Asphaltenes Precipitated by a Two-Step Precipitation Procedure. 1. Interfacial Tension and Solvent Properties

Abstract

Asphaltenes were precipitated into two fractions using a two-step precipitation procedure. The first fraction was obtained by mixing 3:1volumes of n-pentane/crude oil followed by filtration. In the following step the second fraction was precipitated out from the filtrate using 18:1 volumes of n-pentane/crude oil. Whole asphaltenes were precipitated using 40:1 pentane-to-crude oil ratio. Three crude oils were used and the asphaltene fractions obtained were characterized with regard to onset of precipitation, interfacial tension and radius of gyration. The second fraction was more soluble at increasing heptane-to-toluene ratios, more interfacially active and showed different organization properties at the interface between oil and water. Small angle neutron scattering showed that the second fraction formed aggregates with lower radius of gyration. The results show that asphaltenes consist of fractions with different solvent properties and indicates that asphaltenes should be looked at as more than one solubility class.

Model molecules mimicking asphaltenes

“…They then dissolved these fractions in toluene and determined that the size of aggregates formed and their viscometric properties vary in large extents and are different from the unfractionated asphaltene. Similar conclusions on the self-aggregation properties were drawn by Fossen et al 13,86 for fractions obtained by fractionating asphaltenes using different n-alkane/crude oil ratios.…”

“…Different procedures have been used: multiple precipitation of asphaltenes with different nalkane/crude oil volume ratio 13,14 or toluene/n-heptane volume ratio 15,16 , ultracentrifugation 17,18 , ultrafiltration 15,19 … Although this strategy is interesting, the asphaltene fractions obtained are still very complex and polydisperse.…”

Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

“…Most existing work on the asphaltene fractionation are based on their solubility by precipitating different subfractions of asphaltenes using a mixture of aromatic solvent and aliphatic solvent with varying ratios. 25,87,88 However, it is more instructive to fractionate asphaltene molecules according to their problematic properties of research interest. Here, we introduce a new concept of extended-SARA (E-SARA) (Figure 1), the fractionation of asphaltenes based on their adsorption at oil-water and oil-solid interfaces.…”

Asphaltene fractionation based on adsorption onto calcium carbonate: Part 1. Characterization of sub-fractions and QCM-D measurements

“…Several methods exist, for instance some researchers [7][8][9][10][11][12][13][14] initially precipitated asphaltenes by diluting with an n-alkane and then used a binary mixture of solvents (polar solvent + anti-solvent) to fractionate the precipitated asphaltenes. Other fractionation procedures less commonly used include fractionation by varying the crude oil/n-alkane ratios [15][16][17][18], ultracentrifugation [19,20], ultrafiltration [14], supercritical extraction [21] and gel permeation chromatography [22,23]. Yarranton and Masliyah [7] fractionated the asphaltenes from Athabasca bitumens by varying the toluene/nhexane ratio.…”

“…Similarly, Kharrat [12,13] used THF/n-hexane mixtures to fractionate asphaltenes from Athabasca oil and Morgan Oil and observed that the sub-fraction which precipitates first had more condensed aromatic rings but with less alkyl substitution. Fossen et al [15,16] diluted a North Sea crude with different ratios of n-pentane to obtain asphaltene sub-fractions and found that the interfacial activity was higher for sub-fraction which was less aromatic and contained more alcoholic and carboxylic acid groups in the alkyl chain.…”