Polytetrafluoroethylene hollow fiber membrane for membrane contactor as well as preparation method and application of polytetrafluoroethylene hollow fiber membrane

Abstract

The invention discloses a polytetrafluoroethylene hollow fiber membrane for a membrane contactor as well as a preparation method and application thereof, and belongs to the field of membrane separation. The outer surface of the polytetrafluoroethylene hollow fiber membrane is a smooth cylinder, and the inner surface of the polytetrafluoroethylene hollow fiber membrane is of a petal-shaped structure. The preparation method comprises the following steps: mixing polytetrafluoroethylene dispersion resin, curing, compacting, extruding, degreasing, stretching, sintering and shaping to obtain the polytetrafluoroethylene hollow fiber membrane, wherein a central needle of an extrusion die used in the extrusion process is non-circular and has a petal-shaped structure. The prepared polytetrafluoroethylene hollow fiber membrane is suitable for a membrane contactor process with a membrane wire inner cavity medium as a liquid phase, the petal-shaped morphology and the microstructure can reduce the thickness of a liquid phase boundary layer on the surface of the membrane, micro-turbulence and surface renewal are improved, and the mass transfer effect is improved.

Description

Technical Field

[0001] The present application relates to a polytetrafluoroethylene hollow fiber membrane for a membrane contactor, a preparation method thereof, and an application, belonging to the field of membrane separation. Background Art

[0002] Currently, membrane technology has been widely applied in various fields such as environmental protection, chemical engineering, energy, water treatment, etc., and has become one of the most important means in separation science today. The membrane contactor is a new separation process developed in recent years, which is a coupling technology of a membrane and traditional chemical engineering unit operations, and can realize mass transfer between gas-liquid two phases without direct contact. The membrane contactor has problems such as a large mass transfer area, a compact structure, a small equipment volume, no entrainment of mist droplets, and flooding, and has good application prospects in fields such as gas absorption and ammonia nitrogen wastewater treatment.

[0003] The membrane contactor technology is a mass transfer process between gas-liquid two phases without direct contact, and mostly uses hollow fiber hydrophobic microporous membranes. Although the microporous membrane itself has no separation performance, it provides an interface for gas-liquid mass transfer, so its structural design significantly affects the mass transfer effect of the membrane contactor. The most common form of the hollow fiber membrane contactor currently is the flat type, that is, a bundle of hollow fiber membrane filaments are arranged parallel to the length direction of the module and filled in the module housing. This configuration is easy to manufacture, but it brings many adverse effects to the mass transfer process. For example, the random filling of the hollow fiber membrane filaments makes their distribution in the shell side very uneven, and non-ideal behaviors such as channeling, short circuit, and dead zone of the fluid are easily caused during use, and the mass transfer effect of the membrane contactor is not good.

[0004] In order to overcome the above problems of the flat hollow fiber membrane module, research scholars have successively invented new membrane contactors such as baffles and rectangular modules to improve the mass transfer effect of the fluid in the shell side, and have also strengthened the mass transfer process by means of winding, bending, and weaving the membrane filaments, such as CN201320421198.1, CN201610895357.X, etc. These methods have optimized the spatial configuration of the membrane filaments in the module, but none of them have designed from the microscopic structure of the hollow fiber membrane itself, and the hollow fiber membranes are all cylindrical structures. The preparation process of traditional PTFE hollow fiber membranes includes batching, aging, compacting, extrusion, degreasing, stretching, and sintering and shaping, and the prepared hollow fiber membranes are all standard cylindrical ones. Summary of the Invention

[0005] Based on this, the present application prepares a polytetrafluoroethylene hollow fiber membrane with a convex-concave structure on the inner surface, which can essentially reduce the thickness of the liquid phase boundary layer on the membrane surface, improve micro-turbulence and surface renewal, and thus improve the mass transfer effect.

[0006] The present application discloses a polytetrafluoroethylene hollow fiber membrane for a membrane contactor and a preparation method thereof. The outer surface of the hollow fiber membrane is a smooth cylinder, but the inner surface is a non-circular petal shape; the preparation process of the polytetrafluoroethylene hollow fiber membrane includes mixing, aging, compacting, extrusion, degreasing, stretching and sintering and shaping. Its preparation method is similar to the traditional process, but the main difference is that the central needle in the extrusion die is non-circular and has a special petal shape, which is made by 3D printing and its surface is treated with fluorine coating. The polytetrafluoroethylene hollow fiber membrane prepared by the present invention is applicable to the membrane contactor process where the medium in the inner cavity of the membrane filament is a liquid phase.

[0007] According to the first aspect of the present application, there is provided a polytetrafluoroethylene hollow fiber membrane for a membrane contactor.

[0008] A polytetrafluoroethylene hollow fiber membrane for a membrane contactor, wherein the outer surface of the polytetrafluoroethylene hollow fiber membrane is a smooth cylinder and the inner surface is a petal-shaped structure.

[0009] Optionally, the number of the petal-shaped structures is 6 to 10.

[0010] Optionally, the inner diameter of the polytetrafluoroethylene hollow fiber membrane is 0.3 to 1.0 mm and the outer diameter is 0.6 to 2.0 mm.

[0011] Optionally, the ratio of the height of the petal-shaped structure on the inner surface of the polytetrafluoroethylene hollow fiber membrane to the wall thickness of the membrane is 0.1 to 0.25.

[0012] Optionally, the polytetrafluoroethylene hollow fiber membrane is a hydrophobic membrane and the water contact angle > 100°.

[0013] Optionally, the average pore diameter of the polytetrafluoroethylene hollow fiber membrane is 0.05 to 1.0 μm.

[0014] According to the second aspect of the present application, there is provided a preparation method of a polytetrafluoroethylene hollow fiber membrane for a membrane contactor.

[0015] The preparation method of the above-mentioned polytetrafluoroethylene hollow fiber membrane includes the following steps:

[0016] Mixing, aging, compacting, extruding, degreasing, stretching and sintering and shaping the polytetrafluoroethylene dispersion resin to obtain the polytetrafluoroethylene hollow fiber membrane;

[0017] Among them, the central needle of the extrusion die used in the extrusion process is non-circular and has a petal-shaped structure.

[0018] Optionally, the number of the petal-shaped structures of the non-circular central needle is from 6 to 10.

[0019] Optionally, the outer diameter of the non-circular central needle is 0.3 to 1.0 mm.

[0020] Optionally, the non-circular center pin is made of stainless steel and its surface is treated with fluorine coating.

[0021] In this application, the non-circular center pin can be obtained by 3D printing.

[0022] In this application, operations such as mixing, curing, compacting, extruding, debinding, stretching, and sintering and sizing can be carried out by conventional means in the art.

[0023] According to the third aspect of this application, an application of a polytetrafluoroethylene hollow fiber membrane for a membrane contactor is provided. In the present invention, the inner cavity of the polytetrafluoroethylene hollow fiber membrane has a petal-like morphology and microstructure, which can essentially improve the micro-turbulence and renewal of the liquid phase on the membrane surface, thereby greatly improving the mass transfer effect.

[0024] The application of the above-mentioned polytetrafluoroethylene hollow fiber membrane in the process of a membrane contactor where the medium in the inner cavity of the membrane filament is a liquid phase.

[0025] The beneficial effects that this application can produce include:

[0026] For the polytetrafluoroethylene hollow fiber membrane for a membrane contactor provided by this application, its preparation method and application, compared with the current mass transfer improvement solutions for membrane contactors mainly in the component structure design, the polytetrafluoroethylene hollow fiber membrane prepared in this application with a convex-concave structure on the surface can essentially reduce the thickness of the liquid phase boundary layer on the membrane surface, improve the micro-turbulence and surface renewal, and further improve the mass transfer effect. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the non-circular center pin in the extrusion die;

[0028] Figure 2 It is a schematic diagram of the obtained polytetrafluoroethylene hollow fiber membrane with a petal shape on the inner surface;

[0029] Figure 3 It is a schematic diagram of the petal size of the polytetrafluoroethylene hollow fiber membrane. Detailed Embodiments

[0030] The following describes this application in detail with reference to the embodiments, but this application is not limited to these embodiments.

[0031] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels.

[0032] Unless otherwise specified, the testing methods are all conventional methods, and the instrument settings are all the settings recommended by the manufacturers.

[0033] As Figure 1 shown, it is a schematic diagram of the non-circular center pin in the extrusion die, made of stainless steel and its surface is treated with fluorine coating.

[0034] As Figure 2 shown, it is a schematic diagram of a polytetrafluoroethylene hollow fiber membrane with a petal-shaped inner surface, and the number of petal-shaped structures is 6.

[0035] As Figure 3 shown, it is a schematic diagram of the petal size of a polytetrafluoroethylene hollow fiber membrane. d represents the wall thickness of the hollow fiber membrane, r2 represents the inner diameter of the hollow fiber membrane, r1 represents the outer diameter of the petal-shaped structure. The sum of d and r2 is the outer diameter of the hollow fiber membrane. r1 - r2 represents the height of the petal-shaped structure on the inner surface, and the ratio of it to the wall thickness of the membrane (r1 - r2) / d = 0.1 - 0.25.

[0036] Example 1

[0037] Polytetrafluoroethylene dispersion resin (number-average molecular weight 6 million, compression ratio 1000) and isoparaffin Isopar G are formulated into a polytetrafluoroethylene paste according to a mass fraction of 80% and 20%. After curing at 40°C for 24 hours, it is pressed into a paste blank in a pre-pressing device; the central needle in the extrusion die has a petal-shaped structure, with 8 petals and an outer diameter of 0.6 mm. After the blank is extruded by an extruder, degreased at 200°C, stretched 1.5 times at 200°C, and sintered and shaped at 360°C for 3 minutes, a polytetrafluoroethylene hollow fiber membrane is obtained. The inner diameter of the membrane is 0.55 mm, the outer diameter is 1.2 mm. The number of petal-shaped structures on the inner surface of the polytetrafluoroethylene hollow fiber membrane is 8, the ratio of the height of the petal-shaped structure to the wall thickness of the membrane is 0.12, the static water contact angle on the outer surface of the membrane is 110°, and the average pore diameter is 0.05 μm.

[0038] Example 2

[0039] Polytetrafluoroethylene dispersion resin (number-average molecular weight 8 million, compression ratio 600) and isoparaffin Isopar G are formulated into a polytetrafluoroethylene paste according to a mass fraction of 78% and 22%. After curing at 40°C for 24 hours, it is pressed into a paste blank in a pre-pressing device; the central needle in the extrusion die has a petal-shaped structure, with 6 petals and an outer diameter of 1.0 mm. After the blank is extruded by an extruder, degreased at 200°C, stretched 2. :0 times at 200°C, and sintered and shaped at 360°C for 3 minutes, a polytetrafluoroethylene hollow fiber membrane is obtained. The inner diameter of the membrane is 0.9 mm, the outer diameter is 1.8 mm. The number of petal-shaped structures on the inner surface of the polytetrafluoroethylene hollow fiber membrane is 6, the ratio of the height of the petal-shaped structure to the wall thickness of the membrane is 0.2, the static water contact angle on the outer surface of the membrane is 108°, and the average pore diameter is 0.15 μm.

[0040] Example 3

[0041] Polytetrafluoroethylene dispersion resin (number-average molecular weight of 8 million and compression ratio of 600) and isoparaffin Isopar G are formulated into a polytetrafluoroethylene paste according to mass fractions of 78% and 22%. After curing at 40 °C for 24 h, it is pressed into a paste blank in a pre-pressing device; the central needle in the extrusion die has a petal-like structure, the number of petals is 10, and the outer diameter is 0.8 mm. After the blank is extruded by an extruder, degreased at 200 °C, stretched 3.0 times at 200 °C, and sintered and shaped at 360 °C for 3 min, a polytetrafluoroethylene hollow fiber membrane is obtained. The inner diameter of the membrane is 0.7 mm, the outer diameter is 1.5 mm, the number of petal-like structures on the inner surface of the polytetrafluoroethylene hollow fiber membrane is 10, the ratio of the height of the petal-like structure to the wall thickness of the membrane is 0.25, the static water contact angle on the outer surface of the membrane is 112°, and the average pore diameter is 0.5 μm.

[0042] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the technical content disclosed above is equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A polytetrafluoroethylene hollow fiber membrane for a membrane contactor, characterized in that, The outer surface of the polytetrafluoroethylene hollow fiber membrane is a smooth cylinder, and the inner surface is a petal-shaped structure.

2. The polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein The number of the petal-shaped structures is 6 to 10.

3. The polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein The inner diameter of the polytetrafluoroethylene hollow fiber membrane is 0.3 to 1.0 mm, and the outer diameter is 0.6 to 2.0 mm.

4. The polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that, The ratio of the height of the petal-shaped structure on the inner surface of the polytetrafluoroethylene hollow fiber membrane to the wall thickness of the membrane is 0.1 to 0.

25.

5. The polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that, The polytetrafluoroethylene hollow fiber membrane is a hydrophobic membrane, and the water contact angle > 100°.

6. The polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein, The average pore size of the polytetrafluoroethylene hollow fiber membrane is 0.05 to 1.0 μm.

7. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to any one of claims 1 to 6, characterized in that, It includes the following steps: The polytetrafluoroethylene dispersion resin is subjected to mixing, curing, compacting, extrusion, degreasing, stretching and sintering and shaping to obtain the polytetrafluoroethylene hollow fiber membrane; Among them, the central needle of the extrusion die used in the extrusion process is non-circular and has a petal-shaped structure.

8. The preparation method according to claim 7, characterized in that The number of the petal-shaped structures of the non-circular central needle is 6 to 10.

9. The preparation method according to claim 7, characterized in that, The outer diameter of the non-circular central needle is 0.3 to 1.0 mm.

10. Application of the polytetrafluoroethylene hollow fiber membrane according to any one of claims 1 to 6 in the membrane contactor process where the medium in the lumen of the membrane filament is in a liquid phase.

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