CN115246811A - Continuous production method of purified glycolide - Google Patents
Continuous production method of purified glycolide Download PDFInfo
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- CN115246811A CN115246811A CN202110467526.0A CN202110467526A CN115246811A CN 115246811 A CN115246811 A CN 115246811A CN 202110467526 A CN202110467526 A CN 202110467526A CN 115246811 A CN115246811 A CN 115246811A
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- RKDVKSZUMVYZHH-UHFFFAOYSA-N 1,4-dioxane-2,5-dione Chemical compound O=C1COC(=O)CO1 RKDVKSZUMVYZHH-UHFFFAOYSA-N 0.000 title claims abstract description 155
- 238000000034 method Methods 0.000 title claims abstract description 41
- 238000010924 continuous production Methods 0.000 title claims abstract description 27
- 238000002425 crystallisation Methods 0.000 claims abstract description 124
- 230000008025 crystallization Effects 0.000 claims abstract description 124
- 239000000463 material Substances 0.000 claims abstract description 58
- 239000011344 liquid material Substances 0.000 claims abstract description 52
- 239000002904 solvent Substances 0.000 claims abstract description 50
- 239000012452 mother liquor Substances 0.000 claims abstract description 36
- 239000002002 slurry Substances 0.000 claims abstract description 22
- 238000002156 mixing Methods 0.000 claims abstract description 8
- AEMRFAOFKBGASW-UHFFFAOYSA-N Glycolic acid Chemical class OCC(O)=O AEMRFAOFKBGASW-UHFFFAOYSA-N 0.000 claims description 157
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 33
- 239000007787 solid Substances 0.000 claims description 27
- 238000004519 manufacturing process Methods 0.000 claims description 20
- 238000000926 separation method Methods 0.000 claims description 19
- 238000005406 washing Methods 0.000 claims description 19
- 239000007788 liquid Substances 0.000 claims description 11
- 238000004090 dissolution Methods 0.000 claims description 5
- 150000002576 ketones Chemical class 0.000 claims description 4
- FBBDOOHMGLLEGJ-UHFFFAOYSA-N methane;hydrochloride Chemical compound C.Cl FBBDOOHMGLLEGJ-UHFFFAOYSA-N 0.000 claims description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 claims description 3
- 239000011343 solid material Substances 0.000 claims description 3
- 230000003247 decreasing effect Effects 0.000 claims 1
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 99
- 239000000047 product Substances 0.000 description 65
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 29
- 239000012535 impurity Substances 0.000 description 21
- 239000013557 residual solvent Substances 0.000 description 19
- 238000003756 stirring Methods 0.000 description 19
- 238000001816 cooling Methods 0.000 description 17
- 238000001035 drying Methods 0.000 description 13
- 238000001914 filtration Methods 0.000 description 11
- 239000003960 organic solvent Substances 0.000 description 11
- 229920000642 polymer Polymers 0.000 description 10
- 238000000746 purification Methods 0.000 description 8
- 238000011084 recovery Methods 0.000 description 8
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 7
- 238000001953 recrystallisation Methods 0.000 description 7
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 125000004122 cyclic group Chemical group 0.000 description 6
- 239000000539 dimer Substances 0.000 description 6
- 239000006228 supernatant Substances 0.000 description 6
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 5
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 4
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- ZXEKIIBDNHEJCQ-UHFFFAOYSA-N isobutanol Chemical compound CC(C)CO ZXEKIIBDNHEJCQ-UHFFFAOYSA-N 0.000 description 4
- 239000000178 monomer Substances 0.000 description 4
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 3
- 229920000954 Polyglycolide Polymers 0.000 description 3
- 230000001186 cumulative effect Effects 0.000 description 3
- 238000005265 energy consumption Methods 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 239000004633 polyglycolic acid Substances 0.000 description 3
- 238000006116 polymerization reaction Methods 0.000 description 3
- 239000002253 acid Substances 0.000 description 2
- 230000001476 alcoholic effect Effects 0.000 description 2
- 150000001298 alcohols Chemical class 0.000 description 2
- 238000005119 centrifugation Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000004817 gas chromatography Methods 0.000 description 2
- 238000003918 potentiometric titration Methods 0.000 description 2
- 238000007151 ring opening polymerisation reaction Methods 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 description 1
- NTIZESTWPVYFNL-UHFFFAOYSA-N Methyl isobutyl ketone Chemical compound CC(C)CC(C)=O NTIZESTWPVYFNL-UHFFFAOYSA-N 0.000 description 1
- UIHCLUNTQKBZGK-UHFFFAOYSA-N Methyl isobutyl ketone Natural products CCC(C)C(C)=O UIHCLUNTQKBZGK-UHFFFAOYSA-N 0.000 description 1
- XBDQKXXYIPTUBI-UHFFFAOYSA-M Propionate Chemical compound CCC([O-])=O XBDQKXXYIPTUBI-UHFFFAOYSA-M 0.000 description 1
- 150000001242 acetic acid derivatives Chemical class 0.000 description 1
- KXKVLQRXCPHEJC-UHFFFAOYSA-N acetic acid trimethyl ester Natural products COC(C)=O KXKVLQRXCPHEJC-UHFFFAOYSA-N 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 229960001701 chloroform Drugs 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- SWXVUIWOUIDPGS-UHFFFAOYSA-N diacetone alcohol Natural products CC(=O)CC(C)(C)O SWXVUIWOUIDPGS-UHFFFAOYSA-N 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000002198 insoluble material Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000000967 suction filtration Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D319/00—Heterocyclic compounds containing six-membered rings having two oxygen atoms as the only ring hetero atoms
- C07D319/10—1,4-Dioxanes; Hydrogenated 1,4-dioxanes
- C07D319/12—1,4-Dioxanes; Hydrogenated 1,4-dioxanes not condensed with other rings
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a continuous production method of purified glycolide. The method comprises the following steps: (1) treating a crude glycolide product to obtain a pretreated material; (2) Mixing and dissolving the pretreated material and a solvent to obtain a liquid material; (3) Introducing the liquid materials into more than 2 crystallization kettles connected in series one by one to obtain slurry; (4) And (3) separating the slurry to obtain refined glycolide and mother liquor, and returning the mother liquor to the step (2) to participate in mixing.
Description
Technical Field
The invention relates to the field of polymer preparation, in particular to a method for purifying glycolide by continuous crystallization.
Background
Glycolide is a monomer for preparing biodegradable material polyglycolic acid by a ring-opening polymerization method. The purity of glycolide has a crucial influence on the conversion of the ring-opening polymerization, the molecular weight of the product polymer, the molecular weight distribution, etc. Therefore, the content of impurities (e.g., acid, water, glycolic acid dimer or multimer, etc.) of the glycolide monomer used needs to be strictly controlled in the process of producing polyglycolic acid. The crude glycolide produced by the current synthesis process usually cannot reach the high purity required by the polymerization reaction. In addition, the purity of the high purity glycolide monomer product is gradually reduced to be lower than the high purity required by the polymerization reaction, for example, in the case of long storage time, the impurity content of the high purity glycolide monomer product is gradually increased. Therefore, purification of crude glycolide to obtain high-quality refined glycolide is crucial to large-scale continuous production of high-quality polyglycolic acid.
At present, the purification process of crude cyclic lactide mainly comprises a rectification purification process and a recrystallization process, for example, in the aspect of the rectification purification process, US5274073, CN1056689A and the like adopt a gas-assisted evaporation method to separate cyclic lactide as a steam component in gas flow and separate the cyclic lactide from impurities based on the volatility difference between the cyclic lactide and the impurities, but the rectification separation requires a large number of theoretical plates, the temperature of a tower kettle is high, the energy consumption is high, and the polymerization and hydrolysis of the cyclic lactide are accelerated by overhigh temperature, so that the product yield is greatly reduced; in the recrystallization process, CN110511205A and CN100999516 use organic solvents such as ethyl acetate, acetone, and isopropyl alcohol to purify glycolide by recrystallization, but glycolide obtained by 1 recrystallization is not enough in purity, usually needs to be recrystallized 3-5 times, and has large solvent consumption, long purification period, and low product yield. Therefore, the rectification and purification process has the defects of high energy consumption, complex process and equipment, large investment and the like, and the recrystallization process has the problems of large solvent consumption, low product yield and the like.
There is therefore a great need in the art to provide a process for the continuous production of refined glycolide with essentially the same yield of refined glycolide per batch produced and with recycling of most of the mother liquor collected after purification to save solvent.
Disclosure of Invention
The invention aims to provide a process for continuously producing refined glycolide.
The present invention provides a continuous process for the production of purified glycolide, said process comprising the steps of:
(1) Treating the crude glycolide product to obtain a pretreated material;
(2) Mixing and dissolving the pretreated material and a solvent to obtain a liquid material;
(3) Introducing the liquid materials into more than 2 crystallization kettles connected in series one by one to obtain slurry; and
(4) And (3) separating the slurry to obtain refined glycolide and mother liquor, and returning the mother liquor to the step (2) for mixing.
In another embodiment, the treatment in step (1) comprises a solid-liquid separation after washing the crude glycolide product with an alcoholic solvent and retaining the solid.
In another embodiment, the glycolic acid dimer content is no more than 0.25w/w% based on the total weight of the pretreated material obtained in step (1).
In another embodiment, the solvent in step (2) is at least one of an acetate, a ketone, or a methane chloride.
In another embodiment, the glycolic acid dimer content is no more than 500ppm based on the total weight of the liquid feed obtained in step (2).
In another embodiment, the temperature of the first crystallization kettle introduced in step (3) is 5-30 ℃ lower than the dissolution temperature of step (2), and the temperature of the last crystallization kettle introduced is not higher than 0 ℃; for example, the temperature settings from the first to the last crystallization vessel decrease one by one, and the temperature difference between each crystallization vessel and the adjacent crystallization vessel in series is between 5 and 35 ℃.
In another embodiment, the liquid feed is introduced with a residence time in the crystallization vessel of 5 to 150 minutes.
In another embodiment, the amount of solvent added when the mother liquor returned to step (2) in step (4) is 5-50w/w% of the returned mother liquor; preferably 5-15w/w%.
In another embodiment, the slurry is subjected to solid-liquid separation, and the solid material is dried to obtain refined glycolide.
Accordingly, the invention provides a process for continuously producing refined glycolide, the yield of the refined glycolide produced in each batch is basically the same, and most of mother liquor collected after purification can be recycled, so that the solvent can be saved.
Detailed Description
The inventors have made extensive and intensive studies and found that by controlling the content of glycolic acid dimer in the pretreated material and the use of a continuous crystallization vessel, the crystallization mother liquor can be recycled to realize continuous production of purified glycolide. On the basis of this, the present invention has been completed.
The invention provides a continuous production method for purifying glycolide, which comprises the following steps:
firstly, washing a crude glycolide product by using an alcohol solvent to obtain a pretreated material;
secondly, mixing the pretreated material with an organic solvent to fully dissolve the pretreated material to obtain a liquid material;
thirdly, sequentially introducing the liquid material into at least 2 serially connected crystallization kettles of which the temperature is reduced in a stepped manner to cool and crystallize, and obtaining slurry from the last crystallization kettle;
fourthly, carrying out solid-liquid separation on the slurry to obtain refined glycolide and mother liquor;
and step five, returning the mother liquor to the step two to mix with the pretreated material newly obtained from the step one, and then performing the step two to the step four, thereby continuously circulating and obtaining the refined glycolide.
The crude glycolide product in the first step is basically heavy component impurities and light component impurities besides glycolide, the heavy component impurities are glycolic acid polymers with poor solubility, such as tetramers, pentamers or hexamers of glycolic acid, and the light component impurities are glycolic acid, water, other acids or residual solvents. For example, but not limited to, the crude glycolide product comprises about 65-98wt% glycolide, 1-28.5wt% glycolic acid, 0.5-1.5wt% water, 0.5-5wt% glycolic acid polymers.
In the first step, the crude glycolide product is washed by using an alcohol solvent, mainly for preliminarily cleaning light component impurities in the crude glycolide. The alcoholic solvent may be selected from C 1 -C 4 One or more saturated monohydric alcohols; for example, the solvent can be one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol, and ethanol is preferred. In one embodiment of the invention, the washing is carried out with absolute ethanol.
In one embodiment of the invention, the crude glycolide product is washed with an alcohol solvent and then subjected to solid-liquid separation to obtain a solid, namely the pretreated material. The solid-liquid separation method includes, but is not limited to, suction filtration, centrifugation, and the like.
In one embodiment of the invention, the crude glycolide product is washed by an alcohol solvent and then centrifuged, the supernatant is removed, and the solid is retained; this operation can be repeated 1-3 times.
The glycolic acid dimer content is not more than 0.25 wt.%, preferably not more than 0.23 wt.%, based on the total weight of the pretreated material obtained in the above first step.
In one embodiment of the invention, the moisture content (mainly anhydrous ethanol, glycolic acid, water, etc. included in some of the raw crude glycolide product) does not exceed 5w/w%, based on the total weight of the pretreated material obtained in the first step above.
The organic solvent used in the second step may include at least one of acetates, ketones or methane chlorides; alcohols may also be included.
The acetate can be at least one of ethyl acetate and methyl acetate; the ketones may be selected from at least one of acetone, butanone, methyl ethyl ketone and methyl isobutyl ketone; the methane chloride can be selected from at least one of dichloromethane, trichloromethane and carbon tetrachloride; the alcohol can be at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol.
The weight of the organic solvent used in the second step is 4 to 6 times the weight of the crude glycolide product in the first step.
The second step may be carried out by mixing and dissolving in a vessel commonly used in the art, such as, but not limited to, a stirred tank.
In one embodiment of the present invention, the second step is to add the pretreated material into a stirring tank containing the organic solvent, and raise the temperature while stirring to fully dissolve the pretreated material.
The dissolution temperature of the second step is determined depending on the organic solvent used, as long as the pretreated material is completely dissolved, but should be lower than the boiling point of the organic solvent to avoid unnecessary loss of the solvent. In the case of ethyl acetate, the dissolution temperature is generally 50-60 ℃.
In one embodiment of the present invention, the second step is performed by filtering after the pretreated material is sufficiently dissolved to remove insoluble materials (e.g., glycolic acid polymers, etc.) in the crude glycolide product, thereby obtaining a liquid material.
The glycolic acid dimer content thereof is not more than 500ppm based on the total weight of the liquid material obtained in the second step.
The liquid material in the third step is sequentially introduced into more than 2 crystallization kettles which are connected in series and have descending temperature one by one, and the temperature difference between two adjacent crystallization kettles connected in series is favorable for recrystallization, namely, the descending degree of the temperature is favorable for the reduction of the solubility of the glycolide in the liquid material, and the solution is saturated to separate out refined glycolide. The inventor finds that the temperature difference between two adjacent crystallization kettles is too large, so that the material quenching speed is too high or the quenching process is too strong, a large amount of glycolide is rapidly separated out in the process and is rapidly accumulated, so that the glycolide separated out earlier is easily adhered to and stays on the inner wall of the crystallization kettle due to the compression of a large amount of glycolide separated out after relative delay, and the material of the next batch is difficult to carry out the material staying in the previous batch when flowing through the crystallization kettle, thereby causing the waste of the material and greatly reducing the yield of the final glycolide.
And a plurality of crystallization kettles are adopted, before the material reaches the last crystallization kettle, the quenching speed or the quenching degree of the material is properly reduced by utilizing the proper temperature difference between the two adjacent crystallization kettles, so that the glycolide in the material can be separated out mildly, retention of the separated glycolide in the crystallization kettles is favorably reduced or eliminated to the maximum extent, and the retained glycolide is easily carried out by the material of the next batch even if a small amount of retention occurs.
The term "crystallization vessel" is used herein in the usual sense in the art, i.e., to refer to a vessel capable of controlling the temperature within a certain range.
In one embodiment of the invention, the temperature difference between each crystallization vessel and its adjacent crystallization vessel in series is between 5 and 35 ℃.
The temperature of the first crystallization kettle for introducing the liquid material in the third step is 5-30 ℃ lower than the dissolving temperature in the second step, and the temperature of the last crystallization kettle for introducing the liquid material is generally not more than 0 ℃.
In an embodiment of the present invention, the crystallization kettle in the third step is 5 crystallization kettles connected in series and arranged in a descending manner, wherein the temperature of the first crystallization kettle is 42 ℃, the temperature of the second crystallization kettle is 30 ℃, the temperature of the third crystallization kettle is 18 ℃, the temperature of the fourth crystallization kettle is 10 ℃, and the temperature of the fifth crystallization kettle is-5 ℃.
In an embodiment of the present invention, the crystallization kettle in the third step is 4 crystallization kettles connected in series and arranged in a descending manner, wherein the temperature of the first crystallization kettle is set to 35 ℃, the temperature of the second crystallization kettle is set to 18 ℃, the temperature of the third crystallization kettle is set to 5 ℃, and the temperature of the fourth crystallization kettle is set to-5 ℃.
In an embodiment of the present invention, the crystallization kettle in the third step is 3 crystallization kettles connected in series and arranged in a stepwise descending manner, wherein the temperature of the first crystallization kettle is set to 40 ℃, the temperature of the second crystallization kettle is set to 12 ℃, and the temperature of the third crystallization kettle is set to-5 ℃.
In an embodiment of the present invention, the crystallization kettle in the third step is 2 crystallization kettles connected in series and arranged in a temperature descending manner, wherein the temperature of the first crystallization kettle is set to be 32 ℃, and the temperature of the second crystallization kettle is set to be-2 ℃.
The liquid material introduced into the crystallization kettle in the third step needs to stay in the crystallization kettle for a period of time, such as 5-150 minutes; in one embodiment of the invention, the higher the temperature, the longer the residence time in the crystallization vessel is generally.
The solid-liquid separation in the fourth step may be a means commonly used in the art, such as, but not limited to, centrifugation and the like.
In an embodiment of the present invention, the solid material obtained by centrifuging the slurry in the fourth step may be dried to obtain purified glycolide. Drying may be carried out by methods conventional in the art, such as, but not limited to, vacuum drying, e.g., 40-60 ℃ at an absolute pressure of 500Pa or less, for 1-2 hours.
The purity of glycolide in the refined glycolide or the refined glycolide product obtained by the invention can reach more than 99.5%, the solvent residue rate is less than or equal to 0.3%, the content of glycolic acid is less than 0.03wt%, the content of glycolic acid dimer is less than 0.03wt%, and the water content is less than 0.03wt%. The glycolide, residual solvent, and glycolic acid dimer content of the present invention are determined by gas chromatography, as is well known in the art, the water content is determined by a Karl Fischer moisture meter, and the glycolic acid content is determined by potentiometric titration, as is well known in the art (e.g., by an automated potentiometric titrator).
In one embodiment of the present invention, the solvent lost by the fourth step after drying is collected (for example, but not limited to, by using a heat exchanger) and mixed with the mother liquor, and the solvent in the dried refined glycolide may be present in a negligible amount, measured in kg.
In the fifth step, the mother liquor is returned to the container in which the second batch of the pretreated material from the first step, the mother liquor returned from the fifth step and the additional organic solvent are mixed, and then the liquid material obtained by sufficiently dissolving the mixture is subjected to the third step of the second batch or the following steps, thereby performing the second batch of the process for producing purified glycolide, and so on, and the processes of the third batch, the fourth batch and the like are performed, thereby realizing continuous circulation/production. Based on the balance in industrial production, the next batch of circulation brings out the material remained or accumulated in the previous batch of circulation, and the amount of the refined glycolide obtained in the next batch and the amount obtained in the previous batch are basically the same from the appearance.
The determination of how many batches of such recycle/production need to be carried out is generally based on the cumulative glycolic acid dimer content in the mother liquor to be returned to the second step in the fifth step described above or the glycolic acid and/or glycolic acid dimer content of the resulting refined glycolide product.
In one embodiment of the invention, the make-up organic solvent is about 5-50w/w%, such as, but not limited to, about 5-15w/w%, about 8-12w/w%, about 9-11w/w%, etc., of the returned mother liquor.
In one embodiment of the present invention, the fifth step is stopped when the accumulated glycolic acid dimer content in the mother liquor to be returned to the second step exceeds 1000ppm or the glycolic acid and/or glycolic acid dimer content in the resulting refined glycolide product exceeds 0.03% by weight.
Once a round of a continuous production of several batches of purified glycolide according to the invention as described above has been completed, a new round of such a continuous production process can be started, wherein all the newly added organic solvent is used in the second step as described above (instead of the mother liquor and make-up organic solvent returned in the fifth step as described above).
The various solvents used in the present invention are reagent grade and do not require further processing.
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without being limited by any particular theory or mechanism.
All features defined herein as numerical ranges or percentage ranges, such as values, amounts, levels and concentrations, are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.
The features mentioned above, or those mentioned in the embodiments, may be combined in any combination. All features disclosed in this specification may be combined in any combination, and all possible combinations are intended to be included within the scope of the specification as long as there is no conflict between such features and the combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, the features disclosed are merely generic examples of equivalent or similar features.
The main advantages of the invention are:
1. the production method provided by the invention can realize continuous cycle production.
2. The production method provided by the invention obtains high-purity refined glycolide (namely a product) in each round of continuous production, and except for the first batch of continuous production (in an appearance, the first batch of continuous production is used for paving, and the subsequent continuous cyclic production can be realized when the pavement is well paved), the yield of the refined glycolide obtained in each subsequent batch of continuous production is basically the same.
3. Most of the crystallization mother liquor collected after the last cooling crystallization can be recycled, that is, only a small amount of solvent needs to be supplemented in the next circulation to continue the circulation production, so that the use amount of the solvent can be effectively saved.
4. The production method provided by the invention adopts a plurality of serially connected crystallization kettles with the temperature descending in a stepped manner to carry out continuous cooling and crystallization on the pretreated crude glycolide, compared with the conventional recrystallization method, the method can obviously save the using amount of the solvent, does not need to carry out the removal process of the residual solvent, has no waste liquid treatment problem, has no pollution to the environment, has good continuous stability of the whole process flow, can effectively avoid unnecessary material loss, reduces the process cost, has low energy consumption, can realize low-carbonization continuous production, and is convenient for industrial expanded production.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Experimental procedures without specific conditions noted in the following examples, generally according to conventional conditions or according to conditions recommended by the manufacturers. All percentages, ratios, proportions, or parts are by weight unless otherwise specified. The weight volume percentage units in the present invention are well known to those skilled in the art and refer to, for example, the weight (g) of solute in 100 ml of solution. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.
In the following examples, the purified glycolide products obtained were measured for the glycolide, residual solvent, and glycolic acid dimer contents by gas chromatography, a water content by a Karl Fischer moisture meter, and a glycolic acid content by a potentiometric titration method (e.g., an automatic potentiometric titrator), which are well known in the art.
Example 1 (5 crystallization kettles)
In the crude glycolide product to be purified in this example, the glycolide content was about 92.3wt%, the glycolic acid content was about 3.6wt%, the water content was about 0.8wt%, and the glycolic acid polymer content was about 3.3wt%.
Washing 10kg of crude glycolide product to be purified with anhydrous ethanol, centrifuging again, removing supernatant, retaining solids, repeating the above operation 2 times (about 13.5kg of anhydrous ethanol used in each washing) to obtain about 9.57kg of pretreated material with moisture content (mainly anhydrous ethanol, inclusion of some glycolic acid and water impurities in crude glycolide) of less than or equal to 5% and glycolic acid dimer content of less than 0.22wt%, adding the pretreated material to a stirred tank containing 40kg of ethyl acetate solvent, heating to about 60 deg.C while stirring to sufficiently dissolve the pretreated material, filtering to remove solid impurities (very few, essentially negligible), retaining about 49.57kg of liquid material with glycolic acid dimer content of less than or equal to 500ppm, introducing the liquid material to a first crystallization tank at a temperature of about 42 deg.C for a residence time of about 120min, then the mixture is introduced into a second crystallization kettle with the temperature of about 30 ℃ and the residence time is about 90min, then the mixture is introduced into a third crystallization kettle with the temperature of about 18 ℃ and the residence time is about 50min, then the mixture is introduced into a fourth crystallization kettle with the temperature of about 10 ℃ and the residence time is about 35min, then the mixture is introduced into a fifth crystallization kettle with the temperature of about-5 ℃ and the residence time is about 15min, then the slurry of the fifth crystallization kettle is centrifuged for about 49.57kg, the obtained solid is dried for 2 hours under the absolute pressure of less than or equal to 500Pa at 40 ℃, and about 7.09kg of refined glycolide is obtained, the yield is 70.9%, and about 42.48kg of the obtained mother liquor (the solvent lost after drying is collected by a heat exchanger for example) is mixed with the mother liquor, a very small amount of the solvent exists in the dried refined glycolide, and the amount of the solvent can be ignored and can be returned to the stirring kettle, namely about 37.89kg, about 4kg of ethyl acetate solvent is added into the stirring kettle, and the ethyl acetate solvent and the next pretreatment material (note: from the second batch, the selection amount of the crude glycolide product to be purified in each batch is about 8.02kg, after washing with absolute ethanol and centrifugal separation for 2 times, about 7.68kg of pretreatment material is obtained, wherein the content of the glycolic acid dimer is less than 0.22 wt%), stirring and dissolving, filtering to remove solid impurities, and about 49.57kg of liquid material is remained, wherein the content of the glycolic acid dimer in the liquid material is less than or equal to 500ppm, then introducing the liquid material into the first crystallization kettle for subsequent continuous cooling and crystallization, finally, about 49.57kg of slurry obtained from the fifth crystallization kettle is centrifuged, the solid is remained, drying is carried out at 40 ℃ and absolute pressure is less than or equal to 500Pa, namely about 7.09kg of refined glycolide is obtained (continuous circulation is realized, the second batch circulation brings the material remained or accumulated in the first batch circulation process, apparent retention amount of the glycolide product in the first batch is less than or equal to 500Pa, namely about 7.89kg of refined glycolide is obtained), and the yield of the refined glycolide is about 48.89 kg obtained in the second batch, and the continuous circulation is obtained, and the yield is about 37.89kg of the refined glycolide obtained by repeating steps, and the same as the continuous circulation of the continuous production.
Based on the above steps, in the refined glycolide product produced in the first batch of the method in this embodiment, the glycolide content is about 99.91wt%, the residual solvent content is about 0.04wt%, the glycolic acid content is about 0.0107wt%, the glycolic acid dimer content is about 0.0102wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the second batch, the glycolide content is about 99.91wt%, the residual solvent content is about 0.04wt%, the glycolic acid content is about 0.0112wt%, the glycolic acid dimer content is about 0.0105wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the third batch, the glycolide content is about 99.91wt%, the residual solvent content is about 0.04wt%, the glycolic acid content is about 0.0116wt%, the glycolic acid dimer content is about 0.011wt%, and the water content is less than 0.03wt%.
Only three batches of refined glycolide products are listed here, but it should be noted that the liquid material formed in the stirred tank can be continuously introduced into the first crystallization tank for continuous cooling and cooling crystallization, so that the fourth, fifth, sixth batches of 8230can be realized, 82303082303082303030A and even the Nth batch can be realized until the cumulative glycolic acid dimer content in the mother liquor to be returned to the stirred tank exceeds 1000ppm or the glycolic acid and/or glycolic acid dimer content in the obtained refined glycolide product exceeds 0.03wt%, the continuous production is stopped, the ethyl acetate solvent is replaced with new one, and the new continuous production is restarted.
Comparative example
In the crude glycolide product to be purified in this comparative example, the glycolide content was about 92.3wt%, the glycolic acid content was about 3.6wt%, the water content was about 0.8wt%, and the glycolic acid polymer content was about 3.3wt%.
Taking 10kg of crude glycolide product to be purified, washing with absolute ethanol, performing centrifugal separation, removing supernatant, retaining solids, repeating the above operation for 1 time (about 7.5kg of absolute ethanol is used in each washing), obtaining about 9.64kg of pretreated material with moisture content (mainly absolute ethanol, impurities including glycolic acid and water in the crude glycolide) less than or equal to 5% and glycolic acid dimer content of about 0.3 wt%), then adding the pretreated material into a stirring kettle containing 40kg of ethyl acetate solvent, heating to about 60 ℃ while stirring, fully dissolving the pretreated material, filtering, removing solid impurities (few and basically neglecting), retaining about 49.64kg of liquid material, wherein the glycolic acid dimer content in the liquid material is about 630ppm, then introducing the liquid material into a first crystallization kettle with a temperature of about 42 ℃, a residence time of about 120min, then a second crystallization vessel at a temperature of about 30 ℃ for a residence time of about 90min, then a third crystallization vessel at a temperature of about 18 ℃ for a residence time of about 50min, then a fourth crystallization vessel at a temperature of about 10 ℃ for a residence time of about 35min, then a fifth crystallization vessel at a temperature of about-5 ℃ for a residence time of about 15min, then the slurry of the fifth crystallization vessel is centrifuged for about 49.64kg, the resulting solid is dried at 40 ℃ and an absolute pressure of 500Pa or less for 2 hours to obtain about 7.1kg of refined glycolide with a yield of 71.0%, and the resulting mother liquor is about 42.54kg (the solvent lost after drying is collected (for example, by a heat exchanger), mixed with the mother liquor, and the amount of solvent present in the dried refined glycolide is very small, if measured in kg, negligible) of about 89.1% (i.e., about 37.89 kg) was returned to the stirred tank, and about 4kg of ethyl acetate solvent was replenished into the stirred tank, along with the next batch of pretreated material entering the stirred tank (note: from the second time, the selection amount of the crude glycolide product to be purified is about 8.02kg, after washing with absolute ethanol and centrifugal separation for 2 times, about 7.75kg of the pretreated material is obtained, wherein the content of the glycolic acid dimer is about 0.3wt%, after stirring and dissolving, solid impurities are removed by filtration, about 49.64kg of the liquid material is remained, wherein the content of the glycolic acid dimer in the liquid material is about 960ppm, then the liquid material is introduced into the first crystallization kettle for subsequent continuous cooling and cooling crystallization, finally about 49.64kg of the slurry obtained from the fifth crystallization kettle is subjected to centrifugal separation, the solid is remained, and the slurry is dried for 2 hours at 40 ℃ and absolute pressure less than or equal to 500Pa, about 7.1kg of refined glycolide is obtained, the yield is 88.5%, about 89.1% (i.e. about 37.89 kg) of the mother liquor obtained by separation is returned to the stirring kettle, and the continuous production of the refined glycolide is carried out by the same way.
Based on the above steps, the refined glycolide product produced in the first batch of the comparative example method had a glycolide content of about 99.50wt%, a residual solvent content of about 0.4wt%, a glycolic acid content of about 0.0242wt%, a glycolic acid dimer content of about 0.0226wt%, and a water content < 0.03wt%;
in the refined glycolide product produced in the second batch, the glycolide content is about 99.50wt%, the residual solvent content is about 0.4wt%, the glycolic acid content is about 0.0298wt%, the glycolic acid dimer content is about 0.0285wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the third batch, the glycolide content is about 99.50wt%, the residual solvent content is about 0.4wt%, the glycolic acid content is about 0.0386wt%, the glycolic acid dimer content is about 0.0362wt%, and the water content is less than 0.03wt%.
It can be seen from this that, in the comparative example method, since the contents of glycolic acid dimer in the pretreatment material and the liquid material are not strictly controlled, the contents of glycolic acid and glycolic acid dimer in the purified glycolide product produced in the next batch (compared with the purified glycolide product produced in the previous batch) are sharply increased, and only when the process is carried out to the third batch, the contents of glycolic acid and glycolic acid dimer in the obtained purified glycolide product exceed 0.03wt%, which does not meet the product standard, and the production needs to be stopped, and stable and continuous production of purified glycolide cannot be realized.
Example 2 (4 crystallization kettles)
In the crude glycolide product to be purified in this example, the glycolide content was about 84.9wt%, the glycolic acid content was about 12.6wt%, the water content was about 0.9wt%, and the glycolic acid polymer content was about 1.6wt%.
Washing 5kg of crude glycolide product to be purified with anhydrous ethanol, centrifuging again to remove supernatant, retaining solids, repeating the above operations 2 times (about 6.75kg of anhydrous ethanol used in each washing) to obtain about 4.40kg of pretreated material having a moisture content of 5% or less and a dimer of glycolic acid content of less than 0.22wt%, subsequently adding the pretreated material to a stirred tank containing 25kg of ethyl acetate solvent, heating to about 60 ℃ with stirring to dissolve the pretreated material sufficiently, filtering to remove solid impurities (very few, essentially negligible), retaining about 29.40kg of liquid material having a dimer of glycolic acid content of 500ppm or less in the liquid material, introducing the liquid material to a first crystallization tank having a temperature of about 35 ℃ for a residence time of about 100min, introducing to a second crystallization tank having a temperature of about 18 ℃ for a residence time of about 60min, introducing to a third crystallization tank having a temperature of about 5 ℃ for a residence time of about 30min, introducing to a temperature of about 5 ℃ for a residence time of about 5min, introducing to a fourth crystallization tank having a residence time of about 18 ℃ for a residence time of about 60min, introducing to a third crystallization tank having a residence time of about 5 ℃ for a recovery of ethyl acetate solution, drying of about 26.47kg of ethyl acetate in the stirred tank, and recovering the resulting from the ethyl acetate slurry obtained by centrifuging the first crystallization tank (about 2.40 kg of ethyl acetate solution) and drying of about 26.40 kg of ethyl acetate solvent, and the first crystallization tank, and the fourth crystallization tank for about 2kg of about 26.40 kg of ethyl acetate solution, and the first crystallization tank having a recovery time of about 26.40 kg of the first crystallization tank having a recovery time of ethyl acetate solvent, and the first crystallization tank, and the second crystallization tank having a recovery time of about 26.47 hours, and the second crystallization tank having a recovery time of about 6 hours, and a recovery rate of ethyl acetate concentration of about 2kg of ethyl acetate concentration of about 6.47kg of about 6kg of ethyl acetate: starting from the second batch, about 3.8kg of crude glycolide product was selected per batch, and after washing with anhydrous ethanol and centrifuging 2 times, about 3.34kg of pretreated material was obtained, in which the glycolic acid dimer content was less than 0.22 wt.%) was dissolved with stirring, filtering to remove solid impurities, keeping about 29.4kg of liquid material, wherein the content of glycolic acid dimer in the liquid material is less than or equal to 500ppm, then introducing the liquid material into the first crystallization kettle to perform subsequent continuous cooling crystallization, finally centrifuging about 29.4kg of slurry obtained by the fourth crystallization kettle, keeping the solid, drying at 40 ℃ and absolute pressure of less than or equal to 500Pa for 2 hours to obtain about 2.93kg of refined glycolide, wherein the yield is 77.1%, returning about 89% (namely about 23.56 kg) of about 26.47kg of mother liquor obtained by separation to the stirring kettle, and repeating the steps in the same way to continuously produce the refined glycolide.
Based on the above steps, the refined glycolide product produced in the first batch of the method of this embodiment has a glycolide content of about 99.86wt%, a residual solvent content of about 0.06wt%, a glycolic acid content of about 0.011wt%, a glycolic acid dimer content of about 0.0104wt%, and a water content of less than 0.03wt%;
in the refined glycolide product produced in the second batch, the glycolide content is about 99.86wt%, the residual solvent content is about 0.06wt%, the glycolic acid content is about 0.0114wt%, the glycolic acid dimer content is about 0.0107wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the third batch, the glycolide content is about 99.86wt%, the residual solvent content is about 0.06wt%, the glycolic acid content is about 0.012wt%, the glycolic acid dimer content is about 0.0112wt%, and the water content is less than 0.03wt%.
Only three batches of refined glycolide products are listed here, but it should be noted that the liquid material formed in the stirred tank can be continuously introduced into the first crystallization tank for continuous cooling and cooling crystallization, so that the fourth, fifth, sixth batches of 8230can be realized, 82303082303082303030A and even the Nth batch can be realized until the cumulative glycolic acid dimer content in the mother liquor to be returned to the stirred tank exceeds 1000ppm or the glycolic acid and/or glycolic acid dimer content in the obtained refined glycolide product exceeds 0.03wt%, the continuous production is stopped, the ethyl acetate solvent is replaced with new one, and the new continuous production is restarted.
Example 3 (3 crystallization kettles)
In the crude glycolide product to be purified in this example, the glycolide content was about 81.6wt%, the glycolic acid content was about 14.8wt%, the water content was about 1.2wt%, and the glycolic acid polymer content was about 2.4wt%.
Washing 5kg of crude glycolide product to be purified with anhydrous ethanol, centrifuging again to remove supernatant, retaining solids, repeating the above operations 2 times (about 6.75kg of anhydrous ethanol used in each washing) to obtain about 4.22kg of pretreated material having a moisture content of 5% or less and a dimer of glycolic acid content of less than 0.22wt%, adding the pretreated material to a stirred tank containing 28kg of ethyl acetate solvent, heating to about 60 ℃ with stirring to dissolve the pretreated material sufficiently, filtering to remove solid impurities (very few, essentially negligible), retaining about 32.22kg of liquid material having a dimer of glycolic acid content of 500ppm or less in the liquid material, introducing the liquid material to a first crystallization tank having a temperature of about 40 ℃ for a residence time of about 95min, introducing to a second crystallization tank having a temperature of about 12 ℃ for a residence time of about 30min, introducing to a third crystallization tank having a temperature of about-5 ℃ for a residence time of about 10min, returning the third crystallization tank to a third crystallization tank having a temperature of about 5 ℃ for a residence time of about 2 min, drying the third crystallization tank to obtain about 2.85 kg of ethyl acetate concentrate, and drying the crude glycolide in the stirred tank at a yield of about 2.22kg of ethyl acetate solvent (89.22 kg of about 2kg of the next 20 kg of ethyl acetate solvent), and about 2.22kg of ethyl acetate solvent, and 2kg of the stirred tank for a recovery time of the crude glycolide: starting from the second batch, about 3.88kg of crude glycolide product was selected per batch to be purified, after washing with absolute ethanol and centrifuging 2 times, about 3.27kg of pretreated material was obtained, wherein the glycolic acid dimer content was less than 0.22 wt%), after dissolution with stirring, and after filtration, solid impurities were removed, about 32.22kg of liquid material was retained, wherein the content of glycolic acid dimer in the liquid material is less than or equal to 500ppm, then the liquid material is introduced into a first crystallization kettle for subsequent continuous cooling and crystallization, finally about 32.22kg of slurry obtained by a third crystallization kettle is centrifugally separated, the solid is retained, and the slurry is dried for 2 hours at 52 ℃ and under the absolute pressure of less than or equal to 500Pa, so that about 2.89kg of refined glycolide is prepared, the yield is 74.48 percent, about 89.2 percent (namely about 26.15 kg) in about 29.33kg of mother liquor obtained by separation is returned to a stirring kettle, and the rest is done in turn, so as to continuously produce the refined glycolide.
Based on the above steps, in the refined glycolide product produced in the first batch of the method of this embodiment, the glycolide content is about 99.82wt%, the residual solvent content is about 0.09wt%, the glycolic acid content is about 0.0136wt%, the glycolic acid dimer content is about 0.0128wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the second batch, the glycolide content is about 99.82wt%, the residual solvent content is about 0.09wt%, the glycolic acid content is about 0.0145wt%, the glycolic acid dimer content is about 0.0134wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the third batch, the glycolide content is about 99.82wt%, the residual solvent content is about 0.09wt%, the glycolic acid content is about 0.0152wt%, the glycolic acid dimer content is about 0.0139wt%, and the water content is less than 0.03wt%.
Only three batches of refined glycolide products are listed here, but it should be noted that the liquid material formed in the stirred tank can be continuously introduced into the first crystallization tank for continuous cooling and cooling crystallization, so that the yield of the fourth, fifth and sixth batches of \8230 \ 8230and \/8230can be realized, or even the N batch can be realized, until the content of glycolic acid dimer accumulated in the mother liquor to be returned to the stirred tank exceeds 1000ppm or the content of glycolic acid and/or glycolic acid dimer in the obtained refined glycolide product exceeds 0.03wt%, the continuous production is stopped, new ethyl acetate solvent is replaced, and the new continuous production is restarted.
Example 4 (2 crystallization kettles)
In the crude glycolide product to be purified in this example, the glycolide content was about 92.2wt%, the glycolic acid content was about 5.7wt%, the water content was about 0.7wt%, and the glycolic acid polymer content was about 1.4wt%.
Washing 5kg of crude glycolide product to be purified with anhydrous ethanol, centrifuging again, removing supernatant, retaining solids, repeating the above operations 2 times (about 6.75kg of anhydrous ethanol used in each washing) to obtain about 4.78kg of pretreated material having a moisture content of 5% or less and a dimer of glycolic acid content of less than 0.22wt%, subsequently adding the pretreated material to a stirred tank containing 30kg of ethyl acetate solvent, heating to about 60 ℃ with stirring to dissolve the pretreated material sufficiently, filtering to remove solid impurities (very few, essentially negligible), retaining about 34.78kg of liquid material having a dimer of glycolic acid content of 500ppm or less in the liquid material, introducing the liquid material to a first crystallization tank having a temperature of about 32 ℃ for a residence time of about 60min, introducing to a second crystallization tank having a temperature of about-2 ℃ for a residence time of about 15min, then injecting about 34.78kg of slurry from the second crystallization tank for centrifugal separation, drying the resulting solids at 60 ℃ under absolute pressure of 2 hours, drying to obtain about 6.11% or less of ethyl acetate in a stirred tank, and returning the resulting fine ethyl acetate solution to the stirred tank (about 6.78 kg of ethyl acetate solvent), and returning the stirred tank to the stirred tank for about 10kg of ethyl acetate recovery rate of about 6.10 kg: starting from the second batch, the selection amount of crude glycolide products to be purified in each batch is about 3.94kg, after washing with absolute ethanol and centrifugal separation for 2 times, about 3.76kg of pretreatment materials is obtained, wherein the content of glycolic acid dimer is less than 0.22wt percent), after stirring and dissolving, solid impurities are removed by filtration, about 35.44kg of liquid materials is remained, wherein the content of glycolic acid dimer in the liquid materials is less than or equal to 500ppm, and then the liquid materials are introduced into a first crystallization kettle for subsequent continuous cooling and cooling crystallization, and finally, centrifuging about 35.44kg of slurry obtained by the second crystallization kettle, keeping the solid, drying for 2 hours at the temperature of 60 ℃ and under the absolute pressure of less than or equal to 500Pa to obtain about 3.12kg of refined glycolide, wherein the yield is 79.19 percent, returning about 65 percent (about 21 kg) of mother liquor obtained by separation from about 32.32kg of mother liquor to the stirring kettle, and repeating the steps to continuously produce the refined glycolide.
Based on the above steps, the refined glycolide product produced in the first batch of the method of this embodiment has a glycolide content of about 99.80wt%, a residual solvent content of about 0.1wt%, a glycolic acid content of about 0.0142wt%, a glycolic acid dimer content of about 0.013wt%, and a water content of less than 0.03wt%;
in the refined glycolide product produced in the second batch, the glycolide content is about 99.80wt%, the residual solvent content is about 0.1wt%, the glycolic acid content is about 0.0156wt%, the glycolic acid dimer content is about 0.0148wt%, and the water content is less than 0.03wt%;
in the refined glycolide product produced in the third batch, the glycolide content is about 99.80wt%, the residual solvent content is about 0.1wt%, the glycolic acid content is about 0.0172wt%, the glycolic acid dimer content is about 0.0159wt%, and the water content is less than 0.03wt%.
Only three batches of refined glycolide products are listed here, but it should be noted that the liquid material formed in the stirred tank can be continuously introduced into the first crystallization tank for continuous cooling and cooling crystallization, so that the yield of the fourth, fifth and sixth batches of \8230 \ 8230and \/8230can be realized, or even the N batch can be realized, until the content of glycolic acid dimer accumulated in the mother liquor to be returned to the stirred tank exceeds 1000ppm or the content of glycolic acid and/or glycolic acid dimer in the obtained refined glycolide product exceeds 0.03wt%, the continuous production is stopped, new ethyl acetate solvent is replaced, and the new continuous production is restarted.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the scope of the invention, which is defined by the claims appended hereto, and any other technical entity or method that is encompassed by the claims as broadly defined herein, or equivalent variations thereof, is contemplated as being encompassed by the claims.
Claims (10)
1. A continuous process for the production of purified glycolide, characterized in that it comprises the steps of:
(1) Treating the crude glycolide product to obtain a pretreated material;
(2) Mixing and dissolving the pretreated material and a solvent to obtain a liquid material;
(3) Introducing the liquid materials into more than 2 crystallization kettles connected in series one by one to obtain slurry;
(4) And (3) separating the slurry to obtain refined glycolide and mother liquor, and returning the mother liquor to the step (2) to participate in mixing.
2. The production process according to claim 1, wherein the treatment in the step (1) comprises solid-liquid separation after washing the crude glycolide product with the alcohol solvent and retaining the solid.
3. The production process according to claim 1, wherein the glycolic acid dimer content is not more than 0.25w/w% based on the total weight of the pretreated material obtained in step (1).
4. The production method according to claim 1, wherein the solvent in the step (2) is at least one of an acetate, a ketone, or a methane chloride.
5. The production process according to claim 1, wherein the glycolic acid dimer content is not more than 500ppm based on the total weight of the liquid material obtained in the step (2).
6. The production method according to claim 1, wherein the temperature of the first crystallization vessel introduced in the step (3) is 5 to 30 ℃ lower than the dissolution temperature in the step (2), and the temperature of the last crystallization vessel introduced is not higher than 0 ℃.
7. The production process according to claim 6, wherein the temperature setting from the first to the last crystallization vessel is decreased one by one, and the temperature difference between each crystallization vessel and the adjacent crystallization vessel in series is 5 to 35 ℃.
8. The production process according to claim 1, wherein the liquid material is introduced into the crystallization vessel with a residence time of 5 to 150 minutes.
9. The process according to claim 1, wherein the amount of the solvent added while the mother liquor returned to the step (2) is mixed in the step (4) is 5 to 50w/w%, preferably 5 to 15w/w% of the returned mother liquor.
10. The production process according to any one of claims 1 to 9, wherein the slurry is subjected to solid-liquid separation and then the solid material is dried to obtain purified glycolide.
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