This work examines the experimental assessment of the conditions required for sustainable autothermal catalytic combustion of mixtures of lean fuels (methyl ethyl ketone (MEK), acetone, propane, and methane) in a small nonadiabatic laboratory auto-cyclic reactor (ACR) loaded with a combination of laboratory-prepared monoliths and commercial palladium catalyst pellets. Despite the non-optimized physical parameters of this reactor, the experiments demonstrated that, for a given fuel, the domain of autothermal operation is dependent primarily on fuel/catalyst reactivity that, in turn, dictates the minimum heat output (power) requirement of the air/fuel mixture and, to a lesser degree, flow rate. In correlation with the reactivity of individual fuels, the power requirement for a flow rate of 64 L/min (ambient) increased, from 375 W for MEK and acetone to ∼480 W for propane and 613 W for methane. For propane and methane combusted under the limiting conditions, oscillatory behavior was observed with the periods that correlated with the power of the fuel/air mixture. When the methane/air feed mixture was heated to 400 °C before entering the ACR, sustained combustion was assured for 0.6% methane flowing at a rate of 97.2 L/min.
The support effect on the low temperature catalytic oxidation of methane over palladium catalysts was studied by comparing a series of metal oxides as the support. Samples of 0.010 g/g Pd catalysts supported on different grades and/or phases of TiO2, Al2O3, and ZrO2 were prepared via incipient impregnation and their catalytic activity was evaluated using a laboratory plug‐flow reactor. The specific surface area of the supports determined by nitrogen adsorption varied from about 13‐220 m2/g. Initial experiments conducted with titania (anatase) as a support showed a low apparent activity and a poor thermal stability. Focusing on anatase, we have successfully improved its thermal stability by additions of Al2O3 or by doping with CeO2, or La2O3. However, contrary to expectations based on some information in the literature, we have found that the activity decreased in the sequence of Al2O3 > ZrO2 > TiO2, and was not a direct function of specific surface area. This was especially evident in the case of titania. The surface structure of the support and the nature of its interaction with the active component PdO seem to play a far more important role in activity than the apparent specific surface area. Moreover, anatase‐supported catalysts present a very rapid deactivation, whereas rutile‐supported catalysts are relatively stable. The observed phenomena could potentially be related to the interaction between support and the active phase of palladium. Several models have been proposed to describe the strong metal‐support interaction, but either charge transfer or encapsulation seems to be the most probable.
Natural gas represents an environmentally attractive alternative to diesel and gasoline fuels to reduce all automotive emissions. However, a relatively high content of unburned methane in the exhaust gases outweighs these benefits. To treat such emissions, a counter-current type fixed bed autocyclic reactor (ACR) was designed and built for laboratory testing. The efficiency of the ACR, loaded with palladium based catalysts (pellets and monoliths) was evaluated experimentally under a wide range of conditions. As a first step in modeling the ACR performance, a HT1-D model was developed to suit the actual reactor configuration. This model reproduced adequately the axial temperature profiles and methane conversion, but tuning parameters had to be used to account for heat transfer. To permit investigation of radial heat transfer and thus better understanding of the ACR behavior, a two-dimensional model was developed, and successfully validated against experimental data. The new HT2-Dt model allowed a full range of the ACR performance simulations.
A simple experimental fin device was used to develop a laboratory procedure for undergraduate engineering students, in order to enhance their understanding of the transfer of thermal energy. This experiment exposes the student to several important concepts, namely one-dimensional, time-dependent heat transfer in extended surfaces by conduction, convection and radiation. In a few simple steps, students have the opportunity to compare the measured to the predicted temperature profiles obtained at different times using an analytical complex solution and to calculate convective and radiative heat coefficients, such as the relative predominance of convection heat transfer with respect to radiation.
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