(583d) On the Kinetics of Ni-Based Oxygen Carrier Reduction and Oxidation Studied in Thermogravimetric Analysis and Fixed-Bed Reactors | AIChE

(583d) On the Kinetics of Ni-Based Oxygen Carrier Reduction and Oxidation Studied in Thermogravimetric Analysis and Fixed-Bed Reactors

Authors 

Zhou, Z. - Presenter, University of Connecticut
Nordness, O., University of Connecticut
Bollas, G., University of Connecticut



On the kinetics of Ni-based oxygen carrier reduction and oxidation
studied in thermogravimetric analysis and fixed-bed reactors

Zhiquan Zhou, Oscar Nordness, George M. Bollas

NiO is a promising yet
expensive oxygen carrier for chemical-looping combustion (CLC). Knowledge of its
inherent kinetics can greatly facilitate the optimization of the Reducer and
Oxidizer in chemical-looping combustion systems. Reactivity tests with NiO/Al2O3(¦Á-
and ¦Ã-)/SiO2 oxygen carriers were performed in a thermogravimetric
analyzer (see Figure 1) at atmospheric pressure to examine the supported NiO
reduction kinetics by H2 and CH4 under isothermal
conditions (600, 800 and 950 °C). NiO/Al2O3/SiO2
oxygen carriers were prepared via the incipient wetness impregnation method. Table
1 shows the main properties of the fresh (before CLC) materials.

Table 1: Properties of the fresh NiO-based oxygen carriers

Properties

NiO/¦Ã-Al2O3

NiO/¦Á-Al2O3

BET surface area (m2/g)

94

27

Pore size (Å)

116

294

Total NiO content (%)

32

24

Active NiO content (%)

25

21

XRD phases

NiO, NiAl2O4, Al2O3, SiO2

NiO, NiAl2O4, Al2O3, SiO2

Apparent density (g/cm3)

1195

1414

Particle size (µm)

50 ¨C 150

50 ¨C 150

Figure 1: Typical mass and temperature measurement for NiO/¦Ã-Al2O3 oxygen carrier and 4% H2/Ar for reduction and air for oxidation reactions.

Figure 2: Effect of reaction temperature and Curve fitting of Avrami-Erofe'ev and shrinking core models to reduction conversion for NiO/¦Á-, ¦Ã-Al2O3 and 4% H2/Ar reaction at 800 and 950 °C.

            In
this presentation, model-fitting (conversion (X) vs. time and dXdt vs.
conversion) and model-free methods (Hancock and Sharp [1]) are
used to evaluate the kinetics mechanism of the reduction and oxidation
processes. Over 20 solid-state reaction models (nucleation, geometrical
contraction, diffusion, reaction-order, etc.) [2,3] are
applied and compared against reduction and oxidation experiments of bulk Ni and
supported Ni carriers reported in the  literature [4¨C8] and
generated in this work (Figure 2). The F-test and Akaike Information Criterion [9] are
used to statistically compare models with different independent variables. Consistent
kinetic mechanisms are derived that are capable of describing the reactivity
performance of different Ni-based oxygen carriers. 

Acknowledgement:
This material is based upon work supported by the National Science Foundation
under Grant No. 1054718.

References:

[1]      J.D. Hancock, J.H.
Sharp, Method of Comparing Solid-state Kinetic Data and Its Application to the
Decomposition o, (n.d.) 74¨C77.

[2]      B.
Janković, Isothermal reduction kinetics of nickel oxide using hydrogen:
Conventional and Weibull kinetic analysis, Journal of Physics and Chemistry of
Solids. 68 (2007) 2233¨C2246.

[3]      A.
Khawam, D.R. Flanagan, Solid-state kinetic models: basics and mathematical
fundamentals., The Journal of Physical Chemistry. B. 110 (2006) 17315¨C28.

[4]      A.
Abad, J. Ad¨¢nez, F. Garc¨ªa-Labiano, L.F. de Diego, P. Gay¨¢n, J. Celaya, Mapping
of the range of operational conditions for Cu-, Fe-, and Ni-based oxygen
carriers in chemical-looping combustion, Chem. Eng. Sci. 62 (2007) 533 ¨C 549.

[5]      I.
Chen, D.W. Shiue, Reduction of nickel-alumina catalysts, Industrial &
Engineering Chemistry Research. 27 (1988) 429¨C434.

[6]      G.
Plascencia, T. Utigard, The reduction of Tokyo and Sinter 75 nickel oxides with
hydrogen, Chemical Engineering Science. 64 (2009) 3879¨C3888.

[7]      T.
a. Utigard, M. Wu, G. Plascencia, T. Marin, Reduction kinetics of Goro nickel
oxide using hydrogen, Chemical Engineering Science. 60 (2005) 2061¨C2068.

[8]      R.
Chatterjee, S. Banerjee, S. Banerjee, D. Ghosh, Reduction of Nickel Oxide
Powder and Pellet by Hydrogen, Transactions of the Indian Institute of Metals.
65 (2012) 265¨C273.

[9]     H.
Akaike, A new look at the statistical model identification, IEEE Transactions
on Automatic Control. 19 (1974) 716 ¨C 723.

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