Department of Chemical Engineering
Itsaso Auzmendi Murua, Jason Hudzik Joseph W. Bozzelli
Chemical Activation Reactions of Cyclic Alkane and Ether Ring-Opened
Diradicals with O2: Thermochemistry, Reaction Paths, Kinetics
7th International Conference on Chemical Kinetics, July 10-14, 2011
• Cyclic Aliphatic Hydrocarbons are major components in modern fuels:
- Present in reactants:
Commertial jet fuel contains: 26% cycloalkanes and alkylcycloalkanes
Commercial diesel fuel (up to 40%) and gasoline (up to 3%)
- Produced during the gas-phase processes
• During combustion or pyrolisis processes, cycloalkanes can lead to formation of:
- Toxic compounds or soot precursors such as benzene (via dehydrogenation)
- Linear unsaturated species such as acrolein (via ring opening)
• 3 to 6 member cyclic ethers are formed at early times by alkyl radical reactions with
dioxygen in combustion and pre-combustion processes that occur at moderate T.
Introduction
Introduction – s-butane oxidation
c-c-c-co
o
+OH
cc.cc + o2
ccq.cc-19.7-20.7
-3.4-3.2
-0.3-2.4
0.9-0.3ccqc.c
2.22.0
14.914.9
18.017.5
+ OH
-23.1-23.1
-19.8-20.6
+ OH-26.8-27.6
12.613.0
b3lyp/6-31g(d,p)CBS-QB3
5.910.2
3.25.6
7.07.9
ccqcc.
c-c-c-c
c.cqcc
c-c-c-co
Formation of Cyclic Ethers in Alkyl Radical Oxidation R. + O2 => ROO.
Hydrogen atom transfer then Cyclic ether formed with OH elimination
C3CCQjCC2
-41.8
-27.0-31.9
-27.4C3jCCQCC2
C3CCQCjC2
C3CYCOCC2+OH
C3CCQCC2j
-48.4
C3CYCCCOC + OH
-48.5
C2YOXTCC2+OH
-47.9
tst 1
tst 3
tst 2
tst 4
tst 5
tst 6
C3CC.CC2 + O2
-9.1
C-C-C-C
C-O
C
CC C-C-C-C
C
C
CC
OC-C-C-C
C
C
CC
O
C3CCCQ.C2
-46.8
-31.7
C3CCYCCOC2 + OH
-28.5C3CCCQC2
.
C3CY(CCO)C2 + OH-44.4
-29.7
-68.7C2Y(CCCCO)C2 + OH
tst1
tst3
C3CC.CQC2
C3.CCCQC2
-48.5
C-C-C-C
O
C
CC
C
tst2
tst4
tst5
tst6
C-C-C-C
O
C
CC
C
C-C-C-CC
CC
C O
C3CCC.C2
Introduction – s- and t- isooctane oxidation
Formation of Cyclic EthersIn Isooctane Radical + O2 Reactions
• Initial unimolecular dissociation reactions of cyclic alkanes and ethers in
combustion systems are ring opening to form a di-alkyl radical.
• Release of ring strain in small ( 3 to 5 member ring) and bicyclic molecules
reduces the bond energy needed for bond cleavage - ring opening – Diradical
Formation.
• The initial ring opened di-radical or the peroxy – alkyl di-radical can undergo
triplet – singlet conversion by:
- Electronic state crossing
- Collisions of the di-alkyl radical with the bath gas
- Chemical activation reaction of one radical site via association with 3O2
Introduction
Introduction• This study is an attempt to determine the importance of the
diradicals reacting with dioxygen.
• Quantum chemical calculations for thermochemical properties.
• Statistical rate theory for the T and P dependence of the rate coefficient
• Systems Studied :
- Cyclic Alkanes : y(ccc), y(cccc) and y(ccccc)
- Cyclic Ethers : y(cco), y(ccco) and y(cccco)
- TCD (C10H16) Tri-cyclo Decane
Tri-cyclo Decane
Thermochemical Properties• Use of computational chemistry → calculate for radicals and molecules:
- Heats of formation
- Entropies
- Heat capacities
• Heat of formartion from Isodesmic work reactions:
(*) Sirjean, B., et al. . J. Phys. Chem. A 2006, 110, 12693.
Association and addition reactions are treated as:
Chemical activation reactions with:
o Quantum Rice Ramsperger Kassel analysis for k(E)
o Master Equation for fall-off (pressure dependant reactions)
o Steady State Analysis for Activated Species
Input file for Chemaster:
• Thermochemical information on reaction paths
• Temperature and pressures desired for study
• Frequencies of the species involved in the reactions
• High Pressure Rate Constants
• Lennard Jones Collision Parameters of reactants and the bath gas
•ΔEdown and ΔEaverage for the determination of k(E)
Rate Constants
Excited (A)* can:
• Dissociate back to reactants
• Be stabilized by collisions
• React to new products
Chemaster – QRRK and ME analysis
m = bath gas (N2, Air, Ar…)
Diradical + O2 (A)*
(A)o
ks(m)
Species
Reduced Freq. Sets Total (3n-6)
Freq’s Number
Lennard Jones Parameters
σ (Å) ε/k (K)
.cccc.
505.11470.33505.4
10.1812.366.95
4.341 336.95
.ccccc.476.9
1442.83423.5
13.0216.718.77
5.270 383.11
.ccco.549.6
1498.73614.2
8.5510.014.93
5.523 390.07
TCD-H.-H.-12327.0799.3
4000.0
32.4333.395.68
5.320 608.80
Lennard Jones Parameters - Bath gas (N2)
σ (Å) 3.542
ε/k (K) 98.3
∆E (cal) 900.
Ehead (kcal) 75.
Energy levels from one External Rotation included in density of states
P and T dependence of rate constants
Chemical activationDi-radical + O2 only
c.ccc. + o2
-12
-7
-2
3
8
13
0 1 2 3 4
k (c
m3
mol
-1 s-
1)
1000/T (K)
P = 1 atm
c.ccc. + o2
c.cccq. (t)
c.cccq. (s)
y(ccccoo)
o.cccco.
ch2o + c.cco.
-12
-7
-2
3
8
13
0.00001 0.001 0.1 10
k (c
m3
mol
-1 s-
1)
log (P) (atm)
T = 1000 K
c.ccc. + o2
c.cccq. (t)
c.cccq. (s)
y(ccccoo)
o.cccco.
ch2o + c.cco.
• Chemical activation analysis is used for reaction of the diradicals with O2 :
- qRRK for k(E)
- Master Equation Analysis for fall-off
• Chemkin used for analysis of a reaction system of the diradical
• Chemkin analysis includes:
- Results (kinetics) from diradical with O2 (chemical activation association)
- Triplet-Singlet conversion
- Formation of oxygenated ring Hrxn = exothermic ~ 70 kcal mol-1
- Ring opening via cleavage of weak cyclic O-O bond ~ 45 kcal mol-1
- Unimolecular reactions of the diradical: Intramolecular H transfer to form an stable olefin β-scission to form olefins + New Radical
- Reactions of stabilized intermediates β-scission and Ring closure …
Reaction of the diradicals with O2
Systems Num. Rxn
Num. Species
y(cccc) → .cccc. 20 18
y(ccccc) → .ccccc. 26 23
y(ccco) → .cocc. 20 18
TCD → TCD-H.-H.-12 22 19
Reaction Paths – Example - Cyclobutane - y(cccc)
Unimolecular Dissociation
Chemical Activation
Intramolecular H transfers and HO2 elimination reactions
C.CCC.+ O2 → C.CCCQ.
Kinetic Parameters – H transfer and HO2 elimination rxns
Level c.cccq. = c*ccccq c.ccccq. = c.ccc*c + ho2
Ea I freq Ea I freqB3LYP / 6-31g(d,p) 20.50 -1664.97 27.18 -1032.40BMK / 6-31g(d,p) 23.38 -1908.72 35.34 -1022.40B1B95 / 6-31g(d,p) 21.51 -1773.71 28.97 -1007.44
Level c.cccq. = c*cccq c.cccq. = c.cc*c + ho2 o.cccco. = o*ccccoh
Ea I freq Ea I freq Ea I freqB3LYP / 6-31g(d,p) 22.18 -1663.33 27.13 -1026.92 2.33 -826.55BMK / 6-31g(d,p) 24.42 -1826.68 34.94 -1018.74 5.57 -851.21B1B95 / 6-31g(d,p) 22.01 -1726.00 28.35 -1049.43 2.59 -850.53
Level c.ccqj. = c*ccq c.ccq. = c.c*c + ho2 o.ccco. = o*cccoh
Ea I freq Ea I freq Ea I freqB3LYP / 6-31g(d,p) 34.51 -2196.32 22.10 -1073.56 12.65 -1305.53BMK / 6-31g(d,p) 37.57 -2327.19 29.94 -1227.09 16.07 -1653.44B1B95 / 6-31g(d,p) 34.79 -2205.18 23.50 -1150.93 12.59 -1274.35
CHEMKIN MODELING RESULTS
Reaction Paths – Cyclopropane – y(ccc)
Unimolecular Dissociation
Chemical Activation
Reaction Products – Cyclopropane – y(ccc)
1.00E-27
1.00E-24
1.00E-21
1.00E-18
1.00E-15
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+00
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2ch2
ch2
y(cco)
1.00E-27
1.00E-24
1.00E-21
1.00E-18
1.00E-15
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+00
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 1200 K
ch2o
ch2ch2
ch2
y(cco)
Main reaction paths: → Ring closure then reaction to y(cco) + CH2O
At higher temperatures: → Formation of ethylene becomes important by unimolecular dissociation of C.CC.
1 atm
Reaction Paths – Cyclobutane - y(cccc)
Unimolecular Dissociation
Chemical Activation
Small C4 system : 3 kcal mol-1
barrier to beta scission is low
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+00
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
ntime (s)
T = 1200 K
ch2o
ch2ch2
cccdc
y(ccco)
Reaction Products – Cyclobutane – y(cccc)
1 atm
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+000.
00E+
00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2ch2
cccdc
y(ccco)
Unimolecular dissociation to two ethylene moieties is the most important channel under both temperatures.
At 500 K → Oxidation to two formaldehyde plus ethylene is next most important
At 1200 K → Intramolecular H transfer to form stable butene is most important
Formation of oxitane (cy- CCCO) → Some importance at 500K → Negligible at 1200K.
Reaction Paths – Cyclopentane – y(ccccc)
Chemical Activation
Unimolecular Dissociation
Reaction Products – Cyclopentane – y(ccccc)
1 atm
1.00E-18
1.00E-15
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+00
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
ntime (s)
T = 1200 K
ch2o
ch2ch2
ch2
y(cccco)
y(cco)
y(ccc)
cccc=c
1.00E-331.00E-301.00E-271.00E-241.00E-211.00E-181.00E-151.00E-121.00E-091.00E-061.00E-03
1.00E+000.
00E+
00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2ch2
ch2
y(cccco)
y(cco)
y(ccc)
cccc=c
(*) At 500K pentene and y(cccco) are major product and overlapAt 1200K, pentene is mayor product and ch2o, y(cccco), y(ccc) and ch2ch2 are all similar
At 500 K → Formation of pentene and cyclopropane are the main reaction paths. → Formation of two CH2O plus ethylene and singlet diradical 1CH2 are also important
At 1200 K → Intramolecular H transfer - Formation of pentene is the dominant reaction path
Reaction Paths – Oxirane Cyclic ether – y(cco)
Unimolecular Dissociation
Chemical Activation
1.00E-13
1.00E-10
1.00E-07
1.00E-04
1.00E-01
0.00
E+00
1.00
E-0
6
2.00
E-0
6
3.00
E-0
6
4.00
E-0
6
5.00
E-0
6
Mol
e Fra
ctio
n
time (s)
T = 1200 K
ch2o
ch2
hco2.
hco2h
y(coo)
Reaction Products – Oxirane Cyclic ether – y(cco)
1 atm
1.00E-21
1.00E-18
1.00E-15
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+000.
00E+
00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2
hco2.
hco2h
y(coo)
Formation of CH2O and HCO2. are dominant at both temperatures
At 500 K → Ring closure resulting on y(coo) has some importance
At 1200 K→ Formation of a formaldehyde and the singlet diradical 1CH2
Reaction Paths – Oxetane Cyclic ether – y(ccco)
Chemical Activation
Unimolecular Dissociation
1.00E-13
1.00E-10
1.00E-07
1.00E-04
1.00E-01
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 1200 K
ch2o
ch2ch2
o=ccoh
coc=c
y(ccoo)
Reaction Products – Oxetane Cyclic ether – y(ccco)
1 atm
1.00E-16
1.00E-13
1.00E-10
1.00E-07
1.00E-04
1.00E-01
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2ch2
o=ccoh
coc=c
y(ccoo)
Formation of a formaldehyde plus ethylene → most important at both temperatures At 500 K → Ring closure of stabilized intermediate o.cco. has importance
At 1200 K → Formation of coc=c has importance
Reaction Paths – Cyclic Ethers – y(cccco)
It can β-scission to form two different diradicals
Reaction Paths – Cyclic Ethers – y(cccco) 1
Unimolecular Dissociation
Chemical Activation
1.00E-331.00E-301.00E-271.00E-241.00E-211.00E-181.00E-151.00E-121.00E-091.00E-061.00E-03
1.00E+000.
00E+
00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2ch2
ch2
y(cccoo)
y(ccc)
y(cco)
1.00E-18
1.00E-15
1.00E-12
1.00E-09
1.00E-06
1.00E-03
1.00E+00
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
ntime (s)
T = 1200 K
ch2o
ch2ch2
ch2
y(cccoo)
y(ccc)
y(cco)
(*) At 500K ch2o and y(cccoo) are dominant and overlapAt 1200K ch2o and y(ccc)are dominant and overlap
At 500 K → Formation of formaldehyde and ring closure to form y(cccoo) most important
At 1200K → Formation of two formaldehyde plus cyclopropane becomes the dominant path
Reaction channels – Cyclic Ethers – y(cccco) 1
Reaction Paths – Cyclic Ethers – y(cccco) 2
Unimolecular Dissociation
Chemical Activation
1.00E-311.00E-281.00E-25
1.00E-221.00E-19
1.00E-161.00E-13
1.00E-101.00E-07
1.00E-041.00E-01
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2o
ch2ch2
ch2
y(cocco)
y(cco)
1.00E-17
1.00E-14
1.00E-11
1.00E-08
1.00E-05
1.00E-02
0.00
E+00
1.00
E-06
2.00
E-06
3.00
E-06
4.00
E-06
5.00
E-06
Mol
e Fra
ctio
n
time (s)
T = 1200 K
ch2o
ch2ch2
ch2
y(cocco)
y(cco)
(*) At 500K ch2o and y(cocco) are dominant and overlapAt 1200K ch2ch2 and y(cco) are dominant and overlap
Reaction channels – Cyclic Ethers – y(cccco) 2
At 500 K→ Formation of formaldehyde and ring closure to form y(cocco) most important
At 1200 K → Ring closure to form formaldehyde plus the three memebered cyclic ether becomes the dominant reaction path.
JP10 – C10H16 - Tri-cyclodecane (TCD)
Main component of the synthetic fuel JP10, widely used in aircraft
Unimolecular decomposition of TCD is initiated by:
• Breaking of a C-H bond
• Opening of one of the rings, which forms a diradical
- If the diradical is formed, this will:
Further dissociate (β-scission and intramolecular H transfer)
Chemical activation reactions with molecular oxygen
Reaction Paths – JP10 – C10H16 - Tri-cyclodecane
..
(57.8)
(82.5)
(33.9)
TCD12-H.-H
.
YC5E
..
YC5E
+ C=CCC=C
YC5-H.-H
.
(74.0)(8.5)
(-4.9)
YC5YC5E3
(-5.7)
YC5YC5E1YC5YC5E2
(-4.6)
75.6
65.6
77.65
88.2
104.5
Unimolecular Dissociation
+ O2
..
(57.8) .
.
..
(23.3)
(-5.8)
.
.
(-6.7)
..
(-5.1)
(-32.2)
.(-0.6)
.+
(4.5)
TCD12-H.-H
.
TCD12-Q.-H
.
TCD12-YOO
TCD12-O.-O
. Y5O.PN
.=O O*C9
.M
.=O VC
.CCCCHO C
.CCHO
(3.9)
.
.(4.5)+
C.CCHO
VCM.CCCHO
(12.9)
(17.4)
ks [M]
YC5=OYC5OH
(-59.9)
.
+HO2
YC5.YC5E2
(45.3)
.
. Y5O.PN=O
.
(-20.1)
52.8
1.71.7 1.40.8
11.4
24.0
Singlet-Triplet conversion
Chemical Activation
Reaction Paths – JP10 – C10H16 - Tri-cyclodecane
1.00E-22
1.00E-17
1.00E-12
1.00E-07
0.00
E+00
1.00
E-0
6
2.00
E-0
6
3.00
E-0
6
4.00
E-0
6
5.00
E-0
6
Mol
e Fra
ctio
n
time (s)
T = 1200 K
ch2ch2
hco
vccc=o + c=o
yc5yc5e1
yc5yc5e2
yc5yc5e3
yc5=oyc5oh
yc5.pn=o.
yc5jyc5e2
c=ccc=c
c=cc=c
1 atm
Both T → Formation of YC5YC5E is the main reaction path → Formation of butadioene (C=CC=C) has some importance → Formation of 1,4 pentadiene (C=CCC=C) some importance
Lower T → Formation of YC5.PN=O. important reaction path → Formation of YC5=OYC5OH some importance
1.00E-22
1.00E-17
1.00E-12
1.00E-07
0.00
E+00
1.00
E-0
6
2.00
E-0
6
3.00
E-0
6
4.00
E-0
6
5.00
E-0
6
Mol
e Fra
ctio
n
time (s)
T = 500 K
ch2ch2
hco
vccc=o + c=o
yc5yc5e1
yc5yc5e2
yc5yc5e3
yc5=oyc5oh
yc5.pn=o.
yc5jyc5e2
c=ccc=c
c=cc=c
Reaction Products – JP10 – C10H16 - Tri-cyclodecane
Conclusions
• Reformation of cycle → fast function of Ring-Opening → Further reactions
• Most ring opening occurs at high temperature → β-scission
• β-scission and intramolecular H transfer reactions with low barriers exist → these dominant
C.CCC. → 2 C2H4 Ea = 3.0 kcal mol-1
O.CCCCO. → O=CCCCOH Ea = 2.3 kcal mol-1
•Where β-scission and intramolecular H transfer reactions are typical (Ea ~ 14-20 kcal mol-1) → Reactions with O2 become important at low T
• Ring closure from chemical activation intermediate species
Future Work
• Further study of intramolecular H transfers for diradicals
• Development of unimolecular and chemical activation kinetics for TCD
ACKNOWLEDGMENTS
• Naval Office of Research
• Basque Government
