Interfacial Tension

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2.1.6 Interfacial tension. Interfacial tension is a force that holds together the surfaces of the water and оil phases. When an emulsifying agent is not present, the interfacial tension between oil and water is low. When interfacial tension is low water droplets coalesce easily upon contact. Hоwever, when emulsifying agents are present, they increase the interfacial tension and obstruct the coalescence of water drоplets. Everything what lowers the interfacial tension will aid in separation.
2.1.7 Viscosity. Viscоsity plays two primary roles in the stability of an emulsions.
First, as oil viscosity increases, the migration of demulsifying agents to the water droplets oil-water interface is retarded. This results in larger water droplets
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Flocculation is the process in
Master of Science in Petroleum Engineering____________________________________________________________________________ Gaukhar Nauasheva, s206158
CRUDE OIL EMULSION TREATMENT Page - 11 - which emulsion drops aggregate, without rupture of the stabilizing layer at the interface.
Flocculation may also occur under conditions when the Van der Waals attractive energy exceeds the repulsive energy and can be weak or strong, depending on the strength of inter-drop forces. Creaming, sedimentation and flocculation are all reversible phenomena and the original state can often be regained by application of high shear. A much more severe phenomenon is coalescence, a process in which droplets merge into each other. Coalescence is an irreversible phenomenon
The mechanism of coalescence occurs in two stages:
- film drainage
- film rupture
In order to have film drainage there must be a flow of fluid in the film, and a pressure gradient present. However, when the interfacial film between the droplets has thinned to below some critical thickness, it ruptures, and the capillary pressure difference causes the droplets to rapidly fuse into one droplet. Hence, the
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Less is known that asphaltenes are adsorbed on the inorganic the solid particles and may change the contact angle so much that these particles will be wetted with oil more than with water. Result - oil entrainment in the aqueous phase and the difficulty of treating the solids.
Processing of heavy, "reserve" oils may be accompanied by malfunctions in the desalination apparatus - "asphaltene instability", which is expressed in the formation of large flakes. The deposition of solid particles has become so intense that the machine must be shut down for cleaning. The flakes may also form an intermediate layer between the liquid phases, called "lace" or "beard".
Asphaltene dispersants conventionally used as reagents for preventing contamination.
These polymers prove to be useful in dealing with difficulties that accompany the desalting of heavy asphaltic oils. In this case, they are used as additives to the main demulsifiers [31].
Master of Science in Petroleum Engineering____________________________________________________________________________ Gaukhar Nauasheva,
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