Gas Phase Pyrolysis of Freon 12
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Transcript of Gas Phase Pyrolysis of Freon 12
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Gas Phase Pyrolysis of
Freon 12
Grant Allen
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Seminar Outline: Part A
Infrared Laser Powered Homogeneous Pyrolysis (IR LPHP)
Investigative Techniques
Acknowledgements
Results
Conclusion
Introduction
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Introduction
Chlorofluorocarbons (CFCs) are environmentally destructive
Mechanism of gas phase thermal decomposition not fully understood
Initiate gas phase thermal decomposition using IR LPHP
Stable reaction products - IR and GCMS
Short lived intermediates - MIIR and TDL spectroscopy
Proposed mechanism based on:
Freon or R12 (Dichlorodifluoromethane)
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Infrared Laser Powered
Homogeneous Pyrolysis (IR LPHP)
Firebrick
Pyrolysis Cell
Hot Zone
CO2 Laser
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Investigative Techniques
FT-IR Spectroscopy
GC-MS
Matrix Isolation Infrared Spectroscopy
Tuneable Diode Laser Spectroscopy
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Matrix Isolation Infrared
Spectroscopy
Precursor
flow
ZnSe
window
12
= ‘O’ ring vacuum tap (J Young)
= Copper block: Position:
Matrix isolation shroud
Stainless
steel mirror
8 mm o.d.10 mm o.d.
ZnSe window
Vacuum
pump
1: Collection
2: Detection
170 mm
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Tuneable Diode Laser
Spectroscopy
Micrometer
mirror adjustment
screws
CO2 laser
beam
Diode laser
input
Diode laser
output
ZnSe
window
CaF window
250 mm
Al reflective mirror
Au
mirror
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Freon 12
Thermal decomposition of chlorinated organic compounds dominated by HCl elimination and C-Cl bond scission
Pyrolysis of W(CO)6 leads to W(CO)x species (where x < 6)
W(CO)x species are selective and effective abstractors of atomic Cl from a wide variety of organic substrates
Freon 12: C-Cl bond scission
Clean and low energy route into gas phase organic radical chemistry
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Freon 12 pyrolysisA
bsor
banc
e
2000 1800 1600 1400 1200 1000 800
Wavenumber / cm-1
FT-IR spectra of the products of laser pyrolysis of Freon 12 in the absence (—) and presence (—) of W(CO)6
A
A
A
A A
A = CF2Cl2
B B
B = CF2O
C
C = CF3 Cl
D
D = W(CO)6
E
E = C2F4
FF
F
F = C2Cl2F4
G
G = SiF4 Unassigned peaks are attributable to SF6
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Freon 12: Decomposition Scheme
F2C Cl CF3Cl CFCl2
SiF4
SiO2
Cl
Cl
CF2Cl +
CF2Cl2
+1
2
3
4
5
6 7
CF2Cl
CF2
C2F4CF2O Secondary reactions8
C2F4Cl2
CF2
O2
Freon 12 pyrolysis: major products are CF3Cl and CF2 O
Freon 12 copyolysis with W(CO)6: major products are C2F4Cl2 and C2F4 and SiF4
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CF2 : Matrix Isolation IR
Spectroscopy
FT-IR spectra illustrating dimerisation of CF2 to C2F4 A = CF2 Unassigned peaks are attributable to SF6
Abs
orba
nce
1300 1250 1200 1150
Wave number / cm-1
A15 K
35 K
B
B
B = C2F4
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First derivative spectrum centred at ~ 1220 cm-1
Laser off
Laser on
CF2 : Tuneable Diode Laser
Spectroscopy
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Conclusion
A mechanism has been proposed for the gas phase thermal decomposition of Freon 12
CF2, a short lived intermediate, has been detected using matrix isolation infrared spectroscopy and observed directly with tuneable diode laser spectroscopy
Abstraction of atomic Cl from Freon 12 by W(CO)x
species provides a low energy route, permitting the detection of less stable reaction products
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Prof. Douglas Russell
Acknowledgements
Dr Noel Renner
Dr Nathan Hore
Dr Rebecca Berrigan
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Spatial Distribution
of Copper and Iron in
Cardiac Tissue
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Seminar Outline: Part B
Electron Probe Microanalysis
Nuclear Microscopy
Acknowledgements
Secondary Ion Mass Spectrometry
Conclusion
Introduction
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Introduction
Investigate the spatial distribution of Cu and Fe in cardiac tissue
Analytical techniques:
Cardiac tissue that exhibits marked histological damage may
possess elevated levels of Cu and Fe
Electron probe x-ray microanalysis (EPMA)
Secondary ion mass spectrometry (SIMS)
Nuclear microscopy (NM)
Correlate topographical features with chemical composition
UHV techniques influence method of sample preparation
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Electron Probe Microanalysis
Image courtesy of the Microscopy and Microanalysis Facility at the Department of Materials Engineering – Monash University
Detection limit in the region of 100 ppm
Primary ion beam: 5-20 kV electrons
Lateral resolution of 1 µm
Quantitative
Cryochamber
Specimen maintained at 80 K
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Electron Probe Microanalysis
Energy /keV
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Nuclear Microscopy
Rutherford Backscattering Spectroscopy (RBS) - normalisation
Scanning Transmission Ion Microscopy (STIM) - structural information
Particle Induced X-ray Emission (PIXE) - elemental analysis
Secondary electrons – complementary topographical information
Incident beam: 1.0-3.0 MeV H+ or He+
Lateral resolution of between 0.1 and 10 µm
Detection limit: ppb to ppm
Quantitative
UHV chamber
Specimen section freeze dried
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Secondary Ion Mass Spectrometry
Image courtesy of the Bristol University CVD Diamond Group
Detection limit: ppb to ppm
Primary ion beam: 1-30 KeV 133Cs+
Non-quantitative analysis of biological specimens
Lateral resolution of 1 µm is possible
UHV chamber
Specimen section freeze dried
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Secondary Ion Mass Spectrometry
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Conclusion
Nuclear microscopy: provided the specimen is prepared in an
appropriate manner, determination of the spatial distribution of
metals in biological tissue is possible
Secondary ion mass spectrometry: non-quantitative
Electron probe x-ray microanalysis: insufficient sensitivity
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Prof. Garth Cooper (Protemix)
Acknowledgements
Dr Anthony Phillips (Protemix)
Catherine Hobbis (School of Engineering - EPMA)
Dr Marcus Gustafsson (Department of Chemistry - SIMS)
Dr V. John Kennedy (Institute of Geological and Nuclear
Sciences - NM)
Dr Ritchie Sims (Department of Geology - EPMA)