Method for purifying p-dioxanone through vacuum distillation coupled solution crystallization

Abstract

The invention discloses a method for purifying p-dioxanone by coupling vacuum distillation with solution crystallization, which comprises the following steps of: firstly, removing light and heavy impurities from a p-dioxanone crude product in a vacuum distillation manner; and the rectified and purified p-dioxanone enters a crystallizer to be subjected to solution crystallization operation to obtain high-purity p-dioxanone, and crystallization mother liquor is returned to vacuum rectification after the solvent is removed.

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 solution 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 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 view 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 to a solution, 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 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 the 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 0.1-1°C / min, and recovering high-purity p-dioxanone. In order to ensure the high-purity p-dioxanone, 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 solution crystallization process is required.

[0011] Patent application KR100675964B1 further adopts a combination of solution crystallization-solution 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 for reuse, 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 solution 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 solution 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 introduced into the vacuum distillation tower alone or together with the next batch of crude p-dioxanone to be introduced into the vacuum distillation tower for vacuum distillation after the solvent is removed, 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 solution crystallization, filtering after the crystallization, optionally washing the crystals with a small amount of solvent, and removing the solvent in the crystals, and returning the crystallization mother liquor obtained after filtration to the vacuum distillation step after the solvent is removed.

[0016] Another object of the present invention is an apparatus for implementing the above purification method, which comprises a vacuum distillation device, a solution crystallization device, a filtering device, a melt stripping device, and a solvent recovery device for the mother liquor. 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 recrystallizations, or combine solution crystallization with melt crystallization. However, multiple recrystallizations prolong the purification time, which is inefficient and has a low yield, while melt crystallization has high requirements for the purity of the raw materials, large crystal particle size, 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 solution 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 the solvent is removed, 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 the high-purity p-dioxanone of 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 solution 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) adding a solvent to the p-dioxanone purified by vacuum distillation to dissolve it, introducing the solution into a crystallizer, and lowering the temperature of the solution to crystallize it;

[0022] 3) filtering the crystallized 4-dioxanone, and optionally washing the crystals with a solvent to obtain a high-purity 4-dioxanone product,

[0023] 4) heating and melting the obtained p-dioxanone crystals, and performing gas stripping with gas to remove the solvent remaining in the crystals,

[0024] 5) The mother liquor obtained after filtration is returned to the vacuum distillation step after the solvent is removed.

[0025] According to a specific embodiment, in step 1), the purity of the crude p-dioxanone is between 80% and 95%, preferably between 85% and 95%.

[0026] According to a specific embodiment, in step 1), the vacuum distillation tower can be operated in a continuous manner or in a batch manner.

[0027] According to a specific embodiment, in the step 1), the number of theoretical plates of the vacuum distillation tower is 1-200, preferably 10-100.

[0028] According to a specific embodiment, in the step 1), the absolute pressure of the vacuum distillation tower is about 2 kPa-20 kPa, preferably about 5 kPa-15 kPa, and more preferably about 8 kPa-10 kPa.

[0029] According to a specific embodiment, in step 1), the operating temperature of the vacuum distillation tower is about 60°C-200°C, preferably about 80°C-150°C.

[0030] According to a specific embodiment, in the step 1), the reflux ratio of the vacuum distillation tower is 1:1-200:1, preferably 10:1-100:1.

[0031] According to a specific embodiment, in step 1), the purity of p-dioxanone is increased to 95%-99.5%, preferably 97%-99.5%.

[0032] According to a specific embodiment, in step 2), the solvent used is selected from methanol, ethanol, propanol, acetone, butanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethylene glycol methyl ether, ethylene glycol ethyl ether or a mixture thereof.

[0033] According to a specific embodiment, in the step 2), the mass ratio of the solvent to p-dioxanone is about 0.5-10, preferably about 1-5, and more preferably about 1.5-3.

[0034] According to a specific embodiment, in the step 2), p-dioxanone is dissolved in a solvent at a temperature of 28-100°C, preferably 29-50°C.

[0035] According to a specific embodiment, in step 2), the cooling rate of the solution is maintained at about 0.1-50°C / h, preferably about 3-20°C / h, more preferably about 5-10°C / h.

[0036] According to a specific embodiment, in step 2), the crystallization temperature of the solution is maintained at about 0°C-27°C, preferably about 5°C-25°C, more preferably about 10°C-20°C.

[0037] According to a specific embodiment, in step 2), the crystallization time of the solution is 5-20 hours, preferably 7-15 hours, and more preferably 8-12 hours.

[0038] According to a specific embodiment, in the step 4), a stripping tower having a theoretical plate number of 5-50, preferably a theoretical plate number of 10-20 is used.

[0039] According to a specific embodiment, in the step 4), during the gas stripping, the melt flow rate is 100-300 g / h, preferably 150-250 g / h, more preferably 200 g / h, and the gas flow rate is above 0.1 Nl / h, preferably above 0.2 Nl / h, more preferably above 1 Nl / h, and is below 20 Nl / h, preferably below 10 Nl / h.

[0040] According to a specific embodiment, in step 4), the heating and melting temperature is maintained at about 28°C-200°C, preferably about 50°C-150°C.

[0041] According to a specific embodiment, in step 4), the gas used for stripping is selected from hydrogen, nitrogen, helium, methane, ethane or a mixture thereof.

[0042] According to a specific embodiment, the crystallization mother liquor obtained in step 3) is subjected to flash evaporation or rectification operation to remove the solvent and then returned to the vacuum distillation step.

[0043] According to a specific embodiment, in step 4), the purity of the obtained dioxanone is above 99.8%, preferably above 99.9%, and more preferably above 99.93%.

[0044] 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.

[0045] In the method of the present invention, the overall recovery rate of high-purity dioxanone obtained is 80% or more, preferably 85% or more, more preferably 88% or more, or even 90% 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.

[0046] Since the method of the present invention couples vacuum distillation with solution 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 solution 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.

[0047] It is understood that those skilled in the art can reasonably combine the above-mentioned different embodiments 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 conventional equipment and devices commonly used for their purposes in the art.

[0048] Example

[0049] 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.

[0050] Example 1-1

[0051] 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%.

[0052] The p-dioxanone with a purity of 97.2% obtained by distillation was added to 800g of ethanol at 35°C and stirred to completely dissolve it. The solution was placed in a crystallizer, and the temperature of the crystallizer was reduced at a rate of 5°C / h. The temperature was reduced to 10°C and p-dioxanone seed crystals were added to crystallize for 8 hours. After the crystallization was completed, filtration was performed, and the p-dioxanone crystals obtained by filtration were washed with 100g of the above solvent. The p-dioxanone crystals obtained by filtration were heated and melted and the temperature was raised to 150°C. The melt was introduced into a stripping tower with 15 plates at a flow rate of 200g / h, and stripped with 4.0Nl / h of nitrogen to remove residual solvent and possible impurities, thereby obtaining 535g of p-dioxanone with a purity of 99.94%.

[0053] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (impurity content was about 8%, i.e., less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 88%.

[0054] Example 1-2

[0055] The operation of Example 1-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.18 atmospheres (i.e., 18000 Pa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 97.0%.

[0056] The crystallization and melt stripping steps were also carried out in the same manner as in Example 1-1, and 538 g of p-dioxanone with a purity of 99.93% was obtained after melt stripping.

[0057] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (the impurity content was still less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 87%.

[0058] Comparative Example C1

[0059] The operation of Example 1-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.5 atmospheres (i.e., 50 kPa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 95.8%.

[0060] The crystallization and melt stripping steps were also carried out in the same manner as in Example 1-1, and 531 g of p-dioxanone with a purity of 99.88% was obtained after melt stripping.

[0061] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (the impurity content was still less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 84%.

[0062] Comparative Example C2 (Solution Crystallization followed by Rectification)

[0063] 1 kg of crude p-dioxanone with a purity of 85% obtained by the reaction was added to 800 g of ethanol and stirred to completely dissolve it. The solution was placed in a crystallizer, and the crystallizer was cooled at a rate of 5°C / h. The temperature was reduced to 10°C and p-dioxanone seed crystals were added to crystallize for 8 hours. After the crystallization was completed, the p-dioxanone crystals obtained by filtration were washed with 100 g of ethanol. 588 g of p-dioxanone crystals were obtained with a purity of 97.0%.

[0064] After heating and melting the obtained 588g 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 512g of p-dioxanone with a purity of 99.89% was obtained by vacuum distillation.

[0065] 512 g of p-dioxanone obtained by vacuum distillation was melted and heated to 150° C., and the melt was introduced into a stripping tower with 15 plates at a flow rate of 200 g / h, and stripped with 4.0 Nl / h of nitrogen to remove residual solvent and possible impurities, thereby obtaining 502 g of p-dioxanone with a purity of 99.92%.

[0066] Since the crystallization mother liquor obtained after filtration contains a high content of impurities (more than 35%), it is no longer suitable for recovery for vacuum distillation and is discarded. Therefore, the overall recovery rate of dioxanone in the method of this embodiment is about 59%.

[0067] Example 2-1

[0068] The operation of Example 1-1 was repeated, except that propanol was used as the solvent in the solution crystallization step, and 555 g of a 4-dioxanone product with a purity of 99.92% was obtained after melt stripping.

[0069] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (the impurity content was still less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 88%.

[0070] Example 2-2

[0071] The operation of Example 2-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.18 atmospheres (i.e., 18000 Pa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 97.0%.

[0072] The crystallization and melt stripping steps were also carried out in the same manner as in Example 2-1, and 548 g of p-dioxanone with a purity of 99.92% was obtained after melt stripping.

[0073] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 87%.

[0074] Comparative Example C3

[0075] The operation of Example 2-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.5 atmospheres (i.e., 50 kPa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 95.8%.

[0076] The crystallization and melt stripping steps were also carried out in the same manner as in Example 2-1, and 555 g of p-dioxanone with a purity of 99.89% was obtained after melt stripping.

[0077] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent, it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 83%.

[0078] Comparative Example C4 (Solution Crystallization followed by Rectification)

[0079] 1 kg of crude p-dioxanone with a purity of 85% obtained by the reaction was added to 800 g of propanol and stirred to completely dissolve it. The solution was placed in a crystallizer, and the crystallizer was cooled at a rate of 5°C / h. The temperature was reduced to 10°C and p-dioxanone seed crystals were added to crystallize for 8 hours. After the crystallization was completed, the p-dioxanone crystals were filtered and washed with 100 g of propanol. 593 g of p-dioxanone crystals were obtained with a purity of 97.0%.

[0080] After heating and melting the obtained 593g 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 516g of p-dioxanone with a purity of 99.9% was obtained by vacuum distillation.

[0081] 516 g of p-dioxanone obtained by vacuum distillation was heated to melt and the temperature was raised to 150° C., and the melt was introduced into a stripping tower with 15 plates at a flow rate of 200 g / h, and stripped with 4.0 Nl / h of nitrogen to remove residual solvent and possible impurities, thereby obtaining 506 g of p-dioxanone with a purity of 99.93%.

[0082] Since the crystallization mother liquor obtained after filtration contains a high content of impurities (more than 35%), it is no longer suitable for recovery for vacuum distillation and is discarded. Therefore, the overall recovery rate of dioxanone in the method of this embodiment is about 60%.

[0083] Example 3-1

[0084] The operation of Example 1-1 was repeated, except that butanone was used as the solvent in the solution crystallization step, and 552 g of a 4-dioxanone product with a purity of 99.93% was obtained after melt stripping.

[0085] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (the impurity content was still less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 88%.

[0086] Example 3-2

[0087] The operation of Example 3-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.18 atmospheres (i.e., 18000 Pa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 97.0%.

[0088] The crystallization and melt stripping steps were also carried out in the same manner as in Example 3-1, and 549 g of p-dioxanone with a purity of 99.92% was obtained after melt stripping.

[0089] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 87%.

[0090] Comparative Example C5

[0091] The operation of Example 3-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.5 atmospheres (i.e., 50 kPa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 95.8%.

[0092] The crystallization and melt stripping steps were also carried out in the same manner as in Example 3-1, and 537 g of p-dioxanone with a purity of 99.89% was obtained after melt stripping.

[0093] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 83%.

[0094] Comparative Example C6 (Solution Crystallization followed by Rectification)

[0095] 1 kg of crude p-dioxanone with a purity of 85% obtained by the reaction was added to 800 g of butanone and stirred to completely dissolve it. The solution was placed in a crystallizer, and the crystallizer was cooled at a rate of 5°C / h. The temperature was reduced to 10°C and p-dioxanone seed crystals were added to crystallize for 8 hours. After the crystallization was completed, the p-dioxanone crystals obtained by filtration were washed with 100 g of butanone. 603 g of p-dioxanone crystals were obtained with a purity of 97.1%.

[0096] After heating and melting the obtained 603g 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 525g of p-dioxanone with a purity of 99.90% was obtained by vacuum distillation.

[0097] 525 g of p-dioxanone obtained by vacuum distillation was heated to melt and the temperature was raised to 150° C., and the melt was introduced into a stripping tower with 15 plates at a flow rate of 200 g / h, and stripped with 4.0 Nl / h of nitrogen to remove residual solvent and possible impurities, thereby obtaining 515 g of p-dioxanone with a purity of 99.91%.

[0098] Since the crystallization mother liquor obtained after filtration contains a high content of impurities (more than 35%), it is no longer suitable for recovery for vacuum distillation and is discarded. Therefore, the overall recovery rate of dioxanone in the method of this embodiment is about 60.5%.

[0099] Example 4-1

[0100] The operation of Example 1-1 was repeated, except that propyl acetate was used as the solvent in the solution crystallization step, and 575 g of a 4-dioxanone product with a purity of 99.93% was obtained after melt stripping.

[0101] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (the impurity content was still less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 88%.

[0102] Example 4-2

[0103] The operation of Example 4-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.18 atmospheres (i.e., 18000 Pa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 97.0%.

[0104] The crystallization and melt stripping steps were also carried out in the same manner as in Example 4-1, and 571 g of p-dioxanone with a purity of 99.92% was obtained after melt stripping.

[0105] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 87%.

[0106] Comparative Example C7

[0107] The operation of Example 4-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.5 atmospheres (i.e., 50 kPa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 95.8%.

[0108] The crystallization and melt stripping steps were also carried out in the same manner as in Example 4-1, and 563 g of p-dioxanone with a purity of 99.89% was obtained after melt stripping.

[0109] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 83%.

[0110] Comparative Example C8 (Solution Crystallization followed by Rectification)

[0111] 1 kg of crude p-dioxanone with a purity of 85% obtained by the reaction was added to 800 g of propyl acetate and stirred to completely dissolve it. The solution was placed in a crystallizer, and the crystallizer was cooled at a rate of 5°C / h. The temperature was reduced to 10°C and p-dioxanone seed crystals were added to crystallize for 8 hours. After the crystallization was completed, the p-dioxanone crystals were filtered and washed with 100 g of propyl acetate. 598 g of p-dioxanone crystals were obtained with a purity of 96.9%.

[0112] After heating and melting the obtained 598g 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 521g of p-dioxanone with a purity of 99.90% was obtained by vacuum distillation.

[0113] 521 g of p-dioxanone obtained by vacuum distillation was melted and heated to 150° C., and the melt was introduced into a stripping tower with 15 plates at a flow rate of 200 g / h, and stripped with 4.0 Nl / h of nitrogen to remove residual solvent and possible impurities, thereby obtaining 510 g of p-dioxanone with a purity of 99.93%.

[0114] Since the crystallization mother liquor obtained after filtration contains a high content of impurities (more than 35%), it is no longer suitable for recovery for vacuum distillation and is discarded. Therefore, the overall recovery rate of dioxanone in this example is about 60%.

[0115] Example 5-1

[0116] The operation of Example 1-1 was repeated, except that ethylene glycol methyl ether was used as the solvent in the solution crystallization step, and 573 g of a 4-dioxanone product with a purity of 99.93% was obtained after melt stripping.

[0117] After the crystallization mother liquor obtained by filtration was subjected to a flash evaporation operation to remove the solvent (the impurity content was still less than 15%), it was introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps were repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment was about 88%.

[0118] Example 5-2

[0119] The operation of Example 5-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.18 atmospheres (i.e., 18000 Pa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 97.0%.

[0120] The crystallization and melt stripping steps were also carried out in the same manner as in Example 5-1, and 570 g of p-dioxanone with a purity of 99.92% was obtained after melt stripping.

[0121] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 87%.

[0122] Comparative Example C9

[0123] The operation of Example 5-1 was repeated, except that the absolute pressure of the vacuum distillation tower was controlled to be about 0.5 atmospheres (i.e., 50 kPa). A light component with a weight ratio of 8% relative to the total weight was obtained at the top of the tower, and a p-dioxanone fraction accounting for 80% of the total weight of the crude p-dioxanone was obtained at the top of the tower, and a heavy component with a weight ratio of 12% relative to the total weight was left in the bottom of the tower; the purity of the p-dioxanone obtained by the vacuum distillation was 95.8%.

[0124] The crystallization and melt stripping steps were also carried out in the same manner as in Example 5-1, and 555 g of p-dioxanone with a purity of 99.89% was obtained after melt stripping.

[0125] After the crystallization mother liquor obtained by filtration is subjected to flash evaporation or rectification operation to remove the solvent (the impurity content is still less than 15%), it is introduced into a vacuum distillation column together with the next batch of crude p-dioxanone with a purity of 85% for vacuum distillation and the above steps are repeated. Therefore, the overall recovery rate of p-dioxanone in the method of this embodiment is about 83%.

[0126] Comparative Example C10 (Solution Crystallization followed by Rectification)

[0127] 1 kg of crude p-dioxanone with a purity of 85% obtained by the reaction was added to 800 g of ethylene glycol methyl ether and stirred to completely dissolve it. The solution was placed in a crystallizer, and the crystallizer was cooled at a rate of 5°C / h. The temperature was reduced to 10°C and p-dioxanone seed crystals were added to crystallize for 8 hours. After the crystallization was completed, the p-dioxanone crystals obtained by filtration were washed with 100 g of ethylene glycol methyl ether. 591 g of p-dioxanone crystals were obtained with a purity of 97.1%.

[0128] After heating and melting the obtained 591g 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 513g of p-dioxanone with a purity of 99.90% was obtained by vacuum distillation.

[0129] 513 g of p-dioxanone obtained by vacuum distillation was melted and heated to 150° C., and the melt was introduced into a stripping tower with 15 plates at a flow rate of 200 g / h, and stripped with 4.0 Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 501 g of p-dioxanone with a purity of 99.92%.

[0130] Since the crystallization mother liquor obtained after filtration contains a high content of impurities (more than 35%), it is no longer suitable for recovery for vacuum distillation and is discarded. Therefore, the overall recovery rate of p-dioxanone in this example is about 59%.

Claims

1. A method for purifying p-dioxanone, the method comprising: The light and heavy impurity components contained in the crude p-dioxanone are removed by vacuum distillation, the p-dioxanone purified by vacuum distillation is subjected to solution crystallization, and then filtered, the crystals are optionally washed with a small amount of solvent, and the solvent in the crystals is removed, and the crystallization mother liquor after filtration is returned to the previous vacuum distillation step after the solvent is removed.

2. A method for purifying dioxanone according to claim 1, characterized in that: The following steps are involved: 1) feeding the crude p-dioxanone into a vacuum distillation tower to perform vacuum distillation to remove light and heavy impurity components contained in the crude product; 2) adding a solvent to the p-dioxanone purified by vacuum distillation to dissolve it, introducing the solution into a crystallizer, and lowering the temperature of the solution to crystallize it; 3) filtering the crystallized dioxanone, and optionally washing the crystals with a solvent, 4) heating and melting the obtained p-dioxanone crystals, and performing gas stripping with gas to remove the solvent remaining in the crystals; 5) The mother liquor obtained by filtration is returned to the vacuum distillation step after the solvent is removed.

3. A method for purifying dioxanone according to claim 2, characterized in that: In step 1), the purity of the crude p-dioxanone is between 80% and 95%, preferably between 85% and 95%.

4. A method for purifying dioxanone according to claim 2 or 3, characterized in that: In step 1), the number of theoretical plates of the vacuum distillation tower is 1-200, preferably 10-100.

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

6. A method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 2), the solvent used is selected from methanol, ethanol, propanol, acetone, butanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethylene glycol methyl ether, ethylene glycol ethyl ether or a mixture thereof.

7. A method for purifying dioxanone according to claim 2 or 3, characterized in that: In step 2), the cooling rate of the solution is maintained at 0.1-50°C / h, preferably 3-20°C / h.

8. A method for purifying dioxanone according to claim 2 or 3, characterized in that: In step 2), the crystallization temperature of p-dioxanone is maintained at 5°C-25°C, preferably 10°C-20°C.

9. A method for purifying dioxanone according to claim 2 or 3, characterized in that: In step 4), the heating and melting temperature is maintained at 28°C-200°C, preferably 50°C-150°C.

10. A method for purifying p-dioxanone according to claim 2 or 3, characterized in that: In step 4), the gas used for stripping is selected from hydrogen, nitrogen, helium, methane, ethane or a mixture thereof.

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, a solution crystallization device, a filtration device, a melt stripping device, and a solvent recovery device for mother liquor.