Strategies for handling mixtures in a campaign of several multicomponent batch distillations

A method is proposed for optimising the production campaign of several multicomponent batch distillations involving several mixtures having the same components but with different compositions. A general model (based on a superstructure) is proposed, allowing the calculation of the proportion of each mixture to be added to each initial load and to each new batch in order to optimise the global operation. The formulation of several problems leads to non-linear programming (NLP) problems where the set of decision variables are the proportions of each mixture to be added to each batch and the reflux ratios. Three types of criteria (corresponding to the minimum time problem, the problem of the maximum amount to be recovered and the optimal production rate problem) and two types of reflux ratio policies are explored. The results obtained show the necessity for a methodology and the importance of the criterion choice.