Effects of Asphaltene Solvency on Stability of Water-in-Crude-Oil Emulsions

Joseph D. McLean and Peter K. Kilpatrick

Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina, 27695-7905

Received 25 July 1996;  accepted 31 January 1997. ; Available online 7 May 2002.

Abstract

The formation of stable and persistent emulsions and foams in the production and refining of crude petroleum is a challenge which has defied broad and generic resolution for several decades. Rational and systematic approaches to demulsification have been slow to develop due to a lack of fundamental understanding of the molecular origins of emulsion stabilization and the full range of factors which govern emulsion stability. Several studies have shown the importance of resins and asphaltenes, which have the ability to organize and form rigid films at the oil/water interface. We have developed a molecular model in which we propose that the integrity of these films and thus their ability to stabilize water-in-crude-oil emulsions are sensitive to a variety of crude solvency parameters, such as aromaticity, resin-to-asphaltene ratio, and polar functional group concentration. This model was tested by correlating the stability of emulsions formed from a variety of crude oils––Arab Berri (Extra Light), Arab Heavy, Alaska North Slope, and San Joaquin Valley––in which the resin and asphaltene contents vary, as well as their specific characteristics. The results of the elemental and functional group characterization of these crudes and their fractions and the techniques utilized to obtain them were presented previously. Detailed quantitative protocols for gauging relative emulsion stability have been developed to further evaluate the proposed model by blending solvents of varying aromaticity and by doping isolated resins from different crudes into solvent-modified crudes. Dramatic destabilization of emulsions was accomplished by modifying the crude solvency in either fashion. Simple physical and chemical techniques for minimizing emulsion formation such as basic crude blending and solvent-recycle schemes will also be discussed.