Dean, A.M., Craig, B.L., Johnson, R.L., Schultz, M.C., and Wang, E.E. (1979)
Shock Tube Studies of Formaldehyde Pyrolysis
17th Symposium (International) on Combustion, 1979, p.577
Abstract
Formaldehyde decay was followed by IR emission at 3.5 µm behind reflected
shocks at total concentrations near 2.4 and 4.5E+18 molecule/cm3 in a 7.6 cm
diameter shock tube. Data were obtained at 0.5 µs intervals over a
temperature range of 1700-2710 K for mixtures containing 0.1%, 0.5%, and 1.0%
CH2O in Ar. Exponential decay was observed in all cases; at lower temperatures
there was evidence of an induction time prior to the onset of decay. An apparent
rate constant was defined as k=-[d(ln signal)/dt]/[M]; k was observed to be
independent of the total concentration but to decrease with decreasing CH2O
concentration. These data were analyzed in terms of the mechanism consisting of
reactions (-54), (58), (167), and (55). Using literature values for k(58),
k(167), and k(55), a reasonable fit to all the data, both in terms of temperature
and concentration dependence, was obtained with k(-54)= 6.0E-7exp(-364 kJ/RT)
cm3/molecule s. Error considerations suggest this value of k(-54) is accurate to
within a factor of three between 1800-2500 K. However, the uncertainty in the
activation energy may be as high as 40-50 kJ/mole. Evidence is also presented to
suggest that the reaction (-83)
does not play a significant role in the high temperature pyrolysis of formaldehyde.
REACTION RATE COEFFICIENTS SUGGESTED IN THIS WORK:
GRI-Mech
Number
('-' sign
means
reverse) |
Reaction |
Rate Coefficient
A T^n exp(-E/RT) |
Temperature
Range
(K) |
A
(mol,cm3,s) |
n
(T in K) |
E
(cal/mol) |
| -54 |
CH2O + M -> H + HCO + M |
3.61E+17 |
|
87000 |
1700-2710 |