IUPAC Measured - University of Leeds
1
Fig. 2: The HIRAC chamber equipped with recently installed temperature control system. Kinetics of Reactions of Cl atoms with C4-C5 hydrocarbons over a temperature range of 220-320 K L. N. Farrugia , F.A.W. Winiberg, D. E. Heard and P. W. Seakins School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK [email protected] 1. Introduction • Recent observations of high [ClNO 2 ] in inland urban areas in the USA (1) , as well as significant [Cl] in volcanic plumes, have had an impact on the importance of chlorine chemistry outside the marine environment. 2. HIRAC – Highly Instrumented Reactor for Atmospheric Chemistry 3. Relative rate study of Cl + hydrocarbons 4. Temperature dependent study 5. Conclusions • Good agreement with the literature for all experimental Cl+hydrcarbons rate coefficients obtained at 298 K. • Excellent agreement for GC-FID and FTIR data obtained in HIRAC for n-butane, which is also a validation of the method used. • First temperature dependent results for Cl + n-pentane and isopentane, with negative temperature dependence reported for isopentane reaction. Negative temperature dependence observed from isopentane+Cl. • This work provides further validation of suitability of HIRAC temperature control system and relative rate method as a way of generating reliable temperature dependent rate coefficients. 7. References (1) Thornton, J. A. et al., Nature, 464, pp.271-274, 2010. (2) Glowacki, D. R. et al., Atmos. Chem. Phys., 7, pp.5371-5390, 2007. (3) Tyndall, G. S. et al., Int. Journal Chemical Kinetics., 29, 1, pp.43 – 55. 1996. 45.00 45.50 46.00 46.50 47.00 47.50 48.00 48.50 49.00 49.50 50.00 -60 -30 0 30 60 Temperature / o C Vertical Distance / cm (a) 47.00 47.20 47.40 47.60 47.80 48.00 48.20 48.40 48.60 48.80 49.00 -60 -30 0 30 60 Temperature / o C Horizontal Distance / cm (b) -47.00 -46.50 -46.00 -45.50 -45.00 -44.50 -44.00 -43.50 -43.00 -60.00 -30.00 0.00 30.00 60.00 Temperature / o C Vertical Distance / cm (c) -47.00 -46.50 -46.00 -45.50 -45.00 -44.50 -44.00 -60.00 -30.00 0.00 30.00 60.00 Temperature / o C Horizontal Distance / cm (d) Fig. 4: Temperature profile of HIRAC chamber at +48 o C (a + b) and -46 o C (c + d) at 1000 mbar. Fig. 6: Excellent agreement between FTIR and GC measurements in HIRAC for n- butane + ethane + Cl relative rate experiment at 298 K. Table 1: Kinetic data on reactions of Cl with propane, n-butane, isobutane, n-pentane and isopentane at 298 K. Fig. 3:(a) The photolysis lamps and (b) the FTIR Chernin cell present inside the HIRAC chamber. Fig. 1: Nighttime source of Chlorine (Thornton et al., 2010) Hydrocarbon k (Cl+hydrocarbons) / 10 -10 cm 3 molecule -1 s -1 Source propane 1.45±0.28 Wallington et al. (1988) 1.43±0.25 Tyndall et al. (1996) 1.48+0.07 This work (GC) n-butane 2.15±0.15 Tyndall et al. (1996) 2.25+0.10 Lewis et al. (1980) 2.23+0.11 This work (GC) 2.14±0.11 This work (FTIR) isobutane 1.42±0.06 Seakins et al. (1996) 1.46±0.06 Lewis et al. (1980) 1.49±0.08 This work (GC) n-pentane 2.52±0.06 Atkinson et al. (1985) 2.46±0.03 Seakins et al. (2001) 2.65±0.13 This work (GC) isopentane 2.03±0.06 Atkinson et al. (1985) 1.91±0.02 Seakins et al. (2001) 2.05±0.10 This work (GC) 6. Future Work • FTIR analysis for isobutane, n-pentane and isopentane will be performed using the new FTIR data analysis techniques developed. • Product analysis for the GC and FTIR data for all butanes and pentanes studied, and a look into whether there temperature effects product ratios. • Further site-specific rate data and product branching fractions using deuterated compounds are planned for Cl atom reactions with other organics to obtain an insight into product ratios and mechanistic information of these reactions. 0.0030 0.0032 0.0034 0.0036 0.0038 0.0040 0.0042 0.0044 -42.0 -41.5 -41.0 -40.5 -40.0 -39.5 -39.0 -38.5 -38.0 -37.5 Measured IUPAC Herron & Huie Treacy et al. ln(k bim / molecule -1 cm 3 s -1 ) 1/(T / K) Arrhenius plot for propene ozonolysis This work: ln(k bim ) = -2282.4/T - 31.3 IUPAC: ln(k bim ) = -1880/T - 32.8 Fig. 5: Arrhenius plot for propene+O 3 reaction at 1000 mbar and over a temperature range of 233 – 323 K. • ClNO 2 production has an impact on NO x and Cl budgets (Fig.1.). • Cl:OH ratios have been monitored in various sites including the polar regions. Various studies have focused on better understanding the implications of these two cycles. 0.00 0.05 0.10 0.15 0.20 0.25 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 n-butane isobutane n-pentane isopentane ln [hydrocarbon] o /[hydrocarbon] t ln [ethane] o /[ethane] t • A number of these studies are revealing important information on Cl atom chemistry through observing relative hydrocarbon concentrations, in most studies alkanes. • Hydrogen abstraction of hydrocarbons by atomic chlorine have been of interest to kineticists for many years. • Reactions involving chlorine atoms with n-butane, isobutane, n-pentane and isopentane were studied experimentally in an environmental chamber. Experiments were carried out over a temperature range of 225 – 325 K and at 1000 mbar. • The main focus of this study was to obtain a better mechanistic understanding of these reactions and in particular the structural influence of higher hydrocarbons on hydrogen abstraction reactions. • The kinetics of Cl atom hydrogen abstractions from propane, n-butane, isobutane, n-pentane and isopentane has been investigated at room temperature and 1000 mbar in the HIRAC chamber. • GC-FID and FTIR techniques were used in order to analyse the rates of decay of the hydrocarbons. • The relative rate technique was used to measure rate coefficients of these reactions using ethane as a reference compound. • A new FTIR data analysis technique was developed and used to analyse the n-butane data obtained from this study. Lack of suitable reference spectra for other hydrocarbons inhibited analysis of other FTIR data. • A comparison of the kinetic data from this study with other studies is shown in Table 1. • The results obtained for experiments carried out at 298 K were all within good agreement of the literature. Fig. 7.: Relative rate plots for hydrocarbon + Cl reactions at 1000 mbar and at 298 K. • Previous studies for ethane+Cl showed a positive temperature dependence, while no similar trend was found for propane and n-butane. • A temperature dependent study was carried out over ~220 – 320 K in the HIRAC chamber using relative rate method. • Results obtained for isopentane+Cl gave a negative temperature dependence (E a = -1.33 ± 0.02 kJ mol -1 ) • n-pentane, isobutane and n-butane were all found to be temperature independent from this study. Fig. 8: Arrhenius plots for pentanes+Cl reaction at 1000 mbar and over a temperature range of ~ 220 – 320 K. • Recent installation of a temperature control system has enabled studies at temperatures between ~ 223 – 323 K. • System has been tested by conducting a temperature-dependent study for propene+O 3 (Fig.5.). • An Arrhenius plot of the bimolecular rate constant for propene gave E a = 19.84 ± 0.46 kJ mol -1 . This value is within error of the IUPAC and literature data. • A temperature profile of the HIRAC chamber operating at about 233 – 323 K to check the uniformity of the system is shown in Fig.4. • The HIRAC chamber at the University of Leeds (2) allows control of the conditions of temperature, pressure and photolysis rate which are important variables affecting the rate of processes in the atmosphere. • HIRAC is a 2.25 m 3 stainless steel indoor chamber equipped with a range of instruments including a GC- FID , GC-HID, FTIR, FAGE, CRDS as well as commercial NO x , O 3 and CO analysers. • FTIR is coupled to HIRAC via a multipass optical arrangement on the interior of the chamber (Figure 3b). • The mirror systems are robust and able to handle ranges of temperatures and pressures which the chamber is subjected to. • This Chernin cell optical system is a modified multipass matrix system that features three objective mirrors with input and output apertures placed on opposite sides of the small field mirror. (a) (b)
Transcript of IUPAC Measured - University of Leeds
Fig. 2: The HIRAC chamber equipped with
recently installed temperature control system.
Kinetics of Reactions of Cl atoms with C4-C5 hydrocarbons over a temperature range of 220-320 K
L. N. Farrugia , F.A.W. Winiberg, D. E. Heard and P. W. Seakins
School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK [email protected]
1. Introduction
• Recent observations of high [ClNO2] in inland urban areas in the USA(1), as well as
significant [Cl] in volcanic plumes, have had an impact on the importance of chlorine
chemistry outside the marine environment.
2. HIRAC – Highly Instrumented Reactor for Atmospheric Chemistry 3. Relative rate study of Cl + hydrocarbons
4. Temperature dependent study
5. Conclusions
• Good agreement with the literature for all experimental Cl+hydrcarbons rate
coefficients obtained at 298 K.
• Excellent agreement for GC-FID and FTIR data obtained in HIRAC for n-butane,
which is also a validation of the method used.
• First temperature dependent results for Cl + n-pentane and isopentane, with
negative temperature dependence reported for isopentane reaction. Negative
temperature dependence observed from isopentane+Cl.
• This work provides further validation of suitability of HIRAC temperature control
system and relative rate method as a way of generating reliable temperature
dependent rate coefficients.
7. References
(1) Thornton, J. A. et al., Nature, 464, pp.271-274, 2010.
(2) Glowacki, D. R. et al., Atmos. Chem. Phys., 7, pp.5371-5390, 2007.
(3) Tyndall, G. S. et al., Int. Journal Chemical Kinetics., 29, 1, pp.43 – 55. 1996.
45.00
45.50
46.00
46.50
47.00
47.50
48.00
48.50
49.00
49.50
50.00
-60 -30 0 30 60
Te
mp
era
ture
/ o
C
Vertical Distance / cm
(a)
47.00
47.20
47.40
47.60
47.80
48.00
48.20
48.40
48.60
48.80
49.00
-60 -30 0 30 60
Te
mp
era
ture
/ o
C
Horizontal Distance / cm
(b)
-47.00
-46.50
-46.00
-45.50
-45.00
-44.50
-44.00
-43.50
-43.00
-60.00 -30.00 0.00 30.00 60.00
Te
mp
era
ture
/ o
C
Vertical Distance / cm
(c)
-47.00
-46.50
-46.00
-45.50
-45.00
-44.50
-44.00
-60.00 -30.00 0.00 30.00 60.00
Te
mp
era
ture
/ o
C
Horizontal Distance / cm
(d)
Fig. 4: Temperature profile of HIRAC chamber
at +48 oC (a + b) and -46 oC (c + d) at 1000
mbar.
Fig. 6: Excellent agreement between FTIR
and GC measurements in HIRAC for n-
butane + ethane + Cl relative rate experiment
at 298 K.
Table 1: Kinetic data on reactions of Cl with
propane, n-butane, isobutane, n-pentane and
isopentane at 298 K.
Fig. 3:(a) The photolysis lamps and (b) the FTIR
Chernin cell present inside the HIRAC chamber.
Fig. 1: Nighttime source of Chlorine (Thornton et
al., 2010)
Hydrocarbon k (Cl+hydrocarbons) / 10-10
cm3molecule-1s-1 Source
propane
1.45±0.28 Wallington et al. (1988)
1.43±0.25 Tyndall et al. (1996)
1.48+0.07 This work (GC)
n-butane
2.15±0.15 Tyndall et al. (1996)
2.25+0.10 Lewis et al. (1980)
2.23+0.11 This work (GC)
2.14±0.11 This work (FTIR)
isobutane
1.42±0.06 Seakins et al. (1996)
1.46±0.06 Lewis et al. (1980)
1.49±0.08 This work (GC)
n-pentane
2.52±0.06 Atkinson et al. (1985)
2.46±0.03 Seakins et al. (2001)
2.65±0.13 This work (GC)
isopentane
2.03±0.06 Atkinson et al. (1985)
1.91±0.02 Seakins et al. (2001)
2.05±0.10 This work (GC)
6. Future Work
• FTIR analysis for isobutane, n-pentane and isopentane will be performed using the
new FTIR data analysis techniques developed.
• Product analysis for the GC and FTIR data for all butanes and pentanes studied, and
a look into whether there temperature effects product ratios.
• Further site-specific rate data and product branching fractions using deuterated
compounds are planned for Cl atom reactions with other organics to obtain an
insight into product ratios and mechanistic information of these reactions.
0.0030 0.0032 0.0034 0.0036 0.0038 0.0040 0.0042 0.0044
-42.0
-41.5
-41.0
-40.5
-40.0
-39.5
-39.0
-38.5
-38.0
-37.5
Measured
IUPAC
Herron & Huie
Treacy et al.
ln(k
bim
/ m
ole
cu
le-1
cm
3 s
-1)
1/(T / K)
Arrhenius plot for propene ozonolysis
This work: ln(kbim) = -2282.4/T - 31.3
IUPAC: ln(kbim) = -1880/T - 32.8
Fig. 5: Arrhenius plot for propene+O3 reaction at
1000 mbar and over a temperature range of 233
– 323 K.
• ClNO2 production has an impact on NOx
and Cl budgets (Fig.1.).
• Cl:OH ratios have been monitored in
various sites including the polar regions.
Various studies have focused on better
understanding the implications of these
two cycles.
0.00 0.05 0.10 0.15 0.20 0.250.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
n-butane
isobutane
n-pentane
isopentane
ln [
hy
dro
ca
rbo
n] o
/[h
yd
roc
arb
on
] t
ln [ethane]o/[ethane]t
• A number of these studies are revealing important information on Cl atom chemistry
through observing relative hydrocarbon concentrations, in most studies alkanes.
• Hydrogen abstraction of hydrocarbons by atomic chlorine have been of interest to
kineticists for many years.
• Reactions involving chlorine atoms with n-butane, isobutane, n-pentane and
isopentane were studied experimentally in an environmental chamber. Experiments
were carried out over a temperature range of 225 – 325 K and at 1000 mbar.
• The main focus of this study was to obtain a better mechanistic understanding of
these reactions and in particular the structural influence of higher hydrocarbons on
hydrogen abstraction reactions.
• The kinetics of Cl atom hydrogen
abstractions from propane, n-butane,
isobutane, n-pentane and isopentane
has been investigated at room
temperature and 1000 mbar in the
HIRAC chamber.
• GC-FID and FTIR techniques were
used in order to analyse the rates of
decay of the hydrocarbons.
• The relative rate technique was used
to measure rate coefficients of these
reactions using ethane as a reference
compound.
• A new FTIR data analysis technique
was developed and used to analyse
the n-butane data obtained from this
study. Lack of suitable reference
spectra for other hydrocarbons
inhibited analysis of other FTIR data.
• A comparison of the kinetic data from
this study with other studies is shown
in Table 1.
• The results obtained for experiments
carried out at 298 K were all within
good agreement of the literature.
Fig. 7.: Relative rate plots for hydrocarbon + Cl
reactions at 1000 mbar and at 298 K.
• Previous studies for ethane+Cl showed a
positive temperature dependence, while
no similar trend was found for propane
and n-butane.
• A temperature dependent study was
carried out over ~220 – 320 K in the
HIRAC chamber using relative rate
method.
• Results obtained for isopentane+Cl gave
a negative temperature dependence (Ea =
-1.33 ± 0.02 kJ mol-1)
• n-pentane, isobutane and n-butane were
all found to be temperature independent
from this study.
Fig. 8: Arrhenius plots for
pentanes+Cl reaction at 1000 mbar
and over a temperature range of ~
220 – 320 K.
• Recent installation of a temperature
control system has enabled studies at
temperatures between ~ 223 – 323 K.
• System has been tested by
conducting a temperature-dependent
study for propene+O3 (Fig.5.).
• An Arrhenius plot of the bimolecular
rate constant for propene gave Ea =
19.84 ± 0.46 kJ mol-1. This value is
within error of the IUPAC and
literature data.
• A temperature profile of the HIRAC
chamber operating at about 233 –
323 K to check the uniformity of the
system is shown in Fig.4.
• The HIRAC chamber at the University
of Leeds(2) allows control of the
conditions of temperature, pressure
and photolysis rate which are
important variables affecting the rate
of processes in the atmosphere.
• HIRAC is a 2.25 m3 stainless steel
indoor chamber equipped with a
range of instruments including a GC-
FID , GC-HID, FTIR, FAGE, CRDS as
well as commercial NOx, O3 and CO
analysers.
• FTIR is coupled to HIRAC via a
multipass optical arrangement on the
interior of the chamber (Figure 3b).
• The mirror systems are robust and
able to handle ranges of temperatures
and pressures which the chamber is
subjected to.
• This Chernin cell optical system is a
modified multipass matrix system that
features three objective mirrors with
input and output apertures placed on
opposite sides of the small field mirror.
(a) (b)
