Simulation of binary gas separation through multi-tube molecular sieving membranes at high temperatures

An experimentally validated theoretical model was developed to investigate the influence of operating conditions on the performance of a multi-tube membrane module containing cobalt oxide silica (COxS) membranes with molecular sieving properties. The model investigated the separation process for a binary gas mixture consisting of H2 and Ar at 400 °C. Engineering parameters such as feed flow rate, feed pressure, module size and flow configuration were systematically varied in order to optimise the separation performance promoting three main goals: H2 yield, H2 purity and H2 recovery. Changing these parameters led to different flows and H2 fractions in the feed domain, thus altering the driving forces for the preferential permeation of H2. The simulated results suggest that gas separation was greatly improved by reducing the module radius which meets all of the three aforementioned optimisation criteria. Interestingly, increasing the feed flow rate and feed pressure were found to be beneficial but the former led to lower H2 recovery whilst the latter did not deliver the same purity when compared to lower feed pressure. In addition, two flow configurations, counter-current and co-current, were compared. It was observed that the results of counter-current were effectively the same as the co-current. This was attributed to the high gas-through-gas diffusion for high-temperature membrane operation. Finally, neglecting diffusion effects, or considering advection only, leads to over prediction of H2 permeate molar fraction.

• A model was validated for a multi-tube membrane module for binary gas separation. • H2 driving force is greatly affected by process conditions and module design. • The radius of the module influences significantly on H2 purity and recovery. • Similar counter and co-current flows due to high gas-through-gas diffusion.