Membrane gas separations and energy efficiency: Exploring the selective membrane-piston concept

• Membrane Piston is a transient process for simultaneous gas compression and separation. • This new process shows promising results to significantly reduce energy consumption. • It achieves nitrogen purity levels from air exceeding 95 %. A new process call Membrane Piston is proposed to investigate the possible energy efficiency improvement by combining compression and gas separation under unsteady state. The membrane on the piston-head acts as a permeable moving barrier between the two compartments. The movement of the membrane initiates the compression, triggering the mass transfer. The decreasing amount of substance at high pressure leads to lower work requirement. A model based on mass and energy balances provides the temporal evolution of the parameters. This new concept is presented through an air separation case study, operated in isothermal and non-isothermal modes. Compared to a steady-state classical membrane separation at identical purity in N 2 and pressure ratio, this process shows breakthrough energy efficiency improvements, such as 33 to 63 % decrease for 95 to 97 % N 2 purity.