Molecular Dynamics Investigation of Efficient SO2 Absorption by Anion-Functionalized Ionic Liquids

Abstract

Ionic liquids are appropriate candidates for the absorption of acid gases such as SO 2. Six anionfunctionalized ionic liquids with different basicities have been studied for SO 2 absorption capacity by employing quantum chemical calculations and molecular dynamics (MD) simulations. Gas phase quantum calculations unveil that the high uptake of SO 2 in these ionic liquids originates from the basicity of the anions and the consequent enhanced anion-SO 2 interactions. MD simulations of SO 2-IL mixtures reveal the crucial role of both cations and anions in SO 2 dissolution. Multiple-site interactions of SO 2 with the anions have been identified. The calculated solvation free energy substantiates these observations. The order of computed Henry's law constant values with change in the anion is in fair agreement with experimentally determined SO 2 solubility order.

Improved Reversible and Selective SO2 Absorption by a Stable Phosphonium Carboxylate Ionic Liquid

“…This result confirms the hydrogen bond formation between SO 2 and the IL observed by FT-IR at 2362 cm –1 . Similar hydrogen bond formation between [P 2,2,2,1 ] + hydrogen atoms and SO 2 had been previously identified in MD simulations as well …”

“…Similar hydrogen bond formation between [P 2,2,2,1 ] + hydrogen atoms and SO 2 had been previously identified in MD simulations as well. 65 The ideal selectivity of absorption was calculated as the ratio of moles of gas absorbed at a specific pressure with the values reported in Table 2. At 303 K, the quantity of SO 2 absorbed is 60 times higher at 250 mbar (ideal selectivity of 150) and 100 times higher at 343 K (ideal selectivity of 215) than the quantity of CO 2 .…”

Mass Transfer Thermodynamics through a Gas–Liquid Interface

“…Complementary MD PMF studies for [C 4 mim]­[Ace] are strongly needed as a function of x w . While MD PMF studies of gas phase interactions with liquid water have successfully decomposed the enthalpy and entropy contributions as a function of liquid depth, − , this is not the case for ionic liquid MD PMF studies to date. − Future IL MD PMF studies that decompose enthalpy and entropy contributions may provide further insight into the structural dynamics driving the thermodynamic variations across the gas–IL interface.…”

“…The mass transfer of gas phase molecules into a bulk liquid must cross a gas–liquid interface, a process that is ubiquitous in environmental, biological, and engineered liquids . The free energy profile during mass transfer across a gas–liquid interface has been fairly well characterized by molecular dynamics simulations of liquid water − and ionic liquids. − Experimentally measuring the thermodynamic profile across the gas–liquid interface requires the ability to deconvolute the gas–bulk and gas–interface thermodynamics. While measuring gas–bulk liquid thermodynamics is common, the ability to measure directly the surface thermodynamics of gas phase species interacting with a liquid interface under in situ conditions is technologically very challenging .…”

Insight into the interaction between amino acids and SO2: Detailed bonding modes

“…A number of new methods have been proposed so far, such as catalytic redox 7,8 , adsorption on porous media (e.g., activated carbons (ACs), zeolites, MOFs) [9][10][11] , and ionic liquid adsorption. 12 The proposal of these methods greatly reduced the problem of waste liquid generation and also inspired researchers to explore new solutions for SO2 management from more fields. Recently, researchers have invented new techniques for the adsorption of polluted gases using biological processes (e.g., using the metabolism of autotrophic algae to remove SO2), which has the advantages of high efficiency, low energy, and no secondary pollution.…”