engleski

CWAO of phenol over Cu/13X catalysts with hydrogen peroxide as promoter: influence of operating conditions and catalyst pretreatment

Due to its presence in various processes in pharmaceutical, chemical and petrochemical industry, where it is used either as reagent, intermediate substance or solvent, phenol is known as one of the most common organic water pollutants. Its high toxicity and suspected mutagenic and carcinogenic properties prohibit the release of untreated phenolic wastewater into the natural recipients. Therefore, different advanced oxidation processes were investigated as suitable precursors for the biological treatment of industrial effluents containing phenol. Catalytic Wet Air Oxidation (CWAO) is presented as an effective technology to treat aqueous hazardous wastes, especially when these are too diluted to incinerate or too concentrated for a biological treatment. CWAO process uses molecular oxygen as oxidant operates at T ~ 353-475 K and p ~ 10-100 bars. The addition of hydrogen peroxide as a source of free radicals makes the process more attractive by achieving high conversion at considerably lower temperature and pressure thus limiting the investment costs. In this work, the addition of hydrogen peroxide as promoter in the CWAO of phenol with Cu/13X catalysts has been carried out in a modified stainless steel Parr reactor in batch operation mode at the different temperature (313-343 K), different hydrogen peroxide concentration (0.01 - 0.14 mol dm-3) and oxygen pressure (2-20 bars). The catalyst weight was 0.1 g dm-3 and the initial concentration of phenol 0.01 mol dm-3. These parameters were studied to find the optimal conditions for a fast oxidation and mineralization of phenol. The catalysts were prepared from the protonic forms of commercial 13X zeolite by ion exchange method. Post synthesis thermal treatment consisted in calcinations of prepared Cu/13X sample at 1023 K for 5h in order to obtain zeolite based material that exhibit higher stability. The catalysts were characterized by BET, XRD, FTIR and AAS in order to obtain information about their physical and chemical properties. The experimental profiles for phenol and TOC conversions using hydrogen peroxide as promoter in the CWAO have been compared to those obtained in the CWAO and CWPO. Toxicity of the effluents has been also measured because although the same intermediates were identified during phenol oxidation, different intermediate distribution was observed using different treatments. Results show that the effect of hydrogen peroxide on the efficiency of the process is significant and leads to higher pollutant removal conversions than the CWAO and CWPO processes. It can be attributed to synergistic effect between H2O2 and oxygen which leads to higher mineralization of the phenol. It was also found that thermal treatment stabilizes the Cu/13X catalyst from leaching

Catalytic oxidation; hydrogen peroxide; promoting effect; organic aqueous wastes

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