CN112812094A - Method for purifying L-lactide - Google Patents
Method for purifying L-lactide Download PDFInfo
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- CN112812094A CN112812094A CN202110143215.9A CN202110143215A CN112812094A CN 112812094 A CN112812094 A CN 112812094A CN 202110143215 A CN202110143215 A CN 202110143215A CN 112812094 A CN112812094 A CN 112812094A
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- JJTUDXZGHPGLLC-IMJSIDKUSA-N 4511-42-6 Chemical compound C[C@@H]1OC(=O)[C@H](C)OC1=O JJTUDXZGHPGLLC-IMJSIDKUSA-N 0.000 title claims abstract description 91
- 238000000034 method Methods 0.000 title claims abstract description 43
- 238000003860 storage Methods 0.000 claims abstract description 65
- 238000000926 separation method Methods 0.000 claims abstract description 20
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 claims description 34
- 239000012452 mother liquor Substances 0.000 claims description 25
- 235000014655 lactic acid Nutrition 0.000 claims description 17
- 239000004310 lactic acid Substances 0.000 claims description 17
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 claims description 17
- 239000007788 liquid Substances 0.000 claims description 17
- 239000013078 crystal Substances 0.000 claims description 16
- JJTUDXZGHPGLLC-ZXZARUISSA-N (3r,6s)-3,6-dimethyl-1,4-dioxane-2,5-dione Chemical compound C[C@H]1OC(=O)[C@H](C)OC1=O JJTUDXZGHPGLLC-ZXZARUISSA-N 0.000 claims description 10
- 239000002253 acid Substances 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 8
- 230000035900 sweating Effects 0.000 claims description 8
- 238000002844 melting Methods 0.000 claims description 7
- 230000008018 melting Effects 0.000 claims description 7
- 230000003068 static effect Effects 0.000 claims description 6
- 230000001105 regulatory effect Effects 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 4
- 239000012295 chemical reaction liquid Substances 0.000 claims description 3
- 239000002184 metal Substances 0.000 claims description 3
- 238000012856 packing Methods 0.000 claims description 3
- 238000005086 pumping Methods 0.000 claims description 3
- 230000002194 synthesizing effect Effects 0.000 claims description 3
- 239000002994 raw material Substances 0.000 abstract description 4
- 238000009776 industrial production Methods 0.000 abstract description 2
- 239000000203 mixture Substances 0.000 description 7
- 238000000746 purification Methods 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 230000007062 hydrolysis Effects 0.000 description 5
- 238000006116 polymerization reaction Methods 0.000 description 5
- 229920000747 poly(lactic acid) Polymers 0.000 description 4
- 239000004626 polylactic acid Substances 0.000 description 4
- 238000006460 hydrolysis reaction Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000009283 thermal hydrolysis Methods 0.000 description 2
- 238000012719 thermal polymerization Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000006837 decompression Effects 0.000 description 1
- 229920006238 degradable plastic Polymers 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000007151 ring opening polymerisation reaction Methods 0.000 description 1
- 238000007142 ring opening reaction Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 210000004243 sweat Anatomy 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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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
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
- C07B2200/00—Indexing scheme relating to specific properties of organic compounds
- C07B2200/07—Optical isomers
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- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a method for purifying L-lactide, which is carried out in the following device: the device comprises a rectifying tower, a second secondary cold trap, a first storage tank, a first pump, a first crystallizer, a third storage tank, a third pump, a second crystallizer and a fifth storage tank which are connected in sequence; after the separation system and the separation method are used for separation, the L-lactide with the purity higher than 99.0% can be obtained. The separation system provided by the invention can separate high-purity L-lactide from crude L-lactide, and can convert raw materials entering the separation system into useful industrial products to the maximum extent. The method disclosed by the invention is simple to operate, high in product purity, large in treatment capacity and suitable for large-scale industrial production.
Description
Technical Field
The invention relates to the technical field of separation engineering, in particular to a method for purifying L-lactide from crude L-lactide at least containing L-lactide, meso-lactide, lactic acid and lactic acid oligomer.
Background
L-lactide is an intermediate raw material for producing degradable plastic polylactic acid, and along with the implementation of plastic prohibition orders, the production, development and utilization of the L-lactide are more and more widely regarded in recent years, mainly because the ring-opening polymerization of the L-lactide is an effective method for preparing the high-molecular-weight polylactic acid. The lactide used as the intermediate raw material of the polylactic acid has high boiling point and high solidification point, is heat-sensitive, is very easy to absorb water to carry out ring-opening reaction, has great difficulty in refining and purification, is the main technical difficulty of the synthesis process, and the preparation cost, the purity and the concentration of free acid determine the cost and the purity of the high-molecular-quality polylactic acid, which is one of the main factors influencing the industrialization of the lactide.
The separation method of decompression rectification and crystallization is mainly adopted at present for industrially separating the crude L-lactide.
In the current rectification process, two or more rectification towers are generally contained, and the excessive number of the rectification towers in the rectification separation process causes the excessive number of total tower plates, the excessive residence time in a tower system and the corresponding increase of the operation temperature, which bring various problems to the operation and the separation, such as difficult separation caused by the increase of the tower pressure drop and polymerization and decomposition caused by the excessive tower temperature, particularly when crude L-lactide containing water and acid components is rectified, the L-lactide is promoted to carry out thermal polymerization, hydrolysis and other reactions in the tower, so that heavy components with excessive oligomers are extracted from a tower bottom, light components with more L-lactide and decomposed L-lactide are extracted from a tower top, and the concentration of free acid in the L-lactide is excessively high. In addition, the rectification and purification of lactide by a plurality of rectifying towers have certain complexity in the aspects of engineering design and operation.
CN101696203A and CN101857585A both adopt rectification methods to purify lactide, and it was found that the rectification separation requires a large number of theoretical plates, an excessive number of columns, an excessive number of plates, and an excessive residence time, which brings many troubles to the operation, such as an increase in column pressure drop and an increase in column bottom temperature, and particularly when crude L-lactide containing water and acid components is distilled, the crude L-lactide is promoted to undergo thermal polymerization, hydrolysis, and the like in a container, thereby reducing the yield. In addition, due to the high condensation point of the lactide and the great operation difficulty, the lactide can be blocked by carelessness, the process cannot be smoothly carried out, and the purification of the lactide by the single rectification method of a plurality of rectification towers has certain difficulty in the aspects of engineering design and operation.
US6310218 discloses a method for purifying lactide by melt crystallization, crude lactide with a content of 99.2% being melted, crystallized, discharged mother liquor, sweated, discharged sweat. After two-stage purification, the mass fraction of lactide can be increased from 99.2% to 99.99%, meso-lactide can not be detected in the product, and the yield of lactide is about 53%. The method has the advantages of suitability for re-purification of high-purity lactide and low yield.
JP10025288, CN1112559, uses a hydrolysis method to remove meso-lactide from crude lactide to obtain lactide of high optical purity by contacting a meso-lactide-containing mixture with water and hydrolyzing meso-lactide. The method is characterized in that the amount of water and the washing speed are difficult to control, so that the contact time of the product and the water is too long, and hydrolysis is caused; and the melting point and the specific optical rotation can not meet the polymerization requirement, and the product still needs to be further purified after hydrolysis treatment.
Therefore, if a method for purifying L-lactide is developed, the problems in the prior art can be solved, and the method has important significance for the purification of L-lactide and the later popularization and application of products.
Disclosure of Invention
In order to overcome the problems of high-temperature polymerization, excessive residence time and the like in a vacuum rectification method in the prior art, and polymerization and decomposition caused by excessive residence time and the like, the invention provides a method for purifying L-lactide.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides a method for purifying L-lactide, which is carried out in the following device:
the device comprises a rectifying tower T1, a second secondary cold trap E2, a first storage tank V1, a first pump P1, a first crystallizer C1, a third storage tank V3, a third pump P3, a second crystallizer C2 and a fifth storage tank V5 which are connected in sequence;
the rectifying tower T1 is a metal wire mesh plate corrugated structured packing tower, a light component lactic acid discharge port connected with a second discharge pipe 002 through a first secondary cold trap E1 is arranged at the tower top, a crude L-lactide feed port 001 is arranged at the middle part, and a heavy component oligomer discharge port connected with a third discharge pipe 003 is arranged at the tower bottom; an L-lactide-rich discharge port is arranged between the crude L-lactide feed port and the heavy component oligomer discharge port, and the L-lactide-rich discharge port is connected with the first storage tank V1 through the second secondary cold trap E2;
the first crystallizer C1 is a plate or fin static crystallizer; the first crystallizer C1 is provided with a main feed inlet, a first crystal outlet, a first mother liquid outlet and a secondary crystallizer product feed inlet, the main feed inlet of the first crystallizer C1 is connected with the first storage tank V1 through a first pump P1, the first crystal outlet is connected with a second storage tank V2 provided with a delivery pump P2, and the delivery pump P2 is communicated with an external receiving storage tank; the first mother liquor outlet is connected with the third storage tank V3;
the second crystallizer C2 is a plate-type or fin-type static crystallizer; the second crystallizer C2 is provided with a first crystallizer mother liquor feeding hole, a second crystallizer outlet and a second mother liquor outlet, the first crystallizer mother liquor feeding hole is connected with the third storage tank V3 through a third pump P3, the second crystallizer outlet is connected with an inlet of a fifth storage tank V5, and the fifth storage tank V5 is connected with the second-stage crystallizer product feeding hole of the first crystallizer C1 through a fifth pump P5 and a connecting pipe; the second mother liquor outlet is connected with the inlet of a fourth storage tank V4, and the outlet of a fourth storage tank V4 is connected with the crude L-lactide feed inlet 001 through a fourth pump P4;
the method comprises the following steps:
(1) crude L-lactide firstly enters the rectifying tower T1 through a crude L-lactide feeding hole 001 for primary separation, the operating pressure of the top of the rectifying tower T1 is 1-5mbar, the pressure drop is 5-8 mbar, the operating temperature of a tower kettle is 130-150 ℃, and the operating temperature of the top of the tower is 85-100 ℃; the obtained light component is converted from a gas state into a liquid state through a first secondary cold trap E1 from a light component lactic acid discharge port and then is discharged from a second discharge pipe 002, and the obtained heavy component is discharged from a third discharge pipe 003; the L-lactide-rich liquid recovered from the L-lactide-rich discharge port flows into a first storage tank V1 after being converted from a gaseous state into a liquid state through a second secondary cold trap E2, and a first pump P1 pumps the L-lactide-rich liquid in the first storage tank V1 into a first crystallizer C1 in batches; the crude L-lactide is reaction liquid obtained by dehydrating, polycondensing and depolymerizing lactic acid in the process of synthesizing the L-lactide;
(2) cooling the L-lactide-rich liquid in a first crystallizer C1 to 65 ℃ at a speed of 0.02-0.5 ℃/min, then heating to 97 ℃ at a speed of 0.02-0.5 ℃/min for sweating, continuously heating the obtained crystal to 110 ℃ at a speed of 0.1-2.0 ℃/min for melting, then flowing into a second storage tank V2 from the primary crystallizer, and then collecting the L-lactide by a conveying pump P2; the mother liquor of the first crystallizer obtained from the primary crystallizer C1 flows into a third storage tank V3, and then is pumped into a second crystallizer C2 in batches by a third pump P3 to be continuously concentrated;
(3) cooling the mother liquor of the first crystallizer to 50 ℃ at a speed of 0.02-0.5 ℃/min in the second crystallizer C2, then heating to 95 ℃ at a speed of 0.02-0.5 ℃/min for sweating, continuously heating the obtained crystals to 110 ℃ at a speed of 0.1-2.0 ℃/min for melting, then flowing into a fifth storage tank V5, and then pumping the crystals into the first crystallizer C1 in batches by a fifth pump P5 for continuous concentration; the mother liquor obtained by the second crystallizer flows into the fourth storage tank V4 from the second mother liquor outlet, and then is pumped into the rectifying tower T1 by the fourth pump P4 for rectification again.
Further, the crude L-lactide in step (1) consists essentially of: 50-90 wt% of L-lactide, 10-40 wt% of Meso-lactide, 2-8 wt% of lactic acid, 2-12 wt% of oligomer and 400-1000 mmol/kg of free acid.
Further, the crude L-lactide in step (1) consists of the following components: l-lactide 50 wt%, Meso-lactide 37 wt%, lactic acid 5 wt%, oligomer 8 wt% and 603mmol/kg free acid.
Still further, the operating pressure at the top of the rectification column T1 is recommended to be 2mbar, the operating temperature at the bottom of the column is 135 ℃, and the operating temperature at the top of the column is preferably 90 ℃.
Still further, a flow regulating valve is arranged at the crude L-lactide feeding hole (001) in the step (1), and the feeding flow rate of the crude L-lactide in the step (1) is controlled to be 1000-3500 kg/h, preferably 2700kg/h through the flow regulating valve.
Further, the feeding rate of the crude L-lactide in the step (1) was 2700 kg/h.
In the invention, in order to avoid lactide polymerization caused by overhigh temperature of a tower bottom and energy conservation and consumption reduction, the lower the operation pressure of the rectifying tower is, the better the operation pressure is, preferably 0mbar, but the pressure loss of a pipeline cannot be avoided, and the pressure of the tower top is generally within 1-5 mbar.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The components obtained according to the scheme have the following compositions:
compared with the prior art, the invention has the beneficial effects that: after the separation system and the separation method are used for separation, the L-lactide with the purity higher than 99.0% can be obtained. The separation system provided by the invention can separate high-purity L-lactide from crude L-lactide, and can convert raw materials entering the separation system into useful industrial products to the maximum extent. The method disclosed by the invention is simple to operate, high in product purity, large in treatment capacity and suitable for large-scale industrial production.
Drawings
FIG. 1 is a schematic flow chart of an embodiment of the present invention;
the reference numerals are explained below:
rectifying tower T1, first crystallizer C1, second crystallizer C2, crude L-lactide feeding pipe 001, light component lactic acid discharging pipe 002, heavy component oligomer discharging pipe 003, first secondary cold trap E1, second secondary cold trap E2, first storage tank V1, first pump P1, second storage tank V2, second pump P2, third storage tank V3, third pump P3, fourth storage tank V4, fourth pump P4, fifth storage tank V5 and fifth pump P5.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions.
Example 1
The separation system for separating and purifying L-lactide from crude L-lactide provided in this example comprises:
the device comprises a rectifying tower T1, a second secondary cold trap E2, a first storage tank V1, a first pump P1, a first crystallizer C1, a third storage tank V3, a third pump P3, a second crystallizer C2 and a fifth storage tank V5 which are connected in sequence;
the rectifying tower T1 is a metal wire mesh plate corrugated structured packing tower, a light component lactic acid discharge port connected with a second discharge pipe 002 through a first secondary cold trap E1 is arranged at the tower top, a crude L-lactide feed port 001 is arranged at the middle part, and a heavy component oligomer discharge port connected with a third discharge pipe 003 is arranged at the tower bottom; an L-lactide-rich discharge port is arranged between the crude L-lactide feed port and the heavy component oligomer discharge port, and the L-lactide-rich discharge port is connected with the first storage tank V1 through the second secondary cold trap E2;
the first crystallizer C1 is a plate-type static crystallizer; the first crystallizer C1 is provided with a main feed inlet, a first crystal outlet, a first mother liquid outlet and a secondary crystallizer product feed inlet, the main feed inlet of the first crystallizer C1 is connected with the first storage tank V1 through a first pump P1, the first crystal outlet is connected with a second storage tank V2 provided with a delivery pump P2, and the delivery pump P2 is communicated with an external receiving storage tank; the first mother liquor outlet is connected with the third storage tank V3;
the second crystallizer C2 is a plate-type static crystallizer; the second crystallizer C2 is provided with a first crystallizer mother liquor feeding hole, a second crystallizer outlet and a second mother liquor outlet, the first crystallizer mother liquor feeding hole is connected with the third storage tank V3 through a third pump P3, the second crystallizer outlet is connected with an inlet of a fifth storage tank V5, and the fifth storage tank V5 is connected with the second-stage crystallizer product feeding hole of the first crystallizer C1 through a fifth pump P5 and a connecting pipe; the second mother liquor outlet is connected with the inlet of a fourth storage tank V4, and the outlet of a fourth storage tank V4 is connected with the crude L-lactide feed inlet 001 through a fourth pump P4;
the method comprises the following steps:
(1) the crude L-lactide feed port (001) is provided with a flow regulating valve, the crude L-lactide with the feed flow rate of 2700kg/h is firstly fed into the rectifying tower T1 for primary separation through the crude L-lactide feed port 001, the operating pressure at the top of the rectifying tower T1 is 2mbar, the pressure drop is 6mbar, the operating temperature of a tower kettle is 135 ℃, the operating temperature at the top of the tower is 90 ℃, and the pressure of the tower kettle is measured to be 8 mbar; the obtained light component is converted from a gas state into a liquid state through a first secondary cold trap E1 from a light component lactic acid discharge port and then is discharged from a second discharge pipe 002, and the obtained heavy component is discharged from a third discharge pipe 003; detecting that the pressure of an L-lactide-rich discharge port is 6mbar and the temperature is 128 ℃, converting the L-lactide-rich discharged from the L-lactide-rich discharge port from a gas state into a liquid state through a second secondary cold trap E2, and then flowing into a first storage tank V1, and pumping the L-lactide-rich in the first storage tank V1 into a first crystallizer C1 in batches by a first pump P1; the crude L-lactide in the step (1) is a reaction liquid obtained by dehydrating, polycondensing and depolymerizing lactic acid in the process of synthesizing the L-lactide, and is measured to consist of the following components: l-lactide 50 wt%, Meso-lactide 37 wt%, lactic acid 5 wt%, oligomer 8 wt% and 603mmol/kg free acid.
(2) Measuring that the L-lactide rich with the temperature of 100 ℃ is cooled to 65 ℃ at a speed of 0.2 ℃/min in a first crystallizer C1, then raising the temperature to 97 ℃ at a speed of 0.225 ℃/min for sweating, continuously raising the temperature of the obtained crystals to 110 ℃ at a speed of 0.1-2.0 ℃/min for melting, then flowing into a second storage tank V2 from a primary crystallizer, and then extracting by a delivery pump P2; the mother liquor of the first crystallizer obtained from the primary crystallizer C1 flows into a third storage tank V3, and then is pumped into a second crystallizer C2 in batches by a third pump P3 to be continuously concentrated;
(3) measuring that the mother liquor of the first crystallizer with the temperature of 97 ℃ is cooled to 55 ℃ at a speed of 0.25 ℃/min in the second crystallizer C2, then raising the temperature to 95 ℃ at a speed of 0.27 ℃/min for sweating, continuously raising the temperature of the obtained crystals to 110 ℃ at a speed of 0.22 ℃/min for melting, then flowing into the fifth storage tank V5, and then being pumped into the first crystallizer C1 in batches by the fifth pump P5 for continuous concentration; the mother liquor obtained by the second crystallizer flows into the fourth storage tank V4 from the second mother liquor outlet, and then is pumped into the rectifying tower T1 by the fourth pump P4 for rectification again.
The compositions of the components in this example are as follows:
temperature-time relationship table for the first crystallizer C1 in this example:
| Procedure | feeding of the feedstock | Temperature reduction | Sweating | Chemical material |
| Temperature (. degree.C.) | 100 | 100→70 | 70→97 | 110 |
| Time (min) | 35 | 150 | 120 | 90 |
Temperature-time relationship table for the second crystallizer C2 in this example:
| Procedure | feeding of the feedstock | Temperature reduction | Sweating | Chemical material |
| Temperature (. degree.C.) | 97 | 100→55 | 55→95 | 110 |
| Time (min) | 35 | 180 | 150 | 90 |
Example 2
Other process conditions were the same as in example 1 except that the temperature of the bottom of the rectifying column T1 was controlled at 140 ℃ and the temperature of the top of the rectifying column was controlled at 95 ℃.
The compositions of the components in this example are as follows:
example 3
The other process conditions were the same as in example 1 except that the temperature of the bottom of the rectifying column T1 was controlled at 145 ℃ and the temperature of the top of the rectifying column was controlled at 98 ℃.
The compositions of the components in this example are as follows:
comparative example 1
Other process conditions were the same as in example 1 except that the top temperature of the rectifying column T1 was controlled at 102 ℃ and the bottom temperature was controlled at 150 ℃.
The compositions of the components in this example are as follows:
comparative example 2
The other process conditions were the same as in example 1 except that the top temperature of the rectifying column T1 was controlled at 86 ℃ and the bottom temperature was controlled at 130 ℃.
The compositions of the components in this example are as follows:
Claims (8)
1. a method for purifying L-lactide, characterized in that the method is carried out in the following apparatus:
the device comprises a rectifying tower (T1), a second secondary cold trap (E2), a first storage tank (V1), a first pump (P1), a first crystallizer (C1), a third storage tank (V3), a third pump (P3), a second crystallizer (C2) and a fifth storage tank (V5) which are connected in sequence;
the rectifying tower (T1) is a metal wire mesh plate corrugated structured packing tower, a light component lactic acid discharge port connected with a second discharge pipe (002) through a first secondary cold trap (E1) is arranged at the top of the tower, a crude L-lactide feed port (001) is arranged at the middle of the tower, and a heavy component oligomer discharge port connected with a third discharge pipe (003) is arranged at the bottom of the tower; an L-lactide-rich discharge port is arranged between the crude L-lactide feed port and the heavy component oligomer discharge port, and the L-lactide-rich discharge port is connected with the first storage tank (V1) through the second secondary cold trap (E2);
the first crystallizer (C1) is a plate or fin static crystallizer; the first crystallizer (C1) is provided with a main feed inlet, a first crystal outlet, a first mother liquid outlet and a secondary crystallizer product feed inlet, the main feed inlet of the first crystallizer (C1) is connected with the first storage tank (V1) through a first pump (P1), the first crystal outlet is connected with a second storage tank (V2) provided with a delivery pump (P2), and the delivery pump (P2) is communicated with an external receiving storage tank; the first mother liquor outlet is connected with the third storage tank (V3);
the second crystallizer (C2) is a plate or fin static crystallizer; the second crystallizer (C2) is provided with a first crystallizer mother liquid feeding hole, a second crystal outlet and a second mother liquid outlet, the first crystallizer mother liquid feeding hole is connected with the third storage tank (V3) through a third pump (P3), the second crystal outlet is connected with an inlet of a fifth storage tank (V5), and the fifth storage tank (V5) is connected with the secondary crystallizer product feeding hole of the first crystallizer (C1) through a fifth pump (P5) and a connecting pipe; the second mother liquor outlet is connected with the inlet of a fourth storage tank (V4), and the outlet of the fourth storage tank (V4) is connected with the crude L-lactide feed inlet (001) through a fourth pump (P4);
the method comprises the following steps:
(1) the method comprises the following steps that crude L-lactide firstly enters a rectifying tower (T1) through a crude L-lactide feeding hole (001) for primary separation, the operating pressure of the top of the rectifying tower (T1) is 1-5mbar, the pressure is reduced to 5-8 mbar, the operating temperature of a tower kettle is 130-150 ℃, and the operating temperature of the top of the rectifying tower is 85-100 ℃; the obtained light component is converted from gas state to liquid state through a first secondary cold trap (E1) from a light component lactic acid discharge port and then is discharged from a second discharge pipe (002), and the obtained heavy component is discharged from a third discharge pipe (003); the L-lactide-rich liquid recovered from the L-lactide-rich discharge port flows into a first storage tank (V1) after being converted from a gas state into a liquid state through a second secondary cold trap (E2), and a first pump (P1) pumps the L-lactide-rich liquid in the first storage tank (V1) into a first crystallizer (C1) in batches; the crude L-lactide is reaction liquid obtained by dehydrating, polycondensing and depolymerizing lactic acid in the process of synthesizing the L-lactide;
(2) cooling the L-rich lactide to 65 ℃ at a speed of 0.02-0.5 ℃/min in a first crystallizer (C1), heating to 97 ℃ at a speed of 0.02-0.5 ℃/min for sweating, continuously heating the obtained crystal to 110 ℃ at a speed of 0.1-2.0 ℃/min for melting, flowing into a second storage tank (V2) from the primary crystallizer, and then collecting the L-rich lactide by a conveying pump (P2); the mother liquor of the first crystallizer obtained from the primary crystallizer (C1) flows into a third storage tank (V3) and then is pumped into a second crystallizer (C2) by a third pump (P3) in batches for continuous concentration;
(3) cooling the first crystallizer mother liquor to 50 ℃ at a speed of 0.02-0.5 ℃/min in the second crystallizer (C2), heating to 95 ℃ at a speed of 0.02-0.5 ℃/min for sweating, continuously heating the obtained crystals to 110 ℃ at a speed of 0.1-2.0 ℃/min for melting, flowing into a fifth storage tank (V5), and then pumping the crystals into the first crystallizer (C1) in batches by the fifth pump (P5) for continuous concentration; the mother liquor obtained by the second crystallizer flows into the fourth storage tank (V4) from the second mother liquor outlet, and then is pumped into the rectifying tower (T1) by the fourth pump (P4) for rectification again.
2. The method of purifying L-lactide as claimed in claim 1, wherein: in the step (1), the crude L-lactide mainly comprises the following components: 50-90 wt% of L-lactide, 10-40 wt% of Meso-lactide, 2-8 wt% of lactic acid, 2-12 wt% of oligomer and 400-1000 mmol/kg of free acid.
3. The method of purifying L-lactide as claimed in claim 2, wherein: the crude L-lactide in the step (1) consists of the following components: l-lactide 50 wt%, Meso-lactide 37 wt%, lactic acid 5 wt%, oligomer 8 wt% and 603mmol/kg free acid.
4. The method of purifying L-lactide as claimed in claim 1, wherein: the operating pressure at the top of the rectification column (T1) was 2 mbar.
5. The method of purifying L-lactide as claimed in claim 1, wherein: the operating temperature of the bottom of the rectification column (T1) was 135 ℃.
6. The method of purifying L-lactide as claimed in claim 1, wherein: the top operating temperature of the rectification column (T1) was 90 ℃.
7. The method of purifying L-lactide as claimed in claim 1, wherein: and the feeding hole (001) of the crude L-lactide is provided with a flow regulating valve, and the feeding flow of the crude L-lactide in the step (1) is controlled to be 1000-3500 kg/h through the flow regulating valve.
8. The method of purifying L-lactide of claim 7, wherein: the feed flow of the crude L-lactide in step (1) was 2700 kg/h.
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| CN114478471A (en) * | 2022-02-10 | 2022-05-13 | 普立思生物科技有限公司 | Lactide purification system and purification process |
| CN114653086A (en) * | 2022-03-11 | 2022-06-24 | 孝感市易生新材料有限公司 | Device and method for preparing high-purity L-lactide |
| CN115536628A (en) * | 2021-06-29 | 2022-12-30 | 中船重工鹏力（南京）塑造科技有限公司 | Purification method of crude lactide |
| CN115710247A (en) * | 2022-10-28 | 2023-02-24 | 万华化学集团股份有限公司 | Method for producing lactide with low acid value at low cost |
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