The effect of ethanol pre-treatment upon the mechanical, structural and surface modification of ultrafiltration membranes

The in situ ethanol pre-treatment of commercially available polysulfone (PSU) ultrafiltration(UF) membranes resulted in a 3-fold increase in the pure water flux values achieved.Techniques that lead to an increase in flux are of both academic and commercial interest. It ispostulated that the mechanisms for performance improvement can be attributed to swelling ofmembrane skin-layers, as demonstrated by changes in thickness measurements, and consideration ofpolymer solubility parameters, giving a degree of polymer plasticisation. The modification isaccompanied by a hydrophobicity increase – this parameter is linked to a greater fouling tendency.Increases in hydrophobicity contrast with the usual effect of ethanol contact, by enhancing the removalof membrane preservatives and polyvinylpyrrolidone (PVP); a common pore-forming agent.Mechanical property changes were not readily detected, whilst the apparently unaltered sub-layermasked more subtle changes occurring within the dense skin-layer. Directing analysis specifically atthe skin layer using colloidal AFM probes allowed a decoupling of changes against the support,showing that the elastic modulus was reduced as a consequence of PVP removal and plasticisation.Moreover, regional elasticity probing allowed observation of spatial inhomogeneities in elasticity;occurring due to the removal of the previously unevenly distributed PVP and leading to pitting.Consequently, the effects of pre-treatment with ethanol are shown to offer advantages by maximisingthe performance of commercial membranes, though such methods must be used with caution.Elasticity changes that occur may be detrimental to performance if carried out at high transmembranepressures, where compaction could be assisted

Black tea liquor ultrafiltration:effect of ethanol pre-treatment upon fouling and cleaning characteristics

tThis paper reports on the use of polymeric ultrafiltration (UF) membrane ethanol pre-treatment as a strategy toimprove filtration performance in terms of both flux increase, and membrane water flux recovery following cleaning.A 4-fold pure water flux (PWF) increase was observed for a 100 kDa polysulfone membrane. Marked increases inpermeate flux were recorded for ethanol treated UF membranes over a range of molecular weight cut-off values.Ethanol treatment also aided fluxes over multiple foul-clean cycles, and enabled the enhanced transmission ofpolyphenols during UF for the clarification of black tea liquor. Following tea fouling and NaOH cleaning repetitions,PWF values of treated membranes were returned to values of >150% of the untreated virgin membrane PWF over4/5 consecutive cycles, indicating that the ethanol pre-treatment strategy adopted had a prolonged effect uponsubsequent performance