A process for the homogeneous catalytic co-production of methyl ethyl carbonate and diethyl carbonate

Abstract

The present application relates to the technical field of organic synthesis, in particular to a method for homogeneously catalyzing co-production of methyl ethyl carbonate and diethyl carbonate, using 0.5-10% of organic sulfonic acid salt of borderline acid metal ion as catalyst, according to the molar ratio of dimethyl carbonate to ethanol being 1:5-12, reacting for 6-9 hours at 73-80 DEG C; collecting 64-130 DEG C fraction after normal pressure distillation of the reacted material to obtain mixed fraction containing methyl ethyl carbonate and diethyl carbonate. The technical scheme is superior to existing catalysts in catalytic activity, compatibility and stability, can efficiently catalyze transesterification to co-produce methyl ethyl carbonate and diethyl carbonate, ensure the yield of methyl ethyl carbonate being higher than that of diethyl carbonate, and solve the series of problems existing in the existing catalysts.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for homogeneous catalytic co-production of methyl ethyl carbonate and diethyl carbonate. Background Technology

[0002] Ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are characterized by low toxicity and environmental friendliness, and have wide applications in organic synthesis and environmentally friendly solvents. Especially in the field of lithium-ion battery electrolytes, EMC and DEC compound solvents can effectively improve the low-temperature discharge characteristics and high-temperature cycling performance of lithium-ion batteries. The DEC content in the compound solvent is generally lower than that of EMC.

[0003] Currently, the industrial production of EMC and DEC primarily utilizes the transesterification reaction of ethanol and dimethyl carbonate (DMC), which offers advantages such as mild reaction conditions, excellent safety, and environmental friendliness. Co-producing EMC and DEC at a high molar ratio of ethanol to DMC eliminates product separation steps, facilitating the intensive use of shared raw materials and equipment, reducing energy consumption, lowering production costs, and simplifying process management. This aligns with the requirements for cleaner chemical processes and provides a new solution for cost reduction and efficiency improvement in the lithium battery industry. To ensure the production efficiency of the co-production process and meet product application requirements, not only is a high conversion rate of DMC required, but the yield of EMC in the co-production process must also be as high as possible compared to DEC.

[0004] DMC and ethanol cannot react directly and must be accelerated by a catalyst to achieve an effective transesterification reaction. The development of efficient catalysts has always been a research focus in the field of organic carbonate synthesis. Relevant literature has published many catalysts that can be used for transesterification of DMC and ethanol, but there are not many high-performance catalysts with industrial application value. For a long time, industrial production has mainly used sodium alkoxides, represented by sodium methoxide and sodium ethoxide, as homogeneous catalysts. Although sodium alkoxide catalysts have relatively high activity, the following problems still exist in the process of use: (1) Sodium alkoxide is not a completely ideal homogeneous catalyst. Its solubility in the transesterification reaction system of DMC and ethanol is limited. It is very easy to form scale on the walls of towers and reactors, which not only reduces the efficiency of the catalyst, but also increases the thermal resistance of towers, reactors and pipelines, which reduces the heat exchange efficiency of the equipment and may even cause safety hazards in severe cases; (2) Sodium alkoxide will react with water, organic carbonate raw materials or products in the raw materials to generate more insoluble Na2CO3 solid, which not only reduces the catalytic activity and requires frequent replacement of catalysts, but also further aggravates the blockage of towers, reactors and pipelines.

[0005] Furthermore, a common technical drawback of publicly available transesterification catalysts is that, under high ethanol to dimethyl carbonate (DMC) molar ratios, it is difficult to simultaneously achieve high feedstock conversion rates and high EMC yields. A high ethanol to DMC molar ratio is a necessary material condition for the synergistic and efficient co-production of EMC and DEC. In this reaction system, DMC first undergoes transesterification with ethanol to generate EMC, followed by EMC transesterification with ethanol to generate DEC. Both steps are reversible equilibrium reactions with similar mechanisms, and general catalysts exhibit catalytic activity for both transesterification steps. Therefore, under high ethanol to DMC molar ratios, the increased conversion rate of the feedstock DMC inevitably leads to the continuous conversion of EMC to DEC, ultimately resulting in an EMC yield lower than the DEC yield.

[0006] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of limited catalyst solubility and poor stability in the existing transesterification synthesis of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC); at the same time, it overcomes the problem that it is difficult to simultaneously achieve high conversion rate of raw materials and high yield of ethyl methyl carbonate under high molar ratio of ethanol to dimethyl carbonate (DMC), and provides a homogeneous catalytic method for the co-production of ethyl methyl carbonate and diethyl carbonate.

[0008] To achieve the above objectives, this invention discloses a method for the homogeneous catalytic co-production of methyl ethyl carbonate and diethyl carbonate, comprising the following steps:

[0009] S1, dimethyl carbonate, ethanol and organic sulfonic acid metal salt catalyst are mixed evenly to carry out transesterification reaction;

[0010] S2, the material after the reaction in step S1 is subjected to atmospheric distillation, and the fraction at 64-130℃ is collected to obtain a mixed fraction containing methyl ethyl carbonate and diethyl carbonate.

[0011] In step S1, the molar ratio of dimethyl carbonate to ethanol is 1:5 to 12, and the amount of organic sulfonic acid metal salt catalyst used is 0.5 to 10% of the total mass of dimethyl carbonate and ethanol.

[0012] In step S1, the structural formula of the organic sulfonate metal salt catalyst is as follows: Where R is H or an alkyl group; m is the number of hydrogen atoms or alkyl groups, taking a natural number from 0 to 2; X is a halogen atom, n is a positive integer from 1 to 3, and satisfies the relationship m + n = 3; M 2+ It is a boundary acid metal ion with 2 units of positive charge.

[0013] In the structural formula, X is any one of F, Cl, or Br; M 2+ Zn 2+ Fe 2+ Co 2+ Ni 2+ Cu 2+ or Pb 2+ Any one of them.

[0014] In step S1, the organic sulfonate metal salt catalyst is zinc trifluoromethanesulfonate.

[0015] In step S1, the temperature of the transesterification reaction is 73–80°C, and the reaction time is 6–9 hours.

[0016] Transition metal ions, acting as Lewis acids, can coordinate with and activate the carbonyl group in DMC. According to the hard-soft acid theory, the carbonyl group in the DMC molecule is a hard base and requires coordination with a metal ion of sufficient hardness for full activation. This invention is not limited by this theory and selects a salt formed by an organic sulfonate ion and a boundary acid metal ion as the catalyst for the transesterification reaction. On the one hand, boundary acid metal ions, due to their relatively low hardness, can only "limitedly activate" the carbonyl group in the DMC molecule, but this ensures the selectivity of the catalyst. On the other hand, the activation ability of transition metal ions also depends on the tightness of their bond with the counterion; the looser the bond, the more favorable it is for carbonyl activation. Only by selecting organic sulfonates with structures and polarities appropriately matched to the transesterification reaction system can they be dissolved in the reaction medium. Organic sulfonate ions are hard bases and relatively loosely bonded with boundary acid metal ions, easily dissociating into free ions or loose ion pairs in polar solvents, which is beneficial for the coordination activation of the metal ion and carbonyl group, compensating for the relatively soft nature of the boundary acid metal ion. For example, zinc trifluoromethanesulfonate contains a strongly electronegative substituent (trifluoromethyl-CF3), which gives it good solubility in highly polar organic carbonates. It can exist in organic carbonate solvents as free ions or loose ion pairs, laying the foundation for its use as a homogeneous and highly efficient catalyst. The delocalized oxygen anion in the trifluoromethanesulfonate group acts as a hydrogen bond acceptor, forming hydrogen bonds with the hydroxyl hydrogen atoms in the ethanol molecule, which acts as a hydrogen bond donor, as shown in the following equation: This process increases the negative charge density on the oxygen atom in the ethoxy group, enhancing its nucleophilicity. Meanwhile, zinc ions, acting as Lewis acids, provide empty orbitals to coordinate with the lone pair electrons on the carbonyl oxygen atom of the DMC molecule, increasing the positive charge density and electrophilicity of the carbonyl carbon atom. Under this synergistic activation mechanism, dimethyl carbonate and ethanol only need to overcome a relatively low energy barrier to undergo transesterification at a high reaction rate, while maintaining a high yield of EMC in the product.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. This invention uses organic sulfonic acid metal salts as homogeneous catalysts, expanding the range of catalysts for the transesterification reaction of dimethyl carbonate and ethanol. Under similar reaction conditions and transesterification formulations, organic sulfonic acid metal salt homogeneous catalysts, represented by zinc trifluoromethanesulfonate, exhibit catalytic activity similar to that of sodium methoxide.

[0019] 2. The zinc trifluoromethanesulfonate catalyst provided by this invention can maintain excellent catalytic activity and solubility during continuous recycling, continuously converting dimethyl carbonate to EMC and DEC in a high-conversion, homogeneous catalytic manner, demonstrating excellent cycle stability. In contrast, sodium methoxide, during its first use, exhibits a significantly lower EMC yield than DEC yield, and also precipitates on the flask wall due to its poor solubility.

[0020] 3. The catalyst provided by this invention can simultaneously achieve high conversion rate of raw materials and high yield of ethyl methyl carbonate (EMC) in products under high ethanol to dimethyl carbonate (DMC) molar ratio conditions, and always ensure that the yield of EMC is higher than that of DEC, thus achieving synergistic and efficient synthesis of EMC and DEC.

[0021] In summary, the organic sulfonic acid metal salt catalyst provided by this invention has significant advantages in catalytic activity, compatibility, and stability compared to traditional sodium alkoxide catalysts. It can efficiently catalyze transesterification to co-produce methyl ethyl carbonate and diethyl carbonate, and can solve a series of problems associated with sodium alkoxide catalysts. Detailed Implementation

[0022] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the embodiments.

[0023] Example 1

[0024] By mass, 15.1 parts of dimethyl carbonate, 84.9 parts of ethanol (molar ratio 1:11), and 2 parts of zinc trifluoromethanesulfonate were added to a three-necked flask equipped with a reflux condenser, and the mixture was stirred at 75°C for 8 hours. After the reaction was completed, the above materials were distilled under normal pressure, and the fraction collected at 64–130°C was collected. The collected fraction consisted of unreacted dimethyl carbonate, ethanol, and the reacted methyl ethyl carbonate, methanol, and diethyl carbonate.

[0025] Example 2

[0026] By mass, 24.6 parts of dimethyl carbonate, 75.4 parts of ethanol (molar ratio 1:6), and 7 parts of zinc trifluoromethanesulfonate were added to a three-necked flask equipped with a reflux condenser, and the mixture was stirred at 78°C for 6.5 hours. After the reaction was complete, the above materials were distilled at atmospheric pressure, and the fraction collected at 64–130°C was collected. The collected fraction consisted of unreacted dimethyl carbonate, ethanol, and the reacted methyl ethyl carbonate, methanol, and diethyl carbonate.

[0027] Example 3

[0028] By mass, 15.1 parts of dimethyl carbonate, 84.9 parts of ethanol (molar ratio 1:11), and 2 parts of zinc trifluoromethanesulfonate were added to a three-necked flask equipped with a reflux condenser, and the mixture was stirred at 78°C for 8 hours. After the reaction was completed, the above materials were distilled at atmospheric pressure, and the fraction collected at 64–130°C was collected. The collected fraction consisted of unreacted dimethyl carbonate, ethanol, and the reacted methyl ethyl carbonate, methanol, and diethyl carbonate.

[0029] The fractions collected in Examples 1-3 were analyzed using a GC-2010 Pro gas chromatograph. The mass percentages of methyl ethyl carbonate and diethyl carbonate in the fractions were determined using the area normalization method with proportionality factor correction. , Test conditions: N2 as carrier gas, SH-Rtx-1701 capillary column; injection port temperature 200 ℃; split injection, split ratio 25:1; column oven temperature program: 50 ℃ for 2.5 minutes, then increased to 125 ℃ at 25 ℃ / min; FID detector, temperature 250 ℃.

[0030] Calculate the dimethyl carbonate conversion rate according to the following formulas (1) to (3). ethyl methyl carbonate yield and diethyl carbonate yield And the yield ratio of methyl ethyl carbonate to diethyl carbonate.

[0031] (1)

[0032] (2)

[0033] (3)

[0034] In the formula, The total weight of the fractions collected by atmospheric distillation in each embodiment. , The mass percentage of methyl ethyl carbonate and diethyl carbonate in the fraction determined by gas chromatography; , and These are the relative molecular masses of methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate, respectively. The starting amount of DMC in the transesterification formulations of each embodiment is given.

[0035] Dimethyl carbonate conversion rates in Examples 1-3 ethyl methyl carbonate yield and diethyl carbonate yield As shown in Table 1:

[0036] Table 1. Dimethyl carbonate conversion rates in Examples 1-3 ethyl methyl carbonate yield and diethyl carbonate yield

[0037]

[0038] In the transesterification and distillation processes of Examples 1-3, the entire material system was homogeneous, without any precipitation or obvious stratification, indicating that the zinc trifluoromethanesulfonate-zinc transesterification reaction system has good solubility. As shown in Table 1, under suitable material ratios and reaction conditions, zinc trifluoromethanesulfonate can efficiently convert dimethyl carbonate to methyl ethyl carbonate and diethyl carbonate, and the EMC yield in each example is higher than the DEC yield.

[0039] Example 4

[0040] The stability of the zinc trifluoromethanesulfonate catalyst was tested by recycling it 8 times.

[0041] By mass, 19.7 parts of dimethyl carbonate and 80.3 parts of ethanol (molar ratio 1:8) were added to a three-necked flask equipped with a reflux condenser for each cycle, and the transesterification reaction was carried out at 78°C for 7 hours. Four parts by mass of zinc trifluoromethanesulfonate catalyst were added during the first cycle. After each transesterification reaction, the above materials were distilled at atmospheric pressure, and the fractions from 64 to 130°C were collected. The remaining mixture was directly used in the next cycle. The fractions collected from each cycle were analyzed by gas chromatography according to the method described above, and relevant calculations were performed. The results are shown in Table 2.

[0042] Table 2. Recycling of Zinc Trifluoromethanesulfonate

[0043]

[0044] During each cycle of transesterification and distillation in the examples, the material system was entirely homogeneous, without any precipitation or stratification. As can be seen from the data in Table 2, zinc trifluoromethanesulfonate maintained a high DMC conversion rate in all 8 cycles, and the EMC yield was higher than that of DEC, demonstrating good stability.

[0045] Comparative Example

[0046] Sodium methoxide is used as a catalyst for the transesterification co-production of DMC and DEC, and it is recycled.

[0047] By mass, 19.7 parts of dimethyl carbonate and 80.3 parts of ethanol (molar ratio 1:8) were added to a three-necked flask equipped with a reflux condenser for each cycle, and the transesterification reaction was carried out at 76°C for 7 hours. In the first cycle, 1.2 parts by mass of sodium methoxide catalyst were added. After each transesterification reaction, the above materials were distilled at atmospheric pressure, and the fractions from 64 to 130°C were collected. The remaining mixture was directly used in the next cycle. The fractions collected from each cycle were analyzed by gas chromatography according to the method described above, and relevant calculations were performed. The results are shown in Table 3. Table 3 shows that the DMC conversion rate was 65.42% when sodium methoxide was used for the first time, but the EMC yield was significantly lower than the DEC yield. In the fifth cycle, although the ratio of EMC yield to DEC yield was higher, the dimethyl carbonate conversion rate was only 30.65%, indicating a significant decrease in the catalytic activity of sodium methoxide, and its stability was far inferior to the zinc trifluoromethanesulfonate catalyst used in this invention.

[0048] Table 3 Sodium methoxide recycling

[0049]

[0050] When sodium methoxide was used for the first time, a white powdery precipitate was found to form on the flask wall. As the number of uses increased, the amount of precipitate gradually increased.

[0051] Based on the comprehensive analysis of the data from Examples 1-4 and Tables 1-3, it can be seen that the zinc trifluoromethanesulfonate catalyst of the present invention has excellent compatibility in the transesterification reaction system of DMC and ethanol, and can catalyze the transesterification reaction to co-produce methyl ethyl carbonate and diethyl carbonate in a highly efficient homogeneous catalytic manner. Its catalytic activity and stability are higher than those of sodium methoxide, and its EMC yield is higher than that of DEC in both single use and recycling. The catalyst also has high catalytic activity and good stability, which can solve a series of problems existing in sodium alkoxide catalysts in the prior art.

[0052] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for the homogeneous catalytic co-production of methyl ethyl carbonate and diethyl carbonate, characterized in that, Includes the following steps: S1, dimethyl carbonate, ethanol and organic sulfonic acid metal salt catalyst are mixed evenly to carry out transesterification reaction; S2, the material after the reaction in step S1 is subjected to atmospheric distillation, and the fraction at 64-130℃ is collected to obtain a mixed fraction containing methyl ethyl carbonate and diethyl carbonate. In step S1, the organic sulfonate metal salt catalyst is zinc trifluoromethanesulfonate.

2. The method for homogeneous catalytic co-production of methyl ethyl carbonate and diethyl carbonate as described in claim 1, characterized in that, In step S1, the molar ratio of dimethyl carbonate to ethanol is 1:5 to 12, and the amount of organic sulfonic acid metal salt catalyst used is 0.5 to 10% of the total mass of dimethyl carbonate and ethanol.

3. The method for homogeneous catalytic co-production of methyl ethyl carbonate and diethyl carbonate as described in claim 1, characterized in that, In step S1, the temperature of the transesterification reaction is 73–80°C, and the reaction time is 6–9 hours.

Images