JP2023159722A - Method for producing glycolic acid and polyglycolic acid - Google Patents

Abstract

To provide a method for efficiently producing plant-derived glycolic acid from sorghum useful as C4 plant, and a method for producing polyglycolic acid being biodegradable plastic from the plant-derived glycolic acid.SOLUTION: A method for producing glycolic acid includes: a first process of allowing enzyme to act on squeezed juice of sorghum, and saccharifying the squeezed juice to obtain sugar solution; a second process of executing alcohol fermentation on the sugar solution to obtain fermentation liquid containing ethanol; a third process of executing acetic fermentation on the fermentation liquid to obtain acetic acid; and a fourth process of introducing hydroxy group into α carbon of acetic acid to obtain glycolic acid.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing glycolic acid and polyglycolic acid.

In recent years, polyglycolic acid has attracted attention as a biodegradable plastic. Polyglycolic acid has high gas barrier properties (properties that make it difficult for oxygen gas and carbon dioxide gas to permeate), which cannot be achieved with other biodegradable plastics, and is expected to be used in various fields.

It is widely known that glycolic acid, which is the raw material monomer of polyglycolic acid, is manufactured from petrochemical raw materials (for example, Patent Document 1), but from the viewpoint of sustainability, it is difficult to manufacture it from plant raw materials. desired.

A method of obtaining glycolic acid from plant materials by fermentation or the like is known (for example, Patent Document 2), but a method of selectively obtaining glycolic acid with a high yield by a method such as fermentation is not known.

On the other hand, since sorghum is a C4 plant with high photosynthetic efficiency and can be easily cultivated, it is expected to be used as a raw material for processed products such as biodegradable plastics.

Japanese Unexamined Patent Publication No. 8-198802 JP2019-150824A

The present invention was made in view of the above-mentioned circumstances, and provides a method for efficiently producing plant-derived glycolic acid from sorghum, which is useful as a C4 plant, and a method for producing poly, which is a biodegradable plastic, from the plant-derived glycolic acid. An object of the present invention is to provide a method for producing glycolic acid.

In order to solve the above problems, the method for producing glycolic acid of the present invention includes:
A first step of applying an enzyme to the squeezed sorghum juice to saccharify the squeezed juice to obtain a sugar solution;
a second step of alcohol-fermenting the sugar solution to obtain a fermentation liquid containing ethanol;
A third step of fermenting the fermented liquid with acetic acid to obtain acetic acid;
A fourth step of obtaining glycolic acid by introducing a hydroxy group into the α carbon of the acetic acid;
It is characterized by including.

Furthermore, the method for producing polyglycolic acid of the present invention includes:
a step of producing glycolic acid by the method for producing glycolic acid of the present invention;
The method is characterized by comprising a step of dehydrating and polycondensing the glycolic acid to obtain polyglycolic acid.

According to the present invention, it is possible to provide a method for efficiently producing plant-derived glycolic acid from sorghum, which is useful as a C4 plant, and a method for producing polyglycolic acid, which is a biodegradable plastic, from the plant-derived glycolic acid.

FIG. 2 is a process flow diagram of an example of the method for producing glycolic acid according to the present embodiment. 2 is a more detailed process flow diagram of an example of the method for producing glycolic acid shown in FIG. 1. FIG. FIG. 2 is a process flow diagram of an example of the method for producing polyglycolic acid according to the present embodiment. FIG. 2 is a block diagram of an apparatus used in a method for producing polyglycolic acid according to an example.

Embodiments of the present invention will be described below with reference to the drawings as necessary. Note that, although various technically preferable limitations for carrying out the present invention are attached to the embodiments described below, the scope of the present invention is not limited to the following embodiments and illustrated examples.
In this specification, "~" is used to include the numerical values described before and after it as a lower limit value and an upper limit value.

[Production method of glycolic acid]
The method for producing glycolic acid of the present invention includes the following first to fourth steps. FIG. 1 is a process flow diagram of an example of the method for producing glycolic acid according to the present embodiment.

The first step is a step in which an enzyme is applied to the squeezed sorghum juice to saccharify the squeezed juice to obtain a sugar solution. In FIG. 1, the sorghum saccharification step is indicated by S1. Hereinafter, it will also simply be referred to as saccharification step S1.

The second step is a step in which the sugar solution obtained in the first step is subjected to alcohol fermentation to obtain a fermentation liquid containing ethanol. In FIG. 1, the alcohol fermentation step is shown as S2.

The third step is a step of subjecting the fermentation liquid obtained in the second step to acetic acid fermentation to obtain acetic acid. In FIG. 1, the acetic acid fermentation step is shown as S3.

The fourth step is a step of introducing a hydroxy group into the α carbon of the acetic acid to obtain glycolic acid. In FIG. 1, it is shown as step S4 of obtaining glycolic acid by chemical treatment. Hereinafter, it will also simply be referred to as chemical treatment step S4.

In the method for producing glycolic acid of the present invention, in addition to the first to fourth steps described above, additional steps may be included before or after these steps, if necessary.

Each step will be described in detail below with reference to FIG. 2. FIG. 2 is a process flow diagram showing in more detail an example of the method for producing glycolic acid shown in FIG. 1, specifically showing the saccharification step S1 and the chemical treatment step S4 in detail.

(First step; saccharification step S1)
In the first step, first, squeezed sorghum juice is prepared, and then the squeezed juice is saccharified.

The raw material, sorghum (Sorghum bicolor (L.) Moench), is a C4 plant native to northeastern Africa around Ethiopia and Sudan, and is one of the world's five major grains. Although sorghum is native to the tropics, it is currently cultivated as feed for livestock in a wide range of regions, from the tropics to the temperate regions, for example, in EU countries. Sorghum can also be cultivated in Japan. By using it as a raw material in the method for producing glycolic acid of the present invention, the added value of sorghum can be increased and it can also contribute to the effective use of fallow fields.

Sorghum is a C4 plant that belongs to the Poaceae family, looks similar to corn, and reaches a maximum height of about 4 to 5 meters. The growing period is very short, 3 to 4 months, and the dry matter production is 20 to 50 t/ha (total dry matter yield). The plant as a whole contains about 75% complex carbohydrates, accumulates sugar in its stems, and has a Brix value of about 12 to 19 degrees.

There are two types of sorghum: grain sorghum, which mainly uses seeds, and sweet sorghum, which uses stems that accumulate sugar. In the present invention, sorghum may be used partially or the whole plant may be used as a raw material. Considering disposal, it is preferable to use the whole plant.

In the saccharification step, for example, polysaccharides such as starch, pectin, and cellulose are decomposed to obtain oligosaccharides and monosaccharides. Since sorghum contains about 75% by mass of complex carbohydrates as a whole plant, by using an appropriate enzyme or a microorganism or fungus containing the enzyme, it is possible to use the whole plant without wasting it.

The method for obtaining juice from sorghum is not particularly limited, but for example, as shown in FIG. , is preferable because complex carbohydrates can be extracted more effectively from sorghum during juice extraction.

<Crushing sorghum; Step S11>
After harvest, sorghum is typically stored in a dry state. In order to extract juice efficiently, dried sorghum is mechanically crushed into chips (small pieces). Note that "crushing" includes cutting, crushing, shearing, shredding, and the like.

The method for crushing sorghum is not particularly limited, and any conventionally known method can be used. For example, dried sorghum can be crushed using conventionally known crushing devices for dried plants, such as various cutters and crushers. As for the size of chips (small pieces) obtained by crushing sorghum, it is preferable that the maximum diameter is, for example, about 2 to 5 mm. Hereinafter, the chip-shaped sorghum obtained in step S11 will also be referred to as "crushed sorghum."

<Steaming treatment; Step S12>
Next, the crushed sorghum obtained in step S11 is subjected to steaming treatment. Note that the steam treatment refers to heat treatment in an atmosphere of steam.

Sorghum contains 70% by mass or more, preferably about 75% by mass of complex carbohydrates including starch granules. In general, natural starch granules are not susceptible to enzyme action as they are. This is because starch molecules are regularly arranged to form grains (beta starch) and are insoluble in water, which prevents the binding of enzymes and starch molecules. By steaming crushed sorghum, complex carbohydrates can be activated to swell. For example, starch granules can also be heated with water to become gel-like and susceptible to enzymatic action.

The steaming treatment can be performed, for example, with an apparatus capable of heating in a steam atmosphere. Specifically, this is done by storing crushed sorghum in a sealable device, introducing steam into the device, and bringing the crushed sorghum into contact with the steam while stirring the crushed sorghum while keeping the device at a predetermined temperature. I can do it.

Note that the steaming treatment may be performed by supplying high-temperature water to an apparatus containing crushed sorghum. The temperature of the steaming treatment is preferably, for example, 100°C or higher, and more preferably in the range of 80 to 130°C. The device may be evacuated or pressurized as required.

The amount of water for crushed sorghum in the steaming treatment is, for example, 50 to 200 L per 100 L of crushed sorghum, and preferably 80 to 120 L.

The time for the steaming treatment depends on the temperature of water (steam), the amount of water relative to the crushed sorghum, etc., but is generally 1 to 12 hours, preferably about 1 to 2 hours.

<Juicing; Step S13>
After step S12, the mixture of the steam-treated crushed sorghum and the water added in step S12 is squeezed to obtain squeezed juice. The resulting squeezed juice contains the complex carbohydrates that were activated to swell in step S12 in a state dissolved in water. Thus, complex carbohydrates dissolved in water are less susceptible to aging.

In addition, when the obtained squeezed juice contains substances that have not been solubilized (insoluble substances), it is preferable that the insoluble substances are removed by a conventionally known method such as filtration. In addition, the residue (solid material) after squeezing the juice can be used as feed material for livestock.

<Saccharification of juice; Step S15>
Step S15 is a step of saccharifying the squeezed juice obtained in step S13 to obtain a sugar solution. Sorghum juice typically contains a mixture of polysaccharides such as starch, pectin, and cellulose. Juice often also contains oligosaccharides and monosaccharides.

Here, saccharification of squeezed juice refers to hydrolyzing polysaccharides through fermentation treatment to produce oligosaccharides and monosaccharides that can undergo alcoholic fermentation. For example, starch is hydrolyzed according to the following formula to produce glucose.

(C ₆ H ₁₀ O ₅ )n+n(H ₂ O)→nC ₆ H ₁₂ O ₆
According to the above formula, 1.1 kg of glucose is produced from 1 kg of starch. The mass of glucose obtained increases by the amount of water added.

In order to saccharify, that is, hydrolyze the polysaccharides contained in the squeezed juice, for example, a saccharifying enzyme is added to the squeezed juice to perform the saccharification reaction. As the saccharifying enzyme, for example, glucoamylase, α-amylase, cellulase, pectinase, etc. can be used. These enzymes, for example, are activated and used for hydrolysis.

Glucoamylase is an enzyme that cleaves α-1,4 bonds from the non-reducing end of starch into glucose units in exo form. Glucoamylase also has the function of decomposing α-1,6 bonds at branch points, and is an enzyme that can decompose starch into almost all glucose.

α-amylase is an endo-type enzyme that randomly cleaves α-1,4 bonds in starch, glycogen, etc. When it acts on starch gel, its viscosity rapidly decreases and becomes water-like. Also called starch liquefying enzyme.

Cellulases are hydrolytic enzymes that cleave glucosidic bonds in cellulose. Pectinase is an enzyme that acts on and hydrolyzes pectin, which is a polymer of galacturonic acid that fills the space between the cell membranes of fruit and plants.

These hydrolytic enzymes can be used, for example, (1) as purified enzymes, (2) as fermentation broths of enzyme-producing microorganisms containing enzymes produced by bacteria, (3) as extracts of lysed cells of enzyme-producing microorganisms, or , (4) Used as living cells of enzyme-producing microorganisms that have been pretreated to enable both the enzyme reaction and the survival rate (availability of specific cofactors) of the enzyme-producing microorganisms necessary for reaction regeneration. be able to.

In the present invention, for example, any one of the above embodiments (2) to (4) is preferred. The enzyme-producing microorganism is contained, for example, in the crushed sorghum obtained in step S13, and the culture solution in which the crushed sorghum is cultured (aspect (2) or (4)) can also be used for saccharification. It is also possible to carry out the embodiment (3) using the obtained culture solution.

When culturing crushed sorghum, it is preferable to add a component to serve as a medium. As the culture medium, a conventionally known culture medium can be used.

The medium includes carbon sources or carbon substrates, nitrogen sources such as peptone, yeast extract, meat extract, malt extract, urea, ammonium sulfate, ammonium chloride, ammonium nitrate and ammonium phosphate; potassium or dipotassium phosphate; trace elements (e.g. metal salts), such as magnesium salts, cobalt salts and/or manganese salts; as well as amino acids and growth factors such as vitamins essential for the maintenance and/or growth of cells or Media containing beneficial nutrients include, for example, sterile liquid media.

Crushed sorghum can be cultured, for example, by adding the above-mentioned liquid medium to crushed sorghum in an anaerobic culture tank at a preferable temperature range of 25 to 35°C. The addition ratio of the liquid medium to the crushed sorghum can be approximately 5 to 10 times the volume.

In the saccharification of the squeezed juice in step S15, the culture solution of the crushed sorghum cultured as described above is added to the squeezed juice obtained in step S13 as a source of the hydrolytic enzyme, and the saccharification (hydration) is performed. decomposition reaction) takes place.

As conditions for saccharification, it is preferable to adjust the pH to 6 to 7 and the temperature to a range of 30 to 50°C. Saccharification is performed, for example, in a tank (saccharification tank) having a stirring means. The time for the saccharification treatment depends on the capacity of the saccharification tank, etc., but is, for example, the time required for the sugar concentration of the sugar solution to reach the preferred concentration described below, and specifically, about 12 to 24 hours.

In step S15, the supernatant of the saccharification tank is used in the next alcohol fermentation step S2. The bottom liquid at the bottom of the saccharification tank is reprocessed, for example, by returning it to the steaming treatment in step S12. The bottom liquid at the bottom of the saccharification tank may also be used for culturing yeast in the following alcohol fermentation step S2. In addition, when the saccharification treatment is performed while stirring, the mixture in the saccharification tank can be allowed to stand after stirring to separate it into a supernatant and a bottom liquid.

Here, in step S15, in order to make the sugar solution obtained by saccharification have a higher sugar concentration, the sugar solution obtained by saccharification is made to have a higher sugar concentration than the sugar solution obtained by saccharifying squeezed sorghum juice. It is preferable to add the squeezed juice of a plant with a high sugar concentration (hereinafter also referred to as "squeezed juice of other plants") (step S14).

Note that the sugar solution obtained in step S15 may contain disaccharides such as sucrose, sucrose, and lactose in addition to monosaccharides such as glucose, fructose, and galactose. Sugar concentration is measured as the total concentration of these sugars.

The sugar concentration of the sugar solution obtained in step S15 is preferably 20 to 40%, more preferably 30 to 40%. In order to increase the sugar concentration of the sugar solution when saccharifying sorghum juice to 30 to 40%, examples of the juice of other plants mentioned above include stevia, persimmon, sugarcane, etc. , Stevia juice is preferred.

Stevia (Stevia rebaudiana) is a perennial plant of the genus Stevia in the family Asteraceae, native to South America. Stevia juice can be produced, for example, by a method similar to the method for obtaining the above-mentioned sorghum juice.

The ratio of the juice of other plants added to the squeezed sorghum juice is preferably about 3 to 10% by volume based on the total amount of squeezed sorghum juice.

(Second step; Alcohol fermentation step S2)
In the second step S2, the sugar solution obtained in the first step S1 is subjected to alcohol fermentation to obtain a fermentation liquid containing ethanol.

Alcoholic fermentation is a metabolic process in which energy is obtained by decomposing sugars such as glucose, fructose, and sucrose to produce ethanol and carbon dioxide through the action of yeast, and is an anaerobic reaction that does not require oxygen.

Specifically, taking glucose as an example, this is a reaction in which one molecule of glucose is decomposed to produce two molecules of ethanol and two molecules of carbon dioxide, as shown in the following formula.
C ₆ H ₁₂ O ₆ →2C ₂ H ₅ OH+2CO ₂

According to the above formula, about 0.4 kg of ethanol can be obtained from 1 kg of glucose. Since the specific gravity of ethanol is 0.7947, approximately 0.5L can be produced when calculated in terms of volume.

Yeast is used for alcoholic fermentation. The yeast is not particularly limited as long as it is capable of alcoholic fermentation.

For example, Saccharomyces, Candida, Torulopsis, Zygosaccharomyces, Schizosaccharomyces, Pichia ( Pichia), Yarrowia, Hansenula ( Examples include yeasts such as Hansenula, Kluyveromyces, Debaryomyces, Geotrichum, Wickerhamia, and Fellomyces. Yeasts of the genus Saccharomyces are preferred.

Here, the yeast is preferably cultured prior to alcohol fermentation. As mentioned above, yeast obtains energy by decomposing sugar to grow and multiply. The yeast can be cultured, for example, in an anaerobic culture tank by adding a medium and sugar to the yeast. As the sugar, for example, the bottom liquid of the saccharification tank obtained after the saccharification treatment in step S15 can be used.

Conditions for culturing yeast include anaerobic conditions, pH 4 to 6, and temperature 25 to 28°C. As the medium, it is possible to use the same medium as the medium exemplified for culturing the enzyme-producing microorganism during the saccharification.

Alcohol fermentation is performed, for example, in a tank (alcohol fermenter) having a stirring means. The sugar solution obtained in step S15 and the yeast culture solution are put into the alcohol fermentation tank, and alcohol fermentation is performed under, for example, the following conditions.

As conditions for alcoholic fermentation, it is preferable to adjust the pH to a range of 4 to 6 and the temperature to a range of 22 to 28°C. The processing time in alcohol fermentation depends on the capacity of the alcohol fermenter, but is, for example, the time until the ethanol concentration in the mixture in the alcohol fermenter reaches an appropriate concentration, for example, about 15 to 25% by mass, Specifically, about 24 to 48 hours may be mentioned.

(Third step; acetic acid fermentation step S3)
In the third step S3, the fermentation liquid containing ethanol obtained in the second step S2 (hereinafter also referred to as "alcoholic fermentation liquid") is subjected to acetic acid fermentation to obtain acetic acid. Note that the alcoholic fermentation liquid is obtained as the supernatant of the alcohol fermenter. Further, the bottom liquid of the alcohol fermenter can be used, for example, for culturing acetic acid bacteria.

Acetic acid fermentation is a reaction in which acetic acid and water are produced from ethanol and oxygen by the action of acetic acid bacteria, as shown in the following formula.
C ₂ H ₅ OH + O ₂ → CH ₃ COOH + H ₂ O

Acetobacter is a general term for bacteria that incompletely oxidize ethanol and sugar to produce organic acids. Specifically, acetic acid fermentation is a type of oxidative fermentation in which ethanol is aerobically oxidized by the action of acetic acid bacteria that utilize oxygen in the air to produce acetic acid from acetaldehyde. The alcohol oxidation process is in two stages. Alcohol dehydrogenase converts ethanol to acetaldehyde. Acetaldehyde is then converted to acetic acid by aldehyde dehydrogenase.

The acetic acid bacteria are not particularly limited as long as they are capable of acetic acid fermentation. Examples include acetic acid bacteria such as Acetobacter and Gluconacetobacter. Acetic acid bacteria of the genus Gluconacetobacter are preferred.

Here, the acetic acid bacteria are preferably cultured prior to acetic acid fermentation. Cultivation of acetic acid bacteria can be carried out, for example, by adding acetic acid bacteria and a medium to crushed sorghum in an aerobic culture tank. Conditions for culturing acetic acid bacteria include aerobic conditions, pH 4 to 6, and temperature 20 to 30°C. As the medium, it is possible to use the same medium as the medium exemplified for culturing the enzyme-producing microorganism during the saccharification. In culturing acetic acid bacteria, the lower liquid of the alcohol fermenter after the alcohol fermentation step S2 may be further added to the medium.

Acetic acid fermentation is performed, for example, in a tank equipped with stirring means (acetic acid fermenter). The alcohol fermentation liquid obtained in the alcohol fermentation step S2 and the culture liquid of acetic acid bacteria are charged into the acetic acid fermentation tank, and acetic acid fermentation is performed under the following conditions, for example.

The conditions for acetic acid fermentation are preferably adjusted to a pH of 3.5 to 6.5, a temperature of 25 to 30°C, and an alcohol concentration of 5 to 10% by mass. Everything other than temperature is adjusted as appropriate before starting acetic acid fermentation, and it is preferable that temperature is adjusted during acetic acid fermentation. It is preferable to proceed with acetic acid fermentation while performing aeration. Although aeration may be performed continuously, it is preferable to repeat aeration and pause.

The processing time in acetic acid fermentation depends on the capacity of the acetic acid fermenter, but is, for example, the time until the acetic acid concentration in the mixture in the acetic acid fermenter reaches an appropriate concentration, for example, about 10 to 20% by mass, Specifically, about 24 to 48 hours may be mentioned.

In this way, acetic acid is obtained through the acetic acid fermentation step S3. Here, in the acetic acid fermentation step S3, acetic acid after acetic acid fermentation is in the state of an aqueous solution. The acetic acid used in the chemical treatment in step 4 is preferably acetic acid alone. The acetic acid concentration in the fermentation liquor obtained by acetic acid fermentation is, for example, about 10 to 20% by mass. A method for isolating acetic acid from a fermentation liquid includes a method that utilizes the difference in boiling point between acetic acid and components other than acetic acid. Most of the components other than acetic acid in the fermentation liquid are water. The boiling point of acetic acid is 118°C, which has a sufficient boiling point difference from components such as water (boiling point 100°C) and unreacted ethanol (boiling point 78°C), and can be easily purified by distillation, preferably vacuum distillation. It is possible to separate.

An ether extraction method may be used to isolate acetic acid from the fermentation liquid. Specifically, when diethyl ether is added to the fermentation liquid and thoroughly mixed by stirring or the like, a mixed liquid in which acetic acid is dissolved in diethyl ether is obtained. Since diethyl ether is not compatible with water, when this mixture is allowed to stand, it separates into a lower aqueous layer and an upper diethyl ether layer. Acetic acid is present in the upper layer in a state dissolved in the diethyl ether layer.

The diethyl ether layer and the aqueous layer are separated, and diethyl ether and acetic acid are separated from the obtained diethyl ether layer by distillation. The boiling point of ether is 34.6°C, and acetic acid can be easily isolated.

(Fourth step; chemical treatment step S4)
In the fourth step, the acetic acid obtained in the acetic acid fermentation step S3 is chemically treated to obtain glycolic acid. Glycolic acid is a compound having a structure in which one of the hydrogens bonded to the α carbon of acetic acid is replaced with an OH group, as shown below.

The method of obtaining glycolic acid from acetic acid by chemical treatment is not particularly limited. In the present invention, a preferred method is to introduce a chlorine atom into the alpha carbon of acetic acid to obtain monochloroacetic acid, and then replace the chlorine atom of the obtained monochloroacetic acid with a hydroxy group.

In addition, as a method for obtaining monochloroacetic acid by introducing a chlorine atom into the alpha carbon of acetic acid, for example, as shown in FIG. Step S42) may be mentioned. Then, glycolic acid is generated from monochloroacetic acid (step S43).

<Step of obtaining acetic anhydride from acetic acid; Step S41>
The acetic acid obtained in the acetic acid fermentation step S3 is converted into acetic anhydride through chemical treatment in step S41. Acetic anhydride has a structure in which two molecules of acetic acid are dehydrated and condensed, as shown in the following formula. The method for obtaining acetic anhydride, which is an anhydride thereof, from acetic acid is not particularly limited, and conventionally known methods can be used.

_2CH3COOH →( _CH3CO ) _2O + _H2O

As a method for producing acid anhydrides, for example, a method is known in which a carboxylic acid is reacted with methanesulfonyl chloride in the presence of triethylamine (J. Chem. Res., Synop. 3 100 (1984)). In this method, for example, carboxylic acid, specifically 2 moles of acetic acid, 1.05 moles of methanesulfonyl chloride and 3.5 moles of triethylamine are reacted in tetrahydrofuran at -15°C. After the reaction, tetrahydrofuran is distilled off under reduced pressure, ethyl acetate is added, and after washing with an aqueous sodium bicarbonate solution, the organic phase is dried over anhydrous sodium sulfate, and the solvent is distilled off to obtain the desired acid anhydride. , acetic anhydride can be obtained.

Acetic anhydride can also be produced by a method in which ketene (CH ₂ =C=O) generated by thermal decomposition of acetic acid is reacted with acetic acid.

<Step of obtaining monochloroacetic acid from acetic anhydride; Step S42>
Next, in step S42, monochloroacetic acid is produced from acetic anhydride. Monochloroacetic acid has a structure in which one of the hydrogen atoms bonded to the alpha carbon of acetic acid is replaced with a chlorine atom. Monochloroacetic acid can be produced, for example, by reacting acetic anhydride with hypochlorous acid as shown in the following formula. Hypochlorous acid is one of the chlorine oxoacids and has a structure H-OC in which a hydrogen atom and a chlorine atom are bonded to an oxygen atom.

( _CH3CO ) _2O +2HClO→ _2CClH2COOH + _H2O

To produce monochloroacetic acid by reacting acetic anhydride with hypochlorous acid, 2 moles of hypochlorous acid are reacted with 1 mole of acetic anhydride. In this case, hypochlorous acid is used as an aqueous solution. The concentration of hypochlorous acid in the aqueous solution is adjusted to, for example, about 40 to 60% by mass. The reaction temperature includes a range of 80 to 180°C. A catalyst may be used if necessary.

The reaction solution contains monochloroacetic acid (boiling point: 189°C), water, unreacted raw materials, and the like. Examples of the method for isolating monochloroacetic acid (boiling point: 189°C) from the reaction solution include distillation, preferably vacuum distillation.

<Step of obtaining glycolic acid from monochloroacetic acid; Step S43>
Step S43 is a step of obtaining glycolic acid from the monochloroacetic acid obtained in step S42. To obtain glycolic acid from monochloroacetic acid, for example, a reaction shown by the following formula is performed.

CClH ₂ COOH + NaOH → C(OH)H ₂ COOH + NaCl

When sodium hydroxide is reacted with monochloroacetic acid, sodium hydroxide is used as an aqueous solution. The concentration of sodium hydroxide in the aqueous solution is adjusted to, for example, about 20 to 40% by mass. The reaction temperature includes a range of 115 to 145°C. A catalyst may be used if necessary.

The reaction solution contains sodium chloride produced together with glycolic acid in the above reaction. Sodium chloride in the reaction solution can be removed by electrodialysis or the like. Glycolic acid can be isolated from the reaction solution after sodium chloride has been removed by distillation, for example, vacuum distillation.

The method for producing glycolic acid in this embodiment has been described above. According to the production method of this embodiment, it is possible to efficiently produce glycolic acid by combining biochemical reactions such as saccharification and fermentation using enzymes and microorganisms with chemical treatments using sorghum, a plant, as a raw material. It is.

[Production method of polyglycolic acid]
The method for producing polyglycolic acid of the present invention includes a step of producing glycolic acid by the above-described production method of the present invention, and a step of dehydrating and polycondensing glycolic acid to obtain polyglycolic acid. Specifically, the steps for producing glycolic acid by the production method of the present invention include the above-described first step S1 to fourth step S4.

FIG. 3 is a process flow diagram of an example of the method for producing polyglycolic acid according to the present embodiment. The saccharification step S1, the alcohol fermentation step S2, the acetic acid fermentation step S3, and the chemical treatment step S4, which correspond to the first step S1 to the fourth step shown in FIG. 3, can be performed as described above. Specifically, it is preferable to perform the process shown in FIG. 2 described above.

In FIG. 3, step S5 represents the step of dehydrating and polycondensing glycolic acid to obtain polyglycolic acid. In the method for producing polyglycolic acid of the present invention, in addition to the above steps S1 to S5, additional steps may be included before or after these steps, if necessary.

The dehydration polycondensation of glycolic acid in step S5 can be performed by a conventionally known method. Glycolic acid is a compound having both a hydroxy group and a carboxy group in one molecule as shown in the chemical formula below. By repeating ester bonds between hydroxy groups and carboxy groups between molecules, polyglycolic acid is produced as shown by the chemical formula below. In the formula, n indicates the degree of polymerization and is an integer of 2 or more.

Here, in addition to the method of producing polyglycolic acid by dehydration polycondensation using glycolic acid as a monomer, polyglycolic acid may also be produced by ring-opening polymerization of glycolide using glycolic acid as its cyclic diester, glycolide. good.

Methods for producing polyglycolic acid by dehydration polycondensation using glycolic acid as a monomer or by ring-opening polymerization of glycolide include, for example, bulk polymerization, emulsion polymerization, solution polymerization, etc., but solution polymerization is preferred. .

The solvent used for solution polymerization is not particularly limited as long as it can dissolve glycolic acid or glycolide. Specific examples include toluene and xylene.

During polymerization, a catalyst such as tin(II) chloride, 2-ethylhexanetin(II), tin(II) chloride dihydrate, p-toluenesulfonic acid, etc. is added as necessary.

In addition, the catalysts used when producing glycolide by ring-opening polymerization include tin-based compounds such as tin halides and organic tin carboxylates; titanium-based compounds such as alkoxytitanate; aluminum-based compounds such as alkoxyaluminum; zirconium acetylacetone. Known ring-opening polymerization catalysts include zirconium-based compounds such as; and antimony-based compounds such as antimony halides and antimony oxide.

The polymerization temperature is preferably 120 to 300°C, more preferably 130 to 250°C, particularly preferably 140 to 240°C, and most preferably 150 to 230°C. When the polymerization temperature is less than the above lower limit, polymerization tends not to proceed sufficiently, whereas when it exceeds the above upper limit, the produced resin tends to be thermally decomposed.

The polymerization time is preferably 2 minutes to 50 hours, more preferably 3 minutes to 30 hours, and particularly preferably 5 minutes to 20 hours, depending on the molecular weight of the target polyglycolic acid. When the polymerization time is less than the above-mentioned lower limit, polymerization tends not to proceed sufficiently, whereas when it exceeds the above-mentioned upper limit, the produced resin tends to be colored.

Impurities such as the solvent are removed from the reaction solution after the polymerization reaction by distillation, for example, by vacuum distillation to obtain crude polyglycolic acid, and then the water is removed by freeze-drying to obtain purified polyglycolic acid. .

The molecular weight of polyglycolic acid is adjusted as appropriate depending on the application. Regarding the molecular weight of polyglycolic acid, the weight average molecular weight (Mw) is generally in the range of 10,000 to 800,000, and the number average molecular weight (Mn) is generally in the range of 5,000 to 200,000. .

Although several embodiments of the present invention have been described above, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and equivalent ranges thereof. .

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto. In the following examples, unless otherwise specified, operations were performed at room temperature (25° C.).

FIG. 4 shows a block diagram of an apparatus used in the following examples of the method for producing polyglycolic acid. In the following examples, glycolic acid was produced according to the process flowchart shown in FIG. 2, and the obtained glycolic acid was subjected to dehydration polycondensation to produce polyglycolic acid.

<Step S11>
Sorghum was crushed using a crushing device (1). As the sorghum, dried sorghum with a water content of about 40% by mass, which was cultivated in Okayama Prefecture and Okinawa Prefecture and was dried as a whole plant, was used. The maximum diameter of the crushed sorghum was approximately 4 mm on average.

<Step S12>
In the steaming/squeezing equipment (2) (3) (capacity 500L), 100L of circulating water heated to about 80 to 130°C and 100L of crushed sorghum are heated for 1 to 2 hours to expand and activate the complex carbohydrates contained in the crushed sorghum. Steaming treatment with stirring was performed. Note that the circulating water is fed from a water tank containing water discharged from the acetic acid vacuum distillation apparatus shown in FIG. This steaming process makes it more susceptible to enzymatic action, resulting in efficient saccharification. As a result, the productivity of glycolic acid increases.

<Step S13>
After step S12, the processed material in the steaming/juicing devices (2) and (3) is squeezed to obtain squeezed sorghum juice (150 to 180 L) containing circulating water.

<Step S15>
The saccharification step S1 (step S15) is performed in a saccharification tank (4) (capacity 500L). The saccharification tank (4) is charged with the squeezed sorghum juice obtained in step S13 and a culture solution obtained by culturing crushed sorghum in the anaerobic culture tank (11) as described below.

14 L of liquid medium and 2 L of crushed sorghum are put into an anaerobic culture tank (11) (capacity 20 L), stirred at a temperature of around 25° C., and anaerobically cultured for about 24 to 48 hours. The culture solution is sent to the saccharification tank (4). Crushed sorghum contains enzyme-producing microorganisms that produce hydrolytic enzymes that catalyze the hydrolysis of polysaccharides. In anaerobic culture, this enzyme-producing microorganism is cultured.

In addition to the above components, squeezed stevia juice is added to the saccharification tank (4) (capacity 500 L) (step S14). As the stevia, dried stevia with a moisture content of about 50% by mass, which was cultivated in Okayama prefecture and Okinawa prefecture and was dried as a whole plant, was used. Dried stevia is obtained by crushing, steaming, and squeezing the juice in the same manner as the above-mentioned juice is obtained from sorghum.

Stevia juice is added at a ratio of 3 to 10 L per 100 L of sorghum juice. The saccharification treatment was carried out at pH 6-7 and temperature 30-50°C for 24-48 hours with stirring. After the stirring is stopped, the mixture in the saccharification tank (4) is separated into a supernatant and a subnatant by allowing the mixture to stand still. The supernatant liquid is sent as a sugar solution to the next alcohol fermentation tank, a portion of the bottom liquid is used for culturing yeast, which will be described later, and the remainder is returned to the steaming and juice extraction devices (2) and (3). The sugar concentration of the supernatant is about 30 to 40%.

<Step S2>
An alcohol fermentation step S2 is performed in an alcohol fermentation tank (5) (capacity 500 L) using the supernatant of the saccharification tank (4) and a culture solution obtained by culturing yeast in a yeast anaerobic culture tank (13) as described below.

In a yeast anaerobic culture tank (13) (capacity 20 L), yeast of the genus Saccharomyces used for alcohol fermentation is cultured. First, 500 ml of yeast, 14 L of liquid medium, and 2 L of the subnatant from the saccharification tank (4) are added, and the yeast is cultured anaerobically at a temperature of 25 to 28°C for 24 to 48 hours to grow the yeast.

Approximately 150 L of the supernatant from the saccharification tank (4) and the yeast culture solution obtained above were put into the alcohol fermentation tank (5) (capacity 500 L), and the mixture was stirred at 22 to 28°C for 24 to 48 hours to complete alcohol fermentation. I do. The ethanol concentration in the fermentation liquid at the end of alcoholic fermentation was about 20% by mass.

<Step S3>
Using the fermentation liquid (supernatant) of the alcohol fermentation tank (5) and the culture liquid obtained by culturing acetic acid bacteria in the aerobic culture tank (12) as shown below, acetic acid was produced in the acetic acid aerobic fermentation tank (6) (capacity 1000 L). Fermentation step S3 is performed.

In an aerobic culture tank (12) (capacity 20 L), acetic acid bacteria of the genus Gluconacetobacter used for acetic acid fermentation are cultured. First, add 500 ml of acetic acid bacteria, 2 L of the lower liquid from the alcohol fermenter (5), and 14 L of liquid medium, and culture aerobically at a temperature of 25 to 30°C for 24 hours (45 minutes of aeration, 15 minutes of rest). Propagate bacteria.

Approximately 300 L of the alcoholic fermentation liquid diluted with circulating water so that the ethanol concentration was within 10% by mass and the culture solution of the acetic acid bacteria were introduced into the acetic acid aerobic fermentation tank (6) (capacity 1000 L), and the following acetic acid bacteria were added. Under optimal growth conditions, aerobic culture is performed for 24-48 hours with 45 minutes of aeration and 15 minutes of rest.

(Optimal growth conditions for acetic acid bacteria)
pH: 3.5-6.5
Temperature: 25-30℃
Ethanol concentration: 5-10% by mass

The acetic acid concentration in the obtained acetic acid fermentation liquid was about 15% by mass. After removing the solid content from the acetic acid fermentation liquid, acetic acid is obtained. In this way, about 300 L of acetic acid can be produced from 100 L of crushed sorghum. Separation of acetic acid and water is performed by vacuum distillation, and the separated water is sent to a water tank and used as circulating water.

<Step S4>
The acetic acid obtained above was converted to glycolic acid by the same chemical treatment step S4 as shown in FIG. 2, that is, steps S41 to S43.

First, in step S41, acetic anhydride was produced at a ratio of 1 mole to 2 moles of acetic acid. Specifically, half of the obtained acetic acid was converted into ketene (CH ₂ =C=O) by thermal decomposition, and this was reacted with the remaining half of acetic acid to produce acetic anhydride. The obtained acetic anhydride is stored in an acetic anhydride tank (7).

Next, the obtained acetic anhydride and hypochlorous acid water (concentration 40 to 60 mass%;) prepared in a hypochlorous acid water tank were mixed so that the molar ratio of acetic anhydride to hypochlorous acid was 2:1. were mixed in an acetic anhydride/hypochlorous acid mixing tank and reacted at a temperature of 90 to 140°C for 12 to 24 hours (Step S42). Water was removed from the resulting reaction solution using a vacuum distillation apparatus to obtain monochloroacetic acid (boiling point: 189°C). The obtained monochloroacetic acid is stored in a monochloroacetic acid tank (8).

Furthermore, in step S43, the monochloroacetic acid obtained in step S42 is reacted with sodium hydroxide to obtain glycolic acid. The reaction in step S43 is performed in a monochloroacetic acid and sodium hydroxide mixed tank. Sodium hydroxide is prepared in a sodium hydroxide solution tank as an aqueous solution with a concentration of about 20 to 40% by mass. The molar ratio of monochloroacetic acid and sodium hydroxide used in the reaction is 1:1. The reaction in step S43 is performed at a temperature of 115 to 145°C,
It lasted 30-48 hours.

The reaction solution obtained in step S43 contains sodium chloride as a component other than glycolic acid. By applying the reaction solution to an electrodialysis device, sodium chloride is removed from the reaction solution, and purified glycolic acid is obtained using a purification means such as vacuum distillation. The purified glycolic acid is stored in a glycolic acid tank (9). The removed sodium chloride is stored in a sodium chloride tank.

<Production process S5 of polyglycolic acid>
Finally, in step S5, the glycolic acid obtained above is subjected to dehydration polycondensation to produce polyglycolic acid.

Specifically, glycolic acid was weighed, and p-toluenesulfonic acid was added as a catalyst in an amount of 1 to 5 mol % based on the glycolic acid.

A Dean-Stark apparatus was used as the dehydration polycondensation apparatus. After removing oxygen by replacing the atmosphere in the apparatus with argon over 10 to 15 minutes, glycolic acid was subjected to dehydration polycondensation at 110° C. overnight (12 hours). After the reaction was completed, toluene (solvent) was removed using a rotary evaporator. The water bath temperature was 50-60°C. The removed toluene (solvent) is stored in an impurity tank.

For NMR measurement, 1 to 2 mL of DMSO (dimethyl sulfoxide) was added to 5 to 10 g of crude polyglycolic acid after toluene removal, and NMR measurement was performed at 500 MHz to confirm the presence of polyglycolic acid.

The crude polyglycolic acid after the solvent was removed was placed in a freeze-drying device to remove moisture, thereby obtaining purified polyglycolic acid. The purified polyglycolic acid is stored in a polyglycolic acid tank (10). The weight average molecular weight (Mw) of the obtained polyglycolic acid was 10,000 or more.

Claims (5)

A first step of applying an enzyme to the squeezed sorghum juice to saccharify the squeezed juice to obtain a sugar solution;
a second step of alcohol-fermenting the sugar solution to obtain a fermentation liquid containing ethanol;
A third step of fermenting the fermented liquid with acetic acid to obtain acetic acid;
A fourth step of obtaining glycolic acid by introducing a hydroxy group into the α carbon of the acetic acid;
A method for producing glycolic acid comprising: The first step is performed by adding to the squeezed sorghum juice a squeezed juice of a plant whose sugar concentration is higher in the sugar solution obtained by saccharification than the sugar concentration of the sugar solution obtained by saccharifying the squeezed sorghum juice. The manufacturing method according to claim 1, wherein the manufacturing method is carried out. The manufacturing method according to claim 2, wherein the plant contains stevia. 2. The manufacturing method according to claim 1, wherein the fourth step is performed by introducing a chlorine atom into the alpha carbon of the acetic acid to obtain monochloroacetic acid, and then substituting the chlorine atom of the monochloroacetic acid with a hydroxy group. A step of producing glycolic acid by the production method according to any one of claims 1 to 4;
and a step of dehydrating and polycondensing the glycolic acid to obtain polyglycolic acid.

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