Do adsorbent screening metrics predict process performance? A process optimisation based study for post-combustion capture of CO2

Recent interest in carbon dioxide capture has led to the development of hundreds of adsorbents. Adsorbent screening is typically performed either by inspecting the isotherms or by using simple adsorbent screening metrics (selectivities, working capacities, figures of merit, etc.). This work seeks to critically evaluate the efficacy of various adsorption metrics for adsorbent screening through the use of process-optimisation. A case study addressing post-combustion CO2 capture using vacuum swing adsorption (VSA) is presented. Four different adsorbents (Mg-MOF-74, UTSA-16, Zeolite 13X and a type of activated carbon) were subjected to process-optimisation studies on a 4-step PSA cycle with light product pressurisation (LPP). Two kinds of process optimisation studies were performed. The first to maximise purity and recovery; and the second to minimise energy consumption and maximise productivity subject to purity/recovery constraints. This study highlights that most commonly used adsorbent metrics do not correctly rank adsorbents in order of their performance at a process scale. Further, it is also shown that N2 affinity/capacity plays a critical role in deciding the process performance of VSA based post-combustion CO2 capture.