CATALYTIC WET AIR OXIDATION OF PHENOL USING CeO₂AS THE CATALYST. KINETIC STUDY AND MECHANISM DEVELOPMENT

Abstract

Using a CeO2 catalyst prepared from CeCl3.7H2O under high thermal impact, the catalytic wet air oxidation (CWAO) of phenol was effectively implemented. With initial phenol concentrations of between (400 and 2500) mg/L, and at a temperature of 160 degrees C, the rate of phenol conversion increased with increased catalyst loading (0.2g/L-1.0g/L) and oxygen pressure (0.5 MPa-1.5 MPa). Even at an initial concentration of 2500 mg/L, conversion of phenol was as high as 95% after 3 h reaction. The effect of phenol concentration, catalyst loading, and oxygen pressure on the initial rate of phenol conversion was evaluated in a kinetic study. The initial rate equation derived from kinetic study is: Ro=k1 x [Ph]1.3-1.4 x W0.5-0.6 x PO2(0.9-1.1), where k1 is a rate constant, and [Ph], W and PO2 refer to phenol concentration, catalyst loading and oxygen pressure, respectively. A free-radical involved reaction mechanism was proposed and an initial rate expression based on this mechanism was derived: Ro = k2 x [Ph]1.5 x W0.5, where k2 is also a rate constant. Fitting of experimental data with the theoretically derived initial rate equation resulted in good correlation: the coefficient is greater than 0.99.

Catalytic wet air oxidation of phenol over ultrasound-assisted synthesized Ni/CeO2–ZrO2 nanocatalyst used in wastewater treatment

“…The catalytic wet air oxidation of organics is widely acknowledged to proceed via a free-radical chain reaction mechanism Lin et al, 2003;Lin and Weng, 1994;Rivas et al, 1998) and the condition of stationary free radical concentration is usually assumed (Chang et al, 2002; Catalytic wet air oxidation of phenol Weng, 1993). The critical nanocatalyst concentration phenomenon as observed in this work, is one of the characteristics of free radical chain reaction, in which a slight change in nanocatalyst loading (active phase loading and nanocatalyst loading in reactor) induces a noticeable change in the rate of process (Sadana, 1979).…”

Preparation of Granulated Biomass Carbon Catalysts—Structure Tailoring, Characterization, and Use in Catalytic Wet Air Oxidation of Bisphenol A

“…This result is expected to have been caused by the radical scavenging effect wherein higher catalyst loadings reduce the catalyst performance by decreasing the overall oxidation reaction [62]. A widely proposed mechanism that could explain the CWAO reaction process is the free radical chain reaction mechanism [63,64], which is assumed to be stationary [65,66] and wherein a catalyst is seen to play a two-fold role, that is, it acts both as an initiator and a terminator of free radicals. In such a chain reaction cycle, the rate of free radical formation compete with the rate of destruction, and the reaction rate is related to the increase in catalyst loading.…”