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     

Comparative Perfomances of Two Commercial Samples of LiLSX Zeolite for Production of 90% Oxygen from Air by a Novel Rapid Pressure Swing Adsorption System

The performances of a novel rapid pressure swing adsorption system for continuous production of ? 90% O₂ from a compressed air feed were experimentally studied using two different samples of pelletized LiLSX zeolite. Bed size factor (BSF) and O₂ recovery (R) were compared as functions of total process cycle times. The optimum performance by the samples differed substantially—one exhibiting ? 30% smaller BSF and ? 6% higher R than the other, even though the adsorption isotherms and column dynamics for the pure gases were nearly identical. Column pressure drop during the desorption step was the cause.     

Anatomy of a rapid pressure swing adsorption process performance

A detailed numerical study of the individual and cumulative effects of various mass, heat, and momentum transfer resistances, which are generally present inside a practical adiabatic adsorber, on the overall separation performance of a rapid pressure swing adsorption (RPSA) process is performed for production of nearly pure helium gas from an equimolar binary (N₂ +He) gas mixture using 5 A zeolite. Column bed size factor (BSF) and helium recovery (R) from the feed gas are used to characterize the separation performances. All practical impediments like column pressure drop, finite gas‐solid mass and heat transfer resistances, mass and heat axial dispersions in the gas phase, and heats of ad(de)sorption causing nonisothermal operation have detrimental impacts on the overall process performance, which are significantly accentuated when the total cycle time of a RPSA process is small and the product gas helium purity is high. These impediments also prohibit indefinite lowering of BSF (desired performance) by decreasing process cycle time alone. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2008–2015, 2015     

A Pressure Swing Adsorption Process for Production of 23–50% Oxygen-Enriched Air

Abstract

A simple pressure swing adsorption process for direct production of low to medium purity (23–50%) O₂-enriched gas from ambient air is described. The process provides a high O₂ production capacity per unit amount of the adsorbent and a high O₂ recovery combined with a very low energy requirement for the separation. The performance of the process using three different air separation adsorbents is described.     

Efficient Cycle Recovery of Hydrogen from a Low Concentration Pyrolysis Gas Stream by Pressure Swing Adsorption – An Experimental Evaluation

Breakthrough curves, cycle mass balances, and cycle bed productivities (mg H₂ per gram of adsorbent) on three dual adsorbent amounts (g) of 2,892, 1,963, and 1,013 respectively each filling 200 cm, 135 cm, and 70 cm of a 5.0 cm internal diameter stainless steel pipe were performed. The approximate optimum (sludge pyrolysis) synthesis gas with composition in volume % of 45% H₂/35% CO/20% CH₄ was used as the feed gas with molecular sieve 5 Å and activated carbon as adsorbents. Impurity breakthroughs occurred at ～14.9, 12.3, and 5.0 minutes respectively for % cycle recoveries of 72.2, 65.0, and 60.2 using 2,892, 1,962, and 1,013 g of adsorbent respectively. Our results indicated that basing % recycle recovery on cycle bed productivity can enable efficient hydrogen recovery with savings on adsorbent amount. An optimum cycle bed productivity of 2.3 mg H₂/g of adsorbent corresponded to a cycle recovery of 66.2% for 2,300 g of adsorbent used. Only 1.7 mg H₂/g of adsorbent was obtained for a cycle recovery of 72.2% requiring up to 2,800 g of adsorbent. This makes economic sense in the pressure swing adsorption separation of hydrogen from traditionally low hydrogen concentration biomass sources.     

Production of argon free oxygen by adsorptive air separation on Ag‐ETS‐10

The purification of different components of air, such as oxygen, nitrogen, and argon, is an important industrial process. Pressure swing adsorption (PSA) is surpassing the traditional cryogenic distillation for many air separation applications, because of its lower energy consumption. Unfortunately, the oxygen product purity in an industrial PSA process is typically limited to 95% due to the presence of argon which always shows the same adsorption equilibrium properties as oxygen on most molecular sieves. Recent work investigating the adsorption of nitrogen, oxygen and argon on the surface of silver‐exchanged Engelhard Titanosilicate‐10 (ETS‐10), indicates that this molecular sieve is promising as an adsorbent capable of producing high‐purity oxygen. High‐purity oxygen (99.7+%) was generated using a bed of Ag‐ETS‐10 granules to separate air (78% N₂, 21% O₂, 1% Ar) at 25°C and 100 kPa, with an O₂ recovery rate greater than 30%. © 2012 American Institute of Chemical Engineers AIChE J, 59: 982–987, 2013     

Air‐promoted adsorptive desulfurization of diesel fuel over Ti‐Ce mixed metal oxides

Air‐promoted adsorptive desulfurization (ADS) of commercial diesel fuel over a Ti‐Ce mixed oxide adsorbent in a flow system is investigated in this work. The fresh/spent adsorbents were characterized using X‐ray absorption near edge structure spectroscopy. Results show that sulfoxide species are formed during air‐promoted ADS over Ti_0.9Ce_0.1O₂ adsorbent. Adsorption selectivity of various compounds in fuel follows the order of dibenzothiophene sulfone > dibenzothiophene ? benzothiophene > 4‐methyldibenzothiophene > 4,6‐dimethyldibenzothiophene > phenanthrene > methylnaphthalene > fluorene > naphthalene. The high adsorption affinity of sulfoxide/sulfone is attributed to stronger Ti‐OSR₂ than Ti‐SR₂ interactions, resulting in significantly enhanced ADS capacity. Adsorption affinity was calculated using ab initio methods. For Ti‐Ce mixed oxides, reduced surface sites lead to O‐vacancy sites for O₂ activation for oxidizing thiophenic species. Low temperature is preferred for air‐promoted ADS, and the Ti‐Ce adsorbent can be regenerated via oxidative air treatment. This study paves a new path of designing regenerable adsorbents. © 2014 American Institute of Chemical Engineers AIChE J, 61: 631–639, 2015     

Removal of trace quantities of co from H2 using temperature‐swing‐adsorption

A method for the removal of trace quantities (0.2 to 10 ppm) of carbon monoxide in commercial hydrogen using a temperature‐swing‐adsorption system with 0.5 wt% Pt/Al₂O₃, adsorbent has been investigated. The adsorbent could be regenerated by treatment with air at 200°C to 250°C or by treatment with hydrogen at 270°C. The breakthrough curves have been described by a model which considers both the external‐film resistance and the intraparticle diffusion resistance. The model has been validated at the high gas velocities expected in a commercial plant.     

Integrated adsorbent‐process optimization for carbon capture and concentration using vacuum swing adsorption cycles

A novel approach for integrated adsorbent and process design is proposed. The traditional pressure or vacuum swing adsorption (PSA) / vacuum swing adsorption (VSA) process optimization for chosen objectives, where operating conditions are the decision variables, and CO₂ purity and recovery are constraints, is expanded to include adsorbent isotherm characteristics as additional decision variables. Two VSA cycles, namely a four‐step process¹, currently known to have the lowest energy consumption for CO₂ capture and concentration (CCC), and a six‐step process², recently proven to have a wider operating window for the evacuation pressure, have been investigated in the current study. The integrated optimization results simultaneously provide the lower bound of minimum energy and upper bound of maximum productivity for CCC achievable from the two VSA processes along with the operating conditions and the corresponding isotherm shapes necessary to achieve them. It may be viewed as an enabler for adsorbent design or expedient adsorbent search by process inversion. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2987–2995, 2017     

Separation of COCO2N2 gas mixture for high-purity CO by pressure swing adsorption

A pressure swing adsorption (PSA) process for separating CO from a COCO₂N₂ mixture is proposed. The adsorbent used in this process is active carbon supported copper, which has been developed by this laboratory. By cycling the pressure of a bed of this adsorbent between ambient pressure and 20–30 Torr at room temperature, high purity CO can be obtained from the COCO₂N₂ gas mixture with a high recovery. The CO product purity depends crucially on the step of CO cocurrent purge after adsorption in the cycle and the regeneration of sorbent.     

Performance of iron-incorporated A-type zeolites for O2/N2 separation from air by pressure swing adsorption

The performance of various metal ion-exchanged A-type zeolites and metal-incorporated A-type zeolites for O₂ and N₂ adsorption was studied to provide a pressure swing adsorption (PSA) process. Metal-incorporated A-type zeolites adsorbed N₂ in larger quantities than metal ion-exchanged A-type zeolites. Compared with Na-A zeolite, both Cu-incorporated and Ni-incorporated A-type zeolites adsorbed larger quantities of N₂. The incorporation of Cu or Ni enlarged the pore size of the zeolite, while Fe incorporation reduced it. However, the adsorption volume ratio of O₂ to N₂ could be increased to as high as 4.2 on Fe-incorporated A-type zeolite calcined at 750°C, which was the highest value among the samples tested. The amount of adsorption of O₂ was 38.0 ml g⁻¹, which was comparable with ordinary Na-A zeolite. The Fe incorporation markedly improved the performance of ordinary Na-A zeolite in O₂/N₂ separation. Therefore, Fe-incorporated A-type zeolite has a high potential as a good adsorbent for pressure swing adsorption in O₂/N₂ separation from air.     

连续循环式吸附空气取水系统

引　言随着社会的发展,人类的活动范围越来越大.在海岛、沙漠等缺少淡水资源的地区,解决饮用水成为人们在这些地区进行活动的先决条件.空气中的水蒸气含量大、不受空间的限制、可循环再生,因此空气取水是解决这些地区饮用水的渠道之一.空气取水可以采用吸附式空气取水方式,目前     

Efficiency of Nitrogen Desorption from LiX Zeolite by Rapid Oxygen Purge in a Pancake Adsorber

A nonequilibrium, nonisothermal, nonisobaric model was used for numerical simulation of the efficiency of N₂ desorption from a LiX zeolite column by rapid purge with O₂ in a pancake adsorber. The key parameters included desorption time, adsorbent particle size, and the adsorber length to diameter ratio. The efficiency was found to be a complex function of these variables.     

Comparative performance of an adiabatic and a nonadiabatic PSA process for bulk gas separation—a numerical simulation

A detailed numerical model of a Skarstrom‐like PSA process is used to investigate the separation performance of an adiabatic and a nonadiabatic process for removal of bulk CO₂ impurity from inert He. The complexity of the gas phase adsorbate composition, adsorbate loading, and the adsorbent temperature profiles as functions of positions inside an adsorber at the start and end of each step of the PSA process are discussed. The separation performance of a nonadiabatic PSA process is generally inferior to that of the corresponding adiabatic process. Smaller adsorbent column diameter accentuates nonadiabatic operation and hence lower separation efficiency. Furthermore, the separation efficiency decreases more rapidly at short cycle times and smaller column diameters. Insulation of PSA columns of a process development unit operated under these conditions is recommended for reliable data analysis. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4066–4078, 2017     

Cycle synthesis and optimization of a VSA process for postcombustion CO2 capture

A systematic analysis of several vacuum swing adsorption (VSA) cycles with Zeochem zeolite 13X as the adsorbent to capture CO₂ from dry, flue gas containing 15% CO₂ in N₂ is reported. Full optimization of the analyzed VSA cycles using genetic algorithm has been performed to obtain purity‐recovery and energy‐productivity Pareto fronts. These cycles are assessed for their ability to produce high‐purity CO₂ at high recovery. Configurations satisfying 90% purity‐recovery constraints are ranked according to their energy‐productivity Pareto fronts. It is shown that a 4‐step VSA cycle with light product pressurization gives the minimum energy penalty of 131 kWh/tonne CO₂ captured at a productivity of 0.57 mol CO₂/m³ adsorbent/s. The minimum energy consumption required to achieve 95 and 97% purities, both at 90% recoveries, are 154 and 186 kWh/tonne CO₂ captured, respectively. For the proposed cycle, it is shown that significant increase in productivity can be achieved with a marginal increase in energy consumption. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4735–4748, 2013     

CO2 capture from dry flue gas by vacuum swing adsorption: A pilot plant study

The capture and concentration of CO₂ from a dry flue gas by vacuum swing adsorption (VSA) has been experimentally demonstrated in a pilot plant. The pilot plant has the provision for using two coupled columns that are each packed with approximately 41 kg of Zeochem zeolite 13X. Breakthrough experiments were first carried out by perturbing a N₂ saturated bed with 15% CO₂ and 85% N₂ feed, which is representative of a dry flue gas from coal‐fired power plants. The breakthrough results showed long plateaus in temperature profiles confirming a near adiabatic behavior. In the process study, a basic four‐step vacuum swing adsorption (VSA) cycle comprising the following steps: pressurization with feed, adsorption, forward blowdown, and reverse evacuation was investigated first. In the absence of any coupling among the steps, a single bed was used. With this cycle configuration, CO₂ was concentrated to 95.9 ± 1% with a recovery of 86.4 ± 5.6%. To improve the process performance, a four‐step cycle with light product pressurization (LPP) using two beds was investigated. This cycle was able to achieve 94.8 ± 1% purity and 89.7 ± 5.6% recovery. The Department of Energy requirements are 95% purity and 90% recovery. The proposed underlying physics of performance improvement of the four‐step cycle with LPP has also been experimentally validated. The pilot plant results were then used for detailed validation of a one‐dimensional, nonisothermal, and nonisobaric model. Both transient profiles of various measured variables and cyclic steady state performance results were compared with the model predictions, and they were in good agreement. The energy consumptions in the pilot plant experiments were 339–583 ± 36.7 kWh tonne^?1 CO₂ captured and they were significantly different from the theoretical power consumptions obtained from isentropic compression calculations. The productivities were 0.87–1.4 ± 0.07 tonne CO₂ m^?3 adsorbent day^?1. The results from our pilot plant were also compared with available results from other pilot plant studies on CO₂ capture from flue gas. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1830–1842, 2014     

π型向心径向流吸附器变质量流动特性研究

对径向流吸附器内变压吸附(PSA)制氧的变质量流动规律进行研究,有助于准确掌握吸附过程及床层内的变量因素对制氧性能的影响。对π型向心径向流吸附器建立气固耦合的两相吸附模型,并对其PSA制氧过程进行了数值模拟研究,得到了床层内氧气浓度分布、温度分布以及产品气浓度的变化规律。结果表明：首次循环结束时床层内氧气最高摩尔分数可达66.02%,回收率29.2%。非稳定循环期间,氧气摩尔分数从66.02%升高至 97.5%,回收率从29.2%提高至38.5%。循环达到稳定后,床层内氧气摩尔分数最高可达98.6%,回收率38.9%左右,且达到稳定状态后床层内气固两相温差减小,逐渐达到热平衡。获得了吸附器内部气体与吸附剂两相间的传质、传热过程,为π型向心径向流吸附器用于PSA制氧提供技术支持。     

Removal of Cr(VI) from aqueous solution using amino‐modified Fe3O4–SiO2–chitosan magnetic microspheres with high acid resistance and adsorption capacity

A novel, bioadsorbent material of polyethylenimine‐modified magnetic chitosan microspheres enwrapping magnetic silica nanoparticles (Fe₃O₄–SiO₂–CTS‐PEI) was prepared under relatively mild conditions. The characterization results indicated that the adsorbent exhibited high acid resistance and magnetic responsiveness. The Fe₃O₄ loss of the adsorbent was measured as 0.09% after immersion in pH 2.0 water for 24 h, and the saturated magnetization was 11.7 emu/g. The introduction of PEI obviously improved the adsorption capacity of Cr(VI) onto the adsorbent by approximately 2.5 times. The adsorption isotherms and kinetics preferably fit the Langmuir model and the pseudo‐second‐order model. The maximum adsorption capacity was determined as 236.4 mg/g at 25°C, which was much improved compared to other magnetic chitosan materials, and the equilibrium was reached within 60 to 120 min. The obtained thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. Furthermore, the Cr(VI)‐adsorbed adsorbent could be effectively regenerated using a 0.1 mol/L NaOH solution, and the adsorbent showed a good reusability. Due to the properties of good acid resistance, strong magnetic responsiveness, high adsorption capacity, and relatively rapid adsorption rate, the Fe₃O₄–SiO₂–CTS‐PEI microspheres have a potential use in Cr(VI) removal from acidic wastewater. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43078.     

Axial pressure gradients during the pressurization and depressurization steps of a PSA gas separation cycle

An experimental investigation of the pressurization and depressurization of a column packed with an activated carbon adsorbent reveals that for He, Ar and N₂ the dynamics of column filling and exhaustion can be explained by coupling the equation of Darcy describing flow in a packed tube with a differential material balance over an element of the packed tube. However, when CO₂ is admitted to or exhausted from the same packed column, the pressure dynamics can only be explained by taking into account the finite rate of adsorption of CO₂ onto the adsorbent. It appears that mass transfer limitation controls both pressurization and depressurization, and it is interesting to note that the adsorption rate process is very much faster than that of desorption. Such events as described become important for short cycle pressure swing adsorption (PSA) operations.     

Thermal dissociation of compressed ZnO and SnO2 powders in a moving‐front solar thermochemical reactor

The high‐temperature thermal dissociation reaction of ZnO and SnO₂ was investigated, as part of a two‐step thermochemical water‐splitting cycle for H₂ production. A lab‐scale solar reactor (1 kW) was designed, built, and operated for continuous dissociation of volatile oxides under reduced pressure. In this reactor, compressed oxide powders placed in a vertical ceramic cavity are irradiated by highly concentrated solar energy. The reactor design allows moving the reaction front for achieving continuous reactant feeding. ZnO and SnO₂ thermal dissociations were successfully performed at about 1900 K, with the recovery of up to 50% of products as nanopowders with high specific surface area (in the range 20–60 m²/g) and with mass fractions of reduced species up to 48 wt % for Zn and 72 wt % for SnO. The performed O₂ measurements confirmed the kinetics of ZnO dissociation and gave an activation energy of 380 ± 16 kJ/mol, based on an ablation regime of the ZnO surface. © 2010 American Institute of Chemical Engineers AIChE J, 2011