JP2024119778A - Catalyst for dehydration and hydrogenation of alcohol and method for producing same - Google Patents

Abstract

To provide a dehydration hydrogenation catalyst for alcohols that does not require reactions under extremely high pressure conditions or installation of expensive decarboxylation equipment when producing a first fuel gas primarily composed of methane through methanation of hydrogen and carbon oxide in the presence of a methanation catalyst, and is essential for preparing a second fuel gas with reduced hydrogen levels by a simple and economically beneficial method.SOLUTION: A dehydration hydrogenation catalyst for alcohols includes palladium and a solid acid catalyst. The CO adsorption capacity is 0.50 cc or more and 40 cc or less per 1.0 g of the palladium.SELECTED DRAWING: Figure 1

Description

The present invention relates to a catalyst for producing a fuel gas with a high calorific value and mainly composed of methane by methanation reaction of hydrogen and carbon oxides in the presence of a methanation catalyst, and more specifically to a catalyst for producing a fuel gas with a high hydrocarbon concentration and a reduced hydrogen concentration, and a method for producing the same.

In recent years, as a measure to combat global warming, attention has been focused on carbon-neutral fuels, which do not substantially increase the concentration of carbon dioxide in the atmosphere even when burned.

Methane can be obtained by capturing carbon dioxide from exhaust gases generated during industrial processes and thermal power generation, and reacting it with hydrogen obtained through electrolysis using electricity generated by renewable energy sources such as solar and wind power. Methane obtained in this way can be considered a carbon-neutral fuel that does not contribute to global warming, as no additional carbon dioxide is produced when it is burned.

The methanation reaction (Equation 1), in which carbon dioxide reacts with hydrogen to produce methane, is well known.

CO ₂ +4H ₂ → CH ₄ +2H ₂ O (Formula 1)
In Patent Document 1, when a gas containing CO and _H2 is methanated, a methanation reactor having a Cu-Zn-based low-temperature shift catalyst arranged on the upstream side and a methanation catalyst arranged on the downstream side is used. A method for methanating a gas containing CO and _H2 is disclosed, characterized in that the CO shift reaction (Equation 2) proceeds in the upstream low-temperature shift reactor, and the amount of carbon monoxide contained in the raw gas is reduced. Most of the carbon dioxide reacts with water vapor and is converted to carbon dioxide, and it is believed that the methanation reaction of carbon dioxide proceeds on the downstream methanation catalyst.

CO+H ₂ O → CO ₂ +H ₂ (Formula 2)
Methanation reactions have long been used to remove carbon monoxide and carbon dioxide from hydrogen for ammonia synthesis, and catalysts carrying Ni or Ru are known to exhibit high activity (Non-Patent References 1 and 2).

The methanation reaction, in which carbon oxides (carbon monoxide and carbon dioxide) are reacted with hydrogen to obtain methane, is an industrially established technology (e.g., Non-Patent Document 3), but there are still challenges to be overcome in obtaining fuel gas of a quality that can be used as a raw material for city gas.

Natural gas is commonly used as a raw material for city gas, and is composed mainly of methane, with small amounts of ethane, propane, and butane. Natural gas does not normally 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 from liquefied natural gas, hydrogen, carbon monoxide, and carbon dioxide are almost completely removed during the liquefaction refining process, so it contains virtually no hydrogen, carbon monoxide, or carbon dioxide.

The concentration of hydrocarbons other than methane (ethane, propane, and butane) contained in natural gas varies depending on the natural gas's production area and refining method, so when producing city gas, propane or butane is usually added to adjust the calorific value to within a certain range, and an odorant is added to ensure safety before it is sent to consumers through city gas pipelines.

When hydrogen, carbon monoxide and carbon dioxide are present in city gas, they can cause the following problems:

Firstly, carbon monoxide is highly toxic, so if the gas leaks, there is a risk of poisoning. The permissible concentration is 200 ppm, and from a safety standpoint, it is desirable to keep the concentration in fuel gas below this level. Even taking into account dilution with air, it needs to be below 1000 ppm.

Secondly, carbon dioxide is not only non-flammable, but also acts to suppress combustion. Therefore, if it is mixed into fuel gas in high concentrations, it not only reduces the efficiency of gas transport in the ducts, which reduces the heating value of the fuel gas, but it may also cause a decrease in the efficiency of combustion equipment.

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 into a fuel gas whose main component is methane, the calorific value per unit volume decreases. Furthermore, hydrogen is known to have a large impact on combustion equipment due to its fast combustion speed.

As described above, when hydrogen, carbon monoxide and carbon dioxide are mixed into city gas, they have various effects at each stage of gas supply and consumption, so the quality standards for gas accepted into city gas pipeline networks generally set restrictions on the concentrations of hydrogen, carbon monoxide and carbon dioxide.

In pipeline networks with fuel filling stations for natural gas vehicles, there are known examples where the upper limit of hydrogen concentration is set at 2.0% by volume (Non-Patent Document 4). There are also known examples where the hydrogen concentration is set at 4.0% or less by volume, the carbon dioxide concentration at 0.50% or less by volume, and the carbon monoxide concentration at 0.050% 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 at 4.0% or less by volume (Non-Patent Document 6).

The contamination of city gas with hydrogen, carbon monoxide, and carbon dioxide poses problems beyond the quality of the city gas. As mentioned above, city gas is supplied after being adjusted to a certain calorific value range by adding propane or butane to ensure stable use in combustion appliances. Therefore, if high concentrations of hydrogen or carbon dioxide are present, it is necessary to mix in large quantities of propane and butane, which are necessary to adjust the calorific value. This not only increases the cost of gas production, but also undermines the carbon neutrality of the produced gas if fossil fuel-derived propane and butane are used to adjust the calorific value.

The methanation reaction of carbon dioxide (Equation 1) is an equilibrium reaction, and under normal industrial operating conditions, carbon dioxide and hydrogen cannot be completely converted to methane. When a mixed gas with a stoichiometric ratio (hydrogen:carbon dioxide = 4:1) is reacted at normal pressure (0.10 MPa), the equilibrium conversion rate of carbon dioxide to methane is 95.0% when the reaction temperature is 300°C, 97.5% when the reaction temperature is 250°C, and 98.9% when the reaction temperature is 200°C.

Thus, at normal pressure, only fuel gas containing a large amount of hydrogen can be obtained. Because the methanation reaction is an exothermic reaction, the lower the temperature, the higher the equilibrium conversion rate; however, in the case of a catalytic reaction, the lower the temperature, the lower the catalytic activity. For this reason, there is a lower limit to the reaction temperature, and with a typical methanation catalyst, a temperature of 250°C or higher is required to achieve a practical reaction rate (Non-Patent Document 4, Patent Documents 2 and 3).

The methanation reaction of carbon dioxide (Equation 1) is a reaction in which the amount of substance (molar number) decreases, so the higher the pressure, the higher the equilibrium conversion rate. Comparing at 250°C, the equilibrium conversion rate of carbon dioxide to methane (when reacted at a stoichiometric ratio of hydrogen:carbon dioxide = 4:1) is 97.5% at normal pressure (0.10 MPa), but improves to 98.9% at 0.70 MPa and 99.5% at 5.0 MPa. However, even when a mixed gas of hydrogen:carbon dioxide = 4:1 is reacted at 250°C and 5.0 MPa, the equilibrium composition (composition by volume after dehydration excluding the water produced) is 97.45% methane, 2.04% hydrogen, and 0.51% carbon dioxide. Therefore, in order to obtain a fuel gas with 2.0% hydrogen (by volume) or less, the reaction must be carried out under high-pressure conditions exceeding 5.0 MPa.

There are several known methods for reducing the hydrogen concentration in fuel gas obtained by methanation reactions. For example, if methanation reactions are carried out under conditions where the amount of hydrogen is less than the stoichiometric ratio, and excess carbon dioxide is removed by decarbonation treatment, both the hydrogen content and the carbon dioxide content can be reduced (Patent Document 4). There is an example of this method being adopted in the methanation of coke oven gas (Non-Patent Document 3). However, decarbonation equipment generally requires high equipment costs and consumes a large amount of energy to operate, which reduces its economic viability.

As an alternative method, a method is known in which the methanation reaction is carried out in multiple stages, the gas produced in the intermediate stages is cooled, and the water is condensed and separated (Non-Patent Document 4, Patent Documents 2 and 3). By removing the produced water, the methanation reaction can be allowed to proceed further to the production side, improving the conversion rate of carbon dioxide to methane. However, this method requires heat exchange equipment, which increases the equipment costs, and there are also issues with the fact that if too much produced water is removed, the composition will enter the region where equilibrium carbon deposition occurs, making it difficult to control the water separation process.

Furthermore, in both the method of carrying out the methanation reaction under conditions of less hydrogen than the stoichiometric ratio and removing excess carbon dioxide by decarbonation treatment, and the method of carrying out the methanation reaction in multiple stages and cooling the gas produced in the intermediate stages to condense and separate the water, the conditions are favorable for the production of carbon monoxide in equilibrium, resulting in a problem of high carbon monoxide concentrations in the produced fuel gas.

Patent Document 5 and Patent Document 6 describe a method for producing a gas with reduced hydrogen by adding alcohol to a hydrogen-containing gas after a methanation reaction, and then reacting the alcohol with hydrogen in the fuel gas in the presence of a dehydration hydrogenation catalyst. As an example of the catalyst, Patent Document 5 describes a catalyst in which tungstosilicic acid and palladium are supported on a silica carrier (Pd/SiW/silica catalyst), and Patent Document 6 describes a catalyst in which palladium is supported on tungsten oxide zirconia (Pd/WO ₃ /ZrO ₂ catalyst). It is described that the Pd/SiW/silica catalyst and Pd/WO ₃ /ZrO ₂ catalyst exemplified in these documents decompose a part of the alcohol by a steam reforming reaction and convert it into carbon monoxide, carbon dioxide, and hydrogen, but this can be a disadvantage in using the generated fuel gas as city gas.

Japanese Unexamined Patent Publication No. 60-235893 JP 2015-124217 A JP 2018-135283 A JP 2019-26595 A JP 2021-138927 A JP 2022-133257 A

Chemical Engineering Society, ed., Chemical Process Collection, 1970, p. 153 Catalysis Society of Japan, Catalyst Handbook, 2008, p. 535 Kawagoe, Matsuda, Matsushima and Uematsu, Hitachi Review, Vol. 68, No. 10, 1986, p. 73 E. I. Koytsoumpa and S. Karellas, Renewable and Sustainable Energy Reviews, Vol. 94, 2018, p. 536 Biogas Purchasing Guidelines, Osaka Gas Co., Ltd., 2008 Biogas Purchasing Guidelines, Tokyo Gas Co., Ltd., 2008 Catalysis Society of Japan, Reference Catalyst Committee, Catalyst, Vol. 31, No. 5, p. 317, 1989

In view of the above problems, the problem that the present invention aims to solve is to provide an alcohol dehydration/hydrogenation catalyst and a method for producing the catalyst, which are necessary for producing fuel gas with a reduced hydrogen concentration in a simple and economical manner, without requiring reactions under extremely high pressure conditions or the installation of expensive decarbonation equipment, when producing fuel gas mainly composed of methane by a methanation reaction of hydrogen and carbon oxides in the presence of a methanation catalyst.

The alcohol dehydration and hydrogenation catalyst according to the present invention is characterized in that it contains palladium and a solid acid catalyst, and is used to convert a first fuel gas containing 2.0% to 20% hydrogen by volume after dehydration, obtained by methanation reaction of hydrogen and carbon oxides in the presence of a methanation catalyst, into a second fuel gas containing alkanes having 2 to 4 carbon atoms and having a reduced hydrogen concentration, by treating the first fuel gas in the presence of an alcohol having 2 to 4 carbon atoms, and the CO adsorption amount is 0.50 cc to 40 cc per 1.0 g of the palladium.

A catalyst having this characteristic configuration can react hydrogen with alcohols having 2 to 4 carbon atoms at a sufficient rate while suppressing the steam reforming reaction that produces hydrogen, carbon monoxide, and carbon dioxide, effectively producing a second fuel gas having a lower hydrogen concentration on a volumetric basis after dehydration than the first fuel gas. In addition, this catalyst has high resistance to high temperatures and can be used stably for long periods of time even under high temperature conditions. Furthermore, since the amount of CO adsorption is within the above range, the palladium has an appropriate particle size and degree of dispersion on the solid acid catalyst, allowing the dehydration and hydrogenation catalytic reaction of alcohol to be carried out efficiently.

The characteristic feature of the alcohol dehydration hydrogenation catalyst according to the present invention is that the solid acid catalyst is a SiW/silica catalyst or tungsten oxide zirconia.

A catalyst having this characteristic configuration can react hydrogen with alcohol at a sufficient speed, making it possible to produce a catalyst that can effectively produce fuel gas with a reduced hydrogen concentration.

The characteristic configuration of the method for producing an alcohol dehydration hydrogenation catalyst according to the present invention is that it is a method for producing an alcohol dehydration hydrogenation catalyst that contains palladium and a solid acid catalyst, and that converts a first fuel gas containing 2.0% to 20% hydrogen by volume after dehydration, obtained by subjecting hydrogen and carbon oxides to a methanation reaction in the presence of a methanation catalyst, into a second fuel gas containing alkanes having 2 to 4 carbon atoms and having a reduced hydrogen concentration, by treating the first fuel gas in the presence of an alcohol having 2 to 4 carbon atoms. The method includes a step of calcining a catalyst precursor containing palladium at 400°C or higher.

According to this characteristic configuration, the reaction between hydrogen and alcohols having 2 to 4 carbon atoms is carried out at a sufficient rate while the steam reforming reaction that produces hydrogen, carbon monoxide, and carbon dioxide is suppressed, so that a second fuel gas having a lower hydrogen concentration on a volumetric basis after dehydration than the first fuel gas can be effectively obtained, and a catalyst that has high high-temperature resistance and can be used stably for a long period of time even under high-temperature conditions can be produced. Furthermore, according to this characteristic configuration, a good alcohol dehydration and hydrogenation catalyst can be produced in which the CO adsorption amount is within the above range, i.e., palladium has an appropriate particle size and dispersion on the solid acid catalyst.

The characteristic feature of the method for producing an alcohol dehydration hydrogenation catalyst according to the present invention is that the catalyst precursor is a solid acid catalyst impregnated with palladium.

According to this characteristic configuration, the amount of palladium supported can be adjusted by adjusting the concentration of the aqueous solution containing palladium that is impregnated into the solid acid catalyst, so that an excellent alcohol dehydration and hydrogenation catalyst can be produced in which palladium has an appropriate particle size and degree of dispersion on the solid acid catalyst.

The characteristic feature of the method for producing an alcohol dehydration hydrogenation catalyst according to the present invention is that the solid acid catalyst is a SiW/silica catalyst or tungsten oxide zirconia.

This characteristic configuration allows the reaction between hydrogen and alcohol to occur at a sufficient rate, making it possible to produce a catalyst that can effectively produce fuel gas with a reduced hydrogen concentration.

FIG. 1 is a block flow diagram showing a method for producing fuel gas using the alcohol dehydration/hydrogenation catalyst of the present invention. FIG. 1 shows the effect of temperature and pressure on the equilibrium conversion of the methanation reaction of carbon dioxide. FIG. 3 is an expanded view of the region of equilibrium conversion of 80-100% in FIG. 2. 1 is an example of a reactor configuration for a methanation reaction (fixed-bed adiabatic multi-stage reactor). FIG. 2 is a diagram showing the conversion rate of carbon dioxide to methane and the gas temperature in each reaction stage when a methanation reaction is carried out using a fixed-bed adiabatic multi-stage reactor. This is an example of the configuration of a reactor for a methanation reaction (a fixed-bed adiabatic multi-stage reactor having a recycle line that returns the first-stage outlet gas to the first-stage inlet). This is an example of the structure of a reactor for a methanation reaction (a heat exchange reactor). This is an example of the configuration of a reactor for a methanation reaction (the first stage is a fixed-bed adiabatic reactor with a recycle line, and the second stage is a heat exchange type reactor). FIG. 13 is a diagram showing the effect of the inlet hydrogen/carbon dioxide ratio on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of the carbon dioxide methanation reaction (reaction pressure 0.70 MPa). FIG. 13 is a diagram showing the effect of the inlet hydrogen/carbon dioxide ratio on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of the carbon dioxide methanation reaction (reaction pressure 5.0 MPa). FIG. 1 is a diagram showing the effect of the inlet hydrogen/carbon dioxide ratio on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of fuel gas obtained by a fuel gas production method using an alcohol dehydration hydrogenation catalyst of the present invention (ethanol/hydrogen molar ratio: 0.90). FIG. 1 is a diagram showing the effect of the inlet hydrogen/carbon dioxide ratio on the hydrogen and carbon dioxide concentrations in the equilibrium composition (after dehydration) of fuel gas obtained by a fuel gas production method using an alcohol dehydration hydrogenation catalyst of the present invention (ethanol/hydrogen molar ratio: 0.50).

[Embodiment]
Hereinafter, embodiments of the alcohol dehydration/hydrogenation catalyst for producing a fuel gas according to the present invention and the method for producing the alcohol dehydration/hydrogenation catalyst according to the present invention will be described.

Figure 1 is a block flow diagram showing a method for producing fuel gas using the alcohol dehydration/hydrogenation catalyst of the present invention. The method for producing fuel gas using the alcohol dehydration/hydrogenation catalyst of this embodiment has a methanation reaction step (methanation reactor 10) and a dehydration/hydrogenation reaction step (dehydration/hydrogenation reactor 20).

In the methanation reaction process, the 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 a methanation reaction. This methanation reaction produces a fuel gas 2 (an example of a first fuel gas, the same applies below) that is mainly composed of methane and contains 2.0% to 20% hydrogen by volume after dehydration.

In the dehydration hydrogenation reaction process, first, alcohol 3 having 2 to 4 carbon atoms is added to the fuel gas 2 obtained in the methanation reaction process via a flow rate control valve 30. Then, the fuel gas 2 to which alcohol 3 having 2 to 4 carbon atoms is added is fed to the dehydration hydrogenation reactor 20, and the fuel gas 2 to which alcohol 3 having 2 to 4 carbon atoms is added is brought into contact with a dehydration hydrogenation catalyst filled in the dehydration hydrogenation reactor 20, and an alkane having 2 to 4 carbon atoms is produced by a reaction between the alcohol having 2 to 4 carbon atoms and hydrogen. This reaction consumes the hydrogen contained in the fuel gas 2, and a fuel gas 4 (second fuel gas) having a reduced hydrogen concentration is obtained. The obtained fuel gas 4 contains methane as a main component and an alkane having 2 to 4 carbon atoms. The alcohol 3 is one or more alcohols selected from alcohols having 2 to 4 carbon atoms, and the carbon number of the alkane contained in the second fuel gas 4 is the same as that of the alcohol 3 used.

[Methanation reaction process conditions]
The hydrogen and carbon oxides used in the mixed gas 1 in the methanation reaction step may be produced by any method as long as they have a purity and properties that do not interfere with the methanation reaction in the presence of a methanation catalyst. The hydrogen may be electrolytic hydrogen obtained by electrolyzing water, for example. The carbon oxides are carbon monoxide or carbon dioxide, or a mixture thereof. The carbon dioxide may be carbon dioxide recovered from a combustion exhaust gas by a known carbon dioxide recovery method such as an amine absorption method, or may be carbon dioxide contained in a biogas obtained by methane fermentation of organic matter. Biogas is usually obtained as a mixed gas of methane and carbon dioxide, and carbon dioxide may be separated from this mixed gas and used in the methanation reaction, or methane may be supplied to the methanation reaction without being separated.

If the hydrogen and carbon oxides contain sulfur, halogen compounds, siloxane compounds, heavy hydrocarbons, etc., these may cause deterioration of the methanation reaction catalyst, so it is preferable to remove these, if necessary, before subjecting the mixture to the methanation reaction.

The methanation catalyst used in the methanation reaction process can be a known methanation catalyst containing Ni, Ru, or the like.

The type of the methanation reactor 10 used in the methanation reaction step is not particularly limited as long as the hydrogen concentration of the fuel gas 2 after the methanation reaction is 2.0% or more and 20% or less on a volumetric basis after dehydration.
However, the methanation reaction is an equilibrium reaction that generates a relatively large amount of heat, and the equilibrium conversion rate varies greatly with temperature and pressure, becoming higher at lower temperatures and higher pressures, as shown in Figures 2 and 3. On the other hand, there are problems in that it is difficult to ensure the activity of the methanation catalyst at low temperatures, and that the equipment costs are high at high pressures.

In addition, since the methanation reaction generates a relatively large amount of heat, the gas temperature rises as the reaction progresses, and the equilibrium conversion rate decreases accordingly, which cannot be ignored. For these reasons, when using a fixed-bed adiabatic reactor, which is the most commonly used in chemical processes, as the methanation reactor 10, it is usually difficult to obtain the desired conversion rate in one stage, so it is better to connect the reactors in multiple stages and cool the outlet gas, whose temperature has risen due to the heat of reaction, before introducing it into the next stage reactor.

Figure 4 shows an example of the configuration of the methanation reactor 10 when it is set as a fixed-bed adiabatic multi-stage reactor. In this reactor configuration, five sets of reactors (11a-15a) in which the methanation reaction proceeds and heat exchangers (11b-15b) are provided. In the configuration of the methanation reactor 10 shown in Figure 4, when the 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 0.70 MPa, the temperatures 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 the volume after dehydration with moisture removed; the same applies below) is 18.3%, which can be reduced to 20% or less. At the outlet of the fifth stage (15a), the conversion rate of carbon dioxide to methane is 97.7%, and the hydrogen concentration in the gas drops to 8.3%, making it possible to reduce it to 10% or less. Therefore, when methanation is performed by a simple adiabatic multi-stage reaction, under the above temperature and pressure conditions, a four-stage reaction is required to reduce hydrogen to 20% or less by volume, and a five-stage reaction is required to reduce it to 10% or less. In addition, the large heat generated by methanation causes the outlet temperature of the first stage to reach approximately 700°C, which is problematic in terms of catalyst durability.

Figure 6 shows an example of the configuration when the methanation reactor 10 is provided as a fixed-bed adiabatic multi-stage reactor with a recycle line. In this reactor configuration, three sets of reactors (11a-13a) in which the methanation reaction proceeds and heat exchangers (11b-13b) are provided, and the first set of these is provided with a recycle line 11c that returns the product after heat exchange to the reactor 11a. When this reactor configuration is used, the durability of the catalyst is improved because the dilution effect suppresses temperature rise. In addition, the lower reactor outlet temperature has the effect of increasing the equilibrium conversion rate, so that it may be possible to reduce the number of reactor stages compared to a simple multi-stage reactor configuration.

Figure 7 shows an example of the configuration when the methanation reactor 10 is provided as a heat exchange type reactor. In this reactor configuration, the reaction can be carried out while maintaining the catalyst layer temperature at a specified temperature, which makes it possible to obtain a high conversion rate in a single-stage reactor. However, heat exchange type reactors have a complex structure and may require 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 lost, localized high-temperature areas may occur, causing the catalyst to deteriorate in a short period of time.

Figure 8 shows an example of a methanation reactor 10 configured by combining a fixed-bed adiabatic reactor with a recycle line and a heat exchange reactor. In this reactor configuration, the set of reactors (12a, 13a) and heat exchangers (12b, 13b) from the second stage onwards in the example of Figure 6 is replaced with a single heat exchange reactor. With this reactor configuration, it is possible to reduce the number of reactor stages and suppress equipment costs while ensuring the durability of the catalyst.

[Example of methanation reaction process]
In the following description, it is assumed that the methanation reactor 10 has the reactor configuration shown in FIG. 8, a sufficient amount of methanation catalyst is used, and an equilibrium composition for the methanation reaction and the CO shift reaction is obtained under specified conditions.

When the molar ratio of hydrogen to carbon dioxide at the inlet (hydrogen/carbon dioxide molar ratio) is in the range of 3.8 to 4.2 and the second-stage reaction temperature is 250°C, the concentrations of hydrogen and carbon dioxide contained in the gas after the methanation reaction are as shown in Figure 9 when the reaction pressure is 0.70 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%. Reducing the hydrogen/carbon dioxide molar ratio reduces the hydrogen concentration, but even if 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, when the reaction pressure is 0.70 MPa, it is not possible to obtain fuel gas with sufficiently reduced hydrogen and carbon dioxide concentrations.

When the reaction pressure is 5.0 MPa, the hydrogen and carbon dioxide contained in the gas after the methanation 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 can be obtained that generally meets the quality standard of a hydrogen concentration of 2% or less and a carbon dioxide concentration of 0.50% or less (this standard is the strictest among the generally known standards). However, under these conditions, even a slight decrease in the hydrogen/carbon dioxide molar ratio increases the carbon dioxide concentration, and conversely, a slight increase in the hydrogen/carbon dioxide molar ratio increases the hydrogen concentration. In this way, even a slight change in the hydrogen/carbon dioxide molar ratio greatly affects the purity of the resulting fuel gas.

In other words, when obtaining fuel gas whose main component is methane only through the methanation reaction between hydrogen and carbon dioxide, in order to obtain fuel gas that meets the quality standards of a hydrogen concentration of 2.0% or less and a carbon dioxide concentration of 0.50% or less, a high-pressure reaction facility with an operating pressure sufficiently higher than 5 MPa is required.

[Alcohol dehydration hydrogenation catalyst]
The catalyst of the present invention is an alcohol dehydration/hydrogenation catalyst containing palladium and a solid acid catalyst for treating a first fuel gas, which is obtained by subjecting hydrogen and carbon oxides to a methanation reaction in the presence of a methanation catalyst and contains 2.0% or more and 20% or less of hydrogen on a volume basis after dehydration, in the presence of an alcohol having from 2 to 4 carbon atoms to convert the first fuel gas into a second fuel gas which contains alkanes having from 2 to 4 carbon atoms and has a reduced hydrogen concentration, and the catalyst has a CO adsorption amount of from 0.50 cc to 40 cc per 1.0 g of the palladium.
In the present invention, the palladium supported on the carrier is usually considered to be supported in the form of a salt such as a nitrate or chloride before calcination, in the form of palladium oxide after calcination, and in the metallic state after reduction treatment. In the present invention, these various forms of palladium are collectively referred to as palladium.

With the above configuration, the amount of CO adsorption falls within the above range, and the palladium has an appropriate particle size and degree of dispersion on the solid acid catalyst, allowing the dehydration and hydrogenation of alcohol to be carried out efficiently.

Because catalytic reactions often proceed on the surface of a metal, metal-supported catalysts usually support the metal in a highly dispersed manner so that the metal surface area is as large as possible. In particular, for catalysts that use precious metals such as palladium as the active component, it is important to increase the surface area of the precious metal from an economical standpoint, in order to reduce the amount of precious metal used. However, the inventors have discovered that in an alcohol dehydration/hydrogenation catalyst that contains palladium and a solid acid catalyst, the amount of CO adsorption is intentionally reduced, i.e., the surface area of palladium is reduced, allowing the alcohol dehydration/hydrogenation reaction to proceed with high selectivity.

The inventors speculate that the reason why the selectivity of the alcohol dehydration hydrogenation reaction can be improved by reducing the amount of CO adsorption is as follows. As described above, the alcohol dehydration hydrogenation reaction using a catalyst containing palladium and a solid acid catalyst proceeds as follows.

C _n H _{2n + 1} OH → C _n H _2n + H ₂ O (Formula 3)
C _n H _2n + H ₂ → C _n H _2n+2 (Formula 4)

At the same time, the steam reforming reaction of alcohol proceeds as follows.
C _n H _2n+1 OH + (n-1)H ₂ O → nCO + 2nH ₂ (Formula 5)
C _n H _2n+1 OH + (2n-1)H ₂ O → nCO ₂ + 3nH ₂ (Formula 6)
Here, the palladium contained in the catalyst is active in both the hydrogenation reaction of alkenes shown in formula 4 and the steam reforming reaction of alcohols shown in formulas 5 and 6. When the amount of CO adsorption on the catalyst is reduced, that is, the surface area of palladium is reduced, the reaction rates of formulas 4, 5 and 6 are reduced. This makes it difficult for the steam reforming reaction of alcohols to occur, but since it is known that the hydrogenation reaction of alkenes proceeds at a high speed, formula 4 still proceeds at a sufficient speed even if the surface area of palladium is reduced. As a result, it is believed that the selectivity of the dehydration hydrogenation reaction of alcohols is improved.

The CO adsorption amount is an index of the metal surface area contained in the catalyst, and is measured by the CO pulse method (Non-Patent Document 7). In this method, a catalyst analyzer (R6015, manufactured by Hemmi Slide Rule Co., Ltd.) was used to measure by the CO pulse method. The catalyst powder was filled into a glass cell, and as a pretreatment, it was kept at 400 ° C in a _H2 atmosphere for 45 minutes, and the gas was switched to He and kept for another 30 minutes. After the glass tube temperature was lowered to 50 ° C, the measurement was performed using a gas of CO: 10% and He: 90%. He was used as the carrier gas.
In this embodiment, the CO adsorption amount of the catalyst is preferably 0.50 cc or more and 40 cc or less per 1.0 g of palladium, more preferably 1.0 cc or more and 30 cc or less, and even more preferably 2.0 cc or more and 15 cc or less. By setting the CO adsorption amount to 40 cc or less per 1.0 g of palladium, as described above, the steam reforming of alcohol can be suppressed, and the dehydration hydrogenation reaction of alcohol can proceed with high selectivity. If the CO adsorption amount is less than 0.50 cc, there is a risk that the olefin generated by the dehydration reaction of alcohol (formula 3) will not be sufficiently hydrogenated. In addition, if the CO adsorption amount is more than 40 cc, the steam reforming reaction of alcohol cannot be sufficiently suppressed, and the selectivity of the dehydration hydrogenation reaction of alcohol may decrease.

There are no particular limitations on the solid acid catalyst and carrier used, but in order to cause the dehydration and hydrogenation of alcohol at temperatures between 250°C and 350°C, those with high acid strength are suitable. From this perspective, high-silica zeolites, heteropolyacids, and composite oxides are preferred, with silicotungstic acid and tungsten oxide zirconia being even more preferred.

The palladium is in the form of fine particles so that it has sufficient activity for hydrogenating alkenes, but it may also have other shapes, such as coarse particles.

The amount of palladium supported (support concentration) in the solid acid catalyst is 0.050% by mass or more and 5.0% by mass or less, preferably 0.10% by mass or more and 2.0% by mass or less, more preferably 0.10% by mass or more and 1.0% by mass or less, and even more preferably 0.10% by mass or more and 0.50% by mass or less, based on the mass of the dehydration hydrogenation catalyst. If the amount of palladium supported is less than 0.050% by mass, the catalytic activity will be low, whereas if the amount of palladium supported is more than 5.0% by mass, the amount of palladium used will increase, resulting in poor economic efficiency.

[Method for producing an alcohol dehydration/hydrogenation catalyst]
The method for producing a catalyst for dehydration and hydrogenation of alcohols of the present invention includes an impregnation step of impregnating the solid acid catalyst with a solution containing palladium to obtain a catalyst precursor containing palladium (a solid acid catalyst impregnated with palladium), and a calcination step of calcining the catalyst precursor at a predetermined temperature.

[Preparation of solid acid catalyst as support]
First, a solid acid catalyst for supporting the catalyst is prepared. The solid acid catalyst is not particularly limited, and examples thereof include silica, alumina, titania, zirconia, zeolites such as high silica zeolite, heteropolyacids such as tungstosilicic acid, and composite oxides such as tungsten zirconia oxide, but solid acid catalysts such as tungstosilicic acid and tungsten zirconia oxide are preferred.

[Impregnation process]
In the impregnation step, a catalyst precursor containing palladium is obtained by impregnating a solid acid catalyst as a carrier with an aqueous solution containing palladium. The catalyst precursor is dried to fix palladium to the carrier. There is no particular restriction on the method of supporting palladium in the impregnation step, as long as the palladium becomes fine particles having sufficient activity for hydrogenating alkenes in the subsequent calcination step. There is no particular restriction on the concentration of the aqueous solution containing palladium, but in order to support an appropriate amount of palladium on the catalyst, it is preferably 0.10% by mass or more and 20% by mass or less, and more preferably 0.10% by mass or more and 10% by mass or less. When preparing the aqueous solution containing palladium, nitrate salts of palladium, chloride salts of palladium, etc. can be used. The amount of the aqueous solution containing palladium is appropriately determined depending on the water absorption amount of the carrier such as an inorganic oxide.

[Firing process]
In the subsequent calcination step, the catalyst precursor containing palladium is calcined at a predetermined temperature to obtain an alcohol dehydration hydrogenation catalyst containing palladium and a solid acid catalyst. Palladium can also be supported by calcination at 350° C. or less, but in order to achieve appropriate ethane selectivity, that is, to set the CO adsorption amount per 1.0 g of palladium to 0.50 cc or more and 40 cc or less, the predetermined temperature is preferably 400° C. or more and 900° C. or less, more preferably 400° C. or more and 850° C. or less, and even more preferably 600° C. or more and 800° C. or less. By setting the temperature within this range, palladium particles are supported on the inorganic oxide with appropriate particle size and dispersibility, so that an alcohol dehydration hydrogenation catalyst capable of efficiently performing the alcohol dehydration hydrogenation catalytic reaction can be produced. If the calcination temperature is less than 400° C., there is a risk that the impregnated palladium will not be in the form of particles of sufficient size. Furthermore, when the calcination temperature is higher than 900° C., there is a possibility that the structure of the inorganic oxide will be destroyed, that the sintering of the inorganic oxide will proceed, resulting in a significant decrease in the surface area, that the aggregation of palladium will proceed too much, etc. If these phenomena occur, the activity of the catalyst will be significantly reduced, and there is a risk that the dehydration hydrogenation reaction of alcohol will not proceed sufficiently.

[Conditions for the dehydration/hydrogenation reaction step]
As the alcohol 3 having 2 to 4 carbon atoms used in the dehydration hydrogenation reaction step, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and 2-methyl-2-propanol can be used. These may be used alone or in combination.

The alcohol 3 having 2 to 4 carbon atoms may be produced by any method as long as it has a purity and properties that do not interfere with the dehydration hydrogenation reaction. For example, ethanol produced by fermentation using sugar cane or corn as a raw material can be suitably used. In the fuel gas production method according to this embodiment, the alcohol 3 having 2 to 4 carbon atoms may contain a normal amount of water. However, if the water content is too high, evaporation heat is required to vaporize the water, which may reduce the efficiency of fuel gas production. In consideration of this, the water content of the alcohol 3 having 2 to 4 carbon atoms is preferably 50 mass% or less.

The reaction in the dehydration reactor 20 proceeds as follows:

C _n H _{2n + 1} OH → C _n H _2n + H ₂ O (Formula 3)
C _n H _2n + H ₂ → C _n H _2n+2 (Formula 4)
When the amount of the alcohol 3 having 2 to 4 carbon atoms added is small, the reduction in the hydrogen concentration in the fuel gas 4 is insufficient. The extremely low concentration of the alcohol 3 with 2 to 4 carbon atoms causes the hydrogenation reaction (formula 4) of the alkene (ethylene when ethanol is used as the alcohol) produced by the dehydration of the alcohol 3. In addition, since the alkene concentration during the reaction is high, the alkene may polymerize on the catalyst, causing deterioration of the catalyst due to carbon deposition. Therefore, the amount of the alcohol 3 having 2 to 4 carbon atoms to be added is such that the molar ratio of the alcohol 3 having 2 to 4 carbon atoms to the hydrogen contained in the fuel gas 2 obtained in the methanation reaction step (alcohol/hydrogen) is , preferably 0.45 or more and 0.90 or less.

The reaction temperature when converting alcohol to alkanes by reaction with hydrogen using a dehydration hydrogenation catalyst is preferably 200°C or higher and 400°C or lower. Since dehydration hydrogenation catalysts generally exhibit good activity at 200°C or higher, the reaction between alcohol 3 having 2 to 4 carbon atoms and hydrogen (Equation 3 and Equation 4) is likely to proceed when the reaction temperature is 200°C or higher. In addition, the steam reforming reaction of methane, ethane, propane, and butane is easily suppressed when the reaction temperature is 400°C or lower. When the steam reforming reaction of methane, ethane, propane, and butane proceeds, even if hydrogen is reduced by the hydrogenation reaction of alkenes, new hydrogen is generated by the steam reforming reaction of methane, ethane, propane, or butane, so that the hydrogen concentration in the fuel gas may not be reduced. The reaction temperature is more preferably 250°C or higher and 350°C or lower.

It is preferable that the dehydration/hydrogenation catalyst used in the dehydration/hydrogenation reaction step is active in the dehydration reaction of alcohols (Formula 3) and the hydrogenation reaction of alkenes (Formula 4), and is substantially inactive in the steam reforming reaction of methane, ethane, propane, butane, and alcohol. It is also preferable that the dehydration/hydrogenation catalyst can be used stably even at high temperatures. If the catalyst has low high-temperature resistance, the dehydration/hydrogenation reaction cannot proceed stably for a long period of time, and the catalyst needs to be replaced more frequently, resulting in high operating costs for the entire process.

The type of dehydration/hydrogenation reactor 20 used in the dehydration/hydrogenation reaction process is not particularly limited, and may be, for example, a fixed-bed adiabatic reactor, a fixed-bed adiabatic reactor with a recycle line, a heat exchange reactor, etc.

[Example of dehydration hydrogenation reaction process]
8 is used as the methanation reactor 10, and 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, it is assumed that the methanation reaction and the CO shift reaction reach equilibrium in the methanation reactor 10, ethanol is used as the alcohol 3 having a carbon number of 2 to 4, and the dehydration reaction of ethanol and the hydrogenation reaction of ethylene reach equilibrium in the dehydration/hydrogenation reactor 20.

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 set to 250°C so that the reaction proceeded under adiabatic conditions. The reaction pressure was set to 0.70 MPa in both the methanation reactor 10 and the dehydration hydrogenation reactor 20. The hydrogen and carbon dioxide concentrations of the fuel gas 4 obtained in this case are shown in Figures 11 and 12 relative to the hydrogen/carbon dioxide molar ratio of the mixed gas 1 supplied to the methanation reactor 10.

Figure 11 shows the relationship between the composition of mixed gas 1 and the concentrations of hydrogen and carbon dioxide in fuel gas 4 when the molar ratio of ethanol to hydrogen contained in fuel gas 2 is 0.9. When the hydrogen/carbon dioxide molar ratio of mixed gas 1 is 4.0, the hydrogen concentration is 0.44% and the carbon dioxide concentration is 1.09%. When only the methanation reaction process 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 fuel gas 2 obtained by the methanation process is significantly reduced by the dehydration reaction process. Also, when the hydrogen/carbon dioxide molar ratio 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%, and the concentration of hydrocarbons (methane + ethane) exceeds 99%. When only the methanation reaction process was performed, the hydrogen concentration was 5.5% and the carbon dioxide concentration was 0.43%, so even in this case, it can be seen that the hydrogen concentration was significantly reduced by the dehydration reaction process.

Although both the methanation reaction process and the dehydration/hydrogenation reaction process are carried out at the same inlet temperature (250°C), hydrogen remains in the methanation reaction process and decreases in the dehydration/hydrogenation reaction process for the following reason. The methanation reaction of carbon dioxide is an exothermic reaction that generates 41 kJ per mole of hydrogen. On the other hand, the hydrogenation reaction of ethylene is a reaction that generates a slightly large amount of heat (136 kJ of heat per mole of ethylene), and even when combined with the dehydration reaction of ethanol (endothermic heat of 45 kJ per mole of ethanol), it is an exothermic reaction of about 90 kJ per mole of hydrogen. Therefore, the equilibrium between the production of ethylene by dehydration of ethanol and the production of ethane by the subsequent hydrogenation of ethylene is significantly biased toward the production of ethane. For this reason, the dehydration/hydrogenation reaction proceeds sufficiently even under temperature conditions where hydrogen remains in the methanation reaction process.

When 1-propanol is used instead of ethanol as the alcohol 3 having 2 to 4 carbon atoms, the endothermic heat generated by the dehydration reaction is 33.0 kJ per mole of 1-propanol, and the hydrogenation reaction of propylene generates heat of 125.0 kJ per mole of propylene, resulting in an exothermic reaction of approximately 90.0 kJ per mole of hydrogen for the entire dehydration/hydrogenation reaction. When other alcohols having 2 to 4 carbon atoms are used, the entire dehydration/hydrogenation reaction generates heat of approximately 60.0 to 90.0 kJ per mole of hydrogen, and the dehydration/hydrogenation reaction similarly proceeds satisfactorily.

In the dehydration hydrogenation reaction process, carbon dioxide cannot be reduced. If the hydrogen/carbon dioxide molar ratio used in the methanation reaction is slightly higher than 4.0 and the methanation reaction process is performed under conditions of a slight excess of hydrogen, the carbon dioxide concentration in the fuel gas 2 after the methanation reaction process can be reduced. Here, the hydrogen concentration in the fuel gas 2 increases due to the excess addition of hydrogen, but this hydrogen can be reduced in the dehydration hydrogenation reaction process. If the hydrogen/carbon dioxide molar ratio of the mixed gas 1 used in the methanation reaction process is 4.04, the hydrogen concentration in the resulting fuel gas will be 0.55% and the carbon dioxide concentration will be 0.43%. In other words, the quality standards of a hydrogen concentration of 2.0% or less and a carbon dioxide concentration of 0.50% or less, which cannot be achieved even under high-pressure reaction conditions of 5 MPa by the methanation process alone, can be achieved by a reaction at a low pressure of 0.70 MPa using the method according to this embodiment.

If the hydrogen/carbon dioxide molar ratio of the mixed gas 1 to be subjected to the methanation reaction step is further increased, the carbon dioxide concentration in the resulting fuel gas can be further reduced. For example, if the hydrogen/carbon dioxide molar ratio of the mixed gas 1 to be subjected to the methanation reaction step is 4.2, the hydrogen concentration in the resulting fuel gas will be 1.7% and the carbon dioxide concentration will be 0.10% or less. In addition, the methane concentration will be 83.3%, the ethane concentration will be 15.0%, and the calorific value per ^1.0 m3 of fuel gas will be 44.0 MJ, which is a gas with almost the same properties as general natural gas-based city gas.

On the other hand, in addition to the need to add more alcohol 3 having a carbon number of 2 to 4, when the dehydration hydrogenation reaction is performed under adiabatic conditions, the outlet temperature of the dehydration hydrogenation reaction increases, and the alkene concentration increases, which may lead to deterioration of the catalyst due to carbon deposition, and an increase in the concentrations of hydrogen, carbon monoxide, and carbon dioxide due to the simultaneous occurrence of a steam reforming reaction. From this perspective, it is preferable that the hydrogen/carbon dioxide molar ratio of the mixed gas 1 to be subjected to the methanation reaction process does not exceed 4.08. If the hydrogen/carbon dioxide molar ratio is in the range of 4.04 to 4.08, it is easy to achieve the quality standards of a hydrogen concentration of 2% or less and a carbon dioxide concentration of 0.50% or less.

Figure 12 shows the relationship between the composition of the mixed gas 1 and the concentrations of hydrogen and carbon dioxide in the fuel gas 4 when the amount of ethanol added is 0.50 in molar ratio to the hydrogen contained in the fuel gas 2. In the example of Figure 12, the amount of ethanol added is less than that of the example of Figure 11, so the hydrogen concentration in the resulting fuel gas 4 is higher than that of Figure 11, but it can be understood that the hydrogen concentration in the fuel gas 4 is reduced compared to Figure 9. If the hydrogen/carbon dioxide molar ratio of the mixed gas 1 is in the range of 4.04 to 4.08, all of the quality standards of hydrogen concentration 4.0% or less, carbon dioxide concentration 0.50% or less, and components other than hydrocarbons 4.0% or less can be achieved. This condition cannot be achieved in a methanation reaction at 0.70 MPa, no matter how the hydrogen/carbon dioxide molar ratio of the mixed gas to be subjected to the methanation reaction is set, so 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 in the above, when at least one of carbon monoxide and carbon dioxide is contained as carbon oxides, if the ratio of hydrogen to carbon oxides supplied to the methanation reaction process is a ratio that satisfies the value of {(hydrogen) + (carbon monoxide)} / {(carbon monoxide) + (carbon dioxide)} calculated on a substance mass basis of 4.04 or more and 4.08 or less, the above quality standard is easily achieved.

Other embodiments
Finally, other embodiments of the method for producing fuel gas will be described. Note that the configurations disclosed in the following embodiments can be combined with the configurations disclosed in other embodiments as long as no contradiction occurs.

In this embodiment, the methanation reactor 10 used in the methanation reaction process is a combination of a fixed-bed adiabatic reactor having a recycle line and a heat exchange reactor, as shown in FIG. 8. However, the reactor used in the methanation reaction process according to the present invention is not particularly limited as long as it can produce a fuel gas containing 2.0% by volume or more and 20% by volume or less of hydrogen. Examples of such reactors include a fixed-bed adiabatic multi-stage reactor and a single-stage or multi-stage heat exchange reactor.

In this embodiment, an example in which the pressure in the methanation reaction process is 0.70 MPa has been particularly described. However, the pressure in the methanation reaction process according to the present invention is not particularly limited as long as a fuel gas containing 2.0 volume % or more and 20 volume % or less of hydrogen is obtained. However, if the pressure is 0.50 MPa or more, the hydrogen and carbon dioxide contents in the fuel gas obtained in the methanation reaction process are reduced, and therefore the hydrogen and carbon dioxide contents in the final product fuel gas are also likely to be reduced. In addition, since it is easy to reduce the cost of the equipment used in the methanation reaction process, the pressure is preferably 3.0 MPa or less, and more preferably 1.0 MPa or less.

In this embodiment, the dehydration/hydrogenation reactor 20 used in the dehydration/hydrogenation reaction process is configured as a fixed-bed adiabatic reactor. However, the reactor used in the dehydration/hydrogenation reaction process 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 a fixed-bed adiabatic reactor having a recycle line and a heat exchange reactor.

In this embodiment, an example in which the pressure in the dehydration hydrogenation reaction process is 0.70 MPa has been described in particular. However, the pressure in the dehydration hydrogenation reaction process 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 0.50 MPa or more, it is easy to reduce the hydrogen and carbon dioxide contents in the resulting fuel gas without using a large amount of dehydration hydrogenation catalyst. In addition, since it is easy to reduce the cost of the equipment used in the dehydration hydrogenation reaction process, the pressure is preferably 3.0 MPa or less, and more preferably 1.0 MPa or less.

In this embodiment, an example in which the pressure in the methanation reaction process and the dehydration/hydrogenation reaction process are the same (0.70 MPa) has been described in particular. However, in the methanation reaction process and the dehydration/hydrogenation reaction process according to the present invention, the pressure may be the same or different.

The present invention does not exclude the use of conventionally known means for improving methane conversion. For example, the reaction gas may be cooled in the middle 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 hydrogen and carbon dioxide concentrations in the fuel gas without excessively removing water vapor.

In this embodiment, a solid acid catalyst impregnated with palladium through an impregnation process as a catalyst precursor containing palladium is calcined at 400°C or higher in a calcination process to produce an alcohol dehydration/hydrogenation catalyst containing palladium and a solid acid catalyst, but the present invention is not limited to this embodiment. In order to reduce the amount of CO adsorption of the alcohol dehydration/hydrogenation catalyst (0.50 cc or more and 40 cc or less per 1.0 g of palladium), the following can also be done.

Another embodiment of the method for producing an alcohol dehydration/hydrogenation catalyst comprising palladium and a solid acid catalyst of the present invention is a method for producing an alcohol dehydration/hydrogenation catalyst for treating a first fuel gas containing 2.0% to 20% hydrogen on a volume basis after dehydration, which is obtained by subjecting hydrogen and carbon oxides to a methanation reaction in the presence of a methanation catalyst, in the presence of an alcohol having a carbon number of 2 to 4, to convert it into a second fuel gas which contains alkanes having a carbon number of 2 to 4 and has a reduced hydrogen concentration, and includes a mixing step of mixing an inorganic oxide on which palladium is supported and a solid acid catalyst on which no palladium is supported.
The inorganic oxide carrying palladium may be prepared by, for example, impregnating a carrier such as silica, alumina, titania, zirconia, tungsten zirconia, or zeolite with an aqueous solution containing palladium to obtain a catalyst precursor containing palladium (inorganic oxide impregnated with palladium), and then subjecting the catalyst precursor containing palladium to a calcination step of calcining the catalyst precursor at 400° C. or higher.

More specifically, in the case of producing an alcohol dehydration hydrogenation catalyst containing 0.50% by mass of palladium and a solid acid catalyst, an inorganic oxide carrier such as silica, alumina, titania, zirconia, tungsten oxide zirconia, or zeolite is impregnated with an aqueous solution containing palladium to obtain a catalyst precursor containing 5.0% by mass of palladium, and the catalyst precursor is then calcined at 400° C. or higher to obtain an inorganic oxide carrying 5.0% by mass of palladium. There is no particular limit to the concentration of the aqueous solution containing palladium, but in order to carry an appropriate amount of palladium on the catalyst, it is preferably 0.10% by mass or more and 20% by mass or less, and more preferably 0.10% by mass or more and 10% by mass or less. When preparing the aqueous solution containing palladium, nitrate salts of palladium, chloride salts of palladium, or the like can be used.

By subjecting this solid acid catalyst supporting 5.0 mass% palladium to a mixing step of mixing with 9 times the amount, by mass, of a solid acid catalyst, it is possible to produce an alcohol dehydration/hydrogenation catalyst containing 0.50 mass% palladium and the solid acid catalyst.
The inorganic oxide containing palladium produced by calcining a catalyst precursor containing palladium at 400° C. or higher and the solid acid catalyst to be mixed later may be of the same type or different types. In addition, the inorganic oxide does not have to be a solid acid catalyst. In such a case, any inorganic oxide can be selected as a carrier for supporting palladium, and therefore, by selecting an appropriate inorganic oxide, the dispersion degree and supporting concentration of palladium can be widely controlled.

Another embodiment of the method for producing an alcohol dehydration and hydrogenation catalyst containing palladium and a solid acid catalyst is a method for producing an alcohol dehydration and hydrogenation catalyst, which is for converting a first fuel gas containing 2.0% to 20% hydrogen by volume after dehydration, obtained by methanating hydrogen and carbon oxides in the presence of a methanation catalyst, into a second fuel gas containing alkanes having 2 to 4 carbon atoms and having a reduced hydrogen concentration, by treating the first fuel gas in the presence of an alcohol having 2 to 4 carbon atoms, and the first fuel gas is impregnated with an aqueous solution containing palladium on a support, and then calcining the mixture.

By configuring in this way, if the catalyst precursor is impregnated with a relatively high concentration of palladium before mixing, mixing it with a solid acid catalyst precursor that does not support palladium and calcining it will result in a low concentration of palladium in the overall alcohol dehydration hydrogenation catalyst produced, making it possible to produce an economical catalyst.

Another embodiment of the method for producing an alcohol dehydration hydrogenation catalyst containing palladium and a solid acid catalyst is a method for producing an alcohol dehydration hydrogenation catalyst, which is for converting a first fuel gas containing 2.0% to 20% hydrogen on a volumetric basis after dehydration, obtained by subjecting hydrogen and carbon oxides to a methanation reaction in the presence of a methanation catalyst, into a second fuel gas containing alkanes having 2 to 4 carbon atoms and having a reduced hydrogen concentration, in the presence of an alcohol having 2 to 4 carbon atoms, and includes a calcination step of calcining a mixture containing an inorganic oxide carrying palladium and a precursor of the solid acid catalyst. As the inorganic oxide carrying palladium, for example, a commercially available catalyst carrying palladium or a catalyst precursor impregnated with an aqueous solution containing palladium can be used. As the precursor of the solid acid catalyst not carrying palladium, for example, a catalyst that includes a calcination step to function as a catalyst, such as NH ₄ type zeolite, can be used. As a result, the NH ₄ type zeolite becomes a proton type zeolite and exhibits strong solid acidity.

By adopting this configuration, if the inorganic oxide supporting palladium has a relatively high concentration of palladium supported on it before mixing, mixing it with a precursor of a solid acid catalyst that does not support palladium and calcining it will result in a low concentration of palladium in the overall alcohol dehydration hydrogenation catalyst produced, making it possible to produce an economical catalyst.

In another embodiment, in the calcination step, a catalyst precursor containing palladium is calcined at a predetermined temperature to obtain an alcohol dehydration hydrogenation catalyst containing palladium and a solid acid catalyst. Palladium can also be supported by calcination at 350°C or less, but in order to achieve appropriate ethane selectivity, that is, to set the CO adsorption amount per 1.0 g of palladium to 0.50 cc or more and 40 cc or less, the predetermined temperature is preferably 400°C or more and 900°C or less, more preferably 400°C or more and 850°C or less, and even more preferably 600°C or more and 800°C or less. By setting the temperature within this range, palladium particles are supported on the inorganic oxide with appropriate particle size and dispersibility, so that an alcohol dehydration hydrogenation catalyst capable of efficiently performing the alcohol dehydration hydrogenation catalytic reaction can be produced. If the calcination temperature is less than 400°C, there is a risk that the impregnated palladium will not be in the form of particles of sufficient size. Furthermore, if the calcination temperature is higher than 900°C, the structure of the inorganic oxide may be destroyed, the inorganic oxide may be sintered and the surface area may be significantly reduced, or the palladium may be aggregated too much. If these phenomena occur, the activity of the catalyst may be significantly reduced, and the dehydration reaction of alcohol may not proceed sufficiently.

The inorganic oxide carrier may be the same type of solid acid catalyst as the solid acid catalyst not carrying palladium, or may be different from the solid acid catalyst not carrying palladium. The inorganic oxide does not have to be a solid acid catalyst. When producing the catalyst in this way, an inorganic oxide can be freely selected as a carrier for carrying palladium, so that the dispersion degree and carrying concentration of palladium can be widely controlled by selecting an appropriate inorganic oxide.
The carrier to be used may be a commercially available product, or may be prepared by, for example, calcining a precursor of silica, alumina, titania, zirconia, tungsten oxide zirconia, zeolite, or the like.

The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
78 g of zirconium hydroxide (manufactured by Taiyo Koko Co., Ltd.; Z-999-D) and 21 g of an aqueous solution of ammonium metatungstate (manufactured by Nippon Inorganic Chemical Industry Co., Ltd.; MW-2, containing 50% by mass as WO ₃ ) were mixed, and 50 g of pure water was added and wet kneaded. The mixture was evaporated to dryness in a hot water bath, dried overnight in a dryer at 120°C, and then calcined at 800°C for 4 hours to obtain WO ₃ /ZrO _2. 25 g of the obtained WO ₃ /ZrO ₂ was impregnated with an aqueous solution of palladium nitrate containing 0.051 g as Pd. Thereafter, the mixture was evaporated to dryness in a hot water bath, dried overnight in a dryer at 120°C, and then calcined in air at 650°C for 4 hours to obtain catalyst A (0.20% Pd/WO ₃ /ZrO ₂ catalyst) in which 0.2% by mass of palladium was supported on WO ₃ /ZrO ₂ . The CO adsorption amount of catalyst A was 9.7 cc per 1.0 g of palladium.

Catalyst A was tabletted and classified into 1.0-2.5 mm tablets. 6.0 mL of the tablets were filled into a SUS reaction tube (inner diameter 16 mm). The tube was heated in an electric furnace while passing 2.0% hydrogen, the balance nitrogen gas, until the temperature reached 240°C. After that, 10% hydrogen, the balance nitrogen gas was passed through and the temperature was maintained for 1 hour, and then 20% hydrogen, the balance nitrogen gas was passed through and the temperature was maintained for 2 hours, thereby reducing the catalyst. After the reduction process was completed, the temperature of the reaction tube was raised and maintained at 270°C.

Ethanol was added to 400 mL per minute (volume at standard conditions of 0°C and 101.325 kPa) of fuel gas (first fuel gas) consisting of 32.6 vol% methane, 65.3 vol% water vapor, 1.9 vol% hydrogen, and 0.15 vol% carbon dioxide, so that the molar ratio of ethanol to hydrogen in the fuel gas was 0.70. The fuel gas to which ethanol had been added was passed through the catalyst under conditions of a reaction tube temperature of 270°C and a pressure of 0.70 MPa (absolute pressure).

The composition of 32.6 vol% methane, 65.3 vol% water vapor, 1.9 vol% hydrogen, and 0.15 vol% carbon dioxide corresponds to the equilibrium composition when a gas with a (hydrogen)/(carbon dioxide) value of 4.04 calculated on a mass of substance basis is subjected to a methanation reaction at a temperature of 250°C and a pressure of 0.70 MPa (absolute pressure), and simulates the fuel gas (first fuel gas) obtained in the first process (methanation process) that contains approximately 5.5% hydrogen on a volumetric basis after dehydration.

After the reaction, the second fuel gas was cooled to separate the water, and the concentrations of methane, ethane, hydrogen, carbon monoxide, and carbon dioxide were quantified using a gas chromatograph.

The concentrations of each component in the second fuel gas (by volume after dehydration) were: hydrogen 4.63%, carbon dioxide 0.46%, carbon monoxide 1.14%, ethane 2.27%, and the remainder methane.

(Comparative Example 1)
Catalyst B was prepared in the same manner as in Example, except that the calcination temperature was 350° C. The CO adsorption amount of catalyst B was 41.4 cc per 1.0 g of palladium.

A test similar to that in Example 1 was conducted, except that catalyst B was used as the catalyst.

The concentrations of each component in the second fuel gas (by volume after dehydration) were: hydrogen 6.14%, carbon dioxide 0.49%, carbon monoxide 2.00%, ethane 1.41%, and the remainder methane.

(Comparative Example 2)
Catalyst C (0.10% Pd/ _WO3 /ZrO2 catalyst) was prepared in the same manner as in Comparative Example 1, except that an aqueous palladium nitrate solution containing 0.036 g of Pd was impregnated into ₃₅ g of _WO3 / _ZrO2 obtained in Example 1. The CO adsorption amount of catalyst C was 63.1 cc per 1.0 g of palladium.

A test similar to that in Example 1 was carried out, except that catalyst C was used as the catalyst.

The concentrations of each component in the second fuel gas (by volume after dehydration) were: hydrogen 6.26%, carbon dioxide 0.48%, carbon monoxide 2.00%, ethane 1.36%, and the remainder methane.

Example 2
₃₅ g of _WO3 /ZrO2 obtained in the same manner as in Example 1 was impregnated with an aqueous palladium nitrate solution containing 0.35 g of Pd, evaporated to dryness in a water bath, dried overnight in a 120°C dryer, and then calcined in air at 350°C for 4 hours to obtain catalyst D' (1% Pd/ _WO3 / _ZrO2 catalyst) in which 1% by mass of palladium was supported on _WO3 / _ZrO2 . This was mixed with 4 times the amount of _WO3 / _ZrO2 without palladium supported thereon to obtain catalyst D (0.2% Pd/ _WO3 / _ZrO2 catalyst). The CO adsorption amount of catalyst D was 18.8 cc per 1.0 g of palladium.
The same test as in Example 1 was carried out except that Catalyst D was used as the catalyst.
The concentrations of the components contained in the second fuel gas (based on the volume after dehydration) were as follows: hydrogen 2.51%, carbon dioxide 0.45%, carbon monoxide 0.30%, ethane 3.44%, and the balance methane.

Example 3
Catalyst E was prepared in the same manner as in Example 1, except that the calcination temperature was 800° C. The CO adsorption amount of catalyst E was 8.6 cc per 1.0 g of palladium.
The same test as in Example 1 was carried out except that Catalyst E was used as the catalyst and the reaction tube temperature was set to 300°C.
The concentrations of each component contained in the second fuel gas (based on the volume after dehydration) were as follows: hydrogen 1.77%, carbon dioxide 0.46%, carbon monoxide 0.093%, ethane 4.05%, and the balance methane.

(Comparative Example 3)
The same test as in Comparative Example 1 was carried out, except that the reaction tube temperature was set to 300°C.
The concentrations of each component contained in the second fuel gas (based on the volume after dehydration) were as follows: hydrogen 3.83%, carbon dioxide 0.64%, carbon monoxide 0.75%, ethane 2.84%, and the balance methane.
For the examples and comparative examples, the ethane selectivity was calculated according to the following formula, assuming that the carbon-containing products produced using ethanol as a raw material were only carbon dioxide, carbon monoxide, and ethane.
Ethane selectivity (%) = ethane concentration (%) x 2 / [ethane concentration (%) x 2 + carbon monoxide concentration (%) + carbon dioxide concentration (%)] x 100

The conditions and results of the examples and comparative examples are summarized in Table 1.

Comparing Example 1, Example 2, Comparative Example 1, and Comparative Example 2, which were performed under the same reaction conditions, when catalysts A and D, each having a CO adsorption amount of 40 cc or less per 1.0 g of palladium, were used, the ethane concentration in the second fuel gas was high and the carbon dioxide and carbon monoxide concentrations were low, so that the ethane selectivity was high. On the other hand, when catalysts B and C, each having a CO adsorption amount of more than 40 cc per 1.0 g of palladium, were used, the ethane concentration in the second fuel gas was low and instead the carbon dioxide and carbon monoxide concentrations were high, so that the ethane selectivity was low.
Similarly, in a comparison between Example 3 and Comparative Example 3, when catalyst E, in which the CO adsorption amount per 1.0 g of palladium was 40 cc or less, was used, the ethane selectivity was high, whereas when catalyst B, in which the CO adsorption amount per 1.0 g of palladium was more than 40 cc, the ethane selectivity was low.
From these results, it became clear that a catalyst having a CO adsorption amount of 40 cc or less per 1.0 g of palladium promotes the dehydration and hydrogenation reaction of alcohol with high selectivity.

The present invention can be used, for example, as a method for producing fuel gas to be supplied as city gas.

Reference Signs List 1: mixed gas 2: first fuel gas 3: alcohol having 2 to 4 carbon atoms 4: second fuel gas 10: methanation reactor 11a to 15a: reactor 11b to 15b: heat exchanger 11c: recycle line 12d: heat exchange reactor 20: dehydration hydrogenation reactor 30: flow control valve

Claims (5)

A catalyst for dehydration and hydrogenation of alcohol, the catalyst comprising palladium and a solid acid catalyst, for treating a first fuel gas, which is obtained by subjecting hydrogen and carbon oxides to a methanation reaction in the presence of a methanation catalyst and contains 2.0% or more and 20% or less of hydrogen on a volume basis after dehydration, in the presence of an alcohol having 2 to 4 carbon atoms to convert the first fuel gas into a second fuel gas which contains an alkane having 2 to 4 carbon atoms and has a reduced hydrogen concentration, the catalyst comprising:
A catalyst for dehydration and hydrogenation of alcohols, wherein the amount of CO adsorbed is 0.50 cc or more and 40 cc or less per 1.0 g of the palladium. The alcohol dehydration and hydrogenation catalyst according to claim 1, wherein the solid acid catalyst is a SiW/silica catalyst or tungsten oxide zirconia. A method for producing an alcohol dehydration hydrogenation catalyst comprising palladium and a solid acid catalyst, for converting a first fuel gas containing 2.0% to 20% hydrogen by volume after dehydration, obtained by methanation reaction of hydrogen and carbon oxides in the presence of a methanation catalyst, into a second fuel gas containing alkanes having 2 to 4 carbon atoms and having a reduced hydrogen concentration, by treating the first fuel gas in the presence of an alcohol having 2 to 4 carbon atoms. The method comprises the step of calcining a catalyst precursor containing palladium at 400°C or higher. The method for producing an alcohol dehydration hydrogenation catalyst according to claim 3, wherein the catalyst precursor is a solid acid catalyst impregnated with palladium. The method for producing an alcohol dehydration and hydrogenation catalyst according to claim 3 or 4, wherein the solid acid catalyst is a SiW/silica catalyst or tungsten oxide zirconia.

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