Page 252 - Biosystems Engineering

230 Cha pte r Se v e n

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FIGURE 7.10 Schematic representation of a physical model illustrating the
multiphase structure bio-oils.

(see Fig. 7.10) (Garcia-Pérez et al. 2006a, 2006b). The existence of
nanoparticles formed mainly by the association of units of oligomers
has been recently probed by small-angle neutron scattering (SANS)
(Fratini et al. 2006) and by dynamic rheological studies (Garcia-Pérez
et al. 2006a, 2006b).
The complex multiphase properties of bio-oils (Oasmaa and
Czernik 1999; Oasmaa et al. 2003a, 2003b; Oasmaa and Kuoppala 2004;
Ba et al. 2004a, 2004b) could create serious problems during storage
and handling (Boucher et al. 2000a, 2000b). The layering or separation
of bio-oil phases could be a problem in installations that do not have
facilities to homogenize these liquids (Oasmaa and Czernik 1999). The
presence of an aqueous upper layer phase in bio-oils is attributed to the
inability of water to dissolve in the oily matrix (Oasmaa and Czernik
1999; Boucher et al. 2000a, 2000b; Garcia-Pérez et al. 2006a, 2006b). A
separate phase also can be formed due to the presence of wood extrac-
tives (Boucher et al. 2000a, 2000b; Oasmaa et al. 2003a, 2003b; Oasmaa
and Kuoppala 2004; Garcia-Pérez et al. 2004). Specifications must
ensure that bio-oils are supplied as homogeneous liquids.
The main problem encountered in storing bio-oils is the gradual
increase in viscosity and molecular weight with the formation of sep-
arate phases in relatively short periods of time (Diebold and Czernik
1997; Diebold et al. 1999; Ba et al. 2004a, 1994b; Garcia-Pérez et al.
2006a, 2006b). Aging also happens in petroleum but at a much lower
rate. For example, although the shelf life of petroleum exceeds 6 months,
some bio-oils can only be stored for a few months or for a few weeks
in hot environments.