Pervaporation of toluene and toluene/acetone/ethyl acetate aqueous mixtures through dense composite polydimethylsiloxane membranes

The study was aimed at removing organic solvents from aqueous solutions using pervaporation. The tests were carried out on a composite polydimethylsiloxane (PDMS) membrane manufactured by GKSS/ Forschungszentrum Geesthacht, Germany and a polydimethylsiloxane membrane filled with carbon black (PDMS + cb) prepared in a laboratory. There were two runs: the first one tested an aqueous toluene solution as feed, while the other used a mixture of solvents: toluene, acetone and ethyl acetate. It has been found that the PDMS membrane without carbon black removed all the components of the mixture, displaying a very high efficiency of the process. However, the selectivity and enrichment factors turned out to be relatively low. The PDMS + cb membrane produced slightly lower removal degrees as well as acetone and ethyl acetate fluxes compared to the PDMS membrane, yet their concentration at the permeate side of the membrane was considerably higher. It has also been observed that the presence of other solvents did not affect greatly toluene permeation — its final removal seemed to be independent of the composition of the feed used.

The results presented herein reveal that the membrane selected to remove organic solvents from water was the right choice. The PDMS membrane without carbon black yielded a very high efficiency in removing all the components of the mixture, however, both selectivity and enrichment factors for particular components were relatively low. As for the PDMS membrane filled with carbon black, the fluxes were slightly lower, but it correlated with the much better concentration of particular components at the permeate side of the membrane. Regardless of the membrane used, toluene flux remained at almost identical level. In conclusion, the membrane filled with carbon black might be more favourable, provided the process was aimed at concentrating and removing toluene alone. However, if the objective was the removal of all the solvents, the PDMS membrane without carbon black would be better.