Multiple-stage hydrocarbon conversion with gravity-flowing catalyst

Abstract

A multiple-stage catalytic conversion system in which a hydrocarbonaceous charge stock and hydrogen flow serially through a plurality of catalytic reaction zones, in each of which the catalyst particles are downwardly movable via gravity-flow. At least three reaction zones are utilized, with the fresh feed and hydrogen reactant stream being split between the first and second. The flow of that portion introduced into the second zone is restricted. Effluent flow from the first reaction zone is also restricted and combined with the effluent from the second reaction zone; the mixture is introduced into a third reaction zone. Where the catalytic conversion system consists of four reaction zones, the flow of effluent from the third is restricted prior to the introduction thereof into the fourth reaction zone. This technique decreases the mass flow to the first two zones and increases the pressure drop experienced within the entire conversion system, thus serving to alleviate the problems associated with the occurrence of stagnant catalyst areas as a result of catalyst particles being 'pinned' within the reaction zone and thus unable to assume a downward, gravity-flow pattern. Restriction of the second zone feed and first reaction zone effluent insures a higher pressure in the first zone.