Abstract:
An apparatus and method of producing methanol includes reacting a heated hydrocarbon-containing gas and an oxygen-containing gas in a reactor; to provide a product stream comprising methanol; and transferring heat from the product stream to the hydrocarbon-containing gas to heat the hydrocarbon containing gas. After removing methanol and CO 2  from the product stream, unprocessed hydrocarbons are mixed with the hydrocarbon containing gas fro reprocessing through the reactor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 11/319,093 filed on Dec. 27, 2005 which is a continuation-in-part of U.S. application Ser. No. 10/901,717 filed on Jul. 29, 2004. The disclosure of the above application is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a method of and an apparatus for producing methanol.  
         [0003]     Methods and apparatuses for conversion of methane into methanol are known. It is known to carry out a vapor-phase conversion of methane into a synthesis gas (mixture of CO and H 2 ) with its subsequent catalytic conversion into methanol as disclosed, for example, in Karavaev M. M., Leonov B. E., et al “Technology of Synthetic Methanol”, Moscow, “Chemistry”  1984 , pages 72-125. However, in order to realize this process it is necessary to provide a complicated equipment, to satisfy high requirements to purity of gas, to spend high quantities of energy for obtaining the synthesis gas and for its purification, and to have a significant number of intermittent stages from the process. Also, for medium and small enterprises with the capacity less than 2,000 tons/day it is not efficient.  
         [0004]     Russian Patent No. 2,162,460 includes a source of hydrocarbon-containing gas, a compressor and a heater for compression and heating of gas, a source of oxygen-containing gas with a compressor. It further includes successively arranged reactors with alternating mixing and reaction zones and means to supply the hydrocarbon-containing gas into a first mixing zone of the reactor and the oxygen-containing zone into each mixing zone, a recuperative heat exchanger for cooling of the reaction, mixture through a wall by a stream of cold hydrocarbon-containing gas of the heated hydrocarbon-containing gas into a heater, a cooler-condenser, a partial condenser for separation of waste gasses and liquid products with a subsequent separation of methanol, a pipeline for supply of the waste gas into the initial hydrocarbon-containing gas, and a pipeline for supply of waste oxygen-containing products into the first mixing zone of the reactor.  
         [0005]     In this apparatus, however, it is not possible to provide a fast withdrawal of heat of the highly exothermic reaction of oxidation of the hydrocarbon-containing gas because of the inherent limitations of the heat exchanger. This leads to the necessity to reduce the quantity of supplied hydrocarbon-containing gas and, further, it reduces the degree of conversion of the hydrocarbon-containing gas. Moreover, even with the use of oxygen as an oxidizer, it is not possible to provide an efficient recirculation of the hydrocarbon-containing gas due to fast increase of concentration of carbon oxides in it. A significant part of the supplied oxygen is wasted for oxidation of CO into CO 2 , which additionally reduces the degree of conversion of the initial hydrocarbon-containing gas and provides a further overheating of the reaction mixture. The apparatus also requires burning of an additional quantity of the initial hydrocarbon-containing gas in order to provide a stage of rectification of liquid products with vapor. Since it is necessary to cool the gas-liquid mixture after each reactor for separation of liquid products and subsequent heating before a next reactor, the apparatus is substantially complicated, the number of units is increased, and additional energy is wasted.  
         [0006]     A further method and apparatus for producing methanol is disclosed in the patent document RU 2,200,731, in which compressed heated hydrocarbon-containing gas and compressed oxygen-containing gas are introduced into mixing zones of successively arranged reactors, and the reaction is performed with a controlled heat pick-up by cooling of the reaction mixture with water condensate so that steam is obtained, and a degree of cooling of the reaction mixture is regulated by parameters of escaping steam, which is used in liquid product rectification stage.  
         [0007]     Other patent documents such as U.S. Pat. Nos. 2,196,188; 2,722,553; 4,152,407; 4,243,613; 4,530,826; 5,177,279; 5,959,168 and International Publication WO 96/06901 disclose further solutions for transformation of hydrocarbons.  
         [0008]     It is believed that the existing methods and apparatus for producing methanol can be further improved.  
       SUMMARY  
       [0009]     It is accordingly an object of the present invention to provide a method of and an apparatus for producing methanol, which is a further improvement of the existing methods and apparatuses.  
         [0010]     It is another feature of the present teachings to provide a method of and an apparatus for producing methanol which can be used with minimal processing of gas and gas-condensate deposits, and also at any gas consumer, such as power plants, gas distributing and gas reducing stations, chemical production facilities, etc., or small methane producers, (i.e., coal mines, oil production (flares), landfills, farms.)  
         [0011]     In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method of producing methanol, which includes the steps of supplying into a reactor a hydrocarbon-containing gas stream, supplying into the reactor an oxygen containing gas; carrying out in the reactor an oxidation of the hydrocarbon-containing gas by oxygen of said oxygen-containing gas; and, after removing impurities and products of the reaction, recycling un-reacted hydrocarbon gas into the hydrocarbon-containing gas stream for further reaction.  
         [0012]     Another feature of the present teachings is an apparatus for producing methanol, which has a reactor for receiving and reacting a hydrocarbon-containing gas stream with an oxygen-containing gas, to carry out in the reactor oxidation of the heated hydrocarbon-containing gas by oxygen of said oxygen-containing gas. The apparatus also has a means for supplying into the reactor a cold hydrocarbon-containing gas to be mixed directly with a mixture of said heated hydrocarbon containing gas and said oxygen containing gas at a later stage of the reaction to inhibit the decomposition of formaldehyde. Un-reacted hydrocarbon gas is then processed to remove products and contaminants before being recycled back into the hydrocarbon-containing gas stream.  
         [0013]     As can be seen, in accordance with the present teachings, a heated hydrocarbon-containing gas stream and oxygen-containing gas are supplied into a reaction zone or into a reactor, where a gas phase oxidation of the hydrocarbon-containing gas is performed at elevated temperature and pressure in the reaction zone. The reaction mixture is cooled before and is separated into waste gas and liquid product. The waste gas is scrubbed to remove CO 2  and returned to the heated hydrocarbon-containing gas stream. Cold hydrocarbon-containing gas is supplied into a regulation zone of the reactor to reduce the reaction temperature for example by 30-90° C. and thereby to provide a production and a redistribution of the ratio of products to produce corresponding quantities of methanol and formaldehyde.  
         [0014]     In accordance with the present teachings, during cooling of the reaction mixture in the partial condenser, heat is transmitted to an input stream supplied into a formaldehyde rectification column for performing rectification of formaldehyde and simultaneous regeneration of the primary scrubber solvent, methanol. Within the partial condenser, dry gas is separated from raw liquids, including methanol, ethanol, and water. The raw liquids, through the flash drum, are supplied into a rectification column. The temperature of the top of the column is, between about 70 and about 75° C., the pressure in the column is, for example, up to 0.2 MPa. The final product is supplied to storage or further processing. The dry gas is scrubbed to remove CO 2  and formaldehyde and is then returned to the reactor in the hydrocarbon input stream.  
         [0015]     The time of presence of the reaction mixture in the reactor is about 1.2 sec. The period of induction takes approximately 70% of this time, and thereafter a significant temperature increase of the mixture takes place. The content of methanol in the reacted gas is about 40% due to its high stability and selectivity, while the content of the formaldehyde is about 4% due to its lower stability and selectivity. In order to increase the portion of formaldehyde to 8-13% in the final product, the temperature of the reaction is reduced by 30-90° C. after the period of induction (after the formaldehyde has been formed) at 0.7-1.4 sec of reaction due to the injection of the cold hydrocarbon-containing gas into the regulating zone.  
         [0016]     When the temperature of reaction is changed from 370 C.° to 450° C., the content of aldehydes is increased from 5% to 13% and the content of organic acids is increased from 0.5% to 0.7%. The selectivity which is close to a maximum with respect to liquid organic products, including methanol and formaldehyde, is maintained using a concentration of oxygen in the initial gas mixture 2-2.8%.  
         [0017]     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIGS. 1A and 1B  are views schematically showing a system of an apparatus for producing methanol in accordance with the present teachings;  
         [0019]      FIGS. 2 and 3  are views illustrating concentrations of oxygen, formaldehyde and methanol during reactions in accordance with the prior art and in accordance with the present invention correspondingly; and  
         [0020]      FIG. 4  represents a graph depicting the yield oxygenates of the system as a function of recycle ratio 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     An apparatus for producing methanol in accordance with the present invention has a reactor  100  which facilitates a gas phase oxidation of a hydrocarbon-containing gas are shown in  FIGS. 1A and 1B .  FIG. 1B  details the inputs and outputs of the reactor. The reactor  100  has a reaction zone  102  which is provided with a device  104  for introducing a heated hydrocarbon-containing gas stream and a device  105  for introducing an oxygen-containing gas. As explained in detail below, the oxygen-containing gas preferably has greater than 80% oxygen content to reduce the accumulation of inert gases due to the recycling process.  
         [0022]     The reactor  100  further has a regulation zone  108  provided with an optional device  110  for introducing a cold hydrocarbon-containing gas stream for reducing the temperature of reaction during operation of the apparatus. In addition, the reactor  100  is provided with thermal pockets  112  for control and regulation of temperatures in corresponding zones, provided for example with thermocouples.  
         [0023]     The apparatus has a device  114  for cooling the reaction mixture before separation. Additionally, the partial condenser  122  incorporates a gas-liquid heat exchanger to further reduce the temperature of the products. The condenser  122  separates H 2 O and alcohols from a hydrocarbon-CO 2  mixture. The partial condenser  122  is preferably isobaric, as opposed to isothermal, to avoid pressure losses. The product stream enters, and liquid stream and gaseous stream exit the condenser  122 .  
         [0024]     Block  139  represents equipment which is configured to separate contaminants and products from a hydrocarbon-containing recycle gas component. In this regard, the equipment  139  is configured to remove CO 2  from the reduced product stream. The equipment  139  can take the form of a purge valve, absorber, membrane separator, or an adsorber. It is envisioned the equipment  139  can be used to regulate the percentage of other non-reactive components such as N 2  with, for example, a purge valve.  
         [0025]     In the event the system is configured to recover formaldehyde, the gaseous reduced product stream leaves the isobaric condenser  122  and is passed to the scrubber  134 . The scrubber  134  prevents the accumulation of CO 2  and allows the physical capture of formaldehyde. The scrubber  134  can utilize a mixture of methanol and water to physically absorb formaldehyde and CO 2  from the hydrocarbon gas recycle loop  135 . The efficiency of the scrubber  134 , which can operate adequately without refrigeration, is made possible due to the high operating pressure of the recycle loop  135 . This is opposed to cryogenically low temperatures utilized by traditional absorption processes. Other potential methods which can be utilized use materials such as various amines known to remove CO 2  and formaldehyde.  
         [0026]     The gases enter the scrubber  134  as a “dirty” gas with some amount of formaldehyde and CO 2  present. These components will only be present in relatively dilute amounts, so the duty of the methanol absorbent is also relatively small. To fulfill the minimum absorption requirements, modification of the flow rate of methanol or operating temperature of the scrubber column can be used. If it is desirable to operate at extremely low absorbent flow rates, then a lower temperature can be utilized, for example 0° C. If it is desirable to operate at ambient temperatures or temperatures achievable via cooling water, then a high flow rate can be utilized, for example, ten times that of the flow rate for 0° C. In either scenario, the pregnant methanol absorbent stream  14  is completely regenerated by the formaldehyde distillation column  138 . Optionally, the stream  14  from the scrubber  134  can be passed through the condenser  122  to provide cooling of the product stream and preheating of the methanol recycle to improve the energy efficiency of the formaldehyde distillation column  138 .  
         [0027]     The reactor  100  is connected with a compressor  124  and heater  126  for supply of compressed and heated oxygen-containing gas. The raw hydrocarbon-containing gas is mixed with cleaned hydrocarbon gas from the scrubber  134  and is heated using a heater  136 . In the event the raw hydrocarbons have a high CO 2  content, the raw hydrocarbons can be mixed with the reduced product hydrocarbon stream from the condenser  122  prior to the entry of the scrubber  134  for removal of contaminant gases prior to entering the reactor.  
         [0028]     The apparatus further has a unit for rectification of methanol which includes a flash drum  132 , rectification column  128 , and a vessel  130  from which methanol is supplied to storage or further processing. This rectification column  128  is used to separate methanol (light-key component) from ethanol (heavy-key component) and water (non-key component). As before, it is desirable for a portion of the heavy key to enter the distillate stream (as dictated by commercial specification for formalin). For methanol rectification, 99% or higher purity is typical and 99.999% is achievable with multiple columns. Stream  4  enters the column and the distillate, stream  5 , and bottoms, stream  8 , exit the column in liquid phase. Stream  8  has some amount of ethanol (and perhaps methanol, if ultra pure methanol was produced) and will be used as the basis of the aqueous makeup of the commercial formalin stream (stream  11 ). In this manner, some of the ethanol is recovered before the remainder is discarded in the liquid waste stream.  
         [0029]     Disposed between the column  128  and the condenser  122  is a flash drum  132  for removal of CO 2  and formaldehyde from the liquid product stream. The purpose of the flash drum  132  is to drop the pressure to an appropriate level before entry into the methanol rectification column  128  and to substantially remove any dissolved gases, typically CO 2  and formaldehyde, from the liquid product stream.  
         [0030]     In operation, the raw hydrocarbon-containing gas stream with a methane content for example up to 98% and the reduced hydrocarbon product stream are supplied from an installation for preparation of gas or any other source to the heater  136 , in which it is heated to temperature 430-470° C. The heated hydrocarbon-containing gas is then supplied into the reaction zone  102  of the reactor  100 . Compressed air with pressure, for example, of 7-8 MPa and with a ratio 80% to 100% and, preferably, 90% to 95% oxygen is supplied by the compressor  124  also into the reaction zone  102  of the reactor  100 . Oxidation reaction takes place in the reaction zone  102  of the reactor  100 . Between 2.0 and 3.0% O 2  of the total volume of the reactants are reacted with the heated hydrocarbon-containing gas stream as previously described. To limit the amount of N 2  within the system, for example to less than 30%-40%, or reduce the requisite size of the purge stream to achieve the same, the O 2  stream is preferably substantially pure, thus limiting the amount of N 2  entering the system. An optional second stream of cold or in other words a lower temperature hydrocarbon-containing gas than the gases in the reactor is supplied through the introducing device  108  into the regulation zone of the reactor  100 . This stream is regulated by the regulating device  120 , which can be formed as a known gas supply regulating device, regulating valve or the like. This cold stream can be composed of a raw hydrocarbon stream, a recycled stream, or a portion or combination of the two. The regulator is configured to adjust the volume or pressure of cold hydrocarbon-containing gas based on system parameters such as, but not limited to, pressure, temperature or reaction product percentages down stream in the system.  
         [0031]     Depending on the intended mode of operation of the apparatus, in particular the intended production of methanol or methanol and formaldehyde, the reaction mixture is subjected to the reaction in the reactor without the introduction of the cold hydrocarbon-containing gas if it is desired to produce exclusively methanol. The introduction of the cold hydrocarbon containing gas is used when it is desired to produce methanol and formaldehyde. By introduction of the cold hydrocarbon-containing gas, the temperature of the reaction is reduced for example by 30-90° so as to preserve the content of formaldehyde into the separated mixture by reducing the decomposition of the formaldehyde to CO 2 .  
         [0032]     The reaction mixture is supplied into the heat exchanger  114  for transfer of heat to the reactor input stream from the reaction mixture exiting the reactor, and after further cooling is supplied within partial condenser  122 . Separation of the mixture into high and low volatility components, (dry gas and raw liquid, respectively) is performed in the partial condenser  122  which may absorb at least some of the formaldehyde into the raw liquid stream as desired. The dry gas is forwarded to a scrubber  134 , while the raw liquids from the condenser  122  are supplied to the flash drum  132 .  
         [0033]     The scrubber  134  functions to remove the CO 2  and formaldehyde from the dry gas stream. In this regard, the scrubber  134  uses both H 2 O and methanol at between 7-8 MPa pressure and between about 0° C. and about 50° C. to absorb CO 2  and formaldehyde. Once the CO 2  and formaldehyde are removed, the reduced stream of hydrocarbon gas is recycled by mixing the reduced stream with the raw hydrocarbon-containing gas stream either before or within the reactor, as desired. The raw hydrocarbon and reduced streams, individually or in combination, are then inputted into the reaction chamber  100  at input  104  or input  110  after being heated by heat exchanger  116  and heater  136  as previously described.  
         [0034]     The rectification column is used to separate carbon dioxide (non-key component) and formaldehyde (light-key component) from methanol (heavy-key component) and water (non-key components). The pregnant methanol steam, stream  14 , enters the rectification column and is separated into a formaldehyde distillate, stream  16 , and a bottoms stream, stream  15 . Some amount of methanol in the distillate stream is desirable since methanol is used as a stabilizer for the production of commercial grade formalin (6-15% alcohol stabilizer, 37% formaldehyde, and the balance being water). By allowing a portion of the heavy key into the distillate stream the separation is more easily achieved; furthermore, process losses typically experienced during absorbent regeneration are subsequently nullified as methanol within the distillate is used for formalin production. Stream  15  is supplemented by stream  31  so as to replace any methanol which was transferred to the distillate stream, stream  16 . Combining stream  31  and stream  15  results in stream  17 , which then returns to the scrubber  134  as regenerated methanol absorbent. Meanwhile, the formaldehyde distillate, stream  16 , combines with the vapors from flash drum  132 , stream  7 , to form a mixture of formaldehyde, methanol, and carbon dioxide.  
         [0035]     The formaldehyde, water, methanol and CO 2  removed by scrubber  134  are passed to formaldehyde rectification column  138 . Column  138  removes formaldehyde and CO 2  from the methanol-water stream. Small amounts of methanol are combined with produced methanol and are inputted into the scrubber  134  to remove additional amounts of CO 2  and formaldehyde from the reduced hydrocarbon stream.  
         [0036]     Free or non-aqueous formaldehyde is allowed to remain in the gas phase by operation of the isobaric condenser  122 . The liquid methanol product stream, or raw liquids, would then comprise methanol, ethanol, and water by allowing formaldehyde to remain in the gaseous stream. In this case, the liquid stream exiting the isobaric condenser  122  can bypass the formaldehyde rectification portion of the process and enter the methanol rectification column after having optionally passed through the flash drum  132 .  
         [0037]      FIGS. 2 and 3  show diagrams of the concentration of oxygen, formaldehyde and methanol in reactions without cooling and with cooling, respectively.  
         [0038]     As can be seen from  FIG. 2 , approximately after 2 sec, oxygen is burnt completely. At this moment the reaction temperature reaches its maximum and methanol and formaldehyde are produced with their proportions in the reaction mixture. Methanol is a more stable product at the end of the reaction and its concentration remains substantially stable after reaching its maximum concentration. Formaldehyde is less stable, and therefore with a temperature increase (the temperature increases until oxygen is burnt completely) its concentration somewhat reduces.  
         [0039]     In the reaction with the cooling shown in  FIG. 3 , via the introduction of cold gas when the formation of methanol and formaldehyde is completed, the temperature of a final period of the reaction is reduced so as to inhibit the decomposition of formaldehyde.  
         [0040]      FIG. 4  represents a graph depicting the yield of oxygenates for the system as a function of the recycle ratio of the recycling hydrocarbon gasses. Shown is a graph depicting the use of Michigan Antrim gas having 97% CH 4  and 1% N 2 . In this regard, the graph shows a significant increase in product yield using the same input stream and with little increase in capital costs. As the system efficiently manages pressure and integrates process energy usage, energy requirements are minimized, thus increasing the overall system economics.  
         [0041]     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types, of methods and constructions differing from the types described above.  
         [0042]     While the invention has been illustrated and described as embodied in the method of and apparatus for producing methanol, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0043]     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.