Carbon nanotube enhanced selective micro filtration of butanol

Abstract

In this study, we present the development of a carbon nanotube (CNT), immobilized membrane (CNIM) via a phase inversion process for dewatering butanol via microfiltration. The CNTs enhanced membrane hydrophobicity and butanol permeation via adsorption on the CNTs surface leading to relatively high levels of preconcentration, which was not possible using a plain PTFE membrane. The CNIM exhibited a water contact angle of 136 ± 2°, indicating high hydrophobicity. The contact angle decreased with an increase in butanol concentration due to the strong interaction of the CNTs with the latter. The water-butanol mixtures behaved differently at different concentration zones namely water in butanol, WIB (over 80 percent butanol), butanol in water, BIW (below 30 percent butanol), and butanol-water colloidal mixtures, BWCM (30 to 70 percent butanol). At low or high concentrations of butanol, the butanol was strongly hydrogen bonded with the water, and the separation efficiency was relatively lower, between 6.50 and 15.54 % in the WIB and 1.00 to 3.05 % in the BIW regions. In the BWCM regions, water butanol formed colloidal mixtures the separation efficiency was significantly higher. At a feed butanol concentration of 40 %, the water separation reached as high as 43.40 %, with a flux of 118.08 kg/(m2h). The high separation efficiency was attributed to the influence of well-dispersed CNTs on the CNIM which provided sites for the agglomeration of nano water droplets into larger ones that could be removed more easily, as well as the high partition coefficient of the butanol on the CNIM surface.