Environmental Engineering Reference
In-Depth Information
taBle 8.5
Properties of Fast Pyrolysis Bio-oil compared with Petroleum heavy Fuel oil
Properties
Fast Pyrolysis Bio-oil
Petroleum heavy Fuel oil
Bio-oil yield, % by weight of biomass
17-75
NA
Water content, % by weight of bio-oil
0-40
0.1
pH
2.3-5.5
NA
Specific gravity
0.91-1.29
0.94
Elemental composition, % by weight
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
Ash
46-78
5-12
11-47
0-10
Trace
Trace-1.5
85
11
1
0.3
0.5-3.0
0-0.1
Viscosity, centistokes at 50°C
1-50
50
Higher heating value, MJ/kg
14-41
40
Pour point, °C
-36 to 25
-18
Solids, % by weight
0.2-3
1
Stability
Poor
Good
Source:
Czernik, S. and Bridgwater, AV.,
Energy Fuel
, 18, 590-598, 2004 and Mohan, D., Pittman,
CU., and Steele, PH.,
Energy Fuel
, 20, 848-889, 2006.
NA, not applicable.
because these will determine the processing steps needed for upgrading. In addition to H
2
O content,
which was described earlier, fast pyrolysis bio-oil is composed of the following classes of oxygenated
organic compounds in descending order of occurrence (Bridgewater et al. 2001): pyrolytic lignin,
15-25%; aldehydes (formaldehyde, acetaldehyde, hydroxyacetaldehyde, and glyoxal), 10-20%;
carboxylic acids (formic, acetic, propionic, and butyric, etc.), 10-15%; carbohydrates (cellobiosan,
levoglucosan, and oligosaccharides); 5-10%; phenols (phenol, cresols, guaiacols, and syringols),
2-5%; alcohols (methanol and ethanol), 2-5%; ketones (acetol and cyclopentanone), 1-5%; and
furfurals, 1-4%. The key challenge in upgrading these compounds to hydrocarbon transportation
fuels is efficient de-oxygenation through hydrotreating, but to limit consumption of hydrogen,
saturation of aromatic rings should be avoided (NSF 2008).
Properties of pyrolysis bio-oil and comparisons to petroleum heavy fuel oil are shown in Table 8.5.
The ranges of property values in this table are a compilation from a wide diversity of biomass
feedstocks, such as hardwoods, softwoods, bark, bagasse, straw, oil seed feedstocks, microalgae,
and other sources (Mohan et al. 2006). Additional factors that affect the bio-oil properties listed in
Table 8.5 are reaction temperature (400-650°C) and reaction residence time (0.3 s to 30 min).
8.3.2.4 stability of Bio-oil
Diebold (2000) reviewed reactions occurring in pyrolysis bio-oil during long-term storage and
provided recommendations on improving storage stability. Reactions during aging of bio-oil appear
to be catalyzed by organic acids (low pH) and elements found in char. These aging reactions result in
changes to the molecular weight distribution of the bio-oil components, increase in bio-oil viscosity,
and phase separation of higher-molecular-weight oligomers and polymers. Oxygen from air reacts
with organics in bio-oil to form peroxides that catalyze polymerization of olefins and addition of
mercaptans to olefins. Organic acids react with alcohols to form esters and water, and aldehydes
react with components in bio-oil such as water, alcohols, other aldehydes, phenolics, and proteins
to form hydrates, ethers, resins, oligomers, and dimers. In addition, olefins polymerize to form
