Density functional theory (DFT) models for the desulfurization and extraction of sulfur compounds from fuel oils using ionic liquids

The use of DFT computational methodology for the study of ionic liquids (ILs), which could be employed for the desulfurization of fuel oils, can yield a wealth of data. We present preliminary DFT results, which we have conducted on 35 ILs with Gaussian 16 using the 6-311++G(d,2p)/B97X-D basis set. The ILs formed from four N-alkylatedpyridinium cations as examples, namely N-ethyl ([EPy+]), N-butyl ([BPy+]), N-hexyl ([HPy+]), N-octyl ([OPy+]), and three carboxypyridinium cations, namely N-carbomethoxy ([CMePy+]), N-carboethoxy ([CEtPy+]) and N-carbopropoxy ([CEtPy+]) were examined in silico by combinations of each of these cations with the following anions: tetrafluoroborate ([BF4−]), the four conjugate base anions, acetate [Ac−], dihydrogenphosphate, [H2PO4−], hydrogen sulfate [HSO4−] and trifluoroacetate [TFA−]. The four conjugate base anions were chosen in order to ascertain whether their respective pKb values were potentially correlated with their DFT-determined stabilities and/or reactivities and their corresponding ILs toward interacting with DBT and DBTO2. Among the conclusions that could be drawn from such quantum chemical calculations is that experimental conditions can be designed based upon the selection of the optimal ILs thus targeted and which are composed of the appropriate anion(s) chosen with the optimum N-alkylpyridinium or N-carboxyalkylpyridinium cations.