STUDY OF THE COMPOSITION AND PROPERTIES OF THE CUBIC RESIDUES OF PHTHALIC ANHYDRIDE DISTILLATION

Abstract

Phthalic anhydride (PA), obtained directly from freeze condensers (crude), contains 3 to 8% impurities, which are byproducts of the naphthalene oxidation reaction to PA and resinous substances formed during the condensation of these products. The main impurities in crude PA are 1,4-naphthaquinone, maleic anhydride, phthalic and benzoic acids, and resinous substances. If the process conditions for contacting the crude phthalic anhydride are not met, a small amount of naphthalene may be present. Next, the crude PA is purified by heat treatment with the addition of oxidizing or condensing agents, followed by distillation of the molten product. Heat treatment and the addition of oxidizing and condensing agents promote the destruction or polymerization of colored impurities present in phthalic anhydride and their conversion into high-carbon resinous products remaining in the distillation residue.