Combined purification system for bio-based material
Through the use of propylene ester purification, the use of decompression two -level refined distillation coupling and suspension crystalline technology is used to solve the problem of low purification efficiency and low total output rate in existing technology, and achieve efficient and continuous propylene. Pure and ensure high -purity product output.
Patent Information
- Application Number
- CN202420563241.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-22
- Publication Date
- 2025-01-28
- Estimated Expiration
- 2034-03-22
AI Technical Summary
The prior art has problems in the purification process of lactide, such as low efficiency, thermal sensitivity, by-product generation, melt crystallization cannot be continuously operated, and low overall yield.
Using decompression two -level refined distillation coupling suspension crystalline technology, through the combination of a first -class distillation tower and a second -level distillation tower, the continuous purification and purification of propylene esters are realized.
The total revenue of propylene esters is increased, the possibility of energy consumption and side reaction is reduced, the separation effect is ensured, and the high-purity L-Cerites can be effectively separated.
Smart Images
Figure CN222400274U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of bio-based material production, in particular to a combined purification system for bio-based materials. Background Art
[0002] Polylactic acid (PLA) is one of the more mature biodegradable plastics in research and application. Its raw materials come from renewable plant fibers, corn, agricultural by-products, etc., and have good biodegradability. PLA has excellent mechanical properties, similar to polypropylene plastics, and can replace PP and PET plastics in some fields. It also has good gloss, transparency, feel and certain antibacterial properties, and has broad application prospects in the fields of medicine, chemical industry, food, etc.
[0003] Lactide is an intermediate in the synthesis of polylactic acid. Its chemical purity determines the molecular weight and molecular weight distribution of polylactic acid, and its optical purity affects the mechanical properties of polylactic acid materials. Lactide purification and refining is a very important step in the two-step polylactic acid synthesis.
[0004] The production technology of lactide is relatively difficult. Currently, there are only a few companies in the world that have the ability to mass-produce lactide, and my country's lactide production level is relatively low. However, as the global demand for high-end polylactic acid continues to increase, the market is gradually showing a situation of supply exceeding demand.
[0005] The main methods for separating and purifying lactide are solvent extraction, distillation and melt recrystallization. Solvent extraction and solvent recrystallization involve the storage and recycling of solvents, which increases the operating costs, especially the low yield of solvent recrystallization, which cannot be produced on a large scale and continuously. The most commonly used methods in industry are distillation and melt recrystallization processes. However, a simple primary distillation cannot completely remove free acid and m-lactide. At the same time, the thermosensitive nature of lactide determines that it will continue to generate by-products in the distillation tower bottom, resulting in a reduced yield. The purification cycle of the recrystallization process is relatively long, and multiple purifications are required to achieve the purity required for the polymerization reaction. The problem is that after multiple recrystallization purifications, the total yield of lactide is low.
[0006] To this end, we provide a combined purification system for bio-based materials to solve the above-mentioned problems. Utility Model Content
[0007] The utility model aims to provide a combined purification system for bio-based materials, and provides a combined purification system for lactide. The system adopts a vacuum two-stage distillation coupled with a suspended crystallization technology for heat-sensitive materials to achieve continuous purification of lactide, thereby solving the problems of low efficiency of the existing one-stage distillation, easy generation of by-products in the distillation tower due to the heat sensitivity of lactide, inability to continuously operate melt crystallization, and low total yield of lactide.
[0008] In order to solve the above technical problems, the utility model is realized by the following technical solutions:
[0009] The utility model discloses a combined purification system for bio-based materials, comprising a primary distillation tower and a secondary distillation tower; the inlet of the primary distillation tower is a raw material inlet, and the raw material is crude lactide; the top gas phase of the primary distillation tower enters into a first condenser, condenses to form a condensate, and the condensate enters into a first reflux tank, part of the condensate in the first reflux tank is refluxed into the primary distillation tower, and the rest of the condensate is discharged from the system as a top product; a first reboiler is arranged at the bottom of the primary distillation tower, and the first reboiler is used for continuously heating the bottom liquid phase of the primary distillation tower, and the heated bottom liquid phase of the primary distillation tower enters into the secondary distillation tower.
[0010] The gas phase at the top of the secondary distillation tower enters the second condenser and condenses to form a condensate, which enters the second reflux tank. Part of the condensate in the second reflux tank flows back into the secondary distillation tower, and the rest of the condensate enters the crystal growing tank. A second reboiler is provided at the bottom of the secondary distillation tower, and the second reboiler is used to continuously heat the bottom liquid phase of the secondary distillation tower. The bottom liquid phase with a very low lactide content after continuous heating is discharged as a bottom product.
[0011] The crystals at the bottom of the crystal growing tank enter the washing tower for washing, the lower crystals in the washing tower are heated by the melting circuit and enter the finished product tank for storage, and the upper residual liquid in the washing tower enters the crystallization tank for recrystallization; the solid-liquid mixture in the crystallization tank enters the solid-liquid separation tower for separation, the lower crystals in the solid-liquid separation tower enter the crystal growing tank and are mixed with the condensate coming out of the second reflux tank, and the upper residual liquid in the solid-liquid separation tower is returned to the primary distillation tower for recycling.
[0012] The utility model is further configured that the raw material crude lactide is crude lactide obtained through oligomerization and cracking reaction of L-lactic acid.
[0013] The utility model is further configured as follows: the first-level distillation tower is configured as a vacuum packed tower, and the top of the tower is connected to a vacuum system; the top pressure is controlled to be 1kPa, with a maximum value not exceeding 5kPa, and the bottom pressure is 1.5kPa, with a maximum value not exceeding 5kPa; the top temperature is controlled to be 115°C, with a maximum value not exceeding 150°C, and the bottom temperature is 160°C, with a maximum value not exceeding 200°C.
[0014] The utility model is further configured that the packing in the primary distillation tower is a structured packing, a packing support is provided below the packing, a packing pressure ring is provided above the packing, a trough distributor is provided above the packing pressure ring, and a liquid collector is provided above the trough distributor.
[0015] The utility model is further configured such that the first reboiler is temperature controlled by heat transfer oil, and the temperature of the heat transfer oil is controlled at 270°C.
[0016] The utility model is further configured that the secondary distillation tower is also configured as a vacuum packed tower, and the top of the tower is connected to a vacuum system; the top pressure is controlled to be 1kPa, with a maximum value not exceeding 5kPa, and the bottom pressure is controlled to be 2kPa, with a maximum value not exceeding 5kPa; the top temperature is controlled to be 140°C, with a maximum value not exceeding 160°C, and the bottom temperature is 197°C, with a maximum value not exceeding 250°C.
[0017] The utility model is further configured such that the temperature in the crystal growing tank is controlled at 60-80°C.
[0018] The utility model is further configured that a piston is arranged on the upper part of the washing tower, the piston moves up and down, and a filter screen is arranged at the bottom of the piston, and the filter screen has an accuracy of 50-200 meshes.
[0019] The utility model is further configured that the temperature in the crystallization tank is controlled at 60-80°C.
[0020] The utility model has the following beneficial effects:
[0021] 1. The utility model adopts a primary distillation tower and a secondary distillation tower to reduce the pressure of the packing distillation, reduce the operating temperature, can reduce the occurrence of heat-sensitive substances lactide side reaction, and can reduce energy consumption, while ensuring the separation effect.
[0022] 2. The utility model provides a crystal growing tank, a washing tower, a crystallization tank and a solid-liquid separation tower. The medium-purity lactide after distillation is melt-crystallized to effectively separate meso-lactide, ensuring that the content of L-lactide is greater than 99.5%. The unique distillation and crystallization coupling can separate small molecules such as lactic acid and water, as well as large molecules such as oligomers, and can effectively remove meso-lactide at the same time, ensuring that the content of L-lactide reaches the optimal level.
[0023] 3. In the crystallization system of the utility model, the residual liquid of the washing tower enters the crystallization tank for recycling, and the residual liquid of the solid-liquid separation tower enters the primary distillation tower for recycling, which can greatly improve the total yield of lactide.
[0024] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.
[0026] Figure 1 A schematic diagram of a combined purification system for bio-based materials.
[0027] In the accompanying drawings, the components represented by the reference numerals are listed as follows:
[0028] 1-primary distillation tower, 2-first condenser, 3-first reflux tank, 4-first reboiler, 5-secondary distillation tower, 6-second reboiler, 7-second condenser, 8-second reflux tank, 9-crystallization tank, 10-washing tower, 11-finished product tank, 12-crystallization tank, 13-solid-liquid separation tower. DETAILED DESCRIPTION
[0029] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0030] See also Figure 1 The utility model is a combined purification system for bio-based materials, comprising a primary distillation tower 1 and a secondary distillation tower 5; the inlet of the primary distillation tower 1 is a raw material inlet, the raw material is crude lactide, which is crude lactide obtained by oligomerization and cracking reaction of L-lactic acid, the primary distillation tower 1 is set as a vacuum packing tower, the top of the tower is connected to a vacuum system, the top pressure is controlled to be 1kPa, the maximum is not more than 5kPa, the bottom pressure is 1.5kPa, the maximum is not more than 5kPa, the top temperature is controlled to be 115°C, the maximum is not more than 150°C, the bottom temperature is 160°C, the maximum is not more than 200°C; the packing is a regular packing, a packing support is provided below the packing, a packing pressure ring is provided above the packing, a trough distributor is provided above the packing pressure ring, a liquid collector is provided above the trough distributor, the liquid collector collects the liquid flowing down from the top and then disperses it evenly on the packing through the trough distributor, so that the descending liquid is fully in contact with the ascending gas to ensure the mass transfer and heat transfer effect.
[0031] The top gas phase of the primary distillation tower 1 enters the first condenser 2, which is cooled by circulating water to condense into condensate, and the condensate enters the first reflux tank 3. Part of the condensate in the first reflux tank 3 flows back into the primary distillation tower 1, and the rest of the condensate is discharged from the system as the top product, i.e., the distillate.
[0032] After the crude lactide enters the primary distillation tower 1, light components such as lactic acid and water evaporate and rise under controlled temperature and pressure, and mix with the reflux condensate descending from the upper part of the tower in the packing to carry out mass transfer and heat transfer. Part of the heat of the high-temperature gas is transferred to the reflux condensate, so that some of the light components in the reflux condensate evaporate, and at the same time, some of the heavy components in the high-temperature gas condense and release some heat.
[0033] A first reboiler 4 is provided at the bottom of the primary distillation tower 1. The first reboiler 4 is used to continuously heat the bottom liquid phase of the primary distillation tower 1. The first reboiler 4 is temperature-controlled by heat transfer oil. The temperature of the heat transfer oil is controlled at 270°C. After the bottom liquid phase passes through the first reboiler 4, small molecules are continuously vaporized and rise. The heated bottom liquid phase of the primary distillation tower 1 enters the secondary distillation tower 5. The secondary distillation tower 5 is also configured as a vacuum packed tower. The top of the tower is connected to a vacuum system to control the top pressure to 1kPa, with a maximum value not exceeding 5kPa, the bottom pressure to 2kPa, with a maximum value not exceeding 5kPa, the top temperature to 140°C, with a maximum value not exceeding 160°C, and the bottom temperature to 197°C, with a maximum value not exceeding 250°C. The top gas phase of the secondary distillation tower 5 enters the second condenser 7, condenses to form a condensate, and the condensate enters the second reflux tank 8. Part of the condensate in the second reflux tank 8 is refluxed into the secondary distillation tower 5, and the rest of the condensate enters the crystal growing tank 9; a second reboiler 6 is provided at the bottom of the secondary distillation tower 5, and the second reboiler 6 is used to continuously heat the bottom liquid phase of the secondary distillation tower 5. The bottom liquid phase with a very low lactide content after continuous heating is discharged as a bottom product.
[0034] After the material enters the secondary distillation tower 5, the lactide evaporates and rises at the set pressure and temperature, and the purity gradually increases while transferring mass and heat with the reflux condensate. The high-purity gaseous lactide enters the second condenser 7 from the top of the tower, and enters the second reflux tank 8 after condensation. Part of the liquid in the second reflux tank 8 enters the reflux, and part of it enters the crystal growing tank 9 in the melt crystallization system as a raw material. The heavy phase material in the secondary distillation tower 5 is continuously circulated and heated by the second reboiler 6. The lactide content is very low and is discharged as the bottom product.
[0035] The primary distillation tower 1 distills and separates small molecular impurities such as lactic acid, water and other substances, and the secondary distillation tower 5 distills and separates large molecular substances such as oligomers. After the secondary distillation, the content of lactide can reach more than 95%. However, the presence of meso-lactide in lactide reduces the optical purity of the L-lactide product, which has a great impact on the performance of downstream polylactic acid. The boiling point of meso-lactide is similar to that of L-lactide, and the melting point difference is large, so subsequent treatments of the crystal growing tank 9, the washing tower 10, the crystallization tank 12 and the solid-liquid separation tower 13 are carried out.
[0036] The crystals at the bottom of the crystal growing tank 9 enter the washing tower 10 for washing, the lower crystals in the washing tower 10 are heated by the melting circuit and then enter the finished product tank 11 for storage, and the upper residual liquid in the washing tower 10 enters the crystallization tank 12 for recrystallization; the solid-liquid mixture in the crystallization tank 12 enters the solid-liquid separation tower 13 for separation, the lower crystals in the solid-liquid separation tower 13 enter the crystal growing tank 9, and are mixed with the condensate coming out of the second reflux tank 8, and the upper residual liquid in the solid-liquid separation tower 13 is returned to the primary distillation tower 1 for recycling.
[0037] The medium-pure lactide from the second reflux tank 8 enters the crystal growing tank 9. The temperature in the crystal growing tank 9 is controlled at 60-80°C. The temperature needs to be adjusted according to the purity of the medium-pure lactide. The material enters the washing tower 10 from the bottom of the crystal growing tank 9. The crystals accumulate at the bottom of the washing tower 10. A piston is arranged on the upper part of the washing tower 10. The piston moves up and down. The bottom of the piston is a filter screen with a precision of 50-200 meshes, preferably 50 meshes. The residual liquid that has not been crystallized is filtered through the filter screen. During the downward pressure of the piston, the crystals are gradually compacted. A scraper is arranged at the bottom of the crystals. When the piston moves to the bottom , start the scraper, the crystals enter the melting circuit, are heated and enter the finished product tank 11, when the piston moves up, the filtered residual liquid is discharged to the crystallization tank 12 for recycling, the temperature in the crystallization tank 12 is controlled at 60-80°C, which is adjusted according to the purity of the material, preferably 60°C, the material in the crystallization tank 12 enters the solid-liquid separation tower 13, and under the action of the cylinder, the lower crystals in the solid-liquid separation tower 13 enter the crystal growing tank 9 and are mixed with the medium-purity lactide after distillation, and the upper residual liquid in the solid-liquid separation tower 13 is returned to the primary distillation tower 1 for recycling, or is directly discharged for use in other processes.
[0038] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.
[0039] The preferred embodiments of the utility model disclosed above are only used to help explain the utility model. The preferred embodiments do not describe all the details in detail, nor do they limit the utility model to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the utility model, so that technicians in the relevant technical field can well understand and use the utility model. The utility model is limited only by the claims and their full scope and equivalents.
Claims
1. A combined purification system for bio-based materials, comprising a primary distillation tower (1) and a secondary distillation tower (5); characterized in that: The inlet of the primary distillation tower (1) is a raw material inlet, and the raw material is crude lactide; The gas phase at the top of the primary distillation tower (1) enters the first condenser (2) and condenses to form condensate, which enters the first reflux tank (3), part of the condensate in the first reflux tank (3) refluxes into the primary distillation tower (1), and the rest of the condensate is discharged from the system as a top product; A first reboiler (4) is provided at the bottom of the primary distillation tower (1), and the first reboiler (4) is used to continuously heat the bottom liquid phase of the primary distillation tower (1), and the heated bottom liquid phase of the primary distillation tower (1) enters the secondary distillation tower (5); The gas phase at the top of the secondary distillation tower (5) enters the second condenser (7) and condenses to form condensate, which enters the second reflux tank (8), part of the condensate in the second reflux tank (8) flows back into the secondary distillation tower (5), and the rest of the condensate enters the crystal growing tank (9); A second reboiler (6) is provided at the bottom of the secondary distillation tower (5), and the second reboiler (6) is used to continuously heat the bottom liquid phase of the secondary distillation tower (5), and the bottom liquid phase with a very low lactide content after continuous heating is discharged as a bottom product; The crystals at the bottom of the crystal growing tank (9) enter the washing tower (10) for washing, the lower crystals in the washing tower (10) are heated by the melting circuit and enter the finished product tank (11) for storage, and the upper residual liquid in the washing tower (10) enters the crystallization tank (12) for recrystallization; The solid-liquid mixture in the crystallization tank (12) enters the solid-liquid separation tower (13) for separation, the lower crystals in the solid-liquid separation tower (13) enter the crystal growing tank (9) and are mixed with the condensate from the second reflux tank (8), and the upper residual liquid in the solid-liquid separation tower (13) is returned to the primary distillation tower (1) for recycling.
2. A combined purification system for bio-based materials according to claim 1, characterized in that: The raw material crude lactide is crude lactide obtained by oligomerization and cracking reaction of L-lactic acid.
3. The combined purification system for bio-based materials according to claim 1, characterized in that: The primary distillation tower (1) is configured as a vacuum packed tower, the top of which is connected to a vacuum system; Control the tower top pressure to 1kPa, the maximum shall not exceed 5kPa, and the tower bottom pressure to 1.5kPa, the maximum shall not exceed 5kPa; The tower top temperature is controlled at 115°C, with a maximum not exceeding 150°C, and the tower bottom temperature is controlled at 160°C, with a maximum not exceeding 200°C.
4. The combined purification system for bio-based materials according to claim 1, characterized in that: The packing in the primary distillation tower (1) is a structured packing, a packing support is provided below the packing, a packing pressing ring is provided above the packing, a trough distributor is provided above the packing pressing ring, and a liquid collector is provided above the trough distributor.
5. The combined purification system for bio-based materials according to claim 1, characterized in that: The first reboiler (4) is temperature-controlled by heat transfer oil, and the temperature of the heat transfer oil is controlled at 270°C.
6. The combined purification system for bio-based materials according to claim 1, characterized in that: The secondary distillation tower (5) is also configured as a vacuum packed tower, and the top of the tower is connected to a vacuum system; Control the tower top pressure to 1kPa, the maximum shall not exceed 5kPa, and the tower bottom pressure to 2kPa, the maximum shall not exceed 5kPa; The tower top temperature is controlled at 140°C, with a maximum not exceeding 160°C, and the tower bottom temperature is controlled at 197°C, with a maximum not exceeding 250°C.
7. The combined purification system for bio-based materials according to claim 1, characterized in that: The temperature in the crystal growing tank (9) is controlled at 60-80°C.
8. The combined purification system for bio-based materials according to claim 1, characterized in that: A piston is arranged on the upper part of the washing tower (10), and the piston moves up and down. A filter screen is located at the bottom of the piston, and the filter screen has a precision of 50-200 meshes.
9. The combined purification system for bio-based materials according to claim 1, characterized in that: The temperature in the crystallization tank (12) is controlled at 60-80°C.