Method for producing polyhydroxyalkanoate and utilization thereof

Abstract

An object of the present invention is to provide a method for producing PHA that can be obtained by a simple operation. The present invention solves the above problems by providing a method for producing a polyhydroxyalkanoate, the method comprising: (a) a step of preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less; and (b) a step of heating the aqueous suspension of polyhydroxyalkanoate prepared in the above step (a) at a set temperature of 80 to 300 ° C in a twin-screw extruder to cause the polyhydroxyalkanoate to aggregate.

Description

Technical Field

[0001] The present invention relates to a method for producing polyhydroxyalkanoate and its utilization. Background Art

[0002] It is known that polyhydroxyalkanoate (hereinafter sometimes referred to as "PHA") has biodegradability.

[0003] PHA produced by microorganisms accumulates in the cells of the microorganisms. Therefore, in order to utilize PHA in the form of plastic, a process for separating / purifying PHA from the cells of the microorganisms is required. In the process of separating / purifying PHA. After disrupting the cells of the PHA-containing microorganisms or dissolving the bio-derived components other than PHA, PHA can be obtained from the resulting aqueous suspension. At this time, for example, separation operations such as centrifugation, filtration, and drying are performed. For the drying operation, a spray dryer, a fluidized bed dryer, a drum dryer, etc. are used, and from the viewpoint of easy operation, a spray dryer is preferably used (Patent Document 1).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication WO2018 / 070492 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, there is still room for improvement in spray drying.

[0009] Therefore, as a technique alternative to spray drying, an object of the present invention is to provide a method for producing PHA that can be obtained by a simple operation.

[0010] Means for Solving the Problems

[0011] The present inventors conducted intensive studies to solve the above problems and as a result, found the following new insight and completed the present invention. The new insight is that PHA can be easily obtained by heating an aqueous PHA suspension at a specific temperature while extruding it using a twin-screw extruder.

[0012] Therefore, one aspect of the present invention relates to a method for producing polyhydroxyalkanoate, the method comprising: (a) a step of preparing an aqueous PHA suspension having a pH of 7 or less, and (b) a step of heating the aqueous PHA suspension prepared in the above step (a) at a set temperature of 80 to 300°C in a twin-screw extruder and causing PHA to aggregate.

[0013] In addition, one aspect of the present invention relates to a polyhydroxyalkanoate aggregate containing 97% by weight or more of polyhydroxyalkanoate and having a volume median diameter of 300 μm or more.

[0014] Effects of the Invention

[0015] According to one aspect of the present invention, PHA can be obtained by a simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. is a diagram schematically showing a method for producing PHA according to an embodiment of the present invention.

[0017] Figure 2 FIG. is a diagram schematically showing a method for producing PHA according to an embodiment of the present invention.

[0018] Figure 3 FIG. is a diagram schematically showing a method for producing PHA according to an embodiment of the present invention.

[0019] Figure 4 FIG. is a diagram schematically showing a method for producing PHA according to an embodiment of the present invention.

[0020] Figure 5 FIG. is a diagram schematically showing a method for producing PHA according to an embodiment of the present invention.

[0021] Figure 6 FIG. is a diagram schematically showing a method for producing PHA according to an embodiment of the present invention.

[0022] Figure 7 FIG. is a diagram showing a PHA aggregate according to an embodiment of the present invention.

[0023] SYMBOL DESCRIPTION

[0024] 1 Inner region of the extruder

[0025] 2 Screw

[0026] 3 Heater

[0027] 3a High-temperature part

[0028] 3b Medium-temperature part

[0029] 3c Low-temperature part

[0030] 4 Extruder power source part

[0031] 5 Extrusion part (discharge part)

[0032] 6 Pressure reduction part

[0033] 7 Vacuum pump

[0034] 8 Valve

[0035] 9 Screw with reverse feed function (return screw)

[0036] 10 PHA Aqueous Suspension Feeding Section

[0037] 11 Acid Feeding Section

[0038] 12 Pressurized Steam Feeding Section Detailed Embodiment

[0039] Hereinafter, an embodiment of the present invention will be described in detail. It should be noted that in this specification, unless otherwise specified, "A to B" indicating a numerical range means "A or more and B or less". In addition, all the documents described in this specification are incorporated herein by reference.

[0040] [1. Content of the Present Invention]

[0041] The manufacturing method of PHA according to an embodiment of the present invention (hereinafter referred to as "this manufacturing method") includes: (a) a step of preparing a PHA aqueous suspension having a pH of 7 or less; and (b) a step of heating the PHA aqueous suspension prepared in the above step (a) in a twin-screw extruder at a set temperature of 80 to 300 °C to cause PHA to aggregate.

[0042] The present inventors believe that the following problems exist in spray drying during the manufacture of PHA. For example, in the spray drying operation, since it is necessary to evaporate all the water in the aqueous suspension, a large amount of heat energy is required. In addition, the spray dryer used in the spray drying operation tends to become huge, and there is a problem in increasing the equipment installation area. In addition, in order to transport a high-concentration PHA aqueous suspension with a pH of 7 or less to the spray dryer, it is necessary to add a dispersant to the aqueous suspension, and there is still room for improvement from the viewpoint of manufacturing cost.

[0043] Therefore, in order to develop a technology to replace spray drying, in-depth research has been carried out, and as a result, it has been found that the method using a twin-screw extruder is effective. Specifically, the present inventors have first found that by feeding a PHA aqueous suspension into a twin-screw extruder and extruding it, PHA aggregates can be obtained. So far, there has been no report on using a twin-screw extruder in the drying process of a PHA aqueous suspension, and the above-mentioned insight found by the present inventors is unexpected.

[0044] In addition, the present inventors have found that by using this method, PHA aggregates can be obtained more efficiently, and useful PHA aggregates that have not existed in the past (for example, PHA aggregates having new physical properties) can be obtained.

[0045] Thus, PHA can be obtained by a simple operation according to this manufacturing method. In addition, since this manufacturing method is based on a continuous production equipment method, it is possible to save the space of the equipment. As a result, it also has the advantage of being easy to set up and move the manufacturing site. From this point of view, this manufacturing method can also be called a continuous manufacturing method of PHA. As described above, this manufacturing method is extremely advantageous for the manufacture of PHA.

[0046] It should be noted that in this specification, the "twin-screw extruder" used in this manufacturing method also includes a twin-screw kneader. Hereinafter, the configuration of this manufacturing method will be described in detail.

[0047] [2. Manufacturing method of PHA]

[0048] This manufacturing method includes the following steps (a) to (b) as essential steps.

[0049] · Step (a): A step of preparing a PHA aqueous suspension having a pH of 7 or less

[0050] · Step (b): A step of heating the PHA aqueous suspension prepared in the above step (a) in a twin-screw extruder at a set temperature of 80 to 300 °C to cause PHA to coagulate

[0051] (Step (a))

[0052] In step (a) of this manufacturing method, a PHA aqueous suspension having a pH of 7 or less is prepared. In this aqueous suspension, PHA exists in a dispersed state in the aqueous medium. Hereinafter, the aqueous suspension containing at least PHA may sometimes be simply referred to as "PHA aqueous suspension".

[0053] <PHA>

[0054] In this specification, "PHA" is a general term for polymers having hydroxyalkanoic acids as monomer units. As the hydroxyalkanoic acids constituting PHA, there is no particular limitation, and examples thereof include: 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, etc. These polymers may be homopolymers or copolymers containing two or more monomer units.

[0055] More specifically, examples of PHA include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxypentanoate) (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), poly(3-hydroxybutyrate-co-3-hydroxypentanoate-co-3-hydroxyhexanoate) (P3HB3HV3HH), and the like. Among them, from the viewpoint of easy industrial production, P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are preferred.

[0056] In addition, by changing the composition ratio of the repeating units, the melting point, and the crystallinity, as a result, physical properties such as Young's modulus and heat resistance can be changed, and physical properties between polypropylene and polyethylene can be imparted. Moreover, as described above, it is easily produced industrially. From the viewpoint of physically useful plastics, a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, that is, P3HB3HH, is more preferred.

[0057] In one embodiment of the present invention, for the composition ratio of the repeating units of P3HB3HH, from the viewpoint of the balance between flexibility and strength, the composition ratio of the 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit is preferably 80 / 20 to 99 / 1 (mol / mol), more preferably 85 / 15 to 97 / 3 (mol / mol). When the composition ratio of the 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit is 99 / 1 (mol / mol) or less, sufficient flexibility can be obtained, and when it is 80 / 20 (mol / mol) or more, sufficient hardness can be obtained.

[0058] In step (a), the PHA aqueous suspension used as the starting material is not particularly limited. For example, it can be obtained by the following method, which includes a culturing step of culturing a microorganism having the ability to produce PHA intracellularly, and a purification step of decomposing and / or removing substances other than PHA after the culturing step.

[0059] This manufacturing method may include, before step (a), a step of obtaining an aqueous PHA suspension (for example, a step including the above-mentioned culturing step and purification step). The microorganism used in this step may be any microorganism capable of producing PHA intracellularly, and there is no particular limitation. For example, microorganisms isolated from nature, microorganisms preserved in strain preservation institutions (such as IFO, ATCC, etc.), or mutants, transformants, etc. that can be prepared from them can be used. More specifically, examples include bacteria of the genus Cupriavidus, Alcaligenes, Ralstonia, Pseudomonas, Bacillus, Azotobacter, Nocardia, Aeromonas, etc. Among them, microorganisms belonging to the genus Aeromonas, Alcaligenes, Ralstonia, or Cupriavidus are preferred. In particular, strains such as Alcaligenes lipolytica, Alcaligenes latus, Aeromonas caviae, Aeromonas hydrophila, Cupriavidus necator, etc. are more preferred, and Cupriavidus necator is most preferred.

[0060] In addition, in the case where the microorganism originally does not have the ability to produce PHA or the production amount of PHA is low, a transformant obtained by introducing the target PHA synthase gene and / or its mutant into the microorganism can also be used. The PHA synthase gene used for the preparation of such a transformant is not particularly limited. As the above-mentioned PHA synthase gene, the gene of PHA synthase derived from Aeromonas caviae is preferred. By culturing these microorganisms under appropriate conditions, microbial cells in which PHA is accumulated in the cells can be obtained. The culturing method of the microbial cells is not particularly limited. As the above-mentioned culturing method, for example, the method described in Japanese Patent Laid-Open No. 05-93049 can be used.

[0061] The PHA-containing microorganism prepared by culturing the above-mentioned microorganism contains a large amount of cell-derived components as impurities. Therefore, a purification step for decomposing and / or removing impurities other than PHA can usually be carried out. In this purification step, physical treatment, chemical treatment, biological treatment, etc. that can be conceived by those skilled in the art can be applied, and there is no particular limitation. For example, the purification method described in International Publication No. 2010 / 067543 is preferably applied.

[0062] Through the above purification process, the amount of impurities remaining in the final product can be roughly determined. Therefore, it is preferred to minimize these impurities as much as possible. Of course, depending on the use, impurities can be incorporated without impairing the physical properties of the final product. However, in the case of medical uses and other applications that require high-purity PHA, it is preferred to minimize impurities. As an index of the purification degree at this time, for example, the amount of protein in the PHA aqueous suspension can be cited. The amount of this protein is preferably 30,000 ppm or less per unit weight of PHA, more preferably 15,000 ppm or less, further preferably 10,000 ppm or less, and most preferably 7,500 ppm or less. The purification method is not particularly limited. For example, the above-known methods can be applied.

[0063] It should be noted that the solvent (the "solvent" is also referred to as the "aqueous medium") constituting the PHA aqueous suspension in this manufacturing method can be water or a mixed solvent of water and an organic solvent. In addition, in this mixed solvent, the concentration of the organic solvent compatible with water only needs to be below the solubility of the organic solvent to be used in water, and there is no particular limitation. In addition, the organic solvent compatible with water is not particularly limited. As the above-mentioned organic solvent compatible with water, for example, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, and heptanol; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and di alkane; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, piperidine, etc. are not particularly limited. Among the above-mentioned organic solvents compatible with water, from the viewpoint of easy removal, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, di alkane, acetonitrile, propionitrile, etc. are preferred. In addition, among the above-mentioned organic solvents compatible with water, from the viewpoint of easy availability, methanol, ethanol, 1-propanol, 2-propanol, butanol, acetone, etc. are more preferred. In addition, among the above-mentioned organic solvents compatible with water, methanol, ethanol, and acetone are particularly preferred. It should be noted that the aqueous medium constituting the PHA aqueous suspension can contain other solvents, components derived from the bacterial cells, compounds generated during purification, etc. without impairing the essence of the present invention.

[0064] It is preferred that water is contained in the aqueous medium constituting the PHA aqueous suspension of this manufacturing method. The content of water in the aqueous medium is preferably 5% by weight or more, more preferably 10% by weight or more, further preferably 30% by weight or more, and particularly preferably 40% by weight or more.

[0065] <Other>

[0066] The PHA aqueous suspension before step (a) of the present manufacturing method usually undergoes the above purification step and thus has a pH value exceeding 7. Therefore, the pH of the above PHA aqueous suspension is adjusted to 7 or less in step (a) of the present manufacturing method. The adjustment method is not particularly limited, and for example, a method of adding an acid can be cited. The acid is not particularly limited and can be any acid among organic acids and inorganic acids, whether or not it is volatile. More specifically, as the acid, for example, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, etc. can be used.

[0067] Regarding the upper limit of the pH of the PHA aqueous suspension adjusted in the above adjustment step, from the viewpoints of reducing coloring during heating and melting of PHA and ensuring the stability of the molecular weight during heating and / or drying, it is 7 or less, preferably 5 or less, more preferably 4 or less. In addition, 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 further preferably 3 or more. By setting the pH of the PHA aqueous suspension to 7 or less, PHA with reduced coloring during heating and melting and suppressed reduction in molecular weight during heating and / or drying can be obtained.

[0068] In step (a) of the present manufacturing method, the preparation of the pH of the PHA aqueous suspension can be carried out before charging into the twin-screw extruder or after charging into the twin-screw extruder. In the case of carrying out after charging into the twin-screw extruder, first, after charging the PHA aqueous suspension into the twin-screw extruder, the above acid or the like is charged into the twin-screw extruder, thereby enabling the pH of the PHA aqueous suspension to be adjusted to 7 or less. The charging of the acid or the like is preferably carried out before the PHA aqueous suspension is heated in the twin-screw extruder. Thereby, a PHA aggregate with reduced coloring during heating and melting in the twin-screw extruder and suppressed reduction in molecular weight during heating and / or drying can be obtained.

[0069] From the aspect of drying application, the concentration of PHA in the PHA aqueous suspension obtained by step (a) of the present manufacturing method is economically advantageous. In order to improve productivity, it is preferably 30% by weight or more, more preferably 40% by weight or more, and further preferably 50% by weight or more. In addition, regarding the upper limit of the concentration of PHA, since the closest packing is reached, sufficient fluidity may not be ensured, so it is preferably 70% by weight or less, more preferably 65% by weight or less. The method of adjusting the concentration of PHA is not particularly limited, and methods such as adding an aqueous medium and removing a part of the aqueous medium (for example, by removing the supernatant after centrifugation) can be cited. The adjustment of the concentration of PHA can be carried out at any stage of step (a) or at a stage before step (a).

[0070] In one embodiment of the present invention, the concentration of the polyhydroxyalkanoate in the aqueous suspension prepared in step (a) of the present production method is 30 to 70% by weight.

[0071] (Step (b))

[0072] In step (b) of the present manufacturing method, the aqueous suspension of PHA prepared in the above step (a) is heated at a set temperature of 80 to 300°C of a twin-screw extruder to cause PHA to agglomerate. That is, in step (b), the aqueous suspension of PHA is fed into a twin-screw extruder, heated at a specific temperature, and simultaneously moved in the twin-screw extruder, thereby obtaining PHA agglomerates. At this time, pressurized steam can be directly fed into the twin-screw extruder to heat the aqueous suspension of PHA to obtain PHA agglomerates. At this time, PHA is combined due to heat melting, and PHA agglomerates can be obtained. The PHA agglomerates obtained in this step are block-shaped PHA, which has a larger particle size and is easier to handle than the powdered PHA obtained by the spray drying step.

[0073] In one embodiment of the present invention, the set temperature of the twin screw extruder in step (b) (the set temperature of the heater 3 or the temperature of the pressurized steam introduced from the pressurized steam introduction part) is not particularly limited as long as it is a temperature at which PHA agglomerates can be obtained by thermal fusion bonding, and is, for example, 80 to 300° C., preferably 100 to 250° C., more preferably 120 to 240° C., and particularly preferably 140 to 220° C. When the set temperature of the twin screw extruder in step (b) is 80° C. or higher, the water contained in the PHA aqueous suspension can be fully volatilized. When the set temperature of the twin screw extruder in step (b) is 200° C. or lower, the molecular weight reduction caused by the decomposition of the PHA agglomerates can be avoided.

[0074] The heating method in step (b) is not particularly limited, for example, an electric heater, a steam heater, an oil heater, etc. can be used, or pressurized steam can be directly put into a twin-screw extruder. In addition, the heating time is not particularly limited either, and can be appropriately set by those skilled in the art.

[0075] In step (b), the screw speed (also referred to as "shaft speed") of the twin-screw extruder is not particularly limited, and is, for example, 20 to 1000 rpm, preferably 25 to 800 rpm, and more preferably 28 to 700 rpm. When the screw speed of the twin-screw extruder is 20 rpm or more, the adhesion of PHA to the shaft can be suppressed. When the screw speed of the twin-screw extruder is 1000 rpm or less, PHA can be effectively agglomerated.

[0076] In one embodiment of the present invention, a part of the screw of the twin-screw extruder can be a screw with a reverse feeding function (hereinafter sometimes referred to as a "return screw"). By providing the twin-screw extruder with a return screw, pressure is applied to this return screw part. As a result, heat is not only transferred to the surface of the PHA aqueous suspension but also evenly transferred to the interior, and hot melt adhesion can be carried out evenly without water evaporation.

[0077] In one embodiment of the present invention, the number of return screws is not particularly limited and can be 1 or multiple (for example, 2, 3, 4, 5).

[0078] In one embodiment of the present invention, the pressure in the twin-screw extruder in step (b) only needs to be a pressure capable of obtaining PHA aggregates through hot melt adhesion and is not particularly limited. For example, it is 0.01 to 0.5 Mpa, preferably 0.05 to 0.5 Mpa, and more preferably 0.08 to 0.5 Mpa. When the twin-screw extruder is equipped with a return screw, as described above, there is a tendency for the pressure in the twin-screw extruder to increase. When the twin-screw extruder is equipped with a return screw, the pressure in the twin-screw extruder in step (b) is, for example, 0.1 to 0.5 Mpa, preferably 0.2 to 0.5 Mpa, and more preferably 0.25 to 0.5 Mpa.

[0079] In one embodiment of the present invention, in order to obtain a desired PHA aggregate, the set temperature of the above-mentioned twin-screw extruder, the screw rotation speed of the twin-screw extruder, the return screw, the pressure in the twin-screw extruder, etc. can be appropriately combined in step (b).

[0080] In addition, the twin-screw extruder used in this manufacturing method only needs to be able to obtain PHA aggregates from the PHA aqueous suspension and is not particularly limited. Preferably, it is a twin-screw extruder capable of adjusting the set temperature, screw rotation speed, pressure, etc. to a desired range. It should be noted that Figures 1 to 5 FIG. schematically shows a representative twin-screw extruder that can be used in this manufacturing method. As a commercially available twin-screw extruder used in this manufacturing method, there is no particular limitation, and examples include EA-20 manufactured by SUEHIRO EPM used in the examples, S2KRC kneader manufactured by Kurimoto Iron Works Co., Ltd., TEX60α manufactured by Japan Steel Works, Ltd., etc.

[0081] As described above, PHA aggregates can be obtained by this manufacturing method. Here, the obtained PHA aggregates can be represented using the value shown in the following formula (1) as an index:

[0082] Volume median diameter of the PHA aggregate obtained in the above step (b) / Volume median diameter of the PHA primary particles ··· (1)

[0083] It should be noted that in this specification, the "PHA primary particles" refer to the particles of polyhydroxyalkanoate in the aqueous suspension of polyhydroxyalkanoate prepared in step (a). In addition, the "volume median diameter of PHA aggregates" can also be referred to as the "average diameter of PHA aggregates". Furthermore, the "volume median diameter of PHA primary particles" can also be referred to as the "PHA primary diameter".

[0084] In one embodiment of the present invention, the value shown in the above formula (1) is, for example, 50 to 20,000, preferably 100 to 15,000, and more preferably 150 to 10,000.

[0085] The above-mentioned "volume median diameter of PHA aggregates" can be measured by the following method. That is, 0.05 g of sodium dodecyl sulfate as a surfactant is added to 20 ml of ion-exchanged water as a dispersant to obtain an aqueous surfactant solution. Then, 0.2 g of the resin particle group to be measured is added to the above-mentioned aqueous surfactant solution to disperse the above-mentioned resin particle group in the above-mentioned aqueous surfactant solution to obtain a dispersion for measurement. The prepared dispersion is introduced into a laser diffraction / scattering particle size distribution measuring device LA-950 manufactured by HORIBA, Ltd. for measurement.

[0086] In addition, the above-mentioned "volume median diameter of PHA primary particles" can be measured using a laser diffraction / scattering particle size distribution measuring device LA-950 manufactured by HORIBA, Ltd.

[0087] Hereinafter, representative embodiments of this manufacturing method will be described, but this manufacturing method is not limited thereto.

[0088] <Embodiment 1>

[0089] For this Embodiment 1, reference is made to Figure 1 for description.

[0090] The twin-screw extruder used in this Embodiment 1 includes: a screw 2 for conveying the fed sample, an extruder power source unit 4 for supplying power for rotating the screw 2, a heater 3 for adjusting the temperature in the twin-screw extruder, and an extrusion part (discharge part) 5 for extruding the conveyed sample. The set temperature of the heater 3 can be, for example, 140 to 150 °C.

[0091] The PHA aqueous suspension as a sample is fed into the twin-screw extruder from the PHA aqueous suspension feeding section 10. In the present Embodiment 1, the pH of the PHA aqueous suspension before being fed into the twin-screw extruder is adjusted to 7 or less. That is, the PHA aqueous suspension with a pH of 7 or less is fed into the twin-screw extruder. The feeding amount of the PHA aqueous suspension into the twin-screw extruder can be adjusted by the valve 8. The PHA aqueous suspension fed into the inner region 1 of the extruder is conveyed to the extrusion section (discharge section) 5 by the screw 2. During the conveyance, the moisture of the PHA aqueous suspension evaporates by heating at a certain temperature using the heater 3. The PHA in the PHA aqueous suspension is bonded by hot melt adhesion and discharged from the extrusion section (discharge section) 5 in the form of a PHA aggregate. In the present Embodiment 1, the PHA aggregate can be obtained from the PHA aqueous suspension most simply.

[0092] <Embodiment 2>

[0093] For the present Embodiment 2, refer to Figure 2 for the description.

[0094] The twin-screw extruder used in the present Embodiment 2 is the same as the twin-screw extruder used in Embodiment 1.

[0095] The PHA aqueous suspension as a sample is fed into the twin-screw extruder from the PHA aqueous suspension feeding section 10. In the present Embodiment 2, the pH of the PHA aqueous suspension before being fed into the twin-screw extruder is not adjusted to 7 or less. That is, the PHA aqueous suspension with a pH greater than 7 is fed into the twin-screw extruder. The pH of the PHA aqueous suspension fed into the inner region 1 of the extruder is adjusted to 7 or less by feeding an acid from the acid feeding section 11. The amount of the acid fed can be adjusted by the valve 8. The PHA aqueous suspension with a pH adjusted to 7 or less is conveyed to the extrusion section (discharge section) 5 by the screw 2 in the same manner as in Embodiment 1, and a PHA aggregate is obtained. In the present Embodiment 2, the adjustment of the pH of the PHA aqueous suspension and the drying of the PHA aqueous suspension can be concentrated in the inner region 1 of the extruder.

[0096] <Embodiment 3>

[0097] For the present Embodiment 3, refer to Figure 3 for the description.

[0098] In the twin-screw extruder used in the third embodiment, a pressure-reducing section 6 for reducing the pressure in the twin-screw extruder is provided in the twin-screw extruder used in the first embodiment. The pressure-reducing section 6 is connected to a vacuum pump 7. By operating the vacuum pump 7, the air in the twin-screw extruder is discharged via the pressure-reducing section 6 to reduce the pressure in the twin-screw extruder. In addition, the pressure-reducing section 6 can be opened to the atmosphere. By opening to the atmosphere, the moisture in the PHA aqueous suspension evaporated in the twin-screw extruder can be discharged outside the device, improving the evaporation efficiency.

[0099] By using the vacuum pump 7 to reduce the pressure in the twin-screw extruder, the evaporation of the moisture in the PHA aqueous suspension can be promoted. In addition, since the drying of the PHA aqueous suspension can be carried out even when the temperature in the twin-screw extruder is reduced, the decomposition (molecular weight reduction) of PHA can be prevented.

[0100] In addition, as a modification of the third embodiment, the method of providing the acid input section 11 and the valve 8 described in the second embodiment can be cited. In this modification, a PHA aqueous suspension with a pH not adjusted to less than 7 (pH greater than 7) is introduced into the twin-screw extruder, and the pH of the PHA aqueous suspension can be adjusted to less than 7 in the twin-screw extruder.

[0101] <Embodiment 4>

[0102] For this fourth embodiment, reference is made to Figure 4 for description.

[0103] In the twin-screw extruder used in the fourth embodiment, the heater 3 in the twin-screw extruder used in the third embodiment is divided into a plurality of regions with different temperature zones. Specifically, in the fourth embodiment, the heater 3 is divided into respective different temperature zones, which are a high-temperature section 3a, a medium-temperature section 3b, and a low-temperature section 3c. The temperatures of the high-temperature section 3a, the medium-temperature section 3b, and the low-temperature section 3c are respectively represented as T a , T b and T c . T a , T b and T c For example, the relationship is T a > T b > T c . The PHA aqueous suspension introduced into the twin-screw extruder first undergoes moisture evaporation in the region of the high-temperature section 3a, and the remaining moisture evaporates in the regions of the medium-temperature section 3b and the low-temperature section 3c. T a , T b and T cThey can be, for example, 150°C, 120°C, and 80°C. Thus, in the present Embodiment 4, by gradually decreasing the temperature in the twin-screw extruder from the region where the PHA aqueous suspension is introduced to the extrusion section (discharge section) 5, decomposition (molecular weight reduction) of PHA can be prevented.

[0104] The number of different temperature zones of the above-described heater 3 can be appropriately set. In addition, the temperature in each temperature zone can also be appropriately set.

[0105] In addition, as a modification example of Embodiment 4, the method of providing the acid introduction section 11 and the valve 8 described in Embodiment 2 can be cited. In this modification example, a PHA aqueous suspension whose pH is not adjusted to 7 or less (pH > 7) is introduced into the twin-screw extruder, and the pH of the PHA aqueous suspension can be adjusted to 7 or less in the twin-screw extruder.

[0106] <Embodiment 5>

[0107] For this Embodiment 5, reference is made to Figure 5 for description.

[0108] The twin-screw extruder used in this Embodiment 5 is a twin-screw extruder in which a screw (return screw) 9 having a reverse feeding action is provided in a part of the screw 2 of the twin-screw extruder used in Embodiment 1. The screw (return screw) 9 having a reverse feeding action has a function of squeezing the PHA aqueous suspension back in the direction opposite to the direction of conveying the PHA aqueous suspension. The PHA aqueous suspension conveyed by the screw 2 through the internal region 1 of the extruder is pressurized in the region where the screw (return screw) 9 having a reverse feeding action is provided. As a result, heat is not only transferred to the surface of the PHA aqueous suspension but also uniformly transferred to the inside, and uniform hot melting adhesion can be achieved without evaporation of moisture.

[0109] In addition, as a modification example of Embodiment 5, the method of providing the acid introduction section 11 and the valve 8 described in Embodiment 2 can be cited. In this modification example, a PHA aqueous suspension whose pH is not adjusted to 7 or less (pH > 7) is introduced into the twin-screw extruder, and the pH of the PHA aqueous suspension can be adjusted to 7 or less in the twin-screw extruder.

[0110] <Embodiment 6>

[0111] For this Embodiment 6, reference is made to Figure 6 for description.

[0112] The twin-screw extruder used in Embodiment 6 is equipped with a pressurized steam inlet 12 in the twin-screw extruder used in Embodiment 1. By introducing pressurized steam from the pressurized steam inlet 12, the temperature of the PHA aqueous suspension can be rapidly increased, and it can be uniformly melted and adhered without evaporation of moisture.

[0113] In addition, as a modification of Embodiment 6, a mode can be cited in which a screw (return screw) 9 having a reverse feeding function is provided in a part of the screw 2 of the twin-screw extruder described in Embodiment 5.

[0114] Furthermore, as a modification of Embodiment 6, a mode can be cited in which an acid introduction part 11 and a valve 8 are provided as described in Embodiment 2. In this modification, a PHA aqueous suspension whose pH is not adjusted to 7 or less (pH is greater than 7) is introduced into the twin-screw extruder, and the pH of the PHA aqueous suspension can be adjusted to 7 or less in the twin-screw extruder.

[0115] In order to further reduce the water content of the PHA aggregates obtained in the above Embodiments 1 to 6, a drying process can be further added. As the drying method, there is no particular limitation, and examples thereof include using a belt dryer, a conveyor dryer, a rotary dryer, etc.

[0116] 〔3. PHA Aggregates〕

[0117] The PHA aggregate of one embodiment of the present invention (hereinafter referred to as "this PHA aggregate") contains 97% by weight or more of PHA except for the water content, and has a volume median diameter of 300 μm or more. Since this PHA aggregate is manufactured by this manufacturing method, it has the advantage of being able to be obtained by a simple operation. It should be noted that, in other words, "containing 97% by weight or more of PHA except for the water content" means that it contains 97% by weight or more of PHA relative to the total amount of PHA and impurities after removing the water content from all the components (PHA, water, and impurities) contained in this PHA aggregate. In addition, the PHA aggregate in this specification contains PHA particles.

[0118] This PHA aggregate can be manufactured by the above-described specific manufacturing method. Therefore, compared with particles containing PHA powder, it does not require a binder or the like. Thus, PHA can be contained in the PHA aggregate in a high content. This PHA aggregate can also be called a PHA granule.

[0119] The PHA content in the present PHA aggregate only needs to be 97% by weight or more, without any particular limitation. From the perspective of the influence on processability, it is preferably 98% by weight or more, more preferably 99% by weight or more, and further preferably 99.5% by weight or more. In addition, the upper limit value of the PHA content in the present PHA aggregate is not particularly limited, for example, it is 100% by weight or less. The PHA content in the present PHA aggregate can be measured by high performance liquid chromatography.

[0120] In addition, since the present PHA aggregate can be produced by the above-described specific production method, a PHA aggregate with a larger size can be obtained compared to particles containing PHA powder.

[0121] The volume median particle diameter (size) of the present PHA aggregate can be 300 μm or more, without any particular limitation. From the perspective of fluidity, it is preferably 350 μm or more, more preferably 380 μm or more, and further preferably 400 μm or more. In addition, the upper limit value of the volume median particle diameter of the present PHA aggregate is not particularly limited, for example, it is 5 mm or less. The volume median particle diameter of the present PHA aggregate can be measured by the method described above. In addition, the shape of the present PHA aggregate is not particularly limited and can be various shapes such as granular, spherical, irregular, rectangular (polygonal), cylindrical, etc.

[0122] In addition, as long as the present PHA aggregate can exhibit the effects of the present invention, it can contain various components generated or not removed during the process of the present production method.

[0123] It should be noted that in the present embodiment, for parts not specifically described, the content described in the above [2. Production method of PHA] is incorporated by reference.

[0124] The present PHA aggregate can be used for various purposes such as paper, film, sheet, tube, plate, rod, container (for example, bottle container, etc.), bag, component, etc.

[0125] The present invention is not limited to the above-described embodiments, and various changes can be made within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means separately disclosed in different embodiments are also included in the technical scope of the present invention.

[0126] That is, one embodiment of the present invention is as follows.

[0127] <1> A method for producing a polyhydroxyalkanoate, the method comprising:

[0128] (a) A step of preparing a PHA aqueous suspension having a pH of 7 or less; and

[0129] (b) Step of heating the PHA aqueous suspension prepared in the above step (a) at a set temperature of 80 to 300 °C to cause PHA to coagulate.

[0130] <2>The method for producing a polyhydroxyalkanoate according to <1>, wherein the heating method in the above step (b) is a method using a twin-screw extruder heater and / or a method of directly injecting pressurized steam into the twin-screw extruder.

[0131] <3>The method for producing PHA according to <1> or <2>, wherein the value represented by the following formula (1) is 50 to 20,000.

[0132] Volume median diameter of the PHA aggregate obtained in the above step (b) / Volume median diameter of the PHA primary particles ··· (1)

[0133] <4>The method for producing a polyhydroxyalkanoate according to any one of <1> to <3>, wherein in the above step (a), the PHA concentration in the PHA aqueous suspension is 30 to 70% by weight.

[0134] <5>The method for producing PHA according to any one of <1> to <4>, wherein the screw rotation speed of the twin-screw extruder is 30 to 1000 rpm.

[0135] <6>The method for producing PHA according to any one of <1> to <5>, wherein the pressure in the twin-screw extruder is 0.01 to 0.5 Mpa.

[0136] <7>The method for producing PHA according to any one of <1> to <6>, wherein a part of the screw of the twin-screw extruder is a screw having a reverse feeding function.

[0137] <8>A polyhydroxyalkanoate aggregate comprising 97% by weight or more of polyhydroxyalkanoate and having a volume median diameter of 300 μm or more.

[0138] Examples

[0139] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0140] 〔Example 1〕

[0141] (Preparation of Bacterial Cell Culture Solution)

[0142] The Ralstonia eutropha KNK-005 strain described in paragraph

[0049] of International Publication No. 2008 / 010296 was cultured by the method described in paragraphs

[0050] to

[0053] of the same document, and a cell culture solution containing cells containing PHA was obtained. It should be noted that Ralstonia eutropha is now classified as Cupriavidus necator.

[0143] (Sterilization treatment)

[0144] The cell culture solution obtained above was heated / stirred at an internal temperature of 60 to 80 °C for 20 minutes for sterilization treatment.

[0145] (High-pressure homogenization treatment)

[0146] 0.2 wt% sodium dodecyl sulfate was added to the sterilized cell culture solution obtained above. An aqueous sodium hydroxide solution was further added to adjust the pH to 11.0, and then it was kept at 50 °C for 1 hour. Then, a high-pressure homogenizer (high-pressure homogenizer model PA2K, manufactured by Niro Soavi) was used to perform high-pressure homogenization at a pressure of 450 to 550 kgf / cm 2 .

[0147] (Purification treatment)

[0148] An equal amount of distilled water was added to the homogenized lysate obtained above. After centrifugation, the supernatant was removed and it was concentrated 2-fold. An aqueous sodium hydroxide solution (pH 11.0) equal to the amount of the removed supernatant was added to the concentrated aqueous suspension of PHA, and centrifugation was performed. Then, after removing the supernatant, water was added again to suspend it, 0.2 wt% sodium dodecyl sulfate and 1 / 100 wt of protease (Esperase, manufactured by Novozymes) based on PHA were added, and it was stirred at 50 °C while maintaining the pH at 10.0 for 2 hours. Then, the supernatant was removed by centrifugation and it was concentrated 4-fold. Further water was added to adjust the PHA concentration to 53.5 wt%. The volume median diameter of PHA particles (PHA primary particles) in the PHA aqueous suspension was measured, and the result was 2.5 μm.

[0149] (Granulation using a twin-screw extruder)

[0150] Sulfuric acid was added to the obtained PHA aqueous suspension to adjust the pH to 3.0. The resulting slurry was fed into a twin-screw extruder (manufactured by SUEHIRO EPM Co., Ltd., EA-20, barrel length / barrel diameter (L / D) = 12), and the slurry was extruded at a shaft speed (screw speed) of 30 rpm, an internal pressure of the apparatus of 0.1 Mpa, and a heater temperature of 150 °C. During the passage of the slurry through the twin-screw extruder, water in the slurry volatilized, and PHA aggregates were recovered through the outlet part of the apparatus. The obtained PHA aggregates are shown in Figure 7 . The volume median diameter of the obtained PHA aggregates was 883 μm. In addition, the volume median diameter of the PHA aggregates / the volume median diameter of the PHA primary particles was 353.2. Furthermore, the PHA content in the PHA aggregates was 98.9% by weight.

[0151] 〔Example 2〕

[0152] The temperature of the heater of the twin-screw extruder was set to 140 °C, and PHA aggregates were obtained in the same manner as in Example 1 except for this. The volume median diameter of the obtained PHA aggregates was 836 μm. In addition, the volume median diameter of the PHA aggregates / the volume median diameter of the PHA primary particles was 334.4. Furthermore, the PHA content in the PHA aggregates was 98.9% by weight.

[0153] 〔Example 3〕

[0154] A PHA aqueous suspension was obtained in the same manner as in Example 1 up to the purification treatment. Sulfuric acid was added to the PHA aqueous suspension to adjust the pH to 5.0, and the resulting slurry was fed into a twin-screw extruder (manufactured by Kurimoto Iron Works, Ltd., S2KRC mixer, L / D = 13.2) at a rate of 2.5 kg / h, and under the conditions of a shaft speed (screw speed) of 300 rpm, a heater temperature of 150 °C, and opening the decompression part 6 in Figure 3 to the atmosphere, the slurry was extruded, and PHA aggregates were obtained in the same manner as in Example 1 except for this. The volume median diameter of the obtained PHA aggregates was 474 μm. The volume median diameter of the PHA aggregates / the volume median diameter of the PHA primary particles was 189.6. Furthermore, the PHA content in the PHA aggregates was 98.9% by weight.

[0155] 〔Example 4〕

[0156] The slurry feeding rate was set to 5.0 kg / h, and in other respects, PHA aggregates were obtained by the same method as in Example 3. The volume median diameter of the obtained PHA aggregates was 611 μm. In addition, the volume median diameter of the PHA aggregates / the volume median diameter of the PHA primary particles was 244.4. Furthermore, the PHA content in the PHA aggregates was 98.9% by weight.

[0157] 〔Example 5〕

[0158] The shaft rotation speed was set to 100 rpm, and in other respects, PHA aggregates were obtained by the same method as in Example 4. The volume median diameter of the obtained PHA aggregates was 444 μm. In addition, the volume median diameter of the PHA aggregates / the volume median diameter of the PHA primary particles was 177.6. Furthermore, the PHA content in the PHA aggregates was 98.9% by weight.

[0159] 〔Example 6〕

[0160] The slurry feeding rate was set to 10.0 kg / h and the heater temperature was set to 165 °C, and in other respects, PHA aggregates were obtained by the same method as in Example 3. The volume median diameter of the obtained PHA aggregates was 1164 μm. In addition, the volume median diameter of the PHA aggregates / the volume median diameter of the PHA primary particles was 465.6. Furthermore, the PHA content in the PHA aggregates was 98.9% by weight.

[0161] [Comparative Example 1]

[0162] The temperature of the heater of the twin-screw extruder was set to 50 °C, and in other respects, it was carried out by the same method as in Example 1. As a result, a PHA aqueous suspension was discharged from the discharge part of the above twin-screw extruder, and no PHA aggregates were obtained.

[0163] 〔Results〕

[0164] According to the above examples and Figure 7 it can be seen that PHA can be manufactured by a simple operation by this manufacturing method.

[0165] Industrial Applicability

[0166] This manufacturing method can manufacture PHA by a simple operation, and thus can be advantageously used for the manufacture of PHA. In addition, PHA aggregates and the like obtained by this manufacturing method can be suitably used in agriculture, fishery, forestry, horticulture, medicine, hygiene products, clothing, non-clothing, packaging, automobiles, building materials, and other fields.

Claims

1. A method for manufacturing polyhydroxyalkanoate, the method comprising: (a) a step of preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less; and (b) a step of heating the aqueous suspension of polyhydroxyalkanoate prepared in the step (a) at a set temperature of 80 to 300 °C in a twin-screw extruder to cause the polyhydroxyalkanoate to aggregate.

2. The method for manufacturing polyhydroxyalkanoate according to claim 1, wherein the heating method in the step (b) is a method of using a twin-screw extruder heater and / or a method of directly injecting pressurized steam into the twin-screw extruder.

3. The method for manufacturing polyhydroxyalkanoate according to claim 1 or 2, wherein the value represented by the following formula (1) is 50 to 20,000, volume median particle diameter of the polyhydroxyalkanoate aggregate obtained in the step (b) / volume median particle diameter of the polyhydroxyalkanoate primary particles ··· (1).

4. The method for manufacturing polyhydroxyalkanoate according to claim 1 or 2, wherein in the step (a), the concentration of polyhydroxyalkanoate in the aqueous suspension of polyhydroxyalkanoate is 30 to 70% by weight.

5. The method for manufacturing polyhydroxyalkanoate according to claim 1 or 2, wherein the screw rotation speed of the twin-screw extruder is 30 to 1000 rpm.

6. The method for manufacturing polyhydroxyalkanoate according to claim 1 or 2, wherein the pressure in the twin-screw extruder is 0.01 to 0.5 Mpa.

7. The method for manufacturing polyhydroxyalkanoate according to claim 1 or 2, wherein a part of the screw of the twin-screw extruder is a screw having a reverse feeding function.

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