Removal of Ethylene from Agricultural Storage Facilities Using Plasma and Zeolite-Based Adsorbents

This work dealt with treatment of ethylene using zeolite-based adsorbents and regeneration of the ethylene-enriched adsorbent by plasma. So as to maximize the adsorption capacity, ethylene adsorption characteristics of various zeolites (ZSM-5, USY, Y, beta, etc.) were first examined, and then Ag, Pd and Ag-Pd were supported on the zeolite exhibiting the largest adsorption capacity by ion exchange method to find out the best metal component. The prepared adsorbent pellets of about 10g were packed in a ceramic tube in which a high voltage electrode was coaxially installed. A copper foil was wound around the outer surface of the ceramic tube, which served as a ground electrode. The feed gas consisted of 79% nitrogen, 21 % oxygen and 200 ppm ethylene. The flow rates of the gases were controlled by mass flow controllers, and the total flow rate was fixed at 2 L min-1. The breakthrough curves obtained with the above mentioned adsorbents showed that Pd supported on ZSM-5 was the best, and further experiments were carried out using only Pd/ZSM-5. The treatment of ethylene with Pd/ZSM-5 and plasma was a repetitive cycle of adsorption and regeneration. First, the gas mixture containing 200 ppm of ethylene was continuously fed into the reactor for 30 min to adsorb ethylene, and plasma was created inside the zeolite-packed bed for 2 min to regenerate the ethylene-enriched adsorbent by plasma-catalytic oxidation. The measurements of the concentration of CO2 produced as a result of plasma-catalytic oxidation indicated that the adsorbed ethylene was completely oxidized within 5 min, depending on the intensity of plasma discharge. Identical results were obtained by repeating the adsorption and oxidation process several times, demonstrating that the cyclic adsorption-oxidation process using the Pd/ZSM-5 adsorbent and plasma can be applied to agricultural storage facilities for ethylene removal.