To evaluate the membrane performance via gas permeation we decided to immediately measure binary gas mixture of He and CH 4 . A home-built Wicke-Kallenbach membrane permeator is used, which is operated at 60 °C and without feed pressure. Before the experiment, the membranes were activated in a vacuum oven and the membranes were routinely checked for their pressure resistance in the device before measurement. We simulate a mixture of He in a natural gas (CH 4 ) reservoir of 4 %, mimicking the real-world process from a feedstock. In the upstream, the feed gas was adjusted to be 100 ml/min, meaning 4 ml/min He and 96 ml/min CH 4 , controlled by mass flow controllers, while N 2 was used as a sweep gas on the downstream with 1 ml/min, carrying the permeate to the gas chromatograph. This allows for a continuous measurement at equilibrium conditions.