Production Of Bio-ethanol, Levulinic Acid And Its Ester Derivatives

In order to product bioethanol and biomass-based chemicals, several researcheswere carried on including the kinetic model of lignocellulose hydrolysis; pretreatmentmethods of biomass on bioethanol production and enzyme recovery; production oflevulinic acid using feed batch method; synthesis levulinate esters by esterification innon-aqueous systems. The main conclusions in this thesis were summarized asfollowing.Kinetic model of dilute acid hydrolysis of corncob for fractionating pentoseand hexose: Corncob was used as substrate; the kinetics of corncob hydrolysis viadilute acid was investigated with sulfuric acid concentrations between0.1and0.9wt%through a constant solid-liquor ratio of1:10at temperatures of130-170°C in a batchreactor. A nonlinear regression approach has been applied to fitting kinetic parameterswhich obtained a good result. The pentose yield and retained hexose were favored atlow temperature and acid concentration, with best pentose fractionation beingachieved at130°C,0.1wt%H2SO4,82min. Under these conditions, pentoseconcentration reached36.2g/L; the pentose yield and retained percent of hexose were90.7%and96.9%respectively;97.6%of pentosan was released from the corncob.Effect of different pretreatment methods of corncob on bioethanolproduction and enzyme recovery: Corncob was used, and the effects of pretreatmentmethods on glucose and ethanol concentration were analyzed during pre-hydrolysisand the simultaneous saccharification and fermentation (SSF) process. The influenceof each pretreatment on the adsorption and desorption of cellulase and on therecycling effect of cellulase after re-adsorption by fresh substrate were also discussed.The results showed that acid-base coupling pretreatment was much better than asingle acid or alkali pretreatment, i.e. the cellulose content of corncob substrate andcellulose recovery reached at73.84%and85.40%after pretreatment; the desorptionpercent of cellulase after96h of SSF and re-adsorption one time was57.7%and62.4%respectively; ethanol production recovery amounted to62.0%.Acid catalysis production of levulinic acid from glucose using feed-batchmethod: The conditions of acid-catalyzed produced levulinic acid from glucose hasbeen optimized, and then the conditions were used in the followed feed-batchexperiments. The results showed that the high acid concentration, temperature andagitation speed helped to speed up the rate of glucose degradation and levulinic acid generation. The high glucose concentration is not conducive to levulinic acidgenerated, and the higher concentration of substrate, the lower yield of levulinic acid;the yield of levulinic acid increased from44.3mol%to65.9mol%by feed batchmethod on high concentration of glucose(18wt%).Enzyme-catalyzed esterification for levulinate esters synthesis and kineticanalysis: The synthesis of levulinate esters was successfully catalyzed by lipasethrough esterification reaction in a nonaqueous system. Under optimized reactionconditions (Novozym435, MTBE,50oC,0.66U·mL-1of enzyme loading, levulinicacid/ethanol=1:5),96.5%of conversion was obtained and the immobilized lipase canbe reused at least4cycles with half decline of activity. A kinetic model wasestablished based on the classical Ping-Pong Bi-Bi mechanism as well as theexperimental data. The kinetic parameters were obtained through fitting the kineticmodel with the NS fit module in Origin8.5: Vmax=0.290mol·L-1·h-1，KA=0.381mol·L-1，KB=2.340mol·L-1，KiB=2.356mol·L-1.