Composite silica composition containing macropores and process for making same

Abstract

Composite particles are disclosed containing micronized silica particles held together by a binder. The silica particles have a relatively high surface area and can include micropores and mesopores. A binder is selected that produces composite particles with macropores. The macropores serve as highways for access to the pore structure of the silica particles when the composite particles are contacted with a fluid. The composite particles are well suited for adsorption processes.

Description

COMPOSITE SILICA COMPOSITION CONTAINING MACROPORES ANDPROCESS FOR MAKING SAMECROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to the benefit of U.S. Provisional Application No. 63 / 729,656, filed December 9, 2024, which is expressly incorporated herein by reference in its entirety.BACKGROUND

[0002] Porous particles like silica and zeolites have a wide range of applications across various industries due to their high surface area, tunable pore sizes, and chemical stability. For example, the above porous particles are typically used as desiccants and drying agents. The particles, for instance, can control humidity and prevent moisture damage in packaging, electronics, pharmaceuticals, and food products. Porous particles, such as silica particles, are also used in drug delivery systems. Porous particles are also used for odor control.

[0003] Porous particles such as silica particles and zeolites or microporous aluminosilicates are also used for adsorption separation. For instance, the porous particles can be used in gas separation technologies to separate gases like nitrogen, oxygen, hydrogen, and carbon dioxide from mixtures. Zeolites, for instance, have a distinct pore architecture resulting from the crystal lattice, while silica can offer a broad pore size range.

[0004] In the past, silica gels were primarily used as desiccants and sorbents. Silica gels are a granular, porous form of silicon dioxide that can synthetically be produced from sodium silicate. Silica gels do have some limitations when used as adsorbents. For instance, silica gels have little to no intra-particle porosity that can limit their adsorption of a material based on time.

[0005] In view of the above, a need exists for a composition containing silica particles that has enhanced porosity. In particular, a silica-based material is needed that can offer better kinetics in comparison to silica gels used in the past.SUMMARY

[0006] In general, the present disclosure is directed to a composition containing porous composite particles. The composite particles contain very small porous silica particles, such as micronized silica particles, that are bound together. In oneaspect, for instance, the silica particles can be bound together using a binder. In one embodiment, the binder can remain in the final product. In an alternative embodiment, the bound particles can be calcined at a temperature and a time sufficient to remove the most or all of the binder. Calcination of the bound particles can change the pore structure. Thus, calcination can be used to adjust pore sizes based upon the intended use of the particles and the desired result.

[0007] A binder is selected that is not only capable of holding the silica particles together, but also can form mesopores and / or macropores in the resulting composite particle. The mesopores and / or macropores provide access to the silica particles when the composite particles are contacted with an adsorbate. Consequently, the resulting composite particles are well suited for use in adsorption processes in addition to various other processes.

[0008] In one embodiment, for instance, the present disclosure is directed to a silica composition comprising a plurality of composite particles. The composite particles comprise silica particles. The silica particles include micropores and / or mesopores and have an average particle size (D50) of less than about 25 microns, such as from about 1 micron to about 12 microns, such as from about 5 microns to about 10 microns. The silica particles can have a pore volume of greater than about 0.25 ml / g and less than about 2 ml / g, such as from about 0.3 ml / g to about 1 ml / g, such as from about 0.35 ml / g to about 0.75 ml / g. The silica particles are bound together to form the composite particles. The silica particles can be bound together, for instance, by a binder that may or may not remain in the final product. The composite particles include macropores that facilitate access to the silica particles when the composite particles are contacted with a fluid.

[0009] The composite particles can display a surface area of greater than about 2 m2 / g, such as greater than about 3 m2 / g, such as greater than about 4 m2 / g. In addition to macropores, the composite particles can further include mesopores. In one aspect, the macropores on the composite particles include macropores having a pore size from about 100 nm to about 1 ,000 nm. For instance, when tested according to ASTM Test D4404-10, the composite particles can display a peak of greater than about 150 mm3g’1nm at a pore size between about 500 nm and about 1 ,000 nm. In one aspect, the composite particles can also comprise macropores having a diameter of from about 4,000 nm to about 10,000 nm. For instance,when tested according to ASTM Test D4404-10, the composite particles can display a peak of greater than about 100 mm3g’1nm at a pore size of between about 4,000 nm and about 10,000 nm.

[0010] When the composite particles are calcined, however, the calcination process can remove the macropores having a diameter of from about 4,000 nm to about 10,000 nm. For example, when calcined, the resulting particles do not display a peak of greater than 100 mm3g’1nm at a pore size of between about 4,000 nm and about 10,000 nm.

[0011] The composite particles can have any suitable size. In one aspect, the composite particles can have an average particle size (D50) of from about 0.5 mm to about 5 mm, such as from about 1 mm to about 4 mm, such as from about 1 .6 mm to about 2.5 mm.

[0012] The silica particles contained in the composite particles can comprise micronized silica particles. The silica particles can be comprised of amorphous silica. In one aspect, the silica particles can display a surface area of greater than about 300 m2 / g, such as greater than about 400 m2 / g, such as greater than about 500 m2 / g, such as greater than about 600 m2 / g, such as greater than about 700 m2 / g, and less than about 1 ,200 m2 / g, such as less than about 900 m2 / g.

[0013] The binder present in the composite particle can comprise a polysaccharide. For instance, the binder can comprise amylopectin, amylose, or mixtures thereof. Alternatively, the binder can comprise a colloidal silica. The binder can be present in the composite particles in an amount from about 2% by weight to about 15% by weight, such as in an amount from about 2% by weight to about 10% by weight, such as in an amount from about 2.5% by weight to about 7% by weight. When the composite particles are calcined, the amount of binder present in the composite particles can be less than about 1% by weight, such as less than about 0.5% by weight, such as less than about 0.1 % by weight, such as less than about 0.01 % by weight, such as less than about 0.001 % by weight. In one aspect, the binder is completely removed from the composite particles.

[0014] The present disclosure is also directed to a process for removing a component from a fluid stream. The process includes the step of contacting a fluid stream containing the component with a bed of the composite particles as described above. The component is adsorbed onto the silica particles containedwithin the composite particles. In one aspect, the process further includes the step of removing the component from the composite particles through desorption and collecting the component. Desorption, for instance, can occur by changing the temperature and / or the pressure. In one aspect, the component that is adsorbed onto the silica particles comprises carbon dioxide. The process, for instance, can comprise a pressure swing adsorption process.

[0015] The present disclosure is also directed to a process for making composite particles containing silica. The process includes the step of combining micronized amorphous silica particles with a binder. The silica particles can have an average particle size of less than about 25 microns, can include micropores, and can have a pore volume of greater than about 0.25 ml / g. The binder and silica particle mixture is aggregated for forming composite particles. The composite particles are then dried, such as at a temperature of from about 100°C to about 300°C. The formed and dried composite particles include macropores and / or mesopores that facilitate access to the silica particles.

[0016] In one aspect, the binder comprises amylopectin, amylose, or mixtures thereof. The binder, for instance, can be pre-gelled prior to contact with the silica particles.

[0017] In one embodiment, the process can further include the step of calcining the composite particles at a temperature that causes removal of at least a portion of the binder.

[0018] Other features and aspects of the present disclosure are discussed in greater detail below.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:Figure 1 is a graphical representation of some of the results obtained in the example below;Figure 2 is a graphical representation of some of the results obtained in the examples below;Figure 3 is a graphical representation of some of the results obtained in the examples below;Figure 4 is a graphical representation of some of the results obtained in the examples below; andFigure 5 is a graphical representation of some of the results obtained in the examples below.

[0020] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.DETAILED DESCRIPTION

[0021] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present disclosure.

[0022] The present disclosure is generally directed to composite porous particles that can be used in numerous and diverse applications. The composite particles are comprised of relatively small silica particles held together by a binder that can remain in the final product or can be removed. The silica particles are comprised of aggregates of primary particles. The silica particles have a relatively high surface area and can include micropores and mesopores. In accordance with the present disclosure, a binder is selected that holds the particles together without adversely affecting the porous properties of the silica particles. For instance, in one embodiment, the resulting composite particles include macropores that serve as channels or “highways” that allow fluids, such as gases, to interact with the porous structure of the silica particles. The resulting composite particles are not only easy to handle, but offer excellent and controlled porosity characteristics.

[0023] As described above, the composite particles of the present disclosure can be used in numerous and diverse applications. The particles, for instance, can be used as desiccants and drying agents. The particles can be used to control humidity and / or absorb or adsorb odors. In one embodiment, the composite particles can be used to adsorb gases from a fluid stream, such as steam or carbon dioxide. In one aspect, the composite particles can have improved kinetic rates in comparison to porous materials used in the past, such as silica gels.

[0024] As described above, the composite particles of the present disclosure are comprised of relatively small silica particles. In one aspect, the silica particles can comprise micronized amorphous silica. Micronized silica or finely ground silicarefers to silica particles that are ground into very small particle sizes, such as having an average particle size (D50) of less than about 25 microns.

[0025] In one aspect, the silica particles used in the present disclosure are obtained from high-purity silica sources, such as quartz or fumed silica. Optionally, the raw silica can be purified to remove impurities. Purification can include chemical treatments, acid washing, or other processes.

[0026] Once the silica material is collected, the silica is reduced to micron-sized particles through various mechanical grinding methods. For instance, jet milling, ball-milling, attrition milling, or mechanical pulverizing processes can be used. During jet milling, high-speed jet mills use a stream of air or steam to cause particle collisions, which break down the larger silica particles into smaller particles. During ball-milling, a rotating drum with ceramic or steel balls crushes and grinds the silica into fine powder. Attrition milling refers to a process in which the silica particles are ground using a high-speed rotating disk and a stationary disk, which causes grinding. Mechanical pulverizing processes can use hammer mills or pin mills to achieve the fine particle sizes. Grinding can occur according to a dry process, according to a wet process, or can be a combination of both dry and wet processes.

[0027] In one aspect, the silica particles are produced from silica gels. Silica gels, for instance, can be produced by mixing an aqueous solution of an alkali metal silicate (e.g., sodium silicate) with a strong acid such as nitric or sulfuric acid, the mixing being done under suitable conditions of agitation to form a clear silica sol which sets into a hydrogel in less than about one-half hour. The resulting gel is then washed. The concentration of the SiCh in the hydrogel which is formed is usually in the range of typically between about 15 and about 40 weight percent, such as between about 20 and about 35 weight percent, such as between about 30 and about 35 weight percent, with the pH of that gel being from about 1 to about 9, such as from about 1 to about 4. A wide range of mixing temperatures can be employed, this range being typically from about 20 to about 50°C.

[0028] Washing is accomplished simply by immersing the newly formed hydrogel in a continuously moving stream of water which leaches out the undesirable salts, leaving about 99.5 w % pure silica (SiCh) behind.

[0029] During precipitation of the silica gel, the rate of acid addition and thetemperature can be used to control particle sizes, porosity and surface area. Similarly, the temperature, pH, and duration of the washing cycle can influence the physical properties of the resulting silica including surface area and pore volume.In one aspect, the silica gel can be washed at a temperature of from about 40°C to about 90°C and at a pH of from about 3 to about 9 for a period of time of from about 8 hours to about 50 hours. Washing the silica gel at lower pHs, such as from about 3 to about 5 and at lower temperatures, such as from about 45°C to about 70°C for a period of time of from about 12 hours to about 30 hours can produce silica particles having greater surface area and lower pore volumes.

[0030] Once the silica gel particles are formed, the particles can be ground to a desired size. In one aspect, the particles can first be dry milled followed by wet milling in an aqueous slurry.

[0031] The dry milling referred to typically takes particulate inorganic oxide and reduces it in size either by mechanical action, impingement onto a metal surface, or collision with other particles after entrainment into a high-velocity air stream.

[0032] A wet milling procedure is characterized by the presence of liquid, e.g. water, during the milling procedure. Thus, wet milling is typically performed on a slurry of the inorganic oxide particles having a solids content of typically from about 15 to about 25 weight percent based on the slurry weight.

[0033] More specifically, with wet milling, the inorganic oxide is slurried in a media (usually water) and the mixture then subjected to intense mechanical action, such as the high speed metal blades of a hammer mill or rapidly churning media of a sand mill. Wet milling reduces particle size and produces colloidal silica as well.

[0034] Accordingly, the inorganic oxide (typically while still wet from washing) is then subjected to a sequential milling operation as described below.

[0035] In the dry milling procedure, the inorganic oxide is milled in a manner sufficient to reduce its average particle size to typically from about 3 to about 12 microns, such as from about 3 to about 10 microns, such as from about 3 to about 7 microns, and its moisture content is typically less than about 50 weight percent, such as less than about 25 weight percent, such as less than about 15 weight percent. In order to attain the dry milling particle size targets at the higher moisture contents, it may be necessary to conduct dry milling while the particles are frozen.

[0036] The dry milling is also conducted to preferably impart a particle size distribution such that the Distribution Span is typically from about 0.5 to about 3.0, such as from about 0.5 to about 2.0, such as from about 0.7 to about 1.3.

[0037] Thus, the resulting dry milled material exists in the form of a powder prior to being slurried for wet milling.

[0038] The dry milling is preferably conducted in a mill capable of flash drying the inorganic oxide while milling. Flash drying is a standard industrial process where the material to be dried is quickly dispersed into a hot air chamber and exposed to an air stream of from about 370 to about 537°C. The rate of air and material input is balanced such that the temperature of the outgoing air and the material entrained in it is generally from about 121 to about 176°C. The whole process of drying usually takes place in less than 10 seconds, reducing the moisture content to less than about 10% by weight. Alternatively, the inorganic oxide can be separately flash dried to the above described moisture content in a flash dryer and then placed in a dry mill and milled. Ball mills can also be used.

[0039] Flash drying is typically accomplished by exposing the inorganic oxide to conditions of temperature and pressure sufficient to reduce the moisture content thereof to levels as described above over a period of time of typically less than about 60 seconds, such as less than about 30 seconds, such as less than about 5 seconds.

[0040] Dry milling typically does not produce colloidal silica.

[0041] In the wet milling procedure, the previously dry milled inorganic oxide is subjected to a milling procedure well known in the art that is sufficient to produce slurries with the particle sizes specified above. This will result in a further reduction of the average particle size initially imparted by the dry milling procedure. Suitable mills include hammer mills, impact mills (where particle size reduction / control is achieved by impact of the oxide with metal blades and retained by an appropriately sized screen), and sand mills (where particle size control / reduction is achieved by contact of the oxide with hard media such as sand or zirconia beads).

[0042] It should be understood, however, that the above process is provided only for exemplary purposes. For instance, in other embodiments, the silica particles can be micronized using only dry milling or only wet milling.

[0043] After milling or grinding, the resulting silica particles can optionally be fed through classifiers or sieves to separate particles based on their size. For instance, a micronizer or air classifier can be used to obtain uniform particle sizes at average particle sizes of less than about 25 microns. Prior to use, the silica particles can be dried to remove moisture, especially when fed through a wet grinding process.

[0044] In one embodiment, silica particles are selected that are highly porous with a large surface area, high adsorption capacity, and excellent porosity characteristics. As used herein, the average particle size of the silica particles can be determined using a MALVERN MASTERSIZER particle size analyzer, which operates on the principle of laser light diffraction. Similar light diffraction particle size analyzers can also be used. Such particle analyzers can measure the average particle size and can be used to determine a particle size distribution.

[0045] As described above, silica particles used according to the present disclosure generally have an average particle size (D50) of less than about 25 microns. For instance, the particles can have an average particle size of less than about 20 microns, such as less than about 15 microns, such as less than about 12 microns, such as less than about 10 microns, such as less than about 8 microns. The average particle size is generally greater than about 0.1 micron, such as greater than about 0.5 microns, such as greater than about 1 micron, such as greater than about 3 microns, such as greater than about 4 microns, such as greater than about 5 microns.

[0046] The silica particles can display a relatively high surface area. For instance, the surface area of the silica particles can be greater than about 300 m2 / g, such as greater than about 400 m2 / g, such as greater than about 500 m2 / g, such as greater than about 600 m2 / g, such as greater than about 700 m2 / g. The surface area is generally less than about 1 ,000 m2 / g, such as less than about 900 m2 / g. The pore volume of the silica particles is generally greater than about 0.25 ml / g. For instance, the pore volume can be greater than about 0.3 ml / g, such as greater than about 0.33 ml / g, such as greater than about 0.35 ml / g, such as greater than about 0.38 ml / g, and less than about 1 ml / g, such as less than about 0.75 ml / g, such as less than about 0.6 ml / g, such as less than about 0.5 ml / g.Surface area as used herein refers to the BET surface area. BET surface area isdetermined according to ASTM Test D3663-03. Pore volume can be determined by nitrogen adsorption using the BET technique.

[0047] In one aspect, the silica particles can have a relatively narrow particle size distribution span. The particle size distribution span is determined in accordance with the following equation:DQQ — DIQ Distribution Span = — - — - — 50 wherein D10, D50, and D90 represent the 10th, 50th, and 90th percentile, respectively, of the particle size (diameter) distribution, i.e. a Dgoof 100 microns means that 90 volume % of the particles have diameters less than or equal to 100 microns.

[0048] Silica particles made according to the present disclosure can display a particle size distribution span of generally greater than about 0.5, such as greater than about 0.7, such as greater than about 0.8, and less than about 4, such as less than about 3, such as less than about 2, such as less than about 1 .5.

[0049] The silica particles of the present disclosure can display a specific gravity, in one embodiment, of greater than about 1 .5, such as greater than about 1 .8, such as greater than about 1 .9, such as greater than about 2, and less than about 2.5, such as less than about 2.4, such as less than about 2.3, such as less than about 2.2

[0050] As described above, in one embodiment, the silica particles can comprise amorphous particles. The particles, in one embodiment, can display an acidic pH when present in a 5% by weight slurry with water. The pH, for instance, can be less than about 7, such as less than about 6, such as less than about 5, and greater than about 3.

[0051] The silica particles are comprised of aggregate particles containing a plurality of primary particles. The primary particles can be joined and connected at their points of contact to produce the aggregates. In this manner, in one embodiment, the silica particles can contain micropores in combination with mesopores. As used herein, a micropore has a diameter of less than 2 nm, mesopores have a diameter of from 2 nm to 50 nm, and macropores have a diameter of greater than 50 nm. In one aspect, the silica particles can not only include micropores, but can also include a well-defined network of mesopores. Itis believed that the mesopores exist where the primary particles come together to form interstitial void spaces. These interstitial void spaces can comprise channels formed by loosely packed constituent primary particles. The presence of the mesopores within the silica particles enables the particles to adsorb moisture and other molecules more effectively.

[0052] Once the appropriate silica particles are collected, the silica particles in accordance with the present disclosure are bound together to form larger composite particles that are easier to handle for use in various different processes. In accordance with the present disclosure, a binder is selected that does not significantly interfere or block the porous structure of the silica particles. In one aspect, for instance, a binder can be selected that produces macropores and / or mesopores in the composite particle structure which allows fluids contacting the particles to access the porous network of the silica particles. In this way, the silica particles can quickly and efficiently adsorb particular components from a fluid, such as moisture, carbon dioxide, nitrogen, nitrogen oxides, and the like.

[0053] The binder that is used to hold the silica particles together can remain in the final product or can be removed. For instance, it was discovered that subjecting the composite particles to calcination can remove the binder without causing any significant change in particle size. Calcining the composite particles can be used to change the final pore structure of the particles. For instance, calcination, in one embodiment, can remove large macropores from the particles.

[0054] Binders that can be used in accordance with the present disclosure include polysaccharides and colloidal silica.

[0055] In one embodiment, for instance, a polysaccharide binder can be used. The polysaccharide binder can comprise, for instance, amylopectin, amylose, or mixtures thereof. In one aspect, for instance, the binder can comprise a starch, such as a wheat starch. The wheat starch, for instance, can contain from about 60% by weight to about 85% by weight, such as from about 70% by weight to about 80% by weight amylopectin and can contain amylose in an amount from about 40% by weight to about 15% by weight, such as in an amount from about 30% by weight to about 20% by weight.

[0056] One example of a process for producing the composite particles includes combining micronized silica particles with a binder. The binder can bepresent in the mixture and in the final product in an amount from about 2% by weight to about 15% by weight. For instance, the binder can be added in an amount greater than about 2.5% by weight, such as in an amount greater than about 3% by weight, such as in an amount greater than about 3.5% by weight, such as in an amount greater than about 4% by weight, such as in an amount greater than about 4.5% by weight, and in an amount less than about 12% by weight, such as in an amount less than about 10% by weight, such as in an amount less than about 8% by weight, such as in an amount less than about 7% by weight, such as in an amount less than about 6% by weight.

[0057] Once the binder and silica particles are mixed together, the mixture can be granulated using any suitable mixer. In one aspect, the silica can be first added to the mixer followed by the binder. The binder can be added alone or in combination with a liquid carrier, such as water. Mixing the particles together causes the composite particles to form. The resulting particles can then be screened or classified in order to arrive at a desired particle size range. The resulting composite particles can then be dried. For instance, in one embodiment, the composite particles can be dried at a temperature of greater than about 100°C, such as greater than about 150°C, such as greater than about 180°C, and less than about 280°C, such as less than about 250°C, such as less than about 220°C for a period of time of from about 10 minutes to about 5 hours, such as from about 1 hour to about 4 hours. During drying, any moisture or liquid carriers present during the process can be evaporated and removed.

[0058] In one aspect, when using a polysaccharide binder, the polysaccharide binder can optionally be pre-swelled prior to contact with the silica particles. For instance, the binder can be suspended in boiling deionized water and allowed to swell over a period of time of from about 10 minutes to about 30 minutes. The weight ratio between the binder and the water during swelling can be from about 1 : 1 to about 4: 1 , such as from about 1.2: 1 to about 2: 1 . Through this process, a colloidal gel is formed and can optionally be allowed to cool down to room temperature. Greater quantities of water can be added and homogenized in a blender for later mixing with the silica particles.

[0059] It should be understood that the above process for combining the binder with the silica particles is provided for exemplary purposes only. Any suitableprocess can be used for combining the two components together in order to produce the composite particles. For instance, a particular process can be selected that is better suited for a desired final particle size.

[0060] In accordance with the present disclosure, the binder is combined with the silica particles such that the resulting composite particles contain macropores and / or mesopores. The surface area of the composite particles is generally greater than about 1 m2 / g, such as greater than about 2 m2 / g, such as greater than about 3 m2 / g, such as greater than about 4 m2 / g, and less than about 50 m2 / g.

[0061] The macropores that form in the composite particles can have various different sizes depending upon the binder selected and the manner in which the binder and the silica particles are combined. In one embodiment, when the binder remains in the final product, the composite particles can include macropores having a diameter of from about 100 nm to about 1 ,000 nm. In addition, the particles can display macropores having a diameter of from about 4,000 nm to about 10,000 nm, such as from about 4,000 nm to about 7,000 nm. In one embodiment, the particle can display all different sizes of macropores in which many of the macropores have a diameter of from about 100 nm to about 1 ,000 nm and many of the macropores have a diameter of from about 4,000 nm to about 10,000 nm. For instance, when tested according to ASTM Test D4404-10, the composite particles can display a peak of greater than about 150 mm3g’1nm at a pore size of between about 500 nm and about 1 ,000 nm and / or can display a peak of greater than about 100 mm3g’1nm at a pore size of between about 4,000 nm and about 10,000 nm.

[0062] In one alternative embodiment, the process of making the composite particles can further include the step of removing all or at least a portion of the binder. For example, in one embodiment, the composite particles can be subjected to calcination. In particular, the particles can be heated to a temperature sufficient to combust, volatilize, or otherwise remove the binder from the particles. In one aspect, for instance, the composite particles can be heated to a temperature of greater than about 400°C, such as greater than about 500°C, such as greater than about 600°C, such as greater than about 650°C, and less than about 1 ,200°C, such as less than about 1 ,000°C, such as less than about 800°C. It was unexpectedly discovered that calcining the particles does not weaken thecomposite particles and the composite particles remain intact. In addition, the pore structure as described above remains approximately the same except the larger macropores are removed.

[0063] In particular, calcination can produce composite particles that do not display macropores having a diameter of greater than about 4,000 nm, such as greater than about 5,000 nm, such as greater than about 6,000 nm, such as greater than about 7,000 nm, such as greater than about 8,000 nm. The composite particles, however, continue to display macropores having a diameter of from about 100 nm to about 1 ,000 nm and continue to display mesopores. Thus, calcination can be used to adjust the pore structure of the composite particles depending upon the desired result.

[0064] The resulting composite particles can have any suitable particle size depending upon the end use application. In one embodiment, the average particle size of the composite particles can be greater than about 0.5 mm, such as greater than about 1 mm, such as greater than about 1 .6 mm, and less than about 5 mm, such as less than about 4 mm, such as less than about 3 mm, such as less than about 2.5 mm. In other embodiments, however, larger particles or smaller particles can be formed and used.

[0065] The resulting composite particles can be used in all different types of processes and applications. The particles can be used as a desiccant or drying agent. Alternatively, the particles can be used to absorb or adsorb odors. In one embodiment, the composite particles can be used in an adsorption process, including adsorption and desorption processes. It is believed that the particles, for instance, can display fast kinetic rates than porous particles used in the past in similar processes. By increasing the kinetic rates, the particles can be used to reduce bed sizes in adsorption processes. Higher kinetics also establish better recovery in adsorption / desorption processes. Recovery is proportional to energy consumption because the desorption rate depends on the applied pressure during adsorption. Using the composite particles of the present disclosure with higher kinetic rates allow for the adsorption step to be carried out at lower pressures and using smaller bed sizes. The pressure is then reduced for releasing the adsorbed component. Using lower pressures can significantly increase the cycle times and produce product streams having exceptional purity.

[0066] In one embodiment, for instance, the composite particles of the present disclosure can be used in a pressure swing adsorption process. Pressure swing adsorption processes are used to separate a certain fluid from a mixture of fluids, such as a certain gas from a mixture of gases under pressure. The method relies on the preferential adsorption of specific gas molecules in the mixture onto the composite particles of the present disclosure.

[0067] In a pressure swing adsorption process, a gas mixture is passed through a bed of the adsorbent material, which can comprise the composite particles of the present disclosure at an elevated pressure. Specific gas components can then be adsorbed onto the surface of the composite particles. In one embodiment, for instance, the composite particles can be designed to adsorb carbon dioxide from a gas stream. The non-adsorbed gases pass through the bed and are collected as a product gas. The non-adsorbed gases can include, for instance, nitrogen or hydrogen when removing carbon dioxide.

[0068] Once the adsorbent material or composite particles become saturated with the adsorbed gas, the pressure is reduced. The reduction in pressure causes the adsorbed gases to desorb and be released from the composite particles. The desorbed gases, such as carbon dioxide, are then removed from the system which regenerates the adsorbent material for the next cycle. In accordance with the present disclosure, the desorbed gas stream, in one embodiment, can contain carbon dioxide in an amount greater than about 90% by volume, such as greater than about 95% by volume, such as greater than about 98% by volume, such as greater than about 99% by volume.

[0069] Adsorption processes as described above, such as the pressure swing adsorption process, can provide many benefits and advantages when the adsorbent material is well designed for the particular process. For instance, the process can be used to remove greenhouse gases, such as carbon dioxide, from a gas stream. The composite particles of the present disclosure, for instance, can produce high-purity gases (both exit streams) with relatively low energy consumption. Further, the composite particles of the present disclosure can be used in processes of all different scales from small to large scale operations.

[0070] The present disclosure may be better understood with reference to the following example.Example No. 1

[0071] In this example, two different types of composite particles were made in accordance with the present disclosure and tested.

[0072] Sample No. 1 was comprised of composite particles containing a polysaccharide binder in combination with amorphous micronized silica particles. The silica particles had an average particle size of 7 microns and displayed a pore volume of 0.4 ml / g. The Sample No. 1 composite particles contained a polysaccharide binder in an amount of 4% by weight and the silica particles in an amount of 96% by weight. The polysaccharide binder used was wheat starch that was pre-gelled prior to contact with the silica particles. The composite particles had an average particle size of about 2 mm. The resulting particles were subjected to mercury porosimetry according to ASTM Test D4404-10. The results are shown in FIG. 1. As shown, the resulting composite particles displayed macropores. Two different peaks were present. The first peak of macropores was at a diameter of from about 100 nm to about 1 ,000 nm. A peak occurred of greater than about 200 mm3g’1nm, such as greater than about 250 mm3g’1nm.

[0073] As shown in FIG. 1, another peak occurred corresponding to macropores having a diameter of from about 4,000 nm to about 10,000 nm. As shown, the peak was greater than about 150 mm3g’1nm. FIG. 1 demonstrates that the polysaccharide binder produces particles that provides access to the pore structure of the silica particles contained within the composite particles.

[0074] Sample No. 2 made in accordance with the present disclosure comprised the same silica particles as described in Sample No. 1 . In Sample No. 2, however, a colloidal silica binder was used. The colloidal silica used was LUDOX HS-40 colloidal silica commercially available from W. R. Grace & Co. The colloidal silica contained 40% by weight of silica in suspension. The silica particles had an average diameter of about 12 nm. In order to produce the composite particles, the colloidal silica particles were added in an amount of 15% by weight and the micronized silica particles comprised 85% by weight.

[0075] For purposes of comparison, a silica gel was also tested. The silica gel is a granular material known as silica gel grade 40 commercially available from W. R. Grace & Co (Sample No. 3).

[0076] Sample No. 1 and Sample No. 2 were tested for LOD, tapped bulk density, bead crush strength, CO2 adsorption, and water adsorption. Carbon dioxide adsorption was conducted using a ll-tube glassware setup.

[0077] The following results were obtained:

[0078] The results of carbon dioxide adsorption are also illustrated in FIGS. 2 and 3. FIG. 2 illustrates carbon dioxide adsorption capacity versus adsorption pressure at 25°C for all three samples. FIG 3. illustrates the carbon dioxide adsorption breakthrough profile for all three samples. As shown, Sample Nos. 1 and 2 were comparable to the existing commercial product.Example No. 2

[0079] In this example, composite particles (Sample No. 4) were made in accordance with the present disclosure, calcined, and tested.

[0080] The method used to produce Sample No. 1 was repeated. The composite particles contained a polysaccharide binder in an amount of 4% by weight and silica particles in an amount of 96% by weight. The polysaccharide binder used was wheat starch that was pre-gelled prior to contact with the silica particles. The binder was suspended with boiling deionized water [Ratio 163 g [d. b.] / 100 ml water]. The polysaccharide swelled for 20 minutes. After the colloidal gel had been formed and cooled down to room temperature, the same water quantity was added and homogenized with a blender.

[0081] Granulation was done in an EIRICH Lab-Mixer EL5 PROFI PLUS. During mixing the gelled polysaccharide I water mixture [0.09 kg / 1 .1 kg] was added. Target bead size was 1 .6 - 2.5 mm. After screening to the desired particle size range, the material was dried at a temperature of 200 °C at least for three hours in a furnace.

[0082] After granulation, screening, and drying at 200 °C, Sample No. 4 was placed in a furnace. The beaded silica was heated to 700 °C for over one hour and held at this temperature for an additional hour, ensuring complete combustion ofthe organic binder. The resulting white, pure silica was analyzed for its porosity profile using mercury intrusion. The results are shown in FIG. 4. As shown, calcination not only removed the binder but also produced particles that did not show a peak corresponding to macropores having a diameter of from about 4,000 nm to about 10,000 nm.Example No. 3

[0083] Example No. 2 was repeated except the wheat starch was increased from 4 % to 5 % by weight (Sample No. 5). After granulation, screening, and drying at 200°C, the sample was placed in a furnace. The beaded silica was heated to 700°C for over one hour and held at this temperature for an additional hour, ensuring complete combustion of the organic binder. The resulting white, pure silica was analyzed for its porosity profile using mercury intrusion. The results are shown in FIG. 5. As shown, calcination not only removed the binder but also produced particles that did not show a peak corresponding to macropores having a diameter of from about 4,000 nm to about 10,000 nm.

[0084] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to limit the invention so further described in such appended claims.

Claims

What Is Claimed:1 . A silica composition comprising: a plurality of composite particles, the composite particles comprising silica particles, the silica particles having an average particle size (D50) of less than about 25 microns, the silica particles having a pore volume of greater than about 0.25 ml / g, the silica particles being bound together, the resulting composite particles including macropores that facilitate access to the silica particles when the composite particles are contacted with a fluid.

2. A composite composition as defined in claim 1 , wherein the composite particles are held together by a binder.

3. A composite composition as defined in any of the preceding claims, wherein the composite particles further include mesopores.

4. A silica composition as defined in any of the preceding claims, wherein the composite particles display a surface area of greater than about 2 m2 / g, such as greater than about 3 m2 / g, such as greater than about 4 m2 / g.

5. A silica composition as defined in any of the preceding claims, wherein the macropores on the composite particles comprise macropores having a diameter of from about 100 nm to about 1 ,000 nm.

6. A silica composition as defined in any of the preceding claims, wherein, when tested according to ASTM Test D4404-10, the composite particles display a peak of greater than about 150 mm3g’1nm at a pore size of between about 500 nm and about 1 ,000 nm.

7. A silica composition as defined in any of the preceding claims, wherein the macropores on the composite particles comprise macropores having a diameter of from about 4,000 nm to about 10,000 nm.

8. A silica composition as defined in any of the preceding claims, wherein, when tested according to ASTM Test D4404-10, the composite particles display a peak of greater than about 100 mm3g’1nm at a pore size of between about 4,000 nm and about 10,000 nm.

9. A composite composition as defined in claim 1 , wherein the composite particles have been calcined.

10. A silica composition as defined in any of the preceding claims, wherein, when tested according to ASTM Test D4404-10, the composite particlesdo not display a peak of greater than about 100 mm3g’1nm at a pore size of between about 4,000 nm and about 10,000 nm.

11. A silica composition as defined in any of the preceding claims, wherein the silica particles have an average particle size (D50) of from about 1 micron to about 12 microns, such as from about 5 microns to about 10 microns.

12. A silica composition as defined in any of the preceding claims, wherein the silica particles display a pore volume of from about 0.3 ml / g to about 1 ml / g, such as from about 0.35 ml / g to about 0.75 ml / g.

13. A silica composition as defined in any of the preceding claims, wherein the silica particles display a surface area of greater than about 300 m2 / g, such as greater than about 400 m2 / g, such as greater than about 500 m2 / g, such as greater than about 600 m2 / g, such as greater than about 700 m2 / g, and less than about 900 m2 / g.

14. A silica composition as defined in any of the preceding claims, wherein the composite particles have an average particle size (D50) of from about 0.5 mm to about 5 mm, such as from about 1 mm to about 4 mm, such as from about 1 .6 mm to about 2.5 mm.

15. A silica composition as defined in claim 2, wherein the binder is present in the composite particles in an amount from about 2% by weight to about 15% by weight, such as in an amount from about 2% by weight to about 10% by weight, such as in an amount from about 2.5% by weight to about 7% by weight.

16. A silica composition as defined in claim 2, wherein the binder is present in the composite particles in an amount less than about 0.001% by weight.

17. A silica composition as defined in claim 2, wherein the binder comprises a polysaccharide.

18. A silica composition as defined in claim 2, wherein the binder comprises amylopectin, amylose, or mixtures thereof.

19. A silica composition as defined in claim 2, wherein the binder comprises a colloidal silica.

20. A silica composition as defined in any of the preceding claims, wherein the silica particles comprise micronized silica particles.21 . A silica composition as defined in any of the preceding claims, wherein the silica particles comprise amorphous silica.

22. A process for removing a component from a fluid stream comprising: contacting a fluid stream containing the component with a bed of the composite particles as defined in any of the preceding claims, the component being adsorbed onto the silica particles contained in the composite particles.

23. A process as defined in claim 22, wherein the fluid stream comprises a gas stream.

24. A process as defined in claim 22 or 23, wherein the component that is adsorbed onto the silica particles comprises carbon dioxide.

25. A process as defined in any of claims 22-24, wherein the process comprises a pressure swing adsorption process.

26. A process as defined in any of claims 22-25, further comprising the step of removing the component from the composite particles through desorption and collecting the component.

27. A process for making composite particles containing silica comprising: combining micronized amorphous silica particles with a binder, the silica particles having an average particle size (D50) of less than about 25 microns, the silica particles including micropores and having a pore volume of greater than about 0.25 ml / g, the binder and silica particle mixture being aggregated for forming the composite particles; drying the composite particles at a temperature of from about 100°C to about 300°C; and wherein the formed and dried composite particles include macropores that facilitate access to the silica particles when the composite particles are contacted with a fluid.

28. A process as defined in claim 27, wherein the binder comprises amylopectin, amylose, or mixtures thereof.

29. A process as defined in claim 28, wherein the binder is pre-gelled prior to contact with the silica particles.

30. A process as defined in claim 27, wherein the binder comprises a colloidal silica.31 . A process as defined in claim 27, further comprising the step of calcining the particles to remove the binder.

32. A process as defined in any of claims 27-30, wherein the macropores on the composite particles comprise macropores having a diameter of from about 100 nm to about 1 ,000 nm, wherein the binder is present in the composite particles in an amount from about 2% by weight to about 15% by weight, such as in an amount from about 2% by weight to about 10% by weight, such as in an amount from about 2.5% by weight to about 7% by weight, and wherein the composite particles have an average particle size (D50) of from about 0.5 mm to about 5 mm, such as from about 1 mm to about 4 mm, such as from about 1 .6 mm to about 2.5 mm.

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