CN112844262A - Intelligent reaction system and method for preparing lactide from lactic acid - Google Patents
Intelligent reaction system and method for preparing lactide from lactic acid Download PDFInfo
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- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 title claims abstract description 208
- 238000006243 chemical reaction Methods 0.000 title claims abstract description 144
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 title claims abstract description 129
- 239000004310 lactic acid Substances 0.000 title claims abstract description 106
- 235000014655 lactic acid Nutrition 0.000 title claims abstract description 104
- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000000066 reactive distillation Methods 0.000 claims abstract description 91
- 238000006384 oligomerization reaction Methods 0.000 claims abstract description 84
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 75
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 72
- 238000000926 separation method Methods 0.000 claims abstract description 59
- 238000006297 dehydration reaction Methods 0.000 claims abstract description 30
- 238000000746 purification Methods 0.000 claims abstract description 13
- 239000000047 product Substances 0.000 claims description 68
- 239000007795 chemical reaction product Substances 0.000 claims description 36
- 239000000463 material Substances 0.000 claims description 34
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 34
- 239000002994 raw material Substances 0.000 claims description 33
- 239000011552 falling film Substances 0.000 claims description 29
- 239000000203 mixture Substances 0.000 claims description 24
- 239000000126 substance Substances 0.000 claims description 24
- 238000005886 esterification reaction Methods 0.000 claims description 16
- 239000003054 catalyst Substances 0.000 claims description 12
- 230000032050 esterification Effects 0.000 claims description 7
- 238000004821 distillation Methods 0.000 claims description 6
- 230000018044 dehydration Effects 0.000 claims description 4
- 238000010992 reflux Methods 0.000 claims description 4
- 238000007599 discharging Methods 0.000 claims description 2
- 238000006116 polymerization reaction Methods 0.000 description 11
- 230000000694 effects Effects 0.000 description 9
- 239000006227 byproduct Substances 0.000 description 8
- 238000003756 stirring Methods 0.000 description 8
- 239000007788 liquid Substances 0.000 description 5
- 229920000747 poly(lactic acid) Polymers 0.000 description 5
- 239000004626 polylactic acid Substances 0.000 description 5
- 238000012691 depolymerization reaction Methods 0.000 description 4
- 239000000945 filler Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000012856 packing Methods 0.000 description 4
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- 238000004519 manufacturing process Methods 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 238000004939 coking Methods 0.000 description 2
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- 230000002441 reversible effect Effects 0.000 description 2
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- 230000009286 beneficial effect Effects 0.000 description 1
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- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
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- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 1
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- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/009—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping in combination with chemical reactions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/14—Fractional distillation or use of a fractionation or rectification column
- B01D3/143—Fractional distillation or use of a fractionation or rectification column by two or more of a fractionation, separation or rectification step
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/14—Fractional distillation or use of a fractionation or rectification column
- B01D3/32—Other features of fractionating columns ; Constructional details of fractionating columns not provided for in groups B01D3/16 - B01D3/30
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/42—Regulation; Control
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- 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
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- 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
- B01J4/00—Feed or outlet devices; Feed or outlet control devices
- B01J4/001—Feed or outlet devices as such, e.g. feeding tubes
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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
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2204/00—Aspects relating to feed or outlet devices; Regulating devices for feed or outlet devices
- B01J2204/005—Aspects relating to feed or outlet devices; Regulating devices for feed or outlet devices the outlet side being of particular interest
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention provides an intelligent reaction system and method for preparing lactide from lactic acid. This intelligent reaction system includes: the device comprises a lactic acid oligomerization reaction kettle, a first reaction rectifying tower, a lactide synthesis kettle and a second reaction rectifying tower which are connected in sequence; the first reactive distillation tower comprises a first tower kettle reboiler, a purification section and a deep oligomerization dehydration reaction section, wherein the purification section and the deep oligomerization dehydration reaction section are arranged from top to bottom, a first feed inlet is formed in a tower section between the purification section and the deep oligomerization dehydration reaction section, and the first feed inlet is used for introducing products of the lactic acid oligomerization reaction kettle into the first reactive distillation tower. The intelligent reaction system provided by the invention integrates rectification and deep synthesis reaction, optimizes the reaction route, improves the reaction separation efficiency, and further improves the quality and yield of the product.
Description
Technical Field
The invention relates to the field of lactide preparation, in particular to an intelligent reaction system and method for preparing lactide from lactic acid.
Background
The production and exploitation of lactide has gained increasing attention in recent years, mainly because the ring-opening polymerization of lactide is an efficient method for preparing high molecular weight polylactic acid. Polylactic acid is a biodegradable material with a great development prospect, and is an excellent medical high polymer material because the final products decomposed in the natural environment are carbon dioxide and water, so that the polylactic acid is nontoxic and harmless to the environment, and has the advantages of good biocompatibility and biodegradability, excellent mechanical property, easiness in processing and forming and the like. The ring-opening polymerization reaction of lactide is an effective method for preparing high-molecular-weight polylactic acid, and the molecular weight of the polylactic acid of a polymerization product can reach millions.
The existing lactide generation process comprises the following steps:
(1) oligomerization reaction: the lactic acid is subjected to multistage esterification reaction under certain temperature and pressure conditions, and is dehydrated and polycondensed into oligomer;
LACID(MIXED)-->P15(MIXED)+H2O(MIXED)
lactic acid oligomer
(oligomers are mixtures of components with a degree of polymerization of 1 to 30(P1-P30) with gradually increasing boiling points, in which the mixture is replaced by P15)
(2) And (3) synthesis reaction: under certain temperature and pressure conditions, the oligomer is thermally decomposed and broken to form lactide.
P15(MIXED)-->7DLL(MIXED)+LACID(MIXED)
Oligomer lactide lactic acid
Wherein, the oligomerization reaction process of the first step is lactic acid intermolecular dehydration, and because the oligomerization reaction is a reversible reaction, the existence of water can dilute reaction materials and influence the reaction rate, thereby influencing the normal operation of the reaction process.
The lactide synthesis reaction separation system in the second step has low efficiency, and the generated lactide can not be taken out in time to enable the esterification reaction to reach a balanced state due to large system viscosity and small separation interface, so that oligomer is carried out towards the polymerization reaction direction, and the yield of the lactide product is reduced. The retention time in the reaction process is long, so that more byproducts are generated, and the quality of the product is indirectly influenced.
In addition, as informatization is developed more and more rapidly, the application of an intelligent system is more and more extensive, errors are easy to occur by adopting a manual control mode, and the labor cost is higher.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The first purpose of the invention is to provide an intelligent reaction system for preparing lactide from lactic acid, which integrates rectification and deep oligomerization dehydration reaction, optimizes the reaction route, improves the reaction separation efficiency, realizes the effect of timely removing water in the reaction system, avoids the reaction material being diluted by the presence of water to influence the reaction process, and further improves the quality and yield of the oligomerization product; the rectification separation and the lactide reaction synthesis are integrated uniformly, the reaction residence time is shortened, the generation of byproducts is reduced, and the generated lactide can be purified and separated quickly to promote the esterification reaction to proceed in the positive direction, so that the quality and the yield of the product are improved;
meanwhile, the intelligent reaction system can realize the whole process of acquisition, analysis and correction of the operation parameters of the reaction system, does not need manual control, reduces the error rate, improves the production efficiency, reduces the labor cost, and is worthy of wide popularization and application.
The second purpose of the invention is to provide a method for preparing lactide by adopting the intelligent reaction system, and the prepared lactide product has good quality and high yield, and the conversion rate of raw materials is improved to a certain extent.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
the invention provides an intelligent reaction system for preparing lactide from lactic acid, which comprises: the device comprises a lactic acid oligomerization reaction kettle, a first reaction rectifying tower, a lactide synthesis kettle and a second reaction rectifying tower which are connected in sequence;
the first reactive distillation tower comprises a first tower kettle reboiler, a purification section and a deep oligomerization dehydration reaction section, wherein the purification section and the deep oligomerization dehydration reaction section are arranged from top to bottom, a first feed inlet is formed in a tower section between the purification section and the deep oligomerization dehydration reaction section and used for feeding a product of the lactic acid oligomerization reaction kettle into the first reactive distillation tower, a first discharge outlet is formed in a tower kettle of the first reactive distillation tower, a part of the product discharged from the first discharge outlet is heated by the first tower kettle reboiler, and then returns to the deep oligomerization dehydration reaction section, and the other part of the product is directly collected;
the second reaction rectifying tower comprises a rectifying section and a lactide deep synthesis section, wherein the rectifying section comprises a light component separation section for separating water, lactic acid and a small amount of oligomers, a product separation section for separating lactide products and a heavy component separation section for separating oligomers, the light component separation section and the product separation section are arranged on the upper portion of the lactide deep synthesis section from top to bottom, the heavy component separation section is arranged on the lower portion of the lactide deep synthesis section, and a third feed inlet is arranged on a tower section between the product separation section and the lactide deep synthesis section and used for leading products of the lactide synthesis kettle into the second reaction rectifying tower.
The intelligent system comprises an online acquisition module, a feedback control module and an intelligent adjustment module, the online acquisition module sends acquired operation parameters of the reaction system to the feedback control module, and the feedback control module sends set parameters to the intelligent adjustment module after analyzing data so as to adjust the operation parameters of the reaction system.
In the prior art, the oligomerization reaction is a reversible reaction, the reaction materials can be diluted by the presence of water, the reaction rate is influenced, and the normal proceeding of the reaction process is influenced.
In order to solve the technical problems, the deep oligomerization dehydration reaction section is specially arranged in the first reaction rectifying tower, so that the incomplete reaction problem of the lactic acid oligomerization reaction kettle is solved, water is timely removed through the purification section after oligomerization reaction in the first reaction rectifying tower, the problem that reaction materials are diluted by water to influence the reaction process is avoided, and the quality and the yield of an oligomerization product are improved.
In addition, the lactide deep synthesis section is specially arranged in the second reaction rectifying tower, so that the problem of incomplete reaction in the lactide synthesis kettle is solved, and after the lactide deep synthesis reaction is carried out in the second reaction rectifying tower, the product is timely separated from other components through the rectification section, the forward proceeding of the esterification reaction is promoted, the problem of influencing the reaction process is avoided, and the quality and the yield of the lactide product are improved.
The raw material for synthesizing lactide is oligomer with polymerization degree of 1-30, the polymerization degree is an important index for measuring the molecular size of the polymer, and the average value of the number of repeating units contained in a polymer macromolecular chain is based on the number of the repeating units, and the repeating unit of the oligomer is a lactic acid molecule.
For convenience of the present invention, the symbol P indicates that P1-P30 means a polymerization degree of 1-30, for example, P15 means a polymerization of 15 lactic acid molecules.
The intelligent reaction system realizes intelligent adjustment of each operating parameter of the reaction system by introducing the intelligent system, firstly acquires the operating data of the whole reaction system through the online acquisition module and then transmits the operating data to the feedback control module, and then the feedback control module gives the most appropriate operating parameter according to the current working condition through an intelligent analysis mode and feeds the most appropriate operating parameter back to the intelligent adjustment module, thereby achieving the purpose of intelligently adjusting the operating parameter.
Preferably, the online acquisition module is connected with the feedback control module in a wireless manner.
Preferably, the intelligent adjustment module comprises a lactic acid oligomerization reaction kettle pressure control unit, a lactic acid oligomerization reaction kettle temperature control unit, a lactide synthesis kettle pressure control unit and a lactide synthesis kettle temperature control unit, corresponding intelligent modules can be arranged at important control sites in the whole process to realize intelligent adjustment, and the whole intelligent system can adopt a wireless mode to connect all the modules for intelligent control.
For example, the temperature and pressure of the key tower sections of the first reactive distillation tower and the second reactive distillation tower can be detected and controlled.
Preferably, substances accumulated on the top of the first reactive distillation tower and the top of the second reactive distillation tower mainly comprise water, lactic acid and oligomers, substances accumulated on the bottom of the second reactive distillation tower mainly comprise polycondensates, and in order to fully recycle the substances, the substances are returned to the lactic acid oligomerization reaction kettle to be used as raw materials for recycling. In actual operation, the gathered materials are fed from the middle section of the rectifying tower and rectified by the depolymerization rectifying tower, substances gathered at the tower bottom mainly comprise oligomers, lactic acid and the like, and substances at the tower top mainly comprise water.
More preferably, the top of the depolymerization reaction rectifying tower is provided with a tower top condenser, the tower kettle is provided with a tower kettle reboiler, the tower kettle reboiler is preferably a falling film reboiler, after reboiling treatment by the tower kettle reboiler, one part of the reboiler returns to the tower kettle, and the other part of the reboiler enters the lactic acid oligomerization reaction kettle from the lactic acid inlet through a pipeline to be used as a raw material.
Preferably, the first tower kettle reboiler is a falling film reboiler, the top of the falling film reboiler is provided with a second feed inlet, the bottom of the falling film reboiler is provided with a second discharge port, the second feed inlet is communicated with the first discharge port, one part of substances discharged from the second discharge port is introduced into the deep oligomerization and dehydration reaction section, and the other part of the substances is directly collected.
The type of the reboiler of the first tower kettle is selected as the falling film reboiler, and compared with the type of the ordinary reboiler, the reboiler of the type forms a film on the tube wall, so that the heat exchange efficiency is high, the retention time is short, coking is not easy to occur, and the generation of byproducts due to the polymerization of substances in the tower kettle is avoided. And because of the falling film reboiler, the material needs to be fed from the top and discharged from the bottom of the reboiler to improve the evaporation efficiency.
Preferably, the lactic acid oligomerization reaction kettle is provided with a raw material inlet and a first reaction product outlet, the raw material inlet comprises a lactic acid inlet, and the first reaction product outlet is arranged at the bottom of the lactic acid oligomerization reaction kettle;
and the first reaction product outlet is communicated with a first feed inlet on the first reactive distillation tower.
The invention can realize the polymerization of lactic acid to form oligomer through the oligomerization reaction in the lactic acid oligomerization reaction kettle.
The generated oligomer is mainly gathered at the bottom of the lactic acid oligomerization reaction kettle with high density, so that the first reaction product outlet is arranged at the bottom of the kettle, and the lactic acid inlet is arranged on the side wall of the kettle.
Preferably, for the convenience of conveying, a first conveying pump is arranged on a pipeline which is communicated with the second feeding hole and the first discharging hole.
Similarly, for the convenience of conveying, a second conveying pump is arranged on the pipeline of the first reaction product outlet communicated with the first feeding hole.
Preferably, a first circulation pipeline is further arranged on a pipeline communicating the first reaction product outlet with the first feed inlet, so as to return a part of the substances discharged from the first reaction product outlet to the lactic acid oligomerization reaction kettle, and a first heat exchanger is arranged on the first circulation pipeline. At circulating line with the heat exchanger, also control lactic acid oligomerization reation kettle's reaction temperature through the mode of material circulation, can lead to steam when the temperature ratio is lower and realize the heating of material, can lead to the comdenstion water when the temperature ratio and realize the cooling of material, set up the heat exchanger on first circulating line, can play the effect of the interior reaction temperature of control lactic acid oligomerization reation kettle's cauldron mainly.
Preferably, as a further practicable scheme, the top of the first reactive distillation column is provided with a first overhead condenser for refluxing condensation of water, lactic acid and oligomers distilled from the top of the column to enhance the distillation reaction operation.
Preferably, as a further implementable scheme, in the second reactive distillation column of the present invention, a product side draw unit is disposed between the deep lactide synthesis section and the product separation section, and the product side draw unit is connected with a third discharge port.
Preferably, as a further implementable scheme, a mixture side draw unit is arranged between the deep lactide synthesis section and the heavy component separation section, the mixture side draw unit is connected with a third heat exchanger, and a mixture heated by the third heat exchanger enters the second reactive distillation tower again.
The oligomer is thermally decomposed and broken in the lactide deep synthesis section in the second reactive distillation tower to form lactide and lactic acid, after the thermal decomposition and broken chain reaction, the mixture which is not completely reacted is extracted through the mixture side line extraction unit below the lactide deep synthesis section, and then returns to the second reactive distillation tower after being heated by the third heat exchanger, and the lactide and the oligomer are separated through the heavy component separation section.
Preferably, as a further implementable solution, the product sidedraw unit and the mixture sidedraw unit are each constituted by a tray with several sumps. In order to realize the convenient taking out of the products in the second reactive distillation tower, the side line extraction unit is structurally a tower plate with a plurality of liquid collecting grooves, thereby realizing the high-efficiency collection of the products.
Preferably, as a further implementable scheme, the third heat exchanger is a falling film heat exchanger, a fourth feed inlet is formed in the top of the third heat exchanger, a fourth discharge outlet is formed in the bottom of the third heat exchanger, the fourth feed inlet is communicated with the mixture side draw unit, and a substance discharged from the fourth discharge outlet is introduced between the lactide deep synthesis section and the product separation section in the second reactive distillation column.
Preferably, as a further implementable scheme, the second reactive distillation tower further comprises a second tower kettle reboiler, the second tower kettle reboiler is a falling film reboiler, a fifth feed port is arranged at the top of the falling film reboiler, a fifth discharge port is arranged at the bottom of the falling film reboiler, the fifth feed port is communicated with the tower kettle of the second reactive distillation tower, and one part of a substance discharged from the fifth discharge port is introduced into the second reactive distillation tower, and the other part of the substance is directly collected.
The type of the third heat exchanger and the reboiler of the tower kettle is selected to be a falling film type, and compared with the type of the common heat exchanger, the heat exchanger can realize film formation on the pipe wall, has high heat exchange efficiency, short retention time and difficult coking, and avoids the generation of byproducts due to the polymerization of substances in the tower kettle. And because of the falling film heat exchanger, the material needs to be fed from the top and discharged from the bottom of the heat exchanger, thereby further improving the evaporation efficiency.
Preferably, the lactide synthesis kettle is provided with a raw material inlet and a second reaction product outlet, the raw material inlet comprises an oligomer inlet and an esterification catalyst inlet, and the second reaction product outlet is arranged at the bottom of the lactide synthesis kettle;
and the second reaction product outlet is communicated with a third feed inlet on the second reactive distillation tower.
The catalyst introduced into the lactide synthesis kettle is well known in the art and will not be described in detail in the present invention.
The generated lactide and unreacted raw materials have higher density and are mainly gathered at the bottom of the lactide synthesis kettle, so that the second reaction product outlet is arranged at the bottom of the kettle, the esterification catalyst inlet and the oligomer inlet are arranged on the side wall of the kettle in parallel, and the lactide and the unreacted raw materials coming out from the second reaction product outlet are introduced into the middle section of the second reaction rectifying tower to continue to carry out deep reaction and purification separation.
Preferably, as a further implementable scheme, a second circulation pipeline is further arranged on a pipeline through which the second reaction product outlet is communicated with the third feed inlet, so that a part of substances discharged from the second reaction product outlet is returned to the lactide synthesis kettle, and a second heat exchanger is arranged on the second circulation pipeline.
In addition, need add the heat exchanger at the second circulating line, the purpose is to control the reaction temperature of the synthetic cauldron of lactide through the mode of material circulation, can lead to steam when the temperature ratio is lower and realize the heating of material, can lead to the comdenstion water when the temperature ratio and realize the cooling of material, sets up the heat exchanger on the circulating line, can play the effect of the interior reaction temperature of the cauldron of control lactide synthesis cauldron mainly.
In the present invention, the type of the heat exchanger is not particularly limited, and may be a floating head type heat exchanger, a fixed tube-plate type heat exchanger, a U-shaped tube-plate type heat exchanger, a plate type heat exchanger, or the like.
The tubular heat exchanger is preferred, the material passes through a tube pass, and the heat exchange medium passes through a shell pass, because the structure of the heat exchanger is simpler and more compact, and the manufacturing cost is lower.
Preferably, as a further implementable scheme, the lactic acid oligomerization reaction kettle and the lactide synthesis kettle are stirred reaction kettles with jackets. Because the temperatures of oligomerization reaction and esterification reaction need to be controlled to be about 140 ℃, steam needs to be introduced into the jacket to heat the reaction kettle.
In addition, in order to enhance the proceeding degree of the oligomerization reaction and the esterification reaction, a stirrer may be disposed in the kettle, and the stirrer may be a propeller stirrer, an anchor stirrer, a turbine stirrer, or the like, wherein the propeller stirrer has the simplest structure, and the propeller stirrer may be classified into a flat propeller stirrer and a slanted propeller stirrer according to the shape characteristics of the blades. The flat paddle type stirrer generates radial force, the inclined paddle type stirrer generates axial force, and the paddle type stirrer is suitable for stirring low-viscosity liquid, suspension liquid and dissolved liquid.
The paddle stirrer of the present invention is preferably a paddle stirrer with three flat paddles because the stirrer of this configuration is relatively uniform with respect to stirring.
Preferably, as a further practicable aspect, the top of the second reactive distillation column is provided with a second overhead condenser for refluxing condensation of water, lactic acid and oligomers distilled from the top of the column, so that the condensation of water, lactic acid and oligomers distilled from the top of the column is refluxed to enhance the distillation reaction operation.
Preferably, as a further implementable scheme, a transfer pump may be provided on a corresponding pipeline of the entire intelligent reaction system for the convenience of transfer.
The specific type of the transfer pump is not limited, the vacuum pump can also meet the process requirements according to the specific requirements, the cost is low, and the occupied area is small.
The invention also provides a method for preparing lactide by using the intelligent reaction system, which comprises the following steps:
(A) carrying out oligomerization reaction and deep dehydration and rectification on lactic acid to generate oligomer;
(B) the oligomer and a catalyst are subjected to esterification and deep reaction rectification to obtain lactide and lactic acid;
(C) in the operation process of the reaction system, the online acquisition module sends the acquired operation parameters of the reaction system to the feedback control module, and the feedback control module sends the set parameters to the intelligent adjustment module after analyzing the data so as to adjust the operation parameters of the reaction system.
Preferably, as a further implementable scheme, in the step (A), the oligomerization reaction temperature is between 100 and 200 ℃, preferably 130 and 150 ℃, more preferably the reaction temperature is 140 ℃, and the pressure is 0.05MPa, the temperature of the rectification reaction is controlled between 100 and 200 ℃, more preferably 130 and 170 ℃, more preferably 150 ℃, and the pressure is negative pressure, and the specific degree of the negative pressure is not limited at all as long as the negative pressure is negative pressure.
Preferably, as a further implementable scheme, in the step (B), the esterification reaction temperature is 160-240 ℃, preferably the reaction temperature is 170-200 ℃, more preferably 190 ℃ and the pressure is 0.05 MPa.
In the deep dehydration and rectification step, the temperature of the distillate at the top of the tower is 6.6 ℃, the pressure is 0.0006MPa, and the main components are water, lactic acid and oligomer, and the distillate enters a post-treatment working section. Lactide product is extracted from the side of the groove of the tower plate, the temperature is controlled between 160-240 ℃, preferably 180-220 ℃, more preferably 190 ℃, the negative pressure operation is carried out, the tower bottom material is mainly polycondensate (dimeric lactic acid) and a small amount of lactide, a reboiler and a pump are arranged at the tower bottom, the tower bottom mixture is pumped above the packing of the heavy component separation section for further separation, and the separated polycondensate enters the post-treatment section.
The lactide prepared by adopting the lactic acid has good product quality and high yield, the conversion rate of the raw materials is improved by at least 10-20%, the yield and the selectivity are also improved to a certain extent, and the yield is improved by about 10% compared with the prior art.
Compared with the prior art, the invention has the beneficial effects that:
(1) the intelligent reaction system for preparing the lactide disclosed by the invention integrates rectification and reaction synthesis uniformly, so that a reaction route is optimized, the reaction separation efficiency is improved, and the quality and yield of a product are further improved;
(2) the intelligent reaction system for preparing lactide has the advantages of simple structure, less three wastes, realization of full recycling of raw materials and small occupied area;
(3) the invention realizes the effect of controlling the reaction temperature in the lactic acid oligomerization reaction kettle and the lactide synthesis kettle by arranging the circulating pipeline and the heat exchanger;
(4) the reboiler of the tower kettle and the heat exchanger are both selected to be in a falling film type, so that the heat exchange efficiency is improved, and the byproducts generated by the polymerization of substances in the tower kettle are avoided;
(5) the intelligent reaction system disclosed by the invention realizes the effect of timely removing water in the reaction system, avoids diluting reaction materials due to the presence of water, and simultaneously achieves the purpose of quickly purifying and separating lactide generated in the reaction system, promotes the esterification reaction to be carried out in the positive direction, further improves the quality and yield of lactide products, and correspondingly improves the conversion rate of raw materials;
(6) the intelligent system of the invention gets rid of the traditional operation mode of manual operation and control, and realizes the intelligent operation of the whole reaction system through an intelligent control system.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
fig. 1 is a schematic structural diagram of an intelligent reaction system for preparing lactide from lactic acid according to an embodiment of the present invention;
fig. 2 is a functional block diagram of an intelligent system according to an embodiment of the present invention.
Description of the drawings:
a 100-lactic acid oligomerization reaction kettle; a 110-lactic acid inlet;
130-a first reaction product outlet; 140-a second delivery pump;
150-first recycle conduit 160-first heat exchanger;
200-a first reactive distillation column; 210-a purification section;
220-deep oligomerization dehydration reaction section; 230-a first feed port;
240-first discharge hole; 250-a first column kettle reboiler;
251-a second feed port; 252-a second discharge port;
260-a first delivery pump; 270-a first overhead condenser;
a 300-lactide synthesis kettle; 310-oligomer inlet;
320-an esterification catalyst inlet; 330-a second reaction product outlet;
340-a second circulation conduit; 350-a second heat exchanger;
400-a second reactive distillation column; 410-a rectification section;
411-light fraction separation section 412-product separation section;
413-a heavy ends separation section; 420-lactide deep synthesis section;
430-third feed port; 440-a third outlet;
450-a third heat exchanger; 451-fourth feed inlet;
452-a fourth outlet; 460-a second column reboiler;
461-fifth feed inlet; 462-a fifth discharge port;
470-mixture side draw unit; 480-a product sidedraw unit;
490-a second overhead condenser;
500-depolymerization reaction rectifying tower; 510-a third column reboiler;
520-a third overhead condenser;
600-Intelligent system.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are some, not all, of the embodiments of the present invention, and are only used for illustrating the present invention, and should not be construed as limiting the scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In order to more clearly illustrate the technical solution of the present invention, the following description is made in the form of specific embodiments.
Examples
Referring to fig. 1, the intelligent reaction system for preparing lactide from lactic acid according to the embodiment of the present invention includes two main apparatus bodies, namely, a lactic acid oligomerization reaction kettle 100, a first reactive distillation column 200, a lactide synthesis kettle 300, and a second reactive distillation column 400, which are connected in sequence, where the second reactive distillation column 400 includes a distillation section 410 and a lactide deep synthesis section 420.
The first reactive distillation column 200 comprises a first column kettle reboiler 250, a first column top condenser 270, a purification section 210 and a deep oligomerization dehydration reaction section 220 which are arranged from top to bottom;
wherein, the oligomerization reaction kettle 100 is provided with a raw material inlet and a first reaction product outlet 130, and the raw material inlet is a lactic acid inlet 110.
The first reaction rectifying tower 200 is provided with a first material outlet 240 at the bottom, and the first material inlet 230 is arranged on the tower sections of the purifying section 210 and the deep oligomerization dehydration reaction section 220.
The first reaction product outlet 130 on the lactic acid oligomerization reaction kettle 100 is communicated with the first feed inlet 230 on the first reactive distillation column 200, and for the convenience of transportation, a second delivery pump 140 is further disposed on the communicated pipeline for providing power to transport oligomers generated by the lactic acid oligomerization reaction kettle 100 to the first reactive distillation column 200 for further reaction and separation.
In addition, a first reaction product outlet 130 on the lactic acid oligomerization reaction kettle 100 is connected to a pipeline communicated with the first feed inlet 230, the first circulation pipeline 150 is provided with a first heat exchanger 160, the first heat exchanger 160 is a tubular heat exchanger, the material passes through a tube side, the heat exchange medium passes through a shell side, and the material after heat exchange is introduced into the lactic acid oligomerization reaction kettle again through the arrangement of the first circulation pipeline 150 and the first heat exchanger 160, so as to realize temperature control of the lactic acid oligomerization reaction kettle.
In short, a part of the oligomers generated from the reaction in the lactic acid oligomerization reaction kettle 100 is returned to the kettle again through the first circulation pipeline 150, and the other part enters the first reactive distillation column 200 for further reactive distillation.
In addition, the first tower reboiler 250 included in the first reactive distillation tower 200 of another main device is a falling film reboiler, which has high efficiency and avoids the generation of byproducts. The top of the falling film reboiler is provided with a second feed inlet 251, the bottom of the falling film reboiler is provided with a second discharge outlet 252, and the second feed inlet 251 is communicated with the first discharge outlet 240 on the first reactive distillation column, so that a part of the product discharged from the first discharge outlet 240 is returned to the deep oligomerization and dehydration reaction section 220 after being heated by the tower kettle reboiler 250, and the other part is directly collected.
A first delivery pump 260 is further disposed on a pipeline connecting the second feed opening 251 and the first discharge opening 240 for convenient transportation.
It should be noted that the material coming from the first reactive distillation column 200 mainly includes oligomers, raw materials which are not completely reacted, water, and the like, and after entering the first reactive distillation column 200, volatile components of water, lactic acid and a small amount of oligomers gradually gather at the top of the column, and the bottom of the column is P1-P30 oligomers with relatively high density.
The top of the first reactive distillation column 200 is provided with a first top condenser 270, the components at the top of the column mainly comprise water, lactic acid and a small amount of oligomers, one part of the components flows back to the first reactive distillation column 200 through the first top condenser 270, and the other part of the components flows out from the first top condenser 270 for recycling.
The rectification reaction temperature in the first reactive rectification tower 200 is 150 ℃, and the pressure is negative pressure.
The rectifying section 210 and the deep oligomerization and dehydration reaction section 220 of the first reactive rectifying tower 200 are only a preferable arrangement manner, and may be increased or decreased according to the actual rectifying effect, for example, it is also feasible to additionally increase some rectifying sections.
In the second reactive distillation column 400 of this embodiment, the distillation section 410 includes a light component separation section 411 for separating water, lactic acid and a small amount of oligomers, a product separation section 412 for lactide product separation, and a heavy component separation section 413 for separating oligomers, the light component separation section 411 and the product separation section 412 are disposed at the upper portion of the deep lactide synthesis section 420 from top to bottom, and the heavy component separation section 413 is disposed at the lower portion of the deep lactide synthesis section 420; a third feed port 430 is arranged on the tower section between the product separation section 412 and the lactide deep synthesis section 420 and is used for introducing the product of the lactide synthesis kettle into the second reactive distillation tower.
A product side draw unit 480 is arranged between the lactide depth synthesis section 420 and the product separation section 412, and the product side draw unit 480 is connected with a third discharge port 440.
Wherein, the lactide synthesis kettle 300 is provided with a raw material inlet and a second reaction product outlet 330, and the raw material inlet comprises an oligomer inlet 310 and an esterification catalyst inlet 320.
The second reaction product outlet 330 on the lactide synthesis kettle 300 is communicated with the third feed port 430 on the second reactive distillation column 400, and for convenience of transportation, a transfer pump is further arranged on the communicated pipeline for providing power, and unreacted raw materials, catalyst, lactic acid, oligomer (mainly dimeric lactic acid) and lactide generated by the lactide synthesis kettle 300 are transported to the second reactive distillation column 400 for further reaction and separation.
In addition, a second reaction product outlet 330 on the lactide synthesis kettle 300 is connected to a pipeline communicated with the third feed inlet 430, and the second circulation pipeline 340 is connected to a branch of a second circulation pipeline 340, a second heat exchanger 350 is arranged on the second circulation pipeline 340, the heat exchanger is a tubular heat exchanger, a material passes through a tube side, a heat exchange medium passes through a shell side, and the material after heat exchange is introduced into the lactide synthesis kettle again through the arrangement of the second circulation pipeline 340 and the heat exchanger, so that the temperature control of the lactide synthesis kettle is realized.
In summary, a part of the material from the lactide synthesis kettle 300 is returned to the kettle again through the second recycle pipeline 340, and the other part enters the second reactive distillation column 400 for further reactive distillation.
The lactic acid oligomerization reaction kettle 100 and the lactide synthesis kettle 300 are stirring reaction kettles with jackets, steam is introduced into the jackets to control the reaction temperature to be 150 ℃, the pressure to be 0.05MPa, and the stirrers are paddle type stirrers with three flat paddle shapes to improve the stirring force of the reaction.
In addition, in the second reactive distillation column 400, a mixture side draw unit 470 is arranged between the lactide deep synthesis section 420 and the heavy component separation section 413, the mixture side draw unit 470 is connected with a third heat exchanger 450, and the mixture heated by the third heat exchanger 450 enters the second reactive distillation column again, so that the yield of lactide is improved by the arrangement of the circulating synthesis pipeline.
The third heat exchanger 450 is a falling film heat exchanger, the reboiler has high efficiency, and by-products are avoided, the top of the third heat exchanger 450 is provided with a fourth feed port 451, the bottom of the third heat exchanger is provided with a fourth discharge port 452, the fourth feed port 451 is communicated with a mixture side-draw unit 470, and substances discharged from the fourth discharge port 452 are introduced between the lactide deep synthesis section 420 and the product separation section 412 in the second reactive distillation column.
The second kettle reboiler 460 included in the second reactive distillation column 400 is a falling film reboiler, which has high efficiency and avoids the generation of byproducts. The top of the falling film reboiler is provided with a fifth feed inlet 461, the bottom of the falling film reboiler is provided with a fifth discharge outlet 462, and the fifth feed inlet 461 is communicated with the tower kettle on the second reactive distillation tower 400, so that a part of the product coming out of the tower kettle can be returned to the second reactive distillation tower again after being heated by the second tower kettle reboiler 460, and the other part of the product is directly collected.
A delivery pump is further arranged on the pipeline connecting the fifth feed inlet 461 and the tower kettle, so as to facilitate transportation.
The product side draw unit 480 and the mixture side draw unit 470 are each composed of a tray with a plurality of liquid collecting grooves to facilitate the collection and the drawing of the product in the second reactive distillation column.
It should be noted that the material coming from the second reactive distillation column 400 mainly contains unreacted raw material, catalyst, lactic acid, oligomer (mainly dimeric lactic acid), lactide, and the like, and after entering the second reactive distillation column 400, volatile components of water, lactic acid, and a small amount of oligomer gradually accumulate at the top of the column, and at the bottom of the column, oligomer with relatively high density and a small amount of lactide exist.
The rectifying section 210 and the deep oligomerization and dehydration reaction section 220 of the first reactive rectifying tower 200 are mainly composed of tower plates and fillers, the second reactive rectifying tower 400 is sequentially composed of a light component separation section 411, a product separation section 412, a lactide deep synthesis section 420 and a heavy component separation section 413 from top to bottom, each section can be composed of tower plates and fillers in any combination mode, and the types of the fillers can be Raschig rings, pall rings, step rings and the like.
Although the pressure drop of the packing per se is relatively low, the packing has the defect of easy fouling, so that the tower section which is easy to foul is preferably in a tower plate mode.
Among them, the product separation section 412 for lactide is relatively easy to be dirty and blocked, so it is preferably a tray structure, and the other three sections adopt a mode of packing and tray combination.
The second tower top condenser 490 is arranged at the tower top of the second reactive distillation tower 400, the components at the tower top mainly comprise water, lactic acid and a small amount of oligomers, one part of the components flows back to the second reactive distillation tower through the second tower top condenser 490, and the other part of the components flows out from the second tower top condenser 490 for recycling.
The intelligent system 600 is electrically connected to the lactide synthesis kettle, the lactic acid oligomerization reaction kettle, the first reactive distillation column and the second reactive distillation column of the embodiment to achieve the purpose of controlling the pressure and the temperature thereof, and can also perform intelligent control and adjustment after detection and feedback on the flow rate of the material, and the specific control operation flow is shown in fig. 2.
In the above embodiments, the heat exchanger may also be of the floating head type, fixed tube-plate type, U-shaped tube-plate type, or the like.
In the above embodiment, the heating method of the lactic acid oligomerization reaction kettle 100 and the lactide synthesis kettle 300 may be a method of arranging heating pipes on the outer wall of the reaction kettle instead of the jacket, and the type of the stirrer is not limited to three flat paddles and may be a single flat paddle, two flat paddles, or the like, and the type of the stirrer may be a propeller stirrer, an anchor stirrer, a turbine stirrer, or the like.
In the above embodiment, the number of the pump bodies is not specifically required, and the pump bodies may be arranged at corresponding positions as required.
In the above embodiment, the rectifying section 210 and the deep oligomerization and dehydration reaction section 220 of the first reactive distillation column 200 are only a preferable configuration, and may be increased or decreased according to the actual rectifying effect, for example, it is also feasible to additionally add some rectifying sections.
In the above embodiment, the reaction temperature in the lactic acid oligomerization reaction vessel 100 may be 130 ℃, 135 ℃, 145 ℃, 150 ℃ or the like, and the reaction pressure may be 0.03MPa, 0.04MPa, 0.06MPa, 0.07MPa or the like.
Similarly, the temperature in the first reactive distillation column 200 may be 130 ℃, 135 ℃, 145 ℃, 150 ℃ or the like.
In the above examples, the reaction temperature in the lactide synthesis reactor 300 may be 165 ℃, 175 ℃, 185 ℃, 195 ℃ or the like, the reaction pressure may be 0.03MPa, 0.04MPa, 0.06MPa, 0.07MPa or the like, and the reaction temperature is 190 ℃ and the pressure is 0.05MPa most preferably.
Similarly, the temperature of the lactide deep synthesis section 420 in the second reactive distillation column 400 may be 175 ℃, 180 ℃, 185 ℃, 195 ℃ or the like, and the reaction temperature is preferably 190 ℃ and the pressure is a negative pressure condition.
In addition, the tower heights, tower diameters, the numbers of tower plates and the tower section dividing modes of the first reactive distillation tower 200 and the second reactive distillation tower 400 can be adjusted according to actual requirements.
The working process and principle of the intelligent reaction system for lactic acid oligomerization according to the present invention are briefly described as follows:
after nitrogen purges pipelines of the lactic acid oligomerization reaction kettle 100, the first reaction rectifying tower 200, the lactide synthesis kettle 300 and the second reaction rectifying tower 400 and the interiors of the reaction kettles, the lactic acid raw materials are introduced into the lactic acid oligomerization reaction kettle 100 according to the proportion, stirring is carried out by starting stirring equipment of the lactic acid oligomerization reaction kettle 100, the reaction temperature is controlled at 140 ℃, the reaction pressure is 0.05MPa, and oligomers are gradually gathered at the bottom of the kettle along with the reaction.
One part of the oligomers generated at the bottom of the reaction kettle is conveyed into the first reactive distillation column 200 through a pipeline, the other part of the oligomers is circulated through the first circulating pipeline 150, the first circulating pipeline 150 is provided with a first heat exchanger 160, and the oligomers flowing through the first circulating pipeline 150 are heated and cooled to achieve the effect of controlling the reaction temperature in the lactic acid oligomerization reaction kettle.
The generated oligomer and unreacted raw materials enter the deep oligomerization dehydration reaction section 220 from the middle section of the first reactive distillation tower 200 through a pipeline to carry out deep oligomerization dehydration reaction. The operation pressure of the first reactive distillation column 200 is a negative pressure condition, and the temperature at the bottom of the column is about 150 ℃.
After deep oligomerization and dehydration reaction, the generated oligomers P1-P30 with high boiling point gradually gather at the bottom of the tower, volatile components of lactic acid, a small amount of oligomers and water are separated to the top of the tower through a rectifying section 210, one part of the volatile components of lactic acid and a small amount of oligomers and water are refluxed through a first top condenser 270, the other part of the volatile components of lactic acid and a small amount of oligomers and water are discharged through the first top condenser 270, and the volatile components of lactic acid and the small amount of oligomers.
In addition, unreacted raw materials and other substances are still in the oligomer at the bottom of the tower after the deep oligomerization dehydration reaction, and after part of the oligomer passes through a first tower reboiler 250 of the tower kettle, the oligomer is subjected to cyclic deep reaction rectification at the tower kettle, and the other part of oligomer is extracted and post-treated to be used as a subsequent synthetic raw material of lactide.
The first kettle reboiler 250 is a falling film reboiler, and the material enters from the top of the first kettle reboiler 250 and returns to the first reactive distillation column 200 from the bottom of the first kettle reboiler 250 after being evaporated.
Introducing the oligomer extracted from the reboiler 250 of the first tower kettle into the lactide synthesis kettle 300, simultaneously starting the stirring device of the lactide synthesis kettle 300 to stir, controlling the reaction temperature at 240 ℃ and the reaction pressure at 0.05MPa, and gradually gathering the lactide and a small amount of oligomer (mainly dimeric lactic acid) at the bottom of the kettle along with the reaction.
The temperature of the material flowing out of the lactide synthesis kettle 300 is 160-one-material 240 ℃, the pressure is 0.05MPa, the main components are lactide, unreacted raw materials, oligomers, catalysts and the like, the material enters a second reactive distillation column from a second reaction product outlet 330 at the bottom of the kettle, and the second reactive distillation column is sequentially divided into four parts from top to bottom: a light components separation section 411, a product separation section 412, a lactide depth synthesis section 420, and a heavy components separation section 413. The deep lactide synthesizing section 420 in the middle of the second reactive rectifying tower is provided with catalyst stuffing and connected with a pump and a heat exchanger to realize the circulation of the reaction material. The esterification reaction takes place at a temperature of 190 ℃ and under negative pressure.
The oligomer is thermally decomposed and broken to form lactide and lactic acid, and the mixture which is not completely reacted is extracted by a mixture side-line extraction unit 470 below the lactide deep synthesis section 420, heated by a third heat exchanger 450 and then re-enters the second reactive distillation column for further reaction.
Heavy component lactide and polycondensate in the reaction product enter the lower section of the second reactive distillation column 400, namely a heavy component separation section 413 for separating lactide and polycondensate (mainly dimeric lactic acid), a second column bottom reboiler 460 and a pump are arranged at the column bottom, the mixture at the column bottom is pumped above the filler at the lower section of the column for further separation, and meanwhile, the separated polycondensate enters a post-treatment working section.
Light components of lactic acid, water, lactide and oligomers in the reaction product enter the upper section of the second reactive distillation column 400, and separation of the product from the water, lactic acid and oligomers is realized through the product separation section 412 and the light component separation section 411. The temperature of the distillate at the top of the tower is 6.6 ℃, the pressure is 0.0006MPa, the main components are water, lactic acid and oligomer, and the distillate enters a post-treatment working section. The lactide product is withdrawn from the product sidedraw unit 480 below the product separation section 412 at a temperature of 190 ℃ under negative pressure.
Finally, the materials (mainly comprising water, lactic acid and oligomers) from the top of the first reactive distillation column 200, the top of the second reactive distillation column 400 and the bottom of the column are introduced into the depolymerization reactive distillation column 500 for reactive distillation, the high polymers from the first and second reactive distillation columns are decomposed in the depolymerization reactive distillation column 500, and the main product after depolymerization, namely lactic acid, can be returned to the lactic acid oligomerization reaction kettle 100 for reuse, the temperature of the depolymerization reaction is between 100 and 180 ℃, preferably between 140 and 170 ℃, most preferably about 150 ℃, and the operation is carried out under normal pressure or pressurization.
The top of the depolymerization reaction rectifying tower 500 is provided with a third top condenser 520, the tower kettle is provided with a third tower kettle reboiler 510, the third tower kettle reboiler 510 is a falling film reboiler, after reboiling treatment by the tower kettle reboiler, one part returns to the tower kettle, and the other part enters the lactic acid oligomerization reaction kettle 100 from the lactic acid inlet 110 through a pipeline to be used as a raw material.
For the convenience of control, a valve is correspondingly arranged on a pipeline of the reaction process system, the type of the valve can be a ball valve, a butterfly valve and the like, and an electromagnetic valve can also be adopted as an important control point.
The above steps are repeated circularly to make the whole intelligent reaction system run stably.
By adopting the preparation method of the lactide, the conversion rate of the raw materials is increased by 10-20% compared with the prior art, the yield of the lactide is correspondingly improved compared with the prior art, and the effects of reducing energy consumption and improving the conversion rate of the raw materials and the yield of products can be achieved.
Compared with the intelligent reaction system for preparing lactide in the prior art, the intelligent reaction system has the advantages of fewer equipment components, small occupied area, low energy consumption, low cost, controllable reaction and high raw material conversion rate, provides an intelligent reaction system with stronger operability for the subsequent preparation of lactide, and is worthy of wide popularization and application.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. An intelligent reaction system for producing lactide from lactic acid, comprising: the device comprises a lactic acid oligomerization reaction kettle, a first reaction rectifying tower, a lactide synthesis kettle and a second reaction rectifying tower which are connected in sequence;
the first reactive distillation tower comprises a first tower kettle reboiler, a purification section and a deep oligomerization dehydration reaction section, wherein the purification section and the deep oligomerization dehydration reaction section are arranged from top to bottom, a first feed inlet is formed in a tower section between the purification section and the deep oligomerization dehydration reaction section and used for feeding a product of the lactic acid oligomerization reaction kettle into the first reactive distillation tower, a first discharge outlet is formed in a tower kettle of the first reactive distillation tower, a part of the product discharged from the first discharge outlet is heated by the first tower kettle reboiler, and then returns to the deep oligomerization dehydration reaction section, and the other part of the product is directly collected;
the second reactive distillation tower comprises a distillation section and a lactide deep synthesis section, the distillation section comprises a light component separation section for separating water, lactic acid and a small amount of oligomers, a product separation section for separating lactide products and a heavy component separation section for separating oligomers, the light component separation section and the product separation section are arranged at the upper part of the lactide deep synthesis section from top to bottom, the heavy component separation section is arranged at the lower part of the lactide deep synthesis section, and a third feed inlet is arranged on a tower section between the product separation section and the lactide deep synthesis section and used for introducing products of the lactide synthesis kettle into the second reactive distillation tower;
the intelligent system comprises an online acquisition module, a feedback control module and an intelligent adjustment module, wherein the online acquisition module sends acquired operation parameters of the reaction system to the feedback control module, and the feedback control module sends set parameters to the intelligent adjustment module after analyzing data so as to adjust the operation parameters of the reaction system;
preferably, the intelligent adjustment module comprises a lactic acid oligomerization reaction kettle pressure control unit, a lactic acid oligomerization reaction kettle temperature control unit, a lactide synthesis kettle pressure control unit and a lactide synthesis kettle temperature control unit;
preferably, the online acquisition module is connected with the feedback control module in a wireless manner.
2. The intelligent reaction system according to claim 1, further comprising a depolymerization rectification column for depolymerization and rectification of the material from the top of the first reactive rectification column, the top of the second reactive rectification column and the bottom of the column.
3. The intelligent reaction system according to claim 1, wherein the first tower reboiler is a falling film reboiler, a second feed inlet is arranged at the top of the falling film reboiler, a second discharge outlet is arranged at the bottom of the falling film reboiler, the second feed inlet is communicated with the first discharge outlet, a part of the substances discharged from the second discharge outlet is introduced into the deep oligomerization dehydration reaction section, and the other part of the substances is directly collected;
preferably, a first conveying pump is arranged on a pipeline which is communicated with the second feeding hole and the first discharging hole.
4. The intelligent reaction system of claim 1, wherein a raw material inlet and a first reaction product outlet are arranged on the lactic acid oligomerization reaction kettle, the raw material inlet comprises a lactic acid inlet, and the first reaction product outlet is arranged at the bottom of the lactic acid oligomerization reaction kettle;
and the first reaction product outlet is communicated with a first feed inlet on the first reactive distillation tower.
5. The intelligent reaction system of claim 4, wherein a second delivery pump is disposed on the conduit communicating the first reaction product outlet with the first feed inlet.
6. The intelligent reaction system according to claim 5, wherein a first circulation pipeline is further arranged on the pipeline of the first reaction product outlet communicated with the first feed inlet, so as to return a part of the substances from the first reaction product outlet to the lactic acid oligomerization reaction kettle, and a first heat exchanger is arranged on the first circulation pipeline;
preferably, the top of the first reactive distillation column is provided with a first overhead condenser for condensing and refluxing water, lactic acid and oligomers distilled from the top of the column.
7. The intelligent reaction system according to any one of claims 1 to 6, wherein a product side draw unit is arranged between the lactide depth synthesis section and the product separation section, and is connected with a third discharge hole;
preferably, a mixture side-draw unit is arranged between the lactide deep synthesis section and the heavy component separation section, the mixture side-draw unit is connected with a third heat exchanger, and the mixture heated by the third heat exchanger enters the second reactive distillation column again;
preferably, the product sidedraw unit and the mixture sidedraw unit are each comprised of a tray with a plurality of catch basins;
preferably, the third heat exchanger is a falling film heat exchanger, a fourth feed inlet is formed in the top of the third heat exchanger, a fourth discharge outlet is formed in the bottom of the third heat exchanger, the fourth feed inlet is communicated with the mixture side draw unit, and a substance discharged from the fourth discharge outlet is introduced between the lactide deep synthesis section and the product separation section in the second reactive distillation tower.
8. The intelligent reaction system according to any one of claims 1 to 6, wherein the second reactive distillation column further comprises a second kettle reboiler, the second kettle reboiler is a falling film reboiler, a fifth feed inlet is arranged at the top of the falling film reboiler, a fifth discharge outlet is arranged at the bottom of the falling film reboiler, the fifth feed inlet is communicated with the kettle of the second reactive distillation column, and a part of the substance discharged from the fifth discharge outlet is introduced into the second reactive distillation column, and the other part is directly collected;
preferably, a raw material inlet and a second reaction product outlet are formed in the lactide synthesis kettle, the raw material inlet comprises an oligomer inlet and an esterification catalyst inlet, the second reaction product outlet is formed in the bottom of the lactide synthesis kettle, and the second reaction product outlet is communicated with a third feeding port in the second reaction rectifying tower.
9. The intelligent reaction system according to claim 8, wherein a second circulation pipeline is further arranged on a pipeline of the second reaction product outlet communicated with the third feed inlet, so as to return a part of substances discharged from the second reaction product outlet to the lactide synthesis kettle, and a second heat exchanger is arranged on the second circulation pipeline;
and a second tower top condenser is arranged at the tower top of the second reactive distillation tower and is used for condensing and refluxing water, lactic acid and oligomers distilled from the tower top.
10. A method for preparing lactide using the intelligent reaction system of any one of claims 1 to 9, comprising the steps of:
(A) carrying out oligomerization reaction and deep dehydration and rectification on lactic acid to generate oligomer;
(B) the oligomer and a catalyst are subjected to esterification and deep reaction rectification to obtain lactide and lactic acid;
(C) in the operation process of the reaction system, the online acquisition module sends the acquired operation parameters of the reaction system to the feedback control module, and the feedback control module sends the set parameters to the intelligent adjustment module after analyzing the data so as to adjust the operation parameters of the reaction system.
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| US5142023A (en) * | 1992-01-24 | 1992-08-25 | Cargill, Incorporated | Continuous process for manufacture of lactide polymers with controlled optical purity |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5142023A (en) * | 1992-01-24 | 1992-08-25 | Cargill, Incorporated | Continuous process for manufacture of lactide polymers with controlled optical purity |
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