Coated nonwoven porous article

Abstract

Described herein is a porous article comprising: a nonwoven composite comprising oxidized polyacrylonitrile staple fibers and silica aerogel; wherein a coating is disposed on at least a portion of a surface of the nonwoven composite, wherein the coating is derived from an aminoalkoxy silane and wherein the porous article has a surface area of at least 1 m2 / g. Such porous articles may be used to sorb components of interest such as carbon dioxide.

Description

COATED NONWOVEN POROUS ARTICLE TECHNICAL FIELD

[0001] Disclosed herein is a nonwoven composite comprising oxidized polyacrylonitrile staple fibers and silica aerogel, which is coated with an aminoalkoxy silane. Such articles may be used to reversibly bind carbon dioxide. SUMMARY

[0002] Concern over environmental effects of greenhouse gasses has resulted in significant effort to reduce overall atmospheric carbon dioxide (CO2).One such effort is using a sorbent to remove carbon dioxide from gas streams such as plant exhaust or directly from the air. Ideally, these sorbents are reused, wherein carbon dioxide is sorbed from a gas stream onto the sorbent. Then, the carbon dioxide is released from the sorbent and collected and the sorbent is regenerated for use.

[0003] It is advantageous if the sorbent materials can be used over a range of temperatures. One reason is because this would enable any heat generated from a manufacturing plant, geosystem, or renewable energy source to be utilized to extract CO2without requiring additional energy to control or regulate the intake air temperature. Further, actual air streams for removal of CO2are multi-component, comprising in addition to water and CO2, other components such as bacteria, dust, pollen, and / or soot, which can adsorb into the sorbents, impacting sorbent lifetime. Using high temperatures during regeneration of the sorbents can be used to improve lifetimes.

[0004] Thus, there is a desire to identify sorbents for carbon capture that not only provide good initial sorption of CO2and are scalable, but can be used over a wide temperature range and / or have long service times as indicated by good performance over multiple cycles.

[0005] In one aspect, a porous article is discussed. The article comprises a nonwoven composite comprising oxidized polyacrylonitrile staple fibers and silica aerogel. A coating is disposed on at least a portion of a surface of the nonwoven composite, wherein the coating is derived from an aminoalkoxy silane. The disclosed porous article has a surface area of at least 1 m2 / g.

[0006] In another embodiment, a method for capturing carbon dioxide is disclosed. The method comprises contacting carbon dioxide to a nonwoven composite, which has a coating derived from an aminoalkoxy silane thereon, wherein the nonwoven composite comprises oxidized polyacrylonitrile staple fibers and silica aerogel.

[0007] In another embodiment, a use for capturing carbon dioxide and / or a carbonyl-containing compound is disclosed. A nonwoven composite, which has a coating derived from an aminoalkoxy silane thereon, wherein the nonwoven composite comprises oxidized polyacrylonitrile staple fibers and silica aerogel can be used to capture carbon dioxide and / or a carbonyl-containing compound.

[0008] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims. DETAILED DESCRIPTION

[0009] As used herein, the term “a”, “an”, and “the” are used interchangeably and mean one or more; and “and / or” is used to indicate one or both stated cases may occur, for example A and / or B includes, (A and B) and (A or B). Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0010] Also herein, recitation of “at least one” includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0011] As used herein, “comprises at least one of” A, B, and C refers to element A by itself, element B by itself, element C by itself, A and B, A and C, B and C, and all three.

[0012] The present application is directed toward a porous article coated with an aminoalkoxy silane which can be used to capture a desired gas, such as CO2, and / or carbonyl compounds such as formaldehyde, acetaldehyde, acrolein, acetone, etc.

[0013] The porous articles disclosed herein comprise a nonwoven composite, wherein a coating is disposed on at least a portion of the surface of the nonwoven composite and wherein the coating is derived from an aminoalkoxy silane.

[0014] The nonwoven composite disclosed herein comprises a plurality of oxidized polyacrylonitrile fibers and silica aerogel. As used herein, “nonwoven” generally refers to a fibrous web or material characterized by entanglement or point bonding of a plurality of fibers, wherein the fibers are interlaid, but not in an identifiable manner as in a knitted fabric.

[0015] The nonwoven composites used here are known in the art for insulation and fire-resistant applications, such as insulation protection of automobile components and fire protection. Unexpectedly, it has been discovered that these nonwoven composites may also be used to remove components such as CO2, formaldehyde, acetaldehyde, acrolein, and / or acetone from gas streams.

[0016] The fibers are oxidized polyacrylonitrile (PAN) processed into a non-woven fibrous web. In some embodiments, the PAN fiber is heat treated at a high temperature to stabilize the polymer. Such fibers are commercially available under the trade designation ZOLTEK OX from Zoltek Corp., Bridgeton, MO; and PANOX from SGL Group, Meitingen, Germany.

[0017] The oxidized PAN fibers are staple fibers, meaning they are short fibers having a length of at least 20, 30, or even 40 millimeters (mm); and at most 110, 85, or even 65 mm, although shorter and longer fibers (e.g., continuous filaments) may also be useful. The fibers may have a fineness or linear density of at least 1.7, 6, or even 17 decitex (dtex, i.e., grams / 10,000 meters); and at most 560, 280, or even 120 dtex, although fibers having lesser and / or greater linear densities may also be useful.

[0018] The fibers are oxidized, either partially oxidized or fully oxidized. The fibers may be treated thermally at high temperatures to oxidize the PAN fiber.

[0019] In some embodiments, the plurality of oxidized PAN fibers has an average fiber diameter of at least 0.1, 0.5, 1, 5, 10, 50, 100, 200, or even 500 micrometers. In some embodiments, the plurality of oxidized PAN fibers has an average fiber diameter of at most 500, 1000, 2000, 5000, 8000, or even 10000 micrometers.

[0020] In some embodiments, the plurality of oxidized PAN fibers has an average fiber length in the range from 10 mm to 100 mm, from 15 mm to 100 mm, from 25 mm to 75 mm, or in some embodiments, less than, equal to, or greater than 10, 12, 15, 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, or 75 mm. The diameter and length of the fibers can be determined using techniques known in the art such as optical microscopy.

[0021] Typically, to maximize the flame retardancy, commercially available nonwoven composites comprise over 85, 90, or even 95 vol (volume) % of oxidized polyacrylonitrile fibers versus the total volume of fibers present. In some embodiments, at least 50, 60, 70 or even 75% by weight of all of the fibers in the nonwoven composite are oxidized PAN fibers. In some embodiments, at most 99, 98, 95, 90, 85 or even 80% by weight of all of the fibers in the nonwoven composite are oxidized PAN fibers. In some embodiments, the nonwoven composite contains no other fibers other than the oxidized PAN fibers.

[0022] The nonwoven composite further comprises a silica aerogel.

[0023] Silica aerogels are solid, amorphous materials composed of silica. Silica aerogels are typically highly porous material (80 to 99.8%). However, due to the porosity, the materials generally have low mechanical strength and can be composited with the polyacrylonitrile fibers. Exemplary surface areas of aerogels are 500 to 1200 m2 / g.

[0024] In some embodiments, the silica aerogel is physically entangled with the oxidized PAN fibers in the nonwoven composite.

[0025] In some embodiments, the nonwoven composites disclosed herein are made by thermally stabilizing polyacrylonitrile fibers forming the fiber into a nonwoven such as a felt, impregnating the felt with an aerogel sol followed by solvent replacement and supercritical drying to form a nonwoven composite such as disclosed herein.

[0026] The nonwoven composites are known in the art available under the trade designation OX AEROGEL COMPOSITE from Zoltek Corp., Bridgeton, MO and silica aerogel impregnated OX felt from Shanghai Tanchain New Material Technology Co., Ltd., Shanghai, China.

[0027] The nonwoven composite is porous and has a high surface area. For example, in some embodiments, the nonwoven composite has an average surface area of at least 100, 200, 300, 400, or even 500 m2 / g (meters squared per gram) as determined by BET (Brunauer Emmet Teller) nitrogen adsorption.

[0028] In some embodiments, the nonwoven composite comprises at least 10, 15, 20, 25, or even 30 wt % of the silica aerogel. In some embodiments, the nonwoven composite comprises at most 35, 40, 45, 50, 55, or even 60 wt % of silica aerogel.

[0029] In some embodiments, the nonwoven composite further comprises an organic binder. The organic binder melts and / or becomes tacky during processing and can bond components in the nonwoven composite together. In some embodiments, the organic binder is a fiber. In some embodiments, the fibers may be a polyester homopolymer or a polyester copolymer. In some embodiments, the fibers may be a bi- component binder fiber comprising of a core polymer that extends along the axis of the fibers and is surrounded by a sheath of polymer. The sheath polymer typically has a melting temperature less than that of the core polymer, which at elevated temperatures at can become sufficiently soft and tacky to bond to other fibers or particles with which it comes into contact which is added during the manufacture of the nonwoven composite. In some embodiments, the sheath polymer has a melting point between 100°C to 300°C. Exemplary types of polymers that may be particularly useful for the sheath polymer includes thermoplastics such as polyesters or polyolefins (such as polyethylene). These binder fibers can increase the structural integrity of the nonwoven composite by creating a three-dimensional array of nodes where constituent fibers are physically attached to each other. These nodes provide a macroscopic fiber network, which increases tear strength, tensile modulus, preserves dimensional stability of the end product, and minimizes fiber shedding. An exemplary binder fiber that is commercially available is a polyester fiber available under the trade designation TREVIRA T-255 from Trevira GmbH, Bobingen, Germany.

[0030] In some embodiments, the nonwoven composite has a surface area of at least 50, 100, 200, 300, or even 400 m2 / g.

[0031] The nonwoven composites disclosed herein are treated with an aminoalkoxy silane. Not wanting to be limited by theory, but it is believed that the silane portion of the aminoalkoxy silane reacts with the nonwoven composite, specifically the silica aerogel, and the amino portion is directed away from the surface of the nonwoven composite and is able to interact with gases such as CO2.

[0032] Generally, the aminoalkoxy silane should not be sterically bulky to enable higher packing density at the surface of the composite and / or having a lower boiling point to evaporate the molecule onto the surface of the nonwoven composite.

[0033] In some embodiments, the aminoalkoxy silane is of formula (I)   wherein R comprises at least one amine group; and X1, X2, and X3are each independently selected from alkyl and alkoxy groups, wherein at least one of X1, X2, and X3is an alkoxy group.

[0034] Each alkyl and / or alkoxy groups may be linear or branched comprising at least 1, 2, or even 3 carbon atoms and at most 4, 5, 6, 7, 8, or 9 carbon atoms. In some embodiments, X1and X2are the same. In some embodiments, the alkoxy group is a methoxy group. In some embodiments, the alkyl group is a methyl group.

[0035] In some embodiments, R comprises a primary amine, a secondary amine, a tertiary amine, a quaternary amine, or combinations thereof.

[0036] In some embodiments, R is -(CH2)nNH2; -(CH2)oNH(CH2)pNH2; or -(CH2)oNH(CH2)pNH(CH2)qNH2, wherein n is 1, 2, 3, 4, 5, or 6; o is 1, 2, 3, or 4; p is 1, 2, 3, or 4; and q is 1, 2, 3, or 4.

[0037] In some embodiments, the aminoalkoxy silane is a trialkoxy silane. In some embodiments, the aminoalkoxy silane is a monoalkoxy silane. In some embodiments, the aminoalkoxy silane is of formula II: wherein R, X1, r is 0, 1, 2, 3, 4, 5, or even 6; and s is 0, 1, 2, 3, 4, 5, or even 6.

[0038] In some embodiments, the aminoalkoxy silane is selected from 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-aminopropyl methyl dimethoxysilane, 3-aminopropyl methyldiethoxysilane, p-aminophenyl trimethoxysilane, m-aminophenyl trimethoxysilane, 3-(m- aminophenoxy)propyl trimethoxysilane, 4-amino-3,3-dimethylbutyl trimethoxysilane, 2-(2-pyridylethyl) trimethoxysilane, n-(3-trimethoxysilylpropyl)pyrrole, 4-amino-3,3-dimethylbutyl methyldimethoxysilane, 1-amino-2-(dimethylethoxysilyl)propane, n-(2-aminoethyl)-3-aminopropyl trimethoxysilane, n-(2- aminoethyl)-3-aminopropyl trimethoxysilane, n-(6-aminohexyl)aminopropyl trimethoxysilane, n-(2- aminoethyl)-11-aminoundecyl trimethoxysilane, n-(2-n-benzylaminoethyl)-3-aminopropyl trimethoxysilane, n-(2-aminoethyl)-3-aminoisobutyl methyldimethoxysilane, n-(2-aminoethyl)-3- aminopropyl methyldimethoxysilane, n-(2-aminoethyl)-3-aminoisobutyl dimethylmethoxysilane, (3- trimethoxysilylpropyl) diethylenetriamine, 3-(n-allylamino)propyl trimethoxysilane, n-butylaminopropyl trimethoxysilane, t-butylaminopropyl trimethoxysilane, n-methylaminopropyl methyldimethoxysilane, n- methylaminopropyl trimethoxysilane, bis(3-trimethoxysilylpropyl)amine, n,n’-bis[(3- trimethoxysilyl)propyl]ethylenediamine, n,n’-bis[(3-trimethoxysilyl)propyl]ethylenediamine, or 3- (guanidinyl)propyl trimethoxysilane, N-[3-(trimethoxysilyl)propyl]aniline, p- aminophenyltrimethoxysilane, or combinations thereof.

[0039] In some embodiments, the aminoalkoxy silane has a boiling point of no more than 100, 120, 150, or even 175°C at ambient atmospheric pressure (e.g., 100 kPa).

[0040] The surface of the nonwoven composite is at least partially coated with a layer derived from the amino alkoxysilane. Typically, the surface of the nonwoven composite is thinly coated (for example, with a monolayer or dilayer) to prevent clogging of the pores within the aerogel to maximize the surface areaof the article. Generally, the article should not be heavily coated with the aminoalkoxy silane to inhibit the sorption of the desired gas to be removed (e.g., CO2).

[0041] In some embodiments, the nonwoven composite is contacted with an aminoalkoxy silane vapor. In some embodiments, the aminoalkoxy silane is condensed onto the surface of the nonwoven composite. Exemplary radiation to condense the aminoalkoxy silane includes electromagnetic or thermal radiation. In some embodiments, the nonwoven composites are vapor coated with the aminoalkoxy silane. Vapor coating can be conducted by heating the aminoalkoxy silane to vaporize it and placing the nonwoven composite near the vapor. In some embodiments, the vapor coating can be done at ambient pressures. Under these types of conditions, the aminoalkoxy silane may deposit onto the nonwoven composite a mix of partial condensation reactions following anhydrous deposition and partial hydrogen-bonded intermediates. It is postulated that the hydrogen-bonded silane can undergo a condensation reaction and covalently bond firmly with the sample, enabling a strong covalent bond attaching the amino functional group to the nonwoven composite. Following vapor coating, the sample may be heated, for example, at a temperature of at least 50 to at most 120°C to covalently bond the aminoalkoxy silane to the nonwoven composite surface. In some embodiments the vapor coating can be done under controlled vacuum conditions at reduced pressures, which can enable lower temperatures to vapor coat.

[0042] The amount of aminoalkoxy silane deposited onto the nonwoven composite can be controlled by (1) the amount of aminoalkoxy silane used, (2) the duration of the vapor coating, and (3) the temperature used. Aminoalkoxy silanes can modify surfaces under anhydrous conditions consistent with monolayer and vapor phase deposition requirements. Extended vapor coating times (4-12 hours) at elevated temperatures (50-120 °C) are typical.

[0043] In some embodiments, the aminoalkoxy silane (or compound derived therefrom) is disposed on both the surface of the oxidized polyacrylonitrile staple fibers and the surface of the silica aerogel.

[0044] Due to the highly porous nature of nonwoven composite, the nonwoven composites are able to load high amounts of aminoalkoxy silanes. In some embodiments, the porous articles of the present disclosure are able to load (weight gain) at least 15, 20, 30, 40, 50, or even 60 % of the aminoalkoxy silane and at most 65, 70, 75, 80, 90, 100, 110, or even 125 % of the aminoalkoxy silane. Generally, more aminoalkoxy silane is advantageous to capture CO2, but if too much is coated, the pores of the nonwoven composite can become clogged, limiting the available surface area.

[0045] The coated nonwoven composites of the present disclosure are porous. The porous articles of the present disclosure have a high surface area. For example, in some embodiments, the porous articles have an average surface area of at least at least 1, 5, 10, 20, 50, 100, 200, 300, or even 400 m2 / g; and typically, at most 500 m2 / g as determined by BET (Brunauer Emmet Teller) nitrogen adsorption. BET is commonly used to determine surface area and involves adsorbing a monolayer of nitrogen on the surface of the article under cryogenic conditions. The amount of adsorbed nitrogen is proportional to the surface area.

[0046] In some embodiments, the porous articles of the present disclosure have a thickness of at least 1, 2, 5, 10, or even 50 mm.

[0047] In some embodiments, the porous articles of the present disclosure have an initial CO2absorbance of at least 0.5, 0.6, 0.8, 1.0, or even 1.2 mmol CO2 / g at 80°C. In some embodiments, the porous articles of the present disclosure have a percentage difference in CO2absorbance from an initial cycle to a final cycle of less than 10, 8, 5, or even 2% when tested at 80°C.

[0048] Increased heat (for example, 110 °C) may be used to regenerate the porous articles. In some embodiments, the porous articles of the present disclosure have thermal stability up to 110°C, meaning the absorption properties do not deteriorate at temperature below 110°C. Although not wanting to be limited by theory, it is believed that the aminoalkoxy silanes have a strong covalent bond with the nonwoven composite enabling good thermal stability.

[0049] Ideally, the porous articles of the present disclosure can be regenerated and used repeatedly, for example used for at least 10, 20, 50 or even 100 cycles. In some embodiments, the porous articles of the present disclosure after 20 cycles have a CO2absorbance of at least 0.5, 0.6, 0.8, 1.0, or even 1.2 mmol CO2 / g at 50°C.

[0050] In some embodiments, the porous articles disclosed herein may be used in carbon capture, wherein the porous articles are contacted with gas streams. CO2from a gas stream can be sorbed onto the porous articles of the present disclosure. In some embodiments, the porous articles disclosed herein may be used to remove carbonyl-containing contaminates from the air, such as formaldehyde, acetaldehyde, acrolein, and / or acetone. Contaminates from a gas stream can be sorbed onto the porous articles of the present disclosure. In some embodiments, the porous articles disclosed herein may be used in flow through operation-filtration type modules.

[0051] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. EXAMPLES

[0052] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

[0053] These abbreviations are used in the following examples: °C = degree Celsius, cm = centimeter, g = gram, gsm = grams per square meter, µm= micrometer, L = liter, m = meter, mg = milligram, mL = milliliter, mm = millimeter, min = minute, mmol = millimole, MPa = megapascal, rpm = revolutions per minute, psi = pounds per square inch, s = second, and wt = weight.Materials Abbreviation Description Nonwoven A nonwoven composite mat made of oxidized polyacrylonitrile fibers Composite and silica aerogel having an average basis weight of 340 gsm obtained from Nano Tech Co., Ltd., Shaoxing, Zhejiang, China. Fiber Alkaline earth silicate fibers with a mean fiber diameter of 2.5-3.4 micrometers available under the trade designation SUPERWOOL PLUS obtained from Morgan Advanced Materials, Windsor, United Kingdom. Adhesive Aqueous polymer dispersed pressure sensitive adhesive available under the designation VINNAPAS EAF 68 VINYL ACETATE ETHYLENE obtained from Wacker Chemie AG, Miinchen, Germany. Particles Expanded vermiculite obtained from Sun Gro, Agawam, MA, United States. APTMS (3-Aminopropyl)trimethoxysilane obtained from Thermo Scientific Chemicals, Ward Hill, MA, United States.

[0054] Brunauer-Emmett-Teller (BET) Test Method

[0055] The surface area of the composites was determined using the BET method described in J. Am. Chem. Soc., 1938, 60, 309. Samples (20-50 mg) were degassed under vacuum (500 micrometers mercury) using a 0.5 inch (1.27 cm) diameter sample tube at 80°C for 6 hours using Micromeritics VacPrep 061 Sample Degas System (Micromeritics, Norcross, GA). After degassing, the sample was backfilled with nitrogen and transferred to the analysis port. BET surface area was determined using Micrometics Tristar II Plus analyzer (Micromeritics, Norcross, GA) using nitrogen gas as adsorbate at 77 K from relative pressure (P / Po) 0.05 to 0.30 at 0.05 intervals with equilibration time of 10 s each interval.

[0056] Thermogravimetric analysis (TGA) Test Method 1: CO2capture performance

[0057] A hole punch was used to cut out samples from the vapor-coated nonwoven composite weighing approximately 25 mg. The sample was loaded on a clean and tared platinum TGA pan. The thermogravimetric analyzer (a Q500 model from TA Instruments New Castle, DE) was plumbed with house nitrogen (supplied by Praxair, Danbury, CT) in gas line 1 and a mixed gas canister on gas line 2 regulated to 20 psi (0.138 MPa). The mixed gas canister was a 20 volume % CO2with a balance of N2obtained from Airgas, Randor, PA.

[0058] First, house nitrogen was flowed over the sample at 80 °C for 90 minutes at 267 mL / min to drive off CO2and get a baseline weight %.

[0059] Then, the gas composition supplied at a flow rate of 200 mL / min was adjusted (by splitting gas lines 1 and 2) to supply a 15 vol% CO2to the sample in the chamber while holding the chamber at 80°C. The 15 vol% CO2was flowed across the sample for a set time (either 10 or 30 minutes) and the weight gain of the sample was monitored.

[0060] Then, the CO2gas supply was stopped and the sample was regenerated with house nitrogen flow for 10 minutes while held at 80°C.

[0061] Then, the gas in the sample chamber was adjusted to 15 vol% CO2and the chamber was cooled to 65°C. The 15 vol% CO2 was flowed across the sample at a flow rate of 200 mL / min for a set time (either 10 or 30 minutes) and the weight gain of the sample was monitored.

[0062] The sample was then regenerated by flowing house nitrogen and ramping the chamber up to 80 °C at 10°C / min for 10 minutes to remove CO2from the sorbent.

[0063] Then, the gas in the sample chamber was adjusted to 15 vol% CO2and the chamber was cooled to 50°C. The 15 vol% CO2was flowed across the sample at a flow rate of 200 mL / min for a set time (either 10 or 30 minutes) and the weight gain of the sample was monitored.

[0064] The sample was then regenerated by flowing house nitrogen and ramping the chamber up to 80 °C at 10°C / min for 10 minutes to remove CO2from the sorbent.

[0065] Then, the gas in the sample chamber was adjusted to 15 vol% CO2and the chamber was cooled to 35°C. The 15 vol% CO2was flowed across the sample at a flow rate of 200 mL / min for a set time (either 10 or 30 minutes) and the weight gain of the sample was monitored.

[0066] The sample was then regenerated by flowing house nitrogen and ramping the chamber up to 80 °C at 10°C / min for 10 minutes to remove CO2from the sorbent.

[0067] While at 80°C, the gas composition was switched and 15 vol% CO2was flowed across the sample at a flow rate of 200 mL / min for a set time (either 10 or 30 minutes) and the weight gain of the sample was monitored.

[0068] The mmol of CO2per gram of sample at each temperature isotherm (80°C, 65°C, 50°C, 35°C, and 80°C) was calculated based on the difference between peak wt % and baseline wt% from the TGA and then multiplied by the molecular weight of CO2to convert into mmoles of sample and divided by the weight of the initial sample.

[0069] TGA Test Method 2: performance stability

[0070] A sample of EX1 was cut out and tested in the thermogravimetric analyzer similar to TGA Test Method 1, except the following cycling was done.

[0071] After determining the initial baseline weight %, the chamber was cooled to 50°C and 15 vol% CO2was flowed across the sample for 90 minutes at 200 mL / min. Then the CO2gas supply was stopped and the sample was regenerated with house nitrogen flow for 10 minutes while held at 110°C.

[0072] The sample was cycled using the above process (i.e., flowing CO2followed by regeneration) monitoring the weight change of the sample.

[0073] The mmol of CO2per gram of sample at each cycle was calculated based on the difference between peak wt % and baseline (initial) wt% from the TGA and then multiplied by the molecular weight of CO2to convert into mmoles of sample and divided by the weight of the initial sample.

[0074] Vapor Coating Method

[0075] The designated composite was cut into 1.25 in (3.2 cm) by 1.25 in (3.2 cm) square samples using a die cutter. A designated amount of APTMS was placed on an aluminum weighing pan. The pan of APTMS was placed on the top of a hot plate, the composite stood upright right next to the pan tomaximize the vapor exposure. A PYREX 3140 glass dish (70 X 50 mm) was used as a cover for the vapor coating apparatus. The glass dish was sealed on top of the hot plate using a Dow Corning High Vacuum Grease. The hot plate was set to 80°C and the composite was vapor coated for a designated time. After vapor coating, the sample was removed from the vapor coating apparatus was baked at 120 °C for 3 hours in a convection oven to stabilize the APTMS onto the composite by forming a covalent bond.

[0076] Comparative Example 1 (CE1)

[0077] Nonwoven Composite used as-received.

[0078] Comparative Example 2 (CE2)

[0079] 8.92 g of Fiber was placed in a low-shear mixer.1.6 L of warm tap water was added and stirred at 900 rpm for 10 seconds. Then, 1.65 g of Adhesive was added and mixed for an additional 2 minutes. Immediately, 1 g of neutral pH flocculant was added to the mixer and mixed for an additional 10 seconds. Finally, 6.61 g of Particles were added to the mixer and dispersed evenly. Once the mixing was completed, the mixture was quickly removed and immediately poured into a steel square hand sheet former (available under the trade designation FORMAX from Adirondack Machine Corp, Hudson Falls, NY). A vacuum was pulled to remove the water to form a wet sheet. Then, 3 sheets of blotter paper were placed on top and 3 sheets on bottom of the wet sheet to absorb water. The sandwich hand sheet with blotter papers was carefully transferred to a hand sheet press and placed in between two mesh screens. The sandwich was compressed at 40 psi (0.276 MPa) for 30 seconds until the majority of the water was drained. After that, the hand sheet stack with one sheet of blotter paper on each side was placed into a 150 °C oven for 30 minutes to form a composite mat. The weight ratio of fiber / adhesive / particles was 54 / 6 / 40.

[0080] The resulting composite mat was then vapor coated using the Vapor Coating Method. The amount of APTMS used and vapor coating time are shown in Table 1.

[0081] Examples 1-6 (EX1- EX6)

[0082] Nonwoven Composite was vapor coated using the Vapor Coating Method. The amount of APTMS used and vapor coating time for samples EX1-EX6 are shown in Table 1.

[0083] Shown in Table 1 is the weight of the composite before and after vapor coating, and the calculated % weight gain for the vapor coated samples.

[0084] The surface area of CE1 and EX1-EX4 and EX6 was analyzed using the BET Test Method and the results are reported in Table 1. Table 1 Vapor Before After Sample APTMS, coating coating coating % weight Surface milliliters time, weight, weight, gain, % Area, m2 / g hours milligrams milligrams CE1 NA NA NA NA NA 174.58 CE2 1.0 66 386.0 740.9 91.9 NT EX1 1.0 6 283.9 335.5 18.2 76.92 EX2 1.0 6 267.4 321.3 20.2 90.89 EX3 1.0 18 284.2 377.2 32.7 73.71EX4 1.0 66 270.8 411.0 51.8 49.23 EX5 2.5 66 267.5 482.7 80.4 NT EX6 3.0 66 287.5 637.5 121.7 0.57 NA= not applicable NT= not tested

[0085] CE1, CE2, and EX1-EX6 were tested using TGA Test Method 1. The results at the various testing temperatures are shown in Table 2. Table 2 Sample % weight Surface 80 °C, 65 °C, 50 °C, 35 °C, @ 80 °C, gain Area, mmol mmol mmol mmol mmol m2 / g CO2 / g CO2 / g CO2 / g CO2 / g CO2 / g CE1 NA 174.58 0.04 0.05 0.08 0.13 0.02 CE2 91.9% NT 0.11 0.06 0.04 0.03 0.10 EX1 18.2% 76.92 0.63 0.68 0.77 0.83 0.61 EX2 20.2% 90.89 0.68 0.71 0.80 0.86 0.65 EX3 32.0% 73.71 0.73 0.73 0.83 0.86 0.68 EX4 51.8% 49.23 0.83 0.88 0.99 1.05 0.78 EX5 80.4% NT 1.09 1.21 1.35 1.42 1.19 EX6 121.7% 0.57 0.59 0.47 0.52 0.49 0.49

[0086] The first and second 80°C results from Table 2 are compared in Table 3 for samples EX1-EX5. All of the samples in Table 3 have a difference of less than 10%, which is within the experimental error. Table 3 Sample % weight gain 1stcycle at 80 °C, 2ndcycle at 80 °C, % Difference mmol CO2 / g mmol CO2 / g EX1 18.2% 0.63 0.61 3.17% EX2 20.2% 0.68 0.65 4.41% EX3 32.0% 0.73 0.68 6.85% EX4 51.8% 0.83 0.78 6.02% EX5 80.4% 1.09 1.19 9.17%

[0087] EX1 was analyzed by TGA Test Method 2 to evaluate the CO2sorption cyclability run at a sorption temperature of 50°C and a regeneration temperature of 110°C. After 20 cycles of CO2sorption testing, the standard deviation was 1.7%, with no sign of performance degradation with repeated cycles, as shown in Table 4.Table 4 cycle number mmol CO2 / g at 50 °C relative to Cycle 1 Cycle 1 NA Cycle 2 0.98 Cycle 3 1.00 Cycle 4 1.00 Cycle 5 1.00 Cycle 6 0.95 Cycle 7 1.01 Cycle 8 1.00 Cycle 9 0.99 Cycle 10 0.99 Cycle 11 0.99 Cycle 12 1.00 Cycle 13 1.04 Cycle 14 1.01 Cycle 15 0.98 Cycle 16 1.00 Cycle 17 0.99 Cycle 18 1.00 Cycle 19 0.99 Cycle 20 1.02

[0088] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.

Claims

What is claimed is:

1. A porous article comprising: a nonwoven composite comprising oxidized polyacrylonitrile staple fibers and silica aerogel; wherein a coating is disposed on at least a portion of a surface of the nonwoven composite, wherein the coating is derived from an aminoalkoxy silane and wherein the porous article has a surface area of at least 1 m2 / g.

2. The porous article of claim 1, wherein the aminoalkoxy silane is of formula (I)   wherein R comprises at least one amine group; and X1, X2, and X3are independently selected from alkyl and alkoxy groups, wherein at least one of X1, X2, and X3is an alkoxy group.

3. The porous article of claim 2, wherein X1, and X2are the same.

4. The porous article of any one of claims 2-3, wherein the alkoxy group is a methoxy group.

5. The porous article of any one of claims 2-4, wherein R comprises a primary amine, a secondary amine, a tertiary amine, a quaternary amine, or combinations thereof.

6. The porous article of any one of claims 2-5, wherein R is -(CH2)nNH2; -(CH2)oNH(CH2)pNH2; or -(CH2)oNH(CH2)pNH(CH2)qNH2, wherein n is an integer from 1-6, o is an integer from 1-4, p is an integer from 1-4, and q is an integer from 1-4.

7. The porous article of any one of claims 2-6, wherein the aminoalkoxy silane comprises 3- aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-aminopropyl methyl dimethoxysilane, 3-aminopropyl methyldiethoxysilane, p-aminophenyl trimethoxysilane, m- aminophenyl trimethoxysilane, 3-(m-aminophenoxy)propyl trimethoxysilane, 4-amino-3,3- dimethylbutyl trimethoxysilane, 2-(2-pyridylethyl) trimethoxysilane, n-(3- trimethoxysilylpropyl)pyrrole, 4-amino-3,3-dimethylbutyl methyldimethoxysilane, 1-amino-2- (dimethylethoxysilyl)propane, n-(2-aminoethyl)-3-aminopropyl trimethoxysilane, n-(2- aminoethyl)-3-aminopropyl trimethoxysilane, n-(6-aminohexyl)aminopropyl trimethoxysilane, n-(2-aminoethyl)-11-aminoundecyl trimethoxysilane, n-(2-n-benzylaminoethyl)-3-aminopropyl trimethoxysilane, n-(2-aminoethyl)-3-aminoisobutyl methyldimethoxysilane, n-(2-aminoethyl)-3- aminopropyl methyldimethoxysilane, n-(2-aminoethyl)-3-aminoisobutyl dimethylmethoxysilane, (3-trimethoxysilylpropyl) diethylenetriamine, 3-(n-allylamino)propyl trimethoxysilane, n- butylaminopropyl trimethoxysilane, t-butylaminopropyl trimethoxysilane, n-methylaminopropyl methyldimethoxysilane, n-methylaminopropyl trimethoxysilane, bis(3- trimethoxysilylpropyl)amine, n,n’-bis[(3-trimethoxysilyl)propyl]ethylenediamine, n,n’-bis[(3- trimethoxysilyl)propyl]ethylenediamine, 3-(guanidinyl)propyl trimethoxysilane, N-[3- (trimethoxysilyl)propyl]aniline, p-aminophenyltrimethoxysilane, or combinations thereof.

8. The porous article of any one of the previous claims, wherein the aminoalkoxy silane has a boiling point of no more than 175°C.

9. The porous article of any one of the previous claims, wherein the coating is disposed on both the oxidized polyacrylonitrile staple fibers and the silica aerogel.

10. The porous article of any one of the previous claims, wherein the silica aerogel is physically entangled in the nonwoven composite.

11. The porous article of any one of the previous claims, wherein the oxidized polyacrylonitrile staple fibers have an average diameter of at least 0.1 µm and at most 10000 µm.

12. The porous article of any one of the previous claims, wherein the nonwoven comprises about 10- 60 wt % of silica aerogel.

13. The porous article of any one of the previous claims, wherein the nonwoven further comprises an organic binder.

14. The porous article of any one of the previous claims, wherein the organic binder is derived from a multifunctional acrylate or isocyanate.

15. The porous article of any one of the previous claims, wherein the porous article has heat stability of up to at least 110 °C.

16. The porous article of any one of the previous claims, wherein the porous article has an initial CO2absorbance of at least 0.5 mmol CO2 / g at 80°C.

17. The porous article of any one of the previous claims, wherein the porous article after 20 cycles has a CO2 absorbance of at least 0.5 mmol CO2 / g at 50°C.

18. A method of carbon capture, the method comprising contacting carbon dioxide to the porous article according to any one of the previous claims.

19. Use of an aminoalkoxy silane-coated nonwoven composite to capture carbon dioxide, wherein the aminoalkoxy silane-coated nonwoven comprises a nonwoven composite comprising oxidized polyacrylonitrile staple fibers and silica aerogel with a surface coating derived from an aminoalkoxy silane.

20. Use of an aminoalkoxy silane-coated nonwoven composite to capture a carbonyl-containing compound, wherein the aminoalkoxy silane-coated nonwoven comprises a nonwoven composite comprising oxidized polyacrylonitrile staple fibers and silica aerogel with a surface coating derived from an aminoalkoxy silane.

21. The use according to claim 20, wherein the carbonyl-containing compound comprises, formaldehyde, acetaldehyde, acrolein, acetone, or mixtures thereof.

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