A self-repairable ultra-thin polymer / hollow fiber composite membrane module and a preparation method thereof

Abstract

The present application relates to the field of membrane separation, in particular to a self-repairable ultra-thin polymer / hollow fiber composite membrane module and a preparation method thereof, the present application proposes to bind the hollow fibers on the center tube in a "bundling type", to establish a standardized membrane coating production line, to carry out orthogonal cross test on the polymer coating liquid coating process of different materials based on the membrane preparation process of differential pressure pore permeation method, to unify the corresponding membrane preparation parameters, to carry out rapid gas blowing and other post-treatment processes after the coating is completed, so as to realize relatively uniform membrane thickness and dense and defect-free membrane layer, and to avoid the blockage of the inner cavity of the hollow fiber; at the same time, after the crosslinking agent is reacted with the polymer chain amide, a large number of carboxyl groups will still remain on the crosslinking agent, so that the new chemical crosslinking reaction of carboxyl and amino group, carboxyl and carboxyl occurs under a certain temperature and time, so as to realize the self-repair of the membrane layer defects, and the self-repair still maintains good separation performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation, in particular to a self-repairable ultra-thin polymer / hollow fiber composite membrane module and a preparation method thereof. BACKGROUND

[0002] Unlike microfiltration, nanofiltration and other separation processes, the composite membrane composed of a support layer and a separation layer is mainly suitable for gas separation and organic reverse osmosis. At present, the commercialized composite membrane modules mainly include tubular, plate-and-frame, spiral-wound and laminated types, which have the following problems: 1) the production cost of ceramic tubes is high, and the packing density in the membrane module is low; 2) in the design process of the membrane module, although the flat plate composite membrane has different packing modes (plate-and-frame, spiral-wound and laminated types), the mass transfer resistance of the support layer is large, and the length of the membrane module is relatively long, which leads to significant pressure drop loss and high energy consumption. Compared with the tubular composite membrane and the flat plate composite membrane, the hollow fiber composite membrane has the advantages of high packing density, small pressure drop loss, low production cost and protection of the polymer separation layer.

[0003] Compared with the dip-coating method, the blade coating method and the spin coating method, the new differential pressure pore penetration method ensures the reproducibility of the composite membrane preparation and the denseness of the membrane layer. In terms of the difficulty of membrane preparation, the process of large-scale preparation of the composite membrane in the hollow fiber lumen is extremely challenging: first, the inner diameter of the lumen is small (less than 2 mm); second, during the solidification process after the polymer coating, effective and timely subsequent treatment is the key to the success of the polymer / hollow fiber composite membrane module. From the perspective of the reusability of the composite membrane, how to prepare a membrane that can be regenerated after damage and still maintain good separation performance is a research difficulty. SUMMARY

[0004] The technical problem to be solved by the present application is how to make the composite membrane module self-repairable and regenerable after damage, and still maintain good separation performance after self-repairing.

[0005] The present application proposes to bind the hollow fibers on the center tube in a "bundling" manner, establish a standardized membrane coating production line, conduct orthogonal cross tests on the polymer coating process of different materials based on the membrane preparation process of the differential pressure pore penetration method, unify the corresponding membrane preparation parameters, and quickly perform subsequent treatment processes such as gas blowing after the coating of the membrane, so as to realize a relatively uniform membrane thickness and a dense and defect-free membrane layer, and avoid the blockage of the hollow fiber lumen. At the same time, after the crosslinking agent dianhydride reacts with the polymer chain amide, a large number of carboxyl groups will still remain on the crosslinking agent. Therefore, by utilizing the new chemical crosslinking reaction between the carboxyl group and the amino group, and the carboxyl group and the carboxyl group at a certain temperature and time, the self-repairing of the membrane layer defects is realized, and the composite membrane still maintains good separation performance after self-repairing.

[0006] To achieve the above object, the application provides the following technical scheme: a self-repairable ultra-thin polymer / hollow fiber composite membrane assembly, comprising a center tube and a plurality of hollow fibers surrounding the center tube, and a self-repairable polymer separation membrane layer is further arranged on the inner cavity of each hollow fiber, and the film thickness of the polymer separation membrane layer is less than 300 nm.

[0007] Preferably, the self-repairing temperature is 100-160 DEG C, and the time is 0.5-5 h.

[0008] Preferably, the preparation method of the composite membrane assembly comprises the following steps:

[0009] S1: using resin glue to stack and fix the qualified hollow fibers around the center tube layer by layer, after wrapping the outermost layer with a plastic net, the glue is inserted into the membrane shell, and after room temperature curing, the cover is glued on both ends of the membrane shell, thereby obtaining the hollow fiber membrane assembly, and due to the different positions of the feed inlet and the discharge outlet on the cover, two kinds of hollow fiber membrane assemblies with different appearance structures can be obtained.

[0010] S2: blending and stirring the silicone oil, the di-anhydride and the solvent according to the mass ratio to obtain a polymer mixed solution;

[0011] S3: pumping the polymer mixed solution into the inner cavity of the hollow fiber, completing the coating of the polymer separation layer by the differential pressure hole penetration method, and then carrying out gas blowing, curing and drying to obtain the ultra-thin polymer / hollow fiber composite membrane assembly.

[0012] Preferably, the qualified hollow fiber refers to the hollow fiber with CO2 permeability in the range of 10000-25000 Barrer after picking and screening.

[0013] Preferably, the hollow fiber comprises inorganic hollow fiber, organic hollow fiber and hollow fiber with different channel numbers, the inorganic hollow fiber comprises alumina, titania, yttria, zirconia and silica, the organic hollow fiber comprises polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile and polysulfone, and the hollow fiber with different channel numbers comprises 1, 4, 7, 9 and 19 channels.

[0014] Preferably, the material of the center tube comprises stainless steel, polytetrafluoroethylene and polyvinylidene fluoride.

[0015] Preferably, the mass ratio of the silicone oil, the di-anhydride and the solvent is 1-10:1:40-60, the silicone oil comprises one or more of amino silicone oil, hydroxyl silicone oil and vinyl silicone oil, the di-anhydride comprises phthalic anhydride, succinic anhydride, glutaric anhydride, adipic anhydride and maleic anhydride, and the solvent comprises n-heptane, n-hexane, tetrahydrofuran and benzene.

[0016] Preferably, the differential pressure porosimetry method specifically comprises: by controlling the hollow fiber membrane assembly rear valve and peristaltic pump, adjusting the flow rate, pressure and time of the polymer mixed solution pumped into, so as to promote the polymer mixed solution to penetrate into the membrane on the surface of the hollow fiber.

[0017] Preferably, the flow rate is 0-10 L / min, the pressure is 0-100 kPa, preferably 50 Pa-5000 Pa, and the time is 0-30 s.

[0018] Preferably, the gas blowing gas is compressed air, carbon dioxide or nitrogen, and the gas blowing speed is 0-100 L / min.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] (1) The present application effectively enhances the interfacial bonding force between the polymer membrane layer and the support surface by the differential pressure porosimetry method, and forms a dense and defect-free separation membrane.

[0021] (2) The present application can realize self-repairing of the damaged membrane layer by simple heating, and still maintains good separation performance after self-repairing.

[0022] (3) The polymer separation membrane layer of the present application is in the lumen of the hollow fiber, which avoids the physical damage of the composite membrane during the loading process, and the membrane layer shows an ultra-thin film thickness of less than 300 nm.

[0023] (4) The preparation method of the present application has universality and industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figure is a membrane preparation device for the composite membrane assembly of the present application, and there are two forms of the final hollow fiber membrane assembly due to the different positions of the feed inlet and the discharge outlet.

[0025] Figure 2 The figure is a membrane preparation flow chart for the composite membrane assembly of the present application.

[0026] Figure 3 The figure is a post-treatment flow chart for the composite membrane assembly of the present application.

[0027] Figure 4 The figure is a comparison SEM of the cross section of the composite membrane prepared by the common dip-coating method and the new differential pressure porosimetry method.

[0028] Figure 5 The figure is an SEM of the membrane surface damaged after long-term use of the composite membrane in a fermentation solution and an SEM of the membrane surface after self-repairing by heating.

[0029] The figure is a comparison SEM of the cross section of the composite membrane prepared by the common dip-coating method and the new differential pressure porosimetry method.

[0030] 10. Coating liquid tank; 11. Heating and stirring table; 12. Thermometer; 13. Peristaltic pump; 14. Valve; 15. Branch valve; 16. Gas cylinder; 17. Polymer / hollow fiber composite membrane module; 18. Organic solvent waste gas treatment tank. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] Polymer mixed solution formulation: Weigh amino silicone oil, phthalic anhydride, and n-heptane according to a mass ratio of 5:1:50, mix and stir for 5 hours, and pump the mixed solution with a viscosity of 16 lipoise into the four-channel alumina ceramic hollow fiber membrane module at a speed of 2 cm / s using a peristaltic pump. The operating pressure is adjustable to 500 Pa, and the valve opening on the back side of the membrane module is adjusted to 1 / 4. Coating is performed for 10 seconds. The wet four-channel amino silicone oil / ceramic hollow fiber composite membrane module is then purged with air at a speed of 2 cm / s to promote rapid evaporation of the solvent on the surface of the polymer membrane layer. The membrane is then left at room temperature for 2 days.

[0034] like Figure 4 As shown, SEM images were used to compare composite membranes prepared by the common dip-coating method and the novel differential pressure permeation method. It was observed that defects easily appear between the membrane layer and the support layer in the composite membrane prepared by the common dip-coating method, while the composite membrane prepared by the novel differential pressure permeation method shows a tight bond at the interface between the membrane layer and the support layer under 500 Pa pressure. The dip-coating method for coating hollow fiber inner membranes requires wrapping the outer wall of the hollow fiber to prevent the coating solution from penetrating. The hollow fiber is immersed in the coating solution at a certain speed (4 cm / s), held for a certain time (10 s), and then removed at a certain speed (4 cm / s). This method is not suitable for preparing industrial-grade high-viscosity polymer coating solutions due to the limited space within the support cavity.

[0035] The four-channel amino silicone oil / ceramic hollow fiber composite membrane module (effective hollow fiber membrane length 40 cm) prepared in this example was tested. At 30°C and 3 bar, when separating 21% v / v oxygen-containing air, the average gas flux and permeate-side oxygen concentration were 25 L / min and 27.7% v / v, respectively. Through an organic reverse osmosis process at 45°C and 15 bar, when separating 30 wt% dimethyl carbonate-methanol, the average membrane flux and average separation factor were 1.6 kg / m³. 2 h and 1.9.

[0036] Example 2

[0037] Polymer solution formulation: amino silicone oil, phthalic anhydride, n-heptane were weighed according to the mass ratio of 7.5:1:50, and blended and stirred for 1.5 hours. The mixed solution with a viscosity of 11 centipoise was pumped into a polyvinylidene fluoride (PVDF) hollow fiber membrane module at a speed of 0.5 cm / s by using a peristaltic pump. The adjustable operating pressure was 1500 Pa, the valve opening degree of the rear side of the membrane module was adjusted to 2 / 5, and coating was performed for 5 seconds. The amino silicone oil / PVDF hollow fiber composite membrane module in a wet state was blown by air at a speed of 0.1 cm / s to sweep the inner cavity of the hollow fiber, so as to promote the rapid evaporation of the solvent on the surface of the polymer membrane layer, and the module was placed at room temperature for 1 day.

[0038] The amino silicone oil / PVDF hollow fiber composite membrane module (effective hollow fiber membrane length 30 cm) prepared in this example was measured. When separating 21% v / v oxygen-containing air at 30°C and a pressure of 3 bar, the average gas flux and the oxygen concentration on the permeation side were 22 L / min and 29.5% v / v, respectively. Through the organic reverse osmosis process, when separating 10 wt% toluene-methanol at 50°C and a pressure of 10 bar, the average membrane flux and the average separation factor were 1.1 kg / m 2 h and 26, respectively.

[0039] Example 3

[0040] Polymer solution formulation: (amino silicone oil + hydroxyl silicone oil): glutaric anhydride: n-hexane were weighed according to the mass ratio of (5+1):1:50, and blended and stirred for 7.5 hours. The mixed solution with a viscosity of 22 centipoise was pumped into a stainless steel hollow fiber membrane module at a speed of 3 cm / s by using a peristaltic pump. The adjustable operating pressure was 1000 Pa, the valve opening degree of the rear side of the membrane module was adjusted to 1 / 4, and coating was performed for 4 seconds. The silicone oil / stainless steel hollow fiber composite membrane module in a wet state was blown by air at a speed of 0.3 cm / s to sweep the inner cavity of the hollow fiber, so as to promote the rapid evaporation of the solvent on the surface of the polymer membrane layer, and the module was placed at room temperature for 3 days.

[0041] The silicone oil / stainless steel hollow fiber composite membrane module (effective hollow fiber membrane length 15 cm) prepared in this example was measured. When separating 21% v / v oxygen-containing air at 30°C and a pressure of 4 bar, the average gas flux and the oxygen concentration on the permeation side were 17 L / min and 28.0% v / v, respectively. Through the organic reverse osmosis process, when separating 10 wt% dimethyl carbonate-methanol at 50°C and a pressure of 25 bar, the average membrane flux and the average separation factor were 2.6 kg / m 2 h and 9.2, respectively.

[0042] Example 4

[0043] Polymer solution formulation: (0.8+0.1+0.1):1:50 by mass of (amino silicone oil+hydroxyl silicone oil+vinyl silicone oil), succinic anhydride, benzene, were weighed and blended for 5 hours; the mixed solution with a viscosity of 8 centipoise was pumped into a polytetrafluoroethylene (PTFE) hollow fiber membrane module at a speed of 1.5 cm / s by a peristaltic pump, the controllable operating pressure was 1000 Pa, the valve opening degree of the back side of the membrane module was adjusted to 1 / 2, and coating was performed for 25 s; the wet state of the silicone oil / PTFE hollow fiber composite membrane module was blown by air at a speed of 5 cm / s to sweep the inner cavity of the hollow fiber, so as to promote the rapid evaporation of the solvent on the surface of the polymer membrane layer, and the module was placed at room temperature for 1 day.

[0044] The average gas flux and the oxygen concentration on the permeation side of the nine-channel silicone oil / ceramic hollow fiber composite membrane module (effective hollow fiber membrane length 50 cm) prepared in this example were 11 L / min and 28.9% v / v, respectively, when separating 21% v / v oxygen-containing air at 30°C and a pressure of 3 bar; the average membrane flux and the average separation factor were 1.8 kg / m 2 h and 7.5, respectively, when separating 10 wt% dimethyl carbonate-methanol by organic reverse osmosis at 50°C and a pressure of 20 bar.

[0045] Example 5

[0046] Polymer solution formulation: (0.8+0.1+0.1):1:50 by mass of (amino silicone oil+hydroxyl silicone oil+vinyl silicone oil), succinic anhydride, benzene, were weighed and blended for 5 hours; the mixed solution with a viscosity of 8 centipoise was pumped into a polytetrafluoroethylene (PTFE) hollow fiber membrane module at a speed of 1.5 cm / s by a peristaltic pump, the controllable operating pressure was 1000 Pa, the valve opening degree of the back side of the membrane module was adjusted to 1 / 2, and coating was performed for 25 s; the wet state of the silicone oil / PTFE hollow fiber composite membrane module was blown by air at a speed of 5 cm / s to sweep the inner cavity of the hollow fiber, so as to promote the rapid evaporation of the solvent on the surface of the polymer membrane layer, and the module was placed at room temperature for 1 day.

[0047] The average gas flux and the oxygen concentration on the permeation side of the nine-channel silicone oil / ceramic hollow fiber composite membrane module (effective hollow fiber membrane length 50 cm) prepared in this example were 11 L / min and 28.9% v / v, respectively, when separating 21% v / v oxygen-containing air at 30°C and a pressure of 3 bar; the average membrane flux and the average separation factor were 1.8 kg / m 2 h and 7.5, respectively, when separating 10 wt% dimethyl carbonate-methanol by organic reverse osmosis at 50°C and a pressure of 20 bar.

[0048] Repair performance experiment

[0049] To investigate the self-repairing ability of the membrane material, the silicone / PTFE hollow fiber composite membrane module prepared in Example 5 was placed in the fermentation solution for continuous use until the membrane surface was damaged and the membrane performance was affected. After the damaged membrane was removed, the clean surface was heated at 140°C for 1 hour.

[0050] The damaged and self-repaired composite membrane was characterized by SEM, and the results are shown in Figure 5. It can be seen that the damaged composite membrane was well repaired. Figure 5

[0051] The average gas flux and the oxygen concentration on the permeation side of the self-repaired silicone / PTFE hollow fiber composite membrane module (effective hollow fiber membrane length 40 cm) were 22.8 L / min and 29.2% v / v, respectively, when separating 21% v / v oxygen-containing air at 30°C and a pressure of 3 bar. The average membrane flux and the average separation factor were 1.0 kg / m2h and 3.4, respectively, when separating 10 wt% toluene-n-heptane by organic reverse osmosis at 50°C and a pressure of 9 bar. By comparing the separation performance of the original membrane in Example 5, it was proved that the separation performance of the damaged composite membrane was successfully restored after simple heating. 2

[0052] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application, and any reference signs in the claims should not be regarded as limiting the claims involved.​​

Claims

1. A self-healing ultrathin polymer / hollow fiber composite membrane module, characterized in that, It includes a central tube and several hollow fibers surrounding the central tube. Each hollow fiber is also provided with a self-healing polymer separation membrane layer on its inner cavity. The membrane thickness of the polymer separation membrane layer is <300nm. The preparation method of the self-healing ultrathin polymer / hollow fiber composite membrane module includes the following steps: S1: Use resin glue to stack and fix qualified hollow fibers around the central tube layer by layer. After wrapping the outermost layer with plastic mesh, apply glue and stuff it into the membrane shell. After curing at room temperature, glue the caps to both ends of the membrane shell to obtain a hollow fiber membrane module. S2: Weigh out the silicone oil, dianhydride and solvent according to the mass ratio, mix and stir to obtain a polymer mixed solution; S3: The polymer mixture solution is pumped into the inner cavity of the hollow fiber. After the polymer separation layer is coated by differential pressure permeation, the mixture is cured by gas purging and dried to obtain an ultrathin polymer / hollow fiber composite membrane module. The mass ratio of the silicone oil, dianhydride, and solvent is 1-10:1:40-60; the silicone oil includes one or more of amino silicone oil, hydroxyl silicone oil, or vinyl silicone oil; the dianhydride includes phthalic anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, or maleic anhydride; the solvent includes n-heptane, n-hexane, tetrahydrofuran, or benzene. The differential pressure permeation method specifically involves controlling the valves on the back side of the hollow fiber membrane module and the peristaltic pump to adjust the flow rate, pressure, and time of the polymer mixture solution being pumped in, thereby promoting the polymer mixture solution to permeate and form a membrane on the surface of the hollow fibers; the pressure is 50 Pa-5000 Pa, and the time is 0-30 s; The gas used for purging is compressed air, carbon dioxide, or nitrogen.

2. The self-healing ultrathin polymer / hollow fiber composite membrane module according to claim 1, characterized in that, The self-healing temperature is 100-160 ℃ and the time is 0.5-5h.

3. The self-healing ultrathin polymer / hollow fiber composite membrane module according to claim 1, characterized in that, The qualified hollow fiber refers to hollow fiber with a CO2 permeability in the range of 10,000-25,000 Barrers during leak detection and screening.

4. The self-healing ultrathin polymer / hollow fiber composite membrane module according to claim 1, characterized in that, The hollow fiber includes inorganic hollow fiber or organic hollow fiber. The inorganic hollow fiber includes alumina, titanium dioxide, yttrium oxide, zirconium oxide or silicon dioxide; the organic hollow fiber includes polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile or polysulfone.

5. The self-healing ultrathin polymer / hollow fiber composite membrane module according to claim 1, characterized in that, The material of the central tube includes stainless steel, polytetrafluoroethylene, or polyvinylidene fluoride.

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