Process for the production of hydrogen and oxygen from water

A multi-phase thermochemical circulating process for producing hydrogen and oxygen from water is described, using the system of iron and chlorine compounds. Hydrogen is released by the reaction of iron(II)-oxide with water vapor and the oxygen by the reaction of chlorine with water vapor, iron(II)-oxide or iron (II, III)-oxide. Intermediately-formed iron (II)-chloride is hydrolyzed with water vapor to iron(II)-oxide in a multi-stage reaction at a gradually raised temperature, whereby in the hydrolysis the formation of metallic iron or of iron(II, III)-oxide is avoided.

BACKGROUND OF THE INVENTION 
Various thermochemical processes have already been suggested by means of 
which water can be decomposed in several reaction steps into hydrogen and 
oxygen using inorganic iron compounds and chlorine or hydrogen chloride as 
auxiliary agents, whereby these are reacted and regenerated in a closed 
cycle during the carrying out of the processes. However, technical 
problems and industrial material questions often arise so that an 
economical carrying out of the process variants required becomes 
difficult. 
In a known thermochemical process hydrogen is obtained from water by 
reacting, in a first process step, water vapor at about 600-1300 K with 
iron(II)-oxide to form iron (II, III)-oxide and hydrogen. In a further 
process step, oxygen is produced by the reaction of water vapor, iron (II, 
III)-oxide or iron(II)-oxide at about 550-1300 K with chlorine. Iron(II, 
III)-oxide from the first process step is reacted, e.g., with hydrogen 
chloride, while recovering chlorine for use in the second process step, to 
form iron (II)-chloride. From the iron(II)-chloride, iron(II)-oxide is 
formed in a hydrolysis reaction with water vapor. The iron(II)-oxide so 
obtained is returned to the first process step. The hydrogen and oxygen so 
formed are drawn off as product gases from the process. 
The production of oxygen can take place in several different ways. Thus, 
chlorine and water vapor can be converted in a known manner at high 
temperatures, for example, 1000-1100 K, to oxygen and hydrogen chloride. 
If reacting water vapor simultaneously with chlorine and iron oxide, the 
exothermic oxidation of the iron oxide according to the equation: 
EQU 1.5H.sub.2 O + 1.5Cl.sub. 2 + Fe.sub.3 O.sub.4 .fwdarw. 1.5Fe.sub.2 
O.sub.3 + 3HCl+ 1/2 O.sub.2 
can yield the necessary reaction heat. Furthermore, it is possible to react 
iron(II)-oxide or iron(II, III)-oxide directly with chlorine, in which 
case besides oxygen there is obtained iron(III)-chloride. In the last 
instance, iron(III)-oxide is formed, which reacts with further chlorine to 
iron(III)-chloride intermediate which is cleaved into iron(II)-chloride 
and chlorine. 
The recovery of the iron(II)-oxide takes place by means of the intermediate 
step of the iron(II)-chloride formation and is possible in various manners 
at temperatures ranging from 500-1300 K. Thus, iron(II, III)-oxide may be 
converted with hydrogen chloride at temperatures of about 500-1000 K and 
optionally even higher to iron(II)-chloride. The reaction of the iron(II, 
III)-oxide can also take place with a chlorine and hydrogen chloride 
mixture with temperatures of about 800-1300 K prevailing.

DESCRIPTION OF THE INVENTION 
It has now been found that the described process can be much improved if 
the hydrolysis of the iron(II)-chloride is conducted in a certain manner. 
According to the invention, the iron(II)-chloride is converted to 
iron(II)-oxide by a hydrolysis reaction with water vapor at temperatures 
of about 700-1200 K in the presence of hydrogen, whereby the water vapor 
to hydrogen ratio is selected between about 1:3 to 2:1. Advantageously, it 
is 1:1. Higher hydrogen proportions favor the separation of the product 
mixture obtained. The presence of hydrogen involves additional advantages 
with respect to the selection of material, since as a result of the 
reducing requirements, the difficulties of corrosion are reduced. 
Furthermore, the reaction to iron(II)-oxide in the presence of hydrogen is 
conducted in a number of series-connected reaction chambers, e.g., two to 
five, which are maintained sequentially at a given time at a higher 
temperature level within the range of 700-1200 K, for example, with 
respect to two reactors at about 700-950 and 950-1200 K or to three 
reactors at about 700-800, 800-1000 and 1000-1200 K, respectively. Of 
course, depending on the requirements, a variation of these levels is 
possible. By conducting the hydrolysis of the iron(II)-chloride according 
to the invention, surprisingly there does not occur a reduction to iron 
but also no oxidation to iron(II, III)-oxide. 
If in the scope of the cyclic process the coupling of the process heat from 
high-temperature nuclear reactors is desired, it is according to the 
invention of advantage to undertake this in the hydrolysis of the 
iron(II)-chloride into the iron(II)-oxide. In this connection, the working 
with several reactions chambers is advantageous to achieve an optimum 
utilization of the process heat. 
It is then of particular advantage to combine the utilization of the, e.g., 
1300 K hot nuclear reactor coolant with the utilization of the heat in the 
product gases leaving a hydrolysis reactor. The utilization of the heat is 
then flexible over the entire temperature range of the coolant. Said 
combination can be realized for all, but also for only one part, of the 
reactors. Additional flexibility in heat utilization is also obtained if 
the heat of the product gases is utilized only partially with that of the 
hot coolant. Higher temperatures can be achieved in such a manner in the 
hydrolysis reactors. Such a procedure involves the further advantage that 
the partial hydrogen pressure can be adjusted better in the hydrolysis 
reaction chambers, which is of importance because of a dependable 
avoidance of an oxidation and because of the required observance of 
protection of the materials by a carefully set reducing atmosphere. 
Of course in the carrying out of the individual reaction steps, it is 
possible to work at elevated pressures, e.g., up to 60 atmospheres. 
FIG. 1 illustrates in simplified form an advantageous type of conducting 
the hydrolysis reaction according to the invention. In this connection, 
the usual separating and purifying apparatus, required per se, are not 
shown for the sake of clarity. 
Coming through conduit 2, FeCl.sub.2 passes three series-connected 
hydrolysis reactors IIa, IIb and IIc, which are maintained at 740, 830 and 
1020 K. The FeO leaving the reactor IIc by way of conduit 1 is conducted 
to a hydrogen generator (not illustrated). The heating of the hydrolysis 
reactors occurs by means of heat exchangers by hot helium of about 1300 K, 
which had been used as coolant in a high-temperature nuclear reactor, as 
well as partially by the product gases leaving the reactors. The helium 
flows through heat exchangers III, IV and V and transmits its heat to 
hydrolysis exhaust gases or to hydrogen-containing gases from a H.sub.2 
separating apparatus (not shown), supplied through conduits 3, 4 and 5 and 
preheated in heat exchangers VI, VII and VIII, said gases, then completely 
heated, being conducted into the respective reactors. The hydrolysis 
exhaust gases not passing through heat exchangers VI and VII are conducted 
through conduits 6 or 7 into the product gas conduit 8 and reach the 
apparatus for hydrogen separation and thereafter for chlorination of 
Fe.sub.3 O.sub.4 (not illustrated). A side stream of hot helium is 
conducted over conduit 9 and through heat exchanger IX. Therein, water 
vapor, which is used in a further process step, is heated to about 1250 K. 
FIG. 2 illustrates one of the possible forms of carrying out the novel 
improvement in the frame of the known thermochemical process described. 
Introduced into the hydrogen generator XI by means of conduit 11 is 
iron(II)-oxide and by means of conduit 12 is water vapor and they are 
reacted at about 1250-1300 K to iron(II, III)-oxide and hydrogen. Hydrogen 
is drawn off as product gas by means of conduit 13. The iron(II, 
III)-oxide generated in the first process step is supplied to the heat 
exchanger XXI, with the water supplied by means of conduit 14. A portion 
of the water vapor generated in heat exchanger XXI is returned to hydrogen 
generator XI by conduit 12 while another portion is conducted by means of 
conduit 12 into the oxygen generator XV and there is reacted with the 
chlorine supplied by means of conduit 16 at about 900-1300 K to hydrogen 
chloride and oxygen. The resulting gas mixture is then conducted by means 
of conduit 17 into washer XVII, wherein an about 20% aqueous hydrogen 
chloride solution is prepared, while the oxygen is removed as product gas 
by means of conduit 18. 
In the chlorinating apparatus XIII, the iron (II, III)-oxide is reacted 
with hydrogen chloride at about 700-800 K in a mixture consisting of 
gaseous dimeric iron(III)-chloride and an excess of hydrogen chloride 
supplied from the separating container XIV by means of conduit 19. The 
reaction mixture is then conducted to separator XIIIa. There, solid 
iron(II)-chloride is separated, while the gaseous products are returned to 
the separating container XIV by means of conduit 20. Drawn off from 
container XIV by means of conduit 21 is a mixture of hydrogen chloride, 
chlorine and water vapor, which is decomposed into chlorine and water in 
column XVI with a standardization of a cycle of hydrogen chloride through 
conduit 22. The chlorine is conducted by way of conduit 16 into the oxygen 
generator XV; the water is supplied to washers XVII and XVIII by means of 
conduits 23 and 24. The over 20% aqueous hydrogen chloride solution 
obtained in washers XVII and XVIII is conducted into column XVI by means 
of conduits 25 and 26 and is processed there. The hydrogen obtained in 
washer XVIII is supplied to the first reaction chamber XIIa of the 
iron(II)-chloride hydrolysis with water by way of conduit 27 after passing 
heat exchangers XXII and XXb at a respectively elevated temperature. The 
first step of the conversion of the iron(II)-chloride supplied by way of 
conduit 28, to iron(II)-oxide takes place here at about 800 K. The 
reaction mixture subsequently passes reaction chambers XIIb and XIIc, 
maintained at about 1000 K and 1200 K. In this connection, the 
iron(II)-chloride is completely converted to iron(II)-oxide, which is 
supplied by way of conduit 11 to the hydrogen generator XI. The gaseous 
products resulting from this conversion at given times are conducted by 
way of conduit 29 and heat exchanger XIX or by way of conduit 30 and heat 
exchanger XXa and thus brought to the respective higher temperature level. 
In heat exchangers XXa and XXb is utilized the heat of about 1300 K hot 
helium, which was used as the coolant in a high-temperature nuclear 
reactor. The gas mixture drawn off from the conversion step XIIc through 
conduit 31 is conducted, after passing heat exchangers XIX and XXII, to 
washer XVIII where its processing takes place. Thereby both the solids 
cycle as well as the gas cycle are closed. It is obvious that the coupling 
of process heat from the high-temperature nuclear reactor by means of the 
hot helium occurs only in the gas cycle, whereby the very difficult 
problems of the solid and gaseous heat exchange are avoided.