Analysis of mass and heat transfer in transient experiments over heterogeneous catalysts

Abstract

Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract--This article discusses the effects of extra-and intraparticle mass and heat transfer in transient experiments over heterogeneous catalysts. To this purpose, the time-dependent transport in a catalyst particle when introducing a reactant in an inert gas phase has been analyzed. The analysis has led to one criterion assuring the absence of both extra-and intraparticle mass transfer limitations during steady-state experiments. Furthermore, criteria for the absence of mass and heat transport limitations during transient experiments have been developed by extending the criteria for the absence of mass and heat transport limitations during steady-state experiments. As will be shown, transient kinetics are not affected by heat transfer as long as the steady-state criteria for the absence of mass and heat transport limitations are fulfilled.

Non-isothermal reaction-diffusion systems with thermodynamically coupled heat and mass transfer

“…Modeling of spatio-temporal evolution may serve as a powerful complementary tool to experimental non-isothermal reaction-diffusion (RD) systems within a porous catalyst particle and membrane (Weisz and Hicks, 1962, Hlavecek et al, 1969, Aris, 1975, Froment and Bischoff, 1979, Dekker et al, 1995, Pan and Zhu, 1998, Levent et al, 1998, Levent, 2001, Kafarov et al, 1998and Burghardt and Berezowski, 2003Selegny et al, 1995a andSelegny et al, 1995b). Non-isothermal RD systems represent thermodynamically and mathematically coupled transport and chemical processes, and need a through analysis, as they may evolve multiple steady states with unique dynamic phenomena (Burghardt and Berezowski, 2003).…”

Computational fluid dynamics modeling of immobilized photocatalytic reactors for water treatment

“…A common criterion applied to heterogeneous reactions states that if E ex is larger than 0.95, external mass transport limitation is negligible in the system. 61 The analysis of the local E ex distributions in the three reactors shown in Figure 9 reveals that E ex was very low at those areas where surface reaction was taking place (areas with significant UV irradiance). This result implies that at those regions, the surface reaction rate was much higher than the mass transport rate which induced overall a diffusion controlled process.…”

A low-temperature co-fired ceramic micro-reactor system for high-efficiency on-site hydrogen production

“…Therefore, an external mass transfer of propane/air reactants over the surface of catalysts determined the mass diffusion to the CPOX process. Such an external mass transfer behaviour can be practically characterized by the Carberry number (Ca), a ratio between the observed reaction rate and the maximum external mass transfer [44]. As defined in Equation (7) [45], C b stands for the propane species bulk concentration and a 0 represents the specific external surface of used catalyst.…”

“…Dekker et al [44] suggested that Ca should be smaller than 0.05 as a criterion for negligible transport effects in gas phase steady-state heterogeneous catalytic reactions. Therefore, from our estimated Ca value, it was concluded that the LTCC micro-reactor was operating in a kinetics-limited region.…”