Functionalized carbon nanotubes as nanoinhibitors of asphaltene aggregation: a molecular dynamics approach for...

Asphaltene aggregation and deposition pose major challenges in crude oil transport and processing. While extensive experimental studies have explored mitigation strategies, nanomaterials-particularly carbon nanotubes (CNTs)-have emerged as promising inhibitors due to their ability to adsorb asphaltenes and limit their clustering. However, experimental approaches provide limited insight into molecular-scale mechanisms. To address this, molecular dynamics (MD) simulations were performed to investigate interactions between model asphaltenes and CNTs in a toluene/heptane solvent. Five systems were studied: pristine CNTs and CNTs functionalized with carbamoyl (CONH₂), methylcarbamoyl (CONHCH₃), hydroxymethyl (CH₂OH), and carboxylate (COO⁻) groups. Intermolecular interactions and aggregation behavior were analyzed using radial distribution functions (RDF), solvent-accessible surface area (SASA), cluster analysis, hydrogen bonding, and interaction energy decomposition (van der Waals and electrostatic contributions). Results show that CNTs significantly modify asphaltene aggregation, with carboxyl-functionalized CNTs exhibiting the strongest inhibition effect. This performance correlates with enhanced specific interactions between functional groups and asphaltene molecules, leading to reduced aggregation.

Geometry optimizations and vibrational frequency calculations of toluene, heptane, the model asphaltene molecule, and the pristine carbon nanotube were performed using the Gaussian software package. These calculations were carried out within the framework of density functional theory (DFT) using the B3LYP functional and the 6-31G(d,p) basis set. The optimized structures obtained were subsequently used to construct the initial configurations for the molecular dynamics simulations and to derive Mulliken atomic charges for force-field parameterization. All-atom molecular dynamics simulations were performed using GROMACS 2023.3 and the OPLS-AA force field. After energy minimization using the steepest descent algorithm, the systems were equilibrated under NVT and NPT ensembles at 298.15 K and 1 bar. Production simulations were subsequently carried out for 150 ns using periodic boundary conditions and a 2 fs integration time step. Temperature and pressure were controlled using the velocity-rescaling thermostat and the Berendsen barostat, respectively. Long-range electrostatic interactions were treated using the Particle Mesh Ewald (PME) method, while bond constraints were maintained using the LINCS algorithm.