Electric nanofiltration device and electric nanofiltration system

Abstract

The invention relates to the technical field of nanofiltration devices, in particular to an electrical nanofiltration device and an electrical nanofiltration system. According to the invention, the negative charge characteristic of perfluorinated and polyfluoroalkyl compounds in an aqueous solution and the catalytic degradation effect of the perfluorinated and polyfluoroalkyl compounds on an anode are utilized, and an electric field (pointing from an interception side to a permeation side) with the same water molecule pressure difference permeation direction is applied; on one hand, the transmembrane flux of perfluoro and polyfluoroalkyl compounds to penetrating fluid is reduced through electromigration of the perfluoro and polyfluoroalkyl compounds to the anode plate, and meanwhile, the perfluoro and polyfluoroalkyl compounds are electrically adsorbed to the anode plate for electrocatalytic degradation; and on the other hand, as a large amount of positively charged ions in the electrolyte solution move towards the negative plate, a positive charge layer can be formed on the surface of the interception side of the nanofiltration membrane due to an accumulative effect, the electro-adsorption of the nanofiltration membrane to the perfluoro and polyfluoroalkyl compounds is improved, the concentration of the perfluoro and polyfluoroalkyl compounds in the penetrating fluid is further reduced, and the perfluoro and polyfluoroalkyl compounds in the penetrating fluid are further reduced. And the purposes of degrading the perfluorinated and polyfluoroalkyl compounds and improving the rejection rate are synchronously achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration devices, and in particular to an electro-nanofiltration device and an electro-nanofiltration system. Background Art

[0002] The transformation of surface water into safe drinking water is the basic guarantee for ensuring the safety and health of the public. Persistent organic pollutants represented by perfluoroalkyl compounds (PFAs) have become a hot topic and difficulty in current research due to their widespread presence in the environment, potential health risks, and unique physical and chemical properties. Perfluoroalkyl compounds (PFAs), with their hydrophilic and lipophilic amphiphilic properties, can enter drinking water sources through industrial emissions, agricultural runoff, and daily sewage, and migrate with rivers and groundwater, and eventually enter the human body through drinking water. These compounds have bioaccumulation and biomagnification effects in the human body, which can damage the immune system and increase the risk of serious diseases such as cancer.

[0003] For the water environment remediation technology of perfluorinated and polyfluoroalkyl compounds, existing research has mainly focused on the fields of chemical degradation, adsorption and membrane separation. Chemical degradation technologies, such as electrochemical oxidation and photocatalytic reduction, can degrade perfluorinated and polyfluoroalkyl compounds into harmless substances, but they face the challenges of slow reaction kinetics and significant water matrix effects, and the process has low water production efficiency because the conventional electrocatalytic process cannot simultaneously obtain purified water. Porous materials and ion exchange resins are limited in their wide application due to their limited adsorption capacity, high regeneration costs and possible secondary pollution. In contrast, nanofiltration and reverse osmosis technologies have attracted widespread attention for their efficient interception of perfluorinated and polyfluoroalkyl compounds. In existing reports, the interception rate can reach more than 90%. In particular, nanofiltration technology has a wide range of applications in many fields such as seawater desalination. It can provide safe drinking water that meets water quality standards at lower pressure and energy consumption, and has significant economic and environmental advantages. However, due to the technical characteristics of nanofiltration, a retentate with a higher tendency to contaminate is often produced in the process, which faces the need for secondary disposal. Moreover, although it has been reported that the retention rate of nanofiltration for perfluoroalkyl compounds can reach more than 90%, it is limited to treating feed liquid with a lower concentration of perfluoroalkyl compounds. As the concentration of perfluoroalkyl compounds in the initial feed liquid increases, its removal characteristics for perfluoroalkyl compounds with different carbon chain lengths vary. Although a high retention rate for long-chain perfluoroalkyl compounds can be maintained at a higher initial concentration, its retention rate for short-chain perfluoroalkyl compounds is significantly reduced. In general, for conventional nanofiltration, the concentration of perfluoroalkyl compounds with a full carbon chain in the permeate will increase with the feed concentration, resulting in a decrease in the quality of the produced water. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an electro-nanofiltration device and an electro-nanofiltration system to solve the technical problem that the existing nanofiltration membrane has insufficient filtering capacity for high-concentration perfluoro and polyfluoroalkyl compounds, resulting in excessively high concentrations of perfluoro and polyfluoroalkyl compounds in the retentate.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides an electro-nanofiltration device, comprising an anode plate, a cathode plate, and a nanofiltration membrane arranged between the anode plate and the cathode plate, wherein the anode plate and the cathode plate are electrically connected to a DC power supply, respectively. The nanofiltration membrane comprises a base membrane and a modified layer arranged on the surface of the base membrane, wherein the modified layer is composed of a layered double metal hydroxide. The anode plate is provided with a liquid inlet sieve hole and a first liquid outlet sieve hole, and the cathode plate is provided with a second liquid outlet sieve hole. The liquid inlet sieve hole is used to input a solution containing perfluorinated and polyfluoroalkyl compounds, an oxidation reaction occurs on the surface of the anode plate to generate hydroxyl radicals, so as to mineralize and degrade part of the perfluorinated and polyfluoroalkyl compounds to generate a retained liquid, and the first liquid outlet sieve hole is used to output the retained liquid. The nanofiltration membrane is used to adsorb part of the perfluorinated and polyfluoroalkyl compounds that reach the membrane surface with the pressure field to generate a permeate, and the second liquid outlet sieve hole is used to output the permeate.

[0006] Due to the special nanostructure of layered double hydroxide, its Zeta potential in aqueous solution is positive, which can not only promote the electrostatic adsorption of perfluorinated and polyfluorinated alkyl compounds, but also maintain close bonding with the negatively charged base membrane. In addition, the hydrophilic layered structure of layered double hydroxide increases the mass transfer channels inside the membrane, making it easier for water molecules and low-valent ions to pass through the membrane layer, thereby improving the permeability of the membrane.

[0007] In general, the layered double hydroxide layer in this system increases the electrostatic adsorption and steric hindrance of perfluorinated and polyfluorinated alkyl compounds without losing the water molecule transmission flux of the modified nanofiltration membrane.

[0008] Optionally, the electro-nanofiltration device further comprises a first mounting plate and a second mounting plate, wherein the first mounting plate is mounted on the side of the anode plate away from the nanofiltration membrane, and the second mounting plate is mounted on the side of the cathode plate away from the nanofiltration membrane. The first mounting plate is provided with a liquid inlet hole connected to the liquid inlet sieve hole, and a first liquid outlet connected to the first liquid outlet sieve hole. The second mounting plate is provided with a second liquid outlet connected to the second liquid outlet sieve hole.

[0009] Optionally, the liquid inlet sieve hole, the first liquid outlet sieve hole and the second liquid outlet sieve hole are nanopores.

[0010] Optionally, the metal cation of the layered double hydroxide is Mg 2+ and Al3+ , the interlayer anion is CO3 2- .

[0011] Optionally, the anode plate is a transition metal oxide or boron-doped diamond, and the cathode plate is metal titanium.

[0012] The present invention provides an electro-nanofiltration system, comprising the above-mentioned electro-nanofiltration device, a raw material tank for storing a feed liquid containing perfluoro- and polyfluoroalkyl compounds, a temperature control device, a feed valve, a pressure regulating valve, a collecting device, a computer, and a temperature sensor, a first pressure sensor, a second pressure sensor, a first flow sensor, and a second flow sensor electrically connected to the computer respectively.

[0013] The temperature control device is connected to the raw material tank to regulate the temperature of the feed liquid in the raw material tank. When the feed liquid flows along the pipeline through the raw material tank to the electro-nanofiltration device, it first passes through the temperature sensor and the first pressure sensor, and then passes through the feed valve and the first flow sensor.

[0014] The feed liquid is processed by the electro-nanofiltration device to produce retained liquid and permeate. The permeate flows along the pipeline through the second flow sensor and then enters the collecting device. The retained liquid flows along the pipeline through the second pressure sensor and the pressure regulating valve and then returns to the raw material tank. The computer is used to obtain and collect sensor parameters in the electro-nanofiltration system.

[0015] Optionally, the working pressure range is 0MPa to 2.0MPa, and the working temperature range is 5°C to 55°C.

[0016] The beneficial effect of the present invention is that, compared with the prior art, the present invention utilizes the negative charge characteristics of perfluoro and polyfluoroalkyl compounds in aqueous solution and the catalytic degradation reaction that can be carried out near the anode plate, and by applying an electric field in the same direction as the pressure difference penetration of water molecules, on the one hand, the transmembrane flux of perfluoro and polyfluoroalkyl compounds to the permeate is reduced by the electrical migration of perfluoro and polyfluoroalkyl compounds to the anode plate, and at the same time, they are electrically adsorbed to the anode plate for electrocatalytic degradation; on the other hand, due to the large-scale migration of positively charged ions in the electrolyte solution to the cathode plate, a positive charge layer is formed on the interception side surface of the nanofiltration membrane due to the cumulative effect, thereby increasing the electrical adsorption of perfluoro and polyfluoroalkyl compounds by the nanofiltration membrane, thereby further reducing the concentration of perfluoro and polyfluoroalkyl compounds in the permeate, and simultaneously achieving the purpose of degradation of perfluoro and polyfluoroalkyl compounds and improvement of the interception rate, thereby solving the technical problem that the existing nanofiltration membrane has insufficient filtering capacity for high-concentration perfluoro and polyfluoroalkyl compounds, resulting in excessive concentration of perfluoro and polyfluoroalkyl compounds in the intercepted liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a working principle diagram of an electro-nanofiltration device provided by the present invention.

[0018] Figure 2 A schematic structural diagram of an electro-nanofiltration device provided by the present invention.

[0019] Figure 3 A schematic structural diagram of an electro-nanofiltration system provided by the present invention.

[0020] Figure numerals: 1. electro-nanofiltration device; 11. cathode plate; 111. second liquid outlet sieve hole; 12. anode plate; 121. liquid inlet sieve hole; 122. first liquid outlet sieve hole; 13. nanofiltration membrane; 14. first mounting plate; 141. liquid inlet hole; 142. first liquid outlet; 15. second mounting plate; 151. second liquid outlet; 16. terminal; 21. raw material tank; 221. temperature sensor; 222. pressure sensor; 223. flow sensor; 224. computer; 225. feed valve; 226. pressure regulating valve; 23. temperature control device. DETAILED DESCRIPTION

[0021] In order to solve the above technical problems, the present invention provides an electro-nanofiltration device and an electro-nanofiltration system. The technical solutions and embodiments of the present invention are now described in detail in conjunction with the accompanying drawings.

[0022] PFOA, Perfluorooctanoic Acid. PFBS, English full name: PerfluorobutaneSulfonic Acid.

[0023] This study designed an electro-nanofiltration system based on the electro-nanofiltration device 1, and its specific components are as follows: Figure 3 As shown, it includes an electro-nanofiltration device 1, a raw material tank 21 for storing a feed liquid containing perfluoro- and polyfluoroalkyl compounds, a temperature control device 22, a feed valve 23, a pressure regulating valve 24, a collecting device 25, a computer 26, and a temperature sensor 27, a first pressure sensor 281, a second pressure sensor 282, a first flow sensor 291, and a second flow sensor 292 electrically connected to the computer 26 respectively.

[0024] The temperature control device 22 is connected to the raw material tank 21 to control the temperature of the feed liquid in the raw material tank 21. When the feed liquid flows along the pipeline through the raw material tank 21 to the electro-nanofiltration device 1, it first passes through the temperature sensor 27 and the first pressure sensor 281, and then passes through the feed valve 23 and the first flow sensor 291. The feed liquid is processed by the electro-nanofiltration device 1 to produce retentate and percolate. The percolate flows along the pipeline through the second flow sensor 292 and then enters the collection device 25. The retentate flows along the pipeline through the second pressure sensor 282 and the pressure regulating valve 24 and then returns to the raw material tank 21. The computer 26 is used to obtain and collect sensor parameters in the electro-nanofiltration system.

[0025] The operator can monitor and obtain the temperature, pressure and flow data of the electro-nanofiltration system in real time through the computer 26, so that the operator can adjust the feed valve 23, the pressure regulating valve 24 or the temperature control device 22 accordingly through the real-time data to control the temperature, pressure and flow parameters in the electro-nanofiltration system and make the electro-nanofiltration system work normally. The working pressure range of the electro-nanofiltration system is customized to be 0 MPa to 2.0 MPa, the allowable working temperature is 5 ℃ to 55 ℃, the feed flow rate, that is, the membrane surface flow rate is 0 m / s to 10 m / s, and the first pressure sensor 281 and the second pressure sensor 282 cooperate with each other to realize the in-situ monitoring of the transmembrane pressure difference in the electro-nanofiltration device 1, so as to monitor the working condition of the nanofiltration membrane 13 in the electro-nanofiltration device 1 in real time, especially the occurrence process of membrane fouling.

[0026] The structural diagram of the electro-nanofiltration device 1 is shown in FIG. Figure 2 As shown, it includes an anode plate 12, a cathode plate 11, and a nanofiltration membrane 13 arranged between the anode plate 12 and the cathode plate 11, and the anode plate 12 and the cathode plate 11 are electrically connected to a DC power supply respectively. The nanofiltration membrane 13 includes a base membrane and a modified layer arranged on the surface of the base membrane, and the modified layer is composed of a layered double metal hydroxide. The anode plate 12 is provided with a liquid inlet sieve hole 121 and a first liquid outlet sieve hole 122, and the cathode plate 11 is provided with a second liquid outlet sieve hole 111. The liquid inlet sieve hole 121 is used to input a solution containing perfluorinated and polyfluoroalkyl compounds, and an oxidation reaction occurs on the surface of the anode plate 12 to generate hydroxyl radicals to mineralize and degrade part of the perfluorinated and polyfluoroalkyl compounds to produce a retained liquid, and the first liquid outlet sieve hole 122 is used to output the retained liquid. The nanofiltration membrane 13 is used to adsorb part of the perfluorinated and polyfluoroalkyl compounds that reach the membrane surface with the pressure field to produce a permeate, and the second liquid outlet sieve hole 111 is used to output the permeate.

[0027] The electro-nanofiltration device 1 also includes a first mounting plate 14 and a second mounting plate 15. The first mounting plate 14 is mounted on the side of the anode plate 12 facing away from the nanofiltration membrane 13, and the second mounting plate 15 is mounted on the side of the cathode plate 11 facing away from the nanofiltration membrane 13. The first mounting plate 14 is provided with a liquid inlet 141 connected to the liquid inlet sieve hole 121, and a first liquid outlet 142 connected to the first liquid outlet sieve hole 122. The second mounting plate 15 is provided with a second liquid outlet 151 connected to the second liquid outlet sieve hole 111. Specifically, the first mounting plate 14 and the second mounting plate 15 are both provided with a terminal 16, so that the anode plate 12 and the cathode plate 11 are electrically connected to the DC power supply through the terminal 16 respectively.

[0028] The reaction principle in the electro-nanofiltration device 1 is as follows Figure 1As shown, under the action of the electric field, positively charged particles undergo electrophoretic migration toward the cathode plate 11, and negatively charged particles undergo electrophoretic migration toward the anode plate 12. Perfluoroalkyl compounds, due to their negative charge characteristics, will undergo electrophoresis toward the anode plate 12 and be electrically adsorbed on the surface of the anode plate 12. When the power is on, an oxidation reaction occurs on the surface of the anode plate 12, and the generated hydroxyl radicals cause partial perfluoroalkyl compounds to be mineralized and degraded, thereby producing a retained liquid. In addition, due to the migration of cations to the cathode plate 11, some cations will be aggregated on the surface of the nanofiltration membrane 13, and at the same time, the water electrolysis reaction will cause the pH of the solution on one side of the retained liquid to decrease. Under the above two effects, the negative electric density on the surface of the nanofiltration membrane 13 will be reduced. Although this will reduce the electrostatic repulsion of the surface of the nanofiltration membrane 13 to perfluoroalkyl compounds, it will increase the adsorption effect of perfluoroalkyl compounds that reach the surface of the nanofiltration membrane 13 with the pressure field, and the liquid after adsorption and filtration by the nanofiltration membrane 13 is the leachate.

[0029] The present invention is described in detail below through specific examples. The examples are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0030] Example 1 The feed solution was 0.29μM PFOA, the electrolyte solution was 5mM Na2SO4, the system temperature was controlled at 20±0.5℃, the feed flow rate was 3 L / min, the corresponding membrane surface flow rate was 6.9 m / s, the transmembrane pressure was controlled at 1.0 MPa, and the permeate was returned to the raw material tank. The experiment was carried out under the operating electric field strength of 0 V / cm and 8.8 V / cm, and the system was operated for 3h. When the electric field strength was 0V / cm, when the system reached a stable operating state, the PFOA removal rate was 94.96%, and the membrane flux was 21 mL·min -1 ·dm -2 PFOA in the raw liquid was slightly reduced in the initial stage due to the adsorption of hardware such as pipelines, but remained basically constant after the system ran for a period of time; when the electric field strength was 8.8 V / cm, the PFOA removal rate increased slightly to 97.35%, and the membrane flux decreased to 16 mL·min -1 ·dm -2 The PFOA concentration in the raw material solution decreased by nearly 10%, and the concentration reduction rate was 52.7 ng·L -1 ·min -1 , which shows that its concentration can continue to decrease with the extension of running time.

[0031] Example 2 The system was tested for its removal performance of perfluorinated and polyfluorinated alkyl compounds under high concentration conditions. The feed solution was 11.5 μM perfluorinated and polyfluorinated alkyl compounds, including 4.83 μM PFOA and 6.67 μM PFBS. The mass concentration ratio of long-chain PFOA to short-chain PFBS was 1:1. The electrolyte solution used was 5 mM Na2SO4. The system temperature was controlled at 20 ± 0.5 °C. The feed flow rate was 3 L / min, corresponding to a membrane surface flow rate of 6.9 m / s. The transmembrane pressure was controlled at 0.8 MPa. The permeate was returned to the raw material tank. The experiment was conducted under operating electric field strengths of 0 V / cm and 13.6 V / cm, and the system was operated for 3 hours. When the electric field strength was 0 V / cm, when the system reached a stable operating state, the removal rates of PFOA and PFBS were 90.05% and 74.45%, respectively, and the membrane flux was 18.66 mL·min -1 ·dm -2 Due to the adsorption of hardware such as pipelines, the PFOA and PFBS in the raw liquid decreased slightly in the initial stage, but remained basically constant after the system ran for a period of time; when the electric field strength was 13.6 V / cm, the removal rates of PFOA and PFBS were 91.28% and 82.48%, respectively, which shows that the removal rate of short-chain PFBS was significantly improved. In addition, the membrane flux was reduced to 13.93 mL·min under this condition. -1 ·dm -2 , the PFOA concentration in the raw material solution dropped to 18.34%, while the PFBS concentration dropped to 48.45%, and the concentration reduction rates were 1877 ng·L -1 ·min -1 and 4678 ng·L -1 ·min -1 It can be seen that with the extension of operation time, the system can achieve full mineralization of perfluorinated and polyfluoroalkyl compounds.

[0032] The above description is only a preferred embodiment of the present invention, and the above specific embodiment is not intended to limit the present invention. Various deformations and modifications may occur within the scope of the technical concept of the present invention, and any modification, modification or equivalent replacement made by a person of ordinary skill in the art based on the above description shall fall within the scope of protection of the present invention.

Claims

1. An electro-nanofiltration device (1), characterized in that: It comprises an anode plate (12), a cathode plate (11), and a nanofiltration membrane (13) arranged between the anode plate (12) and the cathode plate (11), wherein the anode plate (12) and the cathode plate (11) are respectively electrically connected to a direct current power supply; The nanofiltration membrane (13) comprises a base membrane and a modified layer arranged on the surface of the base membrane, wherein the modified layer is composed of a layered double metal hydroxide; The anode plate (12) is provided with a liquid inlet sieve hole (121) and a first liquid outlet sieve hole (122), and the cathode plate (11) is provided with a second liquid outlet sieve hole (111); The liquid inlet sieve hole (121) is used to input a solution containing perfluorinated and polyfluorinated alkyl compounds, an oxidation reaction occurs on the surface of the anode plate (12) to generate hydroxyl radicals, thereby mineralizing and degrading part of the perfluorinated and polyfluorinated alkyl compounds and generating a retained liquid, and the first liquid outlet sieve hole (122) is used to output the retained liquid; The nanofiltration membrane (13) is used to adsorb a portion of the perfluorinated and polyfluorinated alkyl compounds that reach the membrane surface along with the pressure field and produce a permeate, and the second liquid outlet sieve hole (111) is used to output the permeate.

2. The electro-nanofiltration device according to claim 1, characterized in that: The electro-nanofiltration device (1) further comprises a first mounting plate (14) and a second mounting plate (15), wherein the first mounting plate (14) is mounted on a side of the anode plate (12) facing away from the nanofiltration membrane (13), and the second mounting plate (15) is mounted on a side of the cathode plate (11) facing away from the nanofiltration membrane (13); The first mounting plate (14) is provided with a liquid inlet hole (141) communicating with the liquid inlet sieve hole (121), and a first liquid outlet (142) communicating with the first liquid outlet sieve hole (122); The second mounting plate (15) is provided with a second liquid outlet (151) which is in communication with the second liquid outlet sieve hole (111).

3. The electro-nanofiltration device according to claim 1, characterized in that: The liquid inlet sieve hole (121), the first liquid outlet sieve hole (122) and the second liquid outlet sieve hole (111) are nano-channels.

4. The electro-nanofiltration device according to claim 1, characterized in that: The metal cation of the layered double hydroxide is Mg 2+ and Al 3+ , the interlayer anion is CO3 2- .

5. The electro-nanofiltration device according to claim 1, characterized in that: The anode plate (12) is made of transition metal oxide or boron-doped diamond, and the cathode plate (11) is made of metal titanium.

6. An electro-nanofiltration system, characterized in that: The invention comprises an electro-nanofiltration device (1) as claimed in any one of claims 1 to 5, a raw material tank (21) for storing a liquid containing perfluoro- and polyfluoroalkyl compounds, a temperature control device (22), a feed valve (23), a pressure regulating valve (24), a collecting device (25), a computer (26), and a temperature sensor (27), a first pressure sensor (281), a second pressure sensor (282), a first flow sensor (291), and a second flow sensor (292) electrically connected to the computer (26); The temperature control device (22) is connected to the raw material tank (21) to control the temperature of the feed liquid in the raw material tank (21); in the process of the feed liquid flowing along the pipeline through the raw material tank (21) to the electro-nanofiltration device (1), the feed liquid first passes through the temperature sensor (27) and the first pressure sensor (281), and then passes through the feed valve (23) and the first flow sensor (291); The feed liquid is processed by the electro-nanofiltration device (1) to produce a retentate and a percolate. The percolate flows along a pipeline through the second flow sensor (292) and enters the collecting device (25). The retentate flows along a pipeline through the second pressure sensor (282) and the pressure regulating valve (24) and returns to the raw material tank (21). The computer (26) is used to obtain and collect sensor parameters in the electro-nanofiltration system.

7. The electro-nanofiltration system according to claim 6, characterized in that: The working pressure range is 0MPa~2.0MPa, and the working temperature range is 5℃~55℃.

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