Improvement of Ethylene Removal Performance by Adsorption/Oxidation in a Pin-Type Corona Discharge Coupled with Pd/ZSM-5 Catalyst

Shirjana Saud,Seong Bong Kim,Ho Won Lee,Young Sun Mok,Seung-Geon Kim,Duc Ba Nguyen

doi:10.3390/catal10010133

Abstract

The adsorption and plasma-catalytic oxidation of dilute ethylene were performed in a pin-type corona discharge-coupled Pd/ZSM-5 catalyst. The catalyst has an adsorption capacity of 320.6 μ mol g cat − 1 . The catalyst was found to have two different active sites activated at around 340 and 470 °C for ethylene oxidation. The removal of ethylene in the plasma catalyst was carried out by cyclic operation consisting of repetitive steps: (1) adsorption (60 min) followed by (2) plasma-catalytic oxidation (30 min). For the purpose of comparison, the removal of ethylene in the continuous plasma-catalytic oxidation mode was also examined. The ethylene adsorption performance of the catalyst was improved by the cyclic plasma-catalytic oxidation. With at least 80% of C2H4 in the feed being adsorbed, the cyclic plasma-catalytic oxidation was carried out for the total adsorption time of 8 h, whereas it occurred within 2 h of early adsorption in the case of catalyst alone. There was a slight decrease in catalyst adsorption capability with an increased number of adsorption cycles due to the incomplete release of CO2 during the plasma-catalytic oxidation step. However, the decreased rate of adsorption capacity was negligible, which is less than one percent per cycle. Since the activation temperature of all active sites of Pd/ZSM-5 for ethylene oxidation is 470 °C, the specific input energy requirement by heating the feed gas in order to activate the catalyst is estimated to be 544 J/L. This value is higher than that of the continuous plasma-catalytic oxidation (450 J/L) for at least 86% ethylene conversion. Interestingly, the cyclic adsorption and plasma-catalytic oxidation of ethylene is not only a low-temperature oxidation process but also reduces energy consumption. Specifically, the input energy requirement was 225 J/L, which is half that of the continuous plasma-catalytic oxidation; however, the adsorption efficiency and conversion rate were maintained. To summarize, cyclic plasma treatment is an effective ethylene removal technique in terms of low-temperature oxidation and energy consumption.

Highlights

Volatile organic compounds (VOCs) can be harmful to the environment and human health
The results showed that the cyclic adsorption and plasma-catalytic oxidation provides low-temperature oxidation of C2 H4, improvement of adsorption performance, and energy efficiency for the removal of low-concentration of C2 H4 (30 ppm) in the airflow
The adsorption capacity of the catalyst is a critical factor in a cyclic adsorption-oxidation process, adsorption of the theuse catalyst is a critical factor in and a cyclic adsorption-oxidation i.e., theThe long-term use ofcapacity catalyst or of a catalyst with less weight a decrease in the average process, i.e., the long-term use of catalyst the use a catalyst with less weight In and a decrease power consumption for the oxidation step areor results of aofmassive adsorption capacity

Summary

Introduction

Volatile organic compounds (VOCs) can be harmful to the environment and human health. Among many VOCs, ethylene is produced by agricultural commodities, which causes the ripening of fruits and vegetables [1,2,3,4]. Controlling the ethylene activity can lead to extending the postharvest shelf life. Catalysts 2020, 10, 133 of fruits and vegetables [2]. Conventional techniques like ventilation, controlled atmosphere (CA), ozone treatment, oxidation, suppression of ethylene formation at plant receptor level can be used to control ethylene. Increased ventilation is associated with difficulty in controlling the parameters, like temperature and humidity, and CA is linked with a high cost/benefit ratio. Ozone treatment has been related to the reduction in the commercial value of fruits and vegetables due to injury [4]

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