Application of magnetic alumina-ferric oxide nanocatalyst supported by KOH for in-situ transesterification of microalgae cultivated in wastewater medium

Highlights: • Fabrication of magnetic KOH/Fe₃O₄@Al₂O₃ nanocatalyst by simple method. • Synthesis of the catalyst with uniform particles size and high surface area. • Obtaining well-magnetic properties for simple separation from microalgae carcass. • 95.6% conversion was obtained at the optimized reaction conditions. • Preservation the activity at least for six times with simple recovering process. -- Abstract: Nowadays, use of microalgae as a cheap feedstock and heterogeneous catalysts for biodiesel production has gained considerable interest as they mitigate environmental problems induced by the conventional process of biodiesel production using homogeneous alkali catalysts. However, separation of heterogeneous catalysts from tissues and carcass of microalgae is an important task. For this reason, a magnetic Fe₂O₃–Al₂O₃ nanocatalyst promoted by potassium groups was synthesized using a modified impregnation method and was profoundly studied and compared with nanocatalysts without ferric oxide using X-ray diffraction, Fourier-transform infrared, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda, scanning electron microscopy, transmission electron microscopy and energy-dispersive spectroscopy analyses. The results revealed that the magnetic nanocatalyst with a core-shell structure had suitable surface area, pore size, and particle size and also had no impurity on its structure. The nanocatalyst was used for biodiesel production from microalgae cultivated in a wastewater medium via in-situ transesterification reaction. The nanocatalyst converted 95.6% of microalgae lipids to esters at optimum conditions of 65 °C, 12 mL g⁻¹ of methanol-to-dry biomass, 4 wt% of magnetic catalyst and 6 h of reaction time. The magnetic K/Fe₂O₃–Al₂O₃ core-shell nanocatalyst was reused for several times and presented high stability with less reduction in its activity until six runs.