A Thermodynamic Model for Pure and Binary Adsorption Equilibria of N₂ and O₂ on Lithium-Exchanged Low Silicon-to-Aluminum Ratio X Zeolite

Abstract

To accurately describe the adsorption equilibria of N 2 and O 2 on LiLSX zeolite in the design of air separation by pressure swing adsorption, an applicable model (aNRTL−RAST) was developed. It was based on the real adsorbed solution theory (RAST) in which the activity coefficient was calculated by the nonrandom two-liquid theory (aNRTL). The binary adsorbate− adsorbate interaction parameters of the aNRTL theory were estimated from the pure component isotherms. The aNRTL−RAST model was used to predict the mixed gas equilibrium data under different adsorption conditions and compared with the extended Langmuir (E-L), two-dimensional equation of state (2D-EOS), and ideal adsorbed solution (IAST) models. aNRTL−RAST showed better accuracy than the other models, and the average errors for different adsorption conditions were <5%. Therefore, this model can be used to predict the adsorption equilibrium of mixed gases, avoiding complicated and tedious experiments. This study provides a theoretical basis for the selection of oxygen adsorbents for the separation process design of industrial air separation.

An Upper Bound Visualization of Design Trade‐Offs in Adsorbent Materials for Gas Separations: CO2, N2, CH4, H2, O2, Xe, Kr, and Ar Adsorbents

“…These adsorbent materials are exchanged low silica type X (LSX) Zeolites, specifically Li-exchanged variants which are used industrially (1.3,6.9,-18.5), [127] (1.1,8.5,-26), [128] (1.4,5.8,-21) [129] and (0.8,4.4,-17). [130] Silver, calcium, and strontium-exchanged LSX zeolites also perform well: Ag 3.0 Ca 46.5 -LSX (1.7,6.6,-30), Ag 2.0 Ca 47 -LSX (1.7,4.6,-33) and Ag 3.0 Sr 46.5 -LSX (1.4,4.4,-25). [129] Molecular simulations suggest the reason for this exceptional performance is due to the higher quadrupole moment of nitrogen versus oxygen and the polarizability of the alkali cations promoting interactions at strengths on par with van der Waals interactions.…”

“…These adsorbent materials are exchanged low silica type X (LSX) Zeolites, specifically Li‐exchanged variants which are used industrially (1.3,6.9,‐18.5), [ 127 ] (1.1,8.5,‐26), [ 128 ] (1.4,5.8,‐21) [ 129 ] and (0.8,4.4,‐17). [ 130 ] Silver, calcium, and strontium‐exchanged LSX zeolites also perform well: Ag 3.0 Ca 46.5 ‐LSX (1.7,6.6,‐30), Ag 2.0 Ca 47 ‐LSX (1.7,4.6,‐33) and Ag 3.0 Sr 46.5 ‐LSX (1.4,4.4,‐25). [ 129 ]…”

A short review on recent advances in porous adsorbents for separation of oxygen from atmospheric air

“…Li et al 40 studied the pure N 2 and O 2 adsorption over Li‐LSX zeolite. The adsorption capacity of N 2 was 0.82 and 2.15mmol/g at 1 and 7 bar at 20°C, respectively; and adsorption capacity of O 2 was 0.18 and 0.91 mmol/g under the same conditions, that is, at 1 and 7 bar at 20°C, respectively.…”

“…Adsorption isotherms of N 2 , O 2 , Ar for (a) Li‐LSX 40 (b) AgLi‐LSX at 25°C 1 , and (c) Ag‐ETS‐10 at 30°C 67 …”

Equilibrium Adsorption of Nitrogen, Oxygen, and Argon on Silver-Exchanged Hierarchical ETS-10

“…Several porous adsorbents have been attempted for O 2 separation from air, including Li-exchange low-silica X zeolite (LSX; Si/Al ≈ 1.0), , Ca-LSX, LiCa-LSX, Sr-LSX, and LiSr-LSX . Li et al evaluated the adsorption capacity of Li-LSX for pure N 2 and O 2 . 0.82 and 2.15 mmol g –1 of N 2 adsorption capacity were reported at 1 and 7 bar at 20 °C, respectively; 0.18 and 0.91 mmol g –1 adsorption capacities of O 2 were reported for the same conditions, i.e., at 1 and 7 bar at 20 °C.…”