Method and system for recycling PVP (Polyvinyl Pyrrolidone) and acetic acid prepared by supercritical hydrothermal synthesis of nanoparticles

Abstract

The invention relates to the technical field of nano-material green manufacturing and waste water recycling, in particular to a PVP and acetic acid recycling method and system for nano-particle supercritical hydrothermal synthesis preparation, and the method comprises the following steps: carrying out continuous circulating filtration and concentration on waste liquid to obtain PVP concentrated liquid of membrane concentrated water and permeate liquid containing acetic acid; the PVP concentrated solution of the membrane concentrated water is used for producing nano-particles for reuse; the permeate containing acetic acid is concentrated, an acetic acid concentrated solution and permeate water are obtained, and the permeate water is also used for producing nano-particles for reuse; and reacting the acetic acid concentrated solution with a metal oxide to generate a metal salt solution which is recycled for producing nano-particles. By means of the method, the problems that in the prior art, energy consumption of treatment of waste water containing PVP and acetic acid is high and raw materials are wasted when the nanometer silver powder is prepared through a supercritical hydrothermal method can be effectively solved.

Description

Technical Field

[0001] This invention relates to the field of green manufacturing of nanomaterials and wastewater resource utilization technology, specifically to a method and system for recycling PVP and acetic acid used in the supercritical hydrothermal synthesis of nanoparticles. Background Technology

[0002] Nanomaterials exhibit many unique physical and chemical properties due to quantum effects, small size effects, and surface effects, and are widely used in fields such as catalysts, optoelectronic materials, magnetic materials, and biomedicine.

[0003] Supercritical hydrothermal synthesis is a green synthesis technology for preparing nano-metal powders. The basic principle of supercritical hydrothermal synthesis is to use supercritical water as the reaction medium in a closed, high-pressure vessel to form nano-metal or metal oxide powders with extremely small particle sizes. During the supercritical hydrothermal synthesis of nanoparticles, macromolecular organic compounds are typically used as ligands. These ligands interact with the surface of the growing crystals, inhibiting further crystal growth; polyvinylpyrrolidone (PVP) is commonly used as the organic ligand. PVP acts as a dispersant and protective agent, thereby improving the sphericity and particle size distribution of the nano-metal powders.

[0004] After the supercritical hydrothermal reaction, the fluid is separated, and the separated solid phase is the nano-metal powder. The wastewater contains large-molecule organic PVP and acetic acid, a residue from the decomposition of precursors after the reaction. Current treatment methods mainly involve evaporation and neutralization to ensure the wastewater meets discharge standards. However, this approach increases treatment costs, wastes dissolved PVP, further raises enterprise costs, and causes environmental pollution. Therefore, an effective method is urgently needed to treat this wastewater and recover PVP and acetic acid from the nano-metal powder production wastewater. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles, which addresses the shortcomings of the prior art and solves the technical problems of high energy consumption and waste of raw materials in the existing PVP wastewater treatment methods.

[0006] The objective of this invention is achieved through the following technical solutions: In a first aspect, the present invention provides a method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles, comprising: The waste liquid is continuously circulated, filtered, and concentrated to obtain a PVP concentrate of membrane concentrate and a permeate containing acetic acid; the PVP concentrate of membrane concentrate is used for the production of nanoparticles for reuse. The permeate containing acetic acid is concentrated to obtain acetic acid concentrate and permeate water, which is then used for the production of nanoparticles for reuse. The concentrated acetic acid solution is reacted with a metal oxide to generate a metal salt solution for reuse in the production of nanoparticles.

[0007] As a further improvement of the present invention, the concentration of the PVP concentrate in the membrane concentrate is 20% to 30%.

[0008] As a further improvement of the present invention, the concentration of the acetic acid concentrate is 0.3% to 8%.

[0009] As a further improvement of the present invention, the metal oxide is silver oxide.

[0010] As a further improvement of the present invention, the mass of silver oxide added per liter of concentrated acetic acid solution ranges from 0.015 to 1.93 g.

[0011] In a second aspect, the present invention provides a PVP and acetic acid recycling system for the preparation of nanoparticles by supercritical hydrothermal synthesis, for implementing the PVP and acetic acid recycling method for the preparation of nanoparticles by supercritical hydrothermal synthesis as described in any one of claims 1 to 8, characterized in that it includes a nanofiltration membrane treatment subsystem, a nanoporous adsorption subsystem, and an acetic acid recycling subsystem. The nanofiltration membrane treatment subsystem includes a nanofiltration feed tank, a nanofiltration membrane module, and a nanofiltration concentrate storage tank. The output end of the nanofiltration feed tank is connected to the input end of the nanofiltration membrane module. The nanofiltration membrane module adopts a continuous circulation filtration device, and its output end is divided into two paths. One port is used to connect to the nanofiltration concentrate storage tank to store the generated PVP concentrate. The other port is connected to the nanoporous adsorption subsystem. The nanoporous adsorption subsystem includes a nanoporous adsorption feed tank, a nanoporous adsorption tower, and a nanoporous adsorption concentrate storage tank. The nanoporous adsorption feed tank is connected to the nanofiltration membrane module to receive permeate containing acetic acid. The output end of the nanoporous adsorption feed tank is connected to the input end of the nanoporous adsorption tower to transport the permeate to the adsorption tower. The nanoporous adsorption tower concentrates the acetic acid in the permeate, and the output is divided into two paths. One port is connected to the nanoporous adsorption concentrate storage tank to store the produced acetic acid concentrate. The other port is connected to the acetic acid recycling subsystem. The acetic acid recycling subsystem includes a mixing tank and a feeding device; the mixing tank is connected to a nanoporous adsorption concentrate storage tank through a first input terminal; and is connected to the feeding device through a second input terminal for receiving metal compounds; the mixing tank is a reaction vessel that outputs a metal salt solution generated by the reaction of the metal compound with the acetic acid concentrate for recycling.

[0012] As a further improvement of the present invention, the membrane material used in the nanofiltration membrane module is an organic composite membrane, and the operating temperature of the organic composite membrane is 4-55℃, and the pH range tolerable is 2-11.

[0013] As a further improvement of the present invention, the nanoporous adsorption subsystem includes two nanoporous adsorption towers arranged in parallel. The two nanoporous adsorption towers adopt a continuous operation mode of one adsorption and one desorption, adsorbing acetic acid in the waste liquid to the top of the nanoporous adsorption tower, and then desorbing and regenerating it.

[0014] As a further improvement of the present invention, the interior of the nanoporous adsorption tower is filled with a nanoporous adsorption material, wherein the nanoporous adsorption material is activated carbon, zeolite, MOFs, mesoporous silica, carbon nanotubes or graphene.

[0015] As a further improvement of the present invention, the operating parameters of the nanoporous adsorption tower are: a single feed rate of 1-4 m³ / h. 3 The adsorption time within the cycle is 0.5-1 hour, and the adsorption cycle is 1-10 hours. Desorption and regeneration are carried out using hot nitrogen gas at 100-140℃.

[0016] The beneficial effects of this invention are as follows: This invention provides a method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles. For waste liquid containing PVP and acetic acid, the waste liquid is received and stored in a raw material tank of a nanofiltration membrane subsystem, and then continuously circulated and concentrated through a nanofiltration membrane module. The selective permeation characteristics of the nanofiltration membrane cause large-molecule PVP to be retained, forming membrane concentrate with a concentration of 20%~30%, while small-molecule acetic acid permeates through the nanofiltration membrane into the permeate. This technical principle not only effectively separates PVP and acetic acid but also significantly improves the recovery rate and concentration effect of PVP. The PVP concentrate from the membrane concentrate can be directly returned to the supercritical hydrothermal system for reuse as a stabilizer. Even after more than 5 cycles, the high quality of the nano-silver powder is maintained, reducing raw material costs and achieving closed-loop resource utilization. For the permeate containing acetic acid, this invention further treats it using a nanoporous adsorption subsystem. The nanoporous adsorbent material exhibits high selectivity and adsorption capacity, effectively adsorbing acetic acid from concentrated wastewater with a concentration factor of at least 10 times. Simultaneously, the released permeate can be directly reused in nanoparticle production or used as raw water for pure water systems, further reducing wastewater discharge. Finally, the resulting concentrated acetic acid reacts with metal oxides to generate metal salt solutions, such as silver acetate, which are then reused in subsequent nanoparticle production. This innovative synergistic process significantly reduces energy consumption in wastewater treatment, avoids the waste of raw materials in traditional methods, and achieves near-zero wastewater discharge. Furthermore, the recycling of chemicals significantly improves the system's economic and environmental benefits, providing a new solution for green manufacturing of nanomaterials and wastewater resource recovery. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the process for the recycling of PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles, as described in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives and technical solutions of this invention clearer and easier to understand, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] Example 1 This embodiment provides a method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles. The specific implementation method is as follows.

[0022] A method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles includes: continuously circulating and filtering the waste liquid to obtain a PVP concentrate (membrane concentrate) and a permeate containing acetic acid; using the PVP concentrate to produce nanoparticles; concentrating the permeate containing acetic acid to obtain an acetic acid concentrate and permeate water, which is then used to produce nanoparticles; and reacting the acetic acid concentrate with a metal oxide to generate a metal salt solution for producing nanoparticles.

[0023] In this embodiment, the waste liquid is continuously circulated, filtered, and concentrated. Membrane separation is used to separate PVP and acetic acid, yielding a directly reusable membrane concentrate (PVP concentrate) and a permeate containing acetic acid. The permeate containing acetic acid is then concentrated to further separate an acetic acid concentrate and reusable permeate water. Finally, the acetic acid concentrate is converted into a reusable metal salt solution through a chemical reaction between acetic acid and metal oxides. This achieves the stepwise recovery and conversion of PVP, water, and acetic acid from the waste liquid. The resulting technical advantage is that the PVP, water, and metal salt obtained through acetic acid conversion in the waste liquid can all be reused in the production of nanoparticles, realizing resource recycling, reducing waste liquid discharge, and improving resource utilization.

[0024] This embodiment achieves effective separation of PVP and acetic acid through continuous circulating filtration and concentration using a nanofiltration membrane module. The high selectivity of the nanofiltration membrane ensures the recovery rate and purity of PVP, while the recovery of acetic acid in the permeate is accomplished through a nanoporous adsorption subsystem. This system utilizes the high adsorption performance of nanoporous materials to achieve the concentration and recovery of acetic acid. Nanofiltration membrane technology, based on a dual screening mechanism of membrane pore size and charge, can effectively retain high molecular weight PVP while allowing low molecular weight acetic acid and water to permeate. Nanoporous adsorption technology utilizes the pore size and surface properties of nanoporous materials to selectively adsorb acetic acid. In terms of effectiveness, the technical solution in this embodiment achieves efficient recovery of PVP and acetic acid, reduces raw material costs, and minimizes wastewater discharge, thus realizing closed-loop resource utilization and environmental protection.

[0025] Furthermore, the concentration of PVP concentrate in the membrane concentrate is 20%–30%. By adjusting the operating parameters of the nanofiltration membrane module, such as pressure, flow rate, and temperature, the final concentration of the PVP concentrate can be controlled to ensure that it meets the reuse requirements. High-concentration PVP recovery is based on the retention performance of the nanofiltration membrane and the waste liquid recycling and concentration process. By precisely controlling the concentration factor, the desired PVP concentration can be obtained. The high-concentration PVP concentrate can be directly returned to the supercritical hydrothermal system as a stabilizer for reuse, reducing PVP consumption and lowering production costs.

[0026] Furthermore, the acetic acid in the permeate is concentrated at least 10 times to increase the concentration of the metal salt solution, thereby optimizing the efficiency of chemical recycling. Concentration is achieved using nanoporous adsorption materials, which concentrate the low-concentration acetic acid solution to the required concentration to meet recycling requirements. Acetic acid concentration is based on the high adsorption performance and thermal desorption process of nanoporous materials; by precisely controlling the adsorption and desorption conditions, the desired acetic acid concentration can be obtained. The high-concentration acetic acid concentrate can be directly used to react with metal oxides to generate metal salt solutions, reducing acetic acid consumption and lowering production costs.

[0027] Furthermore, the concentration of the acetic acid concentrate is 0.3%~8%. High-concentration acetic acid concentrate is achieved through efficient concentration using nanoporous adsorption materials, facilitating subsequent chemical reactions. The high specific surface area and unique pore structure of the nanoporous adsorption materials promote dense adsorption of acetic acid molecules, thereby increasing the concentration of the concentrate. The technology in this embodiment not only meets the acetic acid requirements of the supercritical hydrothermal synthesis process but also reduces water consumption and improves overall resource utilization.

[0028] Furthermore, the metal compound is silver oxide, and the metal salt solution generated by reacting it with concentrated acetic acid is a silver acetate solution. By reacting concentrated acetic acid with silver oxide, a silver acetate solution can be generated for subsequent supercritical hydrothermal synthesis of nanoparticles. The reaction between acetic acid and silver oxide is based on acid-base neutralization and redox reactions, and the resulting silver acetate solution exhibits good stability, making it suitable for nanoparticle synthesis. The generation of silver acetate solution realizes the resource utilization of acetic acid, reduces raw material costs, and simultaneously reduces chemical consumption and environmental pollution. In other embodiments, other metal compounds, such as copper oxide and iron oxide, can also be used to generate different types of metal salt solutions for the synthesis of different nanoparticles, solving the technical problem of preparing specific metal salt solutions.

[0029] Furthermore, in order to generate a concentration of 0.01-0.5 mol·L⁻¹ -1 The silver acetate solution was prepared by adding 0.015–1.93 g of silver oxide per liter of concentrated acetic acid. By precisely controlling the reaction ratio of silver oxide to concentrated acetic acid, the desired concentration of silver acetate solution could be obtained to meet the requirements of subsequent synthesis reactions. High-concentration silver acetate solution can be directly used for the synthesis of nanoparticles, improving the efficiency of the synthesis reaction and the quality of the product.

[0030] Example 2 This embodiment provides a PVP and acetic acid recycling system for the supercritical hydrothermal synthesis of nanoparticles. The recycling system includes a nanofiltration membrane treatment subsystem, a nanoporous adsorption subsystem, and an acetic acid recycling subsystem.

[0031] The nanofiltration membrane treatment subsystem includes a nanofiltration feed tank, a nanofiltration membrane module, and a nanofiltration concentrate storage tank. The output of the nanofiltration feed tank is connected to the input of the nanofiltration membrane module and is used to store wastewater. The nanofiltration membrane module employs a continuous circulation filtration device, with its output divided into two paths: one port connects to the nanofiltration concentrate storage tank, storing the generated PVP concentrate in the nanofiltration concentrate storage tank; the other port connects to the nanoporous adsorption subsystem.

[0032] The nanoporous adsorption subsystem includes a nanoporous adsorption feed tank, a nanoporous adsorption tower, and a nanoporous adsorption concentrate storage tank. The nanoporous adsorption feed tank connects to the nanofiltration membrane module to receive the permeate containing acetic acid. The output of the nanoporous adsorption feed tank connects to the input of the nanoporous adsorption tower, delivering the permeate to the tower. The nanoporous adsorption tower concentrates the acetic acid in the permeate, and its output is divided into two paths: one port connects to the nanoporous adsorption concentrate storage tank for storing the produced concentrated acetic acid; the other port connects to the acetic acid recycling subsystem.

[0033] The acetic acid recycling subsystem includes a mixing tank and a feeding device. The mixing tank is connected to a nanoporous adsorption concentrate storage tank via a first input terminal; and to the feeding device via a second input terminal, used to receive metal compounds. The mixing tank serves as a reaction vessel, outputting the metal salt solution generated by the reaction of the metal compounds with the acetic acid concentrate for reuse.

[0034] Furthermore, the nanofiltration membrane module in this embodiment uses an organic composite membrane, which operates at a temperature of 4-55°C and tolerates a pH range of 2-11. The use of the organic composite membrane ensures stable PVP retention and acetic acid permeation under a wide range of temperature and pH conditions, improving the system's adaptability and stability. The structure and properties of the organic composite membrane enable it to maintain good separation performance in complex waste liquids; its temperature and acid / alkali resistance are key to achieving continuous circulation filtration. In terms of effectiveness, this membrane material selection ensures efficient recovery of PVP and acetic acid while reducing the maintenance costs and operational risks of the membrane module. In other embodiments, other types of temperature- and acid / alkali-resistant membrane materials, such as inorganic ceramic membranes and polysulfone membranes, can be used to adapt to different waste liquid treatment requirements and solve membrane module performance problems under specific conditions.

[0035] Furthermore, the nanoporous adsorption subsystem in this embodiment includes two nanoporous adsorption towers arranged in parallel. The two towers operate in a continuous adsorption-desorption mode, adsorbing acetic acid from the waste liquid to the top of the towers before desorption and regeneration. By using parallel nanoporous adsorption towers and the adsorption-desorption mode, continuous acetic acid recovery and regeneration of the nanoporous adsorption material are achieved, improving system operating efficiency and acetic acid recovery rate. The operation of the nanoporous adsorption towers is based on the adsorption and thermal desorption properties of the nanoporous materials. By controlling the adsorption and desorption conditions, acetic acid concentration and recovery can be achieved. The continuous adsorption-desorption mode of the nanoporous adsorption towers ensures continuous recovery of acetic acid from the waste liquid while reducing tower downtime and improving overall system operating efficiency. In other embodiments, the number of nanoporous adsorption towers can be increased or the operating mode changed, such as using three or four towers in parallel, to improve system processing capacity and acetic acid recovery efficiency, solving the technical problems of large-scale waste liquid treatment.

[0036] The operating parameters for the nanoporous adsorption tower are as follows: a single feed rate of 1-4 m³ / min. 3 The adsorption time within the cycle is 0.5-1 hour, and the adsorption cycle is 1-10 hours. Desorption and regeneration are performed using hot nitrogen gas at 100-140℃. Based on the adsorption kinetics of acetic acid and the thermal stability of the nanoporous adsorbent material, efficient concentration and recovery of acetic acid can be achieved by adjusting the parameters. In terms of effectiveness, the technical solution in this embodiment ensures efficient recovery of acetic acid and stable regeneration of the nanoporous adsorbent material, reducing chemical consumption and processing costs.

[0037] Furthermore, the nanoporous adsorption tower is filled with nanoporous adsorption materials. In this embodiment, the nanoporous adsorption materials used include activated carbon, zeolite, MOFs, mesoporous silica, carbon nanotubes, or graphene. The selection of nanoporous adsorption materials is based on their high adsorption performance and stability, which can effectively adsorb acetic acid in waste liquid, ensuring efficient recovery of acetic acid and reducing chemical consumption and treatment costs. In other embodiments, other types of nanoporous materials, such as mesoporous carbon and mesoporous alumina, can be used to adapt to the treatment requirements of different waste liquids and solve the technical problems of acetic acid recovery under specific conditions.

[0038] In addition, the specific surface area of ​​nanoporous materials is greater than 500 m². 2 The nanoporous material, with a pore size of 0.5-5 nm and a high specific surface area, ensures efficient adsorption and selectivity for acetic acid. In principle, the specific surface area determines the adsorption capacity of the material, while the pore size determines its selective adsorption capacity. By controlling these parameters, efficient concentration and recovery of acetic acid can be achieved. In terms of effectiveness, the technical solution in this embodiment ensures efficient recovery of acetic acid and reduces chemical consumption and processing costs.

[0039] Based on the structure of this system, a specific example corresponding to the method of PVP preparation through supercritical hydrothermal synthesis of nanoparticles and acetic acid recycling is given, such as... Figure 1 As shown, it includes the following steps: The nanofiltration feed tank receives 4000 liters of wastewater containing PVP and acetic acid per hour. After passing through the nanofiltration membrane module, the wastewater undergoes continuous circulation filtration and concentration to obtain a PVP concentrate and an acetic acid-containing permeate. The PVP concentrate concentration in the membrane concentrate is 20%~30%, with a recovery rate of 98%.

[0040] The PVP concentrate from the membrane concentrate is output to the nanofiltration concentrate storage tank through a single channel. The PVP concentrate with a concentration of 20% to 30% is then packaged and stored or sold as a product.

[0041] The nanofiltration permeate containing acetic acid is then transported to the nanoporous adsorption feed tank, where it is used in the nanoporous adsorption subsystem (i.e., Figure 1 The nanoporous adsorption tower in the nanoporous adsorption system (of which acetic acid is adsorbed and desorbed) continuously operates to recover acetic acid, yielding a concentrated acetic acid solution with a concentration of 0.3% to 8% and permeate water. The concentrated acetic acid solution is output to the nanoporous adsorption concentrate storage tank through a single channel. The permeate water is used for the production of nanoparticles or as raw water for pure water machines.

[0042] The concentrated acetic acid solution from the adsorption concentrate storage tank is discharged to the mixing tank, where it reacts with silver oxide added in the mixing tank to produce a product with a concentration of 0.01-0.5 mol·L⁻¹. -1 The silver acetate solution is used for subsequent supercritical hydrothermal synthesis of nanoparticles and is reused. Silver oxide is added to the mixing tank via a feeding device.

[0043] During operation, the synergistic effect of the nanofiltration membrane module and the nanoporous adsorption tower enables the efficient recovery and resource utilization of PVP and acetic acid, while reducing wastewater discharge and protecting the environment. By precisely controlling the operating parameters of each subsystem, such as the operating conditions of the membrane module, the operating cycle of the adsorption tower, and the reaction conditions of the reactor, the recovery efficiency and chemical recycling rate of the entire system can be optimized, solving the technical problems of large-scale wastewater treatment and chemical reuse.

Claims

1. A method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles, characterized in that, include: The waste liquid is continuously circulated, filtered, and concentrated to obtain a PVP concentrate of membrane concentrate and a permeate containing acetic acid; the PVP concentrate of membrane concentrate is used for the production of nanoparticles for reuse. The permeate containing acetic acid is concentrated to obtain acetic acid concentrate and permeate water, which is then used for the production of nanoparticles for reuse. The concentrated acetic acid solution is reacted with a metal oxide to generate a metal salt solution for reuse in the production of nanoparticles.

2. The method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles according to claim 1, characterized in that, The concentration of the PVP concentrate in the membrane concentrate is 20%~30%.

3. The method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles according to claim 1, characterized in that, The concentration of the acetic acid concentrate is 0.3% to 8%.

4. The method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles according to claim 1, characterized in that, The metal oxide is silver oxide.

5. The method for recycling PVP and acetic acid in the supercritical hydrothermal synthesis of nanoparticles according to claim 4, characterized in that, The corresponding amount of silver oxide added per liter of concentrated acetic acid solution ranges from 0.015 to 1.93 g.

6. A PVP and acetic acid recycling system for the supercritical hydrothermal synthesis of nanoparticles, used to implement the PVP and acetic acid recycling method for the supercritical hydrothermal synthesis of nanoparticles as described in any one of claims 1 to 5, characterized in that, This includes a nanofiltration membrane treatment subsystem, a nanoporous adsorption subsystem, and an acetic acid recycling subsystem; The nanofiltration membrane treatment subsystem includes a nanofiltration feed tank, a nanofiltration membrane module, and a nanofiltration concentrate storage tank. The output end of the nanofiltration feed tank is connected to the input end of the nanofiltration membrane module. The nanofiltration membrane module adopts a continuous circulation filtration device, and its output end is divided into two paths. One port is used to connect to the nanofiltration concentrate storage tank to store the generated PVP concentrate. The other port is connected to the nanoporous adsorption subsystem. The nanoporous adsorption subsystem includes a nanoporous adsorption feed tank, a nanoporous adsorption tower, and a nanoporous adsorption concentrate storage tank. The nanoporous adsorption feed tank is connected to the nanofiltration membrane module to receive permeate containing acetic acid. The output end of the nanoporous adsorption feed tank is connected to the input end of the nanoporous adsorption tower to transport the permeate to the adsorption tower. The nanoporous adsorption tower concentrates the acetic acid in the permeate, and the output is divided into two paths. One port is connected to the nanoporous adsorption concentrate storage tank to store the produced acetic acid concentrate. The other port is connected to the acetic acid recycling subsystem. The acetic acid recycling subsystem includes a mixing tank and a feeding device; the mixing tank is connected to a nanoporous adsorption concentrate storage tank through a first input terminal; and is connected to the feeding device through a second input terminal for receiving metal compounds; the mixing tank is a reaction vessel that outputs a metal salt solution generated by the reaction of the metal compound with the acetic acid concentrate for recycling.

7. The PVP and acetic acid recycling system for the supercritical hydrothermal synthesis of nanoparticles according to claim 6, characterized in that, The nanofiltration membrane module uses an organic composite membrane material, which has an operating temperature of 4-55℃ and a pH tolerance range of 2-11.

8. The PVP and acetic acid recycling system for the supercritical hydrothermal synthesis of nanoparticles according to claim 6, characterized in that, The nanoporous adsorption subsystem includes two nanoporous adsorption towers arranged in parallel. The two nanoporous adsorption towers adopt a continuous operation mode of one adsorption and one desorption, adsorbing acetic acid in the waste liquid to the top of the nanoporous adsorption tower, and then desorbing and regenerating it.

9. The PVP and acetic acid recycling system for the supercritical hydrothermal synthesis of nanoparticles according to claim 8, characterized in that, The nanoporous adsorption tower is filled with nanoporous adsorption materials, such as activated carbon, zeolite, MOFs, mesoporous silica, carbon nanotubes, or graphene.

10. The PVP and acetic acid recycling system for the supercritical hydrothermal synthesis of nanoparticles according to claim 9, characterized in that, The operating parameters of the nanoporous adsorption tower are: a single feed rate of 1-4 m³ / min. 3 The adsorption time within the cycle is 0.5-1 hour, and the adsorption cycle is 1-10 hours. Desorption and regeneration are carried out using hot nitrogen gas at 100-140℃.

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