thermal cracking of ethylene, propylene and light hydrocarbon

5. Decomposition and pol.wnerization zones in olefines crackins
i:. Propylene cracking
In the thermal cracking of propylene, polyierization and decomposition
processes are in competition (1,2,3,12,13,14). Low tenperatures
and high partial pressures favor polynerization, high tenperatures
and lovr partial pressures fa-ieu*.e 17.
To permit a direct cornp.rison with the literature, the propyhene
partial pressure is expressed in rm Me. From Anano's border line,
it follovis that the present results woulci be conpletely located
in the golpierization zone aid indeed no allene is found. However,
the order of the global disappezrance reaction is not 5/2 but
varies froiii 1/2 to 1 as the teriperature is increased, while the
activation enerfiie varj.es from 31; tn 66 kc~.l/~?:&!.- C!%C r;-ggcr;ts
that the present dat.?. would be located in the trznsition area and
this in turn requires the border line to be shifted towards the
left of t'ne figure. Such a shift could result from a decomposition
of allyl into acetylene instead of allene :
An isothermal, unsteady state radical siniulation of the propylene
experiments (10) led to a frequenc factor of 1.108 and an activation
energy of 32.4 kcal/mol for 77. These values are j?lausj.bl.e,
when compared with Allarals data (9) for the decomposition of c
radicals into C 11 :',ken reaction 7 instead of reaction 6 accoukts
for the/t-behav$o$'of the allylradical, the border line between the
two areas io, calculated from : IC C I1 ) = I: . This is the full
line on Figure 17. Both Kunugi's5t2j Bnd O U ~ experiments are now
located in the transition zone. Tile experiments of Laidler (1)
and Ingold (12) lie in the polyuerization area and these of Szwarc:
(13) and Salcakibarz (14) in the decomposition zone. This is in
agreement with the fact that neither Laidler nor Ingold found
acetylene, while Kunugi and Sakakibara d.id. The results of Szviarc
are doubtful bccause of his rudimentary analytical technique.
At 1200°C and higher, the decomposition of allyl into alleEe
becomes more and more important, became of the high activation
encrm, so that Sakalcibara, whose work is lrlainly situated in the
temperature range 12000c-1400°c, found inore allene and iiiethyl-
140