Photocatalytic reactivity of the titanium oxide loaded on a stainless steel screen
Advancing the chemical engineering fundamentals
Catalysis - II (T2-13b)
Keywords: Photocatalytic decomposition, Spraying method, Film-diffusional resistance, Adsorption, Zeolite
Fumihide SHIRAISHI1*, Takeshi ITOH1, Yasuhiro ODA1, Hideaki NAGAYOSHI2,
Tomohiko HIGUCHI2, and Kenji TATEISHI3
1 Department of Systems Design, Bio-Architecture Center, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
2 FUJICO Co., Ltd., 4-31, Makiyamashinmachi, Kitakyushu 804-0054, Japan
3 I-Quark Corporation, 1-36-14, Matsushima,Higashi-ku, Fukuoka 812-0062, Japan
* Corresponding author
The photocatalytic decomposition of organic compounds is strongly influenced by a large film-diffusional resistance. In the photocatalytic purification of air, this resistance was easily removed by increasing the recirculation flow rate1-3). This operation was also effective in the photocatalytic decomposition of organic compounds in water4,5) (for instance, >0.8 m s-1 in the case of formic acid). However, setting up such a high flow rate of liquid requires an expensive and high-performance pump and consumes a large amount of electricity. In addition, a shearing force by water causes a gradual exfoliation of the photocatalyst film. There is a rust prevention technique called spraying method, in which fine metal particles are shot with a gun so that a strong metallic film is formed on a solid plate. This method may be able to not only deal with the film exfoliation problem described above, but also uniformly distribute the adsorbent particles in the titanium oxide particles such as zeolite since these can be well-mixed before shooting. Thus, there is a possibility that the film-diffusional resistance can be reduced at a lower flow velocity. In the present work, therefore, we examined the performance of a photocatalyst prepared by the spraying method by means of decomposing 2,4-dinitrophenol (DNP) in water.
The batch-recirculation reactor system consisted of a peristaltic pump, perfectly-mixed flow vessel, and annular-flow type reactor with a 6W germicidal lamp in its center. The stainless steel screen (wire diameter; 0.1 mm, space between wires; 0.1 mm) was used as a support, on which titanium oxide particles or 3-10 % zeolite/titanium oxide particles were sprayed. The photocatalyst preparation (14mmx8.8mm) was rounded and then fixed at the inside surface of the reactor. The DNP concentration was determined by a spectrophotometer.
The initial rates of decomposition of DNP, v0, were measured at various linear flow velocities of a reaction mixture in the range of 0-0.051 m s-1. The v0 value for the glass tube loading titanium oxide particles increased with an increase of the linear velocity and indicated the highest value at a linear velocity above 0.037 m s-1. This variation is due to a reduction in the film-diffusional resistance with the increase in the linear velocity. The v0 value of the stainless steel screen loading titanium oxide was remarkably influenced by the zeolite content. Even in the case of no zeolite content, the preparation gave a higher v0 value than the glass tube. In the case of 5%-zeolite content, the v0 value became higher at a lower linear velocity. This is probably because the photocatalytic decomposition was accelerated by the adsorption of DNP on the titanium oxide itself and zeolite. However, the v0 value of the 10 %-zeolite content was lowered, probably because of a decrease in the amount of titanium oxide. A comparison of the experimental data at v0=0.003 m s-1 clearly shows that the photocatalyst prepared by the spraying method enables a higher activity operation at a lower linear velocity.
References
1) F. Shiraishi, S. Yamaguchi, Y. Ohbuchi, Chem. Eng. Sci., 58, pp.929-934 (2003).
2) F. Shiraishi, D. Ohkubo, K. Toyoda, and S.Yamaguchi, and Chem. Eng. J. 114, pp.153-159 (2005).
3) F. Shiraishi, K. Toyoda, and H. Miyakawa, Chem. Eng. J., 114, pp.145-151 (2005).
4) F. Shiraishi, M. Nagano, S. Wang, J. Chem. Technol. Biotechnol., 81, pp.1039-1048 (2006).
5) F. Shiraishi and C. Kawanishi, J. Phys. Chem., 108, pp.10491-10496 (2004).
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Presented Thursday 20, 12:00 to 12:20, in session Catalysis - II (T2-13b).
