Study On Hardwood Biorefinery-Two Pathways

"Biorefinery"aims at full utilization of biomass materials, which is of great significance to relieve the global resource shortage and energy crisis. Eucalyptus and Mixed Southern Hardwood were used in this study, and two pathways were applied for the following research work. One is to explore the influence of hemicelluloses pre-extraction on alkaline pulping and ECF/TCF bleaching, which is based on the IFBR(Integrated Forest Products Biorefinery) concept. The other one is wood to ethanol bioconversion, to optimize acetic acid pretreatment and enzymatic hydrolysis conditions for targeting higher ethanol yield, which is integrated with the acetogenetic fermentation technology used in ZeaChem company. All these results are expected to provide useful information and reference for further research and practice.Alkaline pretreatment and autohydrolysis were carried out on eucalyptus chips, and the effect of alkaline concentration, liquor to wood ratio, temperature and time on the relative pentose yield was studied. Results indicate that autohydrolysis has great superiority on the relative pentose yield compared to alkaline pretreatment. For autohydrolysis, with extended reaction time or increased prehydrolysis factor(P-factor), certain variation trend is shown for the content of xylose, furfural and acid soluble lignin in the liquor. The relationship between direct method(determining pentoses in the extraction liquor) and indirect method(determing the pentosan difference between original and pretreated wood) for evaluating relative pentose yield was investigated, so the pentosan content in pretreated chips can be calculated from the results by direct method.The content of sugars and furfural/hydroxymethyl furfural(HMF) in the pretreatment filtrate is significant for both pulping and bioethanol conversion, so it is necessary to establish rapid and low-cost methods for their analysis. Pentoses, hexoses and total sugars were analyzed by dual-wavelength visible spectroscopy, and furfural and HMF were determined based on dual-wavelength UV method. Furthermore, no significant disturbance from lignin or other probable substances was detected. Under the same cooking conditions, the alkaline pulp from pretreated eucalyptus chips has lower kappa number and lower pulp yield than that from original chips. Based on the (AQ)P bleaching results, autohydrolysis can help improve the pulp bleachability. Conventional KP pulping and MCC pulping were carried out on both autohydrolyzed and original mixed hardwood. Compared to the original wood, lower alkaline charge is needed for the autohydrolyzed wood to obtain similar kappa, with decreased pulp yield and higher bleachability through D0(EP)D1 sequence. Due to partial loss of hemicelluloses, more beating energy is needed for the pulps from autohydrolyzed wood. The pulp strength goes down, while the opacity and scattering coefficient is increased.Based on the fiber morphology results by FQA(Fiber Quality Analysis), after alkaline pretreatment, the mean fiber length in wood goes up, with increased fiber width and lower L/W. As to autohydrolysis, the mean fiber width for both wood and pulps decreases with similar L/W ratio, while the kink and curl index is increased.According to the simulation results by Win/GEMS software, compared to conventional KP pulping, Prehydrolysis-KP pulping process has superiority. Based on the same yearly output of bleached pulp, the latter has relative higher gross margin, in addition, the net present value (NPV) and the internal rate of return(IRR) both increase.Mechanism related to the change of hemicelluoses and lignin during pretreatment was studied. For alkaline pretreatment, the mean molecular weight of hemicelluloses from both extraction liquor and wood is decreased a little bit, but with higher polydispersity. After autohydrolysis, significantly decreased molecular weight of hemicelluloses in wood is shown, with similar polydispersity. EMAL(Enzymolysis-Mild Acid hydrolysis) lignin was prepared from both original and autohydrolyzed chips, and they were analyzed by GPC and quantitative 31P-NMR. For the lignin from autohydrolyzed wood: 1) higher molecular weight and lower polydispersity is shown; 2) the content of total phenolic hydroxyl groups is higher, and the content of condensed phenolic hydroxyl groups increases with extended reaction time; 3) the content of aliphatic hydroxyl groups is lower; 4) higher S/G ratio is shown. To integrate with the acetogenetic fermentation technology applied in ZeaChem, acetic acid pretreatment and enzymatic hydrolysis conditions were optimized to further enhance enzymatic hydrolysis efficiency. Results show that PFI refining has significant effect. Adding acetic acid prehydrolysate into the enzymatic hydrolysis system can increase the total sugar yield, but the sugar produced by pulp itself decreases. Under the optimized conditions, when the enzyme dosage is 5~20 FPU, the total sugar yield is 75~85%, and the theoretical ethanol yield is 503.5~570.6 L ethanol/ODT wood.