CN114672010A - Continuous polymerization devolatilization method and device for polylactic acid - Google Patents
Continuous polymerization devolatilization method and device for polylactic acid Download PDFInfo
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- CN114672010A CN114672010A CN202210347139.8A CN202210347139A CN114672010A CN 114672010 A CN114672010 A CN 114672010A CN 202210347139 A CN202210347139 A CN 202210347139A CN 114672010 A CN114672010 A CN 114672010A
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- devolatilization
- lactide
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- polylactic acid
- continuous polymerization
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- 238000006116 polymerization reaction Methods 0.000 title claims abstract description 32
- 229920000747 poly(lactic acid) Polymers 0.000 title claims abstract description 30
- 239000004626 polylactic acid Substances 0.000 title claims abstract description 30
- 238000000034 method Methods 0.000 title claims abstract description 16
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 claims abstract description 37
- 238000006243 chemical reaction Methods 0.000 claims abstract description 36
- 239000007788 liquid Substances 0.000 claims abstract description 27
- 239000000126 substance Substances 0.000 claims abstract description 21
- 239000011552 falling film Substances 0.000 claims abstract description 17
- 238000001704 evaporation Methods 0.000 claims abstract description 14
- 230000008020 evaporation Effects 0.000 claims abstract description 14
- 239000000155 melt Substances 0.000 claims abstract description 11
- 229920000642 polymer Polymers 0.000 claims abstract description 11
- 238000003756 stirring Methods 0.000 claims abstract description 11
- 239000000654 additive Substances 0.000 claims abstract description 10
- 230000000996 additive effect Effects 0.000 claims abstract description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 10
- 238000009835 boiling Methods 0.000 claims abstract description 8
- 238000002425 crystallisation Methods 0.000 claims abstract description 8
- 230000008025 crystallization Effects 0.000 claims abstract description 8
- 238000002156 mixing Methods 0.000 claims abstract description 8
- 238000009833 condensation Methods 0.000 claims abstract description 5
- 230000005494 condensation Effects 0.000 claims abstract description 5
- 238000005469 granulation Methods 0.000 claims abstract description 5
- 230000003179 granulation Effects 0.000 claims abstract description 5
- 239000010865 sewage Substances 0.000 claims abstract description 5
- 239000007921 spray Substances 0.000 claims abstract description 5
- 230000009471 action Effects 0.000 claims abstract description 4
- 239000000463 material Substances 0.000 claims description 42
- 238000010438 heat treatment Methods 0.000 claims description 32
- 239000007789 gas Substances 0.000 claims description 15
- 238000007599 discharging Methods 0.000 claims description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 8
- 230000005251 gamma ray Effects 0.000 claims description 7
- 239000011261 inert gas Substances 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 230000008676 import Effects 0.000 claims description 3
- 230000008569 process Effects 0.000 claims description 3
- 238000005086 pumping Methods 0.000 claims description 3
- 239000012808 vapor phase Substances 0.000 claims description 3
- 238000012856 packing Methods 0.000 claims description 2
- 230000001502 supplementing effect Effects 0.000 claims description 2
- 230000003631 expected effect Effects 0.000 abstract description 3
- 238000003763 carbonization Methods 0.000 abstract description 2
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 description 10
- 235000014655 lactic acid Nutrition 0.000 description 5
- 239000004310 lactic acid Substances 0.000 description 5
- 238000007151 ring opening polymerisation reaction Methods 0.000 description 4
- 238000006068 polycondensation reaction Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- JVTAAEKCZFNVCJ-REOHCLBHSA-N L-lactic acid Chemical compound C[C@H](O)C(O)=O JVTAAEKCZFNVCJ-REOHCLBHSA-N 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
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- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000002861 polymer material Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- JJTUDXZGHPGLLC-IMJSIDKUSA-N 4511-42-6 Chemical compound C[C@@H]1OC(=O)[C@H](C)OC1=O JJTUDXZGHPGLLC-IMJSIDKUSA-N 0.000 description 1
- 229920002261 Corn starch Polymers 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000012662 bulk polymerization Methods 0.000 description 1
- 238000012824 chemical production Methods 0.000 description 1
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- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
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- 229920006351 engineering plastic Polymers 0.000 description 1
- 238000005886 esterification reaction Methods 0.000 description 1
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- 238000010528 free radical solution polymerization reaction Methods 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
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- 238000006467 substitution reaction Methods 0.000 description 1
- 238000010557 suspension polymerization reaction Methods 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/88—Post-polymerisation treatment
- C08G63/90—Purification; Drying
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D1/00—Evaporating
- B01D1/22—Evaporating by bringing a thin layer of the liquid into contact with a heated surface
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D1/00—Evaporating
- B01D1/30—Accessories for evaporators ; Constructional details thereof
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D5/00—Condensation of vapours; Recovering volatile solvents by condensation
- B01D5/0033—Other features
- B01D5/0036—Multiple-effect condensation; Fractional condensation
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
- C08G63/08—Lactones or lactides
Abstract
The invention discloses a continuous polymerization devolatilization method and a device for polylactic acid, which comprises the following steps: firstly, feeding a polylactic acid melt from a lactide polymerization system into a falling film evaporation heater at the upper part of a vertically arranged devolatilization reaction device to heat the melt; low boiling point substances and lactide gas generated in the devolatilization reaction process are changed into lactide liquid through a condensing device and then are refluxed to a lactide buffer tank; non-condensable gas and low-boiling-point substances are pumped into a vacuum buffer tank for further condensation and crystallization, and are discharged to a sewage system under the action of spray water; and extruding the devolatilized polymer melt to the inlet of a devolatilization discharge pump through a devolatilizer screw, mixing with the modified additive from an additive feeding screw, and conveying to a granulation system through the devolatilization discharge pump. The invention ensures that the chemical components of the melt of the polylactic acid are distributed more uniformly, the expected effect can be achieved by stirring for 30 minutes under the normal condition, and the problems of crystallization, carbonization, melt wall hanging and the like are effectively avoided.
Description
Technical Field
The invention belongs to the technical field of chemical production equipment, and particularly relates to a continuous polymerization devolatilization method and device for polylactic acid.
Background
The polylactic acid is a polymer obtained by polymerizing lactic acid serving as a main raw material, the raw materials mainly comprise plant straws and corn starch, the source is sufficient, the product can be biodegraded, and the polylactic acid is very environment-friendly and is an ideal green high polymer material. The process generally comprises the steps of dehydrating industrial-grade L-lactic acid at high temperature and high vacuum degree to perform esterification reaction to generate linear dimer lactic acid-based lactic acid, further performing dehydration condensation reaction to generate lactic acid oligomer and lactide with high molecular weight, then performing depolymerization degradation on the oligomer with high molecular weight to generate lactide, rectifying and purifying solid-phase crystallization of depolymerized crude lactide to generate high-purity lactide, and performing high-temperature high-pressure polymerization and high-temperature high-vacuum devolatilization on the high-purity lactide to generate high-molecular-weight high-performance polylactic acid slices suitable for engineering plastic grades and fiber grades.
The polylactic acid is a polymer material with good development prospect, not only has degradability and biocompatibility, but also can be produced and processed by most of general processing equipment, and the preparation method of the polylactic acid comprises the following steps: polycondensation, chain extension, lactide ring-opening polymerization, and the like. The direct polycondensation method of lactic acid is the most inexpensive way to prepare polylactic acid, and the ring-opening polymerization of lactide is generally commercially utilized to prepare polylactic acid. The ring-opening polymerization of L-lactide is the best method for preparing high molecular weight polylactic acid because it has the potential to be controlled chemically precisely, which can alter the properties of the final polymer in a more controlled manner. This feature of ring-opening polymerization makes it suitable for large-scale production, and polymerization methods of lactide include melt polymerization, bulk polymerization, solution polymerization, and suspension polymerization, but melt polymerization is the simplest and most reproducible method.
After the polylactic acid polymerization is finished, a devolatilization reaction is needed, and the aim is to remove low-boiling point substances and lactide gas so as to ensure that the purity content of the produced polylactic acid meets the requirement. The reaction generally takes place in horizontal stirring reaction device, and the molecular weight of the product is difficult to further improve after the melt polycondensation of the materials in the equipment reaches a certain stage, the materials are easy to be heated unevenly, side reactions such as thermal oxidation degradation and the like occur, and the residence time distribution is wide.
The present invention has been made in view of this situation.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a continuous polymerization devolatilization method and a device for polylactic acid. In order to solve the technical problems, the invention adopts the technical scheme that:
a continuous polymerization devolatilization method and a device for polylactic acid comprise the following steps:
step 1, feeding a polylactic acid melt from a lactide polymerization system into a falling film evaporation heater at the upper part of a vertically-arranged devolatilization reaction device to heat the melt;
step 2, low boiling point substances and lactide gas generated in the devolatilization reaction process are changed into lactide liquid through a condensing device and then are refluxed to a lactide buffer tank;
step 3, pumping the non-condensable gas and the low-boiling-point substances into a vacuum buffer tank for further condensation and crystallization, and discharging the non-condensable gas and the low-boiling-point substances into a sewage system under the action of spray water;
and 4, extruding the devolatilized polymer melt to the inlet of a devolatilization discharge pump through a devolatilizer screw, mixing with the modified additive from the additive feeding screw, and conveying to a granulation system through the devolatilization discharge pump.
Further, the temperature of the falling film evaporation heater is controlled to be 185-200 ℃, the internal pressure is controlled to be 0.75-0.85KPa, and the liquid level of the internal melt is controlled to be 30%.
Further, the device includes the tower body, the top lid of tower body is equipped with the top cap, and the drain pan is installed to the bottom, tower body, top cap, drain pan enclose jointly and close and form the cavity, be equipped with the material import on the top cap, the drain pan bottom surface is equipped with the discharge gate, fill the material in the cavity, heating system carries out the heat exchange with the material, the inside packing of cavity has inert gas, install mixing system in the cavity, device top vapor phase system is equipped with second grade lactide steam condenser.
Further, the heating system comprises a falling film evaporation heater and a heating medium jacket heating system, the falling film evaporation heater is arranged at the feed inlet, and the heating medium jacket heating system coats the tower body.
Further, the falling film evaporator is provided with a heating system, and the heating system comprises a heat medium circulating pump, a heat medium cooler and a heat medium heating and supplementing adjusting valve.
Further, liquid level control adopts the gamma ray level gauge, the gamma ray level gauge is installed on the inside wall of top cap, pressure sensor, temperature sensor are still installed to the device.
Further, the stirring device is a helical ribbon stirrer, the lower end of the stirrer is connected with a vertical discharging screw rod, the discharging screw rod is installed in the conveying pipeline, and the stirring device is provided with a heater.
Furthermore, the material port is provided with a material conveying pipeline extending downwards, and the end part of the pipeline bends towards the center of the cavity.
Further, the inert gas is nitrogen.
Further, the vacuum of the device adopts a vacuum device of a two-stage roots and a water ring vacuum pump.
After the technical scheme is adopted, compared with the prior art, the invention has the following beneficial effects.
The vertical reaction device is adopted, so that materials with high viscosity and poor fluidity are stirred to be more convenient for full devolatilization reaction; the temperature of the materials is controlled to be about 200 ℃, so that the generation of gel is prevented, and the cleaning frequency of the reaction device is effectively reduced; the liquid level is controlled stably, the adhesion of materials on the wall of the polymerizer is reduced as much as possible, and the feeding speed of the materials is adjusted, so that the constant liquid level of the materials is ensured; the pressure sensor loop controls the rotating speed of the vacuum pump, and the liquid level is prevented from greatly fluctuating due to vacuum degree fluctuation and even flood irrigation is avoided.
According to the invention, the discharge screw is arranged at the discharge hole, so that the melt in the cavity can be subjected to full devolatilization reaction, and the melt after devolatilization reaction can be conveyed out more conveniently. The invention ensures that the chemical components of the melt of the polylactic acid are distributed more uniformly, can achieve the expected effect after being stirred for 30 minutes under the normal condition, and effectively avoids the problems of crystallization, carbonization, melt wall hanging and the like.
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention to the right. It is obvious that the drawings in the following description are only some embodiments and that for a person skilled in the art, other drawings can also be derived from them without inventive effort. In the drawings:
FIG. 1 is a schematic view of the overall structure of the present invention;
fig. 2 is a schematic top view of the present invention.
In the figure: n1, material inlet; n2 and a material outlet; n3, a steam outlet; n4a-c, nitrogen inlet; n5, TEF washing steam outlet; n6, spare port; j1a-c and a heat conduction oil outlet; j2a-c and a heat conduction oil outlet; j3, a heat conducting oil discharge port; p, a pressure gauge port.
It should be noted that the drawings and the description are not intended to limit the scope of the inventive concept in any way, but to illustrate it by a person skilled in the art with reference to specific embodiments.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and the following embodiments are used for illustrating the present invention and are not intended to limit the scope of the present invention.
In the description of the present invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Example one
As shown in fig. 1 and 2, the continuous polymerization and devolatilization method and apparatus for polylactic acid according to this embodiment includes the following steps:
step 1, feeding a polylactic acid melt from a lactide polymerization system into a falling film evaporation heater at the upper part of a vertically-arranged devolatilization reaction device to heat the melt;
step 2, low boiling point substances and lactide gas generated in the devolatilization reaction process are changed into lactide liquid through a condensing device and then are refluxed to a lactide buffer tank;
step 3, pumping the non-condensable gas and the low-boiling-point substances into a vacuum buffer tank for further condensation and crystallization, and discharging the non-condensable gas and the low-boiling-point substances into a sewage system under the action of spray water;
and 4, extruding the devolatilized polymer melt to the inlet of a devolatilization discharge pump through a devolatilizer screw, mixing with the modified additive from the additive feeding screw, and conveying to a granulation system through the devolatilization discharge pump.
The polylactic acid melt from a lactide polymerization system firstly enters a falling film evaporation heater on the upper part of a devolatilization reaction device, the falling film evaporation heater comprises a heat medium circulating pump, a heat medium cooler and a heat medium heating supplement regulating valve bank, and the heating temperature of the heat medium is controlled to be 185-200 ℃. The main task of the polymerization and devolatilization reaction device is to remove low-boiling-point substances and lactide gas. The devolatilization reaction device is provided with a set of vacuum system, low boiling point substances and lactide gas from the devolatilization reaction device are condensed by a primary condenser and a secondary condenser to become lactide liquid to flow back to the lactide buffer tank, non-condensable gas and low boiling point substances are pumped to the vacuum buffer tank for further condensation and crystallization, and the low boiling point substances crystallized on the buffer tank are washed by process spray water and discharged to a sewage system. The non-condensable gas is pumped away by a secondary Roots and water ring vacuum pump, the pressure of the devolatilization reaction device is controlled to be 0.75-0.85KPa, and the pressure is preferably controlled to be 0.8 KPa. The level of the inner melt was controlled at 30%. And extruding the devolatilized polymer melt to the inlet of a devolatilization discharge pump through a devolatilizer screw, mixing with the modified additive from an additive feeding screw, and conveying to a granulation system through the devolatilization discharge pump.
The device includes the tower body, and the top lid of tower body is equipped with the top cap, and the drain pan is installed to the bottom, and tower body, top cap, drain pan enclose jointly and close the formation cavity, are equipped with the material import on the top cap, and the drain pan bottom surface is equipped with the discharge gate, contains the material in the cavity, and heating system carries out the heat exchange with the material, and the cavity is inside to be filled has inert gas, installs mixing system in the cavity, and device top vapor phase system is equipped with second grade lactide steam condenser. The devolatilization reaction device is a vertical cylindrical reaction device with a conical bottom, and a vertical discharge screw is arranged at an outlet of the conical bottom. The upper part of the screw is connected with a helical ribbon stirrer, the stirrer drives materials to rotate downwards to ensure that the polylactic acid melt can be discharged from the bottom of the reaction device smoothly, and meanwhile, the fluidity of the polylactic acid melt in the polymerization devolatilization reaction device can be improved, and the possibility of material stagnation in the reaction device is reduced. The discharge screw pressurizes the polymer and delivers the polymer to a gear metering pump. Preferably, the tower body internal diameter is 1143mm and the tower body depth is 921 mm. The lactide vapor used 75 ℃ hot water as the cooling medium.
The heating system comprises a falling film evaporation heater and a heating medium jacket heating system, the falling film evaporation heater is arranged at the feed inlet, and the heating medium jacket heating system coats the tower body. The falling film evaporator is provided with a heating system, and the heating system comprises a heat medium circulating pump, a heat medium cooler and a heat medium heating supplement adjusting valve. After the polylactic acid melt is heated by high-temperature heat conduction oil when entering the polymerization devolatilization reaction device, unreacted lactide and other low molecular weight components can be better removed, and the molecular weight of the polymer is increased. The temperature of the materials in the devolatilization reaction device can not be directly measured, and only the temperature of the heat-conducting oil can be controlled. The heating medium heating system of the devolatilization reaction device mainly plays a role in keeping the temperature of the materials to be certain, and preferably, the temperature is controlled to be 200 ℃. The liquid level control adopts a gamma-ray liquid level meter which is arranged on the inner side wall of the top cover. The liquid level detection of the devolatilization reaction device adopts a gamma-ray type liquid level meter, and the height of the post-polymerization liquid level is reflected according to the amount of gamma rays absorbed by materials. The rotating speed of a discharge pump at the bottom of the reaction device is adjusted through liquid level signal feedback of a liquid level meter, and the liquid level is controlled at 30%.
The material temperature is controlled at 200 ℃ and is not over high. Prevent the generation of gel and effectively reduce the cleaning frequency of the reaction device. The device is designed and provided with a temperature sensor for detecting the temperature of the material on line. When the material temperature rises or falls, the size of the switch of the heat medium valve is controlled by the loop, so that the constant material temperature is ensured. The liquid level is controlled stably, a gamma-ray liquid level meter is designed and installed on a polymerization reactor wall for reducing the adhesion of materials as much as possible, and the liquid level of the materials is detected on line. When the material liquid level rises or falls, the rotating speed of the frequency converter of the material feeding pump is controlled by the loop, so that the feeding speed of the material is adjusted, and the constancy of the material liquid level is ensured.
The stirring device is a helical ribbon stirrer, the lower end of the stirrer is connected with a vertical discharging screw rod, the discharging screw rod is installed in the conveying pipeline, and the stirring device is provided with a heater. The stirring of the ribbon spiral inside the devolatilization reaction device can ensure that the chemical components of the melt of the polylactic acid are distributed more uniformly, and the stirring is carried out for 30 minutes under the normal condition to achieve the expected effect, so that the low-boiling-point substances and the lactide steam can rapidly reach the surface of the melt. The device is additionally provided with a helical ribbon stirrer, so that the material reaction speed is accelerated. The material port is provided with a material conveying pipeline extending downwards, and the end part of the pipeline is bent towards the center of the cavity. Can make the more even distribution of fuse-element in tower body bottom, the stirring of being convenient for more takes off and volatilizes the reaction. The inert gas is nitrogen, so that oxidation is avoided.
The vacuum of the device adopts a vacuum device of a two-stage roots and water ring vacuum pump. The control of the vacuum is critical to the quality of the product. The unstable vacuum can cause the fluctuation of the liquid level, the materials are attached to the wall of the device, and the gel can be generated after long-time heating. In order to ensure the vacuum stability of the reaction device, a pressure sensor is arranged, and the real-time pressure of the reaction device is detected on line. When the vacuum degree fluctuates, the pressure sensor loop controls the rotating speed of the vacuum pump, so that the phenomenon that the liquid level fluctuates greatly due to the fluctuation of the vacuum degree and even the flooding irrigation is avoided. The vacuum degree is adjusted to control the speed of removing low-boiling-point substances and lactide gas so as to achieve the purpose of adjusting the molecular weight and keeping the molecular weight constant. And according to the feedback signal of the pressure instrument, the rotating speed of the pump is adjusted through the frequency converter, so that the vacuum adjustment is realized. The material stayed in the post-polymerization for 30 minutes, yielding a polymer with a relative viscosity of 65 and a molecular weight of 21000.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A continuous polymerization devolatilization method of polylactic acid is characterized by comprising the following steps:
step 1, feeding a polylactic acid melt from a lactide polymerization system into a falling film evaporation heater at the upper part of a vertically-arranged devolatilization reaction device to heat the melt;
step 2, low boiling point substances and lactide gas generated in the devolatilization reaction process are changed into lactide liquid through a condensing device and then are refluxed to a lactide buffer tank;
step 3, pumping the non-condensable gas and the low-boiling-point substances into a vacuum buffer tank for further condensation and crystallization, and discharging the non-condensable gas and the low-boiling-point substances into a sewage system under the action of spray water;
and 4, extruding the devolatilized polymer melt to the inlet of a devolatilization discharge pump through a devolatilizer screw, mixing with the modified additive from the additive feeding screw, and conveying to a granulation system through the devolatilization discharge pump.
2. The continuous polymerization devolatilization method of polylactic acid as claimed in claim 1, wherein: the temperature of the falling film evaporation heater is controlled to be 185-200 ℃, the internal pressure is controlled to be 0.75-0.85KPa, and the liquid level of the internal melt is controlled to be 30%.
3. A devolatilization process apparatus as claimed in claims 1-2 wherein: the device includes the tower body, the top lid of tower body is equipped with the top cap, and the drain pan is installed to the bottom, tower body, top cap, drain pan enclose jointly and close and form the cavity, be equipped with the material import on the top cap, the drain pan bottom surface is equipped with the discharge gate, fill the material in the cavity, heating system carries out the heat exchange with the material, the inside packing of cavity has inert gas, install mixing system in the cavity, device top vapor phase system is equipped with second grade lactide steam condenser.
4. The continuous polymerization devolatilization device of claim 3, wherein: the heating system comprises a falling film evaporation heater and a heating medium jacket heating system, the falling film evaporation heater is arranged at the feed inlet, and the heating medium jacket heating system coats the tower body.
5. The continuous polymerization devolatilization device as claimed in claim 4, wherein: the falling film evaporator is provided with a heating system, and the heating system comprises a heat medium circulating pump, a heat medium cooler and a heat medium heating and supplementing adjusting valve.
6. The continuous polymerization devolatilization device as claimed in claim 3, wherein: the liquid level control adopts gamma ray level gauge, gamma ray level gauge installs on the inside wall of top cap, still install pressure sensor, temperature sensor on the device inside wall.
7. The continuous polymerization devolatilization device of claim 3, wherein: the stirring device is a helical ribbon stirrer, the lower end of the stirrer is connected with a vertical discharging screw rod, the discharging screw rod is installed in the conveying pipeline, and the stirring device is provided with a heater.
8. The continuous polymerization devolatilization device as claimed in claim 3, wherein: the material port is provided with a material conveying pipeline extending downwards, and the end part of the pipeline is bent towards the center of the cavity.
9. The continuous polymerization devolatilization device as claimed in claim 3, wherein: the inert gas is nitrogen.
10. The continuous polymerization devolatilization device as claimed in claim 3, wherein: the vacuum of the device adopts a vacuum device of a two-stage roots and water ring vacuum pump.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202210347139.8A CN114672010A (en) | 2022-04-01 | 2022-04-01 | Continuous polymerization devolatilization method and device for polylactic acid |
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| CN202210347139.8A CN114672010A (en) | 2022-04-01 | 2022-04-01 | Continuous polymerization devolatilization method and device for polylactic acid |
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| CN114672010A true CN114672010A (en) | 2022-06-28 |
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| CN202210347139.8A Pending CN114672010A (en) | 2022-04-01 | 2022-04-01 | Continuous polymerization devolatilization method and device for polylactic acid |
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| CN (1) | CN114672010A (en) |
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