Solubility of Thiophene and Dibenzothiophene in Anhydrous FeCl₃- and ZnCl₂‑Based Deep Eutectic Solvents

The solubilities of some common refractory-sulfur-containing compounds, namely thiophene and dibenzothiophene, were studied and measured in anhydrous FeCl₃- and ZnCl₂-based deep eutectic solvents (DES) at different temperatures under atmospheric pressure. The aim of this study is to explore the behavior of DESs toward solvation of sulfur-containing compounds so as to set a pace for the successful application of DESs into deep desulfurization of liquid fuels. The studied DESs were screened and prepared by the combination of anhydrous FeCl₃ and ZnCl₂ with different salts and hydrogen bond donors. High pressure liquid chromatography (HPLC) was employed for the quantitative measurements of solubilities of both thiophene and dibenzothiophene. It was found that FeCl₃ based DESs exhibited higher solubilities (from 17 wt % to above 90 wt %) for dibenzothiophene as compared to the ZnCl₂ based DESs (0.084–1.389 wt %). Moreover, FeCl₃ based DESs exhibited complete miscibility with thiophene while ZnCl₂ based DESs showed solubility values in the range of 1–10 wt % for thiophene. The experimental results obtained were further successfully modeled using the nonrandom two liquid (NRTL) model.