JP7782949B2 - Catalyst systems for Fischer-Tropsch reactions - Google Patents

Description

The present invention relates to catalyst technology used in producing hydrocarbons.

One known method for effectively utilizing carbon dioxide contained in exhaust gases, etc., is to produce high-energy-density liquid hydrocarbons from carbon dioxide and hydrogen in the presence of a catalyst (see Patent Document 1). Also known as a method for producing hydrocarbons using hydrogen and carbon monoxide is the Fischer-Tropsch process (hereinafter referred to as the "FT process" where appropriate) (see Non-Patent Document 1).

Japanese Patent Application Publication No. 7-80309

Energy & Fuels, Vol. 23, 4195(2009)

The cobalt-based catalysts typically used in FT reactions selectively produce methane from carbon dioxide. Therefore, when a feedstock containing carbon dioxide is used, a large amount of methane is produced, making it impossible to obtain a high yield of liquid hydrocarbons.

The present invention was made in light of these circumstances, and one of its exemplary purposes is to provide a new catalyst capable of producing liquid hydrocarbons from a feed gas containing at least one of carbon dioxide or carbon monoxide and hydrogen.

In order to solve the above problems, a catalyst according to one embodiment of the present invention comprises a support containing ferric oxide as a main component and an alkali metal supported on the support, wherein the support has a specific surface area of 20 m ² /g or more.

One aspect of the present invention provides a new catalyst capable of producing liquid hydrocarbons from a feed gas containing at least one of carbon dioxide or carbon monoxide and hydrogen, making it possible to obtain liquid hydrocarbons in high yields in hydrocarbon production.

1 is a schematic diagram showing the general configuration of a fixed-bed flow reactor according to the present embodiment.

First, embodiments of the present invention will be described. A catalyst according to one embodiment of the present invention comprises a support containing ferric oxide as a main component and an alkali metal supported on the support. The support has a specific surface area of 20 m ² /g or more.

This embodiment allows for an increased yield of liquid hydrocarbons. Ferric oxide is also known as iron(III) oxide or iron trioxide.

The alkali metal may include at least one selected from the group consisting of sodium and potassium.

The support may have a specific surface area of 40 m ² /g or more and a pore volume of 0.15 cm ³ /g or more, which can further increase the yield of liquid hydrocarbons.

Another aspect of the present invention is a catalyst system. The catalyst system includes a reactor configured to introduce a feed gas from an upstream inlet and discharge hydrocarbons produced from a downstream outlet, a first catalyst that causes a reverse shift reaction and is disposed on the inlet side of the reactor, and a second catalyst that contains the aforementioned ferric oxide-based support and is disposed on the outlet side of the reactor.

According to this embodiment, hydrocarbons can be easily produced from the carbon dioxide and hydrogen contained in the feed gas introduced into the inlet side of the reactor without removing the carbon monoxide produced in the reverse shift reaction from the reactor.

The first catalyst may contain copper and zinc oxide. This allows carbon monoxide to be efficiently produced from carbon dioxide contained in the feed gas. The first catalyst can also be used as a heat absorption component for the second catalyst.

The first catalyst may contain rhodium.

The first catalyst may contain platinum.

The first catalyst may contain iron-chromium.

A temperature adjustment mechanism may be further provided between the first catalyst and the second catalyst to adjust the temperature of at least one of the first catalyst and the second catalyst. This allows the second catalyst to be used at a relatively low temperature even if it generates heat during the catalytic reaction.

Another aspect of the present invention is a method for producing a catalyst. This method includes the steps of: mixing an aqueous solution of iron nitrate with a basic aqueous solution; filtering a precipitate containing iron(III) hydroxide produced in the mixing step; washing the filtered iron(III) hydroxide; calcining the washed iron(III) hydroxide to produce ferric oxide; and supporting an alkali metal on the ferric oxide as a support. The support has a specific surface area of 20 ^m /g or more.

When an aqueous solution containing ammonia is used in the mixing process, the iron(III) hydroxide precipitate produced in the mixing process does not contain alkali metals, compared to when sodium hydroxide or potassium hydroxide is used. If the precipitate contains alkali metals, it is necessary to remove as much of the contained alkali metal as possible to increase the accuracy of the amount of alkali metal loaded in the subsequent loading process, which increases manufacturing costs. In contrast, according to this embodiment, by using an aqueous solution containing ammonia instead of an alkaline aqueous solution, it is possible to reduce the effort required for cleaning during filtration and the effort required to determine the amount of residual alkali metal content.

When using a basic aqueous solution containing the same alkali metal as the alkali metal to be loaded in the mixing step, the amount of alkali remaining in the washing step can be measured and the required amount of alkali can be loaded to shorten the washing step and prevent increases in production costs. In this case, the basic aqueous solution containing the alkali metal may be sodium hydroxide or potassium hydroxide.

In addition, any combination of the above components, or any transformation of the present invention into a method, device, system, etc., is also valid as an embodiment of the present invention. Furthermore, any appropriate combination of the above-mentioned elements may also be included within the scope of the invention for which patent protection is sought through this patent application.

The present invention will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. Identical or equivalent components, parts, and processes shown in the drawings will be designated by the same reference numerals, and redundant explanations will be omitted where appropriate. The scale and shape of each part shown in the drawings are set for convenience to facilitate explanation and should not be interpreted as limiting unless otherwise specified. The same components may have slightly different scales between drawings. Furthermore, when terms such as "first" and "second" are used in this specification or claims, unless otherwise specified, they do not represent any order or importance, but are used to distinguish one configuration from another.

(catalyst system)
Next, a schematic configuration of a reaction apparatus including a catalyst system according to this embodiment will be described. Fig. 1 is a schematic diagram showing the schematic configuration of a fixed-bed flow reactor according to this embodiment. The reaction apparatus 10 shown in Fig. 1 includes, as a catalyst system, a reactor 12 configured to discharge hydrocarbons produced from a feed gas introduced through an upstream inlet 12a from a downstream outlet 12b, a first catalyst 14 arranged on the inlet 12a side of the reactor 12 to cause a reverse shift reaction, and a second catalyst 16 arranged on the outlet 12b side of the reactor 12, which is a catalyst containing a carrier mainly composed of ferric oxide (described below).

In the first catalyst 14, carbon monoxide is produced from carbon dioxide through a reverse shift reaction. In the second catalyst 16, hydrocarbons are produced from carbon monoxide through a reaction using the FT method. This catalyst system can easily produce gaseous or liquid hydrocarbons by introducing a feed gas containing carbon dioxide and hydrogen into the inlet side of the reactor 12.

The reactor 10 produces _CH4 and C2-C4 components, which are gaseous hydrocarbons with 1 to 4 carbon atoms, such as methane, ethane, propane, and butane, and C5+ components, which are hydrocarbons with 5 or more carbon atoms and are liquid oil components at normal pressure (for example, linear alkanes with a carbon number n of 5 or more), and performs gas-liquid separation of the gas components and oil components, and in some cases performs fractional distillation to extract the desired components.

As described above, the catalyst system according to this embodiment includes at least two types of catalysts. The first catalyst 14 is a copper-based catalyst containing copper, and the second catalyst is an iron-based catalyst containing iron. The first catalyst 14 may contain copper and zinc oxide. This allows for efficient production of carbon monoxide from carbon dioxide contained in the feed gas. Furthermore, the reaction caused by the copper-based catalyst according to this embodiment is an endothermic reaction, and the first catalyst 14 can be used as a heat absorption portion of the second catalyst 16. A temperature adjustment mechanism may be provided between the first catalyst 14 and the second catalyst 16 to adjust the temperature of at least one of the first catalyst 14 and the second catalyst 16. The temperature adjustment mechanism may include a medium that absorbs heat itself, or it may be a mechanism that uses a heat transfer medium cooled by another heat source in the plant. This allows the second catalyst to be used at a relatively low temperature even if it generates heat during the catalytic reaction.

The form of each catalyst body is not particularly limited and may be, for example, a powder or a granular compact consisting of powder agglomerates. The shape of the granular catalyst body is not particularly limited and may be, for example, cylindrical, prismatic, spherical, or irregular. The particle size (maximum width) of the granular compact may be 1 mm or more and 50 mm or less. The particle size (maximum width) of the catalyst body powder may be 1 μm or more and less than 1000 μm.

The first catalyst 14 contains metallic copper, copper oxide (CuO), or both. While the copper-based catalyst body functions as a catalyst, it contains at least metallic copper. Therefore, the catalyst is subjected to a reduction treatment before being used in a reaction. Before the reduction treatment, the copper-based catalyst body often contains copper oxide.

The copper content in the copper-based catalyst body is preferably 20 to 100 mass% based on the total mass of the copper-based catalyst body when the amount of copper components contained in the copper-based catalyst body is converted into the amount of metallic copper.

The copper-based catalyst body may further contain zinc oxide (ZnO). By including zinc oxide in the copper-based catalyst body, liquid hydrocarbons can be produced more efficiently. When the amount of copper element contained in the copper-based catalyst body is converted into the amount of copper oxide, the proportion of zinc oxide is preferably 10 to 70 mass%, and more preferably 20 to 50 mass%, based on the total amount of copper oxide and zinc oxide.

The first catalyst 14 may contain at least one metal or alloy selected from the group consisting of rhodium, platinum, or iron-chromium. By containing these metals or alloys, carbon monoxide can be produced more efficiently from the carbon dioxide contained in the source gas.

The copper-based catalyst body may further contain a carrier that supports the copper component. When the copper-based catalyst body contains zinc oxide, the zinc oxide is usually also supported on the carrier. The carrier is preferably alumina, such as gamma-alumina. The content of the carrier in the copper-based catalyst body is, for example, 0.5 to 60 mass%, preferably 1 to 50 mass%, and more preferably 1 to 40 mass%, based on the total content of copper, zinc oxide, and alumina. The copper content here refers to the amount of copper component contained in the copper-based catalyst body converted into the amount of metallic copper.

A copper-based catalyst containing a copper component and zinc oxide can be obtained, for example, by a method including the steps of generating a precipitate containing copper and zinc by coprecipitation and calcining the generated precipitate. The precipitate includes, for example, hydroxides, carbonates, or composite salts of copper and zinc. A copper-based catalyst containing a copper component, zinc oxide, and a support can be obtained by generating a precipitate containing copper and zinc by coprecipitation from a solution containing a support (e.g., alumina).

The fired body containing copper components and zinc oxide formed by firing may be powdered, and the powder may be further molded to form a granular compact. Examples of methods for molding the powder include extrusion molding and tablet molding. A molded body can also be obtained by molding a mixture containing the fired body powder and carbon black.

The second catalyst 16 is an iron-based catalyst body containing a carrier whose main component is ferric oxide and an alkali metal as an additive metal supported on the carrier.

The content of iron components in the iron-based catalyst body is preferably 5 to 100 mass% based on the total mass of the iron-based catalyst body when the amount of iron components contained in the iron-based catalyst body is converted into the amount of iron oxide.

The added metal includes one or more types arbitrarily selected from alkali metals. For example, it is preferable that the added metal includes at least one type selected from the group consisting of sodium, potassium, and cesium. Naturally, two or more types of added metals may be used. When the added metal includes sodium, potassium, or cesium, liquid hydrocarbons can be produced even more efficiently.

The content of the added metal in the iron-based catalyst body is preferably 0.2 to 40 mass%, and more preferably 0.5 to 20 mass%, based on the amount of the portion of the iron-based catalyst body other than the added metal. When the added metal includes sodium, the sodium content in the iron-based catalyst body is preferably 0.2 to 20 mass%, and more preferably 0.5 to 10 mass%. When the added metal includes potassium, the total content of potassium and cesium in the iron-based catalyst body is preferably 0.2 to 40 mass%, and more preferably 0.5 to 20 mass%. When the added metal includes cesium, the cesium content in the iron-based catalyst body is preferably 0.2 to 20 mass%, and more preferably 0.5 to 10 mass%. When the added metal content is within the above range, the conversion rate of carbon monoxide to hydrocarbons tends to be further improved.

The iron-based catalyst body can be obtained, for example, by a method including the steps of generating a precipitate of hydroxide containing trivalent iron from an aqueous solution containing Fe ³⁺ , calcining the precipitate to form a powder containing ferric oxide, mixing the powder with an aqueous solution containing an additive metal, and then drying the aqueous solution containing the additive metal.

The powder containing ferric oxide may be further molded to form a granular compact. Examples of methods for molding the powder include extrusion molding and tablet molding. A mixture containing the sintered powder and carbon black can also be molded to obtain a compact.

One method for producing hydrocarbons according to this embodiment involves producing hydrocarbons from a feed gas containing at least one of carbon dioxide or carbon monoxide and hydrogen in the presence of the above-described catalyst. A catalyst containing a combination of a copper-based catalyst and an iron-based catalyst can produce liquid hydrocarbons at a higher yield from a feed gas containing at least one of carbon dioxide or carbon monoxide and hydrogen, compared to, for example, a catalyst containing a composite oxide containing copper and iron and an alkali metal. The feed gas containing carbon dioxide and carbon monoxide may be, for example, a gas obtained by converting part of the carbon dioxide into carbon monoxide through an electrochemical reaction or a conventional chemical reaction.

While the reaction to produce hydrocarbons from the feed gas is proceeding, each catalyst may be heated. The heating temperature for the reaction is, for example, 200 to 400°C. The feed gas may contain only carbon dioxide or carbon monoxide, or may be a mixed gas containing carbon dioxide and carbon monoxide.

The present invention will be explained in more detail below using examples. However, the present invention is not limited to these examples.

Example 1
1. Preparation of catalyst [Preparation of copper-based catalyst body]
5.0 g of γ-alumina (BK-105, manufactured by Sumitomo Chemical Co., Ltd.) was suspended in 1.0 L of purified water by stirring with a homomixer. 300 mL of an aqueous solution containing 31.7 g of copper nitrate hydrate (manufactured by Nakarai Reagent Co., Ltd.) and 38.1 g of zinc nitrate hydrate (manufactured by Nakarai Reagent Co., Ltd.) was quickly added to the resulting suspension at room temperature, and the suspension was then stirred for an additional hour at room temperature. Subsequently, while continuing to stir with the homomixer, 300 mL of an aqueous solution containing 35.0 g of sodium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise at a rate of 5 mL/min using a roller pump at room temperature. The suspension containing the precipitate formed by the dropwise addition was allowed to stand at 35°C for 24 hours for aging. The supernatant was removed from the aged suspension by decanting, and the remaining precipitate was diluted again with water. This decanting and dilution process was repeated four times.

The precipitate was then removed by suction filtration, suspended again in pure water, and then removed by suction filtration. This procedure was repeated four times. The precipitate was thoroughly washed with water through this process. The resulting precipitate was dried by heating at 120°C for 24 hours. The dried precipitate was calcined by heating under air flow in the following order: 1 hour at 150°C, 1 hour at 200°C, 1 hour at 250°C, 1 hour at 300°C, 1 hour at 350°C, and 4 hours at 400°C. Calcination yielded a black powder, a copper-based catalyst containing copper components and zinc oxide. This black powder was pulverized in a mortar and molded at a pressure of 40 MPa to obtain a cylindrical copper-based catalyst body with a diameter of 3 mm and a height of 3 mm.

[Preparation of iron-based catalyst body]
A solution with an iron ion concentration of 3 mol/L was prepared by dissolving 146.9 g of iron nitrate nonahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 120 ml of purified water with stirring at 70°C. A sodium hydroxide solution (16.6 mol/L) prepared by dissolving 47.9 g of sodium hydroxide in 70 ml of purified water was added dropwise to the solution so that the pH of the solution was 11 to 12, producing a solution containing a precipitate of iron (III) hydroxide (Fe(OH) ₃ ). The precipitate contained in this solution was filtered using a vacuum pump, and the resulting filtrate was repeatedly washed until the alkali metal content was below a predetermined level. This is because if a large amount (unspecified amount) of alkali metal remained, it would be difficult to adjust the amount of alkali metal to be supported on the ferric oxide carrier in the subsequent alkali metal addition step.

The obtained precipitate was then dried by heating at 120°C for 12 to 20 hours. The dried precipitate was calcined by finally heating at 400°C for 5 hours while increasing the ambient temperature at a rate of 5°C/min in an air stream. As a result, 28.7 g of ferric oxide ( _{Fe2O3 )} was obtained.

Next, 5 g of the obtained ferric oxide was dissolved in an aqueous sodium hydroxide solution or an aqueous sodium nitrate solution, dried at 120°C for 12 to 20 hours, and finally calcined by heating to 400°C for 5 hours while raising the ambient temperature at a rate of 5°C/min in an air stream. This produces a powder of an iron-based catalyst body containing a support primarily composed of ferric oxide and an alkali metal supported on the support. Note that if ferric oxide is dissolved in an aqueous sodium hydroxide solution, the calcination step can be omitted and only the drying step can be performed. The powder is then molded to obtain a molded body of the desired shape. The iron-based catalyst body in each of the following examples is in the form of flakes with a diameter of 2 to 3 mm.

When potassium is used as the alkali metal to be supported on ferric oxide, an aqueous solution of potassium hydroxide or potassium nitrate can be used. When cesium is used as the alkali metal to be supported on ferric oxide, an aqueous solution of cesium hydroxide or cesium nitrate can be used.

2. Evaluation [Catalyst reduction treatment]
A fixed-bed reactor tube with an inner diameter of 1.27 cm was sequentially filled with 0.5 g of a copper-based catalyst and 3.5 g of an iron-based catalyst (copper-based catalyst: iron-based catalyst = 1:7), and the copper-based catalyst and iron-based catalyst were arranged in this order from the gas inlet side (upstream side) of the reactor tube. Subsequently, under atmospheric pressure, a flow gas consisting of 1% by volume of hydrogen and nitrogen was circulated through the reactor tube at a flow rate of 200 Ncc/min, while the temperature of the catalyst was raised from room temperature to 150 ° C. over 1 hour. While maintaining the temperature at 150 ° C., the concentration of hydrogen contained in the flow gas was changed in the order of 2% by volume, 10% by volume, 20% by volume, 50% by volume, and 100% by volume. After changing to a flow gas (hydrogen gas) with a hydrogen concentration of 100% by volume, the flow state was maintained for 2 hours. Thereafter, while continuing to pass hydrogen gas, the temperature of the catalyst was raised to 350° C. at a rate of 200° C./hour and maintained at 350° C. for 7 hours, thereby reducing the catalyst.

[Reaction test]
After the reduction treatment, the catalyst was cooled to 320°C while hydrogen gas was passed through at a flow rate of 200 Ncc/min. After the temperature was lowered, the pressure of the flowing gas was increased to 0.8 MPa. After the pressure was increased, carbon dioxide was added at a flow rate of 67 Ncc/min, and the feed gas consisting of hydrogen and carbon dioxide was passed through the reaction tube for 6 hours (gas space velocity: 4000 Ncc·g-cat-1h ^-1 ). The liquid that flowed out of the reaction tube during the 6 hours was collected. In addition, the gas that flowed out of the reaction tube was collected for 5 minutes just before the end of the test. The oil content of the supernatant of the liquid was analyzed by gas chromatography/flame ionization detector (GC-FID). The gas was analyzed by gas chromatography/thermal conductivity detector (GC-TCD) and flame ionization detector (GC-FID). From the analysis results, the product yield relative to the amount of carbon dioxide in the feed gas was calculated.

Table 1 shows the specifications of Carrier 1. Carrier 1 is a 100% Fe ₂ O ₃ (hematite) carrier with a specific surface area of 56.7 ^{m 2} /g and a pore volume of 0.239 cm ³ /g. Example 1 in Table 2 shows the proportions of each component in a hydrocarbon product produced when carbon dioxide and hydrogen are reacted as feed gases in a catalytic system (reactor 10) using an iron-based catalyst body in which sodium (4 wt %: based on the amount of the iron-based catalyst body other than added metals; the same applies below) is supported on Carrier 1. The proportions of each component were calculated for CH ₄ , C2-C4, C5-C9, and C10+. In Tables 2 to 5, "CO ₂ conversion" indicates the conversion rate of carbon dioxide in the feedstock to carbon monoxide, and "CO conversion" indicates the conversion rate of carbon monoxide to hydrocarbons. As shown in Table 2, in Example 1, the yield of hydrocarbon products having 5 or more carbon atoms relative to the amount of carbon dioxide in the feed gas (hereinafter referred to as "C5+ yield") was 15.1%, which is a very good result. In addition, the selectivity of liquid hydrocarbons having 5 or more carbon atoms that can be used as oil (hereinafter referred to as "C5+ selectivity") was 55.1%, which is a very good result.

(Comparative Example 1)
As shown in Table 1, the carrier 2 of Comparative Example 1 is a carrier _made of 100% _Fe3O4 (magnetite), with a specific surface area of 85.9 ^m2 /g and a pore volume of 0.361 ^cm3 /g. Furthermore, Comparative Example 1 in Table 2 shows the proportions of each component of hydrocarbon products produced when carbon dioxide and hydrogen are reacted as feed gases in a catalyst system (reactor 10) using an iron-based catalyst body in which sodium (4 wt%) is supported on the carrier 2. As shown in Table 2, the performance of Comparative Example 1 is equal to or lower than that of Example 1. In other words, the catalyst system of Example 1 can achieve performance equal to or higher than that of Comparative Example 1, even though it uses a carrier 1 (ferric oxide) different from the carrier 2 used in the catalyst system of Comparative Example 1.

(Comparative Example 2)
As shown in Table 1, Carrier 3 according to Comparative Example 2 is a carrier composed of 100% Fe ₃ O ₄ (Magnetite), but has a specific surface area of 4.0 m ² /g and a pore volume of 0.019 cm ³ /g, both of which are smaller than those of Carrier 1 according to Example 1. Therefore, as shown in Table 2, in Comparative Example 2, the C5+ selectivity is less than 50%.

(Comparative Example 3)
As shown in Table 1, carrier 4 according to Comparative Example 3 is a carrier containing 76% _Fe2O3 ( _hematite ) and 24% _{Fe21.16O31.92} (maghemite) _, and has a specific surface area of 4.3 ^m2 /g and a pore volume of 0.020 ^cm3 /g, both of which are smaller than those of carrier 1 according to Example 1. Therefore, as shown in Table 2, in Comparative Example 3, the C5+ selectivity is less than 50%.

(Comparative Example 4)
As shown in Table 1, Carrier 5 according to Comparative Example 4 is a carrier containing 44% _Fe2O3 ( _hematite ) and ₅₆ % _{Fe21.16O31.92} (maghemite), and has a specific surface area of 6.4 ^m2 /g and a pore volume of 0.035 ^cm3 /g, both of which are smaller than those of Carrier 1 according to Example 1. Therefore, as shown in Table 2, in Comparative Example 4, the C5+ selectivity is about 40% and the C5+ yield is about 10%, which is lower in performance than the catalyst system according to Example 1.

As described above, from the results of Example 1 and Comparative Examples 1 to 4, it is clear that the carrier containing ferric oxide as a main component according to this embodiment should have a specific surface area of 20 ^m /g or more, more preferably 40 ^m /g or more. Furthermore, it is also clear that the carrier according to this embodiment should have a pore volume of 0.05 ^cm /g or more, more preferably 0.15 ^cm /g or more. This makes it possible to further increase the yield of liquid hydrocarbons.

Example 2
As shown in Table 3, the catalyst of Example 2 uses the same carrier 1 as the catalyst of Example 1, but differs in that the alkali metal added is potassium instead of sodium. The catalyst system of Example 2 further improves the C5+ selectivity and C5+ yield compared to the catalyst system of Example 1.

(Comparative Example 5)
As shown in Table 1, Carrier 6 of Comparative Example 5 is a _ZnFe2O4 carrier with a _spinel structure, having a specific surface area of 33.9 ^m2 /g and a pore volume of 0.017 ^cm3 _/ g. Here, the _{spinel ZnFe2O4} has the same _AB2O4 crystal structure as _Fe3O4 , with _Zn occupying the A site. It is said that the proximity of Zn to Fe in _ZnFe2O4 with a spinel structure improves the reducibility of Fe and increases activity. However, as shown in Table 3, Comparative Example ₅ exhibits inferior C5+ selectivity and C5+ yield compared to Example 2, which also contained potassium as an alkali metal. In other words, the catalyst system of Example 2 uses Carrier 1 (ferric oxide), which is different from Carrier 6 used in the catalyst system of Comparative Example 5, yet achieves performance equal to or better than that of Comparative Example 5.

(Comparative Example 6)
As shown in Table 1, the carrier 7 of Comparative Example 6 is a carrier made of 100% Fe ₂ O ₃ (hematite), with a specific surface area of 47.1 ^{m 2} /g and a pore volume of 0.202 cm ³ /g. The catalyst system of Comparative Example 6 uses a catalyst in which no alkali metal is supported on the carrier 7. Therefore, as shown in Table 4, in Comparative Example 6, the C5+ selectivity is 14.8% and the C5+ yield is 2.0%, indicating that the performance is lower than that of the catalyst system of Example 1.

Example 3
The catalyst system of Example 3 is different from the catalyst system of Example 1 in that the amount of sodium supported on the carrier 1 is 1.6 wt %, but the other configurations are the same. As shown in Table 4, the catalyst system of Example 3 is equivalent to the catalyst system of Example 1 in C5+ selectivity and C5+ yield.

Example 4
The catalyst system of Example 3 is different from the catalyst system of Example 1 in that the amount of sodium supported on the carrier 1 is 2.6 wt %, but the other configurations are the same. As shown in Table 4, the catalyst system of Example 4 is equivalent to the catalyst system of Example 1 in C5+ selectivity and C5+ yield.

Example 5
The catalyst system of Example 5 is different from the catalyst system of Example 2 in that the amount of potassium supported on the carrier 1 is 1.0 wt %, but the other components are the same. As shown in Table 5, the catalyst system of Example 5 has the same C5+ selectivity and C5+ yield as the catalyst system of Example 2.

Example 6
The catalyst system of Example 6 is different from the catalyst system of Example 2 in that the amount of potassium supported on the carrier 1 is 2.0 wt %, but the other components are the same. As shown in Table 5, the catalyst system of Example 6 is equivalent to the catalyst system of Example 2 in C5+ selectivity and C5+ yield.

Comparing Comparative Example 6 with Examples 1 to 6, it can be seen that loading an alkali metal onto a support primarily composed of ferric oxide significantly improves C5+ selectivity and C5+ yield. The amount of alkali metal loaded should be 0.5 wt% or more, preferably 1.0 wt% or more, and more preferably 1.5 wt% or more. Furthermore, ferric oxide supports loaded with potassium as the alkali metal tend to improve C5+ selectivity and C5+ yield more than those loaded with sodium.

Example 7
Next, differences in the alkaline solutions used in the support manufacturing method will be examined. In the preparation of the iron-based catalyst body in Example 1, sodium hydroxide was used as the alkaline aqueous solution. However, as mentioned above, the iron-based catalyst body in this embodiment requires that the ferric oxide support an alkali metal such as sodium or potassium. If an inconsistent amount of sodium is present in the ferric oxide manufacturing stage, this will affect the washing process and the alkali metal addition process.

Therefore, in Example 7, when preparing a solution containing a precipitate of iron (III) hydroxide (Fe(OH) ₃ ), an aqueous solution containing ammonia but not an alkali metal was used to produce Carrier 7. The other steps were substantially the same as those in the production method of Carrier 1. As shown in Table 1, Carrier 7 is a carrier composed of 100% _Fe2O3 ( _hematite ), and has a specific surface area of 47.1 ^m2 /g and a pore volume of 0.202 ^cm3 /g. The catalyst system of Example 7 using Carrier 7 has the same C5+ selectivity and C5+ yield as the catalyst system of Example 1.

Furthermore, if the preparation method of support 7 in Example 7 is considered as a catalyst manufacturing method, this method includes a mixing step of mixing an aqueous solution of iron nitrate with an aqueous solution containing ammonia, a filtration step of filtering a precipitate containing iron (III) hydroxide produced in the mixing step, a production step of calcining the filtered iron (III) hydroxide to produce ferric oxide, and a step of supporting an alkali metal on the ferric oxide as a support. Furthermore, support 7 has a specific surface area of 20 ^m2 /g or more.

In this method, compared to when sodium hydroxide or potassium hydroxide is used in the mixing process, the iron(III) hydroxide precipitate produced in the mixing process does not contain alkali metals. If the precipitate contains alkali metals, it is necessary to remove as much of the contained alkali metal as possible to increase the accuracy of the amount of alkali metal loaded in the subsequent loading process, which increases manufacturing costs. In contrast, in this embodiment, by using an aqueous solution containing ammonia instead of an alkaline aqueous solution, it is possible to reduce the effort required for cleaning during filtration and the effort required to determine the amount of residual alkali metal content.

On the other hand, if a basic aqueous solution containing the same alkali metal as the alkali metal to be loaded in the mixing process is used, the amount of alkali remaining in the washing process can be measured and the required amount of alkali can be loaded to make up for the deficiency. This makes it possible to shorten the washing process and prevent increases in production costs.

The present invention has been described above with reference to the above-mentioned embodiments and examples, but the present invention is not limited to the above-mentioned embodiments and examples, and appropriate combinations and substitutions of the configurations of the embodiments and examples are also included in the present invention. Furthermore, based on the knowledge of those skilled in the art, it is possible to appropriately rearrange the combinations and processing orders in the embodiments and examples, and to make various design changes and other modifications to the embodiments, and such modified embodiments are also included within the scope of the present invention.

10 Reactor, 12 Reactor, 12a Inlet, 12b Outlet, 14 First catalyst, 16 Second catalyst.

Claims (8)

a reactor configured to discharge hydrocarbons produced from a raw material gas introduced from an upstream inlet through a downstream outlet;
a first catalyst for causing a reverse shift reaction, the first catalyst being disposed on the inlet side of the reactor;
a second catalyst for causing a Fischer-Tropsch reaction, the second catalyst being disposed on the outlet side of the reactor;
the raw material gas contains carbon dioxide and hydrogen,
The second catalyst is
The catalyst comprises a carrier containing ferric oxide as a main component and an alkali metal supported on the carrier,
The catalyst system for a Fischer-Tropsch reaction, wherein the support has a specific surface area of 20 m ² /g or more. The catalyst system for a Fischer-Tropsch reaction according to claim 1, wherein the alkali metal in the second catalyst includes at least one selected from the group consisting of sodium and potassium. 3. The catalyst system for a Fischer-Tropsch reaction according to claim 1, wherein the support in the second catalyst has a specific surface area of 40 m ² /g or more and a pore volume of 0.15 cm ³ /g or more. The catalyst system for a Fischer-Tropsch reaction according to claim 1, wherein the first catalyst contains copper and zinc oxide. The catalyst system for a Fischer-Tropsch reaction according to claim 1, wherein the first catalyst contains rhodium. The catalyst system for a Fischer-Tropsch reaction according to claim 1, wherein the first catalyst contains platinum. The catalyst system for a Fischer-Tropsch reaction according to claim 1, wherein the first catalyst contains iron-chromium. The catalyst system for a Fischer-Tropsch reaction according to any one of claims 1 to 7, further comprising a temperature adjustment mechanism between the first catalyst and the second catalyst that adjusts the temperature of at least one of the first catalyst and the second catalyst.