Evaluation of surface activity of asphaltene and resin fractions of crude oil in the presence of different electrolytes through dynamic interfacial tension measurement
It is generally believed that asphaltenes and resins as the polar components in crude oil can get adsorbed at the oil/water interface and act as a surface active agents. However, due to the complex behavior of asphaltenes and resins, the understanding of their surface properties is challenging. In this work, the effects of addition of six electrolytes: NaCl, KCl, Na2SO4, MgSO4, MgCl2, and CaCl2 have been employed to experimentally evaluate their effect on dynamic interfacial tension of asphaltenic and resinous in oil/water interface. All of the electrolytes had the same ionic strength (0.7 M) and the pedant drop shape method was used for analysis. For this purpose, asphaltene and resin fractions of a crude oil sample with 27 API° are extracted and analyzed with elemental and Fourier-transform infrared spectroscopy (FTIR) analyses. Then, two synthetic oils samples prepared based on dissolution of extracted asphaltene and resin in toluene, their dynamic interfacial tension (IFT) values are measured in the presence of different brines. The adsorption/relaxation reorganization times of asphaltene and resin components at the oil samples/aqueous solution interface are evaluated with exponential decay model. Results suggest that divalent cations, Ca2 and Mg2 , possess higher affinity toward the polar groups of asphaltene and resin components in the presence of Cl− compared to SO42−. Specially, Ca2 is more preferred over Mg2 , particularly for resinous oil sample. Due to the higher affinity of the polar functional groups toward the interface in the presence of CaCl2, the lowest adsorption time was obtained for CaCl2, which refers to the time required for coverage and packing of active agents at the interface.
