Construction of an ab initio kinetic model for industrial ethane pyrolysis

Abstract

The industrial steam cracking of ethane was simulated using an ab initio kinetic model. The reaction network consists of 20 species and 150 reversible elementary reactions. The thermodynamic and kinetic parameters were obtained from ab initio CBS-QB3 and W1U calculations and agree well with available experimental data. Predicted C₂H₆, C₂H₄, and H₂ yields are within 5% of experimental data for the three sets of conditions tested. Though CH₄ yields and outlet temperatures are particularly sensitive to the accuracy of the kinetic parameters, they are simulated with an accuracy of better than 10%. Larger deviations for the C₃H₆ and C₂H₂ yields are attributed to the limited size of the reaction network. The effect of total pressure on the rate coefficients was evaluated using Quantum Rice-Ramsberger-Kassel theory with the Modified Strong-Collision approximation, and was found to be relatively minor for the reaction conditions tested. This study hence demonstrates the feasibility of simulating complex radical reactions using a predictive kinetic model derived from state-of-the-art quantum chemical calculations. © 2010 American Institute of Chemical Engineers AIChE J, 2011