Characteristics Of Mass Transfer And Biochemical Reaction During Hydrogen Production In Microbial Electrolysis Cell Through Lignocellulose Saccharification

At present, traditional methods to produce hydrogen mainly rely on waterelectrolysis, which consume enormous energy, causing excessive consumption of fossilfuels and environmental pollution. However, lignocellulose as one of the most abundant,renewable biomass raw materials in the nature, its usage of for biological hydrogenproduction have many merits such as high burning calorific value, renewability, nopollutants emission, etc. Currently, hydrogen production by microbial electrolysis cellshas become one of the research hots. Most importantly, the simultaneoussaccharification and fermentation of waste materials such as lignocelluloses forhydrogen production can be achieved by using microorganism electrolytic cells (MEC).This new system can also bear these merits such as the integrated use of natureresources and energy resources exploration without pollutant emissions and greatlyimprove the performance of enzymatic saccharification and hydrogen production duringanaerobic fermentation.This thesis strengthened the performance of lignocellulose’s enzymolysisaccording to the features of compositions and structure of lignocellulose, andinvesitgated charification of heat and mass transfer during simultaneous saccharificationand fermentation for hydrogen production in the microbial electrolysis cells usinglignocellulose, which involved interdisciplinary knowledge such as heat and masstransfer, biochemical reaction and electrochemistry in the reaction system. Firstly aparallel electric field was designed and effects of the electric field intensity, watercontent, enzyme loading, pH value, electrode switch time on efficiency of cellulosesaccharification were respectively invesitgated. Then, effects of additives (Tween-80,PEG6000, BSA,[BMIM]Cl) coupled with an electric field on characteristics ofenzymolysis and saccharification of lignocellulsoe were done. Finally, the performanceof MEC used for simultaneous saccharification and fermentation for hydrogenproduction were conducted when considering effects of voltage, substrate, initial pH,reaction temperature in this work. The main results in this thesis are summarized as thefollowing.①A pair of parallel plates with electric field were designed to improve theperformance of enzymatic saccharification of lignocellulose materials. The effects ofelectric field intensity, water content, enzyme loading, pH value, electrode switch time on the efficiency of cellulose saccharification were performed. The optimal efficiencyfor saccharification of cellulose could be obtained at the electric field strength of12V/m (the applied voltage of0.6V) at96h, the supplied water of5.0ml/(g substrate),the cellulase dosage of26.68mg/(g substrate), and pH value of4.5or the electrodeswitch time of every6hours. the corresponding content of reducing sugar under theseconditions were426.6,422.7,446.2,434.5and456.8mg, respectively.②The effects of four additives with synergy of an electric field (Tween-80, PEG6000, BSA and [BMIM]Cl) on enzymatic saccharification of rice straw wererespectively investigated. The results show that the increasing amounts of Tween-80,PEG6000and BSA could significantly improve performance of enzymaticsaccharification of lignocellulose, initially. At200μL/(g substrate) of Tween-80, theamounts of the produced reducing sugar and the consumed lignocellulose,saccharification efficiency were respectively achieved to587.6mg,0.580g and26.4%.At40mg/(g substrate) of PEG6000, the amounts of the produced reducing sugar andthe consumed lignocellulose, saccharification efficiency were respectively fixed at598.8mg,0.599g and26.9%. Meanwhile, at20mg/(g substrate) of BSA, thecorresponding indexes were respectively607.3mg,0.615g and27.3%. However, theionic liquid [BMIM]Cl showed an inhibition to enzymatic saccharification of rice straw,and the saccharification efficiency always decreased with the increase in the amount of[BMIM]Cl.③Here, a double-chamber microbial electrolytic cell was designed, which coulduse lignocellulose for hydrogen production through simultaneous saccharification andfermentation, and hydrogen gas and CO2were respectively produced in the cathodechamber and the anode chamber in the system. Thus, the performance of microbialelectrolysis cells could be improved due to an increase in hydrogen purity and adecrease in cost. This work mainly researches effects of the applied voltage, substratetype, initial pH, temperature on hydrogen production in microbial electrolysis cellssystems. It is found that with the increase in input electricity of MEC systems, hydrogenproduction rate and the consumption of substrate gradually rose due to an increasedtransfer rate of protons and some molecules, while energy recovery efficiency showed atrend of gradual decline. Meanwhile, hydrogen production rate and the consumption ofsubstrates were different from different cellulose materials used in the MEC system.The result also reveals that with the increase of the initial pH, hydrogen production rateand energy recovery efficiency first decreased, then increased during the run of MEC systems, and with the increase of reaction temperature, hydrogen production rate andenergy recovery efficiency first decreased then increased. It indicates that mass transferprocesses and enzymatic activities in the MEC systems were obviously influenced bythe running temperature. The maximal hydrogen production by MEC usinglignocellulose through simultaneous saccharification and fermentation could beobtained individually at these conditions of the input voltage of0.8V, the substrate ofmixing substrate and the initial pH of6.5, the reaction temperature of35°C.Correspondingly, the maximal hydrogen production rates were1.84,2.46,2.46,2.51mmol/L/D, respectively.