JP3502430B2 - Purification method of dialkyl naphthalene dicarboxylate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying crude naphthalenedicarboxylic acid dialkyl ester obtained by esterifying naphthalenedicarboxylic acid (hereinafter sometimes abbreviated as NDCA) in alkyl alcohol. More specifically, the present invention relates to a method for purifying a crude ester, which comprises efficiently removing sulfuric acid or organic sulfonic acid used as a catalyst for an esterification reaction from the crude ester.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to a method for purifying dimethyl naphthalenedicarboxylic acid, which is useful as a raw material for highly functional polyesters. NDCA and its ester (hereinafter sometimes abbreviated as NDM) are substances useful as polymer materials, dye intermediates, and the like. Especially 2,6
Polyethylene naphthalate formed from -NDM and the like and ethylene glycol is more excellent in heat resistance and breaking strength than polyethylene terephthalate, and is attracting attention as a material for films, food packaging materials and the like. Furthermore, since polybutylene naphthalate resin has a higher crystallization rate and higher wet heat resistance than polybutylene terephthalate resin, NDM and the like are useful as a resin raw material.

Conventionally, as a method for producing NDCA, there are many methods in which dialkylnaphthalene and / or its oxidized derivative is oxidized with molecular oxygen in a lower aliphatic carboxylic acid solvent using cobalt, manganese, bromine or the like as a catalyst. Proposed.

Since the naphthalene ring is highly oxidizable unlike the benzene ring, many impurities and condensates such as the formation of trimellitic acid accompanying the cleavage of the aromatic ring are often by-produced.
Therefore, high-purity NDCA cannot be obtained only by the oxidation reaction, and it is usually purified by reacting with methanol in the presence of an acid catalyst such as sulfuric acid to form a dimethyl ester. As a method for purifying NDM, vacuum distillation or a method combining vacuum distillation and recrystallization (Japanese Patent Application Laid-Open No. 4-54152).
JP-A No. 2-96550) and a recrystallization method using an alkyl halide as a solvent are known.

By combining the methods as described above, the organic impurities in the finally obtained NDM can be reduced to a level which can be used for the production of polyethylene naphthalate, but the only problem is that this NDM is Since it is slightly colored, it is difficult to reach a satisfactory level of hue.

The inventors of the present invention have conducted extensive research into this cause, and found that the cause of slight coloration of the purified NDM is
It was clarified that sulfuric acid or organic sulfonic acid, which is generally used as a catalyst for the esterification reaction of NDCA and alkyl alcohol, remains in purified NDM, which causes a coloring phenomenon.

As a measure for avoiding this problem, a means of carrying out the esterification reaction of NDCA without using a catalyst can be considered. In this case, in order to obtain a desired reaction result, the reaction conditions have to be high temperature and high pressure, and the reaction time is long, so that the NDM production method is not only safe but economical. It is hard to say that it is realistic.

On the other hand, it is possible to use metal sulfates such as aluminum sulfate and titanium sulfate as a catalyst capable of preventing the inclusion of sulfonic acid during distillation. However, these metal sulfates have a high unit price and the recovery process Because you will also need
It must be said that use on an industrial scale is extremely unrealistic.

[0009]

The object of the present invention is to eliminate such a situation by using naphthalene dicarboxylic acid as an esterification catalyst in the presence of sulfuric acid or organic sulfonic acid.
When the slurry of the crude naphthalene dicarboxylic acid dialkyl ester obtained by esterification in alkyl alcohol is subjected to solid-liquid separation, and the resulting crude ester is purified by recrystallization in alkyl alcohol and distillation of the recrystallized product, purified ND
It is an object of the present invention to provide a purification method in which the concentration of sulfonate ion in the purified product by distillation is set to 10 ppm or less so that the hue of M reaches a good level.

[0010]

[Means for Solving the Problems] The inventors of the present invention conducted extensive studies to establish the above method, and esterified in an alkyl alcohol in the presence of sulfuric acid or an organic sulfonic acid using naphthalene dicarboxylic acid as an esterification catalyst. When the crude naphthalene dicarboxylic acid dialkyl ester obtained as described above is purified by recrystallization in an alkyl alcohol and distillation of the recrystallized product, solid-liquid separation of the crude ester and the recrystallized cake produced under conditions satisfying the following formula (I): If the distillation is carried out after carrying out, the concentration of sulfonate ions in the distilled NDM will be 1
It was found to be 0 ppm or less, whereby the occurrence of a coloring phenomenon with respect to distilled NDM can be avoided, and the hue of distilled NDM can be remarkably improved, and the present invention was completed.

[0011] A / 100 × B / 100 ≦ 0.08 (I) However, A: Liquid content of produced crude ester B: Liquid content of cake after recrystallization

That is, according to the present invention, crude naphthalenedicarboxylic acid dialkyl ester obtained by esterification in alkyl alcohol in the presence of sulfuric acid or organic sulfonic acid using naphthalenedicarboxylic acid as an esterification catalyst is recrystallized in alkyl alcohol. This is a method for purifying NDM in which, when the recrystallized product is purified by distillation, the crude ester produced and the recrystallized cake are subjected to solid-liquid separation under conditions satisfying the above formula (I) and then subjected to a distillation step.

The present invention will be described in detail below. The NDCA used as the esterification raw material in the present invention may be obtained by any method, but for example, NDCA obtained by oxidizing the aforementioned dialkylnaphthalene, or naphthalene monocarboxylic acid and / or 2,6-form The 2,6-form obtained by thermal disproportionation and / or thermal rearrangement by the so-called Henkel reaction of NDCA other than the above is used.

In the esterification reaction of the present invention, methanol is usually used as the alkyl alcohol. As the esterification catalyst, sulfuric acid or an organic sulfonic acid such as benzenesulfonic acid or paratoluenesulfonic acid is preferable, but sulfuric acid is most preferable from the economical point of view. In this case, the amount of the esterification catalyst used is preferably 1 to 10% by weight with respect to NDCA.

The esterification reaction temperature may be above or below the critical temperature of methanol (240 ° C.). Of course, it is preferable to keep the reaction pressure below the critical temperature and to keep methanol in the liquid phase. The methanol used for the esterification reaction is usually NDCA.
To at least 2 times by weight, preferably 3 to 10 times by weight. In this case, the esterified product is taken out as a methanol solution, so after cooling to a predetermined temperature,
Crude NDM can be obtained by solid-liquid separation.

The esterification reaction may be carried out continuously or batchwise. Further, the reaction time is preferably as short as possible within the range where a desired esterification rate is obtained. If the reaction time is too long, the by-product of dimethyl ether increases, which is not preferable. Esterification rate is 8
0% or more, preferably 90% or more, more preferably 95
% Or more.

After the above esterification reaction, the slurry taken out is subjected to solid-liquid separation by filtration, sedimentation or the like to obtain crude N.
DM can be obtained.

The recrystallization solvent used in the present invention is a solvent whose boiling point at normal pressure is lower than the heating end temperature at the time of recrystallization,
It is preferable to use methanol used for the esterification reaction as a recrystallization solvent. Further, the charging amount is the larger of the amount necessary for enhancing the sufficient refining effect or the amount necessary for handling the slurry, and is at least 2 times the weight of the produced crude ester, preferably 3 to 10 weights. Doubles are used.

[0019]

According to the method of the present invention, the amount of the esterification catalyst (sulfuric acid or organic sulfonic acid) remaining in the purified ester is 10 ppm or less, and the purification is performed while avoiding the coloration of the purified NDM. The NDM can be colorless. In addition, purified NDM having excellent quality can be obtained.

[0020]

EXAMPLES The present invention will be specifically described below based on examples. The parts and% in the examples and comparative examples represent parts by weight and% by weight, respectively. The quality composition was measured using a gas chromatograph, an ion chromatograph, a spectrophotometer and a neutralization titrator.

Example 1 <Esterification> A Hastelloy autoclave equipped with a stirrer was charged with 250 parts of crude 2,6-naphthalenedicarboxylic acid, 1500 parts of methanol, 12 parts of 98% sulfuric acid, and sealed (reaction pressure 20 to 25 kg / cm ² G)
The mixture was reacted at 160 ° C. for 1 hour under stirring. After cooling to room temperature, the slurry was taken out from the autoclave. The esterification was repeated 3 times. After the extracted slurries were combined, they were filtered under reduced pressure at an absolute pressure of 400 mmHg. The cake liquid content obtained from the change in weight when the cake obtained was dried was 28%.
Met. Table 1 shows the quality after drying the esterification product.
Shown in.

<Purification> The esterified product 25 after the drying
A mixture obtained by adding 1500 parts of methanol to 0 part was placed in an autoclave equipped with a stirrer and heated to 120 ° C. to completely dissolve the ester in methanol. Then 3
After cooling to 0 ° C, the contents were removed from the autoclave. It took 3 hours to cool from 120 ° C to 30 ° C. The content taken out was in the form of a slurry.

Methanol was removed from the slurry by vacuum filtration under an absolute pressure of 400 mmHg. The cake was then dried. The liquid content of the cake obtained from the change in weight before and after drying was 21%. The quality of the cake after drying is shown in Table 1. In this case, the value of the formula (I) is 0.0
It was 59.

This dried ester cake was subjected to a column top pressure of 10 mmH using a regular packing-filled distillation column having 10 theoretical plates.
g (abs), tower top temperature 210 ° C., reflux ratio 0.5-1.
It was distilled batchwise at 0. The initial fraction corresponding to 10% of the feed raw material and the fraction excluding the bottom residue corresponding to 10% are 2,6-
It was collected as a naphthalene dicarboxylic acid dimethyl ester fraction. The quality of this fraction is shown in Table 1. The Hazen of this fraction was 10.

[Comparative Example 1] When the slurry after recrystallization was filtered under reduced pressure, the same operation as in Example 1 was performed except that the slurry was filtered under reduced pressure under an absolute pressure of 500 mmHg. At this time, the liquid content of the cake determined from the weight change before and after drying was 29%. The quality after each operation is shown in Table 2. The Hazen of this fraction was 30. The value of the formula (I) was 0.081.

Example 2 When the slurry after the esterification reaction was filtered under reduced pressure, the same operation as in Example 1 was carried out except that the slurry was filtered under reduced pressure under an absolute pressure of 500 mmHg. At this time, the liquid content of the cake calculated from the weight change before and after drying was 3
It was 5%. The quality after each operation is shown in Table 3. The Hazen of this cut was 20. In this case, the value of the formula (1) was 0.074.

[Comparative Example 2] The same as Example 1 except that the slurry after the esterification reaction was filtered under reduced pressure at an absolute pressure of 500 mmHg and the slurry after recrystallization was filtered under a reduced pressure of 500 mmHg. The same operation was performed. At this time, the liquid content calculated from the weight change before and after drying was 35% in the cake after the esterification reaction and 30% in the cake after recrystallization.
Met. The quality after each operation is shown in Table 4. The Hazen of this fraction was 40. The value of the formula (I) is 0.1.
It was 05.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C07B 61/00 300 C07B 61/00 300 (56) References JP-A-3-271256 (JP, A) JP-A-4-54152 (JP, A) JP-A-6-298705 (JP, A) JP-A-5-339210 (JP, A) JP-A-1-117847 (JP, A) JP-A-50-116461 (JP, A) Kai 50-84467 (JP, A) JP-A-48-96550 (JP, A) Special Table 5-508870 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C07C 67 / 48-67/62 C07C 69/76-69/94

Claims (7)

(57) [Claims] 1. A process for producing a naphthalenedicarboxylic acid dialkyl ester using naphthalenedicarboxylic acid using sulfuric acid or organic sulfonic acid as an esterification catalyst and an alkyl alcohol as an esterifying agent, wherein step 1: esterification of naphthalenedicarboxylic acid In the presence of sulfuric acid or an organic sulfonic acid as a catalyst, esterification is carried out with at least 2 times by weight amount of alkyl alcohol of naphthalenedicarboxylic acid to obtain a crude dialkyl ester of naphthalenedicarboxylic acid, Step 2: of the dialkyl ester and the alkyl alcohol Solid-liquid separation of the slurry by filtration or settling, Step 3: recrystallize the ester in at least twice the amount of the alkyl alcohol to obtain a recrystallized cake, Step 4: add the recrystallized cake Solid-liquid separation from rutile alcohol by filtration or settling, and then step 5: thereafter distilling the recrystallized cake, wherein the cake liquid content at the time of solid-liquid separation in steps 2 and 4 respectively. Solid-liquid separation is performed to satisfy the following formula, and the sulfonic acid concentration in the distilled ester is adjusted to 10 p
A method for purifying a naphthalenedicarboxylic acid dialkyl ester having an excellent hue, which is characterized in that it is pm or less. A / 100 × B / 100 ≦ 0.08 However, A: Liquid content of cake after solid-liquid separation in step 2 (wt%) B: Liquid content of cake in solid-liquid separation at step 4 (wt%) 2. The purification method according to claim 1, wherein the alkyl alcohol used in the esterification reaction is methanol. 3. The amount of alkyl alcohol used in the esterification reaction is 3 to 10 relative to naphthalenedicarboxylic acid.
The purification method according to claim 1, which is in a range of weight times. 4. The purification method according to claim 2, wherein the esterification reaction is carried out at a reaction temperature of 240 ° C. or lower and under a reaction pressure higher than the saturated vapor pressure of methanol at the reaction temperature. 5. The amount of sulfuric acid or organic sulfonic acid used in the esterification reaction is 1 with respect to naphthalene dicarboxylic acid.
The purification method according to claim 1, which is in the range of 10% by weight. 6. The purification method according to claim 1, wherein the alkyl alcohol used for recrystallization is methanol. 7. The purification method according to claim 1, wherein the amount of the alkyl alcohol used for recrystallization is in the range of 3 to 10 times by weight with respect to the naphthalenedicarboxylic acid.