Date of Award

Spring 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

James Palmer

Abstract

Cellulosic ethanol is an alternative renewable energy source. Cellulase used in the production of cellulosic ethanol is very expensive. The difficulty in separating cellulase from the cellulose solution after the hydrolysis process limits the reusability of the cellulase, which highly precludes the scales of this application because of the high cost of the enzyme. Immobilization of cellulase provides a promising approach to allow the enzyme to be recycled, thus reducing the production cost. This research focused on immobilizing cellulase for reuse to reduce the cellulosic ethanol cost.

Four immobilization techniques were explored for the immobilization of cellulase on four different immobilization carriers. The immobilized cellulases by Layer-by-Layer Nano-Assembly (LbL) and Ca2+-Al(OH)X modification methods had high initial activities but low reusabilities. Enzyme desorption was observed during the hydrolysis of cellulose solutions by the immobilized cellulases for both LbL and Ca2+-Al(OH)x modification methods. Efforts were focused on improving the reusability of the immobilized cellulase, yet rarely worked. For the immobilized cellulase by the combination of Ca2+-Al(OH)x modification and LbL, the reusability of the immobilized cellulase was improved with the number of enzyme layers. Unfortunately, for the present moment, the initial activity decreased with the number of enzyme layers. Immobilization of cellulase on silica gel by 3-APTES and glutaraldehyde modification showed the highest reusability. No enzyme desorption was observed during the hydrolysis of cellulose solution. It indicated that the cellulase molecules firmly covalent bound to the silica gel. The immobilized cellulase on silica gel by 3-APTES and glutaraldehyde modification had the highest activity per unit mass of immobilization carriers because of the porous structure of the silica gel.

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