JP2010214255A - Separation membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a decrease in permeation flow rate by increasing the hydrophilicity of the filtration surface in a separation membrane used for water treatment. <P>SOLUTION: The separation membrane 1 includes a coating layer 3 comprising a carbon film in which the hydrogen content is 1-80 vol.%, on the surface of a porous body 2 made of a resin such as a fluororesin and a polyolefin system resin to make the surface of the resin porous body 2 hydrophilic and also to fix firmly and integrally to the porous body 2 so as to be difficult to peel. Further, the coating layer 3 provided on the surface of the porous body 2 has strength, durability and chemical resistance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a separation membrane, and more specifically, a porous flat membrane or hollow fiber, a nonwoven fabric or the like suitably used as a filtration membrane for water treatment of sewage, seawater, oil water, etc., a zeolite separation membrane for biofuel production, etc. It is related with the separation membrane which consists of.

Conventionally, a porous resin membrane has been used as a separation membrane for water purification treatment. Among them, fluorine-based resins, particularly tetrafluoroethylene resin (hereinafter referred to as PTFE) are excellent in durability, chemical resistance, and heat resistance, and have a wide range of fields because they retain strength even when thinned. Widely used as a separation membrane.
However, many resins including the fluororesin such as PTFE are generally hydrophobic and water repellent. Therefore, if the pores of the porous film are micropores in order to increase the processing accuracy, there is a problem that the permeability is reduced. For this reason, various hydrophilic treatments have been conventionally applied to the surface of the porous resin membrane.

  For example, in Japanese Patent No. 3809201, a hydrophilic layer is applied by providing a coating layer of polyvinyl alcohol on the surface of PTFE. Further, the surface of the fluororesin porous body may be plasma-treated.

Japanese Patent No. 3809201

  As described in Patent Document 1, both the case where an alcohol-based coating layer is provided on the surface of PTFE or the case where plasma treatment is performed have an advantage that the surface layer can be modified, but the hydrophilic functional group is more deteriorated. It is preferable to reduce and improve so that the permeation | transmission flow rate can be hold | maintained for a long time.

  The present invention has been made in view of the above problems, and can make the surface of a porous body made of resin hydrophilic, and is firmly fixed and integrated with the porous body to prevent peeling, and has strength, durability, and chemical resistance. It is an object of the present invention to provide a separation membrane in which a coating layer having properties is provided on the surface of a porous body.

  In order to solve the above-mentioned problems, the present invention is characterized in that a separation layer is provided on the surface of a resin-made porous body, comprising a coating layer made of a carbon film having a hydrogen content of 1% by volume to 80% by volume. Providing a membrane.

  The coating layer is mainly made of an amorphous film containing 1 to 80% by volume of hydrogen in carbon, so that it is rich in flexibility and slidability, and because it is a carbon film, it has high strength, chemical resistance and durability. It will be excellent. In addition, it is compatible with the resin and can adhere firmly to the porous membrane. Therefore, peeling of the coating layer hardly occurs, the hydrophilicity of the separation membrane can be ensured, and the permeation flow rate does not decrease. The hydrogen contained in the carbon is preferably 20% by volume or more.

The coating layer is preferably a mixture of diamond-like carbon (hereinafter referred to as DLC), fullerene, nanotube, graphite, diamond, crystalline carbon (graphite structure, diamond structure, fullerene structure, nanotube structure) and amorphous carbon. Used for.
Among these, DLC is particularly preferably used because the hydrogen group has high hydrophilicity and high strength. The coating layer may be formed by any method of CVD (chemical vapor deposition), sputtering, arc spraying, plasma spraying PVD, and sintering after coating.
When the DLC is used, it is preferably used because it can be firmly applied to a porous material such as a fluororesin by a CVD method in which vapor deposition is performed at a low temperature plasma of 120 ° C. or lower.

The coating layer has a thickness of 0.01 μm to 100 μm, preferably 0.1 to 10 μm, and more preferably 0.1 to 2 μm.
The reason why the thickness of the coating layer is 0.01 μm or more is that if it is less than 0.01 μm, it is easily affected by the surface, the film is likely to be uneven, and wear due to insufficient adhesion is likely to occur. On the other hand, when the thickness of the coating layer exceeds 100 μm, internal stress is generated due to the difference in linear expansion coefficient from the resin and the influence of the thermal expansion coefficient, and warpage is likely to occur. There is also a problem that the weight increases and the cost increases.

The porous body is composed of a porous sheet for filtration, a hollow fiber of a porous tube or a nonwoven fabric, and is suitably used as a separation membrane for filtration.
Thus, the coating layer is provided on the surface of the porous body as a filtration membrane.For example, when clogging occurs in the sludge treatment, the coating layer is excellent in chemical resistance even after chemical cleaning. Clogging can be easily eliminated, and the cost of medicine can be reduced.
In addition, since the coating layer is hydrophilized, the permeability of raw water to fine pores is good, and the coating layer is difficult to peel off, so that a decrease in permeation flow rate can be prevented.

  In particular, since the coating layer made of DLC is excellent in corrosion resistance to seawater, it is preferably used for seawater treatment, for example, for filtration treatment in which ballast water or oilfield-associated water becomes raw water.

  Further, the porous body is composed of a porous sheet used as a zeolite separation membrane, a hollow fiber of a porous tube or a nonwoven fabric, and is suitably used as a separation membrane for dehydration for biofuel production.

The porous body is not limited as long as it is made of a resin, but a fluorine-based resin or a polyolefin-based resin is preferably used in that it has strength even when a large number of micropores are provided to increase the porosity.
Examples of the fluororesin include PTFE, PVDF (polyvinylidene fluoride), PFA, ETFE, PCTFE, and PVF.
Examples of the polyolefin resin include PE, PP, and ethylene-α olefin copolymer.
In particular, in the case of the fluorine-based resin, by introducing a raw material gas containing F at the initial stage of DLC coating into a reduced-pressure CVD tank and reacting with a gas containing carbon such as acetylene or a gas by introducing a liquid, It is possible to improve adhesion, entrainment, and throwing-in. This F bond can have a gradient F / H ratio by controlling the F / H concentration at the initial stage of vapor deposition to be high and low at the surface part in the latter stage of vapor deposition that requires hydrophilicity.

  In particular, PTFE has a relatively slow decomposition rate even at a melting point peak or higher (327 ° C. or higher), and is most suitably used in terms of durability, chemical resistance, strength, and the like. Note that PTFE may be 80% or more by weight instead of PTFE alone, and other fluororesin may be blended.

Further, the present invention provides a flat membrane having the above-described separation membrane as a flat membrane, with a permeate flow channel provided therebetween and opposed to the permeate flow channel, and a permeate flow outlet communicating with the permeate flow channel. A membrane separation membrane element is provided.
The present invention also provides a flat membrane type separation membrane module in which a plurality of the flat membrane type separation membrane elements are assembled with a gap.

  Further, the separation membrane described above is a hollow fiber, a plurality of hollow fibers are arranged with gaps, and both ends in the length direction of the hollow fibers are connected by a fixing material, and the permeate outlet of the hollow fiber is connected to the one end. A hollow fiber type separation membrane module is provided which communicates with a water collecting section provided on the side fixing member.

  The flat membrane type separation membrane module and the hollow fiber type separation membrane module described above are suitably used for water treatment apparatuses for filtration and the like.

As described above, the separation membrane of the present invention is provided with a coating layer made of carbon containing a large amount of hydrogen on the surface of a porous resin body so as to make it hydrophilic, so that the raw water into the pores of the separation membrane Can improve the permeability. In addition, it has an advantage that it can be firmly and firmly fixed with a resin such as a fluororesin or a polyolefin resin as a porous body, and does not lower the permeation flow rate of the separation membrane.
Furthermore, since the coating layer itself has durability, chemical resistance, and strength, the separation membrane can be cleaned with chemicals, clogging of the separation membrane can be reduced, and the operation efficiency of the separation membrane can be increased.

It is sectional drawing of 1st embodiment of this invention. It is a perspective view of a second embodiment. It is sectional drawing of 3rd embodiment. (A) is a perspective view, (B) is a schematic diagram showing a cross-sectional shape of the BB line of (A), (C) is a partially enlarged view on the permeate inflow side, (D) ) Is a schematic diagram showing a cross section in the thickness direction from the permeate inflow side to the permeate outflow side.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The separation membrane 1 of the first embodiment shown in FIG. 1 is a flat membrane for filtration.

The separation membrane 1 includes a coating layer 3 mainly composed of DLC on the surface of an expanded PTFE porous membrane 2 (hereinafter abbreviated as a porous membrane 2).
The average thickness of the porous membrane 2 is 5 to 200 μm, the average thickness of the coating layer 3 is 0.1 to 100 μm, and the area occupation ratio of the pores 2a on the outer surface of the filtration side that is the liquid to be treated is 40% to It is 85% and the average pore diameter is 0.01 to 20 μm. A coating layer 3 is provided on the outer surface of the porous membrane 2 on the filtration side. The thickness of the coating layer 3 is about 1 to 100% of the thickness of the porous membrane 2 and covers only the surface of the fibrous skeleton surrounding the pores of the porous membrane 2, and thus the surface of the porous membrane 2. It has a hole 3a communicating with the hole 2a.

  The covering layer 3 is made of a DLC film having a hydrogen content of 1 to 80% by volume. The coating layer 3 is firmly fixed to the surface of the porous film 2 and integrated with the porous film 2 by a CVD method (chemical vapor deposition method) that is vapor-deposited at a low temperature plasma of 120 ° C. or lower.

As the porous membrane 2 made of the porous expanded PTFE, in this embodiment, a multilayer porous membrane in which a filtration layer 2A and a support layer 2B are laminated is used.
The filtration layer 2A is arranged on the liquid to be treated side, the area occupation ratio of the pores is 40% to 85% on the outer filtration surface, and the average pore diameter is 0.01 to 20 μm, preferably 0.01 to 0.05 μm. It is said. The support layer 2B has a larger pore diameter and a larger thickness than the filtration layer 2A. Both the filtration layer 2A and the support layer 2B are manufactured by biaxially stretching a molded body obtained by extruding PTFE unsintered powder and a liquid lubricant and then sintering and integrating them.
The filtration layer 2A has an average film thickness of 5 to 200 μm, an average maximum length of a fibrous skeleton surrounding the pores of 5 μm or less, and a particle capture rate of 0.45 μm and a particle capture rate of 90% or more.
The support layer 2B has an average pore diameter of 1 to 15 μm, an average film thickness of 5 to 195 μm, and an average maximum length of a fibrous skeleton surrounding the pores of 15 to 100 μm.
The porous membrane 2 made of the laminate has a tensile strength of 10 N / mm ² or more, 3 mass% sulfuric acid, 4 mass% sodium hydroxide aqueous solution, hypochlorous acid having an effective chlorine concentration of 10%. Even when immersed in each of the aqueous sodium solutions at a temperature of 50 ° C. for 10 days, the amount of permeated water does not decrease and has excellent chemical resistance that is not damaged.
The average pore diameter is measured by a palm porometer (model number CFP-1200A) manufactured by PMI.
The DLC coating layer 3 is provided on the outer surface of the filtration layer 2A for hydrophilic treatment.

  The separation membrane 1 is formed as a flat membrane element having a permeate flow path and opposingly arranged, and the outer periphery is sealed. A flat membrane type separation membrane module in which a large number of flat membrane elements are arranged at intervals is used by being suspended in a filtration tank.

Since the separation membrane 1 composed of a flat membrane for filtration having the above-described configuration is provided with the hydrophilic coating layer 3 on the filtration surface on the liquid to be treated, it can easily permeate water and increase the permeation flow rate.
In addition, since the coating layer 3 is firmly fixed and integrated on the surface of the porous membrane 2, peeling does not occur even when used over time, and the permeation flow rate does not decrease. Furthermore, since the carbon-based coating layer 3 is excellent in strength, durability, and chemical resistance, it can be suitably used as a filtration membrane together with the properties of the porous membrane 2 made of PTFE having similar properties. . In particular, since it can be washed with a high concentration oxidizing agent or alkaline agent, a high permeated water amount can be obtained over a long period of time.

  The porous film 2 is not limited to the structure of the laminate, and may be a single layer in which a dense layer serving as a dense filtration layer is provided on the liquid to be treated and the pores are gradually enlarged toward the opposite side. Furthermore, it may be a single layer in which pores are provided substantially uniformly in the thickness direction.

Since the filtration membrane using the flat membrane made of the separation membrane 1 having the above-described configuration is extremely excellent in chemical resistance and mechanical strength, it can be suitably used for raw water consisting of waste water containing activated sludge. . Especially, it is very excellent at the point which can be used stably with respect to activated sludge (to-be-processed liquid) whose MLSS (mixed-liquid suspension suspended substance) is 5,000-20,000 mg / L.
Moreover, since the coating layer 3 has excellent corrosion resistance against seawater, it is preferably used as a filtration device for seawater filtration, for example, a filtration device in which seawater such as ballast water becomes raw water, or an oily water filtration device such as oilfield-associated water. It is done.

"Example"
DLC was vapor-deposited with a thickness of 1.5 μm on the surface of the flat PTFE porous membrane by low-temperature plasma CVD (120 ° C.).
Water was permeated by suction filtration (0.5 atm) for the example in which the DLC surface layer was provided and the comparative example in which the DLC coating layer was not provided on the same flat membrane.
As a result, the differential pressure of the example was 1/5 that of the comparative example.
Further, 1 ton of sludge drainage was permeated for 30 minutes as raw water. In the comparative example, clogging occurred after 10 minutes, but in the example, clogging occurred only after 30 minutes.

FIG. 2 shows a second embodiment, in which the separation membrane 10 is made of a hollow fiber and is formed as a hollow fiber membrane for filtration.
The hollow fiber used as the porous membrane 11 of the separation membrane 10 is also formed of an expanded PTFE porous body as in the first embodiment. The hollow fiber may be a plurality of layers as in the case of the flat membrane, or may be a single layer, and the pore diameter and the porosity are the same as those of the flat membrane of the first embodiment.
Specifically, a multi-layered porous hollow fiber made of a laminate provided with a support layer and a filtration layer described in JP-A-2006-7224 is preferably used.
In this embodiment, a single layer hollow fiber and a hollow fiber having an outer diameter of 1 to 14 mm, an inner diameter of 0.5 to 12 mm, a wall thickness of 0.2 to 1.0 mm, and a porosity of 60 to 80% are used as the porous membrane 11. ing.

  A coating layer 13 made of DLC similar to the first embodiment is provided on the outer peripheral surface of the porous membrane 11 made of the hollow fiber. The coating layer 13 is applied to the surface of the hollow fiber and then sintered to have a thickness of 0.1 to 2 μm.

A large number of the separation membranes 10 made of hollow fibers are collected into a hollow fiber separation membrane module, and the hollow fiber separation membrane module is suspended in a filtration tank and used in a water treatment apparatus.
Since the separation membrane 10 made of this hollow fiber is also hydrophilically treated with the coating layer 13, the water permeability to the fine pores as described above can be improved, and the permeate flow rate of the raw water can be increased. And since the coating layer 13 is hard to peel from the porous film 11, a permeation | transmission flow rate does not fall.

FIG. 3 shows a third embodiment.
In the separation membrane 20 of the third embodiment, the porous membrane 21 is formed of a nonwoven fabric made of chlorinated polyethylene of polyolefin resin.
A coating layer 23 in which fullerene particles and tubes are dispersed in a nano state is provided in an amorphous DLC membrane matrix on the outer surface on the filtration side of the porous membrane 21. The coating layer 23 had a thickness of 5 to 10 μm.
Since the operation effect of the separation membrane 20 provided with the coating layer 23 is the same as that of the first embodiment, the description is omitted.
When the coating layer 23 of the third embodiment is used, the cost increases by about 30%, but the strength can be improved by 50% compared to the case where the coating layer 23 is not provided.

4A to 4D show a fourth embodiment.
The separation membrane 30 of the fourth embodiment is used as a zeolite separation membrane that dehydrates water and separates ethanol and water.
The zeolite separation membrane 30 uses an expanded PTFE porous sheet as a support for the porous membrane 31, and a coating layer 34 made of a hydrophilic treatment membrane is integrally provided on the surface of the porous membrane 31. The crystal 35 is supported. The coating layer 34 is a DLC coating layer as in the above embodiment. The pore inner surface of the porous film 31 is hydrophilized with crosslinked PVA to provide a hydrophilic film 36. The inner surface of the pores of the porous film 31 may also be provided with a DLC coating layer.

In the zeolite separation membrane 30, one surface of the porous membrane 31 (upper surface in FIGS. 4B to 4C) is a permeate inflow surface 31x, and the other surface (lower surfaces in FIGS. 4B to 4D). ) Is the permeate outflow surface 31y. The fermentation broth separated into water and alcohol permeates in the direction of the arrow from X to Y shown in FIG.
The porous membrane 31 includes a fibrous skeleton 33 composed of fine fibrous structures and nodules in which flexible fibers are connected in a three-dimensional network, and there are a large number of pores 32 surrounded by the fibrous skeleton 33. is doing. The air holes 32 communicate in a three-dimensional manner up to the permeate inflow surface 31x and the permeate outflow surface 31y. The hole diameters of the holes 32 are different in the range of 0.1 to 5.0 μm.

In the schematic diagram of FIG. 4C, a flow path in which the permeate inflow surface 31x and the permeate outflow surface 31y are communicated with each other by a large hole 32a is indicated by a straight through hole 45, and there are many small holes 32b. In addition, a portion where the fibrous skeleton 33 is large is shown as a partition wall portion 46.
The zeolite crystal 35 is A-type. Note that any of PHI type, MER type, LTA type, A type, BEA type or CDO type zeolite may be used, but the A type is used in this embodiment.

As shown in FIGS. 4B to 4D, the zeolite crystal 35 includes a zeolite crystal film 35A supported on the surface of the coating layer 34 on the permeate inflow side and a through-hole 45 made up of a large hole 32a. It consists of a zeolite crystal film 35B carried on the inner peripheral surface and a zeolite crystal part 35C filled in the fine holes 32c among the small holes 32b included in the partition wall part 46.
The zeolite crystal part 35C has the fine holes 32c clogged.
The small holes 32b are not all clogged, but are filled with a hole in which the zeolite crystal film is supported on the surface of the fibrous skeleton 33 and the zeolite crystal part 35C according to the hole diameter. There are also fine pores.

Further, as shown in FIG. 4D, the clogged fine holes 32c filled with the zeolite crystal part 35C are unevenly distributed in the permeate inflow side region and gradually decrease toward the permeate outflow surface 31y. The clogged fine holes 32c do not exist in the region between the intermediate position in the thickness direction and the other surface 31y.
The porous membrane 31 made of the expanded PTFE porous body has a thickness of 30 to 1000 μm and an IPA bubble point of 10 to 200 kPa. The thickness of the coating layer 34 is 0.1 to 1 μm.

The zeolite separation membrane 30 configured as described above includes a hydrophilic coating layer 34 having an affinity for zeolite fine particles and zeolite crystals on the surface of the porous membrane 31. Therefore, the porous membrane 31 made of PTFE which does not originally have affinity and the zeolite crystal 35 have affinity, and the supporting force of the zeolite crystal 35 can be increased. As a result, while the porous membrane 31 made of PTFE is used as a support, the zeolite crystals are not peeled off or dropped off from the porous membrane 31 and can be excellent in durability.
The porous membrane 31 made of PTFE is extremely excellent in physical properties such as strength, bending characteristics, chemical resistance, and the like, and is inexpensive, and therefore excellent in cost.

  As described above, the zeolite separation membrane has excellent physical properties as a support, but a hydrophilic coating layer is provided on a PTFE porous membrane support on which the zeolite is easily peeled, and the zeolite crystal is formed in the coating layer. Since the membrane is supported, the zeolite crystal membrane does not easily peel off. In addition, zeolite crystals are pressed into the micropores in the pores on the permeate inflow side and are packed in a clogged state, so that the zeolite fine particles are not separated from the micropores and can improve the supporting function. it can.

  The zeolite separation membrane is suitably used not only for ethanol but also for producing biofuel from methanol, butanol or the like.

1 Separation membrane 2 Porous membrane 3 Coating layer

Claims (12)

  A separation membrane comprising a coating layer made of a carbon membrane having a hydrogen content of at least 1% by volume to 80% by volume on the surface of a porous body made of resin.   The coating layer is at least one of diamond-like carbon, fullerene, nanotube, graphite, diamond, graphite structure, diamond structure, fullerene structure, and a mixture of crystalline carbon and amorphous carbon of the nanotube structure. Item 2. The separation membrane according to Item 1.   The separation membrane according to claim 1, wherein the coating layer is provided by depositing diamond-like carbon.   The separation membrane according to any one of claims 1 to 3, wherein a thickness of the coating layer is 0.01 µm or more and 100 µm or less.   The separation membrane according to any one of claims 1 to 4, wherein the porous body comprises a porous sheet for filtration, a hollow fiber of a porous tube, or a nonwoven fabric.   The separation membrane according to any one of claims 1 to 3, wherein the porous body is composed of a porous sheet used as a zeolite separation membrane, a hollow fiber of a porous tube, or a nonwoven fabric.   The separation membrane according to any one of claims 1 to 6, wherein the porous body is made of a fluorine resin or a polyolefin resin.   The separation membrane according to any one of claims 1 to 7, wherein the porous body is made of a porous stretched tetrafluoroethylene resin.   The separation membrane according to any one of claims 1 to 5, 7, and 8 is a flat membrane, and a permeate flow path is opened and arranged oppositely, and a permeate flow outlet that communicates with the permeate flow path is opened. A flat membrane separation membrane element that seals the outer periphery.   A separation membrane module comprising a plurality of flat membrane separation membrane elements according to claim 9 assembled with a gap.   The separation membrane according to any one of claims 1 to 5, 7, and 8 is a hollow fiber, a plurality of hollow fibers are arranged with gaps, and both ends in the length direction of the hollow fibers are connected by a fixing material. And a separation membrane module in which the permeate outlet of the hollow fiber communicates with a water collecting portion provided in the fixing member on the one end side.   The water treatment apparatus provided with the separation membrane module of Claim 10 or Claim 11.