Mechanism Of Enhanceing Eucalypt Wood Enzymolysis Efficiency Using Chemimechanical Pretreatment Processes

With rapid consumption of fossil fuels i.e. petroleum and coal, serious environment pollution problems arising globally. For many countries, "to develop bio-energy resource" has been high regarded as national security strategies for sustainable enrgy resource. Ethanol from fermentation process with a long history, is a type of bioenergy, with wide raw materials and mature biotechnology. The second generation bioethanol can be produced from lignocellulosic materials.whereas, it can be relized to converte lignocellulosic raw material into glucose inefficiently by enzymolysis process directly, because of the botanical physiology structure and self pretection mechanism of the lignocellulosic organisms. Therefore, proper pretreatment should be applied prior to efficient enzymolysis process, to increase the ethanol production and decrease its production cost.In this study, eucalypt wood, the common fast growing hardwood species in southern China, was used as the raw material. Investigations on pretreatment of eucalypt wood using different pretreatment processes, for instance, Mechanical, Ammonium hydroxide impregnation/refining, Mg-basd alkali impregnation/refining and acidic salts cooking/refining processes and subsequent enzymolysis saccharification operation were carried out, solids and spent liquors from different pretreatment process were collected, hydrolyzates by enzymolysis operation were prepared, all samples above were analyzed by means of X-ray diffraction meter, specific surface area analyzer, FTIR, UV-Vis and HPLC apparatus applied to evaluate the effects of different pretreamtent processes on the enzymatic saccharification of the pretreated wood fibers. Finally, bioethanol production trials by fermentation of spent liquor from pretreatment process and hydrolyzates from enzymolysis process were investigated. The banlances of biomass and energy were calculated and estimated.For refiner-refining ptrtreatment, the results showed that the dimension of the wood matrix could be decreased by refning, while the specific surface areas and water retention values (WRV) were raised. with more input refining electricity, the specific surface area of the treated material was increased, the enzymolysis efficiency slightly enhanced accordingly. The highest enzymolysis conversion rate was only of 35% when 4-5 times of refining passes at stock consistency of 20-25%. In conclusion, the effect of sole mechnical pretreatment on the enzymatic saachrification was not significant.Pretreatment of wood chips with Mg2+alkali combined wit refining indicates that the refining specific energy consumption was decreased in a great extent, and the enzymolysis efficiency increased gradually, when the Mg(OH)2 dosage of 3% applied in the impregnation stage. However, higher Mg(OH)2 dosage could raise the refining specific energy consumption, and the magnesium hydroxide particels could be absorbed onto fibers, leading to an isolation effect on the contaction between enzymes and cellulose. Therefore, the proper dosage of Mg(OH)2 should by carefully chosen, For instance, when Mg(OH)2 dosage of 3% combined with post-refining, the specific energy consumption was decreased by 53.54%, with contrast to woodchips refining alone, and the yield of reducing sugar was upto 91.53%, because of specific surface areas increment due to genration of more fines and fracments after refining via Mg(OH)2/refining pretreatment. The crystalline structure of the cellulose was also partially destroyed, proven by the cellulose crystallinity analysis.Ammonium hydroxide, a selective delignification regent, was chosen for woodchips imprenation (SAA) prior to post-refning. the SAA impregnation conditions were optimized by a response surface methodology design, the proposed accepteble process paraments were given as follows:ammonia dosage of 79.54%(w/w), reaction temperature of 100℃ and retention time of 10.7 h at the temperature. Under the optimun impregnation condition, about 24.86% of the specific refining energy was saved comparing to the refining of initial wood chips. Further more, while a H2O2 dosage of 5% applied into the SAA impregantion stage (SAAp), the delignification was improved by 6.84%, resulting an obvious increment of enzymolysis reducing sugar convertion rate by 6.2%. the improvement of delignification can be proven by FTIR spectrum of wood samples from SAA and SAAp impregnation.it was found that more delignification function happened during SAAp process. In addition, a small amount of xylan dissolved by SAAp process.To evaluate the applicability of SAA process upon different types of lignocellulosic materials, effects of SAA impregnation on wheat straw, residues and chips of eucalypt wood were compared, results indicate that SAA process is more effective on agricultural residues, due to such type materials, characterized as ess lignin content and high hemicellulose content, and bulky structural property.The acidc salts pretreatment process, a recently development technology, was employed in this study. Investigations on hemicellulose degradation and improvement of enzymolysis efficiency to pretreated substrates were carried out withapplication of the selected seven types of acidic salts, as KCl, NaCl, NH4Cl, CaCl2, MgCl2, FeCl2, FeCl3 individually, the results show that MgCl2 or NH4Cl impregnation could provide treated wood chips with better pretreatment effects on its enzymolysis efficiency.these two types of acidc salts show similar pretreatment effects on the hemicellulose degradation and enzymolysis saccharification.The first order raction kinetics (k) were followed by cellulose and hemicellulose degradtion reactions during the pretreatment of acidc salts, and the k value for cellulose was lower than that of hemicellulsoe, the reaction activation energies for cellulose and hemicellulose were of 46.63 kJ/mol and 82.26 kJ/mol, respectively. Thus it proves that better effect for separating cellulose and hemicellulose in wood matrix can be achieved by using these tow types of acidic salts.Investigations on pretreatment effects, using a combined process (ASPR) of digester cooking with acidic salt plus post refining, were carried out. There are hemicellulose removal rates of 91.97% and 91.14% from woodchips, providing substrates with extremely high cellulose enzymolysis convertion rates of 95.30% or 97.84% by MgCl2 or NH4Cl cooking, respectively. The cooking conditions were optimized and illustrated as acidic dosage of 1.2 mol/(kg o.d. woodchips), liquid to solid ratio of 6:1,reaction at 170℃ for 10 min. After ASPR process, the the surface wood fiber samples were characterized and observed by SEM, it was found that cell walls and surface of fibers were damaged severely, generating more fiber fines and fractions, resulting high WRV values of substrates. The ester and ether linkages of the LCC were damaged that proven by FTIR spectrum, and most of the hemicellulose and less the lignin were dissolve, while only a few of cellulose affected.Bio-enthanol convertion by a fermentation process using yeast from spent liquor of pretreatment and ydrolyzate from enzymolysis process, were carried out. it was found that the spent liquor from pretreatment process was difficult to be fermentated into ethanol, while the glucose in hydrolyzates (substrates by ASPRNH4land ASPRMgCl2) were almost fermentable, with the ethanlo conversion rates of 80.26% and 79.03%, respectively. The balances of biomass and emery were calculated andevaluated, these calculation show that the ethanol productivity was of 5.31 GJ/ton o.d. woodchips he pretreatment process with anenergy efficiency of 0.322 kg o.d. woodchips/MJ, and the energy efficiency (ηenergy) of the holo-process was 277%.