H2 Adsorption Isotherms Research Articles

Pure Hydrogen and Methane Permeation in Carbon-Based Nanoporous Membranes: Adsorption Isotherms and Permeation Experiments.

This paper presents the results of adsorption and permeation experiments of hydrogen and methane at elevated temperatures on a carbon-based nanoporous membrane material provided by Fraunhofer IKTS. The adsorption of pure components was measured between 90 °C and 120°C and pressures up to 45 bar. The Langmuir adsorption isotherm shows the best fit for all data points. Compared to available adsorption isotherms of H2 and CH4 on carbon, the adsorption on the investigated nanoporous carbon structures is significantly lower. Single-component permeation experiments were conducted on membranes at temperatures up to 220 °C. After combining the experimental results with a Maxwell-Stefan surface diffusion model, Maxwell-Stefan surface diffusion coefficients Dis were calculated. The calculated values are in line with an empirical model and thus can be used in future multi-component modeling approaches in order to better analyze and design a membrane system. The published adsorption data fill a gap in the available adsorption data for CH4 and H2.

H2 adsorption isotherms of Mg-MOF-74 isoreticulars: An integrated approach utilizing a thermochemical model and density functional theory

A thermochemical model was developed to calculate the H2 adsorption isotherm of theoriginal Mg-MOF-74 framework, and its computationally designed isoreticular employing the adsorption energies and vibrational frequencies obtained from density functional theory calculations as input variables. The model reasonably replicates the experimental adsorption isotherm of the original framework at -196oC within the pressure range up to 1 bar. The strongest adsorption site of the new Mg-MOF-74 isoreticular exhibits saturation at lower pressure compared to the original one, despite a lower adsorption energy. This emphasizes the importance of vibrational, rotational, and translational contributions for comprehensively assessing the site’s adsorption performance. Because only the strongest adsorption site was taken into account for the site-site interaction, the model is only valid for low coverage rates of secondary sites. Consequently, it strongly overestimates the hydrogen uptake of the original isoreticular at higher temperature and pressure ranges where the cumulative coverage rate of the secondary adsorption sites is comparable to that of the strongest sites. In contrast, the model remains valid for the new isoreticular at a specific temperature between -40oC and 60oC within the pressure range up to 25 bar where the coverage rate of the secondary adsorption site is low. Its predictions highlights the significantly improved performance of the new framework compared to the original framework. Specially, it achieves a gravimetric hydrogen uptake value between 2.8 wt% and 1.9 wt% at a pressure of 25 bar within the mentioned temperature swing which is substantially higher than that of the original framework.

Gaussian process regression for prediction of hydrogen adsorption temperature–pressure dependence curves in metal–organic frameworks

A Gaussian Process Regression (GPR) model was proposed for high-throughput prediction of H2 adsorption isotherms of MOFs at varied temperatures based on classical density functional theory (cDFT) calculations. First, hydrogen adsorption isotherms of 17,644 selected orthorhombic MOFs from 324,426 hypothetical structures at different teperatures were calculated using the cDFT method, while 3- parameter or 4-parameter Langmuir equations were employed to fit those isotherm data and obtain the optimized isotherm parameters of each MOF. Second, the 3-parameter and 4-parameter targeted GPR models were established and trained using seven geometrical features of each MOF as inputs. It was found that our trained GPR models can accurately predict the hydrogen adsorption capacities of MOFs within the range of continuous temperature and pressure variations. Finally, the transferability of our GPR model was further discussed by three different strategies including hydrogen adsorption isotherm validations of unseen MOFs, the experimental MOFs, and the seen MOFs at the extended temperatures, respectively. It was shown that our GPR model exhibits high-performance in predicting hydrogen adsorption isotherms of unseen 306,782 hypothetical MOFs or those of seen hypothetical MOFs at the extended temperatures (258 K and 358 K). The GPR-predicted hydrogen adsorption isotherms of the randomly selected 4 different MOFs from 17,644 orthorhombic MOFs are also good agreement with those calculated by the cDFT method. However, there is still much room for improvement in the prediction accuracy for experimental MOFs such as ZIF-8 and IRMOF-1. The GPR model developed in this work, based on cDFT calculations, will help to advance the design and screening of MOFs for hydrogen separation processes of industrial importance.

Computer-aided design of high-connectivity covalent organic frameworks as CH4/H2 adsorption and separation media

Six novel borophosphonate cube (–B4P4O12–) based covalent organic frameworks (BP-COFs) with high-connectivity have been computationally designed and proposed as CH4/H2 adsorption and separation media. The structural characterization reflects that six BP-COFs own high porosity, low density, applicable pore size, large pore volume and accessible surface area which are beneficial to gas adsorption. The adsorption isotherms for H2 at 77 K and 298 K and for CH4 at 298 K were obtained with grand canonical Monte Carlo (GCMC) simulations. The results reveal that BP-COF-10, -11 and −12 possess the higher CH4 and H2 adsorption capacity versus BP-COF-7, -8 and -9. The CH4/H2 adsorption separation simulation indicated that BP-COF-7, -8 and -9 owns the better CH4/H2 selectivity than BP-COF-10, -11 and −12 at 298 K. It is excited that both CH4/H2 adsorption capacity and selectivity of six BP-COFs are comparable to porous materials owing excellent gas adsorption and separation capacity. We expect this study may motivate researchers’ efforts to develop new high-performance gas adsorption/separation material.

High Efficiency of Na- and Ca-Exchanged Chabazites in D2/H2 Separation by Quantum Sieving

Quantum sieving is a promising approach for separation of hydrogen isotopes using porous solids as sorbents at cryogenic temperatures (<77 K). In the present work, we characterized the properties of two aluminum-rich chabazites: Na-CHA and Ca-CHA (Si/Al = 2.1). The single-gas D2 and H2 adsorption isotherms were measured, and the thermodynamic selectivities were determined through coadsorption experiments in the temperature range 38-77 K. We found that at 38 K, Na-CHA shows a selectivity of 25.8 at a loading of 10.6 mmol·g-1. At the same temperature, Ca-CHA has slightly lower selectivity (18.3), but its uptake (12.9 mmol·g-1) is higher than that for Na-CHA. Comparison with the literature shows that the obtained values of selectivity are among the highest reported so far. This property combined with robustness and availability on the industrial scale of Al-rich chabazites makes them very promising materials for separation of hydrogen isotopes by quantum sieving.

Application of the Dubinin–Radushkevich–Astakhov equation to calculate gases isotherms on zeolite adsorbents (on example of H2, CO2, CO, CH4, N2 adsorption on 13X and 5A)

ABSTRACT The paper demonstrates the prospects of using an approach for calculating adsorption isotherms of gases on micropore industrial zeolites based on the example of H2, CO2, CO, CH4, N2 adsorption on 13X and 5A zeolites using the Dubinin–Radushkevich–Astakhov (DRA) equation. Experimental adsorption isotherms of H2, CO2, CO, CH4, N2 gases on 13X and 5A zeolites of various manufacturers have been obtained, as well as ranges of the limiting adsorption volume and characteristic adsorption energy have been established. It made it possible to correctly calculate isotherms using the DRA equation in the temperature range 293–323 K and pressure range 0–30 atm. The paper proposes and solves the optimization problem of determining affinity coefficients, which allows the calculation of gas adsorption isotherms on zeolites using only one experimental isotherm of standard gas N2. The mismatch between the experimental isotherms and those calculated by the DRA equation is 14.69% for H2 (maximum) and 1.81% for CO2 (minimum). This approach makes it possible to significantly reduce the number of necessary expensive experiments in comparison with the traditional approach (using the Langmuir equations or equations derived from it), at the same time providing acceptable accuracy for practice.

In silico screening and experimental study of anion-pillared metal-organic frameworks for hydrogen isotope separation

Deuterium is a key energy source for fusion reaction and widely used in various application fields. Nevertheless, the separation of deuterium from its isotopic mixture with nearly same physicochemical properties is one of the greatest challenging tasks in industry. Compared with cryogenic distillation, quantum sieving effect based on nanoporous materials has been proposed as a promising strategy for isotopes separation, in which metal-organic frameworks (MOFs) are considered as an ideal platform because of their structural diversity and tailorable functionality. In this work, high-throughput molecular simulations were performed to identify optimal structural features of high-performance materials from a recently-constructed database of anion-pillared MOFs. As a proof-of-concept, the identified material SIFSIX-18-Cd was prepared using a proposed direct mixing method, which can achieve a goal of quickly preparation of such material on a large scale. The experimental pure-component adsorption isotherms of D2 and H2 confirmed the preferential adsorption of SIFSIX-18-Cd for D2 over H2 due to the quantum sieving effect. The advanced cryogenic thermal desorption spectroscopy (ACTDS) measurements further showed that the enrichment factor (EF) of an equimolar D2/H2 mixture in SIFSIX-18-Cd can reach 5.1 at 30 K and 1.0 bar, which is higher than the current cryogenic distillation method (1.5 at 24 K). Along with the proposed efficient preparation method, the high hydrophobic property of SIFSIX-18-Cd also demonstrated a broad industrial prospect of this material for hydrogen isotope separation.

Modulated self-assembly of an interpenetrated MIL-53 Sc metal–organic framework with excellent volumetric H2 storage and working capacity

To achieve optimal performance in gas storage and delivery applications, metal–organic frameworks (MOFs) must combine high gravimetric and volumetric capacities. One potential route to balancing high pore volume with suitable crystal density is interpenetration, where identical nets sit within the void space of one another. Herein, we report an interpenetrated MIL-53 topology MOF, named GUF-1, where one-dimensional Sc(μ2-OH) chains are connected by 4,4′-(ethyne-1,2-diyl)dibenzoate linkers into a material that is an unusual example of an interpenetrated MOF with a rod-like secondary building unit. A combination of modulated self-assembly and grand canonical Monte Carlo simulations are used to optimise the porosity of GUF-1; H2 adsorption isotherms reveal a moderately high Qst for H2 of 7.6 kJ/mol and a working capacity of 41 g/L in a temperature–pressure swing system, which is comparable to benchmark MOFs. These results show that interpenetration is a potentially viable route to high-performance gas storage materials comprised of relatively simple building blocks.

Investigating H2 Adsorption in Isostructural Metal-Organic Frameworks M-CUK-1 (M = Co and Mg) through Experimental and Theoretical Studies.

A combined experimental and theoretical study of H2 adsorption was carried out in Co-CUK-1 and Mg-CUK-1, two isostructural metal-organic frameworks (MOFs) that consist of M2+ ions (M = Co and Mg) coordinated to pyridine-2,4-dicarboxylate (pdc2-) and OH- ligands. These MOFs possess saturated metal centers in distorted octahedral environments and narrow pore sizes and display high chemical and thermal stability. Previous experimental studies revealed that Co-CUK-1 exhibits a H2 uptake of 183 cm3 g-1 at 77 K/1.0 atm [ Angew. Chem., Int. Ed. 2007, 46, 272-275, DOI: 10.1002/anie.200601627], while that for Mg-CUK-1 under the same conditions is 240 cm3 g-1 on the basis of the experimental measurements carried out herein. The theoretical H2 adsorption isotherms are in close agreement with the corresponding experimental measurements for simulations using electrostatic and polarizable potentials of the adsorbate. Through simulated annealing calculations, it was found that the primary binding site for H2 in both isostructural analogues is localized proximal to the center of the aromatic rings belonging to the pdc2- linkers. Inelastic neutron scattering (INS) spectroscopic studies of H2 adsorbed in both MOFs revealed a rotational tunnelling transition occurring at around 8 meV in the corresponding spectra; this peak represents H2 adsorbed at the primary binding site. Two-dimensional quantum rotation calculations for H2 localized at the primary and secondary binding sites in both MOFs yielded rotational energy levels that are in agreement with the transitions observed in the INS spectra. Even though both M-CUK-1 analogues possess different metal ions, they exhibit similar electrostatic environments, modeled structures at H2 saturation, and rotational potentials for H2 adsorbed at the most favorable adsorption site. Overall, this study demonstrates how important molecular-level details of the H2 adsorption mechanism inside MOF micropores can be derived from a combination of experimental measurements and theoretical calculations using two stable and isostructural MOFs with saturated metal centers and small pore windows as model systems.

ON THE ISSUE OF USING THE DUBININ–RADUSHKEVICH–ASTAKHOV EQUATION IN CALCULATING ISOTHERMS OF H2, CO2, CO IN THE PRESSURESWING ADSORPTION PROCESS FOR HYDROGENRECOVERY ON BLOCK ZEOLITES 13X

The calculation of adsorption isotherms of synthesis gas components in the process of pres-sure swing adsorption (PSA) for hydrogen extractionon zeolite adsorbents is traditionally carried out using the Langmuir equation or equations derived from it. Its disadvantage consists in the necessity to obtain experimental adsorption isotherms for each gas in the gas mixture on the used adsorbent. This approach is expensive, especially in the case of multicomponent mixtures, such as synthesis gas. The paper demonstrates the prospects of an alternative method for calculating ad-sorption isotherms of H2, CO2, CO gases in the PSA process for hydrogen extracionfrom synthesis gas on block zeolites 13X using the Dubinin–Radushkevich–Astakhov (DRA) equation. Using zeo-lites 13X made by three samples, experimental adsorption isotherms of H2, CO2, CO at temperatures of 293 and 323 K, and adsorption isotherms of N2ata boiling point of 77.35 K were obtained. Using experimental isotherms, the problems of parametric identification were solved, and the parameters of the DRA equation for H2, CO2, CO gases on block zeolites 13X were determined. It has been found that the calculation of adsorption isotherms of H2, CO2, CO gases on zeolites 13X, the char-acteristics of which fall within the ranges of the limiting adsorption volume 0.258–0.296 cm3/g and the characteristic adsorption energy 10279–13395 J/mol, respectively, can be correctly carried out using the DRA equation in the temperature range of 293–323 K and the pressure range of 0–30 atm.In this case, the maximum value of the mismatch between the experimental gas isotherms and those calculated by the DRA equation is 14.69% for H2; the minimum value is 1.81% for CO2. Certain affinity coefficients make it possible to calculate the adsorption isotherms of H2, CO2, CO gases in the obtained ranges of the limiting adsorption volume and characteristic adsorption energy using only one isotherm of the standard gas (N2) on the zeolite 13X used. The versatility of the DRA equation can be used to calculate the adsorption isotherms of various gases, mixtures, and adsor-bents in cyclic adsorption processes.

Upgrading the Hydrogen Storage of MOF-5 by Post-Synthetic Exchange with Divalent Metal Ions

In metal-organic frameworks (MOFs), mixed-metal clusters have the opportunity to adsorb hydrogen molecules due to a greater charge density of the metal. Such interactions may subsequently enhance the gravimetric uptake of hydrogen. However, only a few papers have explored the ability of mixed-metal MOFs to increase hydrogen uptake. The present work reveals the preparation of mixed metal metal-organic frameworks M-MOF-5 (where M = Ni2+, Co2+, and Fe2+) (where MOF-5 designates MOFs such as Zn2+ and 1,4-benzenedicarboxylic acid ligand) using the post-synthetic exchange (PSE) technique. Powder X-ray diffraction patterns and scanning electron microscopy images indicate the presence of crystalline phases after metal exchange, and the inductively coupled plasma–mass spectroscopy analysis confirmed the exchange of metals by means of the PSE technique. The nitrogen adsorption isotherms established the production of microporous M-MOF-5. Although the additional metal ions decreased the surface area, the exchanged materials displayed unique features in the gravimetric uptake of hydrogen. The parent MOF-5 and the metal exchanged materials (Ni-MOF-5, Co-MOF-5, and Fe-MOF-5) demonstrated hydrogen capacities of 1.46, 1.53, 1.53, and 0.99 wt.%, respectively. The metal-exchanged Ni-MOF-5 and Co-MOF-5 revealed slightly higher H2 uptake in comparison with MOF-5; however, the Fe-MOF-5 showed a decrease in uptake due to partial discrete complex formation (discrete complexes with one or more metal ions) with less crystalline nature. The Sips model was found to be excellent in describing the H2 adsorption isotherms with a correlation coefficient ≅ 1. The unique hydrogen uptakes of Ni− and Co-MOF-5 shown in this study pave the way for further improvement in hydrogen uptake.

Ultrahigh Hydrogen Uptake in an Interpenetrated Zn 4 O-Based Metal–Organic Framework

As a highly promising candidate for hydrogen storage, crucial to vehicles powered by fuel cells, metal–organic frameworks (MOFs) have attracted the attention of chemists in recent decades. H2 uptak...

Water Adsorption Behavior on a Highly Dense Single-Walled Carbon Nanotube Film with an Enhanced Interstitial Space.

In this study, we describe the adsorption behavior of water (H2O) in the interstitial space of single-walled carbon nanotubes (SWCNTs). A highly dense SWCNT (HD-SWCNT) film with a remarkably enhanced interstitial space was fabricated through mild HNO3/H2SO4 treatment. The N2, CO2, and H2 adsorption isotherm results indicated remarkably developed micropore volumes (from 0.10 to 0.40 mL g–1) and narrower micropore widths (from 1.5 to 0.9 nm) following mild HNO3/H2SO4 treatment, suggesting that the interstitial space was increased from the initial densely-packed network assembly structure of the SWCNTs. The H2O adsorption isotherm of the HD-SWCNT film at 303 K showed an increase in H2O adsorption (i.e., by ∼170%), which increased rapidly from the critical value of relative pressure (i.e., 0.3). Despite the remarkably enhanced adsorption capacity of H2O, the rates of H2O adsorption and desorption in the interstitial space did not change. This result shows an adsorption behavior different from that of the fast transport of H2O molecules in the internal space of the SWCNTs. In addition, the adsorption capacities of N2, CO2, H2, and H2O molecules in the interstitial space of the HD-SWCNT film showed a linear relationship with the kinetic diameter, indicating an adsorption behavior that is highly dependent on the kinetic diameter.

Synergistic material and process development: Application of a metal-organic framework, Cu-TDPAT, in single-cycle hydrogen purification and CO2 capture from synthesis gas

We employ a synergistic material and process development strategy to improve the performance of a single-cycle vacuum pressure swing adsorption (VPSA) process for the hydrogen purification and the CO2 separation from reforming-based hydrogen synthesis. Based on process-informed adsorbent selection criteria, including high CO2 cyclic capacity and selective uptake of impurities like CO, N2, and CH4 over H2, a metal organic framework (MOF), Cu-TDPAT, is selected. First, adsorption isotherms of CO2, CO, CH4, N2 and H2 are measured. Subsequently, a column model is used for optimization-based analysis of the VPSA cycle with Cu-TDPAT as the adsorbent to assess both the separation performance, and the process performance in terms of energy consumption and productivity. The adsorption characteristics of Cu-TDPAT require an adaptation of the original VPSA process to increase the CO2 separation performance of the process. After this adaptation, Cu-TDPAT clearly outperforms the benchmark material, zeolite 13X, in several metrics including higher H2 purities and recoveries and fewer columns needed for a continuous separation process. Most importantly, Cu-TDPAT offers a two-fold improvement in CO2 productivities when compared to zeolite 13X, thus substantially decreasing the bed size required to achieve the same throughput. However, zeolite 13X remains the better adsorbent for reaching high CO2 purities and recoveries due to its higher selectivity for CO2 over all other components in the gas stream, which leads to an overall lower energy consumption. The obtained results show that the final performance strongly depends on an interplay of various factors related to both material and process. Hence, an integrated process and material design approach should be the new paradigm for developing novel gas separation processes.

Experimental and simulation study of the effect of surface functional groups decoration on CH4 and H2 storage capacity of microporous carbons

The incorporation of heteroatoms (i.e. N, O, S, F) into the microporous carbon framework is proposed to affect the interactions between adsorbates and adsorbents and improve the efficiency of gas storage. We demonstrate a facile synthesis of coal-derived activated carbons (ACs) modified with oxygen and nitrogen-containing groups for CH4 and H2 storage application. The functionalised ACs showed to have a high surface area of 1617–1924 m2/g, and pore volume of 0.85–0.92 cm3/g. The AC samples prepared by pre-oxidation followed by amination possess comparatively high CH4 adsorption capacity of 13.8 to 14.2 mmol/g at 298 K and 40 bar. However, the pristine AC and the oxidised AC showed the maximum H2 adsorption capacity with 0.6 mmol/g and 0.44 mmol/g, respectively, at 20 bar and 298 K. Density functional theory (DFT) calculations were performed to study the adsorption of CH4 and H2 on the ACs with/without the surface functional groups. In agreement with the experimental results, the computational analysis showed an increase in the gas–solid interaction after surface modification. Finally, a well-known method of Grand Canonical Monte Carlo (GCMC) was used to simulate the studied gas adsorption systems and calculate the adsorption isotherms of CH4 and H2 on different ACs.

Comparisons of activated carbons produced from sycamore balls, ripe black locust seed pods, and Nerium oleander fruits and also their H2 storage studies

Starting materials are very significant to produce activated carbons because every starting material has a different chemical structure; hence they affect the surface functional groups and surface morphologies of obtained activated carbons. In this study, sycamore balls, ripe black locust seed pods, and Nerium oleander fruits have been used as starting materials by ZnCl2 chemical activations for the first time. Firstly, activated carbons were obtained from these starting materials with ZnCl2 chemical activation by changing production conditions (carbonization time, carbonization temperature, and impregnation ratio) also affecting the structural and textural properties of the resultant activated carbons. Then, the starting materials and resultant activated carbons were characterized by utilizing diverse analysis techniques, such as TGA, elemental analysis, proximate analysis, BET surface areas, pore volumes, pore size distributions, N2 adsorption–desorption isotherms, SEM, FTIR spectra, and H2 adsorption isotherms. The highest surface areas were determined to be 1492.89, 1564.84, and 1375.47 m2/g for the activated carbons obtained from sycamore balls, ripe black locust seed pods, and N. oleander fruits, respectively. The yields of these activated carbons with the highest surface areas were calculated to be around 40%. As the carbonization temperature increased with sufficient ZnCl2 amount, N2 adsorption–desorption isotherms began to turn into Type IV isotherms given by mesoporous adsorbents with its hysteresis loops. Also, their hysteresis loops resembled Type H4 loop generally associated with narrow slit-like pores. Moreover, hydrogen uptakes under 750 mmHg at 77 K were determined to be 1.31, 1.48, and 1.24 wt% for the activated carbons with the maximum surface areas produced from sycamore balls, ripe black locust seed pods, and N. oleander fruits, respectively. As a result, the highest surface areas of the activated carbons with different structural properties produced in this study were obtained with different production conditions.

Fabrication of Crystalline Microporous Membrane from 2D MOF Nanosheets for Gas Separation.

Metal-organic frameworks (MOFs)-based membranes have shown great potentials as applications in gas separation. In this work, a uniform membrane based on 2D MOF Ni3 (HITP)2 (HITP=2,3,6,7,10,11-hexaaminotriphenylene) was fabricated on ordered macroporous AAO via the filtration method. To fabricate the membrane, we obtained the Ni3 (HITP)2 nanosheets as building blocks via a soft-physical exfoliation method successfully that were confirmed by AFM and TEM. We also studied the H2 , CO2 and N2 adsorption isotherms of Ni3 (HITP)2 powder at room temperature, which shows Ni3 (HITP)2 has high heats of adsorption for CO2 and high selectivity of CO2 over N2 . Gas permeation tests indicate that the Ni3 (HITP)2 membrane shows high permeance and selectivity of CO2 over N2 , as well as good selectivity of H2 over N2 . The ideal separation factors of CO2 /N2 and H2 /N2 from sing-gas permeances are 13.6 and 7.8 respectively, with CO2 permeance of 3.15×10-6 mol⋅m-2 ⋅s-1 ⋅Pa-1 . The membrane also showed good stability, durability and reproducibility, which are of potential interest for practical applications in the CO2 separations.

Enhanced quantum sieving of hydrogen isotopes via molecular rearrangement of the adsorbed phase in chabazite.

Coadsorption experiments reveal an unexpected increase of the D2/H2 selectivity with loading in pure silica chabazite at 47 K. This effect is correlated with the appearance of a step in the adsorption isotherms of H2 and D2. Grand canonical Monte Carlo simulations show that this phenomenon is related to a molecular rearrangement of the adsorbed phase induced by its strong confinement. In the case of a H2 and D2 mixture, this rearrangement favors the adsorption of D2 having a smaller size due to quantum effects.

PSA purification of waste hydrogen from ammonia plants to fuel cell grade

Industrial hydrogen-rich waste streams hold promises in their upgrading to feed fuel cell stacks. As in the ammonia synthesis process, a stream of up to 180–240 Nm3 per ton of ammonia is purged to keep the inert gases concentration below a threshold value; this stream contains large hydrogen quantities, which could be recovered. In the current work, a four-column PSA unit has been used to produce a high-purity hydrogen stream for fuel cell applications from a synthetic mixture with a molar composition of 58% H2, 25% N2, 15% CH4 and 2% Ar, based on ammonia purge gas. Firstly, a comparative performance of four commercially adsorbents was accomplished to obtain the adsorption isotherms of H2, N2, CH4, and Ar, leading to the selection of 5A zeolite adsorbent. Then, the dynamic behavior of a packed bed was studied by single and multicomponent breakthrough experiments and simulated using Aspen Adsorption®. The results, simulations and experimental, indicate that after H2 the first impurity to break thought the column is Ar, followed by N2 and finally by CH4. Then, a design-of-experiments (DoE) methodology was used to select the best operating conditions of the experimental cyclic PSA unit to reach different target hydrogen product concentrations; the overall PSA performance was evaluated in terms of purity and recovery of H2 product. According to the results, the four-column PSA unit running at 9 bar produced a stream with hydrogen concentration of 99.25% and 99.97% of H2, with a recovery of 75.3% and 55.5%, respectively, where the impurities were mostly Ar and N2. In addition to the technical performance, the economic assessment concluded that the cost to compress, transport and purify waste hydrogen to a concentration of 99.97% using a small-scale PSA unit from ammonia plants has been estimated in the range of 1.17–1.39 € kg H2−1, depending on the dispensing pressure of 350 or 700 bar, respectively. These assessments offer a cost-effective solution to produce high-purity H2 as low cost transportation, allowing hydrogen penetration into the mass markets.

Tuning the Gate-Opening Pressure in a Switching pcu Coordination Network, X-pcu-5-Zn, by Pillar-Ligand Substitution.

Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas-storage applications than the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate-opening and gate-closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine-tune gate-opening and gate-closing pressure. Specifically, three variants of a previously reported pcu-topology MOF, X-pcu-5-Zn, have been prepared: X-pcu-6-Zn, 6=1,2-bis(4-pyridyl)ethane (bpe), X-pcu-7-Zn, 7=1,2-bis(4-pyridyl)acetylene (bpa), and X-pcu-8-Zn, 8=4,4'-azopyridine (apy). Each exhibited switching isotherms but at different gate-opening pressures. The N2 , CO2 , C2 H2 , and C2 H4 adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6, afforded lower gate-opening and gate-closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials.