A polylactic acid intermediate reaction-separation integrated device and a reaction-separation process
By integrating packed tower and plate tower into a single polylactic acid intermediate reaction and separation device, the problem of low efficiency in lactic acid oligomer cracking and lactide purification has been solved, achieving high-efficiency lactide production and improving yield and production efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HENAN LONGDU TORISE BIOMATERIALS CO LTD
- Filing Date
- 2023-08-14
- Publication Date
- 2026-05-29
AI Technical Summary
Existing polylactic acid (PLA) production processes suffer from low production efficiency and insufficient lactide yield. In particular, the cracking of lactic acid oligomers and the purification of lactide require separate processes, resulting in low production efficiency and increased production of heavy polymer components.
An integrated reaction and separation device for polylactic acid intermediates is adopted, which integrates a packed tower and a plate tower. The device generates lactide gas through heating tubes and then purifies it by distillation in the packed tower. This combines the cracking of lactic acid oligomers and the purification of lactide into one process, and improves the reaction efficiency by utilizing gas dilution and heat and mass transfer.
This significantly shortened the process flow, improved production efficiency, reduced the generation of heavy polymer components, increased lactide production, and achieved a continuous and reliable production process.
Smart Images
Figure CN117181175B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polylactic acid production technology, and particularly relates to an integrated device and process for the reaction and separation of polylactic acid intermediates. Background Technology
[0002] Polylactic acid (PLA) is a green functional polymer material with excellent biocompatibility and biodegradability, produced by microbial fermentation of biomass raw materials. It can be completely degraded into water and carbon dioxide. Compared with petroleum-based general-purpose plastics, PLA materials are more in line with the concept of sustainable development. Not only are the products easy to degrade and do not cause environmental pollution, but they can also fundamentally solve the problems of petroleum resource depletion and environmental pollution. It has been widely used in clothing, packaging, agriculture, automobiles, electronics, biomedicine and other fields.
[0003] Currently, there are two main methods for synthesizing polylactic acid: the ring-opening polymerization of lactide and the direct polycondensation of lactic acid.
[0004] Direct polycondensation, also known as the one-step method, refers to the process of preparing polylactic acid (PLA) from lactic acid molecules through dehydration polycondensation. The disadvantage of this method is that the reaction system is in a dynamic equilibrium between polycondensation and depolymerization. The gradual increase in system viscosity makes it more difficult to remove the byproduct water. Water that cannot be removed in time will cause the reaction to proceed towards polymer depolymerization, thus affecting the increase of PLA molecular weight. Simultaneously, under high-temperature and high-vacuum reaction conditions, PLA can also undergo depolymerization, discoloration, and racemization, reducing product properties. While the one-step method for producing PLA has a short production process and low cost, the difficulty in effectively increasing the PLA molecular weight results in poor mechanical properties, limiting its industrial application. Therefore, the mainstream existing production process is the ring-opening polymerization of lactide to synthesize PLA.
[0005] The ring-opening polymerization method can be further divided into three processes: First, lactic acid is polymerized into lactic acid oligomers with a molecular weight of about 1000-5000 under suitable catalyst, temperature, and pressure conditions; Second, the lactic acid oligomers are used to produce lactide under high temperature and high vacuum conditions using distillation, evaporators, or cracking furnaces, and the lactide is further purified using distillation or crystallization techniques to achieve the purity required for polymerization; Third, the lactide is polymerized into polylactic acid with a certain molecular weight under suitable catalyst, temperature, and pressure conditions. The first and second steps are used to produce and purify lactide. Chinese invention patent application CN105646441A specifically discloses a method for preparing lactide, including the following steps: Step 1: Removing free water from lactic acid; Step 2: Adding the lactic acid obtained in Step 1 from the free water reaction to a catalyst to carry out a polycondensation reaction, obtaining lactic acid oligomers; Step 3: Adding an ionic liquid as a solvent to the lactic acid oligomers obtained in Step 2, heating to carry out a depolymerization reaction, and simultaneously collecting the crude product by vacuum distillation; Step 4: Purifying the crude product obtained in Step 3 by recrystallization to obtain the finished lactide product. The above-mentioned method for preparing lactide still requires two separate steps: the pyrolysis of lactic acid oligomers and the purification of lactide. These two steps need to be carried out in different reaction devices, which reduces production efficiency. In addition, during the depolymerization of lactic acid oligomers using devices such as distillation, evaporation or pyrolysis furnaces, as the polymerization reaction and side reactions occur simultaneously, the viscosity of the lactic acid polymer increases, which increases the amount of heavy polymer components that do not produce lactide, and correspondingly reduces the yield of lactide. Summary of the Invention
[0006] Therefore, the purpose of this invention is to provide an integrated reaction and separation device for polylactic acid intermediates to solve the technical problem of low production efficiency and yield in the production of lactide in the prior art; the purpose of this invention is also to provide a reaction and separation process for polylactic acid intermediates that can shorten the process flow and increase the yield of lactide.
[0007] To solve the above problems, the integrated reaction and separation device for polylactic acid intermediates provided by the present invention adopts the following technical solution:
[0008] An integrated reaction and separation device for polylactic acid intermediates includes:
[0009] The reaction tower includes a packed tower body and a plate tower body integrated together and arranged at intervals. A lactic acid oligomer inlet is provided between the packed tower body and the plate tower body. A bottom heavy component outlet is provided at the bottom of the plate tower body and is used to connect with a lactic acid oligomer storage system. A heat exchanger is provided at the top of the packed tower body and a top light component outlet is provided at the top of the reaction tower and is connected to a top condenser.
[0010] The plate tower body is provided with a feed distributor connected to the lactic acid oligomer inlet, and at least two layers of staggered tower plates located below the feed distributor and spaced apart vertically. Each tower plate is provided with a heating pipe for heating the lactic acid oligomer to generate lactide gas; the packed tower body is provided with an intermediate lactide outlet.
[0011] The beneficial effects of the polylactic acid intermediate reaction and separation integrated device of the present invention are as follows: When the lactic acid oligomer is introduced into the reaction tower, it will first be cracked on the plate of the plate tower to generate lactide gas. The lactide gas flows from bottom to top and can bubble and dilute the upper layer of lactic acid oligomer liquid, thereby making the liquid film of lactic acid oligomer thinner, reducing the viscosity of lactic acid oligomer, accelerating the cracking of lactic acid oligomer, and thus avoiding further polymerization of lactic acid oligomer and the generation of side reactions. In a plate column, lactide gas enters the packed column from bottom to top. Under the action of a heat exchanger, lactide and low-molecular-weight lactic acid oligomers in the gas are condensed into liquid and flow downwards into the packing material. There, they exchange heat and mass with the lactide gas entering from bottom to top. The high-boiling-point low-molecular-weight lactic acid oligomers in the lactide gas are condensed into liquid and flow downwards into the plate column for further dilution. Meanwhile, the lighter components of the lactide gas, such as lactic acid and water, which have lower boiling points, flow towards the top of the column and are collected in the top condenser, achieving the distillation and purification of lactide in the packed column. This invention integrates the cracking of lactic acid oligomers and the purification of lactide into a single reaction column, combining these processes into one step. This significantly shortens the process flow, reduces the generation of heavy polymer components, and increases the yield of lactide.
[0012] Furthermore, the heating tubes are provided in at least two layers on the same tower plate, with the two adjacent layers of heating tubes arranged in a cross shape.
[0013] Beneficial effects: It increases the contact area between lactic acid oligomers and heating tubes, thereby accelerating the decomposition reaction of lactic acid oligomers.
[0014] Furthermore, the intermediate outlet of the lactide is located near the heat exchanger in the packed tower body.
[0015] Beneficial effects: The amount of liquid lactide is greatest near the heat exchanger, and the separated lactide has higher purity.
[0016] Furthermore, a packing distributor is provided between the packed tower body and the heat exchanger, as well as between the packed tower body and the feed distributor.
[0017] Beneficial effects: The packing distributor between the packed tower and the heat exchanger can evenly distribute the condensed liquid lactide and low molecular weight lactic acid oligomers throughout the packing layer, which helps improve the uniformity of gas-liquid contact and avoids liquid aggregation or excessive drying. Located between the packed tower and the feed distributor, it also helps to evenly disperse the liquid low molecular weight lactic acid oligomers onto the lactic acid oligomers on the trays, thus diluting the lactic acid oligomers.
[0018] Furthermore, the tray is one of a bubble cap tray, a valve tray, and a sieve tray.
[0019] Beneficial effects: Facilitates material sourcing and installation.
[0020] The technical solution of the polylactic acid intermediate reaction separation process of the present invention is as follows:
[0021] The polylactic acid (PLA) intermediate reaction and separation process, based on the integrated PLA intermediate reaction and separation device in any of the above technical solutions, involves introducing lactic acid oligomers into a reaction tower integrating a packed tower and a plate tower. In the plate tower, the lactic acid oligomers are decomposed to generate lactide gas, which contains low molecular weight lactic acid oligomers, lactide, lactic acid, and water. The lactide gas is used to bubble and dilute the upper layer of lactic acid oligomer liquid by rising from the bottom. The lactide gas is then purified by distillation in the packed tower, allowing the separated low molecular weight lactic acid oligomer liquid to flow into the plate tower to dilute the lactic acid oligomers in the plate tower.
[0022] Furthermore, the plate tower is equipped with two or more layers of trays arranged at intervals, and each tray is equipped with a heating tube for heating the lactic acid oligomers. This allows the lactide gas generated on the lower tray to pass through the upper tray from bottom to top, thereby achieving bubbling dilution of the lactic acid oligomers on the upper tray.
[0023] Furthermore, the distillation and purification of lactide gas involves installing a heat exchanger at the top of the packed column. This allows the lactide gas generated in the plate column to enter the packed column from bottom to top, where it exchanges heat with the heat exchanger. This condenses the lactide and low molecular weight lactic acid oligomers in the lactide gas into a liquid state, which then flows from top to bottom into the packing material in the packed column. There, it exchanges heat and mass with the lactide gas entering the packed column from bottom to top. The high-boiling-point low molecular weight lactic acid oligomers in the lactide gas are condensed into liquid and flow downwards into the plate column to dilute the lactic acid oligomers in the plate column. The lighter components with lower boiling points in the lactide gas flow to the top of the reaction column.
[0024] Furthermore, a light component outlet is set at the top of the reaction tower, and the light component outlet is connected to the top condenser to collect the light components with lower boiling points in the lactide gas in the top condenser; lactide is purified by controlling the reflux ratio between the top condenser and the lactide tower.
[0025] Furthermore, it also includes the process of introducing the heavy component polymer generated inside the plate tower from the bottom of the reaction tower into the lactic acid oligomer storage system.
[0026] The beneficial effects of the polylactic acid intermediate reaction separation process of the present invention are as follows: The present invention can combine the two separate processes of lactic acid oligomer pyrolysis and lactide purification in the prior art into one process, which greatly shortens the process flow and improves production efficiency; in the process of lactic acid oligomer pyrolysis and lactide purification, the lactic acid oligomer liquid can be diluted to reduce the viscosity of the lactic acid oligomer, thereby avoiding further polymerization of the lactic acid oligomer and the generation of side reactions, reducing the generation of heavy component oligomers, and making the whole process continuous and reliable. Attached Figure Description
[0027] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:
[0028] Figure 1 This is a simplified structural diagram of the polylactic acid intermediate reaction and separation integrated device of the present invention.
[0029] Explanation of reference numerals in the attached figures:
[0030] 1-Reaction tower, 2-Packed tower body, 3-Plate tower body, 4-Tower plate, 5-Bottom heavy component outlet, 6-Top light component outlet, 7-Heating tube, 8-Heat exchanger, 9-Lactide intermediate outlet, 10-Packed distributor, 11-Feed distributor, 12-Lactic acid oligomer inlet. Detailed Implementation
[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Those skilled in the art should understand that the embodiments described below are only some, not all, of the embodiments disclosed. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0032] The principles and spirit of the present invention will be explained in detail below with reference to several representative embodiments.
[0033] Example 1 of the integrated reaction and separation device for polylactic acid intermediates provided by the present invention:
[0034] like Figure 1 As shown, the integrated reaction and separation device for polylactic acid intermediates includes a reaction tower 1, which is an integral structure comprising a packed tower body 2 and a plate tower body 3, both integrated together and sharing a single tower body. The plate tower body 3 is located below, and the packed tower body 2 is located above, with a certain gap between them. A lactic acid oligomer inlet 12 is provided on the reaction tower 1 between the packed tower body 2 and the plate tower body 3. A bottom heavy component outlet 5 is provided on the reaction tower 1 at the bottom of the plate tower body 3. A heat exchanger 8 is provided on the reaction tower 1 at the top of the packed tower body 2. A top light component outlet 6 is provided at the top of the reaction tower 1, and the top light component outlet 6 is connected to a top condenser.
[0035] The plate tower body 3 is equipped with a feed distributor connected to the lactic acid oligomer inlet 12. In this embodiment, the plate tower body 3 has two or more layers of trays 4, which are bubble cap trays commonly used in the prior art. Of course, in actual use, the trays 4 can also be floating valve trays or sieve trays commonly used in the prior art. The trays 4 are arranged in a staggered manner in the vertical direction, so that the liquid flow gaps formed between the upper and lower adjacent trays 4 and the inner wall of the plate tower body 4 are staggered in the vertical direction, thereby allowing the liquid to flow from top to bottom in an S-shape.
[0036] Each tray 4 has four layers of heating tubes 7, and the heating tubes 7 on each tray 4 are independent of each other. In this embodiment, U-shaped tubes are used for heating. The U-shaped tubes are arranged vertically, so one set of U-shaped tubes is equivalent to two layers of heating tubes. Another set of U-shaped tubes is sandwiched between the previous set of U-shaped tubes to form four layers of heating tubes, and the adjacent layers of heating tubes are arranged in a cross shape. Heat transfer oil is circulated inside the heating tubes, and the temperature is sufficient to meet the cracking reaction temperature of lactic acid oligomers.
[0037] In actual processing, a high-viscosity melt pump is used to pump lactic acid oligomers from the lactic acid oligomer storage system. After being preheated to a certain temperature by a preheater, the oligomers are continuously fed into the feed inlet. Under the action of the feed distributor, they are evenly distributed on the uppermost tray, forming a liquid film. It should be noted that not only lactic acid oligomers are introduced into the plate column, but also some catalysts required for the reaction. In the high-temperature environment created by the heating tubes, the lactic acid oligomers are decomposed under the action of the catalyst to obtain lactide gas. Lactide gas contains low molecular weight oligomers, lactide, lactic acid, water, and other components, and flows towards the top of the reaction column. The arrangement of the heating tubes increases the contact area between them and the liquid lactic acid oligomers, thereby improving the decomposition efficiency of the lactic acid oligomers.
[0038] Because tray 4 has multiple layers, uncracked lactic acid oligomers overflow from the overflow weir of the upper tray and flow into the downcomer to the lower tray for further cracking. The lactide gas generated on the lower tray then flows upwards through the bubble cap of the upper tray, bubbling, transferring heat and mass to the lactic acid oligomer liquid, thus thinning the liquid film and accelerating the cracking process. The multi-layered trays significantly improve the cracking efficiency of lactic acid oligomers. The upward-flowing lactide gas dilutes the lactic acid oligomers in the upper layer, reducing further polymerization and side reactions. However, a small amount of heavy polymer components may still be generated; these heavy polymer components flow out through the heavy polymer outlet at the bottom of the reaction column. To avoid waste, the bottom recombinant discharge port is connected to the lactic acid oligomer storage system. This recombinant polymer can then flow into the lactic acid oligomer storage system to be diluted and its viscosity reduced. It can then be pumped back into the plate tower 3 and pyrolyzed again under high temperature.
[0039] In this embodiment, the packed tower 2 contains two layers of packing. Packing distributors 10 are installed between the two layers of packing, between the packed tower 2 and the heat exchanger 8, and between the bottom of the packed tower 2 and the feed distributor 11. The packing distributors 10 are liquid distributors. A lactide intermediate outlet 9 is located on the packed tower 2 near the top layer of packing, which is also close to the heat exchanger 8. Of course, in actual production, the packed tower 2 can be designed with a suitable height according to requirements, and then divided into several layers of packing according to the designed height. The aforementioned liquid distributors can be installed between each pair of adjacent packing layers.
[0040] In this embodiment, the heat exchanger 8 is a common shell-and-tube heat exchanger in the prior art. The tubes are exposed at the top of the packed tower 2 and are filled with heat exchange medium. The lactide gas generated in the plate tower 3 enters the packed tower 2 from bottom to top and exchanges heat with the heat exchanger 8 through the packed tower 2. In the lactide gas that exchanges heat with the heat exchanger 8 first, the lactide and low molecular weight lactic acid oligomers with boiling points higher than the temperature of the heat exchange medium will be condensed into liquid and evenly dispersed into the packing by the packing distributor 10 at the top of the packed tower 2. They flow from top to bottom in the packing and take advantage of the large surface contact area of the packing to make full contact with the lactide gas that subsequently enters the packed tower 2 from bottom to top and carry out heat and mass transfer exchange. At this time, the high boiling point low molecular weight lactic acid oligomers and lactide in the lactide gas will be condensed into liquid again during the heat transfer exchange and flow from top to bottom, while the light components such as lactic acid and water with lower boiling points flow towards the top of the tower and enter the top condenser from the light component outlet 6 at the top of the tower for condensation and collection. The low-molecular-weight lactic acid oligomers condensed into liquid can flow from the packed column 2 into the plate column 3 to dilute the lactic acid oligomers in the plate column 3, further reducing their viscosity and lowering the probability of side reactions. The lactide condensed into liquid can then flow out from the lactide outlet for collection. In the packed column 2, there is no need to introduce a liquid medium for heat and mass transfer of the lactide gas; instead, the higher-boiling-point components of the lactide gas are condensed into liquid and then exchange heat and mass with the subsequent lactide gas.
[0041] The liquid light components collected and separated in the overhead condenser can be refluxed as needed, i.e., flowed back into the packed column 2. Here, the liquid light components vaporize through heat transfer within the packed column 2. Thus, by controlling the reflux ratio in the overhead condenser, the purification of lactide can be controlled. Similarly, a certain reflux ratio in the intermediate section of the lactide column can be controlled as needed, allowing the separated liquid lactide to be refluxed back into the packed column 2 for heat and mass transfer.
[0042] This invention integrates the pyrolysis of lactic acid oligomers and the purification of lactide into a single reaction tower, combining the pyrolysis of lactic acid oligomers and the purification of lactide into one process, which greatly shortens the process flow, reduces the generation of heavy component polymers, increases the yield of lactide, and makes the entire process continuous and reliable.
[0043] Example 2 of the integrated reaction and separation device for polylactic acid intermediates provided by the present invention:
[0044] The main difference between this embodiment and Example 1 is that in Example 1, the heating tubes are arranged in a multi-layered cross-shaped distribution, while in this embodiment, the heating tubes are laid out in a single layer. In order to increase the contact area with the lactic acid oligomer, the heating tubes are arranged in a serpentine shape.
[0045] Example 3 of the integrated reaction and separation device for polylactic acid intermediates provided by the present invention:
[0046] The main difference between this embodiment and Example 1 is that in Example 1, the heating tubes on each tray are independent, meaning each heating tube has a heat transfer medium inlet and an outlet, requiring multiple interfaces on the reaction tower. In this embodiment, the heating tubes on each tray are connected, allowing only one heat transfer medium inlet and one outlet to be provided on the reaction tower. Connecting the heating tubes on each tray involves first installing each heating tube on the tray, then welding a connecting pipe to each layer of heating tubes to achieve the connection. The connecting pipe is placed in the gap where the lactic acid oligomer overflows from the upper tray to the lower tray.
[0047] Specific embodiments of the polylactic acid intermediate reaction separation process of the present invention:
[0048] The core of the polylactic acid intermediate reaction separation process is to introduce lactic acid oligomers into a reaction tower that integrates a packed tower and a plate tower. In the plate tower, the lactic acid oligomers are decomposed to generate lactide gas, which contains low molecular weight lactic acid oligomers, lactide, lactic acid, and water. The lactide gas is used to bubble and dilute the upper layer of lactic acid oligomer liquid by rising from the bottom. In the packed tower, the lactide gas is purified by distillation, and the separated low molecular weight lactic acid oligomer liquid flows into the plate tower to dilute the lactic acid oligomers in the plate tower.
[0049] In practice, it is necessary to set up two or more layers of trays arranged at intervals in the plate tower, and to install heating tubes on each tray to heat the lactic acid oligomers, so that the lactide gas generated on the lower tray passes through the upper tray from bottom to top, thereby achieving bubbling dilution of the lactic acid oligomers on the upper tray.
[0050] The distillation purification of lactide gas involves installing a heat exchanger at the top of a packed column. Lactide gas generated in a plate column enters the packed column from bottom to top, exchanging heat with the heat exchanger to condense lactide and low-molecular-weight lactic acid oligomers into a liquid state. This liquid then flows downwards into the packing material within the column, where it exchanges heat and mass with the lactide gas entering from bottom to top. The high-boiling-point low-molecular-weight lactic acid oligomers in the lactide gas are condensed into liquid and flow downwards into the plate column to dilute the lactic acid oligomers already present. The lighter components with lower boiling points flow to the top of the reaction column, exiting through a top light component outlet and being separated and collected by a top condenser. Lactide is collected from an intermediate outlet in the packed column. The purification of lactide is controlled by adjusting the reflux ratio between the top condenser and the lactide column.
[0051] During the pyrolysis of lactic acid oligomers, side reactions inevitably occur, producing a certain amount of heavy polymer components. These heavy polymer components flow to the bottom of the reaction tower. Introducing these heavy polymer components from the bottom of the reaction tower back into the lactic acid oligomer storage system can both dilute and reduce the viscosity of the heavy polymer components and allow them to be reused and reintroduced into the reaction tower for pyrolysis, thus avoiding waste of resources.
[0052] It should be noted that the reaction tower, trays, heating tubes, heat exchangers, and top condenser used in the polylactic acid intermediate reaction and separation process are the same as the corresponding structures in the aforementioned integrated polylactic acid intermediate reaction and separation device.
[0053] The polylactic acid intermediate reaction separation process of the present invention combines the two separate processes of cracking lactic acid oligomers and purifying lactide in the prior art into one process, which greatly shortens the process flow, improves production efficiency, reduces further polymerization of lactic acid oligomers and the generation of side reactions, reduces the generation of heavy component oligomers, and makes the whole process continuous and reliable.
Claims
1. An integrated reaction and separation device for polylactic acid intermediates, characterized in that, include: The reaction tower includes a packed tower body and a plate tower body integrated together and arranged at intervals. A lactic acid oligomer inlet is provided between the packed tower body and the plate tower body. A bottom heavy component outlet is provided at the bottom of the plate tower body and is used to connect with a lactic acid oligomer storage system. A heat exchanger is provided at the top of the packed tower body and a top light component outlet is provided at the top of the reaction tower and is connected to a top condenser. The plate tower body is provided with a feed distributor connected to the lactic acid oligomer inlet, and is also provided with at least two layers of staggered tower plates located below the feed distributor and arranged at intervals between the upper and lower layers. Each tower plate is provided with a heating pipe for heating the lactic acid oligomer to generate lactide gas. The packed tower body is provided with a lactide intermediate outlet.
2. The integrated reaction and separation device for polylactic acid intermediates according to claim 1, characterized in that, The heating tubes are arranged in at least two layers on the same tower plate, with the two adjacent layers of heating tubes arranged in a cross shape.
3. The integrated reaction and separation device for polylactic acid intermediates according to claim 1, characterized in that, The intermediate outlet of the lactide is located near the heat exchanger in the packed tower body.
4. The integrated reaction and separation device for polylactic acid intermediates according to any one of claims 1-3, characterized in that, Packing distributors are provided between the packed tower body and the heat exchanger, and between the packed tower body and the feed distributor.
5. The integrated reaction and separation apparatus for polylactic acid intermediates according to any one of claims 1-3, characterized in that, The tray is one of the following: bubble cap tray, valve tray, and sieve tray.
6. A polylactic acid intermediate reaction and separation process, implemented based on the integrated polylactic acid intermediate reaction and separation device according to any one of claims 1-5, characterized in that, The process involves introducing lactic acid oligomers into a reaction tower that integrates a packed column and a plate column. In the plate column, the lactic acid oligomers are decomposed to generate lactide gas, which contains low molecular weight lactic acid oligomers, lactide, lactic acid, and water. The lactide gas is used to bubble and dilute the upper layer of lactic acid oligomer liquid. In the packed column, the lactide gas is purified by distillation, and the separated low molecular weight lactic acid oligomer liquid flows into the plate column to dilute the lactic acid oligomers in the plate column.
7. The polylactic acid intermediate reaction and separation process according to claim 6, characterized in that, The plate tower is equipped with two or more layers of trays arranged at intervals, and each tray is equipped with a heating tube for heating lactic acid oligomers. This allows the lactide gas generated on the lower tray to pass through the upper tray from bottom to top, thereby achieving bubbling dilution of the lactic acid oligomers on the upper tray.
8. The polylactic acid intermediate reaction and separation process according to claim 7, characterized in that, The distillation and purification of lactide gas involves installing a heat exchanger at the top of a packed column. Lactic acid gas generated in a plate column enters the packed column from bottom to top, exchanging heat with the heat exchanger. This condenses the lactide and low-molecular-weight lactic acid oligomers in the gas into a liquid state, which then flows downwards into the packing material within the column. There, it exchanges heat and mass with the lactide gas entering from bottom to top. The high-boiling-point low-molecular-weight lactic acid oligomers in the lactide gas are condensed into liquid and flow downwards into the plate column to dilute the lactic acid oligomers already present. The lighter components with lower boiling points in the lactide gas flow to the top of the reaction column.
9. The polylactic acid intermediate reaction and separation process according to claim 8, characterized in that, A light component outlet is set at the top of the reaction tower and connected to a top condenser to collect the light components with lower boiling points in the lactide gas. The purification of lactide is controlled by controlling the reflux ratio between the top condenser and the lactide tower.
10. The polylactic acid intermediate reaction separation process according to any one of claims 6-9, characterized in that, It also includes the process of introducing the heavy component polymer generated inside the plate tower from the bottom of the reaction tower into the lactic acid oligomer storage system.