Industry prospect and process technology of N-methylpyrrolidone (NMP)

N-methylpyrrolidone (NMP) is an aprotic solvent, which is characterized by high polarity, high boiling point, low viscosity, low volatility, and high thermal and chemical stability. As a high-performance solvent, it is widely used in lithium-ion battery production, polymer synthesis, electronic chemicals, insulating paints and many other fields.

NMP sources can be divided into two categories: synthetic NMP and recovered NMP. Synthetic NMP refers to NMP products obtained by chemical synthesis. The industrial production route is to produce NMP products by condensation of gamma-butyrolactone (GBL) and monomethylamine as raw materials. Recovery of NMP refers to the recycling of NMP waste liquid used as a solvent after recovery and purification.

The NMP market is huge and on the rise
In the past 5-10 years, due to the rapid development of the lithium battery industry, the scale of NMP consumption has grown rapidly. In 2022, China’s NMP consumption is about 1.52 million tons, of which the consumption in the lithium field is about 1.428 million tons, accounting for about 94.0% of China’s total consumption. With the continuous expansion of the new energy vehicle market, the demand for lithium batteries has also increased. It is expected that by 2025, China’s NMP consumption will reach 3.44 million tons. Between 2022 and 2025, the compound annual growth rate of consumption will be around 31.3%. In addition to being used in the field of lithium-ion batteries, NMP can be used as photoresist removal liquid and semiconductor display panel cleaning agent in the field of electronic chemicals. In polymer synthesis, it can be used as a reaction solvent for special polymers such as para-aramid, polyphenylene sulfide (PPS) and polyimide (PI).

NMP synthesis technology
In NMP synthesis, most manufacturers use 1, 4-butanediol (BDO) dehydrogenation to produce GBL, and then ammoniation and condensation to produce NMP. Mitsubishi Chemical uses maleic anhydride hydrogenation to produce GBL, which is then ammoniated and condensed to produce NMP.
The industrial production of NMP is realized earlier and the production process is mature. At present, the industrial technical route of NMP production in the world is mainly GBL and monomethylamine condensation NMP. According to different reaction conditions, it can be divided into non-catalytic reaction and catalytic reaction, the former is the production process used by most production enterprises.
GBL and monomethylamine catalyst-free condensation NMP was developed by E. path et al in 1936, and was first industrialized by BASF in Germany and GAF in the United States, which is the most commonly used NMP production technology at present. Since the non-catalytic NMP production process often requires high temperature, pressure, high equipment requirements, high energy consumption, and the use of catalysts can reduce reaction conditions and save energy. Therefore, in recent years, many researchers at home and abroad began to pay attention to the role of catalysts in this process. In 2008, South Korea pear tree chemistry adopted ZSM molecular sieve catalytic synthesis technology, which can reduce the reaction conditions to a certain extent.

In China, Sinopec uses Cu-Zn-Cr-Zr as catalyst for BDO dehydrogenation and amination to produce NMP. Although the catalytic process has obvious advantages, due to some engineering problems (such as catalyst life, etc.), there are few industrial applications at present.

The production of NMP adopts catalytic process, and a new zeolite ZSM composite rare-earth cerium catalyst independently developed by Maige Chemical can effectively accelerate the closed-loop speed of intermediate NMH.

NMP recovery and purification market has broad prospects
The NMP industry does not have a high barrier to entry, because the downstream lithium industry continues to boom, more and more enterprises have begun to produce NMP, and the industry is getting larger and larger. Most of the NMP used as a solvent can be recycled, saving costs and reducing environmental impact. According to industry data, it takes 1,500 tons of NMP to produce a 1GWh power battery. With the rapid growth of domestic power battery production, the recycling and purification market of NMP has developed rapidly. Since 2021, the NMP recovery and purification market has witnessed explosive growth, and in the same year, a large number of NMP recovery and purification devices have been mounted in China, with a total annual recovery capacity of more than 400,000 tons. According to the power battery production trend in 2022, 825,000 tons of NMP will need to be recycled and purified throughout the year, and the recycling and purification capacity is expected to exceed one million tons.
At present, new energy vehicles have become the mainstream development trend, China is the largest production market and consumer market for new energy vehicles and power batteries, is expected in the next few years, will grow at a rate of 20% to 30% per year, NMP recycling purification still has good market development potential.

Recycling NMP is mainly divided into two modes, one is that NMP users recycle themselves to form an internal cycle, and the other is to entrust manufacturers to refine, or buy manufacturers refined NMP products. Among NMP manufacturers, there are companies specializing in synthetic products or recycled products, and there are companies with both synthetic and recycling capabilities.

NMP recycling technology
NMP recovery and purification technology includes recovery and purification of two parts, NMP tail gas recovery at present the main treatment processes are: condensation + honeycomb wheel adsorption process, condensation + water spray process and multi-stage water spray process.

1. Condensation + adsorption process: the coating tail gas is cooled first, most of the NMP is collected, and then the tail gas is treated to the standard through the adsorption runner, and the desorbed tail gas is returned to the front end.
   2, water spraying process: the use of NMP water-soluble characteristics, water absorption of NMP, so that the exhaust emission standards. Each process has its own scope of application and advantages and disadvantages, which need to be selected according to the actual production situation and engineering experience. When NMP is transferred from the tail gas to an aqueous solution or condensed into a liquid, the NMP waste liquid is formed, and its purity often fails to meet the requirements of battery production, and it needs to be further purified before it can be reused.

NMP purification technology
NMP waste liquid generally contains NMP, water, amines and other organic impurities, because the battery-grade NMP is directly used for electrode production, in order to maintain the consistency of the battery, the purity of the recovery is very high.
At present, the mainstream recycling electronic grade NMP adopts rectification technology, the difference is that the process and core equipment design are different, and the product quality and recovery rate can be achieved. Under the background of high price and high consumption of NMP, it is a general trend to choose a purification process with high quality, high yield and low consumption.

In China, Tianjin Zhongfu Environmental Protection NMP waste liquid purification system adopts core technologies such as pretreatment technology, precision distillation technology, high-precision filtration and adsorption, heat transfer network optimization and other process strengthening technologies to purify NMP solvent to battery level. It is reported that Zhongfu Environmental Protection is one of the earliest enterprises to develop NMP purification technology, as early as 2014, in cooperation with BYD to carry out NMP solvent purification and resource utilization technology research and development and transformation of results, the first in the country to build NMP solvent purification device, to achieve the reuse of NMP in the plant purification. Since then, a number of NMP solvent purification projects have been put into operation, with more than 30 related cases. It has cooperated with many leading enterprises in the lithium battery industry such as BYD, Yiwei Lithium Energy, Haichen New Energy, Bang Pu Cycle, and has a good market reputation in the field of NMP purification.