Method for purifying p-dioxanone by coupling vacuum rectification with melt crystallization

Abstract

The invention discloses a method for purifying p-dioxanone by coupling vacuum distillation with melt crystallization, which comprises the following steps: removing light and heavy impurity components contained in a crude product of p-dioxanone by vacuum distillation, and carrying out melt crystallization, sweating and filtering on the p-dioxanone subjected to vacuum distillation purification to obtain the p-dioxanone. High-purity p-dioxanone is obtained, and uncrystallized mother liquor is returned to the step of vacuum rectification.

Description

Technical Field

[0001] The invention relates to the technical field of separation and purification in organic chemical industry, and in particular to a method for purifying p-dioxanone by coupling vacuum distillation with melt crystallization. Prior art

[0002] Polydioxanone (PPDO) is an aliphatic polyether ester. Its molecular structure contains both ester bonds and ether bonds. In addition to excellent biodegradability, it also has excellent physical and mechanical properties and thermal properties, and has excellent biodegradability and absorbability.

[0003] Para-dioxanone (PDO) is a monomer of PPDO polymer, and there are generally two synthesis processes. One is to use ethylene glycol as the raw material, chlorinated with chloroacetic acid and then dehydrated and cyclized; the other is to use diethylene glycol as the raw material and catalytically oxidize and dehydrogenate and cyclize. When used for polymerization, the para-dioxanone monomer obtained by the two processes must have a very high purity to obtain high-quality PPDO polymer. Therefore, the refining and purification of para-dioxanone monomer is particularly important.

[0004] Patent application RU2042672C1 discloses a method for purifying p-dioxanone monomer, wherein crude p-dioxanone is distilled once or twice without a catalyst to obtain a product with a purity of 99.5-99.7%, and then a small amount of boric acid is added to continue vacuum distillation to obtain p-dioxanone with a purity of 99.99%. However, this method has a low yield, and the introduction of boric acid substances is prone to side reactions at high temperatures, making it difficult to handle the residual liquid.

[0005] Patent application US5,391,707 proposes a method for producing high-purity p-dioxanone, which is to treat crude p-dioxanone with an alkyl halide under the action of pyridine to cap the hydroxyl group and then obtain high-purity p-dioxanone. However, this method has the following problems. First, benzyl bromide and pyridine are highly toxic, emit unpleasant odors, and are very harmful to the human body. In particular, benzyl bromide has a strong tear-inducing effect, while pyridine can cause infertility. Second, benzyl bromide and pyridine are not easy to be completely separated from p-dioxanone, and trace amounts of residues can still be detected in the high-purity p-dioxanone obtained by distillation.

[0006] Patent application KR100196097B1 discloses a method for purifying p-dioxanone, wherein 200-300 wt % of diphenylmethane diisocyanate (MDI) based on impurities is added to crude p-dioxanone with a purity of 90%, stirred for reaction, and vacuum distilled to obtain a pure p-dioxanone with a purity of more than 99.99%. The reaction temperature is 40-50°C and the reaction time is 3-5 hours. However, the MDI substance added in this method is toxic and harmful, has a certain degree of corrosiveness, has a strong irritating odor, needs to be stored at low temperature and filled with nitrogen, and has poor safety, which forms a sharp contrast with p-dioxanone that can be used for human body.

[0007] Patent application US5,391,768 proposes a method for purifying p-dioxanone using a solvent, wherein p-dioxanone is dissolved in an ethyl acetate aliphatic ester solvent and recrystallized to obtain p-dioxanone with a higher purity. However, since p-dioxanone is completely dissolved at around -3°C, the crystallization temperature must be lowered to -30°C, which makes it difficult to operate at room temperature and results in a low yield.

[0008] Patent application KR100301218B1 proposes a method for purifying p-dioxanone, comprising: (a) dissolving a p-dioxanone mixture in an isopropanol solvent to prepare a mixed solution; (b) crystallizing p-dioxanone from the mixed solution; (c) filtering to obtain p-dioxanone crystals with a higher purity than that of the reaction mixture; (d) repeating steps (a) to (c) to recrystallize; (e) removing isopropanol from the final product obtained in the above steps under reduced pressure and distilling to obtain high-purity p-dioxanone. By this method, p-dioxanone can be purified to more than 99.97%. However, this method also has the problems of low crystallization temperature and low product yield, and requires multiple recrystallizations, resulting in low refining efficiency.

[0009] Patent application KR100567926B1 proposes a method for purifying p-dioxanone, in which, in step (1), crude p-dioxanone is cooled and crystallized, and the cooling temperature of the crude p-dioxanone crystals is about 24°C lower than the melting point of p-dioxanone, preferably -30-20°C, in consideration of crushing and filtering. In step (2), the p-dioxanone crystals obtained in step (1) are crushed to a size of less than 1 cm using a grinder or an extruder, and then filtered under pressure or reduced pressure. When the crushed crystal size is too large, it is difficult to remove impurities mixed in the p-dioxanone crystals and much time is required. In step (3), the filtered p-dioxanone crystal particles are dried under a high vacuum at 10-24°C for 1 to 50 hours. Subsequently, in step (4), the dried p-dioxanone crystals are heated and melted, and then distilled under a reduced pressure of 0.05 to 5 torr, thereby obtaining 99.9% high-purity p-dioxanone. This method requires mechanical crushing, which is likely to cause material loss, and the high vacuum conditions are likely to cause problems such as blockage and high energy consumption.

[0010] Patent application KR100761001B1 provides a purification method, 1) after maintaining a p-dioxanone mixture at 30-40°C, adding seed crystals, cooling to 5-15°C at a cooling rate of 0.1-5°C / min to obtain p-dioxanone crystals; 2) heating the p-dioxanone crystals to 20-35°C at a rate of 0.1-0.5°C / min, and recovering high-purity p-dioxanone. In order to ensure that high-purity p-dioxanone is obtained, the cooling and heating rates of this method are low, the crystallization time is long, and the impurities of specific components in the p-dioxanone crystals are not completely removed, and a multi-stage melt crystallization process is required.

[0011] Patent application KR100675964B1 further adopts a combination of solution crystallization-melt crystallization-reduced pressure distillation. The refining process is too long, the operation is too difficult, and the reliability is reduced. In addition, in this method, since the crystallization mother liquor obtained in the solution crystallization step contains too high an impurity content, they are not suitable for being recovered and reused, so the product yield of this method is low.

[0012] Melt crystallization has high requirements on the purity of raw materials, large crystal particle size, long purification time, and it is difficult to effectively improve the purity of the product; solution crystallization has problems such as low crystallization temperature and low yield.

[0013] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a novel method for refining and purifying polydioxanone, which adopts the method of vacuum distillation coupled with melt crystallization to obtain a high-purity polydioxanone product with high yield, thereby meeting the demand for high-quality polydioxanone. Summary of the invention

[0014] The method of the present invention is based on the following research findings of the applicant: compared with the purification method for p-dioxanone in the prior art, when the p-dioxanone prepared by synthesis is first subjected to vacuum distillation to remove impurities contained therein, and then the obtained p-dioxanone is subjected to simple melt crystallization, the purity of the obtained product is significantly improved, and the purification efficiency is also more significantly improved. In addition, since the crystallization mother liquor obtained after crystallization and filtration still has a sufficiently high p-dioxanone purity and an impurity content significantly lower than 15%, the crystallization mother liquor can be directly introduced into the vacuum distillation tower alone as a raw material or introduced into the vacuum distillation tower together with the next batch of crude p-dioxanone for vacuum distillation, so that the overall recovery rate of p-dioxanone in the method of the present invention is greatly improved, exceeding 80%, or even exceeding 90%.

[0015] Therefore, the first object of the present invention is a method for purifying p-dioxanone, which comprises: removing light and heavy impurity components contained in a crude p-dioxanone product by vacuum distillation, allowing the p-dioxanone purified by distillation to enter a crystallizer for melt crystallization, filtering after the crystallization to obtain high-purity p-dioxanone, and returning the uncrystallized mother liquor to the vacuum distillation step.

[0016] Another object of the present invention is an apparatus for implementing the above purification method, which comprises a vacuum distillation device, such as a packed tower, and a melt crystallization device. DETAILED DESCRIPTION

[0017] The crude p-dioxanone used in the present invention is prepared by the above two synthesis processes: one process is to use ethylene glycol as a raw material, chlorinated with chloroacetic acid and then dehydrated and cyclized to obtain p-dioxanone; the other process is to use diethylene glycol as a raw material, and catalytic oxidation dehydrogenation cyclization is performed to obtain p-dioxanone. More specifically, the crude p-dioxanone used in the present invention is obtained by using diethylene glycol as a raw material and catalytic oxidation dehydrogenation cyclization. The purity of the crude p-dioxanone obtained by these two processes is generally 80%-95%, and the impurities are generally ethylene glycol, dioxane, dioxene, ethylene glycol acetate, diethylene glycol acetate, methoxyethanol, diethylene glycol ethyl ether, etc.

[0018] The inventor has found through research that most of the impurities in the crude p-dioxanone obtained by the above two synthesis processes have strong interference in the crystallization process of p-dioxanone, especially when the crude p-dioxanone contains a high content of impurities. Therefore, in the purification method of the prior art, it is usually necessary to perform multiple solution recrystallizations, or combine solution crystallization with melt crystallization. However, multiple recrystallizations prolong the purification time, are inefficient and have a low yield, while melt crystallization has high requirements for the purity of the raw materials, has a large crystal particle size, a long purification time, and it is difficult to effectively improve the purity of the product. The inventor has surprisingly found through research that if this crude p-dioxanone is first subjected to vacuum distillation to remove most of the interfering impurities and then subjected to melt crystallization, the crystallization efficiency of the p-dioxanone product can be more effectively improved, and the crystallization mother liquor can be introduced into the vacuum distillation tower as a raw material alone after filtration, or introduced into the vacuum distillation tower together with the next batch of crude p-dioxanone for vacuum distillation, so that the overall recovery rate of high-purity p-dioxanone in the method of the present invention is greatly improved.

[0019] According to one embodiment, the present invention relates to a method for purifying p-dioxanone by vacuum distillation coupled with melt crystallization, comprising the following steps:

[0020] 1) sending the crude p-dioxanone product to a vacuum distillation tower to perform vacuum distillation to remove light and heavy impurity components in the crude product;

[0021] 2) maintaining the temperature of the p-dioxanone purified by vacuum distillation above its melting point, entering the crystallizer, and lowering the temperature of the p-dioxanone to below its melting point for crystallization;

[0022] 3) The crystallized p-dioxanone is subjected to a temperature-raising sweating operation, the crystals are filtered out, and the uncrystallized mother liquor is recycled to the vacuum distillation step.

[0023] According to a specific embodiment, the method further comprises melting the p-dioxanone crystals to obtain a high-purity p-dioxanone product.

[0024] According to a specific embodiment, in the step 1), the purity of the crude p-dioxanone is between 80% and 95%, and more preferably between 85% and 95%.

[0025] According to a specific embodiment, in the step 1), the vacuum distillation tower can be operated in a continuous manner or in a batch manner.

[0026] According to a specific embodiment, the number of plates of the vacuum distillation tower is 1-200, and more preferably 10-100.

[0027] According to a specific embodiment, the absolute pressure of the vacuum distillation tower is about 2kPa-20kPa, preferably about 5kPa-15kPa, and more preferably about 8kPa-10kPa; the operating temperature of the vacuum distillation tower is about 60°C-200°C, and more preferably about 80°C-150°C.

[0028] According to a specific embodiment, the reflux ratio of the vacuum distillation tower is 1:1-200:1, preferably 10:1-100:1.

[0029] According to a specific embodiment, in the step 1), the purity of p-dioxanone is increased to 95%-99.5%, preferably 97%-99.5%.

[0030] According to a specific embodiment, in the step 2), the temperature of the p-dioxanone entering the crystallizer is maintained at 27°C-100°C, preferably 30°C-50°C.

[0031] According to a specific embodiment, in the step 2), the cooling rate of dioxanone is maintained at 0.1-50°C / h, preferably 1-10°C / h, and more preferably 3-8°C / h.

[0032] According to a specific embodiment, in the step 2), the crystallization temperature of dioxanone is maintained at 5°C-27°C, preferably 10°C-26°C, and more preferably 15°C-24°C.

[0033] According to a specific embodiment, in the step 2), the melt crystallization time is 5-20 hours, preferably 7-15 hours, and more preferably 8-10 hours.

[0034] According to a specific embodiment, in step 3), the heating rate of dioxanone is maintained at 0.1-50°C / h, preferably 1-10°C / h, and more preferably 3-8°C / h.

[0035] According to a specific embodiment, in step 3), the sweating temperature of dioxanone is maintained at 20°C-27°C, preferably 24°C-27°C.

[0036] According to a specific embodiment, in step 3), the purity of dioxanone is increased to above 99.8%, preferably above 99.9%.

[0037] According to a specific embodiment, the vacuum distillation device can be selected from a baffle tower, a packed tower, a sieve plate tower, a bubble tower, etc., and the melt crystallization device can be selected from a static melt crystallizer and a dynamic tower falling film melt crystallizer, etc.

[0038] In the method of the present invention, the overall recovery rate of high-purity para-dioxanone obtained is 80% or more, preferably 85% or more, and more preferably 88% or more, wherein the overall recovery rate of the product refers to the weight ratio of the total purified product actually obtained to the total purified product theoretically obtained.

[0039] Since the method of the present invention couples vacuum distillation with melt crystallization, compared with the purification method of the prior art, the method of the present invention allows high-purity p-dioxanone products to be obtained with high efficiency and high yield, and has the advantages of simple refining process flow and low refining cost. By removing different impurities through vacuum distillation and melt crystallization, the purity of p-dioxanone is greatly improved, and the energy consumption of the overall process is reduced, which has good prospects for industrial promotion.

[0040] It is understood that those skilled in the art can reasonably combine the above-mentioned different implementation schemes as needed, and the technical solutions obtained by making some non-essential improvements and adjustments to the present invention according to the content of the present invention still fall within the protection scope of the present invention. The equipment and devices used in the method of the present invention are all conventional equipment and devices in the art.

[0041] Example

[0042] The present invention will be described in detail below in conjunction with the examples, but it will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. The purity involved in this specification is by weight and is measured by liquid chromatography.

[0043] Example 1

[0044] After heating and melting 1kg of crude p-dioxanone with a purity of 85% obtained by the reaction, it is placed in a vacuum distillation tower, in which fillers are installed, and the equivalent number of plates is 20. After heating the tower to 80°C, the vacuum pump is turned on, and the absolute pressure of the vacuum distillation tower is controlled to be about 0.1 atmosphere (i.e., 10kPa), and the temperature is slowly increased at 0.5°C / min to perform vacuum distillation operation, and the reflux ratio is controlled at 10:1. First, a light impurity component with a weight ratio of 8% relative to the total weight is obtained at the top of the tower, which is discarded; then the temperature is slowly increased, so that a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone is obtained at the top of the tower, so that a heavy impurity component with a weight ratio of 12% relative to the total weight of the crude p-dioxanone is left in the tower; the purity of the p-dioxanone obtained by vacuum distillation is 97.2%.

[0045] The p-dioxanone with a purity of 97.2% obtained by distillation was heated to 40°C and introduced into a crystallizer. The crystallizer was cooled at a rate of 5°C / h to 24°C for crystallization. After 8 hours of crystallization, the crystals were heated at a rate of 1°C / h in the crystallizer to 26°C for sweating, filtered, and the mother liquor was discharged. After the sweating was completed, the p-dioxanone crystals were heated to 40°C and melted, discharged and collected, and 558g of p-dioxanone with a purity of 99.92% was obtained.

[0046] The mother liquor which was not crystallized and sweated was measured to have an impurity content of about 8%, so it was directly introduced into the vacuum distillation tower kettle together with the crude p-dioxanone with a purity of 85% of the next batch as a raw material to perform vacuum distillation and repeat the above steps. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 89%.

[0047] Example 2

[0048] After heating and melting 1kg of crude p-dioxanone with a purity of 85% obtained by the reaction, it is placed in a vacuum distillation tower, in which fillers are installed, and the equivalent number of plates is 20. After heating the tower to 80°C, the vacuum pump is turned on, and the absolute pressure of the vacuum distillation tower is controlled to be about 0.18 atmospheres (i.e., 18kPa), and the temperature is slowly increased at 0.5°C / min to perform vacuum distillation operation, and the reflux ratio is controlled at 10:1. First, a light impurity component with a weight ratio of 8% relative to the total weight is obtained at the top of the tower, which is discarded; then the temperature is slowly increased to obtain a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone at the top of the tower, so that a heavy impurity component with a weight ratio of 12% relative to the total weight of the crude p-dioxanone is left in the tower; the purity of the p-dioxanone obtained by vacuum distillation is 97%.

[0049] The p-dioxanone with a purity of 97% obtained by distillation was heated to 40°C and introduced into a crystallizer. The crystallizer was cooled at a rate of 5°C / h to 15°C for crystallization. After 8 hours of crystallization, the crystallizer was heated at a rate of 1°C / h to 26°C for sweating, filtered, and the mother liquor was discharged. After the sweating was completed, the p-dioxanone crystals were heated to 40°C and melted, discharged and collected, and 561g of p-dioxanone with a purity of 99.91% was obtained.

[0050] The mother liquor which was not crystallized and sweated was measured to have an impurity content of less than 15%, so it was directly introduced into the vacuum distillation tower kettle together with the next batch of crude p-dioxanone with a purity of 85% as a raw material to perform vacuum distillation and repeat the above steps. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 89%.

[0051] Example 3

[0052] After heating and melting 1kg of crude p-dioxanone with a purity of 85% obtained by the reaction, it is placed in a vacuum distillation tower, in which fillers are installed, and the equivalent number of plates is 15. After heating the tower to 80°C, the vacuum pump is turned on, and the absolute pressure of the vacuum distillation tower is controlled to be about 0.1 atmosphere (i.e., 10kPa), and the temperature is slowly increased at 0.5°C / min to perform vacuum distillation operation, and the reflux ratio is controlled at 10:1. First, a light impurity component with a weight ratio of 8% relative to the total weight is obtained at the top of the tower, which is discarded; then the temperature is slowly increased to obtain a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone at the top of the tower, so that a heavy impurity component with a weight ratio of 12% relative to the total weight of the crude p-dioxanone is left in the tower; the purity of the p-dioxanone obtained by vacuum distillation is 96.5%.

[0053] The p-dioxanone with a purity of 96.5% obtained by distillation was heated to 40°C and introduced into a crystallizer. The crystallizer was cooled at a rate of 5°C / h to 24°C for crystallization. After 8 hours of crystallization, the crystallizer was heated at a rate of 1°C / h to 26°C for sweating, filtered, and the mother liquor was discharged. After the sweating was completed, the p-dioxanone crystals were heated to 40°C and melted, discharged and collected, and 555g of p-dioxanone with a purity of 99.92% was obtained.

[0054] The mother liquor which was not crystallized and sweated was measured to have an impurity content of less than 15%, so it was directly introduced into the vacuum distillation tower kettle together with the next batch of crude p-dioxanone with a purity of 85% as a raw material to perform vacuum distillation and repeat the above steps. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 89%.

[0055] Example 4

[0056] After heating and melting 1kg of crude p-dioxanone with a purity of 85% obtained by the reaction, it is placed in a vacuum distillation tower, in which fillers are installed, and the equivalent number of plates is 15. After heating the tower to 80°C, the vacuum pump is turned on, and the absolute pressure of the vacuum distillation tower is controlled to be about 0.18 atmospheres (i.e., 18kPa), and the temperature is slowly increased at 0.5°C / min to perform vacuum distillation operation, and the reflux ratio is controlled at 10:1. First, a light impurity component with a weight ratio of 8% relative to the total weight is obtained at the top of the tower, which is discarded; then the temperature is slowly increased, so that a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone is obtained at the top of the tower, so that a heavy impurity component with a weight ratio of 12% relative to the total weight of the crude p-dioxanone is left in the tower; the purity of the p-dioxanone obtained by vacuum distillation is 96.0%.

[0057] The p-dioxanone with a purity of 96% obtained by distillation was heated to 40°C and introduced into a crystallizer. The crystallizer was cooled at a rate of 3°C / h to 24°C for crystallization. After 8 hours of crystallization, the crystallizer was heated at a rate of 1°C / h to 26°C for sweating, filtered, and the mother liquor was discharged. After the sweating was completed, the p-dioxanone crystals were heated to 40°C and melted, discharged and collected, and 560g of p-dioxanone with a purity of 99.91% was obtained.

[0058] The mother liquor which was not crystallized and sweated was measured to have an impurity content of less than 15%, so it was directly introduced into the vacuum distillation tower kettle together with the next batch of crude p-dioxanone with a purity of 85% as a raw material to perform vacuum distillation and repeat the above steps. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 89%.

[0059] Comparative Example C1

[0060] After heating and melting 1kg of crude p-dioxanone with a purity of 85% obtained by the reaction, it is placed in a vacuum distillation tower, in which fillers are installed, and the equivalent number of plates is 20. After heating the tower to 80°C, the vacuum pump is turned on, and the absolute pressure of the vacuum distillation tower is controlled to be about 0.5 atmospheres (i.e., 50kPa), and the temperature is slowly increased at 0.5°C / min to perform vacuum distillation operation, and the reflux ratio is controlled at 10:1. First, a light impurity component with a weight ratio of 8% relative to the total weight is obtained at the top of the tower, which is discarded; then the temperature is slowly increased, so that a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone is obtained at the top of the tower, so that a heavy impurity component with a weight ratio of 12% relative to the total weight of the crude p-dioxanone is left in the tower; the purity of the p-dioxanone obtained by vacuum distillation is 96.6%.

[0061] The p-dioxanone with a purity of 96.6% obtained by distillation was heated to 40°C and introduced into a crystallizer. The crystallizer was cooled at a rate of 3°C / h to 24°C for crystallization. After 8 hours of crystallization, the crystallizer was heated at a rate of 1°C / h to 26°C for sweating, filtered, and the mother liquor was discharged. After the sweating was completed, the p-dioxanone crystals were heated to 40°C and melted, discharged and collected, and 545g of p-dioxanone with a purity of 99.87% was obtained.

[0062] The mother liquor which was not crystallized and sweated was measured to have an impurity content of less than 15%, so it was directly introduced into the vacuum distillation tower kettle together with the next batch of crude p-dioxanone with a purity of 85% as a raw material to perform vacuum distillation and repeat the above steps. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 83%.

[0063] Comparative Example C2 (melt crystallization followed by vacuum distillation)

[0064] 1 kg of crude p-dioxanone with a purity of 85% obtained by the reaction was heated to 40°C and introduced into a crystallizer. The crystallizer was cooled at a rate of 5°C / h to 24°C for crystallization. After 8 hours of crystallization, the crystallizer was heated at a rate of 1°C / h to 26°C for sweating, filtered, and the mother liquor was discharged to obtain 578 g of p-dioxanone crystals with a purity of 98.1%. The purity of p-dioxanone in the mother liquor was measured to be less than 70%, which could not be used for recycling and was therefore discarded.

[0065] After heating and melting the obtained 578g of p-dioxanone crystals, the crystals were placed in a vacuum distillation tower, which was filled with packing and had an equivalent number of 20 plates. After heating the tower to 80°C, the vacuum pump was turned on, and the absolute pressure of the vacuum distillation tower was controlled to be about 0.1 atmosphere (i.e., 10kPa). The temperature was continued to be raised for vacuum distillation operation, and the reflux ratio was controlled to be 10:1. First, a light impurity component of 3% relative to the total weight of the p-dioxanone crystals was obtained at the top of the tower and discarded; then the temperature was continued to be slowly raised, so that a p-dioxanone fraction of 87% relative to the total weight of the p-dioxanone crystals was obtained at the top of the tower, and a heavy impurity component of 10% by weight relative to the total weight of the p-dioxanone crude product was left in the tower; about 503g of p-dioxanone with a purity of 99.9% was obtained by vacuum distillation.

[0066] Since the crystallization mother liquor contains a high content of impurities (more than 30%), it is no longer suitable for recovery and is returned to the next vacuum distillation and is discarded. Therefore, the overall recovery rate of dioxanone in this example is about 59%.

Claims

1. A method for purifying dioxanone, characterized in that: The method comprises: removing light and heavy impurity components contained in the crude p-dioxanone by vacuum distillation, subjecting the p-dioxanone purified by vacuum distillation to melt crystallization, sweating, filtering, obtaining high-purity p-dioxanone, and returning the uncrystallized mother liquor to the previous vacuum distillation step.

2. The method for purifying dioxanone according to claim 1, characterized in that: The following steps are involved: 1) sending the crude p-dioxanone product to a vacuum distillation tower to perform vacuum distillation to remove light and heavy impurity components in the crude product; 2) maintaining the temperature of the p-dioxanone purified by vacuum distillation above its melting point, entering the crystallizer, and lowering the temperature of the p-dioxanone to below its melting point for crystallization; 3) The crystallized p-dioxanone is subjected to a temperature-raising sweating operation, the crystals are filtered out, and the uncrystallized mother liquor is recycled to the vacuum distillation step.

3. The method for purifying dioxanone according to claim 2, characterized in that: The method further comprises melting the p-dioxanone crystals to obtain a high purity p-dioxanone product.

4. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 1), the number of plates of the vacuum distillation tower is 1-200, preferably 10-100; the reflux ratio of the vacuum distillation tower is 1:1-200:1, preferably 10:1-100:1; the absolute pressure of the vacuum distillation tower is about 2kPa-20kPa, preferably about 5kPa-15kPa, more preferably about 8kPa-10kPa; the operating temperature of the vacuum distillation tower is about 60°C-200°C, preferably about 80°C-150°C.

5. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 2), the temperature of the p-dioxanone entering the crystallizer is maintained at 27°C-100°C, preferably 30°C-50°C.

6. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 2), the cooling rate of dioxanone is maintained at 0.1-50°C / h, preferably 1-10°C / h.

7. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 2), the crystallization temperature of dioxanone is maintained at 5°C-27°C, preferably 20°C-26°C.

8. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 3), the heating rate of dioxanone is maintained at 0.1-50°C / h, preferably 1-10°C / h.

9. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 3), the sweating temperature of dioxanone is maintained at 20°C-27°C, preferably 24°C-27°C.

10. The method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 3), the purity of p-dioxanone is increased to above 99.8%, preferably above 99.9%.

11. An apparatus for implementing the method for purifying p-dioxanone according to any one of claims 1 to 10, comprising a vacuum distillation device and a melt crystallization device.