THE INFLUENCE OF SO2 AND H2SO4 IMPREGNATION OF WILLOW PRIOR TO STEAM PRETREATMENT

In this investigation steam pretreatment of willow with the addition o f SO2 or H2SO4 was studied, the aim being to recover both the cellulos e and the hemicellulose fr actions. The willow was steamed (1 bar satu rated steam) prior to impregnation with 0-3% H2SO4 or 1% SO2 (w/w subs trate). The pretreatment experiments were performed at temperatures in the range 160-230 degrees C for 10 min.The highest xylose recovery wi th H2SO4 impregnation was obtained using 3% H2SO4 at 190 degrees C, wh ere 80% of the available xylose could be recovered by washing. At thes e pretreatment conditions, a glucose yield after enzymatic hydrolysis of 67%, based on the glucan available in the raw material, was achieve d. The maximum glucose yield, 95%, was obtained when the willow was im pregnated with 1% SO2 and pretreated at 200 degrees C. At these condit ions, 62% of the original xylose was solubilized. As glucan is the mai n constituent of willow, a high yield of glucose is of more importance than a high yield of xylose, leading to the conclusion that impregnat ion with SO2 is better than impregnation with H2SO4.