Method for producing polyhydroxyalkanoate fused product

Abstract

To provide a method for producing PHA, capable of suppressing generation of fine powder without using a binder.SOLUTION: A method for producing a PHA fused body, comprising a step (a) of dehydrating an aqueous PHA suspension to obtain a PHA wet powder having a water content of 5 to 37%, a step (b) of heating the obtained PHA wet powder at 75 °C to 95 °C to obtain a PHA powder having a water content of 0.5% or less, and a step (c) of heating the obtained PHA powder at 100 °C to 150 °C to obtain a PHA fused body.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a fused polyhydroxyalkanoate. [Background technology]

[0002] Polyhydroxyalkanoates (hereinafter sometimes referred to as "PHAs") are known to be biodegradable, and in recent years, their use has been promoted from the viewpoint of environmental considerations.

[0003] One of the advantages of PHA is that it can be produced by microorganisms using renewable plant materials. To utilize PHA produced by microorganisms, first, the microbial cells are disrupted to extract the PHA from the cells, thereby obtaining an aqueous suspension of PHA. The PHA is then recovered and purified from the aqueous suspension by filtration or other methods to obtain a cake-like PHA, after which the PHA cake is dried. For this drying process, a spray dryer, a fluidized bed dryer, a drum dryer, or the like is used, but a spray dryer is commonly used due to its simple operation (e.g., Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2018 / 070492 Summary of the Invention [Problem to be solved by the invention]

[0005] PHA produced by microorganisms is produced as a powder with a fine particle size. When such powdered PHA is dried, a large amount of fine powder is generated, which is a problem. In order to suppress the generation of such fine powder, a technique has been proposed in which PHA is spray-dried while being mixed with a binder. However, when a binder is used, the produced PHA naturally contains the binder as an impurity, which causes a problem of a decrease in the purity of the PHA.

[0006] In view of the above circumstances, one aspect of the present invention aims to provide a method for producing PHA that can suppress the generation of fine powder without using a binder. [Means for solving the problem]

[0007] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a fused PHA can be obtained by carrying out the steps of heating a wet PHA powder obtained by filtering an aqueous PHA suspension at a specific, relatively low temperature until the powder reaches a predetermined moisture content, and then further heating the powder at a specific, relatively high temperature, and that this method makes it possible to dry PHA without using a binder while suppressing the generation of fine powder during the drying process, thereby completing the present invention.

[0008] That is, one aspect of the present invention includes the following configuration.

[0009] [1] A method for producing a polyhydroxyalkanoate fused product, comprising: (a) a step of dehydrating an aqueous suspension of polyhydroxyalkanoate to obtain a wet polyhydroxyalkanoate powder having a moisture content of 5 to 37%; (b) a step of heating the obtained wet polyhydroxyalkanoate powder at 75°C to 95°C to obtain a polyhydroxyalkanoate powder having a moisture content of 0.5% or less; and (c) a step of heating the obtained polyhydroxyalkanoate powder having a moisture content of 0.5% or less at 100°C to 150°C to obtain a polyhydroxyalkanoate fused product. [2] The method for producing a polyhydroxyalkanoate fused body according to [1], which comprises, prior to the step (b), a step (a') of crushing the polyhydroxyalkanoate wet powder obtained in the step (a) so that the maximum diameter is 3.0 mm or less. [3] The method for producing a polyhydroxyalkanoate fused body according to [1] or [2], wherein the step (b) comprises a step of heating the polyhydroxyalkanoate wet powder by indirect heating. [4] A method for producing a polyhydroxyalkanoate fused body according to any one of [1] to [3], wherein the step (c) includes a moving step of heating the polyhydroxyalkanoate powder while moving it. [5] The method for producing a polyhydroxyalkanoate fused body according to any one of [1] to [4], wherein the transferring step includes a step of scraping off the polyhydroxyalkanoate powder using a blade. [6] The method for producing a polyhydroxyalkanoate fused material according to any one of [1] to [5], wherein the step (b) and the step (c) are carried out in the same system. [7] A method for producing a polyhydroxyalkanoate fused material according to any one of [1] to [6], wherein the proportion of polyhydroxyalkanoate microparticles having a particle size of 1 to 10 μm is 28.5% or less relative to the total amount of the dried polyhydroxyalkanoate obtained in step (c). [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a method for producing a PHA (fused body) that can suppress the generation of fine powder without using a binder. DETAILED DESCRIPTION OF THE INVENTION

[0011] One 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)."

[0012] 1. Overview of the Invention A conventional method for drying PHA is known to be spray drying an aqueous PHA suspension. However, as mentioned above, spray drying essentially requires the addition of a binder, which poses the problem of reducing the purity of the resulting PHA.

[0013] The present inventors investigated a new method for drying PHA, in which a PHA aqueous suspension is first dehydrated by filtration to obtain a wet PHA powder, and then the wet PHA powder is heated and dried. However, they discovered that when the wet PHA powder was heated at a relatively high temperature to quickly increase the dryness (reduce the moisture content), some of the dried PHA powder adhered to the inside of the apparatus, resulting in a new problem in that the entire wet PHA powder was not heated sufficiently and could not be dried sufficiently.

[0014] Having found the above problem, the inventors attempted to carry out the drying operation at a temperature lower than the above temperature in order to prevent the dried PHA powder from adhering to the inside of the drying apparatus, but discovered that a new problem arose in that the dried PHA obtained by the drying operation at such a relatively low temperature contained a large amount of fine powder.

[0015] Having encountered the above two new problems related to the drying temperature, the inventors further investigated methods for heating and drying a PHA moist powder. As a result, they discovered that by first heating the PHA moist powder at a relatively low temperature until it reaches a certain moisture content, and then further heating it at a relatively high temperature, the powdered PHA obtained by drying at a relatively low temperature can be fused to obtain a fused PHA, and as a result, the generation of fine powder during the drying process can be suppressed, leading to the completion of the present invention.

[0016] 2. Method for producing PHA fused body A method for producing a PHA fusion-bonded body according to one embodiment of the present invention (hereinafter referred to as "this production method") comprises the steps of: (a) dehydrating a PHA aqueous suspension to obtain a PHA wet powder having a moisture content of 5 to 37%, (b) heating the obtained PHA wet powder at 75°C to 95°C to obtain a PHA powder having a moisture content of 0.5% or less, and (c) heating the obtained PHA powder having a moisture content of 0.5% or less at 100°C to 150°C to obtain a PHA fusion-bonded body.

[0017] Because of the above-described configuration, the present production method can provide a PHA (fused body) without using a binder while suppressing the generation of fine powder. Because the present production method does not require the use of a binder, it can provide a PHA with higher purity, and by suppressing the generation of fine powder, it can improve the yield of PHA and also improve the safety of the production process.

[0018] <Process (a)> The present production method includes (a) a step (sometimes referred to as "step (a)") of dehydrating an aqueous PHA suspension to obtain a wet PHA powder having a moisture content of 5 to 37%.

[0019] (PHA aqueous suspension) First, the PHA aqueous suspension used in step (a) will be described in detail. In this specification, the PHA aqueous suspension refers to a solution in which PHA is suspended (dispersed) in water (aqueous medium) and has fluid properties. In addition to water, the PHA aqueous suspension may contain other solvents (e.g., water-compatible organic solvents), components derived from the PHA-producing microorganism (e.g., cell walls, proteins, etc.), and / or other compounds generated during purification.

[0020] PHA "PHA" is a general term for polymers containing hydroxyalkanoate as a monomer unit (monomer repeat unit) and is generally biodegradable. In particular, "PHA" herein refers to a (co)polymer containing hydroxyalkanoate repeat units at 50 mol% or more of the total monomer repeat units (100 mol%), and a resin composed of such a (co)polymer. Specific examples of hydroxyalkanoate repeat units constituting PHA include 3-hydroxybutanoic acid unit, 4-hydroxybutanoic acid unit, 3-hydroxypropionic acid unit, 3-hydroxypentanoic acid unit, 3-hydroxyhexanoic acid unit, 3-hydroxyheptanoic acid unit, 3-hydroxyoctanoic acid unit, and 2-hydroxypropionic acid unit. In this specification, the term "(co)polymer" encompasses both a homopolymer composed of only one type of monomer and a copolymer composed of two or more types of monomers.

[0021] 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.

[0022] P3HA is a 3-hydroxyalkanoate repeating unit of the formula: [—CHR—CH—CO—O—] (wherein R is C n H 2n+1 and n is an integer of 1 or more and 15 or less.) as an essential repeating unit.

[0023] Specific 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-hydroxyvalerate), poly(3-hydroxy Examples of suitable polyhydroxybutyrates include poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-2-hydroxypropionate), and poly(3-hydroxybutyrate-co-3-hydroxypropionate). Among these, P3HB, P3HB3HH, and P3HB4HB are preferred, with P3HB3HH and P3HB4HB being more preferred, due to the ease of industrial production using microorganisms.

[0024] In this specification, "poly(X-co-Y)" refers to a copolymer containing X repeating units and Y repeating units, 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 a 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 a P3HA may not be reflected in the name of the P3HA, provided that such a monomer does not significantly affect the physical properties of the P3HA. In other words, a P3HA may contain, in addition to the repeating units corresponding to its name, very small amounts of other repeating units.

[0025] 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 the total 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 is advantageous in that a resin product with superior rigidity can be provided. On the other hand, when the composition ratio of 3HB repeating units in P3HA is 99 mol% or less, it is advantageous in that a resin product with superior flexibility can be provided. The monomer composition ratio of P3HA can be measured by gas chromatography or the like (see, for example, WO 2014 / 020838).

[0026] P3HA can be produced by microorganisms. Examples of microorganisms capable of producing P3HA include Bacillus megaterium, a P3HB-producing bacterium discovered in 1925, as well as other naturally occurring microorganisms such as Cupriavidus necator (formerly Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. These microorganisms accumulate P3HB within their cells.

[0027] Known microorganisms 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). To increase P3HB3HH productivity, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bacteriol., 179, pp. 4821-4830 (1997)) is particularly preferred. In addition to the above, genetically modified microorganisms containing various P3HA synthesis-related genes can also be used depending on the desired physical properties of P3HA.

[0028] ·Method of manufacturing PHA aqueous suspension The PHA aqueous suspension used in step (a) is preferably a PHA aqueous suspension derived from a culture medium of a PHA-producing microorganism. Such a PHA aqueous suspension derived from a culture medium of a PHA-producing microorganism can be prepared, for example, by the following method: (1) culturing a microorganism capable of producing PHA; (2) inactivating the culture medium by heating to obtain an inactivated culture medium; (3) treating the inactivated culture medium with hydrogen peroxide to reduce the viscosity of the culture medium; (4) treating the hydrogen peroxide-treated inactivated culture medium with alkali; (5) adding a lytic enzyme (a cell wall-degrading enzyme) to the alkali-treated inactivated culture medium to lyse the microorganism cells and disperse the intracellular substances, including PHA, in the culture medium; (6) adding a protease to the culture medium to decompose the microorganism-derived substances other than PHA (particularly proteins); and (7) further adjusting the pH of the culture medium and adding a surfactant to decompose the microorganism-derived substances other than PHA (particularly cell membranes). Furthermore, the method may further include, if necessary, (8) a step of removing impurities in the aqueous suspension by centrifugation and / or filtration to purify the PHA.

[0029] The present production method may include, prior to step (a), a step of culturing a PHA-producing microorganism and preparing a PHA aqueous suspension from the culture solution, which includes one or more of the above-mentioned operations (a PHA aqueous suspension preparation step). When the present production method includes two or more of the above-mentioned operations, the order in which the operations are performed is not limited to the above-mentioned order.

[0030] (Dehydration operation) In step (a), the method for dehydrating the aqueous PHA suspension is not particularly limited as long as it can produce a wet PHA powder with the desired moisture content. Examples of the method include filtering the aqueous PHA suspension and centrifuging the aqueous PHA suspension.

[0031] The method for filtering the aqueous PHA suspension is not particularly limited as long as it allows the preparation of 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 cost-effective manner. That is, in step (a), it is preferable to dehydrate the aqueous PHA suspension by dead-end filtration to obtain a wet PHA powder. In other words, step (a) preferably includes a dead-end filtration step in which the aqueous PHA suspension is dead-end filtered. In this specification, "dead-end filtration" means "filtration by the dead-end filtration method."

[0032] Specific modes of dead-end filtration are not particularly limited, and examples include suction filtration, pressure filtration, centrifugal filtration, and gravity filtration. Among these, pressure filtration is preferred because it has the advantage of easily reducing the water content, and filter press filtration (FP filtration) is more preferred. That is, the PHA aggregate preparation step preferably includes a filter press filtration step in which the aqueous PHA suspension is filtered through a filter press. Note that filter press filtration is an operation in which the aqueous PHA suspension is squeezed and dehydrated, and a residue (in this production method, a wet PHA powder) is obtained.

[0033] When the PHA aqueous suspension is subjected to filter press filtration in step (a), 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 dehydration efficiency.

[0035] (PHA wet powder) The PHA wet powder obtained by step (a) will be described. The PHA wet powder obtained by step (a) is a residue obtained by dehydrating the PHA aqueous suspension, and is a solid composition containing PHA and water. The PHA wet powder may contain agglomerates formed by aggregation of PHAs due to water being held between the surfaces of multiple PHAs. In other words, the PHA wet powder obtained by step (a) is a concept that includes such agglomerates of PHA (and water).

[0036] The moisture content of the PHA wet powder obtained in step (a) is 5 to 37% by weight. By controlling the moisture content of the PHA wet powder in step (a) within the above range, the drying operation in the subsequent step (b) can be carried out more efficiently. The moisture content of the PHA wet powder obtained in step (a) is not particularly limited as long as it is 5 to 37% by weight, but is preferably 8 to 25% by weight, and more preferably 10 to 20% by weight. Note that the moisture content of the PHA wet powder referred to herein is a wet basis (WB) value, meaning the weight percentage of water in a total amount of 100% by weight of the PHA wet powder. Furthermore, the moisture content of the PHA wet powder referred to herein is a value measured by the method described in the Examples.

[0037] The diameter of the PHA wet powder (including PHA aggregates) obtained in step (a) is not particularly limited, but the maximum diameter is preferably 3.0 mm or less, and more preferably 2.0 mm or less, so that a PHA powder having the desired moisture content can be efficiently obtained in the subsequent step (b) (i.e., efficient heat drying can be achieved).In this specification, whether the maximum diameter of the PHA wet powder (including PHA aggregates) is equal to or less than the desired diameter can be determined by whether the PHA wet powder in question can pass through a sieve with openings of the above-mentioned desired diameter (PHA wet powder that has passed through a sieve with openings of the above-mentioned desired diameter is PHA wet powder whose maximum diameter is equal to or less than the above-mentioned desired diameter).

[0038] (Process (a')) In one embodiment of the present production method, the PHA wet powder obtained in step (a) may contain PHA wet powder (mainly PHA agglomerates) with a diameter exceeding the desired maximum diameter. In such cases, it is preferable to crush the PHA wet powder (mainly PHA agglomerates) and adjust (size) the particles so that their maximum diameter is a desired value or less (e.g., 3.0 mm or less, or 2.0 mm or less) before subjecting them to step (b). That is, the present production method preferably includes step (a') before step (b), in which the PHA wet powder (mainly PHA agglomerates) obtained in step (a) is crushed so that its maximum diameter is a desired value or less (e.g., 3.0 mm or less, or 2.0 mm or less).

[0039] In step (a'), the method for crushing (coarse crushing) the PHA wet powder is not particularly limited, and examples thereof include a method of mechanically breaking the powder using a crusher or screw, or a method of destroying the powder by impact such as dropping.

[0040] <Process (b)> This manufacturing method includes (b) a step (sometimes referred to as "step (b)") of heating the wet PHA powder obtained in step (a) at 75°C to 95°C to obtain a PHA powder having a moisture content of 0.5% or less.

[0041] Step (b) in this manufacturing method can also be said to be a step of heating and drying the above-mentioned PHA wet powder until its moisture content becomes 0.5% or less (basically, PHA wet powder with a moisture content of 0.5% or less will naturally become powdery).

[0042] (heating operation) In step (b), the method for heating the PHA wet powder is not particularly limited as long as it can heat the PHA wet powder within the above temperature range, and either direct heating or indirect heating can be applied, but indirect heating is preferred because it has excellent thermal efficiency and can reduce the cost required for the heating operation. That is, step (b) preferably includes a step of heating the PHA wet powder by indirect heating.

[0043] Specific examples of the method for indirectly heating the PHA wet powder include a method using a plate dryer, a method using a paddle dryer, and a method using a disk dryer.

[0044] In step (b), the temperature to which the wet PHA powder is heated is 75°C to 95°C. By controlling the heating temperature in step (b) within the above range, a portion of the resin (PHA) in the wet PHA powder (particularly the surface portion) is rapidly dried during step (b), preventing it from adhering to the heat transfer surface and inhibiting heat transfer from the heat source. As a result, it becomes possible to obtain a PHA powder from which moisture has been sufficiently removed (water content of 0.5% or less). The heating temperature in step (b) is not particularly limited as long as it is within the above range, but is more preferably 80°C to 93°C, and even more preferably 85°C to 90°C.

[0045] In step (b), the heating time for the PHA wet powder is not particularly limited as long as it can be heated until the moisture content of the PHA wet powder to be heated reaches the desired value (at least 0.5% or less), but it may be, for example, 10 minutes to 1 hour, or 20 to 40 minutes.

[0046] The heating operation in step (b) is preferably carried out while moving the PHA wet powder to be heated within the system (e.g., within a dryer) (i.e., step (b) preferably includes a moving step of moving the PHA wet powder to be heated). By including a moving step in step (b) of heating the PHA wet powder to be heated while moving it, adhesion of the dried PHA powder within the system can be suppressed.

[0047] In step (b), the method for moving the PHA wet powder during heating is not particularly limited, but a suitable example is a method in which the target PHA wet powder is scraped off with a blade. By using a blade to dry the PHA wet powder while scraping it off, uniform drying is possible, and a PHA powder with little unevenness in moisture content can be obtained.

[0048] (PHA powder) Step (b) can also be considered a step for obtaining a PHA powder having a moisture content of 0.5% or less. By reducing the moisture content of the PHA powder obtained in step (b) to 0.5% or less (by drying until the moisture content is 0.5% or less), it becomes possible to fuse the PHA powder particles together in the subsequent step (c), thereby making it possible to obtain a PHA (fused body) while suppressing the generation of fine powder. The moisture content of the PHA powder obtained in step (b) is not particularly limited as long as it is 0.5% or less, but is more preferably 0.4% or less, and even more preferably 0.3% or less. Furthermore, the lower limit of the moisture content is not particularly limited and may be 0%. Note that, in this specification, the moisture content of the PHA powder is a value measured by the method described in the Examples.

[0049] <Process (c)> This production method includes (c) a step (sometimes referred to as "step (c)") of heating the PHA powder having a moisture content of 0.5% or less obtained in step (b) at 100°C to 150°C to obtain a fused PHA body.

[0050] Step (c) in this production method can also be said to be a step of fusing PHA powder particles together to obtain a fused PHA. In this production method, during the fusion process, small particles (particles that can become fine powder) contained in the PHA powder fuse with each other or with relatively large particles, which is thought to reduce the proportion of small particles in the powder and also reduce the proportion of fine powder in the final dried PHA product.

[0051] (heating (fusion) operation) In step (c), the method for heating the PHA powder is not particularly limited as long as it can heat the PHA powder within the above temperature range, and either direct heating or indirect heating can be applied, but indirect heating is preferred because it has excellent thermal efficiency and can reduce the cost required for the heating operation. That is, step (c) preferably includes a step of heating the PHA powder by indirect heating.

[0052] Specific examples of the method for indirectly heating the PHA powder include a method using a plate dryer, a method using a paddle dryer, and a method using a disk dryer.

[0053] In step (c), the PHA powder is heated to a temperature of 100°C to 150°C. By setting the heating temperature in step (c) to 100°C or higher, the resin (PHA) that constitutes the PHA powder can be melted and heat-fused, while by setting the heating temperature to 150°C or lower, complete melting of the PHA powder can be suppressed, resulting in a fused PHA product with a particle shape that is easy to handle. The heating temperature in step (c) is not particularly limited as long as it is within the above range, but is more preferably 105°C or higher, even more preferably 110°C or higher, and even more preferably 115°C or higher, because this allows for the provision of a PHA with a smaller amount of fine powder.

[0054] In step (c), the time for heating the PHA powder is not particularly limited as long as it is possible to melt and heat-fuse the resin (PHA) that constitutes the PHA powder to obtain a fused body, but it is, for example, 1 to 30 minutes, or may be 3 to 10 minutes.

[0055] The heating operation in step (c) preferably includes a transfer step in which the PHA powder to be heated is moved within a system (e.g., a dryer). By including the transfer step in step (c), in which the PHA powder to be heated is heated while being moved, fusion of the molten PHA particles can be promoted and adhesion of the molten PHA to the system can be suppressed.

[0056] In step (c), the method for moving the PHA powder during heating is not particularly limited, but a suitable example is a method in which the target PHA powder is scraped off using a blade. By using a blade to dry the PHA powder while scraping it off, uniform drying and fusion are possible, and a dried PHA product with little unevenness in moisture content and little fine powder can be obtained.

[0057] In this manufacturing method, it is preferable to carry out steps (b) and (c) in the same system, since this can reduce costs related to the transportation of PHA powder (e.g., the time required for transportation and loss of PHA during the transportation process).

[0058] An example of a method for performing steps (b) and (c) in the same system is to use a drying device having two or more temperature zones that can be controlled to different temperatures. An example of such a drying device is a plate dryer. A plate dryer is a drying device consisting of multiple plates, each of which can be individually temperature-controlled, and heats an object to be heated while moving it from the upper plate to the lower plate.

[0059] For example, when using a plate dryer, the upper plate is heated to 75 to 95°C and the lower plate is heated to 100 to 150°C, making it possible to carry out steps (b) and (c) of the present manufacturing method in the same system.

[0060] (PHA fused body and dried PHA) In step (c), a dried PHA product is obtained, which is a mixture of PHA particles, which are fused together to form a fused PHA powder having a certain particle size, and unfused PHA powder or fused PHA particles that are partially fused but still have a small particle size. In other words, the present production method can be said to be a method for producing such a dried PHA product, or a method for obtaining a dried PHA product with a low content of PHA particles.

[0061] In this specification, "fused PHA" refers to fused PHA particles contained in a dried PHA product and having a particle size of more than 10 μm, and "fine PHA particles" refers to fused PHA particles having a particle size of 10 μm or less and unfused powder. The particle sizes of fused PHA and fine PHA particles can be measured using a particle size distribution analyzer.

[0062] In this specification, the amount of fine powder contained in the dried PHA product finally obtained by step (c) can be evaluated based on the ratio of PHA fine particles having a particle size of 1 to 10 μm to the total amount of the dried PHA product (i.e., the total amount of the fused PHA material and the PHA fine particles). In this specification, when the ratio of PHA fine particles having a particle size of 1 to 10 μm to the total amount of the dried PHA product is 28.5% or less, the dried PHA product can be evaluated as a PHA dry product with little fine powder (the generation of fine powder is suppressed), and it can be evaluated that the generation of fine powder is suppressed in the manufacturing process of the fused PHA product.

[0063] The lower the proportion of PHA fine particles having a particle size of 1 to 10 μm relative to the total amount of the dried PHA obtained by step (c), the less fine powder the dried PHA contains, and the more effectively the generation of fine powder during the production process of a fused PHA is suppressed. From the viewpoint of further suppressing the generation of fine powder during the production process of a fused PHA, the proportion of PHA fine particles having a particle size of 1 to 10 μm relative to the total amount of the dried PHA obtained by step (c) is preferably 28.5% or less, more preferably 26.0% or less, more preferably 24.0% or less, more preferably 22.0% or less, even more preferably 20.0% or less, and even more preferably 18.0% or less. There is no particular lower limit to the proportion of PHA fine particles having a particle size of 1 to 10 μm, and it may be, for example, 1.0% or more, or even 0%. In this specification, the ratio of PHA microparticles with a particle size of 1 to 10 μm to the total amount of dried PHA material is a value calculated based on the particle size distribution of the dried PHA material measured using a particle size distribution measuring device, as the abundance ratio of particles with a particle size of 1 to 10 μm, when the abundance ratio of particles with a particle size of 0.01 to 3500 μm is set to 100, and more specifically, it is a value measured and calculated under the conditions described in the examples.

[0064] In the dried PHA obtained by step (c), the higher the proportion of fused PHA particles having a particle size of 100 μm or more relative to the total amount of the dried PHA, the higher the degree of thermal fusion of the PHA powder in step (c). A high degree of thermal fusion in the dried PHA has the advantage of improving the fluidity of the dried PHA and making it easier to handle. Therefore, from the above perspective, the proportion of fused PHA particles having a particle size of 100 μm or more relative to the total amount of the dried PHA obtained by step (c) is preferably 63.0% or more, more preferably 65.0% or more, more preferably 67.0% or more, even more preferably 70.0% or more, and even more preferably 72.0% or less. Furthermore, the upper limit of the proportion of fused PHA particles having a particle size of 100 μm or more is not particularly limited, and may be, for example, 90.0% or more or 100%. In this specification, the ratio of PHA fused bodies having a particle size of 100 μm or more to the total amount of dried PHA is a value calculated based on the particle size distribution of the dried PHA measured using a particle size distribution measuring device, as the abundance ratio of particles of 100 μm or more, where the abundance ratio of particles of 0.01 to 3500 μm is set to 100; more specifically, it is a value measured and calculated under the conditions described in the examples.

[0065] The PHA fusion-bonded material obtained by this production method can be used as a molded product by molding it by a known molding method, such as injection molding, extrusion molding, blow molding, or compression molding. The PHA fusion-bonded material obtained by this production method can also be used as a foamed molded product by foaming it by a known method and then molding it. These molded products and foamed molded products made from the PHA fusion-bonded material obtained by this production method can be used for a variety of purposes, such as paper, film, sheet, tube, plate, rod, container (e.g., bottle container), bag, and parts. [Example]

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "P3HB3HH" is used as "PHA," and "PHA" in the examples can also be read as "P3HB3HH."

[0067] [Measurement method] Measurements in the examples and comparative examples were carried out by the following methods.

[0068] (moisture content) The moisture content of the PHA wet powder and PHA powder was measured using a heat-dry moisture meter ML-50 (manufactured by A&D Co., Ltd.). Specifically, the weight (w1) of the target PHA wet powder or PHA powder was first measured, and the target PHA wet powder or PHA powder after weight measurement was heated at 130°C. Heating was terminated when the rate of weight change fell below 0.05 wt% (WB) / min. The weight (w2) of the target PHA wet powder or PHA powder at the end of heating was measured, and the change in weight of the target PHA wet powder or PHA powder before and after heating (= w1 - w2) was taken as the amount of water contained in the weight of the target PHA wet powder or PHA powder. The moisture content of the target PHA wet powder or PHA powder was calculated using the following formula: Moisture content (wt%) of target PHA wet powder or PHA powder = {(w1-W2) / (w1)} x 100.

[0069] (Particle ratio of dry PHA) The particle proportions of the PHA dried material (proportion of PHA fine particles of 1 to 10 μm and proportion of PHA fused particles of 100 μm or more) were calculated by the following method: (1) The particle size distribution of the target PHA dry material was measured using a particle size distribution analyzer (MASTERSIZER 3000, Malvern Panalytical). The measurement was performed using a dry dispersion unit (AERO S, Malvern Panalytical) with the air pressure set to 1 bar.

[0070] (2) Based on the particle size distribution measured above, the abundance ratio of particles with a particle diameter of 1 to 10 μm was calculated as the proportion of PHA microparticles with a particle diameter of 1 to 10 μm, assuming that the abundance ratio of particles with a particle diameter of 0.01 μm to 3500 μm was 100, and the abundance ratio of particles with a particle diameter of 100 μm was calculated as the proportion of PHA fused bodies with a particle diameter of 100 μm or more.

[0071] (Degree of heat fusion) Based on the percentage of fused PHA particles having a particle size of 100 μm or more calculated by the above method, the degree of thermal fusion of the PHA powder in step (c) was evaluated according to the following criteria: + (Excellent degree of thermal fusion): The percentage of PHA fused particles with particle diameters of 100 μm or more is 63.0% or more. - (Poor degree of thermal fusion): The percentage of PHA fused bodies with particle diameters of 100 μm or more is less than 63.0%.

[0072] Example 1 (Preparation of bacterial culture solution) Ralstonia eutropha, as described in International Publication No. WO 2019 / 142717, was cultured using the method described in paragraphs

[0041] to

[0048] of the same document to obtain a bacterial cell culture broth containing PHA. The obtained PHA was a copolymer consisting of 3HB repeating units and 3HH repeating units (i.e., poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), and the composition ratio of the repeating units in the PHA (3HB unit / 3HH unit composition ratio) was 94 / 6 (mol / mol).

[0073] (inactivation) The bacterial cell culture solution obtained above was sterilized by heating and stirring at an internal temperature of 60-70°C for 7 hours to obtain an inactivated culture solution. The weight-average molecular weight of PHA in the inactivated culture solution was 1,920,000. The water content of the inactivated culture solution was 70% by weight.

[0074] (alkali treatment) To the inactivated culture solution obtained above, a 30 wt% aqueous solution of sodium hydroxide was added to adjust the pH to 9.0±0.5. While maintaining this solution at 65-75°C, 30 wt% aqueous solution of sodium hydroxide was continuously added to maintain the pH at 9.0±0.5 for 6 hours, thereby performing an alkali treatment on the culture solution. After the treatment, the weight-average molecular weight of PHA in the culture solution was 600,000, and the water content was 80 wt%.

[0075] (Neutralization and cell wall decomposition enzyme treatment) 10% sulfuric acid was added to the culture medium obtained above to adjust the pH to 6.5±0.2. Lysozyme (Fujifilm Wako Pure Chemical Industries, Ltd.), a cell wall-degrading enzyme, was added to the neutralized culture medium to a concentration of 100 ppm, and the mixture was kept at 50°C for 2 hours.

[0076] (Proteolytic enzyme treatment) After the lysozyme treatment, the protease Alcalase (Novozymes) was added to the culture medium to a concentration of 300 ppm, and the mixture was then maintained at 50°C for 2 hours while adjusting the pH to 9.0±0.2 using 30% by weight sodium hydroxide.

[0077] (Surfactant addition treatment) To the culture solution after the enzyme treatment obtained above, sodium dodecyl sulfate (Kao Corporation) was added in an amount of 0.6 to 1.0% by weight relative to the weight of the culture solution, and then the mixture was kept at 45°C for 2 hours while adjusting the pH to 11.0±0.2 using an alkaline aqueous solution.

[0078] (Centrifugal washing) The PHA aqueous suspension obtained by the above procedure was centrifuged (4500 rpm, 10 minutes), and the supernatant was removed to obtain a 2x concentrated PHA aqueous suspension. To this concentrated PHA aqueous suspension, an aqueous sodium hydroxide solution (pH 11.0±0.1) in an amount equal to the amount of the removed supernatant was added, and the mixture was centrifuged again (4500 rpm, 10 minutes), and the supernatant was removed. This procedure was repeated three times, and the PHA aqueous suspension was centrifuged and washed.

[0079] (pH adjustment) The PHA aqueous suspension after centrifugation was diluted with water to a solids concentration of 15% by weight, and then 10% sulfuric acid was added to adjust the pH to 3.7±0.2, followed by keeping the mixture at 60°C for 3 hours or more.

[0080] (Step (a)) The PHA aqueous suspension obtained by the above procedure was compressed at a pressure of 0.7 MPa using a filter press (AUTOPAC-PRO-6-14C, manufactured by HITZ Co., Ltd.) to obtain a solid PHA wet powder. The moisture content of the obtained PHA wet powder was 15%.

[0081] (Process (a')) The obtained PHA wet powder was roughly crushed, and the crushed material was passed through a vibrating sieve with 2 mm openings to adjust (size regulation) the maximum particle size of the PHA wet powder to 2.0 mm or less.

[0082] (Step (b) and Step (c)) The sized wet PHA powder obtained in the above step was fed into a plate dryer (manufactured by XingXing Co., Ltd.) at a rate of 20 kg / h. The fed wet PHA powder was dried for 30 minutes on a plate heated to 90°C until the moisture content was 0.3% or less, thereby obtaining a PHA powder (step (b)).

[0083] The resulting PHA powder was then heated for 5 minutes on a plate heated to 105°C in the same plate dryer to obtain a dried PHA product containing a fused PHA (step (c)). The particle ratios in the resulting dried PHA product are shown in Table 1.

[0084] Example 2 A dried PHA product containing a fused PHA was obtained in the same manner as in Example 1, except that the heating temperature in step (c) was changed to 110° C. Table 1 shows the particle ratio in the obtained dried PHA product.

[0085] Example 3 A dried PHA product containing a fused PHA was obtained in the same manner as in Example 1, except that the heating temperature in step (c) was changed to 115° C. Table 1 shows the particle ratio in the obtained dried PHA product.

[0086] Comparative Example 1 A dried PHA product containing a fused PHA was obtained in the same manner as in Example 1, except that the heating temperature in step (c) was changed to 90° C. Table 1 shows the particle ratio in the obtained dried PHA product.

[0087] Comparative Example 2 A dried PHA product containing a fused PHA was obtained in the same manner as in Example 1, except that the heating temperature in step (c) was changed to 95° C. Table 1 shows the particle ratio in the obtained dried PHA product.

[0088] Comparative Example 3 The same procedure as in Example 1 was carried out except that the heating temperature in step (b) was changed to 95°C. At the end of heating in step (b), PHA powder adhered to the inside of the drying device. The moisture content of this PHA powder was 0.92%, and it could not be dried sufficiently. Therefore, step (c) was not carried out, and a fused PHA body could not be obtained.

[0089] [Table 1]

[0090] 〔summary〕 The results of Examples 1 to 3 show that by performing two-stage heating consisting of steps (b) and (c), it is possible to dry and fuse PHA without using a binder while suppressing the generation of fine powder, thereby providing a fused PHA body. Furthermore, a comparison of Examples 1 to 3 with Comparative Examples 1 and 2 shows that when the heating temperature in step (c) is below 100°C, the PHA powder is not sufficiently fused, and as a result, the generation of fine powder cannot be sufficiently suppressed. Furthermore, a comparison of Examples 1 to 3 with Comparative Example 3 shows that when the heating temperature in step (b) is 95°C or higher, some of the dried PHA powder adheres to the inside of the apparatus, resulting in insufficient heating of the entire wet PHA powder and insufficient drying. [Industrial Applicability]

[0091] According to this production method, it is possible to dry PHA without using a binder while suppressing the generation of fine powder, and to provide a fused PHA product. Furthermore, molded articles using the fused PHA product produced 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 a polyhydroxyalkanoate fused material, comprising the steps of: (a) a step of dehydrating an aqueous suspension of polyhydroxyalkanoate to obtain a wet powder of polyhydroxyalkanoate having a moisture content of 5 to 37%; (b) heating the obtained polyhydroxyalkanoate wet powder at 75°C to 95°C to obtain a polyhydroxyalkanoate powder having a moisture content of 0.5% or less; and (c) heating the obtained polyhydroxyalkanoate powder having a moisture content of 0.5% or less at 100°C to 150°C to obtain a polyhydroxyalkanoate fused material.

2. Before the step (b), 2. The method for producing a polyhydroxyalkanoate fused body according to claim 1, further comprising: (a') a step of crushing the polyhydroxyalkanoate wet powder obtained in the step (a) so that the maximum diameter is 3.0 mm or less.

3. 2. The method for producing a polyhydroxyalkanoate fused body according to claim 1, wherein the step (b) comprises a step of heating the polyhydroxyalkanoate wet powder by indirect heating.

4. 2. The method for producing a polyhydroxyalkanoate fused body according to claim 1, wherein the step (c) comprises a moving step of heating the polyhydroxyalkanoate powder while moving it.

5. 2. The method for producing a polyhydroxyalkanoate fused body according to claim 1, wherein the transferring step includes a step of scraping the polyhydroxyalkanoate powder with a blade.

6. 2. The method for producing a polyhydroxyalkanoate fused material according to claim 1, wherein the steps (b) and (c) are carried out in the same system.

7. 2. The method for producing a polyhydroxyalkanoate fused material according to claim 1, wherein the proportion of polyhydroxyalkanoate fine particles having a particle size of 1 to 10 μm is 28.5% or less based on the total amount of the dried polyhydroxyalkanoate obtained in step (c).

Images