Platinum catalysed wet oxidation of phenol in a stirred slurry reactor. The role of oxygen and phenol loads on reaction pathways

The catalytic wet oxidn. of phenol was studied in a slurry phase continuous stirred tank reactor (CSTR) using platinum on graphite support as a catalyst. The investigation was carried out in the temp. range 120-180 DegC and at total pressure of 1.8 MPa, while the phenol feed concn. was varied between 5 and 70 mol/m3, and oxygen partial pressures between 0.01 and 0.8 MPa. It was found that both the oxygen load and the stoichiometric oxygen excess det. the extent of oxygen coverage on the platinum surface, which influences the reaction pathways and selectivity to CO2 and H2O. A fully oxidized platinum surface resulted in catalyst deactivation (over-oxidn.), which favored the formation of p-benzoquinone and polymeric products. Whereas free platinum surface was vulnerable to poisoning by carbonaceous compds., a fully reduced platinum surface favored the formation of acetic and succinic acids which are difficult to oxidize. A reaction scheme for platinum catalyzed phenol oxidn. in liq. phase is proposed. [on SciFinder (R)

Kinetics of malonic acid degradation in aqueous phase over Pt/graphite catalyst

This work aims at describing quantitatively the catalytic decarboxylation of malonic acid over a 5.0 wt.% Pt/graphite catalyst. The study was carried out using a slurry phase continuous flow stirred slurry reactor (CSTR) at a temperature range of 120–160 °C and at a reactor pressure of 1.8 MPa. The conversion of malonic acid during catalytic oxidation was found to proceed via decarboxylation to CO2 and acetic acid, and also oxidation to CO2 and H2O. No indication of deactivation of the platinum catalyst was observed at a maximum residual oxygen pressure in the reactor up to 150 kPa. A reaction mechanism involving elementary steps has been suggested to explain the decarboxylation and oxidation of malonic acid. A kinetic model that accounts for both non-catalysed and catalysed decarboxylation of malonic acid has been developed and validated. The non-catalysed reaction is first order in malonic acid. The activation energies and adsorption enthalpies have been determined. The model is able to describe the experimental data adequately

Platinum catalyzed wet oxidation of phenol in a stirred slurry reactor : a practical operation window

The catalytic performance of graphite supported Pt (5 wt.%) catalyst in liq. phase oxidn. was studied using a continuous flow stirred tank slurry reactor (CSTR) in order to det. the proper operation window. The study was carried out at 120-180 Deg and a total pressure of 1.5-2.0 MPa. Other operational variables were O partial pressure (0.01-0.8 MPa), initial phenol feed concn. (0.005-0.07M), and catalyst concn. 1-10 Kg/m3. It was found that the extent of O coverage on the Pt surface dets. the reaction pathway and selectivity to CO2 and H2O. Complete oxidn. of phenol to CO2 and H2O could be achieved at 150 Deg when the reaction proceeds within the range of wt. specific O loads of 0.15-0.35 mol/KgPt-s and at stoichiometric O excess 0-80%. The activity of the Pt catalyst remained high when the residual partial pressure of O in the reactor was kep

Kinetics of malonic acid degradation in aqueous phase over Pt/graphite catalyst

This work aims at describing quantitatively the catalytic decarboxylation of malonic acid over a 5.0 wt.% Pt/graphite catalyst. The study was carried out using a slurry phase continuous flow stirred slurry reactor (CSTR) at a temperature range of 120–160 °C and at a reactor pressure of 1.8 MPa. The conversion of malonic acid during catalytic oxidation was found to proceed via decarboxylation to CO2 and acetic acid, and also oxidation to CO2 and H2O. No indication of deactivation of the platinum catalyst was observed at a maximum residual oxygen pressure in the reactor up to 150 kPa. A reaction mechanism involving elementary steps has been suggested to explain the decarboxylation and oxidation of malonic acid. A kinetic model that accounts for both non-catalysed and catalysed decarboxylation of malonic acid has been developed and validated. The non-catalysed reaction is first order in malonic acid. The activation energies and adsorption enthalpies have been determined. The model is able to describe the experimental data adequately

Platinum catalyzed wet oxidation of phenol in a stirred slurry reactor : a practical operation window

The catalytic performance of graphite supported Pt (5 wt.%) catalyst in liq. phase oxidn. was studied using a continuous flow stirred tank slurry reactor (CSTR) in order to det. the proper operation window. The study was carried out at 120-180 Deg and a total pressure of 1.5-2.0 MPa. Other operational variables were O partial pressure (0.01-0.8 MPa), initial phenol feed concn. (0.005-0.07M), and catalyst concn. 1-10 Kg/m3. It was found that the extent of O coverage on the Pt surface dets. the reaction pathway and selectivity to CO2 and H2O. Complete oxidn. of phenol to CO2 and H2O could be achieved at 150 Deg when the reaction proceeds within the range of wt. specific O loads of 0.15-0.35 mol/KgPt-s and at stoichiometric O excess 0-80%. The activity of the Pt catalyst remained high when the residual partial pressure of O in the reactor was kep

Support and dispersion effects on activity of platinum catalysts during wet oxidation of organic wastes

Catalytic activity of platinum catalysts such as Pt/graphite, Pt/TiO2, Pt/Al2O3, and Pt/active carbon was studied using a slurry phase CSTR. Three model reactions, namely, phenol, maleic acid, and malonic acid oxidn. were investigated in the temp. range from 120 to 170 °C and at a total reactor pressure of 1.7 MPa. Platinum on graphite was found to be most suitable for aq. phase oxidn. of phenol, maleic acid, and malonic acid. Complete conversion for both phenol oxidn. as well as maleic acid oxidn. to CO2 was obsd. with Pt/graphite at stoichiometric oxygen excess close to 0% and at 150 °C. Deactivation due to over-oxidn. is gradual for Pt/graphite with a metal dispersion of 5.3% as compared to Pt/TiO2, Pt/Al2O3 and Pt/AC, which have metal dispersions of 15.3%, 19.5% and 19.0%, resp. It was further found that in the presence of Pt/graphite catalyst and oxygen, malonic acid reaction proceeds via non-catalyzed decarboxylation, and catalytic decarboxylation to CO2 and acetic acid, and catalytic oxidn. to CO2 and H2O. Acetic acid was found to be difficult to oxidise at temps. below 200 °C