JP2003119168A - Method for producing dimethyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing dimethyl carbonate, capable of giving such a structure of a reactor as the dimethyl carbonate is produced at a low cost, when the dimethyl carbonate is produced by transesterification of ethylene carbonate and methanol. SOLUTION: In this method for producing the dimethyl carbonate by the transesterification of the ethylene carbonate and the methanol, the dimethyl carbonate is produced by using equipment having the following three units (1) to (3): (1) a reaction unit for conducting the transesterification; (2) a gaseous methanol-recovering unit for liquefying the gaseous methanol which is discharged from the reaction unit or a liquid methanol-recovering unit so as to feed the liquefied methanol into the reaction unit; and (c) the liquid methanol-recovering unit for gasifying the methanol in a liquid reaction mixture which is discharged from the reaction unit so as to feed the gasified methanol into the reaction unit or the gaseous methanol-recovering unit.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a dimethyl carbonate by subjecting ethylene carbonate and methanol to transesterification, to obtain a raw material methanol,
The present invention relates to a method for producing dimethyl carbonate by efficiently reacting while circulating between three units of a reaction unit, a gaseous methanol recovery unit and a liquid methanol recovery unit.

[0002]

2. Description of the Related Art Conventional methods of transesterification of ethylene carbonate with methanol include batch reaction and continuous reaction. As the type of reactor, a stirring tank and a continuous flow reactor are generally used, but various methods by reactive distillation have also been proposed (Patent No. 252902).
5, Japanese Patent Publication No. 7-68180, Japanese Patent Laid-Open No. 9-176.
061, JP-A-9-183744, and JP-A-9-1944.
35, JP-A-5-213830, and JP-A-9-27868.
No. 9). In an ideal reactive distillation, both the raw materials methanol and ethylene carbonate had a conversion rate of 1
It becomes 00%, and dimethyl carbonate is obtained from the top of the reactive distillation column and ethylene glycol is obtained from the bottom of the column, but for that purpose, a huge number of stages is required.

[0003]

In such a conventional method for producing dimethyl carbonate by a transesterification reaction, since the transesterification reaction is an equilibrium reaction,
There is a limit to the raw material conversion rate in stirring tanks and continuous flow reactors. Further, in the reactive distillation, since the reaction is carried out while continuously extracting the product, the raw material conversion rate can be improved, but since the low boiling point product dimethyl carbonate is distilled from the upper part of the column, the energy cost becomes large. .
Furthermore, since the distillate composition is an azeotropic mixture of dimethyl carbonate and methanol, it is necessary to separate dimethyl carbonate and methanol to recycle unreacted methanol to the reactive distillation column, and there is also a problem that energy is required there. there were. That is, an object of the present invention is to provide a reactor structure which can be produced at low cost when producing dimethyl carbonate by transesterification reaction of ethylene carbonate and methanol.

[0004]

Means for Solving the Problems As a result of various studies to solve the above problems, the present inventor has combined a transesterification reaction unit, a gaseous methanol recovery unit, and a liquid methanol recovery unit to produce a raw material methanol. By continuously removing the product dimethyl carbonate and ethylene glycol in liquid form while circulating, it is possible to easily increase the conversion rate of ethylene carbonate, which is another raw material, and reduce the required energy. The present invention has been accomplished by the finding that The present inventor has also found that the concentration of dimethyl carbonate in the gaseous methanol recovery unit can be effectively suppressed by using the raw material ethylene carbonate as the extraction solvent.

That is, the gist of the present invention resides in a method for producing dimethyl carbonate from ethylene carbonate and methanol by a transesterification reaction, which is characterized by using an apparatus including the following three units. . (1) Reaction unit for performing the transesterification reaction (2) Gaseous methanol recovery unit that liquefies the gaseous methanol sent from the reaction unit or liquid methanol recovery unit and sends it to the reaction unit (3) Liquid sent from the reaction unit Liquid methanol recovery unit that vaporizes methanol in the reaction mixture and sends it to the reaction unit or gaseous methanol recovery unit

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention comprises a reaction unit for transesterifying ethylene carbonate and methanol, a gaseous methanol recovery unit for liquefying unreacted methanol remaining in a gaseous state and returning it to the reaction unit, and a liquid state. An apparatus including 3 units of a liquid methanol recovery unit which vaporizes the remaining methanol and returns it to the reaction unit is used. In the method of the present invention, the transesterification reaction is not unique while circulating methanol between the reaction unit, the gaseous methanol recovery unit and the liquid methanol recovery unit. The most typical embodiment is as follows. The liquid extracted from the reaction unit is supplied to the liquid methanol recovery unit. If there is any extracted gas, supply it to the gaseous methanol recovery unit. If necessary, the extracted liquid may be flash-separated, and the gas may be supplied to the gaseous methanol recovery unit and the liquid may be supplied to the liquid methanol recovery unit. In the gaseous methanol recovery unit, dimethyl carbonate is separated into a column bottom by extractive distillation using ethylene carbonate as a raw material as an extraction solvent, and methanol is concentrated at a high reflux ratio at the column top. The bottom liquid is supplied to the reaction unit. In the liquid methanol recovery unit, the liquid methanol remaining is cooked up and supplied to the reaction unit or the gaseous methanol recovery unit. On the other hand, the produced dimethyl carbonate is withdrawn in liquid form from the liquid methanol recovery unit together with by-produced ethylene glycol and unreacted ethylene carbonate.

Reaction unit In the reaction unit, transesterification reaction between ethylene carbonate and methanol is carried out. The transesterification reaction is
A liquid phase equilibrium reaction represented by the following formula (1):

[0008]

[Chemical 1]

The presence of a catalyst is preferred to accelerate the reaction. As the catalyst, either a homogeneous catalyst or a heterogeneous catalyst can be used, but it is desirable to use the heterogeneous catalyst in consideration of the ease of separation. Specifically, catalysts such as ion-exchange resins modified with functional groups, amorphous silicas impregnated with alkali metal or alkaline earth metal silicates, ammonium-exchanged Y-type zeolite, and mixed oxides of cobalt and nickel can be used. used.

The pressure of the reaction unit can be arbitrarily set, but considering that it is a liquid phase reaction and that the boiling point of the raw material methanol is about 65 ° C. at normal pressure, it is preferable to set the pressure to 1 MPaA or more. . The temperature of the reaction unit is selected from the boiling temperature of methanol or lower at the pressure of the reaction unit, but considering the reaction rate, it is preferably as high as possible, for example, in the range of 50 to 180 ° C. The molar ratio of methanol to ethylene carbonate is generally 1-5, preferably 1.5-3. When this molar ratio is less than 1, the conversion rate of transesterification decreases,
On the other hand, if it exceeds 5, a large amount of unreacted raw material remains in the system, which requires a large amount of energy such as heating and cooling, and there is a problem that the burden on the equipment when recycling is increased. Furthermore, since the reaction is an endothermic reaction of 130 kJ / mol, it is necessary to supply a sufficient amount of heat to maintain the reaction, and specifically, it is supplied by a heat transfer means such as a jacket. The reaction unit may also be a reactive distillation section (see attached FIG. 2). In that case, the theoretical plate number 1-2
It is desirable that the number of stages is 0, preferably 5 to 15. The operating conditions are set so that almost all the product dimethyl carbonate can be obtained in liquid form from the bottom of the column. The raw material methanol is supplied to the reaction unit in liquid form. In addition,
Depending on the arrangement of the three units (see attached Figure 2),
Part of the vaporized methanol recovered by the liquid methanol recovery unit may be supplied, but this vaporized methanol comes into contact with the liquid in the reaction unit to become partly liquid, and the rest is gaseous methanol recovery unit. It is liquefied and recovered by and is supplied again to the reaction unit. On the other hand, the raw material ethylene carbonate may be directly supplied to the reaction unit in a liquid state, but it is usually preferable to supply it to the reaction unit via the following gaseous methanol recovery unit (see FIGS. 1 and 2 attached). reference).

Gaseous Methanol Recovery Unit In the gaseous methanol recovery unit, the gaseous methanol sent from the reaction unit or the liquid methanol recovery unit is liquefied and sent to the reaction unit. The means for liquefying the gaseous methanol is not particularly limited, but the gaseous methanol sent from the reaction unit or the liquid methanol recovery unit contains dimethyl carbonate, which is a low boiling point product of the azeotropic composition with methanol. Therefore, it is preferable to adopt a means capable of separating by a difference in boiling point, for example, a distillation column type. In that case, it is desirable to set the theoretical plate number to 1 to 20, preferably 2 to 15. Furthermore, it is preferable to reduce the required energy by selecting distillation conditions so that dimethyl carbonate does not escape from the gaseous methanol recovery unit in a gaseous state. For that purpose, the gaseous methanol recovery unit is preferably an extractive distillation column. That is, the required energy can be reduced by supplying the raw material ethylene carbonate as an extraction solvent to the unit and extracting and separating dimethyl carbonate before condensing the methanol. The distillate extracted from the top of the extractive distillation column is high-purity methanol and can be returned to the reaction unit without requiring any particular purification means.
Of course, it is also possible to operate at total reflux without extracting the distillate. In this case, the liquefied methanol is supplied to the reaction unit from the lower part of the extractive distillation column together with ethylene carbonate, which is a raw material and an extracting solvent. The operating pressure of the gaseous methanol recovery unit can also be set independently of the reaction unit. However, if the operating pressure is lowered too much, the boiling temperature of methanol decreases, and ordinary cooling water cannot be used for condensation. Therefore, it is preferably 50 KPaA or more.

Liquid Methanol Recovery Unit In the liquid methanol recovery unit, methanol in the liquid reaction mixture sent from the reaction unit is vaporized and sent to the reaction unit or the gaseous methanol recovery unit. Means for vaporizing methanol in the liquid reaction mixture is not particularly limited, but in the liquid methanol recovery unit, simultaneously with the vaporization of methanol, the transesterification reaction product dimethyl carbonate, ethylene glycol and unreacted ethylene contained in the liquid reaction mixture. In order to obtain the carbonate in a liquid state, it is preferable to adopt a means capable of separating the carbonates depending on the difference in boiling point, for example, a distillation column type. In that case, since the reaction unit or the gaseous methanol recovery unit shares the concentration part of the vaporized methanol by the arrangement of the three units (see the attached FIG. 2 or FIG. 1), the liquid methanol recovery unit has a concentration stage. It may be a recovery tower with no theoretical plate
It is desirable that the number of stages is 30 stages, preferably 5 to 20 stages.
The operating pressure of the unit can be set independently of the reaction unit, but the temperature at the bottom of the column rises as the pressure increases. In particular, when the temperature at the bottom of the column exceeds 200 ° C, the quality of the by-produced ethylene glycol deteriorates, so the operating pressure is 200 KP.
It is preferably aA or less. The column top temperature is usually not higher than the boiling temperature of dimethyl carbonate at the operating pressure. For example, at normal pressure (100 kPa), 75
It will be around ℃.

Arrangement of Units The gaseous methanol recovery unit and the liquid methanol recovery unit can be integrated into one distillation column having a concentrating section and a recovering section (see FIG. 1 attached). In that case, in the gaseous methanol recovery unit, the gaseous methanol sent from the liquid methanol recovery unit is liquefied. Specifically, the reaction liquid extracted from the reaction unit is supplied to the upper portion of the distillation column recovery unit (liquid methanol recovery unit), and the side stream liquid extracted from the distillation column concentration unit (gaseous methanol recovery unit) lower part is used. Supply to the reaction unit. In this case, it is preferable that the operating pressure is around normal pressure due to the restrictions on the condensation temperature and the bottom temperature of methanol. It is also possible to integrate the reaction unit, the gaseous methanol recovery unit and the liquid methanol recovery unit into one distillation column (see attached FIG. 2). In that case, a gaseous methanol recovery unit, a reaction unit, and a liquid methanol recovery unit are arranged in order from the top. The raw material methanol is supplied to the reaction unit, and the reaction liquid extracted from this is supplied to the upper part of the liquid methanol recovery unit. The gaseous methanol vaporized in the unit reaches the reaction unit again, where it is partially consumed by reacting while contacting with gas and liquid, and part of it is returned unreacted to the liquid methanol recovery unit. The remainder passes through the reaction unit in a gaseous state and reaches the gaseous methanol recovery unit where it is condensed and supplied again to the reaction unit. In this case as well, it is preferable to keep the operating pressure near normal pressure due to the limitations of the condensation temperature of methanol and the bottom temperature of the column, but in this case the pressure of the reaction unit cannot be set independently of other units, so the reaction temperature Is reduced. Gaseous methanol recovery unit and liquid methanol recovery unit 1
When installed as a basic distillation column (see Figure 1 attached), the type of column is Sulzer packing, Melapak, MC
Any type such as a packed column packed with ordered packing such as a pack, or a packed column packed with irregular packed materials such as INTPs and Raschig rings, a bubble column, a sieve tray, and a plate column using a valve tray column can be used. Also, when the reaction unit, the gaseous methanol recovery unit and the liquid methanol recovery unit are installed as one distillation column (see attached FIG. 2)
As for the gaseous methanol recovery unit and the liquid methanol recovery unit, it is possible to select the column type similar to the above. The reaction unit can be of a tray column type or a packed column type filled with a catalyst as the reactive distillation section.

The present invention will be described below with reference to examples.

Example 1 According to the flow sheet diagram shown in FIG. 1, transesterification reaction of ethylene carbonate (EC) and methanol was carried out in a reaction unit connected to the first column,
Dimethyl carbonate (DMC) and ethylene glycol (EG), which are transesterification reaction products, were separated and obtained in the second column and the third column, respectively.

(1) In the reaction unit (fixed bed flow reactor, use of catalyst manganese dioxide, reaction temperature 130 ° C.), new EC and recovered EC are collected together with recovered methanol.
It was supplied via the first tower concentrating section, and fresh methanol was directly supplied to carry out the transesterification reaction. Also,
The heat for maintaining this endothermic reaction was supplied through the jacket of the reactor. In the figure, the first column (22 theoretical plates, operating pressure 98 kPa, total reflux) concentrating section (6 theoretical plates)
Corresponds to the gaseous methanol recovery unit, and the recovery part (theoretical 16 stages) corresponds to the liquid methanol recovery unit. That is, (2) in the gaseous methanol recovery unit, the EC supplied to the first stage of the first tower (the uppermost part of the concentration section)
However, while flowing down the concentrating section, the extractive distillation is carried out in contact with the gaseous methanol rising from the column recovery section. The liquid that has flowed down to the sixth stage of the first tower (the lowest part of the concentration section) is sent to the reaction unit through the connecting pipes. Further, (3) in the liquid methanol recovery unit, the liquid reaction mixture withdrawn from the reaction unit is supplied to the seventh stage of the first tower (the uppermost part of the recovery part) through the connecting pipe, and while flowing down this recovery part. In addition, the total amount of methanol in the mixture is vaporized and recovered together with DMC having an azeotropic composition, and rises to a gaseous methanol recovery unit in the tower concentration section,
The remaining liquid mixture (mainly composed of transesterification reaction products DMC and EG and unreacted EC) was continuously withdrawn as a bottom product from the bottom of the first column. This bottom liquid of the first tower is sent to the second tower.

Second tower (17 theoretical plates, operating pressure 19 k
At Pa and a reflux ratio of 1.4), the bottom liquid of the first tower supplied to the seventh stage was distilled, and DMC was separated and obtained from the top of the second tower. The bottoms of the second tower is sent to the third tower. In the third column (15 theoretical plates, operating pressure 8 kPa, reflux ratio 3.5), the bottoms of the second column supplied to the fifth stage was distilled, and EG was converted to EC from the top of the third column. Was obtained separately as an azeotrope. Since high-purity EC is recovered as the third-column bottom liquid, it is circulated to the first column and reused as a raw material.

Under the operating conditions of each of the above columns, the conversion rate of methanol ((the number of DMC moles acquired × 2) / the number of moles of consumed methanol) is 100%, and the conversion rate of EC (the number of obtained EG moles / the consumed EC mole number) is The total amount of energy required for producing 1 kg of DMC is 6,627 kJ (first tower 1,499 kJ, second tower 933 kJ, third tower 3,089).
kJ and reaction unit 1,105 kJ).

[0018]

Example 2 According to the flow sheet diagram shown in FIG. 2, transesterification reaction of EC and methanol is carried out in the first column to obtain DMC and EG which are transesterification reaction products.
Separately acquired in the second and third towers, respectively.

In the figure, the upper part of the first column (32 theoretical plates, operating pressure 297 kPa, total reflux) (11 theoretical plates)
Corresponds to a gaseous methanol recovery unit, and the middle section (10 theoretical plates) is a reaction unit (plate type catalyst packed tower,
Corresponding to the use of catalyst manganese dioxide, reaction temperature 95 ℃,
The lower part (11 theoretical plates) corresponds to the liquid methanol recovery unit. That is, in the first tower, new EC and recovered EC are from the upper part of the gaseous methanol recovery unit (first column second stage), and new methanol is the upper part of the reaction unit (first column twelfth stage). ) From each. Gaseous methanol vaporized from the reaction unit continuously rises to the gaseous methanol recovery unit along with DMC of azeotropic composition, but is contacted with EC flowing down there and extractive distillation is performed to condense and recover the entire amount of DMC. Then, it is returned to the upper part of the reaction unit (the 12th stage of the first tower) along with the EC. Methanol distilled from the top of the column is totally condensed and returned to the upper part of the first column. On the other hand, the liquid reaction mixture reaching from the lower part of the reaction unit to the upper part of the liquid methanol recovery unit (22nd stage of the first tower) is such that while the unit continuously flows down, all the methanol together with DMC having the azeotropic composition are present. It is vaporized and recovered and rises to the reaction unit. The remaining liquid mixture (mainly composed of transesterification reaction products DMC and EG and unreacted EC) was continuously withdrawn as a bottom liquid from the bottom of the first column. This bottom liquid of the first tower is sent to the second tower.

Second tower (17 theoretical plates, operating pressure 16 k
At Pa and a reflux ratio of 1.4), the bottom liquid of the first tower supplied to the seventh stage was distilled, and DMC was separated and obtained from the top of the second tower. The bottoms of the second tower is sent to the third tower. In the 3rd column (15 theoretical plates, operating pressure 8 kPa, reflux ratio 1), the bottoms of the 2nd column supplied to the 5th stage was distilled, and EG was mixed with EC from the top of the 3rd column. Separately obtained as a boiling mixture. Since high-purity EC is recovered as a bottom product from the bottom of the third tower, it is recycled to the first tower and reused as a raw material.

Under the above operating conditions of each column, the conversion rate of methanol ((the number of moles of DMC acquired × 2) / the number of moles of consumed methanol) was 100%, and the conversion rate of EC (the number of obtained EG moles / the consumed EC mole number) was 100%. The total amount of energy required to produce 1 kg of DMC is 7,280 kJ (first tower 5,252 kJ, second tower 710 kJ and third tower 1,32).
It was 0 kJ).

[0022]

Comparative Example 1 According to the flow sheet diagram shown in FIG. 3, transesterification reaction of EC and methanol is carried out in the first tower (reactive distillation tower), unreacted methanol is recovered in the second tower, and transesterification reaction is produced. The substances DMC and EG were separately obtained in the third tower and the first tower, respectively.

The new methanol as a raw material and the recovered methanol are vaporized in a methanol preheater and then vaporized in the first column (a tray-type catalyst packed column, using catalytic manganese dioxide, a reaction temperature of 65 ° C .;
The theoretical number of plates is 42, the operating pressure is 101 kPa, the reflux ratio is 8), and it is supplied in a gaseous state from the lower 32nd stage, and the raw material EC is supplied in a liquid form from the first upper stage of the first column to perform a transesterification reaction. In the first column, the reaction mixture is further distilled, and an azeotropic mixture of reaction product DMC and unreacted methanol is continuously fed from the top of the column, and a reaction product EG and unreacted EC are continuously fed from the bottom of the column. Pull out.

Second column (20 theoretical plates, operating pressure 101)
At kPa and a reflux ratio of 0.93), the first column distillate (azeotropic mixture) supplied to the 15th stage of the column is subjected to extractive distillation using EC as an extraction solvent, and the methanol recovered from the top of the column is The mixture of DMC and EC, which is recycled to the first column and obtained as bottoms from the bottom of the column, is sent to the third column for separation. In the third column (12 theoretical plates, operating pressure 8 kPa, reflux ratio 5), the bottoms of the second column supplied to the 7th column was distilled to separate and obtain DMC from the top of the third column. EC recovered as bottoms from the bottom of the column is circulated to the second column and used as an extraction solvent.

Under the above operating conditions of each column, the conversion rate of methanol ((the number of moles of DMC acquired × 2) / the number of moles of consumed methanol) is 100%, and the conversion rate of EC (the number of obtained EG moles / the consumed EC mole number) is The total energy required to produce 1 kg of DMC is 36,343 kJ (first
Tower 25,515 kJ, second tower 5,169 kJ, third tower 1,818 kJ and methanol preheater 3,840 kJ)
Met.

[0026]

As described above, according to the present invention, when dimethyl carbonate is produced by the transesterification reaction of ethylene carbonate and methanol, the reaction unit for transesterification and the unreacted methanol remaining in the gas By properly combining the gaseous methanol recovery unit that liquefies and returns it to the reaction unit and the liquid methanol recovery unit that vaporizes and returns the remaining methanol in the liquid, a simple and efficient process can be configured. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a flowchart of a first embodiment.

FIG. 2 is a flow sheet diagram of the second embodiment.

FIG. 3 is a flow sheet diagram of a comparative example.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C07C 68/08 C07C 68/08 69/96 69/96 Z // C07B 61/00 300 C07B 61/00 300 F-term (reference) 4D076 AA13 BB05 BB10 BB23 BB30 FA03 FA12 HA20 JA03 JA04 4G070 AA01 AA03 AB01 BB01 CB17 DA23 4H006 AA02 AB84 AC48 AD13 BA16 BA30 BA82 BC14 BD10 BD33 BD52 BD53 BD81 BD82 BD84 KA58 4H039 CA66

Claims (10)

[Claims] 1. A method for producing dimethyl carbonate from ethylene carbonate and methanol by a transesterification reaction, which comprises using an apparatus including the following three units. (1) Reaction unit for performing the transesterification reaction (2) Gaseous methanol recovery unit that liquefies the gaseous methanol sent from the reaction unit or liquid methanol recovery unit and sends it to the reaction unit (3) Liquid sent from the reaction unit Liquid methanol recovery unit that vaporizes methanol in the reaction mixture and sends it to the reaction unit or gaseous methanol recovery unit 2. The production method according to claim 1, wherein the reaction unit is a fixed bed flow reactor or a homogeneous catalyst liquid phase reactor. 3. The gaseous methanol recovery unit is an extractive distillation column using ethylene carbonate as an extractant.
The manufacturing method described in. 4. The production method according to claim 1, wherein the gaseous methanol recovery unit is a distillation column having 1 to 20 theoretical plates. 5. The production method according to claim 1, wherein the liquid methanol recovery unit is a distillation column having 3 to 30 theoretical plates. 6. The production method according to claim 1, wherein the liquid methanol recovery unit is a recovery tower without a concentration stage. 7. The production method according to claim 1, wherein the produced dimethyl carbonate is withdrawn in liquid form from the liquid methanol recovery unit together with by-produced ethylene glycol and unreacted ethylene carbonate. 8. The production method according to claim 1, wherein a distillation column having a gaseous methanol recovery unit as a concentrating section and a liquid methanol recovery unit as a recovering section is used. 9. The production method according to claim 1, wherein a distillation column in which a gaseous methanol recovery unit, a reaction unit, and a liquid methanol recovery unit are arranged in this order from the top is used. 10. The production method according to claim 9, wherein the reaction unit is a reactive distillation section having 1 to 20 theoretical plates.