Immobilized catalyst for transesterification as well as preparation method and application of immobilized catalyst

Abstract

The invention relates to the technical field of organic synthesis, in particular to a preparation method of a transesterification immobilized catalyst, which comprises the following steps: mixing ethylenediamine and citric acid, and reacting to obtain a carbonized polymer point; adding the carbonized polymer point into a solvent, adding acid to adjust the pH value, and adding 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide for activation; adding excessive amine organic matters of which the total carbon number is less than or equal to 5, and reacting to obtain a carbonized polymer dot solid catalyst mixture; and purifying to obtain the carbonized polymer dot solid catalyst. The preparation method comprises the following steps: reacting CPDs with EDC and NHS to activate carboxylic acid in CPDs, and then adding an amine organic matter to react with carboxyl to form a bond so as to obtain amide and form a firm chemical bond; a highly-crosslinked polymer network structure is arranged in the catalyst, a large amount of hydrogen bond acting force can be generated in the structure, and when the catalyst is applied to catalytic transesterification, the content of impurities in a product is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysis technology, in particular to an ester exchange reaction solid catalyst and its preparation method and application. BACKGROUND

[0002] Currently, the catalysts for ester exchange reaction of carbonate products can be divided into two categories: homogeneous catalysts and heterogeneous catalysts. In the homogeneous ester exchange reaction system, the catalyst can be dissolved in the reaction system and form more active centers, so that the conversion rate of reactants and the yield of products are high. However, there are problems such as difficulty in separation of catalyst from product and difficulty in recovery. In addition, the use of homogeneous catalysts in ester exchange reaction can produce a large amount of solid waste, accompanied by increased solid waste treatment costs. The currently developed heterogeneous catalysts include: supported catalysts, molecular sieve catalysts, solid acid catalysts, strong base anion exchange resin catalysts, and anion type columnar material catalysts. Due to the process problems of supported catalysts, the loading amount of active centers is limited, so the amount of catalyst used in the ester exchange reaction is often large, the catalytic effect is general, and the active centers may fall off after a long time of reaction. The strong base anion exchange resin catalyst is generally a polymeric material containing amino groups. The high molecular structure in the resin is easily swollen and damaged when immersed in high-temperature alcohol, ester and other good solvents for a long time, which affects the service life. The other several catalysts also have problems such as low raw material conversion rate and slow catalytic rate. SUMMARY

[0003] In order to solve the above technical problems, the present application provides an efficient and stable ester exchange reaction solid catalyst based on carbonized polymer dots and its preparation method and application. The catalyst can effectively adsorb by-products during the catalytic ester exchange reaction for a long time, greatly improve the sample purity, reduce the energy consumption of product separation, and reduce the production cost of products.

[0004] The present application adopts the following technical solutions:

[0005] A preparation method of an ester exchange reaction solid catalyst, comprising the following steps:

[0006] (1) mixing ethylenediamine and citric acid to obtain carbonized polymer dots (CPDs) by reaction;

[0007] (2) adding the carbonized polymer dots to a solvent, adjusting the pH value of the solution by adding acid, adding 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) for activation, and then adding an excess of amine organic compounds with a total carbon number ≤5 for reaction to obtain a carbonized polymer dot solid catalyst mixture;

[0008] (3) purifying the carbonized polymer dot solid catalyst mixture to obtain a carbonized polymer dot solid catalyst.

[0009] The carbonized polymer dot solid catalyst prepared by the preparation method has a large number of basic groups on the surface, and the basic groups are connected to the surface of the carbonized polymer dot through stable chemical covalent bonds, unlike the traditional solid catalysts which have a serious problem of active center falling off, the catalyst has extremely strong stability, and the active center is not easy to fall off. At the same time, due to the highly cross-linked polymer network structure inside, a large number of hydrogen bond forces can be generated in the structure, and when applied to catalyze ester exchange reaction, the product has less impurities. The main structure is carbon structure, the structure is not easy to be damaged, the service life is long, and except for the surface active center, it is not soluble in organic solvents, can be reused after filtration, and effectively reduces the production cost.

[0010] The carboxylic acid in the carbonized polymer dot is activated by reacting the carbonized polymer dot with 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and then adding an amine organic matter, one amino group in the amine organic matter reacts with the carboxyl group to form an amide, forming a firm chemical bond, and the introduction of a large number of amino groups provides sufficient basic centers for the carbonized polymer dot catalyst.

[0011] In the above amidation reaction process, 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide act together, and one of them is indispensable, otherwise the amino grafting rate will be greatly reduced, and the catalytic effect on ester exchange reaction is poor. Specifically, the principle of the activation of carboxyl groups by the two is as follows: 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride first reacts with the carboxyl group on the surface of the carbonized polymer dot to generate an unstable active intermediate, the intermediate then reacts with N-hydroxysuccinimide to generate a stable ester intermediate, and the ester intermediate then covalently reacts with the amino group to form a stable amide bond, successfully grafting a large number of basic centers on the surface of the carbonized polymer dot.

[0012] Specifically, as an embodiment of the present application, the concentration of the ethylenediamine is 0.33-1 mol / L. The carbonized polymer dots are prepared by the reaction of ethylenediamine and citric acid. If the concentration of the ethylenediamine is greater than 1 mol / L, the reactants are too fully contacted, the degree of polymerization is too high, the molecular weight is too large, which can lead to a relatively low content of carboxyl groups on the surface of the carbonized polymer dots, and further lead to a low content of amino groups and a small number of active sites of the catalyst in subsequent grafting; if the concentration of the ethylenediamine is less than 0.33 mol / L, the reactants are not fully contacted, the degree of polymerization of the carbonized polymer dots is too low, and sufficient polymer network structure cannot be formed, which has limited effect on the adsorption of ester exchange reaction impurities. More specifically, the concentration of the ethylenediamine is 0.33 mol / L, 0.4 mol / L, 0.5 mol / L, 0.67 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.83 mol / L, 0.88 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L or a range value formed by any two of them; preferably, the concentration of the ethylenediamine is 0.5-0.83 mol / L.

[0013] Specifically, as an embodiment of the present application, the concentration of the citric acid is 0.33-1 mol / L. In order to ensure sufficient reaction of raw materials and reduce by-products, the ratio of the input amount of citric acid to the input amount of ethylenediamine in the present application is (0.9-1.1):1. If the input amount of any raw material is significantly too high, it can lead to uneven polymerization and carbonization, and the structure of the carbonized polymer dots is too different, which is not conducive to the preparation of a catalyst with uniform and stable catalytic effect. More specifically, the concentration of the citric acid is 0.33 mol / L, 0.4 mol / L, 0.5 mol / L, 0.67 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.83 mol / L, 0.88 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L or a range value formed by any two of them; preferably, the concentration of the citric acid is 0.5-0.83 mol / L.

[0014] Specifically, as an embodiment of the present application, the concentration of the carbonized polymer dots in step (2) is 5-10 g / L. If the concentration of the carbonized polymer dots is greater than 10 g / L, the concentration is too high, the carboxyl group is not activated sufficiently, the content of ethylenediamine is relatively low, the grafting rate is not high, and the catalytic effect is not good. If the concentration of the carbonized polymer dots is less than 5 g / L, the content of ethylenediamine and other small molecules is too high, and the subsequent dialysis process takes a long time. More specifically, the concentration of the carbonized polymer dots is 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L, 10 g / L, or a range value composed of any two of them; preferably, the concentration of the carbonized polymer dots is 6.5-8 g / L.

[0015] Specifically, as an embodiment of the present application, the concentration of the 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride is 50-100 g / L, and the concentration of the N-hydroxysuccinimide is 50-100 g / L. More specifically, the amount of 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide is 8-12 times the concentration of the carbonized polymer dots, so as to ensure sufficient activation of the carboxyl group. When the amount of 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide is too large, the subsequent dialysis process takes a long time. When the amount of 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide is too small, the carboxyl group is not activated sufficiently in a short time, and the amino grafting rate is reduced. More specifically, the concentration of the 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride is 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, or a range value composed of any two of them; the concentration of the N-hydroxysuccinimide is 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, or a range value composed of any two of them; preferably, the concentration of the 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride is 65-80 g / L, and the concentration of the N-hydroxysuccinimide is 65-80 g / L.

[0016] Specifically, as an embodiment of the present application, in step (2), the mass ratio of the amine organic compound to the carbonized polymer dots is (2-3):1, so as to ensure the complete reaction of the carbonized polymer dots. If the content of the amine organic compound is too high, the subsequent impurity removal takes a long time; if the content of the amine organic compound is too low, the carbonized polymer dots are not fully reacted, and the amount of amino groups grafted is insufficient, and the number of basic centers catalyzing the ester exchange reaction is small. More specifically, the mass ratio of the amine organic compound to the carbonized polymer dots is 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, or a range value composed of any two of them,

[0017] Specifically, as an embodiment of the present application, the total carbon number in the amine organic compound is ≤5. If the total carbon number in the amine organic compound is too large, its solubility in aqueous solution is poor, resulting in low reaction efficiency.

[0018] Specifically, as an embodiment of the present application, the amine organic compound is selected from any one of the following structural formulas:

[0019]

[0020] In formula 1, 1≤n≤5; R is any one of -CH3 and -CH2CH3.

[0021] More specifically, the amine organic compound is selected from any one of the following compounds:

[0022]

[0023] Specifically, as an embodiment of the present application, the reaction in step (1) is a hydrothermal reaction, specifically, the reaction is carried out at 160-230℃ for 4-10h; more specifically, the hydrothermal reaction process is as follows: all the uniformly stirred materials are transferred to a high-pressure reaction kettle, the reaction kettle is placed in an oven, and the reaction is carried out at 160-230℃ for 4-10h.

[0024] If the hydrothermal temperature is greater than 230℃, the polymerization and carbonization degree of the carbonized polymer point is too high, the carbonization degree of the polymer network structure is large, the hydrogen bond force is reduced, the impurities cannot be effectively adsorbed, and part of the surface functional groups is carbonized, so that the grafting site is small, and the amount of subsequent amino grafting is small; if the hydrothermal temperature is less than 160℃, the raw materials are not fully reacted, the polymerization degree is low, the hydrogen bond force is small, and the internal structure of the carbonized polymer point is not effectively carbonized, there are active groups in the crosslinked polymer network structure, which causes side reactions in the ester exchange reaction and reduces the service life. More specifically, the hydrothermal reaction temperature is 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃ or any two ranges; preferably, the hydrothermal reaction temperature is 180-200℃.

[0025] The hydrothermal reaction time is 4-10h, if the reaction time is greater than 10h, the polymerization and carbonization degree is too high, the surface functional group carbonization grafting site is small, which affects the amount of amino grafting; if the reaction time is less than 4h, the raw materials are not completely reacted, the polymerization degree is low, the internal structure of the carbonized polymer point is not effectively carbonized, there are active groups in the crosslinked polymer network structure, which causes side reactions in the ester exchange reaction and reduces the service life. More specifically, the hydrothermal reaction time is 4h, 5h, 6h, 7h, 8h, 9h, 10h or any two ranges; preferably, the hydrothermal time is 5-8h.

[0026] In step (1), after the reaction is completed, a cooling and drying process is further included, specifically including: cooling the hydrothermal reaction product to room temperature, transferring the product solution to a dialysis bag with a molecular weight of 2000-7000Da, sealing the dialysis bag and placing it in pure water, standing and dialysis to separate small molecules, reducing pressure to remove water, and vacuum drying. Specifically, during the standing and dialysis process, the water is replaced every 0.5h, 0.5h, 1h, 1h, 2h, 2h, 3h, 3h, 10h. The molecular weight of the dialysis bag in the present application is between 2000-7000Da, if the molecular weight is higher than 7000Da, the polymerization degree of the screened carbonized polymer point is too high, the proportion of surface hydrophilic groups is low, which is not conducive to subsequent amino grafting; if the molecular weight is lower than 3000Da, the polymer network structure inside the carbonized polymer point is less, which cannot effectively adsorb impurities through hydrogen bond force. Preferably, the molecular weight of the dialysis bag is between 3000-5000Da.

[0027] In step (2), the excess amine organic matter is added at 70-100℃ for 65-75h; preferably, the excess amine organic matter is added at 80℃ for 72h.

[0028] The carbonized polymer dot solid catalyst mixture in step (3) is purified with a 2000-4000 Da dialysis bag for at least 48 h, and then filtered, dried, to obtain the carbonized polymer dot solid catalyst; more specifically, the carbonized polymer dot solid catalyst mixture is purified with a 3000 Da dialysis bag for at least 48 h, to remove small molecules such as amines, EDC and NHS, and then filtered with a microporous filter (0.22 μm), dried, to obtain the carbonized polymer dot solid catalyst with a large number of amino groups on the surface.

[0029] The application further provides an ester exchange reaction immobilized catalyst prepared according to the preparation method.

[0030] The application further provides application of the immobilized catalyst as an ester exchange reaction immobilized catalyst, and the addition amount of the immobilized catalyst is 1-15% of the total mass of ester exchange reaction raw materials.

[0031] Specifically, as an embodiment of the application, the catalytic reaction method based on the immobilized catalyst comprises the following steps:

[0032] Ethylene carbonate (EC), methanol (MA), the CPDs solid catalyst and a magnetic particle are put into a three-necked flask, a reflux condenser is connected, condensed water is introduced, the kettle temperature is set to 70-130 ℃, and heating is continued, samples are taken every 0.5 h, the samples are filtered with a 0.22 μm micro filter, the content of the gas chromatography components is tested, the conversion rate of the raw material EC is calculated according to the gas chromatography data, the conversion rates calculated before and after are similar, which is the reaction equilibrium, and the reaction equilibrium time is recorded.

[0033] Specifically, as an embodiment of the application, the addition amount of the immobilized catalyst is 1-15% of the total mass of ester exchange reaction raw materials; if the addition amount is less than 1%, the catalytic rate is slow; if the addition amount is greater than 15%, the catalytic effect does not obviously increase. Preferably, the addition amount of the immobilized catalyst is 2-5% of the total mass of ester exchange reaction raw materials.

[0034] Specifically, as an embodiment of the application, the kettle temperature of the ester exchange reaction is 70-130 ℃; if the kettle temperature is less than 70 ℃, the material temperature is greatly affected by the environment, and may not reach the reflux temperature, affecting the reaction rate; if the kettle temperature is greater than 130 ℃, the material reflux is insufficient, and the light component material may volatilize. Preferably, the kettle temperature of the ester exchange reaction is 80-100 ℃.

[0035] The preparation method of the transesterification immobilized catalyst of the present application is as follows: the carboxylic acid in the carbonized polymer dots is activated by reacting the carbonized polymer dots with 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and then the amine organic compound is added to react with the carboxyl group to form an amide and a firm chemical bond. The introduction of a large number of amino groups provides sufficient basic centers for the carbonized polymer dot catalyst. In addition, the carbonized polymer dot catalyst has a highly cross-linked polymer network structure, which can generate a large number of hydrogen bonding forces. When the carbonized polymer dot catalyst is applied to catalyze the transesterification reaction, the product has a low impurity content. The main structure of the carbonized polymer dot catalyst is a carbon structure, which is not easy to be damaged and has a long service life. In addition to the surface active center, the carbonized polymer dot catalyst is insoluble in organic solvents and can be reused after filtration, thereby effectively reducing the production cost. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0037] Embodiment 1

[0038] The preparation method of the transesterification immobilized catalyst in the present embodiment includes the following steps:

[0039] (1) 13.4 g of ethylenediamine (0.67 mol / L) and 42 g of citric acid (0.67 mol / L) are added to 300 g of pure water, and stirred uniformly. The materials are all transferred to a high-pressure reaction kettle, and the reaction kettle is placed in an oven for hydrothermal reaction at 200 ℃ for 5 h. After the reaction is completed, the product solution is transferred to a 2000 Da dialysis bag, and the dialysis bag is sealed and placed in 2 L of pure water. After standing for 2 days, small molecules are separated out. During this period, the water is replaced every 0.5 h, 0.5 h, 1 h, 1 h, 2 h, 2 h, 3 h, 3 h, and 10 h. After water is removed under reduced pressure, brown-black carbonized polymer dots (CPDs) are obtained after vacuum drying;

[0040] (2) 1.5 g of the above CPDs (7.5 g / L) is dissolved in 200 mL of deionized water, and the pH of the solution is adjusted to 4 with dilute hydrochloric acid. 15 g of EDC (1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride 75 g / L) and 15 g of NHS (N-hydroxysuccinimide 75 g / L) are added, and the carboxyl groups on the surface of the CPDs are activated for 1 h. 3 g of the amine organic compound shown in compound 1 is added to the above solution, and the solution is transferred to a reaction kettle for reaction at 80 ℃ for 3 days to obtain a carbonized polymer dot solid catalyst mixture;

[0041] (3) The carbonized polymer dot solid catalyst mixture was purified with a dialysis bag (3000 Da) for 48 h to remove small molecules such as ethylenediamine, EDC and NHS, and was filtered through a microporous filter (0.22 μm) and dried to obtain a carbonized polymer dot solid catalyst with a large number of amino groups on the surface.

[0042] The ester exchange reaction was carried out using the catalyst prepared in this example, including the following steps:

[0043] Into a 500 mL three-necked flask were introduced 88 g of ethylene carbonate (EC), 160 g of methanol (MA), 4.96 g of the carbonized polymer dot solid catalyst, and a magnetic stirrer, and a reflux condenser was connected. After cooling water was introduced, the kettle temperature was set to 90°C, and heating was continued under reflux. Samples were taken every 0.5 h, filtered through a 0.22 μm microfilter, and the gas chromatograph component content was tested. According to the gas chromatograph data, the conversion rate of the raw material EC was calculated. When the conversion rates of EC calculated twice in succession were similar, the reaction equilibrium was reached, and the reaction equilibrium time was recorded.

[0044] In this example, the equilibrium time of the ester exchange reaction was 3 h, and the components were: ethylene carbonate (EC) mass content 7.793%, methanol (MA) mass content 54.122%, dimethyl carbonate (DMC) mass content 21.212%, ethylene glycol (EG) mass content 16.828%, 2 types of impurities with a content of 0.045%, and the conversion rate of the raw material EC was 71.16%.

[0045] Table 1 shows the test results of the ester exchange reaction using the carbonized polymer dot solid catalyst of Examples 1-11. The differences between Examples 2-11 and Example 1 are the related data in the catalyst preparation method shown in Table 1.

[0046] Table 1

[0047]

[0048] From the test results of Comparative Examples 1-11, it can be seen that the carbonized polymer dot obtained by the reaction of ethylenediamine and citric acid forms a sufficient polymer network structure, providing a basis for the subsequent activation reaction. From the test results of Example 1 and Examples 6-7, it can be seen that when the content of ethylenediamine and citric acid is too small, the polymerization degree of the carbonized polymer dot is too low, and a sufficient polymer network structure cannot be formed, and the adsorption effect on impurities is limited. When the content of ethylenediamine and citric acid is too large, the polymerization degree is too high, which leads to a low content of carboxyl groups on the surface of the carbonized polymer dot, which is not conducive to subsequent grafting. From the test results of Example 1 and Examples 10-11, it can be seen that when the mass ratio of ethylenediamine and citric acid is too large or too small, the polymerization and carbonization are not uniform, the structure of the carbonized polymer dot differs too much, and the stability of the catalytic effect of the catalyst is affected.

[0049] Table 2 shows the test results of transesterification reaction of carbonized polymer dots solid catalyst of Example 1, Examples 12-21, Comparative Examples 1-2, the difference between Examples 12-21, Comparative Examples 1-2 and Example 1 lies in the relevant data in the catalyst preparation method shown in Table 2.

[0050] Table 2

[0051]

[0052] From the test results of Comparative Example 1, Examples 12-21 and Comparative Examples 1-2, it can be seen that by reacting carbonized polymer dots with 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, the carboxylic acid in the carbonized polymer dots can be activated, and then adding an amine organic matter, the amino and carboxyl form a firm chemical bond, which provides sufficient basic center for the carbonized polymer dot catalyst. From the test results of Example 1 and Comparative Example 1-2, it can be seen that when the carbonized polymer dots are subjected to amidation reaction, 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide act together, and the lack of any one of them will cause the amino grafting rate to be greatly reduced, the corresponding catalytic effect is poor, the EC conversion rate is very low, and it is difficult to reach equilibrium in a short time. From the test results of Example 1 and Examples 16-17, it can be seen that when the concentration of carbonized polymer dots, the concentration of 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride, and the concentration of N-hydroxysuccinimide are too high or too low, the grafting rate will be not high, and the catalytic effect will be poor; or the impurity removal time is long. From the test results of Example 1 and Examples 20-21, it can be seen that when the concentration ratio of 1-ethyl-(3-methylaminopropyl) carbodiimide hydrochloride and carbonized polymer dots is too large or too small, it will also have a significant impact on the catalytic effect or the impurity removal time.

[0053] Table 3 shows the test results of transesterification reaction of carbonized polymer dots solid catalyst of Example 1, Examples 22-30, the difference between Examples 22-30 and Example 1 lies in the relevant data in the catalyst preparation method shown in Table 3.

[0054] Table 3

[0055]

[0056] From the test results of Comparative Example 1, Examples 22-26 and Comparative Example 3, it can be seen that for different types of amine organic compounds with a total carbon number less than or equal to 5, the carbonized polymer dot solid catalyst prepared by the preparation method of the present application can achieve good catalytic effect and low impurity content, which shows that the present application is universal for different amine organic compounds. Most amine organic compounds with a total carbon number greater than 5 are not soluble in water, and the reaction rate with CPD is very low, and it is difficult to reach equilibrium in a short time. Preferably, from the test results of Example 1, Examples 22-26 and Example 27, it can be seen that when the total carbon number of the amine organic compound is ≤5, the catalytic efficiency of the catalyst is relatively better.

[0057] From the test results of Example 1 and Examples 27-30, it can be seen that when the mass ratio of amine organic compound to carbonized polymer dot in step (2) is (2-3) : 1, the reaction of carbonized polymer dot can be further ensured to be complete. If the mass ratio is too large, it is not conducive to impurity removal; if the mass ratio is too small, the catalytic effect is reduced.

[0058] Table 4 shows the test results of ester exchange reaction using carbonized polymer dot solid catalyst of Example 1, Examples 31-33. The difference between Examples 31-33 and Example 1 is the related data in the catalyst preparation method shown in Table 4.

[0059] Table 4

[0060]

[0061] From the test results of Comparative Example 1, Examples 31-33, it can be seen that when ethylenediamine and citric acid are subjected to hydrothermal reaction, good polymerization of carbonized polymer dot can be achieved at a hydrothermal temperature of 160-230°C, which is helpful for the subsequent grafting reaction.

[0062] Table 5 shows the test results of ester exchange reaction using carbonized polymer dot solid catalyst of Example 1, Examples 34-37 and Comparative Examples 4-6. The difference between Examples 34-37 and Comparative Examples 4-6 and Example 1 is the related data in the ester exchange reaction shown in Table 5.

[0063] Table 5

[0064]

[0065] From the test results of Comparative Example 1, Examples 34-37 and Comparative Example 6, it can be seen that when the transesterification reaction is catalyzed by the carbonized polymer dot catalyst of the present application, the catalytic rate and catalytic effect are obviously superior to those of the conventional solid alkali catalyst. From the test results of Example 1, Examples 34-37 and Comparative Examples 4-5, it can be seen that when the addition amount of the catalyst is 1-15% of the total mass of the transesterification reaction raw materials, the catalytic effect is better. If the addition amount is too small, the catalytic rate is slow; if the addition amount is too large, the catalytic effect does not improve obviously.

[0066] Comparative Example 7

[0067] The only difference between this comparative example and Example 1 is that in the catalyst preparation process step (2), no acid is added to adjust the pH value.

[0068] In this comparative example, the equilibrium time of the transesterification reaction is 6h, and the components are: ethylene carbonate (EC) mass content 12.100%, methanol (MA) mass content 66.367%, dimethyl carbonate (DMC) mass content 11.224%, ethylene glycol (EG) mass content 10.258%, 3 types of impurities with a content of 0.051%, and the raw material EC conversion rate is 55.22%.

[0069] From the test results of Example 1 and Comparative Example 7, it can be seen that by adding acid to adjust the pH value of the solution during the preparation of the catalyst, the activation process of the carbonized polymer dot is optimized, and the catalytic effect of the prepared catalyst is better and the equilibrium time is shorter.

[0070] The above has further described the present application with the aid of specific examples, but it should be understood that the specific description herein should not be understood as limiting the spirit and scope of the present application, and various modifications made by those skilled in the art after reading the present specification to the above examples all belong to the scope of the present application.

Claims

1. A method for preparing a supported catalyst for transesterification, characterized in that, Includes the following steps: (1) Mix ethylenediamine and citric acid and react to obtain carbonized polymer dots; (2) The carbonized polymer dots are added to a solvent, the pH of the solution is adjusted by adding acid, and 1-ethyl-(3-methylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide are added for activation; then an excess of amine organic compounds with a total carbon number ≤5 are added to react and a mixture of carbonized polymer dots solid catalysts is obtained. (3) The carbonized polymer spot solid catalyst mixture is purified to obtain the carbonized polymer spot solid catalyst.

2. The method for preparing the supported catalyst for transesterification according to claim 1, characterized in that, The concentration of the ethylenediamine is 0.33–1 mol / L, and the concentration of the citric acid is 0.33–1 mol / L; Preferably, the concentration of ethylenediamine is 0.5–0.83 mol / L, and the concentration of citric acid is 0.5–0.83 mol / L.

3. The method for preparing the supported catalyst for transesterification according to claim 1, characterized in that, In step (2), the concentration of carbonized polymer dots is 5-10 g / L, the concentration of 1-ethyl-(3-methylaminopropyl)carbodiimide hydrochloride is 50-100 g / L, and the concentration of N-hydroxysuccinimide is 50-100 g / L. Preferably, the concentration of the carbonized polymer dots is 6.5–8 g / L, the concentration of 1-ethyl-(3-methylaminopropyl)carbodiimide hydrochloride is 65–80 g / L, and the concentration of N-hydroxysuccinimide is 65–80 g / L.

4. The method for preparing the transesterification supported catalyst according to claim 1, characterized in that, In step (2), the amounts of 1-ethyl-(3-methylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide are both 8 to 12 times the concentration of the carbonized polymer point.

5. The method for preparing the transesterification supported catalyst according to claim 1, characterized in that, In step (2), the mass ratio of the amine organic compound to the carbonized polymer spot is (2-3):

1.

6. The method for preparing the transesterification supported catalyst according to claim 1, characterized in that, The amine organic compound is selected from any one of the following structural formulas: In structural formula 1, 1 ≤ n ≤ 5; R is either -CH3 or -CH2CH3.

7. The method for preparing the transesterification supported catalyst according to claim 1, characterized in that, The reaction in step (1) is a hydrothermal reaction, which is carried out at 160-230°C for 4-10 hours. After the reaction in step (1) is completed, a cooling and drying process is also included. The cooling and drying process includes: cooling the product after the hydrothermal reaction to room temperature, transferring the product solution to a dialysis bag of 2000-7000 Da, sealing it, placing the dialysis bag in pure water, allowing it to stand for dialysis to separate small molecules, removing water under reduced pressure, and drying under vacuum. Preferably, the hydrothermal reaction in step (1) is carried out at 180–200°C for 5–8 hours; Dialysis uses dialysis bags with a capacity of 3000–5000 Da; In step (2), an excess of amine organic compound is added and the reaction is carried out at 70–100 °C for 65–75 h; In step (3), the carbonized polymer dot solid catalyst mixture is purified for at least 48 hours using a dialysis bag with a pressure of 2000-4000 Da, and then filtered and dried to obtain the carbonized polymer dot solid catalyst.

8. A supported catalyst for transesterification, characterized in that, Prepared by the method according to any one of claims 1-7.

9. The application of the supported catalyst according to claim 8 as a supported catalyst for transesterification, characterized in that, The amount of the supported catalyst added is 1 to 15% of the total mass of the transesterification reaction feedstock.

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