(4w) Thermochemical Water Splitting Using Ionic Liquid Solvents

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[1],
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.