A catalyst for synthesizing cyclohexylamine from aniline hydrogenation and preparation method thereof

Abstract

The present invention relates to a modified hydrotalcite-derived cobalt catalyst, the general formula being: M / M1(O)-M2(O)-M3(O), wherein M represents Co, M1 represents an alkaline earth metal, M2 represents a rare earth metal, M3 represents Al, n(Co+M1) / n(Al+M2)=2-4, the molar ratio of Co to M1 is 0.5-1.5, and the molar ratio of M2 to Al is 0.005-0.05. Its preparation method includes: dissolving various metal salts and urea in water to form an aqueous solution, crystallizing the aqueous solution to obtain a solid-liquid mixture, filtering the solid-liquid mixture, washing it with water and a modifier, and then dispersing it in the modifier, ultrasonicating it, filtering it, and drying it to obtain a modified hydrotalcite precursor; roasting and reducing it to obtain the catalyst of the present invention. It is used for synthesizing cyclohexylamine by hydrogenation of aniline, and the aniline conversion rate can reach more than 98%, and the selectivity of dicyclohexylamine is less than 3%.

Description

Technical Field

[0001] The present invention relates to the technical field of organic catalysis, and in particular to a catalyst for synthesizing cyclohexylamine by hydrogenating aniline and a preparation method thereof. Background Art

[0002] Cyclohexylamine is an important organic chemical and fine chemical intermediate used in the production of petroleum product additives, metal corrosion inhibitors, fungicides and pesticides, antistatic agents, rubber accelerators and antioxidants, food and feed additives, and synthesis gas desulfurizers. Due to the rapid development of food additives and rubber accelerators, cyclohexylamine, as a raw material, has long been in short supply.

[0003] Currently, cyclohexylamine is produced primarily through four process routes: aniline hydrogenation, cyclohexanol catalytic amination, cyclohexanone catalytic amination, and nitrocyclohexane reduction. Aniline hydrogenation is a mature process, utilizing inexpensive raw materials, and is adopted by most manufacturers both domestically and internationally. The key to this process lies in the catalyst.

[0004] Patents US5322965, US4943549, US5023226, and US6335470 disclose precious metal catalysts such as Ru, Pd, and Pt for the synthesis of cyclohexylamine and dicyclohexylamine. However, these catalysts are expensive, difficult to recycle, and require harsh reaction conditions. Even under high pressures of 28-30 MPa, more than 3% of dicyclohexylamine is still produced as a byproduct.

[0005] Non-precious metal catalysts primarily use Co as the active component. Patents US5728883 and US5705700 disclose an unsupported cobalt catalyst and a method for synthesizing cyclohexylamine and dicyclohexylamine. The catalyst is made by mixing and tableting powders of Co, Mn, alkaline earth metals, and other transition metal oxides. However, disadvantages of this method include a small specific surface area, poor dispersion of the active components, and significant room for improvement in catalytic activity. The byproduct, dicyclohexylamine, is also high in content. Furthermore, the reaction is carried out under a high pressure of 30 MPa, posing safety risks and hindering industrial production.

[0006] The paper "Comparison of hydrogen adsorption and aniline hydrogenation overco-precipitated Co / Al2O3 and Ni / Al2O3 catalysts" reports that a Co / Al2O3 catalyst prepared by co-precipitation was used for the hydrogenation of aniline to cyclohexylamine. The Co loading was 50%, but the aniline conversion and cyclohexylamine selectivity were only 23% and 67.5%, respectively.

[0007] As mentioned above, during the hydrogenation of aniline to synthesize cyclohexylamine, the byproduct dicyclohexylamine is inevitably generated. The formation of dicyclohexylamine not only affects the yield of cyclohexylamine, but also, due to its strong alkalinity, it adsorbs on the catalyst surface, inhibiting the catalyst. Both US Patent No. 4384142 and German Patent No. 4207314 report adding anhydrous ammonia to the raw materials as a coupling inhibitor to reduce the formation of the byproduct dicyclohexylamine, thereby improving the yield of cyclohexylamine. The shortcomings of these technologies are that the introduction of large amounts of ammonia in industrial equipment can cause equipment corrosion, posing a safety hazard; the post-processing process also requires ammonia recovery and analysis, which increases the process and equipment investment; and there is the problem of handling ammonia-containing waste gas.

[0008] Defects of existing technology:

[0009] 1. The preparation method of precious metal catalysts is simple and the product yield is high, but they are expensive and difficult to recycle.

[0010] 2. Insufficient activity of non-precious metal catalysts: In non-precious metal catalysts prepared using conventional impregnation, co-precipitation and mechanical mixing methods, the active components cannot be evenly dispersed. Therefore, even at a higher loading, the catalyst activity is still unsatisfactory; or the reaction conditions are harsh and cannot meet the needs of industrial production.

[0011] 3. In the reaction of aniline hydrogenation to cyclohexylamine, dicyclohexylamine is generally highly selective. Adding anhydrous ammonia or nitropropane to suppress dicyclohexylamine production can lead to equipment corrosion, increase the number of reaction steps and equipment investment, and create problems with the treatment of ammonia-containing waste gas. Summary of the Invention

[0012] In response to the problems of low conversion rate and low selectivity of non-precious metal catalysts in the prior art, one of the problems to be solved by the present invention is to provide a low-cost, highly active modified hydrotalcite-like derived cobalt catalyst. This catalyst can effectively improve the reaction efficiency, inhibit the formation of the byproduct dicyclohexylamine, and increase the yield of cyclohexylamine.

[0013] The second problem to be solved by the present invention is to provide a method for preparing the modified hydrotalcite-like derived cobalt catalyst.

[0014] The third problem to be solved by the present invention is to provide the use of the modified hydrotalcite-like derived cobalt catalyst in the hydrogenation of aniline to synthesize cyclohexylamine.

[0015] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0016] One aspect of the present invention provides a modified hydrotalcite-like derived cobalt catalyst:

[0017] A cobalt catalyst derived from a modified hydrotalcite-like material has the general formula: M / M1(O)-M2(O)-M3(O), wherein M represents the active metal Co, M1 represents an alkaline earth metal, M2 represents a rare earth metal, M3 represents Al, M1(O) represents an alkaline earth metal oxide, M2(O) represents a rare earth metal oxide, and M3(O) represents Al2O3.

[0018] In the catalyst of the present invention, n(Co+M1) / n(Al+M2)=2-4, most preferably 3; the molar ratio of Co to M1 is 0.5-1.5, preferably 1-1.5; the molar ratio of M2 to Al is 0.005-0.05, preferably 0.01-0.03.

[0019] In the catalyst of the present invention, the alkaline earth metal (M1) is at least one of Mg, Ca, and Sr, preferably two of these elements are simultaneously contained. Preferably, the molar ratio of the two alkaline earth metals added is 0.5-2, more preferably 1.

[0020] The rare earth metal (M2) is at least one of La, Ce, Sc, and Y, preferably two of these elements are included at the same time. Preferably, the molar ratio of the two rare earth metals added is 0.5-2, more preferably 1.

[0021] Another aspect of the present invention provides a method for preparing the catalyst:

[0022] The preparation method of the modified hydrotalcite-like derived cobalt catalyst comprises the following steps:

[0023] (1) Preparation of a modified hydrotalcite precursor: Dissolve cobalt salt, alkaline earth metal salt, rare earth metal salt, aluminum salt, and urea in deionized water according to the catalyst content to form a transparent, uniform aqueous solution. Transfer the aqueous solution to an autoclave and crystallize at a certain temperature for a period of time to obtain a solid-liquid mixture. The obtained solid-liquid mixture is filtered, washed with water and a modifier 2-4 times each, then dispersed in the modifier and ultrasonicated at 20-30°C for 30-60 minutes. Filter the ultrasonicated product and dry it to obtain a modified hydrotalcite precursor.

[0024] (2) Preparation of catalyst: The obtained modified hydrotalcite-like precursor is calcined and reduced to obtain the modified hydrotalcite-like derived cobalt catalyst.

[0025] The metal salt (cobalt salt, alkaline earth metal salt, rare earth metal salt, aluminum salt) in step (1) can be selected from one or more of sulfate, nitrate and organic acid salt, preferably nitrate.

[0026] In the step (1), the molar ratio of urea to the sum of metal ions is 10-15, preferably 10-12.

[0027] In step (1), various metal salts and urea are dissolved in deionized water, and the amount of deionized water used is required to ensure that the concentration of urea is 10-15 mol / L.

[0028] The crystallization temperature in step (1) is 100-120° C., preferably 100-110° C. The crystallization time is 10-24 hours, preferably 12-18 hours.

[0029] In the step (1), the modifier is a low-boiling point organic solvent, including methanol, ethanol, acetone, ether, tetrahydrofuran, etc., preferably methanol. The amount of the modifier used to disperse the sample is 50-60 ml / g 固体 The purpose of using a modifier is to peel off the original stacked structure of hydrotalcite-like particles into a single-layer structure, so that the composite oxide obtained after calcination has a larger specific surface area and more porous structure, which is beneficial to increase the number of active sites exposed on the catalyst surface and improve the reaction efficiency.

[0030] In step (1), the drying temperature range is 55-75°C; the drying time is 6-12 hours, preferably 8-10 hours. The drying temperature varies slightly with the type of modifier. For example, when methanol is used as the modifier, the drying temperature is 60-65°C, preferably 60-62°C.

[0031] The calcination temperature in step (2) is 450-600° C., preferably 500-550° C.; the calcination time is 6-12 hours, preferably 6-8 hours.

[0032] The reduction in step (2) is carried out in a pure hydrogen atmosphere at a temperature of 450-550° C., preferably 450-500° C., at a pressure of 0.1-0.5 MPa (absolute pressure), preferably 0.1-0.2 MPa (absolute pressure), and for a time of 12-36 hours, preferably 24-36 hours.

[0033] The third aspect of the present invention provides the use of the catalyst:

[0034] The catalyst is used for synthesizing cyclohexylamine by hydrogenation of aniline. As a preferred embodiment, the synthesis of cyclohexylamine by hydrogenation of aniline is carried out in a fixed bed reactor, and the method comprises:

[0035] Aniline and hydrogen are mixed and introduced into a preheater for preheating. After preheating, the mixture is added into a fixed bed reactor filled with the above-mentioned cobalt catalyst for reaction to obtain a reaction solution containing cyclohexylamine.

[0036] Furthermore, the feed mass space velocity of the aniline is 0.1-0.6h -1 , preferably 0.2-0.4h -1 The molar ratio of hydrogen to aniline is 10-15:1, preferably 10-12:1.

[0037] Furthermore, the preheater temperature is 155-170° C., preferably 160-165° C. The reaction temperature is 155-170° C., preferably 160-165° C. The reaction pressure is 0.2-0.5 MPa (absolute pressure), preferably 0.2-0.3 MPa (absolute pressure).

[0038] The beneficial effects of the present invention are:

[0039] 1. Using hydrotalcite-like materials as precursors, high-load non-precious metal catalysts can be prepared. The prepared catalysts have a large specific surface area, uniform dispersion of active components, and small metal particle size. Therefore, they can provide more active sites for the reaction, which is beneficial to improving the conversion rate of aniline, which can reach over 98%.

[0040] 2. Using a modifier to treat the hydrotalcite-like material can strip the stacked structure of the hydrotalcite-like material into a single layer. As a result, the modified hydrotalcite-like material, after calcination, produces a composite oxide with a larger specific surface area and a more porous structure, further increasing the number of exposed active sites and improving reaction efficiency.

[0041] 3. The surface of the catalyst prepared by calcining the modified hydrotalcite-like precursor has a large number of basic sites. The addition of rare earth metals can further increase the number of basic sites on the catalyst surface, thereby effectively inhibiting the formation of dicyclohexylamine during the reaction, and the selectivity of dicyclohexylamine is below 3%.

[0042] 4. The use of rare earth metals as additives can effectively improve the dispersion of active components in the catalyst, thereby improving the activity of the catalyst; on the other hand, it can improve the wear resistance of the catalyst, reduce the loss of active components, and inhibit the migration and agglomeration of active metals during the reaction, which is beneficial to improving the stability and service life of the catalyst. DETAILED DESCRIPTION

[0043] The present invention is further described by the following examples, but the present invention is not limited to the examples listed.

[0044] The gas chromatography analysis conditions in the following examples are: Agilent HP-5 chromatographic column, inlet temperature 280°C, FID detector temperature 300°C, column flow rate 1.5 ml / min, hydrogen flow rate 30 ml / min, air flow rate 400 ml / min, and programmed temperature rise mode: hold at 50°C for 2 min, increase the temperature to 80°C at 5°C / min, then increase the temperature to 280°C at 15°C / min and hold for 10 min.

[0045] Example 1

[0046] Preparation of modified hydrotalcite-like precursor:

[0047] First, 72.8 g of cobalt nitrate (Co(NO3)2·6H2O, 291), 128.2 g of magnesium nitrate (Mg(NO3)2·6H2O, 256), 92.9 g of aluminum nitrate (Al(NO3)3·9H2O, 375), 1.1 g of lanthanum nitrate (La(NO3)3·6H2O, 433) and 600.1 g of urea (60) were dissolved in 1000 mL of deionized water to obtain a transparent solution; then the solution was transferred to an autoclave and crystallized at 110 ° C for 12 h; the obtained solid-liquid mixture was filtered and washed with water and methanol three times respectively; then, the separated solid sample was dispersed in methanol (the amount of methanol was 55 ml / g 固体 ), ultrasonicated at 25°C for 1 h; then the sample was filtered and dried at 60°C for 12 h to obtain a modified hydrotalcite-like precursor.

[0048] Preparation of modified hydrotalcite-like cobalt catalyst:

[0049] The hydrotalcite-like precursor was placed in a muffle furnace and heated to 550°C at a rate of 3°C / min, where it was held for 6 hours to obtain a catalyst precursor. 50g of the catalyst precursor was loaded into a fixed-bed reactor with an inner diameter of 20mm and a tube length of 1000mm. The upper and lower ends of the catalyst were filled with 10-20 mesh quartz sand. Hydrogen was introduced for activation at a temperature of 500°C, a pressure of 0.2 MPa (absolute pressure), and a time of 24 hours to obtain a hydrotalcite-like cobalt catalyst.

[0050] Aniline hydrogenation to cyclohexylamine:

[0051] After activation, hydrogen and aniline were mixed in a molar ratio of 15:1 and added to the preheater. After preheating at 165°C, the mixed gas entered the fixed bed reactor filled with the above catalyst. The mass space velocity of aniline was 0.3h -1 The reaction took place at 165°C and 0.2 MPa (absolute pressure). The reaction product, after cooling, entered a gas-liquid separator for gas-liquid separation, with the liquid entering a crude product tank. Gas chromatography analysis of the sample revealed an aniline conversion of 98.1%, a cyclohexylamine selectivity of 96.0%, and a dicyclohexylamine selectivity of 3.0%. The catalyst operated continuously for 400 hours, at which point sampling and analysis revealed no significant change.

[0052] Example 2

[0053] Preparation of modified hydrotalcite-like precursor:

[0054] First, 131.0 g of cobalt nitrate (Co(NO3)2·6H2O, 291), 38.5 g of magnesium nitrate (Mg(NO3)2·6H2O, 256), 35.4 g of calcium nitrate (Ca(NO3)2·4H2O, 236), 91.1 g of aluminum nitrate (Al(NO3)3·9H2O, 375), 3.2 g of lanthanum nitrate (La(NO3)3·6H2O, 433) and 600.1 g (60) of urea were dissolved in 1000 mL of deionized water to obtain a transparent solution; then the solution was transferred to an autoclave and crystallized at 120 ° C for 10 h; the obtained solid-liquid mixture was filtered and washed with water and methanol three times respectively; then, the separated solid sample was dispersed in methanol (the amount of methanol was 55 ml / g 固体 ), ultrasonicated at 25°C for 1 h; then the sample was filtered and dried at 62°C for 10 h to obtain a modified hydrotalcite-like precursor.

[0055] Preparation of modified hydrotalcite-like cobalt catalyst:

[0056] The hydrotalcite-like precursor was placed in a muffle furnace and heated to 550°C at a rate of 3°C / min, where it was held for 6 hours to obtain a catalyst precursor. 50g of the catalyst precursor was loaded into a fixed-bed reactor with an inner diameter of 20mm and a tube length of 1000mm. The upper and lower ends of the catalyst were filled with 10-20 mesh quartz sand. Hydrogen was introduced for activation at a temperature of 500°C, a pressure of 0.2 MPa (absolute pressure), and a time of 24 hours to obtain a modified hydrotalcite-like cobalt-derived catalyst.

[0057] Aniline hydrogenation to cyclohexylamine:

[0058] After activation, hydrogen and aniline were mixed in a molar ratio of 10:1 and added to the preheater. After preheating at 160°C, the mixed gas entered the fixed bed reactor filled with the above catalyst. The mass space velocity of aniline was 0.3h -1 The reaction took place at 160°C and 0.2 MPa (absolute pressure). The reaction product, after cooling, entered a gas-liquid separator for gas-liquid separation, with the liquid entering a crude product tank. Gas chromatography analysis of the sample revealed an aniline conversion of 99.6%, a cyclohexylamine selectivity of 97.2%, and a dicyclohexylamine selectivity of 2.2%. The catalyst operated continuously for 400 hours, at which point sampling and analysis revealed no significant change.

[0059] Example 3

[0060] Preparation of modified hydrotalcite-like precursor:

[0061] First, 109.1g of cobalt nitrate (Co(NO3)2·6H2O, 291), 88.6g of calcium nitrate (Ca(NO3)2·4H2O, 236), 89.3g of aluminum nitrate (Al(NO3)3·9H2O, 375), 5.2g of cerium nitrate (Ce(NO3)3·6H2O, 434) and 600.1g of urea were dissolved in 1000mL of deionized water to obtain a transparent solution. The solution was then transferred to an autoclave and crystallized at 100°C for 18h. The resulting solid-liquid mixture was filtered and washed three times with water and acetone respectively; then, the separated solid sample was dispersed in acetone (the amount of acetone was 55ml / g 固体 ), ultrasonicated at 25°C for 1 h; then the sample was filtered and dried at 55°C for 8 h to obtain a modified hydrotalcite-like precursor.

[0062] Preparation of modified hydrotalcite-like cobalt catalyst:

[0063] The modified hydrotalcite-like precursor was placed in a muffle furnace and heated to 500°C at a rate of 3°C / min, where it was held for 8 hours to obtain a catalyst precursor. 50g of the catalyst precursor was loaded into a fixed-bed reactor with an inner diameter of 20mm and a tube length of 1000mm. The upper and lower ends of the catalyst were filled with 10-20 mesh quartz sand. Hydrogen was introduced for activation at a temperature of 500°C, a pressure of 0.2 MPa (absolute pressure), and a time of 36 hours to obtain a modified hydrotalcite-like cobalt catalyst.

[0064] Aniline hydrogenation to cyclohexylamine:

[0065] After activation, hydrogen and aniline were mixed in a molar ratio of 10:1 and added to the preheater. After preheating at 165°C, the mixed gas entered the fixed bed reactor filled with the above catalyst. The mass space velocity of aniline was 0.3h -1 The reaction took place at 165°C and 0.1 MPa (gauge pressure). The reaction product, after cooling, entered a gas-liquid separator for gas-liquid separation, with the liquid entering a crude product tank. Gas chromatography analysis of the sample revealed an aniline conversion of 99.0%, a cyclohexylamine selectivity of 96.8%, and a dicyclohexylamine selectivity of 2.4%. The catalyst operated continuously for 400 hours, at which point sampling and analysis revealed no significant change.

[0066] Example 4

[0067] Preparation of modified hydrotalcite-like precursor:

[0068] First, 109.1g of cobalt nitrate (Co(NO3)2·6H2O, 291), 96.2g of magnesium nitrate (Mg(NO3)2·6H2O, 256), 92.0g of aluminum nitrate (Al(NO3)3·9H2O, 375), 1.1g of lanthanum nitrate (La(NO3)3·6H2O, 433), 1.1g of cerium nitrate (Ce(NO3)3·6H2O, 434) and 600.1g of urea were dissolved in 1000mL of deionized water to obtain a transparent solution. The solution was then transferred to an autoclave and crystallized at 100°C for 12h. The resulting solid-liquid mixture was filtered and washed three times with water and methanol respectively; then, the separated solid sample was dispersed in methanol (the amount of methanol was 55ml / g 固体 ), ultrasonicated at 25°C for 1 h; then the sample was filtered and dried at 60°C for 12 h to obtain a modified hydrotalcite-like precursor.

[0069] Preparation of modified hydrotalcite-like cobalt catalyst:

[0070] The modified hydrotalcite-like precursor was placed in a muffle furnace and heated to 500°C at a rate of 3°C / min, where it was held for 8 hours to obtain a catalyst precursor. 50g of the catalyst precursor was loaded into a fixed-bed reactor with an inner diameter of 20mm and a tube length of 1000mm. The upper and lower ends of the catalyst were filled with 10-20 mesh quartz sand. Hydrogen was introduced for activation at a temperature of 450°C, a pressure of 0.2 MPa (absolute pressure), and a time of 36 hours to obtain a modified hydrotalcite-like cobalt-derived catalyst.

[0071] Aniline hydrogenation to cyclohexylamine:

[0072] After activation, hydrogen and aniline were mixed in a molar ratio of 10:1 and added to the preheater. After preheating at 165°C, the mixed gas entered the fixed bed reactor filled with the above catalyst. The mass space velocity of aniline was 0.3h -1 The reaction took place at 165°C and 0.1 MPa (gauge pressure). The reaction product, after cooling, entered a gas-liquid separator for gas-liquid separation, with the liquid entering a crude product tank. Gas chromatography analysis of the sample revealed an aniline conversion of 99.2%, a cyclohexylamine selectivity of 97.4%, and a dicyclohexylamine selectivity of 2.0%. The catalyst operated continuously for 800 hours, at which point sampling and analysis revealed no significant change.

Claims

1. A method for synthesizing cyclohexylamine by hydrogenating aniline, using a modified hydrotalcite-derived cobalt catalyst having the general formula: M / M1(O)-M2(O)-M3(O), wherein M represents an active metal Co, M1 represents an alkaline earth metal, M2 represents a rare earth metal, M3 represents Al, M1(O) represents an alkaline earth metal oxide, M2(O) represents a rare earth metal oxide, and M3(O) represents Al2O3; The preparation method of the catalyst comprises: (1) Preparing a modified hydrotalcite-like precursor: dissolving a cobalt salt, an alkaline earth metal salt, a rare earth metal salt, an aluminum salt and urea in water to form an aqueous solution, crystallizing the aqueous solution at a certain temperature for a period of time to obtain a solid-liquid mixture, filtering the obtained solid-liquid mixture, washing it, and then dispersing it in a modifier, ultrasonicating it, filtering the ultrasonicated product, and drying it to obtain a modified hydrotalcite-like precursor; the modifier is selected from methanol, ethanol, acetone, ether and tetrahydrofuran; (2) Preparation of catalyst: The obtained modified hydrotalcite precursor is calcined and reduced to obtain a modified hydrotalcite-derived cobalt catalyst.

2. The method according to claim 1, characterized in that n(Co+M1) / n(Al+M2)=2-4.

3. The method according to claim 2, characterized in that n(Co+M1) / n(Al+M2)= 3.

4. The method according to any one of claims 1 to 3, characterized in that The alkaline earth metal M1 is at least one of Mg, Ca, and Sr; and the molar ratio of Co to M1 is 0.5-1.

5.

5. The method according to claim 4, characterized in that The alkaline earth metal M1 is two of Mg, Ca and Sr, and the molar ratio of the two alkaline earth metals is 0.5-2; the molar ratio of Co to M1 is 1-1.

5.

6. The method according to claim 5, characterized in that The molar ratio of the two alkaline earth metals is 1.

7. The method according to any one of claims 1-3, 5-6, characterized in that The rare earth metal M2 is at least one of La, Ce, Sc, and Y; and the molar ratio of M2 to Al is 0.005-0.

05.

8. The method according to claim 7, characterized in that The rare earth metals M2 are two of La, Ce, Sc and Y, and the molar ratio of the two rare earth metals is 0.5-2; the molar ratio of M2 to Al is 0.01-0.

03.

9. The method according to claim 8, characterized in that The molar ratio of the two rare earth metals is 1.

10. The method according to claim 1, characterized in that In step (1), the molar ratio of urea to the sum of metal ions is 10-15; the concentration of urea dissolved in water is 10-15 mol / L.

11. The method according to claim 10, characterized in that In step (1), the molar ratio of urea to the sum of metal ions is 10-12.

12. The method according to claim 1 or 10, characterized in that In step (1), the crystallization temperature is 100-120°C; and the crystallization time is 10-24h.

13. The method according to claim 12, characterized in that In step (1), the crystallization temperature is 100-120°C; and the crystallization time is 12-18 hours.

14. The method according to claim 1, wherein In step (1), when the washed solid is dispersed in the modifier, the amount of the modifier is 50-60 ml / g. 固体 .

15. The method according to claim 1, wherein In step (1), the modifier is methanol.

16. The method according to claim 1, wherein In step (2), the calcination temperature is 450-600°C and the calcination time is 6-12h; The reduction is carried out in a pure hydrogen atmosphere at a reduction temperature of 450-550° C.; an absolute reduction pressure of 0.1-0.5 MPa; and a reduction time of 12-36 hours.

17. The method according to claim 16, characterized in that In step (2), the calcination temperature is 500-550°C and the calcination time is 6-8h; The reduction temperature is 450-500°C; the absolute pressure of reduction is 0.1-0.2 MPa; and the reduction time is 24-36 hours.