Asphaltene flocculation in crude oil systems

Flocculation points of complex systems of the type crude oil + solvent + precipitant were experimentally and theoretically studied. In this work 6 crude oils are combined with the solvents toluene and cyclohexane and the precipitants n-pentane, n-hexane, n-heptane and i-octane. Experimentally, the oil solution was titrated by the precipitant to determine the precipitant volume necessary for flocculation. Detecting the intensity of a light beam which passes the sample, the flocculation point is assumed to correspond to the maximum of the titration curve. The modeling of the flocculation points is based on the simple Scatchard-Hildebrand solubility theory in the framework of continuous thermodynamics. The crude oil is considered to consist of maltenes and asphaltenes. The composition of these two subsets is described by separate continuous distribution functions. The oil species are identified by their solubility parameters reflecting their degree of aromaticity and their content of heteroatoms. Both maltenes and asphaltenes are assumed to obey Gaussian distribution functions with respect to the solubility parameter. In this way only the polydispersity with respect to the solubility parameter is taken into account. The molar mass polydispersity, here, is much less important and, therefore, it will be neglected. To calculate the flocculation points only a single equation has to be numerically solved. The only fit parameter is the number average of the molar mass of the asphaltenes, the experimental values of which are too inaccurate. The comparison of the calculated and the experimental results are surprisingly reasonable considering the simplicity of the model and the inaccuracies of some input data. (C) 1999 Elsevier Science B.V. All rights reserved.