Preparation method for multi-channel co@cm ceramic catalytic membrane

Abstract

The present invention relates to a preparation method for a new multi-channel Co@CM ceramic catalytic membrane, which belongs to the technical field of catalytic membrane preparation. In the preparation of the catalytic membrane, a multi-channel ceramic membrane is used as a carrier, ZIF-67 is assembled and loaded layer by layer on the surface of the ceramic membrane and inside pore channels, and the catalytic membrane is prepared by means of one-step pyrolysis reduction. The method has the advantages that nano Co particles are loaded on the ceramic membrane instead of precious metals, and the surfaces of the Co particles are coated with carbon and nitrogen, thus effectively inhibiting the loss of the Co particles during the reaction; and the resulting Co@CM ceramic membrane has excellent catalytic activity and stability, and the problem of it being difficult to separate a traditional catalyst from a product in a subsequent process is also solved, so it can be widely used in a hydrogenation reaction process.

Description

A preparation method of multi-channel Co@CM ceramic catalytic membrane Technical Field

[0001] The present invention belongs to the technical field of ceramic membrane catalysis and relates to a method for preparing a multi-channel Co@CM ceramic catalytic membrane. Background Art

[0002] Membrane separation and catalytic reactions can be coupled to form a catalytic membrane reactor, with the catalytic membrane being the core component. The unique feature of catalytic membranes is that they can support active components on the membrane material, separating reactants and products through membrane separation technology while simultaneously carrying out the catalytic reaction. This offers the advantage of in-situ separation of materials and catalysts, thereby simplifying process steps and saving energy. The development of catalytic membranes primarily focuses on membrane surface modification and preparation methods. Patent (CN110841633B) reports a method for preparing a surface-modified catalytic membrane. This involves first modifying a ceramic membrane support with titanium dioxide, then depositing Pd(hfac)2 on its surface via ALD. The precursor is then reduced to Pd using Formalin (a 37% formaldehyde aqueous solution containing 15% methanol), thereby producing a catalytic membrane. This significantly improves the activity and stability of the catalytic membrane. However, precious metals are easily lost during the reaction and are expensive, making large-scale application difficult. Therefore, in addition to these precious metal catalysts, non-precious metal catalysts such as Co are also used in catalytic reactions. In recent years, MOFs have attracted widespread attention as template materials for the preparation of high-porosity carbonaceous materials. MOFs are a new type of ordered nanoporous material assembled from metal ions and organic ligands, which has the characteristics of high specific surface area, ordered pore structure and pore adjustability. It has also been reported that MOFs can be directly carbonized (without adding a carbon source) to prepare MOFs-derived metal or metal oxide-carbon composite materials. Patent (CN113289666A) reports a method for preparing a catalytic membrane, which uses an impregnation method to in situ grow ZIF-67 on the surface of a ceramic membrane, and then calcined in an argon atmosphere. The Co in ZIF-67 is converted to 2+ In situ reduction to catalytically active Co 0Due to the carbonization of organic ligands during the thermal decomposition of MOFs, the agglomeration of metal nanoparticles is effectively avoided, and pyrrole nitrogen is generated during the thermal decomposition process, which effectively improves the catalytic activity of the catalytic membrane. However, compared with powder catalysts, the loading amount of active components on the catalytic membrane is lower, resulting in a lower catalytic efficiency per unit volume. Compared with sheet membranes and single-channel membranes, multi-channel ceramic membranes have richer pore structures and can provide more loading sites for active components per unit volume, thereby achieving the purpose of increasing the loading amount and significantly improving the catalytic efficiency per unit volume of the membrane. However, the combination of MOFs and ceramic membranes to prepare catalytic membranes is still a challenge. The catalytic membranes prepared by conventional methods have fewer active center components per unit volume, and the binding force between the active components and the membrane material is weak, resulting in low catalytic activity of the catalytic membrane and easy deactivation during use, which hinders the large-scale application of catalytic membranes in industry.

[0003] Summary of the Invention

[0004] In view of the problems of low activity and poor stability of traditional catalytic membranes, the present invention proposes a novel method for preparing a multi-channel Co@CM ceramic catalytic membrane.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] A novel method for preparing multi-channel Co@CM ceramic catalytic membrane is described, and the specific steps are as follows.

[0007] Step 1: Dissolve 2-methylimidazole in methanol and stir until the solution becomes clear and transparent to obtain solution A.

[0008] Step 2: Dissolve cobalt nitrate hexahydrate in methanol and stir until the solution becomes clear and transparent to obtain solution B.

[0009] Step 3: First fill the membrane channel with solution A. Under the action of the peristaltic pump, force the solution A in the channel to flow through the membrane pores of the multi-channel ceramic membrane and then flow out of the membrane tube. Design the pipeline so that solution A can be recycled under the action of the peristaltic pump. After the forced circulation time of solution A lasts for one hour, discharge solution A and replace it with solution B and repeat the above operation, alternating at least twice.

[0010] Step 4: After solution A and solution B are discharged, methanol is forced to flow through the membrane tube surface and membrane pores to wash. After washing is completed, the membrane tube is taken out and dried to obtain a multi-channel ZIF-67@CM ceramic membrane.

[0011] Step 5: calcining the ZIF-67@CM ceramic membrane to obtain a multi-channel Co@CM ceramic catalytic membrane.

[0012] Step 6: Use ethanol-water solution to force flow and flush the membrane pores for a period of time to flush out the active components that are not firmly loaded, thereby obtaining a multi-channel Co@CM ceramic catalytic membrane with stable performance.

[0013] Preferably, the concentration of 2-methylimidazole in solution A prepared in step 1 is 0.32-0.64 mol / L.

[0014] Preferably, the concentration of cobalt nitrate hexahydrate in solution B prepared in step 2 is 0.04-0.08 mol / L.

[0015] Preferably, the forced circulation process in step three is kept warm in a water bath at a temperature of 25-45°C, and solution A is preferentially introduced for alternate circulation of solutions. The total time for alternate forced circulation of solution A and solution B is 4-6 hours. The multi-channel ceramic membrane is made of alumina or zirconia, has 7-61 channels, and a pore size of 200-5000 nm.

[0016] Preferably, the washing time in step 4 is 10-20 minutes, the drying temperature is 50-70° C., and the drying time is 12-24 hours.

[0017] Preferably, the calcination temperature in step 5 is in the range of 450-770°C, the calcination atmosphere is argon, the heating rate is 2-10°C / min, and the temperature is raised to the target temperature and kept at this temperature for 4-6 hours.

[0018] Preferably, the forced circulation washing in step six has a flow rate of 2.5 L / h and a time of 45 min. The washing adopts an ethanol-water solution, and the volume ratio of deionized water to ethanol is 5:1.

[0019] The present invention uses the selective hydrogenation of p-nitrophenol to produce p-aminophenol to verify the catalytic performance of the prepared catalyst. During the reaction, a catalytic membrane is fixed in a membrane assembly. After controlling the temperature of the reaction system, a mixed solvent of ethanol and deionized water is added. After the p-nitrophenol raw material is added and dissolved, NaBH4 is added as a reducing agent to proceed with the reaction. Multiple samples can be taken during the reaction, and the product composition is detected using high-performance liquid chromatography (HPLC, Agilent 1200). After the reaction is completed, the liquid in the storage tank is drained, and deionized water is replaced and forced to flow through the membrane pores for 10-15 minutes to wash. The catalytic membrane is removed and dried or oven-dried for storage; alternatively, fresh raw material is added and the reaction is continued.

[0020] The present invention takes the catalytic membrane composited with ZIF-67 and multi-channel ceramic membrane substrate as the research object, and prepares a new type of Co@CM ceramic membrane by high-temperature one-step pyrolysis. It is proved that since ZIF-67 does not contain oxygen atoms, a large number of C and N atoms are retained during the inert gas calcination process, thereby obtaining a nitrogen-rich catalytic membrane, which is conducive to the transmission of electrons and can also effectively inhibit the loss of active components. It shows excellent catalytic performance in the hydrogenation of p-nitrophenol to p-aminophenol. The present invention effectively prepares a composite material with ZIF-67-derived metal-carbon nitrogen by regulating the calcination temperature. The study found that during the calcination process, Co 2+ It will be reduced to Co by the reducing gases generated during the calcination of ZIF-67 and serve as a catalytic active center. The present invention effectively prepares a ZIF-67-derived metal-carbon-nitrogen composite material by regulating the concentration of 2-methylimidazole and cobalt nitrate hexahydrate. Studies have found that the Co loading significantly increases with the increase in raw material concentration. The carbonization of organic ligands during the thermal decomposition of MOFs effectively prevents metal agglomeration. Pyrrolic nitrogen will gradually be generated during the thermal decomposition process, which is beneficial to the conversion of reactants.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are:

[0022] 1. The multi-channel ceramic membrane has a large specific surface area and can provide more loading sites per unit volume, thereby increasing the loading amount of active components and significantly improving the catalytic efficiency per unit volume.

[0023] 2. By adopting a layer-by-layer assembly method, ZIF-67 can be dispersed in an orderly manner on the surface and in the pores of the ceramic membrane, so that the active components are evenly distributed and there are more active centers after calcination.

[0024] 3. Forced circulation can not only force a large amount of solution to flow into the membrane pores, thereby improving the utilization rate of the loadable sites inside the membrane pores, but also remove active components with weak binding force to the ceramic membrane during the forced flow process, thereby further improving the stability of the catalytic membrane.

[0025] Therefore, the Co@CM ceramic catalytic membrane prepared by the present invention has high catalytic activity and high stability, and realizes in-situ separation of catalyst and material, and is suitable for large-scale industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic diagram of the structure of the device used for preparing the multi-channel Co@CM ceramic catalytic membrane and testing the catalytic performance in Example 1.

[0027] Figure 2 is a schematic diagram of the membrane assembly and forced circulation method.

[0028] Figure 3 shows the catalytic performance test results of the multi-channel Co@CM ceramic catalytic membrane under different solution introduction orders.

[0029] FIG4 is an XRD pattern of the multi-channel Co@CM ceramic catalytic membrane prepared in Example 1.

[0030] FIG5 is an EDX image of the multi-channel Co@CM ceramic catalytic membrane in Example 1.

[0031] FIG6 is a stability test result of the catalytic membrane in Example 1.

[0032] The figures are marked as follows: 1 constant temperature water bath, 2 peristaltic pump, 3 peristaltic pump, 4 storage tank jacket, 5 storage tank, 6 membrane reactor jacket, 7 membrane assembly, 8 pressure gauge, 9 material feed pipe, 10 circulating water pipe, 11 normally closed exhaust valve, 12 sampling port, 13 discharge port. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Example 1

[0036] In the present embodiment and the following embodiments, the preparation of the catalytic membrane and the reaction of para-nitrophenol selective hydrogenation to para-aminophenol are carried out using the device shown in Figure 1 (the catalytic membrane preparation and subsequent reactions can also be carried out using other devices. The present embodiment only provides a device that can realize the catalytic membrane preparation and subsequent reaction process, and retains the possibility of other devices that can implement the technical solution of the present invention. The design of other devices is not limited). Figure 1 is a typical structure of a flow-through membrane reactor. The main components include a constant temperature water bath 1, a storage tank 5, a membrane reactor and a pipeline. The lower end of the storage tank 5 is connected to a discharge port 13 for discharging materials. The whole set of equipment includes two-way circulation, which is a water circulation with a constant temperature water bath 1 as the starting point, and a material circulation with a storage tank as the starting point. The outside of the membrane reactor and the storage tank 5 is provided with a jacket, the lower end of the jacket is connected to the inlet pipeline of the constant temperature water pipe, and the upper end of the jacket is connected to the outlet pipeline of the constant temperature water pipe. A peristaltic pump 2 is provided between the constant temperature water bath 1 and the storage tank 5. The constant temperature water flowing out of the constant temperature water bath 1 is pressurized by the peristaltic pump 2 and flows into the storage tank jacket 4 and the membrane reactor jacket 6 in sequence. Then, after flowing out of the membrane reactor, it passes through the circulating water pipe 10 and returns to the constant temperature water bath 1. The temperature of the reaction system is controlled by setting the temperature of the water bath. A membrane assembly 7 (custom-made) is provided inside the membrane reactor. A multi-channel ceramic membrane tube is placed inside the membrane assembly 7. The multi-channel ceramic membrane is fixed in the membrane assembly by putting rubber rings on both ends of the multi-channel ceramic membrane. The flanges at the upper and lower ends are fixed to the membrane assembly by quick-release clamps. The lower opening of the membrane assembly 7 is matched with the material feed pipe 9 as the liquid inlet; the side of the membrane assembly is matched with the material outlet pipe as the outlet, and the top opening of the membrane assembly is matched with the emptying pipeline as the pressure relief port; a peristaltic pump 3 is provided on the material feed pipe 9, a sampling port 12 is provided on the material outlet pipe, a pressure gauge 8 is provided on the emptying pipeline, and a normally closed exhaust valve 11 is provided on the outside of the pressure gauge. When the upper end of the membrane tube needs to be sealed, the normally closed exhaust valve 11 can be closed.

[0037] The specific preparation process of the multi-channel Co@CM ceramic catalytic membrane is as follows.

[0038] (1) Preparation of ZIF-67@CM membrane

[0039] Preparation 200mL concentration is 0.48M 2-methylimidazole methanol solution (solution A), and 200mL concentration is 0.06M hexahydrate cobalt nitrate methanol solution (solution B), by two kinds of solutions respectively by water-bath control temperature is 30 DEG C, treat that solid matter is completely dissolved.Multi-channel ceramic membrane (commercially available, aluminum oxide, 19 channels, pore size is about 1000nm, diameter 3cm, length 8cm) is filled into membrane assembly, 2-methylimidazole methanol solution is added in the storage tank 5 of reactor, constant temperature water bath 1 temperature is continued to be set to 30 DEG C, open peristaltic pump 2, after 5 minutes, open peristaltic pump 3, flow is adjusted to 3.5L / h, force solution to force flow through film pore, after continuing 1h, from discharge port 13, the solution A in storage tank is poured out, and is replaced by solution B, continues to pass into 1h. Passing into 1 solution A and solution B is 1 circulation, and whole preparation process carries out 2 circulations. After 4 hours, peristaltic pumps 2 and 3 were turned off to drain the remaining solution in the reactor. Methanol solution was added to the storage tank, and peristaltic pump 3 was turned on to adjust the flow rate to 3.5 L / h. The membrane tube was cleaned for 15 minutes. The membrane tube was then taken out and placed in a 60°C oven to dry for 18 hours. The obtained sample was labeled ZIF-67@CM-0.06.

[0040] (2) Preparation of Co@CM catalyst

[0041] The treated ZIF-67@CM-0.06 was placed in a tube furnace, and the initial temperature (room temperature) was raised to 550°C for calcination, and the target temperature was kept at 550°C for 5 hours, with a heating rate of 5°C / min and an argon atmosphere. After calcination, the sample was naturally cooled to room temperature. The obtained sample was labeled Co@CM-550-0.06.

[0042] The pores of the multi-channel ceramic catalytic membrane are rinsed to remove loosely loaded active components. The specific operation method is as follows: prepare a sufficient amount of a mixed solution of deionized water and ethanol (the volume ratio of deionized water to ethanol is 5:1) and add it to the storage tank of the flow-through membrane reactor. Turn on peristaltic pump 2 and adjust the flow rate to 2.5L / h. During this process, the solution flowing out of the membrane assembly outlet does not return to the storage tank, but flows directly out of the sampling port shown in Figure 1. The entire process takes 45 minutes. After the rinsing is completed, a multi-channel ceramic catalytic membrane with stable performance is obtained. Since the rinsing liquid and the solvent of the reaction system are the same, the rinsed catalytic membrane can be used directly in the catalytic reaction or dried and stored.

[0043] In order to characterize and verify the effect of the prepared multi-channel ceramic catalytic membrane, multiple catalytic membranes were prepared under the same conditions in this example.

[0044] Figure 4 shows the XRD pattern. The diffraction peak centered at 26.4° is attributed to the (002) plane of graphitic carbon. The distinct derivative peaks at 43.9°, 51.2°, and 75.6° are attributed to the (111), (200), and (220) crystal planes of metallic Co, respectively. This indicates that the Co element in ZIF-67 is reduced to zero-valent Co during pyrolysis and serves as a catalytic active center.

[0045] Figure 5 shows the distribution of Co, C, and N elements in the catalytic membrane prepared in Example 1. As can be seen from the figure, ZIF-67 pyrolyzes into metallic Co after calcination, and these three elements, Co, C, and N, are present and evenly distributed throughout all layers of the multichannel ceramic membrane. Therefore, the multichannel ceramic membrane provides more loading sites for Co, which is the basis for the catalytic membrane's efficient catalytic hydrogenation of p-nitrophenol to p-aminophenol and its ability to facilitate a simple in situ reduction process.

[0046] The catalytic membrane Co@CM-550-0.06 prepared in this example was applied to the experiment of hydrogenating p-nitrophenol to p-aminophenol, and its catalytic performance was tested by a flow-through membrane reactor. First, turn on the constant temperature water bath and set the water bath temperature to 50°C. When the temperature in the water bath reaches the set value, turn on peristaltic pump 2 so that the constant temperature water flows into the storage tank jacket and the membrane reactor jacket in sequence. Then prepare the reaction raw materials: dissolve 1g of p-nitrophenol in a mixed solvent consisting of 240mL of ethanol and deionized water (ethanol and deionized water volume ratio = 1:5), stir manually until the p-nitrophenol is dissolved, and take 0.4mL of the reaction solution as the initial sample. After adding 3.915g of NaBH4 and stirring manually for 5-10 minutes until the solids dissolve, the mixed reaction materials are added to the storage tank of the flow-through membrane reactor. Peristaltic pump 3 is turned on and the flow rate is adjusted to 3.5L / h. When the reaction liquid flows to the outlet of the membrane module, the timer is started. After the reaction liquid flows out of the membrane module, it is circulated into the storage tank. 0.4mL of reaction liquid is taken every 5 minutes. After the reaction is completed, the liquid in the storage tank is drained and replaced with deionized water for forced circulation to wash the membrane pores for 10-15 minutes. The membrane tube is removed and dried or oven-dried for storage; alternatively, fresh raw materials are added and the reaction is continued. The product composition is determined by high-performance liquid chromatography (HPLC, Agilent 1200). The conversion rate and selectivity of the reaction are then calculated based on the standard curve.

[0047] Table 1 shows the turnover frequency (TOF) values ​​of Co@CM catalytic membrane and non-precious metal catalysts reported in recent literature. As can be seen from Table 1, under the condition of consuming a small amount of NaBH4, the Co@CM ceramic catalytic membrane obtained in Example still has a high TOF value (1.69×10 -2 s -1 ), indicating that the Co@CM catalytic membrane has excellent catalytic performance and good application prospects.

[0048] Table 1. Turnover frequency (TOF) of Co@CM catalytic membrane and catalysts reported in the literature

[0049] Note: TOF is calculated as the amount of p-nitrophenol reduced per mole of active component per hour.

[0050] Example 2

[0051] (1) Preparation of ZIF-67@CM membrane

[0052] Prepare 200mL of 0.32M 2-methylimidazole methanol solution and 200mL of 0.04M hexahydrate cobalt nitrate methanol solution, respectively, and place the two solutions in a water bath, control the water bath temperature to 30°C, and wait for the solid matter to be completely dissolved. During this period, a multichannel ceramic membrane (commercially available, zirconium oxide, 7 channels, pore size of about 200nm, diameter 3cm, length 8cm) is filled into the membrane assembly, and the 2-methylimidazole methanol solution is added to the storage tank of the reactor. The temperature is controlled at 25°C by a constant temperature water bath device, and the peristaltic pump is turned on and the flow rate is adjusted to 2.5L / h to force the solution to flow through the membrane pores. After 1 hour, the solution in the reactor is replaced with solution B and passed through for 1 hour. Passing through solution A and solution B once is one cycle, and the entire preparation process is circulated twice. After 4 h, the remaining solution in the reactor was discharged, methanol solution was added to the storage tank, and peristaltic pump 3 was turned on and the flow rate was adjusted to 2.5 L / h. The membrane tube was cleaned for 10 min, and then the membrane tube was taken out and placed in a 70 °C oven to dry for 12 h. The obtained sample was labeled ZIF-67@CM-0.04.

[0053] (2) Preparation of Co@CM catalyst

[0054] The treated ZIF-67@CM-0.04 was placed in a tube furnace, the calcination temperature was set to 450°C, and it was kept at the target temperature for 4 hours, with a heating rate of 2°C / min and an argon atmosphere. The obtained sample was labeled Co@CM-450-0.04.

[0055] The catalytic membrane Co@CM was applied to the experiment of hydrogenating p-nitrophenol to p-aminophenol. The operation method was the same as that in Example 1. After 20 minutes of reaction, the conversion rate reached 84.7% and the selectivity was 100%.

[0056] Example 3

[0057] (1) Preparation of ZIF-67@CM membrane

[0058] In two 500mL beakers, 200mL of 0.64M 2-methylimidazole methanol solution (solution A) and 200mL of 0.08M cobalt nitrate hexahydrate methanol solution (solution B) were prepared respectively, and placed in a water bath, and the water bath temperature was controlled to 30°C until the solid matter was completely dissolved. During this period, a multichannel ceramic membrane (commercially available, alumina, 37 channels, pore size of about 5000nm, diameter 3cm, length 8cm) was filled into the membrane assembly, and the 2-methylimidazole methanol solution was added to the storage tank of the reactor. The temperature was controlled at 45°C by a constant temperature water bath device, and the peristaltic pump was turned on and the flow rate was adjusted to 4.5L / h to force the solution to flow through the membrane pores. After 1 hour, the solution in the reactor was replaced with solution B and continued to be passed for 1 hour. Passing solution A and solution B once is one cycle, and the entire preparation process is circulated twice. After 4 hours, the remaining solution in the reactor was discharged, and methanol solution was added to clean the membrane tube for 20 minutes. The membrane tube was then taken out and placed in a 50°C oven to dry for 24 hours. The obtained sample was labeled ZIF-67@CM-0.10.

[0059] (2) Preparation of Co@CM catalyst

[0060] The treated ZIF-67@CM-0.10 was placed in a tube furnace, calcined to 770°C at the initial temperature (room temperature), and kept at the target temperature for 6 hours with a heating rate of 10°C / min and an argon atmosphere. The obtained sample was labeled Co@CM-770-0.10.

[0061] The catalytic membrane Co@CM was applied to the experiment of hydrogenating p-nitrophenol to p-aminophenol. The operation method was the same as that in Example 1. After 20 minutes of reaction, the conversion rate reached 92.3% and the selectivity was 100%.

[0062] Example 4

[0063] (1) Preparation of ZIF-67@CM membrane

[0064] In two 500mL beakers, 200mL of a 0.64M 2-methylimidazole methanol solution (Solution A) and 200mL of a 0.08M cobalt nitrate hexahydrate methanol solution (Solution B) were prepared respectively, and placed in a water bath, the water bath temperature was controlled to 30°C, and the solid matter was completely dissolved. During this period, a multichannel ceramic membrane (commercially available, alumina, 61 channels, pore size of about 1500nm, diameter 3cm, length 8cm) was filled into the membrane assembly, and the 2-methylimidazole methanol solution was added to the storage tank of the reactor. The temperature was controlled at 30°C by a constant temperature water bath device, and the peristaltic pump was turned on and the flow rate was adjusted to 5.5L / h to force the solution to flow through the membrane pores. After 1 hour, the solution in the reactor was replaced with Solution B and continued to be passed for 1 hour. Passing Solution A and Solution B once is one cycle, and the entire preparation process is repeated twice. After 4 hours, the remaining solution in the reactor was discharged, and methanol solution was added to clean the membrane tube for 15 minutes. The membrane tube was then taken out and placed in a 60°C oven to dry for 12 hours. The obtained sample was labeled ZIF-67@CM-0.08.

[0065] (2) Preparation of Co@CM catalyst

[0066] The treated ZIF-67@CM-0.08 was placed in a tube furnace, calcined to 650°C at the initial temperature (room temperature), and kept at the target temperature for 5 hours, with a heating rate of 5°C / min and an argon atmosphere. The obtained sample was labeled Co@CM-650-0.08.

[0067] The catalytic membrane Co@CM was applied to the experiment of hydrogenating p-nitrophenol to p-aminophenol. The operation method was the same as that in Example 1. After 20 minutes of reaction, the conversion rate reached 85% and the selectivity was 100%.

[0068] Example 5

[0069] The present embodiment adopts the Co@CM-550-0.06 prepared by Example 1 to carry out the test of catalytic stability.Before testing stability, by the device shown in Figure 1, the multichannel ceramic catalytic membrane pores are rinsed to remove the active components that are not firmly loaded.Specific operation method is: prepare enough deionized water, ethanol mixed solution (the volume ratio of deionized water and ethanol is 5: 1), add in the storage tank of flow-through membrane reactor, open peristaltic pump 2, flow regulator is to 2.5L / h, during this process, the solution flowing out of membrane assembly outlet does not return to storage tank, but directly flows out from the sampling port shown in Figure 1.The whole process carries out 45min, and after terminating, the multichannel ceramic catalytic membrane can be directly used for the stability test (i.e., continuous catalytic process) of the present embodiment or air-dry, dry and preserve.

[0070] The specific method of the stability test is as follows: prepare a sufficient amount of 0.5g / L p-nitrophenol solution, add sodium borohydride after the solid substance is completely dissolved (the molar ratio of p-nitrophenol to sodium borohydride is 1:14.4), and stir until the solid is dissolved. Set the temperature of the constant temperature water bath to 50°C. When the temperature reaches the set value, turn on the peristaltic pump 2 so that the constant temperature water flows into the storage tank jacket and the membrane reactor jacket in sequence. Add the reaction raw materials to the storage tank of the flow-through membrane reactor, turn on the peristaltic pump 3, and adjust the flow rate to 3.5L / h. During this process, the solution flowing out of the outlet of the membrane assembly does not return to the storage tank, but flows directly out from the sampling port shown in Figure 1. An additional receiving tank can be set to store the reaction product. Samples are taken every 25 minutes at the sampling port. During this process, when the solution in the storage tank is about to be exhausted, the above-prepared solution is filled to fill the storage tank and continue for 5 hours. As shown in Figure 6, the conversion rate of p-nitrophenol by the catalytic membrane remained at 100% within 5 h without obvious deactivation.

[0071] Comparative Example 1

[0072] (1) Preparation of ZIF-67@CM membrane

[0073] In two 500mL beakers, 200mL of a 0.48M 2-methylimidazole methanol solution (Solution A) and 200mL of a 0.06M cobalt nitrate hexahydrate methanol solution (Solution B) were prepared respectively, and placed in a water bath, the water bath temperature was controlled to 30°C, and the solid matter was completely dissolved. During this period, a multichannel ceramic membrane (commercially available, alumina, 19 channels, a pore size of about 1000nm, a diameter of 3cm, and a length of 8cm) was filled into the membrane assembly, and the 2-methylimidazole methanol solution was added to the storage tank of the reactor. The temperature was controlled at 30°C by a constant temperature water bath device, and the peristaltic pump was turned on and the flow rate was adjusted to 3.5L / h to force the solution to flow through the membrane pores. After 1 hour, the solution in the reactor was replaced with Solution B and continued to be passed for 1 hour. Passing Solution A and Solution B once is one cycle, and the entire preparation process is repeated twice. After 4 hours, the remaining solution in the reactor was discharged, and methanol solution was added to clean the membrane tube for 10 minutes. The membrane tube was then taken out and placed in a 70°C oven to dry for 24 hours. The obtained sample was labeled ZIF-67@CM-0.06.

[0074] (2) Preparation of Co@CM catalyst

[0075] The treated ZIF-67@CM-0.06 was placed in a tube furnace, calcined to 350°C at the initial temperature (room temperature), and kept at the target temperature for 5 hours, with a heating rate of 5°C / min and an argon atmosphere. The obtained sample was labeled Co@CM-350-0.06.

[0076] The catalytic membrane Co@CM was applied to the experiment of hydrogenating p-nitrophenol to p-aminophenol. The operation method was the same as that of Example 1. After 20 minutes of reaction, the conversion rate was 53.1% and the selectivity was 100%.

[0077] Comparative Example 2

[0078] (1) Preparation of ZIF-67@CM membrane

[0079] In two 500mL beakers, 200mL of a 0.16M 2-methylimidazole methanol solution (Solution A) and 200mL of a 0.02M cobalt nitrate hexahydrate methanol solution (Solution B) were prepared, respectively, and placed in a water bath. The water bath temperature was controlled to 30°C until the solid matter was completely dissolved. During this period, a multichannel ceramic membrane (commercially available, alumina, 19 channels, a pore size of approximately 1000nm, a diameter of 3cm, and a length of 8cm) was filled into the membrane assembly. The 2-methylimidazole methanol solution was added to the storage tank of the reactor. The temperature was controlled at 30°C by a constant temperature water bath device. The peristaltic pump was turned on and the flow rate was adjusted to 3.5L / h. The solution was forced to flow through the membrane pores. After 1 hour, the solution in the reactor was replaced with Solution B and continued to be passed through for 1 hour. Passing through Solution A and Solution B once is one cycle, and the entire preparation process is circulated twice. After 4 hours, the remaining solution in the reactor was discharged, and methanol solution was added to clean the membrane tube for 10 minutes. The membrane tube was then taken out and placed in a 70°C oven to dry for 24 hours. The obtained sample was labeled ZIF-67@CM-0.02.

[0080] (2) Preparation of Co@CM catalyst

[0081] The treated ZIF-67@CM-0.02 was placed in a tube furnace, calcined to 550°C at the initial temperature (room temperature), and kept at the target temperature for 5 hours, with a heating rate of 5°C / min and an argon atmosphere. The obtained sample was labeled Co@CM-550-0.02.

[0082] The catalytic membrane Co@CM was applied to the experiment of hydrogenating p-nitrophenol to p-aminophenol. The operation method was the same as that of Example 1. After 20 minutes of reaction, the conversion rate was 42.4% and the selectivity was 100%.

[0083] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a multi-channel Co@CM ceramic catalytic membrane, characterized in that: Here are the steps: Step 1: dissolving 2-methylimidazole in methanol to obtain solution A; Step 2: dissolving cobalt nitrate hexahydrate in methanol to obtain solution B; Step 3: One end of the multi-channel ceramic membrane tube is closed, and solution A is first filled into the channel of the ceramic membrane tube, and pressure is provided to force solution A to circulate from the inside of the membrane tube channel to the outside of the membrane tube for more than 1 hour, and then solution A is switched to solution B, and solution B is forced to circulate from the inside of the membrane channel to the outside of the membrane tube for more than 1 hour, and the process is repeated, so that the number of times solution A and solution B are alternately forced to circulate is at least twice; Step 4: forcing methanol to flow from the inside of the membrane tube channel to the outside of the membrane tube for washing and drying to obtain a multi-channel ZIF-67@CM ceramic membrane; Step 5: calcining the ZIF-67@CM ceramic membrane; Step 6: Use ethanol-water solution to force flow and flush the membrane pores to obtain a stable multi-channel Co@CM ceramic catalytic membrane.

2. The method for preparing the multi-channel Co@CM ceramic catalytic membrane according to claim 1, characterized in that: The concentration of 2-methylimidazole in solution A is 0.32-0.64 mol / L; the concentration of cobalt nitrate hexahydrate in solution B is 0.04-0.08 mol / L.

3. The method for preparing the multi-channel Co@CM ceramic catalytic membrane according to claim 1, characterized in that: In step three, the multi-channel ceramic membrane is made of aluminum oxide or zirconium oxide, the number of channels is 7-61, and the pore size is 200-5000nm; the temperature of solution A, solution B and the multi-channel ceramic membrane tube is maintained at 25-45°C, the total time of alternating forced circulation of solution A and solution B is 4-6h, and the flow rate of alternating forced circulation of solution A and solution B is 2.5-5.5L / h.

4. The method for preparing the multi-channel Co@CM ceramic catalytic membrane according to claim 1, characterized in that: In step 4, the washing time is 10-20 minutes, the drying temperature is 50-70°C, and the drying time is 12-24 hours.

5. The method for preparing the multi-channel Co@CM ceramic catalytic membrane according to claim 1, characterized in that: In step 5, the calcination temperature is 450-770°C, the calcination atmosphere is argon, the heating rate is 2-10°C / min, and the temperature is kept at 4-6 hours after reaching the calcination temperature.

6. The method for preparing the multi-channel Co@CM ceramic catalytic membrane according to claim 1, characterized in that: The flow rate of the forced circulation flushing in step six is ​​2.5 L / h, the flushing time is 45 min, and the flushing adopts ethanol-water solution, in which the volume ratio of deionized water to ethanol in the ethanol-water solution is 5:

1.

7. Use of the ceramic catalytic membrane prepared by the method of any one of claims 1 to 6 in the process of selective hydrogenation of p-nitrophenol to p-aminophenol.

8. A process for preparing p-aminophenol by selective hydrogenation of p-nitrophenol, characterized in that: The ceramic catalytic membrane prepared by any one of claims 1 to 6 is used as a catalyst, and the ceramic catalytic membrane is immersed in a p-nitrophenol solution for intermittent or continuous reaction.

9. The process for preparing p-aminophenol by selective hydrogenation of p-nitrophenol according to claim 8, characterized in that: The recycled multi-channel Co@CM ceramic membrane is used to catalyze the intermittent or continuous reaction of the p-nitrophenol solution. The recycling method is to wash the membrane pores with deionized water for 10-15 minutes, and then take out the ceramic membrane and air dry or bake it.

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