Synthesis of imidazolium based gemini surfactants with ultralow critical micelle concentration for chemical enhanced oil recovery process

A novel imidazolium-based ionic liquid ([HC 14 Im]Br) and two gemini cationic surfactants with different spacers constructed based on this ionic liquid (IL) monomer, abbreviated to [HC 14 Im-S-HC 14 Im]Br 2 , where S represents the spacer including propane 2-bromoacetate S1 (C 7 H 10 O 4 Br 2 ) and hydroxypropane 2-bromoacetate S2 (C 7 H 10 O 5 Br 2 ), were designed and synthesized. The characterization results confirm the structure of obtained surfactants. The results also confirmed that both GSs have higher surface activities compared to the conventional monomeric ionic liquid. Based on the surface tension of surfactant solutions ( γ) and interfacial tensions (IFTs) of crude oil/surfactant solutions (σ), the effect of the hydroxyl functional group in the spacer on CMC, the γ and γ at the CMC point, and surface activities were evaluated. The lowest CMC value with high surface activity was achieved for [HC 14 Im-S-HC 14 Im]Br 2 gemini surfactant with the spacer of C 7 H 10 O 5 Br 2 (CMC = 1.4 × 10 −6 mol/L based on SFT measurement and CMC = 3.13 × 10 −6 mol/L based on IFT measurement). Ultralow IFT value after CMC point (σ < 0.1 mN/m) and wettability alteration toward neutral (θ = 88° at 4.64 × 10 −7 mol/L) and water-wet (θ = 55° at 1.16× 10 −7 mol/L) states lead to outstanding spreading coefficient and capillary number improvements. • Novel gemini surfactants (GS) with ultra- low critical micelle concentration (CMC) were synthesized. • The effect of the hydroxyl functional group in the spacer was evaluated. • Both GSs have higher surface activities compared to the conventional monomeric ionic liquid. • Spreading coefficient and capillary number for the dolomite carbonate rock sample were performed. • [C 14 Im-S-ImC 14 ]Br 2 gemini surfactant with the spacer of C 7 H 10 O 5 Br 2 was proposed for use in EOR.