Hydroxyapatite–CoFe ₂ O ₄ magnetic nanoparticle composites as supports for lipase immobilization in biodiesel production

The application of lipases in biodiesel production is often limited by high operational costs, particularly those associated with catalyst recovery. This study developed magnetic hydroxyapatite (HAP) composites as supports for the immobilization of commercial lipase in biodiesel production. Hydroxyapatite particles were synthesized and incorporated with CoFe 2 O 4 and the resulting structure was selected for lipase immobilization following preliminary evaluation tests. The support was characterized using analytical methods to determine its physical, chemical, and structural properties. Thermomyces lanuginosus (TL) lipase was subsequently immobilized and applied to transesterify refined soybean oil and waste cooking oil. Experimental design results indicated that higher HAP concentrations on the support and temperatures from 40 to 50 °C promoted high ethyl ester conversions (>97%). Under optimal conditions, the biocatalyst also achieved substantial conversion of waste cooking oil (≈89.6% in 24 h), demonstrating its capacity to produce key fatty acid esters from diverse lipid sources. Reuse tests showed that the immobilized lipase retained 63.9% of its activity after three cycles. The biodiesel produced also exhibited density (0.90 g cm −3 ) and viscosity (6.7 mm 2 s −1 ) values compliant with ASTM standards.