CN113292531B - Purification method of mixed lactide of meso-lactide and D, L-lactide - Google Patents
Purification method of mixed lactide of meso-lactide and D, L-lactide Download PDFInfo
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Abstract
The invention belongs to the technical field of high polymer material synthesis, and particularly relates to a purification method of mixed lactide of meso-lactide and D, L-lactide. The invention uses isopropanol as solvent to purify crude lactide by recrystallization. The method comprises the following specific steps: (1) Filtering the crude lactide to obtain a solid part A and a liquid part A; (2) Purifying the liquid fraction a with isopropanol as solvent; (3) Purifying the solid fraction a with isopropanol as solvent, steps (2) and (3) obtaining a lactide mixture containing both meso-lactide and D, L-lactide. The method can simultaneously retain meso-lactide and D, L-lactide in the crude lactide, and compared with the existing method for purifying the crude lactide by recrystallization, the method can remarkably improve the total yield of the lactide and has good application prospect.
Description
Technical Field
The invention belongs to the technical field of high polymer material synthesis, and particularly relates to a purification method of mixed lactide of meso-lactide and D, L-lactide.
Background
Polylactic acid is a degradable polyester, has excellent mechanical properties and processability, and can be used as a substitute for traditional polymer materials. Polylactic acid has been industrially produced, wherein lactide is an important raw material for industrially synthesizing polylactic acid.
The crude lactide synthesized by using D, L-lactic acid as raw material contains both racemic lactide (D, L-lactide) and meso-lactide (meso-lactide), and the ratio of meso-lactide to D, L-lactide is about 40:60. In addition, since crude lactide contains impurities such as lactic acid, lactic acid dimer, lactic acid trimer, and water, crude lactide is a solid-liquid mixture at normal temperature. In the existing polylactic acid production process, only D, L-lactide is used as a production raw material, and thus, the prior art generally purifies crude lactide with the aim of retaining D, L-lactide.
The existing crude lactide purification method mainly comprises a solvent recrystallization method and a rectification method.
The solvent recrystallization method is usually to remove the liquid portion of the solid-liquid mixture by filtration and then to recrystallize and purify the solid portion with ethanol, ethyl acetate, or the like. Since meso-lactide is readily soluble in ethanol and ethyl acetate, purified lactide generally contains only D, L-lactide, while the meso-lactide in the solid fraction is almost entirely lost with the solvent.
The rectification method is based on meso-lactide and D, L-lactide with significant differences in physical properties. The melting point of meso-lactide is 53 ℃, and the melting point of D, L-lactide is 124-128 ℃; at the same pressure, the boiling points of meso-lactide and D, L-lactide differ by about 7 ℃. And under the high vacuum condition, the volatility difference of each component in the crude lactide is utilized to carry out multiple times of partial vaporization and condensation in a rectifying tower, and finally, the low-boiling-point component is enriched in a vapor phase, and the high-boiling-point component is enriched in a liquid phase, so that the separation and the purification of each component are achieved.
However, as the art has developed, it has been found that lactide of different configurations can also be copolymerized. For example, pang et al (lactide ring-opening polymerization stereoselective catalyst: national polymer academy of articles, paper report [ C ], beijing, 2005, china) indicate that atactic and heterogeneous stereoregular polylactic acids, which are amorphous polymers, can be obtained by polymerizing meso-lactide or D, L-lactide (equimolar mixture of L-lactide and D-lactide). It has been found that by copolymerizing L-lactide with other types of lactide (D-lactide, D, L-lactide and meso-lactide), the molecular chain structure of the material can be altered, and thus the material properties can be altered.
Therefore, in some processes for producing polylactic acid, it is desirable to use a mixture of meso-lactide and D, L-lactide as production raw materials. However, in the existing crude lactide extraction process, only D, L-lactide can be remained, or the meso-lactide and D, L-lactide are required to be separated by adopting a rectification method with high cost. The prior art still lacks a simple and efficient process capable of purifying crude lactide from a mixture of meso-lactide and D, L-lactide as the retained target product.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a purification method of mixed lactide of meso-lactide and D, L-lactide, which realizes that the mixture of the purified meso-lactide and D, L-lactide is obtained by a recrystallization method.
A purification method of mixed lactide of meso-lactide and D, L-lactide comprises recrystallizing crude lactide with isopropanol as solvent.
Preferably, the method comprises the following steps:
(1) Filtering the crude lactide to obtain a solid part A and a liquid part A;
(2) Purifying the liquid part A by taking isopropanol as a solvent to obtain a lactide mixture containing meso-lactide and D, L-lactide at the same time;
(3) The solid part a was purified with isopropanol as solvent to obtain a lactide mixture containing both meso-lactide and D, L-lactide.
Preferably, the step (2) specifically includes the following steps:
(2.1) adding isopropanol into the liquid part A at 15-45 ℃, standing for more than 5 hours in an environment of-20-4 ℃, filtering, and collecting solids;
(2.2) dissolving the obtained solid in isopropanol at 15-45 ℃, standing for more than 5 hours in an environment of minus 20-4 ℃ to crystallize and separate out lactide, filtering, and collecting the solid;
and (2.3) repeating the step (2.2) for 2-5 times to obtain the product.
Preferably, in the step (2.1), the dosage volume ratio of the isopropanol to the liquid part A is (2-4): 1; and/or, in the step (2.2), the dosage ratio of the isopropanol to the solid is (1-3) 1mL/g.
Preferably, in the step (2.1), the dosage volume ratio of the isopropanol to the liquid part A is (2-3): 1; and/or, in the step (2.2), the dosage ratio of the isopropanol to the solid is (1-3) 1mL/g.
Preferably, the step (3) specifically includes the following steps:
(3.1) adding isopropanol into the solid part A at 15-45 ℃ and filtering to obtain a solid part B and a liquid part B;
(3.2) repeatedly separating the solid part B for 3-10 times according to the method of the step (3.1) to obtain pure D, L-lactide;
(3.3) combining the liquid part B obtained in the step (3.1) and all the liquid obtained in the step (3.2) to obtain a liquid part C, standing the liquid part C in an environment of-20-4 ℃ for more than 5 hours, filtering, and collecting solids;
(3.4) dissolving the obtained solid in isopropanol at 15-45 ℃, standing for more than 5 hours in an environment of minus 20-4 ℃ to crystallize and separate out lactide, filtering, and collecting the solid;
(3.5) repeating the step (3.4) for 2-5 times to obtain the lactide mixture containing the meso-lactide and the D, L-lactide.
Preferably, in the step (3.1), the dosage ratio of the isopropanol to the solid part B is (1-3): 1mL/g; and/or, in the step (3.4), the dosage ratio of the isopropanol to the solid is (1-3) 1mL/g.
Preferably, in step (3.1), the ratio of the isopropanol to the solid fraction B is 1.67:1mL/g; and/or, in step (3.4), the ratio of the isopropanol to the solid is 1.67:1mL/g.
Preferably, the crude lactide is obtained by cracking and cyclizing with D, L-lactic acid as a raw material. The total content of meso-lactide and D, L-lactide in the crude lactide is 80-90%. The impurities in the crude lactide are lactic acid, lactic acid dimer, lactic acid trimer, water and the like. The crude lactide obtained by cracking and cyclizing the raw material D, L-lactic acid, the total content of meso-lactide and D, L-lactide is usually 80-90%, and the raw material D, L-lactic acid and the raw material D, L-lactide can be purified by the method.
The invention also provides lactide obtained by the purification method.
The invention can simultaneously remove impurities in crude lactide and recover meso-lactide and D, L-lactide by using only one solvent of isopropanol, has no special requirements on equipment, is simple to operate, greatly reduces the loss of meso-lactide and also reduces the cost of lactide. In addition, in the traditional process, the liquid part separated from the crude lactide is usually treated as waste liquid no matter in the rectification method or the recrystallization method, and the invention adopts isopropanol to recover nearly 25% of pure lactide from the liquid part, wherein nearly 76% of the pure lactide is meso-lactide, thereby further improving the yield of the lactide and reducing the cost of the lactide. The recovery rate of the technology of the invention to lactide can reach 68.6%, and when the conventional purification method based on ethanol and ethyl acetate is adopted, the recovery rate of lactide is only 37.2% at most.
It should be apparent that, in light of the foregoing, various modifications, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
The above-described aspects of the present invention will be described in further detail below with reference to specific embodiments in the form of examples. It should not be understood that the scope of the above subject matter of the present invention is limited to the following examples only. All techniques implemented based on the above description of the invention are within the scope of the invention.
Drawings
FIG. 1 is a schematic flow chart of embodiment 1 of the present invention;
fig. 2 is a nuclear magnetic resonance hydrogen spectrum of lactide which is dissolved and recrystallized 3 times at 15 ℃ from the liquid portion of crude lactide.
FIG. 3 is a nuclear magnetic resonance hydrogen spectrum of lactide that was dissolved and recrystallized 3 times at 15℃from the solid portion of crude lactide.
FIG. 4 shows the lactide in Experimental example 1 1 H NMR spectrum (A: D, L-lactide; B-N: lactide obtained during the solid part repeated isopropanol recrystallization).
Detailed Description
The reagents and materials used in the examples of the present invention are commercially available.
Example 1
The purification method of this example is shown in fig. 1, and is specifically as follows:
(1) The total content of meso-lactide and D, L-lactide in the crude lactide in this example was 81%, and the impurities in the crude lactide were lactic acid, lactic acid dimer, lactic acid trimer, water, and the like. The crude lactide solid-liquid mixture was filtered to obtain a solid fraction and a liquid fraction, respectively. The solid fraction was washed 4 to 5 times with isopropanol to remove lactic acid.
(2) The liquid fraction was recrystallized from isopropanol: (1) adding isopropanol into the liquid part at 15-45 ℃, stirring and mixing uniformly, standing for more than 5 hours in an environment of-20-4 ℃, filtering and collecting solids. (2) The solid was dissolved in isopropyl alcohol at 15℃to 45 ℃ (referred to as "dissolution"), and the lactide was crystallized and precipitated by standing at-20℃to 4℃for 5 hours or more (referred to as "crystallization"), followed by filtration, and the solid was collected (referred to as "filtration"). The process of dissolving, crystallizing and filtering the obtained solid is repeated for 2 to 5 times, thus obtaining the lactide mixture containing the meso-lactide and the D, L-lactide at the same time, and realizing the recovery of the meso-lactide.
(3) The solid fraction was recrystallized from isopropanol: (1) adding isopropanol into the solid part at 15-45 ℃, dissolving a large amount of meso-lactide and a small amount of D, L-lactide into the isopropanol, and filtering to obtain a solid part and a liquid part; (2) continuing repeating the process (1)3-10 times to obtain pure D, L-lactide; (3) collecting all liquid parts in the step (1) and the step (2) according to batches, standing for more than 5 hours in an environment of minus 20 ℃ to 4 ℃, filtering, and collecting solids; (4) dissolving the solid in a certain volume of isopropanol (marked as "dissolving") at 15-45 ℃, standing for more than 5 hours at-20-4 ℃ to crystallize and separate out lactide (marked as "crystallization"), filtering, and collecting the solid (marked as "filtering"). The process of "dissolving", "crystallizing" and "filtering" the obtained solid is repeated 2 to 5 times, so as to obtain a lactide mixture containing both meso-lactide and D, L-lactide, and the recovery of meso-lactide is achieved (see fig. 3).
In the above steps, the amount of isopropyl alcohol is determined as follows:
in the step (2) of recrystallizing the liquid portion with isopropyl alcohol, the amount of isopropyl alcohol is selected: the liquid fraction contains a large amount of lactic acid, and the main purpose of adding isopropanol in step (2) (1) is to remove lactic acid and precipitate meso-lactide. The volume of the isopropyl alcohol added is 2-4 times, preferably 2-3 times, the volume of the liquid part, and 2 times is selected in the embodiment; the purpose of adding the isopropyl alcohol in the step (2) and (2) is to dissolve the solid, remove impurities, and the excessive addition of the isopropyl alcohol can cause the lactide to run off more along with the solvent, so that the recovery rate is reduced, and the ratio of the added isopropyl alcohol volume to the solid mass is preferably 1mL/g-3mL/g, and the dosage ratio in the embodiment is 1.67mL/g.
In the recrystallization of the solid portion with isopropyl alcohol in the above step (3), the amount of isopropyl alcohol is selected: the solid fraction contains mainly D, L-lactide and small amounts of meso-lactide with lactic acid. The purpose of adding isopropanol in step (3) (1) (2) is to separate lactic acid and meso-lactide from D, L-lactide to obtain pure D, L-lactide. Therefore, the ratio of the volume of isopropyl alcohol to the mass of the solid to be added is preferably 1mL/g to 3mL/g, and the ratio of the amount to be used in this example is 1.67mL/g. The solid fraction obtained in the steps (3) and (4) mainly contains meso-lactide and a small amount of D, L-lactide, and the purpose of adding isopropyl alcohol in this step is the same as that of adding isopropyl alcohol in the step (3) and (2), so that the ratio of the volume of isopropyl alcohol to the mass of the solid is preferably 1mL/g to 3mL/g, and the ratio of the amount of isopropyl alcohol to the mass of the solid in this example is preferably 1.67mL/g.
The nuclear magnetic resonance hydrogen spectrum of the lactide mixture containing meso-lactide and D, L-lactide obtained in the step (2) is shown in figure 2, wherein A is D, L-lactide, and B is lactide obtained by partially recrystallizing crude lactide liquid for 2 times. -CH of D, L-lactide 3 The double peak is positioned at delta=1.67-1.69 ppm, -CH quartet is positioned at delta=5.01-5.07 ppm, and two peak surfaces are positioned at two positionsThe product ratio was 3:1. meso-lactide is due to the-CH on both sides of its ring 3 Symmetrically distributed, the dual peaks shift to lie at δ=1.71-1.73 ppm. B in fig. 2 shows a double peak at both δ=1.67 to 1.69ppm and δ=1.71 to 1.73ppm, and-CH 3 The peak area ratio to-CH was 3:1, indicating that lactide is a mixture of D, L-lactide and meso-lactide. Recrystallizing the isopropanol to obtain lactide 1 The H NMR spectrum showed no-CH quartet of lactic acid at δ=4.34-4.40 ppm, indicating that isopropanol recrystallization can completely remove lactic acid. By calculating the-CH of meso-lactide with D, L-lactide 3 The area ratio of the double peaks can obtain the content of meso-lactide in the mixed lactide. The lactide mixture obtained in step (2) contains up to 76% meso-lactide.
The nuclear magnetic resonance hydrogen spectrum of the lactide mixture containing the meso-lactide and the D, L-lactide obtained in the step (3) is shown in figure 3, and likewise, the-CH of the meso-lactide and the D, L-lactide in the nuclear magnetic resonance hydrogen spectrum is calculated 3 The area ratio of the double peaks can obtain the content of meso-lactide in the mixed lactide. The lactide mixture obtained in step (3) contains up to 69% meso-lactide.
In the invention, the calculation method of the yield is as follows: yield after purification = mass of lactide after purification/total mass of crude lactide solid-liquid mixture. In this example, the purity of the lactide obtained was 99.9% and the total yield was 68.6%.
Experimental example 1
The experimental example examined the effect of the number of recrystallisation of the solid fraction in step (3) on the retention of lactide. FIG. 4 shows the lactide obtained during the recrystallization of the solid fraction of crude lactide with isopropanol in step (3) 1 H NMR spectrum.
According to 1 The meso-lactide content and the lactide yield of the resulting lactide were calculated by H NMR spectroscopy, and the results are shown in the following table. LA in table ri Refers to lactide obtained by ith recrystallization; d, L-lactide is a solid part obtained by filtering after adding isopropanol for the 12 th time; the total yield after recrystallization is all LA ri Sum of D, L-lactide.
TABLE 1 meso-LA content in lactide obtained by the isopropyl alcohol recrystallization method and lactide yield
The data in table 1 shows that: (1) In the initial several times of recrystallization, the yield of the obtained lactide is higher, and in the recrystallized product, the content of meso-lactide is higher, so that the lactide in the liquid obtained by filtration is necessary to be recovered; (2) The content of meso-LA in the lactide obtained is reduced from 69% to 3% along with the increase of the recrystallization times, and the lactide yield per time is gradually reduced; (3) Since the isopropyl alcohol recrystallization method retains meso-lactide and the D, L-lactide has a smaller solubility in isopropyl alcohol, the total lactide yield of example 1 (68.6%) is significantly higher than that of ethyl acetate recrystallization purification (37.5%) [ feichun, preparation and characterization of star polymers useful for drug sustained release [ D ]. Chongqing university, 2007 ].
As can be seen from the above examples and experimental examples, the purification method provided by the present invention can simultaneously retain meso-lactide and D, L-lactide in crude lactide, and compared with the existing method for purifying crude lactide by recrystallization, the present invention can significantly improve the total yield of lactide.
Claims (6)
1. A process for purifying mixed lactide of meso-lactide and D, L-lactide, characterized by: purifying the crude lactide by using isopropanol as a solvent through a recrystallization method;
the method comprises the following steps:
(1) Filtering the crude lactide to obtain a solid part A and a liquid part A;
(2) Purifying the liquid part A by taking isopropanol as a solvent to obtain a lactide mixture containing meso-lactide and D, L-lactide at the same time;
(3) Purifying the solid part A by taking isopropanol as a solvent to obtain a lactide mixture containing meso-lactide and D, L-lactide at the same time;
the step (2) specifically comprises the following steps:
(2.1) adding isopropanol into the liquid part A at 15-45 ℃, standing for more than 5 hours in an environment of-20-4 ℃, filtering, and collecting solids;
(2.2) dissolving the obtained solid in isopropanol at 15-45 ℃, standing for more than 5 hours at-20-4 ℃ to crystallize and separate out lactide, filtering, and collecting the solid;
(2.3) repeating the step (2.2) for 2-5 times to obtain the product;
the step (3) specifically comprises the following steps:
(3.1) adding isopropanol into the solid part A at 15-45 ℃ and filtering to obtain a solid part B and a liquid part B;
(3.2) repeatedly separating the solid part B for 3-10 times according to the method of the step (3.1) to obtain pure D, L-lactide;
(3.3) combining the liquid part B obtained in the step (3.1) and all the liquid obtained in the step (3.2) to obtain a liquid part C, standing the liquid part C in an environment of-20 ℃ to 4 ℃ for more than 5 hours, filtering, and collecting solids;
(3.4) dissolving the obtained solid in isopropanol at 15-45 ℃, standing for more than 5 hours at-20-4 ℃ to crystallize and separate out lactide, filtering, and collecting the solid;
and (3.5) repeating the step (3.4) for 2-5 times to obtain the lactide mixture containing the meso-lactide and the D, L-lactide.
2. The purification method according to claim 1, wherein: in the step (2.1), the dosage volume ratio of the isopropanol to the liquid part A is (2-4) 1; and/or in the step (2.2), the dosage ratio of the isopropanol to the solid is (1-3): 1mL/g.
3. The purification method according to claim 2, wherein: in the step (2.1), the dosage volume ratio of the isopropanol to the liquid part A is (2-3) 1; and/or, in step (2.2), the dosage ratio of the isopropanol to the solid is 1.67:1mL/g.
4. The purification method according to claim 1, wherein: in the step (3.1), the dosage ratio of the isopropanol to the solid part B is (1-3) 1mL/g; and/or in the step (3.4), the dosage ratio of the isopropanol to the solid is (1-3): 1mL/g.
5. The purification method according to claim 4, wherein: in step (3.1), the dosage ratio of the isopropanol to the solid part B is 1.67:1mL/g; and/or, in step (3.4), the dosage ratio of the isopropanol to the solid is 1.67:1mL/g.
6. The purification method according to claim 1, wherein: the crude lactide is obtained by taking D, L-lactic acid as raw materials for cracking and cyclizing, and the total content of meso-lactide and D, L-lactide in the crude lactide is 80-90%.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5214159A (en) * | 1987-06-16 | 1993-05-25 | Boehringer Ingelheim Gmbh | Meso-lactide |
| JPH07118259A (en) * | 1993-10-26 | 1995-05-09 | Shimadzu Corp | Method for purifying lactide and method for polymerizing the same |
| CN101157680A (en) * | 2007-11-16 | 2008-04-09 | 南京工业大学 | Method for double-solvent lactide recrystallization |
| RU2699801C1 (en) * | 2018-11-20 | 2019-09-11 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Томский государственный университет" (ТГУ, НИ ТГУ) | Lactide purification method |
-
2021
- 2021-05-20 CN CN202110554181.2A patent/CN113292531B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5214159A (en) * | 1987-06-16 | 1993-05-25 | Boehringer Ingelheim Gmbh | Meso-lactide |
| JPH07118259A (en) * | 1993-10-26 | 1995-05-09 | Shimadzu Corp | Method for purifying lactide and method for polymerizing the same |
| CN101157680A (en) * | 2007-11-16 | 2008-04-09 | 南京工业大学 | Method for double-solvent lactide recrystallization |
| RU2699801C1 (en) * | 2018-11-20 | 2019-09-11 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Томский государственный университет" (ТГУ, НИ ТГУ) | Lactide purification method |
Non-Patent Citations (5)
| Title |
|---|
| Nacnac(Bu)CuOiPr:a strained geometry resulting in very high lactide polymerization activity;Whitehorne TJJ等;《CHEMICAL COMMUNICATIONS》;第48卷(第83期);第10334-10336页 * |
| Ring opening polymerization of Rac-lactide using zinc amine-bis(phenolate) complexes;Liu Yi 等;《ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY》;第250卷;第219页 * |
| 内消旋丙交酯及其聚合物的研究进展;牛旭锋等;《高分子材料科学与工程》;第21卷(第4期);第33-36页 * |
| 内消旋丙交酯的研究进展;石英斌等;《嘉兴学院学报》;第17卷(第2期);第55-56页 * |
| 可低温加工聚乳酸的研制;胡雪雪;《中国优秀硕士学位论文全文数据库》;第1-79页 * |
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