A homogeneous polysulfone nanofiltration membrane with excellent chlorine resistance for removal of Na2SO4 from brine in chloralkali process

Abstract

A homogeneous polysulfone nanofiltration membrane with a dense structure was fabricated by solvent evaporation method. Two solvents, tetrahydrofuran (THF) and dimethylacetamide (DMAc), were utilized to prepare the membranes with tunable pores around 1.0nm. The pore size was affected by the solvent species, and it decreased when THF was replaced by DMAc. Correspondingly, the rejections to Na2SO4 of the membranes fabricated with DMAc (80–82%) were higher than those of the membranes fabricated with THF (65–67%). To further improve the performance, by applying a higher membrane formation temperature (110°C), the pore size became even smaller and the rejection to Na2SO4 was improved to 87%. The feasibility of removing sulfate ions from brine by the membrane was proved by rejection to Na2SO4 of 80% and rejection to NaCl of almost zero in the mixed salt solution. The structure of the membrane was independent of the thickness, and thus the flux could be gradually improved by reducing the thickness while maintaining a high rejection. Moreover, the membrane had high mechanical strength larger than 66MPa and excellent chlorine resistance. It kept good separation performance even after exposed to the 50,000ppm sodium hypochlorite solution for 24h.