Page 256 - Biosystems Engineering

234 Cha pte r Se v e n

(e.g., methanol and ethanol). Solvent addition can impact bio-oil
properties by two mechanisms: (1) physical dilution and (2) ester-
ification and acetilazation, preventing chain growth responsible for
the increase in molecular weight and viscosity.
Blending pure pyrolysis oil with high cetane–oxygenated com-
pounds is another effective method for upgrading bio-oils for diesel
engine applications. Tests on blends of pyrolysis oils with up to 56.8
mass% of dyglyme (diethylene glycol dimethyl ether), an oxygenated
compound with a very high cetane number (112 to 130), have been
reported (Chiaramonti et al. 2007). Minor differences were found in
the overall combustion process with diesel fuels. It has been reported
that mixtures of 72 percent of pyrolysis oils, 24 percent methanol, and
4 percent cetane enhancer (tetraethyl glycol dinitrate) also show sim-
ilar performances to that of diesel oil (Suppes et al. 1996). Mixtures
with ethanol and nitrate alcohols have also been studied (Czernik
and Bridgwater 2004, Solantausta et al. 1993). Ethers have been iden-
tified as good fuels for diesel engines. Diglyme (diethylene glycol
dimethyl ether) is suitable for blending with bio-oils (Bertoli et al.
2000). The maximum amount of bio-oil allowed for stable operation
was 44.1 percent (by weight) in these studies. The economic feasibil-
ity of these approaches is limited by the high cost of cetane improv-
ers, solvents, and emulsifiers.
Biodiesel is another renewable fuel derived from triglycerides
that can be used as cetane improvers for bio-oils. Heating value, den-
sity, and viscosity of biodiesels are comparable to those of No. 2 die-
sel from petroleum. Biodiesel is also a very good solvent. Producing
bio-oil/biodiesel blends can be a simple system for using crude bio-
oils as diesel fuel extenders (Garcia-Pérez et al. 2007b).

7.6.3 Producing Chemicals from Bio-Oils
Crude bio-oils are a potential source of chemicals. Although most of
the crude bio-oil are expected to be processed as transportation fuels
or as a source of energy, chemicals could also make an important con-
tribution to the profitability of this technology, mainly because chem-
icals are much more expensive than fuels. In the case of crude petro-
leum oils, about 88 percent is processed as fuel; the other 12 percent
is converted into other materials such as plastic. Detailed reviews on
existing and potential short-term applications of crude bio-oils as a
source for higher-value products can be found elsewhere (Radlein
1999; Czernik and Bridgwater 2004).
Three approaches have been studied to obtain chemicals from
crude bio-oils: using crude bio-oils, using fractions, and isolating
individual compounds (see Fig. 7.11).

Products from Whole Bio-Oils
Useful products can be obtained from crude bio-oil by taking advan-
tage of its most abundant functional groups: carbonyl, carboxyl, and