Degradation of full aromatic polyamide NF membrane by sulfuric acid and hydrogen halides: Change of the surface/permeability properties

Abstract

We investigated the effects of both sulfuric acid (pH 0 to 2) and hydrogen halides (pH 0) on the physical, chemical, and performance properties of full aromatic nanofiltration (NF) polyamide (PA) NE90 membrane. Surface characterizations of the degraded membranes were conducted by Scanning Electron Microscopy (SEM), Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), goniometer, and zeta potential analyzer. No noticeable changes were observed in the surface properties of the membrane exposed to sulfuric acid; however, the permeable characteristics were changed due to the distortion of hydrogen bonding from additionally generated proton bridge for O-protonation and the formation of tetrahedral structure for N-protonation. On the other hand, the membrane's physico-chemical properties were much affected by hydrogen halides compared with sulfuric acid. Amide peaks N-H bending at 1541 cm−1 and C=O stretching at 1663 cm−1 in ATR-FTIR were reduced because of the reaction of the PA with halogens produced by oxidation of hydrogen halides. Molecular halogen gases (Cl2, Br2, I2) generated in the reaction bottle were also analyzed by GC/MS during exposure of the membrane to various types of acids. The increment in halogenation on PA was in the order HCI, HBr, and HI, and it was the same as the order of temporary dipole moment from the effect of molecular size. Water flux after exposure to hydrogen halides was severely decreased due to broken hydrogen bonding by halogenation. Investigation of sulfuric acid and hydrogen halides on the change of the physico-chemical characteristics in the NE90 can be utilized when full aromatic NF membrane is applied to treat/recycle several industrial processes, which include sulfuric acid or hydrogen halides.