Mechanisms of asphaltene aggregation in toluene–heptane mixtures

The kinetics of asphaltene aggregation in toluene–heptane mixtures has been studied by photon correlation spectroscopy (PCS). The PCS technique was adapted for investigation of opaque liquids. We examined the natural asphaltenes of various origin as well as the same ones with chemically modified metal-porphyrin kernels. The concentration of asphaltenes in toluene varied from 1 to 10 g/l. The theoretical model developed employs Smoluchowski fundamental approach. It allowed us to describe quantitatively the experimental curves for which the universal behavior was found. At asphaltene concentrations below the critical micelle concentration the diffusion limited aggregation (DLA) solely is observed. Above the CMC the reaction limited aggregation (RLA) occurs in the initial stage of particle growth. Then, the aggregation mechanism goes to the DLA. The results obtained prove asphaltene aggregation in hydrocarbon solutions is similar to that of typical colloids.