Enhanced Xylooligosaccharides Yields and Enzymatic Hydrolyzability of Cellulose using Acetic Acid Catalysis of Poplar Sawdust

Abstract

To increase the value and promote the utilization of woody processing residues, poplar sawdust was used to produce xylooligosaccharides (XOS) with polymerization degrees of 2–6 by acetic acid catalysis. This process is considered to be an environmental friendly process, and the remaining solid fraction was decomposed to fermentable sugars by enzymatic hydrolysis. Response surface methodology (RSM) was applied to determine the main factors affecting the yield of XOS. XOS production was optimal at 170 ± 3 °C with a 6.5 ± 1% acetic acid concentration and 27 ± 2 min reaction time. These conditions produced a 36.0 ± 0.8% XOS yield from xylan, similar to the predicted value from the model. Careful analysis of the kinetic profile of XOS revealed that xylobiose to xylohexaose were the main products. Detectable degraded chemicals accounted for 71.0% xylan during acidic hydrolysis. When using enzymatic hydrolysis at a cellulase loading of 20 FPU/g cellulose, a 51.0% yield was achieved, which represented an 80% increase relative to pretreated autohydrolysis (28.3%), and reached production yields similar to that of diluted sulfuric acid pretreatment.