Process for the production of high-purity naphthalenedicarboxylic acid

A process for producing a high-purity naphthalenedicarboxylic acid having an improved hue or an excellent hue from a crude naphthalenedicarboxylic acid obtained by the oxidation of dialkyl naphthalene, industrially advantageously at high yields, which comprises dissolving a crude naphthalenedicarboxylic acid obtained by the oxidation of dialkyl naphthalene in an aqueous solution containing an aliphatic amine, an alicyclic amine or acetonitrile, removing heavy metal components contained as impurities until the content of the heavy metal components based on the crude naphthalenedicarboxylic acid is 100 ppm or less, and heating the aqueous solution containing a naphthalenedicarboxylic acid amine salt to distill off the amine.

FIELD OF THE INVENTION 
The present invention relates to a process for the production of a 
high-purity naphthalenedicarboxylic acid from a crude 
naphthalenedicarboxylic acid obtained by the oxidation of 
dialkylnaphthalene. The naphthalenedicarboxylic acid is useful as a raw 
material for a polyethylene naphthalate resin (PEN). 
PRIOR ART OF THE INVENTION 
A polyester obtained by the polymerization of naphthalenedicarboxylic acid 
and a diol such as ethylene glycol is excellent in tensile strength and 
heat resistance, and it finds an industrially important use as a raw 
material for a film, a fiber, a bottle and the like. In particular, a 
polyethylene naphthalate (PEN) obtained by the polymerization of 
2,6-naphthalenedicarboxylic acid and ethylene glycol is expected to find 
an expanded use as an industrial resin in place of polyethylene 
terephthalate. 
Naphthalenedicarboxylic acid can be obtained by oxidizing 
dialkylnaphthalene with molecular oxygen in an acetic acid as a solvent in 
the presence of a heavy metal such as Co or Mn and a bromine compound at a 
high temperature under high pressure. However, the so-obtained crude 
naphthalenedicarboxylic acid inevitably contains hundreds to thousands ppm 
of the metal such as Co or Mn used as a catalyst. The crude 
naphthalenedicarboxylic acid further contains impurities such as formyl 
naphthoic acid and methyl naphthoic acid which are intermediates from the 
oxidation, trimellitic acid which is formed by the decomposition of a 
naphthalene ring, bromonaphthalenedicarboxylic acid which is formed by the 
addition of bromine to naphthalenedicarboxylic acid, and naphthoic acid 
and naphthalenetricarboxylic acid derived from impurities contained in the 
dialkylnaphthalene used as a raw material. Furthermore, coloring 
components of which the structures are not known are also contained. 
When the naphthalenedicarboxylic acid containing the above impurities is 
used as a monomer for the polymerization with a diol, the resultant 
polyester is poor in physical properties such as heat resistance, 
mechanical strength and dimensional stability and has a low softening 
point. Further, there is another defect that the polyester is colored and 
poor in product quality. 
Specifically, when monocarboxylic acids such as naphthoic acid, methyl 
naphthoic acid and formyl naphthoic aicd are contained in an amount over a 
certain limit, the polymerization degree cannot be increased, and gelation 
and coloring take place. It is therefore essential to decrease the above 
amount. That is, a high-purity naphthalenedicarboxylic acid of which the 
impurity content is very small is required for obtaining a polyester 
having a high product quality. Formyl naphthoic acid particularly has the 
above detrimental influence to a great extent. 
Naphthalenedicarboxylic acid cannot be distilled since it is decompsed at 
high temperature, and it is also difficult to purify 
naphthalenedicarboxylic acid by general simple recrystallization since it 
is sparingly soluble in usual solvents. There has therefore not been 
established any industrial method of preparing a high-purity 
naphthalenedicarboxylic acid. In general practice at present, a crude 
naphthalenedicarboxylic acid is reacted with an alcohol such as methanol 
and the resultant naphthalenedicarboxylate ester is purified. However, not 
the naphthalenedicarboxylate ester but naphthalenedicarboxylic acid is 
preferred as a raw material for polyethylenenaphthalate, and it is 
demanded to establish the method of purifying the naphthalenedicarboxylic 
acid. 
As a method of purifying naphthalenedicarboxylic acid by dissolving it in a 
solvent, U.S. Pat. No. 5,256,817 discloses a method in which water or an 
acetic acid aqueous solution is used as a solvent, and 
naphthalenedicarboxylic acid is dissolved in the solvent at a high 
temperature of at least 300.degree. C., hydrogenated and purified by 
crystallization. The problem of this method is that a high temperature is 
required for dissolving a crude 2,6-naphthalenedicarboxylic acid so that 
naphthoic acid is formed due to a decarbonation reaction. Further, an 
expensive rare metal is required as a catalyst for removing formyl 
naphthoic acid, and there is further another problem that 
tetralindicarboxylic acid is formed due to the halogenation of a 
naphthalene ring. 
JP-A-62-230747 discloses a purification method in which a crude 
2,6-naphthalenedicarboxylic acid is dissolved in a solvent such as 
dimethylsulfoxide, dimethylacetamide or dimethylformamide to precipitate 
2,6-naphthalenedicarboxylic acid by crystallization. In this method, 
however, it is required to use a large amount of activated carbon for 
decolorization. Further, a large amount of the solvent is required since 
the solubility of the 2,6-naphthalenedicarboxylic acid in the solvent is 
low. Furthermore, it is difficult to carry out the hydrogenation since the 
solvent is hydrogenated as well when the solution is hydrogenated, and it 
is difficult to remove formyl naphthoic acid which has a detrimental 
effect on the polymerization. Moreover, the yield of the purified 
naphthalenedicarboxylic acid is low. 
JP-A-5-32586 discloses a method in which crude 2,6-naphthalenedicarboxylic 
acid is dissolved in pyridine or a pyridine derivative to precipitate 
2,6-naphthalenedicarboxylic acid by crystallization. Since, however, the 
dependency of the solubility of the 2,6-naphthalenedicarboxylic acid upon 
temperature is low, the yield thereof is low. 
Besides the above methods in which naphthalenedicarboxylic acid is directly 
purified, there have been proposed purification methods in which crude 
2,6-naphthalenedicarboxylic acid is converted to an alkali salt by 
dissolving it in an alkali, to improve the solubility of the 
2,6-naphthalenedicarboxylic acid. For example, JP-B-52-20993 and 
JP-B-48-68554 disclose a method in which crude naphthalenedicarboxylic 
acid is dissolved in an alkaline aqueous solution of KOH or NaOH and 
treated with a solid adsorbent, then, naphthalenedicarboxylic acid is 
precipitated in the form of a monoalkali salt with an acid such as a 
carbon dioxide gas or a sulfurous acid gas, and the monoalkali salt is 
brought into contact with water to cause disproportionation thereby to 
free the 2,6-naphthalenedicarboxylic acid. However, the above method has 
defects that a large amount of a solid adsorbent is required for 
discoloration and further that salts of impurities such as 2,6-formyl 
naphthoic acid, etc., are concurrently precipitated when the monoalkali 
salt is precipitated. There is also another defect that the alkali and the 
acid in large amount should be treated or recovered. 
JP-B-52-20994 and JP-B-48-68555 disclose a method in which crude 
2,6-naphthalenedicarboxylic acid is dissolved in an alkaline aqueous 
solution of KOH or NaOH, the treatment for discoloration with a solid 
adsorbent is carried out, then, a dialkali salt is crystallized by cooling 
or concentration, and further, the dialkali salt is disproportionated to 
obtain a purified 2,6-naphthalenedicarboxylic acid. However, the above 
method has the following defects. A solid adsorbent is required for 
discoloration. The yield of 2,6-naphthalenedicarboxylic acid is low since 
the dependency of solubility of the dialkali salt upon temperature is low 
and since the solubility of the dialkali salt in water at a low 
temperature is very high. Further, a very small amount of an alkali is 
contained in the purified crystal, and it is difficult to remove the 
alkali. 
JP-A-2-243652 discloses a purification method in which crude 
2,6-naphthalenedicarboxylic acid is dissolved in an alkaline aqueous 
solution, and an organic solvent having a high solubility in water such as 
an alcohol or acetone is added to precipitate a crystal of a dialkali salt 
of 2,6-naphthalenedicarboxylic acid. In the above method, however, the 
precipitation rate of the crystal is high so that impurities are liable to 
be included, and when the yield is high, the effect on the removal of 
impurities is insufficient. 
There have been also proposed a variety of purification methods using an 
amine. JP-A-50-135062 discloses a method in which crude 
2,6-naphthalenedicarboxylic acid is dissolved in an aqueous solution of an 
aliphatic amine having 6 carbon atoms or less, the solution is cooled or 
concentrated to precipitate 2,6-naphthalenedicarboxylic acid in the form 
of a diamine salt and the diamine salt is decomposed under heat to obtain 
2,6-naphthalenedicarboxylic acid. Since, however, the yield is low because 
of the very high solubility of the diamine salt in water at a low 
temperature, the above method is impractical in industry. 
JP-A-5-294892 discloses a method in which naphthalenedicarboxylic acid is 
dissolved in mixed solvents of an amine and an alcohol to precipitate a 
crystal of a naphthalenedicarboxylic acid amine salt, and the crystal is 
decomposed under heat at a temperature equivalent to, or higher than, the 
boiling point of the amine, to obtain a purified naphthalenedicarboxylic 
acid. The above method as well has a defect that the yield of 
naphthalenedicarboxylic acid is low since the solubility of the 
naphthalenedicarboxylic acid amine salt in a lower alcohol is high. 
JP-A-50-142542 discloses a method in which crude 
2,6-naphthalenedicarboxylic acid is dissolved in an amine aqueous 
solution, and then an amine compound is distilled off and 
2,6-naphthalenedicarboxylic acid is precipitated to obtain a purified 
2,6-naphthalenedicarboxylic acid. 
In the above method, a large amount of water is used, and a large amount of 
energy is consumed. Further, the yield of 2,6-naphthalenedicarboxylic acid 
in Examples is as low as 63.8 to 72.4%. Further, when the present 
inventors closely studied the above method of JP-A-50-142542, no 
2,6-naphthalenedicarboxylic acid having a sufficiently good hue could be 
obtained when the yield of 2,6-naphthalenedicarboxylic acid is sufficient 
for industrial practice. 
As explained above, in the above conventional methods of purifying 
naphthalenedicarboxylic acid in the presence of an amine, it is required 
to heat-decompose or distill off the amine compound, and the 
naphthalenedicarboxylic acid is therefore exposed to high temperatures. 
The coloring of the naphthalenedicarboxylic acid is accordingly promoted, 
and it is therefore difficult to obtain naphthalenedicarboxylic acid as a 
product having a high quality. Further, since the yield of 
naphthalenedicarboxylic acid is generally low, it is demanded to overcome 
the above defects. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a process for producing 
a high-purity naphthalenedicarboxylic acid having an improved hue or an 
excellent hue from a crude naphthalenedicarboxylic acid obtained by the 
oxidation of dialkyl naphthalene, industrially advantageously at high 
yields. 
It is another object of the present invention to provide a process for 
producing a high-purity naphthalenedicarboxylic acid of which methyl 
naphthoic acid and formyl naphthoic acid contents are small, from the 
above crude naphthalenedicarboxylic acid, industrially advantageously at 
high yields. 
According to the present invention, there is provided a process for the 
production of a high-purity naphthalenedicarboxylic acid, which comprises 
dissolving a crude naphthalenedicarboxylic acid obtained by the oxidation 
of dialkyl naphthalene in an aqueous solution containing an aliphatic or 
alicyclic amine, removing heavy metal components contained as impurities 
until the content of the heavy metal components based on the crude 
naphthalenedicarboxylic acid is 100 ppm or less, and heating the aqueous 
solution containing a naphthalenedicarboxylic acid amine salt to provide a 
high-purity naphthalenedicarboxylic acid by distilling off the amine. 
According to the present invention, further, there is provided a process 
for the production of a high-purity naphthalenedicarboxylic acid, which 
comprises dissolving a crude naphthalenedicarboxylic acid obtained by the 
oxidation of dialkyl naphthalene in an aqueous solution containing an 
aliphatic or alicyclic amine, bringing the aqueous solution into contact 
with a metal belonging to the group VIII of the periodic table in an inert 
gas atmosphere, and heating the aqueous solution containing a 
naphthalenedicarboxylic acid amine salt to provide a high-purity 
naphthalenedicarboxylic acid by distilling off the amine. 
Further, according to the present invention, there is provided a process 
for the production of a high-purity naphthalenedicarboxylic acid, which 
comprises dissolving a crude naphthalenedicarboxylic acid obtained by the 
oxidation of dialkyl naphthalene in an aqueous solution containing an 
aliphatic amine, an alicyclic amine or an acetonitrile, precipitating a 
crystal of a naphthalenedicarboxylic acid amine salt in mixed solvents of 
water with an aliphatic ketone, an alicyclic ketone or an acetonitrile, 
and heating the amine salt of the naphthalenedicarboxylic acid to provide 
a high-purity naphthalenedicarboxylic acid by distilling off the amine. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention 1 is directed to a process for the production of a 
high-purity naphthalenedicarboxylic acid, which comprises dissolving a 
crude naphthalenedicarboxylic acid obtained by the oxidation of dialkyl 
naphthalene in an aqueous solution containing an aliphatic or alicyclic 
amine, removing heavy metal components contained as impurities until the 
content of the heavy metal components based on the crude 
naphthalenedicarboxylic acid is 100 ppm or less, and heating the aqueous 
solution containing a naphthalenedicarboxylic acid amine salt to distill 
off the amine. The present invention 1 provides a production process in 
which heavy metal components are removed so that the 
naphthalenedicarboxylic acid is no longer deteriorated in hue in 
subsequent steps. In the present invention, after the removal of heavy 
metal components, decarbonylation, hydrogenation, crystallization in mixed 
solvents of water and a ketone compound and other treatment can be 
properly carried out as required. 
The present invention 2 is directed to a process for the production of a 
high-purity naphthalenedicarboxylic acid, which comprises dissolving a 
crude naphthalenedicarboxylic acid obtained by the oxidation of dialkyl 
naphthalene in an aqueous solution containing an aliphatic or alicyclic 
amine, bringing aldehyde compounds contained as impurities in the aqueous 
solution into contact with a metal belonging to the group VIII of the 
periodic table in an inert gas atmosphere, thereby causing a 
decarbonylating reaction to convert the aldehyde compounds to naphthoic 
acid, and heating the aqueous solution containing a 
naphthalenedicarboxylic acid amine salt to distill off the amine. The 
present invention 2 provides a high-purity naphthalenedicarboxylic acid of 
which the methyl naphthoic acid and formyl naphthoic acid contents are 
small. When formyl naphthoic acid, etc., are contained in an amount larger 
than a certain limit, the polymerization degree cannot be increased, and 
gelation and coloring take place to deteriorate the product (polyester) 
quality. 
The present invention 3 is directed to a process for the production of a 
high-purity naphthalenedicarboxylic acid, which comprises dissolving a 
crude naphthalenedicarboxylic acid obtained by the oxidation of dialkyl 
naphthalene in an aqueous solution containing an aliphatic amine, an 
alicyclic amine or an acetonitrile, precipitating a crystal of a 
naphthalenedicarboxylic acid amine salt in mixed solvents of water with an 
aliphatic ketone, an alicyclic ketone or acetonitrile, and heating the 
naphthalenedicarboxylic acid amine salt to distill off the amine. The 
present invention 3 provides a high-purity naphthalenedicarboxylic acid 
which is almost completely free of organic impurities, monocarboxylic 
acids in particular, and is excellent in hue. 
The crude naphthalenedicarboxylic acid used as a raw material in the 
present invention is not specially limited so long as it is obtained by 
the oxidation of dialkyl naphthalene. 
The dialkyl naphthalene used for the oxidation includes dimethyl 
naphthalene, diethyl naphthalene, dipropyl naphthalene and diisopropyl 
naphthalene. Each of these dialkyl naphthalenes has 10 isomers with regard 
to the positions of alkyl groups. For a raw material for the polyester, 
2,6-substituted naphthalene and 2,7-substituted naphthalene are useful 
among the above dialkyl naphthalenes, and 2,6-naphthalenedicarboxylic acid 
is particularly preferred. The above dialkyl naphthalenes are oxidized 
with molecular oxygen in the presence of an oxidation catalyst formed 
mainly of a heavy metal and bromine, to give crude napthalenedicarboxylic 
acids. 
Examples of the aliphatic or alicyclic amine (to be sometimes referred to 
as "amine" or "amine compound" hereinafter) used for forming the crude 
naphthalenedicarboxylic acid amine salt are as follows. 
Aliphatic amines such as methylamine, dimethylamine, trimethylamine, 
ethylamine, diethylamine, triethylamine, ethyldimethylamine, 
diethylmethylamine, propylamine, isopropylamine, dipropylamine, 
diisopropylamine, butylamine, isobutylamine, sec-butylamine, 
tert-butylamine, dibutylamine, diisobutylamine, tributylamine, 
pentylamine, dipentylamine, tripentylamine and 2-ethylhexylamine; and 
alicyclic amines such as piperidine, N-methylpyridine, pyrrolidine, 
ethylimine and hexamethyleneimine. 
Of the above amines, methylamines and ethylamines are preferred in view of 
easiness in handling and availability, and trimethylamine and 
triethylamine are particularly preferred since these give amine salts 
having low decomposition temperatures when naphthalenedicarboxylic acid 
amine salts are formed. Further, the above amines may be used alone or in 
combination. 
In the process of the present invention, first, the crude 
naphthalenedicarboxylic acid is dissolved in an aqueous solution 
containing the above amine. The amine compound is preferably used in an 
equivalent weight equivalent to, or greater than, the equivalent weight of 
the crude naphthalenedicarboxylic acid. For economic performance in 
industry, the amount of the amine compound is 1.0 to 1.2 equivalent 
weights per equivalent weight of carboxyl groups. 
The amount of water differs depending upon the kind and amount of the 
amine, the temperature at which the crude naphthalenedicarboxylic acid is 
dissolved and the kind and amount of contained impurities. Generally, the 
amount of water is 0.5 to 50 times, preferably 1 to 20 times, the weight 
of the naphthalenedicarboxylic acid. 
The temperature employed for dissolving the crude naphthalenedicarboxylic 
acid in an aqueous solution containing the above amine to form an amine 
salt is approximately 10.degree. to 100.degree. C. 
In the present invention 1, before the procedure of distilling the amine 
off is carried out, it is required to remove heavy metal components 
contained as impurities in the aqueous solution containing the amine salt 
until the content of the impurities is 100 ppm or less based on the 
naphthalenedicarboxylic acid. When the content of the impurities is higher 
than 100 ppm, the naphthalenedicarboxylic acid as an end product is poor 
in hue, and it is much more colored than the crude naphthalenedicarboxylic 
acid as a raw material. This occurs regardless of yields of the 
naphthalenedicarboxylic acid as an end product, and even if the yield is 
decreased, the naphthalenedicarboxylic acid is inevitably colored. 
The reason for the above coloring is that the heavy metal components 
contained as impurities promote the new formation of coloring components 
when the amine is distilled off. When the mere treatment of adsorption 
with a solid adsorbent is carried out as described in JP-A-52-142542, it 
is possible to remove isomers and bromine derivatives of 
naphthalenedicarboxylic acid, aldehydes and originally existing coloring 
components which are contained as impurities. However, the heavy metal 
components cannot be always removed until the content thereof is 100 ppm 
or less, and it is difficult to prevent the new formation of coloring 
components at a time of distilling off the amine. In the present 
inventions 2 and 3, preferably, the procedure of removing the heavy metal 
components is carried out in advance. 
With a decrease in the content of the heavy metal components, the new 
formation of coloring components is better prevented. When the above 
content exceeds 100 ppm, the coloring takes place to a great extent. It is 
therefore required to remove the heavy metal components until the content 
thereof is 100 ppm or less. 
The heavy metal components contained in the crude naphthalenedicarboxylic 
acid are mainly cobalt and manganese which are components of a catalyst 
used for the oxidation of dialkyl naphthalene, and besides these, there 
are metal components which are from a co-catalyst and titanium, iron, 
nickel, chromium, and the like which are from materials of a reactor. The 
crude naphthalenedicarboxylic acid contains hundreds to thousands ppm of 
cobalt and manganese, and it is particularly essential to remove them. 
When the crude naphthalenedicarboxylic acid is dissolved in an amine 
aqueous solution, most of the above heavy metal components are 
precipitated as insolubles. The insoluble heavy metal components are first 
removed by filtration. The opening diameter of a filter used for the 
filtration is 10 .mu.m or less, preferably 5 .mu.m or less, more 
preferably 1 .mu.m or less. In an industrial apparatus, it is preferred to 
employ a multi-stage filter of which the opening diameters are stepwise 
decreased, for preventing the clogging and securing a stable operation for 
a long period of time. 
Those heavy metal components which are not removable through the above 
filter(s) can be removed by adsorption with a solid adsorbent. The solid 
adsorbent is selected from activated carbon, activated alumina, activated 
clay or an ion-exchange resin. When the solid adsorbent is used with an 
industrial apparatus, a column is packed with the solid adsorbent, and an 
aqueous solution containing a naphthalenedicarboxylic acid amine salt is 
continuously fed to the column. 
When the removal of the heavy metal components is carried out by directly 
feeding the amine aqueous solution to a column packed with the solid 
adsorbent without carrying out the filtering operation in advance, the 
solid adsorbent is overloaded since the amount of the insoluble heavy 
metal components to be removed is too large, and there is obtained no 
continuous effect on the removal of the heavy metal components in the 
operation for a long period of time. Further, since a large amount of the 
heavy metal components deposit in the column and clog the column, no 
stable continuous operation is possible. 
When the adsorption with the solid adsorbent is carried out by a batch 
method, it is required to separate the amine aqueous solution and solid 
components by filtration, and in this case, undesirably, the amount of the 
solid components which are to be treated is large as compared with the 
amount of solid components which are filtered off in the beginning. 
Then, it is preferred to remove formyl naphthoic acid, of which the 
presence causes a problem at a polymerization time, from the aqueous 
solution containing a the naphthalenedicarboxylic acid amine salt from 
which the heavy metal components are removed until the content thereof is 
100 ppm or less. 
For removing the above formyl naphthoic acid, generally, a rare metal 
catalyst is used, and the rare metal catalyst is doped with the heavy 
metal components. By removing the heavy metal components until the content 
thereof is 100 ppm or less, the life of the catalyst used for removing 
formyl naphthoic acid before the amine is distilled off can be maintained 
for a long period of time. 
The formyl naphthoic acid is removed, for example, by hydrogenating 
treatment, in which the formyl group of the formyl naphthoic acid is 
converted to a methyl group. As a catalyst for the hydrogenation, there is 
used a catalyst prepared by dispersing at least one selected from Pt, Pd, 
Rh, Ru, Ni or Co on a carrier having a large surface area such as 
activated carbon, silica or alumina. It is preferred to use a catalyst 
prepared by dispersing Pd or Pt on activated carbon. For removing the 
naphthoic acid, the solution prepared by dissolving the crude 
naphthalenedicarboxylic acid in the amine aqueous solution is subjected to 
hydrogenation in the presence of the above catalyst. The hydrogenation may 
be carried out by any one of a batch method and a continuous flow method. 
The continuous flow method is industrially preferred. The hydrogenation 
conditions differ depending upon the kind and amount of the catalyst and 
the residence time. Generally, the hydrogenation temperature is 70.degree. 
to 250.degree. C. The hydrogen partial pressure is 0.01 to 30 kg/cm.sup.2, 
preferably 0.01 to 10 kg/cm.sup.2. When the hydrogenation is carried out 
under severe conditions at 250.degree. C. or higher, tetralindicarboxylic 
acid may be formed since the ring of the naphthalene is hydrogenated as a 
side reaction, or naphthoic acid may be formed due to decarbonation or 
decarbonylation. 
As described in the present invention 1, decarbonylation may be carried out 
after the heavy metal components are removed. As described in the present 
invention 2, decarbonylation may be carried out without removing the heavy 
metal components. 
The formyl naphthoic acid contained as impurity is converted to naphthoic 
acid by the decarbonylation, and it can be therefore removed. When the 
hydrogenation is carried out without carrying out the decarbonylation, 
methyl naphthoic acid is formed from the formyl naphthoic acid, and the 
methyl naphthoic acid is precipitated together with 
naphthalenedicarboxylic acid when the amine aqueous solution is heated to 
distill off the amine. As a result, the methyl naphthoic acid cannot be 
removed. 
It is therefore useless to carry out the decarbonylation after the 
hydrogenation. The formyl naphthoic acid can be removed by the 
decarbonylation alone without carrying out the hydrogenation depending 
upon the kind and amount of impurities contained in the crude 
naphthalenedicarboxylic acid. Further, usually contained 
naphthalenedicarboxylic acid bromide can be removed by the 
decarbonylation. 
The decarbonylation is carried out in the presence of a catalyst prepared 
by dispersing at least one selected from Pt, Pd, Rh, Ru, Ni or Co on a 
carrier having a large surface area such as activated carbon, silica or 
alumina. It is preferred to use a catalyst prepared by dispersing Pd or Pt 
on activated carbon. 
The decarbonylation is carried out by bringing the above catalyst and the 
amine aqueous solution of the crude naphthalenedicarboxylic acid into 
contact with each other in an inert gas atmosphere. The term "inert gas" 
refers to a gas which is inert to the decarbonylation and substantially 
does not contain hydrogen. The concentration of hydrogen in the inert gas 
does not exceed 10 ppm. The inert gas includes nitrogen, argon and helium, 
while a nitrogen gas is generally used. 
The decarbonylation may be carried out by any one of a batch method and a 
continuous flow method, while the continuous flow method is industrially 
preferred. The pressure for the decarbonylation is not specially limited. 
The temperature for the decarbonylation differs depending upon the kind 
and amount of the catalyst and the residence time, while it is generally 
70.degree. to 250.degree. C. When the decarboxylation is carried out under 
severe conditions at 250.degree. C. or higher, a coloring substance may be 
formed by a side reaction. 
When the aqueous solution containing a the naphthalenedicarboxylic acid 
amine salt, which has been subjected to the decarbonylation, still 
contains formyl naphthoic acid and naphthalenedicarboxylic acid bromide in 
an amount larger than the allowable limit, the aqueous solution is 
subjected to hydrogenation to remove the above impurities. A catalyst 
similar to the catalyst used for the decarbonylation can be used for the 
above hydrogenation. 
The process of the present invention includes two embodiments; in one 
embodiment, the decarbonylation is carried out with one reactor, and in 
the other embodiment, two reactors are connected in series, the 
decarbonylation is carried out in one reactor and the hydrogenation is 
carried out in the other reactor. The decarbonylation and the 
hydrogenation may be separately carried out in one reactor through an 
intermediate portion of which a hydrogen gas is introduced. 
As compared with a conventional case where the purification is carried out 
by hydrogenation alone, the present invention which carries out the 
decarbonylation gives an excellent effect on the purification. 
In the present invention, the precipitation by crystallization may be 
carried out after the removal of the heavy metal components as described 
in the present invention 1, and the naphthalenedicarboxylic acid amine 
salt may be crystallized without removing the heavy metal components as is 
described in the present invention 3. 
The present inventors have found the following. When the aliphatic or 
alicyclic amine salt of the crude naphthalenedicarboxylic acid is 
crystallized in mixed solvents of water with an aliphatic ketone, 
alicyclic ketone or an acetonitrile, there can be obtained a 
naphthalenedicarboxylic acid amine salt which is nearly completely free of 
organic impurities, monocarboxylic acids in particular, and is improved in 
hue. When the above mixed solvents are used, the dependency of solubility 
of the above amine salt upon temperature is high, and 
2,6-naphthalenedicarboxylic acid amine salt can be therefore recovered at 
high yields. When the amine is distilled off by heating the recovered 
naphthalenedicarboxylic acid amine salt, a high-purity 
naphthalenedicarboxylic acid excellent in hue can be obtained at high 
yields. 
In the present invention 3, the purification of the crude 
naphthalenedicarboxylic acid comprises the step of crystallizing a crude 
naphthalenedicarboxylic acid amine salt from mixed solvents of water with 
an aliphatic ketone, alicyclic ketone or an acetonitrile and the step of 
heating the naphthalenedicarboxylic acid amine salt, which is purified by 
the crystallization, to distill off the amine. 
The aliphatic or alicyclic ketone (to be sometimes simply referred to as 
"ketone" hereinafter) used in the present invention are as follows. 
Aliphatic ketones such as acetone, methyl ethyl ketone, methyl propyl 
ketone, diethyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, 
2-heptanone, 4-heptanone, diisobutyl ketone and acetonyl acetone; and 
alicyclic ketones such as cyclohexanone and methylcyclohexanone. 
Of the above ketones, acetone is particularly preferred since the 
dependency of solubility of the above amine salt upon temperature is the 
highest when it is mixed with water and since it is easy in handling and 
availability. 
The above ketones may be used alone or in combination. 
In the crystallization step, first, the crude naphthalenedicarboxylic acid 
amine salt is mixed with the mixed solvents of water with the ketone or an 
acetonitrile, and the resultant mixture is heated. By this procedure, the 
crude naphthalenedicarboxylic acid amine salt is dissolved in the mixed 
solvents of water with the ketone or an acetonitrile. The crude 
naphthalenedicarboxylic acid may be added to the mixed solvents containing 
the amine, water and the ketone or an acetonitrile. 
In the above crystallization of the naphthalenedicarboxylic acid amine 
salt, the water/ketone amount ratio of the mixed solvents is 1 to 99 parts 
by weight/99 to 1 part by weight, preferably, 3 to 15 parts by weight/97 
to 85 parts by weight. In the above crystallization of the 
naphthalenedicarboxylic acid amine salt, the water/acetonitrile amount 
ratio of the mixed solvents is 1 to 99 parts by weight/99 to 1 part by 
weight, preferably, 3 to 25 parts by weight/97 to 75 parts by weight. 
The naphthalenedicarboxylic acid amine salt shows a high solubility in 
water alone. However, the dependency of the solubility upon water is low, 
and the solubility is high even at a low temperature. In the 
crystallization in water alone, therefore, the yield of a crystal of the 
naphthalenedicarboxylic acid amine salt is low. Further, the 
naphthalenedicarboxylic acid amine salt has almost no solubility in the 
ketone or an acetonitrile alone, and the crystallization is therefore 
impossible. In contrast, the present inventors have found a phenomenon 
that when mixed solvents of water with the ketone or acetonitrile are 
used, the naphthalenedicarboxylic acid amine salt is well dissolved at a 
high temperature, and the solubility at a low temperature is low. 
The solubility of 2,6-naphthalenedicarboxylic acid (2,6-NDCA-TEA) 
triethylamine salt was measured in water-acetone mixed solvents having a 
water concentration below. Table 1 shows the results. 
TABLE 1 
______________________________________ 
Water concentration (wt %) in 
Solubilityg-2,6-NDCA- 
water/acetone mixed solvents 
TEA/100 g solvents! 
5 10 20 100 
______________________________________ 
25 (.degree.C.) 0.5 or 1.2 9.5 110 
less 
50 (.degree.C.) 1.0 4.4 23 135 
75 (.degree.C.) 6 17 64 204 
100 (.degree.C.) 
30 63 170 240 
______________________________________ 
For example, 60 g of the ditriethylamine salt of 
2,6-naphthalenedicarboxylic acid is dissolved in 100 g of the mixed 
solvents having a water concentration of 10 wt % at 100.degree. C., and 
then the mixture is cooled to 25.degree. C. In this case, the amount of 
the 2,6-naphthalenedicarboxylic acid triethylamine salt dissolved at 
25.degree. C. is 1.2 g, and a crystal of the diethyltriethylamine salt of 
2,6-naphthalenedicarboxylic acid is precipitated at a recovery of 98% 
(60-1.2)/60=0.98!. 
It is the most preferred to use acetone as a ketone. When 10 wt % 
water/methyl ethyl ketone mixed solvents or 10 wt % water/cyclohexanone 
mixed solvents are used, the dependency of solubility of the amine salt 
upon temperature is smaller than the dependency when the 10 wt % 
water/acetone mixed solvents are used. 
Further, the solubility of 2,6-naphthalenedicarboxylic acid (2,6-NDCA-TEA) 
triethylamine salt, which is obtained when an triethylamine used as the 
amine, was measured in water-acetonitrile mixed solvents having a water 
concentration of 5,10 or 20% by weight and measured in water. Table 2 
shows the results. 
TABLE 2 
______________________________________ 
Water concentration (wt %) in 
Solubilityg-2,6-NDCA- 
water/acetonitrile mixed solvents 
TEA/100 g solvents! 
5 10 20 100 
______________________________________ 
25 (.degree.C.) 0.7 4.3 11 110 
50 (.degree.C.) 4.0 14 44 135 
75 (.degree.C.) 22 45 90 204 
100 (.degree.C.) 
110 140 170 240 
______________________________________ 
For example, 140 g of the ditriethylamine salt of 
2,6-naphthalenedicarboxylic acid is dissolved in 100 g of the 
water-acetonitrile mixed solvents having a water contentration of 10 wt % 
at 100.degree. C., and then the mixture is cooled to 25.degree. C. for 
crystallization. In this case, the amount of the 
2,6-naphthalenedicarboxylic acid triethylamine salt dissolved at 
25.degree. C. is 4.3 g, and a crystal of the diethyltriethylamine salt of 
2,6-naphthalenedicarboxylic acid is precipitated at a recovery of 97% 
(140-4.3)/140=0.97!. 
When above mixed solvents containing water and the ketone or acetonitrile 
are used, the crystallization of the naphthalenedicarboxylic acid amine 
salt at a high recovery ratio, which has been impossible when water alone, 
the ketone alone or acetonitrile alone is used, can be accomplished. 
When the crude naphthalenedicarboxylic acid and the amine or acetonitrile 
are mixed in the above mixed solvents under heat, the 
naphthalenedicarboxylic acid amine salt is readily formed and dissolved in 
the mixed solvents. The amount of the above amine is equivalent to, or 
greater than, the equivalent weight of carboxyl groups of the crude 
naphthalenedicarboxylic acid. For carrying out the above crystallization 
industrially economically, the amount of the amine based on the above 
carboxyl groups is properly 1.0 to 1.2 equivalent weights. 
The amount of the mixed solvents of which the water/ketone or 
water/acentonitrile ratio is specified already is 0.2 to 100 times, 
preferably 0.5 to 10 times, the amount of the crude 
naphthalenedicarboxylic acid. The amount and the ratio of the water/ketone 
or water/acentonitrile mixed solvents are adjusted in the above ranges 
depending upon the crystallization temperature, the recovery and 
purification degree of the naphthalenedicarboxylic acid amine salt and the 
operability and economic performance in a solid/liquid separation. 
The temperature at which the crude naphthalenedicarboxylic acid and the 
mixed solvents of water with the ketone or an acetonitrile are mixed and 
the naphthalenedicarboxylic acid amine salt is formed and dissolved is 
0.degree. to 250.degree. C., preferably 50.degree. to 150.degree. C. The 
pressure in the reaction system in this case is dependent upon the amount 
ratio and the temperature of the mixed solvents, and it is not specially 
limited. 
In the above operation, the heavy metal components such as Co, Mn, etc., 
derived from an oxidation catalyst, are precipitated as insolubles in a 
solution of the crude naphthalenedicarboxylic acid amine salt in the mixed 
solvents of water with the ketone or acetonitrile. For obtaining a 
purified naphthalenedicarboxylic acid having a high quality, it is 
preferred to remove the above heavy metal components by filtration. 
Further, the heavy metal components may be removed by filtration by 
dissolving the naphthalenedicarboxylic acid amine salt in a solvent such 
as water before the step of distilling off the amine by heating the 
naphthalenedicarboxylic acid amine salt purified by the crsytallization. 
Then, a solution of the naphthalenedicarboxylic acid amine salt in the 
mixed solvents of water with the ketone or acetonitrile is subjected to 
crystallization, whereby a purified crystal of the naphthalenedicarboxylic 
acid amine salt is obtained. The crystallization is carried out by 
precipitating the naphthalenedicarboxylic acid amine salt on the basis of 
the dependency of solubility of the amine salt upon temperature, i.e., by 
providing a temperature difference or cooling the solution. 
The temperature to which the solution is cooled ("cooling temperature" 
hereinafter) is in the range of from -50.degree. to 100.degree. C. 
Generally preferably, the cooling temperature which can be industrially 
easily employed is approximately 10.degree. to 60.degree. C. In the 
present invention, the solubility of the naphthalenedicarboxylic acid 
amine salt in the mixed solvents around room temperature is low, and the 
dependency of the solubility upon temperature is high. In the 
crystallization at the cooling temperature in the above range, therefore, 
a naphthalenedicarboxylic acid amine salt having a sufficient purification 
degree can be obtained with a high recovery in an economical amount of the 
mixed solvents. 
By the above procedure, organic impurities contained in the crude 
naphthalenedicarboxylic acid are almost all removed. In particular, 
monocarboxylic acids such as naphthoic acid, methyl naphthoic acid and 
formyl naphthoic acid are nearly completely removed. The process of the 
present invention obviates the particular procedure for the removal of 
formyl naphthoic acid such as hydrogenation or the like, since formyl 
naphthoic acid which is liable to remain in the procedure of general 
crystallization is removed. 
In the above crystallization, further, coloring components contained in the 
crude naphthalenedicarboxylic acid are also removed, and a 
naphthalenedicarboxylic acid amine salt having a remarkably improved hue 
can be obtained. 
For further discoloration, the naphthalenedicarboxylic acid amine salt can 
be treated with a solid adsorbent. For example, the above 
naphthalenedicarboxylic acid amine salt obtained by the crystallization is 
re-dissolved in a solvent such as water, and the resultant solution is 
subjected to a discoloration treatment with a solid adsorbent. Further, 
the above amine salt may be subjected to a purification treatment such as 
hydrogenation. It is uneconomical to carry out the adsorption with a solid 
adsorbent before the crystallization, since the adsorbent is overloaded by 
the discoloration so that a large amount of the solid adsorbent is 
required. 
In the present invention, the crystallization can be carried out by any one 
of a batch method and a continuous flow method, while a continuous flow 
method is superior when a large amount of the naphthalenedicarboxylic acid 
amine salt is treated in an industrial process. The 
naphthalenedicarboxylic acid amine salt is isolated by a solid-liquid 
separation operation such as filtration or centrifugal separation. 
Then, the above-obtained crystal is washed with a solvent which is soluble 
in water and the ketone or acetonitrile but has almost no solubility in 
the naphthalenedicarboxylic acid amine salt, for removing the 
crystallization mother liquor adhering the crystal surface. Generally, a 
ketone alone is used or a ketone containing a small amount of water is 
used as a solvent for the above washing. The crystallization mother liquor 
and the wash liquid are recycled as a crystallization raw material, 
directly or after impurities are removed. 
When the above crystallization is carried out a plurality of times, there 
can be obtained a naphthalenedicarboxylic acid amine salt having a higher 
purity and a more improved hue, while the number of times with which the 
crystallization is carried out is determined by considering the 
purification degree of the amine salt and economic performance. 
According to the present invention 1 and invention 2, an amine compound is 
distilled off from an aqueous solution containing the above-obtained 
naphthalenedicarboxylic acid amine salt. The method of distilling off the 
amine compound includes a method in which the amine aqueous solution is 
externally heated to distill off amine alone or amine and water, a method 
in which the amine aqueous solution is heated with feeding overheated 
steam or water, to distill off the amine compound, a method in which amine 
is distilled of f with blowing an inert gas such as nitrogen gas into the 
amine aqueous solution, and a method in which amine is distilled off under 
reduced pressure. Amine alone or amine and water may be distilled off by 
combining at least two of the above methods. 
The temperature for distilling off amine is preferably at least 50.degree. 
C., particularly preferably at least 80.degree. C., since the 
decomposition rate of the amine salt is low when the above temperature is 
too low. On the other hand, when the above temperature is too high, the 
naphthalenedicarboxylic acid may be altered or colored. The above 
temperature therefore preferably does not exceed 300.degree. C., 
particularly preferably, it does not exceed 250.degree. C. 
The amine compound is distilled off from the aqueous solution containing a 
the naphthalenedicarboxylic acid amine salt by the above method, whereby a 
the naphthalenedicarboxylic acid amine salt is decomposed. The so-formed 
amine is collected by cooling and a nearly total amount thereof can be 
recovered. The collected amine can be purified as required, and re-used. 
As the amine is distilled off, free naphthalenedicarboxylic acid is 
precipitated from the aqueous solution containing the 
naphthalenedicarboxylic acid amine salt. The amount of the precipitated 
naphthalenedicarboxylic acid is in proportion to the amount of the amine 
which is distilled off. The naphthalenedicarboxylic acid can be obtained 
at a high recovery by increasing the distillation amount of the amine. 
Preferably, the distillation is carried out at a recovery of at least 90% 
for achieving an economical industrial process. 
The purified naphthalenedicarboxylic acid which is precipitated by heating 
can be recovered by an operation such as filtration or centrifugal 
separation. Further, the crystal of the purified naphthalenedicarboxylic 
acid may be washed with water as required to remove impurities adhering to 
the crystal surface. Further, the so-obtained crystal is dried to give a 
high-purity naphthalenedicarboxylic acid. 
The naphthalenedicarboxylic acid amine salt obtained by the crystallization 
method in the present invention 3 is also fed to the step of distilling 
off the amine to obtain a purified naphthalenedicarboxylic acid. The 
method of distilling off the amine from a the naphthalenedicarboxylic acid 
amine salt includes a method in which the naphthalenedicarboxylic acid 
amine salt is directly heated and a method in which the 
naphthalenedicarboxylic acid amine salt is heated in the co-presence of a 
solvent. Either method may be used. In the method in which a the 
naphthalenedicarboxylic acid amine salt is directly heated, however, 
organic impurities which cannot be removed in the crystallization step 
still remains in the crystal. 
On the other hand, preferred is the method in which the 
naphthalenedicarboxylic acid amine salt is heated in the co-presence of a 
solvent to distill off the amine, since the above method has an effect 
that the organic impurities which cannot be removed in the crystallization 
step are further removed, so that a purified naphthalenedicarboxylic acid 
having a high product quality can be obtained. The above solvent is not 
specially limited so long as it has no reactivity with the 
naphthalenedicarboxylic acid amine salt at a heating time, while water is 
preferred. 
In the method of distilling off the amine in the co-presence of water as a 
solvent, a the naphthalenedicarboxylic acid amine salt purified by the 
crystallization is dissolved in water. In this case, the resultant 
solution can be treated with a small amount of a solid adsorbent to 
promote discoloration. Further, the above solution can be subjected to 
microfiltration to remove foreign substance and metal components. Then, 
the above solution is heated to distill off the amine together with water. 
The heating method is the same as the above-described method of distilling 
the amine. 
According to the present invention 1, the crude naphthalenedicarboxylic 
acid obtained by the oxidation of dialkyl naphthalene is dissolved in an 
aqueous solution containing the aliphatic amine to remove the heavy metal 
components, and then the aqueous solution is heated to distill off the 
amine. As a result, a high-purity naphthalenedicarboxylic acid having an 
excellent hue can be easily obtained at a high recovery. Further, the 
aqueous solution is subjected to hydrogenation after the removal of the 
heavy metal components, and then the amine is distilled off. As a result, 
formyl naphthoic acid which is to be a problem in polymerization is 
removed, and the hydrogenation catalyst is improved in life, so that a 
high-purity naphthalenedicarboxylic acid can be industrially very 
advantageously produced. The present invention therefore has a remarkably 
great significance in industry. 
According to the present invention 2, the crude naphthalenedicarboxylic 
acid obtained by the oxidation of dialkyl naphthalene is dissolved in an 
aqueous solution containing an aliphatic amine, the resultant aqueous 
solution is subjected to decarbonylation or both decarbonylation and 
hydrogenation, and then the aqueous solution is heated to distill off the 
amine. As a result, a naphthalenedicarboxylic acid almost free of methyl 
naphthoic acid and formyl naphthoic acid can be easily obtained at high 
yields. 
The present invention 3 has the following features 1) to 3). 
1) The crystallization is carried out in mixed solvents of water with an 
aliphatic ketone, an alicyclic ketone or an acetonitrile. As a result, 
organic impurities are almost completely removed, and an amine salt of 
naphthalenedicarboxylic acid having an excellent hue can be obtained. 
2) The dependency of solubility of the naphthalenedicarboxylic acid amine 
salt upon temperature is high when the above mixed solvents are used, or 
the above solubility is low at a low temperature and it is high at a high 
temperature. As a result, a purified amine salt of naphthalenedicarboxylic 
acid can be obtained at a high recovery by the procedure of 
crystallization. 
3) When the above amine salt of naphthalenedicarboxylic acid is heated to 
distill off the amine, a high-purity naphthalenedicarboxylic acid having 
an excellent hue can be obtained at a high recovery. 
According to the present invention, moreover, nearly the whole of the amine 
generated by heating the above amine salt can be easily recovered by 
cooling and collecting it, and it can be recycled. 
Therefore, the present invention provides an industrially excellent process 
and is greatly significant in industry.

EXAMPLES 
The present invention will be explained more in detail with reference to 
Examples hereinafter, while the present invention shall not be limited to 
these Examples. 
Concerning the purity and properties of raw materials and purified 
naphthalenedicarboxylic acid, organic substances were methyl-esterified 
and analyzed by gas chromatography, and inorganic substances were 
wet-decomposed and analyzed by ICP spectrometry. Concerning a hue, 1 g of 
a sample was dissolved in 10 ml of a 1N sodium hydroxide aqueous solution 
and evaluated for an absorbance of light having a wavelength of 500 nm (to 
be abbreviated as "OD.sub.500 " hereinafter) with a 10 mm long quartz 
cell. 
Abbreviations in Examples, Comparative Examples and Tables stand for the 
following. 
______________________________________ 
2,6-NDCA 2,6-naphthalenedicarboxylic acid 
2,6-NDCA-TEA triethylamine salt of 2,6- 
naphthalenedicarboxylic acid 
2-NA 2-naphthoic acid 
2,6-MNA 2,6-methyl naphthoic acid 
2,6-FNA 2,6-formyl naphthoic acid 
TMAC trimellitic acid 
NTCA naphthalenetricarboxylic acid 
Br-2,6-NDCA Bromo-2,6-naphthalenedicarboxylic acid 
TDCA tetralindicarboxylic acid 
L.E. Substance having a low boiling point 
H.E. Substance having a high boiling point 
TEA triethylamine 
TMA trimethylamine 
______________________________________ 
Preparation Example 1 
3.8 Grams of cobalt acetate (tetrahydrate), 32.0 g of manganese acetate 
(tetrahydrate) and 7.43 g of hydrogen bromide (47% aqueous solution) were 
mixed with, and dissolved in, 1,797 g of glacial acetic acid to prepare a 
catalyst liquid. A 5-liter autoclave of titanium having a stirrer, a 
reflux condenser and a feed pump was charged with 740 g of the above 
catalyst liquid. The remaining portion of the catalyst liquid was mixed 
with 180 g of 2,6-dimethylnaphthalene, and the mixture was charged into a 
feed vessel and heated to dissolve the 2,6-dimethylnaphthalene, whereby a 
raw material liquid was prepared. 
The pressure in a reaction system was adjusted to 18 kg/cm.sup.2 G with 
nitrogen, and the reaction system was heated to 200.degree. C. with 
stirring. After the temperature and the pressure were stabilized, the raw 
material liquid and compressed air were supplied to a reactor to initiate 
oxidation. While the flow amount of air was adjusted such that an off-gas 
from the reactor had an oxygen concentration of 0.1% by volume, the raw 
material liquid was continuously fed over 2 hour period. After the 
completion of feeding of the raw material liquid, air was continuously 
supplied for 9 minutes. 
After the reaction, the autoclave was cooled to room temperature, and a 
reaction product was taken out, filtered by means of suction, washed with 
water and with acetic acid and dried to give a crude 2,6-NDCA having a 
composition and a hue shown in Table 3. The crude 2,6-NDCA contained 340 
ppm of Co and 2,400 ppm of Mn. The crude 2,6-NDCA was used as a raw 
material in the following Examples and Comparative Examples. 
Example 1 
A 2-liter four-necked flask formed of glass and equipped with a reflux 
condenser, a stirrer and a temperature measuring tube was charged with 200 
g of 2,6-NDCA, 1,070 g of water and 205.9 g (1.1 equivalent weights based 
on 2,6-NDCA) of TEA, and the mixture was stirred for 30 minutes. Heavy 
metal components which precipitated without being dissolved were filtered 
off through a sintered metal filter having openings having a diameter of 
10 .mu.m, and then the filtrate was further filtered through a filter 
having openings having diameter of 5 .mu.m to give an aqueous solution of 
2,6-NDCA-TEA. 
The above-prepared solution in an amount of 70 g was placed in a 300-ml 
autoclave formed of stainless steel and equipped with a stirrer, a 
pressure filter device and a gas outlet, and the atmosphere in the 
autoclave was replaced with nitrogen. Then, the mixture was heated up to 
200.degree. C., and while water was added at a flow rate of 100 g/hour at 
the same temperature, a distillate was withdrawn, at a rate equivalent to 
the flow rate of water, from the top of the reaction apparatus. This 
procedure was carried out for 2 hours. The total distilate amount was 
about 21 times as much as the amount of NDCA charges in the solution. The 
solution was filtered under pressure at the same temperature to obtain a 
crystal, and the crystal was washed with water and with acetic acid, and 
then dried under vacuum for 5 hours at 120.degree. C., to give a purified 
2,6-NDCA having a composition and a hue shown in Table 3 at a yield of 
94.7% (yield based on the crude 2,6-NDCA). The so-obtained 2,6-NDCA 
contained 10 ppm of Co and 68 ppm of Mn. 
Example 2 
A purified 2,6-NDCA having a composition and a hue shown in Table 3 was 
obtained in the same manner as in Example 1 except that the filter having 
openings having a diameter of 5 .mu.m was replaced with a nitrocellulose 
membrane filter having openings having a diameter of 1 .mu.m. The 
so-obtained 2,6-NDCA contained less than 1 ppm of Co and 20 ppm of Mn. 
Example 3 
A purified 2,6-NDCA having a composition and a hue shown in Table 3 was 
obtained in the same manner as in Example 1 except that the filter having 
openings having a diameter of 5 .mu.m was replaced with a nitrocellulose 
membrane filter having openings having a diameter of 1 .mu.m and further 
that 70 g of the aqueous solution was flowed through a column formed of 
glass and packed with activated carbon to obtain an aqueous solution of 
2,6-NDCA-TEA. The so-obtained 2,6-NDCA contained less than 1 ppm of Co and 
less than 0.5 ppm of Mn. 
Example 4 
A purified 2,6-NDCA having a composition and a hue shown in Table 3 was 
obtained in the same manner as in Example 1 except that the filter having 
openings having a diameter of 5 .mu.m was replaced with a nitrocellulose 
membrane filter having openings having a diameter of 1 .mu.m and further 
that 70 g of the aqueous solution was flowed through a column formed of 
glass and packed with activated clay to obtain an aqueous solution of 
2,6-NDCA-TEA. The so-obtained 2,6-NDCA contained less than 1 ppm of Co and 
less than 0.5 ppm of Mn. 
Comparative Example 1 
A purified 2,6-NDCA having a composition and a hue shown in Table 4 was 
obtained in the same manner as in Example 1 except that an aqueous 
solution of 2,6-NDCA-TEA was obtained without carrying out any filtration 
in the step of obtaining the aqueous solution of 2,6-NDCA-TEA. The 
so-obtained 2,6-NDCA contained 330 ppm of Co and 2,360 ppm of Mn. 
Comparative Example 2 
A purified 2,6-NDCA having a composition and a hue shown in Table 4 was 
obtained in the same manner as in Example 1 except that an aqueous 
solution of 2,6-NDCA-TEA was obtained without carrying out the filtration 
through the filter having openings having a diameter of 5 .mu.m in the 
step of obtaining the aqueous solution of 2,6-NDCA-TEA. The so-obtained 
2,6-NDCA contained 210 ppm of Co and 1,620 ppm of Mn. 
Example 5 
A fixed-bed pressure-flow reaction apparatus having a 13 mm.phi..times.316 
mm reaction tube formed of stainless steel and packed with 5 g of a 0.5% 
Pd/C catalyst having an arranged diameter of 2-3 mm, a gas-liquid 
separator and a raw material feed pump was charged with 10 kg/cm.sup.2 of 
mixed gases of 33.3% by volume of hydrogen and 66.7% by volume of 
nitrogen. While the same gases as above were flowed at a rate of 50 
ml/minute, the reaction tube was maintained at 150.degree. C., and an 
aqueous solution of 2,6-NDCA-TEA obtained in the same manner as in Example 
4 was flowed at 30 g/hour to carry out hydrogenation. 
The aqueous solution of 2,6-NDCA-TEA obtained after the hydrogenation was 
distilled in the same manner as in Example 1 to give a crystal of purified 
2,6-NDCA having a composition and a hue shown in Table 4. The so-obtained 
2,6-NDCA contained less than 1 ppm of Co and less than 0.5 ppm of Mn. 
Comparative Example 3 
The same aqueous solution of 2,6-NDCA-TEA as that obtained in Comparative 
Example 1 was subjected to hydrogenation and distillation in the same 
manner as in Example 5 to give a crystal of purified 2,6-NDCA having a 
composition and a hue shown in Table 4. The so-obtained 2,6-NDCA contained 
270 ppm of Co and 2,200 ppm of Mn. 
TABLE 3 
______________________________________ 
Organic PEx. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 
substances 
(%) (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 98.593 99.746 99.721 99.938 
99.927 
2-NA 0.056 0.003 0.006 0.002 0.003 
2,6-MNA 0.010 0.003 0.002 0.002 0.002 
TMAC 0.630 0.002 0.001 0.001 0.002 
2,6-FNA 0.263 0.210 0.235 0.020 0.020 
TDCA 0.000 0.000 0.000 0.000 0.000 
L.E. 0.097 0.011 0.009 0.010 0.015 
Br-2,6-NDCA 
0.165 0.013 0.012 0.013 0.015 
NTCA 0.164 0.003 0.003 0.002 0.002 
H.E. 0.022 0.014 0.011 0.012 0.014 
Total 100.000 100.000 100.000 
100.000 
100.000 
OD.sub.500 
10.256 0.261 0.256 0.060 0.100 
______________________________________ 
Pex. = Preparation Example, Ex. = Example 
TABLE 4 
______________________________________ 
Organic CEx. 1 CEx. 2 Ex. 5 CEx. 3 
substances (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 99.726 99.721 99.837 
99.828 
2-NA 0.006 0.008 0.007 0.008 
2,6-MNA 0.002 0.003 0.120 0.124 
TMAC 0.221 0.002 0.001 0.002 
2,6-FNA 0.263 0.231 0.006 0.006 
TDCA 0.000 0.000 0.003 0.002 
L.E. 0.012 0.011 0.011 0.011 
Br-2,6-NDCA 0.018 0.011 0.003 0.002 
NTCA 0.002 0.004 0.002 0.002 
H.E. 0.012 0.009 0.012 0.015 
Total 100.000 100.000 100.000 
100.000 
OD.sub.500 0.452 0.338 0.200 0.321 
______________________________________ 
CEx. = Comparative Example, Ex. = Example 
Preparation Example 2 
A 2-liter four-necked flaks formed of glass and equipped with a reflux 
condenser, a stirrer and a temperature measuring tube was charged with 200 
g of the crude 2,6-NDCA obtained in Preparation Example 1, 1,070 g of 
water and 205.9 g (1.1 equivalent weights based on 2,6-NDCA) of TEA, and 
these materials were stirred to obtain an aqueous solution of 
2,6-NDCA-TEA. A heavy metal component, Mn, was floating as an insoluble in 
the aqueous solution. 
Preparation Example 3 
The aqueous solution of 2,6-NDCA-TEA obtained in Preparation Example 2 was 
filtered through a sintered metal filter having openings having a diameter 
of 10 .mu.m, and the heavy metal component was removed by filtering the 
filtrate through a nitrocellulose membrane filter having openings having a 
diameter of 1 .mu.m to prepare an aqueous solution of 2,6-NDCA-TEA. Part 
of the aqueous solution was taken, and water and TEA were distilled off by 
heating the filtrate under vacuum to obtain 2,6-NDCA. The 2,6-NDCA was 
dried to solidness. Table 5 shows the composition of the so-obtained 
2,6-NDCA. The 2,6-NDCA contained 80 ppm of Mn. 
Example 6 
An autoclave formed of stainless steel and equipped with a stirrer and a 
pressure filtration device was charged with 100 g of the aqueous solution 
of 2,6-NDCA-TEA obtained in Preparation Example 3 and a 0.5% Pd/C catalyst 
powder, and the atmosphere in the system was replaced with nitrogen. Then, 
the mixture was stirred at 150.degree. C. for 1 hour to carry out 
decarbonylation, allowed to cool and then filtered to obtain an aqueous 
solution of 2,6-NDCA-TEA. 
A 300-ml autoclave formed of stainless steel and equipped with a stirrer, a 
pressure filtration device and a gas outlet was charged with 70 g of the 
above aqueous solution, and the atmosphere in the autoclave was replaced 
with nitrogen. The aqueous solution was heated up to 200.degree. C., and 
while water was added at a flow rate of 100 g/hour at the same 
temperature, a distillate was withdrawn, at a rate equivalent to the flow 
rate of water, from the top of the reaction apparatus. This procedure was 
carried out for 2 hours. The total distillate amount was about 21 times as 
much as the amount of NDCA charges in the solution. The solution was 
filtered under pressure at the same temperature to obtain a crystal, and 
the crystal was washed with water and with acetic acid, and then dried 
under vacuum for 5 hours at 120.degree. C., to give a purified 2,6-NDCA 
having a composition and a hue shown in Table 5 at a yield of 94.7%. The 
so-obtained 2,6-NDCA contained 40 ppm of 2,6-FNA and 30 ppm of 2,6-MNA. 
Comparative Example 4 
A crystal of purified 2,6-NDCA having a composition shown in Table 6 was 
obtained in the same manner as in Example 6 except that the 
decarbonylation was not carried out. The so-obtained 2,6-NDCA contained 20 
ppm of 2,6-MNA and 2,350 ppm of 2,6-FNA. 
Comparative Example 5 
A crystal of purified 2,6-NDCA having a composition shown in Table 6 was 
obtained in the same manner as in Example 6 except that the replacement of 
the atmosphere in the autoclave with nitrogen was replaced with the 
replacement with 5 kg/cm.sup.2 of hydrogen. The so-obtained 2,6-NDCA had a 
2,6-FNA content of 60 ppm, while 1,230 ppm of 2,6-MNA was formed and 
remained. 
Comparative Example 6 
A crystal of purified 2,6-NDCA having a composition shown in Table 6 was 
obtained in the same manner as in Example 6 except that the aqueous 
solution of 2,6-NDCA-TEA obtained in Preparation Example 6 was replaced 
with the aqueous solution of 2,6-NDCA-TEA in which Mn was floating, 
obtained in Preparation Example 2. In the so-obtained 2,6-NDCA, the 
2,6-FNA content and the 2,6-MNA content were the same as those in Example 
6, while 50 ppm of Mn remained and the 2,6-NDCA was extremely colored. 
Example 7 
A fixed-bed pressure-flow reaction apparatus having a 13 mm.phi..times.316 
mm reaction tube formed of stainless steel and packed with 5 g of a 0.5% 
Pd/C catalyst having an arranged diameter of 2-3 mm, a gas-liquid 
separator and a raw material feed pump was internally pressure-increased 
with nitrogen and maintained at 10 kg/cm.sup.2. While the same gas was 
flowed at a rate of 50 ml/minute, the reaction tube was maintained at 
150.degree. C., and an aqueous solution of 2,6-NDCA-TEA obtained in 
Preparation Example 3 was flowed at 30 g/hour to carry out 
decarbonylation. 
The resultant aqueous solution of 2,6-NDCA-TEA was subjected to 
distillation in the same manner as in Example 6 to give a crystal of 
2,6-NDCA having a composition shown in Table 5. The so-obtained 2,6-NDCA 
contained 40 ppm of 2,6-FNA and 20 ppm of 2,6-MNA. 
Example 8 
The reaction system as that used in Example 7 was internally 
pressure-increased with mixed gases of 33.3 vol % of hydrogen and 66.7% of 
nitrogen in place of nitrogen and maintained at 10 kg/cm.sup.2. While the 
same mixed gases were flowed at a rate of 50 ml/minute, the reaction tube 
was maintained at 150.degree. C., and the aqueous solution of 2,6-NDCA-TEA 
obtained after the decarbonylation in Example 7 was flowed at 30 g/hour to 
carry out hydrogenation. 
The resultant aqueous solution of 2,6-NDCA-TEA was subjected to 
distillation in the same manner as in Example 6 to give a crystal of 
2,6-NDCA having a composition shown in Table 5. The so-obtained 2,6-NDCA 
contained 20 ppm of 2,6-MNA, and no 2,6-MNA was detected. 
Comparative Example 7 
The aqueous solution of 2,6-NDCA-TEA obtained in Preparation Example 3 was 
subjected to the same hydrogenation and the same distillation as those in 
Example 8 without carrying out the decarbonylation, to give a crystal of 
2,6-NDCA. The so-obtained 2,6-NDCA had a 2,6-FNA content of 50 ppm, while 
1,280 ppm of 2,6-FNA was formed and remained. 
TABLE 5 
______________________________________ 
Organic PEx. 1 PEx. 3 Ex. 6 Ex. 7 Ex. 8 
substance (%) (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 98.593 98.593 99.960 99.955 
99.961 
2-NA 0.056 0.056 0.005 0.007 0.006 
2,6-MNA 0.010 0.010 0.003 0.002 0.002 
TMAC 0.630 0.630 0.002 0.003 0.002 
2,6-FNA 0.263 0.263 0.004 0.004 0.000 
TDCA 0.000 0.000 0.000 0.000 0.002 
L.E. 0.097 0.097 0.009 0.011 0.013 
Br-2,6-NDCA 
0.165 0.165 0.003 0.002 0.000 
NTCA 0.164 0.164 0.003 0.0O3 0.002 
H.E. 0.022 0.022 0.011 0.013 0.012 
Total 100.000 100.000 100.000 
100.000 
100.000 
Heavy metal 
(ppm) (ppm) (ppm) (ppm) (ppm) 
component 
Mn 2,400 80 &lt;1.0 &lt;1.0 &lt;1.0 
OD.sub.500 
0.256 0.258 0.220 0.215 0.225 
______________________________________ 
Pex. = Preparation Example, Ex. = Example 
TABLE 6 
______________________________________ 
Organic CEx. 4 CEx. 5 CEx. 6 
CEx. 7 
substances (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 99.721 99.829 99.960 
99.827 
2-NA 0.006 0.005 0.005 0.007 
2,6-MNA 0.002 0.123 0.003 0.128 
TMAC 0.001 0.003 0.002 0.002 
2,6-FNA 0.235 0.006 0.004 0.005 
TDCA 0.000 0.0o1 0.000 0.002 
L.E. 0.009 0.013 0.009 0.012 
Br-2,6-NDCA 0.012 0.003 0.003 0.002 
NTCA 0.003 0.003 0.003 0.002 
H.E. 0.011 0.014 0.011 0.013 
Total 100.000 100.000 100.000 
100.000 
Heavy metal (ppm) (ppm) (ppm) (ppm) 
component 
Mn 5.0 &lt;1.0 50 &lt;1.0 
OD.sub.500 0.230 0.224 0.450 0.218 
______________________________________ 
CEx. = Comparative Example 
Concerning a hue in Examples and Comparative Examples hereinafter, 1 g of a 
sample was dissolved in 10 ml of a 1N sodium hydroxide aqueous solution 
and evaluated for an absorbance of light having a wavelength of 400 nm (to 
be abbreviated as "OD.sub.400 " hereinafter) with a 10 mm long quartz 
cell. 
Example 9 
A pressure filtration apparatus having a volume of 300 ml was charged with 
20.0 g of the crude 2,6-NDCA obtained in Preparation Example 1, 20.0 g 
(1.07 equivalent weights based on 2,6-NDCA) of TEA and 100 g of an acetone 
solution containing 10 wt % of water, and these materials were mixed at 
100.degree. C. to dissolve the 2,6-NDCA. Heavy metal components which were 
insolubles were removed by filtering the solution through a metal filter 
having openings having a diameter of 1 .mu.m. The whole filtrate was 
recharged into a 300-ml autoclave equipped with a stirrer, a filtration 
device and a gas outlet, and the atmosphere in the autoclave was replaced 
with nitrogen. Then, the filtrate was stirred at 100.degree. C. for 30 
minutes. The resultant solution was cooled to 25.degree. C. over 8 hour 
period to precipitate a crystal of 2,6-NDCA-TEA. The crystal of 
2,6-NDCA-TEA was collected by filtration, and washed with 50 g of acetone. 
The recovery of the 2,6-NDCA-TEA was 96.7%. 
Then, 60 g of water was added to the above crystal of 2,6-NDCA-TEA to form 
an aqueous solution, and the aqueous solution was heated up to 200.degree. 
C. While water was added at a flow rate of 100 g/hour at the same 
temperature, a distillate was withdrawn, at a rate equivalent to the flow 
rate of water, from the top of the reaction apparatus. This procedure was 
carried out for 2hours. The total distillate amount was about 21 times as 
much as the amount of 2,6-NDCA in the solution. Then, the solution was 
filtered under pressure at the same temperature to obtain a crystal of 
2,6-NDCA, and the crystal of 2,6-NDCA was washed with water and with 
acetic acid and dried at 120.degree. C. for 5 hours, to give 18.4 g of a 
purified 2,6-NDCA having a composition and a hue shown in Table 7. The 
recovery of the 2,6-NDCA after all the procedures was 92.1%. The 
so-obtained purified 2,6-NDCA had a remarkably improved hue and contained 
almost no organic impurities. 
Example 10 
The same procedures for crystallization and distilling off TEA as those in 
Example 9 were repeated except that 100 g of the acetone solution 
containing 10 wt % of water was replaced with 140 g of an acetone solution 
containing 5 wt % of water. As a result, 18.9 g of a purified 2,6-NDCA 
having a composition and a hue shown in Table 7 was obtained. 
The recovery of 2,6-NDCA-TEA obtained by the crystallization was remarkably 
high, as high as more than 99%, and the recovery of the 2,6-NDCA after all 
the procedures was 94.3%. 
Example 11 
The same procedures for crystallization and distilling off TMA as those in 
Example 9 were repeated except that 20 g of TEA was replaced with 11.7 g 
(1.07 equivalent weights based on 2,6-NDCA) of TMA. As a result, 18.4 g of 
a purified 2,6-NDCA having a composition and a hue shown in Table 7 was 
obtained. The recovery of the 2,6-NDCA-TEA was 92.0%. 
Example 12 
The same procedures for crystallization and distilling off TEA as those in 
Example 9 were repeated except that 100 g of the acetone solution 
containing 10 wt % of water was replaced with 100 g of a methyl ethyl 
ketone solution containing 10 wt % of water. As a result, 16.0 g of a 
purified 2,6-NDCA having a composition and a hue shown in Table 7 was 
obtained. 
The recovery of 2,6-NDCA-TEA obtained by the crystallization was 84.5%, or 
lower than that when the acetone solution containing 10 wt % of water was 
used, and the recovery of the 2,6-NDCA after all the procedures was 80.3%. 
Example 13 
The same procedures for crystallization and distilling off TEA as those in 
Example 9 were repeated except that 100 g of the acetone solution 
containing 10 wt % of water was replaced with 100 g of a cyclohexanone 
solution containing 10 wt % of water. As a result, 15.1 g of a purified 
2,6-NDCA having a composition and a hue shown in Table 7 was obtained. 
The recovery of 2,6-NDCA-TEA obtained by the crystallization was 79.3%, or 
lower than that when the acetone solution containing 10 wt % of water was 
used, and the recovery of the 2,6-NDCA after all the procedures was 75.4%. 
TABLE 7 
______________________________________ 
Organic Ex. 9 Ex. 10 Ex. 11 Ex. 12 
Ex. 13 
substance (%) (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 99.997 99.968 99.973 99.972 
99.973 
2-NA 0.000 0.000 0.001 0.000 0.000 
2,6-MNA 0.000 0.000 0.000 0.000 0.000 
TMAC 0.000 0.000 0.000 0.000 0.000 
2,6-FNA 0.000 0.001 0.001 0.000 0.000 
L.E. 0.003 0.004 0.003 0.003 0.002 
Br-2,6-NDCA 
0.000 0.001 0.000 0.000 0.000 
NTCA 0.000 0.003 0.002 0.003 0.002 
H.E. 0.020 0.023 0.020 0.022 0.023 
Total 100.000 100.000 100.000 
100.000 
100.000 
Heavy metal 
(ppm) (ppm) (ppm) (ppm) (ppm) 
component 
Co &lt;1.0 &lt;1.0 &lt;1.0 &lt;1.0 &lt;1.0 
Mn 3.0 4.3 3.3 3.2 3.5 
Hue value (OD.sub.400) 
(OD.sub.400) 
(OD.sub.400) 
(OD.sub.400) 
(OD.sub.400) 
0.043 0.050 0.045 0.047 0.044 
______________________________________ 
Ex. = Example 
Comparative Example 8 
The same procedures for crystallization and distilling off TEA as those in 
Example 9 were repeated except that 100 g of the acetone solution 
containing 10 wt % of water was replaced with 20 g of water. As a result, 
8.2 g of a purified 2,6-NDCA having a composition and a hue shown in Table 
8 was obtained. 
The recovery of 2,6-NDCA-TEA obtained by the crystallization was very low, 
as low as 43.2%, and the recovery of the 2,6-NDCA after all the procedures 
was 41.0%. 
Comparative Example 9 
An attempt was made to repeat the same procedures for crystallization and 
distilling off TEA as those in Example 9 except that 100 g of the acetone 
solution containing 10 wt % of water was replaced with 100 g of acetone. 
However, the crude 2,6-NDCA was not at all dissolved even by heating at 
100.degree. C., and no purified 2,6-NDCA was obtained. 
Comparative Example 10 
An attempt was made to repeat the same procedures for crystallization and 
distilling off TEA as those in Example 9 except that 100 g of the acetone 
solution containing 10 wt % of water was replaced with 100 g of methyl 
ethyl ketone. However, the crude 2,6-NDCA was not at all dissolved even by 
heating at 100.degree. C., and no purified 2,6-NDCA was obtained. 
Comparative Example 11 
20.0 Grams of the crude 2,6-NDCA obtained in Preparation Example 1 was 
mixed with, and dissolved in, 20.0 g (1.07 equivalent weights based on 
2,6-NDCA) of TEA and 40.0 g of water at room temperature, and the solution 
was filtered through a filter having openings having a diameter of 1 .mu.m 
to remove heavy metal components which were insolubles. While the filtrate 
was stirred at room temperature, 360 g of acetone was added to precipitate 
a crystal of 2,6-NDCA-TEA. The crystal of 2,6-NDCA-TEA was collected by 
filtration, and washed with 50 g of acetone. The recovery of the 
2,6-NDCA-TEA at this time was 87.6%. 
The above-obtained crystal of 2,6-NDCA-TEA was subjected to the same 
distillation as that in Example 9, to give 16.6 g of a purified 2,6-NDCA 
having a composition and a hue shown in Table 8. The recovery of the 
purified 2,6-NDCA was 83.2%. The 2,6-NDCA contained considerable amounts 
of impurities and showed a poor improvement in hue. 
TABLE 8 
______________________________________ 
Organic PEx. CEx. 8 CEx. 9 CEx. 10 
CEx. 11 
substance 
(%) (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 98.593 99.970 No No 99.260 
2-NA 0.056 0.002 purified 
purified 
0.042 
2,6-MNA 0.010 0.000 2,6- 2,6- 0.008 
TMAC 0.630 0.000 NDCA NDCA 0.255 
2,6-FNA 0.263 0.0O1 was was 0.120 
L.E. 0.097 0.004 obtained. 
Obtained. 
0.011 
Br-2,6-NDCA 
0.165 0.000 0.120 
NTCA 0.164 0.000 0.086 
H.E. 0.022 0.023 0.098 
Total 100.000 100.000 100.000 
Heavy metal 
(ppm) (ppm) (ppm) (ppm) (ppm) 
component 
Co 3,400 &lt;1.0 &lt;1.0 
Mn 2,400 3.5 3.9 
Hue value 
(OD.sub.400) 
(OD.sub.400) 
(OD.sub.400) 
(OD.sub.400) 
(OD.sub.400) 
0.930 0.061 0.452 
______________________________________ 
Ex. = Example 
Example 14 
A pressure filtration apparatus having a volume of 300 ml was charged with 
50.0 g of the crude 2,6-NDCA obtained in Preparation Example 1, 50.0 g 
(1.07 equivalent weights based on 2,6-NDCA) of TEA and 100 g of an 
acetonitrile solution containing 10 wt % of water, and these materials 
were mixed at 100.degree. C. to dissolve the 2,6-NDCA. Heavy metal 
components which were insolubles were removed by filtering the solution 
through a metal filter having openings having a diameter of 1 .mu.m. The 
whole filtrate was recharged into a 300-ml autoclave equipped with a 
stirrer, a filtration device and a gas outlet, and the atmosphere in the 
autoclave was replaced with nitrogen. Then, the filtrate was stirred at 
100.degree. C. for 30 minutes. The resultant solution was cooled to 
25.degree. C. over 8 hour period to precipitate a crystal of 2,6-NDCA-TEA. 
The crystal of 2,6-NDCA-TEA was collected by filtration, and washed with 
100 g of acetonitrile twice. The recovery of the 2,6-NDCA-TEA was 95.6%. 
Then, 150 g of water was added to the above crystal of 2,6-NDCA-TEA to 
form an aqueous solution, and the aqueous solution was heated up to 
200.degree. C. While water was added at a flow rate of 200 g/hour at the 
same temperature and nitrogen was added to adjust the whole pressure in a 
reaction system at 30 kg/cm.sup.2 G, a distillate was withdrawn, at a rate 
equivalent to the flow rate of water, from the top of the reaction 
apparatus. This procedure was carried out for 2 hours and a half. The 
total distillate amount was about 10 times as much as the amount of 
2,6-NDCA in the solution. Then, the solution was filtered under pressure 
at the same temperature to obtain a crystal of 2,6-NDCA, and the crystal 
of 2,6-NDCA was washed with water and with acetic acid and dried at 
120.degree. C. for 5 hours, to give 44.5 g of a purified 2,6-NDCA having a 
composition and a hue shown in Table 9. The recovery of the 2,6-NDCA after 
all the procedures was 90.8%. The so-obtained purified 2,6-NDCA had a 
remarkably improved hue and contained almost no organic impurities. 
Example 15 
The same procedures for crystallization and distilling off TEA as those in 
Example 14 were repeated except that 100 g of the acetonitrile solution 
containing 10 wt % of water was replaced with 100 g of an acetonitrile 
solution containing 5 wt % of water. As a result, 46.2 g of a purified 
2,6-NDCA having a composition and a hue shown in Table 9 was obtained. The 
recovery of 2,6-NDCA-TEA obtained by the crystallization was remarkably 
high, as high as more than 99%, and the recovery of the 2,6-NDCA after all 
the procedures was 94.3%. 
Example 16 
The same procedures for crystallization and distilling off TEA as those in 
Example 14 were repeated except that 100 g of the acetonitrile solution 
containing 10 wt % of water was replaced with 100 g of an acetonitrile 
solution containing 20 wt % of water. As a result, 41.3 g of a purified 
2,6-NDCA having a composition and a hue shown in Table 9 was obtained. The 
recovery of 2,6-NDCA-TEA obtained by the crystallization was 88.6%, and 
the recovery of the 2,6-NDCA after all the procedures was 84.2%. 
Example 17 
The same procedures for crystallization and distilling off TMA as those in 
Example 14 were repeated except that 50 g of TEA was replaced with 29.3 g 
(1.07 equivalent weights based on 2,6-NDCA) of TMA. As a result, 44.1 g of 
a purified 2,6-NDCA having a composition and a hue shown in Table 9 was 
obtained. The recovery of the 2,6-NDCA-TEA was 90.1%. 
TABLE 9 
______________________________________ 
Organic Ex. 14 Ex. 15 Ex. 16 
Ex. 17 
substances (%) (%) (%) (%) 
______________________________________ 
2,6-NDCA 99.978 99.966 99.979 
99.974 
2-NA 0.000 0.000 0.000 0.000 
2,6-MNA 0.000 0.000 0.000 0.000 
TMAC 0.000 0.000 0.000 0.000 
2,6-FNA 0.000 0.001 0.000 0.000 
L.E. 0.002 0.004 0.002 0.002 
Br-2,6-NDCA 0.000 0.001 0.000 0.000 
NTCA 0.000 0.003 0.000 0.003 
H.E. 0.020 0.025 0.019 0.021 
Total 100.000 100.000 100.000 
100.000 
Heavy metal (ppm) (ppm) (ppm) (ppm) 
component 
Co &lt;1.0 &lt;1.0 &lt;1.0 &lt;1.0 
Mn 3.5 4.0 3.0 3.2 
Hue Value (OD.sub.400) 
0.041 0.050 0.039 0.044 
______________________________________ 
Ex. = Example 
Comparative Example 12 
The same procedures for crystallization and distilling off TEA as those in 
Example 14 were repeated except that 100 g of the acetonitrile solution 
containing 10 wt % of water was replaced with 50 g of water. As a result, 
20.1 g of a purified 2,6-NDCA having a composition and a hue shown in 
Table 10 was obtained. The recovery of 2,6-NDCA-TEA obtained by the 
crystallization was very low, as low as 43.2%, and the recovery of the 
2,6-NDCA after all the procedures was 41.0%. 
Comparative Example 13 
The same procedures for crystallization and distilling off TEA as those in 
Example 14 were repeated except that 100 g of the acetonitrile solution 
containing 10 wt % of water was replaced with 100 g of acetonitrile. 
Although these materials were mixed under heat at 100.degree. C., the 
crude 2,6-NDCA was not dissolved at all. No purified 2,6-NDCA was 
obtained. 
TABLE 10 
______________________________________ 
Organic PEx. CEx. 12 CEx. 13 
substances (%) (%) (%) 
______________________________________ 
2,6-NDCA 98.593 99.968 No 
2-NA 0.056 0.001 purified 
2,6-MNA 0.010 0.000 2,6- 
TMAC 0.630 0.000 NDCA 
2,6-FNA 0.263 0.002 was 
L.E. 0.097 0.004 obtained. 
Br-2,6-NDCA 
0.165 0.000 
NTCA 0.164 0.000 
H.E. 0.022 0.025 
Total 100.000 100.000 
Heavy metal 
(ppm) (ppm) (ppm) 
component 
Co 3,400 &lt;1.0 
Mn 2,400 3.2 
Hue value 0.930 0.045 
(OD.sub.400) 
______________________________________ 
Ex. = Example