Dense polymer membranes
enable a diverse range of separations
and
clean energy technologies, including gas separation, water treatment,
and renewable fuel production or conversion. The transport of small
molecular and ionic solutes in the majority of these membranes is
described by the same solution-diffusion mechanism, yet a comparison
of membrane separation performance across applications is rare. A
better understanding of how structure–property relationships
and driving forces compare among applications would drive innovation
in membrane development by identifying opportunities for cross-disciplinary
knowledge transfer. Here, we aim to inspire such cross-pollination
by evaluating the selectivity and electrochemical driving forces for
29 separations across nine different applications using a common framework
grounded in the physicochemical characteristics of the permeating
and rejected solutes. Our analysis shows that highly selective membranes
usually exhibit high solute rejection, rather than fast solute permeation,
and often exploit contrasts in the size and charge of solutes rather
than a nonelectrostatic chemical property, polarizability. We also
highlight the power of selective driving forces (e.g., the fact that
applied electric potential acts on charged solutes but not on neutral
ones) to enable effective separation processes, even when the membrane
itself has poor selectivity. We conclude by proposing several research
opportunities that are likely to impact multiple areas of membrane
science. The high-level perspective of membrane separation across
fields presented herein aims to promote cross-pollination and innovation
by enabling comparisons of solute transport and driving forces among
membrane separation applications