Aggregation Behavior of Heavy Crude Oil−Ionic Liquids Solutions by Fluorescence Spectroscopy

Abstract

Asphaltene aggregation is a two-step process concerning phase separation and asphaltene particle growth which provoke crude oil destabilization and significant problems during the production, transport, and refining of heavy and extra heavy crude oils. A recent and innovative approach to overcome this problem is the use of ionic liquids (ILs) as inhibitors or stabilizers of asphaltene aggregation. Since the information concerning the properties of the studied ILs is scarce, we characterized some of their electronic properties and critical aggregation concentration (CAC) by quantum chemistry and spectrofluorometry, respectively. We found that the presence of a complex anion such as [AlCl4]−, [BF4]−, and [PF6]− incremented the HOMO−LUMO gap (ΔH−L), electronegativity (χ), absolute hardness (η), and dipole moment (μ) when compared to [Br]−-containing ILs. Moreover, the ILs’ CAC values showed a linear correlation with the dipole moment. Afterward, we studied the effect of various commercial ILs on the aggregation point (AP) of a heavy crude oil (HCO) due to the increment of (a) its concentration in toluene solutions or (b) the n-heptane volume by means of fluorescence spectroscopy. We have found that the aggregation of HCO occurs at larger crude oil concentration or n-heptane volume in the presence of some ILs. Here, ILs set a polar microenvironment around HCO asphaltenes, which stabilized them against further aggregation and precipitation. The better performance of ILs as inhibitors or stabilizers of asphaltene aggregation was found with those comporting a complex anion, a pyridinium ring, or a shorter alkyl substitution on the cation. Such ILs present the higher values of the calculated electronic properties.