| Rice straw is the critical material for producing biofuel because it is abundant in source, cheap in price and rich in cellulose and hemicellulose. Preparation of bio-ethanol includes mainly the following four steps, pretreatment, saccharification, fermentation, separation and purification. Among them, saccharification is the key procedure to verifying the pretreatment effect and providing matrixes for fermentation. Therefore, how to reach the goal of high sugar yield with low cost has been one of the research focus. From the point of the process parameters optimization, the effects of metal ions action alone and combined action on enzymatic hydrolysis of liquefied rice straw(RS) is investigated, and the action mechanism is also studied. The hydrolysis efficiency of liquefied RS is characterized by sugar yield.Compared with raw materials, the cellulose content of liquefied RS was improved 20.9%, while the content of hemicellulose and lignin were respectively decreased 12.3% and 5.35%. After pretreatment, loose fragments, higher surface area and porosity were observed by scanning electron microscope, which helped cellulase fully contact with liquefied matrixes, results in a better effect of enzymatic hydrolysis.Mn2+ and Fe2+ ions were investigated as catalysts for the enzymatic hydrolysis of rice straw. The hydrolysis efficiency of liquefied RS was characterized by sugar yield. The results indicated that adding metal ions Mn2+ and Fe2+ could improve sugar yield. What’s more, the yield of Mn2+ group was higher than that of blank group but lower than that of Fe2+ group during the same enzymolysis time. The single-factor experiments were suggested that the enzyme loading of Mn2+ group decreased from 25mg/g of blank group to 20mg/g. While Fe2+ group was consistent with blank group. And the proper enzymolysis temperature of Mn2+ and Fe2+ group lowered from 50℃ of blank group to 40℃ and 35℃, respectively. It was concluded that adding Mn2+ and Fe2+ in saccharification process could disorganize the crystalline structure of cellulose, increase contact area of enzyme and substrate as well as improve enzyme activity, which finally enhances the efficiency of enzymolysis and reduces energy consumption.The effects of Mg2+ and Fe3+ ions action alone on the enzymatic hydrolysis of rice straw were studied by single-factor and orthogonal experiments. The optimal process conditions of blank group were following as, 25mg/g of enzyme dosage, 50℃ of enzymolysis temperature, 60 h of enzymolysis time, and the sugar yield reached 343mg/g. Under the conditions of 2mg/g Mg2+ concentration, 20mg/g enzyme dosage, 50℃ enzymatic temperature and 96 h enzymatic time, the sugar yield of Mg2+ group reached 477mg/g. The sugar yield of Fe3+ group reached 400mg/g as 4mg/g of Fe3+ addition, 25mg/g of enzyme loading, 40℃ of reaction temperature and 108 h of reaction time. Compared with blank group, the sugar yield of Mg2+ group and Fe3+ group were separately rose 134mg/g and 57mg/g at the optimum action condition. It was consistent with the conclusion that the sugar yield of Fe3+ group is higher than blank group but lower than that of Mg2+ group through single-factor experiments.On the basis of metal ions individual effect, the combined action effects of Mg2+ and Fe3+ on enzymatic hydrolysis of rice straw were discussed. The optimum conditions were obtained by orthogonal experiments. The highest sugar yield is 346mg/g at the conditions of the ratio between Mg2+ and Fe3+ is one to two, 30mg/g enzyme, 40℃ enzymatic temperature and 84 h enzymatic time. Single-factor experiment results indicate that combined action of Mg2+ and Fe3+ shows the superior effect to their single operation. |
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