N-Methylpyrrolidone (NMP) Instruction:

NMP is a high boiling point liquid with very high solubility for H2S. N-Methylpyrrolidone is particularly suitable for purification of high pressure, high CO2 content synthesis gases in gasification applications.

NMP is a solvent that evaporates very slowly. 1-methyl-2-pyrrolidone has a boiling point of 202°C. NMP takes over 15,000 seconds for a layer of NMP film to evaporate 90% at room temperature. If this is the only solvent used in a PAI or PES based coating, the viscosity will not increase rapidly after application and the coating will tend to run, drip and sag. The most effective fast evaporating solvent for these resins is DMF, but this solvent has serious safety concerns.

NMP Description:

Fortunately, fast evaporating non-solvents can be added to the formulation to provide rapid evaporation and build up viscosity during application. Common examples include hydrocarbons and ketones. Although they are non-solvents, the solubility of the entire solvent system is sufficient to keep PAI and PES in solution. The rapidly evaporating non-solvent is the first to leave the film, leaving NMP, which is a good solvent.

One of the advantages of NMP is its compatibility with water. 1-methyl-2-pyrrolidone is often used in small amounts in water-based primers. nmp absorbs moisture from the air, especially on humid days. Due to the loss of the rapidly evaporating solvent, evaporation cools the coating. On warm, humid days, small droplets of water can condense on the coating. This makes the coating look like it is covered with small raindrops. This should be avoided by either coating in a temperature and humidity controlled room or heating the part being coated to 100-120°F and then baking as soon as possible after coating.