Towards A Science Of Biomass Saccharification

In recent years, utilization of biomass materials as potential biofuel feedstocks to convert carbohydrates to sugars has attracted significant attention. In this thesis, Chlorella biomass, corn stover and Chinese alpine rush were selected as biomass materials to produce fermentable sugars by the technology of acid/salt, ionic liquid, steam explosion as well as enzymatic hydrolysis. The performance of fermentable sugars in the hydrolysate was evalutated by conversing to ethanol.A novel chemical hydrolysis technology was developed to obtain high-yielding fermentable sugars from Chlorella biomass. Using a mixed catalyst of HCl and MgCl2, the highest sugar concentration was close to 12%, and the highest sugar recovery was about 83%, more than the sum of sugar recovery with HCl or MgCl2 as the catalyst, respectively. The results suggested a synergic effect of HCl and MgCl2 during the chemical hydrolysis of Chlorella biomass. Fermentation experiments demonstrated that glucose in the Chlorella biomass hydrolysates was conversed into bioethanol by Sccharomyces cerevisiae with the yield of 0.47 g/g, which is 92% of the theoretical yield. This chemical hydrolysis technology indicated the potential to provide a novel route for biomass to fermentable sugars.Chlorella biomass was then hydrolyzed in the presence of [EMIM]Cl. The effects of dissolution temperature and dissolution time, HCl loading, hydrolysis temperature and hydrolysis time on the formation of fermentable sugars from Chlorella biomass were investigated. After 3 h's dissolution in [EMIM]Cl and then 3 h's hydrolysis in 7 wt% HCl at 105℃,75% of Chlorella biomass could be dissolved, with 48% of total sugar released from Chlorella biomass, a second hydrolysis of the hydrolysates in the presence of 8% H2SO4 would enhance the final sugar yield to nearly 90%. [EMIM]Cl and sugars in the hydrolysate was recovered by using ion-exclusion chromatography, with the recovery of 94% of glucose and 87% of xylose and arabinose. Fermentation experiments demonstrated that the approach used could not introduce much inhibitor that interfered with bioethanol production.Corn stover was treated under different steam explosion pressure (1.5 MPa-2.5 MPa), pressure-retention time (3 min-10 min) and water content (0%-60%), on the base of cellulose content, hemicelluloses content, and enzymatic yield of the treated corn stover, the optimization condition was obtained by using the software of Design Expert, with the steam explosion pressure of 2.4 MPa,8.5 min and 60% of water content. Using the steam explosion treated corn stover obtained at the above condition, enzymatic hydrolysis experiment was carried out in order to get high concentration of fermentable sugar for ethanol production, and the system was gradually increased from 0.5 L,4 Lto 150 L. In 150 L enzymatic hydrolysis system,12%,6%, and 6% of feedstock were introduced at 0 h,24 h and 48 h, with the total sugar concentration increased all the time, while for enzymatic hydrolysis yield and compositions in solid residue, the phenomenon of decrease and increase was observed alternatively. At the end of enzymatic hydrolysis,100.7 g/L of total sugar with the yield of 70.2% was obtained.Different samples of Chinese alpine rush material with different lignin content from a biopulping process was selected as biomass materials to produce fermentable sugars. The enzymatic hydrolysis experiments showed that lignin content in the biomass materials would significantly affect the biomass saccharification. Compared to the sample without lignin degradation, the enzymatic hydrolysis yield of the sample with 71.55% lignin degradation would enhance about 9.58 fold. The addition of xylanse would further enhace the efficiency of enzymatic hydrolysis. However, due to almost intact crystalline structure of cellulose in the test samples, the overall enzymatic hydrolysis yield was less than 40%, which implicated that disrupting the crystalline structure of cellulose in the biomass material was an important key to further enhance the enzymatic hydrolysis of biomass.