CN211384959U - Reaction system for preparing lactide from lactic acid - Google Patents
Reaction system for preparing lactide from lactic acid Download PDFInfo
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- CN211384959U CN211384959U CN201922069340.0U CN201922069340U CN211384959U CN 211384959 U CN211384959 U CN 211384959U CN 201922069340 U CN201922069340 U CN 201922069340U CN 211384959 U CN211384959 U CN 211384959U
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Abstract
The utility model provides a reaction system for preparing lactide by lactic acid. The reaction system 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 the first feed inlet is used for introducing products of the lactic acid oligomerization reaction kettle into the first reactive distillation tower. The utility model provides a reaction system has optimized reaction route through unifying rectification and degree of depth synthesis reaction and is integrated, has improved reaction separation efficiency, and then has improved the quality and the yield of product, has also played save equipment cost in addition, the area's of saving equipment effect.
Description
Technical Field
The utility model relates to a lactide preparation field particularly, relates to a reaction system by lactic acid preparation lactide.
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;
(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.
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 view of this, the present invention is especially provided.
SUMMERY OF THE UTILITY MODEL
The first purpose of the utility model is to provide a reaction system for preparing lactide by 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 existence of water to dilute the reaction materials, influences the reaction process, and further improves the quality and yield of the oligomerization products;
meanwhile, the rectification separation and the lactide reaction synthesis are integrated, the reaction residence time is shortened, the generation of byproducts is reduced, and the generated lactide can be rapidly purified and separated to promote the esterification reaction to be carried out in the positive direction, so that the quality and the yield of the product are improved.
The second objective of the present invention is to provide a method for preparing lactide by using the above reaction system, the prepared lactide product has good quality and high yield, and the conversion rate of raw material is also improved to a certain extent.
In order to realize the above purpose of the utility model, the following technical scheme is adopted:
the utility model provides a reaction system for preparing lactide by lactic acid, include: 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 tower sections of the first reactive distillation tower and the second reactive distillation tower are formed by randomly combining a plurality of tower plates and fillers.
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.
The utility model discloses a solve above-mentioned technical problem, specially set up the oligomeric dehydration reaction section of degree of depth in first reaction rectifying column, not only compensatied lactic acid oligomerization reation kettle incomplete reaction problem, moreover in first reaction rectifying column after oligomerization, in time got rid of moisture through the purification section, avoided the existence of water to dilute the reaction material, the problem of influence reaction process takes place, and then improved the quality and the yield of oligomerizing the product.
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 P1-P30, i.e., P15 indicates polymerization between 15 lactic acid molecules, i.e., polymerization between 1 and 30 polymerization degrees.
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 polycondensate, 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 after depolymerization reaction and rectification are carried out by the depolymerization reaction rectifying tower, substances accumulated 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 utility model discloses a so select the type of first tower cauldron reboiler for falling liquid film formula reboiler, because this type's reboiler compares with ordinary reboiler type, and the film is formed on the pipe wall, and heat exchange efficiency is very high, and the hold-up time is short, is difficult to the coking, and the material of having avoided the tower cauldron takes place the polymerization and has the accessory substance to generate. 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 utility model discloses an oligomerization in lactic acid oligomerization reation kettle can realize the polymerization formation oligomer between the lactic acid.
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 the scheme that further can carry out, in the utility model discloses an in the second reaction rectifying column, lactide degree of depth synthesis section with be provided with product side draw unit between the product separation section, product side draw unit is connected with the third discharge gate.
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 separates the formation of lactide and lactic acid in the lactide degree of depth synthesis section pyrolysis broken chain formation in the second reaction rectifying column, and after the pyrolysis broken chain reaction, after the mixture that does not react completely was through the mixture side extraction unit side extraction of lactide degree of depth synthesis section below, got back to the second reaction rectifying column again after the third heat exchanger heating, separated lactide and oligomer through heavy component segregant section, the utility model discloses in, to the mode of taking out unit and heat exchanger with the mixture side extraction unit and making up, improved the conversion of raw materials conscientiously, also corresponding improvement rectification efficiency.
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 utility model discloses a so select the type of third heat exchanger and tower cauldron reboiler for falling liquid film formula, because the heat exchanger of this type compares with ordinary heat exchanger type, can realize forming a film on the pipe wall, heat exchange efficiency is very high, and the dwell time is short, is difficult to the coking, and the material of having avoided the tower cauldron takes place the polymerization and has the accessory substance to generate. 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 known in the art and is not described in detail in the utility model.
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.
The utility model discloses in, the type of heat exchanger does not have specific restriction, can be for floating head heat exchanger, fixed tube sheet heat exchanger, U-shaped tube sheet heat exchanger, plate heat exchanger etc..
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 utility model is preferably a paddle stirrer with three flat paddles, because the relative stirring of the stirrer with the structure is more uniform.
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 solution, a transfer pump may be provided on the corresponding line of the entire 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 utility model also provides a method for above-mentioned reaction system preparation lactide, including following step:
(A) carrying out oligomerization reaction and deep dehydration and rectification on lactic acid to generate oligomer;
(B) and esterifying the oligomer and a catalyst, and performing deep reaction and rectification to obtain lactide and lactic acid.
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 ℃, 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 product quality of the lactide prepared by lactic acid of the utility model is good, the yield is high, the conversion rate of raw materials is at least improved by 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 beneficial effects of the utility model reside in that:
(1) the reaction system for preparing lactide of the utility model integrates rectification and reaction synthesis, optimizes the reaction route, improves the reaction separation efficiency, and further improves the quality and yield of the product;
(2) the reaction system for preparing lactide has simple structure and less three wastes, realizes the full recycling of raw materials and occupies small area;
(3) the utility model realizes the function 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 utility model discloses a reaction system has realized the effect with the timely desorption of water in the reaction system, avoids the existence of water to dilute reaction material to reach the purpose with the lactide rapid purification separation that generates in the reaction system simultaneously, promote the esterification reaction and go on toward the positive direction, and then improved the quality and the yield of lactide product, also corresponding improvement the conversion ratio of raw materials.
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 a reaction system for preparing lactide from lactic acid according to an embodiment of the present invention.
Description of reference numerals:
a 100-lactic acid oligomerization reaction kettle; a 110-lactic acid inlet;
130-a first reaction product outlet; 140-a second delivery pump;
150-a 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-third overhead condenser.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings and 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. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to 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", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific 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 is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; 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 meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In order to clarify the technical solution of the present invention, the following description is made in the form of specific embodiments.
Examples
Referring to fig. 1, for the reaction system for preparing lactide from lactic acid of the embodiment of the present invention, it includes two main bodies of lactic acid oligomerization reaction kettle 100, first reactive distillation column 200, lactide synthesis kettle 300 and second reactive distillation column 400 connected in sequence, and second reactive distillation column 400 includes distillation section 410 and 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.
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 oligomeric reaction system of lactic acid of 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 reaction system run smoothly.
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, and the yield of the lactide is correspondingly improved compared with the prior art, so that the effects of reducing the energy consumption and improving the conversion rate of the raw materials and the yield of products can be achieved.
Compare with the reaction system of prior art's lactide preparation, the utility model discloses a reaction system equipment subassembly is few, area is little, the energy consumption is low, with low costs, the reaction is controllable, and the raw materials conversion rate is high, provides a stronger reaction system of operability for follow-up preparation lactide, is worth extensively popularizing and applying.
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; although the present invention has been described in detail with reference to the foregoing embodiments, it should 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; such modifications and substitutions do not depart from the spirit and scope of the present invention.
Claims (10)
1. A 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 tower sections of the first reactive distillation tower and the second reactive distillation tower are formed by randomly combining a plurality of tower plates and fillers.
2. The reaction system of claim 1, further comprising a depolymerization rectification column for depolymerization and rectification of 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 reaction system of claim 1, wherein the first tower reboiler is a falling film reboiler, the top of the falling film reboiler is provided with a second inlet, the bottom of the falling film reboiler is provided with a second outlet, the second inlet is communicated with the first outlet, and a part of the substance from the second outlet is introduced into the deep oligomerization and dehydration reaction section, and the other part is directly collected.
4. The 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 reaction system of claim 4 wherein a second transfer pump is provided in the conduit communicating the first reaction product outlet with the first feed port.
6. The reaction system of claim 5, wherein a first circulation pipeline is further arranged on the pipeline of the first reaction product outlet communicated with the first feeding hole, 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.
7. The reaction system of 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 the product side draw unit is connected with a third discharge hole.
8. The 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.
9. The reaction system of claim 8, wherein 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, 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 column.
10. The reaction system according to claim 9, 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 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.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112679465A (en) * | 2021-01-19 | 2021-04-20 | 万华化学(四川)有限公司 | Method for preparing lactide by coupling reaction rectification |
| CN112876453A (en) * | 2021-01-29 | 2021-06-01 | 南京华基塔业有限公司 | Reaction system and method for preparing lactide from lactic acid |
| CN112876452A (en) * | 2021-01-19 | 2021-06-01 | 万华化学(四川)有限公司 | Preparation method and reaction device of lactide |
| CN112898266A (en) * | 2021-01-29 | 2021-06-04 | 安徽丰原生物技术股份有限公司 | Device and method for industrially preparing L-lactide |
| WO2022155762A1 (en) * | 2021-01-19 | 2022-07-28 | 万华化学(四川)有限公司 | Preparation method for lactide and reaction device |
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2019
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112679465A (en) * | 2021-01-19 | 2021-04-20 | 万华化学(四川)有限公司 | Method for preparing lactide by coupling reaction rectification |
| CN112876452A (en) * | 2021-01-19 | 2021-06-01 | 万华化学(四川)有限公司 | Preparation method and reaction device of lactide |
| WO2022155762A1 (en) * | 2021-01-19 | 2022-07-28 | 万华化学(四川)有限公司 | Preparation method for lactide and reaction device |
| CN112679465B (en) * | 2021-01-19 | 2024-06-25 | 万华化学(四川)有限公司 | Method for preparing lactide by coupling reaction rectification |
| CN112876452B (en) * | 2021-01-19 | 2024-08-02 | 万华化学(四川)有限公司 | Preparation method of lactide and reaction device |
| CN112876453A (en) * | 2021-01-29 | 2021-06-01 | 南京华基塔业有限公司 | Reaction system and method for preparing lactide from lactic acid |
| CN112898266A (en) * | 2021-01-29 | 2021-06-04 | 安徽丰原生物技术股份有限公司 | Device and method for industrially preparing L-lactide |
| CN112898266B (en) * | 2021-01-29 | 2021-11-19 | 安徽丰原生物技术股份有限公司 | Device and method for industrially preparing L-lactide |
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