Quantum Chemical Investigation of the Reactivity of Nigerian Crude Oil Asphaltene Fractions with Scale Inhibitors and Implications for Pipeline Chemistry

Asphaltene deposition in crude oil production and transportation pipelines causes blockages that impose enormous economic costs on the Nigerian petroleum industry, and the development of effective scale inhibitors requires detailed quantum chemical understanding of asphaltene molecular structure, aggregation thermodynamics, and inhibitor-asphaltene interaction mechanisms. This study conducted a comprehensive quantum chemical investigation of the reactivity of asphaltene fractions isolated from three Nigerian crude oils of different API gravity and origin, examining their interaction with commercially used and novel inhibitor compounds. Asphaltene fractions were isolated by established precipitation methods and characterised by high-resolution mass spectrometry, nuclear magnetic resonance, and X-ray diffraction. Representative average molecular structures were derived from analytical data and used as input for quantum chemical calculations. Density functional theory calculations at the M06-2X/6-31G level were performed to characterise the electronic structure, dipole moment, HOMO-LUMO gap, and reactivity indices of asphaltene model compounds. Molecular docking studies predicted binding geometries and interaction energies of ten inhibitor molecules with the modelled asphaltene surfaces. Molecular dynamics simulations of asphaltene aggregation in toluene-heptane mixtures with and without inhibitors provided mesoscale thermodynamic insights. The quantum chemical results revealed that heavy Nigerian crude asphaltenes have significantly lower HOMO-LUMO gaps, indicating greater reactivity, compared to light crude counterparts. Phosphonate-based inhibitors showed the highest computed interaction energies with all three asphaltene types. These findings provide an original quantum chemical foundation for the selection and rational design of asphaltene inhibitors for Nigerian heavy crude pipeline applications.

Keywords: asphaltene, quantum chemical calculations, scale inhibitors, pipeline chemistry, Nigerian crude oil