On the application of Diffusion Ordered Spectroscopy - Nuclear Magnetic Resonance combined with Molecular Dynamics simulations to explore the fluid-solid phase change behavior of n-alkanes in synthetic crude oils

We report the use of molecular dynamics (MD) simulation and Diffusion Ordered Spectroscopy - Nuclear Magnetic Resonance (DOSY-NMR) to investigate the incipient solidification of long-chain alkanes in model synthetic crude... [ view full abstract ]

We report the use of molecular dynamics (MD) simulation and Diffusion Ordered Spectroscopy - Nuclear Magnetic Resonance (DOSY-NMR) to investigate the incipient solidification of long-chain alkanes in model synthetic crude oils. We consider pure alkane of tetracosane (C₂₄H₅₀) and triacontane (C₃₀H₆₂), an 8-component wax mixture (C₁₂-C₃₃) and a 12-component model synthetic mixture built upon the compositional information of a waxy crude oil from the Asia Pacific region. It is seen that the DOSY-NMR spectrum captures the appearance of the solid phases by revealing a discontinuity in the diffusion coefficients with decreasing temperature, associated with the formation of glassy (or gel) domains. This transition is predicted by coarse-grained MD simulations employing the SAFT-γ Mie force field. A quantitative agreement is seen between the simulations and the experiments.