Environmental Engineering Reference
In-Depth Information
Fig. 3.1 The relationships between oil properties and the four types of water-in-oil types. a The
differences between stable emulsions (line around shaded area ) and the unstable types or oils that
do not form other types (line around patterned area ). Note the lines indicate the typical boundaries
and the areas are only shown to distinguish the lines. b The relationship between stable emulsions
(line around shaded area) and the entrained type (line around patterned area ). c The relationships
between stable (line around shaded area ) and meso-stable emulsions (line around patterned area ).
d Highlights the relationships between meso-stable emulsions (line around patterned area )and
the unstable type or oils that do not form other types (line around shaded area ). e The property
differences between meso-stable emulsions (line around patterned area ) and the entrained type
(line around shaded area ). Finally, f the relationship between the unstable (line around patterned
area ) and entrained types (line around shaded area )
The values of the stability index are shown in Table 3.1 . This shows that the
stability index can be simply calculated from rheological data and that it can be
used, along with some basic property data such as density and viscosity, to classify
the water-in-oil types.
3.4 Formation of Emulsions
3.4.1 The Role of Asphaltenes
Some researchers reported that asphaltenes were a major factor in water-in-oil emul-
sions more than 45years ago [ 1 ]. The fundamental process is that water-in-oil emul-
sions are stabilized by the formation of high-strength visco-elastic asphaltene films
around water droplets in oil [ 10 ]. Resins could also form emulsions, but resins do
not form stable emulsions, and actually aid in asphaltene emulsion stability by act-
ing as asphaltene solvents and by providing temporary stability during the time of
the slow asphaltene migration. Overall, a wide spectrum of scientists has found that
oil composition is the key factor in water-in-oil emulsion formation including the
amounts and types of asphaltene, resin, and saturate contents.
Asphaltenes represent a very broad category of substances and several scientists
reviewed concluded that the asphaltene content is the most important factor in the
formation of emulsions [ 6 ]. Even in the absence of any other possibly-synergistic
compounds such as resins, asphaltenes were found to be capable of forming rigid,
elastic films which are the primary agents in stabilizing water-in-crude oil emul-
sions. The exact conformations by which asphaltenes organize at oil-water interfaces
and the corresponding intermolecular interactions have not been elucidated. Other
workers have noted that solid particles, such as clays, when present, can stabilize
or enhance the stability of emulsions. This is true of emulsions formed by clay-
containing bitumens. These clay-stabilized emulsions may have differences from
the crude oil and petroleum product emulsions noted in this chapter.
Asphaltenes are a class of substances defined only by their precipitation from oil
in pentane, hexane, or heptane. The specific structure of asphaltenes is unknown,
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