JP2023086457A - Method for producing ethylene carbonate - Google Patents

Abstract

To provide a method for producing ethylene carbonate in which a simple operation and high productivity with low energy can be expected.SOLUTION: There is provided a method for producing ethylene carbonate which comprises bringing ethylene carbonate crystals containing ethylene glycols and a solvent having a boiling point lower than the boiling point of the ethylene glycols into contact with each other. Preferably, the ethylene carbonate crystals containing ethylene glycols or the solvent contains water and the method comprises maintaining the temperature of the solvent before the contact at 36°C or less and the liquid temperature at the end point after contacting the ethylene carbonate crystals and the solvent at 0°C or more.SELECTED DRAWING: None

Description

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

Ethylene carbonate is used as a solvent for various polymer compounds, a reaction solvent for various chemical reactions, an electrolyte solvent for lithium ion secondary batteries, an extractant, a foaming agent, a lubricating oil stabilizer, and the like.
Ethylene carbonate is usually synthesized by reacting ethylene oxide and carbon dioxide at high temperature and high pressure. Therefore, ethylene carbonate contains diols such as ethylene glycol and diethylene glycol derived from these synthetic raw materials. It also contains the catalyst components used in the synthesis and a small amount of water. Moisture further reacts with ethylene carbonate to produce ethylene glycol.

Ethylene carbonate used as various solvents and the like preferably contains as few impurities as possible.
Conventionally, various methods such as a distillation method and a crystallization method have been proposed as methods for purifying ethylene carbonate.

Distillation is the most widely used purification method industrially. However, since the boiling point of ethylene carbonate is as high as 246°C (at normal pressure), when ethylene carbonate is purified by distillation, even if the distillation is carried out under reduced pressure, thermal deterioration occurs, and ethylene carbonate reacts with diols and moisture. It is easy to increase the molecular weight. In addition, since some bonds of ethylene carbonate having a high molecular weight are broken and returned to diol, about 100 ppm of diol may remain in ethylene carbonate even after distillation. Furthermore, the distillation method requires energy for the latent heat of vaporization of the substance, and also requires a large reflux ratio. Therefore, the energy consumption is very large compared to the crystallization method which requires only cooling by removing sensible heat.
In particular, distillation in the presence of a catalyst such as tributylmethylphosphonium iodide (hereinafter sometimes referred to as “TBPMI”)/K ₂ CO ₃ accelerates the decomposition of ethylene carbonate and greatly deteriorates the yield. In addition, when ethylene glycol is contained, ethylene glycol and ethylene carbonate azeotrope, making distillation separation difficult.

The crystallization method is a purification method that utilizes the fact that impurity components that do not crystallize at that temperature do not enter the crystal when the target component is crystallized. In the crystallization method, purification can be performed only by the operation of crystallization by cooling and dissolution by slight heating, so deterioration due to side reactions is unlikely to occur and energy consumption is small.
Patent Document 1 discloses that high-purity ethylene carbonate of 99.999% or more can be obtained by applying the crystallization method described in this document.
However, in order to obtain such high-purity ethylene carbonate by the method of Patent Document 1, it is necessary to adopt a method such as multi-stage crystallization or melt refining, and a long and complicated operation is required to improve the purity. becomes. Therefore, increasing the production volume by this method is not easy and lacks economic efficiency.

JP 2007-284427 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing ethylene carbonate which solves the above-mentioned problems and is expected to have low energy consumption, simple operation, and high productivity.

As a result of intensive studies in view of the above problems, the present inventor found that impurities can be easily removed by washing crude crystals obtained by synthesizing ethylene carbonate and performing primary crystallization with a specific solvent. perfected the invention.
That is, the present invention resides in the following.

[1] A method for producing ethylene carbonate, comprising contacting ethylene carbonate crystals containing ethylene glycols with a solvent having a boiling point lower than that of the ethylene glycols.
[2] The method for producing ethylene carbonate according to [1] above, wherein the ethylene carbonate crystals contain at least one selected from water, quaternary phosphonium salts, alkali metal salts, and alkaline earth metal salts.
[3] The method for producing ethylene carbonate according to [1] or [2] above, wherein the ethylene glycol is monoethylene glycol and/or diethylene glycol.
[4] The method for producing ethylene carbonate according to any one of [1] to [3] above, wherein the solvent is hydrophilic.
[5] The ethylene carbonate crystals containing ethylene glycols or the solvent contains water, the temperature of the solvent before the contact is 36°C or less, and the end point after the ethylene carbonate crystals and the solvent are brought into contact. The method for producing ethylene carbonate according to any one of [1] to [4] above, which comprises maintaining the liquid temperature at 0° C. or higher.

ADVANTAGE OF THE INVENTION According to this invention, the purity of ethylene carbonate can be improved by simple operation, and it becomes possible to manufacture ethylene carbonate with low energy and high productivity.
According to the present invention, ethylene glycols, which are azeotropically distilled with ethylene carbonate and are difficult to separate, can be removed by a simple method, and when it is desired to further improve the purity in applications such as electrolyte solutions, distillation can be combined to achieve high purification. is also possible.
In addition, by using a solvent with a boiling point lower than that of ethylene carbonate, the energy required for distillation can be reduced, and in some cases, high purification can be achieved by drying under reduced pressure or air drying.
In addition, when a catalyst such as a quaternary phosphonium salt, an alkali metal salt, or an alkaline earth metal salt is contained, in the distillation method, ethylene carbonate is distilled from the top, or side-cut to separate the catalyst and ethylene carbonate. However, according to the present invention, since the catalyst can be reduced together with the ethylene glycols, there is no need to remove the ethylene carbonate by distillation, and high purification can be achieved with low energy.
Furthermore, in the present invention, a part of ethylene carbonate may be dissolved by the selected solvent, such as water or alcohol in which ethylene carbonate has high solubility, and the recovery rate may decrease. -208509) or in the production of dialkyl carbonates and diols (see, for example, JP-A-4-198141), the ethylene carbonate dissolved in the solvent can be used without waste.

Embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is an example of the embodiments of the present invention, and the present invention is not limited to these contents. Various modifications can be made within the scope of the gist.

The method for producing ethylene carbonate of the present invention comprises ethylene carbonate crystals containing ethylene glycols (hereinafter sometimes referred to as "crude ethylene carbonate crystals") and a solvent having a boiling point lower than that of the ethylene glycols (hereinafter, "washing (hereinafter, this step may be referred to as the “refining step of the present invention”).

<Crude ethylene carbonate crystal>
Crude ethylene carbonate crystals containing ethylene glycols to be purified in the present invention can be prepared by the following method.
First, carbon dioxide and ethylene oxide are reacted in the presence of a catalyst to produce ethylene carbonate.
The catalyst used in this carbonate reaction includes alkali metal salts such as alkali metal bromides and iodides (for example, those described in JP-B-38-23175), alkaline earth metal halides (for example, US Pat. alkaline earth metal salts such as those described in U.S. Pat. No. 2,667,497), alkylamines, quaternary ammonium salts (e.g., those described in U.S. Pat. No. 2,773,070) , organic tin or germanium or tellurium compounds (for example, those described in JP-A-57-183784), quaternary halogenated organic phosphonium salts (for example, those described in JP-A-58-126884) It may be used by appropriately selecting from known ones such as phosphonium salts.

Among them, it is preferable to use a bromide or iodide of an alkali metal, or a phosphonium salt. Preferred examples include potassium iodide, potassium bromide, quaternary phosphonium iodide or quaternary phosphonium bromide, such as tributylmethylphosphonium iodide (TBPMI), triphenylmethylphosphonium iodide, triphenylpropylphosphonium iodide, triphenyl benzylphosphonium iodide, tributylmethylphosphonium iodide, bromides thereof, and the like.
A compound that forms an alkali metal carbonate with the phosphonium salt can also be used in combination. Alkali metal carbonates are preferred because they suppress the production of by-products other than ethylene glycol and ethylene carbonate in the carbonation reaction. As the alkali metal, a potassium salt having a high solubility is preferable. A preferred example of combined use of a catalyst is as described in JP-A-2000-128814.

Commercially available high-purity ethylene oxide may be used as the ethylene oxide used as a raw material for the carbonation reaction according to the present invention. For example, Ullmanns Encyclopedia of Industrial Chemistry, 5th Ed. As described above, a gas composed mainly of ethylene and oxygen as raw materials and methane as a diluent gas is passed through a multi-tubular reactor filled with a silver catalyst to react and synthesize. , for example, can also be used after being purified as described below. Normally, the selectivity of ethylene to ethylene oxide is about 80%, and the remaining about 20% becomes carbon dioxide gas and water by complete oxidation reaction. The oxidizing reaction gas discharged from the reactor consists of the produced ethylene oxide, unreacted ethylene, carbon dioxide gas, oxygen, diluent gas and the like. The produced ethylene oxide is absorbed into the liquid phase in an absorption tower using water as an absorption liquid. The ethylene oxide absorbed in the absorbing liquid is stripped in the ethylene oxide stripping column, recovered from the top of the column as a highly concentrated aqueous solution of ethylene oxide, and further dehydrated and purified in the distillation column. Alternatively, the high-concentration ethylene oxide aqueous solution obtained from the top of the column can be used directly as a raw material.

Carbonation reaction can be carried out using any device. As an example, the reaction temperature is controlled by circulating the reaction liquid in the column through the liquid circulation conduit using a bubble column having a liquid circulation conduit equipped with a heat removal heat exchanger and a circulation pump in the middle. Then, the raw materials ethylene oxide, carbon dioxide, and the catalyst are continuously supplied from the bottom of the column, and the reaction can be carried out continuously. It is also preferable to use a reactor equipped with an ejector nozzle as disclosed in JP-A-11-269110. The reaction temperature is usually 70 to 200°C, preferably 100 to 170°C.

The reaction pressure is usually 0.6-5.0 MPa, preferably 1.0-3.0 MPa. Water may be added to the carbonation reaction according to the present invention, and in the presence of water, ethylene oxide is converted not only to ethylene carbonate but also to ethylene glycol. Therefore, ethylene glycol is always mixed in the carbonate-forming reaction solution. The reaction proceeds easily even when the amount of carbon dioxide supplied is equimolar or less with respect to ethylene oxide. The feed molar ratio of carbon dioxide to ethylene oxide is usually 5 or less, preferably 0.5 to 3.0.

Also, the molar ratio of water supplied to ethylene oxide is usually 10 or less, preferably 0.5 to 5.0. Since it is inefficient to completely react ethylene oxide in a bubble column, it is also preferable to arrange a tubular reactor after the bubble column to further react ethylene oxide in the liquid. At this time, the amount of the catalyst added is 1/1000 to 1/20, preferably 1/200 to 1/50, in terms of molar ratio to ethylene oxide. A part of the reaction solution obtained by the carbonate-forming reaction is sent to the purification step of the present invention, and the remainder is preferably subjected to a catalyst recovery operation described later, followed by a coloring component removal operation described later to carbonate. It can be circulated to the reactor, or the catalyst recovery operation and the coloring component removal operation may be carried out as separate operations. Examples of the catalyst recovery operation performed to prevent deterioration of the catalyst include the methods described in JP-A-2004-262767, JP-A-2004-284976, JP-A-2004-292384, and the like. The coloring component removing operation includes the method described in International Publication No. 2011/065528.

Next, ethylene carbonate is separated from the carbonation reaction solution by crystallization. Generally, by cooling the carbonate-forming reaction solution, crude ethylene carbonate crystals (“ethylene carbonate crystals containing ethylene glycols” to be purified in the present invention) are precipitated and separated and recovered. The separation method here is not particularly limited, but methods such as centrifugation, vacuum filtration, and pressure filtration can be used.

Generally, the composition of the crude ethylene carbonate crystals obtained as described above has an ethylene carbonate purity of about 85 to 95% by mass, contains 3 to 10% by mass of ethylene glycols, and contains 2 to 5% by mass of water. It is a crude ethylene carbonate crystal containing about 0.001 to 0.5% by mass of a catalyst component.
Ethylene glycols may also typically include monoethylene glycol and/or diethylene glycol. This is because, as mentioned above, water may be added in the carbonation reaction and in the presence of water ethylene oxide is also converted to ethylene glycol. Also, when the abundance ratio of ethylene glycol in the carbonation reaction solution is high, a trace amount of ethylene oxide reacts with ethylene glycol during the carbonation reaction to convert to diethylene glycol.

<Purification process>
In the present invention, the crude ethylene carbonate crystals obtained as described above are brought into contact with a solvent having a boiling point lower than that of the ethylene glycols for purification. Purified ethylene carbonate crystals having a purity of 94% by mass or more, preferably 98% by mass or more can be obtained by this purification step.
When further purification is performed after this purification process, the ethylene glycol and the catalyst are reduced by this purification process, so it is necessary to prevent the inability to separate the ethylene glycol and ethylene carbonate due to azeotropy and the decomposition by the catalyst. can be done.

If the boiling point of the washing solvent used in the refining process is higher than the boiling point of ethylene glycols, the boiling point will be close to that of ethylene carbonate, and separation by distillation will be difficult and a large amount of energy will be required for further purification to a higher degree of purity. . Therefore, in the present invention, a washing solvent having a boiling point lower than that of the ethylene glycols contained in the crude ethylene carbonate crystals is used. The boiling point of the washing solvent should be lower than the boiling point of the ethylene glycols, and the difference in boiling points is not particularly limited. The lower limit of the boiling point of the washing solvent is preferably 40° C. or higher from the viewpoint of easy temperature control during washing purification and storage.

Specific examples of the washing solvent having a lower boiling point than the ethylene glycol used in the purification process of the present invention include water, methanol, ethanol, propanol, butanol, heptane, benzene, normal hexane, cyclohexane, toluene, diethyl ether, and xylene. mentioned. These solvents may be used alone or in combination. Among them, it is preferable to select a solvent having a high affinity with the catalyst such as ethylene glycols, tributylphosphonium iodide, potassium carbonate, potassium iodide and the like. Preferably, it is a hydrophilic solvent, more preferably water, methanol or ethanol.

As a method for contacting the crude ethylene carbonate crystals with the washing solvent, for example, after the above-described centrifugation, centrifugation is performed while contacting with the solvent, and a solvent is further added to the crude ethylene carbonate crystals recovered by filtration. A method of continuing filtration and the like can be mentioned. The separation operation of the crude ethylene carbonate crystals from the carbonate-forming reaction solution after the carbonate-forming reaction and the contacting operation with the washing solvent can be performed intermittently or continuously.

The amount of washing solvent used is preferably set based on the solubility of the selected solvent in ethylene carbonate. Usually, 1.5 times or less of the crystal weight is preferable.
In the case of a hydrophobic solvent such as cyclohexane, since ethylene carbonate hardly dissolves at low temperatures, it is possible to treat with a solvent amount of about 10 times the weight of the crystals.
If the amount of washing solvent used in the purification step is too large, the recovery rate of ethylene carbonate decreases. On the other hand, if the amount of the washing solvent is too small, a sufficient purification effect cannot be obtained, so the amount of the washing solvent used is not particularly limited, but it is preferably 0.5 times or more the weight of the crude ethylene carbonate crystals.

Since the melting point of ethylene carbonate is 36° C., the contact temperature is preferably 36° C. or less. In addition, from the viewpoint of improving the recovery rate of ethylene carbonate, it is preferable to use a small amount of washing solvent and perform the treatment at a low temperature as described above.
On the other hand, since ethylene carbonate absorbs heat when dissolved, in the case of a system containing water, it is desirable to determine the contact start temperature so that the temperature of the solvent after contact is 0° C. or higher. According to Niccolo Peruzzi, et al., J. Phys. Chem. B 2012, 116, 14398-14405, theoretically, an enthalpy change (endotherm) of 13.3 kJ/mol occurs when ethylene carbonate is dissolved. This indicates that the temperature drops by 11° C. when 0.2 parts by mass of ethylene carbonate is dissolved in 0.8 parts by mass of water at once. In reality, ethylene carbonate does not dissolve instantaneously, and the temperature drop is limited. may remain in Since the temperature drop varies depending on the type of solvent, the ratio of the solvent and the crude ethylene carbonate crystals, and the contact method, in the present invention, the end point after contacting the washing solvent and the crude ethylene carbonate crystals, that is, the liquid at the end of the purification process It is preferable to prevent the water from freezing by maintaining the temperature above 0° C., which is the melting point of water.

The contact time between the crude ethylene carbonate crystals and the washing solvent may be determined according to the purity and recovery rate of the finally obtained purified ethylene carbonate crystals. In the present invention, ethylene glycol and water in which catalyst components such as TBPMI, K ₂ CO ₃ and KI are dissolved are subject to reduction by contact with the cleaning solvent. Since they are present in a liquid state on the surface of the crude ethylene carbonate crystals, it is only necessary to bring the crude ethylene carbonate crystals into contact with the washing solvent.
From this point of view, the washing operation according to the present invention is preferably a method in which the washing solvent is passed through the crude ethylene carbonate crystals while continuously performing the filtration operation.

The completion of the contact can be appropriately set by measuring the purity of the purified ethylene carbonate crystals obtained, the amount of ethylene glycol in the washing solvent used for the contact, and the like so that the desired purified ethylene carbonate crystals can be obtained.
Further, if the separation efficiency of impurities by contact is calculated in advance, it is possible to set the completion of cleaning based on the amount of cleaning solvent to be brought into contact.

As described above, according to the present invention, the purity of ethylene carbonate can be improved with a simple operation. To obtain ethylene carbonate of higher purity, the crystallization is repeated. Specifically, for example, as described in Japanese Patent Application Laid-Open No. 7-89905, crystals are deposited on the wall of a cooled vertical tube, and then heated to partially melt the crystals. can be used for recovering crystals with increased purity by flowing down and separating. In addition, as a continuous crystallization method, a countercurrent contact method is also known (Japanese Patent Application Laid-Open No. 2007-284427 and British Patent No. 1086028, Separation Technology Vol. 35, No. 6, pp. 45-49 (2005 year), etc.). The countercurrent contact method is a method of increasing the purity of ethylene carbonate by bringing ethylene carbonate crystals into contact with a liquid.

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

[Example 1]
A crude ethylene carbonate solution containing ethylene carbonate/monoethylene glycol/water/TBPMI/K ₂ CO ₃ was cooled from 20°C to 5°C at a cooling rate of about 7.5°C/h to crystallize and crystallized at 3000 rpm. After centrifugation, crude ethylene carbonate crystals were recovered. The composition of this crude ethylene carbonate crystal was analyzed by the following method, and the results are shown in Table 1.

A tube containing 60 g of the washing solvent shown in Table 1 and a stirrer was cooled to 5°C in a water bath, 40 g of crude ethylene carbonate crystals were added thereto, stirred for 1 hour, and then solid-liquid separated by centrifugation to obtain a The weight of the crystals (purified ethylene carbonate crystals) was measured to calculate the recovery rate (ratio of the weight of the purified ethylene carbonate after solid-liquid separation after washing to 40 g of crude ethylene carbonate crystals before washing), and the composition was analyzed.

The compositions of crude ethylene carbonate crystals and purified ethylene carbonate crystals were analyzed as follows.
Purities of ethylene carbonate and monoethylene glycol were measured by gas chromatography using GC-2025 (DB-WAX ETR column) manufactured by Shimadzu Corporation, and water content, TBPMI concentration, and K ₂ CO ₃ concentration measured by the following methods were subtracted. and expressed as area percentage.
Moisture was measured with a Karl Fischer moisture meter.
Washing solvents other than water were measured by gas chromatography using Shimadzu GC-2025 (DB-WAXETR column).
For TBPMI, iodine was measured by ion chromatography using Metrohm's Eco IC (TSKgel SuperIC-AZ column) and quantified by a calibration curve method.
The potassium concentration of K ₂ CO ₃ was similarly measured by ion chromatography using Metrohm's 883 Basic IC plus (Metrosep C6 column) and quantified by the calibration curve method.
The part where the total does not reach 100% is due to trace impurities on GC.
Table 1 shows the results.
Abbreviations in Table 1 are as follows.
EC: ethylene carbonate MEG: monoethylene glycol The boiling points of the washing solvents and monoethylene glycol used are as follows, and all washing solvents have lower boiling points than the boiling point of monoethylene glycol.
Monoethylene glycol: 197.6°C
Water: 100°C
Methanol: 64.7°C
Ethanol: 78.3°C
Cyclohexane: 80.7°C

From Table 1, it can be seen that ethylene glycols in crude ethylene carbonate crystals can be separated and removed by a simple operation by using a solvent having a boiling point lower than that of ethylene glycols.
Hydrophobic solvents such as cyclohexane do not dissolve ethylene carbonate, but they are also not miscible with ethylene glycol, water, and the catalyst, resulting in insufficient washing. Therefore, it is considered that a hydrophilic solvent is suitable as a washing solvent.
After washing, about 4 to 5% liquid remains on the surface of the purified ethylene carbonate crystals, and about 5% water remains on the crystals when washed with water, but only about 1% when methanol or ethanol is used. Since none remained, most of these solvents are considered to have evaporated before analysis during the process of centrifugation or the like.
As for washing with water, although the purity of ethylene carbonate is not improved, monoethylene glycol, which is an azeotropic component, is reduced. .

Claims (5)

A method for producing ethylene carbonate, comprising contacting ethylene carbonate crystals containing ethylene glycols with a solvent having a boiling point lower than that of the ethylene glycols. 2. The method for producing ethylene carbonate according to claim 1, wherein the ethylene carbonate crystals containing ethylene glycols contain at least one selected from quaternary phosphonium salts, alkali metal salts and alkaline earth metal salts. 3. The method for producing ethylene carbonate according to claim 1, wherein said ethylene glycols are monoethylene glycol and/or diethylene glycol. The method for producing ethylene carbonate according to any one of claims 1 to 3, wherein the solvent is hydrophilic. The ethylene carbonate crystals containing ethylene glycols or the solvent contains water, the temperature of the solvent before the contact is 36 ° C. or less, and the liquid at the end point after contacting the ethylene carbonate crystals with the solvent The method for producing ethylene carbonate according to any one of claims 1 to 4, comprising maintaining the temperature at 0°C or higher.