Method and apparatus for measuring filter membrane pore adhesion

Abstract

The application provides a method and device for measuring solid-liquid adhesion between a filter membrane internal pore wall and a filtering liquid, and specifically comprises the following steps: fully immersing the filter membrane in a good wetting liquid and a filtering liquid to be measured, respectively; loading the filter membrane into a gas-tight membrane assembly, and introducing compressed gas to one side of the membrane assembly; measuring the gas permeation pressure by controlling the flow of the compressed gas, and calculating the solid-liquid adhesion between the filter membrane and the filtering liquid. The method and device are suitable for measuring the solid-liquid adhesion between the filter membrane material and the filtering liquid, have the performance advantages of reflecting the solid-liquid adhesion of the filter membrane internal pore wall and the whole filter membrane, have the operation advantages of being simple and easy to operate, being objective and good in repeatability, and can provide key information for the research and detection of filter membranes in fields such as sewage treatment.

Description

Technical Field

[0001] This invention belongs to the field of interface chemistry and relates to the determination of solid-liquid interfacial adhesion force. Specifically, it relates to a method for determining the solid-liquid adhesion force between the solid wall of the internal pores of a filter membrane material and the filtered liquid, as well as an apparatus based on the method. Background Technology

[0002] Membrane filtration technology has been widely applied in chemical, petroleum, mining, pharmaceutical, and environmental protection fields, with liquid filtration accounting for a large proportion. One of the key performance indicators of membrane filtration is the flow rate of the liquid through the membrane, which depends on the mass transfer resistance of the liquid through the membrane. It is generally believed that a significant factor affecting mass transfer resistance is the wettability of the liquid on the solid surface of the filter membrane. The better the wettability of the liquid on the filter membrane, the higher the liquid flow rate of the filter membrane (Research (2019) 2019, 1). An important mechanical parameter for measuring wettability is adhesion force, also known as adhesion tension. Specifically, adhesion force reflects the force / unit work generated / overcome by the liquid flowing through the pore wall of the filter membrane (i.e., wetting phenomenon). Therefore, accurately measuring the adhesion force between the filter membrane and the liquid is of great significance for the design, development, and application evaluation of filter membranes.

[0003] Currently, the main methods for determining solid-liquid adhesion forces include: 1. Inclined plate method: calculating the solid-liquid adhesion force by observing the movement of a droplet on an inclined plate under gravity, such as CN114858593A; 2. Probe method: calculating the solid-liquid adhesion force by controlling a probe with a droplet at its end to contact the solid surface and then removing the droplet from the solid surface, measuring the change in force on the probe, such as CN113702281A and CN112858161B; 3. Suspended plate method: calculating the solid-liquid adhesion tension by controlling a suspended plate to be immersed in the liquid to be tested to a certain depth, measuring the tension on the suspended plate, such as Acta Phys.-Chim.Sin. (1988) 4, 290. The inclined plate method has relatively low measurement accuracy and is currently rarely used. The probe method has high measurement accuracy, but its measurement range is generally limited to the solid surface within the size of a droplet or microdroplet, making it difficult to reflect the overall adhesion force of the sample. Furthermore, the probe method generally has high requirements for experimental equipment, environment, personnel, and procedures, resulting in high operating costs and significant error risks. The pendant method is more consistent with the wetting process of liquids permeating a filter membrane, but it is generally only suitable for dense solids. Measuring porous materials like filter membranes can lead to strong pore permeation, and the absorbed liquid can greatly interfere with the monitoring of the pendant tension, making it difficult to obtain accurate solid-liquid adhesion force values.

[0004] As an emerging material specializing in filtration, filter membrane materials require well-developed pore structures, ultra-thin thickness and volume, and a greater focus on the overall adhesion of the membrane rather than local adhesion, and the adhesion of internal pore walls rather than surface adhesion. This poses a significant challenge to conventional techniques for measuring solid-liquid adhesion. Therefore, there is an urgent need to develop a suitable method for measuring the solid-liquid adhesion of filter membrane materials. Summary of the Invention

[0005] This invention provides a method for determining the solid-liquid adhesion force between the pore wall of a filter membrane material and the filtered liquid, as well as an apparatus based on this method. One objective of this invention is to address the problems and shortcomings of conventional adhesion force determination methods for filter membrane materials, and to provide at least the advantages described below.

[0006] The present invention is based on the following considerations:

[0007] This invention utilizes the filtration function of filter membranes, specifically their ability to allow a certain amount of fluid to continuously permeate under a certain pressure, to closely approximate the actual application process of filter membranes while simultaneously measuring the solid-liquid adhesion characteristics of the membrane as a whole. This invention leverages the general wettability of filter membranes to their filtered liquids, pre-wetting the membrane to overcome the limitations of traditional adhesion measurement techniques that struggle to penetrate the internal pores of the membrane. The filter membrane is structured as a cluster of irregularly shaped pores, each pore being, according to finite element analysis, a continuous assembly of an infinite number of microcapillaries with varying pore sizes. Under a certain pressure, the liquid can be forced out of the pores. This pressure is related to the pore radius, the adhesion between the liquid and the pore wall, and the friction between the fluid and the pore wall. To eliminate the influence of friction, this invention selects a gas with low solubility that does not chemically react with the sample as the permeation medium. According to Pascal's Law, the maximum pressure required for the gas to permeate the filter membrane when the liquid is completely squeezed out is located at the pore throat, i.e., the narrowest point of the pore radius. The pores and throats of filter membrane materials are generally located inside rather than on the surface. To determine the overall solid-liquid adhesion of the filter membrane, it is necessary to understand the permeation behavior of the pore clusters. Generally, under a given pressure, permeation transitions from the largest pore to the smallest pores, with the maximum pressure required to overcome increasing sequentially. Therefore, based on the above model, capillary pressure formula, and Young's equation, when the number of pores through which gas passes is i, the required escape pressure drop Δp for gas to permeate the filter membrane is... i for:

[0008]

[0009] Where, Δp i σ represents the pressure drop that the gas overcomes when passing through the filter membrane, given that the number of pores is i. i Let be the solid-liquid adhesion force between the filter membrane pores and the liquid when the number of gas channels is i; r is the pore throat radius; Ki Let K be the pore size structure factor when the number of pores through which gas passes is i. i This can be determined using a calibration agent. Common filter membranes generally have a good wetting agent. In this case, the solid-liquid adhesion force between the liquid and the filter membrane is close to its surface tension. For a certain good wetting agent A of the filter membrane, when the number of pores through the gas is i, the required escape pressure drop Δp for the gas to pass through the filter membrane is... A for:

[0010]

[0011] Where γ A The surface tension of the good wetting agent A can be determined using existing instrumental methods. Due to the stability of the filter membrane structure, for both the good wetting agent A and the test liquid wetting scenarios, when the gas flow rate through the filter membrane reaches the same level, their K values ​​are relatively close. Therefore, by controlling the gas flow rate through the filter membrane to reach the same level, the escape pressure drop Δp that the gas needs to overcome to pass through the filter membrane wetted by the test liquid can be obtained as:

[0012]

[0013] The formula for calculating the solid-liquid adhesion force σ between the pore wall of the filter membrane and the liquid is:

[0014]

[0015] Furthermore, by controlling the permeate gas pressure, the solid-liquid adhesion force σQ of the filter membrane under different gas flow rates Q, i.e., different numbers of gas passing through pores i, can be obtained. To better reflect the overall adhesion force of the filter membrane, the solid-liquid adhesion force values ​​at multiple flow rates can be measured. It should be noted that the gas permeate flow rate Q has an upper limit (Qmax). At this limit, all pores of the filter membrane are permeated by gas, and increasing the gas flow rate will no longer change the number of gas passing through pores i. Therefore, the method of this patent is no longer applicable.

[0016] The specific measurement method of the present invention is as follows, and the device based on the method is as follows: Figure 1 As shown:

[0017] 1. Dry the filter membrane sample and immerse it in its good wetting standard solution to ensure that the filter membrane is completely wetted by the standard solution.

[0018] 2. Install the impregnated filter membrane in the sample cell (5) and set the gas mass flow controller (4) according to the required gas flow rate.

[0019] 3. Close the inlet valve (2) and open the exhaust valve (6). Turn on the gas cylinder (1) to supply gas, and open the inlet valve (2) to introduce compressed gas into the gas cylinder (1). Close the exhaust valve (6) to allow the gas to flow through the filter membrane in the sample cell (5). After the pressure value of the monitoring pressure sensor (3) stabilizes, immediately collect and record the pressure value. Close the inlet valve (2), open the exhaust valve (6), and remove the filter membrane from the sample cell (5).

[0020] 4. Dry the filter membrane to be tested and immerse it in the test solution to ensure that the filter membrane is completely wetted by the test solution.

[0021] 5. Install the filter membrane soaked in the test liquid into the sample cell (5). The set flow rate of the gas mass flow controller (4) is exactly the same as in step 2.

[0022] 6. Repeat step 3. Calculate the liquid-solid adhesion force between the filter membrane and the liquid to be tested using formula (4). After the test is completed, close the gas cylinder (1).

[0023] The main components of the filter membrane material pore adhesion testing device proposed in this patent include a gas cylinder (1), an inlet valve (2), a pressure sensor (3), a gas mass flow controller (4), a sample cell (5), an exhaust valve (6), a silencer (7), and a computer (8). The compressed gas in the gas cylinder (1) is dry air, nitrogen, or argon; the inlet valve (2) and exhaust valve (5) are of the type of solenoid valve, electric valve, pneumatic valve, or diaphragm valve; the silencer (7) is used to reduce exhaust noise. The inlet valve (2), gas mass flow controller (4), and exhaust valve (6) are controlled by the computer (8); the signal from the pressure sensor (3) is also collected by the computer (8).

[0024] The present invention also includes at least the following beneficial effects:

[0025] (1) The method and apparatus of the present invention closely resemble the filtration process of the filter membrane and are more in line with actual conditions;

[0026] (2) The method and apparatus of the present invention do not require expensive equipment such as high-speed cameras, miniature probes, and microbalances, and the cost of use is low.

[0027] (3) The method and apparatus of the present invention can measure various types of filter membranes such as tubular, sheet, pleated, capsule, hollow fiber, and multi-channel. It is only necessary to select a suitable sample cell (5) and seal the filter material.

[0028] (4) The method and apparatus of the present invention are easy to operate and can complete a set of experiments in 5 to 7 minutes;

[0029] (5) The method and apparatus of the present invention reduce various human and non-human errors, have better reproducibility, and can automatically complete test operations and data acquisition. Attached Figure Description

[0030] Figure 1 The structural flow diagram of the filter membrane pore adhesion force measuring device is as follows: (1) Gas cylinder; (2) Inlet valve; (3) Pressure sensor; (4) Gas mass flow controller; (5) Sample cell; (6) Exhaust valve; (7) Silencer; (8) Computer.

[0031] Figure 2 The numerical reproducibility graph shows the adhesion force between a stainless steel microfiltration membrane and water measured six times. Detailed Implementation

[0032] The present invention will be further described in detail below through specific embodiments. These embodiments will enable those skilled in the art to have a more comprehensive understanding of the present invention, but will not limit the present invention in any way.

[0033] Example 1

[0034] A cleaned and dried stainless steel sheet microfiltration membrane (316L material, 2μm pore size) was impregnated with a good wettability calibration solution GQ-16 (provided by Nanjing Gaoqian Functional Materials Technology Co., Ltd.). The impregnated membrane was then installed into the module. The pneumatic valve was opened to allow gas to enter the membrane module. The gas flow rate was controlled by adjusting the gas mass flow controller. As the amount of gas entering increased, gas permeation was observed in the membrane osmotic pressure gauge using a bubbler. The gas flow rate was controlled to 50% of its maximum flow rate. The reading on the pressure sensor was then taken as the gas osmotic pressure difference ΔP of the calibration solution-impregnated membrane. A The pressure difference (ΔP) of the tested stainless steel membrane was 9.4 kPa. After drying the membrane in a vacuum oven at 60°C for 1 hour, it was re-wetted with deionized water (the filtrate to be tested). This process was repeated, and the gas osmotic pressure difference (ΔP) of the membrane wetted with deionized water was read as 17.9 kPa. The surface tension (γ) of the calibration solution GQ-16 at room temperature is known. A The value is 16.0 mN / m, and γ A ΔP A Substituting ΔP into formula (4), the adhesion force σ between deionized water and the stainless steel flat-plate microfiltration membrane is 30.4 mN / m. This is not significantly different from the measurement result of 30.6 mN / m obtained by German scientific instrument company Tensiio.

[0035] Example 2

[0036] A stainless steel tubular ultrafiltration membrane (316L material, 0.1μm pore size) that has been stored for a long time was impregnated with ethanol, a standard solution with good wettability. The impregnated tubular membrane was then installed into the module. The pneumatic valve was opened to allow gas to enter the membrane module. The gas flow rate was controlled by adjusting the gas mass flow controller. As the amount of gas entering increased, gas permeation was observed in the membrane osmotic pressure gauge through a bubbler. The gas flow rate was controlled to 80% of its maximum flow rate. The reading on the pressure sensor was taken as the gas osmotic pressure difference ΔP of the membrane impregnated with the standard solution. A The pressure difference is 66.0 kPa. After drying the tested stainless steel membrane in a vacuum oven at 60°C for 1 hour, it is re-wetted with deionized water (the filtrate to be tested). This process is repeated, and the gas osmotic pressure difference ΔP of the membrane wetted with deionized water is read as 138.9 kPa. The surface tension γ of the calibration solution ethanol at room temperature is known. A The value is 22.3 mN / m, and γ A ΔP A Substituting ΔP into formula (4), we obtain that the adhesion tension σ between the deionized water and the stainless steel tubular ultrafiltration membrane is 33.7 mN / m.

[0037] Example 3

[0038] The cleaned and dried organic sheet ultrafiltration membrane (polysulfone material, 0.05μm pore size) was impregnated with GQ-16, a good wettability calibration solution. The impregnated membrane was then installed into the module. The pneumatic valve was opened to allow gas to enter the membrane module. The gas flow rate was controlled by adjusting the gas mass flow controller. As the amount of gas entering increased, gas permeation was observed in the membrane osmotic pressure gauge using a bubbler. The gas flow rate was controlled to 20% of its maximum flow rate. The reading on the pressure sensor was then taken as the gas osmotic pressure difference ΔP of the calibration solution-impregnated membrane. A The pressure difference (ΔP) of the tested organic filter membrane was 198 kPa. After drying the membrane in a vacuum oven at 60°C for 1 hour, it was re-wetted with deionized water (the test solution) and the above steps were repeated. The membrane gas osmotic pressure difference (ΔP) was read as 319.7 kPa. The surface tension (γ) of the calibration solution GQ-16 at room temperature is known. A The value is 16.0 mN / m, and γ A ΔP A Substituting ΔP into formula (4), we obtain that the adhesion tension σ between deionized water and the organic sheet membrane is 25.8 mN / m.

[0039] Example 4

[0040] The cleaned and dried cellulose acetate ultrafiltration membrane (pore size 0.1 μm) was impregnated with the good wettability calibration solution GQ-16. The specific testing procedure was as follows: the impregnated sheet membrane was installed into the module, the pneumatic valve was opened to allow gas to enter the membrane module, and the gas mass flow controller was adjusted to control the gas flow rate. As the amount of gas entering increased, gas permeation was observed in the membrane cell through the bubbler. The gas flow rate was controlled to 5% of its maximum gas flow rate, and the reading of the pressure sensor was taken as the gas osmotic pressure difference ΔP of the membrane impregnated with the calibration solution. A The pressure difference was 49.3 kPa. After drying the tested filter membrane in a vacuum oven at 60°C for 1 hour, it was re-wetted with anhydrous ethanol (the test solution) and the above steps were repeated. The membrane gas osmotic pressure difference ΔP was read as 60.5 kPa. The surface tension γ of the calibration solution GQ-16 at room temperature is known. A The value is 16.0 mN / m, and γ A ΔP A Substituting ΔP into formula (4), we obtain that the adhesion tension σ between anhydrous ethanol and the cellulose acetate membrane is 19.6 mN / m.

[0041] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A method for determining the adhesion force of filter membrane pores, characterized in that: S1 After vacuum drying, the filter membrane is thoroughly wetted with a good wetting standard solution; S2 The filter membrane, after being wetted with the good wetting standard solution, is installed in the sample cell (5) and its airtightness is checked. S3 opens the intake valve (2) and introduces compressed gas. The computer (8) controls the gas mass flow controller (4) to reach the set flow rate and records the pressure drop of the gas through the filter membrane read by the pressure sensor (3). S4 Open the exhaust valve (6) and remove the filter membrane from the sample cell (5); S5 involves vacuum drying the filter membrane and then wetting it with the liquid to be tested. S6 The filter membrane, after being wetted by the liquid to be tested, is installed in the sample cell (5) and its airtightness is checked. S7 controls the repetition of steps S3 and S4 under the same flow rate; The S8 computer (8) calculates the adhesion force σ between the pore wall of the filter membrane and the liquid to be filtered, using the following formula: Where γ A The surface tension of the good wetting standard solution, Δp A Δp is the pressure drop of gas passing through a filter membrane wetted with a good wetting standard solution, and Δp is the pressure drop of gas passing through a filter membrane wetted with the liquid to be tested. The measuring apparatus used in this method includes: a gas cylinder (1), an inlet valve (2), a pressure sensor (3), a gas mass flow controller (4), a sample cell (5), an exhaust valve (6), a silencer (7), and a computer (8).

2. The method for determining the adhesion force of filter membrane pores according to claim 1, characterized in that, The tested filter membranes are suitable for tubular, sheet, pleated, capsule, hollow fiber, or multi-channel configurations.

3. The method for determining the adhesion force of filter membrane pores according to claim 1, characterized in that, The tested filter membranes are suitable for pore sizes of 0.02-100 μm.

4. The method for determining the adhesion force of filter membrane pores according to claim 1, characterized in that, The tested filter membranes are suitable for materials such as metal, ceramic, polymer, or glass.

5. The method for determining the adhesion force of filter membrane pores according to claim 1, characterized in that, The good wetting calibration solution in step S1 includes any liquid with a contact angle of less than 20° with the filter membrane material to be tested.

6. The method for determining the adhesion force of filter membrane pores according to claim 1, characterized in that, The compressed gas in steps S3 and S7 is nitrogen, argon, or air.

7. The method for determining the adhesion force of filter membrane pores according to claim 1, characterized in that, The set flow rate in steps S3 and S7 is 5%-90% of the maximum flow rate that the liquid in the filter membrane pores can withstand.

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