Effect of Crude Oil Fractions on Interfacial Tensions of Novel Sulfobetaine Solutions

The dynamic interfacial tensions (IFTs) of two novel zwitterionic surfactants with different hydrophobic groups, alkyl sulfobetaine (ASB), and xylyl substituted alkyl sulfobetaine (XSB), against kerosene, crude oil, and model oils containing crude oil fractions, such as resins, asphaltenes, saturates, aromatics, and acidic fractions, have been investigated by a spinning drop interfacial tensiometer. The experimental results show that XSB solutions show higher interfacial activity than ASB against kerosene because of the larger size of the hydrophobic part of the XSB molecule. The petroleum acids have high interfacial activity and can adsorb onto the interface. For ASB solutions, the synergism mixed adsorption of betaine and acid molecules lowers IFT values. On the one hand, the partly displacement of XSB molecules by petroleum acid at the interface results in the increase of IFTs. Therefore, resins, aromatics, and acidic fractions show strong effects on IFTs of betaine solutions. On the other hand, asphaltenes and saturates have little effect on interfacial properties. Moreover, the hydrophilic part of the betaine molecule at the interface may vary its orientation from vertical to flat with aging time. Therefore, the dynamic IFT curves of ASB solutions against model oils show "V'' shape for resins, aromatics, and acidic fractions.