Molar masses of both n-pentane-extracted and n-heptane-extracted Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO). The initial asphaltene molar mass, at concentrations below 0.5 kg/m3, is ≈1800 g/mol. The asphaltene molar mass is found to increase with asphaltene concentration until a limiting value is reached at a concentration between 10 and 20 kg/m3. The limiting value ranges from 4000 to 10 000 g/mol and depends on the solvent, temperature, and asphaltene fraction. The results suggest that asphaltenes form aggregates of 2−6 molecules in aromatic solvents. Interfacial tensions of asphaltenes in toluene or 1,2-dichlorobenzene versus water were measured for asphaltene concentrations from 0.3 to 100 kg/m3 using a drop volume tensiometer. The interfacial tension decreases linearly with concentration, indicating that no micelles are formed. Hence, the aggregation observed with VPO does not appear to be micellization. Similar results are obtained for Cold Lake asphaltenes.

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Asphaltene properties vary with separation method and sometimes with individual technique. Factors such as contact time, solvent-to-crude oil ratio, and temperature influence asphaltene precipitation and are somewhat standardized. However, the final step in most separations, washing the asphaltene filter cake with solvent, is not standardized. Asphaltene properties can be very sensitive to small amounts of resins and therefore may be sensitive to the amount of washing. Asphaltenes were extracted with three different levels of washing from four source oils (Athabasca, Cold Lake, Lloydminster, and Peace River). In all cases, increased washing decreased asphaltene yield and slightly increased asphaltene density. Increased washing significantly increased molar mass and decreased the solubility of the extracted asphaltenes. A new washing method using a Soxhlet apparatus removed the largest amount of resinous material and yielded asphaltenes with significantly different properties from conventionally washed asphaltenes. Since more resinous material was removed, the Soxhlet method allows a more direct comparison between asphaltenes from different sources. Asphaltenes were also extracted using three standard separation methods, IP 143, ASTM D4124, and a method proposed by Speight. Some property variations between the methods were observed and a set of criteria to obtain consistent samples is proposed.

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The adsorption of Athabasca and Cold Lake C 7 -asphaltenes on stainless steel (304L), iron, and aluminum powders was measured using UV-vis spectrophotometry. The effects of resins, temperature, and n-heptane-to-toluene ratio were also investigated. In all cases, Langmuir (type I) isotherms were observed, indicating that asphaltenes saturated the available surface area for adsorption. The saturation adsorptions of the asphaltenes on metals (0.25-2.7 mg/m 2 ) were of the same order of magnitude as adsorption of asphaltenes on minerals. The saturation adsorptions were less than the monolayer surface coverage observed on water-in-hydrocarbon emulsion interfaces, indicating that there are a limited number of adsorption sites on the metals. Higher molar saturation adsorptions were observed for resins and low molar mass asphaltenes, suggesting that adsorption was limited by the morphology of the metal surface. In general, higher mass saturation adsorptions were observed when asphaltenes self-associated to greater extents and consequently larger molecules adsorbed on the surface.

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One step in asphaltene extraction is to wash the precipitated asphaltenes with the precipitant to remove trapped resinous material. To assess the effect of washing on asphaltene properties, asphaltenes were extracted with three different degrees of washing. Asphaltenes from three source oils (Athabasca, Cold Lake and Lloydminster) were examined. In all cases, increased washing decreased asphaltene yield and increased asphaltene density slightly. Increased washing increased molar mass and decreased the solubility of the extracted asphaltenes significantly.A new washing method using a soxhlet apparatus removed the greatest amount of resinous material and yielded asphaltenes with significantly different properties from conventionally washed asphaltenes. The asphaltenes from the different source oils exhibited similar properties after conventional washing. However, there were significant differences in their properties after applying the soxhlet method. Hence, the soxhlet method allows for a more sensitive comparison of asphaltenes.