Removal of dilute nitrous oxide from gas streams using a cyclic zeolite adsorption-plasma decomposition process

Removal of dilute N₂O from gas streams by a cyclic adsorption-decomposition using Ca13X (Ca²⁺ exchanged 13X) in combination with N₂ nonthermal plasma was studied in this work. Zeolite 13X was found to be the best for N₂O uptake among tested commercial zeolites including 4A, H-β and 13X. By modifying 13X with Ca²⁺ cation using ion-exchange method, the N₂O adsorption capacity was greatly enhanced from ca. 3.5 × 10^-6 to 80 × 10^-6 molgzeolite-1 due to the stronger interaction of N₂O with Ca²⁺ cation than that with Na⁺ cation. Ca. 96% of N₂O removal efficiency at a SIE_eq (equivalent specific input energy) of 1116 J L^-1 was obtained under the cyclic operation of 60-min N₂O adsorption (initial concentration: 510 ppm, gas flow rate: 0.5 L min^-1) over Ca13X followed by 20-min plasma decomposition of adsorbed N₂O in stationary N₂ atmosphere. In comparison, a similar performance was reached at a relatively high SIE of 1700 J L^-1 as the reactor was operated under continuous plasma condition. The time period of plasma step and therefore the energy consumption could be reduced by properly circulating N₂ gas in the reactor. Also, SIE_eq was found to decrease with increasing the adsorption time, whereby ca. 95% of N₂O removal efficiency could be achieved at a SIE_eq of 298 J L^-1 as the adsorption time was 180 min. The regeneration of N₂O-adsorbed Ca13X by N₂ plasma was initiated by plasma-induced desorption of adsorbed N₂O followed by decomposing the desorbed N₂O in plasma gas phase.