Catalysis

Details Catalysis Catalysis

C - Chemistry, Metallurgy

07

C

260/531.6

C07C 63/26 (2006.01) C07C 51/487 (2006.01)

Patent

CA 1108644

ABSTRACT OF THE DISCLOSURE Improvements are provided in a catalytic process for purifying terephthalic acid which has been prepared by the catalytic oxidation of p-xylene and which includes 4-carboxybenzaldehyde and terephthaldehyde as aldehydic impurities. The purification process involves catalytically hydrogenating the impure terephthalic acid to convert 4-carboxybenzaldehyde and terephthaldehyde therein to p-toluic acid and p-xylene, respectively, by a reaction mechanism which involves first converting the aldehyde (CHO) groups to alcohol (CH2OH) groups and then converting the latter to methyl (CH3) groups. The invention comprises carrying out the hydrogenation of the impure terephthalic acid by contacting an aqueous solution of the impure acid with hydrogen gas, as the sole gaseous reactant, in the presence of a catalyst selected from one of the following metal combinations: palladium:ruthenium; palladium:osmium; palladium:iridium; palladium:rhodium; palladium:platinum; palladium:rhodium; palladium:iron; palladium:nickel; palladium:cobalt; palladium:chromium; palladium:manganese; and palladium:uranium. The catalyst functions to improve the speed at which the alcohol groups are converted to methyl groups without markedly affecting the speed of the initial conversion of aldehyde groups to alcohol groups. The terephthalic acid so produced is of sufficient purity for use in the production of polyester fibres.

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