Effects of carbon chain length of imidazolium-based ionic liquid in the interactions between heavy crude oil and sand particles for enhanced oil recovery

Increasing demand and dwindling supply of crude oil have spurred efforts towards enhancing heavy oil recovery. Recently, applications of ionic liquids (ILs) for heavy oil recovery and catalytic upgrading have been intensively studied due to their novelty as green surfactants. This paper presents the effects of different carbon chain lengths (n = 0, 2, 4, 6, 8, 10, 12) and concentrations from 1000 to 8000 ppm of imidazolium-based ILs on the oil-sand detachment efficiency at room temperature. Overall, the longest carbon chain length (n = 12), 1-dodecyl-3-methylimidazolium chloride ([DODmim][Cl]), showed highest oil-sand detachment efficiency of approximately 80% at 4000 ppm and beyond, indicating that a CMC point has been achieved. In contrary, the IL without carbon chain length (n = 0), 1-methylimidazolium chloride ([Mmim][Cl]), showed lowest oil-sand separation of a mere 5.7% at all concentrations. Interfacial tension (IFT) and zeta potential measurements further verified the above oil-sand detachment efficiencies, whereby the high oil-sand detachment efficiencies correlated to low IFT of approximately 9.78 mN/m for [DODmim][Cl] at 8000 ppm and high net zeta potential measurements of positively charged oil and sand particles. It is interesting to note that while the zeta potential measurements were all positive for oil particles in IL, the zeta potential measurements of sand particles in IL turned to negative for low concentrations of [Omim][Cl] and shorter carbon chain lengths (n ≤ 6), thus resulting in a mild attraction between the oil and sand particles. Further analysis using the Derjaguin-Landau, Verwey Overbeek (DLVO) theory which showed the inter-particle forces further validated the former oil-sand detachment efficiencies whereby repulsive forces between oil and sand particles occurred only for longer carbon chain lengths of [DODmim][Cl] and [Dmim][Cl].