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INFLUENCE OF Cu/ZSM-5 PREPARATION METHOD ON CWPO OF

Phenol and phenol compounds are common and important pollutants found in the effluent streams of variety of chemical plants, including coal processing plants and refineries. In the conventional catalytic wet air oxidation (CWAO) of phenol reaction is performed at high operating pressure (1-10 MPa) and temperature (353-475 K), makes the investment rather costly. By contrast, hydrogen peroxide as an oxidant (a CWPO process) allows oxidation under or almost under the ambient conditions (atmospheric pressure and T 323 K), which reduces the investment. A great variety of solid catalysts, including active carbon, supported and unsupported metal oxides, and metals supported on metal oxides, graphite, clays, and polymers, were tested during oxidation of phenol and its compounds. In this work oxidation of phenol with hydrogen peroxide on Cu/ZSM-5 catalysts was studied. The catalysts samples with different content of catalytic active centers were prepared by two different methods: by ionic exchange from the protonic form of commercial ZSM-5 zeolite, and by direct hydrothermal synthesis. Characterization of the catalysts extends to X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the adsorption techniques were used for the measurement of the specific surface area. The catalytic tests were carried out in a stainless steel Parr reactor in batch operation mode at the atmospheric pressure and the temperature range from 323 to 353 K. The initial concentration of phenol and hydrogen peroxide was 0.01mol dm-3 and 0.1mol dm-3, respectively. After the reaction mixture was heated to the desired temperature, the catalyst and the hydrogen peroxide were added into the reaction system in the appropriate amount. The decrease in phenol concentration was analytically monitored. Phenol was detected and measured by UV absorbance at 254 nm wavelengths by standard 4-aminoantipyrine colorimetric methods. Preliminary experimental data showed that at conditions used in this work reaction external and internal mass transfer resistance not influenced reaction rate, which means that the reaction is performed in kinetic region. The influence of catalyst preparation method and concentration of catalytic active material on phenol elimination is presented on Figs. 1 and 2. It can be seen that the activity of catalyst increases with increasing of copper content on zeolite and that the activity of Cu/ZSM-5 prepared by direct hydrothermal synthesis is higher then the activity of catalyst prepared by ion exchange method. It was also found that the stability of DHS catalyst is also higher in comparison with the stability of II catalyst because the leaching of active ingredient, i.e. copper is lower. The obtained experimental data was tested to a proposed kinetic model for phenol oxidation [1, 2]: Fig.1. Influence of Cu content on phenol elimination (catalyst prepared by ionic exchange method), (cHP = 0.1 mol dm-3, cPh=0.01 mol dm-3, mk=0.1 g dm-3, T=353 K). Fig.2. Influence of Cu content on phenol elimination (catalyst prepared by direct hydrothermal synthesis), (cHP =0.1 mol dm-3, cPh=0.01 mol dm-3, mk=0.1 g dm-3, T=353 K). The kinetic parameters were estimated using the Nelder-Mead method of nonlinear regression. The residual sum of squares calculated from the difference between the experimental and predicted concentrations was minimized in the regression. The results of the model analysis are presented in table 2 and are shown as solid lines in Figures 1 and 2. As can be seen, these kinetic models discriminated fits adequately the experimental data sinew only slight differences were found between the predicted results (curves) and the experimental ones (points). [1] S. Zrncevic, Z. Gomzi, Zrnčević, S. and Gomzi, Z., CWPO: An environmental solution for pollutant removal from wastewater. Ind.Eng.Chem.Res. 44 (2005) 6110-6114. [2] Maduna Valkaj, K., Katović, A. and Zrnčević, S. Investigation of the catalytic wet peroxide oxidation of phenol over different types of Cu/ZSM-5 catalyst, J.Hazard.Mat. (2007) doi:10.1016/.jhazmat. 2007.01.099.

Phenol oxidation; CWPO reaction; Cu/ZSM-5; Wastewater treatment; Pollutant degradation; Kinetics; Modeling

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