Absorption characteristics and molecular mechanism of a low viscosity iron-based ionic liquid for removing H2S

Abstract

Aiming at the problem of by-product salt and volatile solvent component in industrial liquid redox process of H2S removal. A new absorbent, a 1-butyl-3-methylpyridine iron-based ionic liquid (rFeCl3/[BMP]Cl) with three iron-pyridine ratios (r=0.6, 0.8, and 1.0), was synthesized. The physicochemical properties and H2S solubility of rFeCl3/[BMP]Cl were measured and modeled. The molecular mechanism of chemical absorption of H2S by iron-based ionic liquids was explained from the interaction energy, reduced density gradient (RDG) and atoms in molecules (AIM) topology analysis, and standard reaction equilibrium constant by quantum chemical calculation. It was found that rFeCl3/[BMP]Cl have low viscosity, high solubility, and good thermal stability. Its Bronsted acidity avoids by-product salts produced in the absorption of H2S. The hydrophobicity makes the ionic liquid not diluted by the generated water during the absorption. The results of quantum chemical calculations show that rFeCl3/[BMP]Cl-H2S has moderate intermolecular interaction and large reactivity, which is consistent with the experimental results of the Henry's coefficient and reaction equilibrium constant.