This study dealt with the separation of binary water-phenol and water-methanol mixtures and ternary water-phenol-methanol mixtures by pervaporation (PV) with polydimethylsiloxane (PDMS) membranes. The effects of the operating conditions (feed temperature, feed concentration, and feed flow rate) on the separation performance for binary mixtures were investigated. An increase in temperature or concentration increased the total permeation flux and decreased the organic separation factor. In other words, an increase in the temperature or feed organic concentration increased the water flux more significantly than the organic compound flux, which resulted in a separation factor reduction. Also, an increase in the feed flow rate increased the total flux and separation factor because the boundary layer effects diminished. The vaporliquid equilibrium separation factor (alpha(VLE)) and pervaporation separation factor (alpha(PV)) values for the PDMS membrane were calculated, and this showed that alpha(PV) for the water-phenol mixture was greater than alpha(VLE). This means that the membrane was highly efficient for the PV separation of phenol from dilute aqueous solutions relative to the separation of methanol. This was due to the fact that phenol has a higher solubility parameter than methanol in silicone membranes. To study the effect of a third component on membrane performance, PV experiments were also carried out with water-phenol-methanol mixtures. The results for total permeation flux and the phenol separation factor for PDMS membranes in contact with water-phenol-methanol ternary mixtures are similar to those in contact with water-phenol binary mixtures. The phenol separation factor of the membrane in contact with the ternary mixture was slightly lower than that in contact with the binary mixture. (c) 2007 Wiley Periodicals, Inc.