Adsorption equilibria and kinetics of CO2, CH4, CO, N2, and H2 on KOH-treated activated carbon pellets up to 1000 kPa

Abstract

• Adsorption behaviors of CO 2 , CH 4 , CO, N 2 , and H 2 on KOH-treated ACs were studied. • KOH-treated ACs showed improved adsorption capacities, but reduced adsorption rates. • Affinity for CO increased on KACi, in the presence of intercalated K chemicals. • KACi showed higher capacity and selectivity than CAC and KACa based on volume. • Adsorption rate of KACi was faster for CO 2 , CH 4 , and N 2 and slower for CO than KACa. Activated carbon (AC) is critical for bulk separation to produce high-purity H 2 . Coal-based AC pellets (CAC) were modified through KOH activation (KACa) or impregnation (KACi) via bulk preparation. The adsorptive behaviors of CO 2 , CH 4 , CO, N 2 , and H 2 , which are components of various H 2 mixtures, were investigated at 293.15–323.15 K and up to 1000 kPa. The experimental data and model parameters are tabulated for applications by related researchers. The experimental isotherms fitted well to the Sips and dual-site Langmuir models. The improved textural properties of KACa resulted in higher adsorption capacity based on the adsorbent mass. However, based on volume-based evaluation, KACi showed higher adsorption capacities for CO 2 , CO, and CH 4 at low pressures, with capacities almost equivalent to those of KACa at high pressures, despite the deterioration of textural properties due to K impregnation. Furthermore, more favorable isotherms on KACi resulted in higher selectivities toward various H 2 mixtures. From the non-isothermal kinetic model, CO 2 and CH 4 showed a lower adsorption rates than CO and N 2 due to higher heats of adsorption. Compared to those of KACa, the adsorption rates of KACi were faster for CO 2 , CH 4 , and N 2 and slower for CO, but within the same order of magnitude. KACa was found to be more affected by pre-adsorbed molecules than KACi. KACa and KACi exhibited enhanced performances with excellent cyclic stabilities and batch preparation consistencies. Considering its selectivity and adsorption rate, KACi can be used for improving the efficiencies of adsorptive processes for H 2 production.