Comparing the performances of different sulfonating agents in sulfonation of methyl esters synthesized from used cooking oil

Abstract Methyl ester sulfonate (MES) is considered as an efficient and novel surfactant used as main active ingredient in cleansing products. MES is often produced via sulfonation of methyl ester (ME) with sulfonating agent. In this study, ME was synthesized from used cooking oil (UCO) via transesterification and then sulfonated to produce MES using two different sulfonating agents (chlorosulfonic acid (CSA) and sodium bisulfite (NaHSO3)). The influence of various factors (temperature, sulfonating agent/ME molar ratio and time) on MES yield was investigated. Analysis of optimal MES samples was carried out using different techniques (GC-FID, FTIR and 1H NMR). The maximum MES yield of 88.2 % was achieved with CSA/ME molar ratio of 1.2:1 at 70 °C for 3 h while the highest MES yield of 79.4 % was obtained with NaHSO3/ME molar ratio of 1.2:1 at 90 °C for 3 h. FTIR and 1H NMR analyses revealed the presence of methyl (CH2− asymmetric and CH2− symmetric stretching vibrations), esters (C=O, C–O, and O–CH3), and sulfonate (S=O) groups in MESCSA and MESNaHSO3 samples, thereby affirming the desired product. Surface tension analysis showed that the MESCSA and MESNaHSO3 have low critical micelle concentrations of 0.079 g/L and 0.14 g/L, respectively while the corresponding surface tensions were 51.9 mN/m and 30.94 mN/m for MESCSA and MESNaHSO3 respectively.