Yannan Li

Improving CO2 permeability of ceramic hollow fibre-supported composite membranes by blending an ionic liquid in the Pebax/PEGDME selective layer

To improve the permeation performance of a ceramic hollow fiber-supported poly (amide-b-ethylene oxide) (Pebax)/polyethylene glycol dimethylether (PEGDME) composite membrane during CO2 separation from biohydrogen, a room temperature ionic liquid (RTIL), namely, [P66614][2-Op], with a high CO2 capacity, was adopted to blend in the selective layer. An RTIL-blended selective layer without defects was prepared on the surface of the ceramic hollow fibre. The physicochemical properties and CO2/H2 separation performance of the Pebax/PEGDME/RTIL composite membrane were then compared with those of the Pebax/PEGDME composite membrane. Intermolecular hydrogen bonds were produced after blending RTIL with the Pebax/PEGDME selective layer, and the surface roughness of the composite membrane increased. The CO2 permeation rate increased by ∼35% and reached up to ∼75 GPU at 50 °C, and the CO2/H2 selectivity was maintained at a high value of ∼15 at 30 °C. Blending RTIL with the selective layer inhibited the positive effect of CO2-induced plasticisation on H2 permeability. However, this process improved CO2/H2 selectivity in mixed gases relative to the ideal selectivity by enhancing competitive sorption among gas molecules.

In-situ grafting to improve polarity of polyacrylonitrile hollow fiber-supported polydimethylsiloxane membranes for CO2 separation

Surface grafting modification was proposed to improve the surface polarity of polyacrylonitrile hollow fiber-supported polydimethylsiloxane (PDMS) membrane. The initiator 3-aminopropyltriethoxysilane containing one amine group was integrated into PDMS, and polyvinyl pyrrolidone (PVP) with strong polarity was connected to the surface by reacting with amine groups. Surface grafting modification was proven on X-ray photoelectron spectroscopy. The sharp decrease (from ∼98° to ∼28°) in water contact angle of the PDMS membrane indicated the significant improvement in surface polarity after the modification. The surface roughness of the PDMS membrane increased with the modification, and the PDMS surface immersed for 40s was almost covered with PVP. The membrane immersed in PVP solution for 10s improved CO2/H2, CO2/CH4, and CO2/N2 selectivities. While CO2 permeance slightly decreased from ∼2500 GPU to ∼2440 GPU. For the separation of CO2/CH4 and CO2/N2 mixed gases, all CO2/CH4 and CO2/N2 selectivities were improved after the modification. For the separation of CO2/H2 mixed gas, CO2/H2 selectivity was improved when the immersion time was below 30 s.