The possibility of paraffins and C4 olefins mixture separation on membranes made of polyethylene with radiation-grafted sulfonated polystyrene is shown. The selective separation is achieved due to the butenes and isobutene facilitated transfer in the form of a Tr-complex with a proton. Moreover, despite the significantly larger cross-sectional size, obstructing the transfer, isobutene molecules are also transferred much faster than butane, and the separation coefficient reaches 3.8. An unusual fact was discovered of separation selectivity and permeability increase with the separated gases flow humidity rise. (C) 2020 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.