Development of Wastewater Treatment Technique by Catalytic Oxidation in Superheated Steam

¹ Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 4328561, Japan
² Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8561, Japan
³ Nippon Refine Co., Ltd, 2-2-1 Marunouchi, Chiyoda-ku, Tokyo, 100-0005, Japan

^* Corresponding author: okajima.izumi@shizuoka.ac.jp

Abstract

The purpose of this research was the development of a wastewater treatment technique using catalytic oxidation in superheated steam. The target substance was isopropyl alcohol (IPA). The experiment was carried out using a plug-flow reactor filled with MnO₂ catalyst. The optimum decomposition condition was determined, and the kinetics of the catalytic oxidation reaction were analyzed. The experimental results were expressed as total organic carbon (TOC) removal. The dependences of the TOC removal on the reaction temperature and residence time were investigated. The TOC removal increased with the reaction temperature and residence time. It was 99.8% at 300°C, 0.9 MPa, 11 s, and oxidant ratio of 1.2. On the other hand, the TOC removal was constant for a long residence time at low reaction temperatures of 200 and 230°C. This was because acetone and acetic acid were produced via the oxidation of IPA, and they were detected as TOC. The reaction kinetics were examined using the pseudo-first-order reaction model; the TOC removal correlated well with this model. Based on the results of the kinetics, the activation energy (E_a) for TOC decomposition was determined from the Arrhenius equation; it was 56.1 kJ/mol. These results indicate that catalytic oxidation in superheated steam is useful for wastewater treatment.