SE1650013A1 - Reactant system for providing hydrogen using aluminium powder - Google Patents

Abstract

The invention relates to a reactant system comprising in separate compartments, Al powder having a particle size distribution such that 99,8% of the particles have an effective diameter of < 45 jam, water, and a water soluble compound, an aqueous solution of said compound having a pH in the interval 12,5 < pH < 14. The water soluble compound is selected from the group consisting of LiOH, NaOH, KOH, Ca(OH), Mg(OH). Suitably, the water soluble compound is provided in is provided in tablet form having a diameter between 0,25 and 0,5 mm, and a thickness between 0,1 and 0,2 mm. Furthermore, there is suitably provided means adapted to mix the components of the reactant system with each other.

Description

REACTANT SYSTEM The present invention relates to fuel cell technology and in particular to a reactantsystem for providing hydrogen as fuel for fuel cells.

Background Fuels cells have attracted more interest over the last few years for manyapplications, both in automotive technology but also in small scale for theproduction of electricity. One application is for providing charging of electronicequipment, such as mobile phones, laptop computers etcetera, where there is aneed for versatile reactant systems.

In the last few years chemical hydride systems have been developed and been inuse for a number of products.

In adsorption hydrogen storage for fueling a fuel cell, molecular hydrogen isassociated With the chemical fuel by either physisorption or chemisorption.Chemical hydrides, such as lithium hydride (LiH), lithium aluminum hydride(LiAIH4), lithium borohydride (LiBH4), sodium hydride (NaH), sodium borohydride(NaBH4), and the like, are used to store hydrogen gas non-reversibly. Chemicalhydrides produce large amounts of hydrogen gas upon reaction With water asshown below: NaBH4 + QHQO -» NQBOQ + 4H2 To reliably control the reaction of chemical hydrides with water to release hydrogengas from a fuel storage device, a catalyst must be employed along with control ofthe water's pH. Additionally, the chemical hydride is often embodied in a slurry ofinert stabilizing liquid to protect the hydride from early release of its hydrogen gas.

In chemical reaction methods for producing hydrogen for a fuel cell, often hydrogenstorage and hydrogen release are catalyzed by a modest change in temperature orpressure of the chemical fuel. One example of this chemical system, which iscatalyzed by temperature, is hydrogen generation from ammonia-borane by thefollowing reaction: NH3BH3 -> NHQBHQ + H2 -> NHBH + H2 The first reaction releases 6.1 wt.% hydrogen and occurs at approximately 120 °C,while the second reaction releases another 6.5 wt.% hydrogen and occurs atapproximately 160 °C. These chemical reaction methods do not use water as aninitiator to produce hydrogen gas, do not require a tight control of the system pH,and often do not require a separate catalyst material. However, these chemicalreaction methods are plagued with system control issues often due to the commonoccurrence of thermal runaway. See, for example, U.S. Patent 7,682,41 1 , for asystem designed to thermally initialize hydrogen generation from ammonia- boraneand to protect from thermal runaway. See, for example, U.S. Patents 7,316,788 and7,578,992, for chemical reaction methods that employ a catalyst and a solvent tochange the thermal hydrogen release conditions.

Another more recent reaction system is using NaSi, as disclosed in i.a. in WO2015/143212.

However, these systems tend to be relatively bulky and heavy, and there is a needfor simpler light-weight systems.

Summary of the Invention The present inventors have devised a novel system based on a different type ofchemistry than the chemical hydrides.

This novel system is based on well-known chemical reactions of aluminium, butprovided in a novel form. Thus, the inventive use of aluminium is defined in claim1, and comprises use of an Al powder for the production of H2 in a reactor, the Alpowder having a particle size distribution such that 99,8% of the particles have aneffective diameter of < 45 um.

The reactant system comprising the constituent compounds is defined in claim 2,and comprises, in separate compartments, Al powder having a particle sizedistribution such that 99,8% of the particles have an effective diameter of < 45 um,water, and a water soluble compound capable of reacting with Al to form hydrogengas, an aqueous solution of said compound having a pH in the interval 5 14, mostpreferred about 14. The water soluble compound is selected from the groupconsisting of LiOH, NaOH, KOH, Ca(OH)2, Mg(OH)2. At present KOH is preferred.Suitably, the water soluble compound is provided in tablet form, resembling adroplet of water sitting on a non-wetting surface, and having a size of between 0,25and 0,5 mm in diameter and thickness (or height) of between 0,1 and 0,2 mm.However, it is within the inventive concept to use virtually any form of hydroxide aslong as the function is ascertained, i.e. to produce a solution having a desired pH.

Furthermore, there is suitably provided means adapted to mix the components ofthe reactant system with each other.

In a further aspect a method of generating hydrogen gas is also provided, and isdefined in claim 6.

Detailed Description It is well-known that aluminium dissolves in e.g. aqueous sodium hydroxide withthe evolution of hydrogen gas, H2, and the formation of aluminates of the type[Al(OH)4]-, the overall reaction can be written as follows: 2Al(s) + 2NaOH(aq) + 6H2O -> 2Na+(aq) + 2[Al(OH)4]“ + 3H2(g)The various reactions taking place can be described as follows:2Al + 6H2O -> 2Al(OH)3 + 3H2(g)Al(OH)3 + NaOH -> Na* + [Al(OH)4]- A12o3 + zNaoH + 3H2o _» 2Na+ + 2[A1(oH)4]- The bottom line is that When exposed to aqueous solutions under proper conditionsthe aluminium dissolves and hydrogen gas evolves.

The present inventors have carefully optimized the system by selecting proper formsof aluminium and proper composition of the aqueous solution.

In particular it is important to be able to control the rate of hydrogen evolution to fitthe application in which the reactant system is to be used. It has been discoveredthat if the aluminium is provided as a powder having a particle size distributionsuch that 99,8% of the particles have an effective diameter of < 45 um, it is possibleto obtain very efficient reactant system.

The pH of the aqueous solution should also be in the range 12,5 < pH < 14.

The reactant system thus comprises the above mentioned aluminum powder, waterand a water soluble compound which results in an alkaline solution with a pH inthe interval 12,5 < pH < 14, in particular a metal hydroXide such as LiOH, NaOH,KOH, Ca(OH)2 or Mg(OH)2would be usable, KOH at present being the preferred one.

The individual components are preferably provided in a fuel cartridge in separatecompartments, the fuel cartridge having means for providing dissolution of thewater soluble compound in the water and for passing the resulting alkaline aqueoussolution into contact with the aluminium powder.

Preferably the Al powder has a constitution such that it is not reactive when wet. Itshould not react until brought in contact with the alkaline solution. Mostcommercially available powders appear to have this property. However, it ispreferred that powders for use be tested for this property before implementing in areactant system as claimed.

For improving the reactant solution distribution inside the reactor compartmentand to ascertain a rapid distribution within the reactive powder, it has beendiscovered that if small beads of e.g. glass or other inert material is distributed inthe powder a much more efficient spreading occurs, thereby enhancingperformance. In certain applications in fact the beads could also be reactive in asense that they participate in or enhances the reaction in the reactioncompartment.

These glass beads are preferably spherical and suitably 2,5 - 2,8 mm in diameter.Suitable beads that have been used in prototypes are obtainable from Preciosa, andare designed and intended for decorative use, e.g. for necklaces.

Preferably a bead has a hole extending through the bead. This hole preferably has adiameter such the Al powder can enter into the hole and occupy at least a portion ofthe volume inside the hole. It is believed that this enhances the process in thereactor compartment in that the surface to which the powder adheres improveswater flow and thus dissolution rates.

The method according to the invention of producing H2 in a reactor comprisesproviding Al powder having a particle size distribution such that 99,8% of the particles have an effective diameter of < 45 um, and bringing said Al powder incontact With an aqueous solution inside the reactor. The solution has a pH in theinterval 12,5 < pH < 14.

The aqueous solution comprises a dissolved water soluble compound selected fromthe group consisting of LiOH, NaOH, KOH, Ca(OH)2, Mg(OH)2.

The water soluble compound can be provided in various forms and shapes,although particles or grains of a certain size are preferable. Normally the material ofthis type is provided commercially as granules, powders or the like. In a preferredembodiment, the material is provided as tablets, having a diameter of < 4 mm,suitably in the range 2-4, or preferably 3-4 mm and a shape similar to a lens,around 1-2 mm thick.

However, the volume occupied by the material when in the form of the mentionedtablets, will allow only a certain amount of water to enter to fill the void between theparticles. Thus, when the material is dissolved by the water, the total volume ofsolution, at least initially, will not fill up the entire volume of the miXingcompartment, and this will lead to a slowed down delivery from the miXingcompartment to the reactor compartment. In order to avoid this slowing down,there can be provided beads, e.g. of glass or other inert material and preferablyessentially spherical, inter-mixed with the tablets in the voids between them. Thebeads having a smaller size (or diameter) than the tablets will thus occupy thespace between and will therefore provide a smaller “dead volume” than otherwisewould be the case. In this manner the effective volume of the miXing compartmentwill be adapted to the total volume of the produced solution. The relationshipbetween on one hand tablet size and shape and the other bead size can beoptimized for selected tablet size.

In the method the Al powder, the water and the water soluble compound areprovided in separate compartments in a fuel cartridge, and the method comprisespassing water from one compartment to a miXing compartment wherein the watersoluble compound is present whereby the water soluble compound dissolves toprovide an aqueous solution. The aqueous solution is passed to the reactor,wherein the Al powder is present, such that a reaction takes place and hydrogenevolves, and passing the hydrogen through an outlet to a fuel cell device.

Suitably mechanical means are used for feeding the solution through suitablechannels. The mechanical means can be pump means, hydraulic/pneumaticsystems or the like.

Claims (8)

:

1. Use of an A1 powder for the production of H2 in a reactor, the A1 powder having apartic1e size distribution such that 99,8% of the partic1es have an effective diameter< 45 um.

2. Reactant system for the production of hydrogen gas, comprising, in separatecompartments, A1 powder having a partic1e size distribution such that 99,8% of thepartic1es have an effective diameter of < 45 um, water, and a water so1ub1ecompound capab1e of reacting with A1 to form hydrogen, an aqueous so1ution ofsaid compound having a pH in the interval 12,5 < pH < 14, most preferred about14.

3. Reactant system for the production of hydrogen gas according to c1aim 2,wherein the water so1ub1e compound is se1ected from the group consisting of LiOH,NaOH, KOH, Ca(OH)2, Mg(OH)2.

4. Reactant system for the production of hydrogen gas according to c1aim 2,wherein water so1ub1e compound is provided in tab1et form having a diameterbetween 0,25 and 0,5 mm, and a thickness between 0,1 and 0,2 mm.

5. Reactant system for the production of hydrogen gas according to c1aim 2,wherein there is provided means adapted to mix the components of the reactantsystem with each other.

6. Method of producing H2 in a reactor, comprising providing A1 powder having apartic1e size distribution such that 99,8% of the partic1es have an effective diameter< 45 um, bringing said A1 powder in contact inside the reactor with an aqueousso1ution having a pH in the interval 12,5 < pH < 14,.

7. The method according to c1aim 6, wherein the aqueous so1ution comprises adisso1ved water so1ub1e compound se1ected from the group consisting of LiOH,NaOH, KOH, Ca(OH)2, Mg(OH)2.

8. The method according to c1aim 7, wherein the A1 powder, the water and the waterso1ub1e compound are provided in separate compartments in a fue1 cartridge, andwherein the method comprises passing water from one compartment to a mixingcompartment wherein the water so1ub1e compound is present whereby the waterso1ub1e compound disso1ves to provide an aqueous so1ution, passing the aqueousso1ution to the reactor, wherein the A1 powder is present, such that a reaction takesp1ace and hydrogen evo1ves, and passing the hydrogen through an out1et to a fue1ce11 device.