Effects of different alkali metal cations in FAU zeolites on the separation performance of CO2/N2O

Abstract

N2O and CO2 coexist in the exhaust gas of adipic acid production, while their physical properties are extremely similar, making it a big challenge to separate CO2 and N2O mixture. Here, CO2/N2O separation performance on Faujasite (FAU) zeolites with same structure, different Si/Al ratio (zeolite X and Y) and alkali metal cation (Li＋, Na＋, K＋) are researched. With the increase of the alkali metal cation radius (from Li+ to K+), the difference between the adsorption capacity of CO2 and N2O and ideal adsorbed solution theory (IAST) selectivity of CO2/N2O become more significant. Among the zeolite investigated, K-zeolites have bigger difference on CO2 and N2O adsorption capacities and better IAST selectivity (KX: 4.35, KY: 2.15) than Li+ and Na+ exchanged zeolites (NaX: 2.29, LiX: 1.28, NaY: 1.58, LiY: 1.38) at 1 bar and 298 K, and with the increase of K+ exchange degree, the selectivity to CO2 increases. According to the breakthrough experiment, CO2/N2O mixture (50%/50%, v/v) can be separated by KX efficiently with shorter penetration time and relatively longer retention time than KY. Pressure swing adsorption (PSA) simulations further indicate that, by one step enrichment, pristine 50% N2O can be enriched to 80.83% with a recovery of 61.62% on KX.