GB654469A - Methods of recovering phthalic anhydride - Google Patents

Abstract

Phthalic anhydride is removed from gases or vapours containing the same by subjecting the gases or vapours while at an elevated temperature to the action of a water spray or water in the form of fine particles, whereby the phthalic anhydride is condensed and precipitated, the water being supplied in an amount sufficient to condense and precipitate a major proportion of the phthalic anhydride but not in an amount appreciably greater than that required to saturate said vapours or gases. The temperature of the vapours may be above the condensation temperature of phthalic anhydride in the solid phase, or the temperature may be 130 DEG C. or higher and is then reduced to 50 DEG to 95 DEG C. with the water. The gases containing phthalic anhydride may be fed into the upper end of a tower, treated with the water and the precipitated phthalic anhydride removed, e.g. by allowing it to settle at the bottom of the tower and then removing it in a liquid condition by melting. The water employed in the tower may be in the form of particles that are sufficiently small to evaporate before they impinge on any portion of the tower. The phthalic anhydride vapours can be obtained from the vapour phase partial oxidation of polynuclear aromatic compounds, e.g. naphthalene, and the hot reaction gases p are partially cooled to a temperature not lower than 130 DEG C. before being subjected to the water treatment, e.g. by treatment in the tower mentioned above while remaining gases containing unsettled phthalic anhydride may be removed from the tower and the phthalic anhydride separated from said gases.