阅读说明：本技术 一种提高交酯收率的方法 (Method for improving yield of lactide ) 是由 赵春华 袁文博 王文静 牛自芬 于 2021-08-13 设计创作，主要内容包括：本发明属于有机合成技术领域,具体涉及一种提高交酯收率的方法,即羟基酸酯化脱水生成低聚物后先加入高沸点溶剂,然后进行解聚；粗品重结晶前先水洗打浆抽滤,滤饼再进行一次重结晶即可得到高纯度产品。采用本发明减少解聚过程中碳化,提高转化率,减少重结晶次数,最大化的提高原料利用度,提高收率。(The invention belongs to the technical field of organic synthesis, and particularly relates to a method for improving lactide yield, namely, after an oligomer is generated by esterification and dehydration of hydroxy acid, a high-boiling-point solvent is added, and then depolymerization is carried out; and (3) before recrystallization, washing, pulping and filtering the crude product, and recrystallizing the filter cake once again to obtain the high-purity product. The method reduces carbonization in the depolymerization process, improves the conversion rate, reduces the recrystallization times, and maximally improves the utilization rate and the yield of the raw materials.)

1. A method for improving lactide yield is characterized in that after hydroxy acid is esterified and dehydrated to generate oligomer, a high-boiling-point solvent is added, and then depolymerization is carried out; and (3) before recrystallization, washing, pulping and filtering the crude product, and recrystallizing the filter cake once again to obtain the high-purity product.

2. The method for improving the yield of lactide according to claim 1, wherein the hydroxy acid in the filtrate is collected for reuse after removing water and low boiling point impurities by rotary evaporation.

3. A method for increasing yield of lactide as claimed in claim 1, wherein the high boiling point solvent is selected from glycerol or cetyl alcohol or stearyl alcohol or ethylene glycol.

4. The method for improving the yield of lactide according to claim 1, wherein the mass ratio of the high-boiling point solvent to the hydroxy acid is: 0.5-1:1.

5. The method for improving the yield of lactide according to claim 1, wherein the mass ratio of water to crude product in the processes of water washing, pulping and suction filtration is 1-3: 1.

6. A method for increasing yield of lactide as claimed in claim 2, wherein the rotary evaporation temperature of the filtrate is 60-100 ℃.

7. The method for improving the yield of lactide according to claim 1, wherein the solvent used in the recrystallization process is ethyl acetate, and the mass ratio of the ethyl acetate to the filter cake is 1-2.5: 1.

8. The method for improving the yield of lactide according to claim 1, characterized by comprising the following steps:

(1) adding hydroxy acid into a reaction bottle, distilling under reduced pressure to 180 ℃, adding a catalyst and a high-boiling point solvent, stirring and mixing uniformly, depolymerizing at high temperature and in high vacuum, collecting a crude product until no product is distilled off to obtain a crude product I, adding water into the crude product I, pulping, washing and filtering to obtain a filter cake I and a filtrate I;

(2) carrying out rotary distillation on the filtrate I until the volume is not reduced, carrying out reduced pressure distillation on the residues to 180 ℃, depolymerizing at high temperature and in high vacuum, collecting the crude product until no product is distilled off to obtain a crude product II, adding water into the crude product II, pulping, washing and carrying out suction filtration to obtain a filter cake II;

(3) and mixing the filter cake I and the filter cake II, adding ethyl acetate for recrystallization once, and drying in vacuum to obtain the product.

9. A method for increasing the yield of lactide according to claim 8, wherein the high temperature is 230 ℃ and 250 ℃.

10. A method for increasing yield of lactide as claimed in claim 8, wherein the high vacuum is-0.1 MPa.

Technical Field

The invention belongs to the technical field of organic synthesis, and particularly relates to a method for improving lactide yield.

Background

The lactide is ester formed by interactive condensation of two molecules of alpha-hydroxy acid inner hydroxyl (-OH) and carboxyl (-COOH) to remove two molecules of water, and is a six-atom heterocyclic compound. Glycolic acid (α -glycolic acid) and lactic acid (α -hydroxypropionic acid) can be heated to give glycolide and lactide, respectively. Polylactide and polyglycolide and related materials polymerized from the lactide have good biodegradability, biocompatibility and mechanical strength, are ideal biodegradable materials, and have wide application prospects in the aspects of human tissue repair, wound suture and controlled release of medicines and pesticides.

The lactide as the intermediate material of polylactide has the characteristics of high boiling point, low freezing point, heat sensitivity, easy water absorption, ring-opening reaction and the like, has high refining and purification difficulty, and is the main technical difficulty of a synthesis process; the preparation cost and purity of the polylactide modified by the modified starch are determined by the cost and quality of the high-molecular-weight polylactide, and are also one of the main factors influencing the industrialization of the polylactide.

The synthesis process of lactide mainly comprises two stages of reaction synthesis and refining purification. The reaction stage is that hydroxy acid is esterified and dehydrated to generate oligomer (molecular weight is 500-. These impurities can affect the molecular weight, molecular weight distribution, and stability and mechanical properties of the polymer in the next step. Therefore, the crude product is purified and refined to the polymerization level. The prior lactide refining method comprises the following steps: among them, the solvent absorption method, the gas-assisted evaporation method, the recrystallization method and the like are most frequently used, and a method of repeatedly recrystallizing glycolide using an organic solvent such as an alcohol or ethyl acetate is more common, and purification of glycolide by recrystallization is reported in, for example, patent US5223630, CN100999516 and the like. The above method mainly has the following problems: on one hand, when the oligomer generated by esterification and dehydration in the lactide synthesis process is subjected to pyrolysis, the reaction liquid is gradually viscous, darkens in color and even carbonizes with the increase of the temperature (higher than 200 ℃), so that the distillation is not easy to occur, and the yield is reduced. On the other hand, the purification and purification process of lactide generally adopts a repeated recrystallization method, and the amount of used solvent is large, so that the product loss is also large, and the yield is also low.

Therefore, how to improve the synthesis process of lactide, increase the yield and reduce the production cost becomes a hot topic of research.

Disclosure of Invention

Aiming at the problems, the invention provides a method for improving the yield of lactide, which reduces carbonization in the depolymerization process, improves the conversion rate, reduces the recrystallization times, and improves the utilization rate and the yield of raw materials to the maximum extent.

The method for improving the yield of the lactide is characterized in that after the hydroxy acid is esterified and dehydrated to generate oligomer, a high-boiling-point solvent is added, and then depolymerization is carried out; and (3) before recrystallization, washing, pulping and filtering the crude product, and recrystallizing the filter cake once again to obtain the high-purity product.

Furthermore, after water and low-boiling-point impurities in the filtrate are removed by rotary evaporation, the hydroxy acid in the filtrate is collected for reuse, and the utilization rate of the raw materials is improved to the maximum extent.

The high boiling point solvent is selected from glycerol or cetyl alcohol or stearyl alcohol or ethylene glycol.

The mass ratio of the high-boiling-point solvent to the hydroxy acid is as follows: 0.5-1:1, preferably 0.7: 1.

The mass ratio of water to the crude product in the washing, pulping and suction filtration processes is 1-3:1, preferably 2.5: 1.

The rotary evaporation temperature of the filtrate is 60-100 ℃, and the preferable temperature is 70-80 ℃.

The solvent adopted in the recrystallization process is ethyl acetate, and the mass ratio of the ethyl acetate to the filter cake is 1-2.5:1, preferably 1.5-2: 1.

The method comprises the following more specific steps:

(1) adding hydroxy acid into a reaction bottle, distilling under reduced pressure to 180 ℃, adding a catalyst and a high-boiling point solvent, stirring and mixing uniformly, depolymerizing at high temperature and in high vacuum, collecting a crude product until no product is distilled off to obtain a crude product I, adding water into the crude product I, pulping, washing and filtering to obtain a filter cake I and a filtrate I;

(2) carrying out rotary distillation on the filtrate I until the volume is not reduced, carrying out reduced pressure distillation on the residues to 180 ℃, depolymerizing at high temperature and in high vacuum, collecting the crude product until no product is distilled off to obtain a crude product II, adding water into the crude product II, pulping, washing and carrying out suction filtration to obtain a filter cake II;

(3) and mixing the filter cake I and the filter cake II, adding ethyl acetate for recrystallization once, and drying in vacuum to obtain the product.

The high temperature is 230-250 ℃.

The high vacuum is-0.1 MPa.

The invention has the following beneficial effects:

(1) according to the invention, after the hydroxy acid is esterified and dehydrated to generate the oligomer, the high-boiling-point solvent is added firstly, and then depolymerization is carried out, so that carbonization in the depolymerization process is reduced, the conversion rate is improved, and the problem of low yield caused by incomplete distillation is avoided.

(2) The crude product is washed, pulped and filtered before recrystallization, and a high-purity product can be obtained by carrying out primary recrystallization on a filter cake, so that the problems of large solvent consumption, large product loss and low yield caused by a repeated recrystallization method are solved.

(3) And (3) after removing water and low-boiling-point impurities by rotary evaporation, collecting hydroxy acid in the filtrate for reuse, and maximally improving the utilization rate of the raw materials.

Detailed Description

Example 1

Weighing 500g of lactic acid, adding the lactic acid into a three-neck flask, carrying out reduced pressure distillation dehydration to 150 ℃, adding a proper amount of catalyst and 350g of glycerol, stirring and mixing uniformly, carrying out high-temperature (230-;

and (3) carrying out rotary evaporation on the filtrate for 2 hours at the temperature of 80 ℃ until the volume is not reduced, removing most of water and other low-boiling-point impurities, repeating the steps of reduced pressure distillation, high-temperature depolymerization, water adding pulping, washing and suction filtration to obtain 220g of crude filter cake, mixing the two filter cakes, adding 1200ml of ethyl acetate to recrystallize once, and carrying out vacuum drying at the temperature of 40 ℃ for 48 hours to obtain 395g of lactide, wherein the yield is 79%, and the purity is 99.97% by detection.

Example 2

Weighing 500g of glycolic acid, adding the glycolic acid into a three-neck flask, carrying out reduced pressure distillation dehydration to 180 ℃, adding a proper amount of catalyst and 400g of hexadecanol, stirring and mixing uniformly, carrying out high-vacuum depolymerization at high temperature (250-270 ℃), collecting crude glycolide until no product is distilled to obtain 530g of crude glycolide, adding 530ml of water into the crude glycolide, pulping, washing and carrying out suction filtration to obtain 460g of filter cake and 850ml of filtrate;

and (3) carrying out rotary evaporation on the filtrate for 2 hours at the temperature of 80 ℃ until the volume is not reduced, removing most of water and other low-boiling-point impurities, repeating the steps of reduced pressure distillation, high-temperature depolymerization, water adding pulping, washing and suction filtration to obtain 200g of crude filter cake, mixing the two filter cakes, adding 660ml of ethyl acetate to recrystallize once, and carrying out vacuum drying at the temperature of 40 ℃ for 48 hours to obtain 375g of lactide, wherein the yield is 75%, and the purity is 99.95% by detection.

Example 3

Weighing 1000g of lactic acid, adding the lactic acid into a three-neck flask, carrying out reduced pressure distillation dehydration to 150 ℃, adding a proper amount of catalyst and 500g of octadecanol, stirring and mixing uniformly, carrying out high-temperature (190-;

and (3) carrying out rotary evaporation on the filtrate at the temperature of 80 ℃ for 3.5h until the volume is not reduced, removing most of water and other low-boiling-point impurities, repeating the steps of reduced pressure distillation, high-temperature depolymerization, pulping by adding water, washing and suction filtration to obtain 450g of crude filter cake, mixing the two filter cakes, adding 2800ml of ethyl acetate to recrystallize once, and carrying out vacuum drying at the temperature of 40 ℃ for 48 hours to obtain 780g of lactide, wherein the yield is 78%, and the purity is 99.93% by detection.

Example 4

Weighing 1000g of lactic acid, adding the lactic acid into a three-neck flask, carrying out reduced pressure distillation dehydration to 150 ℃, adding a proper amount of catalyst and 1000g of octadecanol, stirring and mixing uniformly, carrying out high-vacuum depolymerization at high temperature (190-;

and (3) carrying out rotary evaporation on the filtrate for 4 hours at the temperature of 80 ℃ until the volume is not reduced, removing most of water and other low-boiling-point impurities, repeating the steps of reduced pressure distillation, high-temperature depolymerization, pulping by adding water, washing and suction filtration to obtain 440g of crude filter cake, mixing the two filter cakes, adding 3420ml of ethyl acetate to recrystallize once, and carrying out vacuum drying at the temperature of 40 ℃ for 48 hours to obtain 710g of lactide, wherein the yield is 71%, and the purity is 99.95% by detection.

Comparative example 1

Weighing 500g of lactic acid, adding the lactic acid into a three-neck flask, carrying out reduced pressure distillation dehydration to 150 ℃, adding a proper amount of catalyst, stirring and mixing uniformly, carrying out high-temperature (230 ℃) and high-vacuum depolymerization, collecting a crude lactide product until no product is distilled off to obtain 500g of the crude product, adding 800ml of ethyl acetate for recrystallization, repeating the steps for 4 times, and carrying out vacuum drying at 40 ℃ for 48 hours to obtain 178g of lactide, wherein the yield is 35.6%, and the purity is 99.52% through detection.

Comparative example 2

Weighing 1000g of lactic acid, adding the lactic acid into a three-neck flask, carrying out reduced pressure distillation dehydration to 150 ℃, adding a proper amount of catalyst, stirring and mixing uniformly, carrying out high temperature (230 ℃.) -250 ℃ C., high vacuum depolymerization, collecting crude lactide until no product is distilled off to obtain 1200g of crude lactide, adding 2400ml of ethyl acetate for recrystallization, repeating the steps for 4 times, and carrying out vacuum drying at 40 ℃ for 48 hours to obtain 382g of lactide, wherein the yield is 38.2%, and the purity is 99.65% through detection.