A method for testing the pore size of a tubular membrane

Abstract

The application discloses a kind of tubular membrane pore size testing methods, comprising the following steps: step 1, from tubular membrane sample middle intercepts a section of membrane tube, makes test sample, and the top of test sample is provided with interface to connect pipeline;Step 2, the test sample obtained in step 1 is connected high pressure gas source and is removed impurity;Step 3, the membrane tube in the test sample obtained in step 2 is infiltrated;Step 4, the test sample obtained in step 3 is ultrasonic negative pressure degassing;Step 5, the test sample obtained in step 4 is connected with pore size measuring instrument, and the test of membrane sample pore size parameter is completed.The ultrasonic dispersion technology and negative pressure impurity removal technology are applied to the testing process of tubular membrane pore size in the application, and the removal problem of gas in complex pore structure is solved.The test sample prepared by the application is suitable for instrument testing of various specifications of tubular membrane pore size, and has universality.The test sample prepared by the application has scientific and reasonable test process, accurate test result and high accuracy.

Description

Technical Field

[0001] This invention relates to the field of separation membrane testing technology, and in particular to a method for testing the pore size of a tubular membrane. Background Technology

[0002] Membrane separation technology, with its advantages of simple operation, high efficiency, speed, energy saving, and environmental friendliness, has been widely used in industrial water treatment, seawater desalination, and biomedicine. Pore size is the most important technical indicator for porous membrane separation products, determining the membrane's flux, rejection rate, and other permeation and separation performance. It is a key parameter for both membrane manufacturers and users. Methods for determining the pore size and distribution of separation membranes include the bubble point and average flow rate method, the permeation method, the standard particle method, mercury intrusion porosimetry, and electron microscopy. GB / T32361—2015 specifies the detailed method and procedure for testing the pore size of separation membranes using the bubble point and average flow rate method. This method is simple to operate, accurate, and precise, and is currently the main and preferred method for determining the pore size of separation membranes. The permeation method, standard particle method, and mercury intrusion porosimetry have complex principles and operating procedures, lower accuracy and precision, and are less commonly used.

[0003] There are many types of tubular membranes, including two main categories: organic tubular membranes and inorganic tubular membranes. Structurally, they can be single-pore (single-cavity, single-channel) or multi-pore (multi-cavity, single-channel). Materials include PVDF, PES, PE, Al2O3, ZrO2, TiO2, and stainless steel. Tubular membranes are generally manufactured in the form of membrane elements and are primary products. They are relatively large, coarse, and lack flexibility. Compared to flat-sheet and hollow fiber separation membranes, tubular membranes have a much thicker structural layer and a more complex pore structure. If the bubble point and average flow rate methods are used to test the pore size of tubular membranes, their large size and high permeate flow rate make it impossible to use currently available commercially available automated testing instruments suitable for testing the pore size of flat-sheet and hollow fiber membranes. Therefore, it is necessary to build a testing device and fabricate operating and testing equipment suitable for the size and specifications of the membrane elements. Fixed-specification equipment is only suitable for the operation and testing of membrane elements of that specific size and lacks universal applicability. The testing process is complex, requiring manual recording of pressure and flow rate changes. This complexity makes stable programmed pressurization and dynamic balancing impossible, resulting in limited data collection points and significant testing errors. Furthermore, the bubble point and average flow rate methods for pore size testing require complete immersion of the membrane sample in the test liquid, with no air remaining in the pores. Due to the greater thickness and complex pore structure of tubular membranes, significant air resistance occurs during pore immersion, making the immersion method specified in GB / T 32361—2015 for flat sheet and hollow fiber membranes unsuitable. During the immersion of tubular membrane samples, gas trapped within the pore structure is difficult to escape, hindering complete immersion and leading to overestimation of the pore size. This results in incomplete characterization of the entire pore structure, especially for extremely fine pores, and a significant deviation between the test results and the true values. Summary of the Invention

[0004] The purpose of this invention is to provide a universal and accurate method for testing the pore size of tubular membranes, addressing various problems existing in current tubular membrane pore size testing processes.

[0005] The technical solution adopted to achieve the purpose of this invention is:

[0006] A method for testing the pore size of a tubular membrane includes the following steps:

[0007] Step 1: Cut a section of membrane tube from the middle of the tubular membrane sample to be tested to make a test sample. The top of the test sample is provided with an interface for connecting the pipeline.

[0008] Step 2: Connect the test sample obtained in Step 1 to high-purity nitrogen gas, adjust the gas pressure so that the gas flow rate through the test sample is 5L / min to 50L / min, maintain constant pressure for 30s, and use high-pressure gas to blow out impurities in the membrane pores to obtain the test sample after impurity removal.

[0009] Step 3: Immerse the membrane tube portion of the test sample obtained in Step 2 in a container filled with test liquid, with the test sample interface facing upwards and above the liquid surface, so that the test liquid can unidirectionally seep into the membrane pores from the outer wall of the membrane, while preventing the test liquid from entering the interior of the test sample from the interface, and immerse for 5 min to 15 min.

[0010] Step 4: Place the container containing the test liquid and test sample obtained in Step 3 into an ultrasonic water bath. Connect the interface of the test sample to a vacuum pump using a transparent tube. Adjust the vacuum level of the system to 0.005 MPa to 0.030 MPa. Observe the rising of bubbles in the transparent tube at the interface of the test sample. If no bubbles containing test liquid emerge within 5 to 10 minutes, further increase the vacuum level of the system to 0.010 MPa to 0.100 MPa until rising bubbles appear in the tube at the interface. Fine-tune the vacuum level. The vacuum level is maintained at zero, ensuring that bubbles emerge from the tube at the interface without causing the liquid level to rise. As gas continuously escapes from the membrane pore structure of the test sample, the bubbles in the tube at the interface gradually become smaller and fewer. When no bubbles emerge, the liquid level in the tube at the interface will slowly rise, and there will be only a very small number of tiny bubbles in the liquid, indicating that there is no gas in the membrane pore structure. After the liquid level rises to 20 mm to 100 mm above the interface, the vacuum level of the system is reduced to zero, the ultrasonic water bath is turned off, and the sample is kept at the set water bath temperature for 1 to 2 hours before being taken out.

[0011] Step 5: Connect the test sample obtained in Step 4 to the pore size measuring instrument through a pipeline, and complete the test of the membrane sample pore size parameters according to the principle of bubble point and average flow rate method specified in GB / T32361—2015.

[0012] In the above technical solution, the membrane tube is obtained by the following method: take a dry, clean tubular membrane sample with no cracks, burrs, or peeling visible to the naked eye, cut a section of membrane tube with a length of 40mm to 150mm from the middle, and grind the end face flat.

[0013] In the above technical solution, the effective length of the membrane tube in the test sample is 5mm-100mm.

[0014] In the above technical solution, the ultrasonic frequency is 20kHz to 100kHz, and the power density is 0.3W / cm². 2 ~1.0W / cm 2 .

[0015] In the above technical solution, the test sample includes a plug, a membrane tube, a connector, an internal threaded mandrel connector, and an external threaded quick-connect connector. Except for the membrane tube, all are standard pipe fittings widely used in engineering. The plug is fixedly connected to one end of the membrane tube, the connector is fixedly connected to the other end of the membrane tube, the external interface of the internal threaded mandrel connector is fixedly connected to the other end of the connector, and the external thread of the external threaded quick-connect connector is connected to the internal thread of the internal threaded mandrel connector. The resulting test sample can be connected to the pipeline through the interface of the external threaded quick-connect connector.

[0016] In the above technical solution, the inner diameter of the plug opening is 1mm to 5mm larger than the outer diameter of the test sample; the specifications of one end of the connector are the same as the specifications of the plug opening, and the specifications of the other end are the same as the specifications of the outer interface of the internal thread core connector; the specifications of the internal thread of the internal thread core connector are the same as the specifications of the external thread of the external thread quick-connect connector; the interface of the external thread quick-connect connector is a quick-connect interface with a diameter of 8mm, 10mm or 12mm.

[0017] In the above technical solution, the connector is a reducing straight connector or a straight connector; the plug, connector, and internal threaded core connector are made of rigid plastic, such as UPVC (PVC-U), ABS, etc.; the external threaded quick-connect connector is made of metal, such as copper, stainless steel, etc.

[0018] In the above technical solution, the test sample is prepared by the following method:

[0019] Step S1: Place the cap with the opening facing upwards on a horizontal surface and inject adhesive into it. Insert one end of the membrane tube vertically into it, ensuring that the membrane tube is in the center of the cap. If adhesive overflows from the cap, wipe off the adhesive on the outer wall of the cap. Otherwise, slowly add adhesive to the inner wall of the cap using a pipette to avoid leaving air in the gap between the membrane tube and the cap. Continue until the adhesive is about to overflow onto the outer wall of the cap. Allow it to cure at room temperature for 24 to 48 hours.

[0020] Step S2: Apply adhesive evenly to the end face and side of the outer interface of the internal threaded connector, insert it into the port of the connector with the same specification as the outer interface of the internal threaded connector, with the internal threaded connector facing down, and place it vertically for 1 hour to cure. Internal threaded connectors can also be connected to each other using threaded connections.

[0021] Step S3: Place the connector and plug of the sample completed in step S2 with the same opening end facing upwards on a horizontal surface. Apply adhesive evenly to the other opening end of the membrane tube of the sample completed in step S1, insert it vertically into the connector, center it, and fix it with external force. After the adhesive has partially cured (cured at room temperature for about 12 hours), use a pipette to slowly add adhesive to the gap between the membrane tube and the connector, avoiding residual air in the gap, until the adhesive is about to overflow to the outer wall of the connector. Cure at room temperature for 24 to 48 hours.

[0022] Step S4: Wrap PTFE raw material tape around the external thread of the quick-connect fitting and screw it into the internal thread of the internal thread connector of the sample completed in step S3 to obtain the test sample.

[0023] In the above technical solution, the adhesives mentioned in steps S1 and S3 are polyurethane two-component adhesives or epoxy resin two-component adhesives; the adhesives mentioned in step S2 are single-component adhesives suitable for pipe fitting materials, such as UPVC special adhesives, ABS special adhesives, etc.

[0024] In the above technical solution, the adhesive in step S3 is injected between the membrane tube and the connector in two steps. First, a small amount of adhesive is used to fix the membrane tube in the center of the connector to seal the gap between the membrane tube and the connector to prevent leakage of the adhesive added later. After the adhesive is semi-cured, adhesive is slowly added to the gap between the membrane tube and the connector.

[0025] In the above technical solution, after the adhesive cures in step S1, a smooth, convex surface is formed at the opening between the membrane tube and the plug. After the adhesive cures in step S3, a smooth, convex surface is formed at the opening between the membrane tube and the connector, thus preventing the test liquid from flowing back into the membrane pore during the pore size test.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. This invention combines ultrasonic dispersion technology and negative pressure impurity removal technology and applies them to the testing process of tubular membrane pore size. By reducing pressure and controlling the flow rate through a programmed decompression method, the influence of gas resistance during the wetting process of tubular membrane samples is greatly reduced. This solves the problem of gas removal within the complex pore structure of tubular membranes, achieving complete sample wetting and meeting the requirements of bubble point and average flow rate method pore size testing. It can measure the structural characteristics of all pores in the membrane structure layer, especially the measurement of ultrafine pores, thus improving the accuracy and precision of the test results.

[0028] 2. This invention utilizes inexpensive, readily available, and widely used standard tubing and adhesives in engineering to fabricate tubular membrane pore size test samples. It enables the use of commercially available automated testing instruments to test the pore size of tubular membranes, and is applicable to testing tubular membrane samples of various specifications, demonstrating versatility and a wide range of applications. The sample size can be flexibly adjusted according to actual conditions. The fabrication process is simple and low-cost, greatly facilitating the testing and research of tubular membranes.

[0029] 3. In the tubular membrane pore size test sample prepared by this invention, the flow direction and process of the fluid during the test are consistent with the actual application process of the membrane product. The test process is scientific and reasonable, and the test results can accurately reflect the pore structure characteristics of the membrane product and predict its permeation and separation performance. The test sample prepared by this invention also has certain reference value for the testing and research of other properties of tubular membranes. Attached Figure Description

[0030] Figure 1 The diagram shown is a structural schematic of the test sample of the present invention.

[0031] Figure 2 The diagram shows a schematic of the apparatus for removing impurities from test samples according to the present invention.

[0032] Figure 3 The diagram shows a schematic of the apparatus for the test sample immersion and ultrasonic negative pressure degassing process of the present invention (the ultrasonic water bath device is omitted in the figure).

[0033] In the diagram: 1-Plug cap, 2-Membrane tube, 3-Connector, 4-Internal threaded connector, 5-External threaded quick-connect connector, 6-Test sample, 7-Gas source, 8-Pressure reducing valve, 9-Pressure regulating valve, 10-Gas mass flow meter, 11-Precision pressure gauge, 12-Container, 13-Vacuum gauge, 14-Vacuum regulating valve, 15-Vacuum pump. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] A method for testing the pore size of a tubular membrane includes the following steps:

[0036] Step 1: Take a dry, clean tubular membrane sample to be tested, with no cracks, burrs, or peeling visible to the naked eye. Cut a section of membrane tube 2 with a length of 40mm to 150mm from the middle, and grind the end face flat. This section will be used to prepare the membrane for testing. Figure 1 Test sample 6 is shown. Based on the outer diameter of the membrane tube 2, one each of a dry, clean rigid cap 1, connector 3, internal threaded core connector 4, and external threaded quick-connect connector 5 is selected. The inner diameter of the open end of cap 1 is 1mm to 5mm larger than the outer diameter of membrane tube 2. One end of connector 3 is the same specification as the open end of cap 1, and the other end is the same specification as the external interface of internal threaded core connector 4. The internal thread of internal threaded core connector 4 is the same specification as the external thread of external threaded quick-connect connector 5. The diameter of the quick-connect interface of external threaded quick-connect connector is 8mm, 10mm, or 12mm. The prepared test sample 6 can be connected to the pipeline through the quick-connect interface of external threaded quick-connect connector 5. The effective length of membrane tube 2 in test sample 6 is 5mm to 100mm (the length of the exposed portion of the membrane tube in the test sample), and test sample 6 is prepared through steps S1-S4.

[0037] Step S1: Place the cap 1 with its opening facing upwards on a horizontal surface. Inject a portion of polyurethane two-component or epoxy two-component adhesive into it (adhesive usage should follow the product instructions). Insert one end of the membrane tube 2 vertically and slowly into it, ensuring the membrane tube 2 is centered. If adhesive overflows from the cap 1, wipe off the adhesive from the outer wall of the cap 1. Otherwise, slowly replenish the adhesive to the inner wall of the cap 1 using a pipette, avoiding air residue in the gap between the membrane tube 2 and the cap 1. Continue until the adhesive is about to overflow onto the outer wall of the cap 1, allowing the adhesive to cure and form a smooth, convex surface at the opening between the membrane tube 2 and the cap 1. This prevents the test liquid from flowing back into the membrane pores during pore size testing. Cure at room temperature for 24-48 hours.

[0038] Step S2: Apply an adhesive suitable for the pipe material, such as UPVC adhesive, evenly to the outer interface (including the end face and side) of the internal threaded connector 4 (use the adhesive according to the product instructions). Insert it into the port of the connector 3, which is the same specification as the outer interface of the internal threaded connector 4, with the internal threaded connector 4 facing downwards, and place it vertically for 1 hour to cure. The internal threaded connector 4 and the connector 3 can also be connected by a threaded connection.

[0039] Step S3: Place the connector 3 and plug 1 (both with the same specifications as the open ends) of the sample completed in step S2 on a horizontal surface with their ends facing upwards. Apply adhesive evenly to the other open end of the membrane tube 2 (from step S1), insert it vertically into the connector 3, centering it, and secure it with external force. After the adhesive has partially cured (approximately 12 hours at room temperature), slowly add adhesive to the gap between the membrane tube 2 and the connector 3 using a pipette, avoiding any residual air in the gap, until the adhesive is about to overflow onto the outer wall of the connector 3. This ensures that the cured adhesive forms a smooth, convex surface at the opening between the membrane tube 2 and the connector 3, preventing the test liquid from flowing back into the membrane pores during pore size testing. Curing time is 24-48 hours at room temperature. The principle for connecting the membrane tube 2 and the connector 3 is as follows: Inject the adhesive between the membrane tube 2 and the connector 3 in two steps. First, use a small amount of adhesive to fix the membrane tube 2 in the center of the connector 3, sealing the gap between the membrane tube 2 and the connector 3 to prevent adhesive leakage. After the adhesive has partially cured, slowly add more adhesive to the gap between the membrane tube 2 and the connector 3.

[0040] Step S4: Wrap PTFE raw material tape around the external thread of the external thread quick-connect connector 5 and screw it into the internal thread of the internal thread core connector 4 of the sample completed in step S3 to obtain the test sample 6.

[0041] Step 2: Connect the quick-connect interface of the test sample 6 completed in step S4 to the high-pressure gas source 7 via a gas tube. The gas source 7 is high-purity nitrogen. Figure 2 As shown. Observe the changes in the readings of the gas mass flow meter 10 and the precision pressure gauge 11. Adjust the gas pressure entering the test sample 6 through the pressure reducing valve 8 and the pressure regulating valve 9 so that the gas flow rate through the test component 6 is 5L / min to 50L / min (the gas mass flow meter can realize the conversion of the mass flow rate of the gas into the volume flow rate under standard conditions). Maintain constant pressure for 30s and use high-pressure gas to blow out impurities in the membrane pores.

[0042] Step 3, as follows Figure 3 As shown, the effective part (below connector 3) of membrane tube 2 in the test sample 6 completed in step 2 is immersed in container 12 containing test liquid, with the test sample interface facing upward and above the liquid surface, so that the test liquid seeps into the membrane pores unidirectionally from the outer wall of membrane tube 2. At the same time, the test liquid is prevented from entering the interior of test sample 6 from quick-connect interface (the liquid entering the membrane cavity will hinder the gas in the membrane pore structure layer from escaping through the membrane cavity). Immersion time is 5 min to 15 min.

[0043] Step 4: Place the container 12 containing the test liquid and test sample 6 from Step 3 into an ultrasonic water bath. The water bath temperature is the temperature required for the aperture test. The ultrasonic frequency is 20kHz~100kHz, and the power density is 0.3W / cm². 2 ~1.0W / cm2 Connect the quick-connect interface of test sample 6 to vacuum pump 15 through a transparent tubing. Observe the reading of vacuum gauge 13 and adjust the vacuum level of the system through vacuum regulating valve 14. Depending on the actual situation of the test sample, first slowly adjust the vacuum level of the system to a lower value, ranging from 0.005MPa to 0.030MPa (generally, the smaller the pore size of the membrane sample, the higher the required vacuum level). Observe the rising of bubbles in the tubing at the interface between the transparent tubing and test sample 6. If no bubbles containing test liquid emerge within 5 to 10 minutes, further slowly increase the vacuum level of the system, ranging from 0.010MPa to 0.100MPa, until rising bubbles appear in the tubing at the interface. Fine-tune the vacuum level to maintain bubbles emerging in the tubing at the interface without causing the liquid level to rise (the more test liquid in the membrane cavity and tubing, the greater the resistance to gas escape from the membrane pore structure layer). As gas continuously escapes from the membrane pore structure in test sample 6, the bubbles in the tubing at the interface will gradually become smaller and fewer. When no bubbles emerge, a slow rise in liquid level will occur inside the tube at the interface, with only a very small number of tiny bubbles in the liquid (for example, when a transparent connecting tube with an outer diameter of 8 mm and an inner diameter of 5 mm is used between test sample 6 and vacuum pump 15, the liquid level rises by 5 mm to 50 mm per minute, and there are 0 to 2 tiny bubbles per 20 mm of liquid, with a bubble diameter of less than 0.2 mm). This indicates that there is no gas inside the membrane pore structure. After the liquid level rises to 20 mm to 100 mm above the interface, the vacuum level of the system is gradually reduced to zero. The water bath ultrasonic test is turned off, and the sample is kept at the set water bath temperature for 1 to 2 hours before being removed.

[0044] Step 5: Connect the test sample 6 obtained in Step 4 to the pore size measuring instrument through the air tube, and complete the test of the membrane sample pore size parameters according to the principle of bubble point and average flow rate method specified in GB / T 32361—2015 (bubble point method to test the maximum pore size, average flow rate method to test the average pore size).

[0045] Application Example 1

[0046] PE sintered tubular microfiltration membrane, outer diameter 35mm, single pore, inner diameter 20mm.

[0047] Procedure: Cut a 75mm long membrane tube 2 from the middle of the membrane sample and grind both ends flat. Select one UPVC plug cap 1 (DN32), one reducing straight connector (DN32×25), one internal threaded core connector 4 (DN25×1 / 2), and one stainless steel external threaded quick-connect connector 5 (8mm×1 / 2). Complete the preparation of test sample 6 according to steps S1-S4 in the specific implementation method. After completion, the effective length of membrane tube 2 in test sample 6 is 15mm. Connect the quick-connect interface of test sample 6 to high-purity nitrogen through a gas tube. When the gas pressure is adjusted to 0.150MPa, the gas flow rate through test sample 6 is 25L / min. Maintain constant pressure for 30s and use high-pressure gas to blow out impurities in the membrane pores. Immerse the effective part of membrane tube 2 in the test sample after impurity removal in a beaker containing isobutanol for 10min (seal the beaker mouth with a plastic bag to reduce the environmental impact of isobutanol volatilization). The quick-connect interface is connected to the vacuum pump 15 via a transparent air tube. The beaker is placed in an ultrasonic water bath at 25°C with a water bath capacity of 3L. The ultrasonic operating frequency is 40kHz, the ultrasonic power is 150W, and the power density is 0.5W / cm³. 2 The vacuum level of the system was adjusted to 0.010 MPa by slowly adjusting the vacuum regulating valve 14. No bubbles emerged from the tube at the quick-connect interface within 5 minutes. The vacuum level was then slowly adjusted to 0.035 MPa. After 2 minutes, a significant number of bubbles rose from the interface. The vacuum level was further fine-tuned to 0.030 MPa, maintaining bubbles at the interface without causing a rise in the liquid level. After 8 minutes, no more bubbles emerged from the interface, and the liquid level began to rise slowly. After 3 minutes, only a few tiny bubbles remained in the liquid. The liquid level slowly rose to 100 mm above the interface. The vacuum level was then gradually reduced to zero, and the ultrasonic bath was turned off. Test sample 6 was kept in a beaker containing isobutanol and kept at a constant temperature of 25°C for 1 hour before being removed and connected to a pore size measuring instrument to complete the pore size test. Test results: Maximum pore size was 1.43 μm, and average pore size was 0.768 μm.

[0048] In comparison, according to the sample immersion method specified in GB / T 32361—2015, the test sample 6 prepared according to the method of this example was immersed in isobutanol for 24 hours and then taken out and connected to a pore size measuring instrument to complete the pore size test. The test results were: the maximum pore size was 4.2 μm and the average pore size was 1.84 μm.

[0049] Application Example 2

[0050] PE sintered tubular microfiltration membrane, outer diameter 19mm, single pore, inner diameter 12mm.

[0051] Operating Procedure: Cut an 80mm long membrane tube 2 from the middle of the membrane sample and grind both ends flat. Select one UPVC plug cap 1 (DN15), one straight connector (DN15), one internal threaded core connector 4 (DN15×1 / 4), and one stainless steel external threaded quick-connect connector 5 (8mm×1 / 4). Complete the preparation of test sample 6 according to steps S1-S4 in the specific implementation method. After completion, the effective length of membrane tube 2 in test sample 6 is 40mm. Connect the quick-connect interface of test sample 6 to high-purity nitrogen through a gas tube. When the gas pressure is adjusted to 0.100MPa, the gas flow rate through test sample 6 is 22L / min. Maintain constant pressure for 30s and use high-pressure gas to blow out impurities in the membrane pores. After impurity removal, the effective portion of membrane tube 2 in test sample 6 was immersed in a beaker containing isobutanol for 5 minutes (the beaker opening was sealed with a plastic bag to reduce the environmental impact of isobutanol volatilization). The quick-connect interface was connected to vacuum pump 15 through a transparent air tube. The beaker was placed in an ultrasonic water bath at 25°C with a water bath capacity of 3L. The ultrasonic operating frequency was 40kHz, the ultrasonic power was 150W, and the power density was 0.5W / cm³. 2 The vacuum level of the system was adjusted to 0.010 MPa by slowly adjusting the vacuum regulating valve 14. No bubbles emerged from the tube at the quick-connect interface within 5 minutes. The vacuum level was then slowly adjusted to 0.030 MPa. After 2 minutes, a significant number of bubbles appeared at the interface. The vacuum level was further fine-tuned to 0.025 MPa, maintaining bubble emergence at the interface without causing a liquid level rise. After 5 minutes, no more bubbles emerged at the interface, and the liquid level began to rise slowly. After 2 minutes, no more bubbles remained in the liquid, and the liquid level slowly rose to 100 mm above the interface. The system vacuum level was then gradually reduced to zero, and the ultrasonic bath was turned off. Test sample 6 was kept in a beaker containing isobutanol and kept at a constant temperature of 25°C for 1 hour before being removed and connected to a pore size measuring instrument to complete the pore size test. Test results: Maximum pore size was 2.57 μm, and average pore size was 1.22 μm.

[0052] In comparison, according to the sample immersion method specified in GB / T 32361—2015, the test sample 6 prepared according to the method of this example was immersed in isobutanol for 24 hours and then taken out and connected to a pore size measuring instrument to complete the pore size test. The test results were: the maximum pore size was 6.44 μm and the average pore size was 2.66 μm.

[0053] Application Example 3

[0054] Tubular ceramic ultrafiltration membrane, outer diameter 22mm, 7 pores, pore inner diameter 2.5mm.

[0055] Operating Procedure: Cut a 65mm long membrane tube 2 from the middle of the membrane sample and grind both ends flat. Select one UPVC plug cap 1 (DN20), one reducing straight connector (DN20×15), one internal threaded core connector 4 (DN15×1 / 4), and one stainless steel external threaded quick-connect connector 5 (8mm×1 / 4). Complete the preparation of test sample 6 according to steps S1-S4 in the specific implementation method. After completion, the effective length of membrane tube 2 in test sample 6 is 20mm. Connect the quick-connect interface of test sample 6 to high-purity nitrogen through a gas tube. When the gas pressure is adjusted to 0.350MPa, the gas flow rate through test sample 6 is 10L / min. Maintain constant pressure for 30s and use high-pressure gas to blow out impurities in the membrane pores. After impurity removal, the effective portion of membrane tube 2 in test sample 6 was immersed in a beaker containing isobutanol for 10 minutes (the beaker opening was sealed with a plastic bag to reduce the environmental impact of isobutanol volatilization). The quick-connect interface was connected to vacuum pump 15 via a transparent air tube. The beaker was placed in an ultrasonic water bath at 25°C with a water bath capacity of 3L. The ultrasonic operating frequency was 40kHz, the ultrasonic power was 150W, and the power density was 0.5W / cm³. 2 The vacuum level of the system was adjusted to 0.030 MPa by slowly adjusting the vacuum regulating valve 14. No bubbles emerged from the tube at the quick-connect interface within 5 minutes. The vacuum level was then slowly adjusted to 0.050 MPa. After 3 minutes, a significant number of bubbles rose from the interface. The vacuum level was further fine-tuned to 0.040 MPa, maintaining bubbles at the interface without causing a rise in the liquid level. After 10 minutes, no more bubbles emerged from the interface, and the liquid level began to rise slowly. After 2 minutes, only a few tiny bubbles remained in the liquid. The liquid level slowly rose to 100 mm above the interface. The vacuum level was then gradually reduced to zero, and the ultrasonic bath was turned off. The test sample 6 was kept in a beaker containing isobutanol and kept at a constant temperature of 25°C for 1 hour before being removed and connected to a pore size measuring instrument to complete the pore size test. Test results: Maximum pore size was 0.234 μm, and average pore size was 0.140 μm.

[0056] In comparison, according to the sample immersion method specified in GB / T 32361—2015, the test component 6 prepared according to the method of this example was immersed in isobutanol for 24 hours and then taken out and connected to a pore size measuring instrument to complete the pore size test. The test results were: the maximum pore size was 0.677 μm and the average pore size was 0.282 μm.

[0057] Application Example 4

[0058] Tubular ceramic ultrafiltration membrane, outer diameter 22mm, 7 pores, pore inner diameter 2.5mm.

[0059] Operating Procedure: Cut a 60mm long membrane tube 2 from the middle of the membrane sample and grind both ends flat. Select one UPVC plug cap 1 (DN20), one reducing straight connector (DN20×15), one internal threaded core connector 4 (DN15×1 / 4), and one stainless steel external threaded quick-connect connector 5 (8mm×1 / 4). Complete the preparation of test sample 6 according to steps S1-S4 in the specific implementation method. After completion, the effective length of membrane tube 2 in test sample 6 is 15mm. Connect the quick-connect interface of test sample 6 to high-purity nitrogen through a gas tube. When the gas pressure is adjusted to 0.500MPa, the gas flow rate through test sample 6 is 25L / min. Maintain constant pressure for 30s and use high-pressure gas to blow out impurities in the membrane pores. After impurity removal, the effective portion of membrane tube 2 in test sample 6 was immersed in a beaker containing isobutanol for 15 minutes (the beaker opening was sealed with a plastic bag to reduce the environmental impact of isobutanol volatilization). The quick-connect interface was connected to vacuum pump 15 through a transparent air tube. The beaker was placed in an ultrasonic water bath at 25°C with a water bath capacity of 3L. The ultrasonic operating frequency was 40kHz, the ultrasonic power was 150W, and the power density was 0.5W / cm³. 2 The vacuum level of the system was adjusted to 0.030 MPa by slowly adjusting the vacuum regulating valve 14. No bubbles emerged from the tube at the quick-connect interface within 5 minutes. The vacuum level was then slowly adjusted to 0.050 MPa. After 5 minutes, no bubbles emerged from the tube at the interface. The vacuum level was then further slowly adjusted to 0.085 MPa. After 3 minutes, bubbles began to emerge from the interface, and the tube at the interface was kept filled with bubbles without any liquid level rise. After 5 minutes, no more bubbles emerged from the tube at the interface, and the liquid level began to rise slowly. After 2 minutes, no more small bubbles remained in the liquid in the tube. The liquid level slowly rose to 100 mm above the interface. The system vacuum level was then gradually reduced to zero. The ultrasonic water bath was turned off. The test sample 6 was kept in a beaker containing isobutanol and kept at a constant temperature of 25°C for 1 hour before being taken out and connected to the pore size measuring instrument to complete the pore size test. Test results: The maximum pore size is 0.130 μm and the average pore size is 0.0626 μm.

[0060] In comparison, according to the sample immersion method specified in GB / T 32361—2015, the test component 6 prepared according to the method of this example was immersed in isobutanol for 24 hours and then taken out and connected to a pore size measuring instrument to complete the pore size test. The test results were: the maximum pore size was 0.644 μm and the average pore size was 0.215 μm.

[0061] As can be seen from the test results of the pore size of four different tubular membrane samples in Examples 1-4, the pore size values ​​measured by the method of this invention are much smaller than those measured by the method specified in standard GB / T 32361—2015. This is because the immersion method specified in the standard is only suitable for wetting flat sheet membranes and hollow fiber membranes with relatively thin membrane structure layers, large pore sizes, and simple pore structures. When applied to the wetting of tubular membranes, due to the presence of surface and interfacial tension, the natural permeation of the test liquid cannot expel the gas within the complex pore structure of the tubular membrane, especially the gas within the ultrafine pores. This causes distortion in the gas flow rate and gas pressure values ​​permeating the membrane during the test, resulting in a shift in the wetted curve, an overestimation of the pore size test results, and test results that cannot accurately reflect the pore structure characteristics of the membrane, thus not matching the actual retention performance of the membrane. This invention combines ultrasonic dispersion technology and negative pressure impurity removal technology and applies them to the testing process of tubular membrane pore size. By reducing pressure and controlling the flow rate through a programmed decompression method, the influence of gas resistance during the membrane sample wetting process is greatly reduced. This solves the problem of gas removal within the complex pore structure of tubular membranes, achieving complete sample wetting and meeting the requirements of bubble point and average flow rate method pore size testing. It can measure the structural characteristics of all pores in the membrane structure layer, improving the accuracy and precision of the test results.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for testing the pore size of a tubular membrane, characterized in that, Includes the following steps: Step 1: Cut a section of membrane tube from the middle of the tubular membrane sample to be tested to prepare a test sample. The test sample includes a plug, membrane tube, connector, internal threaded core connector, and external threaded quick-connect connector. The plug is fixedly connected to one end of the membrane tube, the connector is fixedly connected to the other end of the membrane tube, the external interface of the internal threaded core connector is fixedly connected to the other end of the connector, and the external thread of the external threaded quick-connect connector is connected to the internal thread of the internal threaded core connector. The prepared test sample can be connected to the pipeline through the interface of the external threaded quick-connect connector. Step 2: Connect the test sample obtained in Step 1 to high-purity nitrogen gas, adjust the gas pressure so that the gas flow rate through the test sample is 5 L / min to 50 L / min, maintain constant pressure for 30 s, and use high-pressure gas to blow out impurities in the membrane pores to obtain the test sample after impurity removal. Step 3: Immerse the membrane tube portion of the test sample obtained in Step 2 in a container filled with test liquid, with the test sample interface facing upwards and above the liquid surface, so that the test liquid can unidirectionally seep into the membrane pores from the outer wall of the membrane, while preventing the test liquid from entering the interior of the test sample from the interface, and immerse for 5 min to 15 min. Step 4: Place the container containing the test liquid and test sample obtained in Step 3 into an ultrasonic water bath. Connect the interface of the test sample to a vacuum pump using a transparent tube. Adjust the vacuum level of the system to 0.005 MPa to 0.030 MPa. Observe the rising of bubbles in the transparent tube at the interface of the test sample. If no bubbles containing test liquid emerge within 5 to 10 minutes, further increase the vacuum level to 0.010 MPa to 0.100 MPa until rising bubbles appear in the tube at the interface. Fine-tune the vacuum level to maintain the presence of bubbles in the tube at the interface without causing the liquid level to rise. As the gas continuously escapes from the membrane pore structure of the test sample, the bubbles in the tube at the interface gradually become smaller and fewer. When no bubbles emerge, the liquid level in the tube at the interface will slowly rise, and there will be only a very small number of tiny bubbles in the liquid, indicating that there is no gas in the membrane pore structure. Wait until the liquid level rises to 20 mm to 100 mm above the interface. After mm, reduce the system vacuum to zero, turn off the water bath ultrasonic wave, and take out the sample after keeping it at the set water bath temperature for 1 h to 2 h. Step 5: Connect the test sample obtained in Step 4 to the pore size measuring instrument through a pipeline, and complete the test of the pore size parameters of the tubular membrane sample according to the principle of the bubble point and average flow rate method specified in GB / T 32361—2015.

2. The test method as described in claim 1, characterized in that, The membrane tube is obtained by the following method: Take a dry, clean tubular membrane sample with no cracks, burrs, or peeling visible to the naked eye, cut a section of membrane tube with a length of 40 mm to 150 mm from the middle, and grind the end face flat.

3. The test method as described in claim 1, characterized in that, The effective length of the membrane tube in the test sample is 5mm-100mm.

4. The test method as described in claim 1, characterized in that, The ultrasonic frequency is 20 kHz to 100 kHz, and the power density is 0.3 W / cm² to 1.0 W / cm².

5. The test method as described in claim 1, characterized in that, The inner diameter of the plug opening is 1 mm to 5 mm larger than the outer diameter of the membrane tube; one end of the connector has the same specifications as the plug opening, and the other end has the same specifications as the outer interface of the internal thread connector; the internal thread of the internal thread connector has the same specifications as the external thread of the external thread quick-connect connector; the diameter of the external thread quick-connect connector interface is 8 mm, 10 mm, or 12 mm.

6. The test method as described in claim 1, characterized in that, The connector is a reducing straight connector or a straight connector; the interface is a quick-connect interface; the plug, connector, and internal threaded core connector are made of rigid plastic; the external threaded quick-connect connector is made of metal.

7. The test method as described in claim 1, characterized in that, The test sample was prepared by the following method: Step S1: Place the cap with the opening facing upwards on a horizontal surface, inject adhesive into it, and vertically insert one end of the membrane tube into it, ensuring that the membrane tube is in the center of the cap. If the adhesive overflows from the cap, wipe off the adhesive on the outer wall of the cap; otherwise, use a pipette to add adhesive to the inner wall of the cap to prevent air from remaining in the gap between the membrane tube and the cap. Continue until the adhesive is about to overflow onto the outer wall of the cap. Allow it to cure at room temperature for 24 to 48 hours. Step S2: Apply adhesive evenly to the end face and side of the outer interface of the internal thread repair connector, insert it into the port of the connector with the same specification as the outer interface of the internal thread repair connector, with the internal thread repair connector facing down and placed vertically for 1 hour to cure; or, the internal thread repair connector and the connector are connected by a threaded connection. Step S3: Place the connector of the sample completed in step S2 with the same opening end as the cap opening end facing upwards on a horizontal surface. Apply adhesive evenly to the other opening end of the membrane tube of the sample completed in step S1, insert it vertically into the connector, center it, and fix it with external force. After the adhesive is semi-cured, use a pipette to add adhesive to the gap between the membrane tube and the connector to avoid residual air in the gap, until the adhesive is about to overflow to the outer wall of the connector. Cure at room temperature for 24 h to 48 h. Step S4: Wrap polytetrafluoroethylene raw material tape around the external thread of the external thread quick-connect connector and screw it into the internal thread of the internal thread core connector of the sample completed in step S3 to obtain the test sample.

8. The test method as described in claim 7, characterized in that, The adhesives mentioned in steps S1 and S3 are two-component adhesives; the adhesives mentioned in step S2 are one-component adhesives suitable for pipe fitting materials.

9. The test method as described in claim 7, characterized in that, In step S3, the adhesive is injected between the membrane tube and the connector in two steps. First, a small amount of adhesive is used to fix the membrane tube to the center of the connector and seal the gap between the membrane tube and the connector to prevent leakage of the adhesive added later. After the adhesive is semi-cured, more adhesive is added to the gap between the membrane tube and the connector.

10. The test method as described in claim 7, characterized in that, In step S1, after the adhesive cures, a smooth, convex surface is formed at the opening between the membrane tube and the plug; in step S3, after the adhesive cures, a smooth, convex surface is formed at the opening between the membrane tube and the connector, preventing the test liquid from flowing back into the membrane pore during the pore size test.

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