Simulation Study on the Distillation of Hyper-Pseudoazeotropic HI–I₂–H₂O Mixture

Abstract

The iodine–sulfur thermochemical water splitting process (I–S process) is considered to be one of the most promising clean and large-scale hydrogen production approaches. In the I–S process, the HI distillation step is considerably energy intensive, the heat of which largely affects the overall efficiency of hydrogen production. The present study explored the efficient operating parameters of the distillation column by process simulation assuming the feed solution of hyper-pseudoazeotropic composition which was obtainable by electro–electrodialysis. The Environmental Simulation Program (ESP), the chemical simulation software, was used for the simulation. At first, the vapor–liquid equilibrium database was validated using experimental data reported so far. Then, sensitivity analyses of the operating parameters were carried out, comprised of the HI mole fraction in the distillate, number of stages, feed location of the column, operating pressure, and feed composition. On the basis of the results of the sensitivity analyses, the optimum operation conditions were discussed.

Energy requirement of HI separation from HI–I2–H2O mixture using electro-electrodialysis and distillation

“…1 e Flow sheet of the IS process. i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 9 7 1 e1 3 9 8 2 distillation column, nearly pure HI (the required HI mole fraction in the distillate was assumed to be 0.98) [15] is distilled from the top (stream No. 13) and sent to the HI decomposition subsection.…”

“…Also, technical information on cell voltage has been accumulated through those experiments which used the electrodes made of carbon materials such as graphite, carbon cloth, and glassy carbon [13,14]. In addition, recently, we carried out a distillation analysis for separating HI from the HI x mixture of a hyper-pseudoazeotropic composition which could be obtained by the EED and clarified appropriate column specifications [15]. Flow sheet analyses of HI separation showed similar heat duty using any methods: extractive distillation, reactive distillation, and EED concentration.…”

“…Flow sheet analyses of HI separation showed similar heat duty using any methods: extractive distillation, reactive distillation, and EED concentration. Among them, EED concentration method has advantage of no additional chemicals and relatively moderate environment for component materials [15].…”

Comparison of various circuit designs in the HI decomposition section of the iodine–sulfur process

“…OLI database version 7.0 (OLI systems) [11] was utilized to predict the thermodynamic properties of the process components. The validation of this database for the HI x section has been carried out in our previous work [12].…”

Effect of asymmetric variation of operating parameters on EED cell for HI concentration in I–S cycle for hydrogen production

“…The traditional IeS cycle has lower efficiency compared to the theoretically calculated value primarily due to downstream problems created by these excess of reactants [17,18]. Although highest fraction of total heat required is consumed in the sulfuric acid decomposition section, it is generally believed that there's little room for further optimization of that section [19]. A significant amount of energy is also consumed in the concentration of HI x solution coming out of Bunsen reactor.…”