| (?)High production cost is still the most important factor impedes industrialization of ethanol production from lignocelluloses until now. The cost mainly embodies in high energy consumption of pretreatment and complex treatment or utilization of spent liquor, high cost of cellulase production and low conversion of enzymatic hydrolysis at high solid consistency, few micro-organism can be used to metabolism C5 sugar, low resistant to high concentration of ethanol and inhibitors for micro-organism can metabolized C6 sugar and low utilization of by-products during whole process of ethanol production. Therefore, main factors influencing substrate enzymatic digestibility (SED) and their qualitative relationship, possibility for co-fermentation of solid and liquor from pretreatment and simultaneous production of ethanol and nanocellulose were investigated in this work. It would be significant to clarify the mechanism of woody biomass pretreatment and enzymatic hydrolysis of cellulose, improve the synergism of different processes during ethanol production and energy output efficiency and fasten the pace of commercialization of ethanol production from lignocellulosic biomass.The effect of substrate accessibility on SED and their qualitative relationship were studied firstly in this work. Two SPORL (Sulfite Pretreatment Overcome Recalcitrance of Lignocellulose, shorted as SPORL) pretreated wood substrates and one commercial bleached eucalyptus pulp were used and treated by drying and wet pressing to various degree of hornification. It was found that hornification-reduced cellulose accessibility was one of the most important factors affected SED. SEDs of hornified substrates made from same never treated sample correlate very well to an easily measured parameter, water retention value (WRV), and can be fitted by a Boltzmann function. It was also found that the parameter of WRV in Boltzmann function represent enzyme molecule size, which can be used as a standard parameter to judge whether the accessibility of substrate was significant decreased by hornification or not. The fitting results from three sets of samples suggest that enzyme accessibility to cellulose is mainly through the pores in the cell wall rather than substrate external surface. WRV can correlate to SEDs of hornified substrates resulted from the same never dried or pressed sample independent of the hornification process, e.g., drying or pressing. Cellulase adsorption measurements indicated that accessibility reduction of substrate was the only factor to reduce SED during hornification process.The main factor affects SED at high consistency and corresponding resolvent methods were also conducted in this work. The enzymatic conversion linearly decreased with increasing solids consistency, while it ranged from 8% to 22%. Our finding showed that mass transfer of enzyme components or hydrolysis products limitation caused by insoluble solids was not apparent, at least not at the solids level documented. The conversions of gulcan in SPORL pretreated aspen solid for enzymatic hydrolysis only and simultaneous saccharification and fermentation (SSF) at 18% solid consistency were 60% and 75%, respectively, indicated that hydrolysis products concentration, especially for concentration of glucose, was the major factor affected efficiency of high consistency enzymatic hydrolysis. Furthermore, the enzymatic hydrolysis conversions of glucan at 2% consistency for SPORL low pH and dilute acid (DA) pretreated substreates were very close. But separate enzymatic hydrolysis and SSF for SPORL low pH and dilute acid (DA) pretreated substreates at 18% consistency were 60% and 75%, 28% and 50%, respectively, which verified that aspen wood was more sensitive to SPORL low pH than to DA pretreatment.The possibility for ethanol production from beetle killed lodgepole pine was also examined. Carbohydrates component analysis results suggested that beetle caused mortality enriched glucan content by as much as 3 percentage point in wood. Glucan conversion improvement of 5% to 20% can be captured after SPORL pretreatment followed by enzymatic hydrolysis. An ethanol yielf of 267 L/t of wood was achieved from a tree infested 4 years (labeled as BD4) after SSF of pretreated solid and separate fermentation of pretreatment liquor after detoxification, 7% higher than the 250 L/t of wood from corresponding live tree (labeled as BL). After co-fermentation of solid and pretreatment liquor without detoxification, net energy output (before distillation and lignin energy excluded) from BD4 was 35% higher than from BL, which demonstrated the robustness of SPORL pretreatment and utility of beetle killed lodgepole pine tree for cellulosic ethanol production even after many years of infestation.The process conditions of lodgepole pine SPORL pretreatment was optimized for improving the efficiency of co-fermentation of solid and pretreatment liquor without detoxification. Based on the rules of solid yield and inhibitors concentration in liquor during SPORL pretreatment, SED of solid and recovery of fermentable C6 sugar can be promoted in a certain range of pretreatment conditions, otherwise, they would be decreased. In terms of ethanol yield, the optimization condition for SPORL pretreatment was listed as following: sulfuric acid charge 0.31% (v/v), sodium bisulfate 5.5% (w/w), temperature 180?and duration 38min. However, it differentiated from optimization conditions for enzymatic hydrolysis conversion at 2% consistency and recovery of glucan and mannan from enzymatic hydrolysis and pretreatment liquor. It suggests that some other factors affect fermentation efficiency rather than recovery of fermentable C6 sugar. Systematic experiments for co- fermentation of solid and liquor after SPORL pretreatment indicated that the effect of hydroxymethylfurfural and fufural in pretreatment liquor on ethanol productivity was not apparent if their concentrations were not beyond 1.3 g/L and 2.0 g/L, respectively. But residual SO2 in pretreatment liquor significantly inhibited co-fermentation efficiency, especially the concentration was up to 1.0g/L. After changing the ratio of liquor to wood (od) during SPORL pretreatment, it was found that energy output efficiency for co-fermentation of solid and liquor decreased linearly with the increasing of ratio if substrate enzymatic hydrolysis consistency was below 10% (w/v). However, after solid consistency beyond 20%, in order to guarantee the energy output efficiency and hydroxymethylfurfural and fufural concentration below the limitation of micro-organism resistency, the ratio of liquor to solid during SPORL pretreatment shouldn't below 2.5 and ranges from 2.5 to 3 would be better.The feasibility of integrating the production of nano-fibrillated cellulose (NFC) with sugar/biofuel (ethanol) from wood fibers was evaluated. Although the efficiency of enzyme hydrolysis of cellulose was decreased with the extention of hydrolysis duration and increasing dosage of cellulase, highly crystalline and recalcitrant cellulose is difficult to hydrolyze to sugars but very suitable for producing biobased nanomaterials through mechanical homogenization treatment. It was found that amorphous cellulose was easy to be hydrolyzed to glucose and resulted sugar was also easily converted to ethanol through yeast fermentation with excellent efficiency of 91%. The energy used in homogenizing for NFC production is lower than the energy made from fibers that had not been enzymatic fractionated. The above results from both enzymatic hydrolysis efficiency of eucalyptus bleached pulp and NFC production by mechanic methods demonstrate that the new technology of simultaneous production of ethanol and NFC would be helpful to both of two processes and improve utilization of lignocelluloses. |
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