Adsorption behavior of molecular sieve 3 Å and silica gel for CO₂ separation: equilibrium, breakthrough and mass transfer zone

Abstract

In this study, two types of adsorbents, Molecular sieve 3 Å and Silica gel 8–20 mesh were used for CO₂ separation from CO₂/N₂ mixture in a fixed bed column. The impact of the temperature, superficial velocity and CO₂ partial pressure on the breakthrough behavior, adsorption capacity and mass transfer zone has been thoroughly investigated. The breakpoint time declined with increased temperature, and maximal breakthrough period of 870 s was attained at a temperature of 30 °C using molecular sieve 3 Å, which is significantly higher than that obtained for Silica gel 8–20 mesh. Furthermore, the width of the mass transfer zone (MTZ) increases with reduced bed temperatures, which signifies the extent of utilization of bed capacity at the breakpoint. The breakpoint time increases with reduced superficial velocity, and the prolonged breakthrough time was achieved at a minimal superficial velocity of 0.026 m/s for MS 3 Å. The adsorption capacity reduced considerably with elevated temperature, and the maximal adsorption capacity of 903.8 mmol CO₂/Kg adsorbent was determined at a temperature of 30 °C for MS 3 Å. The capacity increases considerably with increased feed superficial velocity, and the capacities of 792 mmol CO₂/Kg and 152.9 mmol/Kg adsorbent were achieved for MS 3 Å and SG 8–20 mesh, respectively, at a constant superficial velocity of 0.042 m/s. The capacity increases considerably with increased partial pressure of the CO₂, and an adsorption capacity of 894.7 mmol CO₂/Kg adsorbent was acquired with an equilibrium partial pressure of 0.4 bars utilizing MS 3 Å. An adsorption capacity of 167.84 mmol/Kg adsorbent was evaluated at a partial pressure of 0.40 bars by controlling the temperature at 30 °C for SG 8–20 mesh. Owing to its remarkably higher capacity, the MS 3 Å adsorbent can be economically utilized for separation of CO₂ from CO₂/N₂ mixture.