(680a) Removal of Nitric Oxide by Aqueous Solutions of Persulfate in a Bubble Column Reactor
The combustion of fossil fuel releases a large amount of NOx and sulfur dioxide (SO2) into the atmosphere which is a major threat to human health and environment. NOx, together with SO2 is the major contributer to acid rain that harms forest crops and buildings, as well as aquatic life. NOx also constitutes one of the main ingredients involved in the formation of ground-level ozone and urban smog through photochemical reactions, which can trigger serious respiratory problems. The efficient, cost effective and environmentally friendlier removal of NOx and SO2 from flue gases poses a considerable industrial problem. Available control technologies such as Selective Catalytic Reduction (SCR) used for high NOX removal has very high capital cost and suffers from various problems including disposal of spent toxic catalysts. Selective noncatalytic reduction (SNCR, urea injection) is highly temperature dependent and SNCR, ammonia injection (Thermal DeNOX) has moderately high capital cost and ammonia handling problems. Low-NOX burners (LNB) also has moderately high capital cost. Commercial applications of methods involving the chemical conversion of NO into soluble NO2 involving numerous liquid adsorbents in various gas-liquid contactors could prove to be effective if technical complexities and additional costs of chemicals could be reduced. Thus, there is need in the aqueous scrubbing arena for environmentally friendly and cost-effective alternatives for comprehensive treatment of NOx from industrial flue gases. Our research involves the aqueous removal of NOx (NO and NO2) from flue gases utilizing benign inexpensive chemical oxidants, cavitation or combination of the two. Cavitation is the formation, growth and implosive collapse of gas- or vapor-filled microbubbles and can be induced acoustically or hydrodynamically in a body of liquid. Acoustic or ultrasonic cavitation involves the formation and subsequent collapse of microbubbles from acoustical wave-induced compression/rarefaction. On the microscale, the collapse of the bubbles leads to surprisingly high estimated local temperatures and pressures up to and above 5000 C and 500 atmospheres, respectively. These rather extreme conditions are very short lived, but have been shown to produce several highly reactive species in the aqueous systems including hydroxyl (?OH), hydrogen (H?) and hydroperoxyl (HO2?) radicals, and hydrogen peroxide.
In previous studies, we demonstrated that the absorption of NO (50-1040 ppm) into water with simultaneous oxidation to nitrite and nitrate using sodium chlorite, oxone or induced by ultrasonic irradiation at a fixed frequency of 20 kHz could be accomplished using a sonochemical bubble column reactor in the absence and presence of SO2 (52-4930 ppm)at room temperature (23 ± 2oC). Using ultrasound at a fixed frequency of 20 kHz, the fractional conversions of NO were found to range from 60 to 85% while complete removal of SO2 was observed for all the inlet gas concentrations studied. The fractional conversions of NO were found to range from 60 to 85% while complete removal of SO2 was observed for all the inlet gas concentrations studied. It was shown that the presence of about 2520 ppm SO2 in combination with 0.01 M NaCl further enhanced NO removal. Combinative effect of sonication and chemical oxidation using 0.005-0.05M oxone was also studied. It was demonstrated that lower concentrations of HSO5- (0.005 M) enhanced NO removal efficiency. This paper will present new results obtained using aqueous solutions of persulfate.
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