Emulsification of Surfactant on Oil Droplets by Molecular Dynamics Simulation.

Yaoshuang Cheng,Shiling Yuan

doi:10.3390/molecules25133008

Abstract

Heavy oil in crude oil flooding is extremely difficult to extract due to its high viscosity and poor fluidity. In this paper, molecular dynamics simulation was used to study the emulsification behavior of sodium dodecyl sulfonate (SDSn) micelles on heavy oil droplets composed of asphaltenes (ASP) at the molecular level. Some analyzed techniques were used including root mean square displacement, hydrophile-hydrophobic area of an oil droplet, potential of mean force, and the number of hydrogen bonds between oil droplet and water phase. The simulated results showed that the asphaltene with carboxylate groups significantly enhances the hydration layer on the surface of oil droplets, and SDSn molecules can change the strength of the hydration layer around the surface of the oil droplets. The water bridge structure between both polar heads of the surfactant was commonly formed around the hydration layer of the emulsified oil droplet. During the emulsification of heavy oil, the ratio of hydrophilic hydrophobic surface area around an oil droplet is essential. Molecular dynamics method can be considered as a helpful tool for experimental techniques at the molecular level.

Highlights

Asphaltenes are a class of polycyclic aromatic hydrocarbon compounds in crude oil, insoluble in paraffin medium, such as n-heptane, soluble in aromatic crude oil and organic solvent such as o-xylene [1,2]
From the Root mean square displacement (RMSD) of oil droplets in two systems, it can be concluded that the carboxylate asphaltene in system A can enhance the diffusion of sodium dodecyl sulfonate (SDSn) micelle and make the system more stable
The emulsification process of the oil-water emulsion was studied by molecular dynamics simulation when SDSn micelles were mixed with two types of oil droplets

Summary

Introduction

Asphaltenes are a class of polycyclic aromatic hydrocarbon compounds in crude oil, insoluble in paraffin medium, such as n-heptane, soluble in aromatic crude oil and organic solvent such as o-xylene [1,2]. There are many types of asphaltenes [9]. Asphaltenes containing carboxylate are amphoteric, easy to stay at the oil-water interface, and have strong surface activity [10,11], which plays a key role in the emulsification of heavy oil. Micropipette technology [20] was used to study the formation and destruction of the asphaltene molecular membrane at the water/oil interface [21,22,23,24]. Atomic force microscope (AFM) was used to observe the morphology of asphaltene film on the glass or silicon surface [25,26]

Methods

Results

Conclusion