Method for synthesizing methyl ethyl carbonate by using liquid heterogeneous catalyst to catalyze ester exchange

Abstract

The invention relates to the technical field of organic carbonate synthesis, in particular to a method for synthesizing methyl ethyl carbonate by using a liquid heterogeneous catalyst to catalyze transesterification, which comprises the following steps: by taking long-chain tertiary amine as a catalyst, catalyzing dimethyl carbonate and diethyl carbonate to perform transesterification reaction in a liquid heterogeneous manner to synthesize the methyl ethyl carbonate. The liquid heterogeneous catalyst expands the variety of catalysts for synthesizing methyl ethyl carbonate through ester-ester exchange, does not need to be specially filled, is high in equipment utilization rate and free of abrasion and corrosion to equipment, and has the advantages of being easy to disperse uniformly, high in catalytic efficiency, convenient to feed, convenient to use and the like.

Description

Technical Field

[0001] The invention relates to the technical field of organic carbonate synthesis, and in particular to a method for synthesizing ethyl methyl carbonate by catalyzing ester exchange with a liquid heterogeneous catalyst. Background Art

[0002] Ethyl methyl carbonate (EMC) can be used as a lithium battery electrolyte, a raw material for organic synthesis, and an environmentally friendly solvent. Driven by economic, environmental, and safety considerations, industrial EMC synthesis methods and related research have primarily focused on two routes: transesterification of dimethyl carbonate (DMC) with ethanol and transesterification of DMC with diethyl carbonate (DEC). Compared to the former, the synthesis of EMC from DMC and DEC offers milder reaction conditions, and both the raw materials and the product can be directly used in lithium battery electrolytes, eliminating the need for specialized separation and purification, thus conserving energy.

[0003] The effective reaction between DMC and DEC requires a catalyst. Known catalysts include a small number of homogeneous catalysts such as sodium methoxide and Bu2SnO; more heterogeneous catalysts are used, such as solid bases, supported ionic liquids, supported magnesium-aluminum composite oxides, supported solid acid catalysts, and MOF catalysts. Although sodium methoxide has high catalytic activity, its strong alkalinity and corrosiveness to equipment also lead to numerous side reactions. Bu2SnO, on the other hand, is relatively expensive, limiting the industrial application of both. Published heterogeneous catalysts are almost all solid and can be loaded in fixed, fluidized, or slurry beds. Fixed-bed methods require the catalyst particles to be packed in a stationary bed, which not only reduces the available space in the tower but also presents significant pressure drop, low heat transfer efficiency, uneven distribution of the reaction materials, and difficulty in catalyst replacement. Fluidized beds, due to the vigorous movement of catalyst particles, present not only catalyst wear and loss, but also severe equipment wear and high energy consumption. In slurry beds, gravity settling or dead zones in stirring can lead to localized concentration of dense catalyst powder, resulting in uneven distribution. More importantly, most of these heterogeneous catalysts have complex preparation processes, high costs, and low catalytic activity. They are limited to academic research and have low practical application value. Compared with solid heterogeneous catalysts, liquid heterogeneous catalysts do not have the problem of equipment wear and tear. They can be stirred to form micron-sized droplets with a huge specific surface area. The reactants and catalytic active sites can be fully contacted, which is beneficial to improving mass transfer efficiency and catalytic efficiency. Liquid heterogeneous catalysts are immiscible with raw materials and products. In addition to using traditional distillation to separate the catalyst, static stratification or centrifugation can also be used to separate the catalyst. It can combine the high efficiency of traditional homogeneous catalysis with the easy separation characteristics of heterogeneous catalysis, which is beneficial to improving reaction efficiency and saving energy. Therefore, the development of low-cost, easy-to-use liquid heterogeneous catalysts that can be used for ester exchange synthesis of EMC has important industrial application value.

[0004] 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

[0005] The present invention aims to develop a low-cost, easy-to-use liquid heterogeneous catalyst that can be used for transesterification to synthesize EMC, to replace existing solid heterogeneous catalysts; and provides a method for synthesizing ethyl methyl carbonate by transesterification using a liquid heterogeneous catalyst.

[0006] In order to achieve the above object, the present invention discloses a method for synthesizing ethyl methyl carbonate by catalyzing transesterification using a liquid heterogeneous catalyst, comprising the following steps:

[0007] S1, mixing dimethyl carbonate, diethyl carbonate, and a long-chain tertiary amine catalyst, and performing an ester exchange reaction under the condition of fully excluding air;

[0008] S2, after the reaction is completed, the reaction mixture is subjected to atmospheric distillation, the material temperature is controlled not to exceed 165 ° C, and a mixture fraction consisting of dimethyl carbonate, diethyl carbonate and the target product ethyl methyl carbonate is collected.

[0009] In step S1, the mass ratio of dimethyl carbonate to diethyl carbonate is 1:0.35-3.5, and the amount of the long-chain tertiary amine catalyst used is 0.5-10% of the total mass of dimethyl carbonate and diethyl carbonate.

[0010] 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, R2 and R3 are any alkyl groups; and the long-chain tertiary amine catalyst is one long-chain tertiary amine or a mixture of multiple long-chain tertiary amines.

[0011] In the step S1, the long-chain tertiary amine catalyst is any one of N,N-dimethyl-n-octadecylamine and N,N-dimethyl-n-hexadecylamine, or a mixture of the two.

[0012] In step S1, the long-chain tertiary amine catalyst is N,N-dimethyl-n-octadecylamine.

[0013] In step S1, the conditions for the transesterification reaction are as follows: using a sealed inert gas to maintain the system pressure ≥ 0.3 MPa, the transesterification reaction temperature is 100-150° C., the reaction time is 3-8 hours, and the stirring speed is 260-700 r / min.

[0014] The carbonyl oxygen atoms in DEC and DMC molecules have a high electronegativity, which makes the ester carbonyl carbon atom carry a partial positive charge, which is the basis of the transesterification reaction. Tertiary amines can activate the ester carbonyl group through the following pathways, promoting the dissociation of the alkoxy groups in the DMC and DEC molecules and the exchange, ultimately forming EMC: (1) The lone pair of electrons on the nitrogen atom of the tertiary amine can increase the polarization of the ester carbonyl group through dipole-dipole interaction or weak coordination with the carbonyl carbon atom; (2) The tertiary amine undergoes nucleophilic addition to the carbonyl carbon to form an acyl ammonium salt active intermediate. The ability of tertiary amines to activate carbonyl groups mainly depends on the strength of their basicity, and the basicity of tertiary amines is affected by both the electronic effect and steric effect of the alkyl chain: the electron-donating effect of the alkyl chain enhances the basicity of the tertiary amine, but the steric effect of the alkyl chain reduces the basicity of the tertiary amine. The mutual solubility of tertiary amine molecules and organic carbonates depends on the molecular structure of the organic tertiary amine. As the length or volume of the alkyl chain increases, the non-polarity of the alkyl chain will play a dominant role, which will weaken the mutual solubility of tertiary amine molecules with organic carbonates with stronger polarity. Therefore, in order to ensure that the tertiary amine molecules catalyze the transesterification reaction in a heterogeneous catalytic manner, tertiary amines containing longer straight-chain alkyl or branched-chain alkyl groups must be selected as catalysts. Affected by the steric hindrance effect, such tertiary amines have low alkalinity and low catalytic activity, and generally cannot effectively activate carbonyl groups. It can be seen that the core problem that the technical solution of the present invention needs to solve is how to comprehensively balance the alkalinity of the tertiary amine compound and its insolubility in the reaction system to ensure that the transesterification reaction is carried out in an efficient heterogeneous catalytic manner. Based on the principle of structure-activity relationship of substances, the present invention selects long-chain tertiary amines with appropriate alkalinity and insolubility, such as dimethyl n-octadecylamine, as heterogeneous catalysts for transesterification reactions. First, the long alkyl chain makes dimethyl octadecylamine immiscible with the reaction mixture of DMC, DEC and EMC. Second, dimethyl octadecylamine has a melting point of only 23°C and easily melts into a liquid in the transesterification reaction system, forming micron-sized droplets with a huge specific surface area simply by stirring. Third, the strong power supply effect and high flexibility of the appropriately lengthed n-octadecyl group not only give dimethyl octadecylamine a strong alkalinity, but also reduce the activation energy required for its affinity addition to form the active intermediate of acyl ammonium salt, thereby enabling efficient catalysis of the transesterification reaction in a heterogeneous manner.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] 1. The present invention utilizes long-chain tertiary amines as liquid heterogeneous catalysts, expanding the range of catalysts available for ester-to-ester exchange synthesis of ethyl methyl carbonate. Long-chain tertiary amines inherently inhibit corrosion and are non-corrosive to equipment. Their moderate alkalinity and high catalytic activity allow them to efficiently catalyze ester-to-ester exchange reactions with only a small amount, achieving EMC yields similar to those achieved with homogeneous catalysts. Compared to previously disclosed heterogeneous catalysts, the present invention significantly improves equipment utilization.

[0017] 2. The long-chain tertiary amine liquid heterogeneous catalyst of the present invention is convenient and flexible to use, and solves a series of problems existing in existing heterogeneous catalysts. Since the long-chain tertiary amine has a low melting point, it exists in the reaction system in the form of a heterogeneous liquid during the reaction process. It only requires conventional mechanical stirring to be evenly dispersed in the reaction system in the form of small droplets. No special loading is required, and there is no wear on the equipment. The catalytic efficiency can also be controlled by adjusting the stirring speed to control the size of the catalyst droplets, thereby controlling the product composition. Therefore, the liquid heterogeneous catalytic technology of the present invention does not have the problems of low equipment utilization, large pressure drop, and difficulty in catalyst replacement that exist in fixed beds; nor does it have the problems of equipment wear and energy consumption that exist in fluidized beds, and it does not have the problems of local enrichment and uneven distribution of catalysts that exist in slurry beds;

[0018] 3. The long-chain tertiary amine catalysts such as dimethyl n-octadecylamine selected in the present invention are conventional chemical raw materials with a wide range of sources and low prices. In addition, the long-chain tertiary amines have moderate alkalinity, stable chemical properties, safe and simple addition of materials, and high safety in storage and transportation. These advantages are conducive to effectively reducing the production cost of transesterification synthesis of EMC. DETAILED DESCRIPTION

[0019] The above and other technical features and advantages of the present invention are described in more detail below in conjunction with embodiments.

[0020] Example 1

[0021] 27.6 parts by mass of dimethyl carbonate, 72.4 parts by mass of diethyl carbonate, and 3 parts by mass of dimethyl n-octadecylamine were added to a stainless steel reactor. Before the reaction began, the system was purged of air with argon using a five-fill, five-drain procedure: ① Open the system inlet valve, introduce argon, pressurize to 0.4 MPa, and then close the inlet valve; ② Open the exhaust valve, release the system pressure to atmospheric pressure, and then close the exhaust valve. Repeat steps 1 and 2 five times. With the exhaust valve closed, argon was again introduced to 0.4 MPa, and the inlet valve was closed. Heating and stirring were initiated, and the heterogeneous transesterification reaction was stirred at 130°C and 600 rpm for 6 hours. After completion of the reaction, the system temperature was cooled to room temperature, and the exhaust valve was opened to release the system pressure to atmospheric pressure. The reaction mixture was distilled under atmospheric pressure, maintaining the temperature above 165°C. A fraction consisting of dimethyl carbonate, diethyl carbonate, and the desired product, ethyl methyl carbonate, was collected.

[0022] Example 2

[0023] 60.4 parts by mass of dimethyl carbonate, 39.6 parts by mass of diethyl carbonate, and 6 parts by mass of dimethyl n-octadecylamine were added to a stainless steel reactor. Before the reaction began, the air in the system was replaced with argon using a five-fill, five-drain procedure: ① Open the system inlet valve to introduce argon, pressurize to 0.4 MPa, and then close the inlet valve; ② Open the exhaust valve to release the system pressure to atmospheric pressure, and then close the exhaust valve. Repeat steps 1 and 2 five times. With the exhaust valve closed, argon was again introduced to pressurize to 0.4 MPa, and the inlet valve was closed. Heating and stirring were initiated, and the heterogeneous transesterification reaction was stirred at 120°C and 300 rpm for 5 hours. After completion of the reaction, the system temperature was cooled to room temperature, and the exhaust valve was opened to release the system pressure to atmospheric pressure. The reaction mixture was distilled under atmospheric pressure, maintaining the temperature above 165°C. A fraction consisting of dimethyl carbonate, diethyl carbonate, and the target product, ethyl methyl carbonate, was collected.

[0024] Example 3

[0025] 43.3 parts by mass of dimethyl carbonate, 56.7 parts by mass of diethyl carbonate, and 7.5 parts by mass of dimethyl n-octadecylamine were added to a stainless steel reactor. Before the reaction began, the air in the system was replaced with argon using a five-fill, five-drain procedure: ① Open the system inlet valve to introduce argon, pressurize to 0.4 MPa, and then close the inlet valve; ② Open the exhaust valve to release the system pressure to atmospheric pressure, and then close the exhaust valve. Repeat steps 1 and 2 five times. With the exhaust valve closed, argon was again introduced to pressurize to 0.4 MPa, and the inlet valve was closed. Heating and stirring were initiated, and the heterogeneous transesterification reaction was stirred at 110°C and 560 rpm for 7 hours. After completion of the reaction, the system temperature was cooled to room temperature, and the exhaust valve was opened to release the system pressure to atmospheric pressure. The reaction mixture was subjected to atmospheric distillation, maintaining the material temperature above 165°C. A fraction consisting of dimethyl carbonate, diethyl carbonate, and the target product, ethyl methyl carbonate, was collected.

[0026] The fractions collected in Examples 1 to 3 were analyzed using a GC-2010Pro gas chromatograph, and the mass percentages of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate in the fractions were determined using the corrected area normalization method with a proportional factor. Test conditions: N2 as carrier gas, SH-Rtx-1701 capillary column; inlet temperature of 200°C; split injection with a split ratio of 25:1; column oven temperature programmed: 50°C for 2.5 minutes, then increased to 125°C at a rate of 25°C / min; FID detector, temperature of 250°C. The yield of ethyl methyl carbonate in Example 1 was calculated according to (Equation 1), and the yields of ethyl methyl carbonate in Examples 2 and 3 were calculated according to (Equation 2).

[0027] Yield of ethyl methyl carbonate

[0028]

[0029] Where, α EMC , α DMC and α DEC are the mass percentages of ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate measured by gas chromatography; M EMC 、M DMC and M DEC are the relative molecular masses of ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate respectively; or are the starting amounts of DMC or DEC in the transesterification formula, respectively.

[0030] The yield of ethyl methyl carbonate in Examples 1 to 3 is EMC As shown in Table 1.

[0031] Table 1 Ethyl methyl carbonate yield Y of Examples 1 to 3 EMC

[0032] Example 1 Example 2 Example 3 <![CDATA[Yield of ethyl methyl carbonate Y EMC (%)]]> 37.85 44.45 21.61

[0033] As shown in Table 1, dimethyloctadecylamine has a very high catalytic activity for transesterification and can obtain a higher yield of ethyl methyl carbonate in a heterogeneous catalytic manner.

[0034] The above description is merely a preferred embodiment of the present invention and is intended to be illustrative rather than restrictive of the present invention. Those skilled in the art will appreciate that many changes, modifications, and even equivalents may be made to the present invention within the spirit and scope of the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing ethyl methyl carbonate by catalyzing transesterification with a liquid heterogeneous catalyst, characterized in that: The following steps are involved: S1, mixing dimethyl carbonate, diethyl carbonate, and a long-chain tertiary amine catalyst, and performing an ester exchange reaction under the condition of fully excluding air; S2, after the reaction is completed, the reaction mixture is subjected to atmospheric distillation, the material temperature is controlled not to exceed 165 ° C, and a mixture fraction consisting of dimethyl carbonate, diethyl carbonate and the target product ethyl methyl carbonate is collected.

2. The method for synthesizing ethyl methyl carbonate by catalyzing transesterification with a liquid heterogeneous catalyst according to claim 1, wherein: In step S1, the mass ratio of dimethyl carbonate to diethyl carbonate is 1:0.35-3.5, and the amount of the long-chain tertiary amine catalyst used is 0.5-10% of the total mass of dimethyl carbonate and diethyl carbonate.

3. The method for synthesizing ethyl methyl carbonate by catalyzing transesterification with a liquid heterogeneous catalyst according to claim 1, wherein: 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, R2 and R3 are any alkyl groups; and the long-chain tertiary amine catalyst is one long-chain tertiary amine or a mixture of multiple long-chain tertiary amines.

4. The method for synthesizing ethyl methyl carbonate by catalyzing transesterification with a liquid heterogeneous catalyst according to claim 1, wherein: In the step S1, the long-chain tertiary amine catalyst is any one of N,N-dimethyl-n-octadecylamine and N,N-dimethyl-n-hexadecylamine, or a mixture of the two.

5. The method for synthesizing ethyl methyl carbonate by catalyzing transesterification with a liquid heterogeneous catalyst according to claim 1, wherein: In step S1, the long-chain tertiary amine catalyst is N,N-dimethyl-n-octadecylamine.

6. The method for synthesizing ethyl methyl carbonate by catalyzing transesterification with a liquid heterogeneous catalyst according to claim 1, wherein: In step S1, the conditions for the transesterification reaction are as follows: using a sealed inert gas to maintain the system pressure ≥ 0.3 MPa, the transesterification reaction temperature is 100-150° C., the reaction time is 3-8 hours, and the stirring speed is 260-700 r / min.

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