Mohammad Hasan Badizad1, Mohammad Mehdi Koleini2, Remco Hartkamp3, Shahab Ayatollahi4, Mohammad Hossein Ghazanfari5. 1. Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran. Electronic address: mohammadhasan.badizad@che.sharif.edu. 2. Sharif Upstream Petroleum Research Institute (SUPRI), Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran. Electronic address: mmkoleini@che.sharif.edu. 3. Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Leeghwaterstraat 39, 2628CB Delft, the Netherlands. 4. Sharif Upstream Petroleum Research Institute (SUPRI), Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran. Electronic address: shahab@sharif.edu. 5. Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran.
Abstract
HYPOTHESIS: The saltwater-oil interface is of broad implication in geochemistry and petroleum disciplines. To date, the main focus has been on the surface contribution of polar, heavy compounds of crude oil, widely neglecting the role of non-polar hydrocarbons. However, non-polar compounds are expected to contribute to characteristics of oil-brine interfaces. METHODOLOGY: Utilizing molecular dynamics simulation, we aim to characterize ion behavior adjacent to hydrophobic organic phases. Concerning natural environments, NaCl, CaCl2 and Na2SO4 electrolytes at low (5 wt%) and high (15 wt%) concentrations were brought in contact with heptane and/or toluene which account for aliphatic and aromatic constituents of typical crude oils, respectively. The reproduced experimental data for interfacial tension, brines density and ions' diffusivities adequately verify our molecular calculations. FINDINGS: Ions accumulate nearby the intrinsically charge-neutral oil surfaces. A disparate surface-favoring propensity of ions causes the interfacial region to resemble an electrical layer and impose an effective surface charge onto the oil surface. Despite absence of any polar site, the effective surface charge density is hydrocarbon-dependent, with the highest and lowest values observed for toluene and heptane interfaces, respectively. Due to accumulation of toluene molecules nearby the brines, the interfacial characteristics of heptol (toluene-heptane mixture) is comparable to that of the toluene phase.
HYPOTHESIS: The saltwater-oil interface is of broad implication in geochemistry and petroleum disciplines. To date, the main focus has been on the surface contribution of polar, heavy compounds of crude oil, widely neglecting the role of non-polar hydrocarbons. However, non-polar compounds are expected to contribute to characteristics of oil-brine interfaces. METHODOLOGY: Utilizing molecular dynamics simulation, we aim to characterize ion behavior adjacent to hydrophobic organic phases. Concerning natural environments, NaCl, CaCl2 and Na2SO4 electrolytes at low (5 wt%) and high (15 wt%) concentrations were brought in contact with heptane and/or toluene which account for aliphatic and aromatic constituents of typical crude oils, respectively. The reproduced experimental data for interfacial tension, brines density and ions' diffusivities adequately verify our molecular calculations. FINDINGS: Ions accumulate nearby the intrinsically charge-neutral oil surfaces. A disparate surface-favoring propensity of ions causes the interfacial region to resemble an electrical layer and impose an effective surface charge onto the oil surface. Despite absence of any polar site, the effective surface charge density is hydrocarbon-dependent, with the highest and lowest values observed for toluene and heptane interfaces, respectively. Due to accumulation of toluene molecules nearby the brines, the interfacial characteristics of heptol (toluene-heptane mixture) is comparable to that of the toluene phase.