DEVELOPMENT OF ACTIVE AND RECYCLABLE MAGNETIC NANOBIOCATALYSTS FOR GREEN AND SUSTAINABLE CHEMICAL AND FUEL PRODUCTION

Abstract

Enzymatic transformation is widely used as green and sustainable method for chemical and fuel production. However, the practical application of isolated enzymes is hampered by the unsatisfied stability and high cost. Enzyme immobilization technology is known to enhance enzyme stability and enable the recycling of enzymes to significantly decrease the enzyme cost. Immobilization of enzymes on magnetic nanoparticles is highly desirable for efficient biocatalysis due to high enzyme loading and less mass transfer limitation. However, their effective recycling still remains as a big challenge in practical application. In this thesis, we successfully developed novel methods for fabricating highly active, easily recyclable and active magnetic nanobiocatalysts for green and sustainable chemical and fuel production.

Different approaches were demonstrated. 1) A novel concept of using reversible clustering of nanobiocatalysts was developed for efficient biotransformation and easy catalyst separation. Nanobiocatalysts form reversible clusters via non-covalent interactions among enzymes immobilized on neutrally charged magnetic nanoparticles. The clusters were easily dissociated into individual nanobiocatalysts by shaking for efficient biocatalysis (100% activity and enantioselectivity as the free enzyme) in aqueous phase. After the reaction, they were quickly and completely recycled under external magnetic field (80% original productivity after 14 times¿ recycling). 2) Reversible clustering of Cyclohexanone Monooxygenase nanobiocatalysts (RC CHMO-MNPs) and reversible clustering of Glucose Dehydrogenase nanobiocatalyst (RC GDH-MNPs) were coupled for efficient Baeyer-Villiger oxidation (91% and 99% yield for cyclohexanone and 2-hexylcyclopentanone, respectively) with efficient NADPH recycling (TTN = 5,000).

3) Highly active and efficiently recyclable magnetic nanobiocatalyst aggregates (MNA) were developed as the first success on immobilized enzyme-based high-yielding production of biodiesel from waste grease containing high amount of FFA via one-pot esterification and transesterification with methanol. MNA is, by far, the best immobilized enzyme for this transformation (99% yield of biodiesel from grease and 88% productivity retained in cycle 11). The developed methods enable the efficient utilization of waste grease as a sustainable resource for the production of biodiesel. 4) One-pot purification and immobilization of lipase on the magnetic Ni-NTA nanoparticles was successfully developed for fast and simple fabrication of highly active magnetic nanobiocatalysts used in biodiesel production from waste grease (99% yield of biodiesel).