Significant increase of permeation flux and selectivity of poly(vinyl alcohol) membranes by incorporation of crystalline flake graphite

Poly(vinyl alcohol) membranes incorporated crystalline flake graphite (CG-PVA membranes) were prepared by solution blend methods and were characterized by positron annihilation lifetime spectroscopy. The pervaporation properties of CG-PVA membranes for separating benzene/cyclohexane mixtures were investigated by varying graphite content, feed composition and operating temperature. Degree of swelling for CG-PVA membranes increased significantly with graphite content increasing in PVA membrane. The CG-PVA-06 membrane gave the higher separation factor of 100.1 with a flux of 90.7 g/(m2 h) for 50 wt.% benzene in feed at 323 K, and the separation factor of 344.5 with a flux of 40.2 g/(m2 h) for 10 wt.% benzene in feed at 323 K. The fractional free volume of CG-PVA membranes were higher than that of PVA and cross-linked PVA membrane, indicating that incorporation of graphite into PVA membrane facilitates diffusion of benzene and cyclohexane in the membranes. The activation energy values for total and benzene permeation flux were close to each other for all the membranes. The negative sorption heat values (ΔHs) for benzene in the membranes suggested that the sorption process is controlled by the Langmuir's mode.