Effect of diacid stabilizers on kinetics of hydrolytic polymerization of ε-caprolactam in industrial reactors

Abstract

The rate constants in hydrolytic polymerization of ε-caprolactam are dependent on the concentration of carboxylic acid groups in the reaction medium. Therefore, the use of diacid stabilizers for regulating molecular weight are likely to have favorable effect on the kinetics of polymerization compared to monoacid stabilizers, which are traditionally used in such polymerizations. To understand the kinetics of polymerization in the presence of diacid stabilizer compared to monoacid stabilizer, mathematical kinetic models were developed using the end group approach. These models were used to quantify the effect of both stabilizers on nylon-6 synthesis in a closed isothermal batch reactor at different temperatures in the range of 245–265°C. The kinetic model for the diacid-stabilized system was then extended to an industrial VK tube reactor using the process model developed earlier for the monoacid stabilized system. Both the mathematical modeling and experimental results showed that the presence of diacid stabilizer could significantly enhance the overall kinetics of the reaction compared to the monoacid stabilized system and in turn, resulted in reduction of the polymerization time by about 20–25%. The study suggests that diacid stabilizers may be used preferably over monoacid stabilizers in synthesis of nylon-6 to reduce the cost of polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007