An apparatus and method for preparing crude glycolide

Abstract

The present application belongs to the field of polymer preparation process, and relates to a device and method for preparing crude glycolide, which can be implemented in industry, operated continuously and run in large scale. The device comprises a dehydration unit, a polycondensation unit and a depolymerization unit connected in sequence. The dehydration unit comprises a dehydration kettle, a dehydration kettle heater, a dehydration tower and a dehydration tower condenser. The polycondensation unit comprises a polycondensation kettle and an optional pre-polycondensation kettle arranged upstream of the polycondensation kettle. The depolymerization unit comprises a pre-depolymerization kettle, a depolymerization kettle and a crude glycolide condenser. Ethanol acid or ethanol acid ester as raw material is finally obtained into crude glycolide product through dehydration separation, optional pre-polycondensation, polycondensation, pre-depolymerization and depolymerization. At the same time, a small amount of non-condensable gas, depolymerization residue, water or alcohol and other by-products are produced. The device can realize industrial large-scale and continuous production, and the yield of the target product is improved through various strengthening means.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer preparation process, and particularly relates to a preparation of glycolide, and more particularly to a device and method for preparing crude glycolide. BACKGROUND

[0002] Polyglycolic acid (PGA) is the simplest aliphatic polyester in structure, and is widely used in medical polymer materials, such as surgical sutures, drug controlled release, bone fixation and repair, artificial skin and blood vessels, tissue engineering, etc., due to its good biocompatibility and degradability. In recent years, with the increasing production of PGA and the rapid development of modification technology, it is expected to be widely used in the fields of geotextiles, disposable tableware, oil field fracturing balls, etc.

[0003] There are two methods for the synthesis of PGA. One is to directly dehydrate (alcohol) polycondensation of glycolic acid (ester) to obtain PGA, also known as one-step method. The PGA obtained by this method has low relative molecular mass, and has defects in mechanical strength, gas resistance, durability, etc., and the application is limited. The other is to first polycondense glycolic acid (ester) to obtain glycolic acid oligomer, and then depolymerize it to obtain cyclic glycolide, and then use glycolide to perform ring-opening polymerization to obtain a polymer with a relative molecular mass of 10,000-20,000, which is also known as two-step method. At present, the second method is usually used in industry to prepare PGA with high molecular mass. The two-step method is as follows:

[0004]

[0005] Continuous production of glycolide is a key link in the PGA process, and how to improve the yield of glycolide and realize continuous production is a technical difficulty.

[0006] CN104163810B discloses a propylene lactone preparation technology. Under the condition of an acetylacetone metal salt catalyst, polyglycolic acid oligomer, or a mixture of polyglycolic acid oligomer and azeotropic solvent, or a mixture of polyglycolic acid oligomer, azeotropic solvent and cosolvent, is depolymerized to prepare monomer glycolide. Since the temperature is significantly reduced, the yield and purity of glycolide can be significantly improved. The problems of this method are that the preparation of polyglycolic acid oligomer is not involved, the specific process method is not involved, and the large-scale and continuous process technical scheme is not mentioned. In addition, if the solvent is added, the removal of the third monomer will be involved, which increases the difficulty of the glycolide purification process and increases the complexity of the process.

[0007] CN109970702B discloses a production method of high-purity medical glycolide, which uses solid glycolic acid as raw material, and goes through heating dissolution, vacuum dehydration, temperature rising solidification, high temperature and high vacuum cracking, solvent dissolution and crystallization to obtain high-purity glycolide. The process is simple and controllable in operation. However, the method disclosed in the patent is only a laboratory or small-scale intermittent process, which cannot be mass-produced continuously and has limited industrial application.

[0008] US5830991, US6891048B2, US691639B2, CN1496359A, CN1501923A and other Japanese Wu Fei companies mentioned that high-boiling organic solvents can be added to polyglycolic acid oligomers to reduce the viscosity of the reaction system and the depolymerization reaction temperature. Glycolide can be evaporated with high-boiling organic solvents during depolymerization, which well solves the problem of pipeline blockage; at the same time, it is also mentioned that polyglycolic acid oligomers and polar organic solvents are added to the depolymerization system at the same time, and divalent or multivalent cationic form of sulfate or inorganic acid salt stabilizer is introduced to prevent side reactions. However, this method causes the third solvent to be mixed in the crude glycolide product, which increases the difficulty of glycolide purification process and increases the complexity of the process. SUMMARY

[0009] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a glycolide production process which can be implemented industrially, operated continuously and run on a large scale.

[0010] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a device for preparing crude glycolide, which comprises a dehydration unit, a polycondensation unit and a depolymerization unit connected in sequence; the dehydration unit comprises a dehydration kettle, a dehydration kettle heater, a dehydration tower and a dehydration tower condenser; the polycondensation unit comprises a polycondensation kettle and an optional pre-polycondensation kettle arranged upstream of the polycondensation kettle; the depolymerization unit comprises a pre-depolymerization kettle, a depolymerization kettle and a crude glycolide condenser; wherein,

[0011] The dehydration kettle heater is connected to the bottom of the dehydration kettle;

[0012] The top of the dehydration kettle is connected to the dehydration tower, and the bottom is connected to the polycondensation unit;

[0013] The top of the dehydration tower is connected to the dehydration tower condenser, and the bottom is connected to the upper part of the dehydration kettle;

[0014] The polycondensation kettle is provided with a gas phase outlet and a liquid phase outlet, and the liquid phase outlet is connected to the pre-depolymerization kettle;

[0015] The top of the pre-depolymerization kettle is connected to the crude glycolide condenser, and the bottom is connected to the depolymerization kettle;

[0016] The top of the depolymerization kettle is connected to the crude glycolide condenser;

[0017] glycolate feed line is connected to the dehydration unit; a catalyst feed line is connected to the dehydration unit or the depolymerization unit.

[0018] A second aspect of the present application provides a method for preparing crude glycolide, using the device described above, comprising the following steps:

[0019] glycolic acid and / or glycolate ester raw material enters the device through the glycolate feed line, and catalyst enters the device through the catalyst feed line, and the glycolic acid and / or glycolate ester raw material is sequentially subjected to dehydration separation, optional pre-polycondensation, polycondensation, pre-depolymerization, and depolymerization to obtain crude glycolide product.

[0020] The beneficial effects of the present application include:

[0021] 1) The present application realizes the continuous production of crude glycolide by integrating the staged dehydration, polycondensation, depolymerization, and separation sections and pipe equipment, and has industrialization amplification implementation.

[0022] 2) The present application realizes effective control of the molecular weight and distribution of oligomers by forming lactic acid oligomers through pre-polycondensation and polycondensation of one or more stages with step-by-step temperature rise and pressure reduction, ensures the stability of the reaction process, reduces the generation of side reactions, and provides stable raw materials for the pre-depolymerization and depolymerization reaction processes.

[0023] 3) The present application improves process intensification by the dehydration system, ensuring dehydration residence time and heat transfer.

[0024] 4) The present application intensifies the polymerization reaction by the polycondensation reactor, ensuring that the polymerization reaction reaches the required polymerization degree.

[0025] 5) The present application couples pre-depolymerization and depolymerization, and cooperates with the circulating depolymerization process and the reaction-intensifying equipment, ensuring the cracking depth and improving the reaction efficiency.

[0026] 6) The present application ensures the maximum generation of target product glycolide by depolymerization through the reactor and process settings of one or more stages of polymerization and two-stage depolymerization, improves the product yield, and reduces the generation of residues.

[0027] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0028] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which similar reference characters refer to similar elements throughout the several views, and in which:

[0029] Figure 1Flow chart of the device and method for preparing crude glycolide according to the first aspect of the present application.

[0030] Figure 2 Flow chart of the device and method for preparing crude glycolide according to the second aspect of the present application.

[0031] Figure 3 Flow chart of the device and method for preparing crude glycolide according to the third aspect of the present application.

[0032] Explanation of reference signs:

[0033] Dehydrating kettle 1, dehydrating tower 2, dehydrating kettle heater 3, dehydrating tower condenser 4, pre-polycondensation kettle 5, first dehydrating tower 6A, second dehydrating tower 6B, first dehydrating tower condenser 7A, second dehydrating tower condenser 7B, pre-polycondensation kettle heater 8, polycondensation kettle 9, pre-depolymerization kettle 10, crude glycolide condenser 11, depolymerization kettle 12, catalyst 13, glycolic acid / glycolate raw material 14, dehydrating non-condensed gas 15, water and / or alcohol 16, polycondensation non-condensed gas 17, depolymerization residue 18, crude glycolide product 19, depolymerization non-condensed gas mixture 20. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described below, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein.

[0035] The present application provides a device for preparing crude glycolide, which comprises a dehydrating unit, a polycondensation unit and a depolymerization unit connected in sequence; the dehydrating unit comprises a dehydrating kettle, a dehydrating kettle heater, a dehydrating tower and a dehydrating tower condenser; the polycondensation unit comprises a polycondensation kettle and optionally a pre-polycondensation kettle arranged upstream of the polycondensation kettle; the depolymerization unit comprises a pre-depolymerization kettle, a depolymerization kettle and a crude glycolide condenser; wherein,

[0036] The dehydrating kettle heater is connected to the bottom of the dehydrating kettle;

[0037] The top of the dehydrating kettle is connected to the dehydrating tower, and the bottom is connected to the polycondensation unit;

[0038] The top of the dehydrating tower is connected to the dehydrating tower condenser, and the bottom is connected to the upper part of the dehydrating kettle;

[0039] The polycondensation kettle is provided with a gas phase outlet and a liquid phase outlet, and the liquid phase outlet is connected to the pre-depolymerization kettle;

[0040] The top of the pre-depolymerization kettle is connected to the crude glycolide condenser, and the bottom is connected to the depolymerization kettle;

[0041] The top of the depolymerization kettle is connected to the crude glycolide condenser;

[0042] The glycolic acid / ester feed pipeline is connected to the dehydration unit; the catalyst feed pipeline is connected to the dehydration unit or the depolymerization unit.

[0043] According to the present application, the pre-polycondensation kettle is optionally provided, and the optional meaning is that it can be provided or not. When the pre-polycondensation kettle is provided, the pre-polycondensation kettle is arranged upstream of the polycondensation kettle.

[0044] When the pre-polycondensation kettle is not provided, the polycondensation unit comprises a polycondensation kettle, and the bottom of the dehydration kettle is directly connected to the polycondensation kettle; when the pre-polycondensation kettle is provided, the polycondensation unit comprises a pre-polycondensation kettle and a polycondensation kettle, and the bottom of the dehydration kettle is connected to the pre-polycondensation kettle, and the bottom of the pre-polycondensation kettle is connected to the inlet of the polycondensation kettle.

[0045] In the present application, the dehydration tower and the dehydration tower condenser are provided in a set, which can be one group or two groups. When it is one group, the dehydration tower is connected to the top of the dehydration kettle (hereinafter referred to as the dehydration tower at the top of the dehydration kettle), and when it is two groups, one group is connected to the top of the dehydration kettle, and the other group is independently provided; the top of the pre-polycondensation kettle is connected to the dehydration tower at the top of the dehydration kettle or independently provided dehydration tower.

[0046] According to a preferred embodiment of the present application, the bottom discharge pipeline of the dehydration kettle is divided into two branches, one of which is connected to the polycondensation unit, and the other is connected to the inlet of the dehydration kettle heater.

[0047] The meaning that the glycolic acid / ester feed pipeline is connected to the dehydration unit is that it is connected to the dehydration kettle heater or the dehydration kettle.

[0048] In the device of the present application, the catalyst can enter from the dehydration unit or from the depolymerization unit, and accordingly, when it enters from the dehydration unit, the catalyst feed pipeline can be connected to the dehydration kettle heater or the dehydration kettle, and when it enters from the depolymerization unit, the catalyst feed pipeline is connected to the pre-depolymerization kettle, which is a more preferred arrangement.

[0049] According to a preferred embodiment of the present application, the dehydration kettle heater is one of a tube-shell heat exchanger, a plate heat exchanger, and an electric heater.

[0050] According to a preferred embodiment of the present application, the internal parts of the dehydration tower are one or more of sieve plates, float valves, fillers, and bubble caps, preferably fillers.

[0051] According to the present application, preferably, the dehydration tower condenser is provided with a non-condensable gas discharge pipeline for gas phase and a water and / or alcohol discharge pipeline for liquid phase; the water and / or alcohol discharge pipeline is divided into two branches, one of which is connected to the top of the dehydration tower, and the other is used as an external discharge pipeline.

[0052] According to the application, preferably, the pre-polycondensation kettle is provided with a pre-polycondensation non-condensable gas discharge pipeline in gas phase and a pre-polycondensation product discharge pipeline in liquid phase; the pre-polycondensation kettle is connected with the dehydration tower through the pre-polycondensation non-condensable gas discharge pipeline and connected with the polycondensation kettle through the pre-polycondensation product discharge pipeline.

[0053] When the pre-polycondensation kettle top is connected with an independently arranged dehydration tower and dehydration tower condenser, the dehydration tower top is connected with the dehydration tower condenser and the bottom is connected with the upper part of the pre-polycondensation kettle.

[0054] According to a preferred embodiment of the application, the pre-polycondensation kettle is a vertical or horizontal stirred tank provided with a heater and / or a jacket inside, preferably a vertical stirred tank provided with a heater inside.

[0055] According to the application, preferably, the polycondensation kettle is provided with a polycondensation non-condensable gas discharge pipeline in gas phase and a polycondensation product discharge pipeline in liquid phase; the polycondensation kettle is connected with the pre-depolymerization kettle through the polycondensation product discharge pipeline.

[0056] According to a preferred embodiment of the application, the polycondensation kettle is a vertical stirred tank reactor or a horizontal shaft stirred reactor, preferably one of a single-shaft or multi-shaft kneading reactor, a screw type reactor, a surface renewal type reactor, a tubular reactor, a tower type reactor, preferably a horizontal single-shaft or multi-shaft kneading reactor; wherein the surface renewal type reactor is preferably a disc type reactor or a squirrel cage type reactor.

[0057] According to the application, preferably, the pre-depolymerization kettle is provided with a pre-depolymerization non-condensable gas discharge pipeline in gas phase and a pre-depolymerization product discharge pipeline in liquid phase; the pre-depolymerization kettle is connected with the crude glycolide condenser through the pre-depolymerization non-condensable gas discharge pipeline and connected with the depolymerization kettle through the pre-depolymerization product discharge pipeline.

[0058] According to a preferred embodiment of the application, the pre-depolymerization kettle is a horizontal or vertical evaporator with shaft stirring, provided with a heater and / or a jacket inside, preferably a thin film evaporator.

[0059] According to a preferred embodiment of the application, the depolymerization kettle is a vertical or horizontal kettle type reactor with shaft stirring, a screw type reactor or a kneading reactor, preferably a single-shaft or multi-shaft kneading reactor.

[0060] According to the application, preferably, the crude glycolide condenser is provided with a crude glycolide product discharge pipeline and a depolymerization non-condensable gas mixture discharge pipeline.

[0061] According to the application, preferably, the depolymerization kettle is provided with a depolymerization non-condensable gas discharge pipeline in gas phase and a depolymerization residue discharge pipeline in solid-liquid phase; the depolymerization kettle is connected with the crude glycolide condenser through the depolymerization non-condensable gas discharge pipeline.

[0062] The present application also provides a method for preparing crude glycolide, using the device described above, comprising the following steps:

[0063] Glycolic acid and / or glycolate raw materials enter the device through the glycolic acid / ester feed pipeline, and the catalyst enters the device through the catalyst feed pipeline. The glycolic acid and / or glycolate raw materials are sequentially subjected to dehydration separation, optional pre-polycondensation, polycondensation, pre-depolymerization, and depolymerization to obtain a crude glycolide product. At the same time, byproducts such as non-condensable gas, water, or alcohol are obtained at the top of the dehydration column and the (pre) polycondensation kettle, and depolymerization residue byproducts containing coke, polymers, and other impurities are obtained at the bottom of the depolymerization kettle.

[0064] As described above, the optional pre-polycondensation means that pre-polycondensation can be performed or not, depending on the device configuration.

[0065] According to a preferred embodiment of the present application, the method comprises the following steps:

[0066] (a) The aqueous glycolic acid and / or glycolate raw materials enter the dehydration kettle heater inlet or the dehydration kettle inlet through the glycolic acid / ester feed pipeline, and the catalyst enters the dehydration kettle heater inlet or the dehydration kettle inlet or the pre-depolymerization kettle inlet through the catalyst feed pipeline. The dehydration kettle is heated at normal pressure or reduced pressure to evaporate water and / or alcohol, and the evaporated components are separated by reflux in the dehydration column. The overhead stream of the dehydration column enters the dehydration column condenser to obtain liquid-phase water and / or alcohol and dehydration non-condensable gas, and the bottom stream returns to the dehydration kettle. The material at the bottom of the dehydration kettle is divided into two streams, one of which enters the dehydration kettle heater, and the other is extracted to enter the downstream polycondensation unit;

[0067] (b) The polycondensation unit receives the material at the bottom of the dehydration kettle to undergo dehydration and / or alcohol polycondensation to produce glycolic acid oligomers; the step (b) is selected from one of the following two forms:

[0068] (b-1) The polycondensation unit includes a polycondensation kettle, which receives the material at the bottom of the dehydration kettle to undergo dehydration and / or alcohol polycondensation at high temperature and high vacuum to obtain polycondensation non-condensable gas and glycolic acid oligomers; this form corresponds to the case where no pre-polycondensation kettle is provided;

[0069] (b-2) The polycondensation unit includes a pre-polycondensation kettle and a polycondensation kettle, the pre-polycondensation kettle receives the material at the bottom of the dehydration kettle to undergo dehydration and / or alcohol pre-polycondensation at high temperature and low pressure, and the produced water and / or alcohol is discharged through a separate dehydration column or is combined and discharged into the dehydration column at the top of the dehydration kettle; specifically, the step of discharging through a separate dehydration column includes: the produced water and / or alcohol is separated by reflux in the separate dehydration column, the overhead stream of the dehydration column enters the separate dehydration column condenser to obtain liquid-phase water and / or alcohol and dehydration non-condensable gas, and the bottom stream returns to the pre-polycondensation kettle;

[0070] The polycondensation kettle receives the bottom material of the pre-polycondensation kettle, continues the polycondensation reaction through high temperature and high vacuum operation, and obtains polycondensation non-condensable gas and glycolic acid oligomer; and the pre-polycondensation kettle is correspondingly provided;

[0071] (c) The liquid phase at the bottom of the polycondensation kettle enters the pre-depolymerization kettle, and the depolymerization into ring reaction of the glycolic acid oligomer occurs through high temperature and high vacuum operation, to generate a glycolide-containing stream, the glycolide-containing stream enters the crude glycolide condenser through the top of the pre-depolymerization kettle, and the unreacted glycolic acid oligomer in the pre-depolymerization kettle enters the depolymerization kettle through the bottom of the pre-depolymerization kettle;

[0072] (d) The depolymerization kettle continues the depolymerization into ring reaction of the glycolic acid oligomer through higher temperature and higher vacuum operation than the pre-depolymerization kettle, converts the unreacted glycolic acid oligomer in step (c) into glycolide, and discharges from the top gas phase pipeline of the depolymerization kettle to enter the crude glycolide condenser, while producing a depolymerization residue by-product containing coke and polymer, and discharging from the bottom of the depolymerization kettle;

[0073] (e) The crude glycolide condenser condenses the streams from the top of the pre-depolymerization kettle and the top of the depolymerization kettle, to obtain a depolymerization non-condensable gas mixture and a crude glycolide product.

[0074] According to the method of the present application, the catalyst can be at least one of halides of tin, organic acid compounds of tin, oxides of antimony, halides of antimony, organic acid compounds of antimony, oxides of zinc, halides of zinc and organic acid compounds of zinc; and preferably, the catalyst is an organic acid compound of tin.

[0075] The amount of the catalyst used can be 0.001-5% wt of the amount of glycolic acid / glycolate.

[0076] According to the method of the present application, preferably, the number of theoretical plates of the dehydration tower is 2-20, the operating pressure at the top of the tower is 50-130 kPaA, and the operating temperature at the top of the tower is 30-140℃.

[0077] According to the method of the present application, preferably, the operating temperature of the dehydration kettle is 70-140℃, and the operating pressure is 50-150 kPaA.

[0078] According to the method of the present application, preferably, the operating temperature of the pre-polycondensation kettle is 140-200℃, and the operating pressure is 10-50 kPaA.

[0079] According to the method of the present application, preferably, the operating temperature of the polycondensation kettle is 170-210℃, and the operating pressure is 1-20 kPaA.

[0080] According to the method of the present application, preferably, the operating temperature of the pre-depolymerization kettle is 180-250℃, and the operating pressure is 100 PaA-10 kPaA.

[0081] According to the method of the present application, the operating temperature of the depolymerization kettle is preferably 240-300°C, and the vacuum degree is 1-20 kPaA.

[0082] According to the method of the present application, the dehydration kettle mainly removes most of the free water in the glycolic acid / ester raw material, and a small amount of pre-polymerization of the glycolic acid / ester in the dehydration kettle occurs to generate glycolic acid dimers, trimers, etc., and a small amount of pre-polymer is carried into the downstream polycondensation unit with the glycolic acid / ester raw material.

[0083] In the pre-polycondensation kettle, the removal of a small amount of free water and the polycondensation of water and / or alcohol in the glycolic acid / ester continue to occur, and the free water and the water and / or alcohol generated by polycondensation are discharged through a separate dehydration tower or combined into the dehydration tower at the top of the dehydration kettle.

[0084] In the polycondensation kettle, the polycondensation reaction is carried out to polymerize the glycolic acid or glycolic acid ester (when no pre-polycondensation kettle is provided), or the polycondensation reaction is continued to polymerize the remaining glycolic acid or glycolic acid ester (when a pre-polycondensation kettle is provided), and a molecular weight increasing polymerization reaction is carried out, i.e. the molecular weight of the glycolic acid polycondensate is increased, to obtain a glycolic acid oligomer.

[0085] The pre-depolymerization kettle and the depolymerization kettle are used for the depolymerization reaction of the glycolic acid oligomer to obtain crude glycolide and by-products such as coke and polymers.

[0086] In the present application, the term "glycolic acid / ester" refers to glycolic acid and / or glycolic acid ester, wherein the glycolic acid ester is an alkyl glycolate, preferably methyl glycolate and / or ethyl glycolate, and the glycolic acid and / or glycolic acid ester raw material is preferably glycolic acid and / or methyl glycolate.

[0087] The present application is further illustrated by the following examples.

[0088] Example 1

[0089] A device for preparing crude glycolide as shown in Figure 1 The device includes a dehydration unit, a polycondensation unit and a depolymerization unit connected in sequence; the dehydration unit includes a dehydration kettle 1, a dehydration kettle heater 3, a dehydration tower 2 and a dehydration tower condenser 4, the polycondensation unit includes a pre-polycondensation kettle 5 and a polycondensation kettle 9, and the depolymerization unit includes a pre-depolymerization kettle 10, a depolymerization kettle 12 and a crude glycolide condenser 11; wherein,

[0090] The dehydration kettle heater 3 is a shell-and-tube heat exchanger connected to the bottom of the dehydration kettle 1;

[0091] The dehydration kettle 1 is connected to the dehydration tower 2 at the top, and the bottom discharge pipeline is divided into two branches, one connected to the pre-polycondensation kettle 5 and the other connected to the inlet of the dehydration kettle heater 3;

[0092] The dehydration tower 2 is connected to the dehydration tower condenser 4 at the top and to the upper part of the dehydration kettle 1 at the bottom; the inner part of the dehydration tower 2 is filled with packing;

[0093] The dehydration tower condenser 4 is provided with a non-condensable gas discharge pipeline for gas phase and a water and / or alcohol discharge pipeline for liquid phase; the water and / or alcohol discharge pipeline is divided into two branches, one of which is connected to the top of the dehydration tower 2 and the other of which is an external discharge pipeline;

[0094] The pre-polycondensation kettle 5 is a vertical stirring kettle provided with a pre-polycondensation kettle heater 8, a pre-polycondensation non-condensable gas discharge pipeline for gas phase and a pre-polycondensation product extraction pipeline for liquid phase; the pre-polycondensation kettle 5 is connected to the dehydration tower 2 through the pre-polycondensation non-condensable gas discharge pipeline and to the polycondensation kettle 9 inlet through the pre-polycondensation product extraction pipeline;

[0095] The polycondensation kettle 9 is a horizontal single-shaft kneading reactor provided with a polycondensation non-condensable gas discharge pipeline for gas phase and a polycondensation product extraction pipeline for liquid phase; the polycondensation kettle 9 is connected to the pre-depolymerization kettle 10 through the polycondensation product extraction pipeline;

[0096] The pre-depolymerization kettle 10 is a thin film evaporator provided with a pre-depolymerization non-condensable gas discharge pipeline for gas phase and a pre-depolymerization product extraction pipeline for liquid phase; the pre-depolymerization kettle 10 is connected to the crude glycolide condenser 11 through the pre-depolymerization non-condensable gas discharge pipeline and to the depolymerization kettle 12 through the pre-depolymerization product extraction pipeline;

[0097] The depolymerization kettle 12 is a single-shaft kneading reactor provided with a depolymerization non-condensable gas discharge pipeline for gas phase and a depolymerization residue discharge pipeline for solid-liquid phase; the depolymerization kettle is connected to the crude glycolide condenser 11 through the depolymerization non-condensable gas discharge pipeline;

[0098] The crude glycolide condenser 11 is provided with a crude glycolide product extraction pipeline and a depolymerization non-condensable gas mixture discharge pipeline;

[0099] Both the glycolic acid / ester feed pipeline and the catalyst feed pipeline are connected to the dehydration kettle heater 3.

[0100] The method for preparing crude glycolide by using the above device comprises the following steps:

[0101] (a) glycolic acid and / or glycolate feedstock 14, which contains water, enters the dehydration kettle heater 3 inlet via the glycolic acid / ester feed line, and catalyst 13 enters the dehydration kettle heater 3 inlet via the catalyst feed line; the dehydration kettle 1 is heated at normal or reduced pressure to vaporize water and / or alcohol, which vaporized components enter the dehydration column 2 reflux separation, and the dehydration column overhead stream enters the dehydration column condenser 4 to obtain liquid phase water and / or alcohol 16 and dehydration non-condensable gas 15, and the bottom stream returns to the dehydration kettle 1; the bottom material of the dehydration kettle 1 is divided into two streams, one of which enters the dehydration kettle heater 3, and the other is extracted to enter the pre-polycondensation kettle 5;

[0102] (b) the pre-polycondensation kettle 5 receives the bottom material of the dehydration kettle 1, and operates at high temperature and low pressure to cause dehydration and / or alcohol pre-polycondensation reaction, and the generated water and / or alcohol are combined to enter the dehydration column 2 at the top of the dehydration kettle 1 and discharged;

[0103] The polycondensation kettle 9 receives the bottom material of the pre-polycondensation kettle 5, and operates at high temperature and high vacuum to continue the polycondensation reaction, obtaining polycondensation non-condensable gas and glycolic acid oligomers, and the polycondensation non-condensable gas is discharged via the polycondensation non-condensable gas discharge line;

[0104] (c) the bottom liquid phase of the polycondensation kettle 9 containing glycolic acid oligomers enters the pre-depolymerization kettle 10, which operates at high temperature and high vacuum to cause depolymerization of the glycolic acid oligomers to form a stream containing glycolide, which enters the crude glycolide condenser 11 via the top of the pre-depolymerization kettle 10, and the unreacted glycolic acid oligomers in the pre-depolymerization kettle 10 enter the depolymerization kettle 12 from the bottom of the pre-depolymerization kettle 10;

[0105] (d) the depolymerization kettle 12 operates at a higher temperature and higher vacuum than the pre-depolymerization kettle 10 to continue the depolymerization of the glycolic acid oligomers to glycolide, converting the unreacted glycolic acid oligomers from step (c) into glycolide, which is discharged from the top gas phase line of the depolymerization kettle and then enters the crude glycolide condenser 11, while producing depolymerization residue 18 containing coke and polymers, which is discharged from the bottom of the depolymerization kettle 12;

[0106] (e) the crude glycolide condenser 11 condenses the streams from the top of the pre-depolymerization kettle 10 and the top of the depolymerization kettle 12 to obtain a depolymerization non-condensable gas mixture 20 and a crude glycolide product 19.

[0107] The glycolic acid and / or glycolate feedstock 14 is glycolic acid, which comes from outside.

[0108] The catalyst 13 is an organic acid compound of tin, and the amount used is 0.1% wt of glycolic acid.

[0109] The dehydration column has a theoretical plate number of 10, an overhead operating pressure of 100 kPaA, and an overhead operating temperature of 100°C.

[0110] The dehydration kettle operates at a temperature of 120°C and a pressure of 110 kPaA.

[0111] The prepolymerization reactor operates at a temperature of 160°C and a pressure of 50 kPaA.

[0112] The polycondensation reactor operates at a temperature of 190°C and a pressure of 20 kPaA.

[0113] The operating temperature of the pre-depolymerization reactor is 210℃, and the operating pressure is 5kPaA.

[0114] The depolymerization reactor operates at a temperature of 280°C and a pressure of 1 kPaA.

[0115] Using the above apparatus and method, the utilization rate of glycolic acid is 98%, and the yield of glycolide is 88%.

[0116] The formula for calculating the utilization rate of glycolic acid is: (molar flow rate of glycolic acid feed - molar flow rate of remaining glycolic acid) / molar flow rate of glycolic acid feed.

[0117] The formula for calculating the yield of glycolide is: glycolide molar flow rate / (glycolic acid feed molar flow rate - residual glycolic acid molar flow rate).

[0118] Example 2

[0119] use Figure 2 The apparatus shown is for preparing crude glycolide. The apparatus includes a dehydration unit, a polycondensation unit, and a depolymerization unit connected in sequence. The dehydration unit includes a dehydration vessel 1, a dehydration vessel heater 3, a first dehydration tower 6A, a first dehydration tower condenser 7A, a second dehydration tower 6B, and a second dehydration tower condenser 7B. The polycondensation unit includes a pre-polycondensation vessel 5 and a polycondensation vessel 9. The depolymerization unit includes a pre-depolymerization vessel 10, a depolymerization vessel 12, and a crude glycolide condenser 11.

[0120] The dehydration kettle heater 3 is a shell-and-tube heat exchanger, which is connected to the bottom of the dehydration kettle 1;

[0121] The top of the dehydration kettle 1 is connected to the first dehydration tower 6A, and the bottom discharge pipeline is divided into two branches, one of which is connected to the prepolymerization kettle 5, and the other is connected to the inlet of the dehydration kettle heater 3.

[0122] The top of the first dehydration tower 6A is connected to the first dehydration tower condenser 7A, and the bottom is connected to the upper part of the dehydration kettle 1; the internal components of the first dehydration tower 6A are packing materials.

[0123] The first dehydration tower condenser 7A is equipped with a gas phase non-condensable gas discharge pipeline and a liquid phase water and / or alcohol discharge pipeline; the water and / or alcohol discharge pipeline is divided into two branches, one of which is connected to the top of the first dehydration tower 6A, and the other is used as an external discharge pipeline.

[0124] The pre-polycondensation kettle 5 is a vertical stirring kettle with a pre-polycondensation kettle heater 8 inside, provided with a pre-polycondensation non-condensable gas discharge pipeline in gas phase and a pre-polycondensation product extraction pipeline in liquid phase; the pre-polycondensation kettle 5 is connected with the second dehydration tower 6B through the pre-polycondensation non-condensable gas discharge pipeline and connected with the inlet of the polycondensation kettle 9 through the pre-polycondensation product extraction pipeline; the top of the second dehydration tower 6B is connected with the second dehydration tower condenser 7B, and the bottom is connected with the upper part of the pre-polycondensation kettle 5; the inner part of the second dehydration tower 6B is filled with packing; the second dehydration tower condenser 7B is provided with a non-condensable gas discharge pipeline in gas phase and a water and / or alcohol discharge pipeline in liquid phase; the water and / or alcohol discharge pipeline is divided into two branches, one of which is connected with the top of the second dehydration tower 6B, and the other is an external discharge pipeline;

[0125] The polycondensation kettle 9 is a horizontal single-shaft kneading reactor, provided with a polycondensation non-condensable gas discharge pipeline in gas phase and a polycondensation product extraction pipeline in liquid phase; the polycondensation kettle 9 is connected with the pre-depolymerization kettle 10 through the polycondensation product extraction pipeline;

[0126] The pre-depolymerization kettle 10 is a thin film evaporator, provided with a pre-depolymerization non-condensable gas discharge pipeline in gas phase and a pre-depolymerization product extraction pipeline in liquid phase; the pre-depolymerization kettle is connected with the crude glycolide condenser 11 through the pre-depolymerization non-condensable gas discharge pipeline and connected with the depolymerization kettle 12 through the pre-depolymerization product extraction pipeline;

[0127] The depolymerization kettle 12 is a single-shaft kneading reactor, provided with a depolymerization non-condensable gas discharge pipeline in gas phase and a depolymerization residue discharge pipeline in solid-liquid phase; the depolymerization kettle 12 is connected with the crude glycolide condenser 11 through the depolymerization non-condensable gas discharge pipeline;

[0128] The crude glycolide condenser 11 is provided with a crude glycolide product extraction pipeline and a depolymerization non-condensable gas mixture discharge pipeline;

[0129] The glycolic acid / ester feed pipeline is connected with the inlet of the dehydration kettle heater 3; the catalyst feed pipeline is connected with the inlet of the pre-depolymerization kettle 10 (which can be combined with the polycondensation product extraction pipeline).

[0130] The method for preparing crude glycolide by using the above device comprises the following steps:

[0131] (a) glycolic acid and / or glycolate feedstock 14, which contains water, enters the dehydration kettle heater 3 inlet via the glycolic acid / ester feed line, and catalyst 13 enters the pre-polycondensation kettle 10 inlet via the catalyst feed line; the dehydration kettle 3 is heated at atmospheric or reduced pressure to vaporize the water and / or alcohol, and the vaporized components enter the first dehydration column 6A for reflux separation, and the first dehydration column overhead stream enters the first dehydration column condenser 7A to obtain the first water and / or alcohol 16A in liquid phase and the first dehydration non-condensable gas 15A, and the column bottom stream returns to the dehydration kettle 1; the bottom material of the dehydration kettle 1 is divided into two streams, one enters the dehydration kettle heater 3, and the other is withdrawn to the pre-polycondensation kettle 5;

[0132] (b) the pre-polycondensation kettle 5 receives the bottom material of the dehydration kettle 1, and is operated at high temperature and low pressure to cause the pre-polycondensation reaction of the dehydration and / or alcohol, and the produced water and / or alcohol enters the second dehydration column 6B for reflux separation, and the second dehydration column overhead stream enters the second dehydration column condenser 7B to obtain the second water and / or alcohol 16B in liquid phase and the second dehydration non-condensable gas 15B, and the column bottom stream returns to the pre-polycondensation kettle 5;

[0133] The polycondensation kettle 9 receives the bottom material of the pre-polycondensation kettle 5, and is operated at high temperature and high vacuum to continue the polycondensation reaction, to obtain polycondensation non-condensable gas and glycolic acid oligomers, and the polycondensation non-condensable gas is discharged via the polycondensation non-condensable gas discharge line;

[0134] (c) the bottom liquid phase of the polycondensation kettle 9 containing glycolic acid oligomers enters the pre-depolymerization kettle 10, and is operated at high temperature and high vacuum to cause the depolymerization reaction of the glycolic acid oligomers into cyclic reaction to generate a glycolide-containing stream, which enters the crude glycolide condenser 11 via the top of the pre-depolymerization kettle 10, and the unreacted glycolic acid oligomers in the pre-depolymerization kettle 10 enter the depolymerization kettle 12 from the bottom of the pre-depolymerization kettle 10;

[0135] (d) the depolymerization kettle 12 is operated at a higher temperature and higher vacuum than the pre-depolymerization kettle 10 to continue the depolymerization reaction of the glycolic acid oligomers into cyclic reaction to convert the unreacted glycolic acid oligomers of step (c) into glycolide, which is discharged from the top gas phase line of the depolymerization kettle and enters the crude glycolide condenser 11, while producing a depolymerization residue 18 containing coke and high polymers, which is discharged from the bottom of the depolymerization kettle 12;

[0136] (e) the crude glycolide condenser 11 condenses the streams from the top of the pre-depolymerization kettle 10 and the top of the depolymerization kettle 12 to obtain a depolymerization non-condensable gas mixture 20 and a crude glycolide product 19.

[0137] The glycolic acid and / or glycolate feedstock 14 is methyl glycolate, which is from outside.

[0138] The catalyst 13 is an organic acid compound of tin, and the amount is 0.2% wt of the methyl glycolate.

[0139] The first dehydration tower 6A has 5 theoretical plates, a top operating pressure of 125 kPaA, and a top operating temperature of 70°C.

[0140] The second dehydration tower 6B has 5 theoretical plates, a top operating pressure of 50 kPaA, and a top operating temperature of 50°C.

[0141] The dehydration kettle has an operating temperature of 110°C and an operating pressure of 100 kPaA.

[0142] The pre-polycondensation kettle has an operating temperature of 150°C and an operating pressure of 50 kPaA.

[0143] The polycondensation kettle has an operating temperature of 180°C and an operating pressure of 5 kPaA.

[0144] The pre-depolymerization kettle has an operating temperature of 200°C and an operating pressure of 5 kPaA.

[0145] The depolymerization kettle has an operating temperature of 270°C and an operating pressure of 1 kPaA.

[0146] Through the above device and method, the utilization rate of methyl glycolate is 95%, and the yield of glycolide is 85%.

[0147] The utilization rate of methyl glycolate is calculated by the formula: (molar flow rate of methyl glycolate feed - residual molar flow rate of methyl glycolate) / molar flow rate of methyl glycolate feed.

[0148] The yield of glycolide is calculated by the formula: molar flow rate of glycolide / (molar flow rate of methyl glycolate feed - residual molar flow rate of methyl glycolate).

[0149] Example 3

[0150] A device for preparing crude glycolide as shown in Figure 3 The device includes a dehydration unit, a polycondensation unit, and a depolymerization unit connected in sequence; the dehydration unit includes a dehydration kettle 1, a dehydration kettle heater 3, a dehydration tower 2, and a dehydration tower condenser 4; the polycondensation unit includes a polycondensation kettle 9; the depolymerization unit includes a pre-depolymerization kettle 10, a depolymerization kettle 12, and a crude glycolide condenser 11; wherein,

[0151] The dehydration kettle heater 3 is a shell-and-tube heat exchanger connected to the bottom of the dehydration kettle 1;

[0152] The dehydration kettle 1 is connected to the dehydration tower 2 at the top, and the bottom discharge pipeline is divided into two branches, one of which is connected to the polycondensation kettle 9, and the other is connected to the inlet of the dehydration kettle heater 3;

[0153] The dehydration tower 2 is connected to the dehydration tower condenser 4 at the top and to the upper part of the dehydration kettle 1 at the bottom; the inner part of the dehydration tower 2 is filled with packing.

[0154] The dehydration column condenser 4 is provided with a non-condensable gas discharge line for gas phase and a water and / or alcohol discharge line for liquid phase; the water and / or alcohol discharge line is divided into two branches, one of which is connected to the top of the dehydration column 2, and the other is an external discharge line;

[0155] The polycondensation kettle 9 is a horizontal single-shaft kneading reactor, provided with a polycondensation non-condensable gas discharge line for gas phase and a polycondensation product discharge line for liquid phase; the polycondensation kettle 9 is connected to the pre-depolymerization kettle 10 through the polycondensation product discharge line;

[0156] The pre-depolymerization kettle 10 is a thin film evaporator, provided with a pre-depolymerization non-condensable gas discharge line for gas phase and a pre-depolymerization product discharge line for liquid phase; the pre-depolymerization kettle 10 is connected to the crude glycolide condenser 11 through the pre-depolymerization non-condensable gas discharge line and to the depolymerization kettle 12 through the pre-depolymerization product discharge line;

[0157] The depolymerization kettle 12 is a single-shaft kneading reactor, provided with a depolymerization non-condensable gas discharge line for gas phase and a depolymerization residue discharge line for solid-liquid phase; the depolymerization kettle 12 is connected to the crude glycolide condenser 11 through the depolymerization non-condensable gas discharge line;

[0158] The crude glycolide condenser 11 is provided with a crude glycolide product discharge line and a depolymerization non-condensable gas mixture discharge line;

[0159] The glycolic acid / ester feed line is connected to the inlet of the dehydration kettle heater 3; the catalyst feed line is connected to the inlet of the pre-depolymerization kettle 10.

[0160] The method for preparing crude glycolide by using the above device comprises:

[0161] (a) the water-containing glycolic acid and / or glycolic acid ester raw material 14 enters the dehydration kettle heater 3 inlet through the glycolic acid / ester feed line, and the catalyst 13 enters the pre-depolymerization kettle 10 inlet through the catalyst feed line; the dehydration kettle 1 is heated under normal pressure or reduced pressure to evaporate water and / or alcohol, and the evaporated components enter the dehydration column 2 for reflux separation, the dehydration column 2 top stream enters the dehydration column condenser 4 to obtain liquid-phase water and / or alcohol and non-condensable gas, and the bottom stream returns to the dehydration kettle 1; the dehydration kettle 1 bottom material is divided into two streams, one of which enters the dehydration kettle heater 3, and the other is discharged to enter the polycondensation kettle 9;

[0162] (b) the polycondensation kettle 9 receives the dehydration kettle 1 bottom material, and high-temperature and high-vacuum operation is performed to cause dehydration and / or alcohol polycondensation reaction, to obtain polycondensation non-condensable gas and glycolic acid oligomers, and the polycondensation non-condensable gas is discharged through the polycondensation non-condensable gas discharge line;

[0163] (c) the liquid phase at the bottom of the polycondensation kettle 9 containing oligomers of glycolic acid enters the pre-depolymerization kettle 10, and the depolymerization and ring formation of the oligomers of glycolic acid occurs under high temperature and high vacuum operation to generate a stream containing glycolide, which enters the crude glycolide condenser 11 from the top of the pre-depolymerization kettle 10, and the unreacted oligomers of glycolic acid in the pre-depolymerization kettle 10 enter the depolymerization kettle 12 from the bottom of the pre-depolymerization kettle 10;

[0164] (d) the depolymerization kettle 12 is operated under higher temperature and higher vacuum than the pre-depolymerization kettle 10, and the depolymerization and ring formation of the oligomers of glycolic acid continues to convert the unreacted oligomers of glycolic acid in step (c) into glycolide, which is discharged from the top gas phase pipeline of the depolymerization kettle and then enters the crude glycolide condenser 11, while producing a depolymerization residue 18 containing coke and polymers, which is discharged from the bottom of the depolymerization kettle 12;

[0165] (e) the crude glycolide condenser 11 condenses the streams from the top of the pre-depolymerization kettle 10 and the top of the depolymerization kettle 12 to obtain a non-condensable gas mixture 20 and a crude glycolide product 19.

[0166] The raw material 14 of glycolic acid and / or glycolate is glycolic acid from outside.

[0167] The catalyst is an organic acid compound of tin, and the amount used is 0.05% wt of glycolic acid.

[0168] The theoretical plate number of the dehydration tower is 18, the operating pressure at the top of the tower is 70 kPaA, and the operating temperature at the top of the tower is 90°C.

[0169] The operating temperature of the dehydration kettle is 95°C, and the operating pressure is 75 kPaA.

[0170] The operating temperature of the polycondensation kettle is 130°C, and the operating pressure is 40 kPaA.

[0171] The operating temperature of the pre-depolymerization kettle is 230°C, and the operating pressure is 10 kPaA.

[0172] The operating temperature of the depolymerization kettle is 290°C, and the operating pressure is 5 kPaA.

[0173] Through the above device and method, the utilization rate of glycolic acid is 90%, and the yield of glycolide is 82%.

[0174] Among them, the calculation formula of the utilization rate of glycolic acid is: (molar flow rate of glycolic acid feed - molar flow rate of remaining glycolic acid) / molar flow rate of glycolic acid feed.

[0175] The calculation formula of the yield of glycolide is: molar flow rate of glycolide / (molar flow rate of glycolic acid feed - molar flow rate of remaining glycolic acid).

[0176] The above examples show that the device of the present application can realize large-scale and continuous production, and the yield of the target product is improved through various strengthening means.

[0177] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An apparatus for preparing crude glycolide, characterized in that, The apparatus includes a dehydration unit, a polycondensation unit, and a depolymerization unit connected in sequence; the dehydration unit includes a dehydration kettle, a dehydration kettle heater, a dehydration tower, and a dehydration tower condenser; the polycondensation unit includes a polycondensation kettle and optionally a pre-polycondensation kettle located upstream of the polycondensation kettle; the depolymerization unit includes a pre-depolymerization kettle, a depolymerization kettle, and a crude lactide condenser; wherein... The top of the dehydration kettle is connected to the dehydration tower, and the bottom discharge pipeline of the dehydration kettle is divided into two branches, one of which is connected to the polycondensation unit and the other is connected to the heater inlet of the dehydration kettle. The top of the dehydration tower is connected to the dehydration tower condenser, and the bottom is connected to the upper part of the dehydration kettle; The polycondensation reactor is provided with a gas phase outlet and a liquid phase outlet, and the liquid phase outlet is connected to the pre-depolymerization reactor; The top of the prepolymerization reactor is connected to the crude lactide condenser, and the bottom is connected to the depolymerization reactor; The top of the depolymerization reactor is connected to the crude lactide condenser; The glycolic acid / ester feed line is connected to the dehydration reactor heater or the dehydration reactor; the catalyst feed line is connected to the dehydration reactor heater or the dehydration reactor, or connected to the prepolymerization reactor.

2. The apparatus for preparing crude glycolide according to claim 1, characterized in that, The polycondensation unit includes a pre-polycondensation kettle and a polycondensation kettle, the bottom of the dehydration kettle is connected to the pre-polycondensation kettle, and the bottom of the pre-polycondensation kettle is connected to the inlet of the polycondensation kettle; The dehydration tower and the dehydration tower condenser are one or two sets. When there are two sets, one set is connected to the top of the dehydration kettle, and the other set is set independently. The top of the prepolymerization kettle is connected to the dehydration tower at the top of the dehydration kettle or is connected to a separately set dehydration tower.

3. The apparatus for preparing crude glycolide according to claim 1 or 2, characterized in that, The dehydration kettle heater is one of a shell-and-tube heat exchanger, a plate heat exchanger, and an electric heater. The internal components of the dehydration tower are one or more of the following: sieve plate, float valve, packing, and bubble cap; The dehydration tower condenser is equipped with a gas phase non-condensable gas discharge pipeline and a liquid phase water and / or alcohol discharge pipeline; the water and / or alcohol discharge pipeline is divided into two branches, one of which is connected to the top of the dehydration tower and the other is used as an external discharge pipeline.

4. The apparatus for preparing crude glycolide according to claim 3, characterized in that, The internal components of the dehydration tower are packing material.

5. The apparatus for preparing crude glycolide according to claim 2, characterized in that, The prepolymerization reactor is equipped with a gaseous prepolymerization noncondensable gas discharge pipeline and a liquid prepolymerization product collection pipeline; the prepolymerization reactor is connected to the dehydration tower through the prepolymerization noncondensable gas discharge pipeline and to the prepolymerization reactor through the prepolymerization product collection pipeline. The prepolymerization reactor is a vertical or horizontal stirred tank, with a heater and / or jacket installed inside.

6. The apparatus for preparing crude glycolide according to claim 5, characterized in that, The prepolymerization reactor is a vertical stirred reactor with an internal heater.

7. The apparatus for preparing crude glycolide according to claim 1 or 2, characterized in that, The polycondensation reactor is equipped with a gaseous polycondensation non-condensable gas discharge pipeline and a liquid polycondensation product collection pipeline; the polycondensation reactor is connected to the pre-depolymerization reactor through the polycondensation product collection pipeline. The polycondensation reactor is either a vertical stirred tank reactor or a horizontal stirred tank reactor with a shaft.

8. The apparatus for preparing crude glycolide according to claim 7, characterized in that, The polycondensation reactor includes one of the following: a single-shaft or multi-shaft kneading reactor, a screw reactor, a surface renewal reactor, a tubular reactor, or a tower reactor.

9. The apparatus for preparing crude glycolide according to claim 8, characterized in that, The polycondensation reactor is a horizontal single-shaft or multi-shaft kneading reactor.

10. The apparatus for preparing crude glycolide according to claim 8, characterized in that, The surface renewal reactor is either a disc reactor or a cage reactor.

11. The apparatus for preparing crude glycolide according to claim 1 or 2, characterized in that, The pre-depolymerization reactor is equipped with a gaseous pre-depolymerization non-condensable gas discharge pipeline and a liquid pre-depolymerization product collection pipeline; the pre-depolymerization reactor is connected to the crude glycolide condenser through the pre-depolymerization non-condensable gas discharge pipeline and to the depolymerization reactor through the pre-depolymerization product collection pipeline. The pre-depolymerization reactor is a horizontal or vertical evaporator with a shaft stirrer, and is equipped with a heater and / or jacket inside.

12. The apparatus for preparing crude glycolide according to claim 11, characterized in that, The pre-depolymerization vessel is a thin-film evaporator.

13. The apparatus for preparing crude glycolide according to claim 1 or 2, characterized in that, The depolymerization vessel is a vertical or horizontal batch reactor with shaft stirring, a screw reactor or a kneading reactor. The crude lactide condenser is equipped with a crude lactide product collection pipeline and a depolymerization non-condensable gas mixture discharge pipeline. The depolymerization reactor is equipped with a gaseous depolymerization noncondensable gas discharge pipeline and a solid-liquid phase depolymerization residue discharge pipeline. The depolymerization reactor is connected to the crude glycolide condenser through the depolymerization noncondensable gas discharge pipeline.

14. The apparatus for preparing crude glycolide according to claim 13, characterized in that, The depolymerization vessel is a single-axis or multi-axis kneading reactor.

15. A method for preparing crude glycolide, using the apparatus described in any one of claims 1-14, characterized in that, Includes the following steps: Glycolic acid and / or glycolate raw materials enter the device via a glycolic acid / ester feed line, and a catalyst enters the device via a catalyst feed line. The glycolic acid and / or glycolate raw materials are sequentially subjected to dehydration separation, optional pre-condensation, condensation, pre-depolymerization, and depolymerization to obtain crude glycolide product.

16. The method for preparing crude glycolide according to claim 15, characterized in that, The method includes the following steps: (a) Aqueous glycolic acid and / or glycolate feedstocks enter the dehydration reactor heater inlet or dehydration reactor inlet via glycolic acid / ester feed line. Catalyst enters the dehydration reactor heater inlet, dehydration reactor inlet, or prepolymerization reactor inlet via catalyst feed line. The dehydration reactor is heated under normal or reduced pressure to distill off water and / or alcohol. The distilled components enter the dehydration tower for reflux separation. The top stream of the dehydration tower enters the dehydration tower condenser to obtain liquid water and / or alcohol and dehydrated non-condensable gas. The bottom stream is returned to the dehydration reactor. The bottom material of the dehydration reactor is divided into two streams: one stream enters the dehydration reactor heater, and the other stream is collected and enters the downstream polycondensation unit. (b) The polycondensation unit receives material from the bottom of the dehydration reactor, where dehydration and / or alcohol polycondensation reactions occur to produce glycolic acid oligomers; step (b) is selected from one of the following two forms: (b-1) The polycondensation unit includes a polycondensation kettle, which receives the material from the bottom of the dehydration kettle and, under high temperature and high vacuum operation, undergoes dehydration and / or alcohol polycondensation reaction to obtain polycondensation non-condensable gas and glycolic acid oligomers. (b-2) The polycondensation unit includes a pre-polycondensation kettle and a polycondensation kettle. The pre-polycondensation kettle receives the material from the bottom of the dehydration kettle and undergoes a pre-polycondensation reaction of dehydration and / or alcohol under high temperature and low pressure. The water and / or alcohol produced are discharged through a separate dehydration tower or combined and discharged into the dehydration tower at the top of the dehydration kettle. The polycondensation reactor receives the material from the bottom of the pre-polycondensation reactor and continues the polycondensation reaction under high temperature and high vacuum to obtain polycondensation non-condensable gas and glycolic acid oligomers. (c) The liquid phase at the bottom of the polycondensation reactor enters the pre-depolymerization reactor and undergoes a depolymerization and cyclization reaction of glycolic acid oligomers under high temperature and high vacuum operation to generate a glycolide-containing stream. The glycolide-containing stream enters the crude glycolide condenser through the top of the pre-depolymerization reactor, and the unreacted glycolic acid oligomers in the pre-depolymerization reactor enter the depolymerization reactor from the bottom of the pre-depolymerization reactor. (d) The depolymerization reactor operates at a higher temperature and higher vacuum than the pre-depolymerization reactor, and the depolymerization and cyclization reaction of glycolic acid oligomers continues. The unreacted glycolic acid oligomers in step (c) are converted into glycolide, which is discharged from the top gas phase pipeline of the depolymerization reactor and enters the crude glycolide condenser. At the same time, depolymerization residue by-products containing coke and polymers are produced and discharged from the bottom of the depolymerization reactor. (e) The crude glycolate condenser condenses the streams from the top of the prepolymerization reactor and the top of the depolymerization reactor to obtain a mixture of depolymerization noncondensable gases and crude glycolate product.

17. The method for preparing crude glycolide according to claim 15 or 16, characterized in that, The catalyst is at least one of tin halides, tin organic acid compounds, antimony oxides, antimony halides, antimony organic acid compounds, zinc oxides, zinc halides, and zinc organic acid compounds. The amount of catalyst used is 0.001~5%wt of the amount of glycolic acid / glycolate. The glycolate is methyl glycolate and / or ethyl glycolate; The dehydration tower has a theoretical plate number of 2 to 20, an operating pressure at the top of the tower of 50 to 130 kPaA, and an operating temperature at the top of the tower of 30 to 140℃. The dehydration reactor operates at a temperature of 70–140°C and a pressure of 50–150 kPa. The operating temperature of the prepolymerization reactor is 140–200°C, and the operating pressure is 10–50 kPaA. The polycondensation reactor operates at a temperature of 170–210°C and an operating pressure of 1–20 kPa. The operating temperature of the pre-depolymerization reactor is 180–250°C, and the operating pressure is 100 PaA–10 kPaA. The depolymerization reactor operates at a temperature of 240–300°C and a pressure of 1–20 kPa.

18. The method for preparing crude glycolide according to claim 17, characterized in that, The catalyst is an organic acid compound of tin.

19. The method for preparing crude glycolide according to claim 17, characterized in that, The glycolic acid and / or glycolate raw materials are glycolic acid and / or methyl glycolate.

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