Some membrane separation processes are gradually taking over conventional processes such as distillation, evaporation or crystallization as the technology progresses from bench-scale tests to large-scale prototypes. However, membranes for H2 and CO2 separation constitute a daring technology still under development. This overview focuses on mixed matrix membranes (MMMs), a special type of membranes in which a filler is dispersed in a polymer matrix, as a successful strategy to improve their permeability-selectivity performance while keeping the polymer processability. In particular, among all the possible fillers for MMMs, layered materials (porous zeolites and titanosilicates and graphite derivatives) are discussed in detail due to the several advantages they offer regarding selective microporosity, crystallinity and, what is most important, high specific surface area and aspect ratio. In fact, a selective and as thin as possible, i.e. with high aspect ratio, filler would help to develop high performance MMMs.
Chemical and Environmental Engineering Department and Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain.