New Approach for Activation of N₂-Selective ETS-4 Membrane for Nitrogen Separation from N₂/CH₄ Mixture

Microporous titanosilicate ETS-4 zeotype membrane, with its 4 Å pore openings, is an adequate material for the kinetic separation of nitrogen from methane. Obtaining high N₂/CH₄ permselectivity, small-sized ETS-4 powder was synthesized by aging method, and then utilized as membrane seeding powder. Highly N₂-selective ETS-4 membranes were fabricated utilizing a new recipe and the secondary growth approach on α-alumina supports. XRD, FESEM, and EDX studies were used to analyze the synthesized ETS-4 powder and membranes. The effect of membrane activation temperature (80–140 °C) on permeance of N₂ was evaluated. In addition to N₂ and CH₄, the membrane permeance was also evaluated for O₂ and Ar gases. Regarding the ETS-4 membranes, N₂ permeance increased gradually as the activation temperature was raised in the 80–140 °C range, reaching its highest value (i.e., 2.6 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹) after activation at 140 °C. The permeances of N₂ and CH₄ gases were measured at 30, 50, and 70 °C, and a pressure difference up to 600 kPa. N₂/CH₄ permselectivity of 75.19 (N₂ permeance of 1.94 × 10^–8 mol m-² s⁻¹ Pa⁻¹) were obtained at 30 °C and 200 kPa of feed pressure. The results revealed that ETS-4 membranes have great potential for N₂ removal from natural gas due to highest N₂/CH₄ permselectivity among the other membranes. Graphical Abstract: (Figure presented.).