Feedforward and feedback control of a solution copolymerization reactor

Abstract

A control system is designed for a copolymerization reactor using a combination of feedforward, ratio, and feedback control to regulate polymer production rate, copolymer composition, molecular weight, and reactor temperature. The solution copolymerization of methyl methacrylate and vinyl acetate in a continuous stirred tank reactor is used as an illustrative example with the kinetic parameters and reactor operating conditions obtained from the literature. The process includes equipment to recycle unreacted monomers and solvent. The recycle stream introduces disturbances to the reactor feed, which perturb the polymer properties. A feedforward control strategy is proposed to counter these disturbances, and its effectiveness is demonstrated using the model. The mathematical model is used to investigate input /output control pairings in order to identify the fundamental nature of the solution copolymerization control problem and to determine the best control system structure. The combined feedforward /feedback strategy is tested on a nonlinear model of the process for set point changes and compensation of unmeasured reactor disturbances. The performance of the control system design was quite good, and such designs have been found successful in plant operations.

Advanced Control of a Continuous Solution Copolymerization Process

“…The feedforward control equations were obtained by writing component balances around the recycle addition point [1,9,30]. For example, the mole balance for monomer A is:…”

“…The deterministic model, as well as the kinetic mechanism and initial concentrations, is explained in detail in Appendix. More information on the nonlinear model is given in Congalidis et al [1] and Maner and Doyle [30].…”

“…The process considered in this paper is the solution copolymerization of methyl methacrylate with vinyl acetate within a continuous stirred tank reactor [1]. Figure 1 is a qualitative process flow diagram of a copolymerization reactor including the recycle loop (streams 6, 8, and 2).…”

“…Congalidis et al [1] implemented a feedforward controller in the process to compensate for these disturbances by manipulating the fresh feeds to maintain a constant feed composition and flow to the reactor. Feedforward control of the recycle stream enabled the designer to separate the control of the reactor from the rest of the process.…”

“…(1) use a linear model to predict future deviations from a set point over a prediction horizon forming a quadratic objective function to be minimized, (2) adjust a control horizon of manipulated input moves, (3) implement the first move and measure the resulting output at the next sample time, (4) update the model and loop to (1).…”