Effect of the cation structure on the thiophene distribution between the ionic liquid with NTf 2 anion and the hydrocarbon rich phases: A QSPR study Ali Ebrahimpoor Gorji, Mohammad Amin Sobati ⁎ School of Chemical Engineering, Iran University of Science and Technology (IUST), Tehran, Iran abstract article info Article history: Received 10 March 2020 Received in revised form 21 May 2020 Accepted 7 June 2020 Available online 10 June 2020 Keywords: Extractive desulfurization Quantitative Structure-Property Relationship (QSPR) Ionic liquid Cation effect Thiophene distribution G3u descriptor In the present study, the effect of different cation structures has been investigated on the thiophene distribution between the ionic liquids containing NTf 2 anion and hydrocarbon phases in the ternary systems utilizing quanti- tative structure-property relationship (QSPR). The role of cation structure was investigated in the presence of con- stant anion (i.e., NTf 2 ) and different hydrocarbon solvents using three different datasets with 311 experimental data points. The first and second datasets contains {([different cations][NTf 2 ]/thiophene/n-heptane or Toluene}, respectively. The third dataset contains {([different cations][NTf 2 ]/thiophene/different hydrocarbons}. The results demonstrated that the effects of cation structures can vary by changing the involved hydrocarbons in the ternary systems. It was found that “G3u” as a directional WHIM descriptor can take into account the effect of cation struc- ture on the thiophene distribution. “G3u” reflects the relevant molecular 3D information considering symmetry of structure. Therefore, it was tried to propose a predictive QSPR model with two molecular descriptors from the hy- drocarbon structure (i.e., “Pol”) and cation structure (i.e., “G3u”) along with the thiophene mole fraction in the hydrocarbon rich-phase (i.e., X 2 ) to estimate the thiophene mole fraction in the IL rich-phase (i.e., Y 2 variable). The statistical results of internal and external validations confirmed the validity of the developed QSPR model. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Some thiophenic sulfur-containing compounds such as thiophene (T), benzothiophene (BT), and dibenzothiophene (DBT) and their alkylated derivatives can be found in the petroleum-derived fuels [1]. The presence of these compounds leads to some problems in the oil refining process [2] and environmental issues [3,4]. The conventional hydrodesulfurization (HDS) as the main sulfur removal process faced several important chal- lenges for deep removal of this type of sulfur-containing compounds [5]. Therefore, the alternative or complementary HDS processes have been received much attentions [5]. Today, adsorptive desulfurization (ADS) [6,7], oxidative desulfurization (ODS) [8,9], and extractive desul- furization (EDS) [10–17] can be considered as some alternative methods for the desulfurization. Among these methods, EDS has several important advantages including mild operating conditions, and process simplicity. The performance of different solvents such as conventional solvents [12,18] and ionic Liquid (IL) [19–32] were investigated in the different EDS studies. It should be added that the extractive performance of these solvents have been usually investigated in the sulfur removal from model fuels (containing a specific sulfur-containing compound such as thiophene (T) dissolved in a hydrocarbon solvent). Such studies can be conducted in the ternary systems which composed of extractive solvent (1) sulfur-containing compound (2) and hydrocarbon solvent (3). Ionic liquids (IL) as “green solvents” have been applied in the EDS processes [19–21] due to their unique properties such as limited solubil- ity in the hydrocarbon and low vapor pressure [33,34]. There are nu- merous variations of cation and anion structures in such a way that the number of synthesized ILs is forecasted to be about 2000 [35]. Therefore, theoretical studies for selecting the best combination of cat- ion and anion in IL for the desulfurization tasks are welcome. It should be highlighted that the extractive efficiency of ILs depends on the synergy of cation and anion [36]. So, it seems better to investigate the effect of each involved compound by taking into account other involved compounds, simultaneously. For example, our recent study proved that the effect of anion structures on the thiophene distribution depends on the type of present cation [37]. In addition, according to the theoretical re- sults and experimental verifications, it was proved that the effect of a spe- cific cation on the thiophene distribution coefficients depends on the type of the accompanied anion. In other words, changing the alkyl chain length of cation for the Imidazolium-based IL leads to two different behaviors in the presence of two different anions [38]. Therefore, this point implies that the effect of cation structure depend on the accompanied anion structures intensively. In this regard, the exact effect of cation on the thio- phene distribution can be investigated in the presence of a constant anion (e.g., bis (trifluoromethanesulfonyl) imide [NTf 2 ]) as a novel work. Wlazlo Journal of Molecular Liquids 313 (2020) 113551 ⁎ Corresponding author. E-mail address: sobati@iust.ac.ir (M.A. Sobati). https://doi.org/10.1016/j.molliq.2020.113551 0167-7322/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq