GB772478A - Improved process of hydroisomerization of hydrocarbons - Google Patents

Abstract

Hydrocarbons are hydroisomerized by contacting the hydrocarbons and hydrogen in proportions of at least 500, preferably 1000-2000 cubic feet of hydrogen per barrel of hydrocarbon with a catalyst comprising a molybdenum oxide at a pressure above 50 p.s.i., preferably 100-2000 p.s.i., and at a temperature of at least 850 DEG F., preferably between 850 DEG and 1100 DEG F., and including in the charge to the reaction zone an amount of oxygen, steam or carbon dioxide supplying 0.0023 to 0.03 mol. of oxygen per mol. of hydrogen. The hydrogen separated from the product is usually recycled to the reaction zone with or without make-up hydrogen. For optimum results the temperature should be at least 50 DEG F. above the temperature at which an equal amount of liquid product would be obtained from the charge stock without adding oxygen, steam or carbon dioxide. The hydrocarbon charge may comprise singlestraight or branched chain paraffins or mixtures thereof, naphthenes or natural gasolines which are largely paraffinic or straight run petroleum naphthas, e.g. hydrocarbon mixtures boiling within the range of 32-550 DEG F. The process is conducive to isomerization while avoiding excessive cracking and dehydrogenation, e.g. methyl cylopentane is converted to benzene. The molybdenum oxide catalyst may be used alone or with carriers such as activated alumina, alumina gel, silica gel, silica-alumina gels, silica-magnesia gels, magnesia, titania or bauxite. An alumina support stabilized with 5 per cent silica is suitable. The catalyst may be in the form of granules or pellets in a fixed bed or a finely divided catalyst may be used in a fluidized state. Regeneration of the catalyst may take place in the reaction zone but it is preferred to utilize a separate regenerator at about reactor pressure or lower, e.g. atmospheric pressure. Before placing regenerated catalyst on stream it is preferably reduced with a mixture of hydrogen and oxygenic substance. The space velocity in the reactor may vary between 0.25 and 10.0 volumes of hydrocarbon per hour per volume of catalyst. Oxygen may be introduced with the volume of catalyst. Oxygen may be introduced with the hydrogen recycle stream prior to passage through the preheater and preferably in admixture with an inert gas, e.g. methane, ethane and propane. Alternatively oxygen may be introduced directly into the reactor, at the bottom when the catalyst is fluidized or at a number of points when the catalyst is fixed. Oxygen may also be dissolved in the liquid hydrocarbon charge or added to the catalyst transporting gas in a fluidized process. When steam is used, it should be added in double the volume required for pure oxygen, but a steam partial pressure of 50 p.s.i. should not be exceeded. The steam formed in the reactor may be recycled whereupon addition of fresh steam is unnecessary. Thus, the recycle hydrogen may be maintained at a sufficiently high temperature to prevent condensation of water vapour so that the water vapour is recycled to the reaction zone with the hydrogen. It is desirable to employ charge stocks of low sulphur content in order to operate for long periods without regeneration. When high sulphur stock is used, a prior desulphurization may be required or the sulphided catalyst may be regenerated frequently. Detailed examples are given which describe the hydroisomerization of straight run naphtha, of n-pentane to isopentane, of methylcyclopentane to benzene, and of mixtures of n-pentane, cyclohexane and benzene, using a molybdenum - on - alumina catalyst, stabilized with silica, which has been calcined and then reduced in hydrogen, and using hydrogen containing small amounts of oxygen or steam. Comparative examples describe similar processes in which no oxygen or steam is added.