Dynamic interfacial tensions of p-(n-lauryl)-benzyl polyoxyethylene ether carboxybetaine solutions

•The nmin and IFTmin increase with the increase of ethylene oxide group for n-alkane systems.•The electrolyte concentration and ionic type seem to have no effects on ITFs.•The IFT between MEA/C12BExCB and Shengli crude oil can reach ultralow value.•The dispersion of electric charge and the molecular size are the two main factors in dominating ultralow IFT.

The dynamic interfacial tensions (IFT) of four p-(n-lauryl)-benzyl polyoxyethylene ether carboxybetaine C12BExCB (x=0, 1, 2, 3) have been investigated by a spinning drop interfacial tensiometer. The influence factors such as ethylene oxide group, surfactant concentration, organic base, electrolyte concentration and type are explored between C12BExCB solutions and two oils including n-alkane model oil and Shengli crude oil. It is found that the nmin (the minimum alkane carbon number) and IFTmin increase with increase in the ethylene oxide group for n-alkane model oil systems. For Shengli crude oil, the C12BExCB surfactants used alone cannot reduce the IFT to ultralow value. In order to meet the demand, the organic base, monoethanolamine (MEA), is applied together with C12BExCB to form organic base/surfactant system. The results show that there exists a synergistic effect between organic alkaline MEA and C12BExCB surfactant. At optimum MEA concentration (0.10 wt%) and optimum ethylene oxide group number (x=0, 1), the IFT value becomes lower than 10−2 mN/m. All these results show that the interfacial surfactant concentration and the surfactant molecular size are two most important factors in dominating ultralow IFT. Moreover, it is found that electrolyte concentration and type have little effects on IFT and the C12BExCB surfactants exhibit good salinity resistance.