Method for producing high calorific value fuel gas

Abstract

Provided is a method for producing a high calorific value fuel gas, the method comprising: a vapor reforming step in which ethanol is brought into contact with a ruthenium- or nickel-containing catalyst under conditions of a catalyst inlet temperature of 200 °C to 400 °C (exclusive of 400 °C) in the presence of hydrogen in an amount such that the molar ratio of hydrogen / ethanol is 1.0 to 10 and vapor in an amount such that the molar ratio of vapor / ethanol is 1.2 to 5; and a methanation step in which a gas obtained in the vapor reforming step is brought into contact with the ruthenium- or nickel-containing catalyst under conditions of a catalyst outlet temperature of 230 °C to 330°C.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a high-calorific value fuel gas mainly composed of methane by methaneating ethanol in the presence of hydrogen. [Background technology]

[0002] City gas, which is primarily composed of natural gas, emits less carbon dioxide during combustion compared to other fossil fuels such as petroleum, making it an energy source with a low environmental impact. However, in recent years, with environmental problems such as global warming becoming increasingly serious, further reductions in carbon dioxide emissions are desired.

[0003] In recent years, biomass fuels such as bioethanol have attracted attention as a new energy resource. Bioethanol is obtained by alcoholic fermentation of sugars obtained by saccharifying starch contained in sugarcane juice or grains such as corn. Although carbon dioxide is produced when bioethanol is burned, the raw material plants absorb a corresponding amount of carbon dioxide from the air during their growth process. Therefore, it can be considered that, when totaled from the plant's growth process, it does not increase the concentration of carbon dioxide in the atmosphere, and for this reason, bioethanol is considered a carbon-neutral fuel.

[0004] If a method can be established to efficiently produce fuel gas with methane as the main component from ethanol, it would be possible to reduce carbon dioxide emissions by, for example, using bioethanol as a raw material for city gas.

[0005] Patent Document 1 discloses a method for producing fuel gas by catalytic cracking aliphatic alcohols having 2 to 5 carbon atoms, or a mixture of such alcohols and water, in the presence of a ruthenium-based catalyst. According to this document, the catalytic cracking reaction is typically carried out at 400°C to 700°C and at a rate of 2 to 10 kg / cm³. 2It is said that the process is carried out under absolute pressure conditions, where ethanol is catalytically decomposed in the presence of water vapor, resulting in a product containing 32%-44% hydrogen, 29%-40% methane, and 16%-23% carbon dioxide by volume, with a calorific value of 4200-5050 kcal / m³. 3 It has been shown that the fuel gas was obtained.

[0006] Patent Document 2 discloses a method for gasifying ethanol by mixing ethanol with water in a predetermined ratio and passing it through a nickel-based catalyst at 300°C to 600°C. It also states that by cooling the resulting gaseous mixture to 250°C to 350°C and then introducing it into a catalytic methane process, a fuel gas with a high methane concentration that can be used as synthetic natural gas after carbon dioxide removal can be obtained. However, there is no specific description of the catalytic methane process, nor is there any specific description of the fuel gas composition after the catalytic methane process.

[0007] Patent Document 3 discloses a method for producing methane-containing gas from an ethanol-containing raw material containing ethanol and water vapor, the method comprising a reaction step of passing the ethanol-containing raw material once at a reaction temperature of 400°C or higher through a catalyst having rhodium or ruthenium supported on the surface of an inorganic oxide that serves as a support.

[0008] Even with the method described in this document, the methane concentration in the resulting methane-containing gas is only about 55%, making it unsuitable for use as a raw material for city gas.

[0009] 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.

[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 for hydrogen concentration is set at 2% by volume (Non-Patent Document 1). In natural gas transport pipelines in the United States and Canada, there are many examples where the upper limit for carbon dioxide concentration is set at 2 to 4% by volume (Non-Patent Document 2). 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 3), 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 4).

[0016] The production of methane, the main component gas, by steam reforming of ethanol is thought to proceed through the following reaction. Specifically, hydrogen and carbon monoxide are produced by the steam reforming reaction of ethanol (Equation 1). Some of the carbon monoxide is converted to hydrogen and carbon dioxide by the CO shift reaction (Equation 2), and the remainder reacts with hydrogen to produce methane (Equation 3).

[0017] C2H5OH+H2O → 2CO+4H2 (Formula 1) 0.5CO+0.5H2O → 0.5CO2+0.5H2 (Formula 2) 1.5CO+4.5H2→ 1.5CH4+1.5H2O (Formula 3) The overall reaction equation is as shown in Equation 4, in which 1 mole of ethanol produces 1.5 moles of methane and 0.5 moles of carbon dioxide.

[0018] C2H5OH → 1.5CH4+0.5CO2 (Formula 4) In other words, if ethanol is simply subjected to a methane reaction in the presence of water vapor, even if the reaction proceeds ideally, the resulting gas will be a mixture of 75% methane and 25% carbon dioxide. Unless the carbon dioxide is removed by some means, it cannot be used as a raw material for city gas.

[0019] Methods for removing carbon dioxide include the hot potassium carbonate absorption method and the amine absorption method. These carbon dioxide removal systems have been adopted in alternative natural gas production plants that use naphtha and other materials as raw materials. However, all of these carbon dioxide removal methods have high equipment and operating costs, which significantly reduces the economic viability of fuel gas production.

[0020] Patent Document 4 discloses a method for producing hydrogen from ethanol, which includes a step of passing the mixture through a nickel-based catalyst at 300°C to 600°C, with a hydrogen / ethanol molar ratio of 0.1 to 1.0 and a water vapor / ethanol molar ratio of 1.0 to 10.0, to convert it into a flow containing methane, CO, CO2, and H2.

[0021] Table 5 of this document shows that when ethanol was converted on a commercially available methane catalyst under conditions of a water vapor / ethanol molar ratio of 2.8, a hydrogen / ethanol molar ratio of 250, 400°C, and a pressure of 1 atm, the conversion rate was 90.1%, the methane selectivity was 98.8%, and the gasoline selectivity was 1.2% after a reaction time of 15 minutes, showing high methane selectivity. However, after a reaction time of 60 minutes, the conversion rate decreased to 42.1%. However, in the reaction with a hydrogen / ethanol molar ratio of 250, the resulting gas is mainly composed of hydrogen and contains methane, so it cannot be used as a raw material for city gas. Furthermore, Table 7 of this document shows that in ethanol conversion on a commercially available methanation catalyst under conditions of a water vapor / carbon molar ratio of 3, 400°C, and a pressure of 10 atm, when hydrogen was not added, an increase in pressure loss in the catalyst layer due to carbon deposition occurred in a short time, whereas when the hydrogen / ethanol molar ratio was 0.6, no increase in pressure loss was observed. In this case as well, the composition of the resulting gas is 27.2-27.5% methane and 72.3-72.8% hydrogen, making it a gas mainly composed of hydrogen with methane present, and therefore it cannot be used as a raw material for city gas.

[0022] Patent Document 5 describes a method for producing a hydrogen-enriched product by selectively reforming ethanol in the presence of a catalyst, wherein the mixture with a molar ratio of ethanol to hydrogen of 0.2 to 1 is fed into a dehydration / hydrogenation reactor, ethanol is subjected to dehydration / hydrogenation to produce ethane, the produced ethane is adiabatically reformed to produce a stream containing methane, the stream containing methane is subjected to steam reforming to obtain a mixture containing hydrogen and carbon monoxide, and a water-gas shift reaction is further performed to obtain the hydrogen-enriched product.

[0023] However, this document only presents results for the conversion of ethanol to ethane, and no specific description of the methane concentration in the methane-containing stream is found.

[0024] Patent Document 6 describes a method for producing hydrogen, which comprises: mixing a first feed stream containing a mixture of H2 and at least one selected from the group consisting of hydrocarbons having 2 or more carbon atoms and alcohols having 2 or more carbon atoms, wherein the mixture has a hydrogen stoichiometric ratio (λ) of at least 0.1, with a second feed stream containing steam, to produce a first product stream containing CH4 and H2O in a pre-reforming reactor; feeding the first product stream into a reforming reactor; and reacting the first product stream in the reforming reactor to produce a second product stream containing CO and H2.

[0025] However, this document only shows the effect of hydrogen addition on propane conversion when propane is used as the hydrocarbon and the steam reforming reaction over an iridium catalyst is carried out at 450°C, and there is no specific disclosure whatsoever regarding the composition of the produced gas, particularly the concentration of methane.

[0026] Patent Document 7 discloses a method for producing methane by hydrocracking higher hydrocarbons of ethane or higher, wherein petroleum distillate fractions such as LPG, naphtha, kerosene-gas oil, and other hydrocarbon feedstock, and hydrogen gas in an amount of 90% to 150% of the theoretical hydrogen amount required for methane production by hydrogenation of the feed material are passed under heating through a highly active nickel-based solid catalyst layer to generate methane, wherein steam in an amount necessary for controlling the maximum temperature within the range of 400°C to 600°C is mixed with the feed material and added to the catalyst layer, and reaction heat is removed from the catalyst layer by indirect heat exchange so as to keep the outlet temperature of the catalyst layer at least 100°C lower than the maximum temperature. The method is characterized by the above, and it discloses a method for producing high-purity methane.

[0027] This document discloses examples using hexane, light straight-run naphtha, kerosene fraction, or butane as higher hydrocarbons of ethane or higher, but does not disclose the use of alcohol.

[0028] Further, according to this document, in the method for producing high-purity methane, methane is directly obtained from higher hydrocarbons of ethane or higher without going through steam reforming and methanation, and steam is added to control the heat generation of hydrocracking.

[0029] The reaction heat of hydrocracking of ethane (Equation 5) is 66 kJ per mole of ethane, whereas methane production from ethanol (Equation 6) is accompanied by a much larger heat generation of 156 kJ per mole of ethanol. Furthermore, there is a difference in the nature of the reaction because it involves cleavage of carbon-oxygen bonds, so this document does not provide any suggestion for the production of methane from ethanol.

[0030] C2H6+H2→ 2CH4 (Equation 5) C2H5OH+2H2→ 2CH4+H2O (Equation 6) Another problem when obtaining methane as the main component gas by steam reforming of ethanol is the carbon deposition problem described in Patent Documents 3 and 4. Patent Document 3 shows that significant carbon deposition occurred when a nickel catalyst was used in steam reforming with a water / ethanol ratio of 0.78 (by weight). Patent Document 4 shows that carbon deposition occurred in a short time when no hydrogen was added during ethanol conversion on a commercially available methanation catalyst at 400°C with a water / carbon molar ratio of 3. The water / ethanol molar ratio is 2 in Patent Document 3 and 6 in Patent Document 4. To avoid carbon deposition in steam reforming of ethanol, it is necessary to add a large amount of water vapor. The reaction that produces 1.5 moles of methane and 0.5 moles of carbon dioxide from 1 mole of ethanol (Equation 4) is an exothermic reaction, but the heat generated is only 74 kJ (at 25°C), and even if this is used as the heat of vaporization of water, only about 1.7 moles of water vapor can be produced. Therefore, obtaining methane as the main component gas stably through ethanol steam reforming requires an external supply of steam, which is also economically disadvantageous. [Prior art documents] [Patent Documents]

[0031] [Patent Document 1] Japanese Patent Application Publication No. 52-52902 [Patent Document 2] Japanese Patent Application Publication No. 55-144093 [Patent Document 3] Japanese Patent Publication No. 2009-227588 [Patent Document 4] Japanese Patent Publication No. 2013-540674 [Patent Document 5] Japanese Patent Publication No. 2006-82996 [Patent Document 6] Japanese Patent Publication No. 2010-524824 [Patent Document 7] Special Publication No. 46-22749 [Non-patent literature]

[0032] [Non-Patent Document 1] E. Koytsoumpa and S. Karellas, Renewable and Sustainable Energy Reviews, Vol. 94, 2018, p. 536. [Non-Patent Document 2] MMFoss and C. Head, Interstate natural gas - quality specifications & interchangeability, Center for energy economics, 2004. [Non-Patent Document 3] Biogas Purchase Guidelines, Osaka Gas Co., Ltd., 2008. [Non-Patent Document 4] Biogas Purchase Guidelines, Tokyo Gas Co., Ltd., 2008. [Overview of the Initiative] [Problems that the invention aims to solve]

[0033] In view of the above problems, the present invention aims to provide an economically advantageous method for producing a high-calorific value fuel gas that can be used as a raw material for city gas. This method involves obtaining a high-calorific value fuel gas with a high methane concentration that can be used directly as a city gas raw material without using expensive carbon dioxide separation equipment, and is less prone to carbon precipitation. [Means for solving the problem]

[0034] The characteristic configuration of the method for producing high-calorific value fuel gas according to the present invention includes: a steam reforming step in which ethanol is brought into contact with a catalyst containing ruthenium or nickel in the presence of an amount of hydrogen such that the hydrogen / ethanol molar ratio is 1.0 or more and 10 or less, and an amount of water vapor such that the water vapor / ethanol molar ratio is 1.2 or more and 5 or less, under conditions where the catalyst inlet temperature is 200°C or more and less than 400°C; and a methane step in which the gas obtained in the steam reforming step is brought into contact with a catalyst containing ruthenium or nickel under conditions where the catalyst outlet temperature is 230°C or more and 330°C or less. Furthermore, the raw material gas supplied to the steam reforming process further contains at least one of carbon monoxide and carbon dioxide. It's at a single point.

[0035] According to this characteristic configuration, in conventional fuel gas production methods that combine ethanol steam reforming and methane reaction, a large amount of carbon dioxide is produced as a by-product. However, in this method, carbon dioxide is converted into methane through reaction with hydrogen, thus avoiding the large amount of carbon dioxide remaining in the resulting fuel gas. This allows for the production of a high-calorific value fuel gas that can be used as a raw material for city gas without the need for expensive carbon dioxide removal equipment, and carbon deposition is less likely to occur.

[0036] Furthermore, compared to carrying out the ethanol steam reforming process under conditions where hydrogen is absent, the steam reforming process can be started at a lower temperature, and the energy required to preheat the raw material gas for the steam reforming process can be reduced, thus enabling the production of high-calorific value fuel gas more economically.

[0037] In addition, while conventional fuel gas production methods combining ethanol steam reforming and methanation reactions produce only 1.5 moles of methane per mole of ethanol, this unique configuration yields approximately 2 moles of methane per mole of ethanol, making it possible to produce high-calorific value fuel gas more economically.

[0039] Also, The methane reaction of carbon monoxide and carbon dioxide proceeds rapidly even at low temperatures of around 200°C to 250°C, generating a relatively large amount of heat. This leads to a rapid temperature rise in the steam reforming catalyst layer, allowing the steam reforming process to be started at a lower temperature. As a result, the energy required to preheat the raw material gas in the steam reforming process is reduced, making it possible to produce high-calorific value fuel gas more economically.

[0040] A further characteristic feature of the method for producing high-calorific value fuel gas according to the present invention is that the amount of hydrogen supplied to the steam reforming process is such that the value of {(hydrogen) + (ethanol) × 6 + (carbon monoxide)} / {(ethanol) × 2 + (carbon monoxide) + (carbon dioxide)}, calculated on a molar basis, is between 3.9 and 4.1.

[0041] This characteristic configuration makes it possible to keep the residual hydrogen and carbon dioxide in the resulting fuel gas low, and to obtain a high-calorific value fuel gas with high methane purity that is easy to use as a raw material for city gas.

[0042] Method for producing high-calorific value fuel gas according to the present invention special The characteristic composition is, The process includes a steam reforming step in which ethanol is brought into contact with a catalyst containing ruthenium or nickel in the presence of hydrogen in an amount such that the hydrogen / ethanol molar ratio is 1.0 or more and 10 or less, and water vapor in an amount such that the water vapor / ethanol molar ratio is 1.2 or more and 5 or less, under conditions where the catalyst inlet temperature is 200°C or more and less than 400°C; and a methane step in which the gas obtained in the steam reforming step is brought into contact with a catalyst containing ruthenium or nickel under conditions where the catalyst outlet temperature is 230°C or more and 330°C or less. The process further includes a step of preparing a raw material gas by adding hydrogen and water vapor to ethanol such that the molar ratio of hydrogen / ethanol is 1.8 or more and 2.2 or less, and the molar ratio of water vapor / ethanol is 1.2 or more and 4 or less, wherein the raw material gas After being mixed with a portion of the gas obtained in the steam reforming process, The key point is that it is sent to the steam reforming process.

[0043] According to this feature configuration, In conventional fuel gas production methods combining ethanol steam reforming and methanation reactions, a large amount of carbon dioxide is produced as a by-product. However, this is converted to methane through reaction with hydrogen, thus avoiding the large amount of carbon dioxide remaining in the resulting fuel gas. This allows for the production of high-calorific value fuel gas usable as a raw material for city gas without the need for expensive carbon dioxide removal equipment, and carbon deposition is less likely to occur. Furthermore, compared to carrying out the ethanol steam reforming process under conditions without hydrogen, the steam reforming process can be started at a lower temperature, saving energy required for preheating the raw material gas in the steam reforming process, thus enabling the more economical production of high-calorific value fuel gas. In addition, while conventional fuel gas production methods combining ethanol steam reforming and methanation reactions produce only 1.5 moles of methane per mole of ethanol, this characteristic configuration yields approximately 2 moles of methane per mole of ethanol, enabling the more economical production of high-calorific value fuel gas. This method allows for particularly low levels of residual hydrogen and carbon dioxide in the resulting fuel gas, producing a high-calorific value fuel gas with high methane purity that is easily usable as a raw material for city gas. In addition, because carbon deposition on the catalyst is less likely to occur, the fuel gas can be produced stably over a long period of time. Furthermore, even when the steam reforming process is carried out under adiabatic conditions, the peak temperature of the steam reforming catalyst layer can be suppressed, thereby inhibiting thermal degradation of the catalyst.

[0044] Method for producing high-calorific value fuel gas according to the present invention special The characteristic composition is, The process includes a steam reforming step in which ethanol is brought into contact with a catalyst containing ruthenium or nickel in the presence of hydrogen in an amount such that the hydrogen / ethanol molar ratio is 1.0 or more and 10 or less, and water vapor in an amount such that the water vapor / ethanol molar ratio is 1.2 or more and 5 or less, under conditions where the catalyst inlet temperature is 200°C or more and less than 400°C; and a methane step in which the gas obtained in the steam reforming step is brought into contact with a catalyst containing ruthenium or nickel under conditions where the catalyst outlet temperature is 230°C or more and 330°C or less. The process further includes a step of preparing the raw material gas by adding hydrogen and water vapor to ethanol such that the molar ratio of hydrogen / ethanol is 1.0 or more and less than 1.8, and the molar ratio of water vapor / ethanol is 2 or more and 4 or less, and the raw material gas is sent to the water vapor reforming step, and hydrogen is added to the gas obtained in the water vapor reforming step and sent to the methane step.

[0045] According to this feature configuration, In conventional fuel gas production methods combining ethanol steam reforming and methanation reactions, a large amount of carbon dioxide is produced as a by-product. However, in this new method, the large amount of carbon dioxide remaining in the resulting fuel gas is converted to methane through a reaction with hydrogen. This avoids the need for expensive carbon dioxide removal equipment, allowing for the production of high-calorific value fuel gas usable as a raw material for city gas, and minimizing carbon precipitation. Furthermore, compared to performing the ethanol steam reforming process under conditions without hydrogen, the steam reforming process can be started at a lower temperature, reducing the energy required for preheating the raw material gas in the steam reforming process. This allows for the more economical production of high-calorific value fuel gas. In addition, while conventional fuel gas production methods combining ethanol steam reforming and methanation reactions produce only 1.5 moles of methane per mole of ethanol, this new configuration produces approximately 2 moles of methane per mole of ethanol, allowing for the more economical production of high-calorific value fuel gas.Even when the steam reforming process is carried out under adiabatic conditions, the peak temperature of the steam reforming catalyst layer can be suppressed, thereby reducing thermal degradation of the catalyst. As a means of suppressing thermal degradation of the catalyst in exothermic reactions, a method of diluting the raw material gas by a recycling operation, in which a portion of the gas after the reaction is returned to the reactor inlet, is employed. However, by adopting this characteristic configuration, the steam reforming process can be carried out by suppressing the recycling rate or without performing a recycling operation. Therefore, a high-calorific value fuel gas with high methane purity can be obtained more economically.

[0046] A further characteristic feature of the method for producing high-calorific value fuel gas according to the present invention is that the raw material gas, prepared by adding hydrogen and water vapor to ethanol, is mixed with a portion of the gas obtained in the water vapor reforming step and then introduced into the water vapor reforming step.

[0047] According to this feature configuration, even when the steam reforming process is carried out under adiabatic conditions, the peak temperature of the steam reforming catalyst layer can be suppressed, thereby suppressing thermal degradation of the catalyst. [Brief explanation of the drawing]

[0048] [Figure 1] This is a block flow diagram showing one embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 2] This is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 3] This is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 4] This is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 5] This is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 6] This figure shows the relationship between the temperature of the catalyst layer and the carbon activity at the water vapor / ethanol ratio (H2O / EtOH) of Examples 3-6 and Comparative Example 1. [Figure 7]This figure shows the relationship between temperature and carbon activity at the water vapor / ethanol ratio (H2O / EtOH) of Comparative Examples 2-4. [Figure 8] This is a process flow diagram illustrating one embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 9] This is a process flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Figure 10] This is a process flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. [Modes for carrying out the invention]

[0049] [Embodiment] The following describes embodiments of the method for producing high-calorific value fuel gas according to the present invention. Figure 1 is a block flow diagram showing the method for producing high-calorific value fuel gas according to the present invention. The method for producing high-calorific value fuel gas according to this embodiment includes a steam reforming step (steam reforming reaction section 1) in which ethanol is brought into contact with a catalyst containing ruthenium or nickel in the presence of an amount of hydrogen such that the molar ratio of hydrogen / ethanol is 1.0 or more and 10 or less, and an amount of water vapor such that the molar ratio of water vapor / ethanol is 1.2 or more and 5 or less, under conditions where the catalyst inlet temperature is 200°C or more and less than 400°C, and a methane step (methanization reaction section 2) in which the gas obtained in the steam reforming step is brought into contact with a catalyst containing ruthenium or nickel under conditions where the catalyst outlet temperature is 230°C or more and 330°C or less. According to the method for producing high-calorific value fuel gas with such a configuration, a high-calorific value fuel gas can be obtained in which the proportion of methane is 85% or more, more preferably 90% or more, and even more preferably 95% or more, on a volume basis after dehydration.

[0050] The ethanol used in the method for producing high-calorific value fuel gas of the present invention does not necessarily have to be produced by fermentation, but from the viewpoint of producing a fuel gas that can be considered carbon neutral, it is preferable that it be bioethanol produced from raw materials such as sugarcane or corn.

[0051] Ethanol typically contains small amounts of water, and may also contain trace amounts of organic acids, aldehydes, thiols, and other sulfur compounds. Of these, water may make up approximately 20% to 50% of the ethanol by mass. If the ethanol used as a raw material contains water, the amount of water vapor added can be adjusted accordingly.

[0052] While trace amounts of organic acids and aldehydes may cause carbon precipitation and other problems in subsequent steam reforming processes if present in excessive amounts, this is usually not a concern.

[0053] Sulfur compounds such as thiols can cause sulfur poisoning in the subsequent steam reforming process, leading to a decrease in activity. Therefore, if a large amount of sulfur compounds are present, it is desirable to perform desulfurization treatment beforehand.

[0054] In the method for producing high-calorific value fuel gas of the present invention, the hydrogen used can be produced by any method, but hydrogen produced using a water electrolysis device such as an alkaline water electrolysis device, a polymer electrolyte water electrolysis device, or a solid oxide water electrolysis device is preferred because it typically does not contain impurities that would interfere with the steam reforming process.

[0055] There are no particular restrictions on the method or order of mixing hydrogen and water vapor with ethanol, but it is preferable that the hydrogen / ethanol molar ratio be between 1.0 and 10. If the hydrogen / ethanol molar ratio is less than 1.0, it becomes difficult to reduce the carbon dioxide concentration in the fuel gas. If the hydrogen / ethanol molar ratio is greater than 10, it becomes difficult to reduce the hydrogen concentration in the fuel gas.

[0056] The molar ratio of water vapor to ethanol is preferably between 1.2 and 5, more preferably between 1.5 and 4, and even more preferably between 2 and 3.5. If the molar ratio of water vapor to ethanol is less than 1.2, it becomes difficult to suppress carbon deposition on the catalyst. If the molar ratio of water vapor to ethanol is greater than 5, it becomes difficult to save energy required for water vapor generation, which tends to be economically disadvantageous.

[0057] The present invention provides a method for producing a high-calorific value fuel gas, which includes a steam reforming step in which a gas containing ethanol, hydrogen, and water vapor is brought into contact with a catalyst containing ruthenium or nickel under conditions where the catalyst inlet temperature is 200°C or higher and less than 400°C.

[0058] The steam reforming catalyst used in the steam reforming process is a catalyst in which ruthenium or nickel is supported on an inorganic oxide support such as alumina. Catalysts in which ruthenium is supported on an inorganic oxide support such as alumina are particularly preferred because they are less prone to carbon deposition. The steam reforming process may be carried out in an adiabatic reactor, or it may be carried out using a heat exchange reactor while maintaining a nearly constant catalyst layer temperature. The steam reforming catalyst is packed into the steam reforming reaction section 1 to form a steam reforming catalyst layer.

[0059] The steam reforming process is carried out under conditions where the inlet temperature of the steam reforming catalyst layer is between 200°C and 400°C. In the steam reforming process, the endothermic steam reforming reaction of ethanol and the exothermic methane reaction occur simultaneously, resulting in an overall exothermic reaction. When a reactor without a special heat removal mechanism (adiabatic reactor) is used, and the raw material gas is introduced with the inlet temperature of the steam reforming catalyst layer set to around 300°C, and the reaction is carried out under substantially adiabatic conditions, the outlet temperature of the steam reforming catalyst layer is usually around 500°C to 700°C. As a result of diligent research by the inventors, it has become clear that when the raw material gas is introduced with the inlet temperature of the steam reforming catalyst layer set to around 250°C, the reaction proceeds with an increase in temperature, and when the steam reforming catalyst layer temperature is 400°C or higher, the steam reforming reaction of ethanol proceeds rapidly. Therefore, when carried out in an adiabatic reactor, the ethanol reforming reaction is more likely to proceed completely.

[0060] Using a heat exchange reactor, which incorporates a heat exchange function, allows the reaction to proceed while removing the heat generated by the reaction. This suppresses the rise in catalyst layer temperature, which is advantageous in terms of catalyst durability. When the reactor is properly designed and operated, the heat generated by the reaction is removed, and the inlet temperature and outlet temperature of the steam reforming catalyst layer are made nearly identical, allowing the reaction to proceed isothermally. However, it should be noted that even in a heat exchange reactor, there is a temperature distribution in the catalyst layer, and in areas where exothermic reactions are occurring, the temperature may rise to a level close to the outlet temperature of an adiabatic reaction.

[0061] The methanation catalyst used in the methanation process is a catalyst in which ruthenium or nickel is supported on an inorganic oxide support such as alumina. Catalysts in which ruthenium is supported on an inorganic oxide support such as alumina are particularly preferred because they are less prone to carbon deposition. The methanation process may be carried out in an adiabatic reactor, or it may be carried out using a heat exchange reactor while maintaining a nearly constant catalyst layer temperature. The methanation catalyst is packed into the methanation reaction section 2 to form a methanation catalyst layer.

[0062] In the methanation process, the methanation reaction is an exothermic reaction. Therefore, if the reaction is carried out using an adiabatic reactor, the reaction gas will flow out at a temperature higher than the inlet temperature of the methanation catalyst layer. Since the methanation reaction proceeds more towards methane production at lower equilibrium temperatures, it is advantageous to lower the outlet temperature of the methanation catalyst layer from the viewpoint of obtaining fuel gas with high methane purity. The process is carried out under conditions where the outlet temperature of the methanation catalyst layer is 330°C or lower. On the other hand, at low temperatures, the activity of the methanation catalyst decreases, and it becomes difficult to carry out the reaction below 230°C. Therefore, the outlet temperature of the methanation catalyst layer should be 230°C or higher and 330°C or lower, more preferably 230°C or higher and 280°C or lower.

[0063] When a methane reactor is constructed using an adiabatic reactor, multiple reactors are provided, and coolers are installed between the reactors to set the inlet temperature of each reaction stage to 230°C to 330°C, more preferably 230°C to 280°C, so that the outlet temperature of the catalyst layer in the final stage reactor is 230°C to 330°C.

[0064] In the steam reforming process, the pressure inside the steam reforming reaction section 1 should be 0.3 MPa (absolute pressure, the same applies hereinafter) or higher to easily obtain a sufficient reaction rate, and 5 MPa or lower to reduce equipment costs and be economically advantageous. Therefore, it is preferable to set the pressure between 0.3 MPa and 5 MPa, and more preferably between 0.5 MPa and 3 MPa.

[0065] In the methanation process, the pressure inside the methanation reaction section 2 should be 0.3 MPa or higher, as this makes it easier to obtain a sufficient reaction rate and for methanation to proceed in equilibrium. Conversely, a pressure of 5 MPa or lower is economically advantageous as it reduces equipment costs. Therefore, a pressure of 0.3 MPa to 5 MPa is preferable, and a pressure of 0.5 MPa to 3 MPa is even more preferable.

[0066] In both the steam reforming and methanation processes, the pressure in the steam reforming reaction section 1 and the pressure in the methanation reaction section 2 should ideally be between 0.3 MPa and 5 MPa, and more preferably between 0.5 MPa and 3 MPa. Therefore, it is usually not necessary to change the pressure between each process, but if necessary, a process of pressurizing or depressurizing the steam reforming reaction section 1 or the methanation reaction section 2 may be added. Normally, the reaction pressure decreases slightly in accordance with the pressure loss in each process, but this does not pose any particular problem.

[0067] Figure 2 is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. In the method for producing high-calorific value fuel gas according to this embodiment, the raw material gas supplied to the steam reforming step includes ethanol, hydrogen, and water vapor, in addition to at least one of carbon monoxide and carbon dioxide.

[0068] The carbon dioxide may be recovered from combustion exhaust gas or chemical process exhaust gas using known carbon dioxide recovery methods such as the amine absorption method, or it may be carbon dioxide recovered from the atmosphere. If the carbon dioxide contains sulfur compounds, there is a risk of poisoning and degrading the steam reforming catalyst and methane catalyst, so desulfurization treatment of the carbon dioxide will be performed if necessary.

[0069] Carbon monoxide may be synthesized by electrochemically reducing the aforementioned carbon dioxide, or it may be obtained by reducing the aforementioned carbon dioxide with hydrogen (reverse water-gas shift reaction).

[0070] In this embodiment, when the amount of hydrogen supplied to the steam reforming process is added such that the value of {(hydrogen) + (ethanol) × 6 + (carbon monoxide)} / {(ethanol) × 2 + (carbon monoxide) + (carbon dioxide)}, calculated on a molar basis, satisfies 3.9 or more and 4.1 or less, the concentration of components other than methane in the fuel gas obtained after the methane process becomes low, resulting in a fuel gas with high methane purity and high calorific value. If the above value is less than 3.9, there is a risk that the amount of residual carbon dioxide in the obtained fuel gas will be high. If the above value is greater than 4.1, there is a risk that the amount of residual hydrogen in the obtained fuel gas will be high. Figure 3 is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. In addition to the basic embodiment shown in Figure 1, the method for producing high-calorific value fuel gas according to this embodiment further includes a raw material gas adjustment step in the raw material gas adjustment unit 3, in which hydrogen and water vapor are added to ethanol so that the molar ratio of hydrogen / ethanol is 1.8 or more and 2.2 or less and the molar ratio of water vapor / ethanol is 1.2 or more and 4 or less, thereby adjusting the raw material gas, and the adjusted gas after going through the raw material gas adjustment step is sent to the water vapor reforming step.

[0071] The molar ratio of hydrogen to ethanol introduced into the raw material gas adjustment process is preferably between 1.8 and 2.2. This configuration allows for particularly low levels of residual hydrogen and carbon dioxide in the resulting fuel gas, yielding a high-calorific value fuel gas with high methane purity that is easily usable as a raw material for city gas. If the hydrogen / ethanol molar ratio is less than 1.8, it may be difficult to reduce the carbon dioxide concentration in the fuel gas. If the hydrogen / ethanol molar ratio is greater than 2.2, it may be difficult to reduce the hydrogen concentration in the fuel gas. The molar ratio of water vapor to ethanol introduced into the raw material gas preparation process is preferably between 1.2 and 4. The reaction that produces 2 moles of methane and 1 mole of water from 1 mole of ethanol and 2 moles of hydrogen generates 156 kJ (at 25°C). If this is entirely used as the heat of vaporization of water, approximately 3.5 moles of water vapor can be produced. A water vapor / ethanol molar ratio of 1.5 or higher makes it easier to avoid carbon deposition, and a ratio of 3 or lower reduces the amount of water vapor required, which is often economically advantageous. Therefore, a water vapor / ethanol molar ratio of 1.5 or higher is more preferable.

[0072] Furthermore, in order to suppress the outlet temperature of the steam reforming catalyst layer, methane may be added in an amount such that the methane / ethanol molar ratio is between 0.5 and 1.5. In this case, in order to avoid carbon deposition, it is preferable to make the steam / ethanol molar ratio higher than the above, preferably between 2.5 and 4.

[0073] Figure 4 is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. In addition to the basic embodiment shown in Figure 1, the method for producing high-calorific value fuel gas according to this embodiment further includes a raw material gas adjustment step in the raw material gas adjustment unit 3, in which hydrogen and water vapor are added to ethanol so that the molar ratio of hydrogen / ethanol is 1.0 or more and less than 1.8, and the molar ratio of water vapor / ethanol is 2 or more and 4 or less, thereby adjusting the raw material gas. The adjusted gas after passing through the raw material gas adjustment step is sent to the water vapor reforming step, and hydrogen is added to the water vapor reforming reaction outlet gas obtained in the water vapor reforming step before it is sent to the methane step.

[0074] The molar ratio of hydrogen to ethanol supplied to the raw material gas adjustment process shall be 1.0 or more and less than 1.8. This configuration suppresses the peak temperature of the steam reforming catalyst layer when the steam reforming process is carried out under adiabatic conditions. The suppression effect is greater when the hydrogen / ethanol molar ratio is 1.5 or less. If the hydrogen / ethanol molar ratio is less than 1.0, the decrease in hydrogen concentration slows down the progress of the methane reaction, reducing the temperature rise due to the progress of the methane reaction, and there is a risk that the ethanol reforming reaction will not proceed sufficiently. If the hydrogen / ethanol molar ratio is 1.8 or more, the effect of suppressing the peak temperature of the steam reforming catalyst layer becomes poor. In this specification, "peak temperature of the catalyst layer" refers to the maximum temperature of the catalyst layer.

[0075] The molar ratio of water vapor to ethanol is preferably between 2 and 4. However, if the molar ratio is 2.5 or higher, carbon deposition of the catalyst is easily suppressed, and if it is 3 or lower, the amount of water vapor required is reduced, which is economically advantageous. Therefore, it is preferable that the molar ratio of water vapor to ethanol be between 2.5 and 3. If the molar ratio of water vapor to ethanol is less than 2.5, the outlet temperature of the water vapor reforming reaction section will be high, and the carbon activity will exceed 1, which may lead to deterioration of the water vapor reforming catalyst due to thermal degradation and carbon deposition. If the molar ratio of water vapor to ethanol is greater than 4, a large amount of water vapor is required, which may reduce economic efficiency.

[0076] In this embodiment, hydrogen is added to the steam reforming reaction outlet gas obtained in the steam reforming step and then sent to the methane step. The amount of hydrogen added is the total amount of hydrogen mixed with ethanol in the raw material gas preparation step. A molar ratio of 1.8 to 2.2 relative to ethanol is preferable because it is easier to obtain a high-calorific value fuel gas with high methane purity, and a molar ratio of 2.0 to 2.1 is more preferable.

[0077] Figure 5 is a block flow diagram showing another embodiment of the method for producing high-calorific value fuel gas according to the present invention. In addition to the embodiment shown in Figure 3, the method for producing high-calorific value fuel gas according to this embodiment is configured such that the adjusted gas prepared in the raw material gas preparation step and a portion of the steam reforming reaction outlet gas obtained in the steam reforming step are mixed and then sent to the steam reforming step.

[0078] The steam reforming process is an exothermic reaction, and the steam reforming catalyst is exposed to high temperatures, which can sometimes raise concerns about its durability. In this embodiment, a portion of the gas at the outlet of the steam reforming reaction section is mixed with the adjusted gas, diluting the adjusted gas and thus mitigating the temperature rise in the steam reforming process.

[0079] The raw material gas adjustment unit 3 may be equipped with a recycling compressor 5 for recycling a portion of the outlet gas from the steam reforming reaction unit 1 (steam reforming reaction unit outlet gas), and a flow rate adjustment means for adjusting the amount of recycled gas.

[0080] [Examples and Comparative Examples] The following test examples 1 to 4 are test examples relating to the steam reforming process in the method for producing high-calorific value fuel gas according to the present invention.

[0081] [Test Example 1] A temperature measuring sheath tube (6 mm outer diameter) was passed through the center of a stainless steel reaction tube (20 mm inner diameter). 12 mL (approximately 9 g) of catalyst, consisting of activated alumina supports (2-4 mm spherical), supporting 2% by mass of ruthenium, was packed between the reaction tube and the sheath tube to form a catalyst layer. Alumina balls were packed to a height of 30 mm both above and below the catalyst layer. This reaction tube was loaded into an electric furnace and heated until the temperature at the center of the alumina ball layer above the catalyst layer reached 250°C. A reducing gas, a mixture of nitrogen gas and 2% hydrogen gas (by volume), was circulated through the furnace, and the reduction treatment was carried out for 1 hour.

[0082] After the reduction treatment described above, the pressure inside the reaction tube was maintained at 0.7 MPa (absolute pressure), and the catalyst layer was heated so that the temperature at the center of the alumina ball layer, i.e., 15 mm above the top of the catalyst layer, reached 250°C. A raw material gas mixture of 200 mL / min of ethanol (volume at standard conditions of 0°C and 1 atm, the same applies below), 400 mL / min of hydrogen, and 400 mL / min of water vapor was flowed from the inlet of the catalyst layer downwards. The outlet gas of the catalyst layer was separated from condensed components (water, ethanol) using an ice-cooled trap. Carbon monoxide, carbon dioxide, hydrogen, and nitrogen in the gas were analyzed using a gas chromatograph (Agilent Micro-GC with TCD detector), and hydrocarbons (methane, ethylene, ethane, propylene, propane, butane) and ethanol were analyzed using a gas chromatograph (Shimadzu GC-2014 with FID detector). Furthermore, the ethanol in the condensed water obtained by condensing in an ice-cooled trap was analyzed using a gas chromatograph (Shimadzu GC-2014, with FID detector).

[0083] The temperature control point was set not inside the catalyst layer, but in the alumina ball layer above the top of the catalyst layer, because it is difficult to accurately measure the temperature inside the catalyst layer due to the heat generated by the reaction. Since the reaction does not proceed inside the alumina ball layer, the gas temperature at the catalyst layer inlet is approximately the same as that at the center of the alumina ball layer. In the following, when the inlet temperature of the catalyst layer is mentioned, it refers to the temperature at the center of the alumina ball layer above the catalyst layer. The temperature inside the catalyst layer (at three points: top, middle, and bottom) was also measured using a thermocouple inserted into the conduit.

[0084] After the measurement at 250°C was completed, the inlet temperature of the catalyst layer was sequentially changed to 300°C, 350°C, and 400°C while the test gas was still flowing, and the outlet gas of the catalyst layer was similarly analyzed by gas chromatography.

[0085] The ethanol conversion rate in the reaction was calculated using the following formula. The ethanol contained in the outlet gas of the catalyst layer includes not only the gas that passed through the ice-cooled trap, but also the ethanol dissolved in the water condensed in the ice-cooled trap.

[0086] Ethanol conversion rate [%] = 100 × {1 - (amount of ethanol per unit time contained in the catalyst outlet gas) / (amount of ethanol per unit time supplied to the catalyst layer)} Table 1 shows the temperatures of the upper, middle, and lower parts of the catalyst layer for each catalyst layer inlet temperature, as well as the analysis results of the gas composition after condensate separation and the ethanol conversion rate.

[0087] When the catalyst layer inlet temperature was 250°C, the generated gas was primarily methane, containing 88.7% methane, 9.3% hydrogen, and 2.0% carbon dioxide. The ethanol conversion rate was 98.0%, and a small amount of ethanol remained in the condensate. The highest temperature inside the catalyst layer was 339°C (top), and it was 284°C at the catalyst layer outlet. Although the temperature inside the catalyst layer rises above the inlet temperature due to the heat generated by methane production, it can be seen that the temperature inside the catalyst layer decreases due to heat dissipation because the catalyst layer is not sufficiently insulated.

[0088] When the inlet temperature of the catalyst layer was 300°C, the generated gas was a methane-dominant gas containing 87.6% methane. The ethanol conversion rate was 100%, and no ethanol was detected in either the gas or the condensed water. The maximum temperature inside the catalyst layer was 371°C. Compared to when the inlet temperature of the catalyst layer was 250°C, the maximum temperature inside the catalyst layer was higher, which is considered to have resulted in complete conversion of ethanol.

[0089] When the inlet temperature of the catalyst layer was set to 350°C and 400°C, the methane concentration of the generated gas was slightly lower compared to the case where the inlet temperature of the catalyst layer was 300°C, due to the higher outlet temperature of the catalyst layer. [Table 1]

[0090] [Test Example 2] The experiment was conducted in the same manner as in Test Example 1, except that half of the hydrogen in the raw material gases supplied to the catalyst layer was replaced with nitrogen, resulting in a flow rate of 200 mL / min of ethanol, 200 mL / min of hydrogen, 200 mL / min of nitrogen, and 400 mL / min of water vapor. Nitrogen was added to ensure that the total flow rate of gas supplied to the catalyst per unit time was the same as in Test Example 1.

[0091] Table 2 shows the temperatures of the upper, middle, and lower parts of the catalyst layer at each inlet temperature, as well as the analysis results of the gas composition after condensate separation and the ethanol conversion rate.

[0092] When the catalyst layer inlet temperature was 250°C, the generated gas consisted of 51.6% methane, 5.9% hydrogen, and 8.7% carbon dioxide, resulting in a methane-dominant gas with trace amounts (less than 0.02%) of ethane and propane. Even after removing nitrogen, a large amount of carbon dioxide remained in the generated gas; this is because, stoichiometrically, there was insufficient hydrogen to convert all the carbon in the ethanol into methane. The ethanol conversion rate was 97.8%, and in addition to condensed water, some ethanol remained in the gas. The maximum temperature in the catalyst layer was 363°C (upper and middle sections), and 336°C at the bottom of the catalyst layer. When the catalyst layer inlet temperature was 300°C or higher, the ethanol conversion rate was 100%, and the only hydrocarbon in the generated gas was methane. [Table 2]

[0093] [Test Example 3] The test was conducted in the same manner as in Test Example 1, except that the entire amount of hydrogen supplied to the catalyst layer was replaced with nitrogen, resulting in ethanol at 200 mL / min, nitrogen at 400 mL / min, and water vapor at 400 mL / min.

[0094] Table 3 shows the temperatures of the upper, middle, and lower parts of the catalyst layer at each inlet temperature, as well as the analysis results of the gas composition after condensate separation and the ethanol conversion rate.

[0095] At a catalyst layer inlet temperature of 250°C, the ethanol conversion rate was only 11.5%. The ethanol conversion rate increased with increasing catalyst layer inlet temperature, but even at a catalyst layer inlet temperature of 400°C, the ethanol conversion rate remained at 64.6%. At all temperatures, the generated gas (after excluding nitrogen) was mainly hydrogen, with carbon monoxide, carbon dioxide, methane, and small amounts (0.02% to 4.0%) of C2-C4 hydrocarbons (ethylene, ethane, propylene, propane, and butane). [Table 3]

[0096] [Test Example 4] The test was conducted in the same manner as in Test Example 1, except that the pressure inside the reaction tube was set to 0.1 MPa (absolute pressure).

[0097] Table 4 shows the temperatures of the upper, middle, and lower parts of the catalyst layer at each inlet temperature, as well as the analysis results of the gas composition after condensate separation and the ethanol conversion rate.

[0098] The ethanol conversion rate was only 38.4% at a catalyst layer inlet temperature of 250°C, but rose to 98.0% at 300°C and 100% at temperatures above 350°C. The methane concentration of the generated gas was lower compared to Test Example 1. This is thought to be because the reaction proceeds with increasing temperature, and the steam reforming reaction of ethanol proceeds rapidly at steam reforming catalyst layer temperatures above 400°C. [Table 4]

[0099] [Evaluation of Test Examples 1-4] In Test Example 1, hydrogen and water vapor were added to ethanol so that the molar ratio of hydrogen / ethanol and water vapor / ethanol was 2.0, and then the mixture was brought into contact with a ruthenium-containing catalyst. When the inlet temperature of the catalyst layer was 250°C or higher, the ethanol was almost completely converted, and a gas mainly composed of methane was obtained. Furthermore, when the mixture was brought into contact with the catalyst layer under conditions where the inlet temperature was 300°C or higher and the maximum temperature inside the catalyst layer was 370°C or higher, the ethanol could be completely converted into a gas mainly composed of methane.

[0100] In Test Example 2, where the hydrogen / ethanol molar ratio was 1.0, the conversion rate of ethanol was about the same as when the hydrogen / ethanol molar ratio was 2.0, but a large amount of carbon dioxide remained in the generated gas.

[0101] Furthermore, in Test Example 3, where hydrogen is not added, ethanol does not completely convert even when the inlet temperature of the catalyst layer is 400°C (internal temperature of the catalyst layer is 392°C to 398°C). As disclosed in Patent Document 3, in a simple steam reforming reaction of ethanol without hydrogen addition, a temperature of 400°C or higher is required to obtain a sufficient ethanol conversion rate. In Test Example 4, where the reaction pressure was set to 0.1 MPa, the ethanol conversion rate was lower in the temperature range below 300°C compared to Test Example 1. This suggests that the reaction rate of the steam reforming reaction decreased. The lower methane concentration of the generated gas compared to Test Example 1 is likely due in part to the fact that the equilibrium conversion rate of the methanation reaction increases with higher reaction pressure. From the above points, it is understood that, in order to obtain a sufficient ethanol conversion rate even when the steam reforming process is carried out at a relatively low temperature of around 250°C to 300°C at the inlet of the catalyst layer, it is preferable to have a hydrogen / ethanol molar ratio of 1.0 or higher and a reaction pressure higher than atmospheric pressure.

[0102] Examples 1 and 2 are examples in which catalysts are packed in two stages at the inlet and outlet of a long reaction tube, and raw material gases containing ethanol, hydrogen, and water vapor are brought into contact with each catalyst layer at different temperatures. The inlet side is used as the water vapor reforming reaction section 1 to carry out a water vapor reforming reaction, and the outlet side is used as the methane reaction section 2 to carry out a methane reaction, thereby attempting to produce a high calorific value fuel gas.

[0103] [Example 1] A temperature measuring sheath tube (6 mm outer diameter) was passed through the center of a stainless steel reaction tube (20 mm inner diameter). Between the reaction tube and the sheath tube, 12 mL (approximately 9 g) of catalyst, in which 2 mass% of ruthenium was supported on activated alumina supports (2-4 mm spherical), was packed to form a steam reforming catalyst layer. Above the steam reforming catalyst layer, alumina balls were packed to a height of 30 mm. Below the steam reforming catalyst layer, alumina balls were packed to a height of 145 mm to form a cooling zone for cooling the outlet gas of the steam reforming catalyst layer. Further below that, 43 mL (approximately 33 g) of catalyst, in which 2 mass% of ruthenium was supported on activated alumina supports (2-4 mm spherical), was packed to form a methanation catalyst layer. Thermocouples for temperature measurement were installed inside the sheath tube at the center of the alumina ball layer above the steam reforming catalyst layer, at the upper, middle, and lower parts of the steam reforming catalyst layer, and at the upper, middle, and lower parts of the methane catalyst layer.

[0104] The reaction tube was loaded into the electric furnace. The electric furnace consists of three zones: upper, middle, and lower, and the heating output of each zone can be controlled individually. The reaction tube was loaded into the electric furnace so that the lower end of the steam reforming catalyst layer was at the same height as the lower end of the upper heater of the electric furnace, and the upper and lower ends of the lower heater were at the same height as the upper and lower ends of the methane catalyst layer.

[0105] The upper heater was controlled to maintain a temperature of approximately 250°C at the center of the alumina ball layer above the steam reforming catalyst layer, and the lower heater was controlled to maintain a temperature of 250°C at the outlet of the methane catalyst layer. A reducing gas, a mixture of nitrogen gas and 2% hydrogen gas (by volume), was then passed through the system, and the reduction treatment was performed for one hour.

[0106] After the reduction treatment described above, the pressure inside the reaction tube was maintained at 0.7 MPa (absolute pressure). The upper heater was controlled to maintain the temperature at the center of the alumina ball layer above the steam reforming catalyst layer (inlet temperature of the steam reforming catalyst layer) at 300°C, and the lower heater was controlled to maintain the temperature at the outlet (bottom) of the methane catalyst layer at 270°C. A mixture of ethanol (200 mL / min), hydrogen (400 mL / min), and steam (400 mL / min) was circulated from top to bottom through the catalyst layer. The catalyst layer outlet gas was analyzed in the same manner as in Test Example 1.

[0107] Table 5 shows the inlet temperature of the steam reforming catalyst layer, the upper, middle, and lower temperatures of the steam reforming catalyst layer, the upper, middle, and lower temperatures of the methane catalyst layer, the analysis results of the gas composition after condensate separation, and the ethanol conversion rate at 1, 2, 3, and 4 hours after the start of the reaction.

[0108] One hour after the start of the reaction, the inlet temperature of the steam reforming catalyst layer was 295°C, the upper temperature of the steam reforming catalyst was 392°C, and the outlet temperature (lower part) of the methanation catalyst layer was 269°C. The gas after condensation separation consisted of 94.2% methane, 5.3% hydrogen, and 0.5% carbon dioxide, making it a methane-dominant gas with small amounts of hydrogen and carbon dioxide. The ethanol conversion rate was 100%.

[0109] From two hours after the start of the reaction, the inlet temperature of the steam reforming catalyst layer was stably controlled at 299-300°C, the upper temperature of the steam reforming catalyst layer was 397-401°C, and the outlet temperature (lower part) of the methane catalyst layer was 270-271°C, and the reaction continued stably. The gas after condensate separation remained stable at 95% methane, 4% hydrogen, and 1% carbon dioxide, yielding a high-purity methane gas that is easily usable as a raw material for city gas. The ethanol conversion rate remained at 100%. [Table 5]

[0110] [Example 2] The test was conducted in the same manner as in Example 1, except that the gas supplied to the steam reforming catalyst layer was a mixture of 200 mL / min of ethanol, 200 mL / min of hydrogen, and 400 mL / min of water vapor.

[0111] Table 6 shows the inlet temperature of the steam reforming catalyst layer, the upper, middle, and lower temperatures of the steam reforming catalyst layer, the upper, middle, and lower temperatures of the methane catalyst layer, the analysis results of the gas composition after condensate separation, and the ethanol conversion rate at 1, 2, 3, and 4 hours after the start of the reaction.

[0112] The ethanol conversion rate remained stable at 100%. The gas composition after condensate separation remained stable at 85.5% methane, 1.9% hydrogen, and 12.6% carbon dioxide. The resulting gas is mainly methane, but the carbon dioxide concentration is somewhat high. In a typical city gas pipeline network, it is difficult to use it directly as a raw material for city gas, but in city gas pipeline networks with a high upper limit on the permissible carbon dioxide concentration, it may be usable as a raw material for city gas. [Table 6]

[0113] The following is an example of a calculation based on process calculations. Pressure loss and heat loss in each piece of equipment and piping are not considered.

[0114] [Example 3] In this embodiment, as shown in Figure 3, a raw material gas adjustment unit 3 is provided to adjust the composition of the raw material gas before it is supplied to the steam reforming reaction unit 1. Ethanol, hydrogen, and water are supplied to the raw material gas adjustment unit 3 in a molar ratio of 1:2:1.2 and at a pressure of 0.7 MPa (absolute pressure). In the raw material gas adjustment unit 3, these are mixed and heated to 300°C to adjust the raw material gas, and the adjusted gas is then sent to the steam reforming reaction unit 1.

[0115] In the steam reforming reaction section 1, the raw material gas is brought into contact with a steam reforming catalyst under adiabatic conditions, whereby the steam reforming reaction of ethanol, the CO shift reaction and the methanation reaction proceed to reach a chemical equilibrium state, and the produced gas is cooled to 250°C and fed into the methanation reaction section 2.

[0116] In the methanation reaction section 2, the CO shift reaction and the methanation reaction proceed under isothermal conditions of 250°C to reach a chemical equilibrium state, thereby obtaining a fuel gas mainly composed of methane and steam. When this fuel gas is cooled and water is condensed and separated, a fuel gas mainly composed of methane and containing a small amount of hydrogen and carbon dioxide is obtained.

[0117] Table 7 shows the inlet and outlet temperatures in each reaction section, as well as the composition (on a volume basis after dehydration) and carbon activity of the outlet gas. Here, the carbon activity is calculated from the partial pressures of carbon monoxide and carbon dioxide (P CO , P CO2 ) of the outlet gas and the equilibrium constant (K P ) of the thermodynamically calculated disproportionation reaction of carbon monoxide (Equation 7) as K P / (P CO2 / P CO 2 ), and when this value is greater than 1, the carbon deposition reaction proceeds in terms of chemical equilibrium. 2CO → C(solid) + CO₂ (Equation 7) [Table 7]

[0118] The outlet temperature of the steam reforming reaction section 1 is 619°C. The gas composition at the outlet of the steam reforming reaction section 1 is 39.44% methane and 47.48% hydrogen, where the methane concentration is less than 40%, resulting in a gas containing a high concentration of hydrogen.

[0119] The gas composition at the outlet of the methanation reaction section 2 is 96.20% methane, 3.04% hydrogen and 0.76% carbon dioxide, which is a fuel gas with high methane purity (high calorific value fuel gas) that can be used as a city gas raw material.

[0120] At both the outlet of the steam reforming reaction section 1 and the outlet of the methane reaction section 2, the carbon activity is less than 1, and in terms of chemical equilibrium, carbon deposition is avoided.

[0121] In the above, it was assumed that the steam reforming reaction occurs under adiabatic conditions and the methanation reaction occurs under isothermal conditions. However, even in adiabatic reactors, a certain amount of heat is dissipated from the reactor surface, and localized temperature increases can occur even in heat exchange reactors. The catalyst temperature of the methanation catalyst layer is 250°C or higher, and the peak temperature may be 100°C to 200°C higher than 250°C, depending on the balance between heat generation from the reaction and heat removal from heat exchange. The outlet temperature of the steam reforming catalyst layer is 619°C if adiabatic insulation is perfect, but may be 100°C to 200°C lower if adiabatic insulation is not perfect. Therefore, through both the steam reforming catalyst and the methanation catalyst, the minimum temperature of the catalyst layer is 250°C or higher, and the maximum temperature is 619°C or lower. From this perspective, it is desirable that, under conditions where the steam reforming reaction, CO shift reaction, and methanation reaction of ethanol reach equilibrium, the carbon activity is less than 1 in the entire temperature range from 250°C to 619°C, with a molar ratio of ethanol, hydrogen, and water of 1:2:1.2 and a pressure of 0.7 MPa.

[0122] Figure 6 (water vapor / ethanol = 1.2) shows the carbon activity at chemical equilibrium at various temperatures. Since the carbon activity is less than 1 across the entire temperature range from 250°C to 619°C, carbon precipitation is avoided in chemical equilibrium under adiabatic, isothermal, and intermediate conditions.

[0123] [Example 4] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:2:1.5.

[0124] Table 8 shows the inlet and outlet temperatures in each reaction section, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas. [Table 8]

[0125] The outlet temperature of the steam reforming reaction section 1 is 608°C. The gas composition at the outlet of the steam reforming reaction section 1 is 39.14% methane and 47.86% hydrogen. Due to the increase in the amount of added steam, the methane reaction, which produces water as a product, does not proceed in equilibrium, and the methane concentration is slightly lower compared to Example 1.

[0126] The gas composition at the outlet of the methanation reaction section 2 is 95.90% methane, 3.28% hydrogen, and 0.82% carbon dioxide. Although the methane concentration decreases slightly, it becomes a fuel gas (high calorific value fuel gas) with a methane purity high enough to be used as a raw material for city gas.

[0127] At both the outlet of the steam reforming reaction section 1 and the outlet of the methanation reaction section 2, the carbon activity is below 1, which is lower than in Example 3. This is thought to be because increasing the amount of steam added makes carbon precipitation less likely. As shown in Figure 6 (steam / ethanol = 1.5), the carbon activity is below 1 throughout the entire temperature range from 250°C to 608°C, and in equilibrium, carbon precipitation does not occur in the entire temperature range expected for steam reforming and methanation reactions.

[0128] [Example 5] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:2:2.

[0129] Table 9 shows the inlet and outlet temperatures in each reaction section, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas. [Table 9]

[0130] The gas composition at the outlet of the methanation reaction section 2 is 95.42% methane, 3.66% hydrogen, and 0.92% carbon dioxide. Although the methane concentration is slightly lower than in Example 4, it is a fuel gas (high calorific value fuel gas) with a methane purity high enough to be used as a raw material for city gas.

[0131] This gas composition is found to be almost identical to the gas composition obtained in Example 1 (94.9% methane, 4.2% hydrogen, 0.9% carbon dioxide), where the molar ratios of ethanol, hydrogen, and water were the same, and the outlet temperature and reaction pressure of the methanation catalyst layer were almost the same.

[0132] At both the outlet of the steam reforming reaction section 1 and the outlet of the methane reaction section 2, the carbon activity is well below 1. As shown in Figure 6 (steam / ethanol = 2), the carbon activity is below 1 throughout the entire temperature range from 250°C to 591°C, and in equilibrium, no carbon precipitation occurs throughout the entire temperature range expected for the steam reforming and methane reactions.

[0133] [Example 6] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:2:3.

[0134] Table 10 shows the inlet and outlet temperatures in each reaction section, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas. [Table 10]

[0135] The outlet temperature of the steam reforming reaction section 1 is 562°C. This is more than 50°C lower than in Example 3, which is because the temperature rise is mitigated by the increased amount of steam added, and is advantageous in terms of the durability of the steam reforming catalyst.

[0136] The gas composition at the outlet of the methanation reaction section 2 is 94.51% methane, 4.39% hydrogen, and 1.10% carbon dioxide. Although the methane concentration is slightly lower than in Example 5, it is a fuel gas (high calorific value fuel gas) with a methane purity high enough to be used as a raw material for city gas.

[0137] At both the outlet of the steam reforming reaction section 1 and the outlet of the methanation reaction section 2, the carbon activity was well below 1. Furthermore, as shown in Figure 6 (steam / ethanol = 3), the carbon activity remained below 1 throughout the entire temperature range from 250°C to 562°C, indicating that, in equilibrium, carbon deposition does not occur in the entire temperature range expected for steam reforming and methanation reactions.

[0138] [Comparative Example 1] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:2:1.

[0139] Table 11 shows the inlet and outlet temperatures, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas in each reaction section. [Table 11]

[0140] The outlet temperature of the steam reforming reaction section 1 reached 628°C. Furthermore, the carbon activity at the outlet of the steam reforming reaction section 1 exceeded 1. Compared to the example, the lower amount of steam added resulted in a higher outlet temperature and a carbon activity exceeding 1, raising concerns about deterioration of the steam reforming catalyst due to thermal degradation and carbon deposition.

[0141] As shown in Figure 6 (water vapor / ethanol = 1), carbon precipitation does not occur in equilibrium below 580°C. Therefore, it may be possible to avoid carbon precipitation by proceeding with the reaction while removing heat. However, the temperature may locally reach a level close to the outlet temperature of the adiabatic reaction, and controlling this is somewhat difficult.

[0142] [Comparative Example 2] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol and water supplied to the raw material gas adjustment unit 3 was set to ethanol:water = 1:2, and no hydrogen was added.

[0143] Table 12 shows the inlet and outlet temperatures, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas in each reaction section. [Table 12]

[0144] The outlet temperature of the steam reforming reaction section 1 is 518°C. The gas composition at the outlet of the steam reforming reaction section 1 is 49.36% methane and 25.09% hydrogen. The methane concentration is higher compared to Example 1. This is thought to be because the outlet temperature is lower compared to Example 1, making it easier for the methanation reaction to proceed in equilibrium.

[0145] On the other hand, the gas composition at the outlet of the methanation reaction section 2 is 73.87% methane, 1.13% hydrogen, and 25.00% carbon dioxide. Unless the carbon dioxide is removed, it is difficult to use it as a raw material for city gas.

[0146] A further problem is that the carbon activity exceeds 1 at both the outlet of the steam reforming reaction section 1 and the outlet of the methanation reaction section 2, raising concerns about the degradation of the steam reforming catalyst and the methanation catalyst due to carbon deposition. Figure 7 (steam / ethanol = 2.0) shows the carbon activity at each temperature when chemical equilibrium is reached. Since the carbon activity exceeds 1 in the entire temperature range below 700°C, carbon deposition proceeds in chemical equilibrium under adiabatic, isothermal, and intermediate conditions.

[0147] [Comparative Example 3] The calculations were performed using the same method as in Comparative Example 2, except that the molar ratio of ethanol and water supplied to the raw material gas adjustment unit 3 was set to ethanol:water = 1:2.5.

[0148] Table 13 shows the inlet and outlet temperatures in each reaction section, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas. [Table 13]

[0149] The outlet temperature of the steam reforming reaction section 1 reached 502°C, and the carbon activity fell below 1.

[0150] The gas composition at the outlet of the methanation reaction section 2 is 73.66% methane, 1.33% hydrogen, and 25.00% carbon dioxide. Unless the carbon dioxide is removed, it cannot be used as a raw material for city gas. Furthermore, the carbon activity at the outlet of the methanation reaction section 2 exceeds 1, raising concerns about the degradation of the methanation catalyst due to carbon deposition. Figure 7 (water vapor / ethanol = 2.5) shows the carbon activity at chemical equilibrium at various temperatures. Below 340°C, the carbon activity exceeds 1, indicating that if the methanation reaction is carried out at low temperatures to promote methanation, carbon deposition will proceed in chemical equilibrium.

[0151] [Comparative Example 4] The calculations were performed using the same method as in Comparative Example 2, except that the molar ratio of ethanol and water supplied to the raw material gas adjustment unit 3 was set to ethanol:water = 1:3.

[0152] Table 14 shows the inlet and outlet temperatures, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas in each reaction section. [Table 14]

[0153] The temperature at the outlet of the steam reforming reaction section 1 reached 488°C.

[0154] The gas composition at the outlet of the methanation reaction section 2 is 73.46% methane, 1.54% hydrogen, and 25.00% carbon dioxide. Unless the carbon dioxide is removed, it is difficult to use it as a raw material for city gas. At both the outlet of the steam reforming reaction section 1 and the outlet of the methanation reaction section 2, the carbon activity is less than 1, and carbon deposition is avoided in chemical equilibrium. The results of Comparative Examples 2 to 4 show that in simple steam reforming of ethanol without the presence of hydrogen, in order to avoid carbon deposition in equilibrium, it is necessary to add steam so that the molar ratio of steam to ethanol is 3 or more (the molar ratio to the produced methane is 2 or more). Note that, as shown in Figure 5 (steam / ethanol = 3.0), below 245°C, the carbon activity exceeds 1, so if the methanation reaction is carried out below 245°C to advance methanation, carbon deposition may proceed in chemical equilibrium.

[0155] [Example 7] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:2.5:2.

[0156] Table 15 shows the inlet and outlet temperatures, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas in each reaction section. [Table 15]

[0157] The gas composition at the outlet of the methanation reaction section 2 was 80.00% methane and 20.00% hydrogen. Although it contained a relatively high concentration of hydrogen, the concentrations of carbon monoxide and carbon dioxide were both less than 0.01%.

[0158] At both the outlet of the steam reforming reaction section 1 and the outlet of the methane reaction section 2, the carbon activity was well below 1.

[0159] [Example 8] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:1.5:2.

[0160] Table 16 shows the inlet and outlet temperatures, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas in each reaction section. [Table 16]

[0161] The gas composition at the outlet of the methanation reaction section 2 was 91.28% methane, 2.08% hydrogen, and 6.64% carbon dioxide.

[0162] At both the outlet of the steam reforming reaction section 1 and the outlet of the methane reaction section 2, the carbon activity was well below 1.

[0163] [Example 9] The calculations were performed in the same manner as in Example 3, except that the molar ratio of ethanol, hydrogen, and water supplied to the raw material gas adjustment unit 3 was set to ethanol:hydrogen:water = 1:1:2.

[0164] Table 17 shows the inlet and outlet temperatures, as well as the composition (by volume after dehydration) and carbon activity of the outlet gas in each reaction section. [Table 17]

[0165] The gas composition at the outlet of the methanation reaction section 2 was 85.67% methane, 1.63% hydrogen, and 12.70% carbon dioxide.

[0166] This gas composition is found to be almost identical to the gas composition obtained in Example 2 (85.5% methane, 1.9% hydrogen, 12.6% carbon dioxide), where the molar ratios of ethanol, hydrogen, and water were the same, and the methanation catalyst layer outlet temperature and reaction pressure were almost the same.

[0167] At both the outlet of the steam reforming reaction section 1 and the outlet of the methane reaction section 2, the carbon activity was below 1. In Example 2, methane-dominant gas was obtained stably without any change in gas composition over a period of 4 hours. It is presumed that the fact that the carbon activity was well below 1 under these reaction conditions enabled a stable reaction.

[0168] [Example 10] This example shows a calculation example of a fuel gas production process. The process flow is shown in Figure 8.

[0169] The raw material gas adjustment section 3, where the raw material gas adjustment process takes place, is supplied with ethanol, hydrogen, and water at a temperature of 25°C and a pressure of 0.8 MPa, at flow rates of 1 mol / s, 2.0 mol / s, and 2.0 mol / s, respectively. The raw material gas adjustment section 3 is equipped with heat exchangers 31 to 34.

[0170] Ethanol, hydrogen, and water are heated and mixed to form a raw material gas, which is then heated to 300°C and sent to the steam reforming reaction section 1.

[0171] The steam reforming reaction section 1, where the steam reforming process takes place, comprises a steam reforming reactor 11 and a heat exchanger 12. The raw material gas is fed into the steam reforming reactor 11, where the steam reforming reaction of ethanol, the CO shift reaction, and the methane reaction proceed adiabatically. The outlet gas of the steam reforming reactor 11 is cooled to 250°C in the heat exchanger 12 before being fed into the methane reaction section 2.

[0172] The methanation reaction section 2, where the methanation process takes place, comprises a first methanation reactor 21, a heat exchanger 22, a second methanation reactor 23, and a heat exchanger 24.

[0173] The first methanation reactor 21 is an adiabatic reactor, and its outlet gas is cooled to 250°C in the heat exchanger 22 before being sent to the second methanation reactor 23. The second methanation reactor 23 is a heat exchange reactor, and the methanation reaction proceeds while maintaining a temperature of approximately 250°C until the equilibrium composition at 250°C is reached. The outlet gas of the second methanation reactor 23 is cooled in the heat exchanger 24, and after separating the water and dehydrating it, it becomes a fuel gas mainly composed of methane.

[0174] Table 18 shows the temperature and flow rate at key points in the process.

[0175] The composition of the resulting fuel gas (by volume after dehydration) is 95.65% methane, 3.48% hydrogen, 0.87% carbon dioxide, and 2 ppm carbon monoxide. This demonstrates that the method of the present invention can produce a fuel gas with high methane purity (high calorific value fuel gas) that can be used as city gas.

[0176] Furthermore, since the raw material gas is heated to 300°C and introduced into the steam reforming reaction section 1, and the methane reaction proceeds in the second methane reactor 23 while maintaining a temperature of approximately 250°C, the carbon activity at the outlet of each reactor is less than 1, and it is expected that carbon deposition will be avoided in terms of chemical equilibrium. [Table 18]

[0177] [Example 11] The calculations were performed in the same manner as in Example 10, except that the hydrogen flow rate was changed from 2.0 mol / s to 1.0 mol / s. Table 19 shows the temperature and flow rate at key points in the process.

[0178] The composition of the resulting fuel gas (by volume after dehydration) is 85.78% methane, 1.53% hydrogen, 12.69% carbon dioxide, and 18 ppm carbon monoxide.

[0179] Furthermore, since the raw material gas is heated to 300°C and introduced into the steam reforming reaction section 1, and the methane reaction proceeds in the second methane reactor 23 while maintaining a temperature of approximately 250°C, the carbon activity at the outlet of each reactor is less than 1, and it is expected that carbon deposition will be avoided in terms of chemical equilibrium. [Table 19]

[0180] [Example 12] In this embodiment, an example of a fuel gas production process in the form shown in the block flow diagram in Figure 4 is presented. The process flow is shown in Figure 9.

[0181] The raw material gas adjustment section 3, where the raw material gas adjustment process takes place, is supplied with ethanol, hydrogen, and water at a temperature of 25°C and a pressure of 0.8 MPa, at flow rates of 1 mol / s, 1.0 mol / s, and 2.0 mol / s, respectively. The raw material gas adjustment section 3 is equipped with heat exchangers 31 to 34.

[0182] Ethanol, hydrogen, and water are heated and mixed to form a raw material gas, which is then heated to 300°C and sent to the steam reforming reaction section 1.

[0183] The steam reforming reaction section 1, where the steam reforming process takes place, comprises a steam reforming reactor 11 and a heat exchanger 12. The raw material gas is supplied to the steam reforming reactor 11, where the steam reforming reaction of ethanol, the CO shift reaction, and the methane reaction proceed adiabatically. The outlet gas of the steam reforming reactor 11 is cooled to a predetermined temperature in the heat exchanger 12, and then 1.0 mol / s of hydrogen is added from the hydrogen supply line entering the raw material gas adjustment section 3, and the gas is supplied to the methane reaction section 2 at 250°C.

[0184] The methanation reaction section 2, where the methanation process takes place, comprises a first methanation reactor 21, a heat exchanger 22, a second methanation reactor 23, and a heat exchanger 24.

[0185] The first methanation reactor 21 is an adiabatic reactor, and its outlet gas is cooled to 250°C in the heat exchanger 22 before being sent to the second methanation reactor 23. The second methanation reactor 23 is a heat exchange reactor, and the methanation reaction proceeds while maintaining a temperature of approximately 250°C until the equilibrium composition at 250°C is reached. The outlet gas of the second methanation reactor 23 is cooled in the heat exchanger 24, and after separating the water and dehydrating it, it becomes a fuel gas mainly composed of methane.

[0186] Table 20 shows the temperature and flow rate at key points in the process.

[0187] The composition of the resulting fuel gas (by volume after dehydration) is 95.65% methane, 3.48% hydrogen, 0.87% carbon dioxide, and 2 ppm carbon monoxide. This demonstrates that the method of the present invention can produce a fuel gas with high methane purity (high calorific value fuel gas) that can be used as city gas. Furthermore, the carbon activity is less than 1 at the outlet of each reactor, and carbon deposition is avoided in terms of chemical equilibrium.

[0188] Comparing Example 10 and Example 12, the composition of the resulting fuel gas is the same. However, the temperature at the outlet of the steam reforming reactor is 596°C in Example 10, while it is 568°C in Example 12, which is about 30°C lower. This is because, under the conditions of Example 12, there is a stoichiometrically insufficient amount of hydrogen to convert all the carbon in the ethanol into methane, resulting in a lower rate of progress in the exothermic methane reaction. Therefore, introducing some of the hydrogen into the methane reaction inlet, bypassing the steam reforming reactor, has the effect of suppressing the thermal degradation of the catalyst used in the steam reforming reaction. [Table 20]

[0189] [Example 13] In this embodiment, an example of a fuel gas production process is shown in the form of the block flow diagram in Figure 5. The process flow is shown in Figure 10.

[0190] In the raw material gas preparation process, ethanol, hydrogen, and water are supplied at a temperature of 25°C and a pressure of 0.8 MPa, at flow rates of 1 mol / s, 2.0 mol / s, and 2.0 mol / s, respectively. In the raw material gas preparation process, these are heated and mixed, and then mixed with the recycled gas from the outlet of the steam reforming reactor 11. The mixture is heated to 300°C to become the raw material gas, which is then sent to the steam reforming process.

[0191] In the steam reforming process, the raw material gas is introduced into the steam reforming reactor 11, where the reaction proceeds adiabatically. After the outlet gas from the steam reforming reactor 11 is cooled to 250°C, one-third of it is returned to the raw material gas adjustment process via the recycling compressor 5, and the remainder is introduced into the first methanation reactor 21. The first methanation reactor 21 is an adiabatic reactor, and its outlet gas is cooled to 250°C in the heat exchanger 22 before being introduced into the second methanation reactor 23. The second methanation reactor 23 is a heat exchange reactor, where the methanation reaction proceeds while maintaining a temperature of approximately 250°C until the equilibrium composition at 250°C is reached. The outlet gas from the second methanation reactor 23 is cooled in the heat exchanger 24, and after separating the water and dehydrating it, it becomes a fuel gas mainly composed of methane.

[0192] Table 21 shows the temperature and flow rate at key points in the process.

[0193] The composition of the resulting fuel gas (by volume after dehydration) is 95.65% methane, 3.48% hydrogen, 0.87% carbon dioxide, and 2 ppm carbon monoxide. This demonstrates that the method of the present invention can produce a fuel gas with high methane purity (high calorific value fuel gas) that can be used as city gas. Furthermore, the carbon activity is less than 1 at the outlet of each reactor, and carbon deposition is avoided in terms of chemical equilibrium.

[0194] Comparing Example 10 and Example 13, the composition of the resulting fuel gas is the same. However, the temperature at the outlet of the steam reforming reactor is 596°C in Example 10, while in Example 12 it is 559°C, which is about 40°C lower. This is because the temperature rise was suppressed by diluting the reaction gas by recycling a portion of the gas at the outlet of the steam reforming reaction section back to the inlet of the steam reforming reactor. By recycling a portion of the gas at the outlet of the steam reforming reaction section back to the inlet of the steam reforming reactor, the thermal degradation of the catalyst used in the steam reforming reaction is suppressed.

[0195] In Example 13, the molar ratio of hydrogen / ethanol and the molar ratio of water vapor / ethanol at the stage when ethanol is mixed with hydrogen and water vapor are prepared are 2.0. However, because the mixture is mixed with the gas returned from the outlet gas of the water vapor reforming process before being sent to the water vapor reforming process, the molar ratio of hydrogen / ethanol at the inlet of the water vapor reforming process is 2.736 and the molar ratio of water vapor / ethanol is 3.148, which are slightly different. Nevertheless, the value of {(hydrogen) + (ethanol) × 6 + (carbon monoxide)} / {(ethanol) × 2 + (carbon monoxide) + (carbon dioxide)} calculated using the amount of ethanol, hydrogen, carbon monoxide, and carbon dioxide supplied to the water vapor reforming process is 4.0. Therefore, a fuel gas with high methane purity can be obtained because the raw material gases are blended in an appropriate proportion. [Table 21]

[0196] [Example 14] In this embodiment, Figure 2 shows a block flow diagram illustrating an example of a fuel gas production process in which the raw materials supplied to the steam reforming process further contain carbon dioxide. Similar to Example 13, a configuration was adopted in which a portion of the steam reforming reaction outlet gas is returned to the steam reforming reactor inlet.

[0197] In the raw material gas preparation process, ethanol, hydrogen, water, and carbon dioxide are supplied at a temperature of 25°C and a pressure of 0.8 MPa, at flow rates of 1 mol / s, 6.0 mol / s, 2.0 mol / s, and 1.0 mol / s, respectively. In the raw material gas preparation process, these are heated and mixed, and then mixed with the recycled gas from the outlet of the steam reforming reactor 11. The mixture is heated to 300°C to become the raw material gas, which is then sent to the steam reforming process.

[0198] In the steam reforming process, the raw material gas is introduced into the steam reforming reactor 11, where the reaction proceeds adiabatically. After the outlet gas from the steam reforming reactor 11 is cooled to 250°C, one-third of it is returned to the raw material gas adjustment process via the recycling compressor 5, and the remainder is introduced into the first methanation reactor 21. The first methanation reactor 21 is an adiabatic reactor, and its outlet gas is cooled to 250°C in the heat exchanger 22 before being introduced into the second methanation reactor 23. The second methanation reactor 23 is a heat exchange reactor, where the methanation reaction proceeds while maintaining a temperature of approximately 250°C until the equilibrium composition at 250°C is reached. The outlet gas from the second methanation reactor 23 is cooled in the heat exchanger 24, and after separating the water and dehydrating it, it becomes a fuel gas mainly composed of methane.

[0199] Table 22 shows the temperature and flow rate at key points in the process.

[0200] The composition of the resulting fuel gas (by volume after dehydration) is 95.35% methane, 3.72% hydrogen, 0.93% carbon dioxide, and 2 ppm carbon monoxide. This demonstrates that the method of the present invention can produce a fuel gas with high methane purity (high calorific value fuel gas) that can be used as city gas. Furthermore, the carbon activity is less than 1 at the outlet of each reactor, and carbon deposition is avoided in terms of chemical equilibrium.

[0201] In this embodiment, the raw material gas is prepared by mixing ethanol with hydrogen, water vapor, and carbon dioxide. Therefore, the molar ratio of hydrogen to ethanol at the raw material gas preparation stage is 6.0. This is then mixed with the gas returned from the outlet gas of the steam reforming process before being sent to the steam reforming process. As a result, the molar ratio of hydrogen to ethanol at the inlet of the steam reforming process is 7.581, and the molar ratio of water vapor to ethanol is 3.768, which are somewhat high. Nevertheless, the value of {(hydrogen) + (ethanol) × 6 + (carbon monoxide)} / {(ethanol) × 2 + (carbon monoxide) + (carbon dioxide)}, calculated using the molar amounts of ethanol, hydrogen, carbon monoxide, and carbon dioxide supplied to the steam reforming process, is 4.0. Therefore, a fuel gas with high methane purity is obtained because the raw material gas is blended in an appropriate proportion. [Table 22]

[0202] [Other Embodiments] Finally, other embodiments of the method for producing high-calorific value fuel gas 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.

[0203] In the embodiments of Examples 3 to 14, examples in which the steam reforming reactor used in the steam reforming process is configured as an adiabatic reactor were particularly described. However, the reactor used in the steam reforming process according to the present invention is not particularly limited and may be configured as a heat exchange reactor.

[0204] In the embodiments of Examples 10 to 14, examples were particularly described in which the methanation reactor used in the methanation process consisted of an adiabatic first methanation reactor 21 and a heat exchange type second methanation reactor 23. However, the reactor used in the methanation process according to the present invention is not particularly limited as long as the outlet temperature of the catalyst layer at the final stage of the methanation reactor is 230°C or higher and 330°C or lower. It may be configured by connecting two or more adiabatic reactors, or by connecting two or more heat exchange reactors.

[0205] In the embodiments of Examples 10 to 14, examples were particularly described in which the steam reforming reactor and the methane reactor used in the methane process are housed in separate reactors, and further equipped with a heat exchanger, so that the gas exiting the steam reforming reactor is cooled by passing it through the heat exchanger before being inserted into the methane reactor. However, the steam reforming reactor and the methane reactor according to the present invention may be configured as a single unit. For example, by filling a single reactor with the same or different catalysts, and by not providing a heat exchanger near the inlet, or by designing the heat exchange function near the inlet to be smaller than that near the outlet, the reaction may proceed under adiabatic or near-adiabatic conditions in the first half of the reactor, and under isothermal or near-adiabatic conditions in the second half. In this case, the raw material gas is introduced into the steam reforming reactor at 300°C, and the reaction proceeds adiabatically in the first half, with the catalyst layer temperature peaking at, for example, around 400°C. In the second half, the gas produced by the steam reforming reaction is gradually cooled, the methane reaction proceeds, and the reactor is designed to exit at a temperature between 230°C and 330°C. In this case, the steam reforming process is carried out in the first half of the reactor, and the methane process is carried out in the second half.

[0206] 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.

[0207] Furthermore, the present invention does not exclude the use of conventionally known methods for improving methane purity. For example, by adding a small amount of oxygen to the fuel gas after the methane reaction and performing a selective oxidation reaction that selectively oxidizes only hydrogen, it is possible to reduce the amount of hydrogen in the fuel gas after the methane reaction and obtain a fuel gas with higher methane purity.

[0208] In the embodiment of Example 14, the raw material gas contained carbon dioxide, but the embodiment is not limited to this example, and the raw material gas may contain carbon monoxide, or it may contain both carbon monoxide and carbon dioxide.

[0209] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0210] The present invention can be used, for example, as a method for producing fuel gas for supply as city gas. [Explanation of Symbols]

[0211] 1: Steam reforming reaction section 2: Methanation reaction section 3: Raw material gas adjustment section 4: Heat exchanger 5: Recycled compressor 11: Steam reforming reactor 12:Heat exchanger 21: First Methanation Reactor 22: Heat exchanger 23: Second Methanation Reactor 24:Heat exchanger

Claims

1. The process includes: a steam reforming step in which ethanol is brought into contact with a catalyst containing ruthenium or nickel in the presence of hydrogen in an amount such that the hydrogen / ethanol molar ratio is 1.0 or more and 10 or less, and water vapor in an amount such that the water vapor / ethanol molar ratio is 1.2 or more and 5 or less, under conditions that the catalyst inlet temperature is 200°C or more and less than 400°C; and a methane step in which the gas obtained in the steam reforming step is brought into contact with a catalyst containing ruthenium or nickel under conditions that the catalyst outlet temperature is 230°C or more and 330°C or less. A method for producing a high-calorific value fuel gas, wherein the raw material gas supplied to the steam reforming process further contains at least one of carbon monoxide and carbon dioxide.

2. A method for producing a high-calorific value fuel gas according to claim 1, wherein the amount of hydrogen supplied to the steam reforming process is such that the value of {(hydrogen) + (ethanol) × 6 + (carbon monoxide)} / {(ethanol) × 2 + (carbon monoxide) + (carbon dioxide)}, calculated on a molar basis, is 3.9 or more and 4.1 or less.

3. A steam reforming step comprising: contacting ethanol with a catalyst containing ruthenium or nickel in the presence of hydrogen in an amount such that the hydrogen / ethanol molar ratio is 1.0 or more and 10 or less, and water vapor in an amount such that the water vapor / ethanol molar ratio is 1.2 or more and 5 or less, under conditions that the catalyst inlet temperature is 200°C or more and less than 400°C; and a methanation step comprising contacting the gas obtained in the steam reforming step with a catalyst containing ruthenium or nickel under conditions that the catalyst outlet temperature is 230°C or more and 330°C or less. A method for producing a high-calorific value fuel gas, further comprising the step of preparing a raw material gas by adding hydrogen and water vapor to ethanol such that the molar ratio of hydrogen / ethanol is 1.8 or more and 2.2 or less, and the molar ratio of water vapor / ethanol is 1.2 or more and 4 or less, wherein the raw material gas is mixed with a portion of the gas obtained in the water vapor reforming step and then sent to the water vapor reforming step.

4. A steam reforming step comprising: contacting ethanol with a catalyst containing ruthenium or nickel in the presence of hydrogen in an amount such that the hydrogen / ethanol molar ratio is 1.0 or more and 10 or less, and water vapor in an amount such that the water vapor / ethanol molar ratio is 1.2 or more and 5 or less, under conditions that the catalyst inlet temperature is 200°C or more and less than 400°C; and a methane step comprising contacting the gas obtained in the steam reforming step with a catalyst containing ruthenium or nickel under conditions that the catalyst outlet temperature is 230°C or more and 330°C or less, A method for producing a high-calorific value fuel gas, further comprising the step of preparing a raw material gas by adding hydrogen and water vapor to ethanol such that the molar ratio of hydrogen / ethanol is 1.0 or more and less than 1.8, and the molar ratio of water vapor / ethanol is 2 or more and 4 or less, wherein the raw material gas is sent to the water vapor reforming step, and hydrogen is added to the gas obtained in the water vapor reforming step and sent to the methane step.

5. A method for producing a high calorific value fuel gas according to claim 4, wherein the raw material gas prepared by adding hydrogen and water vapor to ethanol is mixed with a portion of the gas obtained in the water vapor reforming step and then sent to the water vapor reforming step.

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