JP3036677B2 - Dimethyl carbonate distillation separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing dimethyl carbonate by efficiently distilling and separating dimethyl carbonate from a mixture of dimethyl carbonate and dimethyl oxalate in the production of dimethyl carbonate and the like. Dimethyl carbonate is a compound useful as a synthetic raw material for aromatic polycarbonates, medical and agricultural chemicals, and the like, and as a solvent.

[0002]

2. Description of the Related Art Dimethyl carbonate is produced, for example, by reacting carbon monoxide, methanol and oxygen in the presence of copper chloride (Japanese Patent Publication No. 55-45555), by subjecting a cyclic carbonate such as ethylene carbonate to an ester in the presence of a catalyst. A method of performing an exchange reaction (for example, Japanese Patent Publication No. 60-27658) and a method of performing a gas phase contact reaction between carbon monoxide and a nitrite in the presence of a catalyst (for example, Japanese Patent Application Laid-Open No. 3-141243).
In any case, it is obtained as a mixture with methanol. For this reason, separation and removal of methanol is indispensable for distilling and separating dimethyl carbonate. However, dimethyl carbonate and methanol have a composition ratio of 3
Since an azeotrope is formed at a ratio of 0:70 (weight ratio), it is not easy to distill and separate dimethyl carbonate from a mixture of dimethyl carbonate and methanol at normal pressure.

As a method of distilling and separating dimethyl carbonate from a mixture of dimethyl carbonate and methanol at normal pressure, for example, this mixture is distilled in the presence of dimethyl oxalate to separate and remove methanol, and then dimethyl carbonate and dimethyl oxalate are removed. A method of distilling and separating dimethyl carbonate from a mixture of the above is known (Japanese Patent Application Laid-Open Nos. 4-270249 and 6-25).
No. 104).

Conventionally, the separation of dimethyl carbonate from the mixture of dimethyl carbonate and dimethyl oxalate by distillation has been carried out in a distillation column at normal pressure. High levels of heat had to be used, requiring large amounts of energy. Also, a dimethyl carbonate production process (Japanese Patent Laid-Open No. 6-25104)
Distillation of dimethyl carbonate from the above mixture of dimethyl carbonate and dimethyl oxalate by means of a single distillation column under reduced pressure, using a low-level heat source of 130 ° C. or lower generated from utility equipment, utility equipment or other chemical manufacturing processes. When the separation is performed, when the temperature at the bottom of the column is 100 ° C. or lower, the temperature at the top of the column becomes 30 ° C. or lower, and there is a problem that ordinary cooling water (about 30 ° C.) cannot be used for the condenser. For this reason, in order to use a low-level heat source as described above, the condenser must be directly cooled by a refrigerating device or cold water cooled indirectly must be used. There was a problem that it was no longer a good idea.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for distilling dimethyl carbonate from a mixture of dimethyl carbonate and dimethyl oxalate obtained by distilling a mixture of dimethyl carbonate and methanol in the presence of dimethyl oxalate. , 130 ° C
Provided is a method for distilling and separating dimethyl carbonate which is advantageous in terms of energy, by effectively utilizing the following low-level heat sources and distilling and separating dimethyl carbonate using ordinary cooling water (about 30 ° C.) for a condenser. It is intended for.

[0006]

An object of the present invention is to distill and separate dimethyl carbonate from a mixture of dimethyl carbonate and dimethyl oxalate obtained by distilling a mixture of dimethyl carbonate and methanol in the presence of dimethyl oxalate. The above is achieved by a method for distilling and separating dimethyl carbonate, which comprises separating and distilling dimethyl carbonate under reduced pressure using two distillation columns having different operating pressures in series.

Hereinafter, the present invention will be described in detail. A mixture of dimethyl carbonate and methanol can be prepared by a known method for producing dimethyl carbonate, for example, a method of reacting carbon monoxide, methanol and oxygen in the presence of copper chloride (Japanese Patent Publication No. 55-45655). In the gas phase in the presence of a catalyst (JP-A-3-141243, JP-A-3-141243)
-25104) as a reaction mixture. Also, a method for producing dimethyl carbonate by subjecting a cyclic carbonate such as ethylene carbonate to a transesterification reaction with methanol in the presence of a catalyst (Japanese Patent Publication No. 60-27658, etc.)
Also, it can be obtained as a distillate during the reaction in a method for producing diphenyl carbonate by transesterifying dimethyl carbonate and phenol (Japanese Patent Application Laid-Open No. 7-101908).

Although the amount of methanol contained in the mixture of dimethyl carbonate and methanol is not particularly limited,
Usually 5 to 30% by weight of methanol is contained in this mixture. If water is present in a mixture of dimethyl carbonate and methanol, dimethyl oxalate is hydrolyzed. Therefore, it is preferable to remove water in advance as necessary.

In consideration of this point, the reaction mixture obtained by the gas-phase catalytic reaction of carbon monoxide and nitrite in the presence of a catalyst contains almost no water and uses a small amount of dimethyl oxalate as a by-product. Therefore, among the above-mentioned mixtures of dimethyl carbonate and methanol, it is the most preferable to produce dimethyl carbonate by applying the method of the present invention. Further, since the distillate obtained when producing dimethyl carbonate or diphenyl carbonate by the transesterification reaction does not contain water, it can be suitably used for separating and purifying dimethyl carbonate by applying the method of the present invention. it can.

Dimethyl oxalate must be present in a mixture of dimethyl carbonate and methanol so that the molar fraction of dimethyl oxalate in the three components is at least 0.3, especially at least 0.5, in order to increase the separation efficiency of methanol. Is preferred. In addition, from the viewpoint of separation efficiency, there is no upper limit, but it may be an industrially practicable range, for example, 0.9.

In the three-component system of dimethyl oxalate-dimethyl carbonate-methanol, dimethyl carbonate and methanol do not form an azeotropic mixture, so that methanol can be separated by ordinary atmospheric distillation. This distillation separation of methanol,
For example, JP-A-4-270249 and JP-A-6-2510
No. 4, methanol and the like are extracted from the top of the distillation column, and a mixture of dimethyl carbonate and dimethyl oxalate is extracted from the bottom of the distillation column.

The mixture of dimethyl carbonate and dimethyl oxalate is then distilled under reduced pressure using two distillation columns in series with different operating pressures. In the first column, a mixture of dimethyl carbonate and dimethyl oxalate from which methanol and the like have been separated as described above, and a distillate withdrawn from the top of the second column are supplied to the center of the column, where distillation is performed under reduced pressure. From the top of the column, dimethyl carbonate having a purity of almost 100% is withdrawn as a distillate, and a mixture of dimethyl carbonate and dimethyl oxalate having a dimethyl carbonate concentration of 3 to 10% by weight is withdrawn from the bottom of the column. Second
Feed to the top of the tower. The distillate at the top of the second column has a high concentration of dimethyl carbonate, and thus is supplied above the mixture of dimethyl carbonate and dimethyl oxalate from which methanol and the like have been separated.

In the distillation in the first column, since ordinary cooling water (about 30 ° C.) is used for the condenser, the operation pressure is such that the top temperature is usually 35 ° C. or higher, preferably 40 to 50 ° C., ie, 70 mmHg. Above, preferably 110-2
At a pressure of 00 mmHg, the reflux ratio is usually 0.1 to 5.0,
Preferably, it is performed under the condition of 0.5 to 2.0. The bottom temperature depends on the temperature of the low-level heat source to be used.
The temperature is 0 ° C or higher, preferably 90 to 100 ° C. If this temperature is raised as high as possible, the concentration of dimethyl carbonate at the bottom of the column is reduced and energy efficiency is improved. However, since the heat transfer area of the reboiler is increased, the bottom temperature is appropriately selected within the above temperature range.

As the distillation column, a usual packed column or plate column is used. As a low-level heat source, a dimethyl carbonate production process (JP-A-6-25104)
And low-level heat sources of 130 ° C. or less generated from utility equipment or other chemical manufacturing processes such as diphenyl carbonate.

In the second column, a mixture of dimethyl carbonate and dimethyl oxalate having a concentration of dimethyl carbonate extracted from the bottom of the first column of 3 to 10% by weight as described above is supplied to the top of the column, and the pressure is reduced. Distillation is performed, and a mixture of dimethyl carbonate and dimethyl oxalate having a dimethyl carbonate concentration of 40 to 60% by weight is withdrawn as a distillate from the top of the column, and dimethyl oxalate having a purity of almost 100% is obtained from the bottom of the column. It is extracted. Then, the mixture of dimethyl carbonate and dimethyl oxalate extracted from the top of the column is circulated and supplied to the center of the first column as described above, and the dimethyl oxalate extracted from the bottom of the column is separated by distillation of methanol in the previous step. It is circulated and supplied to the process.

The distillation in the second column is carried out using the same cooling water, low-level heat source and equipment as in the first column. At this time, the bottom temperature is usually 80 ° C or higher, preferably 90 to 100 ° C, as in the first column. The operating pressure is determined from the liquid composition and the temperature at the bottom of the column, and is usually set at 35 mmHg or more, preferably 50 to 80 mmHg, lower than that of the first column. The reflux ratio is usually 0.1 to 3.0, preferably 0.3 to 1.5, and the overhead temperature is usually 75 to 85 ° C.
It is. In addition, ordinary cooling water (about 30
° C), the condenser outlet temperature is usually 35 ° C
As described above, the temperature is preferably maintained at 40 to 50 ° C.

Next, the process of the present invention will be specifically described with reference to a flow sheet drawing showing one embodiment of the present invention. A mixture of dimethyl carbonate and dimethyl oxalate obtained by distilling and separating methanol in the presence of dimethyl oxalate is supplied to the middle part of the distillation column 1 (first column) through the conduit 3, and at the same time, the distillation column 2 (second column) The distillate withdrawn from the top of (1) is also supplied to the middle of the first column through the conduit 4.
By heating the bottom with a low level heat source and performing distillation under reflux,
Dimethyl carbonate having a purity of almost 100% is withdrawn from the top of the column through a conduit 5. Then, a mixture of dimethyl carbonate and dimethyl oxalate having a concentration of dimethyl carbonate of several percent is withdrawn from the bottom of the column through a conduit 6. A part of the mixture extracted from the bottom of the tower is heated by a reboiler and circulated to the bottom of the tower through a conduit 7.

In the distillation column 2 (second column), a mixture of dimethyl carbonate and dimethyl oxalate extracted from the bottom of the first column through the conduit 6 is supplied to the top of the column, and distillation is performed in the same manner as in the first column. Done. However, the operating pressure of the second column is maintained lower than the operating pressure of the first column. As a result, a mixture of dimethyl carbonate and dimethyl oxalate whose dimethyl carbonate concentration was increased to several tens of percent was extracted from the top of the column, and dimethyl oxalate having a purity of almost 100% was extracted from the bottom of the column through a conduit 8. Will be issued. A part of the dimethyl oxalate is heated by the reboiler and circulated through the conduit 9 to the bottom of the column.

As described above, from the mixture of dimethyl carbonate and dimethyl oxalate obtained by distilling the mixture of dimethyl carbonate and methanol in the presence of dimethyl oxalate,
A low-level heat source of 130 ° C. or less can be effectively used, and dimethyl carbonate can be efficiently distilled and separated using ordinary cooling water (about 30 ° C.) for the condenser.

[0020]

Next, the method of the present invention will be specifically described with reference to examples and comparative examples. Example 1 A mixture of dimethyl carbonate and dimethyl oxalate obtained by distillation of methanol in the presence of dimethyl oxalate obtained according to JP-A-6-25104 (dimethyl carbonate 14.
(3% by weight) 1000 kg / hr is introduced into the middle stage of a distillation column (first column) having an inner diameter of 400 mm and a height of 3000 mm, and at the same time a distillate (dimethyl carbonate 41) withdrawn from the top of the distillation column (second column). 0.01% by weight) of 79.1 kg / hr
It is introduced into the middle stage of the tower, and the bottom temperature is 100 ° C and the top temperature is 40
Distillation was performed at a temperature of 110 ° C. and a pressure of about 110 mmHg. The reflux ratio was 1.13, and normal cooling water (30 ° C.) was used for cooling.
Saturated steam at 120 ° C. was used for the reboiler.

From the top of the first column, 142.3 kg / hr of dimethyl carbonate having a purity of 99.9% by weight was obtained. From the bottom of the first column, dimethyl carbonate having a reduced concentration of dimethyl carbonate and dimethyl oxalate were obtained. 936.8 kg / hr of the mixture (3.6% by weight of dimethyl carbonate) was extracted and the inner diameter was 200 m.
m, and supplied to the upper portion of a distillation column (second column) having a height of 3000 mm.

In the second column, distillation was performed at a bottom temperature of 100 ° C., a top temperature of 84 ° C., and a pressure of about 80 mmHg. The reflux ratio was 0.50, ordinary cooling water (30 ° C.) was used for cooling, and 120 ° C. saturated steam was used for the reboiler. 79.1 kg of a distillate (41.0% by weight of dimethyl carbonate) having a high dimethyl carbonate concentration from the top of the second column
/ Hr was withdrawn and fed to the center of the first column. On the other hand, 857.7 kg / hr of dimethyl oxalate having a purity of 99.9% by weight was obtained from the bottom of the second column.

Comparative Example 1 A mixture of dimethyl carbonate and dimethyl oxalate obtained by distillation of methanol in the presence of dimethyl oxalate obtained according to JP-A-6-25104 (dimethyl carbonate 14.
3 kg) of 1000 kg / hr was introduced into the middle stage of a distillation column having an inner diameter of 200 mm and a height of 6000 mm.
At 90 ° C. and at a top temperature of 90 ° C. under normal pressure. And 142.3 kg of dimethyl carbonate having a purity of 99.9% by weight from the top of the tower.
/ Hr, and 857.7 kg / hr of dimethyl oxalate having a purity of 99.9% by weight was obtained from the bottom of the column. The reflux ratio was 1.36, normal cooling water (30 ° C.) was used for cooling, and high-pressure steam at 200 ° C. was used for the reboiler.
In this method, a high-level heat source of 200 ° C. or more had to be used for the reboiler, and a large amount of energy was required.

Comparative Example 2 A mixture of dimethyl carbonate and dimethyl oxalate obtained by distilling off methanol in the presence of dimethyl oxalate obtained according to JP-A-6-25104 (dimethyl carbonate 14.
3 kg) of 1000 kg / hr was introduced into the middle stage of a distillation column having an inner diameter of 400 mm and a height of 6000 mm.
The distillation was carried out at a temperature of 30 ° C., a top temperature of 30 ° C. and a pressure of about 80 mmHg. Then, 142.3 kg / hr of dimethyl carbonate having a purity of 99.9% by weight was obtained from the top of the tower, and a purity of 92.3 kg / hr was obtained from the bottom of the tower.
97.7% by weight of dimethyl oxalate (857.7 kg / hr) was obtained. The reflux ratio was 1.95, cooling water (15 ° C.) cooled by a refrigeration system was used for cooling, and 120
C. Saturated steam was used. Since this method requires a refrigeration apparatus, using a low-level heat source has not been energetically favorable as a result.

[0025]

According to the method of the present invention, a mixture of dimethyl carbonate and dimethyl oxalate, which is obtained by distilling a mixture of dimethyl carbonate and methanol in the presence of dimethyl oxalate, is subjected to distillation separation of dimethyl carbonate from the mixture of dimethyl carbonate and dimethyl oxalate. A low-level heat source at a temperature of not more than 0 ° C. can be effectively used, and dimethyl carbonate can be separated by distillation using ordinary cooling water (about 30 ° C.) for the condenser. According to the present invention, it is possible to provide a method for distilling and separating dimethyl carbonate which is very advantageous in terms of energy.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention.

[Explanation of symbols]

 Reference numerals 1 and 2 denote distillation columns, and reference numerals 3 to 9 denote conduits.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-228026 (JP, A) JP-A-6-25104 (JP, A) JP-A-4-270249 (JP, A) JP-A-2- 212456 (JP, A) JP-A-57-42656 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 69/96 C07C 68/08

Claims (1)

(57) [Claims] 1. A distillation column having a different operating pressure for distilling and separating dimethyl carbonate from a mixture of dimethyl carbonate and dimethyl oxalate obtained by distilling a mixture of dimethyl carbonate and methanol in the presence of dimethyl oxalate. A method for separating dimethyl carbonate by distillation under reduced pressure using two columns in series.