JP2002371037A - Method for producing dimethyl carbonate having high purity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing dimethyl carbonate having high purity by efficiently removing glycol ether produced as a by-product in the transesterification reaction of ethylene carbonate and methanol. SOLUTION: Dimethyl carbonate is produced in high purity by distilling a transesterification reaction product of ethylene carbonate and methanol with a distillation column having a theoretical plate number of >=10 to concentrate the by-produced glycol ether in the column, extracting the concentrated glycol ether from the side stream and distilling out high-purity dimethyl carbonate from the column top.

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 high-purity dimethyl carbonate, which efficiently separates glycol ether by-produced in the step of producing dimethyl carbonate by subjecting ethylene carbonate and methanol to a transesterification reaction. .

[0002]

2. Description of the Related Art A method for producing dimethyl carbonate includes:
There are a methanol carbonylation method, a urea methanolysis method, a transesterification method and the like, which have been put to practical use or proposed. Among them, the transesterification method for producing dimethyl carbonate by reacting ethylene carbonate and methanol revealed that glycol ether is by-produced in the process of producing dimethyl carbonate by transesterification. Conventional studies have not found any knowledge about the removal of glycol ethers.

[0003]

In the conventional method for producing dimethyl carbonate, separation of glycol ether has not been studied. However, glycol ether is a product because the boiling points of glycol ether and dimethyl carbonate are relatively close. There was a problem that it was easily mixed into the dimethyl carbonate side. That is, an object of the present invention is to provide a method for producing high-purity dimethyl carbonate by efficiently removing glycol ether by-produced in a transesterification reaction using ethylene carbonate and methanol as raw materials.

[0004]

The present inventors have conducted various studies to solve the above-mentioned problems. As a result, glycol ether by-produced has a boiling point close to that of dimethyl carbonate. Causes the purity of dimethyl carbonate to drop with dimethyl carbonate, but by appropriately adjusting the operating conditions of the dimethyl carbonate purification column, the glycol ether is concentrated in the distillation column, preferably at a position above the feed stage. What you can do
In addition, the present inventors have found that glycol ether can be effectively removed by extracting the glycol ether alone or together with other components from the enrichment site, that is, the side stream, and high-purity dimethyl carbonate can be distilled out. The invention has been reached.

[0005] That is, the gist of the present invention is to distill the reaction product liquid obtained by subjecting ethylene carbonate and methanol to a transesterification reaction using a distillation column having 10 or more theoretical plates to convert the by-product glycol ether into a column. The process for producing high-purity dimethyl carbonate is characterized in that the high-purity dimethyl carbonate which does not contain glycol ether is distilled off from the top of the column and concentrated from the side stream.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The transesterification reaction is a reaction in which ethylene carbonate and methanol are subjected to a transesterification reaction in the presence of a catalyst to produce dimethyl carbonate and ethylene glycol. Is done.

[0007]

Embedded image

As the catalyst, a conventional transesterification catalyst can be selected. Specifically, as a homogeneous catalyst, amines such as triethylamine, alkali metals such as sodium, alkali metal compounds such as sodium chloroacetate and sodium methylate, and thallium compound,
Examples of heterogeneous catalysts include ion exchange resins modified with functional groups, amorphous silicas impregnated with alkali metal or alkaline earth metal silicates, ammonium exchanged Y-type zeolites, mixed oxides of cobalt and nickel, and the like. Can be respectively exemplified.

The transesterification reaction conditions are generally as follows: the reaction temperature is 50 to 180 ° C., and the charged molar ratio of methanol to ethylene carbonate is 2 to 20. If the molar ratio is less than 2, the conversion of transesterification decreases, while if it exceeds 20, a large amount of unreacted raw material remains in the system, requiring a large amount of energy such as heating and cooling, or the case of recycling. There are problems such as an increase in the load on the equipment.

This transesterification reaction is an equilibrium reaction, and the reaction product solution contains raw materials such as ethylene carbonate and methanol in addition to the product dimethyl carbonate and ethylene glycol. Further, the above equation (1)
The glycol ether (2-methyethanol) is produced by the side reaction of the following formula (2) at the same time as the main reaction of the formula (2), and the reaction product liquid also contains this by-product glycol ether.

[0011]

Embedded image

[0012] distillation separation in the by-product glycol ether has a boiling point 124.4 ° C., methanol (64.7 ° C.), dimethyl carbonate (9
0.3 ° C) and higher than ethylene glycol (1
97.3 ° C), ethylene carbonate (248.2 ° C)
It has a lower boiling point. Among these components contained in the reaction solution, methanol is removed prior to rectification of dimethyl carbonate, and the methanol is recycled to the transesterification reaction.

The reaction product from which methanol has been removed is subsequently separated by distillation into a high-purity dimethyl carbonate distillate and a bottoms containing by-product ethylene glycol and unreacted ethylene carbonate. The mixture of ethylene glycol and ethylene carbonate separated as a bottom liquid is usually converted into ethylene glycol by hydrolysis, dehydrated, and then commercialized as ethylene glycol. If there is a glycol ether mixed in on the ethylene glycol side, it can be removed together with water by a dehydration operation.

Attention must be paid to the following 1) to 3) in the distillation separation of the present invention. 1) Dimethyl carbonate is a product requiring particularly high purity, and it is not preferable that glycol ether is mixed therein. 2) Since the amount of glycol ether produced is as small as about 0.1 mol% in a reaction at 140 ° C., it is mixed into dimethyl carbonate under ordinary distillation conditions and cannot be separated. 3) Since the boiling point of glycol ether is close to that of dimethyl carbonate, if the glycol ether is to be separated together with ethylene glycol, the dimethyl carbonate is also entrained by ethylene glycol and loss occurs. Therefore, it has been difficult to efficiently separate these components at a degree optimized for general distillation conditions.

Therefore, in the present invention, by setting the distillation conditions including the side distillation, glycol ether is remarkably concentrated in the portion above the feed stage in the distillation column,
It is characterized in that glycol ether is effectively removed by extracting a small amount of liquid from this site.
As the distillation conditions, the number of theoretical plates required for the distillation separation varies depending on the reflux ratio, but in consideration of economy, 10 or more plates are preferable, and 15 or more plates are more preferable. For the concentration of glycol ether, it is necessary to increase it to some extent, but if it is too large, energy consumption increases. Usually, the number of theoretical plates is 100 or less, preferably 50 or less, more preferably 30 or less. The glycol ether is concentrated above the feed stage of the distillation column by selecting a reflux ratio of the distillation column of one or more optimal conditions.
The reflux ratio is preferably from 1 to 10, and more preferably from 3 to 7. In order to commercialize the bottoms from the bottom of the distillation column as ethylene glycol, high operating temperatures will adversely affect the quality of the product ethylene glycol. Avoid. However,
If the pressure is too low, both the separation efficiency and the energy efficiency deteriorate, so it is necessary to select an appropriate pressure. A suitable pressure range is 40 kPa or less, preferably 13-27.
The range is kPa. Further, it is preferable that the number of theoretical sections of the distillation column is three or more, from the viewpoint of preventing dimethyl carbonate from being mixed into ethylene glycol.

The distillation column includes a packed column, a packed packing such as Sulzer packing, Mela pack, MC pack, etc., or IM.
Any type such as a packed tower filled with irregular packing such as TP and Raschig ring, a bubble bell tower, a sieve tray, a tray tower using a valve tray tower, and the like can be used.

[0017]

The reaction product transesterification reactor was 28 cm in diameter and 200 cm in length.
Was charged with a cobalt-yttrium mixed oxide catalyst inside, and the internal temperature was kept at 140 ° C. with a jacket from the outside to carry out a reaction between ethylene carbonate and methanol. The obtained reaction product liquid was separated by distillation at a tower top pressure of 101.3 kPa, a tower top temperature of 64 ° C, and a tower bottom temperature of 160 ° C. From the top, a mixture consisting of 90% by weight of methanol and 10% by weight of dimethyl carbonate was obtained. On the other hand, a mixture having the following composition was obtained from the column bottom as a reaction product liquid obtained by separating and recovering methanol. Dimethyl carbonate 19.7% by weight Glycol ether 0.1% by weight Ethylene glycol 13.6% by weight Ethylene carbonate 66.5% by weight

The distillative separation above methanol separated and recovered reaction product solution, Figure 1
Was fed to a distillation apparatus having 20 theoretical plates as shown in Table 2 to perform distillation separation. Table 1 shows the operating conditions of the distillation column, and Table 2 shows the mass balance. Here, Comparative Example 1 was a case in which only separation of dimethyl carbonate, ethylene glycol and ethylene carbonate was considered without considering removal of glycol ether, and Comparative Example 2 was a case in which glycol ether was concentrated in a distillation column. An example is the case where the glycol ether is removed from the middle stage.

Comparative Example 1 The number of theoretical plates in the distillation column was set to 20 (the condenser was set to the first stage and the reboiler was set to the 20th stage).
The reaction product from which the methanol was separated and recovered was fed to the stage. The reflux ratio was set to 1.2 so that ethylene glycol or ethylene carbonate was not mixed into the overhead distillate, and the dimethyl carbonate in the bottoms was about 0.1% by weight. Under these conditions, all of the glycol ether is mixed into the dimethyl carbonate.

Comparative Example 2 In Comparative Example 2, the feed stage was lowered to the 14th stage and the reflux ratio was increased to 5 in order to facilitate the separation of glycol ether and dimethyl carbonate. As a result, the glycol ether was significantly concentrated around the eleventh stage. As for the glycol ether, 69% of the feed amount was distributed to the bottoms side. In addition, dimethyl carbonate in the bottom was reduced to less than 20 ppm by weight due to the effect of increasing reflux, but glycol ether is still mixed in the distilled dimethyl carbonate.

Example In the example, a sidestream liquid was withdrawn at 50 g / h from the twelfth stage. The side stream contained 28% by weight of glycol ether and 52% by weight of dimethyl carbonate, and 99.9% by weight or more of the fed glycol ether could be removed from the side stream. Since the glycol ether was removed, the dimethyl carbonate concentration in the overhead distillate was 10%.
It was 0% by weight, and a result was obtained in which dimethyl carbonate was not substantially contained in the bottom.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

According to the present invention, it is possible to efficiently remove glycol ether by-produced in a transesterification reaction using ethylene carbonate and methanol as raw materials, thereby efficiently producing high-purity dimethyl carbonate. can get.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a distillation apparatus.

Claims (4)

[Claims] A reaction product obtained by subjecting ethylene carbonate and methanol to a transesterification reaction is treated with a theoretical plate number of 1
Distillation is performed using a zero-stage or more distillation column to concentrate the by-product glycol ether in the column, extract it from the sidestream, and distill high-purity dimethyl carbonate containing no glycol ether from the top of the column. Characteristic method for producing high-purity dimethyl carbonate. 2. The method according to claim 1, wherein the glycol ether is concentrated at a position higher than a feed stage of the distillation column by selecting an optimum condition of a reflux ratio of the distillation column of 1 or more. A method for producing high-purity dimethyl carbonate. 3. The method for producing high-purity dimethyl carbonate according to claim 1, wherein the recovery section of the distillation column has three or more theoretical plates. 4. The method for producing high-purity dimethyl carbonate according to claim 1, wherein the operating pressure of the distillation column is set to an atmospheric pressure or less.