A method for preparing a copper-based catalyst

Abstract

The application belongs to the field of catalyst preparation, and provides a preparation method of a copper-based catalyst. The catalyst is obtained by a method of controlled alkali etching of silicon dioxide and copper carbonate precipitation, the copper oxide content in the catalyst is 15-40 wt.%, the specific surface area of the catalyst is 240-260 m2 / g, and the bulk density of the catalyst is 0.61-0.7 g / mL. The catalyst preparation method is simple, the obtained catalyst has higher cyclohexanol dehydrogenation catalytic activity, and the bulk density is lower, which is beneficial to industrial application and promotion.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a copper-based catalyst and belongs to the technical field of catalyst preparation. BACKGROUND

[0002] Catalytic cyclohexanol dehydrogenation to produce cyclohexanone is an important industrial process, especially for the raw material of nylon-6, epsilon-caprolactam. On the one hand, as people's requirements for the performance of polymer fibers are getting higher and higher, the purity of the raw material is also improved. This puts forward higher requirements for the selectivity of the cyclohexanol dehydrogenation catalyst for producing cyclohexanone. On the other hand, from the perspective of improving the metal utilization rate of the catalyst and the production capacity of the production device, it is the research and development direction of the current industrial solid metal catalyst to prepare a catalyst with lower metal loading and higher metal dispersion to achieve higher catalytic conversion rate. For the cyclohexanol dehydrogenation catalyst, it is also the same. Therefore, it is of important theoretical guiding significance and economic value to develop a more efficient preparation method of the cyclohexanol dehydrogenation catalyst.

[0003] For the hydrogenation and dehydrogenation reaction of organic matter, the reactant and product molecules usually have a large kinetic diameter, for example, the kinetic diameter of a cyclohexane molecule is about 0.6 nm, and the kinetic diameter of a benzene molecule is about 0.65-0.68 nm. In the reaction process, compared with micropores (pore size < 2 nm), the mesopores (pore size of 2-50 nm) of the catalyst have a greater influence on the diffusion and mass transfer of the reactant and product. Therefore, when designing and preparing the catalyst, a reasonable method should be designed to introduce more mesopores.

[0004] Patent CN104437488B discloses a preparation method of a cyclohexanol gas phase dehydrogenation catalyst for preparing cyclohexanone, and the active component of the catalyst is mainly Cu / SiO2. The catalyst is prepared by using a step-by-step precipitation method, that is, a precipitant is mixed with silica sol, and then a copper nitrate solution is added to the above solution for precipitation. After washing, solid-liquid separation, drying and calcination, the catalyst is finally pressed into a tablet.

[0005] The application combines the controllable alkali treatment etching of silicon dioxide with the precipitation of active copper species, effectively increases the mesopore specific surface area of the carrier, increases the contact area between the copper nanoparticles and the carrier, and realizes the purpose of reducing the particle size of the copper nanoparticles. The obtained catalyst exhibits high catalytic activity in the reaction of cyclohexanol gas phase dehydrogenation for preparing cyclohexanone. SUMMARY

[0006] The main technical purpose of the present application is to provide a method for preparing a metal catalyst with silica as a carrier, higher mesopore specific surface area and cyclohexanol catalytic activity. The feature is to introduce a caustic alkali with strong silica etching ability into the precipitant, cooperate with an aluminum species "pore forming indicator", equip a bifunctional mixed solution with suitable silica pore forming ability and copper ion precipitation ability, and use it to first treat the silica carrier, and then precipitate the copper species. In this way, a Cu-Al / SiO2 catalyst with higher mesopore specific surface area, higher cyclohexanol conversion rate and cyclohexanone selectivity, and lower bulk density is prepared, thereby effectively reducing the particle size of copper particles, reducing the use amount of copper raw materials and the loading amount of the catalyst.

[0007] The design principle of the method of the present application is that the caustic alkali added in the precipitant can etch more mesopores on the surface of silica, and the aluminum species in the solution can be present on the newly generated mesopore surface, so that the dispersion and stability of copper nanoparticles in the obtained catalyst are improved due to the increase of the mesopore specific surface area and the presence of the aluminum species.

[0008] The present application provides a preparation method of a copper-based catalyst, which is prepared by a two-step method combining silica alkali etching and copper precipitation.

[0009] The preparation method of the catalyst is as follows: first, a mixed solution of a precipitant, a caustic alkali and an aluminum salt is prepared, then a certain amount of silica sol is mixed with the above-mentioned mixed solution, and the mixture is treated at a certain temperature for 20-240 min; a copper nitrate solution is added to the above-mentioned solution for precipitation, and is aged for 20-30 min, then is washed, dried, calcined and granulated by adding an additive, and finally is tablet-pressed into a shape.

[0010] The content of the active component copper oxide of the catalyst is 15-40 wt.%, the content of silica is 60-85 wt.%, the content of aluminum trioxide is 0.0003-4 wt.%, and the content of sodium oxide is 0-3 wt.%.

[0011] According to some embodiments of the present application, the first-step precipitated silica sol is a JA or JN type silica sol.

[0012] According to some embodiments of the present application, the precipitant is selected from one or more of sodium carbonate, sodium bicarbonate and potassium carbonate.

[0013] According to some embodiments of the present application, the caustic alkali is selected from one or more of potassium hydroxide and sodium hydroxide.

[0014] According to some embodiments of the present application, the concentration of the caustic alkali in the mixture of the precipitant and the silica sol is 0.1-0.3 mol / L.

[0015] According to some embodiments of the present application, the aluminum salt is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate, and sodium metaaluminate.

[0016] According to some embodiments of the present application, the concentration of the aluminum salt in the mixture of the precipitant and the silica sol is 0.0001-0.05 mol / L.

[0017] According to some embodiments of the present application, the alkali treatment temperature of the silica sol is 25-75℃.

[0018] According to some embodiments of the present application, the copper precipitation temperature is 55-75℃.

[0019] According to some embodiments of the present application, the calcination temperature is 350-450℃.

[0020] The bulk density of the catalyst prepared by the present application is 0.40 g / mL-0.65 g / mL, which reduces the catalyst consumption in the production of cyclohexanone and saves social resources.

[0021] Advantages:

[0022] (1) The catalyst preparation cost is low and the preparation process is simple. The catalyst preparation method of the present application has cheap and readily available raw materials and simple preparation process;

[0023] (2) The catalyst has a larger mesopore specific surface area (67-87 m 2 / g) and good catalytic cyclohexanol dehydrogenation activity. The present application combines the mesopore introduction of the carrier and the precipitation of copper species to combine relatively small copper oxide particles to the silica carrier with a relatively high mesopore specific surface area. The catalyst shows good activity, selectivity and stability in the catalytic cyclohexanol dehydrogenation reaction to produce cyclohexanone in a wide temperature range, with a cyclohexanol conversion rate of 65.7% or more and a cyclohexanone selectivity of 99.3% or more;

[0024] (3) The catalyst has good thermal stability. The copper oxide is loaded on the silica carrier with a high mesopore specific surface area, and the aluminum oxide enhances the interaction between the silica carrier and the copper oxide. The sintering resistance of the copper oxide nanoparticles is strong, and the particle size after calcination is small. DETAILED DESCRIPTION

[0025] The present application will be further described below in conjunction with examples. However, the present application is not limited by these examples.

[0026] Raw materials:

[0027] Sodium carbonate, Sigma-Aldrich Trading Co., Ltd., purity 99.5 wt.%.

[0028] Sodium hydroxide, Shanghai Maikelin Biochemical Technology Co., Ltd., content 96 wt.%.

[0029] Potassium hydroxide, Shanghai Aladdin Biochem Technology Co., Ltd., content 95 wt.%.

[0030] Silica sol, Qingdao Haoyang Chemical Factory, JN-25, silica content 25 wt.%, sodium oxide content 3 wt.%, water content 72 wt.%.

[0031] Aluminum nitrate, Hubei Jusheng Technology Co., Ltd., Al(NO3)3·9H2O, purity 99 wt.% Al2O3 content 13.4 wt.%.

[0032] Sodium metaaluminate, Shanghai Yinn Chemical Technology Co., Ltd., content 99 wt.%.

[0033] Copper nitrate solution, self-made, concentration 1.0 M.

[0034] Example 1

[0035] The present embodiment provides a preparation method of a copper-based catalyst, which is prepared by the following method:

[0036] The preparation of the copper-based catalyst of the present application is carried out in an open thermostatic container, and is implemented in the following steps. Take 149 g of sodium carbonate, 25.6 g of sodium hydroxide and 3.6 g of aluminum nitrate nonahydrate, and add deionized water to make 1 L of solution; then take 700 g of silica sol JN-25, and make 2.2 L of aqueous solution. Mix the above two solutions, at this time, the concentration of sodium hydroxide in the mixture is 0.2 M, and the concentration of aluminum nitrate is 0.003 M, control the stirring temperature to be 65℃, and stir vigorously for 30 min. Then take 1 L of 1.0 M copper nitrate solution, and add it to the above mixture, after adding, increase the temperature to 70℃, and continue stirring for 10 min. Finally, add deionized water, and perform natural sedimentation. After washing, drying, crushing, 380℃ calcination, adding appropriate amount of water and graphite, and finally tabletting and forming, the usable catalyst is obtained.

[0037] In the catalyst, the content of copper oxide is 27.6 wt.%, the content of silicon dioxide is 70.5 wt.%, the mass fraction of aluminum oxide (Al2O3) is 1.4 wt.%, and the content of sodium oxide is 0.5 wt.%. The specific surface area of the catalyst is 242.1 m 2 / g, wherein the mesopore specific surface area is 67.3 m 2 / g; the pore volume is 0.42 mL / g; and the average pore diameter is 4.3 nm.

[0038] Example 2

[0039] The present embodiment provides a preparation method of a copper-based catalyst, which is prepared by the following method:

[0040] The preparation of the copper-based catalyst of the present embodiment is carried out in an open thermostatic container, and is implemented by the following steps. In Example 1, 25.6 g of sodium hydroxide is replaced by 35.9 g of potassium hydroxide, 3.6 g of aluminum nitrate nonahydrate is replaced by 0.79 g of sodium metaaluminate, and 1 L of 1.0 M copper nitrate solution is replaced by 0.7 L of 1.0 M copper nitrate solution, and other conditions remain unchanged. At this time, the concentration of potassium hydroxide in the mixture is 0.2 M, and the concentration of sodium metaaluminate is 0.003 M.

[0041] In the catalyst, the content of copper oxide is 19.5 wt.%, the content of silicon dioxide is 78.7 wt.%, the mass fraction of aluminum oxide (Al2O3) is 1.3 wt.%, and the content of potassium oxide is 0.5 wt.%. The specific surface area of the catalyst is 251.1 m 2 / g, wherein the mesopore specific surface area is 82.3 m 2 / g; the pore volume is 0.49 mL / g; and the average pore size is 4.2 nm.

[0042] Example 3

[0043] The present embodiment provides a preparation method of a copper-based catalyst, which is prepared by the following method:

[0044] The preparation of the copper-based catalyst of the present embodiment is carried out in an open thermostatic container, and is implemented by the following steps. In Example 1, 25.6 g of sodium hydroxide and 3.6 g of aluminum nitrate nonahydrate are replaced by 38.4 g of sodium hydroxide and 5.4 g of aluminum nitrate nonahydrate, respectively, and other conditions remain unchanged. In the mixture of the precipitant and the silica sol, the concentration of sodium hydroxide is 0.3 M, and the concentration of aluminum nitrate is 0.0045 M.

[0045] The content of copper oxide in the catalyst is 28.5 wt.%, the content of silicon dioxide is 69.2 wt.%, the mass fraction of aluminum oxide (Al2O3) is 1.5 wt.%, and the content of sodium oxide is 0.8 wt.%. The specific surface area is 236.1 m 2 / g, the mesopore specific surface area is 75.3 m 2 / g, the pore volume is 0.46 mL / g, and the average pore size is 4.5 nm.

[0046] Example 4

[0047] The present embodiment provides a preparation method of a copper-based catalyst, which is prepared by the following method:

[0048] The copper-based catalyst of the present application is prepared in an open thermostatic vessel by the following steps. The two solutions described above in Example 3 are mixed, at which time the concentration of sodium hydroxide in the mixture is 0.2 M and the concentration of aluminum nitrate is 0.003 M, the stirring temperature is controlled at 65°C, and the mixture is stirred vigorously for 30 min. The stirring temperature is changed to 25°C, and the mixture is stirred vigorously for 240 min. The other conditions remain unchanged.

[0049] The copper oxide content of the catalyst is 26.5 wt.%, the silica content is 71.2 wt.%, the mass fraction of aluminum oxide (Al2O3) is 1.6 wt.%, and the sodium oxide content is 0.7 wt.%. The specific surface area is 263.1 m 2 / g, the mesopore specific surface area is 87.6 m 2 / g, the pore volume is 0.51 mL / g, and the average pore diameter is 3.7 nm.

[0050] As can be seen from the above examples, appropriately reducing the caustic soda treatment temperature of the silica carrier, extending the time, increasing the proportion of silica sol, or increasing the concentration of caustic soda and aluminum salt, can be expected to prepare a Cu-Al / SiO2 catalyst with a higher mesopore specific surface area.

[0051] Comparative Example 1

[0052] This comparative example is taken from the patent CN104437488B, Example 3.

[0053] The catalyst is prepared in an open reaction kettle by the following steps. Take 1000 mL of a 1.0 M copper nitrate solution a, and co-precipitate the sodium carbonate solution with 958 grams of silica sol JN-25 in a precipitation tank with stirring, controlling the precipitation temperature at 60°C, then aging at 72°C for 30 min, then adding solution a to the above-mentioned precipitation, controlling the precipitation temperature at 70°C, adding oxalic acid solution to the precipitation endpoint pH value of 7.2, washing, drying, crushing, 380°C calcination, adding an appropriate amount of water and graphite, and finally tabletting to form a catalyst.

[0054] The copper content of the catalyst is 20.6%, the specific surface area is 190.5 m 2 / g, the pore volume is 0.32 mL / g, and the average pore diameter is 3.8 nm.

[0055] The catalyst samples prepared in Examples 1-3 and the Cu-Al / SiO2 catalyst sample prepared in Comparative Example 1 are subjected to reduction treatment using a mixture of hydrogen and nitrogen before the dehydrogenation reaction, the reduction treatment temperature is 180-230°C, the time is 180 h, and the volume concentration of hydrogen in the mixture is 80%. The activity evaluation is carried out in a fixed bed reactor with a size of ￠32x2 mm, and the raw material cyclohexanol space velocity is 0.60 h -1The activity evaluation was performed under the conditions of a reaction temperature of 230°C, a catalyst charge of 50 mL, and the results are shown in Table 1.

[0056] Table 1 Catalyst evaluation results

[0057] Sample Mesopore specific surface area / (m 2 / g) Bulk density / (g / mL) CuO particle size / (nm) Cyclohexanol conversion Cyclohexanone selectivity Example 1 242 0.66 9.5 66.4% 99.5% Example 2 251 0.62 7.8 65.7% 99.5% Example 3 236 0.64 9.2 66.8% 99.3% Example 4 263 0.61 8.6 67.2% 99.7% Comparative Example 1 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 Example 16 Example 17 Example 190 0.72 13.7 60.25% 99.44%

Claims

1. A method for preparing a copper-based catalyst, characterized in that, The catalyst is prepared using a two-step method combining silica alkaline etching and copper precipitation: First, a mixed solution of a precipitant, caustic alkali, and aluminum salt is prepared. Then, a certain amount of silica sol is mixed with the above mixed solution and treated at 25-75℃ for 20-240 min. The concentration of caustic alkali in the mixture of precipitant and silica sol is 0.1-0.3 mol / L, and the concentration of aluminum salt in the mixture is 0.0001-0.05 mol / L. Copper nitrate solution is added to the above solution for precipitation, aged for 20-30 min, washed, dried, calcined, and granulated with additives. Finally, it is pressed into tablets. In the catalyst prepared by the above method, the active component copper oxide content is 15-40 wt.%, the silica content is 60-85 wt.%, the aluminum oxide content is 0.0003-4 wt.%, and the sodium oxide content is 0-3 wt.%.

2. The method for preparing the catalyst according to claim 1, characterized in that, The silica sol precipitated in the first step is of the JA or JN type.

3. The method for preparing the catalyst according to claim 1, characterized in that, The first step of precipitation uses an alkaline precipitant, which can be one or more of sodium carbonate, sodium bicarbonate, and potassium carbonate.

4. The method for preparing the catalyst according to claim 1, characterized in that, The caustic alkali used in the first step is one or more of potassium hydroxide and sodium hydroxide.

5. The method for preparing the catalyst according to claim 1, characterized in that, The added aluminum salt is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate, and sodium aluminate.

6. The method for preparing the catalyst according to claim 1, characterized in that... The copper precipitation temperature is 55~75℃; the calcination temperature is 350~450℃.