JP5825028B2 - Process for producing polyalkylene glycol - Google Patents

Description

  The present invention relates to a method for producing a polyalkylene glycol using an active species comprising an imino group-containing phosphazenium salt and an active hydrogen compound, and more specifically, an active species for producing a polyalkylene glycol comprising an imino group-containing phosphazenium salt. After the polymerization reaction of the alkylene oxide used, the polyalkylene glycol polymerization active species and / or the imino group-containing phosphazenium salt that is the raw material is efficiently separated and recovered by treating with a divalent or higher inorganic acid and solid acid. Thus, the present invention relates to a method for efficiently producing a polyalkylene glycol having a low residual amount of polymerization active species and / or raw materials thereof.

  Polyalkylene glycol is useful as a raw material for polyurethanes and surfactants, and is produced on an industrial scale. As a general production method thereof, there is known a method of addition polymerization of an alkylene oxide to a polyfunctional active hydrogen compound using potassium hydroxide (hereinafter sometimes referred to as KOH) as a catalyst. Consists of a polymerization step for producing a crude polyalkylene glycol by addition polymerization, and a purification step for adding salt to the crude polyalkylene glycol to neutralize KOH, followed by dehydration and drying to remove the deposited salt by filtration. is there.

  However, when a polyalkylene glycol is produced using a KOH catalyst, it is known that a monool having an unsaturated group at the terminal is produced as a by-product with an increase in the molecular weight of the polyalkylene glycol, and a large amount of the monool is contained. When polyalkylene glycol is used as a polyurethane raw material, the resulting polyurethane has low hardness and durability, and its use is limited.

  Therefore, various methods for producing a polyalkylene glycol having a high molecular weight and a small monool amount have been studied, and a method using a specific phosphazene compound as a catalyst has been proposed (for example, see Patent Document 1). When polyalkylene glycol is produced using this phosphazene compound as a catalyst, the productivity is greatly improved. On the other hand, this phosphazene compound is expensive and affects the urethanization reaction. In order to use the obtained polyalkylene glycol as a polyurethane raw material, it was necessary to remove the catalyst.

  The catalyst removal method at that time is 1) a method in which an acid compound is added to the crude polyalkylene glycol to neutralize the catalyst and then treated with an adsorbent, and 2) the crude polyalkylene glycol is washed with water and then the aqueous phase is separated. 3) A method of adding water to the crude polyalkylene glycol and then bringing it into contact with an ion exchange resin, etc. (see, for example, Patent Document 2) has been proposed. Among them, for removing a phosphazene compound that is a large molecule, The use of a solid acid having a specific pore size and specific surface area as an adsorbent has been proposed (for example, see Patent Document 3). As a method for recovering the catalyst, a method of contacting a crude polyalkylene glycol with an acid compound and separating and recovering a phosphazenium compound precipitated after dehydration and drying has been proposed (for example, see Patent Document 4).

  On the other hand, a method of using an imino group-containing phosphazenium salt that is more compact and easier to synthesize than the phosphazene compound as a polyalkylene glycol production catalyst has been proposed (for example, see Patent Document 5).

Japanese Patent Laid-Open No. 10-77289 (see, for example, claims) Japanese Patent Laid-Open No. 11-106500 (for example, refer to the claims) JP 2001-106780 A (see, for example, the claims). Japanese Patent Laid-Open No. 10-330475 (see, for example, claims) Japanese Patent Laying-Open No. 2010-150514 (for example, refer to the claims)

  However, Patent Document 5 does not mention a method for separating and recovering the catalyst. Further, since the imino group-containing phosphazenium salt is basic, if it remains in the polyalkylene glycol, it may adversely affect the moldability and physical properties of the polyurethane. Moreover, imino group-containing phosphazenium salts are expensive. For these reasons, there is a demand for a method for producing a polyalkylene glycol that efficiently separates and recovers an imino group-containing phosphazenium salt from a crude polyalkylene glycol obtained by a polymerization reaction of an alkylene oxide.

  Therefore, as a result of intensive studies to solve the above problems, the present inventors have identified polyalkylene glycol after polymerization under specific conditions when producing polyalkylene glycol using an active species comprising an imino group-containing phosphazenium salt. After separating and recovering the imino group-containing phosphazenium compound after mixing with an inorganic acid, the imino group-containing phosphazenium salt can be separated and recovered efficiently by treating with a solid acid, and the polymerization active species and / or the polymerization The present inventors have found that the present invention provides a method for efficiently producing a polyalkylene glycol having a low residual amount of raw materials of active species, and thus completed the present invention.

That is, this invention relates to the manufacturing method of the polyalkylene glycol characterized by including at least the following (A)-(D) process.
(A) Process; The process of performing the polymerization reaction of alkylene oxide, after preparing the active seed | species for polyalkylene glycol manufacture with the imino group containing phosphazenium salt shown by following General formula (1), and an active hydrogen compound.

（ここで、Ｒ_１、Ｒ_２は、各々独立して、水素原子又は炭素数１〜２０の炭化水素基を表し、また、Ｒ_１とＲ_２が互いに結合して環構造を形成していても良いし、Ｒ_１同士又はＲ_２同士が互いに結合して環構造を形成していても良い。Ｘ⁻は、ヒドロキシアニオン、アルコキシアニオン、カルボキシアニオン、炭素数２〜５のアルキルカルボキシアニオン、又は炭酸水素アニオンを表す。）
（Ｂ）工程；（Ａ）工程により得られたポリアルキレングリコール１００重量部に対して、０．５〜１２重量部の水性媒体と、（Ａ）工程で用いたイミノ含有ホスファゼニウム塩１モルに対して０．５モル以上３．５モル未満の２価以上の無機酸とを混合する工程。
（Ｃ）工程；（Ｂ）工程で得られた混合物から水性媒体を除去し、イミノ基含有ホスファゼニウム化合物を析出し、イミノ基含有ホスファゼニウム化合物を分離する工程。
（Ｄ）工程；（Ｃ）工程で得られたポリアルキレングリコールに固体酸を接触させた後、固体酸を分離する工程。

(Here, R ₁ and R ₂ each independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and R ₁ and R ₂ are bonded to each other to form a ring structure. R ₁ or R ₂ may be bonded to each other to form a ring structure, and X ⁻ represents a hydroxy anion, an alkoxy anion, a carboxy anion, an alkyl carboxy anion having 2 to 5 carbon atoms, or Represents hydrogen carbonate anion.)
(B) step; with respect to 100 parts by weight of the polyalkylene glycol obtained in step (A), 0.5 to 12 parts by weight of an aqueous medium, and 1 mole of imino-containing phosphazenium salt used in step (A) A step of mixing an inorganic acid having a valence of 0.5 to 3.5 with a divalent or higher valent acid.
(C) Process; The process of removing an aqueous medium from the mixture obtained at the (B) process, depositing an imino group containing phosphazenium compound, and isolate | separating an imino group containing phosphazenium compound.
(D) Process; The process of isolate | separating a solid acid, after making a solid acid contact the polyalkylene glycol obtained at the (C) process.

  The present invention will be described in detail below.

  The present invention is capable of efficiently separating and recovering an imino group-containing phosphazenium salt through at least the steps (A) to (D) described above, and the remaining amount of the polymerization active species and / or raw materials of the polymerization active species. The present invention relates to a method for efficiently producing a polyalkylene glycol having a low viscosity.

  The step (A) is a step of producing a polyalkylene glycol by carrying out a polymerization reaction of an alkylene oxide. The active species for producing polyalkylene glycol at that time is prepared from an imino group-containing phosphazenium salt represented by the above general formula (1) and an active hydrogen-containing compound.

In the imino group-containing phosphazenium salt represented by the general formula (1), R ₁ and R ₂ are each independently a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and constitute R ₁ and R ₂ . Examples of the hydrocarbon group having 1 to 20 carbon atoms include methyl group, ethyl group, vinyl group, n-propyl group, isopropyl group, cyclopropyl group, allyl group, n-butyl group, isobutyl group, t-butyl group, Cyclobutyl group, n-pentyl group, neopentyl group, cyclopentyl group, n-hexyl group, cyclohexyl group, phenyl group, heptyl group, cycloheptyl group, octyl group, cyclooctyl group, nonyl group, cyclononyl group, decyl group, cyclodecyl group , Undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octyl Decyl group, mention may be made of a nonadecyl group, and the like. R ₁ and R ₂ may be bonded to each other to form a ring structure. When R ₁ and R ₂ are bonded to each other to form a ring structure, for example, pyrrolidinyl group, pyrrolyl group, piperidinyl group , Indolyl group, isoindolyl group and the like. Furthermore, R ₁ or R ₂ may be bonded to each other to form a ring structure, and R ₁ or R ₂ may be bonded to each other to form a ring structure. In the case where the substituents in the above form an alkylene group such as an ethylene group, a propylene group, and a butylene group, and the other substituents are bonded to each other to form a ring structure. As R ₁ and R ₂ , a methyl group, an ethyl group, and an isopropyl group are preferable because guanidines as raw materials are easily available.

In the imino group-containing phosphazenium salt represented by the general formula (1), X ⁻ represents a hydroxy anion, an alkoxy anion, a carboxy anion, an alkyl carboxy anion having 2 to 5 carbon atoms, or a hydrogen carbonate anion, and constitutes X ⁻ . Examples of the alkoxy anion include a methoxy anion, an ethoxy anion, an n-propoxy anion, an isopropoxy anion, an n-butoxy anion, an isobutoxy anion, a t-butoxy anion, and the like. For example, acetoxy anion, ethyl carboxy anion, n-propyl carboxy anion, isopropyl carboxy anion, n-butyl carboxy anion, isobutyl carboxy anion, t-butyl carboxy anion And the like. Among them, strong basic of the imino group-containing phosphazenium salt, since the polyalkylene glycol producing active species of the polymerization activity obtained is high, X ^- as a hydroxy anion are preferred.

  The imino group-containing phosphazenium salt represented by the general formula (1) can be obtained by any method. For example, an imino group-containing phosphazenium chloride salt, an imino group-containing phosphazenium iodide salt, or an imino group-containing phosphazenium. Examples of the method include ion exchange of a bromide salt using a basic compound or an ion exchange resin. Examples of the basic compound include alkali metal or alkaline earth metal hydroxide, alkali metal or alkaline earth metal. Alkoxides, alkali metal salts or alkaline earth metal salts of carboxylic acids, alkali metal or alkaline earth metal hydrogen carbonates, and the like can be mentioned. Among them, they are easily available, have strong basicity, and facilitate ion exchange. Therefore, an alkali metal or alkaline earth metal hydroxide is preferable, Sodium oxide, potassium hydroxide is particularly preferred.

  In addition, as a method for producing an imino group-containing phosphazenium chloride salt, an imino group-containing phosphazenium bromide salt or an imino group-containing phosphazenium iodide salt, for example, phosphorus pentachloride and a guanidine represented by the following general formula (2) are used. The method of reacting can be mentioned.

（ここで、Ｒ_１及びＲ_２は、上記一般式（１）中のＲ_１及びＲ_２と同じ定義である。）
そして、一般式（１）に示されるイミノ基含有ホスファゼニウム塩としては、例えばテトラキス（テトラメチルグアニジノ）ホスファゼニウムヒドロキシド、テトラキス（テトラメチルグアニジノ）ホスファゼニウムメトキシド、テトラキス（テトラメチルグアニジノ）ホスファゼニウムエトキシド、テトラキス（テトラメチルグアニジノ）ホスファゼニウムカルボキシド、テトラキス（テトラエチルグアニジノ）ホスファゼニウムヒドロキシド、テトラキス（テトラエチルグアニジノ）ホスファゼニウムメトキシド、テトラキス（テトラエチルグアニジノ）ホスファゼニウムエトキシド、テトラキス（テトラエチルグアニジノ）ホスファゼニウムカルボキシド等を例示でき、なかでも、容易に製造でき、アルキレンオキシドの重合反応において高い活性を有する活性種を提供できることから、テトラキス（テトラメチルグアニジノ）ホスファゼニウムヒドロキシドが好ましい。

(Wherein, _{R 1} and _{R 2} are the same definition as _{R 1} and _{R 2} in formula (1).)
Examples of the imino group-containing phosphazenium salt represented by the general formula (1) include tetrakis (tetramethylguanidino) phosphazenium hydroxide, tetrakis (tetramethylguanidino) phosphazenium methoxide, tetrakis (tetramethylguanidino). ) Phosphazenium ethoxide, tetrakis (tetramethylguanidino) phosphazenium carboxyoxide, tetrakis (tetraethylguanidino) phosphazenium hydroxide, tetrakis (tetraethylguanidino) phosphazenium methoxide, tetrakis (tetraethylguanidino) Examples thereof include phosphazenium ethoxide and tetrakis (tetraethylguanidino) phosphazenium carboxyoxide. Among them, they can be easily produced, and are used in the polymerization reaction of alkylene oxide. Because it can provide an active species having high activity Te, tetrakis (tetramethylguanidino) phosphazenium hydroxide are preferred.

  In the step (A), the active hydrogen-containing compound used when preparing the active species for producing the polyalkylene glycol may be any compound having an active hydrogen group in the molecule. An acid compound, a phenol compound, a thiol compound, etc. can be mentioned, More specifically, for example, water, ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4- Hydroxy compounds such as butanediol, 1,6-hexanediol, glycerin, trimethylolpropane, hexanetriol, pentaerythritol, diglycerin, sorbitol, sucrose, glucose; ethylenediamine, N, N′-dimethylethylenediamine, Perijin, amine compounds such as piperazine; benzoic acid, carboxylic acid compounds such as adipic acid; 2-naphthol, phenol compounds such as bisphenol; ethanedithiol, can be exemplified thiol compounds such as butane dithiol. These can be appropriately selected according to the application. For example, when producing polyalkylene glycol for rigid foam, it is preferable to use, for example, pentaerythritol, sorbitol, sucrose, ethylenediamine, etc., and when producing polyalkylene glycol for flexible foam, for example, glycerin, Trimethylolpropane or the like is preferably used.

  Moreover, it is also possible to use the polyalkylene glycol which has a hydroxyl group as an active hydrogen containing compound, for example, polypropylene glycol, polypropylene glycol glycerol ether, etc. can be mentioned. The molecular weight of the polyalkylene glycol used in this case is not particularly limited, and among these, it is desirable that the polyalkylene glycol has a low viscosity, excellent fluidity, and easy handling.

  These active hydrogen-containing compounds may be used alone or in combination of several kinds.

In the step (A), the ratio of the imino group-containing phosphazenium salt represented by the general formula (1) and the active hydrogen-containing compound in preparing the active species for producing polyalkylene glycol is arbitrary, and among these, it is easier Since it becomes possible to produce a polyalkylene glycol having a high molecular weight, the imino group-containing phosphazenium salt represented by the general formula (1) 1 × 10 ⁻⁴ to 1 × 10 ⁻ per 1 mol of the active hydrogen compound. It is preferably used in ¹ mol, and particularly preferably in the range of 5 × 10 ^{−3 to} 5 × 10 ⁻² mol.

  In the step (A), the imino group-containing phosphazenium salt represented by the general formula (1) and the active hydrogen-containing compound are composed of an imino group-containing phosphazenium cation and an anion of the active hydrogen-containing compound. The active species for producing the polyalkylene glycol is prepared, and the preparation conditions at that time are arbitrary. In particular, since it is possible to prepare high-purity active species for producing polyalkylene glycol, it is desirable to efficiently remove the solvent and water as a by-product, particularly at 60 ° C. under reduced pressure of 1.3 kPa or less. It is preferable to prepare at the above temperature.

  Examples of the alkylene oxide used in the step (A) include epoxy compounds such as ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, and cyclohexene oxide. Among these, ethylene oxide, propylene oxide, 1,2-butylene oxide or styrene oxide is preferable, and ethylene oxide and propylene oxide are more preferable. Moreover, this alkylene oxide may be used independently and may use 2 or more types together. When two or more types of alkylene oxide are used in combination, the combined use of propylene oxide and ethylene oxide is particularly preferable. When propylene oxide and ethylene oxide are used in combination, for example, a method of simultaneously adding propylene oxide and ethylene oxide, a method of adding ethylene oxide next to propylene oxide, or a method of repeatedly adding propylene oxide, ethylene oxide and propylene oxide, etc. Can take. Among these, the method of adding ethylene oxide after the polymerization reaction of propylene oxide and further polymerizing is preferable.

  And the reaction temperature and reaction pressure in the case of the polymerization reaction of alkylene oxide in the step (A) can be arbitrarily set. Among these, from the viewpoint of polymerization efficiency and productivity, the reaction temperature is preferably in the range of 40 to 130 ° C, particularly preferably in the range of 80 to 120 ° C. Similarly, the reaction pressure is preferably 0.05 to 1.0 MPa, particularly preferably 0.1 to 0.6 MPa.

  A polyalkylene glycol can be obtained by the step (A). The polyalkylene glycol is a crude polyalkylene glycol, and an imino group-containing phosphazenium salt represented by the general formula (1), an active species for producing a polyalkylene glycol is selected. Contains a large amount.

  The step (B) in the present invention comprises 0.5 to 10 parts by weight of an aqueous medium with respect to 100 parts by weight of the polyalkylene glycol obtained in the step (A) and the general formula (A) used in the step (A). This is a step of mixing 0.5 mol or more and less than 3.5 mol of a divalent or higher inorganic acid with respect to 1 mol of the imino group-containing phosphazenium salt represented by 1). By this mixing step, the neutralization reaction of the active species for producing polyalkylene glycol contained in the polyalkylene glycol and the imino group-containing phosphazenium salt proceeds to become an imino group-containing phosphazenium compound that is insoluble in the polyalkylene glycol. .

  Examples of the divalent or higher inorganic acid include phosphoric acid, phosphorous acid, diphosphoric acid, carbonic acid, sulfuric acid, thiosulfuric acid, boric acid and aqueous solutions thereof. Among them, the neutralization reaction proceeds efficiently. In addition, since the imino group-containing phosphazenium compound to be produced is highly insoluble in polyalkylene glycol and has excellent precipitation / recovery efficiency, it is preferably phosphoric acid and / or sulfuric acid or an aqueous solution thereof, particularly in the step (D) described later. Since it becomes an imino group-containing phosphazenium compound having excellent adsorptivity to a solid acid, phosphoric acid and an aqueous solution thereof are preferable. Here, when a monovalent inorganic acid or organic acid is used, the neutralization reaction does not proceed well, the imino group-containing phosphazenium compound produced by the neutralization reaction is soluble in polyalkylene glycol, etc. Precipitation / recovery as a group-containing phosphazenium compound does not proceed well.

  The added amount of the divalent or higher inorganic acid is 0.5 mol or more and less than 3.5 mol with respect to 1 mol of the imino group-containing phosphazenium salt represented by the general formula (1) used in the step (A). In particular, efficient neutralization is possible, and the precipitation / recovery efficiency of the imino group-containing phosphazenium compound is excellent. Therefore, the amount is preferably 0.5 mol or more and 2.5 mol or less. Here, when the addition amount of the divalent or higher valent inorganic acid is less than 0.5 mol, neutralization of the imino group-containing phosphazenium salt becomes insufficient, and precipitation of the imino group-containing phosphazenium compound becomes difficult. On the other hand, when the amount of divalent or higher inorganic acid used is 3.5 mol or more, it is difficult to precipitate the imino group-containing phosphazenium compound. Even if the imino group-containing phosphazenium compound can be precipitated, it is very fine. When the polyalkylene glycol is used as a raw material for polyurethane, the urethanization reaction is adversely affected and the quality of the polyurethane is poor. It has the problem of becoming.

  In the step (B), 0.5 to 12 parts by weight of an aqueous medium, preferably 3 to 7 parts by weight of an aqueous medium is mixed with 100 parts by weight of the polyalkylene glycol obtained in the step (A). Is. Here, examples of the aqueous medium include water, distilled water, ion-exchanged water, industrial water, and drinking water. The aqueous medium may contain some organic solvent. And when an aqueous medium is less than 0.5 weight part, the efficiency of neutralization reaction falls and precipitation and collection | recovery as an imino group containing phosphazenium compound do not advance well. On the other hand, when the amount of the aqueous medium exceeds 12 parts by weight, it takes a long time to remove the aqueous medium, which not only decreases the efficiency but also may adversely affect the polyalkylene glycol.

  The reaction conditions in the step (B) are arbitrary, and among them, the reaction proceeds more efficiently. Therefore, the reaction temperature is preferably 60 to 110 ° C, particularly preferably 70 to 95 ° C. The reaction time is preferably 1 to 4 hours.

  The step (C) in the present invention is a step of removing the aqueous medium from the mixture obtained in the step (B) and separating the precipitated imino group-containing phosphazenium compound and polyalkylene glycol, and the imino group-containing phosphazenium compound. It is a process to collect.

  In the step (C), the aqueous medium is removed from the mixture obtained in the step (B) to precipitate an imino group-containing phosphazenium compound that is insoluble in polyalkylene glycol. As a removal method, a generally used method can be applied, and among them, it is preferable to perform dehydration under reduced pressure because efficient removal is possible. As an aqueous medium in that case, what was illustrated to the said (B) process can be mentioned, Furthermore, the produced | generated water in the case of a neutralization reaction can also be mentioned. Further, the content of the aqueous medium in the polyalkylene glycol after the removal of the aqueous medium may be any as long as the subsequent precipitation and separation of the imino group-containing phosphazenium compound is possible, and among them, more efficient separation is possible. Since it becomes possible, it is preferable that it is 2500 ppm or less, and it is especially preferable that it is 1000 ppm or less.

  As the method for removing the imino group-containing phosphazenium compound in the step (C), any method can be used as long as the imino group-containing phosphazenium compound precipitated in the polyalkylene glycol can be separated and recovered. Methods such as vacuum filtration, pressure filtration, centrifugal filtration, decantation, and centrifugal decantation can be used. In this case, a filter aid such as diatomaceous earth or cellulite can be used.

  The polyalkylene glycol obtained in the step (C) is obtained by separating the imino group-containing phosphazenium compound liberated in the step (B), but is still a crude polyalkylene glycol containing some imino group-containing phosphazenium compound. I can say that. The liberated imino group-containing phosphazenium compound mentioned here is produced only by the step (B) (neutralization reaction), and is not necessarily an imino group-containing phosphazenium salt and / or polyalkylene glycol represented by the general formula (1). It is not consistent with the active species for production.

  The step (D) in the present invention is a step of separating the solid acid after bringing the solid acid into contact with the polyalkylene glycol obtained in the step (C).

  In the step (D), the polyalkylene glycol obtained in the step (C) is brought into contact with the solid acid to adsorb the imino group-containing phosphazenium compound remaining in the polyalkylene glycol to the solid acid, In this process, the solid acid is separated to form a polyalkylene glycol having a lower residual amount of the imino group-containing phosphazenium compound.

In this case, the solid acid is used to efficiently remove the imino group-containing phosphazenium compound remaining in the polyalkylene glycol, and has a specific surface area of 300 to 1200 m ² / g and an average pore diameter of 50 to Solid acids that are 100 liters are preferred. As the solid acid, any solid acid can be used as long as it belongs to the category of solid acids. Examples thereof include synthetic aluminum silicate, synthetic magnesium silicate, activated clay, zeolite, and acid clay. Particularly preferred solid acids are aluminum silicate, magnesium silicate, and mixtures thereof. Such solid acids are commercially available (trade name) KW-600BUP-S (manufactured by Kyowa Chemical Industry Co., Ltd.), (trade name) KW-700PEL (manufactured by Kyowa Chemical Industry Co., Ltd.), (trade name) ) KW-700SEN-S (manufactured by Kyowa Chemical Industry Co., Ltd.), etc. are available.

  Here, there is no restriction | limiting in the usage-amount of this solid acid, and since an efficient process is attained among them, 0.1-3 weight part is preferable with respect to 100 weight part of polyalkylene glycol, and especially 0.5. It is preferable that it is -2 weight part.

  The method for contacting the polyalkylene glycol and the solid acid in the step (D) is arbitrary, and the temperature at that time is, for example, 60 to 110 ° C, preferably 70 to 100 ° C. In addition, examples of the contact time include 0.5 to 10 hours, preferably 1 to 3 hours.

  When contacting the polyalkylene glycol and the solid acid in the step (D), an aqueous medium may coexist. In this case, the amount of the aqueous medium is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the polyalkylene glycol. When an aqueous medium is used, the polyalkylene glycol and the solid acid may be contacted and dehydrated under reduced pressure, or the solid acid may be separated and then dehydrated under reduced pressure. There is no restriction | limiting in particular in vacuum dehydration conditions at this time, For example, it can carry out at 80-120 degreeC and 0.01-5 kPa.

  In the step (D), the method for separating the polyalkylene glycol and the solid acid is arbitrary, and for example, methods such as vacuum filtration, pressure filtration, centrifugal filtration, decantation, and centrifugal decantation can be used. . In this case, a filter aid such as diatomaceous earth or cellulite can be used.

  In the step (D), it is preferable that an antioxidant is present in order to suppress the generation of peroxides, aldehydes, and the like when the polyalkylene glycol and the solid acid are brought into contact with each other. The addition amount is preferably 100 to 2000 ppm, particularly 600 to 1000 ppm, based on 100 parts by weight of the polyalkylene glycol. Examples of the antioxidant at that time include phenolic compound antioxidants, amine compound antioxidants, phosphite ester compound antioxidants, and the like. As the inhibitor, 2,6-di-tert-butyl-4-methylphenol (hereinafter sometimes abbreviated as BHT), 2-tert-butyl-4-methoxyphenol (hereinafter also abbreviated as BHA). 6) -tert-butyl-2,4-methylphenol, 2,6-di-tert-butylphenol, 2-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-ethyl Phenol and the like. Examples of amine compound antioxidants include n-butyl-p-aminophenol, 4,4-dimethyldiphenylamine, 4,4-dioctyldiphenylamine (hereinafter abbreviated as DOA), 4,4-bis-α, α. Examples include '-dimethylbenzylphenylamine. These antioxidants may be used alone or in combination of two or more. Among these antioxidants, BHT, BHA, and DOA are preferable.

  The method for producing a polyalkylene glycol of the present invention includes the above steps (A) to (D), and any additional steps are included without departing from the present invention as long as these steps are performed. Is also possible.

  According to the production method of the present invention, it is possible to efficiently recover an imino group-containing phosphazenium compound, and it is possible to efficiently produce a polyalkylene glycol having a low residual amount of an imino group-containing phosphazenium compound. It becomes. The imino group-containing phosphazenium compound remaining in the polyalkylene glycol has a high possibility of adversely affecting the reaction with the polyisocyanate compound when used as a polyurethane material. Preferably, the polyalkylene glycol obtained by the production method of the present invention has a residual amount of the imino group-containing phosphazenium compound of 50 ppm or less, particularly 20 ppm or less, more preferably 10 ppm or less. It is preferable that

  Moreover, since the polyalkylene glycol obtained by the production method of the present invention reacts with a polyisocyanate compound to form a polyalkylene glycol which is less colored when made into a polyurethane and can be easily controlled, the pH is 5.5 to 8.0. The polyalkylene glycol is preferably used. In addition, pH here is measured as an apparent pH with a 2-propanol solution (2-propanol / water volume ratio = 100/60) at room temperature using, for example, a pH meter (saturated calomel electrode is a sleep type). Can do.

  Further, the polyalkylene glycol obtained by the production method of the present invention preferably has a hydroxyl value of 5 to 500 mgKOH / g, particularly 10 to 100 mgKOH / g, and more preferably 15 to 50 mgKOH / g. Further, the total unsaturation is preferably 0.05 meq./g or less, and in addition, the molecular weight distribution is preferably 1.1 or less. Moreover, such a polyalkylene glycol can be produced efficiently and easily.

  The polyalkylene glycol obtained by the method for producing polyalkylene glycol of the present invention is useful for polyurethane raw materials, polyester raw materials, surfactant raw materials, lubricant raw materials and the like. In particular, by reacting with various isocyanate compounds, rigid foam used for heat insulating materials, etc., flexible foam used for automobile seats / cushions, bedding, etc., adhesives, paints, sealing materials, thermosetting elastomers, heat Development to plastic elastomer is expected.

  According to the present invention, it has become possible to efficiently produce a polyalkylene glycol having excellent quality expected as a raw material for polyurethane and having a low residual amount of polymerization active species.

  Examples of the present invention will be shown below to clarify aspects of the present invention, but the present invention is not limited to these examples. In addition, the obtained polyalkylene glycol was evaluated by the method shown below.

~ Measurement of residual imino group-containing phosphazenium compounds in polyalkylene glycol ~
The obtained polyalkylene glycol was weighed into a volumetric flask, diluted with cyclohexanone, and then heated using a trace total nitrogen analyzer (Mitsubishi Chemical, (trade name) TN-100), heater temperature T1: 600 ° C., T2 The nitrogen concentration (referred to as c) of the solution was measured under the conditions of: 800 ° C., gas flow rate O ₂ : 500 ml / min, O ₃ : 200 ml / min. From the nitrogen concentration at this time, the concentration of the imino group-containing phosphazenium compound in the solution was calculated from the following formula.

Residual amount of imino group-containing phosphazenium compound in polyalkylene glycol (% by weight) = c / 0.33
-PH measurement of polyalkylene glycol-
According to the measurement method described in JIS K 1557, the pH of the polyalkylene glycol was measured using a pH meter (saturated calomel electrode is a sleep type) and a 2-propanol aqueous solution at room temperature (2-propanol / water volume ratio = 100/60). The apparent pH at was measured.

-Measurement of hydroxyl value and total unsaturation of polyalkylene glycol-
It measured based on the measuring method of JISK1557.

Synthesis Example 1 (Preparation of imino group-containing phosphazenium salt)
-Synthesis of imino group-containing phosphazenium chloride salts-
A 500 ml four-necked flask equipped with a stirring blade was placed in a nitrogen atmosphere, 11.5 g (55 mmol) of phosphorus pentachloride and 225 ml of toluene were added, and the mixture was stirred at -20 ° C. While maintaining the inside of the flask at −20 ° C., 65 g (550 mmol) of tetramethylguanidine was added dropwise, and stirring was continued at −20 ° C. for 1 hour. Furthermore, it heated up at 110 degreeC and stirred for 15 hours. The resulting white suspension was filtered to obtain a white solid as a filtrate. This white solid was dissolved in acetone and filtered to obtain a colorless transparent filtrate. The obtained filtrate was concentrated to obtain a target crude product of tetrakis (tetramethylguanidino) phosphazenium chloride as a white solid.

  The obtained crude product was subjected to liquid separation extraction with chloroform and water. The chloroform phase was concentrated to obtain 25.5 g (48.5 mmol; yield 88%) of the desired tetrakis (tetramethylguanidino) phosphazenium chloride as a white solid.

-Synthesis of imino group-containing phosphazenium salts-
Tetrakis (tetramethylguanidino) phosphazenium chloride 21 g (40 mmol) was added to a 300 ml Schlenk flask equipped with a magnetic rotator, and the inside of the flask was placed under a nitrogen atmosphere. Potassium hydroxide 2.2g (40mmol) and ethanol 80ml were added there, and it stirred at room temperature for 1 hour. The suspension containing the white solid obtained after completion of the reaction was filtered under reduced pressure using a funnel equipped with filter paper. The target tetrakis (tetramethylguanidino) phosphazenium hydroxide (imino group-containing phosphazenium salt in which R ₁ in the general formula (1) is a methyl group, R ₂ is a methyl group, and X ⁻ is a hydroxy anion on the filtrate side) ) Was obtained, and potassium chloride as a by-product salt was obtained on the filtrate side.

  To the resulting tetrakis (tetramethylguanidino) phosphazenium hydroxide-ethanol solution was added 80 ml of ion exchange water, the solvent was removed under reduced pressure, the solution was concentrated to 40 ml, and further 80 ml of ion exchange water was added. The solvent was removed, and the solution was concentrated to 40 ml to obtain an imino group-containing phosphazenium salt aqueous solution. The imino group-containing phosphazenium salt had a purity of 99.6% and an aqueous solution concentration of 50% by weight.

Example 1
(Process A)
In a 2 liter autoclave equipped with a stirring blade, 4.0 g of an imino group-containing phosphazenium salt aqueous solution (50 wt%; tetrakis (tetramethylguanidino) phosphazenium hydroxide) obtained in Synthesis Example 1 and an activated hydrogen compound 175 g (175 mmol) of trifunctional polyalkylene glycol (manufactured by Sanyo Chemical Industries, (trade name) Sannix GP-1000; hydroxyl value 160 mg KOH / g) was added, and the inside of the autoclave was placed in a nitrogen atmosphere, and the internal temperature was 80 ° C. Then, the solvent and by-product water were removed under a reduced pressure of 0.2 kPa to prepare an active species for producing polyalkylene glycol.

  Thereafter, the internal temperature was set to 90 ° C., and 880 g of propylene oxide was intermittently supplied so as to maintain the reaction pressure of 0.3 MPa or less, and the ring-opening polymerization reaction was performed for 8 hours while maintaining the internal temperature of 90 ° C. Next, after removing the residual propylene oxide under a reduced pressure of 0.2 kPa, 210 g of ethylene oxide was intermittently supplied so as to keep the reaction pressure at 0.4 MPa or less, and the internal temperature was maintained at 90 ° C. for 6 hours. A ring polymerization reaction was performed. The residual ethylene oxide was removed under a reduced pressure of 0.2 kPa to obtain 1200 g of a polypropylene glycol-polyethylene glycol block copolymer.

(Process B)
In a nitrogen atmosphere, ion-exchange water corresponding to 5% by weight with respect to the obtained polypropylene glycol-polyethylene glycol block copolymer, 1.1 mol with respect to 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide used. (In the form of a 3% by weight aqueous solution) was added (the water content at that time was 7 parts by weight with respect to 100 parts by weight of the polypropylene glycol-polyethylene glycol block copolymer), and 85 ° C. Then, a neutralization reaction was performed for 3 hours to obtain an imino group-containing phosphazenium compound.

(Process C)
After completion of the neutralization reaction, 750 ppm of 2,6-di-tert-butyl-4-methylphenol (antioxidant) is added to the polypropylene glycol-polyethylene glycol block copolymer, and dehydration is performed while raising the temperature and reducing the pressure. Finally, dehydration under reduced pressure was performed for 3 hours under the conditions of 120 ° C. and 5 kPa to precipitate an imino group-containing phosphazenium compound, and further, the pressure was changed from reduced pressure to atmospheric pressure with nitrogen. Then, pressure filtration was performed with 5A filter paper (manufactured by Advantech Toyo Co., Ltd., holding particles 7 μm) to separate and recover the imino group-containing phosphazenium compound.

  To 100 parts by weight of the recovered imino group-containing phosphazenium compound, 300 parts by weight of diethyl ether (special grade reagent manufactured by Wako Pure Chemical Industries) was added, washed, and dried. The recovery rate of the imino group-containing phosphazenium compound was as high as 71%.

(D process)
(C) Ion exchange water equivalent to 5 parts by weight with respect to 100 parts by weight of the polypropylene glycol-polyethylene glycol block copolymer separated in the step, synthetic aluminum silicate ((trade name) KW-700SEN-S; 1.5 parts by weight of Kyowa Chemical Industry Co., Ltd.) was added and stirred at 85 ° C. for 3 hours. Thereafter, dehydration was started while the temperature was increased and the pressure was reduced, and finally a vacuum dehydration operation was performed at 120 ° C. and 5 kPa for 3 hours. Separation operation of the polypropylene glycol-polyethylene glycol block copolymer A and the solid acid was performed by a filtration operation using a pressure filter.

  The resulting polypropylene glycol-polyethylene glycol block copolymer A had a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.025 meq. / G, the imino group-containing phosphazenium compound residual amount was 6 ppm, pH 6.8. The results are shown in Table 1.

Example 2
In the step (D) of Example 1, an imino group-containing product was prepared in the same manner as in Example 1 except that 0.5 part by weight of synthetic aluminum silicate was used instead of 1.5 parts by weight of synthetic aluminum silicate. The phosphazenium compound was recovered, and a polypropylene glycol-polyethylene glycol block copolymer B was produced. The recovery rate of the imino group-containing phosphazenium compound was as high as 71%. The results are shown in Table 1.

  The resulting polypropylene glycol-polyethylene glycol block copolymer B has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, the imino group-containing phosphazenium compound residual amount was 12 ppm and had a pH of 6.9. The results are shown in Table 1.

Example 3
Instead of using 1.1 mol of phosphoric acid per 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide in the step (B) of Example 1, tetrakis (tetramethylguanidino) phosphazenium hydroxy was used. The imino group-containing phosphazenium compound was recovered in the same manner as in Example 1 except that 2.1 mol of phosphoric acid was used per 1 mol of the catalyst, and a polypropylene glycol-polyethylene glycol block copolymer C was produced. . The recovery rate of the imino group-containing phosphazenium compound was as high as 60%. The results are shown in Table 1.

  The resulting polypropylene glycol-polyethylene glycol block copolymer C has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, the imino group-containing phosphazenium compound residual amount was 6.0 ppm, pH 6.9. The results are shown in Table 1.

Example 4
Instead of using 1.1 mol of phosphoric acid per 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide in the step (B) of Example 1, tetrakis (tetramethylguanidino) phosphazenium hydroxy was used. The imino group-containing phosphazenium compound was recovered in the same manner as in Example 1 except that 0.5 mol of phosphoric acid was used per 1 mol of the catalyst, and a polypropylene glycol-polyethylene glycol block copolymer D was produced. . The recovery rate of the imino group-containing phosphazenium compound was as high as 50%. The results are shown in Table 1.

  The resulting polypropylene glycol-polyethylene glycol block copolymer D had a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, the residual amount of the imino group-containing phosphazenium compound was 6.0 ppm, pH 7.2. The results are shown in Table 1.

Comparative Example 1
Instead of using 1.1 mol of phosphoric acid per 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide in the step (B) of Example 1, tetrakis (tetramethylguanidino) phosphazenium hydroxy was used. Polypropylene glycol-polyethylene glycol block copolymer E was produced in the same manner as in Example 1 except that 0.3 mol of phosphoric acid was used per 1 mol of the catalyst. Precipitation of the imino group-containing phosphazenium compound did not occur, and the imino group-containing phosphazenium compound could not be recovered.

  The resulting polypropylene glycol-polyethylene glycol block copolymer E had a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, pH 6.9, but the residual amount of the imino group-containing phosphazenium compound was as high as 150.0 ppm. The results are shown in Table 2.

Comparative Example 2
Instead of using 1.1 mol of phosphoric acid per 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide in the step (B) of Example 1, tetrakis (tetramethylguanidino) phosphazenium hydroxy was used. Polypropylene glycol-polyethylene glycol block copolymer F was produced in the same manner as in Example 1 except that 3.5 mol of phosphoric acid was used per 1 mol of the catalyst. Although the precipitation of the imino group-containing phosphazenium compound was observed, it was very fine and passed through the filter paper during pressure filtration, and the imino group-containing phosphazenium compound could not be recovered.

  The resulting polypropylene glycol-polyethylene glycol block copolymer F has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, pH 6.6, but the imino group-containing phosphazenium compound residual amount was as high as 250.0 ppm. The results are shown in Table 2.

Example 5
In the step (B) of Example 1, instead of using 1.1 mol of phosphoric acid (in the form of a 3% by weight aqueous solution) with respect to 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide, tetrakis ( Tetramethylguanidino) sulfuric acid (in the form of a 2 wt% aqueous solution) corresponding to 2.5 mol per mol of phosphazenium hydroxide, and in step (D), polypropylene glycol-polyethylene glycol block copolymer 100 wt. In contrast to 1.5 parts by weight of synthetic aluminum silicate as a solid acid, 100 parts by weight of a polypropylene glycol-polyethylene glycol block copolymer, and 2.0 parts by weight of synthetic aluminum silicate as a solid acid. Except that it was used, the imino group-containing photopolymer was prepared in the same manner as in Example 1. The Fazeniumu compound was collected, polypropylene glycol - was produced polyethylene glycol block copolymer G. The recovery rate of the imino group-containing phosphazenium compound was as high as 90%. The results are shown in Table 1.

  The resulting polypropylene glycol-polyethylene glycol block copolymer G has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, the amount of imino group-containing phosphazenium compound remaining was 12.0 ppm, pH 5.8. The results are shown in Table 1.

Comparative Example 3
In the step (B) of Example 1, instead of using 1.1 mol of phosphoric acid (in the form of a 3% by weight aqueous solution) with respect to 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide, tetrakis ( Tetramethylguanidino) sulfuric acid (in the form of a 2 wt% aqueous solution) corresponding to 3.5 mol per mol of phosphazenium hydroxide, and in step (D), 100 weight of polypropylene glycol-polyethylene glycol block copolymer In contrast to 1.5 parts by weight of synthetic aluminum silicate as a solid acid, 100 parts by weight of a polypropylene glycol-polyethylene glycol block copolymer, and 2.0 parts by weight of synthetic aluminum silicate as a solid acid. Except that it was used, the imino group-containing photopolymer was prepared in the same manner as in Example 1. The Fazeniumu compound was collected, polypropylene glycol - was produced polyethylene glycol block copolymer H. The recovery rate of the imino group-containing phosphazenium compound was as high as 80%. The results are shown in Table 2.

  The resulting polypropylene glycol-polyethylene glycol block copolymer H has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. However, the residual amount of the imino group-containing phosphazenium compound was 47.0 ppm and pH 4.0. The results are shown in Table 2.

Comparative Example 4
In the step (B) of Example 1, instead of using 1.1 mol of phosphoric acid (in the form of a 3% by weight aqueous solution) with respect to 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide, tetrakis ( Tetramethylguanidino) phosphazenium hydroxide 1 mol of hydrochloric acid (in the form of a 1 wt% aqueous solution) corresponding to 2.5 mol, and in step (D), polypropylene glycol-polyethylene glycol block copolymer 100 wt. In contrast to 1.5 parts by weight of synthetic aluminum silicate as a solid acid, 100 parts by weight of a polypropylene glycol-polyethylene glycol block copolymer, and 2.0 parts by weight of synthetic aluminum silicate as a solid acid. Polypropylene was prepared in the same manner as in Example 1 except that it was used. Recall - was produced polyethylene glycol block copolymer I. Precipitation of the imino group-containing phosphazenium compound did not occur, and the imino group-containing phosphazenium compound could not be recovered.

  The resulting polypropylene glycol-polyethylene glycol block copolymer I has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, pH 6.0, but the imino group-containing phosphazenium compound residual amount was as extremely high as 200.0 ppm. The results are shown in Table 2.

Comparative Example 5
In the step (B) of Example 1, instead of using 1.1 mol of phosphoric acid (in the form of a 3% by weight aqueous solution) with respect to 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide, tetrakis ( Tetramethylguanidino) phosphazenium hydroxide is used in an amount of 1.1 mol of oxalic acid (in the form of a 2 wt% aqueous solution), and in step (D), polypropylene glycol-polyethylene glycol block copolymer 100 is used. Instead of 1.5 parts by weight of synthetic aluminum silicate as a solid acid based on parts by weight, 2.0 parts by weight of synthetic aluminum silicate as a solid acid based on 100 parts by weight of a polypropylene glycol-polyethylene glycol block copolymer Polypropylene was prepared in the same manner as in Example 1 except that Glycol - was produced polyethylene glycol block copolymer J. Precipitation of the imino group-containing phosphazenium compound did not occur, and the imino group-containing phosphazenium compound could not be recovered.

  The resulting polypropylene glycol-polyethylene glycol block copolymer J had a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, pH 6.8, but the imino group-containing phosphazenium compound residual amount was as extremely high as 300.0 ppm. The results are shown in Table 2.

Comparative Example 6
In the step (B) of Example 1, instead of using 1.1 mol of phosphoric acid (in the form of a 3% by weight aqueous solution) with respect to 1 mol of tetrakis (tetramethylguanidino) phosphazenium hydroxide, tetrakis ( Tetramethylguanidino) phosphazenium hydroxide is used in a step (D) using adipic acid (in the form of a 2 wt% aqueous solution) corresponding to 2.1 mol, and in step (D), polypropylene glycol-polyethylene glycol block copolymer 100 Instead of 1.5 parts by weight of synthetic aluminum silicate as a solid acid based on parts by weight, 2.0 parts by weight of synthetic aluminum silicate as a solid acid based on 100 parts by weight of a polypropylene glycol-polyethylene glycol block copolymer In the same manner as in Example 1, except that Glycol - was produced polyethylene glycol block copolymer K. Precipitation of the imino group-containing phosphazenium compound did not occur, and the imino group-containing phosphazenium compound could not be recovered.

  The resulting polypropylene glycol-polyethylene glycol block copolymer K has a hydroxyl value of 24 mgKOH / g and an unsaturation of 0.024 meq. / G, pH 7.0, but the residual amount of the imino group-containing phosphazenium compound was as high as 350.0 ppm. The results are shown in Table 2.

  According to the production method of the present invention, an expensive imino group-containing phosphazenium salt can be efficiently recovered, and the resulting polyalkylene glycol can provide a polyurethane product having excellent urethanization reactivity and excellent quality. At the same time, it is possible to efficiently supply a polyalkylene glycol having a low residual amount of an imino group-containing phosphazenium salt and excellent in pH characteristics, and the industrial applicability is extremely high.

Claims (7)

A process for producing a polyalkylene glycol, comprising at least the following steps (A) to (D).
(A) Process; The process of performing the polymerization reaction of alkylene oxide, after preparing the active seed | species for polyalkylene glycol manufacture with the imino group containing phosphazenium salt shown by following General formula (1), and an active hydrogen compound.

(Here, R ₁ and R ₂ each independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and R ₁ and R ₂ are bonded to each other to form a ring structure. R ₁ or R ₂ may be bonded to each other to form a ring structure, and X − represents a hydroxy anion, an alkoxy anion, a carboxy anion, an alkyl carboxy anion having 2 to 5 carbon atoms, or Represents hydrogen carbonate anion.)
(B) step; with respect to 100 parts by weight of the polyalkylene glycol obtained in step (A), 0.5 to 12 parts by weight of an aqueous medium, and 1 mole of imino-containing phosphazenium salt used in step (A) A step of mixing an inorganic acid having a valence of 0.5 or more and less than 3.5 mol with a valence of 2 or more.
(C) Process; The process of removing an aqueous medium from the mixture obtained at the (B) process, depositing an imino group containing phosphazenium compound, and isolate | separating an imino group containing phosphazenium compound.
(D) Process; The process of isolate | separating a solid acid, after making a solid acid contact the polyalkylene glycol obtained at the (C) process. The polymerization reaction of alkylene oxide in the step (A) is a method for producing a polypropylene glycol-polyethylene glycol block copolymer in which ethylene oxide is further polymerized after the polymerization reaction of propylene oxide. A method for producing polyalkylene glycol. The method for producing a polyalkylene glycol according to claim 1 or 2, wherein the divalent or higher-valent inorganic acid in step (B) is phosphoric acid and / or sulfuric acid. The method for producing a polyalkylene glycol according to any one of claims 1 to 3, wherein the solid acid in step (D) is synthetic aluminum silicate and / or synthetic magnesium silicate. In the step (D), 0.1 to 3 parts by weight of a solid acid is brought into contact with 100 parts by weight of the polyalkylene glycol, The production of the polyalkylene glycol according to any one of claims 1 to 4 Method. The process for producing a polyalkylene glycol according to any one of claims 1 to 5, wherein a polyalkylene glycol having an imino group-containing phosphazenium compound residual amount of 50 ppm or less and a pH of 5.5 to 8.0 is produced . The pH is measured as an apparent pH with a 2-propanol solution (2-propanol / water volume ratio = 100/60) at room temperature using a pH meter. ] The method for producing a polyalkylene glycol according to any one of claims 1 to 6, wherein a polyalkylene glycol having a hydroxyl value of 10 to 100 mgKOH / g and a total degree of unsaturation of 0.05 meq / g or less is produced.