Continuous microwave-assisted in-situ transesterification of lipids in seeds of invasive Chinese tallow trees (Triadica sebifera L.): Kinetic and thermodynamic studies

Abstract

Continuous in-situ transesterification of Chinese tallow tree seeds into methyl esters using a resonant focusing cavity microwave coupled with a CSTR system was investigated. High production yield of 90% with 97% conversion rate was obtained in 24 min CSTR residence time at a methanol/hexane/Chinese tallow tree seed mass ratio of 47.5:39.3:20, a continuous microwave heating power of 290 W and 14 s exposure time, reaction temperature of 60 °C in presence of sodium hydroxide catalyst (4 g NaOH per 100 g oil). The experimental data fits first order reaction kinetics. The values of rate constants at different temperatures and the corresponding activation energy were found out to be 0.08–0.084 min−1 and 2057.4 J mol−1, respectively. Thermodynamic parameters values such as Gibbs free energy (ΔG), enthalpy (ΔH) and entropy of activation (ΔS) were also determined. The positive values of ΔG and small negative value of ΔH indicated that the reaction has an unspontaneous/endergonic nature and is slightly exothermic.