Immobilized Aspergillus niger lipase over hydrogen titanate nanotubes as a biocatalyst for biodiesel production

Immobilization of lipase enzyme is a promising approach towards cost-effective production of biodiesel to protect the enzyme from denaturation during the transesterification process.

In the present study, hydrogen titanate nanotubes (HTNTs), synthesized by simple hydrothermal method, was used to immobilize lipase from Aspergillus niger via physical adsorption with the following ratios of HTNTs and lipase; 1 T: 1 L, 1 T: 0.75 L, 1 T: 0.5 L, and 1 T: 0.25 L. All prepared samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The catalytic activities of free and immobilized lipases were evaluated for biodiesel production using sunflower oil, methanol to oil molar ratio of 4: 1 at 40 °C for 90 min.

The biodiesel yields (0% water content, 0.877 g/cm³ density, and 0.041 mg acid value) were 79.2 ± 0.01, 82.3 ± 0.9, 79.1 ± 1.2, 81.97 ± 1.4, 78 ± 0.1 percent for 1 T: 1 L, 1 T: 0.75 L, 1 T: 0.5 L, 1 T: 0.25 L, and free lipase (1 L), respectively. Compared with the control (1 L), immobilizing lipase using (HTNTs) enabled a 50- 75% reduction in lipase required quantity while maintaining or even increasing biodiesel production levels. The work establishes a promising method for lipase immobilization in biodiesel production that can be evaluated for large-scale application in further studies.