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

The preferential pervaporation of acetic acid over water is achieved with s ilicalite filled polydimethylsiloxane (PDMS) membranes. The effect of silic alite addition is not positive at the feed temperature of 25 degrees C, but improves with increasing feed temperature. At a feed temperature of 45 deg rees C, silicalite addition enhances not only the separation factor but als o the permeation flux of the pervaporation. This improvement may be attribu ted to the reduction in kinetic limitation on sorption/desorption processes and the enlargement of sorption difference between acetic acid and water t owards silicalite. At 25 degrees C, the sorption ratio of acetic acid to wa ter is 3.9, but 4.9 at 45 degrees C. It is further found that at a silicali te loading of 49.9 wt.%, the separation factor versus feed acetic acid conc entration curve exhibits a maximum and this maximum shifts to lower feed ac etic acid concentrations with increasing feed temperature. Further increasi ng the silicalite loading to 69.2 wt.%, results in the formation of connect ed pores in the membrane and thus failure of the membrane in providing a se parative pervaporation. The addition of silicalite is also found to enhance the thermal stability of the membrane. The pervaporation behavior of the s ilicalitr filled PDMS membrane seems to fall in between those of pure PDMS and pure silicalite membranes. (C) 2000 Elsevier Science B.V. All rights re served.