Production of bioethanol and high value-added products from lignocellulosic biomass

• Main Authors: Yu-Sheng Lin, 林祐生
• Other Authors: Wen-Chien Lee
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/68759660664726075790

博士 === 國立中正大學 === 化學工程研究所 === 99 === The process of simultaneous saccharification and fermentation (SSF) combines the enzymatic hydrolysis of cellulosic matters and ethanol fermentation of hydrolysate within a single stage. It utilizes cellulase enzyme to break down the cellulose and yeast to ferment the resulting glucose. The main disadvantage of SSF lies in different temperature optima for saccharification (50°C) and fermentation (35°C). The aims of this dissertation are to develop the simultaneous saccharification and fermentation process with different lignocellulosic biomass for the production of bioethanol. Initial study dealt with the simultaneous saccharification and fermentation of 10% NaOH-pretreated rice straw under different experiment conditions. With enzyme (Accellerase 1000) dose of 0.20 ml/g-WIS, 10% subtract (WIS) and 1 g/L dry yeast, SSF of 0.1 kg alkali-pretreated rice straw in flask at 40C produced an ethanol concentration of 29 g/L and an ethanol yield of 86% (based on the glucose content in the pretreated raw material) in a 72-h reaction. Also, the SSF scaled up in a 5-L rotary drum reactor with 1 kg substrate under the same WIS percentage and enzyme and yeast loadings resulted in an ethanol yield of 84.4%. In addition, response surface methodology (RSM) based on a three-level three-factor Box-Behnken design was employed for disclosing the optimum SSF conditions of 10% NaOH-pretreated cogongrass. The response surface model arrived at the optimum SSF conditions: cellulase (Accellerase 1000) concentration of 0.255 ml/g-WIS, temperature at 37.5°C, and substrate concentration of 7.28% WIS for obtaining 80.3 % ethanol yield in 72 h. Ethanol yields of 75.0% and 76.2% were obtained from a scaled-up rotary drum reactor filled with 1 and 2 kg of substrate, respectively, under the optimal conditions. For the development of SSF process at higher temperature using 10% NaOH-pretreated sugarcane bagasse (from Taiwan Sugar Corporation) as the substrate, a 72-h SFF from 10% WIS at 42°C with 0.15 ml/g-WIS enzyme (Accelerase 1500) and 1 g/L Ethanol RedTM dry yeast could result in a final ethanol concentration of 24.1 g/L, corresponding to 77.1% of the theoretical ethanol yield from glucan. Compared with 72-h SSF of alkali-pretreated sugarcane bagasse from 10% WIS at 42°C with 0.2 ml/g-WIS enzyme (Accelerase 1500) and 0.5 g/L Kluyveromyces marxianus var. maximanus BCRC 21363, the final ethanol concentration was 23.5 g/L, corresponding to 75.1% of the theoretical ethanol yield. Kluyveromyces marxianus var. maximanus could replace the commercial dry yeast for reducing the cost of SSF. But SSF in a rotary drum reactor containing 1 kg pretreated sugarcane bagasse, a 72-h SSF from 10% WIS at 42°C with 0.2 ml/g-WIS enzyme (Accellerase 1000) and 0.5 g/L Kluyveromyces marxianus var. marxianus could result in a final ethanol concentration of 22.2 g/L, corresponding to only 70.8% of the theoretical ethanol yield from glucan. The wastes of 10% NaOH pretreatment could be used for producing high value-added product. For example, corncob xylan could be extracted from the waste of alkali-pretreated corncobs and xylooligosccharides (XOS) were produced from corncob xylan. The endo-xylanase secreted by the alkaliphilic Bacillus halodurans, in either immobilized or free form, could catalyze the conversion of corncob xylan to XOS by enzymatic reaction. At the end of 24-h reaction, the XOS mixture contained totally 25.2% (w/w) of xylobiose and xylotriose by using immobilized xylanase, while the total amount of xylobiose and xylotriose was 32.5% when free xylanase was used. The conversions for the converting insoluble substrate to soluble XOS with immobilized xylanase on ion-exchanger Lewatit MonoPlus MP64 was determined to be 80.9%, which was lower than that (99.8%) from the use of free xylanase. This study showed the potential applicability of the alkaline reagents (10% NaOH) for the pretreatment of various lignocellulosic feedstocks without adding external energy input. After alkali-pretreatment, SSF was found to be very effective at converting the cellulose in rice straw, cogongrass and sugarcane bagasse into ethanol, even at low enzyme doses and high temperature. The waste from pretreatment could be used for the production of xylooligosaccharides as a high value-added product.