Volume 15 Number 1	December 1998

Research Scholars New Resources Summer Interns Contaminant Spread Liquid-Solid Flow Short Contact-Time Reactors Preconditioning Symposium Mantle Plumes Bioremediation Research Reports eaction engineering and combustion processes are often characterized by a complex interaction of transport and chemical kinetics. The chemistry may include gas-phase as well as surface reactions. Direct partial oxidation of light alkanes, the main components of natural gas, in short contact time reactors have been shown to offer a promising route to convert light alkanes into more useful chemicals such as syngas (H2 and CO), olefins, and oxygenates. Catalysts used for these processes include foam or extruded monoliths, wire gauzes, or sintered spheres that are coated with noble metals such as platinum and rhodium. The reactor can be run autothermally and almost adiabatically with a residence time of approximately one millisecond. Short contact time guarantees a very high throughput using a small amount of catalyst and low energy and capital costs. However, the industrial application needs to operate at higher pressure, but high-pressure experiments in conventional laboratories are expensive and dangerous because reactive mixtures may explode. Detailed modeling and simulation help to clarify complex interactions between reactive flow and catalytic surfaces and can be used to explore reactor conditions beyond available experimental facilities. This work is being carried out by Professor Lanny D. Schmidt and Dimitrios Iordanoglou, a Graduate Student Researcher, of the Chemical Engineering and Materials Science Department at the University of Minnesota and Olaf Deutschmann, a Research Associate, now at Heidelberg University in Heidelberg, Germany. They developed a computer program to simulate short contact time reactors using a two-dimensional flow field description and detailed models for surface and gas-phase chemistry. The program was based on the commercial computational fluid dynamics (CFD) code fluent. The current version of this code, although able to handle multi-species flow including diffusion and heat transfer, is not capable of simulating flows that include a large number of stiff chemical reactions. Therefore, fluent was coupled with models created by the group that simulate gas phase as well as surface chemistry. The extended CFD code was then used to model the partial oxidation of methane on Rh and Pt in a short contact time reactor containing a catalytic foam monolith. The simulation included 22 surface reactions and 164 gas phase reactions. Reaction pathways, interaction between convection, diffusion, adsorption/desorption processes, and surface chemistry were elucidated. The importance of gas phase chemistry at higher pressures were revealed. The figures show how the reactant methane is consumed and CO, one of the desired products, is formed. Furthermore, the formation of OH radicals are shown. These OH radicals act as a precursor to the undesired combustion products carbon dioxide and water. Recently, these researchers also used this computer program to simulate partial oxidation of methane over platinum gauzes. In the future, this group will improve surface reaction mechanisms of hydrocarbon oxidation over noble metals. Group members will also incorporate detailed gas-phase chemistry for larger hydrocarbons in their calculations. These studies are very crucial for a detailed understanding of short-contact-time reactors. This knowledge is necessary for an efficient scale-up of laboratory-scale reactors to commercial applications. Mass fraction of methane in the reactor channel. Mass fraction of carbon monoxide in the reactor channel. Mass fraction of OH radicals in the reactor channel.

HOME | BULLETINS | CONTACT US | PREVIOUS ARTICLE | NEXT ARTICLE | THIS ISSUE