Method for producing fuel gas and catalyst for dehydration and hydrogenation of alcohol

Abstract

To provide a method for obtaining a fuel gas with a reduced hydrogen concentration by a simple and economically advantageous method when producing the fuel gas containing methane as a main component, and a catalyst necessary for realization of the method.SOLUTION: A method for producing a fuel gas comprises: a methanation reaction step of reacting hydrogen and carbon oxides under the presence of a methanation catalyst to obtain a first fuel gas containing 2% or more to 20% or less of hydrogen on a volume basis after dehydration; and a dehydration-hydrogenation reaction step of adding an alcohol to the fuel gas obtained in the methanation reaction step, and then reacting the alcohol with hydrogen in the first fuel gas in the presence of a dehydration-hydrogenation catalyst to obtain a second fuel gas containing an alkane having 2 to 4 carbon atoms, wherein the alcohol is one or more alcohols selected from alcohols having 2 to 4 carbon atoms, and the dehydration-hydrogenation catalyst is formed by supporting palladium on zirconia tungsten oxide, and has activity in a dehydration reaction of the alcohol and a hydrogenation reaction of an alkene.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for producing a high-calorific value fuel gas mainly composed of methane by reacting hydrogen and carbon oxide in the presence of a methanation catalyst, and more specifically to a method for producing a fuel gas with a reduced hydrogen concentration and a high hydrocarbon concentration, and to a catalyst necessary for realizing this method. [Background technology]

[0002] In recent years, carbon-neutral fuels, which do not substantially increase the concentration of carbon dioxide in the atmosphere when burned, have been attracting attention from the perspective of combating global warming.

[0003] Methane can be obtained by recovering carbon dioxide from exhaust gases generated in industrial processes and thermal power plants, and reacting it with hydrogen obtained through electrolysis using electricity from renewable energy sources such as solar and wind power. Since methane obtained by this method does not generate additional carbon dioxide when burned, it can be considered a carbon-neutral fuel that does not contribute to global warming.

[0004] The methanation reaction (Equation 1), which produces methane by reacting carbon dioxide with hydrogen, is well known. CO2+4H2→ CH4+2H2O (Formula 1)

[0005] Patent Document 1 discloses a method for methane production of a gas containing CO and H2, characterized by using a methane reactor in which a Cu-Zn low-temperature shift catalyst is placed upstream and a methane catalyst is placed downstream. In the upstream low-temperature shift reactor, the CO shift reaction (Equation 2) proceeds, so it is thought that most of the carbon monoxide contained in the raw material gas is converted to carbon dioxide by reacting with water vapor, and the methane reaction of carbon dioxide proceeds on the downstream methane catalyst. CO+H2O → CO2+H2 (Formula 2)

[0006] The methanation reaction has long been used to remove carbon monoxide and carbon dioxide from hydrogen used for ammonia synthesis, and catalysts supported with Ni or Ru are known to exhibit high activity (Non-Patent Documents 1, 2).

[0007] The methane reaction, which involves reacting carbon oxides (carbon monoxide and carbon dioxide) with hydrogen to produce methane, is an industrially established technology (for example, Non-Patent Document 3). However, there are still challenges in obtaining fuel gas of a quality suitable for use as a raw material for city gas.

[0008] Natural gas is commonly used as a raw material for city gas, and its main component is methane, with small amounts of ethane, propane, and butane. Natural gas does not usually contain hydrogen or carbon monoxide, and carbon dioxide is removed during the natural gas refining process. In particular, in the case of city gas produced using liquefied natural gas as a raw material, hydrogen, carbon monoxide, and carbon dioxide are almost completely removed during the liquefaction and refining process, so they are practically absent.

[0009] The concentration of hydrocarbons other than methane (ethane, propane, and butane) in natural gas varies depending on the source and refining method of the natural gas. Therefore, when producing city gas, propane or butane is usually added to adjust the calorific value to a certain range, and then an odorant is added to ensure safety before it is sent to consumers through city gas pipelines.

[0010] The presence of hydrogen, carbon monoxide, and carbon dioxide in city gas can cause the following problems:

[0011] First, carbon monoxide is highly toxic, and a gas leak could cause poisoning accidents. Its permissible concentration is 200 ppm, and from a safety standpoint, it is desirable to keep the concentration in fuel gas below this level. Even considering dilution by air, it should be kept below 1000 ppm.

[0012] Next, carbon dioxide is not only non-flammable, but it also inhibits combustion. Therefore, if it is mixed into fuel gas at high concentrations, it may not only reduce the efficiency of gas transport in pipelines due to a decrease in the calorific value of the fuel gas, but also cause a decrease in the efficiency of combustion equipment.

[0013] Finally, although hydrogen is a fuel gas, its calorific value per unit volume is only about one-third that of methane, the main component of city gas. Therefore, when hydrogen is mixed with a fuel gas that is mainly composed of methane, the calorific value per unit volume decreases. Furthermore, because hydrogen burns quickly, it is known to have a significant impact on combustion equipment.

[0014] As described above, hydrogen, carbon monoxide, and carbon dioxide, when mixed with city gas, have various effects at each stage of gas supply and consumption. Therefore, it is common practice to impose restrictions on the concentrations of hydrogen, carbon monoxide, and carbon dioxide in the quality standards for gas accepted into the city gas pipeline network.

[0015] In pipeline networks with fuel refueling stations for natural gas vehicles, there are known examples where the upper limit of hydrogen concentration is set at 2% by volume (Non-Patent Document 4). There are also known examples where the hydrogen concentration is set at 4% or less by volume, the carbon dioxide concentration at 0.5% or less by volume, and the carbon monoxide concentration at 0.05% or less by volume (Non-Patent Document 5), as well as examples where the total concentration of methane and ethane is set at 93% or more by volume, and the total concentration of components other than hydrocarbons is set at 4% or less by volume (Non-Patent Document 6).

[0016] The contamination of city gas with hydrogen, carbon monoxide, and carbon dioxide presents problems beyond just the quality of the city gas itself. As mentioned earlier, city gas is supplied after being adjusted to a certain calorific value range by adding propane or butane so that it can be used stably in combustion equipment. Therefore, if hydrogen or carbon dioxide is present at high concentrations, it becomes necessary to mix in large quantities of propane and butane to adjust the calorific value. This not only increases the cost of gas production, but also compromises the carbon neutrality of the produced gas if fossil fuel-derived propane and butane are used for calorific value adjustment.

[0017] The methane reaction of carbon dioxide (Equation 1) is an equilibrium reaction, and under normal industrial operating conditions, it is not possible to completely convert carbon dioxide and hydrogen to methane. When a mixed gas in a stoichiometric ratio (hydrogen:carbon dioxide = 4:1) is reacted at atmospheric pressure (0.1 MPa), the equilibrium conversion rate of carbon dioxide to methane is 95.0% at a reaction temperature of 300°C, 97.5% at a reaction temperature of 250°C, and 98.9% at a reaction temperature of 200°C.

[0018] Thus, at atmospheric pressure, only fuel gas containing a large amount of hydrogen can be obtained. Since the methanation reaction is an exothermic reaction, the equilibrium conversion rate improves as the temperature decreases. However, in the case of a catalytic reaction, the catalytic activity decreases as the temperature decreases. For this reason, there is a lower limit to the reaction temperature, and in the case of a typical methanation catalyst, a temperature of 250°C or higher is required to obtain a practical reaction rate (Non-Patent Document 4, Patent Documents 2 and 3).

[0019] The methane reaction of carbon dioxide (Equation 1) is a reaction in which the amount of substance (number of moles) decreases, so the equilibrium conversion rate increases with increasing pressure. Comparing at 250°C, the equilibrium conversion rate of carbon dioxide to methane (when reacted with a stoichiometric ratio of hydrogen:carbon dioxide = 4:1) is 97.5% at atmospheric pressure (0.1 MPa), but improves to 98.9% at 0.7 MPa and 99.5% at 5 MPa. However, even when a hydrogen:carbon dioxide = 4:1 mixed gas is reacted at 250°C and 5 MPa, the equilibrium composition (volume-based composition after dehydration excluding the generated water) is 97.45% methane, 2.04% hydrogen, and 0.51% carbon dioxide. Therefore, to obtain a fuel gas with less than 2% hydrogen (volume basis), the reaction must be carried out under high pressure conditions exceeding 5 MPa.

[0020] Several methods are known for reducing the hydrogen concentration in fuel gas obtained by a methane reaction. For example, by carrying out the methane reaction under conditions where the hydrogen concentration is lower than the stoichiometric ratio and removing excess carbon dioxide through decarboxylation, both the hydrogen and carbon dioxide content can be reduced (Patent Document 4). This method has been used in the methane production of coke oven gas (Non-Patent Document 3). However, decarboxylation equipment is generally expensive to install and consumes a large amount of energy to operate, which hinders its economic viability.

[0021] Another method involves carrying out the methanation reaction in multiple stages, cooling the gas produced in the intermediate stages, and condensing and separating the water (Non-Patent Document 4, Patent Documents 2 and 3). By removing the produced water, the methanation reaction can proceed further towards the production side, improving the conversion rate of carbon dioxide to methane. However, this method requires heat exchange equipment, which increases equipment costs. Furthermore, if the produced water is removed excessively, the composition will fall into a region where carbon precipitation occurs in equilibrium, making the control of the water separation process complex.

[0022] Furthermore, in the method of carrying out the methanation reaction under conditions where hydrogen is less than the stoichiometric ratio and removing excess carbon dioxide by decarboxylation treatment, and in the method of carrying out the methanation reaction in multiple stages and cooling the gas generated in the intermediate stage to condense and separate water, in both cases, since the conditions are such that carbon monoxide is likely to be generated in equilibrium, there is also a problem that the concentration of carbon monoxide contained in the produced fuel gas becomes high.

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0024]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

[0025] In view of the above problems, the present invention aims to provide a method for producing a fuel gas mainly composed of methane by methane reaction of hydrogen and carbon oxide in the presence of a methane catalyst, which does not require reactions under extremely high pressure conditions or the installation of expensive decarbonation equipment, and a catalyst necessary for realizing this method. [Means for solving the problem]

[0026] The characteristic configuration of the fuel gas production method according to the present invention comprises a methanation reaction step in which hydrogen and carbon oxide are reacted in the presence of a methanation catalyst to obtain a first fuel gas containing 2% to 20% hydrogen by volume after dehydration, and a dehydration hydrogenation reaction step in which an alcohol is added to the first fuel gas obtained in the methanation reaction step, and the alcohol and the hydrogen in the first fuel gas are reacted in the presence of a dehydration hydrogenation catalyst to obtain a second fuel gas containing an alkane having 2 to 4 carbon atoms, wherein the alcohol is one or more alcohols selected from alcohols having 2 to 4 carbon atoms, and the dehydration hydrogenation catalyst is made of tungsten zirconia oxide with palladium supported on it, and is active in the dehydration reaction of the alcohol and the hydrogenation reaction of the alkene.

[0027] According to this characteristic configuration, the hydrogen contained in the first fuel gas, which is mainly methane and contains a relatively high concentration of hydrogen obtained by performing a methanation reaction while avoiding extremely high pressure conditions, is converted into alkanes with 2 to 4 carbon atoms and water vapor through reaction with alcohol, thereby obtaining a second fuel gas with a reduced hydrogen concentration. Furthermore, since the calorific value per unit volume of alkanes with 2 to 4 carbon atoms is higher than that of methane, the amount of propane or butane added for calorific value adjustment can be reduced when necessary. In addition, if biomass-derived alcohol obtained by fermenting sugars obtained from sugarcane or corn is used as the alcohol, the carbon neutrality of the fuel gas is not compromised. [Brief explanation of the drawing]

[0030] [Figure 1] This is a block flow diagram illustrating the fuel gas production method of the present invention. [Figure 2] This figure shows the effects of temperature and pressure on the equilibrium conversion rate of the methane reaction of carbon dioxide. [Figure 3] This is an enlarged view of the region in Figure 2 where the equilibrium conversion rate is 80-100%. [Figure 4] This is an example of a reactor configuration for a methane reaction (fixed-bed insulated multi-stage reactor). [Figure 5] This figure shows the conversion rate of carbon dioxide to methane and the gas temperature at each reaction stage when carrying out a methane reaction using a fixed-floor insulated multi-stage reactor. [Figure 6] This is an example of a reactor configuration for a methane reaction (a fixed-floor insulated multi-stage reactor with a recycling line that returns the first-stage outlet gas to the first-stage inlet). [Figure 7] This is an example of the structure of a methanation reactor (heat exchange reactor). [Figure 8] This is an example of a reactor configuration for a methane reaction (the first stage is a fixed-bed insulated reactor with a recycling line, and the second stage is a heat exchange reactor). [Figure 9]This figure shows the effect of the hydrogen / carbon dioxide ratio at the inlet on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of the carbon dioxide methane reaction (reaction pressure 0.7 MPa). [Figure 10] This figure shows the effect of the hydrogen / carbon dioxide ratio at the inlet on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of the carbon dioxide methane reaction (reaction pressure 5 MPa). [Figure 11] This figure shows the effect of the hydrogen / carbon dioxide ratio at the inlet on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of the fuel gas obtained by the fuel gas production method of the present invention (ethanol / hydrogen molar ratio 0.9). [Figure 12] This figure shows the effect of the hydrogen / carbon dioxide ratio at the inlet on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of the fuel gas obtained by the fuel gas production method of the present invention (ethanol / hydrogen molar ratio 0.5). [Figure 13] This figure shows the X-ray diffraction patterns of the catalyst according to Example 1 before and after testing. [Figure 14] This figure shows the X-ray diffraction patterns of the catalyst in the comparative example before and after testing. [Modes for carrying out the invention]

[0031] [Embodiment] The following describes embodiments of the catalyst for producing fuel gas and the method for producing fuel gas according to the present invention. Figure 1 is a block flow diagram showing the fuel gas production method of the present invention. The fuel gas production method according to this embodiment comprises a methanation reaction step (metanying reactor 10) and a dehydration hydrogenation reaction step (dehydration hydrogenation reactor 20).

[0032] In the methanation reaction process, a mixed gas 1 of hydrogen and carbon oxides is brought into contact with a methanation catalyst packed in a methanation reactor 10 to carry out the methanation reaction. This methanation reaction yields a first fuel gas 2, which is mainly composed of methane and contains 2% to 20% hydrogen by volume after dehydration.

[0033] In the dehydration hydrogenation reaction step, first, alcohol 3 is added to the first fuel gas 2 obtained in the methanation reaction step via a flow control valve 30. Then, the first fuel gas 2 with added alcohol 3 is sent to the dehydration hydrogenation reactor 20, where it is brought into contact with a dehydration hydrogenation catalyst packed in the dehydration hydrogenation reactor 20, and an alkane is produced by the reaction of alcohol 3 with hydrogen. This reaction consumes the hydrogen contained in the first fuel gas 2, resulting in a second fuel gas 4 with a reduced hydrogen concentration. The obtained second fuel gas 4 mainly consists of methane and contains an alkane derived from alcohol 3. Alcohol 3 is one or more alcohols selected from alcohols with 2 to 4 carbon atoms, and the number of carbon atoms in the alkane contained in the second fuel gas 4 is the same as that of the alcohol 3 used.

[0034] [Conditions for the methanation reaction process] In the methanation reaction step, the hydrogen and carbon oxides used in mixed gas 1 can be produced by any method, as long as they have sufficient purity and properties to carry out the methanation reaction in the presence of a methanation catalyst. The hydrogen may be, for example, electrolyzed hydrogen obtained by electrolyzing water. The carbon oxide is carbon monoxide, carbon dioxide, or a mixture thereof. The carbon dioxide may be recovered from combustion exhaust gas by known carbon dioxide recovery methods such as the amine absorption method, or it may be carbon dioxide contained in biogas obtained by methane fermentation of organic matter. Biogas is usually obtained as a mixed gas of methane and carbon dioxide, but the carbon dioxide may be separated from this mixed gas and used in the methanation reaction, or the methane may be used in the methanation reaction without separation.

[0035] If hydrogen and carbon oxides contain sulfur, halogen compounds, siloxane compounds, heavy hydrocarbons, etc., these can cause degradation of the methanation reaction catalyst. Therefore, it is preferable to remove these before subjecting the mixture to the methanation reaction, if necessary.

[0036] As the methanation catalyst used in the methanation reaction process, known methanation catalysts containing Ni, Ru, etc., can be used.

[0037] There are no particular restrictions on the type of methanation reactor 10 used in the methanation reaction process, as long as the hydrogen concentration of the first fuel gas 2 after the methanation reaction is between 2% and 20% on a volume basis after dehydration. However, the methanation reaction is an equilibrium reaction that generates a relatively large amount of heat, and its equilibrium conversion rate changes greatly with temperature and pressure, as shown in Figures 2 and 3, becoming higher at lower temperatures and higher pressures. On the other hand, there are problems such as difficulty in ensuring the activity of the methanation catalyst at low temperatures and high pressure resulting in high equipment costs.

[0038] Furthermore, since the methanation reaction generates a relatively large amount of heat, the temperature of the gas rises as the reaction progresses, and the resulting decrease in the equilibrium conversion rate cannot be ignored. For these reasons, when using a fixed-bed adiabatic reactor, which is the most commonly used type in chemical processes, as the methanation reactor 10, it is usually difficult to obtain the desired conversion rate in a single stage. Therefore, it is preferable to connect multiple reactors in a multi-stage configuration, cool the outlet gas whose temperature has risen due to the reaction heat, and then introduce it into the next stage reactor.

[0039] Figure 4 shows an example of the configuration when the methanation reactor 10 is installed as a fixed-bed insulated multi-stage reactor. In this reactor configuration, there are five sets of reactors (11a to 15a) where the methanation reaction proceeds and heat exchangers (11b to 15b). In the configuration of the methanation reactor 10 shown in Figure 4, when a raw material gas with a stoichiometric ratio of hydrogen:carbon dioxide = 4:1 (molar ratio) is reacted at an inlet temperature of 250°C and a reaction pressure of 0.7 MPa at each stage, the temperature at the inlet and outlet of each stage and the conversion rate of carbon dioxide to methane are as shown in Figure 5. At the outlet of the fourth stage (14a), the conversion rate of carbon dioxide to methane is 94.3%, and at this stage, the hydrogen concentration in the gas (based on volume after dehydration by removing water; the same applies hereinafter) is 18.3%, which can be kept below 20%. At the fifth stage (15a) outlet, the conversion rate of carbon dioxide to methane reaches 97.7%, and the hydrogen concentration in the gas decreases to 8.3%, which can be reduced to below 10%. Therefore, when performing methanation using a simple adiabatic multi-stage reaction, under the aforementioned temperature and pressure conditions, four stages are required to reduce the hydrogen concentration to below 20% by volume, and five stages to reduce it to below 10%. Furthermore, the high heat generated by methanation causes the outlet temperature of the first stage to reach approximately 700°C, which poses a problem in terms of catalyst durability.

[0040] Figure 6 shows an example of the configuration when the methanation reactor 10 is set up as a fixed-bed insulated multistage reactor with a recycling line. In this reactor configuration, there are three sets of reactors (11a to 13a) where the methanation reaction proceeds and heat exchangers (11b to 13b). The first set of these sets is equipped with a recycling line 11c that returns the product after heat exchange back to reactor 11a. Using this reactor configuration, the temperature rise is suppressed due to the dilution effect, thus improving the durability of the catalyst. In addition, the decrease in the reactor outlet temperature results in an effect that increases the equilibrium conversion rate, which may allow for a reduction in the number of reactor stages compared to a simple multistage reactor configuration.

[0041] Figure 7 shows an example of the configuration when the methanation reactor 10 is installed as a heat exchange reactor. In this reactor configuration, the reaction can be carried out while maintaining the catalyst layer temperature at a predetermined temperature, making it possible to obtain a high conversion rate with a single-stage reactor. However, heat exchange reactors have a complex structure, which can lead to high equipment and maintenance costs. In addition, if the balance between the heat generated by the reaction and the heat removed by heat exchange is disrupted, localized high-temperature areas may occur, causing the catalyst to deteriorate in a short period of time.

[0042] Figure 8 shows an example of a methane reactor 10 configured by combining a fixed-bed insulated reactor with a recycling line and a heat exchange reactor. In this reactor configuration, the pairs of reactors (12a, 13a) and heat exchangers (12b, 13b) from the second stage onward in the example in Figure 6 are replaced with a single heat exchange reactor. This reactor configuration makes it possible to reduce the number of reactor stages and thus control equipment costs while ensuring the durability of the catalyst.

[0043] [Examples of the methanation reaction process] In the following, we assume that the reactor configuration shown in Figure 8 is adopted as the methanation reactor 10, and that a sufficient amount of methanation catalyst is used to obtain the equilibrium composition of the methanation reaction and the CO shift reaction under predetermined conditions.

[0044] When a methanation reaction is carried out with a molar ratio of hydrogen to carbon dioxide (hydrogen / carbon dioxide molar ratio) in the inlet range of 3.8 to 4.2 and a second-stage reaction temperature of 250°C, the concentrations of hydrogen and carbon dioxide in the gas after the methanation reaction are as shown in Figure 9, given a reaction pressure of 0.7 MPa. When the hydrogen / carbon dioxide molar ratio is 4.0, the hydrogen concentration is 4.4% and the carbon dioxide concentration is 1.1%. Lowering the hydrogen / carbon dioxide molar ratio reduces the hydrogen concentration, but even when the molar ratio is reduced to 3.8, the hydrogen concentration does not fall below 2%, and the carbon dioxide concentration rises to 5.6%. In other words, at a reaction pressure of 0.7 MPa, it is not possible to obtain a fuel gas with sufficiently reduced hydrogen and carbon dioxide concentrations.

[0045] When the reaction pressure is 5 MPa, the hydrogen and carbon dioxide contained in the gas after the methane reaction are as shown in Figure 10. When the hydrogen / carbon dioxide molar ratio is 4.0, the hydrogen concentration is 2.04% and the carbon dioxide concentration is 0.51%. Under these conditions, a fuel gas that generally meets the quality standard of a hydrogen concentration of 2% or less and a carbon dioxide concentration of 0.5% or less (this standard is the strictest generally known) can be obtained. However, under these conditions, even a slight decrease in the hydrogen / carbon dioxide molar ratio will increase the carbon dioxide concentration, and conversely, a slight increase in the hydrogen / carbon dioxide molar ratio will increase the hydrogen concentration. Thus, even slight fluctuations in the hydrogen / carbon dioxide molar ratio greatly affect the purity of the resulting fuel gas.

[0046] In other words, when obtaining a fuel gas with methane as the main component solely through the methane reaction of hydrogen and carbon dioxide, obtaining a fuel gas that meets the aforementioned quality standards of a hydrogen concentration of 2% or less and a carbon dioxide concentration of 0.5% or less requires high-pressure reaction equipment with an operating pressure significantly higher than 5 MPa.

[0047] [Conditions for the dehydration and hydrogenation reaction process] Alcohol 3 used in the dehydration hydrogenation reaction step is one or more alcohols selected from alcohols having 2 to 4 carbon atoms. That is, alcohol 3 is one alcohol selected from the group consisting of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-2-butanol, or a mixture of multiple alcohols selected from these groups.

[0048] The alcohol 3 used in the dehydration hydrogenation reaction step can be produced by any method, as long as it has a purity and properties that do not interfere with the reaction proceeding in the dehydration hydrogenation reaction step (details will be described later). For example, alcohol produced by fermentation using sugarcane or corn as raw materials can also be suitably used. In the fuel gas production method according to this embodiment, the alcohol 3 may contain an amount of water that is normally present. However, if the water content is too high, the heat of vaporization required to vaporize the water may decrease the efficiency of fuel gas production. Considering this, the water content of the alcohol 3 is preferably 50% by mass or less.

[0049] The reaction in the dehydration hydrogenation reactor 20 proceeds as follows: In the dehydration hydrogenation reactor 20, the dehydration reaction of alcohols (Equation 3) and the hydrogenation reaction of alkenes (Equation 4) proceed. C n H 2n+1 OH → C n H 2n +H2O (Equation 3) C n H 2n + H2 → C n H 2n+2 (Formula 4) However, n is 2, 3, or 4.

[0050] If the amount of alcohol 3 added is too small, the reduction in hydrogen concentration in the second fuel gas 4 will be insufficient. On the other hand, if the amount of alcohol 3 added is too large, the hydrogen concentration will become extremely low, and the hydrogenation reaction (Equation 4) of the alkene (ethylene in the case of ethanol used as the alcohol) produced by the dehydration of alcohol 3 will not proceed sufficiently, and alkenes may remain in the second fuel gas 4. In addition, because the alkene concentration during the reaction is high, the alkene may polymerize on the catalyst, and degradation of the catalyst due to carbon deposition may become a problem. Therefore, it is preferable that the amount of alcohol 3 added be such that the molar ratio of alcohol 3 to hydrogen contained in the first fuel gas 2 obtained in the methanation reaction step (alcohol / hydrogen) is between 0.45 and 0.9.

[0051] When converting alcohols to alkanes by reaction with hydrogen using a dehydration hydrogenation catalyst, the reaction temperature is preferably between 200°C and 400°C. Dehydration hydrogenation catalysts generally exhibit good activity at temperatures above 200°C, so setting the reaction temperature above 200°C facilitates the reaction between alcohol 3 and hydrogen (Equations 3 and 4). Furthermore, setting the reaction temperature below 400°C tends to suppress the steam reforming reactions of methane, ethane, propane, and butane. If the steam reforming reactions of methane, ethane, propane, and butane proceed, even if hydrogen decreases in the hydrogenation reaction of alkenes, new hydrogen is generated by the steam reforming reactions of methane, ethane, propane, or butane, which may prevent a reduction in the hydrogen concentration in the fuel gas. It is more preferable to set the reaction temperature between 250°C and 350°C.

[0052] [Dehydration Hydrogenation Catalyst] The dehydration hydrogenation catalyst used in the dehydration hydrogenation reaction step is a catalyst consisting of tungsten zirconia oxide supported with palladium. Tungsten zirconia oxide is a known substance, sometimes denoted as WO3 / ZrO2 (for example, Makoto Hino and Kazushi Arata, Surface, Vol. 34, No. 2, p. 51, 1996 (Non-Patent Literature 7)), and can be prepared according to known methods. That is, tungsten zirconia oxide can be obtained, for example, by mixing zirconium oxide and tungstic acid, adding water, kneading, drying, and calcining in air.

[0053] The method of supporting palladium is not particularly limited as long as the palladium is highly dispersed on the support, but preferably, the support is impregnated with an aqueous solution such as a nitrate or chloride salt. The amount of palladium supported is not particularly limited, but is preferably 0.1 to 5%, more preferably 0.5 to 2%, and even more preferably 0.5 to 1%, based on the weight of tungsten zirconia oxide. If the amount of palladium supported is too little, the catalytic activity may be low, while if it is too much, the amount of palladium used may increase, reducing economic efficiency, and the catalytic activity may be lost due to palladium aggregation.

[0054] The dehydration hydrogenation catalyst used in the dehydration hydrogenation reaction step is preferably active in the dehydration reaction of alcohols (Equation 3) and the hydrogenation reaction of alkenes (Equation 4), while being substantially inactive in the steam reforming reactions of methane, ethane, propane, and butane. Furthermore, it is preferable that the dehydration hydrogenation catalyst can be used stably even at high temperatures. If the catalyst has low high-temperature tolerance, the dehydration hydrogenation reaction cannot proceed stably for a long period of time, the frequency of catalyst replacement increases, and the overall operating cost of the process increases.

[0055] The type of dehydration hydrogenation reactor 20 used in the dehydration hydrogenation reaction step is not particularly limited and may be, for example, a fixed-bed insulated reactor, a fixed-bed insulated reactor with a recycling line, a heat exchange reactor, etc.

[0056] [Examples of the dehydration and hydrogenation reaction process] In the following explanation, we will use the reactor configuration shown in Figure 8 as the methanation reactor 10, and provide an example where a dehydration hydrogenation reactor 20 (not shown), configured as a fixed-bed adiabatic reactor, is provided downstream of the methanation reactor 10. In this example, we will assume that the methanation reaction and the CO shift reaction have reached equilibrium in the methanation reactor 10, that ethanol is used as alcohol 3, and that the dehydration reaction of ethanol and the hydrogenation reaction of ethylene have reached equilibrium in the dehydration hydrogenation reactor 20.

[0057] In the following example, the reaction temperature of the heat exchange reactor 12d in the methanation reactor 10 was set to 250°C. The inlet temperature of the dehydration hydrogenation reactor 20 was also set to 250°C to ensure the reaction proceeded under adiabatic conditions. The reaction pressure was set to 0.7 MPa in both the methanation reactor 10 and the dehydration hydrogenation reactor 20. The concentrations of hydrogen and carbon dioxide in the resulting second fuel gas 4, relative to the hydrogen / carbon dioxide molar ratio of the mixed gas 1 supplied to the methanation reactor 10, are shown in Figures 11 and 12.

[0058] Figure 11 shows the relationship between the composition of mixed gas 1 and the concentrations of hydrogen and carbon dioxide in the second fuel gas 4, when the amount of ethanol added is 0.9 in molar ratio to the hydrogen contained in the first fuel gas 2. When the molar ratio of hydrogen to carbon dioxide in mixed gas 1 is 4.0, the hydrogen concentration is 0.44% and the carbon dioxide concentration is 1.09%. If only the methanation reaction step is performed under similar conditions, the hydrogen concentration is 4.4% and the carbon dioxide concentration is 1.1% (Figure 9), so it can be seen that the hydrogen concentration of the first fuel gas 2 obtained by the methanation reaction is significantly reduced by the dehydration hydrogenation reaction step. Furthermore, when the molar ratio of hydrogen to carbon dioxide is 4.04, the hydrogen concentration is 0.55%, the carbon dioxide concentration is 0.43%, the methane concentration is 94.1%, and the ethane concentration is 4.9%, so the concentration of hydrocarbon (methane + ethane) components exceeds 99%. If only the methane reaction step is performed, the hydrogen concentration is 5.5% and the carbon dioxide concentration is 0.43%. Therefore, even in this case, it can be seen that the hydrogen concentration is significantly reduced by the dehydration hydrogenation reaction step.

[0059] Even though both the methanation reaction and the dehydration-hydrogenation reaction (dehydration and hydrogenation) are carried out at the same inlet temperature (250°C), hydrogen remains in the methanation reaction and decreases in the dehydration-hydrogenation reaction for the following reasons: The methanation reaction of carbon dioxide is an exothermic reaction with 41 kJ of heat per mole of hydrogen. On the other hand, the hydrogenation reaction of ethylene is a reaction that involves a slightly larger amount of heat (136 kJ of heat per mole of ethylene), and even when combined with the dehydration reaction of ethanol (45 kJ of heat per mole of ethanol), it is an exothermic reaction with approximately 90 kJ of heat per mole of hydrogen. Therefore, the production of ethylene by the dehydration of ethanol and the subsequent production of ethane by the hydrogenation of ethylene are significantly biased towards ethane production in equilibrium. For this reason, even under temperature conditions that result in residual hydrogen in the methanation reaction, the dehydration-hydrogenation reaction proceeds sufficiently.

[0060] This explanation also holds true for other alcohols that may be included in alcohol 3. For example, when alcohol 3 contains 1-propanol, the endothermic reaction in the dehydration of 1-propanol is 33 kJ per mole of 1-propanol, and the exothermic reaction in the hydrogenation of propylene is 125 kJ per mole of propylene. Therefore, the portion of the dehydration hydrogenation reaction step involving 1-propanol is an exothermic reaction with a discharge rate of 92 kJ per mole of hydrogen. For other alcohols that may be included in alcohol 3, the entire dehydration hydrogenation reaction step is an exothermic reaction with a discharge rate of approximately 65 to 95 kJ per mole of hydrogen. Thus, similar to the explanation for ethanol above, it can be seen that the reaction in the dehydration hydrogenation reaction step proceeds sufficiently for other alcohols that may be included in alcohol 3.

[0061] In the dehydrogenation reaction step, carbon dioxide cannot be reduced. When the methanation reaction is carried out under conditions where the hydrogen / carbon dioxide molar ratio of the hydrogen / carbon dioxide supplied to the methanation reaction is slightly higher than 4.0 and hydrogen is slightly in excess, the carbon dioxide concentration in the first fuel gas 2 after the methanation reaction step can be reduced. Here, although the hydrogen concentration in the first fuel gas 2 increases due to the excessive addition of hydrogen, the hydrogen can be reduced in the dehydrogenation reaction step. When the hydrogen / carbon dioxide molar ratio of the mixed gas 1 supplied to the methanation reaction step is 4.04, the hydrogen concentration in the resulting fuel gas is 0.55% and the carbon dioxide concentration is 0.43%. That is, the quality standards of a hydrogen concentration of 2% or less and a carbon dioxide concentration of 0.5% or less, which cannot be achieved even under the high-pressure reaction conditions of 5 MPa by only the methanation reaction, can be achieved by the reaction at a low pressure of 0.7 MPa using the method according to the present embodiment.

[0062] If the hydrogen / carbon dioxide molar ratio of the mixed gas 1 supplied to the methanation reaction step is further increased, the carbon dioxide concentration in the resulting fuel gas can be further reduced. For example, when the hydrogen / carbon dioxide molar ratio of the mixed gas 1 supplied to the methanation reaction step is 4.2, the hydrogen concentration in the resulting fuel gas is 1.7% and the carbon dioxide concentration is 0.1% or less. Also, the methane concentration is 83.3% and the ethane concentration is 15.0%, and the calorific value per 1 m of the fuel gas 3 becomes 44 MJ, and the gas has substantially the same properties as general natural gas-based city gas.

[0063] On the other hand, in addition to the need for more alcohol 3 to be added, when the reaction (dehydration and hydrogenation) of the dehydrogenation reaction step is carried out under adiabatic conditions, the outlet temperature of the reaction in the dehydrogenation reaction step becomes high, and the alkene concentration becomes high, so there are concerns about the deterioration of the catalyst due to carbon deposition and the increase in the hydrogen and carbon dioxide concentrations accompanying the concurrent steam reforming reaction. From this perspective, it is preferable that the hydrogen / carbon dioxide molar ratio of the mixed gas 1 supplied to the methanation reaction step does not exceed 4.08. If the hydrogen / carbon dioxide molar ratio is in the range of 4.04 or more and 4.08 or less, it is easy to achieve the quality standards of a hydrogen concentration of 2% or less and a carbon dioxide concentration of 0.5% or less.

[0064] Figure 12 shows the relationship between the composition of mixed gas 1 and the concentrations of hydrogen and carbon dioxide in the second fuel gas 4, when the amount of ethanol added is 0.5 in molar ratio to the hydrogen contained in the first fuel gas 2. In the example in Figure 12, although the hydrogen concentration in the resulting second fuel gas 4 is higher compared to Figure 11 because the amount of ethanol added is less, it can be seen that the hydrogen concentration in the second fuel gas 4 is reduced compared to Figure 9. If the molar ratio of hydrogen / carbon dioxide in mixed gas 1 is in the range of 4.04 to 4.08, all quality standards of hydrogen concentration of 4% or less, carbon dioxide concentration of 0.5% or less, and non-hydrocarbon components of 4% or less can be achieved. Since these conditions cannot be achieved in a methanation reaction at 0.7 MPa regardless of how the molar ratio of hydrogen / carbon dioxide of the mixed gas subjected to the methanation reaction is set, it is clear that the method of the present invention is useful for producing high-quality fuel gas without using high-pressure reaction equipment. Even in this case, as described above, if the carbon oxide includes at least one of carbon monoxide and carbon dioxide, the above quality standards are more easily achieved if the ratio of hydrogen to carbon oxide supplied to the methane reaction process satisfies the value of {(hydrogen)+(carbon monoxide)} / {(carbon monoxide)+(carbon dioxide)} calculated on a molar basis to be between 4.04 and 4.08.

[0065] [Other Embodiments] Finally, other embodiments of the fuel gas production method according to the present invention will be described. Note that the configurations disclosed in each of the following embodiments can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise.

[0066] In the above embodiment, an example was described in which the methanation reactor 10 used in the methanation reaction step is configured by combining a fixed-bed insulated reactor with a recycling line and a heat exchange reactor, as shown in Figure 8. However, the reactor used in the methanation reaction step according to the present invention is not particularly limited, as long as a fuel gas containing 2% to 10% by volume of hydrogen can be obtained. Examples of such reactors include fixed-bed insulated multi-stage reactors and single-stage or multi-stage heat exchange reactors.

[0067] In the above embodiment, an example in which the pressure in the methanation reaction step is 0.7 MPa was particularly described. However, the pressure in the methanation reaction step according to the present invention is not particularly limited as long as a first fuel gas containing 2% to 10% by volume of hydrogen is obtained. However, if the pressure is 0.5 MPa or higher, the hydrogen and carbon dioxide content in the first fuel gas obtained in the methanation reaction step is reduced, and therefore the hydrogen and carbon dioxide content in the final product, the second fuel gas, is also easily reduced. Furthermore, since it is easier to reduce the cost of the equipment used in the methanation reaction step, the pressure is preferably 3 MPa or lower, and more preferably 1 MPa or lower.

[0068] In the above embodiment, an example in which the dehydration hydrogenation reactor 20 used in the dehydration hydrogenation reaction step is configured as a fixed-bed insulated reactor has been particularly described. However, the reactor used in the dehydration hydrogenation reaction step according to the present invention is not particularly limited as long as the reactions represented by formulas 3 and 4 proceed. Examples of such reactors include fixed-bed insulated reactors with a recycling line and heat exchange reactors.

[0069] In the above embodiment, an example in which the pressure in the dehydration hydrogenation reaction step is 0.7 MPa was particularly described. However, the pressure in the dehydration hydrogenation reaction step according to the present invention is not particularly limited as long as the reactions represented by formulas 3 and 4 proceed. However, if the pressure is 0.5 MPa or higher, it is easier to reduce the hydrogen and carbon dioxide content in the resulting fuel gas without using a large amount of dehydration hydrogenation catalyst. Furthermore, it is easier to reduce the cost of the equipment used in the dehydration hydrogenation reaction step, so the pressure is preferably 3 MPa or lower, and more preferably 1 MPa or lower.

[0070] In the above embodiment, an example was described in which the pressures of the methanation reaction step and the dehydration hydrogenation reaction step were the same (0.7 MPa). However, in the methanation reaction step and the dehydration hydrogenation reaction step according to the present invention, the pressures may be the same or different.

[0071] Furthermore, the present invention does not exclude the use of conventionally known means for improving the methane conversion rate. For example, a configuration may be used in which the reaction gas is cooled in an intermediate stage of a multi-stage reaction to condense and separate a portion of the water vapor. Even in this case, the method of the present invention can be used to reduce the concentrations of hydrogen and carbon dioxide in the fuel gas without excessively removing water vapor. [Examples]

[0072] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0073] [Example 1] 160g of zirconium hydroxide (manufactured by Hayashi Pure Chemical Industries, Ltd.; containing 85% as ZrO2) and 30g of tungstic acid (manufactured by Mitsuwa Chemical Co., Ltd.; H2WO4) were mixed, and 220g of pure water was added. The mixture was wet-kneaded for 12 hours. After removing the water with an evaporator, it was dried in a 120°C oven for 3 hours, and then calcined at 700°C for 3 hours to obtain WO3 / ZrO2. 30 g was impregnated with an aqueous solution of palladium nitrate containing 0.3 g of Pd, evaporated to dryness on a hot plate at 125°C, dried in a drying oven at 120°C for 1 hour, and then calcined in air at 350°C for 4 hours to obtain a catalyst (1% Pd / WO3 / ZrO2 catalyst) in which 1 mass% of palladium was supported on WO3 / ZrO2.

[0074] The aforementioned 1% Pd / WO3 / ZrO2 catalyst was compressed into tablets and classified into sizes of 1.7 to 3.4 mm. 5 mL of each tablet was packed into a SUS reaction tube (15 mm inner diameter), and heated in an electric furnace while circulating a gas mixture of 10% hydrogen and the remainder nitrogen. The temperature was raised to 250°C and held for 4 hours to reduce the catalyst, after which the temperature was further raised and maintained at 300°C.

[0075] A fuel gas consisting of 32.3% methane, 64.4% water vapor, and 3.3% hydrogen was prepared at a rate of 236 mL / min (volume at standard conditions of 0°C and 101.325 kPa). Ethanol and nitrogen were added to this fuel gas to adjust the molar ratio of ethanol to hydrogen to 0.7 and the nitrogen concentration to 10.0% (volume on a dry basis). This fuel gas with added ethanol and nitrogen was passed through the catalyst at a pressure of 0.8 MPa, and the reaction tube outlet gas was analyzed every 2.5 hours from the start of flow. The analysis was performed by cooling the fuel gas after the reaction to separate water, and then quantifying the concentrations of methane, ethane, ethylene, hydrogen, carbon monoxide, carbon dioxide, and nitrogen using a gas chromatograph. The analysis results are shown in Table 1. The X-ray diffraction patterns of the catalyst before and after the test are shown in Figure 13.

[0076] Table 1: Analysis results of fuel gas (Example 1) [Table 1] -: Not detected

[0077] [Example 2] A catalyst (0.1% Pd / WO3 / ZrO2 catalyst) was prepared by supporting 0.1% by mass of palladium on WO3 / ZrO2, in the same manner as in Example 1, except that the amount of palladium nitrate was changed. The test was carried out in the same manner as in Example 1, except that the 0.1% Pd / WO3 / ZrO2 catalyst was used. The results of the fuel gas analysis are shown in Table 2.

[0078] Table 2: Analysis results of fuel gas (Example 2) [Table 2] -: Not detected

[0079] [Comparative Example] A silica support (CARiACT® G-6, manufactured by Fuji Silysia Chemical Co., Ltd.) was impregnated with an aqueous solution of silitangustic acid (SiO2·12WO3·26H2O) and palladium nitrate. After evaporation to dryness on a hot water bath, the silica support was dried at 120°C and calcined in air at 350°C for 4 hours to obtain a catalyst (Pd / SiW / silica catalyst) in which 20 parts by mass of silitangustic acid and 2 parts by mass of palladium were supported on 80 parts by mass of silica support. The test was carried out in the same manner as in Example 1, except that the Pd / SiW / silica catalyst was compressed into tablets and classified to 1.7-3.4 mm in size. The results of the fuel gas analysis are shown in Table 3. The X-ray diffraction patterns of the catalyst before and after the test are shown in Figure 14.

[0080] Table 3: Analysis results of fuel gas (comparative example) [Table 3]

[0081] As shown in Example 1, when ethanol is added to a hydrogen-containing fuel gas so that the molar ratio of ethanol to hydrogen is 0.7, and then the mixture is passed through a Pd / WO3 / ZrO2 catalyst, the hydrogen reacts quantitatively with the ethanol to produce water vapor and ethane. By cooling the fuel gas and separating the water, the water vapor is removed, thus reducing the hydrogen concentration in the fuel gas and generating ethane. After 50 hours from the start of fuel gas flow, the hydrogen concentration is reduced to 3.7%, which meets the 4% hydrogen concentration standard. Furthermore, while the hydrogen concentration in the reaction tube outlet gas tends to decrease over time and the ethane concentration tends to increase over time until 50 hours from the start of fuel gas flow, the gas composition in the reaction tube outlet gas remains almost constant and stable from 50 hours to 150 hours, and no carbon monoxide or ethylene is produced. These results indicate that Pd / WO3 / ZrO2 is a highly durable catalyst that maintains its performance for extended periods, even at relatively high temperatures of 300°C.

[0082] Similarly, in Example 2, which used 0.1% Pd / WO3 / ZrO2 as a catalyst, the composition of the outlet gas remained stable from 50 hours after the start of fuel gas flow until 145 hours after the start of fuel gas flow, maintaining a hydrogen concentration of 4% or less.

[0083] On the other hand, in a comparative example using a Pd / SiW / silica catalyst, the hydrogen concentration was reduced to 3.7% after 5 hours of fuel gas flow, and 4.7% ethane was obtained. However, the hydrogen concentration increased over time, reaching 4.7% after 154 hours.

[0084] Furthermore, in the X-ray diffraction pattern of 1% Pd / WO3 / ZrO2 (Figure 13, Example 1), only diffraction peaks originating from ZrO2 were observed, and no clear changes were confirmed before and after the test. On the other hand, in the X-ray diffraction pattern of Pd / SiW / SiO2 (Figure 14, Comparative Example), a sharp peak was observed around 23.5° in the X-ray diffraction pattern of the post-tested sample, which was not seen before the test. This is because the siliconungstic acid (SiW) contained in the new catalyst changed to tungsten oxide after the test.

[0085] In Examples 1 and 2, which used Pd / WO3 / ZrO2, the concentration of the ethane produced was maintained for 150 hours (Tables 1 and 2). Furthermore, the X-ray diffraction patterns before and after the test in Example 1 (Figure 13) showed that the structure of Pd / WO3 / ZrO2 did not change before and after use. On the other hand, in the comparative example using the conventional catalyst Pd / SiW / SiO2, a decrease in hydrogen concentration was observed as the reaction continued (Table 3). In addition, a comparison of the X-ray diffraction patterns before and after the test in the comparative example (Figure 14) showed that the structure of Pd / SiW / SiO2 changed during use. These results indicate that the Pd / WO3 / ZrO2 catalyst has higher high-temperature tolerance than conventional catalysts and can be used stably for long periods even under high-temperature conditions (e.g., 300°C).

[0086] [Example 3] 78 g of zirconium hydroxide (Z-999-D, manufactured by Taiyo Kogyo Co., Ltd.) and 21 g of an aqueous solution of ammonium metatungstate (MW-2, manufactured by Nippon Muki Kagaku Kogyo Co., Ltd., containing 50% by mass as WO3) were mixed, and 50 g of pure water was added and wet kneaded. The mixture was evaporated to dryness in a water bath, dried overnight in a 120°C oven, and then calcined at 800°C for 4 hours to obtain WO3 / ZrO2. 35 g of the above WO3 / ZrO2 was impregnated with an aqueous solution of palladium nitrate containing 0.18 g as Pd, evaporated to dryness in a water bath, dried overnight in a 120°C oven, and then calcined in air at 350°C for 4 hours to obtain a catalyst (0.5% Pd / WO3 / ZrO2 catalyst) in which 0.5% by mass of palladium was supported on WO3 / ZrO2.

[0087] The aforementioned 0.5% Pd / WO3 / ZrO2 catalyst was compressed into tablets and classified into 1.0-2.5 mm tablets. 6 mL of these tablets were packed into a SUS reaction tube (16 mm inner diameter), and a gas mixture of 10% hydrogen and the remainder nitrogen was passed through it at 240°C for 1 hour. After holding the tube for 1 hour, the gas mixture was switched to 20% hydrogen and the remainder nitrogen, and the tube was held for another 2 hours to perform the reduction treatment.

[0088] A fuel gas consisting of 32.6% methane, 65.2% water vapor, 2.0% hydrogen, and 0.14% carbon dioxide was prepared at a rate of 400 mL / min (volume at standard conditions of 0°C and 101.325 kPa). Ethanol was added to adjust the molar ratio of ethanol to hydrogen in the fuel gas to 0.7. This ethanol-added fuel gas was passed through the catalyst at a pressure of 0.7 MPa (absolute pressure), heated to 300°C, and held overnight. After the reaction, the fuel gas was cooled and water was separated. The concentrations of methane, ethane, hydrogen, carbon monoxide, and carbon dioxide were then quantified using a gas chromatograph. The concentrations of each component in the fuel gas after the reaction (based on volume after dehydration) were 1.9% hydrogen, 0.47% carbon dioxide, 0.10% carbon monoxide, 4.0% ethane, and the remainder methane.

[0089] As shown in Example 3, when ethanol is added to a hydrogen-containing fuel gas so that the molar ratio of ethanol to hydrogen is 0.7, and then passed through a 0.5% Pd / WO3 / ZrO2 catalyst, the hydrogen reacts quantitatively with the ethanol to produce water vapor and ethane. By cooling the fuel gas and separating the water, the water vapor is removed, thus reducing the hydrogen concentration in the fuel gas and generating ethane. Under the conditions of Example 3, the hydrogen concentration is reduced to 1.9%, which satisfies the criterion of a hydrogen concentration of 4%. [Industrial applicability]

[0090] The present invention can be used, for example, as a method for producing fuel gas for supply as city gas. [Explanation of Symbols]

[0091] 1: Mixed gas 2: Fuel gas 3: Alcohol 4: Fuel gas 10: Methanation reactor 11a~15a: Reactor 11b~15b: Heat exchanger 11c: Recycling Line 12d: Heat exchange reactor 20: Dehydration hydrogenation reactor 30: Flow control valve

Claims

[Claim 1] A methane reaction step in which hydrogen and carbon oxide are reacted in the presence of a methane catalyst to obtain a first fuel gas containing 2% to 20% hydrogen by volume after dehydration, The process includes a dehydration hydrogenation step in which, after adding an alcohol to the first fuel gas obtained in the methane reaction step, the alcohol and hydrogen in the first fuel gas are reacted in the presence of a dehydration hydrogenation catalyst to obtain a second fuel gas containing an alkane having 2 to 4 carbon atoms, The aforementioned alcohol is one or more alcohols selected from alcohols having 2 or more carbon atoms and 4 or fewer carbon atoms. The dehydration hydrogenation catalyst comprises palladium supported on tungsten zirconia oxide, and the method for producing fuel gas is active in the dehydration reaction of alcohol and the hydrogenation reaction of alkenes.

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