Silica Adsorbent

Abstract

To provide a method for efficiently removing silica in a solution.SOLUTION: The present invention discloses new applications based on the silica adsorbing action of cerium hydroxide, wherein one embodiment of the present invention is a silica adsorbent containing cerium hydroxide; and other embodiments involve a silica adsorbent filter and a method for producing the same, a method for removing silica, a method for preventing the occurrence of silica scale in a channel, and a silica remover having the silica adsorbent filter.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an adsorbent that selectively removes silica from a solution. [Background technology]

[0002] The adhesion and accumulation of scale (limescale) is a problem in water circulation systems such as the chilled water systems and cooling water systems of air conditioning equipment, boiler water supply systems, plant cooling water systems, hot spring facilities, etc. If scale adheres and accumulates on piping, it can clog the circulation system, and if it adheres and accumulates on the electric heating surfaces of a heat exchanger, it can cause a decrease in heat exchange efficiency. One of the main causes of scale is silica (silicon dioxide) ions in water, and there is a demand for efficient removal of these ions (Patent Document 1, etc.). Conventionally, methods for removing silica from a solution include ion exchange resins, reverse osmosis membranes, coagulation sedimentation, electrodialysis (EDI), and electrolysis. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2009-541036 Summary of the Invention [Problem to be solved by the invention]

[0004] When removing silica using ion exchange resin, it is usually not efficient because the silica adsorption capacity of ion exchange resin is small. Also, when the ion exchange resin becomes saturated with silica, silica leakage occurs. Therefore, when the silica concentration in the target solution is high, the ion exchange resin needs to be replaced more frequently. In addition, when removing silica using a reverse osmosis membrane, it is difficult to increase the concentration ratio in order to prevent silica fouling. Therefore, when the silica concentration in the target solution is high, the ratio of the treated water obtained to the raw water becomes small, which is not efficient.

[0005] In view of the above circumstances, an object of the present invention is to provide a method for efficiently removing silica from a solution. [Means for solving the problem]

[0006] As a result of intensive research aimed at solving the above problems, the inventors discovered that cerium hydroxide selectively adsorbs silicate ions in a solution, but does not adsorb other ions. This led to the idea that cerium hydroxide could be used as a silica adsorbent, and thus completed the present invention. That is, one aspect of the present invention is a silica adsorbent containing cerium hydroxide. Another aspect is a silica adsorbent filter medium comprising a substrate and the silica adsorbent immobilized on the substrate. Another embodiment is a method for producing a silica adsorbent filter medium, comprising the step of immobilizing the silica adsorbent on a substrate. Another aspect is a method for removing silica from a silica-containing solution, comprising the step of contacting the solution with the adsorbent or the adsorptive filter medium. Another embodiment is a method for preventing the formation of silica scale in a flow passage, comprising removing silica from water flowing through the flow passage by the method of the previous embodiment. Another embodiment is a silica removal device comprising the silica adsorption filter medium. Effect of the Invention

[0007] According to the present invention, silica in a solution can be efficiently removed. Silica is removed by adsorption to an adsorbent containing cerium hydroxide, so it can be easily performed by contacting the solution with the adsorbent, and no large-scale equipment is required. In addition, cerium hydroxide selectively adsorbs silica (silicic acid ions) and does not adsorb other ions normally contained in the target solution, such as sodium ions, magnesium ions, and calcium ions, so the impact of the solution on the system after silica removal is suppressed. [Brief description of the drawings]

[0008] [Figure 1]The silica removing material of the present invention may be installed at any position in the air conditioning system, not limited to the position shown in the figure. [Diagram 2] FIG. 2 is a diagram showing an embodiment in which the silica removing material of the present invention is used for pretreatment of an ion exchange resin. [Diagram 3] FIG. 2 is a diagram showing an embodiment in which the silica removing material of the present invention is used for pretreatment of a reverse osmosis membrane. [Figure 4] FIG. 1 is a diagram showing an embodiment in which the silica removing material of the present invention is used for treating boiler water, hot spring water, geothermal power generation water, etc. [Diagram 5] 2 is a graph showing the silica concentration remaining in tap water after adsorption treatment in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes embodiments of the present invention. The following embodiments are merely examples of the present invention, and the technical scope of the present invention is not limited to the following embodiments.

[0010] <1> Silica Adsorbent The silica adsorbent of the present invention essentially contains cerium hydroxide (Ce(OH)4) as an active ingredient. Cerium hydroxide is usually available in the form of a powder, with particle sizes ranging from about 0.05 μm to 100 μm, and a cumulative median diameter of preferably 0.5 μm to 20 μm. The content of cerium hydroxide in the adsorbent of the present invention is not particularly limited, and can be adjusted arbitrarily within the range of 0.001 to 99.9% by weight. The purity of the cerium hydroxide in the adsorbent of the present invention is preferably 85% by weight or more, and more preferably 90% by weight or more.

[0011] The silica adsorbent of the present invention adsorbs silica in the form of silicate ions in a solution, usually an aqueous solution. Although the term "adsorption" in the present invention is not particularly limited, it usually means adsorbing 11.5 mg or more of silica per 1 g of cerium hydroxide. Furthermore, the silica adsorbent of the present invention does not adsorb other ions such as sodium ions, magnesium ions, calcium ions, etc., and specifically, the adsorption amount is 0.001 mg or less per 1 g of cerium hydroxide. Therefore, the silica adsorbent of the present invention is capable of selectively adsorbing and removing silica from a solution.

[0012] The adsorbent of the present invention may contain other components as long as the effect of the present invention is not impaired. Examples of other components include adsorbents of other components such as activated carbon and diatomaceous earth, binders for forming the adsorbent, antibacterial agents, etc. Examples of binders include inorganic binders such as silica sol and alumina sol, and polymer resins with high hydrophobicity and low reactivity. Examples of polymer resins with high hydrophobicity and low reactivity include polyolefin, nylon, polyethylene terephthalate, polyvinyl chloride, and polyvinylidene chloride.

[0013] <2> Silica adsorption filter material and its manufacturing method The silica adsorbent of the present invention can be contained in the silica adsorbent filter medium in a form immobilized on a substrate. Since cerium hydroxide is usually distributed in the form of powder, when it is immobilized on a substrate, This makes handling and silica removal easier. The shape of the filter material is not particularly limited, but from the viewpoint of the efficiency of the method for removing silica described below, the filter material is usually in a shape suitable for passing a solution therethrough and suitable for installation in a flow path. As such a form, for example, a column packing material or a filter, which can increase the contact area with the solution containing silica, is preferable from the viewpoint of the efficiency of the adsorption reaction.

[0014] More specifically, examples of the method include immobilizing cerium hydroxide on a substrate and filling a container such as a column, and filling a pocket formed by multiple sheets of nonwoven fabric with cerium hydroxide to form a filter structure.

[0015] The cerium hydroxide may be immobilized on the substrate by covalent or non-covalent bonding. For example, the substrate may be a polymer or inorganic material that can be processed into an adsorption filter material, a chromatography carrier, a filter paper, a membrane, a filter, a hollow fiber, a fiber, a nanofiber, etc., which are already known as substrates. More specifically, the substrate may be a polysaccharide such as cellulose, agarose, starch, amylose, dextran, pullulan, glucomannan, etc.; a synthetic polymer such as polyacrylic acid or its derivatives, polyvinyl alcohol, nylon, polysulfone, polyacrylnitrile, polyethylene, polypropylene, polystyrene, etc.; an inorganic material such as glass, porous glass, silica gel, hydroxyapatite, etc.; a porous piece having pores such as activated carbon or zeolite; an inorganic binder such as silica sol or alumina sol; etc. In addition, the substrate may be one type of substrate, or two or more types of substrates may be used in combination.

[0016] The shape of the substrate is preferably a porous body from the viewpoint of contact with and liquid passage through a silica-containing solution, and more preferably includes filter paper, a membrane, a filter, a hollow fiber, a fiber, a nanofiber, a granular shape, a powder shape, and the like. Of these, porous fiber is particularly preferred. The specific surface area of ​​the substrate is 100 to 300 m from the viewpoint of contact with and passage of the silica-containing solution. 2 It is preferable that the molecular weight is 1 / g.

[0017] The silica adsorbent of the present invention can be immobilized on these substrates to produce the silica adsorbent filter medium of the present invention. The immobilization of cerium hydroxide on the substrate can be carried out by any method. For example, there is a method in which cerium hydroxide is precipitated on a substrate by adding an oxidizing agent to an aqueous cerium solution. Another method is to mix cerium hydroxide powder with a binder or the like and solidify it into granular pellets. In this case, the specific surface area of ​​the pellets is set to 100 to 300 m from the viewpoint of contact with and passage of a solution containing silica. 2 The pellet shape is not particularly limited and may be spherical, discoid, crushed, or the like.

[0018] <3> Silica Removal Equipment The adsorptive filter medium of the present invention can be provided in a silica removal device, which can be preferably used to carry out the silica removal method of the present invention described below. In addition to the silica adsorbent filter medium, the device typically includes a flow path for the solution. The mode of use of the device is not particularly limited as long as it is applied to anything that requires the removal of silica from a solution. Examples of the device include devices installed in water circulation systems such as cold water systems or cooling water systems in air conditioning equipment, water supply systems in boilers, cooling water systems in plants, and hot spring facilities.

[0019] <4> How to Remove Silica A step of contacting a silica-containing solution with the silica adsorbent or silica adsorbent filter medium of the present invention is carried out. This makes it possible to remove silica from the solution. The solution is usually an aqueous solution, and the silica is usually contained as silicate ions.

[0020] The pH of the silica-containing solution is preferably from 4 to 9, more preferably from 6 to 7.5. Furthermore, the temperature of the silica-containing solution when the step of contacting the silica-containing solution with the silica adsorbent or silica-adsorbing filter medium is carried out is not particularly limited, and the step can be carried out at any temperature. Furthermore, the time for which the silica-containing solution is brought into contact with the silica adsorbent or silica-adsorbing filter medium is not particularly limited, and may be any time.

[0021] In the step of contacting the silica-containing solution with the silica adsorbent or silica adsorbent filter medium, in order to carry out this step efficiently, it is also preferable to circulate the silica-containing solution in the vicinity of the adsorbent or adsorbent filter medium of the present invention.

[0022] <5> Silica removal application Several application forms of the present invention will be described below, but the present invention is not limited to these.

[0023] The above-mentioned method for removing silica of the present invention can be preferably applied to water flowing through a flow path, thereby making it possible to prevent the formation of silica scale in the flow path. Here, the flow path is not particularly limited, but usually refers to piping through which water flows in a water circulation system such as a cold water system or cooling water system of an air conditioning system, a water supply system of a boiler, a cooling water system of a plant, a hot spring facility, etc. Furthermore, devices, equipment, parts, etc. that come into contact with water in a water circulation system may also be included in the flow path. Here, prevention of silica scale formation includes not only no silica scale formation at all, but also a reduction in the amount of silica scale and a delay in its formation compared to the case where silica removal is not performed.

[0024] Figure 1 shows the use of silica removal in air conditioning piping systems. Air conditioning facilities include a chilled water system, which is a water circulation system that circulates between the chiller and the air conditioner (AHU, FCU, etc.) to carry cold energy, and a cooling water system, which is a water circulation system that circulates between the chiller installed in the machine room inside the building and the cooling tower installed outdoors, and there is a high demand for silica removal. As shown in Figure 1, silica may be removed directly from the makeup water, or a part of the system may be branched off to remove silica. If the silica adsorption filter medium is porous, a branched flow path from the system may be provided for the silica removal filter medium, which may function as a dust removal device in the solution. A similar usage pattern can be adopted in the production cooling water system.

[0025] Figure 2 shows a form of use as a pretreatment for ion exchange resin. When the ion exchange resin becomes saturated with silica, silica leakage occurs. Therefore, it is preferable to remove silica from the aqueous solution before applying it to the ion exchange resin. This can extend the life of the ion exchange resin.

[0026] Figure 3 shows a use form as a pretreatment for reverse osmosis membranes (RO membranes). In reverse osmosis membranes, silica may precipitate during concentration, causing clogging. To prevent clogging, it is necessary to operate the system at a low concentration ratio, which requires a large amount of concentrated water to be discharged, resulting in inefficiency. For this reason, it is preferable to remove silica from the aqueous solution before applying it to the reverse osmosis membrane. This makes it difficult for the membrane to become clogged, and the concentration ratio can be increased, improving treatment efficiency. The silica removal device may be installed in the concentration system in addition to the location shown in the figure.

[0027] Figure 4 shows how water is used in the flow paths for boiler water, hot spring water, geothermal power generation water, etc. By removing silica before the water is passed through each device, it is possible to prevent silica scale from forming in piping, etc. EXAMPLES

[0028] EXAMPLES In the following, examples are shown to specifically explain the present invention, but these examples are merely examples of the present invention and the present invention is not limited to these examples.

[0029] 1 g of sample was added to 100 mL of tap water (collected in Nagaoka City, Niigata Prefecture, pH 6) and shaken in a water bath at 25°C for 24 hours. 2 / g), iron hydroxide III powder (average particle size 1 μm, specific surface area 50 m 2 / g), Or activated alumina fibre (diameter 4mm, specific surface area 150m 2 / g, or 6mm specific surface area 150m 2 / g) was used. The residual silica concentration in the treated tap water was measured using an ICP emission spectrometer (ICPS-7510; Shimadzu Corporation).

[0030] The results are shown in Figure 5. An 85% reduction in silica was observed in tap water with added cerium hydroxide.

Claims

1. A silica adsorbent containing cerium hydroxide, A silica adsorbent used for a silica-containing solution having a pH of 4 to 9 (excluding an embodiment in which it is used for a silica-containing solution having a pH of 9 in the presence of salt).

2. The silica adsorbent described in claim 1, which is used for a silica-containing solution having a pH of 6 to 7.

5.

3. A silica adsorption filter medium comprising a substrate and the adsorbent according to claim 1 immobilized on the substrate, A silica-adsorbing filter material used for a silica-containing solution having a pH of 4 to 9 (excluding an embodiment in which the filter material is used for a silica-containing solution having a pH of 9 in the presence of salt).

4. A silica adsorption filter material as described in claim 3, used for a silica-containing solution having a pH of 6 to 7.

5.

5. A method for producing a silica adsorbent filter medium, comprising the step of immobilizing the adsorbent according to claim 1 on a substrate.

6. A method for removing silica from a solution, comprising a step of contacting the silica-containing solution having a pH of 4 to 9 with the adsorbent according to claim 1 or 2 or the adsorption filter medium according to claim 3 or 4 (excluding an embodiment including a step of contacting with a silica-containing solution having a pH of 9 in the presence of salt).

7. The method of claim 6, wherein the silica-containing solution has a pH of 6 to 7.

5.

8. The method according to claim 6 or 7, wherein silica is removed from water flowing through a flow path. The method for preventing the formation of silica scale in the flow path comprises:

9. A silica removal device comprising the silica adsorption filter material according to claim 3 or 4, The apparatus is used for a silica-containing solution having a pH of 4 to 9 (excluding an embodiment in which the apparatus is used for a silica-containing solution having a pH of 9 in the presence of salt).

10. The apparatus of claim 9, used for a silica-containing solution having a pH of 6 to 7.5.

Images