Study On Enzymatic Hydrolysis Of Lignocellulose And Characteristic Of Nanocellulose Based On Acid Treatment

Lignocellulose is an abundant, renewable and eco-friendly resource, which is a potential alternative to fossil as the source of energies and materials. In this paper, we studied the saccharification of lignocellulose for producing ethanol and nanocellulose isolated from it based on acid treatment.First, different metal chloride aqueous solutions were employed to pretreat bagasse. The metal chloride underwent hydrolysis to keep producing hydrogen ions stabily during pretreatment, which efficiently catalyzed the degradation of hemicellulose, resulting in the improvement of accessability of cellulose on enzyme. Meanwhile, inhibitor factor（IF） was proposed based on the cellase hydrolysis kinetics of pretreated bagasse. The initial velocity and digestibility of enzymatic hydrolysis increased with the decrease of IF. Especially, the cellulose enzymatic digestibility（CED） of FeCl₃-pretreated bagasse would reach 96.7%. Furthermore, the suitability and economic feasibility of FeCl₃ pretreatment were investigated by being applied to herb and wood biomass. Removed hemicellulose based on glucan（RHG） was used to assess the difference among diferent biomass enzymatic hydrolysis.Their CEDs followed this sequence: rice straw（95.1%）>bagasse（91.7%）>eucalyptus（81.5%）, corresponding to their RHG with 83.3%>50.4%>29.6%. Compared with HCl, FeCl₃ pretreatment was more economically and efficiently. At the same cost of chemical comsuption, preteating rice straw with FeCl₃ could abtain 81.9% ethanol converson. In contrast, the converson to ethanol of rice straw pretreated with HCl was only 58.6%. Moreover, FeCl₃ was easily to be recoveried, less impairness on the environment.To overcome the recalcitrance of eucalyptus, degradation kinetics of its xylan was first investigated using combined hydrolysis factor（CHF） of FeCl₃ pretreatment. The correlation between xylan retained in pretreated eucalyptus and CHF was showed as X_R=0.8exp（-CHF） + 0.2 exp（-0.37CHF）. Then solid yield, glucan retained and cellulose enzymatic digestibility could be predicted using CHF. In addition, adding surfactant as Tween 80 during FeCl₃ pretreatment and enzymatic hydrolysis could both improve the digestibility. However, it was must more efficiently and costless through adding Tween 80 during enzymatic hydrolysis, rather than pretreatment.For producing nanocellulose from lignocellulose, we first investigated the effect of concentrated sulfuric acid treatment conditions on characteristic of obtained cellulose nanocrystals（CNC）. It demonstrated that acid concentration was the key parameter to control CNC production. A maximum CNC yield of 75% could be achieved at acid concentration 58wt%, which was sharp transition point. The length, morphology and crystalline can be tailoring through changing the hydrolysis conditions. Under low acid concentration, such 58%, the resultant nanocellulose was more like CNF, and crystalline index unchanged with the CNC yield. Therefore, the surface of CNC produced from high acid concentration seemed smooth, and its Cr I increased linearly with decrease of CNC yield. Then a novel method for simultaneously measuring the length and radius of CNC in an aqueous suspension using UVVisible absorption spectroscopy was tested over a wide range of concentrations.The equationbased on Rayleigh-Gans light scattering（RGS） was The measured length and diameter were 144 nm and 12.6 nm, respectively, comparing well with a length of 114.7 nm) and radius of 13.5 nm（4.3-nm std） measured from Transmission Electron Microscope（TEM） imaging.Three pretreatments including concentrated sulfuric acid, ferric acid and glycidyltrimethylammonium chloride（GTMAC） solution for bleach pulp were compared to producing cellulose nanofibrils（CNF）. They all promoted the isolation of nanocellulose from fibers due to degradation or/and modification of the fiber prior to microfluidzing treatment through 87 um chamber. For ferric chloride solution pretreatment, it only catalyzed the degradation of fiber. The CNF suspension achieved from this pretreatment exhibited a great plastic fluid property with high yield stress and low flow index. Concentrated sulfuric acid solution not only hydrolyzed the fiber, but also modified it. The grafted sulfate group impaired the thermal stability of produced CNF, even it facilitated the processing. GTMAC modified BEP and made it positively charged. It could improve the drainability when using in CNF film preparation.Finally, an efficient method for producing carboxylate CNC and CNF simultaneously was proposed based on the mechanism of nanocellulose production. The carboxylate CNC could be isolated easily when using concentrated（above 50 wt%） oxalic and maleic acid aqueous solution hydrolyzed the bleached pulp at 100-120°C for only 45 min. The rest solid could also be used to produce CNF under weak mechanical treatment. Onset thermal degradation temperature for the CNC was increased to 322°C from 274°C for the feed BEP fibers. And the crystalline index of CNC could reach 82%. Moreover, approximately 95% of the oxalic acid and 80% of the maleic acid in a solution of concentration 70 wt% and 80 wt%, respectively, can be recovered.