GB689005A - Improvements in or relating to a continuous cyclic hydroforming process - Google Patents

Abstract

In a continuous cyclic hydroforming process for improving the octane rating of hydrocarbons in the presence of recycled hydrogen-containing gaseous products and a turbulent dense phase fluidized catalyst which is withdrawn, regenerated by combustion in oxygen-containing gas, and returned to the conversion zone, naphtha vapour is fed to the conversion zone at a weight space velocity of 0.1-2, preferably 0.3-0.6 lbs. per hour per lb. of catalyst in the bed, recycled gaseous products are introduced at an inlet hydrogen partial pressure between 75 p.s.i.a. and the partial pressure at which net consumption of hydrogen begins, generally between 125 and 350 p.s.i.a. or more, regenerated catalyst is added at a catalyst-naphtha charging ratio of less than 0.5 : 1, preferably 0.03-0.15 : 1 by weight, and the product of this ratio and the weight space velocity of naphtha is less than 0.15, preferably 0.02-0.06. Recycled product gases are introduced equivalent to 0.5-10, preferably 1.5-5 mols. of hydrogen per mol. of naphtha. The average temperature of conversion is 825-1025, preferably 900-960 DEG F. The total reaction pressure is desirably at least 150, e.g. 500 p.s.i.g., to provide the desired hydrogen partial pressure without addition of external hydrogen. Contact time is 30-300, preferably 75-175 seconds. Suitable catalysts are sulphides and oxides of left-hand elements of Groups 5 and 6, e.g. chromia-alumina but preferably molybdenum trioxide on alumina gel containing silica or on activated alumina of low soda content. The size may average 200 mesh with few, if any, particles larger than 40 mesh. The feed and recycled gas are separately preheated and fed to the base of a tubular reactor surmounted by a filter housing with automatic flow-back of product gas through the filters in sequence to clear catalyst particles. Partially spent catalyst may be withdrawn periodically from near the base and fresh catalyst fed near the top by gas pressure. The spent catalyst is transported by gas to a regenerator of similar construction to the reactor and held at 700 DEG F. When the regenerator is full, preheated regenerating gas is passed through at 500 p.s.i.g. and the regenerated catalyst may be removed to storage. Alternatively, regenerated catalyst is continuously taken from near the top of the bed, after stripping with, e.g. steam, and conveyed in dense phase while aerated to near the base of the reactor. Spent catalyst from the reactor similarly flows to the base of the regenerator. Valves are provided to control the flow and to prevent back flow if the pressure differential fails. The flow lines are inclined at 45 degrees or more to the horizontal to give free flow. The bed density in the regenerator is lower than in the reactor, while density is greatest in the transfer lines, viz. 40-55 lb./c. ft. The depth of bed in the regenerator is also greater than in the reactor, the tops of the beds preferably being at the same level.