Selective Creaming: A Novel Technique to Isolate Interfacial Organics and Mineral Solids from Water-in-Oil Emulsions

摘要

Characterization of interfacial materials isolated from water-in-crude oil emulsions is a useful tool to reveal the emulsion stability mechanisms. "Heavy water (D_2O) method" is a technique used successfully in the past to isolate the interfacial organics from laboratory-made emulsions containing D_2O droplets. However, isolation of interfacial mineral solids is beyond its capability. The "selective creaming" method proposed in this paper is able to overcome this limitation and is suitable for oilfield/plant emulsions containing H_2O droplets as well. The principle is to modify the density of the hydrocarbon phase first and place a layer of clean D_2O on top. The interfacial material-carrying H_2O droplets are pushed upward through the D_2O layer in a centrifuge. Non-interfacial organics are retained beneath the D_2O layer, and non-interfacial solids sink to the bottom of the hydrocarbon phase. Both contaminants are "selectively" removed from the isolated interfacial materials. This method was applied to a complex industrial system, i.e water-in-diluted Athabasca bitumen froth emulsion. The isolated interfacial organics and solids were characterized using various analytical techniques. The solids concentration on the interface was determined to be 20.9 wt %. The asphaltene concentration was less than 32 wt %. The results suggest that interfacial organics as a whole are the main emulsion stabilizer, but no single organic species dominates the interface. Many other properties of the interfacial materials are consistent with the literature data based on model emulsion studies or bulk solids fractionation. However, the present interfacial sample contains virtually no sodium naphthenates and contains large amounts of 1-5 μm clay platelets, which are significantly larger in size than previous findings. The discrepancies could be due to the differences in sample sources and isolation procedures. Results from this work are likely more relevant to the commercial operations.