Investigation of Asphaltene Association with Vapor Pressure Osmometry and Interfacial Tension Measurements

• Published in: Industrial & engineering chemistry research Vol. 39; no. 8; pp. 2916 - 2924
• Main Authors: Yarranton, Harvey W, Alboudwarej, Hussein, Jakher, Rajesh
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07.08.2000
• Subjects: Applied sciences; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; Asphaltene; Vapor pressure; Chemical precipitation; Interface tension; Crude oil; Measurement method; Osmometry; Experimental study; Bitumen
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie000073r

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.