CN111153886B - Lactide synthesis method and device - Google Patents

Lactide synthesis method and device Download PDF

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CN111153886B
CN111153886B CN202010045269.7A CN202010045269A CN111153886B CN 111153886 B CN111153886 B CN 111153886B CN 202010045269 A CN202010045269 A CN 202010045269A CN 111153886 B CN111153886 B CN 111153886B
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reactor
lactide
oligomer
depolymerization
lactic acid
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CN111153886A (en
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江伟
齐运彪
孙平
黄伟
李爱民
张全兴
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Nanjing University
Nanjing Quankai Research Institute of Biomaterials Co Ltd
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Nanjing University
Nanjing Quankai Research Institute of Biomaterials Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D319/00—Heterocyclic compounds containing six-membered rings having two oxygen atoms as the only ring hetero atoms
    • C07D319/10—1,4-Dioxanes; Hydrogenated 1,4-dioxanes
    • C07D319/12—1,4-Dioxanes; Hydrogenated 1,4-dioxanes not condensed with other rings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/0006—Controlling or regulating processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/0006—Controlling or regulating processes
    • B01J19/0013—Controlling the temperature of the process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B01J3/006—Processes utilising sub-atmospheric pressure; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/0015—Feeding of the particles in the reactor; Evacuation of the particles out of the reactor
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C08J11/12—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by dry-heat treatment only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
    • B01J2208/00008—Controlling the process
    • B01J2208/00017—Controlling the temperature
    • B01J2208/00106—Controlling the temperature by indirect heat exchange
    • B01J2208/00115—Controlling the temperature by indirect heat exchange with heat exchange elements inside the bed of solid particles
    • B01J2208/00132—Tubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
    • B01J2208/00008—Controlling the process
    • B01J2208/00017—Controlling the temperature
    • B01J2208/00106—Controlling the temperature by indirect heat exchange
    • B01J2208/00115—Controlling the temperature by indirect heat exchange with heat exchange elements inside the bed of solid particles
    • B01J2208/0015—Plates; Cylinders

Abstract

The invention discloses a method and a device for synthesizing lactide.A lactic acid single component or lactic acid is added with a catalyst double component and enters an oligomer preparation system through a mixer, the residence time is increased through bottom circulation to synthesize oligomeric lactic acid, and a gas-phase component improves the yield of the oligomeric lactic acid through a rectification system; removing unreacted lactic acid and water from the oligomeric lactic acid by a purification device; adding the lightness-removed oligomeric lactic acid into a catalyst, then passing through a mixer, entering a depolymerization reactor for depolymerization into lactide, returning heavy components to enter the depolymerization reactor again, and passing light components through a purification recovery system to obtain a lactide product. The device can be used for efficiently synthesizing lactide, crude lactide with the yield of 94-98% can be obtained within 0.5-5 minutes of short retention time, the molecular weight of the recombinant polylactic acid is slowly increased, and the recombinant polylactic acid can be returned for depolymerization; the light component is utilized and the lactide product has L-lactide, D-lactide or DL-lactide content of 94-98% and meso-lactide content of 0.5-5.5%.

Description

Lactide synthesis method and device
Technical Field
The invention belongs to the field of environment-friendly/biomedical degradable material synthetic monomers, and particularly relates to a high-efficiency synthesis process of lactide, in particular to a method and a device for quickly synthesizing lactide with high yield.
Background
With the development of the times, petroleum-based non-degradable plastics are more and more widely used, but a plurality of environmental pollution problems are brought along with the use of petroleum-based non-degradable plastics, and meanwhile, the sustainable development problem is influenced by the demand of general plastics on non-renewable petroleum resources. The polylactic acid is a green high polymer material with wide application, is suitable for extrusion, injection molding, plastic suction and other processing, can be degraded into carbon dioxide and water in natural environment after being discarded, has small environmental pollution, and is one of the best choices for solving the 'white pollution'. It has good mechanical strength, chemical stability, biocompatibility and bioabsorbability; meanwhile, it is non-toxic and pollution-free, and its degradation product can be used for human metabolism, and can be extensively used in the fields of medical industry, agriculture, food packaging and daily necessities.
At present, the synthesis method of polylactic acid mainly comprises a one-step method and a two-step method: the one-step method takes lactic acid, glycolic acid and derivatives thereof as raw materials for direct synthesis, for example, lactic acid is directly condensed into polylactic acid as described in JP733861, JP599612 and CN198764C, but the time is long, the molecular weight is not high, and the application value is not high; the two-step process is to obtain lactide from the above raw materials by polycondensation-depolymerization, and to obtain polylactic acid by ring-opening polymerization of the refined and purified monomer, for example, from US5142023, EP261572, JP564688B, WO2009121830, and the synthesized polylactic acid has a relatively high molecular weight. At present, two-step synthesis is mainly used in the industry, and the preparation and purification of lactide as a synthetic intermediate become the key point of research. At present, the lactide synthesis time is longer, such as depolymerization in ZL201510648014.9 for 40min and depolymerization in ZL201310146469.1 for 1-4h, and the efficiency is probably low and the operation cost is high after amplification.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems of long residence time, low efficiency and high cost in the synthesis of commercial lactide in the prior art, the synthesis method for rapidly synthesizing lactide with high yield is provided, so that the residence time of a reactor is shortened, the yield is improved, and a low-cost solution is provided for the industrial production of lactide.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for synthesizing lactide comprises the following steps:
(1) taking L-lactic acid or D-lactic acid or DL-lactic acid as a raw material, carrying out polymerization synthesis reaction at the temperature of 180 ℃ and the pressure of 1-100KPa, recovering lactic acid from a light component to improve the yield, refluxing a heavy component to improve the molecular weight of the oligomeric lactic acid, and obtaining the oligomeric lactic acid with the weight-average molecular weight of 500-3000 Da;
(2) purifying the oligomeric lactic acid obtained in the step (1) to remove unreacted lactic acid and water;
(3) and (3) carrying out depolymerization reaction on the oligomeric lactic acid purified in the step (2) under the action of a catalyst at the temperature of 200 ℃ and 260 ℃ and under the pressure of 0.1-1KPa, purifying and collecting light components to obtain a lactide product, and refluxing and depolymerizing heavy components again.
Further, in step (1), the polymerization reaction may be carried out in the presence of an oligomerization catalyst including, but not limited to, zinc or tin catalysts such as zinc oxide, zinc lactate, zinc acetate, zinc isooctanoate, zinc stearate, stannous oxide, stannic oxide, stannous octoate, and stannous chloride.
The present invention further provides a lactide synthesis apparatus, comprising:
the oligomer preparation system is used for carrying out polymerization synthesis reaction by taking L-lactic acid or D-lactic acid or DL-lactic acid as a raw material to obtain oligomeric lactic acid, and introducing a reaction product into the oligomer purification system;
an oligomer purification system for purifying the reaction product introduced by the oligomer preparation system, removing unreacted lactic acid and water, and introducing the purified oligomeric lactic acid into an oligomer depolymerization system;
the oligomer depolymerization system is used for carrying out depolymerization reaction on the purified oligomeric lactic acid under the action of a catalyst to obtain a crude lactide product and guiding the obtained crude lactide product into the lactide purification system;
the lactide purification system is used for purifying the crude lactide product to obtain a lactide product and a byproduct, and the byproduct is introduced into the recovery system;
a recovery system; the method is used for treating and utilizing the byproducts.
Specifically, the oligomer preparation system comprises an oligomerization reactor, a raw material pump, an oligomerization catalyst feeding pump, a raw material mixer, an oligomerization discharging/circulating pump, a rectifying tower and a condenser;
wherein, lactic acid raw material (85-90% lactic acid aqueous solution) and oligomerization catalyst enter a raw material mixer for mixing through a raw material pump and an oligomerization catalyst feeding pump respectively, and then are fed from the side surface of an oligomerization reactor;
the oligomerization discharging/circulating pump is positioned on a discharging pipe at the bottom of the oligomerization reactor, is connected with a feeding pipe of an oligomer purification system and a lateral line feeding port of the oligomerization reactor through a three-way valve, and controls the reflux ratio of oligomer to be 20:1-1000:1, preferably 30:1-700:1, and most preferably 50:1-200: 1.
A feeding pipeline of the rectifying tower is connected with the top of the oligomerization reactor, a discharging pipe at the top of the rectifying tower passes through a condenser and then is connected with a condensate storage tank, and the side surface of the condensate storage tank is connected with an oligomerization vacuum system; a condensate circulating/discharging pump is arranged on a discharging pipe of the condensate storage tank and is connected to a lateral line feeding pipe line of the rectifying tower through a three-way valve; controlling the pressure of the rectifying tower to be 1-100KPa, preferably 2-50KPa, and optimally 5-20KPa by an oligomerization vacuum system; the temperature is controlled between 40-80 deg.C, preferably 45-75 deg.C, and most preferably 50-70 deg.C.
Specifically, the oligomer purification system comprises an oligomer purification reactor, an oligomer discharge pump and a purification condenser;
a lateral line feeding port of the oligomer purification reactor is connected with a discharging pipe of the oligomer preparation system; a discharge pipe at the top of the oligomer purification reactor passes through a purification condenser and then is connected with a condensate storage tank of a purification system, and the side surface of the condensate storage tank of the purification system is connected with an oligomer purification vacuum system; a purifying system condensate discharging pump is arranged on a discharging pipe at the bottom of the purifying system condensate storage tank;
the oligomer discharging pump is positioned on a discharging pipe at the bottom of the oligomer purification reactor and is connected with a feeding pipeline of the oligomer depolymerization system;
the oligomer purification reactor is a packed rectifying tower; controlling the pressure at the top of the tower to be 1-50KPa, preferably 2-30KPa, and most preferably 3-20KPa by an oligomerization purification vacuum system; controlling the temperature at 20-70 deg.C, preferably 20-50 deg.C, optimally 20-40 deg.C; to reduce impurity acids, water, and a portion of small molecule polymers.
Specifically, the oligomer depolymerization system comprises a depolymerization reactor, a depolymerization catalyst feed pump, a depolymerization feed mixer, and a depolymerization heavy component discharge/circulation pump;
the depolymerization catalyst includes, but is not limited to, zinc or tin catalysts such as zinc oxide, zinc lactate, zinc acetate, zinc isooctanoate, zinc stearate, stannous oxide, stannic oxide, stannous octoate, and stannous chloride. The depolymerization catalyst may be the previously added oligomerization catalyst and may be supplemented subsequently. Simultaneously feeding the purified products generated by the depolymerization catalyst feeding pump and the oligomer purification system into a depolymerization feeding mixer for mixing, and then feeding from the side of a depolymerization reactor; the reaction temperature of the depolymerization feed mixer is controlled at 200-260 ℃, the residence time is 0.5-5 minutes, and the pressure is 0.1-1 Kpa.
The depolymerized heavy component discharging/circulating pump is positioned on a discharging pipe at the bottom of the depolymerizing reactor, is connected to the depolymerizing feed mixer through a three-way valve, returns the heavy components generated in the depolymerizing reactor to the depolymerizing feed mixer to be mixed with reaction raw materials, and reenters the depolymerizing reactor for reaction; the light component generated in the depolymerization reactor is connected with a feed pipeline of a lactide purification system through a discharge hole above the side surface of the depolymerization reactor, so that impurities such as lactic acid, water and the like are removed.
Specifically, the lactide purification system comprises a lactide purification reactor and a lactide storage tank;
the lactide storage tank is connected with a bottom discharge hole of the lactide purification reactor and conveys lactide products outwards through a lactide discharge pump; removing impurities such as lactic acid, water and the like through a lactide purification reactor to obtain a lactide product with the content of L-lactide or D-lactide or DL-lactide of 94-98 percent, wherein the content of meso-lactide is 0.5-5.5 percent;
the non-condensed steam in the lactide purification reactor is connected to a feed line of a recovery system through a discharge hole of a byproduct at the top.
Specifically, the recovery system comprises a recovery system reactor, a recovery liquid storage tank and a recovery liquid discharge pump;
the side surface of the recovery liquid storage tank is connected with a depolymerization vacuum system, a top feed inlet is connected with a bottom discharge port of a recovery system reactor, and uncondensed gas in a lactide purification reactor is recovered through the recovery system reactor to obtain an L-lactic acid or D-lactic acid or DL-lactic acid solution with the concentration of 65-80%; the recovery liquid storage tank discharges the recovery liquid outwards through a recovery liquid discharge pump on a bottom discharge pipe.
Specifically, the oligomerization reactor or the depolymerization reactor is any one of a falling film reactor, a thin film evaporation reactor, a packing reactor and a double falling film reactor.
The lactide purification reactor or the recovery system reactor is any one of a shell-and-tube heat exchanger, a spiral plate heat exchanger and a shell-and-tube heat exchanger.
Has the advantages that:
1. according to the method, lactic acid is used as a reaction raw material, oligomeric lactic acid is synthesized through polymerization reaction, then the oligomeric lactic acid is purified, unreacted lactic acid and water are removed, depolymerization reaction is performed under the action of a catalyst, a crude lactide product is obtained, and finally the crude lactide product is purified to obtain a lactide product.
2. The method adopts lactic acid single component or lactic acid added with catalyst double component, enters an oligomer preparation system through a mixer, increases the retention time through bottom circulation to synthesize oligomeric lactic acid, and improves the yield of the oligomeric lactic acid through a rectification system by gas-phase components; removing unreacted lactic acid and water from the oligomeric lactic acid by a purification device; adding the lightness-removed oligomeric lactic acid into a catalyst, then passing through a mixer, entering a depolymerization reactor, depolymerizing the mixture into lactide under certain pressure and temperature conditions, returning heavy components to the depolymerization reactor again through reflux so as to improve the yield of the lactide, and obtaining a lactide product after purifying and recycling the light components. The device can be used for efficiently synthesizing lactide, crude lactide with the yield of 94-98% can be obtained within 0.5-5 minutes of short retention time, the molecular weight of the recombinant polylactic acid is slowly increased, and the recombinant polylactic acid can be returned for depolymerization; the content of L-lactide, D-lactide or DL-lactide in the lactide product is 94-98% and the content of meso-lactide is 0.5-5.5% after the light component is subjected to a simple purification system, so that the operation is simple, rapid, high-yield and easy for industrialization.
Drawings
The foregoing and/or other advantages of the invention will become further apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.
Fig. 1 is a schematic structural view of a lactide synthesis apparatus according to the present invention.
Wherein each reference numeral represents:
i, preparing an oligomer system; II, an oligomer purification system; III an oligomer depolymerization system; IV, lactide purification system; v, a recovery system; 1, lactic acid raw material; 2, a raw material pump; 3 an oligomerization catalyst; 4 oligomerization catalyst feed pump; 5, a raw material mixer; 6 an oligomerization reactor; 7 oligomerization discharge/recycle pump; 8 oligomerization circulation material; 9 an oligomer; 10 gas phase component; 11 a rectifying tower; 12 a condenser; 13 oligomerization vacuum system; 14 a condensate storage tank; 15 condensate circulation/discharge pump; 16 recycling the condensate; 17 oligomerizing the condensate; 18 oligomer purification reactor; 19 oligomer discharge pump; 20 a depolymerization catalyst; 21 depolymerization catalyst feed pump; 22 purifying the oligomer; 23 oligomer light component; 24 purification condenser; 25 oligomerization purification vacuum system; 26 purifying the condensate storage tank of the system; 27 purifying the system condensate liquid discharge pump; 28 purifying the system condensate; 29 depolymerizing the feed mixer; 30 a depolymerization reactor; 31 depolymerizing the heavies discharge/recycle pump; 32 recycling and depolymerizing heavy components; 33 depolymerizing the heavy fraction; 34 depolymerizing the light components; 35 a lactide purification reactor; 36 a lactide storage tank; 37 lactide discharge pump; 38 a lactide product; 39 is not condensed; 40 recovering the system reactor; 41 de-polymerization of the vacuum system; 42 a recycling liquid storage tank; 43 a recovery liquid discharge pump; 44 recovering the liquid.
Detailed Description
The invention will be better understood from the following examples.
The structures, proportions, and dimensions shown in the drawings and described in the specification are for understanding and reading the present disclosure, and are not intended to limit the scope of the present disclosure, which is defined in the claims, and are not essential to the skilled in the art. In addition, the terms "upper", "lower", "front", "rear" and "middle" used in the present specification are for clarity of description, and are not intended to limit the scope of the present invention, and the relative relationship between the terms and the relative positions may be changed or adjusted without substantial technical changes.
The following examples use the apparatus shown in fig. 1 to prepare lactide. The device mainly comprises an oligomer preparation system I, an oligomer purification system II, an oligomer depolymerization system III, a lactide purification system IV and a recovery system V. The oligomer preparation system I is used for carrying out polymerization synthesis reaction by taking L-lactic acid or D-lactic acid or DL-lactic acid as a raw material to obtain oligomeric lactic acid, and introducing a reaction product into an oligomer purification system II; the oligomer purification system II is used for purifying the reaction product introduced by the oligomer preparation system I, removing unreacted lactic acid and water, and introducing the purified oligomeric lactic acid into the oligomer depolymerization system III; the oligomer depolymerization system III is used for carrying out depolymerization reaction on the purified oligomeric lactic acid under the action of a catalyst to obtain a crude lactide product, and the obtained crude lactide product is introduced into the lactide purification system IV; the lactide purification system IV is used for purifying the crude lactide product to obtain a lactide product and a byproduct, and the byproduct is introduced into the recovery system V; and the recovery system V is used for treating and utilizing the by-products.
The oligomer preparation system I comprises an oligomerization reactor 6, a raw material pump 2, an oligomerization catalyst feeding pump 4, a raw material mixer 5, an oligomerization discharging/circulating pump 7, a rectifying tower 11 and a condenser 12; lactic acid raw material 1 and oligomerization catalyst 3 enter a simultaneous raw material mixer 5 through a raw material pump 2 and an oligomerization catalyst feed pump 4 respectively for mixing, and then are fed from the side of an oligomerization reactor 6; the oligomerization discharging/circulating pump 7 is positioned on a discharging pipe at the bottom of the oligomerization reactor 6, is connected with a feeding pipe of the oligomer purification reactor 18 and a lateral line feeding port of the oligomerization reactor 6 through a three-way valve, and controls the reflux ratio of oligomer to be 20:1-1000: 1; a feeding pipeline of the rectifying tower 11 is connected with the top of the oligomerization reactor 6, a discharging pipe at the top of the rectifying tower 11 passes through a condenser 12 and then is connected with a condensate storage tank 14, and the side surface of the condensate storage tank 14 is connected with an oligomerization vacuum system 13; a condensate circulating/discharging pump 15 is arranged on a discharging pipe of the condensate storage tank 14 and is connected to a lateral line feeding pipe line of the rectifying tower 11 through a three-way valve; the pressure of the rectifying tower 11 is controlled to be 1-100KPa by an oligomerization vacuum system 13, and the temperature is controlled to be 40-80 ℃.
The oligomer purification system II comprises an oligomer purification reactor 18, an oligomer discharge pump 19 and a purification condenser 24; a lateral line feed inlet of the oligomer purification reactor 18 is connected with a discharge pipe of the oligomerization reactor 6; a top discharge pipe of the oligomer purification reactor 18 passes through a purification condenser 24 and then is connected with a purification system condensate storage tank 26, and the side surface of the purification system condensate storage tank 26 is connected with an oligomerization purification vacuum system 25; a purification system condensate discharging pump 27 is arranged on a discharging pipe at the bottom of the purification system condensate storage tank 26; the oligomer discharging pump 19 is positioned on a discharging pipe at the bottom of the oligomer purifying reactor 18 and is connected with a feeding pipeline of the depolymerization reactor 30; the oligomer purification reactor 18 is a packed rectifying tower; the pressure at the top of the tower is controlled to be 1-50KPa by an oligomerization purification vacuum system 25, and the temperature is controlled to be 20-70 ℃ so as to reduce impurity acid, water and a part of small molecular polymer.
The oligomer depolymerization system III comprises a depolymerization reactor 30, a depolymerization catalyst feed pump 21, a depolymerization feed mixer 29 and a depolymerization heavy component discharge/circulation pump 31; the depolymerization catalyst 20 is fed into the depolymerization feed mixer 29 through the depolymerization catalyst feed pump 21 simultaneously with the purified product from the oligomer purification reactor 18, and then fed from the side of the depolymerization reactor 30; the depolymerization feed mixer 29 is controlled at a reaction temperature of 200 ℃ and 260 ℃, a residence time of 0.5-5 minutes, and a pressure of 0.1-1 Kpa. The depolymerized heavy component discharging/circulating pump 31 is positioned on a discharging pipe at the bottom of the depolymerizing reactor 30, is connected to the depolymerizing feed mixer 29 through a three-way valve, returns the heavy components generated in the depolymerizing reactor 30 into the depolymerizing feed mixer 29 to be mixed with reaction raw materials, and enters the depolymerizing reactor 30 again for reaction; the light components produced in the depolymerization reactor 30 are connected to the feed line of the lactide purification reactor 35 through a discharge port above the side of the depolymerization reactor 30 to remove impurities such as lactic acid, water, etc.
The lactide purification system IV comprises a lactide purification reactor 35 and a lactide storage tank 36; the lactide storage tank 36 is connected with a bottom discharge hole of the lactide purification reactor 35, and conveys lactide products 38 outwards through a lactide discharge pump 37; removing impurities such as lactic acid, water and the like through a lactide purification reactor 35 to obtain a lactide product with the content of L-lactide or D-lactide or DL-lactide of 94-98 percent, wherein the content of meso-lactide is 0.5-5.5 percent; the non-condensable gases in the lactide purification reactor 35 are connected to the feed line of the recovery system reactor 40 through the top by-product outlet.
The recovery system V comprises a recovery system reactor 40, a recovery liquid storage tank 42 and a recovery liquid discharge pump 43; the side surface of the recovery liquid storage tank 42 is connected with a depolymerization vacuum system 41, a top feeding hole is connected with a bottom discharging hole of the recovery system reactor 40, uncondensed gas in the lactide purification reactor 35 is recovered through the recovery system reactor 40, and L-lactic acid or D-lactic acid or DL-lactic acid solution with the concentration of 65-80% is obtained; the recycle liquor storage tank 42 discharges recycle liquor 44 outwards through a recycle liquor discharge pump 43 on the bottom discharge pipe.
Example 1
The method comprises the following steps that 90% of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 10g/h, the oligomerization reactor 6 is a TLNS falling film reactor, dehydration oligomerization is carried out under the conditions that the temperature is 80 ℃ and the absolute pressure is 1KPa, the reflux ratio of the dehydration oligomer to a side feed inlet of the oligomerization reactor 6 is controlled to be 1000:1 through an oligomerization discharge/circulating pump 7, the dehydration oligomer flows back to a side feed inlet of the oligomerization reactor 6 for continuous reaction, lactic acid flows back through a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature. The oligomer 9 has a molecular weight of 500 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 1KPa, overhead temperature 20 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst zinc acetate 20 are uniformly mixed through a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 220 ℃, the depolymerization reactor 30 is a WEF thin film evaporation reactor, the residence time is controlled to be 2min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 2:1 through a depolymerized heavy component discharge/circulation pump 31, the back-flow heavy component is mixed with the new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light components 34 are conveyed by heat tracingThen enters a lactide purification reactor 35 which is a common 0.1m reactor2And a shell-and-tube heat exchanger, wherein the heat exchange temperature is controlled to be 20 ℃, and the lactide product of 6.775g/h is obtained by purification, the yield is 94.1 percent, and the content of L-lactide is 98.1 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.1m2The temperature of the plate type heat exchanger is controlled to be 10 ℃, the recovered liquid is 0.1g/h of lactic acid solution, the concentration of L-lactic acid is 70 percent, and the purified L-lactic acid is recycled.
Example 2
The method comprises the following steps of mixing a 90% L-lactic acid raw material 1 with a catalyst zinc oxide 3 at a flow rate of 20g/h through a raw material pump 2, then feeding the mixture into an oligomerization reactor 6, wherein the oligomerization reactor 6 is a TLNS falling film reactor, dehydrating oligomerization is carried out under the reactor operation conditions of 120 ℃ and an absolute pressure of 1KPa, the reflux ratio of the dehydrating oligomer to a side feed inlet of the oligomerization reactor 6 is controlled to be 300:1 through an oligomerization discharge/circulating pump 7, the dehydrating oligomer is refluxed to a side feed inlet of the oligomerization reactor 6 for continuous reaction, and the temperature of the top of the oligomerization reactor 6 is controlled to be 60. The oligomer 9 has a molecular weight of 1100 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 20KPa, overhead temperature 25 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 enters a depolymerization reactor 30 to carry out depolymerization reaction at 0.2KPa and 240 ℃, the depolymerization reactor 30 is an RFJL filler reactor, the residence time is controlled to be 1.5min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 1:1 by a depolymerized heavy component discharging/circulating pump 31, the refluxed heavy component and a new material are mixed and then enter the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to a lactide purification reactor 35 after heat tracing, and the reactor is 0.1m in common use2And (3) purifying by using a plate-type heat exchanger at the heat exchange temperature of 60 ℃ to obtain 14.778g/h of lactide product, wherein the weight yield is 94.9 percent, and the content of L-lactide is 96.9 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery systemReactor 40, reactor 0.1m2The temperature of the spiral plate type heat exchanger is controlled to be 5 ℃, the recovered liquid is 0.2g/h of lactic acid solution, the concentration of L-lactic acid is 65%, and the purified L-lactic acid is recycled.
Example 3
90% of L-lactic acid raw material 1 is mixed with catalyst zinc acetate 3 at a flow rate of 50g/h by a raw material pump 2 and then enters an oligomerization reactor 6, the oligomerization reactor 6 is a WEF film evaporation reactor, dehydration oligomerization is carried out under the operating conditions of 180 ℃ and 100KPa absolute pressure, the reflux ratio of dehydration oligomer to oligomer is controlled by an oligomerization discharging/circulating pump 7 to be 20:1, the dehydration oligomer is refluxed to a side line feed inlet of the oligomerization reactor 6 for continuous reaction, lactic acid is refluxed to a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature at the top of the tower is controlled by reflux to be 70 ℃. The oligomer 9 has a molecular weight of 800 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 40KPa, overhead temperature 40 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 enters a depolymerization reactor 30, depolymerization reaction is carried out under the conditions of 1KPa and 260 ℃, the depolymerization reactor 30 is a TLNS falling film reactor, the residence time is controlled to be 1min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 0.5:1 by a depolymerized heavy component discharging/circulating pump 31, the refluxed heavy component and the new material are mixed and then enter the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) controlling the heat exchange temperature of the spiral plate type heat exchanger to be 20 ℃, and purifying to obtain 36.639g/h of lactide product, wherein the weight yield is 94.1 percent, and the content of L-lactide is 95.1 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2The temperature of the shell and tube heat exchanger is controlled at 25 ℃, the recovered liquid is lactic acid solution with the concentration of 80 percent and is 0.4g/h, and the purified L-lactic acid is recycled.
Example 4
The method comprises the following steps that 90% of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h, the oligomerization reactor 6 is a WEF film evaporation reactor, dehydration oligomerization is carried out under the conditions that the temperature is 170 ℃ and the absolute pressure is 50KPa, the reflux ratio of the dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled to be 50:1 through an oligomerization discharge/circulating pump 7, the dehydration oligomer flows back to the lateral line feed inlet of the oligomerization reactor 6 for continuous reaction, lactic acid flows back through a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature. The oligomer 9 has a molecular weight of 1200 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 50KPa, overhead temperature 70 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst stannous octoate 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 230 ℃, the depolymerization reactor 30 is a WEF thin film evaporation reactor, the residence time is controlled to be 0.5min, the reflux ratio of a depolymerized heavy component 33 is controlled to be 1:1 by a depolymerized heavy component discharge/circulation pump 31, the back-flow heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) purifying by using a tubular heat exchanger at the heat exchange temperature of 50 ℃ to obtain 36.879g/h of lactide product, wherein the weight yield is 94.1 percent, and the content of L-lactide is 97.8 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2A shell-and-tube heat exchanger, the temperature of the heat exchanger is controlled to be 20 ℃, the recovered liquid is 0.45g/h of lactic acid solution, the concentration of L-lactic acid is 75 percent, and the purified L-lactic acid is recycled.
Example 5
The method comprises the following steps that 90% of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h, the oligomerization reactor 6 is a WEF film evaporation reactor, dehydration oligomerization is carried out under the conditions that the reactor operation condition is 160 ℃ and the absolute pressure is 20KPa, the reflux ratio of the dehydration oligomer to the oligomerization reactor 6 is controlled to be 100:1, the dehydration oligomer flows back to a side line feed inlet of the oligomerization reactor 6 to continue reaction, lactic acid flows back to a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature at the top of the tower is controlled to be 60 ℃. The oligomer 9 has a molecular weight of 1500 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 20KPa, overhead temperature 40 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst stannous octoate 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 250 ℃, the depolymerization reactor 30 is an RFJL filler reactor, the residence time is controlled to be 0.7min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 0.1:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2A shell-and-tube heat exchanger, the heat exchange temperature is controlled to be 60 ℃, and 37.121g/h of lactide product is obtained by purification, the weight yield is 95.4%, and the content of L-lactide is 96.2%.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2The temperature of the plate heat exchanger is controlled at 40 ℃, the recovery liquid is lactic acid solution with the concentration of 85 percent and is 0.3g/h, and the L-lactic acid is recycled after purification.
Example 6
The method comprises the following steps that 90% of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h and a catalyst stannous octoate 3, the oligomerization reactor 6 is a WEF film evaporation reactor, dehydration oligomerization is carried out under the operating conditions of 160 ℃ and 20KPa absolute pressure, the reflux ratio of the dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled to be 100:1 through an oligomerization discharge/circulating pump 7, the dehydration oligomer flows back to the lateral line feed inlet of the oligomerization reactor 6 for continuous reaction, lactic acid flows back to a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature at the. The oligomer 9 has a molecular weight of 1500 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 20KPa, overhead temperature 40 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 enters a depolymerization reactor 30 to carry out depolymerization reaction at 0.2KPa and 260 ℃, the depolymerization reactor 30 is a TLNS double-falling-film reactor, the residence time is controlled to be 0.5min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 0:1 by a depolymerized heavy component discharging/circulating pump 31, the refluxed heavy component and a new material are mixed and then enter the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) controlling the heat exchange temperature of the plate type heat exchanger to be 50 ℃, and purifying to obtain 37.297g/h of lactide product, wherein the weight yield is 95.9 percent, and the content of L-lactide is 95.2 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2The temperature of the spiral plate type heat exchanger is controlled to be-20 ℃, the recovered liquid is 0.32g/h of lactic acid solution, the concentration of L-lactic acid is 50%, and the purified L-lactic acid is recycled.
Example 7
90 percent of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 30g/h, the oligomerization reactor 6 is an RFJL filler reactor, the operation conditions of the reactor are that dehydration oligomerization is carried out under the conditions of the temperature of 170 ℃ and the absolute pressure of 50KPa, the reflux ratio of the dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled to be 80:1 by a oligomerization discharging/circulating pump 7, the dehydration oligomer is refluxed to the lateral line feed inlet of the oligomerization reactor 6 for continuous reaction, the lactic acid is refluxed to a rectifying tower 11 at the top of the oligomerization reactor 6, and. The oligomer 9 has a molecular weight of 1600 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 15KPa, overhead temperature 35 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst zinc lactate 20 are uniformly mixed through a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 250 ℃, the depolymerization reactor 30 is a TLNS falling film reactor, the residence time is controlled to be 1.0min, the reflux ratio of a depolymerized heavy component 33 is controlled to be 0:1 through a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) purifying by a spiral plate type heat exchanger at the heat exchange temperature of 60 ℃ to obtain 22.877g/h of lactide product, wherein the weight yield is 98.0 percent, and the content of L-lactide is 96.4 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2The temperature of the shell and tube heat exchanger is controlled at 10 ℃, the recovered liquid is lactic acid solution with the concentration of 75 percent and the recovered liquid is 0.11g/h, and the purified L-lactic acid is recycled.
Example 8
90 percent of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 30g/h, the oligomerization reactor 6 is an RFJL filler reactor, the operation conditions of the reactor are that dehydration oligomerization is carried out under the conditions of 160 ℃ and 50KPa absolute pressure, the reflux ratio of the dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled to be 200:1 through an oligomerization discharging/circulating pump 7, the dehydration oligomer flows back to the lateral line feed inlet of the oligomerization reactor 6 for continuous reaction, the lactic acid flows back through a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature at the top. The oligomer 9 has a molecular weight of 3000 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 15KPa, overhead temperature 35 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst stannous octoate 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 250 ℃, the depolymerization reactor 30 is a WEF thin film evaporation reactor, the residence time is controlled to be 1.5min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 1:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.15m2And (3) purifying by using a shell-and-tube heat exchanger at the heat exchange temperature of 60 ℃ to obtain 22.195g/h of lactide product, wherein the weight yield is 95.2%, and the content of L-lactide is 96.8%.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.15m2A shell-and-tube heat exchanger, the temperature of the heat exchanger is controlled to be 10 ℃, the recovered liquid is 0.2g/h of lactic acid solution, the concentration of L-lactic acid is 80 percent, and the purified L-lactic acid is recycled.
Example 9
90 percent of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 60g/h, the oligomerization reactor 6 is an RFJL filler reactor, the operation conditions of the reactor are that dehydration oligomerization is carried out under the conditions of the temperature of 170 ℃ and the absolute pressure of 50KPa, the reflux ratio of the dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled to be 100:1, the dehydration oligomer flows back to the lateral line feed inlet of the oligomerization reactor 6 for continuous reaction, the lactic acid flows back to a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature at the top of the tower. The oligomer 9 has a molecular weight of 1500 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 20KPa, overhead temperature 30 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst zinc oxide 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 260 ℃, the depolymerization reactor 30 is an RFJL filler reactor, the residence time is controlled to be 1.0min, the reflux ratio of the depolymerized heavy component 33 is controlled to be 0.2:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.25m2A shell-and-tube heat exchanger, the heat exchange temperature is controlled to be 60 ℃, and 42.851g/h of lactide product is obtained by purification, the weight yield is 97.2 percent, and L-The lactide content was 95.1%.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.25m2The temperature of the plate heat exchanger is controlled to be 10 ℃, the recovery liquid is lactic acid solution with the concentration of 78% and 0.4g/h, and the L-lactic acid is recycled after purification.
Example 10
85% of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h, the oligomerization reactor 6 is an RFJL filler reactor, the dehydration oligomerization is carried out under the conditions that the reactor operation condition is 160 ℃ and the absolute pressure is 50KPa, the reflux ratio of the dehydration oligomer oligomerization discharging material/circulating pump 7 is controlled to be 150:1, the dehydration oligomer discharging material/circulating pump flows back to a side line feed inlet of the oligomerization reactor 6 for continuous reaction, the lactic acid flows back to a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature at the top of the tower is controlled to. The oligomer 9 has a molecular weight of 2500 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 15KPa, overhead temperature 35 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst zinc oxide 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.2KPa and 250 ℃, the depolymerization reactor 30 is a double-reduction-film reactor, the residence time is controlled to be 1.0min, the reflux ratio of a depolymerized heavy component 33 is controlled to be 0:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) purifying by using a plate-type heat exchanger at the heat exchange temperature of 60 ℃ to obtain 36.644g/h of lactide product, wherein the weight yield is 94.3%, and the content of L-lactide is 96.7%.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2A spiral plate heat exchanger, the temperature of the heat exchanger is controlled to be 10 ℃, the recovery liquid is 0.24g/h of lactic acid solution, the concentration of L-lactic acid is 75 percent, and the extraction is carried outAnd (4) recycling after purification.
Example 11
The method comprises the following steps that 90% of L-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h, the oligomerization reactor 6 is a double-falling-film reactor, dehydration oligomerization is carried out under the conditions that the temperature is 160 ℃ and the absolute pressure is 50KPa, the reflux ratio of dehydration oligomer to the side feed inlet of the oligomerization reactor 6 is controlled by an oligomerization discharge/circulating pump 7 to be 120:1, the dehydration oligomer flows back to the side feed inlet of the oligomerization reactor 6 to continue reaction, lactic acid flows back to a rectifying tower 11 at the top of the oligomerization reactor 6, and the. The oligomer 9 has a molecular weight of 2000 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 15KPa, overhead temperature 35 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst zinc oxide 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.2KPa and 250 ℃, the depolymerization reactor 30 is a WEF thin film evaporation reactor, the residence time is controlled to be 1.0min, the reflux ratio of a depolymerized heavy component 33 is controlled to be 0:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) purifying by a spiral plate type heat exchanger at the heat exchange temperature of 60 ℃ to obtain 36.828g/h of lactide product, wherein the weight yield is 94.7 percent, and the content of L-lactide is 97.3 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2The temperature of the shell and tube heat exchanger is controlled to be 5 ℃, the recovered liquid is lactic acid solution with the concentration of 75 percent and is 0.3g/h, and the purified L-lactic acid is recycled.
Example 12
The method comprises the following steps that 90% of D-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h, the oligomerization reactor 6 is a double-falling-film reactor, dehydration oligomerization is carried out under the conditions that the temperature is 160 ℃ and the absolute pressure is 20KPa, the reflux ratio of dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled by an oligomerization discharging/circulating pump 7 to be 100:1, the dehydration oligomer flows back to the lateral line feed inlet of the oligomerization reactor 6 to continue reaction, lactic acid flows back to a rectifying tower 11 at the top of the oligomerization reactor 6. The oligomer 9 has a molecular weight of 1400 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 15KPa, overhead temperature 30 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst stannous octoate 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.2KPa and 250 ℃, the depolymerization reactor 30 is an RFJL filler reactor, the residence time is controlled to be 1.5min, the reflux ratio of a depolymerized heavy component 33 is controlled to be 0:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2And (3) purifying by using a shell-and-tube heat exchanger at the heat exchange temperature of 60 ℃ to obtain 36.759g/h of lactide product, wherein the weight yield is 94.5 percent, and the content of L-lactide is 96.1 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2The temperature of the shell and tube heat exchanger is controlled to be 8 ℃, the recovered liquid is lactic acid solution with the concentration of 70 percent and is 0.5g/h, and the purified L-lactic acid is recycled.
Example 13
90% of DL-lactic acid raw material 1 enters an oligomerization reactor 6 through a raw material pump 2 at a flow rate of 50g/h, the oligomerization reactor 6 is an RFJL filler reactor, the reactor operation conditions are that dehydration oligomerization is carried out under the conditions of the temperature of 170 ℃ and the absolute pressure of 20KPa, the reflux ratio of the dehydration oligomer to the lateral line feed inlet of the oligomerization reactor 6 is controlled to be 80:1 by a oligomerization discharge/circulating pump 7, the dehydration oligomer is refluxed to the lateral line feed inlet of the oligomerization reactor 6 for continuous reaction, the lactic acid is refluxed to a rectifying tower 11 at the top of the oligomerization reactor 6, and the temperature. The oligomer 9 has a molecular weight of 1600 Da.
The oligomer 9 enters an oligomer purification reactor 18 which is an RFJL packed rectifying tower, the lateral line is fed, and the operation conditions are as follows: absolute pressure 10KPa, overhead temperature 25 ℃. The removed acid, water and dimer are purified for reuse.
The purified oligomer 22 and the depolymerization catalyst zinc oxide 20 are uniformly mixed by a depolymerization feed mixer 29 and then enter a depolymerization reactor 30 to carry out depolymerization reaction at 0.1KPa and 250 ℃, the depolymerization reactor 30 is a WEF thin film evaporation reactor, the residence time is controlled to be 1.5min, the reflux ratio of a depolymerized heavy component 33 is controlled to be 0:1 by a depolymerized heavy component discharge/circulation pump 31, the refluxed heavy component is mixed with a new material and then enters the depolymerization reactor 30 again, and the depolymerized light component 34 enters a subsequent purification system.
The depolymerized light component 34 is sent to lactide purification reactor 35 after heat tracing, and the reactor is 0.2m2The heat exchange temperature of the shell and tube heat exchanger is controlled at 60 ℃, and the lactide product of 36.81g/h is obtained by purification, the weight yield is 94.6 percent, and the content of L-lactide is 97.7 percent.
The uncondensed steam 39 in the lactide purification reactor 35 enters a recovery system reactor 40 with the reactor diameter of 0.2m2A shell-and-tube heat exchanger, the temperature of the heat exchanger is controlled to be 8 ℃, the recovered liquid is lactic acid solution with the concentration of 0.54g/h and the L-lactic acid is 72 percent, and the purified liquid is recycled.
The present invention provides a method and an apparatus for synthesizing lactide, and a method and a means for implementing the method and the apparatus are many, and the above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, many modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention. All the components not specified in the present embodiment can be realized by the prior art.

Claims (6)

1. A lactide synthesis device is characterized by comprising:
the oligomer preparation system (I) is used for carrying out polymerization synthesis reaction by taking L-lactic acid or D-lactic acid or DL-lactic acid as a raw material to obtain oligomeric lactic acid, and introducing a reaction product into an oligomer purification system (II);
an oligomer purification system (II) for purifying the reaction product introduced by the oligomer preparation system (I), removing unreacted lactic acid and water, and introducing the purified oligomeric lactic acid into an oligomer depolymerization system (III);
an oligomer depolymerization system (III) for carrying out depolymerization reaction on the purified oligomeric lactic acid under the action of a catalyst to obtain a crude lactide product, and introducing the obtained crude lactide product into a lactide purification system (IV);
the lactide purification system (IV) is used for purifying the crude lactide product to obtain a lactide product and a byproduct, and the byproduct is introduced into the recovery system (V);
a recovery system (V); the device is used for treating and utilizing the byproducts;
the oligomer preparation system (I) comprises an oligomerization reactor (6), a raw material pump (2), an oligomerization catalyst feeding pump (4), a raw material mixer (5), an oligomerization discharging/circulating pump (7), a rectifying tower (11) and a condenser (12);
the lactic acid raw material (1) and the oligomerization catalyst (3) enter a simultaneous raw material mixer (5) through a raw material pump (2) and an oligomerization catalyst feeding pump (4) respectively for mixing, and then are fed from the side surface of an oligomerization reactor (6);
the oligomerization discharging/circulating pump (7) is positioned on a discharging pipe at the bottom of the oligomerization reactor (6) and is connected with a feeding pipe of the oligomer purification system (II) and a side line feeding port of the oligomerization reactor (6) through a three-way valve;
a feeding pipeline of the rectifying tower (11) is connected with the top of the oligomerization reactor (6), a discharging pipe at the top of the rectifying tower (11) is connected with a condensate storage tank (14) after passing through a condenser (12), and the side surface of the condensate storage tank (14) is connected with an oligomerization vacuum system (13); a condensate circulating/discharging pump (15) is arranged on a discharging pipe of the condensate storage tank (14) and is connected to a lateral line feeding pipe line of the rectifying tower (11) through a three-way valve;
the oligomer purification system (II) comprises an oligomer purification reactor (18), an oligomer discharge pump (19) and a purification condenser (24);
a lateral line feeding port of the oligomer purification reactor (18) is connected with a discharging pipe of the oligomer preparation system (I); a discharge pipe at the top of the oligomer purification reactor (18) passes through a purification condenser (24) and then is connected with a purification system condensate storage tank (26), and the side surface of the purification system condensate storage tank (26) is connected with an oligomerization purification vacuum system (25); a purification system condensate discharging pump (27) is arranged on a discharging pipe at the bottom of the purification system condensate storage tank (26);
the oligomer discharging pump (19) is positioned on a discharging pipe at the bottom of the oligomer purification reactor (18) and is connected with a feeding pipeline of the oligomer depolymerization system (III);
the oligomer purification reactor (18) is a packed rectifying tower;
the oligomer depolymerization system (III) comprises a depolymerization reactor (30), a depolymerization catalyst feed pump (21), a depolymerization feed mixer (29) and a depolymerization heavy component discharge/circulation pump (31);
wherein, the depolymerization catalyst (20) and the purified product generated by the oligomer purification system (II) enter a depolymerization feed mixer (29) simultaneously through a depolymerization catalyst feed pump (21) to be mixed, and then are fed from the side of a depolymerization reactor (30);
the depolymerized heavy component discharging/circulating pump (31) is positioned on a discharging pipe at the bottom of the depolymerizing reactor (30), is connected to the depolymerizing feed mixer (29) through a three-way valve, returns the heavy components generated in the depolymerizing reactor (30) to the depolymerizing feed mixer (29) to be mixed with reaction raw materials, and reenters the depolymerizing reactor (30) for reaction; the light component generated in the depolymerization reactor (30) is connected with a feed line of the lactide purification system (IV) through a discharge hole above the side surface of the depolymerization reactor (30);
the method for synthesizing lactide by adopting the device comprises the following steps:
(1) taking L-lactic acid or D-lactic acid or DL-lactic acid as a raw material, carrying out polymerization synthesis reaction in an oligomer preparation system (I) at the temperature of 180 ℃ at 100 ℃ and under the pressure of 1-100KPa, recovering lactic acid from a light component to improve the yield, refluxing a heavy component to improve the molecular weight of the oligomeric lactic acid, and obtaining the oligomeric lactic acid with the weight-average molecular weight of 500-3000 Da;
(2) purifying the oligomeric lactic acid obtained in the step (1) by an oligomer purification system (II) to remove unreacted lactic acid and water;
(3) allowing the oligomeric lactic acid purified in the step (2) to enter an oligomer depolymerization system (III) under the action of a catalyst, carrying out depolymerization reaction at the temperature of 200-260 ℃ and under the pressure of 0.1-1KPa to obtain a crude lactide product, introducing the obtained crude lactide product into a lactide purification system (IV) for purification, purifying and collecting light components to obtain a lactide product, and refluxing and depolymerizing heavy components again;
in the step (1), the polymerization synthesis reaction is carried out in the presence of an oligomerization catalyst, wherein the oligomerization catalyst is any one of zinc oxide, zinc lactate, zinc acetate, zinc isooctanoate, zinc stearate, stannous oxide, stannic oxide, stannous octoate or stannous chloride.
2. Lactide synthesis plant according to claim 1, characterized in that the lactide purification system (iv) comprises a lactide purification reactor (35) and a lactide storage tank (36);
the lactide storage tank (36) is connected with a bottom discharge hole of the lactide purification reactor (35) and conveys lactide products (38) outwards through a lactide discharge pump (37);
the top by-product outlet of the lactide purification reactor (35) is connected to the feed line of the recovery system (v).
3. Lactide synthesis plant according to claim 1, characterized in that the recovery system (v) comprises a recovery system reactor (40), a recovery liquid storage tank (42) and a recovery liquid discharge pump (43);
the side surface of the recovery liquid storage tank (42) is connected with a depolymerization vacuum system (41), and a top feed inlet is connected with a bottom discharge outlet of the recovery system reactor (40); the recovery liquid storage tank (42) discharges the recovery liquid (44) outwards through a recovery liquid discharge pump (43) on a bottom discharge pipe.
4. The lactide synthesis apparatus according to claim 1, wherein the oligomerization reactor (6) or depolymerization reactor (30) is any one of a falling film reactor, a thin film evaporation reactor, a packed reactor, and a dual falling film reactor.
5. The lactide synthesis device according to claim 2, wherein the lactide purification reactor (35) is any one of a shell-and-tube heat exchanger, a spiral plate heat exchanger and a shell-and-tube heat exchanger.
6. The lactide synthesis apparatus according to claim 3, wherein the recovery system reactor (40) is any one of a shell-and-tube heat exchanger, a spiral plate heat exchanger, and a shell-and-tube heat exchanger.
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