A process for oxidizing methyl-substituted biphenyl compounds comprises contacting a mixture comprising isomers of at least one methyl-substituted biphenyl compound with a source of oxygen, wherein the mixture comprises at least 20 wt % of isomer(s) having a methyl group at a 2-position or a 3-position on at least one benzene ring and at least 50 wt % of isomer(s) having a methyl group at a 4-position on at least one benzene ring, wherein said percentages are based on the total weight of the at least one methylbiphenyl compound in the mixture.

A process for oxidizing methyl-substituted biphenyl compounds comprises contacting a mixture comprising isomers of at least one methyl-substituted biphenyl compound with a source of oxygen, wherein the mixture comprises at least 20 wt % of isomer(s) having a methyl group at a 2-position or a 3-position on at least one benzene ring and at least 50 wt % of isomer(s) having a methyl group at a 4-position on at least one benzene ring, wherein said percentages are based on the total weight of the at least one methylbiphenyl compound in the mixture.

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.

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.

The present invention relates to a catalyst system for oxidation of o-xylene and/or naphthalene to phthalic anhydride (PA) comprising at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active material of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %. The present invention further relates to a process for gas phase oxidation in which a gas stream comprising at least one hydrocarbon and molecular oxygen is passed through a catalyst system which comprises at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active materials of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %.

The present invention relates to a catalyst system for oxidation of o-xylene and/or naphthalene to phthalic anhydride (PA) comprising at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active material of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %. The present invention further relates to a process for gas phase oxidation in which a gas stream comprising at least one hydrocarbon and molecular oxygen is passed through a catalyst system which comprises at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active materials of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %.

The present invention relates to a catalyst system for oxidation of o-xylene and/or naphthalene to phthalic anhydride (PA) comprising at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active material of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %. The present invention further relates to a process for gas phase oxidation in which a gas stream comprising at least one hydrocarbon and molecular oxygen is passed through a catalyst system which comprises at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active materials of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %.

The present invention pertains to a process for the cross-ketonization (Piria reaction) between an aryl carboxylic acid and an aliphatic carboxylic acid using a metal-based compound and a slight or a moderate excess of aryl carboxylic acid. A good selectivity, up to 99 mol %, can be achieved. The aryl aliphatic ketone can be used for the preparation of surfactants and other downstream products.

The present invention pertains to a process for the cross-ketonization (Piria reaction) between an aryl carboxylic acid and an aliphatic carboxylic acid using a metal-based compound and a slight or a moderate excess of aryl carboxylic acid. A good selectivity, up to 99 mol %, can be achieved. The aryl aliphatic ketone can be used for the preparation of surfactants and other downstream products.

Disclosed herein is a method for producing high-purity terephthalic acid, including steps of dissolving crude terephthalic acid crystal in water and performing catalytic hydrogenation treatment, depressurizing and cooling a reaction liquid after the catalytic hydrogenation treatment in stages with two or more stages of crystallization vessels, to crystallize terephthalic acid to obtain a terephthalic acid slurry, introducing the terephthalic acid slurry into an upper portion of a mother liquor replacement tower, bringing the terephthalic acid crystal into contact with an upward flow of replacement water introduced from a tower lower compartment of the mother liquor replacement tower while making the terephthalic acid crystal settled down in the tower, withdrawing the terephthalic acid crystal as slurry with the replacement water from the tower lower compartment, subjecting the slurry withdrawn from the tower lower compartment to solid-liquid separation into water and the terephthalic acid crystal, and drying the separated terephthalic acid crystal.