JP2014185116A - Production method of glycolide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of glycolide, with which high-purity glycolide is obtained without lowering a rate of glycolide generation and with only a small amount of a by-product.SOLUTION: A production method of glycolide includes respective steps of: I. a step 1 to heat a mixture containing a glycolic acid oligomer and a polar organic solvent to a depolymerization temperature of the glycolic acid oligomer under normal pressure or reduced pressure; II. a step 2 to conduct depolymerization of the glycolic acid oligomer by further continuing heating at the temperature, and to co-distill the glycolide generated by depolymerization from the depolymerization reaction system containing the mixture together with the polar organic solvent to the outside of the depolymerization reaction system; and III. a step 3 to recover glycolide from the co-distillate, in which a catalyst is added in the step 2.

Description

  The present invention relates to a method for producing glycolide, which is a dimer cyclic ester of glycolic acid, and more particularly to a method for producing high-purity glycolide in which a glycolic acid oligomer is heated and depolymerized.

  Polyglycolic acid, which is a polymer of glycolic acid, is a resin material excellent in biodegradability, hydrolyzability, gas barrier properties, strength, and the like, and has been attempted to be used in a wide range of technical fields.

  Polyglycolic acid is a resin having a repeating unit having a structure formed by dehydration polycondensation of glycolic acid. In order to obtain polyglycolic acid with a high degree of polymerization that has strength, durability, melt processability, and an appropriate degradation rate in the natural environment or in vivo, dehydration is performed using glycolic acid (that is, α-hydroxyacetic acid) as a starting material. Rather than the polycondensation method, starting from glycolide, which is a dimer cyclic ester of glycolic acid having a cyclic dimer structure in which two molecules of water are eliminated from two molecules of glycolic acid, the glycolide is opened. A polymerization method is preferred.

  However, even if glycolic acid is subjected to a dehydration reaction, glycolide, which is a dimer cyclic ester, cannot be synthesized, and only a glycolic acid polymer having a low polymerization degree is obtained.

  Therefore, as a method for producing glycolide, a method of depolymerizing a glycolic acid oligomer which is a glycolic acid polymer having a low polymerization degree is known. That is, the following reaction formula (1)

Then, glycolic acid is polycondensed to synthesize glycolic acid oligomers. Next, the following reaction formula (2)

Thus, glycolic acid oligomers are depolymerized to synthesize glycolide, which is a dimer cyclic ester of glycolic acid. Subsequently, when ring-opening polymerization of glycolide, the following reaction formula (3)

According to this, polyglycolic acid can be produced.

  Various proposals have been made on a method for synthesizing glycolide, which is a dimer cyclic ester of glycolic acid (hereinafter sometimes simply referred to as “cyclic ester”) by depolymerization of a glycolic acid oligomer. For example, a solution phase depolymerization method has been proposed as a method suitable for mass production of glycolide. In solution phase depolymerization, a mixture containing glycolic acid oligomer and a high-boiling polar organic solvent is heated to form a solution phase of glycolic acid oligomer, and heating is continued in that state to perform depolymerization. Is the method. When it is necessary to increase the solubility of the glycolic acid oligomer in the high-boiling polar organic solvent, a solubilizer is contained in the mixture.

  Patent Document 1 discloses that α-hydroxycarboxylic acid oligomers such as glycolic acid oligomers are dissolved by heating in a high-boiling polar organic solvent, and heating is continued in this state for depolymerization, and the resulting cyclic ester is A method for producing a cyclic ester is disclosed in which a distillate is distilled together with a boiling-point polar organic solvent, and a cyclic ester such as glycolide is recovered from the distillate. Patent Document 2 discloses a mixture containing an aliphatic polyester (glycolic acid oligomer) such as low molecular weight polyglycolic acid and a specific polyalkylene glycol ether (belonging to a polar organic solvent). Heating to a temperature at which depolymerization occurs, depolymerizing the aliphatic polyester in a uniform solution phase, distilling the cyclic ester produced by the depolymerization together with the polyalkylene glycol ether, from the distillate A method for producing a cyclic ester for recovering a cyclic ester such as glycolide is disclosed. According to the methods disclosed in Patent Documents 1 and 2, in addition to enabling mass production of cyclic esters such as glycolide, the depolymerization reaction can be carried out stably.

  In Patent Document 3, production of a cyclic dimer ester which is obtained by adding an oligomer of α-hydroxycarboxylic acid or an ester or salt thereof to a solvent to which a catalyst is added, and stirring and stirring under heating at a pressure higher than atmospheric pressure. A method is disclosed. Patent Document 3 further includes antimony, zinc or calcium oxides, halides or carboxylates as catalysts, and, as a specific example, an L-lactic acid oligomer is used as an α-hydroxycarboxylic acid oligomer, and oxidation is performed. An example using zinc (catalyst) and dodecane (solvent) is shown.

  On the other hand, in Patent Documents 1 and 2 mentioned above, it is usually unnecessary to use a catalyst for depolymerization (such as a tin compound or an antimony compound), but within the range that does not harm the solution phase depolymerization method, It is disclosed that the use of a catalyst is acceptable.

  Patent Document 4 discloses that by depolymerizing a mixture containing a glycolic acid oligomer, a high-boiling polar organic solvent, and a tin compound that is a catalyst, glycolide can be obtained with high purity and the yield is greatly increased. Has been. In Patent Document 4, as a specific example, a glycolic acid oligomer, a high-boiling polar organic solvent, a solubilizing agent and a catalyst are charged in a flask and heated to 230 ° C. to prepare a uniform solution. The purity and distillation of glycolide in the comparative example in which the depolymerization reaction was carried out in the same manner as in the example except that the purity and distillation amount of glycolide in the example in which the depolymerization reaction was performed were not used. It is disclosed that it is higher or higher than the amount.

  Glycolide, which is a starting material for producing polyglycolic acid, has a higher purity, and is widely recognized for its excellent degradability (biodegradability and hydrolyzability), gas barrier properties and strength. Expectations for getting more efficient are growing. Specifically, in the glycolide production method for depolymerizing glycolic acid oligomers, if a glycolide with a small amount of by-products can be obtained without reducing the production rate of glycolide, the productivity of glycolide is improved. In addition, since purification by recrystallization or the like of the obtained glycolide can be omitted, it is expected that the usable range of polyglycolic acid formed from glycolide will be further expanded, and a method for producing such glycolide is desired. It was.

JP-A-9-328481 International Publication No. 2002/014303 French Patent Invention No. 2692263 International Publication No. 2011/088902

  The subject of this invention is providing the manufacturing method of glycolide which depolymerizes the glycolic acid oligomer which can obtain the highly purified glycolide with few production amounts of a by-product, without reducing the production rate of glycolide. .

  The inventors have studied to solve the above-mentioned object, and in the glycolic acid oligomer depolymerization step, by adjusting the timing of addition of the catalyst, the productivity of glycolide is improved and high purity glycolide is added. The present invention has been completed by finding what can be obtained.

That is, according to the present invention, I.I. Heating the mixture containing the glycolic acid oligomer and the polar organic solvent to a temperature at which the glycolic acid oligomer is depolymerized under normal pressure or reduced pressure;
II. Further heating is continued at the above temperature to depolymerize the glycolic acid oligomer, and glycolide produced by depolymerization from the depolymerization reaction system containing the mixture is co-distilled with the polar organic solvent outside the depolymerization reaction system. Step 2; and III. Recovering glycolide from the co-distillate 3;
Each process, and
In step 2, a method for producing glycolide is provided, which comprises adding a catalyst.

Moreover, according to this invention, the manufacturing method of the glycolide of the following (1)-(5) is provided as an embodiment.
(1) The process for producing glycolide as described above, wherein the catalyst is added after the time point when the production rate of glycolide is reduced to 90% or less of the initial production rate in Step 2.
(2) The polar organic solvent is represented by the following formula X—O— (R—O—) _p —Y
(In the formula, R represents a methylene group or a linear or branched alkylene group having 2 to 8 carbon atoms. X represents a hydrocarbon group. Y represents an alkyl group or aryl having 2 to 20 carbon atoms. P represents an integer of 1 or more, and when p is 2 or more, a plurality of R may be the same or different.
The manufacturing method of the said glycolide which is polyalkylene glycol diether represented by these.
(3) The manufacturing method of the said glycolide whose catalyst is a tin compound.
(4) The method for producing glycolide as described above, wherein the mixture used in Step 1 further contains a solubilizer.
(5) The method for producing glycolide as described above, wherein the solubilizer is a polyalkylene glycol monoether having a boiling point of 180 ° C. or higher.

According to the present invention, I.V. Heating the mixture containing the glycolic acid oligomer and the polar organic solvent to a temperature at which the glycolic acid oligomer is depolymerized under normal pressure or reduced pressure;
II. Further heating is continued at the above temperature to depolymerize the glycolic acid oligomer, and glycolide produced by depolymerization from the depolymerization reaction system containing the mixture is co-distilled with the polar organic solvent outside the depolymerization reaction system. Step 2; and III. Recovering glycolide from the co-distillate 3;
Each process, and
A glycol capable of obtaining a high-purity glycolide with a small amount of by-products without reducing the production rate of glycolide by being a glycolide production method characterized by adding a catalyst in step 2 The effect that the manufacturing method of glycolide which depolymerizes an acid oligomer can be provided is produced.

  The present invention relates to a method for producing glycolide in which a glycolic acid oligomer and a polar organic solvent are heated to depolymerize the glycolic acid oligomer.

1. Glycolic acid oligomer The glycolic acid oligomer used in the method for producing glycolide of the present invention (hereinafter sometimes referred to as “GAO”) has a glycolic acid repeating unit represented by — (O—CH ₂ —CO) —. Polyglycolic acid. GAO can be synthesized by polycondensation of glycolic acid or its ester (for example, lower alkyl ester) or a salt (for example, sodium salt). That is, glycolic acid (including its ester or salt) is heated to a temperature of usually 100 to 250 ° C., preferably 140 to 230 ° C. under reduced pressure or increased pressure in the presence of a condensation catalyst or a transesterification catalyst as necessary. Heating is performed, and a condensation reaction or a transesterification reaction is carried out until the distillation of low molecular weight substances such as water and alcohol substantially disappears. After completion of the condensation reaction or transesterification reaction, the produced GAO can be used as it is as a raw material for the glycolide production method of the present invention. Further, the obtained GAO can be taken out from the reaction system and washed with a non-solvent such as benzene or toluene to remove unreacted substances, low polymer or catalyst, and then used. GAO may be cyclic or linear. The weight average molecular weight of GAO is usually 3000 or more, preferably 5000 or more, more preferably 7000 or more. The upper limit of the weight average molecular weight is usually about 20000, and in many cases about 15000. The weight average molecular weight is a value measured using gel permeation chromatography (GPC).

2. Polar organic solvent Examples of the polar organic solvent used in the method for producing glycolide of the present invention include aromatic dicarboxylic acid diesters, aromatic carboxylic acid esters, aliphatic dicarboxylic acid diesters, polyalkylene glycol diethers, and aromatic dicarboxylic acid diesters. Examples include alkoxyalkyl esters, aliphatic dicarboxylic acid dialkoxyalkyl esters, polyalkylene glycol diesters, and aromatic phosphate esters. Moreover, as a polar organic solvent, the high boiling polar organic solvent whose boiling point under a normal pressure exists in the range of 230-450 degreeC, Preferably it is 255-430 degreeC, More preferably, it is 280-430 degreeC can be used. The molecular weight of the polar organic solvent is preferably in the range of 150 to 450, more preferably 180 to 420, and still more preferably 200 to 400.

Among these polar organic solvents, aromatic dicarboxylic acid diesters, aromatic carboxylic acid esters, aliphatic dicarboxylic acid diesters, and polyalkylene glycol diethers are preferred, and polar organic solvents are represented by the following formulas in that they are less susceptible to thermal degradation. X—O— (R—O—) _p —Y
(In the formula, R represents a methylene group or a linear or branched alkylene group having 2 to 8 carbon atoms. X represents a hydrocarbon group. Y represents an alkyl group or aryl having 2 to 20 carbon atoms. P represents an integer of 1 or more, and when p is 2 or more, a plurality of R may be the same or different.
The polyalkylene glycol diether represented by the formula is more preferable. Further, polyalkylene glycol diether having a molecular weight of 150 to 450 is particularly preferable.

  Examples of the aromatic dicarboxylic acid diester include phthalic acid esters such as dibutyl phthalate, dioctyl phthalate, dibenzyl phthalate, and benzyl butyl phthalate. Examples of the aromatic carboxylic acid ester include benzoic acid esters such as benzyl benzoate. Examples of the aliphatic dicarboxylic acid diester include adipic acid esters such as dioctyl adipate and sebacic acid esters such as dibutyl sebacate.

The following preferred formula X—O— (R—O—) _p —Y
(In the formula, R represents a methylene group or a linear or branched alkylene group having 2 to 8 carbon atoms. X represents a hydrocarbon group. Y represents an alkyl group or aryl having 2 to 20 carbon atoms. P represents an integer of 1 or more, and when p is 2 or more, a plurality of R may be the same or different.
Examples of the polyalkylene glycol diether represented by: Diethylene glycol, triethylene glycol or tetraethylene glycol diethyl ether, dipropyl ether, dibutyl ether, dihexyl ether, dioctyl ether, butyl hexyl ether, butyl octyl ether, butyl decyl ether, Polyethylene glycol dialkyl ether such as butyl 2-chlorophenyl ether or hexyl octyl ether; in the polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether or polybutylene glycol dialkyl ether containing propyleneoxy group or butyleneoxy group instead of ethyleneoxy group A polyalkylene glycol dialkyl ether; Polyethylene glycol alkyl in which the hydrogen group of the phenyl group of tylene glycol, triethylene glycol or tetraethylene glycol, hexyl phenyl ether, hexyl phenyl ether or octyl phenyl ether, or the phenyl group of these compounds is substituted with an alkyl group, alkoxy group, halogen group or the like An aryl ether; in the polyethylene glycol alkyl aryl ether, a polyalkylene glycol alkyl aryl ether such as a polypropylene glycol alkyl aryl ether or a polybutylene glycol alkyl aryl ether containing a propyleneoxy group or a butyleneoxy group instead of an ethyleneoxy group; Diphenyl of triethylene glycol or tetraethylene glycol Polyethylene glycol diaryl ethers such as ethers or compounds in which the phenyl group of these compounds is substituted with alkyl, alkoxy, halogen, etc .; in the polyethylene glycol diaryl ethers, a propyleneoxy group or a butyleneoxy group is substituted for the ethyleneoxy group And polyalkylene glycol diaryl ethers such as polypropylene glycol diaryl ether or polybutylene glycol diaryl ether.

3. Solubilizing agent In the glycolide production method of the present invention, the purity of glycolide obtained by depolymerization is further improved, so that GAO can be heated and depolymerized with a polar organic solvent and a solubilizing agent. The use of a solubilizer is not an essential condition of the present invention. That is, according to the method for producing glycolide of the present invention, for example, there is an effect that it is not necessary to add an additional solubilizer.

The solubilizer means a solvent having higher affinity with GAO than a polar organic solvent, and is more preferably a compound that satisfies any one or more of the following requirements.
(1) It is a non-basic compound. Basic compounds such as amine, pyridine, and quinoline are not preferable because they may react with GAO or glycolide to be generated.
(2) The compound is compatible or soluble in a polar organic solvent such as polyalkylene glycol diether. Any compound that is compatible or soluble in a polar organic solvent may be liquid or solid at room temperature.
(3) A compound having a boiling point of 180 ° C or higher, preferably 200 ° C or higher, more preferably 230 ° C or higher, particularly preferably 250 ° C or higher.
(4) For example, a compound having a functional group such as OH group, COOH group, and CONH group.

  As the solubilizer, monohydric alcohol and polyhydric alcohol are particularly effective. As the monohydric or polyhydric alcohol, a monohydric or polyhydric alcohol having a boiling point of 180 ° C. or higher, preferably 200 ° C. or higher, more preferably 230 ° C. or higher, particularly preferably 250 ° C. or higher can be used. Polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polybutylene glycol; polyalkylene glycol monoethers are more preferred, and polyalkylene glycol monoethers having a boiling point of 180 ° C. or higher are most preferred. According to the present invention, it is possible to obtain a high-purity glycolide with a small amount of by-product generated without decreasing the production rate of glycolide without containing a polyalkylene glycol which is widely used as a solubilizer. .

  Specific examples of the polyalkylene glycol monoether include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polyethylene glycol monopropyl ether, polyethylene glycol monobutyl ether, polyethylene glycol monohexyl ether, polyethylene glycol monooctyl ether, polyethylene glycol mono Polyethylene glycol monoethers such as decyl ether and polyethylene glycol monolauryl ether (hereinafter sometimes referred to as “polyoxyethylene monoether”); in the polyethylene glycol monoether, the ethyleneoxy group is converted to a propyleneoxy group or a butyleneoxy group. Alternative polypropylene glycol monoether and polybutylene Polyalkylene glycol monoethers, such as glycol monomethyl ether; and the like.

  The polyalkylene glycol monoether is more preferably one having an alkyl group having 1 to 18 carbon atoms as the ether group, more preferably one having an alkyl group having 6 to 18 carbon atoms, for example, an octyl group having 8 carbon atoms ( Branched ones such as an ethylhexyl group may be used). These can be used alone or in combination of two or more. Among the polyalkylene glycol monoethers, polyethylene glycol monoalkyl ethers such as triethylene glycol monooctyl ether are preferable. In addition, a mixture of polyethylene glycol monoethers having a different number of repeating oxyethylene units available as a commercially available polyalkylene glycol monoether, such as polyoxyethylene 2-ethylhexyl ether (Newcol 1006 manufactured by Nippon Emulsifier Co., Ltd.), etc. May be used.

4). Step 1 of heating a mixture containing a glycolic acid oligomer and a polar organic solvent to a temperature at which the glycolic acid oligomer is depolymerized under normal pressure or reduced pressure.
[Heating process]
The method for producing glycolide according to the present invention includes a step 1 (hereinafter referred to as “heating step”) in which a mixture containing GAO and a polar organic solvent is heated to a temperature at which GAO is depolymerized under normal pressure or reduced pressure. .) Step 1 (heating step) is a step of heating a mixture containing GAO and a polar organic solvent, and optionally a solubilizer, to a temperature at which GAO is depolymerized under normal pressure or reduced pressure. A polar organic solvent is 30-5000 mass parts normally with respect to 100 mass parts of GAO, Preferably it is used in the ratio of 50-2000 mass parts. If the ratio of the polar organic solvent is too small, the ratio of the GAO solution phase in the mixture containing GAO and the polar organic solvent decreases under the GAO depolymerization temperature condition (the ratio of the GAO melt phase is Increase), and the depolymerization reactivity of GAO decreases. When the proportion of the polar organic solvent becomes too large, the thermal efficiency in the depolymerization reaction is lowered, and the productivity of glycolide by the depolymerization reaction is lowered.

  The mixture in step 1 (heating step) may further contain a solubilizer. When the solubilizer is contained, the solubilizer is usually used at a ratio of 0.1 to 500 parts by mass, preferably 1 to 300 parts by mass with respect to 100 parts by mass of GAO. When the molar ratio of GAO to solubilizer (GAO / solubilizer) is adjusted to a range of preferably 1 to 99, more preferably 3 to 70, and even more preferably 5 to 50, a higher purity glycolide can be obtained. Can be obtained. In addition, the mixture in a heating process does not need to contain a catalyst. When the mixture in the heating step contains a catalyst, the amount of by-products produced may increase, and the glycolide production rate may decrease early.

  In the heating step, a mixture containing GAO, a polar organic solvent, and, if necessary, a solubilizer is heated to a temperature at which GAO is depolymerized under normal pressure or reduced pressure, preferably in an inert atmosphere. . The temperature at which GAO depolymerizes varies depending on the degree of pressure reduction and the type of the polar organic solvent, but is generally a temperature of 200 ° C. or higher. Therefore, the heating temperature is usually 200 to 350 ° C., preferably 210 to 310 ° C. Preferably it is 220-300 degreeC, Most preferably, it exists in the range of 230-290 degreeC.

  In the heating step, it is preferable to form a solution phase of GAO, and the depolymerization reaction is performed under the condition that the residual ratio of the GAO melt phase is 0.5 or less, more preferably 0.3 or less, and particularly preferably zero. It is desirable to implement. That is, the depolymerization reaction is carried out in a substantially homogeneous solution phase state in which the residual ratio of the melt phase of GAO is substantially zero, particularly in order to efficiently obtain high purity glycolide. preferable.

5. Step 2 of continuing the heating to depolymerize the glycolic acid oligomer and co-distilling glycolide produced by the depolymerization from the depolymerization reaction system containing the mixture together with the polar organic solvent to the outside of the depolymerization reaction system
[Distillation process]
In the method for producing glycolide according to the present invention, heating is further continued at the above temperature to depolymerize the glycolic acid oligomer, and glycolide produced by depolymerization from the depolymerization reaction system containing the mixture is mixed with a polar organic solvent. It has the process 2 (henceforth a "distillation process") co-distilled out of the depolymerization reaction system. In step 2 (distillation step), heating is further continued at the heating temperature of the heating step to perform depolymerization of GAO and polarize glycolide generated by depolymerization from a depolymerization reaction system containing the mixture. A co-distillation step of co-distilling with the organic solvent outside the depolymerization reaction system. That is, in the distilling step, the generated glycolide is distilled together with the polar organic solvent, so that the problem that the glycolide is deposited on the inner wall of the distilling line and adheres and the line is blocked does not occur. It is possible to continue for a long time. Since the depolymerization reaction of GAO is a reversible reaction, if glycolide is distilled from the depolymerization reaction system and discharged out of the depolymerization reaction system, the GAO depolymerization reaction proceeds efficiently.

  The heating in the distilling step is carried out under normal pressure or reduced pressure. However, since the depolymerization reaction can be carried out at a low temperature, it is preferably carried out under reduced pressure of 0.1 to 90 kPa, more preferably 1 to 60 kPa. More preferably, it is 1.5-40 kPa, Most preferably, it is 2-30 kPa.

[Catalyst (depolymerization catalyst)]
The method for producing glycolide of the present invention is characterized in that a catalyst (depolymerization catalyst) is added in step 2 (distillation step). That is, the glycolide production method of the present invention is the first step in the glycolide production method in which GAO is heated to depolymerize, that is, GAO that is heated to a temperature at which GAO is depolymerized in Step 1 (heating step). The mixture containing an organic solvent does not contain a depolymerization catalyst. In the glycolide production method of the present invention, a catalyst (depolymerization catalyst) is added in step 2 (distillation step).

As the catalyst (depolymerization catalyst) added in step 2 (distillation step), catalyst compounds conventionally used as GAO depolymerization catalysts such as tin compounds and antimony compounds can be used. Specifically, as the tin compound, oxides such as tin and antimony, halides, carboxylates and the like can be used. More specifically, tin dichloride, tin tetrachloride, tin alkylcarboxylate and the like can be used. The tin compound used as the depolymerization catalyst may be a compound having water of crystallization, and for example, tin dichloride (SnCl ₂ .2H ₂ O) can be used particularly preferably.

  In the method for producing glycolide according to the present invention, the catalyst (depolymerization catalyst) may be added at the time when Step 1 (heating step) is completed and Step 2 (distillation step) is started. From the viewpoint of a high rate improvement (recovery) effect, the glycolide production rate is preferably reduced to 90% or less of the initial production rate, and more preferably the glycolide production rate is 70% of the initial production rate. The catalyst (depolymerization catalyst) may be added after the time point when the production rate is lowered below, more preferably after the time point when the production rate of glycolide is reduced to 50% or less of the initial production rate. There is no particular restriction on the timing of adding the catalyst (depolymerization catalyst), but if the catalyst (depolymerization catalyst) is added after the time when the production rate of glycolide is reduced to 10% or less of the initial rate, it is according to the present invention. There is a possibility that the overall execution time of the glycolide production method in which GAO is heated and depolymerized becomes too long, or the total amount of glycolide recovered is reduced. The catalyst (depolymerization catalyst) in step 2 (distillation step) may be added only once, but the catalyst (depolymerization catalyst) may be added in step 2 (distillation step) in multiple steps. . The production rate of glycolide is usually the amount of glycolide distilled, recovered and obtained from the depolymerization system every hour after the start of the depolymerization reaction (start of step 2). Is measured as the amount of glycolide per unit time (unit: g / hour). The initial production rate of glycolide is usually the production rate of glycolide (unit: g) determined from the amount of glycolide recovered and acquired from the start of the depolymerization reaction (start of step 2) until 1 hour has passed. / Hour).

  In the method for producing glycolide of the present invention, the amount of catalyst (depolymerization catalyst) added in step 2 (distillation step) (the total amount in the case of adding multiple times) is the depolymerization reaction system containing GAO. The amount is usually 100 to 10,000 ppm, preferably 150 to 5000 ppm, more preferably 200 to 3000 ppm, and still more preferably 250 to 2000 ppm. Moreover, it is 0.03-3 mass parts normally with respect to 100 mass parts of GAO, Preferably it is 0.04-1.5 mass parts, More preferably, it is 0.06-1 mass parts, More preferably, it is 0.08-0. About 6 parts by mass, using a relatively small amount of catalyst (depolymerization catalyst) compared to the amount of catalyst used in the conventional method for producing glycolide in which GAO is depolymerized by heating. By doing so, it is possible to obtain a high-purity glycolide with a small amount of by-products generated without reducing the production rate of glycolide.

  In addition, when a catalyst (depolymerization catalyst) was added to the mixture containing GAO and a polar organic solvent, it turned out that the production amount of by-products other than glycolide increases. In the production method of glycolide for depolymerizing GAO, when the amount of by-products such as glycolic acid dimer increases, a side reaction may occur when polyglycolic acid is formed using the resulting glycolide as a starting material. As a result, polyglycolic acid having a high degree of polymerization may not be obtained. In that case, in order to reduce the content of the by-product contained in the obtained glycolide, it is necessary to perform sufficient purification, resulting in an increase in the production efficiency and manufacturing cost of glycolide. As is well known, the content of by-products can be evaluated by the melting point drop (unit: ° C.) with respect to the melting point (83.74 ° C.) of glycolide having a purity of 100%. The content of by-products that are allowed to be contained in glycolide is accumulated during the depolymerization reaction because the by-products are accumulated during the depolymerization reaction. It is desired that the melting point drop be less than 0.5 ° C, preferably less than 0.45 ° C, more preferably less than 0.4 ° C.

6). Step 3 for recovering glycolide from the distillate
[Recovery process]
The method for producing glycolide of the present invention includes a step 3 (hereinafter also referred to as “recovery step”) for obtaining glycolide from the co-distillate following the step 2 (distillation step). Specifically, the distillate is cooled by a heat exchanger (cooler) to be liquefied, and glycolide and the polar organic solvent are liquid-phase separated. When the co-distillate is phase-separated, a glycolide phase (glycolide layer) is formed in the lower layer, and the upper layer becomes a polar organic solvent phase (a layer containing a polar organic solvent). Glycolide can be obtained by separating and recovering the glycolide in the lower layer in a liquid state. In order to phase-separate glycolide and polar organic solvent in a liquid state, the cooling temperature is usually controlled within the range of 70 to 180 ° C, preferably 75 to 150 ° C, more preferably 80 to 120 ° C. If the cooling temperature is too high, side reactions such as ring-opening reactions tend to occur in the glycolide phase during the separation and recovery operation. If the cooling temperature is too low, it is difficult to separate the phases in a liquid state.

  When the depolymerization reaction is continued while controlling the temperature of the co-distillate with a heat exchanger, glycolide co-distilled with the polar organic solvent passes through the solvent phase of the upper layer of the co-distillate as droplets, and the lower layer. The condensed glycolide can be recovered and obtained. The remaining polar organic solvent from which glycolide has been removed from the co-distillate may be refluxed as it is to the depolymerization reaction system, or temporarily stored outside the line, and after purification by activated carbon adsorption or distillation as desired. The depolymerization reaction system may be additionally supplied. When the above-described polyalkylene glycol diether excellent in thermal stability is used as the polar organic solvent, almost the entire amount recovered from the co-distillate can be reused without purification.

  Depolymerization performed by heating GAO supplied to the depolymerization reaction system together with a polar organic solvent is recovered until the generation of glycolide ceases or the production rate of glycolide drops below a predetermined value, that is, recovered in the distillation line. It can continue, adding a catalyst (depolymerization catalyst) suitably until the quantity of glycolide acquired becomes zero or below a predetermined value. Further, when the production rate of glycolide decreases, GAO and / or a polar organic solvent is additionally supplied to the depolymerization reaction system in an amount corresponding to the amount of distillate, so that a catalyst (depolymerization is performed as necessary). The depolymerization reaction can be continued repeatedly while adding the catalyst.

7). Glycolide Glycolide recovered and obtained by the glycolide production method of the present invention is a high-purity glycolide with a small amount of by-products, so that it can be used as a starting material for producing polyglycolic acid without purification. However, if desired, it may be further purified by recrystallization or washing. The content of by-products in glycolide can be confirmed by a melting point drop (unit: ° C.) with respect to the melting point (83.74 ° C.) of glycolide having a purity of 100%. The melting point depression of glycolide that can be used as a starting material for producing polyglycolic acid is usually less than 0.5 ° C, preferably less than 0.45 ° C, more preferably less than 0.4 ° C, and even more preferably 0.35. It is less than ℃. The lower limit of the melting point drop of glycolide is 0 ° C., but high purity glycolide can be said to be about 0.01 ° C.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.

[Example 1]
In a flask with a volume of 500 ml, 110 g of GAO, 120 g of tetraethylene glycol dibutyl ether (hereinafter sometimes referred to as “DBTG”) as a polar organic solvent, and polyoxyethylene 2-ethylhexyl ether (Newcol manufactured by Nippon Emulsifier Co., Ltd.) as a solubilizer 1006. Hereinafter, it may be referred to as “OTeG”.) 90 g was injected and heated to a temperature of 235 ° C. under normal pressure to make the reaction system a uniform solution (step 1: heating step). This solution was decompressed to 3.0 kPa while maintaining the temperature at 235 ° C., and DBTG and the produced glycolide were co-distilled (step 2: distillation step). Glycolide was recovered and obtained from the co-distillate (step 3: recovery step). All the remaining DBTG from which glycolide was recovered from the co-distillate was refluxed to the flask.

  Glycolide production rate (GL production rate; unit: g / hour) is calculated by measuring the amount of glycolide collected and obtained every hour for glycolide produced by heating and depolymerizing GAO. At the same time, the melting point drop (ΔT. Unit: ° C.) relative to the melting point of glycolide having a purity of 100% was calculated by measuring the melting point (unit: ° C.) of the produced glycolide. Note that GAO corresponding to the amount of glycolide distilled was added to the depolymerization reaction system. The calculation results of the glycolide production rate and the melting point drop (ΔT) after 1 hour from the start of the depolymerization reaction (start of step 2), after 20 hours and after 24 hours, are obtained as GL production rate ratio (step 2). Table 1 shows the ratio of the GL generation rate at each elapsed time to the GL generation rate after one hour has elapsed from the start of the above (unit:%).

After 24 hours from the start of the depolymerization reaction (start of step 2), 360 ppm of tin dichloride (SnCl ₂ · 2H ₂ O) as a catalyst (depolymerization catalyst) was added to the total amount of the depolymerization reaction system, and GAO More specifically, step 2 (distillation step) was further continued. The calculation results of the glycolide production rate and melting point drop (ΔT) after 25 hours, 26 hours and 32 hours from the start of the depolymerization reaction (start of step 2) Table 1 shows the generation rate, that is, the ratio of the GL generation rate at each elapsed time to the GL generation rate after 1 hour has elapsed from the start of step 2, in units of%.

  From Table 1, the production rate of glycolide decreased, specifically, from the start of Step 2 by adding a depolymerization catalyst after 24 hours from the start of Step 2 when the GL production rate ratio decreased to 47%. Since the production rate of glycolide after 25 hours has greatly increased to 96.0%, the glycolide production method of the present invention in which a depolymerization catalyst is added in step 2 without reducing the production rate of glycolide. It has been found that glycolide can be obtained.

  Moreover, since melting | fusing point fall increased after adding a depolymerization catalyst, it was confirmed that the production amount of a by-product increases by addition of a depolymerization catalyst. As a result, in Example 1, compared with the case where the depolymerization catalyst is contained in the mixture containing GAO and the polar organic solvent from the beginning of Step 2, the total amount of by-products other than glycolide is generated. It was inferred that there was an effect that there was little. In Example 1, the melting point drop (ΔT) was 0.30 ° C. at the maximum, and it was found that glycolide having a purity with no problem for use as a starting material for the production of polyglycolic acid was obtained.

According to the present invention,
I. Heating the mixture containing the glycolic acid oligomer and the polar organic solvent to a temperature at which the glycolic acid oligomer is depolymerized under normal pressure or reduced pressure;
II. Further heating is continued at the above temperature to depolymerize the glycolic acid oligomer, and glycolide produced by depolymerization from the depolymerization reaction system containing the mixture is co-distilled with the polar organic solvent outside the depolymerization reaction system. Step 2; and III. Recovering glycolide from the co-distillate 3;
Each process, and
A glycol capable of obtaining a high-purity glycolide with a small amount of by-products without reducing the production rate of glycolide by being a glycolide production method characterized by adding a catalyst in step 2 Since the manufacturing method of glycolide which depolymerizes an acid oligomer can be provided, industrial applicability is high.

Claims (6)

I. Heating the mixture containing the glycolic acid oligomer and the polar organic solvent to a temperature at which the glycolic acid oligomer is depolymerized under normal pressure or reduced pressure;
II. Further heating is continued at the above temperature to depolymerize the glycolic acid oligomer, and glycolide produced by depolymerization from the depolymerization reaction system containing the mixture is co-distilled with the polar organic solvent outside the depolymerization reaction system. Step 2; and III. Recovering glycolide from the co-distillate 3;
Each process, and
In the process 2, a catalyst is added, The manufacturing method of the glycolide characterized by the above-mentioned.   The method for producing glycolide according to claim 1, wherein in step 2, the catalyst is added after the time when the production rate of glycolide is reduced to 90% or less of the initial production rate. The polar organic solvent is represented by the following formula X—O— (R—O—) _p —Y
(In the formula, R represents a methylene group or a linear or branched alkylene group having 2 to 8 carbon atoms. X represents a hydrocarbon group. Y represents an alkyl group or aryl having 2 to 20 carbon atoms. P represents an integer of 1 or more, and when p is 2 or more, a plurality of R may be the same or different.
The method for producing glycolide according to claim 1 or 2, wherein the polyalkylene glycol diether is represented by the formula:   The method for producing glycolide according to any one of claims 1 to 3, wherein the catalyst is a tin compound.   The method for producing glycolide according to any one of claims 1 to 4, wherein the mixture used in step 1 further contains a solubilizer.   The method for producing glycolide according to claim 5, wherein the solubilizer is a polyalkylene glycol monoether having a boiling point of 180 ° C or higher.