Removal of dilute ethylene using repetitive cycles of adsorption and plasma-catalytic oxidation over Pd/ZSM-5 catalyst

Abstract

Ethylene removal was investigated using a reactor system combining plasma and a catalyst (Pd/ZSM-5). The catalyst could adsorb ethylene effectively even under harsh conditions of 100% humidity and 10 000 ppm CO2. The air in a 1 m3 container, which was prepared to imitate agricultural storage, was circulated through the reactor. The process of ethylene treatment consists of one cycle comprising adsorption, plasma-catalyst oxidation, and desorption, and this cycle is repeated until the ethylene is completely removed. Among the variables such as initial concentration, amount of catalyst, voltage, adsorption time, and flow rate of the circulating gas, the most influential were the flow rate and the catalyst amount. The lower the initial ethylene concentration is, the less time required for complete removal, although the percent removal was not largely affected by the initial concentration (20–200 ppm). The ethylene removal was improved by injecting 20 ppm ozone into the container once per cycle. In the absence of ozone, using only the plasma-catalytic reactor, it took 20 h for complete removal, whereas all ethylene was removed in about 8 h in the presence of ozone. A mass balance model could provide a good prediction of the temporal variations of ethylene concentration. The long-term storage stability of a Fuji apple in the container was tested for 40 d. A comparison of the control group with the group subjected to ethylene processing revealed that the ethylene concentrations were significantly different from each other, indicating the efficiency of the plasma-catalyst system. After 40 d of storage, the hardness and sugar content were higher in the group from which ethylene was removed than in the control group, and the acidity was higher in the control group. Furthermore, after 40 d, the control group showed a decay rate of 10%, whereas that of the group that underwent ethylene processing was only 1%.