Enhanced synthesis of branched-chain methyl ester sulfonates via surfactant-assisted sulfonation of methyl oleate

Bio-surfactants are gaining recognition as specialized chemicals in the industrial sector, although their manufacture remains underexplored with limited synthetic pathways. This study aims to encourage the development of environmentally friendly bio-based surfactants from renewable feedstocks, offering a sustainable alternative to surfactants derived from fossil fuels. The study presents the production of a bio-based surfactant, specifically branched-chain methyl oleate sulfonates (MOS), through a surfactant-assisted sulfonation process using methyl oleate (MO) and sodium bisulfite. We investigated the impact of surfactant concentration and reaction time on MO conversion and MOS yield. The findings revealed that the addition of MOS as a surfactant at the onset of the reaction significantly accelerated the reaction rate, potentially lowering production costs. The highest MOS yield, ranging from 80 to 82%, was achieved after 20 h without surfactant addition and in just 10 h with 10 wt% surfactant, under conditions of 40 °C, and a 4:1 NaHSO₃-to-MO molar ratio. The presence of 10% MOS reduced the interfacial tension to nearly one-tenth of the value observed in the absence of MOS surfactant. FTIR, NMR, and surface tension measurements were used to characterize the synthesized MOS. The results indicated that the critical micelle concentration (CMC) of branched-chain MOS surfactant is 5 mM, with 30 mN/m at this concentration.