JPS6228942B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an ester by reacting an aromatic carboxylic acid or its anhydride with an alcohol. In the method of producing an ester by reacting an aromatic carboxylic acid or its anhydride with an alcohol in the presence of a catalyst, it is necessary to continuously remove water produced from the reaction system as the reaction progresses. In conventional methods, raw material alcohol is generally used in excess, and reaction product water is azeotroped with the excess alcohol and extracted from the reactor, which is then completely condensed in a condenser, and the condensed liquid is phase-separated to form an aqueous phase. A method was used in which the alcohol phase was separated into an alcohol phase and only the alcohol phase was refluxed into the reactor. However, a considerable amount of water dissolves in the alcohol refluxed in this way, and to prevent this, there is a method in which a certain type of solvent is added as a carrier to reduce the solubility of water in the alcohol phase. cannot be completely prevented, and as a result, the reaction rate is low, especially in the final stage of the esterification reaction, resulting in a disadvantage that it takes a long time to complete the reaction. The present invention solves these drawbacks and provides a method in which water reflux to the reactor is extremely reduced.In a method for producing an ester by reacting an aromatic carboxylic acid or its anhydride with an alcohol, This is a method in which reactor distillate vapor containing reaction product water and alcohol is condensed at a temperature higher than the boiling point of water and lower than the boiling point of alcohol at the internal pressure of the reaction system, and the resulting condensate is returned to the reactor. In the present invention, aromatic carboxylic acids or anhydrides thereof include, for example, phthalic acid, trimellitic acid,
Examples include pyromellitic acid and acid anhydrides thereof. Also, alcohol has a higher boiling point than water,
In particular, alcohols having a boiling point of 130°C or higher under normal pressure are used, such as n-amyl alcohol, i-amyl alcohol, n-hexyl alcohol, heptanol, n-octyl alcohol, 2-ethylhexanol, nonyl alcohol, decyl alcohol, etc. is exemplified. The ester obtained in the present invention can be obtained by reacting the above-mentioned acids and alcohols in appropriate combinations, but the present invention is applicable when producing an ester with a boiling point higher than that of water, especially an ester with a boiling point of 130°C or higher under normal pressure. Yes, it can be applied. In the present invention, the above carboxylic acid or its anhydride and alcohol are reacted by a known method.
In the method for producing ester, the alcohol distilled from the reactor and the water produced by the reaction are heated at a temperature higher than the boiling point of water and lower than the boiling point of alcohol at the internal pressure of the reaction system, especially lower than the temperature at which 90% or more of the charged alcohol condenses. It condenses at a low temperature, and by such means the water content in the condensate can be significantly reduced. The present invention will be explained in more detail with reference to the drawings. The simplest embodiment of the invention is shown in FIG. Here, the vapor distilled from reactor 1 passes through 2 and is transferred to condenser 3.
The condensate, which is mainly alcohol and is cooled to a temperature higher than the boiling point of water and lower than the boiling point of alcohol, is refluxed to the reactor via 4, and the non-condensed vapor, which is mainly water, is discharged to the outside through 5. In Fig. 2, two condensers are installed to recover alcohol escaping into the exhaust gas, and the steam that is not condensed in the primary condenser 3 and is mainly composed of water is guided through 5 to the secondary condenser 6. The condensate is completely condensed at 7, and the condensate is introduced into a phase separator 8 through 7, where the phases are separated.The alcohol phase is returned to the reactor through 9, and the aqueous phase is discharged through 10. In FIG. 1 as well, the condensate may be phase-separated if necessary, and then only the alcohol phase may be returned to the reactor. Although the esterification reaction of the present invention can be carried out without a catalyst, it is more advantageous to use a catalyst. As a catalyst, acidic catalysts such as sulfuric acid and para-toluenesulfonic acid, amphoteric catalysts such as alumina and caustic soda, titanic acid, titanate esters, zinc salts, and tin compounds can be used, and the amount added is 5% by weight based on the raw material carboxylic acid.
The following is sufficient. The reaction temperature is 160℃ when using an acidic catalyst.
The following are preferred. At temperatures above 160°C, the reaction solution may become colored. When no catalyst or an amphoteric catalyst is used, the temperature is preferably 180 to 250°C. At temperatures below 180°C, the reaction rate is slow, and at temperatures above 250°C, the reaction solution may become colored. The molar ratio of alcohol and carboxylic acid is selected so that the alcohol is in excess, and an excess of 10% or more of the theoretical amount is particularly preferred. The reaction pressure may be set at a pressure that maintains the reaction liquid in a liquid phase at the reaction temperature and at the same time allows excess alcohol to reflux. According to the present invention, most of the reaction product liquid generated as the esterification reaction progresses is removed, and the water concentration in the reaction liquid can be kept low, so the reaction rate is increased and the reaction is accelerated compared to conventional methods. It can be completed in a short time. The method of the present invention can be carried out either continuously or batchwise. In the following examples, parts are parts by weight. Example 1 and Comparative Example 1 A raw material liquid consisting of 130 parts of 2-ethylhexanol and 278 parts of mono-2-ethylhexyl phthalate, and a 35% aqueous solution of 0.83% by weight para-toluenesulfonic acid were continuously added to the raw material liquid in a second manner. The mixture was supplied to a reactor as shown in the figure, and reacted at 140°C for a residence time of 50 minutes. Also, the temperature of the primary condenser and the temperature of the secondary condenser
It was kept at 65℃ and 30℃. Reactor pressure 125mmHg (absolute pressure) and 400mmH
g, and the reaction rates were compared. The boiling point of water at 125 mmHg is 56°C, and at 400 mmHg it is 83°C. The reaction results were as shown in Table 1.

[Table] Example 2 and Comparative Example 2 148 parts of phthalic anhydride, 340 parts of linear mixed alcohol having 7 to 9 carbon atoms, 1.2 parts of caustic soda, and 1.2 parts of aluminum hydroxide were charged into a reactor as shown in Fig. 2, and The esterification reaction was carried out in a lower pressure fractional manner. Table 2 shows the reaction rates determined over time when the temperature of the primary condenser was maintained at 130°C and 90°C.

[Table] 〓〓〓〓〓

【table】 [Brief explanation of the drawing]

Figures 1 and 2 show a reaction apparatus used in the method of the present invention. 〓〓〓〓〓

Claims (1)

[Claims] 1. A method for producing an ester by reacting an aromatic carboxylic acid or its anhydride with an alcohol having a boiling point of 130°C or higher under normal pressure,
An ester characterized by condensing reactor distillate vapor containing reaction product water and alcohol at a temperature higher than the boiling point of water and lower than the boiling point of alcohol at the internal pressure of the reaction system, and returning the resulting condensate to the reactor. manufacturing method.