Effect of Impurities on Continuous Solution Methyl Methacrylate Polymerization Reactors. I. Open-Loop Process Identification Results

An automated pilot-scale 1-litre experimental reactor system with facilities for on-line measurement of flow rate, temperature and density has been set up for open-loop process identification of impurity effects on the solution polymerization of methyl methacrylate (MMA) in a continuous stirred tank vessel. The desired conversion level is maintained using the initiator flow rate as the manipulated variable. Monomer, initiator and solvent flow rates are all regulated by computer-controlled variable speed pumps to maintain a prespecified monomer/solvent ratio and residence time. During operation, various levels of 2,2-diphenyl-1-picrylhydrazil (DPPH) are injected into the reactor as disturbances. An on-line densitometer, which relies upon changes in the frequency of oscillation of a fixed volume tube through which liquid is flowing, is used to monitor the density change and therefore conversion in the reactor system. The on-line experimental results have been cross-checked by off-line gravimetry and found in good agreement. The present study sets up the groundwork for the subsequent application of closed-loop real-time control techniques to compensate for known or unknown types and amounts of reactive impurities in continuous polymerization reactors.