ON-LINE COMPUTER CONTROL OF A CONTINUOUS LATEX REACTOR TRAIN

During continuous emulsion polymerization of many monomers, sustained oscillations (limit cycles) occur in all the latex and polymer properties. This creates severe problems with the commercial application of continuous reactors.A mathematical model, based on a particle age distribution analysis and incorporating detailed chemistry and physics of the polymerization phenomena involved, is used to simulate the dynamic behaviour of these reactors. Advanced control theory is shown to be inadequate for controlling these systems. Kathcr, it is shown that the limit cycle behaviour must be eliminated through redesign of the reactor train configuration using the dynamic model. The redesigned reactor configuration is shown to eliminate the oscillations and to offer greatly increased flexibility in controlling the particle size and conversion.Experimental studies which demonstrate the improved dynamic performance of the redesigned reactor system are carried out in a pilot plant stainless steel reactor train. On-line measurements of conversion and particle size are obtained using densitometers and UV-spectrophotometers. Off line measurements of particle size are obtained by turbidity spectra, size exclusion chromatography (SMC) and electron microscopy, and measurements of the molecular weight averages are obtained by gel permeation chromatography (GPC) and low angle laser light scattering (LALLS).Multivariable computer control of the final latex particle size and the monomer conversion is achieved using several algorithms which manipulate the feed rate of initiator to the first reactor, and the split of the monomer and water feed rates between the first two reactors. Control is achieved using a VAX plus PDP-11 front end system interfaced to the pilot plant reactors.