Investigation on Asphaltene Dispersion Activity of Tetrabutylammonium Carboxylate Ionic Liquids

Asphaltene destabilization is still known as one of the main problems of the petroleum industry and imposes many costs on this industry during crude oil production, transportation, and refining. The most important solution to control this problem is using chemical compounds to disperse asphaltene aggregates. Ionic liquids, as an emerging industrial solvent and catalyst, have been used for this purpose in the last two decades. In this work, three ionic liquids having a tetrabutylammonium cation and oleate, stearate, and cinnamate anions were synthesized and used as asphaltene dispersants. The efficiency of the synthesized ionic liquids on the stability of asphaltene aggregates was investigated using cluster size, polydispersity index, zeta potential, and ultraviolet spectroscopy data. It was found that tetrabutylammonium cinnamate and tetrabutylammonium oleate (dispersion indices of 82.5 and 60.2, respectively) have a much higher efficiency than tetrabutylammonium stearate (dispersion index of 20.6). The results of cluster size, polydispersity index, and zeta potential analysis were confirmed by ultraviolet spectroscopy and optical microscopy data. For instance, the mean radius of asphaltene clusters was 2179.8 nm, reduced to 253, 680, and 1402 nm after adding tetrabutylammonium salt of cinnamate, oleate, and stearate, respectively. The same trend was observed in the results of the polydispersity index (0.417, 0.470, and 0.624) and zeta potential analysis (31.4, 1.81, and −0.56). The cinnamate, oleate, and stearate anions have four, one, and no carbon–carbon π bonds, respectively. It seems that the presence of π bonds that can form π–π interactions with π bonds of the asphaltene molecules is an essential factor in asphaltene stabilization by these ionic liquids. In addition, the results showed that the higher the net negative charge of the anion, the greater the ability of the anion to stabilize asphaltene aggregates. This stabilization, which was mainly done through electrostatic interactions between polar groups of asphaltene and the carboxylate anions, was confirmed by zeta potential data.