title: Accurately Predicting CO2 Reactive Absorption Properties in Aqueous Alkanolamine Solutions by Molecular Simulation Requiring No Solvent Experimental Data
author: Javad Noroozi
description: We present a general atomistic simulation framework for efficient reactive equilibrium calculations in dilute solutions, and its application to CO2 reactive absorption in aqueous alkanolamine solutions. No experimental data of any kind are required for the solvents, and no empirical adjustments are required for its implementation. This hybrid methodology calculates reaction equilibrium constants by combining high-level quantum chemical calculations of ideal-gas standard reaction Gibbs energies (ΔG0) with conventional solvation free energy calculations obtained from classical force field methodology. For these quantities we use explicit solvent molecular dynamics simulations with the General AMBER Force Field (GAFF). The resulting equilibrium constants are then coupled with a macroscopic Henry Law based ideal solution model to calculate the solution speciation and the CO2 partial pressure, PCO2. We show results for seven primary amines: monoethanolamine (MEA), 2-amino-2-methylpropanol (AMP), 1-amino-2-propanol (1-AP), 2-amino-2-methyl-1,3-propanediol (AMPD), 2-aminopropane-1,3-diol (SAPD), 2-(2-aminoethoxy)­ethanol or diglycolamine (2-AEE or DGA, respectively), and 2-amino-1-propanol (2-AP). Experimental speciation and PCO2 data for some of these are available, with which we validate our methodology. We predict new results for others in cases when such data are unavailable, and provide explanations for the experimental inability to detect carbamate solution species in relevant cases. Our results for the pK value of the carbamate reversion reaction are within the chemical accuracy limit of 218.546/T units (corresponding to 1 kcal·mol–1 in the corresponding free energy change) in comparison with experimental results when such data exist, which at 298.15 K corresponds to 0.73 pK units. The precision of our pK predictions is comparable to that which can be obtained from conventional experimental methodologies for these quantities. Our results suggest that the presented molecular simulation methodology may provide a robust and cost-efficient tool for solvent screening in the design of post-combustion CO2 capture processes.