Rapid, Selectivity, And Reversibility Absorption of SO ₂  Via Purine-Based Deep Eutectic Solvents and Thermodynamic Analysis

Abstract

Since the advantages of easy preparation, low cost, environmental friendliness, and high absorption capacity, deep eutectic solvents (DESs) are considered to have excellent application potential in the field of SO2 absorption. However, the absorption rate, selectivity, and reversibility of DESs urgently need to be further improved to meet the requirements of industrialization. In this work, five purine-based DESs were designed and prepared by using 1-Ethyl-3-methylimidazolium Chloride (EmimCl) as hydrogen bond acceptors (HBAs) plus Adenine (6-AmP), Hypoxanthine (6-HoP) and 6-Chloropurine (6-ChP) as hydrogen bond donors (HBDs), respectively. The obtained results indicated that the optimal molar ratio of HBAs to HBDs is 7:1, and the absorption capacity of EmimCl + 6-AmP-7 can reach up to 18.118 mol·kg-1, at 298.15 K and 1.0 bar. Notably, the present purine-based DESs not only achieve gas–liquid equilibrium within 40 s, but also exhibit outstanding reversibility (absorb-desorb more than 30 times) and remarkable selectivity of SO2/CO2. Furthermore, a reaction equilibrium thermodynamic model (RETM) equation was employed to investigate the absorption behavior by combining the absorption data under different SO2 partial pressure and temperature. Finally, FT-IR and 1H NMR were employed to further investigate the formation and SO2 absorption mechanism of purine-based DESs. It is revealed that the former is mainly hydrogen bonding interaction between HBAs and HBDs, the latter is mainly Lewis acid-base interaction and strong charge-transfer interaction between DESs and SO2. Based on the obtained data, it could be confirmed that the absorption process includes both physical and chemical absorption.

Keywords: deep eutectic solvents, SO2 absorption, purine derivatives, selectivity and reversibility