WO2019072844A1

WO2019072844A1 - Hydrogen generator with condensation and purification structure

Info

Publication number: WO2019072844A1
Application number: PCT/EP2018/077470
Authority: WO
Inventors: Göran Schack
Original assignee: Myfc Ab
Priority date: 2017-10-12
Filing date: 2018-10-09
Publication date: 2019-04-18
Also published as: SE1751264A1; SE542602C2

Abstract

The invention relates to a hydrogen generator (10), comprising a housing (12) having at least one storage compartment (14, 26) for chemical reaction components, and a reaction compartment (26) in which the chemical reaction components can react. The first compartment (26) houses aluminium, and the second compartment (14) houses water and hydroxide in solution. There is provided means (18) for providing fluid communication between second compartment (14) containing the solution of water and hydroxide and the first compartment (26) containing the aluminium. A condensation structure (20, 22) is provided in which water vapour is removed from the generated hydrogen gas. In particular the first compartment (26) constitutes the reaction compartment. A purification structure (20, 22) comprising zeolite(s), is arranged to receive hydrogen gas from the reaction compartment when formed via an inlet and to feed such purified gas to a fuel cell via an outlet.

Description

HYDROGEN GENERATOR WITH CONDENSATION AND PRUIFICATION STRUCTURE This invention relates generally to hydrogen generators, and in particular to a generator which delivers hydrogen that has been freed from water and contaminants originating from the chemical processes in the generator.

Background of the Invention

Production of hydrogen for fuel cell applications is becoming more interesting as charging of electronic equipment is required in locations where the access to grid power is limited, and the need for mobility in general increases.

So called power banks are very popular and the sales boomed the last couple of years. Still such power banks need recharging via the grid, and thus mobility is restricted.

A number of fuel cell based solutions to mobile charging has been presented over the last decade, most have been based on hydrogen consuming poly-electrolyte membrane fuel cells. Generation of hydrogen is commonly by so called chemical hydrides, e.g. sodium borohydride is allowed to react with water to produce hydrogen.

Most of these solutions are fairly heavy and have not met with any particular success in the market. Thus there is a need for more versatile systems for hydrogen generation.

It is essential that the gas produced be reasonably dry and clean in order not to jeopardize the sensitive membranes in the fuel cells. Summary of the Invention

The present applicants have devised a novel approach using aluminium as a basis reagent for the generation of pure and reasonably dry hydrogen, and provide a single use generator of hydrogen in the form of a flat card type device that is connectable to a fuel cell based power generator. In fact, dryness is not a critical factor, and the gas can have a humidity of up to 80- 90% without a problem as long as the gas is clean and the water does not condense.

In order to provide the clean and dry gas required the present inventors have devised a hydrogen generator comprising a novel purification structure that meets the above mentioned requirements. The novel generator is defined in claim 1.

Thus, it comprises a hydrogen generator ( 10), comprising a housing. The housing contains at least two storage compartments for chemical reaction components, and means for enabling said reaction components to react to generate hydrogen. There is also a condensation structure in which water vapour is removed from the generated hydrogen gas, and a purification structure comprising zeolite (s).

Preferred embodiments are defined in the dependent claims.

Brief Description of the Drawings

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus not to be considered limiting on the present invention, and wherein

Fig. 1 is a perspective exploded view of a housing of the hydrogen generator;

Fig. 2 is a perspective exploded view of a purification and condensation structure;

Fig. 3 schematically illustrates the lay-out of compartments in the generator; and

Fig. 4 schematically illustrates a partioning of the purification and condensation structure.

Detailed Description of Preferred Embodiments

Generally the hydrogen generator comprises a housing, suitably, but not restricted to, made of a polymer material for weight and cost reasons. Inside the housing there are compartments for storing reaction components and for performing the gas generating reaction. There is also provided a structure for removing water vapour from the generated gas and for purifying the gas, i.e. for removing any contaminants that may be withdrawn from the reaction. In particular the present invention makes use of a novel reactant system comprising aluminium that reacts with a reactant solution having a high pH, i.e. very basic, such as NaOH (or other alkali) in water, to generate hydrogen.

Fig. 1 shows the hydrogen generator 10 in a partly exploded view. One part 20 of the generator is shown in broken lines and indicated with reference numeral 20, and will be described separately below.

A generally flat housing 12, i.e. having a width W exceeding the thickness T by a factor of 4 in preferred embodiments, is provided. The flatness ratio W/T is not crucial and the shape of the housing could in principle vary from cylindrical to oval, or square to rectangular over a wide range, depending on the application for which the generator is intended, without the general structure needing any substantial design changes.

Into a distal end DE of housing 12 a water and hydroxide solution container 14 is insertable (illustrated by an arrow A). The container 14 has a bottom part 15 having a peripheral circumferential edge PI which is welded to the periphery P2 of the distal end DE of the housing 12. The opposite end of the housing 12 is consequently referred to as the proximal end PE.

The container 14 is sealed, after filling it with reactant solution, by welding a thin foil 16 to the end opposite to the bottom end of the container 14. This foil 16 is easily penetrated by penetration means 18 to be described below so as to cause a flow of reactant solution into the reaction compartment. The foil is suitably made of a material that is at least impermeable to the ions used in the reaction system, such as Na+ and OH+ ions, one such material being polypropylene, although this is only exemplary and many other foil materials are equally usable. It should preferably also be impermeable to water although some permeability to water may be acceptable.

Adjacent the foil 16 inside the housing 12 said penetration means 18 is provided. In the shown embodiment it comprises a knife member 18 which in the shown embodiment comprises four knives 18' on a supporting structure. When the knife member 18 is mounted in the housing 12 the knives 18' extend across the width of the housing 12 such that when the knife member is pressed against the thin foil 16 in operative mode, the knives 18' will cut open the foil so as to allow solution to flow out from the compartment 14.

Fig. 2 shows the previously mentioned and in Fig. 1 hidden part 20 of the hydrogen generator 10. It constitutes the above mentioned purification structure 20 which is located inside the housing 12 (as shown in broken lines in Fig. 1). The purification structure 20 comprises a further container 22 in which there is provided an amount of preferably granulated zeolites. In particular embodiments it can also contain suitable desiccants, which will be described in further detail below.

There is also provided a safety release valve 23 provided for handling unexpected pressure increase inside the system.

There can also be provided neutralizing components for neutralizing the basic solution used in the reaction system. Such component can be a buffer chemical or an acid, e.g. citric acid.

First a discussion of the merits of zeolites will be given. An issue when using NaOH (or the like: KOH, Ca(OH) ) catalysed systems for hydrogen generation is that due to the very large volume expansion when gas is generated, aerosols of of NaOH can be entrained with the gas formed. The aerosol contains very small particles of NaOH which are very difficult to filter off, and the Na⁺ and OH- ions will then deactivate the electrolyte membrane in the fuel cells to which the gas is fed, which then irreversibly will lose its function. Zeolites have surprisingly been found to be very efficient in eliminating the presence of entrained hydroxide particles in the hydrogen flow.

The zeolites used in the invention are preferably acidic zeolites. At present a preferred, but only exemplary zeolite is H-ZMS-5. ZSM-5 stands for Zeolite Socony Mobil-5 (framework type MFI from ZSM-5 (five)), and is an aluminosilicate zeolite belonging to the pentasil family of zeolites. Its chemical formula is NanAlnSi96- η0192· 16Η20 (0<n<27). It was patented by Mobil Oil Company in 1975. Acidic zeolites consist of a structure containing Si and Al. Si and Al are close to each other in the periodic table of the elements and have practically the same size (Al = 1, 18 A; Si = 1 , 1 1 A), but have different oxidation numbers. When Al replaces a Si in a structure there is needed an anion to neutralize the lower oxidation number of the Al. When a zeolite is synthesized the counter ion is most often Na+. In a finished calcined zeolite the ion can be replaced by other ions such as Cu²⁺ and H⁺. Each Al in the zeolite structure is an acidic site and the zeolite is a Lewis acid. Zeolites consist of a structure similar to a three-dimensional sieving structure having pores or holes of a size in the range 3-5 A. The average size of the zeolite granules is preferably in the range 0,3 to 1 ,0 mm. Porous pellets can also be used which have size of up to 2 mm.

When water vapour containing aerosols of Na+ and OH- ions pass through a zeolite structure having H+ and Al bound to it, the following reaction takes place:

Al-site-H⁺ + Na⁺ + OH- Al site-Na⁺ + H⁺ + OH- -» Al site-Na⁺ H₂0

The first reaction must be regarded as an equilibrium reaction driven by the

concentrations of Na⁺ and H⁺. Due to the access of OH- the concentration of H⁺ will never increase, and hence the reaction will be driven in the desired direction. Using acidic zeolites for cleaning of outflowing water vapour from any aerosols present therein allow a complete neutralization without risk for other ions reaching the membrane and thereby destroying it.

Now, returning to Fig. 2, the container 22 is smaller, both with respect to thickness T and width W, than the interior of the housing 12 and closed off at a proximal end PE' of the container 22 by means of a lid 24 which conforms to the shape of the proximal end PE of the housing 12. At the distal end DE' of the container 22 there is also a lid member 25 which is welded to the container 22 after filling with the zeolites and desiccants, if any. The entire purification structure 20 is inserted in the housing at its proximal end PE (as shown in broken lines in Fig. 1) and welded to the housing along the periphery at the proximal end PE. When the further container 22 is inserted in the housing 12 to provide a finished generator, because of the smaller dimensions of the container 22, there is formed a space between the purification structure 20 and the inner walls of the housing 12. To illustrate this, the contour lines of the housing 12 are shown in broken lines 12'. This space surrounding the container 22 constitutes a reaction chamber in which aluminium is provided.

Fig. 3a illustrates this schematically in a view from above, showing the housing 12, the hydroxide solution container 14, and the purification structure container 22. As mentioned above the space between the housing 12 and the container 22 constitutes a reaction chamber 26, in which aluminium is provided. Notably there is also space in the vertical direction with respect to the plane of the paper, such that the container 22 is surrounded on all sides by a space that is filled with aluminium. This can be seen in the schematic side view in Fig. 3b.

Returning now to Fig. 2, the container 22 as mentioned contains zeolites for purification purposes and optionally also desiccants for drying and purifying the hydrogen generated in the reaction chamber 26. Thus, there is at least one inlet opening 28, in the shown embodiment there are four openings, for admission of generated hydrogen gas into the container 22.

The moisture generated during the reaction that takes place needs to be removed from the gas before feeding to the fuel cells, and therefore these openings 28 should preferably be covered with a filter 30. This filter should be hydrophobic and resistant towards alkaline solutions. It should also preferably be inert, i.e. it should not react with any reaction components to produce gases that potentially could damage the fuel cells. It should also withstand operation temperatures in the range 50 - 130°C. Example of a suitable material for the filter is PTFE (poly-tetra-fluoro- ethylene).

The filter(s) 30 can handle removal of moisture to a certain extent, but it may not be sufficient. Liquid can obstruct the filter if the pore size is small, and if the pore size is too large, solution will pass through. Example of a suitable material for the filter is PTFE (poly-tetra-fluoro-ethylene).

Therefore, in order to avoid this to happen, it is possible to use coarser filters 30 but instead provide desiccants in the container 22 together with zeolites.

In a simple embodiment the zeolites and desiccants are mixed in suitable proportions and placed in the container 22 in a homogenous mixture. However, for a more efficient drying of the gas, preferably the desiccant is provided at different mixing ratios vs the zeolites in different sections inside the container. This is disclosed in Fig. 4 in an exemplary embodiment, wherein the container comprises three sections A, B and C, section A is located at the inlet end IL, section C at the outlet OL and section B between section A and B. All sections contain zeolites, but only section A and B contain desiccant. In the first section A there is a higher concentration of desiccant than in the second section B, whereas section C contains only zeolites. The different concentrations are illustrated by different hatchings.

In a further fourth section D, constituting a part of section C close to the outlet, the components in the container 22 can comprise citric acid, or some other neutralizing component, e.g. other acids or buffer solutions.

The actual mixing ratios can vary depending on dimensions, application etcetera, but exemplary values are 20-30 % desiccant and 80-70 % zeolite in section A, and 5-20 % desiccant and 95-80 % zeolite in section B, whereas there is no desiccant in section C, only zeolites.

Of course it is possible to have another number of sections, other sizes of the sections and other ratios of desiccant vs zeolites. It is also conceivable to have a more or less continuous gradient of components in the container 22, although this is more complicated to achieve from a manufacturing point of view.

The desiccant can be selected from commercially available products, e.g. gypsum or a product sold under the trademark Drierite®. It can be provided as a powder or granulate in a large variation of sizes, although 20 - 40 mesh can be suitable. It can also be provided in pellet format, by mixing several components and sintering to produce pellets.

The present invention also provides a specific reactant system for the generation of hydrogen.

Namely, it is well-known that aluminium will be dissolved in e.g. aqueous sodium hydroxide with the 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) + 6H20→ 2Na+(aq) + 2[Al(OH)4]- + 3H2(g)

The various reactions taking place can be described as follows: 2A1 + 6H20 → 2Al(OH)3 + 3H2(g)

Al(OH)3 + NaOH → Na+ + [Al(OH)4]-

A1203 + 2NaOH + 3H20 → 2Na+ + 2[Al(OH)4]-

The bottom line is that when exposed to aqueous solutions under proper conditions the aluminium dissolves and hydrogen gas evolves.

The present inventors have carefully optimized the system by selecting proper forms of aluminium and proper composition of the aqueous solution. In particular it is important to be able to control the rate of hydrogen evolution to fit the application in which the reactant system is to be used. It has been discovered that if the aluminium is provided as a powder having a particle size distribution such that 99,8% of the particles have an effective diameter of < 45 μπι, it is possible to obtain very efficient reactant system. Also, the purer the aluminium is the better the performance will be. A purity of higher than 95% Al is required, preferably >98 %, and at present a purity of about 99,7% or pure Al or higher is used, the balance being unavoidable contaminants. It is of importance that there be very low amounts of silicon (Si) present, preferably no Si at all. The aluminium is provided in the form of any of a powder, granulates, pellets, sheet, stripes, stretch (expanded) metal foil, or combinations thereof. 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, water and a water soluble compound which results in an alkaline solution with a pH in the interval 12,5 < pH < 14, in particular a metal hydroxide such as LiOH, NaOH, KOH, Ca(OH)2 or Mg(OH)2would be usable.

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

In addition to hydroxides various salts, such as NaCl, KC1, MgCl2, and carbonates, sulphates or phosphates of metals, or other chemicals can be added to the reactant solution. The purpose could e.g. be for controlling reaction rates.

Claims

CLAIMS:

1. A hydrogen generator ( 10), comprising a housing (12), said housing containing: at least two storage compartments for chemical reaction components, and means for enabling said reaction components to react to generate hydrogen: characterized by a condensation structure in which water vapour is removed from the generated hydrogen gas, and

a purification structure comprising zeolite(s).

2. The hydrogen generator according to claim 1 , wherein the zeolite(s) are provided as granules having an average size of 0.3- 1.0 mm, or if porous pellets are used, size can be up to 2 mm.

3. The hydrogen generator according to claim 1 or 2, wherein the zeolite (s) are acidic.

4. The hydrogen generator according to any preceding claim, wherein the means for enabling said reaction components to react is a reaction compartment in which the chemical reaction components can react.

5. The hydrogen generator according to any preceding claim, wherein one storage compartment contains aluminium, and the at least one further compartment contains water and a hydroxide, preferably selected from the group consisting of NaOH, KOH, Ca(OH)₂, Mg(OH)₂, or combinations thereof.

6. The hydrogen generator according to claim 4, wherein the water and the hydroxide are provided in separate compartments.

7. The hydrogen generator according to claim 4, wherein the water and the hydroxide are provided as a solution in one compartment.

8. The hydrogen generator according to any of claim 4-7, wherein the storage compartment for aluminium constitutes a reaction compartment in which the chemical reaction components can react.

9. The hydrogen generator according to any of claims 5-8, wherein the aluminium is provided in the form of any of a powder, granulates, pellets, sheet, stripes, expanded metal foil, or combinations thereof.

10. The hydrogen generator according to any of claims 5-9, wherein the aluminium has a purity of >95 % by weight aluminium, preferably >98 %, most preferred >99,7 % by weight aluminium, the balance being unavoidable contaminants.

1 1. The hydrogen generator according to any of claims 5- 10, wherein the there is no silicon present in the aluminium.

12. The hydrogen generator according to any preceding claim, wherein the purification structure is constituted by a separate compartment housing the zeolite(s), and having an inlet for generated hydrogen and an outlet for feeding purified gas to a fuel cell.

13. The hydrogen generator according to claim 12, wherein the contents in the separate compartment of the purification structure comprises a plurality of sections (A, B, C, D), wherein at least one section contains only zeolite, and the other contain different concentrations of desiccant.

14. The hydrogen generator according to claim 12, comprising three sections, a first section (A) located at the inlet and comprising zeolites and a desiccant, a second middle section (B) comprising zeolites and a desiccant at a lower concentration than in the first section (A), and a third section (C) comprising only zeolites.

15. The hydrogen generator according to claim 13, further comprising a fourth section (D) located close to the outlet and comprising zeolite and citric acid or some other neutralizing component, e.g. other acids or buffer solutions.

16. A hydrogen generator ( 10), comprising a housing ( 12) having at least one storage compartment ( 14, 26) for chemical reaction components, and a reaction compartment (26) in which the chemical reaction components can react, characterized by a first compartment (26) housing aluminium;

a second compartment ( 14) housing water and hydroxide in solution; means ( 18) for providing fluid communication between second compartment ( 14) containing the solution of water and hydroxide and the first compartment (26) containing the aluminium;

a condensation structure (22) in which water vapour is removed from the generated hydrogen gas; wherein the first compartment (26) constitutes the reaction compartment; and further comprising

a purification structure (22) comprising zeolite(s), arranged to receive hydrogen gas from the reaction compartment when formed via an inlet (IL) , and to feed such purified gas to a fuel cell via an outlet (OL).