The synergistic effect of carboxymethylated cellulose nanocrystals -Polyvinyl alcohol- L Arginine in facilitated transport membranes for biogas purification

Abstract

Biogas can be used as a renewable energy source to mitigate the use of conventional fuels. However, for this to happen its quality must be improved. Herein biogas purification was carried out utilising membranes with a biodegradable selective layer of carboxymethylated cellulose nanocrystals (C-CNC)/ Polyvinyl alcohol (PVA)- L Arginine nanocomposite coated over highly porous poly(ether-sulfone) (PESF) hollow fibre substrate. Facilitated transport of CO₂ aided by a mobile carrier (L-Arginine) and NaOH as carriers of CO₂ in the hydrophilic C-CNC/PVA under high relative humidity is the principle of this separation process. Concentrations varying from 0-2 wt% of C-CNC in PVA-LA were considered for the study at 90 % RH and varying feed pressures of 0.8–1 bar. CO₂ permeance and selectivity increased with the increase in C-CNC concentration till 1C-CNC/PVA-LA (1 wt% of C-CNC in PVA-LA) (6226 GPU permeance and selectivity of 19). At further higher C-CNC concentrations, a high chance of creating C-CNC-induced pathways through the selective layer could have created higher swelling, hence a reduction in CO₂ permeance (5244 GPU) and reduced selectivity (11) for 2C-CNC/PVA-LA. Overall, a synergistic effect of the hydrophilicity induced by the C-CNC in PVA along with L-Arginine and NaOH for CO₂ transport helped the attainment of biogas purification at low-pressure conditions.