Cryogenic gas chromatographic separation of hydrogen isotopes using pillared-layer MOFs composites as stationary phase

Hydrogen isotopes are the main fuel in the fusion reactor, and the separation of hydrogen isotope gas mixture is the key process for the operation of fusion reactor. Cryogenic gas chromatography is an effective method which can be used for both separation and analysis of hydrogen isotopes. The chromatographic stationary phase determines the hydrogen isotopes separation performance. In this study, a series of pillared-layer MOFs Ni₂(L)₂ (dabco) (H₂L: 1,4-benzenedicarboxylic acid (H₂bdc), 1,4-naphthalenedicarboxylic acid (H₂ndc), 9,10-anthracenedicarboxylic acid (H₂adc); dabco: 1,4-diazabicyclo-[2.2.2]octane) were synthesized by changing the bridging dicarboxylate ligands with different steric hindrance. The effect of MOFs structure on hydrogen isotope interaction strength was studied by isothermal adsorption experiments of pure H₂ and D₂ at 77 K and 87 K, and programmed temperature desorption experiments of H₂-D₂ mixture from 25 K to 120 K. The enrichment factor for D₂ over H₂ up to 6.8 was obtained for Ni₂(adc)₂ (dabco) by static adsorption experiment of H₂-D₂ mixture. Finally, the MOFs composites Ni₂(L)₂ (dabco)@γ-Al₂O₃ were obtained by in situ solvothermal reaction loading MOFs on γ-Al₂O₃, and cryogenic gas chromatographic separation performance of H₂-D₂ and H₂-HD-D₂ mixtures using three composites-packed columns at liquid nitrogen temperature was investigated. The optimum separation was achieved when Ni₂(adc)₂ (dabco)@γ-Al₂O₃ was used as stationary phase due to strongest interaction strength with hydrogen isotope. The separation resolution R (H₂/HD) and R (HD/D₂) is up to 1.31 and 3.26 respectively.     

Hydrophobic platinum–polytetrafluoroethylene catalyst for hydrogen isotope separation

A composite catalyst, platinum supported on polytetrafluoroethylene (Pt/PTFE), has been successfully prepared by compression moulding forming and used for hydrogen isotope separation by hydrogen–water isotope exchange. The as-prepared Pt/PTFE was characterized by nitrogen adsorption. The results of the catalytic activity for hydrogen–water isotope exchange show that Pt/PTFE has high catalytic activity. The effects of different factors, such as flow rate, temperature, molar flow ratio of hydrogen gas to feed water and time have also been investigated. The present study shows a promising choice of Pt/PTFE as a composite catalyst for hydrogen isotope separation.     

Hydrogen amplification from coke oven gas using a CO2 adsorption enhanced hydrogen amplification reactor

To improve coke oven gas (COG) energy conversion, alternative configurations for amplifying hydrogen from COG are proposed in this paper. In these new configurations, a CO₂ adsorption enhanced hydrogen amplification reactor is combined with a pressure swing adsorption separation unit (PSA) to produce pure hydrogen. Hydrogen production was integrated with desorption gas utilization, in situ CO₂ capture and waste heat recovery to improve COG energy conversion efficiency and decrease CO₂ emissions. To analyze the advantages of the flowsheet modifications, technical and economic performance indicators were used to evaluate and compare the performances of the various system configurations. Simulation results show that the alternative configurations proposed in this paper have higher energy conversion efficiencies, higher hydrogen yields and shorter dynamic payback periods. The variation of technical performance with reaction temperature, pressure, sorbent to carbon ratio and steam to carbon ratio were also analyzed using a sensitivity study. Optimal operating conditions for the CO₂ adsorption enhanced hydrogen amplification reactor were obtained based on the simulation results.     

New gas chromatographic packing ZIF-67@NH2–SiO2 for separation of hydrogen isotope H2/D2

ZIF-67@NH₂–SiO₂ composites were prepared by loading the metal-organic frameworks ZIF-67 on amino modified SiO₂ gel particles (NH₂–SiO₂, 80–100 mesh) through layer-by-layer self-assembly method. Systematic investigation on the effects of ZIF-67 loading amounts on NH₂–SiO₂ packed stainless steel chromatographic column (specification 1.0 m×2.0 mm I.D.), the flow rate of He as carrier gas and the injection amount of mixed gas (H₂/D₂) on the hydrogen isotope H₂/D₂ separation performance at liquid nitrogen temperature, unraveled the optimal conditions for H₂/D₂ isotope separation. The results showed that the optimal stationary phase materials under the optimized conditions can effectively separate H₂ and D₂ with separation resolution R = 1.52 and the separation time t = 10.15 min. The superior performance of the ZIF-67 is tentatively thought to be due to kinetic quantum sieving (pore size 3.3 Å) effect and chemical affinity sieving effect of Co ion in ZIF-67.     

Effect of alumina on thermodynamic performance of palladium-H2 (D2) system

Palladium (Pd) has a strong hydrogen isotope effect, widely used in the Thermal Cycling Absorption Process (TCAP) separation column. However, due to pulverization and high gas resistance, Pd was usually dispersed in backing materials, such as alumina (Al₂O₃), to improve the service performance. In this paper, the microstructure of sponge palladium and Pd–Al₂O₃ pellet was observed by Scanning Electron Microscopy (SEM), and the crystalline structure before and after hydrogeneration was characterized by X-Ray Diffractometer (XRD). To study the support effect of backing material Al₂O₃ on the hydrogen/deuterium thermal absorption performance of palladium, the pressure-composition-temperature (P–C-T) curves were measured by series experiments. The result shows that Al₂O₃ acts as a support material between palladium particles to suppress the effect of the pellet expansion-shrinking during H₂ (D₂) absorption/desorption cycling. Alumina could provide free position for hydrogen atoms. And the inflection points of α phase to α+β phase shift from 0.02 to 0.09 for Pd–Al₂O₃ pellet/hydrogen system. The entropy and enthalpy variation of Pd/H (Pd/D) system in α+β phase are respectively ?18.34 (?16.83) kJ/mol and ?45.65 (?42.44) J/mol/K, which show no correlation with alumina. The H-D separation factor positively correlates with the quantity of hydrogen in the solid phase, and alumina could restrain the separation effect.     

Effect of PTFE coating on enhancing hydrogen embrittlement resistance of stainless steel 304 for liquefied hydrogen storage system application

The phenomenon of hydrogen embrittlement phenomenon is known to be a major obstacle to proposed to overcome this phenomenon. In the present study, polytetrafluoroethylene (PTFE), which is known to be an effective hydrogen adsorption and desorption material, was coated on the surface of stainless steel 304 to improve its hydrogen embrittlement resistance. To make a hydrogen embrittlement environment, electrochemical hydrogen pre-charging was applied to the PTFE-coated stainless steel 304. To investigate the effects of PTFE coating on the hydrogen embrittlement resistance of stainless steel 304, the Charpy V-notch impact (CVN) test was performed under three different temperatures: 25, −83, and −196 °C. Additionally, hydrogen concentration, electron back scatter diffraction (EBSD), and scanning electron microscopy (SEM) evaluations were carried out to verify the results of the CVN impact test. The PTFE coating did not have a significant effect on the quantitative reduction of hydrogen concentration; however, we confirmed its excellent performance in terms of toughness reduction due to the increase in hydrogen loading time at room temperature.     

Highly effective hydrogen isotope separation by cryogenic gas chromatography in a new stationary phase material MnCl2@CPL-1@γ-Al2O3

In this work, metal-organic framework compound CPL-1 of a formula {[Cu₂(pzdc)₂(pyz)]?2H₂O}_n (pzdc = pyrazine-2,3-dicarboxylate, pyz = pyrazine) possessing kinetic quantum sieving effect on H₂/D₂ separation was selected to prepare two new chromatography stationary phase materials CPL-1@γ-Al₂O₃ and MnCl₂@CPL-1@γ-Al₂O₃ by loading CPL-1 on γ-Al₂O₃ particles with size 80–100 mesh through repeating in situ crystallization process, and afterwards by loading MnCl₂ on CPL-1@γ-Al₂O₃ via impregnation approach. The two optimized materials were thoroughly characterized by IR, XRD, SEM, EDS and TG/DTA method. The experimental results showed that, under liquid nitrogen temperature by using just 1-m chromatographic column and cheap He gas as carrier gas, the MnCl₂@CPL-1@γ-Al₂O₃ can solve the problem of long separation time and trailing phenomenon existing in the CPL-1@γ-Al₂O₃ column, can realize highly effective hydrogen isotope H₂/D₂ separation with good separation resolution (R = 1.62) and approximate Gauss distribution of chromatographic peak, can be used for both qualitative and quantitative analysis of hydrogen isotope H₂/D₂ with short separation time of 6.5 min.     

Study of isotope effect on dehydrogenation kinetics of Pd based alloys using differential scanning calorimetry

Owing to the large hydrogen isotope effect, palladium and palladium based alloy are of great technological importance for their application in separation of hydrogen isotopes. The present study deals with the investigation of isotope effect on hydrogen desorption kinetics of Pd, Pd_0.77Ag_0.23 and Pd_0.77Ag_0.10Cu_0.13 alloys, using non-isothermal method by employing Differential Scanning Calorimetry (DSC). Pd_0.77Ag_0.23 and Pd_0.77Ag_0.10Cu_0.13 alloys were prepared by arc melting method and characterised by XRD, TXRF and EDS. Both the alloys are found to have FCC phase similar to Pd lattice. Prior to kinetic measurements, samples were activated by hydriding-dehydriding method. Hydrogen/deuterium desorption kinetic measurements were carried out at four different heating rates (8, 12, 16 and 20 K/min) and Kissinger plots were constructed from peak temperature of DSC curves. Activation energies for hydrogen/deuterium desorption from the corresponding hydride/deuteride were calculated from the slope of Kissinger plot which follows the order; Pd > Pd_0.77Ag_0.23 > Pd_0.77Ag_0.10Cu_0.13. Activation energy for deuterium desorption was found to be lower than that of hydrogen desorption and significant isotope effect was observed for the Pd_0.77Ag_0.10Cu_0.13 alloy which makes it a favorable candidate material for its application in hydrogen isotope separation, employing self-displacement gas chromatography.     

Hydrogen retention and affecting factors in rolled tungsten: Thermal desorption spectra and molecular dynamics simulations

Hydrogen isotope retention of tungsten in nuclear fusion reactors is one of the hot research issues all along. In this paper, tungsten samples in different rolled surfaces were polished by mechanical processing, subsequently subjected to D₂⁺ irradiation and thermal desorption. To better understand the experimental observations, this study also performed molecular dynamics (MD) simulation and investigated the effects of temperature, grain number, grain boundary density, and crystal orientation on hydrogen retention. It is found that the grain number and grain boundary density of rolled tungsten increase successively in RD/TD, RD/ND, and TD/ND surfaces. The RD/ND surface exhibits the best hydrogen radiation resistance, whereas the TD/ND surface is unsatisfactory. MD simulations further indicate that hydrogen retention is more obvious with the increase of grain density in tungsten, and hydrogen atoms are more easily enriched at the grain boundaries. With the increase in temperature, the retention of hydrogen atoms in monocrystalline/polycrystalline tungsten decreases significantly. The average implantation depth of H atoms is deepest along the <111> and <112> crystalline directions, which reveals that hydrogen retention is dependent on the crystal orientations. The good agreement between the experimental data and simulation results reveals that grain boundaries play an important role in hydrogen retention.     

Improvement of hydrogen storage properties of TiCrV alloy by Zr substitution for Ti

The effects of Zr substitution for Ti on the hydrogen absorption–desorption characteristics of Ti_1−xZr_xCrV alloys (x = 0, 0.05, 0.1 and 1.0) have been investigated. The crystal structure, maximum hydrogen absorption capacity, kinetics and hydrogen desorption properties have been studied in detail. While TiCrV crystallizes in body centered cubic (BCC) structure, ZrCrV is a C15 cubic Laves phase compound and the intermediate compositions with 5 and 10 at% Zr substitutions for Ti (x = 0.05 and 0.1) show the presence of a small amount of ZrCr₂ Laves phase along with the main BCC phase. The pressure–composition isotherms have been studied at room temperature. TiCrV shows separation of TiH₂ phase on cycling. A small amount of Zr substitution for Ti is found to have advantageous effects on the hydrogen absorption properties of TiCrV as it suppresses TiH₂ phase separation and decreases hysteresis. It is found that the hydrogen absorption capacity of Ti_1−xZr_xCrV decreases as the Zr content increases due to the increased fraction of Laves phase. Temperature-programmed desorption studies have been carried out on the saturated hydrides in order to find the relative desorption temperatures.     

Influence of Fe addition on hydrogen storage characteristics of Ti–V-based alloy

In order to improve the hydrogen storage properties and reduce the cost of Ti–V-based BCC alloys, the effect of Fe substitution for part V on hydrogen absorption–desorption characteristics of Ti–10Cr–18Mn–32V alloy was investigated. It was found that proper amount of Fe addition was effective in improving the activation performance, enhancing the hydrogen absorption–desorption plateau pressure, reducing the hysteresis of hydrogen absorption–desorption plateau, increasing the hydrogen desorption capacity and decreasing the alloy's cost, while it depressed the hydrogen absorption capacity. X-ray diffraction (XRD) patterns and back scattering electron (BSE) images display that the single BCC phase of Fe-free alloy transformed into two phases of, BCC and C14 Laves, of Fe-containing alloy. Three phase transformations happened in the two alloys during the hydrogen release process, which resulted from the formation of three different hydride phases in the two hydrided alloys.     

Evaluation of hydrogen storage performance of ZrTiVNiCrFe in electrochemical and gas-solid reactions

In the present study, the hydrogen storage performance of multi-principal-component ZrTiVNiCrFe alloy produced through rapid solidification has been examined by electrochemical methods and gas-solid reactions. XRD and EBSD analyses reveal the hexagonal Laves phase structure (type C14) with average grain size of 300 nm and root-mean-square microstrain of 0.19%. Cyclic voltammetry and electrochemical impedance spectroscopy analyses in the hydrogen sorption/desorption region give insight to the sorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The pressure-composition isotherms measured in course of gas-solid reaction confirm the hydrogen storage capacity reaching 1.6 wt% at the first hydrogenation at room temperature, then reducing to 1.3–1.4% during subsequent cycling. According to the calorimetric titration study, there is a significant hysteresis primarily caused by the non-equilibrium character of the hydrogenation process.     

The chromatographic processes for preparation of isotope-free hydrogen

Based on the reviews of the chromatographic processes for hydrogen isotope separation, an expression has been obtained from the derivations concerning the moment analysis to calculate the hydrogen isotope separation factors for porous hydrogen-adsorbing materials. The combination of derivations with experiment data results in a design of the parametric pumping with intermetallic compounds as its absorbents and the organic solutions of hydrogen as its fluid phase for preparation of isotope-free hydrogen. The eigenvalue of the process in the optimized conditions for LaNi₅/n-undecane/hydrogen system is in a range of 0.67–0.75, which is small enough to make the process a competitive one. In discussion of the factors that affect the separation process, the ratio of the hydrogen capacities of solid and liquid phase has been found to be of decisive importance besides the equilibrium separation factor.     

Hydrogen isotope absorption amount and rate of Pd–Al2O3 pellets

A special type of Pd–Al₂O₃ pellet, which included Pd in high weight percent as a hydrogen isotope separation material was prepared by a compression molding method. The pressure–composition isotherm and the plateau pressure of the Pd–Al₂O₃ hydrogen isotope system were determined by a volumetric method. The pellet has high hydrogen absorption ability even at 196 K, and the reaction rate is controlled by surface reaction. The hydrogen absorption capacity and the rate of the Pd–hydrogen system were unchanged by the addition of Al₂O₃. It was found that the Pd–Al₂O₃ pellet has high durability against repeated absorption–desorption cycles. There is no change in the absorption amount and the rate up to 1000 times of absorption–desorption cycles.     

Conceptual design analysis of a compressor‐driven sorption cooling system

The feasibility of using activated carbon/nitrogen pair as an alternative to metal hydride–hydrogen combination in a compressor‐driven sorption refrigerator (CDSR) has been studied in the present article. The motivation behind the selection of this particular adsorbent/adsorbate pair is due to its high heat of adsorption/desorption, in addition to the fact that nitrogen is absolutely eco‐friendly and a nonhazardous gas to handle with. A conceptual design of the cooling system has been envisaged for near room temperature applications with this activated carbon/nitrogen pair. In order to evaluate the performance of the CDSR system, mathematical models have been developed separately for the adsorption and desorption processes involving transient heat and mass transfer analysis. The present analysis also helped to conduct a parametric evaluation of the cooling system. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis by reactive ball milling and cycling properties of MgH2–TiH2 nanocomposites: Kinetics and isotopic effects

MgH₂, MgH₂–TiH₂ nanocomposites and their deuterated analogues have been obtained by reactive ball milling and their kinetic and cycling hydrogenation properties have been analysed by isotope measurements and high-pressure differential scanning calorimetry (HP-DSC). Kinetics of material synthesis depends on both Ti-content and the isotopic nature of the gas. For pure Mg, the synthesis is controlled by isotope diffusion in Mg and therefore MgH₂ forms faster than MgD₂. For the MgH₂–TiH₂ nanocomposites, the synthesis is controlled by the efficiency of milling. Kinetics of reversible hydrogen/deuterium sorption in nanocomposites have been studied at 548 K. The rate limiting step is isotope diffusion for absorption and Mg/MgH₂ interface displacement for desorption. HP-DSC measurements demonstrate that the TiH₂ phase acts as a gateway for hydrogen sorption even in presence of MgO and provides abundant nucleation sites for Mg and MgH₂ phases. The 0.7MgH₂–0.3TiH₂ nanocomposite exhibits steady hydrogen storage capacity after 100 cycles of absorption–desorption.     

High temperature performance of La0.6Ce0.4Ni3.45Co0.75Mn0.7Al0.1 hydrogen storage alloy for nickel/metal hydride batteries

La_0.6Ce_0.4Ni_3.45Co_0.75Mn_0.7Al_0.1 hydrogen storage alloy has been prepared and its electrochemical characteristics and gas hydrogen absorption/desorption properties have been investigated at different temperatures. X-ray diffraction results indicated that the alloy consists of a single phase with CaCu₅-type structure. It is found that the investigated alloy shows good cycle performance and high-rate discharge ability, which display its promising use in the high-power type Ni-MH battery. The exchange current density and the diffusion coefficient of hydrogen in the bulky electrode increase with increasing temperature, indicating that increasing temperature is beneficial to charge-transfer reaction and hydrogen diffusion. However, the maximum discharge capacity, the charge retention and the cycling stability degrade with the increase of the temperature.     

Hydrogen sorption studies of palladium decorated graphene nanoplatelets and carbon samples

With the increasing population of the world, the need for energy resources is increasing rapidly due to the development of the industry. 88% of the world's energy needs are met from fossil fuels. Since there is a decrease in fossil fuel reserves and the fact that these fuels cause environmental pollution, there is an increase in the number of studies aimed to develop alternative energy sources nowadays. Hydrogen is considered to be a very important alternative energy source due to its some specific properties such as being abundant in nature, high calorific value and producing only water as waste when burned. An important problem with the use of hydrogen as an energy source is its safe storage. Therefore, method development is extremely important for efficient and safe storage of hydrogen. Surface area, surface characteristics and pore size distribution are important parameters in determining the adsorption capacity, and it is needed to develop new adsorbents with optimum parameters providing high hydrogen adsorption capacity. Until recently, several porous adsorbents have been investigated extensively for hydrogen storage. In this study, it was aimed to develop and compare novel Pd/carbon, Pd/multiwalled carbon nanotube, and Pd/graphene composites for hydrogen sorption. All the palladium/carbon composites were characterized by t-plot, BJH desorption pore size distributions, N₂ adsorption/desorption isotherms, and SEM techniques. The maximum hydrogen storage of 2.25 wt.% at −196 °C was achieved for Pd/KAC composite sample. It has been observed that the spillover effect of palladium increases the hydrogen sorption capacity.     

Complex hydrides for energy storage

In the past decades, complex hydrides and complex hydrides-based materials have been thoroughly investigated as materials for energy storage, owing to their very high gravimetric and volumetric hydrogen capacities and interesting cation and hydrogen diffusion properties. Concerning hydrogen storage, the main limitations of this class of materials are the high working temperatures and pressures, the low hydrogen absorption and desorption rates and the poor cyclability. In the past years, research in this field has been focused on understanding the hydrogen release and uptake mechanism of the pristine and catalyzed materials and on the characterization of the thermodynamic aspects, in order to rationally choose the composition and the stoichiometry of the systems in terms of hydrogen active phases and catalysts/destabilizing agents. Moreover, new materials have been discovered and characterized in an attempt to find systems with properties suitable for practical on-board and stationary applications. A significant part of this rich and productive activity has been performed by the research groups led by the Experts of the International Energy Agreement Task 32, often in collaborative research projects. The most recent findings of these joint activities and other noteworthy recent results in the field are reported in this paper.     

Effect of Mn on the long-term cycling performance of AB5-type hydrogen storage alloy

Rare-earth AB₅-type hydrogen storage alloys are widely studied due to their extensive application potentials in hydrogen compressors, heat pump, Ni–MH batteries etc. However, their shortcomings such as plateau splitting and capacity degradation during hydrogen absorption/desorption hinder their practical applications. In this paper, we study the effect of Mn partial substitution for Ni on the plateau characteristics and long-term cycling performance of LaNi_5-xMn_x alloys. It is found that Mn addition expands the lattice interstitial for hydrogen accommodation, thus prohibiting the plateau splitting phenomenon. In addition, the substitution of Mn for Ni stabilizes the crystal structure of the alloys against hydrogen absorption/desorption, thus relieving the capacity degradation. The capacity retention of the alloys at the 1000th cycle (S₁₀₀₀) increases from 83.2% (x = 0) to 94.0% (x = 0.75). But when x reaches 1, the hydrogen desorption reversibility is reduced due to the low plateau pressure, resulting in a slight decrease in capacity retention.