Relationship Between Composition And Density Of HI-H₂O-I₂ Solution And Study Of The HI Concentration In The Iodine-sulfur Thermochemical Cycle For Hydrogen Production

Iodine-sulfur cycle is a method of thermalchemical cycle for hydrogen production,which is expected to be great application potential for the use of nuclear energy,solar energy and other clean energy.But for now,because there exists an azeotropic of HI and water in the HIx condensed section,the iodine-sulfur cycle is still difficult to achieve large-scale application in the field of engineering.Based on the large amount of literature reviewing,this paper compared the methods of phosphoric acid extractive distillation,reactive distillation and electro-electrodialysis pre-concentration for HI concentration and separation in iodine-sulfur thermochemical cycle.Electro-electrodialysis for HI pre-concentration could be a promising method because of its easy operation,mild conditions and high efficiency.As a material of the HI decomposition section in indine-sulfur cycle,the significance obviously is there for mastering the basic physicochemical property of HI-H₂O-I₂ solution（HIx）.Using an U-shaped oscillation densimeter,the density of HIx solutions with H2O/HI range from 4.32 to 12.69 and I2/HI range from 1 to 3.30 were determined at 25,40,60 and 80℃.Based on the density data obtained,a composition-density model was established,which enriched the database of HI-H₂O-I₂ ternary system and made a foundation for relevant fluid and process simulation.For the concentration and separation of HIx solution,the research adopted a"transient" method.Totally 18 run of EED experiments were conducted using 1-unit cell,2-unit and 4-unit stacks,with the effective exchanging membrane area of 25 cm² for each unit.The initial molar ratio of HI:I2=1:1.4 or 1:1.6,while the temperature at 100℃ or 80℃,and the current density at 0.10 A/cm² or 0.15 A/cm².The results showed that EED process could concentrate HI effectively,and the concentrating rate was improved drastically by adopting multi-unit EED stacks.The efficiency of EED increased with the increase of I2 molar ratio,current density,and the unit quantity of EED stacks,while decreased with the temperature.Then,azeotropic distillation experiment was carried out,the results show that the electro-electrodialysis pre-concentration method can effectively separate the HIX of iodine,achieve hydroiodic acid over azeotropic composition.