Method for preparing aviation fuel through carbon dioxide hydrogenation

Abstract

The invention relates to the technical field of aviation fuel preparation, in particular to a method for preparing aviation fuel through carbon dioxide hydrogenation, which comprises the following steps: (1) introducing carbon dioxide and hydrogen raw materials into a fixed bed reactor A filled with a solid catalyst a for reaction; (2) introducing a product of the reactor A into a three-phase separator to separate and remove gas and water, and introducing the residual liquid phase into a condensation crystallizer to perform dewaxing operation; (3) introducing the dewaxed oil phase into a hydroisomerization reactor B filled with a solid catalyst b for reaction; and (4) introducing the liquid effluent in the reactor B into a normal-pressure rectifying tower for separation to obtain a light fraction, an aviation fuel component, a low-condensation-point diesel fraction and a high-condensation-point diesel fraction, and according to the method for preparing the aviation fuel through carbon dioxide hydrogenation, the CO2 hydrogenation catalyst is simple to prepare and long in service life, and the investment is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation fuel preparation, in particular to a method for preparing aviation fuel by hydrogenating carbon dioxide. Background Art

[0002] With the global aviation industry urgently pursuing carbon neutrality, the development of sustainable aviation fuel (SAF) has become a key path to reducing carbon emissions. PtL (Power to Liquid) technology, which uses green hydrogen generated by water electrolysis using renewable electricity to hydrogenate CO2 to produce liquid aviation fuel, is a research hotspot for SAF production. Advanced PtL technology can address the challenges of green electricity utilization and green hydrogen transportation, and contribute to the advanced manufacturing of fully green biojet fuel and the high-value utilization of CO2. Currently, the main PtL technology routes include the methanol / olefin intermediate route and the Fischer-Tropsch synthesis route.

[0003] The methanol / olefin intermediate route involves hydrogenating CO2 to produce a methanol / olefin intermediate, which then undergoes C-C coupling / aromatization over a molecular sieve to produce long-chain alkanes / aromatics. Molecular sieves commonly used in this process include SAPO-34, SSZ-13, and ZSM-5. However, CO2 hydrogenation to methanol is more active at relatively low temperatures (<350°C), while the second C-C coupling / aromatization step must be performed above 400°C. This often results in excessive CO selectivity at high temperatures, while CO2 conversion and product yields are low at low temperatures. These low-temperature kinetic limitations and high-temperature thermodynamic limitations make efficient catalytic CO2 hydrogenation to liquid fuels via the methanol / olefin intermediate route extremely challenging. Furthermore, the second C-C coupling or aromatization step to produce multi-carbon hydrocarbons uses a molecular sieve catalyst, which is prone to carbon deposition and requires continuous regeneration in industrial production, placing high demands on the reaction apparatus and process conditions.

[0004] The Fischer-Tropsch synthesis route involves first converting CO2 into CO through the reverse water-gas shift (RWGS) reaction, then hydrogenating the CO into liquid hydrocarbons through the Fischer-Tropsch synthesis (FT) process, and finally refining the resulting full-component aviation kerosene. However, this technical route still faces the technical challenges of RWGS thermodynamic equilibrium limitations and CO2 activation difficulties. Patent CN117019210A discloses a method for catalyzing CO x A bifunctional microsphere catalyst for the synthesis of aromatic chemicals and liquid fuels from (CO2 / CO) and H2 and its preparation method. It closely combines basic metal oxides with molecular sieves to improve the synergistic efficiency of active sites and achieve CO xOne-step conversion of hydrogenation and aromatization. Among the products, the selectivity of aromatics and C6-C12 liquid fuels is greater than 90% and 80% respectively, and the selectivity of methane is less than 3%. However, this technology also has problems such as complex catalyst preparation process, high production cost, and easy carbon deposition and deactivation of molecular sieves. Patent CN114479902A discloses a device and method for catalytic hydrogenation of carbon dioxide to gasoline. After pretreatment, CO2 and H2 enter the reactor and generate gasoline and other by-products under the action of a segmented catalyst; the exhaust gas circulation is combined with membrane separation technology to reduce raw material consumption and separation energy consumption. However, the products of this technology are mainly low-carbon gasoline components, which cannot be used as aviation fuel; at the same time, the CO2 single-pass conversion rate is only 28%-31%, and it is necessary to rely on the circulation system to improve the total conversion rate, which may increase operating costs. Patent CN115555022B discloses a method for preparing an iron-based carbon dioxide hydrogenation catalyst to hydrocarbons. The core of the method is to optimize the grain size and crystal structure of iron oxide or hydroxide through high-temperature heat treatment (800-2000°C), combine it with carriers such as manganese oxide and aluminum oxide, and use alkali metal additives to prepare the catalyst by tableting or extrusion. The catalyst performs excellently in the carbon dioxide hydrogenation reaction, with a single-pass conversion rate of over 40%, a methane and carbon monoxide selectivity of less than 10%, and a high selectivity for long-chain hydrocarbons (C5 + ) selectivity exceeds 50%. However, this method uses high-temperature heat treatment (up to 2000℃) and consumes a lot of energy; although C5 + The selectivity is more than 50%, but the jet fuel components (C9-C 16 ) is still relatively low.

[0005] Therefore, in view of the above situation, there is an urgent need to develop a method for preparing aviation fuel by hydrogenating carbon dioxide to overcome the shortcomings in current practical applications. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing aviation fuel by hydrogenating carbon dioxide to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for preparing aviation fuel by hydrogenating carbon dioxide comprises the following steps: (1) Carbon dioxide and hydrogen are introduced into a fixed bed reactor A loaded with a solid catalyst a for reaction; (2) The product from reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase is passed into a condensation crystallizer for dewaxing operation; (3) The dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction; (4) The liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain a light fraction, a jet fuel component, a low-freezing point diesel fraction, and a high-freezing point diesel fraction.

[0008] As a further solution of the present invention: in step (1), the molar ratio of the raw gas of carbon dioxide and hydrogen is n(CO2):n(H2)=1:5-1:2.

[0009] As a further embodiment of the present invention: the solid catalyst a is composed of a carrier, a metal main active component, an alkali metal / alkaline earth metal additive P1 and a metal additive P2, and its preparation method includes: (1) The salt of the metal main active component is prepared into a solution, loaded onto the carrier by an equal volume impregnation method, dried and calcined at 400-500°C to obtain a catalyst intermediate m; (2) The salts of alkali metal / alkaline earth metal promoter P1 and metal promoter P2 are prepared into a solution, loaded onto the catalyst intermediate m by an equal volume impregnation method, dried, and calcined at 400-450°C to obtain a solid catalyst a.

[0010] As a further solution of the present invention: the main metal active component is Fe, and the loading amount is 10-30 wt%; the carrier is one of ZrO2, MgO, SiO2, TiO2, Al2O3 or CeO2.

[0011] As a further embodiment of the present invention: the alkali metal / alkaline earth metal additive P1 is one or more of Na, K, Cs or Ca, with a loading amount of 1-5 wt%; the metal additive P2 is one or more of Cu, Zn, Co, Mo, Ga, Pt, In or W, with a loading amount of 1-10 wt%.

[0012] As a further solution of the present invention: in step (1), the solid catalyst a needs to be reduced with hydrogen before use, and the reduction temperature is 400-500°C.

[0013] As a further solution of the present invention: in step (1), the reaction temperature of the fixed bed reactor A is 300-400°C, the reaction pressure is 2-8 MPa, and the reaction volume space velocity is 1000-10000 h -1 .

[0014] As a further solution of the present invention: in step (2), the temperature of the three-phase separator is 60°C, and the temperature of the condensation crystallizer is 5°C.

[0015] As a further embodiment of the present invention: in step (3), the solid catalyst b comprises 20-40 wt% Y molecular sieve, 10-20 wt% ZSM-22 molecular sieve, 30-45 wt% nickel and γ-Al2O3, and the sum of the mass fractions of the components is 100%.

[0016] As a further solution of the present invention: in step (3), the reaction temperature of the hydroisomerization reactor B is 250-350°C, and the reaction pressure is 2-8 MPa; the solid catalyst b needs to be reduced with hydrogen before use, and the reduction temperature is 400-500°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention efficiently couples the CO2 reverse water-gas shift reaction (RWGS) and Fischer-Tropsch synthesis (FT) processes by designing a bifunctional catalyst, breaking the thermodynamic equilibrium limitation and solving the technical problem of CO2 activation. The CO2 single-pass conversion rate exceeds 50%, and the jet fuel component selectivity exceeds 50%. 2. The CO2 hydrogenation catalyst designed by the present invention is simple to prepare and has a long service life, which greatly reduces the investment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of a method for preparing aviation fuel by hydrogenating carbon dioxide in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0021] See also Figure 1The method of preparing aviation fuel by hydrogenating carbon dioxide of the present invention efficiently couples the CO2 reverse water gas shift reaction (RWGS) and Fischer-Tropsch synthesis (FT) processes by designing a bifunctional catalyst, thereby breaking the thermodynamic equilibrium limitation and solving the technical problem of difficult activation of CO2. The addition of alkali metal / alkaline earth metal additive P1 helps to improve the adsorption capacity of CO2 on the catalyst surface; the addition of metal additive P2 can adjust the reducibility and electronic structure of the active components of the catalyst; by adjusting the ratio of the two additives P1 and P2, the number of RWGS and FT reaction active sites can be effectively adjusted, thereby efficiently catalyzing the CO2 hydrogenation reaction. Finally, the CO2 hydrogenation product is subjected to isomerization treatment to directly obtain high-quality aviation fuel components. The method of the present invention is implemented by the following steps: (1) Carbon dioxide and hydrogen are introduced into a fixed bed reactor A loaded with solid catalyst a for reaction; (2) The product from reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase enters a condensation crystallizer for dewaxing operation; (3) The dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction; (4) The liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain a light fraction, a jet fuel component, a low-freezing point diesel fraction, and a high-freezing point diesel fraction.

[0022] The molar ratio of raw gas is n (CO2): n (H2) = 1:5-1:2.

[0023] The solid catalyst a is mainly composed of a carrier, a metal main active component, an alkali metal / alkaline earth metal additive P1 and a metal additive P2. The preparation method of the catalyst a is: 1) A solution of a salt of a metal main active component is prepared and loaded onto a support by an equal volume impregnation method, followed by drying and calcination at 400-500°C to obtain a catalyst intermediate m; the metal main active component is Fe, the catalyst support is one of ZrO2, MgO, SiO2, TiO2, Al2O3 or CeO2, and the loading amount of the metal main active component is 10-30 wt%; 2) A solution of salts of an alkali metal / alkaline earth metal promoter P1 and a metal promoter P2 is prepared and loaded onto a catalyst intermediate m by an equal volume impregnation method, followed by drying and calcination at 400-450°C to obtain a catalyst a; the alkali metal / alkaline earth metal promoter P1 is one or more of Na, K, Cs or Ca, and the metal promoter P2 is one or more of Cu, Zn, Co, Mo, Ga, Pt, In or W; the loading amount of the alkali metal / alkaline earth metal promoter P1 is 1-5 wt%, and the loading amount of the metal promoter P2 is 1-10 wt%.

[0024] Catalyst a needs to be reduced with hydrogen at a reduction temperature of 400-500°C.

[0025] The reaction temperature of fixed bed reactor A is 300-400℃, the reaction pressure is 2-8MPa, and the reaction volume space velocity is 1000-10000h -1 .

[0026] The temperature of the three-phase separator is 60°C, and the temperature of the condensation crystallizer is 5°C.

[0027] The solid catalyst b comprises 20-40 wt% Y molecular sieve, 10-20 wt% ZSM-22 molecular sieve, 30-45 wt% nickel, and γ-Al2O3, with the total mass fraction of the Y molecular sieve, ZSM-22 molecular sieve, nickel, and γ-Al2O3 being 100%. The solid catalyst b needs to be reduced with H2 before use at a temperature of 400-500°C.

[0028] The temperature of the fixed bed reactor B is 250-350° C., and the reaction pressure is 2-8 MPa.

[0029] Example 1: A 1M ferric nitrate solution was loaded onto a certain mass of SiO2 carrier by an equal volume impregnation method so that the Fe loading was 15 wt%, and then dried and calcined at 400°C to obtain a catalyst intermediate m; an alkali metal additive KNO3 and a metal additive Cu(NO3)2 were prepared into a solution, loaded onto the catalyst intermediate m by an equal volume impregnation method, and then dried and calcined at 450°C to obtain a catalyst a, wherein the K loading was 1 wt% and the Cu loading was 2 wt%; the catalyst a was loaded into a fixed bed reactor A, and H2 was introduced and reduced at 400°C for 6h; carbon dioxide and hydrogen raw materials were introduced into a fixed bed reactor A loaded with solid catalyst a for reaction, wherein the raw gas molar ratio was n(CO2): n(H2)=1:3, the reaction temperature was 300°C, the reaction pressure was 3MPa, and the reaction space velocity was 3000 h -1 The CO2 single-pass conversion rate of this process is 50%; the product of reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase enters a condensation crystallizer for dewaxing operation; the dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction at a temperature of 350°C and a pressure of 3 MPa; the liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain light fractions, aviation kerosene components, low-freezing point diesel fractions and high-freezing point diesel fractions, among which the selectivity of the aviation kerosene component is 50%.

[0030] Example 2: A 1M ferric nitrate solution was loaded onto a certain mass of SiO2 carrier by an equal volume impregnation method so that the Fe loading was 30 wt%, and then dried and calcined at 450°C to obtain a catalyst intermediate m; an alkali metal additive KNO3, an alkaline earth metal additive Ca(NO3)2, and metal additives Cu(NO3)2 and Ga(NO3)2 were prepared into a solution and loaded onto the catalyst intermediate m by an equal volume impregnation method, and then dried and calcined at 450°C to obtain a catalyst a, wherein the K loading was 1 wt%, the Ca loading was 1 wt%, the Cu loading was 2 wt%, and the Ga loading was 2 wt%; the catalyst a was loaded into a fixed bed reactor A, and H2 was introduced and reduced at 350°C for 6h; carbon dioxide and hydrogen raw materials were introduced into a fixed bed reactor A loaded with solid catalyst a for reaction, wherein the raw gas molar ratio was n(CO2): n(H2)=1:3, reaction temperature is 350℃, reaction pressure is 3MPa, reaction space velocity is 3000h -1 The CO2 single-pass conversion rate of this process is 58%; the product of reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase enters a condensation crystallizer for dewaxing operation; the dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction at a temperature of 350°C and a pressure of 3 MPa; the liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain light fractions, aviation kerosene components, low-freezing point diesel fractions and high-freezing point diesel fractions, among which the selectivity of the aviation kerosene component is 55%.

[0031] Example 3: A 1M ferric nitrate solution was loaded onto a certain mass of CeO2 carrier by an equal volume impregnation method so that the Fe loading was 30 wt%, and then dried and calcined at 450°C to obtain a catalyst intermediate m; an alkali metal additive KNO3, Cs(NO3)2 and a metal additive Zn(NO3)2, Ga(NO3)2 were prepared into a solution and loaded onto the catalyst intermediate m by an equal volume impregnation method, and then dried and calcined at 400°C to obtain a catalyst a, wherein the K loading was 2 wt%, the Cs loading was 1 wt%, the Zn loading was 2 wt%, and the Ga loading was 5 wt%; the catalyst a was loaded into a fixed bed reactor A, and H2 was introduced and reduced at 400°C for 6 h; carbon dioxide and hydrogen raw materials were introduced into a fixed bed reactor A loaded with solid catalyst a for reaction, wherein the raw gas molar ratio was n(CO2): n(H2)=1:3, reaction temperature is 320℃, reaction pressure is 5MPa, reaction space velocity is 5000h -1The CO2 single-pass conversion rate of this process is 60%; the product of reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase enters a condensation crystallizer for dewaxing operation; the dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction at a temperature of 350°C and a pressure of 4 MPa; the liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain light fractions, aviation kerosene components, low-freezing point diesel fractions and high-freezing point diesel fractions, among which the selectivity of the aviation kerosene component is 62%.

[0032] Example 4: A 1M ferric nitrate solution was loaded onto a certain mass of Al2O3 carrier by an equal volume impregnation method so that the Fe loading was 20wt%, and then dried and calcined at 450°C to obtain a catalyst intermediate m; an alkali metal additive NaNO3 and metal additives Cu(NO3)2 and In(NO3)3 were prepared into a solution, loaded onto the catalyst intermediate m by an equal volume impregnation method, and then dried and calcined at 450°C to obtain a catalyst a, wherein the Na loading was 2wt%, the Cu loading was 3wt%, and the In loading was 1wt%; the catalyst a was loaded into a fixed bed reactor A, and H2 was introduced and reduced at 400°C for 6h; carbon dioxide and hydrogen raw materials were introduced into a fixed bed reactor A filled with solid catalyst a for reaction, wherein the raw gas molar ratio was n(CO2):n(H2)=1:4, the reaction temperature was 380°C, the reaction pressure was 3MPa, and the reaction space velocity was 6000h -1 The CO2 single-pass conversion rate of this process is 50%; the product of reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase enters a condensation crystallizer for dewaxing operation; the dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction at a temperature of 350°C and a pressure of 3 MPa; the liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain light fractions, aviation kerosene components, low-freezing point diesel fractions and high-freezing point diesel fractions, among which the selectivity of the aviation kerosene component is 52%.

[0033] Example 5: A 1M ferric nitrate solution was loaded onto a certain mass of ZrO2 carrier by an equal volume impregnation method so that the Fe loading was 25wt%, and then dried and calcined at 500°C to obtain a catalyst intermediate m; an alkali metal additive NaNO3 and a metal additive Cu(NO3)2, H2PtCl6·6H2O were prepared into a solution, loaded onto the catalyst intermediate m by an equal volume impregnation method, and then dried and calcined at 450°C to obtain a catalyst a, wherein the Na loading was 2wt%, the Cu loading was 3wt%, and the Pt loading was 0.5wt%; the catalyst a was loaded into a fixed bed reactor A, and H2 was introduced and reduced at 400°C for 6h; carbon dioxide and hydrogen raw materials were introduced into a fixed bed reactor A filled with solid catalyst a for reaction, wherein the raw gas molar ratio was n(CO2): n(H2)=1:3, the reaction temperature was 300°C, the reaction pressure was 3MPa, and the reaction space velocity was 3000h -1 The CO2 single-pass conversion rate of this process is 55%; the product of reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase enters a condensation crystallizer for dewaxing operation; the dewaxed oil phase is passed into a hydroisomerization reactor B filled with solid catalyst b for reaction at a temperature of 350°C and a reaction pressure of 3MPa; the liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain light fractions, aviation kerosene components, low-freezing point diesel fractions and high-freezing point diesel fractions, among which the selectivity of the aviation kerosene component is 60%.

[0034] It should be noted that, in the present invention, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing aviation fuel by hydrogenating carbon dioxide, characterized in that: The following steps are involved: (1) Carbon dioxide and hydrogen are introduced into a fixed bed reactor A loaded with a solid catalyst a for reaction; (2) The product from reactor A is passed into a three-phase separator to separate and remove gas and water, and the remaining liquid phase is passed into a condensation crystallizer for dewaxing operation; (3) The dewaxed oil phase is passed into a hydroisomerization reactor B filled with a solid catalyst b for reaction; (4) The liquid effluent from reactor B is passed into an atmospheric distillation tower for separation to obtain a light fraction, a jet fuel component, a low-freezing point diesel fraction, and a high-freezing point diesel fraction.

2. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: In step (1), the molar ratio of the raw gas of carbon dioxide and hydrogen is n(CO2):n(H2)=1:5-1:

2.

3. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: The solid catalyst a is composed of a carrier, a metal main active component, an alkali metal / alkaline earth metal additive P1 and a metal additive P2, and its preparation method includes: (1) The salt of the metal main active component is prepared into a solution, loaded onto the carrier by an equal volume impregnation method, dried and calcined at 400-500°C to obtain a catalyst intermediate m; (2) The salts of alkali metal / alkaline earth metal promoter P1 and metal promoter P2 are prepared into a solution, loaded onto the catalyst intermediate m by an equal volume impregnation method, dried, and calcined at 400-450°C to obtain a solid catalyst a.

4. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 3, characterized in that: The main active metal component is Fe, and the loading amount is 10-30 wt%; the carrier is one of ZrO2, MgO, SiO2, TiO2, Al2O3 or CeO2.

5. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 3, characterized in that: The alkali metal / alkaline earth metal additive P1 is one or more of Na, K, Cs or Ca, with a loading amount of 1-5 wt%; the metal additive P2 is one or more of Cu, Zn, Co, Mo, Ga, Pt, In or W, with a loading amount of 1-10 wt%.

6. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: In step (1), the solid catalyst a needs to be reduced with hydrogen before use, and the reduction temperature is 400-500°C.

7. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: In step (1), the reaction temperature of the fixed bed reactor A is 300-400°C, the reaction pressure is 2-8 MPa, and the reaction volume space velocity is 1000-10000h -1 .

8. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: In step (2), the temperature of the three-phase separator is 60°C, and the temperature of the condensation crystallizer is 5°C.

9. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: In step (3), the solid catalyst b comprises 20-40 wt% Y molecular sieve, 10-20 wt% ZSM-22 molecular sieve, 30-45 wt% nickel and γ-Al2O3, and the sum of the mass fractions of each component is 100%.

10. The method for preparing aviation fuel by hydrogenating carbon dioxide according to claim 1, characterized in that: In step (3), the reaction temperature of the hydroisomerization reactor B is 250-350°C, and the reaction pressure is 2-8 MPa; the solid catalyst b needs to be reduced with hydrogen before use, and the reduction temperature is 400-500°C.

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