tapas chakraborty indian association for the cultivation of science calcutta, india mj16, osu isms...
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Tapas Chakraborty
Indian Association for the Cultivation of ScienceCalcutta, India
MJ16, OSU ISMS 2013
Photochemistry of acetone in simulated Photochemistry of acetone in simulated atmosphere atmosphere
Photochemistry of acetone in simulated Photochemistry of acetone in simulated atmosphere atmosphere
Photochemical decomposition (46%)
Annual atmospheric budget of acetone:Annual atmospheric budget of acetone:
Anthropogenic activity: 1.30.7 Tg/year (Industrial Solvents and Automobile exhaust)
~95 Tg (1012 g)/ year flows into atmosphere
MJ16, OSU ISMS 2013
Financial Support:
Department of Science and Technology, Govt. of India
Acknowledgement:
Mr. Aparajeo Chattopadhyay
Ms. Piyali Chatterjee
CHCH33–CO–CH–CO–CH3 3 CHCH33COCO + + CHCH33
CHCH3 3 + CO + + CO + CHCH33
UV light,UV light, λ < 339 nm λ < 339 nm
R G W Norrish 1897-1978
ΔHΔH00 = 84.5 kcal /mol = 84.5 kcal /mol
ΔHΔH00 = 95.5 kcal /mol = 95.5 kcal /mol
UV light,UV light, λ < 299 nm λ < 299 nm
260 280 300 320 3400.00
0.05
0.10
Abs
orpti
on
Wavelength (nm)
Basics of acetone photochemistryBasics of acetone photochemistry
Photo-oxidation CH3CO + CH3 + 2 O2 CH3(CO)OO + CH3OO Photo-oxidation CH3CO + CH3 + 2 O2 CH3(CO)OO + CH3OO
0 km
20 km
Wavelength (nm)
Act
inic
Flu
x (P
ho
ton
s cm
-2 s
-1 n
m -1
)
Early works…. JACS, 59, 2092 (1937)
Early works….
CH3(CO)OO + CH3OO CH3OH, HCHO, CH3O , HO2, OH, etc.
CH3(CO)OO + CH3OO CH3OH, HCHO, CH3O , HO2, OH, etc.
Trans Farad Soc, 49, 1292 (1953)
JACS, 75, 5810 (1953)
JACS, 76, 1979 (1953)
Early works….
JPC, 65, 1622 (1961)
JPC, 67, 1686 (1963)
Whytock et. al, Can. J. Chem, 45, 867 (1967) Queen’s college, Scotland
Cohen, J. Chem. Phys, 47, 3828 (1967) University College, London
Calvert et. al, J. Phys. Chem, 88, 5069 (1984) NCAR, Boulder, Colorado
Ravishankara et. al, Geophys. Res. Lett, 24, 3177 (1997) NOAA, Univ. Colorado,
Ravishankara et. al, Chem. Phys, 231, 229, (1998) NOAA, Univ. Colorado,
Warneck et. al. J. Phys. Chem, 104, 9436 (2000) Max Planck Institut fur Chemie, Mainz, Germany
Francisco et. al, Chem. Phys. Lett, 329, 179 (2000) Purdue University
Pilling et. al, Chem. Phys. Lett, 365, 374 (2002) University of Leeds
Globar SourceDTGS Detector
UV B LampsPhilips TL-01 20W (Emission maximum - 311nm)
SampleVacuum PumpPressure Gauge
Measurement scheme
IFS 66, Bruker Optics
2000 2080 2160 2240
0.00
0.04
0.08
Wavenumber (cm-1)
IR spectroscopy probing of acetone photochemistry in absence of air IR spectroscopy probing of acetone photochemistry in absence of air
Excitation wavelength – 311 nm Excitation wavelength – 311 nm
Ro-vibrational transitions of CO
1000 1500 2000 2500 3000 3500 4000
0.0
0.5
1.0
1.5
2.0
2.5
900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900
0.0
0.5
1.0
1.5
2.0
2.5
O.D
(a.
u)
Wavenumber (cm-1)
In synthetic air
In absence of air
1033 cm-11105 cm-1
O.D
(a
.u)
cm-1
Photo-oxidation in synthetic air yields Photo-oxidation in synthetic air yields HCOOHHCOOH
1020 1080 1140
0.00
0.09
990 1080 1170
0.0
0.4
0.8
acetone
d6 - acetone
Excitation Wavelength = 311 nm
1143 cm-1 1171 cm-1
1033 cm-11105 cm-1
985
945970
980 DCOOH DCOOD
CD3OD
Wavenumber (cm-1)
d6 – acetone + O2
Photo-oxidation of acetone dPhoto-oxidation of acetone d66
Time Variation of products concentrations
0 10 20 30 40 50 600.00
0.01
0.02
0.03
HCOOH CH
3OH
HCHO CO
Time (minutes)
O.D
Acetone:O2:N2 = 1:1:4
(synthetic air)
0 10 20 30 40 50 600.00
0.01
0.02
0.03
Time (minutes)
O.D
Acetone:O2= 1:5
0 20 40 60 80 100 120 140 160 180 2000.00
0.02
0.04
0.06
0.08
0.10
HCOOH CH
3OH
HCHO CO
Longer exposure time
(synthetic air)
Time (minutes)
O.D
Acetone:O2:N2 = 1:1:4
Time Variation of products concentrations
Adsorption of HCOOH on cell walls
0 20 40 60 80 100 120 140
0.06
0.08
0.10
0.12
0.14
0.16 UV light was switched off after 2 hours of exposure
O.D
(H
CO
OH
)
Time (minutes)
0 20 40 60 80 100 120 1400.00
0.05
0.10
0.15
0.20Decrease in concentration of pure HCOOH with time
O.D
(H
CO
OH
)
Time (minutes)
Adsorption of HCOOH on cell walls
A simple Model for estimation of HCOOH yield
An apparent consecutive process
CH3COCH3 + O2 HCOOH HCOOHunadsorbed
k1 k2
Photochemicalreaction
Adsorption
Assumptions:
1.HCOOH formation in step-1 occurs at a constant rate for a particular reaction set
2.Adsorption of HCOOH on cell walls follows 1st order kinetics
Rate of formation of HCOOH, d[HCOOH]/dt = k1 – k2 [HCOOH]
Solving, [HCOOH]t = (k1/k2)[1-exp(-k2t)] ………. (1)
Steps to estimate concentration of HCOOH produced in the reaction:
• k2 is estimated following adsorption kinetics of HCOOH
• Corrected concentration of HCOOH produced at time t, [HCOOH]actual = k1t
0 10 20 30 40 50 60
4.00E+015
6.00E+015
8.00E+015
1.00E+016
1.20E+016
··Original data
Corrected data
H
CO
OH
(m
olec
ule
s cm
-3)
Time (minutes)
Corrected formation rate of HCOOH
Effect of oxygen pressure
0 1 2 3 4
0.03
0.06
0.09
0.12
HCOOH CH
3OH
Ratio of partial pressures (O2 /Acetone)
OD
Total pressure kept fixed
0 1 2 3 4
0.8
0.9
1.0
1.1
1.2
1.3
0 1 2 3 4
1.0
1.1
1.2
1.3
0 1 2 3 40
2
4
6
8
10
CH3OH / HCOOH
CH3OH / HCHO
HCOOH / HCHO
Ratio of partial pressures (O2 /Acetone)
Ratio of partial pressures (O2 /Acetone)
Ratio of partial pressures (O2 /Acetone)
Rela
tive O
D
Rela
tive O
D
Rela
tive O
D
Effect of oxygen pressure
200 400 600 8000.004
0.008
0.012
0.016
HCOOH CH
3OH
HCHO CO
50 100 150 200
0.05
0.10
0.15
HCOOH CH
3OH
Total Pressure (mbar)
Total Pressure (mbar)
OD
OD
Varying total pressure keeping Acetone:O2 fixed
Varying total pressure of synthetic air
Effect of total pressure
Reaction mechanism
0 1 2 3 4
0.03
0.06
0.09
0.12
HCOOH CH
3OH
Ratio of partial pressures (O2 /Acetone)
OD
Total pressure kept fixed CH3-CO-CH3 CH3CO + CH3 UV
+2O2 + M
CH3(CO)OO + CH3OO + M
2CH3OO CH3OH + HCHO + O2
2CH3OO 2CH3O + O2
2CH3O CH3OH + HCHO
CH3 + O2 HCHO + OH
OH + CH3OH HCHO + H2O
HCO-H HCO + H HO2
2 HO2 2OH + O2
CH3CO-OO OH
• We confirm once again that HCOOH is one of the major photoproducts of acetone photoreaction in atmospheric condition under exposure of UV-B light.
• The yields of formic acid for several specific set of reaction conditions have been estimated for the first time.
• The relative yields of CH3OH, HCHO and HCOOH vary differently upon increasing oxygen partial pressure in the reactor cell. The observation suggests that HCHO might be produced via more than one channel, which requires further measurements to settle.
SummarySummary