On the modeling of external mass transfer phenomena in Pd-based membrane separations

In this work, external mass transfer phenomena around hydrogen selective Pd-based membranes were analyzed experimentally and mathematically modelled. A supported Pd-Ag membrane was tested in pure hydrogen and in hydrogen/nitrogen mixtures using three different membrane lengths. Pressure, temperature, gas flow rate and feed composition were varied to obtain an elaborate dataset that could be used for analysis and modelling. Strong influences of concentration polarization and hydrogen depletion were observed. Various empirical correlations describing gas phase mass transfer around a tubular membrane from literature were tested, but none of them yielded a sufficiently accurate prediction of concentration polarization observed in the experiments. Therefore, a new Sherwood correlation was fitted using the dataset. The obtained correlation (Sh=1.846∙Gz^0.60) showed significantly improved predictive behavior for the system used in this work and represents a potentially powerful tool for the modelling of membrane separators for pure hydrogen production.