Page 197 - Advances in bioenergy (2016)

Further, bio-oils can be separated into water-soluble (aqueous phase) and insoluble
components (heavy organic phase). The insoluble heavy organics can be treated to produce
chemicals and the soluble aqueous organic phase can be further steam reformed to produce H .
2
Alternatively, the bio-oil can be treated in an autothermal or steam reformer to produce H .
2
Just by increasing the pyrolysis temperature range above 550–750°C, it is easy to enhance the
gaseous yield to 45–50% compared with the conventional yield of 30–35% at below 500°C.
Demirbas (2002) has discussed about H yield which increased from 27–41% to 41–55% of
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29
the total gas yield on a volumetric basis under the same condition. Catalytic pyrolysis and in
situ pyrolysis vapor upgrading are other routes to achieve higher yield of H , where Vaidya
2
and Rodrigues, reported about the usage of Ca and Cr oxides, and Garcia et al. 20,23 have
discussed about the Ni/Al catalyst to enhance H gas yield. Other methods to avoid the N and
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2
CO dilution and to achieve the energy density of gaseous effluents from pyrolysis of biomass
2
were combined with the secondary decomposition of gaseous intermediate with the
introduction of additional water (>800°C) for production of hydrogen-rich gas (65 g of H /kg
2
of rice husk), known to be a high temperature pyrolysis >600°C, as discussed by Zhao et al. 30
Yield of biomass pyrolysis can be maximized and summarized as follows: (1) charcoal—a
low temperature, low- and moderate heating rate process as followed in slow and intermediate
pyrolysis, (2) liquid products—a medium temperature, high heating rate, short gas residence
time process (as in fast, flash, and intermediate pyrolysis), and (3) fuel gas—a high
temperature, low heating rate, long gas residence time process (high temperature pyrolysis as
in fast and intermediate cases).

GASIFICATION OF BIOMASS FOR H PRODUCTION
2

Coke, coal gasification at higher temperature and blended biomass co-gasification in the
presence of partial O /air and/or steam above 700°C, used as syngas (CO, CO , and H ) can
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2
2
be delivered as output of the process, whereas only air utilization gives rise to producer gas. In
order to maximize H and syngas yield with lower tar formation, catalytic cracking, gasifier
2
type, design, heating rate, temperature, space time, space velocity in catalytic bed, and

residence time can be optimized. Moreover, dolomite and CeO /SiO -supported Ni, Pt, Pd,
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2
Ru, Rh, and alkaline metal oxides can be used to catalyze the gasification process, in order to
reduce tar formation, improve the product gas purity, and to enhance conversion efficiency. As
ICP-MS analysis of biomass and char samples revealed about the inorganic contents of the
biomass such as sodium, potassium, calcium, and other alkali contents, they sometimes act as
catalysts by enhancing the decomposition rate of carbon, further converted to ash which is
collected at the bottom of the gasifier or carried away with the product gas as fly ash. This ash
deposited in the gasifier may cause sintering, fouling, agglomeration, and slogging, which can
be removed periodically to make the process systematic and for better production of

syngas. 30,24-29

When fast or intermediate pyrolysis process is carried out around 700°C, it propagates the