Inhibiting carbon dioxide hydrate formation using deep eutectic solvents

Abstract

The formation of gas hydrates in pipelines during gas and petroleum extraction processes can result in multiphase systems including gas hydrates. These will form as solids in the presence of water and gas under thermodynamically favourable temperature and pressure conditions. Gas hydrates raise safety concerns, hinder process performance, and impact on financial resources as they block pipelines. The formation of gas hydrates can be efficiently prevented by using certain substances referred to as inhibitors. However, most inhibitors are expensive, potentially dangerous, and damaging to the environment. Hence, there is need to investigate environmentally friendly alternatives to mitigate gas hydrates. The objective of this study was to examine the efficiency of green additives referred to as deep eutectic solvents (DES) in inhibiting carbon dioxide gas hydrate formation. Deep eutectic solvents consisting of Tetrapropylammonium bromide + glycerol (DES-1), Tetramethylammonium chloride + glycerol (DES-2), and Tetramethylammonium chloride + ethylene glycol (DES-3) on carbon dioxide hydrates is investigated. These solvents are worth studying because their synthesis, purification, and environmental friendliness offer economic advantages. Molecular Dynamics (MD) simulations were used to theoretically determine the conditions that promote or inhibit the formation and stability of cardon dioxide hydrates in the presence of the selected inhibitors. The conditions investigated include temperature, pressure, and inhibitor concentration. The use of rigorous computational methods for preliminary screening significantly reduces the cost and the duration of experiments. MD simulation results were further validated using experimental gas hydrate equilibrium data. Results obtained in the present study indicated that the various DES solutions have both inhibiting and promoting effects. It was also found that low concentrations promoted hydrate dissociation, whereas high concentration greater than 0,20 stabilised hydrate formation. Pressure and temperature also impacted on the concentration of the DES solutions that inhibited or promoted hydrate formation. The concentration of the DES solutions shifted the hydrate curve to inhibit or promote hydrate formation.