Effect of the addition of tetramethyl ammonium chloride on the solubility and interfacial activity of a sodium linear alkylbenzene sulfonate surfactant

Abstract

The field of action of surfactants encompasses the formulation of dispersed systems in the chemical and petroleum industry and, particularly, in applications such as enhanced oil recovery (EOR) and chemical dewatering (dewatering). In these applications it is necessary to use hydrophilic surfactants that are not sensitive to salinity and water hardness, minimizing their precipitation and improving their performance in terms of interfacial tension decrease. Some of the most widely used surfactants in the industry are linear alkylbenzenesulfonates (LAS-C15-18) due to their low production costs. However, the use of these surfactants in the oil industry has been limited due to problems associated with their precipitation. In this work, we evaluated the action of tetramethyl ammonium chloride (TMACl) as an additive to improve the solubility of the commercial surfactant LAS-C15-18. Solubility tests performed at T = 8, 25 and 40 °C show that the addition of TMACl significantly improves the solubility of the surfactant (Csurf > 1wt%) in moderately-hard-water (Hardness 96.2 ppm Ca, Mg). These results suggest that TMACl acts as a hydrotrope, enhancing the interactions of the LAS-C15-18 surfactant with the aqueous phase. Likewise, the interfacial tension (IFT) curves with respect to theNaCl concentration in the surfactant-heptane-brine system show that the addition of TMACl improves the formulation quality due to the decrease of the interfacial tension in the HLD = 0 condition, from 0.027 mN/m without TMACl to 0.008 mN/m with 1.5 wt% TMACl. In these systems, the addition of TMACl did not result in a change in optimum salinity (S*). Additionally, the IFT-temperature curves of the surfactant/heptane/aqueous phase (NaCl = 1wt%) and surfactant/heptane/moderately-hard-water systems show IFT minima as the TMACl concentration increases in the aqueous phase. Surfactant precipitation was not observed in these systems.