THERMOCHEMICAL CYCLE FOR WATER SPLITTING (Manousiouthakis)
           

Today hydrogen is mainly produced from natural gas through steam reforming and dry reforming, and from coal through gasification.  Hydrogen is also produced through electrolysis.  These production methods however consume fossil fuels and/or electricity.  Alternatively, it is desirable to produce hydrogen by decomposing water and by using renewable energy sources.  Extensive research efforts have been expended to date on identifying sets of reactions that can be used to decompose water.  Such sets of reactions are often referred to as thermochemical cycles.  An extensive literature review on thermochemical cycles has been recently carried out by Beckenbush et al. [1]. The cycle proposed in this project cannot be found in that review or anywhere else in the literature.  Three thermochemical cycles from the literature, that have been or are being implemented in practice, are: the cycle of the University of Tokyo, the so called Sulfur-Iodine cycle and the Calcium-Bromine cycle [1], [2], [3]. 

In this project a novel thermochemical cycle is proposed for the decomposition of water.  One of its obvious uses is the production of hydrogen and or oxygen.  Aside from water, oxygen and hydrogen, it also involves four intermediates X, Y, Z and W.  Its maximum operating temperature can be below 900 ^oC.  A provisional patent application has been submitted for the proposed cycle.  There are many possible realizations of this cycle.  Some involve processing of solids, while others do not.  This realization can be arrived at by considering the kinetic behavior of the reactants, and the separability characteristics of the chemicals involved in the cycle.  The realization shown involves temperature based separations, but other separations may also be considered.

The advantages of the proposed cycle over prior cycles are numerous.  It can be operated so as to avoid the presence and/or movement of solids anywhere in the cycle.  It can operate at temperatures that are attainable through high temperature solar collectors (e.g. 1300 ^oK).  It does not involve complex separations.  It does not involve toxic chemicals. It can have excellent energetic efficiency (about 50% of the cycle’s energy input can be used to create electricity and about 25% can be used to make hydrogen and oxygen).  The invention provides a novel way to produce hydrogen and oxygen.  It can utilize renewable (e.g. solar) energy as its high temperature energy source.  It has the potential to become a more efficient way to produce hydrogen and oxygen than currently used production methods, thus reducing the cost of producing hydrogen. 

Although the individual reactions have been studied experimentally and are known to occur, limited kinetic information exists for a crucial reaction, as a function of temperature. Thus kinetic studies will be undertaken to identify the most suitable operating conditions for that reaction.  Moreover, studies will be undertaken that examine the performance of the cycle as a whole, including the efficiency of the employed separations and the prolonged operation of this hydrogen generating flowsheet.