Control of Emulsion Polymerization Reactors

An overview of some of the research projects on the modelling, optimization and control of emulsion polymerization reactors being carried out at the McMaster Institute for Polymer Production Technology will be presented. The objectives are to optimize production rates and to achieve control over 'product quality variables such as polymer particle size distribution, particle morphology, copolymer composition, sequence length, molecular weights, and long chain branching.The polymer systems under investigation include poly(vinyl acetate) and vinyl acetate copolymers (acrylic acid, butyl acrylate and 2-ethyl hexyl acrylate comonomers) and styrene copolymers (acrylonitrile and butadiene comonomers).One project in particular on the control of oscillations in conversion and latex properties in continuous emulsion polymerization in a CSTR train is discussed in more detail. It is shown that the oscillation phenomenon, which occurs in essentially all Case I emulsion polymerization systems (e.g. vinyl acetate and vinyl chloride emulsion polymerization), is conveniently eliminated with a specially designed reactor train. This design was found with the use of a dynamic model for a latex reactor.The design consists of a train of CSTR's in which the first reactor is a very small nucleating (seed) reactor and the feed streams are split between the first two reactors. The on-line control problem then reduces to the much simpler problem of controlling the "steady-state" generation of particles in the small seed reactor in order to achieve any desired final conversion and particle size. It is shown that this can easily be accomplished in this new reactor configuration by manipulating the split of monomer and water feed between the reactors, and the feedrate of initiator to the first reactor.