Lignocellulose Pretreatment, Cellulase Hydrolysis And Recycling: Process Control And Intensification

For the purpose to intensify the core processes and to reduce the economic costsin cellulosic ethanol bioconversion, this dissertation selects corncobs, a biomassresource from agricultural and forestry waste, as the raw materials to investigate thecomprehensive utilization of lignocellulose in the pretreatment process, to study theintensification approaches of the pretreatment and enzymatic hydrolysis process, todevelop a variety of methods controlling the adsorption/desorption of the cellulase,and finally discovered the operational factors that influence the cellulase quantitation.Alkaline peroxide pretreatment: It established a synchronous pretreating andfraction-recycling process, using corncob feedsotcks and H₂O₂/NaOH solvents, andunder mild temperature. This novel process realized the effective separation andrecovery of three key components whilst attained high lignin removal rate （85.2%）and cellulose retention rate （81.3%）.Ultrasound-assisted soaking in aqueous ammonia: Selecting corncob as rawmaterials, it designed and screened the optimum strategy of ultrasound-assistedsoaking in aqueous ammonia, as well as optimized the process parameters. Theenzymatic hydrolysis rate of corncob samples under the optimum conditions couldincrease34.2%whilst the release rate and equilibrium concentration of reducing sugarwere1.3and1.4times of the non-ultrasound treated samples, respectively.Cellulase adsorption and lignocellulosic hydrolysis controlled by ultrasound:In the isothermal ultrasonic reactor, Spezyme CP enzymes oscillatingly adsorbed onto/desorbed from the soaking in aqueous ammonia treated corncob （SAA-CC）, whichwere reversible and controllable. Through improving the accessibility and removingthe lignin, ultrasound could greatly increase the enzymatic hydrolysis efficiency of thelignocellulosic substrates （SAA-CC）. In addition, the lower energy outputs and themilder ultrasonic temperatures should be employed in lignocellulosic hydrolysis toavoid the inactivation of cellulase.Controllable cellulase adsorption by pH adjustment: Cellulase adsorption anddesorption on the lignocellulosic substrate could be controlled by pH adjustment. Indetail, the acidic pHs were benefit to cellulase adsorption while the neutral and alkaline pHs were more conducive to cellulase desorption. Moreover, adjusting thepH could inactivate cellulase. But, after adjusting the pH back to4.8as long as at lowtemperatures, the cellulase activity could recover reversibly.Design of the strategy of cellulase recycling: After90min incubation with pH7solution and SAA-CC residues, substrate and enzyme mixtures after24h hydrolysis,the91.9%cellulase could be desorbed from solid residues. To substitute this valueinto the recovery rate predictive equation, it is estimated that70.9%of the cellulaseactivity could be recovered in first round readsorption by the employment of pHadjustment.Factors influence the cellulase quantitation: The influence of centrifugationon cellulase quantitation was depended on the centrifugal way. In detail, whenemploying the “aliquot centrifugation” way, the centrifugation did not influencecellulase concentration; but when following the “mixture centrifugation” way, the freeenzyme concentration would decrease. This negative effect could greatly influence thesubsequent quantitation process, such as increased the measured adsorption values,decreased the measured desorption values and accessibility values.