A reactor model was developed to describe the dynamics of continuous solid-
phase polymerization (SPP) of nylon 6,6 in a moving bed. This partial diffe
rential equation (PDE) model was used to simulate the start-up process for
a reactor filled with cold particles. Polymer property profiles (degree of
polymerization and moisture content) along the reactor and inside the polym
er particles are presented at different reaction times. Simulations show th
at approximately two solid-phase residence times are required to reach the
desired steady-state conditions at the reactor outlet. After the process re
ached steady state, operating conditions were adjusted to move the reactor
system to new steady states. Model predictions for the reactor dynamics aft
er the step changes show how adjustments to the operating conditions affect
the SPP process. Variations in the temperature, moisture content and flow
rate of the counter-current nitrogen gas have important effects on the poly
mer properties. (C) 2001 Elsevier Science Ltd. All rights reserved.