Hydrogen can be a viable alternative energy carrier if it can be produced cost effectively from renewable resources. UT-3 thermochemical cycle to produce hydrogen from water is attractive because its temperature requirement is moderate (∼700°C) and it can be operated with solar or nuclear energy. There are still several issues that must be resolved before it becomes viable. These issues include developing high reactive surface area solid reactant structures which are able to go through large volume changes in a cycle while maintaining cyclic reactivity and strength of the solid reactants and speeding up of the hydrolysis reaction of calcium bromide, the rate limiting step in the cycle.

In this study, thermodynamic feasibility investigation of the UT-3 process was conducted to determine the optimal operating conditions for high reaction rate as well as high conversion. A new calcium oxide reactant dispersed and immobilized on a yttria fabric was fabricated via an inexpensive and straightforward immobilization process. The performance of the sample was evaluated in cyclic bromination and hydrolysis reactions experimentally using the optimum conditions determined theoretically. The calcium oxide fabric showed continuous higher reactivity in four bromination reactions and the rate of hydrolysis reaction was faster than that of our calcium oxide pellets and comparable to that of calcium oxide pellets reported in the literature. The thermodynamic efficiency of the UT-3 cycle was estimated considering inert materials and incomplete conversion and heat recovery. It was found that the effects of inert materials and heat recovery on the efficiency were considerable while the influence of incomplete conversion was not significant. With heat recovery, the calculated efficiency for the calcium oxide fabric including inert materials and incomplete conversion was 52.4%.

The use of calcium oxide on fabric was also studied for its application to high temperature carbon dioxide capture. The conventional calcium oxide absorbents could not maintained their performance in cyclic operations due to the reduction of active surface area. On the other hand, the new calcium oxide absorbent on fibrous alumina achieved continuous cyclic carbonation conversion over ten carbonation-calcination cycles under mild calcination condition. However, under the more severe calcination condition, its performance dropped by about eight percent after 12 cycles possibly due to the formation of Ca₁₂Al₁₄O₃₃ by the reaction between calcium oxide and alumina. When calcium oxide was applied to yttria fabric, the absorbent maintained its performance for 12 cycles even under the severe calcination condition.