An efficient and stable magnetic nano-biocatalyst for biodiesel synthesis in recyclable ionic liquids

Abstract

The process of jatropha oil transesterification was studied for biodiesel production. Rhizomucor miehei lipase (RML) immobilized on 3-aminopropyltriethoxysilane functionalized magnetic Fe3O4 was employed as a biocatalyst. The immobilized lipase was confirmed by scanning electron microcopy (SEM), Fourier transform infrared spectra (FT-IR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and confocal laser scanning microscopy (CLSM) techniques. The efficient biodiesel synthesis in ionic liquids using immobilized RML was demonstrated. Fifteen kinds of ionic liquids based on different alkyl chain lengths of the methyl imidazolium cation ([C2MIM], [C4MIM], [C8MIM], [C12MIM], and [C16MIM]) combined with [NTf2], [N(CN)2], [PF6] or [BF4] anions were assayed as reaction media for RML producing biodiesel. The highest synthetic activity of immobilized RML appeared in [BMIM][PF6], which is more than five times higher than the free enzyme. The enzyme catalytic activity remained 60% even after the magnetic nano-biocatalyst and ionic liquid had been reused 5 times in a 48-h reaction cycle. In addition, the immobilized enzyme exhibited excellent storage stability with almost no decrease in catalytic activity after storing at − 20 °C for 98 days.