Solvent extraction is considered as a multi-criteria optimization problem, since several chemical species withsimilar extraction kinetic properties are frequently present in the aqueous phase and the selective extractionis not practicable. This optimization, applied to mixer–settler units, considers the best parameters andoperating conditions, as well as the best structure or process flow-sheet. Global process optimization isperformed for a specific flow-sheet and a comparison of Pareto curves for different flow-sheets is made. Thepositive weight sum approach linked to the sequential quadratic programming method is used to obtain thePareto set.In all investigated structures, recovery increases with hold-up, residence time and agitation speed, while thepurity has an opposite behaviour. For the same treatment capacity, counter-current arrangements are shownto promote recovery without significant impairment in purity. Recycling the aqueous phase is shown to beirrelevant, but organic recycling with as many stages as economically feasible clearly improves the designcriteria and reduces the most efficient organic flow-rate.
展开▼
