CN112574165B - Method for generating lactide by one-step conversion - Google Patents
Method for generating lactide by one-step conversion Download PDFInfo
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- CN112574165B CN112574165B CN202011625907.9A CN202011625907A CN112574165B CN 112574165 B CN112574165 B CN 112574165B CN 202011625907 A CN202011625907 A CN 202011625907A CN 112574165 B CN112574165 B CN 112574165B
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- 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
Abstract
The invention relates to a method for producing lactide by one-step conversion, which comprises the following steps: taking lactic acid as a raw material, carrying out dehydration reaction in an organic solvent under the action of a catalyst, and removing water generated in the reaction process while reacting to obtain a reaction solution containing lactide; the catalyst comprises a stannous-based catalyst. The method provided by the invention has the advantages of mild reaction conditions, simple operation, high product yield and high purity, reduces the consumption of energy and chemicals, and is environment-friendly.
Description
Technical Field
The invention relates to the field of chemical industry, in particular to a method for generating lactide by one-step conversion.
Background
Polylactic acid, also known as polylactide, is a polyester polymer obtained by polymerizing lactic acid as a main raw material, and is a novel biodegradable material. The production process of high molecular weight polylactic acid generally comprises: lactic acid oligomer is generated through lactic acid dehydration and polycondensation, crude lactide is generated through lactic acid oligomer catalytic cracking, the crude lactide is purified to obtain polymer grade lactide, and finally, the polylactic acid with high molecular weight is obtained through the ring opening polymerization reaction of the lactide.
Lactide (C)6H8O4) White needle-shaped, the melting point is 93-95 ℃, the boiling point is 260 ℃, the molecular weight is 144, the polylactic acid is easily soluble in chloroform and ethanol, and is insoluble in water, and the polylactic acid is an intermediate for preparing the polylactic acid. The traditional preparation of lactide mainly comprises a two-step method, lactic acid is dehydrated to generate oligomers, and the oligomers are cracked and cyclized to generate lactide. However, the traditional lactide preparation method has high energy consumption, low selectivity, high separation and purification difficulty and high manufacturing cost of lactide and polylactic acid, and generates a large amount of racemic products.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for producing lactide in one step.
Specifically, the method for generating lactide by one-step conversion provided by the invention comprises the following steps: lactic acid is used as a raw material, dehydration reaction is carried out in an organic solvent under the action of a catalyst, and water generated in the reaction process is removed at the same time of the reaction, so as to obtain a reaction liquid containing lactide.
The method provided by the invention can dehydrate lactic acid into ring under the action of the catalyst to directly generate lactide, and the water dehydrated from lactic acid and the organic solvent form an azeotrope, thereby effectively removing the generated water from the system.
The lactic acid used in the present invention is selected from the group consisting of L-lactic acid and D-lactic acid.
The catalyst used in the present invention comprises a stannous catalyst, i.e., comprises positive divalent (Sn)2+) A catalyst for tin ions. The present invention has surprisingly found that with such catalysts only one conversion step is required to dehydrate lactic acid directly into a ring, producing lactide at a higher conversion rate.
In some embodiments, the stannous-based catalyst is selected from the group consisting of stannous chloride, stannous lactate, and stannous oxide. The invention surprisingly discovers that the stereoselectivity of the reaction can be obviously improved by adopting the catalyst, so that the generation of racemic lactide (namely DL-lactide) is obviously reduced, and the purity of a target substance lactide in a product is improved.
In some embodiments, the catalyst consists of a stannous-based catalyst. Specifically, the catalyst may be one kind of the stannous catalyst, or may be a combination of two or more kinds of the stannous catalysts.
In some embodiments, the catalyst is the stannous-based catalyst and a mixture of a stannous-based catalyst and other types of catalysts.
In some embodiments, the other type of catalyst is a non-metal type catalyst.
In some embodiments, the other type of catalyst is selected from the group consisting of acidic zeolites and activated clays.
In some embodiments, the mass ratio of the lactic acid to the stannous-based catalyst is 1: (0.0001 to 0.1), preferably 1: (0.005-0.05). Specifically, the mass ratio of the lactic acid to the stannous catalyst may be 1: 0.0001,1: 0.0005,1: 0.001,1: 0.005,1: 0.01,1: 0.05,1: 0.1.
in the method provided by the invention, the dehydration reaction is carried out in an organic solvent.
In some embodiments, the organic solvent is a solvent capable of forming an azeotrope with water.
In some embodiments, the organic solvent is a solvent having a boiling point higher than the boiling point of water.
In some embodiments, the organic solvent has a boiling point of no greater than 160 ℃.
In some embodiments, the organic solvent is an ether solvent. Preferably, the ethereal solvent is selected from the group consisting of isopropyl ether, anisole, phenetole, butyl ether, and diphenyl ether.
In some embodiments, the organic solvent is a ketone solvent. Preferably, the ketone solvent is selected from methyl n-butyl ketone, methyl isobutyl ketone, ethyl n-butyl ketone, and the like.
In some embodiments, the organic solvent is a benzene-based solvent. Preferably, the benzene-based solvent is selected from toluene, xylene, and the like.
In some embodiments, the organic solvent is an alkane solvent. Preferably, the alkane solvent is selected from octane, nonane, decane, and the like.
In some embodiments, the mass ratio of lactic acid to organic solvent is 1: (0.1 to 10), preferably 1: (0.2-2). Specifically, the mass ratio of the lactic acid to the organic solvent may be 1: 0.1,1: 0.2,1: 0.3,1: 0.4,1: 0.5,1: 0.6,1: 0.7,1: 0.8,1: 0.9,1: 1,1: 1.1,1: 1.2,1: 1.3,1: 1.4,1: 1.5,1: 1.6,1: 1.7,1: 1.8,1: 1.9,1: 2,1: 5 or 1: 10.
in the method provided by the invention, the dehydration reaction is carried out under the conditions of temperature and pressure which can enable the dehydration of the lactic acid.
In some embodiments, the temperature of the dehydration reaction is above the boiling point of the organic solvent.
In some embodiments, the temperature of the dehydration reaction is 5 to 30 ℃ higher than the boiling point of the organic solvent.
In some embodiments, the dehydration reaction is carried out at 100 to 160 ℃. Specifically, the reaction temperature may be 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃ or 160 ℃.
In some embodiments, the dehydration reaction is carried out at 135 to 155 ℃. Specifically, the reaction temperature may be 135 ℃, 140 ℃, 145 ℃, 150 ℃ or 155 ℃.
In some embodiments, the dehydration reaction is carried out at atmospheric pressure.
In some embodiments, the dehydration reaction is performed under negative pressure conditions, preferably under a pressure of-0.1 MPa to-0.02 MPa.
In the method provided by the invention, the dehydration reaction is carried out, and simultaneously, water generated in the reaction process needs to be removed so as to promote the full progress of the dehydration reaction. The removal of water from the reaction system may be carried out by means known in the art.
In some embodiments, a reflux condenser may be used to collect the water produced during the reaction and remove it from the reaction system.
In some embodiments, the reaction can be confirmed to proceed sufficiently by weighing the amount of water removed from the reaction system.
The present invention may further include the following steps in addition to obtaining a lactide-containing reaction solution: recovering the solvent in the reaction liquid containing lactide to obtain a reaction product rich in lactide. The solvent recovered in this step can be returned to the next reaction for further use.
In some embodiments, the recovery of the solvent is performed using a distillation process.
In some embodiments, when the solvent is recovered by distillation, the distillation temperature is preferably 5 to 30 ℃ higher than the boiling point of the solvent, and preferably not higher than 160 ℃; preferably, the distillation pressure is-0.1 MPa to-0.02 MPa.
The invention can also comprise the following steps on the basis of obtaining the reaction product rich in lactide: and recovering the catalyst in the reaction product to obtain a crude lactide product. The catalyst recovered in the step is returned to the next batch for further use.
The invention can also comprise the following steps on the basis of obtaining the crude lactide product: and purifying the crude lactide product. The purification may be carried out by methods known in the art, such as distillation, recrystallization, and the like.
The operations involved in the present invention are conventional in the art unless otherwise specified, and the separation apparatus involved may be conventional as is well known in the industry.
The above-described preferred conditions may be combined with each other to obtain a specific embodiment, in accordance with common knowledge in the art.
Compared with the prior art, the method provided by the invention has the advantages of mild reaction conditions, simple operation, low requirement on vacuum degree, capacity of generating lactide even under normal pressure, and capability of directly returning the solvent to the next batch of reaction for continuous use without any treatment. The method provided by the invention reduces the generation of racemic lactide, has high yield and high purity of the lactide, reduces the consumption of energy and chemicals, simultaneously reduces the discharge of waste, is environment-friendly and is beneficial to industrial production.
Detailed Description
Preferred embodiments of the present invention will be described in detail with reference to the following examples.
The detection of lactide used in the present invention is gas chromatography.
The calculation method of the lactide conversion rate is as follows: lactide conversion rate (100% × (lactide content × mass of reaction product)/(mass of theoretical lactide);
wherein the lactide content is the lactide content in the reaction product, including the content of L-lactide and racemic DL-lactide; the mass of the reaction product is the mass obtained by weighing the substances left after the solvent is removed after the reaction is finished; the theoretical mass of lactide is the added mass of lactic acid at the beginning of the reaction x 72/90.
Example 1
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) 151.00g L-lactic acid (the concentration is 101.38%), 3.00g of stannous chloride and 100.00g of dimethylbenzene are weighed in sequence and placed in a 1000ml three-neck flask, a stirrer is placed in the flask in advance, and a condensation reflux device is arranged for collecting water generated by the reaction; placing the reaction device in an oil bath kettle at 145 ℃ for dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 24 hours till the reaction is full, and stopping the reaction;
(2) replacing a distillation device, and distilling the reaction liquid obtained in the step (1) at 145 ℃ under the condition that a water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; the colorless and transparent xylene obtained by distillation was collected separately and used for the next reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 124.05 g.
The reaction product was sampled and checked by chromatography, and the results showed that the L-lactide content was 87.31%, the purity of L-lactide was 92.86%, the racemic DL-lactide content was 4.26%, and the calculated lactide conversion was 92.71%.
Example 2
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) sequentially weighing 201.00g of L-lactic acid (the concentration is 102.19%), 4.20g of stannous chloride and 200.00g of n-octane, placing the weighed materials into a 1000ml three-neck flask, placing a stirrer in the flask in advance, and arranging a condensation reflux device for collecting water generated by the reaction; placing the reaction device in an oil bath kettle at 140 ℃ for dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 48 hours to fully react, and stopping the reaction;
(2) replacing a distillation device, and distilling n-octane from the reaction liquid obtained in the step (1) at 140 ℃ under the condition that a water circulating pump is vacuumized by a pump with the pressure p being-0.1 Mpa until no liquid is evaporated; colorless and transparent n-octane obtained by distillation was separately collected and used for the next reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 173.12 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 83.34%, the purity of L-lactide was 95.2%, the content of racemic DL-lactide was 2.62%, and the conversion of lactide was 90.58% by calculation.
Example 3
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) 150.00g of L-lactic acid (the concentration is 100.64 percent), 0.50g of stannous chloride and 200.00g of butyl ether are sequentially weighed and placed in a 1000ml three-neck flask, a stirrer is placed in the flask in advance, and a condensation reflux device is arranged for collecting water generated by the reaction; placing the reaction device in an oil bath kettle at 140 ℃, vacuumizing by using a water circulating pump, performing dehydration reaction under the condition that p is-0.04 Mpa, collecting water generated in the reaction process by using a condensation reflux device during the reaction, fully reacting for 16 hours, and stopping the reaction;
(2) replacing a distillation device, and distilling the butyl ether from the reaction solution obtained in the step (1) at 140 ℃ under the condition that a water circulating pump is vacuumized by a pump with p being-0.1 Mpa until no liquid is evaporated; the colorless and transparent butyl ether obtained by distillation was collected separately and used for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 118.17 g.
The reaction product was sampled and checked by chromatography, and the results showed that the L-lactide content was 92.54%, the purity of L-lactide was 94.53%, the DL-lactide content was 2.91%, and the calculated lactide conversion was 93.39%.
Example 4
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) 2993.00g of L-lactic acid (the concentration is 100.48%), 60.60g of stannous chloride and 1660.00g of toluene are weighed in sequence and placed in a 10L reaction kettle, the reaction kettle is stirred, and a condensation reflux device is arranged for collecting and collecting water generated by the reaction; setting the temperature of a heating jacket on the outer wall of the reaction kettle to be 135 ℃, carrying out dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 39 hours to fully react, and stopping the reaction;
(2) distilling the reaction liquid obtained in the step (1) at 140 ℃ under the condition that the water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; the colorless and transparent toluene obtained by distillation was collected separately and used for the next reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 2411.62 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 95.17%, the purity of L-lactide was 96.06%, the content of racemic DL-lactide was 1.47%, and the conversion of lactide was calculated to be 96.87%.
Example 5
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) 153.00g of L-lactic acid (the concentration is 101.32 percent), 3.00g of stannous oxide and 205.00g of anisole are sequentially weighed and placed in a 1000ml three-neck flask, a stirrer is placed in the flask in advance, and a condensation reflux device is arranged for collecting water generated by the reaction; heating the reaction device in an oil bath at 155 ℃, vacuumizing by a water circulating pump until the pressure is-0.06 Mpa, performing dehydration reaction, collecting water generated in the reaction process by a condensation reflux device during the reaction, performing reaction for 23 hours, and stopping the reaction;
(2) replacing a distillation device, and distilling the anisole from the reaction solution obtained in the step (1) at 155 ℃ under the condition that the water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; colorless and transparent anisole obtained by distillation is separately collected for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 120.17 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 93.65%, the purity of L-lactide was 94.4%, the content of racemic DL-lactide was 4.31%, and the conversion of lactide was calculated to be 94.92%.
Example 6
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) 151.80g of L-lactic acid (the concentration is 101.32%), 3.20g of stannous octoate and 195.60g of butyl ether are weighed in sequence and placed in a 1000ml three-necked bottle, a stirrer is placed in the bottle in advance, and a condensation reflux device is arranged for collecting water generated by the reaction; placing the reaction device in an oil bath kettle at 155 ℃ for dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 24 hours till the reaction is full, and stopping the reaction;
(2) replacing a distillation device, and distilling the butyl ether from the reaction solution obtained in the step (1) at the temperature of 155 ℃ under the condition that the water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; the colorless and transparent butyl ether obtained by distillation was collected separately and used for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 118.00 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 91.55%, the purity of L-lactide was 93.20%, the content of racemic DL-lactide was 5.80%, and the conversion of lactide was calculated to be 93.36%.
Example 7
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) 158.00g of L-lactic acid (the concentration is 100.57%), 0.80g of stannous oxide, 3.20g of activated clay and 213.00g of butyl ether are weighed in sequence and placed in a 1000ml three-necked bottle, a stirrer is placed in the bottle in advance, and a condensation reflux device is arranged for collecting water generated by the reaction; heating the reaction device in 140 deg.C oil bath, vacuumizing with water circulating pump, dehydrating under-0.05 Mpa, collecting water generated during reaction with condensing reflux device, reacting for 23 hr, and stopping reaction;
(2) replacing a distillation device, and distilling the butyl ether from the reaction solution obtained in the step (1) at 140 ℃ under the condition that a water circulating pump is vacuumized by a pump with p being-0.1 Mpa until no liquid is evaporated; the colorless and transparent butyl ether obtained by distillation was collected separately and used for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 120.40 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 91.94%, the purity of L-lactide was 95.83%, the content of racemic DL-lactide was 1.65%, and the conversion of lactide was calculated to be 88.64%.
Example 8
The embodiment provides a method for generating lactide by one-step conversion, which specifically comprises the following steps:
(1) weighing 150.00g of L-lactic acid (the concentration is 101.09%), 3.80g of stannous oxide and 200.40g of butyl ether in sequence, placing the weighed materials into a 1000ml three-necked bottle, placing a stirrer in the bottle in advance, and arranging a condensation reflux device for collecting water generated by the reaction; placing the reaction device in an oil bath at 155 ℃ for heating to carry out dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 18 hours till the reaction is full, and stopping the reaction;
(2) replacing a distillation device, and distilling the butyl ether from the reaction solution obtained in the step (1) at the temperature of 155 ℃ under the condition that the water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; the colorless and transparent butyl ether obtained by distillation was collected separately and used for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 121.97 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 93.33%, the purity of L-lactide was 94.00%, the content of racemic DL-lactide was 3.22%, and the conversion of lactide was calculated to be 96.97%.
Comparative example 1
The comparative example provides a method for generating lactide by one-step conversion, which comprises the following specific steps:
(1) 151g of L-lactic acid (the concentration is 101.32%), 4.4g of zinc oxide and 213g of methyl isobutyl ketone are weighed in sequence and placed in a 1000ml three-necked bottle, a stirrer is placed in the bottle in advance, and a condensation reflux device is arranged for collecting water generated by the reaction; placing the reaction device in an oil bath kettle at 145 ℃ for dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 47 hours to fully react, and stopping the reaction;
(2) replacing a distillation device, and distilling the reaction liquid obtained in the step (1) at 145 ℃ under the condition that a water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; the colorless and transparent methyl isobutyl ketone obtained by distillation is separately collected and used for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 120.70 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 75.22%, the purity of L-lactide was 90.63%, the content of racemic DL-lactide was 8.40%, and the conversion of lactide was calculated to be 82.47%.
Comparative example 2
The comparative example provides a method for generating lactide by one-step conversion, which comprises the following specific steps:
(1) weighing 150.00g of L-lactic acid (the concentration is 102.47%), 7.60g of activated clay and 205.00g of butyl ether in sequence, placing the weighed materials into a 1000ml three-necked bottle, placing a stirrer in the bottle in advance, and arranging a condensation reflux device for collecting water generated by the reaction; placing the reaction device in an oil bath kettle at 155 ℃ for dehydration reaction, collecting water generated in the reaction process by using a condensation reflux device during the reaction, carrying out the reaction for 47 hours to fully react, and stopping the reaction;
(2) replacing a distillation device, and distilling the butyl ether from the reaction solution obtained in the step (1) at the temperature of 155 ℃ under the condition that the water circulating pump vacuumizes p to be-0.1 Mpa until no liquid is evaporated; the colorless and transparent butyl ether obtained by distillation was collected separately and used for the next batch of reaction.
The reaction product obtained in step (2) after distillation of the solvent was weighed to 122.14 g.
The reaction product was sampled and detected by chromatography, and the results showed that the content of L-lactide was 10.85%, the purity of L-lactide was 34.04%, the content of racemic DL-lactide was 0.19%, and the conversion of lactide was 11.05% by calculation.
Although the invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it will be apparent to those skilled in the art that many modifications and improvements can be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (6)
1. The method for generating lactide by one-step conversion is characterized by comprising the following steps of: taking lactic acid as a raw material, carrying out dehydration reaction in an organic solvent under the action of a catalyst, and removing water generated in the reaction process while reacting to obtain a reaction solution containing lactide;
recovering the solvent in the reaction liquid containing the lactide by adopting a distillation method to obtain a reaction product, and returning the recovered solvent to the next batch of reaction for continuous use;
recovering the catalyst in the reaction product to obtain a crude lactide product, and returning the recovered catalyst to the next batch for continuous use;
the catalyst is a stannous catalyst or a mixture of the stannous catalyst and other catalysts, the stannous catalyst is stannous chloride, stannous octoate and stannous oxide, the other catalysts are activated clay, the lactic acid is L-lactic acid, and the mass ratio of the lactic acid to the stannous catalyst is 1: (0.0001 to 0.1);
the temperature of the dehydration reaction is 60-160 ℃;
the mass ratio of the lactic acid to the organic solvent is 1: (0.1 to 10);
the organic solvent is an ether solvent;
the dehydration reaction is carried out under the condition of the pressure intensity of-0.1 Mpa to-0.02 Mpa;
the distillation temperature is 5-30 ℃ higher than the boiling point of the solvent and is not higher than 160 ℃, and the distillation pressure is-0.1 Mpa to-0.02 Mpa;
the reaction was confirmed to proceed sufficiently by weighing the amount of water removed from the reaction system.
2. The method according to claim 1, wherein the mass ratio of the lactic acid to the stannous-based catalyst is 1: (0.005-0.05).
3. The method according to claim 1, wherein the ethereal solvent is selected from the group consisting of isopropyl ether, anisole, phenetole, butyl ether, and diphenyl ether.
4. The method according to claim 1, wherein the mass ratio of the lactic acid to the organic solvent is 1: (0.2-2).
5. The method according to claim 1, wherein the temperature of the dehydration reaction is 120 to 160 ℃.
6. The method of claim 1, wherein the water generated during the reaction is collected by a condensing reflux device and removed from the reaction system.
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| CN104981464A (en) * | 2013-02-08 | 2015-10-14 | 道达尔研究技术弗吕公司 | Process for preparing cyclic esters and cyclic amides |
| US10253012B2 (en) * | 2015-10-12 | 2019-04-09 | Korea Research Institute Of Chemical Technology | Method and apparatus for preparation of lactide using lactide purification process |
| CN109160913A (en) * | 2018-04-27 | 2019-01-08 | 北京理工大学 | A kind of method of the rodlike long crystal of L- lactide of synthesizing optical purity is high |
| CN108610323A (en) * | 2018-06-14 | 2018-10-02 | 中国科学院长春应用化学研究所 | A kind of preparation method of lactide |
| CN111057040A (en) * | 2019-11-05 | 2020-04-24 | 浙江工业大学 | Method for catalytically synthesizing lactide by using shape-selective zeolite supported catalyst |
| CN111039918A (en) * | 2019-12-24 | 2020-04-21 | 安徽丰原发酵技术工程研究有限公司 | Method for preparing D-lactide by one-step gas phase reaction |
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