E.i. Dupont De Nemours and Company

Ronald M Yabroff

Michael Robert Samuels

Processes are provided for the electrodialysis of a (di)alkali metal salt of an aromatic hydroxycarboxylic acid to produce a free aromatic hydroxycarboxylic acid and the alkali metal hydroxide, in the presence of a selected alkali metal salt. These various embodiments represent efficient and economical methods for recovering the alkali metal hydroxide, as well as the parent organic compound, from these dialkali metal salts. These processes also desirably prevent overvoltage during the electrodialysis.

Process for the isolation of aromatic hydroxycarboxylic acids

Alkali metal aryloxides may be speedily dried by removing water while the aryloxide is molten. Such dried alkoxides are useful as chemical intermediates. Molten alkali metal aryloxides may be contacted with carbon dioxide to quickly produce the dialkali metal salts of aromatic hydroxycarboxylic acids, which upon acidification yield the corresponding aromatic hydroxycarboxylic acids. Aromatic hydroxycarboxylic acids are useful as chemical intermediates and as monomers for polymers. Solid metal aryloxides may be reacted with carbon dioxide in a reactor in which the contents, even when pasty, may be agitated so that the reaction is more rapid than in prior methods.

Preparation of aromatic hydroxycarboxylic acids and dialkali metal salts

Separation of 2,4-tolylene diisocyanate from a mixture of 2,4- and 2,6-tolylene diisocyanate by cooling the mixture of isocyanate by passage through a heat exchanger to crystallize a portion of 2,4-tolylene diisocyanate to form a slurry containing no more than about 25% by weight 2,4-tolylene diisocyanate crystals suspended in mother liquor, maintaining the resulting slurry for a nominal residence time of at least about 2 hours at about a constant temperature and centrifuging the slurry to separate 2,4-tolylene diisocyanate crystals from the mother liquor.

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Wilmington, DE, United States of America

Ronald M Yabroff