Lactide preparation device and preparation method

Abstract

The invention provides a lactide preparation device and method, and belongs to the field of degradable materials, the lactide preparation device comprises a dehydration reactor, a pre-polycondensation reactor, a polycondensation reactor, a depolymerization reactor, a lactide rectifying tower and a hydrolysis reactor; the dehydration reactor is used for treating raw materials to form a liquid oligomer; the pre-polycondensation reactor is used for treating an oligomer to form a prepolymer; the polycondensation reactor is at least used for treating low polymers, and the polymer forming depolymerization reactor is at least used for treating polymers and forming high polymers and gaseous depolymerization steam; the lactide rectifying tower is used for treating the depolymerization steam to form lactide; the hydrolysis reactor is used for treating a high polymer to form a hydrolysis product, and the hydrolysis reactor conveys the hydrolysis product to the pre-polycondensation reactor through the liquid-phase material outlet. Not only can continuous production of lactide be realized, but also high-purity lactide can be produced.

Description

Technical Field

[0001] The present application relates to the field of biodegradable materials, and in particular to a lactide preparation device and method. Background Art

[0002] Polylactic acid, as a biodegradable material, has excellent biocompatibility and good mechanical properties, and is widely used in packaging materials and biomedicine.

[0003] High-molecular-weight polylactic acid (PLA) cannot be obtained through direct polymerization of lactic acid but only through the ring-opening polycondensation of lactide. The chemical and optical purity of lactide significantly influence the molecular weight and molecular weight distribution of PLA produced by ring-opening polymerization. Ensuring extremely high chemical and optical purity of the lactide monomer is crucial for producing high-molecular-weight, fiber-grade PLA. Therefore, achieving high-purity lactide production and improving raw material yields have long been areas of research in this field. Summary of the Invention

[0004] The embodiments of the present application provide a lactide preparation device and preparation method to solve the problems of low lactide preparation efficiency and low purity of the prepared lactide.

[0005] In a first aspect, this embodiment provides a lactide production apparatus, comprising a dehydration reactor, a pre-polycondensation reactor, a polycondensation reactor, a depolymerization reactor, a lactide distillation column, and a hydrolysis reactor;

[0006] The dehydration reactor is at least used to process the raw materials to form liquid oligomers;

[0007] The material inlet of the pre-polycondensation reactor is connected to the liquid material outlet of the dehydration reactor, and the pre-polycondensation reactor is at least used to process the oligomer to form a liquid prepolymer;

[0008] The material inlet of the polycondensation reactor is connected to the liquid material outlet of the pre-polycondensation reactor, and the polycondensation reactor is at least used to process the prepolymer to form a liquid polymer;

[0009] The material inlet of the depolymerization reactor is connected to the liquid material outlet of the polycondensation reactor, and the depolymerization reactor is at least used to process the oligomers to form liquid polymers and gaseous depolymerization steam;

[0010] The material inlet of the lactide distillation tower is in communication with the gas phase material outlet of the depolymerization reactor, and the lactide distillation tower is at least used to process the depolymerization steam to form lactide;

[0011] The material inlet of the hydrolysis reactor is connected to the liquid material outlet of the depolymerization reactor. The hydrolysis reactor is at least used to process the polymer to form a hydrolysis product. The hydrolysis reactor transports the hydrolysis product to the pre-condensation reactor through the liquid material outlet.

[0012] In some embodiments of the present application, a hydrolyzed liquid delivery pump is further included, wherein the feed end of the hydrolyzed liquid delivery pump is connected to the liquid phase material outlet of the hydrolysis reactor, and the discharge end of the hydrolyzed liquid delivery pump is connected to the material inlet of the pre-condensation reactor.

[0013] In some embodiments of the present application, an oligomer pump and a reboiler are further included;

[0014] The feed end of the oligomer pump is communicated with the liquid phase material outlet of the dehydration reactor, and the discharge end of the oligomer pump is communicated with the material inlet of the pre-condensation reactor;

[0015] The discharge end of the oligomer pump is reused to communicate with the material inlet of the reboiler, and the material outlet of the reboiler is communicated with the material inlet of the dehydration reactor.

[0016] In some embodiments of the present application, the number of the lactide distillation towers is set to be multiple, and the multiple lactide distillation towers include a first lactide distillation tower and a second lactide distillation tower;

[0017] The material inlet of the first lactide distillation tower is connected to the gaseous material outlet of the depolymerization reactor, the middle fraction outlet of the first lactide distillation tower is connected to the material inlet of the second lactide distillation tower, and the liquid material outlet of the second lactide distillation tower is used to form the lactide.

[0018] In some embodiments of the present application, a spray collection unit is further included; the spray collection unit includes a spray tank, a liquid seal tank, a spray liquid circulation pump and a cooler;

[0019] The spray tank is connected to the gas phase material outlet of the polycondensation reactor, and the material outlet of the spray tank is connected to the liquid seal tank, and the liquid seal tank receives the desalted water containing oligomers after spraying and stabilizes the system pressure;

[0020] The spray liquid circulation pump transports the desalted water in the liquid seal tank to the cooler, and the cooler cools the desalted water and transports the cooled desalted water into the spray tank.

[0021] In some embodiments of the present application, the dehydration reactor processes the feedstock to form gaseous esterification steam;

[0022] The dehydration reactor is provided with a first dehydration tower; the first dehydration tower is connected to the gas phase material outlet of the dehydration reactor, and the first dehydration tower is at least used to process the esterification steam to form lactic acid liquid, and return the lactic acid liquid to the dehydration reactor.

[0023] In some embodiments of the present application, the precondensation reactor is at least used to process the oligomer to form gaseous precondensation steam;

[0024] The precondensation reactor is provided with a second dehydration tower; the second dehydration tower is connected to the gas phase material outlet of the precondensation reactor, and the second dehydration tower is at least used to process the precondensation steam to form lactic acid liquid, and return the lactic acid liquid to the precondensation reactor.

[0025] In some embodiments of the present application, a condensation unit and a vacuum unit are further included;

[0026] The condensing unit is used to process the overhead steam from the dehydration reactor, the pre-condensation reactor, the depolymerization reactor and the lactide distillation tower to form condensate and non-condensable gas;

[0027] The vacuum unit obtains the non-condensable gas from the condensation unit and the spray collection unit.

[0028] In a second aspect, the present invention provides a method for preparing lactide, comprising:

[0029] Processing the feedstock through a dehydration reactor to form oligomers;

[0030] processing the oligomer through a precondensation reactor to form a prepolymer;

[0031] processing the prepolymer through a polycondensation reactor to form a polymer;

[0032] processing the polymer through a depolymerization reactor to form high polymers and depolymerization vapors;

[0033] processing the depolymerization vapor through a lactide distillation column to form lactide;

[0034] The high polymer is treated in a hydrolysis reactor to form a hydrolyzate, and the hydrolyzate is returned to the dehydration reactor as the raw material to participate in the reaction.

[0035] In some embodiments of the present application, after the oligomers are formed in the dehydration reactor, the method includes:

[0036] delivering a first portion of the oligomer to the pre-polycondensation reactor via an oligomer pump;

[0037] delivering a second portion of the oligomers to a reboiler via the oligomer pump;

[0038] The second portion of the oligomers is processed through the reboiler and returned to the dehydration reactor as the raw material to participate in the reaction.

[0039] The embodiments of the present application provide a lactide preparation apparatus and preparation method, which can achieve not only continuous lactide production but also high-purity lactide production by continuously adding reaction raw materials into a dehydration reactor, a pre-polycondensation reactor, a polycondensation reactor, a depolymerization reactor, and a lactide distillation tower that are interconnected in sequence. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0041] Figure 1 A schematic diagram of a lactide production device provided in an embodiment of the present application;

[0042] Figure 2 A schematic diagram of a method for preparing lactide provided in an embodiment of the present application;

[0043] Figure 3 This is a schematic diagram of a method for preparing lactide provided in an embodiment of the present application, wherein a dehydration reactor is used after oligomers are formed.

[0044] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0045] 100, dehydration reactor; 110, oligomer pump; 120, reboiler; 130, first dehydration tower;

[0046] 200, pre-polycondensation reactor; 210, second gas dehydration tower;

[0047] 300, polycondensation reactor; 310, polymer delivery pump;

[0048] 400, depolymerization reactor; 410, depolymerization liquid delivery pump;

[0049] 500a, a first lactide distillation tower; 500b, a second lactide distillation tower;

[0050] 600, hydrolysis reactor; 610, hydrolyzate delivery pump;

[0051] 700, spray capture unit; 710, spray tank; 720, liquid seal tank; 730, spray liquid circulation pump; 740, cooler;

[0052] 800a, first condensing unit; 800b, second condensing unit; 800c, third condensing unit; 800d, fourth condensing unit; 810a, first condenser; 810b, second condenser; 810c, third condenser; 810d, fourth condenser; 820a, first condensate collecting tank; 820b, second condensate collecting tank; 820c, third condensate tank; 820d, fourth condensate collecting tank;

[0053] 900, vacuum unit; 910, first Roots pump; 920, second Roots pump; 930, third Roots pump; 940, fourth Roots pump; 950, liquid ring pump.

[0054] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0055] As mentioned in the background, high-molecular-weight polylactic acid (PLA) cannot be obtained directly through the polymerization of lactic acid but only through the ring-opening polycondensation of lactide. Therefore, the synthesis of lactide has constrained the development of PLA. The chemical and optical purity of lactide significantly influence the molecular weight and molecular weight distribution of PLA produced by ring-opening polymerization.

[0056] In the prior art, the conversion rate and yield of the lactide preparation device are not high, resulting in the inability to efficiently prepare high-molecular-weight fiber-grade polylactic acid using its products. In view of this, the embodiment of the present application provides a lactide preparation device that can continuously add reaction raw materials into a dehydration reactor, a pre-condensation reactor, a condensation reactor, a depolymerization reactor, and a lactide distillation tower that are connected in sequence, thereby not only achieving continuous production of lactide, but also producing high-purity lactide.

[0057] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0058] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0059] refer to Figure 1 An embodiment of the present application provides a lactide preparation device, including a dehydration reactor 100, a pre-polycondensation reactor 200, a polycondensation reactor 300, a depolymerization reactor 400, a lactide distillation tower and a hydrolysis reactor 600.

[0060] The dehydration reactor 100 is at least used to process the raw materials to form liquid oligomers.

[0061] The material inlet of the pre-polycondensation reactor 200 is connected to the liquid material outlet of the dehydration reactor 100. The pre-polycondensation reactor 200 is at least used to process oligomers to form liquid prepolymers.

[0062] The material inlet of the polycondensation reactor 300 is connected to the liquid material outlet of the pre-polycondensation reactor 200. The polycondensation reactor 300 is at least used to process the prepolymer to form a liquid polymer.

[0063] The material inlet of the depolymerization reactor 400 is connected to the liquid material outlet of the polycondensation reactor 300. The depolymerization reactor 400 is at least used to process oligomers to form liquid polymers and gaseous depolymerization steam.

[0064] The material inlet of the lactide distillation tower is connected to the gas phase material outlet of the depolymerization reactor 400. The lactide distillation tower is at least used to process the depolymerization steam to form lactide.

[0065] The material inlet of the hydrolysis reactor 600 is connected to the liquid material outlet of the depolymerization reactor 400. The hydrolysis reactor 600 is at least used to process the polymer to form a hydrolysis product. The hydrolysis reactor 600 transports the hydrolysis product to the pre-condensation reactor 200 through the liquid material outlet.

[0066] It's important to understand that polymers are macromolecules formed by chemically bonding many repeating monomer units. They typically have high molecular weights and complex structures. Oligomers, on the other hand, are molecules composed of relatively few monomer units, typically 2 to 10. Compared to polymers, oligomers have lower molecular weights and simpler structures.

[0067] During use, if Figure 1 As shown, lactic acid is used as the reaction raw material and enters the material inlet of the dehydration reactor 100 along the direction a, and gradually reacts to generate esterification steam and liquid oligomers. The oligomers are output through the liquid material outlet of the dehydration reactor 100 and enter the precondensation reactor 200 through the material inlet of the precondensation reactor 200. At the same time, a composite catalyst is added, and the composite catalyst solution is added into the cavity of the precondensation reactor 200 along the direction e to react to generate precondensation steam and prepolymer.

[0068] The composite catalyst is composed of a tin compound and a zinc compound. The tin compound of the composite catalyst includes at least one of stannous octoate, stannous acetate, stannous oxalate, dibutyltin, dibutyltin dilaurate, stannous chloride, and stannous oxide, with the tin addition amount being 20 to 70 ppm. The zinc compound of the composite catalyst includes at least one of zinc oxide, zinc chloride, zinc acetate, zinc decanoate, and zinc octoate, with the zinc addition amount being 10 to 30 ppm.

[0069] The prepolymer is output from the material outlet of the prepolymer reactor 200, flows into the condensation reactor 300, passes through multiple chambers in the condensation reactor 300 in sequence, reacts to generate condensation steam and polymer, and the polymer is output from the liquid phase material of the condensation reactor 300 and enters the depolymerization reactor 400 through the material inlet of the depolymerization reactor 400.

[0070] The polymer undergoes a depolymerization reaction in the depolymerization reactor 400, forming a small amount of liquid polymer and a large amount of gaseous depolymerization steam. The depolymerization steam containing lactide is output from the gas phase material outlet of the depolymerization reactor 400 and enters the material inlet of the lactide distillation tower for purification to obtain high-purity lactide.

[0071] The bottom of the depolymerization reactor 400 is a high-molecular-weight polymer, which flows out from the material outlet at the bottom of the depolymerization reactor 400 and is sent to the material inlet of the hydrolysis reactor 600, where it undergoes a hydrolysis reaction under high temperature and high pressure to generate oligomers and a small amount of lactic acid, which then flows out from the material outlet of the hydrolysis reactor 600 and re-enters the pre-condensation reactor 200 for reaction.

[0072] In some possible implementations, the pre-polycondensation reactor 200 is provided with a circulating material inlet for liquid reflux. The gas phase outlet and the circulating material inlet of the pre-polycondensation reactor 200 may be the same or different.

[0073] Among them, the condensation reactor 300 includes at least three interconnected cavities. By setting up multiple cavities, the reaction raw materials can flow in the condensation reactor 300 in the form of plug flow, which is conducive to the progress of the condensation reaction, thereby increasing the degree of polymerization and achieving the molecular weight required for depolymerization.

[0074] A polymer delivery pump 310 is provided between the liquid phase outlet of the polycondensation reactor 300 and the material inlet of the depolymerization reactor 400 . The polymer delivery pump 310 can improve the material delivery efficiency.

[0075] Illustratively, each cavity of the polycondensation reactor 300 is independently provided with a heating unit.

[0076] In some possible embodiments, the depolymerization reactor 400 is a scraped film structure, and the depolymerization reactor 400 is heated in sections from top to bottom to control different temperatures.

[0077] The upper part of the depolymerization reactor 400 is a liquid distributor, and the middle part is a scraper assembly. The scraper drive is installed on the top of the depolymerization reactor 400; the bottom of the depolymerization reactor 400 is a depolymerization liquid receiving assembly; the reactor scraper scrapes the polymer flowing down the reactor wall into a film, thereby forming a larger heating and volatilization area, so that the polymer is quickly depolymerized at high temperature and the depolymerization products are quickly vaporized, and the residence time is controlled within 2 minutes; the temperature in the depolymerization reactor 400 is controlled in sections, with the temperature increasing from top to bottom, effectively improving the depolymerization efficiency while preventing the formation of by-products.

[0078] It should be noted that the bottom of the depolymerization reactor 400 is connected to a depolymerization liquid delivery pump 410. The liquid phase material of the depolymerization reactor 400 is discharged from the bottom and enters the depolymerization liquid delivery pump 410. The material at the outlet of the depolymerization liquid delivery pump 410 is divided into two streams. One stream is sent back to the top of the depolymerization reactor 400 to form a forced circulation to make the reaction more complete, and the other stream is sent to the hydrolysis reactor 600.

[0079] The reaction raw materials continuously enter the material inlet of the dehydration reactor 600, stay in the dehydration reactor 600 for the reaction time, and hydrolyze the polymer into oligomers with a degree of polymerization of 2 to 6 and a small amount of lactic acid. The polymer is then discharged from the liquid material outlet of the dehydration reactor 600, flows through the pre-polycondensation reactor 200, the polycondensation reactor 300, and the depolymerization reactor 400, and the gaseous material flows out from the gas phase outlet of the depolymerization reactor 400 and is separated and purified by the lactide distillation tower, thereby realizing continuous reaction and achieving the purpose of continuous production. At the same time, it can also effectively control the polymer molecular weight and depolymerization rate required for the depolymerization reaction, thereby improving the conversion rate of the reaction raw materials.

[0080] It should be noted that the pressure in the dehydration reactor 600 is 30-65 kPa and the temperature is 145-165°C; the pressure in the pre-condensation reactor 200 is 10-20 kPa and the temperature is 160-185°C; the pressure in the condensation reactor 300 is 3-8 kPa, and the temperature of the interconnected cavities in the condensation reactor 300 increases in the direction of sequential connection, and the temperature is 170-185°C; the pressure in the depolymerization reactor 400 is 0.8-3 kPa, and the temperature increases from the top to the bottom of the depolymerization reactor 400, and the temperature is 180-240°C. The polymer flows from top to bottom in the depolymerization reactor 400, and as the temperature rises, a depolymerization reaction occurs to produce lactide; the pressure in the hydrolysis reactor 600 is 150-250 kPa and the temperature is 160-200°C.

[0081] Among them, since the polycondensation reaction in the polycondensation reactor 300 is a reversible reaction, raising the reaction temperature under certain conditions is conducive to improving the conversion rate, but as the temperature reaches a certain level, the temperature increases and the conversion rate decreases instead. Therefore, in addition to the need to control the reaction temperature within a certain range, by controlling the temperature of multiple interconnected cavities to increase in the direction of sequential connection, the polycondensation reaction can be further ensured to be sufficient. For example, along the direction of sequential connection, the polycondensation reactor includes A, B, and C cavities, and the temperature of A, B, and C cavities is controlled to increase. Specifically, the temperature ranges of A, B, and C cavities are 170-175°C, 175-180°C, and 180-185°C, respectively.

[0082] It should be noted that a stirring unit is provided in each cavity of the pre-polycondensation reactor 200, the polycondensation reactor 300, and the hydrolysis reactor 600. The embodiment of the present application does not limit the stirring unit, as long as it can achieve uniformity of the material in the cavity. For example, the stirring unit includes a stirring motor, a stirring shaft, and a stirring blade. The stirring shaft is arranged in the cavity, and one end of the stirring shaft is connected to the stirring motor, and the other end is connected to the stirring blade, and at least one stirring blade is provided in each cavity.

[0083] It can be seen that continuous production of lactide can be achieved by continuously adding reaction raw materials to the dehydration reactor 100, pre-polycondensation reactor 200, polycondensation reactor 300, depolymerization reactor 400, and lactide distillation tower, which are connected in sequence. Due to the provision of multiple cavities in the polycondensation reactor 300, the reaction raw materials can be evenly mixed in the polycondensation reactor 300 and flow in a form close to plug flow, which is conducive to the progress of the polycondensation reaction, improves the esterification rate, and thus achieves the molecular weight required for depolymerization. The depolymerization reactor 400 adopts a vertical scraped film structure, which can provide a large devolatilization area, allowing the depolymerization product to evaporate rapidly, with a residence time controlled to less than 2 minutes. The temperature in the reactor increases from top to bottom, effectively improving the depolymerization efficiency while preventing the formation of by-products. The provision of a lactide distillation tower can achieve purification of crude lactide to obtain high-purity lactide. The hydrolysis reactor 600 re-introduces oligomers and a small amount of lactic acid into the pre-polycondensation reactor 200, eliminating waste from the entire device and improving the utilization rate of raw materials.

[0084] In some possible implementations, an oligomer pump 110 and a reboiler 120 are further included.

[0085] The feed end of the oligomer pump 110 is communicated with the liquid material outlet of the dehydration reactor 100 , and the discharge end of the oligomer pump 110 is communicated with the material inlet of the pre-polycondensation reactor 200 .

[0086] The discharge end of the oligomer pump 110 is reused to communicate with the material inlet of the reboiler 120 , and the material outlet of the reboiler 120 is communicated with the material inlet of the dehydration reactor 100 .

[0087] The reboiler 120 can ensure that the raw materials in the reaction and dehydration reactor 100 are uniformly mixed.

[0088] In some possible embodiments, the dehydration reactor 100 processes the feedstock to form gaseous esterification steam.

[0089] The dehydration reactor 100 is provided with a first dehydration tower 130 ; the first dehydration tower 130 is connected to the gas phase material outlet of the dehydration reactor 100 , and the first dehydration tower 130 is at least used to process the esterification steam to form lactic acid liquid, and return the lactic acid liquid to the dehydration reactor 100 .

[0090] It should be noted that the dehydration reactor 100 , the reboiler 110 and the first dehydration tower 130 are an integrated structure, and the reboiler 110 and the first dehydration tower 130 are directly connected to the upper head pipe opening of the dehydration reactor 100 .

[0091] During use, the dehydration reactor 100 is not equipped with an agitator, and the oligomer product is output through the liquid material outlet of the dehydration reactor 100 and enters the oligomer pump 110. The material at the outlet of the oligomer pump 110 is divided into two streams, one of which is sent to the top of the reboiler 120 to form a forced external circulation, which can increase the amount of rising steam in the tower dehydration reactor 100, thereby improving the separation efficiency and the purity of the separated product, and the other stream is sent to the pre-condensation reactor 200.

[0092] In some possible embodiments, the pre-condensation reactor 200 is used to at least process oligomers to form gaseous pre-condensation steam.

[0093] The precondensation reactor 200 is provided with a second dehydration tower 210; the second dehydration tower 210 is connected to the gas phase material outlet of the precondensation reactor 200, and the second dehydration tower 210 is at least used to process the precondensation steam to form lactic acid liquid and return the lactic acid liquid to the precondensation reactor 200.

[0094] The first dehydration tower 130 and the second dehydration tower 210 each have a gas phase outlet at the top of the tower. The gas phase outlet at the top of the tower is used to discharge water vapor. The second dehydration tower 210 has a liquid phase outlet at the bottom of the tower for discharging lactic acid liquid. The liquid phase outlet of the second dehydration tower 210 is connected to the recycle material inlet of the pre-polycondensation reactor 200, so that the lactic acid liquid separated in the second dehydration tower 210 can be refluxed to the pre-polycondensation reactor 200.

[0095] It should be noted that the esterification steam and pre-condensation steam generated in the dehydration reactor 100 and pre-condensation reactor 200 contain unreacted lactic acid and water and other vapors generated by the reaction. Therefore, the monomers are separated by the first dehydration tower 130 and the second dehydration tower 210, allowing the lactic acid to flow back into the dehydration reactor 100 or the pre-condensation reactor 200 to continue the reaction. This can further improve the utilization rate of the reaction raw materials and increase the conversion rate.

[0096] During operation, the gas phase outlets of the dehydration reactor 100 and the pre-polycondensation reactor 200 are connected to the inlets of the first dehydration tower 130 and the second dehydration tower 120, respectively. Therefore, the esterification vapor and pre-polycondensation vapor output from the gas phase outlets of the dehydration reactor 100 and the pre-polycondensation reactor 200 enter the first dehydration tower 130 and the second dehydration tower 210 through the gas phase outlets. In the first dehydration tower 130 and the second dehydration tower 210, the temperature is maintained above the boiling point of water and below the boiling point of lactic acid, thereby condensing the monomer vapors in the esterification vapor and pre-polycondensation vapor to form a monomer liquid, thereby achieving monomer separation.

[0097] When lactic acid is used as a reaction raw material and sequentially enters the dehydration reactor 100 and the pre-condensation reactor 200 for reaction, the esterification steam and pre-condensation steam generated in the dehydration reactor 100 and the pre-condensation reactor 200 contain unreacted lactic acid and water and other vapors generated by the reaction. Therefore, the monomers are separated by the first dehydration tower 130 and the second dehydration tower 210, allowing the lactic acid to flow back into the dehydration reactor 100 or the pre-condensation exchange reactor 200 to continue the reaction. This can further improve the utilization rate of the reaction raw materials and increase the conversion rate.

[0098] In some possible implementations, there are multiple lactide distillation towers, and the multiple lactide distillation towers include a first lactide distillation tower 500a and a second lactide distillation tower 500b.

[0099] The material inlet of the first lactide distillation tower 500a is connected to the gas phase material outlet of the depolymerization reactor 400, the middle fraction outlet of the first lactide distillation tower 500a is connected to the material inlet of the second lactide distillation tower 500b, and the liquid phase material outlet of the bottom of the second lactide distillation tower 500b is used to form lactide.

[0100] During use, the polymer from the polycondensation reactor 300 enters the depolymerization reactor 400, where chain growth and chain degradation reactions occur simultaneously. Under high temperature and low pressure, the chain degradation reaction becomes dominant, and the polymer is depolymerized. Due to the higher temperature and larger volatilization area, the depolymerization products are rapidly vaporized to form depolymerization steam containing a large amount of lactide.

[0101] The first lactide distillation tower 500a and the second lactide distillation tower 500b are used to purify the depolymerization steam containing lactide. The depolymerization steam enters the first lactide distillation tower 500a, where its temperature is raised above the boiling points of water, lactic acid, and lactide, but below the boiling point of oligomers, thereby separating the components. The overhead vapor from the first lactide distillation tower 500a primarily consists of lactic acid and water, while the bottoms contain oligomers. The mid-stage fraction is a higher concentration of lactide with a small amount of lactic acid. This mid-stage fraction enters the second lactide distillation tower 500b, where its temperature is raised above the boiling points of water and lactic acid, but below the boiling point of lactide. As shown in the figure, the bottoms of the second lactide distillation tower 500b flow in direction b, resulting in high-purity lactide, the desired product.

[0102] The oligomers in the bottom of the first lactide distillation tower 500a flow out from the liquid phase outlet of the bottom and enter the pre-polycondensation reactor 200 to undergo a new reaction, thereby improving the utilization rate of raw materials.

[0103] It should be noted that the first dehydration tower 130, the second dehydration tower 210, the first lactide distillation tower 500a, and the second lactide distillation tower 500b are conventional vacuum separation towers in the art. The specific pressure is determined according to the pressure of the dehydration reactor 100, the pre-condensation reactor 200, and the depolymerization reactor 400 during the actual production process. It is sufficient to ensure that the esterification steam, pre-condensation steam, and depolymerization steam can smoothly enter the first dehydration tower 130, the second dehydration tower 210, the first lactide distillation tower 500a, and the second lactide distillation tower 500b from the dehydration reactor 100, the pre-condensation reactor 200, and the depolymerization reactor 400.

[0104] In some possible embodiments, a hydrolyzed liquid delivery pump 610 is further included, wherein the feed end of the hydrolyzed liquid delivery pump 610 is connected to the liquid phase material outlet of the hydrolysis reactor 600 , and the discharge end of the hydrolyzed liquid delivery pump 610 is connected to the material inlet of the pre-condensation reactor 200 .

[0105] By providing the hydrolyzate delivery pump 610 , the efficiency of returning the hydrolyzate to the pre-polycondensation reactor 200 can be improved.

[0106] In some possible implementations, a spray collection unit 700 is further included; the spray collection unit 700 includes a spray tank 710 , a liquid seal tank 720 , a spray liquid circulation pump 730 and a cooler 740 .

[0107] The spray tank 710 is connected to the gas phase material outlet of the polycondensation reactor 300, and the material outlet of the spray tank 710 is connected to the liquid seal tank 720. The liquid seal tank 720 receives the desalted water containing oligomers after spraying and stabilizes the system pressure.

[0108] The spray liquid circulation pump 730 transports the desalted water in the liquid seal tank 720 to the cooler 740 . The cooler 740 cools the desalted water and transports the cooled desalted water to the spray tank 710 .

[0109] The spray capture unit 700 is used to capture oligomers and lactic acid in the steam from the first dehydration tower 130 .

[0110] It should be noted that the spray tank 710 , the liquid sealing tank 720 , the spray liquid circulation pump 730 and the cooler 740 in the spray capture unit 700 adopt conventional spray condensation devices and can be the same or different.

[0111] During operation, the polycondensation steam discharged from the gas phase outlet of the polycondensation reactor 300 enters the spray capture unit 700. In the spray capture unit 700, the polycondensation steam enters the spray tank 710. After being sprayed with low-temperature water in the cooler 740 in the spray tank 710, the captured liquid and non-condensable gas are formed. The liquid phase enters the liquid seal tank 720 through the liquid phase outlet of the spray tank 710, is cooled by the cooler 740 connected to the liquid seal tank 720, and is recycled by the spray liquid circulation pump 730.

[0112] Since the esterification steam, pre-condensation steam and condensation steam produced by the reaction also contain unreacted lactic acid and generated water and other steam, condensing, separating and recovering them is not only beneficial to the progress of the reaction, but also can further improve the utilization rate of the reaction raw materials.

[0113] In some possible implementations, a condensation unit and a vacuum unit 900 are further included.

[0114] The condensing unit is used to process the overhead steam from the dehydration reactor 100, the pre-condensation reactor 200, the depolymerization reactor 400 and the lactide distillation column to form condensate and non-condensable gas.

[0115] The vacuum unit 900 obtains non-condensable gas from the condensation unit and the spray collection unit 700 .

[0116] It should be noted that the condensing unit includes at least a first condensing unit 800a, a second condensing unit 800b, a third condensing unit 800c and a fourth condensing unit 800d; the first condensing unit 800a includes a first condenser 810a and a first condensate collecting tank 820a; the second condensing unit 800b includes a second condenser 810b and a second condensate collecting tank 820b; 800c includes a third condenser 810c and a third condensate collecting tank 820c; the third condensing unit 800c includes a third condenser 810c and a third condensate collecting tank 820c; 800d includes a fourth condenser 810d and a fourth condensate collecting tank 820d; and the fourth condensing unit 800d includes a fourth condenser 810d and a fourth condensate collecting tank 820d.

[0117] The vacuum unit 900 includes a first Roots pump 910 , a second Roots pump 920 , a third Roots pump 930 , a fourth Roots pump 940 , and a liquid ring pump 950 .

[0118] The gas phase inlet of the first condenser 810a is connected to the gas phase outlet of the first dehydration tower 130; the gas phase inlet of the second condenser 810b is connected to the gas phase outlet of the second dehydration tower 210; the gas phase inlet of the third condenser 810c is connected to the gas phase outlet of the first lactide distillation tower 500a; the liquid phase outlet of the third condensate collection tank 820c is connected to the liquid phase inlet of the dehydration reactor 100; the gas phase inlet of the fourth condenser 810d is connected to the gas phase outlet of the second lactide distillation tower 500b; and the liquid phase outlet of the fourth condensate collection tank 820d is connected to the liquid phase inlet of the dehydration reactor 100.

[0119] The gas phase outlet of the fourth condensate collecting tank 820d is connected to the inlet of the first Roots pump 910; the gas phase outlet of the third condensate collecting tank 820c is connected to the gas phase outlet of the first Roots pump 910 and the inlet of the second Roots pump 920; the non-condensable gas outlet of the spray tank 710 is connected to the gas phase outlet of the second Roots pump 920 and the inlet of the third Roots pump 930; the gas phase outlet of the second condensate collecting tank 820b is connected to the gas phase outlet of the third Roots pump 930 and the inlet of the fourth Roots pump 940; the gas phase outlet of the first condensate collecting tank 820b is connected to the gas phase outlet of the fourth Roots pump 940 and the inlet of the liquid ring pump 950.

[0120] It should be noted that the first condensing unit 800a, the second condensing unit 800b, the third condensing unit 800c, and the fourth condensing unit 800d adopt conventional condensing devices and can be the same or different.

[0121] Specifically, the water vapor discharged from the gas phase outlet of the first dehydration tower 130 is cooled by the first condenser 810a, and then enters the first condensate collection tank 820a. The generated non-condensable gas is discharged through the non-condensable gas outlet in the first condensate collection tank 820a and sent to the vacuum unit. Part of the condensate is sent to the sewage treatment station, and the other part is returned to the first dehydration tower 130 as reflux.

[0122] The water vapor discharged from the gas phase outlet of the second dehydration tower 210 is cooled by the second condenser 810b and then enters the second condensate collecting tank 820b. The non-condensable gas is discharged through the non-condensable gas outlet in the second condensate collecting tank 820b and sent to the vacuum unit. Part of the condensate is sent to the sewage treatment station, and the other part returns to the second dehydration tower 210 as reflux.

[0123] When the lactic acid content in the condensate from the first condensate collecting tank 820a and the second condensate collecting tank 820b is less than 0.3%, the condensate can be directly discharged to a sewage treatment station as wastewater in directions c1 and c2 as shown in the figure.

[0124] The mixed vapor of lactic acid and water discharged from the vapor phase outlet of the first lactide distillation tower 500a is cooled by the third condenser 810c and then enters the third condensate collection tank 820c. The non-condensable gas is discharged through the non-condensable gas outlet of the third condensate collection tank 820c and sent to the vacuum unit 900. A portion of the condensate is sent to the dehydration reactor 100 for further reaction, and the remaining portion is returned to the first lactide distillation tower 500a as reflux. The lactic acid vapor discharged from the vapor phase outlet of the second lactide distillation tower 500b is cooled by the fourth condenser 810d and then enters the fourth condensate collection tank 820d. The non-condensable gas is discharged through the non-condensable gas outlet of the fourth condensate collection tank 820d and sent to the vacuum unit 900. A portion of the condensate is sent to the dehydration reactor 100 for further reaction, and the remaining portion is returned to the second lactide distillation tower 500b as reflux.

[0125] The non-condensable gas generated in the fourth condensate collecting tank 820d is compressed by the first Roots pump 910 and mixed with the non-condensable gas in the third condensate collecting tank 820c and enters the second Roots pump 920. After being compressed, it is mixed with the tail gas generated at the non-condensable gas outlet of the spray pipe 710 in the spray capture unit 700 and continues to enter the third Roots pump 930 for compression. The compressed gas is mixed with the non-condensable gas generated in the second condensate collecting tank 820b and enters the fourth Roots pump 940 for compression. The gas coming out of the fourth Roots pump 940 and the non-condensable gas generated in the first condensate collecting tank 810a are mixed and enter the liquid ring pump 950. Figure 1 As shown, the tail gas from liquid ring pump 950 can be vented at a safe point along direction d. By pressure-matching the four-stage Roots pump 940 and liquid ring pump 950, different vacuum environments can be provided for the dehydration reactor 100, pre-polycondensation reactor 200, polycondensation reactor 300, first lactide distillation column 500a, and second lactide distillation column 500b, thereby improving the utilization rate of the reaction raw materials.

[0126] By allowing the aqueous lactic acid at the liquid phase outlets of the fourth condensate collecting tank 820d and the third condensate collecting tank 920c to re-enter the dehydration reactor 100, no waste is generated in the entire device, thereby improving the utilization rate of raw materials.

[0127] like Figure 2 As shown, the present embodiment provides a method for preparing lactide, comprising:

[0128] Processing the feedstock through a dehydration reactor 100 to form oligomers;

[0129] Processing the oligomer through a precondensation reactor 200 to form a prepolymer;

[0130] Processing the prepolymer through a polycondensation reactor 300 to form a polymer;

[0131] Processing the polymer through a depolymerization reactor 400 to form high polymers and depolymerization vapors;

[0132] Processing the depolymerization vapors through a lactide distillation column to form lactide;

[0133] The high polymer is processed in the hydrolysis reactor 600 to form a hydrolyzate, which is then returned to the dehydration reactor 100 as a raw material to participate in the reaction.

[0134] The above production method not only has the advantage of high utilization rate of reaction raw materials, but also can produce high-purity lactide.

[0135] like Figure 3 As shown, in some possible embodiments, after the dehydration reactor 100 forms oligomers, the method includes:

[0136] The first portion of oligomers is delivered to the pre-polycondensation reactor 200 via the oligomer pump 110 ;

[0137] The second portion of oligomers is delivered to the reboiler 120 via the oligomer pump 110 ;

[0138] The second portion of oligomers is processed through the reboiler 120 and returned to the dehydration reactor 100 as a raw material to participate in the reaction.

[0139] The following describes in detail the lactide preparation device and lactide preparation method according to the embodiments of the present application through specific examples.

[0140] In the following embodiments, the lactide production apparatus used includes at least: a dehydration reactor 100, an oligomer pump 110, a pre-polycondensation reactor 200, a polycondensation reactor 300, a polymer delivery pump 310, a depolymerization reactor 400, a first lactide distillation column 500a, a second lactide distillation column 500b, a reboiler 120, a first dehydration column 130, a second dehydration column 210, a spray collection unit 700, a depolymerization liquid delivery pump 410, a hydrolysis reactor 600, a hydrolyzed liquid delivery pump 610, a first condensing unit 800a, a second condensing unit 800b, a third condensing unit 800c, a fourth condensing unit 800d, a first Roots pump 910, a second Roots pump 920, a third Roots pump 930, a fourth Roots pump 940, and a liquid ring pump 950, which are connected in sequence.

[0141] The dehydration reactor 100 is a vertical reactor with a jacket and heating; the pre-condensation reactor 200 is a vertical reactor with a jacket and coil heating, and is equipped with a stirring unit; the bottom pipe outlet of the first dehydration tower 130 is directly connected to the gas phase outlet at the top of the dehydration reactor 100, and the condensate flows directly back to the dehydration reactor 100; the gas phase outlet of the pre-condensation reactor 200 is connected to the gas phase inlet of the second dehydration tower 210; the circulating material inlet of the pre-condensation reactor 200 is connected to the liquid phase outlet of the second dehydration tower 210; the inlet of the first condensation unit 800a is connected to the gas phase outlet of the first dehydration tower 310; the condensation inlet of the second condensation unit 800b is connected to the gas phase outlet of the second dehydration tower 210; the non-condensable gas outlet of the first condensation unit 800a is connected to the inlet of the liquid ring pump 950; the non-condensable gas outlet of the second condensation unit 800b is connected to the inlet of the fourth Roots pump 940.

[0142] The first condensing unit 800a includes a first condenser 810a and a first condensate collecting tank 820a; the first condenser 810a is used to condense esterification steam, and the first condensate collecting tank 820a is used to collect steam condensate; the second condensing unit 800b includes a second condenser 810b and a second condensate collecting tank 820b; the second condenser 810b is used to condense pre-condensation steam, and the second condensate collecting tank 820b is used to collect steam condensate;

[0143] The polycondensation reactor 300 is a horizontal reactor with a jacket and coil heating. The polycondensation reactor 300 includes three interconnected cavities A, B, and C. Each cavity A, B, and C is independently provided with a heating unit and a stirring unit.

[0144] The spray capture unit 700 includes a spray tank 710, a liquid seal tank 720, a spray liquid circulation pump 730, and a cooler 740. The gas phase outlet of the polycondensation reactor 300 is connected to the gas phase inlet of the spray capture unit 700. The non-condensable gas outlet of the spray capture unit 700 is connected to the inlet of the third Roots pump 930.

[0145] The depolymerization reactor 400 is a vertical reactor with a jacket heating. The depolymerization reactor 400 adopts segmented heating from top to bottom to control different temperatures. The upper part of the depolymerization reactor 400 is a liquid distributor, the middle part is a scraper assembly, and the scraper drive is installed on the top of the reactor. The bottom of the depolymerization reactor 400 is a depolymerization liquid receiving assembly. The reactor scraper scrapes the polymer flowing down the reactor wall into a film, thereby forming a larger heating and volatilization area, so that the polymer is quickly depolymerized at high temperature and the depolymerization product is quickly vaporized.

[0146] The gas phase inlet of the first lactide distillation tower 500a is connected to the gas phase outlet of the depolymerization reactor 400; the liquid phase outlet of the bottom of the first lactide distillation tower 500a is connected to the inlet of the pre-condensation reactor 200; the inlet of the second lactide distillation tower 500b is connected to the outlet of the upper and middle fractions of the first lactide distillation tower 500a; the first lactide distillation tower 500a and the second lactide distillation tower 500b are both vacuum packed towers, and the packing is wire mesh structured packing.

[0147] The gas phase inlet of the third condensing unit 800c is connected to the gas phase outlet at the top of the first lactide distillation tower 500a; the gas phase inlet of the fourth condensing unit 800d is connected to the gas phase outlet at the top of the second lactide distillation tower 500b; the non-condensable gas outlet of the third condensing unit 800c is connected to the inlet of the second Roots pump 920; and the non-condensable gas outlet of the fourth condensing unit 800d is connected to the inlet of the first Roots pump 910.

[0148] The third condensing unit 800c includes a third condenser 810c and a third condensate collecting tank 820c; the third condenser 810c is used to condense the mixed vapor of water and lactic acid, and the third condensate collecting tank 820c is used to collect the condensate of the mixed vapor; the fourth condensing unit 800d includes a fourth condenser 810d and a fourth condensate collecting tank 820d; the fourth condenser 810d is used to condense lactic acid vapor, and the fourth condensate collecting tank 820d is used to collect lactic acid condensate.

[0149] The outlet of the first Roots pump 910 is communicated with the inlet of the second Roots pump 920; the outlet of the second Roots pump 920 is communicated with the inlet of the third Roots pump 930; the outlet of the third Roots pump 930 is communicated with the inlet of the fourth Roots pump 940; the outlet of the fourth Roots pump 940 is communicated with the inlet of the liquid ring pump 500.

[0150] The inlet of the depolymerization liquid delivery pump 410 is connected to the liquid phase outlet of the depolymerization reactor 400, and the polymer inlet of the hydrolysis reactor 600 is connected to the outlet of the depolymerization liquid delivery pump 410; the hydrolysis reactor 600 is a vertical reactor with a jacket and coil heating, equipped with a stirring unit, and a desalted water inlet and a nitrogen inlet on the top; the liquid phase outlet of the hydrolysis reactor 600 is connected to the inlet of the pre-condensation reactor 200 through the hydrolysis liquid delivery pump 610.

[0151] Example 1

[0152] Reference Figure 1, using preheated lactic acid as the reaction raw material, it is added to the dehydration reactor 100 along the direction of a, with a reaction pressure of 50 kPa, a temperature of 158° C., and a residence time of 400 min; the esterification steam generated by the dehydration reactor 100 enters the first dehydration tower 130 from the gas phase outlet at the top of the dehydration reactor 100 for separation to obtain lactic acid liquid and tower top steam. Since the bottom of the first dehydration tower 130 is directly connected to the gas phase outlet of the dehydration reactor 100, the lactic acid liquid directly flows back to the dehydration reactor 100 from the gas phase pipe port, and the tower top steam is condensed by the first condenser 810a of the first condensing unit 800a to obtain water vapor condensate, which is then sent to the first condensate collection tank 820a, and the non-condensable gas is discharged through the gas phase outlet and connected to the liquid ring pump 950. A part of the water vapor condensate is discharged through the liquid phase outlet at the bottom and sent to the sewage treatment station, and the other part of the water vapor condensate returns to the first dehydration tower 130 through the reflux port of the first condensate collection tank 820a for further separation;

[0153] The oligomers coming out from the bottom of the dehydration reactor 100 enter the pre-condensation reactor 200 through the oligomer delivery pump 110, and the composite catalyst (tin compound is stannous octoate, the addition amount is 65ppm, zinc compound is zinc oxide, the addition amount is 28ppm) solution is added into the cavity of the pre-condensation reactor 200 along the direction e. The reaction pressure in the pre-condensation reactor 200 is 18kPa (A), the temperature is 163°C, and the residence time is 200min; the pre-condensation steam generated by the pre-condensation reactor 200 enters the second dehydration tower 21 from the gas phase outlet at the top of the pre-condensation reactor 200 0 is separated to obtain lactic acid liquid and tower top vapor. The lactic acid liquid is refluxed into the pre-polycondensation reactor 200 through the circulating material inlet of the pre-polycondensation reactor 200. The tower top vapor is condensed in the second condenser 810b of the second condensation unit 800b to obtain water vapor condensate, which is then sent to the second condensate collecting tank 820b. The non-condensable gas is discharged through the gas phase outlet and connected to the fourth Roots pump 940. A portion of the water vapor condensate is discharged through the liquid phase outlet at the bottom and sent to the sewage treatment station. The other portion of the water vapor condensate is returned to the second dehydration tower 210 through the reflux port of the second condensate collecting tank 820b for further separation.

[0154] The prepolymer from the pre-condensation reactor 200 enters the polycondensation reactor 300 and flows through the A, B, and C chambers in sequence to obtain polycondensation steam and polymer; the reaction pressure in the polycondensation reactor 3000 is 4 kPa (A), the temperatures in the A, B, and C chambers are 170-175°C, 175-180°C, and 180-185°C, respectively. The exemplary temperatures in the A, B, and C chambers are 170°C, 176°C, and 183°C, respectively. The residence time is 3 50min; the polycondensation steam exits the gas phase outlet of the polycondensation reactor 300 and enters the spray capture unit 700. In the spray capture unit 700, the steam passes through the spray tank 710 and is cooled by the low-temperature desalted water sprayed by the cooler 740 to obtain a capture liquid and non-condensable gas. The capture liquid flows to the liquid seal tank 720 and returns to the cooler 740 via the spray liquid delivery pump 730. The non-condensable gas is connected to the third Roots pump 930 via the non-condensable gas outlet of the spray capture unit 700;

[0155] The polymer exiting the bottom of the polycondensation reactor 300 is fed into the top material inlet of the depolymerization reactor 400 via a polymer delivery pump 310. The polymer then falls along the wall of the reactor through a liquid distributor and is scraped into a film-like shape by a scraper during its fall, causing the polymer to rapidly depolymerize under high temperature and low pressure, generating depolymerization steam. The pressure of the depolymerization reactor 400 is 1.8 kPa(A). The reactor is temperature-controlled in four sections from top to bottom, at 193°C, 204°C, 213°C, and 226°C, respectively. The residence time of the depolymerization steam is 1.8 min.

[0156] The liquid phase flowing out of the bottom of the depolymerization reactor 400 is delivered to the hydrolysis reactor 600 via the depolymerization liquid delivery pump 410. The deionized water is added into the cavity of the hydrolysis reactor 600 along the direction f. The reaction pressure in the hydrolysis reactor 600 is 210 kPa(A), the temperature is 185°C, and the residence time is 100 min. The hydrolyzed liquid generated in the hydrolysis reactor 600 is delivered to the pre-polycondensation reactor 200 via the hydrolyzed liquid delivery pump 610 to participate in the reaction again.

[0157] The depolymerization steam from the depolymerization reactor 400 enters the first lactide distillation tower 500a for preliminary purification. The overhead steam is condensed in the third condenser 810c of the third condensing unit 800c to produce hydrous lactic acid, which is then sent to the third condensate collection tank 820c. The non-condensable gas is discharged through the gas phase outlet and connected to the second Roots pump 920. A portion of the hydrous lactic acid is discharged through the liquid phase outlet at the bottom and sent to the dehydration reactor 100 for further reaction. The remaining portion of the hydrous lactic acid is returned to the first lactide distillation tower 00a5 through the reflux port of the third condensate collection tank 820c for further separation. The oligomers exiting the bottom of the first lactide distillation tower 500a are sent back to the pre-polycondensation reactor 200 for further reaction.

[0158] The fraction flowing out of the upper portion of the first lactide distillation tower 500a enters the second lactide distillation tower 500b for further purification. The overhead vapor is condensed in the fourth condenser 810d of the fourth condensing unit 800d to produce lactic acid, which is then sent to the fourth condensate collection tank 820d. Non-condensable gases are discharged through the vapor phase outlet and connected to the first Roots pump 910. A portion of the lactic acid is discharged through the liquid phase outlet at the bottom and sent to the dehydration reactor 100 for further reaction. The remaining lactic acid is returned to the second lactide distillation tower 500b through the reflux port of the fourth condensate collection tank 820d for further separation. The liquid phase exiting the bottom of the second lactide distillation tower 500b is high-purity lactide.

[0159] Test Example 1

[0160] 1. Analysis methods for lactic acid oligomers, prepolymers and polymers:

[0161] (1) Preparation and calibration of sodium methoxide standard solution

[0162] Accurately weigh 10.80g of sodium methoxide in a 1000ml volumetric flask, add an appropriate amount of anhydrous methanol to dissolve the sample completely, and then dilute to the scale with anhydrous methanol. Weigh 0.1g of naphthol red indicator in a 100ml dropping bottle, add 50ml of anhydrous methanol to dissolve. Weigh 0.5g of standard benzoic acid reagent in a 250ml conical flask, add 20ml of anhydrous methanol to dissolve the sample completely, then add 3 drops of naphthol red indicator, and titrate with the sodium methoxide standard solution to be calibrated until the solution turns light pink. Perform four parallel measurements and take the average value. The concentration of the sodium methoxide standard solution is calculated as follows:

[0163]

[0164] Where:

[0165] m—mass of benzoic acid, g;

[0166] V—volume of sodium methoxide standard solution consumed, ml;

[0167] C—concentration of sodium methoxide standard solution mol / L;

[0168] 122.1—Molecular weight of sodium methoxide.

[0169] (2) Determination and calculation methods of molecular weight and degree of polymerization

[0170] Weigh 0.7-1.5 g of sample into a 250 ml conical flask, add 25 ml of anhydrous methanol to dissolve the sample, add 3 drops of naphthol red indicator, and titrate with sodium methoxide standard solution until it turns light pink.

[0171] The number average molecular weight and degree of polymerization of polylactic acid are calculated as follows:

[0172]

[0173] Where:

[0174] Mn—number average molecular weight

[0175] n—average degree of polymerization

[0176] C—concentration of sodium methoxide standard solution, mol / L;

[0177] m—mass of sample, g;

[0178] V—Volume of sodium methoxide standard solution consumed, ml.

[0179] 2. Analysis method of lactide

[0180] The chemical purity of lactide was determined by gas chromatography.

[0181] (1) Instruments and chromatographic conditions

[0182] Agilent 6820 gas chromatograph,

[0183] Chromatographic column: DB-225 capillary column (50m×0.25mm);

[0184] Column temperature: (programmed temperature rise) initial temperature 140℃, hold for 3min, heating rate 2℃ / min,

[0185] End temperature 160℃, maintain for 35min;

[0186] Vaporization temperature: 280℃;

[0187] Detector temperature: 200°C;

[0188] Split ratio: 80:1;

[0189] Carrier gas: high-purity hydrogen, pressure 0.1 MPa;

[0190] Make-up gas: 29ml / min;

[0191] Injection method: split injection;

[0192] Injection volume: 0.1 μL.

[0193] (2) Determination of correction factor:

[0194] Weigh a certain amount of lactic acid and lactide (chromatographic standard) into a 10ml volumetric flask. Add an appropriate amount of ethyl acetate to completely dissolve the sample and shake well. After the instrument baseline stabilizes according to the above chromatographic conditions, use a microinjector to inject 0.1μL of the mixed standard sample at least 10 times. Calculate the correction factor for lactide relative to lactic acid and take the average value. The measured correction factors are: flactic acid = 1.000; flactide = 0.723. Then, weigh a certain amount of water and lactide (chromatographic standard) into a 10ml volumetric flask. Add an appropriate amount of ethyl acetate dehydrated with molecular sieves to completely dissolve the sample and shake well. Using the same method, determine the correction factors for water and L-lactide. The result is that when flactide = 0.723, the correction factor for water is fwater = 0.283.

[0195] (3) Sample determination:

[0196] Use a microinjector to inject 0.1 μL of sample, record the chromatogram, and record the peak area using a chromatography workstation or integrator. Then calculate the content of lactic acid, lactic acid dimer, meso-lactide and L-lactide in the sample according to the correction factor normalization method.

[0197] The purity of the lactide in Example 1 was measured to be 99.2%.

[0198] Therefore, the lactide preparation device and preparation method provided in the embodiments of the present application can not only achieve continuous production of lactide, but also obtain high-purity lactide.

[0199] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0200] In the description of the present invention, it should be understood that the terms "including" and "having" and any variations thereof used herein are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0201] Unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," "fixed," etc. should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integration; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal connections between two components or interactions between two components. Those skilled in the art will understand the specific meanings of these terms in this disclosure based on the specific circumstances. Furthermore, the terms "first," "second," etc., etc., are used for descriptive purposes only and should not be construed to indicate or imply relative importance or implicitly specify the quantity of the technical features indicated.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lactide production device, characterized in that: It includes a dehydration reactor (100), a pre-polycondensation reactor (200), a polycondensation reactor (300), a depolymerization reactor (400), a lactide distillation tower and a hydrolysis reactor (600); The dehydration reactor (100) is at least used to process the raw materials to form liquid oligomers; The material inlet of the pre-polycondensation reactor (200) is connected to the liquid material outlet of the dehydration reactor (100), and the pre-polycondensation reactor (200) is at least used to process the oligomer to form a liquid prepolymer; The material inlet of the polycondensation reactor (300) is connected to the liquid material outlet of the pre-polycondensation reactor (200), and the polycondensation reactor (300) is at least used to process the prepolymer to form a liquid polymer; The material inlet of the depolymerization reactor (400) is connected to the liquid material outlet of the polycondensation reactor (300), and the depolymerization reactor (400) is at least used to process the oligomers to form liquid polymers and gaseous depolymerization steam; The material inlet of the lactide distillation tower is connected to the gas phase material outlet of the depolymerization reactor (400), and the lactide distillation tower is at least used to process the depolymerization steam to form lactide; The material inlet of the hydrolysis reactor (600) is connected to the liquid material outlet of the depolymerization reactor (400). The hydrolysis reactor (600) is at least used to process the polymer to form a hydrolysis product. The hydrolysis reactor (600) transports the hydrolysis product to the pre-condensation reactor (200) through the liquid material outlet.

2. The lactide production device according to claim 1, characterized in that It also includes a hydrolyzed liquid delivery pump (610), the feed end of the hydrolyzed liquid delivery pump (610) is connected to the liquid phase material outlet of the hydrolysis reactor (600), and the discharge end of the hydrolyzed liquid delivery pump (610) is connected to the material inlet of the pre-condensation reactor (200).

3. The lactide production device according to claim 2, characterized in that: Also included is an oligomer pump (110) and a reboiler (120); The feed end of the oligomer pump (110) is communicated with the liquid phase material outlet of the dehydration reactor (100), and the discharge end of the oligomer pump (110) is communicated with the material inlet of the pre-polycondensation reactor (200); The discharge end of the oligomer pump (110) is reused for the material inlet of the reboiler (120), and the material outlet of the reboiler (120) is communicated with the material inlet of the dehydration reactor (100).

4. The lactide production device according to claim 3, characterized in that The number of the lactide distillation towers is set to be multiple, and the multiple lactide distillation towers include a first lactide distillation tower (500a) and a second lactide distillation tower (500b); The material inlet of the first lactide distillation tower (500a) is connected to the gaseous material outlet of the depolymerization reactor (400), the middle fraction outlet of the first lactide distillation tower (500a) is connected to the material inlet of the second lactide distillation tower (500b), and the liquid material outlet of the second lactide distillation tower (500b) is used to form the lactide.

5. The lactide production device according to claim 4, characterized in that: It also includes a spray collection unit (700); the spray collection unit (700) includes a spray tank (710), a liquid sealing tank (720), a spray liquid circulation pump (730) and a cooler (740); The spray tank (710) is connected to the gas phase material outlet of the polycondensation reactor (300), and the material outlet of the spray tank (710) is connected to the liquid seal tank (720). The liquid seal tank (720) receives the desalted water containing oligomers after spraying and stabilizes the system pressure; The spray liquid circulation pump (730) transports the desalted water in the liquid seal tank (720) to the cooler (740), and the cooler (740) cools the desalted water and transports the cooled desalted water into the spray tank (710).

6. The lactide production device according to claim 5, characterized in that: The dehydration reactor (100) processes the raw material to form gaseous esterification steam; The dehydration reactor (100) is provided with a first dehydration tower (130); the first dehydration tower (130) is connected to the gas phase material outlet of the dehydration reactor (100), and the first dehydration tower (130) is used at least to process the esterification steam to form lactic acid liquid, and return the lactic acid liquid to the dehydration reactor (100).

7. The lactide production device according to claim 6, characterized in that: The pre-condensation reactor (200) is at least used to process the oligomers to form gaseous pre-condensation steam; The pre-condensation reactor (200) is provided with a second dehydration tower (210); the second dehydration tower (210) is connected to the gas phase material outlet of the pre-condensation reactor (200), and the second dehydration tower (210) is at least used to process the pre-condensation steam to form lactic acid liquid, and return the lactic acid liquid to the pre-condensation reactor (200).

8. The lactide production device according to any one of claims 5 to 7, characterized in that: Also included is a condensation unit and a vacuum unit (900); The condensing unit is used to process the overhead steam from the dehydration reactor (100), the pre-polycondensation reactor (200), the depolymerization reactor (400) and the lactide distillation tower to form condensate and non-condensable gas; The vacuum unit (900) obtains the non-condensable gas from the condensation unit and the spray collection unit (700).

9. A method for preparing lactide, characterized in that: include: processing the feedstock through a dehydration reactor (100) to form oligomers; processing the oligomer through a pre-polycondensation reactor (200) to form a prepolymer; processing the prepolymer through a polycondensation reactor (300) to form a polymer; processing the polymer through a depolymerization reactor (400) to form high polymers and depolymerization vapor; processing the depolymerization vapor through a lactide distillation column to form lactide; The high polymer is processed through the hydrolysis reactor (600) to form a hydrolyzate, and the hydrolyzate is returned to the dehydration reactor (100) as the raw material to participate in the reaction.

10. The method for preparing lactide according to claim 9, wherein After the dehydration reactor (100) forms oligomers, the method comprises: delivering a first portion of the oligomer to the pre-polycondensation reactor (200) via an oligomer pump (110); delivering a second portion of the oligomers to a reboiler (120) via the oligomer pump (110); The second portion of the oligomers is processed through the reboiler (120), and the second portion of the oligomers is returned to the dehydration reactor (100) as the raw material to participate in the reaction.

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