Process system and method for purifying and recovering intermediates of degradable materials

Abstract

The application provides a process system for purifying and recycling intermediates of degradable materials, which comprises a pretreatment unit, a crystallization separation unit and a refining unit; the pretreatment unit is used for removing impurities from the crude intermediates of degradable materials, and comprises a dissolving tank, a filter and a first crystallizer; the crystallization separation unit is used for separating and crystallizing the mixed slurry, and comprises a separation and washing device, a sedimentation tank, an evaporation recovery tank and a second crystallizer; and the refining unit is used for refining the slurry, and comprises a centrifugal settling separator, a screw conveyor, a wiped film evaporation device and a rectification device. The process system of the application not only shortens and optimizes the separation process flow of the crude materials, but also makes the separated impurities be reused as raw materials of upstream devices, thereby reducing the operation consumption of the whole device.

Description

Technical Field

[0001] This invention relates to the technical field of biodegradable material purification, and in particular to a process system and method for purifying and recovering biodegradable material intermediates. Background Technology

[0002] Degradable materials are materials that can be degraded in both thermodynamic and kinetic terms over a period of time. They can generally be classified into photodegradable materials, biodegradable materials, etc.

[0003] With economic development, polylactide (PL) and polyglycolic acid (PGA) are increasingly in demand as biodegradable materials. The production process of biodegradable materials requires raw materials to be processed into intermediates through various process devices before polymerization into polymers. For example, the intermediate for PLA is lactide, and the intermediate for PGA is glycolide. The quality of these intermediates (such as purity, water content, and acid content) has a significant impact on the quality of the polymer product. Substandard intermediates cannot be polymerized into qualified biodegradable materials. Therefore, intermediate purification and recycling is one of the most crucial processes in the entire production process, directly determining the quality of the intermediates. Thus, the primary task of the purification process is to produce intermediates that meet the requirements for polymerization. Currently, the purification process typically involves washing the crude intermediate material with a solvent, removing insoluble impurities such as water and acid, and finally crystallizing and drying to obtain the qualified intermediate product. However, the washed glycolide frequently clogs the washing tanks, centrifuges, and other equipment pipelines. This is especially problematic during the separation of the crystallized intermediate slurry, where severe blockages occur in the centrifuge's clear liquid pipeline, hindering continuous process operation and ultimately causing the unit to malfunction. Frequent shutdowns for maintenance and cleaning of equipment and pipelines are necessary, making long-term continuous operation difficult and significantly impacting the production of biodegradable materials. The key reason is that the crystallization mother liquor currently contains a large amount of intermediates. When this mother liquor is directly sent to the solvent distillation system, it causes severe blockages, resulting in extremely low intermediate yields of only about 10%. This portion of intermediates, intended as raw materials for downstream units, is largely wasted due to blockages in the equipment pipelines, preventing recycling and leading to low yields and high consumption.

[0004] Therefore, the purification and separation equipment for intermediates suffers from low yield due to incomplete washing and separation, resulting in significant intermediate loss. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a process system and method for purifying and recovering biodegradable material intermediates.

[0006] To achieve the objectives of this invention, the following technical solution is adopted:

[0007] In a first aspect, this invention provides a process system for purifying and recovering biodegradable material intermediates, the process system comprising a pretreatment unit, a crystallization separation unit, and a purification unit; wherein,

[0008] The pretreatment unit is used to pretreat and remove impurities from the crude intermediate of the biodegradable material, and includes a dissolving tank, a filter and a first crystallizer; the crude material from the depolymerization section is dissolved in the dissolving tank to obtain a mixture, which is then filtered by the filter to obtain impurities and a mixture, and the mixture is crystallized in the first crystallizer to obtain a mixed slurry;

[0009] The crystallization separation unit is used to separate and crystallize the mixed slurry, and includes a separation and washing device, a settling tank, an evaporation recovery tank, and a second crystallizer. After separation in the separation and washing device, the mixed slurry is obtained as intermediate solids and mother liquor. After settling and separation in the settling tank, the mother liquor is obtained as intermediate slurry and clear liquid. The clear liquid is sent to the evaporation recovery tank for evaporation and concentration to obtain concentrated liquid I and concentrated solvent. After crystallization in the second crystallizer, concentrated liquid I is obtained as crystallized slurry.

[0010] The refining unit, used for refining the slurry, includes a centrifugal sedimentation separator, a screw conveyor, a scraped film evaporator, and a distillation unit. The intermediate slurry and the crystallized slurry are sedimented and centrifuged in the centrifugal sedimentation separator to obtain an intermediate and a centrifuged liquid. The intermediate is conveyed by the screw conveyor to the dissolving tank for further dissolution. The centrifuged liquid is evaporated in the scraped film evaporator to obtain concentrated liquid II and a mixed solvent. The mixed solvent and the concentrated solvent are distilled by the distillation unit to obtain a first solvent and a second solvent. The first solvent is recycled to the dissolving tank, and the second solvent is returned to the separation and washing unit.

[0011] In some specific embodiments, the crystallization separation unit further includes a first buffer tank, the inlet of which is connected to the outlet of the settling tank, and the outlet of which is connected to the inlet of the evaporation recovery tank; and / or, the crystallization separation unit further includes a first buffer transfer pump for transferring the clarified liquid to the evaporation recovery tank; and / or, the crystallization separation unit further includes a settling transfer pump for transferring the intermediate slurry to the centrifugal settling separator; and / or, the crystallization separation unit further includes a slurry transfer pump for transferring the crystallized slurry to the centrifugal settling separator.

[0012] In the process system provided by the present invention, the crystallization separation unit further includes a drying system for drying the intermediate solid material; the inlet of the drying system is connected to the intermediate solid material outlet of the separation and washing device, and the outlet of the drying system is connected to the downstream polymerization device.

[0013] In some specific embodiments, the refining unit further includes a second buffer tank, the inlet of which is connected to the outlet of the centrifugal sedimentation separator, and the outlet of which is connected to the inlet of the scraped film evaporator; and the refining unit further includes a second buffer transfer pump for conveying the centrifuged liquid into the scraped film evaporator.

[0014] In the process system provided by the present invention, the impurities filtered out by the filter in the pretreatment unit are sent to the second buffer tank.

[0015] In some specific embodiments, the refining unit further includes a third buffer tank for collecting the first solvent distilled from the distillation apparatus; the inlet of the third buffer tank is connected to the outlet of the distillation apparatus, and the outlet of the third buffer tank is connected to the inlet of the dissolving tank.

[0016] In some specific embodiments, the refining unit further includes a fourth buffer tank for collecting the second solvent distilled from the distillation apparatus; the inlet of the fourth buffer tank is connected to the outlet of the distillation apparatus, and the outlet of the fourth buffer tank is connected to the inlet of the separation and washing apparatus; and / or, the refining unit further includes a circulation pump for providing power to recycle the second solvent to the separation and washing apparatus.

[0017] In a second aspect, the present invention provides a method for purifying and recovering biodegradable material intermediates using the above-described process system, comprising the following steps:

[0018] S1. The biodegradable material intermediate coarse material from the depolymerization section is pretreated to remove impurities to obtain a mixed slurry;

[0019] S2. The mixed slurry obtained in S1 is separated and washed to obtain intermediate solids and mother liquor. The mother liquor is separated by sedimentation to obtain intermediate slurry and clear liquid. The clear liquid is evaporated and concentrated to obtain concentrated liquid I and concentrated solvent. Concentrated liquid I is crystallized to obtain crystalline slurry.

[0020] S3. After sedimentation and separation of the intermediate slurry and crystallized slurry obtained in S2, intermediate and centrifugal liquid are obtained. The intermediate is recycled to S1 for further dissolution. After evaporation, concentrated liquid II and mixed solvent are obtained.

[0021] S4. After separating the mixed solvent and concentrated solvent by distillation, the first solvent and the second solvent are obtained.

[0022] In some specific embodiments, the pretreatment and impurity removal in S1 includes dissolving and filtering the coarse material to obtain impurities and a mixture, and then crystallizing the mixture to obtain the mixed slurry.

[0023] In some specific embodiments, in method S4 of the present invention, the first solvent obtained by distillation is reused as a dissolving solvent in S1, and the second solvent is returned to S2 as a washing solvent for sedimentation separation.

[0024] The above technical solution achieves the following technical effects:

[0025] The process system provided by this invention performs dissolution, filtration and crystallization pretreatment on the intermediate crude material in a pretreatment unit, avoiding the problems of equipment pipeline blockage or even material discharge difficulties caused during the washing process; at the same time, in the crystallization separation unit, the mixed slurry undergoes solid-liquid separation, sedimentation and crystallization concentration in the separation and washing device to obtain crystallized slurry and concentrated solvent, further avoiding the problem of a large amount of solid intermediate entering the distillation unit and causing blockage.

[0026] The process system of the present invention reprocesses the slurry, impurities, and concentrated solvent to obtain intermediates that meet product requirements. At the same time, it can also be used as raw material for the pretreatment device, reducing the loss of intermediates in the crystallization mother liquor and improving the yield of intermediates. Meanwhile, the first solvent is separated and reused as a solvent in the pretreatment unit, and the second solvent is reused in the separation and washing device, reducing raw material consumption. Attached Figure Description

[0027] Figure 1 : A specific embodiment of the process system provided by the present invention;

[0028] The components include: 1. Dissolving tank; 2. Filter; 3. First crystallizer; 4. Separation and washing device; 5. Settling tank; 6. Evaporation and recovery tank; 7. Second crystallizer; 8. Centrifugal settling separator; 9. Screw conveyor; 10. Scraped film evaporator; 11. Distillation device; 12. First buffer tank; 13. First buffer transfer pump; 14. Settling transfer pump; 15. Drying system; 16. Second buffer tank; 17. Second buffer transfer pump; 18. Third buffer tank; 19. Fourth buffer tank; 20. Circulation pump; 21. Slurry transfer pump. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0030] Unless otherwise defined, 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 pertains.

[0031] The present invention provides a process system for purifying and recovering biodegradable material intermediates, such as... Figure 1As shown, it includes a pretreatment unit, a crystallization separation unit and a purification unit connected to the pretreatment unit;

[0032] The pretreatment unit includes a dissolving tank 1, a filter 2, and a first crystallizer 3 located downstream of the depolymerization section. The coarse material from the depolymerization section is mixed and dissolved with the first solvent in the dissolving tank 1 to obtain a mixed material. After being filtered by the filter 2, impurities and a mixed liquid are obtained. The mixed liquid is stirred and crystallized in the first crystallizer 3 to obtain a mixed slurry, thus avoiding the clogging of equipment and pipelines by the mixed slurry.

[0033] The crystallization separation unit is used to separate and crystallize the mixed slurry; specifically, it includes a separation and washing device 4, a settling tank 5, an evaporation recovery tank 6, and a second crystallizer 7. The mixed slurry is washed and separated in the separation and washing device 4 using a second solvent to obtain intermediate solids and mother liquor. The mother liquor containing solid particles is separated by settling in the settling tank 5 to obtain intermediate slurry and clear liquid. The clear liquid is sent to the evaporation recovery tank 6 for evaporation and concentration to obtain concentrated liquid I and concentrated solvent. Concentrated liquid I is crystallized in the second crystallizer 7 to obtain crystallized slurry.

[0034] In some specific embodiments, the crystallization separation unit also includes a first buffer tank 12, which is installed on the overflow pipeline of the settling tank 5 and connected to the settling tank 5 through a pipeline. It is used to collect the clear liquid separated by settling. The outlet of the first buffer tank 12 is connected to the inlet of the evaporation recovery tank 6.

[0035] In some specific embodiments, the crystallization separation unit also includes a first buffer transfer pump 13, the outlet pipeline of which is connected to the evaporation recovery tank 6 for transferring the clarified liquid to the evaporation recovery tank 6.

[0036] In some specific embodiments, the crystallization separation unit also includes a sedimentation transfer pump 14 for conveying intermediate slurry to a centrifugal sedimentation separator 8.

[0037] In some specific embodiments, the crystallization separation unit also includes a slurry delivery pump 21 for delivering intermediate slurry to a centrifugal sedimentation separator 8.

[0038] In some specific embodiments, the crystallization separation unit also includes a drying system 15 for drying the intermediate solid material; the inlet of the drying system 15 is connected to the intermediate solid material outlet of the separation and washing device 4, and the outlet of the drying system 15 is connected to the downstream, so that the qualified intermediate can be sent to the downstream polymerization device for use as raw material.

[0039] The refining unit in the process system provided by this invention is used to refine slurry; specifically, it includes a centrifugal sedimentation separator 8, a screw conveyor 9, a scraped film evaporator 10, and a distillation unit 11. The intermediate slurry separated from the bottom of the sedimentation tank 5 and the crystallized slurry obtained from the second crystallizer 7 are subjected to sedimentation and centrifugal separation in the centrifugal sedimentation separator 8 to obtain an intermediate and a centrifuged liquid. The obtained intermediate is sent to a dissolving tank 1 for continued recycling via a screw conveyor 9 installed on an outlet pipeline of the centrifugal sedimentation separator 8. The obtained centrifuged liquid is evaporated in the scraped film evaporator 10 to obtain concentrated liquid II and a mixed solvent. The mixed solvent obtained from the evaporation in the scraped film evaporator 10 and the concentrated solvent obtained from the evaporation recovery tank 6 are distilled in the distillation unit 11 to obtain a first solvent and a second solvent, respectively. The first solvent is recycled to the dissolving tank 1 as a solvent for dissolution, and the second solvent is returned to the separation and washing unit 4 as a solvent for washing.

[0040] In one embodiment, the refining unit further includes a second buffer tank 16, the inlet of which is connected to the outlet of the centrifugal sedimentation separator 8, and the outlet of which is connected to the inlet of the scraped film evaporator 10; and the refining unit further includes a second buffer transfer pump 17 for conveying the centrifugal liquid into the scraped film evaporator 10.

[0041] Impurities filtered out by filter 2 in the pretreatment unit are also sent to the second buffer tank 16 as another feed for the second buffer tank 16.

[0042] In one embodiment, the refining unit further includes a third buffer tank 18 for collecting the first solvent distilled from the distillation apparatus 11; specifically, the inlet of the third buffer tank 18 is connected to the outlet of the distillation apparatus 11, and the outlet of the third buffer tank 18 is connected to the inlet of the dissolving tank 1.

[0043] In one embodiment, the refining unit further includes a fourth buffer tank 19 for collecting the second solvent distilled from the distillation unit 11; specifically, the inlet of the fourth buffer tank 19 is connected to the outlet of the distillation unit 11, and the outlet of the fourth buffer tank 19 is connected to the inlet of the separation and washing unit 4.

[0044] In some specific embodiments, the refining unit also includes a circulation pump 20 for providing power to transport the second solvent back to the separation and washing unit 4.

[0045] In the process system of this invention, the mixed solvent separated by the evaporation recovery tank 6 and the scraped film evaporator 10 enters the distillation unit 11 for purification. The first solvent and the second solvent are then separated, and dehydration and deacidification of the solvents are also performed. The purified first solvent is sent to the third buffer tank 18 and then to the dissolving tank 1 for dissolution. The purified second solvent is sent to the fourth buffer tank 19 and then via the circulating pump 20 to the separation and washing equipment 20 for use as a washing solvent. In the purification and solvent recovery process of the intermediates of this invention, not only is the problem of blockage in the equipment pipelines of the original intermediate washing system, solvent evaporation recovery system, and solvent distillation system, preventing continuous long-term operation, is solved, but the yield of glycolide is also increased to 50%. The entire process system not only shortens and optimizes the separation process of the crude material but also allows the separated impurities to be reused as raw materials for upstream units, reducing the overall operating costs of the unit.

[0046] The method for purifying and recovering biodegradable material intermediates provided by this invention includes the following steps:

[0047] S1. The biodegradable material intermediate coarse material from the depolymerization section is pretreated to remove impurities to obtain a mixed slurry;

[0048] S2. The mixed slurry obtained in S1 is separated and washed to obtain intermediate solids and mother liquor. The mother liquor is separated by sedimentation to obtain intermediate slurry and clear liquid. The clear liquid is evaporated and concentrated to obtain concentrated liquid I and concentrated solvent. Concentrated liquid I is crystallized to obtain crystalline slurry.

[0049] S3. After sedimentation and separation of the intermediate slurry and crystallized slurry obtained in S2, intermediate and centrifugal liquid are obtained. The intermediate is recycled to S1 for further dissolution. After evaporation, concentrated liquid II and mixed solvent are obtained.

[0050] S4. Distill the mixed solvent and concentrated solvent to obtain a first solvent and a second solvent;

[0051] In some embodiments, pretreatment for impurity removal includes dissolving and filtering the coarse material to obtain impurities and a mixture, and then crystallizing the mixture to obtain the mixed slurry.

[0052] In some embodiments, the first solvent is recycled back to S1 as a dissolving solvent, and the second solvent is returned to S2 as a washing solvent for sedimentation separation.

Claims

1. A process system for purifying and recovering biodegradable material intermediates, characterized in that, The process system includes a pretreatment unit, a crystallization separation unit, and a refining unit; wherein... The pretreatment unit is used to pretreat and remove impurities from the crude intermediate of the biodegradable material, and includes a dissolving tank, a filter and a first crystallizer; the crude material from the depolymerization section is dissolved in the dissolving tank to obtain a mixture, which is then filtered by the filter to obtain impurities and a mixture, and the mixture is crystallized in the first crystallizer to obtain a mixed slurry; The crystallization separation unit is used to separate and crystallize the mixed slurry, and includes a separation and washing device, a settling tank, an evaporation recovery tank, and a second crystallizer. After separation in the separation and washing device, the mixed slurry is obtained as intermediate solids and mother liquor. After settling and separation in the settling tank, the mother liquor is obtained as intermediate slurry and clear liquid. The clear liquid is sent to the evaporation recovery tank for evaporation and concentration to obtain concentrated liquid I and concentrated solvent. After crystallization in the second crystallizer, concentrated liquid I is obtained as crystallized slurry. The refining unit, used for refining the slurry, includes a centrifugal sedimentation separator, a screw conveyor, a scraped film evaporator, and a distillation unit. The intermediate slurry and the crystalline slurry are sedimented and centrifuged in the centrifugal sedimentation separator to obtain an intermediate and a centrifuged liquid. The intermediate is conveyed by the screw conveyor to the dissolving tank for further dissolution. The centrifuged liquid is evaporated in the scraped film evaporator to obtain concentrated liquid II and a mixed solvent. The mixed solvent and the concentrated solvent are distilled in the distillation unit to obtain a first solvent and a second solvent. The first solvent is recycled back to the dissolving tank as a dissolving solvent, and the second solvent is returned to the separation and washing unit as a washing solvent. The crystallization separation unit further includes a first buffer tank, the inlet of which is connected to the outlet of the settling tank, and the outlet of which is connected to the inlet of the evaporation recovery tank. The crystallization separation unit further includes a first buffer transfer pump for transferring the clarified liquid to the evaporation recovery tank; The crystallization separation unit also includes a sedimentation conveying pump for conveying the intermediate slurry to the centrifugal sedimentation separator; The crystallization separation unit also includes a slurry conveying pump for conveying the crystallization slurry to the centrifugal sedimentation separator; The crystallization separation unit also includes a drying system for drying the intermediate solid material; The inlet of the drying system is connected to the intermediate solids outlet of the separation and washing device, and the outlet of the drying system is connected to the downstream polymerization device.

2. The process system according to claim 1, characterized in that, The refining unit further includes a second buffer tank, the inlet of which is connected to the outlet of the centrifugal sedimentation separator, and the outlet of which is connected to the inlet of the scraped film evaporator; and, The refining unit also includes a second buffer transfer pump for transferring the centrifuged liquid to the scraped film evaporator.

3. The process system according to any one of claims 1 to 2, characterized in that, The refining unit also includes a third buffer tank for collecting the first solvent distilled off by the distillation unit; The inlet of the third buffer tank is connected to the outlet of the distillation unit, and the outlet of the third buffer tank is connected to the inlet of the dissolving tank.

4. The process system according to claim 3, characterized in that, The refining unit also includes a fourth buffer tank for collecting the second solvent distilled from the distillation unit; The inlet of the fourth buffer tank is connected to the outlet of the distillation unit, and the outlet of the fourth buffer tank is connected to the inlet of the separation and washing unit.

5. The process system according to claim 4, characterized in that, The refining unit also includes a circulation pump for providing power to recycle the second solvent to the separation and washing apparatus.

6. A method for purifying and recovering biodegradable material intermediates using the process system described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The biodegradable material intermediate coarse material from the depolymerization section is pretreated to remove impurities to obtain a mixed slurry; S2. The mixed slurry obtained in S1 is separated and washed to obtain intermediate solids and mother liquor. The mother liquor is separated by sedimentation to obtain intermediate slurry and clear liquid. The clear liquid is evaporated and concentrated to obtain concentrated liquid I and concentrated solvent. Concentrated liquid I is crystallized to obtain crystalline slurry. S3. After sedimentation and separation of the intermediate slurry and crystallized slurry obtained in S2, intermediate and centrifugal liquid are obtained. The intermediate is recycled to S1 for further dissolution. After evaporation, concentrated liquid II and mixed solvent are obtained. S4. The mixed solvent and concentrated solvent are separated by distillation to obtain a first solvent and a second solvent. The first solvent obtained by distillation is reused as a dissolving solvent in S1, and the second solvent is returned to S2 as a washing solvent for sedimentation separation.

7. The method according to claim 6, characterized in that, The pretreatment and impurity removal in S1 includes dissolving and filtering the coarse material to obtain impurities and a mixture, and then crystallizing the mixture to obtain the mixed slurry.

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