JPH10114716A - Production of dialkyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dialkyl carbonate in a high yield and selectivity by setting pH variability of the reaction liquor at a specified level or lower in the presence of a catalyst when an alcohol is reacted with CO and O2 . SOLUTION: This dialkyl carbonate of the formula is produced by reaction of an aliphatic monoalcohol of the formula ROH (R is a 1-12C aliphatic group) (e.g. CH3 OH, C2 H5 OH) with CO and O2 in the presence of a catalyst. In this case, the pH level of the reaction liquor is set, normally, at >=0 but <14, pref. at 1-10. The pH variation range is set within 1, while the pH variability Q, defined as: Q=d(pHt )/dt((t) is reaction time; pHt is the hydrogen ion exponent of the reaction liquor), is set, normally, at <=3min<-1> , pref. <=2min<-1> . The reaction time is set at 0.001-50 (pref. 0.01-10)h, while the reaction temperature normally at 0-300 deg.C, pref. at 50-200 deg.C. The catalyst to be used is a copper compound such as a copper halide, its concentration being set at 0.001-2mol/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a dialkyl carbonate by reacting an aliphatic monoalcohol, carbon monoxide and oxygen.

[0002]

2. Description of the Related Art Dialkyl carbonate is useful as a raw material for fine chemicals such as various carbonates, carbamates, urethanes, pharmaceuticals and agricultural chemicals, and as a gasoline additive. In particular, it can be used as a substitute for toxic phosgene. Recently, various manufacturing methods have been proposed.

[0003] As a method for producing a dialkyl carbonate, a method of reacting phosgene with an alcohol has been industrially performed. However, this method has drawbacks such as the use of highly toxic phosgene and the reaction of alcohols with phosgene to produce by-products of strongly corrosive hydrochloric acid. As an industrial production method of dialkyl carbonate without using phosgene, a method of reacting an alcohol with carbon monoxide and oxygen in the presence of a catalyst is known. Various proposals have been made for the method, most of which are related to catalysts. The catalyst is VI
A group VIII metal-based catalyst containing a group II metal compound as a main catalyst and a copper-based catalyst containing a copper compound as a main catalyst are roughly classified.

The reaction using a Group VIII metal-based catalyst is described in JP-B-61-8816 and JP-B-61-433.
No. 38, Japanese Unexamined Patent Publication No. 1-287062 and the like. In these methods, a palladium compound is used as a main catalyst, and copper halide or the like is used as a co-catalyst. On the other hand, the reaction using a copper catalyst is described in
No. 11129, Japanese Patent Publication No. 56-8020, Japanese Patent Publication No. 60-58739, and the like. In this reaction, copper halide is usually used as a catalyst.

[0005] In this reaction, water is produced as a by-product. Water in the reaction mixture affects the reaction, such as lowering the yield. To avoid this, a method in which water is used in a specific range of water concentration (JP-A-4-270250, JP-A-7-5347).
No. 5), a method in which a specific water-catalyst ratio is used (Japanese Patent Laid-Open No.
No. 169550) has been proposed. However, even if these methods were used, the yield and selectivity were not always sufficient.

[0006]

The object of the present invention is to eliminate the disadvantages of the previously proposed methods and to reduce the use of oxygen and carbon monoxide in the presence of an aliphatic monoalcohol in the presence of a catalyst. To produce a dialkyl carbonate with high yield and high selectivity by reacting

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when an alcohol is reacted with carbon monoxide and oxygen in the presence of a catalyst to continuously produce a dialkyl carbonate, the reaction liquid It has been found that the reaction proceeds at a high yield and a high selectivity which could not be obtained by the conventional method by setting the pH fluctuation to a certain value or less, and based on this finding, the present invention has been completed. .

That is, the present invention is as follows. (1) In producing a dialkyl carbonate by reacting an aliphatic monoalcohol with oxygen and carbon monoxide in the presence of a catalyst, the pH fluctuation Q defined by the following differential equation
Wherein the reaction is carried out at 3 min ^-1 or less. Q = | d (pH _t ) / dt | (where t represents the reaction time [min] and pH _t represents the hydrogen ion index of the reaction solution at the reaction time t.) (2) The reaction solution is a hydrogen ion buffer. The method for producing a dialkyl carbonate according to 1 above, which has an effect and has a buffering capacity with respect to a hydrogen ion concentration of 0.1 or more. (3) The method for producing a dialkyl carbonate according to the above 1 or 2, wherein the aliphatic monoalcohol is methanol or ethanol. (4) The method for producing a dialkyl carbonate according to the above item 3, wherein the catalyst is a catalyst comprising a copper compound. (5) The method for producing a dialkyl carbonate according to the above (4), wherein the hydrogen ion index is in the range of 0 to 3. (6) The above 1, wherein the pH variation Q is 2 min ^-1 or less.
A process for producing 2, 3, 4 or 5 dialkyl carbonates.

The reason why the production method of the present invention allows the reaction to proceed with higher yield and higher selectivity as compared with the conventional production method is not clear, but the following reasons are presumed. For example, when a homogeneous catalyst is used as the catalyst, if the pH of the reaction solution fluctuates, the frequency of the exchange reaction of the counter anion or ligand of the catalyst species increases, and therefore, the frequency of the original oxidation reaction decreases. It is possible that the production rate decreases. In addition, when a solid catalyst component exists in a slurry state together with a dissolved catalyst component such as a copper-based catalyst, the solubility of the catalyst component fluctuates due to the fluctuation of the pH of the reaction solution, and the catalyst concentration fluctuates. Therefore, it is considered that it is difficult to maintain a stable reaction. On the other hand, it is presumed that the suppression of pH fluctuation, which is the method of the present invention, has the effect of alleviating the above-mentioned phenomenon.

[0010] The reaction of the present invention is carried out in the presence of ROH in the presence of a catalyst.
(Here, R represents a monovalent aliphatic group having 1 to 12 carbon atoms. One or more hydrogen atoms may be substituted with an alkyl group or an aryl group having 1 to 10 carbon atoms.) Is reacted with carbon monoxide and oxygen to obtain a dialkyl carbonate represented by the following general formula (1), which is represented by the following reaction formula (2).

[0011]

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(Where R is as described above)

[0013]

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(Where R is as described above). The aliphatic monoalcohol ROH used in the present invention is
As described above, among them, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, isobutyl alcohol and cyclohexanol are preferably used, and methanol and ethanol are more preferable.

What is produced by the method of the present invention is a dialkyl carbonate represented by the above general formula (1),
Among them, dimethyl carbonate, diethyl carbonate, di (1-propyl) carbonate, di (2-propyl) carbonate, di (1-butyl) carbonate, diisobutyl carbonate and dicyclohexyl carbonate are preferably produced, and more preferably dimethyl carbonate and diethyl carbonate. is there.

The catalyst used in the present invention is obtained by the above reaction formula (2)
Any catalyst can be used as long as it can generate a dialkyl carbonate in the reaction represented by the formula. Usually, a salt or complex of a metal belonging to Group 1B or Group 8 of the periodic table is used.
Cu (OCH ₃ ) Cl, Cu (OCH ₂ CH ₃ ) Cl,
General formula Cu (OR) X (where R is 1 to 4 carbon atoms) such as Cu (OCH ₃ ) Br and Cu (OCH ₂ CH ₃ ) Br
It represents 12 monovalent aliphatic groups, and one or more hydrogens thereof may be substituted with an alkyl group or an aryl group having 1 to 10 carbon atoms. X is a halogen atom, preferably chlorine or bromine. )); Copper (I) halides such as copper chloride (I) and copper (I) bromide; copper (II) oxide, copper (I) oxide, copper hydroxide (I)
I), copper (II) nitrate, copper (II) hydroxycarbonate, copper (II) hydroxynitrate, copper (II) acetate, copper (II) oxalate, copper (II) acetate, copper (II) citrate, copper (II) Copper salts such as acetylacetonate, copper (II) ethoxide, copper (II) methoxide, and copper (II) naphthenate; halides, acetates, nitrates of platinum group elements such as ruthenium, rhodium, palladium, and cobalt; Carboxylate, β-diketonate or platinum group complex; and the like, preferably Cu (OCH ₃ ) Cl, Cu
A copper alkoxy halide such as (OCH ₃ ) Br; a carboxylate or β-diketonate of cobalt; a salt of palladium such as palladium chloride, palladium bromide, palladium acetate, palladium nitrate, palladium sulfate, bis (acetylacetonato) palladium; Is used.

Each of these catalysts can be used alone, or a plurality of catalysts can be used in combination. Further, these catalysts can be used by being supported on a carrier. The carrier is usually activated carbon, silica,
Alumina, silica alumina, titania, zeolite and the like can be used. Also, a redox promoter such as a quinone / hydroquinone-based catalyst can be used in combination.

The pH of the reaction solution varies depending on the type of the catalyst used and the reaction conditions, but is usually from 0 to less than 14, preferably from 1 to 10. In addition, p of the reaction solution
The smaller the fluctuation range of H, the better. Usually, it is 1 or less, preferably 0.5 or less. The smaller the pH fluctuation Q, the more stable the reaction. The reaction is usually carried out at 3 min ^-1 or less, preferably at 2 min ^-1 or less, more preferably at 1 min ^-1 or less.

The method for keeping the pH fluctuation Q within a predetermined range is not particularly limited. For example, the pH fluctuation of the reaction system is measured with a pH meter installed in the reaction system, and a necessary amount of acid or base is added. By adding into the reaction system, the pH of the reaction system can be returned to a predetermined value. The acid is not particularly limited as long as it does not inhibit the reaction of the present invention, and is usually a mineral acid such as sulfuric acid, nitric acid or phosphoric acid; or a halogenated acid such as hydrochloric acid, hydrobromic acid or hydroiodic acid. Hydrogenic acid; carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, oxalic acid, tartaric acid, citric acid, phthalic acid, and terephthalic acid; sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, and methanesulfonic acid Are used.
The base is not particularly limited as long as it does not inhibit the reaction of the present invention, and is usually an alkali metal hydroxide such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, or cesium hydroxide. Substances; alkaline earth metal hydroxides such as magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide;
Hydroxide salts such as magnesium chloride hydroxide and copper trihydroxide; basic carbonate salts such as copper carbonate hydroxide, lead carbonate hydroxide and magnesium carbonate hydroxide; ammonia, methylamine, dimethylamine, trimethylamine, ethylamine; Alkylamines such as diethylamine and triethylamine; aralkylamines such as benzylamine; aromatic amines such as aniline are used.

Further, as another method for keeping the pH fluctuation Q within a predetermined range, the reaction can be carried out by imparting a hydrogen ion buffering action to the reaction solution. That is, by allowing the weak acid (AH) and its conjugate base (A ⁻ ) to be present in the reaction solution, it is possible to use the reaction solution as a buffer solution and suppress the fluctuation of pH. Here, the weak acid includes the conjugate acid (BH ⁺ ) of the weak base (B).

The acid used as the above weak acid includes:
Although it is not particularly limited as long as it is a weak acid that does not inhibit the reaction of the present invention, oxalic acid (1.25), hydrogen sulfate ion (1.96), phosphoric acid (2.12), and phthalic acid (2.7) are usually used.
6), tartaric acid (3.04), citric acid (3.13), hydrogen oxalate ion (4.27), hydrogen tartrate ion (4.37), acetic acid (4.76), dihydrogen citrate ion ( 4.76), hydrogen phthalate ion (4.92), 2
-(N-morpholino) ethanesulfonic acid (6.15),
Hydrogen citrate ion (6.40), collidine conjugate acid (6.69), imidazole conjugate acid (7.06), hydrogen phosphate ion (7.20), 3- (N-morpholino)
Propanesulfonic acid (7.20), conjugate acid of tris (hydroxymethyl) aminomethane (7.70), conjugate acid of triethanolamine (7.76), boric acid (9.2)
4), weak acids such as ammonia conjugate acid (9.24), hydrogen carbonate ion (10.33), hydrogen phosphate ion (12.36) (the numbers in parentheses indicate pKa).
Is used.

The conjugate base of the weak acid is not particularly limited as long as it does not inhibit the reaction of the present invention, and is usually hydrogen oxalate, sulfate, dihydrogen phosphate, hydrogen phthalate, tartaric acid, or the like. Hydrogen ion, dihydrogen citrate ion, oxalate ion, tartrate ion, acetate ion, hydrogen citrate ion, phthalate ion, 2-
(N-morpholino) ethanesulfonic acid ion, citrate ion, collidine, imidazole, hydrogen phosphate ion,
3- (N-morpholino) propanesulfonic acid ion, tris (hydroxymethyl) aminomethane, triethanolamine, borate ion, ammonia, carbonate ion, phosphate ion and the like are used. When these conjugate bases are anions, they have a counter cation other than a proton.

A buffer having an arbitrary pH can be prepared by adjusting the concentration ratio of the weak acid to the conjugate base. However, when the concentration ratio is 10 or more or 0.1 or less, the buffering action is weak.
A combination of a weak acid and its conjugate base having an acid strength pKa in the range of the following formula (3) with respect to a desired pH is usually used. pH-1 <pKa <pH + 1 (3) In the case where the reaction solution has a hydrogen ion buffering action, the buffer capacity is used as a measure indicating the degree of buffering action on the hydrogen ion concentration of the reaction solution. In the present invention,
It is preferable to use a reaction solution having a buffer capacity of 0.1 or more and having a hydrogen ion buffer action, and it is more preferable to use a reaction solution having a buffer capacity of 1 or more.

The reaction time (residence time when a continuous flow reactor is used) varies depending on the reaction conditions such as the reaction temperature, the catalyst used and the concentration of oxygen, but is usually 0.001 to 50 hours, preferably 0.001 to 50 hours. Is 0.01 to 10 hours, more preferably 0.05 to 5 hours. The reaction temperature varies depending on the type of starting materials used and the reaction pressure, but is usually in the range of 0 to 300 ° C, preferably 50 to 200 ° C.

The total pressure of carbon monoxide and oxygen is
Usually expressed as an absolute pressure, 0.5 to 100 kg / c
m ² , preferably ² to 100 kg / cm ² . The value of the ratio of oxygen partial pressure to carbon monoxide partial pressure is typically 0.0
It is carried out at a rate of from 0.5 to 50, preferably from 0.01 to 0.5.
As carbon monoxide, pure carbon monoxide or carbon monoxide containing an inert gas can be used. As the oxygen, pure oxygen or oxygen diluted with an inert gas such as nitrogen (for example, air or oxygen-rich air) can be used.

The concentration of the catalyst is from 0.001 to 2 mol / l. The concentration of the weak acid when the reaction solution has a hydrogen ion buffering action is performed at 0.001 to 2 mol / L. The concentration of the conjugate base of the weak acid when the reaction solution has a hydrogen ion buffering action is 0.001-2.
It is performed in mol / liter. The ratio between the concentrations of the weak acid and its conjugate base is usually 0.11 to 9.9, and the pH is determined so that the desired value is obtained within this range.

In the present invention, it is not necessary to use a solvent, but a suitable inert solvent such as ethers, aliphatic hydrocarbons and aromatic hydrocarbons for the purpose of facilitating the reaction operation and the like. And halogenated aromatic hydrocarbons and the like can be used as a reaction solvent. Further, an inert gas such as nitrogen, helium, argon or the like may be coexisted in the reaction system as a substance inert to the reaction.

The process according to the invention is carried out batchwise or continuously.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be specifically described below. In the following examples, the pH fluctuation Q during the reaction measured at fixed time intervals and 1 second was divided by the time interval to obtain the pH fluctuation degree Q. The analysis of the reaction solution was performed using gas chromatography.

[0030]

Example 1 Dimethyl carbonate was synthesized using an autoclave (capacity: 2 liters) equipped with a stirrer and a pH detection end and covered with Teflon. 20 methanol
0 ml (4.94 mol), 8.84 g (0.0680 mol) of Cu (OCH ₃ ) Cl, 0.355 g (0.0034 mol as HCl) of 35 wt% hydrochloric acid, 0.667 g (0.0068 mol) of sulfuric acid, 0.817 g (0.0068 mol) of sodium hydrogen sulfate was charged. Then, 15% by volume of carbon monoxide, 79% by volume of nitrogen,
20 kg / cm ² -G mixed gas consisting of 6% by volume of oxygen
After inserting, the inside of the autoclave was heated to 120 ° C. and reacted for 1 hour. The pH during the reaction ranges from 1.0 to 1.2, and the maximum value of the pH variability Q during the reaction is 0.2 mi.
n- ¹ . The buffer capacity of the partially sampled reaction solution was 1.3. After completion of the reaction, the autoclave was cooled and the product was analyzed. The yield of dimethyl carbonate based on methanol was 4.5%, and the selectivity for dimethyl carbonate based on methanol was 99% or more.

[0031]

Comparative Example 1 Dimethyl carbonate was produced in the same manner as in Example 1 except that sulfuric acid and sodium hydrogen sulfate were not used. The pH during the reaction ranges from 0.9 to 1.8, and the maximum value of the pH variability Q during the reaction is 4.1 mi.
n- ¹ . The buffer capacity of the reaction solution was 0.03. The yield of dimethyl carbonate based on methanol was 3.1.
%, Dimethyl carbonate selectivity based on methanol is 9
4%.

[0032]

Example 2 Dimethyl carbonate was produced using an experimental apparatus shown in FIG. 1 and comprising an autoclave equipped with a stirrer. In reactor 1 (volume 1000 ml), methanol 300 ml and catalyst (cuprous chloride) 20 g (0.20
2 mol), 1.5 g (0.015 mol) of sulfuric acid, and 1.8 g (0.015 mol) of sodium hydrogen sulfate. 30 kg / cm of reactor with carbon monoxide (conduit 4)
The pressure was increased to ^2- G, and the mixture was heated to 120 ° C. while maintaining the pressure. When the temperature becomes constant, 17 NL / h of carbon monoxide from conduit 4, oxygen 6.8 NL / h from conduit 5, and conduit 6
From nitrogen 146 NL / h, conduit 7 to 35% by weight hydrochloric acid 2
0 g / h were fed. Further, methanol was supplied from the conduit 3 so that the liquid level in the reactor 1 was constant. At the time when the flow rate became stable, the supply amount of methanol was 81 g / h. The pH during the reaction was in the range of 1.0 to 1.1, and the maximum value of the pH variability Q during the reaction was 0.1 min ^-1 .
The buffer capacity of the partially sampled reaction solution was 1.2. The gas discharged from the conduit 8 was cooled by the condenser 9 and passed through the gas-liquid separator 10 to obtain a non-condensable gas from the conduit 12 and a liquid substance from the conduit 13.
When these were analyzed, the yield of dimethyl carbonate based on methanol was 6.9%, and the selectivity for dimethyl carbonate based on methanol was 99% or more. Reaction 7
Continued for 2 h, during which no decrease in yield or selectivity was observed.

[0033]

Comparative Example 2 Dimethyl carbonate was produced in the same manner as in Example 2 except that sulfuric acid and sodium hydrogen sulfate were not used. The pH during the reaction was in the range of 1.0 to 1.7, and the maximum value of the pH variability Q during the reaction was 5.3 min ^-1.
Met. The buffer capacity of the reaction solution was 0.03. The yield of dimethyl carbonate based on methanol was 4.6%, and the selectivity for dimethyl carbonate based on methanol was 94%.

[0034]

Embodiment 3 Cu (OCH ₃ ) Cl8.84 as a catalyst
g (0.0680 mol) together with palladium chloride 0.1 g.
The reaction was carried out in the same manner as in Example 1 except that 60 g (0.0034 mol) was used. The pH during the reaction was 1.
It was in the range of 0 to 1.1, and the maximum value of the pH variability Q during the reaction was 0.2 min ^-1 . The buffer capacity of the reaction solution is 1.5
Met. After completion of the reaction, the autoclave was cooled and the product was analyzed. The yield of dimethyl carbonate based on methanol was 5.1%, and the selectivity for dimethyl carbonate based on methanol was 99% or more.

[0035]

Example 4 Diethyl carbonate was produced in the same manner as in Example 3 except that ethanol was used instead of methanol. The pH during the reaction was in the range of 1.0-1.1, and the maximum value of the pH variability Q during the reaction was 0.22 mi.
n- ¹ . The buffer capacity of the reaction solution was 1.1. After completion of the reaction, the autoclave was cooled and the product was analyzed.
The yield of diethyl carbonate based on ethanol is 5.6.
%, Selectivity of diethyl carbonate based on ethanol is 9
9% or more.

[0036]

Embodiment 5 Q without using sulfuric acid and sodium hydrogen sulfate
Dimethyl carbonate was produced in the same manner as in Example 2 except that 35% by weight of hydrochloric acid was added to the reaction solution by using a metering pump so that the value was within a predetermined range. PH during reaction
Is in the range of 0.8 to 1.2, and the pH variability Q during the reaction is
Was 0.3 min ^-1 . After completion of the reaction, the autoclave was cooled and the product was analyzed. The yield of dimethyl carbonate based on methanol was 6.1%, and the selectivity for dimethyl carbonate based on methanol was 99% or more.

[0037]

COMPARATIVE EXAMPLE 3 35% by weight hydrochloric acid was dissolved in 0.1% by using a metering pump.
Dimethyl carbonate was produced in the same manner as in Example 5, except that it was continuously added to the reaction solution at a rate of 1 ml / min. The pH during the reaction was in the range of 0.9 to 1.3, and the maximum value of the pH variability Q during the reaction was 4 min ^-1 . The yield of dimethyl carbonate based on methanol was 4.2%, and the selectivity for dimethyl carbonate based on methanol was 94%.

[0038]

According to the method of the present invention, dialkyl carbonate can be produced with high yield and high selectivity.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus used in Example 2.

[Description of code field]

 DESCRIPTION OF SYMBOLS 1 Autoclave 2 Stirring motor 3, 4, 5, 6, 7, 8, 12, 13 Conduit 9 Condenser 10 Gas-liquid separator 11 Pressure control valve

Claims (6)

[Claims] When producing a dialkyl carbonate by reacting an aliphatic monoalcohol with oxygen and carbon monoxide in the presence of a catalyst, the reaction is carried out at a pH variation Q defined by the following differential formula of 3 min ^-1 or less. A method for producing a dialkyl carbonate. Q = | d (pH _t ) / dt | (where t represents the reaction time [min] and pH _t represents the hydrogen ion index of the reaction solution at the reaction time t.) 2. The process for producing a dialkyl carbonate according to claim 1, wherein the reaction solution has a hydrogen ion buffering action, and has a buffering capacity with respect to the hydrogen ion concentration of 0.1 or more. 3. The process for producing a dialkyl carbonate according to claim 1, wherein the aliphatic monoalcohol is methanol or ethanol. 4. The method for producing a dialkyl carbonate according to claim 3, wherein the catalyst is a catalyst comprising a copper compound. 5. The method for producing a dialkyl carbonate according to claim 4, wherein the hydrogen ion index is in the range of 0 to 3. 6. The method for producing a dialkyl carbonate according to claim 1, wherein the pH variability Q is 2 min ⁻¹ or less.