Formation, purification and recovery of phthalic anhydride

Details Formation, purification and recovery of phthalic anhydride Formation, purification and recovery of phthalic anhydride

1979-08-29

1980-07-29

Raymond, Richard

Chemistry of carbon compounds

Miscellaneous organic carbon compounds

C-metal

2603464, C07D30789

Patent

active

042150566

ABSTRACT:
Phthalic anhydride of commercially acceptable quality is recovered in high (94-96%) yields from a mixture containing on a weight basis from 70 to 90% o-phthalic acid, 1.5 to 21% water, 0.3 up to 13% benzoic acid, 0.2 up to 2% o-toluic acid, 0.2 to 1% 2-carboxybenzaldehyde, 0.1 up to 2% phthalide and from 1.3 up to 10% higher boiling materials by rapid dehydration of o-phthalic acid to its anhydride and rapid evaporation thereof followed by contact of the resulting vapor mixture with an inert reflux liquid in a fractionation zone to remove water and to provide a partial purification of the anhydride, removal of phthalide therefrom by only heating said partially purified anhydride in the presence of a catalytic amount of an alkali metal hydroxide having a molecular weight of at least 56 followed by fractionation of the phthalide-free mixture. Such process is more commercially attractive than melting said mixture containing 70 to 90% o-phthalic acid to dehydrate it to its anhydride and recovering the anhydride by fractionation because such apparently simple process cannot produce phthalic anhydride of a color or purity to be commercially acceptable nor can it provide an anhydride product substantially free of phthalide.

REFERENCES:
patent: 2670325 (1954-02-01), West et al.
patent: 3402184 (1968-09-01), Berthoux et al.
patent: 3484458 (1969-12-01), Stein et al.
patent: 4165324 (1979-08-01), Schroeder et al.

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