Abstract:
An apparatus and method of producing methanol includes reacting a heated hydrocarbon-containing gas and an oxygen-containing gas in a reactor; and adding a relatively cold hydrocarbon-containing gas, to be mixed directly with a mixture of the heated hydrocarbon-containing gas and the oxygen-containing gas, after formaldehyde is formed to inhibit decomposition of formaldehyde in the reactor, to provide a product stream comprising methanol and formaldehyde; and transferring heat from the product stream to the hydrocarbon-containing gas to heat the hydrocarbon containing gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application 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 herein 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 H2) 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”  1  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, to have a significant number of intermittent stages from the process. Also, for medium and small enterprises with the capacity less than 2000 t/day it is not efficient.  
         [0004]     A method for, producing methanol is also known which includes a separate supply of a hydrocarbon-containing gas heated to 200-500° C. under pressure 2.15 MPa and an oxygen-containing gas in a mixing chamber, subsequent stages of incomplete oxidation of methane with a concentration of oxygen 1-4 volume percent with an additional introduction of reagents (metal oxide catalyst, higher gaseous hydrocarbons or oxygen containing compositions, a cold oxidizer) into the reaction zone of a reactor, cooling of the reaction mixture in a heat exchanger, separation of methanol from liquid reaction products in a partial condenser, supply of gaseous waste products to an input of the reactor as disclosed in the Russian patent no. 2,049,086. However, this method requires the use of a catalyst or additional reagents and an intense heating of the reacting gasses, which leads to a decrease of methanol yield and to an increased possibility of soot formation.  
         [0005]     A further method of producing methanol is known, which includes a separate supply into a mixer of a hydrocarbon-containing gas (natural gas typically) and an oxygen-containing gas (air or oxygen). This mixture a subsequently supplied into a non-catalytic reactor for gas phase incomplete oxidation at pressures of 1-10 MPa during up to 1000 seconds at a temperature 300-500° C. without catalyst, return of waste reaction gasses which contain non-reacted methane for mixing with the initial hydrocarbon containing gas into the first reactor or into the second reactor (which is connected in series with the first reactor), as disclosed in the British patent document GB 2,196,335A. This method provides a high yield of methanol. However, due to significant time of reaction and relatively low per pass conversion (5-15% of methane can reacts during each passage through the reactor) this method has a low efficiency.  
         [0006]     A further method of producing methanol by a separate supply and oxidation of hydrocarbon-containing gas and oxygen-containing gas at temperature 370-450° C. and pressure 5-10 MPa and time of contact in the reactor 0.2-0.22 sec is also known, and includes cooling of the heated reaction mixture to 330-340° C., introduction of methanol into the reactor, as disclosed in the patent document of the Soviet Union SU 1,469,788. Cooling of the reaction mixture without intermediate condensation and separation to 380-400° C. in multi-stage heat exchangers arranged in the reactor with subsequent supply of the mixture to 2-3 successive stages of oxidation is disclosed in the patent document of the Soviet Union 1,336,471. In the first case it is necessary to have an additional consumption and a secondary separation of methanol that leads to unavoidable losses, and in the second case it is necessary to provide additional cooling loops with circulation of additional cooling agent in them.  
         [0007]     An apparatus for producing methanol is known, which includes a plurality of units arranged after one another and connected by pipes, in particular a mixing chamber connected to separate sources of hydrocarbon containing gas and air or oxygen, a reactor composed of an inert material with a heating element for incomplete oxidation of methane in a mixture supplied into the reactor under an excessive pressure, a condenser and a partial condenser for separation of methanol from the products of reaction, a vessel for re-circulated gaseous reaction products with a pipe for their supply into the initial hydrocarbon-containing gas or mixing chamber as disclosed in the British patent no. 2,1 96,335A. However, a significant time of presence of the reagents in the reactor reduces efficiency of the apparatus, and makes the process practically unacceptable in industrial conditions.  
         [0008]     An apparatus which is close to the present invention is disclosed in Russian patent no. 2,162,460. It 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.  
         [0009]     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 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 re-circulation 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 C02, 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 an additional energy is wasted.  
         [0010]     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.  
         [0011]     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 discloses further solutions for transformation of hydrocarbons.  
         [0012]     It is believed that the existing methods and apparatus for producing methanol can he further improved.  
       SUMMARY OF THE INVENTION  
       [0013]     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.  
         [0014]     It is another feature of the present invention to provide a method of and an apparatus for producing methanol which can be used directly on 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.  
         [0015]     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, supplying into the reactor an oxygen containing gas; carrying out in the reactor an oxidation of said heated hydrocarbon-containing gas by oxygen of said oxygen-containing gas; and 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 produce methanol and also formaldehyde.  
         [0016]     Another feature of the present invention is an apparatus for producing methanol, which has a reactor for receiving and reacting a hydrocarbon-containing gas with an oxygen-containing gas, to carry out in the reactor oxidation of said heated hydrocarbon containing gas by oxygen of said oxygen-containing gas; and 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 or the reaction to produce methanol and also formaldehyde.  
         [0017]     As can be seen, in accordance with the present invention, heated hydrocarbon containing gas and air 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 extraction and the cooled reaction mixture is separated into waste gas and liquid product, the liquid products are rectified with separation of methanol, the waste gas is withdrawn, and a liquid is rectified with production of formaldehyde, wherein cold hydrocarbon containing gas is supplied into a regulation zone of the reactor to reduce the reaction temperature for example by 70-90° C. and thereby to provide a production and a redistribution of the ratio of products to produce corresponding quantities of methanol and formaldehyde.  
         [0018]     The reaction is performed in a homogenous phase by a partial combustion without presence of a hydrogenous catalyst.  
         [0019]     The regulating zone is provided with a device for introduction of unheated hydrocarbon containing gas for cooling of the reaction mixture by means of its turbulent mixing with the main stream.  
         [0020]     The device for final cooling of the reaction mixture before separation can include a gas-liquid heat exchanger connected with the reactor, a partial condenser, and formaldehyde and methanol rectification units, and a device for cooling, located one after the other.  
         [0021]     The inner wall of the reaction zone can be coated with a material which is inert to the reaction mixture. The reactor can be provided with thermal pockets for introducing devices for control of temperature in the reaction zone and for control and regulation in the regulating zone, such as for example thermocouples.  
         [0022]     In accordance with a preferred embodiment of the present invention, the required temperature at the inlet of the reactor is provided by heating of the hydrocarbon containing gas to a needed temperature, for example in a tubular oven.  
         [0023]     In accordance with a Preferred embodiment of the Present invention, the introduction of the cold hydrocarbon containing gas for reduction of temperature in the regulating zone can be performed by an introducing device and a temperature regulating valve arranged in the introduction line.  
         [0024]     In accordance with a preferred embodiment of the present invention, during cooling of the reaction mixture in the gas-liquid heat exchanger, heat is transmitted to the raw liquid stream supplied into a formaldehyde rectification column, up to a desired temperature for performing rectification the input of the rectification coolant. The final cooling of the product gas stream is carried out in the cooling device. Then, the cooled gas is supplied into a partial condenser, in which dry gas is separated from raw liquids, including methanol, formaldehyde, ethanol, and water. The raw liquids, through the heat exchanger with temperature 100-120° C., are supplied into a rectification column. The temperature of the top of the column is 70-75° C., the pressure in the column is up to 0.2 MPa. Formaldehyde with a concentration up to 96% is supplied to storage or further processing, while the residue which contains methanol, ethanol, and water is supplied to the methanol rectification column with temperature at its top up to 80°. The final product is supplied to storage or further processing.  
         [0025]     Alternatively, formaldehyde can be separated in the partial condenser from the liquid methanol product stream which would then comprise methanol, ethanol, and water by allowing formaldehyde to remain in the gaseous stream. In this case, the liquid stream exiting the partial condenser can bypass the formaldehyde rectification portion of the process and enter the methanol rectification column after having optionally passed through the gas liquid heat exchanger.  
         [0026]     The time of presence of the reaction mixture in the reactor is 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 exiting gas, due to its high stability is 40%, while the content of the formaldehyde is 4%. In order to increase the portion of formaldehyde to 8-13% in the final product, the temperature of the reaction is reduced by 70-80° in the moment of jump after the period of induction at 0.7-1.4 sec of reaction due to the injection of the cold hydrocarbon-containing gas into the regulating zone.  
         [0027]     When the temperature of reaction is changed from 370° C. to 450° C., the content of aldehydes is increased from 5% to 13% 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 at a concentration of oxygen in the initial gas mixture 2-2.8%.  
         [0028]     In accordance with the present invention, the waste gasses are returned back into the process in the apparatus for gas preparation, with negligible distortion of its operation and quality of gas. Also, when the apparatus is arranged at gas power plants, the returned gas does not substantially change its caloric content.  
         [0029]     The apparatus is ecologically clean and does not produce hazardous wastes. In contrast, in known apparatuses, it is necessary to burn up to 3 million tons per year of formaldehyde mixture when the capacity of the apparatus is 6 million tons per year.  
         [0030]     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  
       [0031]      FIG. 1  is a view schematically showing a reactor of an apparatus for producing methanol in accordance with the present invention;  
         [0032]      FIG. 2A  is a view showing the apparatus for producing methanol, including the reactor and other devices, in accordance with the present invention;  
         [0033]      FIG. 2B  is a view showing the apparatus for producing methanol, including the reactor and other devices, in accordance with an alternative embodiment of the present invention;  
         [0034]      FIG. 2C  is a view showing the apparatus for producing methanol, including the reactor and other devices, in accordance with a further alternative embodiment of the present invention; and  
         [0035]      FIGS. 3 and 4  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.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     An apparatus for producing methanol in accordance with the present invention has a reactor which is shown in  FIG. 1  and identified as a whole with reference numeral  1 . In the reactor a gas phase oxidation of a hydrocarbon-containing gas is carried out. The reactor  1  has a reaction zone  2  which is provided with a device  3  for introducing a heated hydrocarbon containing gas and a device  4  for introducing an oxygen-containing gas, for example air.  
         [0037]     The reactor further has a regulation zone  5  provided with a device  6  for introducing a cold hydrocarbon-containing gas, for reducing the temperature of reaction during operation of the apparatus. In addition, the reactor  1  is provided with thermal pockets  7  for control and regulation of temperatures in corresponding zones, provided for example with thermocouples.  
         [0038]     As can be seen from  FIG. 2A , the apparatus has a device for cooling the reaction mixture before separation, which includes a gas-liquid heat exchanger  8  and an cooling device  9 , as well as a regulator of cold gas supply  10 . The gas-liquid heat exchanger  8  is connected with a rectification unit, in particular with a rectification column  11  and a partial condenser  12 . The rectification column  11  is connected with a cooling device  13 , which is connected with a vessel  14 . Formaldehyde is supplied from the vessel  14  by a pump  21  to storage or further processing.  
         [0039]     The reactor  1  is connected with a compressor  15  for supply of compressed air, and with an oven  16  for heating of hydrocarbon-containing gas. The apparatus further has a unit for rectification of methanol which includes a rectification column  17 , a cooling device  18  and a vessel  19 , from which methanol is supplied to storage or further processing.  
         [0040]     In operation, a hydrocarbon-containing gas with a methane content for example up to 98% is supplied from an installation for preparation of gas or any other source  20  to the oven  16 , in which it is heated to temperature 430-470° C. Then the heated hydrocarbon-containing gas is supplied into the reaction zone  2  of the reactor  1 . Compressed air with pressure for example 8 MPa and with a ratio 1-2.5% of oxygen is supplied by the compressor  15  also into the reaction zone  2  of the reactor  1 . Oxidation reaction takes place in the reaction zone of the reactor  1 . A second stream of cold or in other words not heated hydrocarbon-containing gas from the same source is supplied through the introducing device  6  into the regulation zone  5  of the reactor  1 . This stream is regulated by the regulating device  10 , which can be formed as a known gas supply regulating device, regulating valve or the like.  
         [0041]     Depending on an intended mode of operation of the apparatus, in particular the intended production of methanol or 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, and with the introduction of the cold hydrocarbon containing gas when it is desired to produce also formaldehyde. By introduction of the cold hydrocarbon-containing gas, the temperature of the reaction is reduced for example by 70-90° so as to increase the content of formaldehyde into the separated mixture.  
         [0042]     The reaction mixture is supplied into the heat exchanger  8  for transfer of heat to the raw liquids from the partial condenser  12 , and after further cooling in the cooling device  9  is supplied with temperature 20-30° C. to the partial condenser  12 . Separation of the mixture into highly volatility gases and low volatility liquids is performed in the partial condenser  12  which may condense at least some of the formaldehyde into the raw liquid stream as desired. The dry gas is returned to the gas source  20 , while the raw liquids through the gas-liquid heat exchanger  8  is supplied to the rectification column  11 . From the rectification column  11  vapors of formaldehyde through the cooling device  13  are supplied into the vessel  14 . Formaldehyde is supplied by a pump  21  to storage or further processing. A part of formaldehyde is supplied from the vessel  14  for spraying of the rectification column  11 .  
         [0043]     An alternative embodiment with the present invention would be to use the incoming hydrocarbon stream for cooling of the product gases exiting the reactor. Gas from the hydrocarbon source enters heat exchanger  23 , where it cools the hot gases exiting the reactor, as seen in  FIG. 2B . This process configuration lowers the duty of the cooling device  9  while simultaneously pre-heating the hydrocarbon stream before entering the furnace for heating up to the necessary temperature of the reactor. The heat exchanger may either be internal or external to the reactor.  
         [0044]     Alternatively, at least some of the formaldehyde can be allowed to remain in the gas phase by operation of the partial condenser. The liquid methanol product stream which would then comprise methanol, ethanol, and water by allowing formaldehyde to remain in the gaseous stream. In this case, the liquid stream exiting the partial condenser can bypass the formaldehyde rectification portion of the process and enter the methanol rectification column after having optionally passed through the gas liquid heat exchanger as seen in  FIG. 2C .  
         [0045]     The method in accordance with the present invention and the operation of the apparatus in accordance with the present invention are illustrated by an example of operation of the apparatus with the capacity of 6,000 t/year, with cooling of the reaction mixture by 30° C.  
                       TABLE I                           Example 1 without   Example 2 with       Parameters   cooling   cooling by 30° C.                   Natural gas supply,   56800 (40570)   60208 (43004)       m 3 /hour (kg/hour)       Gas consumption in   1700 (1215)   1700 (1215)       reaction, m 3 /hour       (kg/hour)       Conversion degree,       Oxygen concentration in       reaction entry zones,       Pressure in reactor, MPa   7   7       Cooling in regulation zone   no cooling   direct mixing               with cold gas       Methanol yield, kg/hour   800   800       Formaldehyde yield, kg/hour   115   230       Total organic products   920   1040       yield, kg/hour,       Initial temperature, ° C.       Reaction temperature, ° C.       Temperature in regulation   530   500       zone, ° C.                  
 
         [0046]      FIGS. 3 and 4  show diagrams of concentration of oxygen, formaldehyde and methanol in reactions without cooling and with cooling.  
         [0047]     As can be seen from  FIG. 3 , approximately after 2 sec, oxygen is burnt completely. At this moment the reaction temperature reaches its maximum; and in the reaction mixture methanol and formaldehyde are produced with their proportions. Methanol as a more stable product at the end of the reaction reaches its maximum concentration and maintains it practically stable. Formaldehyde is less stable, and therefore with a temperature increase (the temperature increases until oxygen is burnt completely) its concentration somewhat reduces.  
         [0048]     In the reaction with the cooling shown in  FIG. 4 , with introduction of the cold gas when the formation of methanol and formaldehyde is completed, the temperature of a final period of the reaction is reduced, so that formaldehyde can not decompose and reduce its concentration. Since methanol remains stable, its concentration remains constant (see Table I), while content of formaldehyde increases (on the account of other reaction products).  
         [0049]     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.  
         [0050]     While the invention has been illustrated and described as embodied in 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.  
         [0051]     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.  
         [0052]     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.