The effects of substrate characteristics and pre-wetting agents on PAN–PDMS composite hollow fiber membranes for CO2/N2 and O2/N2 separation

In order to develop high performance poly(dimethylsiloxane)-polyacrylonitrile (PDMS/PAN) hollow fiber composite membranes for the separation of CO2/N2 and O2/N2 gas pairs, we have investigated: (1) the viscosity of PDMS solutions as a function of curing conditions; (2) pore size and pore size distribution of the PAN substrates as a function of spinning conditions and post-treatments and (3) the effects of pre-wetting agents, substrate morphology and PDMS concentration on the gas performance of the selective layer. Based on their complicated relationship, fundamental science and engineering have been elucidated to fabricate PDMS/PAN hollow fiber composite membranes with CO2, N2 and O2 permeances of 3700, 370 and 860 GPU and selectivities of 10 and 2.2 for CO2/N2 and O2/N2 gas pairs at 25 °C and 2 atm, respectively. This O2/N2 separation performance is comparable with the best ever reported results for O2 enrichment. The PAN hollow fibers were prepared by a dry-jet wet spinning process and subsequently coated with PDMS by dip-coating. To increase gas permeance, experimental results show that, in addition to keeping substrate pores open, partially crosslinking PDMS and pre-wetting the PAN substrates by Fluorinert 72 (FC-72) or deionized water before dip coating in order to prevent intrusion are important. This study may provide insights and guidelines to fabricate highly permeable membranes in the industry for O2 enrichment, flue gas separation and CO2 capture.