Demulsification of crude oil/water nanoemulsions stabilized by rhamnolipid biosurfactant using enzymes and pH-swing

Sagheer A.Onaizi

Department of Chemical Engineering and Center of Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran 31216, Saudi Arabia.

Abstract

Emulsification is one of the key mechanisms for the enhancement of crude oil recovery. Although it is desirable to create stable emulsions during the recovery process, the formed emulsions must be easy to break in order to recover the emulsified crude oil before processing. Thus, stable crude oil-in-water (CO/W) nanoemulsions stabilized by rhamnolipid were prepared in this work. The stability of the prepared CO/W nanoemulsions was monitored for at least one month. The prepared CO/W nanoemulsions were very stable with no oil or water separation after 30 days of preparation. Enzymatic demulsification was ineffective in destabilizing CO/W nanoemulsions with less than 10% demulsification even after a month of incubating enzymes in the emulsions. Contrarily, switching the emulsion pH to a lower value using HCl resulted in a complete demulsification within 1 h, irrespective of the bioemulsifier dosage used to stabilize the CO/W nanoemulsion. Surprisingly, switching the emulsion pH to a higher value using NaOH also provided a full destabilization of CO/W nanoemulsions when a lower bioemulsifier dosage was used. However, the efficacy of pH-switching using NaOH decreased with increasing the bioemulsifier dosage. To the best of our knowledge, this is the first study demonstrating the complete breakdown of the CO/W nanoemulsions stabilized by rhamnolipid biosurfactant via pH-swing technique. It is also the first study demonstrating the ineffectiveness of subtilisin A and Alcalase enzymes in breaking the tight CO/W nanoemulsions.

Keywords: Rhamnolipid biosurfactant, Crude oil, Nanoemulsion, Enzyme, pH-Responsive demulsification, Emulsion stability.