Extraction–Stripping Process Synthesis with Multiple Solvent Circulation Loops

Abstract

A flow scheme is suggested for synthesizing solvent extraction–solvent regeneration processes consisting of sets of mixer-settlers. The proposed scheme is based on equal partitioning of the separation capacity between the extraction and stripping cascades with each pair of stages interconnected via an independent solvent circulation loop. A dimensionless linear steady-state model is developed for analysing the behaviour of the proposed multi-loop scheme. It enabled the identification of limiting design conditions and the generation of results relating the combination of strippant consumption and solvent circulation rates required to achieve a given purification duty in a given number of stages. A simple numerical (graphical) method is also suggested for the analysis when equilibrium relations in the extractor and stripper are non-linear. The superiority of the proposed multi-loop scheme over the conventional method of coupling the extraction and stripping cascades via a single solvent circulation loop is illustrated quantitatively. Compared with the conventional scheme the proposed flow structure enables the same purification to be achieved with the same total separation capacity, but at lower solvent circulation rates and strippant consumption. This is obviously reflected as savings in both equipment and operating costs.