Catalytic cracking of alkanes on FAU: Single-event microkinetic modeling including acidity descriptors

Abstract

Single-event microkinetic (SEMK) modeling is applied to catalytic cracking of 2,2,4-trimethylpentane on a series of faujasites with Si/Al ratio ranging from 2.6 to 30. Standard activation entropies of the various elementary reaction families are calculated a priori from transition state theory and statistical thermodynamics, while activation energies are estimated on a reference faujasite by regression to experimental kinetic data. The SEMK model is then extended with two acidity descriptors. The concentration of active sites is available from independent NH₃-TPD measurements, while the change in standard protonation enthalpy, relative to the reference faujasite, is obtained by regression to experimental kinetic data. The latter parameter accounts for the effect of the zeolite average acid strength both on the stability of the intermediates and on the activation energies of the protonation and protolytic scission reactions. For these five commercially available faujasites, a variation in standard protonation enthalpy of 29 kJ mol⁻¹ was found. © 2012 American Institute of Chemical Engineers AIChE J, 2012