The wet oxidation process (water; oxygen and elevated temperature) was
investigated under alkaline conditions for fractionation of hemicellu
lose, cellulose, and lignin from wheat straw. At higher temperature an
d longer reaction time, a purified cellulose fraction (69% w/w) was pr
oduced with high enzymatic convertibility to glucose (66% w/w). At 185
degrees C, nearly three times more hemicellulose was solubilized than
at 150 degrees C. Optimum conditions for hemicellulose solubilization
and cellulose convertibility were for 60 g l(-1) straw: 185 degrees C
: 6.5 g l(-1) Na2CO3, and 12 bar O-2 with a 15-min reaction time. Unde
r these conditions, 55% of the lignin and 80% of the hemicellulose wer
e solubilized, while 95% of the cellulose remained in the solid fracti
on. At 185 degrees C, the reaction kinetics was of pseudo first-order.
The rate constant for hemicellulose solubilization was higher than th
at for lignin, whereas the rate for cellulose was very low. The cellul
ose recovery (95-100%) was significantly higher than that for hemicell
ulose (60%). At temperatures above 185 degrees C, recoveries decreased
due to increased degradation. Only half of the COD-content could be a
ccounted for by saccharides and carboxylic acids; hence, a significant
proportion of reaction products remained unidentified. (C) 1998 Elsev
ier Science Ltd. All rights reserved.