JPH06228026A - Separation of methanol from dimethyl carbonate - Google Patents

Abstract

(57) [Summary] [Purpose] Efficiently separates both from a mixture of methanol and dimethyl carbonate. [Structure] An azeotropic phenomenon can be destroyed by adding an extracting agent selected from a specific compound group to a mixture of methanol and dimethyl carbonate, and each component can be efficiently separated and recovered in high purity by a normal distillation operation. it can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently separating an azeotropic mixture of methanol and dimethyl carbonate by distillation. Dimethyl carbonate is useful as a raw material for various chemical products including aromatic carbonates.

[0002]

2. Description of the Related Art As a method for producing dimethyl carbonate, a method of reacting methanol with phosgene (Japanese Patent Application Laid-Open No. 5-312058)
6-7745), a method of reacting methanol with carbon monoxide and oxygen in the presence of a suitable catalyst (JP-A-51-13).
8620, JP-A-53-44523, JP-A-54-
24827, JP-A-55-45655, and JP-A-56.
-167641, JP-A-60-75447, JP-A-2-19347, JP-A-2-169549, JP-A-3-99041, JP-A-4-108765, JP-A-4-270250 and JP-A-4. -270251), a method by transesterification reaction of cyclic carbonate and methanol (Japanese Patent Publication No. 56-40708, Japanese Patent Publication No. 59-285).
No. 42, Japanese Patent Publication No. 22697, Japanese Patent Publication No. 60-22
698, Japanese Examined Patent Publication No. 61-4381, JP-A-54-48.
715, JP-A-54-48716, and JP-A-54-1.
No. 25617, JP-A-56-10144 and JP-A-63.
-328043, JP-A-3-44354, JP-A-3
-109358, JP-A-4-9356, JP-A-4-9358
198141, U.S. Pat. No. 4,661,609 and U.S. Pat. No. 4,734,518), a method of reacting carbon monoxide and methyl nitrite by vapor phase contact in the presence of a suitable catalyst (JP-A-60-181051, JP-A-3-181051). 141423
No.) In any of these methods, the target product dimethyl carbonate is obtained in the form of a mixture with the raw material methanol, so that a step of separating and recovering each is essential. However, since methanol and dimethyl carbonate have an azeotropic composition with a molar composition ratio of 86:14 under normal pressure, it is difficult to separate them by a normal distillation operation.

Therefore, many proposals have been made so far as a method for separating methanol and dimethyl carbonate. For example, U.S. Pat. No. 3,803,201 presents a method of crystallizing dimethyl carbonate by cooling and then recovering it by distillation, but it requires complicated operations and is impractical from an industrial viewpoint. Japanese Patent Publication Sho 56-1
No. 7333 presents a method of separating by extractive distillation using water as a solvent, but the disadvantage is that loss of dimethyl carbonate occurs due to hydrolysis, and further recovery of methanol from the distilled water and methanol mixture requires a large amount of energy. There is.

Japanese Examined Patent Publication No. 59-3463 suggests distillation separation under pressure, but it has not been completely separated. Further, in JP-A-2-212456,
Methanol and dimethyl carbonate are separated by a combination of a pressure distillation column and an atmospheric distillation column, but the cost of the device is high, and the boiling points of the azeotrope and methanol are very close to each other. It requires energy and is difficult to operate stably. JP-A-54-418
No. 20, JP-A-63-205101, the former is an aliphatic hydrocarbon such as hexane and heptane, and the latter is an azeotropic composition of methanol and an additive by adding benzene to separate it from dimethyl carbonate. However, it is necessary to separate the methanol and the additive from the distillate having the azeotropic composition, which adds a great cost. Japanese Patent Application Laid-Open No. 60-106505 discloses adsorption separation of dimethyl carbonate by a hydrophobic zeolite, but the adsorption concentration is low and not practical. Also, in U.S. Pat. No. 4,798,674, a separation is attempted using a special polymer membrane, but the separation efficiency is not sufficient and it is not industrially suitable. As described above, a method for efficiently separating methanol and dimethyl carbonate has not yet been found.

[0005]

An object of the present invention is to provide a method for separating and recovering methanol and dimethyl carbonate simply and efficiently.

[0006]

In order to solve this problem, the present inventors have added a specific third component (extractant) when distilling and separating two components forming an azeotropic composition. An intensive study was conducted focusing on the extractive distillation method that destroys the azeotropic phenomenon. That is, in the present invention, when distilling and separating an azeotropic mixture of methanol and dimethyl carbonate, (A) a carbonic acid diester having 4 to 15 carbon atoms, (B) a carbon number of 3 To 5 cyclic carbonate, (C) allyloxy compound represented by the general formula (1), Ar-OR (1) (wherein Ar is a phenyl group or a toluyl group, R is an alkyl group having 1 to 3 carbon atoms, or (Representing hydrogen) (D) An aromatic hydrocarbon compound represented by the general formula (2),

[Chemical 2] (In the formula, X, Y and Z are methyl groups, chlorine or hydrogen,
X, Y, and Z are not hydrogen at the same time.) (E) Aliphatic ketone compound having 6 to 8 carbon atoms, (F) Divalent ester compound represented by the general formula (3), R ₁ OOC (CH ₂ ) _n COOR ₂ (3) (wherein n is an integer of 1 to 3 and R ₁ and R ₂ represent an alkyl group having 1 to 3 carbon atoms) and at least one selected from the group is added. Is a method for separating methanol and dimethyl carbonate.

According to the present invention, the azeotropic phenomenon of methanol and dimethyl carbonate is destroyed, and each component can be separated and recovered with high purity by ordinary distillation operation under normal pressure. Specific examples of the extractant (A) include methylphenyl carbonate and diphenyl carbonate, and specific examples of the extractant (B) include ethylene carbonate, propylene carbonate and extractant.
Specific examples of (C), anisole, phenol, specific examples of the extractant (D), mesitylene, paradichlorobenzene, orthochlorotoluene, specific examples of the extractant (E), cyclohexanone, dibutyl ketone, extraction Agent
Specific examples of (F) include dimethyl malonate and dimethyl succinate.

Methanol containing these extractants
Dimethyl carbonate-extractant mixture, since there is no azeotropic relationship between any two components, under normal pressure, when performing a distillation operation at an appropriate number of stages, reflux ratio, the lowest boiling point methanol is first distilled and recovered, Dimethyl carbonate is then recovered, leaving the extractant at the bottom of the distillation column. The extractant of the present invention may be added to the methanol-dimethyl carbonate mixture before distillation, or may be supplied to the distillation column separately from the methanol-dimethyl carbonate mixture. Furthermore, if necessary, the bottoms of the distillation column can be recycled and reused. Also,
It is also possible to continuously perform distillation by combining two distillation columns as shown in FIG. 1 and circulating the bottoms of the second distillation column to the first distillation column for reuse. In any case, since the extractant practically distills in the distillation operation,
It can be said that this is an energy-efficient method.

The amount of the extractant to be added is not particularly limited, but from the viewpoint of separation efficiency, the extractant is added to 5 mol of the total mol of methanol, dimethyl carbonate and the extractant.
It is preferably at least mol%, more preferably at least 20 mol%. The figure shows that the azeotropic phenomenon is destroyed by the addition of the extractant of the invention. That is, FIG. 2 is a vapor-liquid equilibrium diagram of methanol-dimethyl carbonate when no extractant is added, and FIG.
The vapor-liquid equilibrium diagram of methanol-dimethyl carbonate in the case of containing by weight is shown. From these figures, it is understood that when the extractant is added, the azeotropic composition does not exist between methanol and dimethyl carbonate. Such a phenomenon is an action commonly occurring in the addition of the extracting agent of the present invention.

[0010]

EXAMPLES Specific examples will be shown below, but the present invention is not limited to these examples. Example 1 From a 36th stage from the top of a glass Oldershaw type distillation column having a column diameter of 30 mm and 48 stages, a mixed solution of 60% by weight consisting of 30% by weight of methanol and 70% by weight of dimethyl carbonate was introduced at a flow rate of 260 g / Hr. Was continuously fed, and at the same time, preheated methylphenyl carbonate as an extractant was continuously fed at a flow rate of 390 g / Hr from the 10th stage from the top of the column. The column top temperature is 64.
The operation was carried out so as to maintain 5 ° C., and when the steady state was reached, the composition of the distillate and the bottom liquid was analyzed by gas chromatography. As a result, the distillate was methanol 9
The composition was 9.7% by weight, dimethylcarbonate 0.3% by weight, and the bottom liquid had a composition of dimethylcarbonate 31.8% by weight and methylphenylcarbonate 68.2% by weight. In the steady state, the amount of distillate was 79 g / Hr, the amount of bottoms was 571 g / Hr, and the temperature of the liquid in the bottom can was 132 ° C.

Examples 2 to 13 Table 1 shows the results when continuous distillation was carried out under the same conditions as in Example 1 except that the type of extractant and the reflux ratio were changed.

[0012]

[Table 1] Table-1 Examples Extraction agent Reflux ratio Distillate composition (wt%) Bottoms composition (wt%) NO Methanol DMC DMC Extractor 2 Diphenyl carbonate 4.0 99.9 0.1 31.8 68.2 3 Ethylene carbonate 3.0 99.7 0.3 31.8 68.2 4 Propylene carbonate 4.0 99.7 0.3 31.8 68.2 5 Anisole 3.0 99.9 0.1 31.8 68.2 6 Phenol 5.0 99.5 0.5 31.8 68.2 7 Mesitylene 4.0 99.6 0.4 31.8 68.2 8 Paradichlorobenzene 4.0 99.5 0.5 31.8 68.2 9 Orthochlorotoluene 4.0 99.5 0.5 31.8 68.2 10 Cyclohexanone 3.0 99.4 0.6 31.8 68.2 11 Dibutyl ketone 3.0 99.3 0.7 31.8 68.2 12 Dimethyl malonate 3.0 99.8 0.2 31.8 68.2 13 Dimethyl succinate 3.0 99.8 0.2 31.8 68.2 * Distillate: 80 g / Hr, Bottoms: 570 g / Hr

Example 14 The bottom liquor extracted in Example 1 from the 14th stage from the top of the 34-stage Oldershaw type distillation column with a diameter of 30 mm was preheated and continuously heated at a flow rate of 571 g / Hr. I've fed. The operation was performed under the condition that the reflux ratio was 2.0 so that the column top temperature was maintained at 91 ° C., and when the steady state was reached, the composition analysis of the distillate and the bottoms was performed. As a result, the distillate was 100.0% by weight of dimethyl carbonate, the bottoms was 0.1% by weight of dimethyl carbonate, and 9% of methylphenyl carbonate.
It was 9.9% by weight. The amount of distillate in the steady state is 181
g / Hr, the amount of bottoms was 390 g / Hr, and the liquid temperature in the bottom can was 184 ° C.

Examples 15 to 26 The bottoms extracted in Examples 2 to 13 were respectively subjected to continuous distillation under the same conditions as in Example 13 except that the feed temperature, feed amount and reflux ratio were changed. The results are shown in Table-2.

[0015]

[Table 2] Table-2 Examples Feed liquid Reflux ratio Distillate composition (wt%) Bottoms composition (wt%) NO Methanol DMC DMC Extractant 15 Example 2 Bottoms 2.0 100.0 0.0 0.1 99.9 16 Examples 3 bottoms 2.0 100.0 0.0 0.1 99.9 17 Example 4 bottoms 2.0 100.0 0.0 0.1 99.9 18 Example 5 bottoms 2.0 100.0 0.0 0.1 99.9 19 Example 6 bottoms 2.0 100.0 0.0 0.1 99.9 20 Example 7 cans Discharge 2.0 100.0 0.0 0.1 99.9 21 Example 8 bottom discharge 2.0 100.0 0.0 0.1 99.9 22 Example 9 bottom discharge 2.0 100.0 0.0 0.1 99.9 23 Example 10 bottom discharge 2.0 100.0 0.0 0.1 99.9 24 Example 11 bottom discharge 2.0 100.0 0.0 0.1 99.9 25 Example 12 bottom liquor 2.0 100.0 0.0 0.1 99.9 26 Example 13 bottom liquor 2.0 100.0 0.0 0.1 99.9 * Distillate amount: 180 g / Hr, bottom liquor amount: 390 g / Hr

Comparative Example 1 From a 36th stage from the top of a glass-made Oldershaw type distillation column having a column diameter of 30 mm and 48 stages, from a top of the 36th stage, 260 g / 60 g of a mixed solution of 30% by weight of methanol and 70% by weight of dimethyl carbonate was added. It was continuously fed at a flow rate of Hr. The operation was performed under the condition of the reflux ratio of 3.0 so that the overhead temperature was maintained at 64 ° C., and when the steady state was reached, the composition analysis of the distillate and the bottom liquid was performed by gas chromatography. As a result, the distillate was 68.8% by weight of methanol and 31.2% by weight of dimethyl carbonate, and the bottoms was methanol.
The composition was 1% by weight and 99.9% by weight of dimethyl carbonate. The amount of distillate in the steady state is 113 g / H.
r, the amount of canned liquid is 147 g / Hr, the liquid temperature in the bottom can is 9
It was 1 ° C. Next, the obtained distillate is passed through a tower having a diameter of 30 m.
The glass was continuously fed at a flow rate of 113 g / Hr from the 36th stage from the top of a 48-stage glass Oldershaw type distillation column. The operation was performed under the condition that the reflux ratio was 1.0 so that the overhead temperature was maintained at 64 ° C., and when the steady state was reached, the composition analysis of the distillate and the bottoms was performed. As a result, distillate,
Both bottoms were an azeotropic composition mixture of 68.8% by weight of methanol and 31.2% by weight of dimethyl carbonate.

[0017]

EFFECT OF THE INVENTION By adding the extractant shown in the present invention, the azeotropic phenomenon of methanol and dimethyl carbonate is destroyed, and each component can be easily separated and recovered by a normal distillation operation. It is an excellent method that is extremely efficient industrially.

[Brief description of drawings]

FIG. 1 Flowsheet of a continuous extractive distillation process combining two distillation columns.

[Figure 2] Vapor-liquid equilibrium measurement diagram of methanol and dimethyl carbonate

[Fig. 3] Vapor-liquid equilibrium measurement diagram of methanol and dimethyl carbonate when 60% by weight of anisole is contained as an extractant.

[Explanation of symbols]

1 Distillation raw material (main component is methanol and dimethyl carbonate mixture) 2 First tower distillate (main component is methanol) 3 First tower bottom liquid (main component is dimethyl carbonate, extractant mixture) 4 Second tower distillate Liquid (main component is dimethyl carbonate) 5 Second tower bottom liquid (main component is extractant) x Methanol liquid phase mole fraction (two-component basis) y Methanol gas phase mole fraction (two-component basis)

Claims (1)

[Claims] 1. An extractant which destroys an azeotropic phenomenon of methanol and dimethyl carbonate when the azeotropic mixture is separated by distillation, (A) a carbonic acid diester having 4 to 15 carbon atoms, and (B) having 3 to 3 carbon atoms. Cyclic carbonate of 5, (C) allyloxy compound represented by the general formula (1), Ar-OR (1) (wherein Ar is a phenyl group or a toluyl group, R is an alkyl group having 1 to 3 carbon atoms or hydrogen (D) An aromatic hydrocarbon compound represented by the general formula (2), (In the formula, X, Y and Z are methyl groups, chlorine or hydrogen,
X, Y, and Z are not hydrogen at the same time.) (E) Aliphatic ketone compound having 6 to 8 carbon atoms, (F) Divalent ester compound represented by the general formula (3), R ₁ OOC (CH ₂ ) _n COOR ₂ (3) (wherein n is an integer of 1 to 3 and R ₁ and R ₂ represent an alkyl group having 1 to 3 carbon atoms) and at least one selected from the group is added. A method for separating methanol and dimethyl carbonate.