Investigation on the mechanism of air/condensate bubble flotation of emulsified oil droplet

Crude oil droplets in oilfield-produced water are highly emulsified, and the poor attachment between gas bubbles and oil droplets limits the effectiveness of oil-water separation during flotation processes. This paper proposes a new surface-functionalized bubble called a condensate bubble and evaluates its flotation performance based on surface properties and adhesion theory mechanism to address this issue. The surface chemical properties of the oil droplets were characterized using X-ray photoelectron spectroscopy (XPS), contact angle measurement, and zeta potential. Induction time and flotation tests were conducted to compare the attachment effects between air or condensate bubbles and emulsified oil droplets. The interaction forces were calculated using DLVO and extended DLVO theory. The experimental results showed that crude oil contains functional compounds containing oxygen that make it tough to float. However, the contact angle between the oil surface and condensate bubble was greater than 150°, demonstrating that the condensate liquid bubbles have better hydrophobicity than air bubbles. The micro-flotation experiments indicated that condensate bubbles have a strong collection capacity for emulsified oil droplets, which was confirmed by induction time tests. In 70 mM NaCl brine, the oil removal efficiency of condensate bubble flotation could reach 82%, which was a 30% improvement compared to air bubble flotation. However, DLVO theory failed to predict the flotation with a concentration higher than 10 mM NaCl. The extended DLVO theory accounted for hydrophobic interactions, which were observed due to similar solvent extraction and hydrophobicity of the condensate liquid film. As a result, the condensate bubble-oil droplet system exhibited stronger hydrophobic attraction, successfully confirming and illustrating the superiority of the condensate bubble in flotation.