Laser Plasma-immobilized Enzyme Membrane Reactor System For Production Of Ethanol

Conventional first generation bioethanol feedstocks such as corn and sugarcane areunable to meet the current demand of bioethanol production due to their primaryshortage and high cost of food. Therefore, lignocellulosic biomass are attractivefeedstocks for the second bioethanol production. Bioethanol from corn stover could be apromising technology though the process has several challenges and obstacles such asmaterials transport and handling, and efficient pretreatment methods. In addition,cellulase need effective recovery and recycling for cutting the cost, and improving theyield of bioethanol. This thesis presents a detailed research and analysis of producingbioethanol from lignocellulose by the catalysis of laser-plasma.To decrease the cost of bioethanol production, the barrier of biomass degradationneed be overcome so that the conversion of biomass to bioethanol becomes moreefficient. The CO₂laser plasma can disrupt the physical structure of lignocellulose andreduce the average size of fiber. The analyses by FT-IR, specific surface area, and themicrostructure of corn stover were used to elucidate the enhancement mechanism of thepretreatment process by CO₂laser irradiation. The present work demonstrated that theCO₂laser irradiation had potential to enhance the bioconversion efficiency oflignocellulosic waste to renewable bioethanol. The saccharification rate of the CO₂laserpretreatment was significantly higher than that of ultrasonic pretreatment, whichreached27.75%, was1.34-fold of that of ultrasonic pretreatment. The results showedthe CO₂laser pretreatment on corn stover could be more effective than ultrasonicpretreatment.The CO₂laser plasma catalysis to improve the enzymatic hydrolysis oflignocellulose for production of monosaccharide, was investigated. Response surfacemethodology （RSM）, at a three-variable, three-level experiment Box–Behnken design（BBD） established the following optimum pretreatment parameters: time, power andliquid-to-solid ratio are67.53min,264.33W and21.29:1（mL/g）, respectively. Underthese conditions, the total reducing concentration was4.941mg/mL among theproducion of cellulase hydrolysis. This matched the predicted value and cellulasehydrolysis was increased from14.47%to30.84%. Scanning electron microscopy （SEM）showed that the CO₂laser plasma catalysis could make the surface of lignocelluloserough and porous, which promoted the enzyme access and resulted in a high productionrate of reducing sugars.The cellulase adsorption experiment on lignocellulose was done, and the cellulaseadsorption equation with CBD adsorption district of lignocellulose was obtained by transforming Langmuir adsorption isotherm equation. The adsorption experimentsshowed the largest protein fractional value with the combination of lignocellulose in thecellulase protein was about0.43. The result showed that proportion of the effectivecombination of cellulase and wood cellulose fiber protein was43%of the total enzymepreparations. In the process of the laser plasma catalytic corn stover lignocelluloseadsorption with different cellulase concentration, the maximum adsorption value ofcellulase was0.111（g enzyme/g wood cellulose fiber）, which illustrated that1g laserplasma catalytic lignocellulose fiber could combine with cellulase protein of111mg.Then, by studying the enzymatic hydrolysis process of laser plasma catalyzedlignocellulose fiber, the reaction time of the enzymatic hydrolysis and cellulase basickinetic equation were deduced, and obtained the parameters of cellulose enzymatichydrolysis reaction equation k, k ’, K’, and Ymaxvalue. This could effectively predict andcontrol the lignocellulose enzymatic hydrolysis process.To reuse the cellulase, we chose the ultrafiltration membrane module, andscreened PS30hollow fiber membrane as the membrane internal pressure ultrafiltrationmethod for recycling of cellulase protein. The effect was studied on the changes of totalreducing sugars and cellulase protein in the ultrafiltration retentate and through themedium. The results suggested that PS30hollow fiber membrane of recycling cellulasehas a high application value. The recovery rate of cellulase was about78%afterultrafiltration process as well as cellulase could be reused.Immobilized S. cerevisiae bioethanol yield was analysed by single factor and RSMmodel, and the optimal conditions for bioethanol production rate were found. Therusults of the response surface methodology included the three aspects:（1） the additionamount of enzymatic hydrolysis lignocellulose was0.20%;（2） S. cerevisiaeconcentration was about2.08%;（3）Initial pH of the fermentation broth was about4.57.Under the conditions of response surface optimization, the rate of second generationbioethanol production theoretically could reach84.29%in the CO₂laser plasmacatalyzed lignocellulose hydrolysates.