Characteristics and solubility of asphaltenes

Asphaltenes form the most complex solubility class in crude oils. Their solubility behavior and other characteristics are important in applications pertaining to the production, transportation and processing of petroleum materials.; The research is divided into two main sections: the aggregation behavior of asphaltenes and asphaltene solubility issues. The aggregation studies were conducted with separated asphaltenes in mixtures of various solvents (toluene, trichloroethylene, tetrahydrofuran and pyridine), and the solubility studies were carried out with oils.; It has been believed that asphaltenes self-aggregate in organic solvents, in a manner similar to other amphoteric molecules (surfactants). This behavior has been described in terms of critical micelle concentration (CMC) of asphaltenes. Recent studies appear to indicate two widely separated concentration ranges as possible CMC values for asphaltenes. Fundamentally, it is not certain that asphaltene aggregation should, in fact, be termed micellar assembly. This research work aims to provide insights about the asphaltene aggregation process. A new measurement technique that provides data on both the aggregation and the solubility aspects is provided.; The new measurement process employs Near-infrared (NIR) spectroscopy to detect onset of asphaltene precipitation. The onset data inherently provide solubility information. The aggregation aspects are deduced using trends in the onset data. For all of the solvents examined, clear break points in the onset values with respect to asphaltene concentrations in the solvent were observed. These break points or transition points in the data signify a mechanism shift in the asphaltene aggregation process and are called Critical Aggregation Concentrations (CACs). It is difficult to establish these transition points using the traditional surface tension or calorimetric measurements. The mechanism shift observed in this research is similar to the diffusion limited aggregation (DLA)/rate limited aggregation (RLA) transition reported using photon correlation spectroscopy, and is in the same concentration range.; For the asphaltene solubility in oil phase, three different precipitants were used. In the carbon number range studied (5--7), more solvent was necessary to initiate precipitation onset as the carbon number of the solvent increased. Addition of toluene stabilized the asphaltenes and also showed that the oil was undersaturated with respect to the asphaltenes. When aromatic solids (phenanthrene and naphthalene) were initially mixed with the oil, the onset of solid deposition was obtained with more amount of precipitant. In case of the addition of solid n-alkane compounds (eicosane and tetracosane), the onset of solid precipitation was observed with less amount of precipitant. Addition of separated asphaltenes to the oil expedites the precipitation onset.