Environmental Engineering Reference
In-Depth Information
Table 3.1 Stability values
Calculated stability
Starting oil properties
Water-in-oil type Calculated
average stability
Minimum Maximum
4
29
Stable
13
10
5
Meso-stable
2
20
3
Density
>
0.94
Entrained
7
viscosity
>
6000
4
18
Density
<
0.85 or
>
1.0
Unstable
15
viscosity
800,000
Asphaltenes or resins
<
100 or
>
<
1%
however the molecular weight averages about 750Da or more and there is a pla-
nar aromatic structure surrounded by alkane groups, some with heteroatoms, S, N
and O [ 5 ].
The absorption of asphaltenes at the water-oil interface proceeds for a long time
and may still proceed after a year [ 3 ]. This implies that the absorption at the interface
lowers the net energy of the system and thus is favoured thermodynamically. The
bulk concentration of asphaltenes is important and drives the amount that is absorbed
at the interface.
3.4.2 The Role of Resins and Other Components
Several researchers studied the role of resins in water-in-oil formation [ 4 ]. They
noted that the main role appears to be solvation of the asphaltenes in the oil solution.
Others have noted that resins and asphaltenes are somehow correlated in emulsion
stability. Silset et al. [ 9 ] noted that many of the stability differences in emulsions can
be explained by the interactions between asphaltenes and resins. The authors noted
that asphaltenes are believed to be suspended as colloids in the oil with stabilization
by resins. Each particle is believed to consist of one or more sheets of asphaltene
monomers and absorbed resins to stabilize the suspension. Under certain conditions,
the resins can desorb from the asphaltenes leading to increased asphaltene aggrega-
tion and precipitation of the larger asphaltene aggregates.
Some effect from naphthenic acids was also noted, cf. [ 4 ]. Waxes have not been
found to stabilize oil water-in-oil emulsions.
3.4.3 Methods to Study Emulsions
The availability of methodologies to study emulsions is very important. In the
past 15years, dielectric methods and rheological methods and many other methods
 
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