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Sulfite pretreatment (SPORL) for robust enzymatic saccharification of spruce and red pine

Zhu, J.Y., Pan, X.J., Wang, G.S., Gleisner, R.
Bioresource technology 2009 v.100 no.8 pp. 2411
Pinus resinosa, Picea, wood chips, softwood, cellulose, lignocellulose, hemicellulose, sulfites, saccharification, enzymatic hydrolysis, glucans, glucose
This study established a novel process using sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) for robust and efficient bioconversion of softwoods. The process consists of sulfite treatment of wood chips under acidic conditions followed by mechanical size reduction using disk refining. The results indicated that after the SPORL pretreatment of spruce chips with 8-10% bisulfite and 1.8-3.7% sulfuric acid on oven dry (od) wood at 180°C for 30min, more than 90% cellulose conversion of substrate was achieved with enzyme loading of about 14.6 FPU cellulase plus 22.5 CBU β-glucosidase per gram of od substrate after 48h hydrolysis. Glucose yield from enzymatic hydrolysis of the substrate per 100g of untreated od spruce wood (glucan content 43%) was about 37g (excluding the dissolved glucose during pretreatment). Hemicellulose removal was found to be as critical as lignin sulfonation for cellulose conversion in the SPORL process. Pretreatment altered the wood chips, which reduced electric energy consumption for size reduction to about 19Wh/kg od untreated wood, or about 19g glucose/Wh electricity. Furthermore, the SPORL produced low amounts of fermentation inhibitors, hydroxymethyl furfural (HMF) and furfural, of about 5 and 1mg/g of untreated od wood, respectively. In addition, similar results were achieved when the SPORL was applied to red pine. By building on the mature sulfite pulping and disk refining technologies already practiced in the pulp and paper industry, the SPORL has very few technological barriers and risks for commercialization.