Device and method for preparing crude glycolide

Abstract

The invention belongs to the field of polymer preparation processes, and relates to a device and a method for preparing crude glycolide, which can be industrially implemented, can be continuously operated and can be operated on a large scale. The device comprises a dehydration unit, a polycondensation unit and a depolymerization unit which are sequentially connected, 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 at the upstream of the polycondensation kettle, and the depolymerization unit comprises a pre-depolymerization kettle, a depolymerization kettle and a crude glycolide condenser. The raw material glycollic acid or glycollic acid ester is subjected to dehydration separation, optional pre-polycondensation, polycondensation, pre-depolymerization, depolymerization and the like to finally obtain a crude glycolide product. Meanwhile, a small amount of non-condensable gas, depolymerization residues, water or alcohol and other byproducts are produced. The device provided by the invention can realize industrial large-scale continuous production, and improves the yield of the target product through various strengthening means.

Description

Technical Field

[0001] The invention belongs to the field of polymer preparation technology, and in particular, relates to the preparation of glycolide, and more particularly, to a device and method for preparing crude glycolide. Background Art

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

[0003] There are two methods for synthesizing PGA. One is to directly dehydrate (alcoholize) glycolic acid (ester) to obtain PGA, which is also called the one-step method. The PGA obtained by this method has a low relative molecular weight, and is insufficient in mechanical strength, gas barrier properties, durability, etc., and its application is limited. The other is to first condense glycolic acid (ester) to obtain glycolic acid oligomers, and then depolymerize it to obtain cyclic glycolide, and use glycolide for ring-opening polymerization to obtain a polymer with a relative molecular mass of 10,000 to 200,000. This method is also called the two-step method. At present, the second method is usually used in the industry to prepare PGA with a higher molecular weight. An example of the two-step reaction is as follows:

[0004]

[0005] The continuous production of glycolide is a key link in the PGA process. How to improve the yield of glycolide and achieve continuous production is a technical difficulty.

[0006] CN104163810B discloses a lactide preparation technology, which is to depolymerize polyglycolic acid oligomers, or a mixture of polyglycolic acid oligomers and azeotropic solvents, or a mixture of polyglycolic acid oligomers, azeotropic solvents and cosolvents under the catalyst condition of acetylacetone metal salt to prepare monomer glycolide, and because the temperature is significantly reduced, the yield and purity of glycolide can be significantly improved. The problem with this method is that it does not involve the preparation of polyglycolic acid oligomers, does not involve specific process methods, and does not mention large-scale, continuous process technology solutions. In addition, if a solvent is added, the removal of the third monomer will be involved, which increases the difficulty of the glycolide purification process and the complexity of the process.

[0007] CN109970702B discloses a method for producing high-purity medical glycolide, which uses solid glycolic acid as a raw material, undergoes heating dissolution, vacuum dehydration, temperature curing, high-temperature and high-vacuum cracking, solvent dissolution, and crystallization to obtain high-purity glycolide, with a simple process and controllable operation. However, the method disclosed in the patent is only an intermittent process at the laboratory or small-scale test level, and cannot be mass-produced continuously, and has limited industrial application.

[0008] US5830991, US6891048B2, US691639B2, CN1496359A, CN1501923A and other Japanese Kureha companies mentioned that high-boiling-point organic solvents can be added to polyglycolic acid oligomers to reduce the viscosity of the reaction system and the depolymerization reaction temperature. During depolymerization, glycolide can be evaporated together with the high-boiling-point organic solvent, which solves the pipeline blockage problem very well. It also mentioned that polyglycolic acid oligomers and polar organic solvents are added to the depolymerization system at the same time and sulfate or inorganic acid salt stabilizers in the form of divalent or multivalent cations are introduced at the same time to prevent side reactions. However, this method causes the glycolide crude product to be mixed with a third solvent, which increases the difficulty of the glycolide purification process and the complexity of the process. Summary of the invention

[0009] The purpose of the present invention is to provide an industrially feasible, continuously operated, and large-scale glycolide production process in view of the deficiencies of the prior art.

[0010] In order to achieve the above-mentioned object, the first aspect of the present invention 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] 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.

[0018] The second aspect of the present invention provides a method for preparing crude glycolide, using the above-mentioned device, comprising the following steps:

[0019] The glycolic acid and / or glycolic acid ester 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 glycolic acid ester raw materials are sequentially subjected to dehydration separation, optional pre-polycondensation, polycondensation, pre-depolymerization, and depolymerization to obtain a crude glycolide product.

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

[0021] 1) The present invention realizes the continuous production of crude glycolide by integrating graded dehydration, polycondensation, depolymerization and other reaction and separation sections and pipe equipment, and has industrial scale-up feasibility.

[0022] 2) The present invention forms lactic acid oligomers by one-stage or multi-stage polymerization such as pre-condensation and polycondensation with gradual temperature increase and pressure reduction, thereby achieving effective regulation of the molecular weight and distribution of the oligomers, ensuring the stability of the reaction process, reducing the generation of side reactions, and providing stable raw materials for the pre-depolymerization and depolymerization reaction processes.

[0023] 3) The present invention improves process intensification by setting up a dehydration system, thereby ensuring the dehydration residence time and heat transfer.

[0024] 4) The present invention strengthens the polymerization reaction through the reactor of the polycondensation kettle, ensuring that the polymerization reaction reaches the required degree of polymerization.

[0025] 5) The present invention ensures the cracking depth and improves the reaction efficiency by coupling pre-depolymerization and depolymerization, and coordinating the cyclic depolymerization process and the equipment for strengthening the reaction.

[0026] 6) The present invention ensures that the target product glycolide is generated by maximizing depolymerization, improving the product yield and reducing the generation of residues through the reactor and process settings of one or more stages of polymerization and two stages of depolymerization.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0029] Figure 1This is a flow chart of the first device and method for preparing crude glycolide according to the present invention.

[0030] Figure 2 This is a flow chart of the second device and method for preparing crude glycolide according to the present invention.

[0031] Figure 3 This is a flow chart of the third device and method for preparing crude glycolide according to the present invention.

[0032] Description of reference numerals:

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

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

[0035] The present invention 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,

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

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

[0038] 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;

[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 invention, the precondensation kettle is optionally provided, and the meaning of optional is that it can be provided or not provided. When the precondensation kettle is provided, the precondensation kettle is provided upstream of the polycondensation kettle.

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

[0045] In the present invention, the dehydration tower and the dehydration tower condenser are arranged as 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); when it is two groups, one group is connected to the top of the dehydration kettle and the other group is independently arranged; the top of the precondensation kettle is connected to the dehydration tower at the top of the dehydration kettle or is separately connected to an independently arranged dehydration tower.

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

[0047] The glycolic acid / ester feed pipeline connected to the dehydration unit means being connected to the dehydration kettle heater or the dehydration kettle.

[0048] In the device of the present invention, the catalyst can enter from the dehydration unit or from the depolymerization unit. Accordingly, when entering from the dehydration unit, the catalyst feed pipeline can be connected to the dehydration kettle heater or the dehydration kettle. When entering from the depolymerization unit, the catalyst feed pipeline is connected to the pre-depolymerization kettle. The latter is a more preferred setting.

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

[0050] According to a preferred embodiment of the present invention, 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 invention, preferably, the dehydration tower condenser is provided 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 is connected to the top of the dehydration tower, and the other is used as an external discharge pipeline.

[0052] According to the present invention, preferably, the precondensation kettle is provided with a gas phase precondensation non-condensable gas discharge pipeline and a liquid phase precondensation product extraction pipeline; the precondensation kettle is connected to the dehydration tower through the precondensation non-condensable gas discharge pipeline, and is connected to the condensation kettle through the precondensation product extraction pipeline.

[0053] When the top of the precondensation kettle is connected to a dehydration tower and a dehydration tower condenser which are independently arranged, the top of the dehydration tower is connected to the dehydration tower condenser, and the bottom is connected to the upper part of the precondensation kettle.

[0054] According to a preferred embodiment of the present invention, the precondensation reactor is a vertical or horizontal stirred reactor with a heater and / or a jacket disposed therein, preferably a vertical stirred reactor with a heater disposed therein.

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

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

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

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

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

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

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

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

[0063] The glycolic acid and / or glycolic acid ester 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 glycolic acid ester 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, non-condensable gas, water, or alcohol by-products are obtained at the top of the dehydration tower and the top of the (pre) polycondensation reactor, and depolymerization residue by-products containing impurities such as coke and polymers are obtained at the bottom of the depolymerization reactor.

[0064] As mentioned above, the optional pre-polycondensation means that the pre-polycondensation may or may not be performed, depending on the device settings.

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

[0066] (a) The aqueous glycolic acid and / or glycolic acid ester raw material enters 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 enter the dehydration tower for reflux separation, and the top stream of the dehydration tower enters the dehydration tower condenser to obtain liquid water and / or alcohol and dehydrated 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 produced and enters the downstream polycondensation unit;

[0067] (b) the polycondensation unit receives the material at the bottom of the dehydration kettle, and undergoes dehydration and / or alcohol polycondensation reaction 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 and undergoes a dehydration and / or alcohol polycondensation reaction under high temperature and high vacuum operation 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 comprises a pre-polycondensation kettle and a polycondensation kettle. The pre-polycondensation kettle receives the material at the bottom of the dehydration kettle, and undergoes a dehydration and / or alcohol pre-polycondensation reaction through high temperature and low pressure operation. The generated water and / or alcohol are discharged through a separate dehydration tower or are combined and discharged into a dehydration tower at the top of the dehydration kettle. Specifically, the step of discharging through a separate dehydration tower comprises: the generated water and / or alcohol enters a separate dehydration tower for reflux separation, the top stream of the dehydration tower enters a separate dehydration tower condenser to obtain liquid water and / or alcohol and dehydrated non-condensable gas, and the bottom stream returns to the pre-polycondensation kettle;

[0070] The polycondensation kettle receives the material at the bottom of the pre-polycondensation kettle, and continues the polycondensation reaction through high temperature and high vacuum operation to obtain polycondensation non-condensable gas and glycolic acid oligomers; this form corresponds to the case where a pre-polycondensation kettle is provided;

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

[0072] (d) the depolymerization kettle is operated at a higher temperature and a higher vacuum than the pre-depolymerization kettle, and the depolymerization and cyclization reaction of the glycolic acid oligomers continues to occur, and the unreacted glycolic acid oligomers in step (c) are converted into glycolide, which is discharged from the gas phase pipeline at the top of the depolymerization kettle and then enters the crude glycolide condenser, and at the same time, a depolymerization residue by-product containing coke and polymer is produced and discharged from the bottom of the depolymerization kettle;

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

[0074] According to the method of the present invention, the catalyst can be 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; preferably, tin organic acid compounds.

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

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

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

[0078] According to the method of the present invention, preferably, the operating temperature of the pre-polycondensation reactor is 140-200° C., and the operating pressure is 10-50 kPaA.

[0079] According to the method of the present invention, preferably, the operating temperature of the polycondensation reactor is 170-210° C., and the operating pressure is 1-20 kPaA.

[0080] According to the method of the present invention, preferably, the operating temperature of the pre-depolymerization reactor is 180-250° C., and the operating pressure is 100 PaA-10 kPaA.

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

[0082] According to the method of the present invention, the dehydration kettle mainly removes most of the free water in the glycolic acid / ester raw material, and a trace amount of prepolymerization will also occur in the glycolic acid / ester in the dehydration kettle to generate glycolic acid dimers, trimers, etc., and a trace amount of prepolymer enters the downstream polycondensation unit with the glycolic acid / ester raw material.

[0083] In the pre-condensation kettle, the polycondensation reaction continues to remove a small amount of free water and water and / or alcohol in the glycolic acid / ester. The free water and the water and / or alcohol produced by the polycondensation are discharged through a separate dehydration tower or combined into the dehydration tower at the top of the dehydration kettle for discharge.

[0084] In the polycondensation kettle, a polycondensation reaction is carried out to polymerize glycolic acid or glycolic acid ester (when a pre-polycondensation kettle is not set up), or, the polycondensation reaction is continued to polymerize the remaining glycolic acid or glycolic acid ester (when a pre-polycondensation kettle is set up), and a polymerization reaction to increase the molecular weight is carried out, that is, the molecular weight of the glycolic acid polycondensate is increased to obtain glycolic acid oligomers.

[0085] The pre-depolymerization reactor and the depolymerization reactor are used to carry out the depolymerization reaction of glycolic acid oligomers to obtain crude glycolide and produce coke, polymers and the like as by-products.

[0086] In the present invention, the term "glycolic acid / ester" refers to glycolic acid and / or glycolic acid ester, wherein the glycolic acid ester is glycolic acid alkyl ester, 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 invention is further described below by way of examples.

[0088] Example 1

[0089] Use Figure 1 The device for preparing crude glycolide shown in the figure comprises a dehydration unit, a polycondensation unit and a depolymerization unit connected in sequence; the dehydration unit comprises a dehydration kettle 1, a dehydration kettle heater 3, a dehydration tower 2, and a dehydration tower condenser 4; the polycondensation unit comprises a pre-polycondensation kettle 5 and a polycondensation kettle 9; the depolymerization unit comprises 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 top of the dehydration kettle 1 is connected to the dehydration tower 2, and the bottom discharge pipeline is divided into two branches, one is connected to the pre-condensation kettle 5, and the other is connected to the inlet of the dehydration kettle heater 3;

[0092] The top of the dehydration tower 2 is connected to the dehydration tower condenser 4, and the bottom is connected to the upper part of the dehydration kettle 1; the internal parts of the dehydration tower 2 are fillers;

[0093] The dehydration tower condenser 4 is provided 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 2, and the other is used as an external discharge pipeline;

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

[0095] The polycondensation kettle 9 is a horizontal single-shaft kneading reactor, which is provided with a gas phase polycondensation non-condensable gas discharge pipeline and a liquid phase polycondensation product extraction pipeline; 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 is connected to the depolymerization kettle 12 through the pre-depolymerization product extraction pipeline;

[0097] The depolymerization kettle 12 is a uniaxial kneading reactor, provided with a gas phase depolymerization non-condensable gas discharge pipeline and a solid-liquid phase depolymerization residue discharge pipeline, and 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 depolymerized non-condensable gas mixture discharge pipeline;

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

[0100] The method for preparing crude glycolide using the above-mentioned device comprises:

[0101] (a) A hydrous glycolic acid and / or glycolic acid ester raw material 14 enters the inlet of a dehydration kettle heater 3 through a glycolic acid / ester feed pipeline, and a catalyst 13 enters the inlet of a dehydration kettle heater 3 through a catalyst feed pipeline; the dehydration kettle 1 is heated at normal pressure or reduced pressure to evaporate water and / or alcohol, and the evaporated components enter a dehydration tower 2 for reflux separation, and the top stream of the dehydration tower 2 enters a dehydration tower condenser 4 to obtain liquid water and / or alcohol 16 and dehydrated 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 produced and enters a pre-condensation kettle 5;

[0102] (b) the pre-condensation reactor 5 receives the material at the bottom of the dehydration reactor 1, and undergoes a dehydration and / or alcohol pre-condensation reaction through high temperature and low pressure operation, and the generated water and / or alcohol are combined and enter the dehydration tower 2 at the top of the dehydration reactor 1 and discharged;

[0103] The polycondensation reactor 9 receives the material at the bottom of the pre-polycondensation reactor 5, and continues the polycondensation reaction through high temperature and high vacuum operation 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 pipeline;

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

[0105] (d) the depolymerization reactor 12 is operated at a higher temperature and a higher vacuum than the pre-depolymerization reactor 10, and the depolymerization and cyclization reaction of the glycolic acid oligomers continues to occur, and the unreacted glycolic acid oligomers in step (c) are converted into glycolide, which is discharged from the gas phase pipeline at the top of the depolymerization reactor and then enters the crude glycolide condenser 11, and at the same time, a depolymerization residue 18 containing coke and polymer is produced and discharged from the bottom of the depolymerization reactor 12;

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

[0107] The glycolic acid and / or glycolic acid ester raw material 14 is glycolic acid, which comes from outside the world.

[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 tower has 10 theoretical plates, a top operating pressure of 100 kPaA, and a top operating temperature of 100°C.

[0110] The operating temperature of the dehydration kettle is 120°C and the operating pressure is 110 kPaA.

[0111] The operating temperature of the precondensation reactor is 160° C. and the operating pressure is 50 kPaA.

[0112] The operating temperature of the polycondensation reactor is 190°C and the operating pressure is 20 kPaA.

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

[0114] The operating temperature of the depolymerization reactor is 280° C. and the operating pressure is 1 kPaA.

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

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

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

[0118] Example 2

[0119] use Figure 2 The device for preparing crude glycolide shown in the figure comprises a dehydration unit, a polycondensation unit and a depolymerization unit connected in sequence; the dehydration unit comprises a dehydration kettle 1, a dehydration kettle heater 3, a first dehydration tower 6A, a first dehydration tower condenser 7A, a second dehydration tower 6B, a second dehydration tower condenser 7B, the polycondensation unit comprises a pre-polycondensation kettle 5 and a polycondensation kettle 9, the depolymerization unit comprises a pre-depolymerization kettle 10, a depolymerization kettle 12, and a crude glycolide condenser 11; wherein,

[0120] The dehydration kettle heater 3 is a shell and tube heat exchanger 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 is connected to the precondensation kettle 5, and the other is connected to the inlet of the dehydration kettle heater 3;

[0122] The first dehydration tower 6A is connected to the first dehydration tower condenser 7A at the top and connected to the upper part of the dehydration kettle 1 at the bottom; the internal parts of the first dehydration tower 6A are fillers;

[0123] The first dehydration tower condenser 7A is provided 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 precondensation kettle 5 is a vertical stirring kettle with a precondensation kettle heater 8 disposed inside, and is provided with a gas phase precondensation non-condensable gas discharge pipeline and a liquid phase precondensation product extraction pipeline; the precondensation kettle 5 is connected to the second dehydration tower 6B through the precondensation non-condensable gas discharge pipeline, and is connected to the inlet of the polycondensation kettle 9 through the precondensation product extraction pipeline; the top of the second dehydration tower 6B is connected to the second dehydration tower condenser 7B, and the bottom is connected to the upper part of the precondensation kettle 5; the internal parts of the second dehydration tower 6B are fillers; the second dehydration tower condenser 7B is provided 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 is connected to the top of the second dehydration tower 6B, and the other is used as an external discharge pipeline;

[0125] The polycondensation kettle 9 is a horizontal single-shaft kneading reactor, which is provided with a gas phase polycondensation non-condensable gas discharge pipeline and a liquid phase polycondensation product extraction pipeline; the polycondensation kettle 9 is connected to 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 for gas phase and a pre-depolymerization product extraction pipeline for liquid phase; the pre-depolymerization kettle is connected to the crude glycolide condenser 11 through the pre-depolymerization non-condensable gas discharge pipeline, and is connected to the depolymerization kettle 12 through the pre-depolymerization product extraction pipeline;

[0127] The depolymerization kettle 12 is a uniaxial kneading reactor, provided with a gas phase depolymerization non-condensable gas discharge pipeline and a solid-liquid phase depolymerization residue discharge pipeline, and the depolymerization kettle 12 is connected to 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 depolymerized non-condensable gas mixture discharge pipeline;

[0129] 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 (which can be merged with the polycondensation product extraction line).

[0130] The method for preparing crude glycolide using the above-mentioned device comprises:

[0131] (a) The aqueous glycolic acid and / or glycolic acid ester raw material 14 enters the inlet of the dehydration kettle heater 3 through the glycolic acid / ester feed pipeline, and the catalyst 13 enters the inlet of the precondensation kettle 10 through the catalyst feed pipeline; the dehydration kettle 3 is heated at normal pressure or reduced pressure to evaporate water and / or alcohol, and the evaporated components enter the first dehydration tower 6A for reflux separation, and the top stream of the first dehydration tower 6A enters the first dehydration tower condenser 7A to obtain the first liquid water and / or alcohol 16A and the first dehydrated non-condensable gas 15A, and the bottom stream returns to the dehydration kettle 1; the bottom material of the dehydration kettle 1 is divided into two streams, one stream enters the dehydration kettle heater 3, and the other stream is produced and enters the precondensation kettle 5;

[0132] (b) The precondensation reactor 5 receives the bottom material of the dehydration reactor 1, and undergoes a dehydration and / or alcohol precondensation reaction through high temperature and low pressure operation. The generated water and / or alcohol enters the second dehydration tower 6B for reflux separation. The top stream of the second dehydration tower 6B enters the second dehydration tower condenser 7B to obtain the second liquid water and / or alcohol 16B and the second dehydrated non-condensable gas 15B. The bottom stream returns to the precondensation reactor 5;

[0133] The polycondensation reactor 9 receives the material at the bottom of the pre-polycondensation reactor 5, and continues the polycondensation reaction through high temperature and high vacuum operation 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 pipeline;

[0134] (c) the liquid phase at the bottom of the polycondensation reactor 9 containing glycolic acid oligomers enters the pre-depolymerization reactor 10, and undergoes high temperature and high vacuum operation to cause depolymerization and cyclization of the glycolic acid oligomers to generate a glycolide-containing stream, which enters a crude glycolide condenser 11 through the top of the pre-depolymerization reactor 10, and unreacted glycolic acid oligomers in the pre-depolymerization reactor 10 enter a depolymerization reactor 12 from the bottom of the pre-depolymerization reactor 10;

[0135] (d) the depolymerization reactor 12 is operated at a higher temperature and a higher vacuum than the pre-depolymerization reactor 10, and the depolymerization and cyclization reaction of the glycolic acid oligomers continues to occur, and the unreacted glycolic acid oligomers in step (c) are converted into glycolide, which is discharged from the gas phase pipeline at the top of the depolymerization reactor and then enters the crude glycolide condenser 11, and at the same time, the depolymerization residue 18 containing coke and polymer is produced and discharged from the bottom of the depolymerization reactor 12;

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

[0137] The glycolic acid and / or glycolic acid ester raw material 14 is methyl glycolate, which comes from outside the world.

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

[0139] The theoretical plate number of the first dehydration tower 6A is 5, the tower top operating pressure is 125 kPaA, and the tower top operating temperature is 70°C.

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

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

[0142] The operating temperature of the precondensation reactor is 150° C. and the operating pressure is 50 kPaA.

[0143] The operating temperature of the polycondensation reactor is 180°C and the operating pressure is 5 kPaA.

[0144] The operating temperature of the pre-depolymerization reactor is 200° C. and the operating pressure is 5 kPaA.

[0145] The operating temperature of the depolymerization reactor is 270° C. and the operating pressure is 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 calculation formula for the utilization rate of methyl glycolate is: (methyl glycolate feed molar flow rate-remaining methyl glycolate molar flow rate) / methyl glycolate feed molar flow rate.

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

[0149] Example 3

[0150] Use Figure 3 The device for preparing crude glycolide shown in the figure comprises a dehydration unit, a polycondensation unit and a depolymerization unit connected in sequence; the dehydration unit comprises a dehydration kettle 1, a dehydration kettle heater 3, a dehydration tower 2, and a dehydration tower condenser 4; the polycondensation unit comprises a polycondensation kettle 9; the depolymerization unit comprises 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 top of the dehydration kettle 1 is connected to the dehydration tower 2, and the bottom discharge pipeline is divided into two branches, one is connected to the polycondensation kettle 9, and the other is connected to the inlet of the dehydration kettle heater 3;

[0153] The top of the dehydration tower 2 is connected to the dehydration tower condenser 4, and the bottom is connected to the upper part of the dehydration kettle 1; the internal parts of the dehydration tower 2 are fillers;

[0154] The dehydration tower condenser 4 is provided 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 2, and the other is used as an external discharge pipeline;

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

[0156] 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 is connected to the depolymerization kettle 12 through the pre-depolymerization product extraction pipeline;

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

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

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

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

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

[0162] (b) the polycondensation reactor 9 receives the material at the bottom of the dehydration reactor 1, and undergoes a dehydration and / or alcohol polycondensation reaction through high temperature and high vacuum operation to obtain polycondensation non-condensable gas and glycolic acid oligomers, and the polycondensation non-condensable gas is discharged through a polycondensation non-condensable gas discharge pipeline;

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

[0164] (d) the depolymerization reactor 12 is operated at a higher temperature and a higher vacuum than the pre-depolymerization reactor 10, and the depolymerization and cyclization reaction of the glycolic acid oligomers continues to occur, and the unreacted glycolic acid oligomers in step (c) are converted into glycolide, which is discharged from the gas phase pipeline at the top of the depolymerization reactor and then enters the crude glycolide condenser 11, and at the same time, a depolymerization residue 18 containing coke and polymer is produced and discharged from the bottom of the depolymerization reactor 12;

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

[0166] The glycolic acid and / or glycolic acid ester raw material 14 is glycolic acid, which comes from outside the world.

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

[0168] The dehydration tower has 18 theoretical plates, a top operating pressure of 70 kPaA, and a top operating temperature of 90°C.

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

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

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

[0172] The operating temperature of the depolymerization reactor 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] The calculation formula for the utilization rate of glycolic acid is: (glycolic acid feed molar flow rate-remaining glycolic acid molar flow rate) / glycolic acid feed molar flow rate.

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

[0176] The above embodiments illustrate that the device of the present invention can realize large-scale and continuous production, and improve the yield of the target product through various strengthening means.

[0177] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A device for preparing crude glycolide, characterized in that: 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; wherein, The dehydration kettle heater is connected to the bottom of the dehydration kettle; The top of the dehydration kettle is connected to the dehydration tower, and the bottom is connected to the polycondensation unit; 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 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; The top of the pre-depolymerization kettle is connected to the crude glycolide condenser, and the bottom is connected to the depolymerization kettle; The top of the depolymerization kettle is connected to the crude glycolide condenser; 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.

2. The device for preparing crude glycolide according to claim 1, characterized in that: The polycondensation unit comprises 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 dehydration tower condenser are one group or two groups. When there are two groups, one group is connected to the top of the dehydration kettle and the other group is independently set; the top of the precondensation kettle is connected to the dehydration tower at the top of the dehydration kettle or is separately connected to an independently set dehydration tower.

3. The device for preparing crude glycolide according to claim 1, characterized in that: The bottom discharge pipeline of the dehydration kettle is divided into two branches, one is connected to the polycondensation unit, and the other is connected to the inlet of the dehydration kettle heater; The glycolic acid / ester feed pipeline is connected to the dehydration kettle heater or the dehydration kettle; The catalyst feeding pipeline is connected to the dehydration kettle heater or the dehydration kettle, or is connected to the pre-depolymerization kettle.

4. The device for preparing crude glycolide according to any one of claims 1 to 3, 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 parts of the dehydration tower are one or more of a sieve plate, a float valve, a filler and a bubble cap, preferably a filler; The dehydration tower condenser is provided 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 connected to the top of the dehydration tower, and the other as an external discharge pipeline.

5. The device for preparing crude glycolide according to claim 2, characterized in that: The pre-condensation reactor is provided with a gas phase pre-condensation non-condensable gas discharge pipeline and a liquid phase pre-condensation product extraction pipeline; the pre-condensation reactor is connected to the dehydration tower through the pre-condensation non-condensable gas discharge pipeline, and is connected to the polycondensation reactor through the pre-condensation product extraction pipeline; The precondensation reactor is a vertical or horizontal stirring reactor with a heater and / or a jacket disposed therein, preferably a vertical stirring reactor with a heater disposed therein.

6. The device for preparing crude glycolide according to any one of claims 1 to 3, characterized in that: The polycondensation kettle is provided with a gas phase polycondensation non-condensable gas discharge pipeline and a liquid phase polycondensation product extraction pipeline; the polycondensation kettle is connected to the pre-depolymerization kettle via the polycondensation product extraction pipeline; The polycondensation reactor is a vertical stirred tank reactor or a horizontal shaft stirred reactor, preferably a single-shaft or multi-shaft kneading reactor, a screw reactor, a surface renewal reactor, a tubular reactor, a tower reactor, more preferably a horizontal single-shaft or multi-shaft kneading reactor; The surface renewal reactor is preferably a disc reactor or a squirrel cage reactor.

7. The device for preparing crude glycolide according to any one of claims 1 to 3, characterized in that: The pre-depolymerization kettle is provided with a gas phase pre-depolymerization non-condensable gas discharge pipeline and a liquid phase pre-depolymerization product extraction pipeline; the pre-depolymerization kettle is connected to the crude glycolide condenser through the pre-depolymerization non-condensable gas discharge pipeline, and is connected to the depolymerization kettle through the pre-depolymerization product extraction pipeline; The pre-depolymerization kettle is a horizontal or vertical evaporator with shaft stirring, and is provided with a heater and / or a jacket inside, preferably a thin film evaporator.

8. The device for preparing crude glycolide according to any one of claims 1 to 3, characterized in that: The depolymerization reactor is a vertical or horizontal reactor with shaft stirring, a screw reactor or a kneading reactor, preferably a single-shaft or multi-shaft kneading reactor; The crude glycolide condenser is provided with a crude glycolide product extraction pipeline and a depolymerized non-condensable gas mixture discharge pipeline; The depolymerization kettle is provided with a gas phase depolymerization non-condensable gas discharge pipeline and a solid-liquid phase depolymerization residue discharge pipeline, and the depolymerization kettle is connected to the crude glycolide condenser through the depolymerization non-condensable gas discharge pipeline.

9. A method for preparing crude glycolide, using the device according to any one of claims 1 to 8, characterized in that: The following steps are involved: The glycolic acid and / or glycolic acid ester 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 glycolic acid ester raw materials are sequentially subjected to dehydration separation, optional pre-polycondensation, polycondensation, pre-depolymerization, and depolymerization to obtain a crude glycolide product.

10. The method for preparing crude glycolide according to claim 9, characterized in that: The method comprises the following steps: (a) The aqueous glycolic acid and / or glycolic acid ester raw material enters 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 enter the dehydration tower for reflux separation, and the top stream of the dehydration tower enters the dehydration tower condenser to obtain liquid water and / or alcohol and dehydrated 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 produced and enters the downstream polycondensation unit; (b) the polycondensation unit receives the material at the bottom of the dehydration kettle, and undergoes dehydration and / or alcohol polycondensation reaction to produce glycolic acid oligomers; the step (b) is selected from one of the following two forms: (b-1) The polycondensation unit comprises a polycondensation kettle, which receives the material at the bottom of the dehydration kettle and undergoes a dehydration and / or alcohol polycondensation reaction under high temperature and high vacuum operation to obtain polycondensation non-condensable gas and glycolic acid oligomers; (b-2) The polycondensation unit comprises a pre-polycondensation kettle and a polycondensation kettle. The pre-polycondensation kettle receives the material at the bottom of the dehydration kettle and operates at high temperature and low pressure to cause dehydration and / or alcohol pre-polycondensation reaction. The generated water and / or alcohol are discharged through a separate dehydration tower or are combined and discharged into the dehydration tower at the top of the dehydration kettle; The polycondensation reactor receives the material at the bottom of the pre-polycondensation reactor, and continues the polycondensation reaction through high temperature and high vacuum operation to obtain polycondensation non-condensable gas and glycolic acid oligomers; (c) the liquid phase at the bottom of the polycondensation kettle enters the pre-depolymerization kettle, and after high temperature and high vacuum operation, the depolymerization and cyclization reaction of glycolic acid oligomers occurs to generate a glycolide-containing stream, which enters the crude glycolide condenser through the top of the pre-depolymerization kettle, and the unreacted glycolic acid oligomers in the pre-depolymerization kettle enter the depolymerization kettle from the bottom of the pre-depolymerization kettle; (d) the depolymerization kettle is operated at a higher temperature and a higher vacuum than the pre-depolymerization kettle, and the depolymerization and cyclization reaction of the glycolic acid oligomers continues to occur, and the unreacted glycolic acid oligomers in step (c) are converted into glycolide, which is discharged from the gas phase pipeline at the top of the depolymerization kettle and then enters the crude glycolide condenser, and at the same time, a depolymerization residue by-product containing coke and polymer is produced and discharged from the bottom of the depolymerization kettle; (e) The crude glycolide condenser condenses the streams from the top of the pre-depolymerization reactor and the top of the depolymerization reactor to obtain a depolymerized non-condensable gas mixture and a crude glycolide product.

11. The method for preparing crude glycolide according to claim 9 or 10, 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; preferably tin organic acid compounds; The amount of catalyst used is 0.001 to 5%wt of the amount of glycolic acid / glycolate; The glycolic acid ester is 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; The dehydration tower has a theoretical plate number of 2 to 20, a tower top operating pressure of 50 to 130 kPaA, and a tower top operating temperature of 30 to 140°C; The operating temperature of the dehydration kettle is 70-140°C, and the operating pressure is 50-150kPaA; The operating temperature of the precondensation reactor is 140-200°C, and the operating pressure is 10-50kPaA; The operating temperature of the polycondensation reactor is 170-210°C, and the operating pressure is 1-20 kPaA; The operating temperature of the pre-depolymerization reactor is 180-250°C, and the operating pressure is 100PaA-10kPaA; The operating temperature of the depolymerization reactor is 240-300° C., and the operating pressure is 1-20 kPaA.

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