Molecular dynamics simulations of Krytox oil - CO2 gas mixture

Abstract

The power plant, steel and petrochemical industries are large sources of carbon emissions worldwide. For meeting the climate goals of 2030 and 2050, efforts are underway towards pioneering novel technologies. Gas separation by supported liquid membranes is an attractive option for its energy-efficient, continuous and low cost of operation. The separation of gases takes via a solution diffusion mechanism where the gases are separated based on their
selectivity. Krytox oil is a high performance perfluoropolyether polymeric lubricant, originally aimed for its application to supersonic transport aircraft. The lubricant is known for its chemical and thermal stability leading to a longer usable life. The oil has shown an affinity for carbon dioxide (CO2) gas, a weak Lewis acid, owing to the fluorine and oxygen atoms in the polymeric oil which act as Lewis base and is thus envisioned for use in supported liquid membranes for gas separation.
Molecular dynamics simulations serve as a powerful tool of study, overcoming the shortcomings of experimental methods such as the difficulty of measurements at elevated temperatures, pressures or handling dangerous chemicals. This project covers the study of transport properties of Krytox oil namely the oil viscosity and diffusivity of CO2 in the oil for varying conditions of temperature, pressure and polymer chain length using equilibrium molecular dynamics simulations. The suitability of various atomistic force field models for this particular study has been tested, proceeding with the Universal force field (UFF) as the model of choice for studying the oil properties. To shorten the simulation time and study long time scales, coarse-grained simulations have been carried out using state-of-the-art MARTINI force field. In addition to transport properties, Henry’s constant for the solubility of CO2 in Krytox oil
has been predicted via alchemical free energy calculations by molecular dynamics simulations.