JP2000143585A - Production of dialkyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and efficiently obtain without using any highly corrosive/ toxic substance a dialkyl carbonate useful as a solvent, gasoline additive or the like by reaction between a specific cyclic carbonate and a specific alkyl carboxylic ester in the presence of a catalyst followed by distilling and separating the product. SOLUTION: This compound such as dimethyl carbonate is obtained by reaction between a cyclic carbonate of formula I (R1 is a 2-12C alkylene substitutable with an alkyl(s) or the like, or the like) (pref. ethylene carbonate) and an alkyl carboxylic ester of the formula: Q-(COOR2)n (Q is an aromatic ring substitutable with an alkyl(s) or the like, or the like; R2 is a 1-4C alkyl; (n) is 1-3) (pref. dimethyl terephthalate) in the presence of a catalyst such as titanium tetrabutoxide to form the corresponding dialkyl carbonate of formula II which, in turn, is distilled and separated; wherein the temperature and pressure in the above reaction and distillation are pref. 90-350 deg.C and 0.096-0.106 MPa, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a dialkyl carbonate. More specifically, the present invention relates to a method for producing a dialkyl carbonate simply and efficiently by reacting a cyclic carbonate with an alkyl carboxylate and distilling off the produced dialkyl carbonate.

[0002]

2. Description of the Related Art Dialkyl carbonate is a very useful compound as an intermediate material, a solvent, a gasoline additive, an alkylating agent and the like of a melt transesterification polycarbonate.

[0003] As a method for producing this dialkyl carbonate, a carbonyl oxide method, an alkyl nitrite method,
The transesterification method is known.

As an example of the carbonyl oxide method, Japanese Patent Publication No.
JP-A-169549 discloses a method for producing dialkyl carbonate by introducing carbon monoxide and oxygen into an alcohol liquid phase in the presence of a copper chloride slurry catalyst. The alkyl nitrite method is disclosed in Japanese Patent Application Laid-Open No. 4-89458.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-163, a platinum group metal compound such as platinum and a base metal compound such as iron, for example, palladium chloride and copper (II) chloride are supported in the presence of a solid catalyst supported on a carrier such as activated carbon. This is a method for producing dialkyl carbonate by bringing carbon oxide and alkyl nitrite (alkyl nitrite) into gas phase contact.

As described above, both the carbonyl oxide method and the alkyl nitrite method are oxidation reactions using a chlorine compound, and have a drawback that the corrosion of the device material easily occurs and proceeds. Further, the alkyl nitrite method has a problem that the toxicity and corrosiveness of the alkyl nitrite are extremely high.

On the other hand, the transesterification method is a method for producing a dialkyl carbonate by subjecting a cyclic carbonate and a monohydric alcohol as raw materials to a transesterification reaction by catalytic conversion in the presence of a catalyst. With respect to the transesterification method, JP-A-5-78284, JP-A-6-238165, JP-A-9-77706, and the like have a nitrogen-containing heterocyclic group and a part or all of the nitrogen atom. Various conversion catalysts such as a quaternary salified solid catalyst, a composite oxide of magnesium and a metal other than magnesium, and a carbonate of a rare earth element are also disclosed in JP-A-9-194435 and JP-A-10-194435.
-36322, JP-A-9-278689,
JP-A-9-20727, JP-A-10-36322
Japanese Patent Application Laid-Open Publication No. H11-15095 proposes a continuous manufacturing method.

This transesterification method is a mild method in which the reaction proceeds in a liquid phase without using a highly toxic or corrosive chemical substance as in the above-mentioned carbonyl oxide method and alkyl nitrite method. It has the advantage of high security. On the other hand, the transesterification method has some problems that cannot be neglected in terms of production efficiency. As one of them,
Because the transesterification reaction is a reversible equilibrium reaction, the conversion rate of the starting cyclic carbonate and the yield of dialkyl carbonate cannot be sufficiently increased.

In order to largely bias the reversible equilibrium reaction toward the product, it is effective to use at least one of the raw material components in a large excess or to remove the product out of the reaction system simultaneously with the reaction. . However, in the ester reaction system consisting of the starting material cyclic carbonate and monohydric alcohol, the product dialkyl carbonate and dihydric alcohol (by-product derived from the cyclic carbonate), the starting material-side monohydric alcohol is generally used as a product. Is more volatile than the dialkyl carbonate and dihydric alcohol on the side, it is not possible to remove only the substance on the production side from the reaction system by distillation, and further, the melting point of the substance of the production system in the reaction system stands out. Since it is rarely high, it is impossible to remove the product outside the system by precipitation and crystallization at the same time as the reaction.
Further, the method of using a large excess of the raw material components is extremely low in effectiveness because the amount of heat required for heating and the cost of purification and separation after the reaction are greatly increased.

Another major problem of the transesterification method is that the starting monohydric alcohol and the target product, dialkyl carbonate, form an azeotrope at atmospheric pressure (0.1013 MPa, sometimes referred to as normal pressure hereinafter). There are times when you do. Dimethyl carbonate, which is particularly in demand among dialkyl carbonates
(Hereinafter sometimes abbreviated as DMC) by the transesterification method using methanol.

[0010] For this reason, in the method for producing DMC using the transesterification method, DMC is obtained only as an equilibrium composition mixture with methanol. Even if this mixture is subjected to distillation under atmospheric pressure (hereinafter sometimes referred to as atmospheric distillation), only an azeotropic composition mixture having a weight ratio of DMC to methanol of about 3: 7 can be obtained.

In order to obtain pure DMC, the method for continuously producing dialkyl carbonate described in JP-A-10-36322 described above utilizes the fact that the azeotropic composition changes depending on the pressure during distillation. And DMC under high pressure
Is separated by distillation. However, in these cases, the handling and management of the high-pressure distillation apparatus is very troublesome, and furthermore, including the recovery and purification of unreacted methanol and by-produced ethylene glycol, the distillation treatment using a large number of distillation columns and the complicated processing for that purpose are required. Therefore, there is a problem that the production efficiency is extremely low due to the necessity of a proper liquid circulation.

[0012]

As described above, the conventional method for producing dialkyl carbonate requires the use of highly corrosive and toxic substances or the use of very complicated equipment and processes for separation and purification. Although it is a method that has to sacrifice either safety or production efficiency, the present invention is a simple reaction / purification separation device and process without using highly corrosive and toxic substances, efficient It is an object of the present invention to provide a novel method for producing a dialkyl carbonate.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems of the prior art, and as a result, in the presence of a catalyst such as a metal compound, in particular, a titanium alkoxide catalyst, a cyclic carbonate and a carboxylic acid. When the acid alkyl ester was reacted, it was found that the dialkyl carbonate produced without the azeotropic phenomenon could be separated by distillation from the reaction mixture, and the dialkyl carbonate could be efficiently produced, and the present invention was completed. did.

That is, the object of the present invention is to produce a dialkyl carbonate of the following general formula 3 by a transesterification reaction using a metal compound as a catalyst, wherein a cyclic carbonate of the following general formula 1 and a cyclic carbonate of the following general formula 1 are used as raw materials. 2
Characterized in that the dialkyl carbonate produced using the carboxylic acid alkyl ester is separated by distillation.
This can be achieved by a method for producing a dialkyl carbonate.

[0015]

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[0016]

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[0017]

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(In the above general formula 1, R ₁ is an unsubstituted alkylene group or a phenylene group having 2 to 12 carbon atoms or about 1 to 8 carbon atoms, and a part or all of these hydrogens are substituted. At least one of an alkyl group, an alkoxy group, an aryl group and an aryloxy group;
An alkylene group or a phenylene group in which at least two hydrogens have been substituted. In the general formulas 2 and 3, Q represents (1) an unsubstituted or an alkyl group having about 1 to 8 carbon atoms, an alkoxy group, an aryl group, an aryloxy group, a hydroxy group,
An aromatic ring in which at least one hydrogen is substituted by at least one of halogen and the like; or (2) one or more hydrogens by an unsubstituted or at least one of an alkyl group, an alkoxy group, an aryl group, and an aryloxy group Is a substituted alkyl group or alkoxycarbonyl group. When two or more substituents are present in R1 and Q, they may be the same or different. And R
₂ is an unsubstituted alkyl group having 1 to 4 carbon atoms. Also,
n is a natural number of 1, 2, or 3. )

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. The cyclic carbonate used as a raw material in the present invention is a cyclic carbonate represented by the above general formula 1 and a carboxylic acid alkyl ester represented by the above general formula 2.

Specific examples of the cyclic carbonate represented by the general formula 1 include ethylene carbonate, propylene carbonate, 4-ethyl-1,3-dioxolane-
2-one, 4,5-dimethyl-1,3-dioxolane-
2-one, 4,5-diethyl-1,3-dioxolane-
Examples thereof include 2-one, and among these, ethylene carbonate is preferably used because of availability.

Specific examples of the alkyl carboxylate represented by the general formula 2 include methyl ester,
Ethyl ester, propyl ester, isopropyl ester, n-butyl ester, isobutyl ester, s-
Butyl ester and t-butyl ester,
Carboxylic acid methyl ester is preferable since dimethyl carbonate, which is in most demand, can be obtained by using methyl ester.

Examples of the carboxylic acid methyl ester include oxycarboxylic acids such as benzoic acid and the like, in which hydrogen on the aromatic ring is substituted with an alkyl group or the like, long-chain monocarboxylic acids having 4 or more carbon atoms, Methyl esters of polycarboxylic acids such as dicarboxylic acids typified by acids can also be mentioned.However, when dimethyl esters of dicarboxylic acids are used, polycondensation occurs by transesterification with cyclic carbonate to produce a polymer, especially when dimethyl terephthalate is used. In particular, dimethyl terephthalate is particularly preferable because, in addition to the main purpose dialkyl carbonate, polyethylene terephthalate having a wide range of uses such as fibers, resins, and films can be produced together.

In the present invention, it is particularly important to use carboxylic acid alkyl esters here, and for other esters such as carboxylic acid aryl esters, the diaryl carbonate formed is the most volatile component in the reaction mixture. However, since it cannot be separated by distillation from the system, the equilibrium reaction is not advantageous to the diaryl carbonate side which is the target product, and there is a disadvantage that the production efficiency is low, so that the object of the present invention cannot be achieved.

It is preferable to use one kind of each of the above-mentioned cyclic carbonate and alkyl carboxylate, but depending on the case, it is also possible to use a mixture of two or more kinds as one or both raw materials.

In the present invention, the raw material molar ratio of the cyclic carbonate to the carboxylic acid alkyl ester is from 1: 5 to 5: 1.
Is suitable, and particularly preferably 1: 4 to 4: 1.

In the present invention, the above-mentioned raw materials are introduced into a reactor and reacted in the presence of a catalyst. The catalyst used in the present invention is preferably a metal compound. Examples of the metal compound include alkoxides, hydroxides, acetates, hydrochlorides, carbonates, and organic complexes represented by acetylacetonato complexes of various metals, and those satisfying both reactivity and economic efficiency. Alkoxides are particularly preferred. According to the study of the present inventors, any metal on the periodic table can have a reaction activity as a metal species, but it has been found that titanium is preferable in terms of both safety and economy. That is, in the present invention, the reactivity,
Titanium alkoxides such as titanium tetrabutoxide are particularly preferred as a catalyst that satisfies all economic and safety requirements.

The amount of the catalyst used in the present invention may be an amount generally referred to as a catalyst amount, and is not particularly limited. However, considering the economical efficiency and the residual amount when co-producing a polymer, 0 to the weight of the raw material mixture is considered. It is desirable to select within the range of 0.01 to 1.0% by weight.

The temperature for the reaction and the distillation is in a temperature range in which the dialkyl carbonate can be distilled off at the same time as the reaction and the decomposition of the raw materials and products does not occur, that is, 90 to 350.
C is preferred.

The reaction and distillation in the present invention can be carried out under pressure. However, the reaction and distillation can be carried out in a normal pressure reactor and a distillation apparatus which can be easily handled at or near atmospheric pressure, that is, 0.096 to 0.106 MPa. Reaction enough even under pressure
Since distillation can be carried out, it is preferable to adopt this pressure range from the viewpoint of economy and safety.

In the reaction, a transesterification reaction and distillation separation of the resulting dialkyl carbonate can be carried out simultaneously in one reactor. It is also possible to dare to withdraw the reaction solution and lead it to a separate distillation device where the dialkyl carbonate can be separated by distillation.However, from the economical viewpoint, it is naturally better to carry out the reaction and the distillation and separation simultaneously in one reactor. Much more efficient and desirable.

In the present invention, the desired dialkyl carbonate represented by the above-mentioned general formula 3 is efficiently and efficiently prepared.
Manufactured economically.

[0032]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which by no means limit the present invention.

Example 1 A thermometer, a rectification tube equipped with a Liebig condenser, a stirrer, and a nitrogen inlet tube were installed.
In a 0 ml four-necked flask, add ethylene carbonate 13
2.1 g (1.5 mol, manufactured by Wako Pure Chemical Industries, Ltd.), 97.1 g of dimethyl terephthalate (0.5 mol, manufactured by Teijin Limited) and 0.4 g of titanium tetrabutoxide (1.1 mol.
8 mmol, manufactured by Wako Pure Chemical Industries, Ltd.), distilled off the light-boiling components produced and reacted at 250 ° C. and 0.101 MPa under a nitrogen atmosphere, and condensed the resulting steam with water using a Liebig condenser. The liquid was collected. Two hours after the start of the reaction, the collected liquid was analyzed using a gas chromatograph (GC-390 manufactured by GL Sciences) and a mass spectrometer equipped with a gas chromatograph (No. 5890 and 5971A manufactured by Hewlett-Packard), and the yield of dimethyl carbonate was determined. Was 53%.

Further, it was found that polyethylene terephthalate was formed in the flask although the molecular weight was relatively low.

[0035]

According to the method of the present invention, the cyclic carbonate and the alkyl carboxylate are used as raw materials, and the chemical reaction is carried out by a simple reaction apparatus and reaction process without using a high-pressure distillation apparatus which is difficult to handle or a complicated separation and purification process. Industrially useful dialkyl carbonate can be efficiently produced at low cost.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hideo Hasegawa 77, Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Limited Matsuyama Plant F-term (reference) 4H006 AA02 AC48 AD11 BA10 BA32 BC10 BC11 BC51 BC52 BD70 KA58 4H039 CA66 CD40

Claims (11)

[Claims] 1. A method comprising reacting a cyclic carbonate represented by the following general formula 1 with a carboxylic acid alkyl ester represented by the following general formula 2 in the presence of a catalyst, and distilling and separating the resulting dialkyl carbonate represented by the general formula 3. A method for producing a dialkyl carbonate. Embedded image Embedded image Embedded image (In the general formula 1, R ₁ is an alkylene group or a phenylene group having 2 to 12 carbon atoms, and a part or all of these hydrogens are substituted by an alkyl group, an alkoxy group, an aryl group, or an aryloxy group. In the general formulas 2 and 3, Q is unsubstituted or an alkyl group, an alkoxy group, an aryl group, an aryloxy group,
A hydroxy group, an aromatic ring in which one or more hydrogens are substituted by halogen, or an unsubstituted or alkyl group in which one or more hydrogens are substituted by any of an alkyl group, an alkoxy group, an aryl group, an aryloxy group, or an alkoxycarbonyl group, R ₂ is an alkyl group having 1 to 4 carbon atoms. Further, n is a natural number of 1, 2, or 3. ) 2. The method according to claim 1, wherein the cyclic carbonate represented by the general formula 1 is ethylene carbonate. 3. The method according to claim 1, wherein the carboxylic acid alkyl ester represented by the general formula 2 is a carboxylic acid methyl ester. 4. The method according to claim 3, wherein the alkyl carboxylate represented by the general formula 2 is dimethyl dicarboxylate. 5. The method according to claim 4, wherein the alkyl carboxylate represented by the general formula 2 is dimethyl terephthalate. 6. The method according to claim 1, wherein the catalyst is a metal compound. 7. The method according to claim 6, wherein the metal compound of the catalyst is a metal alkoxide. 8. The method according to claim 6, wherein the metal compound of the catalyst is a compound of titanium. 9. The temperature during the reaction and the distillation is 90 to 90, respectively.
The method according to claim 1, wherein the temperature is in the range of 350 ° C. 10. The pressure during reaction and distillation is 0.096 to
The production method according to claim 1, wherein the pressure is 0.106 MPa. 11. The method according to claim 1, wherein the transesterification reaction and the distillation separation of the resulting dialkyl carbonate are carried out simultaneously in one reactor.