Decomposition closed-cycle loops

Evidently, the uncatalyzed direct thermal decomposition is simply too unattractive from both a thermodynamic and kinetic viewpoint to be seriously considered for a practical process. Work has therefore focussed on methods for increasing the reaction yields under more moderate process conditions. Unfortunately, thermodynamics cannot be violated but thermodynamic limitations can be sidestepped, and kinetic limitations can be overcome using catalysts. Four principle types of techniques are being investigated for improved yields including upset equilibrium systems, closed cycle loops, open cycle loops, and electrochemical methods. The advantages and disadvantages of these will now be discussed more fully. 

Because these temperatures are impractical, the thermochemical water-splitting cycles achieve the same result (i.e., separation of water into hydrogen and oxygen) at lower temperatures. A thermochemical water-splitting cycle is a series of chemical reactions tliat sum to the decomposition of water. To be useful, each reaction must be spontaneous and clean. Chemicals are chosen to create a closed loop where water can be fed to the process, oxygen and hydrogen gas are collected, and all other reactants are regenerated and recycled [2]. 

Bunsen reaction, HI decomposition reaction and closed-loop cycle operation are carrying out in KIER. H2SO4 decomposition reaction is carry ing out in KIST... 

A bench-scale test facility for hydrogen production using the thermochemical iodine-sulfur (IS) process has been established at JAERI to verify the hydrogen production, to study the conditions for the reactions, and to gain experience for a large-scale plant [74]. The three reactions (see appendix A.2.3.) are performed in separate sections of the apparatus, the Bunsen reaction and the sulfuric acid decomposition at the same time to avoid SO2 storage (see Fig. 4-8). The process requires temperatures of 800 to 900 °C. Its feasibility was successfully demonstrated in a glass, quartz, and teflon lab-scale apparatus. In the course of six cycles completed, the total amounts of H2 and O2 produced were 16.4 1 and 9.9 1, respectively. The thermal efficiency achieved, however, was much smaller than the theoretical one of 47 - 50 % [44]. In late 1997, the continuous operation of the IS process cycle as a closed loop over 48 h resulted in the production of 44.8 1 of H2 [75]. 

---