A Sulfur-Sulfur Thermochemical Water Splitting Cycle for Thermal-to-Chemical Energy Conversion

Thermochemical water splitting presents a way to store thermal energy in the chemical bonds of a H₂ molecule. Besides becoming an increasingly important energy carrier, hydrogen already has vast importance in petroleum upgrading and ammonia synthesis. In an effort to improve the Sulfur-Iodine Thermochemical Water Splitting Cycle, a novel Sulfur Sulfur Thermochemical Cycle may offer an easier, all fluid route to hydrogen than its predecessor:

Step 1A, liquid phase: 4I₂+4SO₂+8H₂O ↔4H₂SO4 + 8HI

Step 1B, liquid phase: 8HI+H₂SO₄↔H₂S+4H₂O+4I₂

Step 2, gas phase: 3H₂SO₄↔3H₂O+3SO₂+1.5O₂

Step 3, gas phase: H₂S+2H₂O↔SO₂+3H₂

An overall theoretical thermal efficiency assuming a maximum temperature of 1200 K is estimated to be 55%. Here, the I₂ consumed in Step 1A is conveniently regenerated in situ via Step 1B. Furthermore, H₂S easily desorbs from the liquid reaction medium and can then be steam reformed to produce H₂ and SO₂, (Step 3) the latter of which is recycled. The H₂S generation and steam reformation steps (Step 1 and Step 3 respectively) have been demonstrated in our laboratory.[1]

This presentation will focus on the parametric dependence of this highly endothermic, high temperature steam reformation reaction on reactant concentrations, temperature, and residence time in tubular reactor.