Effect of Trace Amounts of Water on Organic Solvent Transport through γ-Alumina Membranes with Varying Pore Sizes

Abstract

The transport behavior of toluene and n-hexane in γ-alumina membranes with different pore diameters was studied. It was shown that the permeability of water-lean hexane and toluene is in agreement with Darcy's law down to membrane pore diameters of 3.5 nm. The presence of molar water fractions of 5−8·10^-4 in these solvents led to a permeability decrease of the γ-alumina layer by a factor of 2−4 depending on pore size. In general, a lower permeability was found for hexane than for toluene. Moreover, in the presence of water a minimum applied pressure of 0.5−1.5 bar was required to induce net liquid flow through the membrane. These phenomena were interpreted in terms of capillary condensation of water in membrane pores with a size below a certain critical diameter. This is thought to lead to substantial blocking of these pores for transport, so that the effective tortuosity of the membrane for transport of hydrophobic solvents increases.