(400b) Hydrogen Production Through a Modified Sulfur-Iodine Thermochemical Water Splitting Cycle in Hydrophobic Ionic Liquid

Hydrogen
Production through a Modified Sulfur-Iodine Thermochemical Water Splitting
Cycle in Hydrophobic Ionic Liquid

Kevin
Caple and Alexandre Yokochi

One
of the most pressing issues of the new millennium is the development of clean,
simple, and renewable energy sources.  Of
the various process that have been studied, thermochemical water splitting is
one that has been conceptualized and researched for over half a century, yet,
at this point, none are commercially viable. 
These thermochemical water splitting cycles include the family of Sulfur
cycles and metal/metal oxide couples.

Of
the Sulfur based cycles, one of the simplest is the Sulfur-Iodine cycle, which
uses sulfur dioxide, iodine, and a large excess of water to produce iodic acid
and sulfuric acid, both of which can be further processed into hydrogen and
oxygen gases, and regenerate the initial sulfur dioxide and iodine for reuse.  Unfortunately, this process has been stalled
due to difficulties separating the azeotropic iodic
acid/water mixture. 

We
have developed an approach to avoid this issue in utilizing what was previously
considered an undesired side reaction that produces hydrogen sulfide.  It has been shown that hydrogen sulfide can
be successfully steam reformed into hydrogen, as well as regenerate sulfur
dioxide to complete this modified Sulfur-Iodine cycle.  The series of reactions is as follows:

I₂
+ SO₂ + 2H₂O -> 2HI + H2_SO₄
(Bunsen Reaction, Low Temp)

8HI
+ H₂SO₄ -> H₂S + 4I₂ + 4H₂O
(Side Reaction Producing H2S, Low Temp)

H₂S
+ 2H₂O -> 3H₂ + SO₂ (Steam Reformation,
High Temp)

In
our work we carry out the two low temperature reactions in an imidazolium based hydrophobic ionic liquid since both
iodine and sulfur dioxide have solubilities in these.  In our presentation, we will discuss recent
experimental results of this reaction in ionic liquid, including kinetic
parameters, the results of  regenerating of the ionic liquid, and
the extent of the cyclic reaction.