Poly(sulfone)/sulfonated poly(ether ether ketone) blend membranes: Morphology study and application in the filtration of alcohol based feeds

Charged nanofiltration membranes were prepared by blending polysulfone (PSf) with the polyelectrolyte sulfonated poly(ether ether ketone) (SPEEK). The blend membranes were applied in the separation of low molecular weight dyes from alcohol based feeds, i.e. methanol, ethanol, 2-propanol and 2-butanol. The charges were easily introduced by blending the polyelectrolyte with PSf during the membrane preparation. Tetrahydrofuran was added to the casting solutions as a tool to tune the filtration properties of the membranes towards lower molecular weight cut-offs. Membrane morphologies - cross-sections, skin-layers as well as surface structures - were studied in detail with SEM and AFM. The results showed that addition of SPEEK leads to a more open membrane structure, and consequently higher solvent fluxes. Due to Donnan exclusion, these charged, high-flux nanofiltration membranes showed the best retention for solutes with the same charge as the polyelectrolyte.