Advanced Kinetic Concepts and Experimental Methods for Catalytic Three-Phase Processes

Abstract

Kinetic studies of catalytic three-phase systems are traditionally performed in autoclaves operating batchwise, and the results are described with rate equations based on the simple Langmuir-Hinshelwood concept. This is not sufficient, as complex organic molecules react on the catalyst surface, and more advanced kinetic models and experimental techniques are needed. Semicompetitive and multicentered adsorption models have been applied to kinetic data, and transient step-response experiments have been carried out for various industrially relevant three-phase systems. The theoretical basis of the advanced kinetic concept is described and successfully applied to several industrially relevant processes, such as hydrogenation of aromatic components and aldehydes on commercial catalysts and enantioselective hydrogenation on modified catalyst surfaces.

Hydrogenation of lactose for the production of lactitol

“…These authors developed a semicompetitive model for the adsorption of organic molecules during the hydrogenation of xylose under the assumption that organic molecules can partially compete and even occupy several primary sites. The rate of adsorption within the semicompetitive model involved the addition of parameters in the adsorption equilibrium equation . For small molecules, an exponential parameter ( j ) was added, and it related the number of sites for adsorption.…”

Catalytic Hydrogenation of d-Xylose Over Ru Decorated Carbon Foam Catalyst in a SpinChem® Rotating Bed Reactor

“…Consequently, the peak at 29.6 min (D-arabinitol) was confirmed as the byproduct present in highest concentration. The fact that no Dxylulose could be identified might imply that herein D-arabinitol can be was formed through D-xylitol isomerization [22] rather than through the hydrogenation of D-xylulose (Fig. 6a).…”

Chemical Reaction Engineering of Biomass Conversion

“…A noncompetitive adsorption model can be justified by the size difference of the reacting molecules (e.g., Wärnå et al, 2006). A general overview of kinetic models is provided by Salmi et al (2004) and Murzin and Salmi (2005), where also a semicompetitive adsorption model is discussed. It has been successfully applied to sugar hydrogenation .…”

“…Moreover, in the catalysis involving complex organic molecules with different functional groups, not only the number of sites but also the mode of adsorption is an important issue. The treatment of kinetics of hydrogenolysis (Bernas et al, 2009) and hydrogenation Grau, 2008a, 2008b;Salmi et al, 2004) on uniform catalyst surfaces involves the concepts of multicentered species. The concept of semicompetitive adsorption of a large molecule and a smaller one implies that the maximum coverage of the large molecule is less than one, and thus some interstitial sites always remain accessible for the smaller molecule (such as hydrogen).…”

“…The competitiveness of adsorption and the state of hydrogen on the catalyst surface have been the subject of intensive discussions in the literature (see, e.g., Salmi et al, 2004), but in this case, the simplest possible model was used, noncompetitive adsorption of hydrogen and organics along with molecular adsorption of hydrogen. Previous comparisons have shown that this approach gives an adequate description of the sugar hydrogenation kinetics, with a minimum number of adjustable parameters.…”