Polymer membranes for gas separation are extensively applied on large scale in many (petro)chemical processes. With the electrification and transition to a circular economy, the number of new applications is expanding, due to their low footprint and low energy consumption for separation. Though as existing membranes are originally designed for other separations, this requires tailoring of membrane performance. In this presentation I will discuss the molecular design of polymer membranes for sustainable process applications. I will show how sophisticated molecular design of membrane chemistry allows controlling the performance of these membranes in sustainable, macroscale applications for gas separation.