KINETICS AND MODELING OF ODOR OXIDATION USING CHLORINE DIOXIDE FOR EMISSION CONTROL UTILIZING WET SCRUBBERS

Abstract

The promulgation of “Odor Control Rules”, increasing public concerns, and EPA air regulations in non-attainment zones, necessitates the remediation of a wide range of volatile organic compounds (VOCs) generated in the rendering industry. Currently, wet scrubbers using oxidizing chemicals, such as ClO2 are utilized to treat VOCs. However, little information is available on the kinetics of ClO2 reaction with rendering air pollutants, limiting wet scrubber design and optimization. Kinetic analysis indicated that ClO2 does not react with hexanal and 2-methylbutanal (aldehydes constitute a major VOC fraction) regardless of pH and temperature, and imply aldehyde removal is primarily via mass transfer. Contrary to the aldehydes, ethanethiol (a model compound for methanethiol) and dimethyl disulfide (DMDS) rapidly reacted with ClO2. The overall reaction was found to be second and third order for ethanethiol and DMDS respectively. Moreover, an increase in pH from 3.6 to 5.05 exponentially increased the reaction rate of ethanethiol (e.g., k2 = 25 to 4200 L/mol/s from pH 3.6 to 5.1) and significantly increased the reaction rate of dimethyl disulfide if increased to pH 9 (k3 = 1.4 x 106 L2/mol2/s). Thus, a small increase in pH could significantly improve wet scrubber operations for removal of odor causing compounds. However, an increase in pH did not improve aldehyde removal. The results explain why aldehyde removal efficiencies are much lower than methanethiol and DMDS in wet scrubbers using ClO2. Wet scrubber models without chemical reaction predicted aldehyde removal within 17-32% of removal efficiencies in an industrial scale scrubber. Incorporating oxidation kinetics into a wet scrubber model predicted increasing removal efficiency with increasing pH (i.e., reaction rate) but did not adequately predict results in an industrial scale scrubber.