Abstract
The digestibility of cellulosic pulps derived by the sulfate process was assessed using commercial multienzyme preparations. Poplar wood pulps of relatively low lignin contents (Kappa numbers of 15.4–24.2), birch, beech and pine wood pulps (Kappa numbers of 25.8–31.4), and wheat straw pulp (Kappa number of 29.5) were efficiently hydrolyzed by a commercial preparation NS-22086 from Novozymes, containing cellulases and xylanases. At around 1.3 % (w/w) substrate concentration, yields of glucose from the poplar pulps were around 80 % on a dry weight (d.w.) basis while for the other four pulps they varied between approximately 70 % (for pine pulp) and 78 % d.w. (for beech and wheat straw pulps). At around 7.4 % (w/w) poplar pulp (Kappa number of 24.2) concentration, glucose yield was around 61 % d.w. The NS-22086 preparation almost completely saccharified fines from a paper mill (around 74 % glucose yields on a dry weight basis) while digestion of poplar chips (particle size of 1.6–2.0 mm) and wheat straw chaff (particle size up to 6 mm) yielded around 5.3 and 14 % d.w. glucose, respectively (total reducing sugars yields of around 16 and 23 % d.w., respectively). These results show that plant biomass may be efficiently converted to glucose-rich hydrolysates by a two-step processing, consisting of kraft pulping followed by treatment with endo- and exo-type cellulases and hemicellulases. Glucose-rich hydrolysates may be also obtained by enzymatic digestion of fines from paper mills.
Highlights
Lignocellulosic biomass has been considered as a renewable, vast, inexpensive and underutilized resource of sugar feedstocks for production of biofuels and valuable chemicals
The NS-22086 preparation almost completely saccharified fines from a paper mill while digestion of poplar chips and wheat straw chaff yielded around 5.3 and 14 % d.w. glucose, respectively. These results show that plant biomass may be efficiently converted to glucose-rich hydrolysates by a two-step processing, consisting of kraft pulping followed by treatment with endo- and exo-type cellulases and hemicellulases
Wood pulps differ in the lignin and hemicelluloses contents and their purity is often described by the Kappa number, which is approximately proportional to the lignin level, and varies between 1 and 100
Summary
Lignocellulosic biomass has been considered as a renewable, vast, inexpensive and underutilized resource of sugar feedstocks for production of biofuels and valuable chemicals. Cellulosic pulps may be regarded as glucose-rich streams for bioethanol production because of the low contents of substances that reduce the digestibility of the cellulose fibers and because of the relatively low price of 700–800 USD per one ton (World Pulp Monthly, January 2014). These pulps are free of typical fermentation inhibitors, like furfural and 5-hydroxymethylfurfural, that are generated by many other pretreatment processes and which considerably reduce conversion yields (Stoutenburg et al 2011). The side products of kraft pulping (lignin-rich streams) are used to provide heat and electricity for paper mills that reduces the overall costs of processing (Chakar and Ragauskas 2004)
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