Method for purifying p-dioxanone

Abstract

The invention discloses a method for purifying p-dioxanone, which comprises the following steps of: fully mixing a p-dioxanone crude product with certain purity with a certain amount of extracting solvent at a temperature higher than the melting point of the p-dioxanone, standing and layering at a certain temperature after mixing, and separating to obtain the p-dioxanone. And after the layering is finished, reducing the temperature of the system to below the melting point of p-dioxanone, starting crystallization, filtering after the crystallization is finished, and removing the solvent in the crystal to obtain the high-purity p-dioxanone product. The invention also relates to a device for carrying out such a purification method.

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 using an extraction crystallization method. Background 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 process uses ethylene glycol as the raw material, chloroacetic acid is hydrochlorinated and then dehydrated and cyclized; the other process uses diethylene glycol as the raw material and is obtained by catalytic oxidation dehydrogenation and cyclization. When used for polymerization, the para-dioxanone monomer obtained by both 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. Crystallization is an effective means of material purification, and it has low energy consumption. Melt crystallization or solution crystallization is often used to purify para-dioxanone.

[0004] 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.

[0005] 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.

[0006] KR100567926B1 proposes a method for purifying p-dioxanone, in which, in step (1), crude p-dioxanone is cooled and crystallized, and in view of crushing and filtering, 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 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.

[0007] 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 0.1-1°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.

[0008] KR100675964B1 further adopts a combination of solution crystallization-melt crystallization-vacuum distillation. The refining process is too long, the operation is too difficult, and the reliability is reduced.

[0009] However, 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, long crystallization time and low yield.

[0010] In view of the shortcomings of the prior art, the object of the present invention is to provide a novel method for purifying polydioxanone, which is simple to operate and allows high-purity polydioxanone products to be obtained with high efficiency and high yield, thereby meeting the demand for preparing high-quality polydioxanone. Summary of the invention

[0011] After studying the purification method of p-dioxanone prepared by the above two synthesis processes, the applicant surprisingly found that if the impurities contained in the p-dioxanone prepared in this way are first extracted and then the p-dioxanone is crystallized at room temperature, the purity of the product obtained after crystallization is significantly improved, and the purification efficiency and yield are also significantly improved.

[0012] Therefore, the first object of the present invention is a method for purifying p-dioxanone, which comprises: fully mixing a crude p-dioxanone with an extraction solvent at a temperature higher than the melting point of the p-dioxanone, wherein the extraction solvent is used to extract impurities contained in the crude p-dioxanone, allowing the mixture to stand for stratification after mixing, and after stratification, optionally discharging most of the extraction solvent, cooling the system to a temperature lower than the melting point of the p-dioxanone for crystallization, filtering after the crystallization, optionally washing the crystals with a small amount of extraction solvent, and removing the solvent in the crystals.

[0013] Another object of the present invention is an apparatus for implementing the above purification method, which comprises an extraction device, a crystallization device, a filtration device and a melt stripping device. DETAILED DESCRIPTION

[0014] The present invention will now be described in detail by way of the following specific embodiments.

[0015] The crude p-dioxanone used in the present invention is prepared by the following two synthetic processes known to those skilled in the art: one process uses ethylene glycol as a raw material, chlorinated with chloroacetic acid, and then undergoes dehydration cyclization to obtain p-dioxanone; the other process uses diethylene glycol as a raw material, and undergoes catalytic oxidation dehydrogenation cyclization 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 undergoing catalytic oxidation dehydrogenation cyclization. The purity of the crude p-dioxanone obtained by these two processes is generally 80%-97%, and the impurities contained are generally ethylene glycol, dioxane, dioxene, ethylene glycol acetate, diethylene glycol acetate, methoxyethanol, diethylene glycol ethyl ether, etc.

[0016] According to a particular embodiment, the removal of the solvent in the crystals is carried out by stripping by passing a gas through the dioxanone melt.

[0017] According to a particular embodiment, the present invention relates to a method for purifying dioxanone, comprising the following steps:

[0018] 1) mixing the crude p-dioxanone with an extraction solvent in a certain proportion at a temperature higher than the melting point of p-dioxanone, and then allowing the mixture to stand for stratification at the temperature; and optionally separating and removing most of the extraction solvent phase containing impurities;

[0019] 2) cooling the system to a temperature lower than the melting point of p-dioxanone to perform crystallization;

[0020] 3) After the crystallization is completed, filter to remove the extraction solvent, and optionally wash the crystals with the extraction solvent in step 1, and then

[0021] 4) heating and melting the crystals, and introducing gas into the melt for stripping to remove the solvent in the crystals, thereby obtaining a high-purity dioxanone product;

[0022] 5) Optionally subjecting the extraction solvent containing impurities to flash or distillation to recover the extraction solvent.

[0023] According to a particular embodiment, in step 1), the purity of the crude p-dioxanone is between 80% and 97%, preferably between 85% and 97%.

[0024] According to a particular embodiment, in step 1), the extraction solvent is selected from butanol, amyl alcohol, isopropyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl tert-amyl ether, methyl isobutyl ketone or a mixture thereof.

[0025] According to a particular embodiment, in step 1), the weight ratio of the extraction solvent to p-dioxanone is about 0.5-10, preferably about 0.5-5, more preferably about 0.8-2, most particularly about 1.

[0026] According to a particular embodiment, in the step 1), the mixing and stratification temperature is maintained at about 27°C-80°C, preferably about 30°C-50°C.

[0027] According to a particular embodiment, in the step 1), the standing and stratification time is about 0.5-3 hours, preferably about 1-2 hours.

[0028] According to a particular embodiment, in step 2), the cooling rate of the system is maintained at about 0.1-50°C / h, preferably about 1-10°C / h, more preferably about 3-7°C / h, most particularly about 5°C / h.

[0029] According to a particular embodiment, in step 2), the crystallization temperature of the system is maintained at about 0°C-26°C, preferably about 5°C-25°C, more preferably about 10°C-25°C, most particularly about 15°C-20°C.

[0030] According to a particular embodiment, in step 2), the crystallization time of the system is about 2-20 hours, preferably about 4-15 hours, more preferably about 5-12 hours, most particularly about 6-10 hours.

[0031] According to a particular embodiment, in step 4), the heating and melting temperature is maintained at 28°C-200°C, preferably 50°C-150°C.

[0032] According to a particular embodiment, in step 4), the stripping gas is selected from hydrogen, nitrogen, helium, methane, ethane or a mixture thereof.

[0033] According to a particular embodiment, in step 4), the purity of the obtained p-dioxanone is above 99.7%, preferably above 99.8%, and more preferably above 99.9%.

[0034] According to a particular embodiment, in the step 4), the stripping column used has a theoretical plate number of 5-50, preferably a theoretical plate number of 10-20.

[0035] According to a particular 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.

[0036] According to a particular embodiment, step 1), step 2) and / or step 3) are implemented in a thermostatic separating funnel with a jacket.

[0037] According to a particular embodiment, at a constant temperature higher than the melting point of dioxanone, dioxanone and an extracting solvent are uniformly mixed in a constant temperature separating funnel with a jacket, and then allowed to stand for separation; optionally, most of the extracting solvent phase is discharged, and the system is cooled to a constant temperature lower than the melting point of dioxanone to crystallize p-dioxanone; after the crystallization is completed, since the p-dioxanone crystals grow into a self-supporting network structure, at least most of the extracting solvent can be directly discharged from the bottom; the crystals are then washed with a small amount of fresh extracting solvent to remove liquid containing impurities on the surface; the jacket temperature is increased to melt the crystals, and the melt is introduced from the top of the stripping tower into a stripping tower equipped with fillers, and gas is introduced from the bottom of the stripping tower to perform a stripping operation, wherein the temperature in the stripping tower is maintained higher than the melting point of p-dioxanone; and the pure PDO product from which the solvent has been removed is collected at the bottom of the stripping tower.

[0038] According to a particular embodiment, the apparatus for implementing the above-mentioned method for purifying dioxanone comprises an extraction device, a crystallization device, a filtration device and a melt stripping device.

[0039] According to a particular embodiment, the extraction device, crystallization device and / or filtration device is a jacketed thermostatic separatory funnel.

[0040] Since the present invention uses extraction crystallization and melt stripping to purify p-dioxanone, compared with 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 characteristics of simple refining process flow and low refining cost. Compared with the melt crystallization method, the method of the present invention has a faster crystallization speed and simpler operation; compared with the solution crystallization method, the method of the present invention has a higher yield of p-dioxanone products and higher efficiency.

[0041] It is understood that those skilled in the art can reasonably combine the above-mentioned different embodiments as needed, and some non-essential improvements and adjustments made to the present invention according to the content of the present invention still fall within the scope of protection 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.

[0042] Example

[0043] The embodiments of the present invention will be described in detail below in conjunction with examples, but those skilled in the art will understand 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.

[0044] Example I-1

[0045] In a constant temperature separating funnel with a jacket, 800 g of butanol was added to 800 g of p-dioxanone with a purity of 97% and mixed thoroughly at 50° C. The mixture was cooled to 30° C. for static stratification. After the stratification was completed, the system continued to cool at a rate of 5° C. / h, and the temperature was reduced to 24° C. for crystallization, and the crystallization time was 7 hours. After the crystallization was completed, the liquid phase was removed by filtration, and the crystals were washed with 200 g of butanol. The p-dioxanone crystals obtained by filtration were heated and melted to 150° C., and the melt was introduced into a stripping tower with a theoretical plate number of 15 at a flow rate of 200 g / h, and stripped with 4.0 Nl / h of nitrogen to remove residual solvents and possible impurities, to obtain 512.5 g of high-purity p-dioxanone, and the purity determined by gas chromatography was 99.93%.

[0046] Example I-2

[0047] The experiment was repeated according to the operation mode of the above-mentioned Example I-1, except that: after the separation was completed, the system was cooled at a rate of 10°C / h to 15°C for crystallization. After the crystallization was completed, the liquid phase was removed by filtration, and the crystals were washed with 200g of butanol. The filtered p-dioxanone crystals were heated and melted to 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 2Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 610g of high-purity p-dioxanone, the purity of which was 99.91% as determined by gas chromatography.

[0048] Example I-3

[0049] The experiment was repeated according to the above Example I-1, except that after the separation, the system was cooled at a rate of 5°C / h to 15°C for crystallization. After the crystallization was completed, the liquid phase was removed by filtration, and the crystals were washed with 200g of butanol. The filtered p-dioxanone crystals were heated and melted to 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 2.5Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 589.3g of high-purity p-dioxanone, the purity of which was 99.92% as determined by gas chromatography.

[0050] Example I-4

[0051] The experiment was repeated according to the above Example I-1, except that after the separation, the system was cooled at a rate of 10°C / h to 5°C for crystallization. After the crystallization was completed, the liquid phase was removed by filtration, and the crystals were washed with 200g of butanol. The filtered p-dioxanone crystals were heated and melted to 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 1.5Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 632g of high-purity p-dioxanone, the purity of which was 99.90% as determined by gas chromatography.

[0052] Example II-1

[0053] In a constant temperature separating funnel with a jacket, 800 g of amyl alcohol was added to 800 g of p-dioxanone with a purity of 97% and mixed thoroughly at 60° C. The mixture was cooled to 40° C. for static stratification. After the stratification was completed, the system continued to cool at a rate of 5° C. / h, and the temperature was reduced to 20° C. for crystallization, and the crystallization time was 7 hours. After the crystallization was completed, it was filtered and the crystals were washed with 200 g of amyl alcohol. The p-dioxanone crystals obtained by filtration were heated and melted to 150° C., and the melt was introduced into a stripping tower with a theoretical plate number of 15 at a flow rate of 200 g / h, and stripped with 4 Nl / h of nitrogen to remove residual solvents and possible impurities, to obtain 584.1 g of high-purity p-dioxanone, and the purity determined by gas chromatography was 99.92%.

[0054] Example II-2

[0055] The experiment was repeated according to the above Example II-1, except that after the separation, the system was cooled at a rate of 10°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of amyl alcohol. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 1.5Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 661.6g of high-purity p-dioxanone, the purity of which was 99.91% as determined by gas chromatography.

[0056] Example II-3

[0057] The experiment was repeated according to the above Example II-1, except that after the separation, the system was cooled at a rate of 5°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of amyl alcohol. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 2.5Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 628.6g of high-purity p-dioxanone, the purity of which was 99.92% as determined by gas chromatography.

[0058] Example II-4

[0059] The experiment was repeated according to the above Example II-1, except that after the separation, the system was cooled at a rate of 10°C / h to 5°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of amyl alcohol. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 1Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 668.0g of high-purity p-dioxanone, the purity of which was 99.90% as determined by gas chromatography.

[0060] Example III-1

[0061] In a constant temperature separating funnel with a jacket, 800 g of methyl tert-butyl ether was added to 800 g of p-dioxanone with a purity of 97% and mixed thoroughly at 40° C. The mixture was cooled to 30° C. for static stratification. After the stratification was completed, the system continued to cool at a rate of 5° C. / h, and the temperature was reduced to 10° C. for crystallization, and the crystallization time was 7 hours. After the crystallization was completed, it was filtered and the crystals were washed with 200 g of methyl tert-butyl ether. The p-dioxanone crystals obtained by filtration were heated and melted to 150° C., and the melt was introduced into a stripping tower with a theoretical plate number of 15 at a flow rate of 200 g / h, and 1 Nl / h of nitrogen was used for stripping to remove residual solvents and possible impurities, and 660.0 g of high-purity p-dioxanone was obtained, and the purity determined by gas chromatography was 99.9%.

[0062] Example III-2

[0063] The experiment was repeated according to the above Example III-1, except that after the separation, the system was cooled at a rate of 5°C / h to 24°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of methyl tert-butyl ether. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 4Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 498g of high-purity p-dioxanone, the purity of which was 99.93% as determined by gas chromatography.

[0064] Example III-3

[0065] The experiment was repeated according to the above Example III-1, except that after the separation, the system was cooled at a rate of 5°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of methyl tert-butyl ether. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 3Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 520g of high-purity p-dioxanone, the purity of which was 99.92% as determined by gas chromatography.

[0066] Example III-4

[0067] The experiment was repeated according to the above Example III-1, except that after the separation, the system was cooled at a rate of 10°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of methyl tert-butyl ether. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 2Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 569.6g of high-purity p-dioxanone, the purity of which was 99.91% as determined by gas chromatography.

[0068] Example IV-1

[0069] In a constant temperature separating funnel with a jacket, 800 g of methyl tert-amyl ether was added to 800 g of p-dioxanone with a purity of 97% and mixed thoroughly at 40° C. The mixture was cooled to 30° C. for static stratification. After the stratification was completed, the system continued to cool at a rate of 5° C. / h, and the temperature was reduced to 10° C. for crystallization, and the crystallization time was 7 hours. After the crystallization was completed, it was filtered and the crystals were washed with 200 g of methyl tert-amyl ether. The p-dioxanone crystals obtained by filtration were heated and melted to 150° C., and the melt was introduced into a stripping tower with a theoretical plate number of 15 at a flow rate of 200 g / h, and stripped with 4 Nl / h of nitrogen to remove residual solvents and possible impurities, to obtain 508.9 g of high-purity p-dioxanone, and the purity determined by gas chromatography was 99.92%.

[0070] Example IV-2

[0071] The experiment was repeated according to the above Example IV-1, except that after the separation, the system was cooled at a rate of 5°C / h to 24°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of tert-amyl methyl ether. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 2.5Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 560.1g of high-purity p-dioxanone, the purity of which was 99.91% as determined by gas chromatography.

[0072] Example IV-3

[0073] The experiment was repeated according to the above Example IV-1, except that after the separation, the system was cooled at a rate of 5°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of tert-amyl methyl ether. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 3.5Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 512.1g of high-purity p-dioxanone, the purity of which was 99.92% as determined by gas chromatography.

[0074] Example IV-4

[0075] The experiment was repeated according to the above Example IV-1, except that after the separation, the system was cooled at a rate of 10°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of tert-amyl methyl ether. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 1Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 632.0g of high-purity p-dioxanone, the purity of which was 99.90% as determined by gas chromatography.

[0076] Example V-1

[0077] In a thermostatic separatory funnel with a jacket, 800 g of methyl isobutyl ketone was added to 800 g of p-dioxanone with a purity of 97% and mixed thoroughly at 40° C. The mixture was cooled to 30° C. for static stratification. After the stratification was completed, the system continued to cool at a rate of 5° C. / h, and the temperature was reduced to 24° C. for crystallization, and the crystallization time was 7 hours. After the crystallization was completed, it was filtered and the crystals were washed with 200 g of methyl isobutyl ketone. The p-dioxanone crystals obtained by filtration were heated and melted to 150° C., and the melt was introduced into a stripping tower with a theoretical plate number of 15 at a flow rate of 200 g / h, and stripped with 3.5 Nl / h of nitrogen to remove residual solvents and possible impurities, to obtain 524 g of high-purity p-dioxanone, and the purity determined by gas chromatography was 99.93%.

[0078] Example V-2

[0079] The experiment was repeated according to the above Example V-1, except that after the separation, the system was cooled at a rate of 10°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of methyl isobutyl ketone. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 2Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 584.0g of high-purity p-dioxanone, the purity of which was 99.91% as determined by gas chromatography.

[0080] Example V-3

[0081] The experiment was repeated according to the above Example V-1, except that after the separation, the system was cooled at a rate of 5°C / h to 15°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of methyl isobutyl ketone. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 3Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 528.3g of high-purity p-dioxanone, the purity of which was 99.92% as determined by gas chromatography.

[0082] Example V-4

[0083] The experiment was repeated according to the above Example V-1, except that after the separation, the system was cooled at a rate of 10°C / h to 5°C for crystallization. After the crystallization was completed, the system was filtered and the crystals were washed with 200g of methyl isobutyl ketone. The filtered p-dioxanone crystals were heated to melt at 150°C, and the melt was introduced into a stripping tower with 15 theoretical plates at a flow rate of 200g / h, and stripped with 1Nl / h of nitrogen to remove residual solvent and possible impurities, to obtain 648.0g of high-purity p-dioxanone, the purity of which was 99.90% as determined by gas chromatography.

[0084] Example V-5 (without melt stripping):

[0085] In a constant temperature separating funnel with a jacket, 800 g of methyl isobutyl ketone was added to 800 g of p-dioxanone with a purity of 97% and mixed thoroughly at 40°C. The mixture was cooled to 30°C for static stratification. After stratification, the temperature was continued to be lowered at a rate of 5°C / h to 24°C for crystallization. After the crystallization was completed, the mixture was filtered and the crystals were washed with 200 g of methyl isobutyl ketone. 675 g of high-purity p-dioxanone with a purity of 99.7% was obtained.

[0086] Comparative Example C1 (without extraction):

[0087] 800 g of p-dioxanone with a purity of 97% was cooled from 35° C. to 24° C. at a rate of 5° C. / h for crystallization. After the crystallization was completed, the crystals were filtered and washed with 200 g of methyl isobutyl ketone. The p-dioxanone crystals obtained by filtration were heated and melted to 150° C., and a stripping operation was performed in a stripping tower with 1 Nl / h nitrogen to remove the residual solvent, thereby obtaining 770 g of high-purity p-dioxanone with a purity of 97.9%.

[0088] Comparative Example C2 (according to US5391768)

[0089] 800 g of 97% pure p-dioxanone was dissolved in 800 ml of ethyl acetate at 40°C. The mixture was then cooled to -20°C. After 10 minutes, 1.0 g of pure p-dioxanone crystals were added to the solution for seeding. After visually confirming that the crystals had formed (about 1 hour), the temperature of the solution was lowered to -34°C and maintained for 2 hours. The mixture was then filtered and the filtrate was dried to obtain about 500 g of a solid containing crystalline p-dioxanone. The solid was dissolved in 375 g of ethyl acetate. The resulting solution was cooled to 0°C and 1 g of pure p-dioxanone crystals were added as seeds. The mixture was kept at -30°C for 12 hours for crystallization and then filtered. 358 g of high-purity p-dioxanone was obtained with a purity of 99.9%.

[0090] Comparative Example C3 (according to KR100301218)

[0091] 800 g of p-dioxanone with a purity of 97% and 1 liter of isopropanol were placed in a container at 40°C, the solution temperature was lowered to 17°C, 1 g of p-dioxanone crystals were added, and the temperature was slowly lowered to -20°C for crystallization for 7 hours. After filtering the crystals at room temperature, the crystals were washed 3 times with 100 ml of an isopropanol solvent precooled to -20°C. 550 g of p-dioxanone was obtained, and the purity measured by gas chromatography was 98%. The obtained product was recrystallized for 10 hours according to the above steps. The obtained recrystallized product was 490 g of p-dioxanone with a purity of 99.1%.

[0092] The recrystallized product was subjected to reduced pressure distillation in a 3 L three-necked flask equipped with a Vigrus column to obtain 410 g (yield 51%) of p-dioxanone with a purity of 99.91%.

[0093] It can be seen from the above examples and comparative examples that the method of the present invention allows a high-purity dioxanone product with a purity exceeding 99.9% to be obtained efficiently and at a relatively high yield, and has the advantages of a simple refining process and low refining cost.

Claims

1. A method for purifying dioxanone, comprising the following steps: The crude p-dioxanone product is fully mixed with an extracting solvent at a temperature higher than the melting point of p-dioxanone, wherein the extracting solvent is used to extract impurities contained in the crude p-dioxanone product, and the mixture is allowed to stand for stratification. After the stratification is completed, most of the extracting solvent is optionally discharged, and then the system is cooled to a temperature lower than the melting point of p-dioxanone for crystallization. After the crystallization is completed, the mixture is filtered, and the crystals are optionally washed with the extracting solvent, and the solvent in the crystals is removed.

2. The method for purifying dioxanone according to claim 1, characterized in that: The following steps are involved: 1) mixing the crude p-dioxanone with an extraction solvent in a certain weight ratio at a temperature higher than the melting point of p-dioxanone, and then allowing the mixture to stand for demixing at the temperature; and optionally separating and removing at least most of the extraction solvent phase containing impurities; 2) cooling the system to a temperature lower than the melting point of p-dioxanone to perform crystallization; 3) After the crystallization is completed, filter to remove the extraction solvent, optionally wash the crystals with the extraction solvent in step 1), and then 4) heating and melting the crystals, and introducing gas into the melt for stripping to remove the solvent in the crystals, thereby obtaining a high-purity dioxanone product; 5) Optionally subjecting the extraction solvent containing impurities to flash or distillation to recover the extraction solvent.

3. The 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 97%, preferably between 85% and 97%.

4. The method for purifying dioxanone according to any one of claims 2 to 3, characterized in that: In step 1), the extraction solvent is selected from butanol, amyl alcohol, isopropyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl tert-amyl ether, methyl isobutyl ketone or a mixture thereof.

5. The method for purifying dioxanone according to any one of claims 2 to 3, characterized in that: In step 1), the weight ratio of the extraction solvent to p-dioxanone is 0.5-10, preferably 0.8-2.

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

7. The method for purifying dioxanone according to any one of claims 2 to 3, characterized in that: In step 2), the crystallization temperature of dioxanone is maintained at 5°C-27°C, preferably 10°C-25°C.

8. The method for purifying dioxanone according to any one of claims 2 to 3, characterized in that: In step 4), the stripping gas is selected from hydrogen, nitrogen, helium, methane, ethane or a mixture thereof.

9. The method for purifying dioxanone according to any one of claims 2 to 3, characterized in that: In the step 2), the crystallization time of the system is about 2-20 hours, preferably about 4-15 hours.

10. The method for purifying dioxanone according to any one of claims 2 to 3, characterized in that Wherein step 1), step 2) and / or step 3) are implemented in a thermostatic separating funnel with a jacket.

11. An apparatus for implementing the method for purifying dioxanone according to any one of claims 1 to 10, comprising an extraction device, a crystallization device, a filtration device and a melt stripping device.