COMPLEX LINEAR POLOCONDENSATION .1. SEMI-BATCH REACTOR

A kinetic model which takes into account the presence of zero and monofunctional as well as bifunctional species was shown to correlate experimental ester interchange reaction data from the literature. In a second study, the two-stage production of poly(ethylene terephthalate) in a well-stirred semi-batch reactor was simulated. Zero and monofunctional species present in the product from the ″monomerization″ stage, which ordinarily result in ″end-capping″ in the second stage, were shown to lead to a higher molecular weight product under certain conditions of the relative reaction rates. A″ mixing film″ model is developed for the case of complex polycondensation in a thick film, i. e. where reaction and simultaneous diffusion of two volatile by-products toward the free surface are coupled with a step to account for periodic complete mixing of the film. Enhancement of the degree of polymerization as high as the 30% reported in the patent literature for commercial reactors can be demonstrated for optimum concentrations of zero and monofunctional reactants initially present. Based on these results it is concluded that the monomerization stage in a polycondensation process should be intentionally operated to yield incompletely converted product. Significant increases in equipment capacity can result, not only in the monomerization stage, but also in the subsequent polymerization stage through enhancement of the coupled reaction-diffusion mechanism governing condensation polymerization rates.