Ethanol has been used to split lignocelluloses into their components to study the structure of lignin, and used as a pulping agent in organosolv pulping. Recently, ethanol fractionation is becoming a major fractionation process among the organosolv fractionation processes for pretreatment lignocellulosic material to produce bioethanol. Generally, ethanol fractionation process is carried out under elevated temperatures without or with the addition of acidic or alkaline catalyst, and some organosolv fraction processes with ethanol are illustrated in Table 11.1 [16-26].

11.3.1 Effect of Treatment on the Structure of Lignocellulosic Material

11.3.1.1 Severity Parameter

Under given conditions in ethanol fractionation (auto — and acid — catalyzed frac­tionation processes), reaction temperature, reaction time and the concentration of H+ are the major contributed parameters to the severity of fractionation. A pro­posed parameter to describe the severity for ethanol fractionation is defined as a severity parameter:

where t is the reaction time (min), and T is the reaction temperature (°C), and [H+] represents the pH of the cooking liquor at 20°C for the solutions.

The effects of severity parameter on the removal of lignin and hemicelluloses are different. Cooking liquor rich in ethanol acts as an effective solubilizer of lignin, but the elution of hemicelluloses is minor. It has been reported that under the highest severity value, about 80% of the original lignin was dissolved into the solution as compared with a low value of around 30% for hemicelluloses [22].