LiLSX Zeolite Research Articles

Mass and Heat Transfer of Pressure Swing Adsorption Oxygen Production Process with Small Adsorbent Particles

Rapid-cycle pressure swing adsorption (PSA) with small adsorbents particles is intended to improve mass transfer rate and productivity. However, the mass transfer mechanisms are changed with reduction of particle size during rapid-cycle adsorption process. A heat and mass transfer model of rapid-cycle PSA air separation process employing small LiLSX zeolite particles is developed and experimentally validated to numerically analyze the effects of mass transfer resistances on the characteristics of cyclic adsorption process. Multicomponent Langmuir model and linear driving force model are employed for characterizing the adsorption equilibrium and kinetic. The results of numerical analysis demonstrate that the dominant mass transfer resistance of small adsorbents particles is a combination of film resistance, axial dispersion effect and macropore diffusion resistance. The oxygen purity, recovery and productivity of the product are overestimated by ~2–4% when the effect of axial dispersion on mass transfer is ignored. As particle size decreases, the front of nitrogen-adsorbed concentration and gas temperature become sharp, which effectively improves the performance. However, the adverse effect of axial dispersion on the mass transfer becomes significant at very small particles conditions. It is nearly identical shapes of nitrogen concentration and gas temperature profiles after adsorption and desorption steps. The profiles are pushed forward near the production end with an increase in bed porosities. The optimal oxygen recovery and productivity are achieved with a particle diameter of 0.45 mm and bed porosity of 0.39 during the PSA process.

Isotherms and Kinetics Study for Adsorption of Nitrogen from Air using Zeolite Li-LSX to Produce Medical Oxygen

This research investigates the adsorption isotherm and adsorption kinetics of nitrogen from air using packed bed of Li-LSX zeolite to get medical oxygen. Experiments were carried out to estimate the produced oxygen purity under different operating conditions: input pressure of 0.5 – 2.5 bar, feed flow rate of air of 2 – 10 L.min-1 and packing height of 9-16 cm. The adsorption isotherm was studied at the best conditions of input pressure of 2.5 bar, the height of packing 16 cm, and flow rate 6 Lmin-1 at ambient temperature, at these conditions the highest purity of oxygen by this system 73.15 vol % of outlet gas was produced. Langmuir isotherm was the best models representing the experimental data., and the model parameters were the maximum monolayer coverage (qm) 200 mg. g-1 and Kl 0.00234 L.mg -1. Also, from the Freundlich isotherm model, the sorption intensity (n) indicated favorable sorption of 1.435. The average free energy estimated from the DRK isotherm model was 0.02 KJ.mol-1, which proved the adsorption process to follow physical nature. The results got from experiments showed a coincidence to the pseudo-first-order kinetic model.

Purification of hydrogen from natural gas/hydrogen pipeline mixtures

• A six-bed PSA cycle is proposed for the purification of hydrogen/natural gas mixture. • A three adsorbent layered bed is able to handle realistic natural gas mixtures. • High purity hydrogen (>99%) was obtained for hydrogen feed concentrations of 5–30%. • PSA compares well with an electrolyzer in providing hydrogen to a refueling station. There is an increasing global attention toward hydrogen as a green energy carrier, primarily because of the environmental concerns associated with global warming issues. It is expected that the produced hydrogen from various sources may be injected to the natural gas grid for economical transportation and use. One interesting option is to evaluate technologies for extracting the hydrogen from the natural gas pipeline for applications using high purity hydrogen. However, natural gas is a complex mixture including CH 4 , C 2 H 6 , CO 2 , N 2 and trace amounts of C 3 -C 6 hydrocarbons. This function requires a natural gas/hydrogen separation technology which must not only operate with low capital and energy cost, but must also provide hydrogen of sufficient purity. The goal of current work therefore was to take a mixture of hydrogen/natural gas of representative concentrations and produce high purity hydrogen using a bespoke pressure swing adsorption (PSA) cycle. A six-bed PSA system with 12 steps was developed and simulated in Aspen Adsorption software to this end. A three-layered adsorption column was designed to capture different groups of components of the mixture selectively within each layer. Informed by measured and literature equilibrium isotherm data, silica gel was chosen as the pre-layer to remove heavy hydrocarbon components and most of the CO 2 ; activated carbon in the main-layer to mainly adsorb methane, and LiLSX zeolite in the top-layer to remove trace nitrogen which had eluted from the earlier layers, for obtaining pure hydrogen product. High purity hydrogen product (>99%) with high recovery (>85%) was achieved with the PSA system for different hydrogen concentrations (5–30%) in the 30 bar feed stream. We also compared the PSA system against an electrolyzer generating hydrogen onsite. Our analysis suggests that the PSA competes favorably, even at a low hydrogen recovery of 40% in cases where the PSA plant is built at a pressure reduction station.

Dynamic ammonia adsorption by FAU zeolites to below 0.1 ppm for hydrogen energy applications

Hydrogen can be released from ammonia (NH3) by cracking, but the residual ammonia is harmful to polymer exchange membrane fuel cells and should be less than 0.1 ppm (μmol/mol). In this paper, the adsorption of NH3 by commercial faujasite (FAU) zeolites to below 0.1 ppm have been investigated. The results show that the Si/Al ratio of zeolite is inversely proportional to the adsorption capacity, and the strength of ammonia adsorption by cation Li+ is more than that of Na+, thus the ammonia adsorption capacity of LiLSX zeolite is greater than that of 13X–HP zeolite. However, the small granule size of crystalline microspheres and the rough surface of 13X–HP zeolite were the factors that lead to the dynamic NH3 adsorption capacity of 13X–HP zeolite close to LiLSX zeolite. In the dynamic 1700 ppm NH3 adsorption, with a breakthrough point of 0.1 ppm, the adsorption capacity is 9.27 wt% for LiLSX zeolite and 8.73 wt% for 13X–HP zeolite.

Flexible oxygen concentrators for medical applications

Medical oxygen concentrators (MOCs) are used for supplying medical grade oxygen to prevent hypoxemia-related complications related to COVID-19, chronic obstructive pulmonary disease (COPD), chronic bronchitis and pneumonia. MOCs often use a technology called pressure swing adsorption (PSA), which relies on nitrogen-selective adsorbents for producing oxygen from ambient air. MOCs are often designed for fixed product specifications, thereby limiting their use in meeting varying product specifications caused by a change in patient’s medical condition or activity. To address this limitation, we design and optimize flexible single-bed MOC systems that are capable of meeting varying product specification requirements. Specifically, we employ a simulation-based optimization framework for optimizing flexible PSA- and pressure vacuum swing adsorption (PVSA)-based MOC systems. Detailed optimization studies are performed to benchmark the performance limits of LiX, LiLSX and 5A zeolite adsorbents. The results indicate that LiLSX outperforms both LiX and 5A, and can produce 90% pure oxygen at 21.7 L/min. Moreover, the LiLSX-based flexible PVSA system can manufacture varying levels of oxygen purity and flow rate in the range 93–95.7% and 1–15 L/min, respectively. The flexible MOC technology paves way for transitioning to an envisioned cyber-physical system with real-time oxygen demand sensing and delivery for improved patient care.

Experimental study on oxygen concentrator with wide product flow rate range: individual parametric effect and process improvement strategy

Improvement on oxygen (O2) 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 O2 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 O2 (purity > 82%). This work studied the individual effects of major PSA process parameters on O2 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 O2 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 N2 breakthrough and O2-rich product waste, and appropriately increasing the feed flow rate to enhance cost-effectiveness. An improved set of parameters rendered O2 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/kgO2) 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 O2 concentrators for practical applications.

Experimental design of a "Snap-on" and standalone single-bed oxygen concentrator for medical applications.

A novel single-bed, “Snap-on” and standalone, medical oxygen concentrator design based on a rapid pressure swing adsorption process was investigated for continuous oxygen supply. The Snap-on concentrator design is easy to hook up to an existing compressed air source, and the unit can then be readily used to produce oxygen for medical applications. It is easily transportable and compared to a traditional oxygen concentrator with its dedicated compressor, the Snap-on concentrator is particularly relevant for the oxygen therapy needs of a larger number of patients in situations such as COVID-19. A commercially available LiLSX zeolite was used for the separation of oxygen from compressed ambient air. The experiments were performed at different feed air pressures using a constant supply of house air in the lab. Further, the device performance was also analyzed using a standalone medium size air compressor. The minimum bed size factor obtained with compressed house air was 100 lb/tons per day contained (TPDc) O2 at a cycle time of 7 s, whereas the minimum bed size factor obtained with a medium size air compressor weighing about 12 lbs was 210 lb/TPDc O2 at a cycle time of 14.5 s under the same feed pressures of 3.1 bar at an oxygen product purity of 90%. The product oxygen flow rate was nearly double for the same amount of adsorbent when using house air for the Snap-on design. The primary reason for this significantly higher oxygen production was the substantially higher and stable air throughput capacity of a typical house air compressor that enabled rapid cycling of the process at near-constant feed pressure compared to a medium size compressor used in a medical oxygen concentrator. The oxygen recovery was approximately 34% for both cases. Thus, the Snap-on oxygen concentrator was found to be easier to build and it delivered more oxygen for medical use compared to standalone units in locations where a constant supply of compressed feed air is available. This is typically the case in facilities such as hospitals, military medical camps and cruise ships. Further, the Snap-on design offers other benefits such as ease of transportation, higher reliability and lower weight.

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

To accurately describe the adsorption equilibria of N2 and O2 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.

Stability of Li-LSX Zeolite in the Catalytic Pyrolysis of Non-Treated and Acid Pre-Treated Isochrysis sp. Microalgae

This paper investigates the use of Li-LSX-zeolite catalyst over three regeneration cycles in presence of non-treated and acid pre-treated Isochrysis sp. microalgae. The spent and regenerated catalysts were characterised by surface analysis, elemental analysis (EA), SEM-EDS, and XRD to correlate their properties with the bio-oil yield and quality. The acid pre-treatment removed alkali metals, reducing gas yield in favour of bio-oil, but, at the same time, led to catalyst deactivation by fouling. Differently, the non-treated microalgae resulted in a bio-oil enriched in C and H and depleted in O, compared to the pre-treated ones, denoting higher deoxygenation activity. After 3 pyrolysis/regeneration cycles, the analyses suggest that there are no major changes on catalyst using non-treated microalgae. Regeneration at 700 °C has been shown to be able to remove most of the coke without damaging the Li-LSX zeolite structure. In summary, Li-LSX zeolite was effective in maintaining deoxygenation activity over three cycles in the pyrolysis of non-treated Isochrysis microalgae, while the algae pre-treatment with sulphuric acid was detrimental on the catalyst activity.

Effect of Li-LSX zeolite, NiCe/Al2O3 and NiCe/ZrO2 on the production of drop-in bio-fuels by pyrolysis and hydrotreating of Nannochloropsis and isochrysis microalgae

The purpose of this work was to investigate the viability of a microalgae catalytic pyrolysis/hydrotreating plant to kerosene, diesel and gasoline using Aspen Plus. A series of 2000 dry tonne per day scenarios were simulated with the final goal of determine the price in USD per litre of the drop-in fuels produced and the economic feasibility of the technique at a large-scale. Different scenarios (mechanical, solar and thermal drying), microalgae (Nannochloropsis and Isochrysis) and catalysts (Li-LSX zeolite, Ni-Ce/Al2O3, Ni-Ce/ZrO2). For this work, a systematic design approach by Douglas was considered and the whole process was actualised with the Marshall and Swift Cost Index of 2016. The lowest minimum fuel selling price (1.418 $/L) was found for Isochrysis and Li-LSX-zeolite. Finally, the sensitivity analysis showed that the bio-oil yield was the most influent factor, leading to a variation of the fuel price between 1.158 $/L to 1.751 $/L assuming a 20% of variation.The techno-economic assessment and sensitivity analysis indicated that Isochrysis and Li-LSX-zeolites are promising for the production of drop-in fuels, but further research is required to further reduce the price of the feedstock production and drying to be competitive with lignocellulosic materials.

Integrated VPSA Processes for Air Separation Based on Dual Reflux Configuration

A six-step, two-bed dual-reflux pressure swing adsorption process for air separation using LiLSX zeolite was first developed and studied systematically. Then two original integrated vacuum pressure...

Li-LSX-zeolite evaluation for post-combustion CO2 capture

Lithium low silica X type (Li-LSX) zeolite is typically used for industrial N2/O2 separation processes, but its potential as a carbon dioxide capture sorbent has not been fully evaluated yet. In this work, Li-LSX zeolite was investigated as CO2 sorbent under post- combustion conditions in TGA and Fixed-bed configurations. The maximum adsorption capacity and CO2/N2 selectivity were determined to be 4.43 mmol g−1 and 85.7 at 60 °C and in presence of 14% CO2, using a packed bed configuration. The CO2 and N2 adsorption capacity was decreased of 10 mol% when the initial calcination temperature was raised from 60 to 300 °C due to a decreased micropore surface. However, the high calcination temperature increased the CO2 selectivity to 128.1 and increased the adsorption rates due to enhanced basicity (1 order of magnitude) and external surface (+75 to 80%) in the Li-LSX zeolite.The sorption stability at 60 °C was found to be excellent during 85 sorption cycles over 35 h period with Li-LSX showing negligible difference in adsorption capacity throughout the cycles and a working capacity of 2.45 mmolCO2/g after an initial calcination at 550 °C (2 min) and cyclic adsorption at 60 °C (6 min) and desorption at 420 °C (5 min). The Avrami kinetic model shows the coexistence of different adsorption mechanisms. CO2 adsorption rate increased with the increasing CO2 partial pressure, as a result of the facilitated CO2 diffusion processes. Film diffusion was determined as the rate-limiting step for CO2 adsorption. Therefore, based on these findings, Li-LSX represents a promising sorbent for post-combustion carbon capture.

Optimization and analysis of the VPSA process for industrial-scale oxygen production

A two-bed, six-step vacuum pressure swing adsorption (VPSA) process using LiLSX zeolite for industrial-scale 80% oxygen production with rapid cycling was investigated by numerical simulation and optimization. keeping the structural parameters of the VPSA devices unchanged and ensuring the purity of oxygen never be lower than 80%, the operating variables were optimized to achieve the target of minimum power consumption and maximum yield, which can maximize the devices’ potential performance for various production requirements. In the case of minimum power consumption, after optimization, the minimum power consumption was reduced from 0.313 to 0.289 kWh Nm−3 O2, meanwhile, the productivity fell from 106.42 to 93.75 Nm3 h−1 ton−1. In the maximum productivity case, a high productivity of O2 was achieved (117.87 Nm3 h−1 ton−1) but the power consumption rose to 0.324 kWh Nm−3 O2. A subsequent detailed analysis was carried out to provide insights into these observations and compare the impact of the decision variables on the process performance.

Single-component structural correlation and self-diffusion of N2 and O2 through nanopores of Li-LSX zeolite: The role of temperature, loading, and Li-III cations

Diffusion-selective N2/O2 separation and competitive adsorption by nanoporous Li-LSX zeolite, as the best commercially available adsorbent, is a scientifically interesting phenomenon with important technological applications. In a recent paper (J. Phys. Chem. C 121, 2017, 1770–1780), we reported the first molecular dynamics (MD) study of the adsorption of the binary N2/O2 mixtures within this zeolite. In the present paper, the microscopic structure and intracrystalline self-diffusion coefficient of N2 and O2 as single-component guest species in Li-LSX zeolite are determined at different temperatures and practical loadings. The simulation results are found to be in very good complementary agreement with experimental adsorption findings as well as with the recent predictions based on the binary air mixture simulations. The influences of the internal surface dynamics of extra-framework Li+ cation in site III (Li-III) on the guest static and dynamic processes within the zeolite are determined. O2 has no significant association with Li-III, while all structural analyses prove remarkable adsorption and hence localization of N2 around the Li-III in the supercages. The degree of localization and the residence time of N2 on Li-III in particular increases with decreasing temperature and also with fixing of Li-III cations during the simulation. As a guide for future design of N2/O2 separation by zeolite frameworks at ambient temperature, an excellent adsorption selectivity ratio can be achieved if it is practically possible to reduce the dynamics of accessible Li-III sorption sites up to extremely fixed situations. The calculated Arrhenius activation energy for N2 diffusion process through Li-LSX zeolite is several times higher than that of O2. These results are due to the larger quadrupole moment of N2 and stronger Coulombic attraction between N2 and Li-III that causes the translational motion of N2 to be significantly hindered. Overall, the intracrystalline self-diffusion coefficients of both N2 and O2 slightly decrease with loading. Current simulations also correctly approve that the Li+ cations in sites I′ and II are inaccessible to interact with guest molecules.

Heats of adsorption on mixed-cation LiNa-LSX: Estimating SIII site occupancy by Li

Li-LSX (low silica type-X) zeolite is the sorbent of choice for air separation by adsorption today. Li-LSX is obtained by ion exchange of Na-LSX. The occupancy of Site III (SIII, which is the open site in the supercage) by Li+ is crucially important for N2 adsorption. In this work, mixed-cation LiNa-LSX zeolites were prepared and N2 adsorption isotherms were measured. The isosteric heats of adsorption of N2 were obtained from the temperature dependence. The heats of adsorption remained at approximately 17.7 kJ/mol (i.e., that for pure Na-LSX) at Li+ exchange below approximately 70%, and increased upon further increase in Li+ exchange, to 22.6 kJ/mol (i.e., that for pure Li-LSX). The increase was not linear (i.e., concave shaped), however, which indicated that one N2 molecule could likely adsorb on two adjacent cation sites. The relationship between heat of adsorption and Li ion occupancy on site SIII was obtained. It is suggested that this relationship may be used to estimate the occupancy by Li+ on SIII of faujasite type of zeolites.

Experiment and simulation study of a dual-reflux pressure swing adsorption process for separating N2/O2

Abstract A dual-reflux pressure swing adsorption (DR-PSA) process using LiLSX zeolite to produce both high purity and recovery of N 2 and O 2 from mimical air (21%O 2 /79%N 2 ) was developed in the commercial software, Aspen Adsorption. In this work, adsorption equilibrium isotherms of pure oxygen and nitrogen on LiLSX zeolite were firstly measured and fitted with the extended Langmuir model in order to describe the behavior of the static adsorption. A total of sixteen experiments were carried out on a laboratory scale DR-PSA apparatus for verifying the reliability of the mathematical model. Finally, an optimal operating condition was obtained by comparing the purity and recovery of products under different experimental conditions. Results revealed that feed or light reflux time (t FE/LR ), heavy reflux flow rate (Q HR ), vacuum pressure (P L ) and feed flow rate (Q F ) all had significant effects on the process performance. O 2 in light product could be enriched to 99.1% with recovery of 98.0% while N 2 in heavy product is 99.0% in concentration with recovery of 99.3% under the optimal experimental condition. All in all, the DR-PSA process could be capable of producing both heavy and light products simultaneously with high purity and recovery.

Tracing Experimentally Compatible Dynamical and Structural Behavior of Atmospheric N2/O2 Binary Mixtures within Nanoporous Li–LSX Zeolite: New Insights to Influence of Extra-Framework Cations by MD Simulations

Along with available adsorption isotherms and uptake kinetic data, microscopic knowledge of the guest self-diffusion and intracrystalline movement of the simple air binary mixture of nitrogen (N2) and oxygen (O2) within Li–LSX zeolite is needed to optimize the design and to reach a breakthrough high-efficiency of air separation process based on the selective adsorption in this zeolite. In the current work for the first time, an all-atom molecular dynamics (MD) simulation is used to study the average single-particle dynamics, self-diffusion, and microscopic structure of the atmospheric binary gaseous mixtures of N2 and O2 in Li–LSX zeolite at temperatures between (260 and 700) K. The common order of magnitude of the computed guest self-diffusion coefficients at different temperatures is in the range of 10–9 - 10–8 m2·s–1 and corresponding activation energies obtained using the Arrhenius equation varied in the range of ∼0.6 for O2 to 1.6–3.3 kcal·mol–1 for N2 in simulations with mobile and with fixed extra-...

Understanding the dynamics, self-diffusion, and microscopic structure of hydrogen inside the nanoporous Li-LSX zeolite

The dynamical and structural properties of hydrogen (H2) guest gas inside nanoporous Li-LSX zeolite were studied by molecular dynamics (MD) simulation for different loadings (8, 12, 16, and 20) of H2 per unit cell at temperatures of 200, 298, 400, and 500 K. Three equal mean-square displacement (MSD) components (in the x, y, and z-directions) for the center of mass of H2 guest molecules show that the translational motion of H2 in this zeolite medium is isotropic due to the high symmetry of the zeolite framework. At these conditions, H2 guest molecules freely move without blocking each other's path into the supercages and channels of the Li-LSX zeolite. The order of calculated self-diffusion coefficient of H2 guest molecules at different temperatures, in the range of 10−9 up to 10−7 m2 s−1, and corresponding activation energy, ∼2 kcal mol−1, followed using the Arrhenius equation is in good agreement with the pores size of Li-LSX zeolite (7.4–12 Å) and compatible with inter-region of well-known Knudsen and Configurational diffusion. The H2 self-diffusion coefficients increase with temperature, while showing no quantifiable changes with loading within this loading range. A further study with a broader guest loading range would be appropriate to fully understand the loading effect on the self-diffusion of H2 guest molecules in the Li-LSX zeolite as the H2 storage candidate. In addition to determining the temperature and loading effects on the H2 guest behavior, current simulations also show that the Li-III cations are specific H2 sorption sites and the structural correlation, dynamics, self-diffusion coefficient, and adsorption of H2 molecules are strongly dependent on the mobility or immobility of the key extraframework Li-III cationic sites of Li-LSX zeolite. The results of the simulation help in the choice of favorable structure, best design, and operative manufacture of zeolites or other microporous materials for similar applications.

Experimental Study of a Novel Rapid Pressure-Swing Adsorption Based Medical Oxygen Concentrator: Effect of the Adsorbent Selectivity of N2 over O2

It was experimentally demonstrated that the performance of a medical oxygen concentrator based on rapid pressure swing adsorption (RPSA) process using a LiLSX zeolite was improved [lower bed size factor (BSF) and higher oxygen recovery (RO)] when the adsorbent exhibited higher selectivity of adsorption of N2 over O2. The effects of N2 selectivity on BSF and RO as functions of the RPSA process cycle times were found to be complex and nonintuitive. The key properties of a LiLSX zeolite sample for adsorption of N2 and O2 (pure and binary gas isotherms, binary selectivity, pure gas isosteric heats, pure gas mass-transfer characteristics, and degrees of adsorbent heterogeneity), which exhibited a relatively higher selectivity of adsorption for N2 over O2 compared to a previously reported sample, were measured and used in this study.

Performance of a medical oxygen concentrator using rapid pressure swing adsorption process: Effect of feed air pressure

The effects of feed air pressure on the steady‐state performance of a medical oxygen concentrator (MOC) were experimentally evaluated using a novel design of a MOC unit which produced a continuous stream of ∼90% O2 employing a rapid pressure swing adsorption (RPSA) process scheme. Dry, CO2 free air containing ∼1% Ar at different feed gas pressures was used in the tests in conjunction with a commercial sample of LiLSX zeolite as the N2 selective adsorbent in the process. The bed size factor (BSF) can be systematically reduced by increasing the feed air pressure for any given total cycle time. The effect of feed air pressure on the oxygen recovery (R) is, however, more complex; it increases with increasing feed pressure only at longer cycle times while the effect is marginal at shorter cycle times. The BSF cannot be indefinitely reduced by lowering total process cycle time at any pressure—a minimum is exhibited in the BSF‐cycle time plot. The minimum value of the BSF decreases as the feed pressure is increased. The cycle time for the minimum BSF is, however, not significantly altered by the feed pressure in the data range of this work. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1212–1215, 2016