Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
  • C01B3/06—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents
  • C01B3/065—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents from a hydride
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L1/00—Liquid carbonaceous fuels
  • C10L1/32—Liquid carbonaceous fuels consisting of coal-oil suspensions or aqueous emulsions or oil emulsions
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• the present invention relates to a blend of borohydride salts for use in the generation of hydrogen.
• borohydride salts for use in the process illustrated in Equation 1.
• Borohydrides generally possess a solubility in water of from about 7% to about 35% by weight at 25° C.
• Lithium borohydride has a solubility of 7%, potassium borohydride is about 19%, and sodium borohydride is soluble at about 35%.
• sodium borohydride is the salt of choice for fuel solutions for a hydrogen generator.
• Sodium borohydride which possesses a high gravimetric hydrogen storage density of about 7.4 wt. percent in a saturated solution at ambient temperature, is preferred in the practice of the present invention as well.
• fuel blends for hydrogen generation comprising a mixture of boron hydrides, including at least one borohydride salt with a positive ion selected from the group consisting of alkali metal cations, alkaline earth metal cations, aluminum cation and ammonium cation such that the mixture possesses a predetermined molar ratio of solvated positive ionic charges ( + IC) to boron atoms, whereby the solubility of the borate is maximized.
• Such fuel blends facilitate fuels with high gravimetric hydrogen storage that can be utilized for the generation of hydrogen with mitigated concern for premature solidification of the borate product in the hydrogen generation apparatus.
• the present invention relates to aqueous fuels for hydrogen generation containing certain mixtures of boron hydrides.
• Boron hydrides in this context refer to boranes, including polyhedral boranes, and anions of borohydrides or polyhedral boranes. More particularly, the present invention relates to aqueous fuels containing blends of boron hydrides having a predetermined molar ratio of solvated positive ionic charges ( + ICs) to boron atoms. It has been found that this ratio results in a solubility maximizing, not of the components of the fuel, but of the borate product of the hydrolysis reaction that results in the generation of hydrogen.
• solubility maximizing in this context is meant achieving optimum solubility of the borate product in relation to the concentration of the borohydrides in the fuel, thereby minimizing the incidence of precipitation of borate product during the generation of hydrogen as a result of the consumption of water in the hydrolysis of boron hydrides, for example, as shown for the borohydrides in Equation (1).
• the ratio of positive ionic charges (+IC) to boron is determined in accordance with the present invention in the following manner, using alkali metal salts as an example.
• Alkali metal borate salts are typically written in the format j M 2 O k B 2 O 3 X H 2 O, wherein M is chosen from lithium, sodium and potassium.
• the values for j, k and X will vary for different borates.
• fuel blends for hydrogen generators are chosen to comprise a mixture of boron hydrides such that the value of the molar ratio of positive ionic charges ( + ICs) to boron atoms is between 0.2 to 0.4, preferably between 0.2 and 0.3, or between 0.6 and 0.99, preferably between 0.7 and 0.8.
• the fuel mixtures in accordance with the present invention are comprised of a boron hydride salt wherein the positive ion (M) is selected from those of an alkali metal such as sodium, lithium, potassium, an alkaline earth metal, aluminum or ammonium in combination with at least one other boron hydride such that the desired ratios are achieved.
• Suitable boron hydrides include, without intended limitation, the group of borohydride salts (MB HA triborohydride salts (MB 3 H 8 ), decahydrodecaborate salts (M B ⁇ oH ⁇ o), tridecahydrodecaborate salts (MB ⁇ oH 13 ), dodecahydrododecaborate salts (M B ⁇ 2 Hi 2 ), and octadecahydroicosaborate salts (M 2 B 2 oH
• M decaborane(14) (BioH )
• Preferred mixtures of positive ion boron hydrides in accordance with the present invention include, without intended limitation: a metal borohydride, preferably sodium borohydride, and decaborane(14); a metal triborohydride and a metal dodecahydrododecaborate; a metal borohydride and a metal triborohydride; and a metal borohydride and a metal dodecahydrododecaborate. It is not critical whether the mixtures of boron hydrides in the subject fuels have an + IC/B ratio falling between 0.2 to 0.4 or between 0.6 and 0.99 as both are advantageous.
• TC/B ratio may be determined by economic considerations, e.g., the relative availability and cost of the individual boron hydride compounds, as well as consideration of the chemical reactivity and human health effects of the individual boron hydride compounds. Whether a particular mixture is within one or the other may be determined by other considerations, such as relative solubility of various boron hydrides, desired operating temperature range of the mixture and the like, and is considered to be within the purview of one of ordinary skill in the art.
• the positive ion component of the higher borohydrides described above may be, in addition to the alkali metal cations as described in reference to the borohydrides, alkaline earth metal cations, or aluminum cation.
• the positive ion is selected from sodium, lithium, potassium, beryllium, magnesium, calcium, or aluminum. It is not a requirement that where the subject fuel mixtures contain more than one borohydride salt, the positive ion components thereof be the same.
• the positive ion component for the metal borohydrides of the subject fuel blends is preferably sodium.
• borohydride salt is present in aqueous fuel mixtures for hydrogen generators, it will readily hydrolyze unless it is stabilized against hydrolysis by the presence of a strong base.
• Suitable bases for this purpose are the hydroxides of the respective metals given above that are strong bases, e.g. sodium hydroxide when the component is sodium borohydride.
• the positive cation component of the stabilizer must enter into the equation when the mole ratio of positive ionic charge ( + IC) to boron is calculated as will be discussed below.
• an alkaline stabilizer in order to prepare stable aqueous solutions of decaborane(14), an alkaline stabilizer must be present; the metal cation component of the stablizer contributes positive ionic charge ( + IC) to the fuel blend.
• the metal cation component of the stablizer contributes positive ionic charge ( + IC) to the fuel blend.
• Many of the boron-rich hydrides (such as the M 2 Bi2H 12 , M 2 B ⁇ oH ⁇ 0 , and M 2 B 20 H 18 ) are stable in neutral aqueous solution.
• the calculation of the mole ratio of positive ionic charge ( + IC) to boron is developed in the following manner.
• an aqueous fuel solution containing 35% by weight sodium borohydride as the only positive ion boron hydride with 3% by weight sodium hydroxide added for stability has a j to k ratio of 1.08 determined as follows using 100 grams of fuel solution as an example.
• all boron comes from the sodium borohydride, therefore the number of moles of boron is calculated directly from the borohydride concentration in the fuel solution as shown below.
• the ratio can be calculated by dividing the total moles of sodium by the total number of moles of boron as illustrated below: f 0.529 mol Na + 0.075 mol Na 1.14 Na : B V 0.529 mol B
• a further advantage of the fuel mixtures of the present invention is that many of the boron-rich higher boron hydrides are stable in aqueous solution and do not require the addition of basic stabilizers as is the case with metal borohydrides, such as sodium borohydride.
• An additional advantage of the subject blended fuel solutions is that some higher boron hydrides hydrolyze in aqueous solution to yield some acidic products which, in turn, could act to partially neutralize any metal hydroxide stabilizer present and produce a less basic discharge stream than the metal metaborate/metal hydroxide mixture that results from using a fuel containing only metal borohydride and metal hydroxide.
• An additional advantage to the novel aqueous fuel blends of the present invention is the fact that, even if some solidification were to take place in the hydrolysis reactor as cooling takes place, the products are readily water soluble.
• the borate mixtures that are formed when the fuel contains only metal borohydride and hydroxide, e.g. sodium borohydride and hydroxide are slow to dissolve and can form a crust in the catalyst chamber that is difficult to remove.
• the borate mixtures formed with use of the fuel mixtures of the present invention can be readily removed by the simple expedient of flushing the chamber and related apparatus with water, thereby prolonging catalyst life and reducing normal maintenance downtime for hydrogen generation systems.
• sodium borate salts having molar ratios of positive ionic charge ( + IC) to boron within the maximum solubility ranges in accordance with the present invention can have positive heats of solvation and, therefore, actually facilitate the dissolution reaction and, thereby, the production of hydrogen, see O'Brien et al, "Amorphous Sodium Borate Composition" USP No. 2,998,310.
• aqueous fuel includes an aqueous liquid in which all the components are dissolved and/or a slurry in which some of the components are dissolved and some of the components are undissolved solids.
• Hydroalcoholic mixtures are also advantageous for preparing the aqueous fuels of the present invention in that they lower the freezing point of the fuel, thereby expanding the operating temperature range thereof.
• the higher boron hydrides tend to be both soluble and stable in hydroalcoholic solutions, especially when a stabilizer is present to raise the pH.
• the alcohols utilized to prepare hydroalcoholic solutions are lower alkanols, particularly methanol and ethanol.
• aqueous fuels prepared in the form of slurries for economy of handling and storage will be combined with sufficient water at time of use to form solutions of the components confirming to the ratios of maximum solubility stated herein.
• the method comprises contacting the subject improved aqueous fuel blend of boron hydrides having specific positive ionic charge ( + IC) to moles of boron ratios with a catalyst for promoting the hydrolysis of the boron hydrides to produce hydrogen.
• the system provided in accordance with the present invention includes means for contacting the aqueous fuel blends of boron hydrides with the catalyst.
• Such means include means to physically separate the catalyst from the fuel when there is no demand for hydrogen gas.
• the aqueous fuel solution can be brought into contact with the catalyst so that the hydrolysis reaction occurs and hydrogen is produced.
• the separation of catalyst can be achieved by using any mechanical, chemical, electrical and/or magnetic method that can readily appreciated by a person skilled in the art.
• different chambers are used to separate the catalyst from the aqueous fuel solution.
• the aqueous fuel can be stored in a fuel reservoir, from which it is pumped into the catalyst chamber to contact the catalyst thereby generating hydrogen through the hydrolysis reaction illustrated in Equation (1) for metal borohydrides.
• the catalyst can be inserted into and removed from a tank containing the subject hydride solution.
• the catalyst for the hydrolysis is an acid and both the fuel and the catalyst are in liquid form which can be pumped into the reaction chamber to generate hydrogen.
• the fuel and the catalyst solution must be stored in separate containers and individually pumped into the reactor to initiate and maintain the hydrolysis reaction.
• Preferred acid catalysts are strong inorganic acids, particularly hydrochloric acid sulfuric acid and phosphoric acid.
• the improved fuel solutions of the present invention may be pumped into the system either batchwise or continuously.
• the catalyst chamber may comprise at least one conduit, through which fuel solution can be directed to flow into and out of the chamber at different stages of the catalysis reaction.
• the conduit may also function as output channel for discharging hydrogen gas generated by the hydrolysis reaction.
• a separate chamber may not be necessary when insoluble metals or metals bound to, entrapped within, and/or coated onto a substrate are used as the catalyst in reaction illustrated in Equation (1).
• Suitable substrates for metal catalysts include, without intended limitation, plastics, polymers, textiles, metals, metal oxides, ceramics, or carbonaceous materials.
• the system of the present invention includes a containment system wherein the catalyst is entrapped by physical or chemical means onto and/or within a porous or nonporous substrate, including metallic meshes and fibers as shown in US Patent No. 6,534,033, which is incorporated by reference herein.
• the hydrogen generation system may comprise only one chamber, wherein the separation of the catalyst from the aqueous fuels can be achieved by removing the insoluble or supported catalyst from the solution thereby interrupting contact between the catalyst and the boron hydrides therein. Consequently, when hydrogen production is desired, the catalyst can simply be reinserted into the aqueous fuel to catalyze reaction (1) as described above. [0024] Since the improved aqueous fuels of the present invention are stable in the absence of a catalyst, the generation of hydrogen in accordance with reaction (1) can be closely controlled by regulating the contact of boron hydrides therein with catalyst.
• the control can be achieved by regulating the flow of aqueous fuel to the catalyst, or by withdrawing the catalyst from the fuel solution, depending on the actual setup of the hydrogen generating system and the configuration thereof.
• hydrogen production can be controlled by contacting with or separating the bound catalyst from the boron hydride fuel solution.
• the catalyst metal can be attached to a piston or the like, which can move in and out of the fuel solution in response to hydrogen demand.
• the supported catalyst can be contained in a separate chamber and the flow of the fuel solution into the chamber is controlled by valves and a suitable regulator means.
• a homogeneous catalyst e.g.
• the control of hydrogen generation is achieved by regulating the flow of either the boron hydride fuel solution, or the catalyst solution, or both.
• a mixing chamber is used wherein the two solutions are injected or pumped into the chamber so that they are mixed and the hydrolysis reaction will occur.
• the acidic salts of polyhedral boron hydrides such as hydronium salts, wherein the positive ion is H +
• ammonium salts wherein the positive ion is NH
• Suitable accelerant components include H2B12H12, H 2 B ⁇ oH ⁇ o, (NH4) 2 B ⁇ 2 H ⁇ 2 , and (NH ) 2 B ⁇ oH ⁇ o. In such a system, no additional catalyst system is required, though one may be incorporated as needed to optimize hydrogen generation rate.
• an acidic polyhedral boron hydride salt is stored separately from a fuel mixture comprising one or more boron hydrides, and the species combined as needed to produce hydrogen. It is preferable that at least one of the accelerant or fuel mixture be an aqueous solutions to facilitate mixing. However, either or both components (the fuel blend and the accelerant) may be stored as a dry powder to eliminate the need for a stabilizer. In such a case, a separate supply of water is required for hydrogen generation, and the dry and liquid components are added in defined proportions to a mixing chamber by using any method known to those skilled in the art.
• the boron hydride species, concentrations and mixing rates are chosen in accordance with the present invention as described above such that the resultant borate salts have the appropriate + IC/B ratio falling between 0.2 to 0.4 or between 0.6 to 0.99.
• the hydronium salts are treated as neutral boron hydrides, e.g. H 2 B 12 H 12 is treated as Bj 2 H 14 in order to determine the boron contribution.
• the accelerant is metered into a reactor to mix with the boron hydride fuel mixture and with any necessary water.
• the acidic polyhedral boron hydride salt thus acts as an accelerant to promote the hydrogen generation reaction, hydrolyzes to produce hydrogen, and, contributes boron atoms, and in the case of the ammonium salts, positive charge, to the fuel blend.
• a gas-liquid separator is used to separate hydrogen gas from the effluent solution.
• a small buffer tank in order to accommodate immediate demand for hydrogen gas, it is preferred to incorporate a small buffer tank into the present system.
• the small buffer tank always contains a supply of hydrogen gas for instantaneous demand for hydrogen. Once hydrogen is withdrawn from the buffer tank, the resulted pressure drop can trigger the system to produce more hydrogen gas so that a constant level of hydrogen gas is maintained therein.
• the hydrogen gas generated by the current system can be directed to a fuel cell or a hydrogen-consuming device for direct use.
• the hydrogen gas can be stored in a gas reservoir or buffer tank as described above for future use.
• the fuel blends prepared in accordance with the present invention are governed by two considerations. The first of these is the mole ratio of positive ionic charge ( + IC) to atomic boron as discussed herein. The second is the relative solubilities of the individual salts utilized to form the mixture. It will be appreciated that one of ordinary skill in the art, given the parameters of the maximum ratios discussed herein and with the relative solubilities of individual salts, which information is readily available, would be able to prepare a fuel solution that would possess a maximum ratio and all components would be soluble in the aqueous vehicle. Such calculations are illustrated by the following examples which are for purposes of illustration and are not intended to be limiting on the scope of the present invention.
• a generic description of a hydrogen generation test is described, using sodium borohydride, decaborane, sodium hydroxide and water in the fuel blend as a sample system. Fuel blends are made in open air. The water and stabilizing sodium hydroxide are initially mixed, decaborane is added thereto, followed by the proper amount of sodium borohydride to deliver the desired ratio.
• a Parr reactor resting on a hot plate is employed.
• the reactor incorporates two thermocouples that operated continuously during the run, one measuring the temperature of the fuel solution, and the other measuring the temperature of the head-space near the top of the reactor.
• the second thermocouple controls a cooling loop circulating through the reactor that is activated when the second thermocouple records a threshold temperature of 95°C.
• a pressure sensor continually measures internal pressure.
• the reactor is first charged with six pieces of ruthenium coated nickel catalyst, each piece weighing between 0.095 and 0.105 g.
• the hydrogen storage capacity of this blend is determined by calculating the total number of moles of H 2 produced and divided by the initial weight of the blend. ( 1 mol NaBH 4 V 4molH2 "2.0158 gH 2
• the + IC:B ratio is calculated as follows: ( lmolNaBH 4 ( I olB
• Example 1 The following were mixed according to the procedure of Example 1 to yield 100 g of a fuel blend capable of delivering 6.8 weight-% H 2 , with a sodium to boron ratio of 0.25: sodium triborohydride 13.74 g; sodium dodecahydrododecaborate 13.74 g and water 76.09 g. Each mole of sodium dodecahydrododecaborate yields twenty-five moles of hydrogen according to equation (3) Na 2 B 12 H 12 + 19 H 2 O ⁇ 2 NaBO 2 + 5 B 2 O 3 + 25 H 2 (3)
• the hydrogen storage capacity of this blend is determined by calculating the total number of moles of H 2 produced and divided by the initial weight of the blend. lmolNa 2 B 12 H 12 V 25 mol H 2 f2.0158gH 2
• this blend has a Na:B mole ratio of 0.25.
• Example 1 The following were mixed according to the procedure of Example 1 to yield 100 g of a fuel blend capable of delivering 5.0 weight-% H 2 , having a metal cation to boron ratio of 0.25: potassium triborohydride 12.95 g; magnesium dodecahydrododecaborate 6.76 g and water 80.03 g.
• the hydrogen storage capacity of this blend is determined by calculating the total number of moles of H 2 produced and divided by the initial weight of the blend. lmolMgB] 2 Hj 2 V 25 mol H 2 V 2.0158gH 2
• the + IC:B ratio can also be calculated as follows:
• the hydrogen storage capacity of this blend is determined by calculating the total number of moles of H 2 produced and divided by the initial weight of the blend.
• the + IC:B ratio can also be calculated as follows:
• the hydrogen storage capacity of this blend is determined by calculating the total number of moles of H 2 produced and divided by the initial weight of the blend.

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