Structure of Monoethanolamine and Diethanolamine Carbamates in Aqueous Solutions Determined by High-Energy X-ray Scattering

Abstract

A more detailed understanding of interactions between amine solution and carbon dioxide (CO2) is required for economical capture and recovery of CO2 emitted from thermal power plants. In order to investigate the molecular structure of the carbamate molecules which originate from CO2 gas, a high-energy X-ray scattering method was applied to monoethanolamine and diethanolamine aqueous solutions with several concentrations of CO2. Distinct peaks attributable to C−O (0.126 nm) and O···O (0.223 nm) interactions within the carbamate molecule were found in the difference distribution function derived from observed interference functions. To our knowledge, this is the first observation of the CO2−captured molecule. The experimental difference distribution functions were well reproduced by theoretical difference distribution functions evaluated from information obtained from NMR and computer conformation analysis. The present results indicate that the X-ray scattering method can contribute to the structural analysis of amine−H2O−CO2 systems.