Collection | recycling process, how to obtain high purity NMP?

N-methylpyrrolidone (NMP) is a clear, colorless, oily liquid with a slight amine odor. Melting point -24.4 ℃, flash point 91 ℃, boiling point 203 ℃; It can be miscible with water, alcohol, ether, ester, ketone, halogenated hydrocarbon and aromatic hydrocarbon. Low volatility, good thermal and chemical stability.

Widely used as aromatics extraction, acetylene concentration, butadiene separation and syngas desulfurization process in the extraction agent, but also pesticides, engineering plastics, coatings, synthetic fibers, integrated circuits and other important industrial solvent production, can also be used as dispersant, dyeing agent and detergent. Especially the battery industry. In recent years, driven by the improvement of the electric vehicle market, the lithium battery industry has developed steadily. The demand for N-methylpyrrolidone (NMP), which is mainly used in the field of lithium batteries, has increased sharply and the price has risen rapidly.

The recycling of NMP by relevant enterprises can also greatly reduce operating costs. Since the boiling point of NMP is relatively high, direct recovery method can not be used, so the solvent recovery system can be used for vacuum decompression rectification. The following process route is to remove the moisture contained in the NMP raw material by decompression distillation to obtain high purity NMP.
Process flow

Give a brief introduction to each section

Neutralization: The waste liquid of NMP to be treated first enters the neutralization tank, and the weak acidity of the raw material is regulated by low price concentrated sulfuric acid. The operating temperature of the neutralization tank is normal temperature and the operating pressure is normal pressure.

The NMP waste liquid after filtration and neutralization goes through the filtration equipment, and the solid residue of the filter element is cleaned regularly. The operating temperature of the filtration process is normal temperature, and the operating pressure is normal pressure.

Primary dehydration, secondary dehydration, refining, reactor residue recovery: the filtered NMP waste liquid enters the primary dehydrating tower after preheating, and the waste water with NMP content less than 400ppm is extracted from the top of the tower, and the tower reactor materials enter the secondary dehydrating tower; The NMP material containing 20% water extracted from the top of the two-stage dehydrating tower is returned to the first-stage dehydrating tower for recycling again, and the materials of the two-stage dehydrating tower still enter the refining tower.

The NMP products are extracted from the top of the refining tower, and the materials of the refining tower are discharged periodically from the residual kettle to the intermittent recovery tower.

After a certain amount of residual in the refining tower is collected, it is put into the intermittent recovery tower for centralized recovery treatment. Most of the NMP in the residual is extracted and returned to the first-level dehydrating tower for recycling again. The remaining residual distillation liquid is regularly packed into the drum for commissioning treatment.

The primary dehydrating tower, the secondary dehydrating tower, the refining tower and the intermittent recovery tower are all operated under negative pressure, and the operating temperature is 50~150 ℃.

Detailed description of process flow

In view of the different pH values of the two NMP raw materials of lithium iron phosphate battery and lithium ternary battery, the process route is slightly different. If the raw material is NMP raw material of lithium iron phosphate battery, the raw material is directly entered into the primary dehydration rectification column through the feed pump for continuous rectification; If the feedstock is a ternary lithium battery NMP feedstock, the feedstock is mixed with the acid from the acid tank in the feed tank, and then fed by the feed pump into the high speed centrifugal equipment. After separation by high-speed centrifugal equipment, solid slag is packed into barrels, liquid materials into a primary dehydration rectification tower for continuous rectification.

The primary dehydration distillation column separates water from the top, and the steam rising from the top realizes phase transformation through the condenser. The condensed water enters a reflux tank and flows into the tower through a reflux pump, and the other part is produced. The produced water is cooled by a middle cooler in the tower and then produced. The NMP content in water is less than 400ppm. After separation by the primary dehydration distillation column, the tank liquid consists of NMP, a small amount of water and high boiling substance, which is pumped to the secondary dehydration distillation column through the first tower tank for continuous distillation. A small amount of water in the feed is separated from the top, and the steam rising from the top realizes phase transformation through the two-tower condenser and two-tower catcher. The condensed material enters the two-tower reflux tank, and part of it flows back into the tower through the two-tower reflux pump. The other part of the production into a tower feed tank, through a tower feed pump back to a tower for separation.

After separation by two towers, the discharge of kettle liquid mainly contains NMP and a small amount of high boiling substance, in which the moisture content is less than 100ppm. It is pumped to NMP product tower by two towers for continuous distillation, and NMP product is separated from the top. The steam rising from the top realizes phase transformation through the NMP product tower condenser and NMP product tower catcher. The condensed material enters the reflux tank of NMP product tower and flows partly back into the tower through the reflux pump of NMP product tower. Part of the condensed material enters the NMP cooler for cooling and then is produced and stored. A small amount of NMP and high boiling mixture is extracted from the tower kettle, which flows to the discharge tank of the tower kettle of NMP product and is extracted by the discharge pump of the tower kettle of the NMP product, and then is barreled for treatment.

The process can achieve NMP purity greater than 99.9 % and water content less than 100 ppm in NMP products.

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