ABSTRACT
The methods utilized for the natural surfactants (NS) isolation suggest that they are adsorbed at the oil-water interface at any pH. The NS are a mixture of high and low average molecular weight (Mw) compounds. Since in the crude oil the low MW acids are part of the asphaltene micelles, so both are adsorbed simultaneously at the interface. The natural surfactants maltenes had lower MW and higher H/C values as expected. These data suggest that the NS are a mixture with bulk properties similar to asphaltenes. Models based on diffusion of NS to the interface, carboxylate formation and its transfer to the aqueous phase were proposed by Rubin and Radke and by Trujillo. The idea behind it is the formation of a water-in-oil emulsion where the continuos phase is washed away with an organic solvent. The surface active NS remain adsorbed at the water-oil interface and they are recovered after breaking the emulsion.
