Preparation method and system of high-molecular-weight polyethylene glycol oxalate

Abstract

The invention relates to a preparation method and system of high-molecular-weight polyethylene glycol oxalate, and the preparation method comprises the following steps: adding oxalic acid diester, ethylene glycol and a first catalyst, and carrying out transesterification to obtain an ester; adding a second catalyst, and carrying out a pre-polycondensation reaction on the esterified product to obtain a glycol oxalate oligomer; polymerizing the ethylene glycol oxalate oligomer, and carrying out final polymerization reaction to obtain polyethylene glycol oxalate; the molar ratio of the oxalic acid diester to the ethylene glycol is (1.05-1.3): 1. Compared with the prior art, by controlling excessive oxalic acid diester in the raw material ratio, namely controlling the molar ratio of oxalic acid diester to ethylene glycol to be greater than 1, the reaction rate of ethylene glycol is improved, self-polycondensation of ethylene glycol is prevented, further increase of molecular weight is facilitated, and meanwhile, the thermal performance of the product is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material synthesis, in particular to a preparation method and system for high molecular weight polyethylene oxalate. Background Art

[0002] Polyethylene oxalate (PEO), the simplest aliphatic dipolymer, is inexpensive and bio-based. Furthermore, PEO's melting point is above 160°C, significantly higher than commercially available biodegradable polymers such as polybutylene succinate (PBS) and polybutylene adipate / terephthalate (PBAT), making it suitable for use at higher temperatures. However, the PEO synthesis process is plagued by the raw materials' tendency to decompose or sublimate, preventing efficient reactions and making it difficult to produce high-molecular-weight PEO. This has significantly limited its development.

[0003] Patent CN115785406B strictly controls the molar ratio of oxalic acid diester to ethylene glycol to 1:1. Through transesterification and pre-polycondensation, crude oligomeric poly(ethylene oxalate) is obtained. This is then washed and dried with a solvent, and finally subjected to final polycondensation to obtain low-color, high-melting-point PEO with a number-average molecular weight of 70 kDa. The preparation process requires the use of organic solvents to wash the intermediate product, which increases costs and may leave chemical residues in the reaction system.

[0004] Patent CN115785416B increases the molar ratio of ethylene glycol to oxalic acid diester, and adds diethylene glycol to the reaction by dehydrating excess ethylene glycol to prepare poly(ethylene glycol oxalate-diethylene glycol ester). The heating rate is slow during the esterification process. At the same time, the introduction of diethylene glycol increases the flexibility of the molecular chain, lowers the melting point of the product, and affects its heat resistance to a certain extent.

[0005] Therefore, there is an urgent need for a method and system for preparing high molecular weight polyethylene oxalate. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method and system for preparing high molecular weight polyethylene oxalate. By controlling the excess of oxalic acid diester in the raw material ratio, that is, controlling the molar ratio of oxalic acid diester / ethylene glycol to be greater than 1, the reaction rate of ethylene glycol is improved, the self-condensation of ethylene glycol is prevented, the molecular weight is further increased, and the thermal performance of the product is improved.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The first object of the present invention is to provide a method for preparing high molecular weight polyethylene glycol oxalate, the method comprising the following steps:

[0009] S1, transesterification stage: under a protective gas atmosphere, adding oxalic acid diester, ethylene glycol and the first catalyst, stirring and dissolving at the dissolution temperature, then heating to the esterification temperature to carry out transesterification reaction to obtain an esterified product;

[0010] S2, pre-polycondensation stage: adding a second catalyst, increasing the temperature and decreasing the pressure, and performing a pre-polycondensation reaction on the esterified product obtained in step S1 under low vacuum conditions to obtain ethylene glycol oxalate oligomers;

[0011] S3, final polymerization stage: further increasing the temperature and decreasing the pressure, and subjecting the oxalate glycol oligomer obtained in step S2 to final polymerization under high vacuum conditions to obtain polyethylene glycol oxalate.

[0012] Furthermore, in step S1, the protective gas is one or more of an inert gas such as argon, and nitrogen.

[0013] Furthermore, in step S1, the molar ratio of the oxalic acid diester to the ethylene glycol is 1.05 to 1.3: 1. More preferably, the molar ratio of the oxalic acid diester to the ethylene glycol is 1.1 to 1.2:1.

[0014] Furthermore, in step S1, the protective gas is nitrogen (N2), helium (He), argon (Ar), etc., and the purge time is 5 to 20 minutes.

[0015] Furthermore, in step S1, the oxalic acid diester is dimethyl oxalate and / or diethyl oxalate. Further preferably, the oxalic acid diester is dimethyl oxalate (DMO).

[0016] Furthermore, in step S1, the first catalyst is one or more of an organic peroxide, a metal oxide, a metal acetate, a metal chlorate, and a metal glycolate. More preferably, the first catalyst is one or more of a metal acetate and a metal chlorate.

[0017] Furthermore, in step S1, the content of the first catalyst is 0.1‰ to 1‰ of the molar amount of ethylene glycol. More preferably, the content of the first catalyst is 0.3‰ to 0.6‰ of the molar amount of ethylene glycol.

[0018] Furthermore, in step S1, the dissolution temperature is 70-95°C. More preferably, the dissolution temperature is 90°C.

[0019] Furthermore, in step S1, the dissolution time is 5 to 60 minutes. More preferably, the dissolution time is 20 to 30 minutes.

[0020] Furthermore, in step S1, the esterification temperature is 100-180°C. More preferably, the esterification temperature is 120-160°C.

[0021] Furthermore, in step S1, the transesterification reaction time is 1 to 4 hours. More preferably, the transesterification reaction time is 2 to 3 hours.

[0022] Furthermore, in step S1, the heating rate to the esterification temperature is 2-10°C / min. More preferably, the heating rate to the esterification temperature is 5-8°C / min.

[0023] Furthermore, in step S2, the second catalyst is one or more of an organic peroxide, a metal oxide, a metal acetate, a metal chlorate, and a metal glycolate. Further preferably, the second catalyst is one or more of a metal oxide, a metal acetate, and a metal chlorate.

[0024] Furthermore, in step S2, the content of the second catalyst is 0.1‰ to 1‰ of the molar amount of ethylene glycol. More preferably, the content of the second catalyst is 0.3‰ to 0.6‰ of the molar amount of ethylene glycol.

[0025] Furthermore, in step S2, the temperature of the pre-polycondensation reaction is 160-180° C. More preferably, the temperature of the pre-polycondensation reaction is 180° C.

[0026] Furthermore, in step S2, the pressure of the pre-polycondensation reaction is 5 kPa to 80 kPa absolute pressure. Further preferably, the pressure of the pre-polycondensation reaction is 5 kPa to 20 kPa absolute pressure.

[0027] Furthermore, in step S2, the pre-polycondensation reaction time is 0.5 to 2 hours.

[0028] Furthermore, in step S2, the pressure reduction rate is 1 kPa / min to 10 kPa / min. More preferably, the pressure reduction rate is 5 kPa / min to 10 kPa / min.

[0029] Furthermore, in step S3, the temperature of the final polymerization reaction is 180-195° C. More preferably, the temperature of the final polymerization reaction is 190° C.

[0030] Furthermore, in step S3, the pressure of the final polymerization reaction is an absolute pressure of 50 to 200 Pa. More preferably, the pressure of the final polymerization reaction is an absolute pressure of 50 to 80 Pa.

[0031] Furthermore, in step S3, the final polymerization reaction time is 5 to 8 hours.

[0032] Furthermore, in step S3, the pressure reduction rate is 0.1 kPa / min to 1 kPa / min. More preferably, the pressure reduction rate is 0.3 kPa / min to 0.7 kPa / min.

[0033] A second object of the present invention is to provide a system for preparing high molecular weight polyethylene oxalate, for implementing the method for preparing high molecular weight polyethylene oxalate, the system comprising:

[0034] An esterification reactor, which is used to carry out an ester exchange reaction between oxalic acid diester and ethylene glycol to obtain an esterified product; a first gas processing unit, which is connected to the esterification reactor and is used to separate and treat the steam generated during the esterification process; a polymerization reactor, which is connected to the esterification reactor and is used to carry out a pre-polycondensation reaction and a final polymerization reaction on the esterified product to obtain polyethylene oxalate; a second gas processing unit, which is connected to the polymerization reactor and is used to separate and treat by-products produced during the pre-polycondensation reaction and / or final polymerization reaction; and a vacuum device, which is connected to the second gas processing unit.

[0035] Furthermore, the first gas processing unit includes a first condenser reflux and a first small molecule alcohol collection tank; the first condenser reflux is connected to the esterification reaction kettle, and the first condenser reflux is provided with a gas phase inlet, a condensate outlet and a gas phase outlet, and the gas phase inlet and the condensate outlet are both connected to the esterification reaction kettle, for condensing the oxalic acid diester vapor and refluxing it into the esterification reaction kettle; the first small molecule alcohol collection tank is connected to the gas phase outlet of the first condenser reflux to collect methanol and / or ethanol.

[0036] Further, according to one embodiment of the present invention, the second gas processing unit includes a by-product buffer tank, a second condenser reflux, a dehumidification tank, an oxalic acid diester collection tank, a filter tank and an ethylene glycol collection tank; the by-product buffer tank is connected to the polymerization reactor; the second condenser reflux is connected to the by-product buffer tank for separating the oxalic acid diester, the second condenser reflux is provided with a gas phase inlet, a condensate outlet and a gas phase outlet, the gas phase inlet and the condensate outlet of the second condenser reflux are both connected to the by-product buffer tank, the gas phase outlet of the second condenser reflux is connected to the dehumidification tank, the oxalic acid diester collection tank and the vacuum device in sequence; the filter tank is connected to the bottom outlet of the by-product buffer tank, and the filter tank is equipped with a cooler for solidifying the oligomers in the by-products; the ethylene glycol collection tank is connected to the bottom outlet of the filter tank for collecting the separated ethylene glycol.

[0037] Furthermore, in the above embodiment, the second gas processing unit further includes a second small molecule alcohol collection tank, which is arranged between the oxalic acid diester collection tank and the vacuum device to capture methanol and / or ethanol in the by-products.

[0038] Furthermore, in the above embodiment, the temperature of the first condenser reflux is set to 50-80°C; in the pre-polycondensation reaction stage, the temperature of the second condenser reflux is set to 125-135°C, and in the final polycondensation reaction stage, the temperature of the second condenser reflux is set to 65-80°C; the temperature of the filter tank is set to 40-65°C.

[0039] Furthermore, according to an embodiment of the present invention, the polymerization reactor comprises a prepolymerization reactor and a final polymerization reactor connected in sequence, and the prepolymerization reactor is connected to the esterification reactor;

[0040] The by-product buffer tank includes a first by-product buffer tank, a second by-product buffer tank and a third by-product buffer tank connected in sequence, a first valve is provided between the bottom outlet of the first by-product buffer tank and the second by-product buffer tank, a second valve is provided between the bottom outlet of the second by-product buffer tank and the third by-product buffer tank, the first by-product buffer tank is connected to the pre-polymerization reactor, and the third by-product buffer tank is connected to the final polymerization reactor;

[0041] The second condenser reflux device and the filter tank are both connected to the third by-product buffer tank;

[0042] The second gas processing unit also includes a second small molecule alcohol collection tank, which is connected to the first by-product buffer tank and is used to collect methanol and / or ethanol in the by-products; the vacuum device includes a first vacuum device connected to the oxalic acid diester collection tank, and also includes a second vacuum device, which is connected to the second small molecule alcohol collection tank.

[0043] Furthermore, in the above embodiment, the first by-product buffer tank, the second by-product buffer tank, and the third by-product buffer tank are arranged in sequence from top to bottom with a height difference, and the by-products in the tanks are easily transferred due to gravity.

[0044] Furthermore, in the above embodiment, the temperature of the first condenser reflux device is set to 50-80°C; the temperature of the second condenser reflux device is set to 65-80°C; the temperature of the filter tank is set to 40-65°C; the temperature of the first by-product buffer tank is maintained at 55-120°C; the temperature of the second by-product buffer tank is maintained at 55-120°C.

[0045] Furthermore, the second small molecule alcohol collection tank may be a cold trap.

[0046] Furthermore, the prepared polyethylene glycol oxalate has a weight average molecular weight of more than 90 kDa, a melting point of more than 180°C, and a thermal decomposition temperature of 5％ Above 230°C, it has higher molecular weight and better heat resistance.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1) The present invention provides a method for preparing high-molecular-weight polyethylene oxalate, wherein the amount of oxalic acid diester (dimethyl oxalate and / or diethyl oxalate) in the raw material ratio is controlled to be excessive, that is, the molar ratio of oxalic acid diester / ethylene glycol is controlled to be greater than 1, which is beneficial to increasing the reaction rate of ethylene glycol, preventing ethylene glycol self-condensation, and facilitating further growth of the molecular weight and improvement of the thermal properties of the product;

[0049] 2) The present invention provides a system for preparing high-molecular-weight polyethylene oxalate. The esterification reactor is externally connected to a first gas processing unit. The oxalic acid diester vapor generated during the esterification process is condensed and refluxed into the esterification reactor, thereby increasing the reaction rate of the oxalic acid diester and reducing the loss of reactants. Thus, the esterification process can be heated rapidly, reducing the esterification cycle.

[0050] 3) The present invention provides a system for preparing high molecular weight polyethylene oxalate, which is provided with a second gas treatment unit. Excess oxalate diester is extracted during the polycondensation process and can be further collected by the second gas treatment unit, thereby improving the utilization rate of the raw materials. Ethylene glycol and oligomers can also be collected separately and further purified for reuse.

[0051] 4) The present invention provides a method for preparing high-molecular-weight polyethylene oxalate. The catalyst is added step by step, and a better catalyst can be selected for the ester exchange reaction and the polycondensation reaction. This prevents the catalyst content from being too high after the catalyst is added at the beginning of the reaction, avoids the occurrence of uncontrollable reactions caused by high catalytic activity, and also avoids the deactivation of the catalyst during the long-term esterification reaction, thereby effectively improving the efficiency of the polycondensation reaction.

[0052] 5) The present invention provides a method and system for preparing high molecular weight polyethylene oxalate, wherein the prepared polyethylene oxalate has a weight average molecular weight of more than 90 kDa, a melting point of more than 180°C, and a thermal decomposition temperature of 0. 5％ Above 230°C, it has higher molecular weight and better heat resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic structural diagram of a preparation system (double kettle) of high molecular weight polyethylene oxalate of the present invention.

[0054] Figure 2It is a schematic structural diagram of a preparation system (three kettles) of high molecular weight polyethylene oxalate of the present invention.

[0055] Figure 3 This is the thermogravimetric curve of the high molecular weight polyethylene oxalate (PEO) sample prepared in Example 2 of the present invention.

[0056] Figure 4 3 is the DSC curve of the high molecular weight polyethylene oxalate (PEO) sample prepared in Example 2 of the present invention.

[0057] in:

[0058] 1. Esterification reactor, 2. Polymerization reactor, 2-1. Prepolymerization reactor, 2-2. Final polymerization reactor, 3. First condenser reflux reactor, 4. First small molecule alcohol collection tank, 5. By-product buffer tank, 5-1. First by-product buffer tank, 5-2. Second by-product buffer tank, 5-3. Third by-product buffer tank, 6. Second condenser reflux reactor, 7. Dehumidification tank, 8. Oxalic acid diester collection tank, 9. Vacuum device, 9-1. First vacuum device, 9-2. Second vacuum device, 10. Filter tank, 11. Cooler, 12. Ethylene glycol collection tank, 13. Second small molecule alcohol collection tank, 14. First valve, 15. Second valve. DETAILED DESCRIPTION

[0059] The present invention is described in detail below with reference to specific embodiments. These embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Any features, such as component models, material names, connection structures, and control methods, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0060] It should be noted that, in the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0061] The present invention provides a method for preparing high molecular weight polyethylene glycol oxalate, which comprises the following steps:

[0062] S1, transesterification stage: under a protective gas atmosphere, adding oxalic acid diester, ethylene glycol (EG) and a first catalyst, stirring and dissolving at a certain temperature, then heating to an esterification temperature to carry out an esterification reaction to obtain an esterified product, wherein the molar ratio of oxalic acid diester:ethylene glycol is 1.05-1.3:1;

[0063] S2, pre-polycondensation stage: adding a second catalyst to the esterified product obtained in step S1, raising the temperature and lowering the pressure, and pre-polycondensing the esterified product under low vacuum conditions to obtain ethylene glycol oxalate oligomers;

[0064] S3, final polymerization stage: further increase the temperature and reduce the pressure, and polymerize the oxalate glycol oligomer obtained in step S2 under high vacuum conditions to perform final polymerization to obtain polyethylene glycol oxalate.

[0065] In the existing polyethylene oxalate preparation process, in order to ensure that the oxalic acid diester (dimethyl oxalate and / or diethyl oxalate) reacts fully, an equal ratio or an excess alcohol method is adopted. However, the boiling point of the oxalic acid diester is lower than that of ethylene glycol and it is easy to evaporate. In particular, the easy sublimation of dimethyl oxalate causes an increase in the alcohol ratio, and the excess ethylene glycol self-polymerizes to produce diethylene glycol, which is more difficult to remove, inhibiting further growth of the molecular weight and reducing the thermal properties of the product, such as the melting point. In the present invention, by controlling the excess oxalic acid diester in the raw material ratio, that is, controlling the molar ratio of oxalic acid diester / ethylene glycol to be greater than 1, the reaction rate of ethylene glycol is improved, ethylene glycol self-condensation is prevented, and further growth of the molecular weight and improvement of the thermal properties of the product are promoted.

[0066] The present invention also provides a preparation system for implementing the above preparation method, such as Figure 1 As shown, the preparation system includes:

[0067] An esterification reaction kettle 1 is used to carry out an ester exchange reaction between oxalic acid diester and ethylene glycol to obtain an esterified product;

[0068] a first gas processing unit, which is connected to the esterification reactor 1 and is used to separate and process the steam generated during the esterification process;

[0069] A polymerization reactor 2, which is connected to the esterification reactor 1 and is used to carry out a pre-polycondensation reaction and a final polymerization reaction on the esterified product to obtain polyethylene oxalate;

[0070] A second gas processing unit, which is connected to the polymerization reactor 2 and is used to separate and process by-products in the pre-polycondensation reaction and / or final polymerization reaction;

[0071] A vacuum device 9 is connected to the second gas processing unit.

[0072] Furthermore, the first gas processing unit includes a first condenser reflux 3 and a first small molecule alcohol collection tank 4; the first condenser reflux 3 is connected to the esterification reaction kettle 1, and the first condenser reflux 3 is provided with a gas phase inlet, a condensate outlet and a gas phase outlet, and the gas phase inlet and the condensate outlet are both connected to the esterification reaction kettle 1, for condensing the oxalic acid diester vapor and refluxing it into the esterification reaction kettle 1; the first small molecule alcohol collection tank 4 is connected to the gas phase outlet of the first condenser reflux 3 to collect methanol and / or ethanol.

[0073] The second gas processing unit includes a by-product buffer tank 5 , a second condenser reflux device 6 , a dehumidification tank 7 , an oxalic acid diester collection tank 8 , a filter tank 10 and an ethylene glycol collection tank 12 .

[0074] Specifically, the by-product buffer tank 5 is connected to the polymerization reactor 2; the second condenser reflux device 6 is connected to the by-product buffer tank 5 for separating oxalic acid diester, and the second condenser reflux device 6 is provided with a gas phase inlet, a condensate outlet and a gas phase outlet, the gas phase inlet and the condensate outlet are both connected to the by-product buffer tank 5, and the gas phase outlet of the second condenser reflux device 6 is connected to the dehumidification tank 7, the oxalic acid diester collection tank 8 and the vacuum device 9 in sequence; the filter tank 10 is connected to the bottom outlet of the by-product buffer tank 5, and the filter tank 10 is equipped with a cooler 11 for solidifying the oligomers in the by-products; the ethylene glycol collection tank 12 is connected to the bottom outlet of the filter tank 10 for collecting the separated ethylene glycol.

[0075] The second gas processing unit further includes a second small molecule alcohol collection tank 13 , which is disposed between the oxalic acid diester collection tank 8 and the vacuum device 9 and is used to capture a small amount of methanol and / or ethanol in the by-products to prevent them from entering the vacuum device 9 .

[0076] Furthermore, the temperature of the first condenser reflux 3 is set to 50-80°C; in the pre-polycondensation reaction stage, the temperature of the second condenser reflux 6 is set to 125-135°C, and in the final polycondensation reaction stage, the temperature of the second condenser reflux 6 is set to 65-80°C; the temperature of the filter tank 10 is set to 40-65°C; the second small molecule alcohol collection tank 13 can be a cold trap with a temperature of -40°C to -20°C.

[0077] During the preparation process, when the esterification reaction kettle 1 is heated from the dissolution temperature to the esterification temperature, the boiling point of the oxalic acid diester is close to the esterification temperature (dimethyl oxalate: 163.5°C, diethyl oxalate: boiling point 185.4°C), and the oxalic acid diester is easy to sublime. By arranging a first condenser reflux device 3 at the gas phase outlet of the esterification reaction kettle 1 and setting the temperature of the first condenser reflux device 3 to 50-80°C, the oxalic acid diester vapor can be condensed and refluxed into the esterification reaction kettle 1, while the by-products of the ester exchange reaction, methanol and / or ethanol, enter the first small molecule alcohol collection tank 4 connected to the gas phase outlet of the first condenser reflux device 3.

[0078] The esterified product obtained in the esterification reactor 1 enters the polymerization reactor 2 through the liquid phase outlet of the esterification reactor 1, and a pre-polycondensation reaction and a final polymerization reaction are carried out in the polymerization reactor 2 to obtain polyethylene oxalate. The raw monomers (including oxalic acid diester and ethylene glycol, especially excess oxalic acid diester) and oligomers are extracted during the pre-polycondensation process and the final polymerization process, and the oxalic acid diester and ethylene glycol are separated by the second gas treatment unit and further collected.

[0079] The specific process is as follows: the gas extracted from the polymerization reactor first enters the by-product buffer tank 5, and then enters the second condenser reflux device 6 through the gas phase outlet of the by-product buffer tank 5. Since the boiling point of the substance is negatively correlated with the vacuum degree, the higher the vacuum degree, the lower the boiling point of the substance. In the pre-polycondensation reaction stage, the temperature of the second condenser reflux device 6 is set to 125-135°C. In the final polymerization reaction stage, the temperature of the second condenser reflux device 6 is set to 65-80°C, so that the oxalic acid diester in the gas is discharged through the gas phase outlet of the second condenser reflux device 6, dehumidified in the dehumidification tank 7, and then enters the oxalic acid diester collection tank 8. A second small molecule alcohol collection tank 13 is provided after the collection tank 8 to capture a small amount of methanol and / or ethanol to prevent methanol and / or ethanol from entering the vacuum device 9; the remaining by-products (including ethylene glycol, oligomers, etc.) are condensed through the second condenser reflux device 6 and returned to the by-product buffer tank 5, and then enter the filter tank 10; the filter tank 10 is externally or internally connected to a cooler 11, and the temperature of the filter tank 10 is set to 40-65°C. The oligomers solidify in the filter tank 10, and ethylene glycol enters the ethylene glycol collection tank 12 from the bottom outlet of the filter tank 10. The solid oligomers are retained at the bottom of the filter tank 10 and discharged regularly.

[0080] The present invention also provides a preparation system for implementing the above preparation method, such as Figure 2 As shown, the preparation system and Figure 1 The preparation system is different in that:

[0081] The polymerization reactor 2 comprises a prepolymerization reactor 2-1 and a final polymerization reactor 2-2 connected in sequence, wherein the prepolymerization reactor 2-1 is connected to the esterification reactor 1;

[0082] The by-product buffer tank 5 includes a first by-product buffer tank 5-1, a second by-product buffer tank 5-2 and a third by-product buffer tank 5-3 connected in sequence, a first valve 14 is provided between the bottom outlet of the first by-product buffer tank 5-1 and the second by-product buffer tank 5-2, a second valve 15 is provided between the bottom outlet of the second by-product buffer tank 5-2 and the third by-product buffer tank 5-3, the first by-product buffer tank 5-1 is connected to the pre-polymerization reactor 2-1, and the third by-product buffer tank 5-3 is connected to the final polymerization reactor 2-2;

[0083] The second condenser reflux device 6 and the filter tank 10 are both connected to the third by-product buffer tank 5-1;

[0084] The second small molecule alcohol collection tank 13 is connected to the first by-product buffer tank 5-1;

[0085] The vacuum device 9 includes a first vacuum device 9 - 1 connected to the oxalic acid diester collecting tank 8 , and also includes a second vacuum device 9 - 2 , and the second vacuum device 9 - 2 is connected to the second small molecule alcohol collecting tank 13 .

[0086] When the first valve 14 is opened and the second valve 15 is closed, the second by-product buffer tank 5-2 is a pre-polymerization by-product tank; when the second valve 15 is opened and the first valve 14 is closed, the second by-product buffer tank 5-2 is a final polymerization by-product tank, and at the same time, the by-products in the second by-product buffer tank 5-2 flow to the third by-product buffer tank 5-3.

[0087] As a preferred solution, the first by-product buffer tank 5-1, the second by-product buffer tank 5-2, and the third by-product buffer tank 5-3 are arranged in sequence from top to bottom with a height difference, and the by-products in the tanks are easily transferred due to gravity.

[0088] The temperature of the first condenser reflux 3 is set to 50-80°C; the temperature of the second condenser reflux 6 is set to 65-80°C; the temperature of the filter tank 10 is set to 40-65°C; the second small molecule alcohol collection tank 13 can be a cold trap with a temperature of -40°C to -20°C. Furthermore, the temperature of the first by-product buffer tank 5-1 is maintained at 55-120°C; the temperature of the second by-product buffer tank 5-2 is maintained at 55-120°C.

[0089] During the preparation process, when the esterification reaction kettle 1 is heated from the dissolution temperature to the esterification temperature, the boiling point of the oxalic acid diester is close to the esterification temperature (dimethyl oxalate: 163.5°C, diethyl oxalate: boiling point 185.4°C), and the oxalic acid diester is easy to sublime. By arranging a first condenser reflux device 3 at the gas phase outlet of the esterification reaction kettle 1 and setting the temperature of the first condenser reflux device 3 to 50-80°C, the oxalic acid diester vapor can be condensed and refluxed into the esterification reaction kettle 1, while the by-products of the ester exchange reaction, methanol and / or ethanol, enter the first small molecule alcohol collection tank 4 connected to the gas phase outlet of the first condenser reflux device 3.

[0090] The esterified product obtained in the esterification reactor 1 enters the prepolymerization reactor 2-1 through the liquid phase outlet of the esterification reactor 1, where a pre-polycondensation reaction occurs to produce ethylene glycol oxalate oligomers. The ethylene glycol oxalate oligomers then enter the final polymerization reactor 2-2 through the liquid phase outlet of the prepolymerization reactor 2-1 for a final polymerization reaction to produce polyethylene oxalate. The raw monomers (including oxalic acid diester and ethylene glycol, especially excess oxalic acid diester) and oligomers in the prepolymerization reactor 2-1 and final polymerization reactor 2-2 are extracted during the pre-polycondensation and final polymerization processes. The oxalic acid diester and ethylene glycol are separated by a second gas treatment unit and further collected.

[0091] The specific process is as follows: in the continuous production process, first the first valve 14 is closed, the second valve 15 is closed, and the gas extracted from the prepolymerization reactor 2-1 enters the first by-product buffer tank 5-1, and the temperature of the first by-product buffer tank 5-1 is maintained at 55-120°C. A small amount of methanol and / or ethanol present in the by-product enters the second small molecule alcohol collection tank 13 through the gas phase outlet of the first by-product buffer tank 5-1, and the remaining by-products are stored in the first by-product buffer tank 5-1 in liquid form; when the amount of by-products in the first by-product buffer tank 5-1 accumulates to a certain amount, the first valve 14 is opened to allow the by-products in the first by-product buffer tank 5-1 to flow into the second by-product buffer tank 5-2. Similarly, the temperature of the second by-product buffer tank 5-2 is maintained at 55-120°C; then the first valve 14 is closed, and the second valve 15 is opened to allow the by-products in the second by-product buffer tank 5-2 to flow into the third by-product buffer tank 5-3.

[0092] The third by-product buffer tank 5-3, in addition to the by-products flowing into the second by-product buffer tank 5-2, also includes the gas extracted from the final polymerization reactor 2-2. After entering the third by-product buffer tank 5-3, the gas enters the second condenser reflux device 6 through the gas phase outlet of the third by-product buffer tank 5-3. The temperature of the second condenser reflux device 6 is set to 65-80°C so that the oxalic acid diester in the gas is discharged through the gas phase outlet of the second condenser reflux device 6, and enters the oxalic acid diester collection tank 8 after dehumidification by the dehumidification tank 7; the remaining by-products (including ethylene glycol, oligomers, etc.) are condensed through the second condenser reflux device 6 and returned to the third by-product buffer tank 5-3, and then enter the filter tank 10; the filter tank 10 is externally or internally connected to a cooler 11, and the temperature of the filter tank 10 is set to 40-65°C. The oligomers solidify in the filter tank 10, and ethylene glycol enters the ethylene glycol collection tank 12 from the bottom outlet of the filter tank 10. The solid oligomers are trapped at the bottom of the filter tank 10 and are discharged regularly.

[0093] In practical applications, the time consumption of each stage can be determined at the beginning of production to determine the feeding time of the next batch of production. It can be recorded how many batches of production have passed before the material in the first by-product buffer tank 5-1 reaches the volume setting value (for example, 70%), and then the first valve 14 is opened to allow the by-product in the first by-product buffer tank 5-1 to flow into the second by-product buffer tank 5-2. According to the time required for the by-product in the first by-product buffer tank 5-1 to flow into the second by-product buffer tank 5-2, the first valve 14 is closed after a certain period of time, and then the second valve 15 is opened; according to the time required for the by-product in the second by-product buffer tank 5-2 to flow into the third by-product buffer tank 5-3, the second valve 15 is closed after a certain period of time.

[0094] It can be understood that the connected components in the above-mentioned preparation system are connected by pipelines. Conventional heating can be configured in the pipeline connecting the reactor and the by-product buffer tank according to actual needs so that the material transported therein is in a flowing state. A melt pump of suitable model / power can be selected to ensure the transportation of the melt material. In addition, the reactor can be equipped with a feeding unit and a stirring unit of suitable form can be selected according to actual needs. A feeding unit can also be configured on the pipeline connecting the reactor, for example, a second catalyst feeding unit can be configured on the pipeline connecting the esterification reactor 1 and the polymerization reactor 2.

[0095] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0096] Determination of weight average molecular weight:

[0097] The sample was dissolved in hexafluoroisopropanol (HFIP) containing 5 mmol / L sodium trifluoroacetate at 60°C to prepare a 0.05-0.3 wt% (mass fraction) solution. After cooling to room temperature, the solution was filtered through a 0.4 μm pore size polytetrafluoroethylene filter. 20 μL of the filtered solution was added to the gel permeation chromatography (GPC) injector to determine the sample's molecular weight. Five molecular weight standards of methyl methacrylate with varying molecular weights were used for molecular weight calibration.

[0098] Determination of melting point:

[0099] The thermal properties of polyesters were studied using a differential scanning calorimeter (DSC). Under a nitrogen atmosphere, 5-10 mg of a sample was heated to 210°C at a rate of 10°C / min and held at that temperature for 10 minutes. The sample was then cooled to 0°C at a rate of 10°C / min and held at that temperature for 10 minutes. Finally, the sample was heated to 210°C at a rate of 10°C / min, and the Tm of the sample was recorded.

[0100] Thermal decomposition temperature determination:

[0101] Use a thermogravimetric analyzer to perform TGA test: In N2 atmosphere, heat 5-10 mg of sample to 600℃ at a heating rate of 10℃ / min, and record the T 5％ .

[0102] The yield of polyethylene oxalate is calculated as follows:

[0103] Yield of polyethylene oxalate = m (actual polymer) / m (theoretical polymer)

[0104] m(theoretical polymer) = m(feed) - m(theoretical amount of methanol and / or ethanol) - m(excess amount of oxalic acid diester)

[0105] Wherein, m (feed) is the total mass of the oxalic acid diester and ethylene glycol added. When the oxalic acid diester: ethylene glycol is added at a molar ratio of 1.05 to 1.3:1, when the added oxalic acid diester is dimethyl oxalate, m (theoretical amount of methanol and / or ethanol) is m (theoretical amount of methanol), m (theoretical amount of methanol) = n * 64.08, n is the molar amount of ethylene glycol; when the added oxalic acid diester is diethyl oxalate, m (theoretical amount of methanol and / or ethanol) is m(theoretical amount of ethanol), m(theoretical amount of ethanol)=n*92.14, where n is the molar amount of ethylene glycol. When the added oxalic acid diester is a mixture of dimethyl oxalate and diethyl oxalate, dimethyl oxalate is theoretically more active than diethyl oxalate and more easily reacts with ethylene glycol. Therefore, m(theoretical amount of methanol) generated by the reaction of all dimethyl oxalate and ethylene glycol is first calculated, and then m(theoretical amount of ethanol) generated by the reaction of the remaining ethylene glycol and diethyl oxalate is calculated.

[0106] Example 1

[0107] The preparation method of high molecular weight polyethylene glycol oxalate provided in this embodiment is as follows Figure 1 The system is implemented as shown, wherein the temperature of the first condenser reflux 3 is set to 60°C, the temperature of the second condenser reflux 6 is set to 130°C in the pre-polycondensation reaction stage, and the temperature of the second condenser reflux 6 is set to 70°C in the final polycondensation reaction stage. A molecular sieve adsorption layer is provided in the dehumidification tank 7, the temperature of the filter tank 10 is set to 40°C, and the temperature of the second small molecule alcohol collection tank 13 is set to -30°C. The preparation method comprises the following steps:

[0108] S1, transesterification stage: After N2 was introduced into the stirred esterification reactor 1 for 10 minutes, 1.1 mol of dimethyl oxalate (DMO), 1 mol of ethylene glycol (EG), and 0.5‰ (molar amount of ethylene glycol) of catalyst zinc acetate were added, the temperature was raised from room temperature to 90°C, heated and stirred for 30 minutes to mix the materials evenly, and then the temperature was raised to 150°C at a rate of 5°C / min to carry out transesterification reaction, and the reaction time was 2 hours;

[0109] S2, pre-polycondensation stage: After the transesterification reaction is completed, the material is transferred to the preheated polymerization reactor 2 while it is hot, 0.5‰ (molar amount of ethylene glycol) of catalyst antimony acetate is added, and vacuum is evacuated at a rate of 5 kPa / min to reduce the pressure, and the temperature in the polymerization reactor 2 is gradually increased and controlled at 160°C and an absolute pressure of 50 kPa, and the reaction is continued for 2 hours;

[0110] S3, final polymerization stage: the polymerization reactor 2 is further heated and depressurized, and vacuumed at a rate of 0.5 kPa / min to reduce the pressure. The temperature is controlled at 180° C. and an absolute pressure of 50 Pa, and the reaction is carried out for 6 hours to obtain polyethylene oxalate.

[0111] After the reaction was completed, the first small molecule alcohol collection tank 4 collected 51.32 g of methanol, the oxalic acid diester collection tank 8 collected 9.63 g of DMO, and the ethylene glycol collection tank 12 collected 0.29 g of ethylene glycol to obtain 61.75 g of polyethylene oxalate.

[0112] The yield of polyethylene oxalate was calculated to be 53.2%.

[0113] The obtained polyethylene glycol oxalate has a weight average molecular weight of 90.6 kDa, a melting point of 183.3 °C, and a thermal decomposition temperature T 5％ It is 235.8℃.

[0114] Example 2

[0115] The preparation system of this embodiment is the same as that of Example 1, and the preparation method includes the following steps:

[0116] S1, transesterification stage: After N2 was introduced into the stirred esterification reactor 1 for 10 minutes, 1.2 mol of dimethyl oxalate (DMO), 1 mol of ethylene glycol (EG), and 0.5‰ (molar amount of ethylene glycol) of catalyst zinc acetate were added, the temperature was raised from room temperature to 90°C, heated and stirred for 30 minutes to mix the materials evenly, and then the temperature was raised to 160°C at a rate of 5°C / min to carry out transesterification reaction, and the reaction time was 2 hours;

[0117] S2, pre-polycondensation stage: After the transesterification reaction is completed, the material is transferred to the preheated polymerization reactor 2 while it is hot, 0.5‰ (molar amount of ethylene glycol) of catalyst antimony acetate is added, and vacuum is applied at a rate of 8 kPa / min to reduce the pressure, and the temperature in the polymerization reactor 2 is gradually increased and controlled at 170°C and an absolute pressure of 10 kPa, and the reaction is continued for 1 hour;

[0118] S3, final polymerization stage: the polymerization reactor 2 is further heated and depressurized, and vacuumed at a rate of 0.5 kPa / min to reduce the pressure. The temperature is controlled at 190° C. and an absolute pressure of 100 Pa, and the reaction is carried out for 5 hours to obtain polyethylene oxalate.

[0119] After the reaction was completed, the first small molecule alcohol collection tank 4 collected 56.27 g of methanol, the oxalic acid diester collection tank 8 collected 10.14 g of DMO, and the ethylene glycol collection tank 12 collected 0.26 g of ethylene glycol to obtain 62.45 g of polyethylene oxalate.

[0120] The yield of polyethylene oxalate was calculated to be 53.8%.

[0121] The weight average molecular weight of the obtained polyethylene glycol oxalate is 122.7 kDa. Figure 3 、 4 As shown, the melting point is 183.4℃ and the thermal decomposition temperature is T 5％ It is 231.6℃.

[0122] Example 3

[0123] The preparation system of this embodiment is substantially the same as that of Example 1, except that the temperature of the second condenser reflux device 6 is set at 160° C. The preparation method comprises the following steps:

[0124] S1, transesterification stage: After N2 was introduced into the stirred esterification reactor 1 for 10 minutes, 1.15 mol of dimethyl oxalate (DMO), 1 mol of ethylene glycol (EG), and 0.5‰ (molar amount of ethylene glycol) of catalyst zinc acetate were added, the temperature was raised from room temperature to 90°C, heated and stirred for 30 minutes to mix the materials evenly, and then the temperature was raised to 120°C at a rate of 3°C / min to carry out transesterification reaction, and the reaction time was 3 hours;

[0125] S2, pre-polycondensation stage: After the transesterification reaction is completed, the material is transferred to the preheated polymerization reactor 2 while it is hot, 0.5‰ (molar amount of ethylene glycol) of catalyst antimony acetate is added, and vacuum is evacuated at a rate of 5 kPa / min to reduce the pressure, and the temperature in the polymerization reactor 2 is gradually increased and controlled at 160°C and an absolute pressure of 80 kPa, and the reaction is continued for 2 hours;

[0126] S3, final polymerization stage: the polymerization reactor 2 is further heated and depressurized, and vacuumed at a rate of 0.6 kPa / min to reduce the pressure. The temperature is controlled at 180° C. and an absolute pressure of 100 Pa, and the reaction is carried out for 7 hours to obtain polyethylene oxalate.

[0127] After the reaction, the first small molecule alcohol collection tank 4 collected 57.44 g of methanol, the oxalic acid diester collection tank 8 collected 10.37 g of DMO, and the ethylene glycol collection tank 12 collected 0.22 g of ethylene glycol to obtain 64.54 g of polyethylene oxalate.

[0128] The yield of polyethylene oxalate was calculated to be 55.6%.

[0129] The obtained polyethylene glycol oxalate has a weight average molecular weight of 134.4 kDa, a melting point of 184.2 °C, and a thermal decomposition temperature T 5％ It is 233.8℃.

[0130] Comparative Example 1

[0131] The preparation process is basically the same as that in Example 1, that is, the preparation method and system are basically the same as those in Example 1, except that 1 mol of DMO is added, that is, the molar ratio of DMO to ethylene glycol is 1:1;

[0132] The first small molecule alcohol collection tank 4 collected 46.92 g of methanol, the oxalic acid diester collection tank 8 collected 7.28 g of DMO, and the ethylene glycol collection tank 12 collected 0.27 g of ethylene glycol to obtain 60.13 g of polyethylene oxalate.

[0133] The yield of polyethylene oxalate was calculated to be 51.8%.

[0134] The obtained polyethylene glycol oxalate has a weight average molecular weight of 82.4 kDa, a melting point of 180.4 °C, and a thermal decomposition temperature of T 5％ It is 227.9℃.

[0135] Comparative Example 2

[0136] The preparation process is basically the same as that of Example 1, that is, the preparation method and apparatus are basically the same as those of Example 1, except that the first condenser reflux device 3 is omitted, and the gas generated during the transesterification process directly enters the first small molecule alcohol collection tank 4;

[0137] The first small molecule alcohol collection tank 4 collected 38.62 g of methanol (actually a mixture of dimethyl oxalate and methanol), the oxalic acid diester collection tank 8 collected 11.47 g of DMO, and the ethylene glycol collection tank 12 collected 0.20 g of ethylene glycol to obtain 53.74 g of polyethylene oxalate.

[0138] The yield of polyethylene oxalate was calculated to be 46.3%.

[0139] The obtained polyethylene glycol oxalate has a weight average molecular weight of 54.4 kDa, a melting point of 178.5 °C, and a thermal decomposition temperature T 5％ It is 225.0℃.

[0140] Comparative Example 3

[0141] The preparation process is basically the same as that of Example 1, that is, the preparation method and system are basically the same as those of Example 1, except that no catalyst is added in the polycondensation stage, that is, 1‰ zinc acetate is added at the beginning of the reaction (in step S1), and no catalyst is added in step S2;

[0142] The first small molecule alcohol collecting tank 4 collected 53.58 g of methanol, the oxalic acid diester collecting tank 8 collected 10.83 g of DMO, and the ethylene glycol collecting tank 12 collected 0.22 g of ethylene glycol to obtain 60.82 g of polyethylene oxalate.

[0143] The yield of polyethylene oxalate was calculated to be 52.4%.

[0144] The obtained polyethylene glycol oxalate has a weight average molecular weight of 76.9 kDa, a melting point of 181.2 °C, and a thermal decomposition temperature T 5％ It is 228.1℃.

[0145] Comparative Example 4

[0146] The preparation process is basically the same as that in Example 1, that is, the preparation method and system are basically the same as those in Example 1, except that 1.5 mol of DMO is added, that is, the molar ratio of DMO to ethylene glycol is 1.5:1;

[0147] The first small molecule alcohol collecting tank 4 collected 57.35 g of methanol, the oxalic acid diester collecting tank 8 collected 56.16 g of DMO, and the ethylene glycol collecting tank 12 collected 0.18 g of ethylene glycol to obtain 58.50 g of polyethylene oxalate.

[0148] The yield of polyethylene oxalate was calculated to be 50.4%.

[0149] The obtained polyethylene glycol oxalate has a weight average molecular weight of 85.2 kDa, a melting point of 180.6 °C, and a thermal decomposition temperature T 5％ It is 226.5℃.

[0150] The above description of the embodiments is intended to facilitate understanding and application of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing high molecular weight polyethylene oxalate, characterized in that: The preparation method comprises the following steps: S1. Under a protective gas atmosphere, adding oxalic acid diester, ethylene glycol and a first catalyst, stirring and dissolving at a dissolution temperature, and then heating to an esterification temperature to carry out an ester exchange reaction to obtain an esterified product; S2, adding a second catalyst, increasing the temperature and decreasing the pressure, and performing a pre-polycondensation reaction on the esterified product obtained in step S1 under low vacuum conditions to obtain ethylene glycol oxalate oligomers; S3, further increasing the temperature and decreasing the pressure, and subjecting the oxalate oligomer obtained in step S2 to a final polymerization reaction under high vacuum conditions to obtain polyethylene oxalate; In step S1, the molar ratio of the oxalic acid diester to the ethylene glycol is 1.05-1.3:

1.

2. The method for preparing high molecular weight polyethylene oxalate according to claim 1, wherein: Step S1 has one or more of the following features: The molar ratio of the oxalic acid diester to the ethylene glycol is 1.1 to 1.2:1; The oxalic acid diester is dimethyl oxalate and / or diethyl oxalate; The first catalyst is one or more of an organic peroxide, a metal oxide, a metal acetate, a metal chlorate, and a metal glycolate; The content of the first catalyst is 0.1‰ to 1‰ of the molar amount of ethylene glycol; The dissolution temperature is 70-95°C; The esterification temperature is 100-180°C; The transesterification reaction time is 1 to 4 hours; The heating rate to the esterification temperature is 2 to 10°C / min.

3. The method for preparing high molecular weight polyethylene oxalate according to claim 1, wherein: Step S2 has one or more of the following features: The second catalyst is one or more of metal oxides, metal acetates, and metal chlorates; The content of the second catalyst is 0.1‰ to 1‰ of the molar amount of ethylene glycol; The temperature of the pre-polycondensation reaction is 160-180°C; The pressure of the pre-polycondensation reaction is an absolute pressure of 5kPa to 80kPa; The pre-polycondensation reaction time is 0.5 to 2 hours; The pressure reduction rate is 1kPa / min to 10kPa / min.

4. The method for preparing high molecular weight polyethylene oxalate according to claim 1, wherein: Step S3 has one or more of the following features: The temperature of the final polymerization reaction is 180-195°C; The pressure of the final polymerization reaction is 50 to 200 Pa absolute pressure; The final polymerization reaction time is 5 to 8 hours; The pressure reduction rate is 0.1kPa / min~1kPa / min.

5. A system for preparing high molecular weight polyethylene oxalate, for implementing the method for preparing high molecular weight polyethylene oxalate according to any one of claims 1 to 4, characterized in that: The preparation system comprises: An esterification reaction kettle (1), wherein the esterification reaction kettle (1) is used to carry out an ester exchange reaction between oxalic acid diester and ethylene glycol to obtain an esterified product; a first gas processing unit connected to the esterification reaction kettle (1) and used for separating and processing steam generated during the esterification process; A polymerization reactor (2) is connected to the esterification reactor (1) and is used to carry out a pre-polycondensation reaction and a final polymerization reaction on the esterified product to obtain polyethylene oxalate; a second gas processing unit connected to the polymerization reactor (2) and used for separating and processing by-products produced during the pre-polycondensation reaction and / or final polymerization reaction; A vacuum device (9), wherein the vacuum device (9) is connected to the second gas processing unit.

6. The preparation system according to claim 5, characterized in that: The first gas processing unit comprises a first condenser reflux device (3) and a first small molecule alcohol collection tank (4); The first condenser reflux device (3) is connected to the esterification reaction kettle (1), and the first condenser reflux device (3) is provided with a gas phase inlet, a condensate outlet and a gas phase outlet, wherein the gas phase inlet and the condensate outlet are both connected to the esterification reaction kettle (1) and are used to condense the oxalic acid diester vapor and reflux it into the esterification reaction kettle (1); The first small molecule alcohol collection tank (4) is connected to the gas phase outlet of the first condenser reflux device (3) to collect methanol and / or ethanol.

7. The preparation system according to claim 6, characterized in that: The second gas processing unit comprises a by-product buffer tank (5), a second condenser reflux device (6), a dehumidification tank (7), an oxalic acid diester collection tank (8), a filter tank (10) and an ethylene glycol collection tank (12); The by-product buffer tank (5) is connected to the polymerization reactor (2); The second condenser reflux device (6) is connected to the by-product buffer tank (5) and is used to separate the oxalic acid diester. The second condenser reflux device (6) is provided with a gas phase inlet, a condensate outlet and a gas phase outlet. The gas phase inlet and the condensate outlet of the second condenser reflux device (6) are both connected to the by-product buffer tank (5). The gas phase outlet of the second condenser reflux device (6) is connected to a dehumidifying tank (7), an oxalic acid diester collecting tank (8) and a vacuum device (9) in sequence. The filter tank (10) is connected to the bottom outlet of the by-product buffer tank (5), and the filter tank (10) is equipped with a cooler (11) for solidifying oligomers in the by-products; The ethylene glycol collection tank (12) is connected to the bottom outlet of the filter tank (10) and is used to collect the separated ethylene glycol.

8. The preparation system according to claim 7, characterized in that: The second gas processing unit further comprises a second small molecule alcohol collection tank (13), which is arranged between the oxalic acid diester collection tank (8) and the vacuum device (9) and is used to capture methanol and / or ethanol in the by-products; The temperature of the first condenser reflux device (3) is set to 50-80°C; In the pre-polycondensation reaction stage, the temperature of the second condenser reflux (6) is set to 125-135° C., and in the final polycondensation reaction stage, the temperature of the second condenser reflux (6) is set to 65-80° C.; The temperature of the filter tank (10) is set to 40-65°C.

9. The preparation system according to claim 7, characterized in that: The polymerization reactor (2) comprises a prepolymerization reactor (2-1) and a final polymerization reactor (2-2) which are connected in sequence, and the prepolymerization reactor (2-1) is connected to the esterification reactor (1); The by-product buffer tank (5) comprises a first by-product buffer tank (5-1), a second by-product buffer tank (5-2) and a third by-product buffer tank (5-3) which are connected in sequence, a first valve (14) is provided between the bottom outlet of the first by-product buffer tank (5-1) and the second by-product buffer tank (5-2), a second valve (15) is provided between the bottom outlet of the second by-product buffer tank (5-2) and the third by-product buffer tank (5-3), the first by-product buffer tank (5-1) is connected to the prepolymerization reactor (2-1), and the third by-product buffer tank (5-3) is connected to the final polymerization reactor (2-2); The second condenser reflux device (6) and the filter tank (10) are both connected to the third by-product buffer tank (5-1); The second gas processing unit further comprises a second small molecule alcohol collection tank (13), which is connected to the first by-product buffer tank (5-1) and is used to collect methanol and / or ethanol in the by-products; The vacuum device (9) includes a first vacuum device (9-1) connected to the oxalic acid diester collection tank (8), and also includes a second vacuum device (9-2), and the second vacuum device (9-2) is connected to the second small molecule alcohol collection tank (13).

10. The preparation system according to claim 9, characterized in that: The temperature of the first condenser reflux device (3) is set to 50-80°C; The temperature of the second condenser reflux (6) is set to 65-80°C; The temperature of the filter tank (10) is set to 40-65°C; The temperature of the first by-product buffer tank (5-1) is maintained at 55-120°C; The temperature of the second by-product buffer tank (5-2) is maintained at 55-120°C.

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