ADSORPTION/DESORPTION STUDIES ON SOLID ACID ALKYLATION CATALYSTS USING A TAPERED ELEMENT OSCILLATING MICROBALANCE (TEOM)

Abstract

Developing economically viable solid acid catalyzed alkylation processes continues to be a grand challenge. Economic and environmental impact assessments of a solid acid/CO2 alkylation process indicate that the solid acid catalyst must be at least four times more active than SiO2-supported Nafion while providing > 80% C 80% C8 alkylates selectivity for the process to be economically viable. A tapered element oscillating microbalance (TEOM) was used to elucidate for the first time the adsorption/desorption characteristics of alkylation reactants and products on promising large-pore beta- and USY-zeolites. A deeper understanding of the limitations of this instrument was gained for diffusivity measurements using large-pore zeolites with small crystal sizes. The desorption rates of 2,2,4-trimethylpentane (224-TMP, the desired alkylate product) from beta-zeolite by helium purging are extremely slow and discontinuous in nature. The significant buildup of 224-TMP causes significant mass transport limitations inside the beta-zeolite pores and will eventually lead to catalyst deactivation by fouling.