A lignin-based membrane fabricated with a deep eutectic solvent

Abstract

Membrane technology is a sustainable process of molecular separation and purification in the chemical and pharmaceutical industries, with lower energy consumption than traditional thermal methods. For sustainability reasons, the membrane fabrication itself needs to align with the 12 principles of green chemistry with low environmental impact, preferentially using natural polymers and green solvents. Membranes are currently mostly produced from petroleum-based polymers and organic solvents like dimethylformamide, which are not expected to be used in large amounts anymore. Lignin is a natural green polymer option, however its low solubility in mild solvents has limited its processability into membranes. We propose a sustainable membrane fabrication method using lignin fully dissolved in a green deep eutectic solvent (DES). The crosslinking with 5% epoxide in the aqueous medium enhanced the membrane stability, enabling its application in an aqueous and organic solvent medium. The resulting membrane had a molecular weight cut-off of 1.3 kg mol⁻¹, a range relevant to molecular separation in the pharmaceutical and chemical industries.