Patent Description:
Polyglycolic acid is a resin material that excels in biodegradability, gas barrier properties, and strength, and is used in a wide range of technical fields such as in sutures, artificial skin, and other polymer materials for medical purposes, bottles, films, and other packaging materials, and resin materials for various industrial products such as injection molded products, fibers, vapor deposition films, and fishing lines.

Such polyglycolic acids are required to have a high degree of polymerization according to the application. A polyglycolic acid with a high degree of polymerization can be produced by a method of subjecting glycolide to ring-opening polymerization. Furthermore, a reduction of the production costs of polyglycolic acid is demanded, and there is also a demand for the mass production of glycolide used as a raw material, that is, there is a demand to enable the production of glycolide at a high production rate.

Glycolide can be produced through <NUM>) subjecting glycolic acid to dehydrating polycondensation to obtain a glycolic acid oligomer (dehydrating polycondensation), and <NUM>) depolymerizing the obtained glycolic acid oligomer (depolymerization).

Examples of methods for producing glycolide with high yield or efficiently include a method of carrying out a depolymerization reaction of a glycolic acid oligomer in the presence of tin octylate as a catalyst (for example, see Patent Document <NUM>), and a method of carrying out a depolymerization reaction of a glycolic acid oligomer in the presence of titanium alkoxide (Ti(OH)<NUM>) solution in methoxyethanol as a catalyst (for example, see Patent Document <NUM>).

In addition, a method is known in which an aqueous solution of <NUM>% glycolic acid is subjected to dehydrating polycondensation while being gradually heated to <NUM> in a reaction vessel made of titanium, and the obtained glycolic acid oligomer is heated under reduced pressure to perform solid-phase depolymerization (for example, see Patent Document <NUM>).

However, with the glycolide production methods described in Patent Documents <NUM> and <NUM>, the production rate of glycolide is insufficient. Moreover, while the glycolide production method described in Patent Document <NUM> can be used to favorably produce glycolide, from the perspective of reducing the cost to produce polyglycolic acid having a high degree of polymerization, there is a demand to further improve the production rate of the glycolide that is used as a raw material.

In light of the foregoing, an object of the present invention is to provide a glycolide production method that can sufficiently increase the production rate of glycolide.

The glycolide production method of the present invention includes: adding metal titanium to an aqueous glycolic acid solution; subjecting glycolic acid contained in the aqueous glycolic acid solution to which the metal titanium is added, to dehydrating polycondensation to obtain a glycolic acid oligomer; and heating and depolymerizing the glycolic acid oligomer to obtain glycolide under the existence of a titanium ion generated from the metal titanium; wherein the metal titanium is a titanium powder, and an addition amount of the metal titanium is from <NUM> ppm to <NUM> ppm relative to the total mass of the glycolic acid.

According to the present invention, a glycolide production method capable of sufficiently increasing the production rate of glycolide can be provided.

The present inventors focused on the addition of metal titanium as a catalyst. Ordinarily, a catalyst is typically added in the depolymerization to increase the rate of production of glycolide. The depolymerization is preferably carried out in an organic solvent from the perspective of being able to stably produce glycolide in large quantities. However, metal titanium cannot be dissolved in an organic solvent even when added in the depolymerization, and thus it is not possible to effectively exhibit the action of the metal titanium.

In contrast, in the present invention, metal titanium is added to the aqueous glycolic acid solution used in the dehydrating polycondensation. Metal titanium typically does not dissolve in an aqueous solution, but since the pH of an aqueous glycolic acid solution is low, the metal titanium favorably dissolves in the aqueous glycolic acid solution, and an aqueous glycolic acid solution containing titanium ions can be obtained. On the other hand, when a known titanium-based catalyst such as a titanium alkoxide or a titanium carboxylate described in Patent Document <NUM> is added to an aqueous glycolic acid solution, the titanium-based catalyst is hydrolyzed and precipitated, and does not function as a catalyst.

In the present description, it is thought that by performing a dehydrating polycondensation using an aqueous glycolic acid solution containing eluted titanium ions, the rate of the dehydrating polycondensation reaction can be increased by the catalytic action of the titanium ions. In addition, it is thought that unlike known titanium-based catalysts such as titanium carboxylates and titanium alkoxides, titanium ions are not affected by ligands, and therefore tend to be highly dispersed in the obtained glycolic acid oligomer. It is also thought that by performing the depolymerization using such a glycolic acid oligomer, the rate of the depolymerization reaction can be effectively increased by the catalytic action of the titanium ions. In particular, titanium (titanium ions) in a highly active state can be supplied into the glycolic acid oligomer by adding metal titanium to the aqueous glycolic acid solution and supplying the metal titanium into the glycolic acid oligomer. It is also thought that as a result, the metal titanium, even added in a low amount, action as a catalyst is easily obtained, and the production rate of glycolide can be dramatically increased.

Furthermore, the addition of metal titanium can also be performed by "heating the aqueous glycolic acid solution in a reaction vessel of which at least the inner surface is constituted by titanium or an alloy thereof, and maintaining the solution at a temperature lower than the boiling point. " Consequently, the production rate of glycolide can be dramatically increased.

The reason for this is thought to be as follows. That is, since the pH of the aqueous glycolic acid solution is low, the titanium is eluted into the aqueous glycolic acid solution from the inner surface of the reaction vessel while the aqueous glycolic acid solution is maintained at a temperature lower than the boiling point. It is thought that by carrying out the dehydrating polycondensation using an aqueous glycolic acid solution containing eluted titanium ions in this manner, the rate of the dehydrating polycondensation reaction is increased by the catalytic action of the titanium ions. Furthermore, titanium ions can be favorably dispersed in the obtained glycolic acid oligomer. It is also thought that by performing the depolymerization using such a glycolic acid oligomer, the rate of depolymerization reaction is increased by the catalytic action of the titanium ions. It is further thought that as a result, the production rate of glycolide is dramatically increased.

In this manner, titanium ions eluted from the reaction vessel are easily and favorably dispersed in the aqueous glycolic acid solution and in the glycolic acid oligomer that is produced, and therefore catalytic action can be effectively obtained.

The glycolide production method according to an embodiment of the present invention includes: <NUM>) adding metal titanium to an aqueous glycolic acid solution (metal titanium addition), <NUM>) subjecting glycolic acid contained in the aqueous glycolic acid solution to which the metal titanium is added, to dehydrating polycondensation to obtain a glycolic acid oligomer (dehydrating polycondensation), and <NUM>) heating and depolymerizing the obtained glycolic acid oligomer to obtain glycolide (depolymerization), whereby the heating and depolymerization is carried out under the existence of a titanium ion generated from the metal titanium; wherein the metal titanium is a titanium powder, and an addition amount of the metal titanium is from <NUM> ppm to <NUM> ppm relative to the total mass of the glycolic acid.

Metal titanium is added to an aqueous glycolic acid solution. Through this, at least a portion of the metal titanium is dissolved in the aqueous glycolic acid solution.

The aqueous glycolic acid solution is an aqueous solution containing glycolic acid. The glycolic acid may be an ester (for example, a lower alkyl ester), a salt (for example, a sodium salt), or the like.

The content of glycolic acid with respect to the total mass of the aqueous glycolic acid solution is, for example, preferably from <NUM> mass% to <NUM> mass%, and more preferably from <NUM> mass% to <NUM> mass%.

The metal titanium is titanium that may contain other components than titanium, but from the perspective of suppressing unnecessary reactions of other components than titanium, the content of the other components than titanium is preferably <NUM> mass% or less. The form of the metal titanium is a titanium powder.

The average particle size of the titanium powder is not particularly limited, but, for example, from the perspective of facilitating uniform dispersion in the aqueous glycolic acid solution, the titanium powder has an average particle size of <NUM> or less, and more specifically, the average particle size is preferably from <NUM> to <NUM>, and more preferably <NUM> or less. The average particle size of the titanium powder can be measured as an arithmetic mean of the volume average particle size distribution using a particle size distribution measurement device.

The addition amount of the metal titanium is from <NUM> ppm to <NUM> ppm, preferably from <NUM> ppm to <NUM> ppm, and more preferably from <NUM> ppm to <NUM> ppm. When the addition amount of the metal titanium is a certain amount or greater, the rate of the dehydrating polycondensation reaction of the glycolic acid and the rate of the depolymerization reaction of the glycolic acid oligomer are easily increased, and as a result, the production rate of glycolide is easily increased. However, when the addition amount thereof is too high, side reactions tend to increase. When the addition amount of the metal titanium is a certain amount or less, the remaining amount of undissolved metal titanium is easily reduced, thereby facilitating a reduction in recovery costs. However, when the addition amount thereof is too low, it becomes difficult to obtain catalytic action.

From the perspective of facilitating uniform dispersion of the metal titanium, the metal titanium may be added while heating the aqueous glycolic acid solution. From a similar perspective, the metal titanium may be added while stirring the aqueous glycolic acid solution.

The metal titanium addition is performed before step <NUM>).

As the aqueous glycolic acid solution, a purified product (high purity grade) having a low content of impurities such as organic material and metal ions is preferably used in order to facilitate production of high purity glycolide.

The method of reflux of the aqueous glycolic acid solution is not particularly limited, and a method such as stirring or circulation can be employed. In the case of stirring, the stirring speed is not particularly limited as long as air bubbles are not mixed in.

The aqueous glycolic acid solution obtained in step <NUM>) described above is heated to subject the glycolic acid to dehydrating polycondensation, and a glycolic acid oligomer is obtained. More specifically, the aqueous glycolic acid solution is heated until the distillation of low molecular weight substances such as water or alcohol is substantially completed, and the glycolic acid is subjected to polycondensation.

The heating temperature during the dehydrating polycondensation reaction (dehydrating polycondensation temperature) is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and even more preferably from <NUM> to <NUM>.

After the dehydrating polycondensation reaction is completed, the produced glycolic acid oligomer can be used as is as a raw material for step <NUM>)
(depolymerization) described below.

The obtained glycolic acid oligomer contains titanium ions dissolved in the aforementioned step <NUM>). Whether titanium is contained in the glycolic acid oligomer can be confirmed by, for example, ion chromatography (IC), ICP emission spectroscopy, and absorptiometric analysis.

The weight average molecular weight (Mw) of the obtained glycolic acid oligomer is preferably from <NUM> to <NUM>, and more preferably from <NUM> to <NUM>, from the perspective of glycolide yield. The weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC).

From the perspective of the yield of glycolide for the depolymerization reaction, the melting point (Tm) of the obtained glycolic acid oligomer is, for example, preferably <NUM> or higher, more preferably <NUM> or higher, and even more preferably <NUM> or higher. The upper limit of the melting point (Tm) of the glycolic acid oligomer is, for example, <NUM>. Here, the melting point (Tm) of the glycolic acid oligomer can be measured from the endothermic peak temperature when the glycolic acid oligomer is heated at a rate of <NUM>/min in an inert gas atmosphere using a differential scanning calorimeter (DSC).

The glycolic acid oligomer obtained in step <NUM>) described above is heated and depolymerized to obtain glycolide.

The depolymerization may be any of solid phase depolymerization, melt depolymerization, or solution depolymerization, but solution depolymerization is preferable from the perspective of being able to stably produce glycolide in large quantities. That is, preferably, the glycolic acid oligomer is heated in an organic solvent and depolymerized to obtain glycolide.

First, the glycolic acid oligomer is added to an organic solvent to be described below, and heated under normal pressure or under reduced pressure to dissolve the glycolic acid oligomer in the organic solvent.

From the perspective of appropriately increasing the depolymerization reaction temperature and facilitating an increase in the production rate of glycolide, the organic solvent is preferably a high boiling point organic solvent having a boiling point of from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and even more preferably from <NUM> to <NUM>.

Examples of such high boiling point organic solvents include aromatic dicarboxylic acid diesters, aromatic carboxylic acid esters, aliphatic dicarboxylic acid diesters, polyalkylene glycol diethers, aromatic dicarboxylic acid dialkoxyalkyl esters, aliphatic dicarboxylic acid dialkoxyalkyl esters, polyalkylene glycol diesters, and aromatic phosphoric acid esters. Among these, aromatic dicarboxylic acid diesters, aromatic carboxylic acid esters, aliphatic dicarboxylic acid diesters, and polyalkylene glycol diethers are preferable, and from the perspective of being less likely to cause thermal degradation, a polyalkylene glycol diether is more preferable.

As the polyalkylene glycol diether, a polyalkylene glycol diether represented by Formula (<NUM>) below is preferable. [Chemical Formula <NUM>].

In Formula (<NUM>), R denotes a methylene group or a linear or branched alkylene group having from <NUM> to <NUM> carbons. X and Y each denote an alkyl group or an aryl group having from <NUM> to <NUM> carbons, and p is an integer from <NUM> to <NUM>. When p is <NUM> or greater, the plurality of R moieties may be mutually the same or different.

Examples of polyalkylene glycol diethers include polyalkylene glycol dialkyl ether, polyalkylene glycol alkyl aryl ether, and polyalkylene glycol diaryl ether.

Examples of polyalkylene glycol dialkyl ethers include diethylene glycol dialkyl ethers such as diethylene glycol dibutyl ether, diethylene glycol dihexyl ether, diethylene glycol dioctyl ether, diethylene glycol butyl-<NUM>-chlorophenyl ether, diethylene glycol butylhexyl ether, diethylene glycol butyloctyl ether, and diethylene glycol hexyloctyl ether; triethylene glycol dialkyl ethers such as triethylene glycol diethyl ether, triethylene glycol dipropyl ether, triethylene glycol dibutyl ether, triethylene glycol dihexyl ether, triethylene glycol dioctyl ether, triethylene glycol butyloctyl ether, triethylene glycol butyldecyl ether, triethylene glycol butylhexyl ether, and triethylene glycol hexyloctyl ether; polyethylene glycol dialkyl ethers such as tetraethylene glycol diethyl ether, tetraethylene glycol dipropyl ether, tetraethylene glycol dibutyl ether, tetraethylene glycol dihexyl ether, tetraethylene glycol dioctyl ether, tetraethylene glycol butylhexyl ether, tetraethylene glycol butyloctyl ether, tetraethylene glycol hexyloctyl ether, and other such tetraethylene glycol dialkyl ethers; and polypropylene glycol dialkyl ethers for which the ethyleneoxy group in the polyalkylene glycol dialkyl ether is substituted with a propyleneoxy group, and polybutylene glycol dialkyl ethers for which the ethyleneoxy group in the polyalkylene glycol dialkyl ether is substituted with a butyleneoxy group.

Examples of polyalkylene glycol alkyl aryl ethers include diethylene glycol butylphenyl ether, diethylene glycol hexylphenyl ether, diethylene glycol octylphenyl ether, triethylene glycol butylphenyl ether, triethylene glycol hexylphenyl ether, triethylene glycol octylphenyl ether, tetraethylene glycol butylphenyl ether, tetraethylene glycol hexylphenyl ether, tetraethylene glycol octylphenyl ether, and polyethylene glycol alkyl aryl ethers for which some of the hydrogen atoms on the phenyl group of these compounds are substituted with an alkyl group, an alkoxy group, or a halogen atom; and a polypropylene glycol alkyl aryl ether for which the ethyleneoxy group in the polyalkylene glycol alkyl aryl ether is substituted with a propyleneoxy group, and a polybutylene glycol alkyl aryl ether for which the ethyleneoxy group in the polyalkylene glycol alkyl aryl ether is substituted with a butyleneoxy group.

Examples of the polyalkylene glycol diaryl ethers include diethylene glycol diphenyl ether, triethylene glycol diphenyl ether, tetraethylene glycol diphenyl ether, or a polyethylene glycol diaryl ether for which some of the hydrogen atoms on the phenyl group of these compounds are substituted with an alkyl group, an alkoxy group, or a halogen atom; and a polypropylene glycol diaryl ether for which the ethyleneoxy group in the polyalkylene glycol diaryl ether is substituted with a propyleneoxy group, and a polybutylene glycol diaryl ether for which the ethyleneoxy group in the polyalkylene glycol diaryl ether is substituted with a butyleneoxy group.

Among these, from perspective of thermal degradation being less likely to occur, a polyalkylene glycol dialkyl ether is preferable, and tetraethylene glycol dibutyl ether, triethylene glycol butyloctyl ether, diethylene glycol dibutyl ether, and diethylene glycol butyl-<NUM>-chlorophenyl ether are more preferable, and from the perspective of the glycolide recovery ratio, tetraethylene glycol dibutyl ether and triethylene glycol butyloctyl ether are even more preferable.

The addition amount of the organic solvent is, for example, preferably from <NUM> to <NUM> parts by mass, more preferably from <NUM> to <NUM> parts by mass, and even more preferably from <NUM> to <NUM> parts by mass, per <NUM> parts by mass of the glycolic acid oligomer.

Furthermore, a solubilizing agent may be further added as necessary to increase the solubility of the glycolic acid oligomer in the organic solvent.

The solubilizing agent is preferably a non-basic organic compound having a boiling point of <NUM> or higher, such as a monohydric alcohol, a polyhydric alcohol, a phenol, a monovalent aliphatic carboxylic acid, a polyvalent aliphatic carboxylic acid, an aliphatic amide, an aliphatic imide, or a sulfonic acid. Among these, from the perspective of being able to easily obtain an effect of a solubilizing agent, a monohydric alcohol and a polyhydric alcohol are preferable.

The boiling point of the monohydric or polyhydric alcohol is preferably <NUM> or higher, more preferably <NUM> or higher, and particularly preferably <NUM> or higher.

Such monohydric alcohols are preferably polyalkylene glycol monoethers represented by Formula (<NUM>) below. [Chemical Formula <NUM>].

In Formula (<NUM>), R<NUM> denotes a methylene group or a linear or branched alkylene group having from <NUM> to <NUM> carbons. X<NUM> denotes a hydrocarbon group. The hydrocarbon group is preferably an alkyl group. q is an integer of <NUM> or greater, and when q is <NUM> or greater, the plurality of R<NUM> moieties may be mutually the same or different.

Examples of polyalkylene glycol monoethers include polyethylene glycol monoethers such as 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 monodecyl ether, and polyethylene glycol monolauryl ether; a polypropylene glycol monoether for which an ethyleneoxy group in the polyethylene glycol monoether is substituted with a propyleneoxy group, and a polybutylene glycol monoether for which an ethyleneoxy group in the polyethylene glycol monoether is substituted with a butyleneoxy group. Among these, a polyalkylene glycol monoether having from <NUM> to <NUM> and preferably from <NUM> to <NUM> carbons in the alkyl group included in the ether group is preferable, and a polyethylene glycol monoalkyl ether such as triethylene glycol monooctyl ether is more preferable.

Since the polyalkylene glycol monoether can increase the solubility of the glycolic acid oligomer, the use of a polyalkylene glycol monoether as a solubilizing agent facilitates a more rapid advancement of the depolymerization reaction of the glycolic acid oligomer.

Polyalkylene glycols represented by Formula (<NUM>) below are preferable as the polyhydric alcohols. [Chemical Formula <NUM>].

In Formula (<NUM>), R<NUM> denotes a methylene group or a linear or branched alkylene group having from <NUM> to <NUM> carbons. r is an integer of <NUM> or greater, and when r is <NUM> or greater, the plurality of R<NUM> moieties may be mutually the same or different.

Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, and polybutylene glycol.

The addition amount of the solubilizing agent is preferably from <NUM> to <NUM> parts by mass, and more preferably from <NUM> to <NUM> parts by mass, per <NUM> parts by mass of the glycolic acid oligomer. When the addition amount of the solubilizing agent is a certain amount or greater, the solubility of the glycolic acid oligomer in the organic solvent can be sufficiently enhanced, and when the addition amount is a certain amount or less, the cost required to recover the solubilizing agent can be reduced.

Next, while the obtained solution is heated under normal pressure or under reduced pressure, the glycolic acid oligomer is depolymerized.

The heating temperature during the depolymerization reaction (depolymerization temperature) may be equal to or greater than the temperature at which depolymerization of the glycolic acid oligomer occurs, and while the heating temperature depends on the degree of depressurization, the type of high boiling point organic solvent, and the like, the heating temperature is generally at least <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, even more preferably from <NUM> to <NUM>, and yet even more preferably from <NUM> to <NUM>.

Heating during the depolymerization reaction is preferably performed under normal pressure or under reduced pressure, and is preferably performed under a reduced pressure from <NUM> kPa to <NUM> kPa. This is because the depolymerization reaction temperature decreases as the pressure is reduced, and therefore a lower pressure facilitates a reduction in the heating temperature, and the recovery ratio of the solvent is increased. The degree of depressurization is preferably from <NUM> kPa to <NUM> kPa, more preferably from <NUM> kPa to <NUM> kPa, and even more preferably from <NUM> kPa to <NUM> kPa.

Next, the produced glycolide is distilled out of the depolymerization reaction system along with the organic solvent. By distilling out the produced glycolide along with the organic solvent, adherence and accumulation of the glycolide on wall surfaces of the reaction vessel and lines can be prevented.

Glycolide is then recovered from the obtained distillate. Specifically, the distillate is cooled and phase separated, and glycolide is precipitated. The precipitated glycolide is separated and recovered from the mother liquor by a method such as filtration, centrifugal sedimentation, or decantation.

The mother liquor from which the glycolide has been separated may be recycled and used as is without purification, or may be recycled and used after being treated with activated carbon and filtered and purified, or after being purified through distillation once again.

When the glycolide is distilled out together with the organic solvent, the volume of the depolymerization reaction system decreases. In contrast, the depolymerization reaction can be performed continuously or repeatedly for a long period of time by adding, to the depolymerization reaction system, a glycolic acid oligomer and an organic solvent in an amount equivalent to the amount that was distilled away.

As described above, in the present invention, metal titanium is added to the aqueous glycolic acid solution to carry out a dehydrating polycondensation reaction and a depolymerization reaction. As a result, the production rate of glycolide can be dramatically increased.

The glycolide (also referred to as crude glycolide) obtained by the production method of an embodiment of the present invention is preferably high in purity. Specifically, the purity of the glycolide is preferably not less than <NUM>%, more preferably not less than <NUM>%, and even more preferably not less than <NUM>%. The purity of glycolide can be measured by gas chromatography (GC) using <NUM>-chlorobenzophenone as the internal standard.

Thus, according to the glycolide production method of an embodiment of the present invention, high purity glycolide can be obtained at a high production rate.

The present invention will be described in further detail below with reference to examples. The scope of the present invention is not to be construed as being limited by these examples and is defined by the current set of claims. Examples which do not fall under the scope of the claims are provided as reference.

A separable flask having a volume of <NUM> was charged with <NUM> of an aqueous solution of <NUM> mass% glycolic acid (available from The Chemours Company), and <NUM> of titanium powder (<NUM> ppm with respect to the glycolic acid, average particle size of <NUM>) was added thereto (step <NUM> described above). Note that the average particle size of the titanium powder was measured from a volume average arithmetic mean using a particle size distribution measurement device.

Next, the mixture was heated under stirring at normal pressure to increase the temperature from room temperature to <NUM>, and a polycondensation reaction was carried out while distilling away water that was produced. Subsequently, the pressure inside the flask was gradually reduced from normal pressure to <NUM> kPa, after which the contents in the flask were heated at <NUM> for <NUM> hours, low boiling point substances such as unreacted raw materials were distilled away, and a glycolic acid oligomer (weight average molecular weight Mw of from <NUM> to <NUM>, melting point of from <NUM> to <NUM>) was obtained (step <NUM> described above).

Next, <NUM> of the obtained glycolic acid oligomer, <NUM> of tetraethylene glycol dibutyl ether (high boiling point organic solvent), and <NUM> of triethylene glycol monooctyl ether (solubilizing agent) were added to a container having a volume of <NUM>, and then heated to <NUM>, and the reaction system was formed into a homogeneous solution. While this reaction system was heated at a temperature of <NUM> under stirring at a speed of <NUM> rpm, a depolymerization reaction was carried out for <NUM> hours under a reduced pressure of <NUM> kPa (step <NUM> described above). During the reaction, every one hour, tetraethylene glycol dibutyl ether and crude glycolide were co-distilled, the crude glycolide was separated and recovered from the co-distillate, and the mass was measured.

Along with the recovery of crude glycolide every one hour, glycolic acid oligomer in an amount equivalent to the mass (one-fold amount) of the recovered crude glycolide was newly fed into the reaction system. The amount of crude glycolide recovered per hour was arithmetically averaged to obtain the production rate (g/h) of the crude glycolide.

The crude glycolide production rate was determined in the same manner as in Example <NUM> with the exception that the addition amount of titanium powder was changed to <NUM> (<NUM> ppm relative to glycolic acid).

The crude glycolide production rate was determined in the same manner as in Example <NUM> with the exception that titanium powder was not added.

The evaluation results for each of Examples <NUM> and <NUM> and Comparative Example <NUM> are shown in Table <NUM>.

As shown in Table <NUM>, in Examples <NUM> and <NUM> in which titanium powder was added, the production rate of crude glycolide was higher than that of Comparative Example <NUM> in which titanium powder was not added.

A reaction vessel made of titanium and having a volume of <NUM><NUM> was charged with <NUM> (<NUM> lbs) of an aqueous solution of <NUM>% glycolic acid (available from The Chemours Company). The solution was then heated from room temperature to <NUM> under stirring at normal pressure, and then maintained at a temperature of from <NUM> to <NUM> for <NUM> days. Note that the boiling point of an aqueous glycolic acid solution typically increases as the concentration of glycolic acid increases. Specifically, since the boiling point of the aqueous solution of <NUM>% glycolic acid is <NUM>, the boiling point of the aqueous glycolic acid solution after reaching <NUM> becomes higher than <NUM> (in association with the increase in concentration). Thus, maintaining a temperature of from <NUM> to <NUM> after reaching <NUM> means maintaining a temperature that is always lower than the boiling point (at the concentration at that time). Next, the solution was further heated to <NUM>, and heating and stirring were performed for three days while water was distilled away. The amount of titanium dissolved in the solution at this time was <NUM> ppm relative to the total mass of the glycolic acid.

Next, the solution was further heated to <NUM>, and a dehydrating polycondensation reaction was carried out while distilling away the water that was produced. Subsequently, the pressure inside the reaction vessel was gradually reduced from normal pressure to <NUM> kPa, after which the contents in the reaction vessel were heated at <NUM> for <NUM> hours, low boiling point substances such as unreacted raw materials were distilled away, and a glycolic acid oligomer was obtained.

A separable flask having a volume of <NUM> was charged with <NUM> of an aqueous solution of <NUM>% glycolic acid (available from The Chemours Company). Next, the solution was heated from room temperature to <NUM> under stirring at normal pressure, and a polycondensation reaction was carried out while distilling away the water that was produced. In this heating process, after a temperature of <NUM> (the boiling point of the aqueous solution of <NUM>% glycolic acid) was reached, the temperature of the aqueous glycolic acid solution was always the same as the boiling point (at the concentration at that time). The stirring speed was set to <NUM> rpm.

Subsequently, the pressure inside the reaction vessel was gradually reduced from normal pressure to <NUM> kPa, after which the contents in the reaction vessel were heated at <NUM> for <NUM> hours to distill away the low boiling substances such as unreacted raw materials, and a glycolic acid oligomer was obtained.

A reaction vessel made of titanium and having a volume of <NUM><NUM> was charged with <NUM> (<NUM> lbs) of an aqueous solution of <NUM>% glycolic acid (available from The Chemours Company). Next, the mixture was heated for approximately <NUM> hours under stirring at normal pressure to increase the temperature from room temperature to <NUM>, and a polycondensation reaction was carried out while distilling away the water that was produced. In this heating process, after a temperature of <NUM> (the boiling point of the aqueous solution of <NUM>% glycolic acid) was reached, the temperature of the aqueous glycolic acid solution was always the same as the boiling point (at the concentration at that time). The amount of titanium dissolved in the solution at this time was <NUM> ppm relative to the total mass of glycolic acid.

The preparation conditions for Synthesis Examples <NUM> to <NUM> are summarized in Table <NUM>.

A flask having a volume of <NUM> was charged with <NUM> of the glycolic acid oligomer obtained in Synthesis Example <NUM>, <NUM> of tetraethylene glycol dibutyl ether, and <NUM> of octyltriethylene glycol, after which the contents were heated to <NUM>, and the reaction system was formed into a homogeneous solution.

Next, the pressure of the reaction system was reduced to <NUM> kPa, and a depolymerization reaction was performed for <NUM> hours while heating and stirring at a temperature of <NUM>. During the reaction, every one hour, tetraethylene glycol dibutyl ether and crude glycolide were co-distilled, the crude glycolide was separated and recovered from the co-distillate, and the mass was measured. Along with the recovery of crude glycolide every one hour, glycolic acid oligomer of the same mass as the recovered crude glycolide was newly fed into the reaction system. The amount of crude glycolide recovered per hour was arithmetically averaged to obtain the production rate (g/h) of the crude glycolide.

A reaction vessel made of SUS and having a volume of <NUM><NUM> was charged with <NUM> of the glycolic acid oligomer obtained in Synthesis Example <NUM>, <NUM> of tetraethylene glycol dibutyl ether, and <NUM> of octyltriethylene glycol, after which the contents were heated to <NUM>, and the reaction system was formed into a homogeneous solution.

Next, the pressure of the reaction system was reduced to <NUM> kPa, and a depolymerization reaction was performed for <NUM> hours while heating and stirring at a temperature of <NUM>. During the reaction, every one hour, tetraethylene glycol dibutyl ether and crude glycolide were co-distilled, and the production amount (kg/h) of the crude glycolide was confirmed using a flow meter.

Glycolide was produced in the same manner as in Example <NUM> with the exception that the glycolic acid oligomer obtained in Synthesis Example <NUM> was used, and the production rate (g/h) of the crude glycolide was calculated.

Glycolide was produced in the same manner as in Example <NUM> with the exception that the glycolic acid oligomer obtained in Synthesis Example <NUM> was used, and the production rate (kg/h) of crude glycolide was calculated.

The evaluation results of Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM> are shown in Table <NUM>.

As indicated in Table <NUM>, it is clear that the production rate of crude glycolide was higher in Example <NUM> in which the glycolic acid oligomer obtained in Synthesis Example <NUM> was used, than in Comparative Example <NUM>, in which the glycolic acid oligomer obtained in Synthesis Example <NUM> was used. It is presumed that the reason for this is that in Synthesis Example <NUM>, there was no elution of the active component from the reaction vessel made of glass, whereas in Synthesis Example <NUM>, titanium ions (which are an active component) were eluted from the reaction vessel made of titanium, dispersed well in the obtained glycolic acid oligomer, and acted as a catalyst.

It is also clear that the production rate of crude glycolide was higher in Example <NUM>, in which the glycolic acid oligomer of Synthesis Example <NUM> (which had undergone a step of maintaining the temperature and stirring in a reaction vessel made of titanium) was used, than in Comparative Example <NUM>, in which the glycolic acid oligomer of Synthesis Example <NUM> (which did not undergo a step of maintaining the temperature and stirring for a certain period of time or longer within a reaction vessel made of titanium). It is presumed that the reason for this is that titanium ions eluted from the titanium reaction vessel were better dispersed in the glycolic acid oligomer obtained in Synthesis Example <NUM> than in the glycolic acid oligomer obtained in Synthesis Example <NUM>, and the dispersed titanium ions acted as a catalyst.

The present application claims priority to <CIT> and <CIT>.

Claim 1:
A glycolide production method comprising:
adding metal titanium to an aqueous glycolic acid solution;
subjecting glycolic acid contained in the aqueous glycolic acid solution to which the metal titanium is added, to dehydrating polycondensation to obtain a glycolic acid oligomer; and
heating and depolymerizing the glycolic acid oligomer to obtain glycolide under the existence of a titanium ion generated from the metal titanium; wherein the metal titanium is a titanium powder, and an addition amount of the metal titanium is from <NUM> ppm to <NUM> ppm relative to a total mass of the glycolic acid.