Abstract: A process for continuously producing high purity terephthalic acid, in particular, useful for direct polymerization, which comprises continuously introducing p-dialkylbenzene as a feed material together with a solvent and an oxidation catalyst into a reactor, subjecting the p-dialkylbenzene to a liquid phase oxidation with oxygen in the reactor to produce terephthalic acid, continuously or intermittently introducing the reaction mixture containing terephthalic acid thus produced into a stabilizer, and oxidizing the reaction mixture in the stabilizer for an extended period of time with a molecular oxygen containing gas of a low oxygen concentration at a temperature and pressure the same as or lower than those in the oxidation reaction while keeping the volume change of the contents in the stabilizer below about 30% by volume of the contents of the stabilizer.

Abstract: A process and an apparatus for producing an aromatic dicarboxylic acid by oxidizing a benzene derivative with molecular oxygen in the liquid phase in a lower aliphatic carboxylic acid as a solvent in the presence of an oxidation catalyst, wherein a starting material liquid e.g., a benzene derivative or a solution thereof in the lower aliphatic carboxylic acid, is fed into the liquid-phase reaction system in a uniformly dispersed state by being passed through a porous material causing the pressure of the starting material liquid just after passing through said porous material to drop more than about 1 kg/m.sup.2 in relation to the pressure of the starting material liquid just before passing through said porous material. The resultant aromatic dicarboxylic acid has high purity and has good color.

Abstract: A process for producing terephthalic acid of high quality suitable for use in direct polymerization comprising oxidizing a para-dialkylbenzene and/or an oxidized intermediate thereof in the liquid phase with molecular oxygen or a molecular oxygen-containing gas in the presence of an oxidation catalyst containing a heavy metal in a lower aliphatic carboxylic acid solvent, the reaction being carried out in the presence of a specified amount of a phenol. Polyesters prepared from the resulting terephthalic acid have good color.

Abstract: In a process for producing terephthalic acid which comprises subjecting p-xylene to a liquid-phase oxidation in a lower aliphatic carboxylic acid solvent in the presence of a cobalt compound-manganese compound-bromine or bromine compound catalyst and molecular oxygen, the improvement which comprisesThe % by weight based on the weight of said lower aliphatic carboxylic acid solvent of the cobalt component (as cobalt) in the catalyst being within the range of-6.00.times.10.sup.-4 t+1.65.times.10.sup.-1 to -2.50.times.10.sup.-3 t+6.25.times.10.sup.-1wherein t is the reaction temperature in .degree. C.;the weight ratio of the manganese component (as manganese) in the catalyst to the cobalt component in the catalyst ranges from 0.25:1 to 1:1 and also the amount of the manganese component in the catalyst is 0.

Abstract: An apparatus for producing an aromatic dicarboxylic acid by oxidizing a benzene derivative with molecular oxygen in the liquid phase in a lower aliphatic carboxylic acid as a solvent in the presence of an oxidation catalyst, wherein a starting material liquid e.g., a benzene derivative or a solution thereof in the lower aliphatic carboxylic acid, is fed into the liquid-phase reaction system in a uniformly dispersed state by being passed through a porous material causing the pressure of the starting material liquid just after passing through said porous material to drop more than about 1 kg/m.sup.2 in relation to the pressure of the starting material liquid just before passing through said porous material. The resultant aromatic dicarboxylic acid has high purity and has good color.

Abstract: A reaction vessel for continuously producing an aromatic carboxylic acid sparingly soluble in a solvent by liquid-phase oxidizing a corresponding alkyl aromatic compound with a molecular oxygen-containing gas in the presence of a lower aliphatic carboxylic acid solvent and an oxidation catalyst. The adhesion of the aromatic carboxylic acid on the inside wall of the reaction vessel at the interface between the vapor-phase portion and the liquid-phase portion is prevented by locating in the reaction vessel a means such as a porous annular pipe for spraying onto the inside wall of the reaction vessel above the level of the reaction liquid a part of a solvent-catalyst mixture supplied continuously to the reaction vessel.

Abstract: A process for producing an aromatic carboxylic acid by liquid-phase oxidizing an alkylbenzene with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid solvent in the presence of a heavy-metal-bromine oxidation catalyst, in which the oxidation reaction is conducted using a material containing as inorganic elements only cobalt, manganese, and bromine as the catalyst components and while withdrawing from the reaction system, at least partially, the condensed liquid of a gaseous mixture discharged from the top of the reactor during the reaction and maintaining the water content of the reaction system below a definite level by introducing fresh solvent (or, preferably, the solvent recovered as a side cut fraction by distilling the condensed liquid) in an amount corresponding to the amount of the solvent withdrawn contained in the condensed liquid, and a reaction mother liquor which is formed by separating the aromatic carboxylic acid from the reaction mixture withdrawn from the reactor is recycl

Abstract: A method of recovering in highly pure states heavy metals such as cobalt, manganese, etc.

Abstract: A method for recovering a heavy metal oxidation catalyst used in a liquid-phase oxidation process for producing terephthalic acid from the residue of the reaction mother liquor by stirring the residue together with water in the presence of molecular oxygen and a sulfur compound, subjecting the extracted mixture to a solid-liquid separation to separate the solid impurities, adding the aqueous solution containing the oxidation catalyst to an alkali metal or ammonium carbonate or an aqueous solution of an alkali metal or ammonium carbonate while maintaining the temperature of the system at about 26.degree.C to 70.degree.C, and recovering the heavy metal catalyst as a carbonate precipitate having high purity and good filterability and washability.