| Summary: | The concern associated with industrial wastes motivated the production quality
bio-oils from pyrolysis of lignocellulosic oil palm wastes with viable mesoporous
catalysts derived from waste steel-slag. This study investigated the thermal and
catalytic pyrolysis of LOPW over zeolite and zeolite-hydroxyapatite based catalysts to
produce quality bio-oils in a slow-heating fixed-bed reactor. Also, the kinetics of the
thermal and catalytic pyrolysis of the LOPW was investigated by using the Coats-
Redfern methods. The reactor was maintained at 450-600 oC pyrolysis temperatures,
200 mL/min N2 flowrate, 10 oC/min heating rate and 0.5-2.5 g catalyst load was used
for the catalytic pyrolysis. The pyrolysis was performed over zeolite and zeolitehydroxyapatite,
as catalysts prepared from electric arc furnace slag. The BET textural
characteristics suggested that the catalysts are hierarchical and highly mesoporous
with average pore diameter ranging from 23-25 nm. The zeolite catalyst has crystallite
structure consistent with that of Faujasite-Ca zeolite, based on authentication by XRD
analysis. Whereas, Faujasite-Ca zeolite and hydroxyapatite crystallite formed the
composite structure of hydroxyapatite-zeolite-based catalysts. The thermal pyrolysis
produced crude bio-oils (CBO) at maximum yield of 40-47 wt% under 500-550 oC
pyrolysis temperatures, whereas, the catalytic pyrolysis over 0.5 g catalyst is 40-47
wt%. The CBO have high heating values from 21-24.68 MJ/kg higher than that of the
corresponding LOPW and comprised of conglomerate of bulky and reactive
oxygenated compounds. But, the catalysts facilitated secondary reactions, which
produced bio-oils pervaded with small and stable oxygenated compounds of specific
families. The phenolics, acids, benzene derivative, esters among others constitute the
light and stable compounds in the bio-oils that the catalysts were selective to. The
decomposition profiles and kinetics of the pyrolysis of LOPW were determined via
thermogravimetry. The thermographs from the thermogravimetric analysis inferred
that pyrolysis reactions decomposed LOPW via stage-wise mode. The kinetics
analysis based on the Coats-Redfern’s methods revealed that diffusion kinetics best
described the second stage (active stage) of thermal and catalytic pyrolysis. While,
the geometrical correlation kinetics best described the second and third stages,
conversely kinetics govern by Avarami-Erofe'ev and Power law described the third
stages of the LOPW pyrolysis. From the kinetics parameters, the catalytic pyrolysis
exhibited the lowest activation energies compared to the corresponding thermal
pyrolysis. Therefore, the pyrolysis of LOPW can be best described to follow complex
multi-step mechanisms. The characteristic decomposition index (D) for the pyrolysis
of LOPW and Fe/HAPAZ blend were higher than those for the LOPW thermal
pyrolysis. The index D revealed that the Fe/HAPAZ profoundly influences the LOPW
thermal pyrolysis.
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