Adsorption dynamics of hydrogen and deuterium in a carbon molecular sieve bed at 77 K

The adsorption equilibrium and rate of H₂ and D₂ on a Carbon Molecular Sieve (CMS) with wide pore size distribution were measured at 77 K using a volumetric method. The adsorption equilibrium or kinetic ratios for D₂ to H₂ decreased with increasing pressure. The adsorption uptake curve showed a slow adsorption rate with time after displaying a fast adsorption rate in the initial period. Adsorption rate constants of D₂ were larger than those of H₂ at low pressure, and the ratio of D₂ to H₂ decreased with an increase in pressure. However, in breakthrough experiments for dynamic separation efficiency of hydrogen isotope separation, the CMS showed higher breakthrough separation factors than the corresponding adsorption equilibrium or kinetic ratios. The breakthrough separation factor reached 1.53 at a total gas pressure of 400.0 kPa and a flow rate of 129.8 cm³/min in the adsorption bed length of 1.0 m. In addition, the shape of D₂ breakthrough curve was slightly affected by the change of flow rate, but that of H₂ breakthrough curve showed almost constant pattern. And meso and macropores of the CMS gave a negative effect on the separation of H₂ and D₂. Therefore, the key factor in separating H₂ and D₂ from the mixture depended not only on their equilibrium selectivity but also on their dynamic diffusional difference in the CMS bed due to the quantum molecular sieving effect in space-limited pore at low temperature.