Crude oil-bubble attachment in aqueous solutions of Deep Eutectic Solvents (DESs)

Abstract

Flotation technology can be employed as a soil remediation technique in the removal of oil from contaminated soil. Studies have demonstrated that the efficiency of flotation technology can be significantly improved by using surfactants. Today, Deep Eutectic Solvents (DESs) which are referred to as “green” solvents are increasingly used as a replacement to traditional surfactants. In this study, the attachment of bubbles to crude oil was investigated in various molar ratios (1:2, 1:3 and 1:4) and concentrations (1000, 8000, 15,000, 18,500 and 22,000ppm) of DES. Characteristics of DESs including surface tension, interfacial tension and pH were initially measured. The attachment between bubble and crude oil was then investigated by measuring the contact angle and zeta potential in DES. These experimental results were then verified using the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory. Results showed that DES is able to reduce the IFT of the crude oil-water system. DES 1:2 demonstrated the highest reduction in IFT at a concentration of 22,000ppm (32.4 mN/m) compared to DES 1:3 (35.3 mN/m) and DES 1:4 (35.8 mN/m) at the same concentration. This is hypothesized to be due to the decreasing proportion of cations (choline) to hydrogen bonds. Although the contact angle showed a decreasing trend with increase in DES concentration, the contact angle displayed good attachment (more than 90°) at all concentrations. Based on zeta potential measurements, the optimum attachment is suggested to occur at concentrations between 18,500 and 22,000ppm for all molar ratios of DESs. The DLVO theory further demonstrated that DES 1:2 exhibited the lowest energy barrier for all concentrations in comparison to DES 1:3 and DES 1:4. This theory also verified that DES concentrations above 18,500ppm are preeminent for optimum attachment between crude oil and bubble.