Effect of different acidic fractions in crude oil on dynamic interfacial tensions in surfactant/alkali/model oil systems

Abstract

Experimental studies have been conducted in order to elucidate the mechanisms responsible for synergism/antagonism for lowering dynamic interfacial tension (IFT) in surfactant/alkali/acidic fraction model oil systems. The dynamic interfacial tensions of different acidic fractions were measured against alkaline and/or surfactant solutions. The relationships between structure and interfacial tensions were studied. We have found that the acid fractions with the lower average molecular weight ( M n<500) have considerable aliphatics in R side chain and show stronger interfacial activities and dynamic interfacial tension behavior with alkaline solutions. The fractions with the higher average molecular weight ( M n>500) have considerable aromaticity in the R side chain and show lower interfacial activities with alkaline solutions. The acidic fractions in oil phase can influence the partition of added surfactants between the oil phase and aqueous phase, which resulted in the change of interfacial tensions. The acidic fractions with the higher average molecular weight, which have high polarity, influenced interfacial tensions more intensively. The synergism in decreasing interfacial tension in acidic fraction model oil/petroleum sulfonate systems and acidic fraction model oil/alkali/petroleum sulfonate systems can be positive or negative according to the character of oil phase and aqueous phase. The EACN values of different model oils have been measured by using petroleum sulfonate mixtures with various n min values. We have found that antagonism was observed generally when EACN/ n min value was far from unity, while synergism was observed when EACN/ n min value was close to unity.