TWI614061B - Composite membrane utilized in membrane distillation - Google Patents

Abstract

A composite membrane applied to membrane distillation, comprising a hydrophobic porous membrane, a first aqueous rubber layer and a second aqueous rubber layer. The hydrophobic porous membrane comprises opposing first and second surfaces, wherein the first surface corresponds to the hot end of the membrane distillation and the second surface corresponds to the cold end of the membrane distillation. The second water layer is connected to the first surface of the first water layer and the hydrophobic porous film, wherein the water content of the second water layer is between 50% and 90%, and the moisture content of the first water layer is greater than The water content of the second water layer.

Description

Composite membrane for membrane distillation

This invention relates to a film for use in membrane distillation.

Due to water shortages, desalination or water recycling has become one of the most important applications for membrane distillation. The membrane distillation technology mainly uses a hydrophobic microporous membrane to separate the high temperature solution from the low temperature solution. The water vapor flows from the high temperature side to the low temperature side through the membrane pore on the membrane due to the vapor pressure difference between the high temperature side and the low temperature side. And then condense into a liquid on the low temperature side. This vapor pressure difference is caused by the temperature gradient between the fluids on both sides.

Since membrane distillation technology can obtain excellent treatment water quality, in addition to seawater desalination treatment, wastewater treatment by membrane distillation technology has also received increasing attention. Since most of the wastewater contains interfacially active substances or large oil stains, the former will cause the surface tension of the wastewater to drop drastically, causing the membrane to be wetted, and the latter will cause the membrane to clog and cause a large drop in flux. Both phenomena cause the membrane distillation process to be terminated, making membrane distillation technology difficult to apply to wastewater treatment.

The invention provides a composite membrane for membrane distillation, which solves the problem that the membrane pores are easily blocked or wetted when the membrane distillation technology is applied to waste water, so as to prolong the operation time of membrane distillation.

其中Ws代表潤濕後的水膠層重量，Wd代表乾燥後的水膠層重量。 One embodiment of the present invention provides a composite membrane for use in membrane distillation comprising a hydrophobic porous membrane, a first aqueous rubber layer and a second aqueous rubber layer. The hydrophobic porous membrane comprises opposing first and second surfaces, wherein the first surface corresponds to the hot end of the membrane distillation and the second surface corresponds to the cold end of the membrane distillation. The second water layer is connected to the first surface of the first water layer and the hydrophobic porous film, wherein the water content of the second water layer is between 50% and 90%, and the moisture content of the first water layer is greater than The water content of the second water layer, wherein the water content is defined as follows:

Where Ws represents the weight of the water layer after wetting, and Wd represents the weight of the water layer after drying.

The composite film contains a two-water gel layer having different water contents to capture the interface active particles (cluster), and the hydrophobic porous film is prevented from being wetted by the interface active particles. The composite membrane contacts the hot-end wastewater with a water-mud layer with a higher water content, so that the oil in the wastewater is less likely to adhere and accumulate on the composite membrane, so as to prevent the composite membrane from being clogging and causing a decrease in flux, thereby effectively prolonging the composite. The operational life of the membrane.

100‧‧‧Composite film

110‧‧‧hydrophobic porous membrane

112‧‧‧ first surface

114‧‧‧ second surface

116‧‧‧ film hole

120‧‧‧First water layer

130‧‧‧Second water layer

200‧‧‧ hot end

210‧‧‧ Wastewater

212‧‧‧ oil stains

220‧‧‧Interfacial active particles (group)

222‧‧‧Hydrophilic end

224‧‧‧Live end

300‧‧‧ cold end

The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood. Schematic diagram of the time.

Figure 2 is a graph of flux-conductivity for a different embodiment of the composite membrane of the present invention after a period of operation.

The spirit and scope of the present invention will be apparent from the following description of the preferred embodiments of the invention. The spirit and scope of the invention are not departed.

Dyeing and finishing wastewater of textile mills is an industrial wastewater with large water volume and high water temperature. It is a kind of object with considerable potential for wastewater recycling and reuse. However, as mentioned above, chemicals added in the dyeing and finishing process, such as leveling agents, softeners, and other organic substances, are substances that easily block or wet the film. If they are not solved, they cannot be directly The membrane distillation technique treats the wastewater. In addition, since the components in the dyeing and finishing wastewater are too complicated to be screened for specific components, the present invention proposes an improved composite membrane for improving the ability of membrane distillation to treat wastewater.

Referring to Figure 1, there is shown a cross-sectional view of an embodiment of a composite membrane for membrane distillation of the present invention in use. The composite film 100 includes a hydrophobic porous film 110 and a first water layer 120 and a second water layer 130 disposed on the hydrophobic porous film 110. The hydrophobic porous membrane 110 includes an opposing first surface 112 corresponding to the hot end 200 and a second surface 114 corresponding to the cold end 300. The second water gel layer 130 is disposed on the first surface 112 of the hydrophobic porous film 110, and the first water gel layer 120 is further disposed on the second water gel On layer 130. More specifically, the first water layer 120 and the second water layer 130 are disposed on one side of the hydrophobic porous film 110 corresponding to the hot end 200, and the second water layer 130 is connected to the first water layer 120 and The hydrophobic porous film 110.

The hydrophobic porous membrane 110 has a plurality of membrane pores 116 that communicate with the first surface 112 and the second surface 114 of the hydrophobic porous membrane 110. The aforementioned hot end 200 refers to a relatively high temperature side of the composite film 100, which contains a fluid having a relatively high temperature for film distillation treatment, such as high temperature wastewater 210. The cold end 300 is a relatively low temperature end of the composite membrane 100, and the water vapor (small liquid water) in the hot end 200 passes through the first water gel layer 120 and the second water gel layer 130 and then passes through the hydrophobic layer. The film pores 116 on the porous membrane 110 reach the cold end 300 and are collected as liquid water at the cold end 300 to be collected. Since the water obtained by such a membrane distillation method is formed by condensation of moisture, there is almost no impurity present.

The first water gel layer 120 and the second water gel layer 130 in the composite film 100 are both high water content water gel layers, wherein the first water gel layer 120 and the second water gel layer 130 respectively have different water content, and the first The water content of the first water gel layer 120 is greater than the water content of the second water gel layer 130. The water content referred to here is defined as:

Wherein Ws represents the wetted water layer, such as the weight of the first water layer 120 or the second water layer 130, and Wd represents the weight of the water layer after drying. The weight of the wetted water gel layer referred to herein is the weight obtained after the water gel layer is immersed in water for a period of time, and the water droplets on the surface of the water gel layer are naturally dripped, and the dried water gel The weight of the layer means that the water layer is dried. After a period of time, it was taken out of the measured weight.

The first water gel layer 120 and the second water gel layer 130 respectively play different roles in the composite film 100, and the first water gel layer 120 has a high water content to provide a lubricating surface of the composite film 100 to prevent oil staining and It is used to prevent the film pores 116 from being wetted by particles having a property of interfacial activity. The second water gel layer 130 has a smaller mesh size to provide further filtration of soiling and to prevent the water mass from passing directly through the film aperture 116.

Since the first water-repellent layer 120 has a high water content, the high-temperature wastewater 210 can be quickly flowed over the surface of the composite film 100. Specifically, the first water layer 120 located in the outer layer, that is, in contact with the wastewater 210 of the hot end 200, has a higher moisture content, which can provide a wetted surface of the composite film 100 to allow the hot end 200 to When the wastewater 210 flows through the composite membrane 100, the dirt in the wastewater 210 includes oil stains 212, interface active particles (groups) 220 having interface-active properties, and other organic or inorganic contaminants, etc., from the surface of the composite membrane 100. Sliding open, and not easily adhering to the surface of the composite film 100 causes clogging. In some embodiments, the first water gel layer 120 having a higher water content than the second water gel layer 130 has a moisture content of between 90% and 98%, for example, the first water gel layer 120. The moisture content can be 90%, 92%, 94%, 96% or 98%. If the moisture content of the first water-repellent layer 120 is too low, for example, less than 90%, the dirt in the wastewater 210 may not be slid away from the surface of the composite film 100, and if the water content of the first water-repellent layer 120 is too high. If it is higher than 98%, it will affect the structural strength of the composite film 100, thus affecting the operating life.

Since the first water gel layer 120 is closer to the hot end 200 than the second water gel layer 130, the first water gel layer 120 has a second water gel layer 130 as compared with the second water gel layer 130. A larger mesh size is used to isolate the larger size of the wastewater 210 from contamination. For example, the first water gel layer 120 has a mesh size of between 0.2 μm and 10 μm. If the mesh size of the first water-repellent layer 120 is too small, such as less than 0.2 μm, the flux of the composite film 100 is greatly reduced, which affects the efficiency of membrane distillation. If the mesh size of the first water-repellent layer 120 is too large, such as greater than 10 μm, since the water content of the first water-repellent layer 120 is high, the structural strength of the composite film 100 is also lowered, which affects the operational life of the composite film 100.

The first water gel layer 120 and the second water gel layer 130 may further serve to further block the interface active particles (sets) 220 having interfacial activity characteristics in the wastewater 210 from passing through the film holes 116 on the hydrophobic porous film 110 to avoid hydrophobicity. The pores 116 of the porous membrane 110 are wetted by the wastewater 210 with the interface-active particles (sets) 220. Specifically, if the interface active particles (clusters) 220 do not slide along the surface of the first water gel layer 120 and enter the first water gel layer 120, the interface active particles (cluster) 220 include the hydrophilic end 222 and At the water-repellent end 224, the interface-active particles (sets) 220 in the wastewater 210 are captured by the first water-based layer 120 having a high water content and remain in the first water-based layer 120. In other words, the interface active particles (sets) 220 are less likely to enter the second water gel layer 130 and the hydrophobic porous film 110. In this way, the problem that the membrane pores 116 are wetted by the interface active particles (cluster) 220 can be solved.

The water content of the second water gel layer 130 is smaller than the water content of the first water gel layer 120. In some embodiments, the second water layer 130 has a water content of between 50% and 90%. For example, the second water layer 130 may have a water content of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%. If the moisture content of the second water-based layer 130 is too low, such as less than 50%, the effect of intercepting the interfacial active particles (sets) 220 cannot be provided.

Since the second water layer 130 is located between the first water layer 120 and the hydrophobic porous film 110, the mesh size of the second water layer 130 is smaller than the mesh size of the first water layer 120 for filtering. Line of defense. In some embodiments, the second water gel layer 130 has a mesh size of between 0.01 μm and 1 μm. If the mesh size of the second water-repellent layer 130 is too small, such as less than 0.01 μm, the flux of the composite film 100 is seriously degraded, which greatly affects the efficiency of membrane distillation. If the mesh size of the second water-repellent layer 130 is too large, such as greater than 1 μm, the water mass will pass directly to wet the film pores 116 of the hydrophobic porous film 110.

The thickness of the first water-based layer 120 and the second water-based layer 130 is as thin as possible in the case where the structural strength permits. The thickness of the first water-based layer 120 is between 0.5 μm and 5000 μm, and the thickness of the second water-based layer 130 is between 0.01 μm and 1000 μm, depending on the mesh size and material selection.

The material of the first water gel layer 120 and the second water gel layer 130 may be a polysaccharide material, a protein material, a polyvinyl alcohol (PVA), or a polyethylene glycol (PEG). Or a polyethylene oxide (PEO) material, an acrylic material, a polyurethane material, a cellulose material, a chitin material, an alginic acid material, a modified product thereof, a copolymer or a combination thereof. The former polysaccharide material may be curdlan, agarose or agar. The monomer in the acrylic material may be 2-hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), hydroxyethoxyethyl methacrylate ( Hydroxyethoxyethyl methacrylate, HEEMA), hydroxydiethoxyethyl methacrylate HDEEMA), methoxyethyl methacrylate (MEMA), methoxyethoxyethyl methacrylate (MEEMA), methoxydiethoxyethyl methacrylate Methacrylate, MDMEEMA), ethylene glycol dimethacrylate (EGDMA), N-vinyl-2-pyrrolidone (NVP), isopropyl olefinamide (N- Isopropyl AAm, NIPAAm), acrylic acid (AA), methyl acrylate acid (MAA), N-(2-hydroxypropyl)methacrylamide (N-(2-hydroxypropyl) Methacrylamide (HPMA), ethylene glycol (EG), poly(ethylene glycol) acrylate (PEGA), poly(ethylene glycol) methacrylate (poly(ethylene glycol) Methacrylate, PEGMA), poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), acrylic acid β- --carboxyethyl acrylate, 2-(dimethyl acrylate) Ethyl 2-(dimethylamino)ethyl acrylate, ethylene glycol methyl ether acrylate, 2-ethoxyethyl acrylate, modified product, copolymerization Or a composition thereof.

The material of the hydrophobic porous film 110 may be polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, polyolefin or a combination thereof. The pore size of the membrane pores 116 in the hydrophobic porous membrane 110 is between 0.01 and 5.00 μm. If it is the film hole 116 If the pore diameter is too small, the flux is too small to reduce the filtration efficiency. If the pore diameter of the membrane pores 116 is too large, the membrane pores are easily passed by other liquids or impurities to lower the filtration purity.

Referring to Figure 2, there is shown a graph of flux-conductivity for a different embodiment of the composite membrane of the present invention after a period of operation. The hollow dots in Fig. 2 indicate the membrane flux (corresponding to the ordinate on the left), the solid dots indicate the conductivity measured at the cold end (corresponding to the ordinate on the right), and the horizontal axis indicates the operation time. The hot end wastewater used in Figure 2 is the wastewater discharged from the dyeing and finishing plant. The temperature of the hot end wastewater is about 60 degrees Celsius, the hot end hot water flow rate is about 2 L/min, and the cold end cold water flow rate is about 2 L. /min, the cold end cold water temperature is about 25 degrees Celsius.

In Fig. 2, the comparative example is a film material having no first water-containing rubber layer, that is, the film material of the comparative example contains a hydrophobic porous film and a water-based rubber layer provided on the surface thereof. The material of the hydrophobic porous film of the comparative example was polytetrafluoroethylene, and the pore diameter of the membrane was 0.1 μm. The material of the water-repellent layer of the comparative example was a 10% by weight polyvinyl alcohol (PVA) having a water content of 69.0% and a mesh size of 0.07 μm. The composite film of Experimental Example 1 to Experimental Example 3 comprises a hydrophobic porous film, a first water-based rubber layer, and a second water-based rubber layer therebetween, and the hydrophobic porous film of Experimental Examples 1 to 3 The material was polytetrafluoroethylene and the pore diameter of the membrane was 0.1 μm. The material of the first water gel layer of Experimental Example 1 was a 10% by weight polyvinyl alcohol (PVA) having a water content of 87.8% and a mesh size of 0.3 μm; the material of the second water gel layer of Experimental Example 1 It is a 10% by weight polyvinyl alcohol (PVA) having a water content of 69.0% and a mesh size of 0.07 μm. The material of the first water gel layer of Experimental Example 2 was 7% by weight of polyvinyl alcohol (PVA), the water content was 90.2%, and the mesh size was 0.5 μm; the material of the second water gel layer of Experimental Example 2 It is a 10% by weight polyvinyl alcohol (PVA) having a water content of 69.0% and a mesh size of 0.07 μm. The material of the first water gel layer of Experimental Example 3 was a weight percent concentration of 5% polyvinyl alcohol (PVA) having a water content of 92.8% and a mesh size of 0.7 μm. The material of the second water gel layer of Experimental Example 3 It is a 10% by weight polyvinyl alcohol (PVA) having a water content of 69.0% and a mesh size of 0.07 μm.

It can be seen from the experimental results that no significant change in the conductivity measured at the cold end of either the comparative example or the experimental example after the operation time of 24 hours. This means that after 24 hours of operation, the pores of the hydrophobic porous membrane are not wetted, reflecting that the addition of a water-based gel layer on the hydrophobic porous membrane can indeed solve the problem that the pores of the membrane are wetted by interfacial active particles. The problem. However, it can be known from the experimental results that as the operation time becomes longer and longer, the membrane having only one layer of water gel layer (ie, the comparative example) has a marked decrease in flux, which may be related to the liquid layer to be filtered. The pollutants are blocked. On the contrary, the use of two composite membranes of water gel layers having different water contents (ie, Experimental Example 1 to Experimental Example 3) showed a lower degree of flux decline than the comparative example. As the water content of the first water gel layer was increased to 90% or more (Experimental Example 2 and Example 3), the effect of maintaining flux was more remarkable (especially Experimental Example 3). Therefore, adding a layer of water-containing glue layer with a higher water content to the hydrophobic porous film and the water-based rubber layer can solve the problem that the oil in the waste water or the clogging of the dirty particle clusters causes the flux to drop, and further Extend the operational life of the composite membrane for membrane distillation. In addition, the operational life of the composite membrane can be more effectively extended as the moisture content of the applied water-based layer is higher.

In summary, the composite film contains a two-water gel layer having different water contents to capture the interface active particles (cluster), and the hydrophobic porous film is prevented from being wetted by the interface active particles (cluster). The composite film contacts the hot end with a water gel layer with a higher water content. The waste water is deposited on the composite membrane so that the oil in the waste water is not easily adhered to prevent the composite membrane from being clogging, thereby reducing the flux, thereby effectively prolonging the operational life of the composite membrane.

Although the present invention has been described above in terms of a preferred embodiment, it is not intended to limit the invention, and it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧Composite film

110‧‧‧hydrophobic porous membrane

112‧‧‧ first surface

114‧‧‧ second surface

116‧‧‧ film hole

120‧‧‧First water layer

130‧‧‧Second water layer

200‧‧‧ hot end

210‧‧‧ Wastewater

212‧‧‧ oil stains

220‧‧‧Interfacial active particles (group)

222‧‧‧Hydrophilic end

224‧‧‧Live end

300‧‧‧ cold end

Claims (10)

A composite membrane for membrane distillation, comprising: a hydrophobic porous membrane comprising opposing first and second surfaces, wherein the first surface corresponds to a hot end of membrane distillation, and the second surface corresponds to membrane distillation a cold water layer; a first water gel layer; and a second water gel layer connecting the first water gel layer and the first surface of the hydrophobic porous film, wherein a moisture content of the second water gel layer Between 50% and 90%, and the water content of the first water layer is greater than the water content of the second water layer, wherein the water content is defined as follows: Where Ws represents the weight of the water layer after wetting, and Wd represents the weight of the water layer after drying. The composite film of claim 1, wherein the first water-based layer has a water content of from 90% to 98%. The composite film of claim 1, wherein the first water-based layer has a mesh size of between 0.2 μm and 10 μm. The composite film of claim 1, wherein the second water-based layer has a mesh size of between 0.01 μm and 1 μm. The composite film of claim 1, wherein the first water-based layer has a thickness of between 0.5 μm and 5000 μm. The composite film of claim 1, wherein the second water-based layer has a thickness of between 0.01 μm and 1000 μm. The composite film according to claim 1, wherein the material of the first water layer and the second water layer comprises a protein material, a polyvinyl alcohol (PVA), a polyethylene glycol system. Polyethylene glycol (PEG) or polyethylene oxide (PEO), acrylic materials, polyurethane materials, cellulose materials, chitin materials, alginic acid materials and their modified materials, copolymers Or a composition thereof. The composite film of claim 1, wherein the material of the first water gel layer and the second water gel layer comprises curdlan, agarose or agar. The composite film according to claim 7, wherein the monomer in the acrylic material is 2-hydroxyethyl acrylate (HEA) or hydroxyethyl methacrylate (HEMA). , hydroxyethoxyethyl methacrylate (HEEMA), hydroxydiethoxyethyl methacrylate Methacrylate,HDEEMA), methoxyethyl methacrylate (MEMA), methoxyethoxyethyl methacrylate (MEEMA), methoxydiethoxyethyl methacrylate (methoxydiethoxyethyl methacrylate, MDMEEMA), ethylene glycol dimethacrylate (EGDMA), N-vinyl-2-pyrrolidone (NVP), isopropyl olefinamide ( N-isopropyl AAm, NIPAAm), acrylic acid (AA), methyl acrylate acid (MAA), N-(2-hydroxypropyl)methacrylamide (N-(2-) Hydroxypropyl)methacrylamide, HPMA), ethylene glycol (EG), poly(ethylene glycol) acrylate (PEGA), poly(ethylene glycol) methacrylate (poly(ethylene) Glycol) methacrylate, PEGMA), poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), acrylic acid --carboxyethyl acrylate, β 2-(dimethylamino)ethyl acrylate, ethylene glycol methyl ether acrylate, 2-ethoxyethyl acrylate And its modified materials, copolymers or combinations thereof. The composite membrane of claim 1, wherein the hydrophobicity The material of the porous membrane comprises polytetrafluoroethylene, polypropylene, polyvinylidene fluoride or a combination thereof.