CN117881717A

CN117881717A - Process for producing polyhydroxyalkanoate and use thereof

Info

Publication number: CN117881717A
Application number: CN202280059009.2A
Authority: CN
Inventors: 平野优; 服部准
Original assignee: Kaneka Corp
Current assignee: Kaneka Corp
Priority date: 2021-09-07
Filing date: 2022-06-27
Publication date: 2024-04-12

Abstract

The purpose of the present invention is to provide a method for producing PHA having good thermal stability in a pH range that does not require the use of a corrosion-resistant device. The present invention solves the above-mentioned problems by providing a method for producing polyhydroxyalkanoate comprising the following steps (a) and (b): (a) A step of preparing an aqueous suspension containing a polyhydroxyalkanoate, an alkylene oxide dispersant, and a specific amount of a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the pH of the aqueous suspension is 3.5 to 7.0; and (b) drying the aqueous suspension prepared in the step (a).

Description

Process for producing polyhydroxyalkanoate and use thereof

Technical Field

The present invention relates to a method for producing polyhydroxyalkanoate and use thereof.

Background

Polyhydroxyalkanoates (hereinafter sometimes referred to as "PHAs") are known to be biodegradable.

Since PHA produced by microorganisms accumulates in microbial cells, a step of separating and purifying PHA from microbial cells is required in order to use PHA as a plastic. In the step of separating and purifying PHA, PHA is removed from the aqueous suspension obtained after the microbial cells containing PHA are broken or the components of biological origin other than PHA are solubilized. At this time, for example, separation operations such as centrifugal separation, filtration, drying and the like are performed. In the drying operation, a spray dryer, a fluidized bed dryer, a drum dryer, or the like can be used, and from the viewpoint of simplicity of operation, a spray dryer is preferably used.

The present inventors have developed the following techniques: in order to prevent aggregation of PHA in an aqueous suspension having a pH of 7 or less and to prevent an increase in viscosity, an alkylene oxide dispersant is added before the pH of the aqueous suspension is adjusted to 7 or less, and then the resulting aqueous suspension having a pH of 7 or less is spray-dried (see patent document 1).

Patent document 2 discloses a method for producing a target product, which comprises mixing a polyhydroxyalkanoate with an acid having a pKa of 3 to 10.

Prior art literature

Patent literature

Patent document 1: international publication No. 2021/085534

Patent document 2: U.S. patent application 2013/0093119

Disclosure of Invention

Problems to be solved by the invention

However, there is still room for further improvement in the technology related to the above-mentioned PHA production process.

Accordingly, an object of one embodiment of the present invention is to provide a method for producing PHA having good thermal stability in a pH range where a corrosion-resistant device is not required.

Means for solving the problems

The present inventors have made intensive studies to solve the above problems, and as a result, have found for the first time that, in the step of producing PHA, PHA having excellent thermal stability can be produced even at a pH at which a corrosion-resistant device is not required by incorporating a specific additive into an aqueous suspension containing PHA (hereinafter, also referred to as "PHA aqueous suspension"), thereby completing the present invention.

Accordingly, a method for producing PHA according to one embodiment of the present invention (hereinafter referred to as "the present production method") comprises: a step (a) of preparing an aqueous suspension containing a PHA, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups is 400 to 15000ppm relative to the amount of the PHA, and the pH of the aqueous suspension is 3.5 to 7.0; and a step (b) of drying the aqueous suspension prepared in the step (a).

The aqueous suspension of PHA according to one embodiment of the present invention (hereinafter referred to as "the present aqueous suspension") contains PHA, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups is 400 to 15000ppm relative to the amount of PHA, and the pH of the aqueous suspension of PHA is 3.5 to 7.0.

The PHA powder (hereinafter referred to as "the present PHA powder") according to one embodiment of the present invention contains PHA, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, and has a thermal stability represented by the following formula (2) of 50% or more:

Thermal stability (%) = weight average molecular weight of PHA tablet obtained by pressing PHA powder at 160 ℃ for 20 minutes under 5 Mpa/weight average molecular weight of PHA powder x 100·· (2).

ADVANTAGEOUS EFFECTS OF INVENTION

According to one embodiment of the present invention, a method for producing PHA having excellent thermal stability can be provided without using a corrosion-resistant device.

Drawings

Fig. 1 is a graph showing the results of thermal stability measurement of an embodiment of the present invention.

Detailed Description

An embodiment of the present invention will be described in detail below. Unless otherwise specified in the present specification, "a to B" representing a numerical range means "a or more and B or less".

[ 1. Summary of the invention ]

In order to improve the thermal stability (molecular weight retention rate upon heating) of PHA, it is generally necessary to reduce the pH (usually about pH2 to 3) of the aqueous PHA suspension using sulfuric acid or the like. However, since a corrosion-resistant device is required for treating an aqueous PHA suspension having a low pH, there is a problem in that the cost of the device increases.

Accordingly, the present inventors have conducted intensive studies on a method for producing PHA that can provide excellent thermal stability without using a corrosion-resistant device, and as a result, have obtained the following new findings: by containing a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups as an additive, PHA having good heat stability can be produced at a pH that does not require a corrosion-resistant device. That is, although it is necessary to set the pH of the aqueous PHA suspension to about 2 to 3 in order to obtain PHA having good heat stability in the prior art, the present invention surprisingly enables the production of PHA having good heat stability in the range of pH3.5 to 7.0.

According to the present production method, PHA having good thermal stability can be produced without using a corrosion-resistant device, and therefore, it is advantageous from the viewpoint of cost. Further, the PHA powder has good thermal stability, and is therefore useful in various applications. Furthermore, the present aqueous suspension has a pH close to neutral and is therefore also advantageous from an operational point of view.

In addition, according to the above-described configuration, the amount of plastic waste generated can be reduced, and thus, for example, it is possible to contribute to realization of sustainable development targets (SDGs) such as the target 12 "ensuring sustainable consumption and production mode", the target 14 "protecting and sustainable use of ocean and ocean resources to promote sustainable development". The following describes the present production method and the constitution of the present aqueous suspension in detail.

[ 2. Method for producing PHA ]

The manufacturing method is a method comprising the following steps (a) - (b):

step (a): a step of preparing an aqueous suspension comprising PHA, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups is 400 to 15000ppm relative to the amount of PHA, and the pH of the aqueous suspension is 3.5 to 7.0

Step (b): and (c) drying the aqueous suspension prepared in the step (a).

(Process (a))

In the step (a) of the present production method, an aqueous suspension is prepared which contains PHA, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups is 400 to 15000ppm relative to the amount of PHA, and the pH of the aqueous suspension is 3.5 to 7.0.

＜PHA＞

In the present specification, "PHA" refers to a generic term for polymers having hydroxyalkanoic acid as a monomer unit. The hydroxyalkanoic acid constituting the PHA is not particularly limited, and examples thereof include: 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxypropionic acid, 3-hydroxyvaleric acid, 3-hydroxycaproic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, and the like. These polymers may be homopolymers or copolymers containing 2 or more monomer units.

More specifically, examples of PHAs include: poly (3-hydroxybutyrate) (P3 HB), poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3 HB3 HH), poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (P3 HB3 HV), poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P3 HB4 HB), poly (3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3 HB3 HO), poly (3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (P3 HB3 HOD), poly (3-hydroxybutyrate-co-3-hydroxydecanoate) (P3 HB3 HD), poly (3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3 HB3HV3 HH), and the like. Among them, P3HB3HH, P3HB3HV, and P3HB4HB are preferable from the viewpoint of easy industrial production.

Further, the copolymer P3HB3HH of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid is more preferable from the viewpoints that the melting point and crystallinity can be changed by changing the composition ratio of the repeating units, and as a result, physical properties such as Young's modulus and heat resistance can be changed, physical properties between polypropylene and polyethylene can be imparted, and the copolymer is industrially easily produced and is a plastic useful in physical properties as described above.

In one embodiment of the present invention, the composition ratio of 3-hydroxybutyrate units/3-hydroxycaproate units is preferably 80/20 to 99.9/0.1 (mol/mol), more preferably 85/15 to 97/3 (mol/mol) in terms of the balance between flexibility and strength with respect to the composition ratio of the repeating units of P3HB3HH. When the composition ratio of 3-hydroxybutyrate units/3-hydroxycaproate units is 99.9/0.01 (mol/mol) or less, sufficient flexibility is obtained, and when 80/20 (mol/mol) or more, sufficient hardness is obtained.

The present production method may include a step of obtaining an aqueous PHA suspension before the step (a). The step of obtaining the aqueous PHA suspension may include, for example: a culturing step of culturing a microorganism having an ability to produce PHA in a cell, and a purifying step of decomposing and/or removing substances other than PHA after the culturing step.

The microorganism used in this step is not particularly limited as long as it is a microorganism capable of producing PHA in the cells. For example, naturally isolated microorganisms and microorganisms deposited in the deposit institution (e.g., IFO, ATCC, etc.) of the strain, mutants and transformants which can be prepared from them, and the like can be used. For example, the bacterial cells of P3HB, which are an example of PHA production, were originally identified as Bacillus megaterium (Bacillus megaterium) found in 1925, and others include: native microorganisms such as copper (Cupriavidus necator) and Alcaligenes eutrophus (Alcaligenes eutrophus) and Ralstonia eutrophus (Ralstonia eutropha) are classified as old, and Alcaligenes broadly (Alcaligenes latus) are classified as broad-spectrum. Among these microorganisms, PHA is known to accumulate in the cells.

Examples of the bacterial cells that produce a copolymer of hydroxybutyrate and other hydroxyalkanoate that is an example of PHA include: aeromonas caviae (Aeromonas caviae) as P3HB3HV and P3HB3HH producer, alcaligenes eutrophus (Alcaligenes eutrophus) as P3HB4HB producer, etc. In particular, regarding P3HB3HH, alcaligenes encoding PHA synthase are more preferably introduced into the strain AC32 (Alcaligenes eutrophus AC, FERM BP-6038) (T.Fukui, Y.Doi, J.Bateriol.,179, P4821-4830 (1997)) of Alcaligenes encoding PHA synthase for improving the productivity of P3HB3 HH. In addition to the above, the bacterial cells may be genetically modified microorganisms into which various PHA synthesis-related genes have been introduced according to PHA to be produced.

Since PHA-containing microorganisms produced by culturing the microorganisms described above contain a large amount of cell-derived components as impurities, a purification step for decomposing and/or removing impurities other than PHA is generally performed. In the purification step, there is no particular limitation, and physical treatment, chemical treatment, biological treatment, and the like which can be considered by those skilled in the art can be applied, and for example, the purification method described in international publication No. 2010/067543 can be preferably applied.

The amount of impurities remaining in the final product can be roughly determined by the above purification step, and therefore it is preferable to minimize these impurities. Of course, impurities may be mixed in depending on the application as long as the physical properties of the final product are not impaired, but in the case of PHA required to have high purity for medical use or the like, it is preferable to reduce impurities as much as possible. The purification degree at this time is an index of, for example, the amount of protein in the PHA aqueous suspension. The amount of the protein is preferably 30000ppm or less, more preferably 15000ppm or less, further preferably 10000ppm or less, and most preferably 7500ppm or less relative to the amount of PHA. The purification method is not particularly limited, and for example, the above known methods can be applied.

The solvent constituting the aqueous suspension of PHA in the present production method ("solvent" is also referred to as "aqueous medium") may be water or a mixed solvent of water and an organic solvent. In addition, the concentration of the organic solvent compatible with water in the mixed solvent is not particularly limited as long as the solubility of the organic solvent to be used in water is not more than. The organic solvent having compatibility with water is not particularly limited, and examples thereof include: alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, heptanol, and the like; ketones such as acetone and methyl ethyl ketone; tetrahydrofuran, twoEthers such as alkanes; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, piperidine, and the like. Among them, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, di +.>Alkane, acetonitrile, propionitrile, and the like. Further, methanol, ethanol, 1-propanol, 2-propanol, butanol, acetone, and the like are more preferable from the viewpoint of easy availability. Furthermore, methanol is particularly preferred Ethanol, acetone. The aqueous medium constituting the aqueous suspension of PHA may contain other solvents, components derived from cells, compounds produced during purification, and the like, as long as the essence of the present invention is not impaired.

The aqueous medium constituting the aqueous suspension of PHA in the present 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, still more preferably 30% by weight or more, and particularly preferably 50% by weight or more.

The concentration of PHA in the aqueous PHA suspension prepared in the step (a) of the present production method is preferably 30% by weight or more, more preferably 32.5% by weight or more, further preferably 35% by weight or more, particularly preferably 37.5% by weight or more, from the viewpoint of economical advantages and improvement in productivity. The upper limit of the concentration of PHA is preferably 65 wt% or less, more preferably 60 wt% or less, from the viewpoint of avoiding the closest packing and securing sufficient fluidity. The method for adjusting the concentration of PHA is not particularly limited, and examples thereof include a method of adding an aqueous medium, removing a part of the aqueous medium (for example, removing a supernatant after centrifugation, and the like). The concentration of PHA may be adjusted at any stage in the step (a), or may be adjusted at a stage preceding the step (a).

< Compounds having multiple carboxyl groups >

In the step (a) of the present production method, PHA having good thermal stability can be produced even when the pH of the aqueous suspension is in the range of 3.5 to 7.0 by including a compound having a plurality of carboxyl groups in the aqueous suspension. In other words, by including a compound having a plurality of carboxyl groups in the aqueous suspension of PHA, PHA having good thermal stability can be obtained without using a corrosion-resistant device.

The compound having a plurality of carboxyl groups in the step (a) of the production method is not particularly limited as long as it is a compound having a plurality of carboxyl groups per 1 molecule on average. The number of carboxyl groups per 1 molecule on average is not particularly limited, and may be, for example, 2, 3, 4, 5, 6, 7, 8, or the like. In the case where the compound having a plurality of carboxyl groups is a polymer, the compound may have a plurality of carboxyl groups as a whole of the polymer. For example, by including one or more carboxyl groups in the monomer units constituting the polymer, the polymer as a whole can have a plurality of carboxyl groups. The form of the compound having a plurality of carboxyl groups is not particularly limited, and may be, for example, a form of a hydrate.

Specific examples of the compound having a plurality of carboxyl groups include, for example: citric acid (e.g., citric acid monohydrate), trisodium citrate (e.g., trisodium citrate dihydrate), tartaric acid, disodium tartrate (e.g., disodium tartrate dihydrate), polyacrylic acid, sodium polyacrylate, and the like. Among them, citric acid and polyacrylic acid are preferable, and citric acid is more preferable. These compounds may be used in an amount of 1 or more.

In the step (a) of the present production method, the amount of the compound having a plurality of carboxyl groups in the aqueous PHA suspension is 400 to 15000ppm, preferably 420 to 10000ppm, more preferably 450 to 8000ppm, relative to the amount of the PHA. When the amount of the compound having a plurality of carboxyl groups in the aqueous PHA suspension is 400 to 15000ppm relative to the amount of PHA, PHA having good thermal stability can be obtained even if the pH of the aqueous PHA suspension is in a higher range (for example, pH3.5 to 7.0).

< Compounds having more than 1 phosphate group >

In the step (a) of the present production method, the aqueous PHA suspension may contain a compound having a plurality of carboxyl groups and contain a compound having 1 or more phosphate groups, or contain a compound having 1 or more phosphate groups instead of the compound having a plurality of carboxyl groups. Preferably, a compound having 1 or more phosphate groups is used instead of the compound having a plurality of carboxyl groups. In the case where the aqueous PHA suspension contains a compound having 1 or more phosphate groups, the same effects as those in the case where the PHA aqueous suspension contains a compound having a plurality of carboxyl groups can be obtained.

The compound having 1 or more phosphate groups in step (a) of the present production method is not particularly limited as long as it has 1 or more phosphate groups per 1 molecule on average. The number of phosphate groups per 1 molecule is preferably plural, but not particularly limited, and may be, for example, 2, 3, 4, 5, 6, 7, 8, or the like.

Specific examples of the compound having a plurality of phosphate groups include, for example: tetrapotassium pyrophosphate, disodium dihydrogen pyrophosphate, tetrasodium pyrophosphate, potassium polyphosphate, sodium polyphosphate, potassium metaphosphate, sodium metaphosphate, tripotassium phosphate, dipotassium hydrogen phosphate, monopotassium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, diammonium hydrogen phosphate, monoammonium phosphate and the like. Among them, sodium polyphosphate, tetrasodium pyrophosphate, and sodium metaphosphate are preferable. These compounds may be used in an amount of 1 or more.

In the step (a) of the present production method, the above-mentioned description of < compound having a plurality of carboxyl groups > is appropriately cited for the content of the compound having a plurality of phosphate groups in the aqueous PHA suspension.

< alkylene oxide dispersant >)

The alkylene oxide dispersant in step (a) of the present production method has the following effects: the PHA can be prevented from agglomerating when the pH of the PHA aqueous suspension is adjusted to 7 or less, and the adhesion to the shaft of the extruder during powder processing can be inhibited.

In one embodiment of the present invention, the alkylene oxide dispersant is not particularly limited as long as it has the above-described effect, and is preferably in the form of PEO-PPO-PEO composed of a block of polyethylene oxide (PEO) and a block of polypropylene oxide (PPO).

In the present specification, the "block of polyethylene oxide (PEO)" refers to a polymer portion formed by polymerization of Ethylene Oxide (EO) in the structure of an alkylene oxide-based dispersant.

In the present specification, the "block of polypropylene oxide (PPO)" means a polymer portion formed by polymerizing 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 dispersant to specific ranges, it is possible to produce PHA (e.g., PHA powder) with high productivity while maintaining the viscosity of the aqueous PHA suspension at a low level.

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

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

That is, in one embodiment of the present invention, the PEO molecular weight in the alkylene oxide dispersant is only 1500 or more, preferably 1750 or more, and more preferably 2000 or more. In one embodiment of the present invention, the upper limit of the PEO molecular weight in the alkylene oxide dispersant is, for example, 30000 or less, preferably 25000 or less, and more preferably 20000 or less.

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

When the PEO molecular weight and the PEO molecular weight/PPO molecular weight of the alkylene oxide dispersant are within the above-mentioned ranges, the alkylene oxide dispersant has hydrophilicity and the number of molecules per the weight of the alkylene oxide dispersant added increases, so that the dispersibility of the aqueous PHA suspension is easily maintained.

In one embodiment of the present invention, the alkylene oxide dispersant has a PEO molecular weight of 1500 or more and a PEO molecular weight/PPO molecular weight of 0.5 to 5.0.

In one embodiment of the present invention, the alkylene oxide dispersant preferably has at least 1 PEO block with a molecular weight of 750 or more, more preferably at least 2 or more. The upper limit is not particularly limited, but is, for example, 4 or less, preferably 3 or less. When the number of PEO blocks is within the above range, the alkylene oxide dispersant has hydrophilicity.

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

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-described effect is achieved, and may be 1 or a plurality (for example, 2, 3, 4).

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

[ chemical formula 1]

In the above formula (1), X is, for example, 17 to 340, preferably 20 to 285, more preferably 22 to 226. When X is 340 or less, the number of molecules per the weight of the alkylene oxide dispersant added increases, so that the dispersibility of the aqueous PHA suspension is easily maintained, and when X is 17 or more, the aqueous PHA suspension has hydrophilicity. Y is, for example, 8 to 115, preferably 10 to 110, more preferably 24 to 107.Y is 115 or less, is easily dissolved in water, and Y is 8 or more, and has hydrophobicity. Z is, for example, 17 to 340, preferably 20 to 285, more preferably 22 to 226. When Z is 340 or less, the number of molecules per the weight of the alkylene oxide dispersant added increases, so that the dispersibility of the PHA aqueous suspension is easily maintained, and when Z is 17 or more, the alkylene oxide dispersant has hydrophilicity.

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 per the weight of the alkylene oxide dispersant added increases, and the dispersibility of the PHA aqueous suspension is easily maintained, and when X is 34 or more, the alkylene oxide dispersant has hydrophilicity.

The alkylene oxide-based dispersant used in step (a) of the present production method is not particularly limited, and for example, commercially available ones can be used. Examples of the commercial products include Pluronic 10400 (manufactured by BASF), pluronic 10500 (manufactured by BASF), genapol PF80 (manufactured by Clariant), UNILUBE DP60-600B (manufactured by Nitro oil Co., ltd.), UNILUBE DP60-950B (manufactured by Nitro oil Co., ltd.), PLONN 208 (manufactured by Nitro oil Co., ltd.), EPAN U105 (manufactured by Nitro oil Co., ltd.), EPAN U108 (manufactured by Nitro oil Co., ltd.), and EPAN 750 (manufactured by Nitro oil Co., ltd.).

The amount of the alkylene oxide dispersant added to the aqueous PHA suspension in the step (a) of the production method is not particularly limited, but 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, based on 100 parts by weight of PHA contained in the aqueous PHA suspension. When the amount of the alkylene oxide dispersant added is in the above range, the dispersion stability of PHA in the PHA aqueous suspension is further improved, and the productivity of PHA tends to be improved.

< aqueous suspension >

In step (a) of the present production method, the pH of the aqueous PHA suspension is 3.5 to 7.0, preferably 3.52 to 6.8, more preferably 3.54 to 6.6. When the pH of the aqueous PHA suspension is 3.5 or more, a corrosion-resistant device is not required for the preparation of the aqueous PHA suspension. In addition, when the pH of the aqueous PHA suspension is 7.0 or less, the thermal stability of the PHA obtained is improved.

In one embodiment of the present invention, when the aqueous PHA suspension comprises polyhydroxyalkanoate, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups, the pH of the aqueous PHA suspension in step (a) of the present production method is preferably 3.5 to 6.0, more preferably 3.52 to 5.8, and even more preferably 3.54 to 5.6.

In one embodiment of the present invention, when the aqueous PHA suspension comprises polyhydroxyalkanoate, an alkylene oxide dispersant, and a compound having 1 or more phosphate groups, the pH of the aqueous PHA suspension in step (a) of the present production method is preferably 3.5 to 7.0, more preferably 3.5 to 6.8, and even more preferably 3.5 to 6.6.

The method for adjusting the pH of the aqueous PHA suspension in the step (a) is not particularly limited, and examples thereof include methods of adding an acid and the like. The acid is not particularly limited, and may be any of an organic acid and an inorganic acid, regardless of whether it is volatile or not. More specifically, as the acid, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, or the like can be used, for example. The compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups may be used as an auxiliary component in the adjustment of the pH of the aqueous suspension of PHA in the step (a).

< others >

In step (a) of the present production method, the temperature at the time of producing the aqueous PHA suspension is, for example, 30 to 80 ℃, preferably 50 to 75 ℃, more preferably 60 to 75 ℃. When the temperature at which the aqueous PHA suspension is prepared is 30 to 80 ℃, the viscosity of the aqueous PHA suspension can be reduced.

(Process (b))

In the step (b) of the present production method, the aqueous PHA suspension produced in the step (a) is dried to obtain PHA. That is, the step (b) may be considered as a step of removing the water contained in the aqueous PHA suspension prepared in the step (a).

The drying method of the aqueous PHA suspension is not particularly limited, and may be performed using, for example, a dryer, an oven, a spray dryer, a flow dryer, a drum dryer, or the like. The drying temperature at the time of drying may be any temperature at which most of the aqueous medium can be removed from the droplets of the aqueous PHA suspension, and the aqueous medium may be dried to a target water content, and may be appropriately set under conditions such as melting and the like without causing deterioration of quality (e.g., reduction of molecular weight and color tone).

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

[ 3. Aqueous suspension of PHA ]

The aqueous suspension comprises PHA, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups is 400 to 15000ppm relative to the amount of PHA, and the pH of the aqueous suspension is 3.5 to 7.0. The present aqueous suspension is at a pH close to neutral and is therefore advantageous from an operational point of view.

In the present aqueous suspension, "PHA", "alkylene oxide dispersant", "compound having a plurality of carboxyl groups", "compound having 1 or more phosphate groups", "pH of the aqueous suspension" can be cited as [ 2.PHA production method ].

The concentration of PHA in the aqueous PHA suspension is preferably 30 wt% or more, more preferably 32.5 wt% or more, further preferably 35 wt% or more, particularly preferably 37.5 wt% or more, from the viewpoint of economical advantage in terms of drying utility and improvement in productivity. The upper limit of the concentration of PHA is preferably 65 wt% or less, more preferably 60 wt% or less, from the viewpoint of avoiding the closest packing and securing sufficient fluidity. The method for adjusting the concentration of PHA is not particularly limited, and examples thereof include a method of adding an aqueous medium, removing a part of the aqueous medium (for example, removing a supernatant after centrifugation, and the like).

The content of the alkylene oxide dispersant in the aqueous PHA suspension is not particularly limited, but 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, based on 100 parts by weight of PHA contained in the aqueous PHA suspension. When the amount of the alkylene oxide dispersant added is in the above range, the dispersion stability of PHA in the PHA aqueous suspension is further improved, and the productivity of PHA tends to be improved.

The amount of protein in the aqueous PHA suspension is preferably 30000ppm or less, more preferably 15000ppm or less, further preferably 10000ppm or less, and most preferably 7500ppm or less, relative to the amount of PHA.

In one embodiment of the present invention, the present aqueous suspension can be produced by the step (a) of the present production method.

The aqueous suspension may contain various components which are generated or removed during the course of the production method as long as it has the effect of the present invention.

[ 4.PHA powder ]

The PHA powder comprises PHA, an alkylene oxide dispersant, a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, and has a thermal stability represented by the following formula (2) of 50% or more:

thermal stability (%) = weight average molecular weight of PHA sheet obtained by pressing polyhydroxyalkanoate powder at 160 ℃ for 20 minutes under 5 Mpa/weight average molecular weight of polyhydroxyalkanoate powder x 100·· (2).

The PHA powder has good thermal stability, and is therefore useful in various applications.

In the present PHA powder, "PHA", "alkylene oxide dispersant", "compound having a plurality of carboxyl groups", "compound having 1 or more phosphate groups" can be cited as [ 2.PHA production method ].

The thermal stability of the PHA powder is 50% or more, preferably 52% or more, and more preferably 54% or more. When the thermal stability is 50% or more, deterioration of the resin obtained by processing the present PHA powder can be suppressed. The upper limit is not particularly limited, and for example, is 95% or less as the thermal stability is higher.

The PHA powder may contain various components that are generated or removed during the course of the present manufacturing method, as long as it has the effects of the present invention.

The PHA powder can be used for various applications such as paper, film, sheet, tube, plate, rod, container (for example, bottle container), bag, and member.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments in which the technical means disclosed in the different embodiments are appropriately combined are also included in the technical scope of the present invention.

That is, one embodiment of the present invention includes the following.

< 1 > a process for producing polyhydroxyalkanoate, which comprises:

(a) A step of preparing an aqueous suspension containing a polyhydroxyalkanoate, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups,

the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups in the aqueous suspension is 400 to 15000ppm relative to the amount of the polyhydroxyalkanoate, and the pH of the aqueous suspension is 3.5 to 7.0; and

(b) And (c) drying the aqueous suspension prepared in the step (a).

The process for producing polyhydroxyalkanoate according to < 2 > to < 1 >, wherein the compound having a plurality of carboxyl groups is at least one selected from the group consisting of citric acid, trisodium citrate, tartaric acid, disodium tartrate, polyacrylic acid and sodium polyacrylate.

The process for producing polyhydroxyalkanoate according to < 3 > to < 1 >, wherein the compound having 1 or more phosphate groups is at least 1 or more selected from sodium metaphosphate and sodium polyphosphate.

The method for producing polyhydroxyalkanoate according to any one of < 1 > - < 3 >, wherein the dispersant is composed of a polyethylene oxide (PEO) block and a polypropylene oxide (PPO) block, and is in the form of PEO-PPO-PEO.

The process for producing polyhydroxyalkanoate according to any one of < 1 > < 4 >, wherein the polyhydroxyalkanoate concentration in the aqueous suspension prepared in the step (a) is 30 to 65 wt%.

The method for producing polyhydroxyalkanoate according to any one of < 1 > - < 5 >, wherein the amount of the dispersant added is 0.1 to 20 parts by weight based on 100 parts by weight of polyhydroxyalkanoate contained in the aqueous suspension.

< 7 > an aqueous suspension of polyhydroxyalkanoate comprising polyhydroxyalkanoate, an oxyalkylene-based dispersing agent, a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups,

the amount of the compound having a plurality of carboxyl groups and/or the compound having 1 or more phosphate groups is 400 to 15000ppm relative to the amount of the polyhydroxyalkanoate,

the pH of the aqueous suspension is 3.5-7.0.

The aqueous suspension of polyhydroxyalkanoate according to < 8 > to < 7 >, wherein the compound having a plurality of carboxyl groups is at least one selected from the group consisting of citric acid, trisodium citrate, tartaric acid, disodium tartrate, polyacrylic acid and sodium polyacrylate.

The aqueous suspension of polyhydroxyalkanoate according to < 7 > or < 8 >, wherein the compound having 1 or more phosphate groups is at least 1 or more selected from sodium metaphosphate and sodium polyphosphate.

The method for producing polyhydroxyalkanoate according to any one of < 7 > - < 9 >, wherein the dispersant is composed of a polyethylene oxide (PEO) block and a polypropylene oxide (PPO) block, and is in the form of PEO-PPO-PEO.

The aqueous suspension of polyhydroxyalkanoate according to any one of < 7 > - < 10 >, wherein the concentration of polyhydroxyalkanoate in the aqueous suspension is 30 to 65 wt%.

The aqueous suspension of polyhydroxyalkanoate according to any one of < 7 > - < 11 >, wherein the content of the dispersant is 0.1 to 20 parts by weight relative to 100 parts by weight of polyhydroxyalkanoate contained in the aqueous suspension.

The aqueous polyhydroxyalkanoate suspension according to any one of < 7 > - < 12 >, wherein the amount of protein in the aqueous polyhydroxyalkanoate suspension is 30000ppm or less relative to the amount of PHA.

< 14 > a polyhydroxyalkanoate powder comprising a polyhydroxyalkanoate, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the polyhydroxyalkanoate powder has a thermal stability represented by the following formula (2) of 50% or more:

Thermal stability (%) = weight average molecular weight of polyhydroxyalkanoate pellet obtained by pressing polyhydroxyalkanoate powder at 160 ℃ and 5MPa for 20 minutes/weight average molecular weight of polyhydroxyalkanoate powder × 100· (2)

Examples

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[ method of measurement and evaluation ]

The measurement and evaluation in examples and comparative examples were performed by the following methods.

(thermal stability)

PHA powder obtained in the following examples and comparative examples was used as a sample for evaluation. The PHA powder was preheated at 160℃for 7 minutes, and then pressed at 5MPa for 20 minutes, thereby producing a PHA sheet. After 10mg of this PHA sheet was dissolved in 10ml of chloroform, insoluble matter was removed by filtration. Molecular weight was measured using a GPC system manufactured by Shimadzu corporation, which was equipped with "Shodex K805L (300X 8mm, 2 series)" (manufactured by Showa Denko Co., ltd.) and using chloroform as a flow against the solution (filtrate). The molecular weight standard sample used was a commercially available standard polystyrene. The molecular weight of the PHA powder was measured by the same procedure as described above, except that the production of the PHA sheet was not performed.

The thermal stability was evaluated based on the following formula (2):

thermal stability (%) = weight average molecular weight of PHA tablet obtained by pressing PHA powder at 160 ℃ and 5MPa for 20 minutes/weight average molecular weight of PHA powder x 100·· (2).

[ example 1 ]

(preparation of cell culture solution)

The Ralstonia eutropha (Ralstonia eutropha) described in International publication No. 2019/142717 was cultured according to the methods described in paragraphs [ 0041 ] to [ 0048 ] of the publication to obtain a bacterial culture solution containing PHA-containing bacterial cells. Note that, ralstonia eutropha is currently classified as copper-pesticidal bacteria.

(Sterilization treatment)

The cell culture solution obtained above was heated and stirred at an internal temperature of 60 to 80℃for 20 minutes, and sterilized.

(high pressure crushing treatment)

To the sterilized cell culture medium thus obtained, 0.2% by weight of sodium dodecyl sulfate was added. Further aqueous sodium hydroxide solution was added to bring the pH to 11.0, followed by incubation at 50℃for 1 hour. Then, a high-pressure crusher (model Homogenizer Model PA K manufactured by Niro Soavi Co., ltd.) was used at a speed of 450 to 550kgf/cm ² Is subjected to high pressure crushing.

(purification treatment)

An equal amount of distilled water was added to the crushed liquid obtained after high-pressure crushing. It was centrifuged and the supernatant was removed and concentrated 2-fold. To the concentrated aqueous suspension of PHA, an aqueous sodium hydroxide solution (pH 11) was added in an amount equivalent to the removed supernatant, and the supernatant was removed by centrifugation. To this was added water again to suspend the mixture, 0.2% by weight of sodium dodecyl sulfate and 1/100 by weight of protease (Novozymes corporation, esperase) of PHA were added, and stirring was performed at pH10 and 50℃for 2 hours. Then, the supernatant was removed by centrifugation, and 4-fold concentration was performed. The pH of the aqueous solution was adjusted to 10 by adding water and the supernatant was removed by centrifugation, and this operation was repeated several times to adjust the PHA concentration to 52.8% by weight. The amount of protein contained in the aqueous PHA suspension thus obtained was 1100ppm relative to the amount of PHA.

To the aqueous PHA suspension thus obtained (solid content concentration 52.8% by weight), 0.95phr (0.95 parts by weight relative to 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: PLONON 208) was added as a dispersant. The dispersant is a dispersant having a form of PEO-PPO-PEO. To this was added a given amount of citric acid monohydrate (manufactured by FUJIFILM Wako Pure Chemical corporation) as a compound having a plurality of carboxyl groups, and stirred at 60 ℃ for 30 minutes. The aqueous PHA suspension was adjusted to a predetermined pH by adding 9% sulfuric acid, and the water of the aqueous PHA suspension was volatilized by a dryer (NDO-600 ND manufactured by EYELA Co.), to obtain PHA powder. The concentration and pH of citric acid monohydrate in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 1.

TABLE 1

Citric acid monohydrate [ ppm ]]	pH[-]	Thermal stability [%]
			850	4.1	82.2
850	5.2	72.1
			1570	5.2	75.5
1570	5.5	76.0
			1570	5.8	59.8

[ example 2 ]

PHA powder was obtained in the same manner as in example 1, except that trisodium citrate dihydrate (manufactured by FUJIFILM Wako Pure Chemical Co.) was used as the compound having a plurality of carboxyl groups. The concentrations and pH of trisodium citrate dihydrate in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 2.

TABLE 2

Trisodium citrate dihydrate [ ppm ]]	pH[-]	Thermal stability [%]
			1230	4.8	80.8
1230	5.2	67.4

[ example 3]

PHA powder was obtained in the same manner as in example 1, except that polyacrylic acid (manufactured by BASF corporation, sokalan PA110s (MW 250,000)) was used as the compound having a plurality of carboxyl groups. The concentration and pH of the polyacrylic acid in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 3.

TABLE 3

Polyacrylic acid [ ppm ]]	pH[-]	Thermal stability [%]
			2300	4.2	82.5
2300	4.4	78.5
			2300	4.7	81.6
2300	5.0	79.7
			2300	5.3	75.7

[ example 4]

PHA powder was obtained in the same manner as in example 1, except that sodium polyacrylate (manufactured by BASF corporation, sokalan PA 40) was used as the compound having a plurality of carboxyl groups. The concentration and pH of sodium polyacrylate in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 4.

TABLE 4

Sodium polyacrylate [ ppm ]]	pH[-]	Thermal stability [%]
			490	3.9	78.7
490	4.5	80.0
			490	5.1	55.2

[ example 5 ]

PHA powder was obtained in the same manner as in example 1, except that disodium tartrate dihydrate (manufactured by FUJIFILM Wako Pure Chemical Co.) was used as the compound having a plurality of carboxyl groups. The concentrations and pH of disodium tartrate dihydrate in the aqueous PHA suspension and the results of evaluating the thermal stability of the resulting PHA powder are shown in table 5.

TABLE 5

Disodium tartrate dihydrate [ ppm ]]	pH[-]	Thermal stability [%]
			1100	3.6	83.8
1100	3.8	83.0
			1100	4.1	77.9
1100	4.4	81.4
			1100	4.8	74.9

Comparative example 1

PHA powder was obtained in the same manner as in example 1, except that the compound having a plurality of carboxyl groups was not added. The pH of the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 6.

TABLE 6

pH[-]	Thermal stability [%]
		4.7	48.9
5.0	32.1
		5.0	21.8

Comparative example 2

PHA powder was obtained in the same manner as in example 5, except that the amount of disodium tartrate dihydrate added was 340 ppm. The concentrations and pH of disodium tartrate dihydrate in the aqueous PHA suspension and the results of evaluating the thermal stability of the resulting PHA powder are shown in table 7.

TABLE 7

Disodium tartrate dihydrate [ ppm ]]	pH[-]	Thermal stability [%]
			340	4.6	44.3
340	5.2	7.0

[ comparative example 3 ]

PHA powder was obtained in the same manner as in example 1, except that the addition amount of citric acid monohydrate was 20000 ppm. The concentration and pH of citric acid monohydrate in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 8.

TABLE 8

Tartaric acid monohydrate [ ppm ]]	pH[-]	Thermal stability [%]
			20000	5	10

[ example 6]

PHA powder was obtained in the same manner as in example 1, except that PolyRINSAN 1A (sodium polyphosphate 26%, sodium metaphosphate 72%, tetrasodium pyrophosphate 2%, and organic Food Tech Co.) was used as the compound having 1 or more phosphate groups. The concentration and pH of PolyRINSAN 1A in the PHA aqueous suspension and the results of evaluating the thermal stability of the PHA powder obtained are shown in Table 9.

TABLE 9

POLYRINSAN 1A[ppm]	pH[-]	Thermal stability [%]
			10000	6.6	72.3
10000	6.0	78.1
			10000	5.5	76.7
10000	4.9	77.9
			10000	4.2	77.9

Example 7

PHA powder was obtained in the same manner as in example 1, except that sodium polyphosphate (manufactured by FUJIFILM Wako Pure Chemical Co.) was used as the compound having a phosphate group. The concentration and pH of sodium polyphosphate in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 10.

TABLE 10

Sodium polyphosphate [ ppm ]]	pH[-]	Thermal stability [%]
			1000	5.6	77.2
1000	5.2	82.5
			1000	4.8	84.4
1000	3.9	82.0
			1000	3.5	82.0

Example 8

PHA powder was obtained in the same manner as in example 1, except that PolyRINSAN 1A was used as the compound having a phosphate group. PolyRINSAN 1A content in PHA aqueous suspension was 10000ppm, and pH was 3.5 to obtain powder. The weight change at 200℃of the obtained powder was measured by TG-DTA (TG-DTA 2000SE, manufactured by NETZCN Co.). The results are shown in FIG. 1.

[ comparative example 4 ]

PHA powder was obtained in the same manner as in example 1, except that the compound having a plurality of carboxyl groups and the compound having a phosphate group were not added. The pH of the aqueous PHA suspension was set to 3.5. The weight change at 200℃of the obtained powder was measured by TG-DTA. The results are shown in FIG. 1.

[ comparative example 5 ]

PHA powder was obtained in the same manner as in example 1, except that the addition amount of citric acid monohydrate was 850ppm and the pH was adjusted to 7.5. The concentration and pH of citric acid monohydrate in the aqueous PHA suspension and the results of evaluating the thermal stability of the obtained PHA powder are shown in table 11.

TABLE 11

Tartaric acid monohydrate [ ppm ]]	pH[-]	Thermal stability [%]
			850	7.5	9.6

< results >

As shown in tables 1 to 6, the PHA powders of examples 1 to 5 have high thermal stability compared with comparative example 1. From this, it was found that by adding a compound having a plurality of carboxyl groups, PHA having good thermal stability can be obtained even if the pH of the PHA aqueous suspension is in a range where a corrosion-resistant device is not required.

Further, tables 5 and 7 show that the PHA powder of comparative example 2 has lower thermal stability than that of example 5. From this, it was found that when the amount of the compound having a plurality of carboxyl groups added was not more than a certain amount, PHA having good thermal stability was obtained. Further, as is clear from tables 1 and 8, even when the amount of the compound having a plurality of carboxyl groups added is a predetermined amount or more, PHA having good thermal stability cannot be obtained. Further, as can be seen from table 11, even when the pH is more than 7.0, PHA with good thermal stability cannot be obtained.

Further, as shown in tables 9 and 10, when a compound having 1 or more phosphate groups was used, PHA powder exhibited high thermal stability. Further, as is clear from FIG. 1, example 8 has less weight change at 200℃and high thermal stability as compared with comparative example 4.

As described above, in the present production method, by adding a predetermined amount of a compound having a plurality of carboxyl groups, even when the pH of the aqueous suspension of PHA is in a range where corrosion resistance is not required, PHA having good thermal stability can be obtained.

Industrial applicability

The present production method can be advantageously used for producing PHA (e.g., PHA powder) having excellent thermal stability. The PHA powder obtained by the present production method can be preferably used in agriculture, fishery, forestry, gardening, medicine, sanitary products, clothing, non-clothing, packaging, automobiles, building materials, and other fields.

Claims

1. A method of making a polyhydroxyalkanoate, the method comprising:

(b) And (c) drying the aqueous suspension prepared in the step (a).

2. The method for producing polyhydroxyalkanoate according to claim 1, wherein,

the compound with a plurality of carboxyl groups is at least one selected from citric acid, trisodium citrate, tartaric acid, disodium tartrate, polyacrylic acid and sodium polyacrylate.

3. The method for producing polyhydroxyalkanoate according to claim 1, wherein,

the compound having 1 or more phosphate groups is at least 1 or more selected from sodium metaphosphate and sodium polyphosphate.

4. The process for producing polyhydroxyalkanoate according to any one of claim 1 to 3, wherein,

the dispersant is composed of a block of polyethylene oxide (PEO) and a block of polypropylene oxide (PPO), and is in the form of PEO-PPO-PEO.

5. The process for producing polyhydroxyalkanoate according to any one of claim 1 to 3, wherein,

the concentration of polyhydroxyalkanoate in the aqueous suspension prepared in the step (a) is 30 to 65 wt%.

6. The process for producing polyhydroxyalkanoate according to any one of claim 1 to 3, wherein,

the dispersant is added in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the polyhydroxyalkanoate contained in the aqueous suspension.

7. An aqueous suspension of a polyhydroxyalkanoate comprising a polyhydroxyalkanoate, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups,

the pH of the aqueous suspension is 3.5-7.0.

8. The aqueous suspension of polyhydroxyalkanoate according to claim 7, wherein,

9. The aqueous suspension of polyhydroxyalkanoate according to claim 7, wherein,

10. The aqueous suspension of polyhydroxyalkanoate according to any one of claims 7 to 9, wherein,

11. The aqueous suspension of polyhydroxyalkanoate according to any one of claims 7 to 9, wherein,

the concentration of polyhydroxyalkanoate is 30 to 65 wt%.

12. The aqueous suspension of polyhydroxyalkanoate according to any one of claims 7 to 9, wherein,

the content of the dispersant is 0.1 to 20 parts by weight relative to 100 parts by weight of the polyhydroxyalkanoate contained in the aqueous suspension.

13. The aqueous suspension of polyhydroxyalkanoate according to any one of claims 7 to 9, wherein,

the amount of protein in the aqueous suspension of polyhydroxyalkanoate is 30000ppm or less relative to the amount of PHA.

14. A polyhydroxyalkanoate powder comprising polyhydroxyalkanoate, an alkylene oxide dispersant, and a compound having a plurality of carboxyl groups and/or a compound having 1 or more phosphate groups, wherein the polyhydroxyalkanoate powder has a thermal stability represented by the following formula (2) of 50% or more,

thermal stability (%) = weight average molecular weight of polyhydroxyalkanoate pellet obtained by pressing polyhydroxyalkanoate powder at 160 ℃ and 5Mpa for 20 minutes/weight average molecular weight of polyhydroxyalkanoate powder x 100·· (2).