Screening of amino acids for enhanced CO2 dissolution in saline aquifers: Molecular dynamics simulation study

Abstract

Research on storing CO₂ in deep saline aquifers with extremely high salinity poses numerous challenges in experimental setup. A key tool for addressing these challenges is molecular dynamic simulation to predict the solubility of CO₂ in brine. This study explores the dissolution behavior of supercritical CO₂ in formation brine, with and without the presence of amino acids. The main focus is to identify a suitable amino acid and find its optimal concentration to enhance dissolution and density. As such, a brine model is developed with a salt concentration of 15 wt%. The model was designed such that it mimics the properties and behavior of an actual brine commonly found in saline aquifers. The density and viscosity of the brine model are compared against actual. The results revealed that the simulated model mimics the density and viscosity of actual brine from saline aquifers. To further ensure accuracy and dependability, the density of CO₂-saturated brine was calculated at a temperature of 338 K and a pressure of 20.5 MPa using solubility model. The result indicates a notable increase in brine density of 0.76% attributed to the dissolution of CO₂, which is also in good agreement with the literature. Next, the performances of six amino acids at concentrations of 0.2%, 1.2%, 2.5%, and 5% are studied in terms of their ability to increase the density of the CO₂-saturated brine to improve CO₂ dissolution. The amino acids considered in this study are L-arginine, L-glycine, L-lysine, L-methionine, L-tryptophan, and L-tyrosine. The simulation findings reveal that each amino acid has the potential to enhance both the dissolution and density of the CO₂-saturated phase. Notably, among the selected amino acids, tyrosine exhibits the highest dissolution rate of −33436.52 kcal/mol and density of 1.088 g/cc at a concentration of 0.2%.