CN215746418U - System for preparing silver powder by continuous formate reduction - Google Patents
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- CN215746418U CN215746418U CN202121840351.5U CN202121840351U CN215746418U CN 215746418 U CN215746418 U CN 215746418U CN 202121840351 U CN202121840351 U CN 202121840351U CN 215746418 U CN215746418 U CN 215746418U
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Abstract
The utility model discloses a system for preparing silver powder by continuous formate reduction. The system comprises a reducing agent subsystem, a silver nitrate subsystem and a reaction subsystem, and comprises an impinging stream reactor and a pipeline reactor, wherein a discharge port of a reducing liquid batching kettle and a liquid outlet of a filtering device of the silver nitrate subsystem are communicated with a feed port of the impinging stream reactor through a pipeline with a control valve; and a post-processing subsystem. The method has the advantages that continuous production is adopted, no ammonia or hydrazine is generated in the reaction process, the method is safer and more reliable than the conventional route, the speed is high, fewer byproducts are generated, the post-treated wastewater can be recycled as a nitrogenous liquid fertilizer and a raw material solution, and finally the obtained product has high purity and concentrated particle size distribution.
Description
Technical Field
The utility model relates to a silver powder preparation system, in particular to a system for preparing silver powder by continuous formate reduction.
Background
The noble metal ultrafine powder is widely applied to optical materials, photocatalysis, microelectrode reaction, electronic slurry, conductive adhesive, printed circuits, bioengineering, medicines, catalytic industry and the like, and attracts the attention of a plurality of researchers. Among them, the ultrafine silver powder is useful for manufacturing paste, printing material, etc. in the microelectronics industry. The nano silver particles have high 3-order nonlinear polarizability and play an important role in the development of microcrystalline semiconductor glass and colored civil glass.
The nano silver powder comprises 2 types of nano flaky silver powder and nano spherical silver powder. The nano silver powder is used for replacing the micron silver powder used in the current market, and has the following advantages:
1. the electronic paste produced by the nano silver powder has smaller granularity of metal particles, and a screen with larger mesh can be used during screen printing, so that a surface coating with better compactness is obtained, and the working efficiency of screen operation is high;
2. can reduce the silver consumption and the production cost. According to a patent of German Laimei application physical research institute, the conductive adhesive prepared by replacing micron silver powder with nano silver powder can be used for welding metal and ceramic, the coating does not need to be too thick, the surface of the coating is flat, and the silver consumption can be saved by 50%;
3. because the melting point of the nano silver powder is usually lower than that of a coarse-grain object, the sintering temperature of the conductive paste prepared from the nano silver powder is usually lower than that of the common paste, so that the requirement on the high-temperature resistance of the substrate material is reduced, and even plastics and the like can be used as the substrate material.
Meanwhile, the formic acid and the salt thereof are convenient and efficient catalytic hydrogen transfer reducing agents and can be applied to various fields of organic synthesis, biochemistry and the like. The formate is low in price, convenient and easy to obtain, non-toxic, good in stability, capable of being used together with various filtering metal catalysts, mild in reaction conditions, easy to separate products, easy to recycle, strong in selectivity and high in yield when the formate is used for catalytic reduction reaction.
The patent publication No. CN1227148A, published as 1999, 09.01, discloses a method for producing high-purity high-dispersibility spherical ultrafine silver powder, which comprises using silver ingot as raw material, dissolving with nitric acid to form silver nitrate solution, reducing with formate, dissolving the silver powder obtained after reduction with nitric acid to form silver nitrate, adding ammonia water to prepare silver ammonia solution, and then re-dispersing and reducing to obtain ultrafine silver powder. Although formate is also used as a reducing agent, ammonia water is introduced into the system, so that the storage and production risks are increased, concentrated nitric acid is used for multiple times in the reaction process, the steps are very complicated, the method is not suitable for producing large-volume silver powder, the obtained silver powder is high in purity and good in dispersity, the particle size is difficult to continue to increase, and the particle size range of the silver powder cannot be effectively regulated.
Publication No. CN102407341A, published as Chinese utility model No. 2/11/2012, provides a method for preparing a surface-modified particle size mixed silver powder, which comprises adding silver nitrate aqueous solution, pH regulator, alcoholic solution of alcohol or ester surface modifier into reducing solution containing hydrazine hydrate or ascorbic acid, and reacting in a stainless steel reaction kettle with high shear stirring to obtain silver powder by one-step reduction and precipitation. Although the obtained silver powder has good dispersibility, high tap density and good filling property, the method has the disadvantages of large reagent dosage, wide particle size distribution range and insufficient silver powder purity, so that the electrical property performance is poor. The silver powder is prepared by using carbonate as a complexing agent and surfactant as a protective agent in the Chinese utility model patent with publication number CN1387968A and publication date 2003, 01.01.2003. Although the silver powder produced by the method has good sphericity, the steps are complicated, and the method has no industrial prospect. The Chinese utility model patent with publication number CN107096927A and publication date of 2017, 08 and 29 adopts ascorbic acid as a reducing agent, maleic acid as a dispersing agent and a reducing agent solution with acidity adjusted by nitric acid, the silver nitrate solution is added into the reducing agent solution for reaction to generate micron-sized silver powder, then ammonia water and ammonium chloride are added into the solution, and the product is obtained by standing and aging after even stirring. The silver powder prepared by the method has good dispersibility, the burning loss rate is lower than 0.5%, the purity of the silver powder is high, but the standing and aging time is too long in the actual production, and meanwhile, the post-treatment is complicated due to more introduced impurities.
At present, there are many methods for preparing silver powder by a liquid phase reduction method. Hydrogen peroxide is used as a reducing agent and organic glue is used as a dispersing agent in the Zheng and Zheng academic forces, silver nitrate is reduced from strong alkali liquor to obtain the ultrafine silver powder with the average particle size of 310nm, and factors influencing the quality of the silver powder are analyzed. The chemical industry college of Fuzhou university utilizes a reverse microemulsion system to obtain nano silver with the particle size of 20-30 nm under the reduction action of hydrazine hydrate at normal temperature (national non-ferrous metals institute, 1998, stage S2). The colleges of materials science and engineering of the university of zhong and nan explored methylcellulose as a dispersant, and in the reaction of preparing silver powder by a chemical liquid phase reduction method using ascorbic acid as a reduction system, the temperature and the concentration of the dispersant were adjusted to finally obtain silver powder with the particle size of 2.21 μm (proceedings of the university of afzechu (natural science edition): 2004, 2 nd year).
However, the existing liquid phase reduction method usually uses substances such as formaldehyde, hydrazine hydrate, sodium borohydride, glucose, polyalcohol, ascorbic acid and the like as reducing agents, a large amount of waste water is generated in the reaction process, and the environmental protection treatment cost is high.
SUMMERY OF THE UTILITY MODEL
The utility model aims to overcome the defects in the prior art and provide a system for preparing silver powder by continuously reducing formate.
The technical scheme adopted by the utility model for solving the problems is as follows:
a system for preparing silver powder by continuous formate reduction comprises a reducing agent subsystem, wherein the reducing agent subsystem comprises a formate batching kettle, an alkali liquor batching kettle and a reducing liquid batching kettle, a sedimentation device and a filtering device are sequentially arranged at the downstream of the formate batching kettle and are sequentially connected through a pipeline with a control valve, and a liquid material outlet of the filtering device and a discharge hole of the alkali liquor batching kettle are communicated with the reducing liquid batching kettle through the pipeline with the control valve;
the silver nitrate subsystem comprises a silver nitrate batching kettle, the reaction subsystem comprises an impinging stream reactor and a pipeline reactor, a sedimentation device and a filtering device are sequentially arranged at the downstream of the formate batching kettle and are sequentially connected through a pipeline with a control valve;
the reaction subsystem comprises an impinging stream reactor and a pipeline reactor, wherein a discharge port of the reducing liquid batching kettle and a liquid outlet of a filtering device of the silver nitrate subsystem are communicated with a feed port of the impinging stream reactor through a pipeline with a control valve;
the post-treatment subsystem comprises a separator, a drying device, an airflow crushing device and a screening machine, wherein a discharge port of the pipeline reactor is communicated with the separator through a pipeline with a control valve, solid materials of the separator are mechanically connected with the drying device through a solid material conveying mechanism, and the drying device, the airflow crushing device and the screening machine are all connected through a solid material conveying mechanism.
Preferably, the pipeline reactor is a normal pressure reaction kettle comprising a formate batching kettle, an alkali liquor batching kettle, a reducing solution batching kettle and a silver nitrate batching kettle, the stirring mode is a turbine type, and the heat transfer structure adopts jacket type heating.
Preferably, the arrangement of the pipelines in the pipeline reactor comprises a parallel mode, a coil mode and a plate mode.
Preferably, the separation mode of the separator adopts centrifugal separation, the drying mode adopts vacuum drying, and the washing solvent is one or more of absolute ethyl alcohol, acetone and deionized water.
A method for preparing silver powder by continuous formate reduction, comprising the following steps:
s1, mixing and dissolving solid formate powder and deionized water in a formate batching kettle, and obtaining a reaction solution A through a settling device and a filtering device;
s2, mixing and dissolving potassium hydroxide or sodium hydroxide and deionized water in an alkali liquor batching kettle to obtain reaction liquid B;
s3, mixing the reaction solution A, B in a reducing solution batching kettle in proportion, adding a surfactant, uniformly mixing to obtain a reducing solution mixed solution, and waiting for entering a reactor of the next step;
s4, mixing and dissolving silver nitrate powder and deionized water in a silver nitrate batching kettle, obtaining silver nitrate solution after passing through a settling device and a filtering device, and waiting for entering a next reactor;
s5, reacting the silver nitrate solution and the reducing solution mixed solution together through an impinging stream reactor to prepare suspension, continuously reacting in the pipeline reactor for a period of time through the pipeline reactor, and finally obtaining a solid-liquid two-phase through a separation device;
and S6, washing the obtained solid-phase filter cake with deionized water, drying the solid-phase filter cake by using a drying device, crushing the solid-phase filter cake into powder by using an airflow crushing device, and finally screening the powder by using a particle size screening device to obtain the product silver powder with the median diameter of 5-4000 nm.
Preferably, the molar ratio of formate ions to hydroxide ions in the mixing of the reaction solution A and the reaction solution B in the step S3 is 1 (0.1-10).
Preferably, the molar ratio of the silver ions to the formate ions in the mixed solution of the silver nitrate solution and the reducing solution in the step S5 is 1 (0.5-2).
Preferably, the temperature of the reaction solution in the impinging stream reactor in step S5 is between 20 ℃ and 300 ℃.
Preferably, the temperature of the suspension in the pipeline reactor in the step S5 is 20-300 ℃, the internal pressure of the pipeline reactor is 0.1-10 MPa, and the circulating reaction time in the pipeline reactor is 20-500 min.
Preferably, the pH value of the reaction solution in the impinging stream reactor and the pipeline reactor in the step S5 is 3-8.
Preferably, the surfactant is a compound having surface activating properties with a molecular weight of less than 2000, including gelatin, tween 80, PVA and PVP.
Preferably, the storage temperature in the formate batching kettle, the reducing liquid batching kettle and the silver nitrate batching kettle is between 20 and 95 ℃ during the reaction.
The utility model has the beneficial effects that:
1. the mode of using the impact reactor and the pipeline reactor realizes continuous production, and is favorable for generating products with narrow, uniform and stable particle size distribution compared with reaction kettle type batch reaction.
2. The product purity and yield are high.
3. The by-product potassium nitrate can be used as potassium-nitrogen liquid fertilizer, and the formate solution can be separated and recycled.
4. The reaction system has no ammonia and hydrazine, so that the method has no fear of generating explosives such as silver fulminate, silver nitride and the like, is convenient to store and transport and is beneficial to safe production.
Drawings
FIG. 1 is a simplified flow diagram of the process of the present invention;
FIG. 2 is a scanning electron microscope image of silver powder prepared according to the first embodiment of the present invention;
FIG. 3 is a scanning electron microscope image of silver powder prepared according to comparative example one of the present invention;
FIG. 4 is a scanning electron microscope image of silver powder prepared according to comparative example II of the present invention;
FIG. 5 is a scanning electron microscope image of silver powder prepared in example two of the present invention;
FIG. 6 is an X-ray diffraction spectrum of silver powder obtained in example III of the present invention.
Detailed Description
The following detailed description of embodiments of the utility model, but the utility model can be practiced in many different ways, as defined and covered by the claims.
A system for preparing silver powder by continuous formate reduction comprises a reducing agent subsystem, wherein the reducing agent subsystem comprises a formate batching kettle, an alkali liquor batching kettle and a reducing liquid batching kettle, a sedimentation device and a filtering device are sequentially arranged at the downstream of the formate batching kettle and are sequentially connected through a pipeline with a control valve, and a liquid material outlet of the filtering device and a discharge hole of the alkali liquor batching kettle are communicated with the reducing liquid batching kettle through the pipeline with the control valve;
the silver nitrate subsystem comprises a silver nitrate batching kettle, the reaction subsystem comprises an impinging stream reactor and a pipeline reactor, a sedimentation device and a filtering device are sequentially arranged at the downstream of the formate batching kettle and are sequentially connected through a pipeline with a control valve;
the reaction subsystem comprises an impinging stream reactor and a pipeline reactor, wherein a discharge port of the reducing liquid batching kettle and a liquid outlet of a filtering device of the silver nitrate subsystem are communicated with a feed port of the impinging stream reactor through a pipeline with a control valve;
the post-treatment subsystem comprises a separator, a drying device, an airflow crushing device and a screening machine, wherein a discharge port of the pipeline reactor is communicated with the separator through a pipeline with a control valve, solid materials of the separator are mechanically connected with the drying device through a solid material conveying mechanism, and the drying device, the airflow crushing device and the screening machine are all connected through a solid material conveying mechanism.
Specifically, a formate batching kettle, an alkali liquor batching kettle, a reducing liquid batching kettle and a silver nitrate batching kettle are all normal-pressure reaction kettles, the stirring mode is a turbine type, and a heat transfer structure adopts jacket type heating; the arrangement mode of the pipelines in the pipeline reactor comprises a parallel mode, a coil pipe mode and a tower plate mode; the separation mode of the separator adopts centrifugal separation, the drying mode adopts vacuum drying, and the washing solvent is one or more of absolute ethyl alcohol, acetone and deionized water.
The following describes an example of the specific size selection of the equipment and the process control parameters through specific embodiments.
Example 1
Dissolving and mixing potassium formate solid powder and deionized water in a formate batching kettle with the volume of 50L, preparing a 2.0mol/L potassium formate solution after the solution passes through a multiple sedimentation filtering device, uniformly mixing the potassium formate solution with a 1.5mol/L potassium hydroxide solution with the same volume in a reducing solution batching kettle with the volume of 100L, simultaneously adding a PVA solution with the mass fraction of 1% as a surfactant, and preheating to 60 ℃; on the other side, mixing high-purity silver nitrate powder and deionized water in a silver nitrate batching kettle with the volume of 100L to prepare 1.5mol/L silver nitrate solution, and preheating to 60 ℃;
respectively enabling a reducing solution and a silver nitrate raw material solution to pass through an impact reactor at feeding flow rates of 30L/min and 35L/min to form gray black slurry, enabling the gray black slurry to enter a parallel pipeline reactor with a reaction temperature of 60 ℃ and a reaction pressure of 0.5MPa at a discharging flow rate of 50L/min to continuously react for 30min, enabling the discharged material to enter a separating device, carrying out centrifugal filtration, washing for 4 times with deionized water, carrying out vacuum drying at 70 ℃ to obtain gray black silver powder, wherein the median diameter is 320nm, the purity is 99.88%, the yield is 99.78%, and an SEM electron microscope image is shown in an attached figure 2.
Comparative example 1
Uniformly mixing 2.0mol/L potassium formate solution and 1.5mol/L potassium hydroxide solution with the same volume to prepare 42L formate reducing solution, introducing the formate reducing solution and 49L silver nitrate solution with the concentration of 1.5mol/L into a 100L horizontal reaction kettle, adding 1% by mass of PVA solution serving as a surfactant, stirring and reacting for 30min in the 100L horizontal reaction kettle at the reaction temperature of 60 ℃, separating and washing, and performing vacuum drying at 70 ℃ to obtain the silver powder, wherein the median particle size is 155nm, the purity is 95.67%, the yield is 87.64%, and an SEM electron microscope picture is shown as an attached figure 3.
Comparing example 1 with comparative example 1, under the same reaction concentration and reaction time conditions, the product particles obtained by continuous production through the impinging stream reactor and the pipeline reactor become uniform spheres under the observation of an SEM (scanning electron microscope), while the product particles directly obtained by sectional heating in a 100L horizontal reaction kettle do not completely react, a large amount of strip-shaped particles remain, the subsequent detection product silver purity is low, and the actual yield is not as high as the result obtained by continuous reaction through the impinging stream reactor and the pipeline reactor.
Comparative example 2
Referring to example 1, 1.5mol/L potassium hydroxide solution introduced into a reducing solution preparation kettle is replaced by deionized water with the same volume to finally obtain the gray black silver powder, wherein the median diameter is 207nm, the purity is 99.13%, the yield is 99.42%, and an SEM electron micrograph is shown in figure 4.
The SEM images of comparative example 1 and comparative example 2 clearly show that a small amount of agglomeration occurs in the SEM image 4 of the product prepared under the conditions of comparative example 2, a plurality of silver powder particles are agglomerated into a ring-like structure, and the uniformity of the product particles is poor. The product obtained in example 1 with potassium hydroxide lye added has clearly dispersed particles and is in an independent spherical structure. The reason is that the potassium hydroxide alkali liquor has a defoaming effect, carbon dioxide gas generated in the reaction process is effectively neutralized, the generation of silver powder particles is not influenced by the gas, the occurrence of agglomeration is reduced, in addition, the addition of the potassium hydroxide alkali liquor can effectively promote the reaction to be continuously carried out, formic acid generated by reduction reacts with potassium hydroxide for the second time to obtain formate again, and the reduction capability of formate reducing solution is improved. The particle size, purity and actual yield of the product added with the potassium hydroxide lye are all improved.
Example 2
Referring to example 1, sodium formate solution with concentration of 2.5mol/L and sodium hydroxide solution with equal volume concentration of 2.5mol/L are mixed to prepare reducing solution, and Tween 80 with mass fraction of 1.5% is added as surfactant and preheated to 80 ℃.
Respectively enabling a reducing solution and a silver nitrate raw material solution with the concentration of 5.0mol/L to pass through an impact reactor at feeding flow rates of 30L/min and 25L/min to form grey black slurry, enabling the grey black slurry to enter a parallel pipeline reactor with the reaction temperature of 80 ℃ and the reaction pressure of 0.8MPa at a discharge flow rate of 50L/min to continuously react for 60min, discharging the slurry to enter a separating device, centrifugally filtering, washing with deionized water for 4 times, and performing vacuum drying at 70 ℃ to obtain the grey-white silver powder, wherein the median diameter is 2.87 mu m, the purity is 99.92%, the yield is 99.46%, and an SEM electron microscope image is shown as an attached figure 5.
Example 3
Referring to example 1, the formula of the reducing solution is changed from the mixing of potassium formate and potassium hydroxide into the mixing solution of ammonium formate and ammonia water, other experimental conditions are not changed, the mixture reacts in a parallel pipeline reactor for 45min, and then the mixture is dried in vacuum to obtain gray black silver powder, wherein the median diameter is 200nm, the purity is 99.98%, the yield is 99.76%, and the X-ray diffraction spectrogram of the silver powder is shown in figure 6.
Example 4
Dissolving and mixing potassium formate solid powder and deionized water in a formate preparation kettle with the volume of 50L, preparing a 1.0mol/L potassium formate solution after the solution passes through a multiple sedimentation filtering device, uniformly mixing the potassium formate solution and a 1.0mol/L potassium hydroxide solution in a reducing solution preparation kettle with the volume of 100L according to the volume ratio of 5:2, simultaneously adding a gelatin solution with the mass fraction of 1% as a surfactant, and preheating to 75 ℃; on the other side, mixing high-purity silver nitrate powder and deionized water in a silver nitrate batching kettle with the volume of 100L to prepare a silver nitrate solution with the volume of 3.0mol/L, and preheating to 75 ℃.
The method comprises the steps of enabling a reducing solution and a silver nitrate raw material solution to pass through an impact reactor at feeding flow rates of 40L/min and 20L/min respectively to form dark brown slurry, enabling the dark brown slurry to enter a parallel pipeline reactor with a reaction temperature of 75 ℃ and a reaction pressure of 1.0MPa at a discharging flow rate of 45L/min to continuously react for 20min, enabling the discharged material to enter a separating device, carrying out centrifugal filtration, washing 3 times with deionized water, washing 1 time with absolute ethyl alcohol finally, and carrying out vacuum drying at 70 ℃ to obtain gray black silver powder, wherein the median diameter is 50nm, the purity is 99.95%, and the yield is 99.81%.
Example 5
Dissolving and mixing potassium formate solid powder and deionized water in a formate preparation kettle with the volume of 50L, preparing a 2.0mol/L potassium formate solution after the solution passes through a multiple sedimentation filtering device, uniformly mixing the potassium formate solution and a 1.5mol/L potassium hydroxide solution in a reducing solution preparation kettle with the volume of 100L according to the volume ratio of 4:3, simultaneously adding 1% of PVP solution as a surfactant, and preheating to 60 ℃; on the other side, mixing high-purity silver nitrate powder and deionized water in a silver nitrate batching kettle with the volume of 100L to prepare 1.5mol/L silver nitrate solution, and preheating to 60 ℃.
The method comprises the steps of enabling a reducing solution and a silver nitrate raw material solution to pass through an impact reactor at feeding flow rates of 20L/min and 30L/min respectively to form grey black slurry, enabling the grey black slurry to enter a parallel pipeline reactor with a reaction temperature of 60 ℃ and a reaction pressure of 0.5MPa at a discharging flow rate of 40L/min to continuously react for 30min, enabling the discharged material to enter a separating device, carrying out centrifugal filtration, washing 3 times with deionized water, washing 1 time with absolute ethyl alcohol finally, and carrying out vacuum drying at 70 ℃ to obtain grey black silver powder, wherein the median diameter is 291nm, the purity is 99.79% and the yield is 99.81%.
Example 6
Dissolving and mixing potassium formate solid powder and deionized water in a formate preparation kettle with the volume of 50L, preparing a 3.0mol/L potassium formate solution after the solution passes through a multiple sedimentation filtering device, uniformly mixing the potassium formate solution and a 3.0mol/L potassium hydroxide solution in a reducing solution preparation kettle with the volume of 100L according to the volume ratio of 3:5, simultaneously adding a PVA solution with the mass fraction of 4% as a surfactant, and preheating to 95 ℃; on the other side, mixing high-purity silver nitrate powder and deionized water in a silver nitrate batching kettle with the volume of 100L to prepare 5.0mol/L silver nitrate solution, and preheating to 95 ℃.
Respectively enabling a reducing solution and a silver nitrate raw material solution to pass through an impact reactor at feeding flow rates of 40L/min and 25L/min to form grey green slurry, enabling the grey green slurry to enter a plate type pipeline reactor with a reaction temperature of 125 ℃ and a reaction pressure of 1.5MPa at a discharge flow rate of 50L/min to continuously react for 120min, enabling the discharged material to enter a separating device, centrifugally filtering, washing for 3 times with deionized water, washing for 1 time with absolute ethyl alcohol, and performing vacuum drying at 70 ℃ to obtain grey white silver powder, wherein the median diameter is 4.47 mu m, the purity is 99.91% and the yield is 99.74%.
Example 7
Dissolving and mixing potassium formate solid powder and deionized water in a formate preparation kettle with the volume of 50L, preparing a 0.5mol/L potassium formate solution after the solution passes through a multiple sedimentation filtering device, uniformly mixing the potassium formate solution and the 0.5mol/L potassium hydroxide solution in a reducing solution preparation kettle with the volume of 100L according to the volume ratio of 3:1, simultaneously adding a PVA solution with the mass fraction of 1% as a surfactant, and preheating to 90 ℃; on the other side, mixing high-purity silver nitrate powder and deionized water in a silver nitrate batching kettle with the volume of 100L to prepare 1.5mol/L silver nitrate solution, and preheating to 90 ℃.
The method comprises the steps of enabling a reducing solution and a silver nitrate raw material solution to pass through an impact reactor at feeding flow rates of 30L/min and 15L/min respectively to form dark gray slurry, enabling the dark gray slurry to enter a plate-type pipeline reactor with a reaction temperature of 100 ℃ and a reaction pressure of 1.0MPa at a discharging flow rate of 50L/min to continuously react for 90min, enabling the discharged material to enter a separating device, carrying out centrifugal filtration, washing 3 times with deionized water, washing 1 time with absolute ethyl alcohol finally, and carrying out vacuum drying at 70 ℃ to obtain gray black silver powder, wherein the median diameter is 680nm, the purity is 99.90%, and the yield is 99.94%.
Example 8
Dissolving and mixing potassium formate solid powder and deionized water in a formate batching kettle with the volume of 50L, introducing 10% formic acid into the solution, adjusting the pH of the solution to be less than 1, preparing a formate solution with the potassium ion concentration of 2.0mol/L through a multiple sedimentation filtering device, uniformly mixing the formate solution with an isovolumetric 1.5mol/L potassium hydroxide solution in a reducing solution batching kettle with the volume of 100L, simultaneously adding a PVA solution with the mass fraction of 1% as a surfactant, and preheating to 80 ℃; on the other side, mixing high-purity silver nitrate powder and deionized water in a silver nitrate batching kettle with the volume of 100L to prepare 1.5mol/L silver nitrate solution, and preheating to 80 ℃.
The method comprises the steps of enabling a reducing solution and a silver nitrate raw material solution to pass through an impact reactor at feeding flow rates of 25L/min and 25L/min respectively to form gray slurry, enabling the gray slurry to enter a coil pipe type pipeline reactor with a reaction temperature of 80 ℃ and a reaction pressure of 0.5MPa at a discharging flow rate of 40L/min to continuously react for 180min, enabling the discharged material to enter a separating device, carrying out centrifugal filtration, washing for 3 times with deionized water, washing for 1 time with absolute ethyl alcohol finally, and carrying out vacuum drying at 70 ℃ to obtain the dark gray silver powder, wherein the median diameter is 1.03 mu m, the purity is 99.96%, and the yield is 99.84%.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A system for preparing silver powder by continuous formate reduction is characterized in that,
the system comprises a reducing agent subsystem, wherein the reducing agent subsystem comprises a formate batching kettle, an alkali liquor batching kettle and a reducing liquid batching kettle, a sedimentation device and a filtering device are sequentially arranged at the downstream of the formate batching kettle and are sequentially connected through a pipeline with a control valve, and a liquid material outlet of the filtering device and a discharge hole of the alkali liquor batching kettle are communicated with the reducing liquid batching kettle through a pipeline with a control valve;
the silver nitrate subsystem comprises a silver nitrate batching kettle, the reaction subsystem comprises an impinging stream reactor and a pipeline reactor, a sedimentation device and a filtering device are sequentially arranged at the downstream of the formate batching kettle and are sequentially connected through a pipeline with a control valve;
the reaction subsystem comprises an impinging stream reactor and a pipeline reactor, wherein a discharge port of the reducing liquid batching kettle and a liquid outlet of a filtering device of the silver nitrate subsystem are communicated with a feed port of the impinging stream reactor through a pipeline with a control valve;
the post-treatment subsystem comprises a separator, a drying device, an airflow crushing device and a screening machine, wherein a discharge port of the pipeline reactor is communicated with the separator through a pipeline with a control valve, solid materials of the separator are mechanically connected with the drying device through a solid material conveying mechanism, and the drying device, the airflow crushing device and the screening machine are all connected through a solid material conveying mechanism.
2. The system of claim 1, wherein the formate batching kettle, the lye batching kettle, the reducing liquid batching kettle and the silver nitrate batching kettle are all normal pressure reaction kettles, the stirring mode is a turbine type, and the heat transfer structure adopts jacketed heating.
3. The system of claim 1, wherein the arrangement of the tubes within the tube reactor comprises a parallel, coil, or tray arrangement.
4. The system of claim 1, wherein the separator is operated in a centrifugal mode and in a vacuum mode.
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