Synthesis of methyl biodiesel by esterification using magnetic nanoparticles coated with sulfonated lignin

Heterogeneous catalysis for biodiesel production via esterification has emerged as a preferred route as it permits to overcome the disadvantages associated to homogeneous catalysis, which presents serious drawbacks that affect biodiesel production and increase its costs such as corrosivity, difficult removal, and non-reuse of the catalyst. This study evaluated the esterification of oleic acid (OA) using CoFe 2 O 4 and MnFe 2 O 4 ferrite magnetic nanoparticles (MNPs) coated with sulfonated lignin (SL). SL was synthesized from sugarcane bagasse lignin employing acetyl sulfate (sulfonating agent). Two different proportions of reactants were adopted, obtaining the solids SL5 and SL7.5—posteriorly incorporated into the MNPs. Reaction parameters evaluated were as follows: time (4 and 6 h) and temperature (80 and 100 °C), with other parameters fixed. The catalysts were characterized by XRD, BET method, SEM, TGA, and elemental analysis. The sulfonic group contents were determined by acid–base titration. The conversion of OA into methyl esters was determined by GC–MS and FTIR. Elemental analysis showed that SL5 and SL7.5 have 2.68% of sulfur content by mass and the following minimal molecular formulas C 9 H 10,52 O 5,62 (SO 3 H) 0,18 and C 9 H 10,52 O 5,62 (SO 3 H) 0,17 . XRD and TGA data evidenced that coated MNPs exhibit incorporation percentage of SL higher than 50%, with the best results for CoFe 2 O 4 -SL5 (79.5%) and CoFe 2 O 4 -SL7.5 (78.5%). GC–MS and FTIR data revealed that the highest OA conversions were achieved under 6 h and 100 °C. In addition, CoFe 2 O 4 -SL5 and MnFe 2 O 4 -SL7.5 exhibited the best catalytic performances in the esterification reactions with conversions of OA into fatty acid methyl esters of approximately 80%. Graphical abstract