JPH0240654B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing esters. Conventionally, acid catalysts such as sulfuric acid and para-toluenesulfonic acid, and metal catalysts such as metal oxides and organometallic compounds have been used as catalysts for producing esters by reacting carboxylic acids or their anhydrides with alcohols. Widely used. Among metal catalysts, titanium-based compounds are a typical catalyst, and are superior to acid catalysts in that they produce high-quality products with almost no side reactions. Because of the low carbon content, it has been difficult to remove, recover, and reuse the catalyst even though a large amount of catalyst is required. In other words, most titanium-based catalysts are homogeneous catalysts, and conventionally, by adding alkali to the reaction system after the reaction, the unreacted carboxylic acid was neutralized and the homogeneous catalyst was simultaneously hydrolyzed. However, this method did not completely hydrolyze the titanium-based compound;
Moreover, the obtained hydrolysis product is a sticky gel-like substance that is difficult to separate, which causes poor separation of the ester layer and water layer during the neutralization washing process, making operations difficult during ester production. At present, there has been no report on the sufficient recovery and reuse of such catalysts. On the other hand, titanium peroxide and the like are known as titanium-based heterogeneous catalysts, but they have low reaction activity and a catalyst dissolution loss of about 10%, so they cannot be said to be advantageous for industrial use. In view of the above-mentioned drawbacks of the conventional method, the present invention provides a product with excellent quality, and also maintains good reaction activity by mechanically separating the used titanium-based catalyst by making it insolubilized through hydrolysis treatment. The purpose of the present invention is to provide a cost-effective method for producing esters by reusing the hydrolyzed product, and its gist is to provide a method for producing esters from tetraalkyl titanates or esters. A carboxylic acid or its anhydride is reacted with an alcohol using a polymer as a catalyst, and after the reaction, 6% by weight or less of water is added to the reaction system to hydrolyze the catalyst under heating, and then an alkali is added to the reaction system. The hydrolysis product obtained by the above hydrolysis is mechanically separated and recovered from the reaction system before neutralizing the reaction system, and then the reaction system is neutralized by adding an alkali to separate the ester. The invention consists in a method for producing an ester. Preferred examples of the tetraalkyl titanate used in the present invention include those in which the alkyl group has 1 to 14 carbon atoms, more preferably tetrapropyl titanate and tetrabutyl titanate, and the tetraalkyl titanate polymer is Usually, general formula

[Formula] (R is an alkyl group, n is an integer), and those in which the alkyl group has 1 to 14 carbon atoms and n is 1 to 10 are preferably used. Examples of carboxylic acids in the present invention include aromatic polyamboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and trimellitic acid; aliphatic saturated polycarboxylic acids such as adipic acid, sebacic acid, and azelaic acid; For example, maleic acid
Aliphatic unsaturated polycarboxylic acids such as fumaric acid and aliphatic monocarboxylic acids such as oleic acid and stearic acid are used. Among these carboxylic acids or anhydrides thereof, aromatic polyhydric carboxylic acids and acid anhydrides thereof are preferably used, and phthalic acid is particularly preferably used. Examples of the alcohol include aliphatic saturated alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, heptyl alcohol, n-octyl alcohol, 2-ethylhexyl alcohol, and isooctanol. Hydrolic alcohols are used, such as aliphatic polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, and mixtures of these alcohols may also be used. Among these alcohols, aliphatic saturated monohydric alcohols having 1 to 13 carbon atoms are particularly preferably used, and 2-ethylhexyl alcohol is particularly preferably used. In the present invention, the reaction between carboxylic acid or its anhydride and alcohol in the presence of the titanium compound catalyst may be carried out according to conventional methods, usually at a temperature of 170°C or higher. . In the present invention, water is added in an amount of about 6% by weight or less, that is, about 60 parts by weight or less based on 100 parts by weight of the reaction system, and heated. Before hydrolyzing the titanium compound catalyst and neutralizing the reaction system described later, the hydrolysis product obtained by the above hydrolysis is mechanically separated and recovered from the reaction system. The reason why the amount of water added to the reaction system is about 6% by weight or less is because if it exceeds about 6% by weight, the activity of the separated and recovered hydrolysis product will decrease when it is used as a catalyst. Furthermore, if the amount of water added is too small, it will be difficult to hydrolyze the catalyst or separate the hydrolysis products, so the amount of water added is usually 0.1% by weight or more, preferably 0.5% by weight or more based on the reaction system. be done. Generally, the heating temperature during hydrolysis is 60 to 98℃,
Preferably, the temperature is 75 to 98°C and the heating time is 30 minutes or more. As a method for mechanically separating the hydrolyzed product of the catalyst obtained by the above-mentioned hydrolysis from the reaction system, for example, a centrifugal separation method is frequently used. The conditions for centrifuging the above hydrolysis product suspended in the reaction system are usually 2000 to 4000 rpm.
×10 to 30 minutes is sufficient, and it is preferable to discharge the hydrolysis product from the solid discharge port of the centrifuge and the crude ester from the liquid discharge port, but in some cases, The supernatant crude ester after centrifugation may be removed from the reaction system by an operation such as decantation. The hydrolysis product of the catalyst thus obtained may be reused as a catalyst for the next step of esterification reaction with the crude ester still attached between the particles, or it may be reused after being heated and dried. Good too. It is presumed that a part of this hydrolysis product is redissolved in the reaction system in the next step, which is usually at a temperature of 170°C or higher, and performs a catalytic action. To neutralize the reaction system from which the hydrolysis products have been separated and recovered, add an alkaline substance such as caustic alkali or alkali carbonate until the system reaches the neutralization point, or add a pre-calculated amount of alkali required for neutralization. Just add it. The alkaline substance at this time may be a solid substance or an aqueous solution. However, when the reaction system containing hydrolyzed products is neutralized, the alkaline content acts on the hydrolyzed products, reducing the resolubility, that is, the activity, of the recovered catalyst, although the detailed reason is unknown. Therefore, neutralization is performed after the hydrolysis products are separated and recovered as described above. Due to neutralization, a small amount of acidic substances remaining in the reaction system become water-soluble alkali metal salts and migrate into the aqueous phase, so they can be removed from the system by washing with water, etc. From then on, the acidic substances remaining in the reaction system can be removed by conventional methods. Therefore, the ester can be separated and purified. For example, after the above neutralization, the aqueous phase is separated, further washed with water, excess alcohol is removed by distillation, and if necessary, treatment with activated clay or the like is performed. The method for producing esters of the present invention is as described above, and in particular, after the reaction, approximately 6% by weight or less of water is added to the reaction system to hydrolyze the catalyst under heating, and then an alkali is added. Since the above-mentioned hydrolysis products are mechanically separated and recovered from the reaction system before neutralizing the reaction system, an alkali is added to the system after the esterification reaction, and at the same time the catalyst is hydrolyzed, the unreacted carboxylic acid is removed. Compared to the conventional method, in which the catalyst is hydrolyzed completely, the hydrolyzed product is suspended in the reaction system without becoming a sticky gel, making it easier to mechanically separate the product. The reason for this is not clear in detail, but there is almost no decrease in activity when used as a catalyst compared to the original catalyst. The above hydrolysis product is obtained. Therefore, according to the method of the present invention, the amount of catalyst residue contained in the final product obtained by refining can be reduced to an extremely small amount, so that the volume resistivity is sufficiently large, for example, it can be used as a plasticizer to improve quality. By repeatedly using the catalyst separated and recovered from the reaction system, the above-mentioned high-quality ester can be produced at low cost. Examples of the present invention are shown below. The volume resistivity value and the hue Hazen value were measured in accordance with JIS-K-6751 (phthalate ester method), and the content of titanium metal in the crude ester was measured by atomic absorption spectrometry. Example 1 222 g (1.5 mol) of phthalic anhydride, 449 g (3.45 mol) of 2-ethylhexanol, and 4.44 g of tetrabutyl titanate as a catalyst were added to the pressure-resistant glass reactor equipped with an electromagnetic rotary stirrer from 1, and the mixture was stirred under reduced pressure.
The temperature was raised to 190℃. The esterification reaction was carried out at a reaction tank temperature of 190° C. for 90 minutes, and the water produced by the reaction was azeotropically distilled with the alcohol and condensed in a condenser, then the water and alcohol were separated and only the alcohol was refluxed to the reaction system. After completion of the reaction, the acid value of the reaction system, that is, the crude ester, was 0.17, and the amount of dissolved titanium in the crude ester was 90 ppm. 23.8g of water (3.70% by weight) for 644g of crude ester obtained
(crude ester) was added and kept at 90°C for 30 minutes to hydrolyze the catalyst at 90°C. Next, centrifugation was performed at a rotational speed of 3000 rpm for 15 minutes to separate the hydrolysis product of the catalyst from the crude ester, and the supernatant crude ester was taken out of the system by decantation. The amount of dissolved titanium in this crude ester is 1.6 ppm,
More than 99.8% of the catalyst used was recovered. Further, 90 g of a 1% by weight aqueous sodium carbonate solution was added to 600 g of this crude ester, and the unreacted mono-2-ethylhexyl phthalate was neutralized at 90°C for 1 hour to separate the crude ester phase and the aqueous phase, followed by washing with water and steaming. The low fraction was removed by distillation, treated with activated clay and filtered to obtain the final product. The acid value of the obtained product is 0.018, and the titanium content in the product is
0.09 ppm, hue Hazen value was 10, and volume resistivity value (30°C) was 3.30×10 ¹² Ωcm. On the other hand, the total amount of hydrolysis products containing a small amount of crude ester recovered by the above centrifugation was about 10 g.
(dry weight about 3g) as a catalyst, and the same amount of phthalic anhydride and 2-ethylhexanol as above.
When the same esterification reaction as above was carried out at 190°C for 90 minutes, the acid value of the crude ester after the reaction was 0.19. Furthermore, in the same manner as above, water is added to the reaction system after the reaction, the redissolved catalyst is hydrolyzed under heating, the hydrolyzed product is separated and recovered, and the ester is neutralized and purified to obtain the final product. Obtained. The acid value of the product is 0.019, the titanium content is 0.09ppm, the hue Hazen value is 10, and the volume resistivity value (30℃) is 3.29×
It was 10 ¹² Ωcm. Thereafter, the same operation was repeated, and the esterification reaction was carried out a total of four times using the hydrolyzed product obtained as above as a catalyst, but there was almost no decrease in the activity of the catalyst, and the quality was equivalent to that of the originally manufactured product. An ester having the following properties was obtained. Example 2 Tetraisopropyl titanate 4.44 as catalyst
At 190°C in the same manner as in Example 1 except that g was used.
The esterification reaction was carried out for 90 minutes. The acid value of the crude ester obtained was 0.15, and the titanium content was
It was 1090ppm. For 644g of this crude ester
Add 31 g of water (4.8% by weight to crude ester) and
The catalyst was hydrolyzed by keeping it at 80° C. for minutes, and the hydrolysis product of the catalyst was centrifuged under the same conditions as in Example 1. The dissolved titanium content in the obtained clear crude ester was 1.1 ppm, and 99.9% of the catalyst used was recovered. The acid value of the product obtained by neutralizing and refining the above crude ester in the same manner as in Example 1 is 0.013, the titanium content in the product is 0.17 ppm, and the hue Hazen value is
10.The volume resistivity value was 3.10×10 ¹² Ωcm. On the other hand, the acid value of the crude ester obtained by carrying out the esterification reaction in the same manner as in Example 1 using the entire amount of the recovered hydrolyzed product as a catalyst was 0.17. Furthermore, the acid value of the product obtained by refining the crude ester in the same manner as in Example 1 was 0.014, the titanium content in the product was 0.18 ppm, the hue was 10, and the volume resistivity value (30°C) was 3.08× It was 10 ¹² Ωcm. Thereafter, the same operation was repeated, and the esterification reaction was carried out a total of four times using the hydrolyzed product obtained as above as a catalyst, but there was almost no decrease in the activity of the catalyst, and the quality was equivalent to that of the originally manufactured product. An ester having the following properties was obtained. Example 3 4.44g of tetrabutyl titanate polymer represented by the following formula was used as a catalyst. 190℃ in the same manner as in Example 1 except that it was used as
The esterification reaction was carried out for 90 minutes. The acid value of the obtained crude ester was 0.14, and the titanium content was
It was 1166ppm. For 644g of this crude ester
Add 7.7 g of water (1.2% by weight to crude ester) and
The catalyst was hydrolyzed by keeping it at 85° C. for a period of time, and the hydrolysis product of the catalyst was centrifuged under the same conditions as in Example 1. The dissolved titanium content in the obtained supernatant crude ester was 2.4 ppm, and 99.8% of the catalyst used was recovered. The acid value of the product obtained by neutralizing and refining the crude ester in the same manner as in Example 1 is 0.020, the titanium content in the product is 0.10 ppm, and the hue Hazen value is
10.The volume resistivity value was 3.58×10 ¹² Ωcm. On the other hand, the acid value of the crude ester obtained by carrying out the esterification reaction in the same manner as in Example 1 using the entire amount of the above-recovered hydrolysis product as a catalyst was 0.14. Furthermore, the product obtained by refining the crude ester in the same manner as in Example 1 had an acid value of 0.021, a titanium content in the product of 0.12 ppm, a hue Hazen value of 10, and a volume resistivity value (30°C) of 3.56. ×10 ¹² Ωcm. Thereafter, the same operation was repeated and the esterification reaction was carried out a total of four times using the hydrolysis product obtained as above as a catalyst, but there was almost no decrease in the activity of the catalyst.
An ester having the same quality as the originally manufactured product was obtained. Comparative Example 1 An esterification reaction was carried out in exactly the same manner as in Example 1 to obtain crude ester 644 with an acid value of 0.17 and a titanium content of 900 ppm.
I got g. To this crude ester, 96.6 g of water (15.0% by weight) was added and the catalyst was hydrolyzed at 90° C. for 1 hour. The obtained hydrolysis product was prepared in Example 1.
After centrifugation in the same manner as above, the amount of dissolved titanium in the supernatant crude ester was measured and found to be 0.88 ppm. An esterification reaction was carried out at 190°C in the same manner as in Example 1 using the above hydrolysis product as a catalyst.
The acid value of the crude ester is 40.8 when the reaction time is 90 minutes.
(Achieved reaction rate 68.7%), 9.76 in 360 minutes (Achieved reaction rate
92.5%), and compared to Example 1, the activity of the recovered catalyst was significantly decreased. Comparative Example 2 An esterification reaction was carried out in exactly the same manner as in Example 2 to obtain a crude ester with an acid value of 0.15 and a titanium content of 1090 ppm.
644g was obtained. To this crude ester, 51.5 g of water (8.0% by weight) was added and the catalyst was hydrolyzed at 85° C. for 30 minutes. Examples of the obtained hydrolysis products
The mixture was centrifuged in the same manner as in 11 to remove the supernatant crude ester, which was used as a catalyst for the next step. 190 in the same manner as in Example 2 using the above recovered catalyst.
The esterification reaction was carried out at ℃, and the acid value of the crude ester was 36.6 (achieved reaction rate 71.9%) after a reaction time of 90 minutes.
It was 7.68 (achieved reaction rate 94.1%) in 360 minutes, and the activity of the recovered catalyst was significantly decreased compared to Example 2. Comparative Example 3 An esterification reaction was carried out in exactly the same manner as in Example 1 to obtain 644 g of crude ester having an acid value of 0.17 and a titanium content of 900 ppm. To this crude ester, 96.6 g of sodium carbonate water with a concentration of 1% by weight was added and the catalyst was hydrolyzed and unreacted mono-2-ethylhexyl phthalate was neutralized at 90°C for 1 hour.
The obtained catalytic hydrolysis product was centrifuged in the same manner as in Example 1, and the amount of dissolved titanium in the supernatant crude ester was measured and found to be 0.13 ppm. In the same manner as in Example 1 using the above hydrolysis product as a catalyst.
The esterification reaction was carried out at 190°C, and the acid value of the crude ester was 47.2 (achieved reaction rate 63.8%) when the reaction time was 90 minutes, and 15.3 (achieved reaction rate 88.3%) when the reaction time was 360 minutes. Compared to No. 1, the activity of the recovered catalyst was significantly decreased.

Claims (1)

[Claims] 1. A carboxylic acid or its anhydride is reacted with an alcohol using a tetraalkyl titanate or its polymer as a catalyst, and after the reaction, approximately 6% by weight or less of water is added to the reaction system, and the reaction is heated. After hydrolyzing the catalyst, before neutralizing the reaction system by adding an alkali, the hydrolysis product obtained by the above hydrolysis is mechanically separated and recovered from the reaction system, and then the reaction system is neutralized by adding an alkali. A method for producing an ester, which comprises neutralizing the ester and separating the ester. 2. The production method according to item 1, wherein the method for mechanically separating the hydrolysis product from the reaction system is a centrifugation method. 3 Paragraph 1 or 2 in which the carboxylic acid is phthalic acid
Manufacturing method described in section. 4. The manufacturing method according to any one of Items 1 to 3, wherein the alcohol is 2-ethylhexyl alcohol.