Adsorption, storage and separation of solid gases

Abstract

The present invention relates to a method of promoting adsorption of one or more gases by a solid particulate material, the method comprising (i) in the presence of one or more gases maintained at a pressure of at least 300 kPa, (ii) using milling balls and the solid particulate material in a ratio of at least 60: 1 and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm.

Description

Technical Field

[0001] The present invention relates generally to the adsorption, storage and separation of solid gases. More particularly, the present invention relates to a method for promoting the adsorption of solid gases, which in turn can promote gas storage and gas separation. Background Art

[0002] Modern society has a long history of developing gas storage technologies. For example, basic storage of fuel gas dates back to the early 19th century.

[0003] Early gas storage technologies included compressing gas into containers to produce compressed gas or liquefied gas. The compressed storage of gas requires the use of specialized high-pressure containers, but there are still disadvantages such as high cost and safety issues.

[0004] The latest technologies for storing gases include so-called solid-state methods, whereby the gas chemically reacts with or physically adsorbs onto a suitable solid matrix material. While these methods do not suffer from the high-pressure methods, they also have disadvantages.

[0005] For example, the so-called chemical reaction technology is to chemically react the gas to be stored with the adsorbent material to form new substances, such as oxides, nitrides, and hydrides. Although the gas is indeed fully stored, its recovery requires a large amount of energy (such as high temperature) input to promote the reversal of the chemical reaction and the reforming / release of the gas. In addition, the combination of gas and feasible chemical reaction adsorbent materials is limited.

[0006] So-called physical adsorption techniques rely on the gas to form a physical bond with the adsorbent material (e.g., via van der Waals forces). While gases adsorbed in this way can be recovered with less energy input (e.g., lower temperatures), the technique has traditionally tended to offer relatively low storage capacities.

[0007] Often associated with gas storage is the need to separate gas mixtures. For example, in addition to the need to store gas, an important requirement in the petrochemical industry is the separation of gas mixtures. A common method of separating gas mixtures is to use a cryogenic distillation process. However, cryogenic distillation is energy-intensive, and it is reported that this type of industry accounts for up to 15% of global energy consumption.

[0008] Therefore, there remains an opportunity to develop alternative technologies to facilitate the storage and separation of gases that address one or more of the shortcomings associated with cutting-edge technologies. Summary of the invention

[0009] The present invention provides a method for promoting the adsorption of one or more gases by a solid particulate material, the method comprising (i) ball milling the solid particulate material in the presence of one or more gases maintained at a pressure of at least 300 kPa, (ii) using a grinding ball to solid particulate material weight ratio of at least 60:1, and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm.

[0010] While ball milling has long been used as a technique to comminute solid materials and / or promote intimate mixing between two or more different materials, it has now surprisingly been found that ball milling can promote high adsorption capacities of gases onto solid particulate materials when a specific combination of parameters is used for ball milling. 3 / g can be achieved. It has been found that this technology is highly efficient, low cost, environmentally friendly, energy-saving, and particularly suitable for scale-up. According to the unique method of the present invention, solid particulate materials are advantageously processed into excellent solid gas storage materials. In addition, the unique gas adsorption that occurs according to the method of the present invention can be advantageously used to promote the separation of gas mixtures.

[0011] Without wishing to be bound by theory, it is believed that ball milling the solid particulate material using a particular combination of operating parameters subjects the particulate material to a unique, energy-intensive process that results in efficient adsorption of gas molecules onto the solid particulate material. The method of the present invention can advantageously be performed without chemically reacting the gas with the solid particulate material, and thus the gas is not converted into new species, such as oxides, nitrides, or hydrides, etc. Instead, it is believed that the method advantageously promotes one or more forms of non-covalent bonding between the gas and the solid particulate material, thereby achieving gravimetric adsorption capacities approaching those of conventional chemical reaction techniques, with the low energy gas release profiles of conventional physical adsorption techniques.

[0012] Furthermore, a given gas is believed to bind uniquely to a given solid particulate material, meaning that other gases have different binding affinities to the solid particulate material combination. These different binding affinities can in turn be used to facilitate separation of gas mixtures.

[0013] It is noteworthy that the method according to the present invention is not believed to promote chemical reactions between the solid particulate material and the gas in the sense that new molecular species are formed between the gas and the solid particulate material. In other words, the gas molecules processed according to the method of the present invention are believed to remain molecularly intact. Without being limited by theory, it is believed that the ball milling process promotes physical adsorption (e.g., by van der Waals forces) and / or electrostatic / ionic bonding of the gas molecules to the solid particulate material.

[0014] Surprisingly, it has now been found that it is possible to store gases at high capacities and to recover them using relatively low energy (cryogenic) inputs through a solid-state storage technique employing controlled ball milling.

[0015] According to the present invention, adsorption of one or more gases by the solid particulate material is not achieved by chemical reaction or covalent bond formation between the one or more gases and the solid particulate material.

[0016] Thus, the combinations of gas and solid particulate material contemplated for use in accordance with the present invention are not intended to include combinations that inherently undergo chemical reactions (such as the combination of metal and hydrogen).

[0017] Therefore, the present invention can also be described as a method for promoting the adsorption of one or more gases by a solid particulate material without chemical reaction between the one or more gases and the solid particulate material, the method comprising (i) ball milling the solid particulate material in the presence of one or more gases maintained at a pressure of at least 300 kPa, (ii) using a grinding ball to solid particulate material weight ratio of at least 60:1 and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm.

[0018] The present invention can also be described as a method for promoting non-covalent adsorption of one or more gases by a solid particulate material, the method comprising (i) ball milling the solid particulate material in the presence of one or more gases maintained at a pressure of at least 300 kPa, (ii) using a weight ratio of grinding balls to solid particulate material of at least 60:1 and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm.

[0019] "Non-covalent" adsorption refers to the adsorption of one or more gases onto a solid particulate material by a bonding mechanism other than covalent bond formation. In this case, the molecules of the gas remain intact.

[0020] Suitable solid particulate materials for use in accordance with the present invention include, but are not limited to, crystalline materials having a layered structure, such as boron nitride, graphite, and transition metal dichalcogenides, such as molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, and molybdenum ditelluride, as well as non-layered materials, such as boron, iron, and silicon.

[0021] In one embodiment, the solid particulate material is selected from the group consisting of boron nitride, graphite, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, molybdenum ditelluride, boron, iron, and silicon.

[0022] In another embodiment, the solid particulate material is selected from the group consisting of boron nitride, graphite, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, and molybdenum ditelluride.

[0023] In yet another embodiment, the one or more gases are selected from hydrogen, carbon dioxide, carbon monoxide, C1-C4 hydrocarbons, ammonia, nitric oxide, nitrogen dioxide, sulfur dioxide and nitrogen.

[0024] In another embodiment, the solid particulate material produced as a product from ball milling has one or more gases adsorbed thereon, and the product is contained in a container to store the one or more gases.

[0025] The present invention also provides a method for solid-state storage of one or more gases, which comprises ball milling the solid particulate material described herein, wherein the solid particulate material produced as a product by the method adsorbs one or more gases, and the product is placed in a container to store the one or more gases.

[0026] The product contained in the container may be processed to release the gas or gases adsorbed on the solid particulate material, thereby recovering the stored gas or gases.

[0027] The one or more gases may also be described as being non-covalently bound to the solid particulate material.

[0028] According to the present invention, the unique and differential adsorption of gases by solid particulate materials advantageously enables separation of gas mixtures.

[0029] In one embodiment, ball milling is performed in the presence of a mixture of two or more gases, and the solid particulate material produced as a product by ball milling is adsorbed with the gas mixture, and the product is processed to selectively release at least one adsorbed gas from the solid particulate material, thereby separating the released gas from the mixture of two or more gases.

[0030] The present invention also provides a method for separating a mixture of two or more gases, which method comprises ball milling the solid particulate material described herein, wherein the solid particulate material produced as a product by ball milling adsorbs the mixture of two or more gases, and the product is processed to selectively release at least one adsorbed gas from the solid particulate material, thereby separating the released gas from the mixture of two or more gases.

[0031] In one embodiment, a solid particulate material product having adsorbed thereon a mixture of two or more gases is processed by increasing the temperature of the solid particulate material to selectively release at least one adsorbed gas from the solid particulate material.

[0032] In a further embodiment, ball milling is performed in the presence of a mixture of two or more gases, and the solid particulate material produced as a product by ball milling (i) adsorbs at least one gas in the gas mixture, and (ii) does not adsorb at least one gas in the gas mixture, thereby separating the at least one gas that is not adsorbed from the mixture of two or more gases.

[0033] The present invention also provides a method for separating a mixture of two or more gases, the method comprising ball milling the solid particulate material described herein, wherein the solid particulate material produced as a product by ball milling (i) adsorbs at least one gas in the gas mixture, and (ii) does not adsorb at least one gas in the gas mixture, thereby separating the at least one gas that is not adsorbed from the mixture of two or more gases.

[0034] Other aspects and features of the invention are discussed in greater detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the present invention will now be described with reference to the following non-limiting drawings, in which:

[0036] Figure 1 .Schematic diagram showing the high energy ball milling effect of the high energy ball mill used.

[0037] Figure 2. Gas adsorption capacity: (a) Hydrocarbon gas pressure reduction during ball milling; (b) Corresponding gas weight uptake as a function of ball milling time. (c) Weight capacity of BN for C2H4 as a function of milling time and intensity (as shown in the figure, the weight ratio of grinding balls to BN is different). (d) Maximum weight uptake of various gases after ball milling BN for 20 hours. (e) Absorption capacity of various materials for carbon dioxide.

[0038] Figure 3 Maximum adsorption capacity of 1 g BN: a) pressure drop curve, b) gravimetric capacity of 1 g BN ground in C2H4.

[0039] Figure 4. Gas mixture separation: (a) g-FTIR spectra of the starting C2H2 / CH4 mixture and the remaining gas after 2 h of grinding. (b) g-FTIR spectra of pure C2H4 and pure C2H6, the starting C2H4 / C2H6 gas mixture (volume ratio of 20:80) and the remaining gas after 2 h and 4 h of grinding. (c) g-FTIR spectra of the starting CO2 / CH4 mixture and the remaining gas after 2.5 h and 5 h. (d) Gas chromatogram of the starting CO2 / N2 gas mixture and the remaining gas after 2.5 h and 5 h.

[0040] Figure 5 .(a) FTIR spectra of BN after grinding for 2 h in CH4 (i) and C2H2 (ii) and C2H2+CH4 gas mixture (iii) (b) FTIR spectra of BN after grinding for 2 h in a gas mixture (C2H4 (20 vol%) + C2H6 (80 vol%)) (i), and analysis of gas released from the ground BN after heating to 550°C using a STA-FTIR coupled system (ii).

[0041] Figure 6. (a) FTIR spectra of the starting BN powder and BN samples after various grinding and heating treatments in C2H4. (b) Full FTIR spectra of BN ground in different hydrocarbon gases. The zoomed-in FTIR spectra show the fingerprint range of hydrocarbon molecules.

[0042] Figure 7 Pressure drop during grinding of (1) fresh BN and (2-3) heated BN in C2H4 (repeated three cycles).

[0043] Figure 8. Nitrogen isotherms of BN ground in C2H4 (a) and CH4 (b); (c) BET surface area of ​​BN ground in two gases (C2H4, CH4) as a function of grinding time.

[0044] Figure 9. Gas adsorption mechanism analysis: (a) SEM images and XRD patterns of BN samples milled in C2H4 and CH4. (b) TGA curves of BN samples milled in C2H4 and CH4. B 1s, N 1s, and C1s XPS spectra of BN samples milled in C2H4 (c, d, e) and CH4 (f, g, h).

[0045] Fig.10 TEM images of BN milled in C2H4 (a) and CH4 (b); Inset: SAED patterns.

[0046] Fig.11 .C2H4 gas absorption performance of hBN with different sizes.

[0047] Fig.12 .C2H4 gas absorption performance of hBN with different sizes.

[0048] Fig.13 (a) Schematic diagram of the ball milling and heating separation process of a mixture containing a single olefin gas and a single alkane gas. (b) Proposed separation of olefin gas and alkane gas by combining ball milling with heating.

[0049] The invention is further described with reference to the following non-limiting examples. DETAILED DESCRIPTION

[0050] The present invention provides a method for promoting the adsorption of one or more gases by a solid particulate material.

[0051] One or more gases undergoing "adsorption" or being adsorbed onto a solid particulate material refers to the gas molecules that make up the one or more gases being bound or adhered to the solid particulate material. In other words, the gas molecules remain molecularly intact and adhere to the solid particulate material without chemically reacting. Without being limited by theory, it is believed that the unique energy-intensive milling process operated in accordance with the present invention promotes physical adsorption and / or electrostatic / ionic bonding of gas molecules to the solid particulate material.

[0052] Thus, reference herein to one or more gases being associated with or adhered to a solid particulate material is intended to mean that the one or more gases are adsorbed on the solid particles.

[0053] It is believed that the method according to the present invention does not promote chemical reactions between the gas molecules and the solid particulate material and does not form covalent bonds.

[0054] Therefore, the method according to the present invention is intended to exclude the use of solid particulate material which chemically reacts with the gas or gases to form covalent bonds between the gas or gases molecules and the solid particulate material.

[0055] In view of the requirement of non-chemical reaction, there is no particular limitation on the gases that can be used according to the present invention. Suitable gases also include those that can or cannot be adsorbed on solid particulate materials. As will be discussed in more detail below, although the present invention must be carried out using at least one gas that adsorbs on solid particulate materials, gases that do not adsorb on solid particulate materials can be used to facilitate the separation of gas mixtures.

[0056] According to the present invention, the affinity of a given gas for adsorption to a solid particulate material depends not only on the properties of the particular gas, but also on the properties of the solid particulate material. A guide to the adsorption affinities of various gases for various solid particulate materials is outlined below. Furthermore, the adsorption affinities of such gases for solid particulate materials can be readily determined experimentally.

[0057] Examples of suitable gases that may be used in accordance with the present invention include, but are not limited to, hydrogen, carbon monoxide, carbon dioxide, C1-C4 hydrocarbons, nitric oxide, nitrogen dioxide, sulfur dioxide, ammonia, and nitrogen.

[0058] Examples of suitable C1-C4 hydrocarbons, such as C1-C2 hydrocarbons and C1-C3 hydrocarbons, include but are not limited to CH4, C2H2, C2H4, C2H6, C3H6, C3H8, C4H8 and C4H 10 .

[0059] There are no particular limitations on the solid particulate materials useful in the present invention, provided that (i) they can adsorb at least one gas, and (ii) do not chemically react with the gas or gases to form covalent bonds between the gas or gases and the solid particulate material.

[0060] The solid particulate material may take any shape, for example it may be in the form of substantially spherical particles, flake-like particles, fibres and rod-like / wire-like particles.

[0061] Examples of suitable materials for the solid particulate material may be derived from, including but not limited to, crystalline materials having a layered structure, such as boron nitride, graphite, and transition metal dichalcogenides, such as molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, and molybdenum ditelluride, and non-layered materials, such as boron, iron, and silicon.

[0062] The ball milling method according to the present invention essentially comminutes the solid particulate material and increases its surface area. As long as the solid particulate material can be properly ball milled, there is no particular limitation on the size of the particulate material that can be used.

[0063] Generally, the average particle size of the solid particulate material prior to ball milling is from about 1 μm to about 5 mm.

[0064] Generally, the average particle size of the solid particulate material after ball milling is from about 10 nm to about 100 μm.

[0065] An important feature of the present invention is the application of ball milling.

[0066] Using a specific combination of operating parameters, the present invention can be advantageously practiced using conventional ball milling equipment.

[0067] Suitable ball milling equipment includes, but is not limited to, planetary ball mills, horizontal ball mills, and vertical ball mills.

[0068] Those skilled in the art will appreciate that ball milling equipment includes a grinding vessel / jar and grinding balls. There are no particular restrictions on the materials of the grinding vessel and grinding balls, as long as they can withstand the operating parameters and are substantially inert to the reagents being processed.

[0069] Suitable grinding vessels include, but are not limited to, vessels made from stainless steel, zirconia, nylon, polytetrafluoroethylene, and agate.

[0070] Suitable grinding balls include, but are not limited to, grinding balls made from silicon carbide, stainless steel, hardened steel, zirconium oxide, and agate.

[0071] The size of the grinding vessel and grinding balls used can be easily adapted by a person skilled in the art to the scale of operation.The present invention can be advantageously carried out on a laboratory, pilot scale and industrial scale.

[0072] In one embodiment, the grinding container has a volume of about 25 ml to about 1000L.

[0073] Those skilled in the art will be readily able to select the size of the grinding balls to suit the task at hand, including consideration of the volume of the grinding vessel and the desired ratio of grinding balls to solid particulate material (as described below).

[0074] In one embodiment, the grinding balls have a diameter of about 1 mm to about 200 mm.

[0075] At least three combinations of ball milling operating parameters are required to promote the desired adsorption of one or more gases onto the solid particulate material.

[0076] According to the present invention, the solid particulate material is ball milled (i.e., subjected to ball milling) in the presence of one or more gases maintained at a pressure of at least 300 kPa. In other words, in order to promote the desired adsorption of the one or more gases, the ball milling is carried out in an atmosphere of one or more gases at a pressure of at least 300 kPa. If desired, gas can be introduced into the ball mill during operation to maintain the desired pressure.

[0077] In one embodiment, the pressure of the one or more gases is maintained at at least about 400 kPa, 500 kPa, 600 kPa, 700 kPa, or 800 kPa.

[0078] In further embodiments, the pressure of the one or more gases is maintained at least about 300 kPa to about 30,000 kPa, 400 kPa to about 30,000 kPa, 500 kPa to about 30,000 kPa, 600 kPa to about 30,000 kPa, 700 kPa to about 30,000 kPa, or 800 kPa to about 30,000 kPa.

[0079] One or more gases may be introduced into the ball milling apparatus to provide the desired pressure using techniques known in the art.

[0080] As the ball milling operation proceeds, the gas pressure in the ball milling apparatus will typically decrease gradually as one or more gases undergo adsorption onto the solid particulate material. The gas pressure can be easily monitored and re-pressurized to at least 300 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa or 800 kPa as needed.

[0081] According to the present invention, the solid particulate material is ball milled using a weight ratio of grinding balls to solid particulate material of at least 60: 1. The required weight ratio can be readily determined using conventional gravimetric measuring equipment.

[0082] In one embodiment, the weight ratio of grinding balls to solid particulate material is at least about 70:1 or about 80:1 or about 90:1 or about 100:1 or about 120:1 or about 150:1.

[0083] In one embodiment, the weight ratio of grinding balls to solid particulate material is at least 60:1 to about 300:1, e.g., about 70:1 to about 300:1, or about 80:1 to about 300:1, or about 90:1 to about 300:1, or about 100:1 to about 300:1, or about 120:1 to about 300:1, or about 150:1 to about 300:1.

[0084] When considering the weight ratio of grinding balls to solid particulate material, the volume of the grinding container and the number of grinding balls also need to be considered to ensure that sufficient space is left in the grinding container to promote the strong energy impact of the grinding balls on the solid particulate material. Generally, the size of the grinding balls will be selected to provide the desired weight ratio of grinding balls to solid particulate material so that about 4 to about 20 grinding balls are used.

[0085] In one embodiment, from about 4 to about 20 grinding balls are used.

[0086] According to the present invention, the solid particulate material is ball milled in the presence of one or more gases at an operating speed of at least 200 rpm.

[0087] In one embodiment, the operating speed is at least about 250 rpm, or at least about 300 rpm, or at least about 400 rpm, or at least about 600 rpm.

[0088] In one embodiment, the operating speed is at least 200 rpm to about 600 rpm, such as about 250 rpm to about 600 rpm or about 300 rpm to about 600 rpm or about 400 rpm to about 600 rpm.

[0089] While ball milling has long been used as a technique for comminuting solid materials and / or promoting intimate mixing between two or more different materials, it has now surprisingly been found that, when ball milling is performed using a specific set of milling parameters, ball milling produces milling energy that promotes adsorption of gases onto solid particulate materials at high capacities. The technique has been found to be efficient, low cost, energy efficient, and particularly suitable for scale-up. By promoting excellent gravimetric adsorption capacity, the gas-adsorbed solid particulate material product produced in accordance with the present invention can be used as an excellent solid-state gas storage material. The product has been found to be advantageously stable at room temperature and pressure, i.e., the bound gas or gases can remain bound to the solid particulate material at room temperature (i.e., about 25°C) and room pressure (i.e., about 1 atmosphere).

[0090] Without being limited by theory, it is believed that a particular combination of ball mill operating parameters causes the particulate material to undergo a unique energy-intensive process whereby gas molecules are physically adsorbed and / or electrostatically bound to the solid particulate material. It is believed that this adsorption process advantageously causes a given type of gas molecule to uniquely bind to a given solid particulate material, meaning that the binding affinities of other gas and solid particulate material combinations are different. As discussed in more detail below, these different binding affinities can in turn be used to facilitate the separation of gas mixtures.

[0091] The method according to the invention can advantageously produce 3 / g or at least 400cm 3 / g or at least 500cm 3 / g or at least 600cm 3 / g or at least 700cm 3 / g or at least 800cm 3 / g or at least 900cm 3 / g or at least 1000cm 3 / g or at least 1100cm 3 / g or at least 1200cm 3 / g or at least 1300cm 3 / g or at least 1400cm 3 / g or at least 1500cm 3 / g of gas adsorption weight capacity of solid particulate material as the product.

[0092] According to the process of the present invention, the adsorption weight capacity of the product can vary depending on the nature of the gas and solid particulate material. Despite such variations, it has been found that the process advantageously provides a substantially higher adsorption weight capacity for a given gas and solid particulate material combination relative to values ​​obtained with conventional techniques.

[0093] For example, the present invention can provide a boron nitride solid particulate material having an adsorption weight capacity for CH4 of at least 580 cm 3 / g, and the adsorption weight capacity for C2H2 is at least 300cm 3 / g or 400cm 3 / g or 500cm 3 / g or 600cm 3 / g or 700cm 3 / g, and the adsorption weight capacity for C2H4 is at least 200 cm 3 / g or 400cm 3 / g or 600cm 3 / g or 800cm 3 / g or 1000cm 3 / g, and the adsorption weight capacity for C2H6 is at least 200 cm 3 / g or 300cm 3 / g or 400cm 3 / g or 500cm 3 / g or 600cm 3 / g, and the adsorption weight capacity for CO2 is at least 800 cm 3 / g or 900cm 3 / g or 1000cm 3 / g or 1100cm 3 / g or 1200cm 3 / g, and the adsorption weight capacity for NH3 is 400cm 3 / g or at least 500cm 3 / g or at least 600cm 3 / g, and the adsorption weight capacity for H2 is 1300cm 3 / g、1400cm 3 / g or 1500cm 3 / g.

[0094] The adsorption gravimetric capacity or simply gravimetric capacity referred to herein is a measured parameter of the solid particulate material ball-milled according to the present invention and is determined according to Formula 1:

[0095]

[0096] Where n is the number of moles, P is the pressure, V is the volume of the mill container, R is the gas constant 8.314, and T is the temperature. Convert the number of moles to liters and then divide by the number of grams of solid particulate material used in the ball mill.

[0097] It has been found that the measured adsorption weight capacity of a given solid particulate material and gas combination increases with increasing ball milling time. However, the solid particulate material eventually reaches a saturation point beyond which further ball milling time does not significantly increase its weight capacity. That is, in addition to providing a higher weight capacity than conventional methods overall, for a given ball milling period, the method according to the present invention also advantageously produces a solid particulate material with a higher weight capacity than conventional methods.

[0098] The amount of time required to perform the ball milling may vary depending upon the nature of the solid particulate material and the gas or gases, and whether the goal is to achieve the saturated adsorption weight capacity of the solid particulate material.

[0099] Typically, ball milling will be performed over a period of time from about 2 hours to about 30 hours.

[0100] In one embodiment, the one or more gases are maintained at a pressure of at least 300 kPa for at least 2 hours, or at least 3 hours, or at least 4 hours, 5 hours, 6 hours, or at least 10 hours, or at least 15 hours, or at least 20 hours, at least 25 hours, or at least 30 hours.

[0101] A particular advantage of the present invention is that not only can a higher adsorption weight capacity be achieved with the present invention relative to the use of conventional techniques, but the higher adsorption weight capacity can be achieved in a shorter period of time than with conventional techniques.

[0102] Since the gas adsorption product produced according to the present invention is stable at room temperature and pressure, in that the bound gas or gases can remain bound to the solid particulate material at room temperature (i.e., about 25° C.) and room temperature (i.e., about 1 atmosphere), the product so formed is particularly suitable for use as a gas storage medium. The solid particulate material product so formed has one or more gases bound thereto, and the product can be easily contained in a container to store the one or more gases.

[0103] Therefore, the present invention also provides a method for solid-state storage of one or more gases, which comprises (i) ball milling the solid particulate material in the presence of one or more gases maintained at a pressure of at least 300 kPa, (ii) using a ratio of grinding balls to solid particulate material of at least 60:1, and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm, wherein the solid particulate material produced as a product by the method has adsorbed one or more gases, and the product is contained in a container for storing the one or more gases.

[0104] Due to the aforementioned stability of the product produced according to the present invention, there is no particular limitation on the type of container that may be used to contain the product and thereby store one or more gases.

[0105] However, if the storage vessel is also to be used as a vessel for releasing one or more bound gases from the solid particulate material (eg for gas recovery), then the vessel may require certain characteristics to make it suitable for the release process.

[0106] Despite the aforementioned stability of the product produced according to the present invention, the adsorbed one or more gases can still be easily released from the solid particulate material. For example, by simply applying heat to the solid particulate material adsorbing the gas, the one or more gases adsorbed on the solid particulate material can be released therefrom. Since the one or more gases are not covalently bound to the solid particulate material, the gas adsorbed on the solid particulate material can be released using relatively low energy input.

[0107] In one embodiment, the product contained in the container is heated to release one or more gases adsorbed on the solid particulate material.

[0108] The product contained in the container can be heated to a temperature of about 50°C to about 500°C to facilitate the release of one or more gases adsorbed on the solid particulate material.

[0109] According to the present invention, the unique and differential adsorption of gases on the solid particulate material advantageously enables the separation of gas mixtures.

[0110] When the method according to the present invention involves the adsorption of two or more gases, those gases have different binding affinities for the solid particulate material. Specifically, while each gas will be adsorbed by the solid particulate material, at least one gas has a stronger binding affinity for the solid particulate material than another gas. For example, it has been found that boron nitride exhibits the following adsorption affinities: CH4 < C2H6 < C2H4 < C2H2, which indicates that boron nitride has a stronger adsorption affinity for olefin gases (C2H2 and C2H4) than for alkane gases (CH4 and C2H6). This difference in binding affinity enables the selective release of a gas from the solid particulate material, and the practical effect advantageously enables the selectively released gas to be separated from the gas mixture adsorbed on the solid particulate material.

[0111] The selective release of a given gas from the solid particulate material can be readily achieved simply by subjecting the solid particulate material to one or more processing steps. Such processing steps can include heating the solid particulate material as described herein. For the purpose of selectively releasing a specific gas species, any given heating adjustment for promoting gas release may need to be carried out in a controlled manner compared to the overall release of all adsorbed gas species. A person skilled in the art can readily carry out such controlled heating adjustment to facilitate the selective release of gas from the solid particulate material.

[0112] In the context of the present invention, "separating out" one or more gases from a gas mixture means that one or more gases are adsorbed by the solid particulate material while one or more other gases are not adsorbed by the solid particulate material. In other words, the one or more gases adsorbed by the solid particulate material actually form part of the solid state, while the one or more gases not adsorbed by the solid particulate material remain in the gaseous state. The combination and non-combination of these gas species result in a separated state of the gases.

[0113] In one embodiment, ball milling is performed in the presence of a mixture of two or more gases, and the solid particulate material produced as a product by ball milling is adsorbed with the gas mixture, and the product is processed to selectively release at least one adsorbed gas from the solid particulate material, thereby separating the released gas from the mixture of two or more gases.

[0114] Therefore, the present invention also provides a method for separating a mixture of two or more gases, which method comprises (i) ball milling the solid particulate material in the presence of a mixture of two or more gases maintained at a pressure of at least 300 kPa, (ii) using a ratio of grinding balls to solid particulate material of at least 60:1, and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm, wherein the solid particulate material as a product produced by the ball milling adsorbs the mixture of two or more gases, and processing the product to selectively release at least one adsorbed gas from the solid particulate material, thereby separating the released gas from the mixture of two or more gases.

[0115] Advantageously, the energy input required to facilitate the separation of one or more gases from the solid particulate material having adsorbed thereon is much lower than conventional methods for separating gases, such as cryogenic distillation.

[0116] Although the practice of the invention is based on the adsorption of one or more gases by a solid particulate material, the invention also exploits the fact that one or more gases are not adsorbed or have low adsorption kinetics on the solid particulate material and are therefore not adsorbed by the solid particulate material.

[0117] For example, when a mixture of two or more gases used in accordance with the present invention contains a gas that has little or no adsorption affinity for a solid particulate material, carrying out the process of the present invention will inherently facilitate separation of the gas mixture because that gas is not adsorbed by the solid particulate material, whereas the remaining gas or gases are adsorbed by the solid particulate material. In such a case, separation of the gases can be achieved by simply carrying out the process of the present invention without the need to perform a dedicated gas release step.

[0118] In one embodiment, ball milling is performed in the presence of a mixture of two or more gases, and the solid particulate material produced as a product by ball milling (i) adsorbs at least one gas in the gas mixture, and (ii) does not adsorb at least one gas in the gas mixture, thereby separating the at least one gas that is not adsorbed from the mixture of two or more gases.

[0119] The present invention also provides a method for separating a mixture of two or more gases, the method comprising (i) ball milling the solid particulate material in the presence of a mixture of two or more gases maintained at a pressure of at least 300 kPa, (ii) using a ratio of grinding balls to solid particulate material of at least 60:1, and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm, wherein the solid particulate material produced as a product by ball milling (i) adsorbs at least one gas in the gas mixture, and (ii) does not adsorb at least one gas in the gas mixture, thereby separating the at least one gas that is not adsorbed from the mixture of two or more gases.

[0120] In one embodiment, the method according to the present invention is used to separate CH4 from C2H2, or to separate C2H2 from C2H6, or to separate CO2 from CH4, or to separate CO2 from N2, or to separate H2 from N2, or to separate H2 from CH4, or to separate C2H2 from C2H6, or to separate C2H4 from CH4, or to separate H2 from NH3.

[0121] Example

[0122] Example 1 - Ball Milling, Materials and Gases

[0123] Hexagonal boron nitride (BN) powder (PT110 grade, purity 99%, particle size ~20 μm) was purchased from Momentive Performance Materials Inc. Graphite (particle size ~15 μm), iron (particle size ~85 μm), boron (particle size ~5 mm), MoS2 (particle size ~6 μm), and silicon (particle size ~2 mm) were purchased from Sigma Aldrich.

[0124] The hydrocarbon gases include acetylene (C2H2), ethylene (C2H4), ethane (C2H6), methane (CH4), ammonia (NH3), hydrogen (H2), carbon dioxide (CO2), and nitrogen (N2) with a purity of 99.99%, purchased from Coregas Pty Ltd, Australia.

[0125] The example uses a vertical planetary ball mill ( Figure 1 ). The grinding jar / grinding vessel has a pressure valve that allows the atmosphere to be controlled. The air pressure is measured by a barometer attached to the jar. In each experiment, the jar is loaded with 2 g to 4 g of material. The jar is then evacuated, purged three times with argon, and finally filled with the target gas or gases at a starting pressure of 400 kPa. The ball mill is rotated at a speed of 160 rpm to 600 rpm.

[0126] Example 2 - Characterization

[0127] After ball milling, the gas-adsorbed solid particle material samples were collected in an argon-filled glove box and stored. For FTIR and TGA experiments, a small amount of sample was taken out of the glove box and tested immediately to avoid contamination.

[0128] The sample morphology was examined using a scanning electron microscope (SEM) with a Hitachi S4500 Zeiss Supra 55VP instrument, operating at 3 kV to 10 kV.

[0129] Thermogravimetric analysis (TGA) was performed using a TA Q50 instrument under 40 ml / min argon flow. The heating rate was 25°C / min.

[0130] The crystal structure of the samples was investigated using X-ray diffraction (XRD) with a PANalytical X'pert powder system (Cu Ka radiation λ = 0.15418 nm), operated at 40 kV with a current of 30 mA.

[0131] For the BET nitrogen adsorption isotherm, the samples were degassed at 110 °C for 4 hours to clean the surface before BET analysis. The pore size distribution was calculated by Barrett-Joyner-Halenda (BJH) desorption. The ball-milled BN samples were heated to 700 °C in a tube furnace and argon atmosphere at a heating rate of 25 °C / min to remove the adsorbed gas molecules. These samples were further used for BET tests.

[0132] The chemical composition of the various samples was studied on a Thermo Scientific K-Alpha instrument (monochromatic Al Kα radiation). The binding energy (BE), i.e., core level and valence band maximum, was corrected in each case using an internal reference peak of the C1s peak centered at 284.5 eV. The core level spectra have been deconvoluted using Thermo Advantage software.

[0133] Fourier transform infrared spectroscopy (FTIR) was used to examine gas molecules. Powder samples were tested using a Bruker Vertex 70 infrared spectrometer in attenuated total reflection mode. Gas samples were analyzed using two different FTIR systems: (1) A Perkin Elmer (Spectrometer Model 100) FTIR system connected to a gas chamber was used to analyze gas samples. The collection resolution was 1 cm -1 4000cm -1 Up to 600cm -1(2) The gases released from the ground BN samples by heat treatment were examined using a combined simultaneous thermal analysis-Fourier transform infrared spectroscopy (STA-FTIR), Perkin Elmer STA 8000 and PerkinElmer Frontier FTIR system via a transfer line connection implemented using a TL9000 interface. The measurements were carried out using about 5 mg of ground material, heated from 30°C to 600°C at a heating rate of 25°C / min. The released gases were immediately transferred to the STA-FTIR via a transfer line (balanced flow escaping gas analyzer, TL9000). The resolution was 4 cm -1 Under, collected at 4000cm -1 Up to 600cm -1 FTIR data in the range.

[0134] Example 3 - Gas Storage / Gas Absorption

[0135] In the absence of grinding, the gas is not adsorbed by the BN powder and no pressure change is observed. Once grinding begins, a significant pressure drop due to gas adsorption is observed, as shown in Figure 2a. In a closed grinding reactor, the pressure of the alkyne gas acetylene (C2H2) dropped from 400 kPa to 20 kPa within 20 hours, indicating that almost all C2H2 gas has been adsorbed by BN. For the olefin gas ethylene (C2H2), the pressure dropped to 95 kPa after 20 hours of ball milling under the same conditions. A relatively slow pressure drop was recorded for the two alkane gases (CH4 and C2H6).

[0136] Figure 2b The weight capacity corresponding to the gas adsorption of four hydrocarbon gases is shown as a function of grinding time. After 20 hours of continuous grinding, BN powder adsorbed 282 cm 3 / g C2H2 and 228cm 3 / g C2H4. The absorption capacity for alkane gases (ethane and methane) is lower: ethane (C2H6) is 188cm 3 / g, methane (CH4) is 152cm 3 / g. Figure 2b The capacity curve showed no flattening within 20 h, indicating that the gas adsorption did not reach saturation after 20 h.

[0137] With further grinding, gas adsorption continued at a reduced adsorption rate due to the decrease in gas pressure in the sealed grinding reactor (Figure 2a).

[0138] To maintain a high adsorption rate, the grinding reactor was refilled with fresh gas (to at least 400 kPa) every five hours during the grinding process.

[0139] When refilled with C2H4 at 5, 10, and 15 h, a higher C2H4 adsorption capacity (412 cm 3 / g) (Figure 2c(i)). The adsorption rate was further improved by increasing the grinding intensity by changing the weight ratio of grinding balls to BN. Higher grinding intensity can provide more energy to BN and accelerate the reaction kinetics during grinding. When the weight ratio increased from 65:1 to 81:1 and 130:1, the adsorption capacity after 20 hours increased to 585 cm 3 / g and 730cm 3 / g, (ii) and (iii) of Figure 2c.

[0140] Prolonging the grinding treatment time can also increase adsorption. For example, extending the grinding in C2H4 gas to 30 hours, the adsorption capacity reached 1048 cm 3 / g (Figure 2c(iii)). Even under mild grinding conditions (i.e., grinding for 20 h at a weight ratio of 130:1), the three-gas refilling grinding process produced 708 cm 3 / g absorption capacity ( Figure 2d After 20 hours of grinding, the total adsorption of CH4 was 564 cm 3 / g. The absorption capacity of C2H6 is 600cm 3 The curve in Figure 2c shows that the C2H4 gas adsorption maintains a high adsorption rate and has not reached saturation after 30 hours.

[0141] If the starting BN is reduced to 1 g, 534.9 cm 3 / g of saturated gas adsorption ( Figure 3 ).

[0142] Therefore, the adsorption capacity is considered to be dependent on the adsorption test conditions (i.e., gas pressure, BN, grinding intensity, and time). Even under average ball milling conditions (e.g., 4 g BN, milled in sufficient gas for 20 h), BN nanosheets achieved an uptake capacity higher than all other materials for olefins and alkynes, ammonia, hydrogen, and carbon dioxide gases. Refilling the gas to 400 kPa every 5 h until the total milling time reached 20 h further enhanced the gas storage. BN storage ( Figure 2d )838.5cm 3 / gCO2,730.1cm 3 / g of C2H4, 708.4cm 3 / g C2H2,600cm 3 / g of C2H6, 592.7cm 3 / g NH3, and 563.8cm3 CH4 at 620 cm / g 3 H2 at / g. It is worth noting that the weight capacities of these gases are not yet saturated, and more gas can be stored by extending the grinding time or fine-tuning the ball-milling parameters. In addition, various materials have also been used to store carbon dioxide ( Figure 2e ).

[0143] Under the same grinding conditions, the adsorption rates of the different gases studied vary ( Figure 2b ). The highest adsorption rate observed was 21.6 cm for C2H2 3 g -1 h -1 , nearly three times that of CH4 (7.2 cm 3 g -1 h -1 ). The trend of adsorption capacity is CH4 < C2H6 < C2H4 < C2H2, indicating that BN shows a stronger affinity for olefin gases (C2H2 and C2H4) than for alkane gases (CH4 and C2H6). These large differences in adsorption capacity and adsorption rate for hydrocarbon gases suggest that they can be separated by selective adsorption on BN under controlled grinding conditions. In addition, the ball-milling process should be applicable to separating other gas groups with different adsorption rates.

[0144] Example 4 - Separation of various gas mixtures

[0145] This example demonstrates the separation of the following gas mixtures, including C2H2 / CH4; C2H4 / C2H6; CO2 / N2; CO2 / CH4.

[0146] High-purity CH4 gas is considered a relatively clean fuel and an important raw material for producing various chemicals; small amounts of C2H2 often occur simultaneously with CH4, so C2H2 needs to be removed. To test the capacity of this method to separate such gases, a mixture of C2H2 (20 vol%) and CH4 (80 vol%) was added to a grinding reactor at 410 kPa containing 4 g of BN and 4 grinding balls. After grinding for 2 hours at a weight ratio of 65:1, the pressure of the gas mixture dropped to 350 kPa, indicating that gas adsorption had occurred. The remaining gas in the grinding reactor was collected in a gas chamber and analyzed by gas-phase FTIR (g-FTIR).

[0147] The g-FTIR spectrum of the initial gas mixture (Figure 4a(i)) showed the presence of both gases, but only CH4 was detected in the remaining gas after 2 hours of grinding (Figure 4a(ii)). The spectral results after 4 hours of grinding confirmed that C2H2 had been completely removed from the gas mixture. The adsorption of C2H2 on the ground BN was confirmed by FTIR analysis ( Figure 5a). Longer milling time is required to remove higher concentrations of C2H2.

[0148] For a mixture containing 30 vol% C2H2 and 70 vol% CH4, at least 4 hours of grinding is required to completely remove C2H2 from the gas mixture, with a pressure drop of 90 kPa. After 2 hours of grinding, the g-FTIR spectrum of the remaining gas (Figure 4a (iii)) shows that both gases are present, but only CH4 is detected in the FTIR spectrum of the remaining gas after 4 hours of grinding (Figure 4a (iv)). This process can also be applied to separate C2H4 and C2H6, which is another industrial product that needs to be purified.

[0149] BN powder was ground in the presence of C2H4 (20 vol%) and C2H6 (80 vol%). After 2 h of grinding, a pressure drop of 60 kPa was observed. The g-FTIR spectrum of the gas mixture after 2 h of grinding ( Figure 4b (iv)) and g-FTIR spectra of individual gases and initial gas mixtures ( Figure 4b (i to iii)) showed that only C2H6 was present in the remaining gas, indicating that C2H4 had been successfully removed. After 4 hours of grinding, the separation of C2H4 and C2H6 was confirmed ( Figure 4b (v) FTIR spectrum of the BN sample ground in the gas mixture for 2 hours ( Figure 5 b(i)) shows that C2H4 is adsorbed on the BN sample. The adsorbed C2H4 gas was extracted by heating the ground BN to 550 °C, and the g-FTIR spectrum of the released gas confirmed that the released gas was C2H4 ( Figure 5 b(ii)).

[0150] In addition, this technique can also separate CO2 from a mixture of CH4 and N2 gases. Figure 4c shows the g-FTIR of the initial CO2 / CH4 gas mixture and the remaining gas after a certain time interval. Figure 4d In the figure, the gas chromatogram confirmed that the separation of CO2 and N2 occurred after 5 h of grinding.

[0151] Example 5 - Proposed gas storage mechanism

[0152] C2H4 molecules were adsorbed onto the BN samples as example gases and further investigated by Fourier transform infrared spectroscopy (FTIR). Figure 6a The FTIR spectrum shown covers the fingerprint region of hydrocarbon molecules (2700 cm -1 -3150cm -1 ) partial spectrum. Featureless FTIR spectrum ( Figure 6a(i)) confirmed that the initial BN powder did not contain any adsorbed C2H4. FTIR spectrum of the BN sample after continuous grinding in the presence of C2H4 for 20 h ( Figure 6a (ii)) shows that at 2850cm -1 and 2920cm -1 There are two peaks at , which represent the sp 3 CH stretching vibration.

[0153] To further confirm the C2H4 adsorption, the ground BN sample was heated from room temperature to 550°C at a rate of 25°C / min using a simultaneous thermal analysis (STA)-FTIR coupled system. The resulting spectra of the gas were collected during the heating to 550°C ( Figure 6a (iii)) showed the same two characteristic peaks attributed to C2H4 molecules, confirming the adsorption of C2H4 gas. The gas collected from the grinding device after heating produced C2H4 with a recovery rate of 82%. FTIR of heated BN ( Figure 6a (iv)) indicates that the BN sample was cleaned after the heat treatment and all adsorbed C2H4 had been removed from the BN surface. When the cleaned BN was reground in C2H4, a similar gas pressure decrease was observed during the subsequent grinding process ( Figure 7 ), and the same sample was subjected to 4 cleaning and grinding cycles, with a pressure / capacity reduction of less than 100 kPa compared to the first grinding treatment. The re-adsorption of C2H4 molecules was confirmed by FTIR ( Figure 6a (v) 3427cm -1 The small NH peak at indicates a weak non-covalent interaction between the hydrogen of the C2H4 molecule and the nitrogen of the BN powder. No NH peak was observed in the spectrum of the released gas ( Figure 6a (iii)). FTIR analysis also confirmed the adsorption of other hydrocarbon gases by BN during ball milling ( Figure 6b ). Figure 6b The complete FTIR spectrum of h-BN shows that -1 and 1336cm -1 There are two characteristic peaks at 673 cm, corresponding to the out-of-plane BN bending vibration and in-plane BN stretching vibration. -1 The unique CH peak at is associated with the C2H2 molecule and is not present in other spectra. The intensities of the other characteristic CH peaks are relatively low, so the spectrum in the hydrocarbon fingerprint region is magnified and displayed at Figure 6b In. At 2925cm -1 、3033cm -1 、3070cm -1 、3089cm-1 The peak at corresponds to the sp 2 CH stretching vibration. Spectrum of BN after grinding in CH4 for 20 hours. -1 、2925cm -1 Up to 2955cm -1 There is a characteristic CH stretching vibration at 2875cm -1 -2958cm -1 The peak at 3427 cm is the CH stretching vibration of the C2H6 molecule. -1 The NH peak is observed at , confirming that multiple gases are non-covalently linked on the BN surface.

[0154] Ball milling uses mechanical energy to achieve gas adsorption by BN at room temperature. The adsorbed gas can be released from the milled sample by heating. The cleaned BN sample can be used again for further adsorption.

[0155] The mechanism of gas adsorption by BN during ball milling was studied. Mechanical grinding of powder can greatly reduce its particle size and increase its surface area; therefore, more gas molecules can be physically adsorbed due to the creation of new surfaces.

[0156] Figure 8 shows the relationship between the Brunauer–Emmett–Teller (BET) surface area of ​​BN powder and the grinding time. The surface area of ​​BN increased to 623.6 m after grinding in CH4 for 20 h. 2 / g, while the surface area of ​​the BN sample ground in C2H4 under the same grinding conditions changed less (99.8 m 2 / g).

[0157] Figure 2a shows that more C2H4 (228 cm 3 / g) is adsorbed on BN with a smaller surface area. In contrast, less CH4 (152 cm 3 / g) was adsorbed by BN with a larger surface area.

[0158] Without being limited by theory, these results indicate that the adsorption capacity is independent of the surface area of ​​the BN samples and suggest that the adsorption mechanism of olefin gases cannot be attributed solely to physical adsorption.

[0159] The X-ray diffraction (XRD) pattern shown in Figure 9a shows that the crystal structure in the milled BN is different, which shows that the h-BN sample milled in C2H4 for 20 hours maintains the hexagonal crystal structure of the initial BN powder. However, the h-BN sample milled in CH4 for the same time has a disordered structure as shown by the diffraction peak (002) with reduced intensity and increased peak width of the sample. Scanning electron microscopy (SEM) analysis confirmed the different morphologies of the two samples. The SEM image of the BN sample in Figure 9a (inset) shows that the BN powder milled in the presence of C2H4 has a nanosheet structure with a size of several microns and a thickness of <30nm, while the BN powder milled in the presence of CH4 has a spherical shape with a diameter of <80nm.

[0160] The corresponding TEM images ( Fig.10 a. Fig.10 b) and selected area electron diffraction (SAED) patterns show consistent results. During the milling process in olefin gas, BN nanosheets were formed due to gas adsorption, because these olefin gases are believed to have a lubricating effect and prevent cross-linking between different layers, and the nanosheets are exfoliated and protected by the olefin molecules adsorbed on the surface.

[0161] For comparison, different starting hBN sizes were tested ( Fig.11 ), confirming that size is not a critical factor for gas adsorption during ball milling.

[0162] The different morphologies and crystal structures of the milled BN samples are believed to indicate different mechanisms leading to the adsorption of olefin and alkane gases.

[0163] To determine the adsorption mechanisms involved in these two different types of gases, BN samples that had been continuously ground in the presence of either CH4 or C2H4 for 20 h were heated to 700 °C ( 25 °C / min) using a thermogravimetric analyzer (TGA) under a constant argon flow rate. Figure 9b ). The desorption of the previously adsorbed CH4 occurred gradually, and a total weight loss of 2.8 wt.% was measured, indicating that CH4 had been physically adsorbed on the BN nanoparticles. Similar gas desorption behavior was observed for C2H6 ( Fig.12 a).

[0164] For BN ground in C2H4, the TGA curve shows a gradual weight loss (2.5 wt.%) at temperatures not greater than 400°C due to the release of physically adsorbed gas, and then the curve changes sharply, indicating a large and rapid weight loss (14.5 wt.%) from 400°C to 550°C ( Figure 9b). This higher desorption temperature and narrower temperature range indicate stronger adsorption of C2H4 on BN nanosheets. The observed desorption temperature range is larger than that of C2H4 on zeolite (350°C to 380°C) and defect-loaded BN (287°C). The desorption energy determined by in situ differential scanning calorimetry (DSC) was 88.7 J / g. A sharp weight loss was also observed in the TGA curve of the BN sample ground in C2H2 ( Fig.12 b).

[0165] These results are considered to indicate that the two gases (olefins and alkanes) have different adsorption energies on the ball-milled BN nanosheets.

[0166] The ball-milled BN was studied using X-ray photoelectron spectroscopy (XPS). For the BN sample ground in C2H4, the B 1s spectrum in Figure 9c shows two BN characteristic peaks at binding energies of 190.3 eV and 191.1 eV. Figure 9d The N1s spectrum in Figure 9e shows that NB bonding is dominant at 397.9 eV, with NC bonding at 398.6 eV. The small peak at 400.1 eV may be attributed to NH bonding. The B1s and N1s spectra of the starting BN powder indicate that the BN does not contain any gas adsorption. The C1s spectrum in Figure 9e shows a major peak at 284.5 eV, which is associated with two CC bondings and CH bondings from adsorbed C2H4 molecules, and a CN bonding peak at 285.3 eV. The NC bonding peak is present in both the N 1s and C1s spectra, while the BC bonding is absent in the B1s spectrum, indicating non-covalent NC bonding between C2H4 molecules and BN nanosheets. As shown by the NH peak in the N1s spectrum and the corresponding FTIR spectrum, a small portion of C2H4 is physically adsorbed on the BN nanosheets through NH bonding, which is also consistent with the smaller weight loss in the low temperature range of <400 °C.

[0167] For the BN sample ground in CH4, the B 1s spectrum ( Figure 9f ) has two BN binding peaks and a larger BO binding peak at 193.1 eV

[38] The milled BN sample has a larger surface area and is more active in ambient gas, which is easily contaminated by oxygen in the air during XPS analysis. The N1s spectrum in Figure 9g has the same NB binding peak as well as a broad and weak shoulder centered at 399.5 eV, which may be caused by NH. Figure 9h The C1s spectrum in Fig. 9 shows major peaks associated with CC and CH bonding at 284.5 eV and a CO peak at 286.3 eV. The obvious NH bonding peak at 399.5 eV in Fig. 9g is believed to indicate that CH4 molecules are physically adsorbed onto the BN surface via NH bonding, which is consistent with the FTIR results.

[0168] XPS results show that alkane molecules are adsorbed on the surface of BN nanoparticles through weak NH bonding. The nitrogen atoms in BN have high electronegativity, while olefin molecules contain unsaturated carbon atoms. Therefore, the adsorption energy of C2H4 on BN is stronger than that of CH4 on BN. XPS studies believe that the nitrogen atoms in BN can form non-covalent bonds with the unsaturated carbon atoms in the olefin gas C2H4. However, these non-covalent CN bonds cannot be formed on BN nanosheets under ambient conditions without the help of ball milling, which provides the required energy for the unique interaction between BN and gas.

[0169] Example 6 - Method of Separating a Gas Mixture

[0170] Fig.13 Figure 4a shows the gas separation process. When a mixture containing alkyne or olefin gases (C2H2 and C2H4) and alkane gases (CH4 or C2H6) is introduced into a grinding reactor, mechanical grinding activates the selective adsorption of alkyne and olefin gases on BN powder. The alkane gas remains in the reaction chamber and can be removed by the vacuum system. The adsorbed alkyne and olefin gases can be recovered by heating the grinding reactor / BN. If fresh gas is continuously supplied, the process can be repeated or continued. The FTIR results in Figures 4a to 4c show that the mixed hydrocarbon gases can be effectively separated by fine-tuning the grinding process (i.e., grinding intensity, time, and gas pressure) to remove all olefin gases, thereby physically enhancing the selective adsorption process. For the case of a mixed gas containing more than two gases, a separation process involving multiple grinding reactors is proposed ( Fig.13 b), provided that these gases have different adsorption rates and capacities. The separation efficiency depends on the selective adsorption capacity.

[0171] Reference in this specification to any prior publication (or information obtained therefrom) or any known matter is not, and should not be taken as, an admission or permission or any form of implication that the prior publication (or information obtained therefrom) or known matter constitutes part of the common general knowledge in the target field covered by this specification.

[0172] Throughout the specification and the claims that follow, unless the context requires otherwise, the word "comprise" and variations such as "comprises" and "comprising" will be understood to imply the inclusion of specified integers or steps or groups of integers or steps but not the exclusion of any other integers or steps or groups of integers or steps.

Claims

1. A method of promoting the adsorption of one or more gases by a solid particulate material, the method comprising (i) ball milling the solid particulate material in the presence of one or more gases maintained at a pressure of at least 300 kPa, (ii) using a weight ratio of grinding balls to solid particulate material of at least 60:1 and (iii) ball milling the solid particulate material at an operating speed of at least 200 rpm.

2. The method of claim 1, wherein the solid particulate material is selected from the group consisting of boron nitride, graphite, molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, molybdenum ditelluride, boron, iron and silicon.

3. The method of claim 1 or 2, wherein the one or more gases are maintained at a pressure of at least about 500 kPa.

4. The method of any one of the preceding claims, wherein the weight ratio of the grinding balls to the solid particulate material is at least about 80:

1.

5. The method of any one of the preceding claims, wherein the operating speed is at least about 300 rpm.

6. A method according to any one of the preceding claims, wherein the solid particulate material has an average particle size of from about 1 μm to about 5 mm prior to ball milling.

7. A method according to any one of the preceding claims, wherein the one or more gases are selected from hydrogen, carbon dioxide, carbon monoxide, C1-C4 hydrocarbons, ammonia, nitric oxide, nitrogen dioxide, sulfur dioxide and nitrogen.

8. A method according to any one of the preceding claims, wherein the solid particulate material produced as a product by the ball milling has adsorbed thereon the one or more gases, and the product is contained in a container to store the one or more gases.

9. The method of claim 8, wherein the product having adsorbed thereon the one or more gases has a gas adsorption weight capacity of at least 500.

10. A process according to claim 8 or 9, wherein the product contained in the container is heated to a temperature of about 50°C to about 500°C to release the one or more gases adsorbed on the solid particulate material.

11. A method according to any one of claims 1 to 7, wherein (i) the ball milling is carried out in the presence of a mixture of two or more gases, and the solid particulate material produced as a product by the ball milling is adsorbed with the gas mixture, and (ii) the product is processed to selectively release at least one adsorbed gas from the solid particulate material, thereby separating the released gas from the mixture of two or more gases.

12. The method according to any one of claims 1 to 7, wherein the ball milling is carried out in the presence of a mixture of two or more gases, and the solid particulate material produced as a product by the ball milling (i) adsorbs at least one gas in the gas mixture, and (ii) does not adsorb at least one gas in the gas mixture, thereby separating the at least one gas that is not adsorbed from the two or more gas mixtures.

Images