Catalytic supercritical water oxidation of aromatic compounds on transition metal oxides

The objective of this research was to study the effect of a catalyst on the destruction of phenol, benzene, and 1,3-dichlorobenzene (DCB) at supercritical water oxidation (SCWO) conditions, specifically, to evaluate the destruction rate and selectivity to CO{dollar}sb2{dollar} at a variety of reaction conditions.; Tests were conducted in a lab-size fixed bed reactor with {dollar}rm Vsb2Osb5/Alsb2Osb3{dollar}, {dollar}rm Crsb2Osb3/Alsb2Osb3{dollar}, or MnO{dollar}sb2{dollar}-{dollar}rm CeOsb2/Alsb2Osb3{dollar} catalysts, and without catalyst at temperatures from 390{dollar}spcirc{dollar}C to 450{dollar}spcirc{dollar}C and a pressure of 3500 psi. The oxidation of phenol gave nearly 100% conversion at all conditions. The conversion of benzene ranged from 5% to 75%, and the conversion of 1,3-DCB ranged from 20% to 85%. Nearly 100% selectivity to CO{dollar}sb2{dollar} on {dollar}rm Vsb2Osb5{dollar}, and 75% on MnO{dollar}sb2{dollar}, for phenol and benzene were reached at 390{dollar}spcirc{dollar}C and 500% excess oxygen, whereas only 20% selectivity to CO{dollar}sb2{dollar} was achieved for phenol and benzene oxidation in conventional SCWO. Selectivity to CO{dollar}sb2{dollar} for phenol oxidation was also enhanced by {dollar}rm Crsb2Osb3{dollar}, but no improvement was seen for benzene oxidation. Limited information was obtained on catalytic 1,3-DCB oxidation because of the fast deactivation of catalyst. Excess oxygen and reaction temperature are the main parameters for conversion and selectivity to CO{dollar}sb2{dollar}, especially in the presence of catalyst.; Homolytic and heterolytic hydrolysis are the main approaches for homogeneous oxidation resulting ring-opening reaction. The hydrolysis mechanism was enhanced with the participation of lattice oxygen in {dollar}rm Vsb2Osb5{dollar} and absorbed oxygen on MnO{dollar}sb2{dollar} catalysts.; Group rate expressions indicated that the rate constants of CO{dollar}sb2{dollar} formation for phenol and benzene SCWO over {dollar}rm Vsb2Osb5{dollar} and MnO{dollar}sb2{dollar} catalysts were one order higher than corresponded conventional SCWO. The kinetic rates from mathematical modeling indicated that {dollar}rm Vsb2Osb5{dollar} catalyst enhanced the directed oxidation from reactants to CO{dollar}sb2{dollar}, while MnO{dollar}sb2{dollar} involved the path from partial oxidation products, and then to CO{dollar}sb2{dollar}.; MnO{dollar}sb2{dollar} is the most stable and active catalyst in SCWO. {dollar}rm Vsb2Osb5/Alsb2Osb3{dollar} has high activity in catalytic SCWO of aromatic compounds, but there is higher vanadium ion in effluent. {dollar}rm Crsb2Osb3/Alsb2Osb3{dollar} might be a good partial oxidation catalyst, although high chromium ion in the effluent was observed during SCWO.