The key parameters for gas separations employing membranes are the permeability of a specific component of the gas mixture and the selectivity. Membrane gas separation employing polymeric membranes has been commercially used since the 1970s generating a significant amount of academic and industrial research activity. It was recognized that an empirical upper limit (the well-known “upper bound”) for the combined selectivity and permeability exists [1]: the selectivity generally decreases with increasing permeability of the more permeable gas component. Molecular sieve membranes with well-defined uniform pore structure would be considered to be the true upper bound limit for polymeric membranes. Recently this upper bound has been updated for relevant gas separations by microporous rigid  polymeric membranes [2, 3].
In this contribution, an analysis of recent findings for industrially relevant gas pairs, such as CO₂/CH₄, CO₂/N₂ is given.

References
[1] L.M. Robeson, Correlation of separation factor versus permeability for polymeric membranes,
J.Membr. Sci. 62 (1991) 165-185; L.M. Robeson, The upper bound revisited, J. Membr. Sci. 320 (2008) 390.
[2] B. Comesaña-Gándara, J. Chen, C. Grazia Bezzu,  Mariolino Carta, Ian Rose, M.-C. Ferrari, E. Esposito, A. Fuoco,  J. C. Jansen  and  N. B. McKeown,  Redefining the Robeson upper bounds for CO₂/CH₄ and CO₂/N₂ separations using a series of ultrapermeable benzotriptycene-based polymers of intrinsic microporosity, Energy Environ. Sci. 12 (2019)  2733-2740. 
[3] M.G. Buonomenna, Microporous Polymers for Gas Separation Membranes: Overview and Advances, pp 1-29  In: Hussain C., Thomas S. (eds) Handbook of Polymer and Ceramic Nanotechnology. Springer, Cham. https://doi.org/10.1007/978-3-030-10614-0_48-1

M. G. Buonomenna (Salerno, 1975), graduated in Chemistry in 1998 (110/110), obtained the license and status of Professional Chemist in 1999 (100/100). She was awarded a Research Fellowship in Membrane Materials and Operations in 1999 from the Institute on Membrane and Technology (ITM) (former IRMERC)-National Research Council of Italy (CNR) and a PhD in Chemical Engineering and Materials in 2005 from the University of Calabria.
In February 2014 and for the second time in October 2018 she obtained the qualification of Associate Professor in Chemical Fundamentals of Technologies from the Italian Ministry for Instruction, University and Research (MIUR).
Her research activities relate to membrane science and technology for sustainable processes.
She is author of more than 70 scientific papers in peer-reviewed international journals, 1 book on nanostructured membranes for energy applications, more than 90 contributions published in conferences proceedings, 10 chapters of scientific books, editor of 1 book on advanced membrane materials, guest-editor of 9 Special Issues in peer-reviewed international journals, and member of the Editorial Boards for a number of international peer reviewed journals. She has been an Invited Speaker in numerous international conferences.
She serves as reviewer for several international scientific journals and  as Expert Evaluator for International Funding Agencies.