A method for recovering organic tin in a transesterification kettle of a vinyl ether compound

Abstract

A method for recovering organic tin in a vinyl ether compound transesterification kettle liquid, comprising the following steps: 1) taking the vinyl ether compound transesterification kettle liquid, cooling to-10-40 DEG C, standing, until crystals are precipitated in the transesterification kettle liquid, filtering, or, cooling to-10-40 DEG C, adding 0.1-5% of organic tin powder in mass fraction to the transesterification kettle liquid, stirring and mixing uniformly, then standing, until crystals are precipitated in the transesterification kettle liquid, filtering; 2) adding a basic solution with a concentration of 5-8 wt% to the crystals obtained by filtering, in a mass ratio of 1:0.5-10, and heating to 25-60 DEG C, until flocculent substances appear on the surface of the basic solution, and filtering the lower aqueous phase; 3) washing the crystals obtained by filtering with water, then washing with an organic solvent, drying, to obtain organic tin. The process condition is mild and the operation is convenient, the recovered organic tin can be used repeatedly, the production cost of enterprises is reduced, and environmental pollution is avoided.

Description

Technical Field

[0001] This invention relates to the chemical industry, and in particular to a method for recovering organotin from transesterification solutions of vinyl ether compounds. Background Technology

[0002] The preparation of vinyl-containing reactive acrylates typically involves transesterification with small-molecule acrylates under conditions where organotin compounds act as catalysts and phenothiazines, nitroxide radicals, etc., act as polymerization inhibitors. The vinyl-containing reactive acrylate fraction is then collected by vacuum distillation. The organotin compounds remaining in the reactor solution are reused.

[0003] Due to the high reactivity of vinyl compounds, a small amount of ester oligomers inevitably occurs during preparation and distillation purification. These oligomers accumulate in the reactor solution, leading to reduced catalyst performance, decreased reaction efficiency, prolonged reaction time, and a further increase in byproduct impurities, resulting in increased reactor solution volume. Unquenched free radicals generated from the prepolymer pose a high risk of initiating chain polymerization reactions.

[0004] Currently, the transesterification reaction liquid of vinyl ether compounds is usually disposed of by incineration, which has a significant environmental impact and cannot recover the organotin compounds. Patent CN201810985389 provides a method for recovering organotin through multiple water washing purification followed by further esterification reaction; however, this method generates a large amount of wastewater and is cumbersome. CN109021008 provides a method for recovering tin by carbonizing tin sludge at 300-800℃; however, this method has harsh operating conditions and requires re-reaction preparation to obtain organotin compounds.

[0005] Therefore, how to recover organotin from the transesterification solution of vinyl ether compounds in a simple, convenient, and low-cost manner is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for recovering organotin from the transesterification reactor of vinyl ether compounds. This method features mild process conditions, convenient operation, and the recovered organotin can be recycled multiple times, reducing enterprise production costs and avoiding environmental pollution.

[0007] The technical solution of this invention is: a method for recovering organotin from the transesterification solution of vinyl ether compounds, comprising the following steps:

[0008] 1) Take the transesterification solution of vinyl ether compounds, cool it to -10-40℃, let it stand until crystals precipitate in the transesterification solution, and filter it; or, cool it to -10-40℃, add 0.1-5% organotin powder by mass of the transesterification solution to the transesterification solution, stir and mix well, let it stand until crystals precipitate in the transesterification solution, and filter it.

[0009] 2) Add an alkaline solution with a concentration of 5-8wt% to the filtered crystals at a mass ratio of 1:0.5-10, heat to 25-60℃ until flocculent matter appears on the surface of the alkaline solution, and filter the lower aqueous phase.

[0010] 3) After the filtered crystals are washed with water, they are then washed with an organic solvent and dried to obtain organotin.

[0011] Further, in step 1), the exchange vessel liquid is cooled to 20-30℃ and allowed to stand for 24-72 hours; or, in step 1), the exchange vessel liquid is cooled to 20-30℃, and 0.5-1% of organotin powder by mass of the exchange vessel liquid is added to the exchange vessel liquid, and the mixture is stirred for 5-15 minutes and allowed to stand for 5-10 hours.

[0012] Furthermore, the molecular structure of organotin in step 1) is as follows:

[0013]

[0014] Among them, M1 and M2 are alkyl branches containing 4-12 carbon atoms.

[0015] Further, in step 2), an alkaline solution is added at a mass ratio of 1:0.5-2, wherein the alkaline solution is any one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and ammonia aqueous solution.

[0016] Further, in step 2), the temperature is raised to 30-40℃ and kept at that temperature for 1-10 hours.

[0017] Furthermore, the organic solvent in step 3) is a light alcohol, an ether, or a cyclic hydrocarbon. The light alcohol is methanol and / or ethanol, the ether is petroleum ether, and the cyclic hydrocarbon is cyclohexane.

[0018] Furthermore, the drying described in step 3) is performed at a temperature of 40-60°C.

[0019] Furthermore, the filtrate separated in step 1) is repeated in step 1).

[0020] The above technical solution has the following beneficial effects:

[0021] 1. The recycling method of the present invention involves first crystallizing the vinyl ether compound containing organotin in an ester exchange vessel, then washing the oligomers mixed in the crystals with an alkaline solution and separating the impurities to recover organotin with no change in molecular structure, thereby achieving the purpose of multiple recycling. During the recycling process, the organotin does not undergo chemical reactions, ensuring that the catalytic activity of the recovered organotin meets the catalytic requirements.

[0022] 2. The recovery method of this invention involves an organotin-containing vinyl ether compound transesterification reactor solution. The solvent, primarily the target product, exhibits high polymerization activity. Typically, when the organotin content reaches approximately 30%, further extraction of lighter components easily leads to reactor solution polymerization, causing significant process damage. The transesterification reactor solution is a near-saturated solution containing an organotin catalyst. After standing at -10 to 40°C, the solution transforms into a supersaturated organotin solution. Slow cooling and standing promote uniform growth of organotin crystal nuclei, resulting in uniform particles of suitable size for easy filtration. Experiments have shown that rapid cooling causes some organotin crystals to incompletely develop, resulting in finer particles that are difficult to filter and may even form an oily substance, reducing the organotin recovery rate. Seed crystals can be added during the crystallization process to promote organotin crystallization. Without seed crystals, the supersaturated solution easily forms an oily substance, prolonging the organotin crystallization time. Typically, the solidification and crystallization of the oily substance takes more than 48 hours, and complete crystal precipitation requires more than 70 hours. If the temperature is too high, the crystallization time is correspondingly prolonged, reducing recovery efficiency and the organotin yield. The crystals precipitated from the crystallization are covered with a small amount of oligomers, mainly low-polyester compounds. Direct reuse of these oligomers would reduce the performance of the organotin catalyst, decrease reaction efficiency, prolong reaction time, and increase process byproducts. Therefore, they need to be removed. This is achieved by adding alkaline solution, controlling the pH between 8 and 14, and maintaining the temperature between 25 and 60°C, and immersing for 3-5 hours. Under alkaline conditions, the ester carbon of the oligomers is attacked by -OH groups, generating carboxylic acid and alcohol anions via the tetrahedral intermediate of the ester carbon. These anions neutralize in the alkaline environment to form carboxylate and alcohol groups, thereby reducing their adhesion to the crystal surface and facilitating separation from the crystal surface. This results in flocculent material that floats on the upper layer of the aqueous phase, achieving efficient separation from the recovered organotin. After purification, the crystals containing the separated oligomers yield organotin that meets the requirements for a catalyst.

[0023] According to the applicant's experiments, the yield of organotin recovered by this invention reaches over 77%. Compared with commercially available organotin, the amount of organotin used to achieve the same catalytic efficiency is only 3%-4%, with no significant increase. The product process yield is ≥93%, and there are no significant differences in product color, impurity generation amount, and types.

[0024] The following is a further explanation of specific implementation methods. Detailed Implementation

[0025] In this invention, the organotin catalyst used is an organotin compound with alkyl branches having 4-12 carbon atoms. For example, the content of dibutyltin oxide (Nantong Aidewang Chemical Co., Ltd.) is ≥98%, the content of diethylene glycol vinyl ether acrylate (produced by Chongqing Chemical Research Institute Co., Ltd.) is ≥99.0%, the content of phenothiazine is ≥99.0%, and the content of nitroxide free radical compounds is ≥98%.

[0026] Example 1:

[0027] 400g of the distillate from vinyl ether acrylate was taken and analyzed by GC. The organotin content was 31.8%, and the mass was approximately 127g. The mixture was allowed to stand at 20℃ for 72 hours until a large amount of crystals precipitated in the residue. After filtration, 280g of filtrate and 120g of crystals were obtained. The filtrate was concentrated to obtain 100g of crude vinyl ether acrylate. The remaining 180g of the residue was combined with the next batch of residue. 80g of 7% NaOH aqueous solution was added to the obtained crystals, and the temperature was raised to 35℃ and maintained for 4 hours until fine flocculent matter floated in the aqueous phase. The upper organic phase was removed, and the aqueous phase was filtered to remove the alkali, yielding 113g of crystals. The crystals were washed with 80g of deionized water, and the filtrate was combined with the alkali solution. 80g of ethanol was used to wash the water and the crystals, which were then filtered to obtain 98g of crystals after drying. The organotin recovery rate was 77.1%.

[0028] Example 2:

[0029] 400g of distilled vinyl ether acrylate reaction vessel liquid was taken. Analysis showed that the organotin content was 31.8%, with a mass of approximately 127g. 4g of dibutyltin oxide powder was added, and the mixture was allowed to stand at 20℃ for 8 hours until a large amount of crystals precipitated in the vessel residue. The mixture was then filtered, yielding 268g of filtrate and 136g of crystals. The filtrate was concentrated to obtain 97g of crude vinyl ether acrylate. The remaining 171g of vessel liquid was combined with the next batch of vessel liquid. 90g of 8% NaOH aqueous solution was added to the obtained crystals, and the mixture was heated to 30℃ and maintained at this temperature for 3 hours until fine flocculent matter floated in the aqueous phase. The upper organic phase was removed, and the aqueous phase was filtered to remove the alkali, yielding 121g of crystals. The crystals were washed with 90g of deionized water, and the filtrate was combined with the alkali solution. The crystals were washed with 80g of cyclohexane and filtered, yielding 105g of dried crystals. The organotin recovery rate was 79.5%.

[0030] Example 3:

[0031] 63g of the organotin compound recovered in Example 1, 1550g of diethylene glycol vinyl ether, 2300g of methyl acrylate, 3.2g of phenothiazine, and 0.4g of nitroxide free radical piperidine alcohol compound were added to a 5L reactor equipped with a distillation column. The mixture was stirred to dissolve, and the temperature was slowly raised to 80-90°C and maintained for 1 hour until a light component slowly distilled from the top of the distillation column (temperature at the top of the column: 45-55°C). Once no more light components distilled, the reactor was slowly evacuated to -0.05 MPa to remove unreacted methyl acrylate. The vacuum was then increased to -0.09 MPa, removing 2120g of the crude product, namely diethylene glycol vinyl ether acrylate, leaving 198g of reactor liquid. GC analysis determined the crude product content to be 93.5%.

[0032] Example 4:

[0033] 63g of the organotin compound recovered in Example 2, 1550g of diethylene glycol vinyl ether, 2300g of methyl acrylate, 3.2g of phenothiazine, and 0.4g of nitroxide free radical piperidine alcohol compound were added to a 5L reactor equipped with a distillation column. The mixture was stirred to dissolve, and the temperature was slowly raised to 80-90°C and maintained for 1 hour until a light component slowly distilled from the top of the distillation column (temperature at the top of the column: 45-55°C). Once no more light components distilled, the reactor was slowly evacuated to -0.05 MPa to remove unreacted methyl acrylate. The vacuum was then increased to -0.09 MPa, removing 2130g of the crude product, namely diethylene glycol vinyl ether acrylate, leaving 200g of reactor liquid. GC analysis showed the crude product content to be 93.3%.

[0034] Compare with Example 1:

[0035] 63g of a commercially available organotin compound, 1550g of diethylene glycol vinyl ether, 2300g of methyl acrylate, 3.2g of phenothiazine, and 0.4g of a nitroxide-free radical piperidine alcohol compound were added to a 5L reactor equipped with a distillation column. The mixture was stirred to dissolve, and the temperature was slowly raised to 80-90℃ and maintained for 1 hour. Light components were slowly distilled from the top of the distillation column, with the column tip temperature at 45-55℃. Once no more light components distilled, the reactor was slowly evacuated to -0.05 MPa to remove unreacted methyl acrylate. The vacuum was then increased to -0.09 MPa, removing 2123g of the crude product, namely diethylene glycol vinyl ether acrylate, leaving 197g of the reactor liquid. GC analysis determined the crude product content to be 93.6%.

Claims

1. A method for recovering organotin from transesterification solutions of vinyl ether compounds, characterized in that, Includes the following steps: 1) Take the transesterification solution of vinyl ether compounds, cool it to -10-40℃, let it stand until crystals precipitate in the transesterification solution, and filter it; or, cool it to -10-40℃, add 0.1-5% organotin powder by mass of the transesterification solution to the transesterification solution, stir and mix well, let it stand until crystals precipitate in the transesterification solution, and filter it. 2) Add an alkaline solution with a concentration of 5-8 wt% to the filtered crystals at a mass ratio of 1:0.5-10, heat to 25-60℃, and maintain the temperature for 1-10 hours until flocculent matter appears on the surface of the alkaline solution. Filter the lower aqueous phase. The molecular structure of organotin is... , Among them, M1 and M2 are alkyl branches containing 4-12 carbon atoms; 3) After the filtered crystals are washed with water, they are then washed with an organic solvent and dried to obtain organotin. The organic solvent is a light alcohol, an ether, or a cyclic hydrocarbon. The light alcohol is methanol and / or ethanol, the ether is petroleum ether, and the cyclic hydrocarbon is cyclohexane.

2. The recycling method according to claim 1, characterized in that, Step 1) Cool the exchange vessel liquid to 20-30℃ and let it stand for 24-72 hours; or, Step 1) Cool the exchange vessel liquid to 20-30℃, add 0.5-1% organotin powder by mass of the exchange vessel liquid to the exchange vessel liquid, stir and mix for 5-15 minutes, and let it stand for 5-10 hours.

3. The recycling method according to claim 1, characterized in that, Step 2) Add an alkaline solution at a mass ratio of 1:0.5-2, wherein the alkaline solution is any one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and ammonia aqueous solution.

4. The recycling method according to claim 1, characterized in that, Step 2) Increase the temperature to 30-40℃.

5. The recycling method according to claim 1, characterized in that, The drying described in step 3) is drying at 40-60℃.

6. The recycling method according to claim 1, characterized in that, Step 1) Repeat step 1 with the separated filtrate.

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