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 gamma-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 x 10(-4) in these solvents led to a permeability decrease of the gamma-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.

Hydrophobisation of mesoporous γ-Al2O3 with organochlorosilanes—efficiency and structure

“…In order to allow comparison of the different samples, the adsorbed amounts are expressed in terms of the volume of the adsorbed N 2 liquid, with a density of 0.8086 g/cm 3 .…”

“…The highly porous -alumina phase has the largest range of applications of the aluminas, and is commonly used for hydrotreating, hydrocracking, hydrogenation, reforming and methanation. In membranes, -Al 2 O 3 can be used either as an intermediate layer between an -alumina support and a selective microporous top-layer or as a selective mesoporous layer on a support [1][2][3]. As the surface is typically occupied by a large number of hydroxyl groups, enabling strong H-bonding with water, -Al 2 O 3 is hydrophilic by nature.…”

“…The N 2 adsorption and desorption isotherms showed a decrease in surface area and micropore volume for membranes silylated with Me 2 Si(OEt) 2 or MeSi(OEt) 3 , indicating that the pore wall had been covered by grafted moieties [26]. Van Gestel [8] reported the effect of surface modification ofAl 2 O 3 /TiO 2 multilayer membranes with difunctional (2 chloride groups) C1 and C8…”

Recovery of Homogeneous Polyoxometallate Catalysts from Aqueous and Organic Media by a Mesoporous Ceramic Membrane without Loss of Catalytic Activity

“…[15,16] In the present investigation a substantial amount of water was present in the reaction mixture; this originates from the H 2 O 2 stock solution and is formed as a by-product of the reaction of H 2 O 2 with cyclooctene. The phenomenon of capillary condensation is also thought to cause a non-zero threshold pressure that needs to be applied at least to initiate a net fluid flow across membranes with relatively small pores.…”

“…Only very low atomic concentrations of W and Zn (0.6 and 0.3 atom %, respectively) were observed. If we consider the specific surface area of g-600 to be 285 m 2 g À1 , [15] with W and Zn residing on the internal pore surface, the surface concentrations of W and Zn atoms per square nanometre of internal pore area are 0.6 and 0.3 nm…”