Abstract
We investigated the potential use of choline chloride/urea and choline chloride/glycerol deep eutectic solvents (DESs) and their individual constituents (the salt and the hydrogen bond donor) as surfactants for enhanced oil recovery. The interfacial tension (IFT) between Saudi medium crude oil and different concentrations of these DESs (and their individual components) in 10 wt% NaCl aqueous solutions were measured as a function of temperature. Results showed that the IFT values decreased with the increase of both the DES concentration and temperature. The effect of adding the salt and the hydrogen bond donor (HBD) separately, without forming the corresponding DES, on IFT values was also explored. It was found that, in most cases, adding the DES or its corresponding constituents separately has the same effect on the IFT. Furthermore, H-1 NMR and different 2D NMR analysis (NOESY and HOESY) were used to examine the nature of molecular interactions that occur in studied DESs and how water affects these interactions. It was found that while the content of water is below 25 wt% the interactions of DES' components become weak. However, the addition of 50 wt% water breaks the hydrogen bonding so that no interactions between the HBD and the salt were observed. (C) 2015 Elsevier B.V. All rights reserved.