The differences in structure and transport mechanisms of nanofiltration (NF) and pervaporation (PV) membranes
were studied by measuring (a) water and ethanol fluxes and raffinose rejections obtained during nanofiltration
with two NF membranes (Desal 5 DK and MPF 50) and two PV membranes (PV 2201 and PV 1070); (b)
water and ethanol fluxes and water/ethanol-n-propanol separation factors obtained during pervaporation with
the same membrane sequence; and (c) gas and vapor (water, ethanol) permeance with the same membrane
sequence. In the nanofiltration experiments, it was observed that transport is determined by hydrophilicity/hydrophobicity of the membrane, the presence of pores and their geometry, membrane thickness, and solvent
properties. Pervaporation experiments confirmed the nanoporosity of the NF membranes; a comparison of
fluxes showed that transport in pervaporation is thought to depend on preferential sorption. Gas permeance
measurements with inert gases provided clear evidence for the porous nature of NF Desal 5 DK and the
dense nature of PV 1070; PV 2201 was found to be porous. However, this membrane swells significantly
when brought in contact with water or ethanol vapors, rendering a dense membrane suitable for pervaporation.
For the other membranes, swelling was also observed, together with plasticization of the polymers.
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