Helium extraction from natural gas using DD3R zeolite membranes

•High He/CH4 selectivity was achieved on all-silica DD3R zeolite membranes.•He/CH4 selectivity was dominated by the diffusion selectivity through DDR pores.•The He concentration increased by 39 times for 0.22% He-containing He/CH4 mixture.•The membrane was stable >130 h in He/CH4 mixture feed even containing 3.6% ethane.