Revisiting the experimental and theoretical upper bounds of light pure gas selectivity–permeability for polymeric membranes

Abstract

Robeson [L.M. Robeson, J. Membr. Sci. 62 (1991) described "upper bounds" correlating the pure gas selectivity with the permeability of the faster gas, P A . The exponential dependence of the selectivity-permeability trade off, −1/n, according to the relationship˛A /B = P A /P B = k . The theoretical model opened the possibility of setting upper bounds for gas pairs for which experimental upper bounds were not reported. Despite quantitative predictions of both −1/n and k −1/n (oř A/B ) calculated values of˛A /B compared poorly with Robeson's upper bounds for many of the gas pairs. This work revisits Robeson's findings as well as those of Freeman and seeks to improve the predictive accuracy of Freeman's model. Robeson had noted that the low precision of many of the kinetic gas diameters could have contributed to the scatter in his correlation of −1/n and A/B . Considering this hypothesis, the gas diameters were re-estimated using the Error in the Variable Method (EVM) with the regression criterion based on the predicted selectivity at three permeabilites compared to Robeson's upper bounds. Very small changes to the gas diameters, typically <0.09 Å, made a significant improvement in the overall accuracy of the predicted selectivity and the correlation of A/B = −1/n. Freeman's f value, a constant in the E D correlation as a function of the gas collision diameter, was revised from 12,600 to 16,909 cal mol −1 (52.7 to 70.7 KJ mol − 1). Recent predictions of the theoretical upper bound are reviewed and corrections proposed based on Freeman's model and parameters for the gas pairs: N 2 /CH 4 and CO 2 /N 2 .Crown

The role of membranes in post-combustion CO2capture

“…membranes with high permeability usually present a low selectivity. The ‘upper bound’ that correlates the ideal permselectivity of a gas pair against the ideal permeability of the more permeable gas has been frequently revisited by Robeson and other researchers for polymeric dense membranes with application in gas permeation . To date, this ‘upper bound’ has shown maximum permeabilities of 10 4 –10 5 Barrer with CO 2 /N 2 selectivities lower than 10.…”

Organic-inorganic hybrid membranes in separation processes: a 10-year review

“…In the last three decades, significant improvements in the performance of polymeric membranes for ultrafiltration, nanofiltration, pervaporation, gas separation, and fuel cells have been made (Malekpour et al, 2011;Yi et al, 2010;Ferraz et al, 2007;Mehta and Zydney, 2005;Nyström et al, 1995;Pagliero et al, 1993;Vittadello et al, 2003;Thayumanasundaram et al, 2010), and our understanding of the relationships between the structure, permeability and selectivity of polymeric membranes has been greatly advanced (Geise et al, 2011;Dal-Cin et al, 2008;Cong et al 2007). Polymeric membrane materials such as polytrimethylsilyl propyne (PTMSP), poly(amide imide) (PAI), polyphosphazene (PPN), Poly(dimethylsiloxane) (PDMS), cross-linked polyethylene glycol (PEG) and polyoctylmethylsiloxane (POMS) have been continuously studied (Ozdemir et al, 2006).…”

Polymeric membrane materials: New aspects of empirical approaches to prediction of gas permeability parameters in relation to permanent gases, linear lower hydrocarbons and some toxic gases

“…As we can see from this table our effective diameters for all gases much less then appropriate Robeson's [32] and Dal-Cin's [53] diameters obtained by correction for upper bound of Robeson's dependences and with using EVM method, respectively. It is a result of Stuart's diameters using.…”