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Preparation of Polyelectrolyte-Coated Magnetic Silica Nanocomposite Particles and Investigation of their Application for Enzyme Immobilization and Biodiesel Production

Esmaeilnejad-Ahranjani, Parvaneh | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47935 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Kazemeini, Mohammad; Arpanaei, Ayyoob; Singh, Gurvinder
  7. Abstract:
  8. In this study, polyelectrolyte-coated magnetic silica nanocomposites were prepared via the covalent attachment of polyelectrolytes onto the as-prepared magnetite-silica particles with core-shell structures and average diameter of 210±50 nm, and subsequently applied for the immobilization of lipase molecules. In this regard, polyethyleneimine (PEI) with two molecular weights of 10000 and 750000 and polyacrylic acid (PAA) with two molecular weights of 1800 and 100000 were utilized. The type and molecular weight of the polyelectrolyte molecules greatly impacted the concentration of binding sites on the particles surface and consequently on the lipase immobilization efficiency and loading capacity as well as the conformation and activity of the immobilized lipases. High lipase immobilization efficiencies (86.2-97.1%) and loading capacities (786-817 mg g-1) were obtained by using the polyelectrolyte-coated particles. The catalytic activity assays of the free and immobilized lipases in hydrolysis reactions indicated that the immobilized lipases exhibit better catalytic performance at broader temperature and pH ranges and higher thermal and storage stabilities as well as reusability in comparison to the free lipase. The higher activities of the immobilized lipases at the elevated temperatures were due to the enhancement of β-sheet contents (5-6.5%) in their structures. Moreover, the type and size of the polyelectrolyte molecules significantly affected the hydrophobic and hydrophilic properties of the particles and consequently the activities of the immobilized lipases for the biodiesel production. The highest biodiesel production yields of 81.2% and 88.3% were achieved through the transesterification of palm oil with methanol or ethanol, respectively, in the solvent-free systems by using the lipase immobilized onto the high molecular weight PEI-coated particles. By addition of n-hexane as a solvent in the aforementioned reaction systems, the biodiesel production yields using methanol or ethanol were increased by 7.7% and 5%, respectively. The assessment of enzyme operational stability over five repeated batches showed that the lipase immobilized onto the high molecular weight PEI-coated particles retains approximately 70.4% and 77.8% of its initial activity for the production of biodiesel in the transesterification reactions of palm oil with ethanol in the solvent-free and n-hexane systems, respectively
  9. Keywords:
  10. Magnetic Nanocomposite ; Silica ; Polyethylenimine ; Lipase Enzyme ; Enzyme Stabilization ; Polyacrylic Acid ; Nanobiocatalyst ; Biodiesel Production

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