Adsorption/Desorption of Water and Ethanol on 3A Zeolite in Near-Adiabatic Fixed Bed

Abstract

A pilot scale adsorber apparatus was designed and constructed to investigate water and ethanol adsorption/desorption kinetics on 3A zeolite for the design purposes of a fuel ethanol dehydration pressure swing adsorption (PSA) process. Equilibrium studies have shown that 3A zeolite adsorbed a significant amount of water while very weak ethanol adsorption was observed. The breakthrough curves were utilized to study the effects of column pressure, temperature, flow rate, pellet size, and adsorbate concentration on the overall mass transfer resistance. Based on experimentally observed trends, both macropore and micropore diffusion were identified as relevant mass transfer mechanisms. A mathematical model for a bench scale adsorption bed included the linear driving force (LDF) adsorption rate model and the variation of axial velocity. A detailed heat transfer model was a necessity since the bed dynamics was affected by heat transfer in the bed wall. The model was used to analyze the experimental data and extract values of pertaining diffusion coefficients.