Green Solvent-Mediated Cyanuric Chloride Crosslinking of Polybenzimidazole (PBI) Nanofiltration Membranes for Improved Acid Stability and Organic Solvent Resistance in Molecular Separation

This study proposes a novel green crosslinking method to improve the performance of polybenzimidazole (PBI) in highly acidic conditions and organic solvent nanofiltration. PBI membranes are modified using cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) as a crosslinker under two distinct solvent conditions: acetone only and in a solvent blend of acetone and water, both recognized as green solvents. The modification process, conducted for 2 h, facilitates sustainable solvent-mediated crosslinking. Comprehensive analyses of membrane properties are conducted using Fourier-transform infrared spectroscopy, energy-dispersive x-ray spectroscopy, scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. In solvent stability experiments conducted at elevated temperature with solvents like N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP), both crosslinked membranes demonstrate exceptional solvent resistance, retaining over 96% after exposure. In organic solvent nanofiltration experiments, both membranes displayed an ethanol permeance of similar to 2.5 LMH/bar at 5.1 bar and a remarkable rejection of around 95% for Rose Bengal (molecular weight: 1017.6 g/mol). After prolonged exposure to DMF for 120 h, both crosslinked membranes demonstrate higher separation efficiency. This green crosslinking approach shows significant potential for advancing the development of robust PBI membranes, achieving high separation efficiency under low-pressure conditions.