Thermochemical Water Splitting Using Ionic Liquid Solvents
Thermochemical water splitting routes such as the Sulfur-Iodine cycle may be greatly improved via the use of ionic liquids as reaction media. In order to enable large scale implementation of this cycle, approaches that simplify product stream management following the initial Bunsen reaction are particularly important, especially with regards to the management of excess water and excess iodine. Using ionic liquids as reaction media allows large amounts of I2 and SO2 to be dissolved while limiting the amount of water. Beyond examining the kinetics of the Bunsen reaction, we identified conditions under which the reaction system may be biased to intentionally produce a stream of H2S based on a normally undesired side-reaction. This led us to the development of a new “Sulfur-Sulfur” Cycle, shown below:
I2 + 2H2O + SO2 = 2HI + H2SO4 eq 1
H2SO4 + 8HI = H2S + 4I2 + 4H2O eq.2
3H2SO4 = 3SO2 + 3H2O + 3/2 O2 eq. 3
H2S + 2H2O = 3H2 + SO2 eq. 4
H2S generation and steam reformation steps (equations 2 and 4 respectively) have been shown to be feasible, and presented here will be the parametric dependence of these two reactions on reactant concentrations, temperature, and residence time. Catalytic activity of several metals in the steam reformation of H2S was also tested. An overall thermal efficiency assuming a steam reformation temperature of 1100 K is estimated to be 55%, and details of these calculations will be presented. The use of ionic liquids in the Hybrid Sulfur (also known as Westinghouse) Cycle will also be discussed.
 A. Yokochi, N. AuYeung, “A Proposed New Sulfur-Sulfur Thermochemical Cycle” 2009 Meeting of the AIChE.