This study deals with the separation of n-butanol from aqueous solutions by pervaporation. The effects of
feed concentration, temperature, and membrane thickness on the separation performance were investigated.
Over the lowfeed butanol concentration range (0.03–0.4 wt%) studied, the butanol fluxwas shown
to increase proportionally with an increase in the feed butanol concentration, whereas the water flux
was relatively constant. An increase in temperature increased both the butanol and water fluxes, and the
increase in butanol flux was more pronounced than water flux, resulting in an increase in separation factor.
While the permeation flux could be enhanced by reducing the membrane thickness as expected for all
rate-controlled processes, the separation factor was compromised when the membrane became thinner.
The effect of membrane thickness on the separation performance was analyzed taking into account the
boundary layer effect. This could not be fully attributed to the concentration polarization, whichwas found
not significant enough to dominate the mass transport. A variation in the membrane thicknesswould vary
the local concentration of permeant inside the membrane, thereby affecting the permeation of butanol
and water differently. Thus, caution should be exercised in using permeation flux normalized by a given
thickness to predict the separation performance of a membrane with a different thickness because the
membrane selectivity can be affected by the membrane thickness even in the absence of boundary layer
effect. |
