Browsing by Author "Masende, Z. P. G."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Kinetics of Malonic Acid Degradation in Aqueous Phase over Pt/Graphite Catalyst
    (2005) Masende, Z. P. G.; Kuster, B. F. M.; Ptasinski, K. J.; Janssen, F. J. J. G.; Katima, Jamidu H. Y.; Schoutena, J. C.
    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.
  • Thumbnail Image
    Item
    Platinum Catalysed Wet Oxidation of Phenol in a Stirred Slurry Reactor: A Practical Operation Window
    (Elsevier, 2003) Masende, Z. P. G.; Kuster, B. F. M.; Ptasinski, Krzysztof J.; Janssen, Frans J. J. G.; Katima, Jamidu H. Y.; Schouten, J. C.
    The catalytic performance of graphite supported platinum (5 wt.%) catalyst in liquid phase oxidation has been studied using a continuous flow stirred tank slurry reactor (CSTR) in order to determine the proper operation window. The study was carried out in a temperature range of 120–180 °C and in a total pressure range of 1.5–2.0 MPa. Other operational variables employed were oxygen partial pressure (0.01–0.8 MPa), initial phenol feed concentration (0.005–0.07 M), and catalyst concentration from 1 to 10 kg m−3. It was found that the extent of oxygen coverage on the platinum surface determines the reaction pathway and selectivity to CO2 and H2O. Complete oxidation of phenol to CO2 and H2O could be achieved at 150 °C when the reaction proceeds within the range of weight specific oxygen loads of 0.15–0.35 mol s−1 kgPt−1 and at stoichiometric oxygen excess in the range of 0–80%. The activity of the platinum catalyst remained high when the residual partial pressure of oxygen in the reactor was kept below 150 kPa. Higher residual oxygen partial pressure resulted into deactivation of the platinum catalyst (over-oxidation), which was temporary and could be reversed at reducing conditions. The formation of p-benzoquinone, followed by the formation of polymeric products was also favoured at higher oxygen load, which resulted into permanent deactivation of the platinum catalyst (poisoning). While the platinum surface was vulnerable to poisoning by carbonaceous compounds when insufficient oxygen was used, a fully reduced platinum surface favoured the formation of acetic and succinic acids which are difficult to oxidize. Higher temperatures can enhance the activity of the platinum catalyst, while at lower temperatures catalyst deactivation occurs with increased formation of polymeric products and lower selectivity to CO2 and H2O. In order to maintain the catalyst within the proper operation window, a CSTR is the preferred reactor.
  • Thumbnail Image
    Item
    Support and Dispersion Effects on Activity of Platinum Catalysts during Wet Oxidation of Organic Wastes
    (Springer Link, 2005) Masende, Z. P. G.; Kuster, B. F. M.; Ptasinski, Krzysztof J.; Janssen, Frans J. J. G.; Katima, Jamidu H. Y.; Schouten, J. C.
    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 oxidation were investigated in the temperature 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 aqueous phase oxidation of phenol, maleic acid, and malonic acid. Complete conversion for both phenol oxidation as well as maleic acid oxidation to CO2 was observed with Pt/graphite at stoichiometric oxygen excess close to 0% and at 150 C. Deactivation due to over-oxidation 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%, respectively. It was further found that in the presence of Pt/graphite catalyst and oxygen, malonic acid reaction proceeds via non-catalysed decarboxylation, and catalytic decarboxylation to CO2 and acetic acid, and catalytic oxidation to CO2 and H2O. Acetic acid was found to be difficult to oxidise at temperatures below 200 C.