JP7781749B2 - Method for producing polyhydroxyalkanoic acid and its use - Google Patents

Description

The present invention relates to a method for producing polyhydroxyalkanoic acid and its use.

Polyhydroxyalkanoic acid (hereinafter sometimes referred to as "PHA") is known to be biodegradable.

Since PHA produced by microorganisms accumulates within the microbial cells, a process for separating and purifying the PHA from the microbial cells is required to use the PHA as a plastic. In the PHA separation and purification process, the PHA-containing microorganism cells are crushed or biological components other than PHA are solubilized, and the PHA is then extracted from the resulting aqueous suspension. This involves separation procedures such as centrifugation, filtration, and drying. For drying, a spray dryer, fluidized bed dryer, drum dryer, or other device is used; however, a spray dryer is preferred due to its ease of operation.

To date, the inventors have developed a technology to prevent aggregation of PHA in aqueous suspensions with a pH of 7 or less by adding polyvinyl alcohol (PVA) as a dispersant before adjusting the pH of the aqueous suspension to 7 or less, and then spray-drying the resulting aqueous suspension with a pH of 7 or less (Patent Document 1). Furthermore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) is known as a suitable example of PHA.

International Publication No. WO2018/070492

While the above technology is excellent, in recent years there has been a demand for PHA with controlled particle size, particularly PHA with large particle size, from the perspective of ease of handling and transport. The inventors have learned from experience that in order to obtain PHA with large particle size, it is necessary to set the hot air temperature during spray drying at a relatively high temperature. However, setting the hot air temperature during spray drying at a high temperature requires more energy, leaving room for improvement from the perspective of energy conservation.

Therefore, the object of the present invention is to provide a manufacturing method and application technology that can obtain PHA (e.g., PHA powder) with large particle size at a lower hot air temperature.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered the novel finding that an aqueous suspension comprising a mixture of two different types of polyhydroxybutyrate copolymers, each having a specific composition ratio of 3-hydroxybutyrate units to 3-hydroxyhexanoate units, can produce P3HB3HH powder with large particle size even when the hot air temperature during spray drying is relatively low, leading to the completion of the present invention. Furthermore, the polyhydroxybutyrate copolymer (A) in the present invention can be a polymer composed only of 3-hydroxybutyrate units.

Therefore, one aspect of the present invention is a method for producing polyhydroxyalkanoic acid, comprising: (a) a step of preparing an aqueous suspension containing polyhydroxybutyric acid copolymer (A) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 100/0 and polyhydroxybutyric acid copolymer (B) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 75/25 to 91/9, and having a pH of 7 or less; and (b) a step of spray-drying the aqueous suspension prepared in step (a).

According to one aspect of the present invention, it is possible to produce PHA (e.g., PHA powder) with large particle size at a lower hot air temperature.

One embodiment of the present invention is described in detail below. Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B." Furthermore, all documents cited in this specification are incorporated herein by reference.

1. Overview of the present invention
A method for producing a polyhydroxyalkanoic acid according to one embodiment of the present invention (hereinafter referred to as "this production method") comprises: (a) a step of preparing an aqueous suspension containing a polyhydroxybutyrate copolymer (A) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 100/0 and a polyhydroxybutyrate copolymer (B) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 75/25 to 91/9, and having a pH of 7 or less; and (b) a step of spray-drying the aqueous suspension prepared in step (a). Hereinafter, "3-hydroxybutyrate" and "3-hydroxyhexanoate" may be referred to as "3HB" and "3HH," respectively.

While conducting research and development into the production of P3HB3HH as an example of PHA, the inventors discovered that in order to produce P3HB3HH with large particle sizes, which has seen increasing demand in recent years, it is necessary to increase the hot air temperature during spray drying. However, increasing the hot air temperature requires more energy, which is undesirable in terms of energy efficiency. Furthermore, increasing the hot air temperature during spray drying increases the likelihood of damage to P3HB3HH production equipment.

Therefore, the inventors conducted extensive research into methods for producing P3HB3HH with large particle diameters while reducing the hot air temperature during spray drying. As a result, they discovered for the first time that by using P3HB and P3HB3HH, or two different types of P3HB3HH (two types of P3HB3HH with different composition ratios of 3HB units to 3HH units), it is possible to obtain P3HB3HH with large particle diameters while reducing the hot air temperature during spray drying. Specifically, they discovered for the first time that by combining a polyhydroxybutyric acid copolymer (A) having a 3HB unit/3HH unit ratio of 92/8 to 100/0 with a polyhydroxybutyric acid copolymer (B) having a 3HB unit/3HH unit ratio of 75/25 to 91/9, it is possible to obtain P3HB3HH with large particle diameters while reducing the hot air temperature during spray drying.

Therefore, this manufacturing method makes it possible to obtain PHA with large particle size (e.g., PHA powder) with high energy efficiency. The configuration of this manufacturing method is described in detail below.

2. PHA Production Method
This production method includes the following steps (a) and (b) as essential steps.
Step (a): preparing an aqueous suspension containing a polyhydroxybutyric acid copolymer (A) having a 3HB unit/3HH unit ratio of 92/8 to 100/0 and a polyhydroxybutyric acid copolymer (B) having a 3HB unit/3HH unit ratio of 80/25 to 91/9, and having a pH of 7 or less; Step (b): spray-drying the aqueous suspension prepared in Step (a) (Step (a)).
In step (a) of this production method, an aqueous suspension containing polyhydroxybutyric acid copolymer (A) and polyhydroxybutyric acid copolymer (B) and having a pH of 7 or less is prepared. In this aqueous suspension, polyhydroxybutyric acid copolymer (A) and polyhydroxybutyric acid copolymer (B) are present in a dispersed state in an aqueous medium. Here, polyhydroxybutyric acid copolymer (A) is P3HB or P3HB3HH. Polyhydroxybutyric acid copolymer (B) is P3HB3HH. Therefore, both polyhydroxybutyric acid copolymer (A) and polyhydroxybutyric acid copolymer (B) fall under the category of PHA. In this specification, an aqueous suspension containing at least polyhydroxybutyric acid copolymer (A) and/or polyhydroxybutyric acid copolymer (B) may be simply referred to as a "PHA aqueous suspension."

<PHA>
As used herein, "PHA" is a general term for polymers containing hydroxyalkanoic acid as a monomer unit. In this production method, the "PHA" used is poly(3-hydroxybutyrate) (P3HB) composed only of 3HB units, or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) composed of 3HB units and 3HH units. Here, P3HB3HH is a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid.

By changing the composition ratio of the repeating units, the melting point and degree of crystallinity of P3HB3HH can be altered, resulting in changes to physical properties such as Young's modulus and heat resistance. P3HB3HH can be given physical properties between those of polypropylene and polyethylene. P3HB3HH is easy to produce industrially and is a plastic with useful physical properties.

In one embodiment of the present invention, the polyhydroxybutyric acid copolymer (A) has a 3HB unit/3HH unit composition ratio of 92/8 to 100/0. By including the polyhydroxybutyric acid copolymer (A) in the PHA aqueous suspension of one embodiment of the present invention, the flexibility and strength of the PHA produced by this production method can be well balanced. From the above perspective, the 3HB unit/3HH unit composition ratio in the polyhydroxybutyric acid copolymer (A) is preferably 92/8 to 99/1, more preferably 93/7 to 99/1, and even more preferably 94/6 to 99/1. When the 3HB unit content in the polyhydroxybutyric acid copolymer (A) is increased, the melting temperature of the resulting PHA (PHA powder) increases, resulting in improved heat resistance. Furthermore, when the 3HB unit content in the polyhydroxybutyric acid copolymer (A) is increased, the crystallization rate of the resulting PHA (PHA powder) increases, resulting in improved processability. From the viewpoint of improving the heat resistance and processability of the PHA (PHA powder), it is particularly preferable that the polyhydroxybutyric acid copolymer (A) has a composition ratio of 3HB units/3HH units of 100/0, i.e., is composed only of 3HB units.

In one embodiment of the present invention, the polyhydroxybutyric acid copolymer (B) has a composition ratio of 3HB units to 3HH units of 75/25 to 91/9. The polyhydroxybutyric acid copolymer (B) has a low melting temperature due to its high composition ratio of 3HH units. Therefore, in the step (b) of spray-drying the PHA aqueous suspension in this production method, the polyhydroxybutyric acid copolymer (B) is in a molten state even when the hot air temperature is low. It is presumed that the molten polyhydroxybutyric acid copolymer (B) functions as a binder to aggregate particles (powder) of the polyhydroxybutyric acid copolymer (A). Therefore, this production method can produce a PHA with a large particle size, in which particles (powder) of the polyhydroxybutyric acid copolymer (A) are aggregated via the fused polyhydroxybutyric acid copolymer (B) acting as a binder, even when the hot air temperature is low. From the above-mentioned viewpoints, the composition ratio of 3HB units/3HH units in the polyhydroxybutyric acid copolymer (B) is preferably 80/20 to 91/9, more preferably 83/17 to 90/10, and even more preferably 85/15 to 90/10.

In one embodiment of the present invention, the content of the polyhydroxybutyric acid copolymer (B) in the PHA aqueous suspension is preferably 1 to 30 parts by weight relative to the content of the polyhydroxybutyric acid copolymer (A).

By ensuring that the content of the polyhydroxybutyric acid copolymer (B) in the PHA aqueous suspension is 1 part by weight or more relative to the content of the polyhydroxybutyric acid copolymer (A), the content of the polyhydroxybutyric acid copolymer (B), which can function as a binder, can be sufficiently ensured, and as a result, PHA with larger particle sizes can be suitably produced at lower temperatures. From the above perspective, it is more preferable that the content of the polyhydroxybutyric acid copolymer (B) in the PHA aqueous suspension is 2 parts by weight or more relative to the content of the polyhydroxybutyric acid copolymer (A), and even more preferable that it is 5 parts by weight or more.

By having the content of the polyhydroxybutyric acid copolymer (B) in the PHA aqueous suspension be 30 parts by weight or less relative to the content of the polyhydroxybutyric acid copolymer (A), the balance between flexibility and strength of the produced PHA can be improved. From the above perspective, it is more preferable that the content of the polyhydroxybutyric acid copolymer (B) in the PHA aqueous suspension be 25 parts by weight or less, and even more preferable that it be 20 parts by weight or less, relative to the content of the polyhydroxybutyric acid copolymer (A).

In one embodiment of the present invention, step (a) preferably includes the following steps (a1) and (a2).
Step (a1): A step of mixing an aqueous suspension containing the polyhydroxybutyric acid copolymer (A) with an aqueous suspension containing the polyhydroxybutyric acid copolymer (B) to prepare a PHA aqueous suspension.
Step (a2): A step of adjusting the pH of the PHA aqueous suspension to 7 or less.

The order in which steps (a1) and (a2) are performed is not particularly limited. Regarding the order in which steps (a1) and (a2) are performed, it is preferable to perform step (a2) after step (a1), from the viewpoint of suppressing aggregation of the PHA in step (a2) and obtaining an aqueous suspension with better PHA dispersion stability.

In step (a), the aqueous suspension containing the polyhydroxybutyric acid copolymer (A) and the aqueous suspension containing the polyhydroxybutyric acid copolymer (B) used as starting materials are not particularly limited. The aqueous suspension can be obtained, for example, by a method including a culture step in which microorganisms capable of producing PHA intracellularly are cultured, and a purification step in which substances other than PHA are decomposed and/or removed after the culture step.

This production method may include, prior to step (a), a step of obtaining an aqueous suspension containing the polyhydroxybutyric acid copolymer (A) and an aqueous suspension containing the polyhydroxybutyric acid copolymer (B). The microorganism used in this step is not particularly limited as long as it is a microorganism capable of producing PHA intracellularly. For example, microorganisms isolated from nature or microorganisms deposited in a depository institution for strains (e.g., IFO, ATCC, etc.), or mutants or transformants prepared from them, can be used. More specifically, examples of the microorganisms include bacteria of the genus Cupriavidus, Alcaligenes, Ralstonia, Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. Among them, microorganisms belonging to the genus Aeromonas, Alcaligenes, Ralstonia, or Cupriavidus are preferred. In particular, Alcaligenes lipolytica, Alcaligenes latus, and Aeromonas caviae are preferred.
Strains such as Aeromonas iae, A. hydrophila, and C. necator are more preferred, with C. necator being the most preferred.

Furthermore, when a microorganism does not inherently have the ability to produce PHA or produces only a low amount of PHA, a transformant obtained by introducing a PHA synthase gene and/or a mutant thereof into the microorganism can also be used. The PHA synthase gene used to prepare such a transformant is not particularly limited. A PHA synthase gene derived from Aeromonas caviae is preferred as the synthase gene. By culturing these microorganisms under appropriate conditions, microbial cells that have accumulated PHA within the cells can be obtained. The method for culturing the microbial cells is not particularly limited. Examples of the culturing method include those described in Japanese Patent Publication No. 05-93049. In one embodiment of the present invention, the aqueous suspension containing the polyhydroxybutyric acid copolymer (A) and the aqueous suspension containing the polyhydroxybutyric acid copolymer (B) can be obtained by the same culturing method from cells of the same bacterial species but with different genetic mutations. For example, the method described in International Publication No. WO 2019/142717 can be used.

Since PHA-containing microorganisms produced by culturing the above microorganisms contain large amounts of bacterial cell-derived impurities, a purification process is typically carried out to decompose and/or remove impurities other than PHA. This purification process is not particularly limited, and physical, chemical, biological, and other treatments that would be considered by a person skilled in the art can be applied. For example, the purification method described in International Publication No. WO 2010/067543 is preferably applied.

The amount of impurities remaining in the final product is largely determined by the purification process described above, so it is preferable to reduce these impurities as much as possible. Naturally, depending on the application, impurities may be present as long as they do not impair the physical properties of the final product. However, in cases where high-purity PHA is required, such as for medical applications, it is preferable to reduce impurities as much as possible. An example of an indicator of the degree of purification is the amount of protein in the aqueous PHA suspension. The protein amount is preferably 30,000 ppm or less per weight of PHA, more preferably 15,000 ppm or less, even more preferably 10,000 ppm or less, and most preferably 7,500 ppm or less. The purification method is not particularly limited. For example, the known methods described above can be used as the purification method.

The solvent (also referred to as "aqueous medium") constituting the PHA aqueous suspension in this manufacturing method may be water or a mixed solvent of water and an organic solvent. Furthermore, the concentration of the water-compatible organic solvent in the mixed solvent is not particularly limited, as long as it is equal to or less than the solubility of the organic solvent used in water. Furthermore, the water-compatible organic solvent is not particularly limited. Examples of water-compatible organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, and heptanol; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, and piperidine. Among these, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile, propionitrile, etc. are preferred because they are easily removed. Furthermore, methanol, ethanol, 1-propanol, 2-propanol, butanol, acetone, etc. are more preferred because they are easily available. Furthermore, methanol, ethanol, and acetone are particularly preferred. Note that the aqueous medium constituting the PHA aqueous suspension may contain other solvents, components derived from bacterial cells, compounds generated during purification, etc., as long as the essence of the present invention is not impaired.

The aqueous medium constituting the PHA aqueous suspension in this production method preferably contains water. The water content in the aqueous medium is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 30% by weight or more, and particularly preferably 50% by weight or more.

<Dispersant>
The aqueous suspension in one embodiment of the present invention may contain a dispersant. That is, the step (a) in one embodiment of the present invention may be a step of preparing an aqueous suspension further containing a dispersant in addition to the polyhydroxybutyric acid copolymer (A) and the polyhydroxybutyric acid copolymer (B). In one embodiment of the present invention, when the dispersant is used, it is preferable to add the dispersant to the PHA aqueous suspension in the step (a1). By including a dispersant in the PHA aqueous suspension in one embodiment of the present invention, the productivity and thermal stability of PHA can be suitably improved.

The dispersant is not particularly limited. Examples of dispersants include alkylene oxide-based dispersants. The dispersant may be of one type or two or more types. For example, the aforementioned Patent Document 1 uses polyvinyl alcohol (PVA) as a dispersant, and the binder effect of the PVA results in a larger PHA particle size. However, when PVA is used, there is a risk of the PVA sticking to the shaft in the twin-screw extruder in the process after spray drying, leaving room for improvement. On the other hand, the present invention allows for the production of PHA with a larger particle size at a lower hot air temperature without the problem of sticking to the shaft.

In one embodiment of the present invention, the dispersant is preferably an alkylene oxide-based dispersant, as this can effectively prevent aggregation of PHA when adjusting the pH of the PHA aqueous suspension to 7 or less, and can effectively suppress adhesion to the extruder shaft during powder processing.

In one embodiment of the present invention, the alkylene oxide dispersant is not particularly limited as long as it exhibits the above-mentioned effects. The alkylene oxide dispersant is preferably composed of poly(ethylene oxide) (PEO) blocks and poly(propylene oxide) (PPO) blocks, and is in the form of PEO-PPO-PEO.

In this specification, "poly(ethylene oxide) (PEO) block" refers to the polymer portion formed by polymerization of ethylene oxide (EO) in the structure of an alkylene oxide-based dispersant.

In this specification, "poly(propylene oxide) (PPO) block" refers to the polymer portion formed by polymerization of propylene oxide (PO) in the structure of an alkylene oxide-based dispersant.

In one embodiment of the present invention, by setting the PEO molecular weight and PEO molecular weight/PPO molecular weight in the alkylene oxide-based dispersant to a specific range, the viscosity of the aqueous suspension can be kept low, and PHA (e.g., PHA powder) can be produced with high productivity.

In one embodiment of the present invention, the PEO molecular weight and PEO molecular weight/PPO molecular weight range in the alkylene oxide-based dispersant are preferably the following combinations:

In this specification, "PEO molecular weight" may be referred to as "EO amount" and "PPO molecular weight" may be referred to as "PO amount."

That is, in one embodiment of the present invention, the molecular weight of PEO in the alkylene oxide-based dispersant may be 1,500 or more, preferably 1,750 or more, and more preferably 2,000 or more. Furthermore, in one embodiment of the present invention, the upper limit of the molecular weight of PEO in the alkylene oxide-based dispersant is, for example, 30,000 or less, preferably 25,000 or less, and more preferably 20,000 or less.

In one embodiment of the present invention, the PEO molecular weight/PPO molecular weight ratio in the alkylene oxide dispersant is preferably 0.5 or greater, more preferably 0.6 or greater, and even more preferably 0.7 or greater. The upper limit of the PEO molecular weight/PPO molecular weight ratio is preferably 5.0 or less, more preferably 4.8 or less, and even more preferably 4.5 or less.

In one embodiment of the present invention, if the PEO molecular weight and PEO molecular weight/PPO molecular weight in the alkylene oxide-based dispersant are within the above ranges, the alkylene oxide-based dispersant will be hydrophilic and the number of molecules relative to the added weight of the alkylene oxide-based dispersant will be large, making it easier to maintain the dispersibility of the aqueous suspension.

In one embodiment of the present invention, the alkylene oxide dispersant has a PEO molecular weight of 1,500 or more and a PEO molecular weight/PPO molecular weight ratio of 0.5 to 5.0.

In one embodiment of the present invention, the alkylene oxide dispersant preferably has at least one PEO block having a molecular weight of 750 or more, and more preferably has at least two PEO blocks. The number of PEO blocks in the alkylene oxide dispersant is not particularly limited, and may be, for example, 4 or less, and preferably 3 or less. If the number of PEO blocks is within the above range, the alkylene oxide dispersant will be hydrophilic.

In one embodiment of the present invention, the molecular weight of the PPO in the alkylene oxide dispersant is not particularly limited. The molecular weight of the PPO in the alkylene oxide dispersant is, for example, 500 or more, and preferably 1500 or more. In another embodiment of the present invention, the upper limit of the molecular weight of the PPO in the alkylene oxide dispersant is, for example, 6700 or less, and preferably 6250 or less. If the molecular weight of the PPO in the alkylene oxide dispersant is within the above range, the alkylene oxide dispersant is hydrophobic.

In one embodiment of the present invention, the number of PPO blocks in the alkylene oxide dispersant is not particularly limited as long as the above-mentioned effects are achieved. The number of PPO blocks in the alkylene oxide dispersant may be one or multiple (e.g., 2, 3, or 4).

In one embodiment of the present invention, the alkylene oxide dispersant is, for example, a compound represented by the following formula (1):

In the above formula (1), X is, for example, 17 to 340, preferably 20 to 285, and more preferably 22 to 226. When X is 340 or less, the number of molecules relative to the weight of alkylene oxide dispersant added increases, making it easier to maintain dispersibility in the aqueous suspension. When X is 17 or more, the compound represented by formula (1) is hydrophilic. Y is, for example, 8 to 115, preferably 10 to 110, and more preferably 24 to 107. When Y is 115 or less, the compound represented by formula (1) is easily soluble in water. When Y is 8 or more, the compound represented by formula (1) is hydrophobic. Z is, for example, 17 to 340, preferably 20 to 285, and more preferably 22 to 226. When Z is 340 or less, the number of molecules relative to the added weight of alkylene oxide-based dispersant is large, making it easier to maintain the dispersibility of the aqueous suspension, and when Z is 17 or more, the compound represented by formula (1) has hydrophilicity.

In addition, in the above formula (1), the sum of X and Z (hereinafter sometimes referred to as "X + Z") is, for example, 34 to 680, preferably 40 to 570, and more preferably 44 to 452. When X + Z is 680 or less, the number of molecules relative to the added weight of alkylene oxide dispersant increases, making it easier to maintain the dispersibility of the aqueous suspension; when X is 34 or more, the compound represented by formula (1) is hydrophilic.

The alkylene oxide dispersant used in step (a) (particularly step (a1)) of this manufacturing method is not particularly limited. Commercially available alkylene oxide dispersants can be used. Examples of commercially available alkylene oxide dispersants include Pluronic 10400 (manufactured by BASF), Pluronic 10500 (manufactured by BASF), Genapol PF80 (manufactured by Clariant), Unilube DP60-600B (manufactured by NOF Corporation), Unilube DP60-950B (manufactured by NOF Corporation), Pronon 208 (manufactured by NOF Corporation), Epan U105 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Epan U108 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and Epan 750 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

The amount of dispersant added to the aqueous suspension in step (a) (particularly step (a1)) of this production method is not particularly limited. The amount of dispersant added is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, and even more preferably 0.75 to 5 parts by weight, per 100 parts by weight of the total content of the polyhydroxybutyric acid copolymer (A) and the polyhydroxybutyric acid copolymer (B) contained in the aqueous suspension. By setting the amount of dispersant added within the above range, the dispersion stability of the PHA in the PHA aqueous suspension is further improved, allowing for efficient spray drying, which tends to result in more favorable improvements in the productivity and thermal stability of the PHA.

<Others>
The PHA aqueous suspension before being subjected to step (a) of the present production method usually has a pH of greater than 7 due to the above-mentioned purification step. Therefore, the PHA aqueous suspension obtained in step (a1) of the present production method has a pH of greater than 7. Therefore, the pH of the PHA aqueous suspension is adjusted to 7 or less in step (a) (particularly, step (a2)) of the present production method. The adjustment method is not particularly limited. For example, a method of adding an acid can be mentioned as the adjustment method. The acid is not particularly limited. The acid may be either an organic acid or an inorganic acid, whether or not it is volatile. More specifically, for example, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, etc. can be used as the acid.

The upper limit of the pH of the PHA aqueous suspension adjusted in the above adjustment step is 7 or less, preferably 5 or less, and more preferably 4 or less, from the viewpoint of reducing discoloration when the PHA is heated and melted, and ensuring molecular weight stability during heating and/or drying. The lower limit of the pH is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, from the viewpoint of acid resistance of the container. By adjusting the pH of the PHA aqueous suspension to 7 or less, discoloration during heating and melting is reduced, and a PHA with suppressed molecular weight reduction during heating and/or drying is obtained.

In one embodiment of the present invention, an aqueous suspension is provided which contains polyhydroxybutyric acid copolymer (A) and the polyhydroxybutyric acid copolymer (B) and has a pH of 7 or less.

The PHA concentration in the PHA aqueous suspension obtained by step (a) of this production method is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more, because this is economically advantageous in terms of drying utility and improves productivity. Here, the PHA concentration in the PHA aqueous suspension refers to the sum of the concentrations of the polyhydroxybutyric acid copolymer (A) and the polyhydroxybutyric acid copolymer (B). The upper limit of the PHA concentration is preferably 65% by weight or less, more preferably 60% by weight or less, because close packing may occur and sufficient fluidity may not be ensured. The method for adjusting the PHA concentration is not particularly limited. Examples of methods for adjusting the PHA concentration include adding an aqueous medium and removing a portion of the aqueous medium (e.g., by centrifuging and then removing the supernatant). The PHA concentration may be adjusted at any stage of step (a) or before step (a).

In one embodiment of the present invention, the concentration of polyhydroxyalkanoic acid in the aqueous suspension prepared in step (a) is 30% by weight or more and 65% by weight or less.

The volume median diameter of the PHA in the aqueous PHA suspension obtained by step (a) of this production method (hereinafter simply referred to as the "volume median diameter of the PHA") is preferably 50 times or less, more preferably 20 times or less, and even more preferably 10 times or less, the volume median diameter of the primary particles of the PHA (hereinafter referred to as the "primary particle diameter"). When the volume median diameter of the PHA is 50 times or less the primary particle diameter, the aqueous PHA suspension exhibits superior fluidity, allowing the subsequent step (b) to be carried out with high efficiency, which tends to further improve PHA productivity.

In one embodiment of the present invention, the volume median diameter of the PHA is preferably 0.5 to 5 μm, more preferably 1 to 4.5 μm, and even more preferably 1 to 4 μm, from the viewpoint of achieving excellent fluidity. The volume median diameter of the PHA is measured, for example, using a laser diffraction/scattering particle size distribution analyzer LA-950 manufactured by HORIBA.

The volume median diameter of the PHA can be used as an indicator of the dispersion state of the PHA in the aqueous PHA suspension. The method for adjusting the volume median diameter of the PHA is not particularly limited. Known means (e.g., stirring) can be used to adjust the volume median diameter of the PHA. For example, if the dispersion state of a PHA aqueous suspension has been disrupted due to exposure to acidic conditions (e.g., when step (a2) is performed before step (a1)), the PHA in the aqueous PHA suspension can be restored to a dispersed state (e.g., a state having the above-mentioned PHA volume median diameter) by subjecting the PHA to a physical, chemical, or biological treatment that would be considered by a person skilled in the art.

(Step (b))
In step (b) of this production method, the PHA aqueous suspension prepared in step (a) is spray-dried. Examples of spray-drying methods include a method in which the PHA aqueous suspension is supplied into a dryer in the form of fine droplets and dried while being brought into contact with hot air in the dryer. The method for supplying the PHA aqueous suspension into the dryer in the form of fine droplets (atomizer) is not particularly limited. Examples of methods for supplying the PHA aqueous suspension into the dryer in the form of fine droplets include known methods such as a method using a rotating disk and a method using a nozzle. The method for contacting the droplets with the hot air in the dryer is not particularly limited. Examples of the method for contacting the droplets with the hot air in the dryer include a parallel flow method, a counterflow method, and a method using both.

The drying temperature during spray drying in step (b) may be any temperature that can remove most of the aqueous medium from the droplets of the PHA aqueous suspension. The drying temperature can be appropriately set so that drying can be performed to the desired moisture content while minimizing deterioration in quality (such as reduction in molecular weight or color tone) and melting.

In one embodiment of the present invention, the hot air temperature is, for example, 200°C or less, preferably 180°C or less, and more preferably 160°C or less. Here, "hot air temperature" refers to the temperature of the hot air blown into the spray dryer used in step (b). Furthermore, the exhaust air temperature is, for example, 114°C or less, preferably 112°C or less, and more preferably 110°C or less. "Exhaust air temperature" refers to the temperature of the exhaust air as it leaves the spray dryer, and can also be interpreted as the "temperature of the PHA particles" being discharged. By keeping the hot air temperature or exhaust air temperature at or below the above-mentioned temperatures, the amount of energy required for the spray drying can be reduced, and as a result, the amount of energy required for producing the PHA can be suitably reduced. This also prevents damage to the PHA production equipment.

In one embodiment of the present invention, the lower limit of the hot air temperature is not particularly limited. The lower limit of the hot air temperature is, for example, 120°C or higher, and preferably 130°C or higher. The lower limit of the exhaust air temperature is also not particularly limited. The lower limit of the exhaust air temperature is, for example, 90°C or higher, and preferably 95°C or higher. By ensuring that the hot air temperature or exhaust air temperature is at or above the above-mentioned temperatures, the polyhydroxybutyric acid copolymer can be suitably melted, and as a result, PHA with a large particle size can be suitably produced.

The volume of hot air inside the dryer can also be set appropriately depending on, for example, the size of the dryer.

The present production method may include, after step (b), a step of further drying the obtained PHA (e.g., PHA powder) (e.g., a step of subjecting it to drying under reduced pressure). The present production method may also include other steps (e.g., a step of adding various additives to the PHA aqueous suspension).

[3. Polyhydroxyalkanoic acid powder]
A polyhydroxyalkanoic acid powder according to one embodiment of the present invention (hereinafter referred to as "the present PHA powder") comprises a polyhydroxybutyric acid copolymer (A) having a composition ratio of 3HB units/3HH units of 92/8 to 100/0, a polyhydroxybutyric acid copolymer (B) having a composition ratio of 3HB units/3HH units of 75/25 to 91/9, and a dispersant.

In this embodiment, the terms "polyhydroxybutyric acid copolymer (A)," "polyhydroxybutyric acid copolymer (B)," and "dispersant" are defined as above.

The median particle size of the PHA powder is not particularly limited. From the viewpoint of achieving excellent fluidity, the median particle size of the PHA powder is preferably 40 to 120 μm, and more preferably 42 to 100 μm. The median particle size of the PHA powder is measured by the method described in the Examples.

The content of the dispersant in the PHA powder is not particularly limited. The content of the dispersant in the PHA powder is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, and even more preferably 0.75 to 5 parts by weight, per 100 parts by weight of the PHA constituting the PHA powder. By adding the dispersant in this range, the productivity of the PHA powder tends to be further improved.

Furthermore, the PHA powder may contain various components that were generated or not removed during the manufacturing process, as long as the effects of the present invention are achieved.

This PHA powder can be used for a variety of purposes, including paper, film, sheets, tubes, plates, rods, containers (e.g., bottle containers), bags, and parts.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

That is, one embodiment of the present invention is as follows.
<1> A method for producing a polyhydroxyalkanoic acid, comprising: (a) a step of preparing an aqueous suspension containing a polyhydroxybutyrate copolymer (A) having a composition ratio of 3-hydroxybutyrate units to 3-hydroxyhexanoate units of 92/8 to 100/0 and a polyhydroxybutyrate copolymer (B) having a composition ratio of 3-hydroxybutyrate units to 3-hydroxyhexanoate units of 75/25 to 91/9, and having a pH of 7 or less; and (b) a step of spray-drying the aqueous suspension prepared in the step (a).
<2> The method for producing a polyhydroxyalkanoic acid according to <1>, wherein the content of the polyhydroxybutyric acid copolymer (B) in the aqueous suspension is 1 to 30 parts by weight relative to the content of the polyhydroxybutyric acid copolymer (A).
<3> The method for producing a polyhydroxyalkanoic acid according to <1> or <2>, wherein the hot air temperature in the spray drying step is 200°C or less.
<4> The method for producing a polyhydroxyalkanoic acid according to any one of <1> to <3>, wherein the aqueous suspension further contains a dispersant.
<5> The method for producing a polyhydroxyalkanoic acid according to <4>, wherein the dispersant is at least one selected from the group consisting of alkylene oxide dispersants and polyvinyl alcohols.
<6> The dispersant is an alkylene oxide-based dispersant,
The method for producing a polyhydroxyalkanoic acid according to <4> or <5>, wherein the alkylene oxide-based dispersant is composed of a poly(ethylene oxide) (PEO) block and a poly(propylene oxide) (PPO) block, and is in the form of PEO-PPO-PEO.
<7> The dispersant is an alkylene oxide-based dispersant,
<4> to <6>, wherein the alkylene oxide dispersant has a PEO molecular weight of 1500 or more, and a PEO molecular weight/PPO molecular weight ratio of 0.5 to 5.0.
<8> The dispersant is an alkylene oxide-based dispersant,
<4> to <7>, wherein the alkylene oxide dispersant is a compound represented by the following formula (1):

(wherein X is 17 to 340, Y is 8 to 115, and Z is 17 to 340.)
<9> The method for producing a polyhydroxyalkanoic acid according to any one of <1> to <8>, wherein the concentration of the polyhydroxyalkanoic acid in the aqueous suspension prepared in the step (a) is 30 to 65% by weight.
<10> The polyhydroxybutyric acid copolymer (A) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 99/1,
<1> - <9> The method for producing a hydroxyalkanoic acid powder according to any one of <1> to <9>, wherein the polyhydroxybutyric acid copolymer (B) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 80/20 to 91/9.
<11> A hydroxyalkanoic acid powder comprising: a polyhydroxybutyrate copolymer (A) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 100/0; a polyhydroxybutyrate copolymer (B) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 75/25 to 91/9; and a dispersant.
<12> The polyhydroxybutyric acid copolymer (A) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 99/1,
The hydroxyalkanoic acid powder according to <11>, wherein the polyhydroxybutyric acid copolymer (B) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 80/20 to 91/9.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. In the examples, "P3HB3HH" is used as "PHA," and "PHA" can be read as "P3HB3HH."

[Measurement and evaluation methods]
Measurements and evaluations in the examples and comparative examples were carried out by the following methods.

(median particle size)
The average particle size of the spray-dried PHA powder obtained by this production method was measured by the following method.

The average particle size was measured using a laser diffraction/scattering particle size distribution analyzer LA-950 (HORIBA). Specifically, 0.05 g of the surfactant sodium dodecyl sulfate was added as a dispersant to 20 ml of ion-exchanged water to obtain a surfactant aqueous solution. 0.2 g of the resin particles to be measured were then added to the surfactant aqueous solution, and the resin particles were dispersed in the surfactant aqueous solution to obtain a dispersion for measurement. The prepared dispersion was introduced into the laser diffraction/scattering particle size distribution analyzer and measurements were performed.

(3HB unit/3HH unit composition ratio)
The composition ratio of 3HB units/3HH units in PHA was measured by the method described in Japanese Patent Laid-Open Publication No. 05-93049.

Example 1
(Preparation of bacterial cell culture solution)
The Ralstonia eutropha KNK-005 strain described in paragraph [0049] of WO 2008/010296 was cultured by the method described in paragraphs [0050] to [0053] of the same document to obtain a fungal cell culture solution containing fungal cells containing PHA. Ralstonia eutropha is currently classified as Capriavidus necator. The composition ratio of repeating units of the PHA contained in the fungal cells (composition ratio of 3HB unit/3HH unit) was 92/8 to 95/5 (mol/mol).

(Sterilization)
The bacterial culture solution obtained above was sterilized by heating and stirring at an internal temperature of 60 to 80°C for 20 minutes.

(High-pressure crushing treatment)
To the sterilized bacterial cell culture solution obtained above, 0.2 wt% sodium dodecyl sulfate was added. Furthermore, aqueous sodium hydroxide solution was added to adjust the pH to 11.0, and the mixture was then incubated at 50°C for 1 hour. The mixture was then subjected to high-pressure homogenization at a pressure of 450 to 550 kgf/ ^cm2 using a high-pressure homogenizer (Nirosoavi High-Pressure Homogenizer Model PA2K).

(Refining process)
An equal volume of distilled water was added to the resulting high-pressure disruption solution. After centrifugation, the supernatant was removed and the suspension was concentrated twice. To this concentrated aqueous suspension of PHA, an equal volume of aqueous sodium hydroxide solution (pH 11) was added, followed by centrifugation and removal of the supernatant. Water was added again to form a suspension, and 0.2 wt% sodium dodecyl sulfate and 1/100 wt% protease (Novozymes, Esperase) of the PHA were added. The suspension was stirred for 2 hours at pH 10 and 50°C. The supernatant was then removed by centrifugation, and the suspension was concentrated four times. Further water was added to adjust the PHA concentration to 52.8 wt%. Hereinafter, this aqueous PHA suspension will be referred to as PHA aqueous suspension (A).

(Preparation of PHA aqueous suspension (B))
A 52.8 wt % aqueous PHA suspension (hereinafter referred to as "aqueous PHA suspension (B)") having a composition ratio of PHA repeating units (composition ratio of 3HB units/3HH units) of 80/20 to 91/9 (mol/mol) was prepared by the method described in WO 2010/067543.

(granulation)
The PHA aqueous suspension (A) and PHA aqueous suspension (B) obtained above were mixed to obtain mixed solution 1. In mixed solution 1, the amount of PHA aqueous suspension (B) added was 5 parts by weight per 100 parts by weight of PHA aqueous suspension (A). Water was added to adjust the concentration of the mixed solution so that the concentration of PHA, which is the solid content of mixed solution 1, was 32.8% by weight, and then 1.0 phr (1 part by weight per 100 parts by weight of PHA present in the aqueous suspension) of an ethylene oxide/propylene oxide copolymer nonionic dispersant (polyethylene oxide molecular weight 8000, polypropylene oxide molecular weight 2000, trade name Pronon 208) was added and mixed to obtain mixed solution 2. Thereafter, water was further added to mixed solution 2 to adjust the solid content concentration to 30% by mass, and mixed solution 3 was obtained. After stirring the mixture 3 for 120 minutes, 0.4 ml of 10 wt % sulfuric acid was added per 100 g of the mixture 3 to obtain a PHA aqueous suspension with a pH of 3.0. The obtained PHA aqueous suspension was spray-dried using a rotary atomizer-type spray dryer (Mobile Minor) manufactured by GEA (hot air temperature: 170°C, exhaust air temperature: 100°C, rotary atomizer rotation speed: 10,000 rpm) to obtain a PHA powder. The median particle size of the obtained PHA powder was 44.3 μm.

Example 2
A PHA powder was obtained in the same manner as in Example 1, except that the amount of PHA aqueous suspension (B) added was 10 parts by weight. The median particle size of the obtained PHA powder was 45.4 μm.

Example 3
A PHA powder was obtained in the same manner as in Example 1, except that the amount of PHA aqueous suspension (B) added was 15 parts by weight. The median particle size of the obtained PHA powder was 58.3 μm.

Example 4
A PHA powder was obtained in the same manner as in Example 1, except that the amount of PHA aqueous suspension (B) added was 20 parts by weight. The median particle size of the obtained PHA powder was 73.4 μm.

Comparative Example 1
A PHA powder was obtained in the same manner as in Example 1, except that the PHA aqueous suspension (B) was not added. The median particle size of the obtained PHA powder was 39.9 μm.

Example 5
An aqueous PHA suspension with a solids concentration of 52.8 wt % was prepared by the same procedure as in Example 1, except that the composition ratio of the repeating units of the PHA (composition ratio of 3HB units/3HH units) was changed to 96/4 to 99/1 (mol/mol). Hereinafter, this aqueous PHA suspension will be referred to as PHA aqueous suspension (C). An aqueous PHA suspension was prepared in the same manner as in Example 1, except that the amount of PHA aqueous suspension (B) added to PHA aqueous suspension (C) was changed to 20 parts by weight. A PHA powder was obtained by spray drying under conditions of a hot air temperature of 180°C, an exhaust air temperature of 105°C, and a rotary atomizer rotation speed of 10,000 rpm. The median particle size of the obtained PHA powder was 58.8 μm.

Comparative Example 2
A PHA powder was obtained in the same manner as in Example 5, except that the PHA aqueous suspension (B) was not added. The median particle size of the obtained PHA powder was 38.5 μm.

[result]
Comparisons of Examples 1 to 4 with Comparative Example 1, and Example 5 with Comparative Example 2, reveal that a PHA powder obtained by spray-drying an aqueous suspension containing, as PHA, a polyhydroxybutyric acid copolymer (A) having a 3HB unit/3HH unit composition ratio of 92/8 to 100/0 and a polyhydroxybutyric acid copolymer (B) having a 3HB unit/3HH unit composition ratio of 75/25 to 91/9 has a larger particle size (median particle size) than a PHA powder obtained by spray-drying an aqueous suspension containing, as PHA, only a polyhydroxybutyric acid copolymer (A) having a 3HB unit/3HH unit composition ratio of 92/8 to 100/0.

In other words, this manufacturing method can produce a larger particle size PHA (e.g., PHA powder) than a method using an aqueous suspension containing only the polyhydroxybutyric acid copolymer (A) as the PHA.

Therefore, it was found that this manufacturing method can produce PHA (e.g., PHA powder) with large particle sizes even when the hot air temperature during spray drying is low.

This manufacturing method can be advantageously used in the production of PHA because it can produce PHA with large particle sizes (e.g., PHA powder) at lower hot air temperatures. Furthermore, the PHA powder obtained by this manufacturing method can be suitably used in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing, packaging, automobiles, building materials, and other fields.

Claims (12)

(a) preparing an aqueous suspension containing a polyhydroxybutyrate copolymer (A) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 100/0 and a polyhydroxybutyrate copolymer (B) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 75/25 to 91/9, and having a pH of 7 or less; and (b) spray-drying the aqueous suspension prepared in the step (a),
The method for producing a polyhydroxyalkanoic acid, wherein the content of the polyhydroxybutyric acid copolymer (B) in the aqueous suspension is 1 to 30 parts by weight relative to the content of the polyhydroxybutyric acid copolymer (A). The method for producing polyhydroxyalkanoic acid according to claim 1, wherein the hot air temperature in the spray drying step is 200°C or less. The method for producing polyhydroxyalkanoic acid according to claim 1 or 2, wherein the aqueous suspension further contains a dispersant. The method for producing polyhydroxyalkanoic acid according to claim 3, wherein the dispersant is at least one selected from the group consisting of alkylene oxide dispersants and polyvinyl alcohol. the dispersant is an alkylene oxide-based dispersant,
The method for producing a polyhydroxyalkanoic acid according to claim 3 or 4, wherein the alkylene oxide-based dispersant is composed of a poly(ethylene oxide) (PEO) block and a poly(propylene oxide) (PPO) block, and is in the form of PEO-PPO-PEO. the dispersant is an alkylene oxide-based dispersant,
The method for producing a polyhydroxyalkanoic acid according to any one of claims 3 to 5, wherein the alkylene oxide-based dispersant has a PEO molecular weight of 1500 or more and a PEO molecular weight/PPO molecular weight ratio of 0.5 to 5.0. the dispersant is an alkylene oxide-based dispersant,
The method for producing a polyhydroxyalkanoic acid according to any one of claims 3 to 6, wherein the alkylene oxide dispersant is a compound represented by the following formula (1):
(wherein X is 17 to 340, Y is 8 to 115, and Z is 17 to 340.) The method for producing polyhydroxyalkanoic acid according to any one of claims 1 to 7, wherein the concentration of polyhydroxyalkanoic acid in the aqueous suspension prepared in step (a) is 30 to 65% by weight. the polyhydroxybutyric acid copolymer (A) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 99/1;
The method for producing a polyhydroxyalkanoic acid according to any one of claims 1 to 8, wherein the composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units in the polyhydroxybutyric acid copolymer (B) is 80/20 to 91/9. a polyhydroxybutyrate copolymer (A) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 100/0, a polyhydroxybutyrate copolymer (B) having a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 75/25 to 91/9, and a dispersant;
The polyhydroxyalkanoic acid powder, wherein the content of the polyhydroxybutyric acid copolymer (B) is 1 to 30 parts by weight based on the content of the polyhydroxybutyric acid copolymer (A). The polyhydroxyalkanoic acid powder according to claim 10 , having a median particle size of 40 to 120 μm. the polyhydroxybutyric acid copolymer (A) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 92/8 to 99/1;
12. The polyhydroxyalkanoic acid powder according to claim 10, wherein the polyhydroxybutyric acid copolymer (B) has a composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units of 80/20 to 91/9.