Wet oxidation is an oxidative pretreatment method that employs oxygen or air as catalyst. It allows reactor operation at relatively low temperatures and short reac­tor times [103]. It has been proven to be an efficient method for solubilization of hemicelluloses and lignin and to increase digestibility of cellulose, specially.

8.3.3.1 Process Description

Typically, the procedure for wet oxidation consists of drying and milling lignocel — lulosic biomass to obtain particles that are 2 mm in length, to which water is added at a ratio of 1 L to 6 g biomass. A compound, usually Na2CO3, is introduced to the mixture to reduce the formation of by-products. Na2CO3 addition has been shown to decrease formation of inhibitory compounds by maintaining pH in the neutral to alkaline range. Air is pumped into the vessel until a pressure of 10-12 bar is reached. This method of pretreatment is performed at 170-200 °C for a range of 10-20 min [104, 105]. The addition of air/oxygen at temperatures above 170 °C makes the process exothermic reducing the total energy demand. In general, low formation of inhibitors and efficient removal of lignin are achieved with wet oxidation pretreat­ment. On the other hand, cost of oxygen and catalyst are considered one of the main disadvantages for wet oxidation development technologies [2].