A new process design for pervaporation is described in which a composite membrane, consisting of a selective hydrophilic toplayer and a microporous hydrophobic sublayer, is used . The feed mixture is brought into contact with the hydrophilic layer. At the permeate side of the membrane a permeate-absorbing liquid is brought into contact with the porous sublayer. The driving force for this process is caused by the thermal gradient that exists between the warm feed side of the membrane and the cold permeate side. The restricting condition of this process design is that the liquid at the downstream side does not penetrate into the pores of the hydrophobic membrane. In this design, the equipment generally needed in conventional pervaporation processes to produce a reduced partial pressure at the permeate side and to condense the permeating vapour is no longer necessary. The performance of the membranes is comparable to those in a conventional pervaporation process.