Driving forces for adsorption of polyols onto zeolites from aqueous solutions

Adsorption isotherms have been developed for C₂-C₆ diols and triols on small (FER), medium (MWW, MFI, BEA) and large (MOR, FAU) pore zeolites as well as on ordered mesoporous materials (MCM-36, 3DOm-MFI, and SBA-15) using gravimetry. Henry's constants for diol and triol adsorption on Silicalite-1 increase exponentially with carbon number demonstrating that confinement of the adsorbate in the zeolite pores is the primary driving force for adsorption. This conclusion is supported by results for propylene glycol adsorption at low coverages on materials differing in topology and chemical composition; it is shown that adsorption decreases with an increase in the adsorbent pore size and lines out to an asymptotic value for mesoporous and large pore zeolitic materials and that aluminum content only has a marginal effect. This study provides evidence that polyol adsorption is primarily a function of dispersion forces and this research will have an impact on the separation and catalytic conversion of oxygenates in the processing of biomass to chemicals and fuels.