In situ Transesterification of Microalgae Parachlorella kessleri Biomass Using Sulfonated Rice Husk Solid Catalyst at Room Temperature

Microalgae are a sustainable raw material for biodiesel production that earned a lot of consideration. Biodiesel from the conventional transesterification (liquid acid based) process of microalgae oil needs pre-treatment before its use as fuel. Moreover, the oil extraction process is energy extensive. In this study, room temperature assisted in situ transesterification method is reported using a solid acid catalyst obtained from sulfonated rice husk (RHS). The RHS catalyst was synthesized by microwave acid treatment of rice husk. The surface characterization of RHS by XRD, FT-IR, Raman, and XPS confirms the presence of −SO₃H, while the pore anatomy and pore structure analysis by FE-SEM and BET substantiate the presence of porous structure and high surface area. Furthermore, the RHS catalyst was successfully employed for the in situ transesterification of the microalgae (Parachlorella kessleri) biomass. Various experimental conditions influencing the in situ transesterification were evaluated. The optimization of catalyst dose revealed that 30 mg RHS produce highest FAME yield after 30-min reaction time at room temperature (25 °C). Performance of the catalyst was compared with rice husk-derived fluorocarbon (RHFC) and conventional acid catalyst (H₂SO₄). Moreover, in the proposed approach, there is no need for oil extraction step and pre-treatment of biodiesel after the reaction. RHS is very effective at room temperature compared with conventional transesterification.