Eucalyptus
Eucalyptus is a diverse genus of flowering trees in the myrtle family. There are more than 700 species of Eucalyptus, mostly native to Australia. Eucalyptus globulus and Eucalyptus grandids are the most common varieties and are generally used in papermaking. The fiber length of eucalyptus is relatively short and uniform with low coarseness compared with other hardwoods commonly used as pulpwood. The fibers are slender, yet relatively thick walled. This gives uniform paper formation and high opacity that are important for all types of fine papers. Eucalyptus is suitable for many tissue papers, as the short and slender fibers gives a high number of fibers per gram and low coarseness contribute to softness of the paper.
Eucalyptus is one of the fastest growing hardwood trees in the world. It is cultivated in more than 90 countries and represents 8% of all planted forests all over the world [237]. Eucalyptus has adequate chemical properties that make it well suited for cellulosic ethanol conversion processes due to the high content in cellulose and hemicellulose [238]. Composition analysis of eucalyptus biomass depends on the species used; there are wide variations between different species, and analysis of Eucalyptus x urograndis is shown in table 3.22 as an example [239, 226]. A number of studies have being carried out concerning eucalyptus biomass production in order to obtain high yielding clones of this species, genetically improved, as well as eucalyptus acclimation to different climate conditions [240242]. In addition, many studies related to ethanol production from eucalyptus biomass at laboratory scale can be found in the literature. However, it was not possible to find pilot plant scale studies using eucalyptus as a feedstock.
The organosolv method is a widely tested pretreatment on eucalyptus [243-247], although experiments with acid pretreatment
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Table 3.22 The average composition analysis of Eucalyptus x urograndis [239, 226].
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[248] and hydrothermal [249] pretreatments are also known. In a more detailed eucalyptus pretreatment experiment, McIntosh and Vancov have studied the effects of combined severity factor of dilute acid pretreatment on the saccharification of eucalyptus forest thinning residues [248].
In another recent study, eucalyptus globulus wood samples were subjected to non-isothermal autohydrolysis in order to solubilize hemicelluloses, leading to treated solids of increased cellulose content and enzyme digestibility. In this study, the auto-hydrolyzed solids obtained were assayed as substrates for bioethanol production by simultaneous saccharification and fermentation (SSF). In this study, Romani et al. reported the production of up to 67.4 g ethanol/L, corresponding to 91% of the stoichiometric amount calculated from the cellulose content of eucalyptus variety studied [250].
In 2011, Gonzalez and coworkers reported their results on a simulated financial evaluation in the conversion of eucalyptus grown in the Southern United States into cellulosic ethanol using dilute acid process, as two publications in the journal, Biomass and Bioenergy [251, 239]. The flow chart of the complete process used in this techno-economic evaluation is shown in Figure 3.3. Their calculations predicted that the cost of ethanol would be
$0.49 per liter, with a capital expenditure (CAPEX) cost of $1.03 per liter. In the cost analysis, they assumed an average ethanol yield of approximately 347.6 L of ethanol per dry Mg of eucalyptus with average carbohydrate content in the biomass around 66.1%. Furthermore, the analysis revealed the main cost drivers as: biomass, enzyme, tax, fuel (gasoline), depreciation and labor. In addition, they predicted that the process is very sensitive to biomass cost, carbohydrate content (%) in biomass and enzyme cost.