Demulsification of Highly Stable Water-in-Oil Emulsions

Abstract

Emulsification and subsequent separation characteristics of water-in-crude-oil emulsions are studied using crude oil from the Norsk Hydro, Norway. In particular, the effects of high pressure, carbon dioxide gas, and electric field on the de-emulsification of water-in-crude-oil emulsions are considered. Emulsions of varying degree of stability were produced, and their natural separation rate under gravity was recorded. Emulsions of known separation characteristics were prepared and subjected to separation tests with electrostatic field, surfactant de-emulsifiers, and high pressure in the absence or presence of carbon dioxide. Purpose-built equipment was used in the electric field and pressure experiments. The different levels of emulsion stability were found to depend on the composition of the oil sample as well as the processing conditions. The heavy fractions formed emulsions much more readily and were significantly more stable. The separation enhancement was achieved through the application of high pressures to the emulsions. But the high pressure was not sufficient to have any significant impact when the emulsion was highly stable. The addition of carbon dioxide from a 50-bar supply did not have any effect, adverse or otherwise, on this improvement. Tests with application of a high-voltage electrostatic field on the oil revealed that lower-stability emulsions at least are susceptible to this method of separation. A number of chemicals were also used as chemical de-emulsifiers and were found to have no effect on enhancing the separation. These studies were conducted in order to provide the background for the intensification of the oil/water separation technique developed by the authors.

Acknowledgment

We are grateful to Professor Johan Sjoblom for helpful discussions and to EPSRC (UK) and Norsk Hydro ASA (Norway) for supporting this research.