Modelling of an industrial autothermal nylon-6 flow reactor

Abstract

Mass- and energy-balance equations that describe the hydrolytic polymerization of nylon-6 in an autothermal industrial reactor are written. These account for both axial and radial variations of the temperature, as well as of the concentrations of the various molecular species. The set of coupled, non-linear partial differential equations are transformed into a set of ordinary differential equations (ODEs) using the finite-difference technique in the radial direction. The resulting stiff ODEs are then solved using Gear's algorithm. The method of successive substitutions is used to obtain convergence to the final results. Sharp radial gradients in temperature and average molecular weights are observed because of near-equilibrium conversions at the reactor walls and the low thermal conductivity of the reaction mass. It is demonstrated that these need to be accounted for in the proper design and analysis of reactors having this configuration. The effects of various operating conditions and parameters are studied. It is found that the hot-spot is parametrically sensitive to the feed-water concentration and to the presence of monofunctional acid in the feed. In addition, product having the same molecular weight can be obtained using two different feed-water concentrations. The results are found to be sensitive to the values of the heat transfer coefficients, and so good estimates of this parameter are required for simulation purposes.