Properties of Venezuelan Asphaltenes in the Bulk and Dispersed State

Abstract

High oil prices have renewed the interest not only in new sources of energy but also in using more efficiently the available oil reserves, which are mostly of the heavy or bituminous type. Many of the problems associated with processing of heavy crude oils come from asphaltenes, roughly defined as fractions which are soluble in aromatic solvents such as toluene and benzene and insoluble in alkanes such as pentane or heptane (1,2). This scientifically vague definition makes difficult a precise characterization of asphaltenes, which composition and structure depends on the source and it is therefore a matter of discussion. In general, the chemical structure consists of an aromatic nucleus with several benzenic rings surrounded by alkyl chains and heteroatoms (1) .However, it is difficult to estimate a precise molecular weight due to association among molecules (3). The behavior of asphaltenes in solution has also 563 JOS

Electrical Conductivity and Dielectric Properties of Solid Asphaltenes

“…40 °C. Figure B shows that this is fairly close to positions of broad endothermic peaks, observed by DSC studies of solid asphaltenes in ref (curve 1) and ref (curve 2). A second increase of derivatives in Figure A commences at 70−80 °C and obviously continues beyond 105 °C, the upper boundary of the studied temperature range.…”

“…Of immediate relevance to conductivity experiments described in this paper are previous studies of microstructural transformations in solid asphaltenes at temperatures below 100−150 °C. These transformations have been revealed by measurements of thermal properties, mainly by differential scanning calorimetry (DSC). − Masson et al concluded that solid asphaltenes lack a crystalline phase but have an ordered amorphous phase (mesophase), which is identified by an endotherm at around 50 °C in the DSC heat flow curves. They also identified two overlapping glass transitions in the amorphous domains of asphaltenes, with the prevalent one at 70 °C apparently controlled by interactions, involving oligo-aromatic structures in asphaltenes.…”

“…Summarizing, the presence of two phase transformations at ≤100−150 °C and the corresponding two-phase behavior observed by various authors appear to be common properties of asphaltenes from diverse geological/geographical origin. The complexity of thermal curves suggests the occurrence of several molecular processes, probably because of variations of the microstructure of asphaltenes, which are inhomogeneous systems and contain microdomains differing in structure and composition . On the other hand, thermal effects may correspond to aggregation−dissociation of certain components of the asphaltene.…”

“…They also suggested that the presence of the overlapping exotherm was consistent with a fraction of solid asphaltenes dissolving into liquid asphaltenes. Rodriguez-Abreu et al 22 identified in bulk asphaltenes a broad endothermic peak centered at around 60 °C. A step-like variation of the DSC curve at around 40 °C was attributed to the occurrence of a second-order phase transition.…”

Effect of the Asphaltene Oxidation Process on the Formation of Emulsions of Water in Oil (W/O) Model Solutions

“…For the O/W emulsions, the average droplet diameter ranged from 13 to 86 µm, while for the W/O systems ranged from 3 to 9 µm. This result could be due to the increase in the polar group concentration at the interface leads to the reduction of interfacial tension and the formation of W/O emulsions [73,74].…”