Effect of Microwave-Assisted Pretreatment Conditions on Hemicellulose Conversion and Enzymatic Hydrolysis of Norway Spruce

The present study investigated the ability of pressurized microwave pretreatment to convert softwood lignocellulose to fermentable monosaccharides. Norway spruce lignocellulose was subjected to microwave pretreatment (600 and 1200 W) under high pressure at different temperatures. Microwave pretreatment at mild acid concentrations (0.05–0.1 % H2SO4), temperatures of 170 and 200 °C, and a very short incubation time (5 min) released 84–100 % of hemicellulosic monosaccharides (mannose, galactose, and xylose). In addition, minimal amounts of degradation products (5-(hydroxymethyl)-2-furaldehyde, levulinic acid) were formed. The highest yield of fermentable sugars was 75 %, after both the pressurized microwave pretreatment with conditions 0.05 % H2SO4/600 W/200 °C/5 min and enzymatic hydrolysis with 20 FPU Celluclast 1.5 L, 400 nkat of Novozyme 188, and polyethyleneglycol (PEG) 4000 (0.3 g/g of pretreated material). Results showed that already 0.05 % H2SO4 used in microwave pretreatment could effectively liberate hemicellulose monosaccharides without serious monosaccharide degradation and form a basis for enzymatic hydrolysis.