Synthesis of novel ethoxylated quaternary ammonium gemini surfactants for enhanced oil recovery application

Two aspects are always considered in the design and development of new surfactants for oilfield application. One of them is that surfactant must be sufficiently stable at reservoir temperature and the other is the solubility of the surfactant in the injection water (usually seawater) and the formation brine. Most industrially applied surfactants undergo hydrolysis at elevated temperature and the presence of reservoir ions causes surfactant precipitation. In relevance to this, a novel series of quaternary ammonium gemini surfactants with different length of spacer group (C8, C10, and C12) was synthesized and characterized using FT-IR, ¹³C NMR, ¹H NMR, and MALDI-TOF MS. The gemini surfactants were prepared by solvent-free amidation of glycolic acid ethoxylate lauryl ether with 3-(dimethylamino)-1-propylamine followed by reaction with dibromoalkane to obtain quaternary ammonium gemini surfactants. The gemini surfactants were examined by means of surface properties and thermal stabilities. The synthesized gemini surfactants showed excellent solubility in the formation brine, seawater, and deionized water without any precipitation for up to three months at 90 ^◦C. Thermal gravimetric data revealed that all the gemini surfactants were decomposed above 227 ^◦C, which is higher than the oilfield temperature (≥90 ^◦C). The decrease in critical micelle concentration (CMC) and surface tension at CMC (γ_cmc) was detected by enhancing spacer length in the order C8 > C10 > C12 which suggested that the larger the spacer, the better the surface properties. Moreover, a further decrease in CMC and γ_cmc was noticed by enhancing temperature (30 ^◦C > 60 ^◦C) and salinity (deionized water > seawater). The current study provides a comprehensive investigation of quaternary ammonium gemini surfactants that can be further extended potentially to use as a suitable material for oilfield application.