Impact of dope extrusion rate and multilayer polydimethylsiloxane coating on asymmetric polyethersulfone hollow fiber membrane for CO₂/N₂ and CO₂/CH₄ separation

Abstract

Carbon dioxide (CO 2 ) emissions to the atmosphere have greatly contributed to climate change as the concentration has increased since the pre-industrial period. Various mitigation strategies have been developed to combat climate change with membrane being one of the growing alternatives. Pristine hollow fiber (HF) membrane typically exhibits lower selectivity as compared to dense flat sheet membrane. In this study, we developed an asymmetric HF polyethersulfone (PES) membrane with critical concentration at two different dope extrusion rate (DER) at 3 and 6 mL/min to be studied for CO 2 /N 2 and CO 2 / CH 4 gas separation for flue gas and biogas upgrading applications by testing the fabricated membrane with pure gas permeation test with variable pressure at room temperature. It was observed that HF membrane extruded with high DER exhibits finger-like structure beneath the skin layer with more pinholes compared to HF extruded with low DER. The gas permeance was observed to increase in linear fashion as function of upstream pressure while the gas selectivity appears to be relatively constant regardless of upstream pressure. Meanwhile, polydimethylsiloxane (PDMS) coated HF PES membrane shows lower gas permeance as compared to its pristine membrane with improved CO 2 /N 2 and CO 2 /CH 4 selectivity. HF PES membrane extruded at 3 mL/min shows relatively low gas permeance, CO 2 /N 2 and CO 2 /CH 4 selectivity as compared to HF PES extruded at 6 mL/min. Additionally, this study shows that sequential coating of PDMS layer does not improve gas selectivity performance of the fabricated asymmetric PES HF membrane while the gas permeance reduction was observed.

Polydimethylsiloxane/Magnesium Oxide Nanosheet Mixed Matrix Membrane for CO2 Separation Application

“…The opposing nature of hydrophobic solvent (n-pentane) and hydrophilic fillers (MgO) may or may not contribute to the sedimentation of the fillers. The sedimentation issue may be mitigated by increasing the polymer dope solution, which in turn increases the viscosity of the polymer solution, as it is known that viscosity of a polymer is a function of its concentration [ 44 , 61 , 62 ]; hence, the higher polymer viscosity may keep higher filler loading suspended during phase separation. However, this will also lead to thicker membrane formation, which in turn will lower the gas permeance due to the increased resistance from the membrane’s thickness.…”

“…The gas performance set-up and its schematic diagram has been described elsewhere [ 44 ]. Pure gas separation performance was conducted at pressure ranging from 2 to 5 bar at room temperature conditions using a constant-volume variable pressure method.…”

“…PDMS is a rubbery polymer with high permeability towards CO 2 gas and with considerably good ideal selectivity against CO 2 /N 2 and CO 2 /CH 4 . It is also cheap and readily available in the market [ 43 , 44 ]. It was hypothesized that inorganic filler with nanosheet structure gives rise to barrier properties, which can enhance gas separation properties [ 45 ].…”