"Fast pyrolysis of elephant grass under different reactive atmospheres and catalytic upgrading of the resulting bio-oil"
Pyrolysis; bio-oil; reactive atmosphere; HZSM-5; deoxygenation
In recent years, due to the progressive depletion of conventional fossil fuels,
renewable energy sources have played an important role in the energy matrix. Among these
sources, the lignocellulosic biomass appears as a viable option, available and relatively
easy to grow, without competing with food production. Fast pyrolysis stands as a route of
transformation of biomass into products of different phases (gas, bio-oil, char and pyrolytic
condensate) with various applications. In this work, bio-oil is produced from elephant-grass
(Schumach Pennisetum Purpureum) in 1.5 and 40 kg/h fluidized bed reactors under different
atmospheres (air, N2 and gas recycled from pyrolysis itself) at a temperature of 500°C. In the
1.5 kg/h reactor, we carried out experiments with and without the HZSM-5 catalyst, both under
N2. Pyrolysis without catalyst was also conducted with recycle (54, 74 and 85%) of gases.
In the 40 kg/h reactor, we conducted experiments under moderate oxidative atmosphere of air
(71% N2 and 21% O2) varying the configurations of a gas-washing column (without heat
exchanger with simple heat exchanger, with multi-pass heat exchanger) and the condensate
recirculation (light products) product of pyrolysis reaction. The bio-oil obtained from
experiments with gas recycling in the bed of 1.5 kg/h were subjected to deoxygenation using
5% Pt/C in a slurry bed reactor. The results showed that the gas recycling caused a 53.96%
increase in carbon content in the regular pyrolysis to 70.89% in the pyrolysis with 74%
recycle and 77.16% in the catalytic pyrolysis with in situ HZMS-5. The oxygen content
decreased from 39.64% to 21.76%. The high heating value (HHV) increased from 26.1 to
33.11 MJ/kg. Mass balance showed that 5.4 to 6.15% of the biomass was converted to CH4,
C2H4, C2H6 and C3H8 with gas recycling. Regarding the liquid phase, all bio-oil samples
were rich in phenols, especially those obtained in the oxidative atmosphere. The other
components and majority functional groups are acetic acid, acetol, sugars and ketones.