A storage method of a multi-channel co@cm catalytic membrane

Abstract

The application relates to a storage method of a p-nitrophenol hydrogenation Co@CM catalytic membrane. By immersing the Co@CM catalytic membrane in ethanol, the surface characteristics of the Co@CM catalytic membrane are changed to a certain extent. The storage method effectively improves the affinity between a reaction solution and the catalytic membrane and reduces the mass transfer resistance, effectively inhibits the loss of the active component cobalt, and realizes efficient recycling of the catalytic membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane catalysis, and relates to a storage method of a multi-channel Co@CM catalytic membrane. BACKGROUND

[0002] A catalytic membrane reactor combines catalytic reaction and membrane process together, has many advantages such as in-situ separation of products and catalysts and enhanced mass transfer. The key of the catalytic membrane reactor is to design and prepare a high-performance catalytic membrane. Many people have devoted to the preparation of the catalytic membrane, including developing a new preparation method, functionalizing a membrane surface and optimizing a membrane module. This makes the development of the catalytic membrane make great progress. In many catalytic membranes for p-nitrophenol hydrogenation reaction, although various catalytic membranes all show excellent catalytic activity, the stability still has room for improvement, and the stability must be ensured in industrial application to improve economic benefits. Therefore, the stability of the catalytic membrane is a key problem to be solved.

[0003] In the research on the catalyst, it is found that the storage method has a significant influence on the stability of the catalyst. For example, Hu et al. store the used Pd@CN catalyst in an inert atmosphere after cleaning, which effectively prevents the catalyst from deactivation and enables the catalyst to be efficiently recycled. Dias et al. find that the CaO catalyst for biodiesel production is sensitive to moisture and carbon dioxide in the air, and therefore storing the catalyst in a controllable atmosphere can ensure the stability during the catalytic reaction. For the catalytic membrane, the storage method also plays a crucial role in the activity and stability. Unfortunately, the research on the storage method of the catalytic membrane is still very limited. SUMMARY

[0004] The application proposes a new storage method of a multi-channel Co@CM catalytic membrane aiming at the problems existing in the storage of the traditional catalytic membrane.

[0005] In order to achieve the above purpose, the application is implemented by using the following technical scheme:

[0006] The application relates to a storage method of a multi-channel Co@CM catalytic membrane, and the multi-channel Co@CM catalytic membrane is applied to p-nitrophenol hydrogenation reaction. After the preparation of the multi-channel Co@CM catalytic membrane is completed, the multi-channel Co@CM catalytic membrane is soaked in a liquid for preservation.

[0007] Preferably, the liquid for soaking the multi-channel Co@CM catalytic membrane after the preparation of the multi-channel Co@CM catalytic membrane is completed is any one of ethanol and methanol.

[0008] Preferably, after the preparation of the multi-channel Co@CM catalytic membrane is completed, the multi-channel Co@CM catalytic membrane is soaked for preservation, and then is taken out and directly applied to p-nitrophenol hydrogenation reaction. The soaking and preservation time is not less than 6h.

[0009] The preparation method of the Co@CM catalytic membrane is consistent with the preparation method of the catalytic membrane in patent 2023111266224.

[0010] The specific steps are as follows.

[0011] Step one: dissolve 2-methylimidazole in methanol, stir until the solution is clear and transparent, and obtain solution A.

[0012] Step two: dissolve cobalt nitrate hexahydrate in methanol, stir until the solution is clear and transparent, and obtain solution B.

[0013] Step three: 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. The pipeline is designed to enable solution A to be recycled under the action of the peristaltic pump. After the forced flow of solution A lasts for one hour, solution A is discharged, and solution B is replaced to repeat the above operation, and solution A is alternately introduced at least twice.

[0014] Step four: after solution A and solution B are discharged, methanol is forced to flow through the surface and membrane pores of the washing membrane tube. After washing is completed, the membrane tube is taken out and dried to obtain a multi-channel ZIF-67@CM ceramic membrane.

[0015] Step five: calcine the ZIF-67@CM ceramic membrane to obtain a multi-channel Co@CM ceramic catalytic membrane.

[0016] After the multi-channel Co@CM ceramic catalytic membrane is prepared by the above steps, it is completely soaked in a solution for storage, preferably soaked in ethanol for at least 6 hours. If long-term storage is required, the container can be sealed. It is found that long-term storage does not affect the catalytic activity and stability of the catalytic membrane. When used, the multi-channel Co@CM ceramic catalytic membrane is directly taken out of the soaking solution and used as a catalytic membrane.

[0017] After the catalytic reaction is completed, the reaction product is taken out, and the catalytic membrane can be fixed in situ in the membrane module for continuous catalysis without separation after the reaction is completed, and new reaction raw materials and solvents can be added for a new catalytic reaction.

[0018] Compared with the prior art, the advantages and positive effects of the present application are as follows:

[0019] The soaking method for storing the Co@CM catalytic membrane proposed in the present application realizes long-term storage of the catalytic membrane, not only solving the problem of conventional storage of the Co@CM catalytic membrane, but also enabling the catalytic membrane to be directly taken out for use after soaking without other treatment. The catalytic activity of the catalytic membrane stored by soaking is better than that of a freshly prepared catalytic membrane, and the catalytic activity of the catalytic membrane remains stable after multiple cycles. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Catalytic performance of Co@CM catalytic membrane soaked in ethanol.

[0021] Figure 2 Catalytic performance of Co@CM catalytic membrane soaked in methanol.

[0022] Figure 3 Catalytic performance of Co@CM catalytic membrane soaked in fresh.

[0023] Figure 4 Catalytic performance of Co@CM catalytic membrane soaked in deionized water.

[0024] Figure 5 Catalytic performance of Co@CM catalytic membrane after flushing with ethanol aqueous solution for 45 min.

[0025] Figure 6 Contact angle of Co@CM catalytic membrane with different storage methods and solvent and time required for solvent to completely penetrate into the membrane pores. DETAILED DESCRIPTION

[0026] In order to enable persons skilled in the art to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application will be further described below in conjunction with specific examples. It should be noted that the examples of the present application and the features in the examples can be combined with each other without conflict.

[0027] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can be practiced in other ways different from those described herein, and therefore, the present application is not limited to the specific embodiments disclosed in the following description.

[0028] Example 1

[0029] The preparation process of the catalytic membrane and the conditions of the catalytic reaction of selective hydrogenation of p-nitrophenol to p-aminophenol are described in detail in patent 2023111266224, and the present application does not make any changes to this part. In the following examples, the preparation process of the catalytic membrane and the catalytic reaction of selective hydrogenation of p-nitrophenol to p-aminophenol are not introduced, and reference can be made to patent 2023111266224.

[0030] 1. Preparation of catalytic membrane

[0031] A 2-methylimidazole methanol solution (solution A) with a concentration of 0.48 M and a 200 mL cobalt nitrate hexahydrate methanol solution (solution B) with a concentration of 0.06 M were prepared and placed in water baths, respectively. After the solid substances were completely dissolved, a multi-channel ceramic membrane (commercially available, alumina, 19 channels, pore size of about 1000 nm, diameter of 3 cm, length of 8 cm) was filled into a membrane module, and the 2-methylimidazole methanol solution was added to a solution storage tank and forced to flow through the membrane pores at a flow rate of 3.5 L / h for 1 h. Then, solution B was switched to flow through the membrane pores for 1 h. One cycle of solution A and solution B was one pass, and the entire preparation process was performed for two cycles. Then, methanol was forced to flow through the membrane pores at a flow rate of 3.5 L / h for 15 min to clean the membrane tube, and then the membrane tube was taken out and dried in an oven at 60 °C for 18 h to obtain a sample, which was labeled as ZIF-67@CM-0.06.

[0032] The treated ZIF-67@CM-0.06 was placed in a tube furnace and calcined at an initial temperature (room temperature) to 550 °C, and the target temperature was 550 °C for 5 h, with a heating rate of 5 °C / min, and the calcination atmosphere was argon. After calcination, the sample was naturally cooled to room temperature, and the sample was labeled as Co@CM-550-0.06.

[0033] 2. Preservation and use of the catalytic membrane

[0034] The prepared multi-channel Co@CM-550-0.06 catalytic membrane was placed in a beaker and immersed in 600 mL of ethanol for 18 h at 30 °C. After the soaking was completed, the multi-channel Co@CM catalytic membrane was taken out of the ethanol and used for the hydrogenation reaction of p-nitrophenol. The reaction raw material was prepared by dissolving 1 g of p-nitrophenol in a mixed solvent of 240 mL of ethanol and deionized water (volume ratio of ethanol to deionized water = 1:5), and manually stirring until the p-nitrophenol was dissolved. 0.4 mL of the reaction solution was taken as the initial sample. Then, 3.915 g of NaBH4 was added and manually stirred for 5-10 min until the solid was dissolved. The reaction temperature of the system was controlled at 50 °C by a super constant temperature water bath. The membrane module was designed so that the reaction raw material flowed through the bottom of the open membrane tube at a flow rate of 3.5 L / h, flowed out of the side membrane pores, and then flowed into the storage tank. The reaction liquid was taken out every 5 min after it flowed out of the membrane module, and the reaction was completed. After the reaction, the membrane tube was taken out and continued to be soaked in ethanol for preservation. Alternatively, the catalytic membrane was fixed in place and fresh raw materials were added for continuous reaction. The results are shown in Figure 1 As shown in the results, the conversion rate reached 100% at 20 min, and the catalytic activity remained basically unchanged in the 5 times of fresh raw material addition for cyclic tests, showing good stability.

[0035] Example 2

[0036] The difference between this example and Example 1 is that the prepared multi-channel Co@CM-550-0.06 catalytic membrane is immersed in methanol for storage. After the end of soaking, the multi-channel Co@CM catalytic membrane is taken out and immediately used for the hydrogenation reaction of p-nitrophenol. The results are shown in Figure 2 After 5 cycles of testing, the conversion rate at 20 min decreased from 96% to 90%. After 25 min, the conversion rate reached 100%. Compared with Example 1, the storage method of this example has a slight effect on the activity of the catalytic membrane in the test range, and the time for complete conversion of the reaction raw material is slightly extended, but it has no effect on the stability of the catalytic membrane.

[0037] Comparative Example 1

[0038] The difference between this comparative example and Example 1 is that the obtained Co@CM-550-0.06 catalytic membrane is not treated and directly used for the hydrogenation reaction of p-nitrophenol. The results are shown in Figure 3 After 5 cycles of testing, the conversion rate at 20 min decreased from 89.7% to 65.4%.

[0039] Comparative Example 2

[0040] The difference between this comparative example and Example 1 is that the obtained Co@CM-550-0.06 catalytic membrane is soaked with an equal amount of deionized water. After the end of soaking, the multi-channel Co@CM catalytic membrane is taken out and used for the hydrogenation reaction of p-nitrophenol. The results are shown in Figure 4 After 5 cycles of testing, the conversion rate at 20 min decreased from 61.6% to 20.1%.

[0041] Comparative Example 3

[0042] The difference between this comparative example and Example 1 is that the obtained Co@CM-550-0.06 catalytic membrane is forced to flow through the catalytic membrane with a sufficient amount of a mixed solution of deionized water and ethanol (volume ratio of deionized water to ethanol is 5:1), and the catalytic membrane is flushed. The flushing flow rate is 3.5 L / h, and the flushing time is 45 min. After flushing, the catalytic membrane is directly used for the hydrogenation reaction of p-nitrophenol, and the results are shown in Figure 5 After 5 cycles of testing, the conversion rate at 20 min decreased from 100% to 94.1%, and the activity remained basically unchanged.

[0043] 1. Contact angle test

[0044] The catalytic membranes obtained in Example 1, Comparative Example 1 and Comparative Example 2 are subjected to contact angle test, and the results are shown in Figure 6 Figure 6 ​It can be seen that the Co@CM catalytic membrane soaked in ethanol has the smallest contact angle with the solvent, indicating that it has the best affinity with the solvent. At the same time, it also has the shortest time for the solvent to penetrate into the membrane pores, indicating that it has the lowest mass transfer resistance in the hydrogenation reaction of p-nitrophenol. Therefore, the Co@CM catalytic membrane soaked in ethanol has the best catalytic performance. The contact angle of the fresh Co@CM catalytic membrane with the solvent is the largest among the three, indicating that its affinity with the solvent is the worst, and the time for the solvent to completely penetrate into the membrane pores is also longer than that of the Co@CM catalytic membrane soaked in ethanol, indicating an increase in mass transfer resistance. Therefore, the catalytic performance decreases. While the Co@CM catalytic membrane soaked in deionized water has a contact angle with the solvent between the two, the solvent cannot penetrate into the membrane pores at all. Therefore, the Co@CM catalytic membrane soaked in deionized water has the worst performance.

[0045] 2. Cobalt loss determination

[0046] In order to analyze the influence of different treatment methods on the active components of the catalytic membrane, the membrane tubes obtained in each example and comparative example were characterized by ICP, and the loss of active component cobalt of the catalytic membrane after the cycle test was calculated based on the cobalt content in the fresh Co@CM catalytic membrane (calcined and cooled catalytic membrane), and the results are shown in Table 1.

[0047] Table 1 Cobalt loss statistics

[0048]

[0049] According to Table 1, after the cycle test, the loss of active component cobalt of the Co@CM catalytic membrane soaked in ethanol is only 7% compared with that before the cycle test, and it always has the most active sites during the reaction. At the same time, it has the best affinity with the solvent. Therefore, the Co@CM catalytic membrane soaked in ethanol has the best catalytic activity and stability. The Co@CM catalytic membrane soaked in methanol has a slightly larger loss of active component cobalt than the Co@CM catalytic membrane soaked in ethanol, so its catalytic activity and stability are slightly reduced. For the fresh Co@CM catalytic membrane and the Co@CM catalytic membrane soaked in deionized water, the loss of active component cobalt after the cycle test is 49% and 38.4%, respectively. A large amount of cobalt loss causes the activity of the two to gradually decrease during the cycle test, so the catalytic performance is not good. For the Co@CM catalytic membrane washed with an ethanol aqueous solution for 45 min and then used for the cycle reaction, the active component with weak binding force in the membrane pores is removed by forced flow, and the active component with strong binding force remaining can stably catalyze the reaction, so it has good stability.

[0050] The ethanol soaking method can change the surface properties of the Co@CM catalytic membrane to some extent, enhance the affinity between the membrane and the reaction solution, reduce the mass transfer resistance in the reaction process, make the active components with weak binding force not easy to flow out, and also participate in the catalytic reaction, thereby greatly improving the catalytic efficiency.

[0051] The above is only the preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution content of the present application, in accordance with the technical essence of the present application, still belong to the protection scope of the technical solution of the present application.

Claims

1. Application of a multi-channel Co@CM ceramic catalytic membrane in the reaction of p-nitrophenol hydrogenation, characterized in that, The prepared multi-channel Co@CM ceramic catalytic membrane is soaked in a liquid for preservation; The liquid used for the soaking is any one of ethanol or methanol; After the preparation of the multi-channel Co@CM ceramic catalytic membrane, the membrane is first soaked for preservation, and then taken out and directly used for the hydrogenation reaction of p-nitrophenol, and the soaking and preservation time is not less than 6 hours; The Co@CM ceramic catalytic membrane is prepared by the following method: Step one: 2-methyl imidazole is dissolved in methanol, and stirred until the solution is clear and transparent to obtain solution A; Step two: cobalt nitrate hexahydrate is dissolved in methanol, and stirred until the solution is clear and transparent to obtain solution B; Step three: solution A is first filled in the membrane channel, and under the action of a peristaltic pump, solution A in the channel is forced to flow through the membrane holes of the multi-channel ceramic membrane, and then flows out of the membrane tube, and the pipeline is designed to enable solution A to be recycled under the action of the peristaltic pump, and the forced flow time of solution A lasts for one hour, then solution A is discharged, solution B is replaced, and the above operation is repeated, and solution A and solution B are alternately introduced for at least two times; Step four: after solution A and solution B are discharged, methanol is forced to flow through the surface of the washing membrane tube and the membrane holes, and after the washing is completed, the membrane tube is taken out and dried to obtain a multi-channel ZIF-67@CM ceramic membrane; Step five: the ZIF-67@CM ceramic membrane is calcined to obtain a multi-channel Co@CM ceramic catalytic membrane.

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