Surfactant molecules are tested as water-in-crude emulsion breakers to attain the quickest separation rate in the so-called “proportional regime”. A concept of demulsifier performance is proposed on the basis of the required demulsifier concentration to offset the effect of a given amount of asphaltenes. The experimental evidence allows one to rank the tested products and relate their performance to their hydrophilicity and molecular weight. Some evidence indicates that the presence of acids in the crude makes it easier to break emulsions and suggests that so-called “extended surfactants” can significantly shorten the demulsifying process.

Hydrophilic surfactant molecules with the proper formulation are able to break W/O emulsions stabilized by asphaltenes and other lipophilic amphiphiles as found in the effluent of petroleum wells. The demulsifier performance is here tested according to two critera. The first one, as in previous research, is the minimum dose of demulsifier used to attain the minimum stability at the so-called optimum formulation in a simplified bottle test. The second criterion is the value of this minimum stability at optimum formulation that has a direct relation with the separation time. Our findings show that in a family of ethoxylated surfactants, the best demulsifier is a hydrophilic one, though not too much. When the demulsifier is a mixture of two surfactants, it usually exhibits an intermediate behavior between the components. However, the mixture sometimes appears to be better than any of the components alone with some synergistic effect that improves the performance.

The performance of several extended surfactants as water-in-crude oil emulsion breakers was evaluated using two criteria: (1) the demulsifier dose required (C D*) to attain the minimum stability at the so-called optimum formulation, and (2) the corresponding low minimum stability value. These surfactants were found to behave in the same way as typical commercial demulsifiers do; i.e., they require a lower dose C D* when their hydrophilicity is slightly greater. The reported data for a dozen different extended surfactants indicate how the two performance indices are altered by changing the structure characteristics, such as the propylene oxide number, the ethylene oxide number, and the ionic polar group (carboxylate, sulfate, phosphate). The best performance as a demulsifier seems to depend on the proper combination of these structures to attain a well-fitting compromise.

Stable water-in-oil emulsions with water volume fraction ranging from 10 to 70 vol % have been developed with mineral oil 70T, Span 80, sodium di-2-ethylhexylsulfosuccinate (AOT), and water. The mean size of the water droplets ranges from 2 to 3 μm. Tests conducted show that all emulsions are stable against coalescence for at least 1 week at 2 °C and room temperature. Furthermore, it was observed that the viscosity of the emulsion increases with increasing water volume fraction, with shear thinning behavior observed above certain water volume fraction emulsions (30 vol % at room temperature and 20 vol % at 1 °C). Viscosity tests performed at different times after emulsion preparation confirm that the emulsions are stable for 1 week. Differential scanning calorimetry performed on the emulsions shows that, for low water volume fraction emulsions (<50 vol %), the emulsions are stable upon ice and hydrate formation. Micromechanical force (MMF) measurements show that the presence of the surfactant mixture has little to no effect on the cohesion force between cyclopentane hydrate particles, although a change in the morphology of the particle was observed when the surfactant mixture was added into the system. High-pressure autoclave experiments conducted on the model emulsion resulted in a loose hydrate slurry when the surfactant mixture was present in the system. Tests performed in this study show that the proposed model emulsion is stable, having similar characteristics to those observed in crude oil emulsions, and may be suitable for other hydrate studies.

Asphaltenes tend to aggregate in different structures depending on the aromatic content of the oil phase. The different aggregates adsorb at the interface as some kind of lipophilic surfactant, which tends to stabilize water-in-oil emulsions. Hydrophilic demulsifier molecules are added to combine with asphaltenes until the optimum formulation is attained at HLD = 0, thus resulting in the emulsion instability. It is found that with the change of asphaltenic aggregate structure produced by the aromatic content of the oil, its surfactant-like effect at the interface is also altered. The performance of dehydration is significantly improved with only 5% of aromatic additive in the oil phase.

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 (HLD N ) 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-incrude 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 HLD N normalized equation in a qualitative way as well as a quantitative way.

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High oil prices have renewed the interest not only in new sources of energy but also in using more efficiently the available oil reserves, which are mostly of the heavy or bituminous type. Many of the problems associated with processing of heavy crude oils come from asphaltenes, roughly defined as fractions which are soluble in aromatic solvents such as toluene and benzene and insoluble in alkanes such as pentane or heptane (1,2). This scientifically vague definition makes difficult a precise characterization of asphaltenes, which composition and structure depends on the source and it is therefore a matter of discussion. In general, the chemical structure consists of an aromatic nucleus with several benzenic rings surrounded by alkyl chains and heteroatoms (1) .However, it is difficult to estimate a precise molecular weight due to association among molecules (3). The behavior of asphaltenes in solution has also 563 JOS