Catalyst, method for producing the same, and method for producing hydrocarbon

Abstract

To provide a catalyst excellent in durability, and capable of stably continuing stable OCM reaction over a comparatively prolonged period of time, and a production method of the same.SOLUTION: A method for producing a catalyst includes the steps of: obtaining catalyst aggregates mutually aggregated in a state where a silica carrier includes a tridymite crystal state and carries an alkali metal, by heating a catalyst precursor made by carrying an alkali metal salt on the silica carrier including a cristobalite crystal state in the presence of water vapor; and obtaining the catalyst by pulverizing the catalyst aggregates.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a catalyst and a method for producing the same, and a method for producing hydrocarbons. [Background technology]

[0002] Oxidative coupling reaction using methane-containing gases such as natural gas A technique for producing hydrocarbons such as olefins by the OCM reaction (Oxidation of Methane Coupling) is known.

[0003] For example, Patent Document 1 proposes a method for producing hydrocarbons having two or more carbon atoms from methane through an OCM reaction using a catalyst (oxidative coupling catalyst) in which an oxide of sodium, manganese, and tungsten or a composite oxide thereof is supported on an inorganic oxide. The invention of Patent Document 1 aims to carry out the OCM reaction with high efficiency and produce hydrocarbons having two or more carbon atoms in high yield. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5493928 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when using conventional catalysts, the catalyst deteriorates within a few tens of hours after the start of the OCM reaction, making it impossible to continue a stable OCM reaction.

[0006] The present invention provides a catalyst having excellent durability that enables stable OCM reactions to continue for a relatively long period of time, a method for producing the catalyst, and a method for producing hydrocarbons using the catalyst. [Means for solving the problem]

[0007] The catalyst according to the present disclosure is a catalyst in which an alkali metal salt is supported on a silica carrier containing tridymite crystals.

[0008] The method for producing a catalyst according to the present disclosure includes the steps of: heating a catalyst precursor, in the presence of water vapor, in which an alkali metal salt is supported on a silica carrier having a cristobalite crystal state, to obtain catalyst agglomerates in which the silica carrier has a tridymite crystal state and supports the alkali metal salt; and pulverizing the catalyst agglomerates to obtain a catalyst.

[0009] The method for producing hydrocarbons according to the present disclosure uses the above catalyst to produce hydrocarbons having two or more carbon atoms from methane through an oxidative coupling reaction of methane. [Effects of the Invention]

[0010] The catalyst according to the present disclosure allows a stable OCM reaction to continue stably for a relatively long period of time. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart illustrating a method for producing a catalyst according to an embodiment of the present disclosure. [Figure 2] 1 is a flowchart illustrating a hydrocarbon production method according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a graph showing the temperature change over time during the OCM reaction of the catalyst prepared in the examples. [Figure 4] FIG. 1 shows the results of an OCM reaction of methane contained in natural gas using the catalyst prepared in the example. [Figure 5] 1 is a photograph showing the results of SEM-EDS analysis of a catalyst prepared in an example. [Figure 6] 1 is an XRD diffraction chart of a catalyst prepared in an example. [Figure 7] 1 is an XRD diffraction chart of a catalyst precursor. [Figure 8] 1 shows XRD diffraction charts before and after a performance evaluation test. DETAILED DESCRIPTION OF THE INVENTION

[0012] Catalyst A first embodiment of the present disclosure is a catalyst in which an alkali metal salt is supported on a silica support containing tridymite in a crystalline state. The term "a silica carrier contains a tridymite crystalline state" means that at least a portion of the silica carrier has a tridymite crystalline structure. Whether or not a silica carrier contains a tridymite crystalline state can be confirmed by observing peaks at specific diffraction angles in XRD. For example, by comparing the XRD diffraction chart of a standard tridymite crystal with the XRD diffraction chart of a silica sample, it can be confirmed by observing the characteristic peaks exhibited by the standard in the sample.

[0013] The catalyst particle size is preferably 300 μm to 5 mm, more preferably 1 to 5 mm, and even more preferably 2 to 4 mm. A larger catalyst particle size can reduce the pressure loss in the catalyst layer during the OCM reaction under pressurized conditions, but the catalyst surface area per unit volume of the catalyst layer is reduced, requiring a larger amount of catalyst to achieve the desired performance. Conversely, a smaller catalyst particle size increases the catalyst surface area per unit volume of the catalyst layer, allowing a smaller amount of catalyst to achieve the desired performance, but increases the pressure loss in the catalyst layer. In OCM reaction facilities (OCM plants), the process gas is pressurized downstream of the OCM reactor using a compressor or other device. The decrease in gas pressure due to pressure loss in the catalyst layer significantly affects the power consumption of the compressor or other device. Therefore, by controlling the catalyst particle size within the above numerical range, the catalyst amount and pressure loss can be optimized. When the particle size of the catalyst varies, it is evaluated by the average particle size, which is given by the median diameter (d50) of the results of measuring the particle sizes of multiple particles measured by a method such as image analysis.

[0014] As the alkali metal salt which is the active component of the catalyst, the active components of conventional oxidative coupling catalysts can be applied, and examples thereof include alkali metal salts of oxides containing at least one of tungsten and zirconium. Examples of oxides containing tungsten or zirconium include tungsten (VI) oxide, tungstic acid, zirconia (ZrO2), and zircon (ZrSiO4). The oxide containing tungsten or zirconium may be a composite oxide of tungsten or zirconium with a metal element other than tungsten or zirconium. The metal elements other than tungsten and zirconium are not particularly limited and include, for example, aluminum, magnesium, calcium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, palladium, silver, indium, tin, iridium, platinum, gold, etc. Among these metal elements, manganese, indium, and tin are preferred because they can further increase the yield of hydrocarbons having 2 to 4 carbon atoms in the OCM reaction, and manganese is more preferred from the viewpoint of increasing the durability of the catalyst.

[0015] Examples of alkali metals constituting the alkali metal salt include sodium, potassium, rubidium, and cesium. Among these alkali metals, potassium is preferred because it has high catalytic activity and excellent heat resistance. This is because sodium tungstate (Na2WO4, melting point 698°C) melts at the operating temperature of the reactor and has poor durability, whereas potassium tungstate (K2WO4, melting point 921°C) does not melt and has excellent durability when the operating temperature of the reactor is set to less than 900°C.

[0016] When the catalyst of this embodiment contains manganese and an alkali metal salt of an oxide, the mass ratio of manganese:alkali metal salt of an oxide:silica is preferably (0.01-5):(0.05-10):(85-99.9), more preferably (0.5-4):(1-8):(88-98.5), and even more preferably (1-3):(2-7):(90-97). When the mass ratio of manganese:alkali metal salt of an oxide:silica is within the above range, the selectivity for hydrocarbons having 2 to 4 carbon atoms in the OCM reaction can be further increased. The mass ratio (mass concentration) of manganese to alkali metal oxide in the mass ratio of manganese to alkali metal oxide to silica can be determined by analyzing the catalyst using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The mass ratio (mass concentration) of silica can be calculated by subtracting the mass ratio (mass concentration) of each active component (manganese and alkali metal) from the total mass of the oxidative coupling catalyst. The mass ratio of manganese:alkali metal oxide:silica can be adjusted by adjusting the concentration and amount of each raw material in the aqueous solution, and the combination thereof.

[0017] When the catalyst of this embodiment contains tin, manganese, and an alkali metal salt of an oxide, the mass ratio of tin:manganese:alkali metal salt of an oxide:silica is preferably (0.01-50):(0.01-5):(0.05-10):(35-99.9), more preferably (2-50):(0.5-4):(1-8):(38-96.5), and even more preferably (10-20):(1-3):(2-7):(70-87). When the mass ratio of tin:manganese:alkali metal salt of an oxide:silica is within the above range, the selectivity to hydrocarbons having 2 to 4 carbon atoms can be further increased in the OCM reaction. The mass ratio (mass concentration) of tin, manganese, and alkali metal in the mass ratio expressed as tin:manganese:alkali metal oxide salt:silica is determined by analyzing the catalyst using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The mass ratio (mass concentration) of silica can be calculated by subtracting the mass ratio (mass concentration) of each active component (tin, manganese, and alkali metal) from the total mass of the oxidative coupling catalyst. The mass ratio of tin:manganese:alkali metal salt of oxide:silica can be adjusted by adjusting the concentration and amount of each raw material in the aqueous solution, and the combination thereof.

[0018] The silica used as the catalyst carrier of this embodiment is not particularly limited as long as it contains a tridymite crystalline state. It may be silica obtained by heat-treating amorphous silica, or silica obtained by heat-treating silica containing cristobalite crystalline state. Examples of amorphous silica include granular silica gel, silica powder, and extrusion-molded calcined silica obtained by extruding a composition in which silica powder is dispersed in a binder to form pellets (extrusion-molded silica), and the like.

[0019] The catalyst of this embodiment is particularly useful as an oxidative coupling catalyst for producing hydrocarbons having two or more carbon atoms from methane.

[0020] <Catalyst manufacturing method> A second embodiment of the present disclosure is a method for producing a catalyst, comprising: a step of heating, in the presence of water vapor, a catalyst precursor including an alkali metal salt supported on a silica carrier having a cristobalite crystal state, to obtain catalyst agglomerates in which the silica carrier has a tridymite crystal state and supports the alkali metal salt; and a step of pulverizing the catalyst agglomerates to obtain a catalyst. Each step (process) will be described in detail below with reference to FIG.

[0021] As shown in FIG. 1 , this embodiment preferably includes the steps of: bringing a silica carrier into contact with an aqueous solution containing an alkali metal salt to obtain an impregnated product in which the silica carrier is impregnated with the aqueous solution; and calcining the impregnated product at 800°C or higher to obtain a catalyst precursor in which the alkali metal salt is supported on a silica carrier in a cristobalite crystalline state.

[0022] The silica carrier used to obtain the impregnated product is preferably amorphous. Examples of amorphous silica include the above-mentioned granular silica gel, silica powder, extruded silica, and extruded calcined silica. The use of amorphous silica facilitates impregnation with an alkali metal salt. By calcining this impregnated product, a catalyst precursor can be easily obtained in which an alkali metal salt is supported on a silica carrier containing cristobalite crystals. Alternatively, a catalyst precursor carrying an alkali metal salt may be obtained by previously impregnating a silica carrier exhibiting cristobalite crystallinity with the aqueous solution.

[0023] The term "cristobalite crystalline state" in a silica carrier means that at least a portion of the silica carrier has a cristobalite crystalline structure. Whether or not the silica carrier contains a cristobalite crystalline state can be confirmed by observing peaks at specific diffraction angles in XRD. For example, by comparing the XRD diffraction chart of a cristobalite crystalline specimen with the XRD diffraction chart of a silica sample, it can be confirmed by observing the characteristic peaks exhibited by the specimen.

[0024] The aqueous solution containing an alkali metal salt to be impregnated into the silica support can be obtained by dissolving an inorganic compound such as a chloride, nitrate, sulfate, carbonate, bicarbonate, or ammonium salt of a metal element, or an organic compound such as an acetate or oxalate, in water. Alternatively, a composite oxide such as potassium tungstate can be dissolved in water to obtain an aqueous solution. The molar concentration of the metal in the aqueous solution can be determined appropriately depending on the performance required of the oxidation coupling catalyst.

[0025] In the step of obtaining the impregnated material, when an impregnated material containing multiple types of metals is used, aqueous solutions each containing one type of metal may be prepared and each aqueous solution may be successively impregnated into the silica support (successive impregnation method), or aqueous solutions each containing multiple types of metals may be co-impregnated into the silica support (co-impregnation method).Of these, the co-impregnation method is preferred because it has excellent production efficiency of the catalyst precursor.

[0026] In the step of calcining the impregnated material to obtain a catalyst precursor, the temperature (calcination temperature) at which the impregnated material is calcined is, for example, 800°C or higher, preferably 850°C or higher, and more preferably 850°C or higher but lower than 900°C. If the calcination temperature is above the lower limit, the alkali metal salt is converted to an oxide or composite oxide containing an alkali metal, and is supported on the calcined silica as a stable active component. Furthermore, amorphous silica becomes crystalline. If the calcination temperature is below the upper limit, melting and volatilization of the active component of the catalyst can be suppressed. In this specification, the "calcination temperature" refers to the set temperature of an oven or the like when calcining an object.

[0027] In the step of calcining the impregnated product to obtain a catalyst precursor, the impregnated product is preferably calcined in an air atmosphere at atmospheric pressure. By calcining at 800°C or higher in this atmosphere, a catalyst precursor containing cristobalite crystals can be easily obtained.

[0028] The time required to calcinate the impregnated product to obtain a catalyst precursor (calcination time) is, for example, preferably 1 to 24 hours, more preferably 2 to 18 hours, and even more preferably 3 to 12 hours. When the calcination time is equal to or greater than the above-mentioned lower limit, the active component is sufficiently supported on the silica. From the viewpoint of productivity, the calcination time is preferably equal to or less than the above-mentioned upper limit. In this specification, the "calcination time" refers to the time during which heating in an oven or the like is maintained after the calcination temperature is reached.

[0029] In the step of heating the catalyst precursor to obtain a catalyst agglomerate, the catalyst precursor is preferably heated in the presence of water vapor. By heating in the presence of water vapor at, for example, 600°C or higher, the desired catalyst agglomerate containing tridymite crystals can be easily obtained.

[0030] The temperature at which the catalyst precursor is heated in the presence of water vapor is preferably 600°C or higher, more preferably 700°C or higher, even more preferably 750°C or higher, and most preferably 800°C or higher but lower than 900°C. At 600°C or higher, tridymite crystal state is easily formed, while at lower than 900°C, melting and volatilization of the active components of the catalyst can be suppressed. In this specification, "heating temperature" refers to the set temperature of the heating device when heating the target.

[0031] When the catalyst precursor is heated in the presence of water vapor, the water vapor concentration is preferably 30 to 90 mol%, more preferably 40 to 80 mol%, even more preferably 50 to 70 mol%, and most preferably 55 to 70 mol% of HO (water vapor) in 100 mol% of an atmospheric gas mixed with an inert gas such as argon or nitrogen. In this case, the inert gas is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, even more preferably 30 to 50 mol%, and most preferably 30 to 45 mol%. With the above preferred water vapor concentration, tridymite crystals are more likely to form.

[0032] The absolute pressure when the catalyst precursor is heated in the presence of water vapor is, in an atmospheric gas mixture of water vapor and an inert gas such as argon or nitrogen, preferably 50 to 500 kPaA, more preferably 100 to 400 kPaA, even more preferably 120 to 300 kPaA, and most preferably 160 to 240 kPaA. At the above preferred absolute pressure, tridymite crystal state is more likely to be formed.

[0033] The time (heating time) for heating the catalyst precursor in the presence of water vapor to obtain a catalyst aggregate is, for example, preferably 10 to 100 hours, more preferably 24 to 72 hours, and even more preferably 30 to 50 hours. The preferred heating time facilitates sufficient formation of tridymite crystals. In this specification, the "heating time" refers to the time during which a predetermined heating temperature is reached and maintained.

[0034] As a method for heating a catalyst precursor to obtain a catalyst aggregate, a method in which the catalyst precursor is heated in the presence of water vapor at 600°C or higher is preferred from the viewpoint of obtaining a catalyst with superior durability, but the production method of the present disclosure is not limited to this. As another method, for example, a raw material gas containing methane and oxygen (methane concentration: 20 to 60 mol%, oxygen concentration: 40 to 80 mol%) may be reacted to generate water vapor, and the heating may be performed under conditions of a heating temperature of 800 to 1100°C, an absolute pressure of 200 to 400 kPaA, and a heating time of 5 to 20 hours.

[0035] Since the catalyst agglomerate obtained after heating is in the form of lumps, it is preferable to crush it and preferably sieve it to make the particle size uniform within the desired range. Crushing and sieving can be performed by a conventional method in this technical field. Sieving is a method of using a mesh sieve to separate particles using a sieve with larger openings than the desired particle size and a sieve with smaller openings than the desired particle size.

[0036] Through the above steps, the catalyst of the first embodiment is obtained in which the silica carrier containing tridymite crystals supports the alkali metal salt and has a uniform particle size of the desired size.

[0037] <Hydrocarbon manufacturing method> A third embodiment of the present disclosure is a hydrocarbon production method in which hydrocarbons having two or more carbon atoms are produced from methane by an oxidative coupling reaction of methane using the catalyst of the first embodiment (see FIG. 2). Specifically, except for using the catalyst of the first embodiment, the method can be carried out in the same manner as a conventional hydrocarbon production method involving an OCM reaction. According to the hydrocarbon production method of this embodiment, the use of the catalyst of the first embodiment allows the oxidative coupling reaction of methane to continue stably for a long period of time.

[0038] The methane used as the reaction feedstock may be pure methane or a methane-containing gas containing other components to the extent that they do not inhibit the OCM reaction. Such methane or methane-containing gas can be obtained from natural gas, methane-containing gas obtained in a high-temperature coal coke oven, methane-containing gas obtained by the hydrogenation reaction of carbon monoxide and carbon dioxide produced from coal cracking gas, or methane-containing gas obtained by the decomposition of hydrocarbons derived from petroleum fractions. Alternatively, methane-containing gas obtained by fermentation or by isolating or purifying the methane from the methane-containing gas can be obtained.

[0039] The OCM reaction can be carried out in an atmosphere in the presence of oxygen, carbon dioxide, nitrous oxide, etc., but is preferably carried out in an atmosphere in the presence of oxygen. Oxygen, air, oxygen-enriched air, and other oxygen-containing gases can be used as the oxygen source for the OCM reaction. Furthermore, it is more preferable to carry out the OCM reaction in an atmosphere where oxygen and water vapor coexist. This is because hydroxyl radicals (OH radicals) are generated from water vapor and active oxygen on the catalyst surface. OH radicals react with methane to generate methyl radicals (CH3 radicals). The oxidative coupling reaction of methane is thought to involve the production of ethane and ethylene from CH3 radicals.

[0040] The water vapor source may be water evaporated in a boiler or the like, or water vapor in the exhaust gas from a boiler or various chemical plants may be used after being isolated or purified as necessary. In addition, water vapor is also produced by the OCM reaction, so this water vapor may also be used.

[0041] The ratio of methane to oxygen and steam used in the OCM reaction is preferably in the range of 0.05 to 0.2 moles of oxygen and 0 to 0.1 moles of steam per mole of methane. When the ratio of oxygen and steam is within the above ranges, hydrocarbons having two or more carbon atoms can be produced safely and in a high yield. In the OCM reaction, an inert gas such as nitrogen, helium, or argon may be present in the reaction atmosphere.

[0042] The temperature (reaction temperature) of the OCM reaction is, for example, preferably 500 to 1100°C, more preferably 600 to 1000°C, and even more preferably 700 to 900°C. When the reaction temperature is equal to or higher than the lower limit, a practical reaction rate can be obtained. When the reaction temperature is equal to or lower than the upper limit, side reactions such as steam reforming reactions, combustion reactions, and polymerization reactions can be suppressed, and the yield of hydrocarbons having two or more carbon atoms can be further increased. In addition, by suppressing melting and volatilization of the active components of the catalyst, the durability of the catalyst can be further improved. In this specification, the "reaction temperature" refers to the temperature inside the catalyst layer of a reactor or the like during the OCM reaction.

[0043] The OCM reaction is preferably carried out under pressurized conditions. This reduces the gas volume, allowing for the downsizing of the reactor used in the OCM reaction. It also reduces the power required for compressors that supply process gas to the purification and separation processes downstream of the reactor. The pressure (reaction pressure) in the OCM reaction is, for example, preferably 0.4 to 1.2 MPa, more preferably 0.5 to 1.1 MPa, and even more preferably 0.6 to 1.0 MPa. When the reaction pressure is equal to or greater than the above lower limit, the reactor in which the OCM reaction is carried out can be made smaller. When the reaction pressure is equal to or less than the above upper limit, side reactions such as combustion reactions and polymerization reactions can be suppressed, and a decrease in the yield of hydrocarbons having two or more carbon atoms can be suppressed. In this specification, the "reaction pressure" is expressed as the total pressure of the raw material gases used in the reaction.

[0044] An example of equipment for carrying out the OCM reaction is a fixed-bed reactor in which a mixture of raw material methane or a methane-containing gas and an atmospheric gas containing oxygen or an oxygen-containing gas, preferably further containing water vapor, is circulated through a reactor packed with a catalyst. The equipment for carrying out the OCM reaction may be a fluidized-bed reactor or a moving-bed reactor. Furthermore, a membrane reactor may be used to suppress combustion of raw material methane by using a high oxygen concentration at the inlet of the catalyst layer, or a reactor that enables a split-feed method in which oxygen is injected separately into each catalyst layer may be used.

[0045] The space velocity in the OCM reaction is, for example, preferably 1,000 to 5,000,000 (1 / h), more preferably 10,000 to 500,000 (1 / h). When the space velocity in the OCM reaction is within the above range, the yield of hydrocarbons having two or more carbon atoms can be further increased. Here, "space velocity" is also called GHSV and means the total volumetric flow rate of the raw material gas per unit volume of the catalyst layer per hour (under conditions of 0°C and 1 atm). The catalyst layer volume means the volume including the catalyst packed in the reaction tube and its voids.

[0046] The reactor may be filled with a single catalyst, or multiple catalysts with different activities may be mixed or layered. If desired, multiple catalysts with different activities, or a single catalyst and an inert inorganic diluent, may be used, so that the activity varies from the inlet to the outlet of the reactor.

[0047] The reactor outlet gas, i.e., the gas containing hydrocarbons with two or more carbon atoms produced by the OCM reaction, has a different composition depending on the reaction raw materials. The target products in the outlet gas, hydrocarbons with two or more carbon atoms, are introduced into known separation and purification equipment and are recovered, purified, recycled, or discharged according to their components to obtain the desired target products, such as ethylene, ethane, propane, propylene, and butane.

[0048] Although the embodiments of the present disclosure have been described in detail above, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present disclosure. Furthermore, the present disclosure is not limited to the embodiments, but is limited only by the scope of the claims. [Example]

[0049] The present disclosure will be described in more detail below using examples, but the present disclosure is not limited to these examples. The raw materials used in this example are as follows:

[0050] [Raw materials used] ·Mn(NO3)2·6H2O: Manganese(II) nitrate hexahydrate. ·Na2WO4: Sodium tungstate. ·SiO2: Silica powder.

[0051] <Production of oxidation coupling catalyst>

[0052] [Example 1] <Catalyst production> 2.09 g of Mn(NO3)2·6H2O raw powder and 1.00 g of Na2WO4 raw powder were added to 9.3 mL of ultrapure water (three times the volume of the raw powder) and stirred to prepare a raw solution. The raw solution was added to 18.6 g of amorphous SiO2 powder, and 54.6 mL of ultrapure water was added. The SiO2 powder was brought into contact with the raw solution, resulting in an impregnated product in which the SiO2 powder was impregnated with the raw solution. The impregnated material was heated at 130°C for 5 hours in an air atmosphere to dry and evaporate the water. After drying, the impregnated material was heated at a temperature increase rate of 2°C / min, calcined at 900°C for 8 hours, and then cooled at a cooling rate of 20°C / min to obtain a catalyst precursor, which was the calcined product of the impregnated material. The obtained catalyst precursor was filled into a hand press with a diameter of 20 mm and compression-molded into cylindrical pellets under a pressure of 40 MPa. The obtained pellets were crushed in a crusher and classified using sieves with openings of 250 μm and 500 μm to obtain catalyst precursors with particle sizes of 250 to 500 μm.

[0053] The rational formula of the catalyst precursor produced here is expressed as Mn(2 wt%)Na2WO4(5 wt%) / SiO2, where "wt%" represents the mass ratio of the metal element to the total mass of the catalyst precursor.

[0054] <Catalyst production> (Heat treatment to form tridymite in the presence of water vapor 1) Regarding the catalyst precursor obtained above: 2Mn / 5Na2WO4 / SiO2 (catalyst particle median diameter is 0.3 mm), a quartz tube with an ID of 4 mm was filled with the catalyst (600 mg), and at a pressure of 201 kPaA, a raw material gas with an Ar concentration of 33.3 mol% and a H2O concentration of 66.6 mol% was flowed at a flow rate of 120 ml / min for 30 hours. The quartz tube was installed inside an electric furnace, and the temperature of the electric furnace was set at 700 °C. After that, since the extracted catalyst aggregate was in a lump, it was crushed and sieved to obtain a catalyst (1) with a median diameter of 0.3 mm. This was filled into the quartz tube again.

[0055] <SEM-EDS Analysis> The results of SEM observation of the above oxidative coupling catalyst are shown in Fig. 5. As the microstructure of the surface of the silica carrier, it was confirmed that the size was about 1 μm in the catalyst precursor, while it was about 10 μm after tridymite treatment. As the catalyst surface structure, the finer the size, the larger the catalyst specific surface area and the higher the reaction rate, so the smaller the size, the more preferable. "Microstructure" refers to the irregularities on the surface of the silica carrier. Here, the size of the microstructure is defined as the average value of 10 or more irregularities observed in the SEM image.

[0056] <XRD Analysis> As a result of performing XRD analysis on the above oxidative coupling catalyst, diffraction peaks indicating the cristobalite crystal state of silica were confirmed in the catalyst precursor, and no diffraction indicating the tridymite crystal state was observed. Fig. 7 shows the crystal peaks of the catalyst precursors adjusted under various active component conditions. On the other hand, in the catalyst (1) obtained under the heat treatment conditions of this example "67 kPa Ar + 134 kPa H2O (700 °C)", as shown in Fig. 6, diffraction indicating the tridymite crystal state of silica was observed overlapping with the diffraction peak of cristobalite. In addition, Fig. 6 shows the diffraction peaks of a standard sample of tridymite crystal of silica and a standard sample of cristobalite crystal of silica for reference. These results indicate that tridymite silica crystals are not contained in the catalyst precursor, but are contained only in catalyst (1).

[0057] [Example 2] (Heat treatment to form tridymite in the presence of water vapor 2) Catalyst (2) was obtained in the same manner as in Example 1, except that the set temperature of the electric furnace was changed to 750°C. The oxidative coupling reaction of methane using the obtained catalyst (2) was stable for a long period of time. When analyzed by XRD, diffraction peaks indicating the tridymite crystalline state of silica were observed overlapping with the diffraction peaks of cristobalite, as shown in Figure 6 for "67 kPa Ar + 134 kPa HO (750°C)."

[0058] [Example 3] <Catalyst production> (Heat treatment to form tridymite in the presence of water vapor 3) Catalyst (3) was obtained in the same manner as in Example 1, except that the set temperature of the electric furnace was changed to 800°C. The oxidative coupling reaction of methane using the obtained catalyst (3) was stable for a long period of time. When analyzed by XRD, diffraction peaks indicating the tridymite crystalline state of silica were observed overlapping with the diffraction peaks of cristobalite, as shown in Figure 6 for "67 kPa Ar + 134 kPa HO (800°C)."

[0059] [Comparative Example 1] (Heat treatment in the presence of water vapor) Catalyst particles were obtained in the same manner as in Example 2, except that the set temperature of the electric furnace was changed to 500°C. When analyzed by XRD, as shown in "67 kPa Ar + 134 kPa HO (500°C)" in Figure 6, no diffraction peak of tridymite of silica was observed, and only diffraction peaks of cristobalite were observed. This is thought to be because the set temperature of the electric furnace was too low.

[0060] Comparative Example 2 (Heat treatment without steam) Catalyst particles were obtained in the same manner as in Example 2, except that a raw material gas with an Ar concentration of 100 mol% was used at a pressure of 201 kPaA. When analyzed by XRD, as shown in "201 kPa Ar (800°C)" in Figure 6, no diffraction peaks of tridymite silica were observed, and only diffraction peaks of cristobalite were observed. This is thought to be due to the absence of water vapor in the raw material gas.

[0061] [Example 4] <Catalyst production> (Tridymite treatment in the presence of water vapor generated from methane) A catalyst precursor (2Mn / 5Na2WO4 / SiO2) (median particle diameter: 0.3 mm) was prepared in the same manner as in Example 1. A quartz tube with a diameter of 4 mm (ID) was filled with 600 mg of catalyst. A source gas containing 40 mol% CH4 and 60 mol% O2 was passed through the tube at a flow rate of 120 mL / min for 10 hours at a pressure of 300 kPaA. The quartz tube was placed inside an electric furnace, which was set at 1000°C. CH4 and O2 were reacted in the presence of the catalyst to generate water vapor. The catalyst aggregates extracted from the quartz tube were then crushed and sieved to obtain catalyst (4) with a median particle diameter of 0.3 mm. This catalyst was then repacked into the quartz tube.

[0062] The oxidative coupling reaction of methane using the catalyst (4) obtained above was stable for a long period of time, as shown in the test described below (Figure 4). XRD analysis showed that the crystal peak position of the tridymite-treated catalyst did not change before and after the test, suggesting that there was no change in the crystalline state of the silica (Figure 8 shows the results).

[0063] <Hydrocarbon production> The catalyst (4) was packed into a pressurizable reactor, and hydrocarbons were produced by the methane oxidative coupling reaction using methane and oxygen as raw materials. An inert quartz tube with no catalytic activity was used as the reactor. The temperature during the reaction in the catalyst bed packed in the quartz tube was observed with an infrared camera. As shown in Figure 3, the high temperature range of 830 to 850 °C observed at the top of the catalyst bed where the feed gas flowed disappeared after the middle stage of the reaction (130 hours), and the entire catalyst bed operated stably at a nearly uniform temperature. A uniform temperature distribution in the catalyst bed can suppress catalyst deterioration and is a necessary condition for stable operation. Although not applicable to this example, a state in which the catalyst bed is hot in spots is undesirable because it causes rapid catalyst deterioration and unstable operation. The methane conversion rate (the proportion of methane converted in the reactor) and C2+ selectivity (the proportion of hydrocarbons with carbon numbers of 2 to 4 among the products obtained) were measured. As shown in Figure 4, the use of catalyst (4) achieved stabilization of the oxidative coupling reaction of methane, and the reaction proceeded particularly stably after 130 hours. Stable performance was confirmed for approximately 270 hours.

[0064] From the above results, it was confirmed that the method for producing hydrocarbons using the catalyst according to the present disclosure has durability that allows the oxidative coupling reaction of methane to continue stably for a long period of time. Furthermore, it was confirmed that the method for producing a catalyst according to the present disclosure can produce a catalyst that contains a tridymite crystal state and has excellent durability.

[0065] <Additional Notes> The catalyst, the method for producing the catalyst, and the method for producing hydrocarbons described in the above-described embodiments can be understood, for example, as follows.

[0066] (1) The catalyst according to the first aspect is a catalyst in which an alkali metal salt is supported on a silica carrier containing tridymite crystals.

[0067] According to the above-mentioned configuration, the catalyst has durability that allows the oxidative coupling reaction of methane to continue stably for a long period of time, and can be used for producing hydrocarbons having two or more carbon atoms.

[0068] (2) A catalyst according to a second aspect is the catalyst according to (1), wherein the size of the microstructure of the silica support is 1 to 10 μm.

[0069] According to the above configuration, the smaller the size, the larger the specific surface area of ​​the catalyst, and the faster the reaction rate.

[0070] (3) A catalyst according to a second aspect is the catalyst according to any one of (1) and (2), wherein the median particle diameter of the silica support is 300 μm to 5 mm.

[0071] According to the above-mentioned configuration, in a usage form in which the reaction tube is filled with a catalyst, the pressure loss of the gas flowing through the reaction tube can be further reduced.

[0072] (4) A catalyst according to a third aspect is any one of the catalysts (1) to (3), which contains sodium or potassium as the alkali metal.

[0073] According to the above configuration, the oxidative coupling reaction of methane can be made more efficient.

[0074] (5) A catalyst according to a fourth aspect is the catalyst according to any one of (1) to (4), wherein the alkali metal salt is an alkali metal salt of an oxide containing at least one of tungsten and zirconium.

[0075] According to the above configuration, the oxidative coupling reaction of methane can be made more efficient.

[0076] (6) A catalyst according to a fifth embodiment is any one of the catalysts (1) to (5), which further supports manganese.

[0077] According to the above configuration, the oxidative coupling reaction of methane can be made more efficient.

[0078] (7) A catalyst according to a sixth embodiment is any one of the catalysts (1) to (6), which is an oxidative coupling catalyst that produces hydrocarbons having two or more carbon atoms from methane.

[0079] According to the above-mentioned configuration, the catalyst has durability that allows the oxidative coupling reaction of methane to continue stably for a long period of time, and can be used for producing hydrocarbons having two or more carbon atoms.

[0080] (8) A method for producing a catalyst according to a seventh aspect includes the steps of: heating a catalyst precursor, in the presence of water vapor, in which an alkali metal salt is supported on a silica carrier having a cristobalite crystal state, to obtain a catalyst agglomerate in which the silica carrier has a tridymite crystal state and supports the alkali metal salt; and pulverizing the catalyst agglomerate to obtain a catalyst.

[0081] According to the above-described configuration, a catalyst having excellent durability and containing tridymite crystals can be produced.

[0082] (9) The eighth aspect of the catalyst production method is the catalyst production method of (8), in which the catalyst precursor is heated at 700° C. or higher in the presence of water vapor.

[0083] According to the above-mentioned configuration, a catalyst containing a larger amount of tridymite crystals and having better durability can be produced.

[0084] (10) A ninth aspect of the catalyst production method is the catalyst production method according to any one of (8) to (9), further comprising a step of sieving the pulverized catalyst.

[0085] According to the above-mentioned configuration, the particle diameter of the catalyst packed in the reaction tube can be made uniform, and the pressure loss of the gas flowing through the reaction tube can be further reduced.

[0086] (11) A tenth aspect of the method for producing hydrocarbons involves using the catalyst according to any one of (1) to (7) to produce hydrocarbons having two or more carbon atoms from methane through an oxidative coupling reaction of methane.

[0087] According to the above-mentioned configuration, the oxidative coupling reaction of methane can be continued stably for a long period of time, and the production efficiency of hydrocarbons having two or more carbon atoms can be increased.

Claims

1. A catalyst comprising an alkali metal salt supported on a silica carrier containing tridymite crystals.

2. 2. The catalyst according to claim 1, wherein the median particle size of the silica support is 300 μm to 5 mm.

3. 2. The catalyst of claim 1, wherein the silica support has a microstructure size of 1 to 10 μm.

4. 2. The catalyst of claim 1, wherein the alkali metal comprises sodium or potassium.

5. 2. The catalyst according to claim 1, wherein the alkali metal salt is an alkali metal salt of an oxide containing at least one of tungsten and zirconium.

6. The catalyst of claim 5, further comprising supported manganese.

7. The catalyst according to any one of claims 1 to 6, which is an oxidative coupling catalyst for producing hydrocarbons having two or more carbon atoms from methane.

8. A method for producing a catalyst, comprising: a step of heating a catalyst precursor, in the presence of water vapor, in which an alkali metal salt is supported on a silica carrier having a cristobalite crystal state, to obtain a catalyst agglomerate in which the silica carrier has a tridymite crystal state and supports the alkali metal salt; and a step of pulverizing the catalyst agglomerate to obtain a catalyst.

9. The method for producing a catalyst according to claim 8, wherein the catalyst precursor is heated at 700°C or higher in the presence of water vapor.

10. The method for producing a catalyst according to claim 9, further comprising the step of sieving the pulverized catalyst.

11. A method for producing hydrocarbons, comprising: using the catalyst according to any one of claims 1 to 6 to produce hydrocarbons having two or more carbon atoms from methane by an oxidative coupling reaction of methane.

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