Controlling and Expanding the Selectivity of Filtration Membranes

Chemical separations account for about 50% of costs and energy use associated with chemical and petrochemical manufacturing, corresponding to about 10% of all energy use in the U.S. Membrane separations are highly energy efficient, simple to operate, scalable, and portable. Broader use of membranes is limited by the selectivity of available membranes, mostly confined to the separation of species about an order of magnitude or more different in size in the liquid phase. This perspective focuses on new approaches for creating liquid filtration membranes that can perform more challenging separations. We first discuss the selectivity mechanisms of currently available membranes and compare them with the operation of biological systems that exhibit enhanced selectivity. Then, we review some approaches for creating isoporous membranes with narrow pore size distributions for enhanced size-based selectivity. We discuss biological systems that exhibit selectivity based on factors beyond size and how they can inspire the design of membranes capable of complex separations. After a review of approaches for creating membranes for separating similarly sized solutes, based on their charge, we discuss the development of membranes that can perform even more challenging separations, differentiating between solutes of similar size and charge based on other molecular criteria. This burgeoning area of research promises to transform chemical and pharmaceutical manufacturing if membranes with sufficient selectivity and permeability for realistic separations can be prepared using scalable manufacturing methods.