Atomic-Scale Revelation of Hydrogen Bond Synergy in Efficient COS Capture by Alkaline DES for Fuel Gas Purification

The clean utilization of industrial fuel gases depends
on the effective
removal of pollutants such as carbonyl sulfide (COS). Although deep
eutectic solvents (DESs) have emerged as potential green absorbents,
the molecular-level mechanism governing COS capture and its selectivity
over CO2 are still poorly understood. Herein, we integrate
molecular dynamics (MD) simulations with spectroscopic validation
(FT-IR, 1H NMR) to elucidate the capture mechanism in an
alkaline TEAC/DEA DES. We conclude that selectivity is primarily driven
by a strong physical affinity for COS over CO2. In a competitive
environment, this changes to a −13.2 kJ/mol interaction energy
advantage for COS, which corroborates the experimentally observed
selectivity of 2.1. This strong, hydrogen-bond-driven physisorption
is further enhanced by a synergistic electrostatic contribution from
the Cl– anion that promotes mass transport. The
excellent COS capacity of the TEAC/DEA DES (88.6 mg/g–1) relative to both neat DEA and its amine-free TEAC/EG analogue experimentally
confirms the operative nature of this synergy. The optimal operating
window at 50 °C is identified, which balances a 15% increase
in initial absorption rate (from 30 °C) with the prevention of
COS hydrolysis at higher temperatures. Under these conditions, the
DES exhibits stable performance over five cycles and low corrosivity.
This work illuminates the COS capture mechanism at the atomic scale,
providing a theoretical foundation for rational design of next-generation
solvents for fuel gas purification.