Abstract:
Systems and methods are provided for generating hydrogen gas using a catalyst or reagent and a boron hydride compound. The preferred hydrogen generation system includes a fuel cartridge and a hydrogen generation system balance of plant (BOP) module. Solid fuel is stored in individual fuel packets in a fuel chamber, and converted into a fuel solution. Fuel is pumped to a reactor where it produces hydrogen and borate. The hydrogen and borate product exit the reactor and are deposited in a hydrogen separation chamber separated from the fuel chamber by a moveable partition. Hydrogen is separated by a membrane and exits the generator. As fuel is consumed, the movable partition is disposed toward the fuel chamber and the borate product is deposited on one side of the movable partition. The controls are preferably contained in the BOP module.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a system for generating hydrogen gas using fuel solutions of borohydride compounds. More particularly, the invention relates to a system for hydrogen generation that produces a fuel solution as needed from dry fuel components. This invention claims priority to U.S. Provisional Application Ser. No. 60/791,215, filed Apr. 12, 2006, which is hereby incorporated herein in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     Although hydrogen is the fuel of choice for fuel cells, its widespread use is complicated by the difficulties in storing the gas. Many hydrogen carriers, including hydrocarbons, metal hydrides, and chemical hydrides, are being considered as hydrogen storage and supply systems. In each case, specific systems need to be developed to release the hydrogen from its carrier, either by reformation as in the case of hydrocarbons, desorption from metal hydrides, or catalyzed hydrolysis from chemical hydrides and water.  
         [0003]     One of the more promising systems for hydrogen storage and generation utilizes borohydride compounds as the hydrogen storage media. Sodium borohydride (NaBH 4 ) is of particular interest because it can be dissolved in alkaline water solutions with virtually no reaction; in this case, the stabilized alkaline solution of sodium borohydride is referred to as fuel. Furthermore, the aqueous borohydride fuel solutions are non-volatile and will not burn. This imparts handling and transport ease both in the bulk sense and within the hydrogen generator itself.  
         [0004]     Various hydrogen generation systems have been developed for the production of hydrogen gas from aqueous sodium borohydride fuel solutions. Such generators typically require at least three chambers, one each to store fuel and borate product, and a third chamber containing a catalyst or other reagent to promote hydrolysis of the borohydride. Hydrogen generation systems can also incorporate additional components such as hydrogen ballast tanks, heat exchangers, condensers, gas-liquid separators, filters, and pumps.  
         [0005]     The development of fuel cells as replacements for batteries is dependent on finding a convenient and safe hydrogen source. A fuel cell power system for small applications needs to be compact and lightweight, have a high gravimetric hydrogen storage density, and preferably be operable in any orientation. Additionally, it should be easy to match the control of the system&#39;s hydrogen flow rate and pressure to the operating demands of the fuel cell.  
         [0006]     The present invention provides, in one embodiment, a fuel cartridge for a hydrogen generation system that stores a solid fuel and incorporates a volume-exchange configuration for the storage of the fuel solution and the product.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The invention relates to a system for generating hydrogen gas using a catalyst or reagent and a boron hydride compound.  
         [0008]     The invention also relates to a system for generating hydrogen gas from a borohydride compound using a catalyst. In one aspect of the present invention, a hydrogen generation system is provided that includes fuel cartridges and a hydrogen generation system balance of plant (BOP) module. Solid fuel is preferably stored in individual fuel packets in a fuel chamber, and converted into a fuel solution. Fuel is pumped to a reactor where it produces hydrogen and borate. The hydrogen and borate product exit the reactor and are deposited in a hydrogen separation chamber separated from the fuel chamber by a moveable partition. Hydrogen is separated by a membrane and exits the generator. Preferably, as fuel is consumed, the moveable barrier is disposed toward the fuel chamber and the borate product is deposited on one side the moveable barrier. All controls are preferably contained in the BOP. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     A complete understanding of the present invention may be obtained by reference to the accompanying drawings when considered in conjunction with the following detailed description, in which:  
         [0010]      FIG. 1  is a fuel cartridge with individual fuel packets in accordance with an embodiment of the present invention.  
         [0011]      FIG. 2  is a fuel cartridge with individual fuel packets and containing a fuel solution in accordance with an embodiment of the present invention.  
         [0012]      FIG. 3  is a schematic illustration of the balance of plant module interface in accordance with another embodiment of the present invention.  
         [0013]      FIG. 4  is a schematic illustration of an overall power system according to the invention comprising fuel cartridge, BOP, water management, control, and power modules.  
         [0014]      FIG. 5  is a schematic as in  FIG. 4  including multiple BOP, fuel cartridge, and power modules. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     A process for generating hydrogen from a stabilized metal hydride solution is described in U.S. Pat. No. 6,534,033, entitled “A System for Hydrogen Generation,” the content of which is hereby incorporated herein by reference in its entirety. In the &#39;033 patent, hydrogen is produced from solutions of borohydride compounds, as shown in Equation (1), where MBH 4  and MBO 2 , respectively, represent an alkali metal borohydride and an alkali metal metaborate. A simplified stoichiometry is provided in Equation (1); wherein n is variable and determined by the temperature and nature of the borohydride, among other factors. For sodium borohydride (NaBH 4 ), n preferably is 2. 
 
MBH 4 +(2+n)H 2 O→MBO 2 .nH 2 O+4H 2 +heat   Equation (1) 
 
         [0016]     The present invention provides a fuel cartridge system that delivers a solid fuel component in conveniently pre-packed dosages, to facilitate dispensing, storage and handling of such solid fuel component, while providing a protective barrier against water and other contaminants. The fuel cartridge system easily delivers pre-measured quantities of the solid fuel for hydrogen generation in conveniently packaged units. The solid fuel is a boron hydride compound that is stored in a dry form and mixed with a liquid, as needed. The liquid may include water. The solid fuel component may be provided in various forms, including but not limited to, granules, pellets and powder, for example.  
         [0017]     Boron hydrides as used herein include boranes, polyhedral boranes, and anions of borohydrides or polyhedral boranes. Suitable boron hydrides include, without intended limitation, neutral borane compounds such as decaborane(14) (B 10 H 14 ); ammonia borane compounds of formula NH x BH y  and NH x RBH y , wherein x and y independently equal 1 to 4 and do not have to be the same, and R is a methyl or ethyl group; borazane (NH 3 BH 3 ); borohydride salts (M(BH 4 ) n ), triborohydride salts (M(B 3 H 8 ) n ), decahydrodecaborate salts (M 2 (B 10 H 10 ) n ), tridecahydrodecaborate salts (M(B 10 H 13 ) n ), dodecahydrododecaborate salts (M 2 (B 12 H 12 ) n ), and octadecahydroicosaborate salts (M 2 (B 20 H 18 ) n ), where M is a cation selected from the group consisting of alkali metal cations, alkaline earth metal cations, aluminum cation, zinc cation, and ammonium cation, and n is equal to the charge of the cation. M is preferably sodium, potassium, lithium, or calcium. The boron hydride fuels may contain a stabilizer component, such as a metal hydroxide having the general formula M(OH) n , wherein M is a cation selected from the group consisting of alkali metal cations such as sodium, potassium or lithium, alkaline earth metal cations such as calcium, aluminum cation, and ammonium cation, and n is equal to the charge of the cation.  
         [0018]     The advantage of fuel cell power systems over batteries is that they are readily refuelable, and therefore can contain a “replaceable” fuel cartridge module, and a “permanent” power module. The fuel cartridge module may be disposable, or may simply be refillable, and comprises fuel storage and hydrogen generation components. The power module comprises the fuel cell module, and more specifically the fuel cell stack and related balance of plant components. The hydrogen generation system&#39;s balance of plant with means for fuel regulation and other controls may be incorporated in the power module or may be a separate component. The elements in the power module may be intended to last the lifetime of the power production device.  
         [0019]     In fuel cartridge modules based on a boron hydride hydrogen generation system, the fuel solutions may be conveyed from a fuel storage area through a reactor chamber to undergo the reaction depicted in Equation (1), the resultant borate byproduct and hydrogen gas separated in a hydrogen separation region, and the hydrogen gas fed to the fuel cell unit. The hydrogen generation process and liquid fuel flow to the reactor are preferably regulated (by a hydrogen generation balance of plant, for example) in accordance with the hydrogen demands of the fuel cell.  
         [0020]     Referring to  FIGS. 1 and 2 , where like elements are designated by like reference numerals, an exemplary fuel system comprises a fuel cartridge  100 , a balance of plant module  200 , and a water management module  300  in accordance with the present invention.  
         [0021]     Preferably, the fuel cartridge  100  comprises a fuel storage chamber  110  and a hydrogen separation chamber  120  separated by a movable partition  130  such that the fuel and the products can occupy the same volume in a volume-exchanging configuration. That is, the fuel storage chamber  110  is initially “full” and the hydrogen separation chamber  120  is initially “empty”. The term “movable partition” as used herein includes moveable walls and pistons as well as flexible walls; it is not necessary for the partition as a whole be moveable, only that at least some portion of the partition be moveable. In some embodiments, the hydrogen separation  120  is a flexible chamber such as a bladder or bag, and at least one wall of the flexible chamber functions as moveable partition; a separate moveable partition element need not be present in such configurations. Examples of such flexible hydrogen separation chambers are disclosed for example, in co-pending U.S. patent application Ser. No. 11/340,484 entitled “Hydrogen Generation System and Method” and U.S. Pat. No. 7,105,033 B2 entitled “Hydrogen Gas Generation System,” the contents of which are hereby incorporated herein by reference in their entirety.  
         [0022]     The fuel storage chamber  110  can further include an optional mixing element  108  and a screen  106 . Generally, any method of mixing can be used and mixing element  108  may comprise a mechanical mixing device such as a tumbler, propeller, magnetic stirrers or blender, or a physical mixing device such as a vibration mixer, sonicator, circulation pump or air nozzle; preferably mixing element  108  is a magnetic stirrer comprised of a magnetic stir bar in the fuel chamber  110  and a rotating magnet within fuel mixer driver  240  in the balance of plant module  200 . Illustratively, the mixing mechanism can start before, at the same time, or after the solid and liquid fuel components are dispensed. The mixing mechanism may run continuously or intermittently.  
         [0023]     The solid fuel is contained within the fuel chamber  110  in one or more individual packets  102 , each connected to an input tube  104  that is in communication with the balance of plant module  200 . Each input tube  104  may comprise a separable interface between the fuel cartridge and the balance of plant with an inlet  104   a  at the fuel cartridge and outlet  104   b  at the BOP module. The number and size of the individual packets  102  can be varied according to, for example, the size of the hydrogen generating system, the desired runtime, and desired power output. As an exemplary system to further explain in more detail a preferred embodiment of the invention, a hydrogen generation system constructed to provide hydrogen to provide about twelve hours of runtime at 500 W of power when connected to a fuel cell power system, the equivalent of 6000 Wh, would use four packets each containing 450 g of solid sodium borohydride fuel blend in each packet. Each would require the addition of approximately 1800 g of water to make an aqueous fuel with a concentration of about 20 wt % NaBH 4 . Alternatively, two packets each containing 900 g of solid sodium borohydride fuel blend could be used.  
         [0024]     In one exemplary embodiment, the fuel packets  102  are composed of a flexible liquid-tight material, such as, but not limited to: nylon; polyurethane; polyvinylchloride (PVC); polyethylene polymers including low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), and ethylene-vinyl acetate copolymers (EVA); natural rubber; synthetic rubber; or metal foil.  
         [0025]     In another exemplary embodiment, the packets  102  may be dissolvable packets of, for example: cellulose, starch, polyvinyl alcohol (PVA), polyurethane, or other dissolvable material.  
         [0026]     Water is delivered to the fuel packets  102  from the water management module  300  using a pump  210 , a regulator  220 , and a water conduit  230  in the balance of plant module  200 . The regulator  220  may comprise a multiplexing valve with multiple ports configured to direct water from the water management module  300  to each fuel packet  102  in succession. That is, water is directed into a single fuel packet  102  at a time.  
         [0027]     Each packet  102  can preferably expand to a capacity sufficient to hold the appropriate amount of water and fuel (thus, in the nonlimiting exemplary case, 1800 g of borohydride fuel and 450 g of water) before rupturing to allow the liquid to escape. Alternatively, the packet  102  may be undersized to rupture prior to receiving the full measured amount of water. Once the fuel packet  102  has filled completely, the system will detect the rupture of the packet, for instance but not limited to, by measuring an increase in the discharge pressure of the water pump  210  just prior to the packet  102  rupturing. As the packet  102  breaks, the discharge pressure will drop and the water pump will stop flowing water into the system. Alternatively, the amount of water input into a given fuel packet  102  could be measured or predetermined, and another means of rupturing the packet  102  (such as a mechanical puncturing) could be employed. Referring to  FIG. 2 , the fuel cartridge  100  is shown with a liquid fuel solution  109 . The level of the liquid fuel solution  109  may fall below the fuel packets  102 , or may submerge one or more of the fuel packets.  
         [0028]     The solid fuel does not need to completely dissolve in the water within the fuel packet, particularly if an optional mixing element  108  is included within the fuel cartridge. The mixing element  108  will engage to ensure that the solids are substantially dissolved into the water to form a fuel solution  109 . The perforated screen  106  prevents the fuel packets  102  from physically interfering with the mixing element  108 .  
         [0029]     The cartridge  100  further comprises a fuel regulator  112 , a fuel conduit  116 , a reaction chamber  118 , a hydrogen separator  122 , and a hydrogen outlet  124 . The cartridge  100  optionally further comprises a memory chip for storing information relevant to the cartridge such as, for example, cartridge identification, amount of fuel remaining, elapsed runtime, and system errors.  
         [0030]     In the operation of the hydrogen gas generating system, fuel regulator  112  feeds the fuel solution  109  from the fuel chamber  110  to the reaction chamber  118  to undergo the reaction depicted in Equation (1). The moveable partition  130  is movable to allow the solid and liquid products to occupy the volume initially occupied by the fuel.  
         [0031]     The reaction chamber  108  used with this embodiment preferably contains a reagent, such as a catalyst metal supported on a substrate. Suitable transition metal catalysts for the generation of hydrogen from a metal hydride solution include metals from Group 1B to Group VIIIB of the Periodic Table, either utilized individually or in mixtures, or as compounds of these metals. Representative examples of these metals include, without intended limitation: transition metals represented by the copper group, zinc group, scandium group, titanium group, vanadium group, chromium group, manganese group, iron group, cobalt group and nickel group. Specific examples of useful catalyst metals include, without intended limitation: ruthenium, iron, cobalt, nickel, copper, manganese, rhodium, rhenium, platinum, palladium, and chromium. The preparation of such supported catalysts is taught, for example, in U.S. Pat. No. 6,534,033 entitled “System for Hydrogen Generation,” the disclosure of which is incorporated herein by reference. Other suitable catalysts or reagents that promote the reaction of boron hydride compounds such as unsupported metals, acids, or heat can alternatively be present in the reaction chamber  118 . These catalysts and reagents can be combined to work in concert for the production of hydrogen; for example, heat may be used with a supported metal catalyst system.  
         [0032]     The products leave the reaction chamber  118  and enter hydrogen separation chamber  120  where the borate is retained while the hydrogen gas passes through an optional hydrogen separator  122  in communication with hydrogen outlet line  124 , and which preferably precedes or is incorporated in the inlet to the hydrogen outlet line  124 .  
         [0033]     The hydrogen occupies any void space in the fuel cartridge  100  until it is removed from the cartridge  100 . The separator  122  may be a hydrogen permeable membrane or filter. Suitable gas permeable membranes include materials that are more permeable to hydrogen than a liquid such as water, such as silicon rubber, polyethylene, polypropylene, polyurethane, fluoropolymers or any hydrogen-permeable metal membranes, such as palladium-gold alloys. Suitable gas permeable membranes include materials that are microporous and hydrophobic and/or oleophobic.  
         [0034]     The hydrogen produced by the fuel cartridge  100  is delivered through hydrogen conduit  124 . The hydrogen can be delivered to a power module comprising a fuel cell or hydrogen-burning engine for conversion to energy, or a hydrogen storage device, such as hydrogen cylinders, metal hydrides, or balloons. Optionally, conduit  124  connects to the balance of plant module  200  and hydrogen can be delivered from the balance of plant module  200 .  
         [0035]     Preferably fuel regulator  122  is the pump head of a peristaltic pump, a piston pump, a diaphragm pump, or other such pump having a pump head that is driven by a motor wherein the pumping mechanism can be external to fuel line  116 . In general, peristaltic and piston pumps operate through the use of a pump head comprised of a series of fingers in a linear or circular configuration or at least one piston which can compress the fuel line  116 ; the fingers may be in a variety of configurations and alternatively referred to as rollers, shoes, or wipers. The compression of the fuel line  116  by the fingers forces the liquid through the line; when the line is not compressed and open, fluid flows into the fuel line. A diaphragm pump configuration comprises a diaphragm in the wall of fuel line  116 , check valves on the upstream and downstream sides of the diaphragm, and a pump head. In general, diaphragm pumps operate through the use of a pump head comprised of a series of cams in a linear or circular configuration or at least one piston which can compress the diaphragm; the compression of the membrane by the fingers forces the liquid through the line; when the membrane expands and is not compressed, fluid is drawn into the fuel line. The cams may be in a variety of configurations and alternatively referred to as rollers, shoes, or wipers. The check valves constrain and control the directional flow through the diaphragm and fuel line  116 .  
         [0036]     In another embodiment of a diaphragm pump configuration, fuel regulator  112  is a diaphragm that further comprises a piezoelectric crystal that is in electrical communication with fuel pump driver  222  which comprises an electrical contact. Upon the application of an oscillating voltage to the piezoelectric crystal, a diaphragm pumps fluid through the conduit line as described previously for the mechanically controlled diaphragm. Alternatively, fuel regulator  112  can comprise a pump and motor driven by an electrical power supplied via fuel pump driver  222 .  
         [0037]     The fuel pump driver  222  preferably resides in the balance of plant module  200  and provides either mechanical or electrical energy to the fuel regulator and may comprise a motor or an electrical contact as described above. The fuel pump driver  222  varies the pumping speed of the fuel regulator  112  in response to control signals from the control unit that may be contained within the balance of plant module  200  or in the power module. For example, when the electrical power demand from the fuel cell  500  ( FIG. 4 ) decreases, the control unit can signal the fuel pump driver  222  to operate its motor at lower speed, thus reducing the fuel flow to reaction chamber  118 , which in turn reduces the rate of hydrogen production. If the electrical demand from fuel cell  500  is zero, the fuel pump driver  222  will operate such that no fuel will be propelled through fuel line  116 . Likewise, when the electrical power demand increases, fuel pump driver  222  operates to increase fuel flow to reaction chamber  118 , and increasing the rate of hydrogen production.  
         [0038]     Referring now to  FIG. 3 , wherein features that are the same as those shown in previous figures are designated by like reference numerals, the balance of plant module  200  comprises a fuel pump driver  222 , fuel mixer driver  240 , at least one optional hydrogen inlet  260  connecting the BOP module  200  with the hydrogen conduit from the fuel cartridge  100  via a hydrogen outlet  265 , and at least one hydrogen outlet  250  configured to deliver hydrogen. The fuel cartridge module  100  may be connected to the balance of plant module  200  in any suitable way.  FIG. 3  also shows electronic interfaces  285  and  280 , water inlet  212  for communication with conduit  310 , and cartridge seat  202 .  
         [0039]     Preferably, the BOP module  200  further includes at least one heat exchanger  270  in communication with the fuel cartridge  100 . The at least one optional heat exchanger  270  can operate to remove heat from at least one of the reaction chamber  118 , the cartridge body as a whole, or the hydrogen stream. In some configurations, the at least one heat exchanger  270  is removably attached to the top of the fuel cartridge  100  and connected by a cable or tether to the BOP module  200 . The at least one heat exchanger  270  can comprise either liquid- or air-cooling loops, fans, radiators and/or heat fins.  
         [0040]     Control electronics for the hydrogen generation modules may be incorporated into the BOP module  200  or may comprise a separate control module  400 , as illustrated in  FIG. 3 . Preferably the control module  400  comprises a battery to handle load prior to operation of the hydrogen generator and associated fuel cell power system during startup. Alternatively, the control module  400  can be in electrical communication with a separate battery. The battery may be recharged by the system during operation. A hybridization battery will also provide for higher peak load capacity as well as allowing the cartridges to be changed during operation without shutting down the system (referred to as “hot-swappable” cartridges).  
         [0041]     Preferably, the control module  400  includes microcontrollers to handle a mix of analog and digital I/O and controls start up, running, and shut down of the system. Components may monitor operating parameters such as, but not limited to, liquid levels, runtime operational errors, and state of charge and energy management of the battery.  
         [0042]     Referring to  FIG. 4 , wherein features that are the same as those shown in previous figures are designated by like reference numerals, an exemplary power system comprises a fuel cartridge module  100 , a balance of plant module  200 , a water management module  300 , a control module  400 , and a fuel cell power module  500 . Optional water conduits  502 ,  504  and  506  may be provided to manage water produced in the power module and convey it to the water management module  300 .  
         [0043]     Water management module  300  comprises a water reservoir  302  and a water filtration system  304  that allows for impure water to be used for hydrogen generation. Various impure waters such as urine, brackish water, sea water, lake water, hard and soft waters, and gray water (wastewater produced by dishwashing, clothes washing and bathing) can be processed by the water filtration system  304  via input  310 . Fresh water may be added directly to the water reservoir  302 , as can water produced by the fuel cell, via input  506 . Water produced by the fuel cell can alternatively be withdrawn for other uses, such as drinking, via water conduit  504 .  
         [0044]     Multiple balance of plant modules  200  and fuel cartridges  100  can be connected to provide sufficient hydrogen fuel for fuel cell power systems as illustrated in  FIG. 5 , wherein features that are the same as those shown in previous figures are designated by like reference numerals. The number of fuel cartridge  100  and balance of plant modules  200  can be varied to fulfill the runtime and/or power demands of the intended use. Preferably, the controller unit can automatically detect the number and identification of the BOP modules  200  and relay status information such as the state of charge of each cartridge  100 , and manage either parallel or serial operation of the balance of plant  200  and fuel cartridge units  100 . Preferably, each balance of plant module  200  comprises at least one valve, such as a solenoid or check valve, to allow an individual BOP module  200  to be isolated from others in a system.  
         [0045]     While the present invention has been described with respect to particular disclosed embodiments, it should be understood that numerous other embodiments are within the scope of the present invention. For example, while the figures illustrate one particular horizontal orientation of the fuel packets and hydrogen separation chamber, additional embodiments wherein the fuel packets and hydrogen separation chamber are oriented vertically or in other spatial arrangements are within the scope of the present invention.