Asphalt flocculation and deposition .3. The molecular weight distribution

Extensive new experimental data are presented for the molecular weight (MW) distributions of the asphalt and asphaltene aggregates formed when a solvent is injected into a crude oil. The effects of various factors such as the nature of the solvent, the solvent-to-oil volumetric ratio and ageing of the solution are all investigated. It is shown that if the asphalt- or asphaltene-containing solution has not been aged for long enough, a bimodal MW distribution is always obtained, which is due to the existence of two different types of aggregates with distinct structures and mechanisms of formation. However, after long enough the MW distribution is unimodal. Based on models proposed for the formation of the structure of the asphalt and asphaltene aggregates, which are based on the analysis of small-angle X-ray and neutron scattering and precipitation data, analytical equations are proposed for the MW distribution of the aggregates which provide accurate predictions of the data. Copyright (C) 1996 Elsevier Science Ltd.