Oxidative and Extractive Desulfurization of Fuel Oils Catalyzed by N-Carboxymethyl Pyridinium Acetate and N-Carboxyethyl Pyridinium Acetate Acidic Ionic Liquids: Experimental and Computational DFT Study

Abstract

This study reports on the synthesis, characterization, and application of two acidic ionic liquids, namely, N-carboxymethylpyridinium acetate ([HO2CCH2Py][CH3CO2] or AIL1) and N-carboxyethylpyridinium acetate ([HO2C(CH2)2Py][CH3CO2] or AIL2), as both extractants and catalysts for the oxidative and extractive desulfurization (OEDS) of model fuel oils containing heteroaromatic sulfur compounds. The structural properties of the synthesized acidic ionic liquids (ILs) were confirmed by 1H NMR, 13C NMR, and FT-IR spectroscopic analysis. To optimize the performance of the acidic AILs in the desulfurization process, the effects of different parameters, such as H2O2 dosage, reaction time, and temperatures, were investigated. The experimental results showed that AIL1 has exceptionally high desulfurization–extraction rates, with values of 99.8%, 97.8%, and 95.4%, for DBT, BT, and 4,6-DMDBT, respectively, under the optimum conditions established. Under the same conditions, the desulfurization-extraction rates using AIL2 reached 91.6%, 87.3%, and 82.4%, respectively, for DBT, 4, 6-DMDBT, and BT. Both ionic liquids can be recycled up to 9 times without a significant decrease in their sulfur removal efficiencies. Furthermore, density functional theory (DFT) calculations were conducted to evaluate the electronic interaction energies (ΔIE) between the AILs with each of the sulfur-containing compounds and their putative oxidized products. The computational findings strongly supported the experimental outcomes.