Abstract:
A closed system for obtaining hydrogen from water is provided by combining a first step of obtaining hydrogen by reacting water and ferrous halide, a second step of converting triiron tetraoxide produced as a by-product in the first step to ferrous sulfate, a third step of obtaining oxygen and by-products by thermally decomposing said ferrous sulfate, and a fourth step of returning said by-products by thermally decomposing said ferrous sulfate, and a fourth step of returning said by-products obtained in the third step to any of the previous steps.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a thermochemical method for producing hydrogen from water. 
     Recently, the shortage of petroleum resources has become a serious problem and, in the field of hydrogen manufacturing industry, in which hereinbefore petroleum has been mainly used as a source of hydrogen, the movement of changing the source from petroleum to water has appeared. As one of the methods for producing hydrogen, there has been an electrolysis of water from of oil. However, since electric power itself is being obtained mainly from petroleum, the electrolysis method may become a problem as well as the case of using directly hydrocarbons as the source of hydrogen when petroleum is dried up. Therefore, a method of using water as a raw material without electric power has been required and, hereinbefore, there have been some proposals. However, a completely closed system in which hydrogen and oxygen are obtained from water and other by-products are not discharged out of the system has not been sufficiently established. It is very important to keep heat energy used in the closed system down as a whole by utilizing thermochemical energy. The known methods have to be improved in this regard. In this field, those skilled in the art have made efforts to establish a closed system with a lowered heat energy consumption. 
     From such a viewpoint, the present invention aims at establishment of a closed system in which water is used as a raw material but an electrolysis method is not utilized and heat energy consumption is very low. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide a method for producing hydrogen by using water as a raw material. 
     Another object of the present invention is to provide a method for producing hydrogen and oxygen by a closed system using water as a raw material. 
     Other objects and advantages will appear from the following description. 
     BRIEF SUMMARY OF THE INVENTION 
     The objects of the present invention are achieved by combining the following steps containing a novel reaction step: 
     (1) A first step in which triiron tetraoxide, hydrogen halide and hydrogen are produced by reacting water and ferrous halide; 
     (2) a second step in which said triiron tetraoxide obtained in the first step is converted to ferrous sulfate; 
     (3) a third step in which said ferrous sulfate obtained in the second step is decomposed to produce diiron trioxide, sulfur dioxide and oxygen; 
     (4) a step in which said hydrogen produced in the first step is recovered and said hydrogen halide is transferred to any of the steps later than the first step; and 
     (5) a step in which said ferrous halide produced in the second step is returned to the first step, a step in which said diiron trioxide and sulfur dioxide produced in the third step are returned to the second step, and a step in which oxygen is recovered. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIGS. 1 to 4 are flow sheets, showing that the present invention can be practiced in various embodiments. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The method of the present invention is explained in accordance with the drawings. 
     Firstly, one of the typical cases is explained in accordance with FIG. 1. 
     The raw material in practicing the method of the present invention is water (hereinafter abbreviated as &#34;H 2  O&#34;) and the reaction of obtaining hydrogen (hereinafter abbreviated as &#34;H 2  &#34;) therefrom is ultimately shown as follows: 
     
         H.sub.2 O→H.sub.2 +1/2O.sub.2                       (1) 
    
     Therefore, in the closed system of the present invention in which H 2  is produced from H 2  O, oxygen (hereinafter abbreviated as &#34;O 2  &#34;) is produced as a by-product. H 2  O supplied through line 1 and ferrous halide (hereinafter abbreviated as &#34;FeX 2  &#34;, in which X stands for halogen) supplied through line 2 are reacted in the reactor 3 to produce triiron tetraoxide (hereinafter abbreviated as &#34;Fe 3  O 4  &#34;), hydrogen halide (hereinafter abbreviated as &#34;HX&#34;) and H 2 . The reaction proceeds in accordance with the following equation: 
     
         3FeX.sub.2 +4H.sub.2 O→Fe.sub.3 O.sub.4 +6HX+H.sub.2 (2) 
    
     The reaction is carried out at a temperature of more than 500° C., more preferably 600°-700° C., and under reduced or elevated pressure, preferably 1-3 kg/cm 2  (abs.). H 2  O is preferably supplied in a form of super heated water steam into the reactor 3 through line 1. 
     From the reactor 3, H 2  and HX are generated. H 2  and HX are separated from each other (the separator is not shown) and taken out. Also, Fe 3  O 4  is taken out through line 6 from the reactor 3. 
     The above mentioned reaction step is called the first step in the present invention and shown as I surrounded by an alternate long, short and short dash line in FIG. 1 (the same as this applies in the following drawings). 
     Fe 3  O 4  produced in the first step is transferred to the reactor 7. Into the reactor 7, HX generated in the reactor 3 is transferred through line 5, and SO 2  is supplied thereto through line 8 and Fe 2  O 3  is supplied thereto through line 9, respectively. The following reaction takes place in the reactor 7: 
     
         Fe.sub.3 O.sub.4 +Fe.sub.2 O.sub.3 +2SO.sub.2 +6HX→3FeX.sub.2 +2FeSO.sub.4 +3H.sub.2 O                                  (3) 
    
     The above reaction is preferably carried out under the following conditions: The reaction pressure is more than 1 kg/cm 2  (abs.), more preferably 5-20 kg/cm 2  (abs.). The reaction temperature is more than room temperature, more preferably 100°-600° C. The amounts of SO 2  and HX are more than their stoichiometrical amounts or theoretical amounts, for example, SO 2  is 1-5 times, more preferably 1.5-3 times, the theoretical amount and HX is 1-5 times, more preferably 1-3 times, the theoretical amount. 
     The reaction products obtained in the above reaction are transferred from the reactor 7 through line 10 into the separator 11 and they are therein separated to FeX 2 , FeSO 4  and H 2  O. 
     The above mentioned reaction step is called the second step in the present invention and shown as II surrounded by an alternate long, short and short dash line in FIG. 1 (the same as this applies in the following drawings). This step is a step of converting Fe 3  O 4  to FeSO 4  and, as is mentioned hereinafter, various embodiments may be included. 
     FeX 2  separated by means of the separator 11 is returned into the reactor 3 of the first step through line 2 and FeSO 4  is transferred into the following third step through line 12. H 2  O is returned into the reactor 3 of the first step through line 13. 
     FeSO 4  taken out of the separator 11 is then supplied into the reactor 14 and is subjected to thermal decomposition in accordance with the following equation. 
     
         2FeSO.sub.4 →Fe.sub.2 O.sub.3 +2SO.sub.2 +1/2O.sub.2 (4) 
    
     Fe 2  O 3 , SO 2  and O 2  produced by thermal decomposition are transferred through line 15 into the separator 16 to be separated and Fe 2  O 3 , through line 9, and SO 2 , through line 8, are returned into the reactor 7 of the second step. O 2  may be separated as a final product and taken out through line 17. 
     The above mentioned step is called the third step in the present invention and shown as III surrounded by an alternate long, short and short dash line in FIG. 1 (the same as this applies in the following drawings). 
     The decomposition reaction of the third step is preferably carried out as a temperature of more than 650° C., more preferably 700°-900° C. and at a pressure of 0.1-3 kg/cm 2  (abs.). 
     The method for producing hydrogen from water in the present invention is completed as a closed system by combining the above mentioned steps. 
     The closed system of the present invention is shown as IV surrounded by an alternate long and short dash line in FIG. 1 (the same as this applies in the following drawings). 
     Moreover, according to the present invention, the embodiment, especially the second step, shown in FIG. 1, may be replaced by other embodiment. That is, even though Fe 2  O 3  generated in the third step is not directly supplied into the reactor 7 in the second step shown in FIG. 1, FeSO 4  can be produced. This method is explained in accordance with FIG. 2. In this method, the yield of S is better than in other methods mentioned below and accordingly S is produced in excess. Therefore, it is preferable that S produced in excess is converted to SO 2  by O 2  which is one of the products of the present invention and the SO 2  thus produced is recycled. 
     Firstly, Fe 3  O 4  and SO 2  are supplied into the reactor 7 and the following reaction is carried out: 
     
         Fe.sub.3 O.sub.4 +4SO.sub.2 →3FeSO.sub.4 +S         (5) 
    
     This reaction is preferably carried out by the following conditions. 
     The reaction pressure is more than 1 kg/cm 2  (abs.), more preferably 5-20 kg/cm 2  (abs.). The reaction temperature is more than 300° C., more preferably 400°-800° C. 
     The amount of SO 2  is 1.5-5.0 times, more preferably 1.5-3 times, the theoretical amount. 
     As a reaction accelerator, H 2  O and HX (X═Cl, Br) are used. 
     The reaction products are separated by means of a separator 11 and FeSO 4  is, as shown above, transferred to the third step, and S is transferred through line 18 into the reactor 19 and therein reacted with Fe 2  O 3  generated in the third step and HX generated in the first step. 
     The reaction is shown as the following equation: 
     
         1/2S+Fe.sub.2 O.sub.3 +4HX→2FeX.sub.2 +1/2SO.sub.2 +2H.sub.2 O (6) 
    
     This reaction is preferably carried out by the following conditions: 
     The reaction pressure is more than 1 kg/cm 2  (abs.), more preferably 5-20 kg/cm 2  (abs.). The reaction temperature is more than 300° C., more preferably 400°-600° C. 
     The amount of sulfur is 1-5 times, more preferably 1-2 times, the theoretical amount. 
     The amount of HX is 1-5 times, more preferably 1.5-3 times, the theoretical amount. 
     The reaction products thus obtained are transferred through line 20 into the separator 21 and separated into FeX 2 , SO 2  and H 2  O. FeX 2  thus separated is returned through line 2 into the reactor 3 and H 2  O is returned through line 13 into the reactor 3. 
     The remaining reaction product, SO 2 , is joined with line 8 through line 22 to be returned into the reactor 7. 
     In the present invention, the above mentioned step is also one embodiment of the second step. 
     In the third step, as in the case of FIG. 1, FeSO 4  is thermally decomposed to produce Fe 2  O 3 , SO 2  and O 2 . Fe 2  O 3  thus produced is transferred into the reactor 19 of the second step through line 9. 
     The third embodiment is that Fe 2  O 3  generated in the third step is converted to FeSO 4  and FeX 2  in the presence of SO 2  and FeX 2  thus obtained is returned to the first step and FeSO 4  is subjected to thermal decomposition. This embodiment is a typical embodiment of the present invention shown in FIG. 1. This embodiment is shown in FIG. 3. That is, Fe 2  O 3  generated in the third step is separated by means of the separator 16 and put in the reactor 23 through line 9. Into the reactor 23, SO 2  and HX are also supplied in which SO 2  is through lines 8 and 24 and HX is through lines 5 and 25. 
     The reaction taken place in the reactor 23 is shown as the following equation: 
     
         Fe.sub.2 O.sub.3 +SO.sub.2 +2HX→FeX.sub.2 +FeSO.sub.4 +H.sub.2 O (7) 
    
     The reaction products thus produced are supplied into the separator 27 through line 26 to be separated to FeSO 4 , FeX 2  and H 2  O. FeSO 4  thus separated is supplied into the reactor 14 through line 28, FeX 2  is joined into line 2 through line 29 and H 2  O is joined into line 13 through line 30. 
     The above mentioned reaction is preferably carried out by the following conditions: The reaction pressure is more than 1 kg/cm 2  (abs.), more preferably 5-20 kg/cm 2  (abs.). The reaction temperature is more than room temperature, more preferably 100°-600° C. The amounts of SO 2  and HX are more than the theoretical amounts, for example, the amount of SO 2  is 1-5 times, more preferably 1.5-3 times, the theoretical amount and the amount of HX is 1-5 times, more preferably 1-3 times. 
     Hereinbefore, the case in which SO 2  is supplied into the reactor 7 of the second step is explained, but it is also possible that S is supplied in place of SO 2  into the reactor 7 to produce SO 2 . In other words, it is possible to carry out the following reaction in the second step: 
     
         Fe.sub.3 O.sub.4 +1/2S+6HX→3FeX.sub.2 +1/2SO.sub.2 +3H.sub.2 O (8) 
    
     This reaction is preferably carried out by the following conditions: The reaction pressure is more than 1 kg/cm 2  (abs.), more preferably 5-20 kg/cm 2  (abs.). The reaction temperature is more than 300° C., more preferably 400°-600° C. The amount of S is 1-5 times, more preferably 1-2 times, the theoretical amount. The amount of HX is 1-5 times, more preferably 1.5-3 times, the theoretical amount. 
     This reaction is shown in FIG. 4. Into the reactor 7, S is supplied through line 8 to be reacted and the reaction products obtained are separated by means of the separator 11 and then FeX 2  and H 2  O are returned into the reactor 3 of the first step. SO 2  is supplied into the reactor 3 and Fe 2  O 3  generated in the third step is also supplied into the reactor 31 through line 9. Thereupon, the following reaction takes place in the reactor 31. 
     
         Fe.sub.2 O.sub.3 +5/2SO.sub.2 →2FeSO.sub.4 +1/2S    (9) 
    
     This reaction is preferably carried out by the following conditions. 
     The reaction pressure is more than 1 kg/cm 2  (abs.), more preferably 5-20 kg/cm 2  (abs.). The reaction temperature is more than 300° C., more preferably 400°-800° C. 
     The amount of SO 2  is 1.5-5 times, more preferably 1.5-3 times, the theoretical amount. As reaction accelerators, H 2  O and HX (X═Cl, Br) are used. 
     The reaction products thus obtained are transferred through line 32 into the separator 33 and FeSO 4  thus separated is supplied through line 34 to the third step and S is returned through line 8 into the reactor 7 of the second step. 
     In the third step, FeSO 4  is thermally decomposed and SO 2  thus obtained is recycled through line 35 into the reactor 31 and Fe 2  O 3  is recycled into the reactor 31 and it results in that Fe 3  O 4  is converted to FeSO 4  in the second step. In other words, this embodiment means that SO 2  generated in the second step is indirectly converted to FeSO 4  and FeSO 4  thus otained is thermally decomposed in the third step. 
     The above explanation is made for explaining the basic technical concept of the present invention and when the present invention is actually practiced, sometimes the reactor and the separator may not be distinguished and sometime two or more separators may be used. Various arrangements of apparatus and various conditions may be easily selected in order to complete the closed system. For instance, both of the reaction products and the unreacted compounds may be recycled by means of a recycle system and recycle pump provided outside the reactor. 
     EXAMPLE 1 
     Into a platinum reactor 3, 3 m mole FeCl 2  and 10 m mole of water steam were supplied and they were reacted at 650°-700° C. and about 1 kg/cm 2  (abs.). Thereafter, 1 m mole of H 2 , 6 m mole of HCl and 1 m mole of Fe 3  O 4  were obtained. (The above is the first step.) 
     Then, 1 m mol of Fe 3  O 4  obtained in the above reaction and 1 m mol of Fe 2  O 3  obtained in the after mentioned third step were put into a quartz tube reactor 7 (inner diameter 15 mm, volume about 40 ml), while chilling it in liquid nitrogen, SO 2  of 3 times the theoretical amount and HCl gas of 1.5 times the theoretical amount were added thereto, the quartz tube is heat sealed and they were maintained at 200° C., 350° C. and 550° C. for about 3 hours to be reacted. In every case, iron oxide of the raw material was reacted with a reaction rate of more than 95% to produce FeCl 2  and FeSO 4 . (The above is the second step.) 
     Then, ferrous sulfate obtained in the second step was put in the platinum boat reactor 14 and heated at 900° C. in an electric furnace in an atmosphere of N 2  of about 1 kg/cm 2  (abs.) to be thermally decomposed and Fe 2  O 3  of 1 m mole, SO 2   of 2 m mole and O 2  of 0.5 m mole were obtained. (The above is the third step.) 
     In the above experiment, the yield of FeCl 2  obtained in the second step was almost equal to the amount of FeCl 2  used in the first step. Also, the yields of Fe 2  O 3  and SO 2  obtained in the third step were almost equal to the amounts of Fe 2  O 3  and SO 2  used in the second step. 
     Independently of the experiment of the second step, using a mixture of 1 m mol of Fe 2  O 3  and 1 m mole of Fe 3  O 4  as a starting material, SO 2  and hydrochloric acid (concentration of HCl, 35% by weight) were added thereto and the reaction was carried out, as mentioned above, in the presence of water at 200° C. for 3 hours. The reaction rate was 70% in a basis of Fe 2  O 3 . This reaction rate was a value obtained under the stationary condition and therefore it seems that the reaction rate may be increased by stirring or shaking. 
     The separation experiments of the reaction products obtained in the reactor 7 of the second step were separately carried out in accordance with the following two methods: 
     The first method 
     20 g of FeSO 4 .7H 2  O and 50 g of FeCl 2 .4H 2  O were added into 10 ml of water and heated to eliminate a little of water and thereafter they showed a constant boiling point at about 120° C. 
     According to the liquid phase analysis at this time, the concentration of iron component was 22% by weight and the concentration of sulfate was 0.9% by weight. These facts mean that the sulfate in all the iron salts present in the liquid phase was only 2.4% by mole and FeCl 2  was selectively dissolved in the liquid phase. 
     The second method 
     10 g of FeSO 4  (anhydride) and 10 g of FeCl 2  (anhydride) were added into 100 ml of ethyl alcohol and heated at about 50° C. FeCl 2  was completely dissolved in the alcohol but FeSO 4  was not dissolved at all. After separating FeSO 4  by filtration, the alcohol solution of FeCl 2  was distilled in an atmosphere of N 2  to obtain 10 g of FeCl 2  solid. 
     EXAMPLE 2 
     A reaction of the first step was carried out in the same manner set forth in Example 1 and 1 m mol of Fe 3  O 4  was obtained (the first step). 
     Then, with the Fe 3  O 4  thus obtained, 12 m mol of SO 2  were reacted, using about 3 m mole of H 2  O and about 1 m mole of HCl as reaction accelerators, at about 650° C. and about 10 kg/cm 2  (abs.) to obtain 3 m mole of FeSO 4  and 1 m mole of S. The obtained S was reacted with HCl and Fe 2  O 3  in the reactor 19 to obtain 3 m mole of FeCl 2 , 3/4 m mole of SO 2  and 3 m mole of H 2  O (the second step). 
     The resulting FeCl 2  was transferred into the reactor 3 of the first step and hydrolysed to yield again Fe 3  O 4 , HCl and H 2 . 
     FeSO 4  obtained in the second step was reacted in the third step to obtain 3 m mole of SO 2 , 3/4 m mole of O 2  and 3/2 m mole of Fe 2  O 3 . 
     EXAMPLE 3 
     A reaction of the first step was carried out in the same manner set forth in Example 1 to obtain 1 m mole of Fe 3  O 4  (the first step). Then, Fe 3  O 4  thus obtained, 6 m mole of HCl and 2 m mole SO 2  were reacted in the quartz tube reactor 7 at 350° C. for 3 hours and Fe 3  O 4  was converted with a reaction rate of more than 95% to FeCl 2  and FeSO 4 . 
     Then, Fe 2  O 3  obtained in the third step, 3 m mole HCl and 2 m mole SO 2  were reacted in the quartz tube reactor 23 at 350° C. for 3 hours and Fe 2  O 3  was converted to FeCl 2  and FeSO 4  (the second step). Next, FeSO 4  obtained in the second step was thermally decomposed in the platinum boat reactor 14 at 900° C. in an atmosphere of N 2  of about 1 kg/cm 2  (abs.) to yield 1 m mole of Fe 2  O 3 , 2 m mole of SO 2  and 0.5 m mole of O 2  (the third step). 
     In the above experiment, the yield of FeCl 2  obtained in the second step was almost equal to the amount of FeCl 2  used in the first step. Also, the yields of Fe 2  O 3  and SO 2  were almost equal to the amounts of Fe 2  O 3  and SO 2 , respectively. 
     EXAMPLE 4 
     A reaction of the first step was carried out in the same manner set forth in Example 1 to obtain 1 m mole of H 2 , 6 m mole of HCl and 1 m mole of Fe 3  O 4  (the first step). 
     Then, to Fe 3  O 4  and HCl obtained in the first step, S was added and the reaction of the second step was carried out in the reactor 7. That is, 1 m mole of Fe 3  O 4 , 1 m mole of S and 8 m mole of HCl were reacted, as in Example 1, in the quartz tube reactor at 550° l C. for 2 hours. The solid product was FeCl 2  only and an excess of S was remained and solidified by chilling. The obtained SO 2 , FeCl 2  and H 2  O were 0.5 m mole, 3 m mole and 3 m mole, respectively. Next, using about 3 m mole of H 2  O and about 1 m mole of HCl as reaction accelerator, SO 2  and Fe 2  O 3  were reacted to obtain 0.5 m mole of S and 2 m mole of FeSO 4  (the second step). 
     The resulting FeSO 4  was thermally decomposed in the thermal decomposition reactor 14 at 900° C. in an atmosphere of N 2  of about 1 kg/cm 2  (abs.) to obtain 0.5 m mole of O 2 , 2 m mole of SO 2  and 1 m mole of Fe 2  O 3  (the third step). 
     According to the above experiment, it became theoretically clear that the yield of HCl generated in the first step is equal to the amount of HCl used in the second step, the yield of FeCl 2  generated in the second step is equal to the amount of FeCl 3  necessary for the first step, the yield of S generated in the reactor 31 is equal to the amount of S necessary for the reactor 7 and the yields of SO 2  and Fe 2  O 3  generated in the third step are equal to the amounts of SO 2  and Fe 2  O 3  necessary for the second step, respectively.