Control of copolymer hydrodynamic volume distribution in a semibatch free radical copolymerization process

In copolymerization processes, molecular weight averages and copolymer comp osition are commonly used as property indices for reactor control purposes. In general, it is difficult to measure the molecular weight distribution o f copolymer accurately by gel permeation chromatography (GPC) because there is no unique relationship between chain length and hydrodynamic volume for a copolymer with a heterogeneity in the composition distribution. In this paper, the hydrodynamic volume distribution is used as a primary control ob jective in a semibatch free radical copolymerization process. The hydrodyna mic volume distribution of copolymer is modeled by computing the weight fra ction of polymers over a number of hydrodynamic volume intervals. Then the target hydrodynamic volume distribution is obtained by designing optimal re actor operating policy. Both copolymer composition and the entire hydrodyna mic volume distribution are controlled by adding reactants as a function of time. A numerical simulation example is presented for a styrene-methyl met hacrylate copolymerization process to illustrate the proposed method. (C) 1 999 Elsevier Science Ltd. All rights reserved.