Fundamental Basis for Action of a Chemical Demulsifier Revisited after 30 Years: HLDNas the Primary Criterion for Water-in-Crude Oil Emulsion Breaking

In the past four decades, many experimental studies have confirmed the systematic events occurring at the so-called optimum formulation of surfactant–oil–water systems. At this particular formulation, the adsorbed surfactant at the interface interacts equally with water and oil phases, which is supposed to occur according to Winsor theory to attain a three-phase behavior. A low minimum interfacial tension has been confirmed to take place at optimum in hundreds of reports on enhanced oil recovery (EOR). It also coincides with a very definite minimum in emulsion stability, which is looked after for chemical dehydration or crude oil desalting. A normalized hydrophilic–lipophilic deviation (HLDN) equation was proposed as a multivariable expression that numerically estimates the difference of the surfactant interactions with oil and water. This concept can be applied in crude oil emulsion breaking by considering asphaltenes as being in part a lipophilic surfactant whose effect must be compensated by a hydrophilic demulsifier surfactant to reach the optimum formulation. This is attained through equivalence effects by changing two or more variables, particularly asphaltenes and demulsifier type and concentration, which can be measured through different techniques. Furthermore, in recent studies, asphaltenes are found to exhibit two different lipophilicity levels depending on their self-gathering at or close to the interface, for example, as flat bidimensional nanoaggregates or as three-dimensional clusters. This review presents the know-how reached after 30 years of studying water-in-crude oil emulsion breaking (also known as chemical dehydration) using a formulation approach with the HLD multivariable expression. The first part reviews the fundamental concepts and advances on the HLD equation in relation to simple and complex mixtures. The second part presents several strategies aimed at increasing performance and decreasing demulsifier dosification using the HLDN normalized equation in a qualitative way as well as a quantitative way.