Experimental Measurement of Pure and Mixed-Gas Kinetics of Ethylene and Ethane Adsorption onto Mordenite, Zeolite 13X, and ZJU-74a: Insights into the Value of Single- vs Mixed-Gas Kinetics, Validity of IAST and Sips Isotherm Models, and Temperature/Pressure Relationships for Process Modeling

Adsorption processes can be appliedto the separationof alkane/alkenemixtures. Process modeling is a key tool used to assess if the operatingand capital cost of these processes can compete with the industrystandard (e.g., cryogenic distillation for ethylene/ethane). Theseprocess models rely on experimental adsorbent data, which, due tosimplicity, is typically gathered using only pure gases at equilibriumconditions. Gas separations are fundamentally mixed-gas processes,raising the following question: is equilibrium pure gas adsorptiondata suitable to predict mixed-gas separation performance? To answerthis, our work provides process modeling data sets for ethylene andethane on Mordenite, Zeolite 13X, and ZJU-74a and illustrates thatpure gas kinetic measurements are sufficient to predict mixed-gasbehavior and provides caution on relying on equilibrium conditionspredicted by the ideal adsorbed solution theory (IAST) and extended-Sipsmethods. Using a modification of the volumetric method for measuringadsorption, we report pure gas kinetics as a function of temperature(20-80 degrees C) and pressure (<100 kPa) for the adsorptionof ethylene and ethane onto Mordenite, Zeolite 13X, and ZJU-74a tosupplement isotherms and aid in process modeling. At 293 K, the pseudo-second-orderadsorption rate constants of ethylene and ethane, respectively, onMordenite (4.2 and 2.0 kg center dot mol(-1)center dot s(-1)) and Zeolite 13X (6.4 and 10 kg center dot mol(-1)center dot s(-1)) increase with increasing pore size,whereas ZJU-74a (4.9 and 6.6 kg center dot mol(-1)center dot s(-1)) does not. Only Mordenite exhibited kinetic selectivity(3.2), with the ratio of rate constants for Zeolite 13X and ZJU-74anear unity, suggesting that process models of Zeolite 13X and ZJU-74awill not benefit from considering kinetics. Rate constants of allmaterials follow an Arrhenius trend with temperature, and the effectof pressure was within measurement error and considered negligible,allowing for simple implementation of these results into process models.Additionally, we show that the extended-Sips isotherm and IAST methodsfor predicting binary equilibria from pure isotherms perform poorlyat predicting the equilibrium condition observed in mixed-gas kineticexperiments.