Transcript Slide 1

Copper Functioning as an Oxygen
Carrier in Chemical Looping
Combustion
Authors:
Richard Baraki,
Dr. Gabor Konya,
Dr. Edward M. Eyring.
Departments of:
Chemistry and
Chemical Engineering
Chemical Looping Combustion
Observed Oxygen Carrier
• Copper
– 2 Cu(s) + O2(g)↔ 2 CuO(s)
http://gwydir.demon.co.uk/jo/minerals/pix/copper1.jpg
Method of Analysis
• Thermogravimetric Analysis
TA Q500
ThermoFisher HP-TGA
Copper
• Overall oxidation
2 Cu(s) + O2(g)↔ 2 CuO(s)
• Cu → Cu(I)
4Cu(s) + O2(g)↔ 2Cu2O(s)
• Cu(I) → Cu(II)
2Cu2O(s) + O2(g)↔ 4 CuO(s)
2 days of looping (200+ loops) @ 850
°C
Looping
Ma
Mass (mg)
25
24
23
22
0
20000
40000
60000
80000
Time (sec)
100000 120000 140000 16
Cu(I) →Cu(II)
Cu(I) →Cu(II) @ 850 °C
Fitted Cu(I) →Cu(II) @ 850 °C
25
Mass (mg)
Mass (mg)
25
24
24
23
23
22
11600 11800 12000 12200 12400 12600 12800 13000 13200 13400 13600
22
11600 11800 12000 12200 12400 12600 12800 13000 13200 13400 13600
Time (sec)
Time (sec)
Residual of Mass
of Y, (mg)
Residual
Residual plot
Residual of Mass
0.4
0.2
0.0
-0.2
11600 11800 12000 12200 12400 12600 12800 13000 13200 13400 13600
Independent Variable
Independent Variable, (sec)
Pseudo first order equation
• First-order reaction
 r = -d[A]/dt = k[A]
• k = rate constant
• A = amount of copper
• Pseudo first order reaction for
 r = k[A][B]1/2 = k΄[A]
•
•
•
•
k = rate constant
k΄ = k[B]1/2
A= amount of copper
B= partial pressure of oxygen
Method of fit
y = Wf + (Wi - Wf) * e(-k * (t-t0))
• Fitted Parameters
• Wf - final weight of oxide
• Wi - initial weight of oxide
• k- rate constant
• Fixed Parameter
• t0- indicates start of reaction
Shifting k values (TA-Q500)
-3
3.00x10
-3
k (1/s)
2.00x10
-3
1.00x10
194-911
553-1270
911-1628
1270-1988
Time window (s)
1626-2347
Full run
Shifting k values (HP-TGA)
-3
3.6x10
-3
3.4x10
-3
3.2x10
-3
3.0x10
-3
k (1/s)
2.8x10
-3
2.6x10
-3
2.4x10
-3
2.2x10
-3
2.0x10
-3
1.8x10
-3
1.6x10
2500-3233
2867-3600
3233-3966
3600-4333
Time window (s)
3966-4700
Full run
Cu2O/CuO/Cu2O system
-2
3.50x10
-2
3.25x10
-2
3.00x10
-2
2.75x10
935°C
-1
 [sec ]
-2
2.50x10
-2
2.25x10
-2
2.00x10
Rate constant of
-2
1.75x10
-2
1.50x10
st
Reduction, 1 order model
Reduction, Avrami-Erofeev model
st
-2
1.25x10
-2
Oxidation, Pseudo 1 order model
Oxidation, Avrami-Erofeev model
1.00x10
-3
7.50x10
-3
5.00x10
-3
2.50x10
0.00
825
850
875
900
Temperature [°C]
925
950
Temperature effects
• Sintering
– Tamman Temperature
Pressure using HP-TGA
• Pressure plots
– 1 atm
– 9 atm
– 16atm
– 25atm
• Oxygen analyzer
Pseudo first order equation
• First-order reaction
 r = -d[A]/dt = k[A]
• k = rate constant
• A = amount of copper
• Pseudo first order reaction for
 r = k[A][B]1/2 = k΄[A]
•
•
•
•
k = rate constant
k΄ = k[B]1/2
A= amount of copper
B= partial pressure of oxygen
Experimental Procedure
• Sample loaded into quartz bucket
– 200mg copper powder
• Chamber closed and purged with pure
nitrogen 15+ min
• Temperature ramp from 21°C to 950°C in
pure nitrogen gas at 25°C/min
– Given experiment, pressure build up
• At desired temperature and pressure, air is
introduced
Observations
• Stoichiometric conversion
• Rate at which sample is being oxidized
Oxidation at different pressures
130
Cu →CuO
125
Mass (%)
120
115
atmospheric
9 atmospheres
16 atmospheres
25 atmospheres
Theoretical yield
110
105
100
1000
2000
3000
4000
Time (sec)
5000
6000
7000
Observations
• Stoichiometric conversion
Oxidation at different pressures
130
Cu →CuO
125
Mass (%)
120
115
atmospheric
9 atmospheres
16 atmospheres
25 atmospheres
Theoretical yield
110
105
100
1000
2000
3000
4000
Time (sec)
5000
6000
7000
Observations
• Stoichiometric conversion
• Rate at which sample is being oxidized
Oxidation at different pressures
130
Cu →CuO
125
Mass (%)
120
115
atmospheric
9 atmospheres
16 atmospheres
25 atmospheres
Theoretical yield
110
105
100
1000
2000
3000
4000
Time (sec)
5000
6000
7000
Reaction Rates for Range of Mass Increases of 101 to 105%:
Decrease in rate with increasing pressure indicative of diffusional limitations
105.0
atmospheric
9 atmospheres
16 atmospheres
25 atmospheres
104.5
104.0
Mass (%)
103.5
103.0
102.5
102.0
101.5
101.0
0
1000
Time (sec)
Theoretical rates versus experimental rates based on the
pseudo-first order model, to be revisited after experimental
constraints eliminated
Cu →CuO
Experimental results of reaction rates
Theoretical pseudo-first order reaction rates
0.32
0.30
0.28
Rate (% mass/seconds)
0.26
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0
5
10
15
Pressure, atm
20
25
Gas cylinders
HP-TGA
Oxygen analyzer
Oxygen concentrations at exit of reactor
corresponding to HP-TGA plots previously shown.
Failure to reach 21% to be explored
25
Oxygen analysis of
25 atm
Cu →CuO
16 atm
9 atm
atmospheric
125
20
120
15
Mass (%)
O2 % in exiting gas
Cu →CuO
130
10
115
atmospheric
9 atmospheres
16 atmospheres
25 atmospheres
Theoretical yield
110
5
105
100
0
0
2000
4000
Time (seconds)
6000
1000
2000
3000
4000
Time (sec)
5000
6000
7000
25
25 atm
16 atm
9 atm
atmospheric
Oxygen analysis of
Cu →CuO
O2 % in exiting gas
20
15
10
5
0
0
2000
4000
Time (seconds)
6000
Conclusion
• Pseudo first order model does not fit
Cu/Cu2O/CuO system
• Data indicate diffusional limitations
Acknowledgements
• Department of Energy
– under Award Number DE-NT0005015.
• Dana Overacker
• Kevin Tucker
• Blake R. Wilde