Phosphorylated cellulose nanocrystals/polyvinyl alcohol-L arginine coating in facilitated transport membranes for biogas purification

Abstract

Biogas is a renewable fuel consisting of CH₄ (∼60–70 %) and CO₂ (∼30–40 %) and can be utilised as a biofuel if CH₄ is enriched. In this work, CNC was phosphorylated and the varied concentrations (0–2 wt.%) of phosphorylated cellulose nanocrystals (PCNC) were dispersed in polyvinyl alcohol (PVA)-L Arginine (PVA-LA) matrix for its utility as a “selective layer” in biogas purification. This selective layer was coated on the surface of highly porous poly(ether-sulfone) (PESF) hollow fibers for the facilitated transport of CO₂ from biogas with l-Arginine as the mobile carrier. These membranes (coated hollow fibers) were stacked straight inside a membrane chamber, spaced 1 mm apart, and biogas was fed over its surface at 90 % RH and different feed pressures (0.8–1 bar) for varying PCNC concentrations. It was observed that CO₂ permeability increased with the increase in PCNC concentration (21177 barrer for 1PCNC/PVA-LA), but the selectivity of 33 decreased after 1PCNC/PVA-LA. At higher PCNC concentrations (2PCNC/PVA-LA), a very high permeability (25772 Barrer) and reduced selectivity (10) was observed. Overall, a combination of hydrophilicity induced by the PCNC in PVA along with l-Arginine for CO₂ transport aided the separation of CO₂ from biogas when operating at low pressure conditions.