Selective Electrophilic Substitution of Halogens into Alkyl-Aromatics using ZSM-5

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9321392 Lund This is a study of the zeolite ZSM-5 as a catalyst for the chlorination of toluene. Of the three possible monochlorination products, p-chlorotoluene is the most valuable; in other reactions involving alkylaromatics, ZSM-5 is selective for formation of the para isomer. In this work, a form of ZSM-5 in which iron cations are present in ion-exchange positions of the zeolite is used. The first (chronologically) objective of the study is to determine whether the catalyst deactivates under reaction conditions, and if so, to measure the severity of the deactivation and determine its origin. The second objective is to probe the active site using sorption capacity and selectivity, Mossbauer spectroscopy, infrared spectroscopy of adsorbed species, transmission electron microscopy, acidity measurements, chemical analysis, ion exchange, and other techniques. Catalysts are prepared with various degrees of dehydration, location of iron, and silicon/aluminum ratios. Reactor studies are performed to measure catalytic activity and selectivity. The third objective is to develop a mechanistic microkinetic model of the reaction kinetics from steady-state and transient kinetics measurements and temperature-programmed desorption data. The performance of ZSM-5 is compared quantitatively to that of conventional Lewis-acid catalysts. Chlorinations and related aromatic substitution reactions are widely used in chemical manufacturing. They are presently done using relatively large amounts of inexpensive (and not very active) catalysts that create large amounts of solid waste that is now recognized to be an environmental problem. This work aims to replace such processes with ones that employ small amounts of more active catalysts that are relatively benign environmentally. ***