Strategies for handling mixtures in multicomponent batch distillations with slop recycle

A methodology is presented for determining the optimal strategy for a production campaign of several multicomponent batch distillations, involving several mixtures having the same components but with different compositions and allowing for the recycling of slop cuts. The methodology involves the construction of a superstructure taking into account all the possible alternatives for handling of different mixtures and the slop cuts obtained. The corresponding mathematical formulation leads to NLP problems which are solved using available optimisation software. The decision variables corresponding to this production campaign are the proportions of each initial mixture and each slop cut introduced into the reboiler at each batch together with the reflux ratios. A series of four problems shows the effectiveness of this procedure. Slop cut recycling allows significant gains in some cases. The optimal strategy depends on the economic value of the different products.