Role of rare earth cations in Y zeolite for hydrocarbon cracking

A FCC unit is the main fuel processing refinery unit that produces olefins. With the addition of rare earth (RE) cations on Y zeolite, refiners manipulate the product mix during cracking and change the olefin-paraffin selectivity. Fundamentally, the rate of the hydride transfer-beta-scission cycle determines to a large extent the olefinicity of the products. The critical role of RE cations in catalytic cracking was studied using isobutane cracking as the model reaction at low temperatures (523-573 K), while simultaneously feeding small controlled amounts (100-400 ppm) of isobutene. Hydride transfer rates depended exponentially on Brønsted acid site density, and thus composite activation energies for these reactions had a linear relationship with site density. Rare earth cations ensure the retention of high Brønsted acid site density under hydrothermal conditions. Therefore, hydride transfer reaction rates were high in the presence of RE cations and led to higher yields of less olefinic gasoline during FCC. This is an abstract of a paper presented at the 229th ACS National Meeting (San Diego, CA 3/13-17/2005).

VIVO