Pervaporation of acetic acid/water mixtures through silicalite filled polydimethylsiloxane membranes

Abstract

The preferential pervaporation of acetic acid over water is achieved with silicalite filled polydimethylsiloxane (PDMS) membranes. The effect of silicalite addition is not positive at the feed temperature of 25°C, but improves with increasing feed temperature. At a feed temperature of 45°C, silicalite addition enhances not only the separation factor but also the permeation flux of the pervaporation. This improvement may be attributed to the reduction in kinetic limitation on sorption/desorption processes and the enlargement of sorption difference between acetic acid and water towards silicalite. At 25°C, the sorption ratio of acetic acid to water is 3.9, but 4.9 at 45°C. It is further found that at a silicalite loading of 49.9 wt.%, the separation factor versus feed acetic acid concentration curve exhibits a maximum and this maximum shifts to lower feed acetic acid concentrations with increasing feed temperature. Further increasing the silicalite loading to 69.2 wt.%, results in the formation of connected pores in the membrane and thus failure of the membrane in providing a separative pervaporation. The addition of silicalite is also found to enhance the thermal stability of the membrane. The pervaporation behavior of the silicalite filled PDMS membrane seems to fall in between those of pure PDMS and pure silicalite membranes.