Purification of 2-Pyrrolidone by Falling Film Melt Crystallization

Industrial grade 2-pyrrolidone with a purity of 99.5% is produced by aminolysis of γ-butyrolactone and subsequent fractional distillation, but it still contains trace amounts of γ-butyrolactone and other impurities. Falling film melt crystallization was applied for further purification of 2-pyrrolidone from 99.5% to a very high purity. The effects of the precooling temperature, feed rate, cooling rate, final crystallization temperature, heating rate, and final sweating temperature on the purity and yield of 2-pyrrolidone were studied. 2-Pyrrolidone was purified by falling film melt crystallization to a purity and yield of more than 99.9 and 73.3%, respectively. The mathematical model of falling film crystallization was applied for simulation of the crystal layer growth of 2-pyrrolidone. The simulated average thickness of the crystal layer was in good agreement with the experimental values, demonstrating the applicability of the model to falling film crystallization of 2-pyrrolidone.