Environmental Engineering Reference
In-Depth Information
2. Inorganic matter
a. Solid, crystalline
minerals, e.g., consisting of phosphates, carbonates,
silicates, chlorides, sulfates, oxyhydroxides, and nitrates
b. Solid, semicrystalline
poorly crystallized mineraloids of certain silicates,
phosphates, hydroxides, etc.
c. Solid, amorphous
phases that are formed as glasses, silicates, etc.
3. Fluid matter
fluid, liquid, and gas (moisture, gas, and gas/liquid inclusions
associated with both organic and inorganic matter)
2.2 MAIN STRUCTURAL ORGANIC CONSTITUENTS
The composition of biomass fuels is associated with a multitude of physical forms, but
for species that belong to the plantcategory, the main structural cell wall components
are nearly always cellulose, hemicellulose and lignin (Klass, 1998). Other major bio-
organic polymer structures that are found in nature are starch (e.g., in maize, banana,
etc.) and chitosan (e.g., shrimp shells).
2.2.1 Cellulose
Cellulose is a homopolysaccharide (C 6 H 10 O 5 ) n of glucose C 6 sugar (hexosan) units that
constitute the main part of the cell walls of plants and synthesized in nature with approx-
imately 10 11 t
year −1 (Kamm et al., 2006); it is the world
s most common organic bio-
polymer. It is naturally incorporated in fibrous products such as cotton and kapok, and
further processed from plants, it forms the raw material for many manufactured goods,
such as paper, paperboard, rayon, cellophane, and celluloid, a product that was used for
making photographic and movie filmmaterial until the mid-1930s (Simon et al., 1998).
Most biomass material consists of about 40
'
50 wt% cellulose on a dry fuel basis. The
cellulose structure consists of up to 14,000 linearly coupled D -glucopyranoside units
connected by
-
-glycosidic linkages in a 1 : 4 fashion (Mohan et al., 2006; Sjöström,
1993; Solomons, 1984). Figure 2.3 depicts this molecular structure, with the repeating
unit consisting of two glucose units called
β
Thus, it is a high-molecular-
weight species, with a molecular mass typically of the order of 10 6 kg
cellobiose.
kmol −1 .The
β
-glycosidic linkages are commonly known as weak bonds that are easily broken
and help initiate the degradation of the cellulose molecule.
The structure shows that
OH groups form both inter- and intramolecular hydro-
gen bonds, which cause different polymer chains to arrange themselves in parallel
configurations to form a crystalline supermolecular structure. This resulting structure
makes cellulose completely insoluble in ordinary aqueous solutions. The linear cel-
lulose chains form bundles that tend to twist so as to make ribbonlike microfibrilic
anisotropic (highly ordered) structures that are highly oriented in the cell wall struc-
ture (Balat et al., 2009). This structure ensures a relatively high stability against ther-
mal and biochemical degradation compared to hemicellulose and starch. These
degradation processes are dealt with in depth in Part III of this topic.
 
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