Green Design of Poly(m-Phenylene Isophthalamide)-Based Thin-Film Composite Membranes for Organic Solvent Nanofiltration and Concentrating Lecithin in Hexane

A green method to fabricate poly(m-phenylene isophthalamide) (PMIA) based thin-film composite membranes has been developed for organic solvent nanofiltration (OSN). For the first time, the porous PMIA membrane substrates are cast from dope solutions prepared by an environmentally benign ionic liquid and the thin-film selective layer is synthesized on top of the glutaraldehyde (GA) modified PMIA substrate (mPMIA) via imine condensation between hyper-branched polyethylenimine (HPEI) using water as the reaction media. Experimental results show that both HPEI and GA concentrations play important roles in controlling the thickness and free volume properties of the selective layer, and thus influence the OSN separation performance significantly. The newly designed composite membranes have an ethanol permeance varying from 3.2 to 21.4 LMH/bar while the corresponding MWCO value changing from 470 to 730 Da when both HPEI and GA concentrations reduce from 1 to 0.5 wt %. In summary, the newly fabricated membranes not only possess satisfactory permeances for solvents like methanol, ethanol, acetonitrile, and hexane but also have good separation performance for concentrating lecithin in hexane, which is in great demand by the food industry. Therefore, this work may offer a green and sustainable method to design environmentally benign composite membranes for OSN.