Waxy Gels with Asphaltenes 1: Characterization of Precipitation, Gelation, Yield Stress, and Morphology

Abstract

We examine the effects of asphaltenes upon the crystallization behavior of a model waxy oil. Yield stress measurements on the model waxy oils with asphaltenes isolated from Shengli crude oil showed that both the relative amount of wax to asphaltenes and the aggregation state of the asphaltenes affected the crystallization properties of the wax. At very low asphaltene concentrations and high wax concentrations, the yield stress of the waxy gel is not significantly affected. At higher asphaltene concentrations, the asphaltenes significantly degraded the microscopic structure of the wax network and drastically reduced the yield stress. There is a threshold ratio of ∼100 paraffin/asphaltene molecules for such behavior. Asphaltenes produced large decreases in yield stress when they were highly aggregated. Oscillatory testing showed that in such cases asphaltene−asphaltene interactions contributed to the gel strength, in addition to the wax platelet interactions. Asphaltenes increased the wax precipitation temperature at high concentrations when large aggregates were present. However, at lower concentrations where the asphaltenes were less aggregated they suppressed precipitation. The aliphatic nature of the Shengli asphaltenes is an important determinant of the observed decrease in precipitation temperature and yield stress.

Liquid-Solid Phase Equilibria of Paraffinic Systems by DSC Measurements

“…It has been reported that flocculated asphaltenes providing nucleation sites for waxes increase WAT [44], but also it has been reported [30] that asphaltenes decreased very slightly the WAT. According with other studies [45] the effect of the asphaltenes on the WAT depends of the aggregation state of the asphaltenes.…”

Influence of the initial cooling temperature on the gelation and yield stress of waxy crude oils

“…In the current section, gelation was determined by using oscillatory tests as proposed by others (Webber 2001;Venkatesan et al 2003;Coutinho 2004, 2007;Kané et al 2004;Visintin et al 2005;Magda et al 2009;Tinsley et al 2009;Phillips et al 2011). Low-amplitude and low-frequency oscillating shear strain was applied to the oil specimen within the linear viscoelastic region.…”

Structural transitions and physical networks in wax-modified bitumens

“…In other words, in the presence of amidic-functionalised waxes there is a greater tendency for re-arranging a solid internal structure where the solid-like units are made by alternation and association of wax crystals and asphaltene molecules. On the other hand, this is not the first time that similar associations and interactions are observed or hypothesised in bituminous materials and oils (Pauli et al, 2011;Thanh, Hsieh, & Philp, 1999;Tinsley et al, 2009).…”

“…Nevertheless, the chemical nature of wax in bitumen is not so simple and somehow conflicts or complies with the conceptual origin of asphaltenes (Redelius, 2009;Tinsley, Jahnke, Dettman, & Prud'homme, 2009). Many studies were carried out about the nature of petroleum waxes and their effects on bitumen quality.…”