On-Line Optimizing Control of Bulk Polymerization of Methyl Methacrylate: Some Experimental Results for Heater Failure RAJU B. MANKAR, DEOKI N. SARAF, SANTOSH K. GUPTA Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208 016, India Received 1 March 2001; accepted 18 October 2001 Published online 18 June 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.10869 ABSTRACT: An experimental unit has been assembled to carry out on-line optimizing control of the bulk polymerization of methyl methacrylate (MMA). A rheometer–reactor assembly is used. Temperature and viscosity measurements are used to describe the state of the system. The polymerization is carried out under an off-line computed optimal temperature history, T op (t). A planned disturbance (heating system failure) is introduced at time t 1 . This disturbance leads to a fall in the temperature of the reaction mass. A new optimal temperature history, T reop (t), is re-computed on-line and is implemented on the reaction mass at time t 2 , when the heating is resumed. This procedure helps ‘save the batch’. A genetic algorithm is used to compute this reopti- mized temperature history in a short period of 2 min of real time. The feasibility of the on-line optimizing control scheme has been demonstrated experimentally. Replicable results for the viscosity history, (t), of the polymerizing mass under several non- isothermal conditions have been obtained. These experimental results are quite trust- worthy, even though the model predictions are only in approximate agreement with them, perhaps because of the extreme sensitivity of results to the values of the model parameters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2350 –2360, 2002 Key words: optimization; genetic algorithm; PMMA; polymerization; on-line optimal control INTRODUCTION The physical properties of any commodity plastic depend largely on its molecular weight distribu- tion (MWD). Generally, from the point of view of product application, it is desirable to have high weight-average molecular weight, M w , products with a narrow MWD. Martin et al. 1 and Nunes et al. 2 have shown that narrowing the MWD im- proves the thermal properties, stress–strain rela- tionships, impact resistance, and hardness and strength of the polymer. To produce such materi- als in industrial reactors, we need to measure the ‘state’ of the reaction mass (e.g., polymer concen- tration, M w , etc.) continuously as the polymeriza- tion proceeds and take corrective action whenever there are any ‘disturbances’ to planned operation. Unfortunately, experimental measurements of the polymer concentration and the MWD (or the average molecular weights) on-line are not easy, particularly for bulk polymerizations, 3,4 and easy- to-measure secondary variables need to be used to provide reliable inferential measurements of these quantities. In our earlier work, 5–7 we re- ported how the viscosity, , of the reaction mass (or any related property, like the electrical power required for stirring the reaction mass) and the temperature, T, at time, t, both of which are easily Correspondence to: S. K. Gupta (skgupta@iitk.ac.in). * Present address: Dr. Babasaheb Ambedkar Technological University, Lonere 402 103, India. Journal of Applied Polymer Science, Vol. 85, 2350 –2360 (2002) © 2002 Wiley Periodicals, Inc. 2350