Boehmite sol-coated membrane preparation for the separation of aqueous alcohol

Abstract

The boehmite-sol-coated membrane was prepared for using the water-repellent characteristics of γ-AlOOH. The stable boehmite sol was prepared in advance of the coating on the porous membrane surface; the preferred molar ratios of i-PrOH, EAcAc, and H 2O to Al(O-sec-Bu) 3 for the stable boehmite sol were 20, 1, and 4, respectively. The membrane coated with boehmite-sol was applied to the separation of alcohol from aqueous ethanol mixture. The separation factors of the sol-coated-membrane vary with ethanol concentrations in feed and numbers of sol-coating; the separation factors of the 5 times boehmite sol-coated-membrane were 1.57, 1.14, 1.06, 1.49, 1.26, and 1.24 at each ethanol concentrations of 1wt.%, 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, and 50 wt.% EtOH in feed; for the 10 times one, 2.26, 1.76, 1.24, 1.10, 1.74, and 1.39. The 10 times coated-membrane showed a little bit higher separation factor than the 5 times one. It was expected that the boehmite-sol-coated membrane would have somewhat higher separation factor; however, the coated membrane did not show so much high separation factor; the existence of air in the hydrophobic pores in the film on glass plate might causes the super-water-repellency. In case of the membrane processes, however, the air could not be trapped inside pores because liquid molecules were passing through the membrane pores. Therefore, it might be concluded that the coated-membrane did not show high separation factor.