The Research On Bioethanol From Lignocellulosic Biomass Of Hardwood

Due to the tight natural structure of the lignocellulose materials, wood cellulose and hemicellulose cannot be directly used in biofuel production. A series of pretreatment and enzymatic hydrolysis process is necessary before the bioconversion of biomass using microorganism. In this paper, the process of pretreatment, enzymatic hydrolysis and ethanol fermentation of lignocellulosic raw materials were studied, and the mechanism of the transformation of monosaccharides was also discussed. The impact with different pretreatment methods on different biomass materials were mainly discussed, including the dilute acid pretreatment, hydrothermal pretreatment, organic acid pretreatment and inorganic acid pretreatment. The conversion efficiency of five carbon sugar ethanol based on different pretreatment methods and the effect of inhibitors on ethanol yield were studied. A new enzymic hydrolysis process was proposed, cellulase plus xylanase and cellobiase can significantly increase the monosaccharide yield. Based on nutritional metabolism mechanism of E. coli K011and S. cerevisiae D5A, the internal relation between biological characteristic, gene express of key enzyme of ethanol conversion and ethanol yield was investigated. A bioethanol production process of different raw material sources was established. The results of this study promote development of the wood cellulose ethanol conversion research and high value of utilization in our country. The results of this study were summarized as follows:1. The cellulose and hemicellulose of triploid populous was45.3%(w/w) and16.3%(w/w), and was significantly higher than diploids. With the optimal dilute acid pretreatment conditions, the concentration of xylose was19.24g/L and the concentration of glucose was3.84g/L in the pretreatment liquor. The results of post-hydrolysis analysis of pretreatment liquor showed that trace amount of cellulose and hemicellulose remained. With the optimal hydrothermal pretreatment conditions, the concentration of xylose was2.71g/L and concentration of glucose was0.20g/L. The results of post-hydrolysis analysis of pretreatment liquor showed that quite amount of cellulose and hemicellulose remained. The fermentation of pretreated liquor was performed by single strain (K011) and mixture strains (D5A+K011), respectively. The theoretical ethanol yield was85.38%by K011and the theoretical ethanol yield was80.20%by mixture strains D5A and K011. The ratios of enzymatic hydrolyzation of pretreatment solid and concentration of cellulase were positively correlated. Enzyme-degradation rate of dilute acid pretreated solid was88.09%and enzyme-degradation rate of hydrothermal pretreated solid was81.08%. Without xylanse, the enzyme-degradation rate of dilute acid pretreated solid was observably higher than that of hydrothermal pretreated solid. The ethanol yield of dilute acid pretreated solid after enzymatic hydrolyzation was101.72%of theoretical yield; however, the ethanol yield of hydrothermal pretreated solid after enzymatic hydrolyzation was88.24%of theoretical yield.2. The cellulose and hemicellulose of maple-wood was42.2%(w/w) and18.2%(w/w). With the optimal mineral acid pretreatment conditions, the concentration of xylose was19.58g/L and the concentration of glucose was4.53g/L in the pretreatment liquor. With the optimal organic acid pretreatment conditions, the concentration of xylose was19.90g/L and concentration of glucose was3.14g/L. The results of post-hydrolysis analysis of pretreatment liquor showed that trace amount of cellulose and hemicellulose remained. The amount of fermentation inhibitors (HMF and furfural) was higher in mineral acid pretreated liquor than that in the organic acid pretreated liquor. Without detoxification treatment, the theoretical ethanol yield was74.04%in mineral acid pretreated liquor; however he theoretical ethanol yield was81.11%in organic acid pretreated liquor. Adding excessive nitrogen source, the ethanol yield climbed to85.26%and93.92%in mineral and organic acid pretreated liquor, respectively. The enzymatic hydrolyzation ratios of pretreatment solid and concentration of cellulase were positively correlated. The enzyme-degradation rate of mineral acid pretreated solid was92.38%and the enzyme-degradation rate of organic acid pretreated solid was92.89%. Xylanse could increase enzyme-degradation rate of cellulase, but not remarkable. The ethanol yield of mineral acid pretreated solid after enzymatic hydrolyzation was95.63%of theoretical yield; however, the ethanol yield of hydrothermal pretreated solid after enzymatic hydrolyzation was95.44%of theoretical yield.3.100g/L glucose could be consumed by S cerevisiae D5A quickly, and no inhibition phenomenon of fermentation. Fermentation activity of D5A was the highest at35℃and decreased when the temperature over40℃. During fermentation process, E. coli K011were strongly influenced by fermentation by-product acetic. When xylose was used as the substrate, K011had the secondary growth. Inhibition phenomenon of fermentation appeared when the concentration of xylose was over80g/L and the concentration of glucose was over40g/L, respectively. The mixture sugar (xylose plus glucose) was fermented by mixture strains D5A and K011. Due to the difference of optimal fermentation conditions between D5A and K011, the ethanol yield did not increase. Nitrogen source could enhance the gene expression of key enzyme in ethanol conversion.