Abstract:
Utilization of process and equipment for oxidation of metal sulfides, preferably two step metal sulfide oxidation reactions, and more preferably with looping back of second step oxide to the first step as an oxidizing agent, to generate sulfur dioxide and a useful metal or metal oxide, and react the sulfur dioxide with halogen (iodine or bromine) and water to produce sulfuric and halogen acid under moderate process conditions and equipment requirements and then dissociating the halogen acids (HI or HBr) to halogen and hydrogen as an overall environmentally and cost efficient and otherwise acceptable safe process for producing hydrogen and other useful products.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of the co-pending U.S. patent application of Lawrence F. McHugh, Ser. No. 12/148,397 (&#39;397) filed Apr. 18, 2008, which has priority from the provisional application Ser. No. 60/992,559 filed Apr. 18, 2007, and is of common assignment with this application, the contents of all of which are incorporated herein by reference as though set out at length herein. 
     
    
     FIELD AND BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a new thermochemical cycle (process and apparatus) for producing hydrogen through coupling the hydrogen cycle by way of hydroiodic acid dissociation to another thermochemical cycle for producing high energy-metal oxidation reactions of industrial scale and providing the sulfur dioxide needed for reaction with halogen to generate the halogen acid and sulfuric acid. The invention also relates to such metal oxidation reactions per se for conversion of metal sulfides to metal oxides with capture of useful sulfur products. These cycles enable new use of known and new forms of certain metal oxidation reactions to produce energy in a way enabling breakthrough advances in hydrogen production, metal oxide, sulfur dioxide, sulfuric acid production, and combinations of such advances and related methods and apparatus. 
         [0003]    The production of hydrogen from thermochemical cycles and hybrid cycles (thermochemical and thermoelectrolytic) is a technology that has been evolving over the past thirty years. Several sulfur based thermochemical cycles that incorporate sulfuric acid decomposition are now known in the art, such as a Sulfur-Iodine cycle developed at General Atomic Corporation in the 1970&#39;s and further developed later at Westinghouse Corporation to a so-called Westinghouse Sulfur Process (“WSP) as cited in the U.S. Pat. No. 7,261,874 by Lahoda and Task/Westinghouse. Such sulfur-iodine cycle and also sulfur-bromine cycles are by now well known. See also, B. Ildiz et al., “Efficiency of Hydrogen Production Systems Using Alternative Nuclear Energy Technologies,” 31 Int&#39;l Jl. Of Hydrogen Energy 77-92 (2006) comparing WSP to other processes of hydrogen production and summarizing the advantages and disadvantages of such cycles. The WSP process uses thermal energy “waste heat” from a nuclear reactor for the decomposition of sulfuric acid or sulfur trioxide to oxygen, water and sulfur dioxide at elevated temperatures 800-1100° C. This step can be described by the following chemical reaction: H 2 SO 4 =&gt;H 2 O+SO 2 (g)+0.5O 2 (g). In the Sulfur-Iodine and Sulfur-Bromine processes sulfur dioxide reacts with water and iodine (or bromine) to form two immiscible liquids: sulfuric acid and hydroiodic acid (or hydrobromic acid). After separation of the two acids (generally by condensation) hydrogen is produced during the thermal decomposition of HI at 320° C. (or HBr at 750° C.) according to the reactions 2HI=&gt;H 2 (g)+I 2 (g) and 2HBr=&gt;H 2 (g)+Br 2 (g). 
         [0004]    In the process described in the U.S. Pat. No. 7,261,874 sulfur dioxide released during the decomposition of sulfuric acid is absorbed in water at about room temperature and sent to an electrolyzer. The sulfur dioxide and water is then electrolyzed to hydrogen as a gas and sulfur trioxide. 
         [0005]    As further described below the present invention recognizes and applies metal oxidation reactions to provide the energy for useful purposes and sulfur dioxide for a WSP or like reaction to produce hydrogen and preferably uses a metal sulfide looping oxidation process to supply high content sulfur dioxide flow, to either a sulfur-iodide or sulfur-bromide process of making hydrogen. 
         [0006]    As a non-limiting illustrative example of state of the prior art, the technology of molybdenum trioxide production has traditionally been oxidizing roasting of molybdenite. (Zelikman A., Korshunov B., Metallurgy of Refractory Metals, Moscow, 1991, pp. 41-60). Typically, the roasting is carried out in a multiple hearth furnace. Molybdenite (MoS 2 ) slowly reacts with oxygen, eventually forming molybdenum trioxide, according to the sum reaction: MoS 2 +3.5O 2 =&gt;MoO 3 +2SO 2 . This reaction is practically irreversible (ΔG° at 600° C.=−210 kcal/mol MoO 3 ) and is highly exothermic (ΔH at 600° C.=−253 kcal/mol). In practice on the top hearths (of a multi-hearth furnace) molybdenum trioxide reacts with molybdenite according to the reaction: MoS 2 +6MoO 3 =&gt;7MoO 2 +2SO 2  (ΔH° at 600°=4.8 kcal/mol). On the lower hearths molybdenum dioxide oxidizes to trioxide, according to the reaction: MoO 2 +0.5O 2 =&gt;MoO 3  (ΔH at 600° C.=−37 kcal/mol). Due to the complexity of the process, it usually requires energy supply to some hearths, even though the sum reaction is highly exothermic. Typically, the SO 2  content in the off-gas varies from 1 to 4% (vol. pct.). Sulfur dioxide, obtained from molybdenite roasting, is typically utilized in an acid plant to make sulfuric acid. Oxidizing roasting in air makes the formation of nitrogen oxides unavoidable and it is detrimental from efficiency, economic and environmental perspectives 
         [0007]    The practice of metal sulfide oxidation via two-step looping sulfide oxidation process is described by L. F. McHugh, R. Balliett and J. Mozolic in “The Sulfide Ore Looping Process: An Alternative to Current Roasting and Smelting Practice,” Journal of Metals (July 2008), pp. 84-87 and http://findarticles.com/p/articles/mi_qa5348/is — 200807/ai_n27998008 and in the PCT Patent Application publication WO 2008/130649 A1 of 30 Oct. 2008 of L. F. McHugh related to the &#39;397 U.S. patent application cited above. In the first step the metal sulfide reacts with a metal oxide to produce a metal suboxide. In a subsequent step the suboxide is further oxidized raising the metal to a higher oxidation state. All or part of the oxide produced in the second step can be recycled to the first step to be reused as an oxidizing agent, indeed as the primary or sole oxidizing agent of the first step. The higher state oxide also can be recovered for other processing. See also, U.S. Pat. No. 4,552,749 granted Nov. 28, 1985 to L. F. McHugh, D. K. Huggins, M. T. Hepworth, and J. M. Laferty (“Process for the Production of Molybdenum Dioxide”) regarding an earlier process of molybdenite looping oxidation that failed in practice. 
       SUMMARY OF THE INVENTION 
       [0008]    We have discovered that for sulfides of certain metals, including, e.g. Mo, V, Pb, Co and certain combined metals, e.g. Fe/Cu the second step reaction (of the two step reaction described above) which is initially endothermic, can become highly exothermic in a certain range of temperatures in a controllable way and can be utilized for gains of energy efficiency, process efficiency and environmental benefits. This makes the looping oxidation process more attractive from the energy generation point. It also creates conditions for the chemical reaction in the first step to become self-propagating and can be used to generate new benefits, described below. 
         [0009]    The thermodynamic analysis of the reaction between MoO 3  and MoS 2  is shown in Table 1, below. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 MoS 2  + 6MoO 3  = 7MoO 2  + 2SO 2 (g) 
               
             
          
           
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
               
               
                 C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 100 
                 5.382 
                 68.333 
                 −20.117 
                 6.07E+11 
               
               
                 200 
                 4.87 
                 67.11 
                 −26.883 
                 2.62E+12 
               
               
                 300 
                 4.422 
                 66.251 
                 −33.55 
                 6.22E+12 
               
               
                 400 
                 3.923 
                 65.451 
                 −40.135 
                 1.08E+13 
               
               
                 500 
                 3.299 
                 64.589 
                 −46.638 
                 1.53E+13 
               
               
                 600 
                 2.521 
                 63.644 
                 −53.05 
                 1.90E+13 
               
               
                 700 
                 1.583 
                 62.629 
                 −59.364 
                 2.15E+13 
               
               
                 800 
                 0.494 
                 61.565 
                 −65.574 
                 2.27E+13 
               
               
                 900 
                 −72.66 
                 −6.356 
                 −65.204 
                 1.41E+12 
               
               
                 1000 
                 −75.62 
                 −8.779 
                 −64.443 
                 1.16E+11 
               
               
                 1100 
                 −78.156 
                 −10.699 
                 −63.465 
                 1.26E+10 
               
               
                 1200 
                 −80.246 
                 −12.17 
                 −62.318 
                 1.76E+09 
               
               
                 1300 
                 −81.862 
                 −13.233 
                 −61.045 
                 3.03E+08 
               
               
                 1400 
                 −82.978 
                 −13.923 
                 −59.684 
                 6.26E+07 
               
               
                 1500 
                 −83.566 
                 −14.265 
                 −58.272 
                 1.52E+07 
               
               
                   
               
             
          
         
       
     
         [0010]    It can be seen from Table 1 that the reaction is thermodynamically favorable in a wide temperature range. At the temperatures typically used for the molybdenum sulfide roasting (500-600° C.), the reaction is slightly endothermic. It can also be seen from this Table that between 800 and 900° C. the reaction becomes exothermic. At the temperatures above 900° C. the reaction is highly exothermic and above 1000 deg. C. generates heat to the external environment rather than needing heat input. This fact creates a unique opportunity for using this reaction not only to produce molybdenum suboxide from molybdenum sulfide, and also serve as an energy generator to power other processes completely aside from production of molybdenum oxide. At 900° C. approximately 65 kcal/per mol of molybdenum sulfide can be converted into useful energy. This works similarly for other metal sulfides, including sulfides of V. Pb, Cu and combined metals such as Fe—Cu. 
         [0011]    The state of the art molybdenite roasting in a conventional multiple hearth furnace process is carried out at relatively low temperatures to avoid sublimation of molybdenum trioxide produced. In the process of the present invention partial vaporization of molybdenum trioxide is very beneficial as it helps drastically improve kinetics of the process and increases desulfurization of molybdenite. 
         [0012]    The plot of  FIG. 1  shows that above 900° C. there is a tangible partial pressure of molybdenum-oxygen bearing species in equilibrium with molybdenum trioxide. An exothermic reaction, where one of the reagents is in the gaseous state, proceeds at higher rate and under certain conditions can become self-propagating. This process can also be carried out in a flash reactor. Other suitable equipment for this process may include a rotary kiln or fluidized bed furnace. 
         [0013]    According to an aspect of the present invention, a breakthrough in production of hydrogen is realized to provide, via looping oxidation of metal sulfide, with the properly employed exotherm, a new source of sulfur dioxide reagent for certain thermochemical or thermolectrolytic reactions ending in hydrogen production. There are known hydrogen production processes but the world market may be poised for orders of magnitude increase through development of market and infrastructure for hydrogen fueling of cars, trucks and trains. Further, nuclear safety concerns will limit the will to expand nuclear energy production and adjunct thermochemical/thermoelectrolytic cycle processes. 
         [0014]    Instead, per the present invention, an output with high percentage of sulfur dioxide, can be produced in combination with a looping metal sulfide oxidation process, preferably with exothermic enhancement as described herein, and the sulfur dioxide can be directly used in the Sulfur-Iodine or Sulfur-Bromine cycles or various other processes (e.g. WSP or like processes) that eventually generate hydrogen. This will eliminate the sulfuric acid decomposition step that requires energy supply by a nuclear plant or like heat generator (e.g. concentrated solar, geothermal, large scale industrial process with waste heat, etc. to the extent practical). Merchant grade or even laboratory grade metal oxide, sulfur dioxide and/or sulfuric acid can become other end products besides the target hydrogen product. Energy costs, capital costs and environmental issues can be reduced to an extraordinary degree by the new approach of the present invention. These reductions occur for various reasons including lower temperatures involved compared to WSP processing and the like in turn yielding lower equipment corrosion issues and lower cost equipment generally, lower risk of catastrophic failure, lower burdens of and risks of waste disposal and more efficient conversion of source materials and derating of source materials specifications. 
         [0015]    Finally, the ability to meet the original purpose of metal sulfide oxidation (e.g., molybdenum sulfide oxidation) is greatly enhanced. The molybdenum dioxide (or other metal oxide) produced during the first step can be used for the molybdenum production. A significant amount of energy, capital investment and labor cost can be saved due to the elimination of hydrogen reduction of molybdenum trioxide. 
         [0016]    Sulfides of other metals, can be oxidized with their higher oxides with energy release, as shown in Tables 2-6. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 6CuO + Cu 2 S =&gt; 4Cu 2 O + SO 2(g)   
               
             
          
           
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
               
               
                 ° C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 500.000 
                 1.008 
                 42.338 
                 −31.726 
                 9.307E+008 
               
               
                 600.000 
                 0.065 
                 41.191 
                 −35.900 
                 9.696E+008 
               
               
                 700.000 
                 −0.802 
                 40.250 
                 −39.971 
                 9.492E+008 
               
               
                 800.000 
                 −1.595 
                 39.474 
                 −43.956 
                 8.963E+008 
               
               
                 900.000 
                 −2.314 
                 38.833 
                 −47.870 
                 8.291E+008 
               
               
                 1000.000 
                 −2.960 
                 38.304 
                 −51.726 
                 7.587E+008 
               
               
                 1100.000 
                 −3.533 
                 37.870 
                 −55.534 
                 6.910E+008 
               
               
                 1200.000 
                 −6.311 
                 35.893 
                 −59.186 
                 6.044E+008 
               
               
                 1300.000 
                 −14.611 
                 29.897 
                 −61.644 
                 3.670E+008 
               
               
                 1400.000 
                 −15.267 
                 29.493 
                 −64.614 
                 2.758E+008 
               
               
                 1500.000 
                 −15.914 
                 29.118 
                 −67.544 
                 2.118E+008 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 CuFeS 2  + 11CuO =&gt; 6Cu 2 O + FeO + 2SO 2(g)   
               
             
          
           
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
               
               
                 ° C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 200.000 
                 1.704 
                 115.083 
                 −52.747 
                 2.324E+024 
               
               
                 300.000 
                 −0.239 
                 111.359 
                 −64.064 
                 2.695E+024 
               
               
                 400.000 
                 −2.208 
                 108.192 
                 −75.038 
                 2.314E+024 
               
               
                 500.000 
                 −4.198 
                 105.436 
                 −85.716 
                 1.705E+024 
               
               
                 600.000 
                 −8.596 
                 100.119 
                 −96.015 
                 1.083E+024 
               
               
                 700.000 
                 −12.179 
                 96.224 
                 −105.820 
                 5.846E+023 
               
               
                 800.000 
                 −14.995 
                 93.469 
                 −115.301 
                 3.043E+023 
               
               
                 900.000 
                 −17.711 
                 91.048 
                 −124.524 
                 1.585E+023 
               
               
                 1000.000 
                 −20.330 
                 88.906 
                 −133.520 
                 8.357E+022 
               
               
                 1100.000 
                 −22.850 
                 87.000 
                 −142.313 
                 4.492E+022 
               
               
                 1200.000 
                 −25.276 
                 85.294 
                 −150.927 
                 2.470E+022 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 10V 2 O5 + V 2 S 3  =&gt; 11V 2 O 4  + 3SO 2(g)   
               
             
          
           
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
               
               
                 ° C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 500.000 
                 −103.382 
                 189.618 
                 −249.985 
                 4.681E+070 
               
               
                 600.000 
                 −103.417 
                 189.590 
                 −268.957 
                 2.117E+067 
               
               
                 700.000 
                 −258.000 
                 27.519 
                 −284.780 
                 9.146E+063 
               
               
                 800.000 
                 −260.784 
                 24.792 
                 −287.389 
                 3.407E+058 
               
               
                 900.000 
                 −263.037 
                 22.781 
                 −289.763 
                 9.667E+053 
               
               
                 1000.000 
                 −264.792 
                 21.343 
                 −291.965 
                 1.327E+050 
               
               
                 1100.000 
                 −266.074 
                 20.371 
                 −294.047 
                 6.371E+046 
               
               
                 1200.000 
                 −266.900 
                 19.789 
                 −296.052 
                 8.405E+043 
               
               
                 1300.000 
                 −267.284 
                 19.535 
                 −298.015 
                 2.542E+041 
               
               
                 1400.000 
                 −267.236 
                 19.563 
                 −299.968 
                 1.533E+039 
               
               
                 1500.000 
                 −266.763 
                 19.837 
                 −301.936 
                 1.653E+037 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 3Pb 2 O 3  + PbS =&gt; 7PbO + SO 2(g)   
               
             
          
           
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
               
               
                 C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 500.000 
                 −66.694 
                 30.722 
                 −90.446 
                 3.706E+025 
               
               
                 600.000 
                 −68.788 
                 28.176 
                 −93.390 
                 2.385E+023 
               
               
                 700.000 
                 −71.027 
                 25.750 
                 −96.085 
                 3.807E+021 
               
               
                 800.000 
                 −73.409 
                 23.421 
                 −98.543 
                 1.176E+020 
               
               
                 900.000 
                 −33.115 
                 58.115 
                 −101.293 
                 7.443E+018 
               
               
                 1000.000 
                 −35.072 
                 56.516 
                 −107.026 
                 2.364E+018 
               
               
                 1100.000 
                 −37.399 
                 54.759 
                 −112.591 
                 8.345E+017 
               
               
                 1200.000 
                 −52.027 
                 44.262 
                 −117.232 
                 2.474E+017 
               
               
                 1300.000 
                 −55.197 
                 42.181 
                 −121.554 
                 7.733E+016 
               
               
                 1400.000 
                 −58.692 
                 40.028 
                 −125.665 
                 2.606E+016 
               
               
                 1500.000 
                 −62.511 
                 37.812 
                 −129.558 
                 9.333E+015 
               
               
                   
               
             
          
         
       
     
         [0017]    An illustrative example of a useful endothermic oxidation reaction is the oxidation of cobalt sulfide (CoS) by cobalt oxide (Co 3 O 4 ) to produce sulfur dioxide. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 CoS + 3Co 3 O 4  &lt;=&gt; 10CoO + SO 2(g)   
               
             
          
           
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
               
               
                 ° C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 500.000 
                 43.710 
                 107.749 
                 −39.596 
                 1.562E+011 
               
               
                 600.000 
                 43.670 
                 107.705 
                 −50.373 
                 4.068E+012 
               
               
                 700.000 
                 43.260 
                 107.264 
                 −61.124 
                 5.350E+013 
               
               
                 800.000 
                 42.518 
                 106.541 
                 −71.816 
                 4.234E+014 
               
               
                 900.000 
                 41.473 
                 105.612 
                 −82.425 
                 2.273E+015 
               
               
                 1000.000 
                 40.155 
                 104.535 
                 −92.934 
                 9.003E+015 
               
               
                 1100.000 
                 38.587 
                 103.351 
                 −103.329 
                 2.800E+016 
               
               
                 1200.000 
                 29.549 
                 96.880 
                 −113.170 
                 6.177E+016 
               
               
                 1300.000 
                 27.495 
                 95.532 
                 −122.791 
                 1.148E+017 
               
               
                 1400.000 
                 25.297 
                 94.178 
                 −132.276 
                 1.904E+017 
               
               
                 1500.000 
                 22.977 
                 92.831 
                 −141.626 
                 2.868E+017 
               
               
                   
               
             
          
         
       
     
         [0018]    According to a further aspect of the invention improvements in sulfur dioxide production (and downstream products such as sulfuric acid) is enhanced and at the same time the production of metal oxide is enhanced. The SO 2  concentration in the off-gas from the first step will be very high (more than 70%). The formation of sulfur dioxide takes place in an inert environment at a relatively low inert gas flow. This prevents or completely eliminates the formation of NO x  compounds that usually occur during traditional molybdenum sulfide roasting and other conventional metal roasting. Such high SO 2  content creates a unique opportunity for its usage. The sulfide conversion from metal sulfide to metal oxide and sulfur dioxide via the looping oxidation process exemplified above yields separate high percent content of both outputs and substantially sequesters contaminants of the sulfide containing starting material to the first step thereby reducing associated clean up steps with economical and environmental benefit. The modification of the looping oxidation utilizing the now recognized exotherm enhances all such benefits. 
         [0019]    The benefit of a new source of sulfur dioxide can also be realized without looping by producing a high recovery essentially uncontaminated sulfur dioxide through use of oxidation of certain metal sulfides (e.g. iron, cobalt or molybdenum sulfides) obtainable as ores or scrap with metal oxides (e.g. iron, cobalt or molybdenum oxides) obtainable as ores or scrap or as merchant products, with the extra cost if any, justifiable in the context of a new beneficial route to hydrogen production and other output products efficiently using the source materials and energy inputs and avoiding undue costs of waste product clean-up or environmentally secure disposition. As a whole the end products can be optimally used. For example, if the end products are sulfur dioxide and molybdenum oxide containing calcium oxide derived from the original sulfide/and/or oxide inputs the molybdenum oxide can be used as a ferro-molybdenum additive in steel making and residual contaminants are removed from the steel and do not materially alter the environment of costs of dealing with residues of the steel making process. 
         [0020]    Other objects, features and advantages of the invention will be apparent form the following detailed description of preferred embodiments above taken in conjunction with the accompanying drawings, in which, 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a plot of molar contents vs. temperature molybdenum trioxide; 
           [0022]      FIG. 2A  (Prior Art) is a schematic diagram of a state of the art by design production process using a nuclear reactor energy source;  FIG. 2B  (Prior Art) is a plot of energy, efficiency vs. temperature for processes of the same general class as the one shown in  FIG. 2A ; and  FIG. 2C  (Prior Art) is a schematic detail of a heat exchanger usable in such processes; 
           [0023]      FIG. 3A  is a block diagrams of a metal oxide two step looping oxidation process per preferred embodiments of the present invention using a looping oxidation process applied to produce hydrogen as well as a metal oxide and sulfur dioxide;  FIG. 3B  is a block diagram of the first part of such a process without the hydrogen production ( 3 B), i.e. a sub-assembly useful on its own; and  FIG. 3C  is a block diagram of certain preferred embodiments of a metal oxidation process without looping applied to produce hydrogen as well as metal oxide and sulfur dioxide. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]      FIG. 2A  is a schematic of a basic sulfur-iodine (SI) process using heat from a nuclear reactor to partially decompose sulfuric acid to water, sulfur dioxide and oxygen 830-900° C. The sulfur dioxide is reacted with iodine and water to produce HI, H 2 SO 4  and H 2 O. The HI and water are fed to a reactor maintained at 450° C. to produce iodine and the iodine is looped back to the latter sulfuric acid producing reactor and give off end product hydrogen. Apart from end product hydrogen (and oxygen if desired) the closed loop system has no effluents. It is described in the above cited Yildiz et al. article (at pp. 83-84) referring to a demonstration by the originator, General Atomics, and improvement by Japan Atomic Energy Research Institute.  FIG. 2B  herein is a projection of energy requirements and efficiency at various temperatures taken from  FIG. 5  of the Yildiz et al. article. The limitations of the basic SI process are apparent. 
         [0025]      FIG. 2C  is a schematic diagram of prior art process of an enhanced hybrid (thermochemical electrolytic) WSP as described in U.S. published patent application of Lahoda and Mazzoccoli (Westinghouse), Ser. No. 11/054,235 filed Feb. 9, 2005 with Jun. 30, 2004 priority and published on Jan. 5, 2006 as US2006/0002845 A1 (&#39;845). The process described in the &#39;845 publication enhances prior sulfur based hydrogen production processes such as WSP by imposing pressure above 1000 psi (preferably 1450 psi, i.e. 10 Mega-Pascals, MPa) on the whole process (&#39;845, par. [0019]). This increases process efficiency (&#39;845, par. [0019]40025D and enables reduction of equipment corrosion ([&#39;845 pars. [0026]-[0035]). These and other advantages are summarized at &#39;845, pars. [0036]-[40048]. 
         [0026]      FIG. 3A  shows schematically a process for hydrogen production per an embodiment of the present invention in which a first furnace reactor  20  (e.g., rotary kiln, tunnel kiln, fluidized bed, multi-hearth roaster) is used to convert an in-feed of a sulfide of a multi-valent metal, e.g. molybdenum sulfide. The sulfide is preferably provided in a particulated form sufficient to provide favorable kinetics but avoiding agglomeration at too fine particle sizes. It is preferably pre-blended (prior to reaction) with looped back molybdenum trioxide to optimize kinetics, reduce residual sulfur content and insure completion of reaction. It is oxidized to produce molybdenum dioxide (MoO 2 ) a lower oxide below higher available oxide of the metal (MoO 3 ) and sulfur dioxide in gas phase, in high percentage yields of separate outputs of 90 wgt-% or more even as high as 99.8 wgt-% conversion of the molybdenum content to MoO 2 . Part of the MoO 2  is removed as a plant output and part is fed to a further furnace reactor  30  and oxidized using air or other oxygen containing reactant to convert the MoO2 to a higher oxide (MoO 3 ). The heating is done at a temperature level to initiate and use the exotherm as described above. The reactor  20  has conventional per se elements of a filter baghouse  19 , packed column scrubber  18 , with NaOH solution in-feed to obtain an output SO 2  gas product at  17 . The operation of the furnaces is substantially continuous (fully continuous or intermittently cycled). 
         [0027]    The portion of the overall process done in reactors  20  and  30  to produce molybdenum oxide and sulfur dioxide is valuable in its own right apart from usage to efficiently produce hydrogen. 
         [0028]    A further more detailed showing of this example of furnace reactors  20 ,  30  with looping back oxidation is shown in  FIG. 3B . In the furnace  20  is a feed hopper  22 , a rotary conveyor  25 , heat source  26  and an exhaust zone  28 , with processing elements  29 A,  29 B to separate end products and providing MoO 2  to a fluidized bed reactor  30  which has a carrier fluid heating zone  32 , a main fluidized bed  34  and an output filter  36 . MoO 2 (s) is oxidized in the reactor to MoO 3  which is looped back to furnace  20 . 
         [0029]    Referring again to  FIG. 3A , all or part of the sulfur dioxide generated in furnace  20  is fed to a further reactor  40  and reacted there with iodine and water feeds to produce hydrosulfuric and hydroiodic acid (or with bromine in lieu of iodine feed to produce hydrobromic acid). The two acids can be separated in a condenser  42  and the hydroiodic acid (or hydrobromic acid) can be dissociated in a furnace reactor to produce hydrogen as an end product (taken up in a condenser  52 ) and iodine (or bromine) all or part of which is fed back to furnace  40  to maintain a substantially continuous process. 
       Example 
       [0030]    An example of a test version of the looping oxidation portion of the process to convert molybdenum oxide and sulfur dioxide was performed as follows: The equipment was essentially as in  FIG. 3B . MoO 3  of the following composition, wgt-% (Mo-63.8, Cu-0.21, C-0.01, S-0.01, Pb-0.01, P-0.01) and MoS 2  of the following composition, wgt-% (Mo-59.5, Cu-0.05, Fe-0.14, Pb-0.01, Insol.-0.4, MoO 3 -0.017, H 2 O-0.0, Oil-0.02, MoS 2 -99.20) were screened to minus 20 mesh and were mixed in a ratio of 11b (0.453 kg) MoS 2  to 5.94 lb (2.7 kg) MoO 3  to achieve a 10% excess stoichiometric amount of MoO 3 . The material was fed into the 5-in. (127-mm) diameter  45  in. (1.14 m) long indirectly fired screw roaster (furnace  20 ). Nitrogen at a rate of 0.35 sft 3 /min (9.91/min) was fed counter currently as a sweep gas to remove the evolving SO 2 . Any entrained fines in the sweep gas were filtered out in a downstream baghouse. 
         [0031]    The feeding-in rate was metered at 10 lb/h with a separate feed screw 2 in. (51 mm) in diameter. 50 lb (22.7 kg) of the blend were charged at a time into the feed hopper. The temperature in the heated section of the furnace was controlled through propane flow to the burners, with the intention of gradually heating the material from the initial zone temperature of 500° C. to the final temperature of 700° C. Local overheating caused the material to agglomerate, thereby making the movement of material difficult. Periodically the screw had to be stopped, cooled down, and cleaned prior to further roasting. After exiting the heated section, the product was conveyed by the flutes to the water jacketed cooling section. Following the cooling section, the material was discharged into a nitrogen purged double valve, cam-locked receiving canister. Periodically, the canister was removed and the replacement canister was nitrogen purged and locked into place. The product continued to cool under a N 2  blanket within the removed canister. 
         [0032]    Once cooled, the material was bagged and a representative sample was taken and analyzed. Overall, a 256 lb (116 kg) blend of MoS 2  and MoO 3  (10% excess MoO 3 ) was processed. The average sulfur content was 0.54%. The residual MoO 3  content was 6%. The calculated SO 2  content in the off-gas was in the range of 72-85%. The sulfur removal reached 98.6% capture of sulfur from the MoS 2  change. 
         [0033]    The processing and equipment of  FIGS. 3A ,  3 B are scalable to industrial needs to produce molybdenum oxide and sulfur dioxide. Also, all or part of the sulfur dioxide so produced can be fed to processing in a sulfur-iodine or sulfur-bromine process with prior art heat exchanges as shown, e.g. in  FIGS. 2A ,  2 C, but with removal of the prior art sulfuric acid production and dissolution steps thereby effecting great enhancement of cost efficiencies and safety in a hydrogen production process. 
         [0034]    The production of sulfur dioxide from metal ores or like sources as a feedstock processes of hydrogen production for the sulfur and/or other uses can also be achieved in processes that do not involve a looping oxidation as in the above described embodiments. Such further embodiments without looping include reactions of metal sulfides with externally provided metal oxides, e.g. ores or scrap materials with sufficiently high concentrations of the metal oxide or refined metal oxides produced by various known processes. Examples of such further embodiments are: 
         [0035]    (a) reaction of iron sulfide with iron oxide: 
         [0000]      FeS 2 +5Fe 2 O 3 =&gt;FeO+2SO 2    
         [0036]    (b) reaction of iron sulfide with vanadium oxide: 
         [0000]      FeS 2 +5V 2 O 5 =&gt;5V 2 O 4+ FeO+2SO 2    
         [0037]    (c) reaction of iron sulfide with molybdenum oxide: 
         [0000]      FeS 2 +5MoO 3 =&gt;FeO+5MoO 2 +SO 2    
         [0038]    (d) reaction of cobalt sulfide with iron oxide: 
         [0000]      CoS+3Fe2O 3 =&gt;CoO+6FeO+SO 2    
         [0039]    (e) molybdenum sulfide with molybdenum trioxide without looping: 
         [0000]      MoS 2 +6MoO 3 =&gt;7MoO 2 +2SO 2    
         [0000]    In all of these and other like reactions, the sulfide and oxide materials are provided as, or converted to particulate form, intermixed and heated to temperatures to drive the above reactions. In each case, the sulfur dioxide is obtained as a gas and of sufficient purity through such phase separation from other reaction inputs/outputs to be suitable for the sulfur based production of hydrogen as described above for previous embodiments. The sulfide oxidizing reactions produce sulfur dioxide and a useful oxide product that can be carried out in single or several steps reactions in any of the rotary kiln, multiple hearth furnace, fluidized bed reactor, flash reactor, plasma reactor or like apparatus, the temperature being controlled to minimize metal oxide vaporization. 
         [0040]    Tables 7-1, through 7-4 below show the thermodynamic considerations and energy balances at temperatures from 600-1300° C. for embodiments (a)-(d) above. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7-1 
               
             
             
               
                   
               
               
                 FeS2 + 5Fe2O3 = 11FeO + 2SO2(g) 
               
             
          
           
               
                 T 
                 deltaH 
                 deltaS 
                 deltaG 
                   
               
               
                 C. 
                 kcal 
                 cal/K 
                 kcal 
                 K = Pso2 
               
               
                   
               
             
          
           
               
                 600.000 
                 171.396 
                 140.779 
                 48.475 
                 7.339E−013 
               
               
                 700.000 
                 167.141 
                 136.162 
                 34.635 
                 1.664E−008 
               
               
                 800.000 
                 166.320 
                 135.349 
                 21.070 
                 5.113E−005 
               
               
                 900.000 
                 166.136 
                 135.184 
                 7.545 
                 3.929E−002 
               
               
                 1000.000 
                 166.107 
                 135.159 
                 −5.971 
                 1.060E+001 
               
               
                 1100.000 
                 166.215 
                 135.241 
                 −19.491 
                 1.266E+003 
               
               
                 1200.000 
                 166.410 
                 135.377 
                 −33.021 
                 7.930E+004 
               
               
                 1300.000 
                 166.659 
                 135.541 
                 −46.567 
                 2.950E+006 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7-2 
               
             
             
               
                   
               
               
                 FeS2 + 5V2O5 = 5V2O4 + FeO + 2SO2(g) 
               
             
          
           
               
                 T 
                 deltaH 
                 deltaS 
                 deltaG 
                   
               
               
                 C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 600.000 
                 −3.514 
                 124.271 
                 −112.021 
                 1.100E+028 
               
               
                 700.000 
                 −80.715 
                 43.334 
                 −122.885 
                 3.978E+027 
               
               
                 800.000 
                 −81.967 
                 42.106 
                 −127.153 
                 7.892E+025 
               
               
                 900.000 
                 −82.907 
                 41.267 
                 −131.319 
                 2.923E+024 
               
               
                 1000.000 
                 −83.553 
                 40.736 
                 −135.417 
                 1.769E+023 
               
               
                 1100.000 
                 −83.916 
                 40.461 
                 −139.475 
                 1.587E+022 
               
               
                 1200.000 
                 −84.007 
                 40.395 
                 −143.516 
                 1.964E+021 
               
               
                 1300.000 
                 −83.838 
                 40.506 
                 −147.560 
                 3.173E+020 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7-3 
               
             
             
               
                   
               
               
                 FeS2 + 5MoO3 = FeO + 5MoO2 + 2SO2(g) 
               
             
          
           
               
                 T 
                 deltaH 
                 deltaS 
                 deltaG 
                   
               
               
                 C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 600.000 
                 19.543 
                 77.208 
                 −47.871 
                 9.620E+011 
               
               
                 700.000 
                 18.676 
                 76.270 
                 −55.546 
                 2.989E+012 
               
               
                 800.000 
                 17.664 
                 75.280 
                 −63.124 
                 7.184E+012 
               
               
                 900.000 
                 −43.430 
                 18.563 
                 −65.207 
                 1.408E+012 
               
               
                 1000.000 
                 −46.057 
                 16.412 
                 −66.952 
                 3.119E+011 
               
               
                 1100.000 
                 −48.363 
                 14.667 
                 −68.503 
                 8.013E+010 
               
               
                 1200.000 
                 −50.336 
                 13.279 
                 −69.897 
                 2.347E+010 
               
               
                 1300.000 
                 −51.959 
                 12.212 
                 −71.169 
                 7.727E+009 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7-4 
               
             
             
               
                   
               
               
                 CoS + 3Fe2O3 = CoO + 6FeO + SO2(g) 
               
             
          
           
               
                 T 
                 deltaH 
                 deltaS 
                 deltaG 
                   
               
               
                 C. 
                 kcal 
                 cal/K 
                 kcal 
                 K 
               
               
                   
               
             
          
           
               
                 600.000 
                 97.530 
                 71.285 
                 35.287 
                 1.469E−009 
               
               
                 700.000 
                 94.932 
                 68.467 
                 28.303 
                 4.397E−007 
               
               
                 800.000 
                 94.379 
                 67.920 
                 21.491 
                 4.198E−005 
               
               
                 900.000 
                 94.194 
                 67.755 
                 14.708 
                 1.819E−003 
               
               
                 1000.000 
                 94.093 
                 67.671 
                 7.937 
                 4.340E−002 
               
               
                 1100.000 
                 94.065 
                 67.650 
                 1.171 
                 6.510E−001 
               
               
                 1200.000 
                 86.838 
                 62.452 
                 −5.163 
                 5.835E+000 
               
               
                 1300.000 
                 86.830 
                 62.446 
                 −11.408 
                 3.845E+001 
               
               
                   
               
             
          
         
       
     
         [0041]    Where ores, ore concentrates or other impure oxide sources are used as an oxidizing agent, there can be other components carried with it such as silica, calcium oxide, iron oxide, iron molybdenum. The sulfur dioxide is nevertheless a clean removal and the metal oxide end product can be separated as a useful product from the processing furnace end product by well known per se refining methods involving physical separation, hydrometallurgy and the like. In some applications ore refining can be minimal (e.g. pyrites, oxidation with MoO 3  leading to a ferrous molybdenum raw material. 
         [0042]      FIG. 3B  shows schematically the operation of such further embodiments to produce hydrogen using, illustratively, the iron sulfide/molybdenum oxide reaction described above. 
         [0043]    In “oxidizing” metal (M) sulfide in the first step of one or more process embodiments described above conditions can be controlled so that the product can be an oxide or a metal (M) or combination of metal M and its (sub)oxide. Preferrably, a second step oxidation reaction is done on the metal or (sub)oxide to create the oxidation agent for looping back to the first step as the sole or primary oxidizing agent therein. But the metal and/or oxide product of the first step can be useful end products (along with the sulfur dioxide end product) without any further steps. 
         [0044]    The present invention is not limited to the examples of its practice described above. It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.