Zeolites are solid acid catalysts currently of use in many industrial chemical processes. A major challenge to zeolite catalysis is the design of catalysts with improved lifetime. As we will show for the alkylation reaction, catalyst lifetime is tuned by choice of reaction conditions, selection of zeolite microporous structure and catalyst acidity. The alkylation reaction produces gasoline from the reaction of isobutane with light alkene molecules. There is need to develop improved heterogenous catalysts for this process that currently is catalyzed by hazardous liquid acids.

Microkinetic simulations are presented that relate kinetics to zeolite structure, and composition. They use as input  DFT quantum-chemical elementary reaction rate constants. The microkinetic equations are solved as a function of time. Reaction initiation, quasi-steady state and deactivation regimes are distinguished.

Furthermore we will introduce a coarse graining approach to microkinetics that enables to relate deactivation times with dimensionless parameters that are functions of elementary reaction rate constants and reaction conditions. The coarse graining approach transforms microkinetic equations into macroscopic chemical engineering kinetic equations. The form of these equations varies with reaction time regime.

We will study the difference in deactivation times in a Continuous Stirred Tank Reactor (CSTR) and Plug Flow Reactor (PFR) respectively.

Simulations show that optimum catalyst functionality for the alkylation reaction requires that the zeolite has micropores with diameter larger than composed of  10 ring Al/Si tetrahedra. Proton affinity has to be high with a deprotonation energy less than 1100 kJ/mol. Catalyst deactivation time in CSTR increases logarithmically with proton concentration. Minimum proton catalyst concentration for long life can be calculated from expressions that depend on deactivating alkene oligomerization reaction rate and reaction rate of alkylation, that critically depends on hydride transfer rate.

Compared to PFR deactivation time in CSTR is longer by two orders of magnitude. Catalyst deactivation of the immobile reaction zone in PFR becomes independent of proton concentration when this exceeds a minimum value. Then conversion of alkene in the alkylation reaction is complete. Proton concentration is a function of catalyst bed length, contact time and reaction rate of alkylation under this condition.

As we will illustrate, kinetics simulations are a useful optimization tool to resolve conflicting structure and composition requirements with respect to different catalyst functionalities.