CROSSOVER KINETICS OF ASPHALTENE AGGREGATION IN HYDROCARBON SOLUTIONS

We have investigated the kinetics of asphaltene aggregation in toluene + n-heptane mixtures with a dynamic light-scattering method adapted t o opaque fluids. Two types of aggregation kinetics have been observed: diffusion-limited aggregation and reaction-limited aggregation. At as phaltene concentrations in toluene below the critical micelle concentr ation of about 3 g l(-1) the aggregation kinetics appears to be solely limited by diffusion. Far above the critical micelle concentration re action-limited aggregation takes place at least in the initial stage o f particle growth. At a concentration of asphaltenes in toluene slight ly above the critical micelle concentration, a crossover between these two types of aggregation kinetics has been observed. We propose a sim ple theoretical expression for the crossover kinetics and also a unive rsal scaled description of the observed phenomena. (C) 1998 Elsevier S cience B.V. All rights reserved.