117q

Abstract

Thermochemical water splitting is considered as an energy-efficient, low-cost process for hydrogen production. Among the large-scale, cost-effective and environmentally-attractive hydrogen production processes, the Sulfur-Iodine (SI) thermochemical cycle appears to be one of the most promising. However, modeling of this process poses many difficulties. Overall, the majority of problems related with the uncertainty in modeling of this thermochemical cycle lies in the prediction of thermodynamic properties in the various sections of the process. Mechanisms should be established to stimulate, collect and validate more physical property experimental and modeling work. This would give the opportunity to researchers doing modeling work to validate their models. One of the major difficulties with modeling the SI cycle is the absence of parameters for the electrolyte thermodynamic models at the conditions of interest. Experimental data become available for some of the process sections, whereas much more are expected in the near future. Hence, a comprehensive framework that deals with all aspects of the thermodynamics of the SI cycle needs to be developed. This framework starts with the development of a self consistent database of thermodynamic properties for the various sections of the SI thermochemical cycle. For this objective, published azeotropic composition data for the solutions of interest together with high temperature P-T-x-y data and heat of mixing and mixture heat capacity data were gathered in a database and evaluated critically for self-consistency.

In this work, a collection of published experimental data for a wide variety of thermophysical properties of aqueous sulfuric acid and hydrogen iodine solutions will be analyzed for their validation based on the generic thermodynamic correlations. The treatment of available data for the development of a comprehensive database follows the works of Zeleznik [1] and Bolsaitis and Elliott [2]. A flexible functional form is chosen for the description of the deviation from ideality of the liquid phase, while the gas phase is treated as ideal. The assumption of an ideal gas phase should be valid up to relatively low pressures, and an equation of state could be used for the extrapolation of the model to higher pressures.

The data will be used to calculate activity coefficients at a wide range of temperature and composition, and to generate expressions for the partial molar heat capacities, which will be used as interpolation formulas for the calculation of basic thermodynamic parameters of aqueous sulfuric acid and hydrogen iodide solutions.

References

[1] F. J. Zeleznik. Thermodynamic Properties of the Aqueous Sulfuric Acid System to 350 K. Journal of Physical and Chemical Reference Data, 20:1157, 1991.

[2] P. Bolsaitis and J. F. Elliott. Thermodynamic activities and equilibrium partial pressures for aqueous sulfuric acid solutions. Journal of Chemical and Engineering Data, 35(1):69–85, 1990.

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