Pyrolysis of propylene over carbon active sites—I: Kinetics

Abstract The influence of carbon active sites on the pyrolysis of propylene was studied in the temperature range 873–1073 K at a starting pressure of 1.6 Pa. Graphon, a graphitized carbon black, was used as a substrate for pyrolysis and subsequent carbon deposition. Pyrolysis was carried out in a static reactor at low pressures where secondary products were less likely to form and complicate the system. The pyrolysis of propylene over the Graphon substrate may be described by the expression d (C 3 H 6 ) dt = (k) (C 3 H 6 ) (ASA) moles/sec where ASA is the active surface area (cm 2 ) of the carbon measured by propylene chemisorption at 573 K, (C 3 H 6 ) is the concentration of propylene in moles/cm 3 , and k is the specific reaction rate constant having a value of 10 9.62 exp (−57 kcal/mole/RT) cm/sec. The carbon active surface greatly enhanced the rate of cracking of hydro-carbons to elemental carbon which was deposited directly on the surface. The carbon was found to deposit on the active sites and become new active sites. Thus, the carbon deposit replicated the active surface area and was autocatalytic.