TWI895209B - Method for producing alkylene carbonate - Google Patents

Abstract

An object of the present invention is to provide a method for producing alkylene carbonate from alkylene oxide and carbon dioxide, in which alkylene carbonate and alkali halide are recovered from waste liquid while reducing entrainment of HB.A method for producing an alkylene carbonate, the method comprising: a reaction step of reacting an alkylene oxide and carbon dioxide in a reactor in the presence of an alkali halide to obtain an alkylene carbonate; a cooling step of cooling a mixture (A) containing the alkylene carbonate and the alkali halide which has been subjected to the reaction step; and a solid-liquid separation step of separating a solid containing the alkylene carbonate and the alkali halide from a mother liquid; wherein the method supplies the alkylene carbonate separated in the solid-liquid separation step and an alkali halide to the reactor.

Description

Method for producing alkyl carbonate

The present invention relates to a method for producing alkyl carbonate.

The reaction of alkylene oxide and carbon dioxide to produce alkylene carbonate (hereinafter referred to as the "reaction") has been extensively studied for its utilizability, and the industry is actively exploring catalysts that can achieve sufficient reaction rates. Numerous reports have used solid acid catalysts, alkaline metal salt catalysts, and homogeneous organometallic catalysts. While catalysts have been improved to some extent, these reactions require relatively large amounts of catalyst to react with carbon dioxide, one of the most stable compounds. Furthermore, they can be deactivated by the formation of low-molecular-weight polymers of alkylene oxide as byproducts under the reaction conditions. Consequently, technologies for reusing the catalysts used in this reaction are required. Regarding this topic, for example, a method has been disclosed in which the residual liquid after separating alkyl carbonate from the reaction mixture is returned to the reactor and used as a catalyst (Patent Document 1). [Prior Art Document] [Patent Document]

Patent Document 1: Japanese Patent Application Publication No. 2006-104092

[Problem to be Solved by the Invention] In the process described in Patent Document 1, the residual liquid contains, in addition to alkyl carbonate, high-boiling-point compounds (hereinafter referred to as "HB") such as polyglycols and polycarbonates, which have higher boiling points than alkyl carbonate. These HBs accumulate as they circulate within the process along with the catalyst. Therefore, to remove these HBs from the process, a portion of the residual liquid must be discharged as waste, resulting in loss of both the alkyl carbonate and the alkaline metal halide used as the catalyst.

The present invention aims to provide a method for producing alkyl carbonate from alkylene oxide and carbon dioxide, wherein the method reduces HB banding while recovering alkyl carbonate and alkali metal halide from wastewater. [Means for Solving the Problem]

To address the aforementioned issues, the inventors of this invention conducted in-depth research and discovered that by cooling the mixture containing alkyl carbonate, catalyst, and HB obtained from the production of alkyl carbonate, the alkyl carbonate and catalyst are precipitated. HB is then discharged from the system as a mother liquor, and the alkyl carbonate and catalyst can be efficiently recovered as precipitates, thereby completing the present invention.

That is, the present invention includes the following embodiments. <1> A method for producing an alkyl carbonate, comprising: a reaction step of reacting an alkylene oxide with carbon dioxide in the presence of an alkali metal halide in a reactor to obtain the alkyl carbonate; a cooling step of cooling the mixture (A) containing the alkyl carbonate and the alkali metal halide after the reaction step; and a solid-liquid separation step of separating a solid containing the alkyl carbonate and the alkali metal halide from a mother liquor, wherein the alkyl carbonate and the alkali metal halide separated in the solid-liquid separation step are supplied to the reactor. <2> The method for producing an alkyl carbonate as described in <1>, further comprising a separation step of obtaining the mixture (A) from the solution subjected to the reaction step. <3> The method for producing an alkyl carbonate as described in <2>, wherein, in the separation step, the alkyl carbonate, unreacted alkylene oxide, and carbon dioxide are separated from the solution subjected to the reaction step to obtain the mixture (A). <4> The method for producing an alkyl carbonate as described in any one of <1> to <3>, wherein a portion of the mother liquor separated in the solid-liquid separation step is returned to the cooling step. <5> The method for producing an alkyl carbonate as described in any one of <1> to <4>, wherein the solid is separated by centrifugal separation in the solid-liquid separation step. <6> The method for producing an alkyl carbonate as described in any one of <1> to <5>, further comprising a heating step of heating the solid containing the alkyl carbonate and the alkali metal halide. <7> The method for producing an alkyl carbonate as described in any one of <1> to <6>, wherein the alkylene oxide is ethylene oxide and the alkyl carbonate is ethyl carbonate. <8> The method for producing an alkyl carbonate as described in any one of <1> to <7>, wherein the alkali metal halide is an alkali metal iodide. <9> The method for producing an alkyl carbonate according to any one of <1> to <8>, wherein the cooling temperature of the mixture (A) in the cooling step is from -30 to 36°C. <10> The method for producing an alkyl carbonate according to any one of <1> to <9>, wherein the slurry concentration of the mixture (A) after the cooling step is from 10 to 40 wt%. [Effects of the Invention]

The present invention provides a method for producing alkyl carbonate from alkylene oxide and carbon dioxide, wherein alkyl carbonate and alkaline metal halide are recovered from waste liquid while reducing HB banding.

The following describes an embodiment of the present invention (hereinafter referred to as the "present embodiment") in detail with reference to the drawings as needed. However, the present invention is not limited thereto and various modifications are possible without departing from the scope of the present invention. Furthermore, in the drawings, positional relationships such as up and down, left and right, unless otherwise specified, are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown.

The method for producing an alkyl carbonate according to this embodiment includes the following steps: a reaction step of reacting an alkylene oxide with carbon dioxide in the presence of an alkali metal halide in a reactor to obtain an alkyl carbonate; a cooling step of cooling the mixture (A) containing the alkyl carbonate and the alkali metal halide after the reaction step; and a solid-liquid separation step of separating the solid containing the alkyl carbonate and the alkali metal halide from the mother liquor. The alkyl carbonate and alkali metal halide separated in the solid-liquid separation step are then supplied to the reactor. According to the above embodiment, a method for producing alkyl carbonate from alkylene oxide and carbon dioxide can be provided, wherein alkyl carbonate and alkaline metal halide are recovered from waste liquid while HB banding is reduced.

Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, vinyl ethylene oxide, hexene oxide, and styrene oxide. Among these, ethylene oxide is preferred.

Alkali metal halides are used as catalysts. Examples of such alkali metal halides include sodium iodide (NaI), potassium iodide (KI), sodium bromide (NaBr), potassium bromide (KBr), and alkaline earth metal halides such as calcium iodide (CaI ₂ ) and calcium bromide. Alkali metal halides are preferred.

Examples of the alkyl carbonate include ethyl carbonate, propyl carbonate, butyl carbonate, vinyl ethyl carbonate, cyclohexene carbonate, and styrene carbonate. Among these, ethyl carbonate is preferred.

Figure 1 is a block diagram showing a schematic process of this embodiment. This embodiment includes a reaction step, a cooling step, and a solid-liquid separation step. This embodiment may further include a separation step.

In the reaction step, the alkylene oxide reacts with carbon dioxide to produce an alkyl carbonate. As described below, the reaction step may have three stages: a first reaction step, a second reaction step, and a third reaction step. The mixture obtained from the reaction step may contain HB.

This embodiment may further include a separation step for obtaining a mixture (A) by separating the alkyl carbonate, unreacted alkylene oxide, and carbon dioxide. The separation step may include a step for separating and removing dissolved carbon dioxide and alkylene oxide, and a separation and recovery step for separating and recovering the alkylene carbonate. The residue after the separation and recovery step may be used as the mixture (A) in the cooling step described below.

In the cooling step, the mixture (A) is cooled to precipitate alkyl carbonate and alkali metal halide. The mixture (A) preferably contains HB. The high-boiling-point compound (HB) refers to an organic compound having a boiling point higher than that of the alkyl carbonate. The cooling step is preferably performed using a crystallization apparatus or the like.

From the viewpoint of sufficiently ensuring the amount of alkali metal halide precipitation and operability, the cooling temperature of the mixture (A) in the cooling step is preferably -30 to 36°C, more preferably -25 to 20°C, even more preferably -20 to 10°C, and even more preferably -15 to 0°C.

The slurry concentration of the mixture (A) after the cooling step is preferably 10 to 40 wt %, more preferably 15 to 30 wt %. The slurry concentration refers to the concentration of the solids precipitated in the mixture (A).

In the solid-liquid separation step, from the viewpoint of improving the processing efficiency, the solid containing alkyl carbonate and alkali metal halide can be separated from the mother liquor by centrifugal separation.

In this embodiment, the reactor in the reaction step is supplied with the alkyl carbonate and alkali metal halide separated in the solid-liquid separation step. However, the alkyl carbonate and alkali metal halide may be supplied to the reactor in a solution state. In this case, a heating step is preferably included to heat the solid containing the alkyl carbonate and alkali metal halide.

The outline of the apparatus used in the method for producing alkylene carbonate according to this embodiment is described.

As shown in Figure 2, the apparatus used in the method for producing alkyl carbonate according to this embodiment may include a first reactor A, a first heat remover B, a second reactor C, a second heat remover D, a third reactor E, a flash evaporation tank F, a separation and recovery device G, and a catalyst preparation tank H. The following describes the method for producing alkyl carbonate according to this embodiment using this apparatus.

<First Reaction Step> In the first reaction step, alkylene oxide is reacted with carbon dioxide in a first reactor A to obtain a reaction mixture containing alkylene carbonate.

The first reactor A can be a reactor of a generally used reaction mode such as a complete mixing reactor or a plug flow reactor. Among these, the first reactor A is preferably a complete mixing reactor.

The reactor for complete mixing is preferably a reactor that dissolves carbon dioxide in the reaction mixture. Examples of the reactor include shower nozzle reactors, eductor reactors, and bubble column reactors. The reactor for complete mixing is preferably a complete mixing tank reactor equipped with a Venturi agitator.

In the first reactor A, alkylene oxide and carbon dioxide are supplied from the top of the first reactor A. The alkali metal halide used as a catalyst is pre-adjusted to a specific concentration using alkyl carbonate as a solvent in a catalyst blending tank H. It is then quantitatively supplied to the catalyst supply line 7 via the supplementary catalyst supply line 9 and then supplied from the top of the first reactor A.

In the first reaction step, an alkaline metal halide is used as a catalyst. Examples of the catalyst include alkaline metal halides such as alkali metal or alkaline earth metal halides, and halides containing a small amount of alcohol or water.

The amount of the catalyst used is preferably 0.1 to 3 wt %, more preferably 0.1 to 2 wt % relative to the total amount of the reaction system.

From the perspective of suppressing the generation of HB, which causes contamination in the device, the reaction temperature in the first reaction step is 150 to 200°C. The reaction temperature in the first reaction step is preferably 155 to 195°C, and more preferably 160 to 190°C.

The reaction pressure in the first reaction step is preferably 2 to 15 MPaG, more preferably 4 to 12 MPaG, and even more preferably 6 to 10 MPaG.

The reaction time in the first reaction step varies depending on the composition ratio of the alkylene oxide and carbon dioxide as raw materials, the type and concentration of the catalyst used, the reaction temperature, etc. The average residence time calculated from the retentate volume and the total feed volume of the fully mixed reactor is preferably 0.5 to 10 hours, more preferably 1 to 5 hours.

The molar ratio of carbon dioxide to alkylene oxide in the first reaction step is preferably 1 to 5, more preferably 1 to 2. It is preferred that the carbon dioxide supply is adjusted so that the pressure of the first reactor A becomes constant.

This reaction is highly exothermic, making it crucial to remove the heat of reaction. A portion of the reaction mixture is withdrawn from first reactor A via first reaction mixture outlet line 1. The cooled reaction mixture, after passing through first heat remover B, is returned to first reactor A for heat removal. Furthermore, at least a portion of the reaction mixture withdrawn to first reaction mixture outlet line 1 is fed to second reactor C.

When using a complete mixing reactor, it is preferred to pump and circulate the reaction mixture at a high flow rate, dissolving a larger amount of carbon dioxide in the reaction mixture. Typically, the circulation rate is 10 to 70 times per hour, preferably 20 to 50 times per hour. Installing a first heat remover B midway through the piping that circulates the reaction mixture to remove the heat of reaction is preferred, as it increases the cooling capacity of the heat exchanger.

<Second Reaction Step> The method for producing alkylene carbonate of this embodiment may include a second reaction step, in which at least a portion of the reaction mixture after the first reaction step is reacted with alkylene oxide and carbon dioxide in a second reactor C to obtain a reaction mixture containing alkylene carbonate.

As shown in Figure 2, the reaction mixture in the second reactor C is discharged through the second reaction mixture discharge line 2, and at least a portion thereof is fed to the second heat remover D. Furthermore, at least a portion of the reaction mixture discharged through the second reaction mixture discharge line 2 is fed to the third reactor E.

The second reactor C is the same as that described above for the first reactor A. To suppress the generation of HB, which can cause contamination within the device, the reaction temperature in the second reaction step is 150 to 200°C. The reaction temperature in the second reaction step is preferably 155 to 195°C, and more preferably 160 to 190°C.

The reaction pressure in the second reaction step is preferably 2 to 12 MPaG, more preferably 4 to 8 MPaG, and even more preferably 4.5 to 6.5 MPaG.

The reaction time in the second reaction step varies depending on the composition ratio of the alkylene oxide and carbon dioxide as the raw materials, the type and concentration of the catalyst used, the reaction temperature, etc. The average residence time calculated from the retentate volume and the total feed volume in the fully mixed reactor is preferably 0.5 to 10 hours, more preferably 1 to 5 hours.

The molar ratio of carbon dioxide to alkylene oxide at the inlet of the second reactor in the second reaction step is preferably 1 to 5, more preferably 1 to 4. In the second reactor C, the reaction mixture from the first reactor A can be directly utilized without supplying new carbon dioxide.

This reaction is highly exothermic, making it crucial to remove the heat of reaction. A portion of the reaction mixture is withdrawn from the second reactor C via the second reaction mixture outlet line 2. The cooled reaction mixture, after passing through the second heat remover D, is returned to the second reactor C for heat removal. Furthermore, at least a portion of the reaction mixture withdrawn to the second reaction mixture outlet line 2 is fed to the third reactor E.

When using a complete mixing reactor, it is preferred to pump and circulate the reaction mixture at a high flow rate, dissolving a larger amount of carbon dioxide in the reaction mixture. Typically, the circulation rate is 5 to 50 times per hour, preferably 10 to 30 times per hour. A second heat remover D is installed midway through the piping that circulates the reaction mixture to remove the heat of reaction. High-flow circulation is preferred because it increases the cooling capacity of the heat exchanger.

<Third Reaction Step> The method for producing alkylene carbonate according to this embodiment may include a third reaction step, in which at least a portion of the reaction mixture after the second reaction step is reacted with alkylene oxide and carbon dioxide in a third reactor E to obtain a reaction mixture containing alkylene carbonate. The third reactor E is preferably a flooded reactor. The third reactor E is provided to allow unreacted alkylene oxide to react with carbon dioxide. Furthermore, the third reactor E preferably does not have an external circulation path.

<Separation and Recovery Step> The method for producing alkyl carbonate according to this embodiment may include a separation and recovery step for separating and recovering alkyl carbonate from the reaction mixture after the first reaction step. Furthermore, the reaction mixture used in the separation and recovery step may have been subjected to either a second reaction step or a third reaction step. Furthermore, the reaction mixture may be provided with a flash evaporator F to separate and remove dissolved carbon dioxide and alkylene oxide prior to the separation and recovery step.

Examples of separation and recovery equipment G used for separation and recovery include distillation towers, distillation towers, and thin-film evaporators. The distillate fraction evaporated in distillation towers, distillation towers, and thin-film evaporators is recovered as the product, while the bottoms and evaporation residue are sent for cooling and crystallization. Of these, thin-film evaporators are preferred from the perspectives of suppressing the decomposition of alkyl carbonate and simplifying the equipment. If the alkyl carbonate is not evaporated in a thin-film evaporator, the amount that can be recovered as the product decreases. Conversely, if excessive evaporation occurs, HB contaminates the alkyl carbonate, and the catalyst concentration exceeds its solubility, causing precipitation. This can lead to pump damage and other problems, making it less desirable. Although the conditions vary depending on the catalyst used, it is preferred to set the distillation conditions so that the catalyst concentration in the distillation residue is approximately 2 to 10 wt% and a certain amount of alkyl carbonate remains at the bottom of the column. This allows for recovery of the alkyl carbonate and maintains a uniform dissolution of the catalyst in the alkyl carbonate.

After the separation and recovery step, the mixture (A) contains alkyl carbonate, catalyst, and HB. However, to prevent the accumulation of HB, which could cause contamination within the apparatus, 0.3 to 30 wt% of the HB is preferably supplied to the cooling step via the waste liquid discharge line 8 relative to the flow rate of the mixture (A), with the remainder being recovered to the first reactor A. To prevent HB from easily accumulating in the reaction system, the amount introduced into the cooling step is preferably set to at least 0.3 wt% relative to the total amount of the mixture (A). To prevent the excessive size of the processing equipment required to discharge a large amount of distillation residue out of the process, the amount introduced into the cooling step is preferably set to no more than 30 wt% relative to the total amount of the mixture (A). Furthermore, fresh catalyst can be supplied from the replenishing catalyst supply line 9, and catalyst that has passed through the cooling step and solid-liquid separation step described later can also be supplied.

The alkyl carbonate production method of this embodiment is preferably carried out on an industrial scale. In this specification, "industrial scale" refers to production of alkyl carbonate at a rate of 1 ton or more per hour. The alkyl carbonate production method of this embodiment preferably produces 1 ton or more per hour, more preferably 2 tons or more per hour, even more preferably 3 tons or more per hour, and even more preferably 4 to 20 tons per hour.

Next, the apparatus used in the cooling and solid-liquid separation steps of this embodiment will be described in detail. Figure 3 schematically illustrates the structure of the crystallization apparatus. The crystallization apparatus of this embodiment comprises a crystallization tank I and a solid-liquid separator J. The crystallization tank I is equipped with a cooling jacket, stirring blades, and an external refrigerant circulation mechanism.

<Crystallization Apparatus> A mixed liquid (A) containing alkyl carbonate, catalyst, and HB is supplied to crystallization tank I via waste liquid discharge line 8. Through external circulation of a refrigerant in the cooling jacket, the mixed liquid (A) introduced into crystallization tank I is typically maintained at -30 to 36°C, preferably -25 to 20°C, more preferably -20 to 10°C, and even more preferably -15 to 0°C. Maintained at this temperature, the mixed liquid (A) precipitates solids containing alkyl carbonate and catalyst (hereinafter referred to as "crystals") due to differences in freezing points and solubility. This solid precipitates as a slurry solution within the tank. The slurry solution is then fed to solid-liquid separator J via extraction piping 10 at the bottom of the crystallization tank. At this time, from the perspective of ensuring a sufficient amount of catalyst precipitation, the temperature of the crystallization tank I is preferably set to 36°C or lower. On the other hand, from the perspective of suppressing the increase in the viscosity of HB caused by low temperatures, improving the stirring performance and slurry transfer performance in the crystallization tank, and maintaining good operability, the temperature is preferably -30°C or higher.

The solid-liquid separator J can be a solid-liquid separator using commonly used separation methods, such as centrifugal filtration, pressure filtration, or reduced pressure filtration. The alkyl carbonate and catalyst crystals separated in the solid-liquid separator J are transported to the catalyst blending tank H via piping 12. However, they can also be heated to form a liquid before being transported to the catalyst blending tank H. The crystals contain alkyl carbonate and catalyst in an inseparable state. However, the alkyl carbonate acts as a solvent for the catalyst, and the catalyst acts as a catalyst in the aforementioned reaction step. Therefore, even if they are transported to the reaction step in an inseparable state, both are still usable. The mother liquor separated in the solid-liquid separator J is discharged outside the process via pipe 13. Furthermore, to adjust the slurry concentration in the crystallization tank I, a portion of the recovered mother liquor can be returned to the crystallization tank I via pipe 11. The slurry concentration in the crystallization tank I is preferably maintained at 10 to 40 wt%, more preferably 15 to 30 wt%. In this case, setting the slurry concentration to 40 wt% or less is preferred to increase the crystallization ratio in the slurry solution and prevent deterioration in the stirring and transferability of the slurry solution within the crystallization tank. Furthermore, by setting the concentration to 10 wt % or more, the crystallization ratio in the slurry solution can be reduced, thereby reducing the amount of mother liquor returned to the crystallization tank 1 through the pipe 11. In other words, the amount of mother liquor recirculation can be reduced. This is preferable from the perspective of not oversizing the size of the crystallization tank or pump. [Example]

The present invention is further described below with reference to the following examples, but the present invention is not limited to the following examples.

[Example 1] This embodiment is specifically described using Figures 2 and 3. Figure 2 shows a schematic configuration of the apparatus used in the method for producing EC. The EC production apparatus of this embodiment comprises a first reactor A, a first deheater B, a second reactor C, a second deheater D, a third reactor E, a flash evaporation tank F, a separation recovery device G, and a catalyst blending tank H. EO is supplied to the first reactor A in a state where it is cooled to approximately 5°C. The supply rate is 2495 kg/h. _CO2 is obtained by vaporizing liquefied _CO2 in a warm water bath type _CO2 evaporator, regulating the temperature at approximately 90°C and a fixed pressure of approximately 9.8 MPaG, and supplying the liquefied CO2 to the first reactor A at a supply rate of 3020 kg/h. After EC is purified in separation recovery unit G, the recovered mixture (A) is blended via catalyst supply line 7 with a supplementary catalyst solution via supplementary catalyst supply line 9 at a ratio of approximately 9:1: mixture (A): supplementary catalyst solution. The catalyst solution is supplied to the first reactor A to achieve a KI concentration of 0.23 to 0.26 wt%. The catalyst solution is fed at a rate of 290 kg/h for mixture (A) and 32 kg/h for supplementary catalyst. Furthermore, supplementary catalyst KI is blended in catalyst blending tank H to a 5 wt% concentration in the EC solution. The reactor temperature is 180°C.

The mixture removed from the third reactor E is supplied to the flash evaporator F via piping 3. Unreacted EO, _CO₂ , and trace amounts of EC are discharged as gases via piping 4 to the outside of the process. Flash evaporator F operates at 760 Torr. Furthermore, a mixture primarily containing EC is removed from the bottom of flash evaporator F via piping 5 and introduced into separation and recovery device G. Evaporated and purified EC is removed at a rate of 4910 kg/h via piping 6, and a mixture (A) containing catalyst and HB is removed via catalyst supply line 7. The composition of mixture (A) is EC: 80 wt%, KI: 5 wt%, and HB: 15 wt%. A portion of this is supplied to the crystallization step via waste liquid discharge line 8 at a rate of 32 kg/h.

FIG3 shows a schematic structure of a crystallization device. The crystallization device of this embodiment comprises a crystallization tank I and a solid-liquid separator J. The crystallization tank I is equipped with a cooling jacket, stirring blades, and an external circulation mechanism for a refrigerant. A mixture (A) containing EC, KI, and HB is supplied to the crystallization tank I through a waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -10°C by external circulation of a refrigerant. The solid-liquid mixed phase of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through a take-out pipe 10. The supply rate of the solid-liquid mixed phase is 100 kg/h, and the slurry concentration is 25 wt%. The crystals separated by solid-liquid separator J have a composition of 96.5wt% EC, 2.6wt% KI, and 1.0wt% HB and are supplied to catalyst blending tank H via pipe 12. The supply rate is 25kg/h. The mother liquor has a composition of 21.8wt% EC, 13.6wt% KI, and 64.6wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 68kg/h and 7kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 2] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus in Figure 2 are the same as those in Example 1. In the crystallization apparatus in Figure 3, a mixture (A) containing EC, KI, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -10°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 62.5 kg/h, and the slurry concentration is 40 wt%. The crystals separated in solid-liquid separator J have a composition of 96.5wt% EC, 2.6wt% KI, and 1.0wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 25kg/h. The mother liquor has a composition of 21.8wt% EC, 13.6wt% KI, and 64.6wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 30.5kg/h and 7kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 3] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus in Figure 2 are the same as those in Example 1. In the crystallization apparatus in Figure 3, a mixture (A) containing EC, KI, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -10°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 250 kg/h, and the slurry concentration is 10 wt%. The crystals separated in solid-liquid separator J have a composition of 96.5wt% EC, 2.6wt% KI, and 1.0wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 25kg/h. The mother liquor has a composition of 21.8wt% EC, 13.6wt% KI, and 64.6wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 218kg/h and 7kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 4] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus in Figure 2 are the same as those in Example 1. In the crystallization apparatus in Figure 3, a mixture (A) containing EC, KI, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to 15°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals precipitated in the crystallization tank I and the mother liquor is supplied to the solid-liquid separator J through the pipe 10. The supply rate of the solid-liquid mixed phase liquid is 110 kg/h, and the slurry concentration is 25 wt%. The crystals separated in solid-liquid separator J have a composition of 97.7 wt% EC, 1.7 wt% KI, and 0.5 wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 22 kg/h. The mother liquor has a composition of 41.0 wt% EC, 12.2 wt% KI, and 46.8 wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 88 kg/h and 10 kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 5] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of Figure 2 are the same as those of Example 1. In the crystallization apparatus of Figure 3, a mixture (A) containing EC, KI, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -20°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 130 kg/h, and the slurry concentration is 25 wt%. The crystals separated in solid-liquid separator J have a composition of 95.1 wt% EC, 3.1 wt% KI, and 1.8 wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 26 kg/h. The mother liquor has a composition of 13.0 wt% EC, 13.6 wt% KI, and 73.4 wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 104 kg/h and 6 kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 6] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus of Figure 2 are the same as those of Example 1, except that NaBr is used as the catalyst. In the crystallization apparatus of Figure 3, a mixture (A) containing EC, NaBr, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -10°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 100 kg/h, and the slurry concentration is 25 wt%. The crystals separated in solid-liquid separator J have a composition of 96.8wt% EC, 2.3wt% NaBr, and 1.0wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 25kg/h. The mother liquor has a composition of 21.5wt% EC, 14.5wt% NaBr, and 63.9wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 68kg/h and 7kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 7] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus of Figure 2 are the same as those of Example 1, except that NaBr is used as the catalyst. In the crystallization apparatus of Figure 3, a mixture (A) containing EC, NaBr, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -10°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 62.5 kg/h, and the slurry concentration is 40 wt%. The crystals separated in solid-liquid separator J have a composition of 96.8wt% EC, 2.3wt% NaBr, and 1.0wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 25kg/h. The mother liquor has a composition of 21.5wt% EC, 14.5wt% NaBr, and 63.9wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 30.5kg/h and 7kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 8] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus of Figure 2 are the same as those of Example 1, except that NaBr is used as the catalyst. In the crystallization apparatus of Figure 3, a mixture (A) containing EC, NaBr, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -10°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 250 kg/h, and the slurry concentration is 10 wt%. The crystals separated in solid-liquid separator J have a composition of 96.8wt% EC, 2.3wt% NaBr, and 1.0wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 25kg/h. The mother liquor has a composition of 21.5wt% EC, 14.5wt% NaBr, and 63.9wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 218kg/h and 7kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 9] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus of Figure 2 are the same as those of Example 1, except that NaBr is used as the catalyst. In the crystallization apparatus of Figure 3, a mixture (A) containing EC, NaBr, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to 15°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 86 kg/h, and the slurry concentration is 25 wt%. The crystals separated in solid-liquid separator J have a composition of 99.4wt% EC, 0wt% NaBr, and 0.6wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 22kg/h. The mother liquor has a composition of 39.5wt% EC, 15.4wt% NaBr, and 45.1wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged outside the process via pipe 13. The supply rates of the mother liquor are 54kg/h and 10kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Example 10] The apparatus shown in Figures 2 and 3 is used in the same manner as in Example 1. The operating conditions of the apparatus of Figure 2 are the same as those of Example 1, except that NaBr is used as the catalyst. In the crystallization apparatus of Figure 3, a mixture (A) containing EC, NaBr, and HB is supplied to the crystallization tank I through the waste liquid discharge line 8. The supply rate of the mixture (A) is 32 kg/h. The crystallization tank I sets the mother liquor temperature to -20°C by external circulation of the refrigerant. The solid-liquid mixed phase liquid of the crystals and the mother liquor precipitated in the crystallization tank I is supplied to the solid-liquid separator J through the take-out pipe 10. The supply rate of the solid-liquid mixed phase liquid is 104 kg/h, and the slurry concentration is 25 wt%. The crystals separated in solid-liquid separator J have a composition of 95.4 wt% EC, 2.8 wt% NaBr, and 1.8 wt% HB, and are supplied to catalyst blending tank H via pipe 12. The supply rate is 26 kg/h. The mother liquor has a composition of 12.9 wt% EC, 14.7 wt% NaBr, and 72.4 wt% HB. A portion of the mother liquor is circulated within crystallization tank I via pipe 11, and a portion is discharged from the process via pipe 13. The supply rates of the mother liquors are 72 kg/h and 6 kg/h, respectively. The process liquid in pipe 13 is a liquid at room temperature of 20°C.

[Comparative Example 1] The process was identical to Example 1, except that the crystallization apparatus shown in Figure 3 was omitted. A mixture (A) containing catalyst and HB was removed via catalyst supply line 7. The composition of mixture (A) was 80 wt% EC, 5 wt% catalyst, and 15 wt% HB. A portion of this mixture was discharged from the process via waste liquid discharge line 8. The discharge rate of mixture (A) was 32 kg/h. The process liquid in waste liquid discharge line 8 was solid at room temperature of 20°C.

[Table 1] Catalyst Cooling step temperature Slurry concentration after cooling step Amount of discharge discharged outside the process EC Catalyst HB EC Catalyst HB - ℃ wt% kg/h kg/h kg/h wt% wt% wt% Example 1 KI -10 25 1.5 1.0 4.6 21.8 13.6 64.6 Example 2 40 Example 3 10 Example 4 15 25 4.1 1.2 4.7 41.0 12.2 46.8 Example 5 -20 0.8 0.8 4.3 13.0 13.6 73.4 Example 6 NaBr -10 25 1.5 1.0 4.6 21.5 14.5 63.9 Example 7 40 Example 8 10 Example 9 15 25 4.1 1.6 4.7 39.5 15.4 45.1 Example 10 -20 0.8 0.9 4.3 12.9 14.7 72.4 Comparative example 1 KI/ NaBr - - 25.6 1.6 4.8 80.0 5.0 15.0

A: First Reactor B: First Heat Remover C: Second Reactor D: Second Heat Remover E: Third Reactor F: Flash Evaporation Tank G: Separation and Recovery Unit H: Catalyst Blending Tank I: Crystallization Tank J: Solid-Liquid Separator 1: First Reaction Mixture Outlet Line 2: Second Reaction Mixture Outlet Line 3, 4, 5, 6, 11, 12, 13: Piping 7: Catalyst Supply Line 8: Wastewater Discharge Line 9: Catalyst Replenishment Supply Line 10: Removal Piping

Figure 1 is a block diagram showing a schematic process of this embodiment. Figure 2 shows a schematic configuration of an apparatus used in the method for producing alkylene carbonate. Figure 3 shows a schematic configuration of a crystallization apparatus.

Claims (10)

A method for producing an alkyl carbonate comprises the following steps: a reaction step of reacting an alkylene oxide with carbon dioxide in the presence of an alkali metal halide in a reactor to obtain the alkyl carbonate; a cooling step of cooling the mixture (A) containing the alkyl carbonate and the alkali metal halide after the reaction step; and a solid-liquid separation step of separating a solid containing the alkyl carbonate and the alkali metal halide from a mother liquor. The alkyl carbonate and alkali metal halide separated in the solid-liquid separation step are then supplied to the reactor. The method for producing an alkyl carbonate as described in claim 1 further comprises a separation step of obtaining the mixture (A) from the solution subjected to the reaction step. The method for producing an alkyl carbonate as claimed in claim 1 or 2, wherein a portion of the mother liquor separated in the solid-liquid separation step is returned to the cooling step. The method for producing an alkyl carbonate as described in claim 2, wherein, in the separation step, the alkyl carbonate, unreacted alkylene oxide, and carbon dioxide are separated from the solution subjected to the reaction step, thereby obtaining the mixture (A). The method for producing an alkyl carbonate according to claim 1 or 2, wherein, in the solid-liquid separation step, the solid is separated by centrifugation. The method for producing an alkyl carbonate as claimed in claim 1 or 2 further comprises a heating step of heating the solid containing the alkyl carbonate and the alkali metal halide. The method for producing alkylene carbonate as claimed in claim 1 or 2, wherein the alkylene oxide is ethylene oxide and the alkylene carbonate is ethylene carbonate. The method for producing an alkyl carbonate as described in claim 1 or 2, wherein the alkali metal halide is an alkali metal iodide. The method for producing an alkyl carbonate as claimed in claim 1 or 2, wherein the cooling temperature of the mixture (A) in the cooling step is -30 to 36°C. The method for producing an alkyl carbonate as described in claim 1 or 2, wherein the slurry concentration of the mixture (A) after the cooling step is 10 to 40 wt%.