GB1042255A - Recovery of maleic anhydride - Google Patents

Abstract

Maleic anhydride of high purity is recovered from aqueous scrubber liquor obtained by scrubbing the effluent gas from a phthalic anhydride oxidation reaction mixture after condensing out at least 98% of the phthalic anhydride from the reaction mixture, by treating the aqueous liquor containing maleic acid in a concentration equivalent up to about 20% maleic anhydride and substantially devoid of solid phthalic anhydride material, with crude maleic anhydride, until the maleic acid concentration is built up to an equivalent of at least 35% maleic anhydride, dehydrating the resulting mixture to produce crude maleic anhydride, treating this at substantially boiling temperature with a strong acid agent for 1-12 hours, and then fractionating it, and recovering maleic anhydride of high purity. The scrubbing liquor may be obtained from a phthalic anhydride effluent gas containing tolualdehyde and may contain maleic acid equivalent to about 7.5% maleic anhydride, and this liquor may be used to scrub maleic anhydride effluent gas obtained by the oxidation of benzene, to give a resulting liquor containing maleic acid in an amount equivalent to about 40% maleic anhydride.