Pervaporation separation of water/isopropanol mixture using sulfonated poly(ether ether ketone) (SPEEK) membranes: transport mechanism and separation performance

Homogeneous membranes based on sulfonated poly(ether ether ketone) (SPEEK) of different sulfonation degrees (SD) were tested for sorption and pervaporation dehydration of water/isopropanol mixtures in a wide range of feed composition. Coupled transport was observed in this pervaporation separation process, the permeation rate of isopropanol increases with the increase of water feed composition. A new transport mechanism considering the coupled transport was proposed, which assumes that there are two types of environments in SPEEK membranes, namely the hydrophilic environment A and hydrophobic environment B. Water can only dissolve in environment A, isopropanol can dissolve in both environments. According to this model, the water percentage in permeate is mainly determined by the relative diffusivity and relative concentration of water to isopropanol in environment A. Some other separation characteristics of the membranes are also discussed based on this mechanism.