Asymmetric or composite polyquinoxaline base membranes, possible application to gaseous permeation and more particularly gaseous mixture fractionation, and mainly dehydration and deacidification of gases, especially gaseous hydrocarbons

An asymmetric gaseous permeation membrane, also applicable to fractionation of a gaseous mixture and in particular dehydration and deacidification of gases, in particular gaseous hydrocarbons, which is obtained from polymers of the polyquinoxaline family presenting the unit:

• ##STR15## and R=H or phenyl radical,
• G=carbon-carbon bond, or --O--, --S--, --SO.sub.2 --, --CO-- ##STR16## presenting a dense "skin" of low thickness ranging from 0.05 to a few microns substantially without defects and any existing pores having a diameter less than 10 .ANG. in order to permit gas molecules to pass through by a dissolution-diffusion mechanism, and having a permeability to methane as measured at 20.degree. C. under 3 bars of 10.sup.-6 to 10.sup.-3 cm.sup.3 /cm.sup.2.sec.cm Hg, together with a separation on factor H.sub.2 O/CH.sub.4 under the same conditions of at least 10.