Abstract

This paper focuses on the determination of optimum control trajectories for the operation of a batch polymerisation reactor. Operating policies needed to achieve pre-specified properties in minimum time are obtained. Two models dealing with the polymerisation of styrene using AIBN as initiator in a batch reactor are considered. The first model (Model I), taken from the literature, is derived from the first principles of the polymerisation system while the other (Model II) is more rigorous involving both mass and energy balances to simulate a batch polymerisation reactor operation.

A dynamic optimisation problem incorporating Model I is formulated and solved to find the optimal temperature trajectory and initial initiator concentrations that will yield desired levels of monomer conversion and number average molecular weight in minimum time. The total batch time is divided into a finite number of intervals and piecewise constant reactor temperature is assumed in each interval. The reaction temperature and the length of each interval are optimised using Control Vector Parameterisation technique. Significant savings in batch time are obtained when these results are compared with those available in the literature obtained using the Pontryagin's Maximum Principle.

Incorporating Model II, a second dynamic optimisation problem is formulated and solved where the coolant flow rates and lengths of the intervals are optimised to minimise the batch time and yield desired levels of monomer conversion and number average chain length. With examples, the results show that although both optimisation problems result in similar product qualities, the optimal operations are significantly different. Batch time is significantly higher for the second optimisation problem. gPROMS modelling software was used to build the process model and perform the dynamic optimisation.

Recommended Citation

Ekpo, Emmanuel E. and Mujtaba, Iqbal M. (2007) "Optimal Control Trajectories for a Batch Polymerisation Reactor," International Journal of Chemical Reactor Engineering: Vol. 5: A4.
Available at: http://www.bepress.com/ijcre/vol5/A4