| Lignocellulosic materials are used to produce bio-energy and fine chemicals as the renewable natural raw material.The complex chemical structure and recalcitrance of plant cell wall make it difficult for bioenergy conversion.Thus,pretreatment is a necessary step to destruction the rigid protective sheath of lignin and hemicelluloses for improved saccharification yield of cellulose hydrolysis.In this study,hybrid Pennisetum,a new herbaceous energy crop,was used as the raw material,and effects of 1-allyl-3-methylimidazolium chloride?[Amim]Cl?system and O2/ 1-ethyl-3-methylimidazolium acetate?[Emim]Ac?systems pretreatment on performance on cellulase hydrolysis of hybrid Pennisetum were investigated.Firstly,central composite design?CCD?wasemployed for design of experimental,and the process parameters were further optimized using response surface methodology?RSM?.In contrast to the control sample,a higher glucose yield of 72.21%was obtained at temperature of 139 ?,retention time of 178 min,and solids loading of 9.06 wt%.The quadratic model for predicting the glucose recovery from hybrid Pennisetum was proposed and verified by variance analysis?ANOVA?.The results of analytical computation showed that the model had high F?65?,and R2?0.9832?with high significance.Moreover,statistical analyses revealed that the interaction of temperature and solid loading had significant effect on glucose recovery.Secondly,the changes of microstructure and enzymatic saccharification of hybrid Pennisetum after [Amim]Cl pretreatment were investigated.The results indicated that the cellulose content of hybrid Pennisetum increased by 22.90%,while the content of hemicelluloses and lignin decreased by 31.25% and 12.78%,respectively.The results of Fourier transform infrared spectroscopy?FT-IR?based on Gaussian fitting function displayed that the bonds of LCC and C=O in xylan were destroyed,the content of inter-molecular hydrogen bonds with O?6?H…O?3`?form in the pretreated samples decreased by 12.9%,while the content of intra-molecular hydrogen bonds of O?2?H…O?6?and O?3?H…O?5?form increased by 2.2% and 10.9%,respectively.The result of X-ray diffraction?XRD?showed that the cellulose crystals of hybrid Pennisetum pretreated by [Amim]Cl changed from cellulose crystalline I transformation into cellulose crystalline transformation II,and the relative crystallinity and the average width of crystallite size decreased by 20.79% and 42.22%,respectively.The results of BET method and scanning electron microscopy?SEM?showed that the surface roughness and porosity increased,and BET specific surface area increased from 0.15 to 10.11 m2/g.In order to further reduce energy consumption and to improve efficiency of the pretreatment process,effect of O2/[Emim]Ac system pretreatment on enzymatic saccharification of hybrid Pennisetum were investigated.The optimal pretreatment conditions were temperature of 120?,time of 30 min,and ratio of solid to liquid of 1?20?w/w?,where glucose yield recovery increased by 9.4 times compared to the unpretreated samples.The [Emim]Ac were reused three times with excellent performance.The results indicated that cellulose content in hybrid Pennisetum after [Amim]Cl pretreatment increased by 17.18%,while the content of hemicelluloses and lignin decreased by 14.63% and 67.36%,respectively.The result of FT-IR showed that LCC bonds and aromatic rings of lignin were destroyed.The XRD result showed that the relative crystals of increased by 15%.The SEM result showed that the pit membrane was ruptured,and a lot of holes were exposed,leading to compact structure of cell wall damaged,for O2/[Emim]Ac biphasic systempretreatment. |
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