No abstract

No abstract

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 :

No abstract

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.

Asphaltenes are a major problem for oil industry. Their variability in size, structure and polarity presents a challenge to develop formulations that are effective against precipitation and deposition for all types of asphaltenes. Also, changes in production systems, such as the rate of water break through, can also impact the efficiency of dispersants. In this paper sophorolipids, a class of microbial surfactants, that are renewable and biodegradable with low aquatic toxicity, are tested as asphaltene dispersants. In order to achieve the objectives of this study, asphaltenes were extracted from a heavy oil and their solubility and stability were evaluated at different concentrations of n-heptane and water. The behavior under n-heptane concentration sweep was found to be in line with previous experimental works and water did not change that behavior. The sophorolipids were able to inhibit ~100 % of the polar asphaltenes precipitation at low concentrations. Under similar conditions dodecylobenzesulfonic acid, which was used as a benchmark for comparison, did not perform at concentrations up to 1000 ppm either with or without water. The high performance of biosurfactants is attributed to their enhanced dispersing properties for organics such as wax and asphaltenes.

No abstract

No abstract