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(259d) Gasification of Glucose in the Reactor CREC-Riser Simulator: Stable Ni-(La or Ce)/g-Alumina Catalysts and Effect of Reaction Time and Steam/Glucose

Serrano, B. Sr., Universidad Autonoma de Zacatecas.
Sanchez, A., Universidad Autonoma de Zacatecas
Gonzalez Castañeda, D. G. Sr., Universidad Autonoma de Zacatecas
Cruz Reyes, I., Universidad Autonoma de Zacatecas
Calzada Hernandez, A. R. Sr., Universidad Autonoma de Zacatecas
de Lasa, H., Western University

Glucose Gasification in the CREC-Riser Simulator Reactor
Using a Ni-(La or Ce)/g-Alumina Fluidizable
Catalyst. Effect of Reaction Time and
Steam/Glucose Ratio.       

A. Sánchez Enríquez1, D.G. González Castañeda1, I. Cruz Reyes1,
A.R. Calzada Hernandez1, H.I. de Lasa2, B. Serrano

Autónoma de Zacatecas, Unidades Académicas de Ingeniería Eléctrica y Ciencias Químicas,
Campus UAZ Siglo XXI, Carr, a Guadalajara km 6, Ejido La Escondida, Zacatecas,

2 Chemical Reactor Engineering
Centre, Department of Chemical and Biochemical Engineering, The University of
Western Ontario, London, ON N6A 5B9, Canada.


Keywords: Hydrogen, Glucose, Nickel,
Cerium, Lanthanum, Gasification  

1.    Introduction     

The gradual depletion of fossil fuels requires
the development of alternative technologies such as biomass gasification [1].
Gasification involves a complex network of heterogeneous reactions, with the use
of catalysts which significantly enhance the gasification reaction network.

Nickel catalysts have been reported as active
for methane and heavy hydrocarbon conversion[2]. Biomass gasification may
require a new class of fluidizable catalytic materials to achieve the desired
syngas composition with minimum amounts of tars. To accomplish this, a 5wt% nickel
catalyst supported on fluidizable g-Al2O3
is proposed in the present study. Furthermore, the influence of lanthanum
and cerium as added promoters, is also examined. Catalysts aresynthesized
using a direct reduction method without catalyst precursor calcination. Various
prepared fluidizable catalysts are evaluated by changing the operating
parameters such as reaction time and steam/glucose ratio. Furthermore, the
influence of oxidation/reduction cycles on catalytic activity is also thoroughly
2.     Experimental Methodology

Catalyst Preparation. - The 5%Ni/g-Al2O3 catalysts were prepared with
a pH of 1 and 4. An incipient wetness impregnation was followed by direct precursor
reduction as follows[3]: a)  The alumina support sample was dried during 12
hours at 110°C, b) A Ni(NO3)₂.6H₂O was
added to a deionized water solution, c) The alumina support was placed under a vacuum,
for 20 minutes, d) The Ni(NO3)solution was added slowly
(drop-by-drop) to the alumina,  e) The resulting paste was dried during 12
hours, e) The nickel impregnated alumina was reduced in a fixed bed using a 160
cm3/min hydrogen flow and a 5°C/min heating ramp. The temperature
was held at 260°C for 1 hour, f) Following this, a second 5°C/min heating ramp was
used until 480°C was reached. This temperature was held for 10 hours, g)
Finally, the catalyst sample was cooled down to room temperature. A similar
procedure was used for the catalyst promoted with Ce and La, with A and B
representing 0.5wt%, 1wt% and 2wt% for Ce and La, respectively. In the case Ce
and La, the promoter addition step b) was modified, using Ni (NO₃)₂.6H₂O
and La or Ce nitrate. These two nitrates were mixed together in deionized water
solution and added to the support in a co-impregnation process [3]. Based on
this methodology, fourteen catalysts were prepared. These catalysts were
characterized using XRD, AA, BET, PSD and SEM.  

Gasification in the CREC – Riser Simulator
. – The CREC Riser
Simulator is a laboratory scale fluidized bed [4], with a 53 cm3 volume.
The temperature in these experiments was 600°C. A glucose solution was injected
into the reactor with and without a catalyst. The reaction times were 5, 10, 20,
30 and 40 seconds. The amount of catalyst used was 0.0500 g. Ratios of steam/glucose
(S/B) of 0.5, 1, and 1.5 g/g were used under an inert atmosphere of argon (1
atm). The samples were analyzed in a GC-AT 7890A, with TCD and FID detectors.
All the catalysts were regenerated first with air (15 min., P = 20 psia) and later
with hydrogen (15 min., P = 20 psia). This was done before each injection. However,
to test catalyst regeneration effectiveness, two additional steps were included:
a) Prior to the runs catalyst was oxidized with air, with reduction being
omitted, b) Before experiments catalyst was not either oxidized or reduced. Operational
conditions were selected based on the results from the already completed runs
obtained by the ANOVA analysis.
Results and discussion

As a first step and as a reference, runs were carried out at 600 °C without the catalyst being loaded in the
catalyst basket. These experiments were designated as thermal runs and the
results were compared to the ones which used the 5%Ni on g-Al2O3 catalyst, with
A=0.5, 1 and 2%.

Figure 1 reports the H2,
CO, CO2 and CH4 molar fractions obtained during the
thermal runs and compare with the syngas molar fractions for three of best catalysts
as follows: a) 5%Ni/g-Al2O3(pH4), b) 5%Ni-2%La/g-Al2O3(pH1), c) 5%Ni-2%Ce/g-Al2O3(pH4). Figure 2
reports the ratios of H2/CH4 for the S/B = 0.5, 1 and 1.5.

Figure 1.- Synthesis gas molar fractions for: a) the thermal case, b) a 5%Ni(pH4) catalyst, c) a 5%Ni-2%La(Ph1) catalyst, d) a 5%Ni-2%Ce(pH4) catalyst. Reaction time: 20 s, Steam/B= 1, Cat/B=3.2, Mass of Catalyst: 50 mg, T=600 °C.

Figure 2.- Effects of Reaction Time and Steam/B on H2/CH4 Ratio for 5%Ni-2%La/g-Al2O3(pH1). Cat/B=3.2,  Mass of Catalyst: 50 mg, T=600 °C.

Figure 1 shows that when using the 5%Ni(pH4) catalyst, hydrogen
production is increased by 32 % and this while compared to the thermal runs. As
well, when using a 5%Ni-2%La(pH1) catalyst, there is an additional hydrogen increase
of 10%. This demonstrates the positive effect of both Ni and La, on catalytic
glucose conversion into H2.  In fact, the performance of the
5%Ni-2%La/g- Al2O3 (pH1)  catalyst 0.73 H2 molar
fraction suggests that there is enhanced steam reforming, methane dry reforming
and water gas shift reactions during glucose gasification.

Figure 2 reports the effects of both reaction time and S/B on the H2/CH4
ratio for the best performing 5%Ni-2%La/g-Al2O3(pH1) catalyst. It is
observed that for all the S/B values, the H2/CH4 ratio augments
with reaction time. This effect is particularly noticeable for the higher S/B
ratios, with hydrogen molar fractions increasing and the methane (a primary
gasification product) molar fraction being reduced.

Figure 3 shows the synthesis gas molar fractions for the 5%Ni-2%La/g-Al2O3 (pH1) catalyst
and their changes with consecutive reaction cycle number. One can observe that
for the freshly reduced catalyst, the first injections led to higher H2.
Hydrogen molar fractions decreased slightly however, for the second and
subsequent injections, remaining close to constant. This consistent trend was
observed (not shown) for the various catalysts of this study. It thus, appears
that oxidization (regeneration) between injections was, in principle, fully adequate
in removing any possible formed coke.

Furthermore, and to further study catalyst stability, 6 consecutive injections
were used with the 5%Ni-2%La/g-Al2O3(pH1)
catalyst, without regeneration
in between injections, as reported
in Figure 4. One can notice that the results in Figure 4 are similar to the
ones in Figure 3. This shows that the 5%Ni-2%La/g-Al2O3(pH1)
catalyst regeneration before
each cycle may not be needed. Based on this, one can speculate that oxidation-reduction
processes coexist in the 5%Ni-2%La/g-Al2O3(pH1) catalyst during every glucose/steam run [5].

As a result, it is anticipated that these efficient and stable catalysts
could simplify the configuration of the industrial gasification plant, without
the need of a catalyst regeneration unit.

Figure 3.- Molar fraction for the 5%Ni-2%La/g-Al2O3(pH1) catalyst, at Steam/B =1, Time = 20 s, Cat/B=3.2, and the mass of catalyst being 50 mg, T=600 °C.

Figure 4. Molar fraction for the 5%Ni-2%La/g-Al2O3(pH1) catalyst, without  regeneration, T = 600°C.


 A 5%Ni-2%La/g-Al2O3(pH1) catalyst was successfully
prepared for H2 production. The performance of this catalyst was
demonstrated in a CREC Riser Simulator.

It is shown that the
prepared catalyst displayed significant improvements (40%) in the hydrogen
molar fractions, and this when compared to those obtained during thermal runs.    

It is proven that the
synthesized catalyst showed a significantly reduced methane molar fraction when
compared to that observed in the thermal experiments.

It is demonstrated that the performance
of the prepared catalyst is favorably affected by increasing both S/B rations and
reaction times.

It is shown that oxidation-reduction processes
take place concurrently during glucose gasification with this leading to stable
hydrogen production.


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