Diffusion of phenolic compounds within high-silica MFI-type zeolite in the mesitylene solution

Abstract

Abstract The intracrystalline diffusivity of phenolic compounds (phenol, p-propylphenol and m-cresol) and toluene within silicalite-1 and MFI-type zeolite with Si/Al = 303 (H-MFI) in the liquid phase (solvent: mesitylene) in the temperature range from 313 to 353 K were measured by using the constant volumetric method. The amounts of phenol, p-propylphenol, and toluene adsorbed onto silicalite-1 at 313, 323 and 353 K were approximately the same, whereas less m-cresol was adsorbed because of its larger kinetic diameter. Unlike adsorbed toluene, adsorbed of phenol displayed stronger interactions in H-MFI than in silicalite-1, indicating that hydrogen bonding between the OH group of phenol and Bronsted acid sites in H-MFI enhanced the adsorption of phenol. Whereas the intracrystalline diffusivity of phenol, p-propylphenol, and toluene within silicalite-1 are approximately the same, m-cresol exhibited lower intracrystalline diffusivity, indicating that the intracrystalline diffusivity was governed by geometrical limitation. The intracrystalline diffusivity of phenol was lower within H-MFI with acid sites than within silicalite-1. The residence time of phenol on the acid sites became longer than that of toluene, which led to a difference in the intracrystalline diffusivity between phenol and toluene within H-MFI.