Catalytic Oxidation of Phenol over Zeolite Based Cu/Y-5 Catalyst: Part 2: Influence of Postsynthesis Thermal and Chemical

Katalitička oksidacija zagađivala organskog podrijetla vodikovim peroksidom u vodenom mediju, poznata kao metoda CWPO (eng. Catalytic Wet Peroxide Oxidation), jedan je od postupaka kojim je moguće postići smanjenje organskog opterećenja otpadnih voda u praksi. U ovom radu zeolit Y-5 izabran je za nosač u koji je kao katalitički aktivna tvar ugrađen bakar. U radu je istražen utjecaj reakcijskih parametara te postsintetske kemijske i termičke obrade katalizatora na njegove katalitičke značajke: aktivnost i stabilnost. Katalizator Cu/Y-5 pripravljen je ionskom izmjenom protoniranog oblika komercijalnog zeolita Y-5. Radi poboljšanja njegovih katalitičkih značajki provođena je postsintetska kemijska (ispiranje sa H2SO4) i termička obrada (kalciniranje). Karakterizacija katalizatora Cu/Y-5 obuhvaćala je rengdensku difrakcijsku analizu na praškastom uzorku (PXRD) i elementnu analizu na atomskom apsorpcijskom spektrometru (AAS) te određivanje specifične površine, obujma pora i raspodjele obujma pora (standardna metoda BET). Aktivnost i stabilnost pripravljenih katalizatora ispitana je u reakciji oksidacije fenola vodikovim peroksidom u vodenoj otopini. Maseni udjel bakra na zeolitu bio je 3,46 % prije postsintetske obrade, odnosno 3,97 % nakon postsintetske termičke obrade te 0,94 % nakon postsintetske kemijske obrade. Eksperimentalni podatci dobiveni provođenjem katalitičkih testova testirani su sljedećim kinetičkim modelima za oksidaciju fenola rPh = k1 cPh cHP i raspad vodikova peroksida rHP = k2 cHP. Za procjenu kinetičkih parametara primijenjena je Nelder-Meadova metoda nelinearnog optimiranja. Oba postupka postsintetske obrade značajno su poboljšala stabilnost pripravljenog Cu/Y-5 katalizatora, dok je istodobno njegova aktivnost ostala nepromijenjena ili je poboljšana.The most important and the most vulnerable part of the global ecosystem are surface waters. Tothis day, numerous scientific investigations have been conducted in to develop new technologies for most effective purification of wastewaters polluted with organic compounds such as phenol and its derivatives. Catalytic wet peroxide oxidation, known as the CWPO process, is one of the methods that can be used for the minimization of organic pollution in practice. With the use of a catalyst (homogeneous or heterogeneous), the process can be successfully operated under mild conditions with low energy consumption (atmospheric pressure and temperatures below 353 K). Zeolites modified with copper possess good catalytic properties when compared to the other types of heterogeneous catalysts tested in CWPO reaction. Based on the literature overview and actual trends in scientific research concerning development of new catalytic oxidation processes for treatment of wastewaters burdened with organic pollutants, Y-5 FAU type of zeolite was selected as catalyst support for copper cations. In this paper, second in a series, investigated was the influence of reaction parameters, synthesis and postsynthesis chemical and thermal treatment of the prepared catalyst on its catalytic properties. The catalyst was prepared by ion exchange method of the protonic form of commercial zeolite. In order to obtain the catalyst with optimum catalytic properties, chemical (H2SO4 wash) and thermal postsynthesis treatment (calcination) was conducted. The catalysts were characterized with powder X-ray diffraction (PXRD) and AAS elemental analysis, while the adsorption techniques were used for the measurement of the specific surface area. Activity and stability of such prepared catalysts was tested in catalytic wet peroxide oxidation of phenol in aqueous medium. The mass fraction of the active metal component on the zeolite was 3.46 %, 3.97 % and 0.94 % before and after postsynthesis thermal and chemical treatment, respectively. The postsynthesis treatment had a profound positive impact on the stability of both the catalytically active component and the support of the catalyst. At the same time, its activity in the CWPO process remained very good or had even improved. With the use of a copper bearing zeolite based catalyst, the complete removal of phenol is obtained even when substoichiometric quantity of oxidant is used. Bearing that in mind, future research will be oriented towards the application of these catalysts in the CWPO process with industrial grade effluents that contain phenol and other phenolic compounds. Good results on model phenolic wastewaters are indicative of its possibly successful integration into the existing industrial and municipal wastewater treatment facilities. CWPO process could be, for example, coupled with the biological treatment in order to reduce the toxicity of the phenolic effluent prior to aerobic/anaerobic digestion. In that case, some of the by-products of CWPO phenol oxidation, such as acetic acid, could be used as a substrate. The obtained experimental data was tested to a proposed kinetic model for phenol oxidation rPh = k1 cPh cHP and hydrogen peroxide decomposition rHP = k2 cHP. The kinetic parameters were estimated using the Nelder-Mead method of nonlinear regression. Good accordance between the experimental (dots) and theoretical data (lines) was obtained. The kinetic model used for hydrogen peroxide decomposition showed somewhat less compliance with the experimental data. This can be attributed to the fact that hydrogen peroxide present in the reactor participates not only in the oxidation of phenol molecules but in other reactions such as oxidation of intermediates, hydrogen peroxide dissociation, decomposition on the reactor wall, which contributes to its ineffective dispense in this reaction system