The oil compatibility model is important for assessing the stability of crudes. The compatibility between maltenes and the corresponding asphaltenes, Asphs, can be assessed from the solubility parameters (Hildebrand and Hansen) of both components of the crude. Solvatochromism is the effect of the medium on the UV/vis spectra of substances (solvatochromic probes) that are sensitive to the properties of the medium, namely, its empirical (or overall) polarity, Lewis acidity and basicity, dipolarity, and polarizability. Therefore, the solubility and solvatochromic parameters of solvents should be related. We synthesized a novel solvatochromic probe (E-2,6-di-tert-butyl-4-(2-(1-hexylquinolin-1-ium-4-yl)­vinyl)­phenolate, HxQMBu 2 ) whose properties are convenient to study in nonpolar and polar solvents. The empirical solvent polarities measured with HxQMBu 2 in 38 solvents correlated linearly with the corresponding Hildebrand solubility parameters. Likewise, the solvent Lewis acidity/basicity, dipolarity, and polarizability correlated linearly with the corresponding Hansen solubility parameters. To test the equivalence of the two scales (solvatochromic and solubility parameters), we determined the solubility of Asphs in 28 solvents, pertaining to different chemical classes. The dependence of Asph solubility on three solvent descriptors (Lewis acidity/basicity, dipolarity, and polarizability) was tested. Our results indicated that alcohols and hydrocarbons are inefficient solvents; solvents of intermediate efficiency carry either a strongly dipolar group or polarized bonds. Aromatic and heterocyclic solvents are most efficient. The most relevant solvent descriptor (for the dissolution of Asphs) is its polarizability.

We extended the oil compatibility model to the dissolution of asphaltenes (Asps) in maltenes from 10 crude oils (COs). As scales for the power of solvents of interest, vide infra, we used solvatochromic parameters, calculated from the UV–vis spectra of solvatochromic compounds (probes), Hildebrand/Hansen solubility parameters, and the colloidal instability index of COs. As the colors of maltenes or asphaltene-free crude oils CO(Asp‑free) were too dark to permit recording the absorption spectra of the probes, we formulated models for these fractions (MCO(Asp‑free)). They were composed of low molar mass hydrocarbons, namely, cis and trans decalines, isooctane, 1-methylnaphthalene and, as model for resins, benzothiazole/n-octyl-1-naphthoate. We based formulations of these MCO(Asp‑free) on SARA analysis of the COs and elemental analysis of the corresponding resins. We validated MCO(Asp‑free) as models for the corresponding CO(Asp‑free) by showing that the correlation between Hildebrand solubility parameter (δt) of (COs) and δt for MCO(Asp‑free) is linear with a slope close to unity. Regarding Asp dissolution, we show that the correlations between log­(dissolved Asp, mass %) and each of the following solvent descriptors is linear: empirical polarity of MCOs(Asp‑free); δt of COs; colloidal instability index of COs. Furthermore, the multiple correlation between log­(dissolved Asp, mass %) and other solvatochromic parameters showed that solvent dipolarity and polarizability are important factors for Asp dissolution, in agreement with our previous results on Asp dissolution in pure solvents. The formulation of a model that successfully mimics maltenes is potentially very useful, e.g., in rationalizing the efficiency of certain classes of additives employed for Asp stabilization.