Kinetic process assessment of H2 purification over highly porous carbon sorbents under multicomponent feed conditions

As a universal energy carrier, the need for pure H-2 is ever increasing due to its ubiquitous role in petrochemical refining, metal reduction, and the up-and-coming fuel cell market. Hydrogen produced from steam methane reforming (SMR) is typically laden with impurities such as CO2, CO, and CH4 and a full efficiency screening for potential H-2 purification sorbents requires evaluating the thermodynamic and kinetic behaviors associated with multicomponent pressure swing adsorption (PSA). As such, in this study we assessed three commercially available activated carbons with high surface area and pore volume for the PSA upgrading of H-2 from simulated SMR off-gas stream consisting of H-2/CO/CH4/CO2 (75/5/5/15 vol%). In addition to high-pressure adsorption isotherms for pure gases, H-2 purity and recovery, and H-2 productivity were estimated from cyclic PSA experiments, while actual (CO + CH4 + CO2)/H-2 selectivity values were estimated from breakthrough experiments. For the best performing material, the results demonstrated H-2 purity and recovery of 99.6 and 55.3 %, respectively with a productivity of 18.3 mol(H2)/kg.h and multicomponent (CO + CH4 + CO2)/H-2 selectivity of 59.86 %. Moreover, the affinity of the different adsorbates toward the activated carbons presented from the most adsorbed to the least adsorbed gas was in the order of CO2 > CH4 > CO >> H-2. The H-2 purification over these carbon-based adsorbents was found to be an equilibrium-controlled process.