JPH10204156A - Production of polyhydroxycarboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent biodegradable plastic by subjecting a mixture mainly comprising a hydroxycarboxylic acid or its oligomer obtd. by the distillation of a hydroxycarboxylic acid or its lactide to polycondensation by dehydration in the presence of a polycondensation catalyst. SOLUTION: An aq. lactic acid soln. having a concn. of 50-90wt.% is dehydrated at 120-150 deg.C and distilled at 130-200 deg.C under a reduced pressure to give a mixture mainly comprising a 2-6C aliph. hydrocarboxylic acid (e.g. lactic acid). A mixture mainly comprising lactic acid is melted by heaing to 120-180 deg.C in a nitrogen atmosphere in the presence of 0.03-10wt.% (based on the mixture) catalyst comprising an inorg. solid acid catalyst (e.g. aluminum silicate) alone or a combination thereof with an alkali metal compd. catalyst and then is subjected to polycondensation at 160-250 deg.C under a reduced pressure, thus giving a polymer having an average mol.wt. of 50,000-300,000. The polymer is used for wrapping films, drink bottles, drug delivery systems, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyhydroxycarboxylic acid, particularly a polyhydroxycarboxylic acid having a weight average molecular weight of 50,000 or more. The polyhydroxycarboxylic acid is used as a biodegradable plastic in food packaging films, beverage bottles, drug delivery systems and the like.

[0002]

2. Description of the Related Art Polyhydroxycarboxylic acids are produced by polymerizing hydroxycarboxylic acids such as lactic acid and glycolic acid. A method of directly dehydrating and polycondensing an acid is known.

In the method by ring-opening polymerization of lactides, U
Although high-molecular-weight polyhydroxycarboxylic acids are produced as described in SP 2,703,316 and US Pat. No. 2,758,987, this method requires high-purity lactides, requires many steps, is complicated, It is not always satisfactory as a typical manufacturing method. On the other hand, the method of directly dehydrating polycondensation of hydroxycarboxylic acid has a small number of steps,
This method is high in yield, low in cost and industrially excellent. For example, JP-A-61-28521 discloses that polycondensation of lactic acid and / or glycolic acid in the presence or absence of an inorganic solid acid catalyst results in a weight average molecular weight of 5,000 or more, usually 5,000 to 5,000. A method for making 30,000 lactic acid or glycolic acid polymers or copolymers is disclosed. However, polymers or copolymers having a weight average molecular weight of 30,000 or less are unsatisfactory in physical properties as a biodegradable plastic.

JP-A-6-65360 discloses that a hydroxycarboxylic acid or an oligomer thereof is subjected to a dehydration-condensation reaction in a reaction mixture containing an organic solvent in the substantial absence of water, and has a weight average molecular weight of 15,000 or more. , Usually 5,000
A method for producing 0 to 200,000 polyhydroxycarboxylic acids is disclosed. However, in this method, the operation of dehydrating the organic solvent distilled off together with the generated water and returning it to the reaction system is complicated.

Further, in the method of dehydration polycondensation in an organic solvent using hydroxycarboxylic acid or its oligomer, it is known that impurities in the raw material lactic acid or hydroxycarboxylic acid containing lactic acid inhibit the increase in molecular weight. Therefore, it has been proposed to increase the molecular weight by using a high-purity raw material. JP-A-7-2987 discloses L-
By using lactic acid obtained by hydrolyzing lactide, a polyhydroxycarboxylic acid having a weight average molecular weight of 120,000 to 340,000 is obtained. However,
In this method, impurities are removed by purification at the L-lactide stage. In this method, the process is longer than in the ring-opening polymerization method of lactide, and it cannot be said that this method is an industrial production method.

[0006] JP-A-6-279577 discloses that acetaldehyde is added to hydroxycarboxylic acid as a raw material in an amount of 0.
3 mol% or less, and in JP-A-7-133344, methanol, ethanol, acetic acid, pyruvic acid, fumaric acid, methyl lactate, ethyl lactate and the like are used in a total of 0.3 mol% with respect to the starting hydroxycarboxylic acid. It discloses a method for obtaining a polyhydroxycarboxylic acid having a weight average molecular weight of 50,000 or more by using the following hydroxycarboxylic acid as a raw material. Not described.

WO 95/28432 discloses that hydroxycarboxylic acid or its oligomer is converted to aluminum oxide 5
A method for producing a polyhydroxycarboxylic acid having a weight average molecular weight of 50,000 or more by polycondensation in the presence of aluminum silicate containing ４０40% by weight is disclosed. However, polyhydroxycarboxylic acids obtained by this method have some problems in terms of hue.

As described above, a method for easily producing a high-quality polyhydroxycarboxylic acid having excellent performance as a biodegradable plastic has not been known.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to directly dehydrate and polycondense a hydroxycarboxylic acid to obtain a polyhydroxycarboxylic acid having a weight average molecular weight of 50,000 or more, which has excellent properties as a biodegradable plastic. A method of manufacturing is provided.

[0010]

The present invention is characterized in that a mixture mainly composed of hydroxycarboxylic acid or its lactide obtained by distilling hydroxycarboxylic acid or its oligomer is used as a raw material for polycondensation. Provided is a method for producing a polyhydroxycarboxylic acid.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the polyhydroxycarboxylic acid includes a polymer of hydroxycarboxylic acid and a copolymer of hydroxycarboxylic acid. The hydroxycarboxylic acid used in the present invention has 2 carbon atoms.
And aliphatic hydroxycarboxylic acids of No. 6 to 6, for example, lactic acid, glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, etc., preferably lactic acid. These may be used alone or as a mixture of two or more. The form of the hydroxycarboxylic acid may be a D-form and an L-form alone, or a mixture of the D-form and the L-form.

When a copolymer is produced, two or more hydroxycarboxylic acids may be arbitrarily mixed or a hydroxycarboxylic acid and a cyclic compound of the hydroxycarboxylic acid may be mixed. γ
-A cyclic compound of a hydroxycarboxylic acid such as butyrolactone and ε-caprolactone may be mixed. Further, the copolymer preferably contains lactic acid.

The lactides used in the production method of the present invention include lactide and glycolide, which are cyclic dimers of the hydroxycarboxylic acid used. Examples of the shape of the hydroxycarboxylic acid used in the present invention include a solid and an aqueous solution. In the case of lactic acid, usually, commercially available 50
A ~ 90% by weight aqueous solution is used.

The raw material for polycondensation in the production method of the present invention can be obtained by distilling hydroxycarboxylic acid or its oligomer. Examples of the distillation format include simple distillation and continuous distillation. As a distillation operation in the production method of the present invention, a case where a commercially available lactic acid aqueous solution is distilled will be described below as an example. First, remove the aqueous lactic acid solution before distillation.
A dehydration operation is performed at 20 to 150 ° C. for 5 to 10 hours to remove coexisting water in advance. At this time, a part of lactic acid causes oligomerization or cyclization reaction to produce lactide, but this does not cause any particular problem. Further, this is heated to 130 to 200 ° C., preferably 140 to 160 ° C., and the pressure is gradually reduced.
0 mmHg, preferably 0.5 to 5 mmHg.
By this distillation operation, a mixture containing lactic acid as a main component is obtained. The obtained mixture can be used as a raw material for a polycondensation reaction.

5 to 20% by weight based on the residue after distillation
After adding water and depolymerizing at 100 to 150 ° C.,
This fraction is heated to 140-160 ° C. and gradually 1-20
By adjusting to mmHg, a mixture containing lactide as a main component is obtained, and this mixture can be used as a raw material for polycondensation. Further, a lactide-forming catalyst is added to an aqueous lactic acid solution, and after the removal of water and the production of the oligomer, cracking distillation is performed at 150 to 250 ° C, preferably 150 to 200 ° C, 1 to 20 mmHg, preferably 1 to 10 mmHg. By
A mixture containing lactide as a main component is obtained, which can be used as a raw material for polycondensation. Examples of the lactide catalyst include metals such as zinc, tin and antimony, and salts, hydroxides and oxides thereof.
The amount of use is 0.0001 to the above lactic acid aqueous solution.
10% by weight is used.

When it is desired to lower the optical purity of the obtained polylactic acid, the lactide-forming catalyst is made of an alkali metal compound or an alkaline earth metal compound,
Decomposition distillation of the oligomer is performed under the conditions of 10 mmHg.
Further, a mixture containing lactide having a low optical purity as a main component obtained by the above method and a mixture obtained by an ordinary method are mixed at an appropriate ratio, and a polylactic acid having a desired optical purity is obtained by performing a condensation reaction. Can be obtained.

Further, the distillation operation of hydroxycarboxylic acid other than lactic acid can be carried out according to the above-mentioned distillation operation of lactic acid. Polyhydroxycarboxylic acid can be obtained by performing dehydration polycondensation in the presence of a polycondensation catalyst using a mixture containing hydroxycarboxylic acid or lactide as a main component obtained by distillation as described above as a raw material for polycondensation. it can.

Examples of the polycondensation catalyst include tin and the like.
Polycondensation can be carried out in the presence of an organic solvent according to the method described in JP-A-6-65360. Preferably, an inorganic solid acid catalyst is used as the polycondensation catalyst. Examples of the inorganic solid acid include aluminum silicate, silica gel, zeolite, aluminum oxide, magnesium silicate, activated clay, acid clay, alumina boria, bentonite, kaolin, talc, silicate and the like. These can be used alone or in combination of two or more. As a polycondensation method using an inorganic solid acid, WO95 / 284
32 can be performed.

More preferably, an inorganic solid acid catalyst and an alkali metal compound catalyst or an alkaline earth metal compound catalyst are used in combination as a polycondensation catalyst. Examples of the alkali metal compound or alkaline earth metal compound catalyst include inorganic salts such as carbonates and bicarbonates of alkali metals such as lithium, sodium and potassium or alkaline earth metals such as magnesium and calcium, lactic acid, and glycolic acid. And the like, an organic acid salt such as acetic acid, an oxide, a hydroxide and the like. The alkali metal compound or alkaline earth metal compound catalyst contains 10 alkali metal or alkaline earth metal dissolved in the reaction solution.
A method is employed in which it is added so as to have a concentration of 1 to 10,000 ppm, preferably 10 to 3000 ppm, or is added to an inorganic solid acid catalyst in advance and eluted during the reaction to the above concentration.

As a method of using an inorganic solid acid catalyst in combination with an alkali metal compound catalyst or an alkaline earth metal compound catalyst, for example, the following method is used. (1) An inorganic solid acid catalyst is treated with an aqueous solution of an alkali metal compound or an alkaline earth metal compound catalyst such as carbonate, bicarbonate or hydroxide to form an alkali metal compound catalyst or an alkaline earth metal catalyst. A method using a metal supported on an inorganic solid acid catalyst, the metal of which is confirmed to be dissolved in a metal dissolution confirmation test similar to Example 1 described below. (2) An inorganic solid acid catalyst which already contains an alkali metal compound catalyst or an alkaline earth metal catalyst and whose metal elution has been confirmed by a metal elution confirmation test similar to Example 1 described later. Without performing the processing of (1) above,
It can be used as it is. As an example of the catalyst, zeolite is used. (3) Whether to add an inorganic solid acid catalyst of the raw material solution and a carbonate, bicarbonate, hydroxycarboxylate, acetate, hydroxide, oxide or the like of an alkali metal catalyst or an alkaline earth metal compound catalyst Of adding a carbonate, bicarbonate, hydroxycarboxylate, acetate, hydroxide, oxide, or the like of an alkali metal compound catalyst or an alkaline earth metal catalyst to a reaction solution containing an inorganic solid acid catalyst .

The inorganic solid acid catalyst is used in an amount of 0.03 to 10% by weight, preferably 0.5 to 7% by weight, more preferably 1 to 3% by weight, based on the hydroxycarboxylic acid and lactide after distillation.
5% by weight is used in one or several portions. The catalyst may be added to the raw material for polycondensation either as a solid or dissolved or dispersed in an appropriate solvent (eg, toluene, xylene, etc.), or may be added to the reaction system as needed during the reaction. Good.

When the raw material for the polycondensation is a mixture containing hydroxycarboxylic acid as a main component, the oligomer is produced by conducting the reaction at 120 to 180 ° C. for 5 to 10 hours under a normal pressure and a nitrogen stream before the polycondensation reaction. I do. When the polycondensation raw material is a mixture containing lactides as a main component, the polycondensation raw material is heated and melted at 120 to 180 ° C. under a normal pressure and a nitrogen stream before the polycondensation reaction.

The polycondensation reaction is carried out at 160 to 250 ° C, preferably 180 to 240 ° C, more preferably 180 to 220 ° C.
° C, 0.05-40 mmHg, preferably 0.1-25
The reaction is carried out at mmHg for 5 to 50 hours, preferably for 10 to 30 hours. After the reaction, it is obtained in a molten state, and then cooled to room temperature to obtain a solidified hydroxycarboxylic acid polymer.

The polycondensation reaction of the production method of the present invention can be carried out by a continuous operation or a batch operation. The lactides recovered from the polycondensation reaction system may be recycled to the raw materials. Various weight-average molecular weights of the polyhydroxycarboxylic acid obtained by the production method of the present invention can be obtained depending on the type and amount of the catalyst, the reaction temperature, the reaction pressure, and the reaction time, but usually about 50,000 to 300, 000. Further, the polyhydroxycarboxylic acid shows a good hue.

Hereinafter, the present invention will be described with reference to Examples.
Of course, the present invention is not limited to these examples.

[0026]

EXAMPLES In the Examples, the weight average molecular weight of the lactic acid polymer, and the tensile strength at break and the tensile elongation at break were measured by the following methods. (1) Measurement of weight average molecular weight of lactic acid polymer The lactic acid polymer was dissolved in chloroform to make a 0.2% by weight chloroform solution, and then subjected to gel permeation chromatography (GPC) using standard polystyrene having a known molecular weight. It was measured. GPC column is TOSO
HG-5000, TOSOH G-3000, TOS
OH G-1000 [Tosoh Corporation] was connected in series, and the column holding temperature was 40 ° C., and the measurement was performed.

(2) Measurement of Tensile Breaking Strength and Tensile Breaking Elongation of Lactic Acid Polymer After dissolving the lactic acid polymer in chloroform, a film (thickness: 50 to 100 μm) was formed by a casting method. A No. 2 test piece was prepared from this film in accordance with JIS K-7127, and the tensile strength at break and the tensile elongation at break were measured at a tensile strength of 1 mm / min.

Example 1 A 90% by weight aqueous solution of L-lactic acid [Stale
y) Co.] was added to a reaction vessel equipped with a stirrer, a Liebig condenser, and a nitrogen inlet tube, and the atmosphere was replaced with nitrogen three times.
And Further, the pressure was finally reduced to 1 mmHg.
286.0 g (recovery rate: 53%) of a mixture containing lactic acid as a main component and distilled out into a receiver cooled with ice water was obtained. 141.4 g remained in the reactor as residue.

The resulting mixture containing lactic acid as a main component was dissolved in acetone, and titrated with a 0.1 N KOH / ethanol solution using BTB (bromthymol blue) as an indicator. The lactic acid content was equivalent to a degree of polymerization of 1.19 as a lactic acid oligomer. This lactic acid-based mixture 25
0.0 g was reacted at 140 ° C. for 5 hours under a nitrogen stream,
208.5 g of lactic acid oligomer was obtained. When the degree of polymerization was measured by titration in the same manner as above, the degree of polymerization was 3.39.

0.43 g of synthetic aluminum silicate [Tomita Pharmaceutical Co., Ltd.] (Note 1) was added to 21.46 g of this oligomer, and the temperature was raised to 200 ° C. and gradually increased to 20 m over 30 minutes.
The pressure was reduced to mHg, and the mixture was stirred at 200 ± 5 ° C. for 1 hour.
Stirred for hours. After cooling to room temperature, 11.43 g of solidified milky white polylactic acid was obtained.

Weight average molecular weight of lactic acid polymer 83,000 (Note 1) Synthetic aluminum silicate [Tomita Pharmaceutical Co., Ltd.]
After adding 2.0 g to 100 g of the oligomer, the mixture was stirred at 80 ° C. for 24 hours under a nitrogen atmosphere. Then, after adding chloroform, the mixture was filtered through filter paper, and further filtered through a 0.1 μm membrane filter. After confirming that the filtrate was transparent, the alkali metal eluted in the filtrate (lactic acid oligomer) was subjected to IPC (inductively coupled high frequency plasma) [apparatus:
UOP-1MARK-II Kyoto Koken Co., Ltd.]. As a result, 490 ppm of sodium was detected from the filtrate. In the following Examples and Comparative Examples, the same synthetic aluminum silicate as described above [Tomita Pharmaceutical Co., Ltd.] was used.

Example 2 90% by weight aqueous L-lactic acid solution [Wako Pure Chemical Industries, Ltd.]
2 g and tin (Sn) powder 0.31 g were added to a reaction vessel equipped with a stirrer, a Dean-Stark tube, and a nitrogen inlet tube,
After performing nitrogen substitution three times, the temperature was raised to an external temperature of 150 ° C. at a rate of 10 ° C./min under a nitrogen stream, and the pressure was gradually reduced to 27 mmHg.
As a result, a lactic acid oligomer was obtained.

Thereafter, the internal temperature was set at 163 to 181 ° C.,
Decomposition distillation was performed under the condition of 6 mmHg to obtain 43.1 g of a mixture containing lactide as a main component. The mixture containing lactide as a main component was analyzed by gas chromatography to find the following analysis values. Lactic acid 2.7% Meso lactide 3.1% L, D lactide 93.0% Lactic acid linear dimer 1.2% 20.0 g of this mixture was added to a 100 ml reaction vessel, and then stirred at 150 ° C. for 3 hours. Heated and melted for hours. 0.4 g of synthetic aluminum silicate [Tomita Pharmaceutical Co., Ltd.]
Was added, and the temperature was raised to 195 ± 5 ° C., and the pressure was gradually reduced over 30 minutes to 20 mmHg, followed by stirring for 1 hour.
Further, gradually increase the degree of decompression over 30 minutes, 1m
The mixture was stirred at 195 ± 5 ° C for 10 hours as mHg. After cooling to room temperature, 14.1 g of a milky white lactic acid polymer was obtained.

Weight average molecular weight of lactic acid polymer 102,000 Tensile breaking strength 295 kg / cm ² Tensile breaking elongation 8%

Comparative Example 1 A 90% by weight aqueous solution of L-lactic acid [Stale
y) (manufactured by a company) is added to a reaction vessel equipped with a stirrer, a Dean-Stark tube, and a nitrogen inlet tube, and after purging with nitrogen three times, the temperature is raised to 150 ° C. under a nitrogen stream to remove distilled water. While concentrating under normal pressure for 6 hours, a lactic acid oligomer was obtained. When the degree of polymerization of this lactic acid oligomer was measured in the same manner as in Example 1, the degree of polymerization was 5.04.

To 20.81 g of the obtained lactic acid oligomer, 0.42 g of synthetic aluminum silicate [Tomita Pharmaceutical Co., Ltd.] was added, and a polycondensation reaction was carried out in the same manner as in Example 1. As a result, a solidified black lactic acid polymer was obtained. Weight average molecular weight of lactic acid polymer 10,000

[0037]

According to the present invention, the weight average molecular weight of 50,0 used as a biodegradable plastic in food packaging films, beverage bottles, drug delivery systems and the like.
More than 00 polyhydroxycarboxylic acids can be produced.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Hotta 2-3-4 Oe, Ichinomiya, Aichi Prefecture

Claims (6)

[Claims] A polycondensation is carried out in the presence of a polycondensation catalyst using, as a raw material for polycondensation, a mixture mainly comprising hydroxycarboxylic acid or its lactide obtained by distilling hydroxycarboxylic acid or its oligomer. A method for producing a polyhydroxycarboxylic acid. 2. The method according to claim 1, wherein the hydroxycarboxylic acid is lactic acid. 3. The method according to claim 2, wherein the raw material for the polycondensation is a mixture containing lactic acid as a main component obtained by distilling an aqueous lactic acid solution. 4. The method according to claim 2, wherein the raw material for the polycondensation is a mixture containing lactide as a main component, which is obtained by producing an oligomer thereof from an aqueous lactic acid solution and then decomposing and distilling the oligomer. 5. The production method according to claim 1, wherein the polycondensation catalyst is a combination of an inorganic solid acid catalyst and an alkali metal compound or an alkaline earth metal compound catalyst. 6. The polyhydroxycarboxylic acid having a weight average molecular weight of 50,000 to 300,000.
5. The production method according to any one of 5.