Method for producing catalyst for fischer-tropsch synthesis

Abstract

The present invention provides a method for producing a catalyst for Fischer-Tropsch synthesis, with which the activity of the catalyst for Fischer-Tropsch synthesis does not deteriorate or is suppressed from deteriorating. More specifically, provided is a method for producing a catalyst for Fischer-Tropsch synthesis, the method comprising: a step for producing a catalyst precursor by causing a carrier to support a cobalt compound; a step for producing an unreduced catalyst containing a cobalt oxide by drying and firing the catalyst precursor; and a step for reducing the unreduced catalyst to obtain a catalyst that is for FT synthesis and that includes a reduced product of the unreduced catalyst. The unreduced catalyst reduction step includes subjecting the unreduced catalyst to a reduction treatment in a reducing gas and at a first temperature, and thereafter, lowering the temperature to a second temperature, followed by substitution with nitrogen. The first temperature is 300-400°C, and the second temperature is 60-210°C.

Description

Method for producing a catalyst for Fischer-Tropsch synthesis REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority based on Japanese Patent Application No. 2024-057623 filed on March 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a method for producing a catalyst for Fischer-Tropsch synthesis.

[0003] The reaction for synthesizing hydrocarbons from synthesis gas mainly composed of hydrogen and carbon monoxide is called Fischer-Tropsch synthesis (hereinafter also referred to as FT synthesis), and is used for producing fuels, etc. As catalysts for use in this FT synthesis reaction, for example, Patent Document 1 discloses a catalyst in which an active metal such as cobalt or iron is supported on a support such as silica or alumina, and Patent Document 2 discloses a catalyst containing cobalt, zirconium or titanium, and silica.

[0004] JP-A-4-227847 JP-A-59-102440

[0005] In catalyst production, from the viewpoint of efficiency, it is desired to reduce the time required for the reaction and the amount of costly reducing gas such as hydrogen used. However, a method for producing a catalyst for Fischer-Tropsch synthesis that reduces the time required for the reaction and the amount of hydrogen gas used has not yet been obtained.

[0006] The present inventors have found that if the reducing gas is switched to nitrogen early during temperature decrease (i.e., at as high a temperature as possible) in order to shorten the time required for the reaction and / or reduce the amount of reducing gas such as hydrogen gas used, the activity of the Fischer-Tropsch synthesis catalyst decreases.

[0007] As a result of extensive research, the present inventors have now found that replacing the reducing gas with nitrogen within a specific temperature range prevents or suppresses the decline in catalytic activity. The present invention is based on this finding.

[0008] Therefore, the present invention provides a method for producing a catalyst for FT synthesis in which the activity of the catalyst for FT synthesis does not decrease or the decrease in the activity of the catalyst is suppressed.

[0009] That is, the present invention provides the following: (1) A method for producing a catalyst for Fischer-Tropsch synthesis, comprising the steps of: supporting a cobalt compound on a carrier to produce a catalyst precursor; drying and calcining the catalyst precursor to produce an unreduced catalyst containing cobalt oxide; and reducing the unreduced catalyst to obtain a catalyst for Fischer-Tropsch synthesis composed of a reduced product of the unreduced catalyst, wherein the unreduced catalyst reduction step comprises reducing the unreduced catalyst under a reducing gas at a first temperature, and then lowering the temperature to a second temperature and replacing the gas with nitrogen, wherein the first temperature is 300 to 400°C, and the second temperature is 60 to 210°C. (2) The production method according to (1), wherein the reducing gas is selected from the group consisting of hydrogen, carbon monoxide, a mixed gas of hydrogen and nitrogen, and a mixed gas of carbon monoxide and nitrogen. (3) The production method according to (1) or (2), wherein the unreduced catalyst reduction step further comprises raising the temperature from room temperature to the first temperature via the second temperature, and wherein the concentration of hydrogen or carbon monoxide in the reducing gas at the second temperature is at least 90% by volume. (4) The production method according to any one of (1) to (3), wherein the difference between the first and second temperatures in the reduction step is 150 to 300°C. (5) The production method according to any one of (1) to (4), wherein the reduction step comprises maintaining the first temperature for 3 to 48 hours. (6) The production method according to any one of (1) to (5), wherein the second temperature in the reduction step is 100 to 200°C. (7) The production method according to any one of (1) to (6), wherein the reduction step comprises maintaining the second temperature for 0.1 to 7 hours during temperature reduction.

[0010] In the production of a Fischer-Tropsch synthesis catalyst, the unreduced catalyst reduction step includes performing a reduction treatment of the unreduced catalyst at a first temperature of 300 to 400°C, followed by cooling to a second temperature of 60 to 210°C and then replacing the gas with nitrogen. This allows the production of a Fischer-Tropsch synthesis catalyst without reducing the activity of the catalyst or while suppressing a decrease in the activity of the catalyst. The present invention is advantageous in that it allows the switching from reducing gas to nitrogen early during temperature reduction (i.e., at as high a temperature as possible), thereby preventing a decrease in the activity of the Fischer-Tropsch synthesis catalyst or suppressing a decrease in the activity of the catalyst. Furthermore, the present invention is advantageous in that it reduces the time required for the reaction (particularly the cooling time during temperature reduction) during the production of a Fischer-Tropsch synthesis catalyst. Furthermore, the present invention is advantageous in that it reduces the amount of reducing gas used during the production of a Fischer-Tropsch synthesis catalyst. Specifically, in the present invention, by switching from reducing gas to nitrogen at an early timing during temperature drop, consumption of reducing gas, which is more expensive than nitrogen, can be reduced compared to the conventional method of switching from reducing gas to nitrogen after the temperature has dropped to room temperature, which is economically advantageous.

[0011] 1 is a conceptual diagram of an embodiment of the present invention regarding the temperature profile of the reduction step (i.e., the temperature increasing step, the reduction treatment step, and the temperature decreasing step). It shows the temperature profile of the reduction step in Example 1 and Comparative Example 1.

[0012] The method for producing a catalyst for Fischer-Tropsch synthesis of the present invention comprises the steps of: supporting a cobalt compound on a carrier to produce a catalyst precursor; drying and calcining the catalyst precursor to produce an unreduced catalyst containing cobalt oxide; and reducing the unreduced catalyst to obtain a catalyst for Fischer-Tropsch synthesis comprising a reduced product of the unreduced catalyst. The unreduced catalyst reduction step comprises reducing the unreduced catalyst in a reducing gas at a first temperature, and then lowering the temperature to a second temperature and purging the catalyst with nitrogen. One of the features of the method is that the first temperature is 300 to 400°C, and the second temperature is 60 to 210°C.

[0013] [Unreduced Catalyst] The unreduced catalyst of the present invention may include a support and a cobalt oxide supported on the support. According to one embodiment of the present invention, the support may be a support containing zirconium oxide, preferably a support containing silica together with zirconium oxide. According to another embodiment of the present invention, the support may be a support obtained by calcining a support precursor containing a zirconium compound, preferably a support obtained by calcining a support precursor containing silica and a zirconium compound.

[0014] The cobalt oxide of the present invention includes tricobalt tetroxide, cobalt (II) oxide, and cobalt (III) oxide, with tricobalt tetroxide being preferred.

[0015] According to one embodiment of the present invention, the cobalt content in the unreduced catalyst is preferably 10 to 40 mass%, and more preferably 10 to 30 mass%, based on the total mass of the unreduced catalyst. Use of such an unreduced catalyst makes it possible to obtain an FT synthesis catalyst with higher reaction activity. According to another embodiment of the present invention, the cobalt oxide content in the unreduced catalyst is preferably 10 to 50 mass%, and more preferably 15 to 35 mass%, calculated as cobalt oxide, based on the total mass of the unreduced catalyst.

[0016] According to one embodiment of the present invention, the zirconium content in the unreduced catalyst may be 0.1 to 10 mass% in terms of zirconium oxide, based on the total mass of the unreduced catalyst. From the viewpoints of improving the reducibility of cobalt and suppressing a decrease in initial activity, the zirconium content in the unreduced catalyst is preferably 0.5 to 8 mass%, more preferably 1 to 7 mass%, and particularly preferably 3 to 6 mass%.

[0017] According to one embodiment of the present invention, the unreduced catalyst of the present invention may further contain a precious metal. The precious metal is preferably one or more of Pt, Pd, Au, and Re, and more preferably Pt. The inclusion of a precious metal can promote the reduction of cobalt. This can suppress the oxidation of cobalt metal by water produced during the Fischer-Tropsch synthesis reaction, which is thought to be a cause of catalyst deterioration.

[0018] In terms of the balance between the above-mentioned effects and economic efficiency, the amount of the noble metal carried is preferably 0.001 to 1 mass %, more preferably 0.001 to 0.5 mass %, based on the total mass of the unreduced catalyst.

[0019] According to one embodiment of the present invention, the specific surface area of ​​the unreduced catalyst of the present invention is 100 m ２ / g or more, and 100 to 400m ２ / g, and more preferably 110 to 200m ２ / g. It is more preferable that the specific surface area is 100 m ２ / g or more, the catalyst deterioration at the initial stage of the reaction tends to be more significantly suppressed. ２ When the average molecular weight is 1 / g or less, catalyst wear is unlikely to occur, and catalyst deterioration due to wear loss during the reaction is further suppressed.

[0020] The specific surface area of ​​the unreduced catalyst is calculated by the following method. First, in order to remove moisture adsorbed on the unreduced catalyst, a pretreatment is carried out, for example, by evacuating the catalyst to a vacuum at 300°C for 5 hours. For the catalyst after this pretreatment, an adsorption / desorption isotherm is obtained by a constant volume gas adsorption method using nitrogen at the temperature of liquid nitrogen (-196°C). From the obtained nitrogen adsorption / desorption isotherm, the surface area (m ) per unit mass of the unreduced catalyst is calculated by the BET equation. ２ The adsorption / desorption isotherm is measured and calculated using, for example, a BELSORP-max manufactured by Microtrac-Bell Corporation.

[0021] According to one embodiment of the present invention, the silica to be used preferably is at least one selected from the group consisting of colloidal silica, water glass, aerosil, aerogel, silica sol, silica gel, powdered silica, and silicates.

[0022] According to one embodiment of the present invention, the carrier precursor can be prepared, for example, by an impregnation method, typically an incipient wetness method, using silica and a zirconium compound.

[0023] The zirconium compound is zirconyl nitrate (ZrO(NO ３ ) ２ ), zirconium oxychloride (ZrOCl ２ ), zirconium hydroxide oxochloride (ZrO(OH)Cl), zirconyl sulfate (ZrOSO ４ ), zirconyl acetate (ZrO(C ２ H ３ O ２ ) ２ ), ammonium zirconyl carbonate ((NH ４ ) ２ ZrO(CO ３ ) ２ Among these, ammonium zirconyl carbonate, zirconyl nitrate, and zirconyl acetate are preferred. The zirconium compounds can be used alone or in combination of two or more.

[0024] According to another embodiment of the present invention, the carrier precursor may contain, as a carrier material other than silica, one or more selected from the group consisting of alumina, titania, magnesia, ceria, zirconia, and composite oxides thereof, such as silica-alumina, silica-titania, alumina-titania, silica-zirconia, alumina-zirconia, and titania-zirconia.

[0025] The carrier precursor can be prepared by an impregnation method, such as the incipient wetness method. After impregnation, the carrier precursor can be dried at a drying temperature of, for example, 50 to 150°C, more preferably 70 to 120°C, for preferably 0.5 to 48 hours, more preferably 1 to 24 hours.

[0026] The support precursor can be calcined after the drying at a calcination temperature of, for example, 200 to 800°C, preferably 350 to 650°C, for, for example, 0.5 to 48 hours, preferably 1 to 24 hours. By calcining the support precursor, a support can be obtained. The calcination temperature is preferably equal to or higher than the decomposition initiation temperature of the zirconium compound used.

[0027] According to one embodiment of the present invention, the unreduced catalyst of the present invention may be produced by a production method including the steps of calcining a carrier precursor containing silica and a zirconium compound to obtain a carrier, producing a catalyst precursor by supporting a cobalt compound on the carrier, and drying and calcining the catalyst precursor to produce an unreduced catalyst comprising a cobalt oxide.

[0028] [Method for Producing a Fischer-Tropsch Synthesis Catalyst] According to one embodiment of the present invention, the method for producing a catalyst for FT synthesis of the present invention comprises a reduction step of obtaining a catalyst for FT synthesis by reducing an unreduced catalyst.

[0029] According to a preferred embodiment of the present invention, the method for producing a catalyst for Fischer-Tropsch synthesis of the present invention comprises the steps of: supporting a cobalt compound on a carrier to produce a catalyst precursor; drying and calcining the catalyst precursor to produce an unreduced catalyst comprising a cobalt oxide; and reducing the unreduced catalyst to obtain a catalyst for Fischer-Tropsch synthesis comprising a reduced product of the unreduced catalyst; wherein the unreduced catalyst reduction step comprises reducing the unreduced catalyst in a reducing gas at a first temperature, and then lowering the temperature to a second temperature and replacing the gas with nitrogen; wherein the first temperature is 300 to 400°C; and the second temperature is 60 to 210°C.

[0030] [Step of Producing a Catalyst Precursor by Supporting a Cobalt Compound on a Support] According to one embodiment of the present invention, an impregnation method, typified by an incipient wetness method or a pore filling method, can be used as a method for producing a catalyst precursor by supporting a cobalt compound on a support.

[0031] As the cobalt compound, a compound having cobalt in the form of a salt or complex in the molecule can be used. Examples include nitrate, hydrochloride, sulfate, formate, acetate, propionate, oxalate, and acetylacetonate. Specific examples include cobalt nitrate, cobalt chloride, cobalt formate, cobalt propionate, cobalt acetate, and cobalt acetylacetonate. The cobalt compound can be used alone or in combination of two or more.

[0032] In the method for producing a catalyst precursor, the content of the cobalt compound in the catalyst precursor is preferably set to 10 to 40 mass% in cobalt equivalent based on the total mass of the unreduced catalyst. From the viewpoint of obtaining high reactivity, the content of the cobalt compound in the catalyst precursor is more preferably 10 to 30 mass% in cobalt equivalent based on the total mass of the unreduced catalyst.

[0033] [Step of drying and calcining the catalyst precursor to produce an unreduced catalyst comprising cobalt oxide] According to one embodiment of the present invention, the catalyst precursor can be dried and calcined to produce an unreduced catalyst comprising cobalt oxide. After impregnation, the catalyst precursor can be dried, for example, at a drying temperature of 50 to 150°C, preferably 70 to 130°C, for preferably 0.5 to 48 hours, more preferably 1 to 24 hours, and even more preferably 8 to 15 hours.

[0034] The calcination temperature of the catalyst precursor is preferably 250 to 650°C, and from the viewpoint of obtaining high dispersibility of the cobalt compound, more preferably 350 to 650°C, and even more preferably 400 to 500°C. The calcination temperature is preferably equal to or higher than the decomposition starting temperature of the cobalt compound used. The calcination time of the catalyst precursor can be, for example, 0.1 to 48 hours, preferably 0.5 to 24 hours, more preferably 1 to 10 hours, and particularly preferably 2 to 5 hours.

[0035] [Step of reducing unreduced catalyst] In the step of reducing the unreduced catalyst, a reduction treatment of the unreduced catalyst can be performed by contacting the unreduced catalyst with a reducing gas. Specific reducing gases used in the reduction treatment include hydrogen gas, carbon monoxide gas, a mixed gas of hydrogen and nitrogen, and a mixed gas of carbon monoxide and nitrogen, with hydrogen gas being preferred. When the reducing gas is a mixed gas of hydrogen and nitrogen, the ratio may be, for example, 90% by volume or more of hydrogen and less than 10% by volume of nitrogen, preferably 95% by volume or more of hydrogen and less than 5% by volume of nitrogen, and more preferably 97% by volume or more of hydrogen and less than 3% by volume of nitrogen.

[0036] Furthermore, the reduction step of the unreduced catalyst described above includes performing a reduction treatment of the unreduced catalyst under a reducing gas at a first temperature, then lowering the temperature, lowering the temperature to a second temperature, and then replacing the atmosphere with nitrogen (preferably, performing a purging treatment), wherein the first temperature is 300 to 400°C and the second temperature is 60 to 210°C.

[0037] The reduction step includes a reduction treatment in which a reducing gas is brought into contact with the unreduced catalyst. Before and after the reduction treatment (usually before the temperature-raising step and after the temperature-lowering step), the environment in which the reduction treatment is performed (for example, inside a catalyst production facility described below, a reduction reactor, a reduction reaction tower, etc.) is filled with nitrogen gas in order to remove hydrogen gas and carbon monoxide gas, which are likely to cause explosive reactions.

[0038] The upper limit of the first temperature in the reduction step of the present invention is 400°C, preferably 390°C, more preferably 380°C, and even more preferably 370°C. The lower limit of the first temperature in the reduction step of the present invention is 300°C, preferably 320°C, more preferably 330°C, and even more preferably 340°C. According to another embodiment of the present invention, the first temperature is 300 to 400°C, preferably 320 to 390°C, more preferably 330 to 380°C, and even more preferably 340 to 370°C.

[0039] According to one embodiment of the present invention, the reduction step of the unreduced catalyst includes a step of increasing the temperature from room temperature to the first temperature (also referred to as a temperature increase step) before the reduction treatment of the unreduced catalyst under a reducing gas at a first temperature. That is, the reduction treatment of the unreduced catalyst under a reducing gas at the first temperature may be performed after increasing the temperature from room temperature to the first temperature. The temperature increase step is preferably a step of increasing the temperature from room temperature to the first temperature via a second temperature.

[0040] In the present invention, the second temperature refers to the "temperature at which the substitution of nitrogen with reducing gas is completed" when the substitution of nitrogen gas with reducing gas is completed during the temperature increase from room temperature to the second temperature, as described below, and refers to the "temperature at which the substitution of reducing gas with nitrogen begins" during the temperature decrease. As described below, when the second temperature indicates a temperature range, the highest temperature in the second temperature range is the "temperature at which the substitution of nitrogen with reducing gas is completed" when the substitution of nitrogen gas with reducing gas is completed during the temperature increase from room temperature to the second temperature, and the highest temperature in the second temperature range during the temperature decrease is the "temperature at which the substitution of reducing gas with nitrogen begins." Here, for example, when the temperature range of the second temperature is 210°C to 60°C, this also includes the case where the highest temperature in the second temperature range during the temperature decrease is 150°C, as in Example 1 of FIG. 2 . The upper limit of the second temperature in the reduction step of the present invention is 210°C, preferably 200°C, more preferably 190°C, even more preferably 180°C, and even more preferably 170°C. Furthermore, the lower limit of the second temperature in the reduction step of the present invention can be 60°C, preferably 80°C, more preferably 100°C, even more preferably 120°C, even more preferably 130°C, and even more preferably 140°C. According to another embodiment of the present invention, the second temperature can be 60 to 210°C, preferably 80 to 200°C or 140 to 210°C, more preferably 100 to 200°C, even more preferably 120 to 190°C, even more preferably 130 to 180°C, and even more preferably 140 to 170°C. That is, when the second temperature indicates a specific temperature, such a temperature can be 60 to 210°C, preferably 80 to 200°C or 140 to 210°C, more preferably 100 to 200°C, even more preferably 120 to 190°C, even more preferably 130 to 180°C, and even more preferably 140 to 170°C. Furthermore, when the second temperature indicates a temperature range, such a temperature range can be 60 to 210°C, preferably 80 to 200°C or 140 to 210°C, more preferably 100 to 200°C, even more preferably 120 to 190°C, even more preferably 130 to 180°C, and even more preferably 140 to 170°C.According to another embodiment of the present invention, the second temperature in the reduction step of the present invention may be 185 to 210°C. That is, when the second temperature indicates a specific temperature, such a temperature may be 185 to 210°C. When the second temperature indicates a temperature range, such a temperature range may be 185 to 210°C. Furthermore, the temperature at which nitrogen substitution is completed after nitrogen substitution from the reducing gas is started at the second temperature is not particularly limited, but is preferably 20°C or higher, more preferably 30°C or higher, even more preferably 40°C or higher, and particularly preferably 50°C or higher. The upper limit of the temperature at which nitrogen substitution is completed is not particularly limited, but may be, for example, 55°C.

[0041] According to one embodiment of the present invention, the difference between the first temperature and the second temperature in the reduction step of the present invention is preferably 150 to 300°C, more preferably 180 to 280°C, and even more preferably 200 to 250°C.

[0042] According to one embodiment of the present invention, the reduction step of the unreduced catalyst may be divided into a temperature-raising step, a reduction treatment step, and a temperature-lowering step. Specifically, as described above, the temperature-raising step of the present invention is preferably a step of raising the temperature from room temperature in the reduction step to a first temperature via a second temperature. The reduction treatment step refers to a step of performing reduction treatment of the unreduced catalyst at the first temperature. The temperature-lowering step of the present invention refers to a step of lowering the temperature from the first temperature via a second temperature to approximately room temperature. Here, room temperature refers to a temperature of 0°C to 50°C, and may be, for example, 10°C, 20°C, 30°C, or 40°C.

[0043] In the present invention, the second temperature reached when the temperature is increased from room temperature to the first temperature does not necessarily have to be the same temperature or temperature range as the second temperature reached when the temperature is decreased from the first temperature, which is 60 to 210° C. For example, the second temperature reached when the temperature is increased from room temperature to the first temperature may be 100 to 120° C., and the second temperature reached when the temperature is decreased from the first temperature may be 150 to 200° C.

[0044] According to one embodiment of the present invention, the temperature increase rate when increasing the temperature from room temperature to the first temperature in the temperature increase step is preferably less than 50°C / min, more preferably less than 30°C / min, and even more preferably less than 20°C / min. The lower limit of the temperature increase rate is not particularly limited, and may be, for example, 5°C / min or more, preferably 10°C / min or more. The same applies to the temperature increase rate when increasing the temperature from room temperature to the second temperature and the temperature increase rate when increasing the temperature from the second temperature to the first temperature in the temperature increase step.

[0045] According to one embodiment of the present invention, the holding time at the second temperature in the temperature-raising step is not particularly limited, but is preferably 0 to 5 hours, more preferably 0 to 3 hours, and even more preferably 0 to 1 hour.

[0046] According to one embodiment of the present invention, the environment at room temperature when the temperature-raising step is started is filled with nitrogen gas, and therefore, in the temperature-raising step, the environment in which the reduction treatment is performed is replaced with a reducing gas at room temperature, and then the temperature is raised from room temperature to the first temperature. According to another embodiment of the present invention, in the temperature-raising step, (i) the unreduced catalyst is heated in a reducing gas while the temperature is raised from room temperature to the first temperature, or (ii) the nitrogen gas is replaced with a reducing gas while the temperature is raised from room temperature to the second temperature, and the unreduced catalyst is heated in a reducing gas while the temperature is raised from the second temperature to the first temperature. From the viewpoint of reducing the time required for the reaction and reducing the amount of reducing hydrogen gas used, it is preferable to treat the unreduced catalyst by replacing the nitrogen gas with a reducing gas while the temperature is raised from room temperature to the second temperature.

[0047] According to a preferred embodiment of the present invention, the temperature-raising step includes passing through a second temperature, and the reducing gas at the second temperature is a mixed gas of hydrogen and nitrogen or a mixed gas of carbon monoxide and nitrogen. The concentration of hydrogen or carbon monoxide in the reducing gas (mixed gas) is, for example, 90 vol% or more, preferably 95 vol% or more, more preferably 97 vol% or more, and the concentration of nitrogen in the reducing gas is, for example, less than 10 vol%, preferably less than 5 vol%, more preferably less than 3 vol%. The reducing gas is preferably a mixed gas of hydrogen and nitrogen.

[0048] According to a preferred embodiment of the present invention, the reducing gas used at the first temperature in the reduction step (preferably the reduction treatment step) is a mixed gas of hydrogen and nitrogen or a mixed gas of carbon monoxide and nitrogen. The concentration of hydrogen or carbon monoxide in the reducing gas (mixed gas) is, for example, 90 vol% or more, preferably 95 vol% or more, more preferably 97 vol% or more, and the concentration of nitrogen in the reducing gas is, for example, less than 10 vol%, preferably less than 5 vol%, more preferably less than 3 vol%. Such a reducing gas is preferably a mixed gas of hydrogen and nitrogen.

[0049] According to one embodiment of the present invention, the reduction step (preferably the reduction treatment step) includes maintaining the first temperature for 3 to 48 hours. In the reduction treatment step, the time (also referred to as the maintenance time) for performing the reduction treatment of the unreduced catalyst in the presence of a reducing gas at the first temperature is not particularly limited, but may be, for example, 1 to 48 hours, preferably 2 to 24 hours, more preferably 3 to 12 hours, and even more preferably 4 to 8 hours.

[0050] As used herein, "maintaining (the temperature)" means, in the case of the first temperature, maintaining a specific temperature (within a range of a constant temperature ±5°C) within the above-mentioned predetermined temperature range, for example, 300 to 400°C, preferably 320 to 390°C, more preferably 330 to 380°C, and even more preferably 340 to 370°C, for a predetermined time, but is not limited to this in the present specification. In other words, it is sufficient to maintain the predetermined temperature range, and for example, the temperature may be increased (for example, the temperature is continuously increased) or decreased (for example, the temperature is continuously decreased) as long as it is within the above-mentioned temperature range, and these are also included as long as they are within a range in which the effects of the present invention can be obtained. In the case of the second temperature, the predetermined temperature range described above, for example, 60 to 210 ° C, is mentioned, preferably 80 to 200 ° C or 140 to 210 ° C, more preferably 100 to 200 ° C, even more preferably 120 to 190 ° C, even more preferably 130 to 180 ° C, even more preferably 140 to 170 ° C, is maintained for a predetermined time at a specific temperature in the range, and it also includes maintaining a predetermined temperature range, for example, the temperature may be raised or lowered as long as it is within the above temperature range. For example, when the temperature range of the second temperature is 210 ° C to 60 ° C, in Example 1 of FIG. 2, maintaining the second temperature includes lowering the temperature from 150 ° C to 60 ° C.

[0051] According to one embodiment of the present invention, the temperature-lowering rate when lowering the temperature from the first temperature to the second temperature and / or the temperature at which nitrogen substitution is completed in the temperature-lowering step is preferably less than 20°C / min, more preferably less than 10°C / min, and even more preferably less than 5°C / min. The lower limit of the temperature-lowering rate is not particularly limited, and may be, for example, 0.5°C / min or more, preferably 1°C / min or more, and more preferably 2°C / min or more. The same applies to the temperature-lowering rate when lowering the temperature from the first temperature to the second temperature (here, if the second temperature indicates a temperature range, the maximum temperature of the second temperature range), the temperature-lowering rate when lowering the temperature from the second temperature (here, if the second temperature indicates a temperature range, the maximum temperature of the second temperature range) to the temperature at which nitrogen substitution is completed, and the temperature-lowering rate when lowering the temperature from the maximum temperature of the second temperature range to the minimum temperature (e.g., 60°C) in the second temperature range (if the second temperature indicates a temperature range).

[0052] According to one embodiment of the present invention, the method includes maintaining the second temperature during the temperature decrease in the reduction step (i.e., during the temperature decrease step). The maintenance time at the second temperature during the temperature decrease step is not particularly limited, but may be 0.1 to 7 hours, preferably 0.5 to 3 hours, and more preferably 1 to 2 hours.

[0053] According to another embodiment of the present invention, the time from the start of replacing the reducing gas with nitrogen to the end of the replacement during temperature reduction in the reduction step (i.e., during the temperature reduction step), i.e., the replacement time from the reducing gas with nitrogen (also referred to as the nitrogen purging time), is not particularly limited, but may be 0.1 to 7 hours, preferably 0.5 to 3 hours, and more preferably 1 to 2 hours.

[0054] According to one embodiment of the present invention, in the temperature-lowering step, from the viewpoint of reducing the time required for cooling and reducing the amount of reducing gas such as hydrogen gas used, it is preferable to cool the reduction catalyst in a reducing gas while lowering the temperature from the first temperature to the second temperature, and to cool the reduction catalyst while substituting the reducing gas with nitrogen gas while lowering the temperature from the second temperature to a temperature at which nitrogen substitution is completed. According to another embodiment of the present invention, it is preferable to cool the reduction catalyst in a reducing gas while lowering the temperature from the first temperature to the second temperature, and to cool the reduction catalyst with nitrogen gas while lowering the temperature from the second temperature to a temperature at which nitrogen substitution is completed.

[0055] FIG. 1 shows an image of the temperature profile of the reduction step (i.e., the temperature-raising step, the reduction treatment step, and the temperature-lowering step) according to one embodiment of the present invention. In one embodiment of the present invention, in the temperature-raising step, the temperature is raised from room temperature to a second temperature (e.g., 150°C) while replacing nitrogen gas with a reducing gas, and the unreduced catalyst is heated in the reducing gas during the period from the second temperature to the first temperature (e.g., 350°C). This temperature profile reduces the amount of reducing gas used during the time indicated by a in FIG. 1 and shortens the time indicated by b. In another embodiment of the present invention, in the temperature-lowering step, the reduced catalyst is cooled in the reducing gas during the period from the first temperature to the second temperature, and then cooled while replacing the reducing gas with nitrogen gas (i.e., while purging with nitrogen) during the period from the second temperature to the temperature at which nitrogen substitution is completed. This process reduces the amount of reducing gas used during the time indicated by c in FIG. 1 and shortens the time indicated by d. This therefore reduces the time required for the entire reduction step or the temperature-lowering step of the reduction step.

[0056] The pressure in the reduction step is not particularly limited, but is selected from the range of atmospheric pressure to about 5 MPa.

[0057] The reduction step of the present invention may be carried out in a catalyst production facility, or may be carried out in a facility where hydrocarbons are produced by the FT synthesis method or in a facility attached thereto.

[0058] The reduction step can be carried out in a commonly known reduction reactor or reduction reactor, for example, in a fixed bed, a fluidized bed, a rotary kiln, etc. From the viewpoint of contact efficiency between the reducing gas and the catalyst, preferred processes include a fluidized bed and a rotary kiln.

[0059] In the reduction process, the GHSV of the reduction gas is 200 h －１ It is preferable that the time is 300 hours or more, and taking into consideration the economic loss －１ More than 1200h －１ It is more preferable that the time is 400 hours or less. －１ Over 1000 hours －１ The GHSV of nitrogen is 200h or less.－１ It is preferable that the time is 200 hours or more. －１ More than 1800h －１ It is more preferable that the time is 400 hours or less. －１ More than 1500h －１ The following is the result.

[0060] In the reduction step, the linear velocity of the reducing gas is preferably 5 mm / s or more, more preferably 5 to 100 mm / s, and even more preferably 10 to 50 mm / s.

[0061] In this specification, the GHSV in the reduction treatment indicates the volumetric flow rate of the reducing gas per unit volume of the unreduced catalyst, and is a value calculated, for example, by "volumetric flow rate of the reducing gas / volume of the unreduced catalyst." Furthermore, the linear velocity in the reduction treatment indicates the velocity of the reducing gas passing through the cross section of the reduction reactor (or reduction reactor tower) filled with the unreduced catalyst, and is a value calculated, for example, by "volumetric flow rate of the reducing gas / cross-sectional area of ​​the reduction reactor (or reduction reactor tower) filled with the unreduced catalyst."

[0062] Next, a preferred embodiment of the process for producing hydrocarbons of the present invention will be described below.

[0063] According to one embodiment of the present invention, a method for producing hydrocarbons includes a step of subjecting carbon monoxide and hydrogen gas to an FT synthesis reaction in the presence of the above-described catalyst for FT synthesis to obtain hydrocarbons.

[0064] The raw material for carrying out the FT synthesis reaction is not particularly limited as long as it is a synthesis gas containing hydrogen and carbon monoxide as main components. However, a synthesis gas having a hydrogen / carbon monoxide molar ratio of 1.5 to 2.5 is preferred, and a synthesis gas having this molar ratio of 1.5 to 2.2 is more preferred.

[0065] The FT synthesis reaction can be carried out in a known reaction process for FT synthesis, such as a fixed bed, a supercritical fixed bed, a slurry bed, a fluidized bed, etc. Preferred processes include a fixed bed, a supercritical fixed bed, and a slurry bed.

[0066] The reaction conditions for the FT synthesis reaction are not particularly limited, and the reaction can be carried out under known conditions. For example, the reaction can be carried out at a reaction temperature of 200 to 280°C, a stirring speed of 500 to 2,000 rpm, a W (catalyst mass) / F (synthesis gas flow rate) of 1 to 10 g h / mol, and an absolute pressure of 1.1 to 5.1 MPa.

[0067] According to a preferred embodiment of the present invention, the activity of the Fischer-Tropsch synthesis catalyst obtained by the production method of the present invention is, in terms of CO conversion (preferably the average hourly CO conversion between 30 and 48 hours after the start of the reaction), 40% or more, preferably 45% or more, and more preferably 50% or more. There is no particular upper limit, but 100% or less is preferred.

[0068] According to a preferred embodiment of the present invention, the reducing gas reduction rate in the preparation of the FT synthesis catalyst is preferably 10% or more, more preferably 15% or more. The reducing gas reduction rate (%) is calculated by the following formula 1, where A is the amount of reducing gas used when nitrogen gas is introduced after the temperature is lowered to room temperature or a predetermined temperature (for example, the temperature at which nitrogen substitution is completed) (i.e., when nitrogen purging is performed), and B is the amount of reducing gas used when nitrogen purging is performed at the second temperature.

[0069] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments.

[0070] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0071] (Example 1) <Preparation of Unreduced Catalyst> Spherical silica particles (average particle diameter: 67 μm, specific surface area: 255 m) were obtained by drying at 100° C. for 24 hours. ２The silica particles (carrier precursor) were impregnated with ammonium zirconyl carbonate in an amount equivalent to 5% by mass of zirconium oxide based on the total mass of the unreduced catalyst by an incipient wetness method. The resulting mixture was then dried at 120°C for 24 hours, and the silica particles (carrier precursor) impregnated with ammonium zirconyl carbonate were calcined in air at 650°C for 3 hours to obtain a carrier (silica particles carrying zirconium oxide).

[0072] The obtained support was impregnated by the incipient wetness method with an aqueous cobalt nitrate solution in an amount such that the cobalt oxide content, calculated as tricobalt tetroxide, based on the total mass of the unreduced catalyst was 30% by mass. The support impregnated with the aqueous cobalt nitrate solution (catalyst precursor) was dried at 120°C for 12 hours and then calcined in air at 450°C for 3 hours to obtain a catalyst having a specific surface area of ​​134 m2 containing tricobalt tetroxide. ２ / g of unreduced catalyst was obtained.

[0073] <Preparation of catalyst for FT synthesis> The unreduced catalyst was packed into a fixed-bed reactor and purged with nitrogen. Then, the nitrogen in the fixed-bed reactor was replaced with hydrogen at room temperature, and the unreduced catalyst was reduced under a hydrogen stream. Specifically, the GHSV of the hydrogen gas used for reduction was 600 h －１ The linear velocity was set to 17.6 mm / s, and the catalyst layer temperature was increased from room temperature to 350°C (first temperature) at a rate of 13°C / min and maintained at 350°C for 5 hours. The temperature inside the reactor was then lowered to 150°C over 30 minutes, and then the temperature was lowered from 150°C to 50°C while purging with nitrogen was performed. That is, the temperature at which the substitution of hydrogen gas with nitrogen began (i.e., purge start temperature, second temperature) was 150°C, and the temperature at which the substitution of nitrogen was completed (i.e., purge end temperature) was 50°C. The GHSV of the nitrogen gas used for purging was 1200 h －１ The linear velocity was set to 35.1 mm / s, and purging was carried out for 2 hours. A catalyst for FT synthesis was obtained by the reduction and purging. The temperature profile in the reduction step of Example 1 is shown in Figure 2.

[0074] <FT synthesis reaction> 2.5 g of the obtained FT synthesis catalyst was removed from the dry box under an inert atmosphere to prevent oxidation and transferred to a 100 mL stainless steel autoclave reactor together with 15 mL of PAO (polyalphaolefin). A Fischer-Tropsch synthesis reaction was initiated using a 2 / 1 (molar ratio) hydrogen / carbon monoxide mixed gas as the feedstock under the following conditions: W (catalyst mass) / F (synthesis gas flow rate) = 3 g h / mol, temperature 220°C, pressure 2.2 MPa, and stirring speed 1,000 rpm. The gas composition at the reactor outlet was analyzed over time by gas chromatography, and the carbon monoxide conversion rate (CO conversion rate) was calculated from this analytical data. The CO conversion rate was calculated every hour from 30 hours to 48 hours after the start of the reaction, and the average values ​​are shown in Table 1.

[0075] The reduction rate (%) of reducing gas (hydrogen gas) in Example 1 is shown in Table 1. The reduction rate (%) of reducing gas was calculated from the following formula 1, where A is the amount of reducing gas used when nitrogen purging was performed after the temperature was lowered to 50°C, and B is the amount of reducing gas used when nitrogen purging was performed at the second temperature.

[0076] Comparative Example 1 An FT synthesis catalyst was prepared in the same manner as in Example 1, except that the temperature of the reduction treatment was changed as shown in Table 1. The temperature profile in the reduction step in Comparative Example 1 is shown in Figure 2. Using the obtained FT synthesis catalyst, the FT synthesis reaction was carried out in the same manner as in Example 1, and the average value of the CO conversion rate was determined every hour from 30 hours to 48 hours after the start of the reaction. The obtained results are shown in Table 1.

[0077]

[0078] (Example 2 and Comparative Examples 2 to 5) In Example 2 and Comparative Examples 2 to 5, FT synthesis catalysts were prepared in the same manner as in Example 1, except that the holding time of the first temperature in the reduction treatment, the second temperature during temperature decrease, and the purging time were changed as shown in Table 2. Using the obtained FT synthesis catalyst, the FT synthesis reaction was carried out in the same manner as in Example 1, and the average value of the CO conversion rate per hour was determined between 30 hours and 48 hours after the start of the reaction. The obtained results are shown in Table 2. Table 2 also shows the reducing gas reduction rates (%) in Example 2 and Comparative Examples 2 and 3.

[0079] In Examples 1 and 2, the reduction gas was reduced compared to Comparative Examples 2 to 5, while the CO conversion rate in the FT synthesis reaction was high, indicating that production was possible while maintaining high catalytic activity.

[0080] Examples 3 to 5 and Reference Example 1 The influence of the nitrogen gas concentration in the mixed gas of hydrogen and nitrogen (reducing gas) used in the reduction treatment on the catalytic activity was investigated.

[0081] Example 3 An FT synthesis catalyst was prepared in the same manner as in Example 1. Here, the nitrogen gas concentration in the mixed gas of hydrogen and nitrogen used in the reduction treatment was set to 0% by volume (i.e., 100% by volume of hydrogen gas). Note that Example 3 and Example 1 are separate tests. Using the obtained FT synthesis catalyst, an FT synthesis reaction was carried out in the same manner as in Example 1, and the average value of the CO conversion rate was determined for each hour from 30 hours to 48 hours after the start of the reaction.

[0082] Example 4 A catalyst for FT synthesis was prepared in the same manner as in Example 1, except that the nitrogen gas concentration in the mixed gas of hydrogen and nitrogen used in the reduction treatment was changed to 5% by volume (i.e., 95% by volume of hydrogen gas).

[0083] Example 5 A catalyst for FT synthesis was prepared in the same manner as in Example 1, except that the nitrogen gas concentration in the mixed gas of hydrogen and nitrogen used in the reduction treatment was changed to 10% by volume (i.e., 90% by volume of hydrogen gas).

[0084] Reference Example 1 A catalyst for FT synthesis was prepared in the same manner as in Example 1, except that the nitrogen gas concentration in the mixed gas of hydrogen and nitrogen used in the reduction treatment was changed to 67% by volume (i.e., 33% by volume of hydrogen gas).

[0085] The FT synthesis reaction was carried out in the same manner as in Example 1 using the FT synthesis catalysts obtained in Examples 3 to 5 and Reference Example 1, and the CO conversion rates were calculated every hour from 30 hours to 48 hours after the start of the reaction, and these values ​​were averaged to obtain the results. Table 3 shows the results.

Claims

1. A method for producing a catalyst for Fischer-Tropsch synthesis, comprising: a step of supporting a cobalt compound on a carrier to produce a catalyst precursor; a step of drying and calcining the catalyst precursor to produce an unreduced catalyst comprising cobalt oxide; and a step of reducing the unreduced catalyst to obtain a catalyst for Fischer-Tropsch synthesis comprising a reduced product of the unreduced catalyst; wherein the unreduced catalyst reduction step comprises reducing the unreduced catalyst in a reducing gas at a first temperature, and then lowering the temperature to a second temperature and replacing the gas with nitrogen; wherein the first temperature is 300 to 400°C, and the second temperature is 60 to 210°C.

2. The method of claim 1, wherein the reducing gas is selected from the group consisting of hydrogen, carbon monoxide, a mixture of hydrogen and nitrogen, and a mixture of carbon monoxide and nitrogen.

3. The method of claim 2, wherein the unreduced catalyst reduction step further comprises raising the temperature from room temperature to a first temperature via a second temperature, and wherein at the second temperature, the concentration of hydrogen or carbon monoxide in the reducing gas is at least 90% by volume.

4. The method according to any one of claims 1 to 3, wherein the reduction step comprises maintaining the first temperature for 3 to 48 hours.

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