Continuous purification process of glycolide, an intermediate product in the production of degradable plastics
The glycolide purification process, which combines melt dehydration and vacuum evaporation, solves the problems of low yield and high solvent consumption in existing technologies, enabling the production of high-purity glycolide and improving the performance of polyglycolic acid.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INNER MONGOLIA RONGXIN CHEM CO LTD
- Filing Date
- 2023-11-23
- Publication Date
- 2026-07-03
Smart Images
Figure CN117624113B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical product purification technology, and relates to a continuous purification process for glycolide, an intermediate product in the production of degradable plastics. Background Technology
[0002] In recent years, polyglycolic acid (PGA) has gradually become a widely used biodegradable material with excellent biocompatibility, machinability, and gas barrier properties. It has begun to be used in packaging, agricultural films, disposable tableware, and medical supplies abroad. PGA is prepared by ring-opening polymerization of glycolide. Glycoide is first polymerized to obtain oligomers from glycolic acid monomers, and then depolymerized to obtain PGA. Currently, in industry, the intermediate product glycolide contains impurities such as water and acid, resulting in low molecular weight and insufficient modulus of PGA products.
[0003] Therefore, the intermediate product glycolide needs to be processed. Existing processing methods are mainly physical extraction methods, which involve obtaining high-purity products through steps such as negative pressure extraction, high-temperature evaporation, and sedimentation. This method is usually simple to operate, highly efficient, and can be recycled and reused in the PGA synthesis process. For example, patent CN116621809A describes a method for purifying glycolide, in which the mother liquor obtained from the subsequent recrystallization is returned to the previous recrystallization as a solvent, and purification is completed by multiple recrystallizations. Patent CN116606277A describes a method and apparatus for purifying glycolide, which uses a combination of solution crystallization and melt crystallization for continuous purification. It is evident that physical removal is a common method for purifying polyesters and intermediate products in the industry. However, this method has the following main problems: (1) Multi-stage crystallization and dissolution of glycolide, and repeated purification cycles result in low yield and high energy consumption; (2) Existing methods use solvent crystallization, which requires a large amount of solvent, and the solvent is an organic solvent, which causes significant pollution; (3) When glycolide containing impurities is removed in a cycle under high vacuum and high temperature conditions, some glycolide will accumulate, resulting in carbon buildup.
[0004] Therefore, it is of great significance to find a process that can overcome the drawbacks of traditional physical purification methods and achieve efficient recycling of intermediate products. Summary of the Invention
[0005] To address the technical problems of low yield and high solvent consumption in the purification of glycolide mentioned above, this invention provides a continuous purification process for glycolide, an intermediate product in the production of degradable plastics.
[0006] This invention improves the yield of glycolide by using melt dehydration, mixing glycolide with fresh polyglycolic acid to remove light components, and evaporation to remove heavy components, resulting in low solvent consumption.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0008] A continuous purification process for glycolide, an intermediate product in the production of biodegradable plastics, includes the following steps:
[0009] 1) The intermediate product glycolide is successively melted and dehydrated;
[0010] 2) Mix the melt-dehydrated glycolide with polyglycolic acid at a mass ratio of 20:1 to 25:1 to remove the light components from the glycolide;
[0011] 3) Under vacuum, the glycolide from which the light component has been removed is evaporated to remove the heavy component, yielding purified glycolide;
[0012] 4) A small portion of the refined glycolide is returned to step 3) for recycling and decomposition of heavy components, while most of the refined glycolide is further processed to obtain purified glycolide.
[0013] Further specifying, in the intermediate product of step 1), the content of glycolide is 65-75%, the moisture content is 400-450 ppm, the content of light components is 5%-6%, and the remainder is impurities.
[0014] Further specified, the impurity content in the dehydrated glycolide is not higher than 1%, and the moisture content is not higher than 200 ppm.
[0015] Further specifying, the impurity is polyglycolic acid.
[0016] Further specifying, in step 2), the molecular weight of polyglycolic acid is 300-500.
[0017] Further specified, the content of light components in the glycolide from which light components have been extracted is not higher than 50 ppm.
[0018] Further specifying, the conditions for evaporating and deweighting components in step 3) are: temperature 180℃~250℃, pressure 1.5KPa, and time 1h~4h.
[0019] Further specifying, in step 4), the subsequent processing includes cooling, washing, and drying in sequence.
[0020] Furthermore, the intermediate product glycolide in step 1) requires pretreatment before melting.
[0021] Further specifying, the pretreatment involves washing and drying the intermediate product glycolide to obtain glycolide particles.
[0022] The beneficial effects of this invention are:
[0023] 1. The continuous purification process of this invention involves melt dehydration, reaction of glycolide with polyglycolic acid to remove light components, and evaporation to remove heavy components. Through a combination of physical and chemical methods, high-quality glycolide is finally obtained with a yield of over 80%. Moreover, the amount of solvent consumed in the purification process is greatly reduced, saving raw material costs.
[0024] 2. In this invention, a small portion of the refined glycolide after de-removing heavy components is returned to the recycling process to improve the purity of glycolide through secondary purification. The process is simple, energy-efficient, and in line with the principle of sustainable development.
[0025] 3. In this invention, fresh polyglycolic acid and dehydrated glycolide are mixed to remove light components from glycolide; the addition of fresh polyglycolic acid ensures the continuity of the reaction and improves the purification speed.
[0026] 4. In this invention, the purified glycolide obtained from the removal of heavy components is returned to the unit for removing light components, thereby achieving secondary purification of glycolide and improving the yield and purity of glycolide.
[0027] 5. The purification process of this invention can greatly avoid the cyclic removal of impurities under high vacuum and high temperature conditions, and the glycolide of ethanol is not easy to accumulate, effectively preventing the occurrence of carbon deposition.
[0028] 6. The purification process provided by this invention reduces the water content in the intermediate product glycolide from 400-450 ppm to below 200 ppm, and increases the glycolide purity from 65%-75% to over 98%, with a maximum increase of 33%. High glycolide purity ensures that the polymerized PGA exhibits good performance. This purification process can be used for the purification of glycolide, an intermediate product in polyglycolic acid production, and has broad application prospects. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the glycolide purification process;
[0030] Figure 2 Schematic diagram of a glycolide purification device;
[0031] in:
[0032] 1—Dyslexic acid storage tank; 2—Dehydration tank; 3—Scraped film evaporator; 4—Kneading reactor. Detailed Implementation
[0033] The technical solution protected by the present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0034] See Figure 1 The present invention provides a continuous purification process for glycolide, an intermediate product in the production of biodegradable plastics, comprising the following steps.
[0035] 1) The intermediate product glycolide is melted and dehydrated sequentially.
[0036] In the intermediate product glycolide, the glycolide content is 65-75% by mass, the moisture content is 400-450 ppm, the light component content is 5%-6% by mass, and the remainder is impurities.
[0037] Specifically, the intermediate glycolide is melted to obtain liquid glycolide containing a small amount of impurities; the impurity content in the liquid glycolide is no more than 1%, and the impurity is polyglycolic acid.
[0038] Liquid glycolide in its molten state is dehydrated under vacuum, and the water content in the dehydrated glycolide is no higher than 200 ppm.
[0039] Preferably, vacuum dehydration is used during dehydration, with a vacuum degree of 8 kPa to 12 kPa. The moisture content in the dehydrated glycolide can be adjusted by regulating the vacuum degree; the higher the vacuum degree, the lower the moisture content.
[0040] In this step, the intermediate product glycolide needs to undergo pretreatment before melting. The pretreatment involves washing and drying the intermediate product glycolide to obtain glycolide particles.
[0041] 2) Mix the melt-dehydrated glycolide with polyglycolic acid at a mass ratio of 20:1 to 25:1 to remove the light components from the glycolide.
[0042] The polyglycolic acid (PGA) used is fresh, low-molecular-weight PGA. The continuity of the purification process is ensured by adding fresh PGA to the purification system. Preferably, the molecular weight of the fresh PGA is 300–500.
[0043] The dehydrated molten glycolide is pumped to the scraped film evaporator 3 via a plunger pump for the removal of light components. The scraped film evaporator can remove light components from a high-viscosity glycolide mixture, and the content of light components in the glycolide is not higher than 50 ppm.
[0044] 3) Under vacuum, the light component of the glycolide is removed by evaporation to remove the heavy component, thus obtaining refined glycolide.
[0045] The glycolide from which the light components have been removed is further fed to kneading reactor 4, where it is evaporated under high vacuum to remove the heavy components. Kneading reactor 4 evaporates the high-viscosity glycolide while separating the impurities of the heavy components to obtain refined glycolide (vapor state).
[0046] The conditions for evaporation and deweighting of the components are: temperature 180℃~250℃, pressure 1.5KPa, and time 1h~4h.
[0047] 4) The refined glycolide is divided into two parts. One part (with a mass ratio of less than 2%) is returned to step 3) for cyclic removal of heavy components, and the other part of the refined glycolide (with a mass ratio of more than 98%) is subjected to subsequent treatment to obtain purified glycolide. The part of the refined glycolide obtained by removing heavy components is returned to the light component removal unit to achieve secondary purification of glycolide, improving the yield and purity of glycolide.
[0048] Specifically, after the glycolide vapor is obtained under a high vacuum state and cooled, it is washed and dried to obtain purified glycolide.
[0049] The above purification process can greatly avoid the cyclic removal of impurities under high vacuum and high temperature conditions. The glycolide of ethanol is not prone to accumulation, effectively preventing the occurrence of carbon deposition.
[0050] The purified glycolide of the present invention is tested, and the purity is more than 98%, and the yield is more than 80%. The purified glycolide is then sent to the polymerization unit, and a high molecular weight polyglycolic acid product is obtained under the action of a catalyst.
[0051] See Figure 2 , this embodiment also provides a purification device配套 to the continuous purification process of the intermediate product glycolide in the production process of degradable plastics, including a glycolide storage tank 1, a dehydration tank 2, a wiped film evaporator 3, and a kneading reactor 4 connected in sequence. The refined glycolide coming out of the kneading reactor 4 is divided into two paths. One path is subjected to subsequent treatment to obtain a purified glycolide product, and the other path is returned to the wiped film evaporator 3 to be mixed with fresh polyglycolic acid for secondary purification, improving the purity and purification speed of glycolide. The subsequent treatment includes a cooling tower, a washing tower, and a drying tower connected in sequence.
[0052] Example 1
[0053] See Figure 1 and Figure 2 , the method of this embodiment is used to continuously purify the intermediate product glycolide, and the specific purification process is as follows.
[0054] 1 kg of glycolide with a purity of about 65% is sent into a water tank, 2 kg of ethyl acetate solvent is added, and it is stirred and washed for 20 min. After removing the oil stain, it is transferred to a dryer and dried at 80 °C to obtain processed glycolide particles.
[0055] After being melt-treated, the glycolide particles enter glycolide storage tank 1 and dehydration tank 2 for vacuum dehydration. Most of the dehydrated glycolide enters the scraped film evaporator 3. Under stirring, the dehydrated glycolide is mixed with fresh polyglycolic acid with a molecular weight of 300 to remove the light components from the glycolide. The light components are discharged from the top of the scraped film evaporator 3, and the glycolide without light components enters the biaxial kneading reactor 4 from the bottom of the scraped film evaporator 3. The reaction is carried out at 180°C and 1.5 kPa for 1 hour. Under vacuum, the heavy components in the glycolide are evaporated to obtain refined glycolide. The refined glycolide is divided into two parts. 2% (mass fraction) is refluxed to the scraped film evaporator 3 and mixed with fresh polyglycolic acid with a molecular weight of 400 to improve the purification efficiency. The remaining 98% of the refined glycolide is cooled, washed, and dried to obtain purified glycolide. The purity of the high-purity glycolide is greater than 98.1%, and the yield is greater than 81.4%.
[0056] Example 2
[0057] See Figure 1 and Figure 2 The intermediate product glycolide is continuously purified using the method of this embodiment. The specific purification process is as follows.
[0058] 1 kg of glycolide with a purity of approximately 65% was placed in a water tank and 2 kg of ethyl acetate was added as solvent. The mixture was stirred and washed for 20 minutes to remove the oil. After removing the oil, the product was transferred to a dryer and dried at 80°C to obtain the treated glycolide granules.
[0059] After being melt-treated, the glycolide particles enter glycolide storage tank 1 and dehydration tank 2 for vacuum dehydration. Most of the dehydrated glycolide enters the scraped-film evaporator 3. Under stirring, the dehydrated glycolide is mixed with fresh polyglycolic acid with a molecular weight of 400 to remove the light components from the glycolide. The light components are discharged from the top of the scraped-film evaporator 3, and the glycolide without light components enters the biaxial kneading reactor 4 from the bottom of the scraped-film evaporator 3. The reaction is carried out at 220°C and 1.5 kPa for 3 hours. Under vacuum, the heavy components in the glycolide are evaporated to obtain refined glycolide. The refined glycolide is divided into two parts. 1.5% (mass fraction) is refluxed to the scraped-film evaporator 3 and mixed with fresh polyglycolic acid with a molecular weight of 400 to improve the purification efficiency. The remaining 98.5% of the refined glycolide is cooled, washed, and dried to obtain purified glycolide. The purity of the high-purity glycolide is greater than 98.4%, and the yield is greater than 85%.
[0060] Example 3
[0061] See Figure 1 and Figure 2 The intermediate product glycolide is continuously purified using the method of this embodiment. The specific purification process is as follows.
[0062] The intermediate product, glycolide, is melted and then transferred to glycolide storage tank 1 and dehydration tank 2 for vacuum dehydration. Most of the dehydrated glycolide enters a scraped-film evaporator 3. Under stirring, the dehydrated glycolide is mixed with fresh polyglycolic acid (PEG) with a molecular weight of 500 to remove the light components. The light components are discharged from the top of the scraped-film evaporator 3, and the glycolide without light components enters a biaxial kneading reactor 4 from the bottom of the scraped-film evaporator 3. The reaction is carried out at 250°C and 1.5 kPa for 4 hours. Under vacuum, the heavy components in the glycolide are evaporated to obtain refined glycolide. The refined glycolide is divided into two parts. 1% (mass fraction) is refluxed to the scraped-film evaporator 3 and mixed with fresh PEG with a molecular weight of 500 to improve the purification efficiency. The remaining 99% of the refined glycolide is cooled, washed, and dried to obtain purified glycolide. The purity of the refined glycolide is greater than 98.6%, and the yield is greater than 82.7%.
[0063] To verify the purification effect, high molecular weight polyglycolic acid (PGA) was synthesized from the high-purity glycolide prepared in the above examples, and its properties were measured.
[0064] The process of synthesizing PGA from glycolide is as follows: purified glycolide is polymerized to obtain low molecular weight polyglycolic acid, which is then depolymerized; then polymerized again and depolymerized; this cycle is repeated until high molecular weight polyglycolic acid (PGA) is finally obtained.
[0065] PGA was prepared using the glycolide prepared in Examples 1 to 3 using the above method. The physical, mechanical and thermodynamic properties of the PGA were tested, as detailed in Table 1.
[0066] The performance of PGA prepared using commercially available glycolide with a purity of 97% was compared, and the test results of the comparison are shown in Table 1.
[0067] The above indicators were all tested using standard testing methods common in this industry.
[0068] Table 1 Performance results of PGA prepared from glycolide of different purities
[0069]
[0070]
[0071] As shown in Table 1, the present invention significantly reduces the use of organic solvents during purification, saving raw materials and lowering costs. Furthermore, it greatly avoids the repeated cyclic removal of impurities under high vacuum and high temperature conditions. Ethanol-derived glycolide is less prone to aggregation, effectively preventing carbon buildup. The purified glycolide has a purity of over 98% and a yield of over 80%. The purified glycolide exhibits high yield, high purity, and the synthesized PGA has a high molecular weight and good mechanical and thermodynamic properties. The purification method of the present invention has broad application prospects.
[0072] The above are preferred embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention. Any equivalent substitutions and modifications made based on the technology of the present invention should fall within the scope of protection of the present invention.
Claims
1. A continuous purification process of glycolide, an intermediate product in the production of degradable plastics, characterized in that, Includes the following steps: 1) The intermediate product glycolide is successively melted and dehydrated; 2) Mix the melt-dehydrated glycolide with polyglycolic acid at a mass ratio of 20:1 to 25:1, and send the mixture to the scraped film evaporator 3 to remove the light components from the glycolide. 3) Under vacuum, the light component of the glycolide is removed and the heavy component is removed by evaporation to obtain purified glycolide; 4) The refined glycolide is divided into two parts. One part is returned to step 3) for recycling and decomposition of heavy components, and the other part is further processed to obtain purified glycolide.
2. The process for the continuous purification of glycolide, an intermediate product in the production of degradable plastics according to claim 1, characterized in that, In the intermediate product of step 1), the content of glycolide is 65%~75%, the moisture content is 400ppm~450ppm, the content of light components is 5%~6%, and the remainder is impurities.
3. The continuous purification process for glycolide, an intermediate product in the production of biodegradable plastics, according to claim 2, is characterized in that... The impurity content of the dehydrated glycolide is not higher than 1%, and the moisture content is not higher than 200 ppm.
4. The continuous purification process for glycolide, an intermediate product in the production of degradable plastics, according to claim 3, is characterized in that... The impurity is polyglycolic acid.
5. The continuous purification process for glycolide, an intermediate product in the production of degradable plastics, according to claim 1, is characterized in that... In step 2), the molecular weight of polyglycolic acid is 300-500.
6. The continuous purification process for glycolide, an intermediate product in the production of degradable plastics, according to claim 5, is characterized in that... The content of light components in the glycolide from which light components have been removed is not higher than 50 ppm.
7. The continuous purification process for glycolide, an intermediate product in the production of biodegradable plastics, according to claim 1, is characterized in that... The conditions for evaporating and decomposing the heavy components in step 3) are: temperature 180℃~250℃, pressure 1.5KPa, and time 1h~4h.
8. The continuous purification process for glycolide, an intermediate product in the production of degradable plastics, according to claim 1, is characterized in that, In step 4), the subsequent processing includes cooling, washing, and drying in sequence.
9. The continuous purification process for glycolide, an intermediate product in the production of degradable plastics, according to any one of claims 1-8, is characterized in that, The intermediate product glycolide in step 1) needs to be pretreated before melting.
10. The continuous purification process for glycolide, an intermediate product in the production of degradable plastics, according to claim 9, is characterized in that... The pretreatment involves washing and drying the intermediate product glycolide to obtain glycolide particles; the intermediate product glycolide in step 1) is glycolide particles.