WO2022155762A1 - 一种丙交酯的制备方法以及反应装置 - Google Patents

一种丙交酯的制备方法以及反应装置 Download PDF

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WO2022155762A1
WO2022155762A1 PCT/CN2021/072593 CN2021072593W WO2022155762A1 WO 2022155762 A1 WO2022155762 A1 WO 2022155762A1 CN 2021072593 W CN2021072593 W CN 2021072593W WO 2022155762 A1 WO2022155762 A1 WO 2022155762A1
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reaction
lactic acid
rectification
distillation column
reactive distillation
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PCT/CN2021/072593
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English (en)
French (fr)
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何岩
车传亮
朱梦瑶
刘杰
朱小瑞
田博
刘英俊
张红涛
杨颖�
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万华化学(四川)有限公司
万华化学集团股份有限公司
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Priority to PCT/CN2021/072593 priority Critical patent/WO2022155762A1/zh
Publication of WO2022155762A1 publication Critical patent/WO2022155762A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D319/00—Heterocyclic compounds containing six-membered rings having two oxygen atoms as the only ring hetero atoms
    • C07D319/10—1,4-Dioxanes; Hydrogenated 1,4-dioxanes
    • C07D319/12—1,4-Dioxanes; Hydrogenated 1,4-dioxanes not condensed with other rings
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
    • C08G63/08—Lactones or lactides

Definitions

  • the present application relates to the technical field of lactide, in particular to a preparation method and a reaction device of lactide.
  • Polylactic acid also known as polylactide
  • PLA polylactic acid
  • polylactide is a typical biodegradable polymer material prepared by chemical synthesis from renewable plant resources.
  • the global market demand for PLA has increased rapidly. It is expected that the demand will double every 3-5 years in the next few years, and it is expected to be in short supply for a long time.
  • the global plastic ban and waste sorting have brought a huge potential market for degradable plastics, especially single-use plastic products.
  • the industrial production of PLA generally adopts the ring-opening polymerization method of lactide.
  • Lactide is a key intermediate in the synthesis of PLA, and its synthesis process and key equipment are the focus of research in the industry.
  • two-step lactic acid method is generally adopted for the industrial synthesis of lactide, that is, the lactic acid is first polymerized to obtain a lactic acid oligomer with a certain molecular weight, and then the lactic acid oligomer is cracked and cyclized in the presence of a catalyst to obtain crude lactide.
  • crude lactide is purified to obtain qualified lactide products, such as US1095205(1914), US2668162(1954), US4835293(1989), US4797468(1989), US5053522(1991), US5247058(1993), WO9509879A1(1995) , CN11122559A (1995), EP98203427.4 (1998), US6005067A (1999), CN1688569A, (2003) CN105814110 (2014) etc. disclosed prior art.
  • qualified lactide products such as US1095205(1914), US2668162(1954), US4835293(1989), US4797468(1989), US5053522(1991), US5247058(1993), WO9509879A1(1995) , CN11122559A (1995), EP98203427.4 (1998), US6005067A (1999), CN1688569A, (2003) CN105814110 (2014) etc. disclosed prior art.
  • the disclosed prior art still has problems such as complicated process, many equipments, and large investment, which increases the production cost of lactide.
  • the lactic acid prepolymerization and lactic acid oligomer depolymerization process includes 5 reactors, 4 sets of rectification towers and 27 auxiliary necessary devices in total. The process is complicated and the number of devices is large.
  • the above-disclosed technology does not mention the recycling of defocal oil. If the tar reuse process is added, the process is bound to become more complicated.
  • the reactor is the core technology for the preparation of lactide.
  • researchers have done a lot of exploration.
  • US5258488 uses a tank reactor
  • JP3083461/93 and EP0893462A2 use a tank reactor with reactive distillation
  • US5023349 and WO9318019A1 use a tower reaction device.
  • a reactor form with strong heat and mass transfer capability and low residence time is particularly required.
  • reactors with enhanced heat transfer and mass transfer especially thin film reactors, such as WO9509879, KP20140023143 disclose horizontal and vertical tubular falling film reactors, etc., and WO9509879, CA2113799 disclose the use of Vertical wiped film reactor with rotating parts, EP1873185 discloses a horizontal wiped film reactor and the like.
  • CN107531663A discloses the technology of maintaining crude lactide under elevated temperature for at least 5 hours to control the content of lactic acid oligomers.
  • WO9509879A1 discloses the use of fractional coagulation to remove lactic acid in crude lactide, thereby reducing the pressure of separation process to remove lactic acid.
  • EP0893462A2, JP308346/93 and CN1894193A for preparing lactide by reactive distillation and depolymerization can significantly reduce the oligomerization of lactic acid in the stream entering the lactide purification process, which is conducive to reducing the difficulty of purification in the refining process and suppressing side effects. reaction to improve the purification yield.
  • the crude lactide is kept at high temperature for at least 5 hours, the equipment investment is large, the efficiency is low, and the yield is reduced along with side reactions such as lactide polymerization; the scheme of partial condensation and delactic acid removal is not effective. good, and there is still room for improvement in energy utilization.
  • a large amount of lactic acid oligomers are refluxed into the depolymerization reactor in the form of liquid phase and then evaporated to the gas phase to re-enter the rectifying tower, causing lactic acid oligomers in the depolymerization reactor.
  • the internal circulation and accumulation in the depolymerization consumes a lot of energy, and significantly increases the acid content in the depolymerization reactor, increasing the side reactions.
  • one of the purposes of this application is to provide a preparation method of lactide.
  • the preparation method greatly simplifies the process and equipment of the lactic acid two-step method, reduces the energy consumption and production cost of the entire lactide production device, and simultaneously can obtain high-quality lactide products.
  • the application provides a preparation method of lactide, and the preparation method comprises the following steps:
  • the following reaction is coupled to the reactive distillation column II and carried out: the first lactic acid oligomer is subjected to an oligomerization reaction to obtain a second lactic acid oligomer, and the second lactic acid oligomer is subjected to the first lactic acid oligomer.
  • Depolymerization reaction obtains lactide primary product;
  • Preliminary polymerization refers to the process of esterification and dehydration of lactic acid to obtain polylactic acid with lower molecular weight.
  • the general initial polymerization molecular weight is 200-800, preferably 200-500.
  • the oligomerization reaction refers to the process in which the preliminary polymerization product undergoes further polymerization reaction to obtain polylactic acid with higher molecular weight.
  • the general oligomeric molecular weight is 1000-2500.
  • the application provides a novel method for preparing lactide, which enables the preliminary polymerization of lactic acid to be carried out in the reactive distillation column I, and couples the oligomerization of lactic acid oligomers and a part of the depolymerization reaction in the reactive distillation column.
  • tower II the process steps are simplified, and high-purity L (or D)-lactide product can be obtained at the same time.
  • the depolymerization reaction is carried out in two steps, and the gas phase composition of the first depolymerization reaction is removed into the gas phase and circulated in the reactive distillation column 1 to the prepolymerization reaction, which can significantly reduce the amount of gas entering the second depolymerization reaction.
  • the content of free lactic acid and lactic acid oligomers in the lactic acid prepolymer can further inhibit the side reaction of the depolymerization reaction, and significantly reduce the key indicators such as moisture and acid value of the crude lactide, the depolymerization reaction product.
  • the weight average molecular weight of the first lactic acid oligomer is 200-800, such as 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, etc., Preferably 250-500.
  • the operating pressure of the reactive distillation column 1 is 10 to 200kPaA (the pressure units appearing in this paper all refer to absolute pressure unless otherwise specified), such as 20kPaA, 30kPaA, 40kPaA, 50kPaA, 60kPaA, 70kPaA, 80kPaA, 90kPaA, 100kPaA, 110kPaA, 120kPaA, 130kPaA, 140kPaA, 150kPaA, 160kPaA, 170kPaA, 180kPaA, 190kPaA, etc., preferably 15-100kPaA.
  • the operating temperature of the reactive distillation column I is 5 to 170°C, such as 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, etc., preferably 40-150°C.
  • the pressure of the preliminary polymerization reaction is 0.1-2BarA, such as 0.2BarA, 0.3BarA, 0.4BarA, 0.5BarA, 0.6BarA, 0.7BarA, 0.8BarA, 0.9BarA, 1BarA, 1.1BarA , 1.2BarA, 1.3BarA, 1.4BarA, 1.5BarA, 1.6BarA, 1.7BarA, 1.8BarA, 1.9BarA, etc., preferably 0.15-1BarA.
  • the temperature of the preliminary polymerization reaction is 100-180°C, such as 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, etc., preferably 120-170°C .
  • the preparation method further comprises: coupling the lactic acid to the reactive distillation column I for de-free water treatment.
  • the method for removing free water treatment includes distillation under elevated temperature and vacuum conditions, or distillation under conditions of atmospheric pressure to higher than atmospheric pressure, or stripping with inert gas such as N 2 .
  • the present application preferably evaporates at a temperature rise, and the temperature for removing free water is generally 100-170°C, preferably 120-150°C, and the pressure It is 10-200kPaA, Preferably it is 15-100kPaA.
  • the preparation method further comprises: coupling the purification reaction of water into the reactive distillation column I to carry out.
  • the method for purification comprises that the overhead condenser is refluxed to the upper packing part of the reactive rectification column 1, and the gas phase containing lactic acid is in countercurrent contact with the rising gas phase in the packing section, and the lactic acid in the gas phase is recovered by rectification, and the final column
  • the top results in an aqueous phase that is practically free of lactic acid.
  • the temperature for realizing the water purification operation is generally 40-150°C, preferably 40-120°C, and the pressure is 10-200 kPaA, preferably 15-100 kPaA.
  • the weight average molecular weight of the second lactic acid oligomer is 800-5000, such as 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000, 3200 , 3400, 3600, 3800, 4000, 4200, 4400, 4600, 4800, etc., preferably 1000-2500.
  • the operating pressure of the reactive distillation column II is 0.1-5kPaA, such as 1kPaA, 2kPaA, 3kPaA, 4kPaA, etc., preferably 0.5-2kPaA.
  • the operating temperature of the reactive distillation column II is 120-180°C, such as 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, etc., preferably 140-170°C .
  • the pressure of the oligomerization reaction is 0.5-5kPaA, such as 1kPaA, 1.5kPaA, 2kPaA, 2.5kPaA, 3kPaA, 3.5kPaA, 4kPaA, 4.5kPaA, etc., preferably 1-2kPaA.
  • the temperature of the oligomerization reaction is 120-180°C, such as 130°C, 140°C, 150°C, 160°C, 170°C, etc., preferably 140-170°C.
  • step (2) the first depolymerization reaction is carried out in the column kettle reboiler of the reactive distillation column II.
  • the conversion rate of the second lactic acid oligomer is ⁇ 20%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, etc., preferably ⁇ 10%, more preferably ⁇ 5% .
  • the conversion rate of the second lactic acid oligomer in the first depolymerization reaction is controlled below 20%, because in the first depolymerization reaction in the reactive distillation column II, the depolymerization The gas-phase product of 2 will rise directly into the upper tray of the rectification tower II, thereby causing the reduction of the single-pass yield of the prepolymerization reaction.
  • the temperature of the first depolymerization reaction is ⁇ 210°C, such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc., preferably 180-200°C.
  • the pressure of the first depolymerization reaction is 0.1-5kPaA, such as 1kPaA, 2kPaA, 3kPaA, 4kPaA, 5kPaA, etc., preferably 0.5-2kPaA.
  • the temperature of the second depolymerization reaction is 170-240°C, such as 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, etc., preferably 180- 220°C.
  • the pressure of the second depolymerization reaction is 0.1-5kPaA, such as 1kPaA, 2kPaA, 3kPaA, 4kPaA, etc., preferably 0.5-2kPaA.
  • the preparation method further comprises: coupling the hydrolysis reaction of the depolymerized oil obtained by the reaction of step (3) into a reactive distillation column I for carrying out. Realize the recycling and reuse of the focused oil, reduce the unit consumption of raw materials, and at the same time do not significantly increase the equipment and investment, which can significantly reduce the total production cost.
  • the temperature of the hydrolysis reaction is 100-170°C, such as 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, etc., preferably 120-150°C.
  • the pressure of the hydrolysis reaction is 10-200kPaA, such as 20kPaA, 40kPaA, 60kPaA, 80kPaA, 100kPaA, 120kPaA, 140kPaA, 160kPaA, 180kPaA, etc., preferably 15-100kPaA.
  • step (3) the column still liquid of the reactive rectification tower II enters the reactive rectification tower III through a thermal insulation pipeline.
  • the temperature of the thermal insulation pipeline is 140-150°C, such as 141°C, 142°C, 143°C, 144°C, 145°C, 146°C, 147°C, 148°C, 149°C, and the like.
  • the preparation method specifically comprises the following steps:
  • reaction is coupled in reactive distillation column 1 to carry out: carry out the dehydration treatment of lactic acid, the preliminary polymerization reaction of lactic acid, the purifying reaction of water and the hydrolysis reaction of depolymerizing oil;
  • the following reaction is coupled to the reactive distillation column II and carried out: the first lactic acid oligomer obtained by the preliminary polymerization reaction is subjected to an oligomerization reaction to obtain a second lactic acid oligomer, and the second lactic acid oligomer is The polymer carries out the first depolymerization reaction to obtain the initial product of lactide;
  • the raw lactic acid is dehydrated, the lactic acid preliminary polymerization reaction, the water purification and the hydrolysis reaction of the depolymerized oil are coupled to the reactive distillation column I to take place; the lactic acid oligomerization reaction, the lactic acid oligomer The partial depolymerization reaction coupled to reactive distillation column II takes place.
  • the reactive distillation column III includes a depolymerization reaction section, a polymerization reaction section and a rectification section from bottom to top.
  • step (3) the following steps are carried out after step (3):
  • step (3) make the lactide that step (3) obtains to carry out the first rectification in the rectifying section of reactive distillation column III, and obtain the liquid phase stream at the bottom of the rectifying section;
  • the residual lactic acid and lactic acid oligomers are converted into polylactic acid with higher molecular weight, And it is decomposed into lactide again when it is recycled back to reactive distillation column III.
  • the technology of the reactive distillation column III disclosed in this application can improve the yield, and finally can obtain L (or D)-lactide with high optical purity products, and further reduce production costs.
  • step (4) further comprises: extracting the first lactide stream in the side line of the reactive distillation column III.
  • the lactide stream is preferably extracted in the side stream of the reactive distillation column, because the content of lactide in the side stream stream is relatively high, and the content of lactic acid and lactic acid oligomers is relatively low, which can further improve the product quality.
  • the first lactide stream is a liquid phase stream.
  • the distance from the position of the side line extraction to the bottom of the reactive distillation column III is 1/3-1/2 of the total height of the reactive distillation column III.
  • the content of lactic acid in the first lactide stream is ⁇ 1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc., preferably ⁇ 0.5%.
  • the lactic acid oligomer content in the first lactide stream is ⁇ 1%, such as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc., preferably ⁇ 0.2%, more preferably ⁇ 0.1%.
  • the temperature of the first rectification is 100-150°C, such as 110°C, 120°C, 130°C, 140°C, and the like.
  • the pressure of the first rectification is 0.1 ⁇ 5kPaA, such as 1kPaA, 1.5kPaA, 2kPaA, 2.5kPaA, 3kPaA, 3.5kPaA, 4kPaA, 4.5kPaA, etc., preferably 0.5 ⁇ 2kPaA.
  • step (4) the pressure of the first rectification is the same as the pressure of the depolymerization reaction in step (3).
  • the polymerization reaction time is ⁇ 1h, such as 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h h, 8h, 8.5h, 9h, 9.5h, etc., preferably 1-10h, more preferably 1-5h, still more preferably 1-2h.
  • the temperature of the polymerization reaction is 100-240°C, such as 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C °C, 210 °C, 220 °C, 230 °C, etc.
  • the time of the polymerization reaction is ⁇ 1 h, and the temperature of the polymerization reaction is 100-240°C.
  • the temperature of the polymerization reaction is lower than the temperature of the second depolymerization reaction.
  • the temperature of the polymerization reaction is higher than the temperature of the side line extraction position.
  • the extraction temperature of the side line, the polymerization temperature and the depolymerization reaction temperature are increased in sequence, so that the polymerization temperature can be controlled in a reasonable range, so as to avoid the polymerization reaction rate being too low when the temperature is too low, or the lactic acid and lactic acid dimerization caused by the temperature being too high.
  • step (5) the polymerization reaction is carried out in a reaction vessel or a reactive distillation tray.
  • the stay time of the column bottom liquid stream in the reactive distillation tray is 1-10h, for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h , 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, etc., preferably 1-5h, more preferably 1-2h.
  • the weight average molecular weight of the lactic acid oligomer obtained by the polymerization reaction is 800-2500, such as 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000 , 2100, 2200, 2300, 2400, etc.
  • the above-mentioned lactic acid oligomers with specific molecular weights are preferably obtained by polymerization. Higher molecular weights can effectively reduce the content of residual lactic acid and lactic acid oligomers in crude lactide, reduce the acid value of the final lactide product, and further improve the The quality of the final lactide product.
  • the preparation method further comprises step (6): entering the first lactide stream into the rectifying tower IV for the second rectification, and extracting the second rectification in the side line of the rectifying tower IV The dilactide stream was crystallized to give the lactide.
  • the temperature of the second rectification is 130°C-160°C, such as 135°C, 140°C, 145°C, 150°C, 155°C, and the like.
  • the pressure of the second rectification is 0.1-5kPaA, such as 0.5kPaA, 1kPaA, 1.5kPaA, 2kPaA, 2.5kPaA, 3kPaA, 3.5kPaA, 4kPaA, 4.5kPaA and the like.
  • the flow rate of the second lactide stream accounts for 60-90% of the feed flow rate of the rectification column IV, such as 65%, 70%, 75%, 80%, 85%, etc., preferably 70-80% .
  • the preparation method comprises the following steps:
  • reaction is coupled in reactive distillation column 1 to carry out: carry out the dehydration treatment of lactic acid, the preliminary polymerization reaction of lactic acid, the purifying reaction of water and the hydrolysis reaction of depolymerizing oil;
  • the following reaction is coupled to the reactive distillation column II and carried out: the first lactic acid oligomer obtained by the preliminary polymerization reaction is subjected to an oligomerization reaction to obtain a second lactic acid oligomer, and the second lactic acid oligomer is The polymer undergoes a first depolymerization reaction;
  • step (3) make the lactide obtained in step (3) enter the rectifying section of reactive distillation column III, carry out the first rectification at 100 ⁇ 150° C. and 0.1 ⁇ 5kPaA, and obtain the liquid phase stream at the bottom of the rectifying section , and extract the first lactide stream with lactic acid content ⁇ 1% and lactic acid oligomer content ⁇ 1% in the side line of the reactive distillation column III;
  • the second purpose of the present application is to provide a reaction device used in the preparation method described in one of the purposes, the reaction device comprises a reactive distillation column I, a reactive distillation column II and a reactive distillation column connected in sequence through pipelines Tower III.
  • the reactive rectification tower I, the reactive rectification tower II and the reactive rectification tower III are each independently provided with at least two plate-type rectification trays.
  • the plate-type rectification tray comprises a sieve tray, a solid valve, a float valve, a bubble cap or a jet tray.
  • the tray-type rectification tray comprises trays, gas-phase channels, overflow weirs, downcomers and guide plates.
  • each stage of the plate rectification tray includes at least two gas phase channels parallel to each other, and the space enclosed by the shell, the tray, the overflow weir and the gas phase channel on the plate rectification tray is a liquid phase channel.
  • a heat exchange tube is provided above the column plate and in the liquid phase height.
  • the gas phase channel is perpendicular to the tray.
  • the height of the gas phase channel is greater than the height of the liquid phase on the rectification tray.
  • a channel for supplying gas and liquid two phases to pass through is provided on the column plate, and a gas-liquid two-phase product is obtained by the reaction, and the liquid-phase reaction liquid flows horizontally through the surface of the column plate in the form of a thin film, and the gas phase passes through the gas phase.
  • the channels pass through the trays and flow perpendicular to the trays.
  • the plate-type rectification tray is located below the feed port of the reactive rectification column I or the reactive rectification column II.
  • a heating pipeline is provided on the plate-type rectification tray.
  • the plate-type rectification tray comprises at least two mutually parallel strip-shaped gas channels arranged in the direction from the liquid receiving tray to the downcomer, and the strip-shaped gas channels do not pass through the liquid layer on the tray;
  • the channels enclosed between the strip-shaped gas-phase channels are liquid-phase channels;
  • the liquid-phase channels are provided with liquid-phase baffles that are perpendicular to the strip-shaped gas-phase channels and alternate high and low.
  • the horizontal viewing angle structure of the plate-type rectification tray is shown in FIG. 1
  • the top viewing angle structure is shown in FIG. 2 .
  • the plug flow of the liquid phase in the reactive rectification tower can be realized, and on the basis of ensuring heat and mass transfer, the residence time distribution caused by liquid phase back-mixing can be significantly reduced, etc.
  • the problem is that lactic acid oligomers with a narrower molecular weight distribution can be obtained, thereby obtaining better lactide yield and product quality in the depolymerization reaction.
  • the reactive rectification column I comprises a column body I and a first reboiler connected with the feed port at the bottom of the column body I.
  • the first reboiler provides the reactive distillation column I with rising steam and the heat required for the reaction.
  • the reactive distillation column I does not contain the first reboiler.
  • the reactive rectification column II comprises a column body II and a second reboiler connected with the feed port at the bottom of the column body II.
  • the second reboiler provides rising steam for the reactive distillation column II, and serves as a reactor for the first depolymerization reaction to provide the heat required for the first depolymerization reaction.
  • the tower still liquid of the reactive distillation column II enters the reactive distillation column III through a thermal insulation pipeline with a heating device to carry out the second depolymerization reaction, and the temperature of the lactic acid oligomer in the thermal insulation pipeline is maintained at 140-150°C to ensure that the lactic acid oligomer flows in a liquid state.
  • the lower section of the reactive distillation column III is provided with a distillation tank.
  • the distillation tank is equipped with a heating interlayer. Oil heating or steam heating is used in the interlayer to maintain the temperature of lactic acid oligomers in the distillation tank at 170-240 °C. It is evaporated in gaseous form.
  • the reactive distillation column III includes a depolymerization reaction section, a polymerization reaction section and a rectification section from bottom to top, the depolymerization reaction section is provided with a depolymerization reactor, and the The polymerization reaction section is provided with a reactive distillation tray.
  • the depolymerization reactor is a thin film reactor, preferably including a falling film depolymerization reactor or a horizontal depolymerization reactor.
  • the horizontal depolymerization reactor is a reaction vessel with a length-to-diameter ratio greater than 1 placed horizontally, wherein a reactive distillation tray is arranged horizontally.
  • the reaction vessel comprises a tank reactor, a tubular reactor or a shell and tube reactor, preferably a shell and tube reactor with a heating function.
  • the reactive rectification tray is a plate type rectification tray.
  • the reactive rectification tray comprises at least two mutually parallel strip-shaped gas channels arranged in the direction from the liquid receiving tray to the downcomer, and the strip-shaped gas channels do not pass through the liquid layer on the tray;
  • the channels enclosed between the strip-shaped gas-phase channels are liquid-phase channels;
  • the liquid-phase channels are provided with liquid-phase baffles that are perpendicular to the strip-shaped gas-phase channels and alternate high and low. Specifically as shown in Figure 3.
  • a plug-flow reactive rectification tray with a large liquid holdup is used, and the liquid-phase reaction vessel at high temperature is integrated into the rectification tower, which increases the degree of integration and simplifies the process. And the flow effect of the plug flow is obtained to the maximum extent, the back mixing and side reactions are reduced, the reaction yield is finally improved, and the production cost is reduced.
  • the reactive distillation column III is provided with a first side-drawing device.
  • the crude lactide product obtained by the side line can significantly reduce the lactic acid, moisture and lactic acid oligomers in the crude lactide, and significantly reduce the technical difficulty and manufacturing cost of the downstream separation process.
  • the distance from the first side line extraction device to the bottom of the reactive distillation column III is 1/3-1/2 of the total height of the reactive distillation column III.
  • the reaction device further comprises a rectification column IV connected to the first side-line extraction device through a pipeline, and a second side-line extraction device is provided on the rectification column IV.
  • the reaction device further includes a crystallization device connected to the second side-drawing device through a pipeline.
  • the application provides a novel method for preparing lactide, which enables the preliminary polymerization of lactic acid to be carried out in the reactive distillation column I, and couples the oligomerization of lactic acid oligomers and a part of the depolymerization reaction in the reactive distillation column.
  • tower II the process steps are simplified, and high-purity L (or D)-lactide product can be obtained at the same time.
  • the method and device provided by the present application significantly reduce equipment investment and production costs, and have outstanding economic advantages.
  • FIG. 1 is a diagram of a reaction apparatus in a specific embodiment of the present application.
  • FIG. 2 is a schematic structural diagram of a horizontal viewing angle of a plate-type rectification tray in a specific embodiment of the present application.
  • FIG. 3 is a schematic structural diagram of a top view of a plate-type rectification tray in a specific embodiment of the present application.
  • FIG. 4 is a horizontal view of the horizontal thin film depolymerization reactor of the depolymerization reaction section of the reactive distillation column III according to an embodiment of the present application.
  • Fig. 5 is a top view of water of the horizontal thin film depolymerization reactor in the depolymerization reaction section of the reactive distillation column III in a specific embodiment of the present application.
  • the L lactic acid raw material used in the examples in this application is from Jiangxi Musashino Company, the chemical purity of L lactic acid is 88%, and the optical purity is 99.7%; the catalyst stannous octoate comes from Aladdin reagent, and the purity is 98%.
  • Characterization equipment the quantitative detection of the composition of the substance in the embodiment adopts gas chromatography (GC), and the chromatographic column and the chromatographic conditions are as follows:
  • the sample concentration was calculated by taking the sample peak area into the standard curve formula. Analytical results are reported in mg/L. The content of lactide isomers was calculated by the external standard curve method:
  • the present embodiment provides a preparation method of lactide, and the preparation method is as follows:
  • reaction is coupled in reactive distillation column 1 to carry out: carry out the dehydration treatment of lactic acid, the preliminary polymerization reaction of lactic acid, the purifying reaction of water and the hydrolysis reaction of depolymerizing oil;
  • the following reaction is coupled to the reactive distillation column II and carried out: the first lactic acid oligomer obtained by the preliminary polymerization reaction is subjected to an oligomerization reaction to obtain a second lactic acid oligomer, and the second lactic acid oligomer is The polymer undergoes a first depolymerization reaction;
  • step (3) obtains carry out the first rectification in the reactive rectification section of reactive rectification tower III, obtain the liquid phase stream at the bottom of the tower, and in the side line of the reactive rectification tower III Produce the first lactide stream;
  • the pressure of reactive distillation tower I is 15kPaA, the temperature at the top of the tower is 40 ° C, and the temperature on the tray is controlled by the temperature of the heat transfer oil heat exchange tube. 130-150°C; reflux ratio 1:1. Reactive distillation column 1 feeds 40kg/h, and the concentration of catalyst stannous octoate is 0.3%.
  • the pressure of reactive distillation column II is 2kPaA
  • the temperature at the top of the column is 120°C
  • the temperature on the tray is controlled by the heat transfer oil heat exchange tube, which is controlled at 150°C from top to bottom, and the reflux ratio is 1:4.
  • the temperature of the reboiler, namely the first depolymerization section, was 180°C.
  • the pressure of the reactive distillation column III is 0.5kPaA
  • the temperature on the tray of the depolymerization section is controlled by the heat transfer oil heat exchange tube
  • the control reaction temperature is 220 ° C
  • the reflux ratio is 1:4
  • the present embodiment also provides a reaction device used in the above-mentioned preparation method, which is specifically as follows:
  • reaction unit as shown in Figure 1, wherein, reactive distillation tower 1 diameter 200mm, the upper part is the ⁇ ring packing of 5*5mm of 1m height, bottom 20 reactive distillation trays, tray structure as shown in Figure 2 and Figure As shown in Fig. 3, the liquid holding height of the tray is 100mm, and the heat-conducting coil is arranged on the tray, and the temperature is controlled by heat-conducting oil.
  • the diameter of the reactive distillation column II is 200mm, and the rectifying section is the ⁇ ring packing of 5*5mm with a height of 1m, and 25 reactive distillation trays are set in the upper part of the rectification as the second prepolymerization section (the tray structure is shown in Figure 2 and Figure 2). 3), the liquid holding height of the tray is 200mm, a heat-conducting coil is arranged on the tray, the temperature is controlled by heat-conducting oil, and the reboiler is the first depolymerization section.
  • Reactive distillation column III includes depolymerization reaction section, polymerization reaction section and rectification section from bottom to top.
  • the diameter of polymerization reaction section and rectification section is 200mm.
  • the polymerization reaction section adopts 20 bubble cap trays, and the tray liquid holding height is 200mm. 200mm, the liquid phase residence time is 1h, the rectification section is filled with 5*5mm ⁇ ring packing with a height of 1m, and the crude lactide product is extracted from the middle side line of the polymerization reaction section and the rectification section.
  • the depolymerization reaction section in the lower part of the reactive distillation column III adopts the horizontal thin-film depolymerization reactor as shown in Figure 4 and Figure 5 as the depolymerization reaction section.
  • the height of the tray weir is 20mm, and there are 4 rows of 30*600mm rectangular gas-phase channels, the height of the gas-phase channel is 80mm, and there are 10
  • the lactic acid 2-5 polymerization products refer to lactic acid dimers, trimers, tetramers and pentamers, and the same is true in the following examples.
  • the present embodiment provides a preparation method and a reaction device of lactide, and the reaction device is the same as that in Example 1, except that the following operating conditions are different:
  • the pressure of reactive distillation tower I is normal pressure
  • the temperature at the top of the tower is 100 ° C
  • the temperature on the tray is controlled by the heat transfer oil heat exchange tube
  • the temperature of the upper 10 trays is 150 ⁇ 160 ° C
  • the temperature of the lower 10 trays is 150-160 ° C. It is 160 ⁇ 170°C
  • the reflux ratio is 1:1.
  • the feed to the reactive distillation column is 20kg/h.
  • the pressure of the reactive distillation column II is 1kPaA
  • the temperature on the tray is controlled by the heat transfer oil heat exchange tube, from top to bottom, it is controlled to be 170°C
  • the temperature of the tower kettle reboiler is 190°C.
  • the conversion of the first depolymerization reaction in reactive distillation column II was 10%.
  • the yield of the second depolymerization reaction in the third column of the reactive distillation column was 63.0%, the optical purity of crude lactide was 96.5%, the lactic acid content was 0.51%, and the total content of the 2-5 lactic acid polymerization products was 1.24%.
  • This embodiment provides a preparation method and reaction device of lactide, the reaction device is the same as that of embodiment 1, the difference is only that the temperature of the reboiler of the first depolymerization reaction section, namely the reactive distillation column II, is controlled to 200°C.
  • the lactic acid content of crude lactide can be regulated by the process of regulating the first depolymerization section, and the content of lactic acid and lactic acid oligomers in crude lactide can be regulated.
  • the content is beneficial to the purification of the downstream lactide and the control of the acid content of the product.
  • This embodiment provides a preparation method and reaction device of lactide, the reaction device is the same as that of embodiment 1, the difference is only that the temperature of the reboiler of the first depolymerization reaction section, that is, the reactive distillation column II, is controlled to be 210°C.
  • the present embodiment provides a preparation method and a reaction device for lactide.
  • the reaction device is the same as that in Example 1, except that the temperature of the reboiler in the first depolymerization reaction section, that is, the reactive distillation column II, is controlled to be 220° C., and the reaction The conversion rate of lactic acid oligomers in the first depolymerization reaction in the rectification column II was 27%.
  • the conversion rate of the first depolymerization reaction stage is controlled within 20%.
  • the present embodiment provides a preparation method and a reaction device for lactide, and the reaction device is the same as that in Example 1, except that the top pressure of the reactive distillation column I is 100 kPaA, the top temperature is 100 °C, and the top 10 The tray temperature is 100-130°C.
  • the molecular weight and molecular weight distribution of the lactic acid oligomer can be adjusted.
  • the reason is that the depolymerization reactor residue of the depolymerization reaction contains a high molecular weight lactic acid polymer, which is mixed with an aqueous lactic acid solution in a reactive distillation column, and undergoes hydrolysis and transesterification to obtain a low molecular weight polymer.
  • the sufficient reaction of ⁇ is beneficial to obtain lactic acid oligomers with narrower molecular weight distribution, which has a significant impact on the reaction rate and yield of the depolymerization reaction.
  • the present embodiment provides a preparation method and reaction device of lactide, the preparation method is the same as that of embodiment 1, the difference is only that the reactive distillation tray is replaced with a traditional bubble cap tray, and the operating conditions are the same as those of embodiment 1.
  • Example 7 It can be seen from the results of Example 7 that good results can still be obtained by using the traditional bubble cap reactive rectification tray, but compared with the preferred plug flow thin film reactive rectification tray of the present application, the molecular weight distribution of lactic acid oligomers Significantly broadened, will affect the reaction yield and product optical purity.
  • the present embodiment provides a preparation method and reaction device of lactide.
  • the preparation method is the same as that of embodiment 2, except that the reactive distillation tray is replaced with a traditional bubble cap tray, and the operating conditions are the same as those of embodiment 2.
  • the conversion rate of the second depolymerization reaction was 63.2%, the optical purity of crude lactide was 95.9%, the lactic acid content was 0.59%, and the total content of the 2-5 lactic acid polymerization products was 1.25%.
  • Example 8 From the results of Example 8, it can be seen that good results can still be obtained by using the traditional bubble cap reactive rectification tray, but compared with the plug flow thin film reactive rectification tray disclosed in this application, the molecular weight distribution of lactic acid oligomers Significantly broadened, will affect the reaction yield and product optical purity.
  • This comparative example provides a kind of preparation method of lactide, specifically as follows:
  • Depolymerization adopts stainless steel tubular falling film evaporator, 32 ⁇ 2mm, length 6m, 3 heat exchange tubes, and effective heat exchange area is about 1.6m 2 .
  • the reaction temperature of the depolymerization reactor was controlled to be 240°C, the pressure was 0.5kPaA, the concentration of the catalyst stannous octoate was 0.5%, and the feed rate was about 2kg/h.
  • the conversion rate of depolymerization was 55.8%, the optical purity of crude lactide was 96.5%, the content of lactic acid was 5.04%, and the total content of 2-5 lactic acid polymerization products was 6.2%.
  • the same stainless steel tubular falling film evaporator as in Comparative Example 1 was used for depolymerization, 32 ⁇ 2mm, 6m in length, 3 heat exchange tubes, and the effective heat exchange area was about 1.6m 2 .
  • the reaction temperature of the depolymerization reactor was controlled at 240° C., the pressure was 0.5 kPaA, the concentration of the catalyst stannous octoate was 0.5%, and the feed rate was about 3 kg/h.
  • the conversion rate of depolymerization was 47.2%, the optical purity of crude lactide was 96.0%, the lactic acid content was 3.69%, and the total content of 2-5 lactic acid polymerization products was 5.7%.
  • the preparation method of lactide provided by the present application greatly simplifies the process and equipment of the two-step lactic acid method, and at the same time, high-quality lactide products can be obtained.

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Abstract

本文公布一种丙交酯的制备方法以及反应装置，所述制备方法包括如下步骤：(1)将如下反应在反应精馏塔I中进行：使乳酸进行初步聚合反应，得到第一乳酸低聚物；(2)将如下反应耦合至反应精馏塔II中进行：使所述第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应，得到丙交酯初产品；(3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，进行第二解聚反应，得到所述丙交酯。相比于目前工业主流的已知技术，本申请极大简化乳酸两步法的流程和设备，显著降低了设备投资和生产成本，具备突出的经济性优势。

Description

一种丙交酯的制备方法以及反应装置 技术领域
本申请涉及丙交酯技术领域，尤其涉及一种丙交酯的制备方法以及反应装置。
背景技术
聚乳酸(PLA)也被称为聚丙交酯，是一种以可再生的植物资源为原料经过化学合成制备的典型可生物降解高分子材料。近年来，PLA的全球市场需求增加迅猛，预计未来几年需求量将以每3-5年翻一番的速度增加，并预计将会长期处于供不应求的情况。全球禁塑和垃圾分类为可降解塑料带来了巨大的潜在市场，特别是一次性塑料制品。
目前，PLA的工业生产一般采用丙交酯开环聚合法。丙交酯作为合成PLA的关键中间体，其合成工艺和关键设备是业内研究的重点方向。目前工业上合成丙交酯一般采用乳酸两步法，即乳酸首先发生聚合得到具有一定分子量的乳酸低聚物，然后该乳酸低聚物在催化剂存在下进行裂解、环化反应获得粗丙交酯，粗丙交酯经提纯获得合格的丙交酯产品，如US1095205(1914)，US2668162(1954)，US4835293(1989)，US4797468(1989)，US5053522(1991)，US5247058(1993)，WO9509879A1(1995)，CN11122559A(1995)，EP98203427.4(1998)，US6005067A(1999)，CN1688569A，(2003)CN105814110(2014)等公开的现有技术。
但是公开的现有技术仍存在流程复杂、设备多、投资大等问题，拉高了丙交酯的生产成本。如CN101096413A公开的流程中，乳酸预聚和乳酸低聚物解聚过程就包括5台反应釜、4套精馏塔以及附属必要的装置共27台设备，流程复杂、设备数量多。另外，以上公开的技术中未提及解聚焦油的回收利用。如果增加焦油回用工序，流程势必将更加复杂。
反应器是制备丙交酯的核心技术，研究人员做了很多的探索，如US5258488采用釜式反应器，JP3083461/93、EP0893462A2采用带反应精馏的釜式反应器，US5023349、WO9318019A1采用塔式反应器。鉴于该反应体系的热敏性，特别需要具有强传热传质能力、低停留时间的反应器形式。因此更多的公开技术采用强化传热、传质的反应器，特别是薄膜式反应器，如WO9509879、KP20140023143公开了卧式、立式管式降膜反应器等，以及WO9509879、CA2113799公开了采用带转动部件的立式刮膜反应器，EP1873185公开了卧式刮膜薄膜反应器等。
虽然现有公开技术在一定程度上解决了聚乳酸解聚制备丙交酯对传热、传质的高要求，并实现了工业化，但仍存在一定问题。如WO9509879、KP20140023143公开的卧式、立式管式降膜反应器，因停留时间短，需要更大的设备投资或者更高的温度、催化剂浓度，从而造成副反应增加、产品品质下降。WO9509879、CA2113799公开了采用带转动部件的立式刮膜 反应器，EP1873185公开了卧式刮膜薄膜反应器，传热效果好，但用动设备强化换热代价高，设备精度要求高、性价比不高，同时也存在停留时间过短，设备处理能力低等问题。
PLA的制备过程中，为了获得更高的分子量和产品性能，对原料丙交酯的杂质如酸份等要求非常严格。如道达尔-科碧恩公司的丙交酯产品一般控制酸份<7meq/kg产品。但是因为物性的关系，酸份的脱除非常困难。CN107531663A公开了粗丙交酯在升温条件下保持至少5小时以控制乳酸低聚物含量的技术。WO9509879A1公开了利用分凝脱除粗丙交酯中的乳酸，进而降低分离工序对脱除乳酸的压力。EP0893462A2、JP308346/93、CN1894193A公开的反应精馏解聚制备丙交酯的技术，使进入丙交酯提纯工序的流股中的乳酸低聚显著降低，有利于减少精制工序的提纯难度，抑制副反应，提高提纯收率。
但是公开的现有技术中，粗丙交酯高温下保持至少5小时，设备投资大，效率低，伴随丙交酯聚合等副反应降低了收率；部分冷凝脱乳酸的方案，脱除效果不佳，且能量利用仍有改善空间。现有反应精馏解聚的已知技术，大量的乳酸低聚物以液相形式回流到解聚反应器中然后被蒸发到气相重新进入精馏塔，造成乳酸低聚物在解聚反应器中的内部循环和累积，消耗了大量的能量，并且显著增加了解聚反应器中的酸份，增加了副反应。
综上，如何在现有技术基础上，进一步地简化流程和设备、降低生产成本是业内仍将继续面对的问题。另外，在控制粗丙交酯中乳酸低聚物等方面，仍存在继续优化的空间。
发明内容
以下是对本文详细描述的主题的概述。本概述并非是为了限制权利要求的保护范围。
针对现有技术的不足，本申请的目的之一在于提供一种丙交酯的制备方法。所述制备方法极大简化乳酸两步法的流程和设备，降低整个丙交酯生产装置的能耗和生产成本，同时又能够得到高质量的丙交酯产品。
为达此目的，本申请采用如下技术方案：
本申请提供一种丙交酯的制备方法，所述制备方法包括如下步骤：
(1)将如下反应在反应精馏塔I中进行：使乳酸进行初步聚合反应，得到第一乳酸低聚物；
(2)将如下反应耦合至反应精馏塔II中进行：使所述第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应，得到丙交酯初产品；
(3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，进行第二解聚反应，得到所述丙交酯。
初步聚合反应指的是乳酸的酯化、脱水得到分子量较低的聚乳酸的过程。一般的初步聚 合分子量为200-800，优选200-500。低聚反应指的是初步聚合产物进一步发生聚合反应，获得更高分子量的聚乳酸的过程。一般的低聚分子量为1000-2500。
本申请提供了一种新型的丙交酯制备方法，使乳酸的初步聚合反应在反应精馏塔I中进行，并将乳酸低聚物的低聚反应和一部分的解聚反应耦合在反应精馏塔II中，简化了工艺步骤，同时又能够得到高纯度的L(或D)-丙交酯产品。
为了进一步简化流程，降低成本，本申请的研究人员尝试将初步聚合与低聚反应设置在两个反应精馏塔中进行，并将低聚反应和一部分的解聚反应耦合在同一个反应精馏塔中，发现在本申请提供的新型工艺以及设备条件下，可以获得和传统工艺相当、甚至更好的结果。设备投资和能耗都得到显著下降，具备显著的经济优势。
此外，解聚反应分两步进行，并将第一解聚反应的气相组成脱除到气相中并进入反应精馏塔I中循环到预聚反应中，能够显著降低进入第二解聚反应的乳酸预聚物的游离乳酸和乳酸低聚物含量，进而抑制解聚反应的副反应，显著降低解聚反应产物即粗丙交酯的水分、酸值等关键指标。
优选地，步骤(1)中，所述第一乳酸低聚物的重均分子量为200-800，例如250、300、350、400、450、500、550、600、650、700、750等，优选250-500。
优选地，步骤(1)中，所述反应精馏塔I的操作压力为10～200kPaA(本文中出现的压力单位如无特殊说明，均指的是绝对压力)，例如20kPaA、30kPaA、40kPaA、50kPaA、60kPaA、70kPaA、80kPaA、90kPaA、100kPaA、110kPaA、120kPaA、130kPaA、140kPaA、150kPaA、160kPaA、170kPaA、180kPaA、190kPaA等，优选15～100kPaA。
优选地，步骤(1)中，所述反应精馏塔I的操作温度为5～170℃，例如10℃、20℃、30℃、40℃、50℃、60℃、70℃、80℃、90℃、100℃、110℃、120℃、130℃、140℃、150℃、160℃等，优选40-150℃。
优选地，步骤(1)中，所述初步聚合反应的压力为0.1～2BarA，例如0.2BarA、0.3BarA、0.4BarA、0.5BarA、0.6BarA、0.7BarA、0.8BarA、0.9BarA、1BarA、1.1BarA、1.2BarA、1.3BarA、1.4BarA、1.5BarA、1.6BarA、1.7BarA、1.8BarA、1.9BarA等，优选0.15～1BarA。
优选地，步骤(1)中，所述初步聚合反应的温度为100～180℃，例如110℃、120℃、130℃、140℃、150℃、160℃、170℃等，优选120-170℃。
优选地，所述制备方法还包括：将乳酸进行脱游离水处理耦合至反应精馏塔I中进行。
优选地，所述脱游离水处理的方法包括在升温、真空条件下的蒸馏，或者在常压到高于大气压的条件下的蒸馏或者采用N 2等惰性气体的气提。为了更好地实现本申请中将脱游离水 处理和预聚等工艺耦合的目的，本申请优选在升温下蒸发，脱除游离水的温度一般为100～170℃，优选120～150℃，压力为10～200kPaA，优选15～100kPaA。
优选地，所述制备方法还包括：将水的纯化反应耦合至反应精馏塔I中进行。
优选地，所述纯化的方法包括塔顶冷凝器回流到反应精馏塔I的上部填料部分，与上升包含乳酸的气相在填料段进行逆流接触，通过精馏作用回收气相中的乳酸，最终塔顶得到几乎不含乳酸的水相。实现水的纯化操作的温度一般为40-150℃，优选40-120℃，压力为10～200kPaA，优选15～100kPaA。
优选地，步骤(2)中，所述第二乳酸低聚物的重均分子量为800-5000，例如1000、1200、1400、1600、1800、2000、2200、2400、2600、2800、3000、3200、3400、3600、3800、4000、4200、4400、4600、4800等，优选1000-2500。
优选地，步骤(2)中，所述反应精馏塔II的操作压力为0.1～5kPaA，例如1kPaA、2kPaA、3kPaA、4kPaA等，优选0.5～2kPaA。
优选地，步骤(2)中，所述反应精馏塔II的操作温度为120～180℃，例如130℃、140℃、150℃、160℃、170℃、180℃等，优选140-170℃。
优选地，步骤(2)中，所述低聚反应的压力为0.5～5kPaA，例如1kPaA、1.5kPaA、2kPaA、2.5kPaA、3kPaA、3.5kPaA、4kPaA、4.5kPaA等，优选1～2kPaA。
优选地，步骤(2)中，所述低聚反应的温度为120-180℃，例如130℃、140℃、150℃、160℃、170℃等，优选140-170℃。
优选地，步骤(2)中，所述第一解聚反应在所述反应精馏塔II的塔釜再沸器中进行。
优选地，步骤(2)中，所述第一解聚反应中，第二乳酸低聚物的转化率≤20％，例如1％、2％、3％、4％、5％、6％、7％、8％、9％、10％、11％、12％、13％、14％、15％、16％、17％、18％、19％等，优选≤10％，进一步优选≤5％。
在本申请的优选技术方案中，将第一解聚反应中第二乳酸低聚物的转化率控制在20％以下，是因为在反应精馏塔II中的第一解聚反应中，解聚的气相产物将直接上升进入精馏塔II的上层塔盘中，从而造成预聚反应的单程收率的降低。在满足本申请的目的基础上，适当控制第一解聚反应的转化率对提高收率是有益的，本申请认为比较合适的数据是20％以内。
优选地，步骤(2)中，所述第一解聚反应的温度≤210℃，例如150℃、160℃、170℃、180℃、190℃、200℃等，优选180-200℃。
优选地，步骤(2)中，所述第一解聚反应的压力为0.1～5kPaA，例如1kPaA、2kPaA、3kPaA、4kPaA、5kPaA等，优选0.5～2kPaA。
优选地，步骤(3)中，所述第二解聚反应的温度为170-240℃，例如180℃、190℃、200℃、210℃、220℃、230℃、240℃等，优选180-220℃。
优选地，步骤(3)中，所述第二解聚反应的压力为0.1～5kPaA，例如1kPaA、2kPaA、3kPaA、4kPaA等，优选0.5～2kPaA。
优选地，所述制备方法还包括：将步骤(3)反应得到的解聚焦油的水解反应耦合至反应精馏塔I中进行。实现了解聚焦油的循环回用，降低了原料单耗，同时未显著增加设备和投资，可显著降低生产总成本。
优选地，所述水解反应的温度为100～170℃，例如110℃、120℃、130℃、140℃、150℃、160℃等，优选120-150℃。
优选地，所述水解反应的压力为10～200kPaA，例如20kPaA、40kPaA、60kPaA、80kPaA、100kPaA、120kPaA、140kPaA、160kPaA、180kPaA等，优选15～100kPaA。
优选地，步骤(3)中，所述反应精馏塔II的塔釜液通过保温管道进入所述反应精馏塔III。
优选地，所述保温管道的温度为140-150℃，例如141℃、142℃、143℃、144℃、145℃、146℃、147℃、148℃、149℃等。
优选地，所述制备方法具体包括如下步骤：
(1)将如下反应耦合至反应精馏塔I中进行：进行乳酸的脱水处理、乳酸的初步聚合反应、水的纯化反应以及解聚焦油的水解反应；
(2)将如下反应耦合至反应精馏塔II中进行：使所述初步聚合反应得到的第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应，得到丙交酯初产品；
(3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，进行第二解聚反应，得到所述丙交酯。
在本申请的优选技术方案中，将原料乳酸脱游离水、乳酸初步聚合反应、水的纯化以及解聚焦油的水解反应耦合到反应精馏塔I中发生；乳酸低聚反应、乳酸低聚物的部分解聚反应耦合到反应精馏塔II中发生。在已经公开的现有技术中，上述的游离水脱除、水的纯化、聚合反应以及解聚焦油的水解，以及乳酸聚合反应和第一解聚反应的反应条件存在较大的差距，所以已经公开的传统工艺采取了多个不同的反应器或其他设备来处理以上不同的工序，造成工艺流程复杂、设备数量多、控制繁琐等问题。但本申请的研究人员发现，在适当的牺牲部分操作偏离最优工艺的条件下，通过巧妙的工艺优化，仍可满足生产的需要，并最终在 优选的工艺取舍的基础上，将以上多个目的、多个工序的操作耦合到2台反应精馏塔中进行，实现了设备和流程的极大简化。
优选地，所述反应精馏塔III自下而上包括解聚反应段、聚合反应段和精馏段。
优选地，在步骤(3)之后进行如下步骤：
(4)使步骤(3)得到的丙交酯在反应精馏塔III的精馏段进行第一次精馏，精馏段底部得到液相流股；
(5)使所述液相流股进入反应精馏塔III的聚合反应段，其中的乳酸和乳酸低聚物在反应精馏塔III的聚合反应段进行聚合反应，得到的产物再在反应精馏塔III的解聚反应段进行解聚反应，解聚液相产物返回至反应精馏塔I。
在本申请的优选技术方案中，通过使精馏塔的液相流股中的乳酸和乳酸低聚物进一步发生聚合反应，将残存的乳酸、乳酸低聚物转化为更高分子量的聚乳酸，并在循环回反应精馏塔III时重新分解为丙交酯。这避免了传统工艺中因乳酸低聚物在解聚反应器和精馏塔或本申请的反应精馏塔III的精馏段与解聚段之间气相、液相内部循环，大量耗能并催化大量副反应。因此，本申请中公开的反应精馏塔III的工艺特别是在反应精馏塔III中设置聚合段的技术，可以提高收率，最终可以得到高光学纯度的L(或D)-丙交酯产品，并进一步降低了生产成本。
优选地，步骤(4)还包括：在所述反应精馏塔III的侧线采出第一丙交酯流股。
本申请优选在反应精馏塔的侧线采出丙交酯流股，是因为侧线流股中丙交酯的含量较高，乳酸以及乳酸低聚物的含量较低，能够进一步提高产品质量。
优选地，所述第一丙交酯流股为液相流股。
优选地，所述侧线采出的位置至反应精馏塔III底部的距离为所述反应精馏塔III总高度的1/3-1/2。
本申请优选在距离反应精馏塔底部的1/3-1/2处进行侧线采出，在该位置，丙交酯的含量最高，乳酸以及乳酸低聚物的含量最低，更进一步提高丙交酯产品的质量。
优选地，所述第一丙交酯流股中乳酸的含量<1％，例如0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％等，优选<0.5％。
优选地，所述第一丙交酯流股中乳酸低聚物含量<1％，例如0.01％、0.02％、0.03％、0.04％、0.05％、0.06％、0.07％、0.08％、0.09％、0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％等，优选<0.2％，进一步优选<0.1％。
优选地，步骤(4)中，所述第一次精馏的温度为100～150℃，例如110℃、120℃、130℃、 140℃等。
优选地，步骤(4)中，所述第一次精馏的压力为0.1～5kPaA，例如1kPaA、1.5kPaA、2kPaA、2.5kPaA、3kPaA、3.5kPaA、4kPaA、4.5kPaA等，优选0.5～2kPaA。
优选地，步骤(4)中，所述第一次精馏的压力与步骤(3)中所述解聚反应的压力相同。
优选地，步骤(5)中，所述聚合反应的时间≥1h，例如1.5h、2h、2.5h、3h、3.5h、4h、4.5h、5h、5.5h、6h、6.5h、7h、7.5h、8h、8.5h、9h、9.5h等，优选1-10h，进一步优选1-5h，更进一步优选1-2h。
优选地，步骤(5)中，所述聚合反应的温度为100～240℃，例如110℃、120℃、130℃、140℃、150℃、160℃、170℃、180℃、190℃、200℃、210℃、220℃、230℃等。
优选地，步骤(5)中，所述聚合反应的时间≥1h，所述聚合反应的温度为100～240℃。
本申请优选上述特定的反应时间和温度。在该范围之内，能够保证乳酸和乳酸低聚物可以充分聚合，同时不会出现过高分子量的聚乳酸产物，从而影响解聚反应的反应速率和产物收率。
优选地，步骤(5)中，所述聚合反应的温度低于所述第二解聚反应的温度。
优选地，步骤(5)中，所述聚合反应的温度高于所述侧线采出位置的温度。
本申请优选侧线采出温度、聚合温度和解聚反应温度依次升高，这样能够将聚合温度控制在较合理的范围，避免温度过低聚合反应速率过低，或者温度过高造成乳酸、乳酸二聚体等的大量气化，以及聚合产物的高温分解，增加了能耗降低了聚合反应的收率，从而进一步提高装置收率和经济性。
优选地，步骤(5)中，所述聚合反应在反应容器或反应精馏塔盘中进行。
优选地，所述塔底液相流股在所述反应精馏塔盘停留的时间为1～10h，例如1.5h、2h、2.5h、3h、3.5h、4h、4.5h、5h、5.5h、6h、6.5h、7h、7.5h、8h、8.5h、9h、9.5h等，优选1～5h，进一步优选1～2h。
优选地，步骤(5)中，所述聚合反应得到的乳酸低聚物的重均分子量为800-2500，例如1000、1100、1200、1300、1400、1500、1600、1700、1800、1900、2000、2100、2200、2300、2400等。
本申请优选聚合得到上述特定分子量的乳酸低聚物，较高的分子量能够有效降低粗丙交酯中残留乳酸以及乳酸低聚物的含量，降低最终丙交酯产品的酸值，从而能够进一步提高最终丙交酯产品的质量。
优选地，所述制备方法还包括步骤(6)：使所述第一丙交酯流股进入精馏塔IV中进行第 二次精馏，并在所述精馏塔IV的侧线采出第二丙交酯流股，结晶，得到所述丙交酯。
优选地，所述第二次精馏的温度为130℃-160℃，例如135℃、140℃、145℃、150℃、155℃等。
优选地，所述第二次精馏的压力为0.1～5kPaA，例如0.5kPaA、1kPaA、1.5kPaA、2kPaA、2.5kPaA、3kPaA、3.5kPaA、4kPaA、4.5kPaA等。
优选地，所述第二丙交酯流股的流量占精馏塔IV进料流量的60-90％，例如65％、70％、75％、80％、85％等，优选70-80％。
优选地，所述制备方法包括如下步骤：
(1)将如下反应耦合至反应精馏塔I中进行：进行乳酸的脱水处理、乳酸的初步聚合反应、水的纯化反应以及解聚焦油的水解反应；
(2)将如下反应耦合至反应精馏塔II中进行：使所述初步聚合反应得到的第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应；
(3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，在反应精馏塔III的解聚反应段进行第二解聚反应；
(4)使步骤(3)得到的丙交酯进入反应精馏塔III的精馏段，在100～150℃、0.1～5kPaA下进行第一次精馏，精馏段底部得到液相流股，并在所述反应精馏塔III的侧线采出乳酸含量<1％、乳酸低聚物含量<1％的第一丙交酯流股；
(5)使所述液相流股进入反应精馏塔III的聚合反应段，其中的乳酸和乳酸低聚物在反应精馏塔III的聚合反应段在100～240℃温度下进行聚合反应至少1h，得到重均分子量为800-2500的乳酸低聚物，得到的产物再在反应精馏塔III的解聚反应段中进行解聚反应，解聚液相产物返回至反应精馏塔I；
(6)使所述第一丙交酯流股进入精馏塔IV中在130℃-160℃、0.1～5kPaA下进行第二次精馏，并在所述精馏塔IV的侧线采出占进料流量70-80％的第二丙交酯流股，结晶，得到所述丙交酯。
本申请的目的之二在于提供一种用于目的之一所述的制备方法中的反应装置，所述反应装置包括通过管线依次连接的反应精馏塔I、反应精馏塔II和反应精馏塔III。
所述反应精馏塔I、反应精馏塔II和反应精馏塔III中各自独立地设置有至少两个板式精馏塔盘。
优选地，所述板式精馏塔盘包括筛板、固阀、浮阀、泡罩或喷射塔盘。
优选地，所述板式精馏塔盘包含塔板、气相通道、溢流堰、降液管和导流板。
优选地，每级板式精馏塔盘包含至少两个相互平行的气相通道，所述板式精馏塔盘上由壳体、塔板、溢流堰和气相通道围成的空间为液相通道。
优选地，所述塔板上方、液相高度内设置有换热管。
优选地，所述气相通道与所述塔板垂直。
优选地，所述气相通道高度大于所述精馏塔盘上的液相高度。
本申请的上述优选技术方案中，塔板上设置供气液两相分别通过的通道，反应得到气液两相产物，液相反应液呈薄膜状水平流过所述塔板表面，气相通过气相通道穿过塔板，与塔板呈垂直方向流动。
优选地，所述板式精馏塔盘位于所述反应精馏塔I或反应精馏塔II的进料口下方。
优选地，所述板式精馏塔盘上设置有加热管道。
优选地，所述板式精馏塔盘包括从受液盘到降液管之间的方向设置至少两个相互平行的条形气体通道，所述条形气体通道不经过塔盘上的液层；所述条形气相通道之间围成的通道为液相通道；液相通道设置有垂直于条形气相通道且高低交替的液相导流板。示例性地，所述板式精馏塔盘的水平视角结构如图1所示，俯视视角结构如图2所示。
通过采用上述板式精馏塔盘，可实现反应精馏塔内液相的平推流流动，在保证传热传质的基础上，可显著减少因液相返混造成的停留时间分布过宽等问题，可获得分子量分布更窄的乳酸低聚物，进而在解聚反应中获得更好的丙交酯收率和产品质量。
所述反应精馏塔I包括塔体I以及与所述塔体I底部进料口相连的第一再沸器。第一再沸器为反应精馏塔I提供上升蒸汽以及反应所需的热量。优选地，所述反应精馏塔I不含所述第一再沸器。
优选地，所述反应精馏塔II包括塔体II以及与所述塔体II底部进料口相连的第二再沸器。第二再沸器为反应精馏塔II提供上升蒸汽，并且作为第一次解聚反应的反应器为第一解聚反应提供反应所需的热量。
在本申请提供的反应装置中，反应精馏塔II的塔釜液通过带有加热装置的保温管道进入反应精馏塔III进行第二解聚反应，保温管道内乳酸低聚物的温度维持在140-150℃，以保证乳酸低聚物呈液态流动。
优选地，所述反应精馏塔III的下段设置有蒸馏罐。蒸馏罐带有加热夹层，夹层内采用油加热或者蒸汽加热的方式维持蒸馏罐内乳酸低聚物的温度在170-240℃，通过真空泵维持蒸馏罐内的真空压力0.1～5kPaA，使丙交酯以气态形式被蒸出。
在本申请的一个优选技术方案中，所述反应精馏塔III自下而上包括解聚反应段、聚合反 应段和精馏段，所述解聚反应段设置有解聚反应器，所述聚合反应段设置有反应精馏塔盘。
优选地，所述解聚反应器为薄膜反应器，优选包括降膜式解聚反应器或卧式解聚反应器。
优选地，所述卧式解聚反应器为长径比大于1的反应容器卧式放置，其中水平设置反应精馏塔盘。
优选地，所述反应容器包括釜式反应器、管式反应器或列管反应器，优选具有加热功能的列管式反应器。
优选地，所述反应精馏塔盘为板式精馏塔盘。
优选地，所述反应精馏塔盘包括从受液盘到降液管之间的方向设置至少两个相互平行的条形气体通道，所述条形气体通道不经过塔盘上的液层；所述条形气相通道之间围成的通道为液相通道；液相通道设置有垂直于条形气相通道且高低交替的液相导流板。具体如图3所示。
在本申请的优选技术方案中，采用大持液量的平推流反应精馏塔盘，将所述的高温下液相反应容器集成到精馏塔中，增加了集成度、简化了流程，并且最大限度地获得平推流的流动效果，减少了返混和副反应，并最终提高了反应收率，降低了生产成本。
优选地，所述反应精馏塔III上设置有第一侧线采出装置。侧线获得粗丙交酯产品，可以显著降低粗丙交酯中的乳酸、水分以及乳酸低聚物，显著降低下游分离工序的技术难度和制造成本。
优选地，所述第一侧线采出装置至反应精馏塔III底部的距离为所述反应精馏塔III总高度的1/3-1/2。
优选地，所述反应装置还包括与所述第一侧线采出装置通过管线连接的精馏塔IV，且所述精馏塔IV上设置有第二侧线采出装置。
优选地，所述反应装置还包括与所述第二侧线采出装置通过管线连接的结晶装置。
相较于现有技术，本申请具有如下有益效果：
本申请提供了一种新型的丙交酯制备方法，使乳酸的初步聚合反应在反应精馏塔I中进行，并将乳酸低聚物的低聚反应和一部分的解聚反应耦合在反应精馏塔II中，简化了工艺步骤，同时又能够得到高纯度的L(或D)-丙交酯产品。相比于目前工业主流的已知技术，本申请提供的方法和装置，显著降低了设备投资和生产成本，具备突出的经济性优势。
在阅读并理解了详细描述后，可以明白其他方面。
附图说明
图1是本申请的一个具体实施方式中的反应装置图。
图2是本申请的一个具体实施方式中板式精馏塔盘的水平视角结构示意图。
图3是本申请的一个具体实施方式中板式精馏塔盘的俯视视角结构示意图。
图4是本申请的一个具体实施方式中反应精馏塔III的解聚反应段的卧式薄膜解聚反应器的水平视图。
图5是本申请的一个具体实施方式中反应精馏塔III的解聚反应段的卧式薄膜解聚反应器的水俯视图。
具体实施方式
为便于理解本申请，本申请列举实施例如下。本领域技术人员应该明了，所述实施例仅仅是帮助理解本申请，不应视为对本申请的具体限制。
原料信息：本申请中实施例采用的L乳酸原料来自江西武藏野公司，L乳酸化学纯度88％，光学纯度99.7％；催化剂辛酸亚锡来自阿拉丁试剂，纯度为98％。
表征设备：实施例中物质的组成定量检测采用气相色谱法(GC)，色谱柱及色谱条件如下：
Figure PCTCN2021072593-appb-000001
绘制各种组分的标准曲线，各组分的定量分析按如下公式进行：
将样品峰面积带入标准曲线公式计算出样品浓度。分析结果以mg/L为单位报告。采用外标曲线法对丙交酯异构体含量进行计算：
Figure PCTCN2021072593-appb-000002
其中，
ω L——样品中L-丙交酯浓度，％
A L——L-丙交酯峰面积
m——称取样品质量，g
Figure PCTCN2021072593-appb-000003
其中，
ω D——样品中D-丙交酯浓度，％
A D——D-丙交酯峰面积
m——称取样品质量，g
Figure PCTCN2021072593-appb-000004
其中，
ω m——样品中m-丙交酯浓度，％
A m——m-丙交酯峰面积
m——称取样品质量，g。
实施例1
本实施例提供一种丙交酯的制备方法，制备方法具体如下：
(1)将如下反应耦合至反应精馏塔I中进行：进行乳酸的脱水处理、乳酸的初步聚合反应、水的纯化反应以及解聚焦油的水解反应；
(2)将如下反应耦合至反应精馏塔II中进行：使所述初步聚合反应得到的第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应；
(3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，在反应精馏塔III的解聚反应段进行第二解聚反应；
(4)使步骤(3)得到的丙交酯在反应精馏塔III的反应精馏段进行第一次精馏，得到塔底液相流股，并在所述反应精馏塔III的侧线采出第一丙交酯流股；
(5)使所述塔底液相流股中的乳酸和乳酸低聚物在反应精馏塔III的反应精馏段进行聚合反应，得到的产物再在反应精馏塔III的解聚反应段中进行解聚反应，解聚产物再次回到精馏塔III的反应精馏段进行精馏；
(6)使所述第一丙交酯流股进入精馏塔IV中进行第二次精馏，并在所述精馏塔IV的侧线采出第二丙交酯流股，结晶，得到所述丙交酯。
上述反应过程的操作参数如下：
反应精馏塔I压力15kPaA，塔顶温度40℃，塔盘上温度通过导热油换热管温度控制，上部10块塔盘热油温度为60～130℃，下部10块塔盘热油温度为130-150℃；回流比1：1。反应精馏塔I进料40kg/h，催化剂辛酸亚锡的浓度为0.3％。
反应精馏塔II压力2kPaA，塔顶温度120℃，塔盘上温度通过导热油换热管来控制，从上到下都控制为150℃，回流比1:4。再沸器即第一解聚段温度为180℃。
反应精馏塔III压力0.5kPaA，解聚段塔盘上温度通过导热油换热管来控制，控制反应温度为220℃，回流比1:4，聚合段塔盘上无换热管。
本实施例还提供了一种用于上述制备方法中的反应装置，具体如下：
上述反应装置如图1所示，其中，反应精馏塔I塔径200mm，上部是1m高度的5*5mm的θ环填料，下部20块反应精馏塔盘，塔盘结构如图2和图3所示，塔盘持液高度100mm，塔盘上布置有导热盘管，用导热油控温。反应精馏塔II塔径200mm，精馏段是1m高度的5*5mm的θ环填料，精馏上部设置25块反应精馏塔盘为第二预聚段(塔盘结构如图2和图3所示)，塔盘持液高度200mm，塔盘上布置有导热盘管，用导热油控温，以及再沸器为第一解聚段。
反应精馏塔III自下而上包括解聚反应段、聚合反应段和精馏段，聚合反应段和精馏段塔径200mm，聚合反应段采用20块泡罩塔盘，塔盘持液高度200mm，液相停留时间为1h，精馏段装填1m高度的5*5mm的θ环填料，聚合反应段和精馏段中间侧线采出粗丙交酯产品。反应精馏塔III下部解聚反应段采用如图4和图5所示卧式薄膜解聚反应器作为解聚反应段，反应器直径1.6m，长度3m，设置5层塔盘，板间距200mm，塔盘堰高20mm，设置4排30*600mm的矩形气相通道，气相通道高度80mm，10根
Figure PCTCN2021072593-appb-000005
长度1.7m导热油管，每层导热油管用一台循环油浴来控温。
反应结果：反应精馏塔I塔釜液乳酸低聚物Mw＝250，PDI＝1.311，反应精馏塔II塔釜液中乳酸低聚物Mw＝800，PDI＝1.552，第一解聚反应的转化率5％。反应精馏塔III塔中第二解聚反 应收率65.0％，粗丙交酯光学纯度97.2％，乳酸含量0.66％，乳酸2～5聚产物总含量1.28％，解聚焦油的平均分子量Mw＝3365g/mol，PDI＝2.48。其中，乳酸2～5聚产物指的是乳酸二聚体、三聚体、四聚体和五聚体，以下实施例同理。
实施例2：
本实施例提供一种丙交酯的制备方法和反应装置，反应装置与实施例1相同，区别仅在于如下操作条件不同：
操作条件：反应精馏塔I压力为常压，塔顶温度100℃，塔盘上温度通过导热油换热管来控制，上部10块塔盘温度为150～160℃，下部10块塔盘温度为160～170℃；回流比1：1。反应精馏塔进料20kg/h。
反应精馏塔II压力1kPaA，塔盘上温度通过导热油换热管来控制，从上到下都控制为170℃，塔釜再沸器温度190℃。
反应结果：反应精馏塔I塔釜液乳酸低聚物Mw＝500，反应精馏塔II塔釜液乳酸低聚物Mw＝2500。反应精馏塔II中第一解聚反应的转化率为10％。反应精馏塔III塔中第二解聚反应的收率63.0％，粗丙交酯光学纯度96.5％，乳酸含量0.51％，乳酸2～5聚产物总含量1.24％。
实施例3
本实施例提供一种丙交酯的制备方法和反应装置，反应装置与实施例1相同，区别仅在于第一解聚反应段即反应精馏塔II的再沸器温度控制为200℃。
反应结果：反应精馏塔II中乳酸低聚物进行第一解聚反应的转化率为10％。反应精馏塔III塔中第二解聚反应收率64.2％，粗丙交酯光学纯度97.3％，乳酸含量0.46％，乳酸2～5聚产物总含量1.05％。
由以上结果可以看到，采用本申请的分步解聚的方法，可以通过调控第一解聚段的工艺来调控粗丙交酯的乳酸含量，粗丙交酯中乳酸以及乳酸低聚物的含量，有利于下游丙交酯的提纯以及产品酸份的控制。
实施例4
本实施例提供一种丙交酯的制备方法和反应装置，反应装置与实施例1相同，区别仅在于第一解聚反应段即反应精馏塔II的再沸器温度控制为210℃。
反应结果：反应精馏塔II中乳酸低聚物进行第一解聚反应的转化率为20％。反应精馏塔III塔中第二解聚反应收率53.8％，粗丙交酯光学纯度97.1％，乳酸含量0.41％，乳酸2～5聚产物总含量0.95％。
从反应结果可以看到，乳酸低聚物进行初步解聚反应的转化率越高，解聚产品的乳酸和乳 酸低聚物可以进一步降低。
实施例5
本实施例提供一种丙交酯的制备方法和反应装置，反应装置与实施例1相同，区别仅在于第一解聚反应段即反应精馏塔II的再沸器温度控制为220℃，反应精馏塔II中乳酸低聚物进行第一解聚反应的转化率为27％。
反应结果：第二解聚反应收率46.8％，粗丙交酯光学纯度96.8％，乳酸含量0.38％，乳酸2～5聚产物总含量0.94％。
从结果可以看到，虽然进一步提高第一解聚反应段的解聚转化率，第二解聚反应得到的粗丙交酯乳酸和乳酸低聚物含量仍可进一步降低，但降低幅度已经不显著。同时，第二解聚反应的收率出现了显著下降。因此，优选第一解聚反应段的转化率控制在20％以内。
实施例6
本实施例提供一种丙交酯的制备方法和反应装置，反应装置与实施例1相同，区别仅在于反应精馏塔I的塔顶压力为100kPaA，塔顶温度为100℃，上部的10块塔盘温度为100～130℃。
反应结果：反应精馏塔I塔釜液乳酸低聚物Mw＝280，PDI＝1.016，反应精馏塔II塔釜液中乳酸低聚物Mw＝800，PDI＝1.520。
可以看到通过调节反应精馏塔I的反应条件，可以调节乳酸低聚物的分子量和分子量分布。究其原因，在于解聚反应的解聚釜残中包含高分子量的乳酸聚合物，其在反应精馏塔中与乳酸水溶液混合，发生水解和酯交换反应获得低分子量的聚合物，解聚焦油的充分反应有利于获得分子量分布更窄的乳酸低聚物，对解聚反应的反应速率和收率有显著的影响。
实施例7
本实施例提供一种丙交酯的制备方法和反应装置，制备方法与实施例1相同，区别仅在于反应精馏塔盘更换为传统的泡罩塔盘，操作条件均与实施例1相同。
反应结果：反应精馏塔I塔釜液乳酸低聚物Mw＝271，PDI＝1.45，反应精馏塔II塔釜液中乳酸低聚物Mw＝810，PDI＝1.75，第一解聚反应的转化率5％。第二解聚反应收率63.6％，粗丙交酯光学纯度96.5％，乳酸含量0.68％，乳酸2～5聚产物总含量1.28％，解聚焦油的平均分子量Mw＝3375g/mol，PDI＝2.54。
从实施例7的结果可以看到，采用传统泡罩反应精馏塔盘仍可以获得不错的结果，但与本申请优选的平推流薄膜反应精馏塔盘比，乳酸低聚物的分子量分布显著变宽，会影响反应收率和产品光学纯度。
实施例8
本实施例提供一种丙交酯的制备方法和反应装置，制备方法与实施例2相同，区别仅在于反应精馏塔盘更换为传统的泡罩塔盘，操作条件均与实施例2相同。
反应结果：反应精馏塔I塔釜液乳酸低聚物Mw＝520，反应精馏塔II预聚反应段出口的液相中乳酸低聚物Mw＝2506，第一解聚反应的转化率10％。第二解聚反应的转化率63.2％，粗丙交酯光学纯度95.9％，乳酸含量0.59％，乳酸2～5聚产物总含量1.25％。
从实施例8的结果可以看到，采用传统泡罩反应精馏塔盘仍可以获得不错的结果，但与本申请公开的平推流薄膜反应精馏塔盘比，乳酸低聚物的分子量分布显著变宽，会影响反应收率和产品光学纯度。
对比例1：
本对比例提供一种丙交酯的制备方法，具体如下：
试验条件：初步聚合和低聚反应均采用间歇搅拌釜，乳酸为原料，控制体系压力为2.5kPaA，反应温度逐渐升高的150℃，并保温2h，反应产物乳酸低聚物Mw＝800。解聚采用不锈钢管式降膜蒸发器，32×2mm，长度6m，3根换热管，有效换热面积约1.6m 2。控制解聚反应器反应温度240℃，压力0.5kPaA，催化剂辛酸亚锡的浓度为0.5％，进料量约2kg/h。
反应结果：
解聚的转化率55.8％，粗丙交酯光学纯度96.5％，乳酸含量5.04％，乳酸2～5聚产物总含量6.2％。
对比例2：
试验条件：预聚采用间歇搅拌釜，乳酸为原料，控制体系压力为2.0kPaA，反应温度逐渐升高到170℃，并保温3h，反应产物乳酸低聚物Mw＝2500。解聚采用与对比例1相同的不锈钢管式降膜蒸发器，32×2mm，长度6m，3根换热管，有效换热面积约1.6m 2。控制解聚反应器反应温度240℃，压力0.5kPaA，催化剂辛酸亚锡的浓度为0.5％，进料量约3kg/h。
反应结果：
解聚的转化率47.2％，粗丙交酯光学纯度96.0％，乳酸含量3.69％，乳酸2～5聚产物总含量5.7％。
对比实施例和对比例1～2的结果可以看出，采用本申请中的耦合反应精馏技术和反应器，可以获得和传统的釜式预聚、降膜解聚相近或更好的收率，同时可以显著降低粗产品中游离乳酸以及乳酸低聚物的含量。
通过上述实施例和对比例可知，本申请提供的丙交酯的制备方法极大简化乳酸两步法的流程和设备，同时又能够获得高品质的丙交酯产品。

Claims (10)

  1. 一种丙交酯的制备方法，其包括如下步骤：
    (1)将如下反应在反应精馏塔I中进行：使乳酸进行初步聚合反应，得到第一乳酸低聚物；
    (2)将如下反应耦合至反应精馏塔II中进行：使所述第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应，得到丙交酯初产品；
    (3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，进行第二解聚反应，得到所述丙交酯。
  2. 根据权利要求1所述的制备方法，其中，步骤(1)中，所述第一乳酸低聚物的重均分子量为200-800，优选250-500。
  3. 根据权利要求1或2所述的制备方法，其中，步骤(1)中，所述反应精馏塔I的操作压力为10～200kPaA，优选15～100kPaA；
    优选地，步骤(1)中，所述反应精馏塔I的操作温度为5～170℃，优选40-150℃；
    优选地，步骤(1)中，所述初步聚合反应的压力为0.1～2BarA，优选0.15～1BarA；
    优选地，步骤(1)中，所述初步聚合反应的温度为100～180℃，优选120-170℃。
  4. 根据权利要求1-3中任一项所述的制备方法，其还包括：将乳酸进行脱游离水处理耦合至反应精馏塔I中进行；
    优选地，所述制备方法还包括：将水的纯化反应耦合至反应精馏塔I中进行。
  5. 根据权利要求1-4中任一项所述的制备方法，其中，步骤(2)中，所述第二乳酸低聚物的重均分子量为800-5000，优选1000-2500。
  6. 根据权利要求1-5中任一项所述的制备方法，其中，步骤(2)中，所述反应精馏塔II的操作压力为0.1～5kPaA，优选0.5～2kPaA；
    优选地，步骤(2)中，所述反应精馏塔II的操作温度为120～180℃，优选140-170℃；
    优选地，步骤(2)中，所述低聚反应的压力为0.5～5kPaA，优选1～5kPaA；
    优选地，步骤(2)中，所述低聚反应的温度为120～180℃，优选140-170℃；
    优选地，步骤(2)中，所述第一解聚反应在所述反应精馏塔II的塔釜再沸器中进行；
    优选地，步骤(2)中，所述第一解聚反应中，第二乳酸低聚物的转化率≤20％，优选≤10％，进一步优选≤5％；
    优选地，步骤(2)中，所述第一解聚反应的温度≤210℃，优选180-200℃；
    优选地，步骤(2)中，所述第一解聚反应的压力为0.1～5kPaA，优选0.5～2kPaA。
  7. 根据权利要求1-6中任一项所述的制备方法，其中，步骤(3)中，所述第二解聚反 应的温度为170-240℃，优选180-220℃；
    优选地，步骤(3)中，所述第二解聚反应的压力为0.1～5kPaA，优选0.5～2kPaA；
    优选地，所述制备方法还包括：将步骤(3)反应得到的解聚焦油的水解反应耦合至反应精馏塔I中进行；
    优选地，步骤(3)中，所述反应精馏塔II的塔釜液通过保温管道进入所述反应精馏塔III；
    优选地，所述保温管道的温度为140-150℃；
    优选地，所述制备方法包括如下步骤：
    (1)将如下反应耦合至反应精馏塔I中进行：进行乳酸的脱水处理、乳酸的初步聚合反应、水的纯化反应以及解聚焦油的水解反应；
    (2)将如下反应耦合至反应精馏塔II中进行：使所述初步聚合反应得到的第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应，得到丙交酯初产品；
    (3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，进行第二解聚反应，得到所述丙交酯。
  8. 根据权利要求1-7中任一项所述的制备方法，其中，所述反应精馏塔III自下而上包括解聚反应段、聚合反应段和精馏段；
    优选地，在步骤(3)之后进行如下步骤：
    (4)使步骤(3)得到的丙交酯在反应精馏塔III的精馏段进行第一次精馏，在精馏段底部得到液相流股；
    (5)使所述液相流股进入反应精馏塔III的聚合反应段，其中的乳酸和乳酸低聚物在反应精馏塔III的聚合反应段进行聚合反应，得到的产物再在反应精馏塔III的解聚反应段进行解聚反应，解聚液相产物返回至反应精馏塔I；
    优选地，步骤(4)还包括：在所述反应精馏塔III的侧线采出第一丙交酯流股；
    优选地，所述第一丙交酯流股为液相流股；
    优选地，所述侧线采出的位置至反应精馏塔III底部的距离为所述反应精馏塔III总高度的1/3-1/2；
    优选地，所述第一丙交酯流股中乳酸的含量<1％，优选<0.5％；
    优选地，所述第一丙交酯流股中乳酸低聚物含量<1％，优选<0.2％，进一步优选<0.1％；
    优选地，步骤(4)中，所述第一次精馏的温度为100～150℃；
    优选地，步骤(4)中，所述第一次精馏的压力为0.1～5kPaA，优选0.5～2kPaA；
    优选地，步骤(4)中，所述第一次精馏的压力与步骤(3)中所述解聚反应的压力相同；
    优选地，步骤(5)中，所述聚合反应的时间≥1h，优选1-10h，进一步优选1-5h，更进一步优选1-2h；
    优选地，步骤(5)中，所述聚合反应的温度为100～240℃；
    优选地，步骤(5)中，所述聚合反应的温度低于所述第二解聚反应的温度；
    优选地，步骤(5)中，所述聚合反应的温度高于所述侧线采出位置的温度；
    优选地，步骤(5)中，所述聚合反应在反应容器或反应精馏塔盘中进行；
    优选地，所述塔底液相流股在所述反应精馏塔盘停留的时间为1～10h，优选1～5h，进一步优选1～2h；
    优选地，步骤(5)中，所述聚合反应得到的乳酸低聚物的重均分子量为800-2500；
    优选地，所述制备方法还包括步骤(6)：使所述第一丙交酯流股进入精馏塔IV中进行第二次精馏，并在所述精馏塔IV的侧线采出第二丙交酯流股，结晶，得到所述丙交酯；
    优选地，所述第二次精馏的温度为130℃-160℃；
    优选地，所述第二次精馏的压力为0.1～5kPaA；
    优选地，所述第二丙交酯流股的流量占精馏塔IV进料流量的60-90％，优选70-80％；
    优选地，所述制备方法包括如下步骤：
    (1)将如下反应耦合至反应精馏塔I中进行：进行乳酸的脱水处理、乳酸的初步聚合反应、水的纯化反应以及解聚焦油的水解反应；
    (2)将如下反应耦合至反应精馏塔II中进行：使所述初步聚合反应得到的第一乳酸低聚物进行低聚反应，得到第二乳酸低聚物，使所述第二乳酸低聚物进行第一解聚反应；
    (3)使所述反应精馏塔II的塔釜液进入反应精馏塔III中，在反应精馏塔III的解聚反应段进行第二解聚反应；
    (4)使步骤(3)得到的丙交酯在反应精馏塔III的精馏段在100～150℃、0.1～5kPaA下进行第一次精馏，在精馏段底部得到液相流股，并在所述反应精馏塔III的侧线采出乳酸的含量<1％、乳酸低聚物含量<1％的第一丙交酯流股；
    (5)使所述液相流股进入反应精馏塔III的聚合反应段，其中的乳酸和乳酸低聚物在反应精馏塔III的聚合反应段在100～240℃温度下进行聚合反应至少1h，得到重均分子量为800-2500的乳酸低聚物，得到的产物再在反应精馏塔III的解聚反应段中进行解聚反应，解聚液相产物返回至反应精馏塔I；
    (6)使所述第一丙交酯流股进入精馏塔IV中在130℃-160℃、0.1～5kPaA下进行第二次精馏，并在所述精馏塔IV的侧线采出占进料流量70-80％的第二丙交酯流股，结晶，得到所述丙交酯。
  9. 一种用于权利要求1-8中任一项所述的制备方法中的反应装置，其包括通过管线依次连接的反应精馏塔I、反应精馏塔II和反应精馏塔III。
  10. 根据权利要求9所述的反应装置，其中，所述反应精馏塔I、反应精馏塔II和反应精馏塔III中各自独立地设置有至少两个板式精馏塔盘；
    优选地，所述板式精馏塔盘包含塔板、气相通道、溢流堰、降液管和导流板；
    优选地，每级板式精馏塔盘包含至少两个相互平行的气相通道，所述板式精馏塔盘上由壳体、塔板、溢流堰和气相通道围成的空间为液相通道；
    优选地，所述塔板上方、液相高度内设置有换热管；
    优选地，所述气相通道与所述塔板垂直；
    优选地，所述气相通道高度大于所述精馏塔盘上的液相高度；
    优选地，所述板式精馏塔盘位于所述反应精馏塔I或反应精馏塔II的进料口下方；
    优选地，所述板式精馏塔盘上设置有加热管道；
    优选地，所述反应精馏塔III自下而上包括解聚反应段、聚合反应段和精馏段，所述解聚反应段设置有解聚反应器，所述聚合反应段设置有反应精馏塔盘；
    优选地，所述解聚反应器为薄膜反应器，优选为降膜式解聚反应器或卧式解聚反应器；
    优选地，所述卧式解聚反应器是长径比大于1的反应容器卧式放置，其中水平设置反应精馏塔盘；
    优选地，所述反应精馏塔盘为板式精馏塔盘；
    优选地，所述反应精馏塔III上设置有第一侧线采出装置；
    优选地，所述第一侧线采出装置至反应精馏塔III底部的距离为所述反应精馏塔III总高度的1/3-1/2；
    优选地，所述反应装置还包括与所述第一侧线采出装置通过管线连接的精馏塔IV，且所述精馏塔IV上设置有第二侧线采出装置；
    优选地，所述反应装置还包括与所述第二侧线采出装置通过管线连接的结晶装置。
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115872970A (zh) * 2022-12-08 2023-03-31 青岛普力机电工程有限公司 一种从乳酸原料到高纯丙交酯连续生产的方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11217425A (ja) * 1998-01-30 1999-08-10 Kobe Steel Ltd ラクチドの連続製造装置及び連続製造方法
JP2009298935A (ja) * 2008-06-13 2009-12-24 Hitachi Plant Technologies Ltd ラクチド及びポリ乳酸の合成方法及び装置
CN111153886A (zh) * 2020-01-16 2020-05-15 南京大学 一种快速高产丙交酯的合成方法及装置
CN111424059A (zh) * 2020-06-08 2020-07-17 中粮营养健康研究院有限公司 利用生物发酵技术制备乳酸以生产高产率、高光纯丙交酯的方法和系统
CN211384959U (zh) * 2019-11-26 2020-09-01 南京华基塔业有限公司 一种由乳酸制备丙交酯的反应系统
CN211384958U (zh) * 2019-11-26 2020-09-01 南京华基塔业有限公司 一种由乳酸制备丙交酯的智能反应系统

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11217425A (ja) * 1998-01-30 1999-08-10 Kobe Steel Ltd ラクチドの連続製造装置及び連続製造方法
JP2009298935A (ja) * 2008-06-13 2009-12-24 Hitachi Plant Technologies Ltd ラクチド及びポリ乳酸の合成方法及び装置
CN211384959U (zh) * 2019-11-26 2020-09-01 南京华基塔业有限公司 一种由乳酸制备丙交酯的反应系统
CN211384958U (zh) * 2019-11-26 2020-09-01 南京华基塔业有限公司 一种由乳酸制备丙交酯的智能反应系统
CN111153886A (zh) * 2020-01-16 2020-05-15 南京大学 一种快速高产丙交酯的合成方法及装置
CN111424059A (zh) * 2020-06-08 2020-07-17 中粮营养健康研究院有限公司 利用生物发酵技术制备乳酸以生产高产率、高光纯丙交酯的方法和系统

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115872970A (zh) * 2022-12-08 2023-03-31 青岛普力机电工程有限公司 一种从乳酸原料到高纯丙交酯连续生产的方法

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