Proposal of Sb-I-Ca Process for Thermochemical Hydrogen Production t

Abstract

A new thermochemical hydrogen production process named "Sb-I-Ca process by modifying the "Sb-I process" previously proposed. The process consists five reaction steps.
4/3 Sb203 + 12→2/3SbI3 Sb204 (4)
2/3 SbI3 Ca0 →CaI2 + 1/3 Sb203 (7 c)
CaI2 + H2O→ Ca0 + 2 HI (6 c)
2 HI → H2 + 12 (2')
Sb204 → Sb203 + 1/2 02 (3')
In the "Sb-I process", a reaction step
1/2 Sb203(s) I2(s) H20(/) 1/2 Sb203 (s) + 2 HI (aq) (1) had been included, which turned out to have drawbacks due to low conversions and side reactions. It was found by preliminary experiments that such drawbacks could successfully be remedied when step (1) was replaced by above steps (4), (7 c), and (6 c). Step (4), a main side reaction of step (1), was found to proceed smoothly at temperatures above some 600 K. However, the produced SbI, could not be hydrolysed to give HI effectively even at 1300 K. So the two-step hydrolysis via reactions (7 c) and (6 c) was invented by introducing calcium compounds as reaction intermediates. As for the intermediates, magnesium and iron compounds whose iodides could be easily hydrolysed at high temperatures were also examined but neither were acceptable for step (7 c), thus leaving only the "Sb-I-Ca process" as an acceptable process.
Discussion was made on thermochemical features of this process.