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