PHOTOCALYTIC DEDRADATION OF MALIC ACID UNDER THIN COATED TiO2 – January 2014
V Rodgher –Graduate Thesis ,The University of Western Ontario, 2012.
Opaque fluids have a limited irradiation transmission. Thus, their decontamination employing near UV irradiation poses significant technical challenges. In the present study, a thin UV-transparent/waterproof glue layer coated with a 1.5 wt% of TiO2 and a new PhotoReactor Cell were implemented. TiO2 irradiation in the PhotoReactor Cell was effected on the TiO2 particle side, not directly in contact with the fluid, allowing the postulation of an “h+” site mobility mechanism on photocatalysis. Photocatalytic degradation experiments with malic and malonic acid in water at 10, 20, 30 and 40 ppm showed the complete degradation of malic acid after 5 to 8 hours. Its minimum concentration was reached with the maximum concentration of malonic acid formed. Mass transfer effects and photolysis were found to be negligible in this setup. Macroscopic balance measurements showed that 92% of the irradiation was absorbed by the TiO2-film and quantum yields as high as 14.2-17.4% were obtained. The “Series-Parallel” kinetic mechanism was found to better predict the photocatalytic degradation of malic acid. It was found that the sensory attributes of apple juice were preserved with irradiation times being limit to 1 hour of exposure time. This time was proved by some authors to be sufficient to promote the 5-log CFU/ml microbial reduction, required by the FDA (21CFR120.24, 2012)… The first set of experiments to shed light into transmission irradiation was performed using the Photo-CREC Water-II Reactor (Figure 4.1). This slurry reactor setup consists of: (1) a stirred tank, (2) a centrifugal pump, (3) a near UV-lamp or BL-lamp, (4) a Pyrex glass with 3.58 cm diameter inner tube, (5) a replaceable Pyrex glass with a 5.6 cm diameter inner tube and (6) fused-silica windows, (7) a StellarNet EPP2000C-25 LT16 Spectrometer and (8) a SpectraWiz Software.
Figure 4.1: Photo-CREC Water-II Reactor Setup Employed in the Light Transmission Experiments with Apple Juice
Figure 5.1: Transmission Spectra for Commercial Allens Apple Juice at Position 4 (Brix: 11.90 0.1, pH: 3.10 0.05, Conc. of malic acid: 3.00 0.1 g/L)
