Analysis of gas phase compounds in chemical vapor deposition of carbon from light hydrocarbons

Product distributions in the pyrolysis of ethylene, acetylene, and propylene are studied to obtain an experimental database for a detailed kinetic modeling of gas phase reactions in chemical vapor deposition of carbon from these light hydrocarbons. Experiments were performed with a vertical flow reactor at 900 °C and pressures from 2 to 15 kPa. Gas phase components were analyzed by both on-line and off-line gas chromatography. More than 40 compounds from hydrogen to coronene were identified and quantitatively determined as a function of the residence time varied up to 1.6 s. Product recoveries were generally more than 90%. Analysis of the kinetics of the conversion of the hydrocarbons resulted in global reaction orders of 1.2 (ethylene), 2.7 (acetylene), and 1.5 (propylene). First order dehydrogenation reactions and third order trimerization reactions leading to benzene are decisive reactions for ethylene and acetylene, respectively. Conversion of propylene should also be based on two simultaneous reactions, a first order dissociation reaction, and second order reactions such as bimolecular reaction of propylene resulting an allyl and a propyl radical. These insights should be useful to develop a reaction mechanism based on elementary reactions in forthcoming studies.