A dry process humidity control structure for hollow membrane spinning and its application

Abstract

The present invention discloses a dry-process humidity control structure for hollow membrane spinning and its application, comprising a through-cavity and several groups of capacitive induction atomizers disposed therein. The present invention controls the humidity of the dry-process cavity between the membrane filaments from the spinneret to the coagulation bath at 100% RH, and controls the ratio of the casting solution so that its phase separation state is close to the cloud point. Liquid-liquid separation occurs immediately after the casting solution contacts the moisture in the dry-process cavity, thereby increasing the mass transfer rate of the solvent in the casting solution to diffuse outward, forming a larger number of macroporous structures on the membrane surface, and improving the looseness of the cross-sectional structure, thereby producing hollow membrane filaments with high pore size and high flux. The process is simple and effectively solves the complex problem of adjusting the formulation and coagulation bath required in the prior art. The capacitive induction atomizer also improves the defect of the steam generator caused by the insufficient exchange of too fine atomized mist.

Description

Technical Field

[0001] The invention belongs to the technical field of hollow membrane preparation, and in particular relates to a hollow membrane spinning dry process humidity control structure and application thereof. Background Art

[0002] With the development of hollow membrane production technology, in order to meet the requirements of high flux of membrane fibers and filtration in special fields, it is generally necessary to prepare microporous membranes with larger membrane pores. Therefore, it is necessary to improve the membrane pore size and flux in terms of formulation and process control. In existing technologies, this is generally achieved by adjusting the composition of the membrane making solution or significantly increasing the solvent in the coagulation bath. For example, the base resin content of the membrane making solution is reduced, the pore former in the membrane making solution is increased, and a large amount of solvent is added to the coagulation bath to slow down its phase separation rate to form macropores. However, the base resin is beneficial to the strength of the membrane fiber, while the excess pore former affects the performance of the membrane fiber, and the coagulation bath with a large amount of solvent also causes industrial problems such as environmental protection. Therefore, it is impossible to significantly reduce the resin or increase the amount of pore former or increase the solvent concentration of the coagulation bath. From this perspective, under the premise of ensuring the performance of the membrane fiber, by increasing the humidity of the membrane fiber from the spinneret to the coagulation bath, the mass transfer rate of the solvent in the membrane making solution to diffuse outward is changed, so that more macroporous structures are formed on the membrane surface and the looseness of the cross-sectional structure is increased, thereby obtaining hollow membrane fibers with high pore size and high flux to solve the problems existing in current production and application.

[0003] The technical solution disclosed in CN105536558A increases the average pore size of the central control fiber membrane to 0.15-0.28 microns and the pure water flux to 2570-4600 L / m by using a steam generator to generate steam and a wet temperature control device in the periphery of the spinneret to control the dry process humidity to 95%-100% RH and the temperature to 60-70°C. 2 Because the mist produced by the steam generator is relatively fine and the contact between the membrane fibers and the mist is small, it is necessary to prepare hollow fiber membranes with a pore size greater than 0.3μm. This requires reconsidering the dry process control equipment and arranging the casting solution near the cloud point. Summary of the Invention

[0004] The present invention aims to overcome the defects of the prior art and provide a humidity control structure for the dry process of hollow membrane spinning.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned large-flux, large-pore hollow membrane.

[0006] The technical solutions of the present invention are as follows:

[0007] A hollow membrane spinning dry process humidity control structure includes a through cavity and a plurality of capacitive induction atomizers arranged therein.

[0008] The bottom of the cavity is immersed in the coagulation bath and connected to the coagulation bath, and the top wall has at least one through groove for the hollow membrane filaments to pass through. The hollow membrane filaments pass through the top wall, the peripheral wall of the cavity and the liquid surface of the coagulation bath entering the bottom of the cavity to form a dry-path cavity, so that the hollow membrane filaments enter the coagulation bath vertically through the at least one through groove and the dry-path cavity in sequence.

[0009] Several groups of capacitive induction atomizers are connected to the coagulation bath, arranged at the lower part of the above-mentioned through cavity and evenly distributed on both sides of the above-mentioned hollow membrane filaments. The liquid level of the coagulation bath submerges its nozzle, and the spraying direction of the nozzle is toward the above-mentioned hollow membrane filaments, and the angle with the hollow membrane filaments is 10-60 degrees, so that after the capacitive induction atomizer is started, the humidity of the above-mentioned dry process cavity reaches 100% evenly within 1-2 minutes, and it is ensured that the atomized liquid sprayed from the nozzle will not be directly sprayed onto the hollow membrane filaments.

[0010] In a preferred embodiment of the present invention, the spray volume of each group of the capacitive induction atomizers is 1.5 kg / h.

[0011] Further preferably, the ratio of the number of groups of the capacitive induction atomizer to the volume of the dry process chamber is 6:3.2-3.3L.

[0012] More preferably, the height of the dry process cavity is 10-20 cm, and the number of the capacitive induction atomizer groups is 6.

[0013] In a preferred embodiment of the present invention, the horizontal distance from the nozzle of the capacitive induction atomizer to the hollow membrane filament is 7-9 cm.

[0014] In a preferred embodiment of the present invention, the horizontal distance from the nozzle of the capacitive induction atomizer to the hollow membrane filament is 8 cm, the height of the dry process cavity is 10-20 cm, the number of groups of the capacitive induction atomizers is 6, the spray volume of each group of the capacitive induction atomizers is 1.5 kg / h, and the angle between the nozzle and the hollow membrane filament is 60 degrees.

[0015] Another technical solution of the present invention is as follows:

[0016] A method for preparing a large-flux, large-pore hollow membrane comprises the following steps: a hollow membrane filament coated with a casting solution near a turbidity point passes through the above-mentioned hollow membrane spinning dry process humidity control structure and then enters a coagulation bath.

[0017] In a preferred embodiment of the present invention, the casting solution consists of dimethylacetamide, polyvinyl pyrrolidone, polyethylene glycol, glycerol and polyvinylidene fluoride.

[0018] More preferably, the mass ratio of dimethylacetamide, polyvinyl pyrrolidone, polyethylene glycol, glycerol and polyvinylidene fluoride is 55:12:5:10:18.

[0019] In a preferred embodiment of the present invention, the coagulation bath is a pure water coagulation bath.

[0020] The beneficial effects of the present invention are:

[0021] 1. The dry process humidity control structure of the hollow membrane spinning of the present invention controls the humidity of the dry process cavity between the membrane filaments from the spinneret to the coagulation bath at 100% RH, and controls the ratio of the casting liquid so that its phase separation state is close to the turbidity point. Liquid-liquid separation can occur immediately after the casting liquid contacts the moisture in the dry process cavity, thereby increasing the mass transfer rate of the solvent in the casting liquid to diffuse outward, forming more macroporous structures on the membrane surface, and increasing the looseness of the cross-sectional structure, thereby preparing hollow membrane filaments with high pore size and high flux. The process is simple and effectively solves the complex problems of the prior art that require adjustment of the formula and the coagulation bath. At the same time, the method of the capacitive induction atomizer is used to improve the defect of the steam generator due to insufficient exchange due to too fine atomization, and prepares a pure water flux greater than 5000L / m 2 h, microporous membrane with an average pore size of 0.3-0.5 μm.

[0022] 3. The humidity control structure for the dry process of hollow membrane spinning of the present invention is simple in structure, easy to operate, and easy to implement in production without adjusting the formula of the casting solution or the coagulation bath conditions.

[0023] 4. The preparation method of the present invention achieves uniformity and effectiveness of humidity during the hollow membrane spinning process by controlling the spray amount and designing the spray angle, thereby increasing the number of pores on the membrane surface and significantly improving the membrane fiber flux. At the same time, the cross-sectional structure of the membrane fiber is changed from conventional finger-like holes to a loose sponge pore structure, thereby improving the anti-pollution ability of the membrane fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the overall structure of the humidity control structure of the hollow membrane spinning dry process in Example 1 of the present invention.

[0025] Figure 2 This is a three-dimensional exploded schematic diagram of the humidity control structure of the hollow membrane spinning dry process in Example 1 of the present invention.

[0026] Figure 3 This is a cross-sectional view of the humidity control structure during the hollow membrane spinning dry process in Example 1 of the present invention.

[0027] Figure 4 These are electron microscope photos of the surface and cross-section of the hollow membrane fiber prepared in Comparative Example 1 of the present invention.

[0028] Figure 5 These are electron microscope photos of the cross section and surface of the hollow membrane fiber prepared in Comparative Example 2 of the present invention.

[0029] Figure 6 These are electron microscope photos of the cross section and surface of the hollow membrane fiber prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further illustrated and described below through specific implementation methods in conjunction with the accompanying drawings.

[0031] Example 1

[0032] like Figures 1 to 3 As shown, a hollow membrane spinning dry process humidity control structure includes a through cavity 1 and a plurality of capacitive induction atomizers 2 arranged therein.

[0033] The cavity 1 has its lower part immersed in the coagulation bath 3 and connected to the coagulation bath 3, and its top wall has at least one through groove 10 for the hollow membrane filament 4 to pass through, and the hollow membrane filament passes through the top wall, the peripheral wall and the liquid surface of the coagulation bath 3 entering the lower part of the cavity 1 to form a dry path cavity 11, so that the hollow membrane filament 4 passes through the at least one through groove 10 and the dry path cavity 11 vertically into the coagulation bath 3 in sequence.

[0034] Specifically, the through cavity 1 is enclosed by two side fixing plates 12, two side sealing plates 13 and a top fixing plate 14. At least one through slot 10 is opened on the top fixing plate 14. The lower end of each side fixing plate 12 is provided with an inclined receiving slot 120.

[0035] Several groups of capacitive induction atomizers 2 are connected to the coagulation bath 3, are arranged in the above-mentioned inclined receiving groove 120 passing through the cavity 1 and are evenly distributed on both sides of the above-mentioned hollow membrane filaments 4. The liquid level of the coagulation bath 3 is above its nozzle, and the spraying direction of the nozzle is toward the above-mentioned hollow membrane filaments 4, and forms an angle with the hollow membrane filaments 4, so that after the capacitive induction atomizer 2 is started, the humidity of the above-mentioned dry process cavity 11 reaches 100% evenly within 1-2 minutes, and it is ensured that the atomized liquid sprayed from the nozzle will not be directly sprayed onto the hollow membrane filaments 4.

[0036] Specifically, the ratio of the number of groups of the capacitive sensing atomizer 2 to the volume of the dry process cavity 11 is 6:3.256L, the horizontal distance from the nozzle of the capacitive sensing atomizer 2 to the hollow membrane filament 4 is 8cm, the height of the dry process cavity 11 is 10-20cm, the number of groups of the capacitive sensing atomizer 2 is 6, the spray volume of each group of the capacitive sensing atomizer 2 is 1.5kg / h, and the angle between its nozzle and the hollow membrane filament 4 is 60 degrees.

[0037] The height of the dry process cavity varies between 10-20 cm, but this embodiment can also be designed to fix the volume of the dry process cavity, such as adjusting the length and width to keep the volume of the dry process cavity unchanged, that is, the number of the capacitive induction atomizer 2 groups remains 6.

[0038] Example 2

[0039] This example uses the hollow membrane spinning dry process humidity control structure of Example 1 to prepare a large-flux, large-pore hollow membrane:

[0040] The power of the capacitive induction atomizer 2 is turned on, and the capacitive induction atomizer 2 starts to mist. After 1 minute, the mist diffuses in the dry process cavity 11 of the hollow membrane spinning dry process humidity control structure. After 1 minute, the humidity in the package area is tested with a humidity agent to be 100% RH (4 different positions).

[0041] Preparation of casting solution: DMAC, PVP-K30, PEG400, glycerol and PVDF were mixed uniformly in a mass ratio of 55:12:5:10:18, and the casting solution was prepared after degassing. PET polyester fiber was used as the support fiber, and pure water was used as the coagulation bath 3.

[0042] The spinning equipment is turned on, and the casting liquid is coated on the surface of the hollow membrane filament 4 through the spinning spinneret, and enters the dry process cavity 11 wrapped in the hollow membrane spinning dry process humidity control structure. The height of the dry process cavity 11 is maintained at 10 cm, and the angle between the nozzle of the capacitive induction atomizer 2 and the vertical hollow membrane filament 4 is adjusted to 60 degrees, and the horizontal distance is 8 cm, so that the spray mist will not be directly sprayed onto the hollow membrane filament 4. After the hollow membrane filament 4 is fully in contact with the mist in the dry process cavity 11, it enters the coagulation bath 3 for coagulation and molding, and the result is as shown below. Figure 6 The formed membrane filament shown has an average pore size of 0.30 μm, a membrane flux of 5099 LMH, and a loose sponge pore structure on the cross section of the membrane filament.

[0043] Example 3

[0044] The preparation was carried out in the same setting as Example 2, except that the height of the dry process cavity 11 was controlled to be 20 cm by the water level, the average pore size of the prepared shaped membrane filaments was 0.50 μm, the membrane filament flux was 5872 LMH, and the membrane filament cross-section had a loose sponge pore structure.

[0045] Comparative Example 1

[0046] In this comparative example, the humidity control structure of the hollow membrane spinning dry process in Example 1 was removed so that the dry process was exposed to the air and kept consistent with the air humidity. The tested dry process humidity was 65% RH.

[0047] Prepare the casting solution by mixing DMAC, PVP-K30:PEG400, glycerol and PVDF in a mass ratio of 55:12:5:10:18. After degassing, the casting solution is prepared. PET polyester fiber is used as the support fiber, and pure water is used as the coagulation bath 3.

[0048] The spinning equipment was turned on and the casting solution was coated on the surface of the inner support tube through the spinning spinneret and entered the air drying process. The drying process length was kept at 10 cm. After the membrane filaments were fully exposed to the air during the drying process, they entered the coagulation bath 3 for coagulation and molding. Figure 4 The formed membrane filament shown has an average pore size of 0.05 μm, a membrane flux of 1180 LMH, and a finger-like pore structure in cross section.

[0049] Comparative Example 2

[0050] The preparation was carried out in the same manner as in Example 2, except that the angle between the nozzle of the capacitive induction atomizer 2 and the hollow membrane filament 4 was 61 degrees.

[0051] Prepared as Figure 5 The formed membrane filament shown in the test has an average pore size of 0.55μm, a membrane flux of 6218LMH, a loose sponge pore structure on the cross section of the membrane filament, and concave defective holes are produced on the part of the membrane filament surface where the spray mist is directly injected.

[0052] Comparative Example 3

[0053] The preparation was carried out in the same manner as in Example 2, except that the spray rate of each group of the capacitive induction atomizer 2 was 1.0 kg / h, and the humidity in the package area was tested with a humidity agent after 1 minute and was 85% RH.

[0054] The obtained membrane filaments had an average pore size of 0.10 μm, a flux of 1428 LMH, and a semi-sponge pore structure in the cross section.

[0055] Comparative Example 4

[0056] The preparation was carried out in the same manner as in Example 3, except that the casting solution was prepared as follows: DMAC, PVP-K30, PEG400, and PVDF were uniformly mixed in a mass ratio of 65:12:5:18 so that the casting solution was not close to the phase separation cloud point, and the casting solution was prepared after degassing.

[0057] The obtained membrane filaments had an average pore size of 0.15 μm, a flux of 1644 LMH, and a sponge pore structure on the cross section.

[0058] Summary table of parameter effects comparison between examples and comparative examples

[0059]

[0060] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A humidity control structure for the dry process of hollow membrane spinning, characterized by: It includes a through cavity and several groups of capacitive induction atomizers arranged therein. The bottom of the cavity is immersed in the coagulation bath and connected to the coagulation bath, and the top wall has at least one through groove for the hollow membrane filaments to pass through. The hollow membrane filaments pass through the top wall, the peripheral wall of the cavity and the liquid surface of the coagulation bath entering the bottom of the cavity to form a dry-path cavity, so that the hollow membrane filaments enter the coagulation bath vertically through the at least one through groove and the dry-path cavity in sequence. A plurality of capacitive induction atomizers are connected to a coagulation bath and are located at the lower portion of the through-cavity and evenly distributed on both sides of the hollow membrane filaments. The liquid level of the coagulation bath is above the nozzles, and the nozzles are oriented toward the hollow membrane filaments at an angle of 10-60 degrees to the hollow membrane filaments. After the capacitive induction atomizers are activated, the humidity of the dry process cavity reaches 100% uniformly within 1-2 minutes, and the atomized liquid ejected from the nozzles is prevented from directly spraying onto the hollow membrane filaments. The spray volume of each group of capacitive induction atomizers is 1.5 kg / h, and the horizontal distance between the nozzle of the capacitive induction atomizer and the hollow membrane filament is 7-9 cm.

2. A hollow membrane spinning dry process humidity control structure according to claim 1, characterized in that: The ratio of the number of groups of the capacitive induction atomizer to the volume of the dry process cavity is 6:3.2-3.3L.

3. A hollow membrane spinning dry process humidity control structure according to claim 2, characterized in that: The height of the dry process cavity is 10-20 cm, and the number of the capacitive induction atomizer groups is 6.

4. A dry-process humidity control structure for hollow membrane spinning according to any one of claims 1 to 3, characterized in that: The horizontal distance from the nozzle of the capacitive induction atomizer to the hollow membrane filament is 8 cm, the height of the dry process cavity is 10-20 cm, the number of groups of the capacitive induction atomizer is 6, the spray volume of each group of the capacitive induction atomizer is 1.5 kg / h, and the angle between the nozzle and the hollow membrane filament is 60 degrees.

5. A method for preparing a large-flux, large-pore hollow membrane, characterized by: The hollow membrane fibers, the surfaces of which are coated with the casting solution near the cloud point, pass through the hollow membrane spinning dry process humidity control structure according to any one of claims 1 to 4 and then enter the coagulation bath.

6. The preparation method according to claim 5, wherein: The casting solution consists of dimethylacetamide, polyvinyl pyrrolidone, polyethylene glycol, glycerol and polyvinylidene fluoride.

7. The preparation method according to claim 6, wherein: The mass ratio of dimethylacetamide, polyvinyl pyrrolidone, polyethylene glycol, glycerol and polyvinylidene fluoride is 55:12:5:10:

18.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The coagulation bath is a pure water coagulation bath.

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