Recovery Process, How To Get High Purity NMP?

N-Methylpyrrolidone (NMP) also called N-Methyl-2-pyrrolidone, cas 872-50-4, is a colorless transparent oily liquid with a slight odor of amine. Melting point -24.4 ℃, flash point 91 ℃, boiling point 203 ℃; miscible with water, alcohols, ethers, esters, ketones, halogenated hydrocarbons, aromatic hydrocarbons, low volatility, good thermal stability and chemical stability.

It is widely used as extractant in the process of aromatic extraction, acetylene extraction, butadiene separation and desulfurization of synthesis gas, etc. It is also an important industrial solvent in the production of pesticides, engineering plastics, coatings, synthetic fibers, integrated circuits, etc. It can also be used as dispersant, dyeing agent and detergent, etc. Especially in the battery industry, in recent years, it has been used as a solvent in the production of the battery industry. Especially in the battery industry, the lithium battery industry has been developing steadily in recent years, driven by the favorable market of electric vehicles. The demand for NMP, which is mainly used in the field of lithium batteries, has increased significantly and the price has risen rapidly.

The recycling of NMP by related enterprises can also greatly reduce operating costs.

The following is the recycling process.

Neutralization: The NMP waste liquid to be treated first enters the neutralization tank, and the pH of the raw material is adjusted to be weakly acidic by low-valent concentrated sulfuric acid, and the neutralization process is carried out at room temperature and pressure.

Filtration: The neutralized NMP waste liquid then passes through the filtration equipment and the solid residue of the cartridge is cleaned periodically, and the filtration process is carried out at room temperature and pressure.

Primary dewatering, secondary dewatering, refining, kettle residue recovery: The filtered NMP wastewater enters the primary dewatering tower after preheating, and the wastewater with NMP content lower than 400ppm is extracted from the top of the tower, and the kettle material enters the secondary dewatering tower; the NMP material with 20% water content is extracted from the top of the secondary dewatering tower and returned to the primary dewatering tower for recycling, and the kettle material of the secondary dewatering tower enters the refining tower.

The NMP product is extracted from the top of the refining tower, and the refining tower kettle material is periodically discharged from the kettle residue to the intermittent recovery tower.

After a certain amount of refining tower kettle residue is accumulated and discharged into the intermittent recovery tower for centralized recovery treatment, most of the NMP in the kettle residue is extracted and returned to the primary dehydration tower for recovery again, and the remaining distillation residue is regularly packaged in drums and commissioned for treatment.

The primary dewatering tower, secondary dewatering tower, refining tower and intermittent recovery tower all operate under negative pressure and operate at 50~150 ℃.

Detailed description of the process

The process route is slightly different for the different pH values of the two NMP feedstocks for LiFePO4 and NCM/NCA. If the raw material is LiFePO4 NMP raw material, then the raw material directly enters the primary dehydration distillation column for continuous distillation through the feed pump; if the raw material is NCM/NCA NMP raw material, then the raw material needs to be mixed with the acid from the acid tank in the feed tank, and then pumped into the high-speed centrifugal equipment by the feed pump. After the separation of high-speed centrifugal equipment, the solid residue is loaded into the barrel, and the liquid material enters the primary dehydration distillation column for continuous distillation.

The water is separated from the top of the primary dehydration distillation tower, and the steam rising from the top is realized by the phase change of the condenser, and the condensed water enters the reflux tank of the first tower through the reflux pump of the first tower and part of it flows back into the tower, and the other part is extracted, and the extracted water is cooled by the intercooler of the first tower and extracted. The NMP content in the water is less than 400ppm. After the separation of the primary dehydration distillation column, the kettle liquid is NMP, a small amount of water and high boiling material, which is pumped to the secondary dehydration distillation column for continuous distillation through the first tower kettle, and a small amount of water is separated from the feed from the top, and the rising steam from the top is passed through the second tower condenser and the second tower trap to achieve phase change, the condensed material enters the second tower reflux tank and flows back into the tower through a part of the second tower reflux pump, and the other part is extracted into a tower feed tank and returned to a tower for separation through a tower feed pump.

After the separation of the second tower, the kettle liquid discharge mainly contains NMP and a small amount of high boiling material, the moisture content of which is less than 100ppm, and is pumped to the NMP product column by the second tower kettle for continuous distillation, and the product NMP is separated from the top, and the rising steam from the top is passed through the NMP product column condenser and the NMP product column trap to achieve phase change, the condensed material enters the NMP product tower reflux tank through the NMP product tower reflux pump and part of it flows back into the tower, part of it is picked up and then enters the NMP cooler for cooling and then picked up and stored; the tower kettle picks up a small amount of NMP and high boiling mixture and flows to the NMP product tower kettle discharge tank and is picked up by the NMP product tower kettle discharge pump and disposed of in barrels.

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