Pt-catalyzed ozonation of aqueous phenol solution using high-gravity rotating packed bed

In this study, a high-gravity rotating packed bed (HGRPB or HG) was used as a catalytic ozonation (Cat-OZ) reactor to decompose phenol. The operation of HGRPB system was carried out in a semi-batch apparatus which combines two major parts, namely the rotating packed bed (RPB) and photo-reactor (PR). The high rotating speed of RPB can give a high volumetric gas-liquid mass transfer coefficient with one or two orders of magnitude higher than those in the conventional packed beds. The platinum-containing catalyst (Dash 220N, Pt/γ-Al2O3) and activated alumina (γ-Al2O3) were packed in the RPB respectively to adsorb molecular ozone and the target pollutant of phenol on the surface to catalyze the oxidation of phenol. An ultra violet (UV) lamp (applicable wavelength λ = 200-280 nm) was installed in the PR to enhance the self-decomposition of molecular ozone in water to form high reactive radical species. Different combinations of advanced oxidation processes (AOPs) with the HGRPB for the degradation of phenol were tested. These included high-gravity OZ (HG-OZ), HG catalytic OZ (HG-Cat-OZ), HG photolysis OZ (HG-UV-OZ) and HG-Cat-OZ with UV (HG-Cat-UV-OZ). The decomposition efficiency of total organic compound (ηTOC) of HG-UV-OZ with power of UV (PUV) of 16 W is 54% at applied dosage of ozone per volume sample mA,in = 1200 mg L−1 (reaction time t = 20 min), while that of HG-OZ without the UV irradiation is 24%. After 80 min oxidation (mA,in = 4800 mg L−1), the ηTOC of HG-UV-OZ is as high as 94% compared to 82% of HG-OZ process. The values of ηTOC for HG-Cat-OZ process with mS = 42 g are 56% and 87% at mA,in = 1200 and 4800 mg L−1, respectively. By increasing the catalyst mass to 77 g, the ηTOC for the HG-Cat-OZ process reaches 71% and 90% at mA,in = 1200 and 4800 mg L−1, respectively. The introduction of Pt/γ-Al2O3 as well as UV irradiation in the HG-OZ process can enhance the ηTOC of phenol significantly, while γ-Al2O3 exhibits no significant effect on ηTOC. For the HG-Cat-UV-OZ process with mS = 42 g, the values of ηTOC are 60% and 94% at mA,in = 1200 and 4800 mg L−1, respectively. Note that the decomposition of TOC via HG-UV-OZ is already vigorous. Thus, the enhancing effect of catalyst on ηTOC is minor.