CN113461915B - Lactic acid oligomer synthesis system and method capable of regulating polymerization degree - Google Patents
Lactic acid oligomer synthesis system and method capable of regulating polymerization degree Download PDFInfo
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- CN113461915B CN113461915B CN202110746387.5A CN202110746387A CN113461915B CN 113461915 B CN113461915 B CN 113461915B CN 202110746387 A CN202110746387 A CN 202110746387A CN 113461915 B CN113461915 B CN 113461915B
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- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
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Abstract
The invention discloses a lactic acid oligomer synthesis system with adjustable polymerization degree and a synthesis method, comprising the following steps: a tower kettle outlet of the first reactive distillation tower is communicated with a feed inlet of the second reactive distillation tower through a first tower kettle extraction pipe; a side line discharge port of the second reactive distillation tower is communicated with a reflux system, and a tower kettle outlet of the second reactive distillation tower is communicated with a second tower kettle extraction pipe; the reflux system comprises a first condenser, an inlet of the first condenser is communicated with a lateral line discharge port of the second reactive distillation tower, and an outlet of the first condenser is respectively communicated with a tower kettle reflux port of the first reactive distillation tower and a tower top reflux port of the second reactive distillation tower through pipelines. According to the invention, the first reaction rectifying tower is used for removing the free water and generating the lactic acid oligomerization intermediate, and the second reaction rectifying tower is used for removing the water and the lactic acid oligomerization intermediate generated by the reaction, so that the lactic acid oligomer with concentrated polymerization degree distribution is obtained, the problem of wide polymerization degree distribution of the lactic acid oligomer is solved, and a high-quality raw material is provided for the subsequent depolymerization reaction.
Description
Technical Field
The invention relates to the technical field of biodegradable material production, in particular to a lactic acid oligomer synthesis system and a lactic acid oligomer synthesis method capable of regulating and controlling polymerization degree.
Background
The lactic acid oligomer is an intermediate in lactide synthesis, is a precursor of degradable biological material polylactic acid, and is an important link in the current polylactic acid production process. Because the lactide does not produce water as a by-product when the ring-opening polymerization reaction is carried out to generate the polylactic acid, and the polymerization degree of the polymerization reaction can be accurately controlled, the production of the polylactic acid by the lactide after the lactic acid is subjected to dehydration polycondensation and depolymerization purification is a more advanced process at present. Meanwhile, the purity of lactide also directly influences the polymerization degree of polylactic acid generated by polymerization of lactide, and further, in the synthesis of lactide, the lactic acid oligomer with more concentrated polymerization degree obtained by condensation polymerization of lactic acid is the most critical step, and the purity and yield of lactide are directly influenced.
The existing synthetic method of the low-polymer lactic acid generally comprises the following steps: heating in inert gas atmosphere to dehydrate and polymerize L-lactic acid, and separating and recovering lactic acid oligomer from reaction product. However, the existing production processes of lactic acid oligomers have the problems of insufficient dehydration and wide polymerization degree distribution, which causes excessive byproducts in the process of depolymerizing to lactide.
Disclosure of Invention
The invention aims to: in order to solve the problems, the invention provides a synthesis system and a synthesis method of lactic acid oligomer with adjustable and controllable polymerization degree. Then, by adjusting the side extraction, the top extraction and other modes, the problem of wide polymerization degree distribution of the lactic acid oligomer in the prior art is better solved, high-quality raw materials are provided for the subsequent depolymerization reaction, and the defects in the prior art are overcome.
The technical scheme adopted by the invention is as follows: a lactic acid oligomer synthesis system capable of regulating and controlling polymerization degree is characterized by comprising:
the first reactive distillation tower is used for carrying out polycondensation and rectification treatment on the lactic acid raw material, the tower top outlet of the first reactive distillation tower is communicated with a first condensation system, and the tower kettle outlet of the first reactive distillation tower is communicated with the feed inlet of the second reactive distillation tower through a first tower kettle extraction pipe;
the second reactive distillation tower is used for carrying out polycondensation and rectification treatment on the material from the first reactive distillation tower, the tower top outlet of the second reactive distillation tower is communicated with a second condensation system, the side line discharge port of the second reactive distillation tower is communicated with a reflux system, and the tower kettle outlet of the second reactive distillation tower is communicated with a second tower kettle discharge pipe;
the reflux system comprises a first condenser, wherein the inlet of the first condenser is communicated with the side line discharge hole of the second reactive distillation tower, and the outlet of the first condenser is respectively communicated with the tower kettle reflux hole of the first reactive distillation tower and the tower top reflux hole of the second reactive distillation tower through pipelines;
the first condensation system is used for condensing the gas phase from the first reactive distillation tower, and an outlet of the first condensation system is communicated with a first tower top output pipe;
and the second condensation system is used for condensing the gas phase from the second reactive distillation tower, and an outlet of the second condensation system is communicated with a feed inlet of the first reactive distillation tower through a second tower top extraction pipe.
Further, the first condensing system comprises a second condenser, an inlet of the second condenser is communicated with an outlet of the first reactive distillation column, and an outlet of the second condenser is respectively communicated with a reflux port of the first reactive distillation column and a discharge pipe of the first column.
Furthermore, the second condensing system comprises a third condenser, an inlet of the third condenser is communicated with an outlet at the top of the second reactive distillation tower, and an outlet of the third condenser is communicated with a feed inlet of the first reactive distillation tower through a second tower top extraction pipe.
Further, a first reboiler is arranged on the first tower kettle extraction pipe, an inlet of the first reboiler is communicated with a tower kettle outlet of the first reactive distillation tower, and an outlet of the first reboiler is respectively communicated with the first tower kettle extraction pipe and a tower kettle reflux port of the first reactive distillation tower.
And further, a second reboiler is arranged on the second tower kettle extraction pipe, an inlet of the second reboiler is communicated with a tower kettle outlet of the second reactive distillation tower, and outlets of the second reboiler are respectively communicated with the second tower kettle extraction pipe and a tower kettle reflux port of the second reactive distillation tower.
Further, the first reactive distillation column and the second reactive distillation column respectively consist of a column bottom reaction section, a stripping section and a rectifying section from bottom to top, and can be a packed column, a plate column or a combination thereof. The reaction section of the tower kettle provides a liquid level space capable of regulating and controlling the reaction residence time for the reaction; the stripping section enables the lactic acid oligomer with smaller polymerization degree to be separated from the reaction section of the tower kettle, so that the polymerization degree of the reaction section of the tower is more concentrated; the rectifying section makes the water extracted from the top of the tower contain less lactic acid.
Preferably, the first reboiler and the second reboiler are falling film reboilers with distributors. The reboiler of this kind is from the top feeding of reboiler, bottom ejection of compact, compares with ordinary reboiler type, can form the film on the heat exchange tube inner wall uniformly, and heat transfer temperature is milder, heat exchange efficiency is higher, residence time is shorter, is difficult to coking and polymerization, has also effectively avoided the material of tower cauldron to take place the polymerization and have the accessory substance to generate when improving evaporation efficiency.
The invention also comprises a synthetic method of the lactic acid oligomer synthetic system with adjustable degree of polymerization, which comprises the following steps:
s1, feeding raw material lactic acid into a first reactive distillation tower for polycondensation reaction and distillation separation, wherein the working pressure is 5-30KPaA, the reaction temperature is 100-170 ℃, the residence time is 1-4h, a first light component and a first heavy component are obtained, the first light component is discharged into a first condensation system, and the first heavy component is fed into a second reactive distillation tower through a first tower kettle extraction pipe;
s2, performing polycondensation reaction and rectification separation on the first heavy component by using a second reactive distillation tower, wherein the working pressure is 0.1-5.0KPaA, the reaction temperature is 160-190 ℃, the retention time is 1-4h, so as to obtain a second light component, a lighter component and a second heavy component, the second light component is discharged into a second condensation system, the main component of the lighter component is a lactic acid oligomerization intermediate with the polymerization degree of less than 10, the lighter component is discharged into a reflux system through a side-stream discharge port of the second reactive distillation tower, and the second heavy component is discharged into a discharge pipe of a second tower kettle as a product.
Further, the raw material lactic acid is an L-lactic acid aqueous solution with the weight percentage of more than 80 percent, and the optical purity of the L-lactic acid is more than or equal to 99.5 percent.
Further, after the lighter components are discharged into a reflux system, the reflux system distributes the flow rate of reflux to the first reactive distillation tower and the second reactive distillation tower, wherein the flow rate of reflux to the first reactive distillation tower is 5-30% of the feeding amount of the raw material lactic acid.
Further, the polymerization degree distribution of the lactic acid oligomer is regulated and controlled by controlling parameters of temperature, pressure, residence time and reflux quantity.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. according to the lactic acid oligomer system with the adjustable polymerization degree, provided by the invention, rectification and deep oligomerization dehydration reaction are integrated uniformly, so that the reaction route is optimized, the reaction separation efficiency is improved, the effect of timely removing water in the reaction system is realized, the reaction material is prevented from being diluted by the presence of water, the reaction process is prevented from being influenced, and the quality and the yield of an oligomerization product are improved;
2. according to the method for synthesizing the lactic acid oligomer with the adjustable polymerization degree, firstly, free water is removed and a lactic acid oligomer intermediate with low polymerization degree is generated through a first reaction rectifying tower, and then the water generated in the reaction and the lactic acid oligomer intermediate with low polymerization degree are removed through a second reaction rectifying tower, and the lactic acid oligomer with concentrated polymerization degree distribution is obtained; meanwhile, the problem of wide polymerization degree distribution of the lactic acid oligomer in the prior art is solved well mainly by adjusting the flow rate of side-draw and top-draw returned to the first reactive distillation column, optimizing the reaction temperature and adjusting the retention time;
3. the synthesis method of the lactic acid oligomer with the adjustable polymerization degree, provided by the invention, not only makes up the problem of incomplete reaction of a lactic acid oligomerization reaction kettle, but also removes water in time through a purification section after oligomerization reaction in the first reactive distillation tower, avoids the problem that the reaction process is influenced by dilution of reaction materials due to the presence of water, further improves the quality and yield of an oligomerization product, enables the polymerization degree to be more concentrated through reactive distillation, enables the temperature of a falling film reactor to be softer, and enables the temperature of a reaction system to be reduced;
4. according to the method and the system for synthesizing the lactic acid oligomer with the adjustable polymerization degree, the fractional polymerization degree of the lactic acid oligomer is mainly between 11 and 25, and high-quality raw materials are provided for subsequent depolymerization reaction and the yield thereof.
Drawings
FIG. 1 is a schematic flow chart of a system for synthesizing lactic acid oligomer with adjustable degree of polymerization according to the present invention;
FIG. 2 is a graph showing the degree of polymerization distribution of a target product obtained in example 1 of the present invention;
FIG. 3 is a graph showing the degree of polymerization distribution of a target product obtained in example 2 of the present invention;
FIG. 4 is a graph showing the degree of polymerization distribution of a target product obtained in example 3 of the present invention;
FIG. 5 is a graph showing the degree of polymerization distribution of a target product obtained in example 4 of the present invention;
FIG. 6 is a graph showing the target product polymerization degree distribution obtained in example 5 of the present invention;
FIG. 7 is a graph showing the degree of polymerization distribution of the target product obtained in example 6 of the present invention;
FIG. 8 is a graph showing the degree of polymerization distribution of a target product obtained in example 7 of the present invention;
the mark in the figure is: 1 is a first reactive distillation tower, 2 is a second reactive distillation tower, 3 is a first tower kettle extraction pipe, 4 is a second tower kettle extraction pipe, 5 is a first condenser, 6 is a first reflux tank, 7 is a first extraction pump, 8 is a first tower top extraction pipe, 9 is a second tower top extraction pipe, 10 is a second condenser, 11 is a third condenser, 12 is a second reflux tank, 13 is a second extraction pump, 14 is a third reflux tank, 15 is a third extraction pump, 16 is a reflux extraction pipe, 17 is a first reboiler, 18 is a first circulating pump, 19 is a fourth extraction pump, 20 is a second reboiler, 21 is a second circulating pump, 22 is a fifth extraction pump, and 23 is a lactic acid feeding pipe.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
As shown in fig. 1, a lactic acid oligomer synthesis system with adjustable degree of polymerization, comprising:
the tower top outlet of the first reactive distillation tower 1 is communicated with a first condensation system, the tower bottom outlet of the first reactive distillation tower 1 is communicated with the feed inlet of a second reactive distillation tower 2 through a first tower bottom extraction pipe 3, and the feed inlet of the first reactive distillation tower 1 is communicated with a lactic acid feed pipe 23;
the top outlet of the second reactive distillation tower 2 is communicated with a second condensing system, the side line discharge port of the second reactive distillation tower 2 is communicated with a reflux system, and the tower kettle outlet of the second reactive distillation tower is communicated with a second tower kettle discharge pipe 4;
the reflux system comprises a first condenser 5, an inlet of the first condenser 5 is communicated with a side line discharge hole of the second reactive distillation tower 2, and an outlet of the first condenser 5 is respectively communicated with a tower kettle reflux hole of the first reactive distillation tower 1 and a tower top reflux hole of the second reactive distillation tower 2 through pipelines;
the outlet of the first condensing system is communicated with a first tower top output pipe 8, and the outlet of the second condensing system is communicated with the feed inlet of the first reactive distillation tower 1 through a second tower top output pipe 9.
In fig. 1, an inlet of a first condenser 5 is communicated with a side line discharge port of a second reactive distillation column 2, an outlet of the first condenser 5 is communicated with a first reflux tank 6, an outlet of the first reflux tank 6 is connected with an inlet of a first extraction pump 7, and the first extraction pump 7 is communicated with a column bottom reflux port of the first reactive distillation column 1 through a reflux extraction pipe 16. The liquid phase obtained after condensation treatment by the first condenser 5 is temporarily stored by the first reflux tank, and then is distributed to the first reactive distillation column 1 and the second reactive distillation column 2 by the first extraction pump 7. Cooling reflux is carried out on the lactic acid and the oligomer distilled from the side line of the tower through a reflux system, so that the rectification reaction operation is enhanced, and the lactic acid oligomer with lower polymerization degree is separated from the second reactive rectification tower 2 and returns to the first reactive rectification tower 1.
Further, in order to recover part of the material in the gas phase and reduce the loss of the material, the first condensation system comprises a second condenser 10, an inlet of the second condenser 10 is communicated with an outlet at the top of the first reactive distillation column 1, and an outlet of the second condenser 10 is respectively communicated with a reflux outlet at the top of the first reactive distillation column 1 and a withdrawal outlet 3 at the top of the first reactive distillation column. As shown in fig. 1, the second condenser 10 is connected to the second reflux drum 12 to temporarily store the liquid phase in the second reflux drum 12, and then the liquid phase is distributed to the first reactive distillation column 1 and the first overhead output pipe 8 by the second output pump 13, and the first overhead output pipe 8 is used for discharging the wastewater containing a trace amount of lactic acid to the outside. The water, the lactic acid and the oligomer distilled from the tower top are subjected to condensation reflux through the first condensation system, so that the rectification reaction operation is enhanced.
Correspondingly, as shown in fig. 1, the second condensation system includes a third condenser 11, an inlet of the third condenser 11 is connected to the top outlet of the second reactive distillation column 2, an outlet of the third condenser 11 is connected to a third reflux drum 14, an outlet of the third reflux drum 14 is connected to a third extraction pump 15, and the third extraction pump 15 is connected to the feed inlet of the first reactive distillation column 1 through a second top extraction pipe 9.
In one embodiment, in order to improve the purity of the material discharged from the first reactive distillation column 1, a first reboiler 17 is provided on the first column bottom withdrawal pipe 3, an inlet of the first reboiler 17 is connected to a column bottom outlet of the first reactive distillation column 1, and outlets thereof are respectively connected to the first column bottom withdrawal pipe 3 and a column bottom reflux port of the first reactive distillation column 1. As shown in fig. 1, a tower bottom outlet of a first reactive distillation tower 1 is connected with an inlet of a first reboiler 17 through a first circulation pump 18, the first circulation pump 18 is used for fully mixing materials, so that the materials are more uniformly distributed in the first reboiler 17, and the reaction is more favorably carried out mildly at a more uniform temperature, the first reboiler 17 is respectively communicated with a tower bottom reflux port of the first reactive distillation tower 1 and a fourth extraction pump 19, so as to respectively convey gas-liquid two phases obtained after the treatment by the first reboiler 17 into the first reactive distillation tower 1 and a first tower bottom extraction pipe 3, and the first tower bottom extraction pipe 3 directly conveys the high-purity materials to a second reactive distillation tower 2 for further treatment. Because the outlet of the first reboiler 17 is gas-liquid two-phase, the light component enters the first reactive distillation column 1 along with the gas phase, the liquid phase containing less light component returns to the column bottom to continue to react, and meanwhile, a part of the liquid phase containing less light component is extracted by the fourth extraction pump 19.
Correspondingly, in order to improve the purity of the material discharged from the second reactive distillation column 1, a second reboiler 20 is arranged on the second column bottom extraction pipe 4, an inlet of the second reboiler 20 is communicated with a column bottom outlet of the second reactive distillation column 2, and outlets of the second reboiler 20 are respectively communicated with the second column bottom extraction pipe 4 and a column bottom reflux port of the second reactive distillation column 2. As shown in fig. 1, a tower bottom outlet of the second reactive distillation tower 2 is connected with the second reboiler 20 through the second circulation pump 21, the second circulation pump 21 is used for fully mixing materials, so that the materials are distributed more uniformly in the second reboiler 20, and the reaction is more favorably performed mildly at a more uniform temperature, the second reboiler 20 is respectively connected with a tower bottom reflux port and a fifth extraction pump 22 of the second reactive distillation tower 2, so as to respectively convey gas-liquid two phases obtained after being processed by the second reboiler 20 into the second reactive distillation tower 2 and the second tower bottom extraction pipe 4, and further obtain a target product.
In one embodiment, the first reactive distillation column 1 and the second reactive distillation column 2 are respectively composed of a bottom reaction section, a stripping section and a rectifying section (not shown in the figure) from bottom to top, and may be, for example, an existing packed column, a plate column or a combination thereof. Further, the first reboiler 17 and the second reboiler 20 are preferably falling film reboilers with a distributor.
The invention also comprises a method for synthesizing the lactic acid oligomer with adjustable and controllable polymerization degree, which comprises the following steps:
s1, feeding raw material lactic acid into a first reactive distillation tower 1 for polycondensation reaction and rectification separation, wherein the working pressure is 5-30KPaA, the reaction temperature is 100-170 ℃, the residence time is 1-4h, a first light component and a first heavy component are obtained, the first light component is discharged into a first condensation system, and the first heavy component is fed into a second reactive distillation tower 2 through a first tower kettle extraction pipe 3;
s2, the second reactive distillation tower 2 carries out polycondensation reaction and rectification separation on the first heavy component, the working pressure is 0.1-5.0KPaA, the reaction temperature is 160-190 ℃, the residence time is 1-4h, a second light component, a lighter component and a second heavy component are obtained, the second light component is discharged into a second condensation system, the main component of the lighter component is a lactic acid oligomerization intermediate with the polymerization degree of less than 10, the lighter component is discharged into a reflux system through a side line discharge port of the second reactive distillation tower 2, and the second heavy component is discharged into a second tower kettle discharge pipe 4 as a product.
Further, taking the embodiment shown in fig. 1 as an example, the specific synthesis method is as follows:
s1, feeding raw material lactic acid into a first reaction rectifying tower 1 through a lactic acid feeding pipe 23, and carrying out polycondensation reaction and rectification separation on the raw material lactic acid by the first reaction rectifying tower 1, wherein the operating pressure is 15KPaA, the operating temperature of a tower kettle is 160 ℃, and the retention time is 3 hours to obtain a first light component in a gas phase and a first heavy component in a liquid phase;
s2, the first light component enters a second condenser 10 from the outlet of the top of the first reactive distillation column 1, is converted from a gas state into a liquid state and then is discharged into a second reflux tank 12, then a small part of liquid phase is distributed to the first reactive distillation column 1 through a second extraction pump 13, and a large part of liquid phase is distributed to a first top extraction pipe 8 and is discharged outside through the first top extraction pipe 8; the test shows that the water content of the liquid phase discharged from the first tower top extraction pipe 8 is 99.9wt%;
s3, the first recombined components are treated by a first reboiler and then discharged into a first tower kettle output pipe 3, tests show that the materials in the first tower kettle output pipe 3 are mainly lactic acid oligomers with the polymerization degree of 5-10, and the materials are discharged into a second reactive distillation tower 2 by the first tower kettle output pipe 3;
s4, performing polycondensation reaction and rectification separation on the material from the first reaction rectifying tower 1 by using a second reaction rectifying tower 2, wherein the operating pressure is 0.5KPaA, the operating temperature of a tower kettle is 185 ℃, and the retention time is 3 hours to obtain a second light component, a lighter component and a second heavy component, wherein the second light component mainly comprises lactic acid and water, the lighter component mainly comprises a lactic acid oligomerization intermediate with the polymerization degree of less than 10, and the second heavy component mainly comprises a lactic acid oligomer with the polymerization degree of 11-25;
s5, the second light component enters a third condenser 11 from the outlet of the top of the second reactive distillation tower 2, is converted from a gas state into a liquid state, is discharged into a third reflux tank 14, and then is distributed to the first reactive distillation tower 1 through a third extraction pump 15;
s6, the lighter components enter a first condenser 5 from a side line discharge port of a second reactive distillation tower 2, are discharged into a first reflux tank 6 after condensation treatment, then reflux a part of liquid phase into the second reactive distillation tower 2 through a first extraction pump 7, reflux the other part of liquid phase into the first reactive distillation tower 2 through a reflux extraction pipe 16, and the reflux flow is 10% of the feeding amount of the raw material lactic acid;
and S7, treating the second heavy component by a second reboiler 20, discharging the treated second heavy component into a second tower kettle extraction pipe 4, and discharging the treated second heavy component as a target product.
In the above synthesis method, the lactic acid oligomer is a reaction solution obtained by dehydrating and polycondensing lactic acid and lactic acid oligomer again, and the target product is obtained by the above synthesis method, the yield is 78.9%, and the distribution rate of polymerization degree is: the polymerization degree is 3% in the range of 0-5, 6% in the range of 6-10, 20% in the range of 11-15, 41% in the range of 16-20, 16% in the range of 21-25, 7% in the range of 26-30, 5% in the range of 31-35, 3% in the range of more than 35, and the distribution of the polymerization degrees is shown in fig. 2.
Example 2
The synthesis method and system adopted in the embodiment are the same as those of the embodiment 1, and the difference is only that the operation temperature of the material in the first reactive distillation tower is 155 ℃ and the operation temperature of the second reactive distillation tower is 180 ℃.
The polymerization degree distribution rate of the target product obtained in this embodiment is: the polymerization degree is 9% in the range of 0-5, 18% in the range of 6-10, 24% in the range of 11-15, 29% in the range of 16-20, 10% in the range of 21-25, 6% in the range of 26-30, 3% in the range of 31-35, 1% in the range of more than 35, and the distribution of polymerization degree is shown in fig. 3.
Example 3
The synthesis method and system adopted in the embodiment are the same as those of the embodiment 1, and the difference is only that the operation temperature of the material in the first reactive distillation tower is 165 ℃ and the operation temperature of the second reactive distillation tower is 190 ℃.
The polymerization degree distribution rate of the target product obtained in this embodiment is: the polymerization degree is 2% in the range of 0-5, the polymerization degree is 3% in the range of 6-10, the polymerization degree is 13% in the range of 11-15, the polymerization degree is 26% in the range of 16-20, the polymerization degree is 28% in the range of 21-25, the polymerization degree is 17% in the range of 26-30, the polymerization degree is 7% in the range of 31-35, the polymerization degree is 4% in the range of more than 35, and the distribution rate of polymerization degrees is shown in FIG. 4.
Example 4
The synthesis method and the system adopted in the embodiment are the same as those in the embodiment 1, and the difference is only that the residence time of the materials in the first reactive distillation tower and the second reactive distillation tower is 2 hours.
The polymerization degree distribution rate of the target product obtained in this embodiment is: the polymerization degree is 12% in the range of 0-5, 34% in the range of 6-10, 24% in the range of 11-15, 16% in the range of 16-20, 8% in the range of 21-25, 3% in the range of 26-30, 2% in the range of 31-35, 1% in the range of more than 35, and the distribution of the polymerization degrees is shown in fig. 5.
Example 5
The synthesis method and the system adopted in the embodiment are the same as those in the embodiment 1, and the difference is only that the retention time of the materials in the first reactive distillation tower and the second reactive distillation tower is 4 hours.
The polymerization degree distribution rate of the target product obtained in this embodiment is: the polymerization degree is 1% in the range of 0-5, 3% in the range of 6-10, 9% in the range of 11-15, 16% in the range of 16-20, 30% in the range of 21-25, 24% in the range of 26-30, 11% in the range of 31-35, 6% in the range of more than 35, and the distribution rate of polymerization degree is shown in fig. 6.
Example 6
The synthesis method and system used in this example are the same as those of example 1, except that the flow rate of the second reactive distillation column returned to the first reactive distillation column is 50% of that of example 1.
The polymerization degree distribution rate of the target product obtained in this embodiment is: the polymerization degree accounts for 12% in the range of 0-5, 20% in the range of 6-10, 27% in the range of 11-15, 21% in the range of 16-20, 10% in the range of 21-25, 6% in the range of 26-30, 3% in the range of 31-35, 1% in the range of more than 35, and the distribution rate of polymerization degrees is shown in FIG. 7.
Example 7
The synthesis method and system adopted in the present example are the same as those of example 1, except that the flow rate of the second reactive distillation column returned to the first reactive distillation column is 200% of that of example 1.
The polymerization degree distribution rate of the target product obtained in this embodiment is: the proportion of the polymerization degree is 4% in the range of 0-5, the proportion of the polymerization degree is 6% in the range of 6-10, the proportion of the polymerization degree is 14% in the range of 11-15, the proportion of the polymerization degree is 20% in the range of 16-20, the proportion of the polymerization degree is 24% in the range of 21-25, the proportion of the polymerization degree is 23% in the range of 26-30, the proportion of the polymerization degree is 6% in the range of 31-35, the proportion of the polymerization degree is 3% in the range of more than 35, and the distribution rate of the polymerization degree is shown in figure 8.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (8)
1. A lactic acid oligomer synthesis system capable of regulating and controlling polymerization degree is characterized by comprising:
the first reactive distillation tower is used for carrying out polycondensation and rectification treatment on the lactic acid raw material, the tower top outlet of the first reactive distillation tower is communicated with a first condensation system, and the tower kettle outlet of the first reactive distillation tower is communicated with the feed inlet of the second reactive distillation tower through a first tower kettle extraction pipe;
the second reactive distillation tower is used for carrying out polycondensation and rectification treatment on the material from the first reactive distillation tower, the tower top outlet of the second reactive distillation tower is communicated with a second condensation system, the side line discharge port of the second reactive distillation tower is communicated with a reflux system, and the tower kettle outlet of the second reactive distillation tower is communicated with a second tower kettle discharge pipe;
the reflux system comprises a first condenser, wherein the inlet of the first condenser is communicated with the lateral line discharge hole of the second reactive distillation tower, and the outlet of the first condenser is respectively communicated with the tower kettle reflux hole of the first reactive distillation tower and the tower top reflux hole of the second reactive distillation tower through pipelines;
the first condensation system is used for carrying out condensation treatment on the gas phase from the first reaction rectifying tower, and an outlet of the first condensation system is communicated with a first tower top output pipe; the first condensation system comprises a second condenser, an inlet of the second condenser is communicated with an outlet of the first reactive distillation column, and an outlet of the second condenser is respectively communicated with a reflux port of the first reactive distillation column and a discharge pipe of the first reactive distillation column;
the second condensation system is used for condensing the gas phase from the second reactive distillation tower, and an outlet of the second condensation system is communicated with a feed inlet of the first reactive distillation tower through a second tower top extraction pipe; the second condensation system comprises a third condenser, an inlet of the third condenser is communicated with an outlet at the top of the second reactive distillation column, and an outlet of the third condenser is communicated with a feed inlet of the first reactive distillation column through a second column top extraction pipe;
the first reactive distillation tower and the second reactive distillation tower respectively consist of a tower kettle reaction section, a stripping section and a rectifying section from bottom to top.
2. The polymerization degree-adjustable lactic acid oligomer synthesis system according to claim 1, wherein a first reboiler is arranged on the first column bottom extraction pipe, an inlet of the first reboiler is connected to the column bottom outlet of the first reactive distillation column, and outlets of the first reboiler are respectively connected to the first column bottom extraction pipe and the column bottom reflux port of the first reactive distillation column.
3. The polymerization degree-adjustable lactic acid oligomer synthesis system according to claim 2, wherein the second tower bottom withdrawal pipe is provided with a second reboiler, an inlet of the second reboiler is connected with the tower bottom outlet of the second reactive distillation tower, and outlets of the second reboiler are respectively connected with the second tower bottom withdrawal pipe and the tower bottom reflux port of the second reactive distillation tower.
4. The system for synthesizing lactic acid oligomer with adjustable degree of polymerization according to claim 3, wherein the first reboiler and the second reboiler are falling film reboilers with distributors.
5. The method for synthesizing a polymerization degree-controllable lactic acid oligomer synthesis system according to any one of claims 1 to 4, comprising the steps of:
s1, feeding raw material lactic acid into a first reactive distillation tower for polycondensation reaction and distillation separation, wherein the working pressure is 5-30KPaA, the reaction temperature is 100-170 ℃, the residence time is 1-4h, a first light component and a first heavy component are obtained, the first light component is discharged into a first condensation system, and the first heavy component is fed into a second reactive distillation tower through a first tower kettle extraction pipe;
s2, a second reactive distillation tower carries out polycondensation reaction and distillation separation on the first heavy component, the working pressure is 0.1-5.0KPaA, the reaction temperature is 160-190 ℃, the retention time is 1-4h, a second light component, a light component and a second heavy component are obtained, the second light component is discharged into a second condensation system, the main component of the light component is a lactic acid oligomerization intermediate with the polymerization degree of less than 10, the light component is discharged into a reflux system through a side line discharge port of the second reactive distillation tower, and the second heavy component is discharged into a second tower kettle discharge pipe as a product.
6. The method for synthesizing lactic acid oligomer with adjustable and controllable degree of polymerization according to claim 5, wherein the raw material lactic acid is an aqueous solution of L-lactic acid with a concentration of more than 80wt%, and the optical purity of the L-lactic acid is more than or equal to 99.5%.
7. The method for synthesizing lactic acid oligomer with adjustable and controllable degree of polymerization according to claim 5, wherein after the lighter components are discharged into the reflux system, the reflux system distributes the flow rate of reflux to the first reactive distillation column and the second reactive distillation column, wherein the flow rate of reflux to the first reactive distillation column is 5-30% of the feeding amount of raw material lactic acid.
8. The method for synthesizing lactic acid oligomer with adjustable degree of polymerization according to claim 5, wherein the distribution of degree of polymerization of lactic acid oligomer is adjusted by controlling parameters of temperature, pressure, residence time and reflux amount.
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| CN112851628A (en) * | 2019-11-26 | 2021-05-28 | 南京华基塔业有限公司 | Reaction system and method for preparing lactide from lactic acid |
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