Polysulfone mixed matrix gas separation hollow fibre membranes filled with polymer and carbon xerogels

This work involves the preparation, tensile testing and gas separation characterization of polysulfone mixed matrix hollow fibres filled with polymeric sol based, and subsequently carbonised, xerogels. The pore characteristics of the xerogels were determined using a surface area and porosity analyser. The xerogel materials were reduced to submicron particles by grinding and wet milling, and the resultant particle size was determined using dynamic light scattering. Using dry/wet forced convection spinning, mixed matrix hollow fibre membranes (MMMs) were spun from solutions of polysulfone loaded with the submicron xerogel particles. At 5% loading, all MMMs exhibited higher strain at break and higher strength than unfilled membranes. Compared to unfilled fibres, MMMs were stiffer when filled with hard xerogel inclusions but became more pliable when filled with soft xerogel particles. Knudsen diffusion becomes an important gas transport mechanism in the membranes filled with mesoporous xerogels. When compared to the unfilled hollow fibres, these membranes showed a strong increase in the permeation of low molecular weight, high kinetic diameter gases, leading to a decline in fast/slow gas selectivities. All types of MMM gave higher CO2/O2 (fast/fast) and CH4/N2 (slow/slow) selectivities than unfilled hollow fibres. The MMMs filled with a microporous xerogel gave a higher CO2 pressure normalized flux when compared to the unfilled fibres without sacrificing the CO2/CH4 selectivity. Future work should focus on the tailoring of the pore size of the xerogels and on the wet milling procedure to obtain smaller filler particles.