Synergetic effect of asphaltenes extracted from polymer containing oil sludge and HPAM at water/toluene interface

The interaction between asphaltenes and hydrolyzed polyacrylamide (HPAM) at the oil-water interface is the key factor leading to the stability of polymer-containing wastewater/oil sludge in the oilfield. In this study, the asphaltenes extracted from polymer-containing oil sludge were systematically characterized and the interaction between asphaltenes and HPAM at the toluene/water interface was studied. We found that asphaltenes had a moderately aromatic structure and a large number of fatty chains. There was a strong π-π stacking interaction among asphaltenes molecules. Asphaltenes and HPAM could reduce the interfacial tension of oil/water, increase the interfacial dilatational modulus, and enhance the stability of emulsion synergistically. Both the asphaltenes concentration and the HPAM concentration affected the interfacial stability. With the changes of the two components concentrations, there was a synergistic or competitive effect between asphaltenes and HPAM at the toluene/water interface. At low concentrations of asphaltenes (C asphaltenes = 100 ppm) the addition of HPAM (C HPAM = 300 ppm) reduced the interfacial tension by 0.52 ± 0.17 mN/m, improved the dilatational modulus by 7.75 ± 0.4 mN/m (the growth rate was 57.33%), asphaltenes molecules and HPAM molecules co-adsorbed on toluene/water interface. For the high concentration of asphaltenes (C asphaltenes = 500 ppm), the addition of HPAM (C HPAM = 300 ppm) rarely reduced the interfacial tension, a few increased the dilatational modulus by 0.69 ± 0.15 mN/m, asphaltenes molecules competed with HPAM molecules to adsorb on toluene/water interface. The presence of HPAM in the aqueous phase changed the emulsion from water-in-oil type (W/O) to oil-in-water type (O/W). The increase of asphaltenes and HPAM concentration is beneficial to the increase of emulsion interfacial film strength (the addition of HPAM increased the yield stress of emulsion interfacial film by 22 times) and the enhancement of emulsion storage stability of 100% maximum. These results provided a theoretical foundation for treating polymer-containing oil sludge in oil fields. • The asphaltene and HPAM can synergistically enhance the interfacial film strength. • The change of concentrations can regulate their synergistic/competitive effect. • The presence of HPAM in the aqueous phase changes the emulsion from W/O to O/W.