Temperature-regulated gas adsorption on LTA zeolites: Observation of sorption isotherms for methane, hydrogen, nitrogen and carbon dioxide

Temperature-regulated gas adsorption of various zeolite LTAs with different cations of Cs2+, 2+ , K+, + , Na+, + , and Ca2+ 2+ (namely, Cs-A, 3A, 4A, and 5A) was analysed in the presence of different gas molecules of H2, 2 , CO2, 2 , N2, 2 , and CH4 4 for pressures up to 800 kPa and temperatures ranging from 77.15 to 363.15 K. Over the range of test conditions, zeolite 5A (containing Ca2+ 2+ cations) exhibited the highest uptake at 800 kPa for CO2, 2 , H2, 2 , CH4, 4 , and N2, 2 , with capacity values of 5.69 mmol.g-1,- 1 , 1.14 mmol.g-- 1 , 6.60 mmol.g-1,- 1 , and 6.10 mmol.g-1,- 1 , at 298.15 K and 201.15 K respectively. Zeolite 4A (containing Na+ + cations) exhibited 0.74 mmol.g-- 1 for H2 2 adsorption at 201.15 K, and 800 kPa. In contrast, pores were inaccessible to H2 2 on ion-exchange Cs-A zeolite at a temperature range of 77.15-343.15 K, due to larger cation Cs2+ 2+ (CsA) comparison with Na+ + (4A). Interestingly, zeolite 3A (containing K+ + cations) showed a negligible capacity for the larger gas molecules, CH4 4 and N2, 2 , ascribed to the pore space blocked by the larger K+ + cations (relative to the smaller Na+ + and Ca2+ 2+ cations). Zeolite 3A exhibited a temperature-dependent behaviour (i.e., presumably a "trapdoor" effect) with H2 2 wherein adsorption was negligible at 77.15 K, but was significant above approximately 200 K. For N2, 2 , zeolite 4A exhibits similar temperature-regulated adsorption characteristics (i.e., presumably a "trapdoor" mechanism as well). These zeolite materials used in various temperature swing processes could be particularly beneficial in natural hydrogen production (with H2/N2 2 /N 2 separation with 3A), the production of synthetic fuels from CO2/H2 2 /H 2 mixtures (with both 3A and 4A), CO2 2 capture from waste streams, and applications for H2/N2 2 /N 2 separation.