(132a) An Unusual State During the Production of Solid Stabilized Emulsions in Stirred Tanks: Paste

An unusual state
during the production of solid stabilized emulsions in stirred tanks: paste

Solid stabilized emulsions (SSEs)
are alternatives to conventional surfactant based emulsions. In SSEs the
particles get adsorbed at the oil-water interface irreversibly, giving a more
stable emulsion than the conventional emulsions. This is advantageous when the
production of an emulsion is targeted. It may, however, be disadvantageous if
undesired emulsions form in the presence of the three phases ? oil-water-solids.
An example of that is in oil sands processing. The small particles adsorbed at
the oil-water interface form very small and very stable water droplets that are
difficult to separate from the oil. In either case, whether the SSEs are the desired
or the undesired product, there is a lack of knowledge of the necessary process
conditions for the production. The current research on SSEs is limited to geometries
that are not directly applicable to industry such as hand-shaken vials or cells
stirred with homogenizers at overwhelmingly high Reynolds numbers, and to
characterizing the emulsions. Our global objective is to demonstrate the impact
of the process conditions on the production of SSEs in stirred tanks. This work
focuses on an unusual state that the SSEs go through during production: paste
state.

Under continuous mixing, when the
three phases, oil and water-solids slurry, are brought together first a normal
SSE forms. Shortly after, the emulsion turns into a paste of particles in oil
and water. Depending on the process conditions the time it takes to reach the
paste state can be very short, or very long. The paste is not a proper
emulsion, but it is not a complete separation of three phases. This paste state
is similar to the rag layer that is seen during oil sands processing. The rag
layer consists of some small droplets, oil and water phases and sand. Over
time, as mixing of the paste is continued the paste turns back into a normal
solid stabilized emulsion. The specific objective of this work is to determine
the parameters that affect the formation of the paste, and to analyze how they
affect the formation, and the time it takes to reach a paste.  

The salt concentration, particle
diameter, wettability of the particles, solids concentration, hydrodynamics and
Reynolds number were found to affect the formation of the paste and time
required for pasting. The tests were run for two impellers, a Rushton turbine
and a pitched blade turbine, at varying Reynolds numbers, with or without
baffles (with an off-centred impeller).  Phase diagrams that show the regions
where paste forms for each impeller at varying oil, water and solids
concentrations were generated. The emulsion formed after continued mixing of
the paste also exhibited surprising behaviour by completely separating into
three phases. The time required for this separation to occur varies based on
the process conditions.