Shock-tube and modeling study of acetaldehyde pyrolysis and oxidation

Shock-Tube and Modeling

Study of Acetaldehyde

Pyrolysis and Oxidation

KENJI YASUNAGA, SATOSHI KUBO, HIROKI HOSHIKAWA, TAKASHI KAMESAWA,

YOSHIAKI HIDAKA

Department of Chemistry, Faculty of Science, Ehime University, Bunkyo-cho, Matsuyama 790-8577, Japan

Received 14 July 2006; revised 30 January 2007, 22 April 2007; accepted 30 August 2007

DOI 10.1002/kin.20294

Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: Pyrolysis and oxidation of acetaldehyde were studied behind reﬂected shock waves

in the temperature range 1000–1700 K at total pressures between 1.2 and 2.8 atm. The study

was carried out using the following methods, (1) time-resolved IR-laser absorption at 3.39 µm

for acetaldehyde decay and CH-compound formation rates, (2) time-resolved UV absorption at

200 nm for CH₂CO and C₂H₄product formation rates, (3) time-resolved UV absorption at 216 nm

for CH₃formation rates, (4) time-resolved UV absorption at 306.7 nm for OH radical formation

rate, (5) time-resolved IR emission at 4.24 µm for the CO₂formation rate, (6) time-resolved IR

emission at 4.68 µm for the CO and CH₂CO formation rate, and (7) a single-pulse technique

for product yields. From a computer-simulation study, a 178-reaction mechanism that could

satisfactorily model all of our data was constructed using new reactions, CH₃CHO (+M) →

CH₄+ CO (+M), CH₃CHO (+M) → CH₂CO + H₂(+M), H + CH₃CHO → CH₂CHO + H₂, CH₃+

CH₃CHO → CH₂CHO + CH₄, O₂+ CH₃CHO → CH₂CHO + HO₂, O + CH₃CHO → CH₂CHO +

OH, OH + CH₃CHO → CH₂CHO + H₂O, HO₂+ CH₃CHO → CH₂CHO + H₂O₂, having assumed

or evaluated rate constants. The submechanisms of methane, ethylene, ethane, f_ꢀormaldehyde,

C

and ketene were found to play an important role in acetaldehyde oxidation.

Periodicals, Inc. Int J Chem Kinet 40: 73–102, 2008

2007 Wiley

etaldehyde oxidation. It is useful to study the py-

rolysis and oxidation mechanisms of acetaldehyde

together.

INTRODUCTION

Acetaldehyde was well known to be an intermediate

in the oxidation of hydrocarbons and alcohols, partic-

ularly ethanol, which is being increasingly used as an

automobile fuel. The mechanism in high-temperature

pyrolysis of acetaldehyde plays a signiﬁcant role in

the overall oxidation/combustion mechanism of these

important fuels. The mechanism of acetaldehyde py-

rolysis is an essential part of the mechanism of ac-

The pyrolysis of acetaldehyde has been studied by

several workers. At high temperatures above 1000 K,

however, there are only a few reports for it [1–3].

Colket et al. [1] have studied the pyrolysis over the

temperature range 1051–1224 K in a turbulent ﬂow

reactor. They found the products, CO, H₂, CH₄, C₂H₄,

and C₂H₆and evaluated the rate constant expres-

sion k₁=7.1 × 10¹⁵exp(−81.8 kcal/RT) s⁻¹for re-

action (1). They showed the following mechanism at

high temperature, which incorporated a Rice–Herzfeld

mechanism [4] along with additional reactions to

Correspondence to: Yoshiaki Hidaka; e-mail: hidaka@dpc.

ehime-u.ac.jp.

c

ꢀ

2007 Wiley Periodicals, Inc.

74

YASUNAGA ET AL.

account for C₂H₄formation.

CH₃CHO(+M) → CH₃+ CHO(+M)

(15), and CH₃CHO + CHO = CH₃CO + CH₂O for

acetaldehyde oxidation.

(1)

(5)

CH₃CHO + O₂→ CH₃CO + HO₂

CH₃CHO + O → CH₃CO + OH

CH₃CHO + OH → CH₃CO + H₂O

CH₃CHO + HO₂→ CH₃CO + H₂O₂

(9)

(11)

(13)

(15)

CH₃CHO + H → CH₃CO + H₂

CH₃CHO + CH₃→ CH₃CO + CH₄

CH₃CO → CH₃+ CO

(7)

(17)

CHO → H + CO (158)

Won [15] has studied acetaldehyde oxidation in the

temperature range 1320–1897 K at total pressures be-

tween 3.3 and 6.0 atm using a shock tube and proposed

a mechanism of 110 reactions to explain the ignition

delay results. They also used reactions (1), (5), (7), (9),

(11), (13), and (15) for acetaldehyde elimination reac-

tions and found that reactions (5), (13), and (15) have

a strong effect on their results. The rate constants of

reactions (5) and (13) were evaluated. Thus, the oxida-

tion mechanism and the rate constant expressions are

now rather clear.

Using Hartree–Fock, Møller–Plesset, and density

functional theories, primary dissociation pathways in

the acetaldehyde pyrolysis have been investigated by

Martell et al. [16]. They evaluated the activation en-

ergies 85 and 84 kcal/mol for reactions (3) and (4),

respectively. Although acetaldehyde decomposition

seems to be in fall off region so that higher energy

channels like reactions (3) and (4) are disfavored in

our experimental conditions, the maximum value of k₃

and the value of k₄will be discussed.

Reactions, CH₃CHO + H, CH₃, O₂, O, OH, HO₂→

CH₂CHO + H₂, CH₄, HO₂, OH, H₂O, H₂O₂have been

neglected in the mechanism recently reported in the

acetaldehyde pyrolysis and oxidation [14,15]. How-

ever, in this study, these reactions were found to be not

negligible in the acetaldehyde pyrolysis and oxidation.

Thus, it can be seen that even the basic framework of

the oxidation mechanism at high temperatures is still

vague. So, we will examine these reactions.

In the present paper, we carry out the study of ac-

etaldehyde pyrolysis and oxidation at higher tempera-

tures by using a shock tube technique. We propose a

detailed reaction mechanism to reproduce our experi-

mental data at temperatures above 1000 K.

CH₃+ CH₃→ C₂H₆

C₂H₆+ H → C₂H₅+ H₂

C₂H₆+ CH₃→ C₂H₅+ CH₄

C₂H₄+ H → C₂H₅

(38)

(39)

(42)

(48)

Ernst et al. [2] have investigated behind reﬂected

shock waves in the temperature range 1350–1650 K.

They found that the decomposition was ﬁrst order in

acetaldehyde concentration and the rate constant ex-

pression was k₁= 1.2 × 10¹⁶exp(−81.7 kcal/RT) s⁻¹

.

Kern et al. [3] have investigated the pyrolysis be-

hind reﬂected shock waves using a TOF-shock tube in

the temperature range 1400–1800 K. A valid mecha-

nism under the above experimental conditions was pro-

posed which modeled the experimental proﬁles. The

proposed rate constant expression was k₁= 3.0 × 10¹⁴

exp(−80.0 kcal/RT) s⁻¹

.

Substantially, all the rate constants of reactions (5),

(7), and (17) reported were evaluated at low tempera-

tures below 1000 K [5–11]. Only a few evaluation and

detailed discussion for them have been done at high

temperatures though they are very important to learn

the combustion mechanism above 1000 K.

At high temperatures above 1000 K, there are sev-

eral reports for acetaldehyde oxidation [12–15]. Colket

et al. [12] have studied the kinetics of the ﬁrst stage

of acetaldehyde oxidation over the temperature range

1030–1115 K with a turbulent ﬂow reactor. They found

that the major and minor products measured were H₂,

CO, CH₄, C₂H₆and CO₂, C₂H₄, CH₂O, respectively,

and proposed a scheme of 26 reactions to explain

the results. Beeley et al. [13] have studied the ig-

nition behind incident shock waves over the higher

temperature range 1550–1850 K and explained the re-

sults with 35 reactions. Recently, two acetaldehyde

oxidation mechanisms were reported [14,15]. Dagaut

et al. [14] have studied acetaldehyde oxidation using

a jet-stirred reactor under a wide range of conditions:

1–10 atm and 900–1300 K. They measured concen-

tration proﬁles of reactant, intermediates, and prod-

ucts of acetaldehyde oxidation by probe sampling and

GC analyses and proposed a detailed reaction mecha-

nism. They used reactions (1), (5), (7), (9), (11), (13),

EXPERIMENTAL

Three shock tubes of 4.1-cm i.d. were used in this

study. The ﬁrst was a magic-hole-type, which had

the facility for both single-pulse and time-resolved

spectroscopy. A simple description only is given be-

low since the apparatus has been described in detail

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

75

previously [17–20]. The reacted gas mixtures heated

by using a single pulse method were extracted into

a pre-evacuated vessel (50 cc) through the valve

near the end plate. The reacted mixture was ana-

lyzed by three serially connected gas chromatographs

each having a thermal-conductivity detector. The gas-

chromatographic analysis, which was similar to that

used previously [18,19], was used to determine the

concentrations of reactant and products. The amounts

of reactant and products were determined within an

accuracy of 4%. An effective heating time t_e(reac-

tion time), which was deﬁned as the time between the

arrival point of the reﬂected shock front and the 80%

point of fall from the reﬂected shock front pressure,

was determined with an accuracy of 5% using the

method described previously [17,18]. The relationship

between the t_eand temperature showed a simple curve:

the t_eincreased with decrease in temperature, as seen

in Fig. 2 of [17]. Hence, the t_evalues at representative

temperatures were evaluated from the relationship be-

tween the observed t_eand temperature. The t_evalues

are shown in the ﬁgure caption. The modeling method-

ology for this comparison was shown in detail in our

previous report [18,19].

The second was a standard-type shock tube con-

nected to laser absorption and IR-emission equipment

[21,22]. A part of the shock tube was modiﬁed: a new

CaF₂window was added to the shock tube to measure

IR emission. This was located at the same distance

from the reﬂected shock plate as the laser-beam win-

dow. The transmitted intensity of a 3.39-µm He–Ne

laser beam through a 4.1-cm path length in the shock

tube and through an interference ﬁlter (λ_max= 3.39 µm,

halfwidth = 0.072 µm) was monitored with an InSb

detector, using the same method as used previously

[21,22]. The 3.39-µm laser beam was absorbed by

many CH-compounds, but mainly by CH₃CHO, C₂H₆,

C₂H₄, and CH₄under our experimental conditions. The

extinction coefﬁcients for the reactant and products

have already been measured previously [21–23]. The

equations between the extinction coefﬁcient of each

species and temperature measured were used for sim-

ulations. In this experiment, an IR-emission technique

similar to that used previously [19] was used to trace

the formation of CO₂. The IR emission was observed

with a Hamamatsu P-5968-200 InSb detector through

a CaF₂window, an interference ﬁlter λ_max= 4.24 µm,

halfwidth = 0.1 µm and two slits with widths 0.8 mm at

each end of a cylindrical tube of length 2 cm. The rela-

tive emission at 4.24 µm comes not only from CO₂, but

also from CH₂CO and CO under our experimental con-

ditions. The relative emission intensity of these com-

pounds against temperature was measured and shown

in [20]. These equations were used for simulations.

The third was a standard-type shock tube con-

nected with UV absorption and IR-emission equip-

ment [18,20,22,23]. The transmitted intensity at 200

or 216 nm of a D₂-lamp through a 4.1-cm path length

in the shock tube, dispersed by a grating monochro-

mator, was monitored with a photomultiplier, using

the same method used previously [22,23]. To observe

the OH radical proﬁle, a light at 306.7 nm of a mi-

crowave discharge of H₂O in He was also used as a

light source instead of the D₂-lamp. The IR emission

at 4.24 or 4.68 µm was observed with a Hamamatsu P-

5968-200 InSb detector through a CaF₂window, an in-

terference ﬁlter (λ_max= 4.24 µm, halfwidth = 0.1 µm

or λ_max= 4.68 µm, halfwidth = 0.1 µm) and two slits

with widths 0.8 mm at each end of a cylindrical tube

of length 2 cm.

Gas mixtures were prepared manometrically. The

compositions of reaction mixtures employed are shown

in Table I. The error in the acetaldehyde, hydrogen,

and oxygen fraction was less than 2% of the respec-

tive fraction. The initial pressure (P₁) of the used gas

mixtures (reactants) was (50

0.1) Torr. The argon

(Teisan Co., Tokyo, Japan), H₂(Chuunenfaiingasu Co.,

Tokyo, Japan) and O₂(Seitetsu Kagaku Co., Tokyo,

Japan) speciﬁed to be 99.999%, 99.99%, and 99.995%

pure, respectively, were used without further puriﬁca-

tion. The acetaldehyde (Wako Pure Chemical Indus-

tries Ltd., Tokyo, Japan), speciﬁed to be 99.5% pure,

was frozen, degassed a number of times and puriﬁed

by trap-to-trap distillation before use.

All temperatures and pressures referred to in con-

nection with the data were calculated from the incident

shock velocity assuming full vibrational relaxation but

no chemical reaction. Uncertainty in the calculated

temperatures is considered to be 1.2%. The com-

puter simulation done in this study was essentially the

same as described previously [18–29]. The computer

routine used was a Gear-type integration of a set of

differential equations describing the chemical kinet-

ics under constant density conditions for a reﬂected

shock wave. Reverse reactions were automatically in-

cluded in the computer program through equilibrium

constants computed from thermochemical data. Since,

Table I Test Gas Mixtures Used

Mixture

CH₃CHO (%)

H₂(%)

O₂(%)

Ar (%)

A

B

C

D

E

F

5.0

4.0

2.0

1.0

0.1

95.0

96.0

93.0

96.0

93.0

94.0

97.9

3.0

2.0

5.0

1.0

G

1.0

International Journal of Chemical Kinetics DOI 10.1002/kin

76

YASUNAGA ET AL.

Table II Experimental Results Used in Fig. 1a

T₅

(K)

P₅

[M]

Effective Heating

Mixture

A

(atm) (10⁻⁵mol cm⁻³

)

Time (µs)

CH₃CHO CH₄

C₂H₆

C₂H₄

C₂H₂

CO

1013

1022

1062

1133

1137

1195

1241

1250

1282

1300

1323

1346

1409

1427

1478

1479

1541

1577

1.26

1.29

1.39

1.57

1.58

1.73

1.86

1.88

1.97

2.02

2.08

2.15

2.33

2.38

2.53

2.72

2.82

1.52

1.54

1.59

1.69

1.77

1.82

1.83

1.87

1.89

1.92

1.94

2.01

2.03

2.09

2.15

2.18

2820

2800

2710

2560

2550

2400

2320

2300

2230

2190

2140

2080

1920

1880

1790

1650

1570

1.00

0.97

0.94

0.85

0.93

0.82

0.66

0.64

0.38

0.35

0.39

0.22

0.12

0.04

0.05

0.00

0.03

0.00

0.01

0.02

0.00

0.13

0.20

0.27

0.34

0.48

0.42

0.50

0.58

0.55

0.59

0.60

0.49

0.00

0.01

0.02

0.03

0.07

0.06

0.05

0.07

0.06

0.04

0.02

0.01

0.00

0.02

0.03

0.02

0.05

0.07

0.11

0.13

0.12

0.13

0.12

0.00

0.01

0.02

0.03

0.02

0.05

0.09

0.00

0.01

0.02

0.00

0.13

0.21

0.30

0.55

0.61

0.50

0.78

0.82

0.95

1.00

0.92

0.99

1.00

under our experimental conditions, temperatures in the

reaction zone are considered to change with reaction

progress, the temperature change should be considered

at the time of calculating the concentration–time vari-

ations and the emission or absorption intensity–time

variations of a species using a computer. The computer

program that contained the expressions relating the

temperature change to the reaction progress was used

for the simulations: the computations were carried out

by changing the rate-constant value for each elemen-

tary reaction every 0.001 K. The time variations of

emission or absorption intensity were also calculated

by the program considering both the concentration

change and the dependence of the emission or absorp-

tion intensity on temperature. The above equations of

the emission or absorption intensity of each species

and temperature were used for these computations.

Assuming that the reaction was frozen perfectly

at the effective heating time, the concentrations of

carbon-containing compounds determined by gas

chromatograph were compared with those simulated.

The validity of this assumption has already been

conﬁrmed in CH₂O and N₂O pyrolysis [24,25]. Since

these pyrolyses proceed through a chain reaction

including steps having low-activation energy, this

assumption is considered to apply to the pyrolysis.

The validity of this assumption was also checked

by a simulation with an assumption of a cooling

rate similar to the observed one. It was found that

the radical reactions in the quenching wave resulted

in a maximum change of about 2.5% of product

distribution under our experimental conditions [29].

The basic thermochemical source was the JANAF

table [30]. Thermochemical data of CH₃CHO and

CH₃CO were adopted from [31]. The heat of formation

of OH was adopted from [32]. Thermochemical data

adopted from other than the JANAF tables and [31,32]

are shown in Table II of [19,23].

RESULTS AND DISCUSSION

Pyrolysis

Mixture A was heated in the temperature range 1000–

1600 K using the single-pulse method. The reacted

mixture was analyzed by gas chromatographs. The

product distribution is shown in Fig. 1a. These ex-

perimental results are also shown in Table II. Under

our experimental conditions, the main products de-

tected were CO, CH₄, C₂H₆, C₂H₄, and C₂H₂. The

species C₃H₄(propyne), AC₃H₄(allene), C₃H₆, C₄H₄,

1,3-C₄H₆, and CH₂CO (ketene) were also detected in

smaller quantities.

A time-resolved IR-laser absorption at 3.39 µm

was observed in the temperature range 1050–1650 K

using mixture B. Typical absorption proﬁles are shown

in Fig. 2a. These experimental results are also shown

in Table III. The absorption intensities increased

rapidly to a given value at the reﬂected shock front,

and then were constant for about 1 ms at temperatures

below 1100 K. At temperatures between 1100 and

1450 K, the absorption intensities increased with time.

Above 1450 K, the absorption intensities increased

with time, arrived at a maximum value, and then

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

77

Figure 1 (a) Product distribution observed with mixture A (symbol) at the effective heating time t at temperature T and

e

P = 50 Torr. The total pressure and density ranges used are 1.2–2.8 atm and 1.5 × 10⁻⁵to 2.2 × 10⁻⁵mol/cm³, respectively.

1

The effective heating times at each temperature are 2850 µs (1000 K), 2630 µs (1100 K), 2410 µs (1200 K), 2190 µs (1300 K),

1970 µs (1400 K), 1750 µs (1500 K), 1520 µs (1600 K), and 1300 µs (1700 K). ——–: calculated with the mechanism described

in Table XII; · · · · · · · · · · · · · · ·: reactions (1), (5), (7), and (17) and the rate constant values reported by Baulch et al. [37,38];

– – – – – -: reactions (1), (5), (7), (17) and CH₃CHO + CHO = CH₃CO + CH₂O and the rate constant values reported by Dagaut

et al. [14]; -·-·-·-·: calculated with the mechanism described in Table XII changing k to k = 1.00 × 10¹⁶exp(−85.0 kcal/RT)

3

s

⁻¹. (b) Sensitivity spectra (pS) [36] of CH₃CHO, C₂H₆, C₂H₄, C₂H₂, and CH₄concentrations for reactions (1)–(20) at 1300

K and at 2000 µs using mixture A. The solid bars show the result of multiplying the indicated rate constants by 0.2, whereas the

open bars show the result of multiplying the indicated rate constants by 5. The horizontal axis shows the reaction numbers.

International Journal of Chemical Kinetics DOI 10.1002/kin

78

YASUNAGA ET AL.

Figure 2 (a) Comparison of the A proﬁles observed using IR-laser absorption with those calculated for mixture B. : observed

◦

t

at 1329 K, 1.97 atm, 1.81 × 10⁻⁵mol/cm³; ꢀ: observed at 1477 K, 2.37 atm, 1.96 × 10⁻⁵mol/cm³; ꢀ, observed at 1589 K,

2.68 atm, 2.05 × 10⁻⁵mol/cm³;———: calculated with the mechanism described in Table XII; · · · · · · · · · reactions (1), (5),

(7), and (17) and the rate constant values reported by Baulch et al. [37,38]; -·-·-·-·-: calculated with the mechanism described in

Table XII changing k to k = 1.00 × 10¹⁶exp(−85.0 kcal/RT) s⁻¹. (b) Comparison of the A_tproﬁle observed at 1589 K using

3

IR-laser absorption with that calculated for mixture B. ꢀ, observed; ———: sum with error bars calculated using uncertainty

of extinction coefﬁcients for acetaldehyde, methane, and ethane; .........., absorption due to CH₃CHO; - - - - - - -: absorption due

ꢁ

to CH₄; -·-·-·-·: absorption due to C₂H₆; •———•: absorption due to C₂H₄; ———: absorption due to CH₂CO. (c) Comparison

of the A_tobserved using IR laser absorption with those calculated at 100, 200, and 300 µs for mixture B. (d) Sensitivity spectra

(pS) [36] of CH₃CHO, C₂H₆, and CH₄concentrations for reactions (1)–(20) at 1589 K and at 100 µs using mixture B. The solid

bars show the result of multiplying the indicated rate constants by 0.2, whereas the open bars show the result of multiplying the

indicated rate constants by 5. The horizontal axis shows the reaction numbers.

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

79

decreased with time. The proﬁles were analyzed using

an equation A_t= log (I_f/I_t) / log (I_f/I₀), where I_fwas

the signal voltage corresponding to the full intensity

and I₀and I_twere the signal voltages corresponding

to the absorption intensities at the reﬂected shock

front (t = 0) and at time t, respectively. To determine

the simulated A_tof the reactant and each product at

3.39 µm, their extinction coefﬁcients were measured

for each mixture, 4% CH₃CHO, 2% C₂H₆, 6% C₂H₄,

6% C₂H₂, 5% CH₄, 3% C₃H₈, 5% C₃H₆, 4% C₃H₄,

4% AC₃H₄, 6% 1,3-C₄H₆, and 6% CH₂CO diluted in

Ar. The equations of extinction coefﬁcients obtained

for the main species were I_a(CH₃CHO) = 5.20 ×

10³cm²mol⁻¹

,

I_a(C₂H₆) = 5.43 × 10⁴–17.5 × T

cm²mol⁻¹

,

I_a(C₂H₄) = 3.38 × T cm²mol⁻¹

,

I_a(C₂H₂) = –1.44 × 10³+ 1.03 × T

cm²

mol⁻¹

I_a(CH₄) = 3.46 × 10⁴– 16.7 × T cm²mol⁻¹(T <

1500 K) or I_a(CH₄) = 1.18 × 10⁴– 2.51 × T cm²

mol⁻¹(T > 1500K), I_a(C₃H₈) = 1.06 × 10⁵–36.0 × T

cm²mol⁻¹, I_a(C₃H₆) = 2.86 × 10⁴– 7.75 × T cm²

mol⁻¹, I_a(C₃H₄) = 1.07 × 10⁴– 3.00 × T cm²mol⁻¹

I_a(AC₃H₄) = 2.20 × 10³+ 0.440 × T cm²mol⁻¹

I_a(1,3-C₄H₆) = 2.35 × 10³+ 4.38 × T cm²mol⁻¹

,

I_a(CH₂CO) = 1.15 × 10³+ 0.875 × T cm²mol⁻¹

respectively. The data spread at the same temperature

was within 5%. The extinction coefﬁcients were

used for simulations. The A_tproﬁle at 1589 K

observed using IR-laser absorption mainly depended

on CH₃CHO, CH₄, C₂H₆, and C₂H₄, as shown in

Fig. 2b.

IR emission at 4.68 µm was also observed using

mixture B. Typical IR emission proﬁles at 4.68 µm

are shown in Fig. 3a. These experimental results

are also shown in Table IV. To determine the sim-

ulated emission intensity E_tof the reactant and

each product at 4.68 µm, the relative emission in-

tensity, E_i(mV cm³mol⁻¹), at 4.68 µm was mea-

sured for each mixture, 0.25% CH₂CO, 1.0% CO,

5% CH₃CHO and each product (5% C_mH_n) di-

luted with Ar and calculated from the emission in-

tensity at the reﬂected shock front. The equations

obtained for the relative emission intensity are log

I_e(CH₃CHO) = 7.49 × 10⁻⁴T + 4.55 mV cm³mol⁻¹

,

log I_e(CH₂CO) = 4.70 × 10⁻⁴T + 6.84 mV cm³

mol⁻¹, and log I_e(CO) = 5.45 × 10⁻⁴T + 5.42 mV

cm³mol⁻¹. These equations were used for simula-

tions. Emission intensities of the other products were

too small to detect. The relative emission intensities of

CH₂CO and CO were larger than that of CH₃CHO and

then the emission proﬁles observed at 4.68 µm mainly

depended on CH₂CO and CO, as shown in Fig. 3b.

Proﬁles of absorption at 200 nm were observed us-

ing mixture B. Typical absorption proﬁles at 200 nm

are shown in Fig. 4a. Proﬁles of total absorption data

International Journal of Chemical Kinetics DOI 10.1002/kin

80

YASUNAGA ET AL.

Figure 3 (a) Comparison of the E /E observed using the IR emission at 4.68 µm with those calculated for mixture B.

,

◦

observed at 1419 K, 2.21 atm, 1.90 ×^t10⁻⁵mol/cm³; ꢀ: observed at 1492 K, 2.41 atm, 1.97 × 10⁻⁵mol/cm³; ———: calculated

with the mechanism described in Table XII; ············: reactions (1), (5), (7), and (17) and the rate constant values reported by

Baulch et al. [37,38]; - - - - - - -: reactions (1), (5), (7), (17), and CH₃CHO + CHO = CH₃CO + CH₂O and the rate constant

values reported by Dagaut et al. [14]; •———•: calculated with the mechanism described in Table XII omitting reactions (4),

(6), and (8); •········•: calculated with the mechanism described in Table XII changing k and k to k = 4.3 × 10¹⁴exp(–10.0

0

6

8

6

kcal/RT) s⁻¹and k = 2.50 × 10¹³exp(–15.0 kcal/RT) s⁻¹and omitting reaction (4). (b) Comparison of the E_t/E observed

8

using the IR emission at 4.68 µm with those calculated for mixture B. ꢀ observed at 1492 K, 2.41 atm, 1.97 × 10⁻⁵⁰mol/cm³;

———, sum calculated using Table XII; ············: emission due to CH₂CO; - - - - - - - - -: emission due to CO; –·–·–·–:

emission due to CH₃CHO. (c) Sensitivity spectra (pS) [36] of CH₃CHO, CH₂CO, and CO concentrations for reactions (1)–(20)

at 1492 K and at 100 µs using mixture A. The solid bars show the result of multiplying the indicated rate constants by 0.2,

whereas the open bars show the result of multiplying the indicated rate constants by 5. The horizontal axis shows the reaction

numbers.

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

81

U_twere determined. U_twas deﬁned as in the following

equation:

U_t= log(I_f/I_t)

where I_fwas the signal voltage corresponding to the

full intensity and I_twere the signal voltages cor-

responding to the absorption intensities at time t.

These experimental results are also shown in Table V.

The beam at 200 nm was absorbed by ketene and

some hydrocarbons. Therefore, it was necessary to

know the molar extinction coefﬁcients for products

and the reactant to be able to compare observed ab-

sorption proﬁles with simulated ones. The extinc-

tion coefﬁcients were measured for each mixture, 5%

CH₃CHO, 0.26% CH₂CO, 1% CH₂O, 0.4% 1,3-C₄H₆,

1% C₃H₆, 1% C₃H₄, 1% AC₃H₄, 1% C₂H₄, 1% C₂H₂,

5% CH₄, and 5% CO diluted in Ar. The extinction

coefﬁcients were calculated from the absorption in-

tensities at the reﬂected shock front. The equations

obtained log I_a(CH₃CHO) = 9.62 × 10⁻⁴T + 2.49

cm²mol⁻¹, log I_a(CH₂CO) = 2.27 × 10⁻⁴T + 5.74

cm²mol⁻¹, log I_a(1,3-C₄H₆) = 6.97 cm²mol⁻¹

log I_a(C₃H₆) = 3.70 × 10⁻⁴T + 5.53 cm²mol⁻¹

log I_a(C₃H₄) = 2.96 × 10⁻⁵T + 5.37 cm²mol⁻¹

log I_a(AC₃H₄) = 2.59 × 10⁻⁴T + 5.52 cm²mol⁻¹

log I_a(C₂H₄) = 8.61 × 10⁻⁴T + 3.94 cm²mol⁻¹

,

log I_a(C₂H₂) = 4.20 × 10⁻⁴T + 4.57 cm²mol⁻¹for

CH₃CHO, CH₂CO, 1,3-C₄H₆, C₃H₆, C₃H₄, AC₃H₄,

C₂H₄, and C₂H₂, respectively. Absorption by CH₂O,

CH₄, and CO was too small to detect. These equations

were used for simulations. It was found that absorption

proﬁle at 1587 K observed at 200 nm mainly depended

on CH₂CO, C₂H₄, and C₃H₆, as shown in Fig. 4b.

Oxidation

The UV-absorption at 306.7 nm was measured with

mixtures G and D. Typical absorption proﬁles at

306.7 nm are shown in Figs. 5a and 6a. Proﬁles of

absorption data log (I_f/I_t) were determined, where I_f

was the signal voltage corresponding to the full inten-

sity and I_twas the signal voltages corresponding to

the absorption intensities at time t. These experimen-

tal results are also shown in Tables VI and VII. The

beam at 306.7 nm was absorbed mainly by OH radi-

cal. The extinction coefﬁcient for OH was determined

as described below. The mixture 1.0% H₂and 1.0%

O₂diluted in Ar was heated behind reﬂected shock

waves in the temperature range 1100–2500 K, 23 times

of experiments being carried out. Any proﬁle showed

partial equilibrium of OH concentration after shock

heating. The OH concentration at partial equilibrium

was estimated by computer simulation, using reactions

International Journal of Chemical Kinetics DOI 10.1002/kin

82

YASUNAGA ET AL.

Figure 4 (a) Comparison of the UV-absorption proﬁles observed at 200 nm with those calculated for mixture B. , observed

◦

at 1327 K, 1.97 atm, 1.81 × 10⁻⁵mol/cm³; ꢀ, observed at 1587 K, 2.67 atm, 2.05 × 10⁻⁵mol/cm³; ——— : calculated with

the mechanism described in Table XII; ···············: reactions (1), (5), (7), and (17) and the rate constant values reported by

Baulch et al. [37,38]; - - - - - -: reactions (1), (5), (7), (17), and CH₃CHO + CHO = CH₃CO + CH₂O and the rate constant

values reported by Dagaut et al. [14]; •———•: calculated with the mechanism described in Table XII omitting reactions (4),

(6), and (8); •··········•: calculated with the mechanism described in Table XII changing k and k to k ˙= 4.6 × 10¹⁴exp(−10.0

6

8

6

kcal/RT) s⁻¹and k = 6.3 × 10¹³exp(−15.0 kcal/RT) s⁻¹and omitting reaction (4). (b) Comparison of the UV-absorption

8

proﬁle observed at 200 nm with those calculated for mixture B. ꢀ: observed at 1587 K, 2.67 atm, 2.05 × 10⁻⁵mol/cm³; ———:

sum calculated at 1587 K calculated with the mechanism described in Table XII; - - - - - - - -: absorption due to CH₂CO;

•———•: absorption due to C₂H₄; -·-·-·-·-·: absorption due to C₂H₂; •········•: absorption due to C₃H₆; ········: absorption due

ꢁ

to CH₃CHO; ········· : absorption due to 1,3-C₄H₆. (c) Sensitivity spectra (pS) [36] of CH₂CO, C₃H₆, and C₂H₄concentrations

for reactions (1)–(20) at 1587 K and at 50 µs using mixture B. The solid bars show the result of multiplying the indicated rate

constants by 0.2, whereas the open bars show the result of multiplying the indicated rate constants by 5. The horizontal axis

shows the reaction numbers.

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SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

83

Figure 5 (a) Comparison of the time-proﬁles observed at

306.7 nm with those calculated for mixture G. , observed at

◦

1321 K, 1.60 atm, 1.43 × 10⁻⁵mol/cm³; ꢀ: observed at 1497

K, 1.89 atm, 1.54 × 10⁻⁵mol/cm³; ———: calculated with

the mechanism described in Table XII; ·········: calculated

with the mechanism described in Table XII changing k₅to k₅

= 4.10 × 10⁹T ^1.16exp(−2.4 kcal/RT) cm³mol⁻¹s⁻¹[37];

-·-·-·-·-·: calculated with the mechanism described in Table

XII changing k and k to k = 2.4 × 10¹⁴exp(−7.0 kcal/RT)

6

cm³mol⁻¹s⁻¹⁵and k = 8.8 × 10¹⁴exp(−7.0 kcal/RT) cm³

5

6

mol⁻¹

s

⁻¹. (b) Sensitivity spectra (pS) [36] of OH concen-

tration for reactions (1)–(20) at 1497 K and at 120 µs using

mixture G. The solid bars show the result of multiplying the

indicated rate constants by 0.2, whereas the open bars show

the result of multiplying the indicated rate constants by 5.

The horizontal axis shows the reaction numbers.

International Journal of Chemical Kinetics DOI 10.1002/kin

84

YASUNAGA ET AL.

Figure 6 (a) Comparison of the time-proﬁles observed at

306.7 nm with that calculated for mixture D. : observed at

◦

1526 K, 2.24 atm, 1.79 × 10⁻⁵mol/cm³; ——–: calculated

with the mechanism described in Table XII; · · · · · · · · · · · ·:

reactions (1), (5), (7), (9), (11), (13), (15), and (17) and

the rate constant values reported by Baulch et al. [37,38];

– – – – – –: reactions (1), (5), (7), (9), (11), (13), (15),

(17), and CH₃CHO + CHO = CH₃CO + CH₂O and the rate

constant values reported by Dagaut et al. [14]. (b) Sensitivity

spectra (pS) [36] of OH concentrations for reactions (1)–(20)

at 1526 K and at 600 µs using mixture D. The solid bars show

the result of multiplying the indicated rate constants by 0.2,

whereas the open bars show the result of multiplying the

indicated rate constants by 5. The horizontal axis shows the

reaction numbers.

(166)–(178) and thermo chemical data adopted

in this study. The equation log ε(OH) = −3.51

× 10⁻⁴T + 7.33 cm²mol⁻¹connected to the OH

concentration estimated above was required to re-

produce absorption proﬁle at 306.7 nm. An induc-

tion time τ_OHwith mixture G was also measured,

where the induction time τ_OHwas deﬁned as the

elapsed time between the reﬂected shock arrival and

the onset of the rapid increase of the OH absorp-

tion at 306.7 nm, determined from the intersection of

the tangent to the curve at its inﬂection point with

the preshock baseline. The induction time is shown

in Fig. 7 together with the results of oxidation of

mixture 1% H₂and 1% O₂diluted with Ar. These

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SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

85

Figure 7 Comparison of induction times observed for mix-

tures, (1.0% H₂, 1.0% O₂, 98.0% Ar: ꢀ), (1.0% H₂, 1.0%

O , 0.1% CH CHO, 97.9% Ar: ) at 306.7 nm with those

◦

2

3

calculated. The total pressure and density ranges used are

1.47–2.25 atm and 1.40 × 10⁻⁵to 1.64 × 10⁻⁵mol/cm³, re-

spectively. ———: calculated with the mechanism described

in Table XII.

experimental results are also shown in Table VIII. It

was found that OH formation below 1600 K was

inhibited by adding acetaldehyde under our experi-

mental conditions. This inhibition was large at low

temperature.

The IR emissions at 4.68 µm were also measured

with mixture C. A typical proﬁle is shown in Fig. 8a.

The experimental result is also shown in Table IV.

These emission proﬁles depended on CH₂CO, CO₂,

and CO as shown in Fig. 8b because the relative emis-

sions of CH₂CO, CO₂, and CO were much larger

than those of the other species; the equations log

I_e(CO₂) = 1.32 × 10⁻³T + 4.44 mV cm³mol⁻¹and

the above equations (see Pyrolysis) were used for

simulations.

Proﬁles of the IR absorption at 3.39 µm with mix-

ture C were observed. Typical absorption proﬁles at

3.39 µm are shown in Fig. 9a. These experimental re-

sults are also shown in Table III. At temperatures below

1100 K, the absorption signal after a rapid rise at the re-

ﬂected shock front remained constant during 1000 µs.

At temperatures between 1100 and 1350 K, the absorp-

tion intensities increased with time. Above 1350 K, the

absorption after a rapid rise slowly increased with time,

arrived at a maximum value, and then decreased with

time. It was found that the A_tproﬁle at 1494 K ob-

served using IR-laser absorption mainly depended on

CH₃CHO, CH₄, C₂H₆, and C₂H₄, as shown in Fig. 9b.

International Journal of Chemical Kinetics DOI 10.1002/kin

86

YASUNAGA ET AL.

Table VIII Experimental Results Used in Fig. 7

coefﬁcients were calculated from the absorption at

the reﬂected shock front. The equations obtained

were log I_a(1,3-C₄H₆) = −1.97 × 10⁻⁴T + 7.26 cm²

Mixture T₅(K) P₅(atm) [M] (10⁻⁵mol cm⁻³) τ (µs)

OH

mol⁻¹

,

log I_a(C₂H₄) = 1.67 × 10⁻³T + 2.10 cm²

G

1280

1290

1301

1312

1321

1373

1421

1449

1497

1523

1601

1660

1677

1.47

1.49

1.51

1.53

1.55

1.65

1.74

1.80

1.89

1.94

2.10

2.22

2.25

1.40

1.41

1.42

1.43

1.46

1.49

1.51

1.54

1.55

1.60

1.63

1.64

1295

1218

1198

1120

1044

814

784

750

499

310

209

129

111

62

mol⁻₋¹₁,log I_a(C₂H₂) = 7.40 × 10⁻⁴T + 3.70 cm²

mol

,

logI_a(CH₂CO) = 7.40 × 10⁻⁴T + 4.50 cm²

mol⁻¹and logI_a(O₂) = 7.46 × 10⁻⁴T + 2.48 cm²

mol⁻¹, logI_a(CO₂) = 7.70 × 10⁻⁴T + 2.68 cm²mol⁻¹

for 1,3-C₄H₆, C₂H₄, C₂H₂, CH₂CO, O₂, and CO₂,

respectively. Absorption by CH₃CHO, CH₂O, and

CO was too small to detect. The equation log I_a

(CH₃) = 6.26 cm²mol⁻¹[33] was used for the CH₃

radical. These equations were used in the simulations.

From the above equations, the absorption of CH₃at

216 nm was found to be much greater than that of

the stable products. Consequently, we could learn

the kinetic behavior of the CH₃radical from the

absorption proﬁles at 216 nm.

51

37

28

36

26

Reaction Mechanism

IR-emission proﬁles at 4.24 µm (CO₂) were mea-

To interpret our data, a computer-modeling study was

performed. By trial and error methods, we determined

a mechanism and rate constant expressions that could

predict all our results. An extended reaction mecha-

nism was constructed combining an acetaldehyde py-

rolysis and oxidation mechanism with a submechanism

of C₁- and C₂-hydrocarbon oxidation. This mecha-

nism included the most recent pyrolysis and oxida-

tion submechanisms for formaldehyde [21], methane

[29], ethane [34], ethylene [22], acetylene [19], and

ketene [20]. It is because these were produced in high

quantity in the acetaldehyde pyrolysis at temperatures

above 1000 K, as shown in Fig. 1a, and because these

products and the radicals produced may play a role in

the pyrolysis and oxidation process. To obtain an in-

sight into the elementary reactions responsible for the

pyrolysis and oxidation of acetaldehyde, pR spectra

[36] were computed based upon the large constructed

mechanism and the product rate constants. The pR

value was deﬁned as the logarithm of the absolute

value of the reaction rate, in molecules per cubic cen-

timeter seconds. On the basis of the pR value of the

elementary reactions, a reduced ﬁnal reaction mecha-

nism with pertinent rate constants for the pyrolysis and

oxidation of acetaldehyde was constructed. The ﬁnal

reaction mechanism and the rate constants developed

in this study are shown in Table XII. It contains 178

elementary reactions and 50 species. The 178-reaction

mechanism including reactions (1)–(20) was able to

predict all our data, including the small quantities of

C₃H₄, AC₃H₄, C₃H₆, C₄H₄, and 1,3-C₄H₆.

sured using mixtures D, E, and F. Typical IR-emission

proﬁles at 4.24 µm for fuel-rich mixture D, stoichio-

metric mixture E, and fuel-lean mixture F are shown

in Figs. 10a, 11a, and 12a, respectively. These exper-

imental results are also shown in Table IX. The CO₂

proﬁles were found to exhibit a rapid increase after

a period from shock heating, as shown in Figs. 10a,

11a, and 12a. An induction time τ_COwas deﬁned as

2

the elapsed time between the reﬂected shock arrival

and the onset of the rapid infrared emission increase,

determined from the intersection of the tangent to the

curve at its inﬂection point with the preshock base line.

Plots of log τ_COvs. 1/T obtained with mixtures D, E,

2

and F are shown in Fig. 13. These experimental results

are also shown in Table X. It can readily be seen that

the values of log τ_COfor each mixture fall on a single

2

line and all the lines are almost parallel. The τ_COval-

2

ues in the fuel-lean mixture F have the similar to the

stoichiometric mixture E. The τ_COvalues in fuel-rich

2

mixture D have the longest induction time.

To examine CH₃radical production, the UV

absorption proﬁles at 216 nm were measured using

mixture D. A typical absorption proﬁle is shown in

Fig. 14a. This experimental result is also shown in

Table XI. To determine the absorption by reactant

and each stable product at 216 nm, the extinction

coefﬁcients were measured using mixtures, 5%

CH₃CHO, 1% CH₂O, 0.4% 1,3-C₄H₆, 4% C₂H₄,

4% C₂H₂, 5% CO, 2% CH₂CO, 5% O₂, and 5%

CO₂, respectively, diluted in Ar. The extinction

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SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

87

Figure 8 (a) Comparison of the E /E observed using the IR emission at 4.68 µm with those calculated for mixture C.

,

◦

t

0

observed at 1393 K, 2.21 atm, 1.94 × 10⁻⁵mol/cm³; ꢀ: observed at 1494 K, 2.49 atm, 2.04 × 10⁻⁵mol/cm³; ꢀ, observed at

1560 K, 2.68 atm, 2.10 × 10⁻⁵mol/cm³; ———–: calculated with the mechanism described in Table XII. (b) Comparison of

the E_t/E observed using the IR emission at 4.68 µm with calculated ones for mixture C. ꢀ: observed at 1494 K, 2.49 atm,

0

and total density 2.04 × 10⁻⁵mol/cm³; ———–: sum calculated with the mechanism described in Table XII; · · · · · · · · · · · · · · ·:

emission due to CH₂CO; - - - - - - - -: emission due to CO; -·-·-·-·-·: emission due to CO₂; •———•: emission due to CH₃CHO.

(c) Sensitivity spectra (pS) [36] of CH₂CO, CO, and CO₂concentrations for reactions (1)–(20) at 1494 K and at 100 µs using

mixture C. The solid bars show the result of multiplying the indicated rate constants by 0.2, whereas the open bars show the

result of multiplying the indicated rate constants by 5. The horizontal axis shows the reaction numbers.

International Journal of Chemical Kinetics DOI 10.1002/kin

88

YASUNAGA ET AL.

Figure 9 (a) Comparison of the A proﬁles observed using IR-laser absorption with those calculated for mixture C.

:

◦

t

observed at 1393 K, 2.21 atm, total density 1.94 × 10⁻⁵mol/cm³; ꢀ: observed at 1494 K, 2.49 atm, 2.04 × 10⁻⁵mol/cm³;

ꢀ, observed at 1560 K, 2.68 atm, 2.10 × 10⁻⁵mol/cm³; ———–: calculated with the mechanism described in Table XII. (b)

Comparison of the A_tproﬁle observed at 1494 K using IR-laser absorption with that calculated for mixture C. ꢀ: observed;

———–: sum with error bars calculated using uncertainty of extinction coefﬁcients for acetaldehyde, methane, and ethane; - -

- - - - - -: absorption due to CH₃CHO; •———•: absorption due to CH₄; -·-·-·-·-·: absorption due to C₂H₆; •········•: absorption

ꢁ

due to C₂H₄; ——— : absorption due to CH₂O; · · · · · · · · · · · ·, absorption due to CH₂CO. (c) Sensitivity spectra (pS) [36] of

CH₃CHO, CH₄, and C₂H₆concentrations for reactions (1)–(20) at 1494 K and at 100 µs using mixture C. The solid bars show

the result of multiplying the indicated rate constants by 0.2, whereas the open bars show the result of multiplying the indicated

rate constants by 5. The horizontal axis shows the reaction numbers.

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SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

89

Figure 11 (a) Comparison of the CO₂proﬁle measured at

4.24 µm with that calculated for mixture E. : observed at

◦

1316 K, 1.81 atm, 1.67 × 10⁻⁵mol/cm³; ꢀ: observed at 1478

K, 2.20 atm, 1.81 × 10⁻⁵mol/cm³; ———–: calculated with

the mechanism described in Table XII;··············: calcu-

lated with the mechanism described in Table XII ch₋an₁ging

k

to k = 3.0 × 10¹³exp(–39.1 kcal/RT) cm³mol

s⁻¹

9

[37]. (b) Sensitivity spectra (pS) [36] of CO₂concentration

for reactions (1)–(20) at 1316 K at 1600 µs using mixture

E. The solid bars show the result of multiplying the indi-

cated rate constants by 0.2, whereas the open bars show the

result of multiplying the indicated rate constants by 5. The

horizontal axis shows the reaction numbers.

Figure 10 (a) Comparison of the CO₂proﬁle measured at

4.24 µm with that calculated using mixture D. : observed at

◦

1526 K, 2.24 atm, 1.79 × 10⁻⁵mol/cm³; ꢀ: observed at 1683

K, 2.62 atm, 1.89 × 10⁻⁵mol/cm³; ———–: calculated with

the mechanism described in Table XII; ··············: calcu-

lated with the mechanism described in Table XII changing

k to k = 3.0 × 10¹³exp(−39.1 kcal/RT) s⁻¹[37]. (b) Sen-

Simulation Using Reactions and the Rate

Constants Reported for Acetaldehyde

Pyrolysis and Oxidation

9

sitivity spectra (pS) [36] for CO₂concentration at 1526 K at

500 µs using mixture D. The solid bars show the result of

multiplying the indicated rate constants by 0.2, whereas the

open bars show the result of multiplying the indicated rate

constants by 5. The horizontal axis shows the reaction num-

bers. Reactions that show a little effect on CO₂concentration

are not shown.

Baulch et al. [37,38] have recommended the rate con-

stant values of reactions (1), (5), (7), and (17) concern-

ing the acetaldehyde pyrolysis, but have not reported

those of reactions (2)–(4), (6), and (8).

International Journal of Chemical Kinetics DOI 10.1002/kin

90

YASUNAGA ET AL.

Figure 12 (a) Comparison of the CO₂proﬁle measured at

4.24 µm with that calculated using mixture F. : observed at

◦

1438 K, 1.96 atm, 1.66 × 10⁻⁵mol/cm³; ꢀ: observed at 1521

K, 2.19 atm, 1.72 × 10⁻⁵mol/cm³; ———–: calculated with

the mechanism described in Table XII ; ··············: reactions

(1), (5), (7), (9), (11), (13), (15), and (17) and the rate constant

values reported by Baulch et al. [37,38]; - - - - - - - -: reactions

(1), (5), (7), (9), (11), (13), (15), (17), and CH₃CHO + CHO

= CH₃CO + CH₂O and the rate constant values reported

by Dagaut et al. [14]. (b) Sensitivity spectra (pS) [36] for

CO₂concentration at 1438 K at 350 µs using mixture F. The

solid bars show the result of multiplying the indicated rate

constants by 0.2, whereas the open bars show the result of

multiplying the indicated rate constants by 5. The horizontal

axis shows the reaction numbers. Reactions that show a little

effect on CO₂concentration are not shown.

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SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

91

Table X Experimental Results Used in Fig. 13

T₅

(K)

P₅

(atm)

M

τco₂

(µs)

Mixture

D

(10⁻⁵mol cm⁻³

)

1399

1401

1479

1526

1580

1633

1647

1683

1703

1276

1308

1316

1322

1329

1370

1393

1401

1410

1414

1428

1468

1478

1481

1501

1547

1621

1304

1370

1397

1403

1438

1442

1462

1466

1476

1483

1521

1547

1548

1553

1568

1.94

2.13

2.24

2.37

2.49

2.53

2.62

2.66

1.71

1.79

1.81

1.82

1.84

1.94

1.99

2.01

2.03

2.04

2.07

2.17

2.20

2.25

2.37

2.55

1.67

1.81

1.87

1.89

1.96

1.97

2.02

2.03

2.05

2.06

2.15

2.21

2.22

2.26

1.69

1.75

1.79

1.82

1.86

1.87

1.89

1.91

1.64

1.67

1.68

1.69

1.72

1.74

1.75

1.76

1.77

1.80

1.81

1.83

1.86

1.92

1.56

1.61

1.63

1.64

1.66

1.67

1.68

1.69

1.70

1.72

1.74

1.75

865

1140

524

396

146

104

133

85

39

E

1630

1190

1283

1090

966

767

615

443

362

393

357

226

183

181

112

66

Figure 13 Comparison of the observed induction times

(symbols) with those (lines) calculated with the mechanism

described in Table XII for mixture D (ꢀ;··············), mix-

ture E ( ; ———), and mixture F (ꢀ; – – – – – –).

◦

First, the Baulch et al. reactions (1), (5), (7), and (17)

and the rate constant values reported for the acetalde-

hyde pyrolysis [37,38] were applied to simulations of

our pyrolysis data, as shown in Figs. 1a, 2a, 3a, and 4a;

reactions (1)–(17) shown in Table XII were exchanged

to reactions (1), (5), (7), and (17) and the rate con-

stant expressions reported by Baulch et al. [37,38]. In

the pyrolysis, the simulated ﬁndings can reproduce the

observed C₂H₆, C₂H₄, and C₂H₂yields within exper-

imental error, but CO and CH₄yields are larger than

those observed, as shown in Fig. 1a. For the observed

A_tproﬁles, the proﬁles calculated using the Baulch

et al. reactions and the rate constant expressions are

much faster than those observed, as shown in Fig. 2a.

Furthermore, the proﬁles calculated using the Baulch

et al. reactions and the rate constant expressions sig-

niﬁcantly differ from those observed, as shown in Figs.

3a and 4a. In the oxidation also, the CO₂proﬁles calcu-

lated using the Baulch et al. reactions (1), (5), (7), (9),

(11), (13), (15), and (17) and the rate constant expres-

sions are much faster than those observed, as shown in

Fig. 12a.

59

21

F

1583

634

510

424

300

408

149

250

106

110

94

54

57

37

42

The Dagaut et al. submechanism [14] was also ap-

plied for simulations of our pyrolysis and oxidation

data, as shown in Figs. 1a, 3a, 4a, and 12a; they did

not use reactions (2)–(4), (6), (8), (10), (12), (14), and

(16), but CH₃CHO + CHO = CH₃CO + CH₂O was in-

cluded in their mechanism. In the pyrolysis, the simu-

lated product distribution except for CH₄and C₂H₄us-

ing their mechanism differs from that observed within

experimental error, as shown in Fig. 1a. Furthermore,

the E_t/E₀and U_tproﬁles calculated using the Dagaut

et al. submechanism [14] differ from the observed ones

in proﬁle shape, as shown in Figs. 3a and 4a. The in-

duction times simulated at each temperature are shorter

than those observed, as shown in Fig. 12a.

International Journal of Chemical Kinetics DOI 10.1002/kin

92

YASUNAGA ET AL.

Figure 14 (a) Comparison of the UV-absorption proﬁle observed at 216 nm with that calculated with the mechanism described

in Table XII using mixture D. : observed at 1544 K, 2.28 atm, 1.80 × 10⁻⁵mol/cm³; ———: sum calculated; •········•:

◦

absorption due to CH₃; •———•: absorption due to CH₂CO; -·-·-·-·-·-·: absorption due to C₂H₄; -------: absorption due to

ꢁ

C₂H₂; ———– : absorption due to 1,3-C₄H₆; ···············: absorption due to O₂. (b) Sensitivity spectra (pS) [36] of CH₂CO

and CH₃concentrations for reactions (1)–(20) at 1544 K and at 50 and 400 µs using mixture D. The solid bars show the result of

multiplying the indicated rate constants by 0.2, whereas the open bars show the result of multiplying the indicated rate constants

by 5. The horizontal axis shows the reaction numbers.

CH₃CHO(+M) → CH₂CO + H₂(+M)

CH₃CHO Reaction

ꢀH₀^◦= 26.5 kcal/mol

CH₃CHO + H → CH₃CO + H₂

ꢀH₀^◦= −15.0 kcal/mol

(4)

(5)

(6)

(7)

(8)

Reactions (1)–(8) were used as consumption reactions

of CH₃CHO in the CH₃CHO pyrolysis under our ex-

perimental conditions.

CH₃CHO + H → CH₂CHO + H₂

CH₃CHO(+M) → CH₃+ CHO(+M)

ꢀH₀^◦= −6.7 kcal/mol

ꢀH ^◦₀= 83.2 kcal/mol

CH₃CHO(+M) → CH₃CO + H(+M)

ꢀH₀^◦= 88.2 kcal/mol

(1)

(2)

(3)

CH₃CHO + CH₃→ CH₃CO + CH₄

ꢀH₀^◦= −15.0 kcal/mol

CH₃CHO + CH₃→ CH₂CHO + CH₄

CH₃CHO(+M) → CH₄+ CO(+M)

ꢀH₀^◦= −6.7 kcal/mol

ꢀH₀^◦= −5.9 kcal/mol

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

93

It has been shown that reaction (1) was the initiation

step and played an important role in the acetaldehyde

pyrolysis. We also adopted reaction (1) as the initi-

ation step. Reaction (1) is sensitive to the consump-

tion of acetaldehyde, as shown in Figs. 1b, 2c, 3c, and

9c, and also to the production of CO₂, as shown in

Figs. 8c, 10b, 11b, and 12b. Reaction (1) plays the

important role in both the acetaldehyde pyrolysis and

oxidation. To explain all our experimental data consis-

tently, the reaction with k₁= 6.00 × 10¹⁴exp(−79.1

kcal/RT) s⁻¹is indispensable. The maximum value,

k₁= 7.50 × 10¹⁴exp(−79.1 kcal/RT) s⁻¹, and mini-

mum value, k₁= 4.50 × 10¹⁴exp(−79.1 kcal/RT) s⁻¹

,

were estimated from the comprehensive reproduction

for data of Figs. 1a, 2a, 3a, 8a, 9a, 10a, 11a, and 12a.

The values of k₁at 1300 and 1600 K at 1 atm were

3.03 × 10 s⁻¹and 9.43 × 10³s⁻¹, respectively. The k₁

values recommended at 1 atm by Baulch et al. [37] were

1.31 × 10²s⁻¹(1300 K) and 4.90 × 10⁴s⁻¹(1600 K).

Our values evaluated for reaction (1) were by a fac-

tor of about 5 lower than those of Baulch et al. [37].

Reaction (2) is a possible initiation reaction under our

experimental conditions. This reaction played a little

role in our results calculated. When the reported value

k₂= 5.00 × 10¹⁴exp(−87.9 kcal/RT) cm³mol⁻¹s⁻¹

[3] was used under our experimental conditions, a little

inﬂuence on species concentration was observed in the

simulations, as shown in Figs. 1b, 2c, 3c, 4c, 5b, 6b,

8c, 9c, 11b, and 14b. However, CH₃CHO consumption

and product yields are not sensitive to the variation of

k₂value. So, we were not able to examine this value

from our experimental results and so used the reported

value k₂= 5.00 × 10¹⁴exp(−88.0 kcal/RT) cm³mol⁻¹

s

⁻¹[3].

Using Hartree–Fock, Møller–Plesset, and density

functional theories, primary dissociation pathways in

the acetaldehyde pyrolysis have been investigated

by Martell et al. [16]. They evaluated the activa-

tion energies 85.0 and 84.0 kcal/mol for reactions

(3) and (4), respectively. We assumed reactions (3)

and (4) with k₃= 1.00 × l0¹⁵exp(–85.0 kcal/RT) s⁻¹

and k₄= 3.00 × l0¹⁴exp(–84.0 kcal/RT) s⁻¹. The use-

fulness of reactions (3) and (4) was examined from

our experimental data. As long as we used the value

k₃= 1.00 × l0¹⁵exp(–85.0 kcal/RT) s⁻¹as one of the

initiation reaction, CH₃CHO consumption and product

yields are not sensitive to the variation of k₃value, as

shown in Fig. 1b. However, if the value k₃= 1.00 × l0¹⁶

exp(–85.0 kcal/RT) s⁻¹was assumed, the calculated

CH₄yield was not reproduced as shown in Fig. 1a.

On the other hand, this value could reproduce A_tpro-

ﬁle better than using the value k₃= 1.0 × l0¹⁵exp(–

85.0 kcal/RT) s⁻¹as shown in Fig. 2a.Hence, the value

International Journal of Chemical Kinetics DOI 10.1002/kin

94

YASUNAGA ET AL.

Table XII Elementary Reactions and Rate Constant Expressions^a

No.

Reaction

A

n

E

a

Reference

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

CH₃CHO = CH₃+ CHO

6.00 × 10¹⁴

5.00 × 10¹⁴

1.00 × 10¹⁵

3.00 × 10¹⁴

1.20 × 10¹⁴

4.40 × 10¹⁴

1.60 × 10¹²

6.00 × 10¹²

2.00 × 10¹³

2.00 × 10¹⁴

5.84 × 10¹²

1.50 × 10¹³

2.34 × 10¹⁰

1.60 × 10¹³

3.00 × 10¹²

1.00 × 10¹²

5.36 × 10²⁷

5.00 × 10¹⁷

1.32 × 10³⁴

6.51 × 10³⁴

3.96 × 10¹⁵

1.80 × 10¹⁴

1.11 × 10⁷

1.00 × 10¹³

2.28 × 10¹²

5.00 × 10¹²

9.00 × 10¹⁰

7.50 × 10¹²

1.00 × 10¹²

3.60 × 10¹³

1.50 × 10¹⁴

9.60 × 10¹³

1.00 × 10¹⁴

4.20 × 10¹⁰

3.00 × 10¹³

2.00 × 10¹²

0.00

0.50

0.00

0.73

0.00

−3.40

0.00

−6.57

−6.87

0.00

2.00

0.00

79,100

87,900

85,000

84,000

7,000

10,000

8,000

11,000

42,200

48,600

1,810

5,000

1,110

2,000

11,900

14,000

18,900

0

49,500

47,200

59,300

8,600

2,000

0

1,350

0

This work

[3]

CH₃CHO = CH₃CO + H

CH₃CHO = CH₄+ CO

See text

This work

See text

[13]

Assumed

[37]

Assumed

[37]

Assumed

[37]

Assumed

[37]

Assumed

[39]

CH₃CHO = CH₂CO + H₂

CH₃CHO + H = CH₃CO + H₂

CH₃CHO + H = CH₂CHO + H₂

CH₃CHO + CH₃= CH₃CO + CH₄

CH₃CHO + CH₃= CH₂CHO + CH₄

CH₃CHO + O₂= CH₃CO + HO₂

CH₃CHO + O₂= CH₂CHO + HO₂

CH₃CHO + O = CH₃CO + OH

CH₃CHO + O = CH₂CHO + OH

CH₃CHO + OH = CH₃CO + H₂O

CH₃CHO + OH = CH₂CHO + H₂O

CH₃CHO + HO₂= CH₃CO + H₂O₂

CH₃CHO + HO₂= CH₂CHO + H₂O₂

CH₃CO + M = CH₃+ CO + M

CH₂CO + H + M = CH₃CO + M

CH₂CHO = CH₂CO + H

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36)

(37)

(38)

CH₂CHO = CH₃+ CO

CH₂CO + M = CH₂+ CO + M

CH₂CO + H = CHCO + H₂

[45]

[20]

[37]

[20]

[45]

[46]

[45]

[37]

[20]

d

CH₂CO + H = CH₃+ CO

CH₂CO + O = CH₂+ CO₂

CH₂CO + O = CH₂O + CO

CH₂CO + OH = CH₂O + CHO

CH₂CO + OH = CH₂OH + CO

CH₂CO + CH₃= C₂H₅+ CO

CH₂CO + CH₃= CHCO + CH₄

CH₂CO + CH₂= C₂H₄+ CO

CH₂CO + CH₂= CHCO + CH₃

CHCO + H = CH₂+ CO

0

13,000

0

11,000

0

850

0

CHCO + O = CO + CO + H

CHCO + OH = CO + CO + H₂

CHCO + O₂= CO + CO + OH

CHCO + CH₂= C₂H₃+ CO

CHCO + CH₃= C₂H₄+ CO

CH₃+ CH₃(+ M)^b= C₂H₆(+M)

0

[45]

k

0

2.12 × 10⁵⁰

−9.70

−1.00

6,220

620

[34]

k

∞

2.12 × 10¹⁶

Troe parameter^c0.5325, 151, 1038, 4970

(39)

(40)

(41)

(42)

(43)

(44)

(45)

(46)

(47)

(48)

(49)

C₂H₆+ H = C₂H₅+ H₂

C₂H₆+ O = C₂H₅+ OH

C₂H₆+ OH = C₂H₅+ H₂O

C₂H₆+ CH₃= CH₄+ C₂H₅

C₂H₅+ H = C₂H₄+ H₂

C₂H₅+ O₂= C₂H₄+ HO₂

1.15 × 10⁸

3.97 × 10¹⁴

6.30 × 10⁶

1.51 × 10⁻⁷

4.50 × 10¹³

5.46 × 10¹¹

1.90

0.00

2.00

6.00

0.00

7,530

10,000

645

6,000

0

3,880

77,200

109,000

64,700

14,900

e

[40]

[37]

[34]

f

C₂H₄+ M = C₂H₂+ H₂+ M

C₂H₄+ M = C₂H₃+ H + M

C₂H₄+ C₂H₄= C₂H + C₂H₃

C₂H₄+ H = C₂H₃+ ⁵H₂

9.33 × 10¹⁶

6.31 × 10¹⁸

5.01 × 10¹⁴

5.40 × 10¹⁴

f

[37]

e

H + C₂H₄(+M)^b= C₂H₅(+M)

Continued

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

95

Table XII Continued

No.

Reaction

A

n

E

a

Reference

k

1.20 × 10⁴²

1.08 × 10¹²

−7.60

6,970

1,820

0

k

∞

0.50

Troe parameter^c0.9753, 210, 984, 4374

1.32 × 10⁷

(50)

(51)

(52)

(53)

(54)

(55)

(56)

(57)

(58)

C₂H₄+ O = CH₃+ CHO

C₂H₄+ O = CH₂CHO + H

C₂H₄+ O = CH₂O + CH₂

C₂H₄+ OH = C₂H₃+ H₂O

C₂H₄+ HO₂= cC₂H₄O + OH

C₂H₄+ CH₃= C₂H₃+ CH₄

C₂H₄+ C₂H = C₄H₄+ H

C₂H₄+ C₂H₃= 1,3-C₄H₆+ H

1.90

0.00

600

700

[22]

[37]

f

6.80 × 10¹¹

1.80 × 10¹³

4,000

5,940

17,200

11,100

0

2.04 × 10¹³

2.23 × 10¹²

4.20 × 10¹¹

[40]

[41]

[22]

1.20 × 10¹³

8.10 × 10¹¹

3,850

C₂H₃(+M)^b= C₂H₂+ H(+M)

k

0

4.98 × 10⁴⁰

−7.50

45,500

39,700

k

∞

2.00 × 10¹⁴

0.00

Troe Fc = 0.350

(59)

(60)

(61)

(62)

(63)

(64)

(65)

(66)

(67)

(68)

(69)

(70)

(71)

(72)

(73)

(74)

(75)

(76)

(77)

(78)

(79)

(80)

(81)

(82)

(83)

(84)

(85)

(86)

(87)

(88)

(89)

(90)

(91)

(92)

(93)

(94)

(95)

(96)

C₂H₃+ H = C₂H₂+ H₂

C₂H₃+ O = CH₂CO + H

C₂H₃+ OH = C₂H₂+ H₂O

C₂H₃+ O₂= C₂H₂+ HO₂

C₂H₃+ O₂= CH₂O + CHO

C₂H₃+ O₂= CH₂CHO + O

C₂H₃+ CH₃= C₂H₂+ CH₄

C₂H₃+ C₂H₃= C₂H₂+ C₂H₄

C₂H₂+ C₂H₂= IC₄H₃+ H

C₂H₂+ O₂= CHO + CHO

C₂H₂+ H = C₂H + H₂

9.60 × 10¹³

3.00 × 10¹³

6.60 × 10²¹

4.00 × 10²¹

9.60 × 10¹³

2.04 × 10¹³

1.44 × 10¹³

1.13 × 10¹⁴

1.00 × 10¹²

2.90 × 10¹⁴

2.08 × 10¹⁴

5.20 × 10¹⁴

1.44 × 10⁴

3.20 × 10¹¹

3.00 × 10¹³

4.20 × 10¹²

9.03 × 10¹³

1.99 × 10¹²

1.80 × 10¹³

3.00 × 10¹³

2.50 × 10¹³

2.52 × 10¹⁵

6.40 × 10¹³

5.00 × 10¹⁵

2.50 × 10¹⁵

4.00 × 10¹⁴

2.00 × 10¹⁴

2.50 × 10¹³

3.00 × 10¹⁵

2.00 × 10¹⁵

3.00 × 10¹³

2.60 × 10⁵

1.30 × 10¹⁴

1.00 × 10¹⁴

1.00 × 10¹³

5.00 × 10¹³

0.00

−3.28

−3.00

0.00

2.68

0.00

2.50

0.00

0

[41]

f

5,410

2,400

12,900

0

[22]

g

0

h

56,000

28,000

25,600

9,900

10,700

12,000

200

g

[19]

[38]

g

C₂H₂+ O = CH₂+ CO

C₂H₂+ O = CHCO + H

C₂H₂+ OH = C₂H + H₂O

C₂H₂+ OH = CH₂CO + H

C₂H₂+ CH = C₃H₃

0

[37]

[19]

g

C₂H₂+ CH₂= C₃H₄

6,620

0

5,000

0

C₂H₂+ C₂H = C₄H₂+ H

C₂H₂+ C₂H₃= C₄H₄+ H

C₂H + O₂= CO + CO + H

2-C₄H₆= 1,3-C₄H₆

f

[35]

[23]

[42]

[27]

[23]

h

65,000

63,000

94,700

77,100

22,800

65,000

75,800

75,000

67,000

1,000

9,400

43,900

0

1,2-C₄H₆= 1,3-C₄H₆

1,3-C₄H₆= C₄H₄+ H₂

1,3-C₄H₆= C₂H₄+ C₂H₂

1,3-C₄H₆+ H = 1,3-NC₄H₅+ H₂

1,3-C₄H₆+ H = 1,3-IC₄H₅+ H₂

1,3-C₄H₆+ CH₃= 1,3-NC₄H₅+ CH₄

1,3-C₄H₆+ CH₃= 1,3-IC₄H₅+ CH₄

1-C₄H₆= 1,2-C₄H₆

1-C₄H₆= C₃H₃+ CH₃

h

1,2-C₄H₆= C₃H₃+ CH₃

2-C₄H₆= 1,2-C₄H₆

[42]

[23]

i

2-C₄H₆+ H = CH₃+ C₃H₄

2-C₄H₆+ H = 2-C₄H₅+ H₂

1,3-NC₄H₅= C₂H₃+ C₂H₂

1,3-NC₄H₅+ C₂H₂= C₆H₆+ H

1,3-IC₄H₅= C₄H₄+ H

[43]

[23]

44,000

Continued

International Journal of Chemical Kinetics DOI 10.1002/kin

96

YASUNAGA ET AL.

Table XII Continued

No.

Reaction

A

n

E

a

Reference

(97)

(98)

(99)

1-NC₄H₅= C₂H + C₂H₄

1-NC₄H₅= C₄H₄+ H

2-C₄H₅= C₄H₄+ H

2.00 × 10¹⁴

3.00 × 10¹³

3.16 × 10¹³

1.26 × 10¹⁵

5.01 × 10⁶

1.00 × 10⁷

3.20 × 10¹⁴

3.16 × 10¹⁵

5.01 × 10¹³

9.00 × 10¹³

3.50 × 10¹²

8.00 × 10¹⁴

4.00 × 10¹³

5.00 × 10¹³

3.40 × 10¹³

6.00 × 10¹²

1.00 × 10¹²

4.70 × 10¹⁸

1.30 × 10⁵

2.00 × 10¹²

2.50 × 10¹²

2.00 × 10¹⁸

4.00 × 10¹²

2.00 × 10¹²

1.40 × 10¹²

3.00 × 10¹¹

0.00

2.00

0.00

2.50

0.00

57,000

45,000

77,100

94,700

6,000

57,200

45,000

0

33,200

70,000

88,000

80,000

3,500

1,500

8,000

80,000

1,000

7,700

59,000

80,000

2,700

7,700

10,000

0

[23]

j

(100)

(101)

(102)

(103)

(104)

(105)

(106)

(107)

(108)

(109)

(110)

(111)

(112)

(113)

(114)

(115)

(116)

(117)

(118)

(119)

(120)

(121)

(122)

(123)

(124)

(125)

C₄H₄= C₂H₂+ C₂H₂

C₄H₄= C₄H₂+ H₂

j

C₄H₄+ H = NC₄H₃+ H₂

C₄H₄+ H = IC₄H₃+ H₂

NC₄H₃= C₂H₂+ C₂H

IC₄H₃+ M = C₄H₂+ H + M

IC₄H₃+ H = C₄H₂+ H₂

NC₃H₇= C₂H₄+ CH₃

C₃H₆= C₂H₂+ CH₄

[43]

k

[43]

h

[44]

l

C₃H₆= C₂H₃+ CH₃

C₃H₆= C₃H₄+ H₂

C₃H₆= AC₃H₅+ H

C₃H₆+ H = C₂H₄+ CH₃

C₃H₆+ H = AC₃H₅+ H₂

C₃H₆+ CH₃= AC₃H₅+ CH₄

C₃H₄+ M = C₃H₃+ H + M

C₃H₄+ H = C₂H₂+ CH₃

C₃H₄+ CH₃= C₃H₃+ CH₄

AC₃H₄= C₃H₄

[44]

[18]

m

[18]

m

AC₃H₄+ M = C₃H₃+ H + M

AC₃H₄+ H = AC₃H₅

AC₃H₄+ CH₃= C₃H₃+ CH₄

AC₃H₄+ C₃H₃= C₆H₆+ H

C₃H₃+ C₃H₃= C₆H₆

H + CH₃(+M)^b= CH₄(+M)

m

[18]

m

k

0

1.42 × 10³³

−4.80

−0.60

2,440

380

[29]

k

∞

1.27 × 10¹⁶

Troe parameter^c0.783, 74, 2941, 6964

(126)

(127)

(128)

(129)

(130)

(131)

(132)

(133)

(134)

(135)

(136)

(137)

(138)

(139)

(140)

(141)

(142)

(143)

(144)

(145)

(146)

CH₄+ O₂= CH₃+ HO₂

CH₄+ H = CH₃+ H₂

3.97 × 10¹⁴

1.19 × 10⁴

2.83 × 10¹⁴

1.57 × 10⁷

9.03 × 10¹²

4.30 × 10¹²

1.90 × 10¹⁶

6.90 × 10¹⁴

2.00 × 10¹⁴

7.00 × 10¹³

1.50 × 10¹³

5.48 × 10¹³

9.00 × 10¹⁴

1.87 × 10¹³

3.60 × 10¹⁰

1.80 × 10¹³

1.00 × 10¹³

1.50 × 10¹²

0.00

56,900

8,040

12,900

2,800

24,700

10,000

91,400

82,500

15,100

0

5,000

2,980

16,000

28,800

8,940

0

[29]

e

3.00

0.00

1.83

0.00

0.10

1.56

0.00

CH₄+ O = CH₃+ OH

CH₄+ OH = CH₃+ H₂O

CH₄+ HO₂= CH₃+ H₂O₂

CH₄+ CH₂= CH₃+ CH₃

CH₃+ M = CH₂+ H + M

CH₃+ M = CH + H₂+ M

CH₃+ H = CH₂+ H₂

[37]

h

CH₃+ O = CH₂O + H

[40]

h

CH₃+ OH = CH₂+ H₂O

CH₃+ OH = CH₂O + H₂

CH₃+ OH = CH₂OH + H

CH₃+ O₂= CH₃O + O

CH₃+ O₂= CH₂O + OH

CH₃+ HO₂= CH₃O + OH

CH₃+ CH₂= C₂H₄+ H

CH₃+ CH₃= C₂H₅+ H

CH₂+ H = CH + H₂

[29]

h

[29]

e

[37]

[29]

g

0

10,600

0

1,000

800

1.00 × 10¹⁸

2.27 × 10¹²

1.20 × 10¹⁴

-

CH₂+ O₂= CO₂+ H + H

CH₂+ CH₂= C₂H₂+ H + H

[20]

[37]

Continued

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

97

Table XII Continued

No.

Reaction

A

n

E

a

Reference

(147)

(148)

(149)

(150)

(151)

(152)

(153)

(154)

(155)

(156)

(157)

(158)

(159)

(160)

(161)

(162)

(163)

(164)

(165)

(166)

(167)

(168)

(169)

(170)

(171)

(172)

(173)

(174)

(175)

(176)

(177)

(178)

CH + O₂= CO₂+ H

2.10 × 10¹³

4.40 × 10¹⁵

5.40 × 10¹³

4.04 × 10¹⁰

5.54 × 10¹⁵

2.52 × 10¹⁶

1.23 × 10⁶

2.18 × 10⁸

3.50 × 10¹³

3.00 × 10¹³

3.32 × 10³

6.95 × 10¹⁷

2.16 × 10¹⁴

3.00 × 10¹³

5.00 × 10¹³

5.10 × 10¹³

1.20 × 10¹⁴

4.40 × 10⁶

1.50 × 10¹⁴

9.75 × 10¹³

5.08 × 10⁴

9.39 × 10⁸

6.40 × 10¹⁷

8.28 × 10²¹

1.20 × 10¹⁴

6.16 × 10¹⁷

1.00 × 10¹⁴

1.50 × 10¹⁴

2.00 × 10¹²

2.00 × 10¹³

4.50 × 10⁴

1.20 × 10¹⁷

0.00

3.00

1.77

0.00

2.80

−1.00

0.00

1.50

0.00

2.67

1.52

−1.00

−2.00

0.00

−0.80

0.00

2.70

0.00

0

30,000

13,490

2,130

75,000

71,500

52,000

3,000

3,510

1,200

5,860

17,000

0

h

CH₂OH + M = CH₂O + H + M

CH₃O + M = CH₂O + H + M

CH₃O + O₂= CH₂O + HO₂

CH₂O + M = CHO + H + M

CH₂O + M = CO + H₂+ M

CH₂O + O₂= CHO + HO₂

CH₂O + H = CHO + H₂

CH₂O + O = CHO + OH

CH₂O + OH = CHO + H₂O

CH₂O + CH₃= CHO + CH₄

CHO + M = CO + H + M

CHO + H = H₂+ CO

f

[37]

[24]

[21]

[41]

[40]

e

[24]

[40]

[41]

[40]

g

CHO + O = OH + CO

0

CHO + OH = H₂O + CO

CHO + O₂= HO₂+ CO

CHO + CH₃= CH₄+ CO

CO + OH = CO₂+ H

1,700

0

−740

23,600

14,850

6,290

18,400

0

CO + HO₂= CO₂+ OH

O₂+ H = OH + O

H₂+ O = OH + H

g

H₂O + H = OH + H₂

g

H + H + M = H₂+ M

[40]

[37]

[40]

[37]

[21]

[40]

h

H + OH + M = H₂O + M

O₂+ M = O + O + M

0

108,000

0

700

1,000

0

H + O₂+ M = HO₂+ M

HO₂+ H = H₂+ O₂

HO₂+ H = OH + OH

HO₂+ HO₂= H₂O₂+ O₂

HO₂+ OH = H₂O + O₂

H₂O + O = OH + OH

14,600

45,500

H₂O₂+ M = OH + OH + M

[40]

^aRate constants in the form, AT exp(−E_a/RT), in cm, mol, cal, and K units.

n

^bThe collision efﬁciency factors are as follows (see [19]): H₂, 2.0; H₂O, 6.0; CH₄, 2.0; CO, 1.5; CO₂, 2.0; C₂H₆, 3.0; Ar, 0.7.

^cTroe parameters are listed in order: a, T ^∗, T ^∗∗∗, T ^∗∗

^dThe reference is in [45].

.

^eThe reference is in [34].

f

The reference is in [22].

^gThe reference is in [19].

^hThe reference is in [29].

ⁱThe reference is in [42].

^jThe reference is in [43].

^kThe reference is in [23].

^lThe reference is in [44].

^mThe reference is in [18].

1.00 × l0¹⁶exp(–85.0 kcal/RT) s⁻¹is considered to be

the maximum value of k₃.

As long as we used reactions (1), (5), (7), and

(17) reported previously [1], IR-emission proﬁles at

4.68 µm were never reproduced, as shown in Fig. 3a.

Also, even if reactions (1)–(3) were used as the initia-

tion reaction and various rate-constant expressions for

reactions, (1)–(3), (5), (7), and (17) were assumed,

the UV-absorption proﬁles at 200 nm and the IR-

emission proﬁles at 4.68 µm were not reproduced

and the calculated values were much smaller than ob-

served ones, as shown in Figs. 3a and 4a; the UV-

absorption proﬁles and the IR-emission proﬁles largely

depended on ketene concentration produced, as shown

International Journal of Chemical Kinetics DOI 10.1002/kin

98

YASUNAGA ET AL.

with k₇= 1.60 × 10¹²exp(–8.0 kcal/RT) cm³mol⁻¹

s⁻¹and 8 with k₈= 6.00 × 10¹²exp(–11.0 kcal/RT)

in Figs. 3b and 4b. The proﬁles shown in Figs. 3a

and 4a were never predicted when reactions (6) and

(8) were omitted from our mechanism without us-

ing unreasonable value of k₄= 3.80 × l0¹²exp(−63.5

kcal/RT) s⁻¹. On the other hand, slightly larger val-

ues of k₆and k₈could compensate the lack of k₄,

namely k₆= 4.60 × 10¹³exp(–10.0 kcal/RT) s⁻¹and

k₈= 6.30 × 10¹³exp(−11.0 kcal/ RT) s⁻¹could ex-

plain experimental results as shown in Figs. 3a and 4a

without reaction (4). Hence, reactions (6) and (8) are

indispensable for reproduction of our observed data.

The produced H atoms may abstract H atoms

from two different positions in CH₃CHO and pro-

duce two different radicals. We used reactions (5)

with k₅= 1.20 × l0¹⁴exp(−7.0 kcal/RT) cm³mol⁻¹

s⁻¹and 6 with k₆= 4.40 × 10¹⁴exp(−10.0 kcal/RT)

cm³mol⁻¹s⁻¹. When a small amount of CH₃CHO is

added to H₂–O₂mixture, reaction (166), O₂+ H →

OH + O, and reactions (5) and (6) are competitive. The

proﬁles calculated for mixtures 1% H₂, 1% O₂, 0.1%

CH₃CHO, and 97.9% Ar are very sensitive to the k₅and

k₆values, as shown in Fig. 5b. The reliability of the

rate constant k₁₆₆= 9.75 × 10¹³exp(−14.9 kcal/RT)

cm³mol⁻¹s⁻¹used for reaction (166) is high, and this

value can reproduce the observed τ_OHin the H₂oxida-

tion, as shown in Fig. 7. Analyzing the data obtained

using the H₂–O₂–CH₃CHO mixture, we were able to

obtain useful information for the rate constant of reac-

tion between the CH₃CHO and H atom. The values k₁,

k₅, and k₆have very high sensitivity to the OH absorp-

tion proﬁle. Since the k₁value was already determined

cm³mol⁻¹⁻¹. CH₄yield shown in Fig. 1a is very

s

sensitive to the k₇and k₈values, as shown in Fig. 1b.

The calculated proﬁle for mixture B is also very sensi-

tive to the k₇value, as shown in Fig. 2c. The CH₄yield

and the A_tproﬁle simulated using k₇= 1.60 × 10¹²

exp(–8.0 kcal/RT) cm³mol⁻¹s⁻¹and k₈= 6.00 × 10¹²

exp(–11.0 kcal/RT) cm³mol⁻¹s⁻¹were the best ﬁt to

our observed data, as shown in Figs. 1a and 2a.

As the reaction of acetaldehyde with O₂, reaction

(9) is reported [13–15].

CH₃CHO + O₂→ CH₃CO + HO₂

ꢀH₀^◦= 40.3 kcal/mol

CH₃CHO + O₂→ CH₂CHO + HO₂

ꢀH₀^◦= 48.6 kcal/mol

(9)

(10)

The proﬁles calculated for mixtures E and F are

very sensitive to the k₉value, as shown in Figs. 11b

and 12b. The simulations using the reported value

k₉= 2.00 × 10¹³T ^0.50exp(−42.2 kcal/RT) cm³mol⁻¹

s

⁻¹[13] are the best ﬁt to our observed data, as shown in

Fig. 11a. However, the reported value k₉= 3.00 × 10¹³

T ^0.50exp(–39.1 kcal/RT) cm³mol⁻¹s⁻¹[37] gives

slower rate than the observed one, as shown in Fig. 11a.

The value k₁₀= 2.00 × 10¹⁴T ^0.50exp(–48.6 kcal/RT)

cm³mol⁻¹⁻¹was assumed for reaction (10). These

s

values were used in Table XII.

as mentioned above, the value k₅= 1.20 × l0¹⁴exp(–

Reactions (11) and (12) played a role in the

CH₃CHO consumption in the oxidation at high tem-

peratures: this reaction may consume about 3.5% of

the CH₃CHO concentration at 1438 K and 200 µs us-

ing mixture F. However, none of our observed data are

sensitive to the above k₁₁and k₁₂values, as shown in

Figs. 5b, 6b, 8c, 9c, 10b, 11b, 12b, and 14b. Even if

the values of 10 × k₁₁and 10 × k₁₂were assumed, the

simulated proﬁles or species concentrations did not

change. So, we are not able to examine this value from

our experimental results.

−1

7.0 kcal/RT) cm³mol

s

⁻¹and k₆= 4.40 × l0¹⁴exp(–

10.0 kcal/RT) cm³mol⁻¹⁻¹, to be able to reproduce

s

the OH absorption proﬁles, were determinedwiththe

ﬁxed value of k₁. The τ_OHsimulated using our values

k₅= 1.20 × l0¹⁴exp(–7.0 kcal/RT) cm³mol⁻¹s⁻¹and

k₆= 4.40 × l0¹⁴exp(–10.0 kcal/RT) cm³mol⁻¹s⁻¹are

also the best ﬁts to our data, as shown in Figs. 5a

and 7. Judging from the difference of simulated re-

sults between k₅= 2.20 × l0¹⁴exp(–7.0 kcal/RT) cm³

mol⁻¹

s

⁻¹, k₆= 4.40 × l0¹⁴exp(–10.0 kcal/RT) cm³

mol⁻¹s⁻¹and the other values, the maximum values,

k₅= 2.40 × l0¹⁴exp(–7.0 kcal/RT) cm³mol⁻¹s⁻¹and

CH₃CHO + O → CH₃CO + OH

k₅= 8.80 × l0¹⁴exp(–10.0 kcal/RT) cm³mol⁻¹s⁻¹

,

ꢀH₀^◦= −13.5 kcal/mol

CH₃CHO + O → CH₂CHO + OH

ꢀH₀^◦= −5.1 kcal/mol

(11)

(12)

were determined as shown in Fig. 5a. The value k₅=

4.10 × 10⁹T ^1.16exp(–2.40 kcal/RT) recommended by

Baulch gives faster rate than the observed one as shown

in Fig. 5a. The proﬁles calculated for mixtures E and F

are also very sensitive to the k₅and k₆values as shown

in Figs. 11b and 12b.

The rate constant expression k₁₁= 5.80 × 10¹²

The CH₃radicals may also abstract the H atoms

from two different positions in CH₃CHO and pro-

duce two different radicals. We used reactions (7)

exp(−1.8 kcal/RT) cm³mol⁻¹s⁻¹

,

recom-

mended by Baulch et al. [37], was used.

The value k₁₂= 1.50 × 10¹³exp(−5.0 kcal/RT)

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

99

cm³mol⁻¹

values were used in Table XII.

s

⁻¹was assumed for reaction (12). These

exp(−14.0 kcal/RT) cm³mol⁻¹s⁻¹was assumed

for reaction (16). These values were used in

Table XII.

Reactions (13) and (14) played a role in the ac-

etaldehyde consumption in the oxidation at high tem-

peratures: this reaction may consume about 15.5%

of the acetaldehyde concentration at 1438 K and

200 µs using mixture F. However, CO₂proﬁles are

marginally sensitive to the k₁₃value, as shown in

Fig. 12b.

CH₃CO and CH₂CHO Radical Reactions

CH₃CO + M → CH₃+ CO + M

ꢀH₀^◦= 9.1 kcal/mol

CH₃CO + M → CH₂CO + H + M

ꢀH₀^◦= 41.5 kcal/mol

(17)

(18)

(19)

CH₃CHO + OH → CH₃CO + H₂O

ꢀH₀^◦= −29.3 kcal/mol

CH₃CHO + OH → CH₂CHO + H₂O

ꢀH₀^◦= −21.0 kcal/mol

(13)

(14)

CH₂CHO → CH₂CO + H

ꢀH₀^◦= 33.2 kcal/mol

The reaction of OH radical with acetaldehyde

has been studied mainly at temperatures be-

low 500 K. Warnatz [40] recommended the

rate constant k₁₃= 1.00 × 10¹²cm³mol⁻¹s⁻¹

in the temperature range 300–2000 K. Baulch

et al. [37] also recommended the rate constant

k₁₃= 2.34 × 10¹⁰T ^0.73exp(+1.1 kcal/RT) cm³mol⁻¹

s⁻¹in the temperature range 250–1200 K. We used

Baulch et al. value [37] for our simulation. This

expression could reproduce all our data. The value

k₁₄= 1.60 × 10¹³exp(−2.0 kcal/RT) cm³mol⁻¹s⁻¹

was assumed for reaction (14). These values were used

in Table XII.

It is known at low temperatures that the CH₃CO rad-

icals produced by reactions (2), (5), (7), (9), (11), (13),

and (15) decompose via reaction (17) to produce CO

and CH₃. Under our experimental conditions, reaction

(17) also played an important role in the CO formation.

However, we were not able to examine the k₁₇value

because none of our observed results were sensitive

to k₁₇. We used reported value k₁₇= 5.4 × 10²⁷T ^−3.40

exp(−18.9 kcal/RT) cm³mol⁻¹s⁻¹[37] in Table XII.

It is inferred that reaction (–18) may occur under

our experimental conditions. However, the rate con-

stant value is not reported. The value k₁₈= 5.0 × 10¹⁷

cm³mol⁻¹s⁻¹was assumed for reaction (18). CO₂pro-

ﬁles are marginally sensitive to the k₋₁₈value, as shown

in Figs. 11b and 12b. We were not able to examine this

value from our experimental results and so used the

CH₃CHO + HO₂→ CH₃CO + H₂O₂

ꢀH₀^◦= 2.0 kcal/mol

CH₃CHO + HO₂→ CH₂CHO + H₂O₂

ꢀH₀^◦= 10.3 kcal/mol

(15)

(16)

assumed value k₁₈= 5.0 × 10¹⁷cm⁶mol⁻²s⁻²

.

Therateconstantsofreactions (19)and(20)werein-

vestigated theoretically [38] in detail, so we used the re-

ported value k₁₉= 1.3 × l0³⁴T ^−6.6exp(−49.5 kcal/RT)

s⁻¹and k₂₀= 6.5 × l0³⁴T ^−6.9exp(−47.2 kcal/RT) s⁻¹

[37].

Reactions (15) and (16) played a little role in the

acetaldehyde consumption in the oxidation at high

temperatures: this reaction may consume about

0.5% of the acetaldehyde concentration at 1438

K and 200 µs using mixture F. However, CO₂

proﬁles are marginally sensitive to the k₁₅value,

as shown in Fig. 12b. Colket et al. [12] reported

k₁₅= 1.70 × 10¹²exp(–10.7 kcal/RT) cm³mol⁻¹s⁻¹

in the temperature range 1030–1115 K. Baulch et al.

[37] recommended the rate constant k₁₅= 3.00 × 10¹²

exp(−11.9 kcal/RT) cm³mol⁻¹s⁻¹in the temper-

ature range 900–1200 K. We used Baulch et al.

value [37] for our simulation. This expression could

reproduce all our data. The Colket et al. value is

also able to reproduce our experimental data within

experimental error. The value k₁₆= 1.00 × 10¹²

Sensitive Reactions of Reactions (20)–(178)

The rate constants of reactions (20)–(178) used in

Table XII are the same as those used in the most recent

pyrolysis and oxidation submechanisms for formalde-

hyde [21], methane [29], ethane [34], ethylene [22],

acetylene [19], and ketene [20], which were main inter-

mediate species in the acetaldehyde oxidation. Under

our experimental conditions, these reactions played a

role in the acetaldehyde oxidation. The CO₂forma-

tion in mixture F (fuel-lean condition) is very sen-

sitive to the rate constants of reactions (1), (5), (6),

(9), (10), (13), (14), (18), (19), (23), (24), (26)–(28),

International Journal of Chemical Kinetics DOI 10.1002/kin

100

YASUNAGA ET AL.

(34), (38), (39), (49), (125), (126), (129), (135), (137)–

(141), (145), (156), (157), (162)–(164), (166)–(168),

(173), and (176), as shown in Fig. 12b.

(162)–(167), and (173), as shown in Fig. 10b.

CH₂CO + M → CH₂+ CO + M

CHCO + H → CH₂+ CO

C₂H₄+ O → CH₃+ CHO

C₂H₄+ O → CH₂O + CH₂

C₂H₃(+M) → C₂H₂+ H(+M)

C₂H₃+ H → C₂H₂+ H₂

C₂H₃+ O₂→ CH₂CHO + O

C₂H₃+ CH₃→ C₂H₂+ CH₄

C₃H₆→ C₂H₃+ CH₃

(21)

(32)

CH₂CO + H → CH₃+ CO

CH₂CO + O → CH₂+ CO₂

CH₂CO + OH → CH₂O + CHO

CH₂CO + OH → CH₂OH + CO

CH₂CO + CH₃→ C₂H₅+ CO

CHCO + OH → CO + CO + H₂

CH₃+ CH₃(+M) → C₂H₆(+M)

C₂H₆+ H → C₂H₅+ H₂

H + C₂H₄(+M) → C₂H₅(+M)

H + CH₃(+M) → CH₄(+M)

CH₄+ O₂→ CH₃+ HO₂

CH₄+ OH → CH₃+ H₂O

CH₃+ O → CH₂O + H

(23)

(24)

(50)

(52)

(26)

(58)

(27)

(59)

(28)

(64)

(34)

(65)

(38)

(110)

(127)

(142)

(143)

(158)

(165)

(39)

CH₄+ H → CH₃+ H₂

(49)

CH₃+ CH₂→ C₂H₄+ H

CH₃+ CH₃→ C₂H₅+ H

CHO + M → CO + H + M

CO + H₂O → CO₂+ OH

(125)

(126)

(129)

(135)

(137)

(138)

(139)

(140)

(141)

(145)

(156)

(157)

(162)

(163)

(164)

(166)

(167)

(168)

(173)

(176)

CH₃+ OH → CH₂O + H₂

CH₃+ OH → CH₂OH + H₂

CH₃+ O₂→ CH₃O + O

CH₃+ O₂→ CH₂O + OH

CH₃+ HO₂→ CH₃O + OH

CH₂+ O₂→ CO₂+ H + H

CH₂O + OH → CHO + H₂O

CH₂O + CH₃→ CHO + CH₄

CHO + O₂→ HO₂+ CO

CHO + CH₃→ CH₄+ CO

CO + OH → CO₂+ H

O₂+ H → OH + O

H₂+ O → OH + H

H₂O + H → OH + H₂

HO₂+ H → H₂+ O₂

HO₂+ OH → H₂O + O₂

On the other hand, the CO₂formation in mixture

D (fuel-rich condition) is very sensitive to the rate

constants of reactions (1), (3), (5)–(9), (21), (23), (24),

(28), (32), (39), (50), (52), (58), (59), (64), (65), (110),

(125)–(127), (129), (135), (137)–(143), (145), (158),

Figure 15 Comparison of the experimental data (symbols)

obtained by JSR [14] at 1 atm with those (curves) calculated

with the mechanism described in Table XII. The initial con-

ditions were CH₃CHO, 0.124%; O₂, 0.375%; N₂, 99.5%;

τ = 0.08 s; φ = 0.82.

International Journal of Chemical Kinetics DOI 10.1002/kin

SHOCK-TUBE AND MODELING STUDY OF ACETALDEHYDE PYROLYSIS AND OXIDATION

101

The CO₂formation is sensitive to the rate con-

stants included in submechanisms of methane, ethy-

lene, ethane, formaldehyde, and ketene, as shown in

Figs. 10b and 12b. The submechanisms of methane,

ethylene, ethane, formaldehyde, and ketene were

found to play an important role in the acetaldehyde

oxidation.

acetaldehyde was constructed using reaction steps and

rate constant expressions that included pyrolysis and

oxidation submechanisms for formaldehyde, ketene,

methane, ethylene, ethane, and acetylene. The pyroly-

sis and oxidation data obtained under our experimental

conditions were predicted well by the proposed mech-

anism of 178 reaction steps and 50 species. The mech-

anism was constructed using new reactions, CH₃CHO

(+M) → CH₄+ CO (+M), CH₃CHO (+M) →

CH₂CO + H₂(+M), CH₃CHO + H → CH₂CHO + H₂,

CH₃CHO + CH₃→ CH₂CHO + CH₄, CH₃CHO + O₂

→ CH₂CHO + HO₂, CH₃CHO + O → CH₂CHO +

OH, CH₃CHO + OH → CH₂CHO + H₂O, CH₃CHO

+ HO₂→ CH₂CHO + H₂O₂. The submechanisms of

methane, ethylene, ethane, formaldehyde, and ketene

were found to play an important role in the acetalde-

hyde oxidation under our experimental conditions.

Application for Jet-Stirred Reactor Data

To test reaction mechanism constructed in this study, it

was applied for the ﬂow reactor data obtained Dagaut

et al. [14]. As is seen in Fig. 15, simulation results

obtained using Chemkin 2 with our reaction mecha-

nism could reproduce the mole fraction of reactant and

products.

The Uncertainty of Absorption Coefﬁcient

at 3.39 µm

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International Journal of Chemical Kinetics DOI 10.1002/kin

Article Doi

Shock-tube and modeling study of acetaldehyde pyrolysis and oxidation

DOI: 10.1002/kin.20294

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Article abstract of DOI:10.1002/kin.20294

Full text of DOI:10.1002/kin.20294

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