DETAILED DESCRIPTION I claim: 1.
A process for the purification of carboxylic acid anhydrides contaminated with halogen and halide values to reduce the quantity of said values in the anhydrides, which comprises treating said anhydrides with a phenyl or an alkyl phosphine in the absence of copper, zinc, silver, and cadmium or their compounds and distilling to recover said anhydrides.
2.
A process as defined in claim 1, wherein the carboxylic acid anhydride contains at least 0.
001, but at most 1,000, ppm of iodine values expressed as I.
Description:
This invention relates to the purification of carbonylation products and is more particularly concerned with the purification of carboxylic acid anhydrides, especially acetic anhydride.
Processes have been developed for the preparation of carboxylic acid anhydrides by the reaction of olefins, esters, and ethers with carbon monoxide in the presence of a catalyst system which comprises a metal catalyst component and an iodide component, generally an alkyl iodide, especially methyl iodide.
Processes of this character involving a Group VIII noble metal catalyst, such as rhodium, palladium, iridium and the like are disclosed, for example, in U.
S.
Pat.
Nos.
3,852,346, 4,115,444, 4,335,059, and 4,358,411, and in British Pat.
Nos.
1,468,940 and 1,523,346.
Catalyst systems of the character indicated wherein the metal component comprises nickel or nickel compounds are employed for the preparation of carboxylic anhydrides in processes which are disclosed, for example, in U.
S.
Pat.
Nos.
4,026,677 and 4,026,678.
Processes have also been disclosed wherein carboxylic anhydrides are co-produced with carboxylic acids in carbonylation systems involving Group VIII noble metal catalysts and an iodide promoter.
In European patent application Nos.
0 087 869 and 0 087 870, for example, there are described processes involving the carbonylation of carboxylic acid esters, such as methyl acetate, hydrocarbyl ethers, such as dimethyl ether, and optionally also an alcohol, together with controlled, limited amounts of water
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