KR20070051348A - Impregnated filter elements, and methods - Google Patents

Abstract

A decontamination filter is provided for removing contaminants (which are acidic, basic or carbonyl containing compounds) from a gas stream (eg air). The filter has a porous or fibrous body comprising a plurality of passages (which provide a flow path) extending from the first inlet face to the second outlet face. The body has an active material impregnated throughout the substrate. The active substance present is selected based on the contaminants to be removed.

Contaminant Removal Filters, Preservatives, Stabilizers, Basics, Accelerators, Reactants

Description

Impregnated filter elements, and methods

This application is a PCT international application of the US company Donaldson Company, Inc. for all country designations except the United States [inventor: Dallas, Andrew James, USA, Dinger Ding, Lefei (China) and Jorman, Jon Dennis (US), Priority: US Utility Model Application No. 10 / 928,776 (April 27, 2008), US Utility Model Application Application No. 10 / 927,708 US Patent Application No. 11 / 016,013 (December 17, 2004) and US Utility Model Registration No. 11 / 016,013, filed August 25, 2005.

The present invention relates to a low-pressure drop filter element for removing contaminants from a gas stream (eg air stream). More particularly, the present invention relates to the removal of contaminants from gas streams using filter elements impregnated with materials selected to specifically remove contaminants.

Gas adsorption products, commonly referred to as members or filters, are used in various industries to remove airborne contaminants to protect humans, the environment, and often important manufacturing processes or products made by such processes. A specific example of use for a gas adsorption product is the semiconductor industry, where the product is manufactured in an ultra-clean environment, commonly known as the "clean room" in the industry. Gas adsorption products are also used in many non-industrial applications. For example, gas adsorption products are present in air movement systems in both malls and homes to provide residents with cleaner breathing air.

Typical airborne contaminants include basic contaminants such as ammonia, organic amines and N-methyl-2-pyrrolidone, acidic contaminants such as hydrogen sulfide, hydrogen chloride or sulfur dioxide, and reactive monomers or non-reactive, often referred to as VOCs (volatile organic compounds). There are common organic contaminants such as solvents. Silicon-containing materials such as silanes, siloxanes, silanols and silazanes may be particularly harmful contaminants in some applications. In addition, many toxic industrial chemicals and chemical weapons must also be removed from the breathing air.

Dirty or contaminated air is often blown through a granular adsorption bed assembly or a packed bed assembly. These layers have a frame and an adsorbent medium (eg, activated carbon) retained in the frame. The adsorption medium adsorbs or reacts with gaseous contaminants from the air stream and allows clean air to be returned to the environment. Removal efficiency and time at specific removal efficiencies are important in order to adequately protect the process and products for long periods of time.

The removal efficiency and capacity of the gaseous adsorption bed depends on a number of factors such as the air velocity through the adsorption bed, the depth of the bed, the type and amount of adsorption medium used, and the activity level and adsorption rate of the adsorption medium. In order to increase or maximize the efficiency, it is important that the air leak through the air gap between the airtight packed adsorbent bed granules and the mold should be reduced to such an extent that there is no such leak. Examples of granular adsorption beds include those taught in US Pat. Nos. 5,290,345 (Osendorf et al.), 5,964,927 (Graham et al.) And 6,113,674 (Graham et al.). This hermetic filled layer creates a warped air flow path through the layer.

However, significant pressure loss occurs due to the hermetically filled layer. Recent solutions for minimizing pressure loss have been to increase bed area to reduce the air velocity through the bed. This can be done by increasing the layer size, forming a V-shaped layer or wrinkling. Unfortunately, however, these methods do not adequately solve the pressure loss problem and can cause additional problems of non-uniform flow rates released from the bed. In addition, the packed bed is quite heavy.

The packed bed contaminant removal system is sufficient for some applications, but there is a need for alternative products that can effectively remove contaminants such as acids, bases or other organic materials while minimizing pressure loss and providing a uniform release rate from the filter.

One example of an unfilled bed adsorbent product is disclosed in US Pat. No. 6,645,271 to Seguin et al. The product described in the above patent has a substrate having a through passage (the surface of the passage is coated or coated with an adsorbent material). The adsorbent material may be retained on the substrate by the polymeric material.

While US Pat. No. 6,071,479 (Marra et al.) Attempts to provide suitable products for removing contaminants from gas streams, products such as Mara have various disadvantages and undesirable features. For example, the medium is not designed for long term liver and / or high purity filtration. According to the invention of Mara et al., Citric acid impregnated paper media is probably a suitable decontamination product, but in practical use such products do not provide acceptable performance. Products such as Mara also include wetting agents or organic amines to increase the water content of the adsorbent and aid the reaction between the acidic impregnant and the basic materials to be removed. Mara and the like also use binders and glues to maintain the structure of the formed medium. Such adhesives are known as gaseous release contaminants, and some may react with or bind to the decontamination material to reduce the amount available to remove contaminants from the gas flowing through.

There is a need for a better decontamination system.

Summary of the Invention

The present invention relates to a decontamination filter wherein contaminant removal actives are present throughout the fibrous substrate. The active substance present in the filter is selected according to the specific contaminants to be removed.

In one embodiment, the filter comprises an acidic substance and a preservative or stabilizer for removing basic contaminants. Applicants have found prior to the present invention that acidic materials in filter elements do not have generally acceptable contaminant removal lifetimes, and the lifetime of prior art filters is shortened by the presence of moisture in the filter. Applicants have found that the inclusion of preservatives or stabilizers with acidic materials can increase the useful life of the filter. Without wishing to be bound by theory, it is believed that preservatives or stabilizers prolong the useful life of the filter by inhibiting the growth of microbial organisms such as fungi, bacteria and viruses in the filter substrate.

Preferred acidic substances are citric acid. Acidic substances react with or otherwise remove the basic contaminants from air or other gaseous fluids in contact with the filter. In addition, at least one preservative or stabilizer is present at least in the substrate surface, preferably in the substrate. In general, such preservatives and / or stabilizers are homogeneously present in the acidic substance. Preferred stabilizers are polyacrylic acids (PAA). Preferred preservative is sodium benzoate.

In another embodiment, the filter comprises a basic or alkaline substance and an accelerator for removing acidic contaminants. Applicants have found prior to the present invention that the basic material in the filter element does not have an acceptable contaminant removal life and the life of the prior art filter is shortened by the moisture present in the filter. It has been found that inclusion of an accelerator in the basic material can increase the service life of the filter. Without wishing to be bound by theory, accelerators are believed to extend the life of the filter by enhancing the oxidation reaction between the acid gas (contaminant to be removed) and the basic or alkaline material of the filter.

Preferred basic substances are potassium carbonate (K ₂ CO ₃ ). Basic materials react with or otherwise remove acidic contaminants from air or other gaseous fluids in contact with the filter. The accelerator is also present at least on the substrate surface, preferably inside the substrate. Generally, such promoters are homogeneously present in the basic material. Preferred promoter is potassium iodide (KI).

In another embodiment, the filter is a substrate having a reactive substance or reactant present therein and on the top for removing carbonyl containing compounds including ketones and aldehydes, wherein the reactive substance is a sulfite, bisulfite, oxidant or derivative of ammonia, specifically It is a stable high molecular weight amine). Strongly alkaline (basic) materials are particularly suitable for aldehyde removal.

Examples of preferred materials for removal of carbonyl containing compounds are activated carbon such as granular or fibrous forms impregnated with reactants such as sulfites, bisulfites, oxidants or derivatives of ammonia, specifically stable high molecular weight amines. Activated carbon granules or fibers impregnated with strong alkalis are particularly suitable for aldehyde removal.

In another embodiment, the filter comprises a substrate comprising activated carbon fibers, wherein the fibers are constituents of the substrate. This filter embodiment is configured for VOC removal such as methanol, toluene, ethanol and the like. Activated carbon fibers are particularly suitable for removing VOCs present at low concentrations (eg less than 100 ppm). All of the embodiments summarized above can use a substrate having carbon fibers therein. Carbon fibers are suitable for impregnation with reactants such as sulfites, bisulfites, oxidants or derivatives of ammonia, specifically stable high molecular weight amines to remove carbonyl containing compounds and VOCs.

The substrate forming the filter is a fibrous or porous material, such as a cellulosic or polymeric material or a combination thereof. The substrate includes activated carbon fibers for VOC removal. The body of the filter formed by the substrate preferably has a plurality of passages (which provide an airflow through path) extending from the inlet face to the outlet face. The active material is present at least on the surface of the substrate, preferably in the substrate.

The active substance, acidic, alkaline or basic or reactive, is applied to the substrate as a mixture or solution of the active substance. Typically, the mixture or solution is applied by impregnation.

The decontamination filter of the present invention can be used for a variety of high purity applications where it is necessary to remove basic contaminants from a gas stream (eg, an air stream). The term “high purity” and variations thereof means that the contaminant concentration of the cleaned gas stream is less than 1 ppm. In many applications, the desired concentration is less than 1 ppb of contaminants. The decontamination filter of the present invention may be a "no high purity" or "high purity medium". In this application, the terms mean a material that not only removes contaminants from the air stream but also does not diffuse or release the contaminants. Examples of materials that are generally not present in the high purity member or high purity medium include adhesives or other polymeric materials that release gas. It should be understood that in some applications adhesive may be present in the decontamination filter.

In general, filters are used in applications such as lithography, semiconductor processing and photographic and heat removal imaging processes. The proper and efficient operation of fuel cells also requires oxidants that do not contain chemical contaminants. Other applications in which the decontamination filter of the present invention may be used include cleaning the ambient air for the benefit of those who breathe air. Often, these areas are enclosed spaces such as residential, industrial or commercial spaces, aircraft cabins, and automobile cabins.

Referring now to the drawings, wherein like reference numerals and symbols indicate corresponding structures throughout the several views,

1 is a schematic perspective view of one embodiment of a decontamination filter according to the present invention,

2 is a schematic perspective view of a second embodiment of a decontamination filter according to the present invention,

3 is a schematic perspective view of a third embodiment of the decontamination filter of the present invention,

4 is a schematic perspective view of a fourth embodiment of the decontamination filter of the present invention,

5 is a schematic diagram of a system incorporating a plurality of decontamination filters in accordance with the present invention with a particulate filter,

6 is a schematic perspective view of a fifth embodiment of a decontamination filter according to the present invention,

7 is a graph showing test results for various decontamination filters according to the present invention,

8 is a graph showing the test results for the decontamination filter according to the present invention,

9 is a graph showing test results for various decontamination filters according to the present invention,

10 is a graph showing test results for various decontamination filters according to the present invention,

11 is a photograph of the inlet side of the filter member according to the present invention after the test by breakthrough test 3,

12 is a photograph of an inlet side of a filter member of a comparative example after the test in Breakthrough Test 3;

13 is a graph showing test results for Example 11 and Comparative Example F. FIG.

Referring to the drawings, specifically to FIG. 1, there is shown a first aspect 10 of a decontamination filter or member according to the present invention. The decontamination filter 10 is defined by a body 12 having a second surface 19 opposite the first surface 17. In general, the gas to be cleaned of the basic contaminants is introduced into the filter 1 through the first side 17 and discharged through the second side 19. In this aspect, the body 12 is formed by alternating the corrugated layer 14 with the opposing layer 16. The corrugated sheet 14 has a circular wave shape and each valley and peak is generally the same. The opposing layer 16 may be a corrugated layer or a non-corrugated (eg flat) sheet, in which embodiment the opposing layer 16 is a flat sheet. Layer 14 and 16 together define a plurality of passages 20 through body 12 extending from first side 17 to second side 19. The filter 10 may be a "straight-through flow" or "serial flow" (in which the gas to be filtered is introduced in one direction through the first side 17 and generally in the same direction from the second side 19). Means to be released). The length L of the passage 20 is measured between the first face 17 and the second face 19, the dimension L being generally the thickness of the body 12 of the filter 10 in the air flow direction. To qualify.

The second structure 10 ′ of the decontamination filter according to the invention is shown in FIG. 2. Similar to the product of FIG. 1, the decontamination filter 10 ′ is defined by a body 12 ′ having a second face 19 ′ opposite the first face 17 ′. The distance between the first face 17 'and the second face 19' is the thickness of the filter 10 '. The main body 12 'is formed by alternating the corrugated layer 14' with the opposing layer 16 '. The corrugated sheet 14 'has an angular wave shape (each valley and peak is generally the same in height). The opposing layer 16 'may be a corrugated layer or a non-corrugated (eg flat) sheet, in which embodiment the opposing layer 16' is a flat sheet. Layer 14 ′ and 16 ′ together define a plurality of passages 20 ′ passing through body 12 ′ extending from first face 17 ′ to second face 19 ′. .

The body 12 of FIG. 1 and the body 12 'of FIG. 2 are similar in configuration in that they both include corrugated layers 14, 14' and opposing layers 16, 16 '. In the case of the body 12, the two layers 14, 16 are alternately stacked to provide a generally planar filter 10. In the case of the body 12 ', the two layers 14', 16 'are wound alternately to generally provide a columnar filter 10'. The illustrated filter 10 'has an acyclic cross section, such as oval, elliptical or racetrack, and other shapes, in particular rings, may be formed by winding the layers 14', 16 '. Furthermore, a shape with two parallel sides, another two parallel sides perpendicular to the two parallel sides mentioned and four rounded corners between them may also be wound. The wound configuration can include a central core to facilitate winding of the layers.

A third aspect 30 of the decontamination filter according to the invention is shown in FIG. 3. The decontamination filter 30 is defined by a body 32 having a second face 39 opposite the first face 37. In general, the gas to be cleaned is introduced into the filter 30 through the first side 37 and discharged through the second side 39. The distance between the first face 37 and the second face 39 is the thickness of the filter 30. The main body 32 is formed by winding the base layer 35 in a spiral manner. Spacers may be used to obtain the desired spacing between adjacent wraps of layer 35. Adjacent envelopes of layer 35 form passages through filter 30. Similar to filter 10 ′ of FIG. 2, filter 30 may have an annular or acyclic cross section and may include a central core to facilitate winding of the layers.

A fourth aspect 50 of the decontamination filter according to the invention is shown in FIG. 4. As with the above aspects, the filter 50 is defined by a body 52 having a second surface 59 opposite the first surface 57. The distance between the first face 57 and the second face 59 is the thickness of the filter 50. The body 52 is generally formed by a number of individual sheets 65 of substrate arranged to form a spiral shape. For example, the body 52 has a first sheet 65a, an adjacent second sheet 65b and subsequent sheets. These sheets 65 are generally flat but may be corrugated. Adjacent sheets 65, such as sheet 65a and sheet 65b, together pass through a plurality of passages 60 through the body 52 extending from the first surface 57 to the second surface 59. To qualify. As with the above aspects, the member 50 can have an annular or acyclic cross section and can include a core to facilitate the placement of the sheets 65.

Another expected aspect of the decontamination filter according to the present invention is that they have the same centered layers formed by the plurality of individual sheets.

Specific characteristics of the decontamination filters are described below. For convenience, only the reference numbers of the filter 10 which is the first aspect are used, but unless stated otherwise, the description of the characteristics is understood to apply to all aspects.

The body of the filter

The body 12 provides the overall structure of the decontamination filter 10, and the body 12 defines the shape and size of the filter 10. The body 12 may have any three-dimensional shape, such as, for example, cube, columnar, cone, truncated cone, pyramid, pyramid, disc, etc., but the first face 17 and the second face 19 have a surface area. It is preferable that the amount to be introduced into the passage 20 is approximately the same as the amount to be discharged from the passage 20. The cross-sectional shape of the body 12 defined by the first side 17, the second side 19 or any cross section between the first side 17 and the second side 19 may be square, rectangular, triangular, Any two-dimensional form is possible, such as annular, star-shaped, dalgal, oval, racetrack, and the like. Angled forms can also be used. Preferably, the cross section of the body 12 is essentially constant along the length L from the first face 17 to the second face 19.

Typically, the first surface 17 and the second surface 19 are equal in area to 1 cm ² or more. Additionally or alternatively, the first surface 17 and the second surface 19 have an area of about 1 m ² or less. In most embodiments, the area of the first side 17 and the second side 19 is about 70-7500 cm ² . The particular application for the filter 10 has a preferred range for area. The thickness L of the body 12 between the first surface 17 and the second surface 19 is generally at least 0.5 cm, and generally at most 25 cm. In most embodiments, L is about 2-10 cm. Two particularly suitable thicknesses of the body 12 are 2.5 cm and 7.5 cm. The dimensions of the body 12 affect the residence time of the gas in the filter and the final removal rate of contaminants from the gas stream.

The body 12 typically has a plurality of passages 20 extending therethrough (see members 10 and 10 'in FIGS. 1 and 2). The passageway 20 may have any shape, for example square, rectangular, triangular, annular, trapezoidal, hexagonal (eg honeycomb), but the preferred shape is generally hemispherical as shown in FIG. . Preferably, the shape of the passageway 20 does not vary significantly from the first face 17 to the second face 19, and each passage 20 in the filter 10 has a similar cross-sectional shape.

Each passageway 20 typically has a cross-sectional area of typically about 50 mm ² or less, which cross section is generally parallel to at least one of the first side 17 and the second side 19. Alternatively or in addition, the passage 20 typically has a cross-sectional area of at least about 1 mm ² . In general, the cross-sectional area of each passage 20 is about 1.5 to 30 mm ² , often about 2 to 4 mm ² . In one preferred embodiment, the cross-sectional area of the hemispherical passageway 20, such as the passageway 20 shown in FIG. 1, is about 7-8 mm ² . In another preferred embodiment, the area of the passageway 20 is 1.9 mm ² .

The longest cross-sectional dimension of the passage 20 is typically 10 mm or less, often 6 mm or less. In addition, the shortest dimension of the passageway 20 is at least 0.25 mm, often at least 1.5 mm.

The total internal surface area of each extension passage 20 is generally at least about 5 mm ² and generally at most about 200 cm ² . The total surface area of the filter 10 defined by the inner surface area of the passage 20 is at least about 200 cm ² or about 250 cm ² to 10 m ² .

In a third aspect (FIG. 3), member 30 has a single passage formed by continuous and adjacent winding of layer 35. In this structure, the total internal surface area of the member 30 is at least about 200 cm ² , typically about 250 cm ² to 10 m ² .

The passage wall defining the shape and size of the passage 20 is defined by the substrate forming the body 12. The substrate is generally at least 0.015 mm thick. Alternatively or in addition, the passage wall is generally 5 mm or less in thickness. Typically, the passage wall is 2 mm or less in thickness. The thickness of the wall depends on the size of the passage 20, the substrate from which the body 12 is made, and the intended use of the filter 10. In configurations where layer 14 and opposing layer 16 define passage 20, the passage wall is defined by layer 14 and opposing layer 16.

In most embodiments, each passage 20 has a size and shape that is continuous along its length. In general, the length of each passageway 20 is essentially equal to the thickness L between the first side 17 and the second side 19. The passage 20 is not considered to be a straight line from the first face 17 to the second face 19, but this is generally not desirable due to the possibility of an undesirable level of pressure drop through the passage 20.

Body 12 (eg, layers 14, 16) is formed from a porous or permeable substrate, with a fibrous material being the preferred material. Examples of substrates suitable for the body 12 include natural materials (such as cellulosic materials) and polymeric materials. The substrate can be a nonwoven fibrous material (eg, a spun-bonded material), a woven fibrous material, a knitted fibrous material, or a continuous or independent bubble foam or sponge material. Specific examples of suitable substrates include glass fiber paper, crepe paper, kraft paper, wool, silk, cellulosic fiber fabrics such as cotton, linen, viscose or rayon, and synthetic fiber fabrics such as nylon, polyester, Polyethylene, polypropylene, polycarbonate, polyvinyl alcohol, acryl and polyamide). Porous ceramic material may also be used for the body 12.

Activated carbon fibers in the body 12 are particularly desirable for removing low concentrations (less than about 100 ppm) of VOCs. The fiber may be present in an amount of 20% to 100% by weight, although 30 to 80% by weight is most common. Activated carbon fibers are generally mixed with one or more other fibers to form the body 12, with combination with thermoplastic fibers being preferred. Thermoplastic fibers add strength and stiffness to the material. Carbon fibers may be present in one or both of layers 14 and 16.

Activated carbon fibers suitable for use in the body 12 for removing VOCs typically have a nominal BET surface area of approximately 800 to 3000 m ² / g, micropore volume of approximately 0.3 to 0.8 cm ³ / g and a fiber diameter of 5 to 100. Μm and an average fiber length of 0.1 to 10 mm.

The material used for the body 12 should not cause the release of contaminants or harmful gas releases that affect the action of the active material (ie acidic, basic or other reactive material) present in the body 12. Examples of materials that are desirable to avoid are adhesives and such other gas release materials. There are several adhesives that are acceptable in certain applications, although there are acceptable adhesives although the gas release levels, amounts and types are not harmful for use.

Preferred substrates for the body 12 have thermoplastic polymeric fibers in combination with cellulose fibers. The two fibers are homogeneously combined or entangled to form a sheet-like substrate. Upon heating, the polymeric fibers soften and at least partially melt to bond the fibers together. Upon cooling, the polymeric fibers are restocked. By using a substrate comprising a polymeric material it is possible to join multiple sheets or layers of the substrate without the use of an adhesive. Specific examples of suitable substrates have about 40 weight percent polyethylene terephthalate (PET) fibers and about 60 weight percent cellulose fibers. Another specific example of a suitable substrate has about 60% by weight activated carbon fiber and about 40% by weight polyester fiber. Other combinations of thermoplastic fibers and non-thermoplastic fibers are also suitable.

An example of a preferred body 12 as shown in FIG. 2 can be made from corrugated sheet 14 and opposing sheet 16 (both have thermoplastic polymeric fibers in combination with cellulose fibers). The sheet 14 and the sheet 16 may be passed through an ultrasonic welder using high frequency sound waves to locally heat the sheet. Pressure is applied to the areas where the sheets 14 and 16 are in contact with each other to bond the sheets 14 and 16 together. Sheet 14 and sheet 16 made using activated carbon fibers and thermoplastic polymeric fibers may be bonded in this manner.

The method of making the body 12 from the corrugated sheet 14 and the opposing sheet 16 is taught, for example, in US Pat. No. 6,416,605 and WO 03/47722, which are incorporated herein by reference. It is. Body 12 is a carrier for acidic material that removes contaminants from air or other gaseous fluids passing through filter 10.

As provided above, the contaminant removal filter 10 includes one or more active materials, such as acidic, basic or alkaline, or reactive materials selected to remove base, acid and carbonyl containing compounds, respectively. The decontamination filter 10 may alternatively or additionally include activated carbon fibers in the body 12 to remove VOCs.

In order to produce a filter 10 in which the active material is provided in and on the body 12 rather than as a fiber in the body 12, it is impregnated in or on a substrate that provides the active material to the liquid carrier and forms a decontamination filter. Let's do it. Typically and preferably, the active substance is impregnated into the substrate in the form of a solution. It is understood that some materials do not dissolve in the solvent but rather disperse. Water is the preferred solvent for the form of solutions, dispersions or other mixtures.

The amount of active substance in the impregnation solution is selected based on the specific active substance and the substrate used. The amount of active substance in the solution is at least about 0.5% by weight and at most about 75% by weight. Preferably, the amount of active substance is 5-50% by weight or 10-50% by weight.

Although the terms "impregnation", "impregnate" and the like are used, it is to be understood that the method of application of the active material to the substrate is not limited to impregnation. Other methods of providing the active material to the substrate can be used. Other alternatives and suitable methods of applying the active material to the substrate include dipping, spraying, brushing, knife coating, kiss coating, and other methods known for applying liquid to the surface of the substrate. do. Impregnation or other application methods can be carried out at atmospheric pressure or under pressure or vacuum.

In a preferred method, the substrate is molded into the body 12 prior to application of the active material. However, it is understood that the body 12 may be molded after the substrate is molded into the body 12. When activated carbon fiber is included in the body 12, it is understood that the substrate is molded with the fiber.

After impregnation, the substrate is at least partially dried to remove solvent (eg water) and to leave the active material inside and on top of the substrate. Preferably, at least 90% of all free water or other solvents are removed, and most preferably at least 95% of all free water or other solvents are removed.

The active material is present above and inside the surface area of at least 50% of the passageway 20 of the member. Preferably, the active material is present on and inside at least 55-70% of the passage wall surface, preferably at least 90% of the surface, and most preferably there is no area free of active areas. The active material is present at least 10% of the thickness of the substrate. Preferably, the active material is present at least 50%, more preferably at least 80% of the substrate. If the active material is an activated carbon fiber in the substrate, the substrate has at least 30% by weight, preferably at least 60% by weight, of activated carbon homogeneously unsaturated throughout the layers 14 and 16. In some embodiments, only one of layers 14 and 16 includes carbon fibers.

Active materials generally do not increase the thickness of the substrate. However, the active material may change the properties of the substrate, such as to make the substrate harder or softer.

Acidic substance as active substance

In one embodiment, the decontamination filter 10 includes an acidic material as the active material. Acidic substances remove basic contaminants from the air passing through the passage by reacting with or otherwise removing the contaminants.

Examples of acidic materials suitable for use in the absence of the present invention include carboxylic acids (mono, di, tri and polyacids, linear, branched and cyclic), such as citric acid, oxalic acid, malonic acid and higher homologues, aromatic carboxylic acids; Sulfonic acids (linear, cyclic and aromatic); Inorganic acids such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid; Heteropolyacids (super acids) are included. Citric acid is a preferred acidic substance.

The amount of acidic material in the impregnation solution is selected based on the acidic material and the substrate used. The amount of acidic material in the solution is at least about 0.5% by weight and at most about 75% by weight. Preferably, the amount of acidic material is 10 to 50% by weight. In the case of citric acid, which is a preferred acidic substance, the amount of citric acid is about 10 to 50% by weight, preferably 15 to 35% by weight. Other amounts of acid may also be suitable.

Low concentrations of acidic materials have generally been found to be preferred over high concentrations. For example, a solution having 5 to 15 weight percent citric acid is preferred over a solution having 20 to 35 weight percent citric acid. As a specific example, it has been found that impregnating a substrate with an aqueous 5% citric acid solution, drying the substrate, and then impregnating with an aqueous 12 wt% citric acid solution provides a better removal of basic contaminants than a one-step impregnation with 25% citric acid solution. . In addition, such a low concentration two-step impregnation process is preferable to the one-step impregnation process.

Additives to avoid when acidic substances are active substances

It is hypothesized that as the moisture content of the substrate increases, the suitable life of the acid impregnated member decreases. Therefore, it is undesirable to use humectants that increase the water content of the dried substrate. Examples of wetting agents to avoid include urea, glycerol, glycerin, alcohols, polyvinylpyridine, polyvinylpyrrolidone, polyvinylalcohols, polyacrylates, polyethylene glycols and cellulosic acetates. It is also undesirable to use organic amines that increase the water content of the dried substrate. Examples of organic amines to be avoided include alkanol amines, hydroxyl amines and polyamines.

Acceptable additives when the acidic substance is the active substance

While not wishing to be bound by theory, the moisture present in the substrate of the filter element is believed to promote the growth of microbial organisms such as fungi, bacteria and viruses on the filter, which microorganisms react with or exacerbate acidic substances. Let's do it. When one or more preservatives or stabilizers are added to the acidic substance, it has been found that the effectiveness of the acidic substance on the life of the member is improved and the life of the filter member is extended.

The amount of stabilizer and / or preservative in the impregnation solution is selected depending on the acidic substance and the stabilizer or preservative used. The amount of stabilizer and / or preservative in the solution is about 0.01% by weight or more and about 20% by weight or less. Preferably, the amount of stabilizer and / or preservative is from 0.01 to 10% by weight, more preferably from about 0.1 to 10% by weight, depending on the additive. Other amounts of stabilizers and / or preservatives may also be suitable.

An example of a suitable stabilizer is polyacrylic acid. The preferred amount of polyacrylic acid in the solution, if present, is about 1 to 10% by weight, preferably 6 to 10% by weight. This amount is particularly suitable when the acidic substance is citric acid. Preferred amounts of polyacrylic acid as a ratio to citric acid are about 1: 1 to 1:10, more preferably about 1: 2 to 1: 4.

Examples of suitable preservatives include benzoic acid, sodium benzoate, potassium nitrate, potassium nitrite, sodium nitrite, sodium nitrate, methyl paraben, ethyl paraben, methyl paraben, ethyl paraben, propyl paraben, butyl paraben, propionic acid, sodium propionate, calcium propane Cypionate, sorbic acid, potassium sorbate, acetic acid, phosphoric acid, sodium sorbate, calcium sorbate, potassium benzoate, calcium benzoate, ethyl parahydroxybenzoate, sodium ethyl parahydroxybenzoate, propyl parahydroxybenzo Ate, biphenyl, diphenyl, orthophenyl phenol, sodium orthophenyl phenol, sodium sulfite and sodium sulfate. The preferred amount of sodium benzoate in the solution, if present, is from about 0.01 to 5% by weight, preferably from 0.1 to 1% by weight, even more preferably from about 0.1 to 0.5% by weight. This amount is particularly suitable when the acidic substance is citric acid. The preferred amount of sodium benzoate as the ratio to citric acid is about 1: 5 to 1: 1000, more preferably about 1:50 to 1: 700.

Alkaline or basic substance as active substance

In another embodiment, the decontamination filter 10 includes a basic material as the active material. Basic substances are removed from the air passing through the passage by reacting or otherwise removing the contaminants from the acidic contaminants.

Examples of basic materials suitable for use in the absence of the present invention include basic salts such as carbonates, bicarbonates, hydroxides, quaternary ammonium compounds (generally in hydroxide form); And metal oxides such as copper oxide, manganese oxide and iron oxide. Ion exchange resins, including polystyrene quaternary ammonium (hydroxide form), polystyrene tertiary amines, grafted polyethylene and grafted polypropylene, are also suitable for removing basic contaminants. In the case of basic salts of alkali metals and alkaline earth metals, lithium, sodium and potassium salts are usually used. Potassium carbonate is a preferred basic material for use in the decontamination member 10. Examples of other preferred basic materials are potassium bicarbonate, sodium carbonate and sodium bicarbonate.

The amount of basic material in the impregnation solution is selected based on the basic material and the substrate used. The amount of basic substance in the solution is about 0.5% by weight or more and about 75% by weight or less. Preferably, the amount of basic material is 10 to 50% by weight. In the case of potassium carbonate, which is the preferred basic substance, the amount thereof is about 10 to 50% by weight, preferably 15 to 35% by weight. Other amounts of basic material may also be suitable.

Additives to avoid if alkaline material is active

It is hypothesized that as the amount of moisture in the substrate increases, the suitable life of the member decreases. Therefore, it is not desirable to use humectants that increase the water content in the dried substrate. Examples of wetting agents to avoid are urea, glycerol, glycerin, alcohols, polyvinylpyridine, polyvinylpyrrolidone, polyvinylalcohols, polyacrylates, polyethylene glycols and cellulosic acetates. It is also undesirable to use organic amines that increase the water content in the dried substrate. Examples of organic amines to avoid are alkanol amines, hydroxyl amines and polyamines.

Acceptable additives when the alkaline substance is the active substance

It has been found that the addition of a promoter to the basic or alkaline material can improve the effectiveness of the basic or alkaline material over the life of the member and extend the life of the filter element.

The amount of promoter in the impregnation solution is selected based on the basic material and the promoter used. Examples of suitable promoters are alkali metal and alkaline earth metal iodides and iodites such as potassium iodide, sodium iodide, lithium iodide, potassium iodide, sodium iodide and lithium iodide. Preferred promoters are potassium iodide, which is particularly suitable for use with potassium carbonate materials.

The amount of accelerator in the solution is at least about 0.01% by weight and at most about 20% by weight. Preferably, the amount of promoter is 0.1 to 10% by weight, more preferably about 0.1 to 5% by weight. This amount is particularly suitable when the basic material is about 5% by weight. Other amounts of promoter may also be suitable. Preferred amounts of promoter as a ratio to basic material are about 1: 1 to 1:50, more preferably about 1: 3 to 1:10.

Reactant as Active Material

In another embodiment, the decontamination filter 10 includes a reactant as an active material. The reactants are removed from the air passing through the passage by reacting or otherwise removing the carbonyl containing compound with the compound.

Examples of suitable reactants for use in the filter elements of the invention include sulfites, bisulfites, oxidants or derivatives of ammonia, specifically stable high molecular weight amines. In the case of the removal of aldehydes, strongly alkaline (basic) substances are preferred.

More specific examples of suitable reactants include sodium sulfite and potassium sulfite for sulfite, sodium bisulfite and potassium bisulfite for bisulfite, derivatives of ammonia, specifically 2,4-dinitro for suitable stable high molecular weight amines Phenyl hydrazine (DNPH), 2-hydroxymethyl piperidine (2-HMP) and tris (hydroxymethyl) aminomethane, in the case of strong alkalis there are sodium hydroxide and potassium hydroxide. Various examples of ways of removing the carbonyl containing compound are provided below.

The reaction example of sulfuric acid and a carbonyl containing compound is as follows.

RCR'O + Na ₂ SO ₃ + H ₂ O → NaOH + HORCR'SO ₃ Na

The reaction example of bisulfite and a carbonyl containing compound is as follows.

RCR'O + NaHSO ₃ → HORCR'SO ₃ Na

Examples of stable high molecular weight amines and aldehydes are as follows.

HCHO + NH ₂ -R → HCNH-R + H ₂ O

Examples of the reaction between strong alkalis and aldehydes are as follows.

2RCH0 + NaOH → RCOONa + RCH ₂ OH

The amount of reactant in the impregnation solution is selected based on the reactant and the substrate used. The amount of reactant in the solution is at least about 0.5% by weight and at most about 75% by weight. Preferably, the amount of reactant is from 5 to 50% by weight. For example, when using tris (hydroxymethyl) aminomethane, its preferred amount in the impregnation solution is about 5% by weight. When using sodium hydroxide, its preferred amount is about 5% by weight. Other amounts of reactant may also be suitable (eg, 10-50% by weight).

Additives to Avoid

It is theorized that as the moisture content of the substrate increases, the suitable life of the member decreases. Therefore, it is undesirable to use humectants that increase the water content of the dried substrate. Examples of wetting agents to avoid include urea, glycerol, glycerin, alcohols, polyvinylpyridine, polyvinylpyrrolidone, polyvinylalcohols, polyacrylates, polyethylene glycols and cellulosic acetates.

All active materials described above are impregnated or otherwise applied to activate the carbon fibers.

play

It has been found that the decontamination filter of the present invention can be regenerated regardless of having acidic, basic or reactive substances. After use or after long periods of inactivity, the member can be impregnated again with an acidic, alkaline or reactive material. This second or subsequent impregnation can be carried out with or without cleaning the preceding contaminants from the filter, and the cleaning of the filter can be carried out, for example, with water washing. As long as the substrate has physical integrity, it is expected that the substrate may be impregnated any number of times.

Use of the decontamination filter 10

The decontamination filter 10 of the present invention can be used for various applications where removal of contaminants from a gas stream (eg an air stream) is desired. The decontamination filter 10 is particularly suitable for high purity, where the removal rate of chemical contaminants from gas is less than 1 ppm. In many high purity applications, the preferred amount of contaminants is less than 1 ppb. The filter 10 itself generally does not add any contaminants such as gas emissions.

Examples of common air basic contaminants that can be removed with acid impregnated filter 10 include ammonia, amines, amides, N-methyl-1,2-pyrrolidone, sodium hydroxide, lithium hydroxide, potassium hydroxide, volatile organic bases. And organic bases such as nonvolatile organic bases. Examples of common aerial acid contaminants that can be removed with the alkali impregnated filter 10 include oxides of sulfur, oxides of nitrogen, HCl (hydrochloric acid), HNO ₃ (nitric acid), H ₂ S (hydrogen sulfide), H ₂ SO ₄ ( Sulfuric acid) and HCN (hydrogen cyanide). Examples of common aerial carbonyl containing compounds are ketones containing acetone, aldehydes including formaldehyde. Carbonyl containing compounds are generally quite malodorous and uncomfortable for many people. Some people have allergic reactions to carbonyl containing compounds.

Generally, the decontamination filter 10 can be used for all applications using packed granule layers, such as lithography processes, semiconductor processing, photographic and heat removal imaging processes. Proper and efficient operation of fuel cells benefits from intake air that does not contain unacceptable basic contaminants. Other uses that may use the decontamination filter 10 include cleaning ambient air for the benefit of those who breathe air. The filter 10 can be used with personal devices such as masks (traditional and motorized masks) and with self contained breathing devices to provide clean breathing air. The decontamination filter 10 can also be used on a large scale for confined spaces such as residential and commercial spaces (eg, rooms and buildings as a whole), aircraft cabins, and automotive cabins. It is also desirable to remove contaminants prior to releasing air to the atmosphere, examples of which include vehicle or other vehicle emissions, exhaust from industrial work or other operations or uses where chemical contaminants may be released to the environment. .

Filter 10 is typically located in a housing, frame, or other type of structure such that gaseous flow (eg, airflow) enters and penetrates passage 20 of filter 10. In many structures, the filter 10 is at least partially surrounded by a circumference of its surroundings by a housing, frame or other structure.

If a decontamination filter 10 made by any of the processes described herein is placed in the system, a pre-filter, post-filter or both may be used with the decontamination filter 10. Can be. The prefilter is located upstream of the filter 10 to remove airborne particles before using the filter 10. The post filter is located downstream of the filter 10 to remove residual particles from the filter 10 before the air is released. These filters are generally located opposite or in proximity to each of the first side 17 and the second side 19. An example of a filter that includes a prefilter is shown in FIG. 5.

In FIG. 5, a system 100 for removing contaminants from a dirty gas stream 101 is shown. System 100 includes a granular filter 105, a first decontamination filter 110, and a second decontamination filter 110 ′. The particulate filter 105 is configured to remove solid particles such as dust and smoke from the gas stream 101. Typically, when using particulate filter 105, particulate filter 105 is located upstream of decontamination filter 110, 101 to reduce the likelihood that filter 110, 110 ′ is clogged or filled with particles. Let's do it. As one example, the first contaminant removal filter 110 is configured to remove basic contaminants from the gas stream 101, and the second contaminant removal filter 110 ′ is configured to remove acidic contaminants from the gas stream 10. do. As another aspect, the filters 110, 110 ′ may be configured in any manner to remove acidic contaminants, basic contaminants or carbonyl containing compounds. After passing through the particulate filter 105, the decontamination filter 110 and the decontamination filter 110 ', respectively, a cleaned gas stream 102 is obtained.

Any or all of the particulate filter 105, filter 110, and filter 110 ′ may be retained in a housing, such as housing 120. The filters 105, 110, 110 ′ may be located adjacent to each other or there may be a gap between the filters.

Another configuration for the combined base contaminant removal filter and particulate filter is shown as filter 70 in FIG. 6. The decontamination filter 70 is defined by a body 72 having a second surface 79 opposite the first surface 77. In general, gas to be cleaned of contaminants is introduced into filter 70 through first side 77 and discharged through second side 79. Body 72 is similar to body 12 of filter 10 ′ in FIG. 2 with alternating corrugated layers 74 and opposing layers 76. Layer 74 and 76 together define a plurality of passageways 80. The first set of passages 80 are blocked or sealed at the first face 79, which is shown as a seal 85. At the opposite end of the seal 85, the passage 80 is open. In addition, the second set of passageways 80 is blocked and sealed at the second face 79 and open at the first face 79.

In use, the particulate fill gas is introduced into the passage 80 open at the first side 79. The particulate is captured in the passage 80 due to the sealed second side 79, while the gas passes through the passage wall formed of the fibrous substrate. Active material in and on the substrate removes airborne contaminants. The cleaned gas is discharged through the second side 70.

The filter 70 is called a z-filter, a direct flow filter, or a series filter. Particulate removal characteristics of filters such as filter 70 are described, for example, in US Pat. Nos. 5,820,646, 6,190,432 and 6,350,291.

If there is contaminant that has not been removed and has passed through the filter 10, an indicator or indicator system for monitoring its amount is located downstream of the filter 10 or one of the other aspects. Such indicators are well known.

The shape and size of the filter 10 is selected to remove the desired amount of contaminants from the penetrating gas or air based on the residence time of the gas in the filter 10. For example, at least 90%, more preferably at least 95% of contaminants are removed. In some embodiments, large amounts of contaminants of at least 98% are removed. The desired amount for the contaminant to be removed is believed to differ depending on the use and the amount and type of contaminant. As an example, in the case of semiconductor processing equipment, the residence time of the introduced air in the filter 10 is typically about 0.06 to 0.36 seconds, which can be achieved using a member having a thickness of about 7.6 to 15 cm.

The following non-limiting examples will further illustrate the present invention. All parts, percentages, ratios, etc. in the examples are by weight unless otherwise indicated.

Two different bodies are used for the decontamination member.

Main body 1: The main body 1 is similar to the main body of FIG. 2 formed by alternating a flat counter sheet and a sinusoidal sheet. Each sheet is made of 100% cellulose fiber. The sheet is wound to form a circumference. The resulting hemispherical passageway is approximately 3.4 mm in height and 5.0 mm in width. The cross-sectional area of each passageway is about 8.5 mm ² . The sheets are joined with a urethane adhesive.

Body 2: Body 2 is similar to Body 1 except that Body 2 has a hemispherical passageway of approximately 1.05 mm in height and 2.90 mm in width. The cross-sectional area of each passageway is about 1.5 mm ² . The sheets are made of 60% cellulose fibers and 40% PET fibers. The sheets are joined with a thermoplastic melted with heat generated from ultrasonic energy.

Acid Impregnated Example

The body is impregnated with an acidic substance in the following manner. A predetermined volume of acidic solution is placed in a beaker. The fibrous body is placed in a beaker to immerse the whole body in the solution. After approximately 60 seconds, the body is removed and dried in the oven for 1 hour. After drying, the resulting filter element is tested to determine its life expectancy.

Breakthrough Test 1

The filter element is placed in a test chamber and sealed to provide the upstream and downstream sides of the filter. An air stream containing 50 ppm of ammonia is delivered to the upstream side of the filter element at a flow rate of 30 l / min. Upstream and downstream ammonia concentrations are monitored using an ammonia detector.

Comparative Example A: An aqueous 35% by weight citric acid solution was prepared. Body 1, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Comparative Example A is tested in Breakthrough Test 1 and the results are shown in the graph of FIG. 7.

Example 1: An aqueous solution of 35% citric acid and 6% polyacrylic acid was prepared. Body 1, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Example 1 is tested by Breakthrough Test 1 and the results are shown in the graph of FIG. 7.

Example 2: An aqueous solution of 35% citric acid and 1% polyacrylic acid was prepared. Body 1, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Example 2 is tested by Breakthrough Test 1 and the results are shown in the graph of FIG. 7.

Example 3: An aqueous solution of 35 wt% citric acid and 0.5 wt% sodium benzoate is prepared. Body 1, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Example 3 is tested by Breakthrough Test 1 and the results are shown in the graph of FIG. 7.

7 shows that the time (minutes) to reach the 10% threshold over time (along the x-coordinate) decreases in both Comparative Example A and Example 2, but not as quickly as Comparative Example A. During the test period, Examples 1 and 3 show no performance loss.

Comparative Example B: An aqueous solution of 15 wt% citric acid and 15 wt% urea is prepared. Body 1, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Comparative Example B is tested by Breakthrough Test 1 and the results are shown in the graph of FIG. 8.

Example 4: An aqueous solution of 15% citric acid and 10% polyacrylic acid is prepared. Body 1, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Example 4 is tested by Break Test 1 and the results are shown in the graph of FIG. 8.

FIG. 8 shows that the time (minutes) to reach the 10% threshold over time (depending on the x-coordinate) decreases for Comparative Example B with humectant. During the test period, Example 4 shows no performance loss.

Example 5: An aqueous solution of 35% by weight citric acid and 0.5% by weight sodium sulfate is prepared. Body 2, about 3.8 cm in diameter and about 2.5 cm in length, is impregnated with the solution. Example 5 is tested by Break Test 1 and the results are shown in the graph of FIG. 9.

Example 6: An aqueous solution of 35% citric acid and 0.5% sodium benzoate is prepared. Body 2, about 3.8 cm in diameter and about 2.5 cm in length, is impregnated with the solution. Example 6 is tested by Breakthrough Test 1 and the results are shown in the graph of FIG. 9.

Example 7: An aqueous solution of 50% citric acid and 0.5% sodium benzoate is prepared. Body 2, about 3.8 cm in diameter and about 2.5 cm in length, is impregnated with the solution. Example 7 is tested by Breakthrough Test 1 and the results are shown in the graph of FIG. 9.

Example 8: An aqueous solution of 35 wt% citric acid and 0.5 wt% sodium sulfate was prepared. Body 2, about 3.8 cm in diameter and about 2.5 cm in length, is impregnated with the solution. The body of Example 8 was dried over the weekend (approximately 48 hours) and then tested according to Breakthrough Test 1. The results are shown in the graph of FIG.

9 shows that, during the test period, Example 5, Example 6, and Example 8 had no performance loss. In Example 7, the breakthrough time increased. This may be due to the small range of test data obtained and the small area of the filters tested. If the diameter is 3.8 cm, the center of the filter is damaged and causes a slight variation in 10% breakthrough time but the overall capability is good.

Alkaline Impregnated Example

The body is impregnated with the basic material according to the following method. The desired volume of basic solution is placed in a beaker. The fibrous body is placed in a beaker to immerse the whole body in the solution. After approximately 60 seconds, the body is removed and dried in the oven for 1 hour. After drying, the resulting filter element is tested to determine its life expectancy. The filter element is placed in a test chamber and sealed to provide the upstream and downstream sides of the filter.

Breakthrough Test 2

For breakthrough test 2, an air stream containing 500 ppb SO ₂ and a relative humidity of 50% is delivered to the upstream side of the filter element at a flow rate of 30 l / min. Sulfur dioxide concentrations upstream and downstream are monitored using a SO ₂ detector.

Breakthrough Test 3

For breakthrough test 3, an air stream containing 50 ppm SO ₂ and a relative humidity of 50% is delivered to the upstream side of the filter element at a flow rate of 30 l / min. Sulfur dioxide concentrations upstream and downstream are monitored using a SO ₂ detector.

Comparative Example C: An aqueous 20% wt potassium carbonate (K ₂ CO ₃ ) aqueous solution was prepared. Body 2, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Comparative Example C is tested in Breakthrough Test 2 and the results are shown in the graph of FIG. 10.

Comparative Example D: A 20 wt% aqueous potassium carbonate (K ₂ CO ₃ ) solution was prepared. Body 2, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Comparative Example D is tested with Breakthrough Test 2 and the results are shown in the graph of FIG. 10.

Example 9 Prepare 20 wt% potassium carbonate (K ₂ CO ₃ ) and 6.6 wt% aqueous KI solution. Body 2, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Example 9 is tested by Break Test 2 and the results are shown in the graph of FIG. 10.

10 shows the amount of SO ₂ passed through the filter element tested over time. Example 9 comprising an accelerator provides better SO ₂ removal than Comparative Example C and Comparative Example D.

Comparative Example E: 20 wt% aqueous potassium carbonate (K ₂ CO ₃ ) solution was prepared. Body 2, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Comparative Example E is tested by Break Test 3. A photograph of the sample tested is shown in FIG. 12.

Example 10 Prepare 20 wt% potassium carbonate (K ₂ CO ₃ ) and 6.6 wt% aqueous KI solution. Body 2, about 3.8 cm in diameter and about 7.5 cm in length, is impregnated with the solution. Example 10 is tested by Break Test 3. A photograph of the sample tested is shown in FIG. 11.

Quantitative test results from breakthrough test 3 for Comparative Example E and Example 10 show that the two filter element lifetimes are similar. However, comparing FIG. 11 and FIG. 12, although the two samples adsorb the same amount of SO ₂ , the pressure drop across the filter is quite different. As can be seen in FIG. 12, the inlet side of Comparative Example E significantly accumulates material and reduces the volume available for airflow penetration. The crystal accumulation at the inlet side of Comparative Example E was found to be K ₂ SO ₃ . No accumulation for Example 10 was observed (FIG. 11). This accumulation is not observed in breakthrough test 2 at low concentrations.

Reactant Impregnation Examples

The body is impregnated with the reactant according to the following method. The desired volume of reactant solution is placed in a beaker. The fibrous body is placed in a beaker and the whole body is immersed in the solution. After approximately 60 seconds, the body is removed and dried in the oven for 1 hour.

After drying, the resulting filter element is tested to determine its life expectancy.

Breakthrough Test 4

For breakthrough test 4, the filter element is placed in a test chamber and sealed to provide the upstream and downstream sides of the filter. An air stream containing 0.7 ppm of formaldehyde and having a relative humidity of 50% is delivered to the upstream side of the filter element at a flow rate of 30 l / min. The filter element is 3.8 cm in diameter and 2.54 cm in length. Formaldehyde concentration downstream is monitored using a detector.

Comparative Example F: A filter element is made from body 1 having a diameter of about 3.8 cm and a length of about 2.54 cm. There is no surface or substrate treatment of the main body substrate.

Example 11: A 5 wt% tris (hydroxymethyl) aminomethane aqueous solution is prepared. Body 1, about 3.8 cm in diameter and about 2.54 cm in length, is impregnated with the solution.

Example 11 and Comparative Example F were tested according to Breakthrough Test 4, and the results are shown in FIG. The graph of FIG. 13 shows that the impregnated filter element (Example 11) has greatly extended its life. The amount of formaldehyde reached 0.5 ppm almost immediately for Comparative Example F, while Example 11 reached 0.5 ppm aldehyde after at least 5000 minutes.

While numerous features and advantages of the invention are set forth in the foregoing Detailed Description, together with the structure and operation of the invention, the disclosure is for illustrative purposes only and in particular the principles of the invention in terms of shape, size and arrangement of the components. It is to be understood that within the scope of the appended claims, the broad general meaning of the terms may be varied to the extent indicated.

Claims (21)

Citric acid and one or more preservatives or stabilizers (a), basic materials and accelerators (b), wherein the filter does not contain a humectant, or sulfites, bisulfites, ammonia throughout the fibrous substrate and throughout the substrate, in particular A contaminant removal filter comprising a body comprising an active material which is one of the reactants (c) selected from the group consisting of stable high molecular weight amines and strong alkalis. The method of claim 1, wherein the preservative, if present, sodium benzoate, benzoic acid, potassium nitrate, potassium nitrite, sodium nitrite, sodium nitrate, methyl paraben, ethyl paraben, propyl paraben, butyl paraben, propionic acid, sodium propionate, Calcium propionate, sorbic acid, potassium sorbate, acetic acid, phosphoric acid, sodium sorbate, calcium sorbate, potassium benzoate, calcium benzoate, ethyl para-hydroxybenzoate, sodium ethyl para-hydroxybenzoate, propyl A decontamination filter selected from the group consisting of para-hydroxybenzoate, biphenyl, diphenyl, orthophenyl phenol, sodium orthophenyl phenol, sodium sulfite, sodium sulfate and combinations thereof. The contaminant removal filter of claim 1, wherein the stabilizer is polyacrylic acid, when present. The contaminant removal filter of claim 1, wherein the citric acid to preservative ratio is from 1: 1 to 5000: 1 when citric acid and preservative are present. The filter of claim 1, wherein the citric acid to stabilizer ratio is between 1: 1 and 50: 1 when citric acid and stabilizer are present. The contaminant of claim 1, wherein the basic substance, when present, is an alkali or alkaline earth metal, a quaternary ammonium compound, a metal oxide, a basic anion ion exchange resin, or a combination thereof selected from the group consisting of carbonates, bicarbonates and hydroxides. Removal filter. The decontamination filter of claim 6, wherein the basic substance is potassium carbonate. The contaminant removal filter according to claim 1, wherein the accelerator, if present, is potassium iodide, sodium iodide, lithium iodide, potassium iodide, sodium iodide or lithium iodide. The decontamination filter of claim 8, wherein the promoter is potassium iodide. The contaminant removal filter of claim 1, wherein the promoter to basic material, when present, has a ratio of promoter to basic material between 1: 1 and 1: 5000. The decontamination filter of claim 10, wherein the ratio of promoter to basic material is 1: 1 to 1:10. 2. A derivative according to claim 1, wherein a derivative of ammonia, if present in 2,4-dinitrophenyl hydrazine (DNPH), 2-hydroxymethyl piperidine (2-HMP) and tris (hydroxymethyl) aminomethane One, decontamination filter. The contaminant removal filter of claim 12, wherein the derivative of ammonia is tris (hydroxymethyl) aminomethane. The contaminant removal filter of claim 1, wherein the sulfite is sodium sulfite or potassium sulfite, when present. The contaminant removal filter of claim 1, wherein the bisulfite, if present, is sodium bisulfite or potassium bisulfite. The decontamination filter according to any one of claims 1 to 15, wherein the fibrous substrate has a first side, a second side, and a plurality of passages extending from the first side to the second side. 17. The decontamination filter of claim 1, wherein the filter is configured for straight-through flow. 18. The decontamination filter of any of claims 1 to 17, wherein the fibrous substrate comprises thermoplastic fibers. The decontamination filter according to any one of claims 1 to 18, wherein the fibrous substrate comprises activated carbon fibers. The contaminant removal filter of claim 1, which contains no humectant. Providing a substrate (a) and 16. A method of making a decontamination filter according to any one of claims 1 to 15, comprising the step (b) of applying the mixture of active substances to the substrate by impregnation.

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