(72d) Adsorption/Desorption Studies of Isobutane in Beta-Zeolite

In developing stable and durable solid acid catalysts for 1-butene+isobutane alkylation, reliable understanding of the adsorption and desorption rates of reactants and products in catalysts is essential to screen potential solid acid catalysts. Toward this end, we are currently investigating the adsorption/desorption phenomena of model compounds (olefins and paraffins) on various solid acid catalysts and supports. Complementary theoretical models are implemented to reliably interpret the experimental data and obtain fundamental parameters. Adsorption and desorption rates of isobutane in beta-zeolite have been experimentally investigated by using a tapered element oscillating microbalance (TEOM) which provides excellent sensitivity, allowing mass changes as little as 10 µg to be detected. Experimental isotherms for isobutane adsorption in beta-zeolite are presented and discussed. At 50 °C and isobutane partial pressure of 0.045 bar in He, the desorption process is much slower than the adsorption process implying that adsorption and desorption occur in the nonlinear region of the isotherm. In contrast, at 100 °C, the desorption is much faster and is complete in about 40-50 seconds at even higher partial pressure (0.4 bar). In general, lower temperatures and higher isobutane partial pressures result in slower desorption rates and therefore adversely affect pore accessibility by other reactants and products. A GCMC (Grand Canonical Monte Carlo) simulation program has been employed to understand the relationship between molecular-level structure and observable macroscopic properties in this adsorption system.