Apparatus for the recovery of vaporized phthalic anhydride from gas

Abstract

Phthalic anhydride is recovered from gases in a multiple heat-pipe exchanger system, one or more for condensing phthalic anhydride from gases containing vapors thereof and one or more simultaneously melting out the condensed phthalic anhydride solids, the exchangers being switched in alternate cycles to melt out from the surfaces of the exchanger tube ends on which the phthalic anhydride solids were first accumulated, and to condense phthalic anhydride solids in the exchanger or exchangers from which the phthalic anhydride was cleared by melting out. The cooling of opposite heat-pipe exchanger ends to recover phthalic anhydride is economical and efficient with ambient air, either alone or with some warm recycle exchanger air to adjust the cooling temperature; and the heating to melt out accumulated phthalic anhydride is effected with hot gases, such as combustion gases, preferably by incineration of residual phthalic anhydride tail gas from which the phthalic anhydride was condensed, or other hot combustion gases, but other sources of heating the air or gases may be optionally substituted. Important advantage is present in superior heat exchange efficiency using the heat-pipe exchanger for this service, in the ready switching from heating to cooling of such exchangers for alternate operation in both condensing and melting out modes, in the elimination of intermediary heat transfer media and the separate auxiliary equipment required for the heating and cooling cycles, in the utilization of waste heat from combustion gases, and in the great economy for phthalic anhydride storage tank vent condensers through elimination of both cooling water and steam requirements.