PNNL

Abstract

The CO2 chemisorption in state-of-the-art sorbents based on oxide/hydroxide/amine moieties is driven by strong chemical bonding formation in the carbonate/bicarbonate/carbamate products, which in turn leads to high energy input in sorbent regeneration. In addition, the CO2 uptake capacity was limited by the active sites’ utilization efficiency, with each active site incorporating one CO2 molecule or less. In this work, a new concept and generation of sorbent was developed to achieve cascade insertion of multiple CO2 molecules by leveraging structure re-arrangement as the driving force, leading to in situ generation of extra CO2-binding sites and significantly reduced energy input for CO2 releasing. The designed ionic liquids (ILs) containing carbanions with conjugated and asymmetric structure, deprotonated (methylsulfonyl)acetonitrile ([MSA]) anion, allowed the cascade insertion of two CO2 molecules via consecutive C-C and O-C bond formations. The proton transfer and structure re-arrangement of the carboxylic acid intermediates played critical roles in stabilizing the 1st integrated CO2 and generating extra electron-rich oxygen sites for the insertion of the 2nd CO2. The structure variation and reaction pathway were illustrated by operando spectroscopy, magnetic resonance spectroscopy (NMR), mass spectroscopy, and computational chemistry. The energy input in sorbent regeneration could be further deduced by harnessing the phase-changing behavior of the carbanion salts in ether solutions upon reacting with CO2, avoiding the energy consumption in heating up the solvent. The fundamental insights obtained herein provide a promising approach to largely improve the CO2 sorption performance via sophisticated molecular-scale structural engineering over the sorbents.