JP2003238479A - Method for producing higher alcohol terephthalic acid ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently producing a high-purity higher alcohol terephthalic acid ester. <P>SOLUTION: Dimethyl phthalate is transesterified with a 6-13C higher monohydric alcohol to give the higher alcohol terephthalic acid ester and the content of methyl ester in the obtained higher alcohol terephthalic acid ester is made to ≤1 wt.%. The production of the higher alcohol terephthalic acid ester is attained, for example, by a method for recovering a liquid consisting essentially of methanol by controlling the temperature of vapor distilled at the boiling point of the higher monohydric alcohol or below until the concentration of methyl ester in the reaction system reaches 20-30%, when the concentration of methyl ester reaches not higher than the range, recovering a mixture of distilled methanol and the higher monohydric alcohol in another container while adding the higher monohydric alcohol to the reaction system. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a terephthalic acid ester of a higher alcohol, and more particularly, to various resins, particularly polyvinyl chloride, additives such as plasticizers and processing aids, and base materials for synthetic lubricating oils. The present invention relates to a method for producing a terephthalic acid ester of a higher alcohol suitable as an oil or the like.

[0002]

2. Description of the Related Art A terephthalic acid ester of a higher alcohol is generally produced by direct esterification of terephthalic acid and a higher monohydric alcohol. It took a long time to proceed to a practical level. In order to solve this problem, a method of reacting under pressure has been proposed (JP-A-60-004151),
Even with this method, the reaction time was at least twice as long as when producing an orthophthalic acid ester.

In the production of terephthalic acid, if the transesterification method using dimethyl terephthalate (hereinafter referred to as "DMT") as a starting material is used, it is insoluble in alcohol which is a problem when terephthalic acid is used as a starting material. Although the problem disappeared, the residual methyl ester in the product ester was emerging as a new problem.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a method for efficiently producing a highly pure terephthalic acid ester of a higher alcohol.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventor has found that when a terephthalic acid ester of a higher alcohol is produced by a transesterification method, by-produced methanol is efficiently separated. The present invention has been completed by finding a method of doing so. That is, the gist of the present invention is dimethyl terephthalate (hereinafter abbreviated as "DMT").
And a higher monohydric alcohol having 6 to 13 carbon atoms are transesterified to produce a terephthalic acid ester of a higher alcohol having a methyl ester content of 1% by weight or less in the obtained terephthalic acid ester of a higher alcohol. Exists on the way.

Another aspect of the present invention resides in a method for producing a terephthalic acid ester of a higher alcohol in which methanol produced in the above transesterification reaction is removed by using a distillation column or a partial condenser. Further, another gist of the present invention is that a liquid containing methanol as a main component is controlled by controlling the vapor temperature to be distilled below the boiling point of the higher monohydric alcohol until the methyl ester concentration in the reaction system becomes 20 to 30%. When the methyl ester concentration is less than the above range, the higher monohydric alcohol is added to the reaction system, and the mixture of methanol and higher monohydric alcohol to be distilled is recovered in a separate container. The method for producing a terephthalic acid ester of a higher alcohol described above, wherein the methyl ester content in the obtained terephthalic acid ester of a higher alcohol is 1% by weight or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a terephthalic acid ester of a higher alcohol according to the present invention comprises DMT and 6 to 6 carbon atoms.
It transesterifies with 13 higher monohydric alcohols. Examples of the higher monohydric alcohol used here include linear or branched hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol and other aliphatic alcohols and cyclohexanol, benzyl alcohol and other cyclic alcohols. To be These alcohols may be used alone or in admixture of two or more.

The content of the methyl ester in the terephthalic acid ester of the higher alcohol of the present invention is 1% by weight or less. Such a high-purity ester is prepared by charging DMT and a higher monohydric alcohol into the reaction system either collectively or separately.
If necessary, a catalyst such as tetraalkyl titanate or dibutyltin oxide is used, with stirring at 150 to 250 ° C.
When the reaction is carried out for about 2 to 5 hours, it can be obtained by removing it using a methanol distillation column or a partial condenser produced by a transesterification reaction.

A liquid containing methanol as a main component distills in the initial stage of this exchange reaction, and a liquid containing a higher monohydric alcohol as a main component distills out at the end of the reaction. In a preferred embodiment of the method of the present invention, when these distillates are separated and purified using a partial condenser or a distillation column having a rectification effect, the methyl ester (of dimethyl ester and monomethyl ester) in the reaction system is Until the concentration of (total) becomes 20 to 30%, the temperature of the steam distilled is not higher than the boiling point of the higher monohydric alcohol, preferably 100.
When the liquid containing methanol as the main component is recovered at a temperature of ℃ or less and the concentration of the methyl ester is less than the above range, higher monohydric alcohol is distilled into the reaction system while adding higher monohydric alcohol. The mixed solution containing alcohol as a main component can be collected in a separate container to increase the exchange rate and obtain a highly pure terephthalic acid ester of higher alcohol. The concentration of methyl ester in the reaction system can be determined by conducting a separate preliminary experiment under the same conditions, collecting the reaction solution at regular intervals, and measuring it by gas chromatography or liquid chromatography analysis method to determine the reaction time or distillation. If it is related to the amount of liquid output, etc., control can be performed based on these during operation.

The liquid mixture containing the higher monohydric alcohol as the main component recovered here is circulated to the transesterification reaction step in the continuous process, or charged to the transesterification reactor in the batch process. It can be effectively used by reusing it as alcohol.

[0011]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. <Example 1> A 1 L four-necked flask equipped with a stirrer, a fractionating tube, a condenser, a thermometer and an alcohol dropping device was used for DMT.
1.0 mol (194 g), 2-ethylhexanol 2.
5 mol (325 g) and 0.2 ml of tetraisopropyl titanate were charged, the reaction system was replaced with nitrogen, and the temperature was raised with stirring to start the transesterification reaction.

Two hours after the start of the distillation of methanol, the temperature of the vapor distilled out was 90 ° C.
The amount of distillate up to this time was 55 g, and the reaction liquid temperature was 198 ° C. When the composition of the distillate was analyzed, the amount of methanol contained was 50 g, and the calculated transesterification rate was 78%. The reaction temperature was gradually raised to 220 ° C., and when the distillation rate of alcohol became slow, 2-ethylhexanol was added from an alcohol dropping device. 195 g (1.5 mol) of 2-ethylhexanol was added over 1 hour, and excess alcohol was distilled under reduced pressure to complete the reaction.

As a result of analysis of the obtained reaction solution, methyl-2
The content of -ethylhexyl terephthalate (MOTP) was 0.2% by weight. The reaction solution was further purified by distillation to obtain bis2-ethylhexyl terephthalate (DOTP).
386 g (yield 98.7%) was obtained. The total reaction time from the start of methanol distillation excluding the purification step was 4 hours and 10 minutes. <Example 2> A rectification column having a theoretical plate number of 3 was set in the same apparatus as in Example 1, and the same raw materials and catalysts as in Example 1 were charged. The distilled steam was introduced into the middle stage of the rectification column, methanol was recovered from the upper part of the rectification column, and 2-ethylhexanol was recovered from the bottom, and the recovered 2-ethylhexanol was circulated and used in the reactor. At this time, the steam temperature at the top of the rectification tower is 80
The temperature was controlled below ℃.

Distillation from the top of the rectification column almost stopped within 3 hours from the start of methanol distillation, so the rectification column was removed and vacuum distillation was carried out to promote the exchange reaction of residual methyl ester and to remove excess 2-ethyl ester. Hexanol was recovered. It took 4 hours and 40 minutes by this time. The obtained reaction product liquid was purified by distillation to obtain 387 g of bis2-ethylhexyl terephthalate (DOTP) (yield 99.0%). The content of methyl ester in this ester was 0.7%. Comparative Example 1 1.0 mol of terephthalic acid was added to a 1 L four-necked flask equipped with a stirrer, a cooler, an oil / water separator, and a thermometer.
(166 g), 2-ethylhexanol 2.5 mol (32
5 g) and 0.2 ml of tetraisopropyl titanate were charged, the reaction system was replaced with nitrogen, and the temperature was raised with stirring. Distilled water and 2-ethylhexanol are separated by an oil-water separator,
The reaction temperature is 220 ° C while refluxing ethylhexanol.
The reaction proceeded at atmospheric pressure until the temperature reached. The time required up to this point was 10 hours. In addition, the reaction product water up to this point is 2
It was 9 g, and the calculated reaction rate was 81%.

Subsequently, the reaction was continued for another 6 hours while refluxing 2-ethylhexanol under reduced pressure while maintaining the temperature at 220 ° C. The water produced by the reaction was 34 g, and the reaction rate was 94%. Unreacted terephthalic acid is filtered off from the reaction solution, and DO
2-Ethylhexanol was removed from the filtrate containing TP by distillation, and further purification such as alkali washing and dehydration was performed to obtain 358 g of DOTP. The reaction was carried out for a total of 16 hours, and the yield was 91.6%.

[0016]

By using the method of the present invention, a highly pure terephthalic acid ester of a higher alcohol can be efficiently produced.

Claims (3)

[Claims] 1. Dimethyl terephthalate (hereinafter referred to as "DM
Abbreviated as “T”) and a higher monohydric alcohol having 6 to 13 carbon atoms, and the content of the methyl ester in the terephthalic acid ester of the higher alcohol obtained is 1% by weight or less. A method for producing a terephthalic acid ester of a higher alcohol, which is characterized. 2. The method for producing a terephthalic acid ester of a higher alcohol according to claim 1, wherein the methanol produced by the transesterification reaction is removed using a distillation column or a partial condenser. 3. The concentration of methyl ester in the reaction system is 20 to
Until the temperature reaches 30%, the temperature of the distilled steam is controlled to be equal to or lower than the boiling point of the higher monohydric alcohol to recover a liquid containing methanol as a main component. While adding the dihydric alcohol to the reaction system, the mixture of the distilled methanol and the higher monohydric alcohol was recovered in a separate container, and the content of methyl ester in the terephthalic acid ester of the higher alcohol obtained was 1% by weight.
The method for producing a terephthalic acid ester of a higher alcohol according to claim 2, wherein: