Interfacial and electrokinetic properties of asphaltenes and alkali/sur- factant/polymer in produced water system Ling Miao a , Feng Li a , Dejun Sun b , Tao Wu b,n,1 , Yujiang Li a,n,2 a Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science & Engineering, Shandong University, Jinan 250100, PR China b Key Laboratory of Colloid & Interface Science of Education Ministry, Shandong University, Jinan 250100, PR China article info Article history: Received 21 January 2015 Received in revised form 18 May 2015 Accepted 22 May 2015 Available online 27 May 2015 Keywords: Asphaltene Emulsion Interface Adsorption abstract Oil-in-water (O/W) emulsions were prepared to mimic water produced by alkali/surfactant/polymer (ASP) flooding. We used a model oil system consisting of asphaltenes precipitated from bitumen and that were then dissolved in toluene–heptane mixtures (6:4, v/v). Different amounts of ASP agents were in- itially added to brine and these solutions were used as the aqueous phase. Static and dynamic interfacial tension, interfacial rheology, and zeta potential measurements were used to investigate emulsion sta- bility. At an asphaltene concentration of 8 g/L, when ASP coexists with asphaltenes in the bulk phase, a much higher elastic modulus was obtained. After aging for 10 h, the nearly constant values of the elastic modulus indicated that the interfacial film was quite stable. The static and dynamic interfacial tension rapidly decreased with an increase in ASP concentrations, which can be attributed to the combination of diffusion, adsorption, and cross-linking interactions between asphaltenes and ASP to form a three-di- mensional network structure. Asphaltene molecules that adsorbed at oil/brine interfaces rearranged with increased aging time. These factors should enhance the elastic modulus. The elastic modulus is an im- portant property of emulsion stability, and a rigid and viscoelastic interfacial film inhibits emulsion droplet coalescence. Addition of ASP had the most significant effect on the zeta potential of the emulsion droplets. The zeta potential of the emulsion droplets became more negative, resulting in an increase in electrostatic repulsion. These observations further confirmed the role of ASP in controlling interfacial electrokinetic properties through specific interactions with hydroxyl groups, hydrophilic headgroups and hydrophobic chains of the surfactant and polymer at oil/brine interfaces. The synergetic effect of elec- trostatic repulsion, adsorption, cross-linking, and molecular rearrangement were the main mechanisms that stabilized the O/W emulsions. & 2015 Elsevier B.V. All rights reserved. 1. Introduction In the petroleum industry, the presence of stable oil-in-water (O/W) or water-in-oil (W/O) emulsions are considered to be un- desirable and have to be separated into oil and water. The for- mation of a viscoelastic, cross-linking network of asphaltene ag- gregates at the oil/water interface has been found to be mainly responsible for the stability of emulsions by forming a physical barrier for droplet–droplet coalescence (Liu et al., 2006; Nen- ningsland et al., 2014; Qiao et al., 2008). Aggregation and ad- sorption of asphaltenes at the oil/water interface is very important with regard to emulsion stability properties. The formation of stable O/W emulsions in the production of crude oil or bitumen from oil sands causes numerous problems because of the diffi- culties in separating oil from water, and has attracted research interest in recent years. Understanding the factors affecting the stability of O/W emulsions is of great importance to the petroleum industry (Bouriat et al., 2004; Gu et al., 2002). The need to mini- mize the formation of diluted asphaltene-in-brine emulsions and the impetus to develop new technologies for effective treatment of produced water from crude oil or bitumen have become more acute for the petroleum and oil sands industries (Gu et al., 2002). One of the main challenges is the loss of asphaltenes due to ad- sorption on displacing fluids followed by discharge into the water environment. In many aquatic systems (lakes, rivers, and oceans), even a low concentration of asphaltenes can become associated with suspended particulate matter present in the system either by physicochemical adsorption or biological uptake. They may act as mediums for other pollutants such as surfactants and chemicals (Nenningsland et al., 2014). Certain asphaltenes are considered harmful and may have undesirable impact on human beings, Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/petrol Journal of Petroleum Science and Engineering http://dx.doi.org/10.1016/j.petrol.2015.05.018 0920-4105/& 2015 Elsevier B.V. All rights reserved. n Corresponding authors. E-mail addresses: wutao@sdu.edu.cn (T. Wu), yujiang@sdu.edu.cn (Y. Li). 1 Fax: þ86 531 88365437. 2 Fax: þ86 531 8 8363358. Journal of Petroleum Science and Engineering 133 (2015) 18–28