Rational design of deep eutectic solvents for absorption of h2s from natural gas

Novel Deep Eutectic Solvents (DESs) are being developed, which are non-flammable and biodegradable. These DESs are used in application for organic synthesis, metal processing, gas absorption, and removal of different undesired impurities in oil & gas industries. For instance, a combination of caprolactam (CPL) and tetrabutylammonium halides (1:1, mole ratio), as the DES, has indicated the highest efficiency for desulfurization of natural gas. We herein implement abinitio and molecular dynamic simulations to explore the formation of CPL based type III DESs. The simulations show ~15% decline in the ionic interactions of tetrabutylammonium halides and ~92% decline in the hydrogen bonds between CPL, thereby explaining the rapid decline in the melting point as noted in experiments during the formation of DES. Moreover, ab-initio and molecular dynamic (MD) simulations of the caprolactam based DES with hydrogen sulfides and methane’s were conducted in order to mimic the industrial natural gas sweetening process. Efficient absorption of hydrogen sulfide from natural gas at various process parameters (5000/10000 ppm H2S, at 25/ 60 C, and at 1/10 bar) can be highlighted from the molecular dynamic simulations. The results revealed strong intermolecular interactions between the anions of the caprolactam based DESs and hydrogen sulfide (H2S), with interaction energies ~10 folds higher than methane (CH4)/hydrogen sulfide (H2S), explaining the mechanism of desulfurization by these DESs. The ab-initio and molecular dynamics simulations were computed via the implementation of GAUSSIAN16, GROMACS software’s. The given work also illustrates that two DESs, namely a combination of choline chloride (ChCl) with urea, and monoethanolamine (MEA) with methyltriphenylphosphonium bromide (MTPPBr) were implemented to compare their capacity to absorb hydrogen sulfide (H2S), however we observed that the CPL based DESs are highly efficient, particularly at low fuel:DES mole ratios, low temperatures, and at low pressures.