AIK FILTRATION MEDIA tX)MPRISlNG MKTAL-DOPED SILICON-BASED GEL MATERIALS WITH OXIDIZING AGENTS

Field of the Invention

The present invention relates generally to an environmental control for use in air handling systems that provides highly effective filtration of noxious gases (such as ammonia). Such a filtration system utilizes novel metal-doped silica-based gels to trap and remove such undesirable gases from an enclosed environment. Such gels exhibit specific porosity requirements and density measurements. Furthermore, in order for the most effective metal doping to take effect, such gels are preferably treated with a multivalent metal salt while in a wet state. The combination of these particular properties and metal dopant permits highly effective noxious gas filtration such that excellent uptake and breakthrough results are attained, particularly in comparison with prior media filtration products. Also included is the presence of an oxidizing agent to aid in capturing nitrogen oxides and preventing conversion of such a product to NO. Methods of using and specific filter apparatuses are also encompassed within this invention.

Background of the Invention

There is an ever-increasing need for air handling systems that include air filtration systems that can protect an enclosure against noxious airborne vapors and particulates released in the vicinity of the enclosure. Even- year there are numerous incidents of noxious vapors contaminating building environments; and causing illness and disruptions There is also a current effort to protect buildings and other significant enclosures against toxic airborne

vapors and particulates being released as part of terrorist acts. As a result, new filter design requirements have been promoted by the military' to protect from certain toxic gases. Generally speaking, whether in a civilian or military setting, a typical air filtration system that contains only a particulate filter (for example, a cardboard framed fiberglass matt filter) provides no protection at all against toxic vapors. Commercially available electrostatic fiber filters exhibit higher removal efficiencies for smaller particles than standard dust filters, bin they have no vapor filtration capability. HEPA ("High-Efficiency Particulate Air") filters are used for high-efficiency filtration of airborne dispersions of ultrafjne solid and liquid particulates such as dust and pollen, radioactive particle contaminants, and aerosols. However, where the threat is a gaseous chemical compound or a gaseous particle of extremely small size (i.e., <0.001 microns), the conventional commercially-available HEPA filters cannot intercept and control those types of airborne agents.

The most commonly used filter technology to remove vapors and gases from contaminated air is activated carbon. Such carbon-based gas filtration has been implemented in a wide variety of vapor-phase filtration applications including gas masks and military vehicle and shelter protection. In these applications, activated carbon impregnated with metal salts is used to remove a full range of toxic vapors (such as arsine, Sarin gas, etc.). These toxic gases require a high filtration efficiency typically not needed for most commercial applications. To the contrary, typical commercial filters generally include activated carbon materials on or incorporated within non-woven fabrics (fiber mats, for instance), with coexisting large fixed beds of packed adsorbent particles. Such commercial filters used for air purification generally are used until an easily measurable percentage (e.g., 10%) of the

challenge cheinicaHs) concentration f^ measured in the effluent Greater loog-teim efficiency is desired for gas masks and/or military vehicle applications

Impregnated, acti\ ated carbons arc used in applications v\ here required to remove gases that would not otherwise be removed through the use of υnimpregnated actuated carbons Such prior art impregnated carbon formulations often contain copper, cluomium and silver impregnated on an acti\ ated carbon These adsorbents are effective in removing a large number of toxic materials, such as Q) anide-bascd gases and vapors

In addition to a number of other inoigank materials which have been impregnated on actuated carbon, various organic impregnates have been found useful in military applications for the removal of cyanogen chloride Examples of these include triethyϊenedi amine { IEDA) and pyridine— i~cart>oxylie acid

Various types of high-efficiency filter systems, both commercial and militaiy types, ha\e been proposed for building protection using copper-silver-zinc-molybdenum- tri ef hylertedi amine impregnated carbon for filtering a broad range of toxic chemical vapors and gases f ϊowes ei such specific carbon-based filteis has e proven ineffective for other gases, such as, ammonia, ethylene oxide, formaldehyde, and nitrogen oxides λs these gases are quite prominent in industry and can be harmful to humans when present in sufficient amounts (particularly within enclosed spaces), and, to date, other filter devices have ptoven unsuitable for environmental treatment and/or removal thereof, there exists a definite need for a filter mechanism to remedy these deficiencies, particularly in both high and low relative humidity (RH) environments Each chemical is affected differently by adsorbed water For ammonia, it is most difficult (design limiting) to filter at a low relative humidity since adsorbed water actually enhances the ammonia affinity of the target adsorbents For ethylene

oxide the reverse is Hue since exposure to high humidity is problematic in designing a proper filter system Io date, no filtration system having a relatively small amount of filter medium present lias been provided that effectively removes such gases at their design limiting RH for long durations of time at relatively high challenge concentrations Ce g , 1 ,000 ppm) without e\ entually el u ting through the filter

It has been realized that silica-based compositions make excellent gas filter media Hov\c\cr, little has been provided within the pertinent prior art that concerns the ability to provide uptake and breakthrough levels b) such filter media on a permanent basis and at levels that are acceptable for long-term usage Uptake basically is a measure of the ability of the filter medium to capture a certain volume of the subject gas, breakthrough is an indication of the saturation point for the filter medium in terms of capture Thus, it is highly desirable to find a proper filter medium that exhibits a high uptake {and thus quick capture of large amounts of noxious gases) and Song breakthrough times (and thus, coupled with uptake, the ability to not only effectuate quick capture but also extensive lengths of time to reach saturation) The standard niters in use today are limited for noxious gases, such as ammonia and nitrous oxide (NO;), to slow uptake and relatively quick breakthrough times There is a need to develop a new filter medium that increases uptake and breakthrough, as a result

The closest art concerning the remo\ al of gases such as ammonia utilizing a potential silica-based compound doped uith a metal is taught within WO 00/40324 to Kcπiira Agro Oy Such a s\ stem, howe\er, is primarily concerned with providing a filter media that permits regeneration of the collected gases, presumably for further utilization, rather than permanent removal from the atmosphere Such an ability to easily regenerate (i e , permit release of captured gases) such toxic gases through increases of temperature or changes in pressure

unfortunately presents a risk to the subject environment. To the contrary, an advantage of a system as now proposed is to provide effective long-duration breakthrough (thus indicating thorough and effective removal of unwanted gases in substantially their entirety from a subject space over time, as well as thorough and effective uptake of substantially all such gases as indicated by an uptake measurement The Kemira reference also is concerned specifically with providing a dry mixture of silica and metal (in particular copper 1 salts, ultimately), which, as noted within the reference, provides the effective uptake and regenerative capacity sought rather than permanent and effective gas (such as ammonia) removal from the subject environment. The details of the inventive filter media are discussed in greater depth below.

Brief Description of the Invention

According to one aspect of this invention, a filter medium comprising multivalent metal- doped silicon-based gel materials, wherein said materials exhibit a BET surface area of between than 100 and 600 m'/g (preferably 100 to 300), a pore volume of between about 0.18 cc/g to about 0,7 cc/g as measured by nitrogen porosimetry; a cumulative surface area measured for all pores having a size between 20 and 40 A of between 50 and 150 nr/g; and wherein the multivalent metal doped on and within said silicon-based gel materials is present in an amount of from 5 to 25% by weight of the total amount of the silicon-based gel materials. Preferably, the filter medium exhibits a BET surface area is between 150 m7g and 250 rn ² Zg; a pore volume of between about 0.25 to about 0.5 cc/g; a cumulative surface area measured for all pores having a size between 20 and 40 λ of between 80 and 120 nr/g; and wherein said multivalent metal is present in an amount of from about S to about 20%.

λccoiding to another aspect of the invention, a multivalent metal-doped silicon-based ge! filter medium that exhibits a breakthrough measurement for an ammonia gas/air composition of at least t>0 minutes a) when present as a filter bed of I cm in height within a flask of a diameter of 4 J cm, b) when exposed to a constant ammonia gas concentration of 1000 mg/m ammonia gas at ambient temperature and pressure, and c) when exposed simultaneously to a relative hυmiditv of 15%, and wherein said filter medium, after breakthrough concentration of 35 mg m'is reached, does not exhibit anx, ammonia gas elutton in excess of said breakthrough concentration Pieferabl) , the bieakthrough time is at least 120 minutes Furthermore, another aspect of this (mention concerns multiv alent metal-doped silicon-based gel materials that exhibit a breakthrough time of at least 60 minutes when exposed to the same conditions as listed above and within the same test protocol, except that the relative humidity is 80% Preferably, the breakthrough time for such a high ieiathe humidity exposure test example is at least 120 minutes, as well

Still another potential aspect of this invention is the inclusion of an oxidizing agent, such as a peimanganate or peroxide, during manufacture of the ge! materials Such a component aids in capturing nitrous oxide and prev ents comersion of that noxious gas to another noxious gas, NO, thereby increasing the viability of the overall filter medium as a dccontaminant of toxic gases from certain environments

According to still another aspect of the invention, a method of producing oxidizer- and metal- doped silicon gel-based particles is provided, said method comprising the sequential steps of a) pro\ iding a silicon-based gel material.

b) wet reacting said silicon-based gel material with at least one multivalent metal salt to produce metal-doped silicon-based gel material; and further reacting with at least one compound capable of acting as an oxidizer to maintain reactive species in an oxidized state, c) drying said oxidizer- and metal-doped silicon-based gel materials. Alternatively, step '"& ^' ' may include a production step for generating said silicon-based gel materials.

One distinct advantage of this invention is the provision of a filter medium that exhibits highly effective ammonia uptake and breakthrough properties when present in a relatively low amount and under a pressure typical of an enclosed space and over a wide range of relative humidity. Among other advantages of this invention is the provision of a filter system for utilization within an enclosed space that exhibits a steady and effective uptake and breakthrough result for ammonia gas and that removes such noxious gases from an enclosed space at a suitable rate for reduction in human exposure below damage levels Yet another advantage is the ability of this invention to irreversibly prevent release of noxious gases once adsorbed, under normal conditions

Also, said invention encompasses a filter system wherein at least 1 5% by weight of such a filter medium has been introduced therein. Furthermore, the production of such metal- doped silica-based material gel-like particles, wherein the reaction of the metal salt is preferably performed while the gel-like particle is in a wet state has been found to be very important in provided the most efficient and thus best manner of incorporating such metal species within the micropores of the subject silica materials As such, u was determined that

such a wet gel doping step was necessary Io provide the most efficient filter medium and overall filter systems for such noxious gas (such as, as one example, ammonia).

One distinct advantage of this invention is the provision of a fsiter medium that exhibits highly effective ammonia uptake and breakthrough properties when present in a relatively low amount and under a pressure typical of an enclosed space and over a wide range of relative humidity. Among other advantages of this invention is the provision of a filter system for utilization within an enclosed space that exhibits a steady and effective uptake and breakthrough result for ammonia gas and that removes such noxious gases from an enclosed space at a suitable rate for reduction in human exposure below damage levels. Yet another advantage is the ability of this invention to irreversibly prevent release of noxious gases once adsorbed, under normal conditions.

In terms of the nitrogen oxide benefits, the oxidized gel materials exhibit excellent removal characteristics of both highly toxic gases nitrous oxide and nitrogen dioxide. The US Department of Labor Occupational Safety and Health Administration ("OSHA") has set stringent guidelines aimed at protecting workers performing operations in an environment potentially contaminated with nitrogen oxide. The Permissible Exposure Limit ("PEL,") for NO2 has been established at 5 ppni, 9 rng/irf ceiling and NO at 25 ppm, 30 mg/nr\ As a result, effective, low cost means of removing nitrogen oxides from ambient streams of air are needed. Of particular interest is the removal capability of nitrogen oxides simultaneously with other potentially toxic industrial chemicals like ammonia.

As noted above, impregnated, activated carbon is known to strongly adsorb a wide variety of organic chemicals from ambient air streams. Such a material is not effective at removing nitric oxide which is a by-product of some reactions with nitrogen oxides. There is

additional!) an inherent benefit from having a combined absorption of multiple compounds from a single absorbent Although mixtures and layered bed filters are effectiv e, they can be complex and costly to produce A single composite particle has distinct advantages from manufacturing, storage, and cυmplcxit) perspectives, at least

The piesem (m ention, according to one embodiment, comprises an adsorbent foi removing NO^ from air over a wide range of ambient temperatures, said process comprising contacting the air with an oxidizer impregnated high surface area silica gel alone or part of a composite matrix for a sufficient time to remove \O> and pievent the formation of other toxic nitrogen oxides, specifically NO

Detailed Description of the Invention

For purposes of this invention, the term "silicon-based gel" is intended to encompass materials that are formed from the reaction of a metal silicate (such as sodium silicate) with an acid (such as sulfuric acid) and permitted to age properly to form a gel material or materials that ate available from a natural source (such as from rice hulls) and exhibit pore structures that are similar to such gels as formed b\ the process above Such synthetic materials ma> be categorized as either silicic acid or poly silicic acid types or silica gel types, whereas the natural souice materials are typical Iv harvested in a certain form and treated to ultimately form the final gel-like product {such a method is provided within U S Pat No 6,638,354) The difference between the two s\ othetie categories lies stricti\ within the measured resultant pH level of the gel after reaction, formation and aging If the gel exhibits a pH of below 3 0 after that stage, the gel is considered silicic oi polysilicic acid in t\ pc If pϊl 3 0 or above, then the material is considered a (traditional) silica gel In any e\ em, as noted abo\ e, the term

"silicon-based gel ^1" is intended to encompass both of these types of gel materials, ϊt has been found that silicon-based gels exhibiting a resultant pH of less than 3 0 (silicic or polysilicie acid gels) contain a larger percentage of micropores of size less than 20 A with a median pore size of about 30 A, while silicon-based geis exhibiting a higher acidic pH, such as pH of 3.0 and above (preferably, though not necessarily, as high as 4) contain a mixture of pore sizes having a median pore size of about 3 OA to about όOA. While not wishing to be held by theory, it is believed that capture of toxic gases, such as ammonia, is accomplished by two separate (but potentially simultaneous) occurrences within the pores of the metal-doped silicon-based gels: acid-base reaction and complexation reaction, Thus silicon-based gels formed at pH <2 contain more residual acid than the gels formed at pH 3-4, however the gels formed at pH 3-4 contain more pores of size suitable to entrap a metal, such as copper, and thus have more metal available for a complexation reaction. It is believed that the amount of a gas such as ammonia that is captured and held by the silicon-based gel results from a combination of these two means. The term "multivalent metal salt" is intended to include any metal salt having a metal exhibiting a valence number of at least three. Such a multivalent metal is particularly useful to form the necessary complexes w ith ammonia; a valence number less than three will not readily form such complexes.

The hydrous silicon-based gels that are used as the base materials for metal doping as well as the basic materials for the desired air filtration medium may be prepared from acid-set silica hydrogels. Silica hydrogel may be produced by reacting an alkali metal silicate and a mineral acid in an aqueous medium to form a silica hydrosol and allowing the hydrosol to set to a hydrogel. When the quantity of acid reacted with the silicate is such that the final pH of the reaction mixture is acidic, the resulting product is considered an acid-set hydrogel

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Sulfuric acid is the most commonly used acid, although other mineral acids such as hydrochloric acid, nitric acid, or phosphoric acid may be used. Sodium or potassium silicate may be used, for example, as the alkali metai silicate. Sodium silicate is preferred because it is the least expensive and most readily available. The concentration of the aqueous acidic solution is generally from about 5 to about 70 percent by weight and the aqueous silicate solution commonly has an SiOj content of about 6 to about 25 weight percent and a molar ratio of SiO: to Na ₂ O of from about i . ! to about 3.4.1 .

The alkali metal silicate solution is added to the mineral acid solution to form a silica hydrosol. The relative proportions and concentrations of the reactants are controlled so that the hydrosol contains about 6 to about 20 weight percent SiOi and has a pH of less than about 5 and commonly between about 1 to about 4. Generally, continuous processing is employed and alkali silicate is metered separately into a high speed mixer. The reaction may be carried out at any convenient temperature., for example., from about 15 to about 80X and is generally carried out at ambient temperatures.

The silica hydrosol will set to a hydrogel in generally about 5 to about 90 minutes and is then washed with water or an aqueous acidic solution to remove residual alkali metal salts which are formed in the reaction For example, when sulfuric acid and sodium silicate are used as the reactants, sodium sulfate is entrapped in the hydrogel. Prior to washing, the gel is normally cut or broken into pieces in a particle size range of from about 1/2 to about 3 inches The gel may be washed with an aqueous solution of mineral acid such as sulfuric add., hydrochloric acid, nitric acid, or phosphoric acid or a medium strength acid such as formic acid, acetic acid, or propionic acid

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Generally, the teinperatuie of the wash medium is from about 2~?^C to about 93 ⁰ C Preferably, the wash medium is at a temperature of from about 27T to about 38T The gel is washed for a period sufficient to reduce the total salts content to less than about 5 weight percent The gel may have, for example, a Na;O content of from about 0 05 to about 3 weight percent and a SO^ content of from about 0 05 to about 3 weight percent, based on the dry weight of the gel The period of time necessary to achieve this salt removal varies with the flow rate of the wash medium and the configuration of the washing apparatus Generally, the period of lime necessary to achieve the desired salt removal is from about 0 5 to about 3 hours Thus, it is preferred that the hydrogel be washed with water at a temperature of from about 2?°C to about 38 ⁰ C for about 0 5 to about 3 hours In one potential embodiment, the washing may be limited in order to permit a certain amount of salt (such as sodium sulfate), to be present on the surface and within the pores of the gel material Such salt is believed, without intending on being limited to any specific scientific theory, to contribute a le\el of hydration that may be utilized for the subsequent metal doping procedure to effectively occur as well as contributing sufficient water to facilitate complexation between the ammonia gas and the metal itself upon exposure

In order to prepare hydrous silicon-based gels suitable for use in the filter media of this invention, the final gei pH upon completion of washing as measured in 5 weight percent aqueous slurry of the gel, may iange from about ! 5 to about S

The washed silica hydrogel generally has a water content, as measured by oven drying at 105 T for about 16 hours, of from 10 to about 60 \\ eight percent and a particle size ranging fiotit about S mi ci on to about 50 millimeters Alternatively the hydrogel is then dcwateied to a desired water content of from about 20 to about 90 weight percent, preferably from about 50

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to about 85 weight percent Any known dewateπng method may be employ ed to reduce the amount of water therein or com ersely increase the so! ids content thereof For example, the washed hydrogei may be dewatercd in a filter, rotary dryer, spray dryer, tunne! dr\ cr. flash dryer, nozzle dryer, fluid bed clτyeτ, cascade dryer, and the like

The a\ eragc particle si/e referred to iluoughout iliis specification is determined in a MICR-OTRACS ¹ particle size analyzer When the water content of the hydrogei is greater than about 90 ueight percent, the hydrogei may be pre-dried in any suitable dryer at a temperature and foτ a time sufficient to reduce the water content of the hydioget to below about 85 weight percent to facilitate handling, processing, and subsequent metal doping

General !γ, the hydrogei materials after formation and aging are of ven coarse sizes and thus should be broken apart to facilitate piopcr metal iniρτ egnation Such a size reduction may be accomplished by various methods, including nulling, grinding, and the like One option, however, is to subject the hydrogei materials to high shear mixing during the metal doping procedure In such a step, the particle sizes can be reduced to the sizes necessary for propeϊ filter utilization Alternatively, the h) drøgei particles may be ground to relatively uniform particles sizes concurrent!) during doping or subsequent to the doping step In such alternative manners, the overall production method can effectuate the desired homogeneous impregnation of the metal foτ the most effective noxious gas removal upon utilization as a filter medium

Thus, in one possible embodiment the silica h\ drogel is wet ground in a mil! in order to provide the desired average particle size suitable for further reaction with the metal dopant and the subsequent production of sufficiently small pore sizes for the most effective ammonia gas Uappirtg and holding while present within a filter medium For example, the h> drogel s

may be concuirenth ground and dried with any standard mechanical grinding des tce, such as a hammer mill, as one non-limiting example The ultimate particle sizes of the multh alent- metal impregnated (doped) silicon-based gel materials are dependent upon the desired manner of providing the filter medium made therefrom Thus, packed media will requite 1 at get particle sizes (from 10 to 100 microns, for example) wheieas relatively small particles sizes (from 1 to 20 microns, for example) may be utilized as extrudates within films or fibers The important issue, however, is not the particle sizes in general, but the degree of homogeneous metal doping effectuated within the pores of the subject hydrogels themselves

The h\drous silicon-based αel product after nrindirm preferably remains in a wet state (although drying and grinding may be undertaken, either separately or simultaneously, pteferabij , though, the materials remain in a high water-content state for further reaction with the rneiai dopant) for subsequent doping with metal salts or oxidizers in order to provide effective toxic chemical trapping and holding capability within a filter medium Such a wet state reaction is thus encompassed within the term "wet reaction" or "wet react" for this invention Without intending on being bound to am specific scientific theorx , it is believed that the wet state doping permits incorporation of sufficient chemical species within the pores of the si I icon -based gel product to permit sufficient points for reaction, complexation or entrapment of the target toxic chemicals hi a wet state, the pores of the subject silicon-based gel product are large enough in volume to allow for a metal salt or chemical moiet> to enter therein Subsequent ώλ ing thus appears to shrink the pores around the resultant compound to a volume that, upon introduction of target toxic gas. causes the gas to condense into a liquid It is apparently this liquid that then exists within the small \ olume pores that will contact with the chemical species to effectuate said remo\ al Thus, it is believed that the production of

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small \ oiuine poies around the chemical species therein to a level wherein the remaining volume within such pores is small enough to permit such condensation of the target toxic chemical species followed b\ reliable contact for the needed substantially permanent removal for effective capture of the molecules is best provided through the wet stale reaction noted above included as one possible altcrnath e within the term "uct reaction" ^" or "wet reacf" is the ability to utilize gel particles that have been dried to a certain extent and reacted witli an aqueous solution of chemical impregnants in a slurry Although the resultant performance of such an alternative filter medium does not equal that of the aforementioned product of pre- dried, wet, gel particles with a metal salt, such a filter medium does exhibit performance results that exceed gels alone, or dn -mixed metal-treated salt materials Such an alternative method has proven effective and is essential when utilizing the natural source materials (from rice bulls, for example, and as noted above) as reaciants with an aqueous impregnate solution

The metals that can be utilized for such a purpose include, as alluded to abo\e, any multivalent metal, such as, without limitation, cobalt iron, manganese, zinc, aluminum, chromium coppei, tin, amimon) , indium, tungsten, silver, gold, platinum, mercury, palladium, cadmium, and nickel For cost reasons, copper and zinc are potential!) preferred, with copper most preferred I he listing above indicates the metals possible for production during the doping step within the pores of the subject silicon-based gel materials The metal salt is pieferab!> water-soluble in nature and facilitates dissociation of the metal from the anion when reacted with silica-based materials Thus, sulfates, chlorides, bromides, iodides, nitrates, and the like, are possible as anions, with sulfate, and thus copper sulfate, most preferred as the metal doping salt (cupric chloride is also potentially preferred as a specific compound, however, the acidic natuie of such a compound may militate against use on

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industrial levels) Without intending on being bound to any specific scientific theory, it is believed that copper sulfate enables doping of copper [ as a copper (I I) species] in some form to the silicon-based gei structure, while the transferred copper species maintains its ability to complex with ammonium ions, and further permits color change within the filter medium upon exposure to sufficient amounts of ammonia gas to facilitate identification of effectiveness of gas removal and eventual saturation of the filter medium, In such a manner, it is an easy task to view the resultant filtration system empirically to determine if and when the filter medium has been saturated and thus requires replacement.

^' The wet state doping procedure has proven to be particularly useful for the provision of certain desired filter efficiency results, as noted above. A dry mixing of the metal salt and silicon-based gel does not accord the same degree of impregnation within the gel pores necessary for ammonia capture and retention. Without such a wet reaction, although capture may be accomplished, the ability to retain the trapped ammonia (in this situation., the ammonia may actually be modified upon capture or within the subject environment to ammonium hydroxide as well as a portion remain as ammonia gas) can be reduced. It is believed, without intending on being limited to such a theory, that in such a product, ammonia capture is slii! effectuated by metal complexation, but the lack of small pore volumes with metal incorporated therein limits the ability for the metal to complex strongly enough to prevent release upon certain environmental changes (such as, as one example, high temperature exposure). Such a result is actually the object of the closest prior art. As in the noted Kemira reference above, a dry mix. procedure produces a regenerable filter medium rather than a permanent capture and retention filter medium The particular wet reaction is discussed more specifically within the examples below, but, in its broadest sense, the reaction entails the

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reaction of a silicon-based gel with intioduced water present in an amount of at least 50 ⁰ O by weight of the gel and metal salt materials Preferably, the amount of water is higher, such as at least 7t)V more preferably at least 80%, and most preferably at least 85% If the reaction is too diy, proper metal doping will not occur as the added vvatei is necessary to transport the metal salts into the pores of the gel materials Without sufficient amounts of metal within such pores, the gas removal capabilities of the filter medium made therefrom will be reduced The term "added" or "introduced" water is intended to include various forms of water, such as without limitation, watei present within a solution of the metal salt or the gel hydrated forms of metal salts, ln drated forms of residual gel react ant salts, such as sodium sulfate, moisture, and relative humidity, basically any form that is not present as an integral part of the either the gel or metal salt itself, or that is not transferred into the pores of the materia! after doping has occuπed Thus, as non-limiting examples, again, the production of gel material, followed by drying initially with a subsequent wetting step (for instance, slurrying within an aqueous solution, as one non-limiting example), followed by the reaction with the multivalent metal salt, ma\ be employed foτ this purpose, as well as the potential!) prefeπed method of retaining the gel materia! in a wet state with subsequent multivalent metal salt reaction thereafter

Water is also important, however, to aid in the complevation of the metal with the subject noxious gas within the gel pores it is belkn ed, without intending on being bound to any specific scientific theory, that upon doping the metal salt is actually retained but complexed, \ia the metal cation, to the silicon-based gel within the pores thereof (and some ma> actual complex on the gel surface but will more readily become dc-comple\ed and thus removed over time, within the pores, the complex with the metal is rclath ely strong and thus

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difficult to break). The presence of x^ater at that point aids in removing the anionic portion of the completed salt molecule through displacement thereof with hydrates. It is believed that these hydrates can then be displaced themselves by, as one example, the ammonia gas (or ammonium ions) thereby producing an overall gel /metal/ammonium complex that is strongly associated and very difficult to break, ultimately providing; not only an effective ammonia gas capture mechanism, but also a manner of retaining such ammonia gases substantially irreversibly The water utilized as such a complexation aid can be residual water from the metal doping step above, or present as a hydrated form on either the gel surface (or within the gel pores) or from the metal salt reactant itself. Furthermore, and in one potentially preferred embodiment, such water may be provided through the presence of humectants (such as glycerol, as one non-limiting example).

Furthermore, of importance as well is the potentially preferred embodiment of contacting and/or reacting the gel materia! with an oxidizing agent to provide extra nitrogen oxide removal capabilities. Any oxidizing material within those categorized in Classes i through 4 would be suitable, with Class i and 2 types preferred due to safety issues in handling during incorporation Examples of Class 1 types include aluminum nitrate, potassium dichromate, ammonium persulfate, potassium nitrate, barium chlorate, potassium persulfate, barium nitrate, silver nitrate, barium peroxide, sodium carbonate peroxide, calcium chlorate, sodium dichloro-s-triaziπetrione, calcium nitrate, sodium dichromate. calcium peroxide, sodium nitrate, cupric nitrate, sodium nitrite, hydrogen peroxide (8-27.5%), sodium perborate, lead nitrate, sodium perborate tetrahydrate, lithium hypochlorite, sodium perchl orate monolrydrate, lithium peroxide, sodium persulfate, magnesium nitrate, strontium chlorate, magnesium perchl orate, strontium nitrate, magnesium peroxide, strontium peroxide.

IS

ϊiicke! nitrate, zinc chtoiate, nitric acid h ⁷ 0% cone ), /uic peroxide, and perchloric acid {- ^' 60% eoneen ) L:\ampies of Class 2 W pes include calcium hypochlorite (-' 50% wgt), potassium permanganate, chromium trioxide (chromic acid), sodium chlorite {'- 40% wgt k nalane, sodium peroxide, hydiogcn peroxide (27 5-52% cone ), sodium permanganate, nitric acid (>70% cone ), and Uichloro-s-tria/iπetrione Hxamples of Class 3 types include ammonium dichromate, potassium chlorate, hs drogen peroxide (52- ^c >l% cone ), potassium dichloroisocyanurate, calcium hypochlorite (>50% wgt }, sodium chlorate, perchloric acid (o0~72 5% cone ), sodium chlorite (>40% wgt ), potassium bromate, and sodium dichloro-s~ tiwinetrione Examples of (.Mass 4 types include ammonium perchJorate, ammonium permanganate, gυanidine nitrate, hydrogen peroxide (>9 i% cone ). perchloric acid (>?2 5%), and potassium superoxide Preferably the oxidizing material is potassium permanganate or calcium peroxide The amount of oxidizing agent contacted there with the gel material particles is from 0 1 to 10% The contacting/reacting may occur during gel production or, and preferably, thereafter, in order to allow sufficient amount of oxidizing agent to attach to sites on the ge! surfaces llie imenth e silicon-based gel particles thus have been doped (impregnated) with at least one multivalent metal salt (such as. as one non-limiting example, copper sulfate) in an amount of from about 2 to about 30 wt%. expressed as the percentage weight of base metals, such as copper, of the entiie dry weight of tlie metal-impregnated (doped) silicon gel-based particles Such resultant metal-doped silicon-based gel materials thus provide a filter medium that exhibits a breakthrough time for an ammonia gas/air composition having a 1000 mg rø* ammonia gas conccntiation when exposed to ambient pressure (i e . from 0 8 to S 2 atmospheres, or roughly from 0 81 to I 25 kPa) and temperatuie Ci e . from 20-25 ⁰ C) of at

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least 35 mg m when applied to a filter bed of at most 2 cm height within a cylindrical lube of 4 1 cm in diameter, and wherein said ammonia gas captured b\ said filter medium does not exhibit any appreciable regeneration upon exposure to a temperature up to 25O ⁰ C at ambient pressure foτ 70 hours And, alternatively, the gel materials also have the aforementioned oxidizer thereon for removal of nitrogen oxides from an environment Such resultant oxidizα metal -doped silicon-based gel materials thus provide a filter medium that exhibits a breakthrough time for an ammonia gas/air composition having a 1000 mg m ^J ammonia gas concentration when exposed to ambient pressure (ι e , from 0 8 to 1 2 atmospheres, or roughly from 0 8 ! to 1 25 LPa) and temperature (i e , from 20-25' C) of at least 35 rag/trT when applied to a filter bed of at most 2 cm height within a flask of 4 I cm in diameter, and wherein said ammonia gas captured by said filter medium does not exhibit any appreciable regeneration upon exposure to a temperature up to 250 ^u C at ambient pressure for 70 hours \nά exhibits a breakthrough time for an nitrous oxides / air composition having a 375 mg/rn* NO; gas concentration when exposed to ambient pressure (i e , from 0 8 to i 2 atmospheres, or roughly from 0 81 to 1 25 kPa) and temperature (i e , from 20-25' C) of at least 9 mg m' when applied to a filter bed of at most 2 cm height within a flask of 4 1 cm in diameter, and wherein said NO; gas captured by said filter medium does not exhibit any appreciable regeneration upon exposure to a temperature up to 250°C at ambient pressure for 70 hours This absorbent also exhibits a breakthrough time for an nitrous oxide that may be present as a contaminant or result from an uncontrolled reaction when exposed to ambient pressure (i e . from 0 8 to 1 2 atmospheres, or roughly from 0 81 to I 25 kPa) and temperature {i e , from 2Q-25 ^J €) of at least >0 mg/m when applied to a filter bed of at most 2 cm height within a flask of 4 I cm in diameter, and wherein said KO; gas captured by said filter medium does not exhibit aπ>

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appreciable regeneration upon exposure to a temperature up to 25(PC at ambient pressure for 7(* hours

The hydrous silicon-based gels (and oxidizer metal -treated gels as well) are employ ed in the filter medium of this invention in an amount from about I to about 90 percent, pieferabi} about 5 to about 70 percent, by weight of the entiie filter medium composition

The filter medium of the invention can also further contain as optional ingredients, silicates, clays, talcs, aluminas, carbons, poly mers, including but not limited to polysaccharides, gums oi other substances used as binder fillers These are conventional components of filter media, and materials suitable for this purpose need not be enumerated for they are well known to those skilled in the art Furthermore, such metal-doped silicon-based gels of the invention may also be introduced within a polymer composition (through impiegnatioπ, or through extrusion) to piovide a polymeric film, composite, or other type of poh meric solid for utilization as a filter medium Additionally, a riotm oven fabric may be impregnated, coated, or otherwise treated with such invention materials, or individual yarns or filaments may be extruded with such materials and formed into a nomvoven. \\o\en or kmt web, all to pro\ ide a filter medium base as well Additionally, the in\ entive filter media may be layered within a filter canister with other tvpes of filter media present therewith (such as layers of carbon black material), oi, alternatively , the filter media may be interspersed together within the same canister Such films and or fabrics, as noted above, may include discrete areas of filter medium, or the same t\ pe of interspersed materials (carbon Mack mixed on the surface, or co-eκtruded, as merely examples, within the same fabric or film) as well

The filter s\ stein utilized for testing of the viability of the medium t) picai!) contains a media bed thickness of from about 1 cm to about 3 cm thickness, preferabh about 1 cm to about 2 cm thickness within a cylindrical tube of 4 i cm in diameter Without limitation. typical filters that ma> actually include such a filter medium, for example, for industrial and/or personal use, will comprise greatei thicknesses (and thus amounts) of such a filter medium, from about i-l 5 cm m thickness and approximately 10 cm in diameter, for example for personal canister filter tvpes, up to i00 cm in thickness and 50 cm in diameter, at least, for industrial uses Again, these aie on!) intended to be iough approximations for such end use applications, any thickness, diameter, width, height, etc , of the bed and/or the container ma> be utilized in actuality, depending on the length of time the filter may be in use and the potential for gaseous contamination the target environment ma> exhibit The amount of tiller medium that may be introduced within a filter system in any amount, as long as the container is structuraih sufficient to hold the filter medium therein and permits proper airflow in order for the filter medium to properly contact the target gases

It is important to note that although ammonia (and m some instances, nitrogen oxide) gases are the test subject for removal by the inventhe filter media discussed herein, such media may also be effective in removing other noxious gases from certain environments as well, including formaldehyde and amines as merely examples

As previous!) mentioned, the filter medium can be used in filtration applications in an industrial setting (such as protecting entire industrial buildings or individual workers, via masks), a military setting (such as filters for \ehicJes or buildings or masks for individual troops), commercial/public settings (office buildings, shopping centers, museums, go\ emmeπtal locations and installations, and the like) Specific examples may include,

??

without limitation, the protection of workers in agricultural environments, such as within poultry houses, as one example, where \ast quantities of ammonia gas can be generated by animal waste Thus, large-scale filters may be utilized in such locations, or individuals mav utilize personal filter apparatuses foτ such purposes Furthermore, such filters mav be utilized at oi around transfoimers that may generate certain noxious gases Generally, such inventive filter media may be included m any type of filter s\ stem that is necessary and useful for the removal of potential noxious gases in any type of environment

Preferred Embodiments of the Invention

Copper content x^as determined utilizing an ICP-OHS model Optima 3(K)O available from PerkinEtmer Corporation, Shehon, Connecticut

The % solids of the adsorbent wet cake wore determined by placing a icpiosemative 2 g sample on the pan of a CHM ^ ⁾ 10700 mi crow a\ e balance and drying the sample to constant weight The weight difference is used to calculate the % solids content Pack or tapped density h determined b\ weighing 100 0 grams of product into a 250-mL plastic graduated cylinder with a flat bottom The cylinder is closed with a rubber stopper, placed on the tap density machine and run for 15 minutes The tap density machine is a conventional motor-gear reducer dri\ e operating a cam at 60 rpm The cam is cut or designed to raise and drop the cylinder a distance of 2 25 in (S 71 S cm) c\ er\ second The cylinder is held in position by guide brackets The volume occupied by the product after tapping was recorded and pack density was calculated and expressed in g ml

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The conductivity of the filtrate was determined utilizing an Orion Model 140 Conductivity Meter with temperature compensator by immersing the electrode epoxy conductivity cell (014010) in the recovered filtrate or filtrate stream. Measurements are typically made at a temperature of 15-2O°C.

Surface area is determined by the BHT nitrogen adsorption methods of Brunaur et al., J, Am. Chem. Soc,, 60, 309 ( 1938).

Accessible porosity has been obtained using nitrogen adsorption-desorption isotherm measurements. The BJH (Barreti-Joiner-Hafender) model average pore diameter was determined based on the desorption branch utilizing an Accelerated Surface Area and Porosimetry System (ASAF 2010} available from Micromeritics Instrument Corporation, Norcross, Georgia. Samples were out gassed at 150 -200 ⁰ C until the vacuum pressure was about Sμrn of Mercury This is an automated volumetric analyzer at 77 ⁰ K. Pore volume is obtained at pressure IVPo ~ 0.99. Average pore diameter is derived from pore volume and

surface area assuming cylindrical pores. Pore size distribution (δV/δD) is calculated using

BJH method, which gives the pore volume within a range of pore diameters. A Haisey thickness curve type was used with pore size range of 1.7 to 300.0 run diameter, with zero fraction of pores open at botli ends.

The N2 adsorption and desorption isotherms were classified according to the 1985 MJPAC' classification for genera! isotherm types including classification of hysteresis to describe the shape and inter connectedness of pores present in the silicon based gel.

Adsorbent micropore area (S _m , _CTO ) is derived from the Haisey isotherm equation used in producing a t-ploi The t-plot compares a graph of the volume of nitrogen absorbed by the adsorbent gel as compared with the thickness of the adsorbent layer to an idea! reference. The

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shape of the (-plot can be used to estimate the micropore surface area Percent microporosity is then estimated by subtracting the external surface area from the total BKT surface area,

where S, _m oro ~ Ban ™ S ₀ \t- Thus %BJH microporosity = S _m , _CTl ,/SBi- r X 100

The level of metal impregnate is expressed on a % elemental basis A sample impregnated with about S \vt% of copper exhibits a level of copper chloride so that the percent Cu added to the si S icon -based ge! is about 5 wf% of Cυ/adsorbent Wt. In the case of cυpric chloride dihydrate, then (CuCb-2H;0), 100 g of tin' adsorbent would be impregnated with dry 1 13,65 g of cupric chloride Thus, the calculation is basically made as % Metal ^::: Weight of elemental metal in metal sa!t/(weight of dry silicon-based gel -+ ^■ weight of total dry metal salt).

Ammonia Breakthrough

The general protocol utilized for breakthrough measurements involved the use of two parallel flow systems having two distinct valves leading to two distinct adsorbent beds (including the filter medium), connected to two different infrared detectors followed by two mass flow controllers The overall system basically permitting mixing of ammonia and air within the same pipeline for transfer to either adsorbent bed or continuing through to the same gas chromatograpli. In such a manner, the uptake of the filter media within the two adsorbent beds was compared for ammonia concentration after a certain period of time through the analysis via the gas chromatograph as compared with the non-filtered ammonia/air mixture produced simultaneously. A vacuum was utilized at the end of the system to force the ammonia/air mixture through the two parallel flow systems as well as the non-filtered pipeline with the How controlled usiny 0-50 Sϊ..PM mass flow controllers

To generate the ammonia/air mixture, two mass flow controllers tienerated chalieone concenti'ation of ammonia, one being a challenge air mass flow controller having a 0-100 SLPM range and the other being an ammonia mass flow controller having a 0- i00 seem range, A third air flow controller was used to control the flow through a heated water sparger to control the challenge air relative humidity ( RIl) Two dew point analyzers, one located in the challenge air line above the beds and the other measuring the effluent RH coming out of one of the two filter beds, were utilized to determine the RH thereof (modified for different levels).

The beds were 4 ! cm glass tubes with a baffled screen to hold the adsorbent The adsorbent was introduced into the glass tube using a fill tower to obtain the best and most uniform packing each time.

The challenge chemical concentration was then measured using an HP 5890 gas chromatograph with a Thermal Conductivity Detector (TCD). The effluent concentration of ammonia was measured using an infrared analyzer (MlRAN), previously calibrated at a specific wavelength for ammonia

The adsorbent was prepared for testing by screening all of the particles below 40 mesh (-425 microns). The largest particles were typically no larger than about 25 mesh (-710 microns).

The valves above the two beds were initially closed. The diluent air flow and the water sparger air flow were started and the system was allowed to equilibrate at the desired temperature and relative humidity (RH). The valves above the beds were then changed and simultaneously the chemical flow was started and kept at a rate of 4 75 SLPM. The chemical flow was set to achieve the desired challenge chemical concentration. The feed chemical

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concentration was constantly monitored using the GC. The effluent concentrations from the two adsorbent beds (filter media) were measured continuously using the previously calibrated infrared detectors. The breakthrough time was defined as the time when the effluent chemical concentration equaled the target breakthrough concentration. For ammonia tests, the challenge concentration was LOOO mg/W at 25°C and the breakthrough concentration was 35 mg/πv at 25 ⁰ C. Ammonia breakthrough was then measured for distinct filter medium samples, with the bed depth of such samples modified as noted, the relative humidity adjusted, and the flow units of the ammonia gas changed to determine the effectiveness of the filter medium under different conditions. A breakthrough time in excess of 40 minutes was targeted. hi a similar manner, using methods described above, the breakthrough time for nitrous oxides were determined The chemical flow was set to achieve the desired challenge chemical concentration by diluting NCK gas to a concentration of 375 mg/m3 with air at the specified relative humidity level. The feed chemical concentration was constantly monitored using a chemi luminescence detector. The effluent concentrations from the two adsorbent beds (filter media) were measured continuously using the previously calibrated chemi luminescence detector to measure simultaneously, NOi, NO and NOx. The breakthrough time was defined as the time when the effluent chemical concentration equaled the target breakthrough concentration. For NOx tests, the challenge concentration was 375 mg/nr at 25°C and the breakthrough concentration was 30 nig/ro ¹ at 25 °C for NO and 9 mg/rø ¹ at 25 °C for NO?.

The breakthrough requirements are summarized in Table K below.

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TABLE- 1 Ammonia and Nitroaen Oxides Breakthrough Targets

Nitrogen Oxide Removal - Metal oxidizer treated Gel Production

The embodiment including an oxidizing material for nitrogen oxide removal including production of the following products'

Inventive Example 1

Particles of silicon-based gel were produced by adding a solution of ! 1.4% sulfuric acid solution to 2000ml 24.7% sodium silicate (3.3 mole ratio) solution with agitation at 300- 400 rpm until the pH of the solution reached the target pH of 3 0. The suspension was then discharged into 5000ml deionized water at S5°C for the 30 minutes to complete gel formation The gel cake was recovered by filtration to form a mass of gel particles with conductivity of less than 3000 μS. Next, the gel was broken apart with further agitation. The washed particles are then filtered and collected and the resulting particles were dried in an oven set at 105°C for 16 hours To form granules and increase product density, 20Og of the dried blend prepared above were compacted in a roller compactor (TF-Laho available from Vector Corporation) using a pressing force 7 bar to form crayon-shaped agglomerates, which were then sized by sieving to recover granules sized between 850 μm and 425 μm

2S

Inventive Example 2

Wet gel cake from Rxample 1 was impregnated with copper by adding ! 500g am aunt of gel wet cake formed above ( 17 35% solids > and Si)Og of deionized water Io this add 1 3g V8% H2SO4 and 3 VOg of CuSO ₄ OH ₂ O (The % solids of the dried gel, determined according to the method described above, was used to estimate the quantify of impregnate icquiied to achieve the desired metal level ) The slurry was then agitated at 3000rpm far 15 minutes at ambient temperature The uniform slurry was then placed directl) in an oven set at 105 ⁰ C and dried overnight ( 16 hours) To form granules and increase product density, 20Og of the dried blend prepared above were compacted in a roller compactor (TF-Labo available from Vector Corporation) using a pressing foτce 7 bar to form crayon-shaped agglomerates, which were then sized b\ siev ing to recover granules sized between 850 μm and 425 μm

Inventive Exam pie 3

To 6 !2g of silicic acid gel from Example 1 having a solids concentration of 16 35 V add 4g of KMnO.4 crystals Blend with a high shear mixer to form a homogeneous slurry Recover and dry for \bh at 105 ^c C To form hard granules and increase product density, 10Og of the dried blend prepaied above were compacted in a roller compactor (TF-Labo available from Vector Corporation } using a pressing force 7 bar to form era\ on-shaped agglomerates, which wore then sired by sieving to recover granules steed between 8^0 μm and 425 μm

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Inventive Example 4

To lOOg of dried silicic acid ge! from Example 1, add 4g calcium peroxide powder and 1Og deionized water dropwise while dispersing in Cuisinart® blender to effect a homogeneous powder. To form hard granules and increase product density, lOOg of the dried blend prepared above were compacted in a roller compactor (TF-Lafao available from Vector Corporation) using a pressing force 7 bar to form crayon-shaped agglomerates, which were then sized by sieving to recover granules sized between 850 μm and 425 μm.

inventive Example 5

The copper impregnated gel of Example 2 was doped with potassium permanganate by mixing 455g of Example 2 slurry (22.45% solids) with 4g KMnO-t crystals. The slurry was stirred at 2000rpm for 20 minutes and dried in an oven for 16 hours at 100 ⁰ C. To form hard granules and increase product density, IOOg of the dried blend prepared above were compacted in a roller compactor (TF-Labo available from Vector Corporation) using a pressing force 7 bar to form crayon-shaped agglomerates, which were then sized by sieving to recover granules sized between 850 μm and 425 μm.

Inventive Example 6

The copper impregnated gel of Example 2 was doped with potassium permanganate by mixing 91Og of Example 2 slurry (22.45% solids) with 8g KMnO ₄ crystals. Using methods described in Example 5 the slurry was dried at 9O ⁰ C and sized granules were produced.

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Comparative Example 1

Particles of commercially available ASZM-TEDA Impregnated carbon particles available from Calgon Corporation, Pittsburgh, Pennsylvania, were sized by sieving as described above to recover granules sized between SSO μm and 425 μm.

Nitrogen dioxide breakthrough and capture: NO conversion

In accordance with the tests run for the ammonia removal above, these samples were tested for both ammonia and nitrogen oxide removal The results were as follows:

TABLE 2 Ammonia and Nitrogen Oxide Breakthrough Data

*NO:; concentration exceeded 5ppm in the firs? minute and peaked out at 32ppm after 5 minutes. The efiϊnent concentration however trended downwards to 18 ppm over the duration of the test with no iiiliic oxide (NO) conversion or breakthrough

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Thus, the inventive examples shew, a clear improvement over the comparative and non-oxidized species in terms of multiple threat gas removal.

While the invention was described and disclosed in connection with certain preferred embodiments and practices, it is in no way intended to limit the invention to those specific embodiments, rather it is intended to cover equivalent structures structural equivalents and all alternative embodiments and modifications as may be defined by the scope of the appended claims and equivalents thereto

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