Carbon membrane performance on hydrogen separation in H2-H2O-HI gaseous mixture system in the sulfur-iodine thermochemical cycle

Sulfur-iodine thermochemical cycle is considered as a promising route for hydrogen production without CO2 emission. In this cycle, the hydrogen iodide conversion rate plays an important role in the total thermal efficiency to some extent. To improve the efficiency of HI decomposition, the homemade carbon membranes supported by a-alumina porous tubes were well-designed in a specific way and evaluated aiming at removing H-2 from HI decomposition reaction side. Permeability, selectivity and stability of self-designed carbon membranes are investigated in some gaseous components in the present work. Firstly, single-component (H-2/Ar) permeance was observed with differential pressure ranging from 0.05 to 0.2 Mpa. The result shows that differential pressure has little effect on H-2 and Ar permeance. Secondly, the hydrogen and argon permeance through carbon membrane is 3.1 x 10(-8) mol m(-2) s(-1) Pa-1 and 5.7 x 10(-10) mol m(-2) s(-1) Pa-1 respectively at 300 degrees C. The separation factor of H-2 and Ar is 54, which is greater than the theoretical value calculated by Knudsen diffusion equation. Thirdly, hydrogen permeability in the H-2-HI-H2O gaseous mixture system owns nearly the same as that of the single-component (H-2) at 300-500 degrees C. Due to the large molecule diameter, most of HI are stopped by carbon membrane. However, H2O molecules could pass through the carbon membrane obviously. The permselectivity of H-2/HI is over 310 at 500 degrees C. Last, after 10 h of stability tests, some slight damage are observed on the surface of carbon membrane according to the scanning electron micrograph (SEM). The structure change of carbon membrane gave rise to a little increase of H-2 permeance at 20-100 degrees C. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.