Reactors and systems for oxidative coupling of methane

In an aspect, the present disclosure provides a method for the oxidative coupling of methane to generate hydrocarbon compounds containing at least two carbon atoms (C2+ compounds). The method can include mixing a first gas stream comprising methane with a second gas stream comprising oxygen to form a third gas stream comprising methane and oxygen and performing an oxidative coupling of methane (OCM) reaction using the third gas stream to produce a product stream comprising one or more C2+ compounds.

BACKGROUND

The modern petrochemical industry makes extensive use of cracking and fractionation technology to produce and separate various desirable compounds from crude oil. Cracking and fractionation operations are energy intensive and generate considerable quantities of greenhouse gases.

The gradual depletion of worldwide petroleum reserves and the commensurate increase in petroleum prices may place extraordinary pressure on refiners to minimize losses and improve efficiency when producing products from existing feedstocks, and also to seek viable alternative feedstocks capable of providing affordable hydrocarbon intermediates and liquid fuels to downstream consumers.

Methane may provide an attractive alternative feedstock for the production of hydrocarbon intermediates and liquid fuels due to its widespread availability and relatively low cost when compared to crude oil. Worldwide methane reserves may be in the hundreds of years at current consumption rates and new production stimulation technologies may make formerly unattractive methane deposits commercially viable.

Ethylene is an important commodity chemical intermediate. The worldwide production of ethylene exceeds that of any organic compound. Ethylene is used in the production of polyethylene plastics, polyvinyl chloride, ethylene oxide, ethylene chloride, ethylbenzene, alpha-olefins, linear alcohols, vinyl acetate, and fuel blendstocks such as, but not limited to, aromatics, alkanes and alkenes. The growth in demand for ethylene and ethylene based derivatives is forecast to increase as the developing world continues to register higher economic growth. The bulk of worldwide annual commercial production of ethylene is based on thermal cracking of petroleum hydrocarbons with stream; the process is commonly called pyrolysis or steam cracking. The feedstocks for steam cracking can be derived either from crude oil (e.g., naphtha) or from associated or natural gas (e.g., ethane, propane, LPG). Ethylene production is primarily limited to high volume production as a commodity chemical in relatively large steam crackers or other petrochemical complexes that also process the large number of other hydrocarbon byproducts generated in the steam cracking process. Producing ethylene from far more abundant and significantly less expensive methane in natural gas provides an attractive alternative to ethylene produced from steam cracking (e.g., naphtha or gaseous feedstocks). Oligomerization processes can be used to further convert ethylene into longer chain hydrocarbons useful as polymer components for plastics, vinyls, and other high value polymeric products. Additionally, these oligomerization processes may be used to convert ethylene to other longer hydrocarbons, such as C6, C7, C8and longer hydrocarbons useful for fuels like gasoline, diesel, jet fuel and blendstocks for these fuels, as well as other high value specialty chemicals.

SUMMARY

Recognized herein is the need for systems and methods for converting methane to higher chain hydrocarbons, such as hydrocarbon compounds with two or more carbon atoms (also “C2+compounds” herein), such as olefins and/or alkanes, in an efficient and/or commercially viable process. An oxidative coupling of methane (“OCM”) reaction is a process by which methane can form one or more C2+compounds.

In an OCM process, methane is oxidized to yield products comprising C2+compounds, including alkanes (e.g., ethane, propane, butane, pentane, etc.) and alkenes (e.g., ethylene, propylene, etc.). Such alkane (also “paraffin” herein) products may not be suitable for use in downstream processes. Unsaturated chemical compounds, such as alkenes (or olefins), may be employed for use in downstream processes. Such compounds may be polymerized to yield polymeric materials, which may be employed for use in various commercial settings.

The present disclosure provides reactors, systems and methods that can be used to react methane in an OCM process to yield products comprising C2+compounds. OCM reactors, systems and methods of the present disclosure can be integrated in various hydrocarbon processes. The efficient and/or commercially viable formation of C2+compounds from methane can be influenced by a number of different parameters that can both affect the progress of the overall reaction of methane to ethylene, as well as provide opportunities for efficiency outside of the reaction progress, e.g., through energy efficient processes and systems, recycling opportunities and the like.

An aspect of the present disclosure provides a process for production of hydrocarbons, the process comprising the steps of: converting at least a feed stream comprising methane (CH4) and oxygen (O2) feed into a conversion effluent by oxidative coupling of methane (OCM); withdrawing one or more product streams from the conversion effluent by at least one product retrieval stage; recycling at least a portion of the remaining conversion effluent as a recycle stream in a recycle loop, the recycle loop comprising a hydrogenation stage and a methanation stage; and adding at least part of the recycle stream to the feed stream.

In some embodiments, the recycle loop further comprises a CO2addition stage. In some embodiments, CO2is added upstream the methanation step at the CO2addition stage and/or directly into the methanation unit. In some embodiments, H2O is at least partially removed upstream and/or downstream one or more of the product retrieval steps. In some embodiments, the recycle loop comprises a pre-methanation step. In some embodiments, CO, CO2is pre-methanated and/or higher alkanes are reformed in the pre-methanation step. In some embodiments, the pre-methanation step is carried out at T<400° C. or >400° C. In some embodiments, at least part of effluent from the pre-methanation is recycled to upstream the pre-methanation step, such as upstream hydrogenation or between hydrogenation and pre-methanation. In some embodiments, the product obtained at the one or more product steps are ethylene, CO2, aromatics and/or raw gasoline. In some embodiments, the recycle stream comprises mainly CH4at the recycle mixing step preferably where the recycle stream comprises 90-99%, such as above 95% CH4. In some embodiments, the recycle stream comprises H2and/or CO at a concentration below 5%, below 1%, below 0.5%, such as below 10 ppm at the recycle mixing point. In some embodiments, the one or more products is obtained by separation from the effluent through pressure swing adsorption, condensation, N2wash and/or distillation or other separation technologies. In some embodiments, the pre-methanation step is carried out over a nickel-based catalyst at a pressure between 0.1 and 80 bars, such as 10-40 bar. In some embodiments, the methanation step is carried out over a nickel-based catalyst at a pressure between 0.1 and 80 bars, such as 10-40 bar. In some embodiments, the methanation step is carried out at T<400° C. or T>400° C., depending on if the unsaturated hydrogenation is desired or not. In some embodiments, the hydrogenation, pre-methanation and/or methanation is carried out in a boiling water reactor preferably in a single boiling water reactor.

Another aspect of the present disclosure provides a plant for production of hydrocarbons, the plant comprising: an OCM stage, one or more product retrieval stages, and a recycle loop comprising at least a hydrogenation stage and a methanation stage.

In some embodiments, the plant comprises a hydrocarbon to aromatics conversion stage. In some embodiments, the recycle loop further comprises a pre-methanation stage. In some embodiments, the methanation stage comprises two or more serially arranged methanation steps. In some embodiments, the methanation stage comprises a H2O removal stage and/or one or more methanation recycles. In some embodiments, the plant comprises a boiling water reactor comprising the hydrogenation, pre-methanation and/or methanation stage.

Another aspect of the present disclosure provides a method for producing hydrocarbon compounds, comprising: (a) directing a feed stream comprising methane (CH4) and an oxidizing agent into an oxidative coupling of methane (OCM) unit to generate from at least a portion of the CH4and the oxidizing agent an OCM effluent comprising the hydrocarbon compounds; (b) recovering a portion of the OCM effluent in one or more product streams; (c) directing an additional portion of the OCM effluent into a recycle loop that comprises (i) a hydrogenation unit that hydrogenates at least a portion of unsaturated hydrocarbons from the additional portion of the OCM effluent, and (ii) a methanation unit that reacts hydrogen (H2) with carbon monoxide (CO) or carbon dioxide (CO2) from the additional portion of the OCM effluent in a methanation reaction to form CH4, wherein the recycle loop outputs a recycle stream comprising the CH4generated by the methanation unit; and (d) directing at least a portion of the recycle stream into the OCM unit.

In some embodiments, the one or more product streams comprise ethylene (C2H4), CO2, and/or hydrocarbon compounds having three or more carbon atoms (C3+compounds). In some embodiments, the method further comprises directing a CO2stream into the methanation unit. In some embodiments, the method further comprises removing water from the OCM effluent. In some embodiments, the method further comprises reducing a concentration of hydrocarbon compounds having carbon-carbon double bonds or triple bonds in the OCM effluent prior to the methanation reaction. In some embodiments, the recycle stream comprises at least about 90% CH4. In some embodiments, the one or more product streams are recovered using pressure swing adsorption (PSA), condensation, and/or membrane separation. In some embodiments, the method further comprises removing water from the recycle stream prior to (d). In some embodiments, at least about 70% of the water is removed from the recycle stream. In some embodiments, the additional portion of the OCM effluent is a part of the portion of the OCM effluent. In some embodiments, the methanation unit comprises a catalyst comprising one or more of ruthenium, cobalt, nickel and iron. In some embodiments, the methanation unit operates at a pressure between about 2 bar (absolute) and 60 bar, and a temperature between about 150° C. and about 400° C. In some embodiments, the carbon efficiency is at least about 50%.

Another aspect of the present disclosure provides a system for producing hydrocarbon compounds, comprising: an OCM unit configured to receive a feed stream comprising methane (CH4) and an oxidizing agent and to generate from at least a portion of the CH4and the oxidizing agent an OCM effluent comprising the hydrocarbon compounds; a product retrieval unit configured to recover a portion of the OCM effluent in one or more product streams; and a recycle loop configured to receive an additional portion of the OCM effluent, wherein the recycle loop comprises (i) a hydrogenation unit that is configured to hydrogenate at least a portion of unsaturated hydrocarbons from the additional portion of the OCM effluent, and (ii) a methanation unit that is configured to react hydrogen (H2) with carbon monoxide (CO) or carbon dioxide (CO2) from the additional portion of the OCM effluent in a methanation reaction to form CH4, wherein the recycle loop is configured to output a recycle stream comprising the CH4generated by the methanation unit, and wherein at least a portion of the recycle stream is directed into the OCM unit.

In some embodiments, the system further comprises an aromatic hydrocarbon unit that converts hydrocarbons to aromatics. In some embodiments, the methanation unit comprises two or more methanation reactors in fluidic communication with one another and connected in series. In some embodiments, the methanation unit comprises a water removal reactor. In some embodiments, the methanation unit comprises a first reactor and a second reactor, wherein the first reactor is configured to react at least a portion of the CO from the additional portion of the OCM effluent to produce a first reactor effluent, and wherein the second reactor is configured to receive the first reactor effluent and react CO from the first reactor effluent with the H2to produce CH4. In some embodiments, the ratio of (1) all carbon atoms output from the system as hydrocarbons to (2) all carbon atoms input to the system is at least about 0.5.

INCORPORATION BY REFERENCE

DETAILED DESCRIPTION

The term “higher hydrocarbon,” as used herein, generally refers to a higher molecular weight and/or higher chain hydrocarbon. A higher hydrocarbon can have a higher molecular weight and/or carbon content that is higher or larger relative to starting material in a given process (e.g., OCM or ETL). A higher hydrocarbon can be a higher molecular weight and/or chain hydrocarbon product that is generated in an OCM or ETL process. For example, ethylene is a higher hydrocarbon product relative to methane in an OCM process. As another example, a C3+hydrocarbon is a higher hydrocarbon relative to ethylene in an ETL process. As another example, a C5+hydrocarbon is a higher hydrocarbon relative to ethylene in an ETL process. In some cases, a higher hydrocarbon is a higher molecular weight hydrocarbon.

The term “OCM process,” as used herein, generally refers to a process that employs or substantially employs an oxidative coupling of methane (OCM) reaction. An OCM reaction can include the oxidation of methane to a higher hydrocarbon and water, and involves an exothermic reaction. In an OCM reaction, methane can be partially oxidized and coupled to form one or more C2+compounds, such as ethylene. In an example, an OCM reaction is 2CH4+O2→C2H4+2H2O. An OCM reaction can yield C2+compounds. An OCM reaction can be facilitated by a catalyst, such as a heterogeneous catalyst. Additional by-products of OCM reactions can include CO, CO2, H2, as well as hydrocarbons, such as, for example, ethane, propane, propene, butane, butene, and the like.

The term “non-OCM process,” as used herein, generally refers to a process that does not employ or substantially employ an oxidative coupling of methane reaction. Examples of processes that may be non-OCM processes include non-OCM hydrocarbon processes, such as, for example, non-OCM processes employed in hydrocarbon processing in oil refineries, a natural gas liquids separations processes, steam cracking of ethane, steam cracking or naphtha, Fischer-Tropsch processes, and the like.

The terms “C2+” and “C2+compound,” as used herein, generally refer to a compound comprising two or more carbon atoms. For example, C2+compounds include, without limitation, alkanes, alkenes, alkynes and aromatics containing two or more carbon atoms. C2+compounds can include aldehydes, ketones, esters and carboxylic acids. Examples of C2+compounds include ethane, ethene, acetylene, propane, propene, butane, and butene.

The term “non-C2+impurities,” as used herein, generally refers to material that does not include C2+compounds. Examples of non-C2+impurities, which may be found in certain OCM reaction product streams, include nitrogen (N2), oxygen (O2), water (H2O), argon (Ar), hydrogen (H2) carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4).

The term “methane conversion,” as used herein, generally refers to the percentage or fraction of methane introduced into the reaction that is converted to a product other than methane.

The term “C2+selectivity,” as used herein, generally refers to the percentage of all carbon containing products of an oxidative coupling of methane (“OCM”) reaction that are the desired or otherwise preferable C2+products, e.g., ethane, ethylene, propane, propylene, etc. Although primarily stated as C2+selectivity, it will be appreciated that selectivity may be stated in terms of any of the desired products, e.g., just C2, or just C2and C3.

The term “C2+yield,” as used herein, generally refers to the amount of carbon that is incorporated into a C2+product as a percentage of the amount of carbon introduced into a reactor in the form of methane. This may generally be calculated as the product of the conversion and the selectivity divided by the number of carbon atoms in the desired product. C2+yield is typically additive of the yield of the different C2+components included in the C2+components identified, e.g., ethane yield+ethylene yield+propane yield+propylene yield etc.).

The term “airfoil” (or “aerofoil” or “airfoil section”), as used herein, generally refers to the cross-sectional shape of a blade. A blade may have one or more airfoils. In an example, a blade has a cross-section that is constant along a span of the blade, and the blade has one airfoil. In another example, a blade has a cross-section that varies along a span of the blade, and the blade has a plurality of airfoils.

The term “auto-ignition” or “autoignition,” as used herein in the context of temperature, generally refers to the lowest temperature at which a substance, given sufficient time, will spontaneously ignite without an external source of ignition, such as a flame or spark. Use of the term “auto-ignites” with reference to oxygen refers to the amount of oxygen that reacts with (e.g., combustion reaction) any or all hydrocarbons that are mixed with oxygen (e.g., methane).

The term “small scale,” as used herein, generally refers to a system that generates less than or equal to about 250 kilotons per annum (KTA) of a given product, such as an olefin (e.g., ethylene).

The term “world scale,” as used herein, generally refers to a system that generates greater than about 250 KTA of a given product, such as an olefin (e.g., ethylene). In some examples, a world scale olefin system generates at least about 1000, 1100, 1200, 1300, 1400, 1500, or 1600 KTA of an olefin.

The term “item of value,” as used herein, generally refers to money, credit, a good or commodity (e.g., hydrocarbon). An item of value can be traded for another item of value.

OCM Processes

In an OCM process, methane (CH4) reacts with an oxidizing agent over a catalyst bed to generate C2+compounds. For example, methane can react with oxygen over a suitable catalyst to generate ethylene, e.g., 2 CH4+O2→C2H4+2 H2O (See, e.g., Zhang, Q.,Journal of Natural Gas Chem.,12:81, 2003; Olah, G. “Hydrocarbon Chemistry”, Ed. 2, John Wiley & Sons (2003)). This reaction is exothermic (ΔH=−67 kcals/mole) and has typically been shown to occur at very high temperatures (e.g., >450° C. or >700° C.). Non-selective reactions that can occur include (a) CH4+2O2→CO2+2 H2O and (b) CH4+½O2→CO+2H2. These non-selective reactions are also exothermic, with reaction heats of −891 kJ/mol and −36 kJ/mol respectively. The conversion of methane to COx products is undesirable due to both heat management and carbon efficiency concerns.

Experimental evidence suggests that free radical chemistry is involved. (Lunsford,J. Chem. Soc., Chem. Comm.,1991; H. Lunsford,Angew. Chem., Int. Ed. Engl.,34:970, 1995). In the reaction, methane (CH4) is activated on the catalyst surface, forming methyl radicals which then couples in the gas phase to form ethane (C2H6), followed by dehydrogenation to ethylene (C2H4). The OCM reaction pathway can have a heterogeneous/homogeneous mechanism, which involves free radical chemistry. Experimental evidence has shown that an oxygen active site on the catalyst activates the methane, removes a single hydrogen atom and creates a methyl radical. Methyl radicals react in the gas phase to produce ethane, which is either oxidative or non-oxidatively dehydrogenated to ethylene. The main reactions in this pathway can be as follows: (a) CH4+O−→CH3*+OH−; (b) 2 CH3*→C2H6; (c) C2H6+O−→C2H4+H2O. In some cases, to improve the reaction yield, ethane can be introduced downstream of the OCM catalyst bed and thermally dehydrogenated via the following reaction: C2H6→C2H4+H2. This reaction is endothermic (ΔH=−144 kJ/mol), which can utilize the exothermic reaction heat produced during methane conversion. Combining these two reactions in one vessel can increase thermal efficiency while simplifying the process.

Several catalysts have shown activity for OCM, including various forms of iron oxide, V2O5, MoO3, Co3O4, Pt—Rh, Li/ZrO2, Ag—Au, Au/Co3O4, Co/Mn, CeO2, MgO, La2O3, Mn3O4, Na2WO4, MnO, ZnO, and combinations thereof, on various supports. A number of doping elements have also proven to be useful in combination with the above catalysts.

Since the OCM reaction was first reported over thirty years ago, it has been the target of intense scientific and commercial interest, but the fundamental limitations of the conventional approach to C—H bond activation appear to limit the yield of this attractive reaction under practical operating conditions. Specifically, numerous publications from industrial and academic labs have consistently demonstrated characteristic performance of high selectivity at low conversion of methane, or low selectivity at high conversion (J. A. Labinger,Cat. Lett.,1:371, 1988). Limited by this conversion/selectivity threshold, no OCM catalyst has been able to exceed 20-25% combined C2yield (i.e., ethane and ethylene), and more importantly, all such reported yields operate at extremely high temperatures (>800° C.). Novel catalysts and processes have been described for use in performing OCM in the production of ethylene from methane at substantially more practicable temperatures, pressures and catalyst activities. These are described in U.S. Patent Publication Nos. 2012/0041246, 2013/0023079, 2013/165728, 2014/0012053 and 2014/0018589, the full disclosures of each of which are incorporated herein by reference in its entirety for all purposes.

An OCM reactor can include a catalyst that facilitates an OCM process. The catalyst may include a compound including at least one of an alkali metal, an alkaline earth metal, a transition metal, and a rare-earth metal. The catalyst may be in the form of a honeycomb, packed bed, or fluidized bed. In some embodiments, at least a portion of the OCM catalyst in at least a portion of the OCM reactor can include one or more OCM catalysts and/or nanostructure-based OCM catalyst compositions, forms and formulations described in, for example, U.S. Patent Publication Nos. 2012/0041246, 2013/0023709, 2013/0158322, 2013/0165728, 2014/0181877 and 2014/0274671, each of which is entirely incorporated herein by reference. Using one or more nanostructure-based OCM catalysts within the OCM reactor, the selectivity of the catalyst in converting methane to desirable C2+compounds can be about 10% or greater; about 20% or greater; about 30% or greater; about 40% or greater; about 50% or greater; about 60% or greater; about 65% or greater; about 70% or greater; about 75% or greater; about 80% or greater; or about 90% or greater.

In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 20% to about 90%. In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 30% to about 90%. In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 40% to about 90%. In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 50% to about 90%. In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 60% to about 90%. In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 70% to about 90%. In some cases, the selectivity of an OCM process in converting methane to desirable C2+compounds is from about 80% to about 90%. The selectivity of an OCM process in converting methane to desirable C2+compounds can be about 10% or greater; about 20% or greater; about 30% or greater; about 40% or greater; about 50% or greater; about 60% or greater; about 65% or greater; about 70% or greater; about 75% or greater; about 80% or greater; or about 90% or greater.

An OCM process can be characterized by a methane conversion fraction. For example, from about 5% to about 50% of methane in an OCM process feed stream can be converted to higher hydrocarbon products. In some cases, about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% of methane in an OCM process feed stream is converted to higher hydrocarbon products. In some cases, at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% of methane in an OCM process feed stream is converted to higher hydrocarbon products. In some cases, at most about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% of methane in an OCM process feed stream is converted to higher hydrocarbon products.

An OCM reactor can be sized, shaped, configured, and/or selected based upon the need to dissipate the heat generated by the OCM reaction. In some embodiments, multiple, tubular, fixed bed reactors can be arranged in parallel to facilitate heat removal. At least a portion of the heat generated within the OCM reactor can be recovered, for example the heat can be used to generate high temperature and/or pressure steam. Where co-located with processes requiring a heat input, at least a portion of the heat generated within the OCM reactor may be transferred, for example, using a heat transfer fluid, to the co-located processes. Where no additional use exists for the heat generated within the OCM reactor, the heat can be released to the environment, for example, using a cooling tower or similar evaporative cooling device. In some embodiments, an adiabatic fixed bed reactor system can be used and the subsequent heat can be utilized directly to convert or crack alkanes into olefins. In some embodiments, a fluidized bed reactor system can be utilized. OCM reactor systems useful in the context of the present invention may include those described in, for example, U.S. patent application Ser. No. 13/900,898 (filed May 23, 2013), which is incorporated herein by reference in its entirety for all purposes.

The methane feedstock for an OCM reactor can be provided from various sources, such as non-OCM processes. In an example, methane is provided through natural gas, such as methane generated in a natural gas liquids (NGL) system.

Methane can be combined with a recycle stream from downstream separation units prior to or during introduction into an OCM reactor. In the OCM reactor, methane can catalytically react with an oxidizing agent to yield C2+compounds. The oxidizing agent can be oxygen (O2), which may be provided by way of air or enriched air. Oxygen can be extracted from air, for example, in a cryogenic air separation unit.

To carry out an OCM reaction in conjunction with some catalytic systems, the methane and oxygen containing gases generally need to be brought up to appropriate reaction temperatures, e.g., typically in excess of 450° C. for some catalytic OCM processes, before being introduced to the catalyst, in order to allow initiation of the OCM reaction. Once that reaction begins or “lights off,” then the heat of the reaction is typically sufficient to maintain the reactor temperature at appropriate levels. Additionally, these processes may operate at a pressure above atmospheric pressure, such as in the range of about 1 to 30 bars (absolute).

In some cases, the oxidizing agent and/or methane are pre-conditioned prior to, or during, the OCM process. The reactant gases can be pre-conditioned prior to their introduction into a catalytic reactor or reactor bed, in a safe and efficient manner. Such pre-conditioning can include (i) mixing of reactant streams, such as a methane-containing stream and a stream of an oxidizing agent (e.g., oxygen) in an OCM reactor or prior to directing the streams to the OCM reactor, (ii) heating or pre-heating the methane-containing stream and/or the stream of the oxidizing agent using, for example, heat from the OCM reactor, or (iii) a combination of mixing and pre-heating. Such pre-conditioning can minimize, if not eliminate auto-ignition of methane and the oxidizing agent. Systems and methods for pre-conditioning reactant gases are described in, for example, U.S. patent application Ser. No. 14/553,795, filed Nov. 25, 2014, which is entirely incorporated herein by reference.

To carry out an OCM reaction in conjunction with preferred catalytic systems, the methane and oxygen containing gases generally need to be brought up to appropriate reaction temperatures, e.g., typically in excess of 450° C. for preferred catalytic OCM processes, before being introduced to the catalyst, in order to allow initiation of the OCM reaction. Once that reaction begins or “lights off”, then the heat of the reaction is typically sufficient to maintain the reactor temperature at appropriate levels. Additionally, these processes may operate at a pressure above atmospheric pressure, such as in the range of about 1 to 30 bars (absolute).

Providing OCM reactants at the above-described elevated temperatures and pressures presents a number of challenges and process costs. For example, as will be appreciated, heating a mixed gas of methane and oxygen can present numerous challenges. In particular, mixtures of methane and oxygen, at temperatures in excess of about 450° C. and a pressure above atmospheric, can be in the auto-ignition zone, i.e., given sufficient time, the mixture can spontaneously combust without the need of any ignition source. Additionally, the provision of thermal energy to heat the reactants prior to entering a catalytic reactor can have substantial costs in terms of energy input to the process.

At least some component of the auto-ignition risk is alleviated by pre-heating the methane containing gas and oxygen containing gas components to reaction temperature separately. While this avoids autoignition in the heated separate gas streams, in some cases, the OCM process necessarily requires the mixing of these two gas streams prior to carrying out the OCM reaction, at which point, the auto-ignition risk resurfaces. Minimizing the residence time of these mixed, heated gases prior to contact with the catalyst bed within the reactor is desired in order to reduce or eliminate the possibility of auto-ignition of the reactant gases, and the consequent negative implications of combustion. Accordingly, in at least one aspect, the present invention provides improved gas mixing devices systems and methods for complete, rapid and efficient mixing of gas streams so that the mixed streams can be more rapidly introduced to the catalyst bed.

The present disclosure provides processes, devices, methods and systems that address these challenges and costs by allowing for the pre-conditioning of reactant gases prior to their introduction into a catalytic reactor or reactor bed, in a safe and efficient manner. Such pre-conditioning can include (i) mixing of reactant streams, such as a methane-containing stream and a stream of an oxidizing agent (e.g., oxygen) in or prior an OCM reactor or prior to directing the streams to the OCM reactor, (ii) heating or pre-heating the methane-containing stream and/or the stream of the oxidizing agent using, for example, heat from the OCM reactor, or (iii) a combination of mixing and pre-heating.

Mixing Devices, Systems and Methods

In an aspect of the present disclosure, pre-conditioning of OCM reactant streams is achieved by mixing using mixer devices, systems and methods for OCM processes. Such devices or systems can overcome the limitations above by i) mixing the methane-containing and oxygen-containing streams with the required degrees of uniformity in terms of temperature, composition and velocity; and ii) mixing the methane-containing and oxygen-containing streams substantially completely, rapidly and efficiently in order to minimize the residence time of the heated mixed gases before they can be contacted with and reacted in the catalyst bed, which will preferably be less than, and more preferably, substantially less than the amount of time for autoignition of the mixed heated gases to occur.

Required composition uniformity can be such that the deviation of the most oxygen-rich and oxygen-poor post-mixing areas in terms of CH4/O2ratio is less than 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% compared to a perfectly mixed stream. Required temperature uniformity can be such that the deviation of the hottest and coldest post-mixing zones from the temperature of the ideally mixed stream is less than about 30° C., 20° C., 10° C., or 5° C. Required velocity uniformity can be such that the deviation in flow of the post-mixing areas with the largest and smallest flow from the flow of the ideally mixed stream is less than 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1%. Any larger deviations of these variables from the average may cause the catalytic bed located downstream of the mixer to perform with a reduced efficiency. Mixers of the present disclosure can aid in achieving a desired degree of compositional, pressure, temperature and/or flow uniformity in a time period lower than the auto-ignition delay time, such as within a time period from about 5 milliseconds (ms) to 200 ms and/or a range of flow rates from about 1 Million standard cubic feet per day (MMSCFD) to 2,000 MMSCFD. In some embodiments, the auto-ignition delay time is from about 10 milliseconds (ms) to 1000 ms, or 20 ms to 500 ms, at a pressure from about 1 bar (absolute) and 100 bars, or 1 bar to 30 bars, and a temperature from about 300° C. to 900° C., or 400° C. and 750° C.

If any portion of the mixed stream is allowed to spend longer than the auto-ignition delay time in the mixing zone before coming in contact with a catalyst in the OCM reactor, this particular portion can auto-ignite and propagate combustion throughout the entire stream. In some cases, 100% of the stream spends less than the auto-ignition time, which may require the mixer to be characterized by a substantially narrow distribution of residence times and the absence of a right tail in the distribution curve beyond the auto-ignition threshold. Such a mixer can provide a non-symmetric distribution of residence times.

An aspect of the present disclosure provides an oxidative coupling of methane process comprising a mixing member or device (or mixer) in fluid communication with an OCM reactor. The mixer is configured to mix a stream comprising methane and a stream comprising oxygen to yield a stream comprising methane and oxygen, which is subsequently directed to the OCM reactor to yield products comprising hydrocarbon compounds. The hydrocarbon compounds can subsequently undergo separation into various streams, some of which can be recycled to the mixer and/or the OCM reactor.

The hydrocarbon compounds can include compounds with two or more carbon atoms (also “C2+compounds” herein). The hydrocarbon compounds can include C2+compounds at a concentration (e.g., mole % or volume %) of at least about 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99%. In some situations, the hydrocarbon compounds substantially or exclusively include C2+compounds, such as, for example, C2+compounds at a concentration of least about 60%, 70%, 80%, 90%, 95%, 99%, or 99.9%.

Mixing can be employed in a mixer fluidically coupled to an OCM reactor. The mixer can be integrated with the OCM reactor, or be a standalone unit. In some examples, the mixer is upstream of the OCM reactor. In other examples, the mixer is at least partly or substantially integrated with the OCM reactor. For example, the mixer can be at least partly or substantially immersed in a reactor bed of the OCM reactor. The reactor bed can be a fluidized bed.

Systems and methods of the present disclosure can maximize the efficiency of an OCM reaction and reduce, if not eliminate, undesired reactions.

Fluid properties can be selected such that methane and an oxidizing agent (e.g., O2) do not auto-ignite at a location that is before the catalyst of the OCM reactor. For instance, a stream comprising methane and oxygen can have a composition that is selected such that at most 5%, 4%, 3%, 2%, 1%, 0.1%, or 0.01% of the oxygen in the mixed gas stream auto-ignites. The fluid properties include the period of time in which methane is in contact with oxygen (or another oxidizing agent). The residence time can be minimized so as to preclude auto-ignition. In some cases, the stream comprising methane and oxygen can have a substantially non-symmetric distribution of residence (or delay) times along a direction of flow of said third stream. The residence (or delay) time is the period in which a stream comprising methane and oxygen does not auto-ignite. In some examples, the distribution of residence times is skewed towards shorter residence times, such as from about 5 ms to 50 ms. Auto-ignition delay time may be primarily a function of temperature and pressure and, secondarily, of composition. In some cases, the higher the pressure or the temperature, the shorter the auto-ignition delay time. Similarly, the closer the composition to the stoichiometry required for combustion, the shorter the auto-ignition delay time. Diagrams based on empirical data and thermodynamic correlations may be used to determine i) the auto-ignition region (i.e., the threshold values of temperature, pressure and composition above or below which auto-ignition may occur); and ii) the auto-ignition delay time inside the auto-ignition region. Once the auto-ignition delay time is determined for the desired or otherwise predetermined operating conditions, the mixer may be designed such that 100% of the mixed stream spends less than the auto-ignition time in the mixer itself prior to contacting the OCM catalyst.

During mixing, flow separation may cause a portion of the flow to spend a substantially long period of time in a limited region due to either the gas continuously recirculating in that region or being stagnant. In at least some cases, flow separation causes this portion of the flow to spend more time than the auto-ignition time prior to contact with the catalyst, thus leading to auto-ignition and propagation of the combustion to the adjacent regions, and eventually, to the entire stream.

Mixers of the present disclosure may be operated in a manner that drastically reduces, if not eliminates, flow separation. In some situations, fluid properties (e.g., flow regimes) and/or mixer geometries are selected such that upon mixing a stream comprising methane with a stream comprising oxygen in a mixer flow separation does not occur between the mixer and the first gas stream, the second gas stream, and/or the third gas stream.

FIG. 32shows an OCM system3200comprising a mixer3201, an OCM reactor3202downstream of the mixer3201, and a separation unit3203downstream of the OCM reactor3202. The arrows indicate the direction of fluid flow. A first fluid stream (“stream”)3204comprising methane (CH4) and a second fluid stream3205comprising oxygen (O2) are directed into the mixer3201, where they are mixed to form a third mixed gas stream106that is directed into the OCM reactor3202. The second fluid stream3205may comprise CH4(e.g., natural gas) and O2mixed and maintained at a temperature below the auto-ignition temperature. In some cases, diluting pure O2with methane may be desirable to enable relatively simpler material of construction for the mixer compared to situations in which pure O2is used. In situations where pure O2is used, materials such as Hastelloy X, Hastelloy G, Nimonic 90, and others can be used as they are high temperature stable and resist metal ignition in oxygen environments. Other materials can be used in the case of oxygen diluted with methane. In the OCM reactor3202, methane and oxygen react in the presence of a catalyst provided within reactor3202, to form C2+compounds, which are included in a fourth stream3207. The fourth stream3207can include other species, such as non-C2+impurities like Ar, H2, CO, CO2, H2O, N2, NO2and CH4. The fourth stream3207is then optionally directed to other unit operations for processing the outlet gas stream3207, such as separation unit3203, used for separation of at least some, all, or substantially all of the C2+compounds from other components in the fourth stream3207to yield a fifth stream3208and a sixth stream3209. The fifth stream3208can include C2+compounds at a concentration (e.g., mole % or volume %) that is at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99%, and the sixth stream3209can include C2+compounds at a concentration that is less than about 99%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10%. The concentration of C2+compounds in the fifth stream3208can be higher than the concentration of C2+compounds in the sixth stream3209. The sixth stream3209can include other species, such as Ar, H2, CO, CO2, H2O, N2, NO2and CH4. At least some, all or substantially all of CH4and/or O2in the sixth stream3209may optionally be recycled to the mixer3201and/or the OCM reactor3202in a seventh stream3210. Although illustrated inFIG. 32as a separate unit operation, the mixer component of the system may be integrated into one or more unit operations of an overall OCM process system. For example, in preferred aspects, mixer3201is an integrated portion of reactor3202, positioned immediately adjacent to the catalyst bed within the reactor3202, so that that the mixed gas stream3206may be more rapidly introduced to the reactor's catalyst bed, in order to minimize the residence time of mixed stream3206.

Methane in the first fluid stream3204can be provided from any of a variety of methane sources, including, e.g., a natural gas source (e.g., natural gas reservoir) or other petrochemical source, or in some cases recycled from product streams. Methane in the first fluid stream may be provided from an upstream non-OCM process.

The product stream3208can be directed to one or more storage units, such as C2+storage. In some cases, the product stream can be directed to a non-OCM process.

Fluid properties (e.g., flow regimes) may be selected such that optimum mixing is achieved. Fluid properties can be selected from one or more of flow rate, temperature, pressure, and concentration. Fluid properties can be selected to achieve a given (i) temperature variation in the third stream3206, (ii) variation of concentration of methane to the concentration of oxygen in the third stream3206, and/or (iii) variation of the flow rate of the third stream3206. Any one, two or all three of (i)-(iii) can be selected. In some cases, the temperature variation of the third stream3206is less than about 100° C., 50° C., 40° C., 30° C., 20° C., 10° C., 5° C., or 1° C. The variation of the concentration of methane to the concentration of oxygen (CH4/O2) in the third stream3206can be less than about 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% compared to a perfectly mixed (or ideal) stream. The variation of the flow rate of the third stream3206can be less than about 50%, 40%, 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1%. Such variations can be as compared to a perfectly mixed or thermally equilibrated stream and may be taken along a direction that is orthogonal to the direction of flow. Variations can be measured at the exit plane of3206, for example.

The mixer3201can mix the first stream3204and the second stream3205to generate a stream characterized by uniform or substantially uniform composition, temperature, pressure and velocity profiles across a cross section of a mixing zone of the mixer3201or reactor3202(e.g., along a direction that is orthogonal to the direction of flow). Uniformity can be described in terms of deviation of the extremes from an average profile. For example, if the various streams possess different temperatures, the resulting profile of the mixed stream can show a maximum deviation of +/−1 to 20° C. between the hottest and coldest areas compared to the ideal (e.g., perfectly mixed) stream. Similarly, if the various streams possess different compositions, the resulting profile of the mixed stream may show a maximum deviation of +/−0.1 to 20 mole % of all reacting compounds compared to the composition of the ideal stream. Similar metrics can be used for velocity and pressure profiles.

In some cases, the system3200can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 separation units. In the illustrated example, the system3200includes one separation unit3203. The separation unit3203can be, for example, a distillation column, scrubber, or absorber. If the system3200includes multiple separation units3203, the separation units3203can be in series and/or in parallel.

The reactors3202can be in series and/or in parallel.

Although described for illustration of preferred aspects as gas streams passing into, through and out of the reactor systems inFIG. 32, it will be appreciated that the streams3204,3205,3206,3207,3208,3209and3210can be gaseous streams, liquid streams, or a combination of gaseous and liquid streams. In some examples, the streams3204and3205are gaseous streams, and the stream3208and3209are liquid streams. In some examples, the streams3204,3205, and3209are gaseous streams, and the stream3208is a liquid stream.

In some cases, the system3200includes multiple OCM reactors3202. The OCM reactors3202can be the same, similar or dissimilar reactors or reactor types arranged in series or parallel processing trains.

The OCM reactor3202can include any vessel, device, system or structure capable of converting at least a portion of the third stream3206into one or more C2+compounds using an OCM process. The OCM reactor3202can include a fixed bed reactor where the combined methane/oxygen gas mixture is passed through a structured bed, a fluidized bed reactor where the combined methane/oxygen mixture is used to fluidize a solid catalyst bed, and/or a membrane type reactor where the combined methane/oxygen mixture passes through an inorganic catalytic membrane.

The OCM reactor3202can include a catalyst that facilitates an OCM process. The catalyst may include a compound including at least one of an alkali metal, an alkaline earth metal, a transition metal, and a rare-earth metal. The catalyst may be in the form of a honeycomb, packed bed, or fluidized bed.

Although other OCM catalysts can be disposed in at least a portion of the OCM reactors3202, in some preferred embodiments, at least a portion of the OCM catalyst in at least a portion of the OCM reactor3202can include one or more OCM catalysts and/or nanostructure-based OCM catalyst compositions, forms and formulations described in, for example, U.S. Patent Publication Nos. 2012/0041246, 2013/0023709, 2013/0158322, 2013/0165728, and pending U.S. Pat. No. 9,055,313 and U.S. Provisional Patent Application No. 61/794,486 (filed Mar. 15, 2013), each of which is entirely incorporated herein by reference. Using one or more nanostructure-based OCM catalysts within the OCM reactor3202, the selectivity of the catalyst in converting methane to desirable C2+compounds can be about 10% or greater; about 20% or greater; about 30% or greater; about 40% or greater; about 50% or greater; about 60% or greater; about 65% or greater; about 70% or greater; about 75% or greater; about 80% or greater; or about 90% or greater.

In the OCM reactor3202, methane and O2are converted to C2+compounds through an OCM reaction. The OCM reaction (e.g., 2CH4+O2→C2H4+2H2O) is exothermic (ΔH=−67 kcals/mole) and may require substantially high temperatures (e.g., temperature greater than 700° C.). As a consequence, the OCM reactor3202can be sized, configured, and/or selected based upon the need to dissipate the heat generated by the OCM reaction. In some embodiments, multiple, tubular, fixed bed reactors can be arranged in parallel to facilitate heat removal. At least a portion of the heat generated within the OCM reactor3202can be recovered, for example the heat can be used to generate high temperature and/or pressure steam. Where co-located with processes requiring a heat input, at least a portion of the heat generated within the OCM reactor3202may be transferred, for example, using a heat transfer fluid, to the co-located processes. Where no additional use exists for the heat generated within the OCM reactor3202, the heat can be released to the environment, for example, using a cooling tower or similar evaporative cooling device. OCM reactor systems useful in the context of the present invention may include those described in, for example, U.S. Pat. No. 9,469,577, which is incorporated herein by reference in its entirety for all purposes.

As described above, in certain aspects, a mixer device or system is provided coupled to or integrated with an OCM reactor or reactor system. Such mixers are described in greater detail below.

In some embodiments, two or more different reactant streams are mixed rapidly and sufficiently for carrying out a reaction involving the two or more streams. In some cases, mixing will be substantially completely within a rapid timeframe within the mixer systems and devices described herein.

In some cases, two or more gaseous streams can be mixed in a mixer within a narrow window of time targeted to be less than the time in which autoignition may occur at the temperatures and pressures of the mixed gas streams. Such narrow window of time can be selected such that the streams are mixed before any OCM reaction has commenced. In some embodiments, the mixing time is no longer than the maximum residence time before auto-ignition occurs. The mixing time can be less than 99%, 95%, 90%, 80%, 70%, 60% or even less than 50% of the maximum residence time. Each and all portions of the mixed stream can spend nearly the requisite amount of time in a mixing zone of a mixer or reactor that is configured to effect mixing. If the reacting mixture spends more time, then undesired reactions, sometimes irreversible, may take place, which may generate undesired products and possibly impede or prevent the formation of the desired products. Such undesired reactions may generate a greater proportion of non-C2+impurities than C2+compounds, which may not be desirable.

In some situations, in order for the optimal residence time to be achieved by each portion of the mixing stream, the distribution of the residence times in the mixing zone can be substantially narrow so as to reduce the possibility for even a small portion of the stream to spend less or more than the allowed time in the mixing area. Such phenomenon can occur if recirculation and/or stagnant areas are formed due to the design of the mixer itself. For example, if the mixing device is a perforated cylinder located in the mainstream of the larger gaseous stream, the cylinder itself can produce significant recirculation zones in the areas immediately downstream, thus generating a wide right tail in the statistical distribution of residence times. Systems and methods of the present disclosure can advantageously avoid such problems.

The present disclosure provides systems and methods for mixing reactant species (e.g., methane and O2) prior to or during reaction to form C2+compounds, such as by an OCM reaction. In some examples, i) two or more gaseous streams are mixed together within a certain time frame and with a given (e.g., minimum) degree of uniformity, and ii) the resulting mixed stream affords a limited overall residence time and a narrow distribution of residence times before operating conditions of the stream are significantly affected by undesired chemical reactions. Prior to or during mixing, reactant species may be preheated.

A mixer can be integrated with an OCM reactor or separate from the OCM reactor, such as a standalone mixer.FIG. 33Ashows an OCM system3300comprising a methane stream3301and an air stream (comprising O2)3302that are each directed through heat exchangers3303and3304, where each of the streams3301and3302is preheated. Next, the streams3301and3302are directed to a mixer3305comprising a plurality of mixing nozzles3306. The nozzles3306can be in two-dimensional array or in concentric circles, for example. The nozzles can each have the shape of an airfoil, as described elsewhere herein. Void space3307between the nozzles3306can be filled with a packing material (e.g., silica) to aid in preventing recirculation of the mixed gas.

The system3300further comprises a catalyst bed3308downstream of the mixer3305. The catalyst bed3308can include an OCM catalyst, as described elsewhere herein. A void space3309between the mixer3305and catalyst bed3308can be unfilled, or filled with an inert medium, such as, for example, aluminum oxide (e.g., alumina) or silicon oxide (e.g., silica) beads. In some cases, the void space can be filled with a material that increases the auto ignition delay time (AIDT), for example by changing the heat capacity of the media and/or interacting with the initial stage of combustion chemistry by scavenging highly reactive species that can act as combustion initiators. Suitable materials can include zirconia beads, ceramic foams, metal foams, or metal or ceramic honeycomb structures. The use of materials that increase the AIDT can be advantageous at elevated pressures (e.g., above about 3, 5, 10, 15, 20, 25, 30, 35, or 40 barg). The system3300can include a reactor liner3310that can insulate the system3300from the external environment. The liner3310can thermally insulate the mixer3305and catalyst bed3308from the external environment.

In each nozzle3306of the mixer3305, methane and air (including oxygen) can be mixed to form a mixed stream that is directed to the catalyst bed3308. In the catalyst bed3308, methane and oxygen react to form C2+compounds in an OCM process. The C2+compounds along with other compounds, such as unreacted methane and oxygen, are directed out of the system3300in a product stream3311.

With reference toFIG. 33B, as an alternative, the void space3309can be precluded and the catalyst bed3308can be directly adjacent to (and in some cases in contact with) the mixer. The nozzles3306can each optionally be positioned above, immediately adjacent, or in some cases even extend into the catalyst bed3308. In such a case, an individual nozzle3306can be surrounded by catalyst material. In some cases, at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, or 50% of the length of an individual nozzle3306can extend into the catalyst bed3308.

In certain examples, oxygen containing gas, e.g., air, can be introduced into the nozzle3306at the top of the nozzle3306, and methane can be introduced into the nozzle3306along the side of the nozzle3306, as shown. As an alternative example, methane can be introduced into a nozzle3306at the top of the nozzle3306, and oxygen containing gas can be introduced into the nozzle3306along the side of the nozzle3306. The location of entry along a side of the nozzle3306can be varied to provide optimal desired mixing, and selected to provide a given mixed gas distribution.

In some situations, the OCM system3300is operated at a reactor inlet temperature of less than about 800° C., less than about 700° C., less than about 600° C., less than about 500° C., or less than about 400° C. In some embodiments, the OCM system3300is operated at a reactor inlet temperature of at least about 800° C., at least about 700° C., at least about 600° C., at least about 500° C., or at least about 400° C.

In some embodiments, the OCM system3300is operated at an inlet pressure less than about 30 bar (gauge), less than about 20 bar, less than about 10 bar, less than about 9 bar, less than about 8 bar, less than about 7 bar, less than about 6 bar, less than about 5 bar, less than about 4 bar, less than about 3 bar, or less than about 2 bar. In some cases, the OCM system3300is operated at an inlet pressure greater than about 30 bar (gauge), greater than about 20 bar, greater than about 10 bar, greater than about 9 bar, greater than about 8 bar, greater than about 7 bar, greater than about 6 bar, greater than about 5 bar, greater than about 4 bar, greater than about 3 bar, or greater than about 2 bar.

In some situations, the OCM system3300is operated at and a methane to oxygen ratio that is at least about 1, at least about 2, at least about 3, at least about 4, at least about 5, at least about 6, at least about 7, at least about 8, at least about 9, or at least about 10.

The OCM catalyst can be operated at a peak bed temperature that is less than about 1100° C., less than about 1000° C., less than about 900° C., less than about 800° C., or less than about 700° C. The OCM catalyst can be operated at a peak bed temperature that is greater than about 1100° C., greater than about 1000° C., greater than about 900° C., greater than about 800° C., or greater than about 700° C. The OCM catalyst temperature may be lower at lower methane to oxygen ratios. The temperature change across the catalyst bed (e.g., from inlet to outlet) can scale with the methane to oxygen ratio. In some cases, a lower methane to oxygen ration can effect a larger temperature change across the catalyst bed.

FIG. 34Ashows an OCM system3400comprising a methane stream3401and an air stream (comprising O2)3402that are each directed through heat exchangers3403and3404, respectively, where each of the streams3401and3402is preheated. In an example, the methane stream3401is preheated to a temperature between about 450° C. and 650° C., and the air stream is preheated to a temperature between about 450° C. and about 650° C. Next, the methane stream3401is directed to a mixer of the OCM system3400. The mixer includes a feed flow distributor3405. The feed flow distributor3405can be, for example, in the form of a showerhead, which can include a plurality of concentric holes. The feed flow distributor3405can provide a uniform flow of methane. The air stream3402is directed into the OCM system3400to an air distributor3406, which provides streams of air upward towards the feed flow distributor and downward towards a catalyst bed3407. The catalyst bed3407can include an OCM catalyst, as described elsewhere herein. As used throughout, references to “air”, “air streams”, and the like should be understood to include enriched air, oxygen, or any other oxidant that can be used to carry out an OCM reaction. Air is but one example of an oxygen source for OCM. When O2is used as the oxidant, the air stream (i.e., O2) can be pre-heated to between about 150° C. and 350° C., or between about 200° C. and 250° C., inlet temperature.

The air distributor3406can be a hollow device that includes a chamber in fluid communication with a plurality of fluid flow paths that lead from the chamber to a location external to the air distributor3406. In an example, the air distributor is a hollow tube that includes a plurality of holes along a length of the tube. In another example, the air distributor is a hollow plate (e.g., circular plate) with a plurality of holes. In either example, some of the holes can point towards the feed flow distributor3405and other holes can point towards the catalyst bed3407.

The system3400can include a reactor liner3408that can insulate the system3400from the external environment. The liner3408can thermally insulate the distributors3405and3406, and catalyst bed3407, from the external environment.

In the catalyst bed3407, methane and oxygen react to form C2+compounds in an OCM process. The C2+compounds along with other compounds, such as unreacted methane and oxygen, are directed out of the system3400in a product stream3409.

In the example ofFIG. 34A, the air distributor3406is disposed at a location between the feed flow distributor3405and the catalyst bed3407. As an alternative, the air distributor3406can be disposed in an inert packing medium or the catalyst bed3407. InFIG. 34B, the air distributor3406is situated in an inert packing medium3410that is situated between the feed flow distributor3405and the catalyst bed3407. The inert packing medium3410can include, for example, aluminum oxide (e.g., alumina) or silicon oxide (e.g., silica) beads. InFIG. 34C, the air distributor3406is situated in the catalyst bed3407. In the illustrated example, the air distributor3406is situated in the catalyst bed3407at a location that is at or adjacent to the point at which methane enters the catalyst bed. However, other locations may be employed. For example, the air distributor3406can be situated at a location that is at or at least about 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the length (i.e., from top to bottom in the plane of the figure) of the catalyst bed3407.

In some embodiments, mixers include one or more airfoils.FIGS. 35A and 35Bshow an OCM system3500comprising a mixer (or injector)3501and a gas distribution manifold3502adjacent to the mixer3501.FIG. 35Bschematically illustrates a cross-section of the system3500, taken along line35B-35B inFIG. 35A. The mixer3501comprises a plurality of ribs3503that are airfoils. An upstream portion of each of the ribs3503has a larger cross-section than a downstream portion of each of the ribs3503. The ribs3503can be hollow.

In some embodiments, a mixer is capable of mixing a first gas (e.g., CH4) and a second gas (e.g., O2) within about 1000 ms, 500 ms, 400 ms, 300 ms, 200 ms, 100 ms, 50 ms, or 10 ms. The mixer can include a plurality of manifolds, such as airfoil-shaped manifolds, distributed across a fluid flow path.

InFIGS. 35A and 35B, a first fluid stream is directed into the gas distribution manifold3502at a first inlet3504. A second fluid stream is directed into the mixer3501at a second inlet3505(along the direction of the arrows (i.e., upstream do downstream), at which point the second fluid stream is directed to along a fluid flow path3506to the ribs3503. The fluid flow path3506can be a chamber that is in fluid communication with the inlet3505and the ribs3503. In some examples, the first fluid stream comprises a hydrocarbon (e.g., methane) and the second fluid stream comprises an oxidizing agent. In an example, the second fluid stream is air and the oxidizing agent is 02.

The system3500further comprises an OCM reactor3507downstream of the mixer3501. The ribs3503are situated along a fluid flow path that leads from the inlet3504to the OCM reactor3507. During use, the first fluid stream enters the system3500at the inlet3504and is directed to the gas distribution manifold3502. The second fluid stream enters the system3500at the inlet3505and is directed along the fluid flow path3506to the ribs3503. As the second fluid stream is directed along the fluid flow path, heat from the OCM reactor3507can heat the second fluid stream. The heated fluid stream enters the ribs3503and is directed out of the ribs to mix with the first fluid stream that is directed towards the OCM reactor3507from the gas distribution manifold3502.

The mixer3501can be close coupled with the OCM reactor3507. In some cases, the OCM reactor3507includes a catalyst that is included in a space between the ribs3503. The OCM reactor3507can have various shapes and sizes. The OCM reactor3507can have a cross-section that is circular, oval, triangular, square, rectangular, pentagonal, hexagonal or any partial shape and/or combination thereof. In an example, the OCM reactor3507is cylindrical in shape. In some examples, the OCM reactor3507has a diameter between about 1 foot and 100 feet, or 5 feet and 50 feet, or 10 feet and 20 feet. In an example, the OCM reactor3507has a diameter that is about 12 feet.

The OCM reactor3507can include a liner3508that can be formed of a refractory material. Examples of refractory materials include the oxides of aluminum (e.g., alumina), silicon (e.g., silica), zirconium (e.g., zirconia) and magnesium (e.g., magnesia), calcium (e.g., lime) and combinations thereof. Other examples of refractory materials include binary compounds, such as tungsten carbide, boron nitride, silicon carbide or hafnium carbide, and ternary compounds, such as tantalum hafnium carbide. Refractory material can be coated and/or doped with rare earth elements or oxides, or other basic alkaline earth and/or alkali metals. This may aid in preventing coking. OCM catalyst nanowires may also be used to coat refractory material to prevent coking. The liner3508can have a thickness from about 0.5 inches and 24 inches, or 1 inch and 12 inches, or 3 inches and 9 inches. In an example, the liner3508has a thickness of about 6 inches.

The inlets3504and3505can have various shapes and sizes. The inlet3505can have cross-section that is circular, oval, triangular, square, rectangular, pentagonal, hexagonal or any partial shape and/or combination thereof. In some examples, the inlet3504has a diameter between about 10 inches and 100 inches, or 20 inches and 80 inches, or 40 inches and 60 inches. In an example, the inlet3504has a diameter that is about 56 inches. In some examples, the inlet3505has a diameter between about 1 inch and 50 inches, or 10 inches and 30 inches, or 15 inches and 20 inches. In an example, the inlet3505has a diameter that is about 18 inches.

Each of the ribs3503can be an airfoil mixer that is configured to bring the second fluid stream in contact with the first fluid stream. This can provide for uniform mixing. Each of the ribs3503can include one or more openings that are in fluid communication with a fluid flow path leading from the inlet3504to the OCM reactor3507. In some examples, each of the ribs3503has an opening on a top or bottom portion of a rib (with respect to the plane of the figure) and/or on opposing side portions—i.e., along a direction that is orthogonal to the direction of fluid flow from the inlet3504to the OCM reactor3507. By introducing the second fluid stream to the first fluid stream prior to the OCM reactor3507, the ribs can enable mixing of the first and second fluid streams prior to an OCM reaction in the OCM reactor3507.

In some cases, the point along a given rib3503at which the second fluid stream is introduced to the first fluid stream, as well as the fluid properties of the respective streams (e.g., pressure, flow rate and/or temperature), is selected such that the auto-ignition (e.g., automatic combustion or partial combustion of methane) prior to the OCM reactor3507is minimized, if not eliminated. This can help ensure that reaction between a hydrocarbon (e.g., methane) and an oxidizing agent (e.g., oxygen) occurs in the OCM reactor3507to yield C2+compounds, and helps reduce, if not eliminate, unwanted reactions, such as the partial or complete combustion of the hydrocarbon. In some examples, the second stream is introduced to the first stream at the top of each of the ribs3503.

A rib can be a blade that is in the shape of an airfoil.FIG. 36shows a blade3601that may be employed for use as a rib. In some examples, the blade can have a width (the widest portion, ‘W’) from about 0.5 inches to 10 inches, and a length from about 0.5 ft. to 10 ft. The blade3601can be part of a mixer upstream of an OCM reactor. The mixer can be integrated with the OCM reactor. The mixer and OCM reactor can be integrated with a heat exchanger (see below). During operation of an OCM system having the blade3601, a first fluid stream is directed along a fluid flow path3602. The first fluid stream can include a hydrocarbon, such as methane. A second fluid stream3603is directed out of the blade3601through openings3604on opposing sides of the surfaces of the blade3601. The openings3604can be holes or slits, for example. The second fluid stream3603can include an oxidizing agent, such as oxygen (O2). In an example, the second fluid stream3603includes air. The second fluid stream can include a mixture of oxygen and methane.

The openings3604can be on the sides of the blade3601. As an alternative or in addition to, the openings3604can be on a top and bottom portion of the blade (with respect to the plane of the figure). The blade3601can have at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, or 100 openings, which can have various sizes and configurations. For example, the openings3604can be holes or slits. The openings can be disposed side-by-side along the length of the blade3601(i.e., along an axis orthogonal to the width of the blade (‘W’) and in the plane of the figure), or side by side along a thickness of the blade3601(i.e., along an axis orthogonal to the width of the blade and orthogonal to the plane of the figure).

The mixer can provide rapid and complete mixing of two or more gas streams.

Additionally, the airfoil shape can help minimize, if not eliminate, stagnant or re-circulation zones in a mixing zone downstream of the mixer. This allows for every portion of the mixed stream to spend the same amount of time within the mixing zone, thus leading to a very narrow and controlled distribution of the residence times in the mixing zone itself.

The present disclosure also provides a reactor system for performing oxidative coupling of methane to generate C2+compounds, comprising a mixer capable of mixing a first gas stream comprising methane with a second gas stream comprising oxygen to provide a third gas stream, and a catalyst that performs an OCM reaction using the third gas stream to produce a product stream comprising one or more C2+compounds. During reaction, the OCM reaction liberates heat. The system further comprises one or more flow reversal pipes in fluid communication with the mixer and at least partially surrounded by the catalyst. The flow reversal pipes comprise an inner pipe circumscribed by an outer pipe along at least a portion of the length of the inner pipe. The inner pipe is open at both ends and the outer pipe is closed at an end that is surrounded by the catalyst. The flow reversal pipes are configured to transfer heat from the catalyst to the second gas stream during flow along the inner pipe and/or a space between the inner pipe and outer pipe.

In some situations, the second gas stream (i) flows through the inner pipe into the catalyst along a first direction and (ii) flows in a space between the inner pipe and outer pipe out of the catalyst along a second direction that is substantially opposite to the first direction. As an alternative, the second gas stream (i) flows through a space between the inner pipe and outer pipe and into the catalyst along a first direction and (ii) flows in the inner pipe and out of the catalyst along a second direction that is substantially opposite to the first direction.

The use of airfoil-shaped manifolds can enable cross-mixing of one stream into another stream, which can aid in providing a high degree of uniformity in a substantially compact space. Spacing, size and number of the airfoil-shaped manifolds can be optimized on a case-by-case basis to produce the desired or otherwise predetermined uniformity at the outlet of the mixer while maintaining the height of the manifold within the maximum allowable height, to minimize the time spent by the mixed stream in the mixer zone.

In some cases, a flow distributor (e.g., a porous packed catalyst bed) is used in conjunction with the manifold to achieve no or limited flow recirculation as captured by negative velocities (e.g., against bulk of flow). The mixing device is not limited to the manifolds alone. In some cases, a flow straightener, an air distribution manifold, packing (e.g., touching the air foils underneath the manifold), and/or an expansion cone with a specified angle are used. In some cases, the manifold is closely coupled with a flow control element such as a metal or ceramic foam, a bed of packed particles or other porous media suppressing flow recirculation in a zone downstream of the manifold.

A wide set of competitive reactions can occur simultaneously or substantially simultaneously with the OCM reaction, including total combustion of both methane and other partial oxidation products. An OCM process can yield C2+compounds as well as non-C2+impurities. The C2+compounds can include a variety of hydrocarbons, such as hydrocarbons with saturated or unsaturated carbon-carbon bonds. Saturated hydrocarbons can include alkanes, such as ethane, propane, butane, pentane and hexane. Unsaturated hydrocarbons may be more suitable for use in downstream non-OCM processes, such as the manufacture of polymeric materials (e.g., polyethylene). Accordingly, at least some, all or substantially all of the alkanes in the C2+compounds may be converted to compounds with unsaturated moieties, such as alkenes, alkynes, alkoxides, ketones, including aromatic variants thereof.

Once formed, C2+compounds can be subjected to further processing to generate desired or otherwise predetermined chemicals. In some situations, the alkane components of the C2+compounds are subjected to cracking in an OCM reactor or a reactor downstream of the OCM reactor to yield other compounds, such as alkenes (or olefins). See, e.g., U.S. patent application Ser. No. 14/553,795, filed Nov. 25, 2014, which is entirely incorporated herein by reference.

The OCM effluent can be cooled after the conversion to ethylene has taken place. The cooling can take place within a portion of the OCM reactor and/or downstream of the OCM reactor (e.g., using at least about 1, 2, 3, 4, 5 or more heat exchangers). In some cases, a heat exchanger is a heat recovery steam generator (HRSG). Cooling the OCM effluent suitably rapidly and to a suitably low temperature can prevent undesirable reactions from occurring with the OCM effluent, including, but not limited to the formation of coke or other by-products.

In some embodiments, the OCM effluent is cooled to a target temperature of equal to or less than about 700° C., equal to or less than about 650° C., equal to or less than about 600° C., equal to or less than about 550° C., equal to or less than about 500° C., equal to or less than about 450° C., equal to or less than about 400° C., equal to or less than about 350° C., equal to or less than about 300° C., equal to or less than about 250° C., or equal to or less than about 200° C. In some cases, the OCM effluent is cooled to the target temperature within about 1 second, within about 900 milliseconds (ms), within about 800 ms, within about 700 ms, within about 600 ms, within about 500 ms, within about 400 ms, within about 300 ms, within about 200 ms, within about 100 ms, within about 80 ms, within about 60 ms, within about 40 ms, or within about 20 ms of the production of the desired or otherwise predetermined concentration of ethylene in the OCM reaction.

In some situations, an OCM system generates ethylene that can be subjected to further processing to generate different hydrocarbons with the aid of conversion processes (or systems). Such a process can be part of an ethylene to liquids (ETL) process flow comprising one or more OCM reactors, separations units, and one or more conversion processes for generating higher molecular weight hydrocarbons. The conversion processes can be integrated in a switchable or selectable manner in which at least a portion or all of the ethylene containing product can be selectively directed to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more different process paths to yield as many different hydrocarbon products. An example OCM and ETL (collectively “OCM-ETL” herein) is provided in U.S. Patent Publication No. 2014/0171707, filed on Dec. 6, 2013, which is entirely incorporated herein by reference.

In an aspect, provided herein is a method for producing hydrocarbon compounds. The method can comprise directing a feed stream comprising methane (CH4) and an oxidizing agent into an oxidative coupling of methane (OCM) unit. An OCM effluent can be generated from at least a portion of the CH4and oxidizing agent in the OCM unit. The OCM effluent can comprise one or more hydrocarbon compounds. Some or all of the OCM effluent can be recovered in one or more product streams. The one or more product streams may comprise ethylene, CO2, and/or hydrocarbon compounds having three or more carbon atoms (C3+compounds) including aromatics and/or gasolines. The one or more product streams may be recovered using pressure swing adsorption (PSA), condensation, distillation and/or membrane separations. In cases where a portion of the OCM effluent is recovered in one or more product streams, the method can further comprise directing an additional portion of the OCM effluent into a recycle loop. The recycle loop may comprise a hydrogenation unit configured to perform a hydrogenation reaction and/or a methanation unit configured to conduct a methanation reaction. In some cases, the hydrogenation reaction and the methanation reaction are two reaction stages/steps which may or may not be performed in the same or different reactor(s) or unit(s). The additional portion of the OCM effluent may or may not be a part of the OCM effluent from which the one or more product streams are recovered. The hydrogenation unit can hydrogenate some or all of unsaturated hydrocarbons from the OCM effluent. The methanation unit can react hydrogen (H2) with carbon monoxide (CO) and/or carbon dioxide (CO2) from the OCM effluent in a methanation reaction to form CH4. Each of the hydrogenation unit and methanation unit may comprise one or more reactors. The reactors may be any type of reactors, such as fixed bed reactors, fluidized reactors, and/or boiling water reactors. In some cases, a concentration of hydrocarbon compounds having carbon-carbon double bonds and/or carbon-carbon triple bonds in the OCM effluent is reduced prior to the methanation reaction. In some cases, the method further comprises directing a CO2stream into the methanation unit. The CO2stream may be added directly into the methanation unit. Additionally or alternatively, the CO2stream may be added in a CO2addition stage upstream of the methanation unit. In some cases, the recycle loop further comprises an additional step which reacts at least a portion of the CO, CO2and/or higher alkanes in the OCM effluent. For example, the CO and/or CO2may be premethanated in the additional step. In some cases, the higher alkanes are reformed in the additional step.

Methanation and premethanation may be employed in the same process. The methanation and premethanation may be performed in the same unit or in separate units. As an alternative, methanation is performed without premethanation. As another alternative, premethanation is performed without methanation.

Premethanation may include reacting CO and/or CO2with H2to generate CH4. As an alternative or in addition to, premethanation may include reforming or premethanating higher hydrocarbons including alkanes such as ethane, propane, butane etc. In some cases, higher hydrocarbons which may form carbon in the methanation unit are premethanated. In some cases, premethanation of CO, CO2and/or H2and premethanation/reforming of higher hydrocarbons may be conducted separately or together, depending upon, e.g., reaction temperatures.

The recycle loop can output a recycle stream comprising the CH4generated by the methanation unit. The recycle stream may comprise at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% CH4or more. In some cases, water is removed from the recycle stream. In some examples, at least about 70%, 75%, 80%, 85%, 90%, 95% of water or more is removed from the recycle stream. The recycle stream may comprises H2, CO and/CO2at low concentrations. For example, the recycle stream may comprise H2, CO and/CO2at a concentration less than or equal to about 10%, 8%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1% or less. At least a portion of the recycle stream can be directed into the OCM unit. In some cases, at least a portion of the recycle stream is added to the OCM feed stream at a recycle mixing point before being directed into the OCM reactor. The recycle stream may comprise at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% CH4or more at the recycle mixing point. The recycle stream may comprise H2, CO and/CO2at a concentration less than or equal to about 10%, 8%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1% or less at the recycle mixing point.

In some cases, the method further comprises removing water from the OCM effluent. The water may be removed from the OCM effluent before, during or after recovering the one or more product streams from the OCM effluent. In some cases, the method further comprises converting higher alkanes (e.g., ethane, propane) into olefins prior to the methanation reaction. In some cases, the higher alkanes may be reformed prior to the methanation reaction in an additional operation, such as a premethanation.

In another aspect, described herein is a system for producing hydrocarbon compounds. The system can comprise an OCM unit. The OCM unit can be configured to receive a feed stream comprising methane (CH4) and an oxidizing agent and to generate from at least a portion of the CH4and oxidizing agent an OCM effluent. The OCM effluent can comprise one or more hydrocarbon compounds. The system can further comprise a product retrieval unit. The product retrieval unit can be configured to recover some or all of the OCM effluent in one or more product streams. In some cases, the system further comprises a recycle loop. The recycle loop can be configured to receive some or all of the OCM effluent. The recycle loop can comprise a hydrogenation unit and/or a methanation unit. The hydrogenation unit can be configured to hydrogenate at least a portion of unsaturated hydrocarbons from the OCM effluent. The methanation unit can be configured to react hydrogen (H2) with carbon monoxide (CO) and/or carbon dioxide (CO2) from the OCM effluent in a methanation reaction to form CH4. The methanation unit may comprise two or more methanation reactors. The methanation reactors may be in fluidic communication with one another. The methanation reactors may be connected in series in parallel, or combinations thereof. In some examples, the methanation unit comprises a first reactor and a second reactor. The reactors may be any type of reactors, such as fixed bed reactors, fluidized reactors, or boiling water reactors. The first reactor and the second reactor may be in fluidic connection with each other. The first reactor may be configured to react at least a portion of CO and/or CO2from the OCM effluent to produce a first reactor effluent. The CO, CO2and/or H2may be premethanated in the first reactor. For example, the first reactor may be configured to react CO and/or CO2with H2to generate CH4. The reaction of the CO and/or CO2with H2may be conducted until a certain approach to equilibrium (e.g., 0° C.-15° C. to equilibrium) is achieved. The reaction of the CO and/or CO2with H2may be operated in the presence of a nickel-based catalyst, at a pressure between about 0.1 bar and 80 bar (e.g., between about 10 bar and 40 bar) and/or at a temperature below or above about 400° C. In some cases, at least a portion of the first reactor effluent is recycled to upstream the first reactor (e.g., upstream of the hydrogenation stage which may be upstream of the first reactor) or between the hydrogenation unit and the first reactor. The second reactor may be configured to receive some or all of the first reactor effluent and react CO and/or CO2from the first reactor effluent with H2to produce CH4.

In some cases, additional CO and/or CO2may be added into the first reactor and/or the second reactor and subjected to one or more additional reactions. The methanation reaction can produce water and/or have water in the methanation effluent. In some cases, it is desirable to remove this water prior to recycling the methanation effluent to the OCM reactor. This can be accomplished by lowering the temperature of the methanation effluent or performing any separation procedure that removes the water. In some cases, the methanation unit comprises a water removal reactor configured to remove water from the methanation effluent. In some cases, at least about 70%, 80%, 85%, 90%, 95%, or 99% of the water is removed from the methanation effluent prior to the OCM reactor. Removing the water can increase the lifetime and/or performance of the OCM catalyst.

In some cases, the recycle loop further comprises an additional unit configured to react at least a portion of the CO, CO2, H2and/or higher alkanes in the OCM effluent. The additional unit may comprise one or more reactors configured to perform the same reactions as the first reactor and/or the second reactor of the methanation unit. For example, the CO, CO2and/or H2may be premethanated in the additional unit. Alternatively or additionally, the higher hydrocarbons may be reformed/premethanated in the additional unit. The additional unit may or may not be upstream/downstream of the hydrogenation and/or methanation unit in the recycle loop. As discussed above and elsewhere herein, it shall be understood that some or all of the above- or below-mentioned stages/steps (including e.g., OCM, hydrogenation, methanation, CO/CO2premethanation, hydrocarbon reformation, hydrocarbon conversion, water removal, CO2removal etc.) may be conducted in the same or different reactor(s) or unit(s). As an example, the recycle loop may comprise a single unit which implements a hydrogenation operation, a methanation operation and an additional operation that premethanates CO/CO2/H2and/or reforms higher hydrocarbon compounds. In another example, the recycle loop may comprise several individual units (or reactors), each of which is configured to operate under a different reaction condition and perform a different reaction.

The recycle loop can be configured to output a recycle stream comprising some or all of the CH4generated by the methanation unit. In some cases, at least a portion of the recycle stream is directed into the OCM unit. In some cases, the system further comprises a conversion unit configured to convert hydrocarbons to compounds such as alkenes, alkynes, alkoxides, ketones, including aromatic variants thereof. For example, the conversion unit may be a hydrocarbon to aromatics unit which is configured to convert at least some, all or substantially all of the C2+compounds in the OCM effluent to aromatics.

In some cases, the systems or methods of the present disclosure have a carbon efficiency of at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, or at least about 90%. In some cases, a system of the present disclosure or method for use thereof has a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system of at least about 0.4, at least about 0.50, at least about 0.55, at least about 0.60, at least about 0.65, at least about 0.70, at least about 0.75, at least about 0.80, at least about 0.85, at least about 0.90, or at least about 0.95.

In some cases, the systems or methods of the present disclosure have a carbon efficiency of between about 50% and about 85%, between about 55% and about 80%, between about 60% and about 80%, between about 65% and about 85%, between about 65% and about 80%, or between about 70% and about 80%. In some cases, a system of the present disclosure or method for use thereof has a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system of between about 0.50 and about 0.85, between about 0.55 and about 0.80, between about 0.60 and about 0.80, between about 0.65 and about 0.85, between about 0.65 and about 0.80, or between about 0.70 and about 0.80.

Reaction heat (e.g., OCM reaction heat) can be used to supply some, most, or all of the energy used to operate systems and perform methods of the present disclosure. In some examples, reaction heat can be used to supply at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% of energy for operating systems and performing processes of the present disclosure. For example, the reaction heat can be used to supply at least about 80% or 90% of all of the energy for operating systems or processes of the present disclosure. This can provide for an efficient, substantially self-contained system with reduced or even minimum external energy input.

OCM Processes for Producing Olefins

An aspect of the present disclosure provides OCM processes that are configured to generate olefins (or alkenes), such as ethylene, propylene (or propene), butylenes (or butenes), etc. An OCM process can be a standalone process or can be integrated in a non-OCM process, such as a natural gas liquids (NGL or NGLs) or gas processing system.

Reference will now be made to the figures, wherein like numerals refer to like parts throughout. It will be appreciated that the figures and features therein are not necessarily drawn to scale. In the figures, the direction of fluid flow between units is indicated by arrows. Fluid may be directed from one unit to another with the aid of valves and a fluid flow system. In some examples, a fluid flow system can include compressors and/or pumps, as well as a control system for regulating fluid flow, as described elsewhere herein.

FIG. 1is a block flow diagram of a system100that is configured to generate olefins, such as ethylene. The system100can be a small scale or world scale system. The system100comprises an OCM sub-system101that can include one or more OCM units in series and/or parallel. The OCM sub-system101can include one or more post-bed cracking (PBC) units for generating olefins (e.g., ethylene) from alkanes (e.g., ethane and/or propane). A PBC unit can be disposed downstream of an OCM unit. The OCM unit and PBC unit can be situated in separate reactor, or included in the same reactor (e.g., a packed bed for OCM disposed upstream of a PBC unit in the same reactor). In some cases, an integrated OCM unit and PBC unit may be collectively referred to as an OCM reactor.

The OCM sub-system101can accept ethane and an oxidizing agent (e.g., O2). In the illustrated example, the OCM sub-system101accepts ethane from ethane stream102and oxygen (O2) from oxygen stream103. Ethane can be injected into the OCM sub-system101at a PBC unit of the OCM sub-system101. Oxygen can be provided by way of air or provided from an oxygen generation unit, such as a cryogenic unit that accepts air and generates individual O2and N2streams, or by O2pipeline. The OCM sub-system101also accepts methane from C1recycle stream104and ethane from C2recycle stream105.

In an OCM unit of the OCM sub-system101, methane can be catalytically reacted with oxygen in an OCM process to generate an OCM effluent stream106comprising C2+compounds and non-C2+impurities. The OCM effluent stream106can be directed to a PBC unit of the OCM sub-system101to convert one or more alkanes in the OCM effluent stream106to alkenes. Next, the OCM effluent stream106can be directed to a process gas compressor (PGC) unit107. Natural gas (NG) is directed along an NG feed108to a sulfur removal unit109, which can remove sulfur-containing chemicals from the NG feed108to yield a sulfur-free methane feed124to the PGC unit107. As an alternative, the sulfur removal unit109can be excluded if the concentration of Sulfur in the incoming natural gas feed stream is very low and acceptable for the OCM process. As another alternative, the methane feed124can be provided from other sources that may not be natural gas. In some cases, for example if the natural gas feed has a considerable quantity of hydrogen, it can be routed to the methanation unit. From the PGC unit107, the OCM effluent can be directed to CO2removal unit110, which can remove CO2from the OCM effluent. At least a portion of the removed CO2can be directed to a methanation unit111along a CO2stream112. At least a portion of the removed CO2can be directed along CO2stream113for other users, such as, for example, storage or purged from the CO2removal unit110. In some cases, the CO2removal system can comprise a pressure swing adsorption (PSA) unit; in other cases, the CO2removal system can be based on any other membrane separation process. The effluent from the CO2removal unit can be treated to remove water. The water removal system can be a molecular sieve dryer, or a series of dryers (not shown in the figure).

Next, the OCM effluent can be directed from the CO2removal unit110to a demethanizer (also “de-methanizer” herein) unit114, which can separate methane from higher molecular weight hydrocarbons (e.g., acetylene, ethane and ethylene). The separated (or recovered) methane can be directed to the methanation unit111along a C1recycle stream115. Alternatively, or in addition to, the separated methane can be directed to the OCM sub-system101. A purge stream123can be directed out of the demethanizer unit114, which is a portion of stream115. The purge stream can contain methane and inert gas, such as, e.g., N2, He or Ar. The purge flow rate may be sufficient such that the inert gas will not accumulate in the system. The purge stream may be required to remove inert gas(es) that are built-up in the recycle loop.

The methanation unit111can generate methane from CO, CO2and H2. Methane generated in the methanation unit111can be directed to the OCM sub-system101along C1recycle stream104. The methanation unit111can be as described elsewhere herein.

In some examples, the demethanizer unit114includes one or more distillations columns in series and/or parallel. A serial configuration can enable the separation of different components. A parallel configuration can enable separation of a fluid stream of greater volumetric flow rate. In an example, the demethanizer unit114comprises a distillation column and is configured to separate methane from C2+compounds in the OCM effluent stream. The demethanizer unit114can be as described elsewhere herein.

Higher molecular weight hydrocarbons separated from methane in the demethanizer unit114can be directed to an acetylene conversion unit116along stream117. The acetylene conversion unit116can react acetylene (C2H2) in the OCM effluent with H2to generate ethylene. The acetylene conversion unit116in some cases can react other alkenes with H2to generate alkanes, such as ethane. The acetylene conversion unit116can be a hydrogenation reactor. The OCM effluent stream can then be directed from the acetylene conversion unit116to a deethanizer (also “de-ethanizer” herein) unit118along stream119. The deethanizer unit118can separate C2compounds (e.g., ethane and ethylene) from C3+compounds (e.g., propane and propylene). Separated C3+compounds can leave the deethanizer unit118along stream120. C2compounds from the deethanizer unit118can be directed to a C2splitter121, which can separate ethane from ethylene. The C2splitter121can be a distillation column. Recovered ethylene can be directed along stream122and employed for downstream use.

OCM effluent can be characterized by a particular ratio or range of ratios of hydrocarbon compounds with three or more carbon atoms (“C3+compounds”) to C2compounds. For example, OCM effluent can have a C3+compounds-to-C2compounds ratio from about 0 to about 1:3. OCM effluent can have a C3+compounds-to-C2compounds ratio of about 0, 1:1000, 1:100, 1:90, 1:80, 1:70, 1:60, 1:50, 1:40, 1:30, 1:20, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, or 1:3.

The systems of the present disclosure, such as the systems ofFIGS. 1-2, can be suited for the production of any olefin, such as, for example, ethylene. Thus, the systems above and elsewhere herein are not limited to ethylene but may be configured to generate other olefins, such as propylene, butenes, pentene, or other alkenes.

Post-bed cracking (PBC) units that may be suitable for use with systems of the present disclosure, such as the systems ofFIGS. 1-2, are described in, for example, U.S. patent application Ser. No. 14/553,795, filed Nov. 25, 2014, which is entirely incorporated herein by reference.

The systems ofFIGS. 1 and 17may employ different unit operations for small scale and world scale olefin production (e.g., ethylene production). The present disclosure provides non-limiting example unit operations and process flows for various units that may be employed for use with the systems ofFIGS. 1 and 17.

Subsystems in an OCM Unit

FIGS. 2-4show various sub-systems that may be suitable for use in a system that is configured for the production of ethylene or other olefins at small scale. Any suitable gas processing technology (e.g., recycle split gas (RSV) or other gas processing technologies may be implemented in the extraction unit to separate methane from NGLs or C2+components with an economic recovery that may be at least about 70%, 80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%.FIG. 2Ashows an OCM reactor201that is configured to generate C2+compounds from oxygen (O2) and methane, which can be directed into the OCM reactor201along an oxygen stream202and a methane stream203, respectively. Ethane can be directed into the OCM reactor201along an ethane recycle stream227. The streams202,203and227can each be pre-conditioned prior to injection into the OCM reactor201. Such pre-conditioning can include pre-heating and/or pre-mixing. For example, the methane stream203can be mixed with the oxygen stream202prior to injection into the OCM reactor201.

The OCM reactor201can include an OCM unit upstream of a PBC unit. The OCM unit can include one or more catalysts for catalyzing an OCM reaction using oxygen and methane directed into the OCM reactor201along streams202and203, respectively. The OCM reactor201can generate an OCM effluent comprising C2+compounds and non-C2+impurities. The OCM effluent can be directed along an OCM effluent stream204from the OCM reactor201to a plurality of heat exchangers, shown in the figure as a single heat recovery block205, which transfers heat from the OCM effluent stream204to the methane stream203to pre-heat the methane stream203. The OCM effluent stream204can be directed to a separator210, which can remove water from the OCM effluent stream204and provide a water stream211comprising water and an OCM effluent stream212comprising C2+compounds and non-C2+impurities. The concentration of water in the stream212may be substantially reduced in relation to the concentration of water in the OCM effluent stream204.

With continued reference toFIG. 2A, CO and/or CO2in a recycle stream206from downstream processes (see below) are directed into a methanation system207and used to generate methane in a methanation process, as described elsewhere herein. Methane generated in the methanation system207is directed along the methane stream203into the OCM reactor201. Recycle methane (C1) is directed along C1recycle stream208into the methanation system207and combined with the methane formed in the methanation system207. The C1recycle stream can be pre-heated in a heat exchanger prior to introduction into the methanation system207.

With reference toFIG. 2B, the OCM effluent stream212is directed into the compression and treatment section. The OCM effluent212is routed to a quench tower213where the OCM effluent gases are quenched with a cooling medium and any process condensates are condensed and removed. The cooled OCM effluent is then fed to the compressor unit214, which can comprise of a single or multiple stages of compression. The compressor unit214can also comprise inter-stage coolers and separator vessels which raise the pressure of the OCM effluent stream212(e.g., by a factor of from about 2.5:1 to 4:1) and remove water from the OCM effluent stream212. The condensate streams from the separator vessels from214are routed along215as the net condensate removed from the unit. The pressurized OCM effluent stream216(which includes C2+compounds) can be mixed with methane from stream228(e.g., natural gas stream) and subsequently directed to a CO2 removal system217for removing CO2from the OCM effluent stream216. The CO2 removal system217can be an amine system, a membrane separation system or a caustic based wash system. The absorption system217comprises an absorption unit218, a regenerator219and a scrubber220. The absorption unit218can employ an aqueous solution of various alkylamines (also “amines” herein) to scrub CO2and H2S from the OCM effluent stream216. Examples of amines include, without limitation, diethanolamine, monoethanolamine, methyldiethanolamine and diisopropanolamine. The resultant “rich” amine is then routed into the regenerator219(e.g., a stripper with a reboiler) to produce regenerated or “lean” amine that is recycled for reuse in the absorption unit218. The separated CO2can be purged221or recycled222(e.g., to the methanation system207in stream206).

The absorption unit218generates an OCM effluent stream that can have a low CO2content, which is directed to the scrubber220. The scrubber removes additional CO2and entrained solvents from the OCM effluent stream, using, for example, a sodium hydroxide stream that is directed through the scrubber220in a counter flow configuration. The OCM effluent stream223is then directed from the scrubber220to a separator224, which removes water from the OCM effluent stream223. The removed water is directed along stream215. The OCM effluent stream is then directed to dryers225and subsequently directed along stream226. The dryers225can remove water from the OCM effluent stream. The OCM effluent stream223may be cooled in a heat exchanger upon heat transfer to a C1recycle stream, for example.

The system ofFIGS. 2A and 2Bmay be employed for use with other systems of the present disclosure. For example, the absorption system217ofFIG. 2Bmay be employed for use as the amine unit110ofFIG. 1. The series of compressors213, heat exchangers and separators ofFIG. 2Bmay be employed for use as the PGC107ofFIG. 1.

FIG. 3is a process flow diagram of a system300that can be used to generate ethane and ethylene from acetylene (C2H2) and subsequently separate ethane from ethylene. The sub-system300may be suitable for the small scale production of ethylene. The system300can be employed for use as the acetylene reactor116, deethanizer118and C2splitter121ofFIG. 1. The system300comprises a hydrogenation reactor unit301, a first separation unit302and a second separation unit303. The first separation unit302and second separation unit303can be distillation columns. The hydrogenation reactor unit301accepts a stream304comprising H2and a stream305comprising C2+compounds, which can include acetylene, and converts any acetylene in the stream305to ethane and/or ethylene. The C2+compounds are then directed in stream306to the first separation unit302, which separates C3+compounds (e.g., propane, propylene, butane, butene, etc.) from C2compounds (ethane and/or ethylene) in the C2+compounds. The first separation unit302may be referred to as a deethanizer. The C3+compounds are directed along stream307and employed for downstream use. The C2compounds are directed to the second separation unit303, which separates ethane from ethylene. The second separation unit303may be referred to as a C2splitter. Ethane from the second separation unit303is directed along stream308and ethylene is directed along stream309. Ethane can be recycled, such as recycled to an OCM reactor. In some examples, the ethane is recycled to a PBC unit of an OCM reactor.

The stream304may be directed to a pressure swing adsorption (PSA) unit (not shown) that is configured to separate H2from N2. H2from the stream304may then be directed to the hydrogenation reactor301. The stream304may be provided by a separation system, such as the system1100ofFIG. 11. In situations in which a PSA is employed, the system300may be suitable for use in world scale olefin production. For small scale olefin production, the PSA may be precluded.

The acetylene hydrogenation reaction can be practiced over a palladium-based catalyst, such as those used to convert acetylene to ethylene in conventional steam cracking (e.g., the PRICAT™ series including models PD 301/1, PD 308/4, PD 308/6, PD 508/1, PD 408/5, PD 408/7 and PD 608/1, which may be commercially available as tablets or spheres supported on alumina). In some cases, the acetylene hydrogenation catalyst is a doped or modified version of a commercially available catalyst.

However, in some cases, applying an acetylene hydrogenation catalyst to the OCM process that has been developed or optimized for another process (e.g., steam cracking separations and purification processes) can result in operational issues and/or non-optimized performance. For example, in steam cracking, the acetylene conversion reactor can either be located on the front end (prior to cryogenic separations) or back end (after cryogenic separations) of the process. In steam cracking, these differences in running front end and back end typically have to do with the ratio of hydrogen to acetylene present, the ethylene to acetylene ratio, and the non-ethylene olefin (e.g., butadiene) to acetylene ratio. All of these factors can impact the catalyst selectivity for forming ethylene from acetylene, the lifetime and regeneration of the catalyst, green oil formation, specific process conditions for the reactor, and additional hydrogen required for the reaction. These factors are also different between steam cracking versus OCM processes, therefore, provided herein is an acetylene hydrogenation catalyst that is designed to be used in an OCM process.

In OCM implementations, the chemical components going into the acetylene reactor can be different than for steam cracking. For example, OCM effluent can include carbon monoxide and hydrogen. Carbon monoxide can be undesirable because it can compete with the acetylene for the active sites on the hydrogenation catalyst and lead to lower activity of the catalyst (e.g., by occupying those active sites). Hydrogen can be desirable because it is needed for the hydrogenation reaction, however that hydrogen is present in the OCM effluent in a certain ratio and adjusting that ratio can be difficult. Therefore, the catalyst described herein provides the desired outlet concentrations of acetylene, desired selectivity of acetylene conversion to ethylene, desired conversion of acetylene, desired lifetime and desired activity in OCM effluent gas. As used herein, “OCM effluent gas” generally refers to the effluent taken directly from an OCM reactor, or having first undergone any number of further unit operations such as changing the temperature, the pressure, or performing separations on the OCM reactor effluent. The OCM effluent gas can have CO, H2and butadiene.

In some embodiments, the catalyst decreases the acetylene concentration below about 100 parts per million (ppm), below about 80 ppm, below about 60 ppm, below about 40 ppm, below about 20 ppm, below about 10 ppm, below about 5 ppm, below about 3 ppm, below about 2 ppm, below about 1 ppm, below about 0.5 ppm, below about 0.3 ppm, below about 0.1 ppm, or below about 0.05 ppm.

The concentration of acetylene can be reached in the presence of carbon monoxide (CO). In some embodiments, the feed stream entering the acetylene hydrogenation reactor contains at least about 10%, at least about 9%, at least about 8%, at least about 7%, at least about 6%, at least about 5%, at least about 4%, at least about 3%, at least about 2%, or at least about 1% carbon monoxide.

When used in an OCM process, the acetylene hydrogenation catalyst can have a lifetime of at least about 6 months, at least about 1 year, at least about 2 years, at least about 3 years, at least about 4 years, at least about 5 years, at least about 6 years, at least about 7 years, at least about 8 years, at least about 9 years, or at least about 10 years.

FIG. 4is a process flow diagram of a sulfur removal system400, which can be employed for use in removing sulfur-containing compounds from a gas stream. The sulfur removal system400can be employed for use as the sulfur removal system109ofFIG. 1, for example. The system400can be employed for use in a system that is configured to generate small scale ethylene. The system400comprises a separation unit401for removing water form a natural gas stream402. Water is removed along stream403. The natural gas stream with decreased water content is directed along stream404to a heat exchanger405, another optional heat exchanger406and an absorption unit408. The heat exchangers405and406raise the temperature of the natural gas stream. The absorption unit removes H2S from the natural gas stream. This can provide a stream409comprising methane and having a substantially low sulfur and H2O content. In some examples, the stream409is directed to an OCM reactor. As an alternative, or in addition to, the stream409can be directed to a natural gas pipeline.

In certain cases, depending on the concentration of sulfur compounds in the natural gas feed stream, the sulfur removal unit can comprise one or more hydrodesulfurization (hydrotreater) reactors to convert the sulfur compounds to H2S, which is then subsequently removed by an amine system.

FIG. 5shows a sulfur removal unit comprising a separation unit501, a hydrogen feed stream502, a natural gas stream503, a flare header504, a methane-containing stream505, a heat exchanger506, a heat recovery steam generator (HRSG) system507, a hydro treating unit508, an absorption unit509, and a product stream510. The separation unit501is configured to remove water from the stream503. Water removed from the stream503is directed to the flare header504. The hydro treating unit508generates H2S from H2provided by the stream502any sulfur in the stream503. Any sulfur-containing compounds in the stream503and generated in the hydro treating unit508can be removed in the absorption unit509. The resulting product stream510can include methane and substantially low concentrations of sulfur-containing compounds, such as H2S. In some examples, the product stream510can be directed to an OCM reactor or a natural gas pipeline.

The HRSG system507is an energy recovery heat exchanger that recovers heat from the stream505. The HRSG system507can produce steam that can be used in a process (cogeneration) or used to drive a steam turbine (combined cycle). The HRSG unit507can be as described herein.

Oxidative coupling of methane (OCM) can convert natural gas to ethylene and other longer hydrocarbon molecules via reaction of methane with oxygen. Given the operating conditions of OCM, side reactions can include reforming and combustion, which can lead to the presence of significant amounts of H2, CO and CO2in the OCM effluent stream. H2content in the effluent stream can range between about 5% and about 15%, between about 1% and about 15%, between about 5% and about 10%, or between about 1% and about 5% (molar basis). The content of CO and CO2can each range between about 1% and about 5%, between about 1% and about 3%, or between about 3% and about 5% (molar basis). In some cases, the ethylene and all the other longer hydrocarbon molecules contained in the effluent stream are separated and purified to yield the final products of the process. This can leave an effluent stream containing the unconverted methane, hydrogen, CO and CO2and several other compounds, including low amounts of the product themselves depending on their recovery rates.

In some cases, this effluent stream is recycled to the OCM reactor. However, if CO and H2are recycled to the OCM reactor along with methane, they can react with oxygen to produce CO2and H2O, causing various negative consequences to the process including, but not limited to: (a) an increase of the natural gas feed consumption (e.g., because a larger portion of it may result in CO2generation instead of product generation); (b) a decrease of the OCM per-pass methane conversion (e.g., because a portion of the allowable adiabatic temperature increase may be exploited by the H2and CO combustion reactions instead of the OCM reactions); and an increase of the oxygen consumption (e.g., because some of the oxygen feed may react with CO and H2instead of methane).

The effluent stream can be exported to a natural gas pipeline (e.g., to be sold as sales gas into the natural gas infrastructure). Given that specifications can be in place for natural gas pipelines, the concentrations of CO, CO2and H2in the effluent can need to be reduced to meet the pipeline requirements. The effluent stream may also be used as a feedstock for certain processes that may require lower concentrations of H2, CO and CO2.

Therefore, it can be desirable to reduce the concentration of H2, CO and CO2in the OCM effluent stream, upstream or downstream of the separation and recovery of the final products. This can be accomplished using methanation systems and/or by separating H2and CO from the effluent stream (e.g., using cryogenic separations or adsorption processes). The disclosure also includes separating CO2from the effluent stream using CO2removal processes, such as chemical or physical absorption or adsorption or membranes. However, these separation processes can require significant capital investments and can consume considerable amounts of energy, in some cases making an OCM-based process less economically attractive.

The present disclosure also provides systems and methods for reducing CO, CO2and H2concentration in a methane stream. Such compounds can be reacted to form methane in a methanation reaction.

An aspect of the present disclosure provides a methanation system that can be employed to reduce the concentration of CO, CO2and H2in a given stream, such as an OCM product stream. This can advantageously minimize the concentration of CO, CO2and H2in any stream that may be ultimately recycled to an OCM reactor. The methanation system can be employed for use with any system of the present disclosure, such as an OCM-ETL system described herein.

In a methanation system, CO reacts with H2to yield methane via CO+3H2→CH4+H2O. In the methanation system, CO2can react with H2to yield methane via CO2+4 H2→CH4+2 H2O. Such processes are exothermic (ΔH=−206 kJ/mol and −178 kJ/mol, respectively) and generate heat that may be used as heat input to other process units, such as heating an OCM reactor of a PBC reactor, or pre-heating reactants, such as methane and/or an oxidizing agent (e.g., 02) prior to an OCM reaction. The methanation reaction can take place in two or more reactors in series, in some cases with intercooling. In some situations, a methanation reactor can be implemented in tandem with an OCM reactor to increase carbon efficiency.

In some cases, to limit the heat release per unit of flow of reactants, methanation can be conducted on streams that contain CO, CO2, H2and a suitable carrier gas. The carrier gas can include an inert gas, such as, e.g., N2, He or Ar, or an alkane (e.g., methane, ethane, propane and/or butane). The carrier gas can add thermal heat capacity and significantly reduce the adiabatic temperature increase resulting from the methanation reactions.

In some examples, methane and higher carbon alkanes (e.g., ethane, propane and butane) and nitrogen are employed as carrier gases in a methanation process. These molecules can be present in an OCM process, such as in an OCM product stream comprising C2+compounds. Downstream separation units, such as a cryogenic separation unit, can be configured to produce a stream that contains any (or none) of these compounds in combination with CO and H2. This stream can then be directed to the methanation system.

A methanation system can include one or more methanation reactors and heat exchangers. CO, CO2and H2can be added along various streams to the one or more methanation reactors. A compressor can be used to increase the CO2stream pressure up to the methanation operating pressure, which can be from about 2 bar (absolute) to 60 bar, or 3 bar to 30 bar. CO2can be added to the inlet of the system in order to create an excess of CO2compared to the amount stoichiometrically required to consume all the available H2. This is done in order to minimize H2recycled to OCM.

Given the exothermicity of the methanation reactions, a methanation system can include various methanation reactors for performing methanation. In some cases, a methanation reactor is an adiabatic reactor, such as an adiabatic fixed bed reactor. The adiabatic reactor can be in one stage or multiple stages, depending, for example, on the concentration of CO, CO2and H2in the feed stream to the methanation system. If multiple stages are used, inter-stage cooling can be performed by either heat exchangers (e.g., a stage effluent can be cooled against the feed stream or any other colder stream available in the plant, such as boiler feed water) or quenching via cold shots, i.e. the feed stream is divided into multiple streams, with one stream being directed to the first stage while each of the other feed streams being mixed with each stage effluent for cooling purposes. As an alternative, or in addition to, a methanation reactor can be an isothermal reactor. In such a case, reaction heat can be removed by the isothermal reactor by, for example, generating steam, which can enable a higher concentration of CO, CO2and H2to be used with the isothermal reactor. Apart from adiabatic and isothermal reactors, other types of reactors may be used for methanation, such as fluidized bed reactors.

FIG. 6Ashows an example methanation system600. The system600may be used in OCM systems that are for small scale or world scale production of ethylene or other olefins. The system600comprises a first reactor601, second reactor602and a heat exchanger603. The first reactor601and second reactor602can be adiabatic reactors. During use, a recycle stream604comprising methane, CO and H2(e.g., from a cryogenic separation unit) is directed to the heat exchanger603. In an example, the recycle stream604comprises between about 65% and 90% (molar basis) methane, between about 5% and 15% H2, between 1% and 5% CO, between about 0% and 0.5% ethylene, and the balance inert gases (e.g., N2, Ar and He). The recycle stream604can have a temperature from about 20° C. to 40° C., or 20° C. to 30° C., and a pressure from about 2 bar to 60 bar (absolute), or 3 bar to 30 bar. The recycle stream604can be generated by a separation unit downstream of an OCM reactor, such as a cryogenic separation unit.

In the heat exchanger603, the temperature of the recycle stream604is increased to about 100° C. to 400° C., or 200° C. to 300° C. The heated recycle stream604is then directed to the first reactor601. In the first reactor601, CO and H2in the recycle stream604react to yield methane. This reaction can progress until all of the H2is depleted and/or a temperature approach to equilibrium of about 0 to 30° C., or 0 to 15° C. is achieved. The methanation reaction in the first reactor601can result in an adiabatic temperature increase of about 20° C. to 300° C., or 50° C. to 150° C.

Next, products from the first reactor, including methane and unreacted CO and/or H2, can be directed along a first product stream to the heat exchanger603, where they are cooled to a temperature of about 100° C. to 400° C., or 200° C. to 300° C. In the heat exchanger603, heat from the first product stream603is removed and directed to the recycle stream604, prior to the recycle stream604being directed to the first reactor601.

Next, a portion of the heated first product stream is mixed with a CO2stream605to yield a mixed stream that is directed to the second reactor602. The CO2stream605can be generated by a separation unit downstream of an OCM reactor, such as a cryogenic separation unit. This can be the same separation unit that generated the recycle stream604.

In the second reactor602, CO and CO2react with H2to yield a second product stream606comprising methane. The reaction(s) in the second reactor602can progress until substantially all of the H2is depleted and/or a temperature approach to equilibrium of about 0 to 30° C., or 0 to 15° C. is achieved. The proportions of CO, CO2and H2in the mixed stream can be selected such that the second product stream606is substantially depleted in CO and H2.

The first reactor601and the second reactor602can be two catalytic stages in the same reactor vessel or can be arranged as two separate vessels. The first reactor601and second reactor602can each include a catalyst, such as a catalyst comprising one or more of ruthenium, cobalt, nickel and iron. The first reactor601and second reactor602can be fluidized bed or packed bed reactors. Further, although the system600comprises two reactors601and602, the system600can include any number of reactors in series and/or in parallel, such as at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, or 50 reactors.

Although the CO2stream605is shown to be directed to the second reactor602and not the first reactor601, in an alternative configuration, at least a portion or the entire CO2stream605can be directed to the first reactor601. The proportions of CO, CO2and H2can be selected such that the methanation product stream is substantially depleted in CO and H2.

Methane generated in the system600can be employed for various uses. In an example, at least a portion of the methane can be recycled to an OCM reactor (e.g., as part of an OCM-ETL system) to generate C2+compounds, including alkenes (e.g., ethylene). As an alternative, or in addition to, at least a portion of the methane can be directed to a non-OCM process, such as a natural gas stream of a natural gas plant. As another alternative, or in addition to, at least a portion of the methane can be directed to end users, such as along a natural gas pipeline.

FIG. 6Bis a process flow diagram of an example of a methanation system that can be employed to generate ethylene. The system ofFIG. 6Bcan be used in other systems of the present disclosure, such as the system100ofFIG. 1. The system comprises compressors607and608, separation units609and610, and methanation reactors611and612. The separation units609and610can be quench towers, which may separate water from a stream comprising CO and/or CO2. During use, a stream613comprising CO and/or CO2is directed to the compressor607and subsequently the separator unit609. In stream614, CO and/or CO2along with H2are directed to the methanation reactor611and are reacted to form methane, which, along with any excess CO, CO2and H2, is subsequently directed to the methanation reactor612, where CO and/or CO2provided in stream615is reacted with H2to form additional methane. The methane generated in the methanation reactors611and612is directed along stream616. The methane in stream616can be, for example, recycled to an OCM reactor.

Use of methanation systems with OCM systems of the present disclosure can reduce the quantity CO and/or CO2that are directed to the environment, which may advantageously decrease overall greenhouse emissions from such systems. In some examples, using a methanation system, the emission of CO and/or CO2from an OCM system can be reduced by at least about 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, or 50%.

The methanation reaction can be practiced over a nickel-based catalyst, such as those used to produce SNG (Substitute Natural Gas or Synthetic Natural Gas) from syngas or used to purify streams containing CO and CO2(e.g., to remove CO and CO2present in the make-up feed to an ammonia synthesis unit). Examples of such catalysts include the KATALCO™ series (including models 11-4, 11-4R, 11-4M and 11-4MR) that may include nickel supported on refractory oxides; the HTC series (including NI 500 RP 1.2) having nickel supported on alumina; and Type 146 having ruthenium supported on alumina. Additional methanation catalysts can include models PK-7R and METH-134. The methanation catalyst can be tableted or an extruded. The shapes of such catalysts can be, for example, cylindrical, spherical, or ring structures, for or partial shapes and/or combinations of shapes thereof. In some cases, ring structures are advantageous due to their reduced pressure drop across the reactor bed relative to cylindrical and spherical commercial forms. In some cases, the methanation catalyst is a doped or modified version of a commercially available catalyst.

In some cases, merely applying a methanation catalyst to the OCM process that has been developed or optimized for another process (e.g., SNG production or gas purification) can result in operational problems and/or non-optimal performance, including carbon formation (or coking) over the methanation catalyst. Coking can lead to de-activation of the catalyst and, eventually, to loss of conversion through the methanation reactor, thus making the methanation process ineffective, severely limiting the performances of the overall OCM-based process and, possibly, preventing the final products from achieving the required specifications.

The selectivity and/or conversion produced by an existing and/or commercially available methanation catalyst at a given process condition (e.g., gas-hourly space velocity, molar composition, temperature, pressure) may not be ideal for OCM implementations. For example, ammonia plants can have between about 100 ppm and 1% CO with a molar excess of H2(e.g., 2, 5, 10, 50, 100-fold or more excess) that drives equilibrium in favor of complete methanation. Methanation systems in ammonia plants have a small temperature difference between inlet and outlet of the adiabatic methanation reactor (e.g., 20 to 30° C.) and can be sized for catalyst lifetime. SNG production does not have a vast molar excess of H2in some cases. Methanation in SNG processes can have an inlet versus outlet temperature difference of greater than 100° C. and be performed in multiple stages. Furthermore, the purpose of methanation can be different for OCM. Ammonia and SNG processes typically perform methanation primarily to eliminate CO and/or CO2(although H2can also be eliminated or substantially reduced in concentration), while methanation is performed in OCM processes primarily to eliminate H2(although CO and/or CO2can also be eliminated or substantially reduced in concentration).

A methanation catalyst and/or catalytic process is described herein that can prevent or reduce carbon formation in the methanation reactor or other operational inefficiencies. The catalyst and/or catalytic process is achieved through any combination of: (a) removing chemical species that can contribute to coke formation from the methanation inlet feed; (b) introducing chemical species into the methanation feed that eliminate or reduce the rate of coke formation; and (c) using the methanation catalyst described herein that reduces or eliminates coke formation and/or is designed to operate at the process conditions of OCM effluent or OCM process streams (e.g., gas-hourly space velocity, molar composition, temperature, pressure).

In some instances, the species present in the OCM effluent stream that can lead to carbon formation in the methanation reactor are removed or reduced in concentration using a separations or reactive process. The typical operating conditions of a methanation reactor can be at a pressure between about 3 bar and about 50 bar and a temperature between about 150° C. and about 400° C. Any hydrocarbon species containing carbon-carbon double bonds or triple bonds may be sufficiently reactive to form carbon deposits (i.e., coke). Examples of such species are acetylene, all olefins and aromatic compounds. Removal or significant reduction of these species can be achieved via different methods including, but not limited to: (a) hydrogenation (i.e., reaction of these species with the hydrogen present in the effluent stream itself to produce alkanes) over suitable catalysts prior to the methanation reactor; (b) condensation and separation of these species from methane prior to the methanation reactor; (c) absorption or adsorption of these species; (d) by utilizing suitable membranes; or (d) any combination thereof. Temperatures of methanation reactions may vary (e.g., below or above about 400° C.), depending upon, for instance, whether it may be desirable to reduce a concentration of hydrocarbon species containing carbon-carbon double or triple bonds (e.g., via hydrocarbon hydrogenation).

In some embodiments, species are introduced into the methanation inlet stream that eliminate or reduce the rate of carbon formation. Molecular species that can create a reducing atmosphere can be used to counteract an oxidation reaction and can therefore reduce the rate of carbon formation. Hydrogen and water are examples of these particular compounds and can be added to the OCM effluent stream prior to methanation to increase their concentration in the methanation reactor.

An aspect of the present disclosure provides a methanation catalyst for an OCM process. Coke formation is typically the product of surface driven reactions. Therefore, the methanation catalyst for OCM alters the local electronic environment around the active site of the catalyst. This can be done by changing the elemental composition (for example via post-impregnation doping, or creating a new mixed metal of nickel and another transition metal), morphology and structure (for example via synthesizing the metal in a non-bulk form factor). Examples of such syntheses include; nanowires of the same material, nanoparticles coated on a support, and vapor deposition of the active material on a support material. Additional modifications to the surface may result from post synthetic processing steps, such as etching of the surface, oxidizing and reducing the metal to create a different surface reconstruction, calcination steps under different atmospheres (e.g., oxidizing or reducing), heating to achieve different crystal phases, and inducing defect formation. The end result of the modifications of the methanation catalyst is specifically designed to minimize carbon (coke) formation, while still effectively at conducting the methanation reactions.

The methanation process and/or methanation catalyst can operate with OCM product gas, either directly or after one or more heat exchangers or separation operations. For example, the methanation feed stream can have the following composition on a molar basis: CH4between about 65% and about 90%; H2between about 5% and about 15%; CO between about 1% and about 5% (molar basis); C2H4between about 0% and about 0.5%; C2H2between about 0% and about 0.1%; and the balance inert gases such as N2, Ar and He. The methanation feed stream typically has a temperature close to ambient temperature and a pressure ranging between about 3 and about 50 bar.

The methanation reaction can produce water and/or have water in the methanation effluent. In some cases, it is desirable to remove this water prior to recycling the methanation effluent to the OCM reactor. This can be accomplished by lowering the temperature of the methanation effluent or performing any separation procedure that removes the water. In some embodiments, at least about 70%, at least about 80%, at least about 70%, at least about 90%, at least about 95%, or at least about 99% of the water is removed from the methanation effluent prior to the OCM reactor. Removing the water can increase the lifetime and/or performance of the OCM catalyst.

A methanation process can be implemented in an OCM-based process using adiabatic reactors. In an example, the process does not require a methanation catalyst specially designed or optimized for OCM. In this example, an OCM-based process is designed to produce ethylene from natural gas. In this case the product and recovery section of the OCM plant (e.g., a cryogenic unit) can be designed to separate ethylene and all other hydrocarbons from methane, CO and H2in the OCM effluent. The mixed stream that contains methane, CO and H2can be fed to the methanation section.

FIG. 7shows an example of a methanation system for OCM. The methanation feed stream700is first sent to a first heat exchanger705where its temperature is increased to the methanation reactor inlet temperature, typically between 150° C. and 300° C. Steam710is injected immediately downstream of the first heat exchanger to increase water concentration in the methanation feed stream. Then the heated stream is fed to a first adiabatic reactor715where ethylene, acetylene and any other hydrocarbon that presents carbon-carbon double or triple bonds are hydrogenated via reaction with the H2present in the stream.

The effluent from the first reactor715is then fed to a second reactor720, where CO reacts with H2until a certain approach to equilibrium is achieved, typically 0° C.-15° C. to equilibrium. The adiabatic temperature increase that results from CO methanation depends on the exact composition of the feed stream and is typically in the 50° C.-150° C. range.

The second reactor720effluent is then sent to the first heat exchanger705and a second heat exchanger725where it is cooled down to a temperature below water condensation. The stream is then fed to a phase separator730where the condensed water735is separated from the vapors740in order to minimize the water concentration in the vapors. It can be important to remove water at this stage to optimize the conditions for the second methanation stage (water is a product of the methanation reaction and is no longer needed in the second stage because all carbon forming species have been either removed or converted at this point).

The vapor stream740is fed to a third heat exchanger745where it is heated up to the temperature required at the inlet of the third adiabatic reactor750, which is the second methanation stage, typically operated at between about 150° C. and about 300° C. Additional CO2755produced in the process is mixed with effluent from the second reactor720and fed to the third reactor750. CO and CO2react with H2in the third reactor750until a 0° C.-15° C. temperature approach to equilibrium is reached. Typically the amount of CO2that is added to the second reactor effluent is more than what may be stoichiometrically required to consume all H2, to push the equilibrium towards CO and H2complete depletion.

The liquid stream from the phase separator735is re-injected into the methanation feed stream alongside the steam. Alternatively, it can be first vaporized and then re-injected, or it can be sent to a water treatment system for water recovery and purification.

The three reactors,715,720and750or any combination of them can be physically situated in the same vessel or can be arranged in separate individual vessels. A portion or even all of the CO2addition may be performed at the inlet of715or720, depending on the type of catalyst used in the two reactors.

OCM System Configurations

An OCM reactor system can comprise a single reactor or multiple reactors in series and/or in parallel. For example, the OCM reactor system includes at least 2, 3, 4, or 5 OCM reactors in series. As another example, the OCM reactor system includes at least 2, 3, 4, or 5 OCM reactors in parallel. As another example, the OCM reactor includes two OCM reactors in parallel, both of which are downstream of another OCM reactor. In some cases, an OCM reactor system can comprise two reactors, three reactors, or four reactors in series. In certain embodiments, the above mentioned number of reactors can be connected in parallel, or a combination thereof (e.g., mixed series and parallel). In addition, either one or more of the OCM reactor can contain a post-bed cracking (PBC) section as a part of the OCM reactor.

The OCM reaction is highly exothermic and the heat produced can be used to generate steam. A heat recovery system can be designed so as to cool down OCM reactor effluent to a temperature of less than or equal to about 600° C., 500° C., 400° C., 300° C. or 200° C., or a temperature between any two of these values (e.g., between 200° C. and 600° C., or 300° C. and 500° C.), and to use that heat as process heat within the OCM unit, to heat boiler feed water (BFW) or steam, or for other processes.

FIGS. 5, 8, and 13show various sub-systems that may be suitable for use in a system that is configured for the production of ethylene at world scale. With reference toFIG. 8A, a system800comprises a first OCM unit801and second OCM unit802. The OCM units801and802are in series—the second OCM unit802receives OCM effluent from the first OCM unit801. Each OCM unit801and802includes and OCM reactor that is configured to react methane with an oxidizing agent to generate C2+compounds. One or both of the OCM units801and802can include a PBC reactor downstream of the OCM reactor. In the illustrated example, the second OCM unit802comprises a PBC reactor downstream of the OCM reactor of the second OCM unit802.

During use, oxygen along stream803is directed into the OCM units801and802.

Methane is directed to the first OCM unit801along stream804. In the first OCM unit801, methane and oxygen react in an OCM process to yield an OCM effluent stream805that is directed to a heat exchanger and subsequently the second OCM unit802. The second OCM unit802generates addition C2+compounds from oxygen and any unreacted methane in the stream805. In addition, the second OCM unit802accepts ethane along stream806into the PCB reactor of the second OCM unit802, and generates ethylene from the ethane. C2+compounds generated in the second OCM unit802, along with any non-C2+impurities are directed out of the second OCM unit802along stream807to multiple heat exchangers and subsequently a separator808, which removes water from the OCM effluent stream. Water is directed out of the separator808along stream809, and C2+compounds and any non-C2+impurities are directed along stream810.

The system800further includes a methanation unit811that generates methane from H2and CO and/or CO2. Methane generated in the methanation unit811is directed along stream804to the first OCM unit801. The methanation unit811may be as described elsewhere herein. Methane, such as recycled methane, is directed along stream812through a heat exchanger and to the methanation unit811. CO and/or CO2are directed to the methanation unit811along stream813.

The system800includes process stream that is used in the heat exchangers. Process steam is directed along stream814to various heat exchangers and is outputted along stream815and816.

Although the system800includes two OCM units801and802, the system800can include any number of OCM units in series and parallel. An OCM unit can be an OCM reactor with an OCM catalyst. The system800can include at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 OCM units.

The stream810may be directed to a hydrogenation reactor and separation train to convert any acetylene in the stream810to ethane and/or ethylene, and separate the ethane from ethylene. For world scale ethylene generation, the system300ofFIG. 3may be employed. A PSA unit may be used to separate H2from N2in a stream comprising H2and N2.

With reference toFIG. 8B, the stream810is directed into a series of compressors817and separators818, which raise the pressure of the stream810(e.g., by a factor of from about 2.5:1 to 4:1) and remove water from the stream810. The separators may be quench towers. Water removed from a first of the separators818is directed along stream819. The pressurized stream820(which includes C2+compounds) can be mixed with methane from stream821(e.g., natural gas stream or methane from a methanation unit) and subsequently directed to an absorption system822for removing CO2from the stream820. The absorption system822can be an amine system. The absorption system822comprises an absorption unit823, a regenerator824and a scrubber825. The absorption unit823can employ an aqueous solution of various akylamines (also “amines” herein) to scrub CO2and H2S from the stream820. Examples of amines include, without limitation, diethanolamine, monoethanolamine, methyldiethanolamine and diisopropanolamine. The resultant “rich” amine is then routed into the regenerator824(e.g., a stripper with a reboiler) to produce regenerated or “lean” amine that is recycled for reuse in the absorption unit823. The separated CO2can be purged826or recycled827(e.g., to a methanation system).

The absorption unit823generates an effluent stream that can have a low CO2content, which is directed to the scrubber825. The scrubber825removes additional CO2from the stream, using, for example, a sodium hydroxide stream that is directed through the scrubber825in a counter flow configuration. The stream828is then directed from the scrubber825to a separator829, which removes water from the stream828. The removed water is directed along stream819and the C2+compounds and non-C2+impurities are directed to dryers830, and subsequently directed along stream831. The OCM effluent stream828may be cooled in a heat exchanger upon heat transfer to a C1recycle stream, for example.

The system ofFIG. 8Bemploys various heat exchangers. A C1/N2stream is directed along stream832to a heat exchanger and removed along streams833and834. Process stream835, which can comprise methane, is directed to another heat exchanger, and a portion of process stream835is then directed along stream834and a remainder is directed along stream836. A C1purge from, for example, a PSA unit, may be directed along stream837to stream834.

InFIGS. 8A-8B, in some examples, the separators808and818can be liquid/liquid separators or gas/liquid separators. For example, the separator808or818can be a gas/liquid separator.

One or more ethylene recovery sections (including, for example, separations units and cryogenic units) can comprise a series of fractionation towers to separate and recover products. The cooling to condense each of the column overhead vapors can be provided by multiple ways. The lowest temperature required is to condense demethanizer overhead vapors. In some cases, the demethanizer overhead vapor is expanded and the chill is utilized to cool the incoming feed streams.

A recycle split vapor (RSV) process can be employed. An RSV process can comprise a full RSV (modified for the OCM plant) with a propylene refrigerant, or a full three-refrigerant system typical of an ethylene plant (methane refrigerant, ethylene refrigerant and propylene refrigerant, or use a mixed refrigerant composed of two or more of these refrigerants). In some cases, a combination of these two options (i.e. RSV or modified RSV combined with utilization of one or more of the three typical refrigeration systems) can be used to provide for the refrigeration duty to the OCM system separation section.

In natural gas processing plants or NGLs fractionation unit, methane can be separated from ethane and higher carbon-content hydrocarbons (conventionally called natural gas liquids or NGLs) to produce a methane-rich stream that can meet the specifications of pipelines and sales gas. Such separation can be performed using cryogenic separation, such as with the aid of one or more cryogenic units, and/or by implementing one of the gas processing technologies (e.g., RSV) for maximum or optimum recovery of the NGLs.

The raw natural gas fed to gas processing plants can have a molar composition of 70% to 90% methane and 4% to 20% NGLs, the balance being inert gas(es) (e.g., CO2and N2). The ratio of methane to ethane can be in the range of 5-25. Given the relatively large amount of methane present in the stream fed to cryogenic sections of gas processing plants, at least some or substantially all of the cooling duty required for the separation is provided by a variety of compression and expansion steps performed on the feed stream and the methane product stream. None or a limited portion of the cooling duty can be supplied by external refrigeration units.

There are various approaches for separating higher carbon alkanes (e.g., ethane) from natural gas, such as recycle split vapor (RSV) or any other gas processing technologies and/or gas sub-cooled process (GSP) processes, which may maximize the recovery of ethane (e.g., >99%, 98%, 97%, 96% or 95% recovery) while providing most or all of the cryogenic cooling duty via internal compression and expansion of portion of the natural gas itself (e.g., at least about 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 50%). However, the application of such approach in separating alkenes (e.g., ethylene) from an OCM product stream comprising methane is novel and may result in a limited recovery in some cases when inert gas in present (e.g., provide less than 95% recovery) of the alkene product, due at least in part to i) the different vapor pressure of alkenes and alkanes, and/or ii) the presence of significant amounts of H2in the OCM product stream, which can change the boiling curve and, particularly, the Joule-Thomson coefficient of the methane stream that needs to be compressed and expanded to provide the cooling duty. Hydrogen can display a negative or substantially low Joule-Thomson coefficient, which can cause a temperature increase or a substantially low temperature decrease in temperature when a hydrogen-reach stream is expanded.

In some embodiments, the design of a cryogenic separation system of an OCM-based plant can feature a different combination of compression/expansion steps for internal refrigeration and, in some cases, external refrigeration. The present disclosure provides a separation system comprising one or more cryogenic separation units and one or more demethanizer units. Such a system can maximize alkene recovery (e.g., provide greater than 95% recovery) from a stream comprising a mixture of alkanes, alkenes, and other gases (e.g., H2), such as in an OCM product stream.

In such separation system, the cooling duty can be supplied by a combination of expansion of the OCM effluent (feed stream to the cryogenic section) when the OCM effluent pressure is higher than a demethanizer column; expansion of at least a portion or all of the demethanizer overhead methane-rich stream; compression and expansion of a portion of the demethanizer overhead methane-rich stream; and/or external propane, propylene or ethylene refrigeration units.

FIGS. 9-12show various separation systems that can be employed with various systems and methods of the present disclosure, including small scale and world scale systems.FIG. 9shows a separation system900comprising a first heat exchanger901, a second heat exchanger902, a demethanizer903, and a third heat exchanger904. The direction of fluid flow is shown in the figure. The demethanizer903can be a distillation unit or multiple distillation units (e.g., in series). In such a case, the demethanizer can include a reboiler and a condenser, each of which can be a heat exchanger. An OCM effluent stream905is directed to the first heat exchanger901at a pressure from about 10 to 100 bar (absolute), or 20 to 40 bar. The OCM effluent stream905can include methane and C2+compounds, and may be provided in an OCM product stream from an OCM reactor (not shown). The OCM effluent stream905is then directed from the first heat exchanger901to the second heat exchanger902. In the first heat exchanger901and the second heat exchanger902, the OCM effluent stream905is cooled upon heat transfer to a demethanizer overhead stream906, a demethanizer reboiler stream907, a demethanizer bottom product stream908, and a refrigeration stream909having a heat exchange fluid comprising propane or an equivalent cooling medium, such as, but not limited to, propylene or a mixture of propane and propylene.

The cooled OCM effluent905can be directed to the demethanizer903, where light components, such as CH4, H2and CO, are separated from heavier components, such as ethane, ethylene, propane, propylene and any other less volatile component present in the OCM effluent stream905. The light components are directed out of the demethanizer along the overhead stream906. The heavier components are directed out of the demethanizer along the bottom product stream908. The demethanizer can be designed such that at least about 60%, 70%, 80%, 90%, or 95% of the ethylene in the OCM effluent stream905is directed to the bottom product stream908.

The demethanizer overhead stream906can contain at least 60%, 65%, 70%, 75%, or 80% methane. The overhead stream906can be expanded (e.g., in a turbo-expander or similar machine or flashed over a valve or similar device) to decrease the temperature of the overhead stream906prior to directing the overhead stream906to the second heat exchanger902and subsequently the first heat exchanger901. The overhead stream906can be cooled in the third heat exchanger904, which can be cooled using a reflux stream and a hydrocarbon-containing cooling fluid, such as, for example, ethylene.

The overhead stream906, which can include methane, can be recycled to an OCM reactor and/or directed for other uses, such as a natural gas pipeline. In some examples, the bottom product stream, which can contain C2+compounds (e.g., ethylene), can be directed to an ETL system.

FIG. 10shows another separation system1000that may be employed for use with systems and methods of the present disclosure. The direction of fluid flow is shown in the figure. The system1000comprises a first heat exchanger1001, demethanizer1002and a second heat exchanger1003. The demethanizer1002can be a distillation unit or multiple distillation units (e.g., in series). An OCM effluent stream1004is directed into the first heat exchanger1001. The OCM effluent stream1004can include methane and C2+compounds, and may be provided in an OCM product stream from an OCM reactor (not shown). The OCM effluent stream1004can be provided at a pressure from about 10 bar (absolute) to 100 bar, or 40 bar to 70 bar. The OCM effluent stream1004can be cooled upon heat transfer to a demethanizer overhead streams1005and1006from the second heat exchanger1003, a demethanizer reboiler stream1007, and a refrigeration stream having a cooling fluid comprising, for example, propane or an equivalent cooling medium, such as, but not limited to, propylene or a mixture of propane and propylene. In some cases, the demethanizer overhead streams1005and1006are combined into an output stream1012before or after passing through the first heat exchanger1001.

Subsequent to cooling in the first heat exchanger1001, the OCM effluent stream1004can be expanded in a turbo-expander or similar device or flashed over a valve or similar device to a pressure of at least about 5 bar, 6 bar, 7 bar, 8 bar, 9 bar, or 10 bar. The cooled OCM effluent stream1004can then be directed to the demethanizer1002, where light components (e.g., CH4, H2and CO) are separated from heavier components (e.g., ethane, ethylene, propane, propylene and any other less volatile component present in the OCM effluent stream1004). The light components are directed to an overhead stream1009while the heavier components (e.g., C2+) are directed along a bottoms stream1010. A portion of the overhead stream1009is directed to second heat exchanger1003and subsequently to the first heat exchanger1001along stream1006. A remainder of the overhead stream1009is pressurized (i.e., pressure is increased) in a compressor and directed to the second heat exchanger1003. The remainder of the overhead stream1009is then directed to a phase separation unit1011(e.g., distillation unit or vapor-liquid separator). Liquids from the phase separation unit1011are directed to the second heat exchanger1003and subsequently returned to the demethanizer1002. Vapors from the phase separation unit1011are expanded (e.g., in a turbo-expander or similar device) and directed to the second heat exchanger1003, and thereafter to the first heat exchanger along stream1005. The demethanizer1002can be designed such that at least about 60%, 70%, 80%, 90%, or 95% of the ethylene in the OCM effluent stream1004is directed to the bottom product stream1010.

FIG. 11shows another separation system1100that may be employed for use with systems and methods of the present disclosure. The direction of fluid flow is shown in the figure. The system1100comprises a first heat exchanger1101, a demethanizer1102, a second heat exchanger1103and a third heat exchanger1104. The system1100may not require any external refrigeration. The demethanizer1102can be a distillation unit or multiple distillation units (e.g., in series). An OCM effluent stream1105is directed to the first heat exchanger1101at a pressure from about 10 bar (absolute) to 100 bar, or 40 bar to 70 bar. In the first heat exchanger1101, the OCM effluent stream1105can be cooled upon heat transfer to demethanizer overhead streams1106and1107, a demethanizer reboiler stream1108and a demethanizer bottom product stream1109. In some cases, the demethanizer overhead streams1106and1107are combined into a common stream1115before or after they are passed through the first heat exchanger1101. The OCM effluent stream1105is then expanded to a pressure of at least about 5 bar, 6 bar, 7 bar, 8 bar, 9 bar, 10 bar, or 15 bar, such as, for example, in a turbo-expander or similar machine or flashed over a valve or similar device. The cooled OCM effluent stream1105is then directed to the demethanizer1102, where light components (e.g., CH4, H2and CO) are separated from heavier components (e.g., ethane, ethylene, propane, propylene and any other less volatile component present in the OCM effluent stream1105). The light components are directed to an overhead stream1110while the heavier components are directed along the bottom product stream1109. The demethanizer1102can be designed such that at least about 60%, 70%, 80%, 90%, or 95% of the ethylene in the OCM effluent stream1105is directed to the bottom product stream1109.

The demethanizer overhead stream1110, which can contain at least 50%, 60%, or 70% methane, can be divided into two streams. A first stream1111is compressed in compressor1112and cooled in the second heat exchanger1103and phase separated in a phase separation unit1113(e.g., vapor-liquid separator or distillation column). Vapors from the phase separation unit1113are expanded (e.g., in a turbo-expander or similar device) to provide part of the cooling duty required in heat exchangers1101,1103and1104. Liquids from the phase separation unit1113are sub-cooled in the third heat exchanger1104and recycled to the demethanizer1102. A second stream1114from the overhead stream1110can be expanded (e.g., in a turbo-expander or similar device) to decrease its temperature and provide additional cooling to the heat exchangers1101,1103and1104.

FIG. 12shows another separation system1200that may be employed for use with systems and methods of the present disclosure. The direction of fluid flow is shown in the figure. The system1200comprises a first heat exchanger1201, a demethanizer1202, and a second heat exchanger1203. An OCM effluent stream1204is directed to the first heat exchanger1201at a pressure from about 2 bar (absolute) to 100 bar, or 3 bar to 10 bar. The first heat exchanger1201can interface with a propane refrigeration unit1215and/or an ethylene refrigeration unit1216. In the first heat exchanger1201, the OCM effluent stream1204can be cooled upon heat transfer to demethanizer overhead streams1205and1206, a demethanizer reboiler stream, a demethanizer pump-around stream, and various levels of external refrigeration, such as using cooling fluids comprising ethylene and propylene. In some cases, the demethanizer overhead streams1205and1206are combined into a single stream1214before or after they are cooled. The cooled OCM effluent stream1204is then directed to the demethanizer1202, where light components (e.g., CH4, H2and CO) are separated from heavier components (e.g., ethane, ethylene, propane, propylene and any other less volatile component present in the OCM effluent stream1204). The light components are directed to an overhead stream1207and the heavier components are directed along a bottom product stream1208. The demethanizer1202can be designed such that at least about 60%, 70%, 80%, 90%, or 95% of the ethylene in the OCM effluent stream1204is directed to the bottom product stream1208.

The demethanizer overhead stream, which can contain at least about 50%, 60%, 70%, or 80% methane, can be divided into two streams. A first stream1213can be compressed in a compressor1209, cooled in the second heat exchanger1203and phase-separated in a phase separation unit1210(e.g., distillation column or vapor-liquid separator). Vapors from the phase separation unit1210can be expanded (e.g., in a turbo-expander or similar device) to provide part of the cooling duty required for the heat exchanger1201and1203. Liquids from the phase separation unit1210can be sub-cooled and flashed (e.g., over a valve or similar device), and the resulting two-phase stream is separated in an additional phase separation unit1211. Liquids from the additional phase separation unit1211are recycled to the demethanizer1202and vapors from the additional phase separation unit are mixed with expanded vapors from the phase separation unit1210prior to being directed to the second heat exchanger1203.

A second stream1212from the overhead stream1207can be expanded (e.g., in a turbo-expander or similar device) to decrease its temperature and provide additional cooling for the heat exchanger1201and1203. Any additional cooling that may be required for the second heat exchanger1203can be provided by an external refrigeration system, which may employ a cooling fluid comprising ethylene or an equivalent cooling medium.

In some cases, recycle split vapor (RSV) separation can be performed in combination with demethanization. In such a case, at least a portion of the overhead stream from a demethanizer unit (or column) may be split into at least two streams (see, e.g.,FIGS. 10-12). At least one of the at least two streams may be pressurized, such as in a compressor, and directed to a heat exchanger.

In some instances, the methane undergoes an OCM and/or ETL process to produce liquid fuel or aromatic compounds (e.g., higher hydrocarbon liquids) and contains molecules that have gone through methanation. In some embodiments, the compounds have been through a recycle split vapor (RSV) separation process. In some cases, alkanes (e.g., ethane, propane, butane) are cracked in a post-bed cracker.

It will be appreciated that systems and methods described herein are provided as examples and that various alternatives may be employed. It will be further appreciated that components of systems described herein are interchangeable. For instance, components for use in small scale production may be employed for use in world scale production, and vice versa.

Air Separation Units (ASU) and Power Production

An OCM reaction can convert a natural gas into a stream containing ethane, ethylene and other short olefins and alkanes, such as propene and propane. Unlike conventional (i.e., non-OCM) cracking-based production technologies for olefin production which may utilize energy to sustain the cracking reaction, the OCM process can generate power from the exothermic OCM reaction itself. Provided herein are systems and methods that can utilize the OCM reaction heat for steam generation, which in turn can be exploited for power generation.

In an OCM process, methane can react with an oxidizing agent such as oxygen over an OCM catalyst to generate ethylene. A wide set of competitive reactions can occur simultaneously over the OCM catalyst, including combustion of both methane and partial oxidations. Natural gas can be the source of methane, and can be combined with one or more recycle streams coming from downstream separation units (e.g., which can contain methane and ethane). Air, enriched air or pure oxygen can be used to supply the oxygen required for the reaction. All these reactions are exothermic and the relevant reaction heat can be recovered in order to cool the reactor effluent and feed the effluent to a downstream compressor, which can then send the effluent stream to downstream separation and recovery units.

Several process configurations can be adopted to enable the efficient recovery of the reaction heat. In some cases, the process utilizes the OCM reaction heat to i) supply the heat for the endothermic cracking reactions that convert the additional ethane feed to ethylene; and ii) generate steam to drive a downstream compressor. This process can achieve energy neutrality (no need for energy import or export to conduct the overall process), however it can require a relatively large number of unit operations which can lead to operational complexity, large capital costs and high pressure drops between the reactor outlet and the compressor suction. When the OCM process is combined with power generation, the integrated OCM-power process can be a simpler and more efficient process when compared to an individual OCM process and a separate power production unit producing the same amounts of ethylene and power.

This flexibility and synergy between olefin and power production can be exploited as a design feature and/or an operating feature. That is, the process configuration of an integrated OCM-power system can be designed in order to maximize ethylene production, or power production, or for any intermediate level of production of the two products. In the case of maximum ethylene production, the flow of the ethane stream injected into the OCM reactor can be maximized to conduct cracking reactions to the maximum allowable extent. If the OCM reactor is adiabatic, the maximum extent of cracking corresponds to designing the system to crack an amount of ethane that results in a decrease in temperature to the minimum viable temperature for cracking. In the case of maximum power production, the system can be designed for minimum ethane injection, which can be limited by the highest possible temperature at the outlet of the OCM reactor and, accordingly, the maximum amount of steam generation. The combined OCM-power system can be designed to operate at any level of power and olefin production in between these two constraints.

The same flexibility and synergy between ethylene and power production can be achieved at an operating level. For example, the combined OCM-power process can be designed to handle both the maximum olefin and the maximum power cases. In such cases, the plant operator has the ability to change the amount of ethylene and power production during operations by deciding at any given time the amount of ethane to be injected into the OCM reactor. This operating feature can be particularly advantageous for optimizing the financial performance of the plant once it is built because it can allow variation of the composition of the product portfolio at any given time based on the real time prices of the respective products.

An aspect of the present disclosure provides an oxidative coupling of methane (OCM) system for production of olefins and power. The system can include an OCM subsystem that takes as input a feed stream comprising methane (CH4) and a feed stream comprising an oxidizing agent such as oxygen, and generates a product stream comprising C2+compounds and heat from the methane and the oxidizing agent. The system can further include a power subsystem fluidically or thermally coupled to the OCM subsystem that converts the heat into electrical power.

The OCM subsystem can have at least one OCM reactor and at least one post-bed cracking unit within the OCM reactor or downstream of the OCM reactor. The post-bed cracking unit can be configured to convert at least a portion of alkanes in the product stream to alkenes. In some cases, the power subsystem has one or more turbines and can be a gas turbine combined cycle (GTCC). In some embodiments, the system further comprises a heat recovery steam generator (e.g., HRSG) for generating steam from the heat and the steam can be converted to electrical power in the power subsystem. In some instances, the power subsystem comprises a gas turbine and un-reacted methane from the OCM subsystem is converted to electrical power using the gas turbine.

Another aspect of the present disclosure provides a method for producing at least one C2+alkene and power. The method can include directing methane and an oxidizing agent into a reactor comprising a catalyst unit, where the catalyst unit comprises an oxidative coupling of methane (OCM) catalyst that facilitates an OCM reaction that produces C2+alkene. The method can include reacting the methane and oxidizing agent with the aid of the OCM catalyst to generate at least one OCM product comprising at least one C2+compound and heat. Electrical power can be generated from the heat.

In some cases, the heat is converted to steam and the steam is converted to power in a steam turbine. In some cases, un-reacted methane from the reactor is converted to electrical power in a gas turbine. In some instances, the reactor includes a cracking unit downstream of the catalyst unit, where the cracking unit generates C2+alkene from C2+alkane. The method can further include providing at least one hydrocarbon-containing stream that is directed through the cracking unit, which hydrocarbon-containing stream has at least one C2+alkane. At least one C2+alkane can be cracked to provide the at least one C2+alkene in a product stream that is directed out of the reactor. In some embodiments, the hydrocarbon-containing stream comprises at least one OCM product. The C2+alkene produced from the hydrocarbon-containing stream in the cracking unit can be in addition to the C2+alkene produced from the methane and the oxidizing agent in the reactor. In some embodiments, the amount of steam produced is varied or the amount of at least one hydrocarbon-containing stream that is directed through the cracking unit is varied to alter the amount of electrical power produced and the amount of C2+alkene produced.

FIG. 13shows an example of a HRSG system1300that may be employed for use as the HRSG507. The HRSG system1300comprises a gas turbine1301, HRSG1302, power generation unit1303and an air separation unit (ASU)1304. The system1300comprises streams1305,1306,1309and1310.

During use, the HRSG1302can transfer heat to a methane-containing stream (e.g., methane-containing stream505). Purge gas from an OCM process can be burned to compress air as feed to ASU unit1304. Additional high pressure steam may be provided along stream1306. Power generated by the power generation unit1303can be directed to an OCM system1307, an energy storage unit or power distribution system1308, and/or the ASU1304. The air separation unit accepts compressed air from the gas turbine1301and separates the compressed air to O2that is directed along stream1309and N2, which can be purged. The HRSG system1300further comprises a purge stream1305that is directed into the gas turbine, and a flue gas stream1310that is directed out of the HRSG1302.

FIG. 14shows an example of an OCM process for producing ethylene and power. Natural gas1402and in some cases, additional ethane1404, can be cleaned of sulfur-containing compounds in a de-sulfurization unit1406and fed into a process gas compressor1408. Carbon dioxide (CO2)1410can be removed in a process gas cleanup module1412and fed to the methanation reactor1426(connection not shown). The gas cleaned of CO2can be fed into a separations module1414where one or more product fractions1416can be isolated (e.g., C2, C3, C4+compounds).

Alkanes such as ethane can be recycled1418from the separations module to the OCM reactor1420, where they can be injected into the post-bed cracking region of the reactor to generate olefins from the alkanes. The alkane recycle stream1418can be heated in a heat exchanger or a heat recovery steam generator (HRSG)1422(for simplicity, connection to HRSG not shown).

Carbon monoxide1424from the separations module1414and carbon dioxide from module1412(connection not shown) can be fed into a methanation reactor1426along with hydrogen1424for conversion to methane. The methane recycle1428can be heated in the HRSG1422and returned to the OCM reactor1420.

The HRSG can provide high-pressure steam1430to a steam turbine1432to produce power1434. The steam and energy to heat the steam can be sourced from any suitable part of the process including from the OCM reactor1436. Additional sources of steam and/or heat can include from combustion of fuel gas1438provided from the separations module, from the exhaust1440from a gas turbine1445, and/or from cooling the effluent from the OCM reactor1420(not shown). Additional fuel gas1450can be provided to the gas turbine1445. The gas turbine can produce electrical power1455and can drive a compressor (e.g., on the same shaft with the power generator) to supply compressed air1460for an air separation unit (ASU)1465or a vacuum pressure swing adsorption (VPSA) unit to supply oxygen to the OCM reactor1420.

The combined OCM-power process shown inFIG. 14can have numerous advantages over processes without power integration (e.g.,FIGS. 26-31). For example, the total number of unit operations can be lower due to the heat recovery section of the combined cycle GTCC (that recovers the heat from the gas turbine exhaust) being utilized for OCM-related services, thus making a feed-product exchanger and a steam superheater redundant. The lower number of unit operations can lead to lower capital cost and operational simplicity. The pressure drop from the OCM reactor outlet to the compressor suction can be reduced by up to 2 bar due to the elimination of two large heat exchangers when integrating OCM with power production. The reduced pressure drop can leads to an increased process efficiency (due to the lower power consumption in compressors) and a lower capital cost (due to the smaller size of the compressors).

Oxidizing Agents

An OCM process requires the presence of an oxidizing agent. The oxidizing agent can be oxygen supplied from air fed to the reactor. In some cases the oxidizing agent can be pure oxygen, supplied by pipeline or recovered from air. In some cases oxygen can be separated from air by cryogenic distillation, as in an Air Separation Unit. In some cases, various membrane separation technologies can be applied to generate an oxygen rich stream. In certain cases, the oxygen stream can be produced by a pressure swing adsorption (PSA) unit or a vacuum pressure swing adsorption (VPSA) unit. In certain cases, while using air as the oxidizing agent, a nitrogen recovery unit (NRU) can be used to reduce the nitrogen content in the OCM reactor system. See, e.g., U.S. patent application Ser. No. 13/739,954 and U.S. patent application Ser. No. 13/936,870, which are entirely incorporated herein by reference.

Systems and methods of the present disclosure can be used to convert both methane and ethane to ethylene, in some cases along with some co-products and by-products. Ethane can be fed directly into a post-bed cracker (PBC), which can be a portion of an OCM reactor downstream of the OCM catalyst, where the heat generated in the OCM reaction can be used to crack the ethane to ethylene. As an alternative, the PBC can be a unit that is separate from the OCM reactor and in some cases in thermal communication with the OCM reactor. The ethane feed stream to the OCM reactor can include (a) ethane recycled to the OCM reactor from an OCM reactor effluent stream, which can be separated in at least one downstream separation module and recycled to the OCM reactor, (b) ethane present in other feed streams (e.g., natural gas), which can be separated in at least one separation module and recycled to the OCM reactor, and (c) any additional (i.e., fresh) ethane feed.

The maximum amount of ethane that can be converted in the PBC can be limited by the flow rate of material exiting the OCM catalyst and/or its temperature. It can be advantageous to utilize a high proportion of the maximum amount of PBC. In some cases, the amount of ethane converted to ethylene is about 50%, about 60%, about 70%, about 80%, about 85%, about 90%, about 95%, or about 99% of the maximum amount of ethane that can be converted to ethylene in the PBC. In some instances, the amount of ethane converted to ethylene is at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, or at least about 99% of the maximum amount of ethane that can be converted to ethylene in the PBC.

Achieving a high proportion (e.g., greater than or equal to about 60%, 70%, or 80%) of the maximum PBC capacity can be accomplished by adding natural gas to the system, which can have a concentration of ethane that depends on many factors, including the geography and type and age of the natural gas well. The treatment and separation modules of the OCM process described herein can be used to purify the OCM effluent, but can be used to treat (e.g., remove water and CO2) and purify the natural gas that is added to the system along with the OCM effluent, such as, e.g., by separating C2+compounds from methane and separating ethane from ethylene. In some cases, ethane contained in the natural gas feed can be recycled to the OCM reactor (e.g., PBC region) as pure ethane and the system may not be sensitive to the purity and composition of the natural gas, making raw natural gas a suitable input to the system.

The maximal PBC capacity can depend on the ratio between methane and ethane in the input to the OCM reactor, including in some instances the PBC portion. In some cases, the PBC capacity is saturated when the molar ratio of methane to ethane is about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, or about 15. In some cases, the PBC capacity is saturated when the molar ratio of methane to ethane is at least about 1, at least about 2, at least about 3, at least about 4, at least about 5, at least about 6, at least about 7, at least about 8, at least about 9, at least about 10, at least about 11, at least about 12, at least about 13, at least about 14, or at least about 15. In some cases, the PBC capacity is saturated when the molar ratio of methane to ethane is at most about 5, at most about 6, at most about 7, at most about 8, at most about 9, at most about 10, at most about 11, at most about 12, at most about 13, at most about 14 or at most about 15. In some cases, the PBC capacity is saturated when the molar ratio of methane to ethane is between about 7 and 10 parts methane to one part ethane.

Natural gas (raw gas or sales gas) can have a concentration of ethane of less than about 30 mol %, 25 mol %, 20 mol %, 15 mol %, 10 mol %, 9 mol %, 8 mol %, 7 mol %, 6 mol %, 5 mol %, 4 mol %, 3 mol %, 2 mol % or 1 mol %. In some cases, natural gas has a methane to ethane ratio greater than about 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1 or 40:1. The ethane skimmer implementation of OCM described herein can be used to inject more natural gas feed into the system than what may be required to produce the desired or predetermined amount of ethylene. The excess methane can be drawn from a stream downstream of the methanation unit and sold as sales gas (which may lack an appreciable amount of ethane but can still meet pipeline specifications and/or can be directed to a power plant for power production). The ethane in the additional natural gas feed can be used to saturate the PBC capacity. Any excess ethane can be drawn from the C2splitter and exported as pure ethane. The ethane skimmer implementation described herein can result in additional product streams from the OCM system (namely sales gas and natural gas liquids). In such a case, the OCM process can be used to achieve both ethylene production and natural gas processing.

The ethane skimmer implementation can be readily understood by reference toFIG. 15(showing additional ethane feed to saturate PBC) andFIG. 16(showing the ethane skimmer implementation). InFIG. 15, at least some or most (e.g., >70%, >80%, >85%, >90%, >95%, or >99%) of the methane in the natural gas (NG) feed1500ends up in the methane recycle1505, at least some or most (e.g., >70%, >80%, >85%, >90%, >95%, or >99%) of the ethane in the NG feed ends up in the ethane recycle stream1510, at least some or most (e.g., >70%, >80%, >85%, >90%, >95%, or >99%) propane in the NG feed ends up in the C3mixed products stream (e.g., Refinery Grade Propylene (RPG))1515, at least some or most (e.g., >70%, >80%, >85%, >90%, >95%, or >99%) of the C4+in the NG feed ends up in the C4mixed stream1520, and ethane is added 1525 up to the point where the PBC cracking capacity1530is saturated or nearly saturated (e.g., >70%, >80%, >85%, >90%, >95%, or >99%). In contrast, in the ethane skimmer implementation (FIG. 16), some of the methane (any proportion) can end up in a sales gas stream1600and if there is excess ethane, it can end up in an ethane product stream1605. The ethane skimmer implementation does not require a separate (i.e., fresh) ethane stream to saturate or nearly saturate the PBC capacity of the system.

Gas Processing Plants

An OCM process for generating olefins (e.g., ethylene) can be a standalone process, or it can be integrated in other processes, such as non-OCM processes (e.g., NGL process).FIG. 17shows a system1700comprising an existing gas plant1701that has been retrofitted with an OCM system1702(or with an OCM-ETL system for the production of other olefins (e.g., propylene)). A raw natural gas (NG) feed1703is directed into the existing gas plant1701, which comprises a treatment unit1704, NGL extraction unit1705, compression unit1706and fractionation unit1707. The NGL extraction unit1705can be a gas processing unit that can use a gas processing recovery technology such as a recycle split vapor (RSV) technology or other technologies. The NGL extraction unit1705can be a demethanizer unit, optionally a demethanizer unit incorporated with a recycle split vapor (RSV) retrofit or standalone unit. The treatment unit1704can remove water, H2S and CO2from the NG feed1703and direct natural gas to the NGL extraction or processing unit1705. The NGL extraction unit1705can remove NGLs (e.g., ethane, propane, butane, etc.) from methane and direct methane (with some traces of NGLs and inert gas) to the compression unit1706along fluid stream1708. NGLs or C2+components can be directed to fractionation unit1707. At least a portion or almost all of the methane (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 99%) from the fluid stream1708is directed along stream1709to an OCM reactor1710of the OCM system1702. This integration of an OCM system (in some other cases OCM-ETL system) with an existing natural gas processing or NGLs extraction plant can improve the recovery of olefin/s production by implementing one of the gas processing technologies (e.g., RSV). This integration is suitable for a small scale and world scale olefin production (e.g., ethylene production).

With continued reference toFIG. 17, the compression unit1706compresses methane in the fluid stream1708and directs compressed methane to a methanation system1711, which converts any CO, CO2and H2in the fluid stream1708to methane, which is then directed to natural gas pipeline1712for distribution to end users. In some cases, the methanation outlet stream can be treated to remove water (not shown). The dryer system can consist one or more of the following. A bed or multiple desiccant (molecular sieve) beds, separator vessels to condense and separate the water.

The NGLs extraction unit1705can extract C2+compounds from the NG feed1703. NGLs or C2+compounds from the NGL extraction unit1705are directed to the fractionation unit1707, which can be a distillation column. The fractionation unit1707splits the C2+compounds into streams comprising various C2+compounds, such as a C2stream along with C3, C4and C5streams. The C2stream can be directed to a C2splitter1713(e.g., distillation column), which separates ethane from ethylene. Ethane is then directed along stream1714to a post-bed cracking (PBC) unit1715of the OCM system1702. In some cases, C3and/or C4compounds can be taken from the C2splitter1713and fed into a downstream region of a post-bed cracking (PBC) reactor for olefin production. In some situations, C4and/or C5streams can be directed to a C4or C5splitter (e.g., a distillation column), which, for example, separate iso-butane (iC4) from normal butane (nC4) and/or separate iso-pentane (iC5) from normal pentane (nC5). In some situations, other alkanes, such as propane and butane, can be directed to the PBC unit1715.

In the OCM system1702, methane from the stream1709and oxygen along stream1716are directed to the OCM reactor1719. The OCM reactor1710generates an OCM product (or effluent) stream comprising C2+compounds in an OCM process, as discussed elsewhere herein. C2+alkanes (e.g., ethane) in the product stream, as well as C2alkanes in the stream1714, may be cracked to C2+alkenes (e.g., ethylene) in the PBC unit1715downstream of the OCM reactor1710. The product stream is then directed to a condenser1717, which removes water from the product stream. The product stream is then directed to a compression unit1718and subsequently another compression unit1719. Methane from the compression unit1719is directed to the NG feed1703along stream1720.

The OCM system1702can include one or more OCM reactor1710. For example, the OCM reactor1710can be an OCM reactor train comprising multiple OCM reactors. The OCM system1702can include one or more PBC reactors1715.

The compression units1718and1719can each be a multistage gas compression unit. Each stage of such multistage gas compression unit can be followed by cooling and liquid hydrocarbon and water removal.

Ethylene Plants

In an aspect, the present disclosure provides a method for producing C2+compounds by performing an oxidative coupling of methane (OCM) reaction to produce an OCM effluent comprising methane (CH4), hydrogen (H2), carbon dioxide (CO2), ethylene (C2H4) and C2+compounds. The OCM effluent can be separated into a first stream comprising C2+compounds and a second stream comprising CH4, CO2, and H2. The second stream can be methanated to produce a first OCM reactor feed comprising additional CH4formed from the CO2and the H2in the second stream. A third stream can be methanated to produce a second OCM reactor feed comprising CH4. The third stream can comprise CH4and H2from demethanizer off-gas from an ethylene cracker. The first and second OCM reactor feeds can then be provided to the OCM reaction.

In some embodiments, the second stream and the third stream are methanated in a single methanation reactor. The method can further comprise providing the first stream to the separation section of the ethylene cracker. The ethylene cracker can be an existing ethylene cracker, which may be present prior to retrofitting with an OCM reactor and additional unit operations. The separation section may be evaluated for available capacity to process the additional feed. In some cases, the cracker operation can be modified to operate at a lower severity, hence making some additional capacity available in the existing separation section, especially C1, C2and C3area. In some cases, the first stream is provided to a gas compressor or a fractionation unit of the ethylene cracker. In some embodiments, the third stream is the overhead stream of a demethanizer of the ethylene cracker. In some cases, separation is performed in a pressure swing adsorption (PSA) unit. In some embodiments, the OCM effluent is compressed prior to separating in the PSA unit. In some cases, the separation section also includes, but is not limited to, a CO2removal system, which typically includes an amine system or a caustic tower and/or dryers to remove water from the OCM effluent.

The method can further comprise feeding oxygen (O2) to the OCM reaction. In some cases, the OCM effluent further comprises carbon monoxide (CO) and the CO is converted into CH4in operation (c). In some instances, the third stream further comprises CO2or CO. The OCM reaction can further react additional CH4from external supply of natural gas. In some embodiments, the third stream further comprises CH4.

In another aspect, the present disclosure provides an oxidative coupling of methane (OCM) system for production of C2+compounds. The system can comprise an OCM subsystem that (i) takes as input a feed stream comprising methane (CH4) and a feed stream comprising an oxidizing agent, and (ii) generates a product stream comprising C2+compounds from the CH4and the oxidizing agent. The system can further comprise a separation subsystem fluidically coupled to the OCM subsystem that separates the product stream into (i) a first stream comprising C2+compounds and (ii) a second stream comprising methane (CH4) hydrogen (H2) and carbon dioxide (CO2) and/or carbon monoxide (CO). The system can further comprise a methanation subsystem fluidically coupled to the second stream and to the OCM subsystem, wherein the methanation subsystem converts H2and CO2and/or CO into CH4. The system can further comprise an ethylene cracker subsystem fluidically coupled to the methanation subsystem that provides additional CH4and H2to the methanation subsystem.

In some embodiments, the methanation subsystem provides CH4for the OCM subsystem. The additional CH4and H2can be derived from the demethanizer overhead of the ethylene cracker subsystem. The first stream comprising C2+components can be fluidically coupled to the ethylene cracker subsystem. The first stream can be fractionated in the ethylene cracker subsystem. The separation subsystem can include a pressure swing adsorption (PSA) unit.

In some instances, the OCM subsystem is supplied additional CH4from a natural gas feed stream. In some cases, the oxidizing agent is O2(e.g., provided by air from an air separation unit or any other type of oxygen concentration unit).

In some embodiments, the OCM subsystem comprises at least one OCM reactor. In some instances, the OCM subsystem comprises at least one post-bed cracking unit within the at least one OCM reactor or downstream of the at least one OCM reactor, which post-bed cracking unit is configured to convert at least a portion of alkanes in the product stream to alkenes. In some cases, the reactor is adiabatic. In some instances, the post-bed cracking unit uses ethane and propane recycle streams from the existing Ethylene cracker subsystem to achieve conversion to ethylene. In some cases, the recycle streams are routed to the cracking furnaces to completely crack the recycle streams.

FIG. 18shows an example of an OCM process integrated with an existing ethylene cracker. The OCM reactor1800takes in methane and oxygen1802and produces an OCM effluent1805having CO2, CH4and C2H4, in some cases amongst other components, such as H2and CO. The OCM reaction can be exothermic and can produce steam1807. The OCM effluent1805can be compressed in a compressor1810and fed into a pressure swing adsorption (PSA) unit1815.

The PSA unit can produce an overhead stream1820that can include H2, CH4, CO2and CO. The overhead stream can be fed into a methanation subsystem1822(e.g., methanation reactor) to provide methane for the OCM reactor1800. Additional methane can be provided by way of a natural gas stream1824.

The process ofFIG. 18further includes an existing ethylene cracker1830with a demethanizer off gas stream. Demethanizer off gas from the existing ethylene cracker1830subsystem can supply additional CH4and H2that may be required for methanation. Methane generated in the ethylene cracker1830can be returned to the OCM reactor1800via stream1826.

Heavier components can exit the PSA separately1825and include ethane, ethylene and C3+compounds, which can be fractionated using existing separations capacity in the ethylene cracker1830. The heavy components can be processed in the fractionation towers of the ethylene cracker, optionally first being compressed in the existing process gas compressor of the ethylene cracker. In some cases, the heavy components stream can be routed to the CO2removal unit of the existing ethylene cracker subsystem to meet the CO2specification.

In processes, systems, and methods of the present disclosure, a Fischer-Tropsch (F-T) reactor can be used to replace a methanation reactor, for example in a methane recycle stream. CO and H2, such as that found in a methane recycle stream, can be converted to a variety of paraffinic linear hydrocarbons, including methane, in an F-T reaction. Higher levels of linear hydrocarbons, such as ethane, can improve OCM process efficiency and economics. For example, effluent from an OCM reactor can be directed through a cooling/compression system and other processes before removal of a recycle stream in a de-methanizer. The recycle stream can comprise CH4, CO, and H2, and can be directed into an F-T reactor. The F-T reactor can produce CH4and C2+paraffins for recycling into the OCM reactor. A range of catalysts, including any suitable F-T catalyst, can be employed. Reactor designs, including those discussed in the present disclosure, can be employed. F-T reactor operation conditions, including temperature and pressure, can be optimized. This approach can reduce H2consumption compared to a methanation reactor.

The combination of a new OCM unit and an existing ethylene cracker is expected to have certain synergistic benefits. In some cases, prior to retrofit of an ethylene cracker with OCM, the entire overhead from the existing demethanizer was being used as fuel gas, and can now be available as one of the feeds to the methanation unit. In some cases, the demethanizer overhead off-gas comprises up to 95% methane which can be converted to Ethylene in the OCM reactor, hence increasing the total ethylene capacity. In some cases, the hydrogen content in the existing demethanizer overhead is substantial, and may be enough to meet the hydrogen requirement of the methanation unit.

In some cases, retrofitting an ethylene cracker with OCM reduces (or allows for reduction of) the severity of cracking in the existing cracker, enabling value addition by increasing the production of pyrolysis gasoline components in the cracker effluent, as the OCM reactor produces the ethylene needed to achieve the total system capacity. The cracker can then be operated on high propylene mode to produce more propylene and at the same time meeting the ethylene production rate by the new OCM unit. This retrofit can result in greater flexibility for the ethylene producer with respect to the existing cracker operation.

In some instances, the overall carbon efficiency is increased as the methane and hydrogen from the existing demethanizer off-gases can be utilized to convert the carbon dioxide and carbon monoxide to methane, which is fed to the OCM reactor.

In some instances, ethane and/or propane recycle streams from the existing cracker can be routed to the OCM unit (e.g., instead of the cracking furnaces). These recycle streams are typically routed to the cracking furnaces where they are “cracked to extinction.” The advantage over routing the recycle streams to OCM over the cracking furnace is higher selectivity to ethylene in the OCM process.

Purge gas from the OCM-methanation system can (at least partially) meet the fuel gas requirements of the existing cracker complex. In some cases, the fuel requirements are met by the existing demethanizer off-gas.

Additional capacity (e.g., for ethylene, propylene or pyrolysis gasoline components) can be gained by integrating an OCM unit and supplying additional natural gas feed to the OCM reactor unit which will increase ethylene production, and the existing cracker can be operated at a reduced severity and/or increased throughput to produce more olefin and/or pyrolysis gas components. Additional fractionation equipment can be used to recover ethylene, for example, if the existing separations section does not have sufficient capacity, or if the existing cracker is operated at a substantially higher throughput than it was built for.

With regard to the present disclosure allowing for reduced severity of cracking, a cracking furnace can thermally crack the hydrocarbon feed comprising of a full range naphtha, light naphtha, ethane, propane or LPG feed to produce ethylene and propylene, along with pyrolysis gas oil, fuel oil and a methane-rich off-gas. The product mix can depend on the feed composition and the process operating conditions. Important process variables can include steam to hydrocarbon ratio (which can vary from 0.3 for ethane and propane feed, And 0.5 for naphtha feed and as high as 0.7 for light vacuum gas oil feeds), temperature (which can vary from 750-850° C.), and the residence time (which can vary, typically in the range of 0.1 to 0.5 seconds). The cracking reaction is favored by low hydrocarbon partial pressure and hence steam can be added to reduce the hydrocarbon partial pressure. Higher steam to hydrocarbon ratio can improve selectivity at the cost of more energy. Severity is the extent or the depth of cracking, with higher severity achieved by operating the cracking furnace at a higher temperature. High severity operation yields more ethylene, and also results in higher rate of coke formation and hence a reduced time between decoking. As the cracking severity is reduced, the yield of ethylene and lighter components decreases and the yield of propylene and heavier components increases. For liquid feeds, severity is measured as the weight ratio of propylene to ethylene in the cracked gases. For gaseous feeds, severity is measured as percentage conversion (mass) of the key components (e.g., percentage disappearance of ethane or propane). The cracking furnace can be operated to maximize ethylene or propylene, depending on the economics and demand. Another process variable in cracker operation is the coil outlet pressure (COP) which is the pressure at the outlet of furnace coils. Low absolute pressure improves selectivity and the pressure is usually kept at about 30 psia for gaseous feeds and 25 psia for liquid feeds.

For example, the influence of pyrolysis temperature can be isolated by keeping the residence time and steam content constant. As the furnace exit temperature increase, ethylene yield also rises, while yields of propylene and pyrolysis gasoline decrease. At very high temperature, residence time can become the controlling factor. Highest ethylene yields can be achieved by operating at high severity (e.g., about 850° C.), with residence time ranging from 0.2 to 0.4 seconds.

There are numerous ways that the synergies between an OCM unit and an existing ethylene cracker can be realized. Depending on the desired product cut, the OCM unit can significantly increase the flexibility of operation and provide additional capacity gain at a lower incremental cost. Based on the existing plant operation, the desired product spectrum and natural gas availability, integrating an OCM unit with an existing ethylene plant (e.g., naphtha cracker or gas cracker) can offer considerable benefits including:

In some cases, natural gas is more economical than naphtha for converting to ethylene and propylene. Integration with OCM can provide the plant the flexibility to operate with a different feedstock at desired severity. In some cases, the integrating with OCM gives an operational flexibility, to operate at the desired throughput and feed mix depending on the option that makes best economic sense for the operator.

Installing more cracking capacity to an existing cracker can require the entire train of process units to be debottlenecked (e.g., quench, gasoline fractionation, compression, refrigeration, and recovery unit). In contrast, gaining capacity by integrating with OCM can result in minimum impact on the existing process unit debottlenecking. For example, since the OCM reaction is highly selective to ethylene (e.g., greater than 50%), there can be a minimum impact on the rest of the system (e.g., especially the hot section and C3+handling unit).

The OCM reaction is highly exothermic and the high heat of reaction can be put to multiple uses. It may be used to crack more ethane (e.g., from the ethane and propane recycle streams of the existing cracker) to further improve conversion to ethylene. The heat of reaction may also be used to generate steam which can be used to meet process requirements or generate power. The OCM unit can be a net exporter of steam and/or power.

Pyrolysis Process Retrofit with OCM

In an OCM process, methane (CH4) reacts with an oxidizing agent over a catalyst bed to generate C2+compounds. The OCM process produces olefins, such as ethylene, and can add to or replace olefin production from a pyrolysis process (e.g., ethane cracking or naphtha cracking). In some cases, a low price natural gas feedstock (used by the OCM process) makes the retrofit to the cracker (which uses expensive feedstock such as naphtha or ethane) an attractive and economical process.

FIG. 19illustrates how a cracker1932can be retrofitted (integrated) with the OCM process. Various unit operations between the blocks and columns are not shown for the purposes of simplification of the drawing. With reference toFIG. 19, the integrated process uses OCM effluent1900from an OCM reactor1902(containing C1, and C2+type hydrocarbons) that utilize a separation train downstream of the cracker1932to produce olefins1904, such as ethylene and propylene. Natural gas1934is fed into the OCM reactor, along with a source of O21936(e.g., air or enriched oxygen). The natural gas can be de-sulfurized in a sulfur removal unit1938.

A lean oil absorber1906using light or heavy pyrolysis gas from the cracker, or any oil stream containing hydrocarbons in the C5to C10range from refining and/or natural gas processing plants, can be used to separate the C1from the C2+hydrocarbons and uses all or some of the unit operations downstream of the quench tower1908of a typical cracker for the cleaning and separations of the hydrocarbons.

The OCM effluent to the process gas compressor (PGC)1910compresses the gas to a pressure between 200-800 psia. Water present in the OCM effluent can be removed. A mole sieve drier is a non-limiting example of a process that may remove water from the system, but any conventional water removal system can be used in this system. The effluent is then cooled to between 50° F. and −80° F., in some cases between −20° F. to −60° F., (depending on C2+purity required by the cracker) and sent to lean oil absorber column1906.

The lean oil absorber1906can run with both a light pyrolysis gas (such as C5+pyrolysis gas) obtained from the quench tower of a typical cracker1912and also a heavy pyrolysis gas (such as C7+pyrolysis gas)1914typically obtained from the heavies fractionator, such as a de-butanizer, de-pentanizer, or gasoline stripper of a cracker, or gasoline from the aromatics extraction plant (either raffinate/light pyrolysis gasoline or the heavy pyrolysis gasoline stream).

The absorber can operate with 40-100 stages, 200-800 psia, and −80° F. to 50° F., providing C2recovery of 75%-100%. The ratio of the lbs of C1/lb ethylene from the bottoms of the absorber can be between 1.0-3.0 lbs C1/lb ethylene depending on the conditions used in the absorber. The lean oil losses in the process are as low as 0.0004-0.001 wt % of lean oil. The ratio of lean oil to OCM effluent is between 0.5-5.5 on a mass basis.

The rich C2+stream can then be sent to the PGC of the cracker1916, treated and separated to produce olefins, such as ethylene. For example, the rich oil can be fed to the compressor's third stage discharge drum, where it can flash lights into the fourth stage suction, while the heavies can be sent to the second stage suction for further recovery of lights. Eventually the oil can be recovered in the Quench tower1980and sent back to the lean oil absorber. Alternatively, the rich oil can be sent to a new stripping column, with the lights then sent to the appropriate suction drum of the PGC.

If the constraints of the cracker are such that a purer C2spec is required or if the demethanizer of the cracker is constrained by methane removal capacity, a C1/C2fractionator1918can be added to recover 60-100% of the methane from the overhead of the fractionator with a much purer C2+stream sent to the either the demethanizer or the deethanizer of the cracker. The C2+can then be separated in the separations train to produce olefins and the C1sent back to the OCM as recycle C11920. Depending on the CO2concentration from the C1/C2fractionator, a caustic wash can be used or the C2+sent to the gas treating section for CO2removal.

The C1/C2fractionator can run between 200-800 psia, and provide 99.0-99.9% recovery of the methane from the C2+stream. This can be sent to gas treating1922before separations1924and/or the demethanizer and/or the deethanizer in the cracker depending on the concentration of CO2and C1in the C2+stream from the fractionator.

Refrigeration power can also be recovered from the C1recycle stream to the OCM depending on the conditions at which the absorber and OCM are running. Refrigeration power anywhere between 0.1 kilowatts (KW)/pound ethylene to 1 KW/pound ethylene can be recovered.

The CO21926from the overhead of either the absorber or the fractionator can be sent to a methanation unit1928in which the CO2and CO react with the H2in the presence of a catalyst to form CH4and recycled back to the OCM reactor.

Natural gas produced in the demethanizer of the cracker train can be sent back to the OCM unit to the methanation section. The H2content in the recycle stream can be methanated in the presence of CO2and CO in the methanation reactor and sent to the OCM reactor as feed natural gas.

The OCM process also produces a purge stream1930, with a heating value in the range of 800 BTU/SCF to 1000 BTU/SCF that can be used as fuel gas, make-up or otherwise. Additional natural gas may also be fed to the cracker furnace through streams1920before methanation of the C1recycle, or stream1944after methanation (such as, e.g., depending on cracker requirements), to provide fuel gas since the fuel oil is utilized in a more efficient manner of producing olefins. The present example shows how olefins1904can be produced from both natural gas1934and cracker feed1940(e.g., as shown inFIG. 19).

In some cases, the cracker1932generates ethane in addition to olefins. The ethane can be recycled to an ethane conversion section of the OCM reactor1902for conversion to olefins.

Control Systems

The present disclosure provides computer control systems that can be employed to regulate or otherwise control OCM methods and systems provided herein. A control system of the present disclosure can be programmed to control process parameters to, for example, effect a given product distribution, such as a higher concentration of alkenes as compared to alkanes in a product stream out of an OCM reactor.

FIG. 20shows a computer system2001that is programmed or otherwise configured to regulate OCM reactions, such as regulate fluid properties (e.g., temperature, pressure and stream flow rate(s)), mixing, heat exchange and OCM reactions. The computer system2001can regulate, for example, fluid stream (“stream”) flow rates, stream temperatures, stream pressures, OCM reactor temperature, OCM reactor pressure, the quantity of products that are recycled, and the quantity of a first stream (e.g., methane stream) that is mixed with a second stream (e.g., air stream).

The computer system2001includes a central processing unit (CPU, also “processor” and “computer processor” herein)2005, which can be a single core or multi core processor, or a plurality of processors for parallel processing. The computer system2001also includes memory or memory location2010(e.g., random-access memory, read-only memory, flash memory), electronic storage unit2015(e.g., hard disk), communication interface2020(e.g., network adapter) for communicating with one or more other systems, and peripheral devices2025, such as cache, other memory, data storage and/or electronic display adapters. The memory2010, storage unit2015, interface2020and peripheral devices2025are in communication with the CPU2005through a communication bus (solid lines), such as a motherboard. The storage unit2015can be a data storage unit (or data repository) for storing data.

The CPU2005can execute a sequence of machine-readable instructions, which can be embodied in a program or software. The instructions may be stored in a memory location, such as the memory2010. Examples of operations performed by the CPU2005can include fetch, decode, execute, and writeback.

The storage unit2015can store files, such as drivers, libraries and saved programs. The storage unit2015can store programs generated by users and recorded sessions, as well as output(s) associated with the programs. The storage unit2015can store user data, e.g., user preferences and user programs. The computer system2001in some cases can include one or more additional data storage units that are external to the computer system2001, such as located on a remote server that is in communication with the computer system2001through an intranet or the Internet.

The computer system2001can be in communication with an OCM system2030, including an OCM reactor and various process elements. Such process elements can include sensors, flow regulators (e.g., valves), and pumping systems that are configured to direct a fluid.

Methods as described herein can be implemented by way of machine (e.g., computer processor) executable code stored on an electronic storage location of the computer system2001, such as, for example, on the memory2010or electronic storage unit2015. The machine executable or machine readable code can be provided in the form of software. During use, the code can be executed by the processor2005. In some cases, the code can be retrieved from the storage unit2015and stored on the memory2010for ready access by the processor2005. In some situations, the electronic storage unit2015can be precluded, and machine-executable instructions are stored on memory2010.

EXAMPLES

Below are various non-limiting examples of uses and implementations of OCM catalysts and systems of the present disclosure.

Example 1: Implementation of OCM

About 1,000,000 metric tons/year of polymer grade ethylene is produced via the oxidative coupling of methane (OCM). The OCM reactor comprises a 2-stage adiabatic axial fixed bed that utilizes an OCM catalyst (e.g., nanowire catalyst) to convert methane and high purity oxygen to ethylene. The methane feed to the OCM reactor is the recycle stream from a downstream demethanizer over-head supplemented by CO and CO2conversion to methane in a two-stage methanation reactor. The hot OCM effluent from a second stage of the reactor effluent is mixed with heated recycle ethane from a downstream C2splitter and cracked to convert ethane primarily into ethylene. Hot reactor effluent is used to heat OCM reactor feed, generate high-pressure steam and heat process condensate. Cold reactor effluent is compressed and mixed with sulfur-free pipeline natural gas and treated to remove CO2and H2O prior to cryogenic separations. The treated process gas is fed to a demethanizer column to recover about 99% of ethylene as column bottoms stream. Demethanizer bottoms steam is separated in deethanizer column to separate C2's from C3+components. Deethanizer column overhead is first treated in selective hydrogenation unit to convert acetylene into ethylene and ethane using H2from a Pressure Swing Adsorption (PSA) Unit. The resulting stream is separated in a C2splitter unit to separate ethylene from ethane. Deethanizer bottoms stream is sent to a De-propanizer to obtain Refinery Grade Propylene (RGP) and mixed C4+stream, both which can be sold for credit. Ethane product stream from C2splitter bottoms is recycled to second stage of the OCM reactor to complete extinction. Polymer grade ethylene product (99.96 wt % ethylene) obtained from the C2splitter overhead is compressed to 1,000 psig and exported as vapor product. A stream factor of 0.95 is used (equal to an installed capacity of 1,059,000 metric tons/yr).

The OCM process generates superheated high pressure (˜1500 psia) steam that is used to run process gas compressors, refrigeration compressors, ethylene heat pump/product compressors, and major pumps. The remainder of the steam and small portion of recycle methane (purge gas) can be exported to combined cycle/gas turbine system to generate power. The OCM process has an energy intensity of −0.89 MMBTU/MT ethylene, while the energy intensity of a comparably sized steam cracking of ethane process is about 31.89 MMBTU/MT.

The reactor consists of a 2-stage adiabatic axial fixed bed with intermediate heat recovery via high-pressure steam generation. The methane stream recycled from the demethanizer overhead becomes the main OCM reactor feed. In both stages high purity oxygen is mixed with the hydrocarbon stream in a proportion of approximately 1:10 on a molar basis to achieve the optimal O2-limited composition for the OCM reaction.

In the OCM reactor, the catalyst enables the partial and highly selective conversion of methane to, primarily, ethylene and ethane, with minor amounts of propylene and propane. Non-selective pathways include high temperature hydrocarbon reactions, such as combustion, reforming and shift. The second stage of the reactor is designed to accommodate an ethane conversion zone immediately downstream of the catalytic bed. Ethane recycled from the deethanizer and, optionally, additional fresh ethane feed are injected into this reactor section where ethane undergoes highly selective adiabatic thermal de-hydrogenation to ethylene.

The OCM reactor effluent flows through a series of heat exchangers to achieve optimal heat recovery and final condensation at ambient temperature, prior to being sent to the Process Gas Compressor (PGC). The natural gas feed stream is mixed with the OCM reactor effluent at the PGC delivery. Gas treating, including CO2removal and drying, follows the compression step. The product recovery train consists of a demethanizer, deethanizer, acetylene converter and C2splitter configuration where the refrigeration and heat integration scheme is designed to optimize heat recovery and minimize power consumption. The product streams comprise of polymer grade ethylene and a C3+mixed stream, similar in composition to Refinery Grade Propylene (RGP), which can be optionally further separated and purified. The C1recycle stream leaving the demethanizer head is sent to a conventional methanation unit where all CO and a portion of the CO2product react with hydrogen to form methane. The integration of the methanation unit into the overall process design is instrumental to maximize the carbon efficiency of the OCM technology.

The OCM process design is energy neutral. The OCM reaction heat is utilized to provide mechanical power to the rotating units required for compression and pumping. The OCM process gets pure oxygen from an adjacent Air Separation Unit (ASU) which also houses a Gas Turbine Combined Cycle (GTCC). The GTCC unit is fed with the purge gas extracted from the demethanizer overhead and provides all the mechanical power and steam required by the ASU.

The final products are 1,000,000 metric tons per annum of polymer grade ethylene and 88,530 metric tons per annum of C3+hydrocarbons. The C3+hydrocarbons are sent to a depropanizer to obtain refinery grade propylene (65% propylene) as distillate.

Example 2: Design Basis of OCM Implementation

The feedstock streams can include a natural gas stream, which supplies the process with the methane and ethane for conversion into ethylene, an oxygen stream, to be supplied by the dedicated Air Separation Unit (ASU) section, an optional ethane stream, which provides extra ethane (in addition to that contained in the natural gas feed) for conversion into ethylene.

As shown inFIG. 21, the ethylene product plant comprises four sections including an OCM reaction section2100(comprising methanation, OCM and heat recover), a process gas compression and treating section2105(comprising PGC, CO2 removal and drying), a product separation and recovery section2110(comprising demethanizer, deethanizer, C2splitter and de-propanizer) and a refrigeration system2115(comprising propylene and ethylene). The process takes in natural gas2120, which can be desulfurized. The process can take in oxygen2125from an air separation unit. Ethane can be added externally2130or as part of a C2recycle2135. The purge gas2140can contain C1compounds and can be recycled2145. Products can include ethylene2150, C4+compounds2155and RGP2160.

Unlike at least some syngas based production processes, the present process is flexible in terms of quality and composition required for the natural gas stream. For example, the process can handle an extremely wide range of natural gas liquids concentration, in particular ethane. None of the typical contaminants present in natural gas, including sulfur, represents a poison for the OCM catalyst. Prior to entering the process, the natural gas feed is treated for sulfur removal in order to prevent contamination of the process outputs and sulfur accumulation in the process. The desulfurization scheme adopted is hydrotreating in a Co/Mo catalyst bed followed by adsorption on a zinc oxide bed. Depending on the actual sulfur content and composition, the adsorption bed may be the only operation. Alternatively other conventional methods of sulfur removal may be used.

The source of the oxygen for the OCM reaction can be air or pure oxygen or any enriched air stream. The presence and concentration of nitrogen may not impact the performances of the OCM reactor system. However, under certain conditions, utilizing pure oxygen as delivered by a conventional Air Separation Unit may minimize the overall process production costs at large scale. Alternatively, enriched air produced via a PSA or air sourced via a compressor may provide the optimal economic solution under other large scale applications.

The OCM reactor has the capability of efficiently processing separate streams of methane and ethane. In the process, the methane stream comes from the demethanizer overhead while the ethane stream, which includes both the unconverted ethane and the ethane contained in the natural gas feed, comes from the deethanizer bottom. Depending on the actual ethane content in natural gas there may be additional ethane processing capacity available in the OCM reactor, which can be saturated with a fresh ethane feed directly mixed with the ethane recycle.

In the particular US Gulf Coast based case presented herein, the natural gas feed is relatively lean (˜4.5% mol ethane), thus additional ethane feed is considered to exploit the available reactor capacity and optimize the overall process economics.

A generic process layout for an ethylene plant based on information described in U.S. Patent Publication No. 2014/0012053 and PCT Patent Application No. US/2013/042480, each of which is herein incorporated by reference in its entirety. The process configurations presented herein are illustrative of a commercial system designed to produce high purity (e.g., 99.96 wt % purity) ethylene via oxidative coupling of methane.

As described in Example 1, the plant is sized to produce at least 1,000,000 metric ton/year (2,214 million lb/yr) of polymer grade ethylene at an on-stream factor of 0.95. Hence, the annual installed capacity is equivalent to 1,059,000 metric t/year (2,330 million lb/yr). The plant also produces 61,185 metric ton/year of refinery grade (65%) propylene and 27,345 metric ton/year of C4+compounds. The reactor system is a 2-stage adiabatic axial fixed bed with intermediate heat recovery via high pressure steam generation; OCM nanowire catalyst with bed height=8.3 ft.; 12″ refractory lining; 2ndstage bottom section used for ethane cracking; and a 2-stage adiabatic methanation unit to convert CO and CO2recycle into methane. The feedstock is pipeline natural gas, 99.5% oxygen (fed in 1:10 molar basis with hydrocarbon stream), and make-up ethane. The operating conditions include OCM reactor inlet conditions: 540° C. (1004° F.), 131 psia; OCM reactor exit temperature: 830° C. (1525° F.); and methanation reactor inlet conditions: 200° C. (392° F.), 161 psia. The overall conversion is 21.5%, which includes conversion of methane and ethane to all reaction products across the OCM reactor. The carbon efficiency is 71% for the ISBL process (specifies carbon utilization for all ISBL units) and 64% overall (includes energy consumption to run OSBL units (mainly ASU)). The selectivity for each reaction product across the OCM reactor is: 55.9% for C2H4; 2.2% for C3H6; 9.7% for CO; 31.3% for CO2; and 0.9% for others.

Example 3: Catalyst Preparation and Catalyst Life

The catalyst is made according to U.S. patent application Ser. Nos. 13/115,082, 13/479,767, 13/689,514 13/757,036 and 13/689,611, and PCT/US2014/028040 filed on Mar. 14, 2014 each of which is entirely incorporated herein by reference. The catalyst is based upon mixed metal oxide catalysts. In some cases, the mixed metal oxide catalysts are comprised of nanowires, mixtures of nanowires and bulk metal oxides, or bulk catalysts. The OCM catalysts can be synthesized via a reaction similar to a standard co-precipitation reaction that takes place in an aqueous solution. The catalysts are then filtered out of the solution, and the resulting solids are calcined.

In order to produce a commercial catalyst, the calcined powder is then mixed with catalyst diluents and binders and formed into commercial forms. Catalyst forming tools are then used to form the combined powder, diluents, and binders into solid cylinders (or other shapes, such as spheres, rings, etc.) with the requisite strength and performance requirements. See, e.g., WO2013177461, which is entirely incorporated herein by reference. Such forming can take place via extrusion or tableting or other conventional catalyst forming techniques.FIG. 22shows an image of the formed cylindrical commercial OCM catalyst.FIG. 23andFIG. 24show Scanning Electron Microscope images of a magnified portion of the commercial catalyst.FIG. 23andFIG. 24show the entire, formed catalyst with nanowires incorporated along with diluents and binders. The white bar in each of the figures designates a scale bar of 5 micrometers (microns).

Under the operating conditions described within this application, an OCM catalyst is stable, with a minimum lifetime of at least 1 year, 2 years, 3 years, 4 years, 5 years, 6 years, 7 years, 8 years, 9 years, 10 years, or 20 years. An OCM catalyst can be regenerated in-situ or regenerated ex-situ. Alternatively, instead of regeneration, an OCM catalyst can be unloaded and returned to the catalyst manufacturer. There, it can be recycled to reclaim its constituent elemental components, or, alternatively, disposed of.

Example 4: OCM Reactors and Reaction Systems

The OCM reactor contains two reaction zones. The entire reactor is a refractory-lined adiabatic reactor. The first reaction zone contains a fixed OCM catalyst bed, to convert methane into ethylene. This is called the methane conversion zone. In the lower section of the reactor, ethane is injected to homogeneously convert ethane to ethylene utilizing the heat generated during methane conversion. This is called the ethane conversion zone. The introduction of reactants into the OCM reactor system is achieved using, extremely low residence time gas mixers. This allows the reactants to be introduced at elevated temperatures, without participating in non-selective side reactions.

In the adiabatic OCM reactor system, the temperature is allowed to rise within a reactor stage through the catalytic bed (methane conversion zone), from approximately 460° C., 470° C., 480° C., 490° C., 500° C., 510° C., 520° C., 530° C., 540° C., 550° C., 560° C., 570° C., 580° C., 590° C., or 600° C. at the inlet to about 850° C., 860° C., 870° C., 880° C., 890° C., 900° C., 910° C., 920° C., 930° C. at the outlet of the bed. Ethane at a lower inlet temperature (about 400° C.-500° C.) is injected into the ethane conversion zone to allow for additional non-oxidative dehydrogenation to take place thereby cooling the reactor effluent. A representative temperature profile of the entire reactor is shown inFIG. 25. The reactor has a methane conversion section (e.g., for OCM) and an ethane conversion section (e.g., for conversion of ethane to ethylene).

In some cases, performance of the process in terms of overall carbon efficiency is higher than that of the OCM reactor alone. The higher carbon efficiency derives from the presence of the catalytic methanation step, which converts all CO and a portion of the CO2product back to methane by utilizing the hydrogen generated in the thermal ethane conversion zone of the OCM reactor.

The methanation unit is a 2-stage adiabatic reaction system, which adopts the same or similar process technology used for Synthetic Natural Gas (SNG) production from syngas. The methanation section is designed to maximize hydrogen consumption and, thus, CO and CO2recovery to methane. Alternative process configurations may include the use of an isothermal reactor in place of the 2-stage adiabatic system.

The design basis also illustrates the impact of the outside battery limits (OSBL) units (mainly the Air Separation Unit) on the overall carbon and energy balance. In the process the purge gas from the demethanizer overhead fuels the GTCC unit, which is used to provide the mechanical power required by the ASU and make the entire process energy neutral.

With reference toFIGS. 26-31, the OCM Reaction System includes two conversion steps: i) the 2-stage OCM Reactor (R-101A&B2650and R-102A&B2651) that converts the methane and ethane recycle streams into ethylene; and ii) the 2-stage Methanation Reactor (R-1032652& R-1042653) that converts the CO and H2present in the methane recycle (and some additional CO2) into methane. A series of feed-product economizers, steam generator and super-heater, BFW pre-heater and cooling water exchangers is also included in this process area to provide optimal heat recovery

The methane recycle feed stream2621coming from the Demethanizer head is first pre-heated to 116° C. (240° F.) in the cross exchanger (E-110)2661with the hot effluent from the 2ndstage of OCM reactor and then further heated to approximately 200° C. (392° F.) in the Methanator Feed/Product Exchanger (E-101)2654. This methane stream is then sent to 1ststage (R-103)2652of the methanation unit where CO is almost completely converted to methane in presence of an excess of hydrogen. Methanation is an exothermic reaction limited by equilibrium and it is carried out over a suitable hydrogenation catalyst in a fixed bed adiabatic reactor. R-1032652effluent2602is cooled in E-1012654against R-1032652feed, mixed with additional CO2coming from CO2removal unit and then fed to the 2ndstage (R-104)2653of methanation. In R-104, H2is the limiting reactant and is almost completely converted in the reaction.

R-104 effluent2603is further pre-heated in the Hot Gas-Gas Exchanger (E-102)2655to achieve the OCM reactor inlet temperature of 540° C. (1004° F.). It is then fed to the 1ststage (R-101)2650of the OCM Reactor to undergo OCM conversion to ethylene. In R-1012650the pre-heated methane feed stream is mixed with the part of the oxygen supplied by the Air Separation Unit2605. The mixed feed flows over the OCM catalytic bed and leaves R-1012650at a temperature of approximately 830° C. (1525° F.). The reaction heat generated in the 1ststage is recovered in the steam generator (E-103)2656by generating high pressure (1500 psia) steam. The high pressure stream from E-1032656is further superheated to 476° C. (889° F.) in exchanger E-1042657.

R-1012650effluent is then fed to the 2ndstage (R-102 A&B)2651of the OCM reactor. It is again mixed with oxygen and fed to the OCM catalyst to carry out the OCM reactions. The ethane feed stream2606comprising of the ethane recycle2634from the C2splitter bottoms and make-up ethane2601is first preheated in the Ethane Gas-Gas Exchanger (E-1072658) and then injected into the bottom section of R-1022651immediately downstream of the OCM catalytic bed to undergo thermal de-hydrogenation to ethylene.

R-1022651effluent at approximately 830° C. (1528° F.) is sent to the Steam Generator and Super-Heater Unit, E-1062657, respectively where the reaction heat generated in the 2ndstage is optimally recovered. The product stream leaving E-1062657flows through the Ethane and the Hot Gas-Gas Exchangers, prior to entering the Boiler Feed Water (BFW) Pre-Heater (E-108)2659. The low temperature fraction of the reaction heat is recovered first in the BFW Pre-Heater E-1082659and then in the Steam Condensate Pre-Heater E-1092660. The product gas leaving2660flows into the Cold Gas-Gas Exchanger (E-110)2661prior to injection into the Quench Tower-I (C-101) 2662.

In the Quench Column (C-101)2662, the product gas is further cooled to ambient temperature and a significant portion of the water produced in the OCM reactors is condensed and separated as Process Condensates2608. The C-1012662overhead gas stream2607is sent to Process Gas Compression and Treating.

Example 5: OCM Process Gas Compression and Treating

The process gas compressor discharge pressure is set to 540 psia to maintain the downstream process gas circuit to a single train with column and vessel sizes limited to a maximum 25 feet diameter. However, the demethanizer can operate as low as 175 psia. This can significantly reduce process gas compression requirements, but requires parallel process gas treatment and demethanizer unit trains and larger propylene and ethylene refrigerant systems. All tradeoffs between capital expense (CAPEX) and operating expense (OPEX) are resolved in a manner that maximizes overall financial return.

Process gas is treated to remove carbon dioxide and water to 0.5 ppmv prior to cryogenic separations using a monoethanol amine-based unit followed by a two-stage caustic wash. Molecular sieve dryers are utilized to remove all moisture from the treated process gas.

With reference toFIGS. 26-31, the Process Gas Compression & Treating section is comprised of four main units: i) The 2-stage (K-201A&B2665and K-2022666) Process Gas Compressors (PGC); ii) a natural gas desulfurization unit2667; iii) the CO2removal Unit2668, including an amine-based absorber and a caustic wash column (G-201); and iv) a drying unit based on molecular sieves absorption (M-201 A-C)2669.

Process gas from the Quench Column C-1012662is compressed in the 2-stage PGC unit (K-2012665&2022666) to a final pressure of 540 psia. The compressed process gas delivered by K-2022666is mixed with the desulfurized natural gas feed stream2615and sent to the Amine system unit (G-201)2668. Pipeline natural gas is first sent through a knockout (KO) drum (V-201)2670, pre-heated to 260° C. (500° F.) in exchanger (E-201)2671against the hot desulfurization reactor (R-201)2672effluent2615and further heated to 316° C. (600° F.) in a process furnace (F-201)2673before entering R-2012672. The reactor R-2012672consists of two beds: the top bed consists of a standard Co/Mo catalyst to convert the sulfur species to H2S and a bottom ZnO bed to adsorb it. The treated natural gas is sent through a turboexpander (S-201)2674to recover some energy.

The rich amine stream leaving the amine absorber bottom is first flashed at an intermediate pressure in the CO2Flash Drum. The CO2vapors leaving flash drum2617are sent to the methanation unit, as described in the previous section. The liquid bottoms leaving flash drum are heated against the lean amine from the Amine Regeneration Columns in the Lean-Rich Solution Exchanger. Medium pressure steam is used to provide the necessary heat for the Regeneration Columns Reboilers. The Regeneration column overhead vapor is cooled and then washed with process water to remove any residual amines prior to CO2venting2618to atmosphere. The overhead process gas from the CO2Absorber is further treated in the Caustic Wash Column, which consists of two stages (rich and lean caustic wash), followed by water-wash stage. The treated process gas from Caustic Wash Column2616is cooled in exchangers, E-2042675and E-2052676, against the methane recycle2623and H2 recycle2624streams from the demethanizer, respectively, and then separated in the Knock-Out Drum V-2022677. The methane recycle streams after exchanging heat through E-2042675, receives part of the H2recycle and the PSA purge stream2631, before being split into the purge gas stream2620and C1recycle stream2621. The purge gas can be sold for credit or alternatively sent to the Gas Turbine Combined Cycle (GTCC) unit housed in an adjacent Air Separation Unit (ASU) to generate mechanical power. Part of the H2recycle stream is sent to the PSA unit2622to recover hydrogen for NG desulfurization in R-2012672and Acetylene dehydrogenation in R-301.

The process gas leaving V-2022677is then fed to the Molecular Sieve Gas Dryers (M-201A-C)2669where all moisture present in the vapors is removed. The dried process gas is then routed to product separation and recovery.

Example 6: OCM Process Gas Separations

The cryogenic separation section of this example utilizes demethanizer and deethanizer technology, but refrigeration is supplemented by expansion-cooling of the olefin-rich process gas as explained in U.S. patent application Ser. No. 13/739,954, which is herein incorporated by reference in its entirety. By utilizing these methods, the amount of refrigeration provided by propylene and ethylene can be reduced, which provides substantial energy savings.

The treated process gas is separated through a demethanizer, deethanizer, ethylene fractionator (C2splitter) and de-propanizer. Treated process gas is cooled using the demethanizer unit overhead product streams and side reboiler and the remainder of the cooling duty is provided by propylene and ethylene refrigeration. The demethanizer recovers 99% of the contained ethylene. The bottoms of the demethanizer are sent to the deethanizer. The overall heat integration scheme for the demethanizer cooling is an aspect of the present disclosure. It includes the adoption of a split vapor process scheme, where a portion of the demethanizer overhead vapor is compressed and then expanded to provide the necessary reflux to the demethanizer. The remaining vapor streams are sent to a turbo-expander to recover refrigeration value and then recycled to the OCM reactor.

The balance between the demethanizer operating pressure, the amount of cooling produced by the internal split vapor scheme and the amount of refrigeration provided by external units constitutes an area of optimization for the trade-off between CAPEX and OPEX. The deethanizer unit is a separation column designed for an ethane recovery of 99 mol %. Deethanizer unit bottoms stream is further fractionated in a de-propanizer to recover a Refinery Grade Propylene (RGP) product stream and a C4mix product stream.

The deethanizer overhead stream is treated for acetylene and fed to the C2splitter, a heat pumped fractionator system. The overhead vapor is compressed and used to provide hot vapor for the reboiler. Liquid from the reboiler is then used to provide refrigerant for the condenser. The C2splitter can have a few trays that serve as a pasteurizing section to remove most of the hydrogen or other inerts that enter the C2splitter unit from the acetylene converter. The C2splitter can recover 99% of the contained ethylene with a purity of 99.95 mol %. The bottoms product is ethane and is recycled back to ethane conversion section of the OCM reactor.

With reference toFIGS. 26-31, the process gas stream2619leaving the Gas Dryers M-201A-C2669is routed to the first cold box E-3012678and cooled against a series of cold streams coming from the Demethanizer system and from the external refrigeration units. The cooled gas stream leaving E-3012678is fed to the Demethanizer Column C-3012679, where the C2+compounds are separated from the lighter components of the process gas (primarily CH4, CO and H2). The Demethanizer Column overhead products2624and2625are re-heated against the Demethanizer Column feed and recycled to the OCM Reaction System.

The overhead reflux necessary for the proper operation of the Demethanizer Column C-3012679is generated via a proprietary refrigeration process scheme, known as the Recycle Split Vapor Unit (G-301)2680that minimizes the need for external refrigeration input. The C-3012679bottom stream2626consists of ethane, ethylene, acetylene and a small fraction (˜5.4%) of heavier (C3+) components. This liquid stream is sent to the Deethanizer Column (C-302)2681. The Deethanizer Column (C-302)2681separates the C3+components in the C-3022681feed from the C2components with minimum loss of ethylene in the C3+stream. C-3022681bottoms stream2627represents the mixed C3+product stream which is sent to a Depropanizer (C-304)2682. Refinery grade propylene (RGP) (˜65% propene) is obtained as C-3042682distillate stream2635and is sent to the appropriate distribution system to obtain by-product credit. Similarly, C-3042682bottoms stream2636contains a mixed C4+stream that can be sold.

The C-3022681overhead stream is cooled in a partial condenser (E-304)2683using propene refrigeration. Liquid condensate is sent as reflux to C-3022681. C-3022681overhead vapor product2628is then heated in E-3022684and routed to a two-stage acetylene hydrogenation reactor R-3012685where all acetylene is hydrogenated to ethylene and ethane.

A pressure swing adsorption (PSA) unit (G-302)2686is installed on a slip stream of the demethanizer overhead vapors to produce the high-purity hydrogen stream required by the acetylene hydrogenation reactor (R-301)2685. The acetylene reactor operates at low temperatures (100° F. Start of run and 150° F. End of run) using a selective palladium catalyst to convert acetylene to ethylene and ethane. R-3012685effluent2632is cooled and sent to the Ethylene Splitter (C-303) 2687. C-3032687produces a 99.96 wt % pure ethylene overhead product2633and a 99% pure ethane stream2634as bottoms. A cold box (E-306)2688serves as the C-3032687condenser and reboiler. A heat pump compressor K-3022689provides hot ethylene vapor to the C-303 reboiler after looping once through the condenser. The condensed ethylene liquid from the reboiler is used in the C-303 condenser.

The high-pressure ethylene product2633from K-3022689is sent to the relevant distribution system. The C-303 bottoms2634are recycled to OCM reaction and injected into the 2ndstage R-1022651of the OCM Reactor.

Example 7: Refrigeration and Steam Generation

The system consists of propylene and ethylene refrigeration systems. Propylene refrigeration system is a three-stage refrigeration system, with three different coolant levels, as illustrated inFIG. 30. Additional utilities are shown inFIG. 31.

Evaporating ethylene from the propylene refrigeration cycle is used to condense the ethylene in the ethylene refrigeration cycle and provide refrigerant to the deethanizer overhead condenser (E-3042683) and the demethanizer cold box (E-3012678).

Ethylene refrigeration system is also a three-stage refrigeration system as illustrated inFIG. 30. This system provides refrigeration to the demethanizer cold box (E-3012678) and to the Recycle Split Vapor Unit (RSV2680).

Superheated, high pressure (HP) steam (1500 psia, 889° F.) generated by the OCM process is used to drive the process gas compressor, the demethanizer overhead compressor, the refrigeration compressors, the ethylene fractionator heat pump and product compressors, half of cooling water and boiler feed water pumps (in offsites), and is fed to medium pressure (MP, 165 psia) and low pressure (LP, 50 psia) reboilers after proper flashing and de-superheating. Any remaining steam can be exported to the Gas Turbine Combined Cycle (GTCC) unit housed in an adjacent Air Separation Unit (ASU) that provides 99.5% O2for the OCM reaction. A purge gas stream is also sent to the GTCC unit to generate the mechanical power required by the ASU unit. In this review, excess steam and purge gas account for utility and by-product credit, respectively

Example 8: Stream Compositions

Table 1 shows the total flow-rate and flow rates of selected molecular entities (e.g., Hydrogen and Argon) for select streams of the example process. Stream numbers correspond to those of Examples 4-7 andFIGS. 26-31.

Table 2 shows the temperatures for select streams of the example process. Stream numbers correspond to those of Examples 4-7 andFIGS. 26-31.

Example 9: Equipment, Materials of Construction and Utilities

The material of construction for the different process units shown inFIGS. 26-31is tabulated in the major equipment list (Tables 3-8). Carbon steel material can be used for construction of at least some or most of the process equipment as the reaction medium is not corrosive. The distillation column shell and, heat exchanger shells can be constructed out of carbon steel (C.S.) or stainless steel (SS). Distillation column internals are made of stainless steel whereas the reactor shells are constructed of carbon steel. The Transfer Line Exchangers used for high pressure steam are made of Mo-Alloy steel.

The process gas compression and treatment section has two pumps and two spares operating at 516 BHP, the product separation and recovery section has four pumps and four spares operating at 1714 BHP, the refrigeration section has one pump and one spare operating at 128 BHP.

All of the compressors in Table 5 are constructed from carbon steel.

In addition, the process has: a natural gas heater (F-201)2673sized 35 MMBTU/HR made of carbon steel; three process gas driers (M-201 A-C)2669each having a capacity of 34,300 gallons made of carbon steel and having molecular sieve beds including all peripheral equipment and one spare column; a treated natural gas expander (S-201)2674of 4200 HP and made of carbon steel; a CO2 removal unit (G-201)2668made of carbon steel and sized to 11.5 MMSCFD CO2 including an amine scrubber, regeneration, caustic scrubber and peripheral units; a recycle split vapor (RSV) unit (G-301)2680made of carbon steel and including a cold box (Width: 4 ft., Height: 5.8 ft. and Length: 14.2 ft.), a compressor, two turboexpanders, and two knockout drums; and a H2 pressure swing adsorption unit (G-302)2686made of carbon steel and having a size of 4.36 MMSCFD.

The utilities consumed by the process shown inFIGS. 26-31are tabulated in Tables 9-10). Table 9 shows the average consumption of the utilities and Table 10 shows peak demands imposed upon the utilities. The utilities are scaled to be able to satisfy both average demands and peak demands.