Preparation method of high-purity ethylene oxalate

Abstract

The invention discloses a preparation method of high-purity ethylene oxalate. The preparation method comprises the steps that a mixed reaction system containing reaction monomers, a catalyst and a heat stabilizer is subjected to a condensation polymerization reaction, the ethylene glycol oxalate polymer is prepared, the reaction monomers comprise ethylene glycol and dimethyl oxalate, and the catalyst comprises an MXene material; and carrying out high-vacuum depolymerization reaction on the ethylene oxalate polymer, carrying out reduced-pressure sublimation to obtain an ethylene oxalate crude product, and purifying to obtain high-purity ethylene oxalate. According to the preparation method of the high-purity ethylene oxalate, the efficient catalyst MXene is used, the ethylene oxalate with the yield larger than 80 wt% and the purity larger than 99 wt% can be obtained by regulating and controlling the introduction amount of the MXene, the reaction temperature, the reaction pressure and the variety of the purification solvent, and the good industrialization prospect is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of oxalate preparation, and in particular relates to a method for preparing high-purity vinyl oxalate. Background Art

[0002] Polyester plastics provide various conveniences for people's lives, but they are not easily degraded in nature, which seriously damages the ecological environment. The lack of microorganisms and environmental temperature that can degrade discarded degradable plastics in the ocean and water makes it difficult to degrade discarded plastics in the aqueous phase. However, literature reports that about 9.5 million tons of plastic waste still enter the ocean every year, so there is an urgent need to develop polyesters that can be degraded in seawater environments. The unique structure of the oxalic acid carbonyl group in the polyoxalate structural unit gives it excellent non-enzymatic hydrolysis ability, and it is a type of material that can be rapidly degraded in seawater environments. In addition, the easy hydrolysis of oxalic acid-based polyesters can give it the ability to be used in a closed loop under mild conditions.

[0003] Vinyl oxalate is a cyclic compound that exhibits high chemical reactivity and can be used in the preparation of oxalic acid-based polyesters. Its molecular structure is shown below:

[0004]

[0005] The main processes for producing vinyl oxalate include: the esterification reaction route of ethylene glycol and oxalic acid catalyzed by concentrated sulfuric acid, the reaction route of oxalyl chloride and ethylene glycol, and the reaction route of oxalate (dimethyl oxalate or diethyl oxalate) and ethylene glycol. The yield of the reaction route of oxalyl chloride and ethylene glycol is 71-87% (Chem. Pharm. Bull. 1993, 41 (2) 408-410), and the yield of other routes has not been reported (Journal of Polymer Science: Polymer Chemistry Edition 1979, 17: 2701-2706; Macromolecules 2023, 56, 3149-3159). However, oxalyl chloride is highly toxic and expensive, which seriously limits the wide application of vinyl oxalate.

[0006] The raw materials of the oxalate (dimethyl oxalate or diethyl oxalate) and ethylene glycol reaction route are cheap, which can significantly reduce the price of the product. In addition, dimethyl oxalate is an intermediate product of the coal-to-ethylene glycol route. Therefore, the most preferred route is to prepare vinyl oxalate from dimethyl oxalate and ethylene glycol as raw materials. In this route, dimethyl oxalate and ethylene glycol are first subjected to an ester exchange reaction and further polycondensed to obtain a hydroxyl-terminated prepolymer, which is then depolymerized under high temperature conditions. However, ethylene glycol oxalate oligomers are easily thermally degraded into ethylene glycol formate compounds at temperatures above 170°C, which not only reduces the yield but also requires the product to be purified. Therefore, the development of efficient polycondensation catalysts and depolymerization catalysts, suitable polymerization and depolymerization routes, and effective purification processes are key technical problems that need to be solved in order to obtain high yields and prepare high-purity vinyl oxalate in this route, and are also the direction that industry researchers have been working towards for a long time. Summary of the invention

[0007] The main purpose of the present invention is to provide a method for preparing high-purity vinyl oxalate to solve the key technical problem that it is difficult to obtain high-yield and high-purity vinyl oxalate through the reaction route of dimethyl oxalate and ethylene glycol, thereby overcoming the shortcomings of the prior art.

[0008] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0009] The embodiment of the present invention provides a method for preparing high-purity vinyl oxalate, which comprises:

[0010] At a first reaction temperature and a first reaction pressure, a mixed reaction system comprising a reaction monomer, a catalyst and a heat stabilizer is subjected to a polycondensation reaction to obtain an ethylene glycol oxalate polymer, wherein the reaction monomer comprises ethylene glycol and dimethyl oxalate, and the catalyst comprises a MXene material;

[0011] At a second reaction temperature and a second reaction pressure, the ethylene glycol oxalate polymer is subjected to a high vacuum depolymerization reaction, and is subjected to reduced pressure sublimation to obtain a crude vinyl oxalate product;

[0012] The crude vinyl oxalate product is purified to obtain high-purity vinyl oxalate.

[0013] In some embodiments, the first reaction temperature is 130-170° C., the first reaction pressure is 50-100000 Pa, the polycondensation reaction time is 5.0-13.5 h, and the second reaction time is 1.5-3.0 h.

[0014] In some embodiments, the second reaction temperature is 200-240° C., and the second reaction pressure is 5-100 Pa.

[0015] Compared with the prior art, the beneficial effects of the present invention include:

[0016] The method for preparing high-purity vinyl oxalate provided by the present invention can prepare vinyl oxalate with a yield of more than 80% and a purity of more than 99wt% by regulating the amount of MXene catalyst introduced, the reaction temperature, the reaction pressure and the type of purification solvent, which is beneficial to the industrial production and application of vinyl oxalate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is a diagram explaining the mechanism of the Ti-based MXene catalyst used in the present invention;

[0019] Figure 2 It is a physical photo and a hue diagram of the product prepared in Example 1 of the present invention;

[0020] Figure 3 It is a schematic diagram of the H NMR spectrum and structural composition of the product prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] In view of the defects of the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. Since the ethylene glycol oxalate oligomers prepared by the polycondensation reaction of dimethyl oxalate and ethylene glycol are easily thermally degraded into ethylene glycol formate compounds at temperatures above 170°C, the yield of vinyl oxalate is reduced and further purification is required. Therefore, the present invention creatively introduces a highly active and environmentally friendly Ti-based MXene catalyst into the polycondensation reaction system of dimethyl oxalate and ethylene glycol, optimizes the reaction route, and uses a low-toxic solvent to purify the crude product, thereby achieving the goal of preparing high-yield, high-purity vinyl oxalate.

[0022] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific implementation methods or embodiments and are not intended to limit the present invention.

[0024] As one aspect of the technical solution of the present invention, it involves the use of MXene materials in catalytic depolymerization of ethylene glycol oxalate oligomers to prepare vinyl oxalate, wherein the vinyl oxalate is formed by the polymerization reaction of ethylene glycol and dimethyl oxalate and the depolymerization reaction of ethylene glycol oxalate oligomers catalyzed by the MXene material as a catalyst.

[0025] As another aspect of the technical solution of the present invention, a method for preparing high-purity vinyl oxalate is mainly: first, dimethyl oxalate is converted into ethylene glycol oxalate polymer, then depolymerized under high temperature conditions and sublimated under reduced pressure to obtain a crude product of vinyl oxalate, and finally the crude product is purified using a low-toxic solvent.

[0026] In some embodiments, the method for preparing high-purity vinyl oxalate specifically comprises:

[0027] At a first reaction temperature and a first reaction pressure, a mixed reaction system comprising at least a reaction monomer and a catalyst is subjected to a polycondensation reaction to obtain an ethylene glycol oxalate polymer, wherein the reaction monomer comprises ethylene glycol and dimethyl oxalate, and the catalyst comprises a MXene material;

[0028] At a second reaction temperature and a second reaction pressure, the ethylene glycol oxalate polymer is subjected to a high vacuum depolymerization reaction, and the depolymerization product is simultaneously sublimated under high vacuum to obtain a crude vinyl oxalate product;

[0029] And, the crude vinyl oxalate product is purified to obtain high-purity vinyl oxalate.

[0030] In some embodiments, the mixed reaction system further includes a thermal stabilizer.

[0031] In some embodiments, the ethylene glycol oxalate polymer has a structure as shown in formula (I):

[0032]

[0033] Among them, n=4~20.

[0034] In some embodiments, the preparation method comprises: dissolving the crude vinyl oxalate product with a low-toxic solvent and purifying it by recrystallization to obtain a high-purity vinyl oxalate product.

[0035] In some more specific preferred embodiments, the method for preparing high-purity vinyl oxalate comprises the following steps:

[0036] (1) Adding a certain ratio of reaction monomers, catalysts and thermal stabilizers into a reactor, and carrying out a polycondensation reaction at a set first reaction temperature and a first reaction pressure to obtain a polymer (ethylene glycol oxalate polymer) having a certain molecular weight as shown in formula (I), wherein n=4 to 20.

[0037]

[0038] (2) performing high vacuum depolymerization on the polymer at a set second reaction temperature and a set second reaction pressure to obtain a crude vinyl oxalate product.

[0039] (3) Purifying the crude product using a low-toxic aprotic solvent, including dissolving, concentrating, filtering and drying.

[0040] In some embodiments, in step (1), the reaction monomers are ethylene glycol and dimethyl oxalate.

[0041] In some embodiments, in step (1), the first reaction temperature is 130-170° C., and the first reaction pressure is 50-100000 Pa.

[0042] Furthermore, in step (1), the polycondensation reaction time is 5.0 to 13.5 hours.

[0043] In some embodiments, in step (1), the molar ratio of ethylene glycol to dimethyl oxalate is 1.1 to 3.0:1, preferably, the molar ratio is 1.1 to 2.2:1.

[0044] In some embodiments, in step (1), the catalyst may include Ti 3 C 2 T x 、Ti 4 C 3 T x 、Ti 2 CT x A mixture of any one or more of the above, preferably Ti 4 C 3 T x .

[0045] Furthermore, the catalyst Ti 3 C 2 T x For example, its mechanism of action is Figure 1As shown in the figure, in the few-layer Ti-MXene planar structure, Ti atoms can be evenly distributed at a high density. This promotes the efficient coordination of ethylene glycol and oxalate bonds with Ti atoms, making the polycondensation reaction very easy. It is also due to this effect that the efficiency of OEO to form vinyl oxalate is very high under the ring-forming temperature conditions, and it is effectively separated under high vacuum conditions, thereby significantly reducing the probability of oxidative degradation of oxalate ethylene glycol ester bonds, and ultimately achieving the preparation of vinyl oxalate with higher yield and purity.

[0046] Therefore, the inventors of this case found that the use of MXene catalysts can not only efficiently promote the condensation reaction of dimethyl oxalate and ethylene glycol, but also efficiently promote the depolymerization of ethylene glycol oxalate polymers into vinyl oxalate cyclic compounds.

[0047] Furthermore, the concentration of the catalyst in the mixed reaction system (ie, the amount introduced) is 50 to 2000 ppm, preferably 500 to 1000 ppm.

[0048] In some embodiments, in step (1), the thermal stabilizer may include but is not limited to any one of phosphoric acid, triphenyl phosphate, phosphorous acid, trimethyl phosphate, triethyl phosphate, etc., or a combination of two or more thereof, preferably a combination of triphenyl phosphate, trimethyl phosphate and triethyl phosphate.

[0049] Furthermore, the concentration of the heat stabilizer in the mixed reaction system (ie, the amount introduced) is 200 to 2000 ppm, preferably 200 to 500 ppm.

[0050] In some embodiments, in step (2), the second reaction temperature is 200-240° C., and the second reaction pressure is 5-100 Pa.

[0051] Furthermore, in step (2), the time of the second reaction is 1.5 to 3.0 hours.

[0052] In some more preferred embodiments, the second reaction temperature is 220-240°C, and the second reaction pressure is 5-60Pa.

[0053] In some embodiments, in step (3), the preparation method includes: purifying the crude vinyl oxalate product using a low-toxic aprotic solvent, wherein the low-toxic aprotic solvent includes at least one of acetone, ethyl acetate, propyl acetate, butyl acetate, dioxane, tetrahydrofuran, cyclohexane, dichloromethane, butanone, cyclohexanone, etc., preferably at least one of acetone, ethyl acetate and dichloromethane, but is not limited thereto.

[0054] Furthermore, the purification includes processes such as dissolution, concentration, filtration and drying.

[0055] In summary, the preparation method of the present invention uses a highly efficient ester exchange catalyst Ti-MXene. By regulating the amount of MXene catalyst introduced, the reaction temperature, the reaction pressure and the type of purification solvent, vinyl oxalate with a yield greater than 80wt% and a purity greater than 99wt% can be obtained, which is beneficial to the industrial production and application of vinyl oxalate.

[0056] In order to facilitate the understanding of the present invention, the technical solution of the present invention is further described in detail below in combination with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific implementation methods or embodiments and are not intended to limit the present invention.

[0058] Unless otherwise specified, all raw materials or reagents used in the examples are commercially available and can be purchased through commercial channels. The main raw materials used in the following examples are analytically pure, ethylene glycol and dimethyl oxalate are purchased from Aladdin, and the Ti-MXene catalyst is homemade.

[0059] Example 1

[0060] Preparation of ethylene glycol oxalate oligomer (OEO1).

[0061] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (118.1 g, 1.903 mol), Ti 3 C 2 Tx (MXene, 12 mg, 100 ppm) and trimethyl phosphate (60 mg, 500 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 4 hours, 150°C for 4 hours, and 165°C for 3 hours, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 150°C and the pressure was 50N100 Pa, the reaction was carried out for 1.5 hours, the material was discharged under nitrogen protection, and cooled to room temperature to obtain the product OEO1. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO1 is 8.0 mol / kg, the degree of polymerization is about 6, and after subtracting the unreacted dimethyl oxalate, its yield is about 95%.

[0062] The temperature of the reaction raw material OEO1 was gradually increased to 170°C, and the pressure was gradually reduced to 60Pa; the temperature was set to 200°C, the heating rate was about 2°C / min, and the reaction was continued for 3 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 80.3% and the purity was >99wt%.

[0063] Structural characterization: AvIII type nuclear magnetic resonance spectrometer (400 MHz) was used with deuterated acetone as solvent and TMS as internal standard. 1 H NMR and structural composition see Figure 3 .

[0064] Color difference measurement: Use WSC-S colorimeter to test the hue of the sample. Figure 2 The actual image and hue value of the vinyl oxalate sample obtained in Example 1 are given.

[0065] Example 2

[0066] The preparation of ethylene glycol oxalate oligomer (OEO1) was the same as in Example 1.

[0067] The temperature of the reaction raw material OEO1 was gradually increased to 170°C, and the pressure was gradually reduced to 60Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 3 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 81.5% and the purity was >99wt%.

[0068] Example 3

[0069] The preparation of ethylene glycol oxalate oligomer (OEO1) was the same as in Example 1.

[0070] The temperature of the reaction raw material OEO1 was gradually increased to 170°C, and the pressure was gradually reduced to 20Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 2 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain the preparation of refined vinyl oxalate ethylene glycol oxalate oligomer (OEO1).

[0071] Example 4

[0072] Preparation of Ethylene Glycol Oxalate Oligomers (OEO2)

[0073] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (118.1 g, 1.903 mol), Ti 3 C 2 Tx (MXene, 24 mg, 200 ppm) and trimethyl phosphate (60 mg, 500 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 4 hours and 150°C for 2 hours, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 150°C and the pressure was 50 to 100 Pa, the reaction was 1.0 h, the discharge was protected by nitrogen, and the product OEO2 was obtained by cooling to room temperature. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO2 is 8.0 mol / kg, the degree of polymerization is about 6, and after deducting the unreacted dimethyl oxalate, its yield is 95%.

[0074] The temperature of the reaction raw material OEO2 was gradually increased to 170°C, and the pressure was gradually reduced to 40Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 2 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 88.0% and the purity was >99wt%.

[0075] Example 5

[0076] Preparation of Ethylene Glycol Oxalate Oligomers (OEO3)

[0077] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (118.1 g, 1.903 mol), Ti 3 C 2 Tx (MXene, 120 mg, 1000 ppm) and trimethyl phosphate (60 mg, 500 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 2 hours and 150°C for 2 hours, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 170°C and the pressure was 50 to 100 Pa, the reaction was 1.0 h, the discharge was protected by nitrogen, and the product OEO3 was obtained by cooling to room temperature. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO3 is 8.4 mol / kg, the degree of polymerization is about 19, and the yield is 93% after deducting the unreacted dimethyl oxalate.

[0078] The temperature of the reaction raw material OEO3 was gradually increased to 170°C, and the pressure was gradually reduced to 40Pa; the temperature was set to 240°C, the heating rate was about 2°C / min, and the reaction was carried out for 2 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 80.0% and the purity was >99wt%.

[0079] Example 6

[0080] Preparation of Ethylene Glycol Oxalate Oligomers (OEO4)

[0081] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (118.1 g, 1.903 mol), Ti 3 C 2 Tx (MXene, 240 mg, 2000 ppm) and trimethyl phosphate (60 mg, 500 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 2 hours and 150°C for 2 hours, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 130°C and the pressure was 50 to 100 Pa, the reaction was performed for 1.5 hours, the discharge was protected by nitrogen, and the product OEO4 was obtained by cooling to room temperature. Nuclear magnetic hydrogen spectrum calculations showed that the oxalic acid unit content of OEO4 was 7.6 mol / kg, the degree of polymerization was about 4, and the yield was 97% after deducting the unreacted dimethyl oxalate.

[0082] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 93.0% and the purity was >99wt%.

[0083] Example 7

[0084] Preparation of ethylene glycol oxalate oligomers (OEO5).

[0085] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (118.1 g, 1.903 mol), Ti 3 C 2Tx (MXene, 6 mg, 50 ppm) and trimethyl phosphate (60 mg, 500 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 6 hours, 150°C for 4 hours, and 165°C for 2 hours, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 150°C and the pressure was 50 to 100 Pa, the reaction was 1.5 hours, the discharge was protected by nitrogen, and the product OEO5 was obtained by cooling to room temperature. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO5 is 8.0 mol / kg, the degree of polymerization is about 6, and after deducting the unreacted dimethyl oxalate, its yield is about 95%.

[0086] The temperature of the reaction raw material OEO5 was gradually increased to 170°C, and the pressure was gradually reduced to 20Pa; the temperature was set to 220°C, the heating rate was about 2°C / min, and the reaction was carried out for 3 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 86.6% and the purity was >99wt%.

[0087] Example 8

[0088] The preparation of ethylene glycol oxalate oligomer (OEO4) is the same as in Example 6.

[0089] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using cyclohexane solution to obtain refined vinyl oxalate. The yield was 91.0%, and the purity was >99wt%.

[0090] Example 9

[0091] The preparation of ethylene glycol oxalate oligomer (OEO4) is the same as in Example 6.

[0092] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a dioxane solution to obtain refined vinyl oxalate. The yield was 86.0%, and the purity was >99wt%.

[0093] Example 10

[0094] The preparation of ethylene glycol oxalate oligomer (OEO4) is the same as in Example 6.

[0095] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using tetrahydrofuran solution to obtain refined vinyl oxalate. The yield was 82.0%, and the purity was >99wt%.

[0096] Embodiment 11

[0097] The preparation of ethylene glycol oxalate oligomer (OEO4) is the same as in Example 6.

[0098] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using ethyl acetate solution to obtain refined vinyl oxalate. The yield was 88.6% and the purity was >99wt%.

[0099] Example 12

[0100] The preparation of ethylene glycol oxalate oligomer (OEO4) is the same as in Example 6.

[0101] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using cyclohexanone solution to obtain refined vinyl oxalate. The yield was 81.5%, and the purity was >99wt%.

[0102] Example 13

[0103] Preparation of ethylene glycol oxalate oligomers (OEO6).

[0104] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (68.2 g, 1.100 mol), Ti 2CTx (MXene, 240 mg, 2000 ppm) and trimethyl phosphate (240 mg, 2000 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 1 hour, 150°C for 2 hours, and 170°C for 0.5 hours, producing about 95% of crude by-product methanol, and 10-30 g of unreacted dimethyl oxalate was collected from the by-product methanol. The reaction was carried out at 170°C and 50-100 Pa for 1.5 hours, the material was discharged under nitrogen protection, and cooled to room temperature to obtain the product OEO6. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO6 is 8.4 mol / kg, the degree of polymerization is about 20, and after deducting the unreacted dimethyl oxalate, its yield is about 91%.

[0105] The temperature of the reaction raw material OEO6 was gradually raised to 220°C, the heating rate was about 2°C / min, and the pressure was gradually reduced to 20Pa; the reaction was continued for 1.5 hours until no obvious material was left in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using acetone solution to obtain refined vinyl oxalate. The yield was 83.5% and the purity was >99wt%.

[0106] Embodiment 14

[0107] Preparation of ethylene glycol oxalate oligomers (OEO7).

[0108] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (136.4 g, 2.200 mol), Ti 4 C 3 Tx (MXene, 12 mg, 100 ppm) and trimethyl phosphate (24 mg, 200 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 1 hour, 145°C for 3 hours, and 150°C for 1 hour, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 135°C and the pressure was 50 to 100 Pa, the reaction was 1.5 hours, the discharge was protected by nitrogen, and the product OEO7 was obtained by cooling to room temperature. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO7 is 7.7 mol / kg, the degree of polymerization is about 4, and after deducting the unreacted dimethyl oxalate, its yield is about 95%.

[0109] The temperature of the reaction raw material OEO7 was gradually raised to 235°C, the heating rate was about 2°C / min, and the pressure was gradually reduced to 20Pa; the reaction was continued for 2.0 hours until no obvious material was left in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a dichloromethane solution to obtain refined vinyl oxalate. The yield was 88.6% and the purity was >99wt%.

[0110] Embodiment 15

[0111] Preparation of ethylene glycol oxalate oligomers (OEO8).

[0112] The reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (186.2 g, 3.000 mol), Ti 4 C 3 Tx (MXene, 12 mg, 100 ppm) and trimethyl phosphate (24 mg, 200 ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 1 hour, 145°C for 3 hours, and 150°C for 1 hour, producing about 95% of crude by-product methanol, and 10 to 30 g of unreacted dimethyl oxalate were collected from the by-product methanol. The temperature was set to 135°C and the pressure was 50 to 100 Pa, the reaction was continued for 2.0 hours, the material was discharged under nitrogen protection, and cooled to room temperature to obtain the product OEO8. Nuclear magnetic hydrogen spectrum calculations show that the oxalic acid unit content of OEO8 is 7.7 mol / kg, the degree of polymerization is about 4, and after deducting the unreacted dimethyl oxalate, its yield is about 95%.

[0113] The temperature of the reaction raw material OEO8 was gradually raised to 235°C, the heating rate was about 2°C / min, and the pressure was gradually reduced to 20Pa; the reaction was continued for 2.0 hours until no obvious material was left in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a dichloromethane solution to obtain refined vinyl oxalate. The yield was 88.6% and the purity was >99wt%.

[0114] Example 16

[0115] The preparation of ethylene glycol oxalate oligomer (OEO8) is the same as in Example 15.

[0116] The temperature of the reaction raw material OEO8 was gradually increased to 170°C, and the pressure was gradually reduced to 5Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using ethyl acetate solution to obtain refined vinyl oxalate. The yield was 89.5%, and the purity was >99wt%.

[0117] Embodiment 17

[0118] The preparation of ethylene glycol oxalate oligomer (OEO8) is the same as in Example 15.

[0119] The temperature of the reaction raw material OEO8 was gradually increased to 170°C, and the pressure was gradually reduced to 100Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 2.0 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using ethyl acetate solution to obtain refined vinyl oxalate. The yield was 82.6%, and the purity was >99wt%.

[0120] Comparative Example 1

[0121] Compared with Example 1, the difference between this comparative example and Example 1 is that the temperature of the reaction raw material OEO1 is gradually increased to 170°C, and the pressure is gradually reduced to 20Pa; the temperature is set to 190°C, the heating rate is about 2°C / min, and the reaction is carried out for 8 hours until there is no obvious material in the reactor. The sublimated product crude vinyl oxalate is collected and recrystallized using a mixed solution of acetone and dichloromethane in a volume ratio of 1:1 to obtain refined vinyl oxalate with a yield of 70.3% and a purity of >99wt%.

[0122] Comparative Example 2

[0123] Compared with Example 1, the difference between this comparative example and Example 1 is that: the temperature of the reaction raw material OEO1 is gradually increased to 170°C, and the pressure is gradually reduced to 60Pa; the temperature is set to 190°C, the heating rate is about 2°C / min, and the reaction is carried out for 10 hours until there is no obvious material in the reactor. The sublimated product crude vinyl oxalate is collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate with a yield of 60.1% and a purity of >99wt%.

[0124] The above results show that the yield of vinyl oxalate can be significantly increased by preparing ethylene glycol oxalate oligomers with a suitable degree of polymerization and increasing the depolymerization temperature, the amount of catalyst Mxene introduced and the vacuum degree.

[0125] Comparative Example 3

[0126] Compared with Example 1, the difference between this comparative example and Example 1 is that the reaction raw materials dimethyl oxalate (118.1 g, 1.000 mol), ethylene glycol (118.1 g, 1.903 mol), Ti 3 C 2 Tx (MXene, 3mg, 25ppm) and trimethyl phosphate (60mg, 500ppm) were added to the reactor. Under nitrogen protection, the temperature of the material was gradually raised to 130°C for 6h, 150°C for 6h, and 165°C for 4h, producing about 95% of crude by-product methanol, and 10-30g of unreacted dimethyl oxalate was collected from the by-product methanol. The temperature was set to 150°C and the pressure was 50-100Pa, the reaction was 1.5h, the discharge was protected by nitrogen, and the product OEO9 was obtained by cooling to room temperature. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO9 is 8.0mol / kg, the degree of polymerization is about 6, and after deducting the unreacted dimethyl oxalate, its yield is about 86%.

[0127] The temperature of the reaction raw material OEO9 was gradually increased to 170°C, and the pressure was gradually reduced to 60Pa; the temperature was set to 200°C, the heating rate was about 2°C / min, and the reaction was continued for 3 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 72.3% and the purity was >99wt%. This is because extremely low amounts of MXene introduced cannot play an effective catalytic role.

[0128] The above results show that the yield of vinyl oxalate can be significantly increased by preparing ethylene glycol oxalate oligomers with a suitable degree of polymerization and increasing the depolymerization temperature, the amount of catalyst Mxene introduced and the vacuum degree.

[0129] Comparative Example 4

[0130] To illustrate the high efficiency of Ti-MXene catalyst, 240 mg of tetrabutyl titanate (TBT) was used to replace Ti 3 C 2 Tx, and repeat the synthesis steps of OEO4 to obtain OEO10. Nuclear magnetic hydrogen spectrum calculation shows that the oxalic acid unit content of OEO10 is 7.5 mol / kg, the degree of polymerization is about 4, and the yield is 93% after deducting the unreacted dimethyl oxalate. Then the temperature of the reaction raw material OEO10 is gradually increased to 170°C, and the pressure is gradually reduced to 35Pa; the temperature is set to 235°C, the heating rate is about 2°C / min, and the reaction is 1.5h until there is no obvious material in the reactor. The sublimated product crude vinyl oxalate is collected and recrystallized using a mixed solution of acetone and dichloromethane with a volume ratio of 1:1 to obtain refined vinyl oxalate with a yield of 75.0% and a purity of >99wt%. The experimental results show that Ti 3 C 2 Tx has better ability to depolymerize ethylene glycol oxalate than TBT.

[0131] Comparative Example 5

[0132] In order to illustrate the high efficiency of low-toxic aprotic solvents, ethanol reported in the literature was used as the purification solvent in this comparative example.

[0133] The temperature of the reaction raw material OEO4 was gradually increased to 170°C, and the pressure was gradually reduced to 35Pa; the temperature was set to 235°C, the heating rate was about 2°C / min, and the reaction was carried out for 1.5 hours until there was no obvious material in the reactor. The sublimated product crude vinyl oxalate was collected and recrystallized from ethanol to obtain refined vinyl oxalate. The yield was 86.0% and the purity was about 98wt%. The results show that due to the high reactivity of vinyl oxalate, proton solvents easily lead to its ring opening, and the ring opening product remains in the refined vinyl oxalate, thereby reducing the purity of the product.

[0134] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing high-purity vinyl oxalate, characterized in that: include: At a first reaction temperature and a first reaction pressure, a mixed reaction system comprising a reaction monomer, a catalyst, and a thermal stabilizer is subjected to a condensation polymerization reaction to produce an ethylene glycol oxalate polymer, wherein the reaction monomer comprises ethylene glycol and dimethyl oxalate, and the catalyst comprises a MXene material; performing a high vacuum depolymerization reaction on the ethylene glycol oxalate polymer at a second reaction temperature and a second reaction pressure, and performing reduced pressure sublimation to obtain a crude vinyl oxalate product; The crude vinyl oxalate product is purified to obtain high-purity vinyl oxalate.

2. The preparation method according to claim 1, wherein: The first reaction temperature is 130-170° C., the first reaction pressure is 50-100,000 Pa, and the polycondensation reaction time is 5.0-13.5 h; and / or the molar ratio of ethylene glycol to dimethyl oxalate is 1.1-3.0:

1.

3. The preparation method according to claim 2, wherein: The molar ratio of ethylene glycol to dimethyl oxalate is 1.1-2.2:

1.

4. The preparation method according to claim 1, wherein: The catalyst includes Ti3C2T x 、Ti4C3T x 、Ti2CT x and / or, the concentration of the catalyst in the mixed reaction system is 50 to 2000 ppm.

5. The preparation method according to claim 2, wherein: The ethylene glycol oxalate polymer has a structure as shown in formula (I): Wherein, n=4 to 20; And / or, the concentration of the catalyst in the mixed reaction system is 500-1000 ppm.

6. The preparation method according to claim 1, wherein: The heat stabilizer comprises any one of phosphoric acid, triphenyl phosphate, phosphorous acid, trimethyl phosphate, and triethyl phosphate, or a combination of two or more thereof; and / or the concentration of the heat stabilizer in the mixed reaction system is 200 to 2000 ppm.

7. The preparation method according to claim 6, characterized in that: The heat stabilizer includes a combination of triphenyl phosphate, trimethyl phosphate and triethyl phosphate; and / or the concentration of the heat stabilizer in the mixed reaction system is 200 to 500 ppm.

8. The preparation method according to claim 1, wherein: The second reaction temperature is 200-240° C., the second reaction pressure is 5-100 Pa, and the second reaction time is 1.5-3.0 h.

9. The preparation method according to claim 8, characterized in that: The second reaction temperature is 220-240° C., and the second reaction pressure is 5-60 Pa; And / or, the preparation method comprises: purifying the crude vinyl oxalate product with a low-toxic aprotic solvent, wherein the low-toxic aprotic solvent comprises at least one of acetone, ethyl acetate, propyl acetate, butyl acetate, dioxane, tetrahydrofuran, cyclohexane, dichloromethane, butanone, and cyclohexanone; And / or, the purification includes dissolving, concentrating, filtering and drying.

10. The preparation method according to claim 9, characterized in that: The low-toxic aprotic solvent includes at least one of acetone, ethyl acetate and dichloromethane; And / or, the yield of the preparation method is greater than 80 wt%; And / or, the purity of the high-purity vinyl oxalate prepared by the preparation method is greater than 99 wt%.

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