A real-time detection device and method for the cleaning effect of a membrane based on electrochemical impedance spectroscopy

Abstract

The present invention discloses a real-time detection device and method for the cleaning effect of a membrane based on electrochemical impedance spectroscopy, belonging to the field of membrane technology. The detection device includes: an electrolytic cell, an electrolytic cell cover, test electrodes, and an electrochemical workstation; the electrolytic cell has a structure with left and right chambers, and the two chambers are respectively filled with a cleaning agent and an electrolyte solution, and a contaminated membrane to be cleaned is fixed at the middle connecting part; wherein, the contaminated side of the contaminated membrane to be cleaned is in direct contact with the cleaning agent, and the uncontaminated side of the contaminated membrane to be cleaned is in direct contact with the electrolyte solution; the electrolytic cell cover is provided with test electrode mounting holes penetrating through it, the test electrode mounting holes are provided with test electrodes, and the front ends of the test electrodes are all located in the cleaning agent or the electrolyte solution; the test electrodes are connected to the electrochemical workstation through wires. The device of the present invention is simple and easy to assemble, and by using this device, the change of the membrane contamination layer during the cleaning process can be effectively detected, and the optimization of the membrane cleaning process can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, and particularly relates to a device and method for real-time detection of the cleaning effect of a membrane based on electrochemical impedance spectroscopy. Background Art

[0002] Membrane separation technology is widely used in the field of water treatment due to its high efficiency and environmental protection characteristics. It has functions such as separation, concentration, and purification, and can be used to treat various complex water bodies. However, due to facing complex water bodies containing a large number of pollutants, even after pretreatment, membrane fouling remains one of the main inevitable problems in the process of membrane separation application. Therefore, it is necessary to clean the fouled membrane to reduce and alleviate membrane fouling and restore its separation performance.

[0003] In the prior art, for the detection methods of the performance recovery of the fouled membrane after cleaning and the cleaning effect, the judgment indexes are mainly based on the recovery of the transmembrane pressure during constant flux operation or the recovery of the flux during fixed pressure operation. For example, the Chinese patent document with the publication number CN111330449A discloses a method for cleaning and regenerating reverse osmosis membrane fouling, and the Chinese patent document with the publication number CN102133505A discloses an enhanced cleaning method for reverse osmosis / nanofiltration membrane fouling. The above methods both use membrane flux and salt rejection rate as indexes to evaluate the cleaning effect. However, in the actual membrane cleaning process, it is usually impossible to directly use the flux test method to judge the membrane cleaning situation in real time, and different membrane fouling situations are different, which is likely to cause over-cleaning of the fouled membrane, resulting in the destruction of the membrane structure and the decrease of the membrane service life.

[0004] The Chinese patent document with the publication number CN107328699A discloses a membrane fouling monitoring device and method based on in-situ spectroscopy-electrochemical analysis technology. Although this method can online monitor and analyze the fouling situation of different separation membrane sheets, combine the optical information obtained by the fiber optic spectrometer with the electrochemical information obtained by the electrochemical workstation to obtain information on the molecular level of the pollutants on the membrane surface and information on the deposition process of the pollutants on the membrane surface, the device is relatively complex, and the application scenario is the monitoring of membrane fouling situation.

[0005] Electrochemical impedance spectroscopy is to measure the change of impedance with the sine wave frequency, and then analyze the electrode process kinetics, double layer and diffusion, etc. Electrochemical methods based on electrochemical impedance spectroscopy have been widely applied in different fields, such as measuring the double layer capacitance on the electrode surface, tracking the formation process of compounds, and optimizing the performance of fuel cells. Applying electrochemical impedance spectroscopy to the detection of the cleaning effect of fouled membranes is a feasible strategy for realizing real-time detection of the membrane cleaning process. Summary of the Invention

[0006] The present invention provides a real-time detection device for the cleaning effect of a membrane based on electrochemical impedance spectroscopy. The device is simple and easy to assemble, suitable for evaluating the cleaning effects of different cleaning agents, and not limited by the types of flat membranes. It can effectively detect the changes in the membrane fouling layer during the cleaning process, realize the real-time evaluation of the membrane cleaning effect, and optimize the cleaning process.

[0007] The specific technical solution adopted is as follows:

[0008] A real-time detection device for the cleaning effect of a membrane based on electrochemical impedance spectroscopy, comprising: an electrolytic cell, an electrolytic cell cover capable of sealingly connecting with the electrolytic cell, a test electrode, and an electrochemical workstation;

[0009] The electrolytic cell has a two-chamber structure on the left and right. The two chambers are respectively filled with a cleaning agent and an electrolyte solution, and a contaminated membrane to be cleaned is fixed at the middle communication part. Among them, the fouled side of the contaminated membrane to be cleaned is in direct contact with the cleaning agent, and the unfouled side of the contaminated membrane to be cleaned is in direct contact with the electrolyte solution;

[0010] A test electrode mounting hole is penetrated through the electrolytic cell cover, a test electrode is installed in the test electrode mounting hole, and the front ends of the test electrodes are all located in the cleaning agent or the electrolyte solution;

[0011] The test electrode is connected to the electrochemical workstation through a wire.

[0012] The present invention constructs a two-electrode electrochemical system, uses the cleaning agent - electrolyte solution system to realize the real-time detection of the electrochemical information of the membrane surface fouling layer, evaluates the cleaning effect of the fouled membrane through the electrochemical characteristic information of the contaminated membrane to be cleaned, obtains the change law of the membrane surface fouling layer during the cleaning process, the device is simple, and the method is accurate and reliable, and can be used to optimize and improve the membrane cleaning process.

[0013] Preferably, the electrolytic cell is an H-type electrolytic cell. The two chambers of the H-type electrolytic cell are respectively filled with a cleaning agent and an electrolyte solution, and are connected through a communicating pipe in the middle. The contaminated membrane to be cleaned is clamped and fixed in the middle of the communicating pipe.

[0014] More preferably, the material of the H-type electrolytic cell is borosilicate glass, and the height is 30 - 40 mm.

[0015] Preferably, the contaminated membrane to be cleaned is a circular flat membrane with a diameter of 10 - 30 mm, the thickness is in millimeters, and the type is one of reverse osmosis membrane, nanofiltration membrane, ultrafiltration membrane, microfiltration membrane, ion exchange membrane or forward osmosis membrane.

[0016] The test electrode is a copper electrode, a platinum electrode or an alloy electrode, and the cleaning agent does not affect the action effect of the test electrode.

[0017] Preferably, the electrolytic cell cover is an acrylic cover.

[0018] Preferably, the active ingredients of the membrane cleaning agent are sodium hydroxide, sodium dodecylbenzenesulfonate, EDTA- tetrasodium, hydrochloric acid, citric acid, phosphoric acid, etc., and the electrolyte solution is a 0.05 - 0.1M KCl solution. The cleaning agent is added to one side of the membrane and the electrolyte solution is added to the other side to specifically clean the contaminated membrane and simultaneously monitor the information of the membrane contamination layer during the cleaning process in real time.

[0019] The present invention also provides a real - time detection method for the cleaning effect of a membrane based on electrochemical impedance spectroscopy, which includes the following steps:

[0020] (1) Use the above - mentioned real - time detection device for the cleaning effect of a membrane based on electrochemical impedance spectroscopy, keep the volumes of the cleaning agent and the electrolyte solution equal, and test the electrochemical impedance spectroscopy;

[0021] (2) Analyze the electrochemical impedance spectroscopy measured in step (1) using an equivalent circuit model to obtain the electrochemical characteristic information of the contaminated membrane to be cleaned, and evaluate the cleaning effect according to the electrochemical characteristic information.

[0022] Preferably, the contaminated membrane to be cleaned is soaked in pure water for 1 - 2h to be fully wetted and then put into the device for cleaning effect detection; the above operation can effectively avoid the influence of solution penetration in the membrane during the initial membrane infiltration process on the test results and ensure the accuracy of the test results.

[0023] The test frequency of the electrochemical impedance spectroscopy is 0.01 - 10 6 Hz. The corresponding test frequency band for different contaminated membranes to be cleaned should be determined according to the specific situation of the membrane. The amplitude of the AC perturbation voltage is 5mV, and the open - circuit voltage before the test is set as the initial voltage of the system.

[0024] The above - mentioned electrochemical characteristic information includes membrane resistance and double - layer structure, etc.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The present invention uses the contaminated membrane to be cleaned to divide the H - type electrolytic cell into a double - electrolytic chamber, so that the contaminated side of the contaminated membrane is in direct contact with the cleaning agent, and the uncontaminated side of the contaminated membrane is in direct contact with the electrolyte solution, simulating the soaking process in membrane cleaning, specifically cleaning the contaminated membrane and simultaneously monitoring the information of the membrane contamination layer during the cleaning process in real time, rather than only monitoring the contaminated layer of the membrane.

[0027] (2) The present invention analyzes the electrochemical characteristic information of the contaminated membrane to be cleaned, including membrane resistance and double - layer, etc., based on the electrochemical impedance spectroscopy method, and then evaluates the membrane cleaning effect and optimizes the membrane cleaning process; the device is simple and easy to assemble, the method is accurate and reliable, and the applicability is good.

[0028] (3) The detection device and method of the present invention are applicable to the evaluation of the cleaning effects of different cleaning agents, and are not restricted by the types of flat membranes, and can effectively detect the changes in the membrane fouling layer during the cleaning process. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of a real-time detection device for the cleaning effect of a membrane based on electrochemical impedance spectroscopy. 1 is a test electrode, 2 is an electrolytic cell cover, 3 is an electrolytic cell, 4 is an electrolyte solution, 5 is a cleaning agent, 6 is a contaminated membrane to be cleaned, and 7 is an electrochemical workstation.

[0030] Figure 2 It is a Nyquist diagram of the contaminated membrane to be cleaned at different soaking and cleaning times.

[0031] Figure 3 It is a graph showing the change of the resistance value of the contaminated membrane to be cleaned with the soaking and cleaning time. Detailed Embodiments

[0032] The present invention will be further clarified below in conjunction with embodiments and the drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0033] The schematic structural diagram of the real-time detection device for the cleaning effect of a membrane based on electrochemical impedance spectroscopy is as Figure 1 shown, including: an electrolytic cell 3, an electrolytic cell cover 2 that can be hermetically connected to the electrolytic cell, a test electrode 1, and an electrochemical workstation 7;

[0034] The electrolytic cell 3 has a left-right two-chamber structure. The two chambers are respectively filled with a cleaning agent 5 and an electrolyte solution 4, and a contaminated membrane 6 to be cleaned is fixed at the middle connection; among them, the fouled side of the contaminated membrane 6 to be cleaned is in direct contact with the cleaning agent 5, and the unfouled side of the contaminated membrane 6 to be cleaned is in direct contact with the electrolyte solution 4;

[0035] The electrolytic cell cover 2 is provided with a test electrode mounting hole penetrating through it. The test electrode mounting hole is provided with a test electrode 1, and the front ends of the test electrodes 1 are all located in the cleaning agent 5 or the electrolyte solution 4;

[0036] The test electrode 1 is connected to the electrochemical workstation 7 through a wire.

[0037] Specifically, a real-time detection method for the cleaning effect of a membrane based on electrochemical impedance spectroscopy includes the following steps:

[0038] (1) Prepare an electrolyte solution and a cleaning agent;

[0039] (2) Assemble the test device: Clamp and fix the contaminated membrane to be cleaned in the middle of the connecting pipe of the H-type electrolytic cell. Add the membrane cleaning agent to the electrolytic chamber on the contaminated side of the contaminated membrane to be cleaned, and add an equal volume of electrolyte solution to the electrolytic chamber on the non-contaminated side. Quickly cover the acrylic cover equipped with the test electrode, keep the volumes of the cleaning agent and the electrolyte solution equal, and adjust the test electrode to be immersed in the cleaning agent and the electrolyte solution. Connect the test electrode to the electrochemical workstation to perform the test of electrochemical impedance spectroscopy; wherein, the test frequency of the electrochemical impedance spectroscopy is 0.01 - 10 6 Hz, and the amplitude of the alternating perturbation voltage is 5 mV;

[0040] (3) Analyze the electrochemical impedance spectroscopy measured in step (1) using an equivalent circuit model to obtain the electrochemical characteristic information of the contaminated membrane to be cleaned, and evaluate the cleaning effect based on the electrochemical characteristic information.

[0041] Example 1

[0042] Cut a contaminated reverse osmosis membrane with a diameter of 30 mm (previously used for surface water treatment), with a membrane thickness of 1 - 2 mm. Immerse it in pure water for 1 - 2 h to fully wet it, clamp and fix it in the middle of the connecting pipe of the H-type electrolytic cell. Add 20 ml of the membrane cleaning agent (the main components are sodium hydroxide and water) to the electrolytic chamber on the contaminated side of the contaminated membrane to be cleaned, and add an equal volume of 0.1 M KCl solution to the electrolytic chamber on the non-contaminated side. Quickly cover the acrylic cover equipped with the platinum plate electrode, and adjust the platinum plate electrode to be immersed in the cleaning agent and the electrolyte solution. Connect the platinum plate electrode to the electrochemical workstation to perform the test of electrochemical impedance spectroscopy.

[0043] During the 0 - 8 h period of the immersion cleaning process, perform the test of electrochemical impedance spectroscopy on the membrane every 1 h to obtain the Nyquist diagram of the contaminated membrane to be cleaned at different immersion cleaning times as Figure 2 shown. It can be seen from the figure that as the cleaning immersion time increases, the Nyquist diagram shifts to the left, indicating that the contaminated layer on the membrane surface gradually becomes loose and even falls off.

[0044] Analyze the electrochemical impedance spectroscopy measured in step (1) using an equivalent circuit model to obtain the variation diagram of the resistance value of the contaminated membrane to be cleaned with the immersion cleaning time as Figure 3 shown. It can be Figure 3 seen that during the immersion process of the contaminated reverse osmosis membrane in the cleaning agent, the resistance value of the contaminated layer gradually decreases. After 5 h, extending the immersion cleaning time has no significant effect on the membrane resistance value, that is, it indicates that the immersion time after 5 h has no obvious improvement on the recovery of the membrane performance during the membrane cleaning process. The optimal immersion time in this cleaning process is 5 h. It shows that the method of the present invention can provide guidance for the cleaning of contaminated membranes, save the cleaning time while effectively restoring the membrane performance, and improve the efficiency of the membrane cleaning process.

[0045] Example 2

[0046] Cut a contaminated reverse osmosis membrane with a diameter of 30 mm (previously used for power plant boiler feed water), with a membrane thickness of 1 - 2 mm. Immerse it in pure water for 1 - 2 h to fully wet it, clamp and fix it in the middle of the connecting pipe of the H-type electrolytic cell. Add 40 ml of membrane cleaning agent (mainly composed of citric acid and water) to the electrolytic chamber on the contaminated side of the contaminated membrane to be cleaned, and add an equal volume of 0.1 M KCl solution to the electrolytic chamber on the non-contaminated side. Quickly cover it with an acrylic cover equipped with platinum sheet electrodes, and adjust the platinum sheet electrodes to be immersed in the cleaning agent and the electrolyte solution. Connect the platinum sheet electrodes to an electrochemical workstation to conduct electrochemical impedance spectroscopy tests.

[0047] During the period of 0 - 8 h in the soaking and cleaning process, conduct electrochemical impedance spectroscopy tests on the membrane every 1 h. Through the analysis of the Nyquist diagram and the equivalent circuit model, it is obtained that the resistance value of the contaminated layer of the contaminated reverse osmosis membrane gradually decreases during the soaking process in the cleaning agent, and after 7 h, extending the soaking time has no significant effect on the membrane resistance value.

[0048] Example 3

[0049] Cut a contaminated reverse osmosis membrane with a diameter of 10 mm (previously used for seawater desalination), with a membrane thickness of 1 - 2 mm. Immerse it in pure water for 1 - 2 h to fully wet it, clamp and fix it in the middle of the connecting pipe of the H-type electrolytic cell. Add 20 ml of membrane cleaning agent (mainly sodium hydroxide and water) to the electrolytic chamber on the contaminated side of the contaminated membrane to be cleaned, and add an equal volume of 0.1 M KCl solution to the electrolytic chamber on the non-contaminated side. Quickly cover it with an acrylic cover equipped with platinum sheet electrodes, and adjust the platinum sheet electrodes to be immersed in the cleaning agent and the electrolyte solution. Connect the platinum sheet electrodes to an electrochemical workstation to conduct electrochemical impedance spectroscopy tests.

[0050] During the period of 0 - 8 h in the soaking and cleaning process, conduct electrochemical impedance spectroscopy tests on the membrane every 1 h. Through the analysis of the Nyquist diagram and the equivalent circuit model, it is obtained that the resistance value of the contaminated layer of the contaminated reverse osmosis membrane gradually decreases during the soaking process in the cleaning agent, and after 6 h, extending the soaking time has no significant effect on the membrane resistance value.

[0051] Example 4

[0052] Cut a contaminated reverse osmosis membrane with a diameter of 10 mm (previously used for reclaimed water reuse), with a membrane thickness of 1 - 2 mm. Immerse it in pure water for 1 - 2 h to fully wet it, clamp and fix it in the middle of the connecting pipe of the H-type electrolytic cell. Add 20 ml of membrane cleaning agent (mainly sodium hydroxide and water) to the electrolytic chamber on the contaminated side of the contaminated membrane to be cleaned, and add an equal volume of 0.05 M KCl solution to the electrolytic chamber on the non-contaminated side. Quickly cover it with an acrylic cover equipped with platinum sheet electrodes, and adjust the platinum sheet electrodes to be immersed in the cleaning agent and the electrolyte solution. Connect the platinum sheet electrodes to an electrochemical workstation to conduct electrochemical impedance spectroscopy tests.

[0053] During the 0 - 8h period of the immersion cleaning process, the membrane was tested for electrochemical impedance spectroscopy every 1h. Through the analysis of the Nyquist plot and the equivalent circuit model, it was found that the resistance value of the contaminated layer of the reverse osmosis membrane gradually decreased during the immersion process in the cleaning agent, and after 6h, extending the immersion time had no significant effect on the membrane resistance value.

[0054] The above - described embodiments have elaborated on the technical solutions of the present invention. It should be understood that the above - described are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A real-time detection method for the cleaning effect of a membrane based on electrochemical impedance spectroscopy, characterized in that, It includes the following steps: (1) Use a real-time detection device for the cleaning effect of the membrane based on electrochemical impedance spectroscopy, keep the volumes of the cleaning agent and the electrolyte solution equal, and test the electrochemical impedance spectroscopy; (2) Analyze the electrochemical impedance spectroscopy measured in step (1) using an equivalent circuit model to obtain the electrochemical characteristic information of the contaminated membrane to be cleaned, and evaluate the cleaning effect based on the electrochemical characteristic information; The real-time detection device for the cleaning effect of the membrane based on electrochemical impedance spectroscopy includes: an electrolytic cell (3), an electrolytic cell cover (2) capable of being hermetically connected to the electrolytic cell, a test electrode (1), and an electrochemical workstation (7); The electrolytic cell (3) has a two-chamber structure on the left and right. The two chambers are respectively filled with a cleaning agent (5) and an electrolyte solution (4), and a contaminated membrane to be cleaned (6) is fixed at the middle connection; among them, the contaminated side of the contaminated membrane to be cleaned (6) is in direct contact with the cleaning agent (5), and the uncontaminated side of the contaminated membrane to be cleaned is in direct contact with the electrolyte solution (4); The electrolytic cell (3) is an H-shaped electrolytic cell. The two chambers of the H-shaped electrolytic cell are respectively filled with a cleaning agent (5) and an electrolyte solution (4), and are connected through a connecting pipe in the middle. The contaminated membrane to be cleaned (6) is clamped and fixed in the middle of the connecting pipe; A test electrode mounting hole is penetrated on the electrolytic cell cover (2), and a test electrode (1) is installed in the test electrode mounting hole. The front ends of the test electrodes (1) are all located in the cleaning agent or the electrolyte solution; The test electrode (1) is connected to the electrochemical workstation (7) through a wire.

2. The real-time detection method for membrane cleaning effect based on electrochemical impedance spectroscopy according to claim 1, wherein, The thickness of the contaminated membrane to be cleaned (6) is in millimeters, and the type is one of reverse osmosis membrane, nanofiltration membrane, ultrafiltration membrane or microfiltration membrane.

3. The real-time detection method for the membrane cleaning effect based on electrochemical impedance spectroscopy according to claim 1, characterized in that The test electrode (1) is a copper electrode, a platinum electrode or an alloy electrode.

4. The real-time detection method for the membrane cleaning effect based on electrochemical impedance spectroscopy according to claim 1, characterized in that, The active ingredients of the cleaning agent include sodium hydroxide, sodium dodecylbenzenesulfonate, EDTA-tetrasodium, hydrochloric acid, citric acid or phosphoric acid.

5. The real-time detection method for the membrane cleaning effect based on electrochemical impedance spectroscopy according to claim 1, wherein The electrolyte solution is a 0.05 - 0.1 M KCl solution.

6. The real-time detection method for the membrane cleaning effect based on electrochemical impedance spectroscopy according to claim 1, characterized in that, The contaminated membrane to be cleaned is soaked in pure water for 1 - 2 h to make it fully wetted and then put into the device for cleaning effect detection.

7. The real-time detection method for the membrane cleaning effect based on electrochemical impedance spectroscopy according to claim 1, wherein, The test frequency of the electrochemical impedance spectroscopy is 0.01 to 10 6 Hz, and the amplitude of the AC perturbation voltage is 5 mV.

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