Gas Separation of Ternary Systems In a Single Permeator with Two Membranes Using Residue Curve Maps

A method for producing residue curve maps for two-membrane (or asymmetric) permeation units is presented, and topographical behaviour of such systems is discussed. It is shown that it is possible, through manipulation of operating conditions, to advantageously modify the topography of such maps. A case study of a ternary mixture is considered for separation, where the two different membranes used are selective to two different components, but share the same intermediate component. It is shown that, under certain operating conditions, the shared intermediate component becomes a stable node of the residue curve map for a two-membrane setup. This implies that this component, under the operating conditions, becomes the slowest permeating species. It is further shown that this phenomenon can be exploited to obtain an intermediate component in high purity from a single unit operation, and improvements in product purity are noted when such a setup is compared to setups consisting of two conventional membrane permeators in series.