Anion and cation effects of ionic liquids and ammonium salts evaluated as dehydrating agents for super-heavy crude oil: Experimental and theoretical points of view

Article abstract of DOI:10.1016/j.molliq.2014.03.044

One series of ionic liquids (IL), [TOA]⁺ [Y] (where [Y] ^- = [Cl]^-, [HSO₄]^- or [H ₂PO₄]^-), and new ammonium salts, [OCD] ⁺ [Y]^- (where [Y] = [HSO₄]^-, [MeSO₃]^- or [MePhSO₃]^-), were evaluated as demulsifying agents for super-heavy crude oil, at API = 6.39° (MO1) and API = 7.13°(MO2), with 8.46 and 8.94 wt.% of asphaltenes, respectively, at dosages of 1000 and 1500 ppm, using a conventional heating bottle test. At 1000 ppm, the ranking of water removal efficiency for the [TOA]⁺ [Y]^- series (in MO1 and MO2, in order to reach 96.7% and 95.4%, respectively) was [Cl]^- > [HSO₄] ^- > [H₂PO₄]^-. For the [OCD] ⁺ [Y]^- series, the rankings for efficiency at 360 min were [HSO₄]^- > [MeSO₃]^-, reaching approximately 27% in MO2, whereas [MePhSO₃]^- reached 1% in MO2. At a dosage of 1500 ppm, the [TOA]⁺ [Y]^- series achieved 100% water removal, showing the same order at 1000 ppm. For [OCD] ⁺ [Y]^-, the order at 24 h was [HSO₄] ^- > [MeSO₃]^- > [MePhSO₃] ^- for MO1 and MO2 at maximums of 85.5% and 92.3%, respectively. [OCD]⁺ [HSO₄]^- was an efficient demulsifier in tests of long duration. Quantum parameters were obtained at the semiempirical RM1 level, in order to establish a correlation with the experimental results. The molecular volume (V_M), molecular refractivity (MR), dipolar moment (μ) and mean polarizability (α) of the cation and anion fragments were important factors driving the dewatering process. V_M, MR and α were shown to have a direct relationship with water removal efficiency. Furthermore, absolute softness and the electrophilicity index of the cation fragments were calculated at the density functional theory (DFT) level. An increase in the softness and electrophilicity of the cations correlated with lesser effectiveness as demulsifiers. Finally, the partition coefficient of the cations showed that if the viscosity of the crude oil is low, it is possible to use ILs with a low partition coefficient (log P), but if the viscosity is high, the log P of IL should be near the [TOA]⁺ [Cl]^- value.