JP2013202215A - Air cleaner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air cleaner using a photocatalyst filter having a large area of a photocatalyst to be irradiated with light and a high air cleaning performance, capable of removing catalyst poisoning components by washing and maintaining the air cleaning performance for a long period of time even when washing is repeated.SOLUTION: An air cleaner includes a photocatalyst filter composed of planar nonwoven fabric of photocatalyst fibers having titanium oxide on a surface and an ultraviolet ray irradiation means capable of radiating ultraviolet rays, the surface of the planar nonwoven fabric and the longitudinal direction of the ultraviolet ray irradiation means are roughly in parallel, and the flow of air is roughly vertical to the planar nonwoven fabric. In the air cleaner, the photocatalyst fiber is a silica-based composite oxide fiber composed of a composite oxide phase of an oxide phase (first phase) mainly composed of a silica component and a metal oxide phase (second phase) containing titanium, and is the fiber in which the presence ratio of the titanium of the metal oxide configuring the second phase is increased gradually toward the surface layer of the fiber.

Description

  The present invention relates to an air cleaning device for removing VOC (volatile organic compounds) contained in air.

  In order to remove VOC in the air, an air cleaning device using a photocatalyst such as titanium oxide is used. In this method, the photocatalyst such as titanium oxide is irradiated with light to excite the photocatalyst to generate OH radicals having strong oxidizing power, thereby removing VOC by oxidative decomposition.

  Since photocatalysts such as titanium oxide are generally in the form of powder, it is necessary to immobilize them in a filter shape in order to use them in an air cleaning device. For example, Patent Document 1 discloses a photocatalytic filter obtained by coating porous ceramics with titanium oxide.

  Further, in order to maintain the performance of the air cleaning device for a long period of time, it is necessary to remove the catalyst poisoning component adhering to the surface of the photocatalyst. For example, Patent Document 2 discloses a photocatalytic filter disclosed in Patent Document 1. An air cleaning device that can remove catalyst poisoning components by washing with water is shown.

JP 2003-053194 A JP 2005-205094 A

As described above, the principle of air purification using a photocatalyst is that OH radicals generated by irradiating and exciting the photocatalyst oxidize and decompose VOC. However, since the lifetime of the OH radical is as extremely short as 10 ⁻⁶ seconds, the OH radical exists only on the photocatalyst irradiated with light. Therefore, in order to exhibit the air cleaning performance, it is necessary to increase the area of the photocatalyst irradiated with light.

  Further, in order for the photocatalyst to maintain the air cleaning performance for a long time, it is necessary that the photocatalyst can recover its initial performance by removing the catalyst poisoning component by washing or the like.

  However, the photocatalytic filter described in Patent Document 1 is a porous ceramic base material coated with a photocatalyst, and since light is not actually irradiated into the pores, the substantial light irradiation area is small and sufficient air is sufficient. The cleaning performance cannot be demonstrated.

  In addition, because the photocatalyst is coated on the ceramic substrate, the photocatalyst filter gradually becomes more photocatalytic performance because the photocatalyst peels off from the ceramic substrate when washing with water to remove the catalyst poisoning component is repeated. Will be reduced.

  The present invention has been made in view of the above problems, and it is possible to remove catalyst poisoning components by washing with water, maintaining air cleaning performance for a long period of time even if washing with water is repeated, and An object of the present invention is to provide an air cleaning device using a photocatalytic filter having a large area of photocatalyst irradiated with light and high air cleaning performance.

  In order to achieve the above object, the present inventors have conducted extensive research, and as a result, a photocatalytic filter comprising a flat nonwoven fabric of a specific photocatalytic fiber, and an ultraviolet irradiation means capable of irradiating ultraviolet rays having a wavelength of 380 nm or less. It has been found that the air purifier comprising the above has a high VOC removal performance, and that the high VOC removal performance can be maintained for a long period of time by repeatedly washing the photocatalytic filter with water.

  That is, the present invention comprises a photocatalytic filter comprising a flat nonwoven fabric of photocatalytic fibers having titanium oxide on the surface, and an ultraviolet irradiation means having a shape extending in the longitudinal direction capable of irradiating ultraviolet rays having a wavelength of 380 nm or less, and the flat plate shape. The surface of the nonwoven fabric and the longitudinal direction of the ultraviolet irradiation means are substantially parallel, and the air flow is substantially perpendicular to the flat nonwoven fabric, wherein the photocatalytic fiber contains a silica component. A silica-based composite oxide fiber comprising a composite oxide phase of a main oxide phase (first phase) and a titanium-containing metal oxide phase (second phase), the metal oxide constituting the second phase The present invention relates to an air purifying apparatus characterized in that the presence ratio of titanium in the product is a fiber in which the proportion of the titanium increases gradually toward the fiber surface layer.

  The photocatalytic fiber is preferably a fiber in which mesopores having an average pore diameter of 2 to 30 nm are formed from the fiber surface toward the inside of the fiber.

  In the mesopores, platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), gold (Au), silver (Ag), copper (Cu), iron (Fe), nickel (Ni) It is more preferable that at least one metal is supported among zinc (Zn), gallium (Ga), germanium (Ge), indium (In), and tin (Sn).

  The present invention also relates to the air cleaning device, wherein the photocatalytic filter is detachable.

  As described above, according to the present invention, the photocatalyst filter having a large area of the photocatalyst irradiated with light, high air cleaning performance and capable of removing catalyst poisoning components by washing with water has high VOC removal performance. It is possible to provide an air cleaning device that can be maintained for a long time.

It is the schematic which shows one Embodiment of the air purifying apparatus of this invention. It is an enlarged view of the photocatalyst filter of this invention. It is a conceptual diagram which shows the desorption method of a photocatalyst filter.

  Although an embodiment of an air cleaning device concerning the present invention is described in detail using a drawing, the present invention is not limited to this embodiment.

  As shown in FIG. 1, the air purifying apparatus according to the present invention includes a casing 1 having an inflow port 5 formed on the top surface from an inflow port 5 formed on the bottom surface, and a casing 1 that is accommodated in the casing 1, and the air flow. Three photocatalytic filters 2 installed parallel to each other so that the surfaces intersect perpendicularly with respect to the direction, and between these photocatalytic filters 2, the surface of the flat nonwoven fabric 10 and the longitudinal direction of the ultraviolet lamp 3 are parallel. And an ultraviolet lamp 3 arranged so as to be.

  The ultraviolet rays irradiated from the ultraviolet lamp 3 have a peak wavelength of 380 nm or less, and the peak wavelength differs depending on the ultraviolet lamp. For example, in the case of black light, the peak wavelength is approximately 350 to 370 nm, and in the case of a low-pressure mercury lamp, it is approximately 250 to 260 nm. Two ultraviolet lamps 3 are arranged between each photocatalytic filter 2 in total, and four ultraviolet lamps 3 can be irradiated on both surfaces of the flat nonwoven fabric 10 provided in each photocatalytic filter. The ultraviolet lamps 3 are arranged in parallel so that their axial directions are parallel to the photocatalytic filter 2. The numbers of the photocatalytic filters 2 and the ultraviolet lamps 3 are determined according to the required VOC removal performance and the like.

  In order to prevent adhesion of inorganic particulate matter such as dust in the air to the photocatalytic filter 2, a dust removal filter 4 is installed between the inlet 5 and the photocatalytic filter 2 in parallel with the photocatalytic filter as necessary. May be. Although there is no restriction | limiting in particular in a dust removal filter, The filter which carried out the pleating process of the electric nonwoven fabric, a HEPA filter, etc. can be utilized.

  As shown in FIG. 2, each photocatalytic filter 2 includes a flat nonwoven fabric 10 and a pair of wire meshes 11, and the flat nonwoven fabric 10 is sandwiched between a pair of stainless steel wire meshes 11. In this way, by using the wire mesh 11 as a support material to form a filter, it is possible to easily remove the photocatalytic filter 2 to which the catalyst poisoning component has adhered and the photocatalytic performance has deteriorated, and attach it again after washing with water. For example, as shown in FIG. 3, the photocatalytic filter 2 is preferably detached from the side surface of the casing 1 or inserted. As described above, since the photocatalyst filter can be detached from the air cleaning device, the photocatalyst filter can be easily washed with water, and the catalyst poisoning substances attached to the photocatalyst filter can be thoroughly removed. It becomes possible. The photocatalytic filter does not peel off the photocatalytic substance even after repeated washing with water, and the photocatalytic performance of the filter is almost restored by washing with water for each filter. Therefore, the air purifier easily provides high VOC removal performance. You can maintain the period.

  In the present embodiment, the number of flat nonwoven fabrics 10 is three, but the number can be arbitrarily determined according to the required VOC removal performance or the like. Further, in the present embodiment, each photocatalytic filter 2 is installed such that its surface intersects perpendicularly to the air flow direction, but it is sufficient that the circulating air passes through the flat nonwoven fabric 10 efficiently. It may be installed at an angle of around 10 °, preferably around 5 °.

  The flat nonwoven fabric 10 is made of a photocatalytic fiber having titanium oxide on its surface, and more specifically, an oxide phase mainly composed of a silica component (first phase) and a metal oxide phase containing titanium (second phase). The composite oxide phase of the silica-based composite oxide fiber is a fiber in which the proportion of titanium of the metal oxide constituting the second phase is increased gradually toward the surface layer of the fiber.

  The first phase is an oxide phase mainly composed of a silica component, and may be amorphous or crystalline, and may be a metal element or metal oxide capable of forming a solid solution or a eutectic compound with silica. It may contain. Examples of the metal element (A) that can form a solid solution with silica include titanium. Examples of the metal element (B) of the metal oxide that can form a solid solution with silica include aluminum, zirconium, yttrium, lithium, sodium, barium, calcium, boron, zinc, nickel, manganese, magnesium, and iron. It is done.

  The first phase forms the internal phase of the silica-based composite oxide fiber and plays an important role in bearing the mechanical properties. The proportion of the first phase relative to the entire silica-based composite oxide fiber is preferably 40 to 98% by weight, fully expressing the desired second phase function, and also exhibiting high mechanical properties. In order to achieve this, it is more preferable to control the proportion of the first phase within the range of 50 to 95% by weight.

  On the other hand, the second phase is a metal oxide phase containing titanium and plays an important role in developing the photocatalytic function. An example of the metal constituting the metal oxide is titanium. The metal oxide may be a simple substance, or may be a co-melting compound or a substance in which a substitutional solid solution is formed with a specific element, but is preferably titania. The second phase forms the surface layer phase of the silica-based composite oxide fiber, and the proportion of the second phase of the silica-based composite oxide fiber varies depending on the type of metal oxide, but is 2 to 60 weights. % Is preferable, and it is more preferable to control the content within the range of 5 to 50% by weight in order to sufficiently exhibit its function and to simultaneously exhibit high strength. The crystal grain size of the metal oxide containing Ti of the second phase is preferably 15 nm or less, particularly preferably 10 nm or less.

  The proportion of titanium in the metal oxide contained in the second phase increases in a gradient toward the surface of the silica-based composite oxide fiber, and the thickness of the region where the gradient of the composition is clearly recognized Is preferably controlled within the range of 5 to 500 nm from the surface layer, but may be about 1/3 of the fiber diameter. Note that the “existence ratio” of the first phase and the second phase is the first of the metal oxide constituting the first phase and the whole metal oxide constituting the second phase, that is, the whole silica-based composite oxide fiber. The weight percentages of the phase metal oxide and the second phase metal oxide are shown.

  The silica-based composite oxide fiber that is more preferable in the present invention is a fiber in which mesopores having an average pore diameter of 2 to 30 nm are formed from the fiber surface toward the inside of the fiber. Such a photocatalytic filter made of a nonwoven fabric of silica-based composite oxide fibers has a higher VOC adsorption capacity, and the air cleaning device of the present invention provided with this photocatalytic filter has a higher air cleaning capacity.

  Further preferred silica-based composite oxide fibers include platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), gold (Au), silver (Ag), copper (Cu), in the mesopores. It is a fiber in which at least one metal is supported among iron (Fe), nickel (Ni), zinc (Zn), gallium (Ga), germanium (Ge), indium (In), and tin (Sn). Such a photocatalytic filter made of a nonwoven fabric of silica-based composite oxide fibers has a higher VOC adsorption capability and higher photocatalytic performance itself, and the air cleaning device of the present invention equipped with this photocatalytic filter is even higher. Has air cleaning ability. The metal is supported on a mesopore having an average pore diameter of 2 to 30 nm from the surface of the silica-based composite oxide fiber toward the inside of the fiber, so that the photocatalyst is formed of a nonwoven fabric of the silica-based composite oxide fiber. Even if the filter is washed repeatedly, the metal does not fall off from the silica-based composite oxide fiber, and the photocatalytic filter can maintain the photocatalytic performance for a long time.

In the air cleaning apparatus according to the present invention, the average intensity of ultraviolet light on the flat nonwoven fabric constituting the photocatalyst filter is preferably is preferably 1~10mW / cm ^2, a further range of 2~8mW / cm ² . When the ultraviolet intensity on the surface of the flat nonwoven fabric is 1 to 10 mW / cm ² , VOC can be removed with high efficiency. In order to make such a range, the distance between the ultraviolet irradiation means and the flat nonwoven fabric may be set to an appropriate range. Here, the average ultraviolet intensity can be obtained by measuring the ultraviolet intensity at a plurality of locations from the center to the end of the nonwoven fabric surface and averaging the values to obtain the average ultraviolet intensity.

  Next, a method for producing the silica-based composite oxide fiber will be described.

(Melt spinning method)
Photocatalytic fibers are mainly of the general formula

(Wherein, R represents a hydrogen atom, a lower alkyl group or a phenyl group, and n represents an integer greater than 1). The number average molecular weight is 200 to 10,000. Step A for obtaining modified polycarbosilane having a structure obtained by modifying carbosilane with an organometallic compound, or a mixture of modified polycarbosilane and organometallic compound, Step B for melt spinning, Step C for infusible treatment , And the D step of baking in air or oxygen.

  Step A is a step of producing a modified polycarbosilane having a number average molecular weight of 1,000 to 50,000 used as a starting material for producing a silica-based composite oxide fiber. The basic method for producing the modified polycarbosilane is very similar to JP-A-56-74126, but it is necessary to carefully control the bonding state of the functional groups described therein.

  The modified polycarbosilane is mainly composed of a polycarbosilane having a main chain skeleton represented by the above chemical formula 1 having a number average molecular weight of 200 to 10,000 and a general formula of M (OR ′) n or MR ″ m (M Is a metal element, R ′ is an alkyl group having 1 to 20 carbon atoms or a phenyl group, R ″ is acetylacetonate, and m and n are integers greater than 1). Is.

  In order to produce a photocatalytic fiber having an inclined structure, it is necessary to select a slow reaction condition in which only a part of the organometallic compound forms a bond with polycarbosilane. For this purpose, it is necessary to react in an inert gas at a temperature of 280 ° C. or lower, preferably 250 ° C. or lower. Under these reaction conditions, even if the organometallic compound reacts with polycarbosilane, it is bonded as a monofunctional polymer (that is, bonded in a pendant form), and no significant increase in molecular weight occurs. The modified polycarbosilane partially bonded with the organometallic compound plays an important role in improving the compatibility between the polycarbosilane and the organometallic compound.

  In addition, when many functional groups more than bifunctional couple | bond together, the bridge | crosslinking structure of polycarbosilane is formed and the remarkable increase in molecular weight is recognized. In this case, a sudden exotherm and a rise in melt viscosity occur during the reaction. On the other hand, when only one function reacts and an unreacted organometallic compound remains, conversely, a decrease in melt viscosity is observed.

  In order to produce a photocatalytic fiber having an inclined structure, it is desirable to select conditions that intentionally leave an unreacted organometallic compound. Mainly, the modified polycarbosilane and the unreacted organometallic compound or the organic metal compound of about 2 to 3 mer are used as starting materials. However, the modified polycarbosilane alone has a very low molecular weight modified polycarbosilane. If a silane component is included, it can be used as a starting material as well.

  In step B, the modified polycarbosilane obtained in step A or a mixture of modified polycarbosilane and a low molecular weight organometallic compound (hereinafter sometimes referred to as a precursor) is melted to prepare a spinning dope. In some cases, this is filtered to remove substances that are harmful when spinning, such as microgel and impurities, and this is spun by a commonly used synthetic fiber spinning device. The temperature of the spinning dope during spinning varies depending on the softening temperature of the raw material modified polycarbosilane, but a temperature range of 50 to 200 ° C. is advantageous. In the above spinning apparatus, a humidification heating cylinder may be provided below the nozzle as necessary. The fiber diameter is adjusted by changing the discharge amount from the nozzle and the winding speed of a high-speed winding device installed at the lower part of the spinning machine.

  In addition to the spinning, the modified polycarbosilane obtained in Step A, or a mixture of the modified polycarbosilane and a low molecular weight organometallic compound is used, for example, benzene, toluene, xylene or other modified polycarbosilane and other low molecular weight compounds. Synthetic fibers that are usually used after dissolving the organometallic compound in a solvent that can be melted to prepare a spinning stock solution, and in some cases filtering it to remove harmful substances such as macrogel and impurities. Spinning may be performed while controlling the winding speed by a dry spinning method with a spinning device.

  In these spinning processes, if necessary, a spinning cylinder is attached to the spinning device, and the atmosphere in the cylinder is mixed with at least one gas of the solvent, or air, inert gas, hot air, By setting the atmosphere of heat inert gas, steam, ammonia gas, hydrocarbon gas, or organosilicon compound gas, solidification of fibers in the spinning cylinder can be controlled.

  In Step C, the spun fiber obtained in Step B is preheated in an oxidizing atmosphere under the action of tension or no tension to infusibilize the spun fiber. The C step is performed for the purpose of preventing the fibers from melting and adhering to adjacent fibers during the firing of the D step. The treatment temperature and treatment time vary depending on the composition and are not particularly limited, but generally, a treatment condition of several hours to 30 hours is selected within a range of 50 to 400 ° C. The oxidizing atmosphere may contain moisture, nitrogen oxides, ozone, or the like that increases the oxidizing power of the spun fiber, and the oxygen partial pressure may be changed intentionally.

  By the way, depending on the ratio of the low molecular weight substance contained in the raw material, the softening temperature of the spun fiber may be lower than 50 ° C. In this case, the fiber surface oxidation is promoted at a temperature lower than the treatment temperature in advance. In some cases, processing is performed. In addition, it is thought that the bleed-out to the fiber surface of the low molecular weight substance contained in a raw material advances in the C process and the B process, and the base | substrate of the target gradient composition is formed.

  In Step D, the fiber infusible in Step C is baked in an oxidizing atmosphere at a temperature range of 500 to 1800 ° C. under tension or no tension, and the target is an oxidation mainly composed of a silica component. It consists of a composite oxide phase of a physical phase (first phase) and a metal oxide phase containing titanium (second phase), and the proportion of titanium in the metal oxide that constitutes the second phase toward the surface layer is inclined. A silica-based composite oxide fiber that increases rapidly is obtained. In Step D, the organic component contained in the infusible fiber is basically oxidized, but depending on the conditions selected, it may remain in the fiber as carbon or carbide. Even in such a state, when the target function is not hindered, it is used as it is. However, when the target function is hindered, further oxidation treatment is performed. At that time, a temperature at which no problem occurs in the target gradient composition and crystal structure and a processing time are selected.

  In the E step, the silica in the vicinity of the surface can be removed by applying treatment to the surface side of the silica-based composite oxide fiber obtained in the D step, and mesopores can be formed on the fiber surface. There is no restriction | limiting in particular in the method of removing this silica, A physical method and a chemical method can be used. Examples thereof include a method of evaporating silica under reduced pressure and high temperature, and a method of eluting silica using an acid. In particular, silica is removed by immersing the silica-based composite oxide fiber obtained in Step D in a 2% by weight hydrogen fluoride aqueous solution for about 10 minutes or in a 10% by weight sodium hydroxide aqueous solution for about 12 hours. Is preferred. Through step E, silica-based composite oxide fibers having mesopores with an average pore diameter of 2 to 30 nm formed from the fiber surface toward the inside of the fiber are obtained.

  In the F step, platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), gold (Au), silver (Ag), copper (Cu), iron (Fe), nickel (Ni) , A silica-based composite oxide obtained through Step E in a solution containing at least one metal of zinc (Zn), gallium (Ga), germanium (Ge), indium (In), and tin (Sn) By irradiating light while contacting the fiber, the metal particles are supported in the mesopores of the silica-based composite oxide fiber, and the silica-based composite oxide fiber supporting the metal is produced. By irradiating the solution with light having energy equal to or higher than the energy corresponding to the band gap of the metal oxide constituting the second phase while contacting the silica-based composite oxide fiber having mesopores formed on the fiber surface. The metal particles can be selectively supported on the metal oxide reduction site (non-light-irradiated surface, that is, in the mesopores). In this case, if necessary, an electron donating sacrificial agent such as ethanol or methanol may coexist in the solution. Through the F step, platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), gold (Au), silver (Ag), copper (Cu), iron (Fe), A silica-based composite oxide fiber carrying at least one metal among nickel (Ni), zinc (Zn), gallium (Ga), germanium (Ge), indium (In) and tin (Sn) is obtained.

  The silica-based composite oxide fiber obtained in the steps up to the D step, the silica-based composite oxide fiber formed with mesopores having an average pore diameter of 2 to 30 nm obtained in the steps up to the E step, Alternatively, platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), gold (Au), silver (Ag), copper (Cu) in the mesopores obtained in the steps up to the Fth step. ), Iron (Fe), nickel (Ni), zinc (Zn), gallium (Ga), germanium (Ge), indium (In) and tin (Sn) on which at least one metal is supported. Any fiber of oxide fibers can be made into a flat nonwoven fabric by performing needle punching after making short fibers.

(Melt blow method)
The flat nonwoven fabric melts the precursor obtained in Step A using a melt blow method, discharges the melt from the spinning nozzle, and spouts heated nitrogen gas from the periphery of the spinning nozzle. The nonwoven fabric can be formed by collecting the spun fibers in a receiver arranged at the lower part of the spinning nozzle, and then the nonwoven fabric is infusible and then fired in an oxidizing atmosphere.

  The diameter of the spinning nozzle is usually about 100 to 500 μm. Nitrogen gas ejection speed is about 30 to 300 m / s, and the higher the speed, the thinner the fiber. The heating temperature of nitrogen gas is not particularly limited as long as a desired spun fiber can be obtained, but nitrogen gas heated to about 500 ° C. is usually ejected. Conventionally, in a general melt-blowing method, air is used as the jet gas, but nitrogen needs to be used to spin the precursor obtained in the step A. Spinning can be performed stably by using nitrogen as the jet gas.

  When collecting the spun fiber in a receiver disposed at the lower part of the spinning nozzle, it is preferable to perform spinning while sucking from the lower side of the receiver using a suckable receiver. By sucking, the fibers are effectively entangled and a high-strength nonwoven fabric is obtained. The suction speed is preferably in the range of about 2 to 10 m / s.

  The obtained nonwoven fabric is subjected to the same infusibilization treatment and firing (step C and step D) as in the melt spinning method, whereby a nonwoven fabric made of silica-based composite oxide fibers is obtained. The silica-based composite oxide fiber produced by the melt blow method has an average fiber diameter of 1 to 20 μm, preferably 1 to 8 μm, more preferably 2 to 6 μm, as compared to the fiber produced by the melt spinning method. It can be thin. Thereby, the surface area of a fiber can also be enlarged and catalyst activity increases. Moreover, the flat nonwoven fabric manufactured by a melt blow method has a long fiber compared with the short fiber manufactured by the melt spinning method about 40-50 mm in length made into the nonwoven fabric by the needle punch method. As a result, the nonwoven fabric has high strength (tensile strength of 2N or more) and has sufficient pleatability when processed into a filter or the like.

The basis weight and thickness of the flat nonwoven fabric are not particularly limited, but it is usually preferable that the basis weight is 30 to 300 g / m ² and the thickness is 0.2 to 10 mm. The thickness can be adjusted by laminating a nonwoven fabric as necessary. If the thickness is less than 0.2 mm, the amount of photocatalyst itself is too small to obtain a sufficient VOC removal effect. When it is thicker than 10 mm, the flat nonwoven fabric becomes a resistance, the pressure loss increases, and the air hardly flows. The shape of the flat nonwoven fabric is not particularly limited, but can be round, square, etc. according to the shape of the casing into which the flat nonwoven fabric is inserted, and corrugated to increase the surface area of the flat nonwoven fabric. It can also be.

  According to the method for producing the flat nonwoven fabric 10 as described above, there is no bridging between fibers, and a silica-based composite having a structure in which photocatalytic components such as titanium oxide are densely deposited on the surface of each fiber. A flat nonwoven fabric 10 made of oxide fibers is obtained. Moreover, since the photocatalyst is not fixed by the coating in this silica-based composite oxide fiber, there is no problem that the photocatalyst component on the fiber surface is dropped. Further, the flat nonwoven fabric 10 made of the silica-based composite oxide fiber has a structure in which each of the fibers is dispersed with a certain amount of voids, so that the contact area between the air and the photocatalyst is very large. Become. Generally, in order to fully exploit the function of the photocatalyst, it is necessary to increase the light irradiation efficiency to the photocatalyst and the contact efficiency with the processing fluid.

  Next, the VOC removal method according to the present embodiment will be described.

  As shown in FIG. 1, air is introduced from the inlet 5, passes through the casing 1, and is discharged from the outlet 6. The flat nonwoven fabric 10 shown in FIG. 2 has a structure in which each of the fibers is dispersed with a certain amount of voids, so that when the air passes through the photocatalytic filter 2, the contact area with the photocatalyst is very large. Big. For this reason, radicals are efficiently generated by the flat nonwoven fabric 10 having a photocatalytic function, and VOC is decomposed. The principle of decomposition of VOC is as follows. Titanium oxide contained in the silica-based composite oxide fiber is excited by ultraviolet irradiation, and electrons in the valence band move to the conduction band. At this time, holes are generated in the valence band of titanium oxide. These holes generate active oxygen species typified by OH radicals having strong oxidizing power by taking electrons from the water around the titanium oxide. This active oxygen species oxidatively decomposes various organic substances. VOC is also an organic substance and is oxidatively decomposed. Radiation can be generated more efficiently by irradiating both the front and back surfaces of the flat nonwoven fabric 10 with ultraviolet rays.

  Hereinafter, the present invention will be described with reference to examples.

(Production Example 1)
A 5-liter three-necked flask was charged with 2.5 liters of anhydrous toluene and 400 g of metallic sodium, heated to the boiling point of toluene under a nitrogen gas stream, and 1 liter of dimethyldichlorosilane was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was heated to reflux for 10 hours to form a precipitate. The precipitate was filtered, washed with methanol and then with water to obtain 420 g of white powder of polydimethylsilane. Polydimethylsilane (250 g) was charged into a three-necked flask equipped with a water-cooled reflux condenser, and heated and reacted at 420 ° C. for 30 hours under a nitrogen stream to obtain polycarbosilane having a number average molecular weight of 1200.

  After adding 100 g of toluene and 64 g of tetrabutoxytitanium to 16 g of the polycarbosilane, preheating it at 100 ° C. for 1 hour, slowly raising the temperature to 150 ° C., distilling off the toluene, and allowing the reaction to proceed for 5 hours. The mixture was heated up to react for 5 hours to synthesize modified polycarbosilane. In order to intentionally allow the low molecular weight organometallic compound to coexist with the modified polycarbosilane, 5 g of tetrabutoxytitanium was added to obtain a mixture of the modified polycarbosilane and the low molecular weight organometallic compound.

  After the mixture of the modified polycarbosilane and the low molecular weight organometallic compound was dissolved in toluene, the mixture was charged into a glass spinning apparatus, the interior was sufficiently purged with nitrogen, and the temperature was raised to distill off the toluene. Melt spinning was carried out at 0 ° C. The spun fiber was heated to 150 ° C. stepwise in air and then infusible, and then fired in air at 1200 ° C. for 1 hour to obtain a titania / silica fiber (photocatalyst fiber) according to Production Example 1.

Example 1
The silica-based composite oxide fiber obtained in Production Example 1 was used as a flat nonwoven fabric to produce a photocatalytic filter as shown in FIG. The size of this filter is 0.3 m × 0.3 m × 0.5 mmt (area: 0.09 m ² ). This was arrange | positioned in a casing and the air purifying apparatus shown by FIG. 1 was produced. The output of the ultraviolet lamp used for this is 40 W, and four were used. In addition, three photocatalytic filters were used, and one dust removal filter made of an electric nonwoven fabric was arranged in parallel with the photocatalytic filter between the inlet and the photocatalytic filter. The ultraviolet lamp has a peak wavelength at 351 nm. The distance between the ultraviolet lamp and the photocatalytic filter was 60 mm, and the average ultraviolet intensity on the photocatalytic filter surface was 3 mW / cm ² . This air purifier was connected to a blower and installed in a sealed room with a volume of 30 m ³ . This sealed chamber is a stainless steel inner wall to prevent adsorption of VOC. After acetaldehyde was filled in the sealed chamber so that the acetaldehyde concentration in the sealed chamber was 5 ppm, the air in the sealed chamber was introduced from the inlet of the air purifier using a blower, and the circulation treatment was performed for 60 minutes. The processing speed of this circulation processing was 10 m ³ / min. The concentration of acetaldehyde in the sealed chamber before and after the circulation treatment was measured using a photoacoustic multigas monitor type 1312 manufactured by INOVA. This test was conducted once a day for 180 days. At this time, the photocatalytic filter was detached from the side surface of the casing every 30 days and washed with water as shown in FIG. As shown in Table 1, the acetaldehyde removal rate was maintained at 80% or more over 180 days, and even when the removal rate was slightly lowered, it was found that the removal rate was completely recovered by washing with water.

(Example 2)
The photocatalyst fiber obtained in Production Example 1 was formed into a flat nonwoven fabric, and this was immersed in a 2 wt% hydrogen fluoride aqueous solution for 10 minutes to elute silica on the fiber surface to form mesopores on the fiber surface. The average pore diameter of this mesopore was 25 nm. The average pore diameter of the mesopore was calculated from the nitrogen adsorption isotherm measured at the liquid nitrogen temperature and the analysis by the BJH method. Similar to Example 1, a photocatalytic filter as shown in FIG. 2 was produced from a flat nonwoven fabric made of photocatalytic fibers having mesopores. The size of this filter is 0.3 m × 0.3 m × 0.5 mmt (area: 0.09 m ² ). This was disposed in the casing, and the air purifier shown in FIG. 1 was produced in the same manner as in Example 1 and a circulation treatment test was performed. As a result, as shown in Table 1, the acetaldehyde removal rate was maintained at 90% or more over 180 days, and the removal rate was higher than that of Example 1. Further, it was found that even when the removal rate slightly decreased, the removal rate was completely recovered by washing with water as in Example 1.

(Example 3)
A flat nonwoven fabric composed of photocatalytic fibers having mesopores with an average pore diameter of 25 nm formed on the fiber surface obtained in Example 2 was immersed in an aqueous solution of palladium (II) chloride trihydrate (palladium concentration: 30 ppm). Then, ultraviolet rays having a central wavelength of 254 nm were irradiated for 3 hours at an intensity of ² mW / cm ² . After irradiation, washing with water and further drying were performed to obtain a palladium-supported photocatalytic fiber. As a result of analysis by ICP, the amount of palladium supported was 2000 ppm. From the result of TEM observation, it was found that the supported palladium was supported in the mesopores. Similar to Example 1, a photocatalytic filter as shown in FIG. 2 was produced from a flat nonwoven fabric made of photocatalytic fibers carrying palladium in the mesopores. The size of this filter is 0.3 m × 0.3 m × 0.5 mmt (area: 0.09 m ² ). This was disposed in the casing, and the air purifier shown in FIG. 1 was produced in the same manner as in Example 1 and a circulation treatment test was performed. As a result, as shown in Table 1, the acetaldehyde removal rate was maintained at 95% or more over 180 days, and the removal rate was higher than that of Example 1 and Example 2. Further, it was found that even when the removal rate slightly decreased, the removal rate was completely recovered by washing with water as in Example 1.

(Comparative Example 1)
Using a glass fiber cloth (plain weave, basis weight: 300 g / m ² ) as a base material, titanium oxide coating was performed using a titanium oxide-containing sol solution (manufactured by Photocatalyst Laboratory, ATN-2) to prepare a photocatalytic filter. Drying and baking were performed at 120 ° C. for 1 hour. The size of this filter is 0.3 m × 0.3 m × 0.5 mmt (area: 0.09 m ² ). Using these three photocatalytic filters, a circulation treatment test was conducted in the same manner as in Example 1. As a result, as shown in Table 1, the acetaldehyde removal rate decreased to 65% at the start of the test and to 55% after 30 days. Although the removal rate recovered to some extent by washing with water, it was found that the removal rate did not completely recover and gradually decreased. This is considered to be because the titanium oxide on the surface of the photocatalytic filter is peeled off by washing with water and the photocatalytic performance is lowered.

DESCRIPTION OF SYMBOLS 1 Casing 2 Photocatalyst filter 3 Ultraviolet lamp 4 Dust removal filter 5 Inlet 6 Outlet 10 Flat nonwoven fabric 11 Wire mesh

Claims (4)

A photocatalytic filter comprising a flat nonwoven fabric of photocatalytic fibers having titanium oxide on the surface, and an ultraviolet irradiation means having a shape extending in the longitudinal direction capable of irradiating ultraviolet rays having a wavelength of 380 nm or less, and the surface of the flat nonwoven fabric and ultraviolet rays An air cleaning device characterized by being substantially parallel to the longitudinal direction of the irradiating means and having a flow of air substantially perpendicular to the flat nonwoven fabric,
The photocatalytic fiber is a silica-based composite oxide fiber composed of a composite oxide phase of an oxide phase (first phase) mainly composed of a silica component and a metal oxide phase containing titanium (second phase), An air cleaning device, wherein the proportion of the metal oxide titanium constituting the second phase is a fiber that increases in a slanting manner toward the surface layer of the fiber.   2. The air cleaning device according to claim 1, wherein the photocatalytic fiber is a fiber in which mesopores having an average pore diameter of 2 to 30 nm are formed from the fiber surface toward the inside of the fiber.   In the mesopores of the photocatalytic fiber according to claim 2, platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), gold (Au), silver (Ag), copper (Cu), iron (Fe) ), Nickel (Ni), zinc (Zn), gallium (Ga), germanium (Ge), indium (In), and tin (Sn), at least one metal is supported. 2. The air purifier according to 2.   The air purifier according to any one of claims 1 to 3, wherein the photocatalytic filter is detachable.

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