PHOTOOXIDATION OF METHYL-TERT-BUTYL ETHER ON TITANIA USING A PLUG-FLOW REACTOR
Shaogang Chu, Chia-Swee Hong, and Rajinder Narang
Wadsworth Center, New York State Department of Health, and School of Public Health, State University of New York at Albany, NY 12201-0509; Phone: (518)473-7299, E-mail: .
The gas-phase photocatalytic degradation of methyl-tert-butyl ether (MTBE) using TiO2-impregnated fiberglass mesh was investigated. The kinetics of the photocatalytic process was measured with a continuous flow of reactants through the plug-flow reactor, which was illuminated with UVA light lamp. A plot of (V/Q)/(C0-C) versus ln(C0/C)/(C0-C) showed a linear relationship by varying C0, the initial concentration of MTBE, and measuring C, the concentration of MTBE in the outlet, where V and Q represent the volume of the reactor and the flow rate through the reactor, respectively. The oxidation kinetics of MTBE followed the Langmuir-Hinshelwood model. The effect of humidity on the photocatalysis was also examined. The adsorption constant K and rate constant k was 92.42 L/mmol and 0.07 mmol/L min-1, respectively, under the humidity of 15% in comparison to the corresponding values of 125.84 L/mmol and 0.14 mmol/L min-1 in dry air condition. Both adsorption constant and rate constant decreased with increasing humidity. It indicated that water produced from the reaction process is enough for the hole scavenging to form hydroxyl radicals and extra water vapor-inhibited MTBE photodegradation. The half-lives of MTBE with initial concentration of 0.14 mmol/L were 1.05 and 0.53 min for 15% humidity and dry air condition, respectively. The reaction by-products have been identified by GC/MS. Acetone and tert-butyl formate (TBF) were the primary intermediates. Other by-products, formaldehyde and tert-butyl alcohol (TBA), were also detected. The degradation pathway of MTBE in the photocatalysis was believed to be similar to that in TiO2 slurries. The concentration of carbon dioxide in the outlet gas was increased rapidly after the reactions were initiated. It showed that MTBE could virtually be completely mineralized after extended reaction time.
Key words: photocatalysis, MTBE, titanium dioxide, GC/MS