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Browsing by Author "Nare, David Nyasha"

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    Spatially Resolved Species and Temperature Profiles in the Oxidative Dehydrogenation of Ethane on Mono and Bimetallic Catalysts at Short Contact Times
    (2010-01) Nare, David Nyasha
    The oxidative dehydrogenation of C2H6 to C2H4 was studied on monometallic and bimetallic 45 PPI foam monoliths at ~8ms contact time. The capillary sampling method was used to measure concentration and temperature profiles along the reactor. Pt and Rh showed quite different product distributions; Rh was highly selective to syngas formation (~80%), whereas Pt produced high selectivity to non-equilibrium C2H4 (~55%). Spatially profiles show that Rh oxidizes feed C2H6 rapidly in the first 3mm of the catalyst to produce H2O, CO and H2 with >99% O2 conversion, followed by endothermic steam reforming, producing more syngas. Pt consumes O2 slower than Rh, with incomplete conversion at all tests. However, Pt shows poor endothermic reforming activity, hence is able to sustain high reactor temperatures, increasing C2H6 dehydrogenation rates. H2 addition tests show a two zone model; preferential oxidation to H2 raising the catalyst temperature while preserving C2H6, followed by C2H4 production. On Rh, H2 addition produced minimal change. The differences in catalytic performances are attributed to the high reforming and oxidation capability of Rh compared to that of Pt. The effect of Sn and Cu addition to Pt was also studied. Results show that bimetallic catalysts exhibit higher C2H6 and O2 conversion and selectivity to C2H4 than Pt. On Pt, production of C2H4 occurs further into the monolith with increase in C/O. In contrast, bimetallic catalysts show C2H4 production almost instantly, particularly because the temperatures would have exceeded 750 degrees C (when homogeneous ignition of C2H6 occurs) closer to the front face. Pt-Sn and Pt-Cu showed that they are superior to Pt in terms of deep oxidation of H2, with higher selectivity to C2H4 (85%). Pt-Sn and Pt-Cu are superior due to improved oxidation rates resulting in attainment of homogenous ignition temperatures earlier into the monolith C2H6 conversion rates. All catalyst show equally poor reforming ability, an attribute desirable in sustaining reactor temperatures, thereby obtaining high selectivity to C2H4. In summary, chapter 1 discusses motivation for research, background on CPO reactors and introduces the capillary sampling technique. Chapter 2 details experimental methods used. Chapter 3 focuses on ODH on Pt and Rh, while chapter 4 discusses ODH on Pt, Pt-Sn and Pt-Cu. Finally, chapter 5 concludes with future directions.