ENEA (Italian National Agency for new Thecnologies, Energy and Environment) is involved in an National R&D program on thermochemical water-splitting cycles to be coupled with solar-thermal power plants. This project is being carried out in the framework of an integrated national program dealing with the sustainable hydrogen production and storage. On the basis of the literature information the sulfur-iodine process was chosen.
The establishment of an efficient scheme for separating HI from HIx (HI-H2O-I2 mixture) in S-I cycle, is left open to further study. Since the solution used in the process has a HI molarity of ca. 4 M/l and an usual distillation column results in a distillate of HI with azeotropic (7,5 M/l) concentration by a large thermal burden.
An extractive distillation using phosphoric acid and a reactive distillation under pressurized condition have so far been proposed to avoid the problem.
Membrane technology may be used to concentrate HI. Here we present our experimental results with assessment of electrodialysis. HI concentration by electrodialysis was examined with a recirculation batch apparatus. Commercial cationic exchange membranes (nafion) and homemade electrode (Ti/TiOx/Rh) have been used. Operative temperature was 80°C and pressure was about 1 atm.
Results showed that the HI concentration at catholyte increase from after 270 min, while the HI concentration at anolyte decrease. The liquid volume of catholyte increases (water permeation from anolyte to catholyte). New membranes are under investigation as well as the energetic process evaluation even at the higher scales. Results obtained will be discussed.