阅读说明：本技术 原位监测膜表面污染状况的电化学方法及监测装置 (Electrochemical method for in-situ monitoring of membrane surface pollution condition and monitoring device ) 是由 张文娟 撖博 王执伟 常晶 王雨菲 王少坡 张宇峰 马军 于 2019-10-22 设计创作，主要内容包括：本发明涉及到一种原位监测膜表面污染状况的电化学方法,该测试体系包括四电极体系监测装置、电化学工作站、控温水浴槽和齿轮泵。将待测膜放入四电极体系装置中使膜面与电解质溶液接触构成串联电路,采用电化学阻抗谱法获得的电流或电压信号反映在电化学工作站软件中形成阻抗谱或导纳谱,然后选用等效电路模型对阻抗谱或导纳谱进行非线性最小二乘法拟合、分析,获得该体系的电化学信息后通过拟合得出所测膜污染过程中污染层及膜-溶液界面层的电化学参数值。本发明的有益效果是：准确性高、简单实用,并且对膜的测量是非损伤性的,有助于提高测试精度和减小膜不均匀性所引起的误差,可以有效表征膜污染过程中膜本身及其界面电化学特性的变化。(The invention relates to an electrochemical method for in-situ monitoring of the pollution condition of a membrane surface. The membrane to be measured is placed in a four-electrode system device to enable the membrane surface to be contacted with an electrolyte solution to form a series circuit, current or voltage signals obtained by an electrochemical impedance spectroscopy are reflected in electrochemical workstation software to form an impedance spectrum or an admittance spectrum, then an equivalent circuit model is selected to perform nonlinear least square fitting and analysis on the impedance spectrum or the admittance spectrum, and electrochemical parameters of a pollution layer and a membrane-solution interface layer in the measured membrane pollution process are obtained through fitting after electrochemical information of the system is obtained. The invention has the beneficial effects that: the method has the advantages of high accuracy, simplicity, practicability, non-damage to the measurement of the membrane, contribution to improving the test precision and reducing the errors caused by the nonuniformity of the membrane, and capability of effectively representing the change of the electrochemical characteristics of the membrane and the interface thereof in the membrane pollution process.)

1. An electrochemical method for in-situ monitoring of the contamination of a membrane surface, comprising the steps of:

(1) preparing an electrolyte solution to be tested;

(2) connecting a test device: connecting a four-electrode testing device with an electrochemical workstation and a gear pump;

(3) operating the membrane to be tested: putting the membrane to be tested into a membrane clamping part in a four-electrode testing device, driving the electrolyte solution prepared in the step (1) into the four-electrode testing device, and starting a gear pump;

(4) measuring current or voltage signals using electrochemical impedance spectroscopy: applying a small-amplitude disturbance signal and sinusoidal alternating voltage or current to the monitoring device through the electrochemical workstation, collecting a response current or voltage signal by the electrochemical workstation, and reflecting the response current or voltage signal in Nova software carried by the electrochemical workstation to form an impedance spectrum EIS or an admittance spectrum;

(5) taking out the test film: stopping the operation of the four-electrode testing device, disconnecting the four-electrode testing device from the electrochemical workstation and the gear pump, and disassembling the four-electrode testing device;

(6) measurement of resistance value of blank solution: reassembling the four-electrode testing device and connecting the four-electrode testing device with an electrochemical workstation and a gear pump, wherein the resistance value of the solution is obtained by a blank experiment, and the measured total resistance minus the resistance value of the blank solution is the resistance of the film, the double electric layers, the diffusion boundary layer and the pollution layer;

(7) performing nonlinear least square fitting and analysis on the impedance spectrum or admittance spectrum obtained in the step (4) by using an equivalent circuit model to obtain electrochemical characteristic information of the test membrane,

is calculated by the formula

Where n is the number of data points selected for calculation, g'_i，g″_iRespectively the real part and the imaginary part of the admittance data;

(8) the electrochemical characteristic information of step (7) includes resistance values of the solution and the membrane, an electric double layer naturally formed by the test membrane in the solution, a diffusion boundary layer, a resistance of a contamination layer, and a resistance value of the electric double layer, the greater the resistance value of the contamination layer, the more easily the membrane is contaminated, and the greater the resistance value of the contamination layer, the more seriously the membrane is contaminated.

2. The electrochemical method for in situ monitoring of membrane surface contamination according to claim 1, wherein: the electrolyte solution in the step (1) is NaCl solution, the purity level of inorganic salt used for preparing the electrolyte solution is superior purity, the used water is deionized water, and the electrolyte solution is added with typical pollutants of bovine serum albumin or sodium alginate with different concentrations to simulate pollutants in natural water.

3. The electrochemical method for in situ monitoring of membrane surface contamination according to claim 1, wherein: the membrane to be tested in the step (3) is an ion exchange membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane or a forward osmosis membrane, and pretreatment is carried out before testing: soaking in 0.5M NaCl solution for 24 hr, and replacing the solution for 4 times to remove residual chemical solvent in the membrane.

4. The electrochemical method for in situ monitoring of membrane surface contamination according to claim 1, wherein: the electrolyte solution in the step (3) is circulated.

5. The electrochemical method for in situ monitoring of membrane surface contamination according to claim 1, wherein: the environmental temperature of the electrolyte solution prepared in the step (3) is 10-40 ℃.

6. The electrochemical method for in situ monitoring of membrane surface contamination according to claim 1, wherein: the EIS testing frequency in the step (4) can be 1000000-0.01 Hz, wherein the testing frequency sections corresponding to different films are different, the amplitude of the alternating voltage is 0.01V, and 50 frequency points are taken in each test; the open circuit potential before the test was started was set to the initial potential of the device.

7. The electrochemical method for in situ monitoring of membrane surface contamination according to claim 1, wherein: the equivalent circuit model in the step (7) is formed by the sum R of the resistances of the solution and the film_m+sThe test membrane is formed by connecting four parts of circuit elements of an electric double layer, a diffusion boundary layer and a pollution layer which are naturally formed in a solution from left to right in series, wherein the membrane and the solution are formed by a resistor R_m+sThe electric double layer is represented by a resistor R_edlAnd phase angle constant element Q_dIn parallel, the diffusion boundary layer is represented by a resistor R_dAnd phase angle constant element Q_dParallel, the contamination layer is represented by a resistor R_foulingAnd phase angle constant element Q_foulingParallel representation; the fitting results in the sum of the resistances R of the solution and the membrane_m+sResistance value R of electric double layer_edlCapacitance value C of the electric double layer_edlResistance value R of diffusion boundary layer_dCapacitance value C of diffusion boundary layer_dResistance value R of the contamination layer_foulingAnd the capacitance C of the contamination layer_foulingThe resistance Rs of the solution is determined by a blank test, the intrinsic resistance R of the pure film_mFrom the sum R of the resistances of the solution and the membrane_m+sMinus the resistance R of the solution_sResult in that R is_m＝R_m+s-R_s. The total resistance R of the film is measured_total＝R_m+R_edl+R_d+R_fouling。

8. A measuring device for in-situ monitoring of the contamination of a membrane surface according to claim 1, wherein: including the rotatory test cell that sets up of bilateral symmetry, press from both sides membrane part (3), four electrode system and outside electrochemistry workstation, gear pump, four electrode system includes working electrode (1), counter electrode (1) and two reference electrode (2), working electrode (1) and counter electrode (1) are the Ag AgCl electrode of disc respectively, two reference electrode (2) are the Ag AgCl electrode of placing in the lujin capillary.

9. The apparatus for in-situ monitoring the contamination of a membrane surface according to claim 8, wherein: the test tank is formed with four water passageways, four water passageways correspond inhalant canal (8,9) that set up and play water passageway (6,7) that upper portion set up for the test tank lower part corresponds, and the gear pump is squeezed into electrolyte solution from inhalant canal (8,9) on test tank both sides lower limit respectively, and electrolyte solution then flows from play water passageway (8,9) on test tank both sides upper limit respectively to guarantee that test membrane both sides environment is unanimous.

10. The apparatus for in-situ monitoring the contamination of a membrane surface according to claim 8, wherein: the diameter of the Ag/AgCl electrode is 10 mm; the effective membrane area of the membrane clamping part (3) is 3.14cm²。

Technical Field

The invention relates to the technical field of membranes, in particular to an electrochemical method for in-situ monitoring of membrane surface pollution condition and a monitoring device thereof.

Background

The membrane separation technology has been widely used in the fields of sewage treatment, seawater desalination, medicine, food processing, medical treatment, chemical industry, bionics and the like due to the characteristics of high efficiency, energy conservation, environmental protection, easy control and the like. However, membrane fouling is one of the main causes that restrict the application of membrane technology. Membrane fouling is the process of depositing contaminants on the membrane surface, where the contaminants in the water can adhere to the membrane surface and/or enter the membrane interior by electrostatic and chemical forces and form a fouling layer on the membrane surface. Membrane fouling causes a decrease in membrane performance such as flux and conductivity, and the phenomena of increased power consumption, shortened membrane life, etc. caused by membrane fouling have become major problems limiting the application and economic feasibility of membrane devices.

Membrane fouling is reported in many documents, most of which focuses on characterization of membrane physical properties and membrane material characteristics, and membrane fouling conditions cannot be monitored in real time. The development and application of a suitable nondestructive online membrane pollution monitoring technology have important application value for effectively quantifying the prevention and treatment of membrane pollution and the effect of membrane cleaning. The membrane pollution process is accompanied by the change of the electrochemical characteristics of the membrane surface, and the degree and the trend of the membrane pollution are related to the physical, chemical and electrochemical characteristics of the membrane surface and the types of pollutants. The pollution tendency and degree of the membrane can be evaluated through the change of electrochemical characteristics of the membrane and the interface thereof in the membrane pollution process.

Disclosure of Invention

The invention aims to provide a simple and reliable electrochemical method for in-situ monitoring of the membrane surface pollution condition and a monitoring device thereof.

In order to solve the technical problems, the invention adopts the technical scheme that: an electrochemical method for in-situ monitoring of the contamination of a membrane surface, comprising the steps of:

(1) preparing an electrolyte solution to be tested;

(2) putting a film to be tested into a film clamping part in a four-electrode testing device;

(3) connecting a four-electrode testing device with an electrochemical workstation and a gear pump, starting the gear pump, pumping the electrolyte solution prepared in the step (1) into the four-electrode testing device, and operating for a period of time to stabilize the condition of a testing membrane;

(4) applying a small-amplitude disturbance signal and sinusoidal alternating voltage or current to a monitoring device through an electrochemical workstation by adopting an electrochemical impedance spectroscopy method, collecting a response current or voltage signal by the electrochemical workstation, and reflecting the response current or voltage signal in Nova software carried by the electrochemical workstation to form an impedance spectrum EIS or an admittance spectrum;

(5) stopping the operation of the four-electrode testing device, disconnecting the four-electrode testing device from the electrochemical workstation and the gear pump, disassembling the four-electrode testing device and taking out the testing membrane;

(6) reassembling the four-electrode testing device, connecting the four-electrode testing device with an electrochemical workstation and a gear pump, and performing a blank experiment to obtain the resistance value of a blank solution;

(7) carrying out nonlinear least square fitting and analysis on the impedance spectrum or the admittance spectrum obtained in the step (4) by using an equivalent circuit model to obtain electrochemical characteristic information of the test membrane, wherein the calculation formula is

Where n is the number of data points selected for calculation, g'_i，g″_iRespectively the real part and the imaginary part of the admittance data;

the electrolyte solution in the step (1) is a NaCl solution, the purity level of inorganic salt used for preparing the electrolyte solution is superior purity, the used water is deionized water, and the electrolyte solution is added with typical pollutants (such as bovine serum albumin or sodium alginate) with different concentrations to simulate pollutants in natural water.

Soaking the membrane to be tested in the step (2) in 0.5M NaCl solution for 24h before testing, and replacing the solution for 4 times to remove the residual chemical solvent in the membrane.

The electrolyte solution in the step (3) is circulated.

The environmental temperature of the electrolyte solution prepared in the step (3) is 10-40 ℃.

The EIS testing frequency in the step (4) can be 1000000-0.01 Hz, wherein the testing frequency sections corresponding to different films are different, the amplitude of the alternating voltage is 0.01V, and 50 frequency points are taken in each test; the open circuit potential before the test was started was set to the initial potential of the device.

The equivalent circuit model in the step (7) is formed by the sum R of the resistances of the solution and the film_m+sThe test membrane is formed by connecting four parts of circuit elements of an electric double layer, a diffusion boundary layer and a pollution layer which are naturally formed in a solution from left to right in series, wherein the membrane and the solution are formed by a resistor R_m+sThe electric double layer is represented by a resistor R_edlAnd phase angle constant element Q_dIn parallel, the diffusion boundary layer is represented by a resistor R_dAnd phase angle constant element Q_dParallel, the contamination layer is represented by a resistor R_foulingAnd phase angle constant element Q_foulingParallel representation; the fitting results in the sum of the resistances R of the solution and the membrane_m+sResistance value R of electric double layer_edlCapacitance value C of the electric double layer_edlResistance value R of diffusion boundary layer_dCapacitance value C of diffusion boundary layer_dResistance value R of the contamination layer_foulingAnd the capacitance C of the contamination layer_foulingThe resistance Rs of the solution is determined by a blank test, the resistance R of the pure film_mFrom the sum R of the resistances of the solution and the membrane_m+sMinus the resistance R of the solution_sAnd (6) obtaining.

The utility model provides a measuring device of electrochemistry method of in situ monitoring membrane surface pollution condition, includes test cell, double-layered membrane part, four electrode system and outside electrochemistry workstation, the gear pump of bilateral symmetry rotation setting, four electrode system includes working electrode, counter electrode and two reference electrodes, working electrode and counter electrode are the Ag AgCl electrode of disc form respectively, two reference electrodes are the Ag AgCl electrode of placing in lujin capillary.

The test tank is formed with four water passageways, and the gear pump is squeezed into electrolyte solution from the water passageway of test tank both sides lower limit respectively, and electrolyte solution then flows from the water passageway of test tank both sides upper limit respectively to guarantee that the test membrane both sides environment that awaits measuring is unanimous.

The diameter of the Ag/AgCl electrode is 10 mm; the effective membrane area of the membrane clamping part is 3.14cm²。

The invention has the beneficial effects that: the method and the device for acquiring the electrochemical characteristics of the membrane surface can measure the electrochemical properties of a test membrane, a surface interface layer and a pollution layer by an EIS method. The resistance value and the capacitance value in the equivalent circuit can reflect the structure of a testing membrane system, so that the equivalent circuit is utilized to fit impedance spectrum data, the conductivity value and the capacitance value of the interface layer and the pollution layer can be quantitatively analyzed, and the pollution tendency and degree of the membrane can be further evaluated. The device is accurate, reliable and simple to operate, and is suitable for in-situ monitoring of the surface pollution conditions of various films.

Drawings

FIG. 1 is a schematic diagram of an experimental setup for an electrochemical method of in situ monitoring of membrane surface contamination according to the present invention;

FIG. 2 is a schematic diagram of the overall structure of the four-electrode system test apparatus of the present invention;

FIG. 3 is a schematic structural diagram of a film clamping component of the four-electrode system testing device of the present invention;

FIG. 4 is an equivalent circuit model of the present invention for non-linear least squares fitting of impedance spectra;

FIG. 5 is electrochemical impedance spectroscopy data and fitted curves of the membrane of the invention after AEM-Type I contamination at a flow rate of 2cm/s, a temperature of 20. + -. 2 ℃, a solution of 0.5mol/LNaCl + 0.5% SA, and a time of 57.4 h;

FIG. 6 is a graph of AEM-Type II membranes of the invention subjected to S at various flow ratesA fouling membrane resistance (R)_m) And total resistance (R) of the system_total) A change over time;

FIG. 7 is the membrane resistance (R) of the membrane AEM-Type II of the invention when contaminated with SA at different NaCl concentrations_m) And film fouling layer property changes;

FIG. 8 is the membrane resistance (R) of the membrane AEM-Type II of the invention_m) And the change in the nature of the fouling layer over time during the contamination by SA/BSA.

In the figure:

1. working electrode, counter electrode 2, reference electrode

3. Film clamping component 4 and electrochemical workstation

5. Computer 6, left side water outlet channel

7. Right side water outlet channel 8 and left side water inlet channel

9. Right water inlet channel

Detailed Description

The invention is described in further detail below with reference to the following figures and detailed description:

as shown in fig. 1, an electrochemical method for in-situ monitoring of the contamination condition of a membrane surface comprises the following steps:

(1) preparing an electrolyte solution to be tested;

(2) putting a film to be tested into a film clamping part in a four-electrode testing device;

(3) connecting a four-electrode testing device with an electrochemical workstation and a gear pump, starting the gear pump, pumping the electrolyte solution prepared in the step (1) into the four-electrode testing device, and operating for a period of time to stabilize the condition of a testing membrane;

(4) applying a small-amplitude disturbance signal and sinusoidal alternating voltage or current to a monitoring device through an electrochemical workstation by adopting an electrochemical impedance spectroscopy method, collecting a response current or voltage signal by the electrochemical workstation, and reflecting the response current or voltage signal in Nova software carried by the electrochemical workstation to form an impedance spectrum EIS or an admittance spectrum;

(5) stopping the operation of the four-electrode testing device, disconnecting the four-electrode testing device from the electrochemical workstation and the gear pump, disassembling the four-electrode testing device and taking out the testing membrane;

(6) reassembling the four-electrode testing device, connecting the four-electrode testing device with an electrochemical workstation and a gear pump, and performing a blank experiment to obtain the resistance value of a blank solution;

(7) and (4) carrying out nonlinear least square fitting and analysis on the impedance spectrum or the admittance spectrum obtained in the step (4) by using an equivalent circuit model to obtain electrochemical characteristic information of the test membrane.

An electrochemical measuring device for obtaining the contamination condition of the membrane surface, which implements the above method, is shown in fig. 2 and 3, and comprises a working electrode, a counter electrode, a reference electrode, and a membrane sandwiching member. And (4) placing the pretreated test membrane into a membrane clamping part, and fixing by using screws. And all the parts are connected in series and fixed by long screws. Electrolyte solution for testing is placed in the constant temperature water bath, two gear pump inlets are connected through rubber guide pipes, then the electrolyte solution is pumped into water inlets 8 and 9 of the testing device, and then returns to the constant temperature water bath from water outlets 6 and 7 of the testing device to flow circularly. The blank experiment is no film in the four-electrode testing device, and the rest steps are the same.