Biodiesel preparation from tiger nut oil utilizing a novel hydroxy-functionalized basic ionic liquid catalytic transesterification procedure: optimization, kinetics, and thermodynamic studies

In this study, six novel hydroxy-functionalized basic ionic liquids (BILs) were prepared using a two-step technique and employed as efficient and recyclable catalysts for the synthesis of biodiesel via catalytic transesterification of tiger nut oil (TNO). The effects of the reaction parameters and their interactions on transesterification were investigated and optimized using a Box-Behnken design (BBD). Among them, 1-(2,3-dihydroxy)-propyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) morpholine ([DPTD][Mo]) was found to be more superior to the other five BILs in terms of catalytic performance. A maximum of 97.9 % biodiesel yield was obtained under the optimal reaction parameters (reaction temperature 65 °C, reaction time 158 min, methanol-to-TNO molar ratio 10.4:1, and catalyst dosage of 1.2 wt%). The transesterification of TNO to biodiesel exhibited an Ea, ΔH, ΔS and ΔG of 36.79 kJ·mol−1, 34.01 kJ·mol−1, −181.42 J·mol−1·K−1 and 93.43 kJ·mol−1 at 333 K, respectively. Additionally, [DPTD][Mo] exhibited satisfactory stability and reusability as the catalytic activity remained at a yield of 80.1 % in biodiesel production for the initial 3 cycles, making it a highly promising catalyst for biodiesel synthesis in industrial scale. After the reaction, an automatic phase separation between biodiesel and the catalyst occurred, minimizing the processes of product isolation and purification. The application of [DPTD][Mo] in this study provides an environmentally friendly technique for biodiesel production. The obtained biodiesel meets the ASTM D6751 and EN 14212 biodiesel standards, enabling its utilization as fuel in diesel engines.