Toward sustainable hydrogen storage and carbon dioxide capture in post-combustion conditions

Abstract

This work addresses two environmental issues of major concern: hydrogen storage for hydrogen economy implementation and CO2 capture to reduce greenhouse gas emissions. For these purposes, two granular activated carbons were synthesized through chemical activation of olive stones by means of potassium salts (KOH and K2CO3). The porosity characterizations reveal typical ultramicroporous carbons with average pore sizes of about 0.53 and 0.69nm for K2CO3 and KOH-activated carbons, respectively. The volumetric measurements of cryogenic hydrogen adsorption show monolayer process. At sub-atmospheric pressures the narrower micropores show stronger binding energy to hydrogen molecules. However, at higher pressures this porosity range saturates and KOH-activated carbon exhibits a H2 storage capacity of 3wt%, 70% of which is achievable at only 1bar. CO2 shows a similar behavior than H2 when it was adsorbed purely at 0°C, and AC_KOH retains its excellence with a capacity of 5.6mmolg−1at 1bar. Finally, the two carbons were tested as CO2 adsorbents in conditions representative of post combustion capture applications (10% CO2 at atmospheric pressure and at 50°C). Both carbons show fast adsorption-desorption kinetics, perfectly described by pseudo-first order model. At these conditions, it was proven that only narrow micropores are essential for CO2 adsorption.