Abstract:
The present invention provides for a method and a reactor for generating hydrogen from a metal hydride. The method includes the steps of: providing a fuel containing a metal hydride and water; catalyzing a reaction of the hydride and water by using a functional membrane system; and thereby generating hydrogen. The reactor for generating hydrogen includes a vessel, and a functional membrane system disposed within the vessel. The functional membrane system compartmentalizes the vessel into two chambers. One of the two chambers is a fuel chamber, and the other chamber is a hydrogen chamber. Fuel, containing a metal hydride and water, is introduced to the fuel chamber, where it undergoes a catalytic reaction to generate hydrogen. The generated hydrogen then passes through the functional membrane system into the hydrogen chamber, and exits the reactor via the hydrogen outlets. The functional membrane system includes a membrane and a catalyst. The catalyst is adapted to promote the removal of hydrogen from a metal hydride.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates to a reactor and a method for generating hydrogen from a metal hydride.  
       BACKGROUND OF THE INVENTION  
       [0002]     Storage of hydrogen gas for use as a fuel in direct hydrogen fuel cells is an important consideration for the development and commercialization of such fuel cells. Some believe that storage of hydrogen gas, a very volatile gas, could limit the introduction of these fuel cells.  
         [0003]     A fuel cell is an electrochemical energy conversion device that produces electricity by converting hydrogen and oxygen into water. As long as fuel and an oxidant are supplied continuously to the fuel cell, the fuel cell continues to operate.  
         [0004]     Fuel cells generally consist of an anode, a cathode, and an electrolyte sandwiched in between the anode and the cathode. The anode and the cathode typically have catalyst to facilitate the oxidation and reduction reactions that produce the electricity. One type of a fuel cell is the polymer electrolyte membrane (“PEM”) fuel cell, which is also known as proton exchange membrane fuel cell.  
         [0005]     In a PEM fuel cell, hydrogen and oxygen are supplied to the cell from the outside sources. Hydrogen then enters the PEM fuel cell on the anode side, where it goes under a oxidation reaction to produce H +  ions and electrons (e − ) The electrons are conducted through the anode to the external circuit (doing useful work such as turning a motor), and then return to the cathode side of the cell. Oxygen enters the cell on the cathode side, where it undergoes a reduction reaction to produce negatively charged oxygen atoms. Two positively charged hydrogen ion combine with a negatively charged oxygen atom and two electrons, which are returning to cathode from the external circuit, to produce a molecule of water.  
         [0006]     If pure hydrogen is used as a fuel, fuel cells emit only heat and water as a byproduct. Since no other byproduct is produced, use of pure hydrogen as fuel, effectively could solve many of the environmental problems associated with fossil fuels.  
         [0007]     As disclosed in U.S. Pat. No. 5,840,329, and U.S. Patent Application Publication 2003/0009942 A1, one of the recognized methods to provide a continuous supply of hydrogen to fuel cells is known as “hydrogen on demand.” Hydrogen on demand technology generates pure hydrogen from water and sodium borohydride, a derivative of borax.  
         [0008]     The chemical reaction of the hydrogen gas generation is: 
 
NaBH 4 +2H 2 O→4H 2 +NaBO 2 +Heat 
 
         [0009]     The hydrogen, generated by the hydrogen on demand technology, can then be utilized to react with oxygen inside a fuel cell to generate electricity that can power a vehicle, a laptop computer, a mobile phone, a personal digital assistant (“PDA”), etc.  
         [0010]     U.S. Patent Application Publication 2003/0009942 A1 discloses an arrangement for generating hydrogen gas utilizing internally generated differential pressure to transport fuel and spent fuel components without requiring an electrically powered fuel delivery.  
         [0011]     U.S. Pat. No. 5,840,329 (“Amendola”) discloses an electroconversion cell in which borohydride is oxidized to generate borate and electrical current. Furthermore, Amendola discloses that borohydride may, in the alternative, be combined with water to generate hydrogen by reduction of water. The hydrogen may then be collected and transported to a hydrogen consumption point.  
         [0012]     While each of the forgoing may have had a measured success in generating hydrogen utilizing “hydrogen on demand” technology, there is still a need for a method for generating hydrogen in a simple and more effective manner.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention is a method and a reactor for generating hydrogen from a metal hydride. The method includes the steps of: providing a fuel containing a metal hydride and water; catalyzing a reaction of the hydride and water by using a functional membrane system; and thereby generating hydrogen. The reactor for generating hydrogen includes a vessel, and a functional membrane system disposed within the vessel. The functional membrane system compartmentalizes the vessel into two chambers. One of the two chambers is a fuel chamber, and the other chamber is a hydrogen chamber. Fuel, containing a metal hydride and water, is introduced to the fuel chamber, where it undergoes a catalytic reaction to generate hydrogen. The generated hydrogen then passes through the functional membrane system into the hydrogen chamber, and exits the reactor via the hydrogen outlets. The functional membrane system includes a membrane and a catalyst. The catalyst is adapted to promote the removal of hydrogen from a metal hydride. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.  
         [0015]      FIG. 1  is a schematic illustration of a reactor made according to the present invention.  
         [0016]      FIG. 2  is a schematic illustration of a flat sheet functional membrane system.  
         [0017]      FIG. 3  is a schematic illustration of a hollow fiber functional membrane system.  
         [0018]      FIG. 4  is a schematic illustration of a flat sheet bi-layer functional membrane system.  
         [0019]      FIG. 5  is a schematic illustration of a hollow fiber bi-layer functional membrane system.  
         [0020]      FIG. 6  is a schematic illustration of a flat sheet multi-layer functional membrane system.  
         [0021]      FIG. 7  is a schematic illustration of a hollow fiber multi-layer functional membrane system.  
         [0022]      FIG. 8  is a schematic illustration of a reactor made according to the present invention utilizing a bundle of hollow fiber multi-layer functional membrane systems. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring to the drawings wherein like numerals indicate like elements, there is shown in  FIG. 1 a  preferred embodiment of the reactor  10 . Reactor  10  includes a vessel  12 , and a functional membrane system  14 . Functional membrane system  14  is disposed within the vessel  12  to form two chambers: fuel chamber  16 , and hydrogen chamber  18 . Fuel chamber  16  includes a fuel inlet  20 , and fuel outlet  22 . Hydrogen chamber  14  includes hydrogen outlets  24 .  
         [0024]     Referring to  FIG. 2 , there is shown a flat sheet functional membrane system  14 . Functional membrane system  14  includes a membrane  26  and catalyst  28 .  
         [0025]     Membrane  26  can be made of synthetic polymers, cellulose or synthetically modified cellulose. Synthetic polymers include, but are not limited to, polyethylene, polypropylene, polybutylene, poly (isobutylene), poly (methyl pentene), polysulfone, polyethersulfone, polyester, polyetherimide, polyacrylnitril, polyamide, polymethylmethacrylate (PMMA), ethylenevinyl alcohol, and fluorinated polyolefins. Membrane  26  is preferably microporous. Membrane  26  is also preferably a hydrophilic membrane, or a hydrophobic membrane with a hydrophilic coating. Membrane  26  may be an asymmetric membrane, or a symmetric membrane; furthermore, membrane  26  may also possess a skin or a coat. Membrane  26  permits only hydrogen to traverse the functional membrane system  14 , and to enter into the hydrogen chamber  18 . Furthermore, membrane  26  prevents fuel and NaBO 2 , a product of the catalytic reaction of the fuel, from crossing the functional membrane system  14 .  
         [0026]     The catalyst  28 , as discussed in greater detail below, is either coated or embedded on the surface of membrane  26 , facing the fuel chamber  16 . The catalyst  28  is adapted to promote the removal of hydrogen from metal hydride; when the catalyst  28  comes in direct contact with the fuel, it catalyzes the catalytic reaction of the fuel to generate hydrogen gas. The functional membrane system  14  contains a sufficient amount of the catalyst  28  to effectively catalyze the reaction of fuel to generate hydrogen gas.  
         [0027]     Catalyst  28 , as described in the U.S. Patent Application Publication 2003/0009942 A1, which is incorporated herein by reference, includes, but is not limited to, transitional metals, transitional metal borides, alloys of these materials, and mixtures thereof. The catalyst  28  is preferably a transitional metal. The transitional metal catalyst may include, but is not limited to, catalysts containing Group IB to Group VIIIB metals of the Periodic Table or compounds made from these metals. Examples of useful transitional metals and compounds include, but are not limited to, ruthenium, iron, cobalt, nickel, copper, manganese, rhodium, rhenium, platinum, palladium, chromium, silver, osmium, iridium, and compounds thereof. Ruthenium, cobalt, and compounds thereof, are most preferred transitional metal catalysts.  
         [0028]     The functional membrane system  14  can be made by coating membrane  26  with catalyst  28 . The coating can be achieved by numerous methods, including dip coating, spraying, deposition, plasma treating, or electrostatic or ionic bonding to a charged or partly charged membrane surface.  
         [0029]     Functional membrane system  14  may also be a hollow fiber. Referring to  FIG. 3 , there is shown a hollow fiber functional membrane system  30 . The hollow fiber functional membrane system  30  has a hydrophilic membrane  26  containing catalyst  28 . Catalyst  28  may be on the inside (lumen) surface of the hollow fiber, the outside surface, or both.  
         [0030]     Referring to  FIG. 4 , there is shown a flat sheet bi-layer functional membrane system  32 . The bi-layer functional membrane system  32  includes a microporous diffusion layer  34 , and a hydrophilic catalyst containing layer  36 .  
         [0031]     The microporous diffusion layer  34  is composed of a microporous membrane. The microporous diffusion layer  34  permits only hydrogen to traverse the bi-layer functional membrane system  32 , and to enter into the hydrogen chamber  18 . Furthermore, the microporous diffusion layer  34  prevents fuel and NaBO 2  from crossing the bi-layer functional membrane system  32 .  
         [0032]     The hydrophilic catalyst containing layer  36  is a hydrophilic membrane that contains catalyst  28 , and, as discussed above, it can be created by coating a hydrophilic membrane with catalyst  28 . The hydrophilic catalyst containing layer  36  faces the fuel chamber  16 . The hydrophilic membrane facilitates the direct contact between the fuel and catalyst  28 .  
         [0033]     The bi-layer functional membrane system  32  can be, additionally, made by utilizing a lamination process to bond the microporous diffusion layer  34  to the hydrophilic catalyst containing layer  36 . In the alternative, the bi-layer functional membrane system  32  can be made by utilizing a co-extrusion process, which can then be made microporous by a stretching technique also known as dry process, or a phase inversion separation or extraction process also known as wet process.  
         [0034]     Referring to  FIG. 5 , there is shown a hollow fiber bi-layer functional membrane system  38 . The hollow fiber bi-layer functional membrane system  38  includes a microporous diffusion layer  34 , and a hydrophilic catalyst containing layer  36 . In  FIG. 5 , microporous diffusion layer  34  is shown on the lumen side and the hydrophilic catalyst containing layer  36  is shown on the exterior; however, microporous diffusion layer  34  can be placed on the exterior side and the hydrophilic catalyst containing layer  36  on the lumen side.  
         [0035]     Referring to  FIG. 6 , there is shown a flat sheet multi-layer functional membrane system  40 . The multi-layer functional membrane system  40  includes a microporous diffusion layer  34 , a metallic catalyst layer  42 , and a hydrophilic layer  44 . The placement of the layers as shown is not limiting, but other combinations, as would be apparent to a person skilled in the art, are possible.  
         [0036]     The microporous diffusion layer  34  is composed of a microporous membrane. The microporous diffusion layer  34  permits only hydrogen to traverse the multi-layer functional membrane system  40 , and to enter into the hydrogen chamber  18 . Furthermore, the microporous diffusion layer  34  prevents fuel and NaBO 2  from crossing the multi-layer functional membrane system  40 .  
         [0037]     The hydrophilic layer  44  is composed of a microporous hydrophilic membrane or coating. The hydrophilic layer  44  faces the fuel chamber  16 . The hydrophilic layer  44  facilitates the direct contact between the fuel and catalyst  28 .  
         [0038]     The metallic catalyst layer  42  is a porous membrane that contains catalyst  28 . The metallic catalyst layer  42  can be made by coating a membrane with catalyst  28 . The metallic catalyst layer  42  facilitates the catalytic reaction of the fuel to generate hydrogen gas.  
         [0039]     The multi-layer functional membrane system  40  can be, additionally, made by a lamination process to bond the following layers to each other: the microporous diffusion layer  34 , the metallic catalyst layer  42 , and the hydrophilic layer  44 . In the alternative, the multi-layer functional membrane system  40  can be made by a co-extrusion process, which can then be made microporous by a stretching technique also known as dry process, or a phase inversion separation or extraction process also known as wet process.  
         [0040]     Referring to  FIG. 7 , there is shown a hollow fiber multi-layer functional membrane system  46 . The hollow fiber multi-layer functional membrane system  46  includes a microporous diffusion layer  34 , a metallic catalyst layer  42 , and a hydrophilic layer  44 . The placement of the layers as shown is not limiting, but other combinations, as would be apparent to a person skilled in the art, are possible.  
         [0041]     Referring to  FIG. 8 , there is shown a preferred embodiment of a reactor  48 . Reactor  48  includes a vessel  50 , and a bundle of hollow fiber multi-layer functional membrane systems  64 . Bundle of hollow fiber functional membrane systems  64 , as used herein, refers to plurality of hollow fiber functional membrane systems. The bundle  64  is held in place within the vessel by tube sheets  53 . The bundle of hollow fiber multi-layer functional membrane systems  64  is disposed within the vessel  50  to form two chambers: fuel chamber  52 , and hydrogen chamber  54 . Fuel chamber  52  preferably refers to the space defined by the interior wall of the vessel  50 , the exterior surfaces of the hollow fibers, and between the tube sheets. Hydrogen chamber  54 , as used herein, refers to the space defined by the lumens hollow fibers  46 , and the headspaces  62 . Fuel chamber  52  includes a fuel inlet  56 , and fuel outlet  58 . Hydrogen chamber  54  includes hydrogen outlets  60 .  
         [0042]     Fuel, as described in the U.S. Patent Application Publication 2003/0009942 A1, which is incorporated herein by reference, refers to a solution of a metal hydride and water. Preferably, fuel refers to a solution of a metal hydride, water, and stabilizing agent. Solution, as used herein, includes a liquid in which all the components are dissolved and/or a slurry in which some of the components are dissolved and some are undissolved solids.  
         [0043]     Metal hydrides, as described in the U.S. Patent Application Publication 2003/0009942 A1, which is incorporated herein by reference, have the general formula MBH 4 . M is an alkali metal selected from Group 1 (formerly Group IA) or Group 2 (formerly Group IIA) of the Periodic Table, examples of which include lithium, sodium, potassium, magnesium, or calcium; and, M in some cases may also be ammonium or organic groups. B is an element selected from the Group 13 (formerly Group IIIA) of the Periodic Table, examples of which include boron, aluminum and gallium. H is hydrogen. Examples of metal hydrides include, but are not limited to, NaBH 4 , LiBH 4 , KBH 4 , Mg(BH 4 ) 2 , Ca(BH 4 ) 2 , NH 4 BH 4 , (CH 3 ) 4 NH 4 BH 4 , NaAlH 4 , LiAlH 4 , KAlH 4 , NaGaH 4 , LiGaH 4 , KGaH 4 , and compounds thereof. The following borohydrides are preferred: sodium borohydride (NaBH 4 ), lithium borohydride (LiBH 4 ), potassium borohydride (KBH 4 ) ammonium borohydride (NH 4 BH 4 ) tetraethyl ammonium borohydride ((CH 3 ) 4 NH 4 BH 4 ), quaternary borohydrides and compounds thereof.  
         [0044]     Stabilizing agents, as described in the U.S. Patent Application Publication 2003/0009942 A1, which is incorporated herein by reference, include the corresponding hydroxide of the cation part of the metal hydride salt. For example, if sodium borohydride were used as the metal hydride salt, the corresponding stabilizing agent would be sodium hydroxide.  
         [0045]     In operation, referring to  FIG. 1 , fuel enters the reactor  10  through the fuel inlet  20 , and into the fuel chamber  16 . Once fuel is in the fuel chamber  16 , the hydrophilic membrane  26  facilitates the direct contact between the fuel and catalyst  28 . Catalyst  28  catalyzes the reaction of the fuel to generate hydrogen. The reaction of the fuel to hydrogen gas can be shown as: 
 
NaBH 4 +2H 2 O→4H 2 +NaBO 2 +Heat 
 
         [0046]     The membrane  26  permits only the hydrogen to traverse the functional membrane system  14 , and to enter into the hydrogen chamber  18 . Furthermore, membrane  26  prevents fuel and NaBO 2 , a product of the fuel reaction, from crossing the functional membrane system  14 . Hydrogen that enters the hydrogen chamber  18  leaves the reactor  10  via the hydrogen outlets  24 . The excess fuel and/or NaBO 2  leave the fuel chamber  16  via fuel outlet  22 .  
         [0047]     In a preferred operation, referring to  FIG. 8 , fuel enters the reactor  48  through the fuel inlet  56 , and into the fuel chamber  52 . Once fuel is in the fuel chamber  52 , it comes in direct contact with the exterior layer of the hollow fibers in bundle  64 . The hydrophilic layer  44  facilitates the direct contact of the fuel and the catalyst layer  42 . The microporous diffusion layer  34  permits the hydrogen to pass through functional membrane system  46 , where it enters the lumen of the hollow. Additionally, the microporous diffusion layer  34  prevents the fuel and/or NaBO 2  from passing through the functional membrane system  46 . The hydrogen, which enters the lumens, travels to the headspaces  62 , and leaves the reactor  10  via the hydrogen outlets  60 . The excess fuel and/or NaBO 2  leave the fuel chamber  52  via fuel outlet  58 .  
         [0048]     The present invention may be embodied in other forms without departing from the spirit and the essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicated the scope of the invention.