A 6FDA based polyamide-imide, 6F-PAI-1, is compared to Pebax (R), a commercially available rubbery polyether/polyamicle block copolymer, for the simultaneous separation of CO2 and H2S from CH4. Feed streams of 20/20/60 and 5/45/50H(2)S/CO2/CH4 were used to compare the effect of acid gas concentration on the separation efficiency of 6F-PAI-1 and Pebae (R) under industrially relevant conditions. 6F-PAI-1 showed CO2/CH4 selectivities at 850 psia total feed pressure of 30 and 40 for the 20/20/60 and 5/45/50 Iced streams, respectively, while selectivity for H2S/CH4 was approximately 20 for both feeds. Pebax showed selectivities of 40 and 10 for H2S/CH4 and CO2/CH4, respectively. Both selectivities were mostly independent of acid gas concentration in the feed, an unsurprising trend considering the non-glassy nature of this material. The selectivities in 6F-PAI-1 translated to less than 6% CH4 lost in the permeate stream for both feeds, while for the 5/45/50 feed, CH4 fraction in the permeate at 850 psia was less than 4%. These promising results suggest that glassy polymers possessing favorable intrinsic plasticization resistance, such as 6F-PAI-1, may be appropriate for the typical case of natural gas sweetening where CO2 concentration in the feed is higher than it is for H2S. (C) 2014 Elsevier B.V. All rights reserve