Chemical and Physical Influences of Salts on CO2 Solubility and Water Phase Changes

This Ph.D. dissertation describes energetic and structural changes in three (3) different physical equilibria scenarios involving aqueous solutions. The first project investigates gas dissolution problems in CO2 sequestration, where it is energetically unfavorable to introduce the gas into brine aquifers. Molecular simulations of the dissolution of carbon dioxide into aqueous solution (i.e. CO2(g) → CO2(aq)), under varying composition and concentration of various simple salts solutions and complex brine solution, give insight into how different ions affect the overall solubility of the gas in a brine solution. This involves developing a method for quantitatively calculating the free energy of solvation through Monte Carlo simulations and developing force-field parameters for CO2(aq). The second project focuses on the simulation of methane clathrates, as a further understanding could lead to new methane mining sources and the prevention of natural gas pipeline blockage. For this study, different temperatures and pressures are simulated using different water models, to give insight into how theses physical changes affect the clathrate cage shape and structural integrity. The third project characterizes the freezing point depression of aqueous solutions under different salt compositions and concentrations. Solution phase free energies are calculated through a standard free energy perturbation to a known thermodynamic state, while the solid phase free energy is calculated through the lattice-coupling expansion method, where the ice lattice is coupled to an Einstein crystal lattice and then adiabatically expanded to the same thermodynamic state as the final solution simulation The freezing point of pure TIP4P-Ew water is determined along with the freezing point depression in various salt solutions