Influence of the Presence of Sulfur and Oxygen Atoms on Molecular, Thermodynamic and Transport Properties in Hydrocarbon Mixtures

Abstract

Introduction: Crude oil is a complex blend of various hydrocarbon families, with compositions that vary depending on the source well and exploitation duration. To categorize its constituents, SARA analysis divides them into saturated, aromatic, resins, and asphaltenes. Heavy asphaltene- rich crude oils can present challenges like viscosity and pipeline blockages, which are often addressed with viscosity-reducing additives. However, a theoretical framework explaining how these additives affect crude oil is lacking, relying primarily on empirical observations. To optimize these additives, it is crucial to understand the underlying chemical and physical processes. This study hypothesizes that asphaltenic crude oils influence viscosity through colloidal properties linked to molecular interactions. Methods: The research aimed to analyze the impact of sulfur in asphaltenes and oxygen in flow improvers on the transport properties of an idealized crude oil, with the goal of predicting additive feasibility. A methodology that combined computational quantum chemistry and statistical thermodynamics was used. An idealized model of crude oil was created, consisting of non-polar alkanes and polar asphaltenes with sulfur atoms. A flow improver was simulated with an aromatic-aliphatic structure containing oxygen and hydroxyl groups, and viscosity was calculated. Results: This study assessed the transport properties of the mixture using principles of statistical thermodynamics. The theoretical insights revealed that reducing viscosity in asphaltene-rich crude oils with additives depends on several critical factors, including the formation of the dispersed phase, the reduced viscosity of the additive, and the effects of dilution. The research identified a strong link between the enhanced effectiveness of these additives and their structural and molecular properties. Conclusion: The theoretical results suggest that additives that act as viscosity reducers in asphalt crudes achieve optimal performance when they possess both higher polarity and reduced viscosity.