Fischer-tropsch synthesis process

Abstract

The application relates to the field of Fischer-Tropsch synthesis, and discloses a Fischer-Tropsch synthesis method, which comprises the following steps: under Fischer-Tropsch synthesis reaction conditions, contacting synthesis gas with a Fischer-Tropsch synthesis catalyst, wherein the Fischer-Tropsch synthesis catalyst comprises zirconium oxide and cobalt, the content of cobalt elements is 5-35 wt% based on the total amount of the Fischer-Tropsch synthesis catalyst, and the content of zirconium oxide is 65-95 wt%; and the content of zirconium oxide in the form of monoclinic phase is more than 50% based on the total amount of zirconium oxide. The method provided by the application can effectively improve the CO conversion rate and the heavy hydrocarbon (C5 + ) selectivity.

Description

Technical Field

[0001] This invention relates to the field of Fischer-Tropsch synthesis, and more specifically to a method for Fischer-Tropsch synthesis. Background Technology

[0002] Fischer-Tropsch synthesis is a process that uses syngas (a certain proportion of carbon monoxide and hydrogen) as raw materials to synthesize hydrocarbons under high temperature, high pressure, and catalysis. In the face of increasing environmental pollution and the oil crisis, utilizing Fischer-Tropsch synthesis to synthesize non-petroleum carbon resources into liquid fuels and high-value chemicals is crucial. Although the raw materials for Fischer-Tropsch synthesis consist only of carbon monoxide and hydrogen, hydrocarbons with different carbon numbers are generated during the reaction, resulting in an extremely complex product distribution. It is generally believed that the product distribution of Fischer-Tropsch synthesis follows the ASF distribution law, that is, except for methane, low-carbon hydrocarbons (C4H4O) account for a large proportion of the product distribution. 2-4 ), gasoline (C 5-11 ), kerosene (C 8-16 ) and diesel (C 11-20 The maximum selectivity values ​​were 58%, 48%, 41%, and 40%, respectively. Commonly used Fischer-Tropsch synthesis catalysts are iron, cobalt, and ruthenium. Among them, cobalt-based catalysts have higher single-pass conversion and higher selectivity and stability for heavy hydrocarbons at lower reaction temperatures. Therefore, the development and utilization of cobalt-based catalysts have attracted widespread attention.

[0003] In practical applications, supported catalysts are commonly used to stabilize and disperse metals. Cobalt-based catalysts often use oxides (silicon oxide, alumina, zirconium oxide, titanium oxide, etc.), molecular sieves, and carbon materials as supports. Adding promoters (K, Na, Mn, etc.) can effectively improve the Fischer-Tropsch performance of the catalyst. Zirconia has abundant oxygen vacancies and a certain degree of acidity and basicity on its surface. Its inertness is stronger than oxides such as silicon oxide and alumina, making it less prone to generating reducible species due to excessively strong interactions with metals. It also possesses three crystalline phases (monoclinic, tetragonal, and cubic), making it a highly promising support. Liu et al. prepared zirconium oxide supports using the sol-gel method and investigated the effect of support pore size on the Fischer-Tropsch performance of cobalt-based catalysts. They found that increasing pore size and calcination temperature weakens the metal-support interaction in the catalyst, effectively promoting metal reduction and increasing catalytic activity and heavy hydrocarbon selectivity (Green Chem., 2007, 9, 611-615). Shi Lihong et al. modified cobalt-based catalysts by changing the calcination temperature of the zirconium oxide support, finding that a support calcined at 400°C was most conducive to the dispersion of metallic cobalt, thus exhibiting the highest activity and heavy hydrocarbon selectivity (Molecular Catalysis, 2007, 21: 107-108). Zhang et al. added CeO2 as a promoter to Co / ZrO2 catalysts and found that the addition of an appropriate amount of CeO2 could promote the dispersion and reduction of metallic cobalt, which was beneficial to improving the activity (Fuel, 2016, 184: 162-168). Chinese patent application CN1460546A prepared Co / ZrO2 catalysts by adjusting the pH of cobalt nitrate solution. This series of catalysts has a simple preparation process and exhibits excellent activity and C 5+ Selectivity.

[0004] No reports have been found on how to effectively optimize the application of zirconium oxide in the Fischer-Tropsch synthesis reaction. Summary of the Invention

[0005] The purpose of this invention is to provide a Fischer-Tropsch synthesis method that can effectively improve CO conversion and the production of heavy hydrocarbons (C5). + Selectivity.

[0006] To achieve the above objectives, the present invention provides a Fischer-Tropsch synthesis method, the method comprising: contacting syngas with a Fischer-Tropsch synthesis catalyst under Fischer-Tropsch synthesis reaction conditions, wherein the Fischer-Tropsch synthesis catalyst comprises zirconium oxide and cobalt, wherein, based on the total amount of the Fischer-Tropsch synthesis catalyst, the content of cobalt is 5-35 wt% and the content of zirconium oxide is 65-95 wt%; and, based on the total amount of zirconium oxide, the content of zirconium oxide existing in monoclinic phase is above 50%.

[0007] Preferably, the calcination temperature during the zirconium oxide preparation process does not exceed 500 °C, the calcination temperature after cobalt loading is not higher than the calcination temperature during the zirconium oxide preparation process, and the reduction temperature of the Fischer-Tropsch synthesis catalyst is not higher than the calcination temperature after cobalt loading, but not lower than 350 °C.

[0008] The inventors of this invention discovered during their research that using a specific ratio of zirconium oxide with a specific amount of cobalt in the Fischer-Tropsch synthesis process is beneficial for the dispersion and reduction of metallic cobalt in the supported cobalt-based Fischer-Tropsch catalyst, thereby resulting in excellent CO conversion and high heavy hydrocarbon (C5) conversion. + Selectivity. Attached Figure Description

[0009] Figure 1 These are the XRD patterns of zirconium oxide from Examples 1-4 and Comparative Example 1. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] This invention provides a Fischer-Tropsch synthesis method, which includes: contacting syngas with a Fischer-Tropsch synthesis catalyst under Fischer-Tropsch synthesis reaction conditions, wherein the Fischer-Tropsch synthesis catalyst comprises zirconium oxide and cobalt, wherein the cobalt content is 5-35 wt% and the zirconium oxide content is 65-95 wt% based on the total amount of the Fischer-Tropsch synthesis catalyst; and the zirconium oxide content existing in monoclinic phase is above 50% based on the total amount of zirconium oxide.

[0012] In this invention, the contents of cobalt and zirconium oxide are determined by X-ray fluorescence (XRF) method.

[0013] In this invention, the crystal form of the zirconium oxide can be determined by X-ray diffraction (XRD). In the XRD pattern of standard monoclinic zirconium oxide (m-ZrO2), the characteristic diffraction peaks at 2θ of 24.1°, 27.9°, and 31.4° can be attributed to (110) of m-ZrO2, respectively. (111) crystal plane (JCPDS 001-0750); In the XRD pattern of standard tetragonal zirconia (t-ZrO2), the characteristic diffraction peaks at 2θ of 30.5°, 35.6°, 51.0°, and 60.5° can be attributed to the (101), (110), (200), and (211) crystal planes of t-ZrO2 (JCPDS 002-0733), respectively. Through the formula... ×100%, the content of monoclinic zirconium oxide was calculated ( X m ).in, and These represent m-ZrO2 in the XRD pattern. The fitting intensity (fitting peak area) of the (111) crystal plane. The fitting intensity (fitting peak area) of the t-ZrO2 (101) crystal plane in the XRD spectrum represents the fitting intensity (fitting peak area).

[0014] According to a preferred embodiment of the present invention, based on the total amount of the Fischer-Tropsch synthesis catalyst, the cobalt content is 16-30 wt%, for example, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, or 30 wt%, and the zirconium oxide content is 70-84 wt%, for example, 70 wt%, 72 wt%, 74 wt%, 76 wt%, 78 wt%, 80 wt%, 82 wt%, or 84 wt%.

[0015] According to the present invention, the Fischer-Tropsch synthesis catalyst is preferably composed of zirconium oxide and the active component cobalt.

[0016] The present invention does not particularly limit the form in which cobalt exists. It can exist in an oxidized state, a reduced state, or a partially oxidized and partially reduced state. Catalysts containing cobalt in different forms are all within the protection scope of the present invention.

[0017] In this invention, preferably, the content of zirconium oxide existing in monoclinic phase is 70-100% based on the total amount of zirconium oxide. This preferred embodiment is more conducive to improving the CO conversion rate and the production of heavy hydrocarbons (C5+) of the catalyst. + Selectivity.

[0018] According to a preferred embodiment of the present invention, the method for preparing the Fischer-Tropsch synthesis catalyst includes the following steps:

[0019] (1) Zirconia was prepared by hydrothermal method;

[0020] (2) The cobalt precursor is introduced into the zirconium oxide by impregnation, followed by drying and calcination;

[0021] (3) Reduce the roasted product obtained in step (2).

[0022] The present invention does not have any particular limitation on the method of preparing zirconium oxide by hydrothermal method in step (1), as long as the zirconium oxide with the crystal form described above can be obtained. Preferably, step (1) includes: reacting zirconium salt precursor solution and precipitant under hydrothermal conditions, and then drying and calcining.

[0023] Preferably, the zirconium salt precursor includes at least one selected from zirconium nitrate, zirconium oxynitrate, zirconium oxychloride, zirconium chloride, and zirconium acetate. This invention uses zirconium oxynitrate as an example for illustrative purposes, but the invention is not limited thereto.

[0024] According to the present invention, preferably, the solvent in the zirconium salt precursor solution includes water and optionally an alcohol, with the water content being 90-100% by volume based on the total amount of solvent. By controlling the water content in the solvent, it is more advantageous to obtain a catalyst with improved performance.

[0025] The present invention has a wide range of choices for the alcohols, and various alcohols commonly used can be used in the present invention, such as C1-C5 alcohols, including but not limited to methanol, ethanol or propanol, with methanol being preferred.

[0026] Preferably, the precipitant is selected from at least one of urea, ammonia, ammonium carbonate and hexadecyltrimethylammonium chloride, more preferably urea.

[0027] According to the present invention, preferably, the molar ratio of the precipitant to the zirconium salt precursor is 3-30, more preferably 8-12.

[0028] According to the present invention, preferably, the hydrothermal conditions include: a hydrothermal temperature of 100-250 °C, more preferably 120-200 °C; and a hydrothermal time of 10-30 hours, more preferably 20-24 hours. The hydrothermal conditions of this preferred embodiment are more conducive to obtaining perfectly crystalline zirconia and to improving the Fischer-Tropsch synthesis performance of the catalyst.

[0029] According to the present invention, the hydrothermal reaction is carried out under closed conditions. The present invention does not particularly limit the equipment used for carrying out the hydrothermal reaction; for example, it can be a hydrothermal reactor, including but not limited to a polytetrafluoroethylene liner within a stainless steel hydrothermal reactor, which is then sealed and placed in an oven for the reaction.

[0030] Preferably, the calcination conditions in step (1) include: a calcination temperature of 300-700°C, preferably 400-500°C; a calcination time of 2-10 hours, preferably 3-8 hours; a calcination heating rate of 1-5 °C / min; and preferably an atmosphere of air, nitrogen, or argon.

[0031] According to the present invention, preferably, before the calcination in step (1), the hydrothermal reaction product is further washed and dried. The washing and drying methods and conditions can be carried out according to conventional techniques in the art. Preferably, in the washing method, after the hydrothermal process is completed, the supernatant is discarded, and the precipitate is washed repeatedly with water and ethanol multiple times, for example, 2-10 times. Preferably, the drying conditions include: using forced-air drying or vacuum drying; drying temperature of 50-150°C, preferably 80-120°C; and drying time of 4-48 hours, preferably 8-16 hours.

[0032] According to the present invention, preferably, the method further includes grinding the dried product after drying in step (1) and then calcining it.

[0033] By controlling the solvent, hydrothermal reaction conditions, precipitant, and zirconium precursor ratio in the above zirconium oxide process, the zirconium oxide crystal phase type and ratio can be effectively controlled, resulting in a catalyst with better Fischer-Tropsch synthesis performance.

[0034] In the method provided by the present invention, there is no particular limitation on the impregnation method. It can be impregnation of equal volume or impregnation of excess volume, and is preferably impregnation of equal volume.

[0035] According to a preferred embodiment of the present invention, the introduction of a cobalt precursor into the zirconium oxide by impregnation specifically includes: impregnating the zirconium oxide with an impregnation solution containing the cobalt precursor, and then performing the drying and calcination described in step (2).

[0036] The present invention does not particularly limit the type of cobalt precursor, but preferably, the cobalt precursor is selected from at least one of cobalt nitrate, cobalt acetate and cobalt chloride.

[0037] Those skilled in the art can select the concentration of the impregnation solution containing the cobalt precursor based on the target cobalt content.

[0038] The present invention has a wide range of choices for the drying method and conditions in step (2). Preferably, the drying method is blower drying or vacuum drying, the drying temperature is 50-150°C, preferably 80-120°C, and the drying time is 4-48 hours, preferably 8-16 hours.

[0039] According to the present invention, preferably, the calcination conditions in step (2) include: a calcination temperature of 300-500 °C, preferably 350-450 °C; a calcination time of 2-8 hours, preferably 4-6 hours; a calcination heating rate of 1-5 °C / min; and preferably an atmosphere of air, nitrogen, argon or nitric oxide.

[0040] In this invention, the roasting in steps (1) and (2) can be carried out independently in a tube furnace or a muffle furnace.

[0041] According to a preferred embodiment of the present invention, preferably, the reduction conditions in step (3) include: being carried out in a hydrogen-containing atmosphere, a reduction temperature of 300-500 °C, preferably 400-450 °C, a pressure of 0.1-1 MPa, preferably 0.1-0.5 MPa, and a time of 3-15 hours, preferably 5-10 hours. More preferably, the hydrogen-containing atmosphere is a pure hydrogen atmosphere.

[0042] According to a preferred embodiment of the present invention, the calcination temperature during the zirconium oxide preparation process (i.e., the calcination temperature described in step (1)) does not exceed 500 °C, the calcination temperature after cobalt loading (i.e., the calcination temperature described in step (2)) is not higher than the calcination temperature during the zirconium oxide preparation process, and the reduction temperature of the Fischer-Tropsch synthesis catalyst (i.e., the reduction temperature described in step (3)) is not higher than the calcination temperature after cobalt loading, and not lower than 350 °C. More preferably, the calcination temperature during the zirconium oxide preparation process is 400-500 °C, the calcination temperature after cobalt loading is 0-100 °C lower than the calcination temperature during the zirconium oxide preparation process, and the reduction temperature of the Fischer-Tropsch synthesis catalyst is 0-50 °C lower than the calcination temperature after cobalt loading. The optimal method for calcining the support can ensure the stability of the zirconia crystal phase and pore structure of the support. The optimal method for calcining the support after cobalt loading can ensure the stability of the support after cobalt loading. The optimal method for the reduction temperature of the Fischer-Tropsch synthesis catalyst can ensure the full reduction of cobalt particles. If the above optimal ranges are not met, for example, if the calcination temperature of the support is too high, it will cause the collapse of the pore structure and a significant decrease in the specific surface area, thereby affecting the subsequent dispersion of cobalt. If the calcination temperature after cobalt loading is too high, it will destroy the support structure and cause cobalt particles to agglomerate. If the reduction temperature is too high, it will also cause cobalt particles to agglomerate. If the reduction temperature is too low, it will not be able to fully reduce cobalt oxide to metallic cobalt, which will affect the full utilization of active sites.

[0043] According to the present invention, preferably, the conditions for the Fischer-Tropsch synthesis reaction include: an H2 / CO volume ratio of 1-2 in the reactant gas, a reaction temperature of 200-250 °C, a reaction pressure of 1.5-4 MPa, and a reaction volume hourly space velocity of 1000-10000 h⁻¹. -1 .

[0044] There are no particular limitations on the reactor used for the Fischer-Tropsch synthesis reaction, but a fixed-bed reactor is preferred. According to one specific embodiment of the invention, the catalyst is packed with a mesh size of 20-40; the dilution ratio of the catalyst to quartz sand is 5-30, preferably 10-15; after the catalyst is packed, the reaction is carried out after in-situ reduction, and the gaseous products are detected by online chromatography, while the liquid products are detected offline.

[0045] The present invention will be described in detail below through embodiments.

[0046] Example 1

[0047] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate, dissolve it in 150 mL of deionized water, stir evenly, then add 15.4 g of urea, stir the mixture evenly, pour it into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven at 160°C for 24 hours. After the reactor cools down, discard the supernatant, wash the precipitate repeatedly with water and ethanol more than 5 times, and dry it in a forced-air oven at 120°C for 12 hours. Grind the dried powder, calcine it in a muffle furnace, introduce air, raise the temperature to 400°C at a rate of 2°C / min, and calcine at 400°C for 3 hours to obtain the support named Z1. Its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that pure monoclinic zirconium oxide can be obtained by using pure water as a solvent.

[0048] (2) Catalyst preparation: Take 2g of Z1 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z1. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain the Co / Z1 catalyst.

[0049] (3) Catalyst reduction: Take 1g of catalyst (20-40 mesh), mix it with quartz sand of the same mesh size at a ratio of 1:10, and then pack it into a fixed-bed reactor. The inner diameter of the reaction tube used is 18 mm, and the length of the isothermal zone is 40 mm. Subsequently, the catalyst is reduced in situ using pure hydrogen gas at a reduction temperature of 400°C, a pressure of 0.1 MPa, and a reduction time of 10 h.

[0050] Example 2

[0051] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate, dissolve it in 150 mL of deionized water, stir evenly, then add 15.4 g of urea, stir the mixture evenly, pour it into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven at 160°C for 24 hours. After the reactor cools down, discard the supernatant, wash the precipitate repeatedly with water and ethanol more than 5 times, and dry it in a forced-air oven at 120°C for 12 hours. Grind the dried powder, calcine it in a muffle furnace, introduce air, and calcine at 500°C for 3 hours to obtain the support named Z2, whose XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that Z2 is still pure monoclinic zirconium oxide.

[0052] (2) Catalyst preparation: Take 2g of Z2 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (25 wt%). Add the prepared cobalt nitrate solution dropwise to Z2. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120°C and then put it into a tube furnace. Air is introduced and the temperature is raised to 450°C at a heating rate of 2°C / min. Keep it for 4 hours to obtain the Co / Z2 catalyst.

[0053] (3) Reduction of catalyst: Same as in Example 1.

[0054] Example 3

[0055] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate, dissolve it in 150 mL of deionized water, stir evenly, then add 15.4 g of urea, stir the mixture evenly, pour it into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven at 160°C for 24 hours. After the reactor cools down, discard the supernatant, wash the precipitate repeatedly with water and ethanol more than 5 times, and dry it in a forced-air oven at 120°C for 12 hours. Grind the dried powder, calcine it in a muffle furnace, introduce air, raise the temperature to 600°C at a rate of 2°C / min, and calcine at 600°C for 3 hours to obtain the support named Z3. Its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that Z3 is still pure monoclinic zirconium oxide, and its crystallinity increases significantly with the increase of calcination temperature.

[0056] (2) Catalyst preparation: Take 2g of Z3 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z3. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain the Co / Z3 catalyst.

[0057] (3) Reduction of catalyst: Same as in Example 1.

[0058] Example 4

[0059] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate and dissolve it in 150 mL of mixed solution (90% methanol by volume). After stirring evenly, add 15.4 g of urea and stir the mixed solution evenly. Pour the solution into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven at 160°C for 24 hours. After the reactor cools down, discard the supernatant and wash the precipitate repeatedly with water and ethanol more than 5 times. Dry it in a forced-air oven at 120°C for 12 hours. Grind the dried powder and calcine it in a muffle furnace. Pour air through the furnace and raise the temperature to 400°C at a rate of 2°C / min. Calcine at 400°C for 3 hours to obtain the support, named Z4. Its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that Z4 exhibits characteristic diffraction peaks of both monoclinic and tetragonal zirconium oxide phases. Calculations show that the monoclinic phase accounts for 70.4%.

[0060] (2) Catalyst preparation: Take 2g of Z4 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z4. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120°C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400°C at a heating rate of 2°C / min. Keep it for 4 hours to obtain the Co / Z4 catalyst.

[0061] (3) Reduction of catalyst: Same as in Example 1.

[0062] Example 5

[0063] (1) Preparation of carrier zirconia: Same as in Example 1.

[0064] (2) Catalyst preparation: Same as in Example 1.

[0065] (3) Reduction of catalyst: The reduction temperature was 550°C, and other conditions were the same as in Example 1. The catalyst was denoted as Co / Z1-R550.

[0066] Comparative Example 1

[0067] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate, dissolve it in 150 mL of methanol, stir well, then add 15.4 g of urea, stir the mixture well, pour it into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven for hydrothermal treatment at 160 °C for 24 hours. After the reactor cools down, discard the supernatant, wash the precipitate repeatedly with water and ethanol more than 5 times, and dry it in a forced-air oven at 120 °C for 12 hours. Grind the dried powder, calcine it in a muffle furnace, introduce air, raise the temperature to 400 °C at a rate of 2 °C / min, and calcine at 400 °C for 3 hours to obtain the support named Z5. Its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that the tetragonal zirconium oxide prepared using pure methanol solvent is pure.

[0068] (2) Catalyst preparation: Take 2g of Z5 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z5. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain the Co / Z5 catalyst.

[0069] (3) Reduction of catalyst: Same as in Example 1.

[0070] Comparative Example 2

[0071] The method is the same as in Example 1, except that the zirconium support in step (1) is replaced with an equal mass of commercial γ-Al2O3 (commercially purchased from Aladdin), denoted as Co / Al2O3 catalyst.

[0072] Comparative Example 3

[0073] The method is the same as in Example 1, except that the zirconium support in step (1) is replaced with an equal mass of commercially available SiO2 (commercially purchased from Aladdin), referred to as the Co / SiO2 catalyst.

[0074] Test case

[0075] The performance of the catalysts prepared in the above examples and comparative examples was evaluated. After the reduction, the hydrogen atmosphere was switched to Fischer-Tropsch reaction feed gas. The H2 / CO volume ratio in the Fischer-Tropsch reaction feed gas was 2, the reaction temperature was 220°C, the reaction pressure was 2 MPa, and the reaction volume hourly space velocity was 4800 h⁻¹. -1 The feed gas and reaction gaseous products were analyzed online using an Agilent 7890A gas chromatograph, while the liquid products were collected, separated, and weighed using both hot and cold traps before offline analysis. All performance evaluation results are shown in Table 1.

[0076] Table 1

[0077]

[0078] As shown in Table 1, the Co / ZrO2 catalyst prepared by the method provided in this invention exhibits excellent Fischer-Tropsch synthesis performance. Pure monoclinic zirconium oxide can be obtained when pure water is used as the solvent. The crystallinity of the support can be altered by changing the calcination temperature of the zirconium oxide. Calcination temperatures exceeding 500 °C cause a decrease in the specific surface area of ​​the zirconium oxide, thus affecting the dispersion of metallic cobalt. Table 1 shows that the catalyst exhibits the highest CO conversion rate when Z1 calcined at 400 °C is used as the support. Comparing Examples 1-3, it is evident that as the calcination temperature increases, the methane selectivity significantly increases while the conversion rate decreases significantly. Pure tetragonal zirconium oxide can be obtained when methanol is used as the solvent. The CO conversion rate of this catalyst, Co / Z5, is significantly lower than that of Co / Z1. When a 90% methanol solution is used as the solvent, a mixed phase of monoclinic and tetragonal zirconium oxide is obtained, with the monoclinic phase accounting for 70.4%, exhibiting significantly better performance than Co / Z5. This indicates that monoclinic zirconium oxide is more favorable for the Fischer-Tropsch reaction than tetragonal zirconium oxide. It is worth noting that, in order to further improve the performance of the catalyst, the calcination temperature and the reduction temperature need to be coordinated. If a reduction temperature higher than the calcination temperature is used, it may lead to the agglomeration of metallic cobalt and instability of the support structure, as seen in Example 5, where the catalyst conversion rate decreased significantly. Compared with the results of the examples, when conventional oxides (Al2O3 and SiO2) were used as supports in the comparative examples, the catalyst activity and heavy hydrocarbon production were inhibited, while the methane selectivity was significantly increased.

[0079] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A Fischer-Tropsch synthesis process characterised in that, The method includes: contacting syngas with a Fischer-Tropsch synthesis catalyst under Fischer-Tropsch synthesis reaction conditions, wherein the Fischer-Tropsch synthesis catalyst comprises zirconium oxide and cobalt, with the cobalt content being 16-26 wt% and the zirconium oxide content being 74-84 wt% based on the total amount of the Fischer-Tropsch synthesis catalyst; and with the zirconium oxide content existing in monoclinic phase being 70-100% based on the total amount of zirconium oxide. The preparation method of the Fischer-Tropsch synthesis catalyst includes the following steps: (1) Zirconia was prepared by hydrothermal method; (2) The cobalt precursor is introduced into the zirconium oxide by impregnation, followed by drying and calcination; (3) Reduce the calcined product obtained in step (2); The calcination temperature during the zirconium oxide preparation process is 400-500°C, and the calcination temperature after cobalt loading is 0-100°C lower than the calcination temperature during the zirconium oxide preparation process. The reduction temperature of the Fischer-Tropsch synthesis catalyst is 0-50°C lower than the calcination temperature after cobalt loading.

2. The method of claim 1, wherein, Step (1) includes reacting the zirconium salt precursor solution and the precipitant under hydrothermal conditions, followed by drying and calcination.

3. The method of claim 2, wherein, The zirconium salt precursor includes at least one of zirconium nitrate, zirconium oxynitrate, zirconium oxychloride, zirconium chloride, and zirconium acetate.

4. The method of claim 2, wherein, The solvent in the zirconium salt precursor solution includes water, with the water content being 90-100% by volume based on the total amount of solvent.

5. The method of claim 2, wherein, The precipitant is selected from at least one of urea, ammonia, ammonium carbonate, and hexadecyltrimethylammonium chloride.

6. The method of claim 2, wherein, The molar ratio of the precipitant to the zirconium salt precursor is 3-30.

7. The method of claim 6, wherein, The molar ratio of the precipitant to the zirconium salt precursor is 8-12.

8. The method of claim 2, wherein, The hydrothermal conditions include: a hydrothermal temperature of 100-250 °C and a hydrothermal time of 10-30 hours.

9. The method of claim 8, wherein, The hydrothermal conditions include: a hydrothermal temperature of 120-200 °C and a hydrothermal time of 20-24 hours.

10. The method of claim 2, wherein, Drying conditions include: using forced air drying or vacuum drying, with a drying temperature of 50-150°C and a drying time of 4-48 hours.

11. The method of claim 10, wherein, The drying conditions include: a drying temperature of 80-120 °C and a drying time of 8-16 hours.

12. The method of claim 2, wherein, Step (1) includes the following roasting conditions: roasting temperature of 400-500°C; roasting time of 3-8 hours.

13. The method of claim 12, wherein, The roasting conditions in step (1) include an atmosphere of air, nitrogen, or argon.

14. The method of claim 1, wherein, The calcination conditions in step (2) include: calcination temperature of 300-500°C; calcination time of 2-8 hours; and calcination heating rate of 1-5 °C / min.

15. The method of claim 14, wherein, The roasting conditions in step (2) include: roasting temperature of 350-450℃; roasting time of 4-6 hours.

16. The method of claim 15, wherein, The roasting conditions in step (2) include: an atmosphere of air, nitrogen, argon or nitric oxide.

17. The method of claim 1, wherein, The reduction conditions in step (3) include: being carried out in a hydrogen-containing atmosphere, with a reduction temperature of 300-500 °C, a pressure of 0.1-1 MPa, and a time of 3-15 hours.

18. The method of claim 17, wherein, The reduction conditions in step (3) include: a reduction temperature of 400-450 °C, a pressure of 0.1-0.5 MPa, and a time of 5-10 hours.

19. The method of any one of claims 1-18, wherein, The conditions of the Fischer-Tropsch synthesis reaction include: the volume ratio of H2 / CO in the reaction raw material gas is 1-2, the reaction temperature is 200-250 °C, the reaction pressure is 1.5-4 MPa, the reaction volume space velocity is 1000-10000 h -1 .

Images