Method and apparatus for purifying dialkyl carbonates

Abstract

The present invention provides a method and apparatus for purifying dialkyl carbonates, which reduces the content of high-boiling-point compounds and yields high-purity dialkyl carbonates. [Solution] A method for purifying dialkyl carbonates, comprising a distillation step in which a mixture containing dialkyl carbonates is supplied to a feed section F of a continuous multi-stage distillation column 1, and a fraction S containing dialkyl carbonates is extracted from a side cut section Sv located below the feed section F, wherein at least a portion of the liquid flowing down inside the continuous multi-stage distillation column 1 passes through a bypass channel 2 that bypasses the side cut section Sv, and the fraction S is distilled out as a gas from the side cut section Sv.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for purifying dialkyl carbonate.

Background Art

[0002] In recent years, dialkyl carbonate has been used as a main component of lithium-ion battery electrolytes. With the development of the electronics and clean energy vehicle industries, the importance of lithium-ion battery electrolytes has been increasing, and accordingly, the market demand for high-purity dialkyl carbonate for lithium-ion battery electrolytes has also been significantly rising. Industrial-grade dialkyl carbonate contains impurities such as water, methanol, ethanol, ethyl methyl carbonate, and high-boiling components. Alcohols and water affect the service life of lithium-ion batteries, and high-boiling components affect the discoloration of electrolytes. Therefore, as dialkyl carbonate for lithium-ion battery electrolytes, it is required to further reduce the content of these impurities and make it extremely high-purity (purity of 99.99 wt% or more).

[0003] As methods for producing such high-purity dialkyl carbonate for lithium-ion battery electrolytes, several have been proposed. For example, a method for obtaining dimethyl carbonate with high purity (purity of 99.99 wt% or more) from the side cut section of a distillation column has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, while the method described in Patent Document 1 can effectively separate high-boiling-point compounds having a boiling point 100°C or more higher than the boiling point of dialkyl carbonates, there is room for improvement in separating high-boiling-point compounds with a smaller boiling point difference.

[0006] Therefore, the present invention aims to provide a method for purifying dialkyl carbonates and a purification apparatus that reduces the content of high-boiling-point compounds and obtains high-purity dialkyl carbonates. [Means for solving the problem]

[0007] As a result of diligent research to solve the aforementioned problems, the inventors have found that by providing a bypass channel in a distillation column for purifying dialkyl carbonates, through which the liquid flowing down the column bypasses the side cut section, the content of high-boiling-point compounds in high-purity dialkyl carbonates can be reduced. In other words, the present invention encompasses the following embodiments. <1> A method for purifying dialkyl carbonates, The distillation process involves supplying a mixture containing dialkyl carbonate to the feed section of a continuous multi-stage distillation column, and extracting the fraction S containing the dialkyl carbonate from a side cut section located below the feed section. At least a portion of the liquid flowing down the continuous multi-stage distillation column passes through a bypass channel that bypasses the side cut section. The aforementioned fraction S is a gas that distills from the side cut portion. A method for purifying dialkyl carbonates. <2> A portion of the fraction S is refluxed to the continuous multi-stage distillation column. <1> The method for purifying dialkyl carbonates as described above. <3> The mixed liquid supplied to the feed section contains 99.00 wt% to 99.95 wt% of dialkyl carbonate. The fraction S contains 99.99 wt% or more of dialkyl carbonate. <1> or <2> The method for purifying dialkyl carbonates as described above. <4> The above fraction S contains no more than 30 wt ppm of high-boiling point compounds. <1> ~ <3> A method for purifying dialkyl carbonates as described in any of the following. <5> The reflux ratio at the top of the continuous multi-stage distillation column is set to 0.2 to 10. <1> ~ <4> A method for purifying dialkyl carbonates as described in any of the following. <6> The reflux ratio in the side cut section is set to 0.02 to 1. <2> ~ <5> A method for purifying dialkyl carbonates as described in any of the following. <7> A liquid collector located above the side cut portion guides the liquid into a bypass channel. <1> ~ <6> A method for purifying dialkyl carbonates as described in any of the above. <8> The dialkyl carbonate is dimethyl carbonate. <1> ~ <7> A method for purifying dialkyl carbonates as described in any of the following. <9> A purification apparatus for dialkyl carbonates, A continuous multi-stage distillation column, A feed section for supplying a mixture containing dialkyl carbonate to the aforementioned continuous multi-stage distillation column, A side cut section is provided below the aforementioned feed section, A purification apparatus having a bypass channel provided such that at least a portion of the liquid flowing down the continuous multi-stage distillation column bypasses the side cut section. <10> Above the side cut section, there is a liquid collector for collecting the liquid flowing down the continuous multi-stage distillation column, The liquid is led from the liquid collector into the bypass channel. <9> The purification apparatus described above. <11> The column has a side-cut reflux section that condenses the fraction from the side-cut section and returns at least a portion of the condensed fraction to the continuous multi-stage distillation column from below the side-cut section. The purification apparatus according to <9> or <10>. <12> The continuous multi-stage distillation column has a top extraction section for extracting a top component from the top of the column, a top reflux section for condensing at least a part of the top component and returning at least a part of the condensed fraction into the continuous multi-stage distillation column, and further has a bottom extraction section for extracting a bottom component from the bottom of the column, where the connection section located above the side cut section of the bypass flow path is defined as an upper connection section, and the connection section located below the side cut section is defined as a lower connection section, the side cut reflux section uses the position where at least a part of the condensed fraction is connected and returned into the continuous multi-stage distillation column as a side cut reflux return section, when the top reflux section uses the position where at least a part of the condensed fraction is connected and returned into the continuous multi-stage distillation column as a top reflux return section, from the top of the continuous multi-stage distillation column, the top extraction section, the top reflux return section, the feed section, the upper connection section, the side cut section, the side cut reflux return section, the lower connection section, and the bottom extraction section are arranged in this order, [[ID=2I]]The purification apparatus according to <11>. <13> a continuous multi-stage distillation column, a feed section for supplying a mixed liquid to be distilled to the continuous multi-stage distillation column, a side cut section provided below the feed section, a bypass flow path provided so that at least a part of the liquid flowing down in the continuous multi-stage distillation column bypasses the side cut section, and has a purification apparatus.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a method for purifying dialkyl carbonate and a purification apparatus that reduce the content of high-boiling compounds and obtain high-purity dialkyl carbonate.

Brief Description of the Drawings

[0009] [Figure 1] Figure 1 is a schematic diagram of the purification apparatus according to this embodiment. [Figure 2] Figure 2 is a schematic diagram of the area around the side cut section of the purification apparatus according to this embodiment. [Figure 3] Figure 3 is a schematic diagram of the purification apparatus used in the comparative example. [Modes for carrying out the invention]

[0010] The embodiments of the present invention (hereinafter referred to as "this embodiment") will be described in detail below, with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from its essence.

[0011] The method for purifying dialkyl carbonate according to this embodiment is as follows: The distillation process involves supplying a mixture containing dialkyl carbonate to the feed section of a continuous multi-stage distillation column, and extracting the fraction S containing the dialkyl carbonate from a side cut section located below the feed section. At least a portion of the liquid flowing down within the continuous multi-stage distillation passes through a bypass channel that bypasses the side cut section. The aforementioned fraction S is a gas and distills out from the side cut section.

[0012] The above-described configuration provides a method for purifying dialkyl carbonates that reduces the content of high-boiling-point compounds and yields high-purity dialkyl carbonates.

[0013] In the dialkyl carbonate purification method according to this embodiment, it is preferable that the mixed liquid supplied to the feed section in the distillation step contains 99.00 wt% to 99.95 wt% of dialkyl carbonate, and the fraction S extracted from the side cut section contains 99.99 wt% or more of dialkyl carbonate. In other words, the content of high-boiling-point compounds in the distillation step to obtain a high-purity dialkyl carbonate with a purity of 99.99 wt% or more from a dialkyl carbonate with a purity of 99.00 to 99.95 wt% can be reduced.

[0014] First, with reference to Figure 1, the purification apparatus according to this embodiment will be described. The purification apparatus according to this embodiment has a continuous multi-stage distillation column 1.

[0015] [Continuous multi-stage distillation column] A continuous multistage distillation column is preferably a distillation column having trays or packing material as an internal component. A multistage distillation column having both a tray and a packing material-filled section can also be used.

[0016] The number of stages in a continuous multi-stage distillation column is not particularly limited, but the theoretical number of internal stages, including the recovery and concentration sections, is preferably 3 to 40. In this specification, "internal" refers to the part of the distillation column where gas and liquid actually come into contact.

[0017] In this specification, "theoretical plate number" means the number of trays or the number of packing units. The side cut section means the space in the middle of the distillation column where the side cut section, which is an outlet for extracting the fraction, is located. If the side cut section is sandwiched between two trays, it means the space between the trays. If packing units are placed in the side cut section, it means the space between the units.

[0018] The tray is not particularly limited, but preferred trays include bubble trays, perforated plate trays, ripple trays, ballast trays, valve trays, counterflow trays, Uniflux trays, Superflax trays, Maxflax trays, DualFloat trays, grid plate trays, TurboGridPlate trays, Kittel trays, and the like.

[0019] The packing material is not particularly limited, but irregular packing materials such as Raschig rings, Lessing rings, Pall rings, Berl saddles, Interox saddles, Dixon packing, McMahon packing, and Helipak are preferred, as are regular packing materials such as Melapack, Gempack, Technopack, Flexipack, Sulzer packing, Goodroll packing, and Glitch Grid.

[0020] A continuous multi-stage distillation column preferably includes a reboiler for heating the distillate and a reflux device.

[0021] The continuous multi-stage distillation column 1 has a feed section F for supplying the mixed liquid to be distilled. The continuous multi-stage distillation column 1 also has a side cut section Sv located below the feed section F. The feed section F is located in the middle of the column. The "middle of the column" refers to the part of the distillation column excluding the top and bottom. The continuous multi-stage distillation column 1 has a bypass channel 2 through which at least a portion of the liquid flowing down the column bypasses the stage of the side cut section Sv. The bypass channel 2 is connected to the continuous multi-stage distillation column 1 by an upper connection section Sl located above the side cut section Sv and a lower connection section Fs located below the side cut section Sv.

[0022] As shown in Figure 2, the continuous multi-stage distillation column 1 has a liquid collector 11 above the side cut section Sv, and the liquid L collected by the liquid collector 11 is guided to the bypass channel 2 and returned to the continuous multi-stage distillation column 1 from the lower connection section Fs located below the side cut section Sv. Thus, the structure around the bypass channel 2 of the continuous multi-stage distillation column 1 is not particularly limited, but the liquid L flowing down the continuous multi-stage distillation column 1 is received by the liquid collector 11, and the received liquid L is flowed from the upper connection section Sl provided on the liquid collector 11 through the lower connection section Fs to the distributor 12b, thereby bypassing the side cut section. For example, a chimney tray can be used as the liquid collector.

[0023] The liquid collector 11 includes a tray 111, a cylindrical portion 112 provided on the tray 111, and a cap 113 over the cylindrical portion 112. The cylindrical portion 112 communicates with the upper and lower spaces of the tray 111 on its inside. Therefore, the gas in the continuous multi-stage distillation column 1 passes through the cylindrical portion 112. On the other hand, the liquid L flowing down the continuous multi-stage distillation column 1 from above is stored outside the cylindrical portion 112. Since the upper end of the cylindrical portion 112 is covered by the cap 113, the liquid L flowing down the continuous multi-stage distillation column 1 does not slip through the inside of the cylindrical portion 112 and fall down, but is stored outside the cylindrical portion 112.

[0024] The continuous multi-stage distillation column 1 preferably has at least one packing material 14a below the side cut section Sv, and the lower connection section Fs is preferably located below the packing material 14a. This arrangement prevents the liquid L returned to the continuous multi-stage distillation column 1 from splashing up to the side cut section Sv along with the vapor in the distillation column 1, thereby reducing the content of high-boiling-point compounds and enabling the production of high-purity dialkyl carbonates.

[0025] The continuous multi-stage distillation column 1 may have a distributor 12b below the lower connection Fs and packing material 14b below the distributor 12b. With this arrangement, the liquid L returned to the continuous multi-stage distillation column 1 from the lower connection Fs is uniformly diffused by the distributor 12b and flows to the packing material 14b, allowing for distillation purification without loss of the dialkyl carbonate contained in the liquid.

[0026] The continuous multi-stage distillation column 1 may have a side-cut reflux section 3 that condenses the fraction S from the side-cut section Sv and returns at least a portion of the condensed fraction S back into the continuous multi-stage distillation column 1 from below the side-cut section Sv. The position where the side-cut reflux section 3 is connected to return at least a portion of the condensed fraction back into the continuous multi-stage distillation column 1 is designated as the side-cut reflux return section Sr. The fraction S is ejected in a gaseous state and condensed by the condensation section Sa. By providing the side-cut reflux section 3, the content of high-boiling-point compounds in the fraction S can be reduced.

[0027] As shown in Figure 2, the continuous multistage distillation column 1 may have a side-cut reflux return section Sr, a distributor 12a, packing material 14a, and a collector 15 in that order from top to bottom. Examples of collectors 15 include a vane liquid collector and a gas riser liquid collector.

[0028] The continuous multi-stage distillation column 1 may have a top extraction section Tv for extracting the top component D. The continuous multi-stage distillation column 1 may also have a top reflux section 4 for condensing at least a portion of the top component D and returning at least a portion of the condensed fraction D back into the continuous multi-stage distillation column 1. The position where the top reflux section 4 is connected to return at least a portion of the condensed fraction back into the continuous multi-stage distillation column 1 is designated as the top reflux return section Tr. The fraction T is ejected in a gaseous state and condensed by the condensation section Ta.

[0029] The continuous multistage distillation column 1 may have a bottom extraction section Bv for extracting bottom component B from the bottom of the column. Bottom component B is heated in a reboiler Br and supplied to the bottom of the continuous multistage distillation column 1, thereby supplying heat to the continuous distillation column.

[0030] It is preferable that the components of the continuous multi-stage distillation column 1 be arranged in the following order from top to bottom: top extraction section Tv, top reflux return section Tr, feed section F, upper connection section Sl, side cut section Sv, side cut reflux return section Sr, lower connection section Fs, and bottom extraction section Bv. This arrangement makes it possible to reduce the content of high-boiling-point compounds in the fraction S while suppressing energy consumption.

[0031] The purification apparatus according to this embodiment is preferably used for purifying a mixture containing dialkyl carbonate, but it may also be used for purifying other mixtures, such as a mixture containing n-octane.

[0032] (Distillation process) In the distillation process, a mixture F containing dialkyl carbonate is supplied to the feed section F of a continuous multi-stage distillation column 1, and the fraction S containing dialkyl carbonate is extracted from the side cut section Sv located below the feed section F.

[0033] In the mixed solution F, the concentration of dialkyl carbonate is preferably 99.00 to 99.95 wt%, more preferably 99.2 to 99.95 wt%, and even more preferably 99.4 to 99.95 wt%. When the concentration of dialkyl carbonate in the mixed solution F is within this range, it becomes easy to achieve a high purity of 99.99 wt% or higher in the final dialkyl carbonate, for example, a level suitable for use in lithium-ion battery electrolytes.

[0034] The mixed solution F may be supplied directly to the continuous multi-stage distillation column, or it may be supplied to an industrial-grade dialkyl carbonate tank and then supplied from the tank to the continuous multi-stage distillation column.

[0035] It is preferable to continuously supply the mixed liquid F to the continuous multi-stage distillation column 1, continuously withdraw the top component D, which is a low-boiling-point component, from the top of the column, continuously withdraw the fraction S, which mainly consists of dialkyl carbonate, from the side cut section Sv, and continuously withdraw the bottom component B, which is a high-boiling-point component, from the bottom of the column. It is also preferable to heat or cool the mixed liquid F to a temperature close to the liquid temperature near the feed section F inside the continuous multi-stage distillation column 1 before supplying it into the continuous multi-stage distillation column 1. The mixed liquid F is preferably supplied into the continuous multi-stage distillation column 1 at a rate of about 2 tons / hour or more.

[0036] The fraction S containing dialkyl carbonate is withdrawn from the side cut section Sv located below the feed section F. The fraction S distills out of the side cut section Sv as a gas. Since it is a gas at the time of withdrawal, the objective of preventing contamination by high-boiling-point components and other non-volatile components is achieved, so it is acceptable if some of the gas liquefies after leaving the column. In the continuous multi-stage distillation column 1, when the fraction S is withdrawn as a gas, the amount of high-boiling-point compounds relative to the dialkyl carbonate in the fraction S tends to be suppressed. In this specification, "high-boiling-point compound" refers to a compound that has a boiling point 50°C or more higher than the boiling point of the main component, dialkyl carbonate, under a pressure of 760 mmHg.

[0037] A portion of the fraction S from the side-cut section Sv may be returned to the interior of the continuous multi-stage distillation column 1 for reflux in the side-cut section Sv. The side-cut reflux return section Sr, which returns the fraction S to the interior of the continuous multi-stage distillation column 1, is preferably located directly below the side-cut section Sv. The purity of the dialkyl carbonate in the fraction S extracted from the side-cut section Sv of the continuous multi-stage distillation column 1 is preferably 99.99 wt% or higher. Such high-purity dialkyl carbonate can be used, for example, as an electrolyte for lithium-ion batteries.

[0038] The content of high-boiling-point compounds in fraction S is preferably 30 wt ppm or less, more preferably 20 wt ppm or less, and even more preferably 10 wt ppm or less.

[0039] The reflux ratio of fraction S is preferably 0.02 to 1, more preferably 0.05 to 0.8, and even more preferably 0.1 to 0.5. In the dialkyl carbonate purification method according to this embodiment, by using such a small reflux ratio, the amount of heat consumed can be reduced, and the content of high-boiling-point compounds can be reduced, making it possible to achieve a high purity of 99.99 wt% or higher in the final dialkyl carbonate, for example, a level that can be used for lithium-ion battery electrolytes.

[0040] In the continuous multi-stage distillation column 1, a bypass channel 2 is provided so that the liquid flowing through the continuous multi-stage distillation column 1 bypasses the side-cut section Sv. For example, in a continuous multi-stage distillation column without a bypass channel 2, when the dialkyl carbonate obtained at the end is purified to a purity of 99.99 wt% or higher and then withdrawn from the side-cut fraction Sv, it becomes clear that the dialkyl carbonate contains high-boiling-point compounds. When used as an electrolyte for lithium-ion batteries, etc., these high-boiling-point compounds lead to a decrease in performance and therefore it is desirable to remove them. According to the dialkyl carbonate purification method of this embodiment, the content of high-boiling-point compounds in the side-cut fraction can be reduced.

[0041] Mixture F contains a dialkyl carbonate and may contain impurities such as aliphatic monohydric alcohols, trace amounts of alkoxy alcohols, trace amounts of aliphatic carbonate ethers, and high-boiling point compounds.

[0042] Conventional distillation columns with side cut sections have the problem that trace amounts of high-boiling-point compounds are included in the fraction S distilled from the side cut section. This is thought to be because some of the high-boiling-point compounds contained in the liquid flowing down the column evaporate at the side cut section, and trace amounts of high-boiling-point compounds are included in the fraction distilled from the side cut section. In this embodiment, the continuous multi-stage distillation column 1 has a bypass channel 2 through which the liquid flowing down the continuous multi-stage distillation column 1 bypasses the side cut section Sv, so that the liquid flowing down containing high-boiling-point compounds bypasses the side cut section. As a result, the liquid flowing down does not pass through the side cut section Sv, so the high-boiling-point compounds contained in it are prevented from evaporating at the side cut section, and consequently the amount of high-boiling-point compounds mixed into the fraction S from the side cut section Sv can be reduced. Regarding the bypass channel 2 through which the liquid flowing down the column bypasses the side cut section, it is desirable that the position of the upper connection part Sl from which the liquid flowing down the column is extracted is one stage above the stage where the side cut section Sv is provided. The position where the liquid flowing down the column is returned to the column, i.e., the position of the lower connection Fs, is preferably a low position from the viewpoint of separation, and preferably a high position from the viewpoint of not consuming excess energy. The appropriate return position depends on the composition of the flowing liquid, but is preferably somewhere midway between the side cut section Sv and the bottom of the column, and more preferably the upper 40-60% of the area between the side cut section Sv and the bottom of the column. By returning the liquid flowing down the column to somewhere midway between the side cut section Sv and the bottom of the column, the liquid flowing down the column comes into gas-liquid contact with reflux at the side cut section Sv, which can reduce the content of high-boiling-point compounds in the fraction S.

[0043] In the purification method according to this embodiment, the low-boiling-point component, component D at the top of the column, may be continuously extracted from the top of the column. The reflux ratio at the top of the continuous multi-stage distillation column is preferably 0.2 to 10, more preferably 0.5 to 5, and even more preferably 1 to 3. In the dialkyl carbonate purification method according to this embodiment, by using such a small reflux ratio, the amount of heat consumed can be reduced, the content of high-boiling-point compounds can be reduced, and the purity of the final dialkyl carbonate can be made high, for example, 99.99 wt% or higher, which is a level that can be used for lithium-ion battery electrolytes.

[0044] Since the other components of the low-boiling-point component D at the top of the column are mainly dialkyl carbonates, these can be reused as aliphatic monohydric alcohols to react with the cyclic carbonate, either as is or mixed with alcohols recovered in other processes. This is one of the preferred embodiments of this model. If the amount of recovered alcohols is insufficient, it is preferable to add more aliphatic monohydric alcohols.

[0045] The high-boiling-point component, bottom component B, may be continuously extracted from the bottom of the column. [Examples]

[0046] The present invention will be described in more detail below with reference to specific examples. However, the present invention is not limited in any way to the examples shown below.

[0047] [Example 1] As a continuous multi-stage distillation column, the continuous multi-stage distillation column shown in Figure 1 was used. In this distillation column, the theoretical number of stages was 18, with a feed section F at the 2nd stage from the top, an upper connection section Sl, a side cut section Sv, a side cut reflux return section Sr at the 13th stage in that order, and a lower connection section Fs at the 16th stage.

[0048] A feed solution consisting of dimethyl carbonate (99.7 wt%), methanol (2000 ppm), and HB (1000 ppm) was continuously supplied from F to a continuous multi-stage distillation column at a rate of 3.62 t / h. The continuous multi-stage distillation column was operated continuously with a top reflux ratio of 1.0 and a side-cut reflux ratio of 0.5. The liquid flowing down the column from the Sl section was completely withdrawn and fed back in from Fs.

[0049] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 95.9 wt% and methanol: 4.1 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 84.9 wt% and HB: 15.1 wt%. The fraction S, continuously withdrawn as gas from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9985 wt%, methanol: 15 ppm, and HB: 0 ppm.

[0050] [Example 2] The continuous multi-stage distillation column used is the same as in Example 1. A feed solution consisting of dimethyl carbonate (99.0 wt%), methanol (6000 ppm), and HB (4000 ppm) was continuously supplied from F to the continuous multi-stage distillation column at a rate of 3.62 t / h. The continuous multi-stage distillation column was operated continuously with a top reflux ratio of 5.0 and a side-cut reflux ratio of 1.0. The liquid flowing down the column from the Sl section was completely withdrawn and fed back in from Fs.

[0051] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 87.7 wt% and methanol: 12.3 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 39.7 wt% and HB: 60.3 wt%. The fraction S, continuously withdrawn as gas from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9999 wt%, methanol: 1 ppm, and HB: 0 ppm.

[0052] [Example 3] The continuous multi-stage distillation column used is the same as in Example 1. A feed solution consisting of dimethyl carbonate (98.0 wt%), methanol (1.4 wt%), and HB (0.6 wt%) was continuously supplied from F to the continuous multi-stage distillation column at a rate of 3.62 t / h. The continuous multi-stage distillation column was operated continuously with a top reflux ratio of 5.0 and a side-cut reflux ratio of 1.0. The liquid flowing down the column from the Sl section was completely withdrawn and fed back in from Fs.

[0053] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 71.2 wt% and methanol: 28.8 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 14.9 wt% and HB: 85.1 wt%. The fraction S, continuously withdrawn as gas from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9860 wt%, methanol: 10 ppm, and HB: 130 ppm.

[0054] [Example 4] The continuous multi-stage distillation column used is the same as in Example 1. A feed solution consisting of dimethyl carbonate (99.95 wt%), methanol (300 ppm), and HB (200 ppm) was continuously supplied from F to a continuous multi-stage distillation column at a rate of 3.62 t / h. The continuous multi-stage distillation column was operated continuously with a top reflux ratio of 0.2 and a side-cut reflux ratio of 0.1. The entire volume of liquid flowing down the column from the Sl section was withdrawn and fed back in from Fs.

[0055] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 99.4 wt% and methanol: 0.6 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 97 wt% and HB: 3 wt%. The fraction S, continuously withdrawn as gas from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9995 wt%, methanol: 5 ppm, and HB: 0 ppm.

[0056] [Example 5] As a continuous multi-stage distillation column, the continuous multi-stage distillation column shown in Figure 1 was used. In this distillation column, the theoretical number of stages was 18, with a feed section F at the 5th stage counting from the top of the column, an upper connection section Sl, a side cut section Sv, a side cut reflux return section Sr in order from the top of the 9th stage, and a lower connection section Fs at the 14th stage.

[0057] A feed solution consisting of n-octane: 90 wt%, n-hexane: 5 wt%, and n-decane: 5 wt% was continuously supplied from F to a continuous multi-stage distillation column at a rate of 1 t / h. The continuous multi-stage distillation column was operated continuously with a top reflux ratio of 10 and a side-cut reflux ratio of 1. The entire volume of liquid flowing down the column in the Sl section was withdrawn and fed back in from Fs. The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of n-octane: 31.7 wt% and n-hexane: 68.3 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of n-octane: 28.8 wt% and n-decane: 71.2 wt%. The fraction S, continuously withdrawn as a gas from the side cut of the continuous multi-stage distillation column at a rate of 860 kg / h, consisted of n-octane: 99.72 wt%, n-hexane: 2600 ppm, and n-decane: 200 ppm.

[0058] [Example 6] The continuous multi-stage distillation column used is the same as in Example 5. A feed solution consisting of n-butanol: 90 wt%, ethanol: 5 wt%, and n-hexanol: 5 wt% was continuously supplied from F to the continuous multi-stage distillation column at a rate of 1 t / h. The continuous multi-stage distillation column was operated continuously with a top reflux ratio of 10 and a side-cut reflux ratio of 1. The liquid flowing down the column from section Sl was completely withdrawn and fed back in from Sl2. The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of n-butanol: 29.6 wt% and ethanol: 70.4 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of n-butanol: 29.5 wt% and n-hexanol: 70.5 wt%. The fraction S, continuously withdrawn as gas from the side cut of the continuous multi-stage distillation column at a rate of 860 kg / h, consisted of n-butanol: 99.85 wt%, ethanol: 800 ppm, and n-hexanol: 700 ppm.

[0059] [Comparative Example 1] As a continuous multi-stage distillation column, the continuous multi-stage distillation column shown in Figure 3 was used. In this distillation column, the theoretical number of stages was 18, with a feed section F at the 2nd stage from the top and a side cut section Sv at the 13th stage.

[0060] A feed solution consisting of dimethyl carbonate (99.7 wt%), methanol (2000 ppm), and HB (1000 ppm) was continuously supplied from F to the continuous multistage distillation column at a rate of 3.62 t / h. The continuous multistage distillation column was operated continuously with a top reflux ratio of 1.0.

[0061] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 95.9 wt% and methanol: 4.1 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 85 wt% and HB: 15 wt%. The fraction S, continuously withdrawn from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9960 wt%, methanol: 15 ppm, and HB: 25 ppm.

[0062] [Comparative Example 2] The continuous multi-stage distillation column used is the same as that used in Comparative Example 1. A feed solution consisting of dimethyl carbonate (99.0 wt%), methanol (6000 ppm), and HB (4000 ppm) was continuously supplied from F to the continuous multistage distillation column at a rate of 3.62 t / h. The continuous multistage distillation column was operated continuously with a top reflux ratio of 0.2.

[0063] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 87.7 wt% and methanol: 12.3 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 40.9 wt% and HB: 59.1 wt%. The fraction S, continuously withdrawn from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9905 wt%, methanol: 1 ppm, and HB: 85 ppm.

[0064] [Comparative Example 3] The continuous multi-stage distillation column used is the same as that used in Comparative Example 1. A feed solution consisting of dimethyl carbonate (98.0 wt%), methanol (1.4 wt%), and HB (0.6 wt%) was continuously supplied from F to the continuous multistage distillation column at a rate of 3.62 t / h. The continuous multistage distillation column was operated continuously at a top reflux ratio of 5.0. The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 71.2 wt% and methanol: 28.8 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 11.5 wt% and HB: 88.5 wt%. The fraction S, continuously withdrawn from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9860 wt%, methanol: 10 ppm, and HB: 130 ppm.

[0065] [Comparative Example 4] The continuous multi-stage distillation column used is the same as that used in Comparative Example 1. A feed solution consisting of dimethyl carbonate (99.95 wt%), methanol (300 ppm), and HB (200 ppm) was continuously supplied from F to the continuous multistage distillation column at a rate of 3.62 t / h. The continuous multistage distillation column was operated continuously at a top reflux ratio of 5.0. The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 176 kg / h, consisted of dimethyl carbonate: 99.4 wt% and methanol: 0.6 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 25 kg / h, consisted of dimethyl carbonate: 97 wt% and HB: 3 wt%. The fraction S, continuously withdrawn from the side cut of the continuous multi-stage distillation column at a rate of 3.42 t / h, consisted of dimethyl carbonate: 99.9990 wt%, methanol: 5 ppm, and HB: 5 ppm.

[0066] [Comparative Example 5] As a continuous multi-stage distillation column, the continuous multi-stage distillation column shown in Figure 3 was used. In this distillation column, the theoretical number of stages was 18, with a feed section F at the 5th stage and a side cut section Sv at the 9th stage, counting from the top of the column.

[0067] A feed solution consisting of n-octane: 90 wt%, n-hexane: 5 wt%, and n-decane: 5 wt% was continuously supplied from F to the continuous multistage distillation column at a rate of 1 t / h. The continuous multistage distillation column was operated continuously at a top reflux ratio of 10.

[0068] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of 31.7 wt% n-octane and 68.3 wt% n-hexane. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of 34.2 wt% n-octane and 65.8 wt% n-decane. The fraction S, continuously withdrawn from the side cut of the continuous multi-stage distillation column at a rate of 860 kg / h, consisted of 99.28 wt% n-octane, 2600 ppm n-hexane, and 4600 ppm n-decane.

[0069] [Comparative Example 6] The continuous multi-stage distillation column used is the same as that used in Comparative Example 5. A feed solution consisting of n-butanol: 90 wt%, ethanol: 5 wt%, and n-hexanol: 5 wt% was continuously supplied from F to the continuous multistage distillation column at a rate of 1 t / h. The continuous multistage distillation column was operated continuously at a top reflux ratio of 10.

[0070] The top component D, continuously withdrawn from the top of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of n-butanol: 29.6 wt% and ethanol: 70.4 wt%. The bottom component B, continuously withdrawn from the bottom of the continuous multi-stage distillation column at a rate of 70 kg / h, consisted of n-butanol: 35.9 wt% and n-hexanol: 64.1 wt%. The fraction S, continuously withdrawn from the side cut of the continuous multi-stage distillation column at a rate of 860 kg / h, consisted of n-butanol: 99.32 wt%, ethanol: 800 ppm, and n-hexanol: 6000 ppm.

[0071] [Table 1] [Explanation of symbols]

[0072] 1…Continuous multi-stage distillation column, 2…Bypass channel, Fs…Lower connection, Sl…Upper connection, 3…Side-cut reflux section, 4…Top reflux section, 11…Liquid collector, 111…Tray, 112…Cylinder section, 113…Shaft, 12a,12b…Distributor, 13…Feed section, 14a,14b…Packing material, 15…Collector, 16…Side-cut reflux return section, B…Bottom components, Br…Reboiler, Bv…Bottom extraction section, D…Top components, F…Feed section, L…Liquid, Sa…Condensing section, Sr…Side-cut reflux return section, Sv…Side-cut section, Ta…Condensing section, Tr…Top reflux return section, Tv…Top extraction section

Claims

1. A method for purifying dialkyl carbonates, The distillation process involves supplying a mixture containing dialkyl carbonate to the feed section of a continuous multi-stage distillation column, and extracting the fraction S containing the dialkyl carbonate from a side cut section located below the feed section. At least a portion of the liquid flowing down the continuous multi-stage distillation column passes through a bypass channel that bypasses the side cut section. The aforementioned fraction S is a gas that distills out from the side cut portion. A method for purifying dialkyl carbonates.

2. The method for purifying a dialkyl carbonate according to claim 1, wherein a portion of the fraction S is refluxed to the continuous multi-stage distillation column.

3. The mixed liquid supplied to the feed section contains 99.00 wt% to 99.95 wt% of dialkyl carbonate. The aforementioned fraction S contains 99.99 wt% or more of dialkyl carbonate. A method for purifying a dialkyl carbonate according to claim 1.

4. The method for purifying a dialkyl carbonate according to claim 1, wherein the content of a high-boiling-point compound in the fraction S is 30 wt ppm or less.

5. The method for purifying a dialkyl carbonate according to claim 1, wherein the reflux ratio at the top of the continuous multi-stage distillation column is 0.2 to 10.

6. The method for purifying a dialkyl carbonate according to claim 2, wherein the reflux ratio in the side cut portion is 0.02 to 1.

7. The method for purifying a dialkyl carbonate according to claim 1, wherein the liquid is guided from a liquid collector located above the side cut portion to a bypass channel.

8. A method for purifying a dialkyl carbonate according to any one of claims 1 to 7, wherein the dialkyl carbonate is dimethyl carbonate.

9. A purification apparatus for dialkyl carbonates, A continuous multi-stage distillation column, A feed section for supplying a mixture containing dialkyl carbonate to the aforementioned continuous multi-stage distillation column, A side cut section is provided below the aforementioned feed section, A purification apparatus having a bypass channel provided such that at least a portion of the liquid flowing down the continuous multi-stage distillation column bypasses the side cut section.

10. Above the side cut section, there is a liquid collector for collecting the liquid flowing down the continuous multi-stage distillation column, The liquid is led from the liquid collector into the bypass channel. The purification apparatus according to claim 9.

11. The column has a side-cut reflux section that condenses the fraction from the side-cut section and returns at least a portion of the condensed fraction to the continuous multi-stage distillation column from below the side-cut section. The purification apparatus according to claim 9.

12. The aforementioned continuous multi-stage distillation column is A top extraction section for extracting the top component from the top of the tower, A top reflux section that condenses at least a portion of the top component and returns at least a portion of the condensed fraction to the continuous multi-stage distillation column, It further includes a bottom extraction section for extracting bottom components from the bottom of the tower, The connection portion located above the side cut portion of the bypass flow path is defined as the upper connection portion, and the connection portion located below the side cut portion is defined as the lower connection portion. The side-cut reflux section is connected to a position where at least a portion of the condensed fraction is returned to the continuous multi-stage distillation column, and this position is designated as the side-cut reflux return section. When the top reflux section is connected to the top reflux section to return at least a portion of the condensed fraction back into the continuous multi-stage distillation column, The following are arranged in the order from the top of the continuous multi-stage distillation column: the top extraction section, the top reflux return section, the feed section, the upper connection section, the side cut section, the side cut reflux return section, the lower connection section, and the bottom extraction section. The purification apparatus according to claim 11.

13. A continuous multi-stage distillation column, A feed section for supplying a mixed liquid to be distilled to the continuous multi-stage distillation column, A side cut section is provided below the aforementioned feed section, A bypass channel is provided such that at least a portion of the liquid flowing down the continuous multi-stage distillation column bypasses the side cut section, A purification apparatus having the following features.

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