Predicting Molecular Weight and Degree of Branching Distribution of Polyethylene for Mixed Systems with a Constrained Geometry Metallocene Catalyst in Semibatch and Continuous Reactors

Abstract

The problem of finding the bivariate chain length (n)/number of branch points (N) distribution for polyethylene produced by a mixed metallocene catalyst system in continuous (CSTR) and semibatch reactors is addressed in two ways. The first uses distinct classes of chains with a certain number of branches, the second the “pseudodistribution” approach, both generating population balances solved with the Galerkin finite element approach of PREDICI. A nine-classes model yields the exact bivariate distribution up to chains of n = 10 000. Until this limit, classes and pseudodistribution models yield identical results, both being based on identical assumptions. Results also coincide with an analytical solution for a CSTR single catalyst system. In view of their importance for deriving architectures and architectural properties, chain statistics were examined by calculating average segment lengths. In the single catalyst CSTR, these turn out to be independent from the number of branches on a chain, which holds un...