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Abstract Adsorption thermodynamics of N 2 and O 2 on two most commonly used zeolites (5A and Li-LSX) under plateau special conditions of wide ranges of temperature (238–298 K) and pressure (0–300 kPa) for pressure swing adsorption (PSA) oxygen production were studied based on molecular simulations and theoretical model fitting. Adsorption isotherms for each adsorbate-adsorbent pair at different temperatures were fitted by Langmuir, Freundlich and Sips models, obtaining equilibrium parameters including adsorption capacity, strength, heterogeneity and N 2 /O 2 selectivity. Thermodynamic parameters such as Gibb's free energy, enthalpy, and entropy changes were numerically derived, and isosteric adsorption heats and distributions of potential energy were simulated. The results suggest that the adsorption capacity and affinity follow the order of N 2 -Li-LSX > N 2 -5A > O 2 -5A > O 2 -Li-LSX, leading to higher N 2 /O 2 selectivity on Li-LSX compared to 5A. For Li-LSX, N 2 /O 2 selectivity increases significantly with temperature above 273 K due to the difference in adsorption thermodynamics of N 2 and O 2 varying with temperature in terms of different adsorption heterogeneities. For 5A, the homogeneous distributions of N 2 and O 2 as well as the wide scopes of affinities from Na+ and Ca2+ exhibit N 2 /O 2 selectivity with negligible temperature dependence, which is beneficial for stable oxygen production with a fixed PSA process under large day-and-night temperature difference. This study provides theoretical basis for obtaining an optimal balance between efficiency and stability of oxygen production by using a proper mixture of Li-LSX and 5A. Highlights • Adsorption equilibrium of N 2 and O 2 on zeolites at plateau conditions are obtained. • N 2 /O 2 selectivity is higher with greater temperature dependence on Li-LSX than on 5A. • Adsorption capacity and affinity follow the order of N 2 -Li-LSX > N 2 -5A > O 2 -5A > O 2 -Li-LSX. • Advantage of thermodynamic stability of 5A over wide temperature range is discussed. [ABSTRACT FROM AUTHOR]

Radial flow is an important type of flow direction for large-scale pressure swing adsorption (PSA) oxygen generation systems. In this study, a numerical simulation of a PSA oxygen generation process based on radial-flow adsorbers was performed with two-dimensional CFD modeling. The gas distribution, the maldistribution factor and the pressure difference were comparatively investigated at each flow type of the radial-flow adsorber. Considering the gas adsorption performance, the results indicated that the centripetal π-flow radial adsorber has the best flow characteristics for the PSA process. The oxygen purity distribution within the adsorption bed was studied to compare centripetal and centrifugal π-flows, and the former was shown to perform better on oxygen enrichment and adsorbent desorption. The steady state was achieved after eight cycles for the centripetal-π adsorber and each of the four steps of the PSA process was explored in detail to show the advantageous properties for oxygen generation in terms of adsorption and desorption. The relationships between the product flow rate and the oxygen purity and recovery were further investigated. [ABSTRACT FROM AUTHOR]

Pressure swing adsorption (PSA) is a suitable method to enrich the concentration of methane in coal mine methane (CMM) separation processes. However, traditional PSA processes for low-concentration CMM can easily increase the concentration of methane to explosive limits, which subsequently increases the risk of explosion. In this paper, a novel PSA process for low-concentration CMM was studied. Using a mixture of activated carbon (AC) and carbon molecular sieve (CMS) as the adsorbent, this method ensures that the gaseous mixture adsorbed does not reach the explosive limits by adsorbing methane and part of the oxygen simultaneously. Using a two-bed vacuum PSA experimental apparatus, the low-concentration CMM was safely enriched from 20% to more than 30%, with CMS and AC mass ratio of 3.4. The results of experimental studies indicate that the mixture adsorbent (AC and CMS) has explosion-suppression and flameproof characteristics. The igniting resource (methane) will not explode even if it appears in the adsorbent layer and, in addition, the explosion will not propagate through the adsorbent layer if it happens in other areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flexible improvement on PSA O 2 production at wide product flow rate range is studied. • Individual effects of process parameters on O 2 production performance are obtained. • Adjusted/unadjusted PSA experiments using appropriate valve settings are conducted. • Process improvement strategies for different product flow rate ranges are proposed. • Higher O 2 purity, recovery and productivity with lower energy consumption are gained. Improvement on oxygen (O 2) concentrator using pressure swing adsorption (PSA) technology according to variable product demands is of great significance, which, for instance, provides the key step for success in practical O 2 therapy for COVID-19 patients who need to be delivered with a wide product flow rate range (1–15 standard liter per minute (SLPM)) of medical O 2 (purity > 82%). This work studied the individual effects of major PSA process parameters on O 2 production performance at the product flow rate of 3.46–19.88 SLPM (0.64–3.68 SLPM per kilogram of adsorbent (SLPM/kg)), based on a self-designed two-bed PSA unit with a modified Skarstom cycle using Li-LSX zeolite adsorbents. The improvement strategies were accordingly proposed based upon influential mechanisms of each parameter: 1) at lower product flow rates (≤2.00 SLPM/kg), increasing the purge flow rate and decreasing the adsorption pressure to suppress excess O 2 adsorption, and decreasing the feed flow rate to ensure low energy consumption; 2) at higher product flow rates (≥2.00 SLPM/kg), decreasing the purge flow rate and increasing the adsorption pressure to eliminate N 2 breakthrough and O 2 -rich product waste, and appropriately increasing the feed flow rate to enhance cost-effectiveness. An improved set of parameters rendered O 2 purity (95.67–74.86%), recovery (11.28–49.05%), productivity (0.47–2.04 mmol/kg/s) increased by up to 3.52–20.08%, 0.36–20.47%, 6.82–19.61%, and energy consumption (4.07–0.95 kWh/kgO 2) decreased by up to 10.56–18.10%, in comparison to two conventional sets, respectively. The results are beneficial for developing intellectualized and flexibly-controlled O 2 concentrators for practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Distillation separation process is proposed to recover NO 2 and SO 2 from flue gases. • The feasibility of NO 2 /SO 2 distillation separation is theoretically verified. • A distillation process with advantageous dual-column liquid-phase feeding is designed. • Process optimization based on robust sensitivity analysis are demonstrated. • Significant economic benefits from the recovered NO 2 and SO 2 products are estimated. High-purity NO 2 and SO 2 have significant economic values and are widely used in many fields. The large amounts of NO 2 and SO 2 in industrial flue gases are worthy of recovery for environmental protection and economic benefits. In this work, a dual-column distillation separation process was proposed to further separate and upgrade NO 2 and SO 2 following a flue gas adsorption capture process. The feasibility of distillation separation of NO 2 /SO 2 from the desorbed gas, and the advantage of liquid-phase feeding way over gas-phase counterpart in terms of lower energy consumption (1286.39 kW) were demonstrated. Key process parameters such as the number of total stages, the feed stage number, the mole flow rate at bottom of column, the reflux ratio and operating pressure for the two columns (15, 6, 16.66 kmol/h, 0.16, 4 bar; 21, 10, 4.43 kmol/h, 0.50, 1 bar) were determined. Heat and mass transfers along the column height as well as the process robustness against feed composition fluctuation indicate its applicability for practical operation and adaptation to industrial needs. An economic analysis shows a significant annual revenue of 14,333.52 thousand USD based on high-purity (>99.5%) SO 2 and NO 2 products recovered from a typical scale (~1000,000 m3/h) of iron-ore sintering flue gas, not only offsetting the total operating cost of the entire adsorption capture-distillation recovery process but also generating net profit. [ABSTRACT FROM AUTHOR]

• Binary adsorption of N 2 and O 2 on FAU zeolites at plateau conditions is obtained. • Water interacting with zeolites via hydrogen bond competes with N 2 and O 2 adsorption. • Effect of water content is greater than that of temperature change on air separation. • Trade-off between N 2 /O 2 selectivity and performance stability is addressed. • X zeolite with Si/Al close to 1.5 is recommended for PSA O 2 production in plateau. Adsorption thermodynamics of N 2 and O 2 on faujasite (FAU) zeolites with different Si/Al molar ratios under plateau conditions of wide ranges of temperature and humidity for pressure swing adsorption (PSA) oxygen production were studied based on validated molecular simulations. Binary adsorption isotherms and N 2 /O 2 selectivity on each adsorbent were obtained. The results suggest that dehydrated feed air with very low dew point of 213 K could still lead to ~10 wt% water adsorption capacity in FAU zeolites. The effect of water content was larger than that of temperature change on N 2 /O 2 separation performance, causing reductions in N 2 /O 2 selectivity of 50.9% and affinities of 15.6% and 10.6% for N 2 and O 2 at 238 K, and those of 45.7%, 13.7% and 11.1% at 298 K on FAU-1.1, respectively. The strong interaction of water with zeolites via hydrogen bond was shown to decrease the pore volume by 25.61%, occupy the cationic sites, and thermodynamically form competitive adsorption over N 2 and O 2. The increase in Si/Al molar ratio suppressed the negative impact of water and temperature change but sacrificed the N 2 /O 2 selectivity. To reach an optimal balance between the air separation performance and the adsorbent robustness, X zeolites with Si/Al molar ratio close to 1.5 would be recommended for PSA O 2 production under the plateau special condition. [ABSTRACT FROM AUTHOR]