Systems and methods for producing dimethyl carbonate

Abstract

This invention relates to a system and method for producing dimethyl carbonate, belonging to the field of organic chemical synthesis technology. The system includes: a methanol source, an ethylene oxide source, a carbon dioxide source, an EC reactor, a condenser, a gas-liquid separator, and a DMC distillation column; the methanol source, ethylene oxide source, and carbon dioxide source are respectively connected to the EC reactor; the gas phase outlet I of the EC reactor is connected to the feed inlet of the condenser, and the liquid phase outlet I is connected to the DMC distillation column; the gas phase outlet II of the condenser is connected to the gas-liquid separator. This invention solves the problems of difficult control of reaction heat, uneven temperature distribution within the reactor, low product conversion rate, low purity, and high color in the ethylene carbonate section of previous technologies. Furthermore, it optimizes the reaction path, using the reaction heat of ethylene carbonate synthesis as the heat source for the dimethyl carbonate section, reducing the energy consumption of the reaction system.

Description

Technical Field

[0001] This invention relates to systems and methods for producing dimethyl carbonate, belonging to the field of organic chemical synthesis technology. Background Technology

[0002] Dimethyl carbonate (DMC) is an important organic compound that was classified as a non-toxic chemical in Europe in 1992. DMC is used as a raw material to synthesize various chemical products, including polycarbonate monomers such as diphenyl carbonate, isocyanates, and carbamates. DMC is non-toxic and contains functional groups such as methyl and carbonyl groups in its structure. It can replace highly toxic dimethyl sulfate, methyl chloroformate, and phosgene in methylation reactions to synthesize many high-value-added downstream products, eliminating the environmental pollution caused by these highly toxic chemicals. It is widely used in the pharmaceutical, pesticide, and other fine chemical industries.

[0003] DMC possesses high dielectric constant, high electrochemical stability, and low viscosity, making it a primary solvent in lithium-ion battery electrolytes. DMC also boasts advantages such as high oxygen content, high octane number, good gasoline / water partition coefficient, low toxicity, and rapid biodegradability, making it an excellent additive for gasoline and diesel fuels. Therefore, DMC is widely used in materials and chemical industries, possessing significant industrial application value. DMC is classified into two categories based on purity: industrial grade (99.9%) and battery grade (above 99.999%), with battery-grade DMC requiring more stringent manufacturing processes.

[0004] Currently, transesterification remains the primary production method for DMC and has been industrially applied. This method first synthesizes propylene carbonate (PC) or ethylene carbonate (EC) from CO2 and propylene oxide (PO) or ethylene oxide (EO). Then, PC or EC undergoes transesterification with methanol to yield DMC and 1,2-propanediol (PG) or ethylene glycol (EG). However, this process presents several technical challenges: First, the reactions for synthesizing PC or EC are exothermic, and strongly exothermic, especially the reaction between EO and CO2. Failure to promptly remove the exothermic reaction heat can cause the reactor to overheat, leading to safety hazards. Second, the transesterification and alcoholysis of EC and methanol to produce DMC is a reversible reaction carried out in a reactive distillation column. Therefore, it is crucial to remove DMC promptly during the reaction process to maintain the equilibrium conversion rate. The molar ratio of methanol to EC is typically 10:1 to 15:1, with methanol in significant excess. This excess methanol forms an azeotrope with the product DMC, which exits from the top of the reactive distillation column, disrupting the equilibrium of the transesterification reaction and thus increasing the conversion rate of PC (or EC). This excess methanol is vaporized in the reactive distillation column, with the energy for vaporization provided by steam from the reboiler. This makes temperature control extremely difficult; excessively high temperatures can exacerbate side reactions, leading to a decrease in the yield and purity of EC or PC.

[0005] Chinese invention patent publication CN113387811A discloses an energy-saving and consumption-reducing method for producing dimethyl carbonate (DMC) via transesterification. The exothermic reaction of propylene oxide (or ethylene oxide) with CO2 to synthesize propylene carbonate (or ethylene carbonate) removes the heat of reaction by vaporizing methanol in a batch evaporator. Excess methanol enters the transesterification reactive distillation column in the gas phase, reducing the steam consumption in the reboiler and lowering the heat load of the reactive distillation column, thus achieving energy savings. However, this invention only focuses on energy saving and consumption reduction in the DMC stage, neglecting the control of the reaction heat in the EC stage. In fact, the level of reaction process control in the EC stage is more important for the final yield and purity of DMC. Summary of the Invention

[0006] The problems to be solved by this invention are as follows: 1) timely removal of reaction heat in the EC section; 2) process control in the EC section; and 3) thermal integration issues in the EC / DMC section. This invention employs the introduction of a solvent into the reaction system, using solvent phase change, vaporization, and evaporation to remove heat and control temperature fluctuations during the reaction process. The introduced solvent can further dilute the reactants, reduce the intensity of the reaction, and thus improve the yield and purity of the EC product.

[0007] The system for producing dimethyl carbonate includes: a methanol source, an alkylene oxide source, a carbon dioxide source, an olefin carbonate reactor, a condenser, a gas-liquid separator, and a DMC distillation column; the olefin carbonate reactor has a gas phase outlet I and a liquid phase outlet I; the condenser has a gas phase outlet II and a reflux condenser II; the methanol source, alkylene oxide source, and carbon dioxide source are respectively connected to the EC reactor; gas phase outlet I is connected to the feed inlet of the condenser, and liquid phase outlet I is connected to the DMC distillation column; gas phase outlet II is connected to the gas-liquid separator; and reflux condenser II is connected to the EC reactor.

[0008] The methanol source described in this invention is a feed pipeline or storage tank that can provide methanol.

[0009] The epoxy alkane source described in this invention can be a feed pipeline or storage tank that can provide epoxy alkane.

[0010] The carbon dioxide source described in this invention is a feed pipeline or storage tank that can provide carbon dioxide.

[0011] Optionally, the methanol source has two parallel branches, namely branch P1 and branch P2; branch P1 is connected to the EC reactor; branch P2 is connected to the DMC distillation column.

[0012] Optionally, the gas phase outlet I is located at the top of the EC reactor, and the liquid phase outlet I is located at the top of the carbonate olefin ester reactor.

[0013] Optionally, the vapor outlet II is located at the top of the condenser, and the condensate return port II is located at the bottom of the condenser.

[0014] Optionally, the alkylene oxide source contains ethylene oxide and / or propylene oxide.

[0015] Optionally, the carbonate olefin ester is ethylene carbonate and / or propylene carbonate.

[0016] Optionally, the methanol source is further provided with a parallel branch P3; branch P3 serves as the cold source for the condenser.

[0017] Optionally, P3 is connected to the shell side of the condenser, and the shell side outlet is connected to the DMC distillation column; the gas phase outlet I of the carbonate olefin ester reactor is connected to the tube side of the condenser.

[0018] Optionally, the system further includes a buffer tank; the methanol source and the epoxide alkane source are respectively connected to the buffer tank, and the buffer tank is connected to the EC reactor.

[0019] Optionally, the system further includes a purification unit, with the gas phase outlet of the DMC distillation column connected to the purification unit.

[0020] The reaction system of this invention mainly consists of an ethylene carbonate synthesis section, a tail gas condensation section, and a dimethyl carbonate synthesis section. Ethylene oxide and carbon dioxide are used as reactants, and methanol is used as a solvent. They enter the EC reactor from the bottom and react using a solid catalyst. Carbon dioxide is continuously introduced, and the reaction is strongly exothermic. The heat generated vaporizes the solvent methanol, which, along with unreacted carbon dioxide, is discharged from the top of the reactor and enters the condenser at the top. Some condensable gases are condensed and returned to the reactor, while non-condensable gases are further separated and absorbed in a separator before being discharged into the tail gas absorption system. The separated liquid returns to the reactor. The reaction product, crude ethylene carbonate, overflows from the top of the reactor and enters the dimethyl carbonate reactive distillation column as feedstock. In the reactive distillation column, it undergoes an ester exchange reaction with methanol to produce dimethyl carbonate. The methanol entering the dimethyl carbonate unit to participate in the reaction first serves as a cold source for the condenser in the ethylene carbonate section, exchanging heat with the gas distilled from the ethylene carbonate section before entering the reactive distillation column.

[0021] Methods for producing dimethyl carbonate include:

[0022] S1 epoxide alkane, methanol, and CO2 enter the carbonate olefin ester reactor and react under the action of catalyst I to obtain gaseous products and liquid phase containing EC;

[0023] The S2 gaseous product flows out of the carbonate olefin ester reactor and enters the condenser for condensation. The condensable gas is then returned to the EC reactor.

[0024] The liquid phase containing carbonated olefin esters generated in the S3 EC reactor enters the DMC reactive distillation column.

[0025] In the S4 DMC reactive distillation column, carbonated olefin esters and methanol undergo transesterification and alcoholysis reaction under the action of catalyst II to generate DMC. The gas phase containing DMC is collected from the distillation column.

[0026] Optionally, in S2, methanol enters the condenser as a cold source, and the gaseous products exchange heat with the methanol in the condenser.

[0027] Optionally, methanol is fed into the DMC reactive distillation column as a reaction feedstock;

[0028] Optionally, both catalyst I and catalyst II are heterogeneous catalysts; preferably, catalyst I is a halogenated hydroxyimidazolium resin (preferably prepared using the method of Example 1 in CN105503608B); preferably, catalyst II is a carboxylimidazolium resin (preferably prepared using the method of Example 1 in CN105503519B).

[0029] Preferably, in the EC reactor, the temperature fluctuation range during the reaction process is 3 to 4 °C.

[0030] Optionally, in the carbonate olefin ester reactor, the molar ratio of alkyl epoxides to methanol is 1:1 to 1:10.

[0031] Optionally, the reaction temperature of the carbonate olefin ester reactor is 100–160°C.

[0032] Optionally, the operating pressure of the carbonate olefin ester reactor is 2.0 to 6.0 MPa.

[0033] Optionally, the minimum flow rate of branch P3 (methanol feed) in the condenser is controlled by the temperature of the gas phase outlet I of the EC reactor, which is 40-100°C.

[0034] Optionally, the reaction temperature in the DMC reactive distillation column is 60–100°C; the top temperature is 67.8–111°C.

[0035] Optionally, the operating pressure in the DMC reactive distillation column is 0.1–0.5 MPa; the top pressure is 0.03–0.4 MPa.

[0036] Optionally, the reflux ratio in the DMC reactive distillation column is 0.05 to 10.

[0037] Optionally, the molar ratio of methanol to carbonate olefin ester in the DMC reactive distillation column is 6:1 to 15:1.

[0038] Optionally, the conditions for the gas-liquid separator are: temperature 40–100°C and pressure 2.0–8.0 MPa. The flow rate of branch P1 is ethylene oxide to methanol in a ratio of 1:1 to 1:10; the flow rate of branch P2 is methanol to olefin carbonate in a molar ratio of 6:1 to 15:1; the flow rate of branch P3 is controlled by the temperature of the gas phase outlet I of the ethylene carbonate reactor. Preferably, the flow rate ratio of P1, P2, and P3 is 1–10:0–12:3–10.

[0039] This invention provides a process for the catalytic production of ethylene carbonate from alkyl epoxides (preferably ethylene oxide) and carbon dioxide in methanol solvent, followed by transesterification and alcoholysis of the generated ethylene carbonate with methanol to produce dimethyl carbonate. This method primarily addresses the problems of uncontrollable reaction heat, uneven temperature distribution within the reactor, low product conversion rate, low purity, and high color in previous ethylene carbonate production processes. Furthermore, it optimizes the reaction path by using the heat of reaction from ethylene carbonate synthesis as the heat source for the dimethyl carbonate process, reducing energy consumption. This invention employs solvent phase change vaporization for heat exchange, effectively controlling temperature fluctuations in the ethylene carbonate reactor. Simultaneously, the continuous flow of carbon dioxide within the reaction system ensures a more uniform flow field distribution within the reactor, eliminating temperature differences and improving overall conversion rate and selectivity, as well as increasing product purity and reducing product color. Another advantage of this invention lies in the rational utilization of heat. Using the heat of reaction from ethylene carbonate as the heat source for the dimethyl carbonate process reduces energy consumption in this process, achieving rational energy utilization and making the co-production process more green and economical.

[0040] (1) The temperature of the reactor has a great influence on the reaction. A temperature difference of 1℃ is very obvious. Existing technologies mainly use external circulation heat removal, jacket heat removal and cooling coil heat removal. These are affected by changes in operation and external conditions, which will significantly increase by-products and make the impurity content in the product high. However, the temperature control of the reactor of the present invention is easier and more stable, with small temperature fluctuations, fewer by-products, lower impurity content, and higher product purity.

[0041] (2) In the current technology, the gas phase in the reactor is basically not flowing and a compensation method is used. In this invention, the gas phase is continuously entering and exiting, which can increase the gas-liquid dispersion in the reaction system and make the reaction temperature more uniform.

[0042] (3) In the process of the present invention, methanol is used as a solvent in the ethylene carbonate section, and there is no need to separate it from the product; in the dimethyl carbonate section, methanol is used as a raw material for reaction and as an azeotropic agent to azeotropically extract the generated dimethyl carbonate, thereby reducing energy consumption and equipment investment.

[0043] (4) In this invention, a portion of the methanol that needs to be replenished in the dimethyl carbonate section is directed to the ethylene carbonate section as a cold source for heat exchange with the high-temperature steam at the top of the ethylene carbonate reactor. Heat exchange is carried out in the condenser, which can make full use of the reaction heat of the ethylene carbonate section. The methanol is overheated and enters the DMC reactive distillation tower, further reducing the overall energy consumption. Attached Figure Description

[0044] Figure 1 The following is a process flow diagram for the synthesis of carbonates according to the present invention:

[0045] Figure 1 The system consists of: 1. Buffer tank; 2. EC reactor; 3. Condenser; 4. Gas-liquid separator; 5. DMC distillation column; 6. Purification unit.

[0046] Reactor streams: 101 is methanol, 102 is the reaction feedstock (mainly methanol and ethylene oxide), 103 is the gaseous effluent from the reactor (mainly methanol, CO2, and small amounts of EC and EO), 104 is non-condensable CO2, 105 is condensable reflux, 106 is reaction product I (mainly EC and solvent methanol), mainly (EC + methanol), 107 is methanol, used as the cold feedstock at the top of the reactor, 108 is methanol after heat exchange, 109 is methanol entering the DMC distillation column, 110 is the top product from the distillation column, 111 is the top product from the purification unit refluxed to the DMC distillation column, 112 is the DMC product effluent, and 113 is the bottom product from the column. Detailed Implementation

[0047] Method for producing carbonates: using the following steps

[0048] Fresh epoxides and methanol are mixed in a buffer tank and then fed into the EC reactor (bubbling bed reactor) from the bottom. CO2 also enters the EC reactor from the bottom, where the reaction takes place under the action of a catalyst.

[0049] The gas phase from the exothermic vaporization of the S2 reaction is condensed by the condenser at the top of the EC reactor. The condensable gas is then returned to the EC reactor to continue participating in the reaction.

[0050] EC and methanol, generated in the S3 EC reactor, overflow from the top of the reactor and enter the DMC reactive distillation column as raw materials for DMC synthesis.

[0051] Methanol flows through the shell side of the S4 condenser. After heat exchange with the vapor phase from the condenser and EC reactor, the methanol enters the DMC reactive distillation column as a reactant.

[0052] In the DMC reactive distillation column, S5 involves the transesterification and alcoholysis reaction of EC and methanol under the action of a catalyst to produce DMC. DMC and methanol form a minimum azeotrope, which is collected from the top of the column by distillation for further purification.

[0053] The present invention will be further illustrated by the following embodiments, but is not limited to these embodiments.

[0054] In the examples, catalyst I is a halogenated hydroxyimidazolium resin, prepared using the method of Example 1 in CN105503608B; catalyst II is a carboxylimidazolium resin, prepared using the method of Example 1 in CN105503519B.

[0055] Example 1: System for producing dimethyl carbonate

[0056] like Figure 1 As shown, the methanol (MEOH) material is connected in parallel through three branches, namely branch 101, branch 107 and branch 109, with a flow ratio of 4:1:5.

[0057] Methanol and fresh ethylene oxide (EO) from branch 101 are mixed in buffer tank 1 and then enter EC reactor 2 from the bottom as reaction feedstock 102. Gas phase CO2 enters EC reactor 2 from the bottom of reactor 2.

[0058] Inside EC reactor 2, EO and CO2 react under the action of a catalyst to produce ethylene carbonate (EC). The reaction releases a large amount of heat, causing the solvent methanol to evaporate. The heat is carried away, and the evaporated gas phase is condensed in condenser 3 at the top of reactor 2. The gas phase enters the tube side of condenser 3, where it exchanges heat with the shell side. The condensable gases (methanol, EO) are then returned to EC reactor 2 to continue the reaction. The reaction product I106 (mainly EC and solvent methanol) generated in reactor 2 overflows from the top of EC reactor 2 and enters DMC distillation column 5 as a feedstock for the preparation of dimethyl carbonate (DMC).

[0059] Methanol from branch 107 enters the shell side of the condenser, where it exchanges heat with the gas phase in the tube side. The resulting methanol, after heat exchange, enters the DMC distillation column 5 as a raw material for DMC preparation.

[0060] The gaseous stream 103 (mainly methanol, CO2 and a small amount of EC and EO) flowing out from the top of the condenser is separated by the gas-liquid separator 4. The gas phase 104 (non-condensable carbon dioxide) 104 is discharged from the top of the gas-liquid separator, and the liquid phase 105 (condensable gas, mainly composed of methanol and EO) is returned to the buffer tank. The temperature is 40-100℃ and the pressure is 2.0-8.0MPa.

[0061] Methanol from branch 109 enters DMC distillation column 5. Inside DMC distillation column 5, EC and methanol undergo transesterification and alcoholysis reaction under the action of a catalyst to generate DMC. DMC and methanol form a minimum azeotrope, i.e., the top product 110 of DMC distillation column (mainly composed of methanol + DMC) is distilled from the top of DMC distillation column 5 and sent to purification unit 6 for further purification (purification separates methanol and DMC; purification adopts a multi-tower distillation mode, and multiple distillation columns are combined for purification according to the required purity of DMC. DMC is collected as a product (112), and methanol is recycled (111)). Finally, DMC product is obtained. 113 is the bottom product, mainly composed of methanol, ethylene glycol, and diethylene glycol.

[0062] Example 2: Method for producing dimethyl carbonate

[0063] according to Figure 1 The described process flow for synthesizing carbonates involves mixing fresh ethylene oxide (EO) and methanol in a buffer tank, then introducing them into the EC reactor from the bottom. The molar ratio of EO to methanol in the EC reactor is 1:4. Gaseous CO2 enters the EC reactor from the bottom and reacts under the action of catalyst I at a temperature of 120°C and a pressure of 2.2 MPa. The reaction releases a large amount of heat, causing the solvent methanol to evaporate, carrying away the heat. The gas phase outlet temperature of the EC reactor is 120°C, and the temperature fluctuation range during the reaction is 118.1–122.2°C. The evaporated gas phase is condensed in a condenser at the top of the EC reactor and flows through the tube side. The temperature of the condensable gas is controlled at 40°C before returning to the EC reactor to continue the reaction. Methanol flows through the shell side of the condenser. After heat exchange with the evaporated gas phase in the condenser, the methanol enters the DMC distillation column as a reactant. EC (monotropic extract) generated in the EC reactor (sampling analysis showed a molar yield of 98.05% for EC product; analysis was performed using chromatographic methods commonly used in the field; impurity ethylene glycol content was 0.0305%, and diethylene glycol content was 0.0150%) and solvent methanol overflowed from the top of the reactor and entered the DMC distillation column as feedstock for DMC production. In the DMC distillation column, EC and methanol underwent transesterification and alcoholysis under the action of catalyst II to produce DMC. The reaction temperature was 88°C, the column top temperature was 67.8°C, the column top pressure was 0.03 MPa, the reflux ratio was 0.05, and the molar ratio of methanol to EC was 1:10. The azeotrope formed by DMC and methanol was distilled off from the top of the column and sent to the purification unit for further purification. The final total yield of DMC and EG products was 98.04 wt%, and the purity of DMC was 99.99%.

[0064] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0065] Comparative Example 1: Method for producing dimethyl carbonate

[0066] according to Figure 1 The process flow for synthesizing carbonates described adopts the method of Example 2, the only difference being that methanol only goes through 101 and 109, and not through 107 and 108.

[0067] Fresh ethylene oxide and methanol are mixed in a buffer tank and then fed into EC reactor 2 from the bottom of EC reactor. The molar ratio of EO to methanol in EC reactor 2 is 1:4. Gaseous CO2 enters EC reactor 2 from the bottom and reacts under the action of catalyst I at a reaction temperature of 120°C. The temperature fluctuation range during the reaction is 118.1–122.2°C, and the reaction pressure is 2.2 MPa. The reaction releases a large amount of heat, causing the solvent methanol to evaporate. The heat is carried away, and the gas phase outlet temperature of EC reactor 2 is 120°C. The evaporated gas phase is condensed by condenser 3 at the top of EC reactor 2. The gas phase flows through the tube side, and the temperature of the condensable gas is controlled at 40°C before returning to EC reactor 2 to continue the reaction. The shell side of condenser 3 uses circulating cooling water for heat removal (methanol does not flow through 107 and 108).

[0068] EC (with a molar yield of 98.03% based on sampling analysis using conventional chromatographic methods, and impurities of 0.0308% ethylene glycol and 0.0154% diethylene glycol) and solvent methanol generated in EC reactor 2 overflow from the top of the reactor and enter DMC distillation column 5 as feedstock for DMC production. In DMC distillation column 5, EC and methanol undergo transesterification and alcoholysis under the action of catalyst II to produce DMC. The reaction temperature is 88°C, the column top temperature is 67.8°C, the column top pressure is 0.03 MPa, the reflux ratio is 0.05, and the molar ratio of methanol to EC is 1:10. The azeotrope formed by DMC and methanol is distilled from the top of the column and further purified in the purification unit, ultimately yielding a total yield of 98.01 wt% for DMC and EG products, with a DMC purity of 99.99%. Energy consumption increased by 10.02% compared to Example 1 (energy consumption is the increased cooling capacity of the utility circulating cooling water and the heat required for methanol evaporation in the DMC distillation column bottom).

[0069] Comparative Example 2: Method for producing dimethyl carbonate

[0070] The method of Example 2 is used, except that methanol only flows through 109 and not through 101, 107 and 108.

[0071] Fresh ethylene oxide enters EC reactor 2 from the bottom (methanol does not enter EC reactor 2; methanol only flows through 109, not 101, 107, or 108). Gaseous CO2 enters EC reactor 2 from the bottom. The reaction takes place under the action of catalyst I at a temperature of 120°C. Heat removal is achieved through a jacket, cooling coils, or external circulation (extracting the liquid in EC reactor 2 from the external reactor for heat removal; the liquid includes liquid ethylene oxide, EC, and gaseous CO2 dissolved in liquid ethylene oxide). The temperature fluctuation range during the reaction is 115.2–126.3°C, and the reaction pressure is 2.2 MPa. EC generated in EC reactor 2 overflows from the top of the reactor (sampling analysis showed a molar yield of 96.83% for the EC product; analysis was performed using chromatographic methods commonly used in the field; the impurity content of ethylene glycol was 0.0624%, and the content of diethylene glycol was 0.0335%). The EC then enters DMC distillation column 5 as a raw material for DMC production. In DMC distillation column 5, EC and methanol undergo transesterification and alcoholysis reaction under the action of catalyst II to produce DMC. The reaction temperature is 88℃, the column top temperature is 67.8℃, the column top pressure is 0.03MPag, the reflux ratio is 0.05, and the molar ratio of methanol to EC is 1:10. The minimum azeotrope formed by DMC and methanol is collected from the top of the column by distillation and sent to the purification unit for further purification. Finally, the total yield of DMC and EG products is 97.64wt%, and the purity of DMC is 98.97%.

[0072] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0073] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A system for producing dimethyl carbonate, comprising: Methanol source, alkyl epoxide source, carbon dioxide source, olefin carbonate reactor, condenser, gas-liquid separator and DMC distillation column; The carbonate olefin ester reactor has a gas phase outlet I and a liquid phase outlet I; The condenser has a vapor phase outlet II and a condensate reflux outlet II; The methanol source, alkyl epoxide source, and carbon dioxide source are respectively connected to the olefin carbonate reactor; Gas phase outlet II is connected to a gas-liquid separator; condenser reflux outlet II is connected to a carbonate olefin ester reactor. Vapor phase outlet I is connected to the feed inlet of the condenser, and liquid phase outlet I is connected to the DMC distillation column; The methanol source has two parallel branches, namely branch P1 and branch P2. Branch P1 connects to the carbonate olefin ester reactor; Branch line P2 connects to the DMC distillation column; The methanol source is also provided with a parallel branch P3; branch P3 serves as the cold source for the condenser. P3 connects to the shell side of the condenser, and the shell side outlet connects to the DMC distillation column; the gas phase outlet I of the carbonate olefin ester reactor connects to the tube side of the condenser.

2. The system for producing dimethyl carbonate according to claim 1, characterized in that, The gas phase outlet I is located at the top of the olefin carbonate reactor, and the liquid phase outlet I is located at the top of the olefin carbonate reactor. And / or, vapor outlet II is located at the top of the condenser; condensate reflux outlet II is located at the bottom of the condenser; And / or, the alkylene oxide source contains ethylene oxide and / or propylene oxide; And / or, the carbonate olefin ester is ethylene carbonate and / or propylene carbonate.

3. The system for producing dimethyl carbonate according to claim 1 or 2, characterized in that, The system also includes a buffer tank; the methanol source and the epoxide alkane source are respectively connected to the buffer tank, and the buffer tank is connected to the carbonate olefin ester reactor.

4. The system for producing dimethyl carbonate according to claim 1 or 2, characterized in that, The system also includes a purification unit, and the gas phase outlet of the DMC distillation column is connected to the purification unit.

5. A method for producing dimethyl carbonate using the system according to any one of claims 1-4, characterized in that, include: S1 epoxide alkane, methanol, and CO2 enter the carbonate olefin ester reactor and react under the action of catalyst I to obtain gaseous products and liquid phase containing carbonate olefin ester; The S2 gaseous product flows out of the olefin carbonate ester reactor and enters the condenser for condensation. The condensable gas that has been condensed flows back into the olefin carbonate ester reactor. The liquid phase containing olefin carbonate generated in the S3 olefin carbonate reactor enters the DMC reactive distillation column. In the S4 DMC reactive distillation column, carbonated olefin esters and methanol undergo transesterification and alcoholysis reaction under the action of catalyst II to generate DMC. The gas phase containing DMC is collected from the distillation column.

6. The method according to claim 5, characterized in that, include: In S2, methanol enters the condenser as a cold source, and the gaseous products exchange heat with the methanol in the condenser. And / or, methanol enters the DMC reactive distillation column as a reaction feedstock; And / or, both catalyst I and catalyst II are heterogeneous catalysts.

7. The method according to claim 6, characterized in that, Catalyst I is a halogenated hydroxyimidazolium resin; And / or, the catalyst II is a carboxyimidazole resin.

8. The method according to claim 6 or 7, characterized in that, In the carbonate olefin ester reactor, the temperature fluctuation range during the reaction process is 3~4℃; And / or, in the carbonate olefin ester reactor, the molar ratio of alkyl epoxides to methanol is 1:1 to 1:10; And / or, the reaction temperature of the carbonate olefin ester reactor is 100~160℃; And / or, the operating pressure of the carbonate olefin ester reactor is 2.0 to 6.0 MPa; And / or, the minimum flow rate of branch P3 in the condenser is controlled by the temperature of the gas phase outlet I of the carbonate olefin ester reactor, which is 40~100℃.

9. The method according to claim 6, characterized in that, The reaction temperature in the DMC reactive distillation column is 60~100℃; the top temperature is 67.8~111℃. Alternatively, the operating pressure in the DMC reactive distillation column is 0.1–0.5 MPa; the top pressure is 0.03–0.4 MPaG. Alternatively, the reflux ratio in the DMC reactive distillation column is 0.05~10; Alternatively, the molar ratio of methanol to carbonate olefin ester in the DMC reactive distillation column is 6:1 to 15:

1.

10. The method according to claim 6, characterized in that, The conditions for the gas-liquid separator are: temperature 40~100 ℃ and pressure 2.0~8.0 MPa.

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