JP2000086652A - Purification of lactide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying a lactide intended obtain a high- purity lactide in high yield using simple equipment and process. SOLUTION: This method for purifying a lactide comprises the following procedure: a crude lactide in a solid or molten state is contacted with ethanol to produce a slurry-like mixture, from which a solid is then separated; the solid thus separated is washed with water to remove the ethanol therefrom, and the resulting solid is subsequently dried under reduced pressures; thereby the objective inexpensive purified lactide suitable for use as a food additive is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying lactide, which is a dimeric cyclic ester of lactic acid, and more particularly to a method for obtaining a purified lactide having a high content of L-lactide and / or D-lactide. About the method. The present invention also relates to the purified lactide obtained by this method.

[0002] Lactide has conventionally been useful as a raw material for producing polylactic acid, which is a biodegradable polymer. That is, polylactic acid is obtained by ring-opening polymerization of lactide. In addition to the use as a raw material for producing polylactic acid, lactide is expected to be used as a food additive such as a food preservation stabilizer, a coloring agent, a coagulant, an acidulant, and a swelling agent.

[0003]

2. Description of the Related Art Lactide is a dimeric cyclic ester of lactic acid and has three kinds of optical isomers, namely, L-lactide composed of two L-lactic acids, D-lactide composed of two D-lactic acids, and L-lactide. There is a meso-lactide composed of lactic acid and D-lactic acid.

[0004] Usually, lactide is obtained by dehydrating and condensing lactic acid to obtain relatively low molecular weight polylactic acid as an intermediate, and then depolymerizing and cyclizing the polylactic acid to produce lactide, which is reacted as steam. It is manufactured by a so-called reactive distillation method that is taken out of the system.

In such a production method, lactide vapor contains L-lactide and / or D lactide and meso-lactide.
As impurities other than lactide, lactic acid monomers, linear lactic acid dimers, low molecular weight lactic acid condensation polymers such as trimers,
And water. Furthermore, impurities such as saccharides, amino acids, and fatty acids other than lactic acid derived from the raw material lactic acid may be included.

Therefore, it is necessary to purify the crude lactide collected by cooling according to the purpose of use to reduce the content of these impurities and meso-lactide. That is, lactide is converted into lactic acid and a linear low molecular weight lactic acid polycondensate by hydrolysis, but meso-lactide has remarkably higher water absorption and hydrolyzability than L-lactide and D-lactide.
Therefore, lactide having a high content of meso-lactide is
Hydrolysis is rapid as a whole, and the content of lactic acid as an acidic component and linear low molecular weight lactic acid polycondensate is increased.

For example, when lactide is used as a food additive, it is more useful to use lactide, which has a low acidity at the initial stage of addition and increases the acidity over time (according to aging of the food). If meso-lactide, lactic acid, or a linear low molecular weight lactic acid polycondensate is contained in a large amount in lactide, the acidity in the initial stage of the addition is increased. Therefore, it is preferable that the contents of meso-lactide, lactic acid, linear low molecular weight lactic acid polycondensate and water in lactide are as small as possible.

The melting points of L-lactide and D-lactide are about 98 ° C., whereas those of meso-lactide are about 40 ° C. The melting point of lactic acid is 16 to 25 ° C., and the linear low molecular weight lactic acid polycondensate is liquid at room temperature. For this reason, when lactide is used in the form of powder or particles, the melting point is lower than or equal to room temperature or near room temperature, meso-lactide, lactic acid, linear low molecular weight lactic acid polycondensate, and the water content is high Thus, there is a problem that the flowability of lactide deteriorates and the workability is impaired. Therefore, the content of these in lactide is preferably as small as possible.

Further, when lactide is used as a food additive, impurities such as saccharides, amino acids, and fatty acids other than lactic acid contained in lactide may make the taste of the food additive worse or change. There is a problem of coloring food additives. Therefore, the content of these impurities in lactide is preferably as small as possible.

Various conventional lactide purification methods are known, such as a method by recrystallization, a method by melt crystallization, a method by rectification, and a method by extraction with water.
For example, Japanese Patent Publication No. 51-6673 discloses a method of recrystallizing lactide using amyl alcohol or butyl alcohol as a solvent. But in this case,
Organic solvents harmful to the human body remain in the purified lactide, which is problematic when used as a food additive.

JP-A-63-101378 discloses that lactide is recrystallized from an alcohol having 1 to 6 carbon atoms, preferably isopropyl alcohol, or that lactide is dissolved and then precipitated using a non-solvent. ing. Japanese Patent Application Laid-Open No. Hei 7-118259 discloses a method in which lactide is recrystallized from a lower alcohol and then recrystallized with benzene or the like. However, in these cases, in the step of heating and dissolving the crude lactide in a solvent or in the step of cooling and depositing lactide from a solution, a large amount of time and utility is required, and a large amount of solvent is required. In addition, since the yield is low, it is disadvantageous in terms of cost. Further, an organic solvent harmful to the human body remains in the purified lactide, which is problematic when used as a food additive.

JP-A-6-256340 discloses a method for purifying crude lactide by a melt crystallization method.
However, the melt crystallization method requires an expensive large-scale apparatus, and requires a large amount of time and utility in the step of cooling and depositing lactide or the step of heating and purifying / dissolving lactide. Disadvantageous. In addition, since purified lactide is separated at a high temperature equal to or higher than the melting point of lactide, lactide is newly decomposed during the purification step, that is, lactic acid, linear low-molecular-weight lactic acid polycondensate, and the like are generated. . In order to obtain lactide of stable quality, strict process control is required.

JP-A-7-505150 discloses a method for obtaining high-purity lactide by rectification.
However, the equipment required for rectification is complicated and expensive, and requires a large amount of utility in the step of heating and vaporizing lactide or in the step of cooling and condensing it.
It is disadvantageous in cost. Further, since purified lactide is separated at a high temperature equal to or higher than the melting point of lactide, lactide is newly decomposed during the purification process, and lactic acid, linear low-molecular-weight lactic acid polycondensate, and the like are generated. In order to obtain lactide of stable quality, strict process control is still required.

Japanese Patent Application Laid-Open (JP-A) No. 7-165753 discloses a method of purifying crude lactide by bringing it into contact with water. In this method, lactide is brought into contact with water to remove meso-lactide.
If an attempt is made to sufficiently remove lactide, L-lactide and / or D-lactide are also partially hydrolyzed and removed, resulting in a low yield. The removed L-lactide and / or D-lactide reacts with water and can be recovered only in the form of lactic acid or a linear low-molecular-weight lactic acid polycondensate. Lactide obtained from lactic acid using a lot of utilities,
It is very disadvantageous in terms of cost that it can be recovered only in the form of lactic acid or linear low molecular weight lactic acid polycondensate.

[0015]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to obtain a highly purified lactide with high yield and high purity by using simple equipment and simple steps. To provide a purification method of Further, an object of the present invention is to provide a method for purifying lactide, which is suitable for food additives without leaving an organic solvent harmful to the human body and obtains a purified lactide having particles having good fluidity. It is in. And the object of the present invention is
An object of the present invention is to provide an inexpensive and highly purified lactide obtained by the present method.

[0016]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that L-lactide and / or D-lactide can be obtained by bringing crude lactide into contact with ethanol and then separating solids.
-It has been found that a purified lactide having a high lactide content can be obtained in a high yield, and the present invention has been completed.

That is, the present invention relates to a method for producing L-lactide and / or L-lactide by contacting crude lactide in a solid state or at least partly in a molten state with ethanol to obtain a slurry-like mixture, and thereafter separating a solid content from the mixture. Or D-
A lactide purification method characterized by obtaining a purified lactide having a high lactide content.

In the present method, it is preferable that after the solid content is separated, the separated solid content is dried under reduced pressure. Also,
In the present method, after the solid content is separated, the separated solid content can be washed with water to remove ethanol. In this case, it is preferable to dry the solid content under reduced pressure after washing with water. In the present invention, both undenatured ethanol and denatured ethanol can be used as ethanol. Further, the present invention is a purified lactide obtained by the above method.

Hereinafter, the present invention will be described in detail. The purification method of the present invention can be applied to crude lactide obtained by a conventionally known method. For example, JP-A-7-138
No. 253, a method of obtaining low molecular weight polylactic acid and depolymerizing this polylactic acid in the presence of a catalyst to obtain lactide. Thin film depolymerization method
504762, U.S. Pat.Nos. 5,274,127, 5,332,839, 5,319,107, 5,42
Any method such as a method for producing lactide directly from lactic acid without passing through a lactic acid oligomer as described in Japanese Patent No. 0,304 may be used. Of course, it is not limited to lactide by these methods.

As the raw material lactic acid for the production of lactide, for example, those having a lactic acid monomer equivalent weight concentration of 50 to 95% obtained by a synthesis method or a fermentation method can be used. Lactic acid obtained by the synthesis method contains an equal amount of an L-lactic acid component and a D-lactic acid component. Lactic acid obtained by the fermentation method is a mixture of an L-lactic acid component and a D-lactic acid component, and there are those mainly containing an L-lactic acid component and those mainly containing a D-lactic acid component. When obtaining a purified lactide for use as a food additive, it is more preferable to use lactic acid obtained by a fermentation method than lactic acid obtained by a synthesis method using a harmful substance such as hydrocyanic acid or acetaldehyde in the production process.

In order to obtain a low molecular weight polylactic acid by polycondensation of lactic acid, the raw material lactic acid is usually dehydrated under heating and reduced pressure in the absence or presence of a catalyst to obtain a weight average molecular weight of 500 to 30,
000 polylactic acid.

The heating temperature in this case is 100 to 250.
° C, preferably 100 to 200 ° C. If the temperature is lower than 100 ° C., it takes too much time for the condensation polymerization. In addition, when lactic acid obtained by fermentation is used to obtain crude lactide having a high optical purity, the optical purity of the crude lactide obtained as the reaction temperature becomes higher becomes lower, so that the racemization reaction is suppressed.
It is carried out at a temperature of 100 to 200 ° C, preferably 100 to 180 ° C. The pressure is 100 Torr or less, preferably 50 Torr or less.

The catalyst used in this case is not particularly limited, but is usually a group IA, IIA or IIB of the periodic table.
Group III, group IVB, group IVA, group IVB, group VB metals,
Oxides, hydroxides, chlorides, other inorganic compounds, organic compounds and the like and acids are used alone or in combination. The amount of the catalyst is usually 5% by weight or less based on the raw lactic acid.

Examples of the group IA catalyst include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium oxide, potassium oxide, lithium oxide, sodium methoxide, potassium ethoxide and the like.

Examples of the Group IIA catalyst include magnesium hydroxide, calcium hydroxide, barium hydroxide, magnesium oxide, calcium oxide, barium oxide, magnesium chloride, barium chloride and the like.

The group IIB catalyst includes zinc hydroxide, zinc oxide, zinc chloride and the like. Examples of the group IIIB catalyst include aluminum oxide, aluminum chloride, aluminum triethoxide, and aluminum octylate.

Examples of the group IVA catalyst include titanium oxide, tetramethyl titanate, tetrabutyl titanate, zirconium, zirconium oxide, zirconium tetramethoxide, zirconium tetrabutoxide and the like.

Examples of Group IVB catalysts include germanium, germanium oxide, tin, tin oxide, tin chloride, tin oxalate, tin octylate, dibutyltin dilaurate, dibutyltin oxide, butyltin chlorooxide, lead oxide, and silicon oxide. Is mentioned. Examples of the VB group catalyst include antimony trioxide, antimony triacetate, and triphenylantimony.

As a catalyst for acids, sulfuric acid, hydrochloric acid, nitric acid,
Examples thereof include phosphoric acid, toluenesulfonic acid, and cation exchange resin. By using the above catalyst, it is possible to accelerate the rate of the polycondensation reaction and shorten the time required for the reaction.
However, since the use of these catalysts also promotes the racemization reaction of lactic acid, when using lactic acid obtained by a fermentation method to obtain lactide with high optical purity, no catalyst is used, or the catalyst is not used. It is preferable to reduce the amount used.

The resulting low-molecular-weight polylactic acid is depolymerized by heating under reduced pressure in the presence of a catalyst to produce lactide, which is taken out of the reaction system as a vapor to produce crude lactide.

The heating temperature in this case is 130 to 300
° C, preferably 160-250 ° C. When the temperature is lower than 130 ° C., it takes too much time for depolymerization, and when the temperature is higher than 300 ° C., the amount of by-products such as acrylic acid and acrylic acid polymer increases, which is not preferable. When a crude lactide having a high optical purity is obtained by using lactic acid obtained by the fermentation method, 130 to 260 ° C, preferably 130 to 220 ° C, more preferably 130 to 180 ° C, in order to suppress the racemization reaction.
It is preferably carried out at a temperature of ° C. The pressure is 100T
orr, preferably 50 Torr or less, more preferably 20 Torr or less.

The depolymerization catalyst is not limited, but is usually selected from groups IA, IIA, IIB, IIIB and IVA of the periodic table.
Group, IVB and VB metals, oxides, hydroxides,
Chlorides, other inorganic compounds, organic compounds, etc. and acids,
Used alone or in combination. Specific examples of each of these catalysts are the same as those described above.

The catalyst is preferably used in an amount of not more than 20% by weight based on polylactic acid. However, when a catalyst is used in the polycondensation step of low-molecular-weight polylactic acid and the catalyst remaining in the polylactic acid provides a sufficient depolymerization reaction rate, it is not necessary to add a new catalyst. Absent.

The crude lactide thus obtained includes
Usually, low-molecular-weight lactic acid polycondensates such as lactic acid monomers, linear lactic acid dimers and trimers, and impurities such as water, and impurities such as saccharides, amino acids, and fatty acids other than lactic acid derived from raw lactic acid are contained. ing. Lactide also has L-
Lactide and / or D-lactide, and meso-lactide are included.

In the present invention, the crude lactide to be purified is brought into contact with ethanol to obtain a slurry-like mixture, after which the solids are separated from this mixture. The crude lactide to be purified may be in a solid state or a molten state. Alternatively, a part may be in a molten state. That is, it is possible to purify the crude lactide once solidified, or to purify the crude lactide obtained by depolymerizing low molecular weight polylactic acid while maintaining the molten state without solidifying it. it can.

Regardless of the state of the crude lactide, when the crude lactide is brought into contact with ethanol, a slurry-like mixture is obtained. The contact between the crude lactide and ethanol can be carried out batchwise or continuously.

The solid content is separated and recovered from the obtained slurry mixture. This operation can be performed in a batch system or a continuous system. Further, the operation of contacting the crude lactide with ethanol and the operation of separating and collecting the solid content can be repeated a plurality of times. That is, after the crude lactide is brought into contact with ethanol, the solid content is separated, the obtained solid content is brought into contact with fresh ethanol again, and then the solid content is separated and recovered, and a repeated operation can be performed.

The ethanol used in the present invention is a liquid mainly containing ethanol, and includes both undenatured ethanol and denatured ethanol. The content of ethanol is 50% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more.

The denatured ethanol is obtained by mixing a denaturant with ethanol. As a modifying agent to be mixed,
Synthetic chemicals and natural substances are included. These denaturants can usually be used in an amount of 1 g to 200 g per liter of ethanol.

As synthetic chemicals, methanol, benzol, toluene, methyl ethyl ketone, denatonium benzoate, ethylene glycol monoethyl ether,
Chloroform, diethyl carbonate, ethyl acetate, ethyl propionate, ethyl butyrate, hexane, industrial ethyl ether, geraniol, octaacetylated sucrose, phenylethyl alcohol, diethyl phthalate, alkylbenzene sulfonate aqueous solution, vinyl acetate monomer, heptane, Isopropyl alcohol, butanol, ethyl acrylate, brucine, linalool, linalool acetate, benzyl acetate, seed vinegar, brewed vinegar, formalin, rhodamine B, white lac, purified shellac, white lac solution, purified shellac solution, paraoxybenzoic acid Butyl and the like can be used.

Natural substances include distilled vinegar, orange recovered aroma, grape recovered aroma, wine recovered aroma,
As a food additive such as natural butter flavor, fermented lactic acid, fermented grain extract, orange oil, lemon oil, lime oil, turmeric orange, vanilla extract, coffee recovery aroma, miso recovery aroma, soy sauce oil essence, malt essence, chicory essence Useable ones are listed. These may be used alone, but are usually used as a mixture.

In order to obtain purified lactide for use as a food additive, among these modifiers, flavors derived from natural substances usable as food additives are particularly preferred. More specifically, flavors H-1 and H- manufactured by Hasegawa Koran Co., Ltd.
2, H-3, H-4, H-6, H-9, H-10, H-
11, H-12, H-13, H-14, flavors T-100, T-101, T-1 manufactured by Takasago International Corporation
02, T-103, T-104, T-105, T-10
6, T-107, EDA-171, flavor S-201 manufactured by Soda Perfume Co., Ltd., and flavor DA-40 manufactured by Riken Perfumery Co., Ltd. can be used. What kind of denaturing agent is used is variously selected depending on the use of the food additive.

As ethanol, a mixture of water and a denaturing agent can be used, but the amount of water to be mixed is 0 to 10 parts by weight, preferably 0 to 5 parts by weight, more preferably 100 parts by weight of ethanol. Is from 0 to 0.1 parts by weight. If the amount exceeds 10 parts by weight, the yield of purified lactide decreases, which is not preferable.

In order to obtain purified lactide for use as a food additive, it is naturally preferable to use undenatured ethanol.

In contact with the crude lactide, ethanol can be used in an amount of usually 10 to 600 parts by weight, preferably 20 to 400 parts by weight, more preferably 30 to 200 parts by weight, based on 100 parts by weight of the crude lactide. If the amount of ethanol is less than 10 parts by weight, separation of meso-lactide and various impurities tends to be insufficient. On the other hand, when the amount exceeds 600 parts by weight, the separation of impurities is sufficient, but the yield of purified lactide decreases, and the cost is disadvantageous because of the large amount of ethanol used.

When the crude lactide in the solid state is brought into contact with ethanol, the coarse lactide particles preferably pass through 4 mesh, preferably through 6 mesh, more preferably through 10 mesh. In the case of coarse lactide particles that do not pass through the 4 mesh, a sufficient contact area between the crude lactide and ethanol cannot be obtained, so that the separation of impurities tends to be insufficient.

Crude lactide previously crushed into particles that have passed through 4 mesh may be used, or lactide may be crushed to 4 mesh or less by a stirrer or the like while contacting the lactide with ethanol.

As a method for previously grinding the crude lactide,
Although not particularly limited, for example, pulverization can be performed using a coarse crusher such as a jaw crusher mill, a hammer crusher mill, a roll crusher mill, a cage mill, a hammer mill, or a medium crusher. If necessary, a particle classifier or the like may be used after the pulverization to remove particles that do not pass through the 4-mesh.

The method for contacting the crude lactide in solid state with ethanol is not particularly limited,
A method in which crude lactide and ethanol are charged into a container and left to contact, a method in which the crude lactide is contacted in a container equipped with a stirrer, a method in which the crude lactide is contacted in a solid-liquid extraction device, and the like are used.
In addition, using a plurality of these devices, the crude lactide can be brought into contact with ethanol in multiple stages.

On the other hand, the method of bringing the crude lactide in liquid state into contact with ethanol is not particularly limited. A method of discharging the crude lactide in a liquid state into ethanol through a nozzle or the like in the form of a shower or a spray is effective.
Further, the slurry obtained by contacting in a vessel equipped with a stirrer to precipitate lactide can be further contacted with fresh ethanol in a solid-liquid extractor.

Examples of the stirring device include a double ribbon blade stirring device, a full zone blade stirring device, a disk turbine blade stirring device, a rotary blade stirring device such as a homomixer, a jet flow, a stirring device using a circulating flow, and a stirring device using a static mixer. Is used. When the crude lactide is pulverized by a stirring device after or simultaneously with the mixing of the crude lactide and ethanol, among these stirring devices, a disk turbine blade stirring device having a large shearing effect, a homomixer, and the like are effective.

A solid-liquid extraction device includes a rotocell extractor,
A Kennedy extractor, a Bonoteau extractor and the like are used. In these solid-liquid extraction devices, ethanol can be brought into contact with the crude lactide, and the solid content can be separated in the same device. However, since the content of ethanol in the separated solid content is large, it is preferable to further perform an operation of re-separating the solid content using another device.

In the present invention, the temperature at which the crude lactide is brought into contact with ethanol is preferably a low temperature in order to suppress the decomposition of L-lactide and / or D-lactide by reaction with ethanol or water. ℃,
Preferably 10 to 50 ° C, more preferably 20 to 40 ° C.
It is about ° C.

When the molten crude lactide is brought into contact with ethanol, or when the temperature rises due to liquid friction due to stirring or the like, it is preferable to contact the crude lactide with ethanol while cooling to prevent the contact temperature from rising. .

The time for bringing the crude lactide into contact with ethanol should be determined according to the capacity of the apparatus and the purity of the purified lactide to be obtained.
0 hours.

In the present invention, a solid content is separated from a slurry mixture obtained by contacting crude lactide with ethanol. In addition, lactide can also be recovered from the ethanol solution after the solid content is separated by crystallization, concentration, or the like. This is one of the great advantages of the present invention, which cannot be realized by the purification method by contact with water described in JP-A-7-165755.

The method of separating solids is not particularly limited, but a method of separating using a centrifugal sedimentation machine, a centrifugal filtration machine, a pressure filtration device or the like is used. When using a device having a function of rinsing solids among these devices, the operation of bringing the solids into contact with ethanol and the operation of separating the solids can be performed in parallel using the same device. Is effective in

As a centrifugal sedimenter, a vertical basket type centrifugal sedimenter, a screw decanter type centrifugal sedimenter or the like is used. As the centrifugal filter, a vertical basket type centrifugal filter, a screw decanter type centrifugal filter, a conical screen type centrifugal filter, or the like is used. As a pressure filtration device,
A gravity filter, a pressure filter, a vacuum filter, or the like is used.
By the above operation, a purified lactide solid content from which meso-lactide and other impurities have been removed is obtained.

In the present invention, after the solid content is separated as described above, it is preferable to wash the separated solid content with water in order to remove ethanol from the solid content.
By washing with water, the content of ethanol in purified lactide can be significantly reduced, and problems such as residual ethanol odor of purified lactide are eliminated.

This water washing may be performed by bringing the solid content into contact with water. The water washing operation can be performed in a batch system or a continuous system. Further, the water washing operation can be repeated a plurality of times. That is, it is also possible to repeat the operation of contacting the solid content with water to separate the solid content, bringing the obtained solid content into contact with fresh water again, and then separating and collecting the solid content.

In this washing operation, water is usually added to 100 parts by weight of a solid content separated after contact with ethanol, and is usually 1 to 10 parts by weight.
0 to 200 parts by weight, preferably 20 to 100 parts by weight, more preferably 30 to 60 parts by weight can be used. If the amount of washing water is less than 10 parts by weight, the action of removing ethanol is somewhat weak. If it exceeds 200 parts by weight, the yield of purified lactide will be low.

The temperature of the water contact washing is preferably low to suppress the decomposition reaction of L-lactide and / or D-lactide, and is usually 0 to 40 ° C., preferably 10 to 3 ° C.
0 ° C, more preferably 10 to 20 ° C.

The washing time with water is preferably short in order to suppress the decomposition reaction of L-lactide and / or D-lactide, and the time required for ethanol to dissolve in water is sufficient. Therefore, it is usually 10 seconds to 20 minutes, preferably 10 seconds to 5 minutes, more preferably 10 seconds to 1 minute.

For the water contact cleaning, an apparatus similar to the above-described apparatus for bringing crude lactide into contact with ethanol can be used. Separation of the solid content from the slurry after contact with water can be performed using the same device as the solid content separation device described above. Among these devices, a centrifugal filter and a pressure filtration device having a function of rinsing solids are particularly preferable because the contact time with water can be shortened and uniform contact with water is possible. It is.

In the present invention, the solid separated after contact with ethanol as described above or the solid obtained after washing with water is preferably dried under reduced pressure. The purified lactide obtained as a solid content usually contains the used ethanol, water, and in some cases substances contained in ethanol (eg, water, methanol, isopropyl alcohol, methyl ethyl ketone, ethyl acetate, etc.).
Is attached. These adhesions may deteriorate the fluidity of the obtained purified lactide particles or may cause a problem of the odor. Therefore, in order to reduce the attached substance, the solid content may be dried under reduced pressure.

The drying under reduced pressure is preferably performed at a low temperature in order to suppress the decomposition of lactide by reaction with ethanol or water due to heating, and is usually performed at a low temperature of 10 to 95.
° C, preferably about 10 to 60 ° C, 0.01 to 1
It can be performed at a pressure of about 00 Torr. Freeze-drying can also be performed at a pressure of about 0.001 to 10 Torr and a temperature of 0 ° C. or less. The drying time should be determined depending on the capacity of the drying apparatus, the amount of lactide to be dried, or the content of ethanol and water in the purified lactide to be obtained, but is usually 5 minutes to 10 hours.

When the drying under heating and reduced pressure is carried out, a tray drying machine, a cylindrical stirring dryer, a conical rotary dryer and the like can be used without limitation. When freeze-drying is performed, a shelf-stage dryer can be used without limitation.

[0068]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. [Synthesis Example 1 of Lactide] Lactic acid (Pu) was placed in a 2 L SUS separable flask equipped with a thermometer, stirrer, condenser, distillate receiver, decompression device, heating temperature control device, etc.
1000 g of HS-88 manufactured by rac: 88.1% by weight in terms of lactic acid monomer: 99.2% ee in optical purity. First, at 130 ° C. for 2 hours at normal pressure, and then 13
The temperature was gradually increased from 0 ° C. to 160 ° C. in 4 hours, and about 703 g of polylactic acid having a weight average molecular weight of 2150 as measured by GPC.
I got

To this low-molecular-weight polylactic acid was added 10.0 g of tin octylate, and the temperature was gradually increased from 160 ° C. to 200 ° C. under reduced pressure.
g was distilled off and collected.

When the composition of the obtained crude lactide was analyzed by high performance liquid chromatography (HPLC), L-lactide and D-lactide: 92.54%, meso-lactide:
3.29%, linear dimer of lactic acid: 0.77%, lactic acid:
It was 3.40%.

Example 1 The crude lactide obtained in Synthesis Example 1 was ground in a mortar and passed through a 10-mesh sieve. 50 g of crude lactide passed through this sieve and 25 ° C.
99 degree 1st grade native ethanol (fermented alcohol) 1
And 5 g thereof in a beaker to obtain a slurry-like mixed solution, which was stirred for 15 minutes with a stirrer. Glass filter mounted on a filter bottle (Buchner type, maximum pore size 20-30 μm)
The slurry was transferred to a filter bottle with an aspirator for about 1 hour.
The pressure was reduced for a minute, and the liquid in the slurry was suction-filtered. After suction filtration, 15 g of 99 ° C. first-grade unmodified ethanol (fermentation alcohol) at 25 ° C. was newly added to the glass filter, and the filtration bottle was subjected to reduced pressure for about 1 minute with an aspirator, followed by suction filtration.

The separated solid was dried using a rotary evaporator at 40 ° C. and 4 Torr for 1 hour to obtain 43.9 g of purified lactide (purification yield: 87.8%).
When the composition of the obtained purified lactide was analyzed by HPLC,
L-lactide and D-lactide: 98.21%, meso-
Lactide: 1.18%, linear dimer of lactic acid: 0.24
%, Lactic acid: 0.37%.

The ethanol content of the purified lactide was determined by gas chromatography (GC) to be 54%.
It was 0 ppm, and a slight ethanol odor was felt. The water content of the purified lactide was 35 ppm as measured by a Karl Fischer moisture meter. In addition, this purified lactide is in the form of particles having good flowability, sealed,
This fluidity was not lost after storing the tubes at 20 ° C. for one month.

Example 2 The crude lactide obtained in Synthesis Example 1 was ground in a mortar and passed through a 10-mesh sieve. 50 g of crude lactide passed through this sieve and 25 ° C.
99 degree 1st grade native ethanol (fermented alcohol) 1
And 5 g thereof in a beaker to obtain a slurry-like mixed solution, which was stirred for 15 minutes with a stirrer. Glass filter mounted on a filter bottle (Buchner type, maximum pore size 20-30 μm)
The slurry was transferred to the flask, and the pressure in the filter bottle was reduced by an aspirator for 1 minute, and the liquid in the slurry was suction-filtered. After suction filtration, another 15 g of 99 ° C. first-grade unmodified ethanol (fermentation alcohol) at 25 ° C. was added to the glass filter, and the filtration bottle was evacuated with an aspirator for 1 minute and suction-filtered.

After suction filtration, the glass filter was newly added to 25 ° C.
Of water was added, and the pressure in the filter bottle was immediately reduced by an aspirator, followed by suction filtration. The separated solid was dried using a rotary evaporator at 40 ° C. and 4 Torr for 2 hours to obtain 43.5 g of purified lactide (purification yield: 87.50 g).
0%). When the composition of the obtained purified lactide was analyzed by HPLC, L-lactide and D-lactide: 98.23
%, Meso-lactide: 1.11%, linear dimer of lactic acid:
0.27%, lactic acid: 0.39%.

The ethanol content of the purified lactide measured by GC was 34 ppm, and almost no ethanol odor was sensed. The water content of the purified lactide was 89 ppm as measured with a Karl Fischer moisture meter. Further, the purified lactide was in the form of particles having good flowability, and the flowability was hardly lost even after sealing and storing the tube at 20 ° C. for one month.

Example 3 (Synthesis of lactide) Thermometer, stirrer, condenser,
Lactic acid (Purac HS-8) was placed in a 1.3 kL reactor equipped with a distillate receiver, a decompression device, a temperature control device, and the like.
8: Lactic acid monomer equivalent concentration 88.1% by weight: Optical purity 9
(9.2% ee) 1000 kg was charged. First, normal pressure,
3 hours at 130 ° C, then gradually from 130 ° C under reduced pressure for 6 hours
The temperature was raised to 160 ° C. over a period of time to obtain about 702 kg of polylactic acid having a weight average molecular weight of 2490 as measured by GPC.

To this low-molecular-weight polylactic acid was added 10.0 kg of tin octylate, and the temperature was gradually increased from 160 ° C. to 200 ° C. under reduced pressure, and 697 kg of crude lactide was obtained in about 3 hours.
Was distilled off and collected. The composition of the obtained crude lactide was determined by HPL
When analyzed by C, L-lactide and D-lactide: 9
1.93%, meso-lactide: 4.18%, linear dimer of lactic acid: 0.64%, lactic acid: 3.25%.

(Purification of lactide) Capacity 1.8 k with disk turbine blade stirring device, thermometer, temperature control device, etc.
530L (418.2kg) 99 degree 1
Grade native ethanol (fermented alcohol)
Cooled to 0 ° C. Mixing tank with disk turbine blade 60r
While stirring at pm, the entire amount of the crude lactide obtained in the above synthesis is maintained in a molten state (103 ° C.), and a four-hole nozzle (each having a diameter of 2 m) capable of discharging in the form of a shower.
m), it was supplied at a discharge rate of about 10 L per minute in about 60 minutes.

While supplying the crude lactide in the molten state,
Cooling was performed by a temperature controller to prevent the temperature inside the mixing tank from rising, but the internal temperature at the end of the supply was 32 ° C due to insufficient cooling capacity.
It became. After the end of the supply, stirring and temperature control (set temperature 20
° C) was continued. One hour after the completion of the supply, the internal temperature was 20 ° C.

One hour after the completion of the supply, about 1/5 of the slurry in the mixing tank was supplied to a vertical basket-type centrifugal filter having a basket diameter of 1000 mm and a basket depth of 400 mm in about 90 seconds. Was isolated. The rotation of the basket during slurry supply was 300 rpm.

After the supply of the slurry is completed, the rotation speed of the basket is set to 800 rpm in order to further improve the solid content separation.
And the liquid was removed for 10 minutes. After the drainage, the rotation speed of the basket was lowered to 500 rpm, and 99% first-grade undenatured ethanol (fermented alcohol) at 20 ° C. was discharged in a spray form from a spray nozzle for rinsing liquid supply, and 71 L of water was discharged.
(56.0 kG) was supplied in about 120 seconds, and fresh ethanol was brought into contact with the solid content in the basket, and at the same time, the solid content was separated.

After the end of the supply of ethanol, the rotation speed of the basket was increased to 800 rpm in order to further improve the separation of solids.
m, and the liquid was removed for 10 minutes. After the completion of the liquid removal, the solid content in the basket was scraped off and charged into a conical rotary dryer (double cone dryer) having a tank volume of 1.1 kL. Thereafter, the operation from the supply of the slurry to the centrifugal filter to the introduction of the solid content to the conical rotary dryer was repeated four times to treat the entire amount of the slurry in the mixing tank.

The conical rotary drier was rotated at 10 rpm, and the charged solid was dried at 50 ° C. and 2 Torr for 6 hours to obtain 611 kg of purified lactide (purification yield: 87.0%).

When the composition of the obtained purified lactide was analyzed by HPLC, L-lactide and D-lactide: 98.7 were obtained.
6%, meso-lactide: 0.82%, linear dimer of lactic acid: 0.19%, lactic acid: 0.23%.

The ethanol content of the purified lactide measured by GC was 360 ppm, and a slight ethanol smell was felt. The water content of this purified lactide was measured using a Karl Fischer moisture meter to be 21 p.
pm. The purified lactide was in the form of particles having good flowability, and the flowability was not lost even after the tube was sealed and stored at 20 ° C. for 1 month.

The present invention may be embodied in various other forms without departing from its spirit or essential characteristics. Therefore, the above-described embodiment is merely an example in every aspect, and should not be construed as limiting. Furthermore, all modifications belonging to the equivalent scope of the claims are within the scope of the present invention.

[0088]

According to the present invention, as described above, a purified lactide having a high content of L-lactide and / or D-lactide can be obtained in a short time and in a high yield by a simple apparatus and operation. Can be. Further, according to the present invention, a purified lactide having good workability can be obtained without leaving an organic solvent harmful to the human body. The purified lactide obtained according to the present invention is inexpensive and suitable for use in food additives.

Claims (6)

[Claims] 1. L-lactide and / or D-lactide by contacting crude lactide in a solid state or at least partly in a molten state with ethanol to obtain a slurry-like mixture, and thereafter separating a solid content from the mixture. A method for purifying lactide, characterized by obtaining a purified lactide having a high content of lactide. 2. The method for purifying lactide according to claim 1, wherein after separating the solid content, the separated solid content is dried under reduced pressure. 3. The method for purifying lactide according to claim 1, wherein after separating the solid, the separated solid is washed with water to remove ethanol. 4. After washing with water, the solid content is dried under reduced pressure.
A method for purifying lactide according to claim 3. 5. The lactide according to claim 1, wherein the crude lactide to be purified is a crude lactide in a molten state obtained by depolymerizing low molecular weight polylactic acid. Purification method. 6. A purified lactide obtained by the method according to any one of claims 1 to 5.