Producing oxygen with purity higher than 95.0% from atmospheric air (78.0% N2, 21.0% O2, and 1.0% Ar) is challenging because of the similar physical properties of oxygen and argon. Silver-exchanged titanosilicates have shown the potential to separate these gases based on their thermodynamic affinities. In this study, various vacuum swing adsorption (VSA) cycle configurations including the simple Skarstrom cycle and more complicated 6-step VSA cycles were simulated using mathematical models to maximize O2 purity and recovery. The simulations were verified by conducting simple 3-step and Skarstrom VSA cycle experiments. A mixture of 95.0%/5.0% O2/Ar feed was considered in the simulations, and a rigorous multiobjective optimization was conducted to maximize O2 purity and recovery. The simulations predicted 27.3% recovery for a product with 99.5% purity for a 6-step cycle with pressure equalization and light product pressurization steps. The recovery for the same level of purity was improved significantly to 91.7% by implementing a heavy product pressurization step. The effect of bed length on O2 purity and recovery and the comparison of VSA with pressure swing adsorption and pressure–​vacuum swing adsorption for high-purity O2 production were also investigated. Rigorous multiobjective optimizations were conducted to maximize oxygen productivity and minimize energy consumption of the VSA cycles, while meeting different purity constraints, and significant improvement in the performance indicators was obtained through process optimization.

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High-purity (>99.5%) O2 production from air with silver-exchanged titanosilicates (Ag-ETS-10) using multiple single- and dual-stage vacuum swing adsorption (VSA) cycle configurations was investigated through process simulation, and optimization. Model predictions for the Skarstrom cycle were validated through experiments and an O2 purity of 98.3 ± 0.5% with a corresponding recovery of 10.6% was achieved. Oxygen purity-recovery Pareto fronts for the Skarstrom cycle and 6-step cycle with pressure equalization (PE) and heavy product pressurization (HPP) with dry air as the feed were obtained. The optimization predicted 82.0% O2 recovery with a product purity of 99.5% for a 6-step cycle with PE and HPP and dry air feed stream. The effect of nitrogen content in the feed on the performance indicators was also studied. Operating conditions for various cycle configurations were optimized through nondominated sorting genetic algorithm technique to achieve low total energy consumption (592.4 kWh/tonne O2) and high overall productivity (1.30 tonne O2/m3 Ag-ETS-10 day). The Pareto fronts of the single- and dual-stage configurations were compared against each other in order to choose the best possible design. The results indicated that the single-stage 6-step cycle with PE and HPP presents a better performance compared to the other single- and dual-stage approaches. A simple graphical scheduling study was also conducted in order to calculate the number of columns required for a continuous process using the better performing configurations.

Breakthrough curves of N 2 , O 2 , and Ar on Silver exchanged titanosilicates (Ag-ETS-10) extrudates and granules were measured using a laboratory scale dynamic column breakthrough (DCB) apparatus. In order to investigate the dynamics of the mass transfer, effect of flow rate, temperature and pressure on the composition and temperature curves were studied. In a separate attempt, N 2 breakthrough curves on two columns filled with Ag-ETS-10 extrudates and granules with two different sizes were obtained. Influence of axial-dispersion, macropore, and film resistance within the column was investigated using fundamentals of mass transfer and fluid dynamics which assisted in classifying the dynamics of this separation. The experimental results indicated the rapid mass transfer and the potential for rapid cycles using Ag-ETS-10 for high-purity O 2 production. A fully predictive mathematical model was shown to describe the experimental curves to a high level of precision. Keywords Breakthrough experiment • Oxygen purification • Air separation • Titanosilicates Abbreviations b Parameter in Langmuir isotherm (m 3 mol −1) b 0 Parameter in Langmuir isotherm (m 3 mol −1) c Fluid phase concentration (mol m −3) C pa Specific heat capacity of the adsorbed phase (J mol −1 K −1) C pg Specific heat capacity of the gas phase (J mol −1 K −1) C ps Specific heat capacity of the adsorbent (J kg −1 K −1) C pw Specific heat capacity of the column wall (J kg −1 K −1) d Parameter in dual-site Langmuir isotherm (m 3 mol −1

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