JPH0737422B2 - Process for producing dialkyl carbonate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a dialkyl carbonate. More specifically, it relates to a method for producing a dialkyl carbonate by reacting a cyclic carbonate with an alcohol.

(Prior Art) Various proposals have been made regarding a method for producing a dialkyl carbonate by reacting a cyclic carbonate with an alcohol in the presence of a catalyst. For example, a method using a tertiary aliphatic amine as a catalyst (Japanese Patent Publication No. 59-2854).
2), a method using an alkali metal or an alkali metal compound (U.S. Pat. No. 3642858), a method using a thallium compound (Japanese Patent Publication No.60-65858), a method using tin alkoxides (Japanese Patent Publication No.56-40708), Method using composite catalyst composed of Lewis acid and nitrogen-containing organic base (Japanese Patent Publication No. 60-
22698) Method using quaternary phosphonium salt
6-10144) and the like are known.

(Problems to be Solved by the Invention) As a catalyst used in a method for producing a dialkyl carbonate by reacting a cyclic carbonate with an alcohol, a homogeneous catalyst has been mainly used conventionally. However, when a homogeneous catalyst is used, it is difficult to separate the reaction mixture and the catalyst. On the other hand, in order to obtain the product dialkyl carbonate as a product,
Usually, distillation is required as a separation operation. Therefore,
When a homogeneous catalyst is used, the reaction mixture is heated and distilled while the catalyst remains. As a result, dehydration condensation of glycol, which is a by-product, occurs, and the selectivity decreases.

In order to prevent this, there is a method of reducing the amount of catalyst used (Japanese Patent Publication No. 61-45616), but the reaction rate is reduced. Furthermore, by using a solid catalyst as the catalyst, it is possible to substantially eliminate side reactions during the separation operation. Examples of such a possible catalyst include a silica-titania solid acid catalyst (Japanese Patent Publication No. 61-5467) and a weakly basic exchange resin containing a tertiary aliphatic amine group (Japanese Patent Publication No. 59-2854).
2) is known, but the catalytic activity is not sufficient and the reaction rate is low.

(Means for Solving the Problems) The inventors of the present invention have earnestly studied a catalyst in the production of a dialkyl carbonate by reacting a cyclic carbonate with an alcohol, and as a result, have found that the catalyst can be easily separated from the reaction solution and has high activity. The present invention has been completed by discovering a new catalyst whose activity lasts for a long time.

That is, the present invention provides a method for producing a dialkyl carbonate, which comprises reacting a cyclic carbonate with an alcohol in the presence of a solid strong basic anion exchanger having a quaternary ammonium group as an exchange group. is there.

In the present invention, as shown in the following formula, a well-known reaction for obtaining a dialkyl carbonate (C) and a glycol (D) by reacting a cyclic carbonate (A) with two molecules of an alcohol (B) can be directly applied. Good.

In the above formula, R ¹ represents a divalent group — (CH ₂ ) m— (m is an integer of 2 to 6), wherein one or more hydrogen atoms are an alkyl group having 1 to 8 carbon atoms or alkylene. Group, CH ₂ n (n is an integer of 1 to 8), which may be substituted with an aryl group,
R ² is a saturated or unsaturated hydrocarbon group having 1 to 12 carbon atoms.

The solid catalyst used in the present invention has higher activity than conventional solid acid catalysts. For example, the activity is higher than that of a base resin containing a tertiary aliphatic amine described in JP-B-59-28542. Although the reason is not clear, it is presumed that the solid catalyst containing a quaternary ammonium group used in the present invention has higher basicity than the tertiary amine.

Further, it is also a feature of the solid catalyst of the present invention that the activity deterioration is small when used for a long time as compared with the case of the base resin containing the tertiary aliphatic amine described above. The reason for this has not been clarified yet. However, the commonly used cyclic carbonates have been synthesized by addition of carbon dioxide to the corresponding epoxides and contain traces of carbon dioxide as acidic impurities. Therefore,
Since the rate of acid anion exchange with the quaternary ammonium group is lower than the rate of acid adsorption with the tertiary aliphatic amine, it is considered that the rate of activity deterioration is low.

Since the catalyst of the present invention is a solid catalyst, it is extremely easy to separate the reaction solution and the catalyst. That is, when the reaction is carried out using a batch reactor, the reaction solution can be separated from the catalyst by passing over or decanting. When a tubular flow reactor is used, only the reaction solution can be taken out by filling the reactor with the solid catalyst of the present invention to form a fixed bed.

The effects of facilitating the separation of the reaction solution and the catalyst by using the solid catalyst are as follows.
That is, in the case of using a homogeneous catalyst, a product is obtained by distilling a reaction liquid containing the catalyst, but this operation causes dehydration condensation of the reaction by-product glycol. If the reaction solution and the catalyst are separated in advance, it is possible to avoid a decrease in selectivity due to such an undesired reaction.

As the cyclic carbonate used in the present invention, for example, ethylene carbonate, alkylene carbonate such as propylene carbonate, and 1.3-dioxacyclohex-2-one, 1,3-dioxacyclohepta-2-one are preferable. Of these, ethylene carbonate and propylene carbonate are particularly preferably used from the viewpoint of easy availability.

Examples of alcohols include carbon numbers such as methanol, ethanol, propanol, 1-methylethanol, allyl alcohol, butanol, 2-butanol, 2-methyl-2-propanol, 3-buten-1-ol, and cyclohexanol. Alcohols of 1 to 12 are preferably used.

The solid strong basic anion exchanger having a quaternary ammonium group as an exchange group, which is used as a catalyst in the present invention, may be any one, for example, a strong solid basic anion exchanger having a quaternary ammonium group as an exchange group. Examples thereof include a basic anion exchange resin, a cellulose strong basic anion exchanger having a quaternary ammonium group as an exchange group, and an inorganic carrier-supporting strong basic anion exchanger having a quaternary ammonium group as an exchange group.

As the strongly basic anion exchange resin having a quaternary ammonium group as an exchange group, for example, a styrene strongly basic anion exchange resin or the like is preferably used. The styrene-based strongly basic anion exchange resin is a strong basic anion exchange resin having a quaternary ammonium (type I or type II) as an exchange group with a copolymer of styrene and divinylbenzene as a matrix. It is shown schematically by a formula.

In the above formula, X Represents an anion, usually X As
Is F , Cl , Br , I , OH , HCO₃ , ▲ CO^Two
_Three▼, CH₃CO_Two , HCO_Two , IO₃ , BrO_Three , ClO_Three
At least one anion selected from among
Preferably Cl , Br , HCO₃ , ▲ CO^Two _ThreeFrom ▼
At least one selected anion is used. Well
Also, the structure of the resin matrix is gel type, macroreticular
Both Yuler type (MR type) can be used, but organic solvent resistance
The MR type is particularly preferable because of its high value.

Cellulose having a quaternary ammonium group as an exchange group
As the strongly basic anion exchanger, for example, cellulose
A part or all of the -OH group of trialkylaminoethyl
Can be obtained byCellulose having an exchange group of However,
R represents an alkyl group, and is usually methyl, ethyl or propyl
And butyl are used, preferably methyl and ethyl
Is used. Also X Is as described above.

The quaternary ammonium group which can be used in the present invention is substituted with a quaternary ammonium group.
Inorganic carrier-supported strong hydrochloric acid-based anion having a substituent
The exchanger is a part of the surface hydroxyl group-OH of the inorganic carrier or
Quaternary ammonium group by modifying allMeans the one introduced. However, R, X Is the above
There is. n is usually an integer of 1 to 6, preferably
Is n = 2. Inorganic carriers include silica and aluminum
Na, silica-alumina, titania, zeolite, etc.
Can preferably be silica, alumina, silica
Alumina is used, particularly preferably silica is used
It Any method can be used to modify the surface hydroxyl groups of the inorganic carrier.
The method of can be used. For example, an inorganic carrier and
Mino Alcohol HC (CH₂) NNR₂Dehydrated in the presence of a base catalyst
After aminoalkoxylation by proceeding the reaction
, An alkyl halide RX '(X' represents halogen,
(Cl, Br, I etc. are usually used)And Furthermore, by performing anion exchange,
Hope Anion X Having a quaternary ammonium groupAnd When n = 2, the inorganic carrier is N, N-
By treatment with dialkylaziridine, N, N-di
Alkylaminoethoxylated to -OCH₂CH₂NR₂After base
By the above methodIt is said that

As the solid strong basic anion exchanger having a quaternary ammonium group as an exchange group, a commercially available one can be used. In that case, it can be used as a catalyst after performing ion exchange with a desired anion species in advance as pretreatment.

The solid strong basic anion exchanger having a quaternary ammonium group as an exchange group can be used even in a state containing water. However, if water is mixed in the reaction system,
Since the raw material ethylene carbonate or the product dimethyl carbonate is hydrolyzed, it is usually dried in advance,
It is preferably used as a catalyst. As the drying method, for example, a method of dehydrating by heating at a temperature below the service temperature under reduced pressure, or an azeotropic solvent that forms a minimum azeotrope with water, such as benzene, toluene, ethylbenzene, etc. For example, a method of removing water by azeotroping at the following temperature is used.

The above-mentioned usage form of the strongly basic anion exchanger is usually used as fine powder or spherical or cylindrical particles having an average particle size of 0.2 to 10 mm.

As a reaction mode, a commonly used method such as a fluidized bed system, a fixed bed system, or a stirring system can be used. Further, either a flow system or a batch system may be used, and the reaction solution and the catalyst can be easily separated.

In carrying out the present invention, the reaction temperature is usually 30 to 300.
℃, preferably 50-260 ℃. However, when the catalyst used has an inherent service temperature, it is preferably carried out in a temperature range lower than that.

The reaction time may vary depending on the type and composition ratio of the starting material cyclic carbonate and alcohol, and the reaction temperature, but for example, it is expressed as a liquid hourly space velocity (LHSV) for all the feed liquids when conducting a flow reaction. , Usually 0.05-40hr ^-1 ,
Preferably 0.1 to 20 hr ^-1 , more preferably 0.2 to 10 hr ^-1
Is used. In the case of batch reaction, it is usually 0.05
~ 60 hours, preferably 0.1-40 hours, more preferably
Used for 0.2 to 20 hours.

The cyclic carbonate as a raw material and the alcohol can be used in a wide range of ratios. However, if the molar ratio of the alcohol to the cyclic carbonate is too large, the amount of alcohol to be recovered becomes too large, which is not realistic. On the other hand, if the molar ratio is too small, the conversion rate of the cyclic carbonate becomes low and the recovery amount increases, which is also not realistic. Therefore, the molar ratio of the alcohol to the starting material cyclic carbonate is usually 0.05 to 100, preferably 0.1 to 40, and more preferably 0.2.
~ 20 is used.

(Effect of the Invention) By the method of the present invention, a dialkyl carbonate can be obtained with a high selectivity using a cyclic carbonate and an alcohol as raw materials, and high activity lasts for a long time. Further, the reaction liquid and the catalyst can be easily separated.

(Example) An example is shown below and the present invention is described concretely.

Example 1 (Pretreatment of catalyst) Dowex MSA-1 [Styrene series manufactured by Dow Chemical Company]
Strongly basic anion exchange resin (type I), anion species Cl ]
The pretreatment of
Seed Cl And

1) 500 ml of Dowex MSA-1 in 4% NaOH aqueous solution 50
After stirring in 0 ml for 1 hour, it was filtered and washed with 3000 ml of water.

2) Furthermore, after stirring in 500 ml of 10% HCl aqueous solution for 1 hour, the mixture was filtered and washed with 3000 ml of water.

3) After repeating 1), 2) was repeated twice.

4) The resin which has been subjected to the treatments 1) to 3) above is heated (120 ° C.) together with 500 ml of ethylene benzene, and ethylbenzene and water are distilled off by an azeotropic composition to remove residual water, and thus the catalyst A Got After removing the excess ethylbenzene by decantation, the catalyst was stored in dry methanol.

(Reaction) The catalyst A obtained above was converted into a tubular reactor (outer diameter 12.7 mm, internal volume
37 ml) and charged with methanol at room temperature. Sent out
Ethylbenzene in methanol is
Almost undetected by analysis by Rafie
(The concentration of ethylbenzene in methanol is 0.01 wt% or less.
Methanol was sent to the bottom). Ethylene carbonate
(Synthesized from ethylene oxide and carbon dioxide,
EC (abbreviated as EC) and methanol mixed solution (MeOH / EC molar ratio =
5) flow rate 110ml / hr (LHSV = 3hr^-1) To start liquid transfer,
The pressure of the reaction system is 7 kg / cm²While keeping (gauge pressure)
The reactor was heated to 100 ° C. When the reaction system becomes steady
As a result of analysis of the reaction solution sent out, ethylene carbonate
Conversion rate of 48%, dimethyl carbonate and ethyl
The selection rates of glycols are 99% and 99%, respectively.
It was Also, Cl in the reaction solution And other anions,
No cationic species were ever present. Distribution reaction as it is
Continued and delivered 120 hours after the reaction became steady
As a result of analyzing the reaction solution, ethylene carbonate
49% conversion, dimethyl carbonate and ethylene
The recall selection rates were 99 and 99%, respectively.

Comparative Example 1 Amberlyst A-21 [made by Rohm and Haas,
The tertiary aliphatic amine type (free base type) was heated to 60 ° C. under reduced pressure to remove water. The reaction was performed in the same manner as in Example 1 except that this catalyst was used. The conversion of ethylene carbonate was 32%, the selectivity of dimethyl carbonate was 98%, and the selectivity of ethylene glycol was 98%. The flow reaction was continued as it was, and the analysis of the delivery reaction solution was carried out 118 hours after the reaction reached a steady state. As a result, the ethylene carbonate conversion rate was 18%, the dimethyl carbonate selectivity was 92%, and the ethylene carbonate selectivity was 92%. The selectivity of glycol was 85%.

Example 2 The reaction was performed in the same manner as in Example 1 except that the reaction temperature was 120 ° C. and the reaction was performed at LHSV = 2 hr ⁻¹ . The conversion rate of ethylene carbonate was 58%, and the selectivities of dimethyl carbonate and ethylene glycol were 99% and 99%, respectively.

Example 3 Dowex MSA-1 was heated under reduced pressure (20 torr) to remove water, thereby obtaining catalyst B. The reaction was carried out in the same manner as in Example 1 except that this catalyst B was used. The conversion rate of ethylene carbonate was 44%, and the selectivities of dimethyl carbonate and ethylene glycol were 99% and 99%, respectively.

Example 4 (Pretreatment of catalyst) 1) 500 ml of Dowex MSA-1 was stirred in 500 ml of 4% aqueous sodium hydrogen carbonate solution for 1 hour and then passed over 300 ml.
It was washed with 0 ml of water.

2) 1) was repeated twice.

3) Heat the above resin with 500 ml of toluene (120 ℃)
And distilling off toluene and water with an azeotropic composition.
To remove residual water and use HCO as anion._Three Basis
A catalyst C having

(Reaction) The reaction was performed in the same manner as in Example 1 except that the catalyst C was used. The conversion rate of ethylene carbonate is 50%, the selectivity of dimethyl carbonate and ethylene glycol is
They were 99% and 99%, respectively.

Example 5 (Pretreatment of catalyst) By the same method as in Example 4 except that sodium carbonate was used instead of sodium hydrogen carbonate, Catalyst D was obtained.

(Reaction) The reaction was performed in the same manner as in Example 1 except that the catalyst D was used. The conversion rate of ethylene carbonate was 52%, and the selectivities of dimethyl carbonate and ethylene glycol were 99% and 99%, respectively.

Example 6 Cl as an anion species as a catalyst And triethylaminoe
Example 1 except that chill cellulose (manufactured by Selva) was used.
The reaction was performed in the same manner as in. Ethylene carbonate
41% conversion, dimethyl carbonate and ethylene
The recall selection rates were 99% and 99%, respectively.

Example 7 Hydrophilic silica gel (quaternary aminoethyl type, manufactured by Toyo Soda Co., Ltd.
TSK-GELQAE-2SW, anion species Cl ) As a catalyst
The reaction was carried out in the same manner as in Example 1 except that the above was used.
Conversion rate of ethylene carbonate is 43%, dimethyl carbo
And the selectivity of ethylene glycol are
It was 99% and 99%.

Example 8 0.5 ml autoclave with a volume of 300 ml ethylene carbonate
0 mol, 2.0 mol of methanol, and 1.0 g of catalyst A (crushed to 80 to 100 mesh) were added, the system was replaced with N ₂ , and stirring and heating were started to bring the reaction temperature to 100 ° C. After 1 hour, the autoclave was cooled and then the reaction solution was passed through to separate from the catalyst. By distilling this solution under atmospheric pressure and reduced pressure, a distillate and a distillation residue were obtained. The distillate contains 0.269 mol of ethylene carbonate and 0.2 dimethyl carbonate.
It contained 13 mol and 0.215 mol of ethylene glycol. In addition, ethylene carbonate 0.016 in the distillation residue
Only moles were present. This result shows that the conversion of ethylene carbonate is 43% and the selectivity of dimethyl carbonate is
99%, the selectivity of ethylene glycol is 99%.

Comparative Example 2 0.5 ml autoclave of ethylene carbonate 0.5
After adding 0 mol and 2.0 mol of methanol and 0.005 mol of sodium methoxide as a catalyst, the system was replaced with N ₂ and stirred.
Heating was started and the reaction temperature was 100 ° C. After 30 minutes, the autoclave was cooled and the reaction solution was analyzed. As a result, sodium methoxide was uniformly dissolved in the reaction solution. The reaction liquid was distilled under atmospheric pressure and reduced pressure to obtain a distillate and a distillation residue. Ethylene carbonate 0.26 for distillate
It contained 0 mol, 0.216 mol of dimethyl carbonate and 0.168 mol of ethylene glycol. The distillation residue contained 0.015 mol of ethylene carbonate and a high boiling by-product. The results show that the conversion of ethylene carbonate is 45%, the selectivity of dimethyl carbonate is 97%, and the selectivity of ethylene glycol is 75%.

Example 9 The reaction was performed in the same manner as in Example 1 except that propylene carbonate was used instead of ethylene carbonate. The conversion rate of propylene carbonate is 51%, the selectivity of dimethyl carbonate and propylene glycol is
They were 99% and 99%, respectively.

Example 10 The reaction was carried out in the same manner as in Example 4 except that ethanol was used instead of methanol. The conversion of ethylene carbonate was 53%, and the selectivities of diethyl carbonate and ethylene glycol were 99% and 99%, respectively.

Example 11 Except that allyl alcohol was used instead of methanol,
The reaction was carried out in the same manner as in Example 5. The conversion of ethylene carbonate was 42%, and the selectivities of diallyl carbonate and ethylene glycol were 99% and 99%, respectively.

Example 12 The procedure of Example 12 was repeated except that a 10% HBr aqueous solution was used instead of the 10% HCl aqueous solution.
As an anion by the same method as the catalyst pretreatment method of Example 1
Br A catalyst E containing was obtained. Implementation using this catalyst
The reaction was carried out under the same conditions as in Example 1. Ethylene carbonate
50% conversion, dimethyl carbonate and ethylene
The glycol selectivities were 99% and 99%, respectively.

Example 13 Using a tubular flow reactor filled with 60 ml of catalyst D, a mixed solution of methanol and ethylene carbonate (MeOH
/ EC molar ratio = 2) was continuously passed at LHSV = 0.33 hr ⁻¹ . The reaction temperature was kept at 60 ° C. to carry out the reaction continuously.
As a result of analyzing the effluent reaction liquid when the reaction system reached a steady state, the conversion rate of ethylene carbonate was 39%,
The selectivities of dimethyl carbonate and ethylene carbonate were 99% each. This reaction was carried out continuously for 8,100 hours, but during this period, the reaction results hardly changed, and no decrease in catalyst activity was observed.

Example 14 As raw materials, methanol and 1,3-dioxacyclohex-2-one (alias: cyclohexene carbonate, CHO
Abbreviated as “) and using a mixed solution (MeOH / CHO molar ratio = 6)
As a result of carrying out the reaction in the same manner as in Example 5 except that SV = 0.05 hr ⁻¹ and a reaction temperature of 90 ° C., the CHO reaction rate was 21%.
Thus, the selectivities of dimethyl carbonate and cyclohexane-1,2-diol were 99%, respectively.

Claims (2)

[Claims] 1. A process for producing a dialkyl carbonate, which comprises reacting a cyclic carbonate with an alcohol in the presence of a solid strong basic anion exchanger having a quaternary ammonium group as an exchange group. 2. The anion is Cl , Br , HCO_Three ,Patent that is at least one anion selected from
The method according to claim 1.