H₂ Separation from CH₄ Using High-Flux DDR Membranes

We explore the separation of H2 from CH4 using ultrathin DDR membranes across various temperatures and feed pressures. Using a membrane that featured a zeolite film around 700 nm thick, we measured an H2 permeance of 7.2 × 10–7 mol/(m2·s·Pa), equivalent to 2.2 × 103 GPU, for a 1/1 H2/CH4 gas mixture at 3 bar(a) under ambient temperature. This permeance exceeds previously reported values for DDR membranes by more than 10-fold and is comparable to the permeance reported for the best palladium membranes. Under the same conditions, H2/CH4 separation selectivity reached 207, well above values earlier reported for DDR membranes. These membranes also demonstrate outstanding performance under high pressures and temperatures of up to 180 °C, and high feed pressure is needed for achieving high H2/CH4 selectivities at elevated temperatures. Interestingly, the experimental data fit a mass-transfer model that incorporates surface diffusion and surface barriers, indicating that the selective surface barrier governs the overall selective transport; meanwhile, the important parameters related to the mass transfer of H2 and CH4 in DDR zeolite are explored.