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Fatty Acid-Asphaltene Interactions at Oil/Water Interface
Xi Wang, Erica Pensini and Zhenghe Xu
*
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4, Canada
#
Sharath Chandra Mahavadi, Simon Ivar Andersen, and Wael Abdallah ,
Schlumberger, DBR Technology Center, Edmonton, AB, T6N 1M9, Canada
#
Schlumberger Dhahran Carbonate Research Center, Dhahran, East Province, 31942, Saudi Arabia
Jan M. Buiting,
Saudi Aramco, Dhahran, Saudi Arabia
(*Corresponding author: [email protected])
Asphaltenes have been shown to stabilize the water-in-oil
emulsions by forming a viscoelastic interfacial film via
molecular aggregation at the oil/water interfaces. Natural
carboxylic acids and their anions present in crude oil are
able to compete with asphaltenes to adsorb at the crude
oil/water interface, decreasing significantly the crude oilwater interfacial tension. In this study, we designed a group
of experiments that systematically probe the molecular
interactions of naphthenic acid with asphaltenes at the
oil/water interface by determining the Langmuir interfacial
isotherms and measuring the crumpling ratio of water
droplets in crude oil.
Figure 1 shows that stearic acid alone is not able to form
rigid films at the toluene/water interface, while asphaltenes
form more rigid interfacial films. Upon mixing of asphaltenes
with stearic acids, non-ideal (non-additive) behavior of
interfacial isotherms was observed. Stearic acid was found
to soften the asphaltene films and make the films more
expanded and flexible at the interface. The rigidity of the
interfacial films was found to be directly proportional to the
amount of the stearic acid present in the system. Washing
experiments of the top phase with solvent showed that both
asphaltenes and stearic acids adsorbed irreversibly at the
toluene/water interface. Experiments conducted by diffusion
of asphaltenes and stearic acids revealed that the stearic
acid is less likely to adsorbed at the interface than
asphaltenes. However, the general trend of non-ideal
adsorption isotherms is the same as in the case of
spreading experiments.
Crumpling experiments were conducted for the same
systems. The crumpling ratio results in Figure 2 support
general conclusions derived from Langmuir interfacial
isotherm measurements, showing a decrease in film rigidity
with the addition stearic acid. In conclusion, the results from
this research provide a more accurate picture on the role of
surface active organic acids in stabilizing oil-water
petroleum emulsions.
Figure 1: Isotherms measured with 12 ml (1 mg/ml)
asphaltenes and 48 ml (1 mg/ml) stearic acid at the
toluene/water interface, showing the synergy (nonadditive) in increasing interfacial activity and film
rigidity.
Asphaltene
Asphaltene+
Stearic acid
Stearic
acid
Before
Crumpling
After
Crumpling
Figure 2: Crumpling of water droplets in toluene,
illustrating the decrease in crumpling by stearic acid
addition.