Nonlinear decoupling control of free-radical polymerization continuous stirred tank reactors

The combination of autoacceleration and poor heat removal in exothermic continuous polymerizations move reactor design towards operation at high state sensitivity with reduced stability margins or unstable operation. A nonlinear temperature control does not guarantee stable operation. Stable control and improved dynamics can be attained when conversion and temperature set-points are regulated by manipulating initiator feedrate and heat removal rate. The use of measured input disturbances (feed conversion and temperature) provides disturbance rejection capabilities. This poses a control design for a multivariable, nonlinear, interactive process with measured input disturbances. It is found that there exists a nonlinear controller which assures a closed-loop operation about a unique attractor with a well-defined domain of stability which accommodates well the region of feasible operation. The methodology is constructive and provides a nonlinear multivariable feedforward—feedback control scheme that cancels both the nonlinearity and the interaction, permitting single-loop tuning with conventional linear techniques. Numerical simulations corroborate the findings and illustrate the performance of the control technique.