阅读说明：本技术 一种三氯蔗糖生产中dmac残液的回收方法 (Method for recovering DMAC (dimethylacetamide) residual liquid in sucralose production ) 是由 张正颂 刘瑞祥 王从春 杨志健 于 2020-05-22 设计创作，主要内容包括：本发明一种三氯蔗糖生产中DMAC残液的回收方法,包括：精馏回收DMF后产生DMAC残液,将残液加入到反应釜加入氢氧化钠进行中和反应,然后进行蒸馏至干后,反应釜内得粉状醋酸钠,蒸馏冷凝后的不含酸DMAC、水、四甲基脲的混合溶液连续泵送至脱水塔进行脱水,塔底得无水的DMAC和四甲基脲的混合物进入精馏塔,塔顶通过冷凝得到高纯度的DMAC产品,塔底得到含量高达60%的四甲基脲溶液,再去进一步回收分离四甲基脲。本发明的工艺过程简单,通过对残液进一步处理,达到回收残液中有价值的DMAC,减少塔底残液的量,减少了残液回收难度,提高了溶剂回收效率,节约能耗,大大降低了生产成本,减少了污染。(The invention relates to a method for recovering DMAC residual liquid in sucralose production, which comprises the following steps: rectifying and recovering DMF to generate DMAC residual liquid, adding the residual liquid into a reaction kettle, adding sodium hydroxide into the reaction kettle for neutralization reaction, distilling until the residual liquid is dry, obtaining powdery sodium acetate in the reaction kettle, continuously pumping the distilled and condensed mixed solution which does not contain acid DMAC, water and tetramethylurea into a dehydration tower for dehydration, obtaining a mixture of anhydrous DMAC and tetramethylurea at the bottom of the tower, entering the mixture into a rectifying tower, obtaining a high-purity DMAC product through condensation at the top of the tower, obtaining a tetramethylurea solution with the content of up to 60% at the bottom of the tower, and further recovering and separating the tetramethylurea. The process is simple, the residual liquid is further treated to recover valuable DMAC in the residual liquid, the amount of the residual liquid at the bottom of the tower is reduced, the difficulty in recovering the residual liquid is reduced, the solvent recovery efficiency is improved, the energy consumption is saved, the production cost is greatly reduced, and the pollution is reduced.)

1. A recovery method of DMAC residual liquid in sucralose production comprises the steps of sending acid-containing DMF recovered in sucralose production to a rectifying tower to react with dimethylamine to generate DMAC, and generating a large amount of residual liquid containing DMAC, acetic acid, tetramethylurea and high-boiling-point impurities at the bottom of the rectifying tower after DMF is recovered by rectification, and is characterized by comprising the following steps of:

a. adding the residual liquid into a reaction kettle, and adding sodium hydroxide according to the amount of acetic acid in the residual liquid with equal molar ratio for neutralization reaction;

b. after the temperature of the reaction liquid in the neutralization reaction is not increased any more, steam is started under the condition of-0.098 MPa to distill the reaction liquid at the temperature of 60-110 ℃, distilled products are condensed to 30-50 ℃ by circulating water to obtain a mixed solution which does not contain acid DMAC, water and tetramethylurea, and after the solvent in the reaction liquid in the reaction kettle is distilled to be dry, dry powdery sodium acetate is formed in the reaction kettle;

c. continuously pumping the mixed solution without the acid DMAC, the water and the tetramethylurea to a dehydrating tower for dehydration, controlling the pressure of the dehydrating tower at-0.098 MPa and the temperature at 60-100 ℃, sending distilled wastewater to a sewage treatment station, and obtaining a mixture of the anhydrous DMAC and the tetramethylurea at the bottom of the tower;

d. feeding a mixture of anhydrous DMAC and tetramethylurea into a rectifying tower for rectification, controlling the pressure of the rectifying tower at-0.098 MPa and the temperature at 80-100 ℃, condensing the rectified gas phase to 30-50 ℃ at the tower top through circulating water, and obtaining high-purity DMAC finished product liquid; the tetramethylurea solution with the content of 60 percent is obtained at the bottom of the rectifying tower.

2. The method for recycling the DMAC raffinate in the sucralose production according to claim 1, wherein 5-10% of the total amount of the DMAC liquid with high purity obtained in step d) is extracted and refluxed into the rectifying tower to exchange heat with the rectified gas phase to form the circular distillation.

3. The method for recovering DMAC raffinate from sucralose production according to claim 1 or 2, wherein the raffinate comprises: 60% DMAC, 20% acetic acid, 20% tetramethylurea and part of high-boiling impurities.

4. The method for recovering DMAC raffinate from sucralose production according to claim 1, 2 or 3, wherein said neutralization reaction pH is from 7 to 8.

5. The method for recovering the DMAC residual liquid in the sucralose production according to claim 1, wherein the DMAC residual liquid at the top of the rectifying tower has the high purity of more than or equal to 99.5 percent by mass and the water content of less than 500ppm, and can be directly sold as a product.

6. The method for recovering the residual liquid of DMAC in the production of sucralose according to claim 1, wherein the tetramethylurea solution with the content of 60 percent is obtained at the bottom of the rectifying tower in the step d), and the light component DMAC is removed firstly through rectification, and then the high-purity tetramethylurea is rectified.

7. The method for recovering the DMAC residual liquid in the sucralose production according to claim 1, wherein the tops of the dehydrating tower and the rectifying tower are sequentially connected with a condenser, a reflux tank and a vacuum pump through pipelines, and the vacuum pump is connected to the tops of the dehydrating tower and the rectifying tower through a pipeline; the bottoms of the dehydration tower and the rectifying tower are respectively connected with the liquid phase inlet of a reboiler at the bottom of the tower, and the gas phase outlet of the reboiler is respectively connected with the middle parts of the dehydration tower and the rectifying tower.

Technical Field

The invention belongs to a method for treating a solvent in a sucralose production process in the technical field of chemical industry, and particularly relates to a method for recovering DMAC (dimethylacetamide) residual liquid in sucralose production.

Background

Sucralose is a fresh sweetener, the sweetness of which is 800 times of that of sucrose, and the sweetness of which is pure and similar to that of sucrose, and sucralose is not absorbed by human body, has no bioaccumulation and high safety, so that the sucralose industry is rapidly developed in this year, production enterprises are gradually increased, and the yield is continuously improved. DMF is used as a solvent in a large amount in the production process of sucralose, the use amount of DMF is increased along with the improvement of yield, the problem of DMF recovery of the solvent is inevitably existed in the current production process, DMF containing acetic acid is inevitably generated in the recovery process, and DMF needs to be treated and recovered, and the latest treatment process is to add dimethylamine to produce DMAC by adopting a reaction rectification method and recover DMF at the same time. But in the process of DMAC rectification, because the acid reaction is incomplete and the system contains tetramethylurea which is a byproduct in the chlorination section, the rectification tower can discharge a large amount of residual liquid which needs to be treated as dangerous waste, the prior art is to add the residual liquid into a reaction kettle according to the amount containing acetic acid with equal molar ratio to carry out neutralization reaction, steam is opened to carry out distillation after the reaction temperature is not increased, after the solvent is distilled to be dry, the residual dry powdery sodium acetate in the reaction kettle can be directly sold as a byproduct, the mixed solution containing no acid DMAC, water and tetramethylurea after distillation and condensation is continuously pumped into a dehydration tower to be dehydrated, partial reflux is extracted after the top of the dehydration tower is subjected to secondary condensation, the mixture of anhydrous DMAC and tetramethylurea at the bottom of the tower enters the rectification tower, partial reflux is extracted at the top of the tower through condensation, and a high-purity DMAC product is obtained, the tetramethylurea solution with the content as high as 60 percent is obtained at the bottom of the tower and then further recycled and separated. The process is simple, the residual liquid is further treated to recover valuable DMAC in the residual liquid, the amount of the residual liquid at the bottom of the tower is reduced, the difficulty in recovering the residual liquid is reduced, the solvent recovery efficiency is improved, the energy consumption is saved, the production cost is greatly reduced, and the pollution is reduced.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for recovering DMAC (dimethylacetamide) residual liquid in sucralose production, which has the advantages of simple operation, high efficiency, high recovery rate and low cost.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

a recovery method of DMAC residual liquid in sucralose production comprises the steps of sending acid-containing DMF recovered in sucralose production to a rectifying tower to react with dimethylamine to generate DMAC, and generating a large amount of residual liquid containing DMAC, acetic acid, tetramethylurea and high-boiling-point impurities at the bottom of the rectifying tower after DMF is recovered by rectification, and is characterized by comprising the following steps of:

a. adding the residual liquid into a reaction kettle, adding sodium hydroxide according to the amount of acetic acid in the residual liquid with equal molar ratio for neutralization reaction, determining the content of the acetic acid through central control analysis, wherein the neutralization has the function of reacting the acetic acid in a system into sodium acetate to fix the acetic acid;

b. after the temperature of the reaction liquid in the neutralization reaction is not increased any more, steam is started under the condition of-0.098 MPa to distill the reaction liquid at the temperature of 60-110 ℃, distilled products are condensed to 30-50 ℃ by circulating water to obtain a mixed solution which does not contain acid DMAC, water and tetramethylurea, and after the solvent in the reaction liquid in the reaction kettle is distilled to be dry, dry powdery sodium acetate is formed in the reaction kettle;

c. continuously pumping the mixed solution without the acid DMAC, the water and the tetramethylurea to a dehydrating tower for dehydration, controlling the pressure of the dehydrating tower at-0.098 MPa and the temperature at 60-100 ℃, sending distilled wastewater to a sewage treatment station, and obtaining a mixture of the anhydrous DMAC and the tetramethylurea at the bottom of the tower;

d. feeding a mixture of anhydrous DMAC and tetramethylurea into a rectifying tower for rectification, controlling the pressure of the rectifying tower at-0.098 MPa and the temperature at 80-100 ℃, condensing the rectified gas phase to 30-50 ℃ at the tower top through circulating water, and obtaining a high-purity DMAC finished product liquid; the tetramethylurea solution with the content of 60 percent is obtained at the bottom of the rectifying tower.

The further technical scheme is that 5-10% of the total amount of the high-purity DMAC liquid obtained in the step d) is extracted and flows back to enter a rectifying tower to exchange heat with the rectified gas phase to form circulating distillation.

The further technical scheme is that the residual liquid comprises the following components: 60% DMAC, 20% acetic acid, 20% tetramethylurea and part of high-boiling impurities.

The further technical proposal is that the PH of the neutralization reaction is 7-8.

The further technical scheme is that the bottoms of the dehydration tower and the rectifying tower are respectively connected with a liquid phase inlet of a reboiler at the bottom of the tower, and a gas phase outlet of the reboiler is respectively connected with the middle parts of the dehydration tower and the rectifying tower.

The further technical scheme is that the mass percent of high-purity DMAC (dimethylacetamide) extracted from the top of the rectifying tower is more than or equal to 99.5%, the water content is less than 500ppm, and the high-purity DMAC can be directly sold as a product.

The further technical scheme is that tetramethylurea solution with the content as high as 60% is obtained at the bottom of the rectifying tower in the step d), and light component DMAC is removed firstly through rectification, and then high-purity tetramethylurea is rectified.

Compared with the prior art, the method has the advantages that the method for treating the rectified residual liquid is found, valuable DMAC in the residual liquid is recovered by further treating the residual liquid, the amount of the residual liquid at the bottom of the tower is reduced, the difficulty in recovering the residual liquid is reduced, the solvent recovery efficiency is improved, pollution caused by treatment of the residual liquid with economic value as hazardous waste is avoided, the energy consumption is saved, and the production cost is greatly reduced. The process is worthy of popularization and application.

Drawings

FIG. 1 is a process flow diagram of the process of the present invention;

FIG. 2 is a schematic view of the dehydration column of FIG. 1;

FIG. 3 is a schematic diagram of the rectifying column structure shown in FIG. 1.

Detailed Description

In order to explain technical contents, structural features, achieved objects and effects of the technical solutions in detail, the following detailed description is given with reference to specific embodiments.