Authors: Kamila Buzała Piotr Przybysz Justyna RosickaKaczmarek Halina Kalinowska
Publish Date: 2015/05/12
Volume: 22, Issue: 4, Pages: 2737-2747
Abstract
Poplar and pine cellulosic pulps derived by the sulfate process Kappa numbers of 154 and 314 respectively and a poplar thermomechanical pulp TMP Kappa number of 1247 as well as 043–08 mm woodchips of various botanical origins poplar birch lime oak beech pine and spruce and poplar chips of five different average particle sizes ranging from 16–20 to 043 mm were digested by a commercial preparation of cellulases and xylanases NS22086 from Novozymes Yields of reducing sugars derived by enzymatic hydrolysis of the poplar and pine pulps that were obtained by the sulfate method achieved 100 and 89 on a dry weight basis 523 and 359 dw wood respectively while glucose yields reached 79 and 707 dw pulp 413 and 286 dw wood respectively Enzymatic hydrolysis of the pine TMP resulted in glucose and reducing sugars yields of only 140 and 367 dw pulp around 13 and 34 dw wood respectively Yields of glucose and soluble reducing sugars released from the poplar chips were inversely proportional to their size and varied between around 53–78 and 157–224 dw respectively Reducing sugars yields from beech birch and lime chips were slightly higher than from the poplar chips of the same size while pine spruce and oak chips were less susceptible to enzymatic digestion The dominating sugars in the hydrolysates of woodchips were glucose and cellobiose 70–90 w/w of the sum of 5 detected sugars while mannose xylose and arabinose concentrations were relatively lowA sustainable production of biofuels and valuable chemicals from renewable lignocellulosic biomass has been considered a safe and ethical alternative to consumption of fossil resources that will be soon exhausted To enhance the recovery of monosaccharides from cellulose and hemicelluloses that are coated by lignin a variety of biomass disintegration and pretreatment methods have been developed Chaturvedi and Verma 2013 All of them require a substantial energy input and their costs strongly affect the economy of plant biomass conversion Furthermore the harsh thermal pretreatment leads to losses in sugars and generates fermentation inhibitors like furfural 5hydroxymethylfurfural 5HMF and phenolic acids Stoutenburg et al 2011 These harmful compounds reducing productivity of fermentation processes need to be removed from biomass hydrolysates that increases overall costs of lignocellulose conversions Recent advances in production and engineering of enzymes that cleave cellulose Wilson 2009 and hemicelluloses Van Dyk and Pletschke 2012 cause that enzymemediated processes are increasingly used for conversion of plant biomass In contrast to cellulose which is characterized by a highly regular structure irrespective of its source the structure of hemicelluloses which are polymers of pentoses and hexoses depends on their botanical origin Xylose and other pentoses derived from hemicelluloses are usually less efficiently converted to fermentation products than glucose Stoutenburg et al 2011 Their content in enzymatic hydrolysates depends on conditions of biomass pretreatment For instance enzymatic hydrolysates of hardwood and softwood cellulosic pulps derived by kraft pulping are rich in glucose constituting above 73 soluble sugars Buzała et al 2015In this study we attempted to assess the digestibility of a thermomechanical pulp TMP and compare it with the digestibility of poplar and pine cellulosic pulps derived by the sulfate process as well as woodchips of various botanical origins and sizes For this purpose we estimated the digestibility of 7 different sorts of 043–08 mm woodchips poplar birch lime oak beech pine and spruce and determined the effect of poplar chips dimensions from 043 to 20 mm on results of enzymatic digestionThermomechanical pulps are made by heating woodchips with steam under high pressure followed by mechanical disintegration These pulps contain much more lignin than kraft pulps and their chemical composition is almost the same as that of woodchips Ma et al 2012 Apart from cellulose hemicelluloses and lignin TMPs contain proteins Hafren 2007 and fatty acids Fleet and Breuil 1998Woodchips derived in large amounts from forestry wastes represent an inexpensive and easily available source of lignocelluloses Chipping and related mechanical methods increase the surface area of lignocellulosic materials but chips are known to be resistant to enzymatic digestion owing to the protective impact of lignin Therefore the energyconsuming mechanical disintegration is usually combined with chemical methods enhancing the access of enzymes to cellulose and hemicelluloses Because of differences in the lignin content the digestibility of chips from various botanical sources may be different Apart from the sort of woodchips also their dimensions may affect the availability of cellulose and hemicellulose fibers to degrading enzymes
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