Kinetic modeling of the photocatalytic degradation of methyl ethyl ketone in air for a continuous-flow reactor

Abstract

This paper reports the study on kinetic modeling of photocatalytic degradation of methyl ethyl ketone (MEK) using TiO2 coated on silica fiber felts. Two different mathematical models, ideal plug flow model and axially dispersed plug flow model (dispersion model), were used to simulate the performance of the PCO reactor. Six kinetic rate equations on the basis of Langmuir-Hinshelwood (L-H) expression were examined to find the best model that fits the experimental data. Moreover, the light intensity distribution on the photocatalyst surface was simulated using the linear source spherical emission model (LSSE) and validated with the experimental data. The Beer-Lambert model was also applied to demonstrate the diminishment of light intensity in the PCO filter. For model prediction validation, a series of experiments was carried out in a bench-scale continuous flow reactor at different concentrations (0.1–1 ppm), relative humidities (17–67%), flow rates (10–30 L/min), and light intensities (7–23.5 W/m2). In addition, adoption tests with MEK at various concentrations (0.25–1 ppm) and relative humidities (15–50%) were conducted under dark condition. Formaldehyde, acetaldehyde, acetone, and propionaldehyde were identified (through HPLC analysis) as by-products of the MEK PCO reaction. Owing to higher concentrations of formaldehyde and acetaldehyde, aldehyde group was considered as the main by-products. The result of carbon balance indicated that 7.2% of MEK mineralized to CO2 (measured by GC-FID) and around 10.8% of that was converted to by-products (for 18.4% removal efficiency). Evaluation of different kinetic rate expressions revealed that the unimolecular L-H model considering inhibitive effect of water vapor and by-products for adsorption provided the best fit. The dispersion model combined with this rate expression had a higher accuracy at all operating conditions while the plug flow model failed to predict the PCO performance at various intensities and air velocities. Evaluation of mass transfer was also performed, and it was concluded that the mass transfer effect on the PCO process is not dominating step; consequently, the PCO reaction is the rate-limiting process.