Biodiesel synthesis through soybean oil transesterification using choline-based amino acid ionic liquids as catalysts

In this study, twelve choline-based amino acid ionic liquids ([Cho][AA]-ILs) were synthesized employing amino acids and choline as raw materials. [Cho][AA]-ILs were effectively employed as catalysts in the biodiesel preparation via the transesterification of soybean oil with methanol. Among the synthesized [Cho][AA]-ILs, cholinium arginate ([Cho][Arg]) was selected as the appropriate catalyst. To optimize the primary experimental reaction conditions (methanol to oil molar ratio, catalyst load, reaction temperature, and reaction time), an experimental design was achieved by the A response surface methodology (RSM) based on the Box-Behnken design (BBD). The maximum biodiesel conversion of 98.58% was achieved with the [Cho][Arg] catalyst under the following optimal conditions: methanol to oil molar ratio of 9.13:1, catalyst load of 14.75%, a reaction time of 56.44 min and temperature 81.41 °C. A first-order kinetic of [Cho][Arg]-catalyzed transesterification of soybean oil with methanol was shown with activation energy and a pre-exponential factor of 10.06 kJ·mol−1 and 1.1707 min−1, respectively. The ionic liquid [Cho][Arg] is a promising, easy to synthesize, and biodegradable catalyst that can replace traditional catalysts for the synthesis of biodiesel.