United States Patent to 11 3,996,342 Ishikawa Et Al
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X2: 33 : s , 42 United States Patent to 11 3,996,342 Ishikawa et al. (45 Dec. 7, 1976 54) METHOD FOR THERMOCHEMICAL PRODUCTION OF HYDROGEN FROM FOREIGN PATENTS OR APPLICATIONS WATER 148,782 1922 United Kingdom ............... 423/471 (75) Inventors: Hiroshi Ishikawa, Ikeda, Masanori Nakane, Takatsuki; Eiichi Ishii; Primary Examiner-Edward Stern Yoshizo Miyake, both of Toyonaka, Attorney, Agent, or Firm-Oblon, Fisher, Spivak, all of Japan McClelland & Maier (73) Assignee: Agency of Industrial Science & 57 ABSTRACT Technology, Tokyo, Japan A method for the thermochemical production of hy (22 Filed: Sept. 2, 1975 drogen from water is disclosed in which barium iodide, carbon dioxide, ammonia and water are allowed to (21 Appl. No.: 609,662 react with one another and give rise to barium carbon (30) Foreign Application Priority Data ate and ammonium iodide, the ammonium iodide thus Sept. 5, 1974 Japan ............................ 49-102767 produced is thermally decomposed to produce hydro gen, iodine and ammonia, and the hydrogen thus pro Dec. 17, 1974 Japan ............................ 49-145475 Dec. 18, 1974 Japan ............................ 49-146169 duced is recovered as the product. The by-produced barium carbonate is allowed to react with the iodine 52 U.S. Cl. ............................... 423/657; 423/356; remaining after the separation of hydrogen thereby to 423/438; 423/470; 423/497; 423/579; produce barium iodide, carbon dioxide and oxygen, 4231507; 423/648 and the barium iodide and carbon dioxide are recycled 51 Int. Cl.' ....................... C01B 1/02; CO1B 1/04 to the reaction system. The ammonia which remains 58) Field of Search .......... 423/657, 648, 470, 471, after the separation of hydrogen is also recycled to the 423/356,500, 507,497 reaction system. By causing the by-products occurring (56) References Cited in the various reactions to be recycled to the relevant reaction systems, hydrogen is efficiently produced from UNITED STATES PATENTS water at a reaction temperature of not more than 800 2003,378 6/1935 MacMullin ........................ 423/471 C. 3,839,550 10/1974 Wentorf, Jr. .................. 423/648 X 3,842,164 10/1974 Wentorf, Jr. .................. 423/657 X 3,929,980 12/1975 Abraham et al. .............. 423f470 X 4 Claims, No Drawings 1. 3.996,342 2 carbonate and ammonium iodide, (b) a step of allowing METHOD FOR THERMOCHEMICAL iodine to react upon the barium carbonate produced in PRODUCTION OF HYDROGEN FROM WATER (a) step thereby producing barium iodide, carbon diox ide and oxygen and (c) a step of thermally decompos BACKGROUND OF THE INVENTION ing the ammonium iodide produced in (a) step thereby The present invention relates to a method for the producing hydrogen, iodine and ammonia, with said thermochemical production of hydrogen from water. reaction cycle continued while causing the barium Establishment of a method for producing hydrogen iodide and carbon dioxide produced in (b) step to be by thermally decomposing water attemperatures below recycled to (a) step, the ammonia produced in (c) step 1000°C, preferably below 800°C, and using as the heat 10 to be recycled to (a) step and the iodine produced in source solar heat or heat from an atomic pile and as the (c) step to be recycled to (b) step. medium such compounds as are available abundantly Further, the ammonium iodide obtained in (a) step is from the standpoint of natural resources is an impor caused to react upon tri-iron tetraoxide to produce tant task to be fulfilled as soon as possible in view of the ferrous iodide, ammonia, water and iodine. The ferrous unavoidable exhaustion of fossil fuel and the conse 15 iodide thus produced is allowed to react with water to quent necessity for securing the source of secondary give rise to tri-iron tetraoxide, hydrogen and hydrogen energy to take its place. iodide. The hydrogen iodide is decomposed into hydro In the circumstances described above, there have gen and iodine. The by-produced tri-iron tetraoxide, heretofore been proposed 60-odd reaction cycles for ammonia, water and iodine which remains after recov the production of hydrogen by thermochemical decom 20 ery of hydrogen are recycled to the relevant reaction position of water. systems. Argonne National Laboratory, for example, has pro In addition, the ammonium iodide obtained in (a) posed a reaction cycle consisting of the following three step is allowed to react with magnesium oxide to pro steps: duce magnesium iodide, ammonia and water, and the 25 magnesium iodide thus produced is allowed to react LiNO + 1 + HO-o-LiNO + 2HI 1. with water to produce hydrogen iodide and magnesium 2H-e-H + 1, 2. oxide and the hydrogen iodide thus formed is decom LiNO-o-LiNO +%O 3. posed into hydrogen and iodine. The by-produced mag nesium oxide, ammonia, water and iodine which re This reaction cycle has not yet been developed to the 30 main after recovery of hydrogen are recycled to the extent of commercial application, because the reaction relevant reaction systems. of Formula (1) proceeds slowly and the reaction of These elementary reactions proceed smoothly at Formula (3) may possibly produce LiO, a highly cor temperatures below 800 C, the reaction products rosive compound, under certain reaction conditions. which occur therein are easily separated and recovered Euratom has proposed a reaction cycle which con 35 and the by-products which simultaneously occur sists of the following three steps: therein can be recycled to relevant elementary reaction systems, enabling hydrogen to be produced easily from water on a commercial scale. Other objects and other characteristic features of the 40 present invention will become apparent from the fol An experiment has shown that the reaction of For lowing detailed description. mula (2) in this reaction cycle does not result in any discernible generation of oxygen, indicating it difficult DETALED DESCRIPTION OF THE INVENTION to have the reaction proceed through the cycle repre The present invention has evolved from a detailed sented by these formulas. The reaction of Formula (3) 45 investigation for a novel reaction cycle for the thermo is problematic in terms of process and heat balance chemical production of hydrogen. In the course of this because the heat of sublimation of FeCla is great and, investigation, the basic reactions involving the reac worse still, the ratio of decomposition is small. tions of halogen containing compounds have been stud As described above, the reaction cycles proposed to ied and it has been found consequently that, of the date invariably entail problems of some sort or other 50 halogens, chlorine exhibits extremely high reactivity and, in their existing status, are difficult of commercial while the reactivity of bromine and that of iodine de application. crease with the increasing atomic numbers thereof. The An object of the present invention is to provide a investigation of the thermal decomposition behavior of method for producing hydrogen by allowing water to hydro-halogen acids has led to the assertion that hydro be thermally decomposed efficiently attemperatures of 55 gen iodide is easily decomposed into hydrogen and not more than 800 C through a combination of com iodine while the thermal decomposition property of mercially quite feasible elementary reactions by using, hydrogen bromide and that of hydrogen chloride are as the medium, elements or compounds which are lower in the order mentioned. available abundantly in nature and which do not exhibit The conclusion, therefore, is that favorable results much toxicity and corrosiveness. 60 cannot be expected from an attempt to obtain hydro gen from hydrogen chloride but that it is advantageous SUMMARY OF THE INVENTION to use either hydrogen iodide or ammonium iodide The present invention accomplishes the object de because hydrogen is easily recovered therefrom by scribed above by providing a method for the produc thermal decomposition or other means. tion of hydrogen by the thermochemical decomposi 65 From the foregoing findings, it has become apparent tion of water, which method comprises (a) a step of that a reaction cycle including 2HI-H + I, as the causing barium iodide, carbon dioxide, ammonia and basic reaction and a reaction cycle including 2NHI-> water to react with one another to produce barium 2NH -- 2HI-2NH -- H -- as the basic reaction 3,996,342 3 4 are advantageous for the hydrochemical production of reaction proves highly advantageous in terms of heat hydrogen. The study behind the present invention con balance (in consideration of the fact that the concen centrated on the development of reaction cycles in tration of aqueous solution by evaporation entails a cluding these basic reactions and it consequently has heavy loss of latent heat of water through evaporation been discovered that the reaction for generating hydro and can be a major cause for degraded heat efficiency). gen through the thermal decomposition of ammonium In the second step, Reaction Formula (2), the barium iodide can be carried out quite effectively by using carbonate obtained in the first step is allowed to react barium iodide, ammonia and carbon dioxide in combi with iodine at 750-800° C. The carbon dioxide gas nation and that the barium iodide, carbon dioxide, generated in this reaction is absorbed in the ammonia ammonia and iodine which are by-products in the reac 10 water and consequently is separated from oxygen and, tions can be recycled to the relevant elementary reac at the same time, there is obtained an aqueous ammo tion systems. nium carbonate solution to be supplied to the first step. It has also been found that when magnesium oxide or In this case, since barium carbonate is in a solid state tri-iron tetraoxide is allowed to take part in these basic and the formed barium iodide is in a liquid state at the reaction cycles, hydrogen can be obtained through the 15 temperature at which the reaction proceeds, the bar thermal decomposition of hydrogen iodide.