Coalescence inhibition and agglomeration initiation near the critical dilution of asphaltene precipitation

In bitumen recovery from oil sands, solvent addition is used to destabilize the water-in-diluted bitumen emulsions and separate the valuable oil product from water and solids. For each solvent, a critical solvent-to-bitumen ratio or critical dilution can be determined that coincides with the onset of bulk asphaltene precipitation, at which the system properties change abruptly. Above the critical dilution, solvent addition promotes bulk asphaltene precipitation and separation by the agglomeration of water droplets, solids and precipitated asphaltenes. Below the critical dilution, separation occurs by the coalescence of water droplets. The properties of the water-diluted bitumen interface could be key to improving the mechanistic understanding of water-in-diluted bitumen emulsions and bitumen recovery. In this work, we explore the behavior of water-in-diluted bitumen emulsions at macro- and microscopic scales, and provide novel insights at conditions below critical dilution. Bench scale bitumen froth treatment settling experiments highlight the possibility to attain effective water and solids separation based on agglomeration, without any noticeable bulk asphaltene precipitation. Light microscopy images reveal the inhibition of water droplet coalescence and the initiation of agglomeration due to the transformation of the oil continuous phase into a gel-like structure in the contact zone between water droplets. Thin liquid film observations show drastic changes in the continuous oil phase properties in the contact zone between water droplets at similar conditions that are attributed to the formation of both asphaltene aggregates at the interface and an oil gel-like structure that expands around them. These findings lead to the proposal that agglomeration can occur below critical dilution by surface asphaltene precipitation at the water-oil interface, without bulk asphaltene precipitation. The multiscale insights highlight opportunities to improve further not only bitumen froth treatment but also other oil-water-solids separation processes.

Automated summary

The study shows that agglomeration can occur below critical dilution by surface asphaltene precipitation at the water-oil interface, without bulk asphaltene precipitation. This finding highlights opportunities to improve not only bitumen froth treatment but also other oil-water-solids separation processes further.