JP2003010612A - Hazardous substance removal filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter capable of removing harmful substances and collecting dust, PM, or the like, at the same time. SOLUTION: This filter is characterized in that a woven textile is made of a silica-group composite oxide fiber, that such fiber is composed of an oxide phase (a first phase) including a silica component as a main constituent and a metal oxide phase (a second phase) other than silica, that the existence ratio of at least one constituent component of the second phase increases in a gradient manner toward the surface layer of the fiber, and that the fiber has an optical and/or thermal function.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a filter for removing harmful substances in the air and water.

[0002]

2. Description of the Related Art In recent years, with increasing interest in environmental protection, catalysts and filters for purifying harmful substances have been required.

Nitrogen oxides generated from internal combustion engines such as automobile engines and industrial plants are atmospheric pollutants harmful to human bodies and the environment, and their reduction is desired. As a technology for removing nitrogen oxides, a three-way catalyst method in a gasoline engine and a selective catalytic reduction method using ammonia in an industrial plant have been put into practical use.

Further, black smoke particulate matter (PM) discharged from a diesel engine has recently been particularly noted as having a serious influence on the human body. As a material for collecting PM, a filter made of silicon carbide fiber has been put into practical use.

Further, regarding the purification of water, as shown in, for example, JP-A-8-103631, a filter obtained by coating titanium oxide on a glass filter is used to purify water by a photocatalytic reaction. Suggested ways to do it.

[0006]

However, these environmental purification technologies have various problems in practical use. Regarding the purification of nitrogen oxides, the three-way catalyst method is applied because the oxidation reaction of reducing agents (CO and hydrocarbons) occurs preferentially when high-concentration oxygen is contained like diesel engine exhaust gas. Is difficult. In addition, the selective catalytic reduction method using ammonia must handle ammonia gas, which is highly toxic and corrosive. Further, in these methods, it is necessary to separately install a dust collecting device such as a filter in order to collect dust and the like in the exhaust gas. P
Regarding the collection of M, the current filter made of silicon carbide fiber has a great effect, but it does not have the function of purifying nitrogen oxides discharged at the same time as PM. Regarding the purification of water, there is a problem that titanium oxide coated in a glass filter is removed by contact with water, and titanium oxide is mixed into the water.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and provides a filter capable of simultaneously purifying harmful substances and collecting soot and PM.

That is, the present invention relates to a fiber comprising a composite oxide phase of an oxide phase (first phase) mainly containing a silica component and a metal oxide phase (second phase) other than silica, A woven fabric of silica-based composite oxide fibers having an increasing proportion of at least one constituent component of the second phase toward the surface layer of the above, and having a light and / or thermal catalytic function. The present invention relates to a harmful substance removing filter characterized by:

In the silica-based composite oxide fiber of the present invention, the oxide phase (first phase) having a silica component as a main component means
It may be amorphous or crystalline, and may contain a metal element or a metal oxide capable of forming a solid solution or a eutectic point compound with silica. The metal element (A) capable of forming a solid solution with silica or the metal element (B) whose oxide can form a compound having a specific composition with silica is not particularly limited, but, for example, titanium as (A), Further, as (B), aluminum, zirconium,
Examples thereof include yttrium, lithium, sodium, barium, calcium, boron, zinc, nickel, manganese, magnesium and iron.

This first phase forms the internal phase of the fibers obtained according to the invention and plays an important role in bearing the mechanical properties. The ratio of the first phase to the whole fiber is 9
It is preferably 8 to 40% by weight, and the target second
In order to fully express the function of the phase and also to express the high mechanical characteristics, the existence ratio of the first phase is 50 to 95.
It is preferable to control within the range of weight%.

On the other hand, the metal oxide constituting the second phase plays an important role in exhibiting a light and / or thermal catalytic function. Examples of the metal forming the metal oxide phase include Ti, Al, V and the like. These metal oxides may be a simple substance, a eutectic compound thereof, a substitutional solid solution formed by a specific element, or the like. The proportion of the second phase constituting the surface layer portion of the fiber varies depending on the type of oxide, but is preferably 2 to 60% by weight, and in order to sufficiently exhibit its function and also to exhibit high strength at the same time. It is preferable to control the content within the range of 5 to 50% by weight.

The abundance ratio of at least one constituent constituting the second phase increases in a gradient toward the surface of the fiber, and the thickness of the region where the composition gradient is clearly recognized is 5 to 5. It is preferable to control in the range of 500 nm, but it may extend to about 1/3 of the fiber diameter. In addition, the second
"Abundance ratio" of a layer means the ratio contained in the whole fiber.

Further, this silica-based composite oxide fiber has a light and / or thermal catalytic function and, at the same time, has excellent heat resistance. For example, the temperature at which 90% or more of the original fiber strength remains after being kept in heated air for 1 hour is 1000 ° C.
Is.

There is no particular limitation on the weaving method of the woven fabric made of the silica-based composite oxide fiber, and there are known weaving methods such as plain weave, satin weave, imitation weave, twill weave, leno weave, bag weave, felt and the like. Can be The basis weight of this woven fabric is 10 to 500 g / m ² . The filtration performance can be adjusted by adjusting the basis weight. The filter-shaped article of the present invention may be used in a planar shape, or may be used in various shapes such as a cylindrical shape, an envelope shape and a conical shape.

Further, in the present invention, a part of the silica-based composite oxide fiber constituting the filter is replaced with another inorganic fiber such as glass fiber, carbon fiber, alumina fiber,
It may be made of silicon carbide fiber or the like. For example, the silica-based composite oxide fiber may be used for the portion of the filter surface that is exposed to the light to exhibit the catalytic function, and the other portions may be used for the inexpensive fiber such as glass fiber.

Next, the method for producing the silica-based composite oxide fiber of the present invention will be described. In the present invention, the general formula

[Chemical 1] (However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.) Polycarbosilane having a main chain skeleton and a number average molecular weight of 200 to 10,000 is modified with an organometallic compound. The modified polycarbosilane having the above structure, or a mixture of the modified polycarbosilane and the organometallic compound is melt-spun, and after the infusibilization treatment, the silica-based composite oxide fiber is produced by firing in air or oxygen. can do.

In the first step, the number average molecular weight used as a starting material for producing the silica-based composite fiber is 1,00.
This is a step of producing 0 to 50,000 modified polycarbosilane. The basic method for producing the modified polycarbosilane is very similar to that in JP-A-56-74126, but in the present invention, it is necessary to carefully control the bonding state of the functional groups described therein. is there. This is outlined below.

The modified polycarbosilane which is the starting material is
Mainly general formula

[Chemical 2] (However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.) A polycarbosilane having a main skeleton represented by a number average molecular weight of 200 to 10,000 and a general formula, M (OR ') n or MR''m (M is a metal element, R'is an alkyl or phenyl group having 1 to 20 carbon atoms, R'is acetylacetonate, m and n are integers greater than 1) It is derived from an organic metal compound having a structure.

Here, in order to produce the fiber having the graded composition of the present invention, it is necessary to select a slow reaction condition in which only a part of the organometallic compound forms a bond with polycarbosilane. Therefore, 280 ° C or lower, preferably 25
It is necessary to react in an inert gas at a temperature of 0 ° C or lower. Under this reaction condition, even if the organometallic compound is reacted with polycarbosilane, it is bonded (that is, pendantly bonded) as a monofunctional polymer, and a large increase in molecular weight does not occur. The modified polycarbosilane in which the organometallic compound is partially bonded plays an important role in improving the compatibility between the polycarbosilane and the organometallic compound.

When a large number of bifunctional or higher functional groups are bonded, a polycarbosilane crosslinked structure is formed and a marked increase in the molecular weight is observed. In this case, a rapid heat generation and a rise in melt viscosity occur during the reaction. On the other hand, when only the above-mentioned monofunctional compound is reacted and the unreacted organometallic compound remains, a decrease in melt viscosity is observed.

In the present invention, it is desirable to select conditions under which unreacted organometallic compound is intentionally left. In the present invention, the above modified polycarbosilane and an unreacted organometallic compound or an organometallic compound in the range of about 2-3 trimers are mainly used as a starting material, but the modified polycarbosilane alone has an extremely low molecular weight. When the modified polycarbosilane component of 1 is contained, it can be similarly used as the starting material of the present invention.

In the second step, the modified polycarbosilane obtained in the first step or a mixture of the modified polycarbosilane and a low molecular weight organometallic compound is melted to prepare a spinning dope, which may be prepared. Filter to remove substances that are harmful to spinning such as microgels and impurities,
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 modified polycarbosilane as a raw material, but is 50 to 200 ° C.
The temperature range of is preferred. In the above spinning device, a humidification heating cylinder may be provided below the nozzle, if necessary. still,
The fiber diameter is adjusted by changing the discharge amount from the nozzle and the winding speed of a high-speed winding device installed in the lower part of the spinning machine.

In the second step, in addition to the melt spinning, the modified polycarbosilane obtained in the first step, or a mixture of the modified polycarbosilane and a low molecular weight organometallic compound, such as benzene, toluene or xylene, is used. Alternatively, the modified polycarbosilane and the low molecular weight organometallic compound are dissolved in a solvent capable of melting to prepare a spinning stock solution, which may be filtered to remove macrogels, impurities and other harmful substances during spinning. The target fiber can be obtained by spinning the stock solution for spinning by a dry spinning method using a synthetic fiber spinning device which is usually used, and controlling the winding speed.

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

In the third step, the spun fiber is preheated in an oxidizing atmosphere under the action of tension or no tension to infusibilize the spun fiber. This step is performed for the purpose of preventing the fibers from being melted and adhering to the adjacent fibers at the time of firing in the subsequent step. The treatment temperature and the treatment time differ depending on the composition and are not particularly specified, but generally, a treatment condition of several hours to 30 hours is selected within the range of 50 to 400 ° C. Also, in the oxidizing atmosphere,
It may contain water, nitrogen oxides, ozone, etc. that enhance the oxidizing power of the spun fiber, and the oxygen partial pressure may be intentionally changed.

By the way, depending on the proportion of low molecular weight substances contained in the raw material, the softening temperature of the spun fiber may be lower than 50 ° C. In that case, the oxidation of the fiber surface may be carried out at a temperature lower than the above treatment temperature in advance. In some cases, a process for promoting It is considered that, in the third step and the second step, bleeding out of the low molecular weight compound contained in the raw material to the fiber surface progresses to form an underlayer having a desired gradient composition. There is.

In the fourth step, the infusibilized fiber is fired under tension or no tension in an oxidizing atmosphere in the temperature range of 500 to 1800 ° C. to obtain a desired oxide mainly composed of a silica component. It is composed of a composite oxide phase of a phase (first phase) and a metal oxide phase other than silica (second phase), and the abundance ratio of at least one constituent component of the second phase gradually increases toward the surface layer. A silica-based complex oxide fiber is obtained. In this step, the organic component contained in the infusibilized fiber is basically oxidized, but it may remain in the fiber as carbon or carbide depending on the selected conditions.
Even in such a state, if the intended function is not hindered, it is used as it is, but if it is hindered, further oxidation treatment is performed. At that time, the temperature and the treatment time must be selected so that the intended graded composition and crystal structure do not cause any problems.

[0028]

EXAMPLES The present invention will be described below with reference to examples. Reference Example 1 2.5 liters of anhydrous toluene and 400 g of sodium metal were placed in a 5 liter three-necked flask and heated to the boiling point of toluene under a nitrogen gas stream, and dimethyldichlorosilane 1 was added.
L was added dropwise over 1 hour. After completion of dropping, the mixture was heated under reflux for 10 hours to generate a precipitate. This precipitate is filtered,
First, it was washed with methanol and then with water to obtain 420 g of white powdery polydimethylsilane. 250 g of polydimethylsilane was charged into a three-necked flask equipped with a water-cooled reflux device, 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.

Example 1 Polycarbosilane 16 synthesized by the method of Reference Example 1
To 100 g of toluene, 100 g of toluene and 64 g of tetrabutoxytitanium were added, preheated at 100 ° C. for 1 hour, then slowly heated to 150 ° C., toluene was distilled off, the reaction was continued for 5 hours, and further heated to 250 ° C. And reacted for 5 hours to synthesize a modified polycarbosilane. To this modified polycarbosilane, 5 g of tetrabutoxytitanium was intentionally added for the purpose of allowing a low-molecular weight organometallic compound to coexist to obtain a mixture of the modified polycarbosilane and the low-molecular weight organometallic compound.

A mixture of this modified polycarbosilane and a low molecular weight organometallic compound was dissolved in toluene and charged into a glass spinning apparatus, and the inside was sufficiently replaced with nitrogen, and then the temperature was raised to distill off the toluene. Melt spinning was performed at 180 ° C. The spun fiber was heated in air stepwise to 150 ° C. to make it infusible and then fired in air at 1200 ° C. for 1 hour to obtain a titania / silica fiber.

The obtained fiber (average diameter: 13 μm) is
As a result of X-ray diffraction, it consisted of amorphous silica and titania of anatase, and the Ti / Si (molar ratio) of the whole fiber was 0.17. Moreover, when the distribution state of constituent atoms by EPMA was examined, it was found that T
i / Si (molar ratio) = 0.87, 3 to 4 μm from the outermost periphery
In the region of Ti / Si (molar ratio) = 0.15, T in the center
It was confirmed that i / Si (molar ratio) = 0.04 and the composition was graded such that titanium increased toward the surface. The tensile strength of the fiber was 1.5 GPa, which was significantly higher than that of the anatase-type titania / silica fiber obtained by the conventional sol-gel method.

The titania / silica fiber obtained was made to have a length of 50.
After making it into mm short fibers, needle punching was performed to obtain a titania / silica fiber felt having a basis weight of 100 g / m ² . This felt is 300mm x 300mm,
A flat filter having a thickness of 1 mm was used.

5 ppm NO from one side of this filter
Containing air was flowed at a flow rate of 10 l / min. At this time, ultraviolet rays of 300 to 400 nm were irradiated from the opposite surface of the filter. When the air after passing through the filter was sampled and the NO concentration was measured by the chemiluminescence method, it was 5 ppb or less.

When exhaust gas from the diesel engine was passed through this filter, 95% of black smoke particulate matter (PM) in the exhaust gas was collected. The filter that trapped PM was heated in the atmosphere at 1000 ° C. for 30 minutes to oxidize and remove the PM, and the filter was regenerated. No damage was found on the filter after regeneration.

Example 2 A titania / silica fiber felt obtained in the same manner as in Example 1 was used as a cylindrical filter shape having a diameter of 200 mm and a length of 300 mm, and water fed with fish from the outside was used as 1
Circulation filtration was performed at a flow rate of 0 liter / min. At this time, ultraviolet light of 300 to 400 nm was irradiated from the inside of the filter. When the number of coliform bacteria in the water before circulation filtration was examined, it was 10
It was 000 pieces / milliliter. In addition, phytoplankton was generated and turbidity of water was observed. The water that had been circulated and filtered for 1 hour was sampled, and the number of coliform bacteria was examined. As a result, the number was 10 / ml or less, and it was possible to almost completely kill the coliform bacteria. No turbidity was observed in the water, and the phytoplankton in the water could be collected almost completely by the filter.

Comparative Example 1 1000 ml of 120 g of titanium tetraisopropoxide
Was diluted with isopropanol, and 40 g of diisopropanolamine and 10 g of water were added with stirring, and further 10 g of polyethylene glycol having a molecular weight of 1000 was added to prepare a transparent titania sol liquid.

A glass fiber woven fabric was impregnated with this titania sol solution, pulled up, dried and fired at 600 ° C. in the atmosphere to obtain a glass fiber woven fabric having titania on the surface. The fabric weight of this woven fabric was 100 g / m ² .
This felt was used as a flat filter having a size of 300 mm × 300 mm and a thickness of 1 mm. Further, the same test as in Example 1 was conducted using this filter.

As a result, the NO concentration after passing through the filter was 5 ppb or less. The PM collection rate was 80%. When the filter that trapped PM was regenerated in the air at 1000 ° C. for 30 minutes, the filter was found to be melted.

Comparative Example 2 The same test as in Example 2 was carried out using the glass fiber woven fabric having titania on the surface obtained in Comparative Example 1 as a cylindrical filter having a diameter of 200 mm and a length of 300 mm.

As a result, the number of coliform bacteria in the water after circulation filtration was 100 / ml, and the killing effect of E. coli was smaller than that in Example 1. In addition, although the phytoplankton was almost completely collected by the filter, titania particles dropped from the filter were observed in the water.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 35/02 B01D 53/36 C 35/06 ZABJ F01N 3/02 301 102D F term (reference) 3G090 AA01 AA02 4D019 AA01 AA03 BA01 BA05 BB02 BC07 BD02 CB06 DA06 4D048 AA06 AA21 BA03Y BA06X BA07X BA23Y BA42X BB08 BB16 CC41 EA01 4G069 AA02 AA08 BA48A BB06A BB06B BC16A BC50A BC50B BC54A BD05A BD05B CA01 CA02 CA03 CA05 CA11 CA13 DA06 EA09 EA10 EC29 FA01 FB30 FB57 FC08

Claims (4)

[Claims] 1. An oxide phase mainly comprising a silica component (first
Phase) and a complex oxide phase of a metal oxide phase other than silica (second phase), wherein the abundance ratio of at least one constituent component of the second phase gradually increases toward the surface layer of the fiber. A harmful substance removing filter comprising a woven fabric of silica-based complex oxide fibers having an increased number of light and / or thermal catalytic functions. 2. The abundance ratio of the first phase to the whole fiber is 98.
The toxic substance removal filter according to claim 1, wherein the presence ratio of the second phase is 2 to 60% by weight. 3. The metal constituting the metal oxide phase is Ti or A.
The harmful substance removing filter according to claim 1 or 2, which is at least one selected from l and V. 4. An oxide phase mainly composed of a silica component (first
Phase) and a complex oxide phase of a metal oxide phase other than silica (second phase), wherein the abundance ratio of at least one constituent component of the second phase gradually increases toward the surface layer of the fiber. A harmful substance removing filter comprising a woven fabric of silica-based composite oxide fibers having an increasing number of and having a light and / or thermal catalytic function, and an inorganic fiber.