Preparation process for producing mixed dibasic acid dimethyl ester by using ionic liquid as catalyst

Abstract

The invention provides a preparation process for producing mixed dibasic acid dimethyl ester by using ionic liquid as a catalyst, which belongs to the technical field of fine chemical engineering, and comprises the following steps: S1, dissolving carbazole in anhydrous acetonitrile, adding bromoethane, reacting, then carrying out rotary evaporation, washing and precipitating, dissolving the precipitate in ethanol, then adding a LiHSO4 solution for ion exchange, centrifuging, and then carrying out vacuum drying to obtain mixed dibasic acid dimethyl ester; the carbazolyl ionic liquid catalyst is obtained; and S2, adding the carbazolyl ionic liquid catalyst, mixed binary acid and methanol into a pre-reactor, reacting to obtain a pre-reaction solution, feeding the pre-reaction solution into an extraction tower, adding an ionic liquid-methanol mixed solution, carrying out countercurrent reaction-extraction to obtain a light-phase product from the top of the extraction tower, carrying out silica gel adsorption, feeding the light-phase product into a rectifying tower, and removing methanol to obtain the carbazolyl ionic liquid. And stirring, adsorbing and filtering to obtain the mixed dibasic acid dimethyl ester. According to the invention, the purposes of high product purity, production process optimization and cost reduction can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemical industry, and in particular to a preparation process for producing mixed dibasic acid dimethyl ester by using ionic liquid as catalyst. Background Art

[0002] Mixed dibasic acid (DBA) is an important by-product in the production process of adipic acid. Its quality is equivalent to 5%-6% of adipic acid. It is large in quantity and low in value. It is worth paying attention to its effective utilization to turn waste into treasure. Mixed dibasic acid dimethyl ester (DBE oil) is a mixture of dibasic acid esters, and its main components are dimethyl succinate, dimethyl glutarate, and dimethyl adipate. DBE oil is a non-toxic, colorless, transparent liquid with a slight aromatic smell. It is a biodegradable, environmentally friendly high-boiling point solvent. It is widely used in coil coatings, baking varnishes, iron printing coatings, automotive coatings, ink industry, resin industry, insulating paint, electrical appliances and metal furniture paints. In addition, it can also be used as a cleaning agent, paint stripper, casting core adhesive, electronic industry flux, and organic synthesis intermediates. The product has high added value. Efficiently, cleanly and economically converting DBA, which is almost a waste, into high-value-added DBE oil has important social, economic and industrial chain value, and is also the key to the sustainable development of the adipic acid industry.

[0003] The synthesis of DBE oil mainly adopts sulfuric acid catalysis, and uses toluene as a water-carrying agent for esterification reaction. Sulfuric acid is oxidizing, dehydrating, and corrosive, which not only corrodes equipment, but also has an important impact on product quality (side reactions lead to more by-products); using toluene as a water-carrying agent will also bring in impurities, which increases the recovery cost on the one hand, and increases the circulation volume of methanol raw materials on the other hand, making the energy consumption and material consumption of the whole process high. The application document with publication number CN101265184A discloses a mixed dibasic acid dimethyl ester production process using a strong acid ion exchange resin as a catalyst, but has the disadvantages of difficulty in catalyst replacement and high energy consumption; the application document with publication number CN101891610A discloses a continuous esterification production method of mixed dibasic acid dimethyl ester using FeCl3 or NaHSO4 as a catalyst, but this method has the disadvantages of high reaction temperature, large circulation volume of intermediate logistics, high energy consumption, and high three wastes.

[0004] Therefore, it is necessary to provide a preparation process for producing mixed dibasic acid dimethyl ester using ionic liquid as catalyst to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0005] In view of this, the present invention provides a preparation process for producing mixed dibasic acid dimethyl ester using ionic liquid as catalyst, which can achieve the purposes of high product purity, optimized production process and reduced cost.

[0006] The specific scheme of the present invention is as follows: a preparation process for producing mixed dibasic acid dimethyl ester using ionic liquid as catalyst comprises the following steps: Step S1, preparation of ionic liquid catalyst: The carbazole is dissolved in anhydrous acetonitrile, ethyl bromide is added, and after the reaction, the precipitate is washed by rotary evaporation, and the precipitate is dissolved in ethanol, and then LiHSO4 solution is added for ion exchange, and the precipitate is centrifuged and vacuum dried to obtain a carbazole-based ionic liquid catalyst; Step S2, preparation of mixed dibasic acid dimethyl ester: A carbazole-based ionic liquid catalyst, a mixed dibasic acid and methanol are added to a pre-reactor, and a pre-reaction liquid is obtained by reaction. The pre-reaction liquid is sent to an extraction tower, and an ionic liquid-methanol mixed liquid is added at the same time to perform a countercurrent reaction-extraction. A light phase product is obtained from the top of the extraction tower, and after silica gel adsorption, it is sent to a distillation tower to remove methanol, and then stirred for adsorption, and filtered to obtain a mixed dibasic acid dimethyl ester.

[0007] The present invention introduces a carbazole-based ionic liquid catalyst, and HSO4 in the carbazole-based ionic liquid - The anion provides strong Brønsted acidity and can effectively catalyze the esterification reaction of mixed dibasic acids and methanol. The aromatic ring structure in the carbazole cation enhances the adsorption capacity of the reactants or their protonated intermediates through π-π stacking, increases the effective collision frequency of the reactants, thereby accelerating the reaction rate, stabilizing the reaction intermediates, inhibiting the production of side reactions, improving the selectivity of the target product, and reducing the production of by-products. In addition, the carbazole-based ionic liquid catalyst has a large non-polar aromatic ring structure and exhibits a certain degree of hydrophobicity. After the reaction is completed, it can form a liquid-liquid phase separation with the product dimethyl dibasic acid, which greatly simplifies the subsequent separation and refining process of the target ester product and reduces the production operation cost.

[0008] The present invention first uses a small amount of ionic liquid to catalyze the reaction of a mixed dibasic acid and methanol to generate a homogeneous pre-reaction liquid. After completing 50%-80% of the entire esterification process, the pre-reaction liquid and the ionic liquid catalyst are further subjected to a countercurrent, differential reaction-separation integrated process in a reaction extraction tower to achieve complete conversion of the mixed dibasic acid and quantitative generation of the mixed dibasic acid dimethyl ester. At the same time, the byproduct water generated by the reaction is bound by the ionic liquid and precipitated in the form of a heavy liquid phase from the light liquid phase mainly composed of the ester product (liquid-liquid phase separation), which not only strengthens the conversion of the raw material to the product, but also greatly simplifies the subsequent separation and refining process of the target ester product. In addition, the process flow is short, the process energy consumption and material consumption are 60% or less of the traditional process, and the discharge amount or concentration of the three wastes is greatly reduced, which is a cleaner production process technology. The process raw materials of the present invention have a wide range of applications, and the ionic liquid catalyst can be recycled after simple concentration, which simplifies the separation process and saves the investment in the separation process. The process of the present invention also has the advantages of mild reaction temperature and pressure conditions, low process energy consumption, etc., and has important application prospects and value in the production of mixed dibasic acid diesters.

[0009] Preferably, in step S1, the reaction temperature is 70-80°C and the reaction time is 6-8h; when adding the LiHSO4 solution, 0.5-2wt% manganese nitrate solution and 0.5-2wt% nickel nitrate solution are also added, and the mixture is heated to 60-80°C and stirred for reaction for 5-6h.

[0010] Manganese nitrate and nickel nitrate provide Mn 2+ and Ni 2+ ions, by ion exchange with HSO4 in carbazole-based ionic liquids - The anions combine to form a binuclear metal coordination structure, which can not only provide Lewis acid sites, promote the activation of reactants (such as methanol, mixed dibasic acids), accelerate the esterification reaction, but also enhance the thermal stability of ionic liquids under high temperature and high pressure.

[0011] Preferably, in step S2, the ratio of the carbazole-based ionic liquid catalyst, the mixed dibasic acid and methanol is 1:10:6; the reaction temperature is 65-80° C., the pressure is 1-2.5 bar, and the reaction time is 1-3 h.

[0012] Preferably, in step S2, the feeding plate position of the pre-reaction liquid is the 5th to 6th plate from the top.

[0013] Preferably, the ratio of ionic liquid to methanol in the ionic liquid-methanol mixture is 1:10; the feed plate position of the ionic liquid-methanol mixture is the first plate from the top to the bottom.

[0014] Preferably, the silica gel adsorption operation uses a two-tower series structure, one of which is in an adsorption operation state and the other is in a regeneration operation state; the adsorbent is a coarse-pore silica gel with a diameter of 2-5 mm; the silica gel adsorption time is 1-2h, the temperature is 30-45°C, and the pressure is 1.5-2.5bar.

[0015] Preferably, after the countercurrent-reactive extraction operation, a heavy phase product is obtained from the bottom of the extraction tower, and the heavy phase product is evaporated, and the evaporation operation is completed by a multi-effect evaporation unit in which a falling film evaporator and a scraper evaporator are connected in series, wherein the operating temperature of the falling film evaporator is 135-145°C and the pressure is 1-2bar; the operating temperature of the scraper evaporator is 100-120°C and the pressure is 0.08-0.12bar.

[0016] A small amount of unreacted methanol and water generated by the reaction are removed by evaporation, so that the ionic liquid can be concentrated. A small part of the concentrated ionic liquid is returned to the pre-reactor for reuse, and most of it is evenly mixed with a small amount of methanol at a certain mass flow rate ratio, and then returned to the upper part of the reaction extraction tower as a catalyst in the reaction-extraction process, thereby constituting the recycling of the catalyst; the steam evaporated from the multi-effect evaporator unit is condensed into liquid, and the condensate is pumped into a methanol recovery tower, methanol is obtained from the top of the recovery tower, and it is returned to the pre-reactor or used as an elution regeneration agent for a silica gel adsorption tower, thereby constituting a methanol recovery cycle, realizing the recycling of materials, optimizing the production process, and reducing costs.

[0017] Preferably, the feed plate position for feeding into the distillation tower is the 15th to 17th plate from the top; the tower top operating pressure is 0.25-0.35 bar, the tower top operating temperature is 35-50°C; the tower top reflux ratio is 1-1.5; and the tower bottom operating temperature is 140-150°C.

[0018] Preferably, in step S2, solid calcium carbonate and activated carbon are added during the stirring adsorption process; the operating temperature of the stirring adsorption is 55-75° C., and the time is 0.5-1.5 h.

[0019] Solid alkali and activated carbon can remove trace acidic substances and colored substances in the product mixed dibasic acid dimethyl ester, and after filtration, a clear and transparent product with qualified acidity and color can be obtained.

[0020] Preferably, the raw material of the mixed dibasic acid dimethyl ester comprises the following components in parts by weight: 7-9 parts of carbazole-based ionic liquid catalyst, 70-90 parts of mixed dibasic acid and 42-54 parts of methanol; The raw materials of the carbazole-based ionic liquid catalyst include 10-15 parts of carbazole, 95-110 parts of anhydrous acetonitrile, 7-10 parts of ethyl bromide and 10-15 parts of LiHSO4 solution; and also include 10-15 parts of nickel nitrate solution and 10-15 parts of manganese nitrate solution.

[0021] The above technical solution of the present invention includes at least the following beneficial effects: (1) The present invention introduces a carbazole-based ionic liquid catalyst, which can effectively catalyze the esterification reaction of a mixed dibasic acid and methanol. The aromatic ring structure in the carbazole cation can enhance its adsorption capacity for reactants or their protonated intermediates through π-π stacking, thereby accelerating the reaction rate, stabilizing the reaction intermediates, inhibiting the production of side reactions, improving the selectivity of the target product, reducing the production of by-products, and improving the product purity and yield.

[0022] (2) The present invention first uses a small amount of ionic liquid to catalyze the reaction of a mixed dibasic acid and methanol to generate a homogeneous pre-reaction liquid. The pre-reaction liquid is then further subjected to a countercurrent, differential reaction-separation integrated process with the ionic liquid catalyst in a reaction extraction tower to achieve complete conversion of the mixed dibasic acid and quantitative generation of dimethyl ester of the mixed dibasic acid. At the same time, the by-product water generated by the reaction is bound by the ionic liquid and precipitated in the form of a heavy liquid phase from the light liquid phase mainly composed of ester products (liquid-liquid phase separation). This not only strengthens the conversion of raw materials into products, but also effectively simplifies the product separation and refining process.

[0023] (3) The process flow of the present invention is short, and the process energy consumption and material consumption are 60% or less of the traditional process. The discharge of three wastes is also greatly reduced, which is a cleaner production process technology. The raw materials of the process of the present invention have a wide range of applications. The ionic liquid catalyst can be recycled after simple concentration, which simplifies the separation process and reduces production costs. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0025] Example 1 Add 10 parts of carbazole and 100 parts of anhydrous acetonitrile into the reactor, stir evenly, then add 7 parts of ethyl bromide, reflux at 75°C for 6 hours, cool to room temperature, remove acetonitrile by rotary evaporation, wash the precipitate with anhydrous ether, and then dissolve the precipitate in ethanol. After fully dissolved, slowly add 10 parts of LiHSO4 solution, then add 10 parts of 2wt% manganese nitrate solution and 10 parts of 2wt% nickel nitrate solution to carry out ion exchange, heat to 70°C, stir for 5 hours, centrifuge and separate the organic layer (ionic liquid layer), vacuum dry, remove moisture, and obtain a carbazole-based ionic liquid catalyst.

[0026] 8 parts of carbazole-based ionic liquid catalyst, 80 parts of mixed dibasic acid and 48 parts of methanol were added into a pre-reactor, and reacted for 2 hours at a reaction temperature of 70° C. and a reaction pressure of 1.5 bar to obtain a pre-reaction liquid.

[0027] The number of plates of the extraction tower is 8. The pre-reaction liquid is fed into the middle of the rotary disc reaction extraction tower, that is, the feed plate position of the pre-reaction liquid is the 6th plate from top to bottom. The mixed liquid with a ratio of methanol to ionic liquid of 1:10 is fed into the upper part of the tower, that is, the first plate from top to bottom. Under the conditions of reaction temperature of 70°C and reaction pressure of 1.5 bar, the countercurrent reaction-extraction process is carried out, and the reaction time is 1.5h. The light phase product at the top of the extraction tower is fed into the silica gel adsorption tower. The adsorbent of the silica gel adsorption tower is selected from coarse-pore silica gel with a diameter of 2-5mm. The silica gel adsorption time is 2h, the temperature is 30°C, and the pressure is 2bar. When the silica gel is saturated with adsorption, it is regenerated. The heavy phase product at the bottom of the extraction tower is fed into the multi-effect evaporator unit for evaporation operation. The operating temperature of the falling film evaporator used in the first effect is 140°C and the pressure is 1bar. The operating temperature of the scraper evaporator in the last effect is 110°C and the pressure is 0.1bar. After the operation is completed, the recovery cycle of ionic liquid and methanol is realized.

[0028] The crude product after silica gel adsorption is sent to a distillation tower. The distillation tower has 25 plates, the feed plate is the 15th plate from the top, the top operating pressure is 0.3 bar, the top operating temperature is 40°C, the top reflux ratio is 1.2, the bottom operating temperature is 145°C, and the collected liquid flow is sent to a stirred adsorption tank, and calcium carbonate solid base powder and activated carbon powder are added at the same time. After filtering, a mixed dibasic acid dimethyl ester is obtained.

[0029] Example 2 Add 15 parts of carbazole and 100 parts of anhydrous acetonitrile into a reactor, stir evenly, then add 10 parts of ethyl bromide, reflux at 70°C for 8 hours, cool to room temperature, remove acetonitrile by rotary evaporation, wash the precipitate with anhydrous ether, and then dissolve the precipitate in ethanol. After fully dissolved, slowly add 15 parts of LiHSO4 solution, then add 15 parts of 1wt% manganese nitrate solution and 15 parts of 1wt% nickel nitrate solution to carry out ion exchange, heat to 60°C, stir for 6 hours, centrifuge and separate the organic layer (ionic liquid layer), vacuum dry, remove moisture, and obtain a carbazole-based ionic liquid catalyst.

[0030] 7 parts of carbazole-based ionic liquid catalyst, 70 parts of mixed dibasic acid and 42 parts of methanol were added into a pre-reactor, and reacted for 3 hours at a reaction temperature of 65° C. and a reaction pressure of 1.5 bar to obtain a pre-reaction liquid.

[0031] The number of plates of the extraction tower is 8. The pre-reaction liquid is fed into the middle of the rotary disc reaction extraction tower, that is, the feed plate position of the pre-reaction liquid is the 5th plate from top to bottom. The mixed liquid with a ratio of methanol to ionic liquid of 1:10 is fed into the upper part of the tower, that is, the first plate from top to bottom. Under the conditions of reaction temperature of 80°C and reaction pressure of 1.0 bar, the countercurrent reaction-extraction process is carried out, and the reaction time is 2.5h. The light phase product at the top of the extraction tower is fed into the silica gel adsorption tower. The adsorbent of the silica gel adsorption tower is selected from coarse-pore silica gel with a diameter of 2-5mm. The silica gel adsorption time is 1.5h, the temperature is 45°C, and the pressure is 2.5bar. When the silica gel is saturated with adsorption, it is regenerated. The heavy phase product at the bottom of the extraction tower is fed into the multi-effect evaporator unit for evaporation operation. The operating temperature of the falling film evaporator used in the first effect is 135°C and the pressure is 2bar. The operating temperature of the scraper evaporator in the last effect is 120°C and the pressure is 0.08bar. After the operation is completed, the recovery cycle of ionic liquid and methanol is realized.

[0032] The crude product after silica gel adsorption is sent to a distillation tower. The distillation tower has 25 plates, the feed plate is the 17th plate from the top, the top operating pressure is 0.25 bar, the top operating temperature is 50°C, the top reflux ratio is 1, and the bottom operating temperature is 140°C. The collected liquid flow is sent to a stirred adsorption tank, and calcium carbonate solid base powder and activated carbon powder are added at the same time. After filtering, a mixed dibasic acid dimethyl ester is obtained.

[0033] Example 3 Add 12 parts of carbazole and 110 parts of anhydrous acetonitrile into the reactor, stir evenly, then add 8 parts of ethyl bromide, reflux at 80°C for 6 hours, cool to room temperature, remove acetonitrile by rotary evaporation, wash the precipitate with anhydrous ether, and then dissolve the precipitate in ethanol. After fully dissolved, slowly add 12 parts of LiHSO4 solution, then add 12 parts of 2wt% manganese nitrate solution and 12 parts of 2wt% nickel nitrate solution to carry out ion exchange, heat to 70°C, stir for 6 hours, centrifuge and separate the organic layer (ionic liquid layer), vacuum dry, remove moisture, and obtain a carbazole-based ionic liquid catalyst.

[0034] 9 parts of carbazole-based ionic liquid catalyst, 90 parts of mixed dibasic acid and 54 parts of methanol were added into a pre-reactor, and reacted for 1 hour at a reaction temperature of 80° C. and a reaction pressure of 2 bar to obtain a pre-reaction liquid.

[0035] The number of plates of the extraction tower is 8. The pre-reaction liquid is fed into the middle of the rotary disc reaction extraction tower, that is, the feed plate position of the pre-reaction liquid is the 6th plate from top to bottom. The mixed liquid with a ratio of methanol to ionic liquid of 1:10 is fed into the upper part of the tower, that is, the first plate from top to bottom. Under the conditions of reaction temperature of 90°C and reaction pressure of 3.0 bar, the countercurrent reaction-extraction process is carried out, and the reaction time is 0.5h. The light phase product at the top of the extraction tower is fed into the silica gel adsorption tower. The adsorbent of the silica gel adsorption tower is selected from coarse-pore silica gel with a diameter of 2-5mm. The silica gel adsorption time is 2h, the temperature is 40°C, and the pressure is 1.5bar. When the silica gel is saturated with adsorption, it is regenerated. The heavy phase product at the bottom of the extraction tower is fed into the multi-effect evaporator unit for evaporation operation. The operating temperature of the falling film evaporator used in the first effect is 145°C and the pressure is 1.5bar. The operating temperature of the scraper evaporator in the last effect is 100°C and the pressure is 0.12bar. After the operation is completed, the recovery cycle of ionic liquid and methanol is realized.

[0036] The crude product after silica gel adsorption is sent to a distillation tower. The distillation tower has 25 plates, the feed plate is the 16th plate from the top, the top operating pressure is 0.35 bar, the top operating temperature is 45°C, the top reflux ratio is 1.4, the bottom operating temperature is 150°C, and the collected liquid flow is sent to a stirred adsorption tank, and calcium carbonate solid base powder and activated carbon powder are added at the same time. After filtering, a mixed dibasic acid dimethyl ester is obtained.

[0037] Example 4 Add 10 parts of carbazole and 95 parts of anhydrous acetonitrile into the reactor, stir evenly, then add 7 parts of ethyl bromide, reflux at 75°C for 7 hours, cool to room temperature, remove acetonitrile by rotary evaporation, wash the precipitate with anhydrous ether, and then dissolve the precipitate in ethanol. After it is fully dissolved, slowly add 10 parts of LiHSO4 solution to carry out ion exchange. After stirring for 4 hours, centrifuge and separate the organic layer (ionic liquid layer), vacuum dry, remove water, and obtain a carbazole-based ionic liquid catalyst.

[0038] 8 parts of carbazole-based ionic liquid catalyst, 80 parts of mixed dibasic acid and 48 parts of methanol were added into a pre-reactor, and reacted for 2 hours at a reaction temperature of 75° C. and a reaction pressure of 1 bar to obtain a pre-reaction liquid.

[0039] The number of plates of the extraction tower is 8. The pre-reaction liquid is fed into the middle of the rotary disc reaction extraction tower, that is, the feed plate position of the pre-reaction liquid is the 5th plate from top to bottom. The mixed liquid with a ratio of methanol to ionic liquid of 1:10 is fed into the upper part of the tower, that is, the first plate from top to bottom. Under the conditions of reaction temperature of 75°C and reaction pressure of 2bar, the countercurrent reaction-extraction process is carried out, and the reaction time is 3h. The light phase product at the top of the extraction tower is fed into the silica gel adsorption tower. The adsorbent of the silica gel adsorption tower is selected from coarse-pore silica gel with a diameter of 2-5mm. The silica gel adsorption time is 1h, the temperature is 45°C, and the pressure is 2.5bar. When the silica gel is saturated with adsorption, it is regenerated. The heavy phase product at the bottom of the extraction tower is fed into the multi-effect evaporator unit for evaporation operation. The operating temperature of the falling film evaporator used in the first effect is 140°C and the pressure is 2bar. The operating temperature of the scraper evaporator in the last effect is 110°C and the pressure is 0.09bar. After the operation is completed, the recovery cycle of ionic liquid and methanol is realized.

[0040] The crude product after silica gel adsorption is sent to a distillation tower. The distillation tower has 25 plates, the feed plate is the 15th plate from the top, the top operating pressure is 0.35 bar, the top operating temperature is 35°C, the top reflux ratio is 1.5, the bottom operating temperature is 140°C, and the collected liquid flow is sent to a stirred adsorption tank, and calcium carbonate solid base powder and activated carbon powder are added at the same time. After filtering, a mixed dibasic acid dimethyl ester is obtained.

[0041] Example 5 Add 12 parts of carbazole and 110 parts of anhydrous acetonitrile into the reactor, stir evenly, then add 9 parts of ethyl bromide, reflux at 80°C for 6.5 hours, cool to room temperature, remove acetonitrile by rotary evaporation, wash the precipitate with anhydrous ether, and then dissolve the precipitate in ethanol. After fully dissolved, slowly add 15 parts of LiHSO4 solution, then add 15 parts of 1.5wt% manganese nitrate solution and 15 parts of 1.5wt% nickel nitrate solution to carry out ion exchange, heat to 80°C, stir for 5 hours, centrifuge and separate the organic layer (ionic liquid layer), vacuum dry, remove moisture, and obtain a carbazole-based ionic liquid catalyst.

[0042] 9 parts of carbazole-based ionic liquid catalyst, 90 parts of mixed dibasic acid and 54 parts of methanol were added into a pre-reactor, and reacted for 1.5 hours at a reaction temperature of 75° C. and a reaction pressure of 2 bar to obtain a pre-reaction liquid.

[0043] The number of plates of the extraction tower is 8. The pre-reaction liquid is fed into the middle of the rotary disc reaction extraction tower, that is, the feed plate position of the pre-reaction liquid is the 5th plate from top to bottom. The mixed liquid with a ratio of methanol to ionic liquid of 1:10 is fed into the upper part of the tower, that is, the first plate from top to bottom. Under the conditions of reaction temperature of 85°C and reaction pressure of 2.5 bar, the countercurrent reaction-extraction process is carried out, and the reaction time is 1.5h. The light phase product at the top of the extraction tower is fed into the silica gel adsorption tower. The adsorbent of the silica gel adsorption tower is selected from coarse-pore silica gel with a diameter of 2-5mm. The silica gel adsorption time is 1h, the temperature is 40°C, and the pressure is 2.5bar. When the silica gel is saturated with adsorption, it is regenerated. The heavy phase product at the bottom of the extraction tower is fed into the multi-effect evaporator unit for evaporation operation. The operating temperature of the falling film evaporator used in the first effect is 135°C and the pressure is 1.5bar. The operating temperature of the scraper evaporator in the last effect is 120°C and the pressure is 0.12bar. After the operation is completed, the recovery cycle of ionic liquid and methanol is realized.

[0044] The crude product after silica gel adsorption is sent to a distillation tower. The distillation tower has 25 plates, the feed plate is the 17th plate from the top, the top operating pressure is 0.35 bar, the top operating temperature is 45°C, the top reflux ratio is 1.2, the bottom operating temperature is 140°C, and the collected liquid flow is sent to a stirred adsorption tank, and calcium carbonate solid base powder and activated carbon powder are added at the same time. After filtering, a mixed dibasic acid dimethyl ester is obtained.

[0045] Example 6 Add 15 parts of carbazole and 100 parts of anhydrous acetonitrile into a reactor, stir evenly, then add 8 parts of ethyl bromide, reflux at 80°C for 6 hours, cool to room temperature, remove acetonitrile by rotary evaporation, wash the precipitate with anhydrous ether, and then dissolve the precipitate in ethanol. After fully dissolved, slowly add 15 parts of LiHSO4 solution, then add 15 parts of 0.5wt% manganese nitrate solution and 15 parts of 0.5wt% nickel nitrate solution to carry out ion exchange, heat to 60°C, stir for 5 hours, centrifuge and separate the organic layer (ionic liquid layer), vacuum dry, remove moisture, and obtain a carbazole-based ionic liquid catalyst.

[0046] 8 parts of carbazole-based ionic liquid catalyst, 80 parts of mixed dibasic acid and 48 parts of methanol were added into a pre-reactor, and reacted for 2.5 hours at a reaction temperature of 75° C. and a reaction pressure of 1.0 bar to obtain a pre-reaction liquid.

[0047] The number of plates of the extraction tower is 8. The pre-reaction liquid is fed into the middle of the rotary disc reaction extraction tower, that is, the feed plate position of the pre-reaction liquid is the 5th plate from top to bottom. The mixed liquid with a ratio of methanol to ionic liquid of 1:10 is fed into the upper part of the tower, that is, the first plate from top to bottom. Under the conditions of reaction temperature of 70°C and reaction pressure of 2.5 bar, the countercurrent reaction-extraction process is carried out, and the reaction time is 2.5 hours. The light phase product at the top of the extraction tower is fed into the silica gel adsorption tower. The adsorbent of the silica gel adsorption tower is selected from coarse-pore silica gel with a diameter of 2-5 mm. The silica gel adsorption time is 2 hours, the temperature is 35°C, and the pressure is 2 bar. When the silica gel is saturated with adsorption, it is regenerated. The heavy phase product at the bottom of the extraction tower is fed into the multi-effect evaporator unit for evaporation operation. The operating temperature of the falling film evaporator used in the first effect is 145°C and the pressure is 1.5 bar. The operating temperature of the scraper evaporator in the last effect is 100°C and the pressure is 0.12 bar. After the operation is completed, the recovery cycle of ionic liquid and methanol is realized.

[0048] The crude product after silica gel adsorption is sent to a distillation tower. The distillation tower has 25 plates, the feed plate is the 16th plate from the top, the top operating pressure is 0.3 bar, the top operating temperature is 35°C, the top reflux ratio is 1.3, the bottom operating temperature is 150°C, and the collected liquid flow is sent to a stirred adsorption tank, and calcium carbonate solid base powder and activated carbon powder are added at the same time. After filtering, a mixed dibasic acid dimethyl ester is obtained.

[0049] The present invention also carries out comparative examples and related tests.

[0050] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, no carbazole-based ionic liquid catalyst is prepared, but a sulfate ionic liquid is used as the ionic liquid catalyst. The other compositions and preparation methods are the same as those in Example 1, and a mixed dibasic acid dimethyl ester is prepared.

[0051] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that no pre-reaction liquid is prepared in Comparative Example 2, but the ionic liquid-catalyzed mixed dibasic acid and methanol are directly put into the extraction tower for reaction. The other compositions and preparation methods are the same as those in Example 1, and mixed dibasic acid dimethyl ester is prepared.

[0052] Performance testing The water vapor consumption in the whole production process of Examples 1-6 and Comparative Examples 1-2 and the purity, yield, acid value and moisture content of the products obtained were tested, and the results are shown in Table 1 below.

[0053] Table 1

[0054] It can be seen from the data in the above table that compared with Example 1, the production process of Comparative Example 1 has a large energy consumption, and the purity and yield of the mixed dibasic acid dimethyl ester produced are low, and the product quality is also significantly reduced, indicating that the carbazole-based ionic liquid catalyst can effectively improve the selectivity of the reaction, reduce by-products, and improve the product purity; Compared with Example 1, the increase in production energy consumption in Comparative Example 2 is not high, but the product purity and product yield are not ideal, and the quality of the product has also declined, indicating that the use of the pre-reaction process can promote the conversion rate of the raw materials, and can simplify the process flow and reduce production costs; In Example 4, nickel nitrate solution and manganese nitrate solution are not added during the preparation of the carbazole-based ionic liquid catalyst, and the purity and yield of the prepared mixed dibasic acid dimethyl ester are reduced compared with other embodiments, indicating that the Ni-Mn binuclear metal coordination structure is conducive to the esterification reaction.

[0055] The above are preferred embodiments of the present invention. A person skilled in the art may make several improvements and modifications without departing from the principles of the present invention. Such improvements and modifications shall also be deemed as the protection scope of the present invention.

Claims

1. A process for producing mixed dibasic acid dimethyl ester using ionic liquid as catalyst, characterized in that: The following steps are involved: Step S1, preparation of ionic liquid catalyst: The carbazole is dissolved in anhydrous acetonitrile, ethyl bromide is added, and after the reaction, the precipitate is washed by rotary evaporation, and the precipitate is dissolved in ethanol, and then LiHSO4 solution is added for ion exchange, and the precipitate is centrifuged and vacuum dried to obtain a carbazole-based ionic liquid catalyst; Step S2, preparation of mixed dibasic acid dimethyl ester: A carbazole-based ionic liquid catalyst, a mixed dibasic acid and methanol are added to a pre-reactor, and a pre-reaction liquid is obtained by reaction. The pre-reaction liquid is sent to an extraction tower, and an ionic liquid-methanol mixed liquid is added at the same time to perform a countercurrent reaction-extraction. A light phase product is obtained from the top of the extraction tower, and after silica gel adsorption, it is sent to a distillation tower to remove methanol, and then stirred for adsorption, and filtered to obtain a mixed dibasic acid dimethyl ester.

2. A process for producing mixed dibasic acid dimethyl esters using ionic liquid as a catalyst according to claim 1, characterized in that: In the step S1, the reaction temperature is 70-80°C and the reaction time is 6-8h; when adding the LiHSO4 solution, 0.5-2wt% manganese nitrate solution and 0.5-2wt% nickel nitrate solution are also added, and the mixture is heated to 60-80°C and stirred for reaction for 5-6h.

3. A process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 2, characterized in that: In the step S2, the ratio of the carbazole-based ionic liquid catalyst, the mixed dibasic acid and methanol is 1:10:6; the reaction temperature is 65-80°C, the pressure is 1-2.5 bar, and the reaction time is 1-3 hours.

4. The process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 1, characterized in that: In the step S2, the feeding plate position of the pre-reaction liquid is the 5th or 6th plate from the top.

5. A process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 4, characterized in that: In the step S2, the ratio of ionic liquid to methanol in the ionic liquid-methanol mixture is 1:10; the feeding plate position of the ionic liquid-methanol mixture is the first plate from the top to the bottom.

6. The process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 1, characterized in that: In step S2, the silica gel adsorption operation uses a two-tower series structure, one of which is in an adsorption operation state and the other is in a regeneration operation state; the adsorbent is a coarse-pore silica gel with a diameter of 2-5 mm; the silica gel adsorption time is 1-2 hours, the temperature is 30-45°C, and the pressure is 1.5-2.5 bar.

7. The process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 1, characterized in that: In the step S2, after the countercurrent-reaction extraction operation, a heavy phase product is obtained from the bottom of the extraction tower, and the heavy phase product is evaporated. The evaporation operation is completed by a multi-effect evaporation unit in which a falling film evaporator and a scraper evaporator are connected in series, wherein the operating temperature of the falling film evaporator is 135-145° C. and the pressure is 1-2 bar; the operating temperature of the scraper evaporator is 100-120° C. and the pressure is 0.08-0.12 bar.

8. The process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 1, characterized in that: In step S2, the feed plates fed into the distillation tower are the 15th to 17th plates from the top; the tower top operating pressure is 0.25-0.35 bar, the tower top operating temperature is 35-50° C.; the tower top reflux ratio is 1-1.5; and the tower bottom operating temperature is 140-150° C.

9. The process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 1, characterized in that: In step S2, solid calcium carbonate and activated carbon are added during the stirring adsorption process; the operating temperature of the stirring adsorption is 55-75° C., and the time is 0.5-1.5 h.

10. The process for producing mixed dibasic acid dimethyl esters using ionic liquid as catalyst according to claim 1, characterized in that: The raw materials of the mixed dibasic acid dimethyl ester include the following components in parts by weight: 7-9 parts of carbazole-based ionic liquid catalyst, 70-90 parts of mixed dibasic acid and 42-54 parts of methanol; The raw materials of the carbazole-based ionic liquid catalyst include 10-15 parts of carbazole, 95-110 parts of anhydrous acetonitrile, 7-10 parts of ethyl bromide and 10-15 parts of LiHSO4 solution; and also include 10-15 parts of nickel nitrate solution and 10-15 parts of manganese nitrate solution.

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