Optimization of chitosan-based demulsifiers via interfacial displacement: A molecular dynamics and principal component analysis approach

Abstract

Chitosan-based materials, distinguished by eco-friendly attributes and tunable side-chain modifications, offer a viable next-generation approach for emulsion separation. The structural properties of asphaltenes, particularly island and archipelago configurations, significantly affect emulsification dynamics in the oil and gas industry. Modifying chitosan enhances its ability to displace asphaltenes at the oil/water interface, thereby expediting emulsion separation. This study focuses on ethylene oxide- and zwitterion-modified chitosan. Experimentally validated molecular dynamics (MD) simulations, coupled with unsupervised learning-based principal component analysis (PCA), are employed to analyze the interfacial displacement. Interfacial tension obtained using pendant drop tensiometry was systematically examined, providing critical validation for the computational predictions. The interfacial tension at varying asphaltene concentrations reveals a strong experimental correlation (R² = 0.95), further confirming the high accuracy of the computational framework. Zwitterion-modified chitosan, despite exhibiting lower interfacial tension, does not show a significant improvement in displacement efficiency. In contrast, ethylene oxide-modified chitosan significantly enhances interfacial displacement efficiency compared to unmodified chitosan, achieving a 22.22–57.15 % increase for island-like asphaltene and a 26.67–44.45 % increase for archipelago-shaped asphaltene. The enhanced performance of ethylene oxide-modified chitosan is attributed to its ability to increase van der Waals interactions with asphaltene, which destabilize asphaltene films and facilitate interfacial displacement. Furthermore, van der Waals interactions between the demulsifier and asphaltenes, rather than electrostatic interactions, are discovered to boost displacement efficiency and demulsification performance. PCA reveals the competitive adsorption between chitosan and asphaltenes at the oil/water interface, driving asphaltene displacement and destabilization, ultimately leading to efficient emulsion separation. This integrated approach not only elucidates the molecular-level mechanistic foundations of chitosan-based demulsification but also provides a versatile framework for the rational design of other biopolymer-based interfacial materials.