Process for the recovery and use of a stream containing methyl 4-acetyloxybutanoate

Abstract

The present application relates to the chemical technology field, disclose a kind of recycling method and application of 4-acetyloxy butyric acid methyl ester material.The method comprises: (1) in the presence of sodium methoxide, the raw material containing γ-butyrolactone and 4-acetyloxy butyric acid methyl ester and methyl acetate are made to carry out acylation reaction, while azeotropic distillation is carried out, obtain the dry material containing α-acetyl-γ-butyrolactone sodium salt;(2) the dry material is extracted after being handled and separated, obtain α-acetyl-γ-butyrolactone crude product;(3) the crude product is subjected to vacuum rectification, separate out γ-butyrolactone and 4-acetyloxy butyric acid methyl ester mixture, obtain α-acetyl-γ-butyrolactone fine product.The method fully recycles 4-acetyloxy butyric acid methyl ester produced by α-acetyl-γ-butyrolactone, reduces waste liquid disposal amount;Avoid 4-acetyloxy butyric acid methyl ester and γ-butyrolactone separation, reduce energy loss;Prepared α-acetyl-γ-butyrolactone has higher yield and purity.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method and application for the recycling of materials containing methyl 4-acetoxybutyrate. Background Technology

[0002] α-Acetyl-γ-butyrolactone is an important organic chemical raw material and an intermediate in the preparation of vitamin B1 and pesticides. Currently, the mainstream process for synthesizing α-acetyl-γ-butyrolactone mainly uses γ-butyrolactone and methyl (or ethyl) acetate as starting materials, undergoing Claisen condensation in the presence of strong bases (sodium metal, potassium metal, sodium alkoxide, sodium amide, etc.) to obtain the target product. However, due to the excessively vigorous reaction involving sodium metal, there are safety hazards such as material spillage, combustion, and explosion during production. Therefore, replacing sodium metal with sodium alkoxide to catalyze the acylation reaction of acetate and γ-butyrolactone to synthesize the target product has become a research hotspot in recent years.

[0003] CN103304519A discloses a method for preparing α-acetyl-γ-butyrolactone with recyclable reactants. The method involves acylation of γ-butyrolactone (I), methyl acetate (II), sodium methoxide, and an inert solvent. Unreacted methyl acetate, methanol (a byproduct), and a small amount of inert solvent are then separated. After neutralization, solvent removal, and distillation, pure α-acetyl-γ-butyrolactone is obtained. However, due to the use of phosphoric acid as an acidifying agent, the cost is high, and the product yield is low.

[0004] CN108129423A discloses a method for preparing α-acetyl-γ-butyrolactone, using solid sodium methoxide as a catalyst and γ-butyrolactone and ethyl acetate as starting materials. An acetylation reaction is carried out, and α-acetyl-γ-butyrolactone is obtained through washing, neutralization, filtration, and vacuum distillation. However, because ethyl acetate is used as the acylation reagent, the system contains a mixture of methanol and ethanol, making recovery difficult.

[0005] While existing technologies disclose the preparation of α-acetyl-γ-butyrolactone using sodium methoxide as a catalyst, the yields are low, all below 85%, and all produce methyl 4-acetoxybutyrate impurities. The formation of methyl 4-acetoxybutyrate impurities mainly proceeds via the following equation:

[0006]

[0007] Due to the existence of equilibrium, methyl 4-acetoxyformate remains in the system, accounting for approximately 2%-3% of the mass of α-acetyl-γ-butyrolactone. During distillation, this impurity accumulates in the pre-boil of the unreacted feedstock γ-butyrolactone. If it can be recovered and utilized, the yield of α-acetyl-γ-butyrolactone and the utilization rate of the feedstock γ-butyrolactone can be further improved.

[0008] Therefore, it is of great significance to study and develop a method for converting methyl 4-acetoxybutyrate into α-acetyl-γ-butyrolactone. Summary of the Invention

[0009] To address the problem of methyl 4-acetoxybutyrate impurities in the production of α-acetyl-γ-butyrolactone in existing technologies, this invention provides a method and application for the recycling of materials containing methyl 4-acetoxybutyrate, which can improve the utilization rate of raw materials and the yield of α-acetyl-γ-butyrolactone.

[0010] To achieve the above objectives, the first aspect of the present invention provides a method for recycling materials containing methyl 4-acetoxybutyrate, wherein the method includes the following steps:

[0011] (1) In the presence of sodium methoxide, the raw material containing γ-butyrolactone and methyl 4-acetoxybutyrate is subjected to an acylation reaction with methyl acetate, and azeotropic distillation is carried out at the same time to recover part of the methyl acetate and the generated methanol, so as to obtain a dry material containing sodium α-acetyl-γ-butyrolactone.

[0012] (2) The dried material is processed and then extracted to obtain crude α-acetyl-γ-butyrolactone;

[0013] (3) The crude product is subjected to vacuum distillation to separate the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate to obtain the refined α-acetyl-γ-butyrolactone.

[0014] A second aspect of the present invention provides the application of the aforementioned method in the preparation of α-acetyl-γ-butyrolactone.

[0015] Through the above technical solution, this invention uses a mixture of methyl 4-acetoxybutyrate and γ-butyrolactone as raw materials to prepare α-acetyl-γ-butyrolactone. This allows for the recovery and reuse of methyl 4-acetoxybutyrate, reducing the amount of waste liquid generated during production. Furthermore, using a mixture saves energy and time in separating methyl 4-acetoxybutyrate and γ-butyrolactone, improving the utilization rate of γ-butyrolactone raw materials and further increasing the yield of α-acetyl-γ-butyrolactone. The product also boasts high purity and an environmentally friendly process. This reduces raw material costs for the large-scale production of α-acetyl-γ-butyrolactone, decreases investment in distillation equipment, shortens the production cycle, and enhances the market competitiveness of α-acetyl-γ-butyrolactone.

[0016] Specifically, the method for recycling materials containing methyl 4-acetoxybutyrate provided by this invention has the following advantages:

[0017] (1) The method provided by the present invention can fully recover and utilize methyl 4-acetoxybutyrate produced by α-acetyl-γ-butyrolactone, reducing the amount of waste liquid disposal, which saves costs and avoids environmental pollution.

[0018] (2) The method provided by the present invention uses a mixture of 4-acetoxybutyrate and γ-butyrolactone as feed, which avoids the problem of difficult separation of 4-acetoxybutyrate and γ-butyrolactone. It eliminates the need for separation between the two, reduces equipment investment and energy consumption, and greatly reduces production costs.

[0019] (3) The method provided by the present invention uses a mixture of methyl 4-acetoxybutyrate and γ-butyrolactone with a high molar fraction as raw material, which can reduce the conversion of γ-butyrolactone to methyl 4-acetoxybutyrate, improve the utilization rate of γ-butyrolactone, effectively reduce the occurrence of side reactions, and the yield of α-acetyl-γ-butyrolactone can reach 99.4% and the purity can reach 99.6 wt%. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of this invention provides a method for recycling materials containing methyl 4-acetoxybutyrate, wherein the method includes the following steps:

[0022] (1) In the presence of sodium methoxide, the raw material containing γ-butyrolactone and methyl 4-acetoxybutyrate is subjected to an acylation reaction with methyl acetate, and azeotropic distillation is carried out at the same time to recover part of the methyl acetate and the generated methanol, so as to obtain a dry material containing sodium α-acetyl-γ-butyrolactone.

[0023] (2) The dried material is processed and then extracted to obtain crude α-acetyl-γ-butyrolactone;

[0024] (3) The crude product is subjected to vacuum distillation to separate the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate to obtain the refined α-acetyl-γ-butyrolactone.

[0025] In this invention, the use of sodium methoxide and methyl acetate prevents the formation of any products other than methanol during the preparation of α-acetyl-γ-butyrolactone, which is more conducive to the recovery of methanol and methyl acetate. Moreover, in this invention, the components form an azeotropic system during the acylation reaction, reacting and azeotropically simultaneously, carrying away methyl acetate and the byproduct methanol through distillation. This eliminates the inhibitory effect of the generated byproduct methanol on the acylation reaction, promotes a more thorough acylation reaction, and improves the yield of α-acetyl-γ-butyrolactone.

[0026] In some embodiments of the present invention, preferably, in step (1), the methyl 4-acetoxybutyrate in the raw materials accounts for 0.5-50% of the total mass fraction of γ-butyrolactone and methyl 4-acetoxybutyrate, more preferably 2-10%.

[0027] In some embodiments of the present invention, preferably, the total amount of methyl 4-acetoxybutyrate and γ-butyrolactone, and the molar ratio of methyl acetate and sodium methoxide are 1:(2-15):(0.5-2), more preferably 1:(3-12):(1-1.5). By controlling the total amount of methyl 4-acetoxybutyrate and γ-butyrolactone, and the feed ratio of methyl acetate and sodium methoxide, a higher yield of α-acetyl-γ-butyrolactone can be achieved.

[0028] In some embodiments of the present invention, preferably, the temperature of the acylation reaction is 60-100°C, more preferably 80-90°C; the pressure of the acylation reaction is 0.01-0.6 MPa, more preferably 0.1-0.3 MPa; and the time of the acylation reaction is 1-30 h, more preferably 3-15 h. Under the preferred time, temperature, and pressure of the acylation reaction of the present invention, methyl 4-acetoxybutyrate and γ-butyrolactone can undergo acylation reactions more effectively, and the components and the byproduct methanol can better azeotropically distill off methyl acetate and methanol, making the acylation reaction more thorough and increasing the yield of α-acetyl-γ-butyrolactone.

[0029] In this invention, the acylation reaction is preferably carried out in a reaction vessel equipped with reflux and distillation devices, and the reaction vessel is preferably equipped with a liquid droplet tank and a solid feed funnel.

[0030] According to the method of the present invention, the methyl acetate serves as both a raw material and a solvent for the acylation reaction. The feeding method and rate of the acylation reaction only need to ensure that the heat of the reaction system can be removed in a timely manner while maintaining the required reaction temperature. Preferably, the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate, along with sodium methoxide, can be added in batches, preferably in six equal portions. Simultaneously, methyl acetate is added during the reaction to ensure that the temperature of the acylation reaction system during the feeding process is within the required temperature range for the acylation reaction.

[0031] In some embodiments of the present invention, preferably, the reflux ratio during the azeotropic distillation is (3-4):1. Controlling the reflux ratio within this range allows for a more complete acylation reaction. The reflux ratio (denoted as R) refers to the ratio of the reflux liquid flow rate L to the product flow rate D during the azeotropic distillation process in the distillation column, i.e., R = L / D. The reflux ratio set by the present invention allows for the timely removal of a portion of the generated alcohol, resulting in a more complete conversion of the γ-butyrolactone and methyl 4-acetoxybutyrate mixture, while also ensuring sufficient reactants in the reaction system.

[0032] According to the method of the present invention, the methyl acetate recovered in step (1) can be directly recycled and reused, and the distilled methanol can be used to prepare sodium methoxide, thereby reducing production costs.

[0033] In this invention, step (2) further performs the vacuum distillation, which can avoid the azeotropic separation problem of methyl acetate, methanol and organic solvent, and significantly reduce energy consumption.

[0034] In some embodiments of the present invention, preferably, step (2) includes: diluting the dried material with water and then neutralizing it with dilute sulfuric acid. In the present invention, the concentration of the dilute sulfuric acid is 10-80 wt%, preferably 30-60 wt%; the pH value of the product obtained by the neutralization reaction is 3-7, preferably 3-5. Under this pH condition, the sodium α-acetyl-γ-butyrolactone can be completely acidified, and its hydrolysis can be effectively reduced, thereby increasing the yield of α-acetyl-γ-butyrolactone.

[0035] In some embodiments of the present invention, preferably, the extractant used in the extraction and separation process is selected from at least one of benzene homologues, carbon tetrachloride, hexane, cyclohexane, and petroleum ether; the benzene homologues are of the general formula C1. n H 2n-6 The compound represented, wherein n>6, is preferably at least one of toluene, ethylbenzene, and xylene, more preferably toluene. In this invention, the toluene enables α-acetyl-γ-butyrolactone sodium salt to be better dispersed in water and does not exhibit a viscous state.

[0036] In some embodiments of the present invention, preferably, the mass ratio of the extractant to the mixture of methyl 4-acetoxybutyrate and γ-butyrolactone is 0.5-5:1; more preferably 2.5:1; and the extraction and separation temperature is 0-5°C. In the present invention, controlling the mass ratio of the extractant to the mixture of methyl 4-acetoxybutyrate and γ-butyrolactone and the extraction and separation temperature within the ranges defined by the present invention enables more complete extraction and separation, thereby improving the yield and purity of α-acetyl-γ-butyrolactone.

[0037] In some embodiments of the present invention, preferably, in step (3), the vacuum distillation process includes: first performing a first vacuum distillation on the crude product at 105-110°C to separate the unreacted mixture of methyl 4-acetoxybutyrate and γ-butyrolactone; and then performing a second vacuum distillation on the resulting concentrate at 120-160°C to obtain a refined α-acetyl-γ-butyrolactone. In the present invention, the concentrate includes α-acetyl-γ-butyrolactone and high-boiling impurities, and the purity of the refined α-acetyl-γ-butyrolactone is greater than 99 wt%.

[0038] In some embodiments of the present invention, preferably, the pressure of the first vacuum distillation is 500-1000 Pa; and the pressure of the second vacuum distillation is 100-500 Pa.

[0039] A second aspect of the present invention provides the application of the aforementioned method in α-acetyl-γ-butyrolactone.

[0040] The present invention will be described in detail below through embodiments.

[0041] The raw materials, acids, bases, solvents, etc. used in the following examples and comparative examples were all commercially available.

[0042] The purity of α-acetyl-γ-butyrolactone was determined by gas chromatography.

[0043] Based on γ-butyrolactone, the yield % of α-acetyl-γ-butyrolactone = (actual amount of α-acetyl-γ-butyrolactone obtained / theoretical yield of α-acetyl-γ-butyrolactone based on the addition of γ-butyrolactone) × 100%.

[0044] Based on the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate, the yield % of α-acetyl-γ-butyrolactone is calculated as follows: (Amount of α-acetyl-γ-butyrolactone actually obtained / Theoretical yield of α-acetyl-γ-butyrolactone based on the addition of γ-butyrolactone and methyl 4-acetoxybutyrate) × 100%.

[0045] Example 1

[0046] (1) The acylation reaction was carried out in a dry 50L stainless steel reaction vessel equipped with a stirring, reflux, and distillation apparatus. The stirring was turned on, the reaction vessel was purged with nitrogen, and 19.7 kg of methyl acetate was added. The temperature inside the reaction vessel was raised to 45°C. 4 kg of raw material (methyl 4-acetoxybutyrate comprising 10% of the total mass of γ-butyrolactone and methyl 4-acetoxybutyrate) and 2.5 kg of sodium methoxide were added sequentially in six equal portions, maintaining the system temperature between 43°C and 48°C. After the sodium methoxide was added, the reaction system was gradually heated to 80°C and the acylation reaction was carried out at a pressure of 0.1 MPa. The valve of the distillation apparatus was slowly opened, controlling the reflux ratio at 4:1. Simultaneously, 8.2 kg of methyl acetate was slowly added, and azeotropic distillation was performed for 6-7 hours. A portion of the methanol and methyl acetate mixture generated from the reaction was collected. The molar ratios of the γ-butyrolactone and methyl 4-acetoxybutyrate mixture, methyl acetate, and sodium methoxide are shown in Table 1.

[0047] (2) The reaction system was monitored by gas chromatography and found to contain approximately 1.1 wt% γ-butyrolactone and 2.0 wt% methyl 4-acetoxybutyrate. The reaction system was distilled to dryness under vacuum of 1000 Pa and 45 °C to obtain a dry material. The remaining methanol and methyl acetate mixture obtained by vacuum distillation was recovered and combined with the methanol and methyl acetate mixture distilled from the acylation reaction stage in step (1) for further fractional distillation.

[0048] In steps (1) and (2), a total of 27.3 kg of a mixture of methyl acetate and methanol was obtained. 20.9 kg of methyl acetate (98 wt% purity, 85% recovery) and 2.3 kg of methanol (99 wt% purity, 86% recovery) were recovered. The methyl acetate recovered by distillation was directly reused in the acylation reaction; the methanol recovered by distillation was used for the production of solid sodium methoxide.

[0049] (3) Add 10 kg of toluene and 10 kg of purified water to the dried material, stir until dispersed at 40-45℃, cool to 0-5℃, add 50 wt% sulfuric acid solution dropwise to adjust the pH to 3-4, using 4.9 kg. After the addition is complete, stir for 30 min to carry out the neutralization reaction. The resulting emulsion is allowed to stand for 0.5 h, the lower aqueous phase is separated, concentrated and crystallized to obtain solid sodium sulfate, which is collected as a by-product; the upper organic phase is concentrated under reduced pressure at 700 Pa and 50℃ to recover toluene, recovering 9.5 kg of toluene (purity 99 wt%, recovery rate 95%), which is reused in the next batch of extraction.

[0050] (4) The remaining liquid in the tank was transferred to a 10L bottle and the mixture of 4-acetoxybutyrate impurity and γ-butyrolactone was distilled under a vacuum of 500Pa and a temperature of 105-110℃. The 4-acetoxybutyrate impurity molar fraction was 48%. The temperature was then raised to 120℃ and the α-acetyl-γ-butyrolactone was obtained by vacuum distillation. Its purity and yield are shown in Table 2.

[0051] Example 2

[0052] (1) The acylation reaction was carried out in a dry 50L stainless steel reaction vessel equipped with a stirring, reflux, and distillation apparatus. The stirrer was turned on, the reaction vessel was purged with nitrogen, and 20.2 kg of methyl acetate was added. The temperature inside the reaction vessel was raised to 45°C. 4 kg of raw material (methyl 4-acetoxybutyrate accounting for 5% of the total mass of γ-butyrolactone and methyl 4-acetoxybutyrate) and 2.5 kg of sodium methoxide were added sequentially in six equal portions, maintaining the system temperature between 43°C and 48°C. After the sodium methoxide was added, the reaction system was gradually heated to 80°C and the acylation reaction was carried out at a pressure of 0.1 MPa. The valve of the distillation apparatus was slowly opened, controlling the reflux ratio at 4:1. Simultaneously, 8.2 kg of methyl acetate was slowly added, and azeotropic distillation was performed for 6-7 hours. A mixture of methanol and methyl acetate generated from the reaction was collected. The molar ratios of the γ-butyrolactone and methyl 4-acetoxybutyrate mixture, methyl acetate, and sodium methoxide are shown in Table 1.

[0053] (2) The reaction system was monitored by gas chromatography and found to contain approximately 1.0 wt% γ-butyrolactone and 2.1 wt% methyl 4-acetoxybutyrate. The reaction system was distilled to dryness under vacuum of 1000 Pa and 45 °C to obtain a dry material. The remaining methanol and methyl acetate mixture obtained by vacuum distillation was recovered and combined with the methanol and methyl acetate mixture distilled from the acylation reaction stage in step (1) for fractional distillation separation.

[0054] In steps (1) and (2), a total of 27.5 kg of a mixture of methyl acetate and methanol was obtained. 21.0 kg of methyl acetate (98 wt% purity, 86% recovery) and 2.6 kg of methanol (99 wt% purity, 90% recovery) were recovered. The methyl acetate recovered by distillation was directly reused in the acylation reaction; the methanol recovered by distillation was used for the production of solid sodium methoxide.

[0055] (3) Add 10 kg of toluene and 10 kg of purified water to the dried material, stir until dispersed at 40-45℃, cool to 0-5℃, add 50 wt% sulfuric acid solution dropwise to adjust the pH to 3-4, using 4.9 kg. After the addition is complete, stir for 30 min to carry out the neutralization reaction. The resulting emulsion is allowed to stand for 0.5 h, the lower aqueous phase is separated, concentrated and crystallized to obtain solid sodium sulfate, which is collected as a by-product; the upper organic phase is concentrated under reduced pressure at 700 Pa and 50℃ to recover toluene, recovering 9.5 kg of toluene (purity 99 wt%, recovery rate 95%), which is reused in the next batch of extraction.

[0056] (4) The remaining liquid in the tank was transferred to a 10L bottle and the mixture of 4-acetoxybutyrate impurity and γ-butyrolactone was distilled under a vacuum of 500Pa and a temperature of 105-110℃. The 4-acetoxybutyrate impurity molar fraction was 52%. The temperature was then raised to 120℃ and the α-acetyl-γ-butyrolactone was obtained by vacuum distillation. Its purity and yield are shown in Table 2.

[0057] Example 3

[0058] (1) The acylation reaction was carried out in a dry 50L stainless steel reaction vessel equipped with a stirring, reflux, and distillation apparatus. The stirring was turned on, the reaction vessel was purged with nitrogen, and 20.5 kg of methyl acetate was added. The temperature inside the reaction vessel was raised to 45°C. 4 kg of raw material (methyl 4-acetoxybutyrate accounting for 2% of the total mass of γ-butyrolactone and methyl 4-acetoxybutyrate) and 2.6 kg of sodium methoxide were added sequentially in six equal portions, maintaining the system temperature between 43°C and 48°C. After the sodium methoxide was added, the reaction system was gradually heated to 80°C and the acylation reaction was carried out at a pressure of 0.1 MPa. The valve of the distillation apparatus was slowly opened, controlling the reflux ratio at 4:1. Simultaneously, 8.2 kg of methyl acetate was slowly added, and azeotropic distillation was performed for 6-7 hours. A mixture of methanol and methyl acetate generated from the reaction was collected. The molar ratios of the γ-butyrolactone and methyl 4-acetoxybutyrate mixture, methyl acetate, and sodium methoxide are shown in Table 1.

[0059] (2) Gas chromatography was used to monitor the reaction system and found that approximately 1.2 wt% of γ-butyrolactone and 2.0 wt% of methyl 4-acetoxybutyrate remained. The reaction system was distilled under reduced pressure at 1000 Pa and 45 °C until dry to obtain a dry material. The remaining methanol and methyl acetate mixture obtained from the reduced pressure distillation was recovered and combined with the methanol and methyl acetate mixture distilled from the acylation reaction stage in step (1) for further fractional distillation.

[0060] In steps (1) and (2), a total of 28.5 kg of a mixture of methyl acetate and methanol was obtained. 22.1 kg of methyl acetate (98 wt% purity, 87% recovery) and 2.5 kg of methanol (99 wt% purity, 88% recovery) were recovered. The methyl acetate recovered by distillation was directly reused in the acylation reaction; the methanol recovered by distillation was used for the production of solid sodium methoxide.

[0061] (3) Add 10 kg of toluene and 10 kg of purified water to the dried material, stir until dispersed at 40-45℃, cool to 0-5℃, add 50 wt% sulfuric acid solution dropwise to adjust the pH to 3-4, using 4.9 kg. After the addition is complete, stir for 30 min to carry out the neutralization reaction. The resulting emulsion is allowed to stand for 0.5 h, the lower aqueous phase is separated, concentrated and crystallized to obtain solid sodium sulfate, which is collected as a by-product; the upper organic phase is concentrated under reduced pressure at 700 Pa and 50℃ to recover toluene, recovering 9.5 kg of toluene (purity 99 wt%, recovery rate 95%), which is reused in the next batch of extraction.

[0062] (4) The remaining liquid in the tank was transferred to a 10L bottle and the mixture of 4-acetoxybutyrate impurity and γ-butyrolactone was distilled under a vacuum of 500Pa and a temperature of 105-110℃. The 4-acetoxybutyrate impurity molar fraction was 47%. The temperature was then raised to 120℃ and the α-acetyl-γ-butyrolactone was obtained by vacuum distillation. Its purity and yield are shown in Table 2.

[0063] Example 4

[0064] (1) The acylation reaction was carried out in a dry 50L stainless steel reaction vessel equipped with stirring, reflux and distillation apparatus. The stirrer was turned on, the reaction vessel was purged with nitrogen, 15.8 kg of methyl acetate was added, and the temperature inside the reaction vessel was raised to 45°C. 4 kg of raw material (methyl 4-acetoxybutyrate accounts for 50% of the total mass fraction of γ-butyrolactone and methyl 4-acetoxybutyrate) was added in 6 equal portions, and 2.0 kg of sodium methoxide was added in sequence, keeping the system temperature between 43°C and 48°C. After adding sodium methoxide, the reaction system was gradually heated to 80°C and subjected to acylation reaction at a pressure of 0.1 MPa. The valve of the distillation apparatus was slowly opened, and the reflux ratio was controlled at 4:1. At the same time, 8.2 kg of methyl acetate was slowly added. Azeotropic distillation was carried out for 6-7 hours, and a mixture of methanol and methyl acetate generated from the reaction was collected. The molar ratio of the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate, methyl acetate, and sodium methoxide is shown in Table 1.

[0065] (2) The reaction system was monitored by gas chromatography and found to contain approximately 2.0 wt% γ-butyrolactone and 3.5 wt% methyl 4-acetoxybutyrate. The reaction system was distilled under reduced pressure at 1000 Pa and 45 °C until dry to obtain a dry material. The remaining methanol and methyl acetate mixture obtained by reduced pressure distillation was recovered and combined with the methanol and methyl acetate mixture distilled from the acylation reaction stage in step (1) for further fractional distillation.

[0066] In steps (1) and (2), a total of 25.0 kg of a mixture of methyl acetate and methanol was obtained. 19.8 kg of methyl acetate (98 wt% purity, 87% recovery) and 2.0 kg of methanol (99 wt% purity, 89% recovery) were recovered. The methyl acetate recovered by distillation was directly reused in the acylation reaction; the methanol recovered by distillation was used for the production of solid sodium methoxide.

[0067] (3) Add 10 kg of toluene and 10 kg of purified water to the dried material, stir until dispersed at 40-45℃, cool to 0-5℃, add 50 wt% sulfuric acid solution dropwise to adjust the pH to 3-4, using 4.9 kg. After the addition is complete, stir for 30 min to carry out the neutralization reaction. The resulting emulsion is allowed to stand for 0.5 h, the lower aqueous phase is separated, concentrated and crystallized to obtain solid sodium sulfate, which is collected as a by-product; the upper organic phase is concentrated under reduced pressure at 700 Pa and 50℃ to recover toluene, recovering 9.5 kg of toluene (purity 99 wt%, recovery rate 95%), which is reused in the next batch of extraction.

[0068] (4) The remaining liquid in the tank was transferred to a 10L bottle and the mixture of 4-acetoxybutyrate impurity and γ-butyrolactone was distilled under a vacuum of 500Pa and a temperature of 105-110℃. The 4-acetoxybutyrate impurity had a molar fraction of 48.5%. The temperature was then raised to 120℃ and the α-acetyl-γ-butyrolactone was obtained by vacuum distillation. Its purity and yield are shown in Table 2.

[0069] Comparative Example 1

[0070] (1) The acylation reaction was carried out in a dry 50L stainless steel reaction vessel equipped with a stirring, reflux, and distillation apparatus. The stirrer was turned on, the reaction vessel was purged with nitrogen, and 20.7 kg of methyl acetate was added. The temperature of the reaction vessel was raised to 45°C. 4 kg of γ-butyrolactone (excluding methyl 4-acetoxybutyrate) and 2.7 kg of sodium methoxide were added in six equal portions in sequence, keeping the system temperature between 43°C and 48°C. After the sodium methoxide was added, the reaction system was gradually heated to 80°C and the acylation reaction was carried out at a pressure of 0.1 MPa. The valve of the distillation apparatus was slowly opened, and the reflux ratio was controlled at 4:1. At the same time, 8.2 kg of methyl acetate was slowly added. Azeotropic distillation was carried out for 6-7 hours. A mixture of methanol and methyl acetate generated in the reaction was collected. The molar ratio of the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate, methyl acetate, and sodium methoxide is shown in Table 1.

[0071] (2) Gas chromatography was used to monitor the reaction system and found that approximately 1 wt% of γ-butyrolactone and 2.2 wt% of 4-acetoxymethyl acetate remained. The reaction system was distilled to dryness under vacuum of 1000 Pa and 45 °C to obtain a dry material. The remaining methanol and methyl acetate mixture obtained from the vacuum distillation was recovered and combined with the methanol and methyl acetate mixture distilled from the acylation reaction stage in step (1) for further fractional distillation.

[0072] In steps (1) and (2), a total of 30.2 kg of a mixture of methyl acetate and methanol was obtained. 23.2 kg of methyl acetate (98 wt% purity, 84% recovery) and 2.7 kg of methanol (99 wt% purity, 88% recovery) were recovered. The methyl acetate recovered by distillation was directly reused in the acylation reaction; the methanol recovered by distillation was used for the production of solid sodium methoxide.

[0073] (3) Add 10 kg of toluene and 10 kg of purified water to the dried material, stir until dispersed at 40-45℃, cool to 0-5℃, add 50 wt% sulfuric acid solution dropwise to adjust the pH to 3-4, using 4.9 kg. After the addition is complete, stir for 30 min to carry out the neutralization reaction. The resulting emulsion is allowed to stand for 0.5 h, the lower aqueous phase is separated, concentrated and crystallized to obtain solid sodium sulfate, which is collected as a by-product; the upper organic phase is concentrated under reduced pressure at 700 Pa and 50℃ to recover toluene, recovering 9.5 kg of toluene (purity 99 wt%, recovery rate 95%), which is reused in the next batch of extraction.

[0074] (4) The remaining liquid in the tank was transferred to a 10L bottle and the mixture of 4-acetoxybutyrate impurity and γ-butyrolactone was distilled under a vacuum of 500Pa and a temperature of 105-110℃. The 4-acetoxybutyrate impurity molar fraction was 54%. The temperature was then raised to 120℃ and the α-acetyl-γ-butyrolactone was obtained by vacuum distillation. Its purity and yield are shown in Table 2.

[0075] Comparative Example 2

[0076] (1) The acylation reaction was carried out in a dry 50L stainless steel reaction vessel equipped with a stirring, reflux, and distillation apparatus. The stirrer was turned on, the reaction vessel was purged with nitrogen, and 11.1 kg of methyl acetate was added. The temperature inside the reaction vessel was raised to 45°C. 4 kg of methyl 4-acetoxybutyrate (excluding γ-butyrolactone) and 1.5 kg of sodium methoxide were added in six equal portions in sequence, keeping the system temperature between 43°C and 48°C. After the sodium methoxide was added, the reaction system was gradually heated to 80°C and the acylation reaction was carried out at a pressure of 0.1 MPa. The valve of the distillation apparatus was slowly opened, and the reflux ratio was controlled at 4:1. At the same time, 8.2 kg of methyl acetate was slowly added. Azeotropic distillation was carried out for 6-7 hours. A mixture of methanol and methyl acetate generated in the reaction was collected. The molar ratio of the mixture of γ-butyrolactone and methyl 4-acetoxybutyrate, methyl acetate, and sodium methoxide is shown in Table 1.

[0077] (2) Gas chromatography was used to monitor the reaction system and found that approximately 3.1 wt% of γ-butyrolactone and 4.0 wt% of 4-acetoxymethyl acetate remained. The reaction system was distilled under reduced pressure at 1000 Pa and 45 °C until dry to obtain a dry material. The remaining methanol and methyl acetate mixture obtained from the reduced pressure distillation was recovered and combined with the methanol and methyl acetate mixture distilled from the acylation reaction stage in step (1) for further fractional distillation.

[0078] In steps (1) and (2), a total of 19.7 kg of a mixture of methyl acetate and methanol was obtained. 16.6 kg of methyl acetate (98 wt% purity, 86% recovery) and 1.4 kg of methanol (99 wt% purity, 90% recovery) were recovered. The methyl acetate recovered by distillation was directly reused in the acylation reaction; the methanol recovered by distillation was used for the production of solid sodium methoxide.

[0079] (3) Add 10 kg of toluene and 10 kg of purified water to the dried material, stir until dispersed at 40-45℃, cool to 0-5℃, add 50 wt% sulfuric acid solution dropwise to adjust the pH to 3-4, using 4.9 kg. After the addition is complete, stir for 30 min to carry out the neutralization reaction. The resulting emulsion is allowed to stand for 0.5 h, the lower aqueous phase is separated, concentrated and crystallized to obtain solid sodium sulfate, which is collected as a by-product; the upper organic phase is concentrated under reduced pressure at 700 Pa and 50℃ to recover toluene, recovering 9.5 kg of toluene (purity 99 wt%, recovery rate 95%), which is reused in the next batch of extraction.

[0080] (4) The remaining liquid in the tank was transferred to a 10L bottle and the mixture of 4-acetoxybutyrate impurity and γ-butyrolactone was distilled under a vacuum of 500Pa and a temperature of 105-110℃. The 4-acetoxybutyrate impurity molar fraction was 46%. The temperature was then raised to 120℃ and the α-acetyl-γ-butyrolactone was obtained by vacuum distillation. Its purity and yield are shown in Table 2.

[0081] Table 1

[0082]

[0083] Table 2

[0084]

[0085] As can be seen from the data in Table 1, the method of the present invention can further react methyl 4-acetoxybutyrate impurities into α-acetyl-γ-butyrolactone, achieving higher utilization of γ-butyrolactone, higher purity of α-acetyl-γ-butyrolactone, and higher yield. From Examples 1-3 in Table 1, it can be seen that a mass fraction of methyl 4-acetoxybutyrate within the preferred range of 2-10% results in a higher yield of α-acetyl-γ-butyrolactone based on γ-butyrolactone. The mass fraction of methyl 4-acetoxybutyrate in Example 4 of Table 1 is not within the preferred range, therefore the yield of α-acetyl-γ-butyrolactone is slightly lower, indicating that the mass fraction of methyl 4-acetoxybutyrate affects the yield of α-acetyl-γ-butyrolactone. The data in Table 1 also show that... Compared with Example 1, the yield of α-acetyl-γ-butyrolactone in Comparative Example 1 was reduced by 4.5% based on γ-butyrolactone. The difference was that methyl 4-acetoxybutyrate was not added to the raw materials of Comparative Example 1. The total molar yield and purity of the product obtained by using the mixed feed were consistent with those of Comparative Example 1 using pure γ-butyrolactone. Compared with Examples 1-4 and Comparative Example 1, the total molar yield and purity of Comparative Example 2 in Table 1 were significantly reduced. The difference was that pure methyl 4-acetoxybutyrate was used as the feed.

[0086] In summary, the use of a mixture of methyl 4-acetoxybutyrate and γ-butyrolactone in this invention results in a higher yield and purity of α-acetyl-γ-butyrolactone, improves raw material utilization, and can significantly reduce production costs and increase economic benefits in large-scale production.

[0087] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing α-acetyl-γ-butyrolactone, characterized in that, The method includes the following steps: (1) In the presence of sodium methoxide, the raw material containing γ-butyrolactone and methyl 4-acetoxybutyrate is subjected to acylation reaction with methyl acetate, and azeotropic distillation is carried out at the same time to recover part of the methyl acetate and the generated methanol, so as to obtain a dry material containing sodium α-acetyl-γ-butyrolactone. In the raw materials, methyl 4-acetoxybutyrate accounts for 2-10% of the total mass of γ-butyrolactone and methyl 4-acetoxybutyrate; the molar ratio of the total mass of methyl 4-acetoxybutyrate and γ-butyrolactone, methyl acetate and sodium methoxide is 1:(2-15):(0.5-2). (2) The dried material is processed and then extracted and separated to obtain crude α-acetyl-γ-butyrolactone; the processing includes: diluting the dried material with water and then neutralizing it with dilute sulfuric acid; (3) The crude product is first subjected to a first vacuum distillation at 105-110℃ to separate the unreacted methyl 4-acetoxybutyrate and γ-butyrolactone mixture, and the resulting concentrate is subjected to a second vacuum distillation at 120-160℃ to obtain α-acetyl-γ-butyrolactone.

2. The method according to claim 1, wherein, The total amount of methyl 4-acetoxybutyrate and γ-butyrolactone, and the molar ratio of methyl acetate and sodium methoxide are 1:(3-12):(1-1.5).

3. The method according to claim 1, wherein, The acylation reaction is carried out at a temperature of 60-100℃; And / or, the pressure of the acylation reaction is 0.01-0.6 MPa; And / or, the acylation reaction takes 1-30 h.

4. The method according to claim 3, wherein, The acylation reaction is performed at a temperature of 80-90℃; And / or, the pressure of the acylation reaction is 0.1-0.3 MPa; And / or, the acylation reaction takes 3-15 hours.

5. The method according to claim 1, wherein, During the azeotropic distillation process, the reflux ratio is (3-4):

1.

6. The method according to claim 1, wherein, The extractant used in the extraction and separation process is selected from at least one of benzene homologues, carbon tetrachloride, hexane, cyclohexane and petroleum ether; The benzene homologues are of the general formula C. n H 2n-6 The compound represented, where n>6.

7. The method according to claim 6, wherein, The benzene homologue is at least one of toluene, ethylbenzene, and xylene.

8. The method according to claim 7, wherein, The benzene homologue is toluene.

9. The method according to claim 6, wherein, The mass ratio of the extractant to the mixture of methyl 4-acetoxybutyrate and γ-butyrolactone is 0.5-5:

1.

10. The method according to claim 9, wherein, The mass ratio of the extractant to the mixture of methyl 4-acetoxybutyrate and γ-butyrolactone is 2.5:

1.

11. The method according to claim 1, wherein, The extraction and separation temperature is 0-5℃.

12. The method according to claim 1, wherein, The pressure of the first vacuum distillation is 500-1000 Pa; the pressure of the second vacuum distillation is 100-500 Pa.

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