CN116272665A - Process system for continuously and efficiently producing polymer grade lactide - Google Patents
Process system for continuously and efficiently producing polymer grade lactide Download PDFInfo
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Abstract
The invention provides a process system for continuously and efficiently producing polymer grade lactide, which comprises the following specific production steps: s1, feeding pure lactic acid and stannous chloride into a lactic acid dehydration reaction system for continuous dehydration to obtain a lactic acid oligomer; s2: and continuously feeding the lactic acid oligomer into a depolymerization purification reaction system, cooling the generated crude lactide, then partially refluxing the cooled crude lactide to a purification tower, and partially extracting the cooled crude lactide to a crude storage tank. The light components are collected by a light component condenser at the top of the purifying tower and discharged through a reflux ratio controller. The heavy component flows back to the bottom of the purifying tower, and the generated residue is discharged through a residue discharge port on one side of the circulating pump; s3: and (3) feeding the crude lactide into a screw filter through a scraper crystallizer to obtain polymer grade lactide and mother liquor. The invention can obtain lactide with optical purity of more than 99%, shortens the residence time of intermediate material lactide, reduces side reaction, and greatly improves the yield of lactide.
Description
Technical Field
The invention relates to the technical field of preparation of degradable materials, in particular to a process system for continuously and efficiently producing polymer grade lactide.
Background
The new material is the basis of modern technological development, and the degradable plastic is an emerging new plastic material. Polylactic acid (PLA) is a thermoplastic polymer with high gloss and high modulus, and can be completely biodegraded. Polylactic acid has good physical and mechanical properties, and can replace the traditional general materials to a certain extent, thus being used as the raw material of degradable products. Two methods for preparing PLA are respectively a lactide ring-opening polymerization method (also called a two-step method) and a direct polycondensation method (also called a one-step method), wherein the two-step method is the most widely used polylactic acid preparation method at present. In the two-step method, lactic acid is dehydrated to generate an oligomer, then depolymerized to generate lactide, and then ring-opening polymerized to prepare PLA, and the key technology is purification of the lactide, energy consumption control of production and improvement of productivity. Lactide is used as an intermediate of degradable materials, has high heat sensitivity, on one hand, side reactions of isomerism interconversion exist among three isomers of L-lactide, meso-lactide and D-lactide caused by optical activity of the lactide, on the other hand, lactide has a tendency to polymerize, particularly a large amount of acidic substances exist in a crude product to catalyze, so that the lactide is easy to polymerize at high temperature to form lactic acid oligomer with low molecular weight, the yield is greatly reduced, and difficulty is increased for purification treatment.
The purification of lactide is the most critical in the whole two-step process, and only lactide with high purity can be used for synthesizing PLA with high molecular weight and good physical properties. The two-step method involves the purification step of lactide, and generally adopts a multistage rectification mode to purify the lactide, for example, patent CN201010180379.0, adopts a three-stage rectification mode to purify the lactide, but the whole process is very high in energy consumption due to three heating and cooling, and byproduct oligomers are easy to generate in the multistage high-temperature heating process, so that the product yield is influenced. For example, in patent CN202110070644.8, lactide is subjected to crude extraction by two-stage rectification (removing light components such as water and free acid, and removing heavy components such as oligomers), and then is subjected to static melt crystallization or solvent recrystallization to perform purification again, so that the process is complex, the energy consumption is high, side reactions are generated, and continuous production cannot be realized. Patent CN115010696a presents a method for continuously preparing purified lactide, but the method adopts fractional distillation and crystallization operations, and the intermittent operation of crystallization fractional heating-heat preservation process leads to low yield, only 75%, and is difficult to meet the requirement of industrial production.
Therefore, there is a need for a lactide production process that can achieve continuous, high efficiency, low energy consumption, and high purity, achieve production of PLA with high molecular weight, controllable chemical structure, and good mechanical properties, and simultaneously reduce process technical difficulties and production costs.
Disclosure of Invention
The technical problems to be solved are as follows: aiming at the characteristic of high heat sensitivity of lactide, the invention aims to provide a process system for continuously and efficiently producing polymer grade lactide, which can generally reduce energy consumption, shorten residence time, reduce side reaction, facilitate the improvement of reaction conversion rate, continuously obtain lactide with the optical purity of more than 99 percent and meet various technical requirements of polymer grade lactide.
The technical scheme is as follows: a system for continuous high efficiency production of polymer grade lactide, the system comprising:
a lactic acid dehydration reaction system, which comprises a lactic acid dehydration reactor 1 and a metering pump 2, and is used for generating lactic acid oligomer;
a depolymerization purification reaction system comprising a falling film reactor 3, a purification tower 4, a circulating pump 5, a product condenser 6, a light component condenser 7, a reflux ratio controller 8 and a vacuum system 12 for decomposing raw materials into crude lactide in a gas phase, light components, heavy components and residues;
the polymerization-grade lactide separation system comprises a crude product storage tank 9, a scraper crystallizer 10 and a screw filter 11, and is used for separating purified polymerization-grade lactide and mother liquor.
Preferably, the lactic acid dehydration reaction system comprises a lactic acid dehydration reactor and a metering pump, wherein the lactic acid dehydration reactor 1 is connected with the metering pump 2.
Preferably, the depolymerization purification reaction system comprises a falling film reactor 3, a purification tower 4, a circulating pump 5, a product condenser 6, a light component condenser 7, a reflux ratio controller 8 and a vacuum system 12, wherein a metering pump 2 in the lactic acid dehydration reaction system is connected with the purification tower 4, the bottom of the purification tower 4 is connected with the circulating pump 5 for continuous feeding, the circulating pump 5 is connected with the falling film reactor 3, one side of the circulating pump 5 is connected with a depolymerization residue discharge outlet, the falling film reactor 3 is connected with the purification tower 4, the top of the purification tower 4 is connected with the light component condenser 7, the light component condenser 7 is connected with the reflux ratio controller 8 and the vacuum system 12, one side of the reflux ratio controller 8 is connected with the purification tower 4, the other side is used for discharging light component substances collected by the light component condenser 7, and a filling section of the purification tower 4 is connected with the product condenser 6.
Preferably, the polymerization-grade lactide separation system comprises a crude product storage tank 9, a scraper crystallizer 10 and a screw filter 11, wherein a product condenser 6 in the depolymerization purification reaction system is connected with the crude product storage tank 9, the crude product storage tank 9 is connected with the scraper crystallizer 10, the scraper crystallizer 10 is connected with the screw filter 11 for separating crystals and mother liquor, the screw filter 11 is connected with the purification tower 4 through a pipeline, the filtered mother liquor is conveyed back to the purification tower 4, and the produced polymerization-grade lactide is extracted through the bottom of the screw filter 11.
A preparation process for continuously and efficiently producing polymer grade lactide is characterized in that: the specific production steps are as follows:
s1, feeding raw material pure lactic acid and catalyst stannous chloride into a lactic acid dehydration reaction system for continuous dehydration to obtain lactic acid oligomer;
s2: the obtained lactic acid oligomer is continuously fed into a depolymerization purification reaction system, the lactic acid oligomer firstly enters a purification tower 4 through a metering pump 2 in a lactic acid dehydration reaction system, then is conveyed to a falling film reactor 3 through a circulating pump 5, gas-phase crude lactide generated in the falling film reactor 3 enters a filling section of the purification tower 4 to generate crude lactide, light components, heavy components and residues, and after the generated crude lactide is cooled by a product condenser 6, a part of the crude lactide is refluxed to the purification tower 4, and a part of the crude lactide is extracted into a crude storage tank 9. The light components are collected by a light component condenser 7 at the top of the purifying tower 4 and discharged through a reflux ratio controller 8. The heavy component is refluxed to the bottom of the purification tower 4 and returned to the depolymerization purification reaction system again, and further depolymerization reaction is carried out to obtain lactide. The residue generated at the same time is discharged through a residue discharge outlet on one side of the circulating pump 5;
s3: and (3) conveying the crude lactide in the crude storage tank 9 into a scraper crystallizer 10 to generate crystals and mother liquor, and finally conveying the crystals and the mother liquor into a screw filter 11 to obtain polymer grade lactide and mother liquor, wherein the polymer grade lactide is extracted by the screw filter 11, and the mother liquor returns to a depolymerization and purification reaction system for further depolymerization and purification.
Preferably, the temperature of the lactic acid dehydration reactor 1 is 100-115 ℃, the pressure is 400kPaA, and the flow rate of the metering pump 2 is 2226.5kg/h.
Preferably, the operation pressure of the falling film reactor 3 is 300-5000 PaA, and the reaction temperature is 150-230 ℃.
Preferably, the pressure of the purifying column 4 ranges from 500 to 7000PaA, and the temperature of the top of the column ranges from 100 to 150 ℃; the bottom heat medium and the top refrigerant adopt conventional public engineering.
Preferably, the temperature of the crude product storage tank 9 is 100-110 ℃, the pressure is 2kPaG, and the crude product storage tank is sealed by adopting nitrogen. Preferably, the feeding amount of the scraper crystallizer 10 is 2154.7kg/h, the pressure is 0-0.5 MPaG, the temperature is 50-100 ℃, and the solid content in the scraper crystallizer 10 can be controlled to be 5-85%.
The beneficial effects are that:
1. the lactide polymerization grade can be continuously produced by the device and the process, and the key equipment is a depolymerization purification reactor, a scraper crystallizer and a screw filter, so that lactide with the optical purity of more than 99% can be continuously obtained, and various technical requirements of the lactide of the polymerization grade are met. The whole set of process system is continuously operated, overheated lactide produced by pyrolysis is used as raw material and energy source in the rectification process, double recovery of materials and energy is realized, energy consumption can be reduced by 30%, and the yield can be improved by about 10% compared with the conventional method;
2. the invention has short residence time in the whole production process, shortens the residence time of the lactide as an intermediate material, reduces the occurrence of side reaction and greatly improves the yield of the lactide. Meanwhile, the emission of byproducts is reduced, the treatment efficiency of the whole production line is improved, and the emission of three wastes and the treatment cost are reduced.
Drawings
Fig. 1 is a schematic process flow diagram, in which a lactic acid dehydration reactor 1, a metering pump 2, a falling film reactor 3, a purification tower 4, a circulating pump 5, a product condenser 6, a light component condenser 7, a reflux ratio controller 8, a crude product storage tank 9, a scraper crystallizer 10, a screw filter 11 and a vacuum system 12 are shown.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples, which are illustrative of the invention and not intended to limit the invention to the examples below:
a system for continuous high efficiency production of polymer grade lactide, the system comprising:
a lactic acid dehydration reaction system, which comprises a lactic acid dehydration reactor 1 and a metering pump 2, and is used for generating lactic acid oligomer;
a depolymerization purification reaction system comprising a falling film reactor 3, a purification tower 4, a circulating pump 5, a product condenser 6, a light component condenser 7, a reflux ratio controller 8 and a vacuum system 12 for decomposing raw materials into crude lactide in a gas phase, light components, heavy components and residues;
the polymerization-grade lactide separation system comprises a crude product storage tank 9, a scraper crystallizer 10 and a screw filter 11, and is used for separating purified polymerization-grade lactide and mother liquor.
The lactic acid dehydration reaction system comprises a lactic acid dehydration reactor and a metering pump, wherein the lactic acid dehydration reactor 1 is connected with the metering pump 2. The depolymerization purification reaction system comprises a falling film reactor 3, a purification tower 4, a circulating pump 5, a product condenser 6, a light component condenser 7, a reflux ratio controller 8 and a vacuum system 12, wherein a metering pump 2 in the lactic acid dehydration reaction system is connected with the purification tower 4, the bottom of the purification tower 4 is connected with the circulating pump 5 for continuous feeding, the circulating pump 5 is connected with the falling film reactor 3, one side of the circulating pump 5 is connected with a depolymerization residue discharge outlet, the falling film reactor 3 is connected with the purification tower 4, the top of the purification tower 4 is connected with the light component condenser 7, the light component condenser 7 is connected with the reflux ratio controller 8 and the vacuum system 12, one side of the reflux ratio controller 8 is connected with the purification tower 4, the other side is used for discharging light component substances collected by the light component condenser 7, and a filling section of the purification tower 4 is connected with the product condenser 6.
The polymerization-grade lactide separation system comprises a crude product storage tank 9, a scraper crystallizer 10 and a screw filter 11, wherein a product condenser 6 in the depolymerization purification reaction system is connected with the crude product storage tank 9, the crude product storage tank 9 is connected with the scraper crystallizer 10, the scraper crystallizer 10 is connected with the screw filter 11 for separating crystals and mother liquor, the screw filter 11 is connected with the purification tower 4 through a pipeline, the filtered mother liquor is conveyed back to the purification tower 4, and the produced polymerization-grade lactide is extracted from the bottom of the screw filter 11.
Example 1
A process system for continuously and efficiently producing polymer grade lactide comprises the following specific production steps:
s1, feeding raw material pure lactic acid and stannous chloride with the feeding amount of 0.5% into a lactic acid dehydration reaction system for continuous dehydration, so as to obtain a lactic acid oligomer with the average molecular weight of 1600 and the temperature of 180 ℃, wherein the temperature of the lactic acid dehydration reactor 1 in the lactic acid dehydration reaction system is 100 ℃, the pressure is 400KPaA, the flow of a metering pump 2 is 2226.5 kg/h;
s2: in the depolymerization purification reaction system, the temperature of the falling film reactor 3 was set at 190℃and the pressure was 1.5kPaA, the temperature at the top of the purification column 4 was set at 128℃and the pressure was 500PaA, the amount taken at the top was 27kg/h of the amount of the fed oligomer, the amount taken from the depolymerization residue was 13.5kg/h of the amount of the fed oligomer, the reflux ratio of the reflux ratio controller 8 was set at 1.5, and the temperature of the product condenser 6 was set at 102 ℃. The obtained lactic acid oligomer is continuously fed into a depolymerization purification reaction system at the speed of 900kg/h, the lactic acid oligomer firstly enters a purification tower 4 through a metering pump 2 in a lactic acid dehydration reaction system, then is conveyed to a falling film reactor 3 through a circulating pump 5, gas-phase crude lactide generated in the falling film reactor 3 enters a filling section of the purification tower 4 to generate crude lactide, light components, heavy components and residues, wherein after the generated crude lactide is cooled by a product condenser 6, a part of the crude lactide is refluxed into the purification tower 4, a part of the crude lactide is extracted into a crude storage tank 9, and the extraction amount is 859.5kg/h. The light components are collected by a light component condenser 7 at the top of the purifying tower 4 and discharged through a reflux ratio controller 8. The heavy component is refluxed to the bottom of the purification tower 4 and returned to the depolymerization purification reaction system again, and further depolymerization reaction is carried out to obtain lactide. The residue produced at the same time was discharged through a residue discharge port on the side of the circulation pump 5, and the amount of the residue recovered was 13.5kg/h of the amount of the oligomer fed. Wherein the L-lactide content in the crude lactide reaches 98%, and the Meso lactide content is 1.7%; the content of the light component is 0.1 percent; the content of the heavy component is 0.2%;
s3: the temperature of the crude product tank 9 was controlled to 100℃and the pressure to 2KPaG, the feed rate to the drag crystallizer 10 was set to 2154.7kg/h, the temperature was 78℃and the pressure to 0.2MPaG. And conveying the crude lactide in the crude storage tank 9 into a scraper crystallizer 10 to generate 645kg/h of crystals and mother liquor, and finally conveying the crystals and the mother liquor into a screw filter 11 to obtain polymer grade lactide and mother liquor, wherein the polymer grade lactide is extracted through the screw filter 11, and the mother liquor is returned to a depolymerization and purification reaction system for further depolymerization and purification. Wherein the L-lactide content is 99.4%, the Meso-lactide content is 0.5%, the rest component content is 0.1%, the water content is 168ppm, the requirements of polymer grade lactide are met, and the mother liquor is discharged for 114.5kg/h.
Example 2
A process system for continuously and efficiently producing polymer grade lactide comprises the following specific production steps:
s1, feeding raw material pure lactic acid and stannous chloride with the feeding amount of 0.5% into a lactic acid dehydration reaction system for continuous dehydration, so as to obtain a lactic acid oligomer with the average molecular weight of 1600 and the temperature of 180 ℃, wherein the temperature of the lactic acid dehydration reactor 1 in the lactic acid dehydration reaction system is 115 ℃, the pressure is 400KPaA, the flow of a metering pump 2 is 2226.5 kg/h;
s2: in the depolymerization purification reaction system, the temperature of the falling film reactor 3 was set at 230℃under a pressure of 5kPaA, the temperature at the top of the purification column 4 was set at 150℃under a pressure of 7KPaA, the amount taken at the top of the column was 32.5kg/h of the amount of the fed oligomer, the amount taken from the depolymerization residue was 18kg/h of the amount of the fed oligomer, the reflux ratio of the reflux ratio controller 8 was set at 1.5, and the temperature of the product condenser 6 was set at 102 ℃. The obtained lactic acid oligomer is continuously fed into a depolymerization purification reaction system at the speed of 900kg/h, the lactic acid oligomer firstly enters a purification tower 4 through a metering pump 2 in a lactic acid dehydration reaction system, then is conveyed to a falling film reactor 3 through a circulating pump 5, gas-phase crude lactide generated in the falling film reactor 3 enters a filling section of the purification tower 4 to generate crude lactide, light components, heavy components and residues, wherein after the generated crude lactide is cooled by a product condenser 6, a part of the crude lactide is refluxed into the purification tower 4, a part of the crude lactide is extracted into a crude storage tank 9, and the extraction amount is 894kg/h. The light components are collected by a light component condenser 7 at the top of the purifying tower 4 and discharged through a reflux ratio controller 8. The heavy component is refluxed to the bottom of the purification tower 4 and returned to the depolymerization purification reaction system again, and further depolymerization reaction is carried out to obtain lactide. The residue produced at the same time was discharged through a residue discharge port on the side of the circulation pump 5, and the amount of the residue recovered was 16.3kg/h of the amount of the oligomer fed. Wherein the L-lactide content in the crude lactide reaches 98.2%, and the Meso lactide content is 1.5%; the content of the light component is 0.1 percent; the content of the heavy component is 0.2%;
s3: the temperature of the crude product tank 9 was controlled to 110℃and the pressure to 2KPaG, the feed rate to the drag crystallizer 10 was set to 2154.7kg/h, the temperature to 100℃and the pressure to 0.5MPaG. And (3) conveying the crude lactide in the crude storage tank 9 into a scraper crystallizer 10 to generate 685kg/h of crystals and mother liquor, and finally conveying the crystals and the mother liquor into a screw filter 11 to obtain polymer grade lactide and mother liquor, wherein the polymer grade lactide is extracted through the screw filter 11, and the mother liquor is returned to a depolymerization and purification reaction system for further depolymerization and purification. Wherein the L-lactide content is 99.3%, the Meso-lactide content is 0.6%, the rest component content is 0.1%, the water content is 176ppm, the requirements of polymer grade lactide are met, and the mother liquor is discharged at 179.4kg/h.
Example 3
The difference between this example and example 1 is that the mother liquor excluded in example 1 was continuously returned to the depolymerization purification reaction system on the basis of the normal operation of example 1.
S1: in the depolymerization purification reaction system, the temperature of the falling film reactor 3 was set at 190℃and the pressure was 1.5kPaA, the temperature at the top of the purification column 4 was set at 128℃and the pressure was 500PaA, the amount taken at the top of the column was 30.5kg/h of the amount of the fed oligomer, the amount taken from the depolymerization residue was 16.8kg/h of the amount of the fed oligomer, the reflux ratio of the reflux ratio controller 8 was set at 1.5, and the temperature of the product condenser 6 was set at 100 ℃. The mother liquor in example 1 was continuously fed into the purification column 4 in the depolymerization purification reaction system at a rate of 900kg/h, and fed into the falling film reactor 3 through the circulating pump 5, and the gas-phase crude lactide produced in the falling film reactor 3 was fed into the packing section of the purification column 4 to produce crude lactide, light components, heavy components and residues, wherein the produced crude lactide was cooled by the product condenser 6, and a part of the crude lactide was refluxed back into the purification column 4, and a part of the crude lactide was recovered into the crude storage tank 9, and the recovery amount was 967kg/h. The light components are collected by a light component condenser 7 at the top of the purifying tower 4 and discharged through a reflux ratio controller 8. The heavy component is refluxed to the bottom of the purification tower 4 and returned to the depolymerization purification reaction system again, and further depolymerization reaction is carried out to obtain lactide. The residue produced at the same time was discharged through a residue discharge port on the side of the circulation pump 5, and the amount of the residue recovered was 16.8kg/h of the amount of the oligomer fed. Wherein the L-lactide content in the crude lactide reaches 97.8%, and the Meso lactide content is 1.9%; the content of the light component is 0.1 percent; the content of the heavy component is 0.2%;
s2: the temperature of the crude product tank 9 was controlled to 100℃and the pressure to 2KPaG, the feed rate to the drag crystallizer 10 was set to 2154.7kg/h, the temperature was 78℃and the pressure to 0.2MPaG. And conveying the crude lactide in the crude storage tank 9 into a scraper crystallizer 10 to generate 765kg/h of crystals and mother liquor, and finally conveying the crystals and the mother liquor into a screw filter 11 to obtain polymer grade lactide and mother liquor, wherein the polymer grade lactide is extracted through the screw filter 11, and the mother liquor is returned to a depolymerization and purification reaction system for further depolymerization and purification. Wherein the L-lactide content is 99.2%, the Meso-lactide content is 0.7%, the rest component content is 0.1%, the water content is 180ppm, the requirements of polymer grade lactide are met, and 202kg/h of mother liquor is discharged.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. A system for continuous high efficiency production of polymer grade lactide, the system comprising:
the lactic acid dehydration reaction system comprises a lactic acid dehydration reactor and a metering pump, and is used for generating lactic acid oligomer;
the depolymerization purification reaction system comprises a falling film reactor, a purification tower, a circulating pump, a product condenser, a light component condenser, a reflux ratio controller and a vacuum system, and is used for decomposing raw materials into gas-phase crude lactide, light components, heavy components and residues;
the polymerization-grade lactide separation system comprises a crude product storage tank, a scraper crystallizer and a screw filter, and is used for separating purified polymerization-grade lactide and mother liquor.
2. The system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the lactic acid dehydration reaction system comprises a lactic acid dehydration reactor and a metering pump, wherein the lactic acid dehydration reactor is connected with the metering pump.
3. The system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the depolymerization purification reaction system comprises a falling film reactor, a purification tower, a circulating pump, a product condenser, a light component condenser, a reflux ratio controller and a vacuum system, wherein a metering pump in the lactic acid dehydration reaction system is connected with the purification tower, the bottom of the purification tower is connected with the circulating pump for continuous feeding, the circulating pump is connected with the falling film reactor, one side of the circulating pump is connected with a depolymerization residue discharge outlet, the falling film reactor is connected with the purification tower, the top of the purification tower is connected with the light component condenser, the light component condenser is connected with the reflux ratio controller and the vacuum system, one side of the reflux ratio controller is connected with the purification tower, the other side of the reflux ratio controller is used for discharging light component substances collected by the light component condenser, and a filler section of the purification tower is connected with the product condenser.
4. The system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the polymerization grade lactide separation system comprises a crude product storage tank, a scraper crystallizer and a screw filter, wherein a product condenser in the depolymerization purification reaction system is connected with the crude product storage tank, the crude product storage tank is connected with the scraper crystallizer, the scraper crystallizer is connected with the screw filter for separating crystals and mother liquor, the screw filter is connected with the purification tower through a pipeline, the filtered mother liquor is conveyed back to the purification tower, and the produced polymerization grade lactide is extracted from the bottom of the screw filter.
5. A preparation process for continuously and efficiently producing polymer grade lactide is characterized in that: the specific production steps are as follows:
s1, feeding raw material pure lactic acid and catalyst stannous chloride into a lactic acid dehydration reaction system for continuous dehydration to obtain lactic acid oligomer;
s2: the obtained lactic acid oligomer is continuously fed into a depolymerization purification reaction system, the lactic acid oligomer firstly enters a purification tower through a metering pump in a lactic acid dehydration reaction system, then is conveyed to a falling film reactor through a circulating pump, gas-phase crude lactide generated in the falling film reactor enters a filler section of the purification tower to generate crude lactide, light components, heavy components and residues, wherein the generated crude lactide is cooled by a product condenser, a part of the crude lactide is refluxed into the purification tower again, and a part of the crude lactide is extracted into a crude storage tank. The light components are collected by a light component condenser at the top of the purifying tower and discharged through a reflux ratio controller. And the heavy component flows back to the bottom of the purification tower and returns to the depolymerization purification reaction system again for further depolymerization reaction to obtain lactide. Simultaneously, the generated residues are discharged through a residue discharge port at one side of the circulating pump;
s3: and (3) conveying the crude lactide in the crude storage tank 9 into a scraper crystallizer to generate crystals and mother liquor, and finally conveying the crystals and the mother liquor into a screw filter to obtain polymer grade lactide and mother liquor, wherein the polymer grade lactide is extracted by the screw filter, and the mother liquor returns to a depolymerization and purification reaction system for further depolymerization and purification.
6. The process system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the temperature of the lactic acid dehydration reactor is 100-115 ℃, the pressure is 400kPaA, and the flow rate of the metering pump 2 is 2226.5kg/h.
7. The process system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the operation pressure of the falling film reactor is 300-5000 PaA, and the reaction temperature is 150-230 ℃.
8. The process system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the pressure range of the purification tower is 500-7000 PaA, and the temperature of the tower top is 100-150 ℃; the bottom heat medium and the top refrigerant adopt conventional public engineering.
9. The process system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the temperature of the crude product storage tank is 100-110 ℃, the pressure is micro-positive pressure 2kPaG, and nitrogen is adopted for sealing.
10. The process system for continuous high-efficiency production of polymer grade lactide according to claim 1, wherein: the feeding amount of the scraper crystallizer 10 is 2154.7kg/h, the pressure is 0-0.5 MPaG, the temperature is 50-100 ℃, and the solid content in the scraper crystallizer can be controlled to be 5-85%.
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| CN202310010705.0A CN116272665A (en) | 2023-01-05 | 2023-01-05 | Process system for continuously and efficiently producing polymer grade lactide |
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