Langmuir surface and interface films of lignosulfonates and Kraft lignins in the presence of electrolyte and asphaltenes: correlation to emulsion stability

The surface and interface properties of lignosulfonate (LS) and Kraft lignin have been studied by means of the Langmuir technique. Surface films at different bulk concentrations and varying pH, the effect of electrolytes and the interaction of LS and multivalent cations has been studied. The asphaltene fraction from a bitumenous Venezuelan crude oil and LS–asphaltene interface films is analyzed by the same method. The emulsifying properties of LS and aluminum-modified LS are also demonstrated. It was found that the surface activity of the lignin fractions varied as a function of pH and that the surface activity of Kraft lignin were higher than LS. Film loss of LS during film-compression was significant especially for the low molecular weight fraction. The formation of LS/cation complexes altered the surface and interface properties of LS. This was utilized in the formation of stable crude oil emulsions containing large amounts of asphaltenes. The polar nature of the asphaltene fraction was demonstrated by varying pH in the aqueous sub-phase.