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 860GPU and selectivities of 10 and 2.2 for CO₂/N₂ and O₂/N₂ gas pairs at 25°C and 2atm, 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.