Preimpregnation: An important step for biomass refining processes

Lignocellulosics treatment via rapid aqueous/steam processes is a heterogeneous reaction that can result in a non-uniform product distribution due to poor contact of reactants within the lignocellulosic matrix. This unfavorable situation could be aggravated when the steam treatment is applied to lignocellulosics using restricted amounts of water such as in "steam explosion" processes. However, by impregnation prior to steam treatment, uniform product distributions can be achieved. In the impregnation steps, reactive agents are forced into the lignocellulosic matrix at relatively low temperatures, preferably below 100 degrees C. This warrants an uniform chemical concentration through the matrix. The advantages of impregnation are more evident when straws are fractionated using aqueous/steam treatments: significant amounts of extractives can be removed in the impregnation steps. We also show that during barley straw impregnation at different levels of NaOH and three temperatures, 25, 60 and 100 degrees C, for 10 min of impregnation, a considerable amount of ash is removed (up to 86 wt% of the initial ash) along with extractives. Therefore, an improved quality of fibers can be obtained from straw by impregnation prior to steam treatment. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.