Taguchi orthogonal design assisted immobilization of Candida rugosa lipase onto nanocellulose-silica reinforced polyethersulfone membrane: physicochemical characterization and operational stability

A greener processing route to replace the current environmentally-unfriendly esterification technique to produce biofuels such as pentyl valerate (PeVa) was explored. This study statistically optimized the covalent immobilization of Candida rugosa lipase (CRL) onto biomass-based nanocellulose-silica (NC-SiO₂) reinforced polyethersulfone (PES) membrane to synthesize PeVa. Raman spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and atomic force microscopy of NC-SiO₂-PES/CRL proved that CRL was successfully conjugated to the membrane. The optimized Taguchi Design-assisted immobilization of CRL onto NC-SiO₂-PES membrane (5% glutaraldehyde, 4 h of immobilization, 20 mg/mL CRL concentration, 40 °C and pH 5) gave 90% yield of PeVa in 3 h. The thermal stability of NC-SiO₂-PES/CRL was ~ 30% greater over the free CRL, with reusability for up to 14 successive esterification cycles. In a nutshell, the greener NC-SiO₂-PES membrane effectively hyperactivated and stabilized the CRL for the esterification production of PeVa. This research provides a promising approach for expanding the use of sustainably sourced NC and SiO₂ nanoparticles, as fillers in a PES for improving CRL activity and durability for an extended catalytic process.