The system Zn2+/DEHPA is a standard test system in reactive extraction [1].From application in emulsion liquid membrane permeation significant water transport from the aqueous feed phase across the membrane due to osmosis has been reported. Present research activities focus on the investigation of supported liquid membranes with the test system Zn2+/DEHPA. For modelling purposes water flux due to osmosis has been subject of investigation. The experiments were carried out in a u-tube membrane cell. DEHPA concentration in the membrane phase was varied within 0-30 [wt%]. Water flux is expected, because osmotic pressure between phase I (stripping phase, cH2SO4 = 1 [mol/L]) and phase III (aqueous feed phase, cZn = 400 [mg/L]) is not in balance. The difference in osmotic pressure between phase I and phase III is deltap = 48 [bar]. Unexpectedly osmosis driven water flux drops with increasing DEHPA concentration. Beyond DEHPA concentration of 5 [w%] no water flux is observed. Transmembrane water flux is blocked by the ion exchanger DEHPA which forms an osmotic sink.

[1] H.-J. Bart, M.J. Slater, Standard Test system for reactive extraction - Zink/D2EHPA, European Federation of chemical engineering working party on distillation, absorption and extraction, 2001