Reimagining gas separation: Drastically improving energy efficiency with the membrane-piston concept

• Energy requirement divided by 2 to 3 compared to a reference steady state. • Open mode offers better energy efficiency. • Optimal piston velocity depends on permeance. • Increased energy efficiency for higher selectivity. • Generic efficiency maps for permeance and selectivity. The use of transient membrane processes has been explored primarily from a separation standpoint, but their energetic performance remains under-investigated. The Membrane Piston concept addresses this gap by integrating gas compression and separation into a single dynamic system. This study presents a detailed model of the Membrane Piston process and conducts a comprehensive parametric analysis, focusing on piston velocity, membrane selectivity, and permeance for both air and biogas separation. The results reveal promising trends. The Membrane Piston generally requires less energy than traditional steady-state separation to reach the same final specifications, with an optimal energy point depending on the piston velocity. Increasing membrane selectivity at fixed permeance reduces the molar work required. Conversely, increasing permeance at fixed selectivity does not reduce the work directly, but allows for higher piston velocities that enable reaching the minimum work condition. These findings are extended across a wide range of ideal membrane materials and inlet compositions, offering valuable insight into system performance for specific applications. In all studied cases, the Membrane Piston achieved substantial energy savings compared to steady-state processes, with the minimum work ratio ranging from 0.63 to 0.19 in favour of the Membrane Piston.