Eﬀects of Block Copolymer Demulsiﬁers on Langmuir Films of Heavy and Light Crude Oil Asphaltenes Marcos D. Lobato, Jose ́ M. Pedrosa,* and Santiago Lago Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Carretera Utrera, km. 1, 41013 Sevilla, Spain ABSTRACT: Three diﬀerent n-heptane (n-C7) asphaltenes were extracted from three crude oils, two heavy and one light, and their ﬁlm-forming properties at the air-water and heptane-water interfaces were investigated using a Langmuir trough. Surface pressure-area isotherms, compression-decompression cycles, and stability curves were carried out to get a better understanding about the asphaltene behavior at these interfaces. Although the light crude oil extract shows more contracted isotherms at the air-water interface that have been associated with a faster association dynamics, its ﬁlms have been found to be more stable with more reproducible compression-decompression cycles. The inﬂuence of two demulsiﬁers (silicone copolymers) on the asphaltene ﬁlm properties has been studied by preparing diﬀerent mixtures of asphaltenes and demulsiﬁers, and the interaction between them at the air-water and liquid-liquid interfaces has been investigated by obtaining surface pressure-area isotherms to check the excess area (deviation from the additivity rule) for diﬀerent mole fractions of demulsiﬁer at a given surface pressure. Signiﬁcant deviations from the additivity rule have been found for almost all mixed ﬁlms studied, which has been attributed to the penetration and dispersion produced by demulsiﬁers in a real mixing with asphaltenes when they are spread at the interface. All these experiments have been completed with Brewster angle microscopy (BAM), where the in situ images at the interface show the eﬀect of the demulsiﬁers on the ability of the asphaltenes to form highly aggregated surface ﬁlms. Clearly, these ﬁlms are already disaggregated and dispersed by a proportion of block copolymers as low as 0.1 mole fraction with total or partial disappearance of bright domains and clusters. 1. INTRODUCTION Asphaltenes are by deﬁnition a solubility class of material that is soluble in toluene but insoluble in n-alkanes such as n-pentane or n-heptane. 1 A typical structure would be formed by aromatic rings, short alkyl chains associated to these rings, heteroatoms (N, O and S), associated metals, and hydrophilic moieties (-OH, -COOH and NHO- groups). 2-7 Because of the surface activity of these compounds, many studies about asphaltenes at the air-water or liquid-liquid interfaces have been carried out. 7-20 In these investigations, the main conclusion that can be drawn is the ability of the asphaltenes to self-organize at the interface, reducing the surface tension when they are spread onto it. Asphaltenes are commonly considered to be responsible, along with resins and particles, for the stabilization of water-in- oil emulsions. 7-22 The destabilization of this kind of emulsions is one of the most important tasks in the petroleum industries. Problems with corrosion in pipelines and reservoirs, along with extra costs of recovery and transport, make the resolution of this problem a fundamental issue for these companies. Also, the great environmental damage produced by marine oil spills as Erika 23 (France, 1999), Prestige 24 (Spain, 2002), or BP 25 (Gulf of Mexico, 2010) motivates the study of this subject in order to understand the emulsiﬁcation process. Traditionally, the mechanisms used to break stable emulsions are electrical dehydrators and mechanical separators combined with added demulsifying agents. 26 This has led to many investigations focused on the use of demulsiﬁers at interfaces. Daniel-David et al. studied the interfacial properties of a water- soluble silicone triblock copolymer at the air-water interface 27 as well as the elastic properties of the crude oil/water interface in the presence of polymeric emulsion breakers. 28 They found that the water-soluble copolymer formed insoluble monolayers on water either by deposition or adsorption from the subphase and conﬁrmed its demulsifying activity on the crude oil ﬁlms. Dalmazzone and co-workers 29 studied the eﬀect of silicone demulsiﬁers on the crude oil/water interface showing the inhibition of the emulsiﬁcation process produced when the demulsiﬁers were added to the oil phase. Djuve et al. 26 used low and high molecular weight demulsiﬁers to destabilize crude oil and asphaltenes based water-in-oil emulsions. They concluded that a signiﬁcant lowering of interfacial tension and adsorption to the interface are necessary but not suﬃcient conditions for an eﬃcient demulsi ﬁer. Kang et al. 30 studied several demulsiﬁers, concluding that the demulsiﬁcation mechanism is based on the partial replacement of the emulsiﬁers in the oil ﬁlm by demulsiﬁers, which leads to a decrease in the interfacial viscosity and elasticity. Recently, Le Follotec and co-workers 31 used Langmuir troughs, optical microscopy and atomic force microscopy to prepare mixed ﬁlms of asphaltenes and triblock copolymers and to check their interfacial and demulsifying properties. There are various investigations carried out to show the inﬂuence of demulsiﬁers on Langmuir ﬁlms built only with asphaltenes as the emulsifying agent. Although the change of operating conditions (performance of emulsions in a natural medium, mixture of oils, etc.) and the scale up, with extrapolation and changes in concentration, can be a problem in a real environment, these studies are useful in obtaining a Received: February 5, 2013 Revised: December 13, 2013 Article pubs.acs.org/EF © XXXX American Chemical Society A dx.doi.org/10.1021/ef402055v | Energy Fuels XXXX, XXX, XXX-XXX