ChemInform Abstract: Millisecond Chemical Reactions and Reactors

Abstract

Short contact time chemical reactors have many features which are very different from conventional packed bed reactors in that temperatures are determined by inlet parameters only, performance is nearly unchanged over wide variations in flow rate, and highly nonequilibrium products can be obtained at high conversions. Chemical reactions occur in regions of large gradients in composition and temperature, so the kinetics of the processes cannot be simply extracted from experiments. We illustrate these systems with recent examples of oxidative dehydrogenation of ethane at 85% ethylene selectivity and cyclohexane partial oxidation to oxygenates and olefins at 80% selectivity. A major feature of both reaction systems is the probable existence of two zones in the monolith where oxidation reactions occur close to the entrance and successive reactions such as homogeneous pyrolysis occur after all O2 is consumed and the surface is passivated with carbon. For the single gauze reactor only homogeneous oxidation occurs after the gauze where the temperature decreases strongly and quenches further decomposition of olefins and oxygenates. Considerations of scaleup of these reactors for large-scale chemicals production are discussed.