WO2015054332A1 - Composite honeycombs for gas storage - Google Patents

Abstract

A composite honeycomb includes a channel-defining honeycomb matrix formed using a first material and a microporous filler made using a second material that is incorporated into a plurality of channels. Mechanical durability provided by the honeycomb matrix and high surface area provided by the microporous filler cooperate to form a gas adsorption platform having both a high gas adsorption capacity and favorable adsorption/desorption kinetics.

Description

COMPOSITE HONEYCOMBS FOR GAS STORAGE

[0001] This application claims the benefit of priority under 35 U.S.C. § 120 of U.S. Application No. 61/889,078, filed on October 10, 2013, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

Field

[0002] The present disclosure relates generally to gas storage media, and more specifically to engineered honeycomb structures and their methods of production.

Technical Background

[0003] Natural gas (methane) is an attractive fuel for motor vehicles. Natural gas engines have lower emissions of NO_x, SO_x, CO and CO2 relative to diesel vehicles. Further, new technologies enabling the economic extraction of "shale gas" are leading to sustained low natural gas prices in North America. To date, natural gas vehicle (NGV) and engine technology has been successfully commercialized using two storage methods: liquefied natural gas (LNG) and compressed natural gas (CNG).

[0004] Activated carbon has been used as filtration media for the abatement of odors, color pigments as well as in various catalytic functions. Recent applications of activated carbon include the removal of impurities from fluid (liquid or gaseous) streams. Impurities in food products such as fruit juices and alcoholic beverages, for example, can be filtered using activated carbon. Activated carbon is also useful for removing gaseous species present in air or gas streams. Activated carbon has particular utility in adsorbing and purifying fluid emissions from internal combustion engines.

[0005] It is desirable to provide low cost and easy-to-manufacture activated carbon-based media for gas storage as well as filtration and purification having good structural integrity, high adsorption capacity per unit volume, and a low pressure drop across the media during use.

BRIEF SUMMARY [0006] In accordance with embodiments of the present disclosure, an adsorbent structure comprises a honeycomb substrate having a plurality of partition walls extending in an axial direction from an inlet end to an outlet end forming a plurality of flow channels, wherein the honeycomb substrate comprises a powder component and a binder; and a microporous filler dispersed within at least some of the flow channels, wherein the partition walls have at least one of (a) a specific surface area from 100 to 2000 m²/g or (b) a thermal conductivity of at least 1 W/mK, the microporous filler specific surface area is from 400 to 15000 m²/g, and the specific surface area of the microporous filler is greater than the specific surface area of the partition walls.

[0007] A method of forming a composite honeycomb comprises providing a batch formulation comprising a carbon precursor and an activating agent, shaping the batch formulation to provide a honeycomb green body having a plurality of parallel channels bounded by channel walls traversing the body from an upstream inlet end to a downstream outlet end, heat treating the honeycomb green body to carbonize and simultaneously activate the carbon precursor, and incorporating a microporous material into a plurality of the channels.

[0008] Additional features and advantages of the subject matter of the present disclosure will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the subject matter of the present disclosure as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0009] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the subject matter of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the subject matter of the present disclosure as it is claimed. The accompanying drawings are included to provide a further understanding of the subject matter of the present disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the subject matter of the present disclosure and together with the description serve to explain the principles and operations of the subject matter of the present disclosure. Additionally, the drawings and descriptions are meant to be merely illustrative, and are not intended to limit the scope of the claims in any manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0011] Fig. 1 is a schematic of a composite honeycomb according to various embodiments;

[0012] Fig. 2 is a cross-sectional view of a composite honeycomb having a porous filler partially filling the channels;

[0013] Fig. 3 is a cross-sectional view of a composite honeycomb having a striated, slit- shaped porous filler within the channels;

[0014] Fig. 4 is a cross-sectional view of a composite honeycomb having filled and unfilled channels;

[0015] Fig. 5 is a cross-sectional view of a composite honeycomb having filled and unfilled channels;

[0016] Fig. 6 is a cross-sectional view of a composite honeycomb having filled and unfilled channels;

[0017] Fig. 7 is a schematic of a composite honeycomb having a striated porous filler within the channels; and

[0018] Fig. 8 is a plot of adsorption/desorption rate versus capacity for comparative porous materials and composite honeycombs according to various embodiments.

[0019] Fig. 9 is a plot of adsorption/desorption rate versus capacity for comparative porous materials and composite honeycombs according to various embodiments.

DETAILED DESCRIPTION

[0020] Reference will now be made in greater detail to various embodiments of the subject matter of the present disclosure, some embodiments of which are illustrated in the accompanying drawings. The same reference numerals will be used throughout the drawings to refer to the same or similar parts.

[0021] Natural gas storage using adsorbed natural gas (ANG) on highly porous solids is a promising alternative to LNG and CNG storage. The US Department of Energy has set target levels for ANG performance at 180 volumes methane at standard temperature and pressure per 1 volume container at 35 bar. Successful ANG storage in on-board vehicle fuel tanks will enable the use of low-cost, single-stage compressors for vehicle refueling, as opposed to relatively expensive multi-stage compression required for CNG (operating at 200+ bar) or cryogenic systems required for LNG (operating near -150°C). Commercialization of ANG could significantly lower the capital investment for fuel station owners to install natural gas refueling pumps, and could even make it cost-effective for consumers to install refueling pumps in their homes. Low-cost refueling systems could dramatically accelerate the adoption of NGV's, as the lack of refueling stations is one of the primary barriers to their wider adoption.

[0022] Many porous materials have been explored as natural gas adsorbents, with the two most promising being activated carbons (AC's) and metal-organic frameworks (MOF's), though each of these materials currently suffer from practical end-use limitations related to gas flow, adsorption/desorption rates, and adsorbent geometry. Typical geometries for the adsorbents include powders, packed pellets, and packed disks.

[0023] Conventionally, activated carbon is used in powdered or granular form. However, powdered or granular activated carbon can be inconvenient or inefficient, particularly in processes where continuous fluid flows are filtered or treated. For example, in applications such as automotive applications where an activated carbon bed is vibrated during use, material attrition may generate fine particles that can become trapped in the material being filtered. Also, the formation of fine particles can change or disrupt flow paths through the bed. This may result in decreased adsorption efficiency. In the case where liquids are being filtered or treated, tightly packed carbon beds can cause a significant unwanted pressure drop and attendant elevated pumping costs.

[0024] Pores less than two nanometers in size (defined here as "micropores") can be used to efficiently adsorb gases such as methane or hydrogen. A powder geometry allows fast access to micropores, but powder packing density can be low with space between powder particles being un-utilized from an adsorption standpoint. Further, packed powder beds suffer from slow gas diffusion and may exhibit poor material utilization due to gas channeling. Pellets, disks, or monoliths, for instance, can include a high volume of adsorbent, but the high surface area and high microporosity requirement for an adsorbent means that diffusion into these pellets, disks, or monoliths will be slow, which slows the adsorption/desorption cycle. The introduction of mesopores (defined here as pores having a size of 2-50 nanometers) or macropores (defined here as pores larger than 50 nanometers) can increase diffusion rates into and out of the adsorption media, but at the same time significantly reduce the available surface area for gas adsorption.

[0025] As disclosed herein, highly microporous, mechanically robust carbon honeycomb- based composite structures can be used for both filtration and storage of liquid and gaseous materials. For instance, the structures are envisioned for use in storage of adsorbed gases, in particular methane or hydrogen for on-board motor vehicle fuel applications. The composite activated carbon-based honeycomb structures forego the use of plural, discrete particles of activated carbon.

[0026] The composite honeycombs comprise a monolithic honeycomb substrate having a plurality of channels and porous filler formed within at least some of the channels. In embodiments, the honeycomb substrate comprises highly microporous activated carbon, and the porous filler comprises a metal organic framework material. The honeycomb geometry enables both a high geometric surface area for media contact/adsorption and a sustainable low pressure drop.

[0027] The composite honeycombs are structurally-rigid, high surface area porous solids. They are characterized by a high volume-filling fraction of microporous material, which maximizes the volume of gas that can be adsorbed. In embodiments they include an optimized volume of relatively large diameter channels that provide fast access to the micropores while minimizing the loss of surface area or volume-filling fraction created by the channels.

[0028] As used herein, a honeycomb structure is a porous monolithic body having a plurality of parallel cell channels bounded by solid or porous channel walls that traverse the body from an upstream end to a downstream end. The geometric shape of the cell channels is not particularly limited and may include, for example, squares, triangles, rectangles, hexagons, octagons, circles, ovals, slits, or any combination of these or similar shapes.

[0029] The channel density of the honeycombs can range from 6 cells per square inch (cpsi) to 1200 cpsi. The wall thickness between the channels can range from 0.001 inch to 0.200 inch, e.g., 0.02 inch to 0.08 inch, for example 0.050 inch. In embodiments, the wall contains interconnected micropores. [0030] The diameter of a honeycomb monolith can range, for example, from about 1 inch to about 30 inches, e.g., from 3 to 15 inches. The body length of the monolith can range from 0.2 inches to 100 inches, e.g., 0.5 to 20 inches.

[0031] In embodiments, a partially-filled honeycomb structure comprises at least two distinct materials. The honeycomb comprises a mechanically-rigid skeleton made from a first material. The honeycomb channels defined by the first material are at least partially- filled with a second material.

[0032] In embodiments, the first material comprises activated carbon and the second material comprises a metal organic framework material. In further embodiments, the first material and the second material each comprise activated carbon. In such a case, however, the respective activated carbons are characterized by at least one different property such as surface area, pore size distribution or average pore size. For example, the first and second materials can have the same chemical and/or elemental composition, but have a different structure or pore size distribution.

[0033] The second material can have a different, for example higher, level of microporosity (i.e., surface area) than the first material. Engineered channels in the honeycomb structure provide fast access to the micropores of the second material, and in some embodiments also the first material.

[0034] In embodiments, the first material provides structural rigidity to the composite, while the second material provides a maximum porosity and attendant surface area for adsorption. A surface area of the first material can range from 100 to 2000 m²/g (e.g., 100, 200, 400, 600, 800, 1000 or 2000 m²/g). A surface area of the second material can range from 400 to 15000 m²/g (e.g., 400, 600, 800, 1000, 2000, 4000, 5000, 10000 or 15000 m²/g). Each of the first and second materials can be microporous materials.

[0035] The first material, which forms the honeycomb skeleton, in embodiments is extrudable and mechanically durable and may have an intermediate surface area and microporosity such that it provides and maintains mechanical integrity. If extruded, the first material may maintain structural rigidity in both the green and the fired states. The first material may be porous or include low or even no porosity, such as in applications where maximum mechanical durability or thermal conductivity is required. These types of "highly filled" honeycombs may be used in applications where high storage capacity, mechanical robustness, and/or high thermal conduction are desired, and fast gas diffusion may be less critical. In embodiments, the first material contains a significant fraction (at least 50%) of microporosity. In further embodiments, the first material has a specific surface area in the range of 100-2000 m²/g, e.g., 400-1500 or 800-1000 m²/g. Additionally, or alternatively, the first material exhibits a high thermal conductivity. For example, in some embodiments, the first material comprises a thermal conductivity of at least about 0.1 W/mK, at least about 0.15 W/mK, at least about 0.2 W/mK, at least about 0.3 W/mK, at least about 0.4 W/mK, at least about 0.5 W/mK, at least about 1 W/mK, at least about 5 W/mK, at least about 10 W/mK, at least about 20 W/mK, at least about 50 W/mK or at least about 100 W/mK. In some embodiments, the first material comprises both a specific surface area in one of the aforementioned ranges and a thermal conductivity as described above.

[0036] With reference to Fig. 1, an example composite honeycomb 11 1 has an inlet end 120 and an outlet end 140. Plural cells 108, 110 extend from the inlet end 120 to the outlet end 140. In the illustrated embodiment, intersecting cell walls 10 extend from the inlet end to the outlet end and define the cells. In the illustrated embodiment, a porous media 200 is disposed in alternating cells, though it will be appreciated that the porous media 200 can be incorporated into any suitable fraction of the honeycomb cells in any suitable configuration. The cell walls 10 are formed from a first material 100 while the porous media 200 is a second material.

[0037] Thermal conduction of the composite honeycomb may be important for some adsorption applications, in particular when fast adsorption/desorption is desired. Because gas adsorption is typically exothermic, during adsorption the adsorbent material will heat up, which may adversely affect the total adsorption capacity of the adsorbent. Conversely, gas desorption is endothermic. A decrease in the temperature of the adsorbent during desorption cycles will decrease the total amount of gas that can be desorbed.

[0038] The second material at least partially fills the honeycomb channels and is not necessarily as extrudable or mechanically durable as the first material. The second material is designed to have a higher level of microporosity and/or surface area than the first material. The second material may have a surface area of 400, 500, 1000, 2000, 3000, 4000 or 5000 m /g. For instance, the second material may have a specific surface area of 400-3000 m²/g, 400-5000 m²/g, 400-10000 m²/g, 400-15000 m²/g, 800-3000 m²/g, 800-10000 m²/g, 1200- 3000 m²/g, 1200-10000 m²/g, and all like ranges and sub-ranges there between.

[0039] In embodiments, engineered axial channels 0.1 to 500 microns in diameter are maintained through the second material to provide fast diffusion paths to more easily access the micropores. These larger axial channels are characterized by a high degree of connectivity (long channels, which may be greater than -500 or even greater than 5000 microns in length). The engineered channels may comprise original, unfilled channels of the honeycomb or sub-channels defined by the second material and formed within the native honeycomb channels. The sub-channels have a lateral dimension (i.e., width or diameter) less than a lateral dimension of the honeycomb channels.

[0040] In a composite honeycomb, long axial channels are maintained to enable fast diffusion paths and access to the micropores of at least the second material. These long, optionally isolated channels also provider high permeability and/or low tortuosity.

[0041] In contrast to conventional adsorption media, the composite honeycomb exhibits both a high volume filling fraction of microporous material for maximum gas storage capacity and fast gas adsorption/desorption.

[0042] In various embodiments, highly microporous carbon honeycomb structures are formed from carbonaceous materials using co-extrusion and in-situ chemical activation. A carbon precursor material, chemical activating agent and binder are mixed together with a liquid carrier into a batch formulation that is extruded to provide the honeycomb form factor, which undergoes thermal processing to simultaneously carbonize the precursor and activate the carbon. A second material can be incorporated into the channels of the honeycomb via dip-coating or slurry impregnation. The second material may partially or completely fill a honeycomb channel. As disclosed in commonly-owned U.S. Patent No. 8,293,010, the entire contents of which being incorporated herein by reference, the second material can be formed within the channels of the honeycomb using a directional solidification (i.e., freeze casting) method.

[0043] A method of forming a adsorbent structure comprises providing an extrudable batch formulation, shaping the batch formulation to provide a honeycomb green body having a plurality of parallel channels bounded by channel walls traversing the body from an upstream inlet end to a downstream outlet end, incorporating a liquid feedstock into the honeycomb channels to form a feedstock-laden honeycomb, directionally solidifying a liquid within the channels to form a secondary array of sub-channels that are smaller than the honeycomb channels; and drying and/or heat treating the adsorbent structure such that the array of subchannels includes a microporous material having a specific surface area that is greater than the honeycomb channel walls, and the microporous material has a specific surface area that is greater than 400 m²/gram.

[0044] In example embodiments, the batch formulation includes i) an organic filler, ii) a chemical activating agent, iii) a cellulosic binder, and iv) a resinous binder. The activated carbon honeycomb may be prepared in a two-stage process that involves pyrolyzing the extruded body to carbonize and activate the carbon precursor content followed by acid washing and drying.

[0045] Example organic fillers include powder materials such as coal-based materials, coconut shells, pecan flour, cherry pit flour, rice hulls, and sawdust.

[0046] Example chemical activating agents include alkali or transition metal compounds such as potassium hydroxide, sodium hydroxide, potassium carbonate and zinc chloride.

[0047] Cellulosic binders, including cellulose ether-based binders, include methylcellulose, hydroxybutylcellulose, ethylcellulose, hydroxybutylmethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, hydro xypropylmethylcellulose, hydroxyethylmethylcellulose, and sodium carboxylmethylcellulose. The cellulose binder acts as a plasticizer and provides wet strength to maintain the structural integrity of the extruded green (un-fired) shape.

[0048] A soluble or dispersible resinous binder may be used as a secondary source of carbon and as a permanent binder. In contrast to the cellulose binder, which provides mechanical strength to the as-extruded green body and which is substantially removed as a result of the heat treatment, the resinous binder may be retained in the final honeycomb.

[0049] The resinous binder may include thermosetting resins and thermoplastic resins (e.g., polyvinylidene chloride, polyvinyl chloride, polyvinyl alcohol, and the like). In particular, phenolic resins, such as resole or novolac resins are readily available at relatively low cost, have low viscosity, high carbon yield, and a high degree of cross-linking upon curing relative to other precursors. [0050] The liquid carrier for the batch formulation may include water, phenolic resins, sugar syrups (e.g., corn syrup) and combinations thereof.

[0051] Example batch formulations that have a resinous liquid carrier in lieu of water may include 20-60 wt.% organic filler, 10-30 wt.% chemical activating agent, 4-10 wt.% cellulosic binder, and up to 40 wt.% of one or more of an extrusion aid and resinous binder.

[0052] Forming aids, e.g., extrusion aids, can also be included in the batch formulation Example forming aids include soaps, polyoxyethylene stearate, sodium stearate, and fatty acids such as oleic acid, linoleic acid, etc. Other additives that are useful for improving the extrusion and curing characteristics are phosphoric acid and oils. Phosphoric acid may improve the cure rate and increase adsorption capacity. If used, phosphoric acid may comprise 0.1% to 5 wt. % of the mixture.

[0053] The extruded body may be dried, cured, and then carbonized by heating. Curing is generally performed in air at atmospheric pressures and typically by heating the green body at a temperature of 100°C to 200°C for 0.5 to 5.0 hours.

[0054] Carbonization is the thermal decomposition of the carbonaceous material, thereby eliminating low molecular weight species (e.g., carbon dioxide, water, gaseous hydrocarbons, etc.) and producing a fixed carbon mass and a rudimentary pore structure in the carbon. Such conversion or carbonization of the cured carbon precursor is accomplished typically by heating to a temperature in the range of 600°C to 1000°C for 1 to 10 hours in a reducing or inert atmosphere (e.g., nitrogen, argon, helium, etc.).

[0055] After carbonization, the monolithic honeycomb is washed to remove the unreacted chemical activating agent. Washing may comprise initially rinsing the activated carbon with de-ionized water, then rinsing with an acid solution, and finally rinsing again with de-ionized water. Such a washing process can reduce residual alkali content in the carbon to less than about 200 ppm (0.02 wt.%), compared with values greater than about 3 wt. % obtained with conventional extraction processes.

[0056] Following the in situ carbonization/activation and washing of the resultant honeycomb, an optional post-carbonization activation step may be used. Post-carbonization activation can further activate the already activated carbon. In an example method, the activated carbon honeycomb is impregnated with a chemical activating agent, heated, for example at a temperature of 650°C to 750°C and then washed. [0057] The geometry of the honeycomb is not particularly limited, but is envisioned as a space-filling skeleton that can be formed by extrusion into various honeycomb geometries. For applications where a high adsorption volume is desired, such as gas storage or gas capture, the filling fraction of microporous material is preferably high, and the filling fraction of void space or non-porous material is low. High gas permeability is not a strict requirement for some applications, meaning the gas channels can be relatively small. In gas storage embodiments, the volume filling fraction of microporous material in the structure can be greater than 50%, 70% or 90%, which can exceed the comparable filling volume that can be achieved with powder beds or randomly-packed pellets.

[0058] Thus, the volume filling fraction of void space can be less than 50%, 30% or 10%. For some gas storage applications, the honeycomb structure is a thick-walled honeycomb. In some embodiments, the internal walls of the honeycomb may have an average thickness that is greater than or equal to the diameter of the neighboring channels. In some cases the honeycomb walls may have an average thickness that is at least twice the diameter of the honeycomb channels.

[0059] As an alternative to activated carbon, the walls of the honeycomb may be formed using a metal or a ceramic material. Example metals include aluminum and copper. Example ceramic materials include alumina, mullite, cordierite, silica, titania, aluminum titanate, silicon carbide, and silicon nitride. In other cases the honeycomb walls can be formed from a metal-ceramic composite, a metal-carbon composite, a ceramic-carbon composite, a carbon-polymer composite, or a metal-polymer composite.

[0060] In embodiments, the honeycomb may be formed from an extruded metal-organic framework material (or an extruded activated carbon material) having relatively thick walls and relatively small channels.

[0061] The honeycomb wall material may have a thermal conductivity that is greater than 0.1 W/mK. For example, in some embodiments, the honeycomb wall material comprises a thermal conductivity that is greater than 0.15 W/mK, greater than 0.2 W/mK, greater than 0.3 W/mK, greater than 0.4 W/mK, greater than 0.5 W/mK, greater than 1 W/mK, greater than 5 W/mK, greater than 10 W/mK, greater than 20 W/mK, greater than 50 W/mK or greater than 100 W/mK. [0062] The composition and geometry of the honeycomb, e.g., the honeycomb walls can be tailored to provide an appropriate balance between microporosity (for gas adsorption) and density (for higher thermal conductivity or higher mechanical durability).

[0063] As an alternative, a supporting structure for the microporous (second) material may have a form factor other than that of a honeycomb. Example porous structures include both regular and irregular geometries and may be formed from polymeric, ceramic, cellulosic, glassy, metallic or carbonaceous material. Suitable supporting structures include 2- dimensional and 3 -dimensional form factors, including porous membranes, porous wools (e.g., steel wool) and lattice structures.

[0064] An adsorbent structure in various embodiments, comprises a porous substrate having a specific surface area of 100 to 2000 m²/g, and a microporous filler dispersed within the porous substrate, wherein the microporous filler specific surface area is from 400 to 15000 m²/g, and the specific surface area of the microporous filler is greater than the specific surface area of the powder component.

[0065] Summarized in Table 1 are textural properties of activated carbon formed by in-situ activated (simultaneous carbonization and activation) using potassium hydroxide.

[0066] Table 1. Textural properties of activated carbon

[0067] A composite honeycomb is formed by incorporating a second porous material into the channels of the honeycomb. The second material in various embodiments is a microporous material. As used herein, "micropores" have an average pore size of less than 2 nm. A microporous material includes at least 50% (e.g., at least 50, 60, 70, 80, 90, 95, 98, 99 or 100%) of its pore volume as micropores.

[0068] The second porous filler may comprise activated carbon, an aerogel, a sol-gel, a metal-organic framework, a porous silicate, a zeolite, a hydrophobic porous siloxane or silsesquioxane, or other highly porous materials. Metal-organic-framework materials are also known as coordination polymers, and typically comprise a crystalline inorganic-organic hybrid structure that includes metal ions or clusters (for example, comprising metals such as Zn, Cu, etc.) assembled with organic ligands (such as carboxylates, sulfonates, benzoates, tetrazolates, etc.)

[0069] Methods of incorporating a second material into the channels of a honeycomb substrate to form a composite honeycomb are disclosed in conjunction with the following discussion of Figs. 2-6.

[0070] Cross-sectional schematic diagrams of composite honeycombs according to various embodiments are shown in Figs. 2-6. The composite honeycomb of Fig. 2, also referred to as "macro-honeycomb HI" includes a first material 100 defining porous walls of the honeycomb and a second material 200 formed within channels defined by the walls. Subchannels 300 can be formed within the second material in some or all of the channels. In the Fig. 2 example, the second material 200 coats the walls of the channels.

[0071] The second material coating can be fabricated using a variety of techniques, such as dip coating, wash coating, spin casting, or impregnation of the extruded honeycomb with a particulate slurry or sol-gel mixture. A coating of the second material can also be formed by vapor deposition techniques, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). Typically, one sub-channel 300 per honeycomb channel is formed using these methods.

[0072] According to a further embodiment, the composite honeycomb of Fig. 3, also referred to as "micro-honeycomb H2" includes a first material 100 defining porous walls of the honeycomb and a directionally-solidified second material 200 formed within channels created by the porous walls. The second material 200 includes a plurality of striated subchannels 310. The resulting structure is illustrated also in Fig. 7. As an alternative to slit- shaped pores, in a non-illustrated embodiment the second material 200 may include a plurality of rounded, capillary pores.

[0073] In the Fig. 3 embodiment, multiple relatively large (compared to the micropore size) gas flow channels are formed within each honeycomb. This allows fast gas diffusion access to the majority of the micropores in the second material (and potentially also the micropores of the first material if the first material is microporous). Maximum gas adsorption capacity can be reached more quickly with such a structure, even if macroscopic gas flow through the honeycomb structure is impeded. The minimum dimension of the gas flow channels may be 0.1 microns, but may be as large as about 1000 microns.

[0074] The composite honeycomb structure of Fig. 3 may be formed using a directional solidification (freeze casting) method. In this method, a particulate slurry, gel or other solution or suspension is gradually frozen from one end of the honeycomb to the other using a controlled temperature gradient. The confined ice crystals grow in continuous or semi- continuous dendrites, pushing the solid or gel material aside as they progress. The ice crystals can then be removed through sublimation (via freeze-drying), leaving behind continuous or semi-continuous gas channels through the porous structure. The gas channels can comprise a two-dimensional array of linear pores, for example micro-lamellae having an inter-lamellae spacing of 1 to 50 microns.

[0075] A batch composition used to form a porous second material via directional solidification is summarized in Table 2.

[0076] Table 2. Batch composition for directionally-solidified porous filler

[0077] Composite honeycombs having still different cross-sectional geometries are illustrated in Figs. 4-6. In the Fig. 4 example, the composite honeycomb includes square channels while the Fig. 5 composite honeycomb includes hexagonal channels. The Fig. 6 composite honeycomb includes a complex cross-sectional geometry made up of square and hexagonal channels. In each of Figs. 4-6, some of the channels are completely filled with a second material 200 while some of the channels are un- filled. Each individual channel may be completely-filled, partially- filled or un-filled by a second material.

[0078] The filling of select channels with the second material can be accomplished, for example, by plugging the ends of the channels with a dissolvable, pyrolizable, or mechanically removable material, immersing or otherwise impregnating the entire honeycomb structure with a slurry or solution containing the second material or a precursor to the second material, drying or otherwise depositing the second material within the channels, and then removing the end-plugs, for example using dissolution, pyrolysis, or mechanical removal.

[0079] The filling fraction and filling pattern of the second material in the honeycomb channels can be designed to have an optimal compromise between total adsorbed gas capacity and gas diffusion speed into and out of the composite honeycomb structure. In applications where slower adsorption or desorption speeds are acceptable (for example, in vehicles that can be refueled slowly overnight), a higher volume filling fraction of microporous material will give the maximum storage capacity. For some applications, it might be desirable to fill all of the channels of the honeycomb with the second material, such as where the composite honeycomb is used primarily for its mechanical durability and/or thermal conductivity.

[0080] In other applications where rapid adsorption and desorption (e.g., refueling) are desired, composite honeycombs having a higher volume fraction or total number of gas channels can be provided. Contemplated structures can be refilled quickly to a lower capacity, or refilled more slowly to a maximum capacity.

[0081] A modeling comparison was made of four gas adsorbent geometries, including conventional pellet and monolith geometries, and the macro- and micro-composite honeycombs discussed above. The results are summarized in Table 3. For the purposes of these calculations and ease of comparison, only the second material of the composite honeycomb is considered as active for gas adsorption, though as mentioned elsewhere, the composite honeycomb performance can be further enhanced by creating microporosity in the honeycomb walls of the first material, which can be available for further gas adsorption. The following additional assumptions were used in the calculations: (1) the density of the active adsorbent phase, p, is the same for each geometry; (2) the specific active surface area for adsorption, S, is the same for each geometry; and (3) the saturation adsorption capacity, λ, is the same for each geometry. [0082] Table 3. Adsorption characteristics for different geometries.

[0083] Important metrics for comparison of the various adsorbent geometries are total adsorbed gas capacity per unit container volume and the speed of adsorption/desorption. These metrics directly relate to the total storage capacity of a fuel tank of a given size, as well as the potential refueling time needed to completely refill an adsorbent storage tank. In addition, the speed of desorption relates to the instantaneous fuel draw that is possible from a tank of a given size that relies on adsorbents. High instantaneous fuel draw may be needed, for example, when a vehicle is accelerating or climbing hills.

[0084] Table 3 summarizes the geometries analyzed, and gives the calculated values of relative total storage capacity and relative adsorption/desorption rate (both normalized to 100 for the micro-honeycomb, H2 geometry). A plot of relative gas storage capacity at saturation versus adsorption/desorption rate is shown in Fig. 8.

[0085] As can be seen with reference to Table 3 and Fig. 8, the micro-honeycomb geometry H2 has the greatest adsorption/desorption rate, exceeding that of the other geometries by ~4-7 orders of magnitude. This means that the micro-honeycomb is the most favorable geometry for applications requiring, for example, fast re-fueling or fast fuel release. At the same time, the micro-honeycomb H2 has a lower total storage capacity than the other geometries by a factor of about 1.5 to 2. In applications where desorption rate is less important, and total storage capacity is more important, the most favorable geometry is likely to be macro-honeycomb HI , which has total storage capacity approaching that of the monolith (stacked disks) Ml, but an adsorption/desorption rate that is ~3 orders of magnitude faster than monolith Ml .

[0086] In some applications, it may be desirable to create a system-level combination of the fast-desorbing micro-honeycomb H2 with a higher-capacity storage medium such as macro-honeycomb HI or monolith Ml . This may be desired in situations where a fast- desorber is needed for "peak load" scenarios, such as vehicle acceleration, but where this is only needed for short periods of time, so the higher-storage medium is used to maximize capacity. This is somewhat analogous to the combined usage of capacitors (for fast discharge) with batteries (for high storage capacity) in electrical systems.

[0087] Without wishing to be bound by theory, we believe that the total adsorbed gas storage of the honeycomb geometries HI and H2 can be increased even further by several means not included in the above calculated results. These include (1) incorporating some amount of micro-porosity into the honeycomb walls, as in the case of using an activated carbon honeycomb scaffold, (2) creating thicker lamellae within the micro-honeycomb H2 structure, relative to the intra-lamellar gap spacing, and (3) using higher-surface area adsorbents within the honeycomb.

[0088] Expanding on point (3), we believe that one of the advantages of the honeycomb support scaffold is that it offers a mechanical support structure that enables higher-surface- area adsorbents to be used than could actually be used in either pellet P I or monolith Ml geometries. This is because the extremely high-surface-area adsorbents that are desirable for maximizing gas storage capacity will, because of their high volume fraction of porosity, tend to have very low mechanical robustness. This means that pellet or monolith geometries are likely to be unstable when used in a moving vehicle, as the pellets or monoliths are likely to become damaged, crushed, or partly converted into powders. These powders will then be likely to block the pathways for gas diffusion and further degrade the adsorption/desorption performance of the pellet or powder geometries. Thus, an advantage of the using the composite honeycomb framework is the mechanical support provided by the first material that enables the usage of the highest-surface-area (second material) adsorbent materials. [0089] Disclosed are methods for forming mechanically robust activated carbon-based honeycombs and the resulting structures. The composite honeycombs are highly microporous and have a high surface area for adsorption. The chemical activation approach, which involves carbonization and activation in a single step, leads to minimal weight loss during the activation process and results in the production of carbon-based honeycombs that are uniformly activated along and across the honeycomb channels.

Examples

[0090] Batch formulations containing different amounts of carbon precursor, chemical activating agent and binder were formulated and evaluated. In various tests, 20 g plasticized formulations were prepared and rheological indicators that can accurately predict the extrudability of the batch were observed over a 24 hour period. The compositions that passed the test were pressed into thin discs, dried and pyrolyzed. The pyrolyzed samples were then acid-washed and dried. Textural properties (e.g., surface area, pore volume and pore size) were obtained from the activated carbon discs.

[0091] Example 1 - extrudable batch containing chemical activating agent

[0092] A 20 g extrudable batch having the composition summarized in Table 4 was prepared by mixing and kneading the ingredients in a crucible. After kneading, the product was pressed into a thin disc, which was dried and cured at 140°C for 2 hours in an air-vented oven. The cured material was heated to 750°C in a nitrogen environment at 5°C/min and held at 750°C for 2 h. After cooling to 25 °C, the activated carbon disc was washed to remove excess potassium. The activated carbon was first washed with water and then acid- washed in 0.5M HC1. Finally, a neutral water wash was used to rinse the carbon until the effluent was pH neutral. The washed disc was dried at 120°C in an air-vented oven.

[0093] The highly-microporous activated carbon was characterized by 2

adsorption/desorption analysis at-196°C using an adsorption analyzer. The activated carbon was initially degassed for 12 hours at 300°C prior to the adsorption analysis. The surface area, total pore volume and average pore size were obtained from the adsorption isotherms. The data are shown in Table 5.

[0094] Example 2 - extrudable batch post-treated with chemical activating agent

[0095] A small (3.2 g, 1 in diameter x 1 inch long) extruded and carbonized (un-activated) honeycomb sample derived from the composition summarized in Table 4 was soaked in KOH solution (45 wt.%) for 24 hours. After clearing the channels to remove the excess solution, the sample was initially dried at 120°C for 1 hour in an air- vented oven and then heated to 650°C at 5°C/min under nitrogen for 2 hours.

[0096] The sample was cooled, washed and analyzed as in Example 1. The textural data are presented in Table 5. The result shows that post-carbonization chemical activation can be used to form a porous honeycomb.

[0097] Table 4. Extrusion Batch Formulations - Examples 1 and 2

[0098] Table 5. Textural Data for Examples 1 and 2

[0099] Example 3 - Activated carbon plus SiC composite batch material

[00100] Activated carbon and SiC were combined to form composite materials with varying SiC content (from 0 to 70 wt%). 0.2 g of the composite material powder was blended with 4 drops of egg white and uniaxially pressed at 3 1 MP A, followed by cold isostatic pressing under 124 MPA into discs of 25 mm diameter and 0.125 mm thickness. The thermal conductivity and surface area of the discs were measured at 27 °C, and the data are presented in Table 6.

[00101] Table 6. Thermal Conductivity and surface area of Activated Carbon-SiC Samples

[00102] Example 4 - Activated Carbon plus Graphite composite batch material

[00103] Activated carbon and graphite were combined to form composite materials with varying graphite contents (from 0 to 60 wt%). Disks were prepared using the method described in Example 3. The thermal conductivity and surface area of the discs were measured at 27 °C, and the data are presented in Table 7.

[00104] Table 7. Thermal Conductivity of Activated Carbon-Graphite

[00105] Example 5 - Extruded activated carbon honeycomb

[00106] Extruded activated carbon honeycombs were fabricated and tested for BET surface area as well as methane adsorption capacity. The honeycomb structures were fabricated using the method described in Example 2. The honeycomb structures had square cells with about 0.5 mm wall thickness and about 2.2 mm unit cell spacing. The BET surface area of the carbon honeycomb structures was measured at 850 m²/g.

[00107] A methane adsorption/desorption was carried out at room temperature at the following pressure steps for both adsorption and desorption: 1 , 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0. At least one minute was allowed at each pressure step for equilibration. The results of the methane adsorption/desorption are shown in Fig. 9.

[00108] Example 6 - Extruded activated carbon honeycomb wash coated with metal- organic framework material.

[00109] Activated carbon extruded honeycombs were fabricated and coated or partially filled with a metal-organic-framework (MOF) material. A coating solution was formulated by mixing MOF powder and liquid carboxymethyl cellulose (CMC) in deionized water. After coating the honeycombs with the coating solution, the honecombs were dried at 140°C for 1 hour and then heated to and held at 200°C for 2 hours. The coated or partially filled honeycombs were tested for BET surface area as well as methane adsorption capacity. The BET surface area of the activated carbon-MOF material was measured at 1100 m²/g.

[00110] A methane adsorption/desorption was carried out at room temperature at the following pressure steps for both adsorption and desorption: 1 , 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0. At least one minute was allowed at each pressure step for equilibration. The results of the methane adsorption/desorption are shown in Fig. 9. [00111] Comparative Example 1- CuMOF plus Activated Carbon Composite (CuMOF-AC) Pellets

[00112] CuBTC-AC composite materials were prepared by adding an appropriate amount of BL® activated carbon, commercially available from Calgon Carbon (Pittsburgh, Pennsylvania, USA), during the synthesis of CuBTC using copper (II) nitrate trihydrate and benzene tricarboxylic acid (BTC). CuMOF-AC pellets were fabricated by extruding the CuBTC-AC composite materials. The extrudate was prepared by mixing 20 g CuMOF-AC composite material with 2 g carboxymethylcelllulose sodium salt (CMC) and a sufficient amount of deionized water to achieve a dough-like extrudable mass. The extrudate was kneaded properly to form uniform dough-like mass. The mass was then extruded using a kitchen machine. After extruding, the green body was dried at 140°C and further heat- treated at 200°C for 2 hours. The BET surface area of the pellets was measured at 1200 m²/g.

[00113] A methane adsorption/desorption was carried out at room temperature at the following pressure steps for both adsorption and desorption: 1 , 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0. At least one minute was allowed at each pressure step for equilibration. The results of the methane adsorption/desorption are shown in Fig. 9.

[00114] Fig. 9 shows the results of the methane adsorption/desorption tests of Example 5, Example 6, and Comparative Example 1. Curves 401 and 402 represent the adsorption and desorption curves, respectively, of Example 5. Curves 403 and 404 represent the adsorption and desorption curves, respectively, of Example 6. Curves 405 and 406 represent the adsorption and desorption curves, respectively, of Comparative Example 1. The honeycomb samples of Examples 5 and 6 exhibit higher total adsorption capacity than the MOF pellet samples of Comparative Example 1. Although some of the higher total adsorption may be attributable to the higher total weight of the honeycomb samples, even when taking the weight differences into account, it is apparent that the honeycomb samples exhibit a faster adsorption and desorption rate in this test (e.g., more gas adsorbed at lower pressure and/or time), as compared to the MOF pellet samples. The honeycomb samples also exhibit closer correspondence between adsorption and desorption curves, indicating less gas is trapped in the adsorbent during desorption. This may be beneficial in that trapped gas is not useful to the system. [00115] The disclosed composite honeycombs beneficially have uniformly high activity (i.e., high surface area) in a given volume of the composite. The composite honeycombs can be used for adsorptive natural gas storage such as in vehicular fuel applications. Additionally, the adsorption properties of the composite honeycombs permit their use in as fractionation of hydrocarbons, purification of industrial gases, anti-pollution devices, liquid- phase purification processes in food and chemical industries, water treatment, and liquid- phase recovery and separation.

[00116] The disclosed batch formulations can be used to form a single-component honeycomb, such as where the chemically-activated extrudable carbon material is the primary adsorbent material, or in a composite honeycomb structure, where the chemically-activated extrudable carbon honeycomb material forms a mechanically robust support for a microporous filler (having a second surface area or microporosity level which may be higher than that of the chemically activated carbon). Such microporous filler may partly or completely fill one or more channels of the honeycomb.

[00117] Gas adsorption applications for the disclosed composite honeycombs, including natural gas storage applications, may be 'pressure swing' applications where the adsorption/desorption cycle is governed primarily by pressure changes in a storage vessel, or 'temperature swing' applications where external heating or cooling is applied to aid the adsorption/desorption cycle. Both 'pressure-swing' and 'temperature swing' types of applications, as well as combinations of the two, may benefit from the composite honeycomb structures of the disclosure. For instance, composite honeycombs that exhibit a relatively high thermal conductivity in the honeycomb wall materials are useful in maximizing the adsorption/desorption yield.

[00118] In embodiments, a gas can be adsorbed and desorbed by a composite honeycomb that is disposed within a sealed pressure vessel. The gas can be introduced into the vessel at an elevated pressure and adsorbed by the composite honeycomb. For example, a gas such as methane or hydrogen can be pumped into the vessel at a pressure greater than 1 atm (e.g., 2, 4, 10, 20, 35, 50, 100 or 200 atm). In addition to or in lieu of providing the gas at an elevated pressure, the composite honeycomb can be cooled to promote gas adsorption into the composite honeycomb. To affect adsorption (storage), a gas can be pumped into the vessel while the composite honeycomb is maintained at a temperature less than 30°C (e.g., 25, 20, 15 or 10°C). Gas can be removed from the tank by reversing the adsorption process, i.e., by reducing the pressure (to less than 1 atm) and/or increasing the temperature (to greater than 30°C, e.g., up to 200°C).

[00119] In embodiments, a method for using the adsorbent structure comprises providing the adsorbent structure in a sealed vessel, and storing gas within the vessel by introducing the gas into the vessel and adsorbing the gas into the adsorbent structure. During the adsorbing the vessel pressure can be greater than 1 atmosphere and/or the adsorbent structure temperature can be less than 30°C. Removal of the gas from the vessel can be affected by desorbing the gas from the adsorbent structure. During the desorbing the vessel pressure can be less than 1 atmosphere and/or the adsorbent structure temperature can be at least 30°C.

[00120] In embodiments, a method for using the adsorbent material comprises removing impurities from an adsorbing gas. For example, contaminants in natural gas such as non-methane higher hydrocarbons (e.g., ethane, propane, butane, etc.) can contaminate adsorbents over time. Moreover, such contaminants can be difficult to desorb, which results in reduction of the total adsorption capacity of the adsorbent over time. In some

embodiments, the method comprises selectively removing one or more contaminants from a gas stream. For example, a secondary adsorption chamber can be used to selectively remove contaminants from a natural gas stream while allowing the majority of the methane to pass through to the primary adsorption or storage tank. The adsorbent material in the secondary adsorption chamber can be replaced periodically or reformed (e.g., using heat or vacuum) to refresh the adsorption capacity used to remove the contaminants. In some embodiments, the secondary adsorption chamber comprises a single-material honeycomb or multi-material honeycomb structure. Additionally, or alternatively, the secondary adsorption chamber comprises activated carbon and/or metal-organic-framework materials.

[00121] As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "carbon precursor" includes examples having two or more such "carbon precursors" unless the context clearly indicates otherwise.

[00122] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, examples include from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[00123] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.

[00124] It is also noted that recitations herein refer to a component being "configured" or "adapted to" function in a particular way. In this respect, such a component is "configured" or "adapted to" embody a particular property, or function in a particular manner, where such recitations are structural recitations as opposed to recitations of intended use. More specifically, the references herein to the manner in which a component is "configured" or "adapted to" denotes an existing physical condition of the component and, as such, is to be taken as a definite recitation of the structural characteristics of the component.

[00125] While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase "comprising," it is to be understood that alternative embodiments, including those that may be described using the transitional phrases

"consisting" or "consisting essentially of," are implied. Thus, for example, implied alternative embodiments to a composite honeycomb that comprises activated carbon and porous filler include embodiments where a composite honeycomb consists of activated carbon and porous filler and embodiments where a composite honeycomb consists essentially of activated carbon and porous filler.

[00126] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

We claim:

1. An adsorbent structure comprising:

a honeycomb substrate having a plurality of partition walls extending in an axial direction from an inlet end to an outlet end forming a plurality of flow channels, the honeycomb substrate comprising a powder component and a binder; and

a microporous filler dispersed within at least some of the flow channels;

wherein the partition walls have at least one of (a) a specific surface area from 100 to 2000 m²/g or (b) a thermal conductivity of at least 0.1 W/mK, the microporous filler specific surface area is from 400 to 15000 m²/g, and the specific surface area of the microporous filler is greater than the specific surface area of the partition walls.

2. The adsorbent structure according to claim 1 , wherein the powder component comprises activated carbon.

3. The adsorbent structure according to claim 1 or claim 2, wherein the microporous filler comprises a metal-organic framework material.

4. The adsorbent structure according to claim 1 or claim 2, wherein the microporous filler comprises a material selected from the group consisting of an aerogel, a sol-gel, a silicate, a siloxane, a silsesquioxane, and combinations thereof.

5. The adsorbent structure according to any of the preceding claims, wherein the microporous filler is a layer coating the partition walls.

6. The adsorbent structure according to claim 5, wherein the layer thickness is less than 50% of the flow channel width.

7. The adsorbent structure according to any of the preceding claims, wherein the microporous filler is a directionally-solidified cast structure.

8. The adsorbent structure according to claim 7, wherein the cast structure comprises a two- dimensional array of linear pores.

9. The adsorbent structure according to claim 7, wherein the cast structure comprises micro- lamellae having an inter-lamellae spacing of 1 to 50 microns.

10. The adsorbent structure according to any of the preceding claims, wherein the powder component comprises a thermal conductivity of at least 0.1 W/mK.

1 1. A method of forming a composite honeycomb, comprising:

providing a batch formulation comprising a carbon precursor and an activating agent;

shaping the batch formulation to provide a honeycomb green body having a plurality of parallel channels bounded by channel walls traversing the body from an upstream inlet end to a downstream outlet end;

heat treating the honeycomb green body to carbonize and simultaneously activate the carbon precursor; and

optionally incorporating a microporous material into a plurality of the channels.

12. The method according to claim 1 1, further comprising incorporating a microporous material into a plurality of the channels.

13. The method according to claim 1 1 or claim 12, wherein the carbon precursor is selected from the group consisting of a coal-based material, coconut shells, pecan flour, cherry pit flour, rice hulls, sawdust, and combinations thereof.

14. The method according to any of claims 1 1 to 13, wherein the activating agent is selected from the group consisting of potassium hydroxide, sodium hydroxide, potassium carbonate, zinc chloride, and combinations thereof.

15. The method according to any of claims 1 1 to 14, wherein the batch formulation further comprises at least one of an acid, an oil, and an extrusion aid selected from the group consisting of soap, polyoxyethylene stearate, sodium stearate, oleic acid, linoleic acid, and combinations thereof.

16. The method according to any of claims 1 1 to 15, wherein the microporous material has a specific surface area of at least 400 m²/g, and the microporous material has a greater specific surface area than the honeycomb channel walls.

17. The method according to any of claims 1 1 to 16, wherein the incorporating comprises: incorporating a liquid feedstock into the honeycomb channels to form a feedstock- laden honeycomb; and

directionally-solidifying a liquid within the channels to form an array of sub-channels that are smaller than the honeycomb channels.

18. An adsorbent structure comprising:

a porous substrate comprising a specific surface area of 100 to 2000 m²/g; and a microporous filler dispersed within the porous substrate and comprising a specific surface area of 400 to 15000 m²/g;

wherein the specific surface area of the microporous filler is greater than the specific surface area of the powder component.

19. A method for using the adsorbent structure according to claim 1, comprising:

providing the adsorbent structure in a sealed vessel; and

storing gas within the vessel by introducing the gas into the vessel and adsorbing the gas into the adsorbent structure, wherein during the adsorbing at least one of:

the vessel pressure is greater than 1 atm, or

the adsorbent structure temperature is less than 30°C.

20. The method according to claim 19, further comprising removing the gas from the vessel by desorbing the gas from the adsorbent structure, wherein during the desorbing at least one of:

the vessel pressure is less than 1 atm, or

the adsorbent structure temperature is at least 30°C.

21. An adsorbent structure comprising:

a honeycomb substrate having a plurality of partition walls extending in an axial direction from an inlet end to an outlet end forming a plurality of flow channels,

wherein the partition walls have both of (a) a specific surface area of at least 400 m²/g and (b) a thermal conductivity of at least 0.2 W/mK.