Abstract
A kinetic model for the olefins synthesis from dimethyl ether on zeolite HZSM-5 based catalysts is developed. The model includes the reaction pathways for the synthesis of olefins from oxygenates in the olefinic and aromatic cycles according to modern concepts of the dual-cycle reaction mechanism. The kinetic parameters were determined for the time-stable hydrothermally treated catalysts of various activities Mg-HZSM-5/Al2O3, HZSM-5/Al2O3, and Zr-HZSM-5/Al2O3. The kinetic parameters determination and the solution of the ordinary differential equations system were carried out in the Python software environment. The preliminary estimation of the kinetic parameters was carried out using the Levenberg-Marquardt algorithm, and the parameters were refined using the genetic algorithm. It is shown that reactions activation energies for different catalysts are close, which indicates that the priority of the reaction paths on the studied catalysts is the same. Thus, the topology of the zeolite plays a leading role in the determination of the synthesis routes, rather than the nature of the modifying metal. The developed model fits the experimental data obtained in an isothermal reactor in the range of temperature 320–360 °C, specified contact time 0.1–3.6 h*gcat/gC with a relative error of less than 15%.
Highlights
Since the 2000s, the proposed models include some features of the mechanism, but to minimize the number of defined kinetic parameters, authors still use the generalization method: combine in a single lump oxygenates, C2 –C4 lower olefins introduce a large number of formal reactions, ignore adsorption effects, and depart from the thermodynamic definition of equilibrium constants [12,13,14,15,16,17,18]
We have developed a lumping kinetic model that reflects the main routes of the dual-cycle mechanism
We have shown that the developed model can be used to describe the kinetics on a series of catalysts based on HZSM-5 zeolite
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Since the 2000s, the proposed models include some features of the mechanism, but to minimize the number of defined kinetic parameters, authors still use the generalization method: combine in a single lump oxygenates, C2 –C4 lower olefins introduce a large number of formal reactions (e.g., direct formation of higher olefins from oxygenates), ignore adsorption effects, and depart from the thermodynamic definition of equilibrium constants [12,13,14,15,16,17,18]. We have developed a lumping kinetic model that reflects the main routes of the dual-cycle mechanism. This model does not contain formal reactions. We have shown that the developed model can be used to describe the kinetics on a series of catalysts based on HZSM-5 zeolite
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