Comprehensive study of the kinetic behavior of CaO carbonation in ...

JA 2011 – SF2M – Nancy
Comprehensive study of the kinetic behavior
of CaO carbonation in isothermal and
isobaric conditions
Lydie Rouchon
Centre : SPIN – Department : PRESSIC
Thesis advisor : Michèle Pijolat (ENSMSE)
Co-advisor : Loïc Favergeon (ENSMSE)

Tertiary Electric
production
Main activities
Agriculture
emitting
CO2 Industry
Residential
Homes
Transports
Partly responsible for
global warming
2
Context
CO 2 (g)
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
CO 2 separation and capture
Sorbent : CaO
CaO (s)
CaCO 3 (s)
CO 2 (g)
Sequestration
Problem : Such a process is limited by the
reversibility of the reaction

Bibliography
Evolution of the capture capacity of CaO over a number of cycles
• CaO rapidly loses activities towards CO 2 *
• Decrease of maximum conversion rate when
the number of cycles increases
• Modelling***
3
Context
• Model of the decay of the carbonation capacity
along cycles based on sintering
* : Abanades, J.C. & Alvarez, D., 2003. Conversion Limits in the Reaction of CO 2 with
Lime. Energy & Fuels, 17(2), 308-315.
** : G.S. Grasa et al, Chemical Engineering Journal, vol. 137, Avr. 2008, pp. 561-567.
*** : E. Bouquet et al, Chemical Engineering Science, vol. 64, 2009, pp. 2136-2146
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
• Microstructural observations**
CaO after 1 calcination
CaO after 30 cycles of
carbonation/decarbonation
• Few studies on carbonation
mechanism and kinetic modelling
Focuse on these points

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• Characterization of CaO divided material
• Decarbonation (800°C -1h00 – He flow) of CaCO 3 powder (Prolabo, Purity :
99.5%)
• Particle size analysis (Laser granulometer – Matsersizer 2000)
• Grains size : 3 µm
Materials and
characterization
• Specific surface area : BET method 6 (Micromeritics ASAP 2000)
S =
ρ × d
• S BET : 8 m 2 .g -1 → d = 2.5 µm
• SEM Observations (Microscope JEOL FEG JSM6400)
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
Agregate Grain
10 µm 1 µm 1 µm
Agregate size : ten µm Grain size : around 1 µm

α d
5
• Kinetic curves
• Thermogravimetric analysis (TAG 16 Setaram)
• Isothermal and isobaric conditions
• Conditions : P CO2 = 5 kPa ; T carbonation = 500°C
Kinetic slowing
down
3. Sluggish stage
1. Determination of an
induction period τ
Experimental
2. “S” shape : nucleationgrowth
process
ad increases when
T increases
α = 1
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
α ( t)
=
Explain this kinetic slowing down
m(
t)
− m(
t0
)
m(
tf ) m(
t )
theo −
0

6
• Morphological and textural studies
• BET analysis
• SEM observations
• BJH analysis
• Kinetic study
• Original kinetic approach
• Based on an experimental test
• Results
• Interpretations
Outline
• Conclusion and perspectives
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011

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Morphological and
textural studies
• Textural and morphological changes
• Specific surface area measurements (Micromeritics ASAP 2000)
• Carbonation in a tube furnace (P CO2 = 5 kPa)
α d-450°C ≈ 0.22α d-550°C ≈ 0.45 α d-650°C ≈ 0.75
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
No direct relation
between strong kinetic
slowing down and
decrease of specific
surface area

• Morphological and textural studies
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• SEM observations(JEOL FEG JSM 6400)
CaO a = 0
α = 0 α =
Ratio of rpthe
molar volume : z = 2,13
0.8
CaO
α = 0.05 α = 0.19
1µm 1µm 1µm
α = 0.36 α = 0.63 α = 0.8
1µm 1µm 1µm
Increase of dense grains size during carbonation
Z = 2,13
rp'
Porosity tends to disapear
CaCO 3
Experimental conditions
P CO2 = 5 kPa
T carbonation = 550°C

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Morphological and
textural studies
• Textural and morphological changes
• BJH analysis (Micromeritics ASAP 2000)
• Carbonation in a tube furnace (T = 550°C ; P CO2 = 5 kPa)
d = 3 nm
d = 5 nm
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
Pores are
not totally
closed
Intermediate
conclusion
- Slowing down not
directly link with decrease
of specific surface area
- Pores are not totally
closed
- Gradient of P CO2 in
aggregates’ pores
Pay attention on
the kinetic of the
reaction

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• Morphological and textural studies
• BET analysis
• SEM observations
• BJH analysis
• Kinetic study
• Original kinetic approach
• Based on an experimental test
• Results of experiment
• Interpretations
Outline
• Conclusion and perspectives
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011

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• « ФS m » test*
• Mechanism of growth process :
• If ONE step is the rate determining step, rate can be written :
• To verify this assumption :
• An experimental test** : the « sudden jump » method
*: M. Pijolat and M. Soustelle, Thermochimica Acta, vol. 478, 2008, pp. 34-40
** : M. Soustelle, Heterogenous kinetics handbook, Wiley-ISTE, 2010.
Kinetic study
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
? ? ? ? ? ? ? ? : Areic growth rate (mol.m2 .s-1 )
S m : « Space function » (m 2 .mol -1 )

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• « Sudden jump » method
Kinetic study
• To change suddenly a physico-chemical variable (P,T) from a value Y 1 to a
value Y 2 , at a given fractional conversion
Jumps
• Verified when the ratio between the rates before and after the physicochemical
variable change is constant
Oxydation of Mg into MgO by
oxygen : ØS m test with temperature
jumps from 773 to 783 K*
Constant ratio
* : K. Surla,, Thèse, Ecole des Mines de Saint-Etienne et Institut national Polytechnique de Grenoble, 1998.
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
One limiting step

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• ØS m assumption : experiments
550°
C
• P CO2 = 5 kPa
• Change of carbonation temperature : increase of 15°C (T 0 + 15°C = T 1 )
Domain I Domain II
Kinetic study
α for R min ≈ 0.5
Domain III
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
α d ≈ 0.5

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• ØE assumption : experiments
• P CO2 = 5 kPa
• Change of carbonation temperature : increase of 15°C (T 0 + 15°C = T 1 )
Inhibiting
effect of
temperature
Kinetic study
R=1
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011

• Sequence of elementary steps
• ? ? ? for rate-determining step
• Reminder, rate ratio :
15
=
Kinetic study
Thermodynamic of reaction
(1)
(4)
(3)
(2)
∆T =15°C
→
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
• Combining of 3 and 4
< 1 > 1

Thermodynamic of reaction
• Quantitative interpretation : 1. CaO particles at the periphery of aggregates
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Kinetic study
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
No inhibiting effect of
temperature

Thermodynamic of reaction
• Quantitative interpretation : 2. At the bottom of pores
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Kinetic study
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
Inhibiting effect of
temperature

• Existence of kinetic slowing down
• Textural and kinetic studies
• Based on the decrease of P CO2 at the bottom of pores
→ Carbonation stop
• 3 domains of carbonation
• An induction period τ
• A very fast carbonation stage up to a breakpoint
• Governed by a rate determining step
Kinetic model (one fitting parameters) : Isotropic growth
model with 1 nucleus per grain
• Kinetic slowing down followed by a sluggish
stage
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Conclusion and
Perspectives
• Study porosity change as function of a
• Modelling of the overall reaction and taking into account
all previous assumptions
Lydie Rouchon – JA 2011 – SF2M – 6/07/2011
3. Sluggish stage
Kinetic slowing down
Model
α =
1
α ≈ 0.3
Experimental
curve
550°C – 5 kpa

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Thank you for your attention