Abstract: The present invention relates to a method for preparing 4,4?-dihydroxy-[1,1?-biphenyl-3,3?-dicarboxylic acid], the method comprising a step for preparing a compound represented by chemical formula 1 by reacting a compound represented by chemical formula 2 with a base according to reaction formula 1. [reaction formula 1] [chemical formula 1] [chemical formula 2] According to the present invention, because use of additional carbon dioxide is unnecessary during the reaction, internal pressure is lowered during same, the reaction can be carried out at a lower temperature, the yield from the synthesis is notably improved as hardening of the resulting substance is absent, and H4dobpdc can be synthesized in large amounts as an additional process for obtaining pure ligands is unnecessary.

Abstract: 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terephthalic acid crystal as slurry with the replacement water from the tower lower compartment, subjecting the slurry withdrawn from the tower lower compartment to solid-liquid separation into water and the terephthalic acid crystal, and drying

Abstract: Methods of purifying crude or contaminated terephthalic acid using ionic liquids are described. Crude or contaminated terephthalic acid is contacted with a solvent in the absence of an oxidizing agent to form a purified product having at least 30 wt % less 4-carboxybenzaldehyde compared to the crude or contaminated terephthalic acid. The solvent consists essentially of an ionic liquid, optionally an ionic solid or a material capable of forming an ionic salt, and optionally an aqueous solvent. The ionic liquid is formed in situ from at least one ionic liquid precursor.

Abstract: A method for producing a purified naphthalenedicarboxylic acid includes steps of mixing a naphthalenedicarboxylic acid-containing material and an amine in a mixed liquid of water and an organic solvent to give a crystal of a naphthalenedicarboxylic acid amine salt; and obtaining a purified naphthalenedicarboxylic acid from the crystal of the naphthalenedicarboxylic acid amine salt, wherein (1) in the step of forming the naphthalenedicarboxylic acid amine salt by adding an amine to the slurry that contains water, an organic solvent and a naphthalenedicarboxylic acid, the amine addition rate is from 0.002 to 0.4 mol/min relative to one mol of the naphthalenedicarboxylic acid, or (2) an amine is added to the aqueous solution prepared by dissolving the naphthalenedicarboxylic acid amine salt in water, or to the liquid prepared through solid-liquid separation of the aqueous solution to insolubilize and precipitate the metal component, and the precipitated metal component is removed through solid-liquid separation.

Abstract: In the present disclosure, a process for separating aryl carboxylic acids from a mixture comprising a plurality of aryl carboxylic acids is provided, wherein the process comprising the steps of heating a first mixture that comprises at least two aryl carboxylic acids wherein each of said aryl carboxylic acids having a pre-determined liquefaction temperature and a pre-determined precipitation temperature, with at least one ionic compound, at a pre-determined temperature to obtain a liquefied composition; and cooling the liquefied composition under controlled temperature conditions to fractionally crystallize and precipitate an aryl carboxylic acid. The precipitated aryl carboxylic acid is isolated and the obtained mother liquor is subjected to iterated cooling steps until each of the remaining aryl carboxylic acids precipitates one by one. The mother liquor remains in liquefied form.

Abstract: In a process/system for the purification of aromatic dicarboxylic acid (ACA), crude ACA solids are slurried with water recycled from at least a filtration step in a feed preparation zone. Flash steam in vapour phase is supplied to the zone from at least one of a crystallisation step, a filtration step, and a drier step. The slurried ACA solids are preheated to form a solution that is then hydrogenated. The ACA is allowed to crystallise and then crystals of pure ACA are filtered out and water is recovered in a single stage filtration process. Recovered water is supplied to the feed preparation zone and the crystals are dried and recovered. The flash steam recovered from the crystallisation step, filtration step and/or drier step is recovered as a vapour phase stream having a pressure from about atmospheric to 5 barg and supplied to the feed preparation zone without phase change.

Abstract: Disclosed herein is a process for purifying aryl carboxylic acids, in particular terephthalic acid, wherein the impure acid is dissolved or dispersed in an ionic liquid and a non-solvent is added to precipitate the purified acid. The present disclosure further relates to compositions comprising terephthalic acid and one or more ionic liquids.

Abstract: A solid terephthalic acid composition and a process for producing terephthalic acid from para-xylene. The process comprises forming a mixture comprising the para-xylene, a solvent, a bromine source, and a catalyst; and oxidizing the para-xylene by contacting the mixture with an oxidizing agent at oxidizing conditions to produce a solid oxidation product comprising terephthalic acid, para-toluic acid, 4-carboxybenzaldehyde. The solvent comprises a carboxylic acid having from 1 to 7 carbon atoms and an dialkyl imidazolium ionic liquid; and the catalyst comprises at least one of cobalt, titanium, manganese, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, and zirconium. The solid terephthalic acid composition comprises, less than about 4,000 ppm-wt 4-carboxybenzaldehyde content, and more than about 2,000 ppm-wt a para-toluic acid.

Abstract: A method for producing a purified naphthalenedicarboxylic acid includes steps of mixing a naphthalenedicarboxylic acid-containing material and an amine in a mixed liquid of water and an organic solvent to give a crystal of a naphthalenedicarboxylic acid amine salt; and obtaining a purified naphthalenedicarboxylic acid from the crystal of the naphthalenedicarboxylic acid amine salt, wherein (1) in the step of forming the naphthalenedicarboxylic acid amine salt by adding an amine to the slurry that contains water, an organic solvent and a naphthalenedicarboxylic acid, the amine addition rate is from 0.002 to 0.4 mol/min relative to one mol of the naphthalenedicarboxylic acid, or (2) an amine is added to the aqueous solution prepared by dissolving the naphthalenedicarboxylic acid amine salt in water, or to the liquid prepared through solid-liquid separation of the aqueous solution to insolubilize and precipitate the metal component, and the precipitated metal component is removed through solid-liquid separation.

Abstract: Embodiments of the present disclosure include methods or processes for purifying CTA, systems for purifying CTA, methods or processes for cooling mother liquor streams, systems for cooling mother liquor streams, methods or processes for treating mother liquor solids, systems for treating mother liquor solids, and the like.

Abstract: Impure aromatic carboxylic acids such as are obtained by liquid phase oxidation of feed materials comprising aromatic compounds with substituent groups oxidizable to carboxylic acid groups, or comprising aromatic carboxylic acid and one or more aromatic carbonyl impurities that form hydrogenated species more soluble in aqueous solvents or with less color or color-forming tendencies than the aromatic carbonyl impurity, are purified to an aromatic carboxylic acid product with lower levels of impurities by a process comprising contacting an aqueous solution comprising the impure aromatic carboxylic acid with hydrogen at elevated temperature and pressure with an attrition-resistance, acid stable catalyst composition comprising at least one hydrogenation catalyst metal and a support comprising relatively high surface area silicon carbide.

Abstract: Disclosed herein is a process for purifying aryl carboxylic acids, in particular terephthalic acid, wherein the impure acid is dissolved or dispersed in an ionic liquid and a non-solvent is added to precipitate the purified acid. The present disclosure further relates to compositions comprising terephthalic acid and one or more ionic liquids.

Abstract: The present invention relates to a method for separating and refining high purity 2,6-naphthalene dicarboxylic acid having an excellent color and purity of 99.9% or more by using crude 2,6-naphthalene dicarboxylic acid. And more particularly, the present invention relates to a method for separating and refining 2,6-naphthalene dicarboxylic acid, in which adjustment of pressure and temperature during multiple-step crystallization process enables controlling nucleation and the crystal growth rate, thereby allowing a particle size distribution and form to be controlled.

Abstract: Disclosed is an optimized process and apparatus for more efficiently producing aromatic dicarboxylic acids (e.g., terephthalic acid). In one embodiment the process/apparatus reduces costs by recovering and purifying residual terephthalic acid present in the liquid phase of an initial oxidation slurry. In another embodiment the process apparatus reduces costs associated with hydrogenation by forming a final composite product containing unhydrogenated acid particles.

Abstract: Disclosed are processes and apparatus for producing a carboxylic acid. The processes employ a concentration section disposed before and/or after a product isolation section, which allows for oxidation byproducts produced in the process to exit the product isolation section with the isolated carboxylic acid product and/or to be combined with the isolated carboxylic acid product downstream of the product isolation section at a rate of at least about 15 percent of the net make rate of the oxidation byproducts in the production process.

Abstract: Disclosed are processes and apparatus for producing a carboxylic acid. The processes employ a concentration section disposed before and/or after a product isolation section, which allows for oxidation byproducts produced in the process to exit the product isolation section with the isolated carboxylic acid product and/or to be combined with the isolated carboxylic acid product downstream of the product isolation section at a rate of at least about 15 percent of the net make rate of the oxidation byproducts in the production process.

Abstract: The present invention relates to a method for separating and refining high purity 2,6-naphthalene dicarboxylic acid having an excellent color and purity of 99.9% or more by using crude 2,6-naphthalene dicarboxylic acid. And more particularly, the present invention relates to a method for separating and refining 2,6-naphthalene dicarboxylic acid, in which adjustment of pressure and temperature during multiple-step crystallization process enables controlling nucleation and the crystal growth rate, thereby allowing a particle size distribution and form to be controlled.

Abstract: There are provided a bottle which has a laminate structure including a glycolic acid polymer layer showing good gas-barrier property in addition to a principal resin layer and is yet provided with excellent recyclability, and also an efficient method of recycling the bottle. More specifically, a bottle having a laminate structure including at least one layer of glycolic acid polymer in addition to a principal resin layer, is obtained. After breaking the bottle, the broken pieces are washed with alkaline water, water or acidic water to remove the glycolic acid polymer layer, thereby recovering the principal resin.

Abstract: Disclosed herein is a process for purifying aryl carboxylic acids, in particular terephthalic acid, wherein the impure acid is dissolved or dispersed in an ionic liquid and a non-solvent is added to precipitate the purified acid. The present disclosure further relates to compositions comprising terephthalic acid and one or more ionic liquids.

Abstract: A process and system for continuous crystallization of a compound using antisolvent addition in which a solution is prepared with an organic compound and a solvent. An antisolvent is added to the solution in a continuous plug flow system comprising at least one process module. The antisolvent can be added in multiple addition points such that the overall amount of antisolvent added to the continuous plug flow reactor remains fixed. The multiple addition point technique provides every process module with an equal volume of antisolvent. Finally, crystals are recovered from the slurry upon exiting the system. Preferably, the mean crystal size is less than 100 ?m.

Abstract: The present invention relates to a process for preparing purified terephthalic acid [PTA,], comprising the steps: dissolving crude terephthalic acid [CTA] in an aqueous medium in a reactor; hydrogenating CTA at a temperature of about 260-320° C. and a pressure of about 1100-1300 psig using a hydrogenation catalyst; crystallizing terephthalic acid in the reactor by lowering the temperature of the solution to about 160° C. without evaporation cooling; transferring the content of the reactor to a filtration unit; filtrating the content at a temperature of about 140-160° C. and a pressure of about 40-100 psig, preferably 80-100 psig to obtain a filter cake, washing the filter cake obtained with water having a temperature of about 140-160° C. in the filtration unit; and drying the filter cake.

Abstract: Disclosed is a method for purifying 2,6-naphthalenedicarboxylic acid (NDA) that is present in a solid state in a solution. According to the method, sintered metal membrane filtration units are used to efficiently separate and purify 2,6-naphthalenedicarboxylic acid separated after hydrogenation and crystallization in a continuous process. An apparatus for implementing the method is further provided.

Abstract: A method of replacing a first dispersion medium in a starting slurry composed of the first dispersion medium and isophthalic acid crystals with a second dispersion medium. The starting slurry is tangentially fed to a vertically extending cylindrical portion of a cyclone-shaped nozzle disposed at an upper portion of a replacement tank of a dispersion medium replacement apparatus, from a tangential direction of the cylindrical portion. The fed starting slurry moves circularly along an inner wall of the cylindrical portion. The slurry circularly moving is then discharged from an opening which is disposed at a vertically lower end of the cylindrical portion and dispersed in a second dispersion medium which is fed from a lower portion of the replacement tank. The replaced slurry composed of isophthalic acid crystals and the second dispersion medium is mainly discharged from the lower portion of the replacement tank, and the first dispersion medium is mainly withdrawn from the upper portion of the replacement tank.

Abstract: The present invention provides a process for the preparation of diphenic acid from phenanthrene which comprises heating phenanthrene and glacial acetic acid, adding drop-wise a pre-determined amount of 30% hydrogen peroxide, heating the resulting mixture after completion of drop wise addition of hydrogen peroxide, distilling the resulting mixture under reduced pressure to make the volume half, cooling the mixture till diphenic acid crystalises out, filtering the cooled mixture and boiling the residue after adding 10% solution of sodium carbonate and activated charcoal, filtering and discarding the residue; acidifying the filtrate with hydrogen chloride; cooling the resultant mixture till more diphenic acid crystallises out; repeating filtration till pure diphenic acid is obtained.

Abstract: The present invention relates to a multi-stage crystallization process which comprises the steps of feeding a solution of terephthalic acid or a slurry (raw slurry) containing terephthalic acid partially precipitated to a first crystallization vessel to precipitate the terephthalic acid therein; and feeding a slurry (crystallization slurry) containing the thus precipitated terephthalic acid sequentially to second and subsequent crystallization vessels, wherein while continuously supplying a cleaning solvent to a delivery conduit connecting the former-stage crystallization vessel and the next latter-stage crystallization vessel to each other, the crystallization slurry is fed through the delivery conduit.

Abstract: A process comprising the steps of dissolving a dihydric phenol in a solvent to form a solution A, contacting the solution A with an adsorbent material selected from the group consisting of metal oxides, modified metal oxides, activated carbons, and clays, filtering the adsorbent material to form a solution B, adding an anti-solvent to the solution B to form a solution C, and distilling the solution C, wherein the dihydric phenol is represented by Formula (I): wherein R is a hydrogen atom or an aliphatic functionality having 1 to 6 carbon atoms and n is an integer having a value of 1 to 4.

Abstract: A process comprising the steps of dissolving a dihydric phenol in a solvent to form a solution A; contacting the solution A with a zeolite; filtering the zeolite to form a solution B; adding an anti-solvent to the solution B to form a solution C; and distilling the solution C; wherein the dihydric phenol is represented by Formula (I): wherein R is a hydrogen atom or an aliphatic functionality having 1 to 6 carbon atoms and n is an integer having a value 1 to 4.

Abstract: The present invention relates to a process for preparing purified terephthalic acid [PTA,], comprising the steps: dissolving crude terephthalic acid [CTA] in an aqueous medium in a reactor; hydrogenating CTA at a temperature of about 260-320° C. and a pressure of about 1100-1300 psig using a hydrogenation catalyst; crystallizing terephthalic acid in the reactor by lowering the temperature of the solution to about 160° C. without evaporation cooling; transferring the content of the reactor to a filtration unit; filtrating the content at a temperature of about 140-160° C. and a pressure of about 40-100 psig, preferably 80-100 psig to obtain a filter cake, washing the filter cake obtained with water having a temperature of about 140-160° C. in the filtration unit; and drying the filter cake.

Abstract: A method for removing impurities from a mother liquor comprising a carboxylic acid, a metal catalyst, impurities by (a) evaporating the mother liquor comprising a carboxylic acid, a metal catalyst, impurities and a solvent in a first evaporator zone to produce a vapor stream and a concentrated mother liquor stream; (b) evaporating the concentrated mother liquor stream in a second evaporator zone to form a solvent rich stream and a super concentrated mother liquor stream; (c) mixing in a mixing zone a water-solvent solution and optionally an extraction solvent with the super concentrated mother liquor stream to form an aqueous mixture; (d) optionally separating organic impurities from the aqueous mixture in a solid-liquid separation zone to form a purified aqueous mixture; and (e) extracting the aqueous mixture or purified aqueous mixture with an extraction solvent in an extraction zone to form an extract stream and the raffinate stream.

Abstract: Disclosed is a process to produce a purified carboxylic acid slurry. The process comprises removing impurities from a crystallized product in a solid liquid displacement zone to form the purified carboxylic acid slurry. The process produces purified carboxylic acid slurry having good color and low impurity levels without the use of purification steps like hydrogenation or an impurity removal process.

Abstract: A method for removing impurities from an aqueous mixture or purified aqueous by extracting the aqueous mixture or purified aqueous mixture with an extraction solvent in an extraction zone to form an extract stream and the raffinate stream; and optionally separating the extract stream and a solvent rich stream in a separation zone to form a high boiling point organic impurities stream and a recovered extraction solvent stream.

Abstract: The present invention relates to a process for oxidizing a slurry composition in a post oxidation zone in the presence of added steam. More specifically, the present invention relates to a process for oxidizing a crude terephthalic acid composition in a post oxidation zone in the presence of added steam in a process for the production of a crystallized post oxidation composition.

Abstract: A method and apparatus for purifying carboxylic acids is disclosed. A mixture containing crude carboxylic acid is contacted with a selective crystallization solvent to form a slurry of a salt complex of the carboxylic acid and the selective crystallization solvent. The salt complex is recovered and optionally processed to recover the free carboxylic acid. The method and apparatus of the invention is particularly suitable for purifying aromatic dicarboxylic acids such as terephthalic acid. The present invention also reduces contamination by carboxybenaldehyde isomers in crude phthalic acids by oxidizing the carboxybenzaldehyde to the corresponding phthalic acid.

Abstract: Disclosed is a process for the production of terephthalic acid by a plurality of process steps including the catalyst oxidation of a dialkylbenzene compound, a second oxidation, a hydrogenation of the product of the second oxidation, and crystallization of the hydrogenation terephthalic acid using a plurality of series-connected crystallizers.

Abstract: This invention provides a process a process for recovering terephthalic acid from pulverized products of spent polyethylene terephthalate.

Abstract: Disclosed is a process to produce a purified carboxylic acid slurry. The process comprises removing impurities from a crystallized product in a solid liquid displacement zone to form the purified carboxylic acid slurry. The purified carboxylic acid slurry is further cooled in a cooling zone and subsequently filtered and dried in a filtration and drying zone. The process produces purified carboxylic acid product having good color and low impurity levels without the use of purification steps like hydrogenation or filtrate purge.

Abstract: The present invention relates to a method for refining 2,6-naphthalene dicarboxylic acid, and particularly to a method for refining 2,6-naphthalene dicarboxylic acid comprising recrystallizing crude 2,6-naphthalene dicarboxylic acid in the form of an amine salt using a solvent comprising a protic polar solvent selected from the group consisting of an alcohol, water, and a mixture thereof, and an acetate. In accordance with the invention, 2,6-naphthalene dicarboxylic acid can be obtained with excellent purity and color, and at the same time, it can be obtained in an economical and environmentally friendly way because the acetate, which is a byproduct of the oxidation process, is used as a solvent.

Abstract: Disclosed is a process to produce a purified carboxylic acid product. The process comprises removing impurities from a crude carboxylic acid slurry in a solid-liquid displacement zone to form a slurry product. The slurry product if further treated in a staged oxidation zone and a crystallization zone to from a crystallized product. The crystallized product is further cooled in a cooling zone and subsequently filtered and dried in a filtration and drying zone. The process produces purified carboxylic acid product having good color and low impurity levels without the use of purification steps like hydrogenation.

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: Disclosed is a process to produce a purified carboxylic acid slurry. The process comprises removing impurities from a crystallized product in a solid liquid displacement zone to form the purified carboxylic acid slurry. The process produces purified carboxylic acid slurry having good color and low impurity levels without the use of purification steps like hydrogenation or an impurity removal process.

Abstract: Crude polycarboxylic acid is slurried in an aqueous medium and the slurry is brought into contact with a metal catalyst while preventing catalyst components thereof from contaminating crystals. Since hydrogenation or decarbonylation of a polymerization inhibitory substance or a substance causing coloration can efficiently proceed at a low temperature while suppressing side reactions, a product having such a quality as to permit direct use thereof as such for polymerization can be obtained with good productivity. Also, since the contact temperature can be lowered, simplification of apparatus and energy saving may be attained.

Abstract: The present invention relates to a process for preparing bromoisophthalic acid compounds, particularly 5-bromoisophthalic acid compounds and 4,5-dibromoisophthalic acid compounds comprising brominating an isophthalic acid compound of the general formula (1) wherein R1 and R2 independently of one another are hydrogen atom or C1-6 alkyl, with bromine in a solvent containing sulfur trioxide. The object of the invention is to provide a process for preparing bromoisophthalic acid compounds, particularly 5-bromoisophthalic acid compounds and 4,5-dibromoisophthalic acid compounds in a highly selective manner by using bromine that is industrially inexpensive.

Abstract: A process for the production of an aromatic carboxylic acid comprising contacting in the presence of a catalyst, within a continuous flow reactor, one or more precursors of the aromatic carboxylic acid with an oxidant, such contact being effected with said precursor(s) and the oxidant in an aqueous solvent comprising water under supercritical conditions or near supercritical conditions close to the supercritical point such that said one or more precursors, oxidant and aqueous solvent constitute a substantially single homogeneous phase in the reaction zone, wherein the contact of at least part of said precursor with said oxidant is contemporaneous with contact of said catalyst with at least part of said oxidant.

Abstract: Crude polycarboxylic acid is slurried in an aqueous medium and the slurry is brought into contact with a metal catalyst while preventing catalyst components thereof from contaminating crystals. Since hydrogenation or decarbonylation of a polymerization inhibitory substance or a substance causing coloration can efficiently proceed at a low temperature while suppressing side reactions, a product having such a quality as to permit direct use thereof as such for polymerization can be obtained with good productivity. Also, since the contact temperature can be lowered, simplification of apparatus and energy saving may be attained.

Abstract: A method for purifying crude 2,6-naphthalenedicarboxylic acid includes a reduction step of reducing crude 2,6-naphthalenedicarboxylic acid containing 6-formyl-2-naphthoic acid with hydrogen and a cleaning step of cleaning the reduction product with alcohol. Preferably, in the reduction step, the crude 2,6-naphthalenedicarboxylic acid and the hydrogen is brought into contact with a hydrogenation catalyst in a liquid phase, and particularly in water. The method makes the purification process less complex and makes it possible to produce high-purity 2,6-naphthalenedicarboxylic acid without damaging equipment or increasing cost.

Abstract: Disclosed is a process to produce a purified carboxylic acid slurry. The process comprises removing impurities from a crystallized product in a solid liquid displacement zone to form the purified carboxylic acid slurry. The process produces purified carboxylic acid slurry having good color and low impurity levels without the use of purification steps like hydrogenation or an impurity removal process.

Abstract: Disclosed is a process to produce a purified carboxylic acid slurry. The process comprises removing impurities from a crystallized product in a solid liquid displacement zone to form the purified carboxylic acid slurry. The purified carboxylic acid slurry is further cooled in a cooling zone and subsequently filtered and dried in a filtration and drying zone. The process produces purified carboxylic acid product having good color and low impurity levels without the use of purification steps like hydrogenation or filtrate purge.

Abstract: A process for forming reactants useful in the manufacture of polyethylene terephthalate includes the steps of: (a) contacting recyclable polyethylene terephthalate with ammonium hydroxide whereby a mixture of ammonium terephthalate and ethylene glycol is formed, (b) separating the ammonium terephthalate, and (c) heating said ammonium terephthalate at a temperature from about 225° C. to about 300° C. to produce terephthalic acid.

Abstract: The present invention relates to a method of recovering a solution comprising the chemical species obtained by depolymerization of PET from a material containing poly(ethylene terephthalate) in the form of bottles, by making said material react, in the absence of water, with a reagent consisting of one or more metal salts of a weaker acid than the terephthalic acid and of ethylene glycol, until a water-soluble intermediate product is obtained, and subsequently carrying out dissolution in water, stirring and filtering.

Abstract: A high-purity naphthalenedicarboxylic acid is produced by a method including Steps [1] and [2]: In Step [I], a raw mixture of crude terephthalic acid and crude naphthalenedicarboxylic acid is dissolved into high-temperature high-pressure water to form a dibasic acid solution wherein the crude naphthalenedicarboxylic acid content is 0.1 to 10 mass percent of the crude terephthalic acid content, the dibasic acid solution is brought into contact with hydrogen in the presence of a catalyst. In Step [II], the resultant in the dibasic acid solution is crystallized by multiple stages while the temperature and the pressure are reduced for each stage, and acid mixtures containing enriched naphthalenedicarboxylic acid or enriched terephthalic acid are obtained by solid-liquid separation.