Carbon membrane performance on hydrogen separation in H2H2O 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 α-alumina porous tubes were well-designed in a specific way and evaluated aiming at removing H2 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 (H2/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 H2 and Ar permeance. Secondly, the hydrogen and argon permeance through carbon membrane is 3.1 × 10−8 mol m−2 s−1 Pa−1 and 5.7 × 10−10 mol m−2 s−1 Pa−1 respectively at 300 °C. The separation factor of H2 and Ar is 54, which is greater than the theoretical value calculated by Knudsen diffusion equation. Thirdly, hydrogen permeability in the H2 HI H2O gaseous mixture system owns nearly the same as that of the single-component (H2) at 300–500 °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 H2/HI is over 310 at 500 °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 H2 permeance at 20–100 °C.