Permeability, permeance and selectivity: A preferred way of reporting pervaporation performance data

A majority of the papers on pervaporation published in the Journal of Membrane Science (JMS) report results as raw data; that is, as fluxes (Ji) and separation factors (βij). These values are not only a function of the intrinsic properties of the membranes used, but also depend on the operating conditions of the experiments (feed concentration, permeate pressure, feed temperature): change the operating conditions and all the numbers change. This makes comparison of pervaporation data sets obtained under different operating conditions difficult. Furthermore, these values can lead to confusion in understanding the real trend of membrane intrinsic properties as operating conditions change. In this paper, the benefits of reporting the results in a normalized form, that is, as permeabilities (Pi), permeances (Pi/ℓ) and selectivities (αij) are described. Data from our laboratory and from two recent papers are used to illustrate these benefits.