JP2001261617A - Method for producing ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an ester with high productivity. SOLUTION: This method for producing the ester is characterized in that refluxing of an alcohol is stopped when the resultant reactional product liquid has 0.2-3.0 mgKOH/g acid value and the following formula (1) Y>=1.2×104X (1) (wherein X denotes the ratio of unreacted carboxyl groups based on the sum total of the unreacted carboxyl groups and esterified carboxyl groups in the reactional product liquid; and Y denotes the equivalent ratio of the unreacted alcohol to the unreacted carboxyl groups in the reactional product liquid) is satisfied and the distilling off of the alcohol is then carried out in the method for producing the ester comprising reacting an organic acid with the excessive alcohol under refluxing conditions of the alcohol while removing water, producing the ester and then distilling off the unreacted alcohol from the resultant reactional product liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an ester, particularly an ester used as a plasticizer. According to the present invention, high-quality esters can be produced with high productivity.

[0002]

2. Description of the Related Art It is well known that an ester is produced by reacting an organic acid (in the present specification, an organic acid also means an organic acid anhydride) with a monohydric alcohol. It is widely used in various fields such as agents, resin additives, synthetic lubricating oils and adhesives.

There are many known methods for producing esters. One of the typical methods is to react an organic acid with an excess amount of a monohydric alcohol in the presence of a catalyst. A method in which an excess monohydric alcohol is removed from a reaction product solution to obtain an ester. Depending on the physical properties required for the ester, the obtained ester is further subjected to a purification treatment in order to remove the remaining catalyst, unreacted organic acid, and by-product impurities. For example, in a typical method for producing a phthalic ester, which is a general-purpose plasticizer, first, phthalic anhydride and an excess amount of a monohydric alcohol are added to the phthalic anhydride.
The ester is formed by reacting in the presence of a catalyst such as tetraisopropyl titanate. During this reaction, the by-product water is removed by evaporation together with the alcohol. The generated vapor is condensed outside the reactor, the condensate is separated into an aqueous phase and an alcohol phase, and the alcohol phase is refluxed to the reactor. If the reaction rate of phthalic anhydride reaches a predetermined value,
The reflux of the alcohol phase is stopped and the remaining alcohol is distilled off under reduced pressure. The crude ester obtained is decomposed by adding water to decompose the catalyst, further adding an alkaline substance to neutralize the acid component, and then performing steam distillation to remove light boiling components such as odor components and to retain the remaining monovalent compound. Reduce alcohol to a very small amount. Finally, filtration to remove solids gives a high quality phthalate suitable as a plasticizer.

[0004]

One of the problems of the above-mentioned method is that the reaction requires a long time and the productivity is slightly low. In addition, a long reaction time causes a secondary problem that the produced ester is easily colored. Accordingly, an object of the present invention is to provide a method for producing an ester with good productivity. It is a further object of the present invention to provide a method for producing an ester having good productivity and little coloring.

[0005]

According to the present invention, an organic acid and an excessive amount of a monohydric alcohol having 4 to 13 carbon atoms are charged into a reactor, and water produced is evaporated together with the alcohol. Condensation outside the reactor, a reaction is carried out while separating the condensate into an aqueous phase and an alcohol phase and refluxing the alcohol phase to the reactor, and then a method for producing an ester in which the alcohol is distilled off under reduced pressure, The reaction product solution has an acid value of 0.2 to 3.0 mgKOH / g and the following formula (1)
Is satisfied, by stopping the reflux of the alcohol phase and distilling off the alcohol, a high-quality ester can be produced with high productivity.

[0006]

[Equation 4] Y ≧ 1.2 × 10 ⁴ X (1)

(Wherein, X is the ratio of unreacted carboxyl groups to the total of unreacted carboxyl groups and esterified carboxyl groups in the reaction product solution, and Y is unreacted alcohol to unreacted carboxyl groups in the reaction product solution) The equivalent ratio of each is shown)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the reaction itself between an organic acid and a monohydric alcohol can be carried out according to a conventional method. Organic acids used as the reaction raw materials include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid and trimellitic acid, aromatic monocarboxylic acids such as benzoic acid, adipic acid, sebacic acid, azelaic acid, and succinic acid. Or unsaturated aliphatic polycarboxylic acids such as maleic acid, fumaric acid, etc .; and saturated or unsaturated aliphatic monocarboxylic acids such as oleic acid and stearic acid. Also, corresponding anhydrides of the above carboxylic acids such as phthalic anhydride and maleic anhydride are used. In the case of an ester for a plasticizer, a polyvalent carboxylic acid or an acid anhydride thereof is usually used.

As the other raw material, a monohydric alcohol is usually n-butyl alcohol, isobutyl alcohol, secondary butyl alcohol, n-pentyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, A straight-chain or branched-chain alcohol having 4 to 13 carbon atoms such as 2-ethylhexyl alcohol, isooctyl alcohol, isononyl alcohol, n-nonyl alcohol, isodecyl alcohol, n-decyl alcohol, undecyl alcohol, and tridecyl alcohol is used. Can be

[0010] The esterification reaction is usually carried out using a catalyst. For example, an acid catalyst such as sulfuric acid, paratoluenesulfonic acid, and methanesulfonic acid is used. Further, alkyl titanates such as tetraisopropyl titanate, tetrabutyl titanate and tetra-2-ethylhexyl titanate, and organic metal catalysts such as dibutyl tin oxide and butyl tin malate are also used. Among them, it is preferable to use an organic titanium compound represented by an alkyl titanate.

The reaction is carried out in a reactor in which a raw material organic acid and a stoichiometric excess thereof are added, usually 1.0 to the stoichiometric amount.
A 5- to 2.0-fold monohydric alcohol is charged, a catalyst is added thereto, and the mixture is heated to react. Since water produced as a by-product of the reaction hinders the reaction, the water is evaporated together with the monohydric alcohol, and is withdrawn outside the reactor as steam.
The extracted vapor is condensed, and the generated condensate is separated into an aqueous phase and an alcohol phase. The aqueous phase is drained out of the system and the alcohol phase is refluxed to the reactor. The reaction is usually 120-2
The reaction is carried out at 50 ° C., but preferably at 150 to 230 ° C. from the viewpoint of dehydration efficiency and ester quality. Further, in order to maintain the reflux state of the alcohol and promote dehydration, it is preferable to gradually reduce the pressure inside the reaction apparatus as the reaction proceeds.

Conventionally, in order to increase the reaction rate of an acid as much as possible, the acid value of the reaction product is reduced to 0.1 under reflux of the alcohol.
1 mg KOH / g or less, usually an acid value of 0.05 mg KO
A method has been performed in which the reaction is carried out until H / g is reached, and then the reflux of the alcohol is stopped to distill off the remaining alcohol. Therefore, the reaction hardly proceeds during the distillation of the alcohol, and the acid value of the reaction product at the time when the reflux of the alcohol is stopped and the acid value of the reaction product at the time when the distillation of the alcohol is completed. Were almost identical. In some cases, especially when the reaction was performed using an organometallic catalyst, the acid value sometimes increased during the distillation of the alcohol. The esterification reaction is considered to proceed more easily when the amount of water in the system is lower and the equivalent ratio of the alcohol to the acid is larger.Therefore, the esterification reaction is conventionally performed under reflux of the alcohol until the final reaction rate is reached, that is, the dehydration operation. The reaction was performed while performing the reaction.

However, according to the study of the present inventors,
Even in the conventional method, at the end of the reaction, the amount of the reaction is extremely small and the amount of by-produced water is also small. Therefore, even if the alcohol is refluxed, almost no water is removed. That is, most of the generated steam is alcohol, so even if the condensate is condensed by condensing it, the water in the condensate does not separate as an aqueous phase, but returns to the reactor as it is contained in the alcohol. It turned out to come. This means that the reflux operation only causes a loss of energy and does not contribute to the improvement of the conversion. Therefore, at the end of the reaction, to reduce the amount of water in the reactor, it is preferable to distill off the alcohol without reflux.

In the present invention, most of the organic acid at the end of the reaction has reacted, but the reaction has not been completed yet, that is, the acid value of the reaction product solution is 0.20 to 3.0 mgKOH / g, preferably 0.1 to 3.0 mgKOH / g. At the time of 25 to 2.0 mgKOH / g, the reflux of the alcohol is stopped and the distillation of the alcohol is started.
Thereby, the reaction time can be shortened, and the productivity can be improved. Further, since the time during which the reaction product liquid is exposed to high temperature is shortened, the quality of the obtained ester can be improved. In order to fully enjoy the advantages of the present invention, it is particularly preferable to start the distillation of the alcohol when the acid value of the reaction solution is 0.5 mgKOH / g or more. Even if the distillation of alcohol is started at such a high acid value,
If the alcohol is properly distilled off, the acid value can be sufficiently reduced in the process.

In the present invention, the unreacted carboxyl group, the esterified carboxyl group and the unreacted alcohol in the reaction product at the time of starting the distillation of the alcohol have the relationship represented by the following formula (1). It is important that there is.

[0016]

[Equation 5] Y ≧ 1.2 × 10 ⁴ X (1)

(Where X is the ratio of unreacted carboxyl groups to the total of unreacted carboxyl groups and esterified carboxyl groups in the reaction product solution, and Y is unreacted alcohol to unreacted carboxyl groups in the reaction product solution) In other words, since the esterification reaction proceeds while distilling off the alcohol, the higher the unreacted rate of the carboxyl group at the start of the distillation of the alcohol, the higher the equivalent ratio of the unreacted alcohol to the unreacted carboxyl group. It is necessary to keep the ratio high.

Since the esterification reaction proceeds more easily as the equivalent ratio of the unreacted alcohol to the unreacted carboxyl group increases, the unreacted carboxyl group in the reaction product at the time of starting the distillation of the alcohol is converted to the esterified one. The carboxyl group and the unreacted alcohol preferably have a relationship represented by the following formula (2).

[0019]

[Equation 6] Y ≧ 1.5 × 10 ⁴ X (2)

(Wherein, X is the ratio of unreacted carboxyl groups to the total of unreacted carboxyl groups and esterified carboxyl groups in the reaction product solution, and Y is unreacted alcohol to unreacted carboxyl groups in the reaction product solution) In a preferred embodiment of the present invention, the alcohol is distilled off so as to satisfy the following formula (3) in order to further promote the esterification reaction during the distillation of the alcohol. .

[0021]

0.4 × T ₁ /T≦M≦1.2×T ₁ / T (3) 0 <T ₁ ≦ 0.5T

(Where M is the ratio of the alcohol distilled off within ₁ hour to the total unreacted alcohol, and T is the time required to distill off 85% of the total unreacted alcohol) The formula (3) means that the first half of the alcohol distillation is performed so that the alcohol is not rapidly distilled to promote the esterification reaction during the alcohol distillation. That is, when alcohol is rapidly distilled off from the beginning during the distillation, the amount of unreacted alcohol is significantly reduced before the esterification reaction proceeds sufficiently, and the esterification reaction is inhibited. If the amount of alcohol removed in the first half of the distillation is too small, the removal of by-produced water becomes insufficient, and the esterification reaction is also inhibited. In contrast,
If the alcohol is distilled off so as to satisfy the condition of the above formula (3), the esterification reaction proceeds easily during the distillation, and the acid value of the reaction product at the time when the distillation is completed is reduced. As in the conventional method, it can be easily reduced to 0.1 mgKOH / g or less, preferably to about 0.05 mgKOH / g.

The ester obtained by removing the alcohol from the reaction solution can be purified by a known method.
For example, when esterification is performed using an organic titanium compound as a catalyst, water is added to the obtained ester to deactivate the catalyst, and then steam distillation is performed to distill off odor components and remaining unreacted alcohol. After neutralizing the acid content by further treating with an alkaline substance, the solid matter is removed by filtration, whereby a high-quality ester can be obtained.

[0024]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. The acid value and hue were measured according to JIS K-6751.

Example 1 A reactor equipped with a stirrer and an alcohol reflux means for condensing distillate vapor, separating a condensate produced and refluxing an alcohol phase was placed in a reactor equipped with 2-ethylhexanol 97.
5 g (7.5 mol), 444 g (3.0 mol) of phthalic anhydride and 0.6 g of tetraisopropyl titanate were charged, and the esterification reaction was allowed to proceed while heating and refluxing the alcohol at 220 ° C. The acid value of the reaction product liquid is 1.0
The reaction was stopped when 3 mg KOH / g was reached. As a result of analyzing the reaction solution, the ratio (X) of the unreacted carboxyl group to the total of the unreacted carboxyl group and the esterified carboxyl group in the reaction product solution was 0.004. Further, the content of 2-ethylhexanol was 14.5% by weight, and therefore, the equivalent ratio (Y) of the unreacted alcohol to the unreacted carboxyl group was 63.5. The elapsed time from the start of heating to the stop of the reaction was 3 hours and 15 minutes.

The obtained reaction product liquid was divided into three equal parts, and the alcohol was distilled off over 45 minutes while sequentially increasing the degree of vacuum for one of the liquids. The temperature of the reaction solution gradually decreased from 220 ° C. to 180 ° C. The relationship between the distillation time and the amount of alcohol distilled off was as follows.

[0027]

[Equation 8] _{T 1 = 0.1T M = 0.06 T} 1 = 0.3T M = 0.20 T 1 = 0.5T M = 0.44

The properties of the obtained ester were as follows. Acid value 0.040mgKOH / g Hue 10APHA Alcohol content 1.23% by weight

Example 2 The other reaction solution obtained in Example 1 was divided into three equal parts, and the alcohol was distilled off over 40 minutes while gradually increasing the degree of vacuum. The relationship between the distillation time and the amount of alcohol distilled off was as follows.

[0030]

[Equation 9] _{T 1 = 0.1T M = 0.16 T} 1 = 0.3T M = 0.38 T 1 = 0.5T M = 0.68

The properties of the obtained ester were as follows. Acid value 0.072mgKOH / g Hue 20APHA Alcohol content 1.45% by weight

Example 3 The alcohol was distilled off over 40 minutes while gradually increasing the degree of vacuum in the other three equal parts of the reaction product liquid obtained in Example 1. The relationship between the distillation time and the amount of alcohol distilled off was as follows.

[0033]

T ₁ = 0.1 T M = 0.03 T ₁ = 0.3 T M = 0.07 T ₁ = 0.5 T M = 0.15

The properties of the obtained ester were as follows. Acid value 0.063mgKOH / g Hue 10APHA Alcohol content 1.53% by weight

COMPARATIVE EXAMPLE 1 A reaction apparatus equipped with a stirrer and an alcohol reflux means for condensing distillate vapor, separating a condensate produced and refluxing an alcohol phase was placed in a reactor equipped with 2-ethylhexanol 325.
Mol (2.5 mol), 148 g (1.0 mol) of phthalic anhydride and 0.2 g of tetraisopropyl titanate were charged, and the esterification reaction was allowed to proceed while heating and refluxing the alcohol at 220 ° C. The acid value of the reaction product solution is 0.0
The reaction was stopped when it reached 55 mgKOH / g. As a result of analyzing the reaction product liquid, the ratio (X) of the unreacted carboxyl group to the total of the unreacted carboxyl group and the esterified carboxyl group was 0.0001. Also 2
The content of -ethylhexanol was 14.3% by weight, so that the equivalent ratio (Y) of unreacted alcohol to unreacted carboxyl groups was about 2500. The elapsed time from the start of heating to the stop of the reaction was 4 hours and 35 minutes. While gradually increasing the degree of reduced pressure of the obtained reaction solution, 30
The alcohol was distilled off over a period of minutes. The relationship between the distillation time and the amount of alcohol distilled off was as follows.

[0036]

T ₁ = 0.1 T M = 0.07 T ₁ = 0.3 T M = 0.23 T ₁ = 0.5 T M = 0.45

The properties of the obtained ester were as follows. Acid value 0.0038 mgKOH / g Hue 25 APHA Alcohol content 1.35% by weight Compared with Example 1, the reaction proceeded to almost the final reaction rate under alcohol reflux, so the reaction time was long and the hue was deteriorated. .

Example 4 2-Ethylhexanol 286 was added to a reactor equipped with a stirrer and an alcohol reflux means for condensing distillate vapor, separating the condensate produced and refluxing the alcohol phase.
g (2.2 mol), 148 g (1.0 mol) of phthalic anhydride and 0.2 g of tetraisopropyl titanate were charged, and the esterification reaction was allowed to proceed while heating and refluxing the alcohol at 220 ° C. The acid value of the reaction product solution is 0.3
The reaction was stopped when 2 mg KOH / g was reached. As a result of analyzing the reaction product solution, the ratio (X) of the unreacted carboxyl group to the total of the unreacted carboxyl group and the esterified carboxyl group was 0.0011. Further, the content of 2-ethylhexanol was 6.98% by weight, and therefore, the equivalent ratio (Y) of the unreacted alcohol to the unreacted carboxyl group was 92. The elapsed time from the start of heating to the stop of the reaction was 4 hours and 5 minutes. With respect to the obtained reaction solution, alcohol was distilled off over 35 minutes while sequentially increasing the degree of vacuum. The relationship between the distillation time and the amount of alcohol distilled off was as follows.

[0039]

[Number 12] _{T 1 = 0.1T M = 0.09 T} 1 = 0.3T M = 0.25 T 1 = 0.5T M = 0.49

The properties of the obtained ester were as follows. Acid value 0.045mgKOH / g Hue 15APHA Alcohol content 1.02% by weight

Comparative Example 2 Phthalic anhydride and 2-ethylhexanol were reacted in exactly the same manner as in Example 4, and the acid value of the reaction solution was 0.984.
The reaction was stopped when mg KOH / g was reached. As a result of analyzing the reaction product solution, the ratio (X) of the unreacted carboxyl group to the total of the unreacted carboxyl group and the esterified carboxyl group was 0.0035. Also 2
The content of -ethylhexanol was 6.92% by weight, so that the equivalent ratio (Y) of unreacted alcohol to unreacted carboxyl groups was about 30. The elapsed time from the start of heating to the stop of the reaction was 3 hours and 50 minutes. About the obtained reaction liquid, alcohol was distilled off for 35 minutes in the same manner as in Example 4. The relationship between the distillation time and the amount of alcohol distilled off was as follows.

[0042]

[Number 13] _{T 1 = 0.1T M = 0.09 T} 1 = 0.3T M = 0.28 T 1 = 0.5T M = 0.53

The properties of the obtained ester were as follows. Acid value 0.124mgKOH / g Hue 20APHA Alcohol content 1.02% by weight

Compared with Example 4, the acid value is inferior to that of Example 4 because the equivalent ratio of alcohol to acid at the start of alcohol distillation is too small.

Claims (4)

[Claims] 1. An organic acid and an excessive amount thereof having 4 to 4 carbon atoms.
The monohydric alcohol of No. 13 was charged into the reactor, the produced water was evaporated together with the alcohol and condensed outside the reactor, the condensate was separated into an aqueous phase and an alcohol phase, and the alcohol phase was refluxed to the reactor. In the method for producing an ester, wherein the alcohol is distilled off under reduced pressure, the reaction product solution has an acid value of 0.2 to 3.0 mg KOH / g.
And when the following formula (1) is satisfied, the reflux of the alcohol is stopped and the alcohol is distilled off. [Formula 1] Y ≧ 1.2 × 10 ⁴ X (1) (in the formula, X is an unreacted carboxyl group based on the total amount of unreacted carboxyl groups and esterified carboxyl groups in the reaction product solution) , Y indicates the equivalent ratio of unreacted alcohol to unreacted carboxyl groups in the reaction product liquid) 2. The reaction product solution has an acid value of 0.25 to 2.0 m.
When gKOH / g and the following formula (2) are satisfied,
The method for producing an ester according to claim 1, wherein the reflux of the alcohol is stopped to distill off the alcohol. Y ≧ 1.5 × 10 ⁴ X (2) (where X is an unreacted carboxyl group relative to the total of unreacted carboxyl groups and esterified carboxyl groups in the reaction product solution) , And Y represents the equivalent ratio of unreacted alcohol to unreacted carboxyl groups in the reaction product liquid.) 3. The distillation of alcohol such that the amount of alcohol distilled out of the system within T ₁ hour from the time when the reflux of alcohol is stopped and the distillation of alcohol is started, satisfies the following formula (3). 3. The method for producing an ester according to claim 1, wherein the ester is removed. ## EQU3 ## 0.4 × T ₁ /T≦M≦1.2×T ₁ / T (3) 0 <T ₁ ≦ 0.5T (where T is the reaction product liquid) 85 of all unreacted alcohol
%, Where M is the ratio of alcohol distilled off within ₁ hour to the total unreacted alcohol. ) 4. The organic acid according to claim 1, wherein the organic acid is a polycarboxylic acid or a polycarboxylic anhydride.
The method for producing an ester according to any one of the above.