WO2021132899A1 - Ultra-hydrophobic composite membrane for membrane aerated biofilm reactor process and manufacturing method therefor - Google Patents

Abstract

The present invention relates to an ultra-hydrophobic composite membrane for a membrane aerated biofilm reactor (MABR) process, the membrane comprising: a porous polyvinylidene fluoride (PVDF) hollow fiber membrane; a non-porous silicone envelope membrane formed on the external surface of the hollow fiber membrane; and a silicone impregnation membrane embedded at a predetermined depth in the inner direction of the hollow fiber membrane from a side in contact with the non-porous silicone envelope membrane. The ultra-hydrophobic composite membrane according to the present invention is free from exfoliation of the silicone envelope membrane, causes no swelling of the silicone envelope membrane even under a high supply pressure, has high oxygen permeability, and has significantly improved durability due to excellent mechanical properties, and thus is commercially usable through the application to the MABR process.

Description

Ultra-hydrophobic composite membrane for membrane aeration biofilm process and manufacturing method thereof

The present invention relates to an ultra-hydrophobic composite membrane for a membrane aeration biofilm process and a method for manufacturing the same, and more particularly, a silicone outer film formed on the outer surface of a porous polyvinylidene fluoride (PVDF) hollow fiber membrane, and an inner direction of the hollow fiber membrane It relates to a technology for applying a very hydrophobic composite film having a structure in which a silicon-impregnated film embedded with a cross-locking structure is applied to a membrane aerated biofilm (MABR) process.

In general, in a membrane aerated biofilm reactor (MABR) process, oxygen is transferred from the inside of the membrane to the outside in a bubbleless state by permeating air or oxygen in water through a homogeneous membrane without pores. At this time, aerobic microorganisms grow on the outer surface of the membrane, and an anaerobic biofilm in which anaerobic microorganisms grow is formed from the outer wall of the aerobic microorganism biofilm that has consumed all of oxygen. According to this mechanism of action, pollutants based on carbon and nitrogen atoms in wastewater can be removed with low energy.

A lot of research has been done on polyethylene (PE) or polypropylene (PP)-based porous hollow fiber membranes, which are hydrophobic materials, in the first generation as a separator for the conventional MABR process. However, these hollow fiber membranes have been conducted in various research directions to attach specific microorganisms and treat wastewater by delivering gases such as hydrogen, oxygen, or air in a bubbleless state in water due to the characteristics of hydrophobic materials despite the presence of pores. However, after a short period of operation, contaminants such as inorganic substances were attached to the pores of the membrane, and the properties of the hydrophobic membrane were changed to hydrophilic.

In other words, in order to be commercialized as a separation membrane for the MABR process, it must have good gas permeability such as oxygen, and as a hydrophobic material, water should not penetrate even if the membrane is contaminated because there are no pores in the membrane. do. Recently, there is a case of commercialization for MABR process by using a homogeneous membrane without pores in order to meet these conditions.

OXYMEM manufactured and commercialized a hydrophobic silicone-based hollow fiber homogeneous membrane with excellent gas permeability, but since it is a hollow fiber single membrane type, it cannot withstand pressure below a certain thickness and swells. There is a downside to

In addition, SUEZ manufactured a very thin hollow fiber membrane with a material of 4-methyl-1-pentyl, wound it in a twisted form inside a support, and commercialized it as a membrane for the MABR process. Compared to silicone, it does not swell even under pressure. However, there is a problem in that it is impossible to use the membrane itself because the mechanical strength is weak because a thin and thin hollow fiber membrane is manufactured.

The present inventors have focused on the development of membranes for wastewater treatment for decades, and have held about 20 registered patents. Recently, hydrophobic polyvinylidene fluoride (PVDF) multi-bore hollow fiber membranes have been developed. It has been successfully developed and applied to the wastewater treatment process, which has been registered as Patent No. 1848817. Based on this patented technology, the present inventors have conducted research on the development of a membrane that can be applied to the above-described MABR process as a wastewater treatment process. As a result, the outer surface of the porous polyvinylidene fluoride (PVDF) hollow fiber membrane has a silicone outer surface. The present invention was completed by forming a membrane, embedding a silicon-impregnated membrane in the inner direction of the hollow fiber membrane, and manufacturing an ultra-hydrophobic composite membrane having a structure in which the silicone outer film and the silicon-impregnated membrane were cross-locked.

[Prior art literature]

[Patent Literature]

Patent Document 1. US Patent Publication US 2017-0088450

Patent Document 2. US Patent Publication US 2016-0009578

Patent Document 3. Korean Patent No. 10-1848817

The present invention has been devised in view of the above problems, and an object of the present invention is to provide an ultra-hydrophobic composite membrane for a membrane aerated biofilm (MABR) process with high oxygen permeability and excellent mechanical properties and greatly improved durability, and a method for manufacturing the same that you want to provide.

The present invention for achieving the object as described above, a porous polyvinylidene fluoride (PVDF) hollow fiber membrane; a non-porous silicone outer film formed on the outer surface of the hollow fiber membrane; and a silicon-impregnated membrane embedded to a predetermined depth in the inner direction of the hollow fiber membrane from the side in contact with the non-porous silicone outer membrane.

The porous polyvinylidene fluoride (PVDF) hollow fiber membrane forms a channel having a plurality of holes (multi-bore) in the short fibers constituting the hollow fiber, and the outer peripheral surface of the short fibers including the plurality of holes is not circular. It is characterized in that the concave portion and the convex portion have a repeating pattern.

The porous polyvinylidene fluoride (PVDF) hollow fiber membrane is characterized in that the pore size is 0.05 to 0.45 μm.

The thickness of the non-porous silicone outer film is characterized in that 0.5 to 20 ㎛.

The silicon-impregnated membrane is characterized in that it is embedded in a depth of 1 to 100 μm in the inner direction of the hollow fiber membrane.

The silicone is characterized in that polydimethylsiloxane (PDMS).

In addition, the present invention comprises the steps of (I) obtaining a porous polyvinylidene fluoride (PVDF) hollow fiber membrane; (II) forming a non-porous silicone outer film on the outer surface of the hollow fiber membrane by wetting and evaporating only the surface of the hollow fiber membrane in a hydrophilic medium, and then coating the silicone; and (III) after forming the non-porous silicone outer film, blowing in strong air to adjust the thickness of the outer film and impregnating with silicon to form a silicon-impregnated film in the inner direction of the hollow fiber film from the side in contact with the non-porous silicon outer film It provides a method for manufacturing an ultra-hydrophobic composite membrane for a membrane aerated biofilm (MABR) process comprising a.

The hydrophilic media of step (II) is characterized in that it is selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol and n-butanol.

The silicone of step (II) or (III) is characterized in that it is polydimethylsiloxane (PDMS).

The ultra-hydrophobic composite membrane according to the present invention has a structure in which a silicone outer film formed on the outer surface of a porous polyvinylidene fluoride (PVDF) hollow fiber membrane and a silicon impregnated membrane embedded in the hollow fiber membrane are cross-locked. Due to this, the silicone outer film does not peel off, the silicone outer film does not swell even when the supply pressure is high, the oxygen permeability is high, and the durability is greatly improved due to excellent mechanical properties, so it can be applied to the MABR process and commercialized.

1 is a block diagram showing a typical membrane aerated biofilm (MABR) process.

2 is a 3D conceptual diagram showing a structure in which a silicon outer film and a silicon impregnated film are cross-locked according to the present invention;

Hereinafter, the ultra-hydrophobic composite membrane for a membrane aeration biofilm process according to the present invention and a method for manufacturing the same will be described in detail with the accompanying drawings.

The present invention is a porous polyvinylidene fluoride (PVDF) hollow fiber membrane; a non-porous silicone outer film formed on the outer surface of the hollow fiber membrane; and a silicon-impregnated membrane embedded to a predetermined depth in the inner direction of the hollow fiber membrane from the side in contact with the non-porous silicone outer membrane.

The porous polyvinylidene fluoride (PVDF) hollow fiber membrane preferably has a pore size of 0.05 to 0.45 μm, an inner diameter of the membrane of 0.2 to 2.0 mm, and a thickness of the membrane of 0.1 to 3.0 mm. The polyvinylidene fluoride (PVDF) hollow fiber membrane is hydrophobic and has the advantage of being easily discharged without being condensed inside even if moisture is contained when gas such as air is supplied to the inside of the membrane.

In particular, the shape of the hollow fiber constituting the porous polyvinylidene fluoride (PVDF) hollow fiber membrane may be a single-bore hole in the single fiber constituting the hollow fiber, and preferably a plurality of holes (multi-bore). bore) is formed, and the outer peripheral surface of the short fiber including the plurality of holes has a pattern in which concave and convex portions are repeated rather than circular, which is shown in FIGS. 7 may be a porous hollow fiber membrane.

In addition, a non-porous silicone outer film is formed on the outer surface of the porous polyvinylidene fluoride (PVDF) hollow fiber membrane. The thinner the silicon outer film, the better the oxygen permeability, but peeling may occur due to the continuous supply pressure. In order to prevent this, peeling durability is improved as the thickness of the silicone outer film is increased, while oxygen permeability is lowered. Therefore, the silicon outer film must be as thin as possible and have a structure stable for peeling. Therefore, the thickness of the non-porous silicone outer film is preferably 0.5 to 20 μm, more preferably 3 to 8 μm.

In addition, a silicon-impregnated film embedded to a predetermined depth in the inner direction of the hollow fiber film is formed from the side in contact with the non-porous silicon outer film, and the non-porous silicon outer film and the embedded silicon-impregnated film are cross-locked. By having a structured structure, the silicone outer film does not peel off, and the silicone outer film does not swell even when the supply pressure is high.

Silicon has a very high oxygen permeability. After oxygen is initially adsorbed to silicon, it diffuses through the silicon thickness and then goes through three stages of dissolution in water, and the diffusion rate is faster as the thickness becomes thinner. Making the thickness as thin as possible is the key to increasing the oxygen transfer ability.

That is, the silicone is cross-locked in the pores of the porous polyvinylidene fluoride (PVDF) hollow fiber membrane, which serves as a support for the silicone outer film and the composite film, so that the silicon outer film is not peeled off, the size of the pores The larger the size, the higher the holding effect, but if the pores are too large, the depth of the silicon-impregnated film to be embedded deepens, and the oxygen permeability drops sharply. Therefore, in order to control the depth of the silicon-impregnated film to be embedded while exhibiting a cross-locking effect, the size of the pores is preferably controlled to 0.05 to 0.45 μm. In this case, the silicon-impregnated membrane is preferably embedded to a depth of 1 to 100 μm in the inner direction of the hollow fiber membrane, and more preferably, the depth is 5 to 15 μm.

In addition, polydimethylsiloxane (PDMS) is preferably used as a silicone material for forming the silicone outer film and the silicone impregnated film.

2 is a 3D conceptual diagram illustrating a structure in which the silicon outer film and the silicon impregnated film are cross-locked according to the present invention as described above.

In addition, the present invention comprises the steps of (I) obtaining a porous polyvinylidene fluoride (PVDF) hollow fiber membrane; (II) forming a non-porous silicone outer film on the outer surface of the hollow fiber membrane by wetting and evaporating only the surface of the hollow fiber membrane in a hydrophilic medium, and then coating a silicone; and (III) after forming the non-porous silicone outer film, blowing in strong air to adjust the thickness of the outer film and impregnating with silicon to form a silicon-impregnated film in the inner direction of the hollow fiber film from the side in contact with the non-porous silicon outer film It provides a method for manufacturing an ultra-hydrophobic composite membrane for a membrane aerated biofilm (MABR) process comprising a.

In step (I), a porous polyvinylidene fluoride (PVDF) hollow fiber membrane having a single hole in a single fiber forming a hollow fiber according to a known conventional hollow fiber membrane manufacturing method may be prepared and obtained. , preferably, a porous polyvinylidene fluoride (PVDF) hollow fiber membrane of a multi-bore type may be obtained by manufacturing according to the method disclosed in [Experimental Example] of the present inventor's Patent No. 1848817 as described above. .

In step (II), after wetting the porous polyvinylidene fluoride (PVDF) hollow fiber membrane in a hydrophilic medium and evaporating only the surface, silicone is coated to form a non-porous silicone outer film on the outer surface of the hollow fiber membrane, As the hydrophilic media, one selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol and n-butanol may be used.

In step (III), after forming the non-porous silicone outer film, strong air is blown in to control the thickness of the outer film, and silicon is impregnated to form a silicon-impregnated film in the inner direction of the hollow fiber film from the side in contact with the non-porous silicon outer film. Bar, the silicon-impregnated membrane is embedded in a depth of 1 to 100 μm in the inner direction of the hollow fiber membrane, and more preferably to a depth of 5 to 15 μm. Cross-locking of the non-porous silicone outer coating and the embedded silicon-impregnated membrane. The effect of locking) can be maximized.

Hereinafter, specific examples and comparative examples according to the present invention will be described.

( Example 1 to 2)

A porous (7-bore) porous polyvinylidene fluoride (PVDF) hollow fiber membrane was obtained according to the method disclosed in [Experimental Example] of Patent Registration No. 1848817. After the obtained hollow fiber membrane was wetted with isopropanol and only the surface was evaporated, a polydimethylsiloxane (PDMS) solution was coated to form a non-porous polydimethylsiloxane outer film on the outer surface of the hollow fiber membrane. Then, the thickness of the outer film is adjusted by blowing in strong air (0.5 to 20 μm), and a polydimethylsiloxane solution is impregnated to form a polydimethylsiloxane-impregnated film in the inner direction of the hollow fiber film from the side in contact with the polydimethylsiloxane outer film. A composite membrane was prepared.

(Comparative Example 1)

A porous (7-bore) porous polyvinylidene fluoride (PVDF) hollow fiber single membrane was prepared according to Example 1.

(Comparative Example 2)

A composite membrane in which only the surface of the porous (7-bore) porous polyvinylidene fluoride (PVDF) hollow fiber single membrane prepared in Comparative Example 1 was coated with polydimethylsiloxane (a polydimethylsiloxane impregnated membrane was not formed) was prepared.

Table 1 below shows the oxygen permeability measurement and bubble test (at 3 bar) of the hollow fiber composite membranes or single membranes prepared from Examples 1 and 2 and Comparative Examples 1 and 2 according to the present invention.

Sample	PDMS envelope thickness (μm)	PDMS impregnated film depth (μm)	oxygen permeability (g/m 2 day)	bubble test (at 3 bar)
Example 1	8	15	2,800	No bubble
Example 2	20	70	700	No bubble
Comparative Example 1	-	-	100,000	bubble
Comparative Example 2	30	-	1,820	No bubble

A commercially available homogeneous silicon film with a thickness of 1 μm ^{is known to have a pure oxygen permeability of 56,283 g/m 2} ·day. As shown in Table 1, Examples 1 and 2 and Comparative Examples 1 and 2 are all theoretical oxygen permeability. It was measured with a value similar to the transmittance, and it was confirmed that no bubbles were generated in the water at 3 bar.

On the other hand, when only the oxygen permeability was considered, Comparative Examples 1 and 2 in addition to Examples 1 and 2 showed sufficient oxygen permeability. However, due to the characteristics of actually applying the composite membrane according to the present invention to a wastewater treatment process, continuous use for more than 5 years is possible In order to be commercialized in the MABR process, the oxygen permeability and durability (at 3 bar, the swelling of the PDMS outer film was observed) while varying the pressure conditions in water (at 3 bar and at 0.5 bar; initial and after 3 months) was tested, and the results are shown in Table 2 below.

Sample	oxygen permeability (g/m 2 day) at 3 bar	oxygen permeability (g/m 2 day) at 0.5 bar initial	oxygen permeability (g/m 2 day) at 0.5 bar after 3 months	Part development of PDMS envelope
Example 1	430	72	72	not bloated
Example 2	106	18	18	not bloated
Comparative Example 1	100,000	126	-	-
Comparative Example 2	258	45	45	intumescence

Normally, the oxygen permeability of the membrane developed by SUEZ or OXYMEM is 8~20 g/m ² ·day, and the amount of oxygen supplied to the biofilm required for the MABR process ^{exceeds 20 g/m 2} ·day You do not have to do. There is a limit to the amount of oxygen consumed by microorganisms present in the biofilm, so it is unnecessary to deliver too much. Due to the characteristics of wastewater treatment, durability should be maintained for more than 5 years in contaminated water, so it is more important to maintain the same performance for a long time without damaging the silicon film rather than oxygen permeability. Oxygen permeability increases when the supply pressure is high, but it is required to have an appropriate permeability to enable operation at low pressure. It is possible to maintain about 1 bar for a short period using a blower, but it is recommended to adjust it to 0.5 to 0.8 bar for long-term operation. desirable.

In Examples 1 and 2 of Table 2, oxygen permeability in water was measured by continuously pressurizing at 3 bar (Na ₂ SO ₃ was added in excess to remove dissolved oxygen because dissolved oxygen in water interferes with oxygen permeability) This is a method of measuring the amount of oxygen consumed in the absence of dissolved oxygen by measuring and calculating the oxygen permeability). Oxygen permeability was measured under the conditions of 3.0 bar and 0.5 bar, and it was confirmed that there was no change in oxygen permeability compared to the initial stage even after 3 months as well as 1 year.

Comparative Example 1 is a porous (7-bore) porous polyvinylidene fluoride (PVDF) hollow fiber single membrane that is not coated with silicone, wherein oxygen permeates in a bubble state at 3 bar and oxygen permeates in water but in air Similarly, the oxygen permeability was measured to ^{be 100,000 g/m 2 ·day.} On the other hand, at 0.5 bar, no bubbles were generated and oxygen was transferred to the porous membrane without resistance ^{, showing a high oxygen permeability of 126 g/m 2} ·day. However, after 3 months, the pores of the porous membrane were wetted by water. Oxygen was not permeated.

Comparative Example 2 is a composite membrane in which polydimethylsiloxane is coated only on the surface of a porous (7-bore) porous polyvinylidene fluoride (PVDF) hollow fiber single membrane (polydimethylsiloxane impregnated membrane is not formed). It was measured to be 258 g/m ² ·day at 3 bar and 45 g/m ^{2 ·day at 0.5 bar.} In addition, as a result of observing the swelling of the PDMS outer film, the swelling of the outer film occurred after 1 month at 3 bar and after 7 months at 0.5 bar.

However, in the ultra-hydrophobic composite membranes prepared in Examples 1 and 2 of the present invention, it was confirmed that the polydimethylsiloxane outer film did not peel off even after one year or more, and the silicone outer film did not swell even when the supply pressure was high. found it possible

Therefore, the ultra-hydrophobic composite membrane according to the present invention has a structure in which a silicon outer film formed on the outer surface of a porous polyvinylidene fluoride (PVDF) hollow fiber membrane and a silicon impregnated membrane embedded in the hollow fiber membrane are cross-locked. Due to this, the silicone outer film does not peel off, the silicon outer film does not swell even when the supply pressure is high, and the oxygen permeability is high and the durability is greatly improved due to excellent mechanical properties. .

Claims (9)

1. porous polyvinylidene fluoride (PVDF) hollow fiber membrane;

   a non-porous silicone outer film formed on the outer surface of the hollow fiber membrane; and

   The ultra-hydrophobic composite membrane for a membrane aeration biofilm (MABR) process comprising a; a silicon-impregnated membrane embedded to a predetermined depth in the inner direction of the hollow fiber membrane from the side in contact with the non-porous silicone outer membrane.
2. According to claim 1, wherein the porous polyvinylidene fluoride (PVDF) hollow fiber membrane forms a channel having a plurality of holes (multi-bore) in the short fibers constituting the hollow fiber,

   An ultra-hydrophobic composite membrane for a membrane aerated biofilm (MABR) process, characterized in that the outer circumferential surface of the short fibers including the plurality of holes has a pattern in which concave and convex portions are not circular.
3. The ultra-hydrophobic composite membrane for a membrane aeration biofilm (MABR) process according to claim 1, wherein the porous polyvinylidene fluoride (PVDF) hollow fiber membrane has a pore size of 0.05 to 0.45 μm.
4. The ultra-hydrophobic composite membrane for a membrane aerated biofilm (MABR) process according to claim 1, wherein the non-porous silicone outer coating has a thickness of 0.5 to 20 μm.
5. The ultra-hydrophobic composite membrane for a membrane aeration biofilm (MABR) process according to claim 1, wherein the silicon-impregnated membrane is embedded to a depth of 1 to 100 μm in the inner direction of the hollow fiber membrane.
6. The ultra-hydrophobic composite membrane for a membrane aerated biofilm (MABR) process according to claim 4 or 5, wherein the silicone is polydimethylsiloxane (PDMS).
7. (I) obtaining a porous polyvinylidene fluoride (PVDF) hollow fiber membrane;

   (II) forming a non-porous silicone outer film on the outer surface of the hollow fiber membrane by wetting and evaporating only the surface of the hollow fiber membrane in a hydrophilic medium, and then coating the silicone; and

   (III) after forming the non-porous silicone outer film, blowing in strong air to adjust the thickness of the outer film and impregnating with silicon to form a silicon-impregnated film in the inner direction of the hollow fiber film from the side in contact with the non-porous silicon outer film; A method of manufacturing a very hydrophobic composite membrane for a membrane aerated biofilm (MABR) process comprising a.
8. The method of claim 7, wherein the hydrophilic media is selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol and n-butanol.
9. The method of claim 7, wherein the silicone is polydimethylsiloxane (PDMS).

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