1.Project Background
NMP (N-methylpyrrolidone) is a key solvent in fields such as lithium battery electrode coating and semiconductor photoresist manufacturing, featuring strong solubility and a high boiling point (202℃). With the rapid development of the new energy and semiconductor industries, the amount of impure waste liquid generated after the use of NMP has increased sharply. The traditional recovery methods have problems such as high energy consumption, low recovery rate and insufficient product purity. Moreover, the organic matter and trace metal impurities in the NMP waste liquid cause severe corrosion to the equipment. To achieve the recycling and utilization of NMP resources, reduce the production costs and environmental protection pressure of enterprises, a certain enterprise has built a 30,000-ton-per-year NMP recovery device, adopting high vacuum distillation technology and selecting 304 stainless steel as the main equipment material to ensure efficient, stable and corrosion-resistant operation.
2.Technological process
(1) Pretreatment stage
The NMP waste liquid first passes through a filter to remove solid particles, fibers and other impurities to prevent clogging of subsequent equipment. Then, through the ion exchange resin column, trace metal ions (such as Fe³⁺, Cu²⁺) in the waste liquid are adsorbed to prevent them from affecting the quality of NMP and accelerating equipment corrosion during the distillation process; Finally, adjust the pH of the waste liquid to neutral to reduce the erosion of acidic or alkaline substances on the distillation column.
(2) High vacuum distillation system
The pre-treated waste liquid enters the high vacuum distillation column (operating pressure 5-10 kpa). Under the low vacuum environment, the boiling point of NMP drops to 120-140 ℃, which is significantly lower than that under normal pressure, effectively reducing energy consumption. The tower is filled with high-efficiency structured packing to ensure full contact between gas and liquid. The light components with lower boiling points (such as water and low-boiling-point organic solvents) are distilled out from the top of the tower first, and then collected as by-products after being cooled by the condenser. High-purity NMP is enriched at the bottom of the tower and further enhanced in purity through reboiler heating and circulating distillation.
(3) Product refining and Recycling
The crude NMP product flowing out from the bottom of the distillation column enters the finished product refining tower for secondary distillation to further remove the remaining high-boiling-point impurities. The final obtained NMP product with a purity of ≥99.9% can be directly reused in processes such as lithium battery electrode coating and semiconductor photoresist production. The condensate water produced during the distillation process is discharged or reused after being treated to meet the standards, achieving the goals of resource recycling and environmental protection.
3.Technical advantage
(1) High efficiency and energy conservation
High vacuum distillation reduces the boiling point of NMP, decreases the energy required for heating, and saves more than 35% energy compared with traditional atmospheric pressure distillation. By optimizing the structure and operating parameters of the distillation column, the thermal energy utilization rate was improved, and the steam consumption was reduced to 1.2 tons per ton of NMP product.
(2) High recovery rate and purity
By adopting multi-stage distillation and vacuum environment, the recovery rate of NMP reaches over 98%, and the product purity is ≥99.9%, meeting the strict requirements for NMP quality in high-end fields and can replace imported products.
(3) Strong corrosion resistance
The main equipment is made of 304 stainless steel, which has good resistance to organic acids, alkaline additives and other substances in NMP waste liquid. The service life of the equipment is extended to more than 10 years, reducing the cost of equipment replacement and maintenance.
(4) Automation and Security Assurance
Equipped with an advanced automatic control system, it can monitor parameters such as pressure, temperature and liquid level inside the tower in real time, and automatically adjust operating conditions such as reflux ratio and heating capacity. Install vacuum system protection devices and emergency pressure relief valves to prevent equipment damage or safety accidents caused by abnormal vacuum degrees, and ensure the stable operation of the device.
4.Application field
(1) Lithium battery manufacturing industry
The recycled high-purity NMP is used in the formulation and coating process of lithium battery electrode slurry, reducing the raw material costs of enterprises, facilitating large-scale production and cost control of lithium batteries, and promoting the development of the new energy vehicle industry.
(2) Semiconductor and Electronics Industry
To meet the demand for high-purity NMP in semiconductor photoresist manufacturing and electronic component cleaning, improve the coating accuracy of photoresist and the cleaning effect of electronic components, and support the high-end development of the semiconductor industry.
(3) Other chemical engineering fields
In the fields of polyimide film production, synthesis of pesticides and pharmaceutical intermediates, etc., it is recycled as a solvent to enhance the utilization rate of enterprise resources and reduce the emission of organic solvents, which is in line with the development trend of green chemical engineering.
