Patent GB-684649-A (GB)
Title: Recovery of molten phthalic anhydride
IPC: C07C51/573
Filed: 1951-02-27
Abstract: <PICT:0684649/IV (b)/1> In the vapour phase oxidation of a phthalic anhydride convertible hydrocarbon the effluent from the oxidation zone is countercurrently contacted with a downwardly moving mass of solid granular heat exchange material whereby the phthalic anhydride is condensed on said material.  In the preferred apparatus (Fig. 1) the effluent from the oxidation of a hydrocarbon (e.g. naphthalene, o-dialkylbenzene or phenanthrene with vanadium oxide catalyst) enters the chamber 1 at 3 and meets a downwardly moving stream of pebbles. The latter are initially cool (around 100 DEG  F.) and cause condensation of phthalic anhydride from the injected gaseous material which is at 400-1000 DEG  F.  Solid phthalic anhydride first condenses on the pebbles at the upper part of the chamber and as they pass downward it is re-evaporated, causing an enrichment of the upwardly-flowing gas.  When a steady state is reached the temperatures are such that liquid phthalic anhydride is formed in the central portion of the chamber.  The gases from this section are removed via 5 and thence blown into the heat exchanger 2 from which liquid phthalic anhydride is removed. Gases substantially free from phthalic anhydride are removed at 14 (below 200 DEG  F.), scrubbed if necessary and released to the atmosphere.  In a modification (Fig. 2 (not shown), phthalic anhydride is condensed in liquid form in a trap-out tray in the middle of the chamber and removed as such.  The pebbles pass via 15 to the chamber 17 whence they are lifted to the fountain separator 22 and cooled before re-entry to the separation chamber. Lifting may be done by air as shown, or by steam, by the effluent from 14 or by a mechanical elevator.  Fine particles produced by abrasion are removed via 23 and fresh pebbles added as necessary from 27.  After prolonged use the pebbles become covered with non-volatile by-products which are periodically burnt off.  The pebbles may be of gravel, silica-alumina, glass, carborundum, quartz, alundum, mullite, kaolin, ceramic or metals that are not oxidation catalysts at the working temperature.  Examples are given of the operation of the process.  Maleic anhydride may also be recovered by using water-wetted non-porous pebbles whereby maleic and/or fumaric acid is formed and subsequently re-converted to maleic anhydride lower down.  The mixed anhydrides are removed together and subsequently separated by fractional distillation. The water should not be sufficient to form phthalic acid.ALSO:<PICT:0684649/III/1> In the vapour phase oxidation of a phthalic anhydride convertible hydrocarbon the effluent from the oxidation zone is countercurrently contacted with a downwardly moving mass of solid granular heat exchanger material whereby the phthalic anhydride is condensed on said material.  In the preferred apparatus, Fig. 1, the effluent from the oxidation of a hydrocarbon (e.g. naphthalene, o-dialkylbenzene or phenanthrene with vanadium oxide catalyst) enters the chamber 1 at 3 and meets a downwardly moving stream of pebbles.  The latter are initially cool (around 100 DEG F) and cause condensation of phthalic anhydride from the injected gaseous material which is at 400-1000 DEG F.  Solid phthalic anhydride first condenses on the pebbles at the upper part of the chamber and as they pass downward it is re-evaporated causing an enrichment of the upwardly flowing gas. When a steady state is reached the temperatures are such that liquid phthalic anhydride is formed in the central portion of the chamber. The gases from this section are removed via 5 and thence blown into the heat exchanger 2 from which liquid phthalic anhydride is removed. Gases substantially free from phthalic anhydride are removed at 14 (below 200 DEG F), scrubbed if necessary and released to the atmosphere.  In a modification, Fig. 2 (not shown), phthalic anhydride is condensed in liquid form in a trap-out tray in the middle of the chamber and removed as such.  The pebbles pass via 15 to the chamber 17 whence they are lifted to the fountain separator 22 and cooled before re-entry to the separation chamber. Lifting may be done by air as shown or by steam, by the effluent from 14 or by a mechanical elevator.  Fine particles produced by abrasion are removed via 23 and fresh pebbles added as necessary from 27.  After prolonged use the pebbles become covered with non-volatile by-products which are periodically burnt-off.  The pebbles may be gravel, silica-alumina, glass, carborundum, quartz, alundum, mullite, kaolin, ceramic or metals that are not oxidation catalysts at the working temperature.  Examples are given of the operation of the process. Maleic anhydride may also be recovered by using water-wetted non-porous pebbles whereby maleic and/or fumaric acid is formed and subsequently re-converted to maleic anhydride lower down.  The mixed anhydrides are removed together and subsequently separated by fractional distillation.  The water should not be sufficient to form phthalic acid.