7-46: Cellulase immobilization on magnetic particles enables enzyme recycling during lignocellulose hydrolysis

An important step for the production of lignocellulosic derived ethanol is the conversion of cellulose to glucose which can be achieved enzymatically, by the combined action of endoglucanases, exoglucanases and beta-glucosidases. However, enzyme cost is one of the main obstacles for enabling an economically viable large-scale process of lignocellulosic ethanol. Consequently, different approaches for decreasing the cost of the enzymatic step are being considered. Enzyme immobilization could reduce the enzyme cost by improving operational stability of the enzyme and allowing enzyme re-use. Recycling of the enzyme may however be difficult when treating crude particulate containing lignocellulosic feedstocks. One approach to overcome the difficulty in recycling would be to use enzymes immobilized on small magnetically susceptible particles.

The aim of this study was to evaluate the possibility of covalently immobilizing cellulases on magnetic particles. The magnetic particles used were commercial, non-porous silica based ones and activated with polyglutaraldehyde, cyanuric acid or tosyl chloride groups. The average diameter size of the particles was 1 µm, however smaller particle sizes was examined in order to increase surface area/g particle. Immobilization was conducted by mixing the particles and a cellulase mixture (Celluclast 1.5 L from Novozymes) at varying reaction time (between 2-24 h). The immobilized activity (filter paper units) was compared with immobilization of purified endoglucanases, exoglucanases and beta-glucosidases (obtained from Megazyme). Recyclability of the immobilized enzyme was tested on sulphite pretreated spruce and alkali pretreated wood. The results confirmed possibilities for re-use of cellulases immobilized on magnetic particles.