Method for producing dried polyhydroxyalkanoic acid granules a nd use thereof

Abstract

The present invention addresses the problem of providing a method for producing dried PHA granules whereby PHA having excellent meltability and excellent energy efficiency can be provided. The problem is solved by a method for producing PHA, the method comprising: a step (a) for dehydrating an aqueous suspension of PHA to prepare a moist PHA powder including 5-37 wt% of water; a step (b) for subjecting the moist PHA powder obtained in step (a) to compression granulation and / or extrusion granulation to obtain moist PHA granules including 5-37 wt% of water; and a step (c) for drying the moist PHA granules obtained in the step (b) to obtain dried PHA granules.

Description

Method for producing dry polyhydroxyalkanoic acid granules and use thereof

[0001] The present invention relates to a method for producing dry polyhydroxyalkanoic acid granules and the use thereof.

[0002] Polyhydroxyalkanoic acid (hereinafter, sometimes referred to as "PHA") is known to be biodegradable, and in recent years, efforts have been made to utilize it from the standpoint of environmental consideration.

[0003] One of the advantages of PHA is that it can be produced by microorganisms using renewable plant materials. To use PHA produced by microorganisms, it is first necessary to destroy the microbial cells, extract the PHA from the cells, and then process the PHA into a form suitable for use, such as granules or pellets, by removing moisture and the like.

[0004] As a technology relating to the production and processing of PHA, for example, Patent Document 1 discloses a technology for producing PHA granules by extruding an aqueous suspension of PHA (aqueous PHA suspension) using a twin-screw extruder while heating it at a specific temperature. Patent Document 2 discloses a technology for processing dry PHA powder into granules. Furthermore, Patent Document 3 discloses a technology for obtaining PHA agglomerates by heating and then filtering an aqueous PHA suspension to which specific additives have been added.

[0005] International Publication No. WO2021 / 176941 Japanese Patent Publication No. 7387950 International Publication No. WO2023 / 120310

[0006] Although each of the above technologies is excellent, the technology described in Patent Document 1 requires heating the PHA aqueous suspension at a high temperature to remove moisture, which requires a lot of energy for heating, and therefore there is room for improvement from the viewpoint of energy efficiency.

[0007] The technique described in Patent Document 2 has difficulty in obtaining a uniform wet PHA powder and granulated material because moisture is added to a dry PHA powder. Non-uniform PHA granulated material is likely to have an excessive increase in melt viscosity and kneading temperature during melt-kneading. From this perspective, there is room for improvement in the technique described in Patent Document 2.

[0008] The technology described in Patent Document 3 sizes the PHA agglomerates by crushing them, and since it is difficult to achieve uniform sizing, a lot of energy is required to dry the PHA agglomerates after crushing, leaving room for improvement in terms of energy efficiency.

[0009] In view of the above circumstances, one aspect of the present invention aims to provide a PHA that is excellent in melting property and a method for producing a PHA that is excellent in energy efficiency.

[0010] As a result of intensive research into solving the above-mentioned problems, the inventors have discovered a new finding that a method of preparing a wet PHA powder containing a specific amount of water from an aqueous PHA suspension, compressing and / or extruding the wet PHA powder to obtain wet PHA granules containing a specific amount of water, and further drying the obtained wet granules does not require heating during granulation of the wet PHA granules (in other words, is energy efficient), and furthermore, can provide uniform wet PHA granules, thereby providing dry PHA granules with excellent melting properties, which has led to the completion of the present invention.

[0011] That is, a method for producing polyhydroxyalkanoic acid dry granules according to one embodiment of the present invention comprises the steps of: (a) dehydrating an aqueous suspension of PHA to prepare a polyhydroxyalkanoic acid wet powder containing 5 to 37% by weight of water; (b) compression-granulating and / or extrusion-granulating the polyhydroxyalkanoic acid wet powder obtained in step (a) to obtain polyhydroxyalkanoic acid wet granules containing 5 to 37% by weight of water; and (c) drying the polyhydroxyalkanoic acid wet granules obtained in step (b) to obtain polyhydroxyalkanoic acid dry granules.

[0012] According to one aspect of the present invention, it is possible to provide dry PHA granules that have excellent melting properties, and also to provide a method for producing dry PHA granules that is excellent in energy efficiency.

[0013] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0014] 1. Method for Producing PHA A method for producing a PHA according to one embodiment of the present invention (hereinafter, the "method for producing a PHA according to one embodiment of the present invention" may be referred to as "this production method") includes the steps of: dehydrating an aqueous PHA suspension to prepare a wet PHA powder containing 5 to 37% by weight of water; compression-granulating and / or extrusion-granulating the wet PHA powder obtained in step (a) to obtain wet PHA granules containing 5 to 37% by weight of water; and drying the wet PHA granules obtained in step (b) to obtain dry PHA granules.

[0015] Since this manufacturing method includes the above steps (a) to (c), it does not require heating during granulation of wet PHA granules, and therefore it is possible to provide dry PHA granules that are excellent in energy efficiency and meltability.

[0016] <PHA> First, the PHA constituting the PHA dry granules provided by this production method will be specifically described. "PHA" is a general term for polymers containing hydroxyalkanoate as a monomer unit (monomer repeating unit), and is generally biodegradable. In particular, in this specification, "PHA" refers to a (co)polymer containing 50 mol% or more of hydroxyalkanoate repeating units out of all monomer repeating units (100 mol%), and a resin composed of such a (co)polymer. The PHA is preferably a (co)polymer containing 60 mol% or more of hydroxyalkanoate repeating units out of all monomer repeating units (100 mol%), and more preferably a (co)polymer containing 70 mol% or more. In this specification, the term "(co)polymer" is used to refer to both a homopolymer composed of only one type of monomer and a copolymer composed of two or more types of monomers.

[0017] Examples of PHAs provided by this production method include poly(3-hydroxyalkanoate) (hereinafter, sometimes referred to as "P3HA"), poly(4-hydroxyalkanoate), etc. Among these, P3HA is preferred because it is suitable for use in molded articles.

[0018] P3HA has the formula: [-CHR-CH ２ -CO-O-] (wherein R is C ｎ H ２ｎ＋１ where n is an integer of 1 to 15.) as an essential repeating unit. In this specification, "P3HA" refers to a (co)polymer containing 50 mol % or more of the 3-hydroxyalkanoate repeating units out of all monomer repeating units (100 mol %).

[0019] Specific examples of P3HA include homopolymers of one or more monomers selected from the group consisting of 3-hydroxybutanoic acid (hereinafter sometimes referred to as "3HB"), 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, and 3-hydroxyoctadecanoic acid, or copolymers of two or more of these monomers. Furthermore, P3HA may be a copolymer of the above-mentioned P3HA-based repeating unit and a repeating unit other than P3HA. For example, P3HA may be a copolymer of the above-mentioned P3HA-based repeating unit and one or more monomers selected from the group consisting of 4-hydroxybutanoic acid, 4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoic acid, 4-hydroxyoctanoic acid, 4-hydroxynonanoic acid, 4-hydroxydecanoic acid, 4-hydroxyundecanoic acid, 4-hydroxydodecanoic acid, 4-hydroxytridecanoic acid, 4-hydroxytetradecanoic acid, 4-hydroxyhexadecanoic acid, and 4-hydroxyoctadecanoic acid.

[0020] More specifically, examples of P3HA include poly(3-hydroxybutyrate) (hereinafter sometimes referred to as "P3HB"), which is a homopolymer of 3HB, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as "P3HB3HH"), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter sometimes referred to as "P3HB4HB"), poly(3-hydroxybutyrate-co-3-hydroxypropionate), etc. Among these, P3HB, P3HB3HH, and P3HB4HB are preferred, with P3HB3HH and P3HB4HB being more preferred, due to the ease of industrial production using microorganisms.

[0021] In this specification, "poly(X-co-Y)" refers to a copolymer containing an X repeating unit and a Y repeating unit, and is intended to mean a copolymer obtained by copolymerizing a monomer from which the X repeating unit is derived and a monomer from which the Y repeating unit is derived. As described above, the name of P3HA is determined by the repeating units contained in the P3HA. However, a very small amount (about 1 mol% or less) of a monomer contained in P3HA may not be reflected in the name of the P3HA, provided that it does not significantly affect the physical properties of the P3HA. In other words, P3HA may contain, in addition to the repeating units corresponding to its name, very small amounts of other repeating units.

[0022] When P3HA contains 3HB repeating units, from the viewpoint of the balance between flexibility and strength, the composition ratio of 3HB repeating units to repeating units other than 3HB repeating units (other repeating units) in all monomer repeating units (100 mol%) in the P3HA (3HB repeating units / other repeating units) is preferably 99 / 1 (mol% / mol%) to 60 / 40 (mol% / mol%), more preferably 97 / 3 (mol% / mol%) to 70 / 30 (mol% / mol%), and even more preferably 95 / 5 (mol% / mol%) to 80 / 20 (mol% / mol%). When the composition ratio of 3HB repeating units in P3HA is 60 mol% or more, it has the advantage of being able to provide resin products with superior rigidity. On the other hand, when the composition ratio of 3HB repeating units in P3HA is 99 mol% or less, it has the advantage of being able to provide resin products with superior flexibility. The monomer composition ratio of P3HA can be measured by gas chromatography or the like (see, for example, WO 2014 / 020838).

[0023] P3HA can be produced by microorganisms. Examples of microorganisms capable of producing P3HA include P3HB-producing bacteria, such as Bacillus megaterium, which was first discovered in 1925, as well as other naturally occurring microorganisms such as Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. In these microorganisms, P3HB accumulates intracellularly.

[0024] Furthermore, known bacteria that produce P3HA, a copolymer of 3HB and other hydroxyalkanoic acids, include Aeromonas caviae, which produces P3HB3HH, and Alcaligenes eutrophus, which produces poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In particular, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bacteriol., 179, pp. 4821-4830 (1997)), into which genes encoding P3HA synthases have been introduced, is preferred for increasing the productivity of P3HB3HH. In addition to the above, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced can also be used depending on the desired physical properties of P3HA.

[0025] Methods for culturing these microorganisms capable of producing P3HA are known, and for example, the conditions described in the examples of WO 2019 / 142845 can be adopted.

[0026] <Step (a)> This production method includes step (a), which is a step of dehydrating an aqueous PHA suspension to prepare a wet PHA powder containing 5 to 37% by weight of water. In this specification, the term "aqueous PHA suspension" refers to a solution in which PHA is suspended (dispersed) in water (aqueous medium) and has fluid properties. The term "wet PHA powder" refers to a composition containing powdered PHA and water, in which the weight percentage of PHA (solids) is 60% or more but less than 100%, the weight percentage of water is 0.5% or more but less than 40%, and the composition does not have fluid properties in a static state. The water in the wet PHA powder may contain, in addition to water, other solvents (e.g., organic solvents compatible with water), components derived from PHA-producing microorganisms (e.g., cell walls, proteins, etc.), and / or other compounds generated during purification. That is, the PHA wet powder prepared in step (a) may contain, in addition to PHA and water, each of the components present in the water.

[0027] As the PHA aqueous suspension that can be used in step (a), a PHA aqueous suspension derived from the culture solution of a microorganism capable of producing PHA can be suitably used.Such a PHA aqueous suspension derived from the culture solution of a microorganism capable of producing PHA can be prepared, for example, by the following method: (1) culturing a microorganism capable of producing PHA; (2) inactivating the culture solution of the microorganism by heating to obtain an inactivated culture solution; (3) treating the inactivated culture solution with alkali; (4) neutralizing the inactivated culture solution that has been alkali-treated, and adding a lytic enzyme (cell wall-degrading enzyme) to lyse the microorganism cells, and dispersing the intracellular substances including PHA in the culture solution; (5) adding a protease to the culture solution to decompose and / or remove substances derived from the microorganism cells other than PHA (particularly proteins); (6) further adjusting the pH of the culture solution and adding a surfactant to decompose and / or remove substances derived from the microorganism cells other than PHA (particularly cell membranes). As specific conditions for each of these operations, for example, the conditions described in the examples of WO 2023 / 120310 can be adopted.

[0028] The present production method may include, prior to step (a), a step of culturing a microorganism capable of producing PHA, including each of the above-mentioned operations, and preparing a PHA aqueous suspension from the culture solution (PHA aqueous suspension preparation step).

[0029] In the step (a), the method for dehydrating the aqueous PHA suspension is not particularly limited, and examples thereof include a method of filtering the aqueous PHA suspension, a method of centrifuging the aqueous PHA suspension, and the like.

[0030] The method for filtering the aqueous PHA suspension is not particularly limited as long as it can prepare a wet PHA powder with the desired water content, but dead-end filtration is preferred because it allows filtration to be performed with simple equipment and operations, and can be performed in a more space-saving and low-cost manner. That is, in step (a), it is preferable to prepare a wet PHA powder by dead-end filtering the aqueous PHA suspension. In other words, it is preferable that step (a) includes a dead-end filtration step in which the aqueous PHA suspension is dead-end filtered. In this specification, "dead-end filtering" means "performing filtration by the dead-end filtration method."

[0031] Specific modes of dead-end filtration are not particularly limited, and examples include suction filtration, pressure filtration, centrifugal filtration, gravity filtration, etc. Among these, pressure filtration is preferred, and filter press filtration is more preferred, because it allows for easy discharge of the PHA wet powder after filtration. That is, step (a) preferably includes a filter press filtration step in which the PHA aqueous suspension is filtered through a filter press. Note that filter press filtration is an operation in which the PHA aqueous suspension is squeezed and dehydrated, and a residue (in this production method, the PHA wet powder) is obtained.

[0032] The filter material used in the dead-end filtration step is not particularly limited, and can be selected from various materials, such as paper, filter cloth (woven or nonwoven), screen, sintered plate, bisque, polymer membrane, punched metal, wedge wire, etc. From the viewpoints of cost and ease of cleaning, filter cloth is preferably used.

[0033] When filter press filtration is carried out in the dead-end filtration step, the filtration operation can be carried out using a known filter press filtration device.

[0034] Methods for centrifuging the PHA aqueous suspension include basket centrifugation, decanter centrifuges, disk centrifuges, liquid cyclones, etc. Among these, basket centrifugation is preferred because it has superior dewatering efficiency.

[0035] Step (a) may further include a step of adjusting the moisture content of the PHA wet powder after filtration or centrifugation. Examples of methods for adjusting the moisture content of the PHA wet powder include a method of further pushing out moisture from the PHA wet powder with air blown in, and a method of drying the PHA wet powder with a dryer.

[0036] In this production method, the PHA moist powder is not heated (dried) at a high temperature during the granulation process (step (b)) of the PHA moist powder (in other words, the moisture content of the PHA moist powder is not adjusted), thereby saving the energy consumed in heating the PHA moist powder in conventional methods, and as a result, the energy required for granulating the PHA moist powder and, ultimately, for the entire production process of the PHA final product can be reduced. Furthermore, in this production method, the moisture content of the PHA moist powder does not change in step (b), so the moisture content of the PHA moist powder prepared in step (a) becomes the moisture content of the PHA moist granules prepared in the subsequent step (b). Therefore, in step (a), it is necessary to control the moisture content of the PHA moist powder obtained in the subsequent step (b) to a range that will allow the PHA moist granules to be prepared to provide PHA moist granules with excellent melting properties.

[0037] From the above viewpoints, the moisture content of the PHA wet powder prepared in step (a) is 5 to 37 wt %, preferably 10 to 25 wt %, and more preferably 15 to 20 wt %, based on 100 wt % of the total amount of the PHA wet powder. Note that the moisture content of the PHA wet powder in this specification refers to the weight percentage of water in 100 wt % of the total amount of the PHA wet powder on a wet basis (W.B.), and is a value measured by the method described in the Examples.

[0038] The median diameter of the PHA wet powder obtained in step (a) is not particularly limited, but is preferably 2.0 mm or less, more preferably 1.5 mm or less, so that it can be easily fed to a granulator in step (b). The lower limit of the median diameter of the PHA wet powder obtained in step (c) is also not particularly limited, but from the viewpoint of ease of handling, it is preferably 0.05 mm or more, more preferably 0.1 mm or more. In this specification, the median diameter of the PHA wet powder is a value measured by the method described in the Examples.

[0039] The PHA wet powder prepared in step (a) may contain various additives, such as a crosslinking agent, a crystal nucleating agent, a cell adjusting agent, a lubricant, a plasticizer, an antistatic agent, a flame retardant, a conductive agent, a heat insulating agent, an antioxidant, an ultraviolet absorber, a colorant, an inorganic filler, an organic filler, a hydrolysis inhibitor, a dispersant, and a nonionic water-soluble polymer.

[0040] <Step (b)> This production method includes step (b), in which the PHA wet powder obtained in step (a) is compression-granulated and / or extrusion-granulated to obtain PHA wet granules containing 5 to 37% by weight of water. In this specification, PHA granules refer to a composition having a secondary particle-like structure composed of a large number of PHA primary particles (in this production method, the PHA particles constituting the above-mentioned PHA wet powder). In this specification, PHA granules having a moisture content of 5% or more but less than 40% are referred to as PHA wet granules, and those having a moisture content of less than 5% are referred to as PHA dry granules. PHA granules having a moisture content of more than 40% are not considered to be granules because they have the properties of a fluid (i.e., an aqueous suspension).

[0041] In step (b), the wet PHA powder is granulated by compression granulation and / or extrusion granulation. By compression granulation and / or extrusion granulation of a wet PHA powder containing 5 to 37% by weight of water, granulation can be performed with more energy savings (i.e., energy efficiency) and a uniform wet PHA powder can be obtained. As a result, it is possible to provide wet PHA granules that can be dried uniformly in a short time and in which the generation of fine powder during drying is suppressed. In addition, the wet PHA granules obtained by such granulation can provide dry PHA granules with a high bulk density. In step (b), either compression granulation or extrusion granulation or both may be performed. However, it is particularly preferable that step (b) includes a step of compression granulating the wet PHA powder, as this allows granulation to be performed in a more space-saving manner.

[0042] When step (b) includes a step of compressing and granulating the PHA wet powder, the compression granulation operation can be carried out using a known compression granulation device. Examples of such compression granulation devices include plate-type, tablet-type, briquette-type, compacting-type, screw extrusion-type, roll extrusion-type, blade extrusion-type, moving die-type, ram extrusion-type, and disk pelleter-type. Among these, a briquette-type granulator is preferably used because it has a high compression force and can further reduce fine powder. Examples of briquette-type granulators include briquetting-type and compacting-type, and either may be used.

[0043] When step (b) includes a step of compressing and granulating the PHA wet powder, such a step may include two steps: a step of compressing the PHA wet powder, and a step of crushing (granulating) the compressed PHA wet powder.

[0044] When step (b) includes a step of extrusion granulating the PHA wet powder, the extrusion granulation operation can be carried out using a known extrusion granulation apparatus, such as a twin-screw extruder, a wet extrusion granulator, or a rotary multi-hole die granulator.

[0045] In step (b), the temperature at which the wet PHA powder is granulated (granulation temperature) is preferably 10 to 55°C, more preferably 15 to 40°C, and even more preferably 20 to 30°C (room temperature). Granulating the wet PHA powder at a temperature of 10 to 55°C means that the granulation temperature is kept relatively low compared to conventional granulation methods in which the wet PHA powder is not heated (granulation is carried out at room temperature) or is heated at temperatures above 60°C. By controlling the granulation temperature in step (b) within the above range, evaporation of water during granulation can be suppressed, making it possible to obtain wet PHA granules with a desired moisture content, and reducing the energy required for granulation, making it possible to obtain wet PHA granules, and ultimately dry PHA granules, more energy efficiently.

[0046] In step (b), the temperature of the resulting PHA wet granules immediately after granulation (post-granulation temperature) is preferably 10 to 55°C, more preferably 10 to 50°C, even more preferably 15 to 40°C, and even more preferably 20 to 35°C (room temperature). A temperature of 10 to 55°C immediately after granulation of the resulting PHA wet granules means that the PHA wet powder is hardly or not heated at all during step (b). Therefore, from the viewpoint of providing PHA wet granules with greater energy efficiency, the temperature of the PHA wet granules obtained in step (b) immediately after granulation is preferably within the above range.

[0047] The present inventors have conducted extensive research into PHA and PHA resin particles obtained by melt-kneading PHA, and have found that drying wet PHA granules containing 5 to 37% by weight of water can suppress the generation of fine powder during drying, and that the dried granules obtained after drying melt quickly when subjected to melt-kneading, and are able to suppress excessive increases in viscosity and kneading temperature during kneading, making them PHA dry granules with excellent melting properties, compared to conventional PHA consisting of PHA granules obtained by extrusion granulation of a PHA aqueous suspension heated at a high temperature.

[0048] From the viewpoint of suppressing the generation of fine powder during drying and providing a PHA with excellent melting property, the moisture content of the wet PHA granules prepared in step (b) is 5 to 37 wt %, preferably 10 to 25 wt %, and more preferably 15 to 20 wt %, based on 100 wt % of the total amount of the wet PHA granules. Note that the moisture content of the wet PHA granules in this specification refers to the weight percentage of water in 100 wt % of the total amount of the wet PHA granules, based on the wet base, and is a value measured by the method described in the Examples.

[0049] The median diameter of the PHA wet granules obtained in step (b) is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.2 mm or more, since it is easy to obtain PHA dry granules with excellent handleability. The upper limit of the median diameter of the PHA wet granules obtained in step (b) is also not particularly limited, but is preferably 5.0 mm or less, more preferably 4.0 mm or less, and even more preferably 3.0 mm or less, from the viewpoint of ease of drying. In this specification, the median diameter of the PHA wet granules is a value measured by the method described in the Examples.

[0050] (Step (c)) The present production method includes step (c), which is a step of drying the wet PHA granules obtained in step (b) to obtain dry PHA granules.

[0051] In step (c), the method for drying the PHA wet granules is not particularly limited, and examples include drying methods using a tray dryer, band dryer, conveyor dryer, spray dryer, fluidized bed dryer, flash dryer, vibration dryer, plate dryer, or rotary dryer.

[0052] In step (c), the wet PHA granules may be dried until the moisture content of the resulting dry PHA granules is 5% by weight or less. However, from the viewpoint of preventing a decrease in the molecular weight of the PHA, it is preferable to dry the wet PHA granules until the moisture content of the resulting dry PHA granules is 0.5% by weight or less. From the above viewpoint, the moisture content of the dry PHA granules obtained in step (c) is preferably 0.5% by weight or less, more preferably 0.4% by weight or less, and even more preferably 0.3% by weight or less. Furthermore, the lower limit of the moisture content of the dry PHA granules is not particularly limited and may be 0% by weight. In this specification, the moisture content of the dry PHA granules refers to the weight percentage of water in a total amount of 100% by weight of the wet base of the dry PHA granules, and is a value measured by the method described in the Examples.

[0053] In step (c), the temperature at which the wet PHA granules are dried is not particularly limited, but from the viewpoint of efficiently providing dry PHA granules with a sufficiently low moisture content (0.5% by weight or less), it is preferably 60°C or higher, and more preferably 80°C or higher.

[0054] The median diameter of the PHA dry granules obtained in step (c) is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more, since this results in PHA dry granules with excellent handleability. The upper limit of the median diameter of the PHA dry granules obtained in step (c) is not particularly limited, but is, for example, 5.0 mm or less. In this specification, the median diameter of the PHA dry granules is a value measured by the method described in the Examples.

[0055] The bulk density of the dried PHA granules obtained in step (c) is not particularly limited, but is preferably 0.32 g / cm ３ It is preferable that the density is 0.35 g / cm or more. ３ It is more preferable that the bulk density of the PHA dry granules is 0.32 g / cm or more. ３ From the above viewpoint, the higher the bulk density of the PHA dry granules obtained in step (c), the better. The upper limit of the bulk density is not particularly limited, but it may be, for example, 1.0 g / cm. ３ In this production method, a high-density PHA wet powder obtained by compression granulation and / or extrusion granulation of the PHA wet powder is dried to obtain PHA dry granules. Therefore, it is possible to provide PHA dry granules having a high bulk density that satisfies the above range. In this specification, the bulk density of the PHA dry granules is a value measured by the method described in the Examples.

[0056] [2. Method for producing PHA-based resin particles] In one embodiment of the present invention, there is provided a method for producing PHA-based resin particles (hereinafter, sometimes referred to as "the present resin particle production method"), which includes a step of melt-kneading the dried PHA granules produced by the present production method (melt-kneading step).

[0057] PHA produced by conventional methods has problems with meltability and is difficult to melt during melt-kneading, resulting in an excessive increase in the torque (viscosity) of the kneaded product, and therefore an excessive increase in the temperature of the kneaded product. On the other hand, the PHA dry granules produced by the present production method have excellent meltability, so they melt easily during melt-kneading, and can suppress excessive increases in the torque and temperature of the kneaded product. In the melt-kneading operation, the energy required to knead the kneaded product increases in proportion to the increase in the torque of the kneaded product. Therefore, the present production method using PHA dry granules produced by the present production method, which can be kneaded with low torque, can reduce the energy required for the melt-kneading operation and provide PHA-based resin particles with greater energy efficiency.

[0058] The torque of the kneaded material in the melt-kneading step can be evaluated by the melt torque of the kneaded material.Specifically, from the viewpoint of reducing the energy required for the melt-kneading operation and providing PHA-based resin particles with energy efficiency, the melt torque of the melt-kneaded material in the present resin particle manufacturing method is preferably 100 N m or less, more preferably 80 N m or less, and even more preferably 65 N m or less.The lower the melt torque of the melt-kneaded material, the lower the energy required for the melt-kneading operation.The lower the melt torque of the melt-kneaded material, the more preferable it is, and its lower limit is not particularly limited, but it can be, for example, 20 N m or more.

[0059] In this specification, the temperature of the kneaded product in the melt-kneading step refers to the stable torque temperature of the kneaded product. From the viewpoint of providing PHA-based resin particles with energy efficiency, the stable torque temperature of the melt-kneaded product in the present resin particle production method is preferably less than 125°C, more preferably 123°C or less, and even more preferably 121°C or less. The lower the stable torque temperature of the melt-kneaded product, the more energy-efficient the melt-kneading operation can be carried out. The lower the stable torque temperature of the melt-kneaded product, the more preferable it is, and the lower limit is not particularly limited, but it can be, for example, 90°C or more. In this specification, the stable torque temperature of the melt-kneaded product in the melt-kneading operation is a value measured by the method described in the examples.

[0060] The melt-kneading operation in the present method for producing resin particles can be carried out using a known melt-kneading device, such as an extruder, a kneader, a Banbury mixer, or a roll.

[0061] In the melt-kneading step of the present resin particle production method, the PHA dry granules produced by the present production method may be melt-kneaded in a state where they are mixed with various additives, such as crosslinkers, crystal nucleating agents, cell regulators, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, antioxidants, UV absorbers, colorants, inorganic fillers, organic fillers, hydrolysis inhibitors, and nonionic water-soluble polymers.

[0062] In this method for producing resin particles, the PHA dry granules melt-kneaded in the melt-kneading step are formed into PHA-based resin particles by a known method, for example, by being discharged from a die nozzle provided in a melt-kneading device and cut by a cutting device simultaneously with or after discharge.

[0063] The particle shape of the PHA resin particles obtained by the present method for producing resin particles is not particularly limited, and may be cylindrical, elliptical cylindrical, spherical, cubic, rectangular parallelepiped, or the like.

[0064] The PHA-based resin particles obtained by the method for producing resin particles of the present invention can be used as a molded article by molding it by a known molding method, for example, injection molding, extrusion molding, blow molding, or compression molding.The PHA-based resin particles obtained by the method for producing resin particles of the present invention can also be used as a foamed molded article by foaming it by a known method and then molding it.The molded articles and foamed molded articles made from the PHA-based resin particles obtained by the method for producing resin particles of the present invention can be used for various purposes, such as paper, film, sheet, tube, plate, rod, container (e.g., bottle container), bag, parts, etc.

[0065] [Others] One aspect of the present invention may include the following configuration.

[0066] [1] A method for producing polyhydroxyalkanoic acid dry granules, comprising: step (a) of dehydrating an aqueous suspension of PHA to prepare a polyhydroxyalkanoic acid wet powder containing 5 to 37% by weight of water; step (b) of compressing and / or extruding the polyhydroxyalkanoic acid wet powder obtained in step (a) to obtain polyhydroxyalkanoic acid wet granules containing 5 to 37% by weight of water; and step (c) of drying the polyhydroxyalkanoic acid wet granules obtained in step (b) to obtain polyhydroxyalkanoic acid dry granules.

[0067] [2] The method for producing polyhydroxyalkanoic acid dry granules according to [1], wherein in the step (b), the wet polyhydroxyalkanoic acid powder is compression granulated and / or extrusion granulated at a temperature of 10 to 55°C.

[0068] [3] The method for producing polyhydroxyalkanoic acid dry granules according to [1] or [2], wherein the water content of the polyhydroxyalkanoic acid dry granules is 0.5% by weight or less.

[0069] [4] The method for producing dry polyhydroxyalkanoic acid granules according to any one of [1] to [3], wherein the step (a) comprises a step of dead-end filtration of an aqueous suspension of polyhydroxyalkanoic acid.

[0070] [5] The method for producing polyhydroxyalkanoic acid-based resin particles according to any one of [1] to [4], wherein the median diameter of the wet polyhydroxyalkanoic acid granules is 1.0 to 5.0 mm.

[0071] [6] The method for producing a polyhydroxyalkanoic acid according to any one of [1] to [5], wherein the polyhydroxyalkanoic acid is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0072] [7] The method for producing a polyhydroxyalkanoic acid according to any one of [1] to [6], wherein the polyhydroxyalkanoic acid is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0073] [8] A method for producing polyhydroxyalkanoic acid-based resin particles, comprising a step of melt-kneading the polyhydroxyalkanoic acid dry granules produced by the method for producing polyhydroxyalkanoic acid dry granules according to any one of [1] to [7].

[0074] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0075] [Measurement Method] Measurements in the examples and comparative examples were carried out by the following methods.

[0076] (Moisture Content) The moisture contents of the wet PHA powder, wet PHA granules, and dry PHA granules were measured using a heat-dry moisture meter ML-50 (manufactured by A&D Co., Ltd.) Specifically, the weight (w1) of the target wet PHA powder, wet PHA granules, or dry PHA granules was first measured, and the target wet PHA powder, wet PHA granules, or dry PHA granules after weight measurement was heated at 105°C, and heating was terminated when the rate of weight change fell below 0.05 wt% (W.B.) / min. The weight (w2) of the target PHA wet powder, PHA wet granules, or PHA dry granules was measured at the end of heating, and the change in weight of the target PHA wet powder, PHA wet granules, or PHA dry granules before and after heating (= w1 - w2) was taken as the amount of water contained in the weight of the target PHA wet powder, PHA wet granules, or PHA dry granules. The moisture content of the target PHA wet powder, PHA wet granules, or PHA dry granules was calculated using the following formula: Moisture content (wt%) of the target PHA wet powder, PHA wet granules, or PHA dry granules = {(w1 - W2) / (w1)} × 100.

[0077] (Median Diameter) The median diameters of the PHA wet powder, PHA wet granules, and PHA dry granules were measured using a metal mesh sieve and / or a laser diffraction particle analyzer (Malvern, MASTERSIZER3000) based on JIS Z 8801-1:2000. More specifically, (1) among the measurement objects (PHA wet powder, PHA wet granules, or PHA dry granules), those that passed through a metal mesh sieve with a mesh opening of 2 mm and those that did not were selected. (2) For those that passed through the mesh sieve, the under-sieve cumulative distribution was measured using a laser diffraction particle analyzer. For those that did not pass through the mesh sieve, the under-sieve cumulative distribution was measured again using a metal mesh sieve. (3) The weight (A1) of the particles that did not pass through a 2 mm metal mesh sieve and the weight (A2) of the particles that did pass through were measured, and the median diameter of the object to be measured was determined based on the following method: If A2 < A1, the particle size of the object to be measured in the cumulative frequency [%] of the particles that did not pass through a 2 mm metal mesh sieve in the cumulative distribution that passed through the sieve = [{A1 - (A1 + A2) x 0.5} / A1] x 100 was used as the median diameter of the object to be measured. If A1 ≦ A2, the particle size of the object to be measured in the cumulative frequency [%] of the particles that passed through a 2 mm metal mesh sieve in the cumulative distribution that passed through the sieve = [1 - {A2 - (A1 + A2) x 0.5} / A2] x 100 was used as the median diameter of the object to be measured. Note that in the above calculations, the density of the object to be measured is considered to be constant.

[0078] (Melt Torque) The melt torque of the PHA dry granules was measured using a melt kneading (test) device (Labo Plastomill (registered trademark) 3S150, manufactured by Toyo Seiki Seisakusho). Specifically, the PHA dry granules were supplied to the device, melt kneading was started, and the torque of the melt kneaded product 20 seconds after the start of melt kneading was measured as the melt torque. During the measurement, the temperature inside the device was set to 100°C.

[0079] (Stable Torque Temperature) The stable torque temperature of the dried PHA granules was measured using a melt-kneading (test) device (Labo Plastomill (registered trademark) 3S150, manufactured by Toyo Seiki Seisaku-sho, Ltd.) Specifically, the dried PHA granules were supplied to the device, melt-kneading was started, and the temperature of the melt-kneaded product at the time when the torque stabilized (i.e., the time when the change in torque per 5 seconds became less than 1 N m) was measured as the stable torque temperature.

[0080] (Bulk Density) The bulk density of the dried PHA granules was measured using a bulk specific gravity measuring instrument (product name: Standard Type Bulk Specific Gravity Meter, manufactured by Kuratori Scientific Instruments) based on JIS K 7365:1999.

[0081] Example 1 Preparation of PHA Aqueous Suspension Based on the method described in Example 1 of International Publication No. WO 2019 / 142845, the PHA-producing microorganism Ralstonia eutropha (currently classified as Capriavidus necator) was cultured to obtain a culture solution containing PHA-containing fungal cells. The obtained PHA was poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and the composition ratio of its repeating units (3HB unit / 3HH unit) was 94 / 6 (mol% / mol%).

[0082] The resulting culture solution containing PHA-containing bacterial cells was treated under the conditions described in paragraphs

[0114] to

[0118] of WO 2023 / 120310 to obtain an aqueous PHA suspension.

[0083] (Step (a)) The PHA aqueous suspension obtained by the above operation was dehydrated by pressure filtration using a pressure filter (YTO type filter press, manufactured by Yabuta Kikai) to obtain a PHA wet powder. This PHA wet powder was further dried in a tray dryer (WFO-700 manufactured by Tokyo Rikakikai Co., Ltd.) to adjust the moisture content. The moisture content and median diameter of the PHA wet powder after drying are shown in Table 1.

[0084] (Step (b)) The PHA wet powder (after drying) obtained by the above operation was supplied to a briquette machine compactor (HCS-25, manufactured by Hosokawa Micron Corporation), which is a compression granulator having a vertical screw and two rotating rolls, and compressed. The obtained compressed PHA wet powder was crushed using a feather mill (FM-1S, manufactured by Hosokawa Micron Corporation) to obtain PHA wet granules. The moisture content and median diameter of the obtained PHA wet granules are shown in Table 1. The above compression and crushing operations were carried out at room temperature (25°C), and the temperature of the PHA wet powder subjected to the operations was 24°C, and the temperature of the PHA wet granules immediately after crushing (granulation) was 34°C.

[0085] (Step (c)) The wet PHA granules obtained by the above procedure were dried at 80°C using a tray dryer (Tokyo Rikakikai WFO-700) to obtain dry PHA granules. The moisture content, bulk density, and median diameter of the obtained dry PHA granules are shown in Table 1.

[0086] (Resin particle preparation process) The PHA dry granules obtained by the above operation were melt-kneaded using a melt-kneading device (Toyo Seiki Seisakusho, Labo Plastomill (registered trademark) 3S150) to prepare PHA resin particles. The melt torque and torque stability temperature during this melt-kneading operation were measured. The results are shown in Table 1.

[0087] Example 2 (Preparation of PHA Aqueous Suspension) A PHA aqueous suspension was obtained in the same manner as in Example 1.

[0088] (Step (a)) The PHA aqueous suspension obtained by the above operation was dehydrated by pressure filtration using a pressure filter (YTO type filter press, manufactured by Yabuta Kikai) to obtain a PHA wet powder. This PHA wet powder was further dried in a tray dryer (WFO-700 manufactured by Tokyo Rikakikai Co., Ltd.) to adjust the moisture content. The moisture content and median diameter of the PHA wet powder after drying are shown in Table 1.

[0089] (Step (b)) The PHA wet powder (after drying) obtained by the above operation was granulated using a wet extrusion granulator (EXDS-60 manufactured by Fuji Paudal Co., Ltd.) to obtain PHA wet granules. The moisture content and median diameter of the obtained PHA wet granules are shown in Table 1. The above granulation operation was carried out at room temperature (25°C), and the temperatures of the PHA wet powder and PHA wet granules subjected to the operation immediately after granulation were both 25°C.

[0090] (Step (c)) The wet PHA granules obtained by the above procedure were dried at 80°C using a tray dryer (Tokyo Rikakikai WFO-700) to obtain dry PHA granules. The moisture content, bulk density, and median diameter of the obtained dry PHA granules are shown in Table 1.

[0091] (Resin particle preparation process) The PHA dry granules obtained by the above operation were melt-kneaded using a melt-kneading device (Toyo Seiki Seisakusho, Labo Plastomill (registered trademark) 3S150) to prepare PHA resin particles. The melt torque and torque stability temperature during this melt-kneading operation were measured. The results are shown in Table 1.

[0092] Example 3 (Preparation of PHA Aqueous Suspension) A PHA aqueous suspension was obtained in the same manner as in Example 1.

[0093] (Step (a)) The PHA aqueous suspension obtained by the above operation was dehydrated by dead-end filtration (pressure filtration) using a pressure filter (YTO type filter press, manufactured by Yabuta Kikai) to obtain a PHA wet powder. The water content and median diameter of the obtained PHA wet powder are shown in Table 1.

[0094] (Step (b)) The PHA wet powder obtained by the above operation was granulated using a wet extrusion granulator (EXDS-60 manufactured by Fuji Paudal Co., Ltd.) to obtain PHA wet granules. The moisture content and median diameter of the obtained PHA wet granules are shown in Table 1. The above granulation operation was carried out at room temperature (25°C), and the temperatures of the PHA wet powder and PHA wet granules subjected to the operation immediately after granulation were both 25°C.

[0095] (Step (c)) The wet PHA granules obtained by the above procedure were dried at 80°C using a tray dryer (Tokyo Rikakikai WFO-700) to obtain dry PHA granules. The moisture content, bulk density, and median diameter of the obtained dry PHA granules are shown in Table 1.

[0096] (Resin particle preparation process) The PHA dry granules obtained by the above operation were melt-kneaded using a melt-kneading device (Toyo Seiki Seisakusho, Labo Plastomill (registered trademark) 3S150) to prepare PHA resin particles. The melt torque and torque stability temperature during this melt-kneading operation were measured. The results are shown in Table 1.

[0097] Comparative Example 1 (Preparation of PHA Aqueous Suspension) A PHA aqueous suspension was obtained in the same manner as in Example 1.

[0098] (Dehydration step) The PHA aqueous suspension obtained by the above operation was dehydrated using a filter cloth, and the obtained dehydrated product was further dried at 80°C using a tray dryer (WFO-700 manufactured by Tokyo Rikakikai Co., Ltd.) to obtain a PHA powder. The moisture content and median diameter of the obtained PHA powder are shown in Table 1. As shown in Table 1, the moisture content of the obtained PHA powder was less than 0.5%, and it was not a wet powder.

[0099] (Granulation step) The PHA powder obtained by the above operation was supplied to a briquette machine compactor (HCS-25 manufactured by Hosokawa Micron Corporation), which is a compression granulator having a vertical screw and two rotating rolls, and compressed. The obtained compressed PHA powder was crushed with a feather mill (FM-1S manufactured by Hosokawa Micron Corporation) to obtain PHA wet granules. The moisture content and median diameter of the obtained PHA wet granules are shown in Table 1. The above compression and crushing operations were performed at room temperature (25°C), the temperature of the PHA powder subjected to the operations was 24°C, and the temperature of the PHA wet granules immediately after crushing (granulation) was 45°C.

[0100] (Drying step) The wet PHA granules obtained by the above operation were dried at 80°C using a tray dryer (WFO-700 manufactured by Tokyo Rikakikai Co., Ltd.) to obtain dry PHA granules. The moisture content, bulk density, and median diameter of the obtained dry PHA granules are shown in Table 1.

[0101] (Resin particle preparation process) The PHA dry granules obtained by the above operation were melt-kneaded using a melt-kneading device (Toyo Seiki Seisakusho, Labo Plastomill (registered trademark) 3S150) to prepare PHA resin particles. The melt torque and torque stability temperature during this melt-kneading operation were measured. The results are shown in Table 1.

[0102] Comparative Example 2 (Preparation of PHA Aqueous Suspension) A PHA aqueous suspension was obtained in the same manner as in Example 1.

[0103] (Dehydration step) The PHA aqueous suspension obtained by the above operation was dehydrated using a filter cloth. The moisture content of the obtained dehydrated product is shown in Table 1. As shown in Table 1, the moisture content of the obtained dehydrated product was more than 40% and had fluid properties, and was not a wet powder but an aqueous suspension. Therefore, granulation itself could not be performed, and wet granules could not be obtained.

[0104] [Summary] The results of Examples 1 to 3 show that the PHA dry granules produced by the present production method including steps (a) to (c) are not heated during the production process, are produced energy-efficiently, and yet have low melt torque and stable torque temperature, and excellent meltability. On the other hand, the results of Comparative Example 1 show that when the moisture content of the PHA wet granules is below 5%, the resulting PHA dry granules have high melt torque and stable torque temperature, resulting in a PHA with poor meltability. Furthermore, the results of Comparative Example 2 show that when the moisture content of the PHA wet powder exceeds 40%, it becomes an aqueous suspension with fluid properties, making granulation itself impossible.

[0105] According to this production method, dry PHA granules with excellent melting properties can be provided in an energy-efficient manner. Therefore, this production method can be advantageously used in the production of PHA. Furthermore, molded articles using the dry PHA granules obtained by this production method can be suitably used in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing, packaging, automobiles, building materials, and other fields.

Claims

1. A method for producing polyhydroxyalkanoic acid dry granules, comprising: step (a) of dehydrating an aqueous suspension of polyhydroxyalkanoic acid to prepare a polyhydroxyalkanoic acid wet powder containing 5 to 37% by weight of water; step (b) of compressing and / or extruding the polyhydroxyalkanoic acid wet powder obtained in step (a) to obtain polyhydroxyalkanoic acid wet granules containing 5 to 37% by weight of water; and step (c) of drying the polyhydroxyalkanoic acid wet granules obtained in step (b) to obtain polyhydroxyalkanoic acid dry granules.

2. The method for producing polyhydroxyalkanoic acid according to claim 1, wherein in step (b), the wet powder of polyhydroxyalkanoic acid is compression granulated and / or extrusion granulated at a temperature of 10 to 55°C.

3. The method for producing polyhydroxyalkanoic acid according to claim 1, wherein the water content of the dried polyhydroxyalkanoic acid granules is 0.5% by weight or less.

4. The method for producing polyhydroxyalkanoic acid according to claim 1, wherein step (a) comprises subjecting the aqueous suspension of polyhydroxyalkanoic acid to dead-end filtration.

5. The method for producing polyhydroxyalkanoic acid resin particles according to claim 1, wherein the median diameter of the wet polyhydroxyalkanoic acid granules is 1.0 to 5.0 mm.

6. The method for producing a polyhydroxyalkanoic acid according to claim 1, wherein the polyhydroxyalkanoic acid is one or more selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

7. The method for producing a polyhydroxyalkanoic acid according to claim 1, wherein the polyhydroxyalkanoic acid is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

8. A method for producing polyhydroxyalkanoic acid-based resin particles, comprising a step of melt-kneading dry polyhydroxyalkanoic acid granules produced by the method for producing polyhydroxyalkanoic acid according to any one of claims 1 to 7.

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