Views: 4 Author: Site Editor Publish Time: 2023-05-09 Origin: Site
N-Methylpyrrolidone (NMP), (N-Methyl-2-pyrrolidone) is a non-protonic solvent characterised by high polarity, high boiling point, low viscosity, low volatility, high thermal and chemical stability. It has a wide range of applications as a high-performance solvent in the production of lithium-ion batteries, polymer synthesis, electronic chemicals, insulating paints and many other fields.
NMP sources can be divided into two categories: synthetic NMP and recycled NMP. Synthetic NMP refers to the chemical synthesis of NMP products, the industrial production route is the condensation of γ-butyrolactone (GBL) and monomethylamine as raw materials to produce NMP products; recycled NMP refers to the recovery and purification of NMP waste liquid used as a solvent to achieve recycling.
In the past 5 to 10 years, due to the rapid development of the lithium industry, the scale of NMP consumption has grown rapidly. 2022 China's NMP consumption will be about 1.52 million tons, of which the lithium sector will consume about 1.428 million tons, accounting for about 94.0% of China's total consumption. As the scale of the new energy vehicle market continues to expand, the demand for lithium batteries also increases. It is expected that by 2025, China's NMP consumption will reach 3.44 million tonnes. between 2022 and 2025, the consumption compound annual growth rate is around 31.3%.
In addition to lithium-ion batteries, NMP is used in electronic chemicals as a photoresist stripper and a cleaning agent for semiconductor display panels. In polymer synthesis, it is used as a reaction solvent for specialty polymers such as para-aramids, polyphenylene sulfide (PPS) and polyimide (PI).
In NMP synthesis, the majority of producers use a process route of dehydrogenation of 1,4-butanediol (BDO) to produce GBL, followed by ammoniacal condensation to prepare NMP. Mitsubishi Chemical uses maleic anhydride hydrogenation to produce GBL, followed by ammoniacal condensation to obtain NMP.
The industrial production of NMP has been achieved earlier and the production process is mature, currently the main technical route of NMP production worldwide is the condensation of GBL and monomethylamine to produce NMP.
The catalyst-free condensation of GBL and monomethylamine to NMP was developed by E. Spath et al. in 1936 and later industrialised by BASF in Germany and GAF in the USA, and is currently the most commonly used technology for NMP production. As the catalyst-free NMP production process often requires high temperature and pressure, high equipment requirements and energy consumption, and the use of catalysts can reduce the reaction conditions and save energy. In 2008, Irisu Chemical in Korea adopted the ZSM molecular sieve catalytic synthesis technology, which can reduce the reaction conditions to a certain extent.
The NMP industry does not have a high barrier to entry and as the downstream lithium industry continues to boom, more and more companies are producing NMP and the industry is getting bigger and bigger. The vast majority of NMP used as a solvent can be recycled, saving costs and reducing the impact on the environment. According to industry data, the production of 1GWh power battery requires the consumption of 1,500 tons of NMP. with the rapid growth of domestic power battery production, the NMP recycling and purification market is developing rapidly. since 2021, the NMP recycling and purification market is growing explosively, in the same year, China launched a large number of NMP recycling and purification devices, the total annual recycling capacity of more than 400,000 tons. According to the trend of power battery production in 2022, there will be 825,000 tons of NMP 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, the annual growth rate of 20% to 30%, NMP recovery and purification still has a good market development potential.
There are two main modes of recycling NMP: one is for NMP users to recycle themselves, forming an internal cycle, and the other is to commission manufacturers to refine, or to purchase refined NMP products from manufacturers. Among the NMP producers, there are both those specialising in synthetic or recycled products, and those with both synthetic and recycling capabilities.
NMP recovery and purification technology includes two parts: recovery and purification. The current main treatment processes for NMP tail gas recovery are: condensation + honeycomb rotor adsorption process, condensation + water spraying process and multi-stage water spraying process.
1. Condensation + adsorption process:
The coating tail gas is first cooled to collect most of the NMP in it, and then the tail gas is treated to meet the standard by means of an adsorption rotor, while the desorbed tail gas is returned to the front end.
2、Water spraying process:
Using the characteristics of good water solubility of NMP, water is used to absorb NMP so that the tail gas can meet the emission standards.
Each process has its own scope of application and advantages and disadvantages, and needs to be selected according to the actual production situation and engineering experience. When NMP is transferred from the tail gas from the aqueous solution or condensed into a liquid, it forms an NMP waste stream, the purity of which often fails to meet the requirements of battery production and needs to be further purified before it can be reused.
NMP waste streams generally contain NMP, water, amines and other organic impurities. As battery-grade NMP is used directly in electrode fabrication, the purity requirements are extremely high in order to maintain cell consistency and therefore the purity requirements for recycling are strict.
At present, the mainstream recycling system for electronic grade NMP uses distillation technology, the difference lies in the process and core equipment design, the product quality and recovery rate that can be achieved varies greatly. In the context of the high price of NMP and the surge in usage, the trend is to choose a high quality, high yield, low consumption purification process.