Evaluation of the interfacial tension of binary surfactant mixtures and crude oil using the response surface method

Abstract

Since it is possible to improve the surface activity of surfactants and mixing them to reduce their critical micelle concentration (CMC), this study is aimed to evaluate the binary mixture of different surfactants types including cationic quaternary ammonium surfactant (CTAB), anionic surfactant (AOT) and nonionic dispersing agent (Tween 80) with a cationic imidazolium-based ionic liquid (ILs) including 1-dodecyl-3-methyl imidazolium chloride ([C12mim]Cl). To optimize the interfacial tension (IFT) of crude oil/surfactant solutions and to evaluate the IFT trend as a function of salt concentrations, a central composite design approach (CCD) is used as the design of experiment approach (DoE) using the response surface methodology (RSM). In this way, effects of surfactants concentrations (170–430 ppm), salt concentration (650–38350 ppm), types of surfactants (Tween 80, CTAB, AOT), and volume ratio of [C12mim]Cl: surfactants (1: 2, 1:1, and 2: 1) are being investigated. The statistical data and the interaction of factors is investigated using analysis of variance (ANOVA) approach based on the rotatable CCD design and a quadratic model using total experimental IFT data points of 117. The excellent coefficient of determination (R2 = 0.9984) and adjusted R2 (0.9980) reveal the accurate IFT values prediction using RSM. According to the DoE approach, optimal conditions are obtained with CTAB surfactant with a concentration of less than 200 ppm with a slight change as the salt concentration and its volume ratio with IL is changed.