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| Identifier |
000428734 |
| Title |
Ατμοσφαιρική δραστικότητα και επίδραση φθορίωσης ακόρεστων ενώσεων : κινητική και μηχανιστική μελέτη της αντίδρασης ατόμων Cl, με τις απλούστερες φθοριωμένες ολεφίνες, CH2=CFX (X:H, F), στην αέρια φάση |
| Alternative Title |
Atmospheric reactivity and fluorination impact of unsaturated compounds: kinetic and mechanistic study for the gas-phase reaction of Cl atoms, with the simplest fluorinated olefins, CH2=CFX (X:H, F) |
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Author
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Αντωνοπούλου, Γεωργία Ε.
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Thesis advisor
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Μήλιος, Κωνσταντίνος
Παπαδημητρίου, Βασίλειος
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Reviewer
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Άγγλος, Δημήτριος
Κανακίδου, Μαρία
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| Abstract |
In this work, kinetics and mechanisms for the reactions of Cl atoms (Cl) with two fluorinated
ethylenes, i.e., fluoroethylene (CH2=CHF) and 1,1-difluoroethylene (CH2=CF2), were studied.
Fluorinated ethylenes belong to a class of gases referred to as hydro-fluorinated-olefins (HFO) that
were recently proposed as potential alternatives for ChloroFluoroCarbons (CFC). The presence of
the double bond in their molecule is expected to lead to an increased atmospheric reactivity, since
besides hydrogen metathesis, HFO’s can be additionally decomposed via electrophilic association
reaction mechanism. The simplest members of HFO (C-2 compounds) were selected as starting
point to evaluate the impact of position and degree of fluorination on HFO reactivity.
Two experimental setups were used in the kinetic studies, performed based on: 1. The technique
of the Thermostated Photochemical Reactor coupled with Fourier-transformed Infrared
Spectroscopy (TPCR/FT-IRS) and 2. The continuous flow technique of the Very-Low-Pressure
Reactor coupled with Quadrupole Mass Spectrometry (VLPR/QMS). In the kinetic study for the
reactions Cl + CH2=CHF (1) and Cl + CH2=CF2 (2) rate coefficients were determined in the
temperature range 253 –363 Κ and at pressure between 0.002 and 700 Torr. Increasing the degree
of fluorination leads to reduced reactivity in the ethylenes studied, with room temperature (296 K)
rate coefficient values, at pressure extremes, being k1(296 Κ,700 Torr) = (8.14±0.17) × 10-11 and
k1(296 Κ, 2 mTorr) = (6.61 ± 0.66) × 1013 cm3 molecule-1 s-1 and k2(296 Κ,700 Torr) = (7.57 ±
0.16) × 10-11 and k2(296 Κ, 2 mTorr) = (1.70 ± 0.25) × 1013 cm3 molecule-1 s-1. Quoted error limits
are given at 95.4 % level of confidence (2σ) and do not include systematic uncertainties. With
regard the reaction mechanisms, it was proven that both reactions proceed via a Chemical
Activation Mechanism (CAM). Based on CAM mechanism, rate coefficient dependence on
temperature and pressure is given by the following expressions.
Combining experimental results with thermochemical parameters for the studied reaction
systems that were calculated using molecular quantum calculations (Gaussian03), at
CCSD(T)/AUG-cc-pVDz//B3LYP/6-311++G(2df,2p) level of theory, branching-ratios for the two
possible reaction pathways during the addition of Cl atoms in the two chemically different carbon
atoms of the double bond were determined and the impact of positioning and degree of fluorination
on products distribution was evaluated. In particular, Cl atoms were added 5 out of the 6 times into
the fluorinated carbon in the case of CH2=CHF (~83 %), while 2 out of 3 times, in CH2=CF2 (~70%).
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| Language |
Greek |
| Subject |
Hydrofluoroolefins |
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Υδροφθοροολεφίνες |
| Issue date |
2020-03-27 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses
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Type of Work--Post-graduate theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/a/b/6/metadata-dlib-1583223676-504417-16456.tkl
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| Views |
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