Page 248 - Biosystems Engineering

226 Cha pte r Se v e n

burner to heat two horizontal plates over which the biomass is con-
veyed (Bridgwater and Peacocke 2000; Garcia-Pérez et al. 2002).

7.6 Crude Bio-Oils
Fast pyrolysis can convert up to 70 mass% of the biomass into crude
bio-oils. This section describes the physicochemical characteristics of
these oils as well as their potential uses as fuels and chemicals.

7.6.1 Chemical Composition of Crude Bio-Oils
The chemical composition of bio-oil depends on feedstock composi-
tion, pyrolysis conditions, and upgrading technology used in its pro-
duction. The elemental composition of bio-oil on an anhydrous basis
is not very different than that of the feedstock: carbon content, 44 to
47 mass%; hydrogen content, 6 to 7 mass%; oxygen content, 46 to 48
mass%; and nitrogen content, 0 to 0.2 mass%. The content of water is
usually between 10 and 30 mass%.
More than 300 organic compounds have been identified in these
oils (Evans and Milne 1987a, 1987b; Diebold et al. 1999; Boucher et al.
2000 Oasmaa et al. 2003a, 2003b; Ba et al. 2004a, 2004b; Czernik et al.
2004, Garcia-Pérez et al. 2002, 2007b). A detailed chemical character-
ization based on the quantification of individual species is almost
impossible to achieve and has limited practical application. A charac-
terization strategy based on the quantification of macrofractions or
chemical families instead of individual species is more useful to get
an overview of bio-oil composition (Garcia-Pérez et al. 2007b). The fit-
ting of thermogravimetry (DTG) curves, like the one seen in Fig. 7.9,
suggests that these materials could be broadly described as a mixture
of seven macrogroups (Garcia-Pérez et al. 2007a, 2007b, Garcia-Pérez
et al. 2008). The overall differences in the chemical composition of

9 9
550°C 580°C
8 8
7 6 7 6
DTG (mass%/min) 5 4 DTG (mass%/min) 5 4

2 3 3 2 B
B E F A E F
1 1 C
A C D D
0 0
0 100 200 300 400 500 0 100 200 300 400 500
Temperature (°C) Temperature (°C)
FIGURE 7.9 Deconvolution of DTG curves of bio-oils produced at two pyrolysis
temperatures (Garcia-Pérez et al. 2008).