GB2627446A - Method for the generation of hydrogen - Google Patents

Abstract

A process is disclosed for the reaction of aluminium with water which comprises the steps of adding aluminium metal to an aqueous solution comprising potassium hydroxide at a concentration of between 0.1M and 0.4M and a surfactant; agitating the mixture of previous step; and collecting generated hydrogen. Also disclosed is a composition for use in such a process for reacting aluminium with water, comprising potassium hydroxide and a surfactant. The surfactant may be a non-ionic surfactant selected from silicone, siloxane, polysiloxane, polyethylene-polypropylene glycol, polypropylene glycol, alkyl polyethylene glycol ether, polyethylene glycol, and dipropylene glycol.

Description

METHOD FOR THE GENERATION OF HYDROGEN

The present invention relates to the field of chemistry and chemical engineering. In particular, the invention relates to a process of aluminium hydrolysis to produce aluminium hydroxide, hydrogen gas, and heat. The invention also relates to a catalyst for use in such a process.

Background of the Invention

It is known that aluminium undergoes an exothermic reaction with water to generate hydrogen and aluminium hydroxide (Al(OH)3). Such reactions can be very useful, in particular, to power fuel cell devices, and also as a heat source for thermal engines.

However, known processes are not optimal for a number of reasons; in particular because of the presence of a protective layers of oxide or hydroxide on the surface of aluminium which impedes the reaction.

Aluminium hydrolysis has also been widely studied for the production of aluminium hydroxide. Aluminium hydroxide is used in many industries, including the textile industry, pharmaceutical industry, cosmetic industry, etc. Aluminium hydroxide is usually produced by the Bayer process. In the Bayer process, bauxite is heated in a pressure vessel along with a sodium hydroxide solution at a temperature of 150 to 200 °C. At these temperatures, the aluminium is dissolved as sodium aluminate (primarily [Al(OH)4]-). After separation of the residue by filtering, gibbsite is precipitated when the liquid is cooled and then seeded with fine-grained aluminum hydroxide crystals from previous extractions. The resulting product is of low purity. Additionally, the process consumes a lot of energy which makes it uneconomical and environmentally unfriendly.

A process of hydrogen production is also mentioned in "Hydrogen generation by oxidation of coarse aluminum in low content alkali aqueous solution under intensive mixing"; International Jorurnal of Hydrogen Energy; 2016; Issue 41; Page 1721617224. However, this method is not feasible because it uses a lot of energy required in vigorous mixing, and the aluminium metal needs to be activated prior to its use for hydrogen production which makes the process costly and has greater environmental impacts.

US6506360B1 discloses a method for producing hydrogen consisting of reacting aluminium with water in the presence of sodium hydroxide as a catalyst. The apparatus for carrying out the method uses the pressure and temperature of the reaction to control the degree of immersion of a fuel cartridge in water and consequently to control the vigour and duration of the reaction.

US6638493 B2 discloses a process for producing hydrogen gas which consists of reacting aluminium with water in the presence of sodium hydroxide as a catalyst. In one aspect of the present invention, there is provided a process for producing hydrogen gas, comprising the steps of: providing an aqueous solution containing 1.0 between 0.26 M and 19 M NaOH in a vessel.

US714456 B2 provides a renewable energy carrier system and method wherein the aluminium metal is the carrier. Aluminium metal is reacted with water in a catalytic reaction, thereby splitting the water into hydrogen, oxygen and forming a clean aluminium derivative. The hydrogen is converted into useful energy and the aluminium derivative is recycled back into aluminium metal.

W002/14213A2 relates to a method of producing hydrogen by reacting a metal selected from the group consisting of aluminium (Al), magnesium (Mg), silicon (Si) and zinc (Zn) with water in the presence of an effective amount of a catalyst at a pH of between 4 and 10 to produce Hydrogen. The catalyst or other additive is selected to prevent or slow down deposition of the reaction products on the metal that tend to passivate the metal and thereby facilitates the production of hydrogen.

The present invention aims to alleviate at least one of the aforementioned disadvantages. In particular, the aim of the present invention is to upscale the process of aluminium hydrolysis to industrially produce aluminium hydroxide, hydrogen gas, and heat in a cost-effective and resource-efficient manner.

Summary of the Invention

According to a first embodiment, the invention provides a process for the reaction of aluminium with water, the process comprising the steps of: i. adding aluminium metal to an aqueous solution comprising potassium hydroxide at a concentration of between 0.1 M and 0.4M, and a surfactant; ii. agitating the mixture of step i whilst maintaining the temperature of the mixture at between 60°C and 90°C; collecting generated hydrogen.

s According to a second embodiment, the invention provides a composition for use in a process for reacting aluminium with water, comprising potassium hydroxide and a surfactant.

Brief Description of the Figures

Figure 1 is a schematic representation of a system of continuous process of aluminium hydrolysis.

Figure 2 is a graphical representation of level of foam produced with increased concentration of surfactant.

Figure 3 is a graphical representation of settling speed of aluminium hydroxide with increasing concentration of surfactant.

Figure 4 illustrates the hydrogen flow rate with differing agitation speed.

Definitions Some of the terms used to describe the invention are explained below. A person skilled in the art would have sufficient understanding of these terms, at least from the definitions provided below.

zo A "surfactant" is a chemical substance that reduces surface tension between two chemical species.

The term "non-ionic surfactant" is referred to surfactants which do not undergo ionisation when dissolved in water.

"Scrap aluminium" is recycled aluminium, such as, used beverage cans, used automotive spare parts, etc.

Detailed Description of the Preferred Embodiments

According to one embodiment, the invention relates to a process of reacting aluminium with water to produce aluminium hydroxide Al(OH)3, hydrogen gas 1-12, and heat in the presence of a composition comprising potassium hydroxide and a surfactant.

The overall reaction, as is well known, proceeds according to the following formula: Al + 3H20 3 1.5 H2 + Al(OH)3 + At In a preferred embodiment, the process takes place in a closed environment, such as a sealed reactor in which the aluminium metal is mixed with an aqueous solution comprising the dual-part catalyst -potassium hydroxide and surfactant. Venting means are generally provided to collect hydrogen produced.

Potassium hydroxide reacts with carbon dioxide to form potassium carbonate: 10 CO2 + 2KOH K2CO3 + H2O The formation of potassium carbonate degrades the efficacy of the catalyst and reduces its effective half-life. Therefore, it is important to protect potassium hydroxide from ambient atmosphere, and hence a sealed reactor is preferred.

Additionally, hydrogen ignites when mixed with air or oxygen. Therefore, it is preferable that the reactor is sealed, and that hydrogen gas is vented from the reactor as it is produced.

The water making up the aqueous solution is preferably selected from deionised water, distilled water and ultrapure water. This ensures that the aluminium hydroxide produced is of a higher purity. It also helps extend the working life of the potassium hydroxide catalyst.

Preferably, potassium hydroxide has a molarity of 0.1 M to 0.4M. More preferably, the molarity of potassium hydroxide is 0.3M to 0.4M, as it is observed that the reaction rate between aluminium and water is optimal with this concentration of potassium hydroxide. Unexpectedly, recovery of alumina from the reaction mixture is significantly greater when the concentration of potassium hydroxide is between 0.3M to 0.4M.

The surfactant reduces surface tension of liquid-solid interface at the surface of the aluminium metal. Preferably, surfactant may be a non-ionic surfactant which assists in removing the passivating layer of aluminium oxide covering the aluminium metal and increases the overall rate of reaction.

The surfactant may have the concentration of 0.01% v/v to 0.5% v/v. Preferably, the surfactant has the concentration of 0.08% v/v to 0.1% v/v.

In preferred embodiments of the present invention, the nonionic surfactants comprise alkoxylates such as polyglycol ethers, fatty alcohol polyglycol ethers, alkylphenol polyglycol ethers, end-capped polyglycol ethers, mixed ethers and hydroxy mixed ethers, and fatty acid polyglycol esters or mixtures thereof. Ethylene oxide/propylene oxide block polymers, fatty acid alkanolamides and fatty acid polyglycol ethers may be comprised as well. Another important class of nonionic surfactants that may be comprised are the polyol surfactants and in particular the glycol surfactants, such as io alkyl polyglycosides and fatty acid glucamides.

Preferred alcohol ethoxylates include the condensation products of aliphatic alcohols with 1 to 60 moles, preferably 5 to 30, more preferably 6 to 25, of an alkylene oxide, especially ethylene oxide or propylene oxide or mixtures thereof. Most preferred is ethylene oxide. The alkyl chain of the aliphatic alcohol can either be straight or is branched, primary or secondary, and generally contains from about 8 to about 22 carbon atoms, preferably 8 to 16, more preferably 8 to 12. Examples of such ethoxylated alcohols include the condensation product of myristyl alcohol condensed with about 10 moles of ethylene oxide per mole of alcohol and the condensation product of about 9 moles of ethylene oxide with coconut alcohol (a mixture of fatty alcohols with alkyl chains varying in length from about 10 to 14 carbon atoms). Other examples are those C6 to C22 straight-chain alcohols having 3 to 6 moles of ethylene oxide. Commercially available products include Alfonic® 810-4.5, comprising C8 to 010 straight-chain alcohols having 4.85 moles E0 (in the following EO is used as abbreviation for ethoxylation units = degree of ethoxylation); Alfonic® 810-2, comprising C8 to 010 straight-chain alcohols having 2.1 moles EO; and Alfonic® 610-3.5, having 3.1 moles EO. Other examples of alcohol ethoxylates are C10 oxo-alcohol ethoxylates available from BASF under the Lutensol® ON tradenamelike Lutensol® ON 30; Lutensol® ON 50; Lutensol® ON 60; Lutensol® ON 65; Lutensol® ON 66; Lutensol® ON 70; Lutensol® ON 80; and Lutensol® ON 110.

Other examples of ethoxylated alcohols include the Neodol ® 91 series non-ionic surfactants available from Shell Chemical Company which are described as C9 to C11 ethoxylated alcohols, like Neodol® 91-2.5, Neodol® 91-6, and Neodol® 91-8. Neodol® 91-2.5 have been described as having about 2.5 EO; Neodol® 91-6 has been described as having about 6 E0; and Neodol® 91-8 has been described as having about 8 E0. Further examples of ethoxylated alcohols include the Rhodasurf® DA series non-ionic surfactants available from Rhodia which are described to be branched isodecyl alcohol ethoxylates, like Rhodasurf® DA-530 having 4 moles ED; Rhodasurf® DA-630 having 6 moles ED; and Rhodasurf® DA-639 is a 90% solution of DA-630. Further examples of ethoxylated alcohols include those from Tomah Products (Milton, WI) under the Tomadol®. A further class of useful nonionic surfactants include primary and secondary linear and branched alcohol ethoxylates, such as those based on C6 to C18 alcohols which further include an average of from 2 to 80 moles of ethoxylation per mol of alcohol. These examples include the Genapol® UD like Genapol® UD 030 with 3 E0; Genapol® UD 050 with 5 EO; Genapol® UD 070 with 7 ED; Genapol® UD 080 with 8 E0; Genapol® UD 088 with 8 ED; and Genapol® UD 110 with 11 EO. Exemplary useful nonionic surfactants include the condensation products of a secondary aliphatic alcohols containing 8 to 18 carbon atoms in a straight or branched chain configuration condensed with 5 to 30 moles of ethylene oxide, like commercially available under the trade name of Tergitol®. Examples include Tergitol 15-S-12 having 9 EO, or Tergitol 15-S-9 which having 12 EO.

Most preferred fatty alcohol alkoxylates are unbranched or branched, saturated or unsaturated C8 to C22 alcohols alkoxylated with ethylene oxide (E0) and/or propylene oxide (PO) with a degree of alkoxylation 2 to 30, preferably ethoxylated C12 to 22 fatty alcohols with a degree of ethoxylation of 10 to 30, preferably 12 to 28, particularly 20 to 28, particularly preferably 25, for example C16 to 18 fatty alcohol ethoxylates containing 25 EO.

Alkyl polyglycosides which are as well suitable for the composition of the present invention are surfactants that can be obtained by the reaction of sugars and alcohols using appropriate methods of preparative organic chemistry, whereby according to the method of preparation, one obtains a mixture of monoalkylated, oligomeric or polymeric sugars. They are for example commercially available under the trade name Pluronics® (ex. BASF). The compounds are formed by condensing ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide with propylene glycol. The molecular weight of the hydrophobic portion of the molecule is of the order of 950 to 4,000 and preferably 200 to 2,500. The addition of polyoxyethylene radicals of the hydrophobic portion tends to increase the solubility of the molecule as a whole so as to make the surfactant water-soluble. Preferably, these surfactants are in liquid form at 25°C and particularly satisfactory surfactants are available as those marketed as Pluronics® L62 and Pluronics® L64. Preferred alkyl polyglycosides are the alkyl polyglucosides, wherein the alcohol is particularly preferably a long-chain fatty alcohol or a mixture of long-chain fatty alcohols with branched or unbranched C8 to C18 alkyl chains and the degree of oligomerization (DP) of the sugar is between 1 and 10, advantageously 1 to 6, particularly 1.1 to 3, most preferably 1.1 to 1.7, for example C8 tol 0 alkyl-1.5-glucoside (DP of 1.5). Their preparation is known to the skilled person.

Fatty alcohol ethoxylates are preferably employed in amounts of 0.1 to 10 wt.-%, particularly preferably 0.5 to 8 wt.-%, and particularly preferably from 1 to 5 wt.-%. Additional nonionic surfactants, such as fatty acid monoalkanolamides and/or alkyl polyglycosides, may be included in amounts of 0.1 to 10 wt.-%, preferably 0.5 to 6 wt.-%, more preferably 1 to 4 wt.-% based on the total weight of the composition.

In a preferred embodiment the nonionic surfactants can comprise polyalkylene oxide condensates of alkyl phenols. These compounds include the condensation products of alkyl phenols having an alkyl group containing from about 6 to 12 carbon atoms in either a straight chain or branched chain configuration with an alkylene oxide, especially an ethylene oxide, the ethylene oxide being present in an amount equal to to 25 moles of ethylene oxide per mole of alkyl phenol. The alkyl substituent in such compounds can be derived, for example, from polymerized propylene, diisobutylene and the like. Examples of compounds of this type include nonyl phenol condensed with about 9.5 moles of ethylene oxide per mole of nonyl phenol; dodecylphenol condensed with about 12 moles of ethylene oxide per mole of phenol; dinonyl phenol condensed with about 15 moles of ethylene oxide per mole of phenol and diisooctyl phenol condensed with about 15 moles of ethylene oxide per mole of phenol.

The nonionic surfactants can alternatively be selected from alkoxylated alkanolamides, preferably C8 to C24 alkyl di(C2 to C3 alkanol amides), as described in WO 2007148054 Al.

Alternatively, the nonionic surfactants preferably comprise nonionic amine oxide surfactants. Exemplary amine oxides include: A) Alkyl di (lower alkyl) amine oxides in which the alkyl group has about 10 to 20, and preferably 12 to16 carbon atoms, and can be straight or branched chain, saturated or unsaturated. The lower alkyl groups include between 1 and 7 carbon atoms.

Examples include lauryl dimethyl amine oxide, myristyl dimethyl amine oxide, and those in which the alkyl group is a mixture of different amine oxide, dimethyl cocoamine oxide, dimethyl (hydrogenated tallow) amine oxide, and myristyl/palmityl dimethyl amine oxide; B) Alkyl di (hydroxy lower alkyl) amine oxides in which the alkyl group has about 10 to 20, and preferably 12 to 16 carbon atoms, and can be straight or branched chain, saturated or unsaturated.

In a preferred embodiment, the surfactant has anti-foaming properties. It allows the microbubbles of hydrogen gas forming on the surface of the aluminium metal to quickly coalesce thus increasing their critical mass and escape through floatation.

is Thus, the surfactant reduces the formation of insulating layer formed by the gathering of hydrogen gas microbubbles on the surface of aluminium metal that slows down the reaction.

Verification of the foaming power was carried out by the method described in the examples.

In a preferred embodiment, the surfactant is a non-ionic surfactant which can withstand high pH environments of the reactor. Preferred non-ionic surfactant are silicone derived surfactants. Silicone based surfactants have been found to exhibit good levels of foam suppression and resist degradation in the alkaline environment of the reaction mixture compared to alcohol-based alternatives.

The silicone derived surfactants may be selected from any of a silicone, a siloxane (such as polydimethylsiloxane), and a polysiloxane. It is observed that silicone derived surfactants achieve the best results at low level dosing. Preferably, the concentration of silicone derived surfactants is between 0.01% v/v to 0.5% v/v.

Without wishing to be bound by any such assertion, amongst the advantages of using the composition comprising potassium hydroxide and the surfactant are: -It accelerates the reaction between aluminium and water; It enhances the wetting of aluminium due to reduced surface tension between the surface of the aluminium metal and the aqueous solution; It enables hydrogen bubbles to escape easily and quickly; It assists in the precipitation of aluminium hydroxide by suppressing foaming; Both potassium hydroxide and the surfactant are largely not consumed in the process, and they can be added together which makes the whole process simpler and economical.

Preferably, the pH of the aqueous solution is between 11 and 14. In a preferred embodiment, the aqueous solution has the pH of 13.4 to 13.6.

io In a preferred embodiment, the aluminium metal used in this process comes from scrap aluminium which is easily available, cost-effective, and environmentally-friendly.

The surface covering the scrap aluminium may be composed of a mixture of aluminium metal (Al), aluminium oxide (A1203) and aluminium hydroxide (Al(OH)3). A coating of a plastics material, paint, or other non-metallic substance may be present.

Thus, the following reactions are believed to take place in the reactor: Aluminium metal reacts with water to produce aluminium hydroxide, hydrogen gas, and heat as mentioned above.

Aluminium oxide reacts with potassium hydroxide to form potassium tetrahydroxoaluminate(III) (K[Al(OH)4]). However, the levels of aluminium oxide on the surface of the scrap metal is very low and hence, very little amount of potassium hydroxide is consumed by aluminium oxide. In return, it exposes a clean surface of aluminium for further hydrolysis.

Aluminium hydroxide reacts with potassium hydroxide present in the aqueous solution and forms tetrahydroaluminate, Al(OH)4-. However, this aluminium hydroxide ion having an additional hydroxyl group is unstable and hence decomposes into aluminium hydroxide that precipitates. Potassium hydroxide is regenerated. This whole process also results in the formation of hygrogen gas: Al(OH)3 + KOH + H2O 4 (aq)A1(OH)4-+ K+ + H2 The ultimate outcome of the above reactions is that these will remove the protective coating from the aluminium metal exposing a clean aluminium surface available to react with water inside the reactor. The hydrolysis continues until all of the aluminium metal is consumed to produce aluminium hydroxide, hydrogen gas, and heat.

Thus, scrap aluminium can be used for this process without requiring any cleaning steps to remove the protective surface.

In an alternative embodiment, the scrap aluminium may have a resinous and polymeric coating. Such coatings need to be removed for the aluminium to be available for the hydrolysis reaction.

Conventional technology involves heating the metal prior to smelting and capturing the noxious fumes with filters. Other methods may entail the use of acetone, hot organic or synthetic oils, etc. However, these methods are environmentally damaging, and uneconomical.

In the present invention, such coating is removed in a simpler, environmentally friendly, and cost-effective manner. Aluminium having resinous and polymeric coating are exposed to the temperatures of 350°C to 390°C (below the flash-point of the coating) for a very brief amount of time. This super-sets the coating making it hard and brittle. The hot particles are then plunged into a weak solution of aqueous potassium hydroxide such as the aqueous solution mentioned above.

The thermal shock damages or blows the layer of super-set coating from the surface of the aluminium while the corrosive nature of the aqueous potassium hydroxide serves to further clean the surface. The solution of aqueous potassium hydroxide does not need to be strong because cleaning is accelerated by virtue of the temporarily elevated temperature of the metal particles which quickly cool and so the reaction dwindles.

Hydrogen and any steam evolving from this cleaning process can be captured and 25 filtered and the hydrogen can be used for the system pre-heating the aluminium particles. This makes the process clean and economical.

The aluminium metal used for aluminium hydrolysis preferably have an average particle size of 5mm to 12 mm. Generally, the smaller the size of aluminium particles, the greater the rate of reaction. Preferably, the aluminium used is shred particles of 30 varying thickness having an average of around 0.75mm.

In a preferred embodiment, the process of aluminium hydrolysis comprises a step of agitating the mixture of aluminium metal and the aqueous solution comprising the composition of surfactant and potassium hydroxide.

Agitation may be mild and provided in the form of paddles, impellors, mild s electrolysis, or ultrasonic energy. The aluminium particles have sharp edges and so when they are moved even at a low speed by agitation, they effectively abrade each other. This cleans the aluminium surface at regular intervals which exposes further metal for reaction with water. Additionally, mild agitation means that the process consumes very little energy.

Preferably, the mixing speed is at least 10 rpm, such as at least 50 rpm or at least rpm. More preferably, the mixing speed is between 100 and 150 rpm. In a preferred embodiment, smaller reactors, such as those of around 20-30 litres of capacity, may have the agitation speed of at least 100 rpm. In a more preferred embodiment, larger reactors, such as those having the capacity of 500 to 700 litres, may have the agitation speed of 20 rpm to 30 rpm.

The low stirring speed also reduces the formation of foam within the reactor which, when coupled with the anti-foaming action of the surfactant, ensures that the reactor and filtration environment for aluminium hydroxide remains efficient.

According to one embodiment, the process of aluminium hydrolysis is a continuous 20 process wherein the reactants are fed into the reactor and the products are extracted from the reactor in a continuous flow. Such a process results in a cost-effective, simpler and an automated system for hydrogen production.

In a continuous process, the hydrogen gas may be extracted out of the reactor when the pressure exceeds a predetermined pressure inside the reactor.

Aluminium hydroxide may be separated and filtered out of the reactor in a continuous manner so that its concentration inside the reactor remains less than 50% at all times.

The excess heat produced during this process may be extracted by converting it into electrical energy. Thus, the temperature inside the reactor may be set so that it is maintained between 60 °C to 90 °C and when the ambient temperature exceeds this unit, excess heat is extracted out of the reactor. However, depending on the construction of the reaction vessel, the temperature can be maintained at a higher level, such as above 90 °C, above 100 °C, above 150 °C or above 180 °C. The reaction would inevitably proceed at a faster rate at these temperatures.

The pressure inside the reaction vessel is preferably maintained at a constant level s to achieve the desired rate of hydrogen evolution and solid product purity.

Preferably, the pressure is maintained at at least 100 kPa, such as at least 200 kPa, or at least 1,000 kPa.

Heat would typically be extracted with a heat exchanger as part of the cooling process to maintain a safe operating temperature and pressure. In an industrial model the cooling liquid might typically be an alcohol that has a low boiling point and that pressure be used to drive a low pressure steam turbine to generate electricity. Alternatively the cooling system could be run at a vacuum where water might typically boil at 20° Centigrade or lower and the pressure developed by the "boil" event used to drive a steam turbine.

As shown in Figure 1, in a preferred embodiment, there is provided a system of continuous process of aluminium hydrolysis, continuous filtration of aluminium hydroxide, continuous recirculation of the composition comprising surfactant, and continuous extraction of hydrogen gas and excess heat.

Aluminium hydroxide has a specific gravity of 2.42 at 20°C which means that it rapidly settles after precipitation. Its relatively high gravimetric weight also lends itself to centrifugal filtration with the aid of a hydrocyclone filter. The advantage of a hydrocyclone filter is that there are no moving parts, it is self-cleaning, can operate as part of a sealed and closed loop system.

Any dense impurities may be removed using a sump. Floating impurities such as 25 plastic may be removed by skimming.

Various modifications and improvements will be apparent to those skilled in the art without departing from the scope of the invention. Relative terms such as "mild", "high", "strong", etc. are used for illustrative purposes only and are not intended to limit the scope of the invention.

Examples

Example 1

Aluminium was reacted with water containing a range of concentrations of KOH and a silicone-based DOWSILTM AFE-7600 Antifoam Emulsion surfactant at a concentration of 1000ppm. A 10-litre reactor was charged with 5 litres of water.

Each run was conducted with 100 grams of mixed engineering aluminium swarf particles ranging between 5mm -12mm of varying thickness but no greater than 0.75mm. The speed of agitation was 100 RPM. The measurements were taken using a hydrogen mass flow gauge (Sierra Instruments, Sierra Instruments, Monterey, CA, USA) calibrated to 20 LPM. The results are shown in Table 1 below: Aluminium KOH/ Litre (Grams) KOH j Molar Peak H2 j Mass of AI Remaining Grams of Swart Mass Value pH How Duration (Grams) IPM Al(OH(3 (Gram) LPIVI (iViins) Remaining Activity recovered 5.6 0.1 13 3.5 45 60 1 45 11.2 0.2 13.3 4.75 45 45 0.5 90 16.8 0.3 13.48 6 45 12 0.4, 135 1()0 22.4, 0 4 45 8 0.3 140 28.1 0.5 13.7 7.5 45 5 0.2 110 39.3 0,7 113.78 8.25 45 4 0.2 92 103 39 3 0.7 13.85 9 45 3 0 81 103 44.9 0.8; 13.9 10.2 45 0 72 103 50.5 0.9 113.95 11 45 2 0 60 56.1 1 1 14 12.5 45 2 0 45 Recovery of alumina was greatest in the highlighted columns at a KOH concentration of between 0.3 M and 0.4 M

Example 2

This example assessed the suitability of two silicone-based surfactants for use in the process of the invention.

DOWSILTM AFE-7600 Antifoam Emulsion (DOW Chemicals, Midland, Michigan, United States) was introduced into a 2 litre glass beaker filled to 1 litre of 0.4 mol KOH and 50 cc of Al(OH)3 to create a liquid Al(OH)3 emulsion. A small volume of liquid soap (0.25m1) was added to assist in the formation of bubbles.

The beaker was heated to 80 °C on a heat plate and stirred with an overhead stirrer at 100 RPM.

Hydrogen was bubbled through the beaker at 1 litre per minute.

Foam bubbles were allowed to form and fill the upper portion of the beaker. The relative foam mass above the liquid level was measured. The results are tabulated below and are shown in Figures 2 and 3: Foam Test: Temperature 80' C H2 Flow rate 1 IPM KOH mol / litre a4 Dosing CC 0 0.2 0.3 0.4 0.5.6 0.7 0.8 OS Level of foam (ml) 1000 900 700 500 300 200 10 0 0 0 Settle Speed (minutes) 13 10 8 7.5 6 6 4 4 Total foam suppression was achieved at a concentration of surfactant of over 0.08% v/v. The alumina settle speed was also optimal at these concentrations.

Example 3

A 10-litre reactor was charged with 50 grams of aluminium particles and 5 litres of 10 aqueous KOH (concentration 0.4 M) containing 0.08% DowsilTM AFE-7600 at a temperature of 80 °C. The stirring speed was varied (RPM), and the rate of hydrogen production was measured (LPM). The results are shown in the table below and Figure 4.

Temperature 80C Diameter of paddle 150 Mass of Aluminium S'starf 50g RPM 10 20 30 40 50 60 70 80 90 00 110 120 130 140 150 LP WI 2.5 2.6 2.7 2.71J 2.72 2.73 2.73 2.74 2.74 2.75 2.75 2.75 2.75 2.75 2.75 The rate of hydrogen production increased up to about 100 RPM, beyond which no further improvement was observed.

Claims (25)

1. Claims 1. A process for the reaction of aluminium with water, the process comprising the steps of: i. adding aluminium metal to an aqueous solution comprising potassium hydroxide at a concentration of between 0.1 M and 0.4M and a surfactant; ii. agitating the mixture of step i; iii. collecting generated hydrogen.
2. 2. A process according to claim 1, wherein the agitation occurs at a temperature of between 60 °C and 90 °C.
3. 3. A process according to claim 1 or 2, wherein the surfactant has wetting properties.
4. 4. A process according to any preceding claim, wherein the surfactant has defoaming properties.
5. 5. A process according to any preceding claim, wherein the surfactant is a non-ionic surfactant.
6. 6. A process according to any of the preceding claims wherein the surfactant is selected from a non-ionic silicone derived surfactant and a non-ionic alcohol derived surfactant.
7. 7. A process according to claim 6, wherein the surfactant is selected from a silicone, a siloxane, and a polysiloxane, or a combination thereof.
8. 8. A process according to claim 6, wherein the surfactant is selected from polyethylene-polypropylene glycol, polypropylene glycol, alkyl polyethylene glycol ether, polyethylene glycol, and dipropylene glycol. is
9. 9. A process according to any of the preceding claims, wherein the potassium hydroxide is at a concentration of between 0.3M to 0.4M.
10. 10.A process according to any of the preceding claims, wherein the temperature of the reactor is maintained at between 75°C and 85°C.
11. 11.A process according to any of the preceding claims, wherein the aluminium metal is scrap aluminium.
12. 12.A process according to any preceding claim, wherein the agitation is achieved by one or more of mechanical agitation, rotary mixing, and sonication.
13. 13.A process according to claim 12, wherein the rotary mixing speed is at least 100 rpm, such as between 100 and 150 rpm.
14. 14.A process according to any of the preceding claims, wherein the water is selected from any of deionised, distilled, and ultrapure water.
15. 15.A process according to any of the preceding claims wherein the process comprises a step of separating solid product from the reaction mixture.
16. 16.A process according to claim 15 wherein the solid product is aluminium hydroxide.
17. 17.A process according to claim 15 or 16 wherein the solid product is separated using a hydrocyclone.
18. 18.A process according to any of the preceding claims wherein the process comprises a step of removing dense impurities using a sump.
19. 19.A process according to any of the preceding claims wherein the process comprises a step of removing floating impurities such as plastic by skimming.
20. 20.A process according to any preceding claim wherein the process is conducted in a sealed reactor which allows hydrogen to be vented and collected.
21. 21.A process according to any preceding claim, wherein the process is operated in a continuous fashion.
22. 22.A process according to any preceding claim, wherein heat generated by the reaction is captured.
23. 23.A process according to any of the preceding claims, wherein the aluminium metal is provided in the form of particles of 5mm to 12mm.
24. 24.A composition for use in a process for reacting aluminium with water, comprising potassium hydroxide and a surfactant.
25. 25.A composition according to claim 23, wherein the surfactant is selected from any of silicone, siloxane, polysiloxane.