Adsorption equilibria and kinetics of ethane and ethylene on zeolite 13X pellets

Abstract

To establish a design basis of the cyclic adsorption process for ethylene purification, the adsorption equilibria and kinetics of ethane and ethylene on zeolite 13X pellets were measured by a volumetric method at 303–343 K under pressure up to 600 kPa. The Sips model showed better prediction of ethane in the full pressure range, but the dual-site Langmuir (DSL) model was more accurate for ethylene in the pressure range of <250 kPa. The strong cation-π interaction between ethylene and Na+ in zeolite 13X led to higher adsorption capacity and affinity than those of ethane. It resulted in a greater isosteric heat of adsorption (Qst) of ethylene at a low loading amount, while Qst variance in ethane was almost linearly increased with a dominant lateral interaction. At 303 K, the adsorption amount and affinity of ethylene at <5 kPa were slightly greater than those of propane but lower than those of propylene. However, the adsorption isotherms of ethane/ethylene became higher than those of propane/propylene above a certain pressure. The experimental uptake curves of ethane and ethylene were well predicted by a non-isothermal sorption model, considering the adsorption thermal effects. The difference in the apparent reciprocal diffusional time constant (Dapp/R2) between ethane and ethylene was mainly attributed to the thermal effects by the heat of adsorption. The comparison of Dapp/R2 values between zeolite 13X pellet and powder indicated that macropore diffusional resistance also contributed to the adsorption kinetics.