Solutions Of Asphaltenes In Toluene Research Articles

Solubility and Binding of Water in Toluene Solutions of Asphaltenes

The solubility of water in toluene solutions of asphaltenes is determined, and the state of water molecules in these solutions is studied spectroscopically. A number of water molecules bound to an asphaltene molecule is estimated from the experimental data. Aggregation in the system asphaltene-water-toluene is simulated using the pseudophase approximation, and the Flory-Huggins parameters are estimated for the pair asphaltene-water. The potentiality of this model for simulation of mixed aggregates in the asphaltene-water-toluene systems is discussed.

Electrokinetic Characterization of Asphaltenes and the Asphaltenes−Resins Interaction

The electrophoretic mobility of asphaltene particles formed by precipitation induced by the addition of n-heptane to asphaltene solutions in toluene was measured in water and in nonpolar media. Dispersed in water, the particles presented a negative electrophoretic mobility, whereas in toluene their mobility was positive and around 2.0 × 10-9 m2/V s. When resins were present in the precipitating medium, a coprecipitation of these fractions occurred, indicating an adsorption or binding process of the resins on the nascent asphaltene particles. This interaction, however, did not significantly change the electrophoretic mobility of the asphaltene particles. In contrast with commercial dispersants, resins fail to stabilize asphaltene dispersions. This result indicate that the descriptions representing asphaltenes as a solid phase intrinsically insoluble in hydrocarbon media dispersed by adsorbed resins molecules does not accurately represent the structure of these fractions

Changes in Asphaltene Microenvironments Evidenced by Fluorescence Solvatochromism

This work presents a novel and sensitive procedure to study the behavior of asphaltene solutions in toluene and o-dichlorobenzene. Fluorescence solvatochromism was used to observe changes in asphaltene microenvironments with the increase in asphaltene concentration. The environmentally sensitive molecular probe PRODAN (6-propionyl-2-(N,N-dimethylamino)naphthalene) was selected as the reporter molecule to provide clues as to the polarizability in the vicinity of asphaltene molecules. PRODAN displays substantial polarizability-induced shifting of its maximum fluorescence intensity, a feature that was exploited to characterize the various microenvironments found in asphaltene systems. A preaggregation model was developed to explain the experimental solvatochromic observations, and a definition for the critical aggregation concentration was proposed.

SANS Study of Asphaltene Aggregation: Concentration and Solvent Quality Effects

The structure of asphaltene solutions in toluene was studied by small-angle neutron scattering (SANS) as a function of temperature and concentration. Temperature alters solvent quality, flocculation being expected at low temperature. SANS measurements were carried out at four different temperatures (from 73 down to 8 °C) for solute (asphaltene) volume fractions Φ ranging from ≃0.3 to ∼10%. Asphaltenes were found to form nanometric aggregates, whose average masses (Mw) and radii of gyration (RGZ) increased as temperature decreased. These parameters hardly varied with concentration in the dilute regime Φ ≤ 3−4%, in which no evidence of dissociation was found. At higher Φ, apparent values of the same parameters (Mw and RGZ) decreased as repulsive interactions or aggregate interpenetration reduced the normalized intensity, I/Φ, a phenomenon reminiscent of the semidilute regime of polymers and fractal aggregates. At the two lowest temperatures studied, 8 and 20 °C, a strong scattering at low q signaled flocculation, as some of the asphaltenes formed dense domains of micronic size. This phenomenon occurred throughout the studied concentration range and entailed some limited hysteresis for time scales of the order of a few hours.

Nonlinear optical evidences of aggregation in asphaltene–toluene solutions

Evidences of asphaltene aggregation are presented through the application of the Z-scan technique to study the nonlinear optical response of solutions of asphaltenes in toluene. Strong dependence of the two photon absorption coefficients ( β) with the input intensity was observed for concentrated solutions, as opposed to the observed behavior at low concentration. The results suggest that a change in ( β) occurs as a consequence of aggregation. The results are of importance for the study of dark samples like those relevant for crude oils.

Interaction and Solubilization of Water by Petroleum Asphaltenes in Organic Solution

The relation between the often reported micellization of petroleum asphaltenes in organic solvents and the content of trace water in the solvent was investigated using calorimetric titration. The content of trace water in toluene (ranging from 0 to 0.047%) was found to be the driving force in establishing a measurable critical micelle concentration in the concentration range between 0.2 and 8 g/L solvent. It was determined that, for the three different asphaltenes analyzed, the calorimetric trace in the presence of 0.01% water more likely indicates a stepwise association rather than a classical micelle formation mechanism. On the basis of this result, thesolubilization of water into solutions of asphaltenes in toluene was studied, and a quasi-linear relation between asphaltene concentration and water uptake was observed. From this, the Gibbs free energy of the transference of water into the solution or asphaltene micelle was determined to be around −13.4 kJ/mol at 293 K, which is in the range of hydrogen ...

Viscosity of base-treated asphaltene solutions

The viscosity behaviour of base-treated Ratawi asphaltene-toluene solutions was compared with that of untreated solutions. NaOH solutions (1, 3 and 6 M) were used to treat the asphaltene solutions by mechanical mixing followed by overnight two-phase equilibrium. The treatment noticeably affected the viscosity, particularly for asphaltene volume fractions ( ø) > 0.13. The simple Pal-Rhodes analysis indicated that the systems became very non-ideal, even at ø < 0.1, probably owing to the charges introduced into the asphaltene colloids. The Dougherty-Krieger formula failed to explain the data. The Mooney equation qualitatively characterized the particle polydispersity but not the interactions. The interaction was interpreted by a two-fluid model. The results showed that the interaction potential, V( r), between the asphaltene colloids was extensively modified, corresponding to a longer-range interaction potential, which leads to a much smaller maximum packing volume fraction ø m .

Polydispersity analysis of asphaltene solutions in toluene

We performed a series of small angle neutron scattering (SANS) measurements on asphaltene solutions in toluene at various temperatures to study the structure and polydispersity of asphaltene colloids. In order to extract the polydispersity unambiguously, we developed a method to self-consistently evaluate our analysis. From our polydispersity analysis we found that the SANS data were best interpreted using a spherical model for particle structure and a Schultz distribution for particle sizes. A possible thermodynamic origin of the polydispersity is suggested.

Peptization of asphaltene by various oil soluble amphiphiles

The dispersion of asphaltene in heptane by different oil soluble amphiphiles was investigated. Alkyl phenols show good peptizing properties and partially lose their capacity when oxyethylenic groups are incorporated into the molecule. Primary aliphatic amines also show some ability to disperse asphaltene, but long chain aliphatic alcohols and alkyl benzenes are rather inefficient. Asphaltene solutions in toluene containing alkyl phenols are less sensitive to precipitation by the addition of low molecular weight alkanes. The asphaltene adsorption onto quartz was also reduced by the addition of amphiphiles.