A NormalizedHydrophilic–LipophilicDeviation ExpressionHLDNIs Necessary to Avoid Confusion Close to the Optimum Formulation ofSurfactant‐Oil–WaterSystems

Abstract

AbstractThe physicochemical conditions to attain a minimum interfacial tension between oil and water were intensively studied in the 1970s when the chemical‐enhanced oil recovery became an emergency with the increase in petroleum cost. Correlations between the formulation variables (salinity, oil nature, surfactant and co‐surfactant nature, temperature, and pressure) required to attain a minimum interfacial tension or a three‐phase behavior, so‐called optimum formulation, were related to the chemical potential concept in the late 1970s. They were then transformed in a generalized hydrophilic–lipophilic deviation (HLD) expression in 2000. Some confusion in the ranking and classification of the surfactant parameters with different scales has occurred in recent years. The aim here is to propose a normalized HLDNexpression with the alkane carbon number (ACN) variable scale to clear up the current misunderstanding in the use of different HLD expressions. The use of a single HLDNexpression for all systems improves the prediction of formulation effects, but does not eliminate the limitations due to the partitioning of species in surfactant mixtures.