Method of preparation of diolefins by dehydrogenation of the monoolefins

摘要

Diolefines are prepared by the dehydrogenation of mono-olefines containing at least four carbon atoms in contact with an oxide of iron, cobalt or nickel in a high oxidation state, i.e. one capable of being reduced to an oxide in which the metal is in a lower oxidation state, preferably Fe2O3, Ni2O3 or Co2O3, at 260-540 DEG C. for less than 40 seconds. The metal oxide may be supported on alpha or gamma alumina of surface area 20-150 sq. metres per gram, titania, zirconia, magnesia, silica, natural or synthetic clays, diatomaceous earth or magnetite, the composite containing 10-95% of the metal oxide. The oxide is reduced during the reaction and is frequently regenerated by contact with an oxygen-containing gas, e.g. air, at 260-650 DEG C. for 0.1-5 minutes. Preferably the oxide is treated with a non-oxidizing gas before and after the oxidizing step, suitable gases being nitrogen, flue gas, steam, hydrogen or carbon monoxide. The oxide only becomes fully active after activation by 1-100 cycles of alternate contact with a reducing agent such as hydrocarbon feed at 315-540 DEG C. and an oxidizing agent such as air at up to 650 DEG C., contact times being in the same range as in the process itself. Conversions which may be effected include 1- or 2-butene to 1,3-butadiene, 1- or 2-pentene to 1,3-pentadiene, 2- or 3-methyl-1-butene or 3-methyl-2-butene to isoprene and (methyl)cyclopentene to (methyl) cyclopentadiene. The hydrocarbon should be in the vapour phase and contact times of 0.3-20 seconds are preferred at 0.35-4.2 kg./cm.2 absolute. The contact between solid and vapour may be effected in a co-current up-flow or down-flow reactor or counter-current, the vapours flowing up and the solid down. Amounts of hydrocarbon passed during a reaction cycle may be 0.1-2 parts per 100 parts by weight of solid. Diluents may be employed, e.g. up to 4 times the amount of hydrocarbon of nitrogen, carbon dioxide or steam may be added.