Fabrication of thin-film composite hollow fiber membranes in modules for concentrating pharmaceuticals and separating sulphate from high salinity brine in the chlor-alkali process

Abstract

Nanofiltration (NF) has been widely used for sulphate removal in chlor-alkali industries and concentrating ingredients in pharmaceutical industries, but the fabrication and applications of thin-film composite (TFC) NF hollow fiber membranes and modules are still lagged behind those NF membranes in other configurations. In this work, the pressure-assisted interfacial polymerization (IP) is employed to fabricate TFC NF hollow fiber membranes in 1-inch modules through tailoring the reaction conditions. By firstly circulating a piperazine (PIP) solution in the lumen side under a positive pressure and then circulating a trimesoyl chloride (TMC) solution at atmosphere pressure, a strong, uniform and defect-free polyamide selective layer is formed on the inner surface of hollow fiber membranes. The optimal TFC NF hollow fiber membranes in 1-inch modules exhibit a pure water permeability of 8.93 L m−2 h−1 bar−1 and a molecular weight cut-off (MWCO) of 175 Da. They also show a rejection of 98.3% to MgSO4 and a high rejection of around 98% to cephalexin (molecular weight = 437 g mol−1). The optimal membranes exhibit a consistent Na2SO4 rejection of ∼85% and nearly no NaCl rejection over a 30-day performance test using a high salinity feed solution containing 200 g/L NaCl and 10 g/L Na2SO4. The impressive performance suggests that the newly developed TFC NF hollow fiber membrane has great potential to be used in the chlor-alkali and pharmaceutical industries.