Low-temperature catalytic oxidation of volatile organic compounds using novel catalysts
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Exhaust gases from poultry rendering facilities contain volatile organic compounds (VOCs) that are a nuisance, odorous, and smog and particulate matter precursors. Present treatment options, such as wet scrubbers, do not eliminate a significant fraction of the VOCs emitted including, 2-methylbutanal (2-MB), 3-methylbutanal (3-MB), and hexanal. Other available treatment options, such as thermal and catalytic incineration require temperature intensive inputs and form additional greenhouse gases. Hence, an inexpensive alternative technology is needed to eliminate these air pollutants. This research investigated the low-temperature (25-160°C) catalytic oxidation of aldehyde vapors using novel catalysts derived from renewable carbon sources. In the first phase, 8-150 ppmv of 2-MB, 3-MB, and hexanal were oxidized using wood fly ash as a catalyst and molecular oxygen as an oxidant. The oxidation rates of 2-MB, 3-MB, and hexanal were between 3.0 and 3.5 x 10 mol/g-s at 25°C. The activity of wood fly ash in oxidizing aldehydes was comparable to other commercially available metal and metal-oxide catalysts. It is theorized that wood fly ash catalyzed a free radical reaction in which acetone and 2-butanone were formed as end products of 3-MB and 2-MB oxidation respectively, while pentanal and butanal were formed as end products of hexanal oxidation. When tested as a binary mixture at 25°C, the presence of 2-MB increased the oxidation rate of hexanal. However, under identical conditions, hexanal inhibited the oxidation of 2-MB. Additionally, when 1500 ppmv ozone was tested as an oxidant at 160°C, 100 % removal was achieved for all aldehydes within a 4-second reaction time. In the second part of this research, nickel and cobalt oxide catalysts were dispersed on activated carbon using electrochemical deposition. When tested for oxidation of 50-250 ppmv propanal vapors using 1500 ppmv ozone, the electrochemically deposited catalysts exhibited significantly higher (25-50 %) activities (-r=100-450 x 10 mol/g-s) than activated carbon. The results from this research may be used to design catalytic oxidation processes for VOC removal at poultry rendering facilities and potentially replace energy and intensive air pollution treatment technologies currently in use.