Process for the manufacture of butadiene

摘要

546,709. Catalytic dehydrogenation. MOND, A. L. (Universal Oil Products Co.). April 3, 1940. No. 5997. [A Specification was' laid open to inspection under Sect. 91 of the Acts, Oct. 12, 1940.] [Class 1 (i)] [Also in Group IV] Butadiene is prepared from normal butane in a two stage dehydrogenation process, in the first stage of which butane is subjected to contact with a catalyst composed of from 99 to 80 per cent. of aluminous oxide and from 1-20 per cent. of oxide of chromium at a temperature between 550‹ C.-650‹ C. under a pressure of between ¢ and 2.5 atmospheres absolute for a time of contact of between 0.05 and 1 seconds to produce a substantial conversion of butane to butenes, and then in the second stage subjecting the reaction products of the first stage to contact with a separate portion of the same catalyst at a temperature within the range 500‹-700‹ C. under sub-atmospheric pressure and a time of contact not exceeding one second. The preferred time of contact for the first stage is one second and for the second stage 0.1 second. The preferred pressure for the second stage is 0.06 to 0.33 atmospheres absolute. It is also preferred to separate the butenes from the unconverted butanes after the first operation before proceeding to the second stage of the process, although this separation-may be omitted. The catalyst may be prepared by preparing an aqueous solution of a chromium compound such as chromium trioxide or chromium nitrate and impregnating the alumina and then reducing, or chromium hydroxide may be precipitated on to suspended particles of the carrier using such precipitating agents as the hydroxides and carbonates of the alkali metals or ammonium. The aluminium oxide used as the carrier may be obtained from natural aluminium oxide minerals or ores such as bauxite or dawsonite or it may be prepared byprecipitation of aluminium hydroxide from solutions of aluminium suphate, nitrate, chloride, or other salt. The preferred form of aluminium oxide is gamma-alumina which is obtained by the dehydration of the mono-hydrate bohmite (AlO-OH) or the trihydrate hydrargillite of gibbsite (Al(OH)3) at temperatures of the order of 350‹-500‹. The preferred proportions of chromium oxide in the catalyst range from 15 per cent.-20 per cent. The products from the second stage of the dehydrogenation are fractionated, and unconverted butanes recycled. The catalysts used in the present invention may be reactivated by oxidizing: with air or other oxidizing gas at a moderately elevated temperature. In an example a catalyst was prepared by adding chromic acid to a granular activated alumina, and contacting with hydrogen at approximately 350‹ C., the composition of the catalyst being 92 per cent. by weight of alumina and 8 per cent. of chromium sesquioxide. Normal butane is passed over this catalyst at 610‹ C. at a slightly superatmospheric pressure using a space velocity of 8260 volumes per volume of catalyst space per hour. The catalyst is reactivated at intervals of one hour. The reaction products from the primary stage were fractionated and the butane fraction was recycled. The butene fraction was passed over a similar catalyst containing 4 per cent. of chromium sesquioxide at 650‹ C. using space velocities of 2380-3350 per hour and absolute pressures of 60 mm. Specification 481,646 is referred to. The Specification as open to inspection under Sect. 91 includes also the modification of using a different catalyst for the dehydrogenation step. In addition a wider range of catalysts are included comprising a major amount of alumina or other base capable of acting as a refractory carrier, and a minor amount of one of the oxides of chromium or other active catalyst. Alternatively the invention also includes the use of a catalyst composed of a minor amount of carrier and a major proportion of carrier. This subjectmatter does not appear in the Specification as accepted.