L-lactide purification device and L-lactide purification method

Abstract

The invention provides an L-lactide purification device and an L-lactide purification method. The L-lactide purification device comprises a crystallization unit, an evaporation unit, a condensation unit and an extraction unit, the crystallization unit is at least used for crystallizing, sweating and melting the raw materials to form L-lactide and crystallization raffinate; the inlet of the evaporation unit is communicated with the crystallization residual liquid outlet of the crystallization unit, and the evaporation unit is at least used for evaporating the crystallization residual liquid to form evaporation gas; an inlet of the condensation unit is communicated with a gas phase outlet of the evaporation unit, and the condensation unit is at least used for condensing the evaporation gas to form condensate; a liquid phase inlet of the extraction unit is communicated with a liquid phase outlet of the condensation unit, and the extraction unit is at least used for extracting condensate to form a first component containing L-lactide; the outlet of the extraction unit is communicated with the crystallization unit, so that the crystallization unit adopts the first component as a raw material for crystallization. According to the embodiment of the invention, the yield of the L-lactide can be improved, and the L-lactide with high chemical purity and high optical purity can be obtained.

Description

Technical Field

[0001] The present application relates to the field of biodegradable materials, and in particular to an L-lactide purification device and an L-lactide purification 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 an L-lactide purification apparatus and an L-lactide purification method to solve the problems of low L-lactide raw material yield and low purity of the purified L-lactide.

[0005] In a first aspect, this embodiment provides an L-lactide purification device, comprising a crystallization unit, an evaporation unit, a condensation unit, and an extraction unit;

[0006] The crystallization unit is at least used to crystallize the raw material to form L-lactide and a crystal residue;

[0007] The inlet of the evaporation unit is connected to the outlet of the residual crystallization liquid of the crystallization unit, and the evaporation unit is at least used to evaporate the residual crystallization liquid to form evaporated gas;

[0008] The inlet of the condensing unit is communicated with the gas phase outlet of the evaporating unit, and the condensing unit is at least used to condense the evaporated gas to form condensate;

[0009] The liquid phase inlet of the extraction unit is connected to the liquid phase outlet of the condensation unit, and the extraction unit is at least used to extract the condensate to form a first component containing L-lactide;

[0010] The outlet of the extraction unit is further connected to the crystallization unit, so that the crystallization unit uses the first component as raw material for crystallization.

[0011] In some embodiments of the present application, the crystallization unit includes a crystallizer, an L-lactide collection tank, an L-lactide delivery pump, and a residual liquid delivery pump;

[0012] The crystallizer is configured as a pulse tube-and-shell crystallizer, which is used to cool and heat the raw materials to crystallize, sweat, and melt the raw materials to form at least L-lactide and a crystal residue;

[0013] The inlet of the L-lactide collecting tank is connected to the crystallizer, and the outlet of the L-lactide collecting tank is connected to the L-lactide delivery pump, and the L-lactide delivery pump outputs the L-lactide in the L-lactide collecting tank;

[0014] The inlet of the residual liquid delivery pump is communicated with the crystallizer, and the outlet of the residual liquid delivery pump is communicated with the inlet of the evaporation unit. The residual liquid delivery pump delivers the crystallized residual liquid of the crystallizer to the evaporation unit.

[0015] In some embodiments of the present application, the pulse tube crystallizer is used to at least heat the raw material to crystallize the raw material to form at least a mother liquor;

[0016] The crystallization unit includes a mother liquor collecting tank and a mother liquor delivery pump. The mother liquor collecting tank is at least used to collect the mother liquor of the crystallizer. The mother liquor delivery pump is at least used to deliver the mother liquor in the mother liquor collecting tank to the crystallizer, so that the crystallization unit uses the mother liquor as raw material for crystallization.

[0017] In some embodiments of the present application, the evaporation unit includes a residual liquid evaporator, an oligomer collection tank, and an oligomer delivery pump;

[0018] The residual liquid evaporator is at least used to evaporate the crystallization residual liquid to form liquid oligomers and evaporated gas;

[0019] The liquid phase outlet of the residual liquid evaporator is communicated with the oligomer collecting tank, and the oligomer collecting tank collects the oligomers; the gas phase outlet of the residual liquid evaporator is communicated with the condensing unit.

[0020] In some embodiments of the present application, the condensing unit includes a steam condenser and a condensate collection tank;

[0021] The inlet of the steam condenser receives the evaporated gas from the evaporation unit, and the steam condenser is at least used to condense the evaporated gas to form condensate;

[0022] The inlet of the condensate collecting tank is communicated with the outlet of the steam condenser, and the outlet of the condensate collecting tank is communicated with the liquid phase inlet of the extraction unit.

[0023] In some embodiments of the present application, the extraction unit includes an extraction kettle and a centrifuge;

[0024] The extraction kettle is used to extract the condensate to form a first component containing L-lactide and a second component that is incompatible with the first component;

[0025] The centrifuge is used to separate at least the first component and the second component.

[0026] In some embodiments of the present application, the extraction unit includes a first delivery pump, a second delivery pump, a first component collection tank, and a second component collection tank;

[0027] The first delivery pump is used at least to deliver the first component from the centrifuge from the first component collecting tank to the crystallization unit, and the second delivery pump is used at least to deliver the second component from the centrifuge from the second component collecting tank out of the L-lactide purification device.

[0028] In some embodiments of the present application, a vacuum unit is further included;

[0029] The vacuum unit is at least used to make the evaporation process of the crystallization residual liquid in a negative pressure state;

[0030] And / or, the vacuum unit is at least used to place the evaporation gas condensation process in a negative pressure state.

[0031] In a second aspect, the present invention provides a method for purifying L-lactide, comprising:

[0032] The raw material is crystallized to obtain L-lactide and a crystal residue;

[0033] Evaporating the crystallization residue to obtain evaporated gas;

[0034] condensing the evaporated gas to obtain a condensate;

[0035] The condensate is subjected to extraction treatment to form a first component containing L-lactide, and the first component is recycled as the raw material to participate in the crystallization.

[0036] In some embodiments of the present application, the raw material is subjected to a crystallization process, including an intermittent multi-stage process, where each stage of the process includes:

[0037] subjecting the raw material to nitrogen blast treatment;

[0038] performing crystallization treatment on the raw material after the nitrogen blast treatment;

[0039] performing a sweating treatment on the raw material after the crystallization treatment;

[0040] The raw material after the sweating treatment is melted.

[0041] The L-lactide purification apparatus and L-lactide purification method provided in the embodiments of the present application, through a combined process of multi-stage separation (crystallization, evaporation, condensation, and extraction), can solve the problems of low purification rate and conversion rate of the L-lactide purification apparatus, and can produce L-lactide with high chemical purity and high optical purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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.

[0043] Figure 1 A schematic diagram of an L-lactide purification device provided in an embodiment of the present application;

[0044] Figure 2 A schematic diagram of a method for purifying L-lactide provided in an embodiment of the present application;

[0045] Figure 3 This is a schematic diagram of a method for crystallizing a raw material in a method for purifying L-lactide provided in an embodiment of the present application.

[0046] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0047] 100, crystallization unit; 110, crystallizer; 120, L-lactide collection tank; 130, L-lactide delivery pump; 140, residual liquid delivery pump; 150, mother liquor collection tank; 160, mother liquor delivery pump; 170, residual liquid collection tank; 180, crude lactide collection tank; 190, crude lactide delivery pump;

[0048] 200, evaporation unit; 210, residual liquid evaporator; 220, oligomer collection tank; 230, oligomer delivery pump;

[0049] 300, condensing unit; 310, steam condenser; 320, condensate collecting tank;

[0050] 400, extraction unit; 410, extraction kettle; 420, centrifuge; 430, first delivery pump; 440, second delivery pump; 450, second component collection tank; 460, first component collection tank; 470, extract delivery pump;

[0051] 500, vacuum unit; 510, spray tank; 520, liquid seal tank; 530, spray liquid circulation pump; 540, spray liquid cooler; 550, liquid ring pump.

[0052] 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

[0053] As mentioned in the background, high-molecular-weight polylactic acid (PLA) cannot be obtained through direct polymerization of lactic acid but can only be obtained through the ring-opening polycondensation of lactide, particularly L-lactide. The chemical and optical purity of L-lactide significantly influence the molecular weight and molecular weight distribution of PLA produced by ring-opening polymerization. Impurities in L-lactide primarily consist of lactic acid, oligomers, and trace amounts of water. Lactic acid and oligomers are acidic impurities, and their presence complicates the synthesis and storage of the polymer, easily disrupting the molecular chain and causing it to hydrolyze back into lactic acid, resulting in a decrease in polymer molecular weight. The presence of water accelerates the hydrolysis of L-lactide and the polymer, similarly reducing the polymer's molecular weight. Furthermore, due to the unique chiral properties of L-lactide, its optical purity, in addition to chemical purity, significantly influences the steric properties of the polymer, resulting in polymers with varying physical properties. Therefore, only by ensuring extremely high chemical and optical purity of the L-lactide monomer can high-molecular-weight, fiber-grade PLA be produced.

[0054] Chirality refers to the property of an object or molecule that its mirror image cannot be superimposed on itself. Molecules with chirality typically contain one or more chiral centers, the most common of which is a carbon atom attached to four different substituents. Such a carbon atom is called a chiral carbon or stereocenter.

[0055] In the prior art, L-lactide purification devices suffer from poor stability, low purification rates, and low conversion and yield rates, resulting in the inability to efficiently produce high-molecular-weight, fiber-grade polylactic acid using their products. In view of this, the present invention provides an L-lactide purification device that, through a combined multi-stage separation process, can address the issues of low purification and conversion rates in L-lactide purification devices and produce L-lactide of high chemical and optical purity.

[0056] 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.

[0057] 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.

[0058] refer to Figure 1 , an embodiment of the present application provides an L-lactide purification device, including a crystallization unit 100, an evaporation unit 200, a condensation unit 300 and an extraction unit 400.

[0059] The crystallization unit 100 is used to at least crystallize the raw material to form L-lactide and a crystal residue.

[0060] The inlet of the evaporation unit 200 is connected to the outlet of the residual crystallization liquid of the crystallization unit 100. The evaporation unit 200 is at least used to evaporate the residual crystallization liquid to form evaporated gas.

[0061] The inlet of the condensing unit 300 is communicated with the gas phase outlet of the evaporating unit 200 . The condensing unit 300 is at least used to condense the evaporated gas to form condensate.

[0062] The liquid phase inlet of the extraction unit 400 is connected to the liquid phase outlet of the condensation unit 300. The extraction unit 400 is at least used to extract the condensate to form a first component containing L-lactide.

[0063] The outlet of the extraction unit 400 is connected to the crystallization unit 100, so that the crystallization unit 100 uses the first component as a raw material for crystallization.

[0064] It should be noted that the raw material is crude lactide produced by a lactide synthesis unit, and the crude lactide contains water, lactic acid, L-lactide, M-lactide and oligomers.

[0065] The chemical purity and optical purity of L-lactide can be effectively improved through a combined multi-stage separation process (crystallization, evaporation, condensation, and extraction). The crystallization process initially separates high-purity L-lactide, the evaporation and condensation processes remove volatile impurities, and the extraction process further purifies it. The first fraction containing L-lactide then enters the crystallization unit 100 again to begin a cyclic purification process, thereby continuously improving the chemical purity and optical purity of L-lactide and its utilization rate while avoiding waste of raw materials.

[0066] In some possible implementations, the crystallization unit 100 includes a crystallizer 110 , an L-lactide collection tank 120 , an L-lactide delivery pump 130 , and a residual liquid delivery pump 140 .

[0067] The crystallizer 110 is configured as a pulse tube-in-tube crystallizer 110, which is used to cool and heat the raw materials to crystallize, sweat, and melt the raw materials to form at least L-lactide and a crystal residue.

[0068] The inlet of L-lactide delivery pump 130 is connected to crystallizer 110 , and the outlet of L-lactide delivery pump 130 is connected to L-lactide collection tank 120 . L-lactide delivery pump 130 delivers L-lactide from crystallizer 110 to L-lactide collection tank 120 .

[0069] The inlet of L-lactide collection tank 120 is connected to crystallizer 110, and the outlet of L-lactide collection tank 120 is connected to L-lactide delivery pump 130. L-lactide delivery pump 130 outputs the L-lactide in L-lactide collection tank 120 into the desired product.

[0070] The inlet of the residual liquid delivery pump 140 is connected to the crystallizer 110 , and the outlet of the residual liquid delivery pump 140 is connected to the inlet of the evaporation unit 200 . The residual liquid delivery pump 140 delivers the crystallized residual liquid of the crystallizer 110 to the evaporation unit 200 .

[0071] Crystallizer 110, a pulsed shell-and-tube crystallizer, utilizes pulsed flow and a shell-and-tube structure to optimize crystallization conditions, improving product purity and crystallization efficiency. This helps control temperature and pressure conditions to crystallize L-lactide from the feedstock, resulting in high-purity L-lactide and a residual crystallization liquid. The residual crystallization liquid contains water, lactic acid, L-lactide, and oligomers, as well as a portion of L-lactide that requires further recovery. Therefore, the residual crystallization liquid is delivered to evaporation unit 200 by liquid delivery pump 140.

[0072] In some possible embodiments, the pulse tube crystallizer 110 is used to at least heat the raw material to crystallize the raw material and at least form a mother liquor.

[0073] The crystallization unit 100 includes a mother liquor collecting tank 150 and a mother liquor delivery pump 160. The mother liquor collecting tank 150 is at least used to collect the mother liquor of the crystallizer 110, and the mother liquor delivery pump 160 is at least used to deliver the mother liquor in the mother liquor collecting tank 150 to the crystallizer 110, so that the crystallization unit 100 uses the mother liquor as raw material for crystallization.

[0074] The mother liquor collecting tank 150 is used to collect the uncrystallized mother liquor in the crystallizer 110. These mother liquors usually contain incompletely crystallized liquids, which can be sent to the crystallizer 110 through the mother liquor delivery pump 160 for re-crystallization, thereby improving the utilization rate of the raw materials.

[0075] By recycling the mother liquor, L-lactide can be recovered to the maximum extent, the utilization efficiency of raw materials can be improved, and waste can be reduced.

[0076] In some possible embodiments, the crystallization unit 100 further includes a residual liquid collecting tank 170 , which is used to collect crystallization residual liquid from the crystallizer 110 . An outlet of the residual liquid collecting tank 170 is connected to the evaporation unit 200 via a residual liquid delivery pump 140 .

[0077] In some possible embodiments, the crystallization unit 100 further includes a crude lactide collection tank 180 , which can collect the raw materials and keep them warm. A crude lactide delivery pump 190 is connected to the bottom of the crude lactide collection tank 180 , and the crude lactide delivery pump 190 is used to deliver the raw materials in the crude lactide collection tank 180 into the crystallizer 110 .

[0078] It should be understood that, depending on the actual production scale, additional crystallizers 110 may be added, and the present embodiment does not limit the number of additional crystallizers 110. The liquid phase raw material inlet and nitrogen outlet of the crystallizer 110 are arranged at the top, and the liquid phase material outlet and pulse nitrogen inlet are arranged at the bottom.

[0079] The raw material of the present invention is crude lactide produced by a lactide synthesis unit. The crude lactide contains water, lactic acid, L-lactide, M-lactide, and oligomers. The crude lactide enters crystallizer 110 and undergoes multi-stage crystallization to obtain high-purity L-lactide and a crystalline residue. The crystalline residue contains not only water, lactic acid, M-lactide, and oligomers, but also a portion of L-lactide. Therefore, the crystalline residue needs to be further recovered and introduced into evaporation unit 200.

[0080] During use, the raw material, i.e., crude lactide, enters the crystallizer 110 for crystallization. The crystallizer 110 adopts an intermittent multi-stage operation process with three stages. Each stage of operation consists of five steps: feeding, nitrogen blowing, crystallization, sweating, and melting.

[0081] like Figure 1 As shown, crude lactide is added into the crude lactide collecting tank 180 along the direction of a. The crude lactide collecting tank 180 is maintained at a temperature of 65° C. and a pressure of normal pressure. The crude lactide residence time is 30 minutes.

[0082] Feeding the crystallization unit 100: The liquid phase outlet valve of the crystallizer 110 is closed, and crude lactide flows out from the bottom of the crude lactide collection tank 180 and is delivered to the crystallizer 110 via the crude lactide delivery pump 102. Nitrogen is pumped into the crystallizer 110: After the tubes in the crystallizer 110 are filled with crude lactide, the valve of the liquid phase inlet pipe of the crystallizer 110 is closed, and a heat medium is introduced into the shell side of the crystallizer 110 for heating. Nitrogen is then introduced into the tube side of the crystallizer 110 via a pulse valve to enhance heat and mass transfer. The temperature of the crystallizer 110 is maintained at 70-98°C, illustratively at 96°C, for 15 minutes to completely melt the crude lactide material.

[0083] Crystallization in the crystallizer 110: A cold medium is introduced into the shell side of the crystallizer 110 to cool the material, and the material begins to crystallize. The temperature difference is controlled at 16 to 23°C, illustratively at 18°C, and the crystallization time is 110 minutes.

[0084] The crystallizer 110 is sweated: after the crystallization is completed, the liquid phase outlet valve of the crystallizer 110 and the liquid phase inlet valve of the mother liquid collecting tank 150 are opened, and the uncrystallized liquid flows into the mother liquid collecting tank 150. The liquid phase inlet valve of the mother liquid collecting tank 150 and the liquid phase outlet valve of the crystallizer 110 are closed, and the heat medium is re-introduced into the shell side of the crystallizer 110 to increase the temperature, so that the low-melting-point substances in the crystal layer are sweated and melted. The temperature difference of sweating is controlled within 10°C, and the final sweating temperature is 92-105°C, illustratively 93°C, and the sweating time is 60 minutes;

[0085] Melting of the crystallizer 110: Open the outlet valve of the crystallizer 110 and the liquid phase inlet valve of the mother liquor collecting tank 150, discharge the low-melting-point material into the mother liquor collecting tank 150, close the liquid phase outlet valve of the crystallizer 110 and the liquid phase inlet valve of the mother liquor collecting tank 150, continue to increase the temperature of the heat medium, and completely melt the high-concentration material remaining in the crystallizer 110 tube. The melting temperature is 110-130° C., illustratively, 125° C., and the melting time is 40 min.

[0086] Open the liquid phase outlet valve of the crystallizer 110 and the liquid phase inlet valve of the L-lactide collection tank 120 to discharge the molten liquid into the L-lactide collection tank 120, completing the primary crystallization;

[0087] The liquid phase outlet valve of crystallizer 110 is closed, and the liquid phase inlet valve of crystallizer 110 is opened. The mother liquor in mother liquor collection tank 150 is fed into crystallizer 110 by mother liquor transfer pump 160, and the above-mentioned feeding, nitrogen blowing, crystallization, sweating, and melting operations are repeated to perform secondary crystallization. Tertiary crystallization is then repeated. The uncrystallized liquid and sweated low-melting-point liquid from the third stage operation flow as the crystallization residue into the residue collection tank 170. The L-lactide collection tank 120 stores L-lactide of high chemical purity and high optical purity.

[0088] Since the content of L-lactide is 42% to 68%, the L-lactide in the crystallization residue needs to be recovered; the crystallization residue in the residue collection tank 170 enters the evaporation unit 200 through the residue delivery pump 140.

[0089] Among them, the L-lactide collection tank 120 stores L-lactide of high chemical purity and high optical purity, which is output along direction A by the L-lactide delivery pump 130 to produce the desired product, that is, L-lactide of high chemical purity and high optical purity.

[0090] In some possible implementations, the evaporation unit 200 includes a residual liquid evaporator 210 , an oligomer collection tank 220 , and an oligomer delivery pump 230 .

[0091] The residual liquid evaporator 210 is used to evaporate at least the crystallization residual liquid to form liquid oligomers and evaporate gas.

[0092] The liquid phase outlet of the residual liquid evaporator 210 is communicated with the oligomer collecting tank 220 , and the oligomer collecting tank 220 collects oligomers; the gas phase outlet of the residual liquid evaporator 210 is communicated with the condensing unit 300 .

[0093] It can be seen that the main function of the residual liquid evaporator 210 is to evaporate the crystallized residual liquid from the intermediate residual liquid collecting tank 170. By heating and reducing pressure, oligomers and other impurities in the crystallized residual liquid are evaporated and separated to form liquid oligomers and mixed evaporated gas.

[0094] The residual liquid evaporator 210 may be a vertical scraping film structure, which can improve the evaporation efficiency and process viscous or heat-sensitive materials, and is provided with an independent heating unit.

[0095] During use, the crystallized residual liquid in the residual liquid collection tank 170 enters the residual liquid evaporator 210 through the residual liquid delivery pump 140, and falls along the cylinder wall of the residual liquid evaporator 210 through the liquid distributor. During the falling process, it is scraped into a film by a scraper, so that the crystallized residual liquid is rapidly vaporized under high temperature and low pressure to generate mixed steam; the pressure of the residual liquid evaporator 210 is set to 1~3.5kPa, exemplarily, 1.3kPa (A), the temperature is 200~250℃, exemplarily, 215℃, and the residence time of the steam is 1.5min.

[0096] The unvaporized liquid phase in the residual liquid evaporator 210 is oligomers, which flows out from the bottom of the residual liquid evaporator 210 and enters the oligomer collection tank 220; Figure 1 As shown, the oligomers in the oligomer collection tank 220 flow out from the bottom c and can be sent back to the lactide synthesis device through the oligomer delivery pump 230 to participate in the reaction, thereby improving the utilization rate of raw materials and avoiding waste.

[0097] The mixed steam generated by the residual liquid evaporator 210 mainly includes lactic acid, L-lactide and M-lactide, and the mixed steam enters the condensing unit 300 .

[0098] Through the treatment of the evaporation unit 200, oligomers and other impurities in the crystallization residue can be effectively removed, further improving the chemical and optical purity of lactide; by removing impurities such as oligomers and water, the negative impact of these components on the synthesis and stability of polylactic acid is reduced.

[0099] In some possible implementations, the condensing unit 300 includes a steam condenser 310 and a condensate collecting tank 320 .

[0100] The inlet of the steam condenser 310 receives the boil-off gas from the evaporation unit 200 . The steam condenser 310 is at least used to condense the boil-off gas to form condensate.

[0101] The inlet of the condensate collecting tank 320 is communicated with the outlet of the steam condenser 310 , and the outlet of the condensate collecting tank 320 is communicated with the liquid phase inlet of the extraction unit 400 .

[0102] During use, the mixed steam generated from the residual liquid evaporator 210 enters the condensate collection tank 320, and the condensate collection tank 320 condenses the mixed steam to obtain steam condensate. The steam condensate enters the condensate collection tank 320, and the liquid phase is discharged from the liquid phase outlet of the condensate collection tank 320 and sent to the extraction unit 400.

[0103] The condensate in the condensate collecting tank 320 contains water, lactic acid, L-lactide, and M-lactide. Therefore, the condensate flows out from the bottom of the condensate collecting tank 320 and enters the extraction unit 400 for further extraction to purify L-lactide.

[0104] In some possible implementations, the extraction unit 400 includes an extraction tank 410 and a centrifuge 420 .

[0105] The extraction kettle 410 is used to extract the condensate to form a first component containing L-lactide and a second component that is immiscible with the first component.

[0106] The centrifuge 420 is used to separate at least the first component and the second component.

[0107] Extraction vessel 410 processes the condensate collected from condensation unit 300. In extraction vessel 410, an appropriate solvent or extractant is used to separate the L-lactide from other impurities in the condensate, forming a two-phase system: a first fraction containing L-lactide and a second fraction that is insoluble in L-lactide. Centrifuge 420 separates the two-phase system formed in the extraction vessel. Through high-speed rotation, the centrifuge effectively separates the two phases of varying densities, separating the first fraction containing L-lactide from the second fraction containing insoluble impurities. The centrifugal separation process is fast and efficient, significantly improving the purity of the L-lactide.

[0108] Through extraction and centrifugal separation, insoluble impurities can be effectively removed to obtain high-purity L-lactide.

[0109] In some possible implementations, the extraction unit 400 includes a first delivery pump 430 , a second delivery pump 440 , a second component collection tank 450 , and a first component collection tank 460 .

[0110] The first delivery pump 430 is used to deliver at least the first component from the centrifuge 420 from the first component collection tank 460 to the crystallization unit 100 , and the second delivery pump 440 is used to deliver at least the second component from the centrifuge 420 from the second component collection tank 450 out of the L-lactide purification device.

[0111] The first delivery pump 430 transfers the first component from the centrifuge 420 from the first component collection tank 460 along the Figure 1 The molten metal is transported to the crystallization unit 100 in the middle d direction.

[0112] During use, the condensate in the condensate collecting tank 320 contains water, lactic acid, L-lactide and M-lactide. The condensate flows out from the liquid phase outlet at the bottom of the condensate collecting tank 320 and enters the extraction kettle 410. Deionized water is used as the extraction agent. Figure 1 As shown, deionized water is added to the extraction kettle 410 along the direction b. In the extraction kettle 410, M-lactide enters the aqueous phase and is hydrolyzed in the water, and lactic acid enters the aqueous phase at the same time. The operating temperature of the extraction kettle 410 is 20-45° C., illustratively, 28° C., the temperature is normal pressure, and the residence time is 55 minutes.

[0113] The bottom of the extraction kettle 410 is provided with an extract delivery pump 470. The extract in the extraction kettle 410 flows out from the bottom and is delivered to the centrifuge 420 through the extract delivery pump 470.

[0114] The extract is separated by centrifuge 420 into a first component and a second component. The first component is a heavy component containing L-lactide, and the second component is a light component containing lactic acid and water. The second component flows out of the second component outlet of centrifuge 420 into second component collection tank 450, and is then delivered by second delivery pump 440 along direction e to the outside of the L-lactide purification device. For example, the second component is delivered to the lactide synthesis device to allow lactic acid to participate in the synthesis of lactide again, thereby improving the utilization rate of raw materials. The first component flows out of the first component outlet of centrifuge 420 into first component collection tank 460, and is then delivered by first delivery pump 430 to crude lactide collection tank 180 of crystallization unit 100 for further purification.

[0115] By transporting the first component back to the crystallization unit 100, the yield of L-lactide can be further improved; the centralized collection and treatment of the second component reduces the interference of impurities on the production process, and fully utilizes the second component containing lactic acid, avoiding waste of resources.

[0116] In some possible implementations, a vacuum unit 500 is further included.

[0117] The vacuum unit 500 is at least used to keep the evaporation process of the residual crystallization liquid in a negative pressure state.

[0118] And / or, the vacuum unit 500 is at least used to place the evaporation gas condensation process in a negative pressure state.

[0119] The vacuum unit 500 includes a spray tank 510 , a liquid seal tank 520 , a spray liquid circulation pump 530 , a spray liquid cooler 540 and a liquid ring pump 550 .

[0120] During use, the condensate collection tank 320 also has a gas phase outlet, and the steam condenser 310 also generates tail gas during the condensation process. The tail gas contains lactic acid and water. The tail gas goes out from the gas phase outlet of the condensate collection tank 320 and enters the spray tank 510 of the vacuum unit 500. After cooling through the spray tank 510 and the low-temperature desalted water sprayed by the spray liquid cooler 540, the captured liquid and non-condensable gas are obtained. The captured liquid flows to the liquid seal tank 520 and returns to the spray liquid cooler 540 through the spray liquid circulation pump 530. The non-condensable gas is connected to the liquid ring pump 550 through the non-condensable gas outlet of the spray tank 510. The tail gas at the outlet of the liquid ring pump 550 can be sent to a safe point for discharge along the f direction.

[0121] It should be noted that the embodiments of the present application do not limit the positions of the material inlets and outlets of the crude lactide collection tank 180, the mother liquor collection tank 150, the L-lactide collection tank 120, the residual liquid collection tank 170, the second component collection tank 450, the extraction kettle 410, the first component collection tank 460, and the second component collection tank 450, as long as the liquid material can flow from the material inlet to the material outlet.

[0122] The embodiment of the present application does not limit the specific types of the crude lactide collection tank 180 , the oligomer collection tank 220 , the second component collection tank 450 , the first component collection tank 460 , and the extraction kettle 410 , which can be conventional equipment in the art.

[0123] For example, the crude lactide collection tank 180, the oligomer collection tank 220, the second component collection tank 450, and the first component collection tank 460 can be vertical storage tanks with jackets and / or coil heating; the residual liquid evaporator 210 of the embodiment of the present application is a vertical scraped film structure, which can be a vertical cylindrical reactor with jacket heating, with a material distributor provided on the upper part of the cylinder and a plurality of scrapers provided in the middle, and the scraper drive is installed on the top of the reactor.

[0124] To ensure uniform mixing of the raw materials and heat transfer, the crude lactide collection tank 180, oligomer collection tank 220, second component collection tank 450, first component collection tank 460, and extraction kettle 410 are each equipped with a stirring unit. The stirring unit in this embodiment is not limited to any specific stirring unit, as long as it can achieve uniform distribution of the materials within the cavity. For example, the stirring unit includes a stirring motor, a stirring shaft, and stirring blades. The stirring shaft is disposed within the cavity, with one end of the stirring shaft connected to the stirring motor and the other end connected to the stirring blades. At least one stirring blade is provided in each cavity.

[0125] like Figure 2 As shown, the embodiment of the present application provides a method for purifying L-lactide, comprising:

[0126] The raw material is crystallized to obtain L-lactide and a crystal residue;

[0127] Evaporating the crystallization residue to obtain evaporated gas;

[0128] Condensing the evaporated gas to obtain condensate;

[0129] The condensate is subjected to extraction treatment to form a first fraction containing L-lactide, and the first fraction is recycled as a raw material to participate in crystallization.

[0130] like Figure 3 As shown, in some possible embodiments, the raw material is subjected to a crystallization process, including an intermittent multi-stage process, each stage of the process including:

[0131] Nitrogen blasting treatment of raw materials;

[0132] Performing crystallization treatment on the raw materials after nitrogen blast treatment;

[0133] Performing sweating treatment on the raw materials after crystallization treatment;

[0134] The raw materials after the sweating treatment are melted.

[0135] The L-lactide chemical purity and L-lactide optical purity of the product output by the L-lactide delivery pump 130 are measured:

[0136] 1. Determination of chemical purity of L-lactide

[0137] The chemical purity of L-lactide was determined by gas chromatography.

[0138] (1) Instruments and chromatographic conditions

[0139] Agilent 6820 gas chromatograph,

[0140] Chromatographic column: DB-225 capillary column (50m×0.25mm);

[0141] Column temperature: (programmed temperature rise) initial temperature 140℃, hold for 3min, heating rate 2℃ / min,

[0142] End temperature 160℃, maintain for 35min;

[0143] Vaporization temperature: 280℃;

[0144] Detector temperature: 200°C;

[0145] Split ratio: 80:1;

[0146] Carrier gas: high-purity hydrogen, pressure 0.1 MPa;

[0147] Make-up gas: 29ml / min;

[0148] Injection method: split injection;

[0149] Injection volume: 0.1 μL.

[0150] (2) Determination of correction factor:

[0151] 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 fL-lactide = 0.723, the correction factor for water is fwater = 0.283.

[0152] (3) Sample determination:

[0153] 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.

[0154] 2. Determination of optical rotation of L-lactide

[0155] Instrument: WZZ-1 automatic polarimeter

[0156] Reagent: Ethyl acetate (analytical grade).

[0157] Accurately weigh 1.5g of sample into a 25ml volumetric flask, dissolve it in ethyl acetate, and bring to volume. Adjust the instrument as specified. Once the instrument stabilizes, fill a clean, dry polarimeter tube with ethyl acetate, carefully removing any bubbles. Place the polarimeter tube in the polarimeter and calibrate the polarimeter to zero at 20±0.5°C. Wash the polarimeter tube three times with the sample solution, then fill the polarimeter tube with the sample solution. Measure the optical rotation of the sample solution using the same method. Repeat the measurement twice and take the average value. The two results should not exceed 0.04°. Left-hand rotation is indicated by a "-".

[0158] The specific rotation of the sample is calculated according to the following formula:

[0159]

[0160] Where:

[0161] [α]-specific optical rotation of the sample solution, (°)·m2 / kg;

[0162] α-optical rotation of sample solution, °;

[0163] C-concentration of sample solution, g / ml;

[0164] L- length of the polarimeter tube, dm.

[0165] The chemical purity of the L-lactide product output by the L-lactide delivery pump 130 is 99.8%, and the optical purity is 99.5%. This embodiment of the present application can obtain L-lactide with high chemical purity and high optical purity.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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. An L-lactide purification device, characterized in that: It includes a crystallization unit (100), an evaporation unit (200), a condensation unit (300) and an extraction unit (400); The crystallization unit (100) is at least used to crystallize, sweat and melt the raw materials to form L-lactide and crystal residue; The inlet of the evaporation unit (200) is connected to the outlet of the residual crystallization liquid of the crystallization unit (100), and the evaporation unit (200) is at least used to evaporate the residual crystallization liquid to form evaporated gas; The inlet of the condensing unit (300) is in communication with the gas phase outlet of the evaporating unit (200), and the condensing unit (300) is at least used to condense the evaporated gas to form condensate; The liquid phase inlet of the extraction unit (400) is connected to the liquid phase outlet of the condensation unit (300), and the extraction unit (400) is at least used to extract the condensate to form a first component containing L-lactide; The outlet of the extraction unit (400) is further connected to the crystallization unit (100), so that the crystallization unit (100) crystallizes the first component as a raw material.

2. The L-lactide purification device according to claim 1, characterized in that: The crystallization unit (100) includes a crystallizer (110), an L-lactide collecting tank (120), an L-lactide delivery pump (130), and a residual liquid delivery pump (140); The crystallizer (110) is configured as a pulse tube-shell crystallizer (110), and the pulse tube-shell crystallizer (110) is used to cool and heat the raw material to crystallize the raw material to form at least L-lactide and a crystal residue. The inlet of the L-lactide collecting tank (120) is in communication with the crystallizer (110), and the outlet of the L-lactide collecting tank (120) is in communication with the L-lactide delivery pump (130), and the L-lactide delivery pump (130) delivers the L-lactide in the L-lactide collecting tank (120) into a desired product; The inlet of the residual liquid delivery pump (140) is connected to the crystallizer (110), and the outlet of the residual liquid delivery pump (140) is connected to the inlet of the evaporation unit (200). The residual liquid delivery pump (140) delivers the crystallized residual liquid of the crystallizer (110) to the evaporation unit (200).

3. The L-lactide purification device according to claim 2, characterized in that: The pulse tube crystallizer (110) is used at least to cool and heat the raw materials, so as to crystallize, sweat and melt the raw materials to form at least a mother liquor; The crystallization unit (100) includes a mother liquor collecting tank (150) and a mother liquor delivery pump (160), wherein the mother liquor collecting tank (150) is at least used to collect the mother liquor of the crystallizer (110), and the mother liquor delivery pump (160) is at least used to deliver the mother liquor in the mother liquor collecting tank (150) to the crystallizer (110), so that the crystallization unit (100) crystallizes using the mother liquor as raw material.

4. The L-lactide purification device according to claim 1, characterized in that: The evaporation unit (200) includes a residual liquid evaporator (210), an oligomer collection tank (220), and an oligomer delivery pump (230); The residual liquid evaporator (210) is at least used to evaporate the crystallization residual liquid to form liquid oligomers and evaporated gas; The liquid phase outlet of the residual liquid evaporator (210) is communicated with the oligomer collecting tank (220), and the oligomer collecting tank (220) collects the oligomers; the gas phase outlet of the residual liquid evaporator (210) is communicated with the condensing unit (300).

5. The L-lactide purification device according to claim 1, characterized in that: The condensing unit (300) includes a steam condenser (310) and a condensate collecting tank (320); The inlet of the steam condenser (310) receives the evaporated gas from the evaporation unit (200), and the steam condenser (310) is at least used to condense the evaporated gas to form condensate; The inlet of the condensate collecting tank (320) is communicated with the outlet of the steam condenser (310), and the outlet of the condensate collecting tank (320) is communicated with the liquid phase inlet of the extraction unit (400).

6. The L-lactide purification device according to claim 1, characterized in that: The extraction unit (400) includes an extraction kettle (410) and a centrifuge (420); The extraction kettle (410) is used to extract the condensate to form a first component containing L-lactide and a second component that is incompatible with the first component; The centrifuge (420) is used to separate at least the first component and the second component.

7. The L-lactide purification device according to claim 6, characterized in that: The extraction unit (400) includes a first delivery pump (430), a second delivery pump (440), a second component collection tank (450) and a first component collection tank (460); The first delivery pump (430) is at least used to deliver the first component from the centrifuge (420) from the first component collecting tank (460) to the crystallization unit (100), and the second delivery pump (440) is at least used to deliver the second component from the centrifuge (420) from the second component collecting tank (450) out of the L-lactide purification device.

8. The L-lactide purification device according to any one of claims 1 to 7, characterized in that: Also included is a vacuum unit (500); The vacuum unit (500) is at least used to place the evaporation process of the residual crystallization liquid in a negative pressure state; And / or, the vacuum unit (500) is at least used to place the evaporation gas condensation process in a negative pressure state.

9. A method for purifying L-lactide, characterized in that: include: The raw material is crystallized to obtain L-lactide and a crystal residue; Evaporating the crystallization residue to obtain evaporated gas; condensing the evaporated gas to obtain a condensate; The condensate is subjected to extraction treatment to form a first component containing L-lactide, and the first component is recycled as the raw material to participate in the crystallization.

10. The method for purifying L-lactide according to claim 9, wherein: The raw materials are crystallized, including intermittent multi-stage treatment, each stage of treatment includes: subjecting the raw material to nitrogen blast treatment; performing crystallization treatment on the raw material after the nitrogen blast treatment; performing a sweating treatment on the raw material after the crystallization treatment; The raw material after the sweating treatment is melted.

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