Verfahren zum Behandeln von rohem Phthalsäure-Anhydrid

摘要

Crude phthalic anhydride (PSA) is catalytically produced from oxygen-containing gas and orthoxylol or naphthalene at temperatures in a range from 300 to 500 DEG C. The mixture containing gas and PSA vapour withdrawn from the reactor is first led through a cooled, continuously operating liquid separator. A first liquid, PSA-rich stream is withdrawn from the liquid separator, as well as a separate residual mixture of gas and vapour. The residual, PSA-containing mixture is led through at least one among a plurality of cooled solid separators to separate solid PSA, which is then periodically liquefied again. A second PSA-rich stream is thus withdrawn from the solid separators. The amount per unit in time ratio between the first and second streams ranges from 1:5 to 2:1. The first stream is led at temperatures from 250 to 300 DEG C through a first dwelling vessel, in which it is subjected under stirring to a preliminary thermal treatment for at least 3 hours. The second, PSA-rich stream is purified by distillation together with the first, thermally pre-treated stream, bypassing the first dwelling vessel.