JP2006016353A - Method for producing aromatic compound and hydrogen from lower hydrocarbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently producing aromatic hydrocarbons and hydrogen from a biogas. <P>SOLUTION: The method for producing the aromatic compounds and hydrogen comprises removing hydrogen sulfide in the biogas containing a lower hydrocarbon and hydrogen sulfide so that the remaining hydrogen sulfide content is a desired value, preferably, 1.25-10 ppm, and the obtained hydrogen sulfide-remaining biogas is treated in the presence of a catalyst. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an aromatic compound and hydrogen from a biogas generated when various organic wastes are processed by methane fermentation using a catalyst.

  In recent years, with the generalization of fuel cell technology, the importance of hydrogen energy has been recognized, and methods for obtaining aromatic compounds and hydrogen from lower hydrocarbons such as methane (see Patent Documents 1 to 3) have been developed. Yes.

  On the other hand, there is a methane fermentation treatment using microorganisms as one of methods for treating various organic wastes. This method is an effective method for treating organic wastes using methane bacteria, etc., and a gas mainly composed of lower hydrocarbons such as methane and carbon dioxide (hereinafter referred to as “biogas”). Can be obtained.

  In addition to a method of using a gas turbine or the like to obtain heat and electric energy, biogas can be used in addition to aromatic compounds such as aromatic hydrocarbons and hydrogen in the presence of a catalyst using biogas as a lower hydrocarbon source. (See Patent Document 4) and the like.

Japanese Patent Laid-Open No. 11-60514 JP 10-272366 A Japanese Patent Laid-Open No. 11-47606 JP 2001-316302 A

  Biogas contains hydrogen sulfide, ammonia and the like in addition to the main components of lower hydrocarbons such as methane and carbon dioxide. Among them, it is known that hydrogen sulfide may poison the catalyst and cause a significant loss of catalytic activity. Therefore, conventionally, when an aromatic compound such as an aromatic hydrocarbon is obtained from biogas using a catalyst, the sulfide has been completely removed (Patent Document 4). General methods for removing sulfides include physical and / or chemical operation methods, for example, chemical treatment using iron oxide or the like, and biological desulfurization method using ion-oxidizing bacteria. However, the chemical treatment method has a problem that enormous energy and cost are required to completely remove hydrogen sulfide. Further, the biological desulfurization method has a problem that the treatment is unstable and complete removal of hydrogen sulfide cannot be expected.

  Then, an object of this invention is to provide the method of manufacturing an aromatic compound and hydrogen efficiently from biogas.

The present invention includes the following inventions.
(1) Hydrogen sulfide in a biogas containing lower hydrocarbons and hydrogen sulfide is removed so that the residual hydrogen sulfide concentration becomes a desired value, and the obtained hydrogen sulfide residual biogas is treated in the presence of a catalyst. To produce an aromatic compound and hydrogen.
(2) The method according to (1), wherein hydrogen sulfide in the biogas is removed so that the residual hydrogen sulfide concentration is 1.25 to 10 ppm.
(3) The method according to (1) or (2), wherein the catalyst is obtained by carbonizing a metallosilicate supporting molybdenum with a reducing gas.

  According to the present invention, energy and cost required for reducing the hydrogen sulfide concentration can be reduced in a method for producing an aromatic compound and hydrogen by treating biogas in the presence of a catalyst. In addition, the energy and cost required for the overall production of the aromatic compound and hydrogen by this method can be minimized.

  The present invention removes hydrogen sulfide in a biogas containing lower hydrocarbons and hydrogen sulfide so that the residual hydrogen sulfide concentration has a desired value, and the obtained hydrogen sulfide residual biogas is removed in the presence of a catalyst. The present invention relates to a method for producing an aromatic compound and hydrogen by treatment.

  As shown in Examples, the present inventors have found that the reaction rate of production of aromatic compounds and hydrogen (that is, catalytic activity) depends on the concentration of hydrogen sulfide in the reaction system. Specifically, it has been found that the catalyst activity decreases as the concentration of coexisting hydrogen sulfide increases. Furthermore, it has been found that the catalytic activity decreases as the reaction time (ie, throughput) increases.

  From this knowledge, it can be seen that when an aromatic compound and hydrogen are produced by treating a hydrogen sulfide-containing biogas in the presence of a catalyst, the catalytic activity decreases as the hydrogen sulfide concentration and the treatment amount increase. Then, it is necessary to regenerate the catalyst when the activity drops below a certain level. Since the regeneration process takes energy and cost, it is better to reduce the number of regeneration processes. For this purpose, a method of reducing the concentration of hydrogen sulfide in biogas is effective. However, the energy and cost required for hydrogen sulfide reduction increase as the hydrogen sulfide concentration is reduced. This relationship is schematically shown in FIG. If this knowledge is applied, an efficient operation of producing aromatic compounds and hydrogen can be performed as described below.

  Compare the energy and cost required for the catalyst regeneration treatment with the energy and cost required to reduce the concentration of hydrogen sulfide in the biogas, and the energy and cost required to produce aromatic compounds and hydrogen from the biogas. The most efficient production of aromatic compounds and hydrogen is achieved by calculating the hydrogen sulfide concentration that can minimize the total cost and performing a catalytic reaction using the biogas obtained by removing hydrogen sulfide according to the calculated value. Can do. That is, the present invention is based on the relationship between the residual hydrogen sulfide concentration (that is, the amount of hydrogen sulfide removed) obtained in advance and the energy and cost required for the entire aromatic compound and hydrogen production process. Determine the residual hydrogen sulfide concentration to the extent (usually minimal), remove the hydrogen sulfide in the biogas so that the determined desired residual hydrogen sulfide concentration is achieved, and obtain the resulting hydrogen sulfide residual biogas In the presence of a catalyst to produce an aromatic compound and hydrogen. In the present specification, the “desired value” of the residual hydrogen sulfide concentration means the residual hydrogen sulfide concentration when the energy and cost required for the entire production process of the aromatic compound and hydrogen become a desired level.

  A more preferable embodiment of the present invention is characterized by including a step of removing hydrogen sulfide in the above-described hydrogen sulfide-containing biogas so that the residual hydrogen sulfide concentration is 1.25 to 10 ppm. The inventors have surprisingly produced aromatic compounds and hydrogen in the presence of a catalyst using biogas that has been removed so that the residual hydrogen sulfide concentration is within these ranges as a lower hydrocarbon source. In this case, the same aromatic compound production rate and hydrogen production rate can be achieved as when a biogas from which hydrogen sulfide has been completely removed (that is, the residual hydrogen sulfide concentration is 0) is used as the lower hydrocarbon source. I found out that Although a great deal of energy and cost is required to completely remove hydrogen sulfide, according to this preferred embodiment of the present invention, the same reaction rate can be achieved while suppressing the energy and cost required for hydrogen sulfide reduction. This is very advantageous in terms of energy and cost. In this form of the invention, the upper limit of residual hydrogen sulfide concentration is more preferably 3 ppm, and the lower limit is more preferably 1.50 ppm, more preferably 2.0 ppm, more preferably 2.7 ppm, most preferably 3.0 ppm. It is. When the lower limit of the residual hydrogen sulfide concentration is within these ranges, it is more advantageous because the energy or cost required for removing hydrogen sulfide is relatively small.

  The biogas that can be used in the present invention can be obtained, for example, by treating various organic wastes with microorganisms. Biogas generated in landfills containing various organic wastes can also be used. Various organic wastes are not particularly limited as long as they are organic wastes, and examples thereof include livestock manure, garbage, waste / drainage from various factories, sewage, human waste, sludge, weeds, and the like. The microorganism treatment method is not particularly limited as long as it is a method capable of converting an organic substance into a lower hydrocarbon such as methane using microorganisms. For example, the UASB method (Upflow Anaerobic Sludge Blanket = upflow anaerobic sludge blanket method) ), Dry methane fermentation and the like. For the production of biogas, anaerobic bacteria (methane bacteria) that can undergo methane fermentation are usually used.

  The biogas that can be used in the present invention contains lower hydrocarbons such as methane and hydrogen sulfide. More specifically, the biogas used in the present invention is usually at least 40% by volume, preferably 60% or more methane gas, 55% or less, preferably 35% or less carbon dioxide, and volume by volume. % Contains 0.01 to 1% hydrogen sulfide.

  The method for removing hydrogen sulfide in the biogas is not particularly limited as long as hydrogen sulfide can be reduced to a predetermined concentration, and normal physical and / or chemical methods can be employed. For example, a method using iron oxide (dry desulfurization method), a method of circulating biogas in a sodium carbonate aqueous solution or water (wet desulfurization method), and a method of converting hydrogen sulfide into sulfate ions using microorganisms and removing them are exemplified. it can.

  Biogas may contain several ppm of ammonia. However, as is clear from Example 3, it is known that if the ammonia content is 100 ppm or less, the production rate of the aromatic compound and hydrogen is not affected, and therefore, it is not necessary to remove ammonia.

  Further, as described above, the biogas contains a considerable amount of carbon dioxide. When the carbon dioxide contained in the biogas has a high concentration or a low concentration, the production rate of the aromatic compound and hydrogen may decrease. In such a case, the carbon dioxide concentration in the biogas can be controlled to 0.01 to 10% by volume, preferably 1 to 3%, as necessary. The adjustment method is not particularly limited as long as it is a method for controlling the carbon dioxide concentration. For example, a method using an alkali adsorbent, a PSA method (Pressure Swing Adsorption), or the like can be used.

  In the present invention, “treating biogas in the presence of a catalyst” means that a reaction for converting a lower hydrocarbon such as methane contained in the biogas into an aromatic compound and hydrogen is performed in the presence of the catalyst. .

  In the present invention, a catalyst having a catalyst material supported on a carrier can be used. Preferably, the catalyst is further carbonized by mixing a reducing gas. The catalyst carrier is preferably a porous metallosilicate having an angstrom-scale pore size such as HZSM-5 or MCM-22, but is not particularly limited as long as it can support a catalyst material. As the catalyst material, at least one selected from the group consisting of metals such as molybdenum, rhenium, tungsten, cobalt, rhodium, compounds thereof, and carbides thereof can be used, but is not limited thereto. The amount of catalyst material supported is suitably about 6 to 20% by weight of the total weight. These catalyst materials can be supported on a carrier by a usual method. For example, a method in which a water-soluble inorganic salt of a metal serving as a catalyst material is supported on a carrier by an impregnation method, or volatility can be achieved. It is preferable to carry out by a chemical vapor deposition method using an organometallic complex of a metal as a catalyst material. As the reducing gas, methane, hydrogen, methane-hydrogen mixed gas, or the like can be used, but is not limited thereto. Further, in the present invention, “carbonization treatment” means a treatment for obtaining a carbide by heating / reducing the catalyst material or its precursor under a flow of the reducing gas while keeping the temperature rising rate constant. The carbonization treatment can also be performed on a catalyst material or a precursor thereof supported on a carrier. Examples of the precursor of the catalyst material include oxides.

  The reaction treatment for obtaining aromatic compounds and hydrogen from lower hydrocarbons in biogas is usually carried out in a batch or flow type reaction mode, but a flow type reaction mode such as a fixed bed, moving bed or fluidized bed. It is preferable to carry out. In the reaction, for example, a catalyst is filled in a fixed bed flow type reaction tube (for example, made of quartz), preferably at a temperature of 600 to 850 ° C, more preferably 700 to 750 ° C, preferably 1 to 10 atm, more preferably 3 to 3. It is carried out by supplying a predetermined biogas at a pressure of 5 atm, preferably at SV (weight hourly space velocity) 1000-10000, more preferably 3000-5000.

  By the above reaction, an aromatic compound mainly containing an aromatic hydrocarbon such as benzene and toluene can be obtained. In addition, the kind and ratio of the aromatic compound obtained can be changed according to the raw material. In addition, high-purity hydrogen is obtained with this reaction.

  Figure 2 shows the change in benzene production rate over time when an aromatic compound and hydrogen are produced using a gas containing 1% by volume of carbon dioxide and 0-100 ppm of hydrogen sulfide with respect to pure methane gas. The change with time is shown in FIG. The catalyst used was a catalyst in which 6% by weight of molybdenum was supported on HZSM-5. This catalyst was filled in a reaction vessel, and the gas was passed through with SV (weight hourly space velocity) = 3000 (mL / (g · h)), and reacted at a reaction temperature of 750 ° C. and 3 atm. As is clear from FIGS. 2 and 3, the time-dependent changes in the benzene production rate and the hydrogen production rate were almost the same as when hydrogen sulfide was 0 ppm even when hydrogen sulfide was mixed up to 10 ppm. From this, it has been clarified that under the condition where carbon dioxide is present at 1%, the benzene production rate and the hydrogen production rate comparable to those obtained when hydrogen sulfide is completely removed can be achieved by setting hydrogen sulfide to 10 ppm or less.

  FIG. 4 shows the change over time in the benzene production rate when an aromatic compound and hydrogen are produced using a gas in which 6% by volume of hydrogen and 0 to 100 ppm of hydrogen sulfide are added to pure methane gas. The change over time is shown in FIG. The catalyst used was a catalyst in which 6% by weight of molybdenum was supported on HZSM-5. This catalyst was filled in a reaction vessel, and the gas was passed through with SV (weight hourly space velocity) = 3000 (mL / (g · h)), and reacted at a reaction temperature of 750 ° C. and 3 atm. As apparent from FIGS. 4 and 5, the benzene production rate and the hydrogen production rate over time were almost the same as those when hydrogen sulfide was 0 ppm even when hydrogen sulfide was mixed up to 3 ppm. From this, it has been clarified that under the condition where 6% hydrogen is present, by setting the hydrogen sulfide to 3 ppm or less, it is possible to achieve the same benzene production rate and hydrogen production rate as when hydrogen sulfide is completely removed.

  FIG. 6 shows changes over time in the benzene production rate when hydrogen and an aromatic compound are produced using a gas in which carbon dioxide is added at a volume of 1% and ammonia is added at 0 to 100 ppm with respect to pure methane gas. The change over time is shown in FIG. The catalyst used was a catalyst in which 6% by weight of molybdenum was supported on HZSM-5. This catalyst was filled in a reaction vessel, and the gas was passed through with SV (weight hourly space velocity) = 3000 (mL / (g · h)), and reacted at a reaction temperature of 750 ° C. and 3 atm. As apparent from FIGS. 6 and 7, the benzene production rate and the hydrogen production rate over time were almost the same as those when hydrogen sulfide was 0 ppm even when hydrogen sulfide was mixed up to 100 ppm. In view of the fact that the ammonia concentration in the biogas is usually about several ppm, when the aromatic compound and hydrogen are produced from the biogas as a raw material, the ammonia is completely removed without providing an ammonia removal step. It has been found that aromatic compounds and hydrogen can be produced to the same extent as in the case.

It is a conceptual diagram which shows the relationship between residual hydrogen sulfide concentration, energy and cost which are required for catalyst regeneration and hydrogen sulfide concentration reduction. It is the figure which showed the influence of the hydrogen sulfide density | concentration with respect to a benzene production | generation rate when carbon dioxide exists 1%. It is the figure which showed the influence of the hydrogen sulfide density | concentration with respect to a hydrogen production rate when a carbon dioxide exists. It is the figure which showed the influence of the hydrogen sulfide density | concentration with respect to benzene production | generation speed | velocity when hydrogen exists 6%. It is the figure which showed the influence of the hydrogen sulfide density | concentration with respect to a hydrogen production | generation rate when hydrogen exists 6%. It is the figure which showed the influence of ammonia concentration with respect to benzene production | generation speed | velocity when carbon dioxide exists 1%. It is the figure which showed the influence of the ammonia concentration with respect to the hydrogen production | generation speed | velocity when carbon dioxide exists 1%.

Claims (3)

  Hydrogen sulfide in the biogas containing lower hydrocarbons and hydrogen sulfide is removed so that the residual hydrogen sulfide concentration becomes a desired value, and the resulting hydrogen sulfide residual biogas is treated in the presence of a catalyst to produce an aroma. Group compounds and methods for producing hydrogen.   The method according to claim 1, wherein hydrogen sulfide in the biogas is removed so that the residual hydrogen sulfide concentration is 1.25 to 10 ppm.   The method according to claim 1 or 2, wherein the catalyst is obtained by carbonizing a metallosilicate supporting molybdenum with a reducing gas.

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