Humidity effect on ion behaviors of moisture-driven CO2 sorbents

Xiaoyang Shi; Hang Xiao; Xiangbiao Liao; Mitchell Armstrong; Xi Chen; Klaus S Lackner

doi:10.1063/1.5027105

Humidity effect on ion behaviors of moisture-driven CO₂ sorbents

J Chem Phys. 2018 Oct 28;149(16):164708. doi: 10.1063/1.5027105.

Authors

Xiaoyang Shi¹, Hang Xiao¹, Xiangbiao Liao¹, Mitchell Armstrong², Xi Chen¹, Klaus S Lackner²

Affiliations

¹ Department of Earth and Environmental Engineering, Columbia University, New York, New York 10027, USA.
² School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, Arizona 85287-9309, USA.

PMID: 30384735
DOI: 10.1063/1.5027105

Abstract

Ion hydration is a fundamental process in many natural phenomena. This paper presents a quantitative analysis, based on atomistic modeling, of the behavior of ions and the impact of hydration in a novel CO₂ sorbent. We explore moisture-driven CO₂ sorbents focusing on diffusion of ions and the structure of ion hydration complexes forming inside water-laden resin structures. We show that the stability of the carbonate ion is reduced as the water content of the resin is lowered. As the hydration cloud of the carbonate ion shrinks, it becomes energetically favorable to split a remaining water molecule and form a bicarbonate ion plus a hydroxide ion. These two ions bind less water than a single, doubly charged carbonate ion. As a result, under relatively dry conditions, more OH^- ions are available to capture CO₂ than in the presence of high humidity. Local concentrations of dissolved inorganic carbon and water determine chemical equilibria. Reaction kinetics is then driven to a large extent by diffusion rates that allow water and anions to move through the resin structure. Understanding the basic mechanics of chemical equilibria and transport may help us to rationally design next-generation efficient moisture-driven CO₂ sorbents.