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Methodology for Estimating Ea for Catalyst Deactivation · 2017. 6. 14. · Apply the protocol to...

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Bukky Oladipo.pptBukky Oladipo, Tom Pauly, Marco Lopez
May 2, 2012
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¶ Assessing catalyst system performance deterioration over in-use lifetime very costly and time-consuming
¶Need to correctly reflect impact of thermal aging and chemical exposure can complicate bench aging acceleration to mimic field aging
¶ Typically, aging acceleration simulated through oven-, burner-, and engine bench-aging with select time @ temperature specifications
¶ For gasoline application, Arrhenius expression has been a successful tool used for determining equivalent aging acceleration over the years
¶ Industry interest is growing to develop appropriate protocol for accelerating diesel catalyst system aging to demonstrate end-of-life performance for various heavy-duty applications
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
3
Objectives
¶ Employ the Arrhenius expression as a tool for developing accelerated aging protocol for diesel catalyst systems
¶ Apply the protocol to SCR catalyst aging and evaluate applicability of the Arrhenius expression for representing loss of overall NOx conversion with aging and/or the inherent functionalities of the SCR
¶ Establish Ea (energy of activation) for the deactivation of the catalyst and establish the variants related to functional deactivation due to thermal aging and chemical exposure
¶ Identify conditions under which the global Arrhenius method is not sufficient to determine the required aging acceleration
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
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Arrhenius Time and Temperature Dependency of Catalyst System Aging
Arrhenius equation relates rate of a reaction to temperature
Example: Ea = 96.5 kJ/mol for CO oxidation on Pt 111 face (gasoline) Source: SwRI – HD-DAAAC Consortium EPA Presentation, 17 March 2009
RT Ea
5
Our Ultimate Objective is to Establish Performance DF for the Catalyst
AGING DURATION
NO x
CO NV
ER SI
O N
NOx Conversion Deterioration With Oven-Aging at 675 °C; Evaluation Testing at 250 deg C SCR Inlet Temp
• Aging model effectively establishing DF for simulating end-of-life (EUL) performance
•HD Truck: 435,000 miles (~8,000 hrs)
• Locomotive line-haul: >64,000 hours EUL
•Can Arrhenius-type expression work to predict EUL activity?
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
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In the literature on catalyst simulation, inhibition terms are usually expressed in the Arrhenius form:
For NO oxidation over DOC as an example,
where the inhibition terms K1, K2, K3, & K4 have Arrhenius dependence just like the main reaction rate term k3
Source: Pandya, Mmbaga, Hayes, Hauptmann and Votsmeier, “Global Kinetic Model and Parameter Optimization for a Diesel Oxidation Catalyst,” National Research Council Canada, Pan2009
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
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For simulation purposes, can we then separate deactivation into distinct sources?
);( poisoningagingthermalfonDeactivati =
8
8.5 L = 17.0 L
Performance evaluation with NO2
17.0 L
A simple example with hydrothermal aging: Fe-Zeolite SCR over short to long aging duration
Aged 16H @ 750C
¶Space Velocity
¶SCR Volume
¶33.0 k
¶25.5 k
¶21.5 k
¶19.5 k
¶17 L
Time Dependence of Thermal Aging: 550 C 200h 550 C 400h 550 C 800h Temperature Dependence of Thermal Aging: § 16 hr 550°C § 16 hr 700°C 16 hr 800°C
SCR2
9
Approach
¶ Arrhenius expression to describe performance loss due to aging:
¶ For (global) SCR NOx conversion reaction, consider: • Deactivation = Change in NOx conversion from Fresh to Aged State
= Function (time, temperature) • Assuming:
§ Linearity with aging time
§ Exponential with temperature
• Deactivation where Δη/taging is the rate of loss of NOx conversion efficiency and


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Variation of NOx Conversion Efficiency with Aging Temperature (Aging Duration = 16 hrs)
α = 1.0
100
N O
x C
on ve
rs io
N H
]
16 hr @ 550 C 16 hr @ 800 C 16 hr @ 700 C NH3-Slip 16 hr @ 550 C NH3-Slip 16 hr @ 800 C NH3-Slip 16 hr @ 700 C
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
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Variation of NOx Conversion Efficiency with Aging Duration (Aging Temperature = 550 C)
30 40 50 60 70 80 90
100
N O
x C
on ve
rs io
N H
]
16 hr @ 550 C 200 hr @ 550 C 400 hr @ 550 C 800 hr @ 550 C NH3-Slip 16 hr @ 550 C NH3-Slip 200 hr @ 550 C NH3-Slip 400 hr @ 550 C NH3-Slip 800 [email protected] 550 C
Two Major Observations: There is no significant loss of NOx conversion except @ 400 deg C temperature; Aging temperature influences deactivation more than aging duration
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
12
Estimating Ea for Degreened & Aging Modes (NOx Eff)ref, % 100 Time Aged Temp NOx Eff Eff Deac. Inv Temp Deac/time (D) ln(D) hr deg C % - 1/K 1/s 16 550 94.38 5.62 0.00121 9.757E-07 -13.84
16 700 91.25 8.75 0.00103 1.519E-06 -13.40 16 800 80.5 19.5 0.00093 3.385E-06 -12.60 16 550 94.44 5.56 0.00121 9.653E-07 -13.85 200 550 92.68 7.32 0.00121 1.017E-07 -16.10 400 550 90.17 9.83 0.00121 6.826E-08 -16.50 800 550 90 10 0.00121 3.472E-08 -17.18
y = -2392.9389188x - 10.9384323 R2 = 0.9995698
y = -14121.1373361x + 0.5625532 R2 = 0.9530623
-18.00
-17.00
-16.00
-15.00
-14.00
-13.00
-12.00
-11.00
-10.00
1/T
y = -10496x - 2.7345 R2 = 0.4878
-18.00
-17.00
-16.00
-15.00
-14.00
-13.00
-12.00
-11.00
-10.00
LN (D )
All Aging Levels Linear (All Aging Levels)


−=
Normal aging mode Degreened mode
Degrn'd Aging -Ea/R -2,393 -14,121 R 8.314 8.314 kJ/kmol Ea 19,894.9 117,403.1 kJ/kmol ln(A) -10.93843 0.562553 A 1.78E-05 1.755148 1/s
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
13
Fe-SCR example shows aging influence only at the high end (400 deg C) of aging temperature
¶ This is likely due to loss of NH3 storage capability; dealumination of Zeolite or other mechanisms
¶Must look at component functionalities rather than global NOx conversion efficiency • NO oxidation • NH3 storage capacity • Surface coverage dependent NOx conversion • NH3 oxidation
¶ Attempt to correlate the component processes (functionalities) using the Arrhenius expression
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
14
0
10
20
30
40
50
60
70
80
90
100
100 150 200 250 300 350 400 450 500 550 600 650
T in front of SCR [°C]
N O
c on
ve rs
io n,
n or
m ed
b y
al ph
]
4h/800°C hydrothermal 4h/850°C hydrothermal 4h/875°C hydrothermal 4h/900°C hydrothermal 4h/950°C hydrothermal
Short hydrothermal aging reaching up to 950 deg C
Estimating Ea for Aging Modes (NOx Eff)ref, % 100
Time Aged Temp NOx Eff Eff Deac. Inv Temp Deac/time (D) ln(D) hr deg C % - 1/K 1/hr
4 800 98.0 2.0 0.00093 1.389E-06 -13.49 4 850 92.0 8.0 0.00089 5.556E-06 -12.10 4 875 83.0 17.0 0.00087 1.181E-05 -11.35 4 900 57.5 42.5 0.00085 2.951E-05 -10.43 4 950 6.5 93.5 0.00082 6.493E-05 -9.64
Performance Deterioration at 200 deg C


−=
15
Potential to Identify Transition Points for Change in Aging (Deactivation) Mechanism
Inverse Temp (1/K)
• Loss of catalytic sites
16
Identifying Aging Limit for SCR Deactivation Source: “CLEERS SCR Teleconference,” Stephen J Schmieg, GM R&D
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
17
Need to look at inherent “component” processes rather than global NOx conversion only
¶Recall that the Fe-SCR example shows aging influence only at relatively high operating temperature (400 deg C)
¶ It suggests potential benefit of looking at the detailed processes
¶Component functionalities to consider: • NO oxidation • NH3 storage capacity • Surface coverage dependent NOx conversion • NH3 oxidation
¶Can these inherent processes (functionalities) be correlated with the Arrhenius even when overall NOx conversion shows no impact?
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
18
19
0
50
100
150
200
250
300
Time
p
Temp NO NH3 Step Temp NO NH3 Step Temp NO NH3 Step
Influence of 650 °C Hydrothermal Aging Change in NH3 storage at 175 °C reveal impact of aging
Aging hours as indicated on the curves
NH3 storage capacity is almost entirely gone after 1000 hrs of hydrothermal aging at 650 deg C
NO Efficiency almost unchanged
250 hrs 1000 hrs
20
Influence of 650 °C Hydrothermal Aging No change in NH3 storage at 400 °C with the aging
Aging hours as indicated on the curves
0
50
100
150
200
250
300
350
400
450
Time
Temp NO NH3 Temp NO NH3 Temp NO NH3 Step
16 hrs 250 hrs 1000 hrs
NO Efficiency equal
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We decide to employ a DoE approach involving aging temperature and duration
5
10
1
8
3
7 Relevant aspects to consider: • Response of SCR component functionalities
to aging level (time @ temp)
• Contribution of exposure to chemical poisoning elements (P, S, Zn, Ca, etc.)
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
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If Successful, Potential Application of the Arrhenius Correlation for Aging Representation
§ Estimate likely performance deactivation for aging duration and temperature of a given application





−−=
k1 = deactivation rate at temperature T1
k2 = deactivation rate at temperature T2
With Ea known, calculate k2 corresponding to given aging temperature T2
2012 DOE Crosscut Workshop on Lean Emissions Reduction Simulation
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¶Complete performance testing and analysis of the aging DoE
¶ Establish impact of chemical exposure and attempt to correlate combined thermal and chemical aging effects
¶Determine suitability of the procedure for extrapolating required accelerated aging for extended-duration applications e.g. locomotive
¶ Apply same principle to DOC and CDPF aging

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