A hybrid distillation–pervaporation system in a single unit for breaking distillation boundaries in multicomponent mixtures

Abstract This work presents a theoretical investigation of an integrated pervaporation and distillation column within a single column. The pervaporation section consists of hollow fibres, with the separation layer on the outer diameter. Vapour and liquid flow facing the separation layer while the permeate stream is removed from the inside lumen. Several advantages have been identified from the process integration. There is no need for inter-stage heating since the latent heat required for pervaporation is supplied by condensation of the vapour in the pervaporation section. Additionally, vapour induces turbulence in the liquid phase enhancing the mass and heat transfer between the liquid and the membrane surface. Also, the liquid phase within the column is close to saturated conditions, and thus its components are also close to their maximum driving force for pervaporation at the operation pressure. As a consequence, the membrane area is reduced compared to an externally connected pervaporation–distillation hybrid system (ECPDS). Due to a higher amount of liquid that is in contact with the membrane than in an ECPDS, the driving force of the transported component is improved, reducing the required membrane area. It is shown that the hybrid column is able to overcome the distillation boundaries for multicomponent mixtures and, therefore, perform separations that are not possible in a single distillation column. Two case studies of ternary mixtures are analysed. The hybrid system behaviour is studied as function of the membrane area, position of the pervaporation section and membrane wetting.