ИСТИНА

We present a scheme for multi-scale simulations of asphaltene precipitation from crude oil. Asphaltenes are formed by one or two polyaromatic “cores” with aliphatic, mostly alkyl, “tails” and heteroatoms and have molecular weight of 600 to 1400 Da. In oil, they are suspended in a form of semicrystalline primary nanoaggregates of 2-3 nm in diameter. In this work, asphaltene aggregation is simulated with dissipative particle dynamics (DPD), for which we develop a forcefield quantitatively fitting to experimental data. We generally follow the “top-down” approach: the parameters are chosen to provide the best match to common thermodynamic properties of reference bulk solutions of hydrocarbons: molar volumes, activity coefficients, and solubilities. Bonded parameters are chosen from the geometrical considerations and atomistic simulation results. With the forcefield, we compose models of characteristic asphaltenes of different molecular mass and geometry and model their aggregation in presence of resins and different solvents. Generally, the results agree with experimental observations [1]. To upscale the simulations of precipitation, asphaltene nanoaggregates are modelled as separate particles, which agglomerate to fractal structures of gradually increasing fractal dimension, slowly forming gel-like and then semi-crystalline bitumen [2]. The models developed for the precipitation problem can be used for the inverse process of precipitate dissolution, which will be the next stage of our studies.