Adsorbents containing potassium hydroxide and potassium carbonate, and related methods and apparatus

Abstract

Described is an adsorbent material useful for removing airborne molecular contaminants from gas streams, comprising a porous adsorbent substrate having potassium hydroxide ions and potassium carbonate applied to the surface of the adsorbent substrate, as well as an apparatus comprising the adsorbent and related methods of preparing and using the adsorbent.

Description

[Technical Field]

[0001] This specification relates to adsorbent materials useful for removing airborne molecular contaminants from gas streams and comprising porous adsorbent substrates impregnated with potassium hydroxide and potassium carbonate, as well as devices comprising the adsorbents and related methods of preparing and using the adsorbents. [Background technology]

[0002] Airborne molecular contaminants (AMCs) are molecular-scale impurities present at low levels (e.g., "trace") in gases such as air in highly controlled and purified environments, such as cleanroom air.

[0003] The presence of airborne molecular contaminants in semiconductor and microelectronic device manufacturing environments is becoming more and more significant as the dimensions of integrated circuits, disk drives, etc. become smaller and smaller. As manufacturing processes become more precise, smaller concentrations of airborne molecular contaminants become relevant to the quality and yield of products prepared in the controlled environments.

[0004] Molecular-scale chemical contaminants can be present in gases due to various factors, such as the gas's processing history or exposure to surfaces that generate gaseous molecular-scale contaminants. For example, airborne molecules are emitted from almost all materials present in cleanrooms. Molecular-scale organic and inorganic (acids, bases, etc.) materials enter the cleanroom environment from surfaces, processing materials, etc. used in the cleanroom. As part of the cleanroom environment, these molecules may eventually be deposited on the surfaces of microelectronic devices being processed. At the surface, the molecules can act as contaminants or impurities that can have detrimental effects on further processing of the device surface or the operation of the finished device. As an example, contaminants can alter the electrical or optical properties of fabricated devices. Contaminants include molecular acids, molecular bases, cohesive molecules, organic compounds, ozone, and molecular dopants, among others. Airborne molecular contaminants have sizes in the nanoscale range (e.g., approximately 0.2 to 3.0 nanometers) and therefore can evade particle filters.

[0005] Continuing improvements in cleanroom environments have significantly reduced the presence of particulate contamination, as filtration technology can reduce hundreds of thousands of submicron particles per liter to virtually zero per liter using the highest grade ULPA filters. However, airborne molecular contamination remains a challenge.

[0006] Airborne molecular contamination is an important research topic, including in the context of cleanrooms and microelectronic device manufacturing. See, for example, Robert, Jurgen, M., Srivastana, R., and Belanger, F., "Airborne molecular contamination: Formation, impact, measurement, and removal of nitrous acid (HNO2)," ASCM 2018, pp. 180–185. As noted, airborne molecular contamination can contribute to yield reductions in semiconductor processing. For example, weak acids as molecular contaminants can impact processing technologies at the 22-nanometer node and below. One such weak acid is nitrous acid (HNO2 or HONO), which has not demonstrated a direct impact on processing or equipment, but has nevertheless been the subject of airborne molecular contamination filtration removal. Nitrous acid (HNO2) is commonly formed on surfaces from nitrogen dioxide (NO2) gas and is one of the primary nitrogen oxides formed from combustion processes and atmospheric photochemistry. Summary of the Invention

[0007] The following description focuses on the extraction of nitrogen oxide compounds (including nitrogen dioxide (NO2)) from a gas flow such as air. x The present invention relates to novel adsorbents, devices, systems, and processes that can be used to remove nitric oxide compounds (e.g., nitrogen dioxide) from gases. The adsorbent comprises a porous adsorbent substrate impregnated with potassium hydroxide and potassium carbonate. A useful method involves contacting a gas with the adsorbent to adsorb nitric oxide compounds, e.g., nitrogen dioxide, onto the surface of the porous adsorbent. The adsorbent is effective in adsorbing nitric oxide molecules contained in the gas and removing the nitric oxide molecules from the gas. The adsorbent further comprises a process for removing nitric oxide molecules from the gas by converting the adsorbed nitric oxide molecules into HNO x It has been found to be particularly effective in releasing acid compounds from the adsorbent by preventing them from being converted to derivative acid compounds, referred to as hydroxybenzoates.

[0008] In one known method for removing nitric oxide compounds from gases, nitric oxide molecules adsorbed on an adsorbent surface (e.g., granular activated carbon (GAC)) are converted to derivative acids such as HNO (HNO x Nitrogen dioxide, NO2, adsorbed on the adsorbent surface and then chemically converted to HNO2, is released from the adsorbent surface as a derivative acid, e.g., HNO2. The acid then enters the purified gas effluent stream (e.g., "filtrate") flowing from the adsorbent and can be released as a contaminant in the purified gas stream. x This will result in the undesirable presence of HCl (especially HNO2).

[0009] It has been shown herein that the described sorbents containing both potassium carbonate and potassium hydroxide are effective for adsorbing nitrogen dioxide and advantageously result in relatively low amounts of acid derivatives of the nitric oxide compounds being released from the sorbent after the nitric oxide is adsorbed onto the sorbent surface. For example, a relatively large amount of the nitric oxide compounds can be adsorbed onto the sorbent before the sorbent begins to release significant amounts of the derivative acids.

[0010] In one aspect, the present invention relates to a porous adsorbent comprising a porous adsorbent substrate, potassium hydroxide on the surface of the porous adsorbent substrate, and potassium carbonate on the surface of the porous adsorbent substrate.

[0011] In another aspect, the present invention relates to a filter device containing an adsorbent, the adsorbent comprising a porous adsorbent substrate, potassium hydroxide on the surface of the porous adsorbent substrate, and potassium carbonate on the surface of the porous adsorbent substrate.

[0012] In another aspect, the present invention relates to a method for preparing a sorbent comprising a sorbent substrate, potassium hydroxide, and potassium carbonate, the method including applying an aqueous K2CO3 solution to the sorbent substrate, applying an aqueous KOH solution to the sorbent substrate, and removing water from the aqueous K2CO3 and KOH solutions applied to the porous sorbent substrate.

[0013] In yet another aspect, the present invention relates to a method for removing nitric oxide compounds from a gas, the method comprising contacting the gas with a porous adsorbent substrate and a porous adsorbent comprising potassium hydroxide and potassium carbonate on the surface of the porous adsorbent substrate. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 illustrates an example of a filter as described. [Figure 2] FIG. 1 illustrates an example of a filter as described. [Figure 3A] 1 is a graph showing filtration performance data for the described filters and for comparative filters. [Figure 3B] 1 is a graph showing filtration performance data for the described filters and for comparative filters. [Figure 3C] 1 is a graph showing filtration performance data for the described filters and for comparative filters. [Figure 3D] 1 is a graph showing filtration performance data for the described filters and for comparative filters. [Figure 3E] 1 is a graph showing filtration performance data for the described filters and for comparative filters. [Figure 4A] 1A-1C illustrate exemplary filters herein and comparative filters. [Figure 4B] 1A-1C illustrate exemplary filters herein and comparative filters. [Figure 5] 1 is a graph showing filtration performance data for the described filters and for comparative filters. [Figure 6A] 1A-1C illustrate exemplary filters herein and comparative filters. [Figure 6B] 1A-1C illustrate exemplary filters herein and comparative filters. [Figure 7] 1 is a graph showing filtration performance data for the described filters and for comparative filters. DETAILED DESCRIPTION OF THE INVENTION

[0015] All figures are schematic and not to scale.

[0016] NO is removed from a gas flow, such as air, by contacting the gas with a sorbent material that has been treated to contain potassium hydroxide and potassium carbonate at the surface of the sorbent. x Described herein are novel adsorbents, devices, systems, and processes that can be used to remove compounds (e.g., nitrogen dioxide or "NO2").

[0017] According to an exemplary process, a gas containing one or more NOx compounds can be contacted with the treated sorbent material, and NO x Compounds, particularly nitrogen dioxide, are adsorbed onto the surface of the adsorbent material and removed from the gas.

[0018] Advantageously, NO x After the compounds are adsorbed on the adsorbent surface, the adsorbent releases NO, such as HNO, when compared to the amount of acid-derivative compounds released by other adsorbents. x The adsorbents described herein release relatively low amounts of acid derivatives of the compounds. In particular, known carbon adsorbents used to remove nitrogen dioxide from gases convert nitrogen dioxide to acid derivatives (e.g., HNO) on the adsorbent surface, which are then released in the effluent stream of gas filtered from the adsorbent. The treated adsorbents described herein can reduce or prevent this effect. Compared to known adsorbents, the adsorbents described herein may be able to adsorb a greater amount of nitrogen dioxide molecules before a significant amount of their acid derivatives is released from the surface.

[0019] NO xThe gas treated to remove compounds can be any gas containing a quantity of one or more nitric oxide compounds that is desired to be removed from the gas. In a particular example, the gas is air from a clean room environment used in the processing of semiconductor and microelectronic devices. In the semiconductor processing and microelectronics industries, as well as other manufacturing industries, a "clean room" comprises atmospheric air that is highly purified and has a controlled composition. In clean rooms used to process microelectronic and semiconductor devices, the clean room atmosphere is continuously treated to remove not only particulate contaminants but also "airborne molecular contamination" (also "AMC," "airborne molecular contaminants").

[0020] In addition to the typical components of air (approximately 78 percent nitrogen, 21 percent oxygen, and about 0.9 percent argon and 0.3 percent carbon dioxide), the air may optionally contain water vapor. According to this specification, the cleanroom air atmosphere also contains very low concentrations of one or more different types of airborne molecular contaminants, such as nitric oxide compounds (e.g., nitrogen dioxide), each individually present at concentrations below 100 parts per billion, or below 50 parts per billion (ppb), or below 1, 0.5, or 0.1 ppb (measured for the individual contaminant molecules). The air may also contain other airborne molecular contaminants, such as molecular acids (e.g., organic acids such as acetic acid or inorganic acids such as sulfuric acid), ammonia (NH), or organic compounds (e.g., aromatic compounds such as toluene), at concentrations (individually) below 100 parts per billion or below 50, 10, 5, 2, 0.5, or 0.1 parts per billion (ppb). The described adsorbents can be effective in removing contaminants such as these from the air of cleanroom environments and maintaining the concentration of one or more of these contaminants at a maximum in the parts per billion range noted above.

[0021] A typical cleanroom atmosphere for processing semiconductor and microelectronic products will have a relative humidity in the range of 20 to 60 percent, such as below 60 percent, e.g., below 50 percent, e.g., 40 to 50 percent, at ambient temperature, e.g., approximately 22 degrees Celsius (e.g., 20 to 25 degrees Celsius), and atmospheric pressure (approximately 1 atmosphere).

[0022] The amount of an airborne molecular contaminant in a volume of air can be described as a percentage, or alternatively, in units of parts per billion. The term "parts per billion" is used herein to be consistent with the use of this term in the chemical arts. In this regard, parts per billion ("ppb") is commonly used as a measure of small levels (concentrations) of impurities in gases, expressed as milligrams of impurity per liter of fluid (mg / L), measuring the mass of contaminant per volume of fluid. One part per billion ("ppb") is 1 x 10 of the total substance. -9 or equal to 0.0000001 percent.

[0023] This novel adsorbent material contains potassium hydroxide and potassium carbonate, and is capable of removing NOx, including nitrogen dioxide. x The present invention includes a solid porous adsorbent "substrate" structure that can be used as a porous substrate for supporting a combination of potassium hydroxide and potassium carbonate on the surface of the substrate structure so that the combination is effective as an adsorbent for removing impurity containing compounds from a gas flow.

[0024] The porous sorbent substrate can be any useful porous sorbent material to which potassium hydroxide and potassium carbonate can be added, after which the porous sorbent substrate and the applied potassium hydroxide and potassium carbonate will be effective as a sorbent material for removing airborne molecular contaminants from a gas flow.

[0025] Examples of adsorbent materials that may be useful as porous adsorbent substrates include known types of porous adsorbent materials, such as carbon-based adsorbent media, polymeric adsorbent media, silica, etc. Specific examples include metal-organic frameworks ("MOFs"), including, among other things, zeolitic imidazolate framework ("ZIF") adsorbents; zeolites (aluminosilicates), silica and silica-based particles; alumina and alumina-based particles; and porous carbon adsorbent particles, including carbon adsorbent materials commonly referred to as "activated carbon particles," among other types of carbon particles.

[0026] Non-limiting examples of porous carbon adsorbent materials useful as porous adsorbent substrates include synthetic polymers such as hydrocarbons, halocarbons (e.g., chlorocarbons), or hydrohalocarbon resins, e.g., polyacrylonitrile, polystyrene, sulfonated polystyrene divinylbenzene, polyvinylidene chloride (PVDC), and the like; cellulose char; charcoal; and carbons formed by pyrolysis of activated carbons formed from natural raw materials such as coconut shells, pitch, wood, petroleum, coal, and the like.

[0027] The porous adsorbent substrate can be of any shape, form, size, etc., to support potassium hydroxide and potassium carbonate on the surface of the substrate, and the combination of the substrate structure and the added potassium hydroxide and potassium carbonate is effective in adsorbing airborne molecular pollutants from gases. The size, shape, and physical properties of the porous adsorbent substrate, such as pore characteristics (pore size, porosity, surface area), can affect the substrate's ability to adsorb airborne molecular pollutants.

[0028] For example, activated carbon particulate adsorbent substrates can be characterized by relatively high surface areas, e.g., at least 500, 600, or 700 square meters per gram, e.g., in the range of 700 to 1000 square meters per gram or more. This type of surface area measurement can be performed by known methods, such as the nitrogen BET surface area measurement technique.

[0029] The pores of the adsorbent substrate can have any useful pore size, i.e., any pore size that enables the desired adsorption performance. Pore sizes of adsorbent materials are typically classified into ranges based on the average pore size of a population of particles. Particles having an average pore size greater than 50 nanometers (nm) are typically referred to as macroporous. Particles having an average pore size in the range of 2 to 50 nanometers (nm) are typically referred to as mesoporous particles. Particles having an average pore size less than 2 nanometers are typically referred to as microporous. These terms are defined by IUPAC terminology. Substrate particles used in accordance with this specification may have an average pore size, or pore size range, that falls within any of these size range designations.

[0030] The porous adsorbent substrate is treated with a useful amount of a combination of potassium hydroxide (KOH) and potassium carbonate (KCO), such that the potassium hydroxide and potassium carbonate are located on the surface within the pores of the porous adsorbent, i.e., "impregnated" into the porous adsorbent substrate. According to one useful technique, the potassium hydroxide and potassium carbonate can be applied to the porous adsorbent by incipient wetness impregnation. According to these techniques, an aqueous solution containing potassium hydroxide is prepared, and another aqueous solution containing potassium carbonate is prepared. The aqueous solutions are incorporated (e.g., "impregnated") into the porous adsorbent, e.g., separately, so that they penetrate the pores of the porous adsorbent. The solution within the pores of the porous adsorbent is dried to remove the water, and after the water from the aqueous solution is removed, the potassium hydroxide and potassium carbonate remain within the pores of the adsorbent. The potassium hydroxide and potassium carbonate impregnated into the porous substrate may be present, partially or entirely, in ionic form; with respect to potassium hydroxide, the surface is dominated by potassium ions (KCO). + ) and hydroxide ions (OH - ), and for potassium carbonate, the surface contains potassium ions (K + ), carbonate ions (CO 3- ) contains.

[0031] According to a specific method, the aqueous potassium carbonate solution can be applied first, and the solution can be dried to remove water. The aqueous potassium hydroxide solution can be applied after the potassium carbonate solution has dried. The aqueous potassium hydroxide solution can then be dried to remove water.

[0032] According to other variations of the wet impregnation technique, the aqueous solutions can be applied in a different order, such as applying the potassium carbonate solution first, then drying the solution, then applying the potassium hydroxide solution, and drying the aqueous potassium hydroxide solution, etc. In yet another variation, a single aqueous solution containing both potassium hydroxide and potassium carbonate may be applied in a single application and then dried.

[0033] Advantageously, the wet impregnation process can be useful for applying aqueous solutions of potassium hydroxide or potassium carbonate (or both) in a very efficient manner, without the need for pressure or agitation. In an exemplary method, one or more aqueous solutions can be applied to the porous adsorbent substrate by a useful application method, such as spraying. The aqueous solution is drawn into and infiltrates the porous adsorbent without the need for excessive amounts of solution and without the need for high temperatures, agitation, or pressure. The efficient nature of the wet impregnation process avoids the need to apply excessive amounts of aqueous solution to the porous adsorbent, reducing the amount of aqueous solution wasted.

[0034] A solution containing an aqueous potassium carbonate solution and an aqueous potassium hydroxide solution, or both, can be applied to the adsorbent at room temperature using the aqueous solution and the adsorbent substrate. For example, when the aqueous solution is applied to the adsorbent substrate, the adsorbent substrate may be at a temperature in the range of 20 to 25 degrees Celsius, and the aqueous solution may be at a temperature in the range of 20 to 25 degrees Celsius.

[0035] The step of drying the applied aqueous solution can be carried out at any useful temperature and for any amount of time effective to completely remove water from the aqueous solution, for example, at a temperature in the range of 100-200 degrees Celsius, and for an amount of time in the range of several hours (e.g., in the range of 5-20 hours).

[0036] The sorbent material treated with potassium hydroxide, potassium carbonate, or both can be identified by chemical analytical techniques and instruments. For example, the hydroxide ion (OH - ) and carbonate ions (CO 3- ) can be detected on the adsorbent surface by Fourier transform infrared spectroscopy (FTIR) techniques. + ) ions can be detected on the adsorbent surface by ion chromatography (IC).

[0037] The amounts and relative amounts of potassium carbonate and potassium hydroxide added to the porous adsorbent substrate can be any amount useful for providing a useful capacity for adsorbing nitric oxide compounds such as nitrogen dioxide. In a preferred example, the amounts of potassium carbonate and potassium hydroxide result in improved adsorption performance compared to an equivalent adsorbent without potassium hydroxide. The adsorbent can contain amounts and relative amounts of potassium carbonate and potassium hydroxide that result in increased capacity for adsorbing nitric oxide compounds such as nitrogen dioxide compared to an equivalent adsorbent containing potassium carbonate but not potassium hydroxide. Furthermore, compared to an adsorbent without potassium hydroxide, an adsorbent containing both potassium carbonate and potassium hydroxide can adsorb a greater amount of nitric oxide molecules such as nitrogen dioxide before the adsorbent begins to release significant amounts of derivative acids of the nitric oxide molecules, such as HNO. For example, an adsorbent containing both potassium carbonate and potassium hydroxide will have a longer "breakthrough time" to derivative acids such as HNO compared to the breakthrough time of an adsorbent containing only potassium carbonate.

[0038] An exemplary sorbent can contain 10 to 40 weight percent potassium hydroxide and 60 to 90 weight percent potassium carbonate, based on the total weight of the potassium hydroxide and potassium carbonate, for example, 15 to 35 weight percent potassium hydroxide and 65 to 85 weight percent potassium carbonate, based on the total weight of the potassium hydroxide and potassium carbonate.

[0039] The sorbent can be prepared to contain a combination of potassium hydroxide and potassium carbonate. Useful sorbents can optionally contain additional chemical components, such as other salts, acids, bases, and the like, including the addition of potassium compounds. However, according to certain useful examples, the sorbent can contain only potassium carbonate and potassium hydroxide, without other potassium compounds and other additional application chemical materials. The chemicals added to the sorbent can include, consist of, or consist essentially of potassium hydroxide and potassium carbonate, with no other potassium compounds added, or with no other chemical compounds added, or with only small or trace amounts of other potassium compounds or other chemical compounds added.

[0040] Exemplary sorbents may contain at least 90, 95, 98, or 99 weight percent potassium carbonate and potassium hydroxide, based on the total weight of all potassium compounds applied to the sorbent, and may contain, for example, less than 10, 5, 2, or 1 weight percent potassium compounds other than potassium hydroxide and potassium carbonate.

[0041] Exemplary sorbents may contain at least 90, 95, 98, or 99 weight percent potassium carbonate and potassium hydroxide, and may contain, for example, less than 10, 5, 2, or 1 weight percent of chemical compounds different from potassium hydroxide and potassium carbonate, based on the total weight of all chemical compounds applied to the sorbent.

[0042] The described adsorbents can be used alone or in combination with one or more additional adsorbent materials in adsorbent beds, filter membranes, or other forms of filter products or devices. A second type of adsorbent that can be combined with the described adsorbents can be, for example, activated carbon adsorbents, MOFs, zeolites, ZIFs, polymers, etc., or ion exchange resins (either cation exchange resins or anion exchange resins).

[0043] Ion exchange resins are known materials capable of adsorbing and desorbing ionic compounds. Exemplary ion exchange resins are made of polymers, such as cross-linked polystyrene, and contain ion exchange sites as part of the polymer. Ion exchange resins may be in the form of polymer beads or polymer membranes. Various types of ion exchange resins are known, differing with respect to the functional groups of the polymer component, including: strongly acidic ion exchange resins containing sulfonic acid functional groups, e.g., sodium polystyrene sulfonate (polyAMPS); strongly basic ion exchange resins typically characterized by quaternary amino functional groups, e.g., trimethylammonium groups; weakly acidic ion exchange resins typically containing carboxylic acid groups; and weakly basic ion exchange resins that can contain primary, secondary, or tertiary amino groups, e.g., polyethyleneamines.

[0044] In some exemplary products, the adsorbents herein (containing potassium carbonate and potassium hydroxide) can be present in a blended combination or physical mixture with a different adsorbent, such as an ion exchange resin, and gas can be flowed through the mixture to simultaneously contact both adsorbents in the mixture. See, for example, layer 62 of multi-layer filter 60 in FIG. 2. Ion exchange resin can be combined with the described adsorbents containing potassium hydroxide and potassium carbonate to form a mixture of the two adsorbents containing any useful relative amounts of the two adsorbents, for example, ratios (by weight) ranging from 90:10 to 10:90, or 25:75 to 75:25, or 40:60 to 60:40.

[0045] Alternatively, the described adsorbent can be present as the sole (only) adsorbent in a filter bed or membrane, and another layer or bed of the filter system can contain a different adsorbent. Two different layers or beds of adsorbent can be arranged in series to allow gas to flow first through one type of adsorbent and then through the second type of adsorbent. See, for example, multi-layer filter 60 in FIG. 2.

[0046] The described adsorbents can be included in a filter assembly or filter system (commonly referred to as a "filter") and used to remove one or more airborne molecular contaminants from a gas (e.g., air) by contacting the gas with the adsorbent. Airborne molecular contaminants present in the gas are adsorbed onto the surface of the adsorbent, separating the molecular contaminants from the gas. The gas flows from the filter as a filtrate containing a reduced concentration of airborne molecular contaminants compared to the concentration of contaminants in the gas before the gas contacted the filter.

[0047] One example of a filter layer can have a sorbent that is the only (consisting of, or consisting essentially of) sorbents containing potassium hydroxide and potassium carbonate. See, e.g., FIG. 1. Another example of a filter layer can contain a mixture of a sorbent containing potassium hydroxide and potassium carbonate with a different sorbent, such as a cation exchange resin. See, e.g., FIG. 2. A filter or filter system can contain two layers of different sorbents, such as a layer containing a sorbent that is the only (consisting of, or consisting essentially of) sorbents containing potassium hydroxide and potassium carbonate, and a layer containing a blend of a sorbent containing potassium hydroxide and potassium carbonate with a different sorbent, such as a cation exchange resin. See, e.g., FIG. 2.

[0048] In exemplary processes, airborne molecular contaminants may be present in the gas prior to contact with the adsorbent at concentrations of (individually) less than 10 parts per million, less than 5 parts per million, less than 1 part per million, or less than 500 parts per billion, or less than 100, 50, 10, 5, 1, or 0.5 parts per billion (ppb). After the gas contacts the adsorbent as part of a filter, a certain amount of airborne molecular contaminants is removed from the gas, and the gas exiting the filter (or "filtrate") may contain significantly reduced amounts of contaminants (considered individually), e.g., the amount of contaminant may be reduced by at least 50, 70, 80, 90, or 95 percent or more. In terms of concentration, the filtrate may contain one or more airborne molecular contaminants at concentrations of less than 10 parts per billion, 1, 0.5, or 0.1 parts per billion (individually) (ppb).

[0049] 1 shows an exemplary filter 60 including an inlet 46, an outlet 48, and a sorbent 42 between the inlet and outlet. The inlet 46 allows a gas 50 to flow into the interior of the filter 60 and contact the sorbent 42. The gas 50 may be any gas containing one or more airborne molecular contaminants, such as NO, for example, air from a clean room environment used for processing semiconductor and microelectronic devices. As the gas passes through the filter 60 and contacts the sorbent 42, the one or more airborne molecular contaminants are adsorbed onto the sorbent particles 42. The gas exits the filter 60 as filtrate 52 and contains a reduced concentration of one or more airborne molecular impurities.

[0050] FIG. 2 illustrates an example of a filter containing two different types of adsorbents: adsorbent particles 42 containing a combination of potassium carbonate and potassium hydroxide, and cation exchange resin particles 44. Referring to FIG. 2, an exemplary filter 60 includes an inlet 46, an outlet 48, and two layers (or "segments" or "beds") of adsorbent (62, 64) between the inlet and outlet. Layer 62 is positioned upstream from layer 64 (as shown). Layer 62 contains a physical mixture of two different types of adsorbents, e.g., adsorbent 42 containing potassium hydroxide and potassium carbonate, and adsorbent 44 in the form of a cation exchange resin (denoted by a "+" inside a circle). Layer 64 contains only (e.g., consists of, or consists essentially of) adsorbent 42 containing potassium hydroxide and potassium carbonate.

[0051] Inlet 46 allows gas 50 to enter filter 60 and contact adsorbents 42 and 44 in layer 62, and then adsorbent 42 in layer 64. Gas 50 may be any gas containing one or more airborne molecular contaminants, such as NO, for example, air from a clean room environment used for processing semiconductor and microelectronic devices. As the gas passes through filter 60 and contacts adsorbents 42 and 44, the one or more airborne molecular contaminants are adsorbed onto particles 42 or 44. The gas exits filter 60 as filtrate 52, containing a reduced concentration of one or more airborne molecular impurities. [Example]

[0052] Example 1 3A shows the filtration performance of a single layer filter (Example 1 or "GAC B") containing an example of a sorbent herein in the form of an activated carbon sorbent containing a combination of potassium hydroxide and potassium carbonate on the surface of the sorbent. The "comparative sorbent" ("GAC A") is a single layer activated carbon sorbent containing only potassium carbonate and no potassium hydroxide.

[0053] 3A and 3B show that the single layer filter containing the adsorbent of Example 1 of the present invention (GAC B) reduces NOx Regarding the adsorption of NO x HNO after adsorption x This shows improved performance in terms of reducing (retarding) the release of

[0054] Both filters have NO x Each monolayer filter was contacted with a flow of air containing 1 ppm NO at a rate of 1 liter per minute. x For several hours, both filters absorbed significant amounts of HNO x No. x After absorbing HNO for a certain period of time, each filter finally releases x (The time when this occurs is sometimes referred to as the "breakthrough time.") After approximately 200 hours, the comparative adsorbent (GAC A) began to release increased amounts, e.g., more than 0.5 ppb of HNO. x The adsorbent of Example 1 began to release HNO into the filtrate stream at a concentration of at least 0.5 ppm. x Without releasing NO x The amount of time that the sorbent was adsorbed was significantly longer.

[0055] Referring to FIG. 3B, the graph shows that the adsorbent GAC B has superior NO2 removal capacity compared to GAC A. Regarding the performance of GAC A, the graph shows that the concentration of NO2 in the filtrate increased sharply after the adsorbent was exposed to the NO2 gas flow for approximately 350 hours. On the other hand, the GAC B adsorbent did not result in such an increase in the concentration of NO2 gas in the filtrate over the same amount of time, suggesting that the GAC B adsorbent has a higher ability to adsorb NO2.

[0056] Figure 3C compares the acetic acid adsorption performance of GAC A and GAC B. The results show that adsorbent GAC B has effective capacity for acetic acid adsorption.

[0057] Figure 3D compares the toluene adsorption performance of GAC A and GAC B. The results show that adsorbent GAC B has a significantly higher adsorption capacity for toluene compared to adsorbent GAC A.

[0058] Figure 3E compares the performance of GAC A and GAC B in adsorbing SO2. The results show that adsorbent GAC B has significantly higher SO2 adsorption capacity compared to adsorbent GAC A.

[0059] Example 1 shows that an exemplary sorbent herein (GAC B) reduces NO2 by 200% compared to an equivalent sorbent (GAC A) containing potassium carbonate but not potassium hydroxide. x The adsorbent of Example 1 also has an increased ability to adsorb compounds such as HNO as indicated by the longer breakthrough time. x Example 1 also shows that the GAC B sorbent provides improved (reduced or delayed) release of non-NOx sorbents, including acetic acid, toluene, and SO2. x This indicates that it is effective in adsorbing molecular pollutants.

[0060] Example 2 In this example, the exemplary filter (Example 2, "Media B") contains two adsorbent-containing layers. As shown in Figure 4B, filter 80 of Example 2 includes a first layer 82 containing activated carbon adsorbent 84 treated with potassium hydroxide and potassium carbonate (GAC B, 67 weight percent) in combination with a cation exchange resin 86 (33 weight percent). A second layer 90 contains only activated carbon adsorbent 84 treated with potassium hydroxide and potassium carbonate (GAC B).

[0061] A two-layer comparative filter (Comparative Example 2 or "Media A") 100 includes a first layer 102 containing activated carbon sorbent 104 (GAC A) treated with potassium carbonate only (no potassium hydroxide). A second layer 106 contains activated carbon sorbent 104 (GAC A) treated with potassium carbonate only (no potassium hydroxide) (31 weight percent) in combination with cation exchange resin 86 (69 weight percent). See Figure 4A.

[0062] The performance of the two-layer filter of Example 2 and the two-layer filter of Comparative Example 2 were tested against each other, and the results are shown in Figure 5. During the test, both two-layer filters were charged with NO x The mixture was contacted with a flow of air containing 1 ppm of ...

[0063] In the filter of Example 2 (Media B, see FIG. 4B), air first contacted a first layer 82 containing activated carbon sorbent 84 treated with potassium hydroxide and potassium carbonate in combination with a cation exchange resin 86. The air passed through first layer 82 and then entered and passed through a second layer 90 containing treated activated carbon sorbent 84 without the cation exchange resin.

[0064] In Comparative Example 2, the filter first contacted air with a first layer 102 containing activated carbon adsorbent 104 treated only with potassium carbonate, rather than potassium hydroxide, and no cation exchange resin. The air passed through the first layer 102 and then entered and passed through a second layer 106 containing activated carbon adsorbent 104 treated only with potassium carbonate (no potassium hydroxide), in combination with a cation exchange resin 86.

[0065] The graph in FIG. 5 shows that the filter of Example 2 (Media B) x After adsorption, HNO is released x Both of the two-layer filters show improved performance in reducing or delaying the amount of NO compared to the filter of Comparative Example 2 (Media A). xEach two-layer filter was contacted with an identical flow of air containing 1 ppm NO at a rate of 1 liter per minute. x Both filters effectively adsorbed significant amounts of HNO for several hours. x After approximately 500 hours, the filter of Comparative Example 2 released no HNO. x The amount of HNO x Without releasing NO x The amount of time it continued to adsorb was significantly longer, i.e., approximately 1000 hours.

[0066] Example 3 In this example, Media B, which contains a sorbent of the present invention, is compared to a different comparative filter ("Media C") containing two filter layers. See Figures 6A and 6B. In Media C of Figure 6A, the top layer contains 67 weight percent GAC A and 33 weight percent resin. Media B is the same Media B as in Example 2 (see Figure 4B).

[0067] As shown in FIG. 7, Media B (containing the adsorbent of the present invention) performed better than both Media A and Media C.

[0068] Adsorbent Preparation Method To prepare the adsorbent, specific percentages of K2CO3 and KOH were incorporated into activated carbon via a two-step initial impregnation method. First, 27.1 g of granular activated carbon (GAC) derived from coconut shells was placed in a Petri dish and treated with 45 mL of K2CO3 solution prepared by adding 2.1 g of K2CO3 to 45 mL of DI water. The prepared K2CO3 solution was sprayed onto the carbon with a syringe, allowed to stand in contact with the carbon at room temperature for 6 hours, then placed in an oven at 150 °C for 16 hours, and then cooled to room temperature for the second step. Next, a KOH solution was prepared by adding 0.8 g of KOH to 45 mL of DI water. The KOH solution was sprayed onto the carbon, allowed to stand in contact with the carbon at room temperature for 6 hours, and then placed in an oven to dry at 120 °C for 16 hours.

[0069] Experimental Test Methods The adsorbent absorbs NO containing approximately 1 ppm NO2 and approximately 10 ppb NO in air at 45 percent relative humidity. x The test was conducted under a continuous gas flow of 1000 kJ / s. Nitrite, nitric acid, nitrite, and nitrate were measured using the wet impinger method, in which the upstream and downstream air streams were bubbled through water to dissolve water-soluble compounds such as acids (e.g., HNO2 and HNO3). By passing the air stream through water for at least 1 hour, water-soluble compounds accumulated in the water and were detected by ion chromatography (IC). Details of the wet impinger method are described in Robert et al., "Virtual NOx - A measurement artifact in wet impinger air sampling," Jurgen Robert, Anatoly Grafer, Oleg Kishkovich, Entegris Inc., 2006. Additionally, the upstream and downstream air streams were continuously recorded using a gas analyzer (Model 17i, Thermo Scientific).

Claims

1. a porous adsorbent substrate; potassium hydroxide on the surface of the porous adsorbent substrate, and potassium carbonate on the surface of the porous adsorbent substrate; A porous adsorbent comprising:

2. The adsorbent of claim 1 , wherein the porous adsorbent substrate comprises a carbon adsorbent.

3. 10. The adsorbent of claim 1, comprising 10 to 40 weight percent potassium hydroxide and 60 to 90 weight percent potassium carbonate, based on the total weight of the potassium hydroxide and potassium carbonate.

4. Nitrogen dioxide (NO ) was reduced compared to an equivalent adsorbent containing potassium carbonate but not potassium hydroxide. ２ 4. The adsorbent of claim 1, wherein the adsorbent has an increased capacity to adsorb .

5. 4. The adsorbent of any one of claims 1 to 3, which exhibits reduced release of acid derivatives of adsorbed nitrogen dioxide compared to an equivalent adsorbent containing potassium carbonate but not potassium hydroxide.

6. K ２ CO ３ applying an aqueous solution to the porous adsorbent substrate; K applied to the porous adsorbent substrate ２ CO ３ removing water from the aqueous solution; applying an aqueous KOH solution to the porous adsorbent substrate; removing water from the aqueous KOH solution applied to said porous adsorbent substrate; 4. The adsorbent of claim 1, prepared by a process comprising:

7. The method is K ２ CO ３ applying an aqueous solution to the porous adsorbent substrate; Next, the K applied to the porous adsorbent substrate ２ CO ３ removing water from the aqueous solution; then applying an aqueous solution of KOH to the porous adsorbent substrate; then removing water from the aqueous KOH solution applied to the porous adsorbent substrate; 7. The adsorbent of claim 6, comprising, in order:

8. Nitrogen dioxide (NO) from nitrogen dioxide-containing air ２ 4. A method for removing toluene, toluene- ...

9. a porous adsorbent substrate; potassium hydroxide on the surface of the porous adsorbent substrate, and potassium carbonate on the surface of the porous adsorbent substrate; 1. A filter device containing an adsorbent, comprising:

10. The device of claim 9 , wherein the porous adsorbent substrate comprises activated carbon.

11. a first internal inlet, a first internal outlet, and a porous adsorbent substrate; potassium hydroxide on the surface of the porous adsorbent substrate, and Potassium carbonate on the surface of the porous adsorbent substrate a first interior including an adsorbent comprising a second interior including a second interior inlet, a second interior outlet, and a second adsorbent; a second interior having a second interior inlet facing the first interior outlet; 11. The apparatus of claim 9 or 10, comprising:

12. The first interior is the porous adsorbent substrate, potassium hydroxide on the surface of the porous adsorbent substrate, and potassium carbonate on the surface of the porous adsorbent substrate; an adsorbent comprising Cation exchange resin 12. The device of claim 11, comprising a combination of:

13. The second adsorbent is the porous adsorbent substrate, potassium hydroxide on the surface of the porous adsorbent substrate, and potassium carbonate on the surface of the porous adsorbent substrate; The apparatus of claim 11 , comprising:

14. 1. A method for preparing an adsorbent comprising an adsorbent substrate, potassium hydroxide, and potassium carbonate, comprising: K ２ CO ３ applying an aqueous solution to the adsorbent substrate; applying an aqueous KOH solution to the adsorbent substrate; K applied to porous adsorbent substrate ２ CO ３ removing water from the aqueous solution and the aqueous KOH solution; A method comprising:

15. K ２ CO ３ applying an aqueous solution to the porous adsorbent substrate; Next, the K applied to the porous adsorbent substrate ２ CO ３ removing water from the aqueous solution; then applying an aqueous solution of KOH to the porous adsorbent substrate; then removing water from the aqueous KOH solution applied to the porous adsorbent substrate; 15. The method of claim 14, comprising, in order:

16. K at temperatures between 20 and 25 degrees Celsius ２ CO ３ applying an aqueous solution; applying an aqueous solution of KOH at a temperature in the range of 20-25 degrees Celsius; 16. The method of claim 14 or 15, comprising:

17. 16. The method of claim 14 or 15, wherein the porous adsorbent substrate comprises an activated carbon adsorbent.

18. 16. The method of claim 14 or 15, wherein the adsorbent comprises 10 to 40 weight percent potassium hydroxide and 60 to 90 weight percent potassium carbonate, based on the total weight of the potassium hydroxide and potassium carbonate.

19. 1. A method for removing nitric oxide compounds from a gas, the method comprising contacting the gas with a porous adsorbent substrate and a porous adsorbent comprising potassium hydroxide and potassium carbonate on a surface of the porous adsorbent substrate.

20. 20. The method of claim 19, wherein the adsorbent comprises 10 to 40 weight percent potassium hydroxide and 60 to 90 weight percent potassium carbonate, based on the total weight of the potassium hydroxide and potassium carbonate.

21. 21. The method of claim 19 or 20, wherein the method has an increased capacity to adsorb nitrogen dioxide compared to an equivalent adsorbent containing potassium carbonate but not potassium hydroxide.

22. Adsorbed HNO compared to an equivalent adsorbent containing potassium carbonate but not potassium hydroxide ２ 21. The method of claim 19 or 20, wherein the release of

23. 21. The method of claim 19 or 20, wherein the gas is air containing less than 1 part per million nitrogen dioxide, and the method removes at least 90 percent of the nitrogen dioxide.

24. 21. The method of claim 19 or 20, wherein the gas is air containing less than 1 part per million of acetic acid, and the method removes at least 90 percent of the acetic acid.

25. 21. The method of claim 19 or 20, wherein the gas is air containing less than 1 part per million toluene, and the method removes at least 90 percent of the toluene.

26. The gas is SO at a rate below 1 part per million. ２ and by this method, at least 90 percent of the SO ２ 21. The method of claim 19 or 20, wherein

27. contacting a gas with a first volume of adsorbent, the first volume of adsorbent comprising: Porous adsorbent substrate, and potassium hydroxide and potassium carbonate on the surface of said porous adsorbent substrate a porous adsorbent comprising: an ion exchange resin; contacting the gas with a first volume of adsorbent comprising a mixture comprising: then contacting the gas with the porous adsorbent substrate and a second volume of adsorbent comprising potassium hydroxide and potassium carbonate on the surface of the porous adsorbent substrate; 21. The method of claim 19 or 20, comprising:

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