The role of boundary layer mass transfer in partial oxidation selectivity

• Published in: Journal of catalysis 1992-08, Vol.136 (2), p.300-308
• Main Authors: Hickman, D.A., Schmidt, L.D.
• Format: Article
• Language: English
• Subjects: 01 COAL, LIGNITE, AND PEAT; 010408 - Coal, Lignite, & Peat- C1 Processes- (1987-); 03 NATURAL GAS; 030300 - Natural Gas- Drilling, Production, & Processing; 10 SYNTHETIC FUELS; 100200 - Synthetic Fuels- Production- (1990-); ALKANES; AMMONIA; BOUNDARY LAYERS; CARBON COMPOUNDS; CARBON MONOXIDE; CARBON OXIDES; Catalysis; CATALYSTS; CATALYTIC EFFECTS; Catalytic reactions; CHALCOGENIDES; CHEMICAL REACTIONS; CHEMICAL REACTORS; Chemistry; CYANIDES; ELEMENTS; Exact sciences and technology; FLOW RATE; FLUID FLOW; FLUIDS; GAS FLOW; GASES; General and physical chemistry; GEOMETRY; HYDRIDES; HYDROCARBONS; HYDROCYANIC ACID; HYDROGEN; HYDROGEN COMPOUNDS; INORGANIC ACIDS; LAYERS; MASS TRANSFER; MATHEMATICAL MODELS; MATHEMATICS; METALS; METHANE; NITROGEN COMPOUNDS; NITROGEN HYDRIDES; NONMETALS; OPTIMIZATION; ORGANIC COMPOUNDS; OXIDATION; OXIDES; OXYGEN COMPOUNDS; PLATINUM; PLATINUM METALS; REACTION INTERMEDIATES; RHODIUM; SURFACE PROPERTIES; SYNTHESIS GAS; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TIME DEPENDENCE; TRANSITION ELEMENTS
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(92)90063-N

Simple models predict that mass transfer in the boundary layer over a catalyst surface should have a large influence on reactor selectivity for any fast series reaction, but few experimental cases demonstrate this explicitly. In this paper, we show experimentally that selectivities of CH 4 oxidation to CO and H 2 over Pt-Rh gauzes and HCN synthesis from CH 4, NH 3, and air over Pt-coated ceramic monoliths are strongly affected by the gas flow rate and the catalyst geometry. For any series reaction in which the desired product is an intermediate species, such as HCN synthesis, an optimal residence time exists where the production of the desired component is maximized, and the selectivity of formation of the intermediate product improves with increasing rates of mass transfer. For parallel and series-parallel reactions, mass transfer may improve or reduce selectivity of formation of the intermediate product, with the effect of mass transfer depending strongly on the reaction orders of the kinetics. However, typical series-parallel partial oxidation reactions such as the partial oxidation of CH 4 to synthesis gas require high rates of mass transfer for maximum reactor selectivity.