How to produce hydrogen

Abstract

A process for reacting aluminum with water, comprising the steps of adding metallic aluminum to an aqueous solution containing potassium hydroxide at a concentration of 0.1 M to 0.4 M and a surfactant, stirring the mixture obtained in the previous step, and recovering the hydrogen produced. A composition containing potassium hydroxide and a surfactant for use in such a process for reacting aluminum with water.

Description

[Technical Field]

[0001] The present invention relates to the fields of chemistry and chemical engineering. In particular, the present invention relates to a process for the hydrolysis of aluminum to produce aluminum hydroxide and hydrogen gas, and to generate heat. The present invention also relates to a catalyst for use in such a process. [Background technology]

[0002] It is well known that aluminum reacts exothermically with water to produce hydrogen and aluminum hydroxide (Al(OH)3). Such a reaction could be very useful, particularly for driving fuel cell devices and as a heat source for heat engines. However, the known process is less than optimal for several reasons, in particular because a protective layer of oxide or hydroxide present on the surface of aluminum inhibits the reaction.

[0003] The hydrolysis of aluminum has also been widely studied to produce aluminum hydroxide, which is used in many industries, including textiles, pharmaceuticals, and cosmetics. Aluminum hydroxide is typically produced by the Bayer process, in which bauxite is heated with sodium hydroxide solution in a pressure vessel at 150-200°C. At these temperatures, aluminum is converted into sodium aluminate (mainly [Al(OH)4]). - The residue is separated by filtration, the solution is cooled, and then fine aluminum hydroxide crystals from the previous extraction are added as seeds, resulting in the precipitation of gibbsite. The resulting product is of low purity. Furthermore, the process is energy-intensive, uneconomical, and environmentally harmful.

[0004] The hydrogen production process is also mentioned in "Hydrogen Production by Oxidation of Coarse Aluminum in a Low-Concentration Alkaline Aqueous Solution under Vigorous Stirring" (International Journal of Hydrogen Energy; 2016; Issue 41; Pages 17216-17224). However, this method requires a large amount of energy during vigorous stirring, and the aluminum metal must be activated before it can be used for hydrogen production, which increases the process cost and the environmental impact, making it impractical.

[0005] U.S. Patent No. 6,506,360 discloses a method for producing hydrogen by reacting aluminum with water in the presence of sodium hydroxide as a catalyst. The apparatus for carrying out this method uses reaction pressure and reaction temperature to control the degree of immersion of the fuel cartridge in water, thereby controlling the intensity and duration of the reaction.

[0006] U.S. Patent No. 6,638,493 discloses a process for producing hydrogen gas by reacting aluminum with water using sodium hydroxide as a catalyst. In one aspect of the present invention, a process for producing hydrogen gas is provided, the process comprising providing an aqueous solution of NaOH in a vessel, the aqueous solution having a concentration ranging from 0.26 M to 19 M.

[0007] U.S. Patent No. 714,456 describes a renewable energy carrier system and method using metallic aluminum as a carrier. The metallic aluminum reacts with water in a catalytic reaction, decomposing the water into hydrogen and oxygen and producing a clean aluminum derivative. The hydrogen is converted into useful energy, and the aluminum derivative is recycled back to metallic aluminum.

[0008] WO 02 / 14213 relates to a method for producing hydrogen by reacting a metal selected from the group consisting of aluminum (Al), magnesium (Mg), silicon (Si) and zinc (Zn) with water in the presence of an effective amount of a catalyst at a pH ranging from 4 to 10. The catalyst or other additive is selected to prevent or inhibit the deposition of reaction products on the metal surface that tend to passivate the metal, thereby facilitating the production of hydrogen.

[0009] The present invention aims to alleviate at least one of the above-mentioned drawbacks, and in particular to scale up the process of aluminum hydrolysis to industrially produce aluminum hydroxide, hydrogen gas and heat in a cost-effective and resource-efficient manner. Summary of the Invention

[0010] According to a first embodiment, the present invention provides a process for the reaction of aluminum with water, the process comprising: (i) adding metallic aluminum to an aqueous solution containing potassium hydroxide and a surfactant at a concentration of 0.1M to 0.4M; (ii) stirring the mixture obtained in step (i) while maintaining the temperature of the mixture between 60°C and 90°C; (iii) recovering the produced hydrogen.

[0011] According to a second embodiment, the present invention provides a composition containing potassium hydroxide and a surfactant for use in a process for reacting aluminum with water. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a system for continuous processing of aluminum hydrolysis. [Figure 2] FIG. 2 is a graph showing foam volume with increasing surfactant concentration. [Figure 3]FIG. 3 is a graph showing the sedimentation rate of aluminum hydroxide with increasing surfactant concentration. [Figure 4] FIG. 4 shows the hydrogen flow rate at different stirring speeds.

[0013] definition Below are explained some of the terms used in describing the present invention, which will be fully understood by those of ordinary skill in the art from at least the definitions set forth below.

[0014] "Surfactant" refers to a chemical that reduces the interfacial tension between two chemical species.

[0015] "Nonionic surfactant" refers to a surfactant that does not ionize when dissolved in water.

[0016] "Aluminum scrap" refers to recycled aluminum, such as used beverage cans, used automobile parts, etc. DETAILED DESCRIPTION OF THE INVENTION

[0017] In one embodiment, the present invention relates to a process for producing aluminum hydroxide (Al(OH)), hydrogen gas (H), and heat by reacting aluminum with water in the presence of a composition comprising potassium hydroxide and a surfactant.

[0018] The overall reaction, as is well known, proceeds according to the following equation: Al + 3H2O → 1.5H2 + Al(OH)3 + Δt

[0019] In a preferred embodiment, the process is carried out in a closed environment, such as a sealed reactor in which aluminum metal is mixed with an aqueous solution containing a binary catalyst (potassium hydroxide and a surfactant), typically with a vent means for collecting the hydrogen produced.

[0020] Potassium hydroxide reacts with carbon dioxide to produce potassium carbonate. CO2+2KOH→K2CO3+H2O

[0021] The formation of potassium carbonate reduces the activity of the catalyst and shortens its effective half-life, therefore it is important to protect the potassium hydroxide from the ambient atmosphere, and for this reason a closed reactor is preferred.

[0022] Furthermore, hydrogen ignites when mixed with air or oxygen, so the reactor is preferably sealed and hydrogen gas is preferably vented to the outside of the reactor as soon as it is produced.

[0023] The water constituting the aqueous solution is preferably selected from the group consisting of deionized water, distilled water, and ultrapure water, which ensures higher purity of the produced aluminum hydroxide and contributes to extending the useful life of the potassium hydroxide catalyst.

[0024] Preferably, the molarity of potassium hydroxide is in the range of 0.1 M to 0.4 M. More preferably, the molarity of potassium hydroxide is in the range of 0.3 M to 0.4 M, since it has been observed that the reaction rate between aluminum and water is optimal at these concentrations. Surprisingly, the recovery of alumina from the reaction mixture is significantly higher when the potassium hydroxide concentration is in the range of 0.3 M to 0.4 M.

[0025] The surfactant reduces the interfacial tension of the liquid-solid interface at the surface of the aluminum metal, and preferably is a non-ionic surfactant that aids in the removal of the passivating layer of aluminum oxide that covers the aluminum metal and enhances the overall reaction rate.

[0026] The concentration of the surfactant can be from 0.01% (v / v) to 0.5% (v / v), preferably from 0.08% (v / v) to 0.1% (v / v).

[0027] In a preferred embodiment of the present invention, the nonionic surfactant comprises an alkoxylate (e.g., polyglycol ether, fatty alcohol polyglycol ether, alkylphenol polyglycol ether, end-capped polyglycol ether, mixed ether, hydroxy mixed ether, etc.) and a fatty acid polyglycol ester, or a mixture thereof. Further, ethylene oxide / propylene oxide block copolymers, fatty acid alkanolamides, and fatty acid polyglycol ethers may also be included. Another important class of nonionic surfactants that may be included are polyol-based surfactants, particularly glycol-based surfactants, such as alkyl polyglycosides and fatty acid glucamides.

[0028] Preferred alcohol ethoxylates include condensation products of aliphatic alcohols with 1 to 60 moles (preferably 5 to 30 moles, more preferably 6 to 25 moles) of alkylene oxide, particularly ethylene oxide, propylene oxide, or a mixture thereof. Ethylene oxide is most preferred. The alkyl chain of the aliphatic alcohol may be linear or branched. The aliphatic alcohol may be primary or secondary. The alkyl chain generally contains about 8 to about 22 carbon atoms, preferably about 8 to about 16 carbon atoms, and more preferably about 8 to about 12 carbon atoms. Examples of such ethoxylated alcohols include the condensation product of myristyl alcohol with about 10 moles of ethylene oxide per mole, and the condensation product of coconut alcohol (a mixture of fatty alcohols having an alkyl chain of about 10 to 14 carbon atoms) with about 9 moles of ethylene oxide per mole. Other examples include adducts of 3 to 6 moles of ethylene oxide with linear alcohols having 6 to 22 carbon atoms. Commercially available products include Alfonic® 810-4.5 (a C8-C10 linear alcohol with 4.85 moles EO (hereinafter EO is used as an abbreviation for ethoxylated units [=degree of ethoxylation]), Alfonic® 810-2 (a C8-C10 linear alcohol with 2.1 moles EO), and Alfonic® 610-3.5 (with 3.1 moles EO). Other examples of alcohol ethoxylates include C10 oxoalcohol ethoxylates available from BASF under the trade name Lutensol® ON. Typical examples include 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 of nonionic surfactants available from Shell Chemical Company, which are described as C9 to C11 ethoxylated alcohols.Examples include Neodol® 91-2.5, Neodol® 91-6, and Neodol® 91-8. Neodol® 91-2.5 is described as having approximately 2.5 EO, Neodol® 91-6 is described as having approximately 6 EO, and Neodol® 91-8 is described as having approximately 8 EO. Further examples of ethoxylated alcohols include the Rhodasurf® DA series of nonionic surfactants available from Rhodia, which are described as branched isodecyl alcohol ethoxylates. Examples include Rhodasurf® DA-530 (having 4 moles of EO), Rhodasurf® DA-630 (having 6 moles of EO), and Rhodasurf® DA-639 (a 90% solution of DA-630). Further examples of ethoxylated alcohols include those available under the Tomadol® brand from Tomah Products, Inc. (Milton, Wisconsin). A further group of useful nonionic surfactants includes linear and branched primary and secondary alcohol ethoxylates, including those based on, for example, C6-C18 alcohols and having an average of 2 to 80 moles of ethoxylated units per mole of alcohol. Examples include Genapol® UD, such as Genapol® UD030 (with 3 EO), Genapol® UD050 (with 5 EO), Genapol® UD070 (with 7 EO), Genapol® UD080 (with 8 EO), Genapol® UD088 (with 8 EO), and Genapol® UD110 (with 11 EO). Examples of useful nonionic surfactants include condensation products of secondary aliphatic alcohols having a linear or branched chain structure and containing 8 to 18 carbon atoms with 5 to 30 moles of ethylene oxide, such as those commercially available under the trade name Tergitol®.Examples include Tergitol® 15-S-12 (with 9 EO) or Tergitol® 15-S-9 (with 12 EO).

[0029] The most preferred fatty alcohol alkoxylates are those in which a linear or branched, saturated or unsaturated C8 to C22 fatty alcohol is alkoxylated with ethylene oxide (EO) and / or propylene oxide (PO) to an alkoxylation degree of 2 to 30, preferably a C12 to 22 fatty alcohol ethoxylate having an ethoxylation degree of 10 to 30, more preferably 12 to 28, even more preferably 20 to 28, and particularly preferably 25, such as a C16 to 18 fatty alcohol ethoxylate having 25EO.

[0030] Alkyl polyglycosides, which are also suitable for the compositions of the present invention, are surfactants obtained by the reaction of sugars with alcohols using suitable methods of organic synthesis, resulting in mixtures of mono-, oligo-, or polyalkyl glycosides. These are commercially available, for example, under the trade name Pluronics® (BASF). These compounds are obtained by condensing ethylene oxide with a hydrophobic group obtained by condensation of propylene oxide with propylene glycol. The molecular weight of the hydrophobic portion of the molecule ranges from 950 to 4,000, preferably 200 to 2,500. The introduction of polyoxyethylene radicals into the hydrophobic portion tends to increase the solubility of the entire molecule, making the surfactant water-soluble. Preferably, these surfactants are liquid at 25°C. Particularly suitable surfactants include those commercially available under the names Pluronics® L62 and Pluronics® L64. Preferred alkyl polyglycosides are alkyl polyglucosides, in which the alcohol is particularly preferably a long-chain fatty alcohol having a branched or linear C8-C18 alkyl chain, or a mixture thereof, and the degree of polymerization (DP) of the sugar is from 1 to 10, preferably from 1 to 6, more preferably from 1.1 to 3, and most preferably from 1.1 to 1.7, such as C8-C10 alkyl-1.5-glucoside (DP=1.5). Their preparation is well known to those skilled in the art.

[0031] The fatty alcohol ethoxylate is preferably used in an amount of 0.1 to 10% by mass, particularly preferably 0.5 to 8% by mass, and even more particularly preferably 1 to 5% by mass. Furthermore, a nonionic surfactant such as a fatty acid monoalkanolamide and / or an alkyl polyglycoside may be contained in an amount of 0.1 to 10% by mass, preferably 0.5 to 6% by mass, and more preferably 1 to 4% by mass, based on the total weight of the composition.

[0032] In a preferred embodiment, the nonionic surfactant may comprise a polyalkylene oxide condensate of an alkylphenol. These compounds include condensation products of alkylphenols having a linear or branched alkyl group containing about 6 to 12 carbon atoms with an alkylene oxide (especially ethylene oxide). The amount of ethylene oxide is equivalent to 5 to 25 moles per mole of alkylphenol. The alkyl substituents in such compounds may be derived, for example, from polymers of propylene or diisobutylene. Examples of this type of compound include nonylphenol, which is condensed with about 9.5 moles of ethylene oxide per mole of nonylphenol; dodecylphenol, which is condensed with about 12 moles of ethylene oxide per mole of phenol; dinonylphenol, which is condensed with about 15 moles of ethylene oxide per mole of phenol; and diisooctylphenol, which is condensed with about 15 moles of ethylene oxide per mole of phenol.

[0033] The nonionic surfactant may alternatively be selected from alkoxylated alkanolamides, preferably alkoxylated C8-C24 alkyldi(C2-C3 alkanolamides), as disclosed in WO 2007 / 148054.

[0034] Alternatively, the nonionic surfactant preferably comprises a nonionic amine oxide surfactant. Exemplary amine oxides include: A) alkyl di(lower alkyl) amine oxides, in which the alkyl group contains about 10 to 20 carbon atoms (preferably 12 to 16 carbon atoms), which may be straight or branched chain and saturated or unsaturated. Lower alkyl groups include alkyl groups containing 1 to 7 carbon atoms.

[0035] For example, lauryl dimethylamine oxide, myristyl dimethylamine oxide, and mixtures of amine oxides with different alkyl groups (e.g., dimethyl coco amine oxide, dimethyl (hydrogenated beef tallow) amine oxide, myristyl / palmityl dimethylamine oxide; B) alkyl di(lower hydroxyalkyl) amine oxides, in which the alkyl group has about 10 to 20 carbon atoms (preferably 12 to 16), and may be linear or branched, saturated or unsaturated.

[0036] In a preferred embodiment, the surfactant has antifoaming properties, which allow hydrogen gas microbubbles generated on the surface of the aluminum metal to coalesce quickly, increasing their critical mass and allowing them to float away from the surface. Thus, the surfactant prevents the formation of an insulating layer on the surface of the aluminum metal that slows down the reaction.

[0037] The evaluation of foaming power was carried out by the method described in the Examples.

[0038] In a preferred embodiment, the surfactant is a nonionic surfactant that can withstand the high pH environment in the reactor. Preferred nonionic surfactants are silicone-based surfactants. Silicone-based surfactants have been found to exhibit better foam suppression than alcohol-based alternatives and to be resistant to degradation in the alkaline environment of the reaction mixture.

[0039] The silicone-derived surfactant may be selected from silicones, siloxanes (e.g., polydimethylsiloxanes), and polysiloxanes. It has been observed that silicone-derived surfactants provide the best results at low dosages. Preferably, the concentration of the silicone-derived surfactant ranges from 0.01% to 0.5% v / v.

[0040] Although it is not intended to be limiting in any way by the following description, advantages of using a composition containing potassium hydroxide and the surfactant include the following: -Accelerates the reaction between aluminum and water, - Improve the wettability of aluminum metal by reducing the interfacial tension between the surface of aluminum metal and the aqueous solution; - Allows hydrogen bubbles to desorb easily and quickly, - By suppressing foaming, it promotes the precipitation of aluminum hydroxide, Potassium hydroxide and surfactant are not substantially consumed during the process, and both can be added simultaneously, which simplifies the overall process and makes it more economical.

[0041] Preferably, the pH of the aqueous solution is from 11 to 14. In a preferred embodiment, the pH of the aqueous solution is from 13.4 to 13.6.

[0042] In a preferred embodiment, the metallic aluminum used in the present process is obtained from readily available, cost-effective, and environmentally friendly aluminum scrap.

[0043] The surface coating of the aluminum scrap may consist of a mixture of metallic aluminum (Al), aluminum oxide (Al2O3), and aluminum hydroxide (Al(OH)3). A coating layer of plastic material, paint, or other non-metallic material may also be formed. Therefore, the following reaction is believed to occur in the reactor: As mentioned above, metallic aluminum reacts with water to form aluminum hydroxide, as well as evolving hydrogen gas and heat. -Aluminum oxide reacts with potassium hydroxide to form potassium tetrahydroxoaluminate(III) (K[Al(OH)4]). However, the amount of aluminum oxide present on the surface of scrap metal is very small. Therefore, only a small amount of potassium hydroxide is consumed by the aluminum oxide. This exposes a clean aluminum surface, allowing for further hydrolysis. -Aluminum hydroxide reacts with potassium hydroxide in aqueous solution to form tetrahydroxoaluminate ions (Al(OH)4 - However, this hydroxide ion with its additional hydroxyl group is unstable and therefore decomposes to form aluminum hydroxide, which precipitates. Potassium hydroxide is regenerated. This entire process also results in the evolution of hydrogen gas. Al(OH)3 + KOH + H2O → (aq)Al(OH)4 - +K + +H2

[0044] The net result of the above reactions is that they remove the protective coating on the aluminum metal, exposing a clean aluminum surface that can react with the water in the reactor. Hydrolysis continues until all of the aluminum metal is consumed, producing aluminum hydroxide, hydrogen gas, and heat in the process.

[0045] Therefore, aluminum scrap can be used in the process without requiring a cleaning step to remove the protective surface coating.

[0046] In other embodiments, the aluminum scrap may have a resin or polymer coating that must be removed in order to subject the aluminum to the hydrolysis reaction.

[0047] In conventional techniques, metals are heated before smelting and harmful fumes are collected with a filter. Other methods include using acetone or heated organic or synthetic oils. However, these methods are environmentally hazardous and uneconomical.

[0048] This invention provides a simpler, more environmentally friendly, and more cost-effective method for removing these coatings. Aluminum coated with resinous and polymeric coatings is exposed to temperatures between 350°C and 390°C (below the flash point of the coating) for a very short period of time. This causes the coating to overcure, becoming hard and brittle. The hot particles are then immersed in a dilute potassium hydroxide solution, such as the one mentioned above.

[0049] The thermal shock damages or spalls or blows off the over-cured coating layer from the aluminum surface, while the corrosive properties of the potassium hydroxide solution contribute to further cleaning of the surface. The potassium hydroxide solution does not need to be highly concentrated because the temporary increase in temperature of the metal particles accelerates cleaning, but the particles cool quickly, damping the reaction.

[0050] The hydrogen and (possibly) water vapor generated from this cleaning process can be collected and filtered, and the hydrogen can be used in the system to preheat the aluminum particles, making the process clean and economical.

[0051] The metallic aluminum used for aluminum hydrolysis preferably has an average particle size of 5 mm to 12 mm. Generally, the smaller the aluminum particle size, the faster the reaction rate. Preferably, the aluminum used is in the form of fine pieces of varying thickness, the average thickness being about 0.75 mm.

[0052] In a preferred embodiment, the aluminum hydrolysis process comprises stirring a mixture of metallic aluminum and an aqueous solution containing a surfactant and potassium hydroxide.

[0053] Agitation can be gentle and can come in the form of paddles, impellers, mild electrolysis, or ultrasonic energy. Because aluminum particles have sharp edges, they effectively wear down even at slow agitation speeds. This repeatedly cleans the aluminum surface, exposing new metal surfaces available for water reaction. Furthermore, because the agitation is gentle, the energy consumption of the process is very low.

[0054] Preferably, the mixing speed is at least 10 rpm, e.g., at least 50 rpm or at least 100 rpm. More preferably, the mixing speed is in the range of 100 to 150 rpm. In a preferred embodiment, in a small reactor, e.g., about 20-30 liters in capacity, the stirring speed may be at least 100 rpm. In a more preferred embodiment, in a large reactor, e.g., 500-700 liters in capacity, the stirring speed may be 20-30 rpm.

[0055] Additionally, the slow agitation reduces foam generation within the reactor, which, combined with the anti-foaming action of the surfactant, maintains the efficiency of the reactor and filtration environment for the aluminum hydroxide.

[0056] According to one embodiment, the aluminum hydrolysis process is a continuous process in which reactants are continuously fed to a reactor and products are continuously removed from the reactor, resulting in a cost-effective, simpler, and more automated system for hydrogen production.

[0057] In a continuous process, hydrogen gas may be removed from the reactor when the pressure inside the reactor exceeds a predetermined pressure.

[0058] The aluminum hydroxide may be continuously removed from the reactor by separation and filtration so that its concentration in the reactor is always maintained below 50%.

[0059] Excess heat generated in this process can be recovered by converting it into electrical energy. Therefore, the temperature within the reactor may be set to be maintained in the range of 60°C to 90°C, and if the ambient temperature exceeds this range, excess heat can be removed from the reactor. However, depending on the configuration of the reaction vessel, the temperature can be maintained higher, for example, above 90°C, 100°C, 150°C, or 180°C. At these temperatures, the reaction necessarily proceeds at a higher rate.

[0060] The pressure in the reactor is preferably maintained constant to achieve the desired hydrogen production rate and purity of the solid product. Preferably, the pressure is maintained at 100 kPa or more, for example 200 kPa or more, or 1,000 kPa or more.

[0061] To maintain safe operating temperatures and pressures, heat is typically removed via a heat exchanger as part of the cooling process. In industrial embodiments, the coolant may typically be a low-boiling alcohol, the pressure of which can be used to drive a low-pressure steam turbine to generate electricity. Alternatively, the cooling system may operate under vacuum, boiling water at a vacuum level where the boiling point of water is typically below 20°C, and the pressure generated by this "boiling" event may be used to drive a steam turbine.

[0062] As shown in FIG. 1, in a preferred embodiment, a system is provided for continuous hydrolysis of aluminum, continuous filtration of aluminum hydroxide, continuous circulation of a surfactant-containing composition, and continuous recovery of hydrogen gas and excess heat.

[0063] Aluminum hydroxide has a specific gravity of 2.42 at 20°C, which allows it to settle quickly after precipitation. Its relatively high specific gravity also makes it suitable for centrifugation using hydrocyclone filters. The advantages of hydrocyclone filters are that they have no moving parts, are self-cleaning, and can operate as part of a sealed, closed-loop system.

[0064] Any high density impurities can be removed using a sump, and floating impurities such as plastics can be removed by skimming.

[0065] It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the scope of the present invention. Relative terms such as "mild," "high," and "strong" are used for descriptive purposes only and are not intended to limit the scope of the present invention.

[0066] Example Example 1 Aluminum was reacted with water containing various concentrations of KOH and a silicone antifoam emulsion surfactant (DOWSIL™ AFE-7600) at a concentration of 1000 ppm. Five liters of water were charged to a 10-liter reactor. Each test was performed using 100 g of mixed industrial aluminum swarf particles ranging from 5 to 12 mm in size and varying thicknesses, not exceeding 0.75 mm. The stirring speed was 100 rpm. Measurements were performed using a hydrogen mass flow meter (Sierra Instruments, Monterey, CA, USA) calibrated to 20 LPM. The results are shown in Table 1 below.

[0067] [Table 1]

[0068] The recovery of alumina was greatest in the highlighted column from 0.3M to 0.4M KOH concentration.

[0069] Example 2 In this example, two silicone surfactants were evaluated for suitability for use in the process of the present invention.

[0070] DOWSIL™ AFE-7600 antifoam emulsion (DOW Chemicals, Midland, Michigan, United States) was added to a 2 L glass beaker containing 1 L of 0.4 M KOH and 50 cc of Al(OH) to create a liquid Al(OH) emulsion. A small amount (0.25 mL) of liquid soap was added to promote foam production.

[0071] The beaker was heated to 80° C. on a hot plate and stirred at 100 rpm using an overhead stirrer.

[0072] Hydrogen gas was bubbled into the beaker at a flow rate of 1 L / min.

[0073] Foam was allowed to form and fill the headspace in the beaker. The relative mass of foam above the liquid surface was measured. The results are tabulated below and shown in Figures 2 and 3.

[0074] [Table 2]

[0075] When the surfactant concentration was above 0.08% (v / v), foaming was completely suppressed, and the settling rate of alumina was also optimal within this concentration range.

[0076] Example 3 A 10 L reactor was charged with 50 g of aluminum particles and 5 L of a 0.4 M KOH aqueous solution containing 0.08% DOWSIL™ AFE-7600 at 80°C. The stirring speed (RPM) was varied to measure the hydrogen production rate (LPM). The results are shown in the table below and in Figure 4.

[0077] [Table 3]

[0078] The hydrogen production rate increased until the rotational speed reached approximately 100 revolutions per minute (RPM), beyond which no further improvement was observed.

Claims

1. A process for the reaction between aluminum and water, (i) Adding metallic aluminum to an aqueous solution containing potassium hydroxide at a concentration of 0.1 M to 0.4 M and a surfactant selected from silicone, siloxane, and polysiloxane, or a combination thereof; (ii) A step of stirring the mixture obtained in step (i), (iii) A process for recovering the generated hydrogen, A process that includes this.

2. The process according to claim 1, wherein the stirring is performed at a temperature between 60°C and 90°C.

3. The process according to claim 1 or 2, wherein the concentration of the potassium hydroxide is between 0.3 M and 0.4 M.

4. The process according to claim 1 or 2, wherein the reactor temperature is maintained between 75°C and 85°C.

5. The process according to claim 1 or 2, wherein the metallic aluminum is aluminum scrap.

6. The process according to claim 1 or 2, wherein the stirring is performed by at least one selected from mechanical stirring, rotary mixing, and ultrasonic treatment.

7. The process according to claim 6, wherein the rotational mixing speed is at least 100 rpm, for example, 100 to 150 rpm.

8. The process according to claim 1 or 2, wherein the water is selected from deionized water, distilled water, and ultrapure water.

9. The process according to claim 1 or 2, wherein the process includes a step of separating a solid product from the reaction mixture.

10. The process according to claim 9, wherein the solid product is aluminum hydroxide.

11. The process according to claim 9, wherein the solid product is separated using a hydrocyclone.

12. The process according to claim 1 or 2, further comprising the step of removing high-density impurities using a sump.

13. The process according to claim 1 or 2, wherein the process includes a step of removing suspended impurities, such as plastic, by skimming.

14. The process according to claim 1 or 2, wherein the process is carried out in a closed reactor capable of exhausting and recovering hydrogen.

15. The process according to claim 1 or 2, wherein the process is carried out continuously.

16. The process according to claim 1 or 2, wherein the heat generated by the reaction is recovered.

17. The process according to claim 1 or 2, wherein the metallic aluminum is supplied in the form of particles with a particle size of 5 mm or more and 12 mm or less.

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