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Study on Pretreatment and Cellulase Saccharification for Both Banana Pseudo-stem and Bagasse

Author: LiKun
Tutor: FuShiYu
School: South China University of Technology
Course: Pulp and Paper
Keywords: banana pseudo-stem bagasse sulfite pretreatment delignification
CLC: TS745
Type: Master's thesis
Year: 2010
Downloads: 221
Quote: 1
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Abstract

The shortage in fossil energy resources is a tough obstacle for the development of economy and society. Biomass is considered as a promising substitute for traditional energy sources because it is rich in resources and environmentally friendly. Banana pseudo-stem and bagasse are abounding natural resources in south China. Production of bioethanol from banana pseudo-stem and bagasse will bring about high economic, environmental and social benefits by making full use of waste bioresources, protecting environment and increasing peasants’income. This paper is mainly focused on the alkalescent sulfite pretreatment of banana pseudo-stem and bagasse, especially the delignification discipline, decomposition of hemicellulose and sulfonation of lignin. The research work will provide the fundamental knowledge for biorefinery of banana pseudo-stem and bagasse, as well as technical support.An analysis of chemical composition and anatomical structure of banana pseudo-stem was carried out using Light Microscopy (LM), Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). The chemical analysis indicated there is a high holocellulose content and low lignin content in banana pseudo-stem compared with some non-wood fiber resources. Glucose is the predominant monomer in this raw material with 71.76%, followed by xylose, 11.20%. These results demonstrate that the banana pseudo-stem has potential value for pulping and biorefinery. However, the membrane on fibers may pretend fibers from cellulase and result in low biorefinery efficiency. In order to improve the biorefinery efficiency, this membrane should be removed by pretreatment.In order to study the delignification during alkalescent sulfite pretreatment, the waster liquid was analyzed by UV spetra, and the sulfite concentration was determined by chemical titration as well. The delignification expirical model and kinetic model in alkalescent sulfite pretreatment of bagasse was build up. The delignification expirical model was described as D ? 0 .8359H0 .2?(C0?C1)?6.699. The good linear relation between predicted value and measured value revealed that this expirical model was highly accurate. In the initial stage of pretreatment, the delignification process was fast and the delignification rate increased rapidly. When H﹥239,the delignification rate increased slowly.The kinetic model for alkalescent sulfite pretreatment of bagasse was build up, which was described as the equation L0 ?L?0 ?1 .544S?H?. Which can predict the degree of delignification during the pretreatment with alkalescent sulfite.The hydrolysis yields of bagasse after sulfite pretreatment and cellulosic hydrolysis was determined by analyzing the hydrolysates with Ion Chromatograph. In order to get high hydrolysis yields, the pretreatment technologies were optimized as follows: sulfite dosage 18%, maximum temperature 160oC, holding time 60min, cellulase load 30u/g with a littleβ-glucosidase, hydrolysis temperature 50 oC, pH 4.8, rotation speed 150rpm, hydrolysis time 72h. After the optimized sulfite pretreatment and cellulosic hydrolysis, the glucose yields of bagasse was 50.9%, while the xylose yields reached 23%, which was higher than steam explode and AFEX pretreatments. The hydrolysis yields of banana pseudo-stem was improved from 12.6% to 46% after the alkalescent sulfite pretreatment, which illustrated that the sulfite pretreatment was highly beneficial in the improving biorefinery efficiency of banana pseudo-stem. However, the membrane covering fibers may pretend fibers from cellulase and result in low biorefinery efficiency, which required removing to increase the hydrolysis yields.The hemicellulose in the bagasse after pretreatment was determined by Ion Chromatograph, while the amount of sulfonic acid group was analyzed by conductimetric method. The influence of delignification, decomposition of hemicellulose and sulfonation of lignin on the alkalescent sulfite pretreatment of banana pseudo-stem and bagasse was also studied in this paper. Under same temperature, the hydrolysis yields increased while delignification rate increased, and it increased faster when the delignification rate was higher. This result illustrated that delignification was positive to process of enzymatic hydrolysis. However, the hemicellulose was degraded simultaneously when delignification was carried out, which would result in the low hydrolysis yields. Conclusively, the lignocellulosic material with high delignification rate and little decomposition of hemicellulose could bring about high hydrolysis yields. Additionally, the results suggested that sulfonation of lignin was positive to process of enzymatic hydrolysis.

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