阅读说明：本技术 一种废溶剂的处理方法 (Treatment method of waste solvent ) 是由 陈国平 林辉荣 何睿鸣 左姣 倾彩霞 毛小英 阳杨 于 2020-07-17 设计创作，主要内容包括：本发明涉及废液处理领域,公开了一种废溶剂的处理方法,包括以下步骤：(1)减压蒸馏：将清洗后的废溶剂通入到蒸发器中进行减压蒸馏,使废溶剂蒸汽经蒸发器顶部冷凝后液体进入到溶剂接收中间槽内；(2)干燥回收：将固液混合杂质通入到干燥器中进行加热,使气相部分溶剂经冷凝后流入到溶剂接收中间槽内；(3)初次减压精馏：将溶剂接收中间槽内的溶剂通入到精馏塔一中,精馏塔一的塔顶采出轻组分杂质,精馏塔一的塔釜采出产品混合物；(4)二次减压精馏：将产品混合物通入到精馏塔二中,精馏塔二的塔顶采出单乙醇胺,精馏塔二的塔釜采出乙二醇。本发明能够用以解决现有技术中采用焚烧方式处理废溶剂而造成废溶剂中有价值的成分浪费的问题。(The invention relates to the field of waste liquid treatment, and discloses a waste solvent treatment method, which comprises the following steps: (1) and (3) reduced pressure distillation: introducing the cleaned waste solvent into an evaporator for reduced pressure distillation, and condensing waste solvent steam through the top of the evaporator to obtain liquid which enters a solvent receiving intermediate tank; (2) drying and recovering: introducing solid-liquid mixed impurities into a dryer for heating, and enabling the gas-phase partial solvent to flow into a solvent receiving intermediate tank after being condensed; (3) primary vacuum rectification: introducing the solvent in the solvent receiving intermediate tank into a first rectifying tower, extracting light component impurities from the top of the first rectifying tower, and extracting a product mixture from the bottom of the first rectifying tower; (4) and (3) secondary vacuum rectification: and introducing the product mixture into a second rectifying tower, extracting monoethanolamine from the top of the second rectifying tower, and extracting ethylene glycol from the bottom of the second rectifying tower. The invention can be used for solving the problem of waste of valuable components in the waste solvent caused by treatment of the waste solvent by adopting an incineration mode in the prior art.)

1. A method for treating a waste solvent, which is characterized by comprising the following steps: the method comprises the following steps:

(1) and (3) reduced pressure distillation: introducing the cleaned waste solvent into an evaporator for reduced pressure distillation, condensing waste solvent steam through the top of the evaporator, and introducing liquid into a solvent receiving intermediate tank, wherein solid-liquid mixed impurities are extracted from the bottom of the evaporator;

(2) drying and recovering: introducing solid-liquid mixed impurities into a dryer for heating, condensing a gas phase part of solvent, flowing into a solvent receiving intermediate tank, discharging dried solid phase impurities, and performing hazardous waste treatment;

(3) primary vacuum rectification: introducing the solvent in the solvent receiving intermediate tank into a first rectifying tower for vacuum rectification, collecting light component impurities from the tower top of the first rectifying tower, and collecting a product mixture from the tower bottom of the first rectifying tower;

(4) and (3) secondary vacuum rectification: and introducing the product mixture into a second rectifying tower for vacuum rectification, wherein monoethanolamine is extracted from the tower top of the second rectifying tower, and ethylene glycol is extracted from the tower bottom of the second rectifying tower.

2. The method for treating a waste solvent according to claim 1, wherein: in the step (1), the internal vacuum degree of the evaporator is 10-30 kPa, and the temperature of the top of the evaporator during condensation is 40-60 ℃.

3. The method for treating a waste solvent according to claim 2, wherein: the evaporator is a scraper film evaporator.

4. A method for treating a used solvent according to claim 3, wherein: in the step (1), the non-condensable gas condensed from the top of the evaporator is absorbed by a tail gas collecting device.

5. The method for treating a waste solvent according to claim 1, wherein: in the steps (3) and (4), continuous rectification is adopted for the reduced pressure rectification.

6. The method for treating a waste solvent according to claim 5, wherein: in the step (3), the light component impurities comprise ethylene glycol methyl ether, propylene glycol methyl ether, dimethylformamide, water and residual trimethylamine.

7. The method for treating a waste solvent according to claim 6, wherein: in the step (3), the product mixture comprises monoethanolamine, ethylene glycol and residual light component impurities.

8. The method for treating a waste solvent according to claim 7, wherein: the amount of the residual light component impurities is controlled to be less than 0.005 percent.

9. The method for treating a waste solvent according to claim 1, wherein: in the step (3), the number of feeding tower plates is 20-30, the number of tower plates of the first rectifying tower is 40-60, the reflux ratio is 1.5-4, and the tower top pressure of the rectifying tower is 5-20 kPa.

10. The method for treating a waste solvent according to claim 9, wherein: in the step (4), the number of feeding tower plates is 25-30, the number of tower plates of the second rectifying tower is 50-70, the reflux ratio is 3-5, and the tower top pressure of the second rectifying tower is 3-10 kPa.

Technical Field

The invention relates to the field of waste liquid treatment, in particular to a method for treating a waste solvent.

Background

The PI (polyimide) film is a uniform alignment film on the surfaces of the TFT and CF substrates, and can make the liquid crystal molecules arranged according to a certain pretilt angle, thereby controlling the light passing direction and achieving the purpose of display through proper driving voltage. In the actual PI film coating process, the coating effect of the PI film is often affected by the state of the TFT or CF substrate surface. The PI solution is generally a hydrophilic substance and tends to diffuse unevenly on the surface where many organic substances remain, and such uneven diffusion is generally referred to as PI non-staining. Due to the non-sticking existence of PI, the broken bright points of the TFT-LCD product are often caused, and the quality of the product is influenced. Therefore, before the PI is coated on the TFT or CF substrate, the substrate is usually cleaned by using a cleaning agent, in order to slightly modify organic substances on the surface of the substrate, thereby increasing the coatability of the substrate and forming a uniform and dense PI film on the surface of the substrate. The waste solvent after cleaning contains more organic matters, such as: trimethylamine, ethylene glycol methyl ether, propylene glycol methyl ether, monoethanolamine, dimethylacetamide, ethylene glycol and the like, and if the trimethylamine, ethylene glycol methyl ether, monoethanolamine, dimethylacetamide and ethylene glycol are directly discharged, environmental pollution is caused.

The existing treatment method is mainly incineration disposal, but because the waste solvent contains a large amount of nitrogen, a large amount of nitrogen oxides NO are generated after combustion_XAnd carbon dioxide CO₂The waste solvent contains valuable components such as ethylene glycol, monoethanolamine and the like, so that the waste solvent is lost by direct incineration, and further energy waste is caused by consumption of a large amount of energy required by incineration.

Disclosure of Invention

The invention aims to provide a method for treating a waste solvent, which aims to solve the problem that valuable components in the waste solvent are wasted due to the fact that the waste solvent is treated in an incineration mode in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme: a method for treating a spent solvent, comprising the steps of:

(1) and (3) reduced pressure distillation: introducing the cleaned waste solvent into an evaporator for reduced pressure distillation, condensing waste solvent steam through the top of the evaporator, and introducing liquid into a solvent receiving intermediate tank, wherein solid-liquid mixed impurities are extracted from the bottom of the evaporator;

(2) drying and recovering: introducing solid-liquid mixed impurities into a dryer for heating, condensing a gas phase part of solvent, flowing into a solvent receiving intermediate tank, discharging dried solid phase impurities, and performing hazardous waste treatment;

(3) primary vacuum rectification: introducing the solvent in the solvent receiving intermediate tank into a first rectifying tower for vacuum rectification, collecting light component impurities from the tower top of the first rectifying tower, and collecting a product mixture from the tower bottom of the first rectifying tower;

(4) and (3) secondary vacuum rectification: and introducing the product mixture into a second rectifying tower for vacuum rectification, wherein monoethanolamine is extracted from the tower top of the second rectifying tower, and ethylene glycol is extracted from the tower bottom of the second rectifying tower.

The principle and the advantages of the scheme are as follows: in practical application, impurities such as solid, non-condensable gas and the like in the waste solvent are removed through reduced pressure distillation, then liquid in the waste solvent is heated and evaporated to form a gas phase through drying solid-liquid mixed impurities at the bottom of an evaporator, and the gas phase is condensed and then returned to a solvent receiving intermediate tank to recover the solvent discharged in the reduced pressure distillation process, so that the loss of the solvent is reduced, and the yield of the ethylene glycol and the monoethanolamine is improved. Then, carrying out vacuum rectification twice, carrying out rectification for the first time to remove light component impurities in the waste solvent to obtain a product mixture of monoethanolamine and ethylene glycol, and carrying out rectification separation and purification for the second time to obtain monoethanolamine and ethylene glycol.

1. According to the scheme, valuable solvents such as ethylene glycol, monoethanolamine and the like in the waste solvent are recycled through reduced pressure distillation and rectification, waste is changed into valuable, a new economic growth point is created, the environmental protection is facilitated, and the emission of CO2 and NOX is reduced; meanwhile, the relative volatility can be changed through vacuum rectification, and monoethanolamine (atmospheric boiling point 165 ℃) and dimethylacetamide (atmospheric boiling point 170 ℃) which are difficult to separate under normal pressure are separated and purified to obtain a monoethanolamine product; further, the occurrence of polymerization between substances caused by an excessively high heating temperature can be prevented by reducing the pressure.

2. According to the scheme, drying is arranged between distillation and rectification, solid-liquid mixed impurities extracted by distillation are heated and dried, so that liquid in the solid-liquid mixed impurities is heated and evaporated to form a gas phase, and then the gas phase is condensed and returned to a solvent receiving intermediate tank to recover the solvent discharged from the bottom of an evaporator in the vacuum distillation process, so that the loss of the glycol and monoethanolamine solvent is reduced, and the yield of the glycol and monoethanolamine is improved; in addition, organic solvents such as waste solvents and the like are removed from the dried solid-phase impurities, so that the solid-phase impurities can be better treated, and the negative influence of the waste solvents in the treatment process is avoided.

Preferably, as an improvement, in the step (1), the vacuum degree in the evaporator is 10-30 kPa, and the temperature of the top of the evaporator during condensation is 40-60 ℃. Under the condition, the waste solvent can be better distilled, and the subsequent purification influenced by the reaction among substances can be avoided by utilizing reduced pressure distillation.

Preferably, as a refinement, the evaporator is a wiped film evaporator. The waste solvent is subjected to solid removal, impurity removal and decoloration through the scraper film evaporator, so that the energy consumption can be reduced, and the efficiency can be improved.

Preferably, as an improvement, in the step (1), the non-condensable gas condensed from the top of the evaporator is subjected to absorption treatment by a tail gas collecting device. The non-condensable gas is mainly a trimethylamine solvent, and is subjected to adsorption treatment through the tail gas paving device, so that the non-condensable gas is prevented from being directly discharged to cause environmental pollution.

Preferably, as an improvement, in the steps (3) and (4), the vacuum distillation adopts continuous distillation. So as to carry out continuous production, the in-process need not artifical feeding many times, is favorable to reducing staff occupational disease's risk, and practices thrift the energy consumption, improves production efficiency.

Preferably, as an improvement, in the step (3), the light component impurities include ethylene glycol methyl ether, propylene glycol methyl ether, dimethylformamide, water and residual trimethylamine. The relative volatility among all the components is changed through vacuum rectification, so that the components are separated from the product, particularly the dimethyl formamide and the monoethanolamine in the impurities can be well separated, and the purity and the yield of the monoethanolamine are improved.

Preferably, as a refinement, in step (3), the product mixture includes monoethanolamine, ethylene glycol and residual light component impurities. The main product obtained from the bottom of the second kettle of the rectifying tower after primary rectification and a small amount of residual light component impurities.

Preferably, as an improvement, the amount of the remaining light component impurities is controlled to 0.005% or less. The amount of residual light component impurities is strictly controlled, and excessive impurities in the feed of the second rectifying tower are avoided, so that the quality of the final product is ensured, and the final product can reach the standard better.

Preferably, as an improvement, in the step (3), the number of feed trays is 20-30, the number of trays in the first rectifying tower is 40-60, the reflux ratio is 1.5-4, and the top pressure of the rectifying tower is 5-20 kPa. Under this condition, can separate light component impurity and product better, the edulcoration effect is best, can also guarantee the quality of product simultaneously.

Preferably, as an improvement, in the step (4), the number of feed trays is 25-30, the number of trays of the second rectifying tower is 50-70, the reflux ratio is 3-5, and the tower top pressure of the rectifying tower is 3-10 kPa. Under the condition, the ethylene glycol and the monoethanolamine can be better separated, and the purity and the yield of the ethylene glycol and the monoethanolamine are improved.

Detailed Description

The following is further detailed by way of specific embodiments: