Reaction vessel

Abstract

A method of making functionalised nano-silica particles by supplying silane and one of carbon dioxide, sulphur dioxide and nitrogen dioxide into a reaction vessel where one of the reactants has been e

Description

This invention relates to a reaction vessel. 5 Background of the Invention Typically, exhaust gas from combustion and energy transformation processes, mainly for propulsion and energy generation, is released into the atmosphere and invariably contains various undesirable noxious air pollutants that causes adverse effects to the environment, on both a local and global scale. Oxides of carbon 10 (COx), nitrogen (NOx) and sulphur (SOx) are all prime examples of the types of air pollutants found in exhaust gases from combustion and energy transformation processes. Conventional methods for producing nano-silica and hydrogen require high 15 temperatures. Nano-silica produced from such methods is typically not hydrophobic, and at least a further high temperature and / or pressure processing step is required in order to provide the nano-silica with hydrophobic properties. Hydrophobic properties are useful in nano-silica because nano-silica is commonly used as a primary or additive material in industries that can benefit from materials 20 being made with or have a film of nano-silica applied thereto to render the material hydrophobic, such as cements, glasses, screens and pharmaceutical &Rheological processes etc. Flame hydrolysis deposition is an example of a conventional method for producing 25 nano-silica, which requires high temperature to produce nano-silica. This is typically achieved using a Hydrogen-Oxygen reaction. The use of these reactants means other reaction compounds introduced must be non-reactive with the initial Hydrogen-Oxygen mixture to prevent reactions occurring under the wrong conditions or prior to the introduction of these reactants into a reaction chamber. 30 This process requires ignition, and nebulised silicon chloride to be present, which is costly and inconvenient. Further, hydrochloride gas is produced from this process, which is toxic and must be disposed of. The present invention aims to overcome or at least ameliorate one or more of the problems set out above. 5 Summary of the Invention In a first aspect of the invention, there is provided a reaction vessel for producing functionalised nano-silica from silane and an oxide of at least one of Nitrogen, Sulphur and Carbon comprising: a mixing chamber for mixing said silane and said oxide, the mixing chamber having a containment region arranged in the upper part 10 of the mixing chamber for containing the Hydrogen and monoxide reaction products produced from the reaction of the silane and oxide gases; a Silane delivery system for delivering the silane into the containment region via an opening proximate to and below the containment region; an oxide delivery system for delivering the oxide to an oxide inlet of the mixing chamber wherein the inlet for the 15 oxide is arranged below said opening such that the Oxide gas must travel up via a lower part of the containment region through the contained Hydrogen and monoxide reaction products before it interacts with the Silane gas introduced via the opening further up the containment region, for facilitating the production of functionalised nano-silica; and charging means arranged to charge at least one of 20 the silane and the oxide. By providing a charge on at least one of the silane and oxide within a chamber, functionalised nano-silica can be produced from a one-step reaction between the silane and the oxide. In particular, when carbon dioxide (CO2) is used as the oxide, 25 hydrophobic nano-silica is produced. This is because electrostatically charging the gases increases the electron density of the reacting mixed gas, which causes the bonds of the oxide and silane to break more easily when reacting to produce silicas, hydrogens and monoxides. As a result, due to the increased electron density of the reacting mixed gases, the outer layer of silica is coated with a functional group, 30 which in the case CO2 is used, imbues the nano-silica with a hydrophobic property. A first part of the reaction vessel, relative to a ground surface, comprises a containment region for containing hydrogen and monoxide produced from the reacting mixed gas proximate to the reacting mixed silane and oxide gases for facilitating the production of functionalised nano-silica. In this way, due the relative 5 buoyancy of hydrogen and monoxide produced from the reacting mixed gas, the hydrogen and monoxide are contained in a region proximate to the reacting mixed gas. This helps to facilitate the production of hydrophobic nano-silica because the hydrogen and monoxide are utilised during the nucleation of the nano-silica to produce functionalised nano-silica. 10 Preferably, the delivery system is also arranged to deliver hydrogen and monoxide to the mixing chamber proximate to the reacting mixed gas for facilitating the production of functionalised nano-silica. In this way, hydrogen and monoxide are provided to the reacting mixed gas to facilitate the production of hydrophobic nano-15 silica. Preferably, the containment region is the first part of the reaction vessel. Preferably, the first part of the reaction vessel is shaped such that delivered silane 20 and oxide converges. In this way, gases delivered to the mixing chamber converge near the first part of the mixing chamber. Preferably, at least the first part of the reaction vessel is bell-shaped. 25 Preferably, said at least one of the silane and oxide is arranged to be charged prior to being delivered to the mixing chamber. Preferably, the delivery system includes a portion made of at least one of: a triboelectrically sensitive material and a dielectric material, for charging the silane 30 and / or oxide. In this way, the silane and / or oxide can be passively charged via the triboelectric material and / or actively charged via the dielectric material of the delivery system as the gases are delivered to the mixing chamber. Preferably, the delivery system is a delivery tube and / or a storage vessel of the silane and / or oxide. 5 Preferably, a portion of the reaction vessel is made from at least one of: a triboelectrically sensitive material and a dielectric material for charging at least one of the silane and oxide. In this way, the silane and / or oxide can be passively charged via the triboelectric material and / or actively charged via the dielectric material of the vessel as the gases are in the mixing chamber. 10 Preferably, the delivery system is arranged to deliver the silane and oxide to the mixing chamber via inlets provided in the reaction vessel; and wherein at least one of said inlets is arranged to deliver the silane or oxide to the mixing chamber in a turbulent flow. Delivering the oxide and / or silane to the mixing chamber in a 15 turbulent flow ensures a greater degree of collisions occur between silane and the oxide, as well, in the case of the vessel comprising triboelectrically sensitive material, increasing the amount of contact that occurs between the oxide and the surface of the vessel for better charging, thus increasing the efficacy of the production of functionalised nano-silica. 20 Preferably, the reaction vessel is elongate having a longitudinal axis, and at least one inlet is arranged to supply gas at an angle between 45 and 90 degrees relative to a longitudinal axis of the reaction vessel such that the inlet generally directs the gas towards the first part of the reaction vessel. In this way, the flow of oxide being 25 delivered to the mixing chamber is turbulent and flows towards the opening of the delivery chamber. Further, this arrangement reduces the likelihood of gases, such as silane, flowing back up into the inlets, which is undesirable. Preferably, the at least one inlet is the inlet for said oxide. Preferably, the inlet for silane is in the first part of the reaction vessel and arranged at an angle parallel to the longitudinal axis of the reaction vessel such that the inlet for silane generally faces the ground surface. In this way, silane is delivered to the delivery chamber, which allows control of the flow of silane such that a direct flow path from the silane to the reacting mixed gas can be achieved. 5 Preferably, the mixing chamber comprises a delivery means for delivering the silane to below the containment region. In this way, the flow of silane can be controlled and a direct flow path from the silane to the reacting mixed gas can be achieved. 10 Preferably, the inlet for silane extends into the mixing chamber, and the delivery means includes a cylinder that extends towards the inlet for silane, the cylinder having an opening to receive the inlet for silane into a confined space within the cylinder; and the cylinder is arranged to provide a flow path to below the containment region. In this way, the flow of silane can be controlled and a direct 15 flow path from the silane to the reacting mixed gas can be achieved. Preferably, the opening of the cylinder is proximate to below the containment region. In this way, silane is delivered directly to the reacting mixed gas. 20 Preferably, the opening is between the inlet for oxide and the containment region. In this way, silane is delivered below the containment region to the reacting mixed gas. Preferably, the reaction vessel comprises a separation means for separating the 25 produced hydrogen, oxide and functionalised nano-silica. Preferably, the oxide is at least one of carbon dioxide, nitrogen dioxide and sulphur dioxide. 30 In a second aspect of the invention, there is provided a method of producing functionalised nano-silica comprising the steps of: supplying silane to a containment region arranged in the upper part of a mixing chamber for containing the Hydrogen and monoxide reaction products produced from the reaction of the silane and oxide gases, the silane being delivered via an opening proximate to and below the containment region; supplying an oxide of at least one of Nitrogen, Sulphur and Carbon into said mixing chamber, wherein said oxide is delivered into 5 said mixing chamber below the containment region and said opening such that the Oxide gas must travel up via a lower part of the mixing chamber to a lower part of the containment region through the contained Hydrogen and monoxide reaction products before it interacts with the Silane gas introduced further up the mixing chamber in the containment region, for facilitating the production of functionalised 10 nano-silica; arranging for at least one of the silane and oxide to be charged; and mixing the silane and oxide to produce a reacting mixed gas. 15 20 Preferably, hydrogen and monoxide produced from the reacting mixed gas are contained proximate to the reacting mixed gas for facilitating the production of functionalised nano-silica. Preferably, the silane is supplied to a region in the confined space that is proximate to the reacting mixed gas. Preferably, at least one of the silane and oxide are arranged to be charged prior to being supplied to the confined space. Preferably, at least one of the silane and oxide are arranged to be charged in the confined space. 25 Preferably, at least one of the silane and oxide is supplied to the confined space so as to cause it to flow turbulently. Preferably, the method further comprises the step of separating produced hydrogen, oxide and functionalised nano-silica from one another. Preferably, the produced hydrogen, oxide and functionalised nano-silica are separated via a batch process. Brief Description of the Drawings 5 Embodiments of the invention will now be described by way of example, with reference to the drawings in which: - Figure 1 is a cross-sectional view of an embodiment of the reaction vessel; Figure 2a is a schematic view of hydrophobic nano-silica whereby the functional 10 group is represented by R and Figure 2b is a schematic view of hydrophobic nano-silica whereby the functional groups are methyl groups; and Figure 3 is a perspective view showing the reaction vessel attached to a temperature-controlled flow reactor and a separation device. 15 Detailed Description As illustrated in Figure 1, the vessel 2 comprises a mixing chamber 4. The mixing chamber 4 comprises a reactant inlet 8, for receiving silane, and a pair of oxidizer inlets 10a, 10b, for receiving an oxide gas. The inlets 8,10a, 10b allow the delivery of silane and an oxidiser into the mixing chamber 4 from a delivery system (not 20 shown). In some cases, the reactant inlet 8 may be a plurality of inlets and / or there may be more or less than two oxidiser inlets 10a, 10b. In this embodiment, the oxide is carbon dioxide (CO2). In other embodiments, the oxide may be other oxides, such as nitrogen dioxide (NO2) or sulphur dioxide (SO2), 25 or a mixture of at least two different oxides such as CO2, NO2 and SO2. The oxide(s) may form part of an exhaust gas from a combustion and / or energy transformation industrial process The reaction vessel 2, and thus the mixing chamber 4, is elongate having a top end 30 16, relative to a ground surface (i.e., generally parallel relative to a ground surface of the earth), and an opposing bottom end 18 connected to the top end 16 via a diverging wall 20. In this embodiment, the top end 16 of the vessel 2 is bell-shaped, the advantage of which will be described later on. The reactant inlet 8 is in the top end 16 of the vessel 2 and extends into the mixing 5 chamber 4 at an angle parallel to a longitudinal axis of the reaction vessel such that the inlet 8, i.e. the interface of the inlet at which gas is delivered into mixing chamber 4, generally faces the ground surface. In other embodiments, the inlet 8 may not be substantially parallel to a longitudinal axis of the reaction vessel. 10 The mixing chamber 4 comprises a substantially cylindrical delivery chamber 6 that is mounted to the mixing chamber 4 via mounting arms 7 such that the delivery chamber 6 is suspended centrally within the mixing chamber 4. The delivery chamber 6 is substantially concentric with the inlet 8 and has an opening 9 into a If) CM confined space 11 within the delivery chamber 6. The inlet 8 extends into the 15 confined space 11 via the opening 9. In this way, silane being delivered to the mixing chamber 4 is arranged to flow into the mixing chamber 4 via the opening. The advantage of this flow path will be described later on. CM The oxide inlets 10a, 10b are configured at an angle of 45 degrees relative to the 20 longitudinal axis of the vessel 2 such that the inlets 10a, 10b generally direct oxide being delivered to the mixing chamber 4 towards the top end 16 of the vessel 2. In this way, the flow of oxide being delivered to the mixing chamber 4 is turbulent and flows towards the opening 9 of the delivery chamber 6. Further, this arrangement reduces the likelihood of gases, such as silane, flowing back up into the inlets 10a, 25 10b, which is undesirable. In this document, the term ‘turbulent’ means a flow having a sufficiently high Reynolds number such that a reaction occurs between the oxide and silane. Preferably, the flow of oxide being delivered to the mixing chamber 4 has a 30 Reynolds number greater than the point of laminar transition of the flow into turbulent flow. In other embodiments, at least one of the oxide inlets is configured at an angle between 45 and 90 degrees relative to a longitudinal axis of the reaction vessel, and / or may be tangential relative to the vessel, such that the inlet generally directs the gas it is delivering to the mixing chamber towards the top end of the vessel 2. LD The delivery system (not shown) comprises delivery tubes (not shown) that supply silane and oxide to the reactant inlet 8 and oxide inlets 10a, 10b respectively from respective storage vessels of oxide and silane (not shown). In this embodiment, the delivery tubes are made from silicone, which is a material that is able to receive 10 and impart a charge triboelectrically onto the particles of gas via contact between the material and particles (herein such material is referred to as triboelectrically sensitive material). In this way, the silane and CO2 are electrostatically charged prior to being delivered to the mixing chamber 4 due to sufficient contact between the gases and the triboelectrically sensitive material of the delivery tubes. In other 15 words, silane and CO2 become electrically charged as they pass through the delivery tubes. In this arrangement, silicone is used as the triboelectrically sensitive material. In other arrangements, a triboelectrically sensitive material other than silicone, such 20 as PTFE, VITON or Buna-N, may be used. The triboelectrically sensitive material should be compatible with at least silane and oxides, particularly oxides of carbon, nitrogen or sulphur. Preferably, the triboelectrically sensitive material is towards the negative end the triboelectric series spectrum. In some embodiments, only one of the delivery tubes comprises a triboelectrically sensitive material such that at 25 least one of the silane or oxide is charged prior to being delivered to the mixing chamber 4. Further, in some arrangements, the delivery tubes are not made from silicone. In these cases, the delivery tubes are instead cladded with triboelectrically sensitive material, such as silicone. Further, in some arrangements, a charge may be imparted triboelectrically onto the particles of gas flowing through the delivery 30 tubes via one or more meshes of triboelectrically sensitive material that are mounted within at least one of the delivery tubes. In some cases, the triboelectric material of the meshes are a dielectric material that can be polarized with an applied electric field. In this way, a charge may be imparted triboelectrically from the polarised dielectric mesh onto the particles of gas. In some arrangements, these meshes (i.e. a mesh made of at least one of a triboelectric and dielectric material) may also be mounted within the vessel 2 such that charge is imparted 5 from the mesh onto the particles of gas within the vessel. Thus, charge is imparted triboelectrically onto the particles of gas at least either via triboelectrically sensitive material and / or via dielectric material that is polarised with an applied electric field. In other words, the particles of gas can be charged 10 triboelectrically in a passive manner via contact with triboelectrically sensitive material and / or in an active manner via contact with dielectric material that is polarised with an applied electric field. The triboelectrically sensitive material may also be a dielectric material this allowing both passive and active charging of the particles of gas. The importance of charging silane and CO2 in this way will be 15 described later on. The mechanism of triboelectric charging between materials is well known to the skilled person. In the technical field of chemical processing, triboelectric charging is generally perceived as an undesirable effect because inadvertent discharging of 20 static charge can occur. This is often managed by grounding parts of the chemical processing apparatus to remove any build of static charge on the apparatus. As silane and the CO2 are delivered into the mixing chamber 4, the two gases flow towards a mixing region 12 that is proximate to and surrounds the opening 9 of the 25 delivery chamber 6, where the gases mix together and begin to react. The reaction results in the production of nano-silica, as will be described later on. The delivery system is also arranged to deliver silane and CO2 to the mixing chamber 4 under pre-determined conditions, such as pressure, speed etc, and at 30 a suitable stoichiometric ratio of silane to CO2. The pre-determined conditions and stoichiometric ratio of silane to CO2 are controlled by adjusting the pressure and / or temperature of silane and CO2 being delivered to the vessel 2. The mixing chamber 4 is an enclosed area, in communication with the inlets 8, 10a, 10b, for which mixing can occur between silane and the CO2. The reaction may also be controlled by adjusting the temperature and / or pressure 5 of the silane and the temperature and / or pressure of the CO2 being delivered via the delivery system. For example, a decrease in the temperature and / or pressure of the CO2 being delivered can be compensated for by an increase in temperature and / or pressure of silane being delivered to maintain a desired mass flow rate or pressure of the flow of gases in the mixing chamber 4. In this way, the 10 stoichiometric ratio, the Reynolds number of the flows of silane and CO2, and the reaction of silane and the CO2 can be controlled. A control system (not shown) is arranged to monitor the stoichiometric ratio and / or pressure of the mixed gases in the mixing chamber 4. This is achieved by 15 monitoring the mass flow rate and / or pressure and / or temperature of the mixed gas and adjusting the mass flow rate and / or pressure and / or temperature of the silane being delivered accordingly to maintain the desired stoichiometric ratio and / or pressure of the mixed gas. 20 In this embodiment, the temperature and / or pressure of the silane is adjusted to control the stoichiometric ratio and / or pressure of the mixed gas. In other embodiments, the control system may control the mass flow rate and / or pressure and / or temperature of at least one of the silane and the CO2 being delivered accordingly to maintain the desired stoichiometric ratio and / or pressure of the 25 mixed gas. In some embodiments, the mixing chamber 4 may comprise swirlers and / or a pintle and / or a mesh to facilitate the mixing of silane with CO2 in the mixing chamber 4. The swirlers, pintle or a mesh may comprise triboelectrically sensitive material to 30 also facilitate electrostatically charging the silane and CO2 in the mixing chamber 4. The reaction that occurs between silane and the CO2 will now be described. Silane is pyrophoric in nature, allowing an instant hypergolic reaction to occur with oxides when the turbulence of the fluid mixture is sufficiently high. In other words, the reaction occurs when the two gases mix together above a predetermined Reynold’s 5 number, which, as discussed above, is determined by controlling the mass flow rate at which silane and CO2 are delivered to the mixing chamber 4. In this way, it is ensured that collisions occur between silane and CO2 such that silane reacts with the CO2. 10 This reaction produces silicon dioxide (silica), hydrogen, heat energy and a monoxide of the initial oxide, i.e. an oxygen atom is stripped from the oxide. This would provide nitrogen oxide (NO) when NO2 is the initial oxide, sulphur oxide (SO) when SO2 is the initial oxide and carbon monoxide (CO) when CO2 is the initial oxide. This reaction can be generally summarised as: 15 SiH4 + 2X02 = SiO2 + 2X0 + 2H2 + E (1) whereby X may denote carbon, nitrogen or sulphur and E denotes the release of energy. 20 As the mixture reacts, silica reacts with compounds such as the monoxide and the hydrogen to produce Si-C-R and / or Si-O-R bonds particularly on its surface structure, whereby R represents organic functional groups such as methyl, alkyls, carbonyls etc. Nucleation and aggregation of this silica with these bonds begins to 25 occur to form silica having an organic functional group, such as methyl, alkyl, carbonyl, etc groupings, coating on the surface of the silica particle giving the surface a functional property, such as a hydrophobic property. In other words, the reaction produces functionalised silica, i.e., silica having a functional chemical group attached to it. The type of functional chemical group attached will depend 30 on the type of oxide used in the reaction, as well as the reaction conditions. In this embodiment, silane is used with carbon dioxide to produce hydrogen, silica, carbon monoxide and heat energy: SiH4 + 2CO2 = SiO2 + 2CO + 2H2 + E (2) 5 However, as the gases initially mix a number of intermediate reactions may take place which can lead to the production of carbon, silicon, water and other products. Typical reactions are as follows: 10 SiH4 + CO2 = SiO2 + C + 2H2O (3) SiH4 + CO2 = Si + CO + 2H2O (4) These products may only exist transiently before taking part in further reactions. 15 Carbon as an example in a nano state can react with steam and re-form to make hydrogen and carbon monoxide. During these reactions, transient hydrogen and carbon compounds or radicals are produced which may also combine with each other to produce methyl, alkyl, and 20 other functional groups, which can bond to the silica being produced to form a functionalised coating on the surface which can provide hydrophobic properties to the silica, as described in more detail below. As illustrated in Figure 2b, in this case, the organic functional group coatings 25 formed on the surface are primarily methyl groups, giving the surface a hydrophobic property. Other groups, such as ethyl groups, may also be formed on the surface. Figure 2a illustrates a schematic view of nano-silica whereby the functional group is represented by R. 30 When CO2 is used as the oxide, the functional groups that are commonly formed are such as alkanes, aldehydes, ketenes or ethers. Other functional groups may from such as alkynes, alcohols, carboxylic acids, esters and acid anhydrides, although these are likely to be rarely. Depending on conditions and available materials haloalkenes, aryls, epoxides and acyl halides might be formed although this is less likely. 5 When Nitrogen dioxide (NO2) is used as the oxide, the functional groups that are likely to form may include nitrides, amines and amides. Other functional groups that might be formed are nitrate, nitrosos, cyanates, isocyanates, azos, imines and imides and to a lesser extent azides and nitro compounds. 10 When Sulphur dioxide (SO2) is used as the oxide, the functional groups that are likely to form may be thiol and sulfide. Other functional groups that might be formed are disulphides, sulfoxides, sulphenes as well as compounds of sulphinic acid, sulphonic acid and sulfonate ester and to a lesser extent thiocyanates, thials, isothiocyanates and thioketones. 15 The particle size of the silica produced from the above reaction is between 50 -125nm - the silica is therefore considered nano-silica. The particle size is influenced by the magnitude of the electric field within the vessel 2. The electric field in the vessel 2 is generated as a result of the charged particles and / or any 20 charging of the vessel 2. The particle size can thus be manipulated by controlling the magnitude of the electric field within the vessel 2, for example by controlling a voltage applied to the vessel 2 when charging the vessel 2, which is described later on. The collision rates between the particles of silica and the particles of hydrogen and carbon define the shape and size of the particles after the nucleation process 25 concludes. An example of the molecular weight of the produced nano-silica is around 60.08 g mol1 with a specific surface area (SSA) of around 40 m2g’1. The formation of the functional chemical group, which in this arrangement is an alkyl group such as a methyl group, on the nano-silica occurs due to the silane and 30 CO2, and / or the vessel being electrostatically charged. Charging the gases in this way increases the electron density of the reacting mixed gas, which causes the bonds of the carbon dioxide and silane to break more easily when reacting to produce silicas, hydrogens and carbon / carbon monoxides. As a result, due the increased electron density of the reacting mixed gases, the outer layer of silica is coated with a hydrophobic methyl group or other functional group. 5 The agglomeration rate of the nano-silica is influenced by the degree to which the gases and / or the vessel are electrostatically charged. Generally, the greater the degree of electrostatic charge imparted on the reacting particles, the greater the agglomeration rate will be of nano-silica. The phobicity of the hydrophobic nano-silica and the size distribution of the nano-silica are both influenced by the degree 10 and rate at which the nano-silica has agglomerated. Thus, controlling the degree to which the gases and / or the vessel are triboelectrically charged allows these aspects of the nano-silica to be controlled as desired by the user. This control may be achieved by adjusting the length and / or the thickness of the triboelectrically in sensitive material being used to impart the electrostatic charge on the reacting 15 particles, such as the length and / or thickness of the delivery tubes. In some arrangements, this control may also be achieved by adjusting the type of triboelectrically sensitive material used. CM As discussed above, the silane and CO2 are triboelectrically charged prior to being 20 delivered into the mixing chamber 4 via the delivery tubes that deliver the silane and CO2 to the reactant inlet 8 and oxide inlets 10a, 10b respectively from their respective storage vessels. In other embodiments, at least one of the storage vessels may comprise triboelectrically sensitive material, such as Polytetrafluoroethylene (PTFE), instead of or in addition to the delivery tubes. In 25 yet other embodiments, the vessel 2 may comprise triboelectrically sensitive materials like dielectrics that do not chemically react with silane or other products of the reaction, instead of or in addition to the delivery tubes and / or the at least one storage vessel. 30 In the case only the vessel 2 comprises triboelectrically sensitive material, silane and CO2 particles are triboelectrically charged as they contact and rub the surface of the vessel 2. This arrangement may be beneficial when used in combination with the delivery tubes and / or the storage vessels comprising triboelectrically sensitive material. In some embodiments, the vessel 2 may be made of a conductive material that is 5 charged, such as via a voltage generator, prior to and / or during the reaction. In this case, the vessel 2 may also comprise insulation to prevent any sparking that may occur as the vessel 2 is charged. In some cases, the insultation is a dielectric material that separates the mixing chamber from the conductive material. The dielectric material is thus polarized as the conductive material is charged such that 10 the dielectric material imparts a charge onto particles within the mixing chamber 4 as previously described. In this way, electrostatic charging of silane and CO2 within the mixing chamber 4 can be achieved (if the particles are not already triboelectrically charged) or supplemented (if the particles are already triboelectrically charged). In the latter case, this improves the efficacy of the 15 production of hydrophobic nano-silica. Alternatively, or additionally, in some cases, an inside surface of the vessel 2 may be cladded with triboelectrically sensitive material, such dielectric, to facilitate electrostatically charging the silane and CO2 in the mixing chamber 4 20 The addition of organic groups to the nano-silica, which in this arrangement are alkyl groups, imbues the nano-silica with a hydrophobic property because the organic outer layer changes the chemical structure of the material from the Si-OH grouping on typical hydrophilic silica, blocking ingress of water through the structure of the material. 25 The formation of the hydrophobic methyl group on the silica is supplemented by the arrangement of the vessel 2, as will now be described. As explained above, silane is delivered to the mixing chamber 4 via the delivery chamber 6, which has an opening 9 that allows silane to flow into the mixing region 12, which is proximate 30 to and surrounds the opening 9 of the delivery chamber 6. CO2 is delivered to the mixing chamber 4 such that it also flows towards the mixing region 12. It is at this region that silane and CO2 meet, mix, and begin to react. Due to their relative buoyancy to the silane and CO2, the hydrogen and carbon monoxide produced from the reaction flow towards the top end 16 of the vessel 2. The hydrogen and carbon monoxide are thus trapped or contained in a 5 containment region 14 between the top end 16 of the vessel 2 and the opening 9. In this way, hydrogen and carbon monoxide produced from the reacting mixed gas are trapped proximate to the reacting mixed gas, and silane is delivered to the mixing region 12 below the trapped hydrogen and carbon monoxide. This helps to facilitate the production of hydrophobic nano-silica because, as explained above, 10 hydrogen and carbon monoxide are utilised during the nucleation of the nano-silica, hydrogen and carbon to produce functionalised nano-silica. In some arrangements, the vessel 2 may comprise vents for removing excess carbon monoxide and hydrogen from the trapping region. LO CM 15 The distance between the top end 16 of the vessel 2 and the opening 9 of the delivery chamber 6 can be optimised during manufacture of the vessel 2 such that trapped hydrogen and carbon monoxide are suitably proximate to the reacting mix £\J gas. The location of trapped hydrogen and carbon monoxide can also be influenced by controlling the mass flow rates of the silane and CO2 being delivered 20 to the mixing chamber 4, the dimensions and pressure of the mixing chamber 4, as well as the permeability of material of the vessel for hydrogen and carbon monoxide. As explained above, the vessel 2, and thus the mixing chamber 4, is bell-shaped. 25 This allows gases delivered to the mixing chamber 4 to converge near the top end 16 of the mixing chamber 4. In other embodiments, the vessel 2, and thus the mixing chamber 4, may be another suitable shape, such as cylindrical, that allows hydrogen and carbon monoxide to be contained proximate to the mixing region 12. 30 The production of hydrophobic nano-silica is further facilitated by the turbulence induced in the delivered CO2, due to configuration of the oxide inlets 10a, 10b. Delivering the oxide to the mixing chamber 4 in a turbulent flow ensures a greater degree of collisions occur between silane and CO2, as well, in the case of the vessel comprising triboelectrically sensitive material, increasing the amount of contact that occurs between the CO2 and the surface of the vessel for better charging, thus increasing the efficacy of the production of hydrophobic nano-silica. Although in the embodiment above, silane is delivered via the top end of the vessel 2, alternatively, silane could be delivered to the mixing chamber 4 from the bottom and / or sides of the delivery chamber 6. 10 In some embodiments, there may be no delivery chamber 6. In this case, the reactant inlet 8 may not extend into the mixing chamber 4. Here, silane is delivered to the mixing chamber 4 at the top end 16 of the vessel 2. This arrangement may be less favourable, because less silane may react with CO2 as it descends towards the bottom end 18 of the vessel 2. In some embodiments, the delivery of silane and oxide may be done in reserve such that oxide is delivered via the inlet 8 and silane is delivered via the inlets 10a,10b. 20 As noted above, oxides other than carbon dioxide may be used, for example, nitrogen dioxide: SiH4 + 2NO2 = SiO2 + 2NO + 2H2 + E (5) 25 In this case, the organic functional group coatings formed on the surface are amine groups. The vessel 2 comprises a material that has a catalytic effect on the reaction between silane and the CO2. In the case where the mixing chamber 4 comprises 30 a pintle, the pintle may comprise the catalytic material to increase the surface contact between the mixed gases and the catalytic material. In some embodiments, one or more additional gases, such as inert gas or catalytic gas, may be injected into the vessel 2 to further control the rate of reaction between silane and CO2. The rate of reaction of silane with the CO2 can be increased or decreased depending on the one or more additional gases supplied to the vessel 5 2. In this case, the vessel 2 comprises one or more additional inlets supplying the one or more additional gases to the mixing chamber 4. For example, the vessel 2 may comprise an additional inlet for supplying a catalytic gas, such as nitrogen, to increase the rate of reaction. The catalytic gas may be another type of noble gas, such as Argon. 10 The bottom end 18 may provide a surface for supporting the vessel 2 in an orientation such that gravity facilitates the flow of products created by the reacting mixed gas (i.e. nano-silica, hydrogen and carbon monoxide), from the top end 16 to the bottom end 18. 15 The products descend, facilitated by gravity, from the top end 16 towards the bottom end 18. The nano-silica may further collide as it descends towards the bottom end 18 causing further agglomeration. In some cases, the vessel 2 may be arranged to actively facilitate the flow of the products to the bottom end 18 of the 20 vessel 2. For example, the vessel 2 may comprise earthed or negatively charged conductive material at the bottom end 18 to facilitate the flow of the products towards the bottom end 18 of the vessel 2. The bottom end 18 of the mixing chamber 4 is wider than the top end 16 such that 25 the dimensions of the chamber 4 proximate to the top end 16 increases towards the bottom end 18. This results in a pressure differential between the top and bottom ends 16, 18 which facilitates the flow of the products towards the bottom end 18 from the top end 16. The increase in dimensions between the top and bottom ends 16, 18 of the mixing chamber 4 may also facilitate agglomeration of 30 the nano-silica. As illustrated in Figure 3, the bottom end 18 of the vessel 2 is coupled to and in fluid communication with a plug flow reactor 22. Here, nano-silica, hydrogen and carbon monoxide flow through the plug flow reactor until it reaches a particulate separator 24, which is arranged to separate these products from one another. The 5 plug flow reactor 22 induces a turbulent flow on the products flowing within it (i.e. the nano-silica, hydrogen and carbon monoxide), which assists in further agglomeration of the nano-silica. In some embodiments, the vessel 2 may not be coupled to a plug flow reactor and 10 particulate separator. In this case, nano-silica, monoxide and hydrogen are removed from the vessel 2 once the amount of nano-silica produced reaches a particular threshold amount. In other words, removal of nano-silica, monoxide and / or hydrogen from the vessel 2 can be achieved using a batch process, for example using a liquid trap with ethanol to trap the nano-silica. In some cases, all 15 of these gases are separated from one another. In other cases, nano-silica is separated from the hydrogen and carbon monoxide resulting a mixture of hydrogen and monoxide. Extracting and separating the gases in this way is useful because both hydrogen and the monoxide, in particular carbon monoxide, are valuable products that can be utilised in various industrial chemical processes, either as 20 separate gases or as a mixture. Therefore, the method of reacting silane with oxide as described by the present invention results in not only desirable functionalised nano-silica, but also valuable by-products of hydrogen and monoxide. 25 In some arrangements, the vessel 2 may be an input structure / portion of a plug flow reactor. In this case, charged silane and / or CO2 are delivered to the input portion of the plug flow reactor, which is equivalent to a mixing chamber, to produce functional nano-silica. This arrangement may be more beneficial in allowing for 30 large scale quantities of nano-silica to be produced. In this case, hydrogen and carbon monoxide are injected into the plug flow reactor at one or more locations along the reactor to facilitate the reaction between silane and CO2. The length of the plug flow reactor is optimised to ensure sufficient reaction and agglomeration occurs to produce the functionalised nano-silica. In some embodiments, the agglomeration of the nano-silica due to the variation in 5 dimensions of the mixing chamber 4 can also be influenced by adjusting the degree of said variations along the length, i.e. by having a narrower or wider bell-shaped mixing chamber 4. Controlling the agglomeration of the nano-silica, via selection of the dimensions of the mixing chamber 4, is advantageous as will be described in more detail further below. 10 15 The design parameters of the vessel 2 and the conditions under which the reaction of silane and the CO2 occurs influences the agglomeration of the nano-silica. In other words, the design parameters and reaction conditions can be controlled to produce variations of nano-silica as desired by the user. Therefore, in other embodiments, the design parameters of the vessel 2 and the conditions under which the reaction occurs may be varied to calibrate the output of nano-silica being extracted from the vessel as desired by a user. The design parameters may be decided during manufacture of the vessel 2. 20 As described above, the design parameters and conditions used to calibrate the output of nano-silica include: the shape of the mixing chamber 4; the differing dimensions between the ends 16, 18 of the chamber 4; the distance between the ends 16, 18 of the chamber 4; the temperature and / or pressure of the delivered silane and / or oxide; the temperature and / or pressure of within the chamber 4; and 25 the stoichiometric proportion of silane and CO2. Other embodiments may have a different combination and / or degree of any of the above-mentioned design parameters and / or conditions depending on the particular output of nano-silica desired by the user. 30 In some cases, additional gases may be delivered to the mixing chamber 4 along with silane and the oxide and / or the vessel 2 may be flushed with other gases before the silane and the oxide are delivered to the mixing chamber 4. For example, the vessel 2 may be flushed with nitrogen before silane and CO2 are delivered to the mixing chamber 4 and / or nitrogen may be delivered to the chamber 4 along with silane and CO2. This introduces a unique nitrogen-based bond structure in the produced nano-silica that can be detected, for example using 5 infrared (IR) detection. This type of nano-silica has applications in the security industry. Items can be coated with this nano-silica, allowing IR detection systems to detect the unique nitrogen-based bond within the coating on the item. In this way, counterfeit items not having the applied coating can be identified. 10 27 01 25

Claims

1. A reaction vessel for producing functionalised nano-silica from silane and an oxide of at least one of Nitrogen, Sulphur and Carbon comprising:5 a mixing chamber for mixing said silane and said oxide, the mixingchamber having a containment region arranged in the upper part of the mixing chamber for containing the Hydrogen and monoxide reaction products produced from the reaction of the silane and oxide gases;a Silane delivery system for delivering the silane into the containment 10 region via an opening proximate to and below the containment region;an oxide delivery system for delivering the oxide to an oxide inlet of the mixing chamber wherein the inlet for the oxide is arranged below said opening such that the Oxide gas must travel up via a lower part of the containment region through the contained Hydrogen and monoxide reaction products before it interacts with15 the Silane gas introduced via the opening further up the containment region, for facilitating the production of functionalised nano-silica; andcharging means arranged to charge at least one of the silane and the oxide.20 2. A reaction vessel according to claim 1, wherein the containment region ofthe reaction vessel is shaped such that delivered silane and oxide converges.

3. A reaction vessel according to claim 2, wherein at least the containment region of the reaction vessel is bell-shaped.

4. A reaction vessel according to any of claims 1 to 3, wherein said charging means is arranged to charge said at least one of the silane and oxide prior to being delivered to the mixing chamber.30 5. A reaction vessel according to claim 4, wherein the delivery system includesa portion made of at least one of a triboelectrically sensitive material and a dielectric material, for charging at least one of the silane and the oxide.

6. A reaction vessel according to claim 5, wherein the delivery system includes at least one of: a delivery tube and a storage vessel for at least one of the silane and the oxide.

7. A reaction vessel according to any of claims 1 to 6, wherein a portion of the reaction vessel is made from at least one of: a triboelectrically sensitive material and a dielectric material, for charging at least one of the silane and oxide.10 8. A reaction vessel according to any of claims 1 to 7, wherein at least one inletof said Silane and oxide inlets is arranged to deliver the silane or oxide to the mixing chamber in a turbulent flow.

9. A reaction vessel according to claim 8, wherein the reaction vessel is 15 elongate having a longitudinal axis, and said at least one inlet is arranged to supply gas at an angle between 45 and 90 degrees relative to a longitudinal axis of the reaction vessel such that the inlet generally directs the gas towards the containment region of the reaction vessel.20 10. A reaction vessel according to claim 8 or 9, wherein said at least one inlet isthe inlet for said oxide.

11. A reaction vessel according to claim 10, wherein the silane is delivered into a delivery chamber of the reaction vessel through a tube parallel to the longitudinal 25 axis of the reaction vessel such that the silane inlet is nearer the lower part of the delivery chamber and generally faces the bottom of the delivery chamber, such that the Silane fills the delivery chamber before emerging from the upper part of the delivery chamber into the containment region.30 12. A reaction vessel according to claim 11, wherein the delivery means includesa cylinder that extends towards the inlet for silane, the cylinder having an opening to receive the inlet for silane into a confined space within the cylinder; andwherein the cylinder is arranged to provide a flow path to the containment region.

13. A reaction vessel according to any of claims 1 to 12, wherein the reaction 5 vessel comprises a separation means for separating the produced hydrogen, oxide and functionalised nano-silica.

14. A reaction vessel according to any preceding claim, wherein the delivery system is also arranged to deliver hydrogen and monoxide to the mixing chamber 10 proximate to the reacting mixed gas for facilitating the production of functionalised nano-silica.

15. A method of producing functionalised nano-silica comprising the steps of: supplying silane to a containment region arranged in the upper part15 of a mixing chamber for containing the Hydrogen and monoxide reaction products produced from the reaction of the silane and oxide gases, the silane being delivered via an opening proximate to and below the containment region;supplying an oxide of at least one of Nitrogen, Sulphur and Carbon into said mixing chamber, wherein said oxide is delivered into said mixing chamber20 below the containment region and said opening such that the Oxide gas must travel up via a lower part of the mixing chamber to a lower part of the containment region through the contained Hydrogen and monoxide reaction products before it interacts with the Silane gas introduced further up the mixing chamber in the containment region, for facilitating the production of functionalised nano-silica;25 arranging for at least one of the silane and oxide to be charged; andmixing the silane and oxide to produce a reacting mixed gas.

16. A method according to claim 15, wherein the silane is supplied to a region in the confined space that is proximate to the reacting mixed gas.3017. A method according to claim 15 or 16, wherein said at least one of the silaneand oxide are arranged to be charged prior to being supplied to the confined space.27 01 2518. A method according to any of claims 15 to 17, wherein said at least one of the silane and oxide are arranged to be charged in the confined space.5 19. A method according to any of claims 15 to 18, wherein at least one of thesilane and oxide is supplied to the confined space so as to cause it to flow turbulently.

20. A method according to any of claims 15 to 19, further comprising the step of 10 separating produced hydrogen, oxide and functionalised nano-silica from one another.

21. A method according to claim 20, wherein the produced hydrogen, oxide and functionalised nano-silica are separated via a batch process.15

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