Table 14.2 represents some organosolv pretreatment processes, their effects on the substrate features and their susceptibilities to enzymatic hydrolysis. Although a pre­cise comparison is difficult to make from the data given in this table due to differences in the natures of lignocellulose and the reaction conditions employed, a rough evalu­ation is possible. By varying the process effective factors, such as the type of solvent (ethanol, acetone, butanol, glycerol, or other high boiling solvents) and aqueous content (50-90 %, w/w), catalyst type (H2SO4, NaOH, or MgCl2) and concentration (0.5-1.5 %, w/w), reaction temperature (140-200 °C) and time (10-60 min), ratio of biomass to solvent (1:5-1:15, w/w), the organosolv pretreatment produces a range of substrates with varying enzymatic digestibility of 10-90 %. As shown in the table, the organosolv pretreatment could increase the hydrolysis yields to 1.5-10 times that of the untreated substrate. Most of the previous work defined the delignification, recovery of hemicellulose and cellulose as well as hydrolysis rate and yield of the pretreated materials as the indicators to evaluate the efficiency of the process. To most kinds of biomasses 10 % (w/w) biomass loading, using the aqueous ethanol or aqueous acetone (around 50%, w/w), with 0.5-1.0% H2SO4 as catalyst, under 160-180 °C for 30 min appear to be the most effective parameters for organosolv pretreatment efficiency.

Reaction conditions were optimized to achieve the highest yield of them. Nev­ertheless, these reaction factors should not only be optimized to maximize the enzymatic saccharification yield, but also to take into account the energy cost and reduction of the formation of fermentation inhibitors. Using less severe pretreatment conditions for better processing economy, as well as minimizing the generation of fermentation inhibitors (furfural and 5-HMF), have to be taken into consideration [22, 72].