9.3 Hydrogen Production Using a Thermochemical Process Made Possible with the Use of a Ceramic Membrane


Fig. 9-6 Thermochemical hydrogen production system concepts

Hydrogen is thermochemically generated from water decomposed by nuclear heat at high temperature. The IS process is named after the initials of each element used.


Fig. 9-7 The relation between separation factor of H2 from HI and temperature

The trial membrane product of ceramics was successfully made and the hydrogen trans-missibility was found to be several hundred times greater than that for hydrogen iodide.


Fig. 9-8 Structure of separation membrane for hydrogen

Separation membrane was prepared by repeatedly coating silica on a porous tube of ceramic by CVD method.



Hydrogen, as one of the lightest elements, like uranium as one of the heaviest, is ready to play the lead in the next generation of energy production methods. We have studied a new thermochemical process of hydrogen production using nuclear energy. The process used in our study is illustrated in Fig. 9-6.
Thermochemical decomposition of water results in hydrogen and oxygen through a process that allows an endothermic reaction to be induced at high temperatures and an exothermic reaction at low temperatures. The high temperature reactors, such as HTTR are fitted as the source of high temperatures.
Thermal decomposition of hydrogen iodide produces hydrogen. If the hydrogen produced is removed from the reaction process apparatus by a separation membrane, the efficiency of the reaction improves. However, the high temperatures of 400°C or greater and the highly corrosive gases in the system exclude the use of any ordinary separation membrane for hydrogen. In our laboratory, high thermal and high corrosion resistant hydrogen separation ceramic membranes have been prepared, and hydrogen has been successfully isolated from hydrogen iodide at high temperatures.
Figure 9-7 shows separation factor against temperature, that is, the ratio of hydrogen transmission to hydrogen iodide transmission through the membrane. The rate of transmission at high temperature for hydrogen through the membrane is several hundred times greater than that for hydrogen iodide.
Figure 9-8 shows the structure of the membrane, which is prepared by the chemical vapor deposition (CVD) of silicone layers on
a porous alumina tube. Both high transmissibility and high separability membrane characteristics are required throughout the process of separation of gases by the membrane. It has been recognized that the characteristics are determined by the conditions of the CVD. New processes of hydrogen production using this excellent membrane will be subsequently investigated.


Reference
G.J. Hwang* et al., Separation of Hydrogen from a H2-H2O-HI Gaseous Mixture Using a Silica Membrane, AIChE J., 46(1), 92 (2000).
*post doctoral fellow

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