JPH0791233B2 - Method for producing dialkyl carbonate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a dialkyl carbonate.

[Conventional technology]

Various proposals have been made as 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. 59-28542).
JP), a method using an alkali metal or an alkali metal compound (US Pat. No. 3,642,858), a method using a thallium compound (JP-B-60-27658), and a method using tin alkoxides (JP-B-SHO). 56-40708), a method of using a mixture of a Lewis acid and a nitrogen-containing organic base (JP-B-60-22698), a method of using a quaternary phosphonium salt (JP-A-56-10144), etc. There is.

Usually, distillation is required as a separation operation in order to obtain the product dialkyl carbonate as a product. However, when such a homogeneous catalyst is used, it is difficult to separate the reaction mixture from the catalyst, and the reverse equilibrium reaction is likely to occur due to the presence of the catalyst during the distillation, so that the azeotropic distillation of the dialkyl carbonate and alcohol occurs. There are problems that it can be obtained only with the composition and that dehydration condensation of the co-product glycol occurs.

In order to prevent this, a method using a heterogeneous catalyst has been published. For example, a silica-titania solid acid catalyst (Japanese Patent Publication No. 61-5467), a weakly basic exchange resin containing a tertiary aliphatic amine group (Japanese Patent Publication No. 59-28542), and a quaternary ammonium group are exchanged. A strong basic exchange resin having a group (Japanese Patent Laid-Open No. 63-238043), a cation exchange resin having a sulfonic acid group or a carboxylic acid group as an exchange group (Japanese Patent Laid-Open No. 64
-31737 gazette) and the like. That is, when the reaction is carried out using a batch reactor, the reaction solution is subjected to a catalyst separation operation by filtration or decantation, and when a flow reactor is used, the catalyst is charged into the reactor. And by making it a fixed bed (in this case,
After the reaction and the catalyst separation operation are simultaneously performed), the catalyst is almost separated from the reaction solution and then subjected to distillation. For example, according to JP-A-64-31737, first, ethylene carbonate (abbreviated as EC) and methanol (abbreviated as MeOH)
After reacting with and in a tubular reactor (the catalyst separation operation here corresponds to the case of the flow reactor described above), the obtained dimethyl carbonate (abbreviated as DMC), ethylene glycol (abbreviated as EG), MeOH , The reaction solution consisting of EC is subjected to distillation,
The MeOH and DMC mixture obtained as the overhead liquid was further distilled under pressure (about 10 atm) to obtain pure DMC.

[Problems to be Solved by the Invention]

However, in the case of a flow reactor, it is not possible to completely avoid mixing of catalyst components (which refers to eluates and decomposed products of the catalyst) into the reaction liquid, and also in the case of a batch reactor, filtration or The catalyst component cannot be completely separated from the reaction solution by a method such as decantation. Therefore, after the reaction, the reaction liquid obtained by the catalyst separation operation, that is, the four-component alcohol / dialkyl carbonate / glycol / cyclic carbonate liquid mixture containing a trace amount of the catalyst component should be separated by distillation at a higher temperature. Then, generation of high boiling components in the distillation column,
There was a problem that the reverse equilibrium reaction of the dialkyl carbonate to the cyclic carbonate occurs and the recovery amount of the dialkyl carbonate is reduced.

[Means for Solving the Problems]

The present inventors have achieved the present invention as a result of intensive studies aimed at solving the conventional problems relating to the production of dialkyl carbonates and obtaining dialkyl carbonates in high yield.

That is, the present invention, after reacting the cyclic carbonate and alcohol in the presence of a heterogeneous catalyst, performs the separation operation of this heterogeneous catalyst, the reaction solution containing a trace amount of catalyst components even after the catalyst separation operation. A method for producing a dialkyl carbonate, which comprises distilling while introducing carbon dioxide gas.

In the present invention, the cyclic carbonate is represented by the following general formula (1).

[In the formula, R ₁ represents a divalent group — (CH ₂ ). m is 2-6
Is an integer. Further, one or more hydrogen atoms in R ₁ may be substituted with an alkyl group having 1 to 8 carbon atoms, an alkylene group or an aryl group. ) Specific examples include alkylene carbonates such as ethylene carbonate and propylene carbonate; 1,3-dioxacyclohex-2-one and 1,3-dioxacyclohepta-2-one. It may also be a mixture thereof.

In the present invention, the alcohol is one which reacts with a cyclic carbonate to give a carbonic acid ester. Preferably, the general formula R ₂ OH [R ₂ is a saturated or unsaturated hydrocarbon group having 1 to 18 carbon atoms or the like. Further, the hydrogen atom of R ₂ may be substituted with an alkoxy group or the like. ] Is represented. Specific examples include methanol, ethanol, propanol, 1-methylethanol, allyl alcohol, butanol, 2-butanol, 2-methyl-2-propanol, 3-buten-1-ol, cyclohexanol, benzyl alcohol, 2-methoxyethanol. And so on. Also,
A mixture of these may be used.

In the present invention, as shown in the following formula (2), the cyclic carbonate (1) is reacted with two molecules of the alcohol (2) to prepare the dialkyl carbonate (3) and the co-product glycol (4). A well-known reaction to be obtained may be applied.

In the present invention, the heterogeneous catalyst is a known heterogeneous catalyst capable of reacting a cyclic carbonate with an alcohol to produce a dialkyl carbonate.

Specific examples thereof include a basic resin containing a tertiary aliphatic amine group or a basic resin containing a quaternary ammonium group, and such a tertiary aliphatic amine group or quaternary ammonium group. A solid base having a group supported on an inorganic carrier may be used. Further, these may be mixed and used.

A basic resin containing a tertiary aliphatic amine group means a tertiary resin
Weakly basic functional groups such as primary amines or tertiary amines,
It is a giant reticulated and gel type ion exchange resin having amide functional groups. In such resins, the terminal amine groups are attached to the organic polymer either directly or via one or more carbon atoms or via a combination of carbon and nitrogen bonds. Tertiary amine or tertiary amine, amide functional group is, for example, dimethylamine group, diethylamine group, dimethylaminobenzyl group, diethylaminobenzyl group, dimethylaminopropyl group, dimethylaminopropylamide group, diethylaminopropyl group,
Dipropylamino and dimethylaminohexylamide, dimethylaminomethylamide, and dimethylaminomethyl groups.

An example of such a resin is Amberlyst A-21 (a macroreticular weak basic anion exchange resin obtained by copolymerizing styrene and divinylbenzene, which is marketed by Rohm and Haas Co., Exchange group is dimethylamine group) (Amberlyst is a registered trademark)
Is mentioned.

As the basic resin containing a quaternary ammonium group,
A resin in which a quaternary ammonium group is bonded to an organic polymer substrate either directly or through one or more carbon atoms. The quaternary ammonium group is, for example, a trimethylammonium hydroxide group, a trimethylammonium chloride group or a trimethylammonium bromide group. Examples of commercially available resins of this type are Amberlyst A-26, A-27, Amberlite IRA-904 (macroreticular type strongly basic anion exchange resin obtained by copolymerizing styrene and divinylbenzene). Yes, the exchange group is a trimethylammonium group), Amberlite IR
A-410 (a gel-type strongly basic anion exchange resin in which styrene and divinylbenzene are copolymerized, and the exchange group is a trimethylammonium group), Dowex MSA-1
(A strongly basic anion exchange resin that is a copolymer of styrene and divinylbenzene, and the exchange group is a trimethylammonium group) and DIAION PA316 (a strongly basic anion exchange resin that is a copolymer of styrene and divinylbenzene). And the exchange group is a trimethylammonium group) (Amberlite is from Rohm and Haas,
Dowex is a trademark of Dow Chemical Company, and Diaion is a registered trademark of Mitsubishi Kasei Co., Ltd.). The anion species of the quaternary ammonium salt group may be exchanged with ion species other than chlorine ion and bromine ion, such as iodine ion, carbonate ion, bicarbonate ion, hydroxyl ion, acetate ion, formate ion and the like.

Further, a part or all of the hydroxyl groups of cellulose may be trialkylaminoethylated. Methyl, ethyl, propyl, butyl and the like are used as the alkyl group. The anion species in this case are as described above.

In the present invention, the inorganic support carrying solid base which can be used, by modifying some or all of the surface hydroxyl groups of the inorganic _{support, -O (CH 2) n N} (R) 2 or -O
(CH ₂ ) n N (R) ₃ X group (R is methyl, ethyl, propyl, butyl or the like is used, and X is an anion species and is as described above. Further, n is usually 1 to It is an integer of 6). As the inorganic carrier, silica, alumina, silica-alumina, titania,
Zeolite or the like is used, and silica or silica alumina is preferably used. As a method for modifying the surface hydroxyl groups of the free carrier, any method can be used. For example, an inorganic carrier and amino alcohol HO (CH ₂ ) n N (R) ₂
In the presence of a base catalyst to give an aminoalkoxylation to give a solid basic catalyst having a tertiary amine group, which is further reacted with an alkyl halide to give a solid having a quaternary ammonium group. A basic catalyst is obtained. This may be used after converting the anion species by a conventional method.

These catalysts may be used in combination.

In the present invention, the catalyst component contained in the reaction liquid in a trace amount even after the catalyst separation operation is a heterogeneous catalyst mixture, catalyst eluate, catalyst decomposition product, or the like.

The amount of the catalyst component contained in the reaction solution after the catalyst separation operation is
0.01 to 10,000 ppm by weight, preferably 0.01 to 1,000 pp
It is in the range of m.

In the reaction of the present invention, a batch reactor or a flow reactor may be used. In either case, the reaction-terminated liquid is subjected to a catalyst separation operation. That is, when the reaction is carried out using a batch reactor, the reaction solution is subjected to catalyst separation operation such as filtration or decantation, and when a flow reactor is used, the catalyst is filled in the reactor. Then, the reaction solution is separated from the catalyst by taking a fixed bed or the like, and then taken out. However, complete separation of the catalyst component from the reaction solution is complicated and requires many steps.

The amount ratio of cyclic carbonate and alcohol in the raw material liquid used in the reaction can be used in a wide range. However, preferably the molar ratio of alcohol to starting cyclic carbonate is from 0.2 to 20. More preferably, it is 1-5.

The reaction temperature of the present invention is usually 30 to 300 ° C, preferably 50 to 2
60 ° C. However, when the catalyst used has an inherent service temperature, it is preferable to carry out the reaction within a temperature range below the inherent service temperature.

The reaction time of the present invention may vary depending on the type and composition ratio of the starting material cyclic carbonate and alcohol, and the reaction temperature. For example, when expressed in terms of liquid hourly space velocity (LHSV) (feed volume velocity of reaction liquid per unit volume of reactor) for all feed liquids when conducting a flow reaction, usually 0.05 to 40 hr ^-1 ,
Preferably 0.2 to 10 hr ^-1 is used. In the case of a batch reaction, it is usually 0.05 to 60 hours, preferably 0.2 to 20 hours.
Time is used.

In the present invention, the pressure during the reaction is not important and may be the pressure of the self-generated reaction substance depending on the size of the reactor and the reaction temperature, but here it is preferably normal pressure to 20 kg / cm.
² (gauge pressure) is used, more preferably atmospheric pressure to 10 k
g / cm ² is used.

In the case of a batch system, the amount of the catalyst used in the reaction of the present invention is 0.01 to 20% by weight, preferably 0.5 to 10% by weight, based on the raw materials. Also, in the case of the distribution type, it should be within the above-mentioned LHSV range.

Under the reaction conditions described above, a cyclic carbonate is reacted with an alcohol, and a catalyst separation operation is performed to obtain a reaction liquid composed of an unreacted cyclic carbonate and an alcohol, and a reaction product of a dialkyl carbonate and a glycol. This reaction solution contains 0.01 to 10,000 ppm of catalyst components (a trace amount of catalyst, catalyst decomposition products, etc.) and may also contain by-products and the like. Also, the temperature of the reaction,
The reaction may be allowed to reach equilibrium or stopped before equilibration by adjusting the time or the amount of catalyst.

In the present invention, the distillation operation may use a batch type apparatus or a flow type apparatus.

The distillation apparatus of the present invention is preferably operated at a distillation column bottom temperature of room temperature to 250 ° C, more preferably 50 to 180 ° C.

The pressure at the time of distillation varies depending on the type of reaction raw material and the liquid composition of the distillate, but may be any of reduced pressure, normal pressure and increased pressure as long as it falls within the range of the above-mentioned distillation temperature.

In the present invention, it is necessary to introduce carbon dioxide gas into the distillation system. By introducing carbon dioxide gas, it is possible to suppress the formation of high boiling components during distillation and the reverse equilibrium reaction of dialkyl carbonate to cyclic carbonate.

Various methods can be used for introducing carbon dioxide into the distillation system, and there is no particular limitation. For example, a method of introducing from the bottom of the distillation column during distillation, or a method of introducing carbon dioxide gas by dissolving it in the reaction solution before distillation is used.

If the amount of carbon dioxide gas introduced is too small with respect to the amount of the reaction liquid to be distilled, there is no effect, and if too large, it is economically wasteful. Usually, 0.001Nl ~ 4 for 1 distillate throughput
Introduce 00Nl, preferably 0.01Nl-40Nl. Carbon dioxide is
It may be diluted with an inert gas and introduced.

〔Example〕

 Hereinafter, the present invention will be specifically described with reference to examples.

Example 1 (Pretreatment of catalyst) Amberlyst A-21 (Rohm and Haas,
A weakly basic anion exchange resin obtained by copolymerizing styrene and divinylbenzene and having a dimethylamine group as an exchange group) was heated at 60 ° C. under reduced pressure for preliminary drying. Next, a tubular reactor (outer diameter 12.7 mm, inner volume 37 ml) was filled with the above dry anion exchange resin, and dry methanol was fed at 60 ° C. The delivered methanol was analyzed by gas chromatography, and dry methanol was introduced until the water content was 0.01% by weight or less.

(Reaction) The tubular reactor containing the dry catalyst was used for the reaction. A mixed solution of ethylene carbonate (EC) and methanol (MeOH) (MeOH / EC molar ratio = 2) with a flow rate of 55 ml / hr (LHSV = 1.5 h
The liquid transfer was started at r ⁻¹ ), and the reactor was heated to 100 ° C. while maintaining the pressure of the reaction system at 7 kg / cm ² (gauge pressure). The delivered liquid was analyzed by gas chromatography, and when the composition of the delivered liquid reached a steady state, the reaction liquid to be subjected to distillation in the next step was collected. The conversion rate of EC was 32%. The amount of catalyst component was 3.8 ppm.

(Distillation) 300.0 g of the reaction solution was charged into a 500 ml glass distillation apparatus for distillation. Insert the gas inlet tube into the bottom of the glass container and raise the temperature under normal pressure to distill it while introducing 0.1 Nl / hr of carbon dioxide gas. After the temperature reached 150 ° C over 2 hours, the distillation pressure was kept constant. Decrease pressure and take MeOH / D over 2 hours
MC azeotrope, DMC, EG and EC were sequentially extracted. The high boiling residue was less than 0.1 g. As a result of analysis by gas chromatography, 300.0 g of the reaction solution contained 56.8 g of DMC, and the distillation recovery fraction, that is, the DMC / MeOH azeotropic fraction, and the total of DMC in the DMC fraction were 56.3 g. .

Comparative Example 1 Using 300.0 g of the same reaction solution as in Example 1, the same distillation operation as in Example 1 was performed while introducing nitrogen gas instead of carbon dioxide gas. The high boiling residue was 0.1 g or less, but only 50.6 g of DMC recovered by distillation was obtained.

Example 2 (Catalyst pretreatment) 500 ml of Dowex MSA-1 (manufactured by Dow Chemical Co., a strong base anion exchange resin obtained by copolymerizing styrene and divinylbenzene) and having a trimethylammonium group as an exchange group. The anion species is chlorine ion), the mixture was stirred in 500 ml of a 4% sodium carbonate aqueous solution for 1 hour, filtered, and washed with 3,000 ml of water. This series of operations was repeated twice more. The resin thus obtained was heated at 60 ° C. under reduced pressure to be pre-dried, which was then charged into a tubular reactor in the same manner as described in Example 1 and dried by feeding dry methanol. .

(Reaction) The flow rate of the raw material fed into the tubular reactor was 37 ml / hr (LHSV = 1 hr
^-1 ) except that the reaction was carried out in the same manner as in Example 1. The conversion rate of EC was 42%. The amount of the catalyst component in the collected reaction liquid was 9.5 ppm.

(Distillation) Distillation was performed by the same operation as in Example 1. Reaction liquid 300.
The recovered DMC was 73.9 g, compared with 74.4 g of DMC in 0 g. The distillation residue was 0.1 g or less.

Comparative Example 2 The reaction solution obtained in Example 2 was used for distillation in the same manner as described in Comparative Example 1. 68.1 g of DMC recovered by distillation,
The distillation residue was 0.4 g.

Example 3 Using 300.0 g of the reaction solution obtained in Example 2, the amount of introduced carbon dioxide gas was increased to 0.5 Nl / hr and the temperature was raised to 180 ° C. for distillation operation. 73.7 g of DMC could be recovered and the distillation residue was 0.3 g.

Comparative Example 3 The same operation as in Example 3 was performed except that nitrogen gas was used instead of carbon dioxide gas. The recovered DMC was 53.9 g and the distillation residue was 7.2 g.

Example 4 The same operation as in Example 2 was performed except that ethanol was used instead of methanol. The conversion rate of EC was 43%, and the catalyst component in the reaction solution was 10.4 ppm. 84.6 g of diethyl carbonate was contained in 300.0 g of the reaction solution, and 84.1 g was recovered by distillation. The distillation residue was 0.1 g or less.

〔The invention's effect〕

The present invention makes it possible to distill a dialkyl carbonate without causing an inverse equilibrium reaction, and as a result, a dialkyl carbonate can be obtained in a high yield.

Claims (1)

[Claims] 1. A cyclic carbonate and an alcohol are reacted in the presence of a heterogeneous catalyst, and then the separation operation of the heterogeneous catalyst is carried out. A method for producing a dialkyl carbonate, which comprises distilling while introducing gas.