Kinetic Modeling of the Methanol to Olefins Process. 1. Model Formulation

Detailed kinetic models at the elementary step level have been formulated for the methanol to olefins (MTO) process over HZSM-5 catalyst with a Si/A1 ratio of 200. Starting from plausible mechanisms, the formation of primary products has been modeled rigorously by means of the Hougen−Watson formalism. The formation of higher olefins has been expressed in terms of carbenium ion mechanisms. A computer algorithm has been used to generate the reaction network. The rate coefficient of each elementary step has been formulated according to the single-event approach. The number of single events for each elementary step was calculated from the structure of the activated complex determined by quantum chemical calculations. Activation energies for each elementary step were obtained through the Evans−Polanyi relation that accounts for the various energy leve1s of carbenium ions and olefin isomers. The single-event kinetics combined with the Evans−Polanyi relation provides a tremendous reduction of the number of parameters to be estimated. Thermodynamic constraints further restrict the number of independent parameters to 33.