Molecular mechanics and dynamics calculations were carried out for asphaltenes and resins from crude oils of different origins. Average structural models were used in order to study the forces that determine the association process of asphaltenes and resins in crude oils. The stabilization energies obtained for asphaltene and resin associates were due mainly to the van der Waals forces between the molecules. Comparatively, the contribution of the hydrogen bonding to the stabilization energy was low. It was also found that few structural changes occur in the molecules due to aggregation. Therefore, the contribution of the conformation changes to the stabilization energy was also very low. According to the results obtained, the stabilization energy of the associates depends on the structural characteristics of the molecules. In particular, the stabilization energy is more favorable for those molecules with lower hydrogen-to-carbon ratio, higher aromaticity, and higher aromatic condensation degree. When diff...

Simulation of Interactions in Asphaltene Aggregates

Adsorption of asphaltenes and resins onto montmorillonite occurs rapidly and to a large extent irreversibly under near-anhydrous laboratory conditions. Factors which influence the adsorption are the exchangeable cation on the clay, the basic nitrogen components of the molecules, and the solvent. As a result of this adsorption, the physical and chemical properties of the clay are drastically altered. The fundamental principles revealed in this study lead to a better understanding of the physical and chemical behavior of clays in petroleum reservoirs.

Interaction of petroleum heavy ends with montmorillonite

Electrokinetic and adsorption properties of asphaltenes

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

Electrokinetic characterization of asphaltenes and the asphaltenes-resins interaction

Electrophoresis is the movement of charged particles suspended in a liquid under the influence of an applied electric field. The usual aims of electrophoresis experiments are the obtaining of information on the electrical double layer surrounding the particles, the analysis of a mixture, or the identification of surface components on the particles (e.g., biological cells).

Electrophoresis of Particles in Suspension

The electrophoretic mobility of asphaltenes in nitromethane

Samples of polyester plastics, upon exposure to solar or carbon-arc radiant energy, were found to form oxidation products which, when reacted with N,N-dimethyl-p-phenylenediamine (DMPDA), produced yellow to brown reaction products. The extent of the reaction was determined directly by the amount of diamine reacted or indirectly by differential colorimetry. Research with this color reaction was extended into the development of tests for measuring the photooxidative degradation of polyesters, rigid poly(vinyl chloride), acrylics, and cellulose acetate–butyrate plastics. The basic colorimetric method was modified as needed for each of these plastics types, by directly measuring the absorbance of the DMPDA solution instead of measuring the amount of DMPDA reacted, by the use of o-, m-, and p-phenylenediamines as replacements for DMPDA in the color reaction, or by a change in the solvent. The reliability of “yellowness” as an indicator of the photochemical stability of plastics was examined.

Measurement of photochemical degradation in certain plastics by color reactions with phenylenediamines

Chemical changes occurring in thermoset polyesters during exposure to solar and carbon-arc radiant energy were determined quantitatively by a color reaction with a diamine, N,N-dimethyl-p-phenylenediamine, in a methanol–benzene solution. The amount of diamine reacting with a specimen and the color change of the treated specimen, as measured by differential reflectance, varied directly with exposure time. Three commercial polyesters (glass fiber-reinforced) exposed under identical conditions showed widely different degradation rates as measured by the amount of N,N-dimethyl-p-phenylenediamine used per specimen. The relative stability of the three materials was independent of irradiation source. The color of the treated specimen was dependent on exposure time.

James R Wright

Papers

The electrophoretic mobility of asphaltenes in nitromethane

Measurement of photochemical degradation in certain plastics by color reactions with phenylenediamines

Colorimetric method for measuring polyester degradation due to weathering

Velocity-depth relationship in microelectrophoresis cell for asphaltenes in nitromethane