Abstract: The present invention proposes a crystallization process comprising the steps of feeding a slurry solution in which a terephthalic acid solution or a part of the terephthalic acid is precipitated to a crystallization vessel, precipitating the terephthalic acid in the crystallization vessel, generating a slurry containing crystals and solvent, discharging the slurry, and further comprising the steps of introducing the slurry in a tangential the direction of a hydrocyclone, returning the slurry flowing out as a downward swirling flow from a lower part of the hydrocyclone to the vessel, and discharging the slurry overflowing from the upper part of the hydrocyclone. According to the present invention, crystals of large particle size is obtained and a stable driving ranging long term can be achieved because any adhesion or accumulation of the terephthalic acid crystals does not appear at all in the crystallization vessel.

Abstract: The present invention proposes a crystallization process comprising the steps of feeding a slurry solution in which a terephthalic acid solution or a part of the terephthalic acid is precipitated to a crystallization vessel, precipitating the terephthalic acid in the crystallization vessel, generating a slurry containing crystals and solvent, discharging the slurry, and further comprising the steps of introducing the slurry in a tangential the direction of a hydrocyclone, returning the slurry flowing out as a downward swirling flow from a lower part of the hydrocyclone to the vessel, and discharging the slurry overflowing from the upper part of the hydrocyclone. According to the present invention, crystals of large particle size is obtained and a stable driving ranging long term can be achieved because any adhesion or accumulation of the terephthalic acid crystals does not appear at all in the crystallization vessel.

Abstract: There is disclosed a process for continuously producing an aromatic carboxylic acid comprising the steps of (A) subjecting a poly-alkyl aromatic hydrocarbon to a liquid-phase oxidation by continuously supplying an oxidation reactor with said hydrocarbon, a catalyst, a reaction accelerator, acetic acid containing water and a gas containing molecular oxygen; (B) continuously taking out from the oxidation reactor, the reaction products containing aromatic carboxylic acids, and separating the same into crude aromatic carboxylic acids and acetic acid containing water; and (C) continuously taking out from the oxidation reactor, the oxidative reaction exhaust gas containing evaporated acetic acid containing water, introducing the above gas in a condenser, and condensing the above evaporated acid, wherein acetic acid containing water is supplied to an oxidative reaction exhaust gas inlet line leading to the condenser.

Abstract: A process for recovering crystals from a slurry which comprises supplying a slurry comprising crystals and a solvent to a rotary vacuum filter and successively conducting filtration under suction, washing, filtration under suction and cleavage of a cake continuously by rotation of a cylindrical filter medium, wherein a vapor having a same composition as that of the solvent is supplied as a blowing gas for cleaving the cake. The crystals can be continuously recovered for a long period of time without clogging of a filter medium when the crystals are recovered from a slurry by using a rotary vacuum filter.

Abstract: There is disclosed a process for continuously producing an aromatic carboxylic acid comprising the steps of (A) subjecting a poly-alkyl aromatic hydrocarbon to a liquid-phase oxidation by continuously supplying an oxidation reactor with said hydrocarbon, a catalyst, a reaction accelerator, acetic acid containing water and a gas containing molecular oxygen; (B) continuously taking out from the oxidation reactor, the reaction products containing aromatic carboxylic acids, and separating the same into crude aromatic carboxylic acids and acetic acid containing water; and (C) continuously taking out from the oxidation reactor, the oxidative reaction exhaust gas containing evaporated acetic acid containing water, introducing the above gas in a condenser, and condensing the above evaporated acid, wherein acetic acid containing water is supplied to an oxidative reaction exhaust gas inlet line leading to the condenser.

Abstract: A process for recovering crystals from a slurry which comprises supplying a slurry comprising crystals and a solvent to a rotary vacuum filter and successively conducting filtration under suction, washing, filtration under suction and cleavage of a cake continuously by rotation of a cylindrical filter medium, wherein a vapor having a same composition as that of the solvent is supplied as a blowing gas for cleaving the cake.

Abstract: A process for producing 2,6-naphthalenedicarboxylic acid comprising oxidizing 2,6-dimethylnaphthalene with a gas containing oxygen in a solvent comprising a lower aliphatic carboxylic acid in the presence of a catalyst comprising cobalt, manganese, and bromine, wherein the total amount of cobalt and manganese in the catalyst is 50 to 300 mg atom per 1 g mol of 2,6-dimethylnaphthalene, a ratio by g atom of manganese to cobalt in the catalyst is 20:1 to 4:1, and the oxidation is conducted at a temperature of 200 to 250.degree. C.; and a process as described above, wherein a mother liquor which is obtained from a slurry of a product of the oxidation via a step of solid-liquid separation is recyled to a step of oxidation after heat treatment at a temperature of 150.degree. C. or higher. In accordance with the processes, accumulation of substances which affect the oxidation adversely is prevented.

Abstract: A process for the production of high-purity isophthalic acid, which enables easy treatment of the PIA mother liquor, enables the recovery of the useful materials contained in the PIA mother liquor, decreases the discharge amount of water and enables the recycling of water to be used as a solvent, without additional investment and expenses, the process comprising the steps ofa) separating a liquid-phase oxidation solution into an oxidation mother liquor and a crude isophthalic acid by crystallization and evaporating the oxidation mother liquor to form acetic acid vapor or a condensate thereof,b) dissolving the crude isophthalic acid in water, then catalytically hydrogenating, catalytically treating or oxidizing the resultant solution of isophthalic acid in water to form a purified solution, cooling the purified solution to crystallize isophthalic acid and separating the purified solution into a PIA mother liquor and a crystal of the isophthalic acid, andc) feeding the acetic acid vapor or condensate prepared b

Abstract: There are disclosed a method for replacing a dispersion medium wherein an original slurry comprising solid particles and an original dispersion medium is introduced in a dispersion medium replacement column at the top thereof, a replacing dispersion medium is introduced in the column at the bottom thereof to replace the original dispersion medium with the replacing dispersion medium, the resultant replaced slurry comprising the solid particles and the replacing dispersion medium is taken out from the column at the bottom thereof, and the original dispersion medium is taken out from the column at the top thereof, which method comprises dividing the fluid in the intermediate portion into a plurality of parallel streams, stirring the slurry in the bottom of the column to uniformize the slurry, and controlling the feed rates of the replacing dispersion medium and the replaced slurry to maintain the slurry in the bottom portion of the column at a concentration higher than that of the slurry in the intermediate por

Abstract: A process for producing highly pure terephthalic acid comprising: (a) oxidizing a p-phenylene compound in the liquid phase in the presence of acetic acid, to produce a liquid-phase oxidation product, (b) separating the liquid-phase oxidation product into the following: (i) a first mother liquid containing acetic acid and (ii) a crude terephthalic acid, (c) evaporating, in whole or in part, the first mother liquid, to produce a vapor, (d) feeding the vapor, or a condensate thereof, to an intermediate stage of a distillation tower, carrying out an azeotropic distillation and withdrawing through a bottom of the distillation tower a concentrated acetic acid, (e) subjecting the crude terephthalic acid to a refining treatment, which is a catalytic hydrotreatment, a catalytic treatment or a recrystallization, which is carried out in the presence of is water, (f) cooling and crystallizing the resultant liquid from step (e), to produce a pure terephthalic acid and a second mother liquor, (g) subjecting the second moth

Abstract: There is disclosed a process for producing highly pure terephthalic acid by converting a slurry of terephthalic acid crystals in acetic acid solvent which crystals are obtained by liquid-phase oxidation of p-alkylbenzene, into a slurry thereof in water solvent by mother liquor replacement and then subjecting the latter slurry to a catalytic hydrogenation treatment which process comprises the steps of introducing the slurry of terephthalic acid crystals in acetic acid into a mother liquor replacement column at the top portion; forming an accumulation layer of the terephthalic acid crystals at the bottom portion by the sedimentation of the crystals; feeding replacing water sufficient for the formation of upward rising stream of water to the inside of the column at the bottom portion; and withdrawing the accumulation layer of the crystals from the bottom portion of the column.

Abstract: There is disclosed a process for producing terephthalic acid which comprises oxidizing in a liquid-phase a starting raw material comprising p-xylene incorporated with 3 to 35% by weight of p-tolualdehyde based on the same at a temperature in the range of 120.degree. to 240.degree. C. by means of a molecular oxygen-containing gas by using a lower aliphatic monocarboxylic acid as a solvent in the presence of a catalyst comprising a manganese compound having 50 to 1000 ppm by weight of manganese atoms, a cobalt compound having 50 to 2000 ppm by weight of cobalt atoms and a bromine compound having 100 to 4000 ppm by weight of bromine atoms, each based on the solvent. By virtue of the above specific constitution, it is made possible to produce high-quality terephthalic acid with a high residual rate of the lower aliphatic monocarboxylic acid as a solvent minimized in its loss, thereby enabling the production of high-quality polyester with high whiteness from the above terephthalic acid and a glycol.