Hemicellulose hydrolysis remaining

Xylan remaining in solid residues was also analyzed. As seen in Fig.5, increasing velocity significantly increased xylan removal, especially in the first 8 min. For example, xylan removal for operation at 2.8,5.2, and 10.7 cm/ min was 60, 70, and 82% for hot water only pretreatment of corn stover at 200°C after 8 min. However, after 16 min, the differences in xylan removal were less for all velocities run, suggesting that fluid velocity has less impact on the overall degree of hemicellulose hydrolysis. 

The effect of solids loading on hemicellulose hydrolysis was studied by Jacobsen and Wyman (37) and Stuhler (71), Water-only batch tube experiments with com stover were performed at 200°C for 15 minutes at solids loadings of 5 and 21%, and a number of performance criteria including total solids remaining and total soluble xylan oligomer yields were evaluated (71). Statistically significant differences in several results were observed at a 95% confidence level, as summarized in Figure 3. 

A second effect on hydrogen ion activity not previously considered in dilute-acid hydrolysis of hemicellulose is the shift to bisulfate that occurs with neutralization. Neutralization products are water and mineral sulfates (Eq. 5). These mineral sulfates, if not removed from the system, will form bisulfates from some of the remaining hydronium ions to reestablish equilibrium as follows (Eq. 7) ... 

Note from these tables that all pretreatments significantly reduce the ash content of the raw biomass on a weight percentage basis (12 to 37%). The ash that remains is insoluble in acid and is assumed to be mainly silica. Acid hydrolysis shows the smallest reduction in ash content of the three pretreatments. In fact, acid hydrolysis is probably very efficient in removing alkali but it also removes carbohydrate from the feedstock in the form of pentose sugar hydrolyzed from hemicellulose. In this case, the percentage change in ash... 

The synergy between cellulases, hemicellulases, and accessory enzymes has been explored in some depth but is still not fully understood. Studies utilizing purified cellulases and hemicellulases have shown that when some of the hemicellulose component in lignocellulose remains intact following pretreatment, the enzymatic hydrolysis of the remaining xylan and substituted xylan moieties improves cellulose hydrolysis by cellulases (Selig et al., 2008, 2009). This improvement in cellulose... 

The hemicellulose and cellulose polymers are hydrolyzed with enz5unes Cellulases or Hemicellulases to release monomeric sugars. The sugars from the pretreatment and enzymahc hydrolysis steps are fermented by bacteria, yeast, or filamentous fungi, although enzymatic hydrolysis and fermentation can also be performed in a combined step called simultaneous saccharification and fermentation. After a final purification (by distillation and molecular sieves), the ethanol is ready to be used as a fuel, either neat or blended with petrol. A part of the lignin (remaining biomass) can be burned to provide heat and electricity for the process, whereas the rest is retained as a valuable coproduct. The most probable use today would be as an ash-free solid fuel (Fernando et al., 2006). 

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