Reactive Oxygen-assisted Alkali Pretreatment Of Sugarcane Bagasse And Its Enzymatic Saccharification

Sugarcane bagasse,a primary by-product of sugar industry,contains carbohydrate in large quantities.Thus,the conversion of sugarcnae bagasse into ethanol and other energy chemicals is of great significance.However,sugarcane bagasse is difficult to degradation directly due to complex structure of bagasse fiber raw material.It is necessary for enzymatic hydrolysis to damage its inherent structure by appropriate pretreatment.For this reason,pretreatment method will be the first key for ethanol production from sugarcane bagasse,which directly affects the subsequent enzymolysis efficiency and ethanol fermentation.In this paper,the state-of-the-art in cellulosic ethanol at home and abroad,as well as developed pretreatment technology of sugarcnae bagasse for ethanol production were summarized.Based on the current situation,sugarcane bagasse pretreated by combining active oxygen reagent(O2/H2O2)and alkali was conducted to improve its enzymatic digestibility and sugar recovery.To obtain the optimized pretreatment process,the effects of oxygen reagent and their loading,the kind and dosage of alkali,temperature and time during the pretreatment on composition change and enzymatic saccharification of sugarcnae bagasse were systematically examined.Firstly,sugarcane bagasse pretreated by combining oxygen reagent(O2/H2O2)and NaOH with different variables was carried out,and the results were compared with sole NaOH pretreatment.Research shows that lignin removal for combining oxygen reagent and NaOH pretreatment was about 10%higher than that for sole NaOH pretreatment at the same conditions,and resulted in higher glucan recovery in the solid remain.Subsequently,combining oxygen reagent and NaOH pretreated sugarcane bagasse presented more efficient enzymatic digestibility than sole NaOH pretreatment.Taking O2-NaOH pretreatment as an example,under the moderate pretreatment conditions of combining 1%NaOH and 0.5 MPa O2 at 80 OC for 120 min,a high glucan conversion of 95%was achieved after 48 h enzymatic hydrolysis.Coupled with the operations of pretreatment and enzymatic hydrolysis,an admirable total sugar recovery of 89%was obtained.The susceptibility of the substrates to enzymatic digestibility was explained by their physical and chemical characteristics.Cellulose crystallinity,porosity and lignin barrier seem to be crucial in enzymatic digestibility.Based on the above findings,sugarcnae bagasse pretreated by combinding O2 and various alkalis,and its enzymatic saccharification were investigated.The result indicates that the pretreatment efficiency of O2-alkali pretreatment was closely related to the water solubility of the alkali and alkalinity of medium,and fine water solubility and strong alkalinity of medium were beneficial to pretreatment process.Compared with sole alkali pretreatment,O2-alkali pretreatment could remove lignin more effectiviely and improve enzymatic saccharification of substrate.The lignin removal was:NaOH>KOH>NH3·H2O>Ca(OH)2>Ba(OH)2>Mg(OH)2,and enzymolysis yield of glucose was:NaOH>KOH>Ca(OH)2>NH3·H2O>Ba(OH)2>Mg(OH)2.Increasing pretreatment tempeature to 130 ?,there was a considerable increase in lignin removal and enzymolysis efficiency for O2-NH3 H2O pretreatment,and the enzymolysis yield of glucose was higher than that of O2-Ca(OH)2 pretreatment.In conclusion,the pretreatment of combining active oxygen(O2/H2O2)and NaOH is appropriate for sugarcane bagasse.Compared with sole NaOH pretreatment,it has distinct advantages in pretreatment conditions,lignin removal,enzymolysis efficiency,and total sugar recovery.The findings of this dissertation can provide theoretical guidance and technical reference for the exploitation of pretreatment process during the ulilization of sugarcane bagasse for bioethanol production.