Process for the low-temperature directed decarbonylation of dimethyl oxalate to dimethyl carbonate and catalyst used therefor

Abstract

This application discloses a low-temperature directional decarbonylation process for dimethyl oxalate to dimethyl carbonate and the catalyst used. The catalyst is an imidazole salt-based strong basic catalyst, which has the advantages of high activity at low temperature, high selectivity, and high thermal stability. The process method is a continuous decarbonylation process, which can achieve continuous feed replenishment, continuous product output, and continuous catalyst replacement, ensuring that the catalyst in the reactor remains highly active. The gaseous mixture of dimethyl oxalate and dimethyl carbonate is simply separated by a cooling separation device to obtain crude dimethyl carbonate with a purity of over 80%. It can also be further purified by high-pressure reaction-distillation to obtain dimethyl carbonate with a purity of over 98%. Further purification by distillation can then continuously produce electronic-grade dimethyl carbonate. The high-purity carbon monoxide byproduct of this process can be directly recovered for dimethyl oxalate production after alkali washing and drying, achieving complete utilization of carbon atoms. This significantly reduces production costs and has extremely high industrial application value.

Description

Technical Field

[0001] This invention belongs to the technical field of chemical industrial catalysis, specifically relating to a process for the low-temperature directional decarbonylation of dimethyl oxalate to produce dimethyl carbonate and the catalyst used therein. Background Technology

[0002] Dimethyl carbonate (DMC) is an important, non-toxic, and environmentally friendly solvent and chemical raw material. Its structural formula includes carbonyl, methyl, methoxy, and carbonylmethyl groups, giving it excellent reactivity and earning it the reputation of a "new cornerstone" of organic synthesis. Due to its superior physicochemical properties, it has a wide range of applications, including as an environmentally friendly solvent for paints and coatings, in the preparation of fine chemicals for pharmaceuticals and pesticides, as a gasoline and diesel additive, as a substitute for phosgene in the synthesis of polycarbonate, and as an electrolyte for lithium-ion batteries in the new energy field. In recent years, with the rapid advancement of China's new energy vehicle industry, the demand for new energy batteries has expanded rapidly, leading to a significant increase in the market demand for DMC.

[0003] The process systems for the directed decarbonylation of dimethyl oxalate to dimethyl carbonate mainly include two types: gas-phase and liquid-phase methods. Gas-phase method: First, liquid-phase dimethyl oxalate is vaporized and then, under certain temperature and pressure conditions, passes through a porous solid-phase catalyst, resulting in gas-phase decarbonylation to produce gas-phase dimethyl carbonate. For the gas-phase decarbonylation method, there are extremely high requirements for the activity, selectivity, stability, and lifespan of the catalyst; otherwise, frequent catalyst replacement not only increases the complexity of the operation but also increases costs and production efficiency, thus limiting the application of the catalyst. Liquid-phase method: The decarbonylation reaction can be achieved by liquid-phase dimethyl oxalate and a catalyst under certain temperature and pressure conditions. Although the catalyst and raw materials can have sufficient contact in the liquid-phase method, there are problems such as the separation and recovery of products and catalysts from the reactants, intermittent reaction, and low production efficiency.

[0004] Patent CN112724020A discloses a method and apparatus for the decarbonylation of dimethyl oxalate and dimethyl carbonate. It employs a primary reactor and a secondary reactor connected in series. The primary reactor operates in a one-on-one standby mode, transferring the feed to the secondary reactor once the initial conversion rate reaches 60%. One primary reactor is used for normal reaction, while the other is used for catalyst replacement and regeneration in preparation for the next feed. Although this invention achieves a seemingly continuous reaction, it is essentially still a batch reaction. The increased equipment adds to the fixed asset investment rate, limiting its application.

[0005] In the directed decarbonylation of dimethyl oxalate to produce dimethyl carbonate, process design and development are crucial, but the catalyst is the key to the success of the entire reaction. Patent CN105413726B discloses an alkaline catalyst embedded in carbon materials, its preparation method, and its applications. Through reverse replication technology, it achieves the preparation of an alkaline catalyst with alkali metal carbonate nanoparticles embedded in carbon materials. Patent CN113181894A discloses a catalytic system for the direct decarbonylation of dimethyl oxalate to dimethyl carbonate. It achieves the preparation and composite of alkali / alkaline earth metal Group III and IV inorganic acid salt catalysts and their supports through volume impregnation followed by in-situ calcination, thus obtaining the catalytic system. This catalytic system exhibits good reactivity and can produce dimethyl carbonate with high catalytic selectivity and high conversion rate.

[0006] Currently, reports on these catalysts are limited to laboratory research, and the active components used are all carbonates. These active components are hygroscopic and easily decompose upon heating. Compared to existing processes for the decarbonylation of dimethyl oxalate to dimethyl carbonate, these catalysts are highly susceptible to deactivation, significantly impacting their performance. Furthermore, the industrial-scale preparation of these catalysts involves complex processes and theoretically could cause environmental pollution. Additionally, the catalytic activity and selectivity of existing catalysts still fall short of the requirements for large-scale industrial production. Therefore, it is essential to develop catalyst systems with high catalytic activity, high selectivity, and convenient preparation, as well as to design complementary production processes tailored to the characteristics and performance of these new catalysts. Summary of the Invention

[0007] This application aims to address the problems of existing catalysts for the decarbonylation of dimethyl oxalate to dimethyl carbonate, such as harsh reaction conditions, thermal decomposition of active components, easy deactivation, low activity, and difficult preparation processes. It also addresses the difficulties in separating the product and catalyst from the system in existing liquid-phase production processes, including intermittent reactions, low production efficiency, complex operation, and low purity of DMC products. The application provides a catalyst for the low-temperature directional decarbonylation of dimethyl oxalate to dimethyl carbonate.

[0008] The following technical solution is adopted to solve the above problems: A catalyst for the low-temperature directional decarbonylation of dimethyl oxalate to dimethyl carbonate, wherein the catalyst is a strongly basic imidazole salt.

[0009] Optionally, the strongly basic imidazole salt is prepared by the following method: Add a strong base to molten imidazole and stir until the color changes. Then add solvent I to dissolve and filter to obtain the filtrate. The filtrate was distilled under reduced pressure to obtain a crude product. The crude product was washed and filtered with solvent II and dried to obtain the strongly basic imidazole salt.

[0010] Optionally, the strong base is at least one selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0011] Optionally, solvent I and solvent II are independently at least one of methanol, ethanol, acetonitrile, acetone, and cyclohexane.

[0012] Optionally, the weight ratio of the imidazole to the strong base is 1:0.2~3.

[0013] Optionally, the weight ratio of the imidazole to the strong base is any one of 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, or 1:3, or a range between any two.

[0014] Optionally, the conditions for vacuum distillation include a negative pressure of -0.4 to -0.005 MPa.

[0015] According to another aspect described above, a process for the low-temperature directional decarbonylation of dimethyl oxalate to produce dimethyl carbonate is provided, comprising the following steps: S1. A feed liquid containing dimethyl oxalate and a strong basic imidazole salt catalyst is fed into a reactor for decarbonylation reaction. The upper part of the slurry bed reactor yields the decarbonylation gas phase product, and the lower part of the slurry bed reactor yields the decarbonylation liquid-solid phase mixture product; the reactor is a slurry bed reactor. S2. The decarbonylation gaseous product from step S1 enters the separation device and is separated to obtain a gaseous product containing carbon monoxide and a liquid mixture I containing dimethyl carbonate, dimethyl ether, and methanol. The gaseous product containing carbon monoxide is absorbed by an alkaline solution and dried to obtain high-purity carbon monoxide for discharge. As described above, the high-purity carbon monoxide obtained is recycled for the production of the feedstock dimethyl oxalate.

[0016] The separation device also separates a mixture containing dimethyl oxalate and dimethyl carbonate, which is then returned to the reactor for recycling. Optionally, the purpose of the separation process in the separation device is to remove most of the dimethyl oxalate and carbon monoxide components from the decarbonylation gas phase products.

[0017] In step S3 and S2, mixture I is introduced into a distillation system for separation and purification to obtain electronic-grade dimethyl carbonate.

[0018] Optionally, the feed solution in step S1 is prepared online by introducing dimethyl oxalate from the dimethyl oxalate feed tank and a strongly basic imidazole salt catalyst from the catalyst feeding device into the feed solution preparation tank; In step S1, the decarbonylating liquid solid-phase mixture product is separated by a catalyst solid-liquid separation device to remove the deactivated strong basic imidazole salt catalyst and then returned to the feed liquid preparation tank. Optionally, in step S3, the dimethyl oxalate-containing liquid phase obtained by the distillation system is refluxed to the dimethyl oxalate feed tank.

[0019] Optionally, in step S1, the solid-liquid separation device is one of a filter, a centrifuge, or an evaporation tower.

[0020] Optionally, in step S2, the separation device is one or more combinations of a distillation column, an alcohol washing column, a hot trap, and a cold trap.

[0021] In step S3, the distillation system includes a light-light product column and a product column connected in sequence. The process in step S3 where the liquid mixture I enters the distillation system for separation and purification to obtain electronic-grade dimethyl carbonate is as follows: In step S2, liquid phase mixture I enters the light phase removal tower from the middle, undergoes distillation I, and discharges liquid phase product II containing dimethyl carbonate from the bottom of the light phase removal tower; Liquid product II enters the product column from the middle, followed by distillation II. Premium grade dimethyl carbonate is discharged from the top of the product column, while electronic grade dimethyl carbonate is discharged from the middle of the product column.

[0022] Optionally, in step S1, the conditions for the decarbonylation reaction include: a reaction temperature of 100~250℃ and a reaction pressure of 0~1.5MPa.

[0023] Optionally, in step S1, the reaction temperature of the decarbonylation reaction is any value among 100℃, 150℃, 200℃, and 250℃, or a range between any two.

[0024] Optionally, the weight ratio of the strongly basic imidazole salt catalyst to dimethyl oxalate is 0.01 to 0.5:1.

[0025] Optionally, the weight ratio of the strongly basic imidazole salt catalyst to dimethyl oxalate is any one of 0.01:1, 0.03:1, 0.5:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, or 0.5:1, or a range between any two.

[0026] Optionally, in step S2, the separation conditions of the separation device include: a cooling separation temperature of 80~200℃ and a separation pressure of 0~1.5MPa.

[0027] Optionally, the slurry bed reactor is a batch reactor.

[0028] Optionally, the stirring method of the batch reactor is one of paddle, propeller, or anchor.

[0029] Optionally, the heating method of the batch reactor is either external coil heating or internal coil heating.

[0030] Optionally, in step S3, the separation conditions of the distillation system include: operating pressure of -80~600kPa, top temperature of 40~120℃, and bottom temperature of 70~140℃. Optionally, in step S3, the conditions for distillation I include: operating pressure of 0~600kPa, top temperature of 60~90℃, and bottom temperature of 100~120℃. Optionally, in step S3, the conditions for distillation II include: operating pressure of -80 to 10 kPa, top temperature of 40 to 95°C, and bottom temperature of 90 to 115°C.

[0031] As mentioned above: Industrial grade dimethyl carbonate products refer to dimethyl carbonate products with a purity of 99.5% or higher. Premium grade dimethyl carbonate products refer to dimethyl carbonate products with a purity of 99.9% or higher. Electronic grade dimethyl carbonate products refer to dimethyl carbonate products with a purity of 99.99% or higher.

[0032] The beneficial effects that can be produced as described above include: The catalyst provided above for the low-temperature directional decarbonylation of dimethyl oxalate to dimethyl carbonate is a strongly basic imidazole salt catalyst. Its preparation process does not require calcination, is simple, has high thermal stability, high low-temperature catalytic efficiency, and the active component is stable and not easily decomposed.

[0033] The process of using the aforementioned strongly basic imidazole salt catalyst for the low-temperature directional decarbonylation of dimethyl oxalate to produce dimethyl carbonate uses dimethyl oxalate as a raw material to produce high-value-added dimethyl carbonate. The crude dimethyl carbonate product produced has a dimethyl carbonate content of over 80 wt%, and the target product content is relatively high. This can significantly reduce the steam consumption in the subsequent distillation stage, thereby reducing costs. 99.99% electronic-grade dimethyl carbonate can be directly obtained through multi-stage distillation. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the process flow for the low-temperature directional decarbonylation of dimethyl oxalate to produce dimethyl carbonate in Example 6 of the present invention.

[0035] Figure 2 This is a schematic diagram of the process flow for the low-temperature directional decarbonylation of dimethyl oxalate to produce dimethyl carbonate in Example 7 of the present invention.

[0036] Figure 1 The labels in the attached diagram are as follows: 1. Dimethyl oxalate, 2. Strongly basic imidazole salt catalyst, 3. Feed liquid, 4. Decarbonylation gaseous product, 5. Decarbonylation liquid-solid mixed product, 6. Deactivated strongly basic imidazole salt catalyst, 7. Mixture of dimethyl oxalate, dimethyl carbonate, carbon monoxide, dimethyl ether, and methanol, 8. Dimethyl oxalate, 9. Carbon monoxide and carbon dioxide gas, 10. Dimethyl carbonate, a small amount of dimethyl oxalate, dimethyl ether, and methanol mixture, 11. Dimethyl carbonate and dimethyl oxalate mixture, 12. Mixture containing dimethyl ether and methanol, 13. Dimethyl carbonate product with a purity of ≥99.5%, 14. Dimethyl oxalate mixture, 15. Dimethyl carbonate product with a purity of ≥99.9%, 16. Dimethyl carbonate product with a purity of ≥99.99%, 17. Dimethyl carbonate residue, 18. Dimethyl oxalate, V1. Dimethyl oxalate feed tank. V2. Feed liquid preparation tank; V3. Catalyst solid-liquid separator; V4. Catalyst feeding device; R1. Reactor; E1. Primary cooling separation device; E2. Secondary cooling separation device; T1-1. Light weight removal tower; T1-2. Product tower 1; T1-3. Product tower 2; P1. Feed liquid inlet pump; P2. Primary condenser outlet pump; P3. Secondary condenser outlet pump; P4. Light weight removal tower outlet pump; P5. Product tower 1 outlet pump; P6. Product tower 2 outlet pump.

[0037] Figure 2 The labels in the attached diagram are as follows: 1. Dimethyl oxalate, 2. Strongly basic imidazole salt catalyst, 3. Feed liquid, 4. Decarbonylation gaseous product, 5. Decarbonylation liquid-solid mixed product, 6. Mixture of dimethyl carbonate, dimethyl ether, methanol, and carbon monoxide gas, 7. Carbon monoxide and carbon dioxide gas, 8. Mixture of dimethyl carbonate, dimethyl ether, and methanol, 9. Mixture of dimethyl carbonate, dimethyl ether, and methanol, 10. Mixture containing dimethyl ether and methanol, 11. Dimethyl carbonate product with a purity of ≥99.5%, 12. Dimethyl carbonate product with a purity of ≥99.9%, 13. Dimethyl carbonate product with a purity of ≥99.99%, 14. Dimethyl carbonate residue, 15. Dimethyl oxalate, 16. Dimethyl oxalate, 17. Deactivated strongly basic imidazole salt catalyst, V1. Dimethyl oxalate feed tank, V2. Feed liquid preparation tank; V3. Catalyst solid-liquid separator. V4. Catalyst feeding device; V5. Reflux tank; R2. Reactor; T2-1. Separation device; E1. Condenser; T2-2. Light weight removal tower; T2-3. Product tower; P1. Feed pump; P2. Primary separation unit discharge pump; P3. Reflux discharge pump; P4. Light weight removal tower discharge pump; P5. Product tower discharge pump. Implementation

[0038] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to these embodiments; Unless otherwise specified, the raw materials used in the embodiments of the present invention were all purchased through commercial channels; Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0039] The conversion rate is calculated as follows in this invention: X =(n a + n b + n c + 0.5n d ) / (n e + n a + n b + n c + 0.5n d )×100 The selective calculation method is as follows: S a =n a / (n a + n b + n c + 0.5n d )×100 The table yield is calculated as follows: Y a = X × S a ×100 in: X The conversion rate of dimethyl oxalate is expressed in % (%). S a Selectivity of dimethyl carbonate, measured in % %. Y a Yield of dimethyl carbonate, unit of measurement: % n a This refers to the amount of substance of dimethyl carbonate, measured in mol. n b This refers to the amount of dimethyl ether, measured in mol. n c This refers to the amount of substance of methyl formate, measured in mol. n d This refers to the amount of methanol, measured in mol. n eThis represents the amount of unreacted dimethyl oxalate, measured in mol.

[0040] Example 1: 10 g of imidazole was weighed and heated in an induction cooker at 90 °C for 3 h to melt it, obtaining molten imidazole. 3.52 g of lithium hydroxide was weighed and ground into powder in a mortar, then added to the molten imidazole. The mixture was stirred for 20 min under magnetic stirring until the solution changed color, and then ethanol was added. The mixture was filtered, and the filtrate was distilled under reduced pressure at -0.2 MPa and 80-100 °C for 40 min to obtain crude lithium imidazole. The crude product was placed in 12 g of methanol solution and stirred at room temperature for 10 min. The mixture was filtered and the above operation was repeated 3 times. After filtration, the product was placed in a vacuum drying oven at 100 °C for 8 h and then placed at room temperature to obtain 9.92 g of lithium imidazole catalyst, which was named Catalyst No. 1.

[0041] Example 2: 10 g of imidazole was weighed and heated in an induction cooker at 90 °C for 3 h to melt it, obtaining molten imidazole. 5.88 g of sodium hydroxide was weighed and ground into powder in a mortar, then added to the molten imidazole. The mixture was stirred for 25 min under magnetic stirring until the solution changed color, and then methanol was added. The mixture was filtered, and the filtrate was distilled under reduced pressure at -0.2 MPa and 80-100 °C for 40 min to obtain crude imidazole sodium. The crude product was placed in 14 g of methanol solution and stirred at room temperature for 10 min. The mixture was filtered and the above operation was repeated 3 times. After filtration, the product was placed in a vacuum drying oven at 100 °C for 8 h and then placed at room temperature to obtain 11.77 g of imidazole sodium catalyst, which was named Catalyst No. 2.

[0042] Example 3: 10 g of imidazole was weighed and heated in an induction cooker at 90 °C for 3 h to melt it, obtaining molten hot imidazole; 8.24 g of potassium hydroxide was weighed and ground into powder in a mortar, then added to the molten imidazole, and stirred for 25 min under magnetic stirring until the solution changed color, then cyclohexane was added; the above mixture was filtered, and the filtrate was distilled under reduced pressure, maintaining a pressure of -0.2 MPa and a temperature of 80-100 °C for 40 min to obtain crude imidazole potassium product. The crude product was placed in 16 g of methanol solution, stirred at room temperature for 10 min, filtered, and the above operation was repeated 3 times. After filtration, it was placed in a vacuum drying oven at 100 °C for 8 h, and placed at room temperature to obtain 14 g of imidazole potassium catalyst, named Catalyst No. 3.

[0043] Example 4: 10 g of imidazole was weighed and heated in an induction cooker at 90 °C for 3 h to melt it, obtaining molten imidazole. 15.05 g of rubidium hydroxide was weighed and ground into powder in a mortar, then added to the molten imidazole. The mixture was stirred for 30 min under magnetic stirring until the solution changed color, and then ethanol was added. The mixture was filtered, and the filtrate was distilled under reduced pressure at -0.2 MPa and 80-100 °C for 50 min to obtain crude imidazole rubidium product. The crude product was placed in 23 g of methanol solution and stirred at room temperature for 10 min. The mixture was filtered and the above operation was repeated 3 times. After filtration, the product was placed in a vacuum drying oven at 100 °C for 8 h and then placed at room temperature to obtain 15.73 g of imidazole rubidium catalyst, which was named Catalyst No. 4.

[0044] Example 5: 10 g of imidazole was weighed and heated in an induction cooker at 90 °C for 3 h to melt it, obtaining molten imidazole. 22.05 g of cesium hydroxide was weighed and ground into powder in a mortar, then added to the molten imidazole. The mixture was stirred for 25 min under magnetic stirring until the solution changed color, and then cyclohexane was added. The mixture was filtered, and the filtrate was distilled under reduced pressure at -0.2 MPa and 80-100 °C for 40 min to obtain crude imidazole cesium product. The crude product was placed in 30 g of methanol solution and stirred at room temperature for 10 min. The mixture was filtered and the above operation was repeated 3 times. After filtration, the product was placed in a vacuum drying oven at 100 °C for 8 h and then placed at room temperature to obtain 18.69 g of imidazole cesium catalyst, which was named Catalyst No. 5.

[0045] Example 6: The process flow for the low-temperature directional decarbonylation preparation of dimethyl carbonate is as follows: Figure 1 As shown, labels 1-18 represent the products in the process. The specific process is as follows: Dimethyl oxalate feedstock comes from dimethyl oxalate feedstock tank V1. Imidazole salt-based strong basic catalyst feedstock is added to feedstock preparation tank V2 via catalyst feeding device V4. Stirring is performed under the action of electrode M to prepare a mixture feedstock solution 3 of dimethyl oxalate 1 and imidazole salt-based strong basic catalyst 2. The prepared feedstock solution 3 is then fed into slurry bed reactor R1 via feedstock feed pump P1 for decarbonylation reaction. The decarbonylation reaction temperature is 165℃ and the pressure is 0.35MPa. The decarbonylation liquid solid-phase mixture 5 exiting from the bottom of slurry reactor R1 is recycled back to slurry reactor R1 via catalyst solid-liquid separator V3, or after the deactivated strong basic imidazole salt catalyst is discharged through solid-liquid separator V3, dimethyl oxalate 18 is recycled back to slurry reactor R1. The product exiting from the top of slurry reactor R1... The decarbonylated gaseous product 4 passes through a primary cooling separation unit E1, set at 110°C, separating a large amount of dimethyl oxalate 8. This product is then returned to the dimethyl oxalate raw material tank V1 via a primary condenser discharge pump P2. The remaining gaseous mixture 7 (a mixture of dimethyl oxalate, dimethyl carbonate, carbon monoxide, dimethyl ether, and methanol) enters a secondary cooling separation unit E2, set at 30°C, separating crude dimethyl carbonate product 10 (a mixture of dimethyl carbonate, a small amount of dimethyl oxalate, dimethyl ether, and methanol). This crude product is mainly dimethyl carbonate, containing small amounts of byproducts methanol and dimethyl ether, as well as a small amount of entrained dimethyl oxalate. The gaseous phase is mainly composed of carbon monoxide and a small amount of carbon dioxide gas 9. After alkaline washing and drying to remove a small amount of carbon dioxide, high-purity carbon monoxide is obtained and directly discharged to the dimethyl oxalate production workshop.The separated crude dimethyl carbonate product enters the light component removal tower T1-1 via the secondary condenser discharge pump P3. At the top of tower T1-1, a light component (a mixture of dimethyl ether and methanol) 12 is roughly separated from the by-products. The operating pressure of tower T1-1 is 0.25 kPa, the top temperature is 87.5℃, and the bottom temperature is 105℃. By controlling the top temperature of the product tower, dimethyl carbonate products (a mixture of dimethyl carbonate and dimethyl oxalate) 11 of different purities are obtained. These products then enter product tower 1 T1-2 via the light component removal tower discharge pump P4. The operating pressure of product tower 1 T1-2 is 5 kPa, the top temperature is 92.5℃, and the bottom temperature is 110℃. The operating pressure of product tower 2 T1-3 is 10 kPa, the top temperature is 87.5℃, and the bottom temperature is 102.5℃. The top of product tower T1-2 yields dimethyl carbonate product 13 with a purity of over 99.5%, i.e., industrial-grade dimethyl carbonate. The bottom of product tower T1-2 yields a dimethyl oxalate mixture 14, which is recycled back to the dimethyl oxalate raw material tank V1 via product tower 1 discharge pump P5. The bottom of product tower T1-3 yields dimethyl carbonate residue 17, which is discharged via product tower 2 discharge pump P6. The top of product tower T1-3 yields dimethyl carbonate product with a purity of over 99.9%, i.e., premium-grade dimethyl carbonate. The side sample from product tower T1-3 yields dimethyl carbonate product with a purity of over 99.99%, i.e., electronic-grade dimethyl carbonate.

[0046] Example 7: The process flow for the low-temperature directional decarbonylation preparation of dimethyl carbonate is as follows: Figure 2 As shown, labels 1-17 represent the products in the process. The specific process is as follows: Dimethyl oxalate feedstock comes from dimethyl oxalate feedstock tank V1. Imidazole salt-based strong basic catalyst feedstock is added to feedstock preparation tank V2 via catalyst feeding device V4. Stirring is performed under the influence of electrode M to prepare a mixture feedstock solution 3 of dimethyl oxalate 1 and strong basic imidazole salt catalyst 2. The prepared feedstock solution 3 is then fed into slurry bed reactor R1 via feedstock feed pump P1 for decarbonylation reaction. The decarbonylation reaction temperature is 165℃ and the pressure is 0.35MPa. The decarbonylation liquid solid-phase mixture 5 exiting from the bottom of slurry reactor R1 is recycled back to slurry reactor R1 via catalyst solid-liquid separator V3, or after deactivating the strong basic imidazole salt catalyst, dimethyl oxalate 16 is discharged from solid-liquid separator V3 and recycled back to slurry reactor R1. The decarbonylation gas phase product 4 exiting from the top of slurry reactor R1 is cooled and separated by device T2-1, with a set temperature of 165℃ and a pressure of 0.35MPa. The bottom product of the tower, dimethyl oxalate 15, is refluxed to the slurry reactor R1 via the discharge pump P2 of the separation unit. The gas mixture 6 of dimethyl carbonate, dimethyl ether, methanol, and carbon monoxide at the top of the tower is condensed by E1, and carbon monoxide and carbon dioxide gases 7 are discharged. The high-purity carbon monoxide obtained after alkali washing and drying is sent to the dimethyl oxalate production workshop. A large amount of the mixture 8 of dimethyl carbonate, dimethyl ether, and methanol separated by condenser E1 flows to the reflux tank V5. The mixture 9 of dimethyl carbonate, dimethyl ether, and methanol after passing through reflux tank V5 is partially refluxed to the separation unit T2-1 via the discharge pump P3. A portion of the crude dimethyl carbonate product enters the light-light product removal tower T2-2 via the discharge pump P3. The operating pressure of the light-light product removal tower T2-2 is 0.25 kPa. a. The top temperature of the column is 87.5℃ and the bottom temperature is 105℃. At the top of the light component removal column T2-2, a light component 10 containing dimethyl ether and methanol as a byproduct is roughly separated. At the bottom of the column, dimethyl carbonate product 11 with a purity of over 99.5% is obtained. This product enters the product column T2-3 through the discharge pump P4 of the light component removal column T2-2. The operating pressure of the product column T2-3 is 10 kPa, the top temperature is 87.5℃, and the bottom temperature is 102.5℃. At the top of the product column T2-3, dimethyl carbonate product 12 with a purity of over 99.9% is obtained, which is the premium grade dimethyl carbonate product. At the side of the product column T2-3, dimethyl carbonate product 13 with a purity of over 99.99% is obtained, which is the electronic grade dimethyl carbonate product.

[0047] Test Example 1: The catalysts prepared in Examples 1-5 were selected and used in the process flow of low-temperature directional decarbonylation to prepare dimethyl carbonate in Example 6. The reaction performance evaluation method for the low-temperature directional decarbonylation of dimethyl oxalate to dimethyl carbonate was as follows: In the decarbonylation reactor, dimethyl oxalate and solid base catalyst were mixed at a mass ratio of 10:1. The temperature was raised and, after reaching the target reaction temperature, the stirring was started and the speed was adjusted to 800 rpm for thorough stirring. The reaction was carried out for 20 minutes at a controlled temperature of 165°C. The catalyst performance was then examined, and the results are shown in Table 1.

[0048] Table 1. Catalytic performance of the catalysts obtained in Examples 1-5 for the directed synthesis of dimethyl carbonate. Catalyst No. 1 165 80.04 1.54 15.37 16.22 66.87 53.52 Catalyst No. 2 165 80.88 0.48 7.23 23.34 68.95 55.76 Catalyst No. 3 165 83.48 0.08 4.21 19.91 75.79 63.27 Catalyst No. 4 165 82.34 0.57 6.83 17.95 74.65 61.39 Catalyst No. 5 165 80.88 0.48 7.23 23.34 68.95 55.76 Catalyst No. 5 120 21.65 0.77 13.77 59.93 25.54 5.53 In the table above, X represents conversion, S represents selectivity, and Y represents yield; DMO is dimethyl oxalate, MeOH is methanol, DMC is dimethyl carbonate, DME is dimethyl ether, and MF is methyl formate.

[0049] Test Example 2: The catalysts prepared in Examples 1-5 were used in the process flow of low-temperature directional decarbonylation to prepare dimethyl carbonate in Example 6. The optimization experiment of the temperature for the decarbonylation synthesis of dimethyl carbonate from dimethyl oxalate was conducted. The reaction performance evaluation method was as follows: In the decarbonylation reactor, dimethyl oxalate and solid base catalyst were mixed at a mass ratio of 10:1. The temperature was raised to the target temperatures of 120℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, and 185℃, respectively. The reaction was then carried out for 20 minutes with the stirring speed adjusted to 800 rpm. The optimal reaction temperature was screened. The experimental results are shown in Table 2.

[0050] Table 2. Reaction performance of catalytic directed synthesis of dimethyl carbonate at different reaction temperatures. 1 120 5.37 0 3.04 84.48 12.48 0.67 2 155 15.73 0 6.11 43.24 50.65 7.97 3 160 43.56 0.16 7.03 21.69 71.13 30.98 4 165 83.48 0.08 4.21 19.91 75.79 63.27 5 170 85.73 0.57 8.93 16.43 74.07 63.49 6 175 89.22 0.64 9.33 22.87 72.16 64.38 7 180 89.48 0.42 3.65 24.24 71.68 64.13 8 185 89.64 0.00 0.99 30.77 68.24 61.17 In the table above, T represents the reaction temperature, P represents the final reaction pressure, X represents the conversion rate, S represents the selectivity, and Y represents the yield; DMO is dimethyl oxalate, MeOH is methanol, DMC is dimethyl carbonate, and DME is methyl ethyl carbonate.

[0051] Test Example 3: The catalysts prepared in Examples 1-5 were selected for the low-temperature directional decarbonylation process for preparing dimethyl carbonate in Example 7. The optimization experiment of the temperature for the decarbonylation synthesis of dimethyl carbonate from dimethyl oxalate was conducted. The reaction performance evaluation method was as follows: In the decarbonylation reactor, dimethyl oxalate and solid base catalyst were mixed at a mass ratio of 10:1. The temperature was raised to the target temperature of 165℃. After the temperature was raised to the target temperature, the rotation speed was adjusted to 800 rpm. The optimal reaction time was screened under the condition of full stirring at reaction times of 10 min, 20 min, 40 min, 60 min, 80 min, 120 min, 160 min, and 200 min. The experimental results are shown in Table 3.

[0052] Table 3. Reaction performance of catalytic directed synthesis of dimethyl carbonate under different reaction times. 1 10 39.2 0.4 9.62 28.11 61.87 24.25 2 20 57.24 0.09 6.06 17.5 76.35 43.7 3 40 85.66 0.61 11.23 16.83 71.32 61.09 4 60 88.85 0.32 6.15 20.32 73.21 65.04 5 80 91.55 0.27 4.83 21.43 73.48 67.26 6 120 91.89 0.01 3.24 22.88 73.87 67.87 7 160 93.59 0.34 3.79 23.29 72.58 67.93 8 200 97.18 0.43 3.44 21.41 74.72 72.61 In the table above, t represents reaction time, P represents final reaction pressure, X represents conversion, S represents selectivity, and Y represents yield; DMO is dimethyl oxalate, MeOH is methanol, DMC is dimethyl carbonate, and DME is methyl ethyl carbonate.

[0053] Test Example 4: The catalysts prepared in Examples 1-5 were selected for the process of low-temperature directional decarbonylation to prepare dimethyl carbonate in Example 6. The optimization experiment of the catalyst dosage for the decarbonylation synthesis of dimethyl carbonate from dimethyl oxalate was conducted. The reaction performance evaluation method was as follows: Dimethyl carbonate and solid base catalyst were added to the decarbonylation reactor. The catalysts were mixed and fed in a mass ratio of dimethyl oxalate to solid base catalyst of 8%, 10%, and 12%, respectively. The temperature was raised to the target temperature of 165°C, the rotation speed was adjusted to 800 rpm, and the reaction time was controlled at 20 min. The catalyst dosage was screened under the condition of thorough stirring.

[0054] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementations and fall within the scope of protection of the claims.

Claims

1. Use of a strong basic imidazolium salt catalyst in the low-temperature directed decarbonylation of dimethyl oxalate to dimethyl carbonate, characterized in that, The imidazole to strong base in the strongly basic imidazole salt catalyst has a weight ratio of 1:

1. 0.2-3, its preparation method is as follows: S1: Add a strong base to molten imidazole and stir until the color changes, then add solvent I to dissolve and filter to obtain the filtrate; S2: The filtrate is distilled under reduced pressure to obtain a crude product. The crude product is washed and filtered with solvent II and dried to obtain the strongly basic imidazole salt.

2. Use of a catalyst according to claim 1, characterised in that, The strong base is at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

3. The application of the catalyst according to claim 1, characterized in that, Solvent I and Solvent II are independently at least one of methanol, ethanol, acetonitrile, acetone, and cyclohexane.

4. The application of the catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: S1: The feed liquid containing dimethyl oxalate and a strong basic imidazole salt catalyst is fed into the reactor for decarbonylation reaction. The upper part of the slurry bed reactor yields the decarbonylation gas phase product, and the lower part of the slurry bed reactor yields the decarbonylation liquid-solid phase mixture product. The reactor is a slurry bed reactor; S2: The decarbonylation gaseous product from step S1 enters the separation device and is separated to obtain a gaseous product containing carbon monoxide and a liquid mixture I containing dimethyl carbonate, dimethyl ether, and methanol. The gaseous product containing carbon monoxide is absorbed by an alkaline solution and dried to obtain high-purity carbon monoxide for discharge. The obtained high-purity carbon monoxide is recycled for the production of the raw material dimethyl oxalate. The separation device also separates a mixture containing dimethyl oxalate and dimethyl carbonate, which is then returned to the reactor for recycling. S3: In step S2, mixture I enters the distillation system for separation and purification to obtain electronic-grade dimethyl carbonate product.

5. The application of the catalyst according to claim 4, characterized in that, The raw material solution in step S1 is prepared online by adding dimethyl oxalate from the dimethyl oxalate raw material tank and a strongly basic imidazole salt catalyst from the catalyst feeding device into the raw material solution preparation tank.

6. The application of the catalyst according to claim 4, characterized in that, In step S2, the separation device is one or more combinations of a distillation column, an alcohol washing column, a hot trap, and a cold trap.

7. The application of the catalyst according to claim 4, characterized in that, In step S3, the distillation system includes a light-light product column and a product column connected in sequence. The process in step S3 where the liquid mixture I enters the distillation system for separation and purification to obtain electronic-grade dimethyl carbonate is as follows: In step S2, liquid phase mixture I enters the light phase removal tower from the middle, undergoes distillation I, and discharges liquid phase product II containing dimethyl carbonate from the bottom of the light phase removal tower; Liquid product II enters the product column from the middle, followed by distillation II. Premium grade dimethyl carbonate is discharged from the top of the product column, while electronic grade dimethyl carbonate is discharged from the middle of the product column.

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