Why is membrane selectivity often prioritized over permeability in practical gas separation applications? Recommendations for relevant research articles are appreciated.
Siraj Ahmad, there can be more answers but probably the best reason is that you can never achieve a better separation in a single step if your selectivity is not enough but you can easily increase the flow rate by increasing the total membrane area or the number of membrane modules if your permeability is not high enough.
Depending on whether you are interested in the permeate or the retentate, you can play with the stage cut, feed pressure or even the permeate pressure to optimize your separation but the final purity will always be limited by the membrane selectivity.
Once you have reached your limit, you can still improve the final purity of the gases and limit the losses of the desired product by connecting more modules in series or in parallel, with additional recycle streams, but this is going to impact the total complexity of the separation process, and thus the total costs (see for instance the commercial biogas upgrading process where both high purity methane and high purity CO2 are desired, with minimum methane losses: Article Simultaneous production of biomethane and food grade CO2 fro...
).For the average researcher, selectivity will probably dominate, but for
In practical gas separation, selectivity is prioritized because it determines the membrane’s ability to produce a high-purity product stream. While high permeability allows faster flux, it is of little use if the membrane cannot discriminate between gases. Industrial processes demand strict purity standards, and low selectivity would require multiple stages or costly downstream treatment. Thus, a moderately permeable but highly selective membrane is often more valuable than a highly permeable but poorly selective one. Perhaps Dr. Muhd Izzudin Fikry Zainuddin should have better explanation on this.
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