Stable oxygen-selective sorbents for air separation

Commercial sorption-based air separation is usually done using nitrogen selective zeolites in pressure swing adsorption (PSA) systems. Separation of air by adsorption of less abundant oxygen is more desirable. In this study we have developed some stable oxygen selective sorbents with silver and cerium salts. AgCl, AgBr, AgI and CeCl₃ all showed stable adsorption characteristics with pure component selectivity of O₂/N₂∼2.0-3.0 at 1 atm. For these salts heat of adsorption of oxygen was found to be slightly higher than that of nitrogen, which was also predicted by ab initio molecular orbital calculations by Chen and Yang (Ind. Eng. Chem. Res. 35 (1996) 4020). The adsorption capacity of these salts was increased by thermal dispersion on high surface area SiO₂ support. AgBr thermally spread on SiO₂ is the best sorbent obtained in this study. AgBr/SiO₂ (1.0 g/g) showed a pure component oxygen selectivity of ∼3 at 1 atm and ∼5 at 7 atm. PSA simulations were used to show the feasibility of nitrogen production using AgBr/SiO₂.