  Solvent exchange is a controlled process for dilution-induced phase
separation. This work utilizes the solvent exchange method to reveal the effect
of the mixing dynamics on the asphaltene precipitation process under 20
different mixing conditions using a model system of n-heptane and asphaltene in
toluene. The external mixing between the asphaltene solution and the paraffinic
solvent is strictly controlled. We employed a high-spatial-resolution total
internal reflection fluorescence microscope to detect asphaltene precipitates
with a resolution up to 200 nm. A multiphysics model is used to simulate the
evolution of the oversaturation pulse in the solvent exchange process. Based on
the simulation results, we predicted the effect of the flow rate, dimension,
the orientation of the microfluidic chamber, and temperature on the surface
coverage and size distribution of asphaltene precipitates. The model
predictions of all factors corroborate with the experimental observations.
Local concentration of the solvent and shear forces are found to be the two
main reasons for the change of asphaltene precipitation caused by mixing
dynamics. However, the influence of thermodynamics is more critical than the
mixing dynamics as temperature changes. Through a combination of experimental
and simulation studies, this work illuminates the significance of the
transportation process for the final morphology of asphaltene precipitates and
provides an in-depth insight into the mechanism of mixing dynamics on the
asphaltene precipitation. A smart mixing may be to boost new phase formation
without excessive solvent consumption.
