(124a) Molecular Separations in Organic Liquid Systems: The Selectivity Challenge

Organic liquids are ubiquitous in chemical-science-based industries, which range in scale from refining to pharmaceutical production. It is generally accepted that 40-70% of capital and operating costs in these industries are dedicated to separations. Membrane technology has the potential to provide game changing alternatives to conventional concentration and purification technologies such as evaporation, liquid extraction, adsorption, crystallisation and chromatography. To achieve this, membranes must offer resilience in organic environments, and have good permeance. Crucially, in many applications to molecular separations in liquids a membrane system should also offer an outstanding selectivity between solutes to provide an efficient process. This paper will explore materials science and engineering based approaches to improving selectivity, and illustrate the effect of selectivity on overall process complexity and feasibility.

Materials science approaches to improving selectivity between solutes revolve around designing materials for the membrane separating layers which can discriminate cleanly between two solutes. Approaches include incorporating pre-structured materials with microporosity, such as MOFs, COFs, and POCs into the separating layers of membranes, or designing membranes with increasingly rigid polymer networks which build-in desired microporosities.

An engineering-based approach to improving system selectivity is to use multiple separation stages. In these systems, the permeate from one stage is typically fed into a subsequent stage for further solute fractionation. This idea has been explored through simulation and a limited number of experimental demonstrations – these latter requiring the control of pressures and flows.

The impact of these approaches will be considered in the context of high value molecules from pharmaceutical contexts, and the potential for each approach to achieve desired outcomes will be assessed.