Method for producing metal nanoparticles and apparatus for producing metal nanoparticles

Abstract

To provide a method for efficiently producing metal nanoparticles and an apparatus for performing the method.SOLUTION: There is provided a method for continuously synthesizing metal nanoparticles by irradiating microwaves while feeding a raw material solution into a pipe, wherein in an apparatus where the piping includes a first piping and a second piping, the method comprises: a first synthesis step of synthesizing metal nanoparticles by irradiating microwaves to the first pipe while feeding the raw material solution into the first pipe until a fixed amount of the raw material solution and / or metal nanoparticles adheres to the inner wall of the first pipe; a switching step of switching the piping for supplying the raw material solution from the first piping to the second piping; a second synthesis step of synthesizing metal nanoparticles by irradiating microwaves to the second piping while feeding the raw material solution into the second piping; and a cleaning step of cleaning the first piping.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing metal nanoparticles. [Background technology]

[0002] Metal nanoparticles are being used and investigated for a variety of applications, such as catalysts, ink materials, and electronic component materials.

[0003] For example, Patent Document 1 discloses a method for producing metal nanoparticles, which includes a step of synthesizing metal nanoparticles by circulating a reaction liquid, which is a mixture of a first liquid containing at least a raw material salt of the metal nanoparticles and a second liquid containing a reducing agent for the raw material salt, through a reaction tube. The method includes a step of providing at least one of a reaction status determination means and a classification means as part of the synthesis step of the metal nanoparticles, and which uses a multiphase flow of gas and liquid in the reaction liquid in at least one reduction step.

[0004] Patent document 2 discloses a method for producing metal microparticles, in which a reaction liquid containing a metal precursor is circulated through a flow pipe, and electromagnetic waves are irradiated uniformly and intensively into the flow pipe along the length of the flow pipe, thereby uniformly heating the electromagnetic wave-irradiated space within the flow pipe along the flow direction, thereby generating metal microparticles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-104749 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-137226 Summary of the Invention [Problem to be solved by the invention]

[0006] A method for producing metal nanoparticles using a flow system in which a raw material solution is circulated through a resin tube and heated using a microwave heating device has been investigated. However, this method tends to result in adhesion of the metal nanoparticles and raw materials to the inner walls of the tube, causing clogging of the tube, abnormal heating, and reduced yield.

[0007] The present invention aims to provide a method for efficiently producing metal nanoparticles and an apparatus for carrying out the method. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and have discovered that in a method for continuously synthesizing metal nanoparticles by irradiating microwaves while feeding a raw material solution through a pipe, a first pipe and a second pipe are prepared as the pipes, a reaction is first carried out in the first pipe, and when a certain amount of raw material solution and / or metal nanoparticles adheres to the inner wall of the first pipe, the pipe for feeding the raw material solution is switched from the first pipe to the second pipe, and a reaction is carried out in the second pipe while simultaneously cleaning the first pipe, thereby making it possible to efficiently produce metal nanoparticles without reducing the productivity of the metal nanoparticles, and have arrived at the present invention.

[0009] An example aspect of this embodiment is described as follows. (1) A method for continuously synthesizing metal nanoparticles by irradiating microwaves while feeding a raw material solution into a pipe, the method comprising: a first synthesis step in an apparatus in which the pipes include a first pipe and a second pipe, in which microwaves are irradiated onto the first pipe while feeding the raw material solution into the first pipe, thereby synthesizing metal nanoparticles until a certain amount of raw material solution and / or metal nanoparticles adhere to the inner wall of the first pipe; a switching step in which the pipe for feeding the raw material solution is switched from the first pipe to a second pipe; a second synthesis step in which microwaves are irradiated onto the second pipe while feeding the raw material solution into the second pipe, thereby synthesizing metal nanoparticles; and a cleaning step in which the first pipe is cleaned. (2) The method according to (1), wherein the washing step is carried out simultaneously with the second synthesis step. (3) An apparatus for producing metal nanoparticles by irradiating a raw material solution with microwaves, the apparatus comprising a raw material solution storage tank, a cleaning liquid storage tank, a microwave irradiation device, a first recovery tank, and a second recovery tank, the raw material solution storage tank and the first recovery tank being connected by a first pipe, the raw material solution storage tank and the second recovery tank being connected by a second pipe, the first pipe and the second pipe comprising a microwave irradiation unit in which the microwave irradiation device is disposed, the cleaning liquid storage tank and the first pipe being connected at a portion upstream of the microwave irradiation unit by a third pipe, and the cleaning liquid storage tank and the second pipe being connected at a portion upstream of the microwave irradiation unit by a fourth pipe. (4) The apparatus according to (3), further comprising a device for detecting the raw material solution and / or metal nanoparticles attached to the inner wall of the pipe. (5) The apparatus described in (4), wherein when the detection device detects adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the pipe, the microwave irradiation device arranged in the microwave irradiation section moves between the microwave irradiation section of the first pipe and the microwave irradiation section of the second pipe. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for efficiently producing metal nanoparticles and an apparatus for carrying out the method. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing an outline of an embodiment of a manufacturing apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. The method and apparatus for producing metal nanoparticles of the present invention are not limited to the following embodiments, and can be embodied in various forms incorporating modifications and improvements that can be made by those skilled in the art without departing from the spirit of the present invention. Furthermore, although each embodiment described in this specification is independent, two or more of each embodiment can also be combined to form one embodiment of the present invention.

[0013] The symbol "to" used herein means a range having the numerical values ​​before and after it as the upper and lower limits. In numerical ranges described in stages in this specification, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit described in another stage. The upper or lower limit of a numerical range described herein may be replaced with a value shown in the examples.

[0014] First, the method for producing metal nanoparticles of the present invention will be described. The method of the present invention relates to a method for continuously synthesizing metal nanoparticles by irradiating a raw material solution with microwaves while feeding the raw material solution through a pipe.

[0015] In the present invention, the raw material solution is not particularly limited as long as it is a solution from which metal nanoparticles can be obtained by heating with microwaves.

[0016] The solvent is not limited as long as it dissolves materials such as a metal nanoparticle precursor, an organic dispersant, and a reducing agent, and is a polar solvent or ionic liquid that can absorb microwaves. Examples of solvents used in the raw material solution include low-boiling-point solvents with a boiling point of 300°C or less at one atmosphere. Examples of low-boiling-point solvents include, but are not limited to, water, alcohols such as methanol and ethanol, polyhydric alcohol solvents such as ethylene glycol, ketone solvents such as acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), other organic solvents, and mixtures of two or more of these low-boiling-point polar solvents.

[0017] The metal nanoparticle precursor is not limited as long as it dissolves in a solvent and generates metal ions, such as ions of precious metals, base metals, and alloys, such as gold, silver, platinum, copper, nickel, iron, and cobalt, or ions of two or more of these metals. Examples of metal nanoparticle precursors include inorganic metal salts such as metal halides (e.g., fluorides, chlorides, bromides, and iodides), metal sulfates, metal nitrates, metal phosphates, and metal cyanides; organic metal salts such as metal carboxylates and metal sulfonates; and metal complexes, including metal complex salts. Inexpensive metal nitrates, such as nickel nitrate and silver nitrate, are preferred as metal nanoparticle precursors. Alternatively, formates with reducing properties, such as nickel formate, can be used as the metal nanoparticle precursor.

[0018] The concentration of metal ions in the raw material solution is not limited as long as it is equal to or less than the saturated concentration, but is usually 0.05 mol / L (M) or more and usually 2.0 M or less, for example, 0.05 M to 2.0 M, 0.05 M to 1.0 M in one embodiment, 0.05 M to 0.5 M in one embodiment, and 0.05 M to 0.3 M in another embodiment.

[0019] The raw material solution contains an organic substance as a dispersant. Examples of dispersants include, but are not limited to, one or more dispersants selected from polyvinylpyrrolidone (PVP), dodecylamine (DDA), thiol-based polymers, polyvinyl alcohol (PVA), polyacrylic acid, polyacrylates, cyclodextrin, aminopectin, methylcellulose, polyethyleneimine cellulose, aliphatic amines, aliphatic carboxylic acids, and tannic acid. When the dispersant is a polymer, the molecular weight of the dispersant is, but is not limited to, for example, a weight-average molecular weight (Mw) of typically 1,000 or more, in one embodiment 8,000 or more, and in one embodiment 10,000 or more, and typically 50,000 or less, in one embodiment 40,000 or less, for example 1,000 to 50,000, in one embodiment 8,000 to 50,000, and in one embodiment 10,000 to 40,000.

[0020] The concentration of the dispersant in the raw solution is not limited, but is usually 3000 mmol / L (mM) or less, and in one embodiment, 1000 mM or less. Since the amount of dispersant in the raw solution is preferably small, the lower limit is not limited, but is usually 0.1 mM or more.

[0021] Furthermore, the raw material solution may contain a reducing agent.

[0022] The reducing agent is not limited. Examples of the reducing agent include citric acid or citrates such as trisodium citrate, disodium citrate, and monosodium citrate; oxalic acid or oxalate salts such as sodium oxalate; ascorbic acid or ascorbate salts such as sodium ascorbate; formic acid or formate salts such as sodium formate; DMF, NaBH4, hydrazine, and mixtures of two or more thereof. In one embodiment, the reducing agent for metal ions, particularly silver ions, is DMF. When the raw material solution contains DMF, DMF can function as both a solvent and a reducing agent.

[0023] The amount of reducing agent is not limited as long as it can reduce metal ions to a metal whose oxidation number is 0 through a redox reaction, but is typically 1.0 equivalent or more, and in one embodiment 4.0 equivalents or more, and typically 20 equivalents or less, and in one embodiment 15 equivalents or less, for example, 1.0 to 20 equivalents, and in one embodiment 4.0 to 15 equivalents, relative to the metal ions. Note that when the reducing agent for metal ions contains one or more functional groups capable of interacting with metals, such as a carboxy group, a hydroxy group, or an ether group, it can also function as a dispersant.

[0024] The raw material solution may further contain a base. The base functions as a pH adjuster, and examples thereof include 2-amino-1-butanol, sodium hydroxide, magnesium hydroxide, potassium hydroxide, and calcium hydroxide. The base may be a mixture of two or more types. The base may be used as a basic solution containing a base dissolved in a solvent such as water or alcohol. When the raw material solution contains a base, it is possible to promote the reduction reaction and increase the reaction rate, thereby enabling metal nanoparticles to be produced efficiently at a high concentration.

[0025] When the raw material solution further contains a base, the concentration of the base in the raw material solution is not limited as long as it is not more than the saturated concentration, but is usually 1 mmol / L (mM) or more, and in one embodiment, 50 mM or more and usually 250 mM or less. The concentration of the base in the raw material solution is, for example, 1 mM to 250 mM, and in one embodiment, 50 mM to 250 mM.

[0026] The pH of the raw material solution is not limited, but is usually pH5 to pH14.

[0027] The raw material solution may be composed of the metal nanoparticle precursor, solvent, dispersant, and optionally a reducing agent and base described above. In addition to these materials, the raw material solution may further contain additives that are commonly used in conventional methods for producing metal nanoparticles by microwave irradiation, such as chelating agents, such as ethylenediaminetetraacetic acid (EDTA) and / or salts thereof. The amount of additive is not limited. The amount of additive is typically 10 wt % or less, and in one embodiment, 3 wt % or less, based on the total weight of the raw material solution. Because additives do not necessarily need to be added, there is no lower limit for the amount of additive. However, if the raw material solution further contains an additive, the amount of additive is typically 0.1 wt % or more, based on the total weight of the raw material solution.

[0028] In the present invention, the order of addition of the materials, the addition temperature, the mixing method, the mixing time, etc. in preparing the raw material solution are not limited, and the materials are mixed so as to prepare a uniform raw material solution.

[0029] Next, in the first synthesis step in an apparatus equipped with a first pipe and a second pipe, the prepared raw material solution is sent to the first pipe, and the raw material solution flowing through the first pipe is irradiated with microwaves to heat the raw material solution and cause the reaction to proceed.

[0030] The first pipe may be a straight pipe or a spiral pipe. The size and shape of the first pipe are not limited as long as the microwaves are uniformly irradiated throughout the pipe.

[0031] The average inner diameter of the first pipe is usually 2 mm or more, and in one embodiment 4 mm or more, and usually 10 mm or less, and in one embodiment 8 mm or less, for example, 2 mm to 10 mm, and in one embodiment 4 mm to 10 mm.

[0032] The length of the first pipe is not limited, and is usually 1 m to 30 m, and in one embodiment, 10 m to 20 m.

[0033] The thickness of the first pipe is not limited, and is usually 1 mm to 3 mm, and in one embodiment, 1 mm to 2 mm.

[0034] The first pipe is provided with a microwave irradiation section for irradiating microwaves. The microwave irradiation section is the section of the pipe where microwaves are irradiated, and during synthesis, a microwave irradiation device is provided, and the microwave irradiation device is used to irradiate microwaves to the raw material solution flowing through the pipe, and the irradiated raw material solution in the pipe is heated. The raw material solution is usually reduced by the heating, thereby obtaining metal nanoparticles.

[0035] The material of the first pipe, particularly the material of the microwave irradiation section of the first pipe, is not limited as long as it can uniformly irradiate the raw material solution with microwaves. The material of the microwave irradiation section of the first pipe is, for example, a material that transmits microwaves, i.e., does not absorb microwaves, such as ceramic materials, ceramic materials made of silicon oxide such as glass and quartz, and non-conductive materials with a small relative dielectric constant ε and dielectric loss angle tanδ, such as resin.

[0036] Examples of the resin include fluororesins such as PFA (perfluoroalkoxy fluororesin), PTFE (polytetrafluoroethylene), and FEP (tetrafluoroethylene-hexafluoropropylene copolymer), nylon resin, silicone resin, polyethylene resin, acrylic resin, or mixtures thereof.

[0037] The arithmetic mean roughness Ra of the inner wall of the first pipe is usually 0.01 μm or more and usually less than 0.1 μm. The maximum height roughness Rz of the inner wall of the first pipe is usually 0.1 μm or more and usually less than 1.0 μm. By using a first pipe whose inner wall Ra and Rz are within the above ranges, it is possible to prevent the produced metal nanoparticles from adhering to the pipe.

[0038] The microwave irradiation device placed in the microwave irradiation section during synthesis is not particularly limited as long as it is a device capable of irradiating microwaves to the microwave irradiation section of the piping, but usually a device capable of continuously irradiating microwaves is used.

[0039] The microwave absorption power (E) of the raw material solution is usually 20 W / mL or more and usually 500 W / mL or less, for example, 20 W / mL to 500 W / mL, relative to the volume of the raw material solution.

[0040] Here, the microwave absorption power E of the raw material solution is calculated by dividing the microwave intensity (W) absorbed by the raw material solution, i.e., the value obtained by subtracting the reflected wave power irradiated and reflected from the raw material solution from the output of the microwave irradiation source (output - reflected wave power), by the volume (mL) of the raw material solution irradiated with that output. The reflected wave power can be measured using a power monitor in the microwave irradiation device.

[0041] In the microwave irradiation section of the first pipe, the raw material solution is heated to the reaction temperature during synthesis. The reaction temperature to which microwave irradiation raises the temperature can be appropriately changed depending on the reaction conditions (such as the type of solvent and the pressure during the reaction) and is not limited. The reaction temperature is usually 25°C or higher, and in one embodiment, 80°C or higher. The upper limit of the reaction temperature is not limited, but is usually below the boiling point of the solvent. For example, when the solvent is water, the reaction temperature is usually in the range of 25°C or higher and lower than 100°C at atmospheric pressure, and in one embodiment, 80°C to 90°C. Note that, in the present invention, when pressure is applied to the raw material solution, the reaction temperature can be higher than the boiling point of the solvent under atmospheric pressure. The boiling point of the solvent under the applied pressure may vary depending on the pressure. Therefore, in one embodiment, the reaction temperature is equal to or higher than the boiling point of the solvent under atmospheric pressure and lower than the boiling point of the solvent under the applied pressure.

[0042] The length of the microwave irradiation section in the first pipe is not limited and can be changed depending on the microwave irradiation device configured. The length of the microwave irradiation section is usually 0.1 m to 0.5 m.

[0043] The first pipe may be provided with a heat-retaining / cooling section downstream of the microwave irradiation section. The heat-retaining / cooling section is a section for keeping the metal nanoparticles (post-reaction suspension) produced in the raw material solution warm.

[0044] The heat-retaining / cooling section in the first pipe may be composed of pipes alone, or may include a heat-retaining device such as a heater or a cooler.

[0045] The insulation temperature in the heat-retaining / cooling section in the first pipe is not limited, but is usually below the reaction temperature, and the heat-retaining / cooling section has a temperature gradient from the reaction temperature to room temperature, for example, usually 80°C to 0°C. The lower limit of the insulation temperature is not limited, but is usually 0°C or higher, and in one embodiment, 20°C or higher. For example, when the solvent is water, the insulation temperature is usually in the range of 80°C to 10°C, and in one embodiment, 60°C to 20°C, at atmospheric pressure.

[0046] The length of the heat-retaining / cooling section in the first pipe is not limited. In one embodiment, the length of the heat-retaining / cooling section is long enough to cool from the reaction temperature to room temperature at room temperature. The length of the heat-retaining / cooling section is usually 1 m to 10 m.

[0047] By keeping the post-reaction suspension warm using a heat-retaining device, the growth of nuclei of metal nanoparticles in the resulting post-reaction suspension can be promoted, and the metal nanoparticles can be further homogenized (ripened).

[0048] The method of flowing the raw material solution is not limited as long as the raw material solution flows, for example, from the microwave irradiation section (upstream) of the first pipe to the heat-retaining / cooling section (downstream). The raw material solution can be flowed at a constant speed through a pipe, for example, a straight pipe or a spiral pipe.

[0049] The flow rate of the raw material solution flowing through the first pipe is not limited, but is usually 70 mL / min to 300 mL / min, and in one embodiment, 120 mL / min to 180 mL / min.

[0050] In one embodiment, pressure may be applied to the raw material solution. By applying pressure, the flow rate can be easily adjusted. In one embodiment, the pressure is 0.1 MPa to 1.0 MPa.

[0051] In the present invention, a reaction proceeds in the microwave irradiation section of the first pipe, producing metal nanoparticles in the raw material solution. After a certain amount of raw material solution and / or metal nanoparticles adheres to the inner wall of the first pipe, particularly the microwave irradiation section where the reaction is occurring, a switching step is performed in which the pipe for transporting the raw material solution is switched from the first pipe to the second pipe. After the pipe switching step is completed, a second synthesis step is performed in which microwaves are irradiated onto the transported raw material solution in the second pipe, as in the first pipe, to synthesize metal nanoparticles. The configuration of the second pipe (such as the microwave irradiation section and the heat-retaining / cooling section) and the synthesis conditions (such as microwaves, reaction temperature, flow rate, and pressure) are the same as those of the first pipe described above.

[0052] The adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the first pipe can be detected, for example, by visual inspection, pressure, reaction temperature, reaction time, or the like.

[0053] The term "certain amount" refers to an amount of the precursor solution and / or metal nanoparticles deposited on the inner wall of the pipe that makes it impossible to maintain the synthesis conditions for metal nanoparticles. In one embodiment, the term "certain amount" refers to an amount of the precursor solution and / or metal nanoparticles deposited on the inner wall of the pipe that accounts for 1% or more of the cross-sectional area of ​​the pipe (the area through which the precursor solution flows). In one embodiment, the term "certain amount" refers to an amount of deposition when the pressure applied to the precursor solution is 5% or more higher than the set pressure. In one embodiment, the term "certain amount" refers to an amount of deposition when the reaction temperature is 5% or more higher than the set temperature. In one embodiment, the term "certain amount" refers to an amount of deposition when the reaction time exceeds a certain time, for example, 30 minutes, 1 hour, 2 hours, or 3 hours. When the amount of deposition is determined based on the reaction time, the amount of deposition may be empirically determined through experiments. A person skilled in the art can calculate the amount of the precursor solution and / or metal nanoparticles deposited on the inner wall of the pipe per unit of time through several experiments and determine the reaction time required to reach the certain amount.

[0054] The adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the first pipe, particularly the microwave irradiation section, may be detected by, but is not limited to, a detection device such as a pressure gauge, a thermometer, or a clock. The installation location of the detection device is not limited, and it is installed in a location where each condition and physical property can be appropriately measured.

[0055] By switching from the first pipe to the second pipe, metal nanoparticles can be produced continuously without reducing productivity.

[0056] After the step of switching from the first pipe to the second pipe, the raw material solution and / or the metal nanoparticles adhering to the first pipe are washed in the washing step while the metal nanoparticles are synthesized in the second pipe.

[0057] The cleaning process is not limited as long as it can remove the raw material solution and / or metal nanoparticles adhering to the first pipe, and examples include sending pure water or a solution in which the synthesized metal nanoparticles dissolve, such as an acidic solution (hydrochloric acid, sulfuric acid, nitric acid, acetic acid, citric acid, etc.), for example, 10% nitric acid, or a basic solution (aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, etc.) to the first pipe.

[0058] The timing for starting the cleaning step is not limited as long as it is completed immediately after the switching step from the first pipe to the second pipe and before a certain amount of raw material solution and / or metal nanoparticles are confirmed to adhere to the inner wall of the second pipe in the second synthesis step. For example, if the second synthesis step takes 60 minutes and the cleaning step takes 10 minutes, the timing for starting the cleaning step is between immediately after the switching step and 50 minutes after the switching step. The cleaning step is preferably carried out immediately after the switching step from the first pipe to the second pipe, simultaneously with the second synthesis step. Note that "immediately after the switching step" generally means within one minute of the completion of the switching step.

[0059] By performing the cleaning step, in the second synthesis step, once a certain amount of raw material solution and / or metal nanoparticles has been confirmed to adhere to the inner wall of the second pipe, as in the first synthesis step, the pipe for delivering the raw material solution can be switched back from the second pipe to the cleaned first pipe. Microwaves can be irradiated onto the cleaned first pipe to synthesize metal nanoparticles again. After the step of switching to the first pipe, the second pipe to which the raw material solution and / or metal nanoparticles have adhered can be cleaned in the same manner as in the above-mentioned cleaning step, in preparation for switching back from the first pipe. This method allows for continuous production of metal nanoparticles without reducing productivity.

[0060] Next, one embodiment of a metal nanoparticle production apparatus for carrying out the production method of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the production apparatus produces metal nanoparticles by irradiating a raw material solution L with microwaves. FIG. 1A is a schematic illustration of the production apparatus showing the synthesis of metal nanoparticles in the first pipe 30 (and pipe cleaning in the second pipe 31) before a certain amount of raw material solution L and / or metal nanoparticles adheres to the inner wall of the first pipe 30 (first synthesis). FIG. 1B is a schematic illustration of the production apparatus showing the synthesis of metal nanoparticles in the second pipe 31 and pipe cleaning of the first pipe 30 after a certain amount of raw material solution L and / or metal nanoparticles adheres to the inner wall of the first pipe 30 (second synthesis). The metal nanoparticle production method of this embodiment can be easily carried out by using the metal nanoparticle production apparatus of this embodiment.

[0061] The production apparatus includes a raw solution tank 10 that stores a raw solution L, a pump 20 that sucks and pumps the raw solution L from the raw solution tank 10, a first recovery tank 50 and a second recovery tank 51 that collect and store a slurry suspension containing the generated metal nanoparticles or a cleaning waste liquid, a cleaning liquid tank 11 that stores a cleaning liquid, and a pump 21 that sucks and pumps the cleaning liquid L' from the cleaning liquid tank 11. In the production apparatus, the raw solution tank 10 and the first recovery tank 50 are connected by a first pipe 30, and the raw solution tank 10 and the second recovery tank 51 are connected by a second pipe 31. As shown in FIG. 1 , the raw solution tank 10 may be connected to the first pipe 30 or the second pipe 31 using a single pump 20 via selector valves 60, 61, and 62, such as a three-way cock, so that the raw solution tank 10 can be switched between the first pipe 30 and the second pipe 31, respectively. In this case, the raw material solution L can be transferred from the raw material solution storage tank 10 through (1) the switching valves 60 and 61 and the first pipe 30 to the first recovery tank 50 (FIG. 1A), or (2) the switching valves 60 and 62 and the second pipe 31 to the second recovery tank 51 (FIG. 1B). Alternatively, the raw material solution storage tank 10 may be connected to the first pipe 30 or the second pipe 31 separately using two different pumps (not shown). When the raw material solution storage tank 10 is connected to the first recovery tank 50 or the second recovery tank 51, a slurry-like suspension containing the generated metal nanoparticles is recovered in the first recovery tank 50 or the second recovery tank 51. The first pipe 30 and the second pipe 31 are each equipped with a microwave irradiation unit 40, which can serve as a reaction field. The microwave irradiation unit 40 includes a housing 42 for accommodating the microwave irradiation unit 40 through which the raw material solution L flows during synthesis, and an irradiation device 41 for irradiating microwaves to the microwave irradiation unit 40 in the housing 42. As described above, the manufacturing apparatus, for example, the microwave irradiation unit 40, may also include a detection device (not shown) for detecting the raw material solution L and / or metal nanoparticles adhering to the inner wall of the piping. Furthermore, a third pipe 32 connects the cleaning liquid-storage tank 11 to a portion of the first pipe 30 upstream of the microwave irradiation unit 40, and a fourth pipe 33 connects the cleaning liquid-storage tank 11 to a portion of the second pipe 31 upstream of the microwave irradiation unit 40.1, the cleaning liquid-storage tank 11 may be connected to the third pipe 32 or the fourth pipe 33 via selector valves 61, 62, and 63, such as three-way cocks, so that the cleaning liquid L' can be switched between the third pipe 32 and the fourth pipe 33 using a single pump 21. In this case, the cleaning liquid L' can flow from the cleaning liquid-storage tank 11 either (1) through the selector valve 63, the third pipe 32, the selector valve 61, the first pipe 30, and then to the first collection tank 50 (FIG. 1B), or (2) through the selector valve 63, the fourth pipe 33, the selector valve 62, the second pipe 31, and then to the second collection tank 51 (FIG. 1A). Alternatively, the cleaning liquid-storage tank 11 may be connected to the third pipe 32 or the fourth pipe 33 separately using two different pumps (not shown). When the cleaning liquid storage tank 11 is connected to the first recovery tank 50 or the second recovery tank 51, the cleaning waste liquid is recovered in the first recovery tank 50 and the second recovery tank 51. The first pipe 30 and the second pipe 31 may be provided with a heat-retaining / cooling unit downstream of the microwave irradiation unit 40. In this embodiment, for convenience, the fluids flowing through the first pipe 30 and the second pipe 31 are referred to as the raw material solution L (before and after the reaction) or the cleaning liquid L' (before and after cleaning). Furthermore, "upstream" refers to the direction of the location where the raw material solution L or the cleaning liquid L' before the synthesis of metal nanoparticles starts to flow, and "downstream" refers to the direction of the location where the suspension after the synthesis of metal nanoparticles or the cleaning waste liquid is finally recovered and stored.

[0062] As shown in FIG. 1A , in the first synthesis run, raw material solution L is pumped from raw material solution storage tank 10 by pump 20 and flows through microwave irradiation section 40 of first pipe 30. As it passes through microwave irradiation section 40, it is irradiated with microwaves by irradiation device 41 along with microwave irradiation section 40, forming a slurry-like suspension containing metal nanoparticles, which then flows to first recovery tank 50. The materials for first pipe 30, particularly microwave irradiation section 40, are as described above. Furthermore, the materials for the first pipe 30 other than microwave irradiation section 40 may be metals such as aluminum and stainless steel, in addition to the above-described materials. Furthermore, microwave irradiation section 40 may be a straight pipe, but it may also be a spiral pipe, for example. This allows for higher microwave irradiation efficiency compared to a straight pipe. The average inner diameter, thickness, length, and other properties of the pipe are as described above.

[0063] The raw material solution L is fed in the first pipe 30 until the synthesis of metal nanoparticles progresses and a certain amount of the raw material solution L and / or metal nanoparticles adheres to the inner wall of the first pipe 30 .

[0064] As described above, the production apparatus is configured so that the pipe for delivering the raw solution L can be switched from the first pipe 30 to the second pipe 31, and once a certain amount of raw solution L and / or metal nanoparticles have adhered to the inner wall of the first pipe 30, the pipe for delivering the raw solution L is switched from the first pipe 30 to the second pipe 31, as shown in Fig. 1B. For this switching, the raw solution storage tank 10, the first pipe 30, and the second pipe 31 may be connected by a three-way cock as described above.

[0065] 1B, in the second synthesis by this switching, raw material solution L is pumped from raw material solution storage tank 10 by pump 20, flows through microwave irradiation section 40 of second pipe 31, and is irradiated with microwaves by irradiation device 41 together with microwave irradiation section 40 as it passes through microwave irradiation section 40, becoming a slurry-like suspension containing metal nanoparticles, which flows to second recovery tank 51. The configurations of first pipe 30 and second pipe 31 are the same as described above.

[0066] In addition, in the microwave irradiation units 40 of the first pipe 30 and the second pipe 31, the housing 42 and the irradiation device 41 may be disposed in both of the microwave irradiation units 40. However, the housing 42 and the irradiation device 41 may be disposed only in the microwave irradiation unit 40 of the pipe where synthesis is occurring, depending on the pipe switching. For example, in the first pipe 30, as the synthesis of metal nanoparticles progresses, once a certain amount of raw material solution L and / or metal nanoparticles adhere to the inner wall of the first pipe 30, the housing 42 and the irradiation device 41 provided in the microwave irradiation unit 40 of the first pipe 30 may be configured to be movable to a location that will become the microwave irradiation unit 40 of the second pipe 31. For example, the housing 42 and the irradiation device 41 may be programmed to be movable to a location that will become the microwave irradiation unit 40 of the second pipe 31 once a detection device detects the adhesion of a certain amount of raw material solution L and / or metal nanoparticles to the inner wall of the first pipe 30.

[0067] 1B, a cleaning liquid storage tank 11 that stores a cleaning liquid L' is connected to the first pipe 30 upstream of the microwave irradiation unit 40 via a third pipe 32. Therefore, after the pipe for transporting the raw solution L is switched from the first pipe 30 to the second pipe 31, the cleaning liquid L' is pumped from the cleaning liquid storage tank 11 by a pump 21 to the first pipe 30, particularly to the portion of the pipe inner wall where a certain amount of raw solution L and / or metal nanoparticles are attached, for example, to the microwave irradiation unit 40, as shown in FIG. 1B, to clean the inside of the first pipe 30, and finally, as a cleaning waste liquid, flows to the first recovery tank 50. 1A, the fourth pipe 33 connecting the cleaning liquid-containing tank 11 with the second pipe 31 at a portion upstream of the microwave irradiation unit 40 is intended to clean the second pipe 31 when a certain amount of raw material solution L and / or metal nanoparticles adheres to the inner wall of the second pipe 31, particularly the microwave irradiation unit 40. Therefore, in order to switch between the third pipe 32 and the fourth pipe 33, the cleaning liquid-containing tank 11, the third pipe 32, and the fourth pipe 33 may be connected by a three-way cock as described above.

[0068] In this way, the production apparatus of the present invention makes it possible to easily carry out the method of the present invention, and to continuously produce metal nanoparticles without reducing productivity.

[0069] The raw material solution L sent by the pump 20 is pumped into the microwave irradiation unit 40. At this time, the pumped raw material solution L may be adjusted to a pressurized state by providing a pressure adjusting device (not shown) on the downstream side of the first pipe 30 and the second pipe 31. [Example]

[0070] The present embodiment will be described below with reference to examples, but the present invention is not limited to these examples.

[0071] Metal nanoparticles were synthesized according to the table below. The raw material solution used was silver nitrate as a precursor for the metal nanoparticles, PVP as a dispersant, and DMF as a reducing agent. The synthesis temperature was 90°C. The apparatus shown in Figure 1 was used for the synthesis in Example 1. In Table 1, in Example 1, "stage change" means a switching step, and washing is also carried out simultaneously with "synthesis." As a result, it was found that in Example 1, even if the synthesis time was shortened by 0.8 hours, metal nanoparticles could be synthesized while suppressing the occurrence of abnormal heating in the microwave irradiation part.

[0072] [Table 1]

[0073] The method and manufacturing apparatus of the present invention can deal with the adhesion of metal nanoparticles and the like to piping immediately after the adhesion, and therefore can synthesize metal nanoparticles continuously without significantly reducing the manufacturing efficiency.

Claims

1. A method for continuously synthesizing metal nanoparticles by irradiating a raw material solution with microwaves while feeding the raw material solution through a pipe, comprising: In an apparatus in which the piping includes a first piping and a second piping, a first synthesis step of synthesizing metal nanoparticles by irradiating microwaves onto the first pipe while feeding the raw material solution into the first pipe until a predetermined amount of the raw material solution and / or metal nanoparticles adheres to the inner wall of the first pipe; a switching step of switching the pipe for sending the raw material solution from the first pipe to the second pipe; a second synthesis step of synthesizing metal nanoparticles by irradiating the second pipe with microwaves while sending the raw material solution to the second pipe; and A cleaning step of cleaning the first pipe A method comprising:

2. 10. The method of claim 1, wherein the washing step is carried out simultaneously with the second synthesis step.

3. An apparatus for producing metal nanoparticles by irradiating a raw material solution with microwaves, The apparatus includes a raw material solution storage tank, a cleaning solution storage tank, a microwave irradiation device, a first recovery tank, and a second recovery tank; the raw material solution storage tank and the first recovery tank are connected by a first pipe, the raw material solution storage tank and the second recovery tank are connected by a second pipe; The first pipe and the second pipe include a microwave irradiation unit in which a microwave irradiation device is disposed, the cleaning liquid storage tank and the first pipe at a portion upstream of the microwave irradiation portion are connected by a third pipe; The cleaning liquid storage tank and the second pipe upstream of the microwave irradiation section are connected by a fourth pipe.

4. The apparatus according to claim 3 , further comprising a device for detecting the raw material solution and / or metal nanoparticles attached to the inner wall of the pipe.

5. The apparatus according to claim 4, wherein when the detection device detects adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the pipe, the microwave irradiation device arranged in the microwave irradiation section moves between the microwave irradiation section of the first pipe and the microwave irradiation section of the second pipe.

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