A hydrogen inhibition model of carbon deposition from light hydrocarbons

Carbon depositions from ethene, ethine, propene, butadiene and benzene were studied in a flow reactor at a temperature of 1000 degrees C, constant hydrocarbon partial pressures and increasing hydrogen partial pressures. Analogous studies with methane were performed at 1100 degrees C. Carbon deposition rates and corresponding compositions of the gas phase were determined. In the case of the C-2- to C-6-hydrocarbons the deposition rates are decreased by hydrogen addition, but the influence on the gas phase compositions is less significant. Hydrogen inhibition of carbon deposition is very sensitive as to the carbon/hydrogen ratio in the case of light, linear hydrocarbons, and the molecular structure if light, linear hydrocarbons are compared with aromatic hydrocarbons. It can be described by a strongly simplified heterogeneous inhibition model. The model exhibits a physico-chemical meaning in the case of ethene, propene and butadiene. In the case of methane the gas phase composition changes by hydrogen addition; nevertheless, hydrogen inhibition of carbon deposition from this hydrocarbon as well as that from ethine and benzene is perfectly described by the model in a formal manner. (C) 2000 Elsevier Science Ltd. All rights reserved.