Dynamic interfacial tension measurement of heavy crude oil±alkaline systems The role of the counterion in the aqueous phase

Abstract

The dynamic behaviour of the interfacial tension at the oil±water interface g (t) for oleic acid and a 90% v/v Cerro Negro±xylene solution had been studied under alkaline conditions. For the system oleic acid in paraf®n, aqueous sodium carbonate with or without added sodium chloride, the usual g (t) behaviour was observed, i.e. g drops to low or ultralow values at short times, remains low during a short period, and then rises to high ( . 1 N m21) values. However, when alkyl amines (ethyl, diethyl and triethyl amine) were used as alkalis in the aqueous phase, g (t) ®rst dropped to a relatively high value (1.5,g,3 N m21) and then remained almost constant afterwards. The presence of sodium chloride in the aqueous phase was required to observed the aforementioned usual g (t) behaviour. From these results it is clear that the presence of sodium ions is esential for both reducing (to very low values) and increasing g (t). It is suggested that ultralow transient (values and the formation of spontaneous emulsion are due to a phase inversion (from w/o to o/w) going through a microemulsion intermediate. q1999 Elsevier Science Ltd. All rights reserved.