Two recent texts (Becher, 1965, Sherman, 1968 have dealt in some detail with emulsions, but little attention has been given to mechanisms of emulsion stabilization by non-ionic materials, in spite of the widespread industrial use of non-ionic surfactants. Emulsions stabilized by these non-ionic compounds present interesting problems not encountered in systems which contain ionic surfactants.At first sight it would appear that stability cannot be explained by the electrostatic repulsive forces which operate in many dispersions, but it is known that pure hydrocarbon droplets dispersed in pure water possess a net negative charge. The problems which arise in the theory of non-ionic dispersions are these. To what extent do electrostatic forces contribute to stability? How is any charge on the dispersed particles affected by the presence of non-ionic detergents or polymer molecules at the interface? What is the nature of other stabilizing forces? Lyklema (1968) recently discussed the principles of stability of colloidal dispersions in non-aqueous media. Much of what he has written is relevant here, although we will restrict our discussion mainly to oil-in-water emulsions. The outline of the theories of stability will thus be kept to a minimum.It is the purpose of this review to consider relevant aspects of colloid stability theory and the relation of some recent experiments to this theory, and to discuss this with regard to the use of these emulsion systems. We will deal mainly with stabilizers which are derivatives of polyoxyethylene glycols.
ASPECTS OF EMULSION STABILITYEmulsions have been defined as heterogeneous systems of one liquid dispersed in another in the form of droplets usually exceeding 0.1 pm (Becher, 1965) in diameter. The two liquids are immiscible, chemically unreactive, and form systems characterized by a minimal thermodynamic stability.Unless the free energy of the oil-water interface is zero, an emulsion cannot be a thermodynamically stable system, since reduction of the area of oil in contact with the water will always result from coalescence of the droplets. "Stability" is therefore a relative term; but the degree of stability can be assessed by observing the rate of change of a parameter such as interfacial area or droplet diameter. Unstabilized emulsions, referred to as oil hydrosols by King (1941), coalesce rapidly, while stabilized emulsions can retain a highly dispersed internal phase for months or years. As the free energy of the interface is the driving force for coalescence, emulsions can be stabilized by the inclusion of a surface-active substance in the * The first of two articles, the second of which will appear on p. 233 et seq. and includes all the references. t Present address :
Asphaltenes and waxes can precipitate and deposit in reservoirs, wells and equipment increasing production and operation costs. Previous studies showed the co-precipitation of these heavy organic compounds under field conditions and that the chemical treatment for one fraction can affect the deposition mechanism of the other fraction. These facts led to a key question: Can solvents that are normally used for asphaltenes remediations affect wax deposition? In this paper, we dealt with the impacts of aromatic solvents addition to a waxy crude and studied characteristics of wax deposits obtained from Cold Finger testing at different ratios of solvent/oil. The results showed that depending on solvent concentration the Wax Appearance Temperature (WAT), composition of paraffins and deposition rate have significantly changed. It was also shown that a biodegradable and low toxicity biosurfactant demonstrated a remarkable efficiency as wax dispersant to control and reduce organics deposition.
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