A method for removing vinyl acetate from ethylene-vinyl acetate resolution

Abstract

The present application relates to the technical field of recovery of methyl acetate and methanol, and discloses a method for removing vinyl acetate in vinyl alcoholysis of ethylene-vinyl acetate, which comprises the following steps: in the preparation of polyethylene-vinyl acetate resin, the mixed solution of crude methyl acetate and first vinyl acetate generated by alcoholysis is subjected to an ester exchange reaction through an alkaline anion exchange resin to remove part of the vinyl acetate; wherein the crude methyl acetate comprises a mixed solution containing methyl acetate, first acetaldehyde and methanol, and the alkaline anion exchange resin is a weak alkaline styrene. The method can reduce the content of vinyl acetate in the crude methyl acetate, which is crucial for improving the subsequent recovery of methanol and product quality.

Description

Technical Field

[0001] This invention relates to the field of methyl acetate and methanol recovery technology, and more specifically to a method for removing vinyl acetate from ethylene-vinyl acetate alcoholysis. Background Technology

[0002] Polyvinyl alcohol (EVOH) polymer is currently the synthetic resin material with the best barrier properties and is widely used in packaging materials. Furthermore, EVOH is a green and environmentally friendly material, free of nitrogen and dioxins, consisting only of carbon, oxygen, and hydrogen, and does not produce toxic or harmful gases when burned. Global demand for EVOH continues to grow rapidly, and its applications are constantly expanding.

[0003] The production of EVOH resin mainly involves the polymerization of ethylene and vinyl acetate, the removal of polymerization residues, and the alcoholysis of ethylene-vinyl acetate. Because vinyl acetate monomer cannot be completely removed during the polymerization residue removal process, a small amount of vinyl acetate residue enters the alcoholysis process along with the polymerization resin solution. Hundreds of ppm of vinyl acetate are carried out of the alcoholysis resin solution system along with a mixed solution of methyl acetate and methanol (also called crude methyl acetate) produced in the alcoholysis process. Since ethyl acetate and methanol form an azeotrope, which is difficult to separate by ordinary distillation, the vinyl acetate in the crude methyl acetate affects the subsequent recovery of methanol and the quality of the final product.

[0004] In existing technologies, it is difficult to recover vinyl acetate and methanol azeotropes using ordinary distillation. In industrial production, water is mainly used as an extractant for extractive distillation. However, when components are introduced into water, the water will also form an azeotrope with the residual methyl acetate. Therefore, industrial purification methods using water as an extractant are obviously not advisable.

[0005] Therefore, it is of great significance to research and develop a method to reduce the vinyl acetate content in crude methyl ester. Summary of the Invention

[0006] The purpose of this invention is to overcome the defect in the removal of vinyl acetate monomers after polymerization of EVOH in the prior art, where a small amount of vinyl acetate monomer cannot be completely removed and enters the alcoholysis process with the polymerization resin liquid. This invention provides a method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate, which can reduce the vinyl acetate content in crude methyl ester, and is crucial for improving the subsequent recovery of methanol and product quality.

[0007] To achieve the above objectives, the present invention provides a method for removing vinyl acetate from the alcoholysis of ethylene-vinyl acetate, wherein the method comprises: in the preparation of polyethylene-vinyl alcohol resin, subjecting a mixed solution of crude methyl acetate and first vinyl acetate produced by alcoholysis to an ester exchange reaction via an alkaline anion exchange resin to remove part of the vinyl acetate; wherein the crude methyl acetate is a mixed solution containing methyl acetate, first acetaldehyde and methanol, and the alkaline anion exchange resin is a weakly basic styrene.

[0008] The above technical solution utilizes an alkaline anion exchange resin to catalyze the transesterification reaction of vinyl acetate and methanol, producing vinyl alcohol and methyl acetate. Furthermore, in a preferred embodiment, Purolite resin is used to effectively adsorb acetaldehyde. Therefore, this method can reduce the vinyl acetate content in crude methyl acetate, which is crucial for improving the subsequent recovery of methanol and the quality of the product. Attached Figure Description

[0009] Figure 1 This is a schematic diagram illustrating the removal of vinyl acetate in the alcoholysis of ethylene-vinyl acetate according to the present invention.

[0010] Explanation of reference numerals in the attached figures

[0011] I: A mixed solution of crude methyl ester and vinyl acetate produced during the alcoholysis process;

[0012] II: After passing through storage tank (A), it is a mixed solution mainly containing methyl acetate, methanol, a small amount of vinyl acetate and diacetaldehyde;

[0013] III: A mixed solution containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde after passing through storage tank (B);

[0014] A: A storage tank (A) containing an alkaline anion exchange resin;

[0015] B: Storage tank (B) containing Purolite resin. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] As previously stated, the present invention provides a method for removing vinyl acetate from the alcoholysis of ethylene-vinyl acetate, wherein the method comprises: in the preparation of polyethylene-vinyl alcohol resin, subjecting a mixed solution of crude methyl acetate and first vinyl acetate produced by alcoholysis to an ester exchange reaction via an alkaline anion exchange resin to remove part of the vinyl acetate; wherein the crude methyl acetate is a mixed solution containing methyl acetate, first acetaldehyde and methanol, and the alkaline anion exchange resin is a weakly basic styrene.

[0018] The inventors of this invention discovered that in the preparation of polyethylene-vinyl alcohol resin (EVOH resin), a small amount of entrained vinyl acetate needs to be removed before distilling the methanol solution of methyl acetate. Based on this, the inventors employed a basic anion exchange resin to catalyze the transesterification reaction of vinyl acetate and methanol, producing vinyl alcohol and methyl acetate. Vinyl alcohol is unstable and rearranges to acetaldehyde. Preferably, a weakly basic styrene 704 anion exchange resin is used, which can react effectively in acidic, neutral, and alkaline media. In contrast, the strongly basic styrene quaternary ammonium 703 resin, being an ion exchange resin with quaternary ammonium groups [-N(CH3)3] on a styrene-vinylbenzene copolymer cross-linked polymer matrix, has a lower working exchange capacity and lower anti-fouling ability than the weakly basic anion exchange resin, resulting in poorer performance. Furthermore, Purolite resin can effectively adsorb acetaldehyde. Therefore, the vinyl acetate content in crude methyl acetate can be reduced, which is crucial for improving subsequent methanol recovery and product quality.

[0019] According to the present invention, since the basic anion exchange resin has a high catalytic effect on the esterification reaction of vinyl acetate, it can better remove vinyl acetate.

[0020] In this invention, it should be noted that the basic anion exchange resin has a weak alkalinity, with an alkalinity pH of 7-10; it can react effectively in acidic, neutral, and alkaline media, and can be used in non-aqueous solutions. This resin has advantages such as high regeneration efficiency, large exchange capacity, strong anti-fouling ability, and good mechanical strength.

[0021] According to the present invention, preferably, the basic anion exchange resin has a wet apparent density of 0.65-0.75 g / ml, a wet true density of 1.03-1.06 g / ml, and a particle size range of 0.3-1.5 mm. This basic anion exchange resin was purchased from the chemical plant of Nankai University.

[0022] Additionally, in this invention, it should be noted that wet apparent density is the density of the resin in a hydrated state, while wet true density is the resin density obtained after removing the water from the resin; particle size refers to the diameter of the resin particles.

[0023] According to the present invention, the basic anion exchange resin is a weakly basic styrene 704 type anion exchange resin; in the present invention, the weakly basic styrene 704 type anion exchange resin is purchased from Tianjin Nankai University Chemical Plant.

[0024] According to the present invention, the content of the first vinyl acetate in the mixed solution is 100-1200 ppm, preferably 100-1000 ppm.

[0025] According to the present invention, the content of the first acetaldehyde in the mixed solution is 15-100 ppm, preferably 15-60 ppm.

[0026] According to the present invention, in the preparation of polyethylene-vinyl alcohol resin (EVOH resin), the crude methyl ester produced in the alcoholysis step contains methyl acetate, acetaldehyde, and methanol; preferably, based on the total weight of the crude methyl ester, the content of methyl acetate is 10-35% by weight, and the content of methanol is 65-90% by weight; more preferably, based on the total weight of the crude methyl ester, the content of methyl acetate is 20-35% by weight, and the content of methanol is 65-80% by weight.

[0027] According to the present invention, the conditions for the transesterification reaction include: a temperature of 35-70°C and a time of 20-60 min; preferably, a temperature of 40-65°C and a time of 20-40 min. In this invention, limiting the conditions of the transesterification reaction to the aforementioned range enables better removal of vinyl acetate; if the temperature is too high, the adsorption effect will deteriorate, and the resin will fail; if the temperature is too low, the adsorption effect will be poor.

[0028] According to the present invention, in the liquid after the transesterification reaction, the content of the second vinyl acetate is 20-100 ppm and the content of the second acetaldehyde is 20-1000 ppm; preferably, the content of the second vinyl acetate is 20-60 ppm and the content of the second acetaldehyde is 20-800 ppm.

[0029] According to the present invention, the method further includes: subjecting the liquid after the transesterification reaction to adsorption treatment with Purolite resin.

[0030] In this invention, Purolite resin was chosen because it has good adsorption properties for acetaldehyde and can better adsorb acetaldehyde.

[0031] According to the present invention, the Purolite resin is of type C100 and is purchased from Purolite, a British manufacturer.

[0032] In this invention, it should be noted that Purolite C100 ion exchange resin is a gel-type styrene gel sodium cation exchange resin with a highly cross-linked three-dimensional network structure. This structure endows the resin with good chemical stability, wear resistance, compressive strength, and other physical strengths, as well as high exchange capacity and high selectivity, ensuring high efficiency in formaldehyde removal. Purolite C100 resin has a transformation expansion rate of less than 10%, and the resin volume change is small during the conversion between different ion forms, which directly affects the stability of the resin bed and the ease of operation. The low expansion rate reduces mechanical stress on the resin during exchange and regeneration, lowers the risk of resin particle breakage, and thus extends the resin's service life. Furthermore, a stable resin bed also helps improve the overall adsorption efficiency, reduces the frequency of maintenance and regeneration, and lowers operating costs. In contrast, Purolite A110 has a polystyrene macroporous structure, and its acetaldehyde adsorption performance is lower than that of C100. Its pore size is larger than that of C100, making it unsuitable for the exchange of small molecules and relatively pure liquids.

[0033] According to the present invention, preferably, the Purolite resin has a wet apparent density of 0.77-0.87 g / ml, a wet true density of 1.24-1.28 g / ml, and a resin particle size of 0.315-1.25 mm.

[0034] According to the present invention, the conditions for the adsorption treatment include: a temperature of 25-60°C and a time of 20-60 min; preferably, a temperature of 35-50°C and a time of 25-40 min. In this invention, limiting the adsorption treatment conditions to the aforementioned range allows for better adsorption of acetaldehyde; if the temperature is too high, the adsorption effect will be poor, or even the resin will fail; if the temperature is too low, the adsorption effect will also be poor.

[0035] According to the present invention, the content of vinyl acetate tertiary in the liquid after the adsorption treatment is 10-100 ppm and the content of acetaldehyde tertiary is 10-80 ppm; preferably, the content of vinyl acetate tertiary is 20-60 ppm and the content of acetaldehyde tertiary is 10-60 ppm.

[0036] According to the present invention, the content of the partial vinyl acetate is the difference between the content of the first vinyl acetate and the content of the second vinyl acetate.

[0037] According to a particularly preferred embodiment of the present invention, such as Figure 1 As shown, Figure 1 This is a schematic diagram illustrating the removal of vinyl acetate from ethylene-vinyl acetate alcoholysis according to the present invention; the method for removing vinyl acetate from ethylene-vinyl acetate alcoholysis provided by the present invention includes:

[0038] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of crude methyl acetate and first vinyl acetate produced by alcoholysis is passed through a storage tank (A). The storage tank (A) contains a basic anion exchange resin (weakly basic styrene 704 type). The basic anion exchange resin catalyzes the transesterification reaction between the first vinyl acetate and methanol to produce vinyl alcohol and methyl acetate, and removes some vinyl acetate. The vinyl alcohol is unstable and rearranges to acetaldehyde. The mixed solution (II) after passing through the storage tank (A) mainly contains methyl acetate, methanol, a small amount of second vinyl acetate and second acetaldehyde.

[0039] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which is equipped with Purolite C100 resin for adsorption treatment to remove part of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde.

[0040] In this invention, it should be noted that the content of the acetaldehyde is the difference between the content of the first acetaldehyde and the content of the third acetaldehyde.

[0041] The present invention will be described in detail below through embodiments.

[0042] In the following examples and comparative examples:

[0043] The parameters of methyl acetate and acetaldehyde were determined by gas chromatography.

[0044] Unless otherwise specified, all other ingredients are commercially available products.

[0045] The strongly basic styrene quaternary ammonium 703 resin involved in Comparative Example 1 has a pH range of 8-14, a wet apparent density of 0.66-0.75 g / ml, a wet true density of 1.06-1.11 g / ml, and a resin particle size of 0.315-1.25 mm. This strongly basic styrene quaternary ammonium 703 resin was purchased from the chemical plant of Nankai University.

[0046] The Purolite A110 resin involved in Comparative Example 2 has the following parameters: wet apparent density 0.75-0.83 g / ml, wet true density 1.27-1.38 g / ml, and particle size range 0.30-1.21 mm. This Purolite A110 resin was purchased from Purolite (China) Co., Ltd.

[0047] Example 1

[0048] This embodiment illustrates the removal of vinyl acetate from ethylene-vinyl acetate alcoholysis using the method of the present invention.

[0049] like Figure 1As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0050] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 40°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 30% by weight and the content of methanol is 70% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 1.

[0051] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 40°C for 20 min, producing vinyl alcohol and methyl acetate, and removing some vinyl acetate. The vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0052] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 45°C for 25 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 1.

[0053] Table 1

[0054]

[0055] Example 2

[0056] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0057] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0058] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 50°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 30% by weight and the content of methanol is 70% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 2.

[0059] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 50°C for 20 minutes to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. Vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0060] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 45°C for 25 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 2.

[0061] Table 2

[0062]

[0063] Example 3

[0064] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0065] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0066] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 60°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 30% by weight and the content of methanol is 70% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 3.

[0067] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 60°C for 20 min to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. Vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0068] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 45°C for 25 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 3.

[0069] Table 3

[0070]

[0071] Example 4

[0072] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0073] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0074] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 70°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 35% by weight and the content of methanol is 65% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 4.

[0075] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 70°C for 30 minutes to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. Vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0076] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 45°C for 25 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 4.

[0077] Table 4

[0078]

[0079] Example 5

[0080] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0081] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0082] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 60°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 35% by weight and the content of methanol is 65% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 5.

[0083] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 60°C for 25 min to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. Vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0084] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 60°C for 30 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 5.

[0085] Table 5

[0086]

[0087] Example 6

[0088] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0089] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0090] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 60°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 25% by weight and the content of methanol is 75% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 6.

[0091] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 60°C for 35 minutes to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. The vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0092] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 55°C for 35 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 6.

[0093] Table 6

[0094]

[0095] Example 7

[0096] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0097] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0098] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, acetaldehyde and vinyl acetate produced by alcoholysis is cooled to 60°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 23% by weight and the content of methanol is 77% by weight, based on the total weight of the crude methyl acetate. The contents of acetaldehyde and vinyl acetate are shown in Table 7.

[0099] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 60°C for 45 min to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. Vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0100] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 55°C for 60 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 7.

[0101] Table 7

[0102]

[0103] Example 8

[0104] This embodiment illustrates the removal of vinyl acetate using the method of the present invention.

[0105] like Figure 1 As shown, the method for removing vinyl acetate in the alcoholysis of ethylene-vinyl acetate includes:

[0106] (1) In the preparation of polyethylene-vinyl alcohol resin, a mixed solution (I) of methyl acetate, methanol, first acetaldehyde and first vinyl acetate produced by alcoholysis is cooled to 60°C by a heat exchanger and then enters a storage tank (A). The content of methyl acetate is 28% by weight and the content of methanol is 72% by weight, based on the total weight of the crude methyl acetate. The contents of first acetaldehyde and first vinyl acetate are shown in Table 8.

[0107] The storage tank (A) contains an alkaline anion exchange resin (weakly basic styrene 704 type). The alkaline anion exchange resin catalyzes the transesterification reaction of vinyl acetate and methanol at 60°C for 60 min to produce vinyl alcohol and methyl acetate, removing some vinyl acetate. The vinyl alcohol is unstable and rearranges into acetaldehyde. Therefore, the solution after passing through the storage tank (A) mainly contains a mixed solution (II) of methyl acetate, methanol, a small amount of vinyl acetate, and acetaldehyde.

[0108] (2) The mixed liquid (II) after the transesterification reaction in step (1) is passed through a storage tank (B), which contains Purolite resin C100, and is subjected to adsorption treatment at 60°C for 60 min to remove some of the acetaldehyde; wherein, after passing through the storage tank (B), there is a mixed solution (III) containing methyl acetate, methanol, a small amount of vinyl acetate and a small amount of acetaldehyde; as shown in Table 8.

[0109] Table 8

[0110]

[0111] Comparative Example 1

[0112] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 1, except that the "basic anion exchange resin (weakly basic styrene 704 type)" was replaced with "strongly basic styrene quaternary ammonium 703 type resin." This strongly basic styrene quaternary ammonium 703 type resin is an ion exchange resin with quaternary ammonium groups [-N(CH3)3] on a styrene-vinylbenzene copolymer cross-linked polymer matrix. Its basicity is equivalent to that of a general quaternary ammonium base, exhibiting ion exchange function in acidic, neutral, and even alkaline media.

[0113] The results are shown in Table 9.

[0114] Table 9

[0115]

[0116]

[0117] Comparative Example 2

[0118] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 2, except that “Purilet C100” was changed to “Purilet A110 resin”.

[0119] The results are shown in Table 10.

[0120] Table 10

[0121]

[0122] Comparative Example 3

[0123] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 3, except that the time spent passing through the alkaline anion exchange resin was 15 minutes.

[0124] The results are shown in Table 11.

[0125] Table 11

[0126]

[0127]

[0128] Comparative Example 4

[0129] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 4, except that the time spent passing through the alkaline anion exchange resin was 90 minutes.

[0130] The results are shown in Table 12.

[0131] Table 12

[0132]

[0133] Comparative Example 5

[0134] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 5, except that the time spent passing through Purolite resin was 15 minutes.

[0135] The results are shown in Table 13.

[0136] Table 13

[0137]

[0138]

[0139] Comparative Example 6

[0140] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 6, except that the time spent passing through Purolite resin was 90 minutes.

[0141] The results are shown in Table 14.

[0142] Table 14

[0143]

[0144] Comparative Example 7

[0145] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 7, except that the temperature of the Purolite resin was 20°C.

[0146] The results are shown in Table 15.

[0147] Table 15

[0148]

[0149]

[0150] Comparative Example 8

[0151] Vinyl acetate was removed from the ethylene-vinyl acetate alcoholysis using the same method as in Example 8, except that the temperature of the Purolite resin was 70°C.

[0152] The results are shown in Table 16.

[0153] Table 16

[0154]

[0155] The results above show that the method of the present invention can reduce the vinyl acetate content in crude methyl ester.

[0156] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for removing vinyl acetate from ethylene-vinyl acetate alcoholysis, characterized in that, The method includes: in the preparation of polyethylene-vinyl alcohol resin, passing a mixed solution of crude methyl acetate and vinyl acetate produced by alcoholysis through an alkaline anion exchange resin for transesterification to remove part of the vinyl acetate; wherein the crude methyl acetate includes a mixed solution containing methyl acetate, acetaldehyde and methanol, and the alkaline anion exchange resin is a weakly basic styrene.

2. The method according to claim 1, wherein, In the mixed solution, the content of the first vinyl acetate is 100-1200 ppm, preferably 100-1000 ppm; And / or, the content of the first acetaldehyde is 15-100 ppm, preferably 15-60 ppm.

3. The method according to claim 1, wherein, Based on the total weight of the crude methyl ester, the content of methyl acetate is 10-35% by weight, and the content of methanol is 65-90% by weight. Preferably, based on the total weight of the crude methyl ester, the content of methyl acetate is 20-35% by weight, and the content of methanol is 65-80% by weight.

4. The method according to claim 1, wherein, The conditions for the transesterification reaction include: a temperature of 35-70℃ and a time of 20-60 min; preferably, a temperature of 40-65℃ and a time of 20-40 min.

5. The method according to any one of claims 1-4, wherein, The liquid after the transesterification reaction contains 20-100 ppm of vinyl acetate and 20-1000 ppm of acetaldehyde. Preferably, the content of the second vinyl acetate is 20-60 ppm, and the content of the second acetaldehyde is 20-800 ppm.

6. The method according to any one of claims 1-5, wherein, The method further includes: subjecting the liquid after the transesterification reaction to adsorption treatment with Purolite resin.

7. The method according to claim 6, wherein, The Purolite resin is a gel-type styrene gel-type sodium acid cationic resin.

8. The method according to claim 6 or 7, wherein, The conditions for the adsorption treatment include: a temperature of 25-60℃ and a time of 20-60 min; preferably, a temperature of 35-50℃ and a time of 25-40 min.

9. The method according to any one of claims 6-8, wherein, The liquid after the adsorption treatment contains 10-100 ppm of vinyl acetate and 10-80 ppm of acetaldehyde. Preferably, the content of the third vinyl acetate is 20-60 ppm, and the content of the third acetaldehyde is 10-60 ppm.

10. The method according to claim 1, wherein, The content of the aforementioned vinyl acetate is the difference between the content of the first vinyl acetate and the content of the second vinyl acetate.

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