Abstract
The main limitation preventing the use of enzymatic cellulosic ethanol in industrial production is its higher cost which is mainly due to the elevated price of β-glucosidase (BG). Herein, we report on a simple strategy for the in-situ encapsulation of BG for repeated cellulosic ethanol production. In this strategy, BG was net-immobilized into a poly(ethylene glycol) (PEG) net-cloth layer on a PP nonwoven fabric by way of the visible light-induced surface controlled/living graft cross-linking polymerization. The visible light and mild reaction conditions could ensure the activity retention of BG during immobilization, while the non-swelling uniform net-mesh formed by living cross-linking polymerization could prevent the leakage of BG effectively (at the immobilization rate of more than 98.6% and the leakage rate of only 0.4%). When the BG-loaded fabric was used in combination with free cellulase (CEL), the results of the catalytic reaction demonstrated that these BG-loaded fabrics could not only give a 40% increase in cellulose conversions but also be reused for more than fifteen batches without losing the activity. These BG-loaded fabrics with characteristics including easy separation, excellent operation stability, a low cost of the polymeric matrix and a simple fabrication process are particularly interesting for a future bio-fuel production strategy.
Highlights
The growing demand for energy combined with diminishing fossil fuel reserves have stimulated a tremendous interest in finding alternative renewable energy sources1,2.“Cellulosic ethanol”, obtained by turning all kinds of plant material into fuels[3,4,5,6,7,8,9,10,11], is a promising sustainable substitution for fossil fuel
The hydrolysis of cellulose comes from the synergistic effect of the multi-enzyme systems
BG catalyzes the hydrolysis of cellobiose, which is known to be a strong inhibitor of the activities of the other two enzymes[22,23]
Summary
The growing demand for energy combined with diminishing fossil fuel reserves have stimulated a tremendous interest in finding alternative renewable energy sources1,2.“Cellulosic ethanol”, obtained by turning all kinds of plant material (from waste straw to useless wood) into fuels[3,4,5,6,7,8,9,10,11], is a promising sustainable substitution for fossil fuel. One mild and green way to produce “cellulosic ethanol” is to convert cellulose into fermentable sugars by a complex enzyme hydrolysis and ferment the sugars into ethanol[12,13,14,15]. Cellulase (CEL) is a complex enzyme system that includes endo-glucanase (EG, EC 3.2.1.4), cellobiohydrolase (CBH, EC 3.2.1.91), and β-glucosidase (BG, EC 3.2.1.21). BG catalyzes the hydrolysis of cellobiose, which is known to be a strong inhibitor of the activities of the other two enzymes[22,23]. Due to the fact that the content of BG is much lower than that of the other two enzymes of the CEL system, the rate that converting cellobiose into glucose is relatively slow[24]. To develop an efficient “BG immobilization” technique and permit multiple reuse without loss of activity would greatly reduce the cost of cellulosic ethanol[28,29,30,31,32,33]
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