Study on the effect of crosslinking temperature on microporous polyamide membrane structure and its nitrogen/cyclohexane separation performance

Membrane performance is a vital factor for the membrane-based waste VOCs treatment, which is not only affected by the properties of monomers or polymers, but also by crosslinking temperature during the membrane-forming procedure. However, little attention has been paid to the latter. In this work, the effect of the crosslinking temperature on membrane structure and separation performance was studied. The properties of polymers and membranes were first characterized by X-ray photoelectron spectroscopy, positron annihilation lifetime spectra, and so on. Apparent differences in physicochemical properties between polymers and membranes can be observed. Different crosslinking temperatures were thus chosen to investigate their effects on the membrane structure, and the separation performances of membranes obtained under different crosslinking temperatures for the molecular sieving of nitrogen over cyclohexane were also evaluated. Results showed that higher temperature leads to higher crosslink and smaller pore size so that 99% rejection can be obtained when the crosslinking temperature over 80 °C was used. While the permeability of nitrogen slightly decreases with increasing temperature from 50 to 120 °C.