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

Tuesday, October 18, 2011: 2:35 PM
208 A (Minneapolis Convention Center)
Nick AuYeung, Malachi D. Bunn and Alexandre F.T. Yokochi, School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, OR

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. 

[1] Yokochi, A., AuYeung, N. In A Proposed New Sulfur-Sulfur Thermochemical Cycle, AIChE National Meeting, Nashville, Tennessee, Nashville, Tennessee, 2009. 

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