Solvent Induced Volumetric Changes on Solid Asphaltenes

摘要

The volumetric changes experienced by coals exposed to solvents have been widely studied and reported in the open literature. These studies aim to understand coal structure, the way soluble hydrocarbons are trapped inside the solid matrix and to assess means to improve the yield of valuable products obtained from coal liquefaction processes. The purpose of this work is to investigate the volumetric changes experienced by solid asphaltenes exposed to solvents. Asphaltene samples were isolated from crude oils with diverse operational stability, virgin and cracked residua and tubing deposits as well. The volumetric changes observed for the studied samples were the basis for improving our knowledge on asphaltene aggregation as well as its relation with asphaltene structural properties and crude oil stability. Physicochemical parameters such as aromaticity, density, hydrogen deficiency and heteroatom content were the properties correlated with the observed volumetric changes. At this point of the investigation, all findings suggest that solvent dispersive forces appear to be the properties that influence the behavior the most. Asphaltene swelling in non-polar solvents was successfully fitted using the Flory-Rehner equation. This procedure allows estimating the solubility parameters for the samples, which turned out relatively low. However, solvent donor properties and asphaltene acceptor properties also played an important role in the swelling phenomenom. The former results allowed us to present a structural model for solid asphaltenes. This model proposes the solids to be composed by inner aromatic cores that are impermeable to solvents, surrounded by a aliphatic moieties capable of incorporationg solvents and swell.