Environmental Engineering Reference
In-Depth Information
Table 1. Composition of some lignocellulosic feedstocks.
Unit
(dry)
Parameter
Softwood
Switchgrass
Corn stover
Wheat straw
Water % 15 15 15 15
LHV MJ/kg 19.6 18.6 18.51 17.56
Cellulose % 44.55 35.39 38.12 32.64
Glucan (C6) % 44.55 35.39 38.12 32.64
Hemicellulose % 21.9 26.52 25.29 22.63
Xylan (C5) % 6.3 22.44 20.25 19.22
Arabinan (C5) % 1.6 2.73 2.03 2.35
Galactan (C6) % 2.56 0.96 0.74 0.75
Mannan (C6) % 11.43 0.39 0.41 0.31
Lignin % 27.67 18.17 20.24 16.85
Acids % 2.67 2.15 4.84 2.24
Extractives % 2.88 11.46 4.78 12.95
Ash % 0.32 4.28 8.59 10.22
C % 50.26 46.9 46.75 43.88
H % 5.98 5.54 5.49 5.26
O % 42.14 41.96 38.4 38.75
N % 0.03 0.62 0.67 0.63
S % 0.01 0.7 0.1 0.16
Sources: softwood Hammelinck et al., 2005; swithgrass EERE 2008 (biomass sample type: Switchgrass
Alamo Whole Plant #94); corn stover EERE 2008 (biomass sample type: Corn Stover Zea Mays
Stalks and Leaves w/o cobs #55); wheat straw EERE 2008 (biomass sample
type: Wheat Straw (Triticum Aestivum) Thunderbird Whole Plant #154).
3.2. Technological Processes
Biomass must be chemically converted for production of biofuels and biochemicals.
Obviously, changes are necessary to convert biomass from a solid to a liquid state. As
discussed in the previous section, fundamental is the biomass feedstock composition: it
generally has too little hydrogen (which must be added), too much oxygen (which must be
rejected), and other undesirable elements (such as nitrogen and sulphur) which also must be
rejected (Cherubini and Jungmeier, 2008). The aim of each technological process which acts
on raw biomass can be summarized in depolymerising and deoxygenating the biomass
components. Especially for producing fuels, deoxygenation is particularly important as the
presence of oxygen reduces the heat content of the molecules, while some chemical products
may require much less deoxygenation, because the presence of oxygen often provides
valuable physical and chemical properties to the compound (Lange, 2007).
In order to convert biomass feedstock into valuable products within a biorefinery
approach, several technological processes must be jointly applied in multiple steps. These
