Steady State Size Distribution of Asphaltenes by Flocculation From Toluene–n-Heptane Mixtures

The aggregation mechanisms of asphaltenes have been the subject of several recent studies. In this work, we have studied the effect of inhibitors on size distribution of asphaltene particles, in solutions containing toluene and mixtures of n-heptane and toluene. The asphaltenes used have been extracted from Marlim crude oil, using a modified procedure IP-143/82. Several solutions containing one percent volume of asphaltenes have been prepared in pure toluene and in toluene and n-heptane mixtures with and without inhibitors and have been homogenized during a period of 24 h. The particles sizes were determined by filtering the solutions through a set of standard filters ranging from 0.45 to 0.02 µm pore size. In addition, from the saturated filtered solution of asphaltene in toluene, three other solutions were prepared having 10, 20, and 30% volume of n-heptane and were homogenized for 24 h. Again the size distribution of precipitated particles was obtained by filtering. The concentration of asphaltenes remaining in the solution was measured directly by evaporation or by spectroscopy. The results have shown that large part of asphaltenes remain as colloidal particles in the size range tested in toluene solution without inhibitor. On the solutions in which inhibitors were used, one of the inhibitors effectively prevented flocculation, concentrating the asphaltene particles on the smaller size range even on mixtures containing 20 and 30% volume of n-heptane, which is a strong flocculating agent.