engleski

TREATMENT OF PHENOLIC EFFLUENTS BY PP-CWAO OVER Cu/13X CATALYST

The increasing complexity of wastewater streams as well as the unfavourable public opinion about some conventional waste management techniques, e.g. incineration and adsorption is forcing the development of cost-competitive and environmentally acceptable waste treatments. To overcome the inconveniences of conventional treatment methods various chemical oxidation techniques have emerged in the past last decades. Wet air oxidation (WAO) is an attractive method for the treatment of waste streams which are too diluted to incinerate and too toxic to treat biologically. The use of catalysts makes the process more attractive by achieving high conversion at considerably lower temperature (353 – 473 K) and pressure (1-10 MPa). An alternative process which allows oxidation at the ambient or close-to-the-ambient conditions, thus limiting the investment costs, involves hydrogen peroxide as an oxidant in the so-called catalytic wet peroxide oxidation (CWPO). The main objective of this work is to integrate the benefits CWAO and CWPO in an intensified process, named Peroxide Promoted Catalytic Wet Air Oxidation (PP-CWAO) keeping high conversion of pollutant in wastewater and to give an effluent that could be easier biologically treated. The catalyst choice is the core for an efficient and cost competitive performance. Activity and stability of prepared Cu/13X catalyst was tested in CWAO, CWPO and PP-CWAO of phenol in aqueous medium. The catalyst was prepared from the protonic forms of commercial 13X zeolite (13X-APG Molsiv™ UOP Italy, SiO2/Al2O3 = 3.2) by ion exchange method and was calcined in air at 1023 K for 5 hours to increase its stability. The catalyst was characterized by BET, XRD and AAS in order to obtain information about their physical and chemical properties. The catalytic tests were carried out in a modified stainless steel Parr reactor in batch operation mode at constant temperature (333 K), different hydrogen peroxide concentration (0.01 - 0.14 mol dm-3) and different air pressure (2 - 20 bar). The catalyst weight was 0.1 g dm-3 and the initial concentration of phenol 0.01 mol dm-3. It was found that the PP-CWAO process leads to higher pollutant removal conversions than the CWAO and CWPO processes. The results were influenced by the Ph: H2O2 : air molar ratio. A synergistic effect was found when H2O2 is combined with air which leads to higher mineralization of the phenol.

phenol; hydrogen peroxide; catalytic oxidation; promoting effect

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