JP2016216380A - Method for producing dialkyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing dialkyl carbonate where azeotropy between the generated dialkyl carbonate and raw material is prevented, the number of steps for obtaining dialkyl carbonate of product quality is efficiently reduced, and also, production-equipment costs are reduced.SOLUTION: Provided is a method for producing dialkyl carbonate comprising: the first synthesis step where at least one or more alcohols selected from ethanol, propanol, butanol and pentanol and ketone are used as raw material, and the raw material is reacted in the presence of a catalyst to generate ketal; and the second synthesis step where the generated ketal and COare reacted in the presence of a catalyst to generate dialkyl carbonate. Each step is provided with a separation step of, after the passage of the separation regeneration step of the unreacted raw material, it is made into the raw material in each step.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a dialkyl carbonate, and more particularly to a method for producing a dialkyl carbonate for producing a dialkyl carbonate which is a raw material for polycarbonate from an alcohol.

  Polycarbonate, which is a resin with excellent transparency, impact resistance, heat resistance, etc., has been steadily growing in demand for industrial materials. It has been reported that the dialkyl carbonate used as a raw material for such a polycarbonate can be synthesized by various methods. As a main synthesis method of such a dialkyl carbonate, there is a phosgene method in which a phosgene and an alcohol are reacted to produce a dialkyl carbonate. However, since phosgene has strong toxicity, a production method that does not use phosgene is eagerly desired.

As such a production method, a method of producing dimethyl carbonate by producing acetone dimethyl acetate from methanol and reacting it with CO ₂ is known (for example, Patent Document 1).

  However, the example shown in Patent Document 1 has a problem that the dialkyl carbonate to be produced and the raw material existing during the production azeotrope to form an azeotrope. In addition, there are many steps for separating and purifying dialkyl carbonate, making it difficult to obtain product-quality dialkyl carbonate and increasing production and equipment costs.

Japanese Patent No. 4616589

  In light of the above circumstances, the present invention prevents the azeotropy between the dialkyl carbonate to be produced and the raw material, efficiently reduces the number of steps for obtaining product-quality dialkyl carbonate, and reduces the manufacturing and equipment costs. It aims at providing the manufacturing method of.

In order to achieve the above object, a method for producing a dialkyl carbonate according to the present invention uses at least one alcohol selected from the group consisting of ethanol, propanol, butanol and pentanol and a ketone as raw materials in the presence of a catalyst. It comprises at least a first synthesis step for reacting to produce a ketal and a second synthesis step for reacting the produced ketal with CO ₂ in the presence of a catalyst to produce a dialkyl carbonate.

  Further, the present invention provides a first separation in which a ketone is separated from a first mixture comprising a ketal, a by-product and an unreacted product produced in the first synthesis step, and sent to the first synthesis step as a raw material. -Separation / regeneration of ketal by separating the ketal from the second mixture consisting of the regeneration step and the dialkyl carbonate, by-product and unreacted product produced in the second synthesis step, and sending them to the second synthesis step as raw materials And a process.

  By providing such a step, the ketone after the first synthesis step is recycled to reduce the amount of ketone required for the synthesis of the required amount of ketal, and the ketal after the second synthesis step is recycled, The amount of ketal required for the synthesis of the required amount of dialkyl carbonate can be reduced. As a result, the production efficiency of dialkyl carbonate can be further improved and the production cost can be reduced.

  Furthermore, in the present invention, in another embodiment, the by-product water is removed from the first mixture of the first synthesis step using at least two dehydration towers, and sent to the first synthesis step as a raw material. It can be set as the form further provided with a process.

  If it is such a form, while reducing the moisture content in a raw material and improving the synthesis | combination efficiency of the ketal in a 1st synthetic | combination process, the unreacted substance of a 1st synthetic | combination process can be recycled. As a result, the production efficiency of dialkyl carbonate can be further improved and the production cost can be reduced.

  Furthermore, it is preferable that the present invention further includes a second separation / regeneration step of separating the ketone and alcohol from the second mixture and sending them as raw materials to the first synthesis step.

  By providing such a process, for example, the ketone and alcohol after the second synthesis step are recycled between the ketal production facility and the ketone production facility, and necessary in the first synthesis step. The amount of ketone required to synthesize the amount of ketal can be reduced. As a result, the production efficiency of dialkyl carbonate can be further improved and the production cost can be reduced.

Furthermore, it is preferable that the present invention further includes a CO ₂ separation / regeneration step of separating CO ₂ from the second mixture and sending it as a raw material to the second synthesis step.

By providing such a process, it is also necessary to provide expensive equipment and processes for fixing CO ₂ in the production plant without discharging CO ₂ generated in the production plant of dialkyl carbonate. Absent. For this reason, while reducing an installation and manufacturing cost, the manufacturing efficiency of dialkyl carbonate can be improved more.

  It is preferable that the alcohol is butanol, the ketone is acetone, the ketal is acetone dibutyl acetate, and the dialkyl carbonate is dibutyl carbonate.

  With such a raw material, it is possible to produce dibutyl carbonate, which is a raw material for polycarbonate, using butanol having a large number of carbons as a raw material, and reliably preventing alcohol and dialkyl carbonate from constituting an azeotropic composition. it can. In addition, dibutyl carbonate can be easily separated and purified, and it is not necessary to purify butanol after the first synthesis step. Therefore, the number of processes and equipment for increasing the purity of butanol to product quality can be reduced as compared with the case where methanol is used as a raw material. As a result, equipment and manufacturing costs can be further reduced. In industrial production of dialkyl carbonate, especially dibutyl carbonate, it is very important to suppress production / equipment costs, energy consumption, and the like.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the dialkyl carbonate which prevents the azeotropy of the dialkyl carbonate to produce | generate and raw material, reduces the number of processes for obtaining the product quality dialkyl carbonate efficiently, and reduces manufacturing and equipment cost. Provided.

FIG. 1 is a conceptual diagram for explaining the outline of the system of the first embodiment of the method for producing dialkyl carbonate according to the present invention. FIG. 2 is a conceptual diagram for explaining the outline of the system of the second embodiment of the method for producing dialkyl carbonate according to the present invention. FIG. 3 is a conceptual diagram of a system for explaining an embodiment of the method for producing dialkyl carbonate according to the present invention.

  Hereinafter, the manufacturing method of the dialkyl carbonate which concerns on this invention is demonstrated in detail, referring an accompanying drawing. The present invention is not limited to the embodiments described below.

[First embodiment]
The method for producing a dialkyl carbonate according to the present invention includes at least a first synthesis step and a second synthesis step.

First, in the first synthesis step, an alcohol having 2 to 5 carbon atoms and a ketone, for example, acetone, are used as a first raw material, and reacted in the presence of the first catalyst as shown in the following formula (1). Generate.

In the subsequent second synthesis step, the produced ketal, for example, acetate and CO ₂ is used as a second raw material and reacted in the presence of the second catalyst as shown in the following formula (2) to produce a dialkyl carbonate. .

One of the raw materials for the first synthesis step is ethanol (C ₂ H ₅ OH), propanol (C ₃ H ₇ OH), butanol (C ₄ H ₉ OH), and pentanol (C ₅ H ₁₁ OH). And at least one alcohol having 2 to 5 carbon atoms selected from the group consisting of: More specifically, as the alcohol, ethanol, 1-propanol (CH ₃ CH ₂ CH ₂ OH), 1-butanol (CH ₃ CH ₂ CH ₂ CH ₂ (OH)) and 1-pentanol (CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ (OH)). Among these, while being able to reliably avoid azeotropy during the production of dialkyl carbonate, butanol is preferable and linear 1-butanol is more preferable from a practical viewpoint.

One of the raw materials for the first synthesis step is a ketone. There is no limitation as long as it is capable of producing a dialkyl carbonate together with alcohol. More specifically, examples of the ketone include acetone (CH ₃ COCH ₃ ), methyl ethyl ketone (CH ₃ COC ₂ H ₅ ), and diethyl ketone (CH ₃ CH ₂ COCH ₂ CH ₃ ). Among these, acetone is preferable from a practical viewpoint, because when the number of carbon atoms increases, the amount of by-products generated may increase.

The products and raw materials of the first and second synthesis steps are not limited as long as they can produce a dialkyl carbonate from an alcohol having 2 to 5 carbon atoms. More specifically, the ketal is preferably an acetal using acetone as a raw material as a ketone. As the acetal, when acetone and an alcohol having 2 to 5 carbon atoms are used as the first raw material, acetone diethyl acetate ((C ₂ H ₅ O) ₂ C (CH ₃ ) ₂ ), acetone dipropyl acetate ((C ₃ H ₇ O) ₂ C (CH ₃ ) ₂ ), acetone dibutyl acetate ((C ₄ H ₉ O) ₂ C (CH ₃ ) ₂ ), and acetone dipentyl acetate ((C ₅ H ₁₁ O) ₂ C (CH ₃ ) ₂ ). Of these, acetone dibutyl acetate is preferred from a practical viewpoint.

The dialkyl carbonate that is the product of the second synthesis step is not particularly limited as long as it is generated according to the starting alcohol. More specifically, dialkyl carbonate is obtained by using diethyl carbonate ((C ₂ H ₅ O) ₂ CO), dipropyl carbonate ((C ₃ H) when acetone and alcohol having 2 to 5 carbon atoms are used as the first raw material. ₇ O) ₂ CO), dibutyl carbonate ((C ₄ H ₉ O) ₂ CO), and dipentyl carbonate ((C ₅ H ₁₁ O) ₂ CO). Of these, dibutyl carbonate is preferred from the practical point of view because azeotropy can be reliably avoided.

  The temperature and pressure in the first or second synthesis step may be any temperature and pressure at which ketal can be synthesized from the first raw material and dialkyl carbonate can be synthesized from the second raw material. The temperature in the first synthesis step is, for example, −50 ° C. to 50 ° C., preferably −20 ° C. to 0 ° C., and the pressure is, for example, 0.01 MPa to 1.0 MPa, preferably normal pressure. It is. Moreover, the temperature in a 2nd synthetic | combination process is 100 degreeC-300 degreeC, for example, Preferably it is 150 degreeC-200 degreeC, The pressure is 10 MPa-50 MPa, for example, Preferably it is 10 MPa-30 MPa. If it is such a range, the production | generation efficiency of dibutyl carbonate at the time of using butanol can be improved.

In the first and second synthesis steps, predetermined catalysts are used as the first and second catalysts. As a 1st catalyst, what is necessary is just to use the catalyst which can produce | generate a ketal from a C2-C5 alcohol and ketone, It is not limited. For example, a strong acid catalyst (such as a strong acid cation exchange resin) obtained by supporting a strong acid on a carrier made of a compound having a solid acid point can be used. Moreover, what is necessary is just to use the catalyst which can produce | generate dialkyl carbonate from a ketal and CO2 as a _2nd catalyst. For example, a catalyst in which an acid such as phosphoric acid, sulfuric acid, or sulfonic acid is supported on a carrier made of a compound such as ZrO ₂ , TiO ₂ , or SiO ₂ having a solid acid point can be used. Among these, a catalyst in which phosphoric acid is supported on an amphoteric oxide such as ZrO ₂ is preferable. With such a catalyst, the amount of by-products relative to the amount of dialkyl carbonate produced can be reduced, and separation and purification of dialkyl carbonate can be performed more efficiently.

As described above, when the raw materials of the first synthesis step are acetone and butanol, and the raw materials of the second synthesis step are acetone dibutyl acetate (ADBA) and CO ₂ , the first and second synthesis are performed. The said dialkyl carbonate produced | generated through a process turns into dibutyl carbonate (DBC: Dibutyl carbonate).

Moreover, the manufacturing method of the dialkyl carbonate which concerns on this invention can be equipped with the process of the following iv.
i) a first separation / regeneration step in which a ketone is separated from a first mixture composed of a ketal, a by-product and an unreacted product produced in the first synthesis step, and sent to the first synthesis step as a raw material;
ii) a ketal separation / regeneration step for separating the ketal from the second mixture comprising the dialkyl carbonate, by-product and unreacted product produced in the second synthesis step, and sending the ketal as a raw material to the second synthesis step;
iii) a removal step of removing by-product water from the first mixture of the first synthesis step using at least two dehydration towers and sending it as a raw material to the first synthesis step;
iv) a second separation / regeneration step in which a by-product ketone and an unreacted alcohol are separated from the second mixture and sent to the first synthesis step as a raw material, and / or
v) A CO ₂ separation / regeneration step of separating CO ₂ from the second mixture and sending it as a raw material to the second synthesis step.
The first and second separation / regeneration steps, the ketal separation / regeneration step, the removal step, and the CO ₂ separation / regeneration step will be described in detail below with specific examples.

  Next, the method for producing dialkyl carbonate according to the present invention will be described in detail with reference to the system configuration shown in FIG. In the illustrated system, the alcohol is butanol, the ketal is acetone dibutyl acetate (hereinafter also referred to as ADBA), and the dialkyl carbonate is dibutyl carbonate (hereinafter also referred to as DBC).

  A dialkyl carbonate production system 10 shown in FIG. 1 includes an ADBA synthesizer 20 (first synthesizer), an ADBA separation / purification tower 30 (first separator), and a DBC synthesizer 40 (second synthesizer). And a DBC separation / purification tower 50 and an ADBA separation / purification tower 60 (second separation device).

A first raw material containing at least acetone and butanol in a liquid phase state that has been cooled to a predetermined temperature, for example, a temperature of 25 ° C. and cooled and aggregated, is introduced into the ADBA synthesizer 20.
In the ADBA synthesizer 20, ADBA is generated from acetone and butanol introduced as the first raw material under a first catalyst filled therein, for example, at normal pressure and a temperature of −20 ° C. (first Synthesis process). The mixed solution (first mixture) discharged from the ADBA synthesizer 20 contains generated ADBA, by-product water, and unreacted acetone and butanol.
The mixed liquid is introduced into a dehydrating tower 22 equipped with a dehydrating agent such as molecular sieve, and dehydrated by separating by-product water. The separated by-product water is discharged out of the system, and a mixed liquid composed of dehydrated ADBA, acetone and butanol is sent to the ADBA separation / purification tower 30.

The ADBA separation / purification tower 30 can employ at least one distillation tower of a plate system or a packing system, and includes at least a reboiler 31, a cooler 32, and a recovery tower 33.
In the ADBA separation / purification tower 30, a mixed liquid composed of ADBA, acetone and butanol is introduced, and the mixed liquid at the bottom of the tower is heated by the reboiler 31 and refluxed to the separation / purification tower 30. Thereby, it evaporates from a substance with a low boiling point among the mixed liquid in ADBA separation and purification tower 30, and rises in the tower. As a result, the liquid mixture newly introduced into the ADBA separation / purification tower 30 and falling inside the tower comes into vapor-liquid contact with the rising steam.
In the upper part of the ADBA separation / purification tower 30, the concentration of acetone, which is a substance having a low boiling point in the vapor mixture, is high, and the concentration of ADBA and butanol, which are substances having a high boiling point, is high in the lower part. Distribution occurs. Then, acetone is discharged from the upper part of the ADBA separation / purification tower 33, and the discharged steam is condensed by the cooler 32, whereby the acetone can be recovered in the recovery tower 33 in a liquid phase state. The heating temperature by the reboiler 31 is preferably in the range of 50 ° C. or higher and 200 ° C. or lower, and within this range, acetone can be efficiently separated and recovered from a mixed solution composed of ADBA, acetone and butanol. The recovered acetone is mixed with the first raw material, refluxed to the ADBA synthesizer 20, and recycled as the raw material for the first synthesis step.
In this manner, the ADBA separation / purification tower 30 separates acetone from the first mixture of acetone dibutyl acetate, by-products and unreacted products generated in the first synthesis step in the ADBA synthesizer 20, The raw material is sent to the first synthesis step (first separation / regeneration step).

  On the other hand, a mixed liquid of ADBA and butanol obtained by separating acetone from the mixed liquid is sent to the DBC synthesizer 40 from the lower part of the ADBA separation / purification tower 30.

The DBC synthesizer 40 is introduced with CO ₂ in a liquid phase pressurized to, for example, 30 MPa by a compressor 41, and a mixed liquid composed of ADBA and butanol. In the DBC synthesizer 40 filled with the second catalyst, ADBA and CO ₂ are added under a predetermined catalyst at a predetermined pressure (second pressure) higher than normal pressure, for example, a pressure of 30 MPa and a temperature of 200 ° C. To produce DBC. The mixed liquid (second mixture) discharged from the DBC synthesizer 40 contains generated DBC, by-product acetone, and unreacted ADBA, butanol, and CO ₂ .
In this way, in the DBC synthesizer 40, CO ₂ is reacted with ADBA generated in the first synthesis step in the ADBA synthesizer 20 and passed through the first separation / regeneration step in the ADBA separation / purification tower 30. To generate DBC (second synthesis step).

The liquid mixture discharged from the DBC synthesizer 40 is sent to the CO ₂ separation device 42 in a high pressure state. At this time, the mixed liquid contains the produced DBC, by-product acetone, and unreacted ADBA, butanol and CO ₂ .
In the CO ₂ separation device 42, under a predetermined pressure (third pressure) higher than normal pressure and lower than the second pressure at which the reaction is performed in the DBC synthesizer 40, for example, at a pressure of 5 MPa and a temperature of 180 ° C. The CO ₂ in the mixture is separated from ADBA, acetone and butanol.

As the CO ₂ separation device 42, a CO ₂ stripper provided with a heat source (not shown) for heating the liquid or a flash tank can be suitably used.
The CO ₂ stripper has a configuration similar to that of a so-called tray type or packed type distillation column, and raises a mixture of dibutyl carbonate, acetone, and CO ₂ under high pressure. As a result, the liquid phase DBC, ADBA, acetone, and butanol remain as they are, and only the CO ₂ in the gas phase rises and is separated. The separated CO ₂ is discharged from the upper part of the CO ₂ stripper, mixed with the second raw material via the compressor 43 and the cooler 44, refluxed to the DBC synthesizer 40, and recycled. The flash tank is a device that evaporates high-pressure liquid and separates it into low-pressure steam and low-pressure condensate. Similarly to the CO ₂ stripper, the flash tank also separates only the CO ₂ that has become vapor, mixes it with the second raw material via the compressor 43 and the cooler 44, and recycles it to the DBC synthesizer 40.
In this way, the second mixture for synthesizing DBC is obtained by separating CO ₂ from the second mixture generated in the second synthesis step in the DBC synthesizer 40 and returning it to the DBC synthesizer 40 again. As a raw material for the synthesis process (CO ₂ separation / regeneration process).

CO ₂ discharged from the CO ₂ separation device 42 maintains the high pressure. For this reason, it is possible to reduce the degree of boosting for circulation to the DBC combiner 40 for recycling. For example, the pressure of CO ₂ is increased from 5 MPa to 30 MPa by the compressor 43. Thus, the energy required for the compressor 43 used for boosting can be greatly reduced as compared with the case of boosting from normal pressure. Note that ADBA and butanol that merge with CO _{2 in} front of the DMC reactor 40 are in a liquid phase, so even if the pressure is increased, less energy is required for compression than in the gas phase. That's it. Thereby, the energy required for manufacturing dialkyl carbonate can be suppressed. As a result, effects such as cost saving and suppression of environmental deterioration can be obtained.

Subsequently, CO ₂ separation device 42 to separate the CO ₂ from the second mixture, DBC, ADBA, discharged in the state of acetone and butanol liquid phase, and sends it to the DBC separation and purification column 50.

The DBC separation / purification tower 50 can employ at least one distillation tower of a plate system or a packing system, and includes a reboiler 51, a cooler 52, and a recovery tower 53.
In the DBC separation / purification tower 50, when a mixed liquid of DBC, ADBA, acetone and butanol is introduced, the liquid mixture at the bottom of the tower is heated by the reboiler 51 and refluxed to the DBC separation / purification tower 50. Thereby, it evaporates from a substance with a low boiling point among the mixed liquid in DBC separation and purification tower 50, and goes up in the tower. The liquid mixture newly introduced into the DBC separation / purification tower 50 and falling inside the tower comes into vapor-liquid contact with the rising steam.
On the upper side of the DBC separation / purification tower 50, the concentration of ADBA, acetone and butanol, which are substances having a low boiling point, is high in the mixed solution, and the concentration of DBC, which is a substance having a high boiling point, is high on the lower side. Concentration distribution occurs. Then, the vapors of ADBA, acetone and butanol are discharged from the upper part of the DBC separation / purification tower 50, and the discharged steam is condensed by the cooler 52, thereby being recovered in a liquid phase state by the recovery tower 53. Can do. On the other hand, DBC having product quality (for example, purity: 95% or more) can be recovered from the lower portion of the DBC separation / purification tower 50 in a liquid phase state. The heating temperature by the reboiler 51 is preferably in the range of 150 ° C. or more and 250 ° C. or less, and within this range, DBC can be efficiently recovered from a mixed solution composed of DBC, ADBA, acetone and butanol.

  Subsequently, the DBC is separated by the DBC separation / purification tower 50, and the mixture containing ADBA, acetone and butanol which has passed through the recovery tower 53 is sent to the ADBA separation / purification tower 60.

The ADBA separation / purification tower 60 can employ at least one distillation tower of a plate system or a packing system, and includes a reboiler 61, a cooler 62, and a recovery tower 63.
In the ADBA separation / purification tower 60, a mixed liquid composed of ADBA, acetone and butanol is introduced, and the mixed liquid at the bottom of the tower is heated by the reboiler 61 and refluxed to the separation / purification tower 60. Thereby, it evaporates from a substance with a low boiling point among the mixed liquid in ADBA separation / purification tower 60, and rises in the tower. The mixed liquid newly introduced into the ADBA separation / purification tower 60 and falling inside the tower comes into vapor-liquid contact with the rising steam.
On the upper side of ADBA separation / purification tower 60, the concentration distribution of acetone and butanol, which are substances having a low boiling point, is high in the mixed solution, and the concentration distribution of ADBA, which is a substance having a high boiling point, is high on the lower side. Occurs. Then, the acetone and butanol vapors are discharged from the upper part of the ADBA separation / purification tower 60, and the discharged steam is condensed by the cooler 62, whereby the acetone and butanol are recovered in the recovery tower 63 in a liquid phase state. it can. The heating temperature by the reboiler 61 is preferably in the range of 100 ° C. or more and 200 ° C. or less. In this range, ADBA and acetone and butanol are efficiently separated from the mixed solution consisting of ADBA, acetone and butanol for recycling. It can be recovered.

Acetone and butanol recovered in the recovery tower 63 are mixed with the first raw material, refluxed to the first ADBA synthesizer 20, and recycled as a raw material for generating ADBA. Further, ADBA recovered from the lower part of the ADBA separation / purification tower 60 is mixed with the second raw material, refluxed to the DBC synthesizer 40, and recycled as the raw material of the second synthesis step for generating DBC.
In this way, acetone and butanol are separated from the second mixture and sent as raw materials to the first synthesis step (second separation / regeneration step). Also, acetone dibutyl acetate is separated from the second mixture consisting of dibutyl carbonate, by-products and unreacted products produced in the second synthesis step, and sent to the second synthesis step as a raw material (acetal separation / regeneration step). .

[Second Embodiment]
A second embodiment of the method for producing dialkyl carbonate according to the present invention will be described with reference to the system of FIG. The dialkyl carbonate production system according to the present embodiment can include at least an ADBA synthesizer 120 (first synthesizer) and at least two dehydration towers 121 and 122.

In the form shown in FIG. 2, two dehydration towers 121 and 122 each filled with a dehydrating agent for dehydrating the first mixture are provided. As the dehydrating agent, for example, a dehydrating agent such as molecular sieve or silica gel can be used. The two dehydration towers 121 and 122 are arranged in parallel and are provided with on-off valves 121a and 121b and 122a and 122b, respectively. The on-off valves 121a to 122b may be manual valves or automatic on-off valves.
In this embodiment, the dehydration towers 121 and 122 are provided, and one of them is used for adsorption and the other is used for regeneration of the adsorbent, whereby dehydration from the mixed liquid after ADBA synthesis in an operating system, The regeneration process of the adsorbent is performed simultaneously.

  For example, in the illustrated dehydration tower 121, the on-off valves 121a and 121b are opened, and the by-product water is removed from the first mixture by the dehydrating agent therein. At the same time, in the dehydration tower 122, the on-off valves 122a and 122b are closed and the by-product water contained in the internal dehydrating agent is removed by heat treatment. The dehydrating tower 122 is disposed as a dehydrating tower that is used when the dehydrating efficiency of the dehydrating tower 121 is reduced.

With the above configuration, by-product water in the first mixture generated in the first synthesis step in the ADBA synthesis tower 120 is removed by the dehydration towers 121 and / or 122. Part of the first mixture dehydrated in the dehydration towers 121 and / or 122 is refluxed to the ADBA synthesis tower 120 to be used as a raw material for the first synthesis step. The remainder is sent to the dehydration tower 22 via a flow rate controller 123 (FIC: Flow Indication Controller).
The method of feeding the first mixture during dehydration to ADBA synthesis 120 and / or dehydration tower 22 may be batch or continuous. Moreover, what is necessary is just to implement liquid feeding to the dehydration tower 22 when the water content in a liquid mixture becomes below a predetermined amount. It is preferable to carry out the first synthesis step by dehydrating the water content in the first mixed solution within the range of, for example, 0.01% by weight or more and 1.0% by weight or less.
In this way, by-product water is removed from the first mixture of the first synthesis step using at least two dehydration towers, and the raw water is sent to the first synthesis step as a raw material (removal step).

  According to the second embodiment, the first mixture after the first synthesis step is supplied to the dehydration tower for dehydration, and then recycled as a raw material for the first synthesis step. Thereby, the water | moisture content in the raw material in the 1st synthetic | combination process in ADBA synthesizer 20 decreases, and the amount of ADBA synthesis | combination can be increased.

  In addition, according to the second embodiment, by installing at least two dehydration towers and operating one for dehydration while using the other for dehydrating agent regeneration, efficient dialkyl carbonate can be efficiently Manufacturing is possible. Furthermore, since the amount of by-product water to the dehydration tower 22 located downstream is reduced, the deterioration rate of the dehydrating agent in the dehydration tower 22 can be suppressed. This enables long-term implementation of the dialkyl carbonate production method.

  Hereinafter, the effects of the present invention will be clarified by specifically describing the present invention with reference to Examples. The method for producing a dialkyl carbonate according to the present invention is not limited by this example.

FIG. 3 shows a dialkyl carbonate production system 10 used in the dialkyl carbonate production method according to the present invention. As shown in FIG. 3, the DBC synthesis process by the production system 10 of dialkyl carbonate is one form of the production method of dialkyl carbonate according to the present invention, ADBA is produced from butanol, and this is reacted with CO ₂ . This is a process for synthesizing DBC. The required amount of steam required for each heat exchanger (cooler), reboiler 21, 31, 44, 51, 61, etc. in the DBC synthesis process by the system 10 was calculated by a process simulator. In addition, in FIG. 3, the location which calculated required steam using the arrow is shown.

As a comparative example, the amount of steam required for each heat exchanger (cooler), reboiler, etc. in a dimethyl carbonate synthesis process (hereinafter also referred to as DMC synthesis process) was calculated by a process simulator. The DMC synthesis process is a process in which acetone dimethyl acetate (ADA) is generated from methanol in an ADA synthesizer, CO ₂ is reacted therewith, and DMC is synthesized in the DMC synthesizer.

  The amount of steam required for each heat exchanger (cooler) and reboiler in the DBC synthesis process was compared with the amount of steam required for each heat exchanger (cooler) and reboiler in the DMC synthesis process. The required amount of steam was compared as the amount of steam per 1 ton of DMC or as the amount of steam per 1 ton of DBC. The results are shown in Table 1 below.

  From the results, when the required steam amount required for the DMC synthesis process is 1, the required steam amount required for the DBC synthesis process is 0.42. Thus, it was found that the required steam amount can be reduced to ½ or less in the DBC synthesis process as compared with the DMC synthesis process. Therefore, according to the manufacturing method of the dibutyl carbonate which concerns on this invention, it confirmed that manufacturing cost could be reduced rather than the manufacturing method of the conventional dimethyl carbonate.

  According to the method for producing dialkyl carbonate according to the present invention, it is possible to prevent azeotropy between the dialkyl carbonate to be produced and the raw material. In addition, the number of steps for obtaining product-quality dialkyl carbonate can be efficiently reduced. As a result, the manufacturing / equipment cost required for the dialkyl carbonate can be reduced.

10: Dialkyl carbonate production system 20, 120: ADBA synthesizer (first synthesizer)
21, 32, 44, 52, 62: Cooler (heat exchanger)
22, 121, 122: Dehydration tower 30, 60: ADBA separation / purification tower 31, 51, 61: Reboiler 33, 53, 63: Recovery tower 40: DBC synthesizer (second synthesizer)
41, 43: Compressor 50: DBC separation / purification tower

Claims (6)

A first synthesis step in which at least one alcohol selected from the group consisting of ethanol, propanol, butanol and pentanol and a ketone are used as raw materials to react with each other in the presence of a catalyst to produce a ketal;
A method for producing a dialkyl carbonate, comprising: a second synthesis step in which the produced ketal and CO ₂ are reacted in the presence of a catalyst to produce a dialkyl carbonate. A first separation / regeneration step of separating a ketone from a first mixture comprising a ketal, a by-product and an unreacted product produced in the first synthesis step, and sending the ketone as a raw material to the first synthesis step;
A ketal separation / regeneration step of separating the ketal from the second mixture composed of the dialkyl carbonate, by-product and unreacted product generated in the second synthesis step, and sending the ketal as a raw material to the second synthesis step; The method for producing a dialkyl carbonate according to claim 1.   3. The method further comprises a removal step of removing by-product water from the first mixture of the first synthesis step using at least two dehydration towers and sending the by-product water as a raw material to the first synthesis step. The manufacturing method of dialkyl carbonate described in 2.   The method further comprises a second separation / regeneration step of separating a by-product ketone and an unreacted alcohol from the second mixture and sending them as raw materials to the first synthesis step. 4. The method for producing a dialkyl carbonate according to any one of 3 above. The carbon dioxide according to any one of claims 2 to 4, further comprising a CO ₂ separation / regeneration step of separating CO ₂ from the second mixture and sending it as a raw material to the second synthesis step. A method for producing dialkyl.   The carbonic acid according to any one of claims 1 to 5, wherein the alcohol is butanol, the ketone is acetone, the ketal is acetone dibutyl acetate, and the dialkyl carbonate is dibutyl carbonate. A method for producing dialkyl.

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