Primary submicron particles from early stage asphaltene precipitation revealed in situ by total internal reflection fluorescence microscopy in a model oil system

Paraffinic froth treatment (PFT) is an essential step in oilsands extraction. The ability to quantitatively understand and control asphaltene precipitation induced by solvent dilution is key to technology innovation in PFT process. In this work, we investigate the early stage of asphaltene precipitation in a model oil system in response to diffusive solvent addition in quasi-2D confinement. Using total internal reflection fluorescence microscope, we provide direct visualization of the size distribution and structural characteristics of asphaltene precipitates with a spatial resolution of ~200 nm and temporal resolution of 250 ms. Our results show the correlation between the size and number of the asphaltene particles and the concentration of the paraffinic solvent in the diluent. Notably the aggregates were found to consist of primary submicron particles with a similar size from 200 nm to 400 nm in radius. These particles may be the primary elementary units that aggregate and form bigger particles via aggregation. The growth time of asphaltene particles decreases with increase n-pentane concentration in the observation area. The findings from this work provide new insight into the effects of solvent mixing on the size distribution and morphological characteristics of asphaltene precipitates that are important for association with water and solids and separation properties.