GB789414A - Recovery of maleic anhydride from hot gaseous mixtures - Google Patents

Abstract

Maleic anhydride is recovered from hot gases comprising the vapour of the anhydride and water-vapour by cooling the gases to a temperature, between 70 DEG and 20 DEG C., at which a large proportion of the anhydride condenses but the water-vapour does not condense, stripping the remainder of the anhydride from the cooled gases by washing them with water, and subjecting the anhydride obtained by condensation to distillation, preferably under reduced pressure, together with the solid maleic acid obtained from the aqueous wash solution by evaporation. The first runnings of the distillate comprise aqueous maleic acid; but solid maleic anhydride, free from fumaric acid and other impurities, is obtained as main product. The process may be applied to the hot gases obtained in the vapour-phase oxidation of benzene, crotonaldehyde, di- or tetrahydrofurane, or aliphatic hydrocarbons with 4 or more carbon atoms per molecule with oxidizing gases, e.g. air. The examples relate to the separation of maleic anhydride from the hot gases obtained by the oxidation of benzene with air in the presence of vanadium pentoxide catalyst.ALSO:Maleic anhydride is recovered from hot gases comprising the vapour of the anhydride and water-vapour by cooling the gases to a temperature, between 70 DEG and 20 DEG C., at which a large proportion of the anhydride condenses but the water-vapour does not condense, stripping the remainder of the anhydride from the cooled gases by washing them with water, and subjecting the anhydride, obtained by condensation, to distillation together with the solid maleic acid obtained from the aqueous wash solution by evaporation. The first runnings of the distillate contain aqueous maleic acid; but solid maleic anhydride, free from fumaric acid and other impurities, is obtained as main product. The process may be applied to the hot gases obtained in the vapour-phase oxidation of benzene, crotonaldehyde, di- or tetrahydrofurane, or aliphatic hydrocarbons with 4 or more carbon atoms per molecule with oxidizing gases, e.g. air. The cooling stage is preferably effected in such a manner that considerable turbulence is created in the gases. In an example, a gas obtained by the oxidation of benzene with air in the presence of V2O5 and containing 17 grm. of maleic anhydride and 23 grm. of water per cubic metre is fed, at a temperature of 90 DEG C., into a tubular cooler (2 metres in length) with tubes (40 mm. I.D.) in which spirals of sheet iron are accommodated. Water at a temperature between 20 DEG and 30 DEG C. is passed through the shell of the cooler. The total cooling surface is 30 square metres over which 900 cubic metres of gas are passed per hour. The gas is cooled down to 30-35 DEG C. on passing through the system, and 98 per cent maleic anhydride separates out as a brown solid. The feed of gas is discontinued after every two hours, the solid anhydride is melted and discharged from the cooler, and the feed of gas is then resumed. The cooled gas is washed with water in a tower, 0.05 to 0.1 litres of water being used per cubic metre of gas, to dissolve out the residual anhydride. The resultant solution is concentrated by evaporation, and 98 per cent maleic acid is obtained by centrifuging. The maleic acid is united with the crude maleic anhydride, and the resultant mixture is distilled at a pressure of 110 mm. Hg in a still provided with a stirrer and a short fractionating column. The vapours are condensed at 55 DEG to 60 DEG C.; the first runnings comprise maleic acid solution, and this is followed by 99 per cent maleic anhydride. Turbulence during the cooling stage may be effected by introducing the hot gas with sufficient speed tangentially into a cylindrical vessel, or by means of moving members, e.g. bucket wheels or gyroscopes.