AFEX pretreatment does not require small particle size for efficacy (Holtzapple et al., 1990). CO2 explosion is also used for pretreatment of lignocellulosic materials. It was hypothesized that CO2 would form carbonic acid and increase the hydrolysis rate. The yield was relatively low compared to steam or ammonia explosion pretreatment, but high compared to the enzymatic hydrolysis without pretreatment (Dale and Moreira, 1982). Zheng et al. (1998) compared CO2 explosion with steam and ammonia explosion for pretreatment of recycled paper mix, sugarcane bagasse and repulping waste of recycled paper and found that CO2 explosion was more cost effective than ammonia explosion and did not cause the formation of inhibitory compounds that could occur in steam explosion