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The effect of chemical and physical characteristics of spruce SEW pulps on enzymatic hydrolysis

Yamamoto, Minna, Iakovlev, Mikhail, van Heiningen, Adriaan
Cellulose 2014 v.21 no.5 pp. 3395-3407
Picea, biofuels, biomass, cellulose, conifers, enzymatic hydrolysis, enzymes, forests, glucose, hemicellulose, hydrolysis, lignin, lignocellulose, polymerization, pulp, softwood, stemwood, Canada, Russia, Scandinavia, United States
Conifers, which are the most abundant biomass species in Nordic countries, USA, Canada and Russia, exhibit strong resistance towards depolymerization by cellulolytic enzymes. At present, it is still not possible to isolate a single structural feature which would govern the rate and degree of enzymatic hydrolysis. On the other hand, the forest residues alone represent an important potential for biochemical production of biofuels. In this study, the effect of substrate properties on the enzymatic hydrolysis of softwood was studied. Stem wood spruce chips were fractionated by SO₂–ethanol–water (SEW) treatment to produce pulps of varying composition by applying different operating conditions. The SEW technology efficiently fractionates different types of lignocellulosic biomass by rapidly dissolving hemicelluloses and lignin. Cellulose remains fully in the solid residue which is then treated by enzymes to release glucose. The differences in enzymatic digestibility of the spruce SEW pulp fibers were interpreted in terms of their chemical and physical characteristics. A strong correlation between the residual lignin content of SEW pulp and enzymatic digestibility was observed whereas cellulose degree of polymerization and hemicellulose content of pulp were not as important. For the pulps containing about 1.5 % (w/w) lignin, 90 % enzymatic digestibility was achieved at 10 FPU enzyme charge and 24 h of hydrolysis time.