A novel magnetic bifunctional hydrochar catalyst derived from palm leaf residue for biodiesel production: kinetic and thermodynamic studies

Abstract

BACKGROUND

Novel magnetic bifunctional hydrochar-based catalysts were produced from activated hydrochar derived from palm leaf residue (PLRAH) via a wet impregnation technique and used to perform one-step waste cooking oil (WCO) transesterification to produce biodiesel. The magnetic bifunctional hydrochar-based catalysts were evaluated for their acid–base properties, crystallinity, functional groups, magnetism, textural properties, thermal stability, chemical composition, and morphology.

RESULTS

The PLRAH-Fe₂O₃/K₂O magnetic catalyst performed well in thermal testing, with a large specific surface area of 111.08 m² g⁻¹ and its high basicity value of 7.34 mmol g⁻¹, as well as an acidity value of 12.67 mmol g⁻¹, significantly contributed to the WCO transesterification. An optimum biodiesel yield of 98.36% was obtained under the following conditions: catalyst loading of 3 wt%, a methanol-to-WCO molar ratio of 12:1, and a reaction temperature of 75 °C for a duration of 4 h and biodiesel yields maintained at >80% after five cycles. The produced biodiesel complied with the physicochemical properties stated in ASTM D6751. The kinetic study also revealed that WCO transesterification using the one-step approach had a pseudo-first order and activation energy ($E_a$) of 24.27 kJ mol⁻¹. Furthermore, the thermodynamic variables, including Gibbs free energy (∆G^o), enthalpy (∆H^o), and entropy (∆S^o) of WCO transesterification, were found to be 7.60 kJ mol⁻¹, 24.27 kJ mol⁻¹, and −21.78 J mol⁻¹ K, respectively. This suggests that WCO transesterification was an endothermic and non-spontaneous process.

CONCLUSION

The synthesized magnetic bifunctional hydrochar-based catalyst demonstrated outstanding performance for WCO transesterification, highlighting its potential for efficient biodiesel production. © 2024 Society of Chemical Industry (SCI).