Water filter and manufacturing method thereof

Abstract

A method of making a water filter comprising: preparing a solution comprising a polymer, an adsorbent, and a first solvent, the polymer being soluble in the first solvent; casting the solution onto a substrate to form a thin film; dissolving the first solvent in a second solvent to precipitate a polymer from the solution; removing the film from the substrate; and winding the film to form a cylindrical filter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 493,367, filed on March 31, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to water filters and methods of making water filters. Background Art

[0004] Water filters constructed using activated carbon can remove unwanted chemicals, such as disinfection byproducts, from drinking water. A common type of such filter is made by enclosing granular activated carbon (GAC) in a container. While cost-effective, such filters typically have low performance and must be large or replaced frequently. Another type of such filter is a carbon block filter, which is made by extruding or compression-molding GAC with a binder. This carbon block filter performs slightly better, but has increased cost and an undesirable high pressure drop. Therefore, there is still room for improvement. Summary of the Invention

[0005] In one embodiment, a method for preparing a water filter includes: preparing a solution comprising a polymer, an adsorbent, and a first solvent, wherein the polymer is soluble in the first solvent; casting the solution onto a substrate to form a film; dissolving the first solvent in a second solvent to precipitate the polymer from the solution; removing the film from the substrate; and winding the film to form a cylindrical filter.

[0006] In another embodiment, a water filter comprises a cylindrical inner surface, a cylindrical outer surface, and a filter body positioned between the cylindrical inner surface and the cylindrical outer surface, the filter body consisting essentially of a polymer-bound adsorbent, wherein at least 70% by weight of the adsorbent is powdered activated carbon (PAC) having a particle size <180 μm.

[0007] Other features and aspects of the disclosure will become apparent by consideration of the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a flow chart illustrating in detail a method of manufacturing a water filter.

[0009] Figure 2 is a schematic diagram of a manufacturing apparatus for manufacturing a water filter according to one embodiment.

[0010] Figure 3 is a schematic diagram of another manufacturing apparatus for manufacturing a water filter according to the first embodiment.

[0011] Figure 4 is a cross-sectional view of a layer of a water filter prior to polishing via Figure 3

[0012] Figure 5 is a cross-sectional view of a layer of a water filter after polishing via Figure 3

[0013] Figure 6 is a schematic view of another manufacturing apparatus for polishing a membrane of a water filter.

[0014] Figure 7 A shows a water filter formed via the method of Figure 1

[0015] Figure 7 B shows a zoomed-in view of a portion of the water filter of A. Figure 7

[0016] Figure 8 is a schematic view of a manufacturing apparatus for manufacturing a water filter according to another embodiment.

[0017] Figure 9 is a cross-section of a first membrane having a sorbent.

[0018] Figure 10 is a cross-section of a second membrane having a sorbent. DETAILED DESCRIPTION

[0019] Before any embodiments of the present disclosure are explained in detail, it is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The present disclosure is capable of other implementations and is capable of being practiced or being carried out in various ways.

[0020] Figure 1 A method for manufacturing a water filter 110, such as an activated carbon filter, is shown. As a non-limiting example, activated carbon filters can be used for water treatment to remove free chlorine, organic materials, and other contaminants from water passing through the filter. Some examples of activated carbon filters include granular activated carbon filters, carbon block filters, and activated carbon fiber filters. The methods and manufacturing apparatuses shown and described herein relate to the manufacture of activated carbon filters, such as carbon block filters, and result in a resulting filter 110 having increased filter porosity, which results in increased flow and improved efficiency of contaminant removal by increasing the surface area of the activated carbon in the filter 110. Additionally, the methods and manufacturing apparatuses 200 can be used to manufacture carbon filters 110 having different shapes, including flat sheet filters and pleated filters.

[0021] ​​​​The manufacturing method includes manufacturing a high-density activated carbon membrane (HDACM) 114 (as shown in Figure 2 and further includes a process of forming a cylindrical carbon block filter 110 from the HDACM 114 (as shown in Figure 3 The flowchart of Figure 1 detailed method steps 100-108 associated with the manufacturing process. In a first method step 100 of forming the membrane 114, a polymer is dissolved in an organic solvent. The first solvent can be N,N-dimethylformamide, chloroform, dimethylacetamide, or N-methyl-2-pyrrolidone. The polymer can be a polysulfone, polystyrene, polyethersulfone, polyvinylidene fluoride, or polyvinyl chloride.

[0022] Further, in the first method step 100, an adsorbent is added to the polymer and organic solvent mixture, thereby forming an activated carbon solution 118. The ratio of adsorbent to polymer (e.g., by weight) is at least 4:1, and in some embodiments can be at least 85% adsorbent (to 15% polymer). In one embodiment, the adsorbent is activated carbon. In other embodiments, the adsorbent can be activated alumina, zeolite, ion exchange resin, or a mixture of activated carbon and one or more of activated alumina, zeolite, and ion exchange resin. The activated carbon (or other adsorbent) is used to remove contaminants within the membrane 114 for water purification, and different adsorbents can be selected to remove specific contaminants. The activated carbon is preferably a powdered activated carbon (PAC) having a particle size of less than 180 microns. In contrast, conventional carbon block filters produced by manufacturing methods such as extrusion and compression molding use granular activated carbon (GAC) having a particle size of greater than 200 microns. In some embodiments, some (e.g., 5-10%) of the adsorbent can be replaced by activated carbon fibers (or another fiber) having a length of 2-10 millimeters to increase the flexibility of the membrane 114.

[0023] Within the activated carbon solution 118 produced in the method step 100, the polymer is provided to adhere the adsorbent together in the final water filter 110, the organic solvent is used to dissolve the polymer and provide fluidity to the solution, and the adsorbent provides the water purification function of the final water filter 110 produced via the manufacturing method. The activated carbon solution 118 is provided at a temperature of 20-80 °C and is provided to the manufacturing apparatus 200 as shown in Figure 2 as shown in Figure 2As shown, the manufacturing apparatus 200 includes a substrate 122 that extends from a first end 208 of the manufacturing apparatus 200 to a second end 212 of the manufacturing apparatus 200 and is configured to transfer the activated carbon solution 118 from the first end 208 to the second end 212. As shown, the substrate 122 (e.g., on a roll) is disposed at the first end 208 of the manufacturing apparatus 200, and a container 216 containing the activated carbon solution 118 is also disposed at the first end 208 of the manufacturing apparatus 200. The substrate 122 is provided as a thin sheet (e.g., having a thickness of 50-1000 microns) of non-woven fiber, warp knit fabric, or filter paper made of, for example, polyethylene terephthalate (PET), polypropylene (PP), or polyethylene (PE). The free end of the sheet is attached to a motorized reel 232 at the second end 212 so that the substrate 122 can be pulled from the roll at the first end 208 to the roll at the second end 212.

[0024] In method step 101 ( Figure 1 ), the activated carbon solution 118 is provided to the substrate 122 at the first end 208 of the manufacturing apparatus 200. In some embodiments, the activated carbon solution 118 is poured onto the substrate 122 via a casting operation. As the substrate 122 and the activated carbon solution 118 move from the first end 208 of the manufacturing apparatus 200 toward the second end 212 of the manufacturing apparatus 200, a film applicator 220 (e.g., a casting blade) provides a uniform thin film of the mixture solution 118 onto the substrate 122. In some embodiments, the casting thickness (i.e., the distance between the film applicator 220 and the substrate 122) is 300-4000 microns, wherein the thickness of the resulting thin film of the activated carbon solution 118 is 300-2000 microns.

[0025] like Figure 2 As shown, the manufacturing apparatus 200 includes a bath 224 located between the first end 208 and the second end 212. The bath 224 is a container that holds a solvent 126 (i.e., a second solvent) that is different from the solvent in the activated carbon solution 118 (i.e., the first solvent). In the embodiment shown, the second solvent 126 is water. The bath 224 is a water bath set at 5°C to 60°C and is configured to remove the organic solvent from the activated carbon solution 118 (on the substrate 122) as the activated carbon solution 118 passes through the bath 224. In method step 102 ( Figure 1 ), the first solvent is dissolved by moving the activated carbon solution 118 and the substrate 122 through the bath 224. Figure 2 As shown, the activated carbon solution 118 and substrate 122 pass through a bath 224 such that the substrate 122 and activated carbon solution 118 are immersed in a solvent 126 (water) within the bath 224. The first solvent is dissolved in the bath 224 to precipitate the polymer from the solution 118, causing the polymer within the film to coagulate, thereby adhering the activated carbon together and forming a high-density activated carbon membrane 114 (HDACM).

[0026] like Figure 2 As shown, the manufacturing apparatus 200 includes an oven 228 located between the bath 224 and the second end 212 of the apparatus 200 (i.e., downstream of the bath 224). The substrate 122 passes through the oven 228, causing the HDACM 114 on the substrate 122 to pass through the oven 228. In method step 103 ( Figure 1 ), the HDACM 114 is passed through an oven 228, thereby drying. The oven 228 is set at a temperature higher than ambient temperature, to absorb moisture from the HDACM (after passing through the bath 224 from the residual solvent 126 on the HDACM 114). Once dry, the substrate 122 and the HDACM 114 advance to the reel 232 at the second end 212 of the manufacturing equipment 200. In method step 104, the HDACM 114 and the substrate 122 are wound onto the reel 232, spirally wound around the reel 232. In some embodiments, the method step 103 of the dry HDACM 114 and the use of the oven 228 are omitted.

[0027] The roll of HDACM 114 and substrate 122 is removed from the fabrication facility 200 and moved to another fabrication facility 240, such as Figure 3 The HDACM 114 and the substrate 122 mounted at the first end 244 of the apparatus 240 are mounted in step 105 ( Figure 1 ) is unfolded. The polishing system 256 is introduced into the apparatus 240 between the first end 244 and the second end 252. In method step 106, the HDACM 114 is polished via the polishing system 256. In some embodiments, the polishing system 256 includes a polishing roller 260 and a blower 264, such as Figure 6 As shown in more detail in .

[0028] like Figure 4As shown, the HDACM 114 has an upper surface 130 (i.e., the surface opposite the substrate) that has 0.1-0.5 micron pores that are composed of a polymer and are created from a polymer that has a lower density than the density of the sorbent. Such pores have a size through which water can pass, and larger particles (i.e., particles larger than 0.1-0.5 microns) will be blocked by the membrane 114. However, the relatively small pore size limits the rate of water flow through the membrane 114, which will result in a high pressure drop in the water filter 110 due to the many rolled-up layers of the HDACM 114. The polishing process eliminates the upper surface 130 of the HDACM 114, causing an increase in the water flow rate through the membrane 114. The upper surface 130 of the membrane 114 is polished by a polishing roller 260, where the polishing roller 260 is rotated as the HDACM 114 passes over the roller 260. More specifically, the polishing roller 260 is counter-rotated relative to the membrane 114 (i.e., as the polishing roller 260 rotates clockwise above the membrane 114, the membrane 114 moves to the right Figure 4 The polishing roller 260 can have a contact surface 268 (for contacting the upper surface 130 of the HDACM 114) formed from 500-2000 grit sandpaper or equivalent surface roughness. The relative speed of the polishing roller 260 and the HDACM 114 (i.e., the difference between the speed of the outer surface of the roller 260 and the speed of the HDACM 114) is 2-20 cm / s.

[0029] A blower 264 is installed downstream of the roller 260 (i.e., between the roller 260 and the second end 252 of the apparatus 240) and blows air or water onto the HDACM 114 to remove polishing powder / debris from the polished upper surface 134 of the HDACM 114. The resulting polished upper surface 134 Figure 5 ) has a reduced density relative to the unpolished upper surface 130 Figure 4 ) such that water can more freely pass through the membrane 114. The thickness of the HDACM 114 after polishing is reduced by less than 50 microns (e.g., 5-50 microns), while the flux of the HDACM 114 is increased by more than 100% relative to the unpolished HDACM 114. In some embodiments, the final thickness of the HDACM 114 (without the substrate 122) is 300 microns to 2000 microns (e.g., 300 microns to 1000 microns, 400 microns to 1000 microns). In some embodiments, the final thickness is at least 400 microns to limit tearing of the HDACM 114.

[0030] The polishing roller 260 can be lifted or otherwise moved away from the HDACM 114 to pause the polishing process at a specified time. Thus, in some embodiments, the rolled carbon block filter 110 can be constructed as a partially polished filter. For example, in some embodiments, the polishing step is omitted on the water inlet side of the rolled membrane 114 (e.g., outer layer 138) to maintain a top surface with small pores on the outer layer 138, thereby more effectively removing particles and bacteria without applying a significant additional pressure drop through the filter. In the same embodiment, the remainder of the filter body, including the water outlet side (e.g., inner layer 142), is polished to minimize the pressure drop across the filter 110. The number of unpolished layers can vary based on the bacterial removal requirements, with higher requirements being associated with more unpolished layers. In other embodiments where the direction of water flow through the rolled carbon block filter 110 is radially outward, the unpolished layer can alternatively be provided on the innermost layer.

[0031] In some embodiments, the HDACM 114 is removed from the substrate 122 and / or polished before the substrate 122 is wound, so that the winding and unwinding (method steps 104 and 105) are omitted. Figure 2 and Figure 3 The manufacturing equipment 200, 240 in FIG. 5 is a single manufacturing equipment, while in other embodiments, the manufacturing equipment 200, 240 may be separate (eg, spaced apart) from each other.

[0032] After the polishing step, as in method step 107 ( Figure 1 ), as outlined in Figure 3 As shown, the substrate 122 is separated (e.g., peeled) from the HDACM 114. The manufacturing apparatus 240 includes a first reel 276 for winding the substrate 122 and a second reel 280 for winding the HDACM 114. At the separation point 272, the HDACM 114 is peeled from the substrate 122 as each of the substrate 122 and the HDACM 114 is wound around their respective reels 276, 280. Method step 108 includes winding the filter 110, which includes winding (i.e., spirally winding) the HDACM 114 around the reel 280 to form the final filter 110 as a rolled carbon block filter.

[0033] Figure 7 A-7B shows the Figure 11. A filter 110 is formed by the method shown in . As shown, the filter 110 comprises a cylindrical inner surface 142 having a first diameter and a cylindrical outer surface 138 having a second diameter greater than the first diameter. A filter body 150 formed by a thin spirally wound HDACM 114 is formed between the cylindrical inner surface 142 and the cylindrical outer surface 138. The filter body 150 includes an adsorbent bound by a polymer, wherein at least 70% (by weight) of the adsorbent is powdered activated carbon with a median particle size of less than 180 microns. In some embodiments, the median particle size of the powdered activated carbon is less than 100 microns or less than 50 microns. In some embodiments, the filter body 150 has a porosity of 3-15% by volume. The thickness of each spirally wound layer of the filter 110 is 300 microns to 2000 microns (400 microns to 1000 microns in some embodiments) and has a particle size of 50-1000 g / m 2 (e.g. at least 200 g / m 2 , at least 250 g / m 2 ) carbon loading. In some embodiments, the water inlet side of the filter 110 (which may be at the cylindrical inner surface 142 or the cylindrical outer surface 138) is unpolished, such that the pore size at the water inlet side is 0.05-0.5 microns. The water outlet side of the filter at the other of the cylindrical inner surface 142 or the outer surface 138 (opposite the water inlet side) is polished, such that the pore size is larger than that of the water inlet side.

[0034] pass Figures 1 to 6 The method described in detail Figure 7 The water filter 110 shown in A-7B has been shown through testing to have a performance level of 6 mg / g (6 mg of chloroform adsorbed onto the filter 110 per gram of adsorbent (e.g., carbon). Conventional carbon block filters (e.g., those manufactured by extrusion and compression molding) have a chloroform adsorption capacity of only about 3 mg / g (3 mg of chloroform adsorbed per gram of adsorbent). Thus, the filter 110 and the method of making the filter 110 provide significant performance improvements over those formed by conventional methods.

[0035] Figure 8 Shown Figure 2 An alternative manufacturing apparatus 200' is shown in FIG. 200. Apparatus 200' is similar to apparatus 200 except as otherwise described. Figure 2The apparatus shown in FIG. 1 1 1. This apparatus does not include a bath, but rather a shower 224' configured to spray solvent 126 (e.g., water) onto the activated carbon solution 1 18 to perform a similar function as the bath 224. Additionally, since the activated carbon solution 1 18 does not pass through a bath, the substrate 122 can be omitted so that the activated carbon solution 1 18 rests directly on the continuous belt 204. The shower 224' sprays solvent 126 onto the activated carbon solution 1 18 to precipitate the polymer out of the solution 1 18 so that the polymer within the thin film coagulates, thereby adhering the activated carbon together and forming a high density activated carbon membrane 1 14 (HDACM). The HDACM 1 14 is then wound onto a spool 280' without a substrate to form a filter 1 10'. Although not shown in FIG. 1 1 1, a polishing step 106 can be provided after the drying oven 228. Figure 8

[0036] Figure 9 10 Reverse osmosis (RO) membranes 300, 400 are shown having a thin film 304, 404 with adsorbent formed by the method described in Figures 1 to 6 Figure 9 Figure 10 Figure 9 The thin film 304 is shown as a support layer. Figure 10 The thin film 404 is shown on the back of the support layer 408 in addition to a conventional porous layer 416 between the active layer 412 and the support layer 408.

[0037] Membranes such as reverse osmosis (RO) / nanofiltration (NF) and RO / NF / ultrafiltration (UF) membranes are used to remove various contaminants from water because these membranes are more environmentally friendly to use than other conventional water treatment methods. Such contaminants include salts and / or volatile organic compounds (VOCs). RO / NF membranes are typically thin film composite (TFC) membranes and can include three layers: a base fabric layer 308, 408; a porous layer 304, 404, 416; and a top active layer 312, 412 (i.e., a desalination layer). Figure 9 10 The membranes shown in FIGS. 1 1 1 and 1 12 contain adsorbent within the porous layer 304, 404.

[0038] ​​​​​​In particular, the membranes 300, 400 include an active layer 312, 412, a fabric layer 308, 408, and at least one porous layer 304, 404, 416. The porous layer 304, 404 contains at least one type of adsorbent. As noted above with reference to Figures 1 to 8 The adsorbent can be, such as, activated carbon, zeolite, activated alumina, or a mixture of different adsorbents. When the membrane 300, 400 containing activated carbon is exposed to volatile organic compounds (VOCs) in water, the VOCs are adsorbed by the adsorbent in the membrane, thereby being removed from the feed water.

[0039] Various features of the present disclosure are set forth in the claims that follow.

Claims

1. A method of manufacturing a water filter, the method comprising the steps of: formulating a solution comprising a polymer, an adsorbent, and a first solvent, the polymer being soluble in the first solvent; casting the solution onto a substrate to form a thin film; dissolving the first solvent in a second solvent to precipitate the polymer from solution; removing the thin film from the substrate; and winding the thin film to form a cylindrical filter.

2. The method of claim 1, wherein the second solvent is water.

3. The method of claim 1, wherein the weight ratio of the adsorbent to the polymer is at least 4:

1.

4. The method of claim 1, wherein the adsorbent comprises powdered activated carbon (PAC) having a particle size < 180 pm.

5. The method of claim 4, wherein the PAC has an average particle size < 50 pm.

6. The method of claim 1, further comprising the step of drying the thin film to remove the second solvent prior to removing the thin film from the substrate.

7. The method of claim 1, further comprising the step of removing a top layer of at least a portion of the thin film prior to winding the thin film to form a cylindrical filter.

8. The method of claim 7, wherein the removed top layer has a thickness of 5 pm to 50 pm.

9. The method of claim 1, wherein the polymer is selected from the group consisting of a polysulfone, a polystyrene, a polyethersulfone, a polyvinylidene fluoride, and a polyvinyl chloride.

10. The method of claim 1, wherein the first solvent is selected from the group consisting of N,N-dimethylformamide, chloroform, dimethylacetamide, and N-methyl-2-pyrrolidone.

11. A water filter, comprising: a cylindrical inner surface; a cylindrical outer surface; and a filter body between the cylindrical inner surface and the cylindrical outer surface, the filter body consisting essentially of an adsorbent bound by a polymer, wherein at least 70% by weight of the adsorbent is powdered activated carbon (PAC) having a particle size < 180 pm.

12. The water filter of claim 11, wherein the PAC has a median particle size < 100 pm.

13. The water filter of claim 11, wherein the PAC has a median particle size < 50 pm.

14. The water filter of claim 11, wherein the filter body comprises a spirally wound thin film.

15. The water filter of claim 14, wherein the spirally wound thin film has a thickness of 300 pm to 2000 pm.

16. The water filter of claim 14, wherein the spirally wound thin film has a thickness of 400 pm to 1000 pm.

18. The water filter of claim 11, wherein at least one of the cylindrical inner surface and the cylindrical outer surface comprises a filtration layer having a pore size of 0.05 pm to 0.5 pm.

17. The water filter of claim 14, wherein the spiral wound membrane has a carbon loading of at least 200 g / m 2 .

19. The water filter of claim 11, wherein the water filter has a chloroform adsorption capacity of at least 6 mg per gram of adsorbent. ​ 20. The water filter of claim 11, wherein the filter body has a porosity of 3-15 volume percent.

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