One-step direct transesterification of wet yeast for biodiesel production catalyzed by magnetic nanoparticle-immobilized lipase

To develop a method for direct transesterification of wet yeast using immobilized lipase, the oleaginous yeast Saitozyma podzolica Zwy-2-3 and the lipase producing Burkholderia pyrrolica WZ10-3 were used as materials for production of biodiesel. Fe3O4@SiO2-CHO prepared by modifying Fe3O4 with TEOS, APTES and glutaraldehyde. The biocatalysts covalently cross-linked with WZ10-3 lipase by Fe3O4@SiO2-CHO were characterized by FTIR, XRD and TEM. When the enzyme dosage, glutaraldehyde concentration, temperature and time were 30.22 mL, 2.0%, 40 °C and 4 h, the immobilized lipase activity and immobilization rate reached 10038.0 U/g and 96.9%, respectively. The optimum temperatures for immobilized and free lipase were 60 °C and 40 °C. The immobilized enzyme still had 80% enzymatic activity after 48 d storage at 4 °C. The optimized conditions for the direct conversion of immobilized lipase to esterified wet yeast (one-step) were: enzyme dosage 2.5 g, reaction temperature 35 °C; water content 15%; and molar ratio of n-hexane to methanol 3: 1. The transesterification rates of one-step method for oil and biomass were 98.12% and 56.11%, respectively. In contrast, the two-step method was only 88.75% and 51.21%. The immobilized enzyme had 90% enzyme activity after 10 times of reuse.