Polyhydroxyalkanoic acid particles and method for producing the same

Abstract

To provide a production method of PHA particle suppressing the generation of fine powder.SOLUTION: A production method of PHA particle includes a step (a) of preparing a PHA aqueous suspension having a pH of 7 or less and a viscosity of 1 to 5 Pa s under a shear rate of 10 1 / s, a step (b) of forming a PHA droplet having a droplet diameter of 2 to 10 mm and a height of 1 to 5 mm from the PHA aqueous suspension obtained in the step (a), and a step (c) of vaporizing water in the PHA droplet formed in the step (b).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to polyhydroxyalkanoic acid particles and a method for producing the same. [Background technology]

[0002] Polyhydroxyalkanoic acid (hereinafter sometimes referred to as "PHA") is known to be biodegradable.

[0003] PHA produced by microorganisms accumulates within the microbial cells. Therefore, in order to use PHA as a plastic, a process for separating and purifying PHA from the microbial cells is required. In the process of separating and purifying PHA, the cells of PHA-containing microorganisms are crushed or biological components other than PHA are solubilized, and then the PHA is extracted from the resulting aqueous suspension. Separation procedures, such as centrifugation, filtration, and drying, are then performed. For drying, a spray dryer, fluidized bed dryer, drum dryer, or the like can be used; however, a spray dryer is preferred due to its ease of operation.

[0004] To date, the present inventors have developed a technique for preventing aggregation of PHA in an aqueous suspension having a pH of 7 or less, in which polyvinyl alcohol (PVA) is added as a dispersant before adjusting the pH of the aqueous suspension to 7 or less, and then the resulting aqueous suspension having a pH of 7 or less is spray-dried (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 070492 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the techniques described above are all excellent, there is still room for further improvement.

[0007] Therefore, an object of the present invention is to provide a method for producing PHA particles that suppresses the generation of fine powder. [Means for solving the problem]

[0008] As a result of intensive research into solving the above-mentioned problems, the inventors have discovered the novel finding that the generation of fine powder can be suppressed by preparing a PHA aqueous suspension of a specific viscosity in the PHA manufacturing process and forming PHA droplets (granules) having a specific particle size and a specific height from the PHA aqueous suspension, and have thus completed the present invention.

[0009] Therefore, one aspect of the present invention is a method for producing PHA particles (hereinafter referred to as "this production method"), comprising the steps of: (a) preparing a PHA aqueous suspension having a pH of 7 or less and a viscosity of 1 to 5 Pa·s when subjected to a shear rate of 10 1 / s; (b) forming PHA droplets having a diameter of 2 to 10 mm and a height of 1 to 5 mm from the PHA aqueous suspension obtained in step (a); and (c) volatilizing the water from the PHA droplets formed in step (b).

[0010] Another aspect of the present invention is PHA particles having a particle density of 0.3 to 0.5 g / mL, a particle diameter of 2 to 10 mm, and a height of 1 to 5 mm (hereinafter referred to as "the present PHA particles"). [Effects of the Invention]

[0011] According to one aspect of the present invention, a method for producing PHA particles that suppresses the generation of fine powder can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a granulation apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less." In addition, all documents described in this specification are incorporated herein by reference.

[0014] 1. Overview of the Invention As described in the above-mentioned Patent Document 1, granulation of PHA by spray drying is well known. The present inventors, in the course of conducting detailed studies on spray drying of PHA, discovered that fine powder may be generated, which, in turn, causes problems in handling. As a result of extensive research aimed at solving the above problem, the present inventors have discovered for the first time that the generation of fine powder can be suppressed by preparing an aqueous PHA suspension of a specific viscosity in the PHA production process and forming PHA droplets having a specific particle size and a specific height from the aqueous PHA suspension.

[0015] According to the present production method, the generation of fine powder can be suppressed, and therefore PHA particles with excellent handleability can be obtained, making the present production method extremely advantageous for the production of PHA particles.

[0016] Furthermore, the above-described configuration can reduce the amount of plastic waste generated, thereby contributing to the achievement of Sustainable Development Goals (SDGs), such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans and marine resources for sustainable development." In particular, it is preferable in terms of energy efficiency if step (c) of this production method does not include a heating step. The present invention will be described in detail below.

[0017] 2. PHA Manufacturing Method The present production method includes the following steps (a) to (c) to produce PHA particles. Step (a): A step of preparing a PHA aqueous suspension having a pH of 7 or less and a viscosity of 1 to 5 Pa·s when subjected to a shear rate of 10 1 / s. Step (b): A step of forming PHA droplets having a diameter of 2 to 10 mm and a height of 1 to 5 mm from the PHA aqueous suspension obtained in step (a). Step (c): A step of volatilizing the water from the PHA droplets formed in step (b). In this specification, "PHA particles" refers to PHA aggregates formed after volatilizing water from PHA droplets. Also, in this specification, "suppressing the generation of fine powder" refers to the proportion of PHA particles with a particle size of 10 μm or less being 2% or less.

[0018] (Step (a)) In step (a) of this production method, a PHA aqueous suspension is prepared having a pH of 7 or less and a viscosity of 1 to 5 Pa·s when subjected to a shear rate of 10 1 / s. In this aqueous suspension, the PHA is present in a dispersed state in the aqueous medium. In this specification, an aqueous suspension containing at least PHA may be abbreviated as "PHA aqueous suspension."

[0019] <pha> As used herein, "PHA" is a general term for polymers containing hydroxyalkanoic acid as a monomer unit. Hydroxyalkanoic acids constituting PHA are not particularly limited, but examples include 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, and 3-hydroxyoctanoic acid. These polymers may be homopolymers or copolymers containing two or more types of monomer units.

[0020] More specifically, examples of PHAs include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (P3HB3HOD), poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (P3HB3HD), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH). Among these, P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are preferred because they are easy to produce industrially.

[0021] Furthermore, by changing the composition ratio of the repeating units, it is possible to change the melting point and degree of crystallinity, and as a result, physical properties such as Young's modulus and heat resistance can be changed. It is also possible to impart physical properties between those of polypropylene and polyethylene. Furthermore, as described above, from the viewpoint of being an easily produced industrially and physically useful plastic, P3HB3HH, which is a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, is more preferred.

[0022] In one embodiment of the present invention, the composition ratio of the repeating units of P3HB3HH is preferably 80 / 20 to 99 / 1 (mol / mol) of 3-hydroxybutyrate units / 3-hydroxyhexanoate units, and more preferably 83 / 17 to 97 / 3 (mol / mol), from the viewpoint of the balance between flexibility and strength. A 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit composition ratio of 99 / 1 (mol / mol) or less provides sufficient flexibility, while a 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit ratio of 80 / 20 (mol / mol) or more provides sufficient hardness. Increasing the content of 3HB units in the P3HB3HH increases the melting temperature of the resulting PHA (PHA sheet), thereby improving heat resistance. Furthermore, increasing the content of 3HB units in the P3HB3HH increases the crystallization rate of the resulting PHA (PHA sheet), thereby improving processability. From the viewpoint of improving the heat resistance and processability of the PHA (PHA sheet), it is particularly preferable that the composition ratio of 3HB units / 3HH units in the P3HB3HH is 100 / 0, that is, P3HB.

[0023] In step (a), the PHA aqueous suspension used as the starting material is not particularly limited, but can be obtained, for example, by a method including a culture step in which a microorganism capable of producing PHA intracellularly is cultured, and a purification step in which substances other than PHA are decomposed and / or removed after the culture step.

[0024] The present production method may include a step of obtaining an aqueous PHA suspension (e.g., a step including the above-mentioned culturing and purification steps) prior to step (a). The microorganisms used in this step are not particularly limited, as long as they are 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 such microorganisms, can be used. More specifically, examples of such microorganisms include bacteria of the genera Cupriavidus, Alcaligenes, Ralstonia, Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. Among these, microorganisms belonging to the genera Aeromonas, Alcaligenes, Ralstonia, and Capriavidus are preferred. In particular, strains such as Alcaligenes lipolytica (A. lipolytica), Alcaligenes latus (A. latus), Aeromonas caviae (A. caviae), Aeromonas hydrophila (A. hydrophila), and C. necator are more preferred, with C. necator being the most preferred.

[0025] 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 the desired PHA synthase gene and / or its mutant into the microorganism can be used. The PHA synthase gene used to prepare such a transformant is not particularly limited, but a PHA synthase gene derived from Aeromonas caviae is preferred. 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, but the method described in JP-A-05-93049, for example, can be used.

[0026] Since the PHA-containing microorganisms produced by culturing the above-mentioned microorganisms contain a large amount of bacterial cell-derived impurities, a purification step is usually carried out to decompose and / or remove impurities other than PHA. This purification step is not particularly limited, and physical, chemical, biological, and other treatments that a person skilled in the art can consider can be applied. For example, the purification method described in WO 2010 / 067543 can be preferably applied.

[0027] 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, when high-purity PHA is required, such as for medical applications, it is preferable to reduce the impurities as much as possible. An example of an index 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, more preferably 15,000 ppm or less, even more preferably 10,000 ppm or less, and most preferably 7,500 ppm or less, per weight of PHA. The purification method is not particularly limited, and the known methods described above can be used, for example.

[0028] In addition, the solvent (the "solvent" is also referred to as the "aqueous medium") constituting the PHA aqueous suspension in this production method may be water or a mixed solvent of water and an organic solvent. In the mixed solvent, the concentration of the organic solvent compatible with water is not particularly limited as long as it is not more than the solubility of the organic solvent used in water. The organic solvent compatible with water is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butanol, 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, piperidine, and the like. Among them, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile, propionitrile, etc. are preferable in terms of easy removal. Further, methanol, ethanol, 1-propanol, 2-propanol, butanol, acetone, etc. are more preferable because they are easily available. Furthermore, methanol, ethanol, and acetone are particularly preferable. 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.

[0029] It is preferable that the aqueous medium constituting the PHA aqueous suspension in this production method 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.

[0030] <Viscosity of PHA aqueous suspension> In one embodiment of the present invention, the viscosity of the PHA aqueous suspension obtained by step (a) of the production method is such that the viscosity when a shear rate of 10 1 / s is applied is 1 to 5 Pa·s, preferably 1.2 to 4.8 Pa·s, more preferably 1.4 to 4.6 Pa·s, and even more preferably 1.6 to 4.4 Pa·s. When the viscosity of the PHA aqueous suspension is within the above range, in step (b), it becomes possible to form appropriate PHA droplets. The viscosity of the PHA aqueous suspension is measured by the method described in the examples.

[0031] <pH adjustment> In step (a) of the production method, the PHA aqueous suspension used as a starting material usually has a pH exceeding 7 through the above purification step. Therefore, in step (a) of the production method, the pH of the PHA aqueous suspension is adjusted to 7 or less. The adjustment method is not particularly limited, and examples include a method of adding an acid. The acid is not particularly limited and may be either an organic acid or an inorganic acid, regardless of volatility. More specifically, for example, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, etc. can be used as the acid.

[0032] Regarding the upper limit of the pH of the PHA aqueous suspension adjusted in the above adjustment step, from the viewpoint of reducing coloring when PHA is heated and melted and ensuring the molecular weight stability during heating and / or drying, it is 7 or less, preferably 5 or less, and more preferably 4 or less. Regarding the lower limit of the pH, from the viewpoint of the acid resistance of the container, it is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. By setting the pH of the PHA aqueous suspension to 7 or less, PHA with reduced coloring during heat melting and suppressed molecular weight decrease during heating and / or drying can be obtained.

[0033] In one embodiment of the present invention, in step (a), a dispersant may be added to the PHA aqueous suspension. Thereby, when adjusting the pH of the PHA aqueous suspension to 7 or less, aggregation of PHA can be prevented.

[0034] <Viscosity adjustment> The method for adjusting the viscosity of the PHA aqueous suspension to a predetermined value is not particularly limited, and various methods can be used, such as adding a dispersant to achieve the predetermined viscosity in step (a) of the present production method, or adjusting the PHA concentration (solids concentration) of the PHA aqueous suspension used as a starting material.

[0035] Dispersants include, but are not limited to, polyvinyl alcohol, modified polyvinyl alcohol, water-soluble cellulose derivatives (e.g., methylcellulose such as hydroxyethylmethylcellulose and carboxymethylcellulose), alginic acid, water-soluble alginic acid derivatives (e.g., sodium alginate, potassium alginate, ammonium alginate), agar, gelatin, carrageenan, polyacrylic acid derivatives (e.g., sodium polyacrylate, butyl polyacrylate, polyacrylic acid ester), alkylene oxide-based dispersants (e.g., those described in WO 2021 / 085534), and the like.

[0036] The PHA concentration (solids concentration) in the PHA aqueous suspension obtained by step (a) of the present production method is, for example, 20 wt % or more, preferably 22.5 wt % or more, more preferably 25 wt % or more, even more preferably 27.5 wt % or more, particularly preferably 30 wt % or more, particularly preferably 32.5 wt % or more, especially preferably 35 wt % or more, and even more especially preferably 37.5 wt % or more, because this is economically advantageous in terms of drying utility and improves productivity. The upper limit of the PHA concentration is, for example, 70 wt % or less, preferably 65 wt % or less, more preferably 60 wt % 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, and examples include adding an aqueous medium or 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).

[0037] (Step (b)) In step (b) of this production method, PHA droplets having a diameter of 2 to 10 mm and a height of 1 to 5 mm are formed from the PHA aqueous suspension obtained in step (a). By forming PHA droplets having the above-mentioned specific diameter and height in step (b), it is possible to suppress the generation of fine powder.

[0038] The formation of PHA droplets in step (b) is carried out using, for example, a granulator. Step (b) will be described with reference to FIG. 1 as an example of a granulator.

[0039] The PHA aqueous suspension 1 obtained in step (a) is delivered to a perforated container 4 by a PHA aqueous suspension supply pump 2. The perforated container 4 has a plurality of holes in its bottom. The PHA aqueous suspension 1 is continuously added to the perforated container 4 so that the suspension reaches a constant height. At the same time, the perforated container 4 is vibrated by a vibrator 3, causing PHA droplets 6 having a specific diameter and height to form on a conveyor 5. As the PHA droplets 6 are transported on the conveyor 5, they are exposed to hot air 7 (step (c)), which causes the water to evaporate, yielding PHA particles having a specific diameter and height.

[0040] The granulation apparatus in step (b) is not limited to the granulation apparatus in Fig. 1, and is not particularly limited as long as it can form PHA droplets from the PHA aqueous suspension. In addition to the granulation apparatus in Fig. 1, examples of the granulation apparatus in step (b) include the granulation apparatus described in JP-A-2017-535640 (particularly those described in Figs. 1, 4, and 5), pastillation systems (e.g., ROTOFORMER), and the like. From the viewpoint of producing uniform particle size, the granulation apparatus is preferably a pastillation system (e.g., ROTOFORMER).

[0041] The droplet diameter of the PHA droplets is 2 to 10 mm, preferably 2.2 to 9 mm, more preferably 2.5 to 8 mm, and even more preferably 2.8 to 7 mm. When the droplet diameter of the PHA droplets in step (b) is within the above range, the generation of fine powder can be efficiently suppressed. The droplet diameter of the PHA droplets is measured by the method described in the Examples.

[0042] The height of the PHA droplets is 1 to 5 mm, preferably 1.2 to 4.5 mm, more preferably 1.5 to 4 mm, and even more preferably 1.8 to 3.5 mm. When the height of the PHA droplets in step (b) is within the above range, the generation of fine powder can be efficiently suppressed. The height of the PHA droplets is measured by the method described in the Examples.

[0043] The PHA droplet density is preferably 0.7 to 1.5 g / mL, more preferably 0.7 to 1.3 g / mL, and even more preferably 0.7 to 1.1 g / mL. When the PHA droplet density in step (b) is within the above range, a high granulation rate can be achieved. The PHA droplet density is measured by the method described in the Examples.

[0044] (Process (c)) In step (c) of this production method, water is evaporated from the PHA droplets formed in step (b) above. In step (c), some of the fine PHA particles in the PHA droplets are thermally fused together (particularly, the PHA particles on the surfaces of the PHA droplets are thermally fused together), thereby suppressing the generation of fine powder.

[0045] In step (c), the method for volatilizing water from the PHA droplets is not particularly limited, and examples thereof include heating, vacuum drying, and room temperature drying. For example, water from the PHA droplets can be volatilized by heating and drying the PHA droplets while bringing them into contact with hot air in a dryer. The method for bringing the PHA droplets into contact with hot air in the dryer is not particularly limited, and examples include a parallel flow method, a counterflow method, and a method combining these. In step (c), the method for volatilizing water from the PHA droplets is preferably performed by heating, from the viewpoint of appropriate thermal fusion.

[0046] When step (c) is carried out by heating, the heating temperature is preferably 50 to 160°C, more preferably 55 to 155°C, and even more preferably 60 to 150°C. When the heating temperature in step (c) is within the above range, thermal fusion within the PHA droplets is adequately achieved, enhancing the effect of suppressing the generation of fine powder. The heating method is not particularly limited, and examples include hot air heating, microwave heating, and infrared heating. Note that if the 3HH ratio of the PHA used is high, the melting point of the PHA will be low, making it possible to dry at a lower temperature within the above heating temperature range. On the other hand, if the 3HH ratio of the PHA used is low, the melting point of the PHA will be high, making it possible to dry at a higher temperature within the above heating temperature range.

[0047] When step (c) is performed by vacuum drying or room temperature drying, the conditions can be appropriately set by those skilled in the art. For example, when a dryer is used, the volume of hot air can be appropriately set depending on the size of the dryer. Furthermore, room temperature drying is advantageous in terms of energy efficiency.

[0048] In one embodiment of the present invention, the present production method may further include a step of drying the obtained PHA particles (e.g., a step of subjecting them to drying under reduced pressure) after step (c). The present production method may also include a step of transporting the obtained PHA particles after step (c). The PHA particles obtained in step (c) have a uniform particle size, and are therefore easy to handle during transportation.

[0049] [3.PHA particles] The PHA particles have a particle density of 0.3 to 0.5 g / mL, a particle diameter of 2 to 10 mm, and a height of 1 to 5 mm.

[0050] The particle density of the present PHA particles is 0.3 to 0.5 g / mL, preferably 0.31 to 0.49 g / mL, more preferably 0.32 to 0.48 g / mL, and even more preferably 0.33 to 0.47 g / mL. When the particle density of the present PHA particles is within the above range, they are easy to handle during transportation. The particle density of the present PHA particles is measured by the method described in the Examples.

[0051] The particle diameter of the present PHA particles is 2 to 10 mm, preferably 2.2 to 9 mm, more preferably 2.5 to 8 mm, and even more preferably 2.8 to 7 mm. When the particle diameter of the present PHA particles is within the above range, they are easy to handle during transportation. The particle diameter of the PHA particles is measured by the method described in the Examples.

[0052] The height of the PHA particles is 1 to 5 mm, preferably 1.2 to 4.5 mm, more preferably 1.3 to 4 mm, and even more preferably 1.4 to 3.5 mm. When the height of the PHA particles is within the above range, they are easy to handle during transportation. The height of the PHA particles is measured by the method described in the Examples.

[0053] In one embodiment of the present invention, the PHA particles are produced by the production method.

[0054] Furthermore, the present PHA particles may contain various components that are generated or not removed during the production process of the present invention, as long as the effects of the present invention are achieved.

[0055] The PHA particles can be used in a variety of applications, including paper, films, sheets, tubes, plates, rods, containers (such as bottle containers), bags, and parts.

[0056] 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.

[0057] That is, one embodiment of the present invention is as follows. <1> (a) preparing an aqueous PHA suspension having a pH of 7 or less and a viscosity of 1 to 5 Pa·s when subjected to a shear rate of 10 1 / s; (b) forming PHA droplets having a diameter of 2 to 10 mm and a height of 1 to 5 mm from the PHA aqueous suspension obtained in the step (a); and (c) a step of volatilizing water from the PHA droplets formed in the step (b). <2> The step (b) is carried out using a granulation device. <1> The manufacturing method described in <3> The step (c) is a heating step in which water in the PHA droplets is volatilized by heating. <1> or <2> The manufacturing method described in <4> The heating temperature in the heating step is 60 to 160°C. <3> The manufacturing method described in <5> The PHA droplet density in the step (b) is 0.7 to 1.5 g / mL. <1> ~ <4> 1. The manufacturing method according to any one of the preceding claims. <6> (PHA particles having a particle density of 0.3 to 0.5 g / mL, a particle diameter of 2 to 10 mm, and a height of 1 to 5 mm. [Example]

[0058] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0059] [Measurement and evaluation methods] Measurements and evaluations in the examples and comparative examples were carried out by the following methods.

[0060] (Viscosity of PHA aqueous suspension) The viscosity of the PHA aqueous suspension was measured by the following method. Specifically, the viscosity was measured using a coaxial double cylinder with an Anton Paar MCR302. The PHA aqueous suspension was poured into a 20 mL cylinder, and the liquid temperature was adjusted to 25°C. After reaching the target shear rate, the viscosity was measured when the change in torque with time became less than 1%.

[0061] (Droplet diameter and height of PHA droplets) The droplet diameter and height of the PHA droplets were measured using a ruler.

[0062] (PHA droplet density) The PHA droplet density was calculated from the weight of the aqueous PHA suspension measured using a measuring cylinder and was defined by the following formula (1): PHA droplet density (g / ml) = PHA aqueous suspension weight / PHA aqueous suspension volume (1) (PHA particle density) The PHA particle density was calculated using the PHA particle volume measured with a vernier caliper and is defined by the following formula (2). PHA particle density (g / ml) = PHA particle weight (g) / PHA particle volume (ml) (2) Example 1 (Preparation of bacterial culture solution) The fungal culture medium containing PHA was obtained by culturing the fungal cells according to the method described in International Publication No. 2010 / 067543. Ralstonia eutropha is currently classified as Capriavidus necator.

[0063] (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.

[0064] (High-pressure crushing treatment) To the sterilized bacterial culture solution obtained above, 0.2% by weight of sodium dodecyl sulfate was added. Furthermore, an aqueous solution of sodium hydroxide was added to adjust the pH to 11.0, and the mixture was then kept at 50°C for 1 hour. Thereafter, the mixture was crushed at 450 to 550 kgf / cm using a high-pressure homogenizer (Nirosoavi High-Pressure Homogenizer Model PA2K). 2 High-pressure fracturing was carried out at a pressure of .

[0065] (Refining process) An equal volume of distilled water was added to the disruption solution obtained after high-pressure disruption. After centrifugation, the supernatant was removed and the solution was concentrated two-fold. To this concentrated aqueous suspension of PHA, an aqueous sodium hydroxide solution (pH 11) in an amount equal to the removed supernatant was added, followed by centrifugation and the supernatant was removed. 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 mixture was stirred for 2 hours at pH 10 and 50°C. The supernatant was then removed by centrifugation and the solution was concentrated four-fold. Further water was added to adjust the PHA concentration to 40.0 wt%.

[0066] Sulfuric acid was added to the PHA aqueous suspension obtained above to adjust the pH to 3.5. The viscosity of the PHA aqueous suspension at 25°C when subjected to a shear rate of 10 1 / s was 2379 mPa·s (approximately 2.4 Pa·s). The obtained PHA aqueous suspension was fed into a ROTOFORMER (IPCO), and PHA droplets with a diameter of 3.3 mm and a height of 2 mm were obtained. The PHA droplet density was 0.8 g / mL. The PHA droplets were dried by exposure to hot air at 150°C to obtain PHA particles. The particle diameter and height of the PHA particles were 3.1 mm and 1.5 mm, respectively. Furthermore, no particle crushing occurred, and the generation of fine powder was suppressed. The PHA particle density was 0.39 g / mL.

[0067] Comparative Example 1 An aqueous PHA suspension was obtained under the same conditions as in Example 1, except that the PHA concentration was adjusted to 30.0 wt% by purification. The viscosity of the aqueous PHA suspension was 720 mPa s (approximately 0.7 Pa s) when a shear rate of 10 1 / s was applied. When the obtained aqueous PHA suspension was fed into a ROTOFORMER, the discharged droplets spread and were unable to maintain their particle shape.

[0068] Comparative Example 2 An aqueous PHA suspension was obtained under the same conditions as in Example 1, except that the PHA concentration was adjusted to 50.0 wt % by purification. The viscosity of the aqueous PHA suspension was 9097 mPa·s (approximately 9.1 Pa·s) when a shear rate of 10 1 / s was applied. When the obtained aqueous PHA suspension was fed into a ROTOFORMER, the discharged droplets did not assume a spherical shape. The PHA droplet density was 1.0 g / ml. The droplets were dried by exposure to hot air at 150°C to obtain PHA particles, but the particles were crushed during the drying process, resulting in the generation of fine powder of 10 μm or less.

[0069] Example 2 An aqueous PHA suspension was obtained by purification under the same conditions as in Example 1, except that the PHA concentration was adjusted to 50.0 wt% during the purification process. To the resulting aqueous PHA suspension, 0.375 phr (0.375 parts 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 the pH was adjusted to 2.8. The viscosity of the aqueous PHA suspension at 25°C when subjected to a shear rate of 10 1 / s was 2095 mPa·s. The resulting aqueous PHA suspension was subjected to droplet formation and hot air drying in the granulator shown in Figure 1 to obtain PHA particles. An OLI vibrator (Type: OT36, air supply pressure 0.4 MPaG) was used as the vibrator 3. The resulting PHA droplets had a diameter of 6 mm and a height of 3 mm. The PHA droplet density was 1.0 g / mL. The PHA droplets were irradiated with hot air 7 at 130°C to obtain PHA particles. The particle diameter and height of the PHA particles were 5 mm and 2 mm, respectively. Furthermore, no particle crushing occurred, and the generation of fine powder was also suppressed. The PHA particle density was 0.45 g / mL.

[0070] <Result> From Examples 1 and 2 and Comparative Examples 1 and 2, it was found that by preparing a PHA aqueous suspension with a specific viscosity in the PHA production process, PHA droplets with a specific particle size and a specific height could be formed, and as a result, the generation of fine powder could be suppressed. [Industrial Applicability]

[0071] According to the present production method, PHA particles that are easy to handle can be produced, and therefore, the method can be suitably used in various fields where PHA is used. [Explanation of symbols]

[0072] 1. PHA aqueous suspension 2 PHA aqueous suspension supply pump 3. Vibrator 4 Perforated container 5 Conveyor 6 PHA droplets 7 Hot air< / pha>

Claims

1. (a) preparing an aqueous suspension of polyhydroxyalkanoic acid having a pH of 7 or less and a viscosity of 1 to 5 Pa s when subjected to a shear rate of 10 1 / s; (b) forming polyhydroxyalkanoic acid droplets having a diameter of 2 to 10 mm and a height of 1 to 5 mm from the polyhydroxyalkanoic acid aqueous suspension obtained in the step (a); and (c) a step of volatilizing water from the polyhydroxyalkanoic acid droplets formed in the step (b), A method for producing polyhydroxyalkanoic acid particles, wherein the step (c) is a heating step of volatilizing water from the polyhydroxyalkanoic acid droplets by heating.

2. The method according to claim 1 , wherein step (b) is carried out using a granulator.

3. The method according to claim 1 or 2, wherein the heating temperature in the heating step is 60 to 160°C.

4. The method according to any one of claims 1 to 3, wherein the density of the polyhydroxyalkanoic acid droplets in step (b) is 0.7 to 1.5 g / mL.

5. Polyhydroxyalkanoic acid particles having a particle density of 0.3 to 0.5 g / mL, a particle diameter of 2 to 10 mm, and a height of 1 to 5 mm.

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