Synergism/Antagonism between Crude Oil Fractions and Novel Betaine Solutions in Reducing Interfacial Tension

The Shengli crude oil fractions of saturates, aromatics, resins, and asphaltenes (SARA) were obtained by the classic SARA method, and acidic fractions were extracted by ethanol/water (7:3, v/v) solution mixed with 1.5 mass % NaOH. The interfacial tensions (IFTs) of solutions of two different betaines with different structures against n-alkanes, kerosene, and crude oil fractions dissolved in kerosene were studied in this paper. The experimental results show that, for linear betaine, a small quantity of crude oil fractions, especially acidic fractions and resins, can decrease IFTs of the system by forming a mixed adsorption film, which enhances the dynamic behavior and the compactness of interfacial films to some degree. Therefore, it has a synergistic effect between crude oil fractions and linear betaine. However, for the branched betaine with a larger hydrophobic part, it displays the absolutely opposite tendency because a small amount of active substances present in kerosene can have a synergistic effect with the surfactant to achieve ultralow IFTs and the addition of crude fractions relatively affect the arrangement of surfactant molecules on the interface, leading to the obvious increase of IFT values. As a result, it has an obvious antagonistic effect between crude oil fractions and branched betaine.