Thermal hydrogen, solar

Additionally, there are a number of useful electrochemical reactions for desulfurization processes (185). Solar—thermal effusional separation of hydrogen from H2S has been proposed (188). The use of microporous Vicor membranes has been proposed to effect the separation of H2 from H2S at 1000°C. These membrane systems function on the principle of upsetting equiUbrium, resulting in a twofold increase in yield over equiUbrium amounts. 

Steinfeld, A. et al., Production of filamentous carbon and hydrogen by solar thermal catalytic cracking of methane, Chem. Eng. Sci., 52,3599, 1997. 

Dahl, J. et al., Solar thermal dissociation of methane in a fluid-wall aerosol flow reactor, Int. J. Hydrogen Energ., 29, 725, 2004. 

Different strategies have evolved for thermochemical hydrogen production to effectively utilize the potentials of, in particular, nuclear and solar thermal energy sources. These strategies, which we discuss below, can be categorized depending upon the number of process steps involved and whether electrolysis is employed in a reaction. 

Perkins C, Weimer AW (2004) Likely near-term solar-thermal water splitting technologies. Int J Hydrogen Energy 29 1587-1599... 

Baykara SZ (2004) Hydrogen production by direct solar thermal decomposition of water, possibilities for improvement of process efficiency. Int J Hydrogen Energy 29 1451-1458... 

Kogan A, Spiegler E, Wolfshtein M (2000) Direct solar thermal splitting of water and on-site separation of the products. III. Improvement of reactor efficiency by steam entrainment. Int J Hydrogen Energy 25 739-745... 

In the US, two programs were reported High Temperature Solar Splitting of Methane to Hydrogen and Carbon, and Rapid Solar-thermal Dissociation of Natural Gas in an Aerosol Flow Reactor. 

Kogan, A., E. Spiegler, M. Wolfshtein (2000), Direct Solar Thermal Splitting of Water and On-site Separation of the Products. III. Improvement of Reactor Efficiency by Steam Entrainment , International Journal of Hydrogen Energy, 25, 739-745. 

Besides the traditional markets for carbon, some novel applications for the carbon produced via methane decomposition are discussed in the literature. Kvaemer has initiated R D program to investigate the potential of novel grades of carbon black as a storage medium for hydrogen, and as a feedstock for the production of solar grade silicone.35 The production of carbon nanotubes and nanofibers via solar thermal decomposition of methane over supported Co and Ni catalysts, respectively, was also reported.36... 

Thermochemical splitting of water involves heating water to a high temperature and separating the hydrogen from the equilibrium mixture. Unfortunately the decomposition of water does not proceed until temperatures around 2500 K are reached. This and other thermal routes are discussed in Chapter 5. Solar thermal processes are handicapped by the Carnot efficiency limits. On the other hand, solar photonic processes are limited by fundamental considerations associated with band-gap excitation these have been reviewed in Refs.32 and 33. 

Direct Solar Thermal Water Splitting to Generate Hydrogen Fuel... 

Theory of Direct Solar Thermal Hydrogen Generation... 

Kogan has calculated that, at a pressure of 0.05 bar, water dissociation is barely discernible at 2000 K.1 By increasing the temperature to 2500 K, 25% of water vapor dissociates at the same pressure. A further increase in temperature to 2800 K under constant pressure causes 55% of the vapor to dissociate.1 These basic facts indicate the difficulties that must be overcome in the development of a practical hydrogen production by solar thermal water splitting ... 

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