A continuous production apparatus and process for silver nanowires

Abstract

This invention belongs to the field of new material preparation / nanomaterial synthesis technology, and relates to a continuous production device and process for silver nanowires. Addressing the problems of poor batch stability, high energy consumption at scale, and insufficient product uniformity in existing technologies, this invention employs a modular and compact layout of raw material pretreatment, microchannel reaction, continuous flow purification, and drying and packaging units. Through ultra-turbulent mixing with a cluster of microchannel mixers, dynamic temperature control in multiple temperature zones, and a flexible reagent substitution scheme, efficient continuous production is achieved. The product is highly crystalline silver nanowires, suitable for flexible electronic devices, transparent conductive films, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of new material preparation / nanomaterial synthesis technology, specifically involving an industrial preparation process and system for silver nanowires based on continuous hydrothermal synthesis. It focuses on solving problems such as poor batch stability, high energy consumption in large-scale production, and insufficient product uniformity in existing technologies. Through the integrated innovation of dynamic pressure balance control, enhanced mass and heat transfer, and continuous flow purification system, it achieves high-efficiency production at the ton level per year. Background Technology

[0002] This invention relates to the field of silver nanowire synthesis, and more particularly to the background technology of chemical synthesis processes in industrial-scale preparation. Silver nanowires, due to their excellent electrical, optical, and mechanical properties, have wide applications in flexible electronic devices, transparent conductive films, and biosensors. However, while existing chemical synthesis processes can achieve large-scale production, they each have their own technical bottlenecks, making it difficult to achieve the optimal balance between high yield, high uniformity, low energy consumption, and environmental friendliness.

[0003] The chemical synthesis technology of industrial-grade silver nanowires mainly includes the following four types of method systems: The polyol method uses ethylene glycol as a bifunctional solvent and reducing agent, silver nitrate as a precursor, and polyvinylpyrrolidone (PVP) as a dispersant, and carries out the reduction reaction at high temperatures of 160–200℃. However, this method easily generates byproducts such as silver particles and nanorods, requiring complex purification processes such as multi-stage centrifugation and recrystallization. Furthermore, residual halides can reduce product purity, and the high-temperature, long-duration reaction significantly increases energy consumption.

[0004] The hydrothermal / solvothermal method relies on a closed high-pressure reactor to construct a high-temperature and high-pressure environment for reducing silver precursors. However, it is highly sensitive to parameters such as the sealing of the reaction system and the volume of the solution, resulting in insufficient batch stability. At the same time, it is difficult to achieve large-scale production due to the limited reactor volume.

[0005] Microwave-assisted methods achieve rapid and uniform heating of the reaction system through microwave radiation, and can complete the reduction of silver precursors in organic solvents such as ethylene glycol within minutes, significantly reducing energy consumption; however, dedicated microwave reaction equipment is required, resulting in high initial investment costs, and uneven microwave field distribution can easily lead to local over-reduction, affecting the uniformity of nanowire morphology.

[0006] Electrochemical methods deposit nanowires in situ on the electrode surface by electrolyzing silver salt solutions, which has the advantage of mild process conditions. However, they also have technical bottlenecks such as low yield and the need for excessive surfactants to maintain growth stability. In addition, the treatment of electrolysis byproducts is difficult and the environmental compatibility is poor. At present, it is still mainly in the laboratory research stage.

[0007] Existing nanowire synthesis technologies generally suffer from bottlenecks in continuous production: laboratory-scale batch reactors suffer from significant temperature gradients due to insufficient mass transfer efficiency, and are limited by reactor volume, making industrial scale-up difficult. To overcome these common technical obstacles, it is urgent to develop a systematic solution integrating equipment, process, and control to achieve efficient, stable, and low-cost continuous production of silver nanowires.

[0008] Current industrial-scale preparation technologies for silver nanowires heavily rely on silver nitrate as a precursor, but these technologies suffer from issues such as the risk of halide residues, limitations in reduction kinetics, and sensitivity to cost fluctuations. The decomposition of silver nitrate may introduce nitrate residues, reducing product purity, and its reduction rate is difficult to precisely control, leading to the formation of byproducts (such as silver particles and nanorods).

[0009] Furthermore, the traditional process of using ethylene glycol as the sole solvent / reducing agent and PVP as the sole dispersant suffers from bottlenecks such as limited solvent selection and dispersant functionality. Ethylene glycol is prone to carbonization at high temperatures, leading to coking in the reactor after long-term use, while PVP struggles to simultaneously achieve nanowire morphology control and surface functionalization. Therefore, there is an urgent need to develop flexible synthesis systems that are compatible with multiple precursors and allow for solvent-dispersant substitution, in order to improve process stability and expand application scenarios.

[0010] The chemical synthesis processes and problems described in this section should not be considered an exhaustive list of existing technologies or an exclusive description of any unmentioned directions for improvement. Unless otherwise stated, those skilled in the art should not interpret the processes and problems described in this section as generally known or adopted technical solutions. Summary of the Invention

[0011] This disclosure provides an industrial-scale production system for silver nanowires, a dedicated reaction device, and an optimized production process, covering key technologies such as scaled-up reaction process, selection of reaction equipment, enhancement of mass and heat transfer, and continuous production control.

[0012] The first aspect relates to a scaled-up production process for silver nanowires, characterized by comprising: By calculating the selection parameters of the core mixing unit, the pressure vessel level is matched by comprehensively considering the ethylene glycol vapor pressure, air expansion partial pressure, and the amount of chemical reaction gas generated. The core mixing unit adopts a double-layer hydraulic self-tightening flange seal, and is equipped with pressure monitoring instruments, exhaust processors, and exhaust pressure setting valves to achieve precise control of the internal pressure of the unit at 0.8-1.2MPa.

[0013] A high-temperature, high-pressure static metal microchannel mixer cluster is adopted, integrating a point jet flow mixing module. The microchannel array has a channel diameter of 1-3mm, and the inner wall is uniformly sprayed with a 0.2μm polytetrafluoroethylene coating to improve corrosion resistance and mass transfer efficiency. The top cover of the mixer has three one-way valves with uniformly distributed inlets in a ring, which are used to introduce solvent, silver precursor and dispersant respectively. The heterogeneous system is ultraturbulently mixed by chaotic flow sedimentation technology to ensure the uniformity of nanowire morphology.

[0014] A multi-temperature zone dynamic temperature control strategy is established: an external circulation plate heat exchanger is used in the 80℃ melting zone, and a positive temperature coefficient (PTC) heating film (heating power adjustable range of 500-1500W) built into the heating layer of the mixing device is activated in the 160℃ reaction stage. An integrated embedded thermocouple (temperature measurement accuracy ±0.5℃) is used to achieve precise temperature control. A 5-10mm thick perfluoroether rubber filler insulation layer is set under the top cover of the mixing device to reduce heat loss, reduce the temperature gradient, and adjust the material residence time through flow feedback.

[0015] The second aspect provides industrial-grade mixing and separation equipment, specifically including: The system is equipped with a pre-sealed centrifuge tube system (500 mL per tube), and uses a large-capacity refrigerated high-speed floor-standing multi-stage variable speed centrifuge with a speed of 300-30000 rpm and a temperature of 4℃–10℃, combined with pulsed ultrasonic dispersion (20kHz ultrasonic probe array, pulse mode 5s working / 2s intermittent).

[0016] The modular production line features a compact layout of a high-temperature, high-pressure static metal microchannel mixer cluster (with a fixed base), centrifugal unit, and drying and packaging unit. The microchannel array is connected below the heating layer of the mixing device, and a drain valve is connected in series behind the array to regulate the product discharge rate. A spiral 316L stainless steel coil or an external heat exchange unit is added to the oil bath device to reduce energy consumption in the preheating stage through a segmented temperature control strategy.

[0017] The third aspect involves building a production verification and quality control system, using a UV-Vis absorption spectrometer to provide real-time feedback on nanowire diameter distribution data, and establishing a production batch traceability database to record key parameters such as aspect ratio, surface roughness, and crystallinity for each batch of products.

[0018] The fourth aspect provides methods for equipment selection and cost control, specifically implemented as follows: The modular equipment layout enables the high-temperature, high-pressure static metal microchannel mixer cluster unit, centrifugal purification unit, and drying and packaging unit to form a compact production line.

[0019] This technical solution achieves a scale-up of silver nanowire production from laboratory level to industrial level through systematic innovation in equipment, process, and control; the overall production cost is significantly reduced compared to traditional scale-up solutions, providing an industrial foundation for the large-scale application of flexible micro-nano materials.

[0020] The silver nanowire preparation system of this invention supports various alternatives to silver sources and chemical reagents. Conventional alternatives include silver perchlorate and silver acetate, achieved by precisely controlling the reaction temperature and concentration to match the reduction kinetics of different silver salts. For example, silver acetate requires a higher concentration and longer reaction time, as its residual acetate ions are easily volatilized at high temperatures, reducing surface contamination; silver perchlorate requires a lower concentration and controlled temperature to suppress side reactions caused by strong oxidation. The innovative solution uses sodium silver thiosulfate instead of silver ammonia complex, combined with a microfluidic reactor, avoiding the explosion risk caused by ammonia decomposition at high temperatures, achieving precise control of nanowire diameter, and is suitable for the preparation of ultrafine transparent electrodes.

[0021] Regarding solvent / reducing agent substitution, the high-temperature solvent propylene glycol requires an anchor stirrer and an increased stirring rate of 300–400 rpm to overcome the high viscosity mass transfer limitation; the ethanol-acetone fractional precipitation method can replace the supercritical CO2 system to achieve rapid purification of nanowires and reduce energy consumption.

[0022] Dispersants include hydroxypropyl cellulose and functionalized ionic liquids. The former allows for controllable thickness of the surface coating layer through substitution degree regulation, while the latter, such as 1-butyl-3-methylimidazolium hexafluorophosphate, has both dispersing and hydrophobic modification functions. Attached Figure Description

[0023] The accompanying drawings exemplify embodiments and form part of the specification, serving together with the textual description to explain exemplary implementations of the embodiments. The illustrated embodiments are for illustrative purposes only and do not limit the scope of the claims. Throughout the drawings, the same reference numerals refer to similar but not necessarily identical elements.

[0024] Figure 1 This is a schematic diagram of the silver nanowire raw material mixing device of the present invention.

[0025] Figure 2 This is a schematic cross-sectional view of the silver nanowire raw material mixing device of the present invention.

[0026] As shown in the figure: 1. Inlet check valve; 2. Top cover; 3. Insulation layer; 4. Heating layer; 5. Base; 6. Liquid level gauge; 7. Pressure monitoring instrument; 8. Exhaust processor; 9. Exhaust pressure setting valve; 10. Drain valve.

[0027] Figure 3 This is an industrial system flow diagram of the continuous preparation process of silver nanowires described in this invention.

[0028] As shown in the figure: 11. Raw material; 12. Mixing device; 13. Multi-tube reactor; 14. Stream divider; 15. Solid-liquid separator; 16. Waste liquid; 17. Cleaning agent; 18. Product.

[0029] Figure 4 This is a scanning electron microscope image of the product of this invention.

[0030] Figure 5 X-ray powder diffraction pattern of the product of this invention Detailed Implementation

[0031] The industrial production implementation scheme of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are used to exemplify the core technical innovations and large-scale implementation path of the present invention. Those skilled in the art can make adaptive adjustments within the scope defined by the claims.

[0032] Combined with appendix Figures 1 to 2 The mixer body is made of 316L stainless steel and has an internal microchannel array with an equivalent diameter of ≤1000μm. The inner wall of the channel is uniformly sprayed with a 0.2μm diamond coating to improve its resistance to ethylene glycol corrosion.

[0033] The core mixing zone employs a chaotic flow settling design, inducing superturbulent mixing through a multi-stage baffle structure and radial turbulence fins to ensure homogenization of the silver halide precursor and solvent / dispersant. The sealing system utilizes perfluoroether rubber packing combined with a double-layer hydraulic self-tightening flange to achieve pressure resistance stability. The cross-sectional view shows the integrated location of the built-in PTC heating film, which achieves precise temperature control via an embedded thermocouple.

[0034] Microchannel reactor selection and pressure balance model, specifically including the following explanations: Operating conditions calculation: The operating temperature is 160℃, the vapor pressure of the raw material ethylene glycol is about 30kPa, the partial pressure of air expansion at 160℃ is about 145kPa, the total internal pressure is 175kPa, and a high-temperature and high-pressure static metal microchannel mixer with a pressure resistance of not less than 420kPa (safety factor 1.5) (316L stainless steel body, perfluoroether rubber sealing packing, double-layer hydraulic self-tightening flange seal) is selected; by adjusting the exhaust pressure setting valve, the internal pressure of the device is precisely controlled at 0.8–1.2MPa.

[0035] The operating temperature is 160℃, the vapor pressure of the raw material ethylene glycol is about 30kPa, the expansion partial pressure of air at 160℃ is about 145kPa, the total internal pressure gauge is 175kPa, and a high-temperature and high-pressure static metal microchannel mixer (316L stainless steel body, FFKM sealing packing) with a pressure resistance of not less than 420kPa (safety factor 1.5) is selected.

[0036] Structural parameters: The dimensions of a single high-temperature and high-pressure static metal microchannel mixer are 75×70mm. The bottom is fixed to the base, and six units are connected in parallel to form a reaction cluster. The top cover of the mixer is equipped with three one-way valves for liquid inlet, which respectively introduce ethylene glycol, silver nitrate and PVP dispersant. The microchannel array has a diameter of 1-3mm, and the inner wall is sprayed with a 0.2μm polytetrafluoroethylene inert coating, which can withstand long-term corrosion from ethylene glycol.

[0037] High-shear premixing unit: A rotor-stator disperser (10,000 rpm) is added to the front end of the one-way valves at the three inlets of the mixing device to achieve micron-level dispersion of PVP / silver salt (particle size D90≤5μm).

[0038] Zoned temperature control device: The dissolution zone (80℃) adopts external circulation heat exchange, and the reaction zone (160℃) uses PTC thin film heating (power 1000W, response time <10s), with embedded thermocouples to achieve temperature control accuracy of ±0.5℃; the perfluoroether rubber insulation layer under the top cover is 8mm thick, which effectively reduces the temperature gradient inside the device.

[0039] Centrifuge unit: The first stage separation uses a large-capacity refrigerated high-speed centrifuge (25,000-35,000 rpm, G value ≥2,000g), with a single batch processing capacity of 5L; a pulsed ultrasonic disperser is used to improve the recovery rate of silver nanowires.

[0040] Ultrasonic dispersion optimization: A 20kHz ultrasonic probe array is used, and the temperature is controlled to ≤45℃ in pulse mode (5s working / 2s intermittent) to prevent nanowire breakage.

[0041] Continuous flow reactor: A PTFE tubular reactor (6mm inner diameter, 200m total length, multi-channel parallel connection) is used to improve the production rate of silver nanowires.

[0042] Equipment layout: The oil bath device, reaction vessel, centrifuge unit, and drying tower are arranged in a U-shaped assembly line.

[0043] Combined with appendix Figure 3As shown in the diagram, this schematic exemplifies the integrated production line layout and core equipment composition. The system begins with the supply and pretreatment unit (including preheating or premixing) of raw materials (including silver halide precursors, solvent ethylene glycol, dispersant PVP, etc.). The core reaction stage employs a parallel-configured cluster of high-temperature, high-pressure static metal microchannel mixers, designed based on a precise pressure balance model, to achieve ultraturbulent mixing and precise temperature control in heterogeneous systems. The reacted slurry then enters a continuous flow purification unit, primarily consisting of a large-capacity refrigerated high-speed centrifuge unit for primary separation, combined with a pulsed ultrasonic dispersion device to optimize nanowire recovery. The purified wet silver nanowire material is then transported to the drying and packaging unit to complete the final product preparation. The diagram illustrates the compact U-shaped flow line layout of each functional module (microchannel reaction cluster, centrifuge unit, ultrasonic dispersion, drying and packaging, etc.), as well as the flow direction of materials and possible energy / control signals.

[0044] This flowchart illustrates how the present invention achieves large-scale, efficient, and stable production of high-purity, highly uniform silver nanowire products from raw materials through modular equipment integration, continuous flow operation, and dynamic control strategies. It should be noted that this diagram is merely an illustrative representation of the process flow and equipment association; specific implementation details (such as valves, instruments, auxiliary pipelines, etc.) may be adjusted according to actual engineering requirements and do not constitute a limitation of the present invention.

[0045] Combined with appendix Figure 4 and Figure 5 As shown, numerous nanowires with a diameter of approximately 5 nanometers are visible. These nanowires are non-oriented and dispersed, with uniform diameters and lengths exceeding 5 micrometers. The diffraction peaks of the face-centered cubic silver crystals are also visible, with 2θ values ​​at 38.1 degrees (indicating the 111 crystal plane), 44.3 degrees (indicating the 200 crystal plane), 64.4 degrees (indicating the 220 crystal plane), and 77.5 degrees (indicating the 311 crystal plane). Based on these characterization results, the product is clearly a highly crystalline pure silver nanowire.

[0046] The above embodiments are merely illustrative, and those skilled in the art can make equivalent substitutions within the scope of the claims.

Claims

1. A continuous production apparatus for silver nanowires, characterized in that, The system includes a core mixing unit, a purification unit, a drying and packaging unit, and a modular connection structure. The core mixing unit is a high-temperature, high-pressure static metal microchannel mixer cluster. Each mixer in the cluster includes: a mixer body made of 316L stainless steel, fixedly connected to a base at the bottom, and sealed to a top cover via a double-layer hydraulic self-tightening flange; a top cover with three evenly distributed one-way valves at the inlet in a ring shape, and a level gauge and pressure monitoring instrument symmetrically arranged in the center. A vent pressure setting valve and a vent outlet are connected in series on one side of the pressure monitoring instrument. The mixer comprises: a heat insulation layer, located below the top cover and attached to the inner wall of the main body, made of perfluoroether rubber filler with a thickness of 5-10mm; a heating layer, located below the heat insulation layer, internally fitted with a PTC heating film with a heating power adjustment range of 500-1500W, wherein the PTC heating film integrates an embedded thermocouple with a temperature measurement accuracy of ±0.5℃; and a microchannel array, connected to the bottom of the main body of the mixer, with a channel diameter of 1-3mm and a 0.2μm polytetrafluoroethylene coating uniformly sprayed on the inner wall, wherein a drain valve is connected in series behind the microchannel array.

2. The continuous production apparatus for silver nanowires according to claim 1, characterized in that, The mixer cluster consists of 6 individual mixers connected in parallel, with each mixer having dimensions of 75×70mm.

3. The continuous production apparatus for silver nanowires according to claim 1, characterized in that, The purification unit includes a pre-sealed centrifuge tube system with a single tube capacity of 500 mL, a large-capacity refrigerated high-speed floor-standing multi-stage variable speed centrifuge with a rotation speed of 300-30000 rpm and a temperature of 4℃–10℃, and a pulsed ultrasonic dispersion device composed of a 20kHz ultrasonic probe array. The ultrasonic dispersion device adopts a pulse mode of 5s working / 2s intermittent.

4. The continuous production apparatus for silver nanowires according to claim 1, characterized in that, The modular connection structure arranges the mixer cluster, purification unit, and drying and packaging unit in a U-shaped assembly line layout.

5. The continuous production apparatus for silver nanowires according to claim 1, characterized in that, It also includes an oil bath device, which is equipped with a spiral 316L stainless steel coil or an external heat exchange unit, as well as an external circulation plate heat exchanger for the 80°C melting section.

6. A continuous production process for silver nanowires based on the apparatus of any one of claims 1-5, characterized in that, Includes the following steps: (1) Raw material pretreatment: Solvent, silver precursor and dispersant are introduced through three inlet check valves respectively. The raw materials are pretreated by a rotor-stator disperser with a speed of 10,000 rpm before being introduced; (2) Pressure balance control: Calculate the ethylene glycol vapor pressure, air expansion partial pressure and chemical reaction gas generation in the mixing device, match the pressure vessel level of not less than 420 kPa, and accurately control the pressure in the device at 0.8–1.2 MPa through the exhaust pressure setting valve; (3) Multi-temperature zone reaction: The 80℃ dissolution zone is temperature controlled by an external circulation plate heat exchanger, and the 160℃ reaction zone is temperature controlled by a PTC heating film and an embedded thermocouple. The material residence time is adjusted by flow feedback, and the heterogeneous system is mixed by superturbulent flow sedimentation technology; (4) Continuous purification: The slurry after reaction enters the purification unit and is treated by freeze high-speed centrifugation and pulse ultrasonic dispersion; (5) Drying and packaging: The purified silver nanowire wet material is transported to the drying and packaging unit to complete the preparation of the finished product.

7. The continuous production process for silver nanowires according to claim 6, characterized in that, The silver precursor is selected from one or more of silver nitrate, silver perchlorate, silver acetate, or sodium silver thiosulfate; the solvent is selected from one of ethylene glycol, propylene glycol, or an ethanol-acetone mixture; and the dispersant is selected from one of polyvinylpyrrolidone (PVP), hydroxypropyl cellulose, or 1-butyl-3-methylimidazolium hexafluorophosphate.

8. The continuous production process for silver nanowires according to claim 7, characterized in that, When silver acetate is used as a precursor, the raw material concentration is increased and the reaction time is extended; when silver perchlorate is used as a precursor, the raw material concentration is reduced and the reaction temperature is controlled; when sodium silver thiosulfate is used as a precursor, a microfluidic reaction module is used.

9. The continuous production process for silver nanowires according to claim 6, characterized in that, It also includes quality control steps: using a UV-Vis absorption spectrometer to provide real-time feedback on the diameter distribution data of nanowires, establishing a production batch traceability database, and recording the aspect ratio, surface roughness, and crystallinity parameters of each batch of products.

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