Abstract: A system for dehydrogenating a C3 or C4 hydrocarbon feed stream containing a first and second layer of catalysts placed in the hydrocarbon feed stream, wherein the feed stream first passes through the first layer and then the second layer of catalysts and wherein the catalysts of the first layer contain from about 50 to about 90 percent by weight of an eta-alumina carrier, from about 10 to about 50 percent by weight of chromia and from about 0.1 to about 5 percent by weight of a zirconium compound and wherein the catalysts of the second layer of catalysts contain from about 50 to about 90 percent by weight of an eta-alumina carrier and from about 10 to about 50 percent by weight of chromia, without an added zirconium compound.

Abstract: The present development relates to a modification of the Houdry process for the dehydrogenation of aliphatic hydrocarbons, whereby the dehydrogenation cycle is extended, or lengthened, and hydrogen gas is added into the reaction. The combination of the extended cycle with the hydrogen introduction results in a surprising stabilization of the production rate in the dehydrogenation process. The hydrogen gas may be introduced through a recycle step. The process of the present development is demonstrated for the dehydrogenation of propane to propylene.