(33f) Solar FUEL Synthesis in the Molten Metal Reactors

The broad chemical perspective of synthesizing fuel based chemicals through photochemical reactions is collected under the solar fuels generic title since the seminal paper of Bolton¹.  Since then, the indirect conversion of solar energy to chemical bonds via solar thermal processes and electrochemical routes after a photovoltaic process are also included under the same generic title.  Solar to chemical conversion is a very promising strategy of energy storage, as it has been adopted by nature almost 3.5 Billion years ago. 

As trying to imitate the nature, we arrive at many hurdles imposed by thermodynamics, kinetics, or transport phenomena. In the computer aided, biological and biomolecular chemical engineering era, we rediscover the unsolved mysteries of Chemical Reaction Engineering² while our objective function has shifted to sustainability, imposing lower temperatures and pressures, efficient use of (if possible) non-fossil energy.      

Along these lines, this presentation will cover the use of solar chemical looping reactors^3,4 for syn-gas manufacture. These new types of solar reactors use solar concentrators to reach high temperatures such that a soft oxide releases its oxygen.  The oxygen depleted structure is then regenerated by carbon dioxide to form CO or water to form hydrogen at a lower temperature.  As the system cycles between a high temperature and a lower temperature, a power cycle generates work and/or electricity as well.  Our unique contribution in this field is to develop mixed oxide catalysts which can release its oxygen at lower temperatures thus decreasing the need for expensive solar concentrators.  We based our starting point on the excellent molten metal mixed oxide catalyst we have developed for diesel soot oxidation⁵ which can exchange its oxygen at much faster rates than CeO₂.  How we met the design challenge of a molten metal reactor that involves a power cycle will be presented.  

References:

1. J.R. Bolton, Solar Fuels, Science 202(1978)705.
2. J. Wei, Chem. Eng. Sci., 47(1992) 2983.
3. W. C. Chueh, C. Falter, M. Abbott, D. Scipio, P. Furler, S. M. Haile, A. Steinfeld Science 330 (2010) 1797.
4. R. B. Diver, J. E. Miller, M. D. Allendorf, N.P. Siegel, R. E. Hogan, J. Solar Energy Eng. -Transactions of ASME , 130, Article Number: 041001(2008). 
5. D. Uner, M.K. Demirkol, and, B. Dernaika, App. Catal. B: Environ. 61(2005) 359-370.