Multiobjective optimization of an industrial wiped film poly(ethylene terephthalate) reactor: some further insights

Multiobjective optimization of an industrial third-stage, wiped-film poly(e thylene terephthalate) reactor is carried out, using a pre-validated model. The two objective functions minimized are the acid and vinyl end group con centrations in the product. These are two of the undesirable side products produced in the reactor. The optimization problem incorporates an end-point constraint to produce polymer having a desired value of the degree of poly merization (DP). In addition, the concentration of the di-ethylene glycol e nd group in the product is constrained to lie within a certain range of val ues. The possible decision variables for the problem are the reactor pressu re, temperature, catalyst concentration, residence time of the reaction mas s in the reactor and the speed of rotation of the agitator. The nondominate d sorting genetic algorithm (NSGA) is used to solve this multiobjective opt imization problem. It is found that this algorithm is unable to converge to the correct solution(s) when two or more decision variables are used, and we need to run the code several limes over (with different values of the co mputational variable, S,, the seed for generating the random numbers) to ob tain the solutions. In fact, this is an excellent test problem for future m ultiobjective optimization algorithms. It is found that when temperature is kept constant, Pareto optimal solutions are obtained, while, when the temp erature is included as a decision variable, a global unique optimal point i s obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.