Abstract: Processes are described for separating 3,4?- and 4,4?-dimethylbiphenyl from a mixture comprising at least 3,3?-, 3,4?- and 4,4?-dimethylbiphenyl. In the processes, the mixture is cooled to produce a crystallization product comprising at least of the 4,4?-dimethylbiphenyl from the feed mixture and a first mother liquor product. The first mother liquor product is distilled to produce a bottoms stream enriched in 4,4?-dimethylbiphenyl as compared with the first mother liquor product and an overhead stream deficient in 4,4?-dimethylbiphenyl as compared with the first mother liquor product. The overhead stream is then cooled to produce a second crystallization product comprising at least part of the 3,4?-dimethylbiphenyl from the overhead stream and a second mother liquor product.

Abstract: Processes are described for purifying a biphenyldicarboxylic acid product containing one or more impurities, particularly at least formylbiphenylcarboxylic acid. In the processes, a mixture comprising the biphenyldicarboxylic acid product is contacted with hydrogen in the presence of a hydrogenation catalyst under conditions to selectively reduce at least part of the formylbiphenylcarboxylic acid to produce a hydrogenation effluent comprising (i) hydroxymethylbiphenylcarboxylic acid and/or methylbiphenylcarboxylic acid, and (ii) biphenylcarboxylic acid. At least a portion of the biphenyldicarboxylic acid is then separated from the hydrogenation effluent. Advantageously, a polyester product may be produced from the separated biphenyldicarboxylic acid.

Abstract: Processes are described for separating 3,4?- and 4,4?-dimethylbiphenyl from a mixture comprising at least 3,3?-, 3,4?- and 4,4?-dimethylbiphenyl. In the processes, the mixture is cooled to produce a crystallization product comprising at least of the 4,4?-dimethylbiphenyl from the feed mixture and a first mother liquor product. The first mother liquor product is distilled to produce a bottoms stream enriched in 4,4?-dimethylbiphenyl as compared with the first mother liquor product and an overhead stream deficient in 4,4?-dimethylbiphenyl as compared with the first mother liquor product. The overhead stream is then cooled to produce a second crystallization product comprising at least part of the 3,4?-dimethylbiphenyl from the overhead stream and a second mother liquor product.

Abstract: Processes are described for purifying a biphenyldicarboxylic acid product containing one or more impurities, particularly at least formylbiphenylcarboxylic acid. In the processes, a mixture comprising the biphenyldicarboxylic acid product is contacted with hydrogen in the presence of a hydrogenation catalyst under conditions to selectively reduce at least part of the formylbiphenylcarboxylic acid to produce a hydrogenation effluent comprising (i) hydroxymethylbiphenylcarboxylic acid and/or methylbiphenylcarboxylic acid, and (ii) biphenylcarboxylic acid. At least a portion of the biphenyldicarboxylic acid is then separated from the hydrogenation effluent. Advantageously, a polyester product may be produced from the separated biphenyldicarboxylic acid.

Abstract: Processes are described for purifying a biphenyldicarboxylic acid product containing one or more impurities, particularly at least formylbiphenylcarboxylic acid. In the processes, at least a portion of the biphenyldicarboxylic acid product is contacted with an alcohol under conditions effective to esterify at least part of the biphenyldicarboxylic acid and at least part of the formylbiphenylcarboxylic acid and produce an esterification effluent containing biphenyldicarboxylic acid diester and formylbiphenylcarboxylic acid ester. At least part of the biphenyldicarboxylic acid diester is then separated from the esterification effluent by crystallization. Advantageously, a polyester product may be produced from the separated biphenyldicarboxylic acid diester.