JPH107621A - Method for producing carboxylic acid ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a carboxylic acid ester, wherein the ester yield is good, the titanium elution from the catalyst is small, and the catalyst can be reused. SOLUTION: When a carboxylic acid ester is produced by reacting a carboxylic acid and / or an anhydride thereof with an alcohol, a partial hydrolyzate of an alkoxysilane and / or a silicon halide is mixed with a hydrolyzable titanium compound. Of a carboxylic acid ester using a silica titania catalyst prepared by hydrolyzing carboxylic acid in the presence of a basic catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a carboxylic acid ester. More specifically, the present invention relates to a method for producing a carboxylic acid ester used as a plasticizer such as a vinyl chloride resin or a vinyl acetate resin.

[0002]

2. Description of the Related Art Conventionally, when a plasticizer such as dialkyl phthalate is industrially produced by esterifying (anhydrous) phthalic acid and an aliphatic alcohol, sulfuric acid and paratoluenesulfonic acid are used as a catalyst for the esterification reaction. And other strong acids and tetraalkyl titanates. In particular, tetraalkyl titanates are widely used because they have less side reactions such as dehydration of alcohols than strong acid catalysts and can provide high-quality carboxylic esters without coloring.

[0003] However, since tetraalkyl titanate is a homogeneous catalyst, there is a problem that it is difficult to separate the product ester from the product. That is, since it is difficult to distill and separate a high boiling point carboxylic acid ester such as dialkyl phthalate, a method of hydrolyzing and depositing the catalyst after the reaction is completed, and then a method of separating by filtration is generally used. However, there has been a problem that the catalyst is not recovered and reused, and the hydrolyzed tetraalkyl titanate becomes a viscous gel, so that it takes a long time for filtration and separation.

To solve such problems, various heterogeneous titanium catalysts such as supported alkyl titanate catalysts and titanium-containing metal oxide catalysts have been proposed. Supported alkyl titanate catalysts are those in which an alkyl titanate is supported using an inorganic compound having a hydroxyl group on the surface as a carrier. For example, JP-A-52-75684 discloses a catalyst in which a tetraalkyl titanate is supported on silica or alumina. Are disclosed. In addition, Japanese Patent Application Laid-Open No. 2-628
No. 49 discloses a methyl titanate catalyst supported on silica magnesia. These catalysts exhibit an activity comparable to that of the homogeneous titanate catalyst, but have a problem in that titanium is eluted because the bond between the carrier and the titanate is weak. Particularly when used in the production of phthalic diesters, which are mainly used as plasticizers for plastic products, the elution of titanium causes a reduction in the volume resistivity of the product, which may adversely affect the quality of the final product such as poor insulation. Is not preferred.

[0005] On the other hand, various studies have been made on the esterification reaction using a titanium-containing metal oxide catalyst, mainly on titania and silica titania. However, in general, the activity is insufficient, and In the case of a catalyst having a high esterification activity, such as titania, it is possible to use the method described in Collect. Cz
ech. Chem. Commun. (1984), 49
(1) As reported in 253, there was a problem that a large amount of titanium was eluted as in the case of the supported alkyl titanate catalyst. In addition, Japanese Patent Application Laid-Open No.
No. 01 discloses that a silica titania catalyst obtained by a method of coprecipitating a titanium compound and a silicon compound under a high acid concentration exhibits high esterification activity, but the activity decreases with time. There is a problem in that occurs.

In the case of such a heterogeneous titanium catalyst,
The compatibility between the catalyst activity (esterification activity, ester yield) and the stability of the catalyst (the amount of titanium eluted) is insufficient, and has not yet reached a level that can be industrially implemented.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a carboxylic acid ester, which has a good ester yield, little titanium elution from the catalyst, and enables the recovery and reuse of the catalyst. It is in.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, when producing a carboxylic acid ester by reacting a carboxylic acid and / or an anhydride thereof with an alcohol, It has been found that the object can be achieved by using a silica titania catalyst obtained by producing the catalyst by a specific production method, and the present invention has been completed.

That is, the gist of the present invention is to provide a method for producing a carboxylic acid ester by reacting a carboxylic acid and / or an anhydride thereof with an alcohol, wherein a partial hydrolyzate of an alkoxysilane and / or a silicon halide is produced. A hydrolyzable titanium compound and a method for producing a carboxylic acid ester characterized by using a silica titania catalyst prepared by hydrolyzing in the presence of a basic catalyst, wherein the silica titania catalyst further comprises A process for producing the above-mentioned carboxylate which is amorphous silica titania containing titanium having a tetrahedral coordination structure, a process for producing the above-mentioned carboxylate wherein the carboxylic acid is phthalic acid, and wherein the alcohol has 4 carbon atoms. The present invention also provides a method for producing the above carboxylic acid ester which is an aliphatic monohydric alcohol of No. 18 to No. 18.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for preparing a silica titania catalyst according to the present invention will be described in detail. The silica titania catalyst of the present invention comprises a two-stage hydrolysis step, a first step of partially hydrolyzing alkoxysilanes and / or silicon halides, and then adding a hydrolyzable titanium compound, It is prepared by a second step of hydrolysis in the presence of a basic catalyst. In order to minimize hydrolysis by moisture in the air, the catalyst is preferably prepared under an atmosphere of an inert gas such as nitrogen.

The alkoxysilanes used in the present invention include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-n-butoxysilane, tetrakis (2-ethoxyethoxy) silane, tetrakis (2-methoxy) Ethoxy) silane, tetrakis (2-ethylbutoxy) silane, tetraphenoxysilane, di-t-butoxydiacetoxysilane and the like. Examples of the silicon halide include tetrachlorosilane, tetrafluorosilane, tri-n-butoxychlorosilane, tri-i-propoxychlorosilane, and the like. Particularly, tetraethoxysilane is preferably used because it is easily available.

In the partial hydrolysis step (first step) of alkoxysilanes and / or silicon halides (hereinafter referred to as “alkoxysilanes and the like”), in order to prevent the hydrolysis from proceeding unevenly, In general, hydrolysis is performed after diluting an alkoxysilane or the like with an alcohol such as ethanol or 2-propanol. As the hydrolysis catalyst, acids such as hydrochloric acid, sulfuric acid, nitric acid and acetic acid or bases such as ammonia, sodium hydroxide, potassium hydroxide and potassium carbonate are used. For uniform hydrolysis, it is preferable to use an acid. The amount of the catalyst used is not particularly limited, but is usually 0.01 to 1 equivalent, preferably 0.05 to 0.5 equivalent, relative to the alkoxysilanes and the like.

The amount of water to be added is less than 4 equivalents, usually 0.5 to 3.5 equivalents, and preferably 1 to 2.5 equivalents to alkoxysilanes and the like. If the amount of water is too small or too large, the dispersion of titanium and silicon at the atomic level in silica titania tends to be nonuniform, and a silica titania catalyst having good stability (less titanium elution amount) cannot be obtained.
By adjusting the amount of water to be added in this way, a partial hydrolyzate such as alkoxysilanes can be obtained. The degree of partial hydrolysis is preferably from 10 to 90%, more preferably from 25 to 65%. If the hydrolysis proceeds excessively, the resulting hydrolysis product is polymerized and an oligomer of silica is formed, so that a stable silica titania catalyst as described above cannot be obtained.

Examples of the hydrolyzable titanium compound (hereinafter simply referred to as “titanium compound”) include, for example, tetramethyl titanate, tetraethyl titanate, tetra-n
Alkyl titanates such as -propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-t-butyl titanate, tetra-2-ethylhexyl titanate and titanium di-n-butoxide (bis-2,4-pentane And titanium diketonates such as titanium oxide (bis-2,4-pentanedionate) and titanium halides such as titanium tetrachloride and titanium trichloride. Preferably, a tetraalkyl titanate having an alkyl group having 4 to 8 carbon atoms, which is easy and inexpensive to use, is used. The molar ratio of the titanium compound / alkoxysilanes is usually 0.1.
1 / 99.9 to 50/50, preferably 1/99 to 10
A range of / 90 is appropriate. If the proportion of the titanium compound is small, the activity of the silica titania decreases, and if it is too large, the dispersion of titanium in the silica titania becomes nonuniform and the stability is lowered, which is not preferable.

The titanium compound is usually dispersed in an alcohol such as ethanol or 2-propanol and then mixed with a partially hydrolyzed alkoxysilane or the like. The mixing method is not particularly limited, but a method in which a titanium compound is gradually added to alkoxysilanes or the like to uniformly disperse titanium and silicon in silica titania is preferable.

The hydrolysis (second step) performed after the addition of the titanium compound is required to proceed in the presence of a basic catalyst in order to obtain a silica titania catalyst having a high esterification activity.

Examples of the basic catalyst include ammonia, ammonium carbonate, urea, sodium hydroxide, potassium hydroxide, potassium carbonate and the like. Ammonia is preferred because it can be easily removed by drying and calcining. When an acidic catalyst is used in the above partial hydrolysis, the amount of the basic catalyst is usually 1.1 to 5 of the acidic catalyst.
The equivalent is preferably double equivalent, preferably 1.5 to 3 equivalents. When a basic catalyst is used, the reaction system is basic, so that it is not necessary to newly add a basic catalyst. The amount of water used for the hydrolysis is usually 0.25 to 100 equivalents, preferably 2 to 10 equivalents, based on the total amount of the titanium compound and the alkoxysilanes. If the amount of water is small, the formation of a crosslinked structure of silica titania by hydrolysis becomes insufficient, and the stability of the silica titania catalyst decreases. In addition, even if a large amount of water is used, there is no particular advantage because only the load of the subsequent filtration step increases. By adding the above amount of water,
The degree of hydrolysis (second step) is theoretically 100%, but in fact, there are sites that are taken into the inside of the crosslinked structure during the process of forming the crosslinked structure and are not easily susceptible to hydrolysis. Usually, it is about 95% to 99%. Usually, it is convenient and convenient to add the basic catalyst to the system in the form of an aqueous solution. However, the aqueous solution may be further diluted with an alcohol such as ethanol or 2-propanol.

The sol-form silica titania gradually gels due to hydrolysis in the presence of a basic catalyst and subsequent dehydration condensation. For aging of gel, usually 15 ~
It is good to leave at a temperature of 50 ° C. for 1 to 14 days. The gel thus formed is filtered, washed and dried by a conventional method,
Further, calcination is performed in air as needed. The firing temperature is usually from 150 ° C to 800 ° C, particularly preferably from 150 ° C to 400 ° C.

According to the above-mentioned preparation method, a silica titania catalyst suitable for producing a carboxylic acid ester can be obtained. The silica titania catalyst thus prepared is amorphous, and mainly contains titanium having a tetrahedral coordination structure. If the titanium has a tetrahedral coordination structure instead of an octahedral coordination structure, excellent esterification activity is provided. Titanium having such a tetrahedral coordination structure is XANE
S (X-ray Absorption NearEd)
The peak is detected as a pre-edge portion (a portion immediately before a portion where X-ray absorption greatly changes) in a spectrum (ge Structure: structure near the X-ray absorption edge).

Next, a method for producing a carboxylic acid ester using the catalyst of the present invention will be described. The carboxylic acid and / or its anhydride are mixed with the alcohol under an inert gas atmosphere, and the silica titania catalyst obtained as described above is added thereto.
７760 mmHg, set according to the vapor pressure of the alcohol used. ) At a temperature of 60-250 ° C., preferably 100
The esterification reaction is performed at a temperature of 220 ° C. The generated water is removed from the reaction system by azeotropy with the alcohol. At this time, it is also possible to use an azeotropic agent such as toluene.

The carboxylic acid in the present invention includes benzoic acid, toluic acid, α- and β-naphthoic acid, o-, m-
-And monovalent aromatic carboxylic acids having 7 to 30 carbon atoms such as p-ethylbenzoic acid, o-, m- and p-phenylbenzoic acid; and aliphatic divalent acids such as adipic acid, azelaic acid and sebacic acid. Carboxylic acid, phthalic acid, isophthalic acid,
And aromatic polycarboxylic acids such as terephthalic acid, trimesic acid, trimellitic acid, and pyromellitic acid. Particularly, (phthalic anhydride), (trimellitic anhydride), and adipic acid are useful as a raw material of the plasticizer and are preferably used in the present invention.

Examples of the alcohol include methanol, ethanol, propanol, isopropanol, n-butanol, t-butanol, isoamyl alcohol, n-hexanol, 2-ethylhexanol, n-octanol, n-decanol, isodecanol, 2-octanol and lauryl. Examples include aliphatic saturated monohydric alcohols such as alcohol and stearyl alcohol, and aliphatic polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, trimethylolpropane, sorbitol, glycerol, and pentaerythritol. Further, a mixture of these alcohols may be used. Among them, 4 to 4 carbon atoms
A single or mixture of the ten aliphatic saturated monohydric alcohols is useful as a raw material for the plasticizer. In particular, the above-mentioned carboxylic acid esters obtained from phthalic acid (anhydride), trimellitic acid (anhydride) or adipic acid and the above-mentioned alcohols alone or in a mixture are preferably used as a plasticizer.

In such a case, the molar ratio of alcohol / carboxylic acid (including its anhydride) is usually from 1/1 to 10 /.
1, preferably in the range of 2/1 to 5/1. If the value of the molar ratio is too small, the conversion of carboxylic acid and / or its anhydride into an ester is difficult to increase, while if the value is too large, the amount of unreacted alcohol increases and burdens the circulation system. This is not desirable.

The silica titania catalyst can be easily separated from the product by filtration, and the separated catalyst can be reused as it is. Therefore, the esterification reaction can be carried out not only by a batch method but also by a continuous method.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof.

Example 1 (Preparation of silica titania catalyst) Under a nitrogen atmosphere, 60.6 g (291 mmol) of tetraethoxysilane and 150 ml of ethanol were weighed into a separable flask (1 liter) and stirred at room temperature at 300 rpm. Then, an alcoholic dilute hydrochloric acid solution (3
3.03 g of 5 wt% hydrochloric acid, 10 g of demineralized water, ethanol 2
0 ml) with a dropping funnel over 30 minutes to partially hydrolyze tetraethoxysilane. After stirring for further 30 minutes, a mixture of 3.06 g (9 mmol) of tetra-t-butyl titanate and 20 ml of ethanol was added dropwise over 30 minutes. After stirring was continued for further 30 minutes, a mixed solution of 3 ml of 28 wt% ammonia water and 20 ml of demineralized water was added over 30 minutes to carry out hydrolysis (second step) to gel.
Then, the gel was aged by standing still for 10 days. The obtained precipitate was separated by filtration, washed with water until chloride ions and ammonium ions were not detected in the filtrate, and dried under reduced pressure at 70 ° C. The obtained solid was pulverized using a milk stick until it passed through a JIS 50 mesh sieve, and calcined at 200 ° C. for 3 hours under an air stream to obtain 18.1 g of silica titania. In addition, the XANES spectrum of this silica titania (Ti K
-Edge) (a situation in which titanium atoms absorb X-rays and emit K-shell electrons), a peak was detected at the pre-edge portion (around 4.962 keV) as shown in FIG. It was found to contain titanium with a body coordinated structure.

(Synthesis of carboxylic acid ester (dioctyl phthalate)) In a flask equipped with a stir bar, a thermometer, a reflux tube, and an ester tube, 37 g (0.25 mol) of phthalic anhydride and 81.4 g of 2-ethylhexanol ( 0.625
Mol) was added thereto, and the mixture was kept at 210 ° C. under a normal pressure and a nitrogen atmosphere, and the reaction was carried out for 0.5 hour while removing generated water outside the system. At this time, the conversion of phthalic anhydride was measured by measuring the NMR (nuclear magnetic resonance spectrum analysis: using UNITY-300 manufactured by Varian Inc.), the acid value and the reaction rate by using liquid chromatography (using LC-6A manufactured by Shimadzu Corporation). Rate is 100
%, And the yield of dioctyl phthalate (DOP) was 68%. Then, 4 g of the silica titania catalyst obtained as described above was added, and the mixture was again kept at 210 ° C. for 1 hour at normal pressure, and then gradually reduced in pressure (560 mm).
(Hg for 0.5 hour, 460 mmHg for 0.5 hour, and 360 mmHg for 0.5 hour). The yield of dioctyl phthalate (DOP) was determined by acid value measurement and liquid chromatography, and the yield was 99.7.
%Met. Further, the reaction solution after the completion of the esterification reaction is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES: J
As a result of measurement with an OBINYVON JY-38S type), the amount of titanium eluted was 2.5 ppm.

Example 2 Instead of tetra-t-butyl titanate, tetra-2-
18.3 g of silica titania was obtained in the same manner as in Example 1 except that 5.08 g (9 mmol) of ethylhexyl titanate was used. When a carboxylic acid ester was synthesized in the same manner as in Example 1 using this as a catalyst,
The yield of DOP was 99.0%. The amount of titanium eluted in the reaction solution after the completion of the esterification reaction was 3.0 ppm.

Example 3 Instead of tetra-t-butyl titanate, tetra-n-
18.2 g of silica titania was obtained in the same manner as in Example 1, except that 3.06 g (9 mmol) of butyl titanate was used, and that the obtained silica titania was calcined at 600 ° C. in an air flow. Example 1 using this as a catalyst
When a carboxylic acid ester was synthesized in the same manner as in the above, the yield of DOP was 99.9%. The amount of titanium eluted in the reaction solution after the esterification reaction was 9.7 pp.
m.

Example 4 Instead of tetra-t-butyl titanate, tetra-n-
Except that 3.06 g (9 mmol) of butyl titanate was used and that the obtained silica titania was not calcined, silica titania 18.9 was used in the same manner as in Example 1.
g was obtained. When a carboxylic acid ester was synthesized in the same manner as in Example 1 using this as a catalyst, the yield of DOP was 99.6%. The amount of titanium eluted in the reaction solution after the completion of the esterification reaction was 3.7 ppm.

Example 5 In Example 4, silica titania used after completion of the esterification reaction was recovered by filtration, and the same reaction as in Example 1 was carried out using this as a catalyst. The yield of DOP was 9%.
It was 9.6%. The amount of titanium eluted in the reaction solution after the completion of the esterification reaction was 6.3 ppm.

Comparative Example 1 (When no basic catalyst was used for the preparation of the silica titania catalyst) 60.6 g of tetraethoxysilane under a nitrogen atmosphere
(291 mmol) and 150 ml of ethanol were weighed into a separable flask (1 liter) and stirred at room temperature at 300 rpm. Next, an alcoholic dilute hydrochloric acid solution (35 wt% hydrochloric acid 3.0) prepared in advance was used.
3 g, demineralized water 10 g, and ethanol 20 ml) were added by a dropping funnel over 30 minutes to perform partial hydrolysis. After further stirring for 30 minutes, 3.06 g (9 mmol) of tetra-n-butyl titanate and ethanol 2
0 ml of the mixture was added dropwise over 30 minutes. After stirring was further continued for 30 minutes, 20 ml of demineralized water was added over 20 minutes to carry out hydrolysis (second step). After standing for 1 day, the solvent was distilled off under reduced pressure to gel. The obtained precipitate was washed with water until no chloride ion was detected in the filtrate, and then dried at 70 ° C. under reduced pressure.
The obtained solid was pulverized using a milk stick until it passed through a JIS 50 mesh sieve, and calcined at 600 ° C. for 3 hours in an air stream to obtain 17.2 g of silica titania. A carboxylic acid ester was synthesized in the same manner as in Example 1 using the silica titania obtained as described above as a catalyst, and the yield of DOP was 90.7%. Before the reaction, the XANES spectrum (Ti K-ed
Ge) was measured, and no peak was detected in the pre-edge portion (around 4.962 keV) as shown in FIG.

Comparative Example 2 (In the case where the alkoxysilanes and the like were not partially hydrolyzed at the time of preparing the silica titania catalyst) Under nitrogen atmosphere, 60.6 g (291 mmol) of tetraethoxysilane and 1.71 g (9 mmol) of titanium tetrachloride were used. ) And 200 ml of deionized water were placed in a separable flask (1 liter) and stirred at room temperature at 300 rpm. After stirring was continued for 30 minutes, 10 ml of 28 wt% ammonia water was added to 30 ml.
Over a period of minutes, hydrolysis was carried out. Then, the gel was aged by standing still for 10 days. The obtained precipitate was separated by filtration, washed with water until chloride ions and ammonium ions were not detected in the filtrate, and dried under reduced pressure at 70 ° C. The obtained solid was pulverized using a milk stick until it passed through a JIS 50 mesh sieve, and calcined at 500 ° C. for 3 hours in an air stream to obtain 18.8 g of silica titania. Then, a carboxylic acid ester was synthesized in the same manner as in Example 1 using this as a catalyst, and the yield of DOP was 99.9%.
The amount of titanium eluted in the reaction solution after the completion of the esterification reaction was 25.5 ppm.

Comparative Example 3 (In the case of synthesizing a carboxylic acid ester using a crystalline composite oxide of titanium and silicon as a catalyst) Titanosilicate was synthesized by the method described in US Pat. No. 4,410,501, and this was used as a catalyst. A carboxylic acid ester was synthesized in the same manner as in Example 1 except that
The yield of DOP was 93.2%. The amount of titanium eluted in the reaction solution after the completion of the esterification reaction was 5.0 ppm.

Comparative Example 4 (Synthesis of carboxylic acid ester using titania as catalyst) Synthesis of carboxylic acid ester in the same manner as in Example 1 except that titania (IT-S manufactured by Idemitsu Kosan Co., Ltd.) was used as a catalyst. , The yield of DOP was 97.8.
%Met. The amount of titanium eluted in the reaction solution after completion of the esterification reaction was 21.3 ppm.

[0036]

According to the present invention, a high-quality carboxylate with a low yield and a low level of titanium contamination can be obtained.
The used catalyst can be reused.

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[Procedure amendment]

[Submission date] August 22, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of an XANES spectrum of silica titania prepared and used in Example 1 and Comparative Example 1.

Claims (4)

[Claims] When a carboxylic acid ester is produced by reacting a carboxylic acid and / or an anhydride thereof with an alcohol, a partial hydrolyzate of an alkoxysilane and / or a silicon halide and a hydrolyzable titanium compound are used. Using a silica titania catalyst prepared by hydrolyzing the above in the presence of a basic catalyst. 2. A silica titania catalyst prepared by hydrolyzing a partial hydrolyzate of an alkoxysilane and / or a silicon halide and a hydrolyzable titanium compound in the presence of a basic catalyst is used as a catalyst. An amorphous silica titania containing titanium having a tetrahedral coordination structure.
The method for producing a carboxylic acid ester according to the above. 3. The method for producing a carboxylic acid ester according to claim 1, wherein the carboxylic acid is phthalic acid. 4. The method for producing a carboxylic acid ester according to claim 1, wherein the alcohol is an aliphatic monohydric alcohol having 4 to 18 carbon atoms.