Process modeling and optimization of vacuum pressure swing adsorption for ethane and ethylene separation using Cu(Qc)2 MOF

The separation of ethylene from ethane/ethylene mixtures is of prime significance, and replacing the energyintensive cryogenic distillation used in the petrochemical industry is challenging. The aim of this study is to separate ethane and ethylene using a vacuum pressure swing adsorption (VPSA) process on a Cu(Qc)2 metal-organic framework (MOF) synthesized as a spheroidal adsorbent. To quantify the adsorption equilibrium, single isotherms of ethane and ethylene were measured at 283 and 298 K up to 5 bar. A Quadratic Langmuir adsorption model was employed to predict equilibrium adsorption. Dynamic adsorption experiments were conducted for a single-component and a binary mixture of different feed compositions and flow rates. The mass-transfer coefficients of ethane and ethylene were estimated to be 0.1 sec-1 and 1.0 sec-1, respectively. Based on these parameters, a two-bed, five-step VPSA mathematical model was developed, and the nominal operating conditions were determined from the length of the unused bed. It showed ethylene purity, recovery, and productivity of 99.68 mol%, 65.28%, and 1.84 mol/kg/hr. Sensitivity analyses of purity and recovery were performed using six critical operating variables. The time and rate of the rinse step had the most significant influence on the results, followed by those of the PU, AD and BLW steps. The particle swarm optimization methodology was applied to optimize the operating variables to maximize ethylene recovery. After optimization, the ethylene purity, recovery, and productivity were attained at 99.60 mol%, 76.57%, and 1.98 mol/kg/hr.