Method and device for testing liquid-phase in-situ morphology of flat filtering membrane

Abstract

The invention discloses a method and a device for testing the liquid phase in-situ morphology of a flat filtering membrane. The device comprises a feed liquid box, a pressure pump and an in-situ sample table which are connected through a pipeline, wherein the pressure pump is connected with a liquid injection channel of the in-situ sample table through a pipeline. The method adopts an in-situ morphology testing method, is suitable for in-situ micro-morphology analysis of the pressure-driven flat plate filtering membrane in a liquid phase environment, can adjust various factors such as filtering pressure, filtering time, filtering feed liquid types and testing temperature, and has the advantages of integrated testing, real-time operation, wide applicability, simple steps and the like.

Description

Technical Field

[0001] The invention relates to filter membrane testing, in particular to a liquid phase in-situ morphology testing method and device for a flat filter membrane. Background Art

[0002] With the continuous advancement of science and technology and the increasing significance of environmental protection, membrane separation technology has become one of the widely used technologies in the fields of environmental protection and production due to its advantages of energy saving, environmental protection, small footprint, mild operating conditions, and easy scale-up. Membrane structure design and development is an inevitable trend in the research of high-performance filtration membrane materials. The accurate analysis of its micromorphology is crucial to improving the performance and service life of membrane materials. At present, the test of the evolution of membrane micromorphology during the filtration process is still a difficult problem, and there is a lack of corresponding in-situ test methods. Therefore, the development of test methods that can be used to characterize membrane materials in situ and determine membrane performance and life has become an urgent problem to be solved.

[0003] The changes in membrane micromorphology during membrane filtration usually occur at the micrometer or even nanometer scale, requiring the observation equipment to have extremely high resolution and sensitivity. During the in-situ observation process, it is necessary to ensure the stability of the membrane in the liquid phase environment driven by pressure, and to capture the morphological changes on the membrane surface in real time. Conventional scanning electron microscopes provide high-resolution surface imaging, which often requires high vacuum and dry testing conditions, and cannot truly capture the micromorphological changes during membrane filtration. Cryo-scanning electron microscopy does not require chemical fixation, can fix samples at low temperatures, and observe samples under vacuum. It can maintain the original morphology and structure of the material containing the filtration liquid, avoiding problems such as decomposition, shrinkage or drying that may occur in conventional electron microscopes. However, there are some technical obstacles to the in-situ characterization of filtration membranes, including observing the morphology of the membrane under operating pressure and isolating it from air contact during sample preparation. Summary of the invention

[0004] The present invention designs and proposes a liquid phase in-situ morphology testing method for a flat filter membrane, which fully considers factors such as the electronic signal acceptability, temperature controllability, and filtration pressure controllability of the sample, and has the characteristics of integrated testing, high precision, and easy operation. It brings a new entry point for research institutions and production enterprises, which will greatly promote the development of membrane separation technology, improve the level of membrane separation technology, and promote the development of environmental protection and industrial production.

[0005] The present invention provides the following technical solution: a liquid phase in-situ morphology testing method for a flat filter membrane, comprising the following steps: (1) Placing a flat filter membrane in an in-situ sample stage; the in-situ sample stage is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and a liquid outlet channel for discharging the filter liquid; the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate for supporting the flat filter membrane; (2) Driven by the pressure pump, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane and the support plate in turn, and is discharged through the liquid outlet channel; (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage in the supercooled liquid nitrogen for freezing; (4) Transferring the in-situ sample stage to a vacuum environment, breaking, sublimating, and spraying the frozen flat filter membrane; (5) Place the in-situ sample stage carrying the flat filter membrane into the cold stage of a scanning electron microscope for morphological observation.

[0006] Further, the flat filter membrane is one of polysulfone, polyethersulfone, polyamide, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, graphene oxide, chitosan, and alumina; the filter liquid is one of water, an organic solvent, an alcohol-water mixture, an aqueous solution of organic pollutants, an electrolyte solution, or an aqueous protein solution; the organic solvent includes N,N-dimethylformamide, N-methylpyrrolidone, ethylene glycol, ethylene glycol monomethyl ether, butanol, octanol, octyl acetate, and dimethyl sulfoxide; the alcohol-water mixture includes a mixture of methanol and water, a mixture of ethanol and water, a mixture of ethylene glycol and water, a mixture of octanol and water, a mixture of isopropanol and water, a mixture of benzyl alcohol and water, a mixture of isopentanol and water, a mixture of isobutanol and water, a mixture of n-propanol and water, and n-butanol. A mixture of alcohol and water or a mixture of sec-butyl alcohol and water; an aqueous solution of organic pollutants includes an aqueous solution of methyl blue, an aqueous solution of methyl red, an aqueous solution of ethyl formate, an aqueous solution of alkaline green, an aqueous solution of direct red, an aqueous solution of direct yellow, and an aqueous solution of direct ash; an electrolyte solution includes an aqueous solution of sodium hydroxide, an aqueous solution of potassium sulfate, an aqueous solution of sodium sulfate, an aqueous solution of magnesium sulfate, an aqueous solution of calcium sulfate, an aqueous solution of sodium chloride, an aqueous solution of magnesium chloride, an aqueous solution of calcium chloride, and an aqueous solution of potassium chloride; an aqueous protein solution includes an aqueous solution of fibrin, an aqueous solution of globulin, an aqueous solution of collagen, an aqueous solution of myoglobin, and an aqueous solution of polyaspartic acid; the concentrations of the alcohol-water mixture, the aqueous solution of organic pollutants, the electrolyte solution, and the aqueous protein solution are all 0.5-5 g·L -1 .

[0007] Furthermore, the support plate includes a first support plate and a second support plate, and the flat filter membrane, the second support plate and the first support plate are sequentially attached; the flat filter membrane divides the pressure tank into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate and the second support plate have a plurality of evenly distributed through holes, the first support plate is located on one side of the liquid outlet part, and the flat filter membrane is located on one side of the liquid injection part.

[0008] Furthermore, the temperature of the filtered liquid in step (1) and step (2) is 20-30°C.

[0009] Furthermore, the pressure of the pressure pump is 1-5 bar, and the driving time of the pressure pump is 0.5-36 h.

[0010] Furthermore, the breaking is to cut off the ice on the surface of the flat filter membrane with a sharp cold knife in a frozen state, so that the flat filter membrane is mechanically broken by the breaking of the ice.

[0011] Furthermore, the freezing temperature is -20~-165°C, the sublimation is that the flat filter membrane sublimates in a vacuum at -10~-135°C, the temperature during sublimation is 10~50°C higher than the temperature during freezing, and the sublimation time is 1~10 min; the spraying is to spray platinum particles on the flat filter membrane, the spraying current is 5~20 mA, and the spraying time is 10~60 s.

[0012] A device for implementing the above-mentioned liquid phase in-situ morphology testing method of a flat filter membrane comprises a liquid tank, a pressure pump, and an in-situ sample stage connected by pipelines, wherein the pressure pump is connected to a liquid injection channel of the in-situ sample stage by a pipeline.

[0013] Furthermore, the feed liquid box controls the temperature of the filtered feed liquid through a temperature control system, and the liquid outlet channel of the in-situ sample stage is connected to the feed liquid box through a pipeline.

[0014] Furthermore, the support plate includes a first support plate and a second support plate, and the flat filter membrane, the second support plate and the first support plate are sequentially attached; the aperture of the through hole on the first support plate is 0.8~1 mm, and the aperture of the through hole on the second support plate is 50~100 mesh.

[0015] The beneficial effects of the present invention are: The present invention adopts an in-situ morphology testing method, which is suitable for in-situ microscopic morphology analysis of pressure-driven flat filter membranes in a liquid environment. It can adjust multiple factors such as filtration pressure, filtration time, type of filtration liquid, test temperature, etc., and has the advantages of integrated testing, real-time operation, wide applicability, and simple steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of the liquid phase in-situ morphology testing device of the flat filter membrane in Example 1; Figure 2 is a schematic diagram of the structure of the first support plate, the second support plate and the flat filter membrane; Figure 3 It is a schematic structural diagram of the liquid phase in-situ morphology testing device of the flat filter membrane in Example 5; Figure 4 It is a schematic structural diagram of the liquid phase in-situ morphology testing device of the flat filter membrane in Example 6; Figure 5In situ cryo-scanning electron microscope images of the cross-sections of the flat filter membranes in Examples 1 to 4 and Comparative Examples 1 to 8 of the present invention, wherein a is an image of Example 1, b is an image of Example 2, c is an image of Example 3, d is an image of Example 4, e is an image of Comparative Example 1, f is an image of Comparative Example 2, g is an image of Comparative Example 3, h is an image of Comparative Example 4, i is an image of Comparative Example 5, j is an image of Comparative Example 6, k is an image of Comparative Example 7, and l is an image of Comparative Example 8; Figure 6 The following are the frozen scanning electron microscope images of the unfiltered flat filter membrane in Example 9-Comparative Example 10 of the present invention and the room temperature scanning electron microscope cross-sectional images after drying. Figure 6 a and b are cryo-SEM images of the unfiltered membrane of Comparative Example 9 of the present invention at different magnifications; Figure 6 c and d are scanning electron microscope images of the unfiltered membrane section after drying at different magnifications at room temperature in Comparative Example 10 of the present invention;

[0017] Among them, there are a liquid tank 1, a pressure pump 2, an in-situ sample table 3, a support plate 4, a first support plate 4-1, a second support plate 4-2, a flat filter membrane 5, and a temperature control system 6. DETAILED DESCRIPTION

[0018] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0019] The present invention simulates the real working condition of the flat filter membrane by controlling multiple factors such as filtration pressure, filtration time, type of filtration liquid, test temperature, etc., thereby realizing the liquid phase in-situ morphology test method of the flat filter membrane, so that the test of the flat filter membrane is completely consistent with the real working condition.

[0020] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0021] Example 1 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0022] The testing method includes the following steps: (1) Place a flat filter membrane 5 in the in-situ sample stage 3. The flat filter membrane 5 is made of polyamide. Inject the filter liquid into the pressure tank through the injection channel and discharge the filter liquid through the outlet channel. The filter liquid is 1 g·L -1 An aqueous solution of methyl blue; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 5 bar, and the driving time of the pressure pump 2 is 0.5 h. The temperature of the filtered liquid in step (1) and step (2) is 25°C.

[0023] After the pressure pump 2 is driven for 0.5h, i.e., in the micro-pollution stage, the membrane flux is calculated by calculating the produced liquid volume per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=1.5*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=3.0 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0024] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-5*10 -3 g•L -1 / 1 g•L -1 )×100%=99.5%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0025] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, the freezing temperature is -140 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -100 °C, the temperature during sublimation is 40 °C higher than the temperature during freezing, and the sublimation time is 5 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 10 mA, and the spraying time is 10 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope at -140 °C for morphological observation.

[0026] Figure 5 Figure a is an in-situ cryo-scanning electron microscope image of the membrane cross section in an embodiment of the present invention, and the intermediate pore structure shows partial blockage. Figure 6 The following are the frozen scanning electron microscope images of the unfiltered flat filter membrane in Example 9-Comparative Example 10 of the present invention and the room temperature scanning electron microscope cross-sectional images after drying. Figure 6 a and b are cryo-SEM images of the unfiltered membrane of Comparative Example 9 of the present invention at different magnifications; Figure 6 Figures c and d are room temperature scanning electron microscope images of the unfiltered membrane section in comparative example 10 of the present invention after drying at different magnifications. The two have similar morphologies, both including a top blade structure, a dense porous structure in the middle, and a loose porous structure in the lower layer. By comparison, it can be seen that micro-pollution in this example leads to a decrease in pore volume. Example 2

[0027] A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0028] The testing method includes the following steps: (1) A flat filter membrane 5 is placed in the in-situ sample stage 3. The flat filter membrane 5 is made of polyamide. The in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting the filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid. The filter liquid is 1 g•L -1 An aqueous solution of methyl blue; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 5 bar, and the driving time of the pressure pump 2 is 6 hours; The temperature of the filtered liquid in step (1) and step (2) is 25°C.

[0029] After the pressure pump 2 was driven for 6 h, i.e., in the filtration pollution stage, the membrane flux was calculated by calculating the production liquid volume per unit time, and the retention rate was calculated by the difference in concentration between the filtered feed liquid and the production liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=0.75*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=1.5 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0030] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-5*10 -3 g•L -1 / 1 g•L -1 )×100%=99.5%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0031] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, and the freezing temperature is -140 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -100 °C, the temperature during sublimation is 40 °C higher than the temperature during freezing, and the sublimation time is 5 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 10 mA, and the spraying time is 10 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope at -140 °C for morphological observation.

[0032] Figure 5 Figure b is an in-situ cryo-scanning electron microscope image of the membrane cross section in the embodiment of the present invention. Due to the long-term operation of the pollutant solution in the membrane, the middle pores and the loose pores in the lower layer are partially blocked.

[0033] Example 3 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0034] The testing method includes the following steps: The steps include: (1) A flat filter membrane 5 is placed in the in-situ sample stage 3. The flat filter membrane 5 is made of polyamide. The in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid. The filter liquid is 1 g•L -1 An aqueous solution of methyl blue; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 5 bar, and the driving time of the pressure pump 2 is 6 h. The temperature of the filtered liquid in step (1) and step (2) is 25°C.

[0035] After the pressure pump 2 was driven for 6 h, i.e., in the filtration pollution stage, the driving was stopped and backwashed with deionized water for 0.5 h. The membrane flux was calculated by calculating the production volume per unit time, and the retention rate was calculated by the difference in concentration between the filtered feed liquid and the production liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=1.25*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=2.5 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h-1 •bar -1 .

[0036] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-5*10 -3 g•L -1 / 1 g•L -1 )×100%=99.5%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0037] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, the freezing temperature is -140 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -100 °C, the temperature during sublimation is 40 °C higher than the temperature during freezing, and the sublimation time is 5 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 10 mA, and the spraying time is 10 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope at -140 °C for morphological observation.

[0038] Figure 5 Figure c is an in-situ cryo-scanning electron microscope image of the membrane cross section in the embodiment of the present invention. The pore blockage problem is alleviated after backwashing, and the middle pores and the loose pores in the lower layer are partially restored. The reason is that the pollution is reduced after backwashing and the volume of the contaminated pores is increased.

[0039] Example 4 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0040] The testing method includes the following steps: (1) A flat filter membrane 5 is placed in the in-situ sample stage 3. The flat filter membrane 5 is made of polyamide. The in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid. The filter liquid is 5 g·L -1 An aqueous solution of sodium hydroxide; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 5 bar; The temperature of the filtered liquid in step (1) and step (2) is 25°C.

[0041] Pressure pump 2 drives the filtration to calculate the interception rate and permeation flux data every 0.5 h until the flux suddenly increases by more than 10%, that is, the membrane is damaged, and the experiment is stopped. The membrane flux is calculated by calculating the production volume per unit time, and the interception rate is calculated by the difference in concentration between the filtered feed liquid and the production liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=2.25*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=4.5 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar-1 .

[0042] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-0.15 g•L -1 / 1 g•L -1 )×100%=85.0%; Among them C p is the concentration of produced liquid, C f The concentration of the filtered liquid is characterized by a conductivity meter or an ion meter.

[0043] (3) Vacuum the liquid nitrogen, wait for it to form solid liquid nitrogen mud, then release the pressure to form supercooled liquid nitrogen, immerse the in-situ sample stage in the supercooled liquid nitrogen for freezing, and the freezing temperature is -140 °C; (4) The in-situ sample stage is transferred to a vacuum environment, and the frozen flat filter membrane is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane in a vacuum at -100 °C, the temperature during sublimation is 40 °C higher than the temperature during freezing, and the sublimation time is 5 min; the spraying is to spray platinum particles on the flat filter membrane, the spraying current is 10 mA, and the spraying time is 10 s; (5) The in-situ sample stage 3 carrying the flat filter membrane was placed in the cold stage of a scanning electron microscope at -140 °C for morphological observation.

[0044] Figure 5 d in the figure is an in-situ cryo-SEM image of the membrane cross section in the embodiment of the present invention. The corrosive solution causes a large degree of damage to the membrane structure, and the middle pores and the lower loose pores are deformed and damaged. In-situ characterization shows that there is ice support in the pores, which can fully display the damage morphology.

[0045] Example 5 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 3The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines. The pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline, and the liquid tank 3 controls the temperature of the filtered liquid through a temperature control system 5. The in-situ sample stage 3 is provided with a pressure tank, and the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure tank into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0046] In some embodiments, the temperature of the filtered liquid may not be controlled by the temperature control system 5 , but the filtered liquid with a pre-controlled temperature may be injected into the liquid tank 3 .

[0047] The testing method includes the following steps: A method for testing the liquid phase in-situ morphology of a flat filter membrane comprises the following steps: (1) placing a flat filter membrane 5 in an in-situ sample stage 3, wherein the flat filter membrane 5 is polysulfone; the in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and a liquid discharge channel for discharging the filter liquid, wherein the filter liquid is water; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 1 bar, and the driving time of the pressure pump 2 is 6 hours; The temperature of the filtered liquid in step (1) and step (2) is 20°C.

[0048] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, and the freezing temperature is -20 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -10 °C, the temperature during sublimation is 10 °C higher than the temperature during freezing, and the sublimation time is 1 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 5 mA, and the spraying time is 10 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope for morphology observation.

[0049] Example 6 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 4 The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines. The pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline, and the liquid outlet channel is connected to the liquid tank 1 through a pipeline. The liquid tank 3 controls the temperature of the filtered liquid through a temperature control system 5. The in-situ sample stage 3 is provided with a pressure tank, and the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially attached; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 60 mesh. The flat filter membrane 5 divides the pressure tank into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0050] The testing method includes the following steps: The steps include: (1) placing a flat filter membrane 5 in an in-situ sample stage 3, wherein the flat filter membrane 5 is polyvinylidene fluoride; the in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid, wherein the filter liquid is ethylene glycol; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 2 bar, and the driving time of the pressure pump 2 is 13.5 hours; The temperature of the filtered liquid in step (1) and step (2) is 22°C.

[0051] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, and the freezing temperature is -60 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -10 °C, the temperature during sublimation is 50 °C higher than the temperature during freezing, and the sublimation time is 3 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 9 mA, and the spraying time is 20 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope for morphology observation.

[0052] Example 7 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 4 The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines. The pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline, and the liquid outlet channel is connected to the liquid tank 1 through a pipeline. The liquid tank 3 controls the temperature of the filtered liquid through a temperature control system 5. The in-situ sample stage 3 is provided with a pressure tank, and the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially attached; the aperture of the through hole on the first support plate 4-1 is 0.9 mm, and the aperture of the through hole on the second support plate 4-2 is 80 mesh. The flat filter membrane 5 divides the pressure tank into an injection part and a liquid outlet part, the injection channel is arranged in the injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the injection part;

[0053] The testing method includes the following steps: (1) A flat filter membrane 5 is placed in an in-situ sample stage 3. The flat filter membrane 5 is made of cellulose acetate. The in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid. The filter liquid is a mixture of ethanol and water. The concentration of ethanol in water is 0.5 g·L -1 ; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 3 bar, and the driving time of the pressure pump 2 is 21 hours; The temperature of the filtered liquid in step (1) and step (2) is 24°C.

[0054] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, and the freezing temperature is -100 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -60 °C, the temperature during sublimation is 40 °C higher than the temperature during freezing, and the sublimation time is 5 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 13 mA, and the spraying time is 30 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope for morphology observation.

[0055] Example 8 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 3 The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines. The pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline, and the liquid outlet channel is connected to the liquid tank 1 through a pipeline. The liquid tank 3 controls the temperature of the filtered liquid through a temperature control system 5. The in-situ sample stage 3 is provided with a pressure tank, and the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially attached; the aperture of the through hole on the first support plate 4-1 is 0.9 mm, and the aperture of the through hole on the second support plate 4-2 is 80 mesh. The flat filter membrane 5 divides the pressure tank into an injection part and a liquid outlet part, the injection channel is arranged in the injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the injection part;

[0056] The testing method includes the following steps: (1) A flat filter membrane 5 is placed in an in-situ sample stage 3. The flat filter membrane 5 is chitosan. The in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid. The filter liquid is an aqueous solution of sodium chloride, and the concentration of sodium chloride in water is 2 g·L -1;;The pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate 4 for carrying a flat filter membrane 5; the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.9 mm, and the aperture of the through hole on the second support plate 4-2 is 80 mesh; the flat filter membrane 5 divides the pressure tank into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 4 bar, and the driving time of the pressure pump 2 is 28.5 hours; The temperature of the filtered liquid in step (1) and step (2) is 26°C.

[0057] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, the freezing temperature is -140 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -120 °C, the temperature during sublimation is 20 °C higher than the temperature during freezing, and the sublimation time is 7 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 17 mA, and the spraying time is 40 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope for morphology observation.

[0058] Example 9 A method for testing the liquid phase in-situ morphology of a flat filter membrane, using Figure 4The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines. The pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline, and the liquid outlet channel is connected to the liquid tank 1 through a pipeline. The liquid tank 3 controls the temperature of the filtered liquid through a temperature control system 5. The in-situ sample stage 3 is provided with a pressure tank, and the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 1mm, and the aperture of the through hole on the second support plate 4-2 is 100 mesh. The flat filter membrane 5 divides the pressure tank into an injection part and a liquid outlet part, the injection channel is arranged in the injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the injection part;

[0059] The testing method includes the following steps: (1) A flat filter membrane 5 is placed in an in-situ sample stage 3. The flat filter membrane 5 is made of polyacrylonitrile. The in-situ sample stage 3 is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and an outlet channel for discharging the filter liquid. The filter liquid is an aqueous solution of fibrin. The concentration of fibrin in water is 3 g·L -1 ; (2) Driven by the pressure pump 2, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane 5, the second support plate 4-2, the first support plate 4-1, and is discharged through the liquid outlet channel. The pressure of the pressure pump is 5 bar, and the driving time of the pressure pump 2 is 36 h; The temperature of the filtered liquid in step (1) and step (2) is 30°C.

[0060] (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage 3 in the supercooled liquid nitrogen for freezing, the freezing temperature is -165 °C; (4) The in-situ sample stage 3 is transferred to a vacuum environment, and the frozen flat filter membrane 5 is fractured, sublimated, and sprayed; the fracture is to cut off the ice on the surface of the flat filter membrane 5 with a sharp cold knife in the frozen state, and the flat filter membrane 5 is mechanically fractured by the fracture of the ice; the sublimation is to sublimate the flat filter membrane 5 in a vacuum at -135 °C, the temperature during sublimation is 30 °C higher than the temperature during freezing, and the sublimation time is 10 min; the spraying is to spray platinum particles on the flat filter membrane 5, the spraying current is 20 mA, and the spraying time is 60 s; (5) The in-situ sample stage 3 carrying the flat filter membrane 5 is placed in a cold stage of a scanning electron microscope for morphology observation.

[0061] Comparative Example 1 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage and then performing a cryo-electron microscopy test. Figure 1 , Figure 2 The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 by pipelines. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0062] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0063] 2) Place two membranes into the membrane performance evaluation device for pressure-driven filtration experiment. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 1 g•L -1 The methyl blue dye solution is the filtered feed liquid.

[0064] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=1.55*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=3.1 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0065] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-0.02 g•L -1 / 1 g•L -1 )×100%=98.0%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0066] 3) 0.5 h after the start of the pressure-driven filtration experiment, i.e., the micro-pollution stage, the retention rate and permeation flux data were calculated and the membrane was removed from the test membrane pool.

[0067] 4) One of the membrane samples is broken, sublimated, and sprayed. The specific operation steps include: fixing the membrane on the sample stage, cooling it to -140 ℃, applying force from the side of the membrane with a sharp cold knife, and based on the mechanical fixation of the ice on the membrane in the frozen state, the ice breaks and drives the membrane to mechanically break, exposing the internal section. The sample stage is heated to -100 ℃ and vacuum treated for 5 min to complete the sublimation process of the ice layer covering the surface. Finally, platinum particles are sprayed on the surface of the sample to enhance conductivity, with a spraying current of 10 mA and a spraying time of 10 s. Put the other membrane sample back into the membrane evaluation device, carry out the filtration experiment according to steps 2)~3), and calculate the retention rate and permeation flux data.

[0068] 5) Place the flat filter membrane in the cold stage of a scanning electron microscope and observe its morphology at -140 °C.

[0069] Figure 5 e in the figure is a cryo-SEM image of the cross section of the membrane taken out from the membrane pool in the comparative example of the present invention, which has no dense pores and is a loose pore structure. Table 1 shows that the membrane retention rate decreases and the flux increases after being removed and then put back into the membrane pool, indicating that the membrane structure undergoes irreversible changes after removal. However, the test results of the removal and freezing method in this comparative example do not form a responsive relationship with the performance, mainly because the membrane structure undergoes irreversible changes, resulting in the disappearance of dense pores during freezing observation. Therefore, even if the membrane is immediately frozen in situ after being taken out, it cannot reflect the original structure of the membrane.

[0070] Comparative Example 2 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage and then performing a cryo-electron microscopy test. Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 by pipelines. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0071] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0072] 2) Place two membranes in a membrane performance evaluation device for pressure-driven filtration experiments. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 1 g·L -1 The methyl blue dye solution is the filtered feed liquid.

[0073] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=0.8*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=1.6 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0074] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-0.02 g•L -1 / 1 g•L-1 )×100%=98.0%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0075] 3) 6.0 h after the start of the pressure-driven filtration experiment, i.e., the filtration pollution stage, the retention rate and permeation flux data were calculated and the membrane was removed from the test membrane pool.

[0076] 4) One of the membrane samples is broken, sublimated, and sprayed. The specific operation steps include: fixing the membrane on the sample stage, cooling it to -140 ℃, applying force from the side of the membrane with a sharp cold knife, and based on the mechanical fixation of the ice on the membrane in the frozen state, the ice breaks and drives the membrane to mechanically break, exposing the internal section. The sample stage is heated to -100 ℃ and vacuum treated for 5 min to complete the sublimation process of the ice layer covering the surface. Finally, platinum particles are sprayed on the surface of the sample to enhance conductivity, with a spraying current of 10 mA and a spraying time of 10 s. Put the other membrane sample back into the membrane evaluation device, carry out the filtration experiment according to steps 2)~3), and calculate the retention rate and permeation flux data.

[0077] 5) Place the flat filter membrane in the cold stage of a scanning electron microscope and observe its morphology at -140 °C.

[0078] Figure 5 Figure f is a cryo-scanning electron microscope image of the cross section of the membrane after it was taken out from the membrane pool in the comparative example of the present invention. Since the pollutant solution circulates in the membrane for a long time, the loose pores are blocked.

[0079] Comparative Example 3 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage and then performing a cryo-electron microscopy test. Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 by pipelines. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0080] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0081] 2) Place two membranes in a membrane performance evaluation device for pressure-driven filtration experiments. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 1 g·L -1 The methyl blue dye solution is the filtered feed liquid.

[0082] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=1.3*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=2.6 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0083] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-0.02 g•L -1 / 1 g•L-1 )×100%=98.0%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0084] 3) 6.0 h after the start of the pressure-driven filtration experiment, i.e., the filtration contamination stage, the experiment was stopped, deionized water was used for backwashing for 0.5 h, the retention rate and permeation flux data were calculated, and the membrane was removed from the test membrane pool.

[0085] 4) One of the membrane samples is broken, sublimated, and sprayed. The specific operation steps include: fixing the membrane on the sample stage, cooling it to -140 ℃, applying force from the side of the membrane with a sharp cold knife, and based on the mechanical fixation of the ice on the membrane in the frozen state, the ice breaks and drives the membrane to mechanically break, exposing the internal section. The sample stage is heated to -100 ℃ and vacuum treated for 5 min to complete the sublimation process of the ice layer covering the surface. Finally, platinum particles are sprayed on the surface of the sample to enhance conductivity, with a spraying current of 10 mA and a spraying time of 10 s. Put the other membrane sample back into the membrane evaluation device, carry out the filtration experiment according to steps 2)~3), and calculate the retention rate and permeation flux data.

[0086] 5) Place the flat filter membrane in the cold stage of a scanning electron microscope and observe its morphology at -140 °C.

[0087] Figure 5 g in the figure is a cryo-SEM image of the cross section of the membrane after it is taken out in the comparative example of the present invention. The problem of loose pore blockage is partially alleviated, and the degree of pore recovery is weaker than that in Example 3. Table 1 shows that the membrane retention rate decreases and the flux increases after the membrane is removed and then put back into the membrane pool, indicating that the membrane structure undergoes irreversible changes after removal. The test results of the removal and drying method in this comparative example have a weaker degree of pore recovery than that in Example 3, mainly due to the reduction of pollution after backwashing, the irreversible change of the membrane structure after removal, and the deformation of the loose pores. Therefore, the freezing test after the membrane is taken out cannot fully reflect the original structure of the membrane.

[0088] Comparative Example 4 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage and then performing a cryo-electron microscopy test. Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 by pipelines. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0089] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0090] 2) Place two membranes into the membrane performance evaluation device for pressure-driven filtration experiment. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 5g L -1 The aqueous solution of sodium hydroxide is the filtrate.

[0091] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J=V / (S×Δt×ΔP)=2.3*10 -3 L / (1.2*10 -4 m 2 ×5 / 6 h×5 bar)=4.6 L•m -2 •h -1 •bar -1 ; Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0092] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%=(1-0.17 g•L -1 / 1 g•L-1 )×100%=83.0%; Among them C p is the concentration of produced liquid, C f The concentration of the solution can be characterized by a conductivity meter or an ion meter.

[0093] 3) From the beginning of the pressure-driven filtration experiment, the retention rate and permeation flux data were calculated every 0.5 h until the flux suddenly increased by more than 10%, indicating that the membrane was damaged. The experiment was stopped and the membrane was removed from the test membrane pool.

[0094] 4) One of the membrane samples is broken, sublimated, and sprayed. The specific operation steps include: fixing the membrane on the sample stage, cooling it to -140 ℃, applying force from the side of the membrane with a sharp cold knife, and based on the mechanical fixation of the ice on the membrane in the frozen state, the ice breaks and drives the membrane to mechanically break, exposing the internal section. The sample stage is heated to -100 ℃ and vacuum treated for 5 min to complete the sublimation process of the ice layer covering the surface. Finally, platinum particles are sprayed on the surface of the sample to enhance conductivity, with a spraying current of 10 mA and a spraying time of 10 s. Put the other membrane sample back into the membrane evaluation device, carry out the filtration experiment according to steps 2)~3), and calculate the retention rate and permeation flux data.

[0095] 5) Place the flat filter membrane in the cold stage of a scanning electron microscope and observe its morphology at -140 °C.

[0096] Figure 5 h in the figure is a cryo-SEM image of the cross section of the membrane after it is taken out in the comparative example of the present invention. The pores are deformed and collapsed, and the damage is lighter than that in Example 4. Table 1 shows that the membrane retention rate decreases and the flux increases after the membrane is removed and then put back into the membrane pool, indicating that the membrane structure undergoes irreversible changes after removal. The test results of the removal and freezing method in this comparative example are lighter in pore damage than those in Example 4, mainly because the mechanical support of ice is lost after removal, and the damaged tissue collapses together, and the damage is "pseudo" reduced. Therefore, the freezing test after the membrane is taken out cannot fully reflect the original structure of the membrane.

[0097] Comparative Example 5 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage, drying it, and performing a common electron microscope test. Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0098] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0099] 2) Place two membranes in a membrane performance evaluation device for pressure-driven filtration experiments. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 1 g·L -1 The methyl blue dye solution is the filtered feed liquid.

[0100] 3) 0.5 h after the start of the pressure-driven filtration experiment, i.e., the micro-pollution stage, the retention rate and permeation flux data were calculated, and the membrane was taken out of the test membrane pool and placed in a room temperature forced air oven for drying.

[0101] 4) One of the membrane samples was broken and sprayed. The specific operation steps include: brittle fracture treatment of the membrane in liquid nitrogen to expose the internal section, spray platinum particles on the sample surface to enhance conductivity, spray current 10 mA, spray time 10s. The other membrane sample was placed back into the membrane evaluation device, and the filtration experiment was carried out according to steps 2) to 3) to calculate the retention rate and permeation flux data.

[0102] 5) Place the flat filter membrane into the room temperature sample stage of a scanning electron microscope for morphological observation.

[0103] Figure 5i in the figure is a scanning electron microscope image of the cross section of the membrane taken out and dried in the comparative example of the present invention. The intermediate pore structure shows partial blockage, which is less severe than that in Example 1. Table 1 shows that the membrane retention rate decreases and the flux increases after being removed and then put back into the membrane pool, indicating that the membrane structure undergoes irreversible changes after removal. The test results of the removal and drying method in this comparative example show less blockage than that in Example 1, mainly due to the irreversible changes in the membrane structure, the shrinkage of the pores after drying, the reappearance of "pseudo" intermediate pores, the shrinkage of the volume of pollutants due to water loss, and the "pseudo" reduction of blockage. Therefore, after the membrane is taken out and dried, it cannot fully reflect the original structure of the membrane.

[0104] Comparative Example 6 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage, drying it, and performing a common electron microscope test. Figure 1 , Figure 2 The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0105] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0106] 2) Place two membranes in a membrane performance evaluation device for pressure-driven filtration experiments. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 1 g·L -1 The methyl blue dye solution is the filtered feed liquid.

[0107] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J = V / (S × Δt × ΔP); Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0108] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0109] 3) 6.0 h after the start of the pressure-driven filtration experiment, i.e., the filtration pollution stage, the retention rate and permeation flux data were calculated, and the membrane was taken out of the test membrane pool and placed in a room temperature forced air oven for drying.

[0110] 4) One of the membrane samples was broken and sprayed. The specific operation steps include: brittle fracture treatment of the membrane in liquid nitrogen to expose the internal section, spray platinum particles on the sample surface to enhance conductivity, spray current 10 mA, spray time 10s. The other membrane sample was placed back into the membrane evaluation device, and the filtration experiment was carried out according to steps 2) to 3) to calculate the retention rate and permeation flux data.

[0111] 5) Place the flat filter membrane into the room temperature sample stage of a scanning electron microscope for morphological observation.

[0112] Figure 5 J in the figure is a scanning electron microscope image of the cross section of the membrane in the comparative example of the present invention after it was taken out and dried. The middle pores and the loose pores in the lower layer showed partial blockage, and large particles appeared. The blockage was lighter than that in Example 2. Table 1 shows that the membrane retention rate decreased and the flux increased after it was removed and then put back into the membrane pool, indicating that the membrane structure changed irreversibly after it was taken out. The test results of the removal and drying method in this comparative example showed that the blockage was lighter than that in Example 1. The membrane was blocked by dirt, and the pores shrank after drying, and the "pseudo" middle pores appeared again. The volume of the pollutants shrank due to water loss, and the blockage was "pseudo" reduced. Therefore, after the membrane is taken out and dried, it cannot fully reflect the original structure of the membrane.

[0113] Comparative Example 7 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage, drying it, and performing a common electron microscope test. Figure 1 , Figure 2The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0114] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0115] 2) Place two membranes in a membrane performance evaluation device for pressure-driven filtration experiments. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 1 g·L -1 The methyl blue dye solution is the filtered feed liquid.

[0116] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J = V / (S × Δt × ΔP); Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L•m -2 •h -1 •bar -1 .

[0117] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0118] 3) 6.0 h after the start of the pressure-driven filtration experiment, i.e., the filtration contamination stage, the experiment was stopped, deionized water was used for backwashing for 0.5 h, the retention rate and permeation flux data were calculated, and the membrane was taken out of the test membrane pool and placed in a room temperature forced air oven for drying.

[0119] 4) One of the membrane samples was broken and sprayed. The specific operation steps include: brittle fracture treatment of the membrane in liquid nitrogen to expose the internal section, spray platinum particles on the sample surface to enhance conductivity, spray current 10 mA, spray time 10s. The other membrane sample was placed back into the membrane evaluation device, and the filtration experiment was carried out according to steps 2) to 3) to calculate the retention rate and permeation flux data.

[0120] 5) Place the flat filter membrane into the room temperature sample stage of a scanning electron microscope for morphological observation.

[0121] Figure 5 k in the figure is a scanning electron microscope image of the membrane section after being taken out and dried in the comparative example of the present invention. The pore blockage problem is alleviated, and the dense pores in the middle become larger, mainly because the pollution is reduced after backwashing, but the membrane structure undergoes irreversible changes, and the loose pores are partially deformed. Therefore, the morphology test after the membrane is taken out and dried cannot fully reflect the original structure of the membrane.

[0122] Comparative Example 8 This comparative example relates to a non-in-situ liquid phase in-situ morphology test method for a flat filter membrane, which is achieved by removing the flat filter membrane from the in-situ sample stage, drying it, and performing a common electron microscope test. Figure 1 , Figure 2 The device shown is implemented, and the device includes a liquid tank 1, a pressure pump 2, and an in-situ sample stage 3 connected by pipelines, and the pressure pump 2 is connected to the injection channel of the in-situ sample stage 3 through a pipeline. The in-situ sample stage 3 is provided with a pressure groove, and the pressure groove is sealed by a cover plate; the pressure groove has an inserted support plate 4 for carrying a flat filter membrane 5, wherein the support plate 4 includes a first support plate 4-1 and a second support plate 4-2, and the flat filter membrane 5, the second support plate 4-2 and the first support plate 4-1 are sequentially fitted; the aperture of the through hole on the first support plate 4-1 is 0.8 mm, and the aperture of the through hole on the second support plate 4-2 is 50 mesh. The flat filter membrane 5 divides the pressure groove into a liquid injection part and a liquid outlet part, the liquid injection channel is arranged in the liquid injection part, and the liquid outlet channel is arranged in the liquid outlet part, the first support plate 4-1 is located on one side of the liquid outlet part, and the flat filter membrane 5 is located on one side of the liquid injection part;

[0123] The specific steps include: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0124] 2) Place two membranes into the membrane performance evaluation device for pressure-driven filtration experiment. The test temperature is set to 25°C, the operating pressure is adjusted to 5 bar, and 5g L -1 The aqueous solution of sodium hydroxide is the filtrate.

[0125] The membrane flux is calculated by calculating the volume of produced liquid per unit time, and the retention rate is calculated by the difference in concentration between the filtered feed liquid and the produced liquid. The calculation process is as follows: J = V / (S × Δt × ΔP); Where V is the total volume of liquid produced within Δt time after the flux stabilizes, in L; S is the effective filtration area, in m 2 ; Δt is the time for collecting the produced liquid, in h. ΔP is the transmembrane pressure difference, which is simplified to the pressure setting value of the test element, in bar. Therefore, the flux J is in L·m -2 ·h -1 bar -1 .

[0126] The retention rate R can be calculated by the following formula: R=(1-C p / C f )×100%; Among them C p is the concentration of produced liquid, C f is the concentration of the filtered solution. The concentration of the solution was characterized by a UV-visible spectrophotometer.

[0127] 3) From the beginning of the pressure-driven filtration experiment, the retention rate and permeation flux data were calculated every 0.5 h until the flux suddenly increased by more than 10%, indicating that the membrane was damaged. The experiment was stopped and the membrane was removed from the test membrane pool and dried in a room temperature forced air oven.

[0128] 4) One of the membrane samples was broken and sprayed. The specific operation steps include: brittle fracture treatment of the membrane in liquid nitrogen to expose the internal section, spray platinum particles on the sample surface to enhance conductivity, spray current 10 mA, spray time 10s. The other membrane sample was placed back into the membrane evaluation device, and the filtration experiment was carried out according to steps 2) to 3) to calculate the retention rate and permeation flux data.

[0129] 5) Place the membrane on the sample stage of a scanning electron microscope and observe its morphology at room temperature.

[0130] Figure 5 1 in the figure is a scanning electron microscope image of the cross section of the membrane in the comparative example of the present invention after being taken out and dried. Some pores are deformed, and the deformation is lighter than that of Example 4 and Comparative Example 4. This is mainly due to the shrinkage of the pores after drying, which intensifies the collapse of the damaged tissue and "pseudo" reduces the damage. Therefore, the morphology test of the membrane after being taken out and dried cannot fully reflect the original structure of the membrane.

[0131] Comparative Example 9 This comparative example relates to a non-in-situ flat filter membrane morphology testing method, which is achieved by subjecting an unfiltered membrane to a cryo-electron microscopy test, and specifically comprises the following steps: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0132] 2) Fracture, sublimate, and spray the membrane sample. The specific operation steps include: fix the membrane on the sample stage, cool it to -140 ℃, use a sharp cold knife to apply force from the side of the membrane, and based on the mechanical fixation of ice on the membrane in the frozen state, the ice breaks and drives the membrane to mechanically break, exposing the internal section. Heat the sample stage to -100 ℃ and vacuum treat it for 5 minutes to complete the sublimation process of the ice layer covering the surface. Finally, spray platinum particles on the sample surface to enhance conductivity, the spraying current is 10 mA, and the spraying time is 10 s.

[0133] 3) Place the flat filter membrane in the cold stage of a scanning electron microscope and observe its morphology at -140 °C.

[0134] Figure 6 a and b in the figure are cryo-scanning electron microscope images of the unfiltered membrane in the comparative example of the present invention, including the top leaf structure, the middle dense porous structure and the lower loose porous structure.

[0135] Comparative Example 10 This comparative example relates to a non-in-situ flat filter membrane morphology testing method, which is achieved by taking out the unfiltered membrane and drying it, and then performing a common electron microscope test, and specifically includes the following steps: 1) Soak the polyamide flat filter membrane in deionized water, select a membrane with no obvious defects on the surface, and cut multiple membranes at similar positions.

[0136] 2) The membrane sample is fractured and sprayed. The specific operation steps include: brittle fracture treatment of the membrane in liquid nitrogen to expose the internal cross-section, and platinum particles are sprayed on the surface of the sample to enhance conductivity, with a spraying current of 10 mA and a spraying time of 10 s.

[0137] 3) Place the membrane on the sample stage of a scanning electron microscope and observe its morphology at room temperature.

[0138] Figure 6 Figures c and d are scanning electron microscope images of the unfiltered membrane cross-section after drying in the comparative example of the present invention, including the top blade structure, the middle dense porous structure and the loose porous structure of the lower layer, which are consistent with comparative example 9.

[0139] In order to explore the effect of freezing treatment on the membrane permeation retention performance, it is necessary to obtain the filtration test performance of the flat filter membrane 5 after freezing and warming up. Steps 1 to 3 in Example 1 to Example 4 are repeated respectively, and then the in-situ sample stage 3 is placed at room temperature for one hour to restore it to room temperature, and then step 2 is repeated to test its permeation retention performance, that is, the performance after freezing and warming up. The results are shown in Table 1.

[0140] Table 1 Membrane separation performance data of polyamide flat filter membranes in Examples 1 to 4 and Comparative Examples 1 to 4 at different filtration stages, after freezing and warming up, and after removal and reassembly

[0141] The test conditions of Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1 are: operating pressure of 5 bar, concentration of filtered liquid in the micro-pollution and fouling stages of 1 g·L -1 Methyl blue solution, the concentration of the filtered liquid at the membrane damage stage is 5 g L -1 NaOH; cleaning conditions: backwash the membrane with deionized water at an operating pressure of 5 bar for half an hour.

[0142] Table 2 Cross-sectional morphology and conclusions of polyamide membranes after different treatment methods at different filtration stages in Examples 1-4 and Comparative Examples 1-10

[0143] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. As an equivalent replacement of the present invention, in some implementations, the flat filter membrane can also be one of polyethersulfone, polyamide, graphene oxide, and aluminum oxide.

[0144] As an equivalent replacement of the present invention, in certain embodiments, the filtered liquid can also be N,N-dimethylformamide, N-methylpyrrolidone, ethylene glycol monomethyl ether, butanol, octanol, octyl acetate, dimethyl sulfoxide, a mixture of methanol and water, a mixture of ethylene glycol and water, a mixture of octanol and water, a mixture of isopropanol and water, a mixture of benzyl alcohol and water, a mixture of isopentanol and water, a mixture of isobutanol and water, a mixture of n-propanol and water, a mixture of n-butanol and water or a mixture of sec-butanol and water, an aqueous solution of methyl red, an aqueous solution of ethyl formate, an aqueous solution of alkaline green, an aqueous solution of direct red, an aqueous solution of direct yellow, an aqueous solution of direct ash, an aqueous solution of potassium sulfate, an aqueous solution of sodium sulfate, an aqueous solution of magnesium sulfate, an aqueous solution of calcium sulfate, an aqueous solution of magnesium chloride, an aqueous solution of calcium chloride, an aqueous solution of potassium chloride, an aqueous solution of globulin, an aqueous solution of collagen, an aqueous solution of myoglobin, an aqueous solution of polyaspartic acid.

[0145] Although the present invention has been disclosed as above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for testing the liquid phase in-situ morphology of a flat filter membrane, characterized in that: The steps include: (1) Placing a flat filter membrane in an in-situ sample stage; the in-situ sample stage is provided with a pressure tank, an injection channel for injecting a filter liquid into the pressure tank, and a liquid outlet channel for discharging the filter liquid; the pressure tank is sealed by a cover plate; the pressure tank has an inserted support plate for supporting the flat filter membrane; (2) Driven by the pressure pump, the filtered liquid is injected into the pressure tank sealed by the cover plate through the liquid injection channel, and then passes through the flat filter membrane and the support plate in turn, and is discharged through the liquid outlet channel; (3) Vacuuming the liquid nitrogen, and after it forms solid liquid nitrogen mud, depressurizing it to form supercooled liquid nitrogen, and immersing the in-situ sample stage in the supercooled liquid nitrogen for freezing; (4) Transferring the in-situ sample stage to a vacuum environment, breaking, sublimating, and spraying the frozen flat filter membrane; (5) Place the in-situ sample stage carrying the flat filter membrane into the cold stage of a scanning electron microscope for morphological observation.

2. The method according to claim 1, characterized in that The flat filter membrane is one of polysulfone, polyethersulfone, polyamide, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, graphene oxide, chitosan, and alumina; the filter liquid is one of water, an organic solvent, an alcohol-water mixture, an aqueous solution of organic pollutants, an electrolyte solution, or an aqueous protein solution; the organic solvent includes N,N-dimethylformamide, N-methylpyrrolidone, ethylene glycol, ethylene glycol monomethyl ether, butanol, octanol, octyl acetate, and dimethyl sulfoxide; the alcohol-water mixture includes a mixture of methanol and water, a mixture of ethanol and water, a mixture of ethylene glycol and water, a mixture of octanol and water, a mixture of isopropanol and water, a mixture of benzyl alcohol and water, a mixture of isopentanol and water, a mixture of isobutanol and water, a mixture of n-propanol and water, and a mixture of n-butanol and water. or a mixture of sec-butyl alcohol and water; the aqueous solution of organic pollutants includes an aqueous solution of methyl blue, an aqueous solution of methyl red, an aqueous solution of ethyl formate, an aqueous solution of alkaline green, an aqueous solution of direct red, an aqueous solution of direct yellow, and an aqueous solution of direct ash; the electrolyte solution includes an aqueous solution of sodium hydroxide, an aqueous solution of potassium sulfate, an aqueous solution of sodium sulfate, an aqueous solution of magnesium sulfate, an aqueous solution of calcium sulfate, an aqueous solution of sodium chloride, an aqueous solution of magnesium chloride, an aqueous solution of calcium chloride, and an aqueous solution of potassium chloride; the aqueous protein solution includes an aqueous solution of fibrin, an aqueous solution of globulin, an aqueous solution of collagen, an aqueous solution of myoglobin, and an aqueous solution of polyaspartic acid; the concentrations of the alcohol-water mixture, the aqueous solution of organic pollutants, the electrolyte solution, and the aqueous protein solution are all 0.5-5 g·L -1 .

3. The method according to claim 1, characterized in that The support plate comprises a first support plate and a second support plate, and the flat filter membrane, the second support plate and the first support plate are sequentially attached.

4. The method according to claim 1, characterized in that The temperature of the filtered liquid in step (1) and step (2) is 20-30 °C.

5. The method according to claim 1, characterized in that The pressure of the pressure pump is 1-5 bar, and the driving time of the pressure pump is 0.5-36 h.

6. The method according to claim 1, characterized in that The freezing temperature is -20~-165°C.

7. The method according to claim 1, characterized in that The fracture is to cut off the ice on the surface of the flat filter membrane with a sharp cold knife in a frozen state, so that the flat filter membrane is mechanically fractured by the fracture of the ice; the sublimation is to sublime the flat filter membrane in a vacuum at -10~-135°C, the temperature during sublimation is 10~50°C higher than the temperature during freezing, and the sublimation time is 1~10 min; the spraying is to spray platinum particles on the flat filter membrane, the spraying current is 5~20 mA, and the spraying time is 10~60 s.

8. A device for implementing the liquid phase in-situ morphology testing method of the flat filter membrane according to claim 1, characterized in that: The invention comprises a material liquid box, a pressure pump and an in-situ sample table which are connected through pipelines. The pressure pump is connected to a liquid injection channel of the in-situ sample table through pipelines.

9. The device according to claim 8, characterized in that The feed liquid box controls the temperature of the filtered feed liquid through a temperature control system, and the liquid outlet channel of the in-situ sample stage is connected to the feed liquid box through a pipeline.

10. The device according to claim 8, characterized in that The support plate includes a first support plate and a second support plate, and the flat filter membrane, the second support plate and the first support plate are sequentially attached; the aperture of the through hole on the first support plate is 0.8~1 mm, and the aperture of the through hole on the second support plate is 50~100 mesh.

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