Abstract
In order to meet the world’s growing energy demand and reduce the impact of greenhouse gas emissions resulting from fossil fuel combustion, renewable plant-based feedstocks for biofuel production must be considered. The first-generation biofuels, derived from starches of edible feedstocks, such as corn, create competition between food and fuel resources, both for the crop itself and the land on which it is grown. As such, biofuel synthesized from non-edible plant biomass (lignocellulose) generated on marginal agricultural land will help to alleviate this competition. Eucalypts, the broadly defined taxa encompassing over 900 species of Eucalyptus, Corymbia, and Angophora are the most widely planted hardwood tree in the world, harvested mainly for timber, pulp and paper, and biomaterial products. More recently, due to their exceptional growth rate and amenability to grow under a wide range of environmental conditions, eucalypts are a leading option for the development of a sustainable lignocellulosic biofuels. However, efficient conversion of woody biomass into fermentable monomeric sugars is largely dependent on pretreatment of the cell wall, whose formation and complexity lend itself toward natural recalcitrance against its efficient deconstruction. A greater understanding of this complexity within the context of various pretreatments will allow the design of new and effective deconstruction processes for bioenergy production. In this review, we present the various pretreatment options for eucalypts, including research into understanding structure and formation of the eucalypt cell wall.
Highlights
Approximately 40% of the world’s transportation fuels are derived from non-renewable sources, the combustion of which directly contributes to global climate change (Simmons et al, 2008; González-García et al, 2012)
This study demonstrates eucalypt biomass conversion from debarked biomass, bark accounts for approximately 10–12% of tree biomass residue processed from a plantation (Perlack et al, 2005; Zhu and Pan, 2010), which contains considerable levels of glucose (40%) and xylose (10%) (Lima et al, 2013)
This study demonstrates how combining methods can effectively reduce the severity of the pretreatment required to deconstruct biomass, which will lessen the formation of inhibitory products and the costs associated with enzymatic saccharification
Summary
Approximately 40% of the world’s transportation fuels (fossil fuels) are derived from non-renewable sources, the combustion of which directly contributes to global climate change (Simmons et al, 2008; González-García et al, 2012). As structural polysaccharides represent the non-edible portions of plants, fuel synthesized from cellulose and hemicellulose can help alleviate the competition between energy and agriculture. Crops intended for this purpose are known as the second-generation biofuel feedstocks. Monomeric subunits of cellulose and hemicellulose degrade in low pH conditions, generating aldehydes [furfural and 5-hydroxymethyl-2-furaldehyde (5-HMF)] and organic acids Formation of these degradation products inhibits fermentation by reducing available sugars and limiting microbial growth (Zheng et al, 2009; Soccol et al, 2011; Puri et al, 2012).
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