Solvent Extraction for Heavy Oil from Carbonate Asphalts─Experiment and Molecular Dynamics Study

Abstract

We have systematically studied the effects of solvents such as benzene, toluene, isooctane, and cyclooctane on the selective separation of four heavy oil components (saturates, aromatics, resins, asphaltenes), aiming to clarify the molecular mechanism of solvent extraction as an oil–solid separation method in heavy oil extraction. However, the time-dependent extraction kinetics and the detachment behavior of different saturates, aromatics, resins, and asphaltenes (SARA) fractions from mineral surfaces under solvent action remain insufficiently understood. In this work, solvent extraction experiments were combined with molecular dynamics simulations to analyze solvent-dependent extraction behavior from the perspectives of SARA-selective recovery, molecular diffusion, solvent–solute interaction, and oil–solid interfacial detachment. In terms of experiments, we used SARA component analysis, contact angle measurement, and oil–solid interaction force test to comprehensively characterize the extraction efficiency and interface behavior. In addition, we used Materials Studio 2022 software and COMPASS II force field to simulate molecular dynamics. By analyzing the evolution of molecular conformation, mean-square displacement (MSD), radial distribution function (RDF), and concentration distribution, the diffusion and interaction kinetics of molecular scale are revealed. Based on comprehensive experimental and simulation results, we found that four solvents showed remarkable selectivity: toluene was the best solvent for asphaltenes, while isooctane excelled in separating saturates. The MSD analysis revealed the diffusion order of “saturates > aromatics > asphaltenes > resins”, and the RDF results indicate structure-dependent solvent–solute interactions among different SARA fractions. On this basis, we propose that the solvent extraction behavior can be interpreted by a combined mechanism involving molecular structure matching, solvent–solute interactions, diffusion behavior of SARA fractions, and oil–solid interfacial detachment. This mechanism, together with the established correlative interpretation of solvent-heavy oil component interaction, provides a mechanistic reference for the reasonable design of efficient heavy oil extraction process. Compared with previous studies that mainly focused on solvent screening, extraction yield, or process optimization, this work provides an integrated experimental-simulation interpretation of solvent-dependent extraction behavior by linking SARA-selective recovery, extraction kinetics, oil–solid interfacial detachment, and MD-derived diffusion/RDF evidence in carbonate asphalt systems.