Process-wide integration of solvent mixtures
This paper presents a systematic design approach to the generation of batch process flowsheets with integrated solvent recovery and recycling. The approach is based on the proposition that highly non-ideal phase behavior, in particular azeotropy, creates barriers to solvent recovery and recycling, and that solvent mixtures that cannot be recycled inevitably become toxic waste. The systematic alteration of the mixtures formed in a batch process in order to facilitate solvent recovery and recycling is therefore investigated. The design approach is realized as a mathematical programming problem. The primary objective is to design the compositions of stream candidates that will (or can be) subject to recovery such that the quantity of solvents crossing the plant boundary is minimized, subject to a variety of constraints such as reaction stoichiometry, solvation of reactions, selectivity achievable, etc. The advantage of a mathematical programming formulation is that it facilitates the analysis and integration of very complex networks where the trade-offs are not obvious. For this approach to be valuable, the model employed must be abstract but reflect accurately the complex physical behavior that drives the decision process (e.g. azeotropy), the resulting mathematical program must be compact and solvable efficiently for problem sizes of industrial relevance, and the results must be generated in a form that can be interpreted easily by the engineer to improve the process design. The formulation presented satisfies all these criteria. The novel design methodology has been successfully demonstrated in two realistic case studies. (C) 1999 Elsevier Science Ltd. All rights reserved.
batch processing solvent recovery mathematical programming azeotropes batch distillation composition simplex