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Energy efficient synthesis of boranesRelated Patent Categories: Chemistry Of Inorganic Compounds, Boron Or Compound Thereof, Nitrogen And Hydrogen Containing, Ternary CompoundEnergy efficient synthesis of boranes description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070189950, Energy efficient synthesis of boranes. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This application claims the benefit of copending U.S. Provisional Patent Application No. 60/771,739, filed Feb. 8, 2006 and entitled "Energy Efficient Synthesis of Boranes," which is incorporated by reference herein. FIELD OF THE INVENTION [0003] The present invention relates generally to hydrogen storage, and more particularly to an energy efficient synthesis of boranes (boron compounds having at least one B--H bond). BACKGROUND OF THE INVENTION [0004] Hydrogen (H.sub.2) is currently the leading candidate for a fuel to replace gasoline/diesel fuel in powering the nation's transportation fleet. There are a number of difficulties and technological barriers associated with hydrogen that must be solved in order to realize this "hydrogen economy". Inadequate storage systems for on-board transportation hydrogen are recognized as a major technological barrier (see, for example, "The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs," National Academy of Engineering (NAE), Board on Energy and Environmental Systems, National Academy Press (2004). [0005] One of the general schemes for storing hydrogen relates to using a chemical compound or system that undergoes a chemical reaction to evolve hydrogen as a reaction product. In principle, this chemical storage system is attractive, but systems that have been developed to date involve either: (a) hydrolysis of high-energy inorganic compounds where the evolution of hydrogen is very exothermic (sodium borohydride/water as in the Millennium Cell's HYDROGEN ON DEMAND.RTM., and lithium (or magnesium) hydride as in SAFE HYDROGEN.RTM., for example), thus making the cost of preparing the inorganic compound(s) high and life-cycle efficiency low; or (b) dehydrogenation of inorganic hydride materials (such as Na.sub.3AlH.sub.6/NaAlH.sub.4, for example) that release hydrogen when warmed but that typically have inadequate mass storage capacity and inadequate refueling rates. [0006] Inorganic compounds referred to in (a), above, produce hydrogen according to the chemical reaction MH.sub.x+XH.sub.2O.fwdarw.M(OH).sub.x+XH.sub.2 (1) where MH.sub.x is a metal hydride, and M(OH).sub.x is a metal hydroxide. This reaction is irreversible. [0007] Inorganic hydride materials referred to in (b), above, produce hydrogen according to the following chemical reaction, which is reversible with H.sub.2 (hydrogen gas): MH.sub.X=M+x/2H.sub.2 (2) where MH.sub.x is a metal hydride, M is metal and H.sub.2 is hydrogen gas. By contrast to the first reaction, which is irreversible with H.sub.2, the second reaction is reversible with H.sub.2. [0008] A practical chemical system that evolves hydrogen yet does not suffer the aforementioned inadequacies would be important to the planned transportation sector of the hydrogen economy. This same practical chemical system would also be extremely valuable for non-transportation H.sub.2 fuel cell systems, such as those employed in laptop computers and other portable electronic devices, and in small mechanical devices such as lawnmowers where current technology causes significant pollution concerns. [0009] Any heat that must be input to evolve the hydrogen represents an energy loss at the point of use, and any heat that is evolved along with the hydrogen represents an energy loss where the chemical storage medium is regenerated. Either way, energy is lost, which diminishes the life-cycle efficiency. For most organic compounds, such as in those shown in equations 3-5 below, hydrogen evolution reactions are very endothermic, and the compounds are incompetent to evolve hydrogen at ambient temperature (i.e. thermodynamically incapable of evolving H.sub.2 at significant pressure at ambient temperature). For temperatures less than about 250-400 degrees Celsius, the equilibrium pressure of hydrogen over most organic compounds is very small. As a consequence, most common organic compounds require heating above about 250 degrees Celsius, and the continual input of high-grade heat to maintain this temperature, in order to evolve hydrogen at a useful pressure. TABLE-US-00001 CH.sub.4 .fwdarw. C + 2H.sub.2 .DELTA.H.sup.0 = +18 kcal/mol (3) .DELTA.G.sup.0 = +12 kcal/mol 6CH.sub.4 .fwdarw. cyclohexane + 6H.sub.2 .DELTA.H.sup.0 = +69 kcal/mol (4) .DELTA.G.sup.0 = +78 kcal/mol cyclohexane .fwdarw. benzene + 3H.sub.2 .DELTA.H.sup.0 = +49 kcal/mol (5) .DELTA.G.sup.0 = +23 kcal/mol [0010] Most organic compounds have hydrogen evolution reactions that are endergonic (i.e. having a net positive standard free energy of reaction change, i.e. .DELTA.G.sup.0>0) and their ambient temperature equilibrium hydrogen pressure is very low, practically unobservable. Thus, most organic compounds are unsuitable for hydrogen storage, based on both life-cycle energy efficiency and delivery pressure considerations. Decalin, for example, evolves hydrogen to form naphthalene when heated to about 250 degrees Celsius in the presence of a catalyst (see, for example, Hodoshima et al. in "Catalytic Decalin Dehydrogenation/Naphthalene Hydrogenation Pair as a Hydrogen Source for Fuel-Cell Vehicle," Int. J. Hydrogen Energy (2003) vol. 28, pp. 1255-1262, incorporated by reference herein). Hodoshima et al. use a superheated "thin film" reactor that operates at a temperature of at least 280 degrees Celsius to produce hydrogen from decalin at an adequate rate and pressure. Thus, this endothermic hydrogen evolution reaction requires both a complex apparatus and high-grade heat, which diminishes the life-cycle energy efficiency for hydrogen storage. [0011] Boranes have high hydrogen storage capacities and have attracted interest for use as hydrogen storage materials for transportation, but the difficulty of manufacturing borane compounds, and the life-cycle energy inefficiency of the chemical process presently used for their manufacture, has prevented their widespread use. [0012] Owing to its commercial availability, NaBH.sub.4 (sodium borohydride) is a starting material typically used to prepare borane compounds. Diborane (B.sub.2H.sub.6), for example, is prepared by reacting NaBH.sub.4 with BF.sub.3. Borohydride compounds (i.e. compounds containing the BH.sub.4 anion or other anionic B--H groups) are generally prepared by reacting alkoxyborates with active metal hydrides e.g. NaH or NaAlH.sub.4. Sodium borohydride itself (NaBH.sub.4), for example, is commercially prepared using the known Schlessinger process, which involves reacting sodium hydride (NaH) with trimethoxyboron (B(OCH.sub.3).sub.3). While convenient to practice on a small or intermediate laboratory or commercial scale, these reactions are not energy-efficient; the reaction of NaH with B(OCH.sub.3).sub.3 is exothermic, and NaH is itself formed in the exothermic reaction of Na metal with H.sub.2, so overall, about 22 kcal of heat are released per B--H bond that is formed. [0013] Other means are known for forming B.sub.2H.sub.6. The best known is the reaction of BCl.sub.3 with H.sub.2 at high temperature to make BHCl.sub.2 and HCl. Significant equilibrium conversion is possible only if the temperature is on the order of about 600 degrees Celsius or more, and the product mixture must be rapidly quenched, typically within a few seconds, to a temperature below about 100 degrees Celsius to allow BHCl.sub.2 to disproportionate to B.sub.2H.sub.6 and BCl.sub.3. The quenched mixture must be separated rapidly before the B.sub.2H.sub.6 back reacts with the HCl coproduct. BCl.sub.3 and HCl are both highly corrosive. Their corrosive properties in combination with the difficulties of heat management make this process costly to practice. [0014] Presently, there is no energy efficient means available for preparing boranes. [0015] Methods and systems that employ chemical compounds for storing and evolving hydrogen at ambient temperature with minimal heat input remain highly desirable. SUMMARY OF THE INVENTION [0016] In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention includes a method for synthesizing a BH.sub.3-containing compound. The method involves synthesizing at least one halo-boron compound from a boron-containing precursor; reacting the at least one halo-boron compound with an inorganic hydride material, thereby generating at least one B--H compound; and disproportionating the at least one B--H compound to at least one BH.sub.3-containing compound. [0017] The invention also includes a method for making a metal hydride, comprising thermolyzing a reactive metal formate. The reactive metal hydride may be a compound of the formula (R').sub.n(R'').sub.m(X).sub.3-n-mSn(H) wherein R' is alkyl; wherein R'' is aryl or aryl attached to a polymer backbone; wherein X is F, Cl, Br, or I; wherein n is 0, 1, 2, or 3; wherein m is 0, 1, 2, or 3; and wherein n+m.ltoreq.3. [0018] The invention also includes a method of forming BH.sub.3NH.sub.3 and related materials containing BH.sub.3 and amine compounds. The method involves reacting a monohydrido boron compound with a selected ligand whereby the monohydrido boron compound disproportionates to a BH.sub.3-containing compound; and thereafter reacting the BH.sub.3-containing compound with ammonia. [0019] The invention also includes a method of forming halo-boron compounds suitable for reduction to boranes. The method involves reacting a boron compound selected from the group consisting of alcoholato-boron compounds, catecholato-boron compounds, amino-boron compounds, and anilino-boron compounds with a compound of the formula HX wherein X is selected from the group consisting of halogens; and thereafter separating a product halo-boron compound. [0020] The invention also includes a method of forming halo-boron compounds suitable for reduction to boranes. The method involves reacting a boron compound selected from the group consisting of alcoholato-boron compounds, catecholato-boron compounds, amino-boron compounds, and anilino-boron compounds with an oxidizing agent, the oxidizing agent comprising a corresponding halo-boron compound or halide salt of the boron compound; and thereafter separating a product halo-boron compound. [0021] The invention also includes a method for synthesizing a BH-containing compound. The method includes synthesizing at least one halo-boron compound from a boron-containing precursor; and reacting the at least halo-boron compound with an inorganic hydride material, thereby generating at least one B--H compound. Continue reading about Energy efficient synthesis of boranes... Full patent description for Energy efficient synthesis of boranes Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Energy efficient synthesis of boranes patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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