Robust polybenzimidazole (PBI) hollow fiber membranes for organic solvent nanofiltration

Abstract

Design and fabrication of solvent resistant hollow fiber membranes with great mechanical and thermal stability are highly demanded for sustainable manufacturing in chemical and pharmaceutical industries. Herein, we propose a facile and novel acid doping procedure to synthesize highly stable and selective polybenzimidazole (PBI) hollow fibers for organic solvent nanofiltration for the first time. PBI hollow fibers were spun through a dry-jet wet-spinning method. Subsequently, the hollow fibers were acid doped with a 2 wt% H2SO4 solution so that the acid molecules form hydrogen bonds with the PBI backbone and build an integrated structure which becomes insoluble in organic solvents. Comprehensive characterizations were conducted to study the impact of acid doping on PBI hollow fibers. The acid doping not only reduced the molecular weight cut off (MWCO) of the fibers from 2000 g mol‒1 to 500 g mol‒1 but also significantly enhanced their chemical and mechanical stability, as well as flexibility. In addition, for the first time, the conventional solute‒rejection experiments utilized to determine the MWCO and pore size distribution of membranes in aqueous solutions were modified to estimate them in organic solvents. By using tetracycline/methanol and L-α-lecithin/hexane mixtures as feeds, the newly developed PBI hollow fibers showed rejections of > 98% and permeances of 3.5 and 7.1 L m−2h−1bar−1 towards methanol and hexane, respectively. Therefore, they have great potential for solvent recovery in food and pharmaceutical industries.