Patent GB-790559-A (GB)
Title: Process for the manufacture of maleic acid and/or maleic anhydride
Filed: 1955-05-20
Abstract: Maleic anhydride and/or maleic acid are obtained by passing the vapour, which may contain water, of an organic compound containing at least 4 carbon atoms and which is oxidizable to maleic anhydride and/or maleic acid under the reaction conditions, together with an oxidizing gas consisting of or comprising molecular oxygen at a raised temperature, and if desired, under superatmospheric pressure, over an oxidation catalyst, and after introducing the gaseous mixture into the reaction vessel introducing further vapour of the initial organic compound, and if desired of oxidizing gas, into the reaction vessel at at least one point other than that at which the initial gaseous mixture is introduced into the reaction vessel.  The further vapour of the initial organic compound and if desired oxidizing gas is preferably introduced at a plurality of places spaced from one another at intervals in the direction of flow of the gaseous mixture, e.g. at 3 to 5 successive places, and they are advantageously introduced in such an amount as to maintain approximately the initial concentration of the organic compound at its point of introduction. Specified oxidizable organic compounds are benzene, toluene, xylene, cyclohexane, butane, n-butene, 1,3-butadiene, n-butanol, diols containing 4 carbon atoms, aldols, e.g. acetaldol, crotonaldehyde, mineral oil fractions boiling within the range of 80 DEG  to 100 DEG C., tetrahydrofuran, furfural, and 2-methyl-2,4-pentadiene. Specified oxidation catalysts include the higher difficulty reducible oxides of vanadium and molybdenum alone or in admixture, and if desired activated by the addition of oxides of chromium, cerium, or phosphorus.  The catalyst may if desired be supported on a carrier or directly on the wall of the reaction vessel and may be in the form of a static bed or a fluidized bed.  In the latter case a plurality of fluidized beds is used through which the vapour passes in succession, and the further vapour of the organic compound, and if desired oxidizing gas, is introduced into the fluidized bed or beds which succeed the first bed.  The oxidizing gas may be oxygen itself or any gas containing oxygen, e.g. air, and traces of gaseous oxidation accelerators, e.g. chlorine, may be present.  In examples: (1) a catalyst is applied to the inner walls of a reaction furnace consisting of six tubes by evaporating an aqueous solution containing ammonium vanadate, ammonium molybdate, and a small amount of ammonium diphosphate and the catalyst is then activated in a current of air at raised temperate.  A gaseous mixture of crotonaldehyde vapour, oxygen, nitrogen, and a small amount of water vapour is passed through the furnace and further amounts of crotonaldehyde vapour are introduced through each of two additional inlet openings which are arranged apart beyond the inlet to the furnace.  The furnace temperature is 355 DEG  C. and maleic anhydride and a small amount of maleic acid are recovered from the gaseous reaction product; (2) and (3) maleic anhydride is obtained by oxidation of 1,4-butanediol and n-butanol respectively using the same procedure as in (1) except that the reaction temperatures are 325 DEG  C. and 345 DEG  C. respectively.ALSO:An oxidation catalyst used for the production of maleic anhydride by air oxidation of, for example, crotonaldehyde, 1,4-butane-diol, or n-butanol (see Group IV (b)) is obtained by evaporating a solution of 14.2 parts ammonium vanadate, 2.8 parts ammonium molybdate, and 0.4 part ammonium diphosphate in 250 parts of water and then activating in a current of air at raised temperature.