WO2003006418A1

WO2003006418A1 - Method for producing dialkylcarbonate

Info

Publication number: WO2003006418A1
Application number: PCT/JP2002/006959
Authority: WO
Inventors: Takashi Kanamaru
Original assignee: Mitsubishi Chemical Corporation
Priority date: 2001-07-10
Filing date: 2002-07-09
Publication date: 2003-01-23

Abstract

A method for producing a dialkylcarbonate through the transesterification of an alkylene carbonate and an alcohol, wherein a purified alkylene carbonate having a purity of 80 wt % or more is used as a raw material of the transesterification, characterized in that the purified alkylene carbonate is obtained by purifying, by the use of a single distillation unit, a crude alkylene carbonate from an alkylene carbonate production process and an unreacted alkylene carbonate mixture separated from a transesterification reaction mixture. The method can be employed for producing a dialkylcarbonate with improved energy efficiency at a reduced cost, in the production of the dialkylcarbonate through the transesterification of an alcohol and an alkylene carbonate produced by the reaction of an alkylene oxide with carbon dioxide.

Description

Description Manufacturing method of dialkyl carbonate

The present invention relates to an improved method for producing a dialkyl carbonate by subjecting an alkylene carbonate and an alcohol to a transesterification reaction. More specifically, the present invention relates to an improvement in a method for producing a steal exchange dialkyl carbonate using a crude alkylene carbonate containing an alkylene dalicol and an alkylene carbonate production catalyst as a raw material source. Background art

As a method for producing a dialkyl carbonate, particularly dimethyl carbonate, for example, a carbonylation method of methanol, a methanolysis method of urea, a transesterification method of ethylene carbonate, and the like have been put to practical use or proposed. Among these methods, a method of producing a dialkyl carbonyl by transesterification of an alkylene carbonate and an alcohol is described by a method employing a batch reaction (US Pat. No. 3,648,588; No. 4,837,15), a method in which a distillation column is installed at the top of a reaction vessel to carry out the reaction while removing continuously produced dialkyl carbonate (US Pat. No. 3,830,201). Specification etc.) and a method employing a continuous reaction using a tubular reactor (JP-A-63-41432, etc.). All of these methods are based on the assumption that high-purity alkylene carbonate is used as a raw material.

When transesterification is performed between ethylene carbonate and methanol, equimolar amounts of dimethyl carbonate and ethylene dalicol are produced. This transesterification reaction is an equilibrium reaction, and the reaction product mixture contains the product dimethyl carbonate, by-product ethylene dalicol, and unreacted raw materials methanol and ethylene carbonate. Conversion of ethylene carbonate by increasing the ratio of methanol in feedstock ^ But the remaining ethylene carbonate can be reduced, but it is not economical because the recovery of methanol requires a lot of energy. Therefore, the raw material ethylene carbonate is usually recovered from the reaction mixture and reused.

Methods for separating and purifying the raw material ethylene carbonate from the reaction product mixture include distillation and crystallization (Japanese Patent Application Laid-Open No. 7-89905). Distillation requires energy costs, and crystallization requires equipment costs. However, there is a drawback that it takes.

That is, in the conventional method for producing dimethyl carbonate, in order to obtain a purified ethylene carbonate raw material, crude ethylene carbonate obtained from the ethylene carbonate production process is purified and ethylene carbonate is separated. It was necessary to separate and purify ethylene carbonate from the mixture of unreacted ethylene carbonate and by-product ethylene dalicol separated from the liquid. Furthermore, since these separation and purification are usually performed by distillation, there is a problem that energy costs are required.

An object of the present invention is to provide an energy-efficient method, a low-cost dialkyl carbonate, and a low-cost method for producing alkyl carbonyl by subjecting an alkylene carbonate obtained by a reaction between an alkylene oxide and carbon dioxide to a transesterification reaction with an alcohol. It is to provide a method by which ponates can be produced. Disclosure of the invention

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have conducted the same distillation on the crude alkylene carbonate obtained from the alkylene carbonate production process and the unreacted alkylene carbonate mixture separated from the transesterification reaction solution. apparatus more distillation, by using the obtained pure 8 0 wt ^_0/0 or more purification alkylene carbonate as a raw material of S. ether exchange reaction, discovered that it energy efficient production of dialkyl carbonates, leading to the present invention .

Further, a reaction unit for performing a transesterification reaction, a gas alcohol recovery unit for liquefying gaseous alcohol and sending it to the reaction unit, and a reaction apparatus including a liquid alcohol recovery unit for vaporizing alcohol in the liquid reaction mixture are provided. To use The present inventors have found that dialkyl carbonate can be produced efficiently and at low cost, and have led to the present invention. .

That is, a first gist of the present invention is a method for producing a dialkyl carbonate by subjecting an alkylene carbonate and an alcohol to a transesterification reaction,

Upon using the 8 0 weight ^_0/0 or more purification alkylene carbonate as a raw material of the transesterification reaction, the purified alkylene carbonate, a crude alkylene carbonate derived from the alkylene carbonate Manufacturing process, released from the transesterification reaction mixture min An unreacted alkylene carbonate mixture is purified by the same distillation apparatus.

Further, a second gist of the present invention is: (a) a step of producing an alkylene carbonate by reacting an alkylene oxide with carbon dioxide in the presence of a catalyst;

(b) recovering the alkylene oxide from the reaction product mixture,

(c) a distillation step of supplying the residual liquid to the distillation column and obtaining a purified alkylene carbonate having a purity of 80% by weight or more from the side of the column;

(d) a step of producing a dialkyl carbonate by subjecting a purified alkylene carbonate and an alcohol to a transesterification reaction,

(e) circulating unreacted alcohol to step (d),

(f) recovering dialkyl carbonate 1 from the transesterification reaction solution, and supplying the residual liquid of step (f) to the distillation column of step (c). It is in.

Further, a third aspect of the present invention is a method for producing a dialkyl carbonate from an alkylene carbonate and an alcohol by an ester exchange reaction, wherein (i) a reaction unit for performing the ester exchange reaction, (ii) a reaction unit or a liquid alcohol. A gaseous alcohol recovery unit that liquefies the gaseous alcohol sent from the collection unit and sends it to the reaction unit, and (iii) vaporizes the alcohol in the liquid reaction mixture sent from the reaction unit to recover the reaction unit or gaseous alcohol. A method for producing a dialkyl carbonate, characterized by using an apparatus including three units of a liquid alcohol recovery unit to be sent to a unit. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow sheet diagram showing the first embodiment.

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

FIG. 3 is a flow sheet diagram showing Comparative Example 1.

Figure 4 is a flow sheet diagram of the E-C reaction step,

FIG. 5 is an explanatory diagram of the DMC manufacturing process.

FIG. 6 shows the distillation column of Reference Example 1.

FIG. 7 shows the distillation column of Reference Example 2.

FIG. 8 shows the distillation column of Reference Example 3.

FIG. 9 shows the distillation column of Reference Example 4.

FIG. 10 is a flow sheet diagram of the fifth embodiment.

FIG. 11 is a flow sheet diagram of the sixth embodiment.

FIG. 12 is a flow sheet diagram of Reference Example 8. BEST MODE FOR CARRYING OUT THE INVENTION

Manufacturing process of dialkyl carbonate

Transesterification step>

The transesterification reaction between alkylene carbonate and alcohol in the presence of a catalyst is represented by the following formula (1):

(In the formula, R ¹ represents a hydrogen atom, a saturated hydrocarbon having 1 to 3 carbon atoms, and R ² represents a saturated hydrocarbon having 1 to 5 carbon atoms.)

To produce a dialkyl carbonate and an alkylene glycol. The alkylene carbonate is a compound represented by the above formula (1), wherein R ¹ is a hydrogen atom and a saturated hydrocarbon having 1 to 3 carbon atoms. Specifically, ethylene carbonate, propylene carbonate, butylene carbonate and the like can be mentioned, among which ethylene carbonate is preferable.

Alcohol is a monohydric alcohol, and R ² is a saturated hydrocarbon having 1 to 5 carbon atoms. Specific examples include methanol, ethanol, n-propanol, i-propanol, n-butanol, and i-butanol, and among them, methanol is preferable.

Dialkyl carbonate specifically includes dimethyl carbonate, getyl carbonate, di-n-propyl carbonate, di-i-propyl carbonate, di-n-butyl carbonate, di-i-butyl carbonate and the like. Dimethyl carbonate is preferred.

Specific examples of the alkylene glycol include ethylene glycol, propylene glycol, and polyethylene glycol.

Hereinafter, a method for producing dimethyl carbonate by subjecting ethylene carbonate and methanol to a transesterification reaction will be mainly described.

As the catalyst for the transesterification reaction, a conventional transesterification catalyst can be selected. Specifically, as homogeneous catalysts, amines such as triethylamine, alkali metals such as sodium, alkali metal compounds such as sodium sodium chloroacetate methylate, and thallium compounds, and heterogeneous catalysts include: Examples thereof include ion-exchange resins modified with functional groups, amorphous silicas impregnated with alkali metal or alkaline earth metal silicates, ammonium-exchanged Y-type zeolites, and mixed oxides of cobalt and nickel. When a homogeneous catalyst is used, it is preferable to separate the catalyst prior to the distillation separation in order to avoid the progress of the reverse equilibrium reaction and the occurrence of side reactions.

The reaction conditions of the transesterification reaction, the reaction temperature is 5 0~1 8 0 ° C, _c the molar ratio is generally the molar ratio of methanol and ethylene carbonate and 2-2 0 If it is less than 2, the conversion rate of transesterification decreases, while if it exceeds 20, it becomes large. A large amount of unreacted raw material remains in the system, which requires a lot of energy such as heating and cooling, and increases the load on the equipment when it is recycled.

The transesterification reaction is based on a batch reaction (US Pat. No. 3,642,588, the specification, JP-A-54-48715, etc.), and a distillation column is installed at the top of the reactor. Which reacts while removing dimethyl carbonate formed continuously by the process (US Patent No.

No. 3,830,201), continuous reaction using a tubular reactor (JP-A-63-4111)

Any type of reaction is applicable.

Preferred embodiments of the reaction apparatus will be described below by taking transesterification of ethylene carbonate and methanol as an example.

A reaction unit for transesterification, a gaseous methanol recovery unit that liquefies unreacted methanol remaining in gaseous form and returns it to the reaction unit, and a liquid methanol recovery unit that vaporizes remaining methanol in liquid form and returns to the reaction unit. Use a device containing three units. The most typical mode in which the ester exchange reaction is carried out while circulating methanol between the reaction unit, the gaseous methanol recovery unit and the liquid methanol recovery unit is as follows.

The withdrawn liquid of 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 withdrawn liquid may be flash-separated and the gas supplied to the gaseous methanol recovery unit and the liquid supplied to the liquid methanol recovery unit.

In the gaseous methanol recovery unit, dimethyl carbonate is separated at the bottom of the column by extraction distillation using ethylene carbonate as a raw material as an extraction solvent, and methanol is concentrated at the top at a high reflux ratio. The bottom liquid is supplied to the reaction unit.

In the liquid methanol recovery unit, the remaining methanol in the liquid state is cooked and supplied to the reaction unit or the gaseous methanol recovery unit. On the other hand, the produced dimethyl carbonate is extracted from the liquid methanol recovery unit together with the by-produced ethylene glycol and unreacted ethylene carbonate in a liquid state.

Reaction cut: Transesterification between ethylene carbonate and methanol

Five. The pressure of the reaction unit can be set arbitrarily.However, considering the liquid phase reaction and the fact that the starting methanol has a boiling point of about 65 ° C at normal pressure, the pressure should be IMP a A or higher. Is preferred. The temperature of the reaction unit is selected from the boiling temperature of methanol or lower at the pressure of the reaction unit. However, considering the reaction rate, the temperature is as high as possible, for example, 50 to 180. C is preferably within the range. The molar ratio between methanol and ethylene-ponate is generally from 1 to 5, preferably from 1.5 to 3. If this molar ratio is less than 1, the conversion of transesterification decreases, while if it exceeds 5, a large amount of unreacted raw material remains in the system, requiring a lot of energy such as heating and cooling, or when recycling. There are problems such as an increase in the load on the equipment.

The reaction cut may be a reactive distillation section. In this case, the number of theoretical plates is preferably 1 to 20 stages, and more preferably 5 to 15 stages. The operating conditions are set so that almost all of 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 a liquid state. Depending on the arrangement of the three units (see Fig. 10), some of the vaporized methanol recovered by the liquid methanol recovery unit may be supplied, but this vaporized methanol is vaporized in the reaction tube. Part of the liquid comes into contact with the liquid, and the remaining part is liquefied and recovered by the gaseous methanol recovery unit, and is supplied again to the reaction unit. On the other hand, the raw material ethylene carbonate can be supplied directly 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 Fig. 10). And Figure 11).

Gaseous methanol recovery unit: Gaseous methanol sent from the reaction unit or liquid methanol recovery unit is liquefied and sent to the reaction unit.

The means for liquefying 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 product of an azeotropic composition with methanol. Since it is contained, it is preferable to employ a means capable of separating according to the difference in boiling point, for example, a distillation column type. In such a case, the number of theoretical plates is desirably 1 to 20 stages, preferably 2 to 15 stages.

Further, dimethyl carbonate is converted from the gaseous methanol recovery unit into gas. It is preferable to reduce the required energy by selecting the distillation conditions so as not to escape as it is. For this purpose, the gaseous methanol recovery unit is preferably used as an extractive distillation column. That is, the required energy can be reduced by supplying the raw material ethylene carbonate to the unit as an extraction solvent and extracting and separating dimethyl carbonate before condensing the methanol.

The distillate withdrawn from the top of the extractive distillation column is high-purity methanol, and can be returned to the reaction unit without particularly requiring any purification means. Of course, it is also possible to operate at full reflux without extracting the distillate. In this case, the liquefied methanol is supplied to the reaction unit from the lower part of the extraction distillation column together with ethylene carbonate as a raw material and an extraction solvent.

The operating pressure of the gaseous methanol recovery unit can be set independently of the reaction unit. However, if the operating pressure is lowered too much, the boiling temperature of methanol decreases, and it becomes impossible to use ordinary cooling water for condensation. Therefore, it is preferable to use 50 KPa A or more.

Liquid methanol recovery unit: The methanol in the liquid reaction mixture sent from the reaction unit is vaporized and sent to the reaction unit or gaseous methanol recovery unit. The means for vaporizing methanol in the liquid reaction mixture is not particularly limited, but in the liquid methanol recovery unit, at the same time as the vaporization of methanol, the transesterification reaction product dimethyl carbonate, ethylene dalicol, and ethylene glycol contained in the liquid reaction mixture. In order to obtain the ethylene carbonate in a liquid state, it is preferable to employ a means capable of separating ethylene carbonate by a difference in boiling point, for example, a distillation column. In that case, the concentrated unit for the vaporized methanol is shared by the reaction unit or the gaseous methanol recovery unit (see attached Fig. 2 or Fig. 1) due to the arrangement of the three units. A recovery tower without a concentration stage may be used, and the number of theoretical plates is preferably 3 to 30 plates, and more preferably 5 to 20 plates.

The operating pressure of the unit can be set independently of the reaction unit, but the higher the pressure, the higher the temperature at the bottom of the column. In particular, if the temperature at the bottom of the column exceeds 200 ° C, the quality of by-product ethylenic alcohol will be reduced, so the operating pressure shall be 200 KPa a A or less. Is preferred.

Arrangement of each unit: The gaseous methanol recovery unit and the liquid methanol recovery unit can be integrated into one distillation column, each of which serves as a concentration section and a recovery section (see Fig. 10). 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 section (liquid methanol recovery unit), and is extracted from the lower portion of the distillation column concentration section (gaseous methanol recovery unit). The side stream liquid is supplied to the reaction unit. In this case, it is preferable that the operating pressure be around normal pressure due to the restrictions on the methanol condensation temperature and the bottom temperature.

The reaction unit, gaseous methanol recovery unit and liquid methanol recovery unit can be integrated into one distillation column (see Fig. 11). In that case, gaseous methanol recovery unit (2), reaction unit (2), and liquid methanol recovery unit (3) are arranged in order from the top. The raw material methanol is supplied to the reaction unit (2), and the reaction liquid extracted therefrom is supplied to the upper part of the liquid methanol recovery unit (3). The gaseous methanol vaporized in the unit reaches the reaction unit again, where it is partially reacted and consumed while in gas-liquid contact, and returns to the liquid methanol recovery unit ③ partly unreacted . The remainder passes through the reaction unit in a gaseous state, reaches the gaseous methanol recovery unit ①, where it is condensed and supplied again to the reaction unit ②. In this case, too, it is preferable that the operating pressure be around normal pressure due to the restriction of the methanol condensation temperature and the bottom temperature, but in this case, the pressure of the reaction unit cannot be set independently of other units. The reaction temperature decreases.

When the gaseous methanol recovery unit and the liquid methanol recovery unit are installed as a single distillation column (see Fig. 10), the type of column may be structured packing such as Sulza packing, Mela pack, MC pack, etc. Alternatively, any type such as a packed tower filled with irregular packing such as IMTP or Raschig ring, a bubble tower, a sieve tray, a tray tower using a valve tray tower, or the like can be used. Also, when the reaction unit, gaseous methanol recovery unit and liquid methanol recovery unit are installed as one distillation column (see Fig. 11 attached), gaseous methanol recovery unit II and liquid methanol recovery unit ① The same tower type as above can be selected for the waste collection unit ③. In addition, the reaction unit (2) can be a tray column type packed with a catalyst or a packed column type as a reactive distillation unit.

In the above reactor, since the entire amount of the raw material methanol is consumed while circulating in the reactor, it is not necessary to separately provide a methanol separation step.

Combining the above reactor with the purification process described in this specification results in a more economical method for producing dialkyl carbonate.

Alcohol separation and circulation process>

If a usual known reactor is used, the alcohol is separated from the reaction mixture and recycled to the reaction step. As a method for separating the alcohol from the reaction mixture, for example, distillation and the like can be mentioned.

When methanol is used as the starting alcohol, methanol and dimethyl carbonate form an azeotrope. For this reason, for example, a method using a plurality of distillation columns having different pressures for separation, an extractive distillation method, and the like are employed.

Ku dialkyl carbonate recovery process>

In this step, dimethyl carbonate is separated from the reaction mixture obtained from the above reactor.

Since dimethyl carbonate is the object of the process, high purity is required, but since there is no azeotrope with dimethyl carbonate in the reaction mixture, high purity dimethyl carbonate can be obtained by ordinary distillation. It is possible.

Ethylene dalicol is contained in the reaction mixture, and when mixed with dimethyl carbonate, a reverse reaction of transesterification may occur. Therefore, it is necessary to make the treatment temperature of this step 180 ° C or less, preferably 170 ° C or less, and to make the heating time as short as possible. As the above reverse reaction proceeds, methanol is mixed into dimethyl carbonate.However, when dimethyl carbonate is ester-exchanged with phenol to produce diphenyl carbonate, a polycarbonate raw material, the reaction produces methanol. Methanol contamination that does not affect the progress of the reaction is acceptable. Manufacturing process of alkylene carbonate

The alkylene carbonate, which is a raw material of the transesterification reaction, is obtained from an alkylene oxide and carbon dioxide in the presence of a catalyst by the following formula (2)

(Wherein, R ¹ is as defined above)

It is produced by the reaction represented by

Specific examples of the alkylene oxide include ethylene oxide, propylene oxide, and polyethylene oxide, and among them, ethylene oxide is preferable. Hereinafter, a reaction for producing ethylene carbonate from ethylene oxide and carbon dioxide will be described as a main example, and this reaction may be referred to as an “EC conversion reaction”.

As the EC conversion reaction catalyst, a phosphonium salt is preferable because of its high activity and reusability.

The type of reactor used for the EC conversion reaction is not particularly limited, but a reaction containing ethylene oxide, carbon dioxide and a catalyst, or, in some cases, water supplied from the bottom and ethylene carbonate generated from the top. It is effective to use a bubble column reactor in which the liquid and unreacted carbon dioxide are distilled off.

The EC conversion reaction is performed at a temperature of 70 to 200 ° C, preferably 100 to 170 ° C, and a pressure of 49.

It is generally carried out at 0-4900 kPa-G (gauge pressure), preferably at 980-2940 kPa-G. The supply amounts (molar ratio) of carbon dioxide and water to ethylene oxide are usually 0.1 to 5 and 0 to 10, respectively, preferably 0.5 to 3 and 0.5 to 0.5, respectively. 5 is recommended.

Also, since the EC conversion reaction is an exothermic reaction, a part of the reaction solution is extracted to the outside and It is preferable to control the reaction temperature by an external circulation system, in which the reaction temperature is returned after cooling in the heat exchanger.

The addition reaction represented by the above formula (2) has the advantage of proceeding at a high selectivity in a non-aqueous system, but has the disadvantage of a low reaction rate. When the addition reaction represented by the above formula (2) is performed in the presence of water, the reaction rate can be improved as compared with a non-aqueous system. Further, when the addition reaction represented by the above formula (2) is performed in the presence of water, alkylene carbonate is generated by a hydrolysis reaction of the alkylene carbonate generated in the reaction system.

That is, in the reaction system of the EC conversion reaction, the above addition reaction and hydrolysis reaction proceed simultaneously. Since the addition reaction has a higher reaction rate than the hydrolysis reaction, the content of ethylene carbonate changes according to the progress of the EC conversion reaction. In the region where the conversion of ethylene oxide is high, the generated ethylene carbonate is hydrolyzed according to the reaction time in the EC conversion reactor and converted to ethylene glycol. The ethylene carbonate content is low and the ethylene glycol content is high.

In the EC conversion reaction of the present invention, the lower limit of the conversion of ethylene oxide is 50 ° / ₀ , preferably 70%, and the upper limit is 95. Is preferably 9 °° / ₀ . It is preferable to use ethylene carbonate separated from all or a part of the reaction product as a raw material for the transesterification reaction.

Ethylene oxide remains in the E-Cation reaction product without being completely consumed. In order to use ethylene carbonate as a raw material for the transesterification reaction, it is necessary to remove residual ethylene oxide. Examples of the removal method include a method of performing flash separation using a difference in boiling point from ethylene carbonate, and a method of stripping using a part or all of carbon dioxide supplied to an EC conversion reactor. The removed ethylene oxide can be reused in the EC conversion reaction.

When performing the EC conversion reaction in the presence of water, the resulting ethylene carbonate mixture After removing water, it is preferable to use it as a raw material for a transesterification reaction. Water is not required in the dialkyl carbonate production process, and water reduces the yield of dialkyl carbonate in the transesterification reaction. As a method for removing water, vacuum distillation and the like can be mentioned. The removed water can be reused for the EC conversion reaction or used for the hydrolysis reaction of the alkylene carbonate.

In a preferred embodiment of the present invention, in a method for producing dimethyl carbonate by subjecting ethylene carbonate and methanol to a transesterification reaction, a conversion of ethylene oxide obtained by reacting ethylene oxide with carbon dioxide gas in the presence of water; From unreacted ethylene oxide from 50% to 95% of the reaction product, and then water and ethylene dalicol are removed by distillation to use ethylene carbonate as the raw material for the transesterification reaction. Is preferred.

In the present invention, as described above, since the alkylene carbonate separated from the reaction product in the low conversion stage is used as a raw material of the dialkyl carbonate, the alkylene oxide separated from the reaction product in which the alkylene oxide is completely consumed is used. Compared to the case where carbonate is used as a raw material, the amount of alkylene glycol passing through the process for producing dialkyl carbonate is reduced.

The alkylenedalycol contained in the raw material for the transesterification reaction can be separated from the dialkyl carbonate production step and supplied to the alkylene glycol production step together with the alkylene glycol by-produced in the transesterification reaction. Examples of the separation method include distillation.

Typically, ethylene dalicol forms an azeotrope with ethylene carbonate. Reducing the amount of ethylene glycol in the transesterification feedstock leads to a reduction in the energy required in the dialkyl ponate production process. In other words, energy consumption can be reduced efficiently. Distillation process

Since the transesterification represented by the formula (1) is an equilibrium reaction, the transesterification reaction solution contains the dialkyl carbonate and by-product alkylene diaryl carbonate on the right side of the same formula. In addition to the coal, the alkylene carbonate and alcohol on the left side of the formula remain unreacted. However, in the reactor described above as a preferred embodiment of the present invention, the alcohol is circulated in the reactor and consumed in its entirety, so that a mixture of the product dialkyl carbonate, by-product alkylene glycol and raw material alkylene carbonate is obtained.

The components are usually separated by distillation to remove the product from the reaction mixture and reuse the unreacted raw materials. In particular, the transesterification reaction liquid after separation of low-boiling components such as product dimethyl carbonate (boiling point 90.3 ° C) and Z or unreacted methanol (boiling point 64.7 ° C) is not It consists of reacted ethylene carbonate (boiling point: 248.2 ° C) and by-produced ethylene glycol (boiling point: 197.3 ° C). Unreacted ethylene carbonate is usually recovered from the reaction solution by distillation. By separation.

In the present invention, as the raw material ethylene carbonate for the transesterification reaction, one obtained from the purified distillation of the crude ethylene carbonate obtained by the EC conversion reaction is used, and the above-mentioned purified distillation is carried out by separating the unreacted ethylene carbonate by distillation. This is performed simultaneously in the distillation tower.

The crude ethylene carbonate purified and distilled in this distillation column may contain water, but may be dehydrated in advance by a suitable means and contain no water. In terms of energy efficiency, it is slightly advantageous to feed crude ethylene carbonate containing water directly to the distillation column, but if crude ethylene carbonate containing no water is supplied to the distillation column, the condensation temperature Can be kept high, so that refrigeration equipment for cooling is not required. The means for dehydration is not particularly limited, but is usually distillation under reduced pressure. In the case where the crude ethylene carbonate contains water, at the time of the above-mentioned distillation separation, water and a low-boiling component mainly composed of ethylene glycol are separated from the top, and ethylene carbonate containing an EC conversion catalyst is separated from the bottom of the column. It is preferable that the purified ethylene carbonate is fractionated from the side stream while being fractionated.

When the crude ethylene carbonate does not contain water, an azeotropic mixture of ethylene glycol and ethylene carbonate is collected from the top of the column and ethylene carbonate containing an EC conversion reaction catalyst is collected from the bottom of the column during the distillation. while doing, It is preferred to fractionate the purified ethylene carbonate from the side stream.

In this distillation separation, it is important to pay attention to the following points.

1) The purified ethylene carbonate fractionated from the side stream weighs 80% because the less ethylene glycol contained, the more the transesterification equilibrium shifts to the production system. It is necessary to have a purity of / ₀ or more. Preferably, it has a purity of 90% by weight or more, more preferably 95% by weight or more. The upper limit of the purity of ethylene carbonate in the purified ethylene carbonate is not particularly limited, but is preferably 99.9% by weight.

2) It is necessary to minimize mixing of the EC conversion catalyst in the components collected from the bottom of the column into the purified ethylene carbonate. This is why purified ethylene carbonate is fractionated from the sidestream, especially in the gas phase.The fractionated gas phase is returned to the liquid phase by means such as condensation and used as a raw material for transesterification. Is done.

The distillation column has a gas-liquid contact part divided into two flow paths, and supplies the crude alkylene carbonate to the gas-liquid contact part of the first flow path, and supplies the crude alkylene carbonate to the gas-liquid contact part of the second flow path. When using a distillation column that supplies unreacted alkylene carbonate separated from the ester exchange reaction solution, the distillation column is extracted from the gas-liquid contact portion of the second flow path for the same reason as described above.

3) The components collected from the top of the column are preferably used for the production of EG described below, together with the components collected from the bottom of the column, from the viewpoint of economy, and the EC conversion catalyst in the components collected from the bottom is recovered. It is preferred to reuse.

The number of stages required for the distillation separation (the column body excluding the reboiler and condenser) varies depending on the reflux ratio, but is preferably 5 or more, more preferably 10 or more in consideration of economy. The reflux ratio is preferably from 0.1 to 5, more preferably from 0.3 to 0.7. The operating pressure of the distillation column shall be lower than atmospheric pressure to prevent a decrease in product purity due to an increase in operating temperature. However, if the pressure is lowered too much, both separation efficiency and energy efficiency will deteriorate, so it is necessary to select an appropriate pressure. A suitable pressure range is less than 27 kPa, preferably between 4 and 13 kPa.

Distillation towers are packed with regular packings such as Sulzer packing, Mela pack, MC pack, etc., and irregular packings such as IMTP, Raschig ring, etc. Any type, such as a tray tray type using a tray tray and a valve tray tower, can be used.

Further preferred embodiments of the distillation column are shown below. That is, a distillation column having a gas-liquid contact section divided into two flow paths is used, and the reaction solution is supplied to the gas-liquid contact section of the first flow path, and the gas-liquid contact section of the second flow path is used. To extract a cyclic alkylene carbonate liquid having a purity of 80% by weight or more from the liquid.

Having the gas-liquid contact section divided into two flow paths means that two flow paths are formed between predetermined stages of the distillation column (hereinafter, sometimes referred to as “divided sections”), It means that the liquid contact portions are separated from each other, and a distillation column having such a gas-liquid contact portion is generally called a Petruk type. Here, the two flow paths may be of a so-called vertical split type formed in the same distillation column, or may be of a type formed of one in another distillation column. And the ascending gaseous phase are combined or arranged in a distillation stage above and below the dividing section (hereinafter, sometimes referred to as a “non-dividing section”) to form a single flow path. Need to be done. In a vertical division type in which both flow paths are formed in the same distillation column, the flow paths are divided using partition walls. Specifically, it is common practice to provide a vertical plane partition at a dividing portion in the tower and divide the partition into left and right sides, or to provide a vertical cylindrical partition and divide the inside and outside of the partition. As the type of the gas-liquid contact part of each flow path of the divided part and the type of each gas-liquid contact part of the upper and lower non-divided parts, an arbitrary one such as a packed tower, a tray tower and the like is selected.

Further, in the present invention, the reaction liquid containing the cyclic alkylene force-ponate, the by-product alkylene glycol, water and the catalyst is supplied to the gas-liquid contact part of the first flow path, and the gas-liquid contact part of the second flow path is provided. While supplying the unreacted alkylene carbonate separated from the transesterification reaction solution, the cyclic alkylene carbonate liquid is withdrawn from the lower part of the gas-liquid contact portion of the second flow path. The reaction liquid supplied to the distillation column is concentrated in a gas-liquid contact portion of the first flow path, in which water and alkylenedaricol, which are light boiling distillates, are concentrated and an ascending flow accompanied by cyclic alkylene carbonate, and cyclic alkylene carbonate The concentrated catalyst is separated into a down stream with alkylene glycol. The ascending flow of the first flow path is further subjected to gas-liquid separation at the gas-liquid contact portion of the upper non-divided portion, and water and alkylene glycol A distillate whose main component is toluene is obtained from the top of the column. At this time, a small amount of cyclic alkylene carbonate also azeotropically distills with the alkylene glycol. On the other hand, the cyclic alkylene carbonate liquid phase containing a small amount of alkylenedalycol flowing down from the upper non-divided portion flows down the second flow passage while the lower non-divided portion in the gas-liquid contact portion of the second flow passage. It comes into contact with the gaseous phase mainly composed of cyclic alkylene carbonate, which rises from the gas-liquid contact part, and is concentrated and separated.

Therefore, by appropriately adjusting these operating conditions of the respective gas-liquid contact portion, from the gas-liquid contact portion of the second passage, purity 8 0 wt ^_0/0 or more, preferably 9 0 wt% or more cyclic § Ruki The lencarbonate liquid can be withdrawn. Since the cyclic alkylene carbonate production reaction catalyst is not mixed into the second flow path, the position at which the cyclic alkylene carbonate liquid is withdrawn is preferably the lowest stage of the gas-liquid contact portion of the flow path.

In the lower undivided portion, the descending flow of the first flow path and the descending flow of the second flow path merge, and the slightly remaining alkylenedalycol is vaporized, and the cyclic alkylene carbonate and the catalyst are further concentrated. It is withdrawn from the bottom as a catalyst solution. A suitable catalyst concentration range in the solution is between 20 and 90% by weight.

The number of stages required for the above-mentioned distillation separation (the tower body excluding the reboiler and condenser) varies depending on the return flow ratio. However, considering the separation capacity and economic efficiency, the first passage for supplying the reaction liquid is provided in the division section. The gas-liquid contact part of the second flow path from which the cyclic alkylene carbonate liquid is extracted is preferably at least three theoretical stages and at most 20 theoretical stages. . Further, it is preferable that the number of theoretical plates of the gas-liquid contact portion of the second flow path is larger than the number of theoretical plates of the gas-liquid contact portion of the first flow passage. In addition, it is preferable to install a gas-liquid contact portion having one or more theoretical plates in each of the non-divided portions above and below the divided portion. The operating pressure of the distillation column should be kept at less than atmospheric pressure to keep the operating temperature below 200 ° C in order to prevent the catalyst from deteriorating due to the rise in operating temperature. However, if the pressure is too low, the separation efficiency and energy efficiency will deteriorate, so it is necessary to select an appropriate pressure. A suitable overhead pressure range is below 27 kPa, preferably in the range of 2 to 13 kPa.

Sulza packing (wire mesh molding type) Mela pack (porous metal sheet molding type), MC pack (wire mesh molding type or metal sheet molding type) and the like are exemplified. Examples of the irregular packing include IMTP, Dickson packing, Raschig ring and the like. In the case of a vertical division type with vertical cylindrical bulkheads, the inner tower is filled with ordered packing or irregular packing, and the outer tower is packed with random packing in terms of the ease of manufacturing the equipment. preferable. In addition, in the case of a vertical split type with a vertical plane partition and a type in which a flow path is formed in another distillation column, there are few restrictions on the production, so the packing shall be either a regular packing or an irregular packing. Either may be used. When a tray type distillation column is used, a general distillation column such as a sieve tray and a bubble bell tower can be used. Use in recall manufacturing process

Examples of the method for producing alkylenedaricol, particularly ethylene dalicol, include a method of hydrolyzing ethylene carbonate, a method of direct hydration of ethylene oxide, and the like. Among these, the method of hydrolyzing ethylene carbonate has the advantage that monoethylene dalicol can be produced with high selectivity because the production of dimers and trimers such as diethylene glycol and triethylene dalicol is extremely small. There is.

In the above-mentioned ethylene carbonate production process in the presence of water, in the dimethyl carbonate production process using the ethylene carbonate produced in this process as a raw material, etc., ethylene dalicol separated and recovered, water-containing ethylene glycol and / or ethylene Since all ethylene glycol containing carbonate is manufactured using ethylene carbonate as a raw material, by supplying them to the ethylene carbonate manufacturing process, the economics of both the ethylene carbonate manufacturing process and the ethylene dalicol manufacturing process are improved. Acts favorably.

More specifically, in the distillation step, a low-boiling component containing water and ethylene glycol as main components, or an azeotropic mixture of ethylene glycol and ethylene glycol, collected from the top of the column, and a fraction from the bottom of the column The ethylene carbonate containing the EC conversion reaction catalyst and the water separated in advance prior to the distillation separation can be used for the production of ethylene glycol by hydrolysis of ethylene carbonate. The hydrolysis reaction of ethylene carbonate is usually carried out at a temperature of 100 to 180 ° C and a normal pressure to 2000 kPa'G, preferably a normal pressure to 1960 kPa 1G. Carbon dioxide as a by-product is separated in a gas phase from the obtained ethylene glycol aqueous solution containing the EC conversion catalyst. In the aqueous solution from which carbon dioxide has been removed, water is removed from the top of the column by distillation, and high-boiling components containing an EC conversion catalyst and ethylene glycol are separated by gas-liquid separation. Ethylenedalicol is obtained as a product, and the reusable components are each reused in suitable processes. The use of such ethylene glycol production steps is particularly desirable in order to ensure the economic efficiency of the method of the present invention. Example

Hereinafter, the present invention will be described in more detail by way of examples, but it should be understood that the present invention is not limited to the examples. In the examples, ethylene oxide is referred to as "EOj, carbon dioxide as" CO 2 ", ethylene carbonate as" EC ", ethylene glycol as" G ", methanol as" MeOH ", and dimethinore carbonate as "DMCJ is sometimes called. Example 1

According to the flow sheet diagram shown in Fig. 1, EO was removed from the crude EC containing water, EG, and the EC conversion catalyst, and distilled together with unreacted EC and by-product EG separated from the transesterification reaction solution. Separation was performed, and the obtained purified EC was used as a raw material for a transesterification reaction. In the figure, the numbers surrounded by 〇 indicate the stream numbers. same as below.

Table 1 shows the temperature and composition of each stream in the case of producing 5.04 T / h of product DMC using crude EC (stream 1). The six main components of the composition shown are gas carbonate, EO, EC, monoethylene glycol (MEG), water, and catalyst (EC conversion catalyst). table 1

EO 4.5 weight ⁰ /. The crude EC containing (stream 1) is fed to the top of the stripping tower (EO separation tower) and brought into countercurrent contact with CO 2 (stream 2) fed at a pressure of 2MPa from the bottom. A stream 4 from which EO was removed to 0.3% by weight or less was obtained. Here, the stream 3 of CO 2 accompanied by E〇 removed from the top is effectively used in the EC conversion process.

The crude EC from which EO had been removed (stream 4) was continuously fed to the EC separation column together with the by-product EG separated from the transesterification reaction solution and unreacted EC (stream 5). In the DMC production facility, light boiling components such as MeOH were removed during the above separation, and the product DMC was obtained.

The EC separation tower (number of theoretical plates: 18) has an operating pressure of 8 kPa and a reflux ratio of 0.05, feeds the above stream 4 to the first stage, and feeds the above stream to the ninth stage. 5 was fed, and high-purity EC (stream 7) was removed from the 17th stage with a vapor. After being condensed, it is transferred to the DMC production facility and used as a raw material for the transesterification reaction. In addition, a mixture of water, EG and EC (stream 6) was obtained from the top of the tower, and a mixture of EC and an EC conversion catalyst (stream 8) was obtained from the bottom of the column. These streams obtained from the top and bottom are effectively used in the EG production process.

The top composition is 33 weight of water. /. , EG 5 1% by weight, EC 16% by weight, the bottom composition is E

It contained 69% by weight of C and 28% by weight of an EC conversion catalyst, and about 3% by weight of high molecular weight ethylene dalicol such as diethylene dalicol. The EC purity of the sidestream par

97 weight ⁰ /. And 3% by weight of diethylene dalicol. The energy required to produce the product DMC in this way was 7.9 MJ / kg. Example 2

According to the flow sheet diagram shown in Fig. 2, the crude EC from which water was removed was separated from the ester exchange reaction solution by distillation with unreacted EC and by-product EG, and the resulting purified EC was esterified. The method used as a raw material of the exchange reaction was performed.

Table 2 shows the temperature and composition of each stream when the product DMC was produced using crude EC (stream 1). Table 2

Crude EC (Stream 1) was continuously fed to the dehydration tower. The dehydration tower (theoretical plate number: 8) has an operating pressure of 23 kPa and a reflux ratio of 0.03, and feeds the above stream 1 to the 4th stage to reduce the water content from the bottom of the column to 10 wtp or less. Obtain the removed stream 3. The overhead stream 2 containing most of the EO and water contained in the crude EC is effectively used in the EG production process.

The dehydrated crude EC (stream 3) was continuously fed to the EC separation tower together with the by-product EG and unreacted EC (stream 4) separated from the transesterification reaction solution. In the DMC production facility, light boiling components such as MeOH were removed during the above separation, and the product DMC was obtained.

The EC separation tower (the number of theoretical plates is 13) has an operating pressure of 8 kPa and a reflux ratio of 0.43, and feeds the above-mentioned streams 3 and 4 to the 4th stage. High Purity EC (stream 6) was extracted with a vapor. After being condensed, it is transferred to the DMC production facility and used as a raw material for transesterification. Furthermore, an azeotropic mixture of EG and EC (stream 5) was obtained from the top of the column, and a mixture of EC and an EC conversion catalyst was obtained from the bottom of the column (stream 7). These streams obtained from the top and bottom are effectively used in the EG production process.

Top composition EG 8 1 wt%, with EC 1 9 wt%, the bottom composition EC 73 wt%, with EC-forming reaction catalyst 25 weight ^_0/0, other Echire glycol of high molecular weight, such as diethylene da recalled Of about 2% by weight. The EC purity of the side stream is 98.6% by weight, and 1.3 weight of diethylene glycol is added. /. Included.

The energy required to produce product DMC in this way was 9.5 MJ / kg. Comparative Example 1

According to the flow sheet diagram shown in Fig. 3, the crude EC having the same composition as in Example 2 was first subjected to catalyst separation and then to EC purification distillation. As a by-product EG and unreacted EC separated from the reaction solution, a method of recycling only an azeotropic mixture to the EC purification distillation was performed. Table 3 shows the temperature and composition of each stream when a product DMC was produced using the crude EC (stream 1) having the same composition as that of Example 2 for 5.04TZh.

First, the crude EC (stream 1) was subjected to flash separation of the EC conversion catalyst in the catalyst separation tank. After flashing, the vapor (stream 2) was reduced at 100 ° C. to obtain a stream 5 from which 78% of water was removed, and fed to an EC purification tower. On the other hand, the condensed water (stream 7) is effectively used in the EG manufacturing process because it is accompanied by EG and EC.

The EC purification tower (theoretical stage 13 stage) has an operating pressure of 9 kPa, a reflux ratio of 0.5, feeds the stream 5 to the third stage, and feeds the EC separation column (described later) to the fifth stage. The azeotropic mixture of EG and EC (stream 11) was fed to purify EC. The purified EC (stream 9) is transferred to the DMC production facility and used as a raw material for the transesterification reaction. The overhead distillate containing 63% by weight of EG (stream 8) is effectively used in the EG production process I do.

MeOH and DMC were separated from the transesterification reaction liquid in a DMC production facility, and the obtained by-product EG and unreacted EC (stream 10) were fed to an EC separation tower.

The EC separation tower (theoretical plate number: 8) has an operating pressure of 8 kPa, a reflux ratio of 1, and 5 stages. The stream 10 was fed to the eye, and EC was extracted from the bottom of the tower (stream 12). This can be recycled as a DMC raw material and used as an extractant to separate MeOH from the transesterification reaction liquid by extractive distillation at the DMC production facility. An azeotropic mixture of EG and EC (stream 11) was obtained from the top of the column, and was recycled to the EC purification column to separate purified EC as described above.

The energy required to produce the product DMC in this way was 15.7 MJ / kg. Example 3

EC reaction: An example of the EC reaction step is shown in FIG. E06 5 kg / h, carbon dioxide 140 kg / h, water 47 kg / h, and potassium iodide 9.3 kgZh were dissolved in EG 16.5 kgZh in the first-stage EC reactor. The catalyst solution was fed, and reacted at a temperature of 110 to a conversion of 86% at £ 0.

The reaction solution obtained from the EC first reactor is supplied to the tubular EC second reactor, and the EO conversion is performed at 110 ° C and a pressure of 1960 kPa. The reaction was performed to 99.9 ° / ₀ .

The reaction liquid composition (% by weight) at the outlet (A) of the first-stage reactor and the outlet (B) of the second-stage reactor in this process was as shown in the table below.

Table 4 Composition of EC reaction solution

Transesterification: The DMC production process is shown in FIG. The ester exchange reaction and the purification operation were performed according to the procedure shown in this figure, and the energy required for the production of DMC was obtained. The raw material liquid with an EO conversion rate of 86% extracted from the outlet (A) of the first-stage EC reactor is stripped of EO with carbon dioxide gas, and the top is adjusted to a pressure of 23 kPa. Dehydration was performed in the retained distillation column. The liquid after dehydration is fed to an EC separation column, and is separated by distillation together with EG and unreacted EC by-produced in the transesterification reaction between MeOH and EC, and EG is converted from the top of the column with an azeotropic composition of EG and EC. Then, the EC conversion catalyst was removed from the tower bottom together with EC. The distillation column was operated at a top pressure of 8 kPa and a reflux ratio of 0.5. EC to be supplied to the transesterification reactor as a DMC raw material was withdrawn as a gas from a side stream of the EC separation column. The EC purity in this extracted mixture was 98.3 weight. /. Met.

In this operation, the amount of EG separated from the DMC manufacturing process was 1.2 kg per 1 kg DMC. The amount of heat required to obtain EC for producing 1 kg of DMC was 3.0 MJ for the dehydration tower and 4.9 MJ for the EC separation tower, for a total of 7,9 MJ. Example 4

In Example 3, EO conversion was withdrawn from the EC second stage reactor outlet (B) instead of the raw material liquid with an EO conversion rate of 86% extracted from the EC first stage reactor outlet (A). The ester exchange reaction and the purification operation were performed in exactly the same manner as in Example 3 except that the reaction solution was used at a rate of 99.9%. The E C purity in the mixture withdrawn from the E C separation column was 98.6% by weight.

In this operation, the amount of EG separated from the DMC manufacturing process was 2.1 kg per 1 kg of DMC. The amount of heat required to obtain EC for producing 1 kg of DMC was 2.4 MJ for the dehydration tower and 6.9 MJ for the EC separation tower, for a total of 9.3 MJ.

As described above, according to Examples 3 and 4, the amount of EG passing through the DMC production process is further reduced by using EC separated from the reaction product in a specific EO conversion range as a DMC raw material. be able to. In addition, the energy required in the DMC manufacturing process can be further reduced. Reference example 1

EC generation reaction: E065 kgZh, carbon dioxide 140 kg / h, water 47 kgZh and triptyl methylphosphonium iodide 9.3 kg / h with carbon dioxide power at the bottom of the first reactor of the EC type of bubble column type A catalyst solution obtained by dissolving 0.373 kg / h of lithium in 16.5 kg / h of EG was fed, and reacted at a temperature of 110 ° C. and a pressure of 1960 kPa to an EO conversion of 86%. The reaction liquid obtained from the outlet at the top of the first EC reactor is fed to a tubular EC second reactor. At a temperature of 110 ° C and a pressure of 1960 kPa, the conversion rate of £ 〇99 It was reacted to 9%. The reaction solution was then reduced in pressure to normal pressure to remove the remaining carbon dioxide.

Distillation separation: Distillation separation was performed while supplying the reaction solution obtained in the EC conversion reaction to the distillation column shown in FIG.

The distillation column was divided into the first to third layers from the top of the column, and the first and third layers were gas-liquid contact parts corresponding to one theoretical plate. The second layer is divided into two equal parts on the left and right by a vertical planar partition wall to form two flow paths, and the first flow path for supplying the reaction solution is equivalent to three theoretical plates, and the side flow is drawn out. A gas-liquid contact part equivalent to eight theoretical stages was installed in the flow path. The gas-liquid contact part in the tower is a packed tower type. The first channel of the first, third and second layers is a porous metal sheet molded type structured packing (product name: Melapak), the second layer The second flow path was filled with a wire netting type structured packing (product name Sulza one packing BX). The reaction solution was continuously supplied to the first stage of the first flow path, and the sidestream liquid was continuously extracted from the seventh stage of the second flow path. The pressure at the top of the distillation column was 5 kPa, and the reflux ratio was 0.3. The liquid phase flowing down from the first layer was distributed in approximately equal amounts to the two channels. The distribution of the gas phase rising from the third layer was a consequence.

Under the above conditions, the system was operated to a substantially steady state, and EC was manufactured. Table 5 shows the mass balance in the steady state. The purity of the sidestream EC liquid extracted from the second flow path was about 91% by weight, and contained about 9% by weight of EG. The reboiler calorie required for distillation was 2.34 MJ per kg of the sidestream EC solution.

Reference example 3

EC was obtained in the same manner as in Reference Example 1 except that the distillation column in FIG. 8 was used instead of the distillation column in FIG. 6 to perform distillation separation.

The distillation column shown in Fig. 8 is provided with a gas-liquid contact part equivalent to 12 theoretical plates, filled with a wire mesh molding type structured packing (product name Sulzer Packing BX). Then, the sidestream gas was continuously extracted from the first stage. The distillation was operated at a reflux ratio of 4.7 while maintaining the pressure at the top of the distillation column at 5 kPa, and the mass balance in Table 7 was obtained. I got The EC purity of the sidestream gas at this time is about 91% by weight, about 9% by weight. /. Of EG. The reboiler calorie required for distillation was 8.02 MJ per kg of sidestream gas.

Reference example 4

EC was obtained in the same manner as in Reference Example 1, except that the distillation column in FIG. 9 was used instead of the distillation column in FIG. 6 to perform distillation separation.

The distillation column shown in Fig. 9 is provided with a gas-liquid contact section filled with a wire mesh type structured packing (product name Sulza-I Packing BX) .The first column has one theoretical plate in the concentration section and one theoretical plate in the recovery section. As a third stage, a distillation operation was performed at a reflux ratio of 0.001 while maintaining the top pressure at 5 kPa, and the liquid distilled from the top was supplied to the second stage of the second column. In the second column, distillation was performed at a reflux ratio of 0.1 while maintaining the top pressure at 5 kPa with a theoretical stage of 1 stage in the enrichment section and 7 stages in the recovery section. As a result, the concentrated EC solution was continuously extracted. At this time, the EC purity of the second column bottoms was about 91% by weight and contained about 9% by weight of EG. The calorific value of the reboiler required for distillation was 3.76 MJ per kg of the bottoms discharged from the second column. Table 8

Reference example 5

The second layer of the distillation column is divided inside and outside by a vertical cylindrical partition wall, and the outside is used as the first flow path, filled with irregular packing (product name: Dickson packing, outer diameter 3 mm, length 3 mm, cylindrical). Distillation and separation were performed under the same conditions as in Reference Example 1 except that the inside was used as the second flow path. The result of the distillation was the same as in Reference Example 1. Reference example 6

Distillation and separation were performed under the same conditions as in Reference Example 1 except that the distillation column was a tray column of a sieve tray, and the liquid depth on the first flow path side was larger than that on the second flow path side to correct pressure imbalance. The result of the distillation was the same as in Reference Example 1. Reference Example 7

The entire second layer of the distillation column is used as the first channel, and another distillation column connected at the lower part of the first layer and the upper part of the third layer is used as the second channel. Distillation and separation were performed under the same conditions as in Reference Example 1, except that the gas was introduced into the upper part of the second flow path, and about half of the gas phase rising from the third layer was introduced into the lower part of the second flow path. The result of the distillation was the same as in Reference Example 1.

As described above, according to Reference Examples 1 to 7, in separating and purifying cyclic alkylene carbonate from a reaction product obtained by reacting alkylene oxide and carbon dioxide in the presence of water, a single distillation column was used. The effect of being able to separate with low energy is obtained. Example 5

According to the flow sheet diagram shown in FIG. 10, the transesterification reaction between EC and MeOH was carried out in the reaction unit connected to the first tower, and the transesterification products DMC and EG were converted to Separated and obtained in the second and third towers.

(1) In the reaction unit (fixed-bed flow reactor, using manganese dioxide catalyst, reaction temperature of 130 ° C), new EC and recovered EC are supplied to the reaction unit together with recovered MeOH through the first column enrichment section. Also, new MeOH was directly supplied and transesterification was performed. The reaction temperature was kept constant by flowing a heat medium through the jacket of the reactor.

In the figure, the enrichment section (6 theoretical levels) of the first column (22 theoretical levels, operating pressure 98 kPa, total reflux) corresponds to the gaseous methanol recovery unit, and the recovery section (16 theoretical levels). Corresponds to the liquid methanol recovery unit.

That is, (2) In the gaseous methanol recovery unit, EC supplied to the first stage of the first column (top of the enrichment section) rises from the column recovery section while flowing down the enrichment section Extractive distillation is performed in contact with gaseous methanol. Almost all of the liquid that has flowed down to the sixth stage of the first tower (the lowermost part of the concentrated section) is sent to the reaction unit through the connection pipe.

(3) In the liquid methanol recovery unit, the liquid reaction mixture extracted from the reaction unit is supplied to the seventh stage of the first tower (the top of the recovery section) through the connecting pipe, and flows down the recovery section. In the meantime, all of the methanol in the mixture is vaporized and recovered together with DMC having an azeotropic composition, and rises to the gaseous methanol recovery unit in the enrichment section of the column, and the remaining liquid mixture (mainly, the transesterification reaction product) DMC and EG and unreacted EC) were continuously withdrawn from the bottom of the first column as bottoms. The liquid discharged from the first column is sent to the second column.

In the second column (17 theoretical plates, operating pressure 19 kPa, reflux ratio 1.4), the bottoms of the first column supplied to the seventh column are distilled and the top of the second column is distilled. DMC was obtained from The bottoms of the second column are sent to the third column.

In the third column (15 theoretical plates, operating pressure 8 kPa, reflux ratio 3.5), the fifth column The bottom liquid of the second column supplied to the stage was distilled, and EG was separated and obtained from the top of the third column as an azeotrope with EC. Since high-purity EC is recovered as the bottom liquid of the third column, it is recycled to the first column and reused as a raw material.

Under the above operating conditions for each column, the conversion of methanol ((moles of DMC acquired x 2) / moles of methanol consumed) is 100%, and the conversion of EC (moles of DMC acquired / moles of EC consumed) is 97 °. / ₀ , and the total energy required to produce 1 kg of DMC is 6.6 MJ (1.5 MJ for the first tower, 0.9 MJ for the second tower, 3.1 MJ for the third tower, and 1.1 MJ for the reaction unit). ) Met. Example 6

According to the flow chart shown in Fig. 11, the ester exchange reaction between EC and MeOH was performed in the first column, and the transesterification products DMC and EG were converted to the second and third columns, respectively. Was obtained separately.

In the figure, the upper part of the first column (theoretical stage number 32, operating pressure 297 kPa total reflux) (theoretical stage number 11 stage) ① corresponds to the gaseous methanol recovery unit, and the middle part (theoretical stage number 10 0 Step (2) corresponds to the reaction unit (a tray-type catalyst packed tower, using catalytic manganese dioxide, reaction temperature 95 ° C), and the lower part (the number of theoretical plates is 11) ③ corresponds to the liquid methanol recovery unit.

That is, in the first tower, new EC and recovered EC are supplied from the upper part of the gaseous methanol recovery unit II (second stage of the first tower), and new methanol is supplied to the reaction unit.

Raw materials are supplied from the upper part of ② (first and second stages of the first tower). The gaseous methanol vaporized from the reaction unit とともに continuously rises to the gaseous methanol recovery unit とともに together with the DMC having an azeotropic composition. The entire amount is condensed 'recovered and returned to the upper part of the reaction unit II (1st and 2nd stages of the first column) with EC. The 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 the upper part of the liquid methanol recovery unit ③ (first stage, 22nd stage) from the lower part of the reaction unit ② is continuously flowing down the unit ③. Then, methanol is vaporized and recovered together with the DMC having the azeotropic composition, and rises to the reaction unit (2). The remaining liquid mixture (mainly composed of transesterification products DMC and EG and unreacted EC) was continuously withdrawn from the bottom of the first column as bottoms. The liquid discharged from the first column is sent to the second column.

In the second column (17 theoretical plates, operating pressure 16 kPa, reflux ratio 1.4), the bottoms of the first column supplied to the seventh column are distilled and the top of the second column is distilled. DMC was obtained from The bottoms of the second column are sent to the third column.

In the third column (15 theoretical plates, operating pressure 8 kPa, reflux ratio 1), the bottom liquid of the second column supplied to the fifth column is distilled, and EG is collected from the top of the third column. Separated and obtained as an azeotrope with EC. Since high-purity EC is recovered from the bottom of the third column as bottom product, it is recycled to the first column and reused as raw material.

Under the above operating conditions, the conversion of methanol ((acquired DMC moles x 2) Z consumed methanol moles) was 100%, and the EC conversion rate (acquired DMC moles consumed EC moles) was 94%. The total energy required to produce 1 kg of DMC is 7.3 MJ (5.3 MJ for the first tower, 0.7 MJ for the second tower, and 1.3 MJ for the third tower). Reference Example 8

According to the flow sheet diagram shown in Fig. 12, transesterification between EC and MeOH is performed in the first column (reactive distillation column), unreacted MeOH is recovered in the second column, and the transesterification product Certain DMCs and EGs were separated and obtained in the third tower and the first tower, respectively.

New Me OH and recovery of raw material Me OH is vaporized by a MeOH preheater, and then converted to the first column (using a tray-type catalyst packed column, using catalytic manganese dioxide, reaction temperature 65-190 ° C; theoretical plate number) 42 stages, operating pressure 101 kPa, reflux ratio 8) Supplied in gaseous form from lower third stage 2 and raw material EC supplied in liquid form from upper stage 1 in upper stage 1 and transesterification I do. In the first column, the reaction mixture is further distilled, and an azeotropic mixture of the reaction product DMC and unreacted MeOH is provided from the top of the column, and the reaction product EG is provided from the bottom of the column. Unreacted ECs are continuously extracted.

In the second column (20 theoretical plates, operating pressure: 101 kPa, reflux ratio: 0.93), the first column distillate (azeotropic mixture) supplied to the first and fifth stages was converted to an EC. The MeOH recovered from the top of the column is recycled to the first column, and the mixture of DMC and EC obtained as bottoms from the bottom Send to the tower. In the third column (12 theoretical plates, operating pressure 8 kPa, reflux ratio 5), the bottoms of the second column supplied to the seventh column are distilled, and DMC is removed from the top of the third column. Acquired separately. EC recovered as bottoms from the bottom is recycled to the second column and used as an extraction solvent. Under the operating conditions of each column above, the conversion of Me OH ((moles of acquired DMC x 2) / moles of methanol consumed) is 100%, and the conversion rate of EC (moles of acquired DMC / moles of consumed EC) is 99%. ° / ₀ , and the energy required to produce 1 kg of DMC is 36.3 MJ in total (25.5 MJ in the first tower, 5.2 MJ in the second tower, 1.8 MJ in the third tower and 1.8 MJ in the methanol preheater 3 8MJ).

As described above, according to Examples 5, 6 and Reference Example 8, further simplification can be achieved by appropriately combining a reaction unit for transesterifying ethylene carbonate with methanol, a gaseous methanol recovery unit, and a liquid methanol recovery unit. Thus, an efficient process can be configured. Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

This application was filed on July 10, 2001 (Japanese Patent Application No. 2001-209502), filed on July 27, 2001 in Japanese Patent Application (No. 2001-227395), and filed on October 103, 2001 Of Japanese Patent Application No. 2001-312743, and Japanese Patent Application No. 2001-377811 filed on December 11, 2001, the contents of which are incorporated herein by reference. Industrial applicability

According to the present invention, for example, unreacted crude ethylene carbonate containing ethylene glycol and an EC conversion reaction catalyst, which is obtained as an intermediate stream for the EC conversion reaction of a catalytic ethylene glycol production process, is separated from a transesterification reaction solution. By using purified ethylene carbonate having a purity of 80% by weight or more obtained by distillation separation together with ethylene carbonate and by-product ethylene glycol as a raw material for transesterification, dimethyl carbonate can be efficiently produced with little energy. In addition to the above, the effect of being able to manufacture the equipment and simplifying the equipment can be obtained.

Claims

S = te Range of requests

1. In a method for producing a dialkyl carbonate by subjecting an alkylene carbonate and an alcohol to a transesterification reaction, when a purified alkylene carbonate having a purity of 80% by weight or more is used as a raw material for the transesterification reaction, the purified alkylene carbonate is used. Wherein the crude alkylene carbonate obtained from the alkylene carbonate production step and the unreacted alkylene carbonate mixture separated from the transesterification reaction liquid are purified by the same distillation apparatus. Manufacturing method.

2. The alkylene carbonate production step is a step in which alkylene oxide is reacted with carbon dioxide gas in the presence of water and a catalyst to obtain a reaction product having a conversion of the alkylene oxide of 50% or more and 95% or less. The method according to claim 1, wherein:

3. The method according to claim 2, wherein the step of producing an alkylene carbonate includes a step of removing unreacted alkylene oxide from the reaction product.

4. When purifying the alkylene carbonate by distillation, distill water and low-boiling components mainly composed of Z or alkylenedalicol from the top of the distillation column, and contain an alkylene-force-ponation reaction catalyst from the bottom of the column. The method according to any one of claims 1 to 3, wherein the alkylene carbonate is withdrawn and purified alkylene carbonate is removed from a side stream.

5. The supply line of the crude alkylene carbonate obtained from the alkylene carbonate production process to the distillation column is above the supply line of the unreacted alkylene carbonate separated from the transesterification reaction solution. The method described in.

6. When purifying the alkylene carbonate by distillation, the distillation column has a gas-liquid contact part divided into two flow paths, and the crude alkylene carbonate is supplied to the gas-liquid contact part of the first flow path. The method according to any one of claims 1 to 4, wherein the purified alkylene carbonate is supplied from the gas-liquid contact portion of the second flow path.

7. The method according to claim 6, wherein unreacted alkylene carbonate separated from the transesterification reaction solution is supplied to the gas-liquid contact portion of the second flow path.

8. The method according to claim 6 or 7, wherein the distillation column is a vertical division type in which two flow paths are formed by using partition walls in the same distillation column.

9. (a) reacting alkylene oxide with carbon dioxide in the presence of a catalyst to produce alkylene carbonate;

(b) recovering the alkylene oxide from the reaction product mixture,

(c) a distillation step of supplying the residual liquid to a distillation column and obtaining a purified alkylene force-ponate having a purity of 80% by weight or more from the column side;

(e) circulating unreacted alcohol to step (d),

(f) a step of recovering the dialkyl carbonate from the transesterification reaction solution, wherein the residual liquid of the step (f) is supplied to the distillation column of the step (c).

10. The supply line of the crude alkylene carbonate obtained from the alkylene carbonate production process to the distillation column is higher than the supply line of the unreacted alkylene carbonate separated from the transesterification reaction solution. A gas-liquid contact section divided into two flow paths, and the crude liquid: Supplying unreacted alkylene carbonate separated from the transesterification reaction solution to the gas-liquid contact portion of the second flow path, and extracting the purified alkylene carbonate from the gas-liquid contact portion of the second flow path. 10. The method according to claim 9, wherein:

11. A reactor for transesterifying an alkylene carbonate with an alcohol comprises: (i) a reaction unit for performing the transesterification; (ii) a gaseous alcohol sent from a reaction tube or a liquid alcohol recovery unit 1. (Iii) vaporizing the alcohol in the liquid reaction mixture sent from the reaction unit and sending it to the reaction unit or gaseous alcohol collection unit. 10. The method according to claim 1 or 9, wherein the apparatus comprises three units.

12. A method for producing a dialkyl carbonate by transesterification from an alkylene carbonate and an alcohol, wherein (i) a reaction unit for carrying out the transesterification reaction, (ii) a gaseous alcohol sent from the reaction unit or the liquid alcohol recovery unit. A gaseous alcohol recovery unit that is liquefied and sent to the reaction unit and (iii) a liquid alcohol recovery unit that vaporizes the alcohol in the liquid reaction mixture sent from the reaction unit and sends it to the reaction unit or the gaseous alcohol recovery unit A method for producing dialkyl carbonate, comprising using an apparatus containing the above three buttes.