A membrane separation unit for a membrane separation process for separating a gas mixture, wherein the membrane separation unit has a pressure vessel and a membrane provided inside the pressure vessel in a membrane arrangement, and wherein the pressure vessel has an inlet nozzle for a feed gas mixture, an outlet nozzle for a permeate and an outlet nozzle for a retentate, wherein measurement means that are arranged at least partially inside the pressure vessel and/or inside the inlet nozzle for the feed gas mixture and/or inside the outlet nozzle for the permeate and/or inside the outlet nozzle for the retentate and are set up to record one or more parameters relevant to operation.