阅读说明：本技术 一种用于dmac废液回收的高效节能精馏工艺 (Efficient energy-saving rectification process for recycling DMAC waste liquid ) 是由 陈小祥 朱志坤 王大春 周靖鑫 赵崇键 程维 陈利斌 许可 杨玉宇 吴水祥 于 2019-11-20 设计创作，主要内容包括：本发明公开了一种用于DMAC废液回收的高效节能精馏工艺,本发明高效节能精馏的装置系统包括浓缩塔、精馏塔、脱酸塔,其均为填料塔。为降低精馏过程中DMAC的分解,本发明高效节能精馏的装置系统采用真空操作。浓缩塔与精馏塔之间设置第一蒸发器、第二蒸发器及汽液分离罐,精馏塔塔顶上升汽相作为浓缩塔再沸器的热源,脱酸塔上升汽相作为第一蒸发器的热源,以实现热量的回收,降低精馏能耗。浓缩塔采用塔釜进料,避免液体物料中的杂质流经浓缩塔塔体,造成填料堵塞,同时进精馏塔采用气相进料,避免废液中的聚合物树脂和醋酸盐堵塞精馏塔和脱酸塔。(The invention discloses an efficient energy-saving rectification process for recovering DMAC waste liquid. In order to reduce the decomposition of DMAC in the rectification process, the device system for high-efficiency energy-saving rectification adopts vacuum operation. A first evaporator, a second evaporator and a vapor-liquid separation tank are arranged between the concentration tower and the rectification tower, the ascending vapor phase at the top of the rectification tower is used as a heat source of a reboiler of the concentration tower, and the ascending vapor phase at the deacidification tower is used as a heat source of the first evaporator, so that the heat recovery is realized, and the rectification energy consumption is reduced. The concentration tower adopts tower cauldron feeding, avoids the impurity among the liquid material to flow through the concentration tower body, causes the filler to block up, and the rectifying column adopts gaseous phase feeding simultaneously, avoids polymer resin and acetate in the waste liquid to block up rectifying column and deacidification tower.)

1. An efficient energy-saving rectification process for recovering DMAC waste liquid is characterized by comprising the following steps of:

s1: a concentration tower reboiler (3) for heating the kettle material is arranged at the bottom of the concentration tower (1); performing pretreatment of neutralizing and filtering the DMAC waste liquid from the waste liquid tank area by using alkali liquor, feeding the DMAC waste liquid into a concentration tower (1) from the tower bottom, performing distillation concentration until the DMAC waste liquid contains 45-55 wt%, and discharging the DMAC waste liquid from the tower bottom of the concentration tower (1);

s2: mixing a material discharged from the bottom of the concentration tower (1) with a liquid discharged from a vapor-liquid separation tank (6), feeding the mixture into a first evaporator (4) for preliminary heating, then feeding the mixture into a second evaporator (5) for continuous heating to partially vaporize the mixed material, feeding the partially vaporized mixed material into the vapor-liquid separation tank (6) for vapor-liquid separation, discharging gas from the top of the vapor-liquid separation tank (6), discharging the liquid from the lower part of the vapor-liquid separation tank (6), mixing the liquid with the material discharged from the bottom of the concentration tower (1), and returning the liquid into the first evaporator (4) again for heating;

s3: gas discharged from the top of the gas-liquid separation tank (6) enters a rectifying tower (7) for rectification, a rectifying tower reboiler (8) for heating kettle materials of the rectifying tower (7) is arranged at the bottom of the rectifying tower (7), steam at the top of the rectifying tower (7) is condensed and then divided into two parts to be discharged, one part of the steam flows back into the top of the rectifying tower (7), and the other part of the steam is taken as a top product to be discharged;

s4: the deacidification tower (9) and the rectification tower (7) share one reboiler, part of vapor rising from the tower kettle of the rectification tower (7) flows out of the rectification tower (7) and enters the tower kettle of the deacidification tower (9), and liquid in the tower kettle of the deacidification tower (9) flows back to the tower kettle of the rectification tower (7); the vapor at the top of the deacidification tower (9) is condensed and then divided into two parts to be discharged, one part of the vapor flows back to the top of the deacidification tower (9), and the other part of the vapor is taken as a DMAC finished product and is extracted;

wherein in step S2, the bottom of the vapor-liquid separation tank (6) periodically discharges the deposited solid-containing materials.

2. The efficient energy-saving rectification process for recovering the DMAC waste liquid according to claim 1, characterized in that in the step S1, the theoretical plates of the concentration tower (1) are 10-30, the operation reflux ratio is 0.5-2, the tower operation pressure is controlled to be 5-15 kpa, the tower bottom temperature is 45-60 ℃, and the tower top temperature is 40-50 ℃; the concentration tower (1), the rectifying tower (7) and the deacidification tower (9) all adopt packed tower devices.

3. The efficient energy-saving rectification process for recovering the DMAC waste liquid according to claim 1, wherein in the step S3, the number of theoretical plates of a rectification tower (7) is 15-35, the operational reflux ratio of the rectification tower is 0.4-2.5, the tower operational pressure is controlled to be 25-40 kpa, the tower bottom temperature is 110-130 ℃, and the tower top temperature is 60-75 ℃; in step S2, the mixed material is heated to 80-90 ℃ by the first evaporator (4), and then enters the second evaporator (5) to be continuously heated to 85-100 ℃.

4. The high-efficiency energy-saving rectification process for recovering the DMAC waste liquid according to claim 3, wherein in the step S3, the gas discharged from the top of the vapor-liquid separation tank (6) enters the rectification tower from 8 th to 12 th theoretical plates of the rectification tower (7) for rectification.

5. The high-efficiency energy-saving rectification process for recovering the DMAC waste liquid according to claim 1, characterized in that the operating reflux ratio of the deacidification tower (9) is 0.3-1.5, the operating pressure of the tower is 25-40 kpa, the temperature of the bottom of the tower is 125-130 ℃, and the temperature of the top of the tower is 120-125 ℃.

6. The high-efficiency energy-saving rectification process for recovering the DMAC waste liquid according to claim 1, characterized in that the concentration tower reboiler (3) adopts a tubular heat exchanger structure, the bottoms of the concentration tower (1) enter a tube side of the concentration tower reboiler (3), and the overhead vapor of the rectification tower (7) enters a shell side of the concentration tower reboiler (3) for condensation and is used as a heat source for heating the bottoms of the concentration tower (1).

7. The high-efficiency energy-saving rectification process for recovering the DMAC waste liquid according to claim 1, characterized in that the first evaporator (4) adopts a tubular heat exchanger structure, and the vapor at the top of the deacidification tower (9) enters the shell side of the first evaporator (4) for condensation and is used as a heat source for heating the tube side material of the first evaporator (4).

8. The efficient energy-saving rectification process for DMAC spent liquor recovery as claimed in claim 1, wherein in step S1, the DMAC spent liquor from the spent liquor tank field is composed of the following components in percentage by weight: 10% -40% of DMAC, 0.5% -2% of polymer resin, 0.5% -3% of acetate and 55% -88% of water.

9. The efficient energy-saving rectification process for DMAC waste liquid recovery as claimed in claim 1, wherein in step S1, the DMAC waste liquid is neutralized to neutrality by lye.

Technical Field

The invention relates to the field of DMAC separation and purification, in particular to an efficient energy-saving rectification process for DMAC waste liquid recovery.

Background

Dimethylacetamide (DMAC) is a strong polar aprotic solvent, can be completely dissolved with water, ether, ketone, ester and the like, has the characteristics of high thermal stability, low possibility of hydrolysis, low corrosivity and the like, and has wide application. The compound has good solubility to various resins, particularly polyurethane resin and polyimide resin, is commonly used for producing polyimide films, soluble polyimide, polyimide-polyfluorinated ethylene propylene composite films, polyimide (aluminum) films, soluble polyimide molding powder, macromolecular synthetic fiber spinning and other excellent polar solvents for organic synthesis and the like, and generates a large amount of DMAC-containing wastewater in the using process, so that the DMAC recovery treatment of the wastewater is of great significance.

At present, extraction method and rectification method are main treatment methods for wastewater containing DMAC. Wherein, the extraction method needs to additionally introduce an extractant, the rectification product often contains a small amount of the extractant, which causes great influence on secondary use, and the use amount of the extractant is large, which causes secondary pollution. The rectification method is another common DMAC recovery method, and the recovery process generally adopts a two-tower purification method, so that the DMAC recovery rate can reach 98%. Chinese patent CN108276302 discloses a process and system for dewatering, refining and recovering DMAC, DMF or DMSO waste liquid, which is used for treating DMAC, DMF or DMSO or similar waste liquid containing metal elements, acids and the like. Although the technology adopts a multi-effect energy-saving process, the steam heat at the top of the deacidification tower is not utilized, and the energy consumption is still high. Meanwhile, DMAC is subjected to higher temperature in the production process of the film, part of DMAC is decomposed to generate dimethylamine and acetic acid, usually, NaOH is added into the wastewater for neutralization before rectification and recovery, so that the wastewater contains a small amount of sodium acetate; meanwhile, as DMAC is contacted with a large amount of resin in the using process, part of the resin can be carried out along with the solvent, so that the waste water can contain a small amount of resin. The technology can not effectively treat the waste water containing resin and acetate, and easily causes the blockage of the rectifying tower filler and the reboiler, and the defects are obvious.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention aims to provide an energy-saving and emission-reducing efficient energy-saving rectification process for DMAC waste liquid recovery by combining a double-effect rectification method and heat integration.

In order to solve the problems, the device system adopted by the invention for realizing the process method is as follows:

a three-tower double-effect rectification system for recovering DMAC wastewater comprises a concentration tower, a rectification tower and an acid removal tower which are all packed towers. A first evaporator, a second evaporator and a vapor-liquid separation tank are arranged between the concentration tower and the rectification tower, an ascending vapor phase at the top of the rectification tower is used as a heat source of a reboiler of the concentration tower, and an ascending vapor phase at the deacidification tower is used as a heat source of a first reboiler, so that heat recovery is realized, and the energy consumption of rectification is reduced. In order to reduce the decomposition of DMAC in the rectification process, the system adopts vacuum operation.

The high-efficiency energy-saving rectification process for recovering the DMAC waste liquid is characterized by comprising the following steps of:

s1: a reboiler of the concentration tower for heating the kettle material is arranged at the bottom of the concentration tower; performing pretreatment of neutralizing and filtering DMAC waste liquid from a waste liquid tank area by using alkali liquor, feeding the DMAC waste liquid into a concentration tower from the tower bottom of the concentration tower, distilling and concentrating until the DMAC waste liquid contains 45-55 wt%, and discharging from the tower bottom of the concentration tower;

s2: mixing the material discharged from the bottom of the concentration tower with the liquid discharged from the vapor-liquid separation tank, then entering a first evaporator for preliminary heating, then entering a second evaporator for continuous heating to partially vaporize the mixed material, then entering the vapor-liquid separation tank for vapor-liquid separation, discharging the gas from the top of the vapor-liquid separation tank, discharging the liquid from the lower part of the vapor-liquid separation tank, mixing the liquid with the material discharged from the bottom of the concentration tower, and then returning the liquid back to the first evaporator for heating;

s3: gas discharged from the top of the vapor-liquid separation tank enters a rectifying tower for rectification, a rectifying tower reboiler for heating kettle materials of the rectifying tower is arranged at the bottom of the rectifying tower, vapor at the top of the rectifying tower is condensed and then is divided into two parts to be discharged, one part of the vapor flows back into the top of the rectifying tower, and the other part of the vapor is taken as a tower top product;

s4: the deacidification tower and the rectification tower share one reboiler, part of vapor rising from the tower kettle of the rectification tower flows out of the rectification tower and enters the tower kettle of the deacidification tower, and liquid in the tower kettle of the deacidification tower flows back to the tower kettle of the rectification tower; condensing the tower top vapor of the deacidification tower, dividing the condensed tower top vapor into two parts, discharging the two parts, refluxing one part of the condensed tower top vapor to the tower top of the deacidification tower, and extracting the other part of the condensed tower top vapor as a DMAC finished product; wherein in step S2, the bottom of the vapor-liquid separation tank periodically discharges the deposited solid-containing material.

The efficient energy-saving rectification process for recovering the DMAC waste liquid is characterized in that in the step S1, 10-30 theoretical plates of a concentration tower are arranged, the operating reflux ratio is 0.5-2, the tower operating pressure is controlled to be 5-15 kpa, the tower bottom temperature is 45-60 ℃, and the tower top temperature is 40-50 ℃; the concentration tower, the rectifying tower and the deacidification tower all adopt packed tower devices.

The efficient energy-saving rectification process for recovering the DMAC waste liquid is characterized in that in the step S3, 15-35 theoretical plates of a rectification tower are arranged, the operational reflux ratio of the rectification tower is 0.4-2.5, the operational pressure of the rectification tower is controlled to be 25-40 kpa, the temperature of the bottom of the tower is 110-130 ℃, and the temperature of the top of the tower is 60-75 ℃; in step S2, the mixed material is heated to 80-90 ℃ by the first evaporator and then enters the second evaporator to be continuously heated to 85-100 ℃.

The efficient energy-saving rectification process for recycling the DMAC waste liquid is characterized in that in the step S3, gas discharged from the top of the vapor-liquid separation tank enters a rectifying tower from 8 th to 12 th theoretical plates of the rectifying tower for rectification.

The efficient energy-saving rectification process for recovering the DMAC waste liquid is characterized in that the operating reflux ratio of the deacidification tower is 0.3-1.5, the tower operating pressure is 25-40 kpa, the tower bottom temperature is 125-130 ℃, and the tower top temperature is 120-125 ℃.

The efficient energy-saving rectification process for recycling the DMAC waste liquid is characterized in that a tube type heat exchanger structure is adopted in a reboiler of the concentration tower, kettle materials of the concentration tower enter a tube pass of the reboiler of the concentration tower, steam at the top of the rectification tower enters a shell pass of the reboiler of the concentration tower to be condensed, and the steam is used as a heat source to heat the kettle materials of the concentration tower.

The efficient energy-saving rectification process for recycling the DMAC waste liquid is characterized in that the first evaporator adopts a tubular heat exchanger structure, and vapor at the top of the deacidification tower enters the shell side of the first evaporator to be condensed and is used as a heat source to heat materials on the tube side of the first evaporator.

The high-efficiency energy-saving rectification process for recovering the DMAC waste liquid is characterized in that in the step S1, the DMAC waste liquid from the waste liquid tank area consists of the following components in percentage by weight: 10% -40% of DMAC, 0.5% -2% of polymer resin, 0.5% -3% of acetate and 55% -88% of water.

The high-efficiency energy-saving rectification process for recycling the DMAC waste liquid is characterized in that in the step S1, the DMAC waste liquid is neutralized to be neutral by alkali liquor.

Compared with the prior art, the invention has the following advantages:

1) the invention adopts a double-effect rectification process, effectively recovers the condensation heat at the tower top of the deacidification tower, and has obvious energy-saving effect compared with the traditional process;

2) the concentration tower adopts tower cauldron feeding, avoids the impurity among the liquid material to flow through the concentration tower body, causes the filler to block up, and the rectifying column adopts gaseous phase feeding simultaneously, avoids polymer resin and acetate in the waste liquid to block up rectifying column and deacidification tower.

Drawings

FIG. 1 is a schematic diagram of the apparatus flow of an energy-efficient rectification process for DMAC spent liquor recovery.

Wherein: 1-a concentration column; 2-condensation tower condenser; 3-a concentration tower reboiler; 4-a first evaporator; 5-a second evaporator; 6-a vapor-liquid separation tank; 7-a rectifying tower; 8-rectifying column reboiler; 9-deacidifying tower.

Detailed Description

The present invention is further illustrated by the following examples, which should not be construed as limiting the scope of the invention.