Optimization of microreactor-intensified transesterification reaction of sesame cake oil (sesame waste) for biodiesel production using magnetically immobilized lipase nano-biocatalyst

Enzyme-catalyzed transesterification to produce biodiesel is a time-consuming reaction. This study aimed to use a recoverable nanomagnetic immobilized enzyme and microreactor-intensified process to design a significantly rapid transesterification reaction. Immobilization of Candida Rugosa lipase (CRL) on GO-Fe₃O₄@TiO₂ nanocomposite was optimized using response surface methodology-box–Behnken design (RSM-BBD). Results showed the highest immobilization efficiency of 92.73% at the optimum condition of CRL concentration of 2.59 mg/mL, time of 4.96 h, and temperature of 37.61 °C. Newly synthesized GO-Fe₃O₄@TiO₂@CRL nano-biocatalyst (NBC) was characterized using FTIR, XRD, VSM, FE-SEM, EDX and elemental mapping. Immobilized CRL showed improved stability under different parameters, including pH, thermal, and methanol medium compared to free CRL. Freshly synthesized NBC was used in a microreactor to intensify the transesterification reaction of sesame cake oil to produce biodiesel. The RSM-BBD optimization of the transesterification reaction showed a maximum conversion rate of 97.03%, achieved at the NBC amount of 4.47 wt%, residence time of 13.29 min, and Me/oil molar ratio of 4.28. The generated biodiesel has all characteristics well within the ASTM D6751, demonstrating its good quality. The results of this study showed that using a microreactor could sufficiently intensify the transesterification reaction and reduce the reaction time using GO-Fe₃O₄@TiO₂@CRL NBC.