Catalytic Dehydrogenation of Cyclohexane Using Coated Silica Oxide Ceramic Membranes

Abstract

Experiments were conducted to characterize US Filter ceramic membranes used in the catalytic dehydrogenation of cyclohexane to benzene. The reaction yield was studied as a function of membrane pore size for 50, 100, 200, and 2000 A membranes. The effect on reaction yield, membrane permeability, and membrane selectivity of altering pore size by addition of successive thin film layers (silica oxide particles in an iron(III) supported solution) to the membrane surfaces was the primary focus of the study. The membranes were also characterized with a nonreactive He/N2 separation to determine the effect of successive thin film layers on the extent of Knudsen diffusion as the transport mechanism. This characterization demonstrated that Knudsen behavior could be obtained in a large pore diameter membrane by adding thin film layers to the surface. Reaction experiments showed a 300% increase in yield from that which was obtained in an impermeable reactor under similar conditions. Most significantly, the coated membranes operating in the Knudsen regime rendered a higher reaction yield than the uncoated 50 A membrane, whose transport mechanism was also Knudsen dominated. This phenomena can be explained by favorable surface effects between the thin film material and the reaction species. Thus, it was concluded, that a thin film (added to the surface membrane), which operates in the Knudsen regime and creates favorable surface effects to enhance membrane selectivity, can shift reaction equilibrium to a higher product yield than a membrane which only exhibits Knudsen diffusion.