Carbon dioxide emissions in industrial flue gases have traditionally been mitigated using amine scrubbing, wherein an aqueous alkanolamine solvent is typically utilized to absorb carbon dioxide. These alkanolamines are synthesized via ring-opening of an epoxide by an amine in an aqueous solution at ambient temperature and pressure. A key challenge with their synthesis is maintaining control over the product distribution, since ring-opening of asymmetric epoxides can lead to the formation of multiple isomers that can subsequently react to produce secondary and tertiary amines. In addition, previous studies have reported a catalytic influence of water on the reaction and potential autocatalytic behavior of product alkanolamines, further adding to the complexity of the reaction system
1. Therefore, a fundamental understanding of the mechanism and kinetics of aminolysis of epoxides is essential for the directed synthesis of alkanolamines. To that end, we focus on the development of a computational model that leverages mechanistic insights and reaction energetics from molecular-scale simulations for the prediction of experimental observables, such as product concentrations, using continuum-scale microkinetic modeling.
In this study, we consider a class of reactions between propylene oxide and alkylamines of varying complexity. Molecular dynamics and conformational sampling approaches are utilized to solvate reacting species with explicit solvent molecules. Reaction energetics are calculated using DFT for unsolvated and solvated structures to clarify the role of solvent species in catalyzing the epoxide ring-opening reaction. In addition, the influence of changing solvent composition on proton shuttling is investigated. Lastly, kinetic parameters calculated using transition state theory are employed in a detailed microkinetic model to predict the evolution of species concentrations.
[1] Holubka, J. W.; Bach, R. D.; Andres, J. L. Theoretical Study of the Reactions of Ethylene Oxide and Ammonia: A Model Study of the Epoxy Adhesive Curing Mechanism. Macromolecules 1992, 25 (3), 1189–1192.
