Preparation of High-Flux Nanoporous Solvent Resistant Polyacrylonitrile Membrane with Potential Fractionation of Dyes and Na₂SO₄

In this study, a high-flux organic solvent nanofiltration (OSN) membrane with the permeance of 66.7 Lm^–2 h^–1 bar^–1 in methanol and 38.0 Lm^–2 h^–1 bar^–1 in ethanol was successfully prepared from nanoporous PAN by phase inversion and hydrolyzation in sodium hydroxide solution. The polymer concentration and hydrolysis time were varied to control the final morphology and performance. The ternary phase diagram and viscosity measurements were used to describe precipitation thermodynamics and kinetics of the phase inversion process. The prepared membranes had a typical asymmetric structure, which could be observed from images of the cross section, comprising a dense skin layer and a porous substructure in the sublayer. It was found that the polymer concentration has an apparent influence on the morphology, selectivity and permeability of the prepared membranes. FTIR analysis, ζ-potential and water contact angle measurements confirm a molecular chain rearrangement as hydrogen bonds were formed between CONH₂ and COOH groups during the carboxyl modification process. Moreover, an increase of the surface hydrophilicity was obtained by hydrolysis. A good solvent resistance and a satisfactory separation performance in the nanofiltration range were achieved with hydrolyzed PAN membranes in polar as well as nonpolar solvents. The relationship between solvent permeation and combined solvent properties (viscosity, molar diameter and solubility parameter) indicated a strong interaction of selected solvents with polymers except alkanes. The hydrolyzed PAN membrane was applied to fractionation of dyes and Na₂SO₄ solution compared to commercial NF membrane. The high dye rejection and salt permeance remained constant with the salt addition for high flux hydrolyzed PAN showing the fractionation potential for dyes and divalent salts, and establishing the strong advantage over commercial NF membranes