CO2 was used to break several water-in-crude oil and water-in-model oil emulsions stabilized
by asphaltenic films. The stability of asphaltenic films in model oils having varying H/C ratios
(aromaticities) was also studied upon contact with liquid or supercritical CO2. The efficacy and
kinetics of demulsification appeared to be enhanced with increased CO2 density and mole fraction.
The proposed mechanism by which CO2 destabilizes water-in-crude oil emulsions involves
asphaltene flocculation and precipitation. The emulsions break by flocculating the adsorbed
asphaltenes, leading to film defects, film thinning, film rupture, and water coalescence. The
various factors influencing asphaltene precipitation and emulsion destabilization were studied
in model solvent systems containing asphaltenes and resins. Increasing CO2 pressure, residence
time, temperature, and degree of mixing were found to increase the rate of asphaltene
precipitation. Asphaltene precipitation by CO2 was found to increase in the presence of water
as compared to precipitation from water-free systems. It is apparent that CO2 preferentially
precipitates the most surface-active portion of asphaltenes, leading to a substantial weakening
of the viscoelastic asphaltenic film built around the dispersed water droplets in the emulsion.
The rate of the demulsification process was greatly enhanced when the emulsion was injected
under pressure into compressed CO2 as a result of the enhanced CO2/emulsion volume ratio
and mass transfer rates.