Method for homogeneous catalytic synthesis of dimethyl carbonate by using liquid separation method to separate catalyst

Abstract

The invention relates to the technical field of organic synthesis, in particular to a method for homogeneous catalytic synthesis of dimethyl carbonate by using a liquid separation method to separate a catalyst, which comprises the following steps: by using 0.3-15% long-chain tertiary amine as a homogeneous catalyst, carrying out homogeneous reaction on cyclic carbonate and methanol in a mass ratio of 1: (1.2-5.5) at 60-80 DEG C for 4-7 hours. And after the homogeneous transesterification reaction is completed, carrying out atmospheric distillation on the reaction mixture, and collecting fractions to obtain the target product dimethyl carbonate. Carrying out liquid separation on the heterogeneous atmospheric distillation residual liquid, and collecting a lower-layer material to obtain a by-product; and the collected material is a catalyst which can be directly recycled subsequently. The dimethyl carbonate synthesis method provided by the invention has the characteristics of high catalytic efficiency, easy catalyst separation, environmental protection, energy saving and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and particularly relates to a method for homogeneous catalytic synthesis of dimethyl carbonate that can separate catalysts by liquid separation method. Background Art

[0002] Dimethyl carbonate (DMC) has wide applications in the fields of organic synthesis, medicine, environmentally friendly solvents, and lithium battery electrolytes. Developing efficient synthesis technologies for DMC has important application values. Compared with other technical routes, using ethylene carbonate (EC) or propylene carbonate (PC) to transesterify with methanol (MeOH) can not only produce the target product DMC, but also co-produce ethylene glycol or propylene glycol with important uses, which is the main route for industrial production of DMC currently. The reaction barrier between cyclic carbonate EC or PC and MeOH is relatively high, and an effective reaction can only be achieved with the aid of a catalyst; the performance of the catalyst directly determines the yield and selectivity of the target product.

[0003] In existing research, catalysts such as triethylamine and sodium acetate have been used to catalyze the transesterification of PC and MeOH to synthesize DMC. It is found that under the condition of sufficient reaction, the single-pass conversion rate of PC by the triethylamine catalyst can only reach 7.3% (Journal of Chemical Engineering of Oil and Gas, 2000, 29(01): 5-7+10), far from meeting the requirements of industrial applications. Notably, the triethylamine catalyst not only has extremely low catalytic efficiency, but also its normal boiling point is the same as that of the target product DMC (both are 90°C), making it difficult to effectively separate the catalyst and the product by distillation process.

[0004] In addition to the above catalysts, the disclosed transesterification catalysts also include: (1) strong bases such as NaOH and KOH; (2) alkali metal Na and K oxides, alkoxy compounds, amino compounds, carbonates, silicates; (3) quaternary ammonium halides, ionic liquids, tertiary phosphines chemically bonded to polymer skeletons, etc. Among them, sodium methoxide is the most commonly used homogeneous catalyst for industrial production of DMC by transesterification currently, but there are still the following problems in actual use: (1) Sodium methoxide is a strongly corrosive solid powder, which is easy to react with moisture and carbon dioxide in the air; the feeding operation, storage, and transportation are inconvenient; (2) The solubility of sodium methoxide in the reaction system is limited, and it is easy to scale on the inner wall of the reaction tower, resulting in a decrease in heat and mass transfer efficiency; (3) Sodium methoxide will react with organic carbonates and the moisture in the raw materials to generate more insoluble Na2CO3 solids; as the number of recycling times increases, the solubility of the sodium methoxide catalyst will continue to deteriorate, further aggravating the problem of fouling on the reactor wall, and seriously causing blockage of the tower kettle and pipelines, bringing potential safety hazards.

[0005] In a homogeneous catalytic system, since the catalyst and the reactant are in the same phase, the catalyst can be evenly dispersed in the reaction system in the form of molecules or ions, all active sites can contact the reactants, and the reaction efficiency is high. In the prior art, after the homogeneous reaction is completed, the distillation method is often used to separate and recover the homogeneous catalyst, which requires a large amount of heat energy, not only increasing the production cost, but also causing the catalyst to decompose due to repeated heating during the distillation separation process, shortening the life of the catalyst. Therefore, the efficient and energy-saving separation of homogeneous catalysts has always been a key technical problem that needs to be broken through. This problem is particularly prominent in the process of homogeneous catalytic synthesis of DMC using EC and methanol as raw materials.

[0006] Homogeneous catalysts other than sodium alcohol used in the prior art generally have good solubility in the reaction mixture and in the mixture of EC and ethylene glycol (EG). The reaction of EC and methanol itself is a reversible reaction with a small equilibrium constant. The homogeneous mixture obtained after the synthesis stage contains the catalyst, the target product DMC, the by-product EG, and the unreacted EC and methanol. In order to save costs, the catalyst must be separated and recovered, and then the recovered catalyst is recycled in the next reaction. Methanol and DMC have low atmospheric boiling points, while EC and ethylene glycol have atmospheric boiling points of up to 243-244°C and 195-198°C, respectively. Therefore, in the separation stage, methanol and DMC are generally separated by atmospheric distillation, and then EC and EG are distilled from the residual mixture of atmospheric distillation by multiple cycles of high-temperature vacuum distillation, and then the separated catalyst is catalyzed in the next cycle. The high-temperature vacuum distillation separation method not only consumes a lot of energy, but also causes the catalyst to decompose and discolor, and shortens its service life. At the same time, the catalyst decomposition products will also affect the purity and color of the target product DMC, resulting in a decrease in product quality.

[0007] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the invention

[0008] The purpose of the present invention is to solve the problem that in a homogeneous catalytic system, a high-temperature vacuum distillation method is often used to separate and recover a homogeneous catalyst, which consumes a large amount of heat energy, not only increasing the production cost, but also causing the catalyst to undergo side reactions such as decomposition due to repeated heating during the vacuum distillation separation process, thereby shortening the catalyst life. A method for synthesizing dimethyl carbonate by homogeneous catalysis is provided, in which the catalyst can be separated by a liquid separation method.

[0009] In order to achieve the above object, the present invention discloses a method for synthesizing dimethyl carbonate by homogeneous catalysis, which can separate the catalyst by liquid separation method, comprising the following steps:

[0010] S1, React the cyclic carbonate, methanol, and long-chain tertiary amine catalyst by stirring at 60 - 80 °C for 4 - 7 hours;

[0011] S2, After cooling the reaction mixture in step S1 to room temperature, perform atmospheric distillation. Collect the mixed fraction composed of methanol and the target product dimethyl carbonate within the range of 64 °C - 91 °C. Control the material temperature not to exceed 120 °C and distill until no more fractions are distilled out. Use the liquid separation method to separate the long-chain tertiary amine catalyst for reuse in the next cycle.

[0012] In step S1, the cyclic carbonate is a five-membered cyclic carbonate.

[0013] In step S1, the cyclic carbonate is any one or a mixture of ethylene carbonate and propylene carbonate.

[0014] In step S1, the mass ratio of the cyclic carbonate to methanol is 1:1.2 - 5.5, and the dosage of the long-chain tertiary amine catalyst is 0.3 - 15% of the total mass of methanol and the cyclic carbonate.

[0015] In step S1, the structural formula of the long-chain tertiary amine catalyst is wherein, R1 is an alkyl group containing at least 12 carbon atoms, and R2 and R3 are any alkyl groups; the long-chain tertiary amine catalyst is any one long-chain tertiary amine or a mixture composed of multiple long-chain tertiary amines.

[0016] In step S1, the long-chain tertiary amine catalyst is any one or a mixture of N,N-dimethyl-n-octadecylamine and N,N-dimethyl-n-hexadecylamine.

[0017] In step S1, the long-chain tertiary amine catalyst is N,N-dimethyl-n-octadecylamine.

[0018] In step S2, the remaining residue that has not been distilled out under atmospheric distillation is in a heterogeneous liquid mixture state when the temperature is higher than room temperature. No special treatment is required, and only static settling is needed to separate the layers.

[0019] In step S2, the method for separating the long-chain tertiary amine catalyst is any one of liquid separation using a separating funnel, centrifugal acceleration for liquid separation, decantation separation, and sedimentation separation.

[0020] The specific process of liquid separation using a separating funnel is as follows: Cool the atmospheric distillation residue to below 100 °C, add it to the separating funnel, let it stand still to separate the catalyst from the unevaporated reaction mixture into layers. Open the lower piston of the separating funnel and release all the lower-layer materials to obtain a homogeneous mixture formed by by-products and unreacted cyclic carbonate; close the piston, and the remaining materials in the separating funnel are the long-chain tertiary amine catalyst for reuse in the next cycle.

[0021] As another technical solution of the present invention, in the step S2, the method for separating the long-chain tertiary amine catalyst can also adopt the vacuum distillation method. The boiling point of the long-chain tertiary amine is much higher than that of EC or PC, and by-products ethylene glycol or propylene glycol. For example, the boiling point of N,N-dimethyloctadecylamine is 347 °C respectively, and the volatility is extremely low. Therefore, the catalyst can be separated from the reaction mixture by vacuum distillation.

[0022] The specific process of the vacuum distillation method is as follows: By vacuum distillation, the by-products and unreacted cyclic carbonates are distilled out, and the remaining undistilled matter is the long-chain tertiary amine catalyst.

[0023] The nitrogen atom in the tertiary amine molecule can activate the methanol molecule through hydrogen bonding, reducing the energy barrier for its attack on the carbonyl carbon atom in the cyclic carbonate to undergo transesterification reaction. The catalytic mechanism is as follows: The tertiary amine nitrogen atom, as a hydrogen bond acceptor, increases the negative charge density of the oxygen atom in the alcohol molecule, thereby enhancing the nucleophilic ability. The long-chain tertiary amine molecule structure contains a non-polar long alkyl chain and a polar amine group. Within a certain range, the electron-donating effect of the long alkyl chain is beneficial to increasing the basicity of the tertiary amine, thus increasing the catalytic activity. On the other hand, the long alkyl chain also causes the solubility of the tertiary amine to change with the composition and polarity of the solvent system. Long-chain tertiary amines such as dimethyloctadecylamine have excellent solubility in the initial reaction mixture containing methanol and can catalyze the transesterification reaction between methanol and cyclic carbonate in a homogeneous catalytic manner. When the transesterification reaction target products DMC and excess methanol are distilled off, the long-chain tertiary amine is immiscible with the remaining undistilled reaction mixture, and its specific gravity is relatively small (~0.8). After standing, the long-chain tertiary amine catalyst will float on the upper layer of the remaining homogeneous reaction mixture, quickly forming two layers of liquids with a clear and flat interface, and there is no diffusion or gradual transition phenomenon. The technical solution of the present invention skillfully combines the catalytic activity of the catalyst, its dynamic miscibility with the reaction mixture, and the density difference, enabling the organic tertiary amine catalyst to catalyze the transesterification reaction in a homogeneous and efficient manner during the reaction process, and can be separated by a simple and easy liquid separation method such as gravity separation (static liquid separation method) during post-treatment. The corresponding liquid separation method can adopt liquid separation with a separating funnel, or can adopt centrifugal acceleration for liquid separation, or adopt decantation separation, or sedimentation separation and other methods. These catalyst separation methods are all based on gravity to make the immiscible liquids naturally separate, and then are discharged through different outlets.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The long-chain tertiary amine homogeneous catalyst provided by the present invention has strong catalytic activity and high catalytic efficiency (comparable to sodium methoxide), has excellent solubility in the transesterification reaction system of cyclic carbonate and methanol, can ensure that the transesterification reaction process always proceeds in a homogeneous reaction manner, and can still maintain excellent solubility and catalytic efficiency during continuous multiple recycling, without precipitation and adhesion to the reactor wall. However, the sodium methoxide catalyst adheres and scales on the flask wall due to unsatisfactory solubility during the first use; moreover, with the increase in the number of recycling times, the solubility of the sodium methoxide catalyst in the reaction system continuously deteriorates, resulting in an increasing amount of precipitation. Therefore, the long-chain tertiary amine catalyst of the present invention effectively solves a series of problems existing in the alcohol sodium catalyst in the prior art, such as limited solubility, side reactions with reaction raw materials and products to generate precipitation and scale on the reactor wall, leading to a decrease in heat and mass transfer efficiency;

[0026] 2. The long-chain tertiary amine homogeneous catalysis transesterification technology provided by the present invention balances and combines the catalytic activity of the catalyst, the dynamic miscibility with the reaction mixture and the density difference, and only needs to adopt a simple and easy static separation and liquid separation method to separate the catalyst. For example, the tertiary amine catalyst can be simply separated from the reaction mixture by using a separating funnel. Therefore, the long-chain tertiary amine catalyst combines the high efficiency of homogeneous catalysts and the easy separation of heterogeneous catalysts, and solves the problems that traditional homogeneous catalysts need to be separated and recovered by distillation processes, consuming a large amount of heat energy, increasing production costs, reducing the activity of the catalyst and shortening the service life;

[0027] 3. The long-chain tertiary amine catalyst provided by the present invention has relatively mild and stable chemical properties, is easy to store, and has the advantages of low melting point and high boiling point. For example, the melting point and boiling point of dimethyl n-octadecylamine are 23°C and 347°C respectively; it only needs a little heat to be transformed into a liquid state, which is convenient for pumping and feeding; and the boiling points of the catalyst and the raw materials and products in the transesterification reaction system are quite different, and it has excellent heat resistance. Even after experiencing multiple vacuum distillation separations, it can still maintain stable high catalytic activity in the transesterification reaction. Detailed Embodiments

[0028] The following examples are used to illustrate the above and other technical features and advantages of the present invention in more detail.

[0029] Example 1

[0030] The long-chain tertiary amine homogeneous catalyst was separated by the separating funnel liquid separation method and recycled 7 times according to the following steps.

[0031] (1) In each cycle, 23.4 parts by mass of ethylene carbonate and 76.6 parts by mass of methanol of the same quality were added to a three-necked flask equipped with a reflux condenser, and the mixture was stirred and reacted at 67 °C for 5 hours. In the first cycle, 12 parts by mass of dimethyl octadecylamine were added, and the changes in the color and state of the reaction system in each cycle reaction were listed in Table 1.

[0032] (2) After cooling the above materials to room temperature, atmospheric distillation was carried out, controlling the material temperature not to exceed 120 °C, and collecting the mixture fraction composed of methanol and dimethyl carbonate in the range of 64 °C to 91 °C, and the weight was recorded as m 馏 .

[0033] (3) The atmospheric distillation residue in step (2) (composed of catalyst, ethylene glycol by-product and unreacted ethylene carbonate) was cooled to below 100 °C and added to a separatory funnel, and left to stand to separate the catalyst from the reaction mixture; the lower piston of the separatory funnel was opened to release all the lower-layer liquid to obtain a homogeneous and mutually soluble substance composed of ethylene glycol and ethylene carbonate; the piston was closed, and the remaining material in the separatory funnel was the catalyst, which was directly added to the next transesterification reaction system.

[0034] Gas chromatography analysis was carried out on the atmospheric distillation fractions obtained in step (2) of each cycle to determine the mass percentage content α MeOH 、α DMC of methanol and dimethyl carbonate products therein. The quantitative method was the corrected area normalization method with a proportionality factor. Test conditions: N2 was used as the carrier gas, and a SH-Rtx-1701 type capillary chromatographic column was used; the injection port temperature was 200 °C; split injection was used, and the split ratio was 25:1; the column oven was programmed to heat: hold at 50 °C for 2.5 minutes and rise to 125 °C at a rate of 25 °C / min; FID detector, temperature 250 °C.

[0035] Substitute the measured results into (Equation-1) to calculate the dimethyl carbonate yield Y of each cycle of catalyst reuse DMC As shown in Table 1.

[0036] Dimethyl carbonate yield In the formula, α DMC is the mass percentage content of dimethyl carbonate in the atmospheric distillation fraction measured by gas chromatography; M DMC 、M EC are the relative molecular masses of dimethyl carbonate and ethylene carbonate respectively, is the EC dosage in each transesterification formulation, and m 馏 is the weight of the fraction collected by atmospheric distillation in step (2) of each cycle.

[0037] Table 1 DMC yield Y of catalyst reuse separated by liquid separation method DMC

[0038]

[0039] As can be seen from Table 1, DMC maintained a high yield in each cycle. The liquid separation method can effectively separate the dimethyloctadecylamine catalyst. This liquid separation process is a physical process without heating, which can effectively avoid side reactions such as oxidation of the catalyst due to heat, and is beneficial to extending the service life of the catalyst.

[0040] Example 2

[0041] (1) Take 21.55 parts by mass of ethylene carbonate, 78.45 parts by mass of methanol, and 0.5 part by mass of dimethyloctadecylamine as the catalyst, and add them to a three-necked flask equipped with a reflux condenser. Stir and react at 70 °C for 5 hours.

[0042] (2) After cooling the above materials to room temperature, carry out atmospheric distillation, control the material temperature not to exceed 120 °C, and collect the mixture fraction composed of methanol and dimethyl carbonate in the range of 64 °C to 91 °C.

[0043] Perform gas chromatography analysis and calculation according to the method described in Example 1. The DMC yield Y in Example 2 DMC was 78.75%.

[0044] Example 3

[0045] (1) Take 18.65 parts by mass of ethylene carbonate, 81.35 parts by mass of methanol, and 1.0 part by mass of dimethyloctadecylamine as the catalyst, and add them to a three-necked flask equipped with a reflux condenser. Stir and react at 70 °C for 6 hours.

[0046] (2) After cooling the above materials to room temperature, carry out atmospheric distillation, control the material temperature not to exceed 120 °C, and collect the mixture fraction composed of methanol and dimethyl carbonate in the range of 64 °C to 91 °C.

[0047] Perform gas chromatography analysis and calculation according to the method described in Example 1. The DMC yield Y in Example 3 DMC was 79.37%.

[0048] Example 4

[0049] (1) Take 23.39 parts by mass of ethylene carbonate, 76.61 parts by mass of methanol, and 5.0 parts by mass of dimethyloctadecylamine as the catalyst, and add them to a three-necked flask equipped with a reflux condenser. Stir and react at 66 °C for 7 hours.

[0050] (2) After cooling the above materials to room temperature, carry out atmospheric distillation, control the material temperature not to exceed 120 °C, and collect the mixture fraction composed of methanol and dimethyl carbonate in the range of 64 °C to 91 °C.

[0051] Perform gas chromatography analysis and calculation according to the method described in Example 1. The DMC yield Y in Example 4 DMC is 67.05%.

[0052] Example 5

[0053] Separate the dimethyloctadecylamine catalyst of the present invention by the vacuum distillation method in the prior art, and recycle it 8 times to investigate its recycling stability.

[0054] Take 21.6 parts by mass of ethylene carbonate and 78.4 parts by mass of methanol of the same mass in each cycle, add them to a three-necked flask equipped with a reflux condenser, and carry out transesterification reaction at 70 °C for 5 hours; add 3 parts by mass of dimethyloctadecylamine catalyst in the first cycle. After each transesterification reaction is completed, cool the reaction material to room temperature and then carry out atmospheric distillation, control the material temperature not to exceed 120 °C, and collect the mixture fraction composed of methanol and dimethyl carbonate in the range of 64 °C to 91 °C; then transfer the remaining mixture after atmospheric distillation to a rotary evaporator, and carry out rotary evaporation under reduced pressure at 150-160 °C for 2 h. The remaining mixture (composed of catalyst and a small amount of EC and ethylene glycol) is directly used for the next cycle.

[0055] Perform gas chromatography analysis on the atmospheric distillation fractions in each cycle according to the method described in Example 1, and calculate the DMC yield Y in each cycle DMC , and the results are shown in Table 2.

[0056] Table 2 Test results of the recycling stability of the dimethyloctadecylamine catalyst in Example 5

[0057]

[0058] In the 8-cycle test, the transesterification reaction system in each cycle was homogeneous and transparent, and the reaction proceeded in a homogeneous reaction manner. As can be seen from Table 2, the solubility and DMC yield of dimethyloctadecylamine were basically unchanged in the 8 transesterification reactions, indicating that the dimethyloctadecylamine catalyst can maintain basically unchanged solubility and catalytic activity even when separated by the vacuum distillation method in the prior art, showing excellent stability.

[0059] Comparative Example

[0060] Use sodium methoxide as the comparative example catalyst and recycle it 8 times.

[0061] For each cycle, 21.6 parts by mass of ethylene carbonate and 78.4 parts by mass of methanol of the same quality were taken and added to a three-necked flask equipped with a reflux condenser. Transesterification reaction was carried out at 70 °C for 7 hours; 1.66 parts by mass of sodium methoxide catalyst was added in the first cycle. After the transesterification reaction was completed in each cycle, the reaction material was cooled to room temperature and then subjected to atmospheric distillation. The material temperature was controlled not to exceed 120 °C, and the mixture fraction of methanol and dimethyl carbonate in the range of 64 °C to 91 °C was collected; then the remaining mixture after atmospheric distillation was transferred to a rotary evaporator and rotary evaporated under reduced pressure at 150 - 160 °C for 2 h. The remaining mixture (composed of catalyst and a small amount of EC and ethylene glycol) was directly used for the next cycle.

[0062] The atmospheric distillation fractions in each cycle were subjected to gas chromatography analysis according to the method described in Example 1, and the DMC yield Y in each cycle was calculated DMC , and the results are shown in Table 3.

[0063] Table 3 Test results of the cycle stability of sodium methoxide in the comparative example

[0064]

[0065] As can be seen from Table 3, a small amount of white powder precipitated on the side wall of the flask when sodium methoxide was used for the first time. During the second cycle, powdery precipitates began to appear at the bottom of the flask. As the number of cycles increased, the powdery precipitates at the bottom of the flask continued to increase, indicating that the solubility of sodium methoxide continued to deteriorate during the cycle.

[0066] It should be noted that in Examples 2 - 4, due to the small amount of catalyst used, it was inconvenient to separate and recover the catalyst by the liquid separation method in the laboratory small-scale test. It can be foreseen that when carrying out pilot-scale or industrial production according to the formulations and reaction conditions of Examples 2 - 4, the catalyst can be separated and recovered by an appropriate liquid separation method. From the experimental results in Examples 1 - 5, it can be seen that the catalytic activity of dimethyloctadecylamine is equivalent to that of sodium methoxide, and the solubility of dimethyloctadecylamine remains stable during recycling, which is far better than that of sodium methoxide. Therefore, long-chain tertiary amines such as dimethyloctadecylamine can solve the problems existing in the sodium methoxide catalyst in the prior art.

[0067] The above are only the preferred embodiments of the present invention, which are merely illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims

1. A method for the homogeneous catalytic synthesis of dimethyl carbonate by using a liquid separation method to separate the catalyst, characterized in that, It includes the following steps: S1. Stir and react cyclic carbonate, methanol, and long-chain tertiary amine catalyst at 60-80 °C for 4-7 hours; S2. Cool the reacted material in step S1 to room temperature and then perform atmospheric distillation. Collect the mixed fraction composed of methanol and the target product dimethyl carbonate within the range of 64 °C - 91 °C, and distill until no fraction distills out with the material temperature not exceeding 120 °C. Separate the long-chain tertiary amine catalyst from the atmospheric distillation residue for reuse in the next cycle.

2. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating catalysts by liquid separation according to claim 1, characterized in that, In step S1, the cyclic carbonate is a five-membered cyclic carbonate.

3. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating catalysts by liquid separation according to claim 1, characterized in that, In step S1, the cyclic carbonate is any one or a mixture of ethylene carbonate and propylene carbonate.

4. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating catalysts by liquid separation according to claim 1, characterized in that, In step S1, the mass ratio of cyclic carbonate to methanol is 1:1.2 - 5.5, and the dosage of the long-chain tertiary amine catalyst is 0.3 - 15% of the total mass of methanol and cyclic carbonate.

5. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating catalysts by liquid separation according to claim 1, characterized in that, In the step S1, the structural formula of the long-chain tertiary amine catalyst is wherein, R1 is an alkyl group containing at least 12 carbon atoms, and R2 and R3 are arbitrary alkyl groups; the long-chain tertiary amine catalyst is any one long-chain tertiary amine or a mixture composed of multiple long-chain tertiary amines.

6. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating a catalyst by a liquid separation method according to claim 1, characterized in that, In step S1, the long-chain tertiary amine catalyst is any one or a mixture of N,N-dimethyl-n-octadecylamine and N,N-dimethyl-n-hexadecylamine.

7. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating a catalyst by a liquid separation method as claimed in claim 1, wherein In step S1, the long-chain tertiary amine catalyst is N,N-dimethyl-n-octadecylamine.

8. A method for the homogeneous catalytic synthesis of dimethyl carbonate that can separate the catalyst by liquid separation according to claim 1, characterized in that In step S2, the method for separating the long-chain tertiary amine catalyst is any one of separating funnel liquid separation method, centrifugal acceleration liquid separation, decantation separation, and sedimentation separation.

9. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating catalysts by liquid separation according to claim 8, characterized in that, The specific process of the separating funnel liquid separation method is as follows: Cool the atmospheric distillation residue to below 100 °C, add it to the separating funnel, let it stand to separate the catalyst from the unevaporated reaction mixture, open the lower piston of the separating funnel, and discharge all the lower-layer materials to obtain a homogeneous mixture formed by by-products and unreacted cyclic carbonate; close the piston, and the remaining material in the separating funnel is the long-chain tertiary amine catalyst for reuse in the next cycle.

10. The homogeneous catalytic synthesis method of dimethyl carbonate capable of separating a catalyst by a liquid separation method as described in claim 1, characterized in that, In step S2, the method for separating the long-chain tertiary amine catalyst is the vacuum distillation method; the specific process of the vacuum distillation method is as follows: Evaporate by-products and unreacted cyclic carbonate through vacuum distillation, and the remaining unevaporated material is the long-chain tertiary amine catalyst.

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