Calcium oxide-based catalysts for conventional and supercritical water gasification of palm fruit bunches in hydrogen production
Hydrogen shows great potential as a clean and alternative energy resource that could reduce the dependency of fossil fuel consumption.Commercially,hydrogen is produced from natural gas reforming and coal gasification.Apart from this,biomass conversion via gasification method is regarded as a prom...
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| Format: | Thesis |
| Language: | English |
| Published: |
2015
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/68173/1/FS%202015%2087%20IR.pdf |
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| Summary: | Hydrogen shows great potential as a clean and alternative energy resource that could
reduce the dependency of fossil fuel consumption.Commercially,hydrogen is produced
from natural gas reforming and coal gasification.Apart from this,biomass conversion
via gasification method is regarded as a promising technique for hydrogen
production.Empty palm fruit bunches (EFB) are considered as an abundant biomass
wastewhich is apotential feedstock for gasification process.
In this investigation,catalytic EFB conversion into hydrogen were studied in two
different prominentgasification methodsthatincludes conventional (900ºC in partial O2
environment) and supercritical water gasificationreaction (380 ºC). Hence, a series
ofCaO based catalysts were synthesized via wet impregnation method using bulk CaO
as a base added with primary (Ni) and secondary (La, Mg, Ba, Nd, Na, K, Zn, Co and
Fe) dopants.The prepared catalysts were characterized by x-ray diffraction (XRD), N2
adsorption-desorption (BET), thermal gravimetric analysis (TGA), temperature
programmed reduction (TPR-H2)and temperature programmed desorption(TPD-CO2).
Furthermore,the effects of catalyst in EFB conversion to hydrogen were tested in both
gasification techniques.
Preliminary catalytic studies show thatBaO doped NiO-CaO catalyst was found to be
very active in conventional gasification while ZnO doped NiO-CaO catalysts in
supercritical water gasification reaction (SCWG). Both catalysts exhibit high
selectivity towards hydrogen production. This is due to improvements in catalytic
activity ofNiO-CaO with additions of BaO or ZnO dopants that enhances gasification
of EFB and promote hydrogen favored reactions. In comparison with both techniques
SCWG reaction shows several advantages over conventional gasification such as lower
reaction temperature, higher hydrogen yield, tolerate high moisture content feedstock
(EFB), reduce tar production and shorter reaction time. Therefore, SCWG reactionwas
selected for EFB conversion using ZnO doped NiO-CaO catalysts with both unreduced
and reduced catalysts.The catalytic results of reduced ZnO/Ni-CaO catalyst
showsignificant improvement in terms of hydrogen selectivity. Formation of Ni.8Zn.2O solid solution phase on the CaOsurface was found to be the active in catalyzing water
gas shift reaction while the presence of metallic Ni promotescarbon gasification and
reforming reactions.
The highest hydrogen concentration (105.7 mmol mL-1)was observedwith 5wt.%ZnO
doped 5wt% Ni-CaO catalyst and found to be increased with increasing reaction
time.Further, Ni and ZnO loading were increased in catalyst formulationeven though
concentration of hydrogen didn’t displayed any significant difference. This is due to
the possible particle agglomerations on the CaO surface.However, only slight
improvement in carbon gasification is observed with 8 wt.% of Ni loading.
Therefore,based on the information obtained Ni loading in the range of 5-8 wt.% with
5wt.% of ZnO on CaO was predicted as an optimum catalyst formulations that provide
high catalytic activity and selectivity towards hydrogen production. |
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