Kinetic modeling and prediction of the deactivation mechanism in zeolite-catalyzed alkylation of isobutane with 2-butene

In the present work, the kinetic modeling of the liquid phase alkylation of isobutane with 2-butene over a faujasite (FAU) zeolite was performed. Since under liquid phase conditions the alkylation reaction is severely diffusion limited, effects of diffusion on the rate of reaction and deactivation pathways were considered. By implementing morem appropriate assumptions in comparison with previous investigations, an attempt was made in order to properly model the catalyst deactivation in a mixed reactor. Accordingly, spatial variation of diffusivity in the pores of the catalyst wasconsidered as a function of time on stream. The obtained profiles of intrapellet butene concentration and point activity implied that at later stages of conversion drop, a transition from individual site poisoning into pore mouth plugging mechanism might occur. It was also found that the assumption of the shell progressive mechanism was not valid during the earlier stages of the deactivation. Furthermore, the values of the reactio and deactivation rate constants, as well as the diffusivity in the poisoned region of the pores were determined through fitting and sensitivity analysis of theestimated parameters were performed. Results revealed that the diffusivity in the poisoned region of the pores had a pronounced effect on the deactivation behavior of the catalyst.

Keywords:

Isobutane alkylation , Catalyst deactivation , Kinetics , Modeling , Zeolites