(63c) Kinetic Modeling and Reaction Pathways of C2 to C7 Olefin Transformation over an H-ZSM-5 Catalyst

The interconversion reactions of olefins on zeolite catalysts are important in many petrochemical processes such as, e.g., catalytic naphtha cracking or in methanol downstream processes for the production of light olefins such as the MTO or MTP processes [1, 2]. Due to the complexity of the reaction mechanism and a high number of involved components it still remains challenging to establish reliable kinetic models suitable for process design, particularly in terms of applicability for reactor optimization purposes.

This work aims at kinetic modelling based on extensive own experimental measurement data. We propose a novel reaction network scheme for the interconversion reactions of the olefins including cracking, oligomerization and disproportionation reactions. Additionally, a reaction kinetic model for the formation of side products has been developed based on a new mechanism to precisely describe the hydrogen transfer reactions.

Reaction kinetics of C2 to C7 olefin cracking over a commercial H-ZSM-5 catalyst were studied in detail using a Berty-type reactor. The reactor concept allows for gradient free kinetic measurements and therefore is an excellent choice to establish intrinsic reaction kinetic models.

To investigate the behavior of olefins, dosing of pure (individual) olefins as well as different olefin mixtures was performed over a wide range of conversion. The structure of the reaction mechanism of olefin cracking was systematically analyzed to identify the best suitable model, taking into account both, the reaction network and the reaction kinetic model approach. The numerical regression of the kinetic parameters was carried out using state-of-the-art solvers. The formation of side products was analyzed in detail using a custom-made gas chromatograph which was capable of separating and analyzing more than 100 hydrocarbon species. Based on this high degree of information for the product distribution, a new reaction mechanism for modeling the hydrogen transfer reactions has been proposed in this work. Considered side products include paraffins, naphthenes, cycloolefins and BTX aromatics.

1. Liu, D., et al., Inter-conversion of light olefins on ZSM-5 in catalytic naphtha cracking condition. Catalysis Today, 2014. 226: p. 52-66.
2. Huang, X., D. Aihemaitijiang, and W.-D. Xiao, Reaction pathway and kinetics of C3–C7 olefin transformation over high-silicon HZSM-5 zeolite at 400–490°C. Chemical Engineering Journal, 2015. 280: p. 222-232.