Optical method for non-contact regulation of macropores in hollow fiber membranes and device therefor

Abstract

The present invention provides a non-contact optical method and apparatus for controlling macropores within hollow fiber membranes. The method comprises the following steps: 1) ejecting a hollow tubular membrane filament through a spinneret; 2) radiating a laser beam radially from the outside toward the axial center of the membrane filament within the air layer of the spinning machine; the laser beam's focus is modulated within the membrane filament's wall thickness, generating a periodic thermal effect within the wall thickness, thereby forming and controlling macropores. The present invention utilizes laser-induced Marangoni convection during the initial phase separation phase to precisely control the location, speed, direction, and volume of macropore growth within the membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hollow fiber membrane preparation, in particular to a non-contact optical method for regulating the macrovoids in hollow fiber membranes and a device thereof. BACKGROUND

[0002] Hollow fiber membranes are a kind of filtration materials, which have important applications in water treatment, chemistry, medicine, etc.

[0003] In the non-solvent induced phase inversion membrane preparation process, macrovoids in the shape of fingers or pears or other irregular shapes can be formed, which are caused by Marangoni convection during phase separation. The position, shape, size and distribution of the macrovoids will affect the performance of the hollow fiber membranes. Therefore, precise control of the macrovoids is a process problem for improving the performance of the hollow fiber membranes.

[0004] In the existing wet spinning process, the macrovoid structure in the membrane is often regulated by adjusting the air path length, the composition of the dope, the convection conditions of the coagulation bath and the tensile tension conditions of the membrane filaments. However, these methods can only roughly control the size and density of the pores, and cannot achieve precise regulation of the growth of the macrovoids in the membrane. The volume and position of the macrovoids cannot be precisely controlled. SUMMARY

[0005] The present application aims to solve the problems in the prior art by providing a non-contact optical method for regulating the macrovoids in hollow fiber membranes and a device thereof. The method of laser-induced Marangoni convection at the initial stage of phase separation is used to achieve precise control of the growth location, growth speed, growth direction and growth volume of the macrovoids in the membrane.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A non-contact optical method for regulating the macrovoids in hollow fiber membranes, comprising the following steps:

[0008] 1) The hollow tubular membrane filaments are ejected through the spinneret;

[0009] 2) The laser beam is emitted radially from the outside towards the axis of the membrane filaments at the air layer position in the spinning machine; the focal point of the laser beam is modulated inside the wall thickness of the membrane filaments, a periodic thermal effect is generated inside the wall thickness, thereby forming and regulating the macrovoids.

[0010] Further, the step 2) is implemented according to the following steps:

[0011] 2-1) The focal point of the laser beam is modulated inside the membrane filaments, at a distance of 10-50 microns from the inner surface of the membrane filaments, forming the nucleation point of the macrovoids, and promoting the growth of the macrovoids inward from the focal point;

[0012] 2-1') reversely, the focal point of the laser beam is modulated inside the membrane filament, at a distance of 10-50 microns from the inner wall of the membrane filament, to form a nucleation point of the large hole, and to promote the growth of the large hole from the focal point outward.

[0013] Further, the multiple laser beams are distributed in a ring shape around the liquid column of the membrane filament.

[0014] Further, the focal point of the laser beam has a focusing range of 20-50 microns.

[0015] Further, the emission power of a single laser beam is less than 5 milliwatts.

[0016] Further, the spot diameter emitted by the laser beam is 10-30 microns.

[0017] The optical device for non-contact regulation of the large hole in the hollow fiber membrane according to one or more of the above, comprises a spinneret, a ring-shaped base, a laser head module, a fixed-focus lens, and a controller; the spinneret is vertically downward; the ring-shaped base is arranged around the lower part of the spinneret, at the periphery of the membrane filament sprayed by the spinneret, and coaxially arranged with the spinneret; a plurality of laser head modules are evenly installed on the base, arranged in a ring shape, and the laser head modules are arranged towards the axis of the membrane filament; a replaceable fixed-focus lens is arranged on the laser head module for focusing; all the laser head modules are connected with the controller.

[0018] Further, the base is composed of two semi-circular ring-shaped sub-bases, which can be opened and closed and installed together.

[0019] The optical method of the present application uses laser induction after the membrane filament is sprayed by the spinneret and before the coagulation bath, and regulates the nucleation point, growth volume and shape of the large hole by generating periodic thermal effects on the corresponding focal point of the membrane filament, so as to accurately control the growth of the large hole and improve the performance of the hollow fiber membrane. The optical device of the present application is installed with a ring-shaped laser head module, which can accurately control the growth of the large hole around the membrane filament by 360°. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a principle schematic diagram of a non-contact optical method for regulating the large hole in the hollow fiber membrane provided by the first embodiment of the present application.

[0021] Figure 2 is a focal point schematic diagram of step 2).

[0022] Figure 3 is a structure schematic diagram of an optical device for non-contact regulation of the large hole in the hollow fiber membrane provided by the second embodiment of the present application. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be described in detail below with reference to the drawings and specific embodiments. EMBODIMENT

[0024] As Figures 1 to 2 shown, the present application provides a non-contact optical method for regulating the growth of macropores in hollow fiber membranes, comprising the following steps:

[0025] 1) a hollow tubular membrane filament 1 is extruded through a spinneret 10;

[0026] 2) a laser beam is emitted radially from the outside towards the axis of the membrane filament 1 at the air layer position in the spinning machine; the focal point 4 of the laser beam is modulated inside the wall thickness of the membrane filament 1, generating a periodic thermal effect inside the wall thickness, thereby forming and regulating the macropores 2.

[0027] The membrane filament 1 is a polymer solution, which is completely transparent before being solidified in the coagulation bath. The laser induction occurs after the membrane filament 1 is extruded through the spinneret 10 in the spinning machine and before the coagulation bath. By modulating the focal point 4, power and switching frequency of the laser beam, a weak periodic thermal effect can be generated at different depths of the membrane filament 1, thereby controlling the location of the Marangoni convection and inhibiting or enhancing the Marangoni convection generated during phase separation, and then controlling the growth of the macropores 2 in the membrane filament 1.

[0028] As Figure 2 shown, in particular,

[0029] The step 2) is implemented according to the following steps:

[0030] 2-1) the focal point 4 of the laser beam is modulated inside the membrane filament 1, at a distance of 10-50 microns from the outer wall of the membrane filament 1 towards the inside, forming a nucleation point of the macropores 2 and promoting the growth of the macropores 2 from the focal point 4 towards the inside;

[0031] 2-1') reversely, the focal point 4 of the laser beam is modulated inside the membrane filament 1, at a distance of 10-50 microns from the inner wall of the membrane filament 1 towards the outside, forming a nucleation point of the macropores 2 and promoting the growth of the macropores 2 from the focal point 4 towards the outside.

[0032] By modulating the focal point 4 of the laser beam to the position close to the outer wall of the membrane filament 1, the convection at the outer wall is enhanced due to the weak thermal effect of the laser, thereby forming a nucleation point of the macropores 2, and the macropores 2 grow from this position. By continuously heating at the nucleation point, the left-right symmetry of the macropores 2 can be controlled, forming an approximately elliptical macropore 2 instead of a finger-shaped pore with different sizes at both ends. If the focal point 4 of the laser beam is moved to the position close to the inner wall of the membrane filament 1, the nucleation point of the macropores 2 can be controlled, thereby controlling the distribution position of the macropores. In addition, by controlling the power of the laser beam, the size of the growing macropores 2 can be adjusted.

[0033] As an improvement, the multiple laser beams are distributed in a ring around the liquid column of the membrane filament 1, by distributing the laser beam emitting points evenly along the circumference, the distribution of nucleation points in the circumference of the membrane embryo can be controlled, and by controlling the light beam emitting frequency, large holes 2 can be generated at certain intervals in the stretching direction of the membrane filament 1.

[0034] Preferably, the focal point 4 of the laser beam has a focusing range of 20-50 microns. The emission power of a single laser beam is less than 5 milliwatts. The spot diameter emitted by the laser beam is 10-30 microns. Embodiment

[0035] As Figure 3 As shown in the drawings, the application also provides a non-contact optical device for regulating large holes in hollow fiber membranes, comprising a spinneret 10, a ring-shaped base 20, a laser head module 3, a fixed focus lens, and a controller. The spinneret 10 is vertically downward. The ring-shaped base 20 is arranged around the lower part of the spinneret 10 and is located at the periphery of the membrane filament 1 emitted by the spinneret 10, and is coaxially arranged with the spinneret 10. A plurality of laser head modules 3 are evenly installed on the base 20, arranged in a ring shape, and the laser head modules 3 are arranged towards the axis of the membrane filament 1. The laser head module 3 is provided with a replaceable fixed focus lens for focusing. All laser head modules 3 are connected with the controller.

[0036] The ring-shaped laser head module 3 can implement laser induction in all directions around the circumference of the membrane filament 1. The installation position of the base 20 is kept coaxial with the spinneret 10, so as to ensure that the laser beams are evenly distributed along the circumference of the hollow fiber membrane. The plurality of laser head modules 3 are uniformly regulated by the controller, and the power of the laser and the focal point 4 of the focusing can be adjusted by the controller, so that all the laser head modules 3 work cooperatively and precisely control the growth of the large holes 2 of the membrane filament 1.

[0037] As an improvement, the base 20 is composed of two semi-circular ring-shaped sub-bases 21, which can be opened and closed together. When installed, the two semi-circular ring-shaped sub-bases 21 are closed together to surround the membrane filament 1 emitted from the spinneret 10.

[0038] The application also provides a non-contact optical method for regulating large holes in hollow fiber membranes, which uses laser-induced Marangoni convection to subtly affect the growth of large holes 2, thereby achieving precise control of large holes 2. This process is precise and efficient, solving the problem of irregular and uncontrollable large holes 2 in hollow fiber membranes, and significantly improving the performance of hollow fiber membranes. The optical device for realizing this method can precisely operate all laser head modules 3 through the controller.

[0039] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A non-contact optical method for controlling the macropores in a hollow fiber membrane, characterized in that: The following steps are involved: 1) Hollow tubular membrane filaments are ejected through the spinneret; 2) At the air layer position in the spinning machine, a laser beam is emitted radially from the outside toward the axis of the membrane filament; the focus of the laser beam is modulated inside the wall thickness of the membrane filament, generating a periodic thermal effect within the wall thickness, thereby forming and regulating macropores.

2. The optical method for non-contact control of macropores in hollow fiber membranes according to claim 1, characterized in that: Step 2) is implemented as follows: The focus of the laser beam is modulated inside the membrane filament, 10-50 microns inward from the outer wall of the membrane filament, to form a nucleation point for the macropore, thereby promoting the macropore to grow inward from the focus; Alternatively, the focus of the laser beam is modulated inside the membrane filament, 10-50 microns outward from the inner wall of the membrane filament, to form a nucleation point for the macropore, thereby promoting the macropore to grow outward from the focus.

3. The non-contact optical method for controlling macropores in hollow fiber membranes according to claim 1, characterized in that: Multiple laser beams are distributed in a ring shape around the liquid column of the membrane filament.

4. The non-contact optical method for controlling macropores in hollow fiber membranes according to claim 1, characterized in that: The focal point of the laser beam is in the range of 20-50 microns.

5. The non-contact optical method for controlling macropores in hollow fiber membranes according to claim 1, characterized in that: The emission power of a single laser beam is less than 5 milliwatts.

6. The non-contact optical method for controlling macropores in hollow fiber membranes according to claim 1, characterized in that: The diameter of the light spot emitted by the laser beam is 10-30 microns.

7. An optical device for use in the optical method for non-contact control of macropores in hollow fiber membranes according to any one of claims 1 to 6, installed below a spinneret, characterized in that: It includes an annular base, a laser head module, a fixed-focus lens and a controller; the spinneret is arranged vertically downward; the annular base is arranged below the spinneret, located on the periphery of the membrane filament ejected by the spinneret, and is coaxially arranged with the spinneret; multiple laser head modules are evenly distributed on the base in an annular layout, and the laser head modules are arranged towards the axis of the membrane filament; the laser head module is provided with a replaceable fixed-focus lens for focusing; all laser head modules are connected to the controller.

8. The optical device for non-contact control of macropores in hollow fiber membranes according to claim 7, characterized in that: The base is composed of two semicircular ring-shaped sub-bases, and the two sub-bases can be opened and closed and installed together.

Images