Evaluation of ammonia modified and conventionally activated biomass based carbons as CO2 adsorbents in postcombustion conditions

Abstract

Low cost carbons obtained from biomass residues, olive stones and almond shells, were evaluated as CO2 adsorbents in postcombustion conditions (low CO2 partial pressure). These carbons were prepared from biomass chars by means of two different methods: physical activation with CO2 and amination. All the prepared carbons present a high CO2 adsorption capacity at 303 K, although carbons developed from almond shells show a superior CO2/N2 selectivity (lower N2 adsorption) than those obtained from olive stones. In general, activated samples present faster adsorption kinetics due to the presence of transport pores, although they have lower densities. On the other hand, aminated samples have narrower porosities but higher volumetric capacities. Among the samples studied, aminated almond shells were selected as the most promising adsorbent, due to their high CO2 adsorption capacity and selectivity and their good adsorption kinetics. To assess the performance of these samples in cyclic adsorption/desorption processes, basic two-step cycle configurations were evaluated by the following regeneration strategies: temperature swing adsorption (TSA), vacuum swing adsorption (VSA) and a combination of both (VTSA). Aminated almond shells showed no sign of deactivation after 13 h of continuous TSA cycling between 303 and 373 K, nor during VSA or VTSA cycling.