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 cobalt and manganese components from a product stream or a residue stream that resulted from a process which employs a catalyst system containing the cobalt and manganese components for oxidizing pseudocumene to trimellitic acid includes the steps of adding a precipitating agent to the product stream or the residue stream in an effective amount to react with the cobalt and manganese components in the product stream or the residue stream.

Abstract: Processes for producing aromatic monomers useful for forming polyesters are disclosed. Cost effective steps employed in the processes permit small amounts of process-related materials typically removed from monomer to remain in an aromatic monomer product. In many cases, the presence of the process-related materials left in the monomer product by the cost effective process steps can enhance the performance of the monomer in certain applications.

Abstract: A process for recovering components of a catalyst from a mother liquor of liquid phase oxidation in production of aromatic carboxylic acids by liquid phase oxidation of aromatic hydrocarbons having substituents with a gas containing oxygen in a presence of a catalyst comprising cobalt, manganese and bromine in acetic acid or acetic acid containing water as a solvent, which process comprises adding a compound generating an ion of an alkali metal to the mother liquor of liquid phase oxidation obtained after separating crystals of the aromatic carboxylic acid from a reaction fluid of the liquid phase oxidation, bringing the mother liquor containing the compound into contact with an ion exchange resin so that the components of the catalyst are adsorbed to the ion exchange resin and recovering the components of the catalyst comprising cobalt, manganese and bromine ion by passing an elution liquid through the ion exchange resin.

Abstract: A process for purifying a naphthalenic carboxylic acid comprising contacting at a temperature below about 575° F. a mixture comprising an impure naphthalenic carboxylic acid and a solvent in the presence of hydrogen gas with a noble metal on carbon catalyst. The process results in reduced amounts of organic impurities in the purified acid when compared to other purification processes.

Abstract: An aromatic carboxylic acid, aromatic aldehyde, and aromatic alcohol are simultaneously and efficiently prepared by liquid phase oxidizing an aromatic compound represented by formula (I) with a gas containing molecular oxygen, in a presence of a catalyst comprising transition metal compound, tertiary amine and bromide compound: 1

Abstract: Improved process for producing carboxylic acids or their esters by catalytic liquid phase oxidation of a corresponding precursor in a suitable solvent comprising feeding the reactants to a first oxidation reaction zone at high pressure and high solvent ratio, wherein uptake of oxygen is limited to less than 50% of the oxygen required for full conversion of the precursor to its corresponding carboxylic acid, and then feeding the resulting reaction medium to a second oxidation reaction zone.

Abstract: This invention relates to methods and reactor devices for controlling the oxidation of hydrocarbons to dibasic acids, in the presence of a cobalt catalyst and a monobasic acid, such as acetic acid, by treating the catalyst from the reaction mixture, outside the oxidation zone, after the oxidation has taken place at least partially. In one preferred embodiment, the catalyst is reduced to contain, preferably predominantly and more preferably substantially, cobalt ions in valence II, and at least partially precipitated by de-watering and/or thermal treatment. In a different preferred embodiment, the catalyst in the reaction mixture is first oxidized or maintained, preferably predominantly and more preferably substantially, at valence III, the reaction mixture is de-watered, the catalyst is reduced, preferably predominantly and more preferably substantially, to valence II, causing precipitation either spontaneously at a predetermined temperature or after further thermal treatment.

Abstract: Process for producing mono- and poly-carboxylic aromatic acids by oxidation of the corresponding precursors with molecular oxygen and/or air in the presence of a catalytic complex formed by a combination of at least one metal selected from ruthenium, iridium, platinum and palladium, and/or at least one metal of Group VIIA, principally rhenium; and/or cerium, and B at least one metal belonging IVA of the periodic table of elements, principally zirconium and/or hafnium.

Abstract: A process to produce terephthalic acid is provided, the process including the steps of: providing a feed stream comprising a dialkyl substituted aromatic and in an organic acid solvent: contacting the feed stream with an oxidant, the oxidant containing at least 50% by volume oxygen and at an oxygen partial pressure of at least 1 psia, at a temperature between about 80.degree. C. and about 130.degree. C.

Abstract: A method for recovering methyl acetate and residual acetic acid in a two-stage process for producing pure terephthalic acid having a first oxidation stage and a second purification stage.

Abstract: Process for producing pure terephthalic acid having improved means for recovering and/or recycling terephthalic acid precursors, residual acetic acid and other reaction by-products, such as methyl acetate.

Abstract: Disclosed is a method for preparing isophthalic acid from metaxylene and especially for purifying crude isophthalic acid (IPA) produced in the course of such method, or otherwise, from a liquid dispersion thereof also containing impurities selected from unreacted starting materials, solvents, products of side reactions and/or other undesired materials. The purifying portion of the method comprises the step of: (1) filtering the dispersion to form a crude IPA filter cake; (2) dissolving the filter cake in a selective crystallization solvent at an elevated temperature to form a solution; (3) crystallizing purified IPA from the solution in the crystallization solvent by reducing the temperature, or pressure, or both of the solution; (4) separating the crystallized purified IPA from the solution; and (5) re-dissolving or soaking the washed purified IPA cake at elevated temperature, to remove the final traces of the crystallization solvent and obtain the desirable particle sizes and shape.

Abstract: A process for producing 2,6-naphthalenedicarboxylic acid by the liquid phase, exothermic oxidation of 2,6-dimethylnaphthalene comprising adding to a reaction zone oxidation reaction components comprising 2,6-dimethylnaphthalene, a source of molecular oxygen, a solvent comprising an aliphatic monocarboxylic acid, and a catalyst comprising cobalt, manganese and bromine components wherein the atom ratio of cobalt to manganese is at least about 1:1 and the total of cobalt and manganese, calculated as elemental cobalt and elemental manganese added to the reaction zone, is less than about 0.

Abstract: A method and apparatus for preparing purified terephthalic acid and, optionally, isophthalic acid from mixed xylenes. The method of the present invention purifies the oxidation reactor effluent containing a mixture of terephthalic acid and isophthalic acid as well as minor amounts of 4-carboxybenzaldehyde (4-CBA), 3-carboxybenzaldehyde (3-CBA), and toluic acid isomers, to produce purified terephthalic acid and, optionally, purified isophthalic acid in an integrated process.

Abstract: A process for producing pure carboxylic acids by catalytic liquid phase oxidation of a suitable precursor in a solvent in which the oxidation reaction is carried out in a plug flow reaction zone at a high solvent:precursor ratio and reaction conditions sufficient to maintain the pure acid in solution as it is formed, and product produced from such process.

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: There is disclosed a process for producing an aromatic carboxylic acid (e.g.iso-or-tere-phthalic acid) by liquid-phase oxidation of an alkyl-group-substituted aromatic compound (e.g. p-or-m-xylene) in acetic acid which comprises dehydrating water-containing acetic acid by azeotropic distillation in an azeotropic distillation dehydration tower to recycle the dehydrated acetic acid as the solvent, and suppressing the concentration of the alkyl-group-substituted aromatic compound in the entrainer (e.g. n-butyl acetate) which is fed at the top portion of the above tower, to at most 10% by weight by removing the above aromatic compound. The process makes it possible to proceed with efficient dehydration of water-containing acetic acid for a long period of time by preventing the separation efficiency between acetic acid and an azeotropic component from being deteriorated by the alkyl-group-substituted aromatic compound remaining in the azeotropic component.

Abstract: An improved separation process for the continuous catalytic oxidation of aromatic alkyls for the production of aromatic carboxylic acids in a liquid solvent medium, wherein the reactor product stream is withdrawn from the oxidation process, then separated to produce a product containing stream, mother liquor stream and a catalyst containing purge stream which is then passed through a filtration system and series of sorption vessels to remove the oxidation catalyst and separate the impurities from the catalyst. The solvent is then separated from the reaction by-products by conventional distillation methods. The solvent is recycled to the process while the reaction by-product residue is disposed of by incineration. The oxidation catalyst is eluted from the ion exchange columns and returned to the process.

Abstract: A process for producing an aromatic dicarboxylic acid by simple operations using a simple apparatus is disclosed, which enables to effect separation and washing of the product crystals efficiently without suffering from clogging of the apparatus, while permitting recovery of the reaction solvent and catalyst with permission of an efficient replacement of the solvent.

Abstract: A process for the production of a trimellitic acid by oxidizing dialkyl aromatic aldehyde and/or its oxide derivative in a liquid phase, the oxidation being carried out in a lower aliphatic carboxylic acid solvent having a water content of 5 to 70% by weight in the presence of a catalyst containing a heavy metal and bromine or being carried out in a solvent containing a lower aliphatic carboxylic acid in the presence of a bromine-manganese catalyst system containing zirconium and/or cerium, and a process for the production of high-quality trimellitic acid anhydride from the trimellitic acid.

Abstract: A process for continuously producing an aromatic carboxylic acid comprising oxidizing an aromatic compound substituted with alkyl groups with molecular oxygen gas in the liquid phase in a solvent containing a lower aliphatic carboxylic acid in the presence of a catalyst comprising heavy metal compounds and a bromine compound, wherein a mother liquor which is obtained after removal of crystals from a reaction liquid of the liquid phase oxidation and contains heavy metal ions and bromine ion as catalyst components is brought into contact with a chelate resin of an anion exchange type to recover the catalyst components.The catalyst components are efficiently recovered, and auxiliary agents in an amount exceeding the equivalent amount and excessive labor are not necessary.

Abstract: A terephthalic acid slurry in acetic acid is produced by oxidising p-xylene in acetic acid, removing water by evaporation of a stream of water and acetic acid, and returning acetic acid to the oxidation step. The terephthalic acid is separated from the reaction medium in a first zone to leave a deposit on a band, the deposit is washed with a first aqueous medium in a second zone, removed from the band in a third zone, and admixed with a second aqueous medium. Reaction medium is passed from the first zone to the oxidation step and terephthalic acid is recovered, preferably after further purification.

Abstract: Purified terephthalic acid is prepared by a process of subjecting an aqueous solution of crude terephthalic acid to hydrogenation to reduce impurities, crystallizing this solution to produce a slurry of purified terephthalic acid in an aqueous liquor, and carrying out an integrated separation washing process.

Abstract: A method for separating oxidation catalysts used for producing trimellitic acid, which comprises the steps of: adding water to a reactor effluent in a volume ratio of water to the reactor effluent of 0:1 to 11:1, the reactor effluent being in a slurry state and resulting from oxidizing pseudocumene with air in an acetic acid and in the presence of cobalt, manganese and bromine catalysts; heating the mixture of water and the reactor effluent to a temperature of 25.degree. to 140.degree. C. to make the slurry be a diluted reactor effluent in a liquid phase; passing the diluted reactor effluent through ion exchange resins, to adsorb cobalt, manganese and bromine ions on the resins; regenerating the resins with an eluting solution; and isolating the oxidation catalysts from an effluent, shows recoveries of at least 99 wt % for cobalt, at least 99 wt % for manganese and at least 90 wt % for bromine.

Abstract: Economical processes are disclosed for preparing relatively pure polycarboxylic acid from typical crude products of liquid phase oxidation, which do not involve intermediate steps of ester formation or require any alkanol containing solvent, for purification of "crude" polycarboxylic acid containing impurities which include one or more monofunctional aromatic compounds, trifunctional aromatic compounds, and/or color causing organic compounds formed by oxidation of a corresponding substituted aromatic compound in a liquid phase, e.g. 2,6-naphthalene dicarboxylic acid by liquid phase oxidation of 2,6-dimethyl naphthalene. The invention provides integrate processes which comprise reacting crude oxidation product with a polyalkyl amine amine, e.g. trialkylamine, forming an aqueous solution of the salts thus obtained, separating deleterious compounds from the solution, and recovering the polyalkyl amine and a relatively pure polycarboxylic acid product.

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: A method and apparatus for purifying crude terephthalic acid from a liquid dispersion thereof also containing impurities selected from unreacted starting materials, solvents, products of side reactions and/or other undesired materials is provided. The method comprises the steps of filtering the dispersion to form a crude terephthalic acid filter cake, dissolving the filter cake in a selective crystallization solvent at an elevated temperature to form a solution, crystallizing purified terephthalic acid from the solution in the crystallization solvent by reducing the temperature of the solution, and separating the crystallized purified terephthalic acid from the solution. According to the invention, the selective crystallization solvent is non-aqueous, non-corrosive and essentially non-reactive with terephthalic acid. Preferably, the selective crystallization solvent is N-methyl pyrrolidone.

Abstract: A process for producing an aromatic carboxylic acid, which comprises oxidizing an alkylaromatic hydrocarbon with a molecular oxygen-containing gas in a liquid phase in an acetic acid solvent in the presence of catalyst components comprising cobalt, manganese and bromine, wherein(1) the reaction temperature is from 140.degree. to 180.degree. C.,(2) the cobalt component is in an amount of from 400 to 3,000 ppm by weight to the acetic acid solvent, as calculated as cobalt metal,(3) the manganese component is in an amount of from 0.001 to 0.4 time in the atomic ratio to cobalt,(4) the bromine component is in an amount of from 0.1 to 5.

Abstract: The process that involves liquid phase catalytic oxidation of a mono- or poly-substituted alkyl aromatic compound comprises: (i) microdispersion of the air in the reactor at a pressure between 15 and 25 atmospheres and at a rate between 200 and 500 kg/sec.m.sup.2 ; and (ii) recycling the catalyst by evaporation of the purge that contains it and leaching the resulting paste with distilled water at 20.degree.-40.degree. C. to dissolve the catalyst separating it from the rest of the components.Aromatic carboxylic acids are basic products used in a large number of industrial fields.

Abstract: A method for preparing an alkylbenzoic acid is herein disclosed which comprises subjecting an alkylbenzene having at least two alkyl groups of 1 to 3 carbon atoms to a liquid phase oxidative reaction with a molecular oxygen-containing gas in the presence of a soluble heavy metal catalyst to convert one alkyl group into a carboxylic acid, thereby preparing the alkylbenzoic acid, and impurities contained in the alkylbenzene recovered from the reaction solution are removed therefrom by distillation, water washing, alkali washing, a treatment with an anion exchange resin or a treatment with a solid adsorbent, and the impurities-free fraction is reused as a raw material.Furthermore, the conversion of the desired product is regulated to 25% or less in the liquid phase oxidative reaction, whereby the reaction is carried out in a boiling heat removal state and reaction heat is removed as the heat of vaporization.

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: Purified terephthalic acid is prepared by a process of subjecting an aqueous solution of crude terephthalic acid to hydrogenation to reduce impurities, crystallizing this solution to produce a slurry of purified terephthalic acid in an aqueous liquor, and carrying out an integrated separation washing process using a centrifuge having washing facilities.

Abstract: Terephthalic acid is produced by reacting paraxylene with oxygen in a reactor having several vertical stages, the reaction taking place in the liquid phase using acetic acid as solvent and a cobalt-manganese-bromine complex catalyst. During the reaction, a carbon dioxide-containing gas phase is withdrawn from the vapor space of the reactor. The gas phase is cooled to condense vaporized acetic acid therefrom and carbon dioxide is separated from the gas phase and recycled to the vapor space or to the liquid phase or to both of these. In an alternate embodiment, the gas remaining after condensing acetic acid is subjected to catalytic oxidation to oxidize carbon monoxide and methane, if present, to carbon dioxide, and some or all of the carbon dioxide is recycled to the reactor.

Abstract: A terephthalic acid slurry in acetic acid is produced by oxidizing p-xylene in acetic acid, removing water by evaporation of a stream of water and acetic acid, and returning acetic acid to the oxidation step. The terephthalic acid is separated from the reaction medium in a first zone to leave a deposit on a band, the deposit is washed with a first aqueous medium in a second zone, removed from the band in a third zone, and admixed with a second aqueous medium. Reaction medium is passed from the first zone to the oxidation step and terephthalic acid is recovered, preferably after further purification.

Abstract: A process for preparing purified 2,6-naphthalenedicarboxylic acid which comprises hydrolyzing a dialkyl-2,6-naphthalenedicarboxylate with water at a reaction temperature of at least about 450.degree. F. under liquid phase condition, the amount of water present being sufficient to solubilize, at the reaction temperature, at least about 10 percent of the 2,6-naphthalenedicarboxylic acid formed; and a process for purifying 2,6-naphthalenedicarboxylic acid comprising combining impure 2,6-naphthalenedicarboxylic acid with a purification solvent, heating the resulting mixture under liquid phase conditions at a temperature of at least about 500.degree. F. to form a product mixture and thereafter recovering from the product mixture purified 2,6-naphthalenedicarboxylic acid.

Abstract: In the purification of an off-gas stream originating from a process of oxidizing a liquid mixture of para-xylene with methyl para-toluate with an oxygen-containing gas under pressure, the off-gas being contaminated with at least one of an aliphatic and an aromatic impurity, which comprises expanding the off-gas stream in an expansion turbine for generating mechanical or electrical energy so as to obtain an at least partial recovery of the energy contained in the off-gas, the improvement comprising subjecting the off-gas to at least one absorption step under pressure to remove at least one component from the off-gas and subjecting the resultant off-gas stream to combustion under a pressure of more than 3 bar prior to expanding the off-gas stream in the expansion turbine.

Abstract: It is contemplated by the present invention to produce a high quality aromatic carboxylic acid by a liquid phase oxidation of an alkylbenzene by contacting it with a molecular oxygen-containing gas in a solvent containing a lower aliphatic carboxylic acid, under exclusion of any acceleration of decomposition of the solvent molecules and danger of explosion accident.

Abstract: A process for preparing o-nitroaromatic acids by direct oxidation of the corresponding o-nitroalkylaromatic compounds, utilizing salts of certain catalytic metals in the presence of an oxygen-containing gas and an aliphatic aldehyde or ketone at elevated temperature and pressure, is provided. The process allows catalyst recovery and reuse.

Abstract: A process for producing 2,6-naphthalenedicarboxylic acid (NDCA) is disclosed. This process comprises oxidizing a 2,6-dialkylnaphthalene with a gas containing molecular oxygen in a solvent containing a lower aliphatic carboxylic acid in the presence of a catalyst comprising heavy metal compounds and a bromine compound, and is characterized in that an ester mixture containing dimethyl 2,6-naphthalenedicarboxylate (NDCM) is added to the oxidation reaction. The low boiling distillate, the high boiling still residue, and the residue of the mother liquor after recrystallization, occurring during purification of the crude NDCM, are also used as additives to the oxidation reaction. According to the present invention, NDCA with large particle size and bulk density can be obtained. Therefore, solid-liquid separation of the crystals, drying of the separated crystals and transportation of the dried crystals are made easier.

Abstract: Purified terephthalic acid is prepared by subjecting an aqueous solution of crude terephthalic acid to hydrogenation to reduce impurities, crystallizing this solution to produce a slurry of purified terephthalic acid in an aqueous liquor, and carrying out an integrated separation and washing process. The integrated separation is performed by exchanging the acidic reaction medium with water to produce a water containing cake of terephthalic acid.

Abstract: A terephthalic acid slurry in acetic acid is produced by oxidizing p-xylene in acetic acid, removing water by evaporation of a stream of water and acetic acid, and returning acetic acid to the oxidation step. The terephthalic acid is separated from the reaction medium in a first zone to leave a deposit on a band, the deposit is washed with a first aqueous medium in a second zone, removed from the band in a third zone, and admixed with a second aqueous medium. Reaction medium is passed from the first zone to the oxidation step and terephthalic acid is recovered, preferably after further purification.

Abstract: A process for preparing an aqueous slurry of terephthalic acid, which comprises oxidizing p-xylene with molecular oxygen in a liquid phase in an acetic acid solvent in the presence of a catalyst, to obtain an acetic acid slurry of terephthalic acid, separating terephthalic acid crystals from the acetic acid slurry, washing the terephthalic acid crystals containing acetic acid, with p-xylene or an acetic acid ester, and then mixing water thereto.

Abstract: A terephthalic acid slurry in acetic acid is produced by oxidizing p-xylene in acetic acid, removing water by evaporation of a stream of water and acetic acid, and returning acetic acid to the oxidation step. The terephthalic acid is separated from the reaction medium in a first zone to leave a deposit on a band, the deposit is washed with a first aqueous medium in a second zone, removed from the band in a third zone, and admixed with a second aqueous medium. Reaction medium is passed from the first zone to the oxidation step and terephthalic acid is recovered, preferably after further purification.

Abstract: Disclosed is an improved process for the continuous production of aromatic carboxylic acids by the liquid-phase oxidation of an alkyl aromatic compound with an oxygen-containing gas in the presence of oxidation catalyst which effectively utilizes the heat of reaction in the process of removing excess water generated from the reaction and minimizes the loss of solvent used as the carrier for the reaction catalyst. Operation of the process is improved by removing reactor off-gas directly into a water removal column for distillation. A portion of distillate condensed from the overhead aqueous vapors of the water removal column is refluxed to the fractionating zone of the water removal column.

Abstract: A process and an apparatus for producing terephthalic acid economically by oxidizing paraxylene supplied to an oxidizing reactor connected with a compactly designed distillation column in an acetic acid-based solvent, while effecting the distillatory recovery of the paraxylene and acetic acid efficiently without suffering from stuffing of the distillation column.

Abstract: A process for making relatively high purity eulfonylbis(phthalic anhydride) is provided. 3,3',4,4'-tetramethyl diphenyl sulfone is catalytically oxidized in a solvent under liquid phase elevated temperature and pressure conditions. The catalyst is constituted by cobalt, manganese, zirconium, and bromine. Sulfonylbis(phthalic) acid is recovered by crystallization and is then heated to produce the anhydride. Preferably, the acid is purified prior to dehydration.

Abstract: Terephthalic acid is produced by oxidation of para xylene, purified in an aqueous phase and recovered by precipitating a purified product from the aqueous phase, the aqueous phase mother liquor is then cooled or evaporated to produce a further less pure precipitate and a second mother liquor and the less pure precipitate is returned to the reaction medium and/or the water of the second mother liquor is used to dissolve the crude solid and/or the second mother liquor is treated to recover water which is used to wash the precipitate recovered from the aqueous solution. The process produces better yields of terephthalic acid, reduces the use of water and reduces problems in the disposal of polluted waste water.

Abstract: A process is disclosed for counter-current positive displacement of an aliphatic carboxylic acid of 1 to 5 carbon atoms from a filter cake of an aromatic polycarboxylic acid containing the aliphatic carboxylic acid wherein mother liquor retained by the aromatic polycarboxylic acid has a concentration of the aliphatic carboxylic acid of 5000 ppmw, or less, based upon weight of the aromatic polycarboxylic acid present. This method is useful for the manufacture of crude terephthalic acid which is used after purification for the preparation of polyesters used for the manufacture of fabrics, fibers and plastic bottles.

Abstract: Terephthalic acid is produced by oxidation of para xylene, purified in an aqueous phase and recovered by precipitating a purified product from the aqueous phase, the aqueous phase mother liquor is then cooled or evaporated to produce a further less pure precipitate and a second mother liquor and the less pure precipitate is returned to the reaction medium and/or the water of the second mother liquor is used to dissolve the crude solid and/or the second mother liquor is treated to recover water which is used to wash the precipitate recovered from the aqueous solution. The process produces better yields of terephthalic acid, reduces the use of water and reduces problems in the disposal of polluted waste water.