Kinetic decomposition of ozone, geosmin, and 2-methylisoborneol during catalytic ozonation

Kinetic decomposition of ozone, geosmin, and 2-methylisoborneol during catalytic ozonation
Winn-Jung Huang,^1,* Cheng-Feng Hsu² and Yao-Ming Wang^1
1 Department of Safety, Health and Environmental Engineering, Hungkuang University, Taichung 433, Taiwan

² Department of Soil and Water Conservation, National Chung Hsing University, Taichung 402, Taiwan
ABSTRACT

Two taste and odor (T&O) causing compounds, geosmin (GSM) and 2- methylisoborneol (2-MIB) were oxidized by zinc oxide (ZnO) catalyzed ozonation. The use of a 2.5 mg O3L^-1 (52 μM) and 500 mg ZnO L^-1 catalyst yields 96-97% GSM and 2-MIB conversion in 30 min; this experimental result compares favorably with the 53-58% obtained without a catalyst. The overall reaction rate was enhanced by the presence of ZnO; the most significant improvement in the overall rate constants (k_overall) was observed at 500 mg ZnO L^-1, whereby over four-fold increases in k_overall value was observed. The experimental electron paramagnetic resonance (EPR) spectra confirmed that the formation of more hydroxyl radicals (•OH) in the ZnO catalytic ozonation process increases the T&O removal rate. Based on ozone decomposition kinetics and adsorption capacity of ZnO, the initial rate of disappearance of T&O correlates with the Langmuir-Hinshelwood kinetic model. The relationships between reaction rates and reactant concentrations were derived from the kinetic parameters determined experimentally for each reaction system. A comparison indicates that the kinetic rate constant for catalytic ozonation is 175-260% higher than that of the system of ozonation process due to increased production of hydroxyl radicals by an ozone combined with ZnO catalyst.

KEYWORDS: Taste, odor, geosmin, 2-methylisoborneol, zinc oxide, catalytic ozonation, hydroxyl radical