SAPO-34 Membranes for N2/CH4 separation: Preparation, characterization, separation performance and economic evaluation

SAPO-34 membranes were synthesized by several routes towards N2/CH4 separation. Membrane synthesis parameters including water content in the gel, crystallization time, support pore size, and aluminum source were investigated. High performance N2-selective membranes were obtained on 100-nm-pore alumina tubes by using Al(i-C3H7O)3 as aluminum source with a crystallization time of 6h. These membranes separated N2 from CH4 with N2 permeance as high as 500 GPU with separation selectivity of 8 at 24°C for a 50/50 N2/CH4 mixture. Nitrogen and CH4 adsorption isotherms were measured on SAPO-34 crystals. The N2 and CH4 heats of adsorption were 11 and 15kJ/mol, respectively, which lead to a preferential adsorption of CH4 over N2 in the N2/CH4 mixture. Despite this, the SAPO-34 membranes were selective for N2 over CH4 in the mixture because N2 diffuses much faster than CH4 and differences in diffusivity played a more critical role than the competitive adsorption. Preliminary economic evaluation indicates that the required N2/CH4 selectivity would be 15 in order to maintain a CH4 loss below 10%. For small nitrogen-contaminated gas wells, our current SAPO-34 membranes have potential to compete with the benchmark technology cryogenic distillation for N2 rejection. •The membranes are selective for N2 over CH4 with selectivity of 8.•This separation performance is superior to those of the state-of-the-art membranes.•Membranes have high potential to compete with benchmark technology.