Page 260 - Biosystems Engineering

238 Cha pte r Se v e n

from the oily insoluble fraction was an economically viable activity
until the 1940s (Klar and Rule 1925). The technologies to recover these
compounds are well known but not currently used because most of
these compounds can be produced at a lower cost from other feed-
stocks derived from natural gas, crude oil, or coal.

7.6.4 Production of Transportation Fuels
There are five major concepts under study today to produce transpor-
tation fuels from bio-oils: (1) gasification of the whole bio-oils at a cen-
tralized unit followed by the synthesis of Fischer–Tropsch fuels (van
Rossum et al. 2007), (2) steam reforming of whole bio-oils or the water-
soluble fractions to produce hydrogen (Czernik et al. 2002; Takanabe
et al. 2006; Basagiannis and Verykios 2007; Bleeker et al. 2007; David-
ian et al. 2007; Iojoiu et al. 2007; Ramos et al. 2007), (3) hydrotreatment
of whole bio-oils or the water-insoluble fractions to produce green
gasoline and green diesel (Baker and Elliott 1988; Yu and Zhang 2003;
Zhang et al. 2006; Elliott 2007; Mahfud et al. 2007a, 2007b), (4) hydro-
lysis, neutralization, detoxification, and fermentation of pyrolytic sug-
ars (Prosen et al. 1993; Yu and Zhang 2003, 2004; Bhatia 2005; Muyafuji
et al. 2005; Helle et al. 2007), (5) aqueous phase catalytic processes to
produce hydrogen and/or alkanes (Huber and Dumesic 2006).

Bio-Oil Gasification
Synthesis gas can be produced by reacting bio-oil with oxidizing
°
agents (steam, oxygen) at temperatures over 600 C. Several nickel-
based catalysts have been tested to enhance the selectivity toward the
formation of synthesis gas (van Rossum et al. 2007). During bio-oil
gasification, an important fraction of bio-oils is converted to coke.
These coke-formation problems can be handled by using fluidized-
bed reactors. Van Rossum et al. (2007) proposed the use of a twin-bed
setup for the coupling of endothermic reactions (cracking, reforming)
and exothermic reactions (coke burning). The proposed system uncou-
ples the atomization/cracking of the oil and the catalytic conditioning
of the produced gases (van Rossum et al. 2007). This synthesis gas can
be further converted to produce green diesel via Fischer–Tropsch reac-
tions over ion, cobalt, nickel, and ruthenium catalysts.
Steam Reforming
Studies on steam reforming of bio-oil and several of its model com-
pounds to produce hydrogen have shown promising results (Garcia
et al. 2000; Takanabe et al. 2006; Basagiannis and Verykios 2007;
Czernik et al. 2007; Davidian et al. 2007; Iojoiu et al. 2007). The main
problem observed is the rapid formation of carbon deposits, which
seriously limits reforming times to less than 4 h, after which regen-
eration is needed (Davidian et al. 2007). The use of two reactors in
parallel operation in reforming-regeneration successive cycles has been
proposed. Although fluidized-bed reactors have shown good results