Patent Publication Number: US-7915463-B2

Title: Process for the conversion of natural gas to hydrocarbon liquids

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 11/669,451 filed on Jan. 31, 2007, entitled “Process For The Conversion of Natural Gas to Hydrocarbon Liquids,” which is a divisional application of U.S. application Ser. No. 10/844,852 filed on May 13, 2004, now Pat. No. 7,183,451, claiming benefit of U.S. Provisional Application Ser. No. 60/505,204, filed Sep. 23, 2003, entitled “Process For the Conversion of Natural Gas to Hydrocarbon Liquids and Ethylene;” all applications are hereby incorporated herein by reference in their entirety for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to processes for the conversion of natural gas to hydrocarbon liquids. More particularly, this invention relates to processes for the conversion of natural gas to hydrocarbon liquids wherein natural gas is first converted to reactive hydrocarbon products and the reactive hydrocarbon products are then reacted further to produce the hydrocarbon liquids. 
     2. Description of the Related Art 
     Natural gas typically contains about 60-100 mole percent methane, the balance being primarily heavier alkanes. Alkanes of increasing carbon number are normally present in decreasing amounts. Carbon dioxide, hydrogen sulfide, nitrogen, and other gases may be present in relatively low concentrations. 
     The conversion of natural gas into hydrocarbon liquids has been a technological goal for many years. This goal has become even more important in recent years as more natural gas has been found in remote locations, where gas pipelines cannot be economically justified. A significant portion of the world reserves of natural gas occurs in such remote regions. While liquefied natural gas (LNG) and methanol projects have long attracted attention by making possible the conversion of natural gas to a liquid, in recent years the advent of large-scale projects based upon Fisher-Tropsch (F-T) technology have attracted more attention. A review of proposed and existing F-T projects along with a discussion of the economics of the projects has recently been published (Oil and Gas J., Sep. 21 and Sep. 28, 1998). In this technology, natural gas is first converted to “syngas,” which is a mixture of carbon monoxide and hydrogen, and the syngas is then converted to liquid paraffinic and olefinic hydrocarbons of varying chain lengths. 
     The conversion of natural gas to unsaturated hydrocarbons and hydrogen by subjecting the hydrocarbons in natural gas to high temperatures produced by electromagnetic radiation or electrical discharges has been extensively studied. U.S. Pat. No. 5,277,773 (Exxon Research &amp; Eng. Co.) discloses a conversion process that treats methane and hydrocarbons with microwave radiation so as to produce an electric discharge in an electromagnetic field. U.S. Pat. No. 5,131,993 (The Univ. of Conn.) discloses a method for cracking a hydrocarbon material in the presence of microwave discharge plasma and a carrier gas, such as oxygen, hydrogen, and nitrogen and, generally, a catalyst. Expired U.S. Pat. No. 3,389,189 (Westinghouse Electric Corp.) is an example relating to the production of acetylene by an electric arc. 
     The traditional methods of converting lower molecular weight carbon-containing molecules to higher molecular weights are numerous. There are many patents that teach reactor designs with the purpose of converting hydrocarbon containing gases to ethylene, acetylene, or syngas. The most prevalent methods involve oxidative coupling, partial oxidation, or pyrolysis. Each method has its own benefits and its own challenges. 
     Oxidative coupling is a technique wherein a lighter hydrocarbon is passed through a reaction bed containing a catalyst that encourages partial oxidation of the hydrocarbon. The primary advantage of oxidative coupling is that relatively mild conditions of temperature and pressure are required. Another real advantage of oxidative coupling is that liquid hydrocarbons (and other liquids) can be formed in substantial quantity. The distinguishing disadvantage of oxidative coupling is the necessity for a solid phase catalyst, which has a short useful life and must be regenerated often. U.S. Pat. No. 4,704,493 (Chevron Corp.) discloses the use of Group IIA metal oxides on various supports to convert methane into light aromatic compounds and light hydrocarbons. Although methane conversions of up to 40% are reported, there is a strong correlation between increased conversion and increased tar and coke production. U.S. Pat. No. 4,705,908 (Gondouin) teaches the conversion of natural gas containing components of C 1  through C 4 -C 5+  hydrocarbons and hydrogen by first splitting the stream of natural gas into a C 1 -C 2  portion and a heavier portion, and then reacting these streams separately using a single non-silica based catalyst that includes mixed oxides. The reactions are performed at different temperatures and residence times. Disadvantages of this process include expected low conversion, excessive recycling of gases, continuous movement, and regeneration of the solid catalyst. U.S. Pat. No. 5,012,028 (The Standard Oil Co.) presents a process whereby natural gas is separated into methane and C 2+  hydrocarbons and other gases, and the methane is introduced along with oxygen to a reactor operated to perform oxidative coupling. The products of oxidative coupling are then combined with the other gases and non-methane hydrocarbons in a pyrolysis reactor. A quench step and a product recovery step follow. A disadvantage of this process is that the overall conversion to liquids is low (&lt;10%). U.S. Pat. No. 5,288,935 (Institut Francais du Petrole) teaches separating natural gas into methane and other gases rich in C 2+ . The methane is subjected to oxidative coupling. The C 2+  fraction is fed to the reactor before all of the oxygen is consumed. The product from this reactor is conveyed to an aromatization reactor, containing a catalyst comprising an MFI zeolite containing gallium. Conversion to heavier components is about 10% to 15%. U.S. Pat. No. 6,518,476 (Union Carbide Chem. &amp; Plas. Tech. Corp.) teaches effective oxidative dehydrogenation of natural gas at elevated pressure, generally between 50 psi and 400 psi (about 340-2800 kPa) and below 600° C., using a rare earth oxycarbonate catalyst. The olefin yield is increased through recycling of the non-olefin containing product. The olefin is removed using silver ion-containing complexation agents or solutions. Conversions are generally on the order of 20% but can be as high as 40%, depending upon the method of operation of the reactor. Selectivity declines with increased conversion. U.S. Pat. No. 6,566,573 (Dow Global Tech., Inc.) teaches conversion of paraffinic hydrocarbons with two or more carbon atoms to olefins in the presence of oxygen, hydrogen, and a supported platinum catalyst. It is recognized that preheating of the feedstreams reduces the required flow of oxygen, with a resulting reduction in oxygen-containing byproducts such as CO and CO 2 . Conversion of ethane to ethylene is about 55%, while acetylene production is less than 1%. 
     Non-catalytic partial oxidation is widely practiced because the technique is simpler as there is no catalyst to regenerate. Products generally include only gas phase components, which will generally include ethylene, carbon monoxide, carbon dioxide, and acetylene. There are many reactor designs and methods for partial oxidation. U.S. Pat. No. 4,575,383 (Atlantic Richfield Co.) discloses a unique reactor design, namely a reciprocating piston engine. Conversion of methane to ethylene and acetylene is less than 1% however, which is very low. U.S. Pat. Nos. 4,599,479 and 4,655,904 (Mitsubishi Jukogyo Kabushiki Kaisha) teach a technique to increase the yield of BTX (benzene/toluene/xylene) compounds in one reactor by first burning a hydrocarbon with less-than-stoichiometric oxygen to make a hot gas containing steam and hydrogen, and then feeding methane and hydrogen to the hot gas formed, followed by a quench. More BTX can be made by feeding an intermediate stream containing liquid hydrocarbons which have a normal boiling point above 350° C. It is taught that the methane to hydrogen ratio is very important, as the hydrogen tends to consume olefins generated while at the same time generating methyl radicals that lead to the formation of heavier hydrocarbon species. The reaction time of 15 milliseconds is relatively long. U.S. Pat. No. 5,068,486 (Mobil Oil Corp.) reveals a partial oxidation process that operates at very high pressure (20-100 atm), necessitating very high compression costs. The conversion of methane, which is the hydrocarbon feed, is reported as 12.6%, with hydrocarbon selectivity of 32%. The overall conversion of methane to ethylene, acetylene, and propane were 1.4%, 0.4% and 0.1%, respectively. U.S. Pat. Nos. 5,886,056 and 5,935,489 (Exxon Res. and Eng. Co.) teach a multi-nozzle design for feeding a partial oxidation reactor. The multiple nozzles allow introduction of a pre-mix of oxidant and fuel at the burner face so that these gases are premixed and of uniform composition. Alternatively, the plurality of injection nozzles allows one to feed different pre-mix compositions to the partial oxidation reactor burner face, for example allowing one nozzle to act as a pilot due to a higher than average oxygen feed concentration, and those nozzles on the periphery to have a greater hydrocarbon concentration resulting in a lower temperature. A major disadvantage of such a design is that the control and operation of multiple feeds increases the probability of failure or shutdown of the reactor and also increases the cost of building the reactor. U.S. Pat. No. 6,365,792 (BASF AG) teaches that operation of a partial oxidation cracker at less than 1400° C. but for longer residence times provides similar acetylene conversion but at reduced energy costs and with less solid carbon being formed. 
     Pyrolysis of hydrocarbons generally requires higher temperatures than the other techniques because there are normally no oxidative or catalytic species present to facilitate dehydrogenation of the hydrocarbon. As in oxidation processes, the products are generally limited to gas phase components. 
     There are many ways to propagate pyrolysis reactions and some are described here. Expired U.S. Pat. No. 3,663,394 (The Dow Chem. Co.) claims use of a microwave generated plasma for converting methane and ethane to acetylene. Although conversions ranged up to 98% with about 50% acetylene being formed, the process performed best at pressures below 40 torr and especially at 10 torr, which would be difficult to achieve economically at industrial scale. Expired U.S. Pat. No. 3,697,612 (Westinghouse Elec. Corp.) describes an arc heater of complex design that can convert methane to higher hydrocarbons, wherein the conversion is about 40%. Of the total converted, acetylene accounted for 74% of the product. The energy required to create a pound of acetylene was more than 5 kilowatts, which is comparable to other methods for making acetylene using electrical discharge. Expired U.S. Pat. No. 3,703,460 (U.S. Atomic Energy Commission) teaches that ethylene and ethane can be made in an induced electric discharge plasma reactor. The process operates at atmospheric pressure or below and provides less than 6% conversion of the feed methane. A disadvantage of the process is the need for vacuum pumps, which are expensive to operate. U.S. Pat. No. 4,256,565 (Rockwell Int&#39;l. Corp.) discloses a method to produce high yields of olefins from heavy hydrocarbon feedstock by commingling a stream of hot hydrogen and water vapor with a spray of liquefied heavy hydrocarbon consisting preferentially of asphalts and heavy gas oils. Yields of olefins are strongly dependent upon rapid heating and then cooling of the fine spray droplets, to initiate and then quench the reactions. U.S. Pat. No. 4,288,408 (L.A. Daly Co.) teaches that for cracking of heavy hydrocarbons, which tend to coke heavily, injection of an inert gas such as nitrogen or CO 2  just downstream of the liquid feed atomizers will decrease accumulation and formation of coke on the walls of the reactor and downstream in the gas cooler. U.S. Pat. No. 4,704,496 (The Standard Oil Co.) relates to the use of nitrogen and sulfur oxides as reaction initiators for pyrolysis of light hydrocarbons in reactors such as tubular heaters. Conversion of methane is reportedly as high as 18.5%, with selectivity to liquids as high as 57.8% and selectivity to acetylene as high as 18.7%. No mention of liquid composition is provided, so it is reasonable to suspect that some heteroatom incorporation into the liquid molecules occurs. U.S. Pat. No. 4,727,207 (Standard Oil Co.) teaches that the addition of minor amounts of carbon dioxide to methane or natural gas will assist in the conversion of the methane or natural gas to higher molecular weight hydrocarbons as well as reduce the amount of tars and coke formed. The examples were run at 600° C., which is a relatively low temperature for pyrolysis of methane, and the reported conversions were generally low (about 20% or less). A drawback of this technique is that the addition of CO 2  adds another component that must then be removed from the product, which increases both gas scrubbing costs and transmission equipment size. 
     U.S. Pat. No. 5,749,937 (Lockheed Idaho Tech. Co.) discloses that acetylene can be made from methane using a hydrogen torch with a rapid quench, with conversions of methane to acetylene reportedly 70% to 85% and the balance being carbon black. U.S. Pat. No. 5,938,975 (Ennis et al.) discloses the use of a rocket engine of variable length for pyrolysis of various feeds including hydrocarbons. Various combinations of turbines are disclosed for generating power and compressing gas, purportedly allowing a wide range of operating conditions, including pressure. An obvious drawback of such a rocket powered series of reactors is the complexity of the resulting design. U.S. Patent No. Application Publication No. 20030021746, U.S. Pat. Nos. RE37,853E and 6,187,226 (Bechtel BWXT Idaho, LLC), and U.S. Pat. No. 5,935,293 (Lockheed Martin Idaho Tech. Co.) all teach a method to make essentially pure acetylene from methane via a plasma torch fueled by hydrogen. The disclosed design employs very short residence times, very high temperatures, and rapid expansion through specially designed nozzles to cool and quench the acetylene production reaction before carbon particles are produced. The disclosed technique purportedly enables non-equilibrium operation, or kinetic control, of the reactor such that up to 70% to 85% of the product is acetylene. Approximately 10% of the product is carbon. A drawback of this process is that high purity hydrogen feed is required to generate the plasma used for heating the hydrocarbon stream. 
     Interesting combinations of processes have also been developed. For example, U.S. Pat. No. 4,134,740 (Texaco Inc.) uses carbon recovered from the non-catalytic partial oxidation reaction of naphtha as a fuel component. A complex carbon recovery process is described wherein the reactor effluent is washed and cooled with water, the carbon is extracted with liquid hydrocarbon and stripped with steam, and then added to an oil to form a slurry that is fed back to the partial oxidation reactor. This process does not appear to be applicable to the partial oxidation of gas-phase hydrocarbons, however. The handling and conveying of slurries of carbon, which clogs pipes and nozzles, is a further drawback. U.S. Pat. No. 4,184,322 (Texaco Inc.) discusses methods for power recovery from the outlet stream of a partial oxidation cracker. The methods suggested include: 1) heat recovery steam generation with the high temperature effluent gas, 2) driving turbines with the effluent gas to create power, 3) directly or indirectly preheating the partial oxidation reactor feeds using the heat of the effluent, and 4) generating steam in the partial oxidation gas generator to operate compressors. Integration of these methods can be difficult in practice. For example, when preheating feed streams depends on the downstream temperature and effluent composition, there will be periods when the operation is non-constant and the product composition is not stable. However, no external devices are disclosed to assist in the start-up or trim of the operation to achieve or maintain stable operation and product quality. U.S. Pat. No. 4,513,164 (Olah) discloses a process combining thermal cracking with chemical condensation, wherein methane is first cracked to form acetylene or ethylene, which is then reacted with more methane over a superacid catalyst, such as tantalum pentafluoride. Products are said to consist principally of liquid alkanes. U.S. Pat. No. 4,754,091 (Amoco Corp.) combines oxidative coupling of methane to form ethane and ethylene with catalytic aromatization of the ethylene. The ethane formed and some unreacted methane is recycled to the reactor. Recycle of the complete methane stream did not provide the best results. The preferred lead oxide catalyst achieved its best selectivity with a silica support, and its best activity with an alpha alumina support. Residual unsaturated compounds in the recycle gas were said to be deleterious in the oxidative coupling reaction. It is also taught that certain acid catalysts were able to remove ethylene and higher unsaturates from a dilute methane stream, without oligomerization, under conditions of low pressure and concentration. Expired U.S. Pat. No. 4,822,940 (The Standard Oil Co.) discloses the conversion of a feedstock containing hydrogen, ethylene, and acetylene to a product with a substantial liquid content in a conventional non-catalytic pyrolysis reactor, when the contents are maintained at about 800° to 900° C. for about 200 to 350 milliseconds. One of the reported examples shows 30% ethylene conversion and 70% acetylene conversion to liquids, with more than 80% selectivity to liquids. 
     U.S. Pat. No. 5,012,028 (The Standard Oil Co.) teaches the combination of oxidative coupling and pyrolysis to reduce external energy input. Oxidative coupling is used to form an intermediate, principally ethylene and ethane, which is an exothermic process. The product of the oxidative coupling reaction is converted to heavier hydrocarbons, which is endothermic, in a pyrolysis reactor. Pyrolysis of C 2+  hydrocarbons to liquids does not require as high a temperature as does the pyrolysis of methane, therefore the required energy input is reduced. Because both process steps occur at temperatures below 1200° C., equipment can be readily designed to transfer heat between the processes for heat integration. A major drawback of this combination of technologies however, is controlling the composition of the intermediate because residence times are less than ½ second in both systems. Feed or control fluctuations could easily result in loss of operation and heat transfer between the units. If the units are closely coupled, such a loss of heat transfer could easily result in reactor damage. U.S. Pat. No. 5,254,781 (Amoco Corp.) discloses oxidative coupling and subsequent cracking, wherein the oxygen is obtained cryogenically from air and the products, principally C 2 &#39;s and C 3 &#39;s, are liquefied cryogenically. Effective heat integration between the exothermic oxidative coupling process step and the endothermic cracking process step is also said to be obtained. U.S. Pat. No. 6,090,977 (BASF AG) uses a hydrocarbon diluent, such as methane, to control the reaction of a different, more easily oxidized hydrocarbon, such as propylene. The more easily oxidized hydrocarbon is converted by heterogeneously catalyzed gas phase partial oxidation. After the partial oxidation reaction, combustion of the effluent gas is used to generate heat. An advantage of a hydrocarbon diluent is that it can absorb excess free radicals and thereby prevent run-away reaction conditions caused by the presence of excess oxygen. The hydrocarbon also increases the heating value of the waste gas, thus its value as a fuel. Of course, this technique cannot be utilized when the reaction conditions are such that methane reacts and/or is the predominant reactant. U.S. Pat. No. 6,596,912 (The Texas A&amp;M Univ. System) employs a recycle system with a high recycle ratio of (8.6:1) to achieve a high conversion of methane to C 4  and heavier products. The initial process employs an oxidative coupling catalyst to produce primarily ethylene, and a subsequent process step using an acid catalyst such as ZSM-5 to oligomerize the ethylene. A drawback of this relatively high recycle ratio is that larger compressors and reactors are required to produce the final product. 
     To produce liquids after cracking, oligomerization of the unsaturated cracked hydrocarbons can produce a desirable liquid composition. U.S. Pat. No. 5,118,893 (Board of Regents, The Univ. of Texas System) for example, discloses a high conversion of acetylene directly to other hydrocarbons using a nickel or cobalt modified ZSM catalyst. Conversions of 100% are reported for up to 8 hours of operation. Conversion to liquid products after several hours of operation appears to stabilize between 10 and 20%. Data for longer times are not given for the modified catalysts. U.S. Pat. No. 4,424,401 (The Broken Hill Prop. Co. Ltd.; Commonwealth Scientific; and Industrial Res. Org.) teaches use of a ZSM-5 zeolite with a minimum ratio of silica to alumina of 800:1 to convert acetylene and hydrogen to liquid hydrocarbons. Many oligomerization catalysts are highly sensitive to the presence of water. However, U.S. Pat. No. 4,982,032 (Amoco Corp.) teaches that acetylene can be oligomerized while water is in significant abundance by HAMS-1B crystalline borosilicate modified molecular sieve promoted by zinc oxide. The catalyst is also said to be tolerant of CO, CO 2 , O 2  and alcohols. Although the reported conversions are high, the optimum selectivity to organic liquids is reported to be only about 73%. The use of gas streams low in acetylene content resulted in much lower acetylene conversion. 
     Following cracking, some unsaturated compounds are desirably converted to hydrogenated species. The hydrogenation of unsaturated compounds is known in the art. For example, U.S. Pat. No. 5,981,818 (Stone &amp; Webster Eng. Corp.) teaches the production of olefin feedstocks, including ethylene and propylene, from cracked gases. U.S. Pat. No. 5,414,170 (Stone &amp; Webster Eng. Corp.) discloses a mixed-phase hydrogenation process at very high pressure. A drawback of this technique is that the concentration of acetylene must be low to enable the proper control of temperature in the hydrogenation step. U.S. Pat. No. 4,705,906 (The British Petroleum Co.) teaches hydrogenation of acetylene to form ethylene in the gas phase using a zinc oxide or sulphide catalyst. Conversions up to 100% and selectivities to ethylene up to 79% were reported. 
     Separation of the products of cracking is often desirable when a specific component has particular value. For example, separation of acetylene from ethylene is beneficial when the ethylene is to be used in making polyethylene. U.S. Pat. No. 4,336,045 (Union Carbide Corp.) proposes the use of liquid hydrocarbons to separate acetylene from ethylene, using a light hydrocarbon at temperatures of below −70° C. and elevated pressure. 
     The cogeneration of electrical power can substantially improve the economics of cracking processes. For example, U.S. Pat. No. 4,309,359 (Imperial Chem. Ind. Ltd.) describes the use of a catalyst to convert a gas stream containing hydrogen and carbon monoxide to methanol, whereby some of the gas is used to create energy via reaction in a fuel cell. 
     Chemical production prior to the complete separation of the products of the cracking reaction can also be used to reduce the cost of purification. U.S. Pat. No. 4,014,947 (Volodin et al.) describes a process for the pyrolysis of hydrogen and methane with conversion of the produced acetylene and ethylene to vinyl chloride. The acetylene and ethylene are reacted with chlorine or hydrogen chloride, during the pyrolysis formation of the unsaturated hydrocarbons, and rapidly quenched with a liquid hydrocarbon. 
     U.S. Pat. Nos. 6,130,260 and 6,602,920 (The Texas A&amp;M Univ. Systems) and U.S. Pat. No. 6,323,247 (Hall et al.) describe a method in which methane is converted to hydrogen and acetylene at temperature, quenched, and catalytically converted to, inter alia, pentane. While an advance over conventional art processes, the method disclosed still suffers from a number of drawbacks with respect to the preferred embodiments of the process of the present invention, as will be further described herein. In particular, the production and integration of carbon monoxide and carbon dioxide within the process is not contemplated by the reference. Carbon monoxide is produced in preferred embodiments of the present invention that include a partial oxidation step, and it provides additional value to the inventive processes as both a downstream feedstock and a fuel. Carbon dioxide that can be used to reduce the carbon formation in process equipment and increase the overall process yield is also produced in preferred embodiments of the present invention that include direct heating. 
     Further advantages are provided by the employment of the various separation processes described in preferred embodiments of the present invention. For example, preferred embodiments of the present invention provide for the separation of acetylene from other gas components prior to hydrogenation, with corresponding reductions in the quantity of gas that must be treated in the hydrogenation steps. Improvements in catalyst life may also be expected therefrom. Ethylene management in accordance with preferred embodiments of the present invention provides additional advantages, as illustrated by inventive preferred embodiments comprising removal of ethylene from acetylene-deprived streams, with their subsequent combination with ethylene-rich hydrogenator product streams. In some preferred embodiments of the present invention, fractionation of the natural gas feed prior to conversion steps allows different reaction conditions for the various fractions, thus improving the performance of the overall process and optimization of the product mix. 
     Additional advantages are provided by the unit operations uniquely employed in accordance with preferred embodiments of the processes of the present invention. Direct heat exchange, but one such example, is utilized to enhance conversion and reduce carbon formation in certain preferred embodiments of the present invention by placing the heating medium in direct contact with the reactant gas, thus enabling chemical reactions and equilibria that would not otherwise obtain. Similarly, the above-mentioned conventional processes do not disclose the recycle of gas components other than hydrogen to the combustor for the indirect transfer of heat, or for combination with the incoming natural gas feed stream. Preferred embodiments of the present invention however, provide for the separation of non-hydrogen components upstream of the hydrogenator and downstream of the catalytic reactor with recycle for improving the acetylene yield, with the further option of recycle to the combustion stage, if the heating value of the stream provides an economic advantage. 
     Numerous methods for cracking hydrocarbons, particularly natural gas and methane, are known in the art. Likewise, many methods have been developed for separation of the products from cracking reactions, and many designs have been disclosed for producing ethylene and acetylene from cracking processes. However, no economical and integrated method is presently known in the art for the conversion of methane and natural gas to ethylene, hydrocarbon liquids, and other valuable final products, through the intermediate manufacture of acetylene, such that the final products can be either transported efficiently from remote areas to market areas (or used at the point of manufacture). 
     Although the prior art discloses a broad range of methods for forming acetylene or ethylene from natural gas, an energy-efficient process for converting natural gas to liquids that can be transported efficiently from remote areas to market areas has not previously been available. A way of overcoming these problems is needed so that production of transportable liquids from natural gas is practical for commercial industrial-scale applications. Accordingly, research has focused on developing new processes that can reduce or eliminate the problems associated with the prior art methods. The processes of the present invention in their various preferred embodiments are believed to both overcome the drawbacks of the prior art and provide a substantial advancement in the art relating to the conversion of natural gas to transportable hydrocarbon liquids. The present invention has been developed with these considerations in mind and is believed to be an improvement over the methods of the prior art. 
     BRIEF SUMMARY 
     It is thus an object of the present invention to overcome the deficiencies of the prior art and thereby to provide an integrated, energy-efficient process for converting natural gas to readily transportable upgraded liquids. Accordingly, provided herein is a process for the conversion of natural gas to either a hydrocarbon liquid, for transport from remote locations, or a stream substantially composed of ethylene. 
     In some preferred embodiments, natural gas is heated to a temperature at which a fraction is converted to hydrogen and one or more reactive hydrocarbon products such as acetylene or ethylene. The product stream is then quenched to stop any further reactions, and reacted in the presence of a catalyst to form the liquids to be transported. The liquids comprise predominantly liquid hydrocarbons, a significant portion of which is naphtha or gasoline or diesel. In some preferred embodiments, hydrogen may be separated after quenching and before the catalytic reactor. Heat for raising the temperature of the natural gas stream may preferably be provided by burning a gas recovered from downstream processing steps, or by burning a portion of the natural gas feed stream. Hydrogen produced in the reaction is preferably available for further refining, export, or in generation of electrical power, such as by oxidation in a fuel cell or turbine. 
     In some preferred embodiments, heat produced from a fuel cell is preferably used to generate additional electricity. In other preferred embodiments, the acetylene portion of the reactive hydrocarbon is reacted with hydrogen, to form ethylene prior to the reactions forming the liquid to be transported. In other preferred embodiments, some of the produced hydrogen may be burned to raise the temperature of the natural gas stream, and the acetylene portion of the reactive hydrocarbon may be reacted with more hydrogen to form ethylene prior to its reaction to form the liquid to be transported. 
     In other preferred embodiments, hydrogen produced in the process may be used to generate electrical power, the electrical power may be used to heat the natural gas stream, and the acetylene portion of the reactive hydrocarbon stream may be reacted with hydrogen to form ethylene prior to forming the liquid to be transported. In certain other preferred embodiments, acetylene may be separated from the stream containing reactive hydrocarbon products prior to subjecting the acetylene to hydrogenation, while in other preferred embodiments the stream containing acetylene is subjected to hydrogenation. 
     In still other preferred embodiments, the stream from which the acetylene has been removed is subjected to further separation such that ethylene is removed, making this ethylene available for combination with the acetylene. In other preferred embodiments, the ethylene stream and the product of the acetylene hydrogenation step may be combined for processing in the catalytic reactor for production of hydrocarbon liquids. 
     In another preferred embodiment, either separate or combined ethylene streams may be separated for further processing such that heavier hydrocarbons are not made from the ethylene. In certain other preferred embodiments, the heating of one portion of the natural gas feed is accomplished by the complete combustion of a second portion of the natural gas, which is accomplished within a reactive structure that combines the combusted natural gas and natural gas to be heated. 
     In other preferred embodiments, the heating of a portion of the natural gas is accomplished by mixing with an oxidizing material, such that the resulting incomplete combustion produces heat and the reaction products may comprise reactive hydrocarbon products. 
     In other preferred embodiments, the carbon monoxide that is produced by the incomplete combustion of natural gas or other hydrocarbons is recycled to a section or sections of the reactor as a fuel component. In yet other preferred embodiments, the carbon monoxide that is produced by the incomplete combustion of the natural gas feed or other hydrocarbons is used in subsequent chemical processing. In another preferred embodiment, hydrogen that is produced in the reactor is separated from the reactive components and then used in subsequent chemical processing. 
     In another preferred embodiment, hydrogen and carbon monoxide produced in the process are subsequently combined to form methanol. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which a first portion of the natural gas is heated to reaction temperature by essentially complete combustion of a second portion of the natural gas upstream, with subsequent mixing of the streams to convey heat from the second stream to the first stream in a mixed stream reactor. 
         FIG. 2  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by incomplete combustion in a mixed stream reactor after which the reactive hydrocarbon products are separated from the non-hydrocarbons and non-reactive hydrocarbons and the reactive hydrocarbon products are subjected to liquefaction. 
         FIG. 3  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by burning a stream comprising natural gas and a portion of the stream comprising hydrogen and, in some cases, carbon monoxide produced with the reactive hydrocarbon products in the mixed stream reactor, after which the reactive hydrocarbon products are separated from the non-hydrocarbons and non-reactive hydrocarbons, and the reactive hydrocarbon products are subjected to liquefaction. 
         FIG. 4  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by a furnace. Acetylene is separated from the reaction products and hydrogenated and the remaining gas components may be vented, reserved for subsequent processing, or returned to the process to be burned or further reacted. 
         FIG. 5  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by incomplete combustion in a mixed-stream reactor. The reaction products containing acetylene are subjected to separation, such that the acetylene is separated from the other gas components, and the acetylene stream is then hydrogenated and subjected to liquefaction. The other (non-acetylene) gas components may be vented, reserved for subsequent processing or chemical conversion, or returned to the process to be burned, further reacted or, after further separation, certain components of the reaction products gas stream may be combined with the acetylene hydrogenation product stream. 
         FIG. 6  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by burning a stream of natural gas and a portion of the stream comprising hydrogen (and, in some preferred embodiments, carbon monoxide produced with the reactive hydrocarbon products) in a mixed-stream reactor. The reaction products containing acetylene are subjected to separation, such that the acetylene is separated from the other gas components, and the acetylene stream is then hydrogenated and subjected to liquefaction. The other (non-acetylene) gas components may be vented, reserved for subsequent processing or chemical conversion, or returned to the process to be burned, further reacted or, after further separation, certain components of the reaction products gas stream may be combined with the acetylene hydrogenation product stream. 
         FIG. 7  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by burning a portion of the natural gas in a furnace. Acetylene is separated from the reaction products, hydrogenated, and subjected to liquefaction. The other (non-acetylene) gas components may be vented, reserved for subsequent processing or chemical conversion, or returned to the process to be burned or further reacted. 
         FIG. 8  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by an electrical heating device. 
         FIG. 9  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by means that may include hydrogen combustion in a combustion device. 
         FIG. 10  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by an electrical heater via the electrical energy produced from hydrogen and a portion of the natural gas. 
         FIG. 11  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the natural gas is heated to reaction temperature by incomplete combustion in a mixed stream reactor. Acetylene is separated from the reactive hydrocarbon products and non-hydrocarbons remaining in the quenched stream and then hydrogenated. The product of this hydrogenation is liquefied or separated for later conversion to other products. Excess hydrogen may be removed in a hydrogen separation step downstream of the hydrogenator. The remaining components of the hydrogenator outlet stream are reacted in a catalytic reactor. Carbon dioxide may be removed from the process. The gas products or residual products from the catalytic reactor may be conveyed, after separation, back to the mixed stream reactor, to a location downstream of the quench section, or both. The hydrogen-rich stream from the hydrogen separation step may be conveyed to an electrical generator or combined with hydrogen from the acetylene separation, or they may be utilized separately, as fuel in the electrical generator, as fuel in the process, or in subsequent chemical conversion steps. This process description applies equally to complete combustion, pyrolysis, and partial oxidation, as well as other direct and indirect heating methods that may be used to reach reaction temperature, except that stream compositions may be expected to vary accordingly. 
         FIG. 12  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention that further comprise process steps in which ethylene is separated from the gas stream exiting the acetylene separation step that follows the quench section. The ethylene that is separated may be used in subsequent processing or chemical conversion. 
         FIG. 13  is a schematic process flow diagram illustrating preferred embodiments of the process of the present invention in which the produced natural gas is split into at least two streams; one containing mostly methane, and at least one containing ethane and heavier components. These at least two streams can be reacted separately in two different reactors (or reacted in the same reactor but in different sections) that maintain different process conditions, depending on process needs. The separated natural gas fractions may be used to make the same product or different products. The use of a portion of the liquid product as fuel is also provided in contemplation of applications in which the most valuable or locally useful product is ethylene. A preferred embodiment of the process of the present invention is also illustrated in which a separation of unsaturated hydrocarbons from the product recycle stream is provided such that these components are not returned to the reactor, to improve conversion and reduce carbon production. 
     
    
    
     DETAILED DESCRIPTION 
     Herein will be described in detail specific preferred embodiments of the present invention, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. The present invention is susceptible to preferred embodiments of different forms or order and should not be interpreted to be limited to the specifically expressed methods or compositions contained herein. In particular, various preferred embodiments of the present invention provide a number of different configurations of the overall gas to liquid conversion process. 
     Referring now to  FIG. 1 , shown therein are certain preferred embodiments for producing a liquid product such as naphtha or gasoline or diesel from natural gas in accordance with the present invention. In these preferred embodiments, impurities and contaminants may be first removed from the inlet natural gas stream. Thereafter, a portion of the natural gas feed is diverted from the feed stream to a burner, which may preferably be an in-line upstream burner, where the diverted natural gas is burned, preferably with oxygen enriched air such that NO x  production from the combustion section of the reactor is minimized. As shown in  FIG. 1 , produced gas stream  8  may be first cleaned of contaminants in natural gas contaminant removal  10  to produce clean gas stream  12 . Clean gas stream  12  may preferably be separated into inlet gas feed stream  14  and inlet gas burn stream  16 . Inlet gas feed stream  14  is conveyed to the reaction section  210  of the reactor  200 . Inlet gas burn stream  16  is conveyed to the combustion section  110  of the reactor  200 . Oxygen or oxygen-containing gas is provided to combustion section  110  via oxygen line  6 . Nitrogen via nitrogen line  3  and/or steam via steam line  5  preferably may also be provided to reaction section  210  via inlet stream  4 . Inlet gas feed stream  14  is preferably pre-heated in pre-heaters (not shown) before it is heated to the preferred reaction temperature by direct heat exchange through combination with the hydrocarbon-combustion gas. The flame temperature of inlet gas burn stream  16  is preferably adequate to reach a desired reaction temperature preferably between 1000K and 2800K with air or oxygen or a combination of air and oxygen. The addition of water or steam (not shown) to the combustion section  110  of the reactor may be used to lower and thereby control the combustion gas temperature. The residence time of the combined combustion and feed gas in the reaction section  210  of the reactor should be sufficient to convert inlet gas feed stream  14  to acetylene, ethylene, and other reactive compounds, and not so long as to allow significant further reactions to occur before quenching, which is discussed below. It is preferred to maintain the residence time to under 100 milliseconds and, more preferably, under 80 milliseconds, to minimize coke formation. Residence times in excess of 0.1 milliseconds and more desirably 0.5 milliseconds are preferred to obtain sufficient conversion. The desired products from this series of reactions are ethylene and acetylene and most preferably acetylene. 
     Suppression of the production of other components may be required to achieve the desired reactive products. This may be accomplished by such methods as adjusting the reaction temperature and pressure, and/or quenching after a desired residence time. It is preferred to maintain the pressure of the natural gas within the reaction section  210  of the reactor  200  to between 1 and 20 bar (100-2000 kPa) to achieve the preferred reactive products. The reactive products resulting from reaction in reaction section  210  of the reactor leave with the combustion products and any unconverted feed through the reaction section outlet stream  212 . The desired reactive products of the reactions are designated herein as “reactive hydrocarbon products.” 
     The temperature rise in the feed, combustion, or combined gas should preferably occur in a short period of time. The reactor  200  may preferably be designed to accommodate one or more natural gas feed streams, which may employ natural gas combined with other gas components including, but not limited to: hydrogen, carbon monoxide, carbon dioxide, ethane, and ethylene. The reactor  200  may preferably have one or more oxidant feed streams, such as an oxygen stream and an oxygen-containing stream such as an air stream, which employ unequal oxidant concentrations for purposes of temperature or composition control. As is well known to those skilled in the art, Reactor  200  may comprise a single device or multiple devices. Each device may comprise one or more sections. In the example shown in  FIG. 1 , products from combustion section  110  go to reaction section  210  schematically as stream  112 . Depending on the type and configuration of reactor  200  used, stream  112  may not be isolatable. 
     To stop the desired reactions taking place in reaction section  210 , prevent the reverse reactions, or prevent further reactions to form carbon and other hydrocarbon compounds, rapid cooling or “quenching” is preferred in quench  310 , and it is more preferred that quenching take place within about 1 to 100 milliseconds. As shown in, for example,  FIG. 1 , reaction section outlet stream  212  is directed to quench section  310  where it is quenched before exiting through quench outlet stream  312 . The quench system  310  preferably achieves quenching of reaction section outlet stream  212  by any of the methods known in the art including, without limitation, spraying a quench fluid such as steam, water, oil, or liquid product into a reactor quench chamber; conveying through or into water, natural gas feed, or liquid products; preheating other streams such as  6 ,  12 , or  14  of  FIG. 1 ; generating steam; or expanding in a kinetic energy quench, such as a Joule Thompson expander, choke nozzle, or turbo expander. Use of certain quench fluids may induce further chemical reactions to occur, possibly creating additional reactive hydrocarbon products, thereby increasing the overall energy and economic efficiency of the process, particularly when recovered or recycled streams from downstream processing steps are used as the quench fluids. Quenching can be accomplished in multiple steps using different means, fluids, or both. Accordingly, quench section  310  may be incorporated within reactor  200 , may comprise a separate vessel or device from reactor  200 , or both. 
     Referring again to  FIG. 1 , it is to be noted that “lean” natural gas, i.e., gas with 95% or greater methane, reacts to mostly acetylene as a reactive product. Where the produced natural gas stream  8  is lean, it is preferred to operate the reaction section  210  in the upper end of the available temperature range to achieve a higher content of alkynes in the product, in particular acetylene. In contrast, with a richer natural gas stream, it may be preferable to operate reaction section  210  at a temperature lower in the desirable range to achieve a higher content of alkenes in the product, primarily ethylene. 
     In certain preferred embodiments illustrated in  FIG. 1 , a portion of the product of hydrogen separator  20  represented by stream  26  may be recycled and burned in the combustion section  110  of reactor  200 . Stream  22  comprising hydrogen from hydrogen separator  20  may be used in any number of processes (not shown) or may be burned as fuel. A portion of stream  22 , shown as stream  23 , may preferably be used in electrical generator  50 , which may comprise a fuel cell or fuel cells, or any other hydrogen-fed electrical power generation device as known in the art to, for example, generate water and electricity by combination with oxygen, or by burning with oxygen in a combustion turbine. It is also within the scope of this invention that the aforementioned hydrogen can be used indirectly to generate electricity by any method known to those skilled in the art, including burning or pressure reduction, wherein the energy from burning or pressure reduction is used first to impart energy to a second substance, such as water to create steam or steam to create higher pressure steam, such that the second substance is used to generate electrical energy. The particular equipment employed in electrical generator  50  is not important to the embodiment of the invention, and any mechanism reasonably known to those skilled in the art may preferably be employed herein without departing from the scope of the invention. The term “portion” as used throughout this document is intended to mean a variable quantity ranging from none to all (i.e. 0% to 100%) with the specific quantity being dependent upon many internal factors, such as compositions, flows, operating parameters and the like as well as on factors external to the process such as desired products and by-products, or availability and cost of electrical power, fuel, or utilities. Where “portion” is used to refer to none or 0% of a chemical component in the context of a process step, thus indicating that the process step is not performed, it should be understood to be synonymous with the term “optionally” in the context of the process step. 
     As further shown in  FIG. 1 , hydrogen separator outlet stream  28 , which comprises the reactive hydrocarbon products, is conveyed from hydrogen separator  20  to catalytic reactor  30 . Catalytic reactor  30  is a catalytic liquefaction reactor that may include internal recycle and is designed to convert the reactive hydrocarbon products to hydrocarbon liquids such as naphtha or gasoline. This reaction preferably is catalyzed to suppress the reaction of acetylene to benzene and to enhance the conversion of reactive hydrocarbon products to hydrocarbon liquids such as naphtha or gasoline, which are preferred for the method of this invention. 
     Catalytic reactor  30  shown in, for example,  FIG. 1 , preferably produces predominantly naphtha or gasoline, but may also produce some aromatic and cyclic compounds. The vapor pressure of naphtha or gasoline is about 1 bar (100 kPa) at 40° C. Thus, the products can be transported easily via truck or ship. Heavier hydrocarbons such as crude oil may optionally be blended with the liquid products to reduce the vapor pressure of liquids to be transported, as is known in the art. 
     The reaction(s) in catalytic reactor  30  to produce naphtha or gasoline is/are thermodynamically favorable. The equilibrium thermodynamics for the reactions of acetylene and ethylene with methane are more favorable at low to moderate temperatures (300K-1000K). It is well known in the chemical art that the C 2+  hydrocarbons can be converted to higher molecular weight hydrocarbons using acid catalysts, such as the zeolites H-ZSM-5 or Ultrastable Y (USY). 
     Applicants have discovered that the amount of Brønsted (or “Broenstead”) Acid sites on the catalyst should be maximized in comparison to the Lewis acid sites. This may be accomplished by increasing the silica to alumina ratio in the catalyst (Y Zeolites typically have Si/Al ratios of 2-8, whereas ZSM-5 typically has an Si/Al ratio of 15-30,000). Other alkylation catalysts are known in the chemical industry. In some preferred embodiments of the present invention, the reactions of acetylene and ethylene to benzene are suppressed, and the reactions of these reactive hydrocarbon products with methane is enhanced. The inlet streams, including the natural gas streams, may be preheated if desired, using methods such as electric arc, resistance heater, plasma generator, fuel cell, combustion heater, and combinations thereof, as will be recognized by those skilled in the art. The preferred reaction conditions comprise temperatures in the range of from about 300K to about 1000K, and pressures in the range of from about 2 bar (200 kPa) to about 30 bar (3 MPa). The products of the liquefaction reaction leave catalytic reactor  30  through catalytic reactor outlet stream  32 . 
     Referring still to  FIG. 1 , catalytic reactor outlet stream  32  may preferably be sent to product separator  40 . The primary purpose of product separator  40  is to separate the desired hydrocarbon liquid products from any lighter, primarily gaseous, components that may remain after the liquefaction reactions. It should be understood that internal cooling (not shown) is considered a part of product separator  40 . Depending upon the method of final separation and the optimum conditions for that separation, cooling of the liquefaction reactor outlet stream  32  after the reaction may be desired and is within the scope of the present invention. 
     Product separator  40 , which may be considered a part of the catalytic reactor  30 , may preferably comprise any appropriate hydrocarbon gas-liquid separation methods as will be known to, and within the skill of, those practicing in the art. If the product separator  40  is simply a gas-liquid or flash separation, cooling may be necessary. Distillation, adsorption or absorption separation processes, including pressure-swing adsorption and membrane separation, may also be used for the product separator  40 . The liquid hydrocarbons/products separated in product separator  40  may preferably be sent to storage or transport facilities via liquid product stream  42 , which is the outlet stream comprising liquid product from product separator  40 . A portion of the primarily gaseous components separated in product separator  40 , shown as stream  43 , may preferably be sent to combustion section  110  of reactor  200  via stream  44  as fuel for combustion, allowing for the reduction in whole or in part of the required flow of fuel stream  16 . A portion of stream  43  may be sent via stream  45  to reaction section  210  of reactor  200  as a recycle to feed. Stream  43  may be burned as fuel or used for other purposes, such as electrical power generation (not shown). Vapor or liquid may be removed from product separator  40  as stream  46 . Depending on its composition and quantity, stream  46  may be either sent to quench section  310  via stream  461  for reaction quenching or subsequent cooling, or recycled via stream  462  to the quench section  310  outlet stream  312 . In some cases, it may be more efficient instead to recycle stream  46  to other points in the process (not shown), such as to catalytic reactor  30 . 
     Note that processing steps may be added after catalytic reactor  30  and before product separator  40  or, after product separator  40 , to convert the hydrocarbon liquids such as naphtha or gasoline to heavier compounds such as diesel fuel. 
     In other preferred embodiments, shown in  FIG. 2 , feed and fuel are introduced to the reactor  200  together via inlet gas stream  12 . Oxidant, insufficient for complete combustion, is introduced to the reactor  200  via stream  6 , providing for incomplete combustion in combustion section  110 . Reactive products, comprising the desired reactive hydrocarbon products, are then formed during and within the incomplete combustion process. The preferred products from this series of reactions comprise ethylene and acetylene, and most preferably acetylene. Suppression of the production of other components may be required to achieve the desired reactive hydrocarbon products. This may be accomplished by such methods as adjusting the reaction temperature and pressure and/or quenching after a desired residence time. Carbon dioxide may be removed from outlet stream  312  via carbon dioxide separator  410  to stream  414 , by which it may be removed from the process, or a portion of stream  414  may be recycled to the reaction section  210  via stream  416  and inlet stream  4  to reduce carbon formation or improve reaction yield. Carbon dioxide may be separated from other streams or locations (not designated in  FIG. 2 ) within the process to be either removed from the process or recycled, where such separation may be either ‘in addition to’ or ‘in place of’ carbon dioxide separator  410 . As mentioned above, the desired hydrocarbon products of the reactions are designated herein as “reactive hydrocarbon products”. It is preferred to maintain the pressure of the natural gas within the reaction section  210  of the reactor between 1 and 20 bar (100-2000 kPa) to achieve the reactive hydrocarbon products. The reactive hydrocarbon products resulting from reaction in reaction section  210  of the reactor  200  leave with the combustion products and any unconverted feed through the reaction section outlet stream  212 . 
     In other preferred embodiments, shown in  FIG. 3 , natural gas in stream  12  to be burned in combustion section  110  is combined in the reactor  200  with at least hydrogen that has been produced in the reactor with the reactive hydrocarbon products and removed downstream. The hydrogen-containing stream  124  may be preferably separated from the outlet stream  412  in H 2 /CO separator  120  by conventional means including, but not limited to, pressure swing absorption, membrane separation, cryogenic processing, and other gas separation techniques commonly practiced by those skilled in the art. When insufficient oxygen via stream  6  is introduced to combustor  110  to provide for complete combustion of either the separate stream of natural gas  12  intended as combustion gas or the combined stream of natural gas which serves as feed gas and combustion gas, carbon monoxide may be formed. If formed, this carbon monoxide may be combined in whole or in part with the hydrogen-containing stream  124  that may be separated in separator  120  and recycled to the combustion section  110 . Use of carbon monoxide in this manner may supply additional energy to the combustion process that would otherwise not be available, and may preferably provide a source of control for the combustion temperature of the natural gas mixture in combustion section  110  as the combustion of carbon monoxide will, in general, deliver less energy to the combustion process than the natural gas hydrocarbon components or hydrogen, and may preferably provide a reactant that will alter and diminish the severity of reaction conditions that lead to coke formation, thus reducing coke formation. Separator  120  outlet stream  122  comprising the reactive hydrocarbon products is sent to catalytic reactor  30  for liquefaction. A stream comprising at least hydrogen and carbon monoxide can be taken from H2/CO separator  120  as stream  126  and sent to further processing (not shown), such as, for example, methanol production or Fisher-Tropsch reactions or units. Depending on composition, stream  126  may comprise syngas, or synthesis gas. It is well known that syngas and methanol are intermediates in the production of many different chemical and fuel production processes. A portion of stream  126  as stream  128  may be subjected to further separation in separator  20 , yielding a stream  22  comprising hydrogen. Portions of stream  126 , or many of their components if separated, can also be used to generate electricity, burned as fuel, flared, or vented, as can the hydrogen lean gas stream  27  from separator  20 . 
     In other preferred embodiments, such as those shown in  FIG. 4 , outlet stream  114  from furnace  111  goes to reaction section  210 . Depending on the configuration of reactor  200  used, stream  114  may not be isolatable. Section  210  outlet stream  212  produced by pyrolysis, and containing reactive hydrocarbon components that comprise reactive hydrocarbon products comprising acetylene and ethylene, as well as hydrogen, unreacted hydrocarbons, carbon monoxide, and carbon dioxide, is quenched in quench section  310 . Carbon dioxide may be removed in carbon dioxide separator  410 , and resulting stream  412  may be subjected to selective separation at non-acetylene removal  600  such that principally acetylene, the preferred reactive hydrocarbon, is separated from stream  412 . The stream  602  that contains acetylene may be selectively subjected to hydrogenation in hydrogenator  700  apart from the stream  412  from which it was removed. Hydrogenator  700  outlet stream  702  comprising ethylene may be sent to reactor  30 . A portion of the acetylene lean gas from non-acetylene removal  600  represented by stream  604  may be burned in furnace  111 . Depending upon composition, the stream  606  from which acetylene is removed may comprise syngas, or synthesis gas, and could be, for example, used for methanol production or in Fisher-Tropsch reactions or units. Stream  606  may be returned in part or whole via stream  607  and recycle stream  295  to furnace  111  to be burned as fuel, recycled as feed, or both. A portion of stream  606  may be sent via stream  605  to separator  20 . Stream  22  comprising hydrogen can be returned, in whole or in part, as streams  25  and  295  to furnace  111 . A portion of the hydrogen recovered in separator  20  may be supplied to hydrogenator  700  via stream  24 . A portion of stream  606  may be sent to further processing (not shown), burned as fuel, used to generate electricity, flared, or vented. 
     In other preferred embodiments, shown in  FIG. 5 , the reactor outlet stream produced by partial oxidation, containing reactive hydrocarbon components, which preferably comprise reactive hydrocarbon products such as acetylene and ethylene, as well as hydrogen, unreacted hydrocarbons, carbon monoxide, carbon dioxide and, depending on the operation conditions, nitrogen, may be subjected to selective separation such that principally acetylene, the preferred reactive hydrocarbon, is separated from the remaining products at non-acetylene removal  600 . This separation may be performed according to known methods such as absorption, distillation, selective membrane permeation, pressure swing absorption, or other gas separation techniques known to those skilled in the art. The stream  602  that contains acetylene may be selectively subjected to hydrogenation at  700  apart from the stream  412  from which it was removed. This acetylene rich stream may be wholly acetylene or combined with other gas fractions or liquid fractions used for, or to enhance, the separation process. A portion of the acetylene lean gas from non-acetylene removal  600  represented by stream  604  may be burned in combustion section  110  of reactor  200 . Hydrogenator  700  outlet stream  702  may be sent to catalytic reactor  30  for liquefaction and subsequent product separation. A portion of stream  702  may be sent via stream  704  to ethylene storage  900 . The stream  606  that has been reduced in acetylene concentration may be subjected to gas separation techniques whereby the ethylene fraction, if in sufficient concentration, may be separated at ethylene separator  800  from the stream  802  of remaining components. If formed, this stream  804 , either alone or in combination with stream  704 , can be reserved at ethylene storage  900  for recycle, conversion, purification or export. If desired, streams sent to ethylene storage  900  can be subjected to liquefaction by means of a catalyst to form liquid hydrocarbons independent of catalytic reactor  30  (not shown). Remaining components stream  802 , including but not limited to hydrogen, carbon dioxide, and carbon monoxide, and potentially unreacted hydrocarbons, nitrogen, and unseparated ethylene, as examples of components of this stream, can be recycled to reactor  200  via stream  807  and recycle stream  295 . Stream  802  can also be sent to further processing (not shown). Depending on composition, stream  802  may comprise syngas, or synthesis gas, and could be, for example, used for methanol production or in Fisher-Tropsch reactions or units. It is well known that syngas and methanol are intermediates in the production of many different chemical and fuel production processes. Stream  802  can also be subjected to further separation, in some cases yielding a hydrogen stream, such as, for example, when a portion is sent via stream  805  to hydrogen separator  20 . Stream  802 , or streams separated from stream  802 , can also be burned as fuel, used to generate electricity, flared, or vented. 
     In other preferred embodiments, shown in  FIG. 6 , the reactor outlet stream produced by pyrolysis, containing reactive hydrocarbon components which comprise acetylene and ethylene as well as hydrogen, unreacted hydrocarbons, carbon monoxide, carbon dioxide and depending on the operation conditions, nitrogen, may be subjected to selective separation such that principally acetylene, the preferred reactive hydrocarbon product, is separated from the remaining products at non-acetylene removal  600 . The stream  602  that contains acetylene may be selectively subjected to hydrogenation at  700  apart from the stream  412  from which it was removed. The stream  606  that has been reduced in acetylene concentration may be subject to gas separation techniques whereby the ethylene fraction, if in sufficient concentration, may be separated at ethylene separator  800  from the stream  802  of remaining components. If formed, this stream  804  of separated ethylene may be recombined via stream  803  with the stream  702  formed by hydrogenation of acetylene at  700  to form a combined ethylene stream. This combined ethylene stream can be subjected to liquefaction by means of catalytic reactor  30  to form stream  32  as feed to product separator  40 . Either ethylene stream  704  or  804 , or both (separately or combined), can be reserved at ethylene storage  900  for recycle, conversion, purification, or export. Remaining components stream  802 , including but not limited to hydrogen, carbon dioxide, and carbon monoxide, and potentially unreacted hydrocarbons, nitrogen, and unseparated ethylene, as examples of components of this stream, can be recycled as feed, fuel, or both to reactor  200  via stream  807  and recycle stream  295 , either entering the reactor directly or mixing with one or more of the other inlet streams. Stream  802  can also be sent to further processing (not shown). Depending on composition, stream  802  may comprise syngas, and could be, for example, used for methanol production or in Fisher-Tropsch reactions or units. Stream  802  can also be subjected to further separation, in some cases yielding a hydrogen stream. Stream  802 , or streams separated from stream  802 , can also be burned as fuel, used to generate electricity, flared, or vented. 
     In other preferred embodiments, shown in  FIG. 7 , the natural gas stream  12  is directed through furnace  111 , which is heated in part by combustion with oxidant provided by oxidant stream  6 , preferably comprising air or oxygen, such that sufficient temperature is created for a sufficient yet controlled time to convert a portion of the natural gas stream to reactive hydrocarbon products, preferably comprising ethylene and acetylene, and most preferably acetylene, in reactor  200 . The reaction duration is limited, as described above, by quench section  310  wherein a fluid, such as water, heavy hydrocarbon, inorganic liquid, steam or other fluid is added in sufficient quantity to abate further reaction. As previously stated, quenching can be accomplished in multiple steps using different means, fluids, or both, or can be done in a single step using a single means or fluid. The gas stream  312  that emerges from the quench section  310  may be subjected to non-acetylene removal  600  such that the acetylene containing stream  602  is passed on to catalytic reactor  30  via hydrogenator  700 . The product stream  32  of the catalytic reactor  30  may be subjected to separation in product separator  40  in which the liquid hydrocarbons and water are removed. Gas removed from separator  40  as stream  43  may be recycled via stream  45  to the reaction section  210  of reactor  200  as supplemental feed, sent via stream  44  to furnace  111  of reactor  200  as fuel for combustion, or both. A portion of the gas removed from separator  40  as stream  46  may be recycled to catalytic reactor  30  through stream  463 , particularly if the gas contains substantial quantities of hydrocarbons known in the art as being beneficial to the liquefaction process. Stream  46  may be combined via stream  464  in whole or in part with stream  606  from non-acetylene removal  600  and sent to further processing. Depending on composition, stream  606 , or the combination of streams  606  and  464 , may comprise syngas. A portion of stream  46  may be routed to hydrogen separator  20  either directly via stream  465  or indirectly via streams  464 ,  606  and  605 , particularly, for example, in cases in which stream  46  contains substantial but impure hydrogen. A portion of stream  46  can also be burned as fuel, used to generate electricity, sent to further processing, flared, or vented. 
     In other preferred embodiments, shown in  FIG. 8 , the natural gas stream  16  is directed through an electrical heater  113  and is heated by electrical energy such that adequate temperature is created for a sufficient yet controlled time to convert a portion of the natural gas stream to reactive hydrocarbon products, preferably comprising ethylene and acetylene, and most preferably acetylene, in reactor  200 . Depending on the configuration of reactor  200  used, outlet stream  116  from electrical heater  113  to reaction section  210  may not be isolatable. A portion of the gas removed from separator  40  as stream  46  may be recycled to reactor  200  through stream  466 , particularly if the gas contains substantial quantities of hydrocarbons. The acetylene-lean stream  606  via stream  605  may be subjected to further separation at separator  20  such that a hydrogen stream  22  is created, a portion of which as stream  23  can be used to generate electricity in electrical generator  50  as described previously. A notable but not exclusive use for the electrical power produced in generator  50 , schematically shown as energy stream  52 , is to provide the energy required by heater  113  such as depicted with energy stream  54 . Various streams created in the process, such as, for example, streams  22 ,  27 ,  43 ,  46 , and  606 , may be used to generate electricity in external facilities not shown. Power produced either in generator  50  or in external facilities may be used to satisfy a portion of the electrical needs of the process. 
     In other preferred embodiments, shown in  FIG. 9 , the process is enhanced by utilization of a portion of the recovered hydrogen via stream  29  as fuel to be used in combustion section  110 . 
     In other preferred embodiments, shown in  FIG. 10 , the process as described in  FIG. 8  is practiced such that natural gas via stream  18  may be utilized as fuel for the electrical generator  60  that provides power via energy stream  62  to the electrical heater  113 . Other streams created in the process that are suitable for generation of electricity may be sent in whole or in part to generator  60  as supplemental fuel to reduce the flow of stream  18 . Hydrogen produced in the various steps of the process, such as cracking and catalytic reaction, may be separated out and utilized for purposes other than electrical power generation exclusively, for example, as further illustrated in the drawing figures. 
     In other preferred embodiments, shown in  FIG. 11 , natural gas is heated to reaction temperature by incomplete combustion in reactor  200 . The reactor outlet stream is quenched in quench section  310  to substantially stop chemical reaction(s). Acetylene may be separated at non-acetylene removal  600  from the other reactive hydrocarbon products and non-hydrocarbons, and the acetylene-rich stream  602  may be subjected to hydrogenation at hydrogenator  700 . The product of hydrogenation, principally ethylene, may be subjected thereafter to liquefaction at catalytic reactor  30  (via hydrogen separator  290 ) or sent via stream  704  to ethylene storage  900  for later processing. Hydrogen, if there is excess, may be removed at separator  290  from the outlet stream  702  of the hydrogenator via stream  292 . The remaining components of the separator  290  outlet stream  294  may be conveyed to catalytic reactor  30  wherein the reactive hydrocarbon products are converted in reactor  30  and then product separator  40  to liquid product stream  42 , comprising principally naphtha, diesel and gasoline. An intermediate reaction stream  34  may be taken from reactor  30  and sent to alternate processing (not shown). Stream  34  may be comprised of components such as hydrogen, carbon monoxide, carbon dioxide, ethylene, other hydrocarbons, and liquefaction reaction intermediates and products. A portion of the acetylene lean gas from non-acetylene removal  600  represented as stream  604  may be sent through carbon dioxide separator  450 , where some of the carbon dioxide present may be removed as stream  452 , prior to sending the gas as stream  454  to be burned in combustion section  110  of reactor  200 . Carbon dioxide may be removed from acetylene lean stream  606  via carbon dioxide separator  410  to stream  414 , by which it may be removed from the process, or a portion of stream  414  may be recycled to reaction section  210  of reactor  200  via stream  416  and inlet stream  4  to reduce carbon formation or improve reaction yield. Sources of carbon dioxide other than stream  414  may be used, including, but not limited to, a portion of stream  452 , another carbon dioxide recovery location within the process (not shown), or an external source. Outlet stream  412  from separator  410  may be returned in whole or in part via stream  413  and recycle stream  417  to reactor  200  to be burned as fuel, recycled as feed, or both. A portion of stream  412  may be burned as fuel, used to generate electricity, flared, or vented. Depending on composition, stream  606  or stream  412  may comprise syngas, or synthesis gas. A portion of either stream  606  or stream  412  may be sent to further processing (not shown). A portion of steam  412  may be sent via stream  418  to hydrogen separator  20 . Stream  22  comprising hydrogen can be returned, in whole or in part, as streams  25  and  417  to reactor  200 . A portion of hydrogen stream  22  may be sent to electrical generator  50  via stream  23 . Hydrogen stream  292  from separator  290  may have the same disposition options as stream  22 . Streams  292  and  22  can be combined as shown and used jointly, or they can be kept separate and used independently for the same purpose or different purposes. A portion of hydrogen lean gas outlet stream  27  from separator  20  can be recycled via streams  272  and  417  to be burned in combustion section  110  of reactor  200 . Portions of stream  27  can also be used to generate electricity, burned as fuel, flared, or vented. This process description applies to complete combustion or pyrolysis as well as partial oxidation, with the exception that stream compositions may be expected to vary, as will be known to those skilled in the art. 
     In other preferred embodiments, such as those shown in  FIG. 12 , the process described above and illustrated in  FIG. 11  may be modified such that the acetylene lean stream  606  formed from removal of acetylene at non-acetylene removal  600  downstream of the quench section  310  is subjected to separation techniques at ethylene separator  800  whereby the ethylene fraction, if in sufficient concentration and quantity, may be separated from the stream  802  of remaining components. If formed, this stream  804  of separated ethylene may be recombined in whole or in part via stream  803  with the hydrogen separator  290  outlet stream  294  to form a combined ethylene stream. This combined ethylene stream can be subjected to liquefaction in catalytic reactor  30 . Streams  294  and  803  may also be sent separately to reactor  30  (not shown). Either ethylene stream  704  or stream  804 , or both (separately or combined), can be reserved at ethylene storage  900  for recycle, conversion, purification, or export. A portion of separator  800  outlet stream  802  may be recycled to reactor  200  via stream  807  and recycle stream  817 . It may be desirable to remove some carbon dioxide from stream  802 , which may be done by sending a portion of stream  802  via stream  806  through carbon dioxide separator  410 , such as, for example, to limit accumulation of carbon dioxide in the process when recycling a portion of the outlet stream  412  to reactor  200  via stream  413  and recycle streams  417  and  817 . Another example for desiring some carbon dioxide removal would be to benefit the hydrogen separator  20  by increasing performance or efficiency, or by reducing equipment size or costs, or some combination thereof. Since streams  802  and  412  may comprise syngas, still another example for desiring some carbon dioxide removal would be to alter the stoichiometric ratio of the syngas, as is well understood in the art, prior to sending to further processing (not shown). It will be easily recognized that carbon dioxide may be separated from other streams or locations within the process that are not designated in  FIG. 12  as removal sites. It will also be easily recognized by those skilled in the art that separator  410  could be located upstream of separator  800  and fed with a portion of stream  606 , which is the reverse order from that shown. A portion of stream  452  comprising carbon dioxide may be added to reactor  200  via stream  453  and inlet stream  4 . 
     In other preferred embodiments, shown in  FIG. 13 , the process described above and shown in  FIG. 12  is modified such that the natural gas stream  9 , which may have been subjected to contaminant removal at natural gas contaminant removal  10 , is separated at natural gas separator  170  into at least two streams, one stream  172  that is rich in methane and one stream  176  that is lean in methane; a portion of the liquid product stream  42  may be recirculated via product recycle stream  47  to combustion section  110  through stream  471 , to reaction section  210  through stream  472 , or to quench section  310  through stream  473 , or to some combination of these three recycle points; the unsaturated components of product separator outlet stream  43  may be removed as stream  432  at unsaturates removal  430  prior to recycling the remaining components via stream  434  to combustion section  110  through stream  435 , to reaction section  210  through  436 , or both. The separation of natural gas into two or more streams of different composition allows additional flexibility in selection of the manner in which each stream will be utilized in subsequent processing, such as, by way of illustration and not limitation, combustion, cracking, or quenching. A portion of methane rich stream  172  may be sent to reactor  200  via stream  174 . A portion of the methane lean stream  176 , comprising ethane and heavier hydrocarbons, may be sent to combustion section  110  through stream  177 , to reactor section  210  through stream  178 , to quench section  310  through stream  179 , or to any combination of these. The separation of natural gas into two or more streams also allows for alternate, parallel, or separate processing of the different streams (not shown) as well as set aside for storage. Processing paths may be recombined at any location within the process judged to be efficient or economical or beneficial. Reverting a portion of the liquid product stream  42  to the reactor  200  or to quench section  310  may be useful when the liquid has much less or no value compared to the gaseous products. The liquid product stream  42  may contain solids in slurry form. The removal of the unsaturated components at unsaturates removal  430  from the vapor fraction removed from separator  40  that is recycled to the reactor  200  may preferably have the effect of reducing carbon formation and increasing acetylene formation. 
     In other preferred embodiments, electricity generator  50  may comprise a fuel cell or cells. With respect to fuel cells, any fuel cell design that uses a hydrogen stream and an oxygen steam may preferably be used, for example by way of illustration and not limitation, polymer electrolyte, alkaline, phosphoric acid, molten carbonate, and solid oxide fuel cells. The heat generated by the fuel cell or a turbine or turbines, may be used to boil the water exiting the fuel cell, thus forming steam. This resulting steam may then preferably be used to generate electricity, for instance in a steam turbine (not shown but within the scope of electrical generator  50 , as is well known in the art). The electricity may then be sold or, as shown in for example  FIG. 8 , may be used to provide heat to preheat any of the appropriate feed, fuel, or oxidant streams, or to provide heat to other process equipment, such as, but not limited to, pumps, compressors, fans, and other conventional equipment that may be employed to accomplish the goals of the embodiments of the above-described processes of the present invention. In other preferred embodiments, such as those shown in  FIG. 3 , hydrogen as indicated at stream  22  from hydrogen separator  20  may preferably be produced as a saleable product. In still other preferred embodiments, such as those illustrated in  FIG. 11 , recycle stream  417  may preferably be burned directly in combustion section  110 . In other preferred embodiments, such as those illustrated in  FIG. 10 , a portion of inlet gas stream  12  may be separated and routed via supplemental gas stream  18  to electrical generator  60 . In this way, additional electrical power may be generated as described above. As will be understood by those skilled in the art, the electrical generators  50  or  60 , or both of the above-described preferred embodiments may be eliminated from the process entirely so as to maximize hydrogen production for other purposes, such as, for example, direct combustion, storage, or alternate chemical conversion. 
     In still other preferred embodiments, as shown for example in  FIGS. 11 and 12 , the acetylene containing stream may be directed to hydrogenation reactor  700 , where alkynes, preferably acetylene, may be converted into a preferred intermediate product, preferably comprising ethylene and other olefins. The non-acetylene containing stream(s) that flow(s) from the non-acetylene removal  600  may be redirected to the combustion section  110  of the reactor  200  via stream  604 , and/or further separated into its components via stream  606 , which preferably substantially comprises hydrogen, but which may comprise some carbon monoxide and smaller amounts of nitrogen, methane, ethylene, ethane, and other light gases, as is known in the art. The hydrogen, carbon monoxide, or mixture can be reserved for subsequent chemical reaction or conversion, or returned to the combustion section  110  of reactor  200 , or used to produce electrical power through combustion or other means as have been described above, or conventional methods that are known to those skilled in the art. If sufficient ethylene is present in the stream from which acetylene is removed, as shown in the case of stream  606  in the preferred embodiments illustrated in  FIG. 12 , this ethylene may be separated out at ethylene separator  800  and returned for example to the inlet of the catalytic reactor  30 , thus joining the product of the hydrogenator  700 , which preferably comprises substantially ethylene, with that of the upstream ethylene separator  800 , and thereby maximizing the amount of ethylene conveyed to the catalytic reactor  30 . 
     Traditional catalysts for conversion of alkynes to alkenes may preferably be used to convert acetylene to ethylene. These include nickel-boride, metallic palladium, and bimetallic catalysts such as palladium with a Group  1 B metal (copper, silver or gold). Some natural gas feed streams may contain trace amounts of sulfur compounds that may act as a poison for the hydrogenation catalyst. Accordingly, incoming sulfur compounds may react to form catalyst poisons, such as COS and H 2 S. It is preferable to remove or reduce the concentration of these catalyst poisons by processes well known to those in the art, such as activated carbon or amine based processes, and most preferably by zinc oxide processes. 
     In accordance with the above preferred embodiments, it should be noted that the products of the reactions within hydrogenator  700  are preferably conveyed to hydrogen separator  290  through hydrogenation outlet stream  702 . Because the conversion from acetylene to ethylene may not always be complete, hydrogenation outlet stream  702  may contain both acetylene and ethylene, as well as hydrogen and some higher molecular weight alkynes and alkenes. 
     In other preferred embodiments, product stream  606  from non-acetylene removal  600  may be routed variously to a secondary hydrogen separator  20 , illustrated for example in  FIGS. 11-13 . Like hydrogen separator  290 , this hydrogen separator  20  may be operated according to any of a variety of processes, including membrane or pressure swing processes, described for example in A. Malek and S. Farooq, “Hydrogen Purification from Refinery Fuel Gas by Pressure Swing Adsorption”, AIChE J. 44, 1985 ( 1998 ), which is hereby incorporated herein by reference for all purposes. 
     In an alternate preferred embodiment, the produced natural gas  8  provided may be sufficiently pure that contaminant removal is not required. In such a case, the contaminant removal  10  may preferably be by-passed or eliminated. The necessity of performing contaminant removal will depend upon the nature of the contaminants, the catalyst used, if any, in the hydrogenator  700 , the catalyst used in the catalytic reactor  30 , the materials of construction used throughout the process, and the operating conditions. 
     In another alternate preferred embodiment, some portion of ethylene may not be converted to liquid hydrocarbons by the direct route described herein. In such cases, the downstream equipment comprising the catalytic reactor  30  and product separator  40 , may preferably not be operated continuously or even at all. 
     While the preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. 
     The examples provided in the disclosure are presented for illustration and explanation purposes only and are not intended to limit the claims or embodiment of this invention. While the preferred embodiments of the invention have been shown and described, modification thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Process design criteria, pendant processing equipment, and the like for any given implementation of the invention will be readily ascertainable to one of skill in the art based upon the disclosure herein. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Use of the term “optionally” with respect to any element of the invention is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the invention. 
     The discussion of a reference in the Description of the Related Art is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.