Ay. Starikovsky et al., Soot formation in the pyrolysis of halogenated hydrocarbons. Part I, binary mixtures of carbon tetrachloride with hydrogen and iron pentacarbonyl, BER BUN GES, 102(12), 1998, pp. 1815-1822
Citations number
11
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
BERICHTE DER BUNSEN-GESELLSCHAFT-PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Measurements on carbon particle growth during CCl4 thermal decomposition we
re carried out behind both incident and reflected shock waves. Three kind o
f mixture compositions have been investigated: 4000 ppm CCl4 in argon; 200
to 4000 ppm CCl4 and 200 to 8000 ppm Fe(CO)(5) in argon; 4000 ppmCCl(4) and
4000 ppm hydrogen in argon. The temperature range 1200<T/K<3200, pressure
around 25 bar. Kinetics of the particle growth was detected via the attenua
tion of the laser beam (He-Ne laser, 632.8 nm).
The low temperature boundary for soot particles detection and magnitude of
soot yield in CCl4 pyrolysis is the same as that for most of the hydrocarbo
ns studied. The temperature change during CCl4 pyrolysis is an important fa
ctor for its kinetic interpretation. The first order rate constants of soot
growth k(f)/[C] are higher than those for all hydrocarbons, including benz
ene under comparable conditions. At T<2200 K the induction times bind an cl
ose to those for hydrocarbons with respect to both, absolute values and act
ivation energy. In the middle temperature range studied, 2200<T/K<2500, an
"induction-less behaviour" of soot growth was observed: t(ind) at T>2500 K
show a negative activation energy. Hydrogen additives significantly act on
soot formation characteristics depending on H/Cl-ratio.
Chemical reaction in mixtures CCl4/Fe(CO)(5) was observed even at relativel
y low temperatures behind incident shock waves. However, iron additives onl
y slightly change the soot yield as compared to CCl4 pyrolysis. A qualitati
ve interpretation of experimental findings observed is suggested based on t
he consideration of the hierarchy of characteristic times in reacting syste
ms followed by the growth of soot particles.