315
Water Dissociation Technologies for Hydrogen
The second reaction is a two-step reaction is as follows:
H 2 SO 4 → H 2 O + SO 3
(400°C − 600°C)
(11.42)
1
SO 3 → SO 2 + O 2
(800°C − 900°C)
(11.43)
2
The first exothermic reaction is called Bunsen reaction and is operated at 120°C. The
second endothermic reaction needs a temperature of about 850°C (in two steps as
shown above). The last endothermic reaction runs at temperatures between 300°C
and 450°C. Three reactors that are a part of the cycle are called Gibbs reactor,
Bunsen reactor, and equilibrium reactor. The separation of H 2 SO 4 –HI mixture is the
most critical part of the S–I cycle [107,129,130].
This cycle has been investigated by several research teams because the cycle
involves only liquids and gases. General Atomics has discovered that it is possible to
separate two acids in the presence of excess iodine and water. However, an efficient
separation of HI from water and excess iodine at the outcome of Bunsen reaction still
remains an issue. The high-temperature decomposition of acids is also an issue. The
cycle was successfully tested in Japan to produce 45 l of hydrogen. It was also tested
in France at the capacity of 50 l/h [107,129,130].
11.4.1.8 the Westinghouse Process
The Westinghouse process is one of the “sulfur family” of thermochemical cycles
being considered for the generation of hydrogen [91,107,108]. It is a sulfur cycle using
hybrid electrochemical/thermochemical process for decomposing water into hydrogen and oxygen. Sulfurous acid and water are reacted electrolytically to produce
hydrogen and sulfuric acid. The resulting sulfuric acid is vaporized to produce steam
and sulfur trioxide, which is subsequently reduced at higher temperatures into sulfur
dioxide and oxygen. The process may be seen as a variant of the S–I process, in which
iodine reactions are substituted for by sulfur dioxide electrolysis as follows:
SO 2 + 2H 2 O → H 2 SO 4 + H 2
(20°C − 110°C, P = 2 − 10 bar) (11.44)
Following the separation of the water and sulfur dioxide for recycle to the electrolyzer,
oxygen is available as a by-product. This has the advantage of requiring only one
intermediate element. Sulfur was used because it is relatively inexpensive, its properties are well known, and it can assume a variety of valence states, thereby facilitating
its use in oxidation–reduction reactions. The process requires electric energy that
restricts its efficiency. Electrolysis is carried out in a strong acid medium, leading
to corrosion issues. Moreover, this would require several compartments to restrict
parasitic sulfur and H 2 S production at the cathode [91,107].
11.4.1.9 Copper–Chlorine Cycle
The copper–chlorine (Cu–Cl) cycle is an important cycle due to its requirement for
relatively low-temperature heat compared to other thermochemical water decomposition cycles [91,104,107]. It was identified by Atomic Energy of Canada Ltd. as a highly
promising cycle for hydrogen production. The advantages of this cycle are (1) reduced
Water Dissociation Technologies for Hydrogen
The second reaction is a two-step reaction is as follows:
H 2 SO 4 → H 2 O + SO 3
(400°C − 600°C)
(11.42)
1
SO 3 → SO 2 + O 2
(800°C − 900°C)
(11.43)
2
The first exothermic reaction is called Bunsen reaction and is operated at 120°C. The
second endothermic reaction needs a temperature of about 850°C (in two steps as
shown above). The last endothermic reaction runs at temperatures between 300°C
and 450°C. Three reactors that are a part of the cycle are called Gibbs reactor,
Bunsen reactor, and equilibrium reactor. The separation of H 2 SO 4 –HI mixture is the
most critical part of the S–I cycle [107,129,130].
This cycle has been investigated by several research teams because the cycle
involves only liquids and gases. General Atomics has discovered that it is possible to
separate two acids in the presence of excess iodine and water. However, an efficient
separation of HI from water and excess iodine at the outcome of Bunsen reaction still
remains an issue. The high-temperature decomposition of acids is also an issue. The
cycle was successfully tested in Japan to produce 45 l of hydrogen. It was also tested
in France at the capacity of 50 l/h [107,129,130].
11.4.1.8 the Westinghouse Process
The Westinghouse process is one of the “sulfur family” of thermochemical cycles
being considered for the generation of hydrogen [91,107,108]. It is a sulfur cycle using
hybrid electrochemical/thermochemical process for decomposing water into hydrogen and oxygen. Sulfurous acid and water are reacted electrolytically to produce
hydrogen and sulfuric acid. The resulting sulfuric acid is vaporized to produce steam
and sulfur trioxide, which is subsequently reduced at higher temperatures into sulfur
dioxide and oxygen. The process may be seen as a variant of the S–I process, in which
iodine reactions are substituted for by sulfur dioxide electrolysis as follows:
SO 2 + 2H 2 O → H 2 SO 4 + H 2
(20°C − 110°C, P = 2 − 10 bar) (11.44)
Following the separation of the water and sulfur dioxide for recycle to the electrolyzer,
oxygen is available as a by-product. This has the advantage of requiring only one
intermediate element. Sulfur was used because it is relatively inexpensive, its properties are well known, and it can assume a variety of valence states, thereby facilitating
its use in oxidation–reduction reactions. The process requires electric energy that
restricts its efficiency. Electrolysis is carried out in a strong acid medium, leading
to corrosion issues. Moreover, this would require several compartments to restrict
parasitic sulfur and H 2 S production at the cathode [91,107].
11.4.1.9 Copper–Chlorine Cycle
The copper–chlorine (Cu–Cl) cycle is an important cycle due to its requirement for
relatively low-temperature heat compared to other thermochemical water decomposition cycles [91,104,107]. It was identified by Atomic Energy of Canada Ltd. as a highly
promising cycle for hydrogen production. The advantages of this cycle are (1) reduced