Adsorption/Desorption Studies of 224-Trimethylpentane in β-Zeolite and Mesoporous Materials Using a Tapered Element Oscillating Microbalance (TEOM)

The facile desorption of C-8 and heavier products from solid acid alkylation catalysts is essential to thwart catalyst deactivation by fouling. To better understand this phenomenon, a tapered element oscillating microbalance (TEOM) was employed to investigate the adsorption/desorption characteristics of 224-trimethylpentane (224-TMP), a proxy C-8 alkylate product, on beta-zeolite and mesoporous materials (T = 298-473 K, P224-TMP = 0-0.3 bar) It is found that the 224-TMP desorption rates from saturated beta-zeolite (by helium purging) are characterized by a rapid initial burst of 224-TMP followed by a rather long desorption phase. Complementary experimental and modeling investigations using pelletized beta-zeolites of known sizes indicate that the adsorption rate and initial desorption (during the burst phase) rate of 224-TMP are controlled by meso-/macropore diffusion resistance external to the beta-zeolite crystals and that the long transient could be due to pore diffusion resistance within the beta-zeolite crystals. In contrast, mesoporous silica materials provide facile pore accessibility for large alkylate molecules such as 224-TMP, as evidenced by complete desorption of 224-TMP even at mild temperatures These insights provide guidance for rational engineering of stable solid acid alkylation catalysts