engleski

Hydrogen Peroxide Promoted Cwao of Phenol Over Cu/13X Catalyst

The disposal of wastewater streams containing highly toxic organic pollutants generated by many industrial processes has emerged as a topic of mounting concern in recent years. Among the numerous classes of pollutants, phenols are of particular importance due to their widespread discharge in the environment from pharmaceutical, chemical and petrochemical processes, where are used either as reagent, intermediate substance or solvent. The effective removal of such pollutants, for safe discharged is a challenging task as environmental lows and regulations are becoming more and more stringent. To meet the requirements of these regulations, bio treatment, adsorption and incineration are traditionally used. However, toxic pollutants are lethal to the microorganisms employed in bioprocesses, whereas incineration or adsorption merely transfers the pollutants from the liquid to air or to the solid leaving combustion by-products or contaminated adsorbent for further disposal. Therefore, there is clear need to test and set-up emerging alternative technologies that can deal with highly concentrated and/or toxic non-biodegradable organic water pollutants. Wet air oxidation (WAO) is an attractive method for the treatment of waste streams which are too dilute to incinerate and too toxic to treat biologically. Unfortunately, the efficient removal of pollutants via WAO requires excessive pressures (20-200 bars) as well as high temperatures (473-598K). The use of catalysts makes the process more attractive by achieving high conversion at considerably lower temperature and pressure CWAO). In order to increase oxidation efficiency at mild conditions, hydrogen peroxide can be used as powerful source of highly reactive hydroxyl radicals which act as promoters (PP-CWAO). In this work catalytic activity and stability of Cu/13X zeolite in PP-CWAO of phenol was examined. The catalysts were prepared by ion exchange from commercial 13X zeolite. Post synthesis thermal treatment consisted in calcinations of prepared Cu/13X samples at 523, 773 and 1023 K for 5h (ramp 2 K min-1) was conducted in order to obtain zeolite based materials that exhibit higher stability to the loss of active metal component during the reaction. The catalytic tests were carried out in a modified stainless steel Parr reactor in batch operation mode at constant temperature (353 K), oxygen pressure (20 bars) and catalyst weight (2.5 g dm-3). The initial concentration of phenol was 0.01 mol dm-3 and hydrogen peroxide 0.05, 0.10 and 0.14 mol dm-3. It was found that the PP-CWAO process leads to higher pollutant removal conversions than the CWAO and CWPO processes. A synergistic effect was found when H2O2 is combined with oxygen which leads to higher mineralization of the phenol.

zeolite; phenol; catalytic oxidation; promoted oxidation

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