Preparation of Polysulfone Support for Higher-Performance Reverse Osmosis Membranes

Abstract

We prepared a polysulfone (PSf) support by applying a coating of a PSf-N,N-dimethylformamide (DMF) solution on 91 μm thick nonwoven paper and then set it in water (the phase inversion reaction). The prepared PSf-substrate sheet was 280 mm wide and 10 m long. We then investigated the effects of the preparation conditions (i.e., the concentration of the PSf-DMF solution and the coating thickness) on the water permeability of the resulting PSf support. The thickness of the PSf layer increased almost linearly with the increase in the coating thickness, and the water permeability decreased monotonically with the increase in the PSf layer's thickness. A bubble point analysis revealed that the pore size dia. of the membranes was approx. 20-60 nm, depending on the PSf-DMF solution's concentration. Using these PSf membranes as the support, we prepared a reverse-osmosis (RO) membrane, the active layer of which consisted of aromatic polyamide (PA) that contained carbon nanotubes. The salt rejection rate 99.7% and water permeability at 0.56 L m^-2 h^-1 bar^-1 were achieved at 5.5 MPa for a 3.2% NaCl solution with the RO membrane, the support of which was prepared from a 17.0% PSf-DMF solution.

Keywords: RO support, polysulfone, UF membrane, phase inversion, carbon nanotube