Removal of N2O from industrial gaseous streams by selective adsorption over metal-exchanged zeolites

The behavior of ZSM5 zeolites in the acid, sodium form or ion-exchanged with various metal ions (Cs, Sr, Pa, Mg, Fe, Co, Cu, Ag, Ph, Ga, In, La, and Ce) and that of Y and X zeolites ion-exchanged with Ba ions are discussed with reference to their behavior in the adsorption of N2O from gaseous industrial streams containing low (<0.1-0.2%) concentrations of N2O, to produce a concentrated (>5%) stream of N2O for either autothermic operation of the decomposition of N2O or use of N2O as a selective oxidant. Ba-ZSM5 show significantly better performances than other metal-exchanged zeolites in the adsorption of N2O, although water competes with N2O for adsorption. However, the adsorption of N2O is faster than that of water, and thus it is possible to adsorb N2O even in the presence of larger (40 times higher) amounts of water in the feed. It is also shown that it is possible to have a dual-bed selective adsorption, where first water adsorbs selectively on an alumina bed and then N2O is adsorbed on a Ba-ZSM5 bed. It is suggested that the enhanced adsorption properties of Ba-ZSM5 are related to the presence of naked Ba2+ ions that creates a strong electrostatic field within the zeolite cavities which allows the orienting of the N2O molecule and its trapping inside the zeolite.