Amino-acid-functionalized methanesulfonate ionic liquids as effective and reusable catalysts for oleic acid esterification

Abstract

Five new amino-acid-functionalized methanesulfonate ionic liquids ([AAH][CH₃SO₃]-ILs) were prepared using methanesulfonic acid and amino acids (AAs). The catalytic performances of the five synthesized [AAH][CH₃SO₃]-ILs were evaluated for biodiesel synthesis via the esterification of oleic acid with methanol. Among them, IL [GluH][CH₃SO₃] exhibited the optimal catalytic activity in the oleic acid esterification. An experimental design based on the RSM-BBD was used to optimize the reaction conditions. A conversion rate of 96.8 % was attained using the [GluH][CH₃SO₃] catalyst for the oleic acid esterification at a catalyst load of 12 wt%, a molar ratio of 19.6:1, a reaction time of 3.5 h and a temperature of 103 °C. The [GluH][CH₃SO₃]-catalyzed oleic acid esterification followed first-order kinetics with the activation energy and frequency factor of 9.86 kJ·moL⁻¹ and 0.47 min⁻¹, respectively. The catalytic activity of the [GluH][CH₃SO₃] catalyst did not considerably change during ten consecutive cycles of the esterification reaction. Operational simplicity, high conversion rate along with good reusability makes the IL [GluH][CH₃SO₃] a promising catalyst for replacing traditional catalysts for the biodiesel preparation via the fatty acids esterification.