GOALI: A Fundamental Study of Hydrocarbon Cracking on Acidic Zeolites

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ABSTRACT Proposal Title: GOALI: A Fundamental Study of Hydrocarbon Cracking on Acidic Zeolites Proposal Number: CTS-9807333 Principal Investigators: Harold H. Kung, Jeffrey Miller and Randall Q. Snurr Institution: Northwestern University This GOALI proposal is a collaboration between Northwestern University (H. H. Kung and R. Q. Snurr) and Amoco Chemicals R&D (Jeffrey Miller). Its objective is the determination of the mechanisms responsible for the enhancement of catalytic cracking activity produced by the steam dealumination of HY zeolite. In the proposed model of catalytic cracking of alkanes, three reaction mechanisms are operative: monomolecular cracking involving a non-classical carbocation, bimolecular cracking involving hydride transfer and beta-scission, and oligomeric cracking involving alkylation, oligomerization, hydride transfer and beta-scission. While both the bimolecular and oligomeric cracking are strongly dependent on alkane partial pressure, the monomolecular cracking is strongly dependent on acidic strength, and the oligomeric cracking is diffusion limited. Experimentally, the dominant mechanism would be manifested in the product distribution, and could be controlled by the operating condition. Therefore, various possible causes of enhanced activity in dealuminated HY will be studied under conditions that correspond to a predetermined mechanism. The formation of new acid sites will be tested by means of the monomolecular cracking rate. The role of extra-framework Al will be determined by contrasting the rates of monomolecular and bimolecular-oligomeric cracking. The role of internal diffusion in mesopores and defects will be elucidated by contrasting monomolecular, bimolecular, and oligomeric rates. Also to be studied are the effects of selective poisoning of acid sites, e.g., Na; of zeolite type (Y, ZSM-5, ferrierite, mordenite); of adsorption heat contribution to apparent activation energy; of adsorption of reactant alkanes on the selectivity of c ompeting cracking reactions. The experimental adsorption study will be supported by theoretical calculations and simulations of binary adsorption isotherms.