A New Phase-Equilibrium Model for Simulating Industrial Nylon-6 Production Trains

Abstract

This paper presents a thermodynamically consistent model for the phase equilibrium of water/caprolactam/nylon-6 mixtures, based on the POLYNRTL (polymer nonrandom two-liquid) activity-coefficient model. Our model predicts phase equilibrium for any binary or ternary mixture containing water, ε-caprolactam, and nylon-6 at industrially relevant temperatures and pressures with an average error of 1%. This paper also demonstrates its application to simulate a melt train and a bubble-gas kettle train for industrial production of nylon-6. Prior literature makes simplifying assumptions about liquid-phase (molten polymer) activities of water and ε-caprolactam; these assumptions are shown to be unrealistic.