A method for purifying dioxanone

Abstract

The application discloses a method for purifying p-dioxanone, which comprises the following steps: mixing a crude p-dioxanone product with a certain amount of extraction solvent at a temperature higher than the melting point of the p-dioxanone; allowing the mixture to stand at a certain temperature to separate into layers; lowering the temperature of the system to below the melting point of the p-dioxanone to start crystallization; filtering the mixture after the crystallization is completed; and removing the solvent in the crystals to obtain a high-purity p-dioxanone product. The application also relates to an apparatus for implementing the purification method.

Description

Technical Field

[0001] This invention relates to the field of separation and purification technology in organic chemical engineering, and in particular to a method for purifying p-dioxanone using extraction crystallization. Background Technology

[0002] Poly(p-dioxanone) (PPDO) is an aliphatic polyether ester. Its molecular structure contains both ester and ether bonds, giving it excellent biodegradability, physical and mechanical properties, and thermal properties. It also exhibits excellent biodegradability and absorbability.

[0003] p-Dioxane (PDO) is the monomer of PPDO polymer and is generally synthesized using two processes. One process uses ethylene glycol as a raw material, followed by hydrochlorination with chloroacetic acid and then dehydration cyclization. The other process uses diethylene glycol as a raw material and obtains it through catalytic oxidative dehydrogenation cyclization. For polymerization, the p-dioxane monomer obtained from both processes must have high purity to yield high-quality PPDO polymers. Therefore, the purification of p-dioxane monomer is particularly important. Crystallization is an effective method of material purification with low energy consumption; melt crystallization or solution crystallization are commonly used for the purification of p-dioxane.

[0004] US5,391,768 describes a method for purifying p-dioxanone using a solvent. The method involves dissolving p-dioxanone in an aliphatic ester solvent, ethyl acetate, and recrystallizing to obtain p-dioxanone with high purity. However, since p-dioxanone dissolves completely around -3°C, the crystallization temperature must be lowered to -30°C, making room temperature operation difficult and resulting in low yields.

[0005] KR100301218B1 proposes a method for purifying p-dioxanone, comprising: (a) dissolving a mixture of p-dioxanone in isopropanol 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 the reaction mixture; (d) repeating steps (a) to (c) recrystallization; and (e) removing isopropanol from the final product obtained in the above steps under reduced pressure and distilling to obtain high-purity p-dioxanone. This method can purify p-dioxanone to over 99.97%. However, this method also suffers from low crystallization temperature, low product yield, and requires multiple recrystallizations, resulting in low purification efficiency.

[0006] KR100567926B1 proposes a method for purifying p-dioxanone. In step (1), crude p-dioxanone is cooled and crystallized. Considering crushing and filtration, the cooling temperature of the crude p-dioxanone crystallization is about 24°C below the melting point of p-dioxanone, preferably -30 to 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 extruder, and then filtered under pressure or reduced pressure. When the size of the crushed crystals is too large, it is difficult to remove impurities mixed in with the p-dioxanone crystals and it takes a lot of time. In step (3), the filtered p-dioxanone crystal particles are dried under 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 reduced pressure of 0.05 to 5 torr to obtain p-dioxanone with a high purity of 99.9%. This method requires mechanical crushing, which can easily lead to material loss, and the high vacuum conditions can easily cause blockages and high energy consumption.

[0007] KR100761001B1 provides a purification method: 1) After maintaining a mixture of p-dioxanone at 30-40°C, seed crystals are added, and the mixture is cooled to 5-15°C at a cooling rate of 0.1-5°C / min to obtain p-dioxanone crystals; 2) The p-dioxanone crystals are then heated to 20-35°C at a rate of 0.1-1°C / min to recover high-purity p-dioxanone. To ensure high-purity p-dioxanone, this method has a low cooling and heating rate, a long crystallization time, and does not completely remove impurities of specific components from the p-dioxanone crystals, requiring an additional multi-stage melt crystallization process.

[0008] KR100675964B1 further adopts a combination of solution crystallization-melt crystallization-reduced pressure distillation, which results in an excessively long refining process, excessive operational difficulty, and reduced reliability.

[0009] However, melt crystallization requires high purity of raw materials, has large crystal particle size, long purification time, and is difficult to effectively improve product purity; solution crystallization has problems such as low crystallization temperature, long crystallization time and low yield.

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide a novel purification method for p-dioxanone, which is simple to operate and allows for the efficient and high-yield production of high-purity p-dioxanone products, thereby meeting the demand for the preparation of high-quality p-dioxanone. Summary of the Invention

[0011] After studying the purification methods of p-dioxanone prepared by the above two synthetic processes, the applicant surprisingly discovered 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 objective of this invention is a method for purifying dioxane, the method comprising: thoroughly mixing crude dioxane with an extraction solvent at a temperature above the melting point of dioxane, wherein the extraction solvent is used to extract impurities contained in the crude dioxane; allowing the mixture to stand and separate into layers after mixing; optionally discharging most of the extraction solvent after separation; cooling the system to a temperature below the melting point of dioxane for crystallization; filtering after crystallization; optionally washing the crystals with a small amount of extraction solvent to remove the solvent from the crystals.

[0013] Another object of the present invention is an apparatus for carrying out the above-described purification method, comprising an extraction apparatus, a crystallization apparatus, a filtration apparatus, and a melt stripping apparatus. Detailed Implementation

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

[0015] The crude p-dioxanone used in this invention is prepared by two synthetic processes known to those skilled in the art: one process uses ethylene glycol as a raw material, chloroacetic acid is converted to hydrochloric acid, and then dehydrated and cyclized to obtain p-dioxanone; the other process uses diethylene glycol as a raw material, and obtains p-dioxanone by catalytic oxidative dehydrogenation cyclization; more specifically, the crude p-dioxanone used in this invention is obtained by catalytic oxidative dehydrogenation cyclization using diethylene glycol as a raw material. The purity of the crude p-dioxanone obtained by these two processes is typically 80%-97%, and the impurities typically include ethylene glycol, dioxane, dioxene, ethylene glycol acetate, diethylene glycol acetate, methoxyethanol, diethylene glycol ethyl ether, etc.

[0016] According to a particular embodiment, the solvent removal from the crystal is carried out by gas stripping through a gas stream passing through a dioxane melt.

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

[0018] 1) The crude p-dioxanone product is thoroughly mixed with the extraction solvent in a certain proportion at a temperature higher than the melting point of p-dioxanone, and then allowed to stand for layering at that temperature; optionally, most of the extraction solvent phase containing impurities is separated and removed.

[0019] 2) Cool the system to a temperature below the melting point of dioxane to allow for crystallization;

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

[0021] 4) The crystal is heated and melted, and gas is introduced into the melt for stripping to remove the solvent in the crystal, so as to obtain a high-purity p-dioxanone product.

[0022] 5) Optionally, the extraction solvent containing impurities is flash-distilled or distilled to recover the extraction solvent.

[0023] According to a particular embodiment, in step 1), the purity of the crude dioxane 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, pentanol, isopropyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl tert-pentyl ether, methyl isobutyl ketone, or mixtures 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, and most particularly about 1.

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

[0027] According to a particular implementation, in step 1), the settling 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, and 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, and 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, and most particularly about 6-10 hours.

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

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

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

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

[0035] According to a particular embodiment, in step 4), during the gas stripping process, 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 0.1 Nl / h or more, preferably 0.2 Nl / h or more, more preferably 1 Nl / h or more, and 20 Nl / h or less, preferably 10 Nl / h or less.

[0036] According to a particular embodiment, steps 1), 2) and / or 3) are carried out in a jacketed thermostatic separatory funnel.

[0037] According to a particular embodiment, dioxane and extraction solvent are mixed uniformly in a jacketed thermostatic separatory funnel at a constant temperature above the melting point of dioxane, and then allowed to stand for stratification. Optionally, most of the extraction solvent phase is discharged, and the system is cooled to a constant temperature below the melting point of dioxane to allow dioxane to crystallize. After crystallization, since the dioxane crystals grow into a self-supporting network structure, at least most of the extraction solvent can be discharged directly from the bottom. The crystals are then washed with a small amount of fresh extraction solvent to remove liquid containing impurities from 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 packed stripping tower, and gas is introduced from the bottom of the stripping tower for stripping operation, wherein the temperature inside the stripping tower is maintained above the melting point of dioxane. The solvent-removed pure PDO is collected at the bottom of the stripping tower.

[0038] According to a particular embodiment, the equipment for carrying out the above-described purification method for dioxane includes 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] Because this invention employs extraction crystallization and melt stripping methods to purify p-dioxanone, compared to existing technologies, the method of this invention allows for the efficient and high-purity production of p-dioxanone products in high yields, and features a simple purification process and low purification costs. Compared to melt crystallization methods, the method of this invention has a faster crystallization speed and simpler operation; compared to solution crystallization methods, the method of this invention has a higher yield and higher efficiency of p-dioxanone products.

[0041] It is understood that those skilled in the art can reasonably combine the different embodiments described above as needed, and that some non-essential improvements and adjustments made to the present invention based on the content of this invention are still within the scope of protection of this invention. The equipment and apparatus used in the method of this invention are all conventional equipment and apparatus in the art.

[0042] Example

[0043] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. All purity levels mentioned in this specification are by weight.

[0044] Example I-1

[0045] In a jacketed, isothermal separatory funnel, 800 g of butanol was added to 800 g of 97% pure p-dioxanone and mixed thoroughly at 50 °C. The mixture was then cooled to 30 °C and allowed to stand for phase separation. After phase separation, the system was further cooled at a rate of 5 °C / h to 24 °C for crystallization over 7 hours. After crystallization, the liquid phase was removed by filtration, and the crystals were washed with 200 g of butanol. The filtered p-dioxanone crystals were heated to 150 °C and the melt was introduced into a stripping column with 15 theoretical plates at a flow rate of 200 g / h. Stripping was performed with nitrogen at a rate of 4.0 Nl / h to remove residual solvent and possible impurities, yielding 512.5 g of high-purity p-dioxanone with a purity of 99.93% as determined by gas chromatography.

[0046] Example I-2

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

[0048] Example I-3

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

[0050] Example I-4

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

[0052] Example II-1

[0053] In a jacketed, isothermal separatory funnel, 800 g of 97% pure p-dioxanone was mixed thoroughly at 60°C with 800 g of pentanol. The mixture was then cooled to 40°C and allowed to stand for phase separation. After phase separation, the system was further cooled at a rate of 5°C / h to 20°C for crystallization over 7 hours. After crystallization, the mixture was filtered, and the crystals were washed with 200 g of pentanol. The filtered p-dioxanone crystals were heated to 150°C and melted. The melt was introduced into a stripping column with 15 theoretical plates at a flow rate of 200 g / h, and stripped with 4 Nl / h of nitrogen to remove residual solvent and possible impurities, yielding 584.1 g of high-purity p-dioxanone with a purity of 99.92% as determined by gas chromatography.

[0054] Example II-2

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

[0056] Example II-3

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

[0058] Example II-4

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

[0060] Example III-1

[0061] In a jacketed, isothermal separatory funnel, 800 g of methyl tert-butyl ether was added to 800 g of 97% pure p-dioxanone and mixed thoroughly at 40 °C. The mixture was then cooled to 30 °C and allowed to stand for phase separation. After phase separation, the system was further cooled at a rate of 5 °C / h to 10 °C for crystallization over 7 hours. After crystallization, the mixture was filtered, and the crystals were washed with 200 g of methyl tert-butyl ether. The filtered p-dioxanone crystals were heated to 150 °C and the melt was introduced into a stripping column with 15 theoretical plates at a flow rate of 200 g / h. Stripping was performed with 1 N / h of nitrogen to remove residual solvent and possible impurities, yielding 660.0 g of high-purity p-dioxanone with a purity of 99.9% as determined by gas chromatography.

[0062] Example III-2

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

[0064] Example III-3

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

[0066] Example III-4

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

[0068] Example IV-1

[0069] In a jacketed, isothermal separatory funnel, 800 g of methyl tert-amyl ether was added to 800 g of 97% pure p-dioxanone and mixed thoroughly at 40 °C. The mixture was then cooled to 30 °C and allowed to stand for phase separation. After phase separation, the system was further cooled at a rate of 5 °C / h to 10 °C for crystallization over 7 hours. After crystallization, the mixture was filtered, and the crystals were washed with 200 g of methyl tert-amyl ether. The filtered p-dioxanone crystals were heated to 150 °C and the melt was introduced into a stripping column with 15 theoretical plates at a flow rate of 200 g / h. Stripping was performed with 4 Nl / h of nitrogen to remove residual solvent and possible impurities, yielding 508.9 g of high-purity p-dioxanone with a purity of 99.92% as determined by gas chromatography.

[0070] Example IV-2

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

[0072] Example IV-3

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

[0074] Example IV-4

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

[0076] Example V-1

[0077] In a jacketed, isothermal separatory funnel, 800 g of methyl isobutyl ketone (MBE) was added to 800 g of 97% pure p-dioxanone and mixed thoroughly at 40 °C. The mixture was then cooled to 30 °C and allowed to stand for phase separation. After phase separation, the system was further cooled at a rate of 5 °C / h to 24 °C for crystallization over 7 hours. After crystallization, the mixture was filtered, and the crystals were washed with 200 g of MBE. The filtered p-dioxanone crystals were heated to 150 °C and the melt was introduced into a stripping column with 15 theoretical plates at a flow rate of 200 g / h. Stripping was performed with 3.5 Nl / h of nitrogen to remove residual solvent and possible impurities, yielding 524 g of high-purity p-dioxanone with a purity of 99.93% as determined by gas chromatography.

[0078] Example V-2

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

[0080] Example V-3

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

[0082] Example V-4

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

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

[0085] In a jacketed, isothermal separatory funnel, 800 g of methyl isobutyl ketone was added to 800 g of p-dioxanone (97% purity) and mixed thoroughly at 40°C. The mixture was then cooled to 30°C and allowed to stand for phase separation. After phase separation, the temperature was further reduced at a rate of 5°C / h to 24°C for crystallization. After crystallization, the mixture was filtered, and the crystals were washed with 200 g of methyl isobutyl ketone. 675 g of high-purity p-dioxanone (99.7% purity) was obtained.

[0086] Comparative Example C1 (no extraction):

[0087] 800g of 97% pure p-dioxanone was cooled from 35°C to 24°C at a rate of 5°C / h for crystallization. After crystallization, the crystals were filtered and washed with 200g of methyl isobutyl ketone. The filtered p-dioxanone crystals were then heated to 150°C and stripped in a stripping column with 1Nl / h nitrogen to remove residual solvent, yielding 770g 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 as seed crystals. After visual confirmation that crystals had formed (approximately 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 approximately 500 g of 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 seed crystals. The mixture was maintained at -30 °C for 12 hours to crystallize, and then filtered. 358 g of high-purity p-dioxanone with a purity of 99.9% was obtained.

[0090] Comparative Example C3 (according to KR100301218)

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

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

[0093] As can be seen from the above embodiments and comparative embodiments, the method of the present invention allows for the efficient and high-yield production of high-purity p-dioxanone products with a purity exceeding 99.9%, and has the advantages of simple refining process and low refining cost.

Claims

1. A method for purifying dioxanone comprising the steps of: At a temperature above the melting point of dioxane, crude dioxane is thoroughly mixed with an extraction solvent, which is used to extract impurities contained in the crude dioxane. After mixing, the mixture is allowed to stand and separate into layers. After separation, the extraction solvent is removed, and the system is then cooled to a temperature below the melting point of dioxane to allow crystallization. After crystallization, the mixture is filtered, and the crystals are washed with the extraction solvent to remove the solvent from the crystals. The weight ratio of the extraction solvent to p-dioxanone is 0.5-10. The crystallization temperature of p-dioxanone is maintained at 5℃-27℃. The mixing and standing separation temperature is maintained at 27℃-80℃. The extraction solvent is selected from butanol, pentanol, methyl tert-butyl ether, methyl tert-amyl ether, methyl isobutyl ketone or mixtures thereof.

2. The method for purifying dioxane according to claim 1, characterized in that, Includes the following steps: 1) The crude dioxane was thoroughly mixed with the extraction solvent at a temperature above the melting point of dioxane, and then allowed to stand for phase separation at that temperature; the extraction solvent phase containing impurities was then separated and removed. 2) Cool the system to a temperature below the melting point of dioxane to allow for crystallization; 3) After crystallization, filter to remove the extraction solvent, wash the crystals with the extraction solvent from step 1), and then... 4) The crystal is heated and melted, and gas is introduced into the melt for stripping to remove the solvent in the crystal, so as to obtain a high-purity p-dioxanone product. 5) Optionally, the extraction solvent containing impurities may be flash-distilled or distilled to recover the extraction solvent.

3. The method for purifying dioxane according to claim 2, characterized in that, In step 1), the purity of crude dioxane is between 80% and 97%.

4. The method for purifying dioxane according to claim 2, characterized in that, In step 1), the purity of crude dioxane is between 85% and 97%.

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

6. The method for purifying dioxane according to any one of claims 2-3, characterized in that, In step 2), the cooling rate of the system is maintained at 0.1-50℃ / h.

7. The method for purifying dioxane according to any one of claims 2-3, characterized in that, In step 2), the cooling rate of the system is maintained at 1-10℃ / h.

8. The method for purifying dioxane according to any one of claims 2-3, characterized in that, In step 2), the crystallization temperature of p-dioxanone is maintained at 10℃-25℃.

9. The method for purifying dioxane according to any one of claims 2-3, characterized in that, In step 4), the gas used for gas stripping is selected from hydrogen, nitrogen, helium, methane, ethane, or mixtures thereof.

10. The method for purifying dioxane according to any one of claims 2-3, characterized in that, In step 2), the crystallization time of the system is 2-20 hours.

11. The method for purifying dioxane according to any one of claims 2-3, characterized in that, In step 2), the crystallization time of the system is 4-15 hours.

12. The method for purifying dioxane according to any one of claims 2-3, characterized in that... The steps 1), 2) and / or 3) are carried out in a jacketed thermostatic separatory funnel.