GB727828A - Recovery of polycarboxylic acid anhydrides - Google Patents

Abstract

Maleic and phthalic anhydrides are recovered from a gaseous mixture containing them by passing the mixture in contact with dibutyl phthalate at a minimum of 40 DEG C. for simultaneous absorption of the anhydrides, and thereafter stripping the absorbed anhydrides from the solution. The absorption may be effected under conditions such that the resultant solution contains both the anhydrides, which can then be separated by fractionation, or the absorption may be accompanied by simultaneous stripping of the maleic anhydride by passing a countercurrent of an inert gas through the solvent. For details of operation (see Group III). U.S.A. Specification 2,574,644 is referred to.ALSO:<PICT:0727828/III/1> Maleic and phthalic anhydrides are separated from a gaseous mixture containing them by passing said mixture into dibutyl phthalate solvent at least 40 DEG C. for simultaneous absorption of both anhydrides, and thereafter stripping the absorbed anhydrides from the solution. The absorption may be effected so that the solution contains both the anhydrides, the stripping then producing a mixture of maleic and phthalic anhydrides which may then be fractionated; or the absorption may be accompanied by simultaneous stripping of the maleic anhydride (e.g. by employing a counter-current of an inert gas), leaving phthalic anhydride to be stripped from a solvent substantially free of maleic anhydride. Flow-sheets for the alternative methods above are provided. In Fig. 2, for operation of the latter method, reaction gases are fed into an absorber-stripper 26, down which dibutyl phthalate is passed. Inert gases from the base of the stripper strip maleic anhydride from the solvent, and the remaining substantially maleic anhydride-free solution of phthalic anhydride in dibutyl phthalate is introduced into a stripper 29 to strip the anhydride from the solvent, which is recycled. U.S.A. Specification 2,574,644 is referred to.