Lightweight Substrate with a Glass Bubble Skeleton Having Mixed Porosity for Carbon Capture and Fabrication Method

Abstract

The porous structure includes a plurality of glass bubbles sintered together such that adjacent glass bubbles are physically directly bonded to each other. The glass bubbles have surfaces that define voids throughout the porous structure. The voids include closed voids that are not open to the surface of the porous structure. At least 50% of the glass bubbles are closed glass bubbles, and each closed glass bubble defines a cavity sealed therein. The porous structure has a closed porosity of at least 10% and an open porosity of at least 40%. The closed porosity includes the sealed cavities and the closed voids. A method for fabricating the porous structure includes the step of heating the glass bubbles. Substantially all of the glass bubbles are closed glass bubbles prior to heating. At least 50% of the glass bubbles remain closed after heating such that the sintered closed glass bubbles form the porous structure.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority under 35 U.S.C. § 119 to Chinese Patent Application No. 202210837104.2, filed on July 15, 2022, the content of which is hereby incorporated by reference in its entirety. Technical Field The present disclosure relates to a porous inorganic structure, and more particularly to a porous structure having a high proportion of fused closed glass bubbles that define an inorganic framework with a mixed porosity.

Background Art

[0002] The production of composite materials using micro glass bubbles (which may also be referred to as "hollow" and / or "glass", and may be used interchangeably with any of "spheres", "microspheres", "beads" or "balloons", and are also referred to as "cenospheres", etc.) is known. Such glass bubbles are commercially available, for example, from Dennert Poraver GmbH, 3M, Zhongke Yali Technology, Ltd, Fibre Glast Developments Corp., Potters Industries LLC, etc. The glass bubbles can be incorporated into composite materials for buoyant load - bearing structures, such as supports for surfboards or marine drilling equipment. The glass bubbles can also be incorporated into concrete. In these and other typical uses, the glass bubbles are included as fillers for cost reduction and / or for adjusting the mass or density of the resulting composite structure. The amount of glass bubbles in the composite structure can be limited to ensure mechanical integrity.

[0003] The area where benefits can be obtained from the use of glass bubbles is a substrate or structure for the capture of a target gas, such as carbon dioxide (CO2). CO2 has been gradually increasing in the atmosphere since the Industrial Revolution due to fossil fuel combustion technologies such as coal-fired power plants and gasoline / diesel-based automobiles. In response to concerns about global warming associated with increasing CO2 levels, the international community has agreed to reduce CO2 emissions and / or capture CO2 in order to achieve net-zero CO2 emissions in the future. One solution is to capture CO2 directly from the air using solid sorbents (known as direct air capture or DAC), or to capture CO2 from high-concentration sources such as power plant flue gases (also known as point source capture). Ceramic honeycomb structures are considered an important potential carrier for solid sorbents for CO2 capture. However, any potential implementation of a CO2 capture device or system needs to consider important factors such as performance and economics.

[0004] Some existing ceramic honeycomb structures that can be useful for CO2 capture applications capture particulate matter and / or SO2 and NO from diesel and gasoline engine exhaust gases x and are ceramic honeycomb structures integrated into engine aftertreatment systems to decompose them. Such ceramic honeycomb structures have several advantages, including lower pressure drop, lower energy consumption over their lifetime on the other hand, the ability to be regenerated, long life, less solid waste, and lower ownership costs over their life cycle. The honeycomb structures used in such engine aftertreatment systems are typically ceramic-based (e.g., cordierite, aluminum titanate (AT), silicon carbide (SiC), etc.) and are configured to withstand high temperatures (e.g., 800 °C or higher) and high thermal shock. However, such temperature-related properties are not necessary for CO2 capture from ambient air or combustion exhaust gases. Further, CO2 is typically desorbed from the solid adsorbent after capture using methods such as temperature swing adsorption (TSA), which is often used in low CO2 concentration applications such as DAC. The thermal energy input for desorption is one of the largest costs in the operation of such TSA-based capture systems. Thus, lightweight and low density are important attributes of the carrier structure implemented for CO2 capture. As a result, it is advantageous to develop low-cost porous structures having these and other attributes that enable scaling up of the CO2 capture system. SUMMARY OF THE INVENTION

[0005] A first aspect of the present disclosure is a porous structure including a plurality of glass bubbles, wherein the glass bubbles are sintered together such that adjacent glass bubbles are physically directly bonded to each other, the glass bubbles have a surface defining a gap throughout the porous structure, the gap includes a closed gap that is not open to the surface of the porous structure, at least 50% of the glass bubbles are closed glass bubbles, each closed glass bubble defines a cavity sealed therein, the porous structure has a closed porosity of at least 10% in terms of volume, the closed porosity includes the sealed cavities and the closed gaps, and the porous structure has an open porosity of at least 40% in terms of volume. A second aspect of the present disclosure includes the porous structure according to the first aspect, which substantially comprises glass in terms of mass. A third aspect of the present disclosure includes the porous structure according to the first or second aspect, which comprises at least 90% glass in terms of mass. A fourth aspect of the present disclosure includes the porous structure according to any one of the first to third aspects, which comprises at least 85% amorphous phase glass in terms of mass.

[0006] A fifth aspect of the present disclosure includes the porous structure according to any one of the first to third aspects, which comprises approximately 100% amorphous phase glass in terms of mass. The sixth aspect of the present disclosure includes a porous structure according to any one of the first to fifth aspects, in which about 65% to about 100% of the glass bubbles are closed. The seventh aspect of the present disclosure includes a porous structure according to any one of the first to fifth aspects, in which about 75% to about 100% of the glass bubbles are closed. The eighth aspect of the present disclosure includes a porous structure according to any one of the first to fifth aspects, in which about 85% to about 100% of the glass bubbles are closed. The ninth aspect of the present disclosure includes a porous structure according to any one of the first to fifth aspects, in which about 90% to about 100% of the glass bubbles are closed. The tenth aspect of the present disclosure includes a porous structure according to any one of the first to ninth aspects, including about 0% to about 40% additional inorganic substance in terms of mass and at least about 55% glass bubbles. The eleventh aspect of the present disclosure includes a porous structure according to the tenth aspect, including about 20 to about 40% additional inorganic substance in terms of mass.

[0007] The twelfth aspect of the present disclosure includes a porous structure according to the tenth aspect, including at least about 95% glass bubbles in terms of mass. The thirteenth aspect of the present disclosure includes a porous structure according to any one of the first to twelfth aspects, having a closed porosity of at least 20% in terms of volume. The fourteenth aspect of the present disclosure includes a porous structure according to any one of the first to twelfth aspects, having a closed porosity of at least 30% in terms of volume. The fifteenth aspect of the present disclosure includes a porous structure according to any one of the first to twelfth aspects, having a closed porosity of about 10% to about 40% in terms of volume. The sixteenth aspect of the present disclosure includes a porous structure according to any one of the first to fifteenth aspects, having an open porosity of about 40% to about 70% in terms of volume. The seventeenth aspect of the present disclosure includes a porous structure according to any one of the first to sixteenth aspects, having a cellular honeycomb geometry with a web thickness in the range of about 2 to about 15 mils and a cell density in the range of about 50 to about 400 cells per square inch.

[0008] The 18th aspect of the present disclosure includes a porous structure according to any one of the 1st to 17th aspects, having a bulk density within the range of about 0.4 g / cm 3 to about 0.6 g / cm 3 . The 19th aspect of the present disclosure includes a porous structure according to any one of the 1st to 18th aspects, in which the gaps include open gaps that open to the surface of the porous structure so as to define pores, and the pores have a pore size distribution having a central pore size within the range of about 0.008 μm to about 40 μm. The 20th aspect of the present disclosure is a porous structure including an inorganic skeleton containing a plurality of glass bubbles of at least about 55% by mass based on the total mass of the inorganic skeleton and a further inorganic substance of about 0% to about 40% by mass, wherein the glass bubbles are sintered together such that adjacent glass bubbles are physically directly bonded to each other, most of the glass bubbles are closed, and the porous structure has a total porosity of at least 50% in terms of volume. The 21st aspect of the present disclosure includes a porous structure according to the 20th aspect, including an inorganic skeleton of at least 90% by mass based on the total mass of the porous structure. The 22nd aspect of the present disclosure includes a porous structure according to the 21st aspect, in which about 75% to about 100% of the glass bubbles are closed. The 23rd aspect of the present disclosure includes a porous structure according to any one of the 20th to 22nd aspects, including at least 90% by mass of amorphous phase glass in terms of mass.

[0009] The 24th aspect of the present disclosure includes a porous structure according to any one of the 20th to 23rd aspects, including a further inorganic substance of about 20 to about 40% by mass in terms of mass. The 25th aspect of the present disclosure includes a porous structure according to any one of the 20th to 23rd aspects, including at least about 95% by mass of glass bubbles in terms of mass. The 26th aspect of the present disclosure includes a porous structure according to any one of the 20th to 25th aspects, including a closed porosity of about 10% to about 40% in terms of volume. The 27th aspect of the present disclosure includes a porous structure according to any one of the 20th to 26th aspects, including an open porosity of about 40% to about 70% in terms of volume. The 28th aspect of the present disclosure is a method for producing a porous structure, including the steps of joining a plurality of glass bubbles to each other, the glass bubbles having a central particle size in the range of about 1 μm to about 100 μm, the plurality including at least 1000 glass bubbles, and heating the glass bubbles, substantially all of the glass bubbles being closed before heating, substantially all adjacent glass bubbles sintering to each other during heating, and at least 50% of the glass bubbles remaining closed after heating such that the sintered closed glass bubbles form a porous structure as a whole. Each of the closed glass bubbles defines a cavity sealed therein, the surface of the sintered glass bubbles defines the gaps of the whole porous structure, the gaps include closed gaps that are not open to the surface of the porous structure, the porous structure has a closed porosity of at least 10% in terms of volume, and the closed porosity includes the sealed cavities and the closed gaps.

[0010] The 29th aspect of the present disclosure includes the method according to the 28th aspect, in which about 75% to about 100% of the glass bubbles remain closed after heating. The 30th aspect of the present disclosure includes the method according to the 28th aspect, in which about 90% to about 100% of the glass bubbles remain closed after heating. The 31st aspect of the present disclosure includes the method according to any one of the 28th to 30th aspects, in which the step of heating includes heating the glass bubbles to at least the softening temperature of the amorphous glass of the glass bubbles. The 32nd aspect of the present disclosure further includes, before heating, the step of extruding a raw material including glass bubbles, an organic binder, and any additional inorganic substances, and substantially all of the glass bubbles remaining closed after extrusion, including the method according to any one of the 28th to 31st aspects. The 33rd aspect of the present disclosure includes the method according to the 32nd aspect, in which the step of extruding includes extruding thousands of glass bubbles connected to each other by an organic binder.

[0011] A 34th aspect of the present disclosure includes a method according to the 32nd or 33rd aspect, wherein the raw material further includes a liquid portion containing one or more of oil and water, and glass bubbles, an organic binder, and any additional inorganic substances define a solid portion of the raw material, and the solid portion is more in mass than the liquid portion. A 35th aspect of the present disclosure includes a method according to the 34th aspect, wherein the solid portion is at least 10% more in mass than the liquid portion of the raw material. A 36th aspect of the present disclosure includes a method according to the 34th or 35th aspect, wherein the raw material occupies at least 55% of the solid portion in terms of mass. A 37th aspect of the present disclosure includes a method according to any one of the 34th to 36th aspects, wherein the ratio of the mass of the solid portion to the mass of the liquid portion is in the range of about 1.2 to about 1.7. A 38th aspect of the present disclosure includes a method according to any one of the 34th to 37th aspects, wherein, in terms of mass, the raw material includes at least about 30% glass bubbles, about 3% to about 10% organic binder, about 0% to about 25% any additional inorganic substances, and about 35% to about 45% liquid portion.

[0012] A 39th aspect of the present disclosure includes a method according to any one of the 34th to 38th aspects, wherein the step of heating one or more burns or chemically changes most of the organic binder and the liquid portion. A 40th aspect of the present disclosure includes a method according to any one of the 32nd to 39th aspects, wherein the additional inorganic substances include one or more of clay, talc, sepiolite, bentonite, CaCO3, Na2CO3, NaHCO3, ZrO2, Al2O2, MgO, and SiO2. A 41st aspect of the present disclosure includes a method according to any one of the 28th to 40th aspects, wherein during heating, the glass bubbles are heated for a first residence time to a first temperature range and then for a second residence time to a second temperature range, the first temperature range is about 200°C to about 400°C, and the first residence time is in the range of about 2 hours to about 6 hours. A 42nd aspect of the present disclosure includes the method according to the 41st aspect, wherein during heating, the second temperature range is from about 450 °C to 800 °C and the second residence time is within the range of about 3 hours to 7 hours.

[0013] A 43rd aspect of the present disclosure includes the method according to the 41st aspect, wherein during heating, the second temperature range is from about 500 °C to 700 °C and the second residence time is within the range of about 3 hours to 7 hours. A 44th aspect of the present disclosure includes the method according to the 41st aspect, wherein during heating, the second temperature range is above 400 °C and below the devitrification temperature of the amorphous glass of the glass bubbles, and the second residence time is within the range of about 3 hours to 7 hours. A 45th aspect of the present disclosure includes the method according to any one of the 28th to 44th aspects, further comprising the step of cooling a plurality of glass bubbles having adjacent closed glass bubbles physically directly bonded to each other.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

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Modes for Carrying Out the Invention

[0015] Here, for the purpose of facilitating the understanding of the principles of the present disclosure, reference is made to the embodiments shown in the drawings and described in the specification below. It is understood that it is not intended to limit the scope of the present disclosure thereby. Further, the present disclosure includes any modifications and corrections to the illustrated embodiments, and also includes further applications of the principles disclosed herein that would be ordinarily contemplated by those skilled in the art related to the present disclosure. As used herein, the term "and / or" when used in a listing of two or more items means that any one of the listed items may be used alone or any combination of two or more of the listed items may be used. For example, if a composition is described as containing components A, B, and / or C, the composition may contain A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C. In this specification, relative terms such as first and second, top and bottom, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual such relationship or order between such entities or operations.

[0016] As used herein, the term "about" means that quantities, sizes, formulations, parameters, and other quantities and characteristics are not exact and need not be exact, but reflect tolerances, conversion factors, rounding, measurement errors, etc., and other factors known to those skilled in the art, and may be approximate and / or larger or smaller as desired. When the term "about" is used in describing a single point of a value or range, it should be understood that the present disclosure includes the particular value or single point being referenced. Whether or not a numerical value or single point of a range in the specification lists "about", the numerical value or single point of the range is intended to include two embodiments, namely, those modified by "about" and those not modified by "about". Further, each endpoint of a range is understood to be significant in relation to and independent of the other endpoint. The terms "substantially", "substantially identical" and variations thereof, as used herein, are intended to indicate that the recited feature is equal to, or approximately equal to, a value or description, unless otherwise defined elsewhere in connection with a particular term or phrase. For example, a "substantially flat" surface is intended to indicate a surface that is flat or approximately flat. Further, "substantially" is intended to indicate that two values are equal or approximately equal. In some embodiments, "substantially" may indicate values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0017] As used herein, directional terms such as up, down, right, left, front, back, top, bottom, above, below, etc. are used only with reference to the figures as depicted and are not intended to imply an absolute orientation. As used herein, the terms "the", "a", or "an" mean "at least one" and should not be limited to "only one" unless explicitly stated to the contrary. Thus, for example, reference to "a component" includes embodiments having two or more such components, unless a different meaning is explicitly set forth in the context.

[0018] As used herein, "particle size distribution" or "PSD" is a series of values, a histogram, or a mathematical function that defines the relative quantity of particles such as glass bubbles disclosed herein as a function of size. The PSD is a useful technique for describing the size of particles in a collection of particles. The PSD can be described by many characteristics of the distribution, such as the mean, median, mode, and width or span. The mean is a calculated value similar to the concept of the arithmetic mean. Since the mean value is related to the basis of distribution calculations (number, surface, volume), there are several definitions of the mean. Various mean calculations are defined by known standards such as ISO9276-2:2001. The median is defined as the value at which half of the population exists above this point and half exists below this point. With respect to the particle size distribution, the median is called D50. D50 is the size (diameter) in microns that bisects the distribution, where half is above this diameter and half is below this diameter. D90 and D10 are other common values reported in the PSD. D90 is the size (diameter) at which 90% of the distribution is below this diameter, and D10 is the size (diameter) at which 10% of the distribution is below this diameter. The mode is the peak of the frequency distribution, or the highest peak observed in the distribution. The mode represents the particle size (or size range) most commonly seen in the distribution. The particle size values disclosed herein refer to the diameter of the particle or the equivalent spherical diameter, unless otherwise specified.

[0019] As used herein, "pore size distribution" is an analysis of the pores of a porous material, such as the porous structure of the present invention disclosed herein, for characterizing the pore diameters for which a specified percentage of the total pore volume is of finer pore diameters. Thus, for example, d1, d5, d10, d50, d90, d95, and d99 each represent the pore diameter for which 1%, 5%, 10%, 50%, 90%, 95%, and 99% of the total pore volume is of finer pore diameters. The volume percent porosity and pore size distribution, as used herein, are measured by mercury porosimetry for examples of the porous materials of the present invention in accordance with known standards such as ASTM D4284-12. All pore size distributions are based on pore volume. In particular, among other parameters, the parameters d10, d50, and d90 are used herein to define the relative narrowness of the pore size distribution. The parameters (i.e., d10, d50, and d90) used to describe the pore size distribution are conceptually similar to the parameters (i.e., D10, D50, and D90) used to describe the particle size distribution. For example, the quantity d50 is the median pore diameter based on pore volume and is measured in μm. Thus, d50 is the pore diameter into which 50% of the open porosity of the ceramic honeycomb article is intruded by mercury. The quantity d90 is the pore diameter for which 90% of the pore volume is composed of pores having a diameter smaller than the value of d90. Thus, d90 is equal to the pore diameter into which 10 volume % of the open porosity of the ceramic is intruded by mercury. The quantity d10 is the pore diameter for which 10% of the pore volume is composed of pores having a diameter smaller than the value of d10. Thus, d10 is equal to the pore diameter into which 90 volume % of the open porosity of the ceramic is intruded by mercury. The values of d10 and d90 are also in units of microns.

[0020] FIG. 1 shows a lightweight porous substrate or structure 100 according to the present disclosure for use in a variety of applications such as CO2 capture. The porous structure 100 can include a plurality of porous partitions 120 that define a plurality of open channels 122. Each of the porous partitions 120 has a thickness T between opposite surfaces that define the plurality of open channels 122. The open channels 122 can extend axially 90 from an inlet end 112 to an outlet end 114 of the porous structure 100. In an embodiment, as shown in FIG. 1, a plurality of partitions 120 intersect to form a honeycomb structure. The porous structure 100 is shown in FIG. 1 as having channels 122 with a substantially circular cross-section (e.g., in a plane perpendicular to the axial direction 90), but in embodiments, the channels can have any suitable geometry, such as hexagonal, square, triangular, rectangular, or sinusoidal cross-sections, or any combination thereof. Further, the porous structure 100 is shown as having a substantially cylindrical shape, but such a shape is merely illustrative, and it should be understood that the porous structure can have any kind of shape, including but not limited to spherical, oval, pyramidal, cubic, or block-shaped, etc.

[0021] The open channels 122 in an embodiment can have a relatively high aspect ratio, such as length to width or length to diameter, with the length being oriented axially 90 along the flow path of the open channels 122. In an embodiment, the open channels 122 are elongated such that the aspect ratio, defined as the length of the open channels 122 relative to the widest cross-sectional dimension of each open channel 122 orthogonal to the length, is at least 10, at least 20, at least 50, at least 100, and / or 50,000 or less for at least some (e.g., most, more than 90%, all) of the length of the open channels 122. The porous structure 100 can also have any kind of configuration and design, including but not limited to flow-through monoliths, wall-flow monoliths, or partial flow monolith structures. Exemplary flow-through monoliths include open channels 122, porous networks, or any structure with other passages through which fluid can flow from one end of the structure 100 to the other. Exemplary wall-flow monoliths include, for example, open channels 122, or any monolith structure with a porous network or other passages that may be open or closed at opposite ends of the structure, thereby directing the flow of fluid through the partition wall 120 (a "wall flow") from one end of the structure to the other. Exemplary partial flow monoliths can include any combination of wall-flow monoliths and flow-through monoliths that have, for example, several channels or passages that are open at both ends and through which fluid can flow through the channels without being blocked.

[0022] As shown in FIG. 1, the porous structure 100 can also include a porous skin 116 along or around its periphery. The skin 116 can have a thickness of from about 0.1 mm to about 3.5 mm, or from about 0.5 mm to about 2.5 mm, or even from about 1 mm to about 2 mm. The skin 116 can have properties similar to those of the partition wall 120 (e.g., pore diameter, pore diameter distribution, material, etc.). In embodiments, the skin 116 can be formed by converging the partition wall 120. The skin 116 can be applied during or after the formation of the porous structure 100. FIG. 2 shows a porous structure 200 having an overall geometry different from that of the porous structure 100 of FIG. 1 and a different channel geometry. In FIG. 2, features of the porous structure 200 that are substantially similar to those of the porous structure 100 of FIG. 1 are denoted using the same reference numbers incremented by 100 only. The porous structure 200 includes a plurality of porous partitions 220 that define a plurality of open channels 222. Each of the porous partitions 220 has a thickness T between opposite surfaces that define the plurality of open channels 222. The open channels 222 extend in the axial direction 190 from an inlet end 212 to an outlet end 214 of the porous structure 200. In an embodiment, as shown in FIG. 2, a plurality of the partitions 220 intersect to form a honeycomb structure.

[0023] The open channels 222 are shown as having a substantially square cross-section (e.g., in a plane perpendicular to the axial direction 190), but in an embodiment, the channels can have any suitable geometry, such as that described with respect to the porous structure 100 of FIG. 1. The porous structure 200 is shown as having a substantially square shape, but in an embodiment, the structure 200 can have any kind of shape, such as that described with respect to the porous structure 100 of FIG. 1. The porous structure 200 can have the same or a different configuration (e.g., a flow-through monolith, a wall-flow monolith, or a partial-flow monolith structure) as that described with respect to the porous structure 100 of FIG. 1. The porous structure 200 can also include a porous skin 216 along its periphery. The skin 216 may be configured substantially the same as or differently from the skin 116 of the porous structure 100 of FIG. 1. According to an embodiment, a porous structure, such as the porous structure 100 of FIG. 1 and the porous structure 200 of FIG. 2, includes a plurality of glass bubbles and / or is substantially formed from a plurality of glass bubbles (see the glass bubbles 312, 312' in FIGS. 3-5). As used herein, "a plurality" can include more than 100, such as more than 1000. The porous structure of the present disclosure, when formed from glass bubbles under the amounts and processing conditions disclosed herein, is lightweight and has a porosity beneficial for applications such as CO2 capture. For example, the porous structure of the present disclosure has a very low density and a mixed porosity, and a relatively high closed porosity that can allow for the introduction of carriers such as gamma Al2O3 on the walls for adsorbents such as polyethyleneimine (PEI).

[0024] The glass bubbles can be characterized by a "diameter", which refers to the diameter when the volume of the glass bubble is arranged in a perfect spherical geometry. However, in reality, the glass bubbles can be merely approximately spherical, for example, having a potato-like shape. The size of the glass bubbles can be selected and characterized based on the diameter related to the particle size distribution of the glass bubbles. The glass bubbles can have a median or D50 particle size within the range of about 1 μm to about 1000 μm, or about 2.5 μm to about 500 μm, or about 5 μm to about 250 μm, or about 7.5 μm to about 100 μm, or about 1 μm to about 100 μm, or about 7.5 μm to about 50 μm, or about 10 μm to about 30 μm. The glass bubbles can also have D10 and D90 particle sizes as shown in Table 1 below, in relation to the exemplary glass bubbles used to form the porous structure by the methods disclosed herein.

[0025] The glass bubbles may include (e.g., consist of, consist essentially of, contain) glass such as soda-lime glass, borosilicate glass, aluminosilicate glass, and / or other glasses. The glass of the glass bubbles is, in an exemplary embodiment, substantially or completely amorphous. In such an exemplary embodiment, the glass of the glass bubbles is substantially or completely amorphous before heating and remains substantially (i.e., 85% or more) or completely (i.e., about 100%) amorphous after heating according to the methods disclosed herein. In some contemplated embodiments, the glass of the glass bubbles may be completely or partially amorphous, crystalline, polycrystalline, etc., such as a two-phase glass-ceramic. In such contemplated embodiments, the glass of the glass bubbles may be amorphous before heating and may then devitrify and / or crystallize. In some contemplated embodiments, the glass bubbles may include and / or be formed from other materials such as synthetic materials, polymers, ceramics, fly ash / cenospheres, metals, etc. In an embodiment, the glass bubbles have a softening temperature in the range of about 425 °C to about 825 °C, or about 450 °C to about 800 °C, or about 475 °C to about 750 °C, or about 500 °C to about 700 °C, or about 400 °C to about 675 °C, or above 400 °C and below the devitrification temperature of the amorphous glass of the glass bubbles. In an embodiment, the softening temperature corresponds to the peak or maximum temperature of the firing cycle used to form the porous structure according to the methods disclosed herein. In an embodiment, the softening temperature is less than about 600 °C.

[0026] In an embodiment, the glass bubbles are about 0.66 g / cm 3 to about 0.90 g / cm 3 , or 0.60 g / cm 3 to about 1.00 g / cm 3 , or about 0.54 g / cm 3 to about 1.10 g / cm 3 , or about 0.42 g / cm 3 to about 1.30 g / cm 3 , or about 0.30 g / cm 3 to about 1.50 g / cm3 or 0.48 g / cm 3 to about 1.00 g / cm 3 or about 0.36 g / cm 3 to about 1.00 g / cm 3 or about 0.24 g / cm 3 to about 1.00 g / cm 3 and has a density within the range of. The glass bubbles, in an exemplary embodiment, have a density of less than 1.0 g / cm 3 . Density, as used herein, describes the mass per volume including the internal bubble volume. In an embodiment, the glass bubbles are particularly elastic and have, for example, an average hydrostatic pressure crushing strength of at least 1000 psi, for example at least 2000 psi, for example at least 3000 psi, for example at least 4000 psi, or higher than any of these listed strength values. Such crushing strength can be measured according to the technique described in the paper "Measuring Isostatic Pressing Strength of Hollow Glass Microspheres by Mercury-injection Apparatus" by Yun, W. and Shou, P., Key Engineering Materials, vol. 544, pp. 460-5 (2013). The methods disclosed herein can enable the formation of porous structures from glass bubbles having various compositions, physical attributes, and / or properties.

[0027] The porous structure of the present disclosure containing a relatively large amount of glass bubbles, which will be described later, has a pore size distribution beneficial for various applications such as CO2 capture. The pore size distribution is described with reference to the parameters d10, d50, and d90, which can be used to characterize various attributes of the pore size distribution such as the pore distribution width and the d factor. In embodiments, the porous structure of the present disclosure has a median or d50 pore size within the range of about 0.005 μm to about 10 μm, or about 0.010 μm to about 8 μm, or about 0.010 μm to about 6 μm, or about 0.015 μm to about 5 μm, or about 0.015 to about 4 μm, or within a range larger or smaller than those shown herein. The pore distribution width db, as used herein, is a measure of the overall width of the pore size distribution of the porous partition walls of the porous structure, i.e., a measure of the overall narrowness of the coarse / coarse pore fraction (above d50) of the pore size distribution of the material forming the partition walls. The pore distribution width db is given by the following relationship: db = (d90 - d10) / d50. According to embodiments, the porous structure containing glass bubbles has a pore distribution width db within the range of about 1.00 to about 1000, or about 1.50 to about 975, or about 2.00 to about 950. In embodiments where the porous structure contains additional inorganic substances (e.g., MgO or a source of magnesium or other inorganic substances disclosed herein), the pore distribution width db is within the range of about 1.50 to about 50.0, or about 1.75 to about 25.0, or about 2.00 to about 10.0, or about 2.25 to about 5.00, or about 2.25 to about 3.25.

[0028] The d factor df, as used herein, is a measure for characterizing the relative narrowness of the micropore size portion (below d50) of the pore size distribution. The d factor df is given by the following relationship: df = (d50 - d10) / d50. According to embodiments, the porous structure containing glass bubbles has a d factor df within the range of about 0.10 to about 1.00, or about 0.15 to about 0.95, or about 0.20 to about 0.90, or about 0.25 to about 0.85, or about 0.3 to about 0.80, or about 0.35 to about 0.75, or about 0.30 to about 1.00, or about 0.10 to about 0.75. In an embodiment, the porous structure of the present disclosure is substantially glass in terms of mass, for example, at least 70% by mass, or at least 80% by mass, or at least 90% by mass glass. Such a mostly porous structure formed from the glass of glass bubbles may be surprising or counterintuitive as an industrial product because such a structure is particularly fragile and / or may be expected not to maintain mechanical integrity. However, in some intended uses, the open porosity of the porous structure of the present disclosure can be at least partially filled by other materials (e.g., solid adsorbents for CO2 capture), while the porous structure coalesces mainly due to the methods of making such structures disclosed herein.

[0029] FIG. 3 is a micrograph of a “raw” (e.g., before firing, before sintering) structure 308, with a surface portion, e.g., surface portion 310, shown on the front of the micrograph. The raw structure 308 is configured to form the body of a porous structure, such as the porous structure 100 of FIG. 1 and the porous structure 200 of FIG. 2, after firing the raw body 308 according to the methods disclosed herein. The surface portion 310 can form the outer wall or inner wall (or web) of the porous structure after firing.

[0030] The raw structure 308 in an exemplary embodiment can be formed from an extruded batch material that includes glass bubbles 312 held in a binder 314 (e.g., an organic binder, or a mostly organic binder). The glass bubbles 312 are hollow and preferably have walls configured to be relatively elastic. Such elasticity allows the glass bubbles 312 to remain closed (i.e., intact and not ruptured) during extrusion and after firing, resulting in a mixed porosity structure with a relatively high closed porosity. As previously mentioned, the methods disclosed herein can allow the porous structure to be formed from a wide range of readily available glass bubbles. Some exemplary glass bubble attributes configured for use in the methods disclosed herein are shown in Table 1 below. Attribute values marked with an asterisk (*) were estimated according to SEM results.

[0031]

Table 1

[0032] Exemplary glass bubbles of Table 1 may have a composition described by the following non-limiting ranges: about 40 wt% to about 90 wt% SiO2; about 2 wt% to about 10 wt% CaO; about 3 wt% to about 35 wt% B2O3; about 0 wt% to about 5 wt% Al2O3; about 0 wt% to about 1 wt% Fe2O3; about 4 wt% to about 20 wt% Na2O; about 0 wt% to about 1 wt% K2O; and about 0 wt% to about 5 wt% MgO. In embodiments, the porous structure of the present disclosure can be formed from glass bubbles having a composition with different amounts of the indicated constituents and / or a composition having different constituents in amounts that may differ from or be similar to the indicated constituents. The glass bubbles 312 in the batch material can have a particle size distribution width Db given by the following relationship: Db = (D90 - D10) / D50. In embodiments, the glass bubbles 312 have a particle distribution width Db of less than 3, or less than 2.75, or less than 2.5, or less than 2.4, or less than 2.3, or less than 2, or less than 1.75, or less than 1.6, or less than 1.5, or less than 1.3, or less than 1. The glass bubbles 312 in the batch material can have a d factor Df given by the following relationship: Df = (D50 - D10) / D50. In embodiments, the glass bubbles 312 have a d factor Df of less than 1.25, or less than 1.2, or less than 1.1, or less than 1.0, or less than 0.95, or less than 0.85, or less than 0.75, or less than 0.7, or less than 0.65, or less than 0.6, or less than 0.55, or less than 0.5, or less than 0.4.

[0033] In an embodiment, the batch material forming the as - fabricated structure 308 may include various additives to facilitate processing, such as extrusion. For example, the batch material may include a slip agent and / or a lubricant, such as oil. In an embodiment, one or more sintering aids, such as sodium stearate, etc., may be added to the batch material. In an embodiment, the binder may include methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, and / or other binders. In an embodiment, the batch material may include a pore - forming agent, such as an organic pore - forming agent, such as starch (e.g., corn starch, pea starch). To facilitate processing, water, such as deionized water or DIW, may be added to the batch material. In an embodiment, oil and water define the liquid portion of the batch material. In an embodiment, the batch material includes substantially (i.e., more than 50% by mass) inorganic constituents, based on the total mass of the inorganic and organic constituents (i.e., the organic binder) in the batch material. For example, the batch material may include at least 55% by mass, or at least 60% by mass, or at least 75% by mass, or at least 80% by mass, or at least 85% by mass, or at least 90% by mass of inorganic constituents, while the remainder of the batch material substantially includes organic constituents. In an exemplary embodiment, the glass bubbles 312 may have a "separate" composition with respect to the inorganic constituents such that the batch material includes at least 55% by mass, or at least 60% by mass, or at least 75% by mass, or at least 80% by mass, or at least 85% by mass, or at least 90% by mass of the glass bubbles 312.

[0034] In an embodiment, the batch material forming the as - fabricated structure 308 may include additional or further inorganic materials (hereinafter “further inorganic substances”), such as clay, talc, silica, alumina, minerals, synthetic oxides, other types of glass or ceramic particles and / or bubbles. In an embodiment, the further inorganic substance has a softening temperature different from that of the glass bubbles so as to affect the softening temperature of the inorganic constituents in the batch material. In an exemplary embodiment, the further inorganic substance includes a source of magnesium (such as MgO). In an embodiment, the further inorganic substance is one or more of clay, talc, sepiolite, bentonite, CaCO3, Na2CO3, NaHCO3, ZrO2, Al2O2, and SiO2. In an embodiment, the further inorganic substance is one or more of clay, talc, sepiolite, bentonite, CaCO3, Na2CO3, NaHCO3, ZrO2, Al2O2, MgO, and SiO2.

[0035] The glass bubbles, organic binder and any further inorganic substances may define the solid portion of the batch material. In an embodiment, the batch material includes a substantially (i.e., more than 50% by weight) solid portion based on the total weight of the solid and liquid portions of the batch material. For example, the batch material in an embodiment may include a solid portion of about 50.1% to about 70% by weight, or about 51% to about 69% by weight, or about 52% to about 67% by weight, or about 53% to about 65% by weight, or about 54% to about 64% by weight, or about 55% to about 63% by weight, while the remainder of the batch material substantially includes a liquid portion. In an embodiment, the batch material has a ratio of the mass of the solid portion to the mass of the liquid portion. For example, the ratio in terms of the mass of the solid portion and the liquid portion is greater than 1, such as at least 1.05, or 1.1, or 1.2, or 1.3, or 1.4, and up to 2.5, or 2, or 1.9, or 1.8, or 1.7.

[0036] In an embodiment, the batch material may include glass bubbles, additional inorganic substances, and an organic binder. For example, the batch material in an embodiment may include glass bubbles in an amount of about 25% by mass to about 60% by mass, or about 27% by mass to about 58% by mass, or about 29% by mass to about 55% by mass, or about 30% by mass to about 53% by mass, or about 31% by mass to about 50% by mass, or about 32% by mass to about 49% by mass, or about 33% by mass to about 48% by mass, based on the total mass of the batch material. The batch material in an embodiment may include additional inorganic substances and / or a source of magnesium in an amount of about 0% by mass to about 35% by mass, or about 3% by mass to about 33% by mass, or about 5% by mass to about 30% by mass, or about 7% by mass to about 29% by mass, or about 10% by mass to about 25% by mass, or about 15% by mass to about 20% by mass, or about 0% by mass to about 25% by mass, based on the total mass of the batch material. The batch material in an embodiment may include an organic binder in an amount of about 2.5% by mass to about 10% by mass, or about 2.75% by mass to about 9% by mass, or about 2.9% by mass to about 8.5% by mass, or about 3% by mass to about 8% by mass, or about 3% by mass to about 10% by mass, or about 3.1% by mass to about 7.75% by mass, or about 3.2% by mass to about 7.5% by mass, based on the total mass of the batch material. The batch material in an embodiment may include oil in an amount of about 0.5% by mass to about 4% by mass, or about 0.75% by mass to about 3% by mass, or about 1% by mass to about 2% by mass, or about 1.25% by mass to about 2% by mass, or about 1.3% by mass to about 1.9% by mass, based on the total mass of the batch material. The batch material in an embodiment may include water in an amount of about 25% by mass to about 55% by mass, or about 27.5% by mass to about 50% by mass, or about 29% by mass to about 48% by mass, or about 30% by mass to about 46% by mass, or about 32.5% by mass to about 45% by mass, or about 33% by mass to about 44% by mass, or about 35% by mass to about 41% by mass, based on the total mass of the batch material.

[0037] In embodiments that include glass bubbles and additional inorganic materials, the amount of glass bubbles is greater than the amount of additional inorganic materials in the batch material. For example, the amount of glass bubbles is at least 5 wt%, or at least 10 wt%, or at least 15 wt%, or at least 20 wt% greater than the amount of additional inorganic materials, based on the total mass of the inorganic and organic components in the batch material. Some exemplary batch compositions of the batch material are shown in Table 2 below. The exemplary batch compositions include the exemplary glass bubbles disclosed in Table 1. The header of the column "Glass bubble sample" in Table 2 refers to the identification of the samples of the exemplary glass bubbles disclosed in Table 1 (i.e., sample A, B, or C). For example, the batch compositions of samples 2-3 include the glass bubbles of sample A, the batch compositions of samples 2-1 and 2-2 each include the glass bubbles of sample B, and the batch composition of sample 2-4 includes the glass bubbles of sample C. The mass percentages (wt%) listed in Table 2 are based on the total mass of the batch material. The abbreviations "MC", "CMC", and "HPMC" in the header "Type of binder" in Table 2 refer to methylcellulose, carboxymethylcellulose, and hydroxypropylmethylcellulose, respectively. In Table 2, any aqueous portion of the binder is included in the header of the row "Water (g)", and the remaining solid portion is included in the header of the row "Binder mass (g)".

[0038] [Table 2]

[0039] According to an embodiment, the glass bubbles 312 in the binder 314 are extruded at a rate and pressure configured to maintain the integrity of most (e.g., more than 75%, or more than 80%, or more than 85%, or more than 90%, or more than 95%) of the glass bubbles 312 in the batch material (e.g., via a twin-screw extruder). As shown in FIG. 3, most of the glass bubbles 312 appear to be completely intact. By maintaining the integrity of the glass bubbles 312, the glass bubbles can occupy a relatively large volume of space within the as-formed structure 308, gaps are defined between the glass bubbles 312, and respective sealed cavities are defined within each closed glass bubble 312. It is understood that the rate and pressure through the corresponding extruder can vary depending on the size of the glass bubbles, the material of the glass bubbles, and the extrusion device. In an embodiment, the extrusion pressure is in the range of less than 2500 psi, such as less than 2000 psi, and / or at least 500 psi.

[0040] The extrusion of the as-formed structure 308 can be particularly efficient for forming through-channels (e.g., channel 122 in FIG. 1, channel 222 in FIG. 2) within a porous structure, such as the porous structures 100 and 200 of FIGS. 1 and 2, or other through-features within the as-formed structure 308. However, in contemplated embodiments, such porous structures containing glass bubbles in the binder can be molded, tape cast, or otherwise shaped or processed, which can better or alternatively maintain the integrity of the glass bubbles 312. In contemplated embodiments, porous structures having shapes substantially different from the shapes of the porous structures 100, 200 may be extruded or otherwise formed. In an embodiment, the as - fabricated structure 308 is dried and heated (e.g., fired / sintered in a furnace, laser - heated) according to the methods described herein to form the porous structure of the present disclosure. The heating is configured to combust substantially all of the liquid portion including oil and water. The heating is configured to combust, carbonize, chemically transform, or otherwise affect the binder 314. In an embodiment, the heating is such that at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or more of the binder is removed during heating. Table 3 shows the estimated composition from the firing of the as - fabricated structure 308 including each batch composition of Table 2 after about 90% of the binder and substantially all (e.g., about 100%) of the liquid portion have been removed during heating according to the methods described herein.

[0041]

Table 3

[0042] The compositions listed in Tables 2 and 3 are related in that the estimated compositions of Examples 2 - 1’ to 2 - 4’ in Table 3 are based on the batch compositions of Examples 2 - 1 to 2 - 4 in Table 2, respectively. Considering this relationship, it is understood that the composition ranges discussed above in relation to embodiments of the batch materials can be adjusted to provide the composition of the fired porous structure based on the amount of binder and / or liquid portion removed during heating. For example, the porous structure of the present disclosure may include from about 0 wt% to about 40 wt% additional inorganic material (e.g., MgO) and at least about 55 wt% glass bubbles, based on the total mass of inorganic and organic materials in the porous structure after heating / firing. In an embodiment, the porous structure may include from about 20 wt% to about 40 wt% additional inorganic material (e.g., MgO), based on the total mass of inorganic and organic materials in the porous structure after heating / firing. In an embodiment, the porous structure may include at least about 95 wt% glass bubbles, based on the total mass of inorganic and organic materials in the porous structure after heating / firing.

[0043] In an embodiment, the as - received structure 308 is heated to at least the softening temperature of the (amorphous) glass of the glass bubbles 312 and up to but less than the devitrification temperature of the (amorphous) glass of the glass bubbles 312 at most. The conditions and handling of the as - received structure 308 during heating are configured such that adjacent glass bubbles 312 physically interact with each other, for example, bond directly to each other (e.g., sinter, weld, melt), but do not completely lose their individual structures. In other words, the conditions and handling of the as - received structure 308 are such that the glass bubbles 312 do not completely liquefy and / or do not completely lose their structure, and instead, the glass bubbles 312 are bonded to each other such that the resulting structure as a whole aggregates and has rigidity. This aggregated and rigid structure substantially containing fused / bonded glass bubbles after heating defines the inorganic skeleton of the porous structure of the present disclosure. Since the heating is below the devitrification temperature, the glass of the glass bubbles 312 forming the inorganic skeleton remains substantially or completely amorphous after heating. In an embodiment, the porous structure after heating / firing contains at least 80%, or at least 85%, or at least 90%, or at least 95%, or more of the amorphous - phase glass in terms of mass.

[0044] In an embodiment, the as - received structure 308 is heated using a unique firing process configured to allow a large amount (e.g., 50% or more) and / or substantially a large amount (e.g., 75% or more) of the glass bubbles 312 therein to remain closed (i.e., intact and not broken) during heating / firing. In an embodiment, during heating, the as - received structure 308 can be heated from ambient temperature to a first temperature (e.g., a fixed temperature and / or a temperature within a specified range) at a first dwell time. For example, the first temperature is at least about 200°C, e.g., about 300°C to about 400°C, and the first dwell time is at least 1 minute, e.g., 1 hour to 10 hours, or about 1 hour to about 8 hours or about 2 hours to about 6 hours, or about 3 hours to about 5 hours.

[0045] In some such embodiments, after heating to the first temperature for the first residence time, the as - fabricated structure 308 can be heated from the first temperature to the second temperature for the second residence time. For example, the second temperature is greater than about 400°C, such as from about 400.5°C to about 850°C, or from about 450°C to about 800°C, or from about 475°C to about 775°C, or from about 500°C to about 700°C, or from about 570°C to about 670°C, or from about 400.5°C to about 675°C, and the second residence time is at least 1 minute, such as from 1 hour to 10 hours, or from about 1 hour to about 8 hours, or from about 2 hours to about 8 hours, or from about 2 hours to about 6 hours, or from about 4 hours to about 6 hours, or from about 3 hours to about 5 hours, or from about 3 hours to about 7 hours. In an embodiment, the second temperature is in the range from at least the softening temperature of the glass of the glass bubbles 312 in the as - fabricated structure 308 to less than the devitrification temperature of the glass of the glass bubbles 312 in the as - fabricated structure 308. Thus, the second temperature in an embodiment can depend on the composition and / or properties of the glass bubbles 312 in the as - fabricated structure 308.

[0046] After heating, the as - fabricated structure 308 can be cooled to a temperature that is, for example, at least 100°C lower than the temperature at which the as - fabricated structure 308 was heated, such as less than 100°C, for example less than 50°C. During cooling, adjacent glass bubbles 312 remain physically bonded to each other, for example directly bonded and / or indirectly bonded via any additional inorganic materials present if any. In some such embodiments, the cooling includes a residence at a temperature above room temperature (e.g., the annealing point of the glass of the glass bubbles) but below the heating temperature. The residence can be in incremental steps or in the form of a temperature ramp down within a particular temperature range. Regardless of the cooling profile, the cooling can be configured to promote relaxation of residual stresses via annealing while avoiding formation of crystals in the material of the glass bubbles 312. In an exemplary embodiment, the heating rate is generally faster than the cooling rate. For example, in one embodiment, the heating to the first temperature and / or the second temperature may be at a ramp rate of at least 200 °C / hour, such as from about 200 °C / hour to about 400 °C / hour. In such an embodiment, the cooling from the second temperature may be at a ramp rate of less than 200 °C / hour, such as from 50 °C / hour to about 175 °C / hour.

[0047] Referring now to FIG. 4, a scanning electron microscope (SEM) image of the porous structure 308’ associated with the as-received structure 308 of FIG. 3 is shown. More specifically, the porous structure 308’ of FIG. 4 is formed after firing the as-received structure 308 according to the method disclosed herein. Thus, the porous structure 308’ is not an “as-received” structure. Similar to the as-received structure 308, the fired porous structure 308’ has a surface portion including a surface portion 310’ shown on the front of the SEM image. The surface portion 310’ may form the outer wall or inner wall (or web) of the fired porous structure 308’. The porous structure 308’ includes a plurality of glass bubbles 312’ corresponding to the glass bubbles 312 of the as-received structure 308. The glass bubbles 312’ within the porous structure 308’ are fused and / or sintered together without, or substantially without, any organic constituents (such as binders) such that adjacent glass bubbles are physically directly bonded to each other.

[0048] Figure 5 is an enlarged portion of the SEM image of Figure 4. The glass bubbles 312' of the porous structure 308' shown in Figure 5 may not be as spherical after firing as the glass bubbles 312 of the as-received structure 308 of Figure 3. Despite any gentle change in shape, Figures 4 and 5 show that after firing of the as-received structure 308, substantially all of the fused / sintered glass bubbles 312' of the porous structure 308' are closed (i.e., intact and not broken) such that the respective shells of each glass bubble define a cavity sealed therein. Such glass bubbles that are closed after firing and / or remain closed may be interchangeably referred to as "closed glass bubbles". In contrast, an "open glass bubble" may have a shell that is broken or otherwise discontinuous so as to define an exposed cavity therein (see 316 in Figure 5). In embodiments, most (e.g., more than 50%) of the fused / sintered glass bubbles 312' within the porous structure 308' are closed glass bubbles. In embodiments, more than 50%, or at least 65%, or at least 75%, or at least 85%, or at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or up to 100% of the glass bubbles 312' within the porous structure 308' are closed glass bubbles.

[0049] In an embodiment, the percentage of closed glass bubbles can be estimated. In one embodiment, an image of the porous structure (e.g., a micrograph, SEM, etc.) can be configured to capture a minimum number (e.g., about 500, or 750, or 1000) of distinguishable glass bubbles within the image display so that the number of closed glass bubbles and the total number of all glass bubbles can be counted within the image. The percentage of closed glass bubbles is then estimated by dividing the number of individual closed glass bubbles by the total number of glass bubbles (closed and open / broken) within the display and then multiplying by 100. In another embodiment, open (broken) glass bubbles can be indicated by volume during the mercury porosimetry method, and the highest (or theoretical) pore volume is obtained if all of the glass bubbles are open (broken). Thus, the closed pore ratio can be estimated by volume, and the closed pore volume ratio is equal to the theoretical pore volume (e.g., about 66 - 96 volume%) - the open pore volume (by mercury porosimetry).

[0050] Referring further to FIG. 5, the shell or surface of the glass bubble 312' defines a gap 318 throughout the porous structure 308'. In an embodiment, some of the gaps 318 can be formed by cavities left from the burned binder (see binder 314 in FIG. 3). In an embodiment, some of the gaps 318 and / or open glass bubbles interconnect (define an intricate path) to form the open porosity of the porous structure 308' and can open to the surface of the porous structure 308'. In an embodiment, some of the gaps 318 do not open to the surface of the porous structure 308' and instead are isolated within the porous structure 308' and separated from its surface. Such gaps 318 isolated within the porous structure 308' can be interchangeably referred to as "closed gaps". The sealed cavities of the closed glass bubbles 312' and the closed gaps 318 form the closed porosity of the porous structure 308'. Table 4 shows the beneficial open porosity achieved by the fired samples of Table 3 and the attributes of the resulting pore size distribution of the fired samples.

[0051] [Table 4]

[0052] As shown in Table 4, the porous structure 308' can achieve an open porosity measured by the mercury porosimetry method of at least 35%, or at least 40%, or at least 45%, or at least 50%, or at least 55%, or at least 60%, or at least 65%, or more, up to about 70% by volume. In embodiments, the closed porosity of the porous structure 308' from the sealed cavities of the closed gaps and closed glass bubbles can be estimated with reference to the maximum open porosity of about 80% achieved by the applicant when all or substantially all of the glass bubbles were broken during firing, as described in International Application No. PCT / CN2020 / 083460, filed on April 7, 2020 and published as WO2021 / 203232 on October 14, 2021, which is the exact opposite of the teachings herein. The difference between the measured open porosity, e.g., the measured porosity in Table 4 and the maximum open porosity, provides an estimate of the closed porosity of the porous structure 308'. In such embodiments, the porous structure 308' has a closed porosity of at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35%, or at least 40%, or more, up to about 50% by volume. In embodiments, the porous structure 308' has a total porosity that includes the sum of the open porosity and the closed porosity shown herein. In other embodiments, the closed porosity can be estimated with reference to the measured density. In further embodiments, the total porosity including the open porosity and the closed porosity can be measured using techniques such as small angle x-ray scattering (SAXS).

[0053] In an embodiment, the porosity of the fired porous structure 308' can be adjusted by using different blends of glass bubbles in the batch composition. For example, glass bubbles of a particular product name from a supplier (i.e., glass bubble samples A, B, or C from Table 2) can be sieved to provide different groups of glass bubbles of the same glass bubble sample having different particle size distributions with different size attributes. Thereafter, the batch composition can be formulated using different proportions (i.e., blends) of different groups of glass bubbles to adjust the resulting porosity of the fired porous structure formed from such a batch composition. Similarly, the batch composition can be formulated using glass bubbles of different glass bubble samples. For example, the batch composition of Sample 2-1 in Table 2 containing glass bubbles of glass bubble sample B can be modified to further include glass bubbles of glass bubble sample A and / or sample C to adjust the resulting porosity of the fired porous structure formed from such a batch composition.

[0054] In an embodiment, a beneficial mixed (i.e., open and closed) porosity is enabled by the porous structure 308' having a very low density, such as less than 0.75 g / cm3, or less than 0.7 g / cm3, or less than 0.65 g / cm3, or less than 0.6 g / cm3, or less than 0.575 g / cm3, or less than 0.55 g / cm3, or less than 0.525 g / cm3, or less than 0.52 g / cm3, and having a density of at least about 0.4 g / cm3. FIG. 6 is a graph showing the pore size distribution associated with the open pores of the fired samples of Tables 3 and 4. In an embodiment, the pores of the porous structure 308' have a pore size distribution with a median pore size within the range of about 0.008 μm to about 40 μm, or about 0.01 μm to about 40 μm, or about 0.05 μm to about 36 μm, or about 0.09 μm to about 32 μm, or about 0.13 μm to about 28 μm, or about 0.17 μm to about 24 μm, or about 0.21 μm to about 20 μm, or about 0.01 μm to about 38 μm, or about 0.01 μm to about 30 μm, or about 0.01 μm to about 22 μm, or about 0.03 μm to about 40 μm, or about 0.11 μm to about 40 μm, or about 0.19 μm to about 40 μm, and including all sub-ranges and sub-values between the endpoints of these ranges. In an embodiment, the mode of the pore size distribution is less than 15 μm, or less than 14 μm, or less than 12 μm, or less than 10 μm, and at least 0.1 μm, or at least 0.5 μm, or at least 1 μm.

[0055] Referring again to FIGS. 1-4, the inner wall formed between the open channels of the porous structure 308' may be particularly thin (T), for example, in an embodiment, less than 1 millimeter (mm), for example, less than 500 micrometers (μm), for example, less than 100 μm, for example, less than 50 μm, for example, less than 10 μm, for example, less than 5 μm in thickness. In the contemplated embodiments, the processes and techniques disclosed herein are used, for example, as a lightweight porous honeycomb structure for introducing a solid adsorbent for CO2 capture applications. The glass bubbles have a crush strength and a sufficiently small geometry to facilitate the extrusion of a honeycomb structure having a web thickness of at least 50 cells per square inch (cpsi), such as at least 100 cpsi, such as at least 200 cpsi, such as at least 300 cpsi, such as at least 400 cpsi, or even higher cpsi (e.g., 600, 700, 800, or 900 cpsi), and / or at least about 2 mils (i.e., 1 / 1000 of an inch) and 15 mils or less, such as about 11 mils or less, such as about 10 mils or less, such as about 8 mils or less, such as about 7 mils or less, such as about 6 mils or less, such as about 5 mils or less, and are selected to have a cell geometry of at least the same density as that value, a density less than that value, or about that value, such as, for example, cpsi over web thickness in mils of about 200 / 8, 400 / 7, 400 / 6, 400 / 5, 400 / 4, 400 / 3, 400 / 2, 300 / 7, 300 / 6, 300 / 5, 300 / 4, 300 / 3, 300 / 2, 250 / 10, 200 / 7, 200 / 6, 200 / 5, 200 / 4, 100 / 8, 100 / 7, 100 / 6, 100 / 5, 50 / 8, 50 / 7, 50 / 6, etc.

[0056] At least some such embodiments have a cylindrical geometry and have a diameter of at least 4 inches, such as at least 6 inches, such as at least 8 inches, such as at least 12 inches, such as at least 24 inches, and / or 64 inches or less, such as 36 inches or less. Other such embodiments have a cross-section of a generally square, rectangular, or other polygonal geometry and have sides of at least 4 inches, such as at least 6 inches, such as at least 8 inches, such as at least 12 inches, such as at least 24 inches, and / or 64 inches or less, such as 36 inches or less. Other contemplated embodiments have other sizes or shapes. Such geometries can promote a low pressure drop.

[0057] Embodiments of the porous structure, assembly, and method of forming them offer many advantages over existing structures, assemblies, and methods. In embodiments, the firing temperature can be lowered (e.g., 500 °C), while existing structures are typically fired at higher temperatures (e.g., above 800 °C). The unique firing process beneficially enables the use of glass bubbles widely available in the market, providing an immediate cost advantage. When used in certain applications, e.g., CO2 capture applications, the resulting mixed porosity of the formed porous structure having both relatively high open porosity and closed porosity simplifies the firing process while providing further cost reduction. Furthermore, the fired porous structure by the method disclosed herein has a very low density (e.g., about 0.5 g / cm 3 ) and a similarly low heat capacity (e.g., about 0.5 kJ / K), which is lower than many other ceramic honeycomb structures. Additionally, the fired porous structure formed according to the method disclosed herein may enable on-wall / intra-wall coating for (solid) adsorbents, e.g., introduction of PEI for CO2 capture applications.

[0058] The configuration and arrangement of the porous structure, assembly, and structure and method of forming them are merely exemplary, as shown in various embodiments. Although only some embodiments are described in detail in this disclosure, many modifications are possible without departing significantly from the novel teachings and advantages of the subject matter described herein (e.g., variations in size, dimensions, structure, shape, and proportions of various elements, values of parameters, mounting arrangements, use of materials, color, orientation). Some elements shown as integrally formed may be constructed of multiple parts or elements, the positions of the elements may be reversed, or otherwise changed, and the nature or number of separate elements or positions may be modified or changed. The order or sequence of any process, logical algorithm, or method step may be changed or rearranged according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the various exemplary embodiments without departing from the scope of the technology of the present invention.

[0059] In some modifications, different forming processes (i.e., other than extrusion) are contemplated to form a raw structure that includes a relatively large amount of glass bubbles as disclosed herein. For example, the raw structure can be formed using additive manufacturing techniques to build individual layers of the raw structure using a batch material that includes a relatively large amount of glass bubbles dispensed through a nozzle or similar orifice. In some embodiments, the batch material can include additional inorganic materials, such as polymers, carbon, ceramics, and / or metals added to and / or in place of the materials. In such modifications, the relative proportion of glass bubbles in terms of mass in the batch material remains similar to the proportions disclosed herein.

Claims

1. A porous structure containing multiple glass bubbles, Glass bubbles are sintered together so that adjacent glass bubbles are physically directly bonded to each other. Glass bubbles have surfaces that define the gaps throughout the porous structure, and these gaps include closed gaps that are not open to the surface of the porous structure. At least 50% of glass bubbles are closed glass bubbles, and each closed glass bubble defines a sealed cavity inside. The porous structure has a closed porosity of at least 10% in terms of volume, and the closed porosity includes sealed cavities and closed gaps. A porous structure is a porous structure having an open porosity of at least 40% in terms of volume.

2. The porous structure according to claim 1, comprising substantially glass in terms of mass.

3. The porous structure according to claim 1, comprising at least 85% by mass of amorphous phase glass.

4. The porous structure according to claim 1, wherein approximately 65% ​​to approximately 100% of the glass bubbles are closed.

5. In terms of mass, Approximately 0% to approximately 40% of further inorganic substances, At least about 55% glass bubbles and The porous structure according to claim 1, including the above.

6. The porous structure according to claim 5, comprising about 20 to about 40% further inorganic material in terms of mass, or comprising at least about 95% glass bubbles.

7. The porous structure according to claim 1, having one or more closed porosity of about 10% to about 40% and open porosity of about 40% to about 70% in terms of volume.

8. A porous structure according to any one of claims 1 to 7, having a cellular honeycomb geometric shape with a web thickness in the range of about 0.051 to about 0.381 mm (about 2 to about 15 mils) and a cell density in the range of about 50 to about 400 cells per 6.452 cm² (square inch).

9. Approximately 0.4 g / cm 3 ~Approx. 0.6g / cm 3 A porous structure according to any one of claims 1 to 7, having a bulk density within the range of [specified range].

10. The porous structure according to any one of claims 1 to 7, wherein the gaps include open gaps that are open to the surface of the porous structure so as to define the pores, and the pores have a pore size distribution having a central pore size in the range of about 0.008 μm to about 40 μm.

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