Removal of metal ion impurities from N-methyl**** (NMP) —— Ion exchange method

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N-methyl**** (NMP) is a colorless and transparent oily liquid with a slight amine odor; it is highly hygroscopic and miscible with solvents such as water, alcohols, and ethers. Its melting point is -24°C, and its boiling point is 202°C; it decomposes easily in strong acidic or alkaline environments. It is widely used in the refining of high-grade lubricants, the synthesis of polymers, insulating materials, pesticides, pigments, and cleaners, among others. This solvent is an excellent dispersant for pigments (paints); it can be used in water-based coatings as well as in solvent-based coatings. The “ultimate threshold for impurities” in electronic-grade N-methyl**** (NMP) – that is, the typical limits that must be met – is currently governed in the industry by a dual standard of “SEMI C12 (G4) + internal controls of leading wafer manufacturers.” This can be summarized as “four zeros and one low”:

- Target limit for impurity categories (for product release):
- Purity ≥99.9% (on a dry basis), determined using chromatographic area normalization.
- Moisture ≤100 ppm, measured by KF titration.
- Individual metal ions ≤1 µg/kg (1 ppb); 32 elements including Fe, Cu, Na, K, Ca, Al, etc., are detected using ICP-MS.
- Individual anions (Cl⁻, SO₄²⁻, NO₃⁻) ≤50 ppb, measured by ion chromatography.

- Particle size: ≥0.1 µm and ≤100 particles per mL, as determined by an online laser particle counter.

- Chroma ≤5, measured using the platinum-cobalt colorimetry method.

- Total organic impurities ≤50 ppm, determined by GC-MS with area normalization.

On-site data from leading domestic projects such as Pingmei Shenma and Jingrui Electric Materials show that after using a combination of resin treatment, distillation, and nanofiltration, the levels of Fe³⁺ are 0.003 ppm, Cu²⁺ is 0.001 ppm, moisture content is 80 ppm, and the particle count is less than 10 particles per mL at 0.1 µm size – thus these standards can be consistently met. Summary: Achieving NMP at “99.9% + 100 ppm water + 1 ppb metals + 100 particles/mL” represents the ‘passing standard’ for electronic-grade materials” ； At the next lower level of 0.1 ppb, it represents the \"perfect score\" for 3 nm nodes. Experimental data and examples of resin \"impurity removal\": Resin used: Tulsimer® T-42H (sulfonic acid cation exchange resin). Removal efficiency: Cu²⁺ removal rate: 99.86%, residual amount: 0.0006 mg/L; Fe³⁺ removal rate: 99.83%, residual amount: 0.0049 mg/L; Zn²⁺ removal rate: 99.78%, residual amount: 0.0011 mg/L. Purity requirements met: The conductivity of the wastewater after treatment dropped to 0.98 μS/cm, which is far below the standard for high-purity analytical NMP (1.13 μS/cm), thus satisfying the purity requirements for metal ions in electronic-grade NMP solvents. Data verification: ICP-OES analysis confirmed that the T-42H resin exhibits an impressive removal efficiency for the major metal ions in wastewater. The NMP wastewater from a new energy battery manufacturer had an initial conductivity of 3.58 μS/cm and contained various metal ions. Innovative exploration: A systematic study on the ion exchange resin method. The research team innovatively turned its attention to ion exchange resin technology. This technology achieves selective adsorption through a displacement reaction between the functional groups of the resin (such as sulfonic acid groups - SO3H) and metal cations in the solution, and can be recycled via regeneration. Its potential advantages for purifying NMP waste liquid are significant: low energy consumption potential – operation at normal temperature and pressure results in a significant reduction in energy use. Avoiding heat denaturation risk: Preventing potential damage to NMP caused by high temperatures. Deep purification potential: Particularly suitable for the efficient removal of ions at low concentrations. Electronic-grade isopropyl alcohol production process: Industrial-grade IPA → Pre-filtration → Boron-removing resin column → Distillation system → Final filtration → G5-grade IPA. N-methyl**** (NMP) production process: Two-stage dehydration + ion exchange resin unit + multi-stage distillation + polishing mixed-bed. Common combination processes include molecular sieve dehydration, distillation, ion exchange, precision filtration, etc. For more project case discussions and technical exchanges, contact 13247215317. Ke Haishi, Du Sheng Resins, Liang Sheng