Modeling and Simulation of a Semi-batch Reactor

Magazine article, 2007

The operation of an industrial semi-batch reactor, in which the bulk chemical EHEC, ethyl hydroxyethyl cellulose, is produced, is studied and simulated. In the reactor a strongly exothermic polymerization reaction takes place followed by a slightly exothermic reaction, and we want to minimize the duration of the operation of the process. Various operational as well as quality and safety related constraints have to be met during the batch. The complete process model, derived from measurements, first principles, and reasoning about effects on molecular level, is stated. The model includes heat and mass balances of the reactor, a pressure model, models of PID controllers, the jacket and the condenser. Technical limitations, for instance maximal and minimal jacket temperature changes due to limitations in the heat exchanger, have been modeled as constraints. The equations have been implemented in SIMULINK, MATLAB and the model predicts the process variables rather well over time. During the first reaction, the model is not able to reproduce the jacket temperature to the desired accuracy, but the other variables have acceptable predictions. An optimization problem is formulated, wherein the total batch time is minimized under the constraints of the differential algebraic equation system and other constraints originating from the process, for instance limited pump capabilities. As a first step in optimizing the operation of the process, a series of simulations has been performed in order to decrease the total batch time. It is concluded that a 10 % shorter batch time than today is possible if the quality is discarded, and a 5 % shorter batch time can be reached while using the existing requirements for the quality.