The influence of water on butanol isomers pervaporation transport through polyethylene membrane

Pervaporation transport of binary mixtures of four butanol isomers (n-butanol, sec-butanol, iso-butanol and tert-butanol) with water through polyethylene membrane was studied. The pervaporation experiments were performed with butanol water binary mixtures of wide concentration range and at different temperatures. The effects of temperature, feed composition and molecular shape of the permeating species on pervaporation characteristics were investigated. The obtained results shown that in comparison with pure butanols, the butanol permeation fluxes initially steeply decreases with increase of water concentration in the feed but then at higher water concentration levels. In the case of higher content of water in mixtures (15-95 wt.%) they remained practically constant. It was found that the butanol fluxes decrease in the following order: sec-butanol, n-butanol, tert-butanol to iso-butanol. Butanol diffusivities with small increase of water concentration in the feed increase only slightly, for higher water concentration they appear approximately concentration independent. From the comparison of butanol isomers flux and diffusivity it follows that diffusivity decreases as expected with decreasing of "linearity" of butanol molecules in the sequence - n-butanol, sec-butanol, iso-butanol and tert-butanol. The temperature dependencies of butanol isomers sorption in polyethylene membrane were measured and compared. The sorption of isomers corresponds to their vapor pressure the sorption amount decreases from tert-butanol, sec-butanol, iso-butanol to n-butanol. Calculated butanol fluxes using the first Fick's law under the assumption constant diffusion coefficient and equilibrium concentration of permeant at the feed side of the membrane are in very good agreement with experimental values. (C) 2013 Elsevier B.V. All rights reserved.