Use of Agitator Power as a Soft Sensor for Bulk Free-Radical Polymerization of Methyl Methacrylate in Batch Reactors

The histories of the temperature T of the reaction mass and the agitator current C required for stirring it in a batch polymerization reactor at constant speed are used to develop a soft sensor for online estimation of the state variables, namely, the monomer conversion ( x m ) and the weight average molecular weight ( M w ). Methyl methacrylate (MMA) is used as a sample system. Bulk polymerization of MMA is performed in a 1-L stainless steel (SS) reactor instrumented using virtual instrumentation techniques. Experimental data on x m ( t ), M w ( t ), C ( t ), and T ( t ) are obtained at different values of times t, under various near-isothermal and nonisothermal conditions. A semiempirical model is developed that relates C ( t ) and T ( t ) to the state of the polymerization mass. The feasibility of using this as a soft sensor, along with the kinetic model, is demonstrated.