Adsorption, diffusion and reaction in FCC catalysts

This dissertation offers a new perspective into the fundamental mechanisms of catalytic cracking. Adsorption and diffusion are studied under reaction conditions similar to those of fluid catalytic cracking; an approach advancing the study of adsorption and diffusion of reactants on zeolitic catalysts. This method surpasses traditional studies done at lower temperatures with lower reactivity zeolites.; Experiments are performed in a CREC riser simulator using FCC catalysts of different crystallite sizes. Catalyst characterization is done at different stages of the catalyst preparation process using several surface science techniques.; The complex composition of heavy gas oil feedstock and the multitude of reaction pathways have limited previous attempts to model fluid catalytic cracking. The demand for more detailed kinetic information motivates the use of pure components to first clarify the dominant pathways and mechanisms, and then determine the associated rate parameters.; Catalytic cracking reactions of various model compounds are performed, and distribution of products is reviewed considering potential shape-selectivity effects. Catalytic and thermal runs allow the development of heterogeneous kinetic models while assessing intrinsic kinetic constants, adsorption, and diffusional parameters. Different operating conditions are applied and their simultaneous effects on adsorption, reaction, and diffusion are discussed. In addition, adsorption constants and heats of adsorption remain unchanged throughout the reaction time. The formation of coke does not hinder adsorption, although it significantly affects the reactivity of model compounds.; Heterogeneous models for the catalytic cracking of gas oil are proposed and implemented in computational fluid dynamic simulations of a typical FCC unit. Differences in fluid dynamics and catalytic conversion of gas oil are indicated by comparing a homogeneous and a heterogeneous model. This comparison shows that lower values of gas-phase velocity are predicted by heterogeneous models, translating to longer gas-phase residence time in the reactor and deeper catalytic cracking of gas oil.