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The right part of Figure 2 shows the results for TF=45°C,
above the critical formation temperatures. The effects of such a
strong pre-heating are rather small. For all flow temperatures the
activation energies are reduced approximately to the level, ob-
served at 20–30°C in case formation at TF=20°C.
The most pronounced changes of activation energies were reg-
istered (central part of Figure 2) after formation of emulsions at
TF=36°C, close to the critical temperature in the matrix crude oil.
In this case activation energies for the W/O emulsion and the crude
sharply increase from 10–12 kcal/mol (42–50 kJ/mol) to
70–100 kcal/mol (290–420 kJ/mol) with flow temperatures decreas-
ing from 30°C to 10–12°C. In contrast, activation energies for bi-
tumen emulsion sharply decrease at low flow temperatures, down
to 1.5 kcal/mol (6.3 kJ/mol) at 13°C. The observed large variations
of activation energies are indicative of notable modifications of the
emulsion’ molecular structures induced by formation in the critical
TF range. These structural modifications we attribute primarily to
the specific molecular processes involving asphaltenes.
Discussion
It is known that asphaltenes may stabilise water (oil) droplets in
emulsions formed by recovery of crudes [4–7] and in bitumen
emulsions [8, 9]. It is mostly the aggregation state of the asphalte-
nes and not their amount that controls the stability of an emulsion.
When asphaltenes start to form large aggregates, their impact on
emulsion stability is the greatest [10, 11]. Accordingly, when the
asphaltene particles/aggregates are dissolved to substantially
smaller units, they no longer produce stabilising effects.
Based on these results, it can be concluded that the asphal-
tene fractions, are primarily responsible for the stability of the
emulsion’s inner structure. The degree of asphaltene aggregation
determines the strength of this structure. Hence the observed
sharp variations of viscosity may be attributed to some specific ag-
gregation processes involving asphaltene molecules.
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