JP2000351789A - Purification of phosphoric ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a purified phosphoric ester of reduced content of polar solvents, and extremely reduced amount of impurities, for example, water, the starting alcohol and the like by treating a specific phosphoric ester with an crystalline aluminosilicate hydrate of an alkali metal or the like. SOLUTION: (A) A phosphoric ester that is represented by the formula (R1 to R3 are each methyl, ethyl, an aryl) and includes a polar solvent contaminated with at least one selected from water, methanol and ethanol, as impurities, is treated with (B) a crystalline alumino-silicate hydrate of alkali metal or an alkaline earth metal to obtain phosphoric ester of high purity. In a preferred embodiment, the component B has a spherical shape with a particle size of 7-10 mesh and the resultant purified phosphoric ester has >=100 ppm of water content, and <=50 ppm of the total content of methanol and ethanol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying a phosphate ester having a low water content and a low alcohol content, which is expected to be used as an electrolyte in a battery industry in the industry.

[0002]

2. Description of the Related Art In general, esters of phosphoric acid and alcohol are widely used in resin additives such as plasticizers or flame retardants, and lubricant components. Among the esters of phosphoric acid and alcohol, phosphate esters, which are esters of alcohol and phosphoric acid selected from methanol or ethanol, such as trimethyl phosphate or triethyl phosphate, have recently been used for lithium batteries or polymer. It is expected to be used as an electrolyte component of batteries.

For example, JP-A-8-321313 discloses that a solvent containing a high dielectric constant solvent selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate contains lithium trifluoromethanesulfonate or hexafluorophosphate. It describes dissolving lithium to obtain a non-aqueous electrolyte, and adding a phosphorus compound such as trimethylphosphine, trimethyl phosphite, or trimethyl phosphate to the non-aqueous electrolyte.

Japanese Patent Application Laid-Open No. 9-223516 describes a non-aqueous electrolyte for a secondary battery containing a negative electrode material mainly composed of an oxide, a positive electrode material, a lithium salt and a phosphate triester. Further, the publication describes that when the electrolytic solution contains a phosphate triester, the charge / discharge cycle characteristics can be improved without impairing the high capacity of the nonaqueous electrolyte secondary battery.

However, trimethyl phosphate or triethyl phosphate expected to be used as an electrolyte component as described above has a high adsorptivity to polar solvents such as water or alcohol. Therefore, when trimethyl phosphate or triethyl phosphate is purified by a conventional method (for example, a distillation method or a membrane separation method), water or alcohol derived from the production process or the raw material can be sufficiently removed from trimethyl phosphate or triethyl phosphate. Was difficult to remove. Thus, the phosphate esters purified by such conventional methods typically contained about 200 to about 1000 ppm water and about 1000 to about 5000 ppm alcohol.

As described above, when a phosphoric acid ester containing a large amount of a polar solvent such as water or alcohol is used for an electrolytic solution, the water or alcohol reacts with the phosphoric acid ester or reacts with lithium hexafluorophosphate or lithium hexafluorophosphate. When a compound such as lithium hexafluorosulfonate is present in the electrolytic solution, water or alcohol reacts with a compound such as lithium hexafluorophosphate or lithium hexafluorosulfonate, which tends to shorten the battery life. In addition, there are problems such as easy ignition.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above problems. That is, a method of purifying a crude phosphate ester containing a large amount of a polar solvent to obtain a purified phosphate ester having a small content of a polar solvent, and a phosphate ester having a very small content of impurities such as water and raw material alcohol. To provide.

[0008]

Means for Solving the Problems The purification method of the present invention is a method for purifying a phosphoric ester, which comprises the general formula (I)

[0009]

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(Wherein R ¹ , R ² and R ³ are each independently a methyl group, an ethyl group or an aryl group, except that all of R ¹ , R ² and R ³ are aryl groups) ), And treating the phosphate ester containing a polar solvent as an impurity with a treating agent to obtain a phosphate ester of high purity, wherein the polar solvent is water, methanol, And at least one selected from ethanol and the treating agent is a crystalline hydrous aluminosilicate of an alkali metal or an alkaline earth metal.

[0011] In one embodiment, the shape of the treatment agent is spherical.

[0012] In one embodiment, the particle size of the treatment agent is 7 to 10 mesh.

According to another aspect of the present invention, there is provided a phosphate ester purified by any of the methods described above.

In another aspect of the present invention, the water content is 100 ppm or less, and the sum of the methanol content and the ethanol content is 50 ppm or less, represented by the general formula (I). A phosphate ester is provided.

[0015]

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(Wherein R ¹ , R ² and R ³ are each independently a methyl group, an ethyl group or an aryl group, except that all of R ¹ , R ² and R ³ are aryl groups) .).

In one embodiment, the above phosphate ester is used as an electrolyte component for a battery.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below.

(Phosphate) As used herein, unless specifically stated otherwise, an ester of phosphoric acid with methanol or ethanol or an aromatic hydroxy compound, wherein at least one A compound having an ethyl group or at least one methyl group is referred to as “phosphate ester”. Among the phosphoric acid esters, in particular, a triester of phosphoric acid and methanol or ethanol or an aromatic hydroxy compound,
It is called "phosphate triester".

The phosphate ester that can be purified by the method of the present invention is represented by the general formula (I).

[0021]

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Where R¹, R^TwoAnd R^ThreeIs German
It is a methyl group, an ethyl group or an aryl group. However
Then R¹, R^TwoAnd R^ThreeAre all aryl groups
Excludes When intended for use in electrolyte applications
Therefore, in order to provide sufficient flame retardancy to the electrolyte,
Til group is preferred to increase conductivity and charge / discharge cycle characteristics
For this purpose, an ethyl group is preferred. To bring out the merits of each
To R¹, R^Two, And R ^ThreeIs a mixture of methyl and ethyl groups
May be used as the phosphoric acid ester. R¹, R^Two,and
R^ThreeWhere one or two of
The aryl is phenyl, naphthyl, or aromatic
One or more of the hydrogen atoms on the ring may be an alkyl having 1 to 4 carbon atoms.
Or halogen-substituted aryl, e.g.
, Xylyl, mesityl, chlorophenyl, etc.
It is. Phosphate esters are usually single compounds
If desired, a plurality of compounds represented by the above general formula
A mixture of seeds may be used. With such a mixture
For example, trimethyl phosphate and triethyl phosphate
And mixtures with sulfates.

Preferred specific examples of the phosphoric ester include trimethyl phosphate, triethyl phosphate, dimethyl monoethyl phosphate and diethyl monomethyl phosphate.

[0024] In this specification, the term "crude phosphate ester" refers to a phosphate ester containing a large amount of a polar solvent as an impurity. Further, the purified phosphate ester refers to a phosphate ester having a low polar solvent content after purification.

(Polar solvent) In the present specification, the polar solvent is
Unless specifically stated to be used in other ways,
It means at least one polar solvent selected from water, methanol, and ethanol.

(Alcohol) As used herein, the alcohol means at least one alcohol selected from ethanol and methanol, unless otherwise specified.

(Treatment agent) In the present specification, a treatment agent means a crystalline hydrous aluminosilicate of an alkali metal or an alkaline earth metal, unless otherwise specified. The crystalline hydrous aluminosilicate of an alkali metal or alkaline earth metal has the formula: Me _{2 / x} .Al ₂ O
It is represented by ₃ · mSiO ₂ · nH ₂ O. Here, Me represents an alkali metal or an alkaline earth metal. If only methanol is used as the raw material alcohol for the phosphate ester, the treating agent preferably has Me as potassium and / or sodium. x represents the valence of Me. For m, any positive number can be adopted, and preferably 2 to 3. n represents the number of moles of water of crystallization, and 0 or any positive number can be adopted. Preferably, n is
0.

Such treating agents include zeolite, zeolite,
Or it is sold under a trade name such as molecular sieve. Some are naturally occurring and others are synthesized industrially, both of which can be used in the present invention.

The shape of the treating agent is classified into a spherical shape, a columnar shape, a powdery shape, and the like, and a spherical shape is preferred in that impurities can be removed efficiently, and particularly preferably a 4 to 12 mesh (diameter of about 2.1 mm to about 6 mm). .2 mm), more preferably 7-1.
It is a spherical processing agent having a particle size of 0 mesh (about 2.5 mm to about 3.6 mm in diameter). If the treating agent is too small, the treating agent tends to be crushed, which may reduce the filterability. Conversely, if the treating agent is too large, the adsorption effect tends to decrease, and as a result, it is difficult to obtain a sufficient polar solvent removing effect.

The amount of the treating agent used may be any amount and is determined so that impurities can be sufficiently removed from the phosphate ester.
Impurities can be efficiently removed by using 1 to 10 parts by weight with respect to 00 parts by weight.

(Production of phosphate ester) The phosphate ester can be produced by any conventionally known production method. Phosphate esters are generally prepared by reacting phosphorus oxytrihalide with an aromatic hydroxy compound such as methanol and / or ethanol and, if necessary, phenol or xylenol, and subjecting the resulting reaction mixture to known means. It is manufactured by purification.

Examples of the phosphorus oxytrihalide include phosphorus oxychloride and phosphorus oxybromide.

Since phosphorus oxytrihalide is very easily reacted with methanol or ethanol, it is not usually necessary to use a catalyst, but a catalyst may be used in some cases. Examples of such catalysts include aluminum chloride, magnesium chloride, titanium chloride,
Examples include Lewis acid compounds such as calcium chloride, Bronsted acid compounds such as sulfuric acid and hydrochloric acid, and amine compounds such as triethylamine and tributylamine.

[0034] The reaction temperature is not particularly limited, but is preferably in the range of about -10 ° C to 50 ° C, more preferably -5 ° C to 10 ° C, in that the reaction can proceed slowly.
Range.

The reaction time may be any time depending on the production scale and the desired purity of the phosphate ester. When considering industrial use, about 3 to 20 hours is appropriate.

The reaction ratio between phosphorus oxytrihalide and methanol and / or ethanol may be any ratio. It is preferable to use methanol and / or ethanol in an equimolar amount or more per 1 mol of phosphorus oxytrihalide.

The reaction mixture obtained by carrying out the esterification reaction as described above contains by-products and a large amount of unreacted raw materials. The reaction mixture, if necessary, is water,
It is washed with an alkaline aqueous solution or an acidic aqueous solution. This washing step may be performed once, but is preferably performed a plurality of times. This washing step removes unreacted raw materials or by-products.

The crude phosphate ester thus produced usually contains about 5,000 to 10,000 ppm of water, and usually contains 1000 to 1000 parts of alcohol as the remaining raw material.
It contains about 5000 ppm.

The crude phosphate is usually purified by distillation to reduce impurities consisting of water and alcohol. Preferably, it is purified by distillation using a rectification column. According to distillation purification using a rectification column, water is reduced to 200 ppm to 1 ppm.
A phosphate ester containing about 000 ppm and about 100 ppm to 500 ppm of alcohol as a residual raw material can be obtained.

(Treatment Step) The purification method of the present invention includes a step of treating a phosphate ester with a treating agent to obtain a high-purity phosphate ester.

For example, the water containing 200 ppm or more and the alcohol of 100 pp obtained as described above are used.
By treating the crude phosphate ester containing m or more with a treating agent, impurities which are polar solvents such as water or alcohol can be removed from the crude phosphate ester.

Various conditions for contacting the phosphoric acid ester with the treating agent will be described below. These conditions are based on the impurity concentration in the crude phosphoric acid ester before the treatment and the desired purified phosphoric acid ester in the phosphoric acid ester. It can be used after being appropriately changed according to the allowable amount of impurities and the like.

The contact temperature between the phosphate ester and the treating agent is as follows:
Preferably, from 10 ° C to 60 ° C, more preferably from 20 ° C to
It is determined within the range of 40 ° C. in consideration of the shape or amount of the treatment agent. It is not necessary to be within the above range, but within the above preferable range, impurities can be efficiently removed.

As a specific method for contacting the crude phosphoric ester and the treating agent, any method capable of sufficiently contacting both can be used. For example, a method of filtering a crude phosphoric acid ester using a treating agent as a filter medium, and a method of filling a crude phosphoric acid ester and a treating agent into a treatment can, stirring or shaking, or a known method such as a method of shaking and having such a function. The devices can be used alone or in combination.

The contact time between the phosphate ester and the treating agent is as follows:
Preferably, it is determined within the range of 6 to 8 hours in consideration of the shape or amount of the treatment agent. It is not necessary to be within the above range, but within the above preferable range,
Impurities can be efficiently removed.

The contact between the phosphoric ester and the treating agent may be performed once, but may be repeated a plurality of times as necessary.

After the crude phosphate and the treating agent are sufficiently contacted with each other and then separated by, for example, filtration, the purified phosphoric acid ester and the used treating agent are separated from each other. Can be obtained.

According to a method in which a treating agent is filled in a funnel or column as a filtering agent and a crude phosphate ester is passed through the funnel or column, the purified phosphate ester can be used without providing an independent separation step. Obtainable.

According to the above-mentioned method, a high-quality phosphate ester having extremely few impurities composed of a polar solvent can be obtained.

The content of the polar solvent in the obtained phosphoric ester can be adjusted by appropriately adjusting the above various contact conditions.
Adjusted easily.

For example, by adopting the above-mentioned various preferable conditions, the water content is 100 ppm or less or 50 ppm or less, and the alcohol content is 5 ppm or less.
Phosphate esters of 0 ppm or less or 20 ppm or less are obtained.

The used treating agent can be reused by washing with water or alcohol, and then heating and drying under reduced pressure or normal pressure.

(Phosphate Esters of the Present Invention) The phosphate esters of the present invention are high-quality phosphate esters that have never been seen before. That is, it is a phosphate ester having a water content of 100 ppm or less and a methanol and / or ethanol content of 50 ppm or less. Such a phosphoric ester can be obtained by appropriately adjusting the above-mentioned various conditions by the above-mentioned method.

Further, by further adjusting the above conditions, a phosphate ester having a water content of 50 ppm or less and / or an alcohol content of 20 ppm or less can be easily obtained.

When the phosphoric acid ester is used for an electrolytic solution, if the phosphoric acid ester contains too much water, the discharge capacity of the battery tends to decrease due to the reaction of water with lithium over time. In addition, the charge / discharge cycle tends to decrease. Furthermore, there is a danger that the internal pressure of the battery tends to increase due to heat generated during the reaction, and in the worst case, the battery tends to burst.

(Use in Electrolyte Solution) As described above, a phosphate ester which has been purified to significantly reduce the content of a polar solvent, for example, a phosphate ester purified by the method of the present invention, is used in a battery electrolyte solution. It is preferably used. In particular,
It can be preferably used for an electrolyte containing a lithium salt.

As a lithium salt in such an electrolytic solution,
Is any known lithium salt for lithium batteries.
Titium salts can be used. For example, LiCF_ThreeSO_Three,
LiC _FourF₉SO_Three, LiPF₆, LiClO_Four, LiBF_Four
Etc. can be used. In particular, LiCF_ThreeSO_Three, LiC
_FourF₉SO_Three, LiPF₆Are preferred.

The content of the lithium salt is preferably 0.1 to 3 mol / l, more preferably 0.5 to 2 mol / l, as the concentration in the electrolytic solution. When the amount of the lithium salt is small, the conductivity tends to decrease.

The electrolyte may contain an organic solvent other than the phosphoric acid ester, if necessary. Examples of such an organic solvent include organic solvents having a high dielectric constant. this is,
It is used for the purpose of increasing the solubility and conductivity of the electrolyte and consequently improving the electric capacity. Specifically, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate;
cyclic esters such as γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane,
3-dioxolan, tetrahydrofuran, 2-methyl-
Ethers such as tetrahydrofuran and diethyl ether; Of these, carbonates are preferred.

In such an electrolytic solution containing a lithium salt,
The use of phosphates with significantly reduced polar solvent content does not impair the properties of phosphates, which have excellent flame retardancy, and does not require special electrode materials or additives. In addition, a non-aqueous electrolyte for a secondary battery that can improve cycle characteristics can be provided.

For example, a suitable electrolytic solution can be obtained by mixing a phosphoric acid ester having a significantly reduced polar solvent content, the above-mentioned lithium salt, and if necessary, the above-mentioned other organic solvent. If an electrolytic solution using a phosphoric acid ester whose polar solvent content is significantly reduced is employed, the life of the secondary battery is improved because the lithium metal rarely reacts with water and loses its activity.

That is, there is provided a non-aqueous electrolyte for a secondary battery capable of improving the charge / discharge efficiency and cycle characteristics of a battery without the need for a special electrode material or additive.

The electrolytic solution thus obtained can be applied to any type of secondary battery using a lithium salt as an electrolyte, as a non-aqueous electrolytic solution for a secondary battery.

The types of secondary batteries include small batteries used for devices such as mobile phones and notebook computers, stationary batteries of 2-3 kWh used for flattening the power demand load, and electric batteries. Secondary batteries used for mobile objects such as automobiles and hybrid vehicles are exemplified.

By using an electrolyte containing a phosphate ester having a significantly reduced polar solvent content in such a battery, high capacity, long life, cycleability, flame retardancy, safety, and storage stability can be obtained. A high-performance secondary battery with excellent performance can be obtained.

(Function) The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the phosphate ester is treated with a crystalline hydrous aluminosilicate of an alkali metal or an alkaline earth metal. The present inventors have found that it is possible to efficiently remove polar solvents such as water and alcohol from phosphate esters by the method, and have completed the present invention.

Here, it is considered that the treating agent acts as an adsorbent for the polar solvent.

The phosphoric acid ester of the present invention has extremely low water content and alcohol content as compared with the phosphoric acid ester obtained by the conventional method, and was used as an electrolyte component for a polymer battery or a lithium battery. In this case, it is possible to reduce the risk of ignition without shortening the life of the battery while maintaining characteristics such as flame retardancy or storability.

[0069]

The following are non-limiting examples of the present invention.

In the following examples, the water content was measured by a Karl Fischer titration type moisture meter (manufactured by Hiranuma Sangyo Co., Ltd., trade name: Hiranuma Automatic Moisture Analyzer AQV-5S). The detection limit (ND) was 5 ppm or less.

The methanol content and the purity of the phosphoric ester were measured by gas chromatography (manufactured by Shimadzu Corporation, trade name: GC-14B). The detection limit (ND) was 5 ppm or less.

(Example 1) Stirrer, thermometer, additional device,
A 3000 L reactor having a condenser and a hydrochloric acid recovery device was charged with 1320 kg of methanol and 1407 kg of phosphorus oxychloride, and stirred at -2 ° C / 33 ° C.
The reaction was performed while recovering hydrochloric acid generated at 9 mmHg for 9 hours with a hydrochloric acid recovery apparatus. Next, 880 kg of methanol was added in 7 hours, and the reaction was performed for 4 hours. Subsequently, unreacted methanol and hydrochloric acid are collected in a purification tower at 50 ° C./33 mmHg, and as a residue, crude trimethyl phosphate having a water content of ND (detection limit) and a methanol content of 3000 ppm. 1298 kg were obtained.

To 1298 kg of this crude trimethyl phosphate, 2
31.8 kg of an 8% aqueous sodium hydroxide solution was added, and 1
The rectification was performed at 70 ° C./30 to 10 mmHg for 8 hours, the water content was 200 ppm, and the methanol content was 8%.
There was obtained 1168 kg of trimethyl phosphate at 0 ppm.

Next, a packed tower filled with 17.5 kg of a treating agent (crystalline hydrous aluminosilicate of K and Na (spherical, 8 to 10 mesh)) was installed in a circulation line of a treatment can having a circulation mechanism. The rectified trimethyl phosphate (350 kg) was charged into a treatment can, and was pump-circulated at room temperature for 6 hours to be brought into contact with the adsorbent to adsorb moisture and methanol to the treatment agent. After circulation, the solution is filtered using a 1 micron wound filter (line filter). The content of water is 50 ppm, the content of methanol is ND (detection limit), and the purity of trimethyl phosphate is 99.9% by weight. 340 Kg were obtained.

[0075]

According to the present invention, it is possible to obtain a phosphate ester having a low water content and a low alcohol content, which cannot be obtained by a conventional purification method. Further, the phosphate ester of the present invention has a particularly high utility value as an electrolyte component of a battery because of its low moisture content and low alcohol content.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4H050 AA01 AA02 AA03 AB78 AD30 BC50 BD20 BE90 5H024 BB11 BB18 FF11 HH00 HH08 HH13 HH15 5H029 AJ01 AM03 CJ28 DJ16 EJ11 HJ02 HJ05 HJ10

Claims (6)

[Claims] 1. A method for purifying a phosphate ester, comprising the steps of: (Wherein, R ^1, R ² and R ³ are each independently a methyl group, an ethyl group or an aryl group. However, R ^1,
Except when all of R ² and R ³ are aryl groups. ) And treating the phosphate ester containing a polar solvent as an impurity with a treating agent to obtain a phosphate ester of high purity, wherein the polar solvent comprises water, methanol, and A method comprising at least one selected from ethanol, wherein the treating agent is a crystalline hydrous aluminosilicate of an alkali metal or an alkaline earth metal. 2. The method according to claim 1, wherein the shape of the treatment agent is spherical. 3. The method according to claim 1, wherein the particle size of the treating agent is 7 to 10 mesh. 4. A phosphate ester purified by the method according to claim 1. 5. The water content is 100 ppm or less,
And a phosphate ester represented by the general formula (I) wherein the sum of the content of methanol and the content of ethanol is 50 ppm or less. (Wherein, R ^1, R ² and R ³ are each independently a methyl group, an ethyl group or an aryl group. However, R ^1,
Except when all of R ² and R ³ are aryl groups. ). 6. The phosphate according to claim 4, which is used as an electrolyte component for a battery.