Patent Application
20120034154
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.
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'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'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: H2SO4=>H2O+SO2(g)+0.5O2(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=>H2(g)+I2(g) and 2HBr=>H2(g)+Br2(g).
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.
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.
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 (MoS2) slowly reacts with oxygen, eventually forming molybdenum trioxide, according to the sum reaction: MoS2+3.5O2=>MoO3+2SO2. This reaction is practically irreversible (ΔG° at 600° C.=−210 kcal/mol MoO3) 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: MoS2+6MoO3=>7MoO2+2SO2 (ΔH° at 600°=4.8 kcal/mol). On the lower hearths molybdenum dioxide oxidizes to trioxide, according to the reaction: MoO2+0.5O2=>MoO3 (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 SO2 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
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 '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.
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.
The thermodynamic analysis of the reaction between MoO3 and MoS2 is shown in Table 1, below.
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.
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.
The plot of
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.
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.
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.
Sulfides of other metals, can be oxidized with their higher oxides with energy release, as shown in Tables 2-6.
An illustrative example of a useful endothermic oxidation reaction is the oxidation of cobalt sulfide (CoS) by cobalt oxide (Co3O4) to produce sulfur dioxide.
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 SO2 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 NOx compounds that usually occur during traditional molybdenum sulfide roasting and other conventional metal roasting. Such high SO2 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.
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.
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,
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.
A further more detailed showing of this example of furnace reactors 20, 30 with looping back oxidation is shown in
Referring again to
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
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 N2 blanket within the removed canister.
Once cooled, the material was bagged and a representative sample was taken and analyzed. Overall, a 256 lb (116 kg) blend of MoS2 and MoO3 (10% excess MoO3) was processed. The average sulfur content was 0.54%. The residual MoO3 content was 6%. The calculated SO2 content in the off-gas was in the range of 72-85%. The sulfur removal reached 98.6% capture of sulfur from the MoS2 change.
The processing and equipment of
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:
(a) reaction of iron sulfide with iron oxide:
FeS2+5Fe2O3=>FeO+2SO2
(b) reaction of iron sulfide with vanadium oxide:
FeS2+5V2O5=>5V2O4+FeO+2SO2
(c) reaction of iron sulfide with molybdenum oxide:
FeS2+5MoO3=>FeO+5MoO2+SO2
(d) reaction of cobalt sulfide with iron oxide:
CoS+3Fe2O3=>CoO+6FeO+SO2
(e) molybdenum sulfide with molybdenum trioxide without looping:
MoS2+6MoO3=>7MoO2+2SO2
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.
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.
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 MoO3 leading to a ferrous molybdenum raw material.
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.
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.
This application is a continuation-in-part of the co-pending U.S. patent application of Lawrence F. McHugh, Ser. No. 12/148,397 ('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.
| Number | Date | Country | |
|---|---|---|---|
| 60912550 | Apr 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12148397 | Apr 2008 | US |
| Child | 13176268 | US |
