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.     

Ag–AgBr/g-C3N4/ZIF-8 prepared with ionic liquid as template for highly efficient photocatalytic hydrogen evolution under visible light

In this study, a ternary photocatalyst named Ag–AgBr/g-C₃N₄/ZIF-8 (A/g/Z) was prepared by ionic liquid assisted in-situ growth method. The structure and composition of samples are studied by means of XRD, SEM, XPS, TEM, EIS, etc. The AgBr prepared by ionic liquid assisted method has good dispersion, and the protonated carbon nitride has better specific surface area and morphology structure. The structure of the composites is optimized by modifying g-C₃N₄ with MOFs and noble metals, and the existence of Ag⁺ can play a bridging role, so as to form multi-path electronic transmission route. The high efficiency of electron transfer greatly improved the efficiency of hydrogen evolution. It is worth noting that the surface plasmon resonance (SPR) effect produced by silver ions on the surface of g-C₃N₄ can improve the absorption of visible light. The A (1.1)/g/Z (6.5) exhibit high hydrogen evolution efficiency (2058 μmol g^?1 h^?1, which is 49 times than g-C₃N₄) at the absence of Pt co-catalyst. Furthermore, the transient photocurrent density of the composites is much higher than that of g-C₃N₄ and AgBr, the semicircle radius of EIS is also less than both. Through the five cycle experiment, the photocatalytic efficiency of the composite material remained above 91%.     

Hydrogen storage in 1D nanotube-like channels metal–organic frameworks: Effects of free volume and heat of adsorption on hydrogen uptake

Metal–organic Frameworks generate significant interest for their potential application as Hydrogen storage materials. Grand Canonical Monte Carlo (GCMC) simulations were performed at two different temperatures 77 and 300 K over a wide range of pressures to describe H₂ adsorption in 7 metal–organic frameworks (MOFs), which all have the same framework topology but different surface chemistry and different pore sizes. DREIDING and UFF force fields were identified to be able to predict adsorption isotherms for H₂ in MOFs in a reasonable agreement with the experimental data from the literature. This work reveals that at 77 K the total amount of H₂ adsorbed correlates mainly with: the heat of adsorption at low pressure and the free volume at high pressure. While at 300 K the amount adsorbed mainly correlates with the available free volume at both low and high pressure. None of the MOFs studied fulfils DOE requirement, this is due to their low heat of adsorption. The required adsorption energy to meet the DOE targets is estimated to be 34 kJ/mol.     

Novel experimental methods for assessment of hydrogen storage capacity and modelling of sorption in Cu-BTC

Novel experimental procedures for hydrogen adsorption studies are presented. The methods provide an important advantage: pure material sorption behaviour can be directly determined without the use of equations of state (EOS) at low temperatures. The storage properties of Cu-BTC [Cu₃(BTC)₂, BTC – 1,3,5-benzenetricarboxylate] were investigated under different thermodynamic conditions. The maximum hydrogen uptake of 4.6 wt% was observed at 25 K. We compared the results obtained in this work with previously reported experimental data to prove the validity of the novel methods for the hydrogen sorption measurements. The experimental data of the present work show a good agreement with the results reported in the literature. Additionally, the modelling of the hydrogen sorption processes in Cu-BTC was carried out. The simulations were performed in the form of isotherms and isobars. Fairly good agreement with experimental data has been achieved. Uncertainties in MOF-H₂ interactions are most likely the major reasons for the remaining difference between simulations and experiments.     

An insight into hydrogen isotopic separation on iron-alumina and chromium-alumina as stationary phase in gas chromatographic method

In gas chromatographic separation of hydrogen isotopes iron-alumina as a stationary phase is conventionally used. Further, Chromium-alumina as an alternative stationary phase has also been mentioned in the literature. In this present study, a detail comparative study of both the stationary phases in terms of their hydrogen isotope separation ability has been carried out. This study shows that chromium-alumina is better alternative than iron-alumina which might be attributed to its improved resolution, higher column efficiency, easy mode of preparation and shorter retention time along with equally simple regeneration procedure for regaining the performance of column material. To understand the basis behind their difference in ability of hydrogen isotope separation, hydrogen adsorption/desorption phenomenon at experimentally condition along with different surface related properties of both stationary phases have been evaluated. These experimental findings have been correlated with hydrogen isotope separation ability in terms of its retention time and resolution obtained during hydrogen isotopic separation and it illustrates the fact that hydrogen adsorption/desorption phenomenon is one of the governing factor in deciding the performance of the column materials.     

Hydrogen isotopes separation validation of frontal displacement chromatography for various compositions of feed gas and tritium extraction simulation for TBM

Based on the previous study in frontal displacement chromatography (FDC) packed with Pd-Al₂O₃, three groups of separation tests were carried out to verify the separation performance of the constituted FDC device for various compositions of feed gas and to validate the application probability of FDC in the Tritium Extraction System (TES) of ITER and China Fusion Engineering Test Reactor (CFETR). The separations were conducted by the FDC procedure with characteristics of the feed gas one-time flushing though the column and then reasonable separation performance had been obtained. The results indicate that the FDC process could be applied to deal with the desorbed gas mixtures from TES and/or further to extract and thereafter enrich the breeding tritium in ITER or CFETR, which would take the advantages of system compactness and efficiency over the present route of TES. Comparing to other related displacement chromatography procedures, the FDC process could be applied in tritium pre-enrichment for the mixtures of low tritium concentrations, which is highlighted by the outstanding merit of operation simplicity.     

Efficient hydrogen production over MOFs (ZIF-67) and g-C3N4 boosted with MoS2 nanoparticles

MOFs (ZIF-67) and g-C₃N₄ catalyst-modified MoS₂ nanoparticles are prepared by means of doping g-C₃N₄ in the process of ZIF-67 formation and then introducing MoS₂ nanoparticles on the surface of collaborative structure between MOFs and g-C₃N₄. The MOFs (ZIF-67) and g-C₃N₄ catalyst-modified MoS₂ photocatalyst exhibits efficient hydrogen production with about 321 μmol under visible light irradiation in 4 h, which is almost about 30 times higher than that of over the pure g-C₃N₄ photocatalyst. A series of characterization studies such as SEM, XRD, TEM, EDX, XPS, UV–vis DRS, FTIR, transient fluorescence and electro-chemistry show that the novel structure of g-C₃N₄ and MOF is formed, the more active sites appears and the efficiency of photo-generated charge separation is improved. MoS₂, as a narrow band semiconductor, is grafted on the surface of g-C₃N₄/MOF, which could effectively harvest visible light and swift charge separation. The results are well mutual corroboration with each other. In addition, a eosin Y-sensitized reaction mechanism is introduced.     

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.     

Permeability,solubility and diffusivity of hydrogen isotopes in stainless steels at high gas pressures

In this report, we provide a framework for describing the permeability, solubility and diffusivity of hydrogen and its isotopes in austenitic stainless steels at temperatures and high gas pressures of engineering interest for hydrogen storage and distribution infrastructure. We demonstrate the importance of using the real gas behavior for modeling permeation and dissolution of hydrogen under these conditions. A simple one-parameter equation of state (the Abel–Noble equation of state) is shown to capture the real gas behavior of hydrogen and its isotopes for pressures less than 200 MPa and temperatures between 223 and 423 K. We use the literature on hydrogen transport in austenitic stainless steels to provide general guidance on and clarification of test procedures, and to provide recommendations for appropriate permeability, diffusivity and solubility relationships for austenitic stainless steels. Hydrogen precharging and concentration measurements for a variety of austenitic stainless steels are described and used to generate more accurate solubility and diffusivity relationships.     

Improved hydrogen desorption properties of ammonia borane by Ni-modified metal-organic frameworks

Ammonia borane (AB) has attracted intensive study because of its low molecular weight and abnormally high gravimetric hydrogen capacity. However, the slow kinetics, irreversibility, and formation of volatile materials (borazine and ammonia) of AB limit its practical application. In this paper, new strategies by doping AB in metal-organic framework MIL-101 (denoted as AB/MIL-101) or in Ni modified MIL-101 (denoted as AB/Ni@MIL-101) are developed for hydrogen storage. In AB/MIL-101 samples, dehydrogenation did not present any induction period and undesirable by-product borazine, and decomposition thermodynamics and kinetics are improved. For AB/Ni@MIL-101, the peak temperature of AB dehydrogenation was shifted to 75 °C, which is the first report of such a big decrease (40 °C) in the decomposition temperature of AB. Furthermore, borazine and ammonia emissions that are harmful for proton exchange membrane fuel cells, were not detected. The interaction between AB and MIL-101 is discussed based on both theoretical calculations and experiments. Results show that Cr-N and B-O bonds have generated in AB/MIL-101 nanocomposites, and the decomposition mechanism of AB has changed.     

Exergy analysis on the simulation of a small-scale hydrogen liquefaction test rig with a multi-component refrigerant refrigeration system

This study investigates the simulation of a proposed small-scale laboratory liquid hydrogen plant with a new, innovative multi-component refrigerant (MR) refrigeration system. The simulated test rig was capable of liquefying a feed of 2 kg/h of normal hydrogen gas at 21 bar and 25 °C to normal liquid hydrogen at 2 bar and −250 °C. The simulated power consumption for pre-cooling the hydrogen from 25 °C to −198 °C with this new MR cycle was 2.07 kWh/kg_GH2 from the ideal minimum of 0.7755 kWh per kilogram of feed hydrogen gas. This was the lowest power consumption available when compared to today’s conventional hydrogen liquefaction cycles, which are approximately 4.00 kWh/kg_GH2. Hence, the MR cycle’s exergy efficiency was 38.3%. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was found that the majority of the losses were from the compressors, heat exchangers, and expansion valves. Suggestions are provided for how to reduce exergy in each component in order to reduce the exergy loss. Finally, further improvements for better efficiency of the test rig are explained to assist in the design of a future large-scale hydrogen liquefaction plant.     

Strategies for stationary and portable fuel cell markets

In the future, hydrogen-based stationary and portable fuel cell systems can help supply some or all of the power demanded with additional advantages of higher reliability, lower emissions, independence from the general grid, and cogeneration capability. In order to understand how to prepare the future for this technology, this paper describes a thorough investigation of past alternative stationary and portable power projects in order for an assessment of the opportunities for stationary and portable fuel cell markets, as well as interactions with transportation hydrogen systems. The lessons learned from the programs are used to establish best practices and recommendations for a hydrogen strategy that addresses opportunities for hydrogen in power generation systems, as well as to make recommendations for market transformation within the hydrogen fuel cell industry.     

Liquid hydrogen production via hydrogen sulfide methane reformation

Hydrogen sulfide (H₂S) methane (CH₄) reformation (H₂SMR) (2H₂S + CH₄ = CS₂ + 4H₂) is a potentially viable process for the removal of H₂S from sour natural gas resources or other methane containing gases. Unlike steam methane reformation that generates carbon dioxide as a by-product, H₂SMR produces carbon disulfide (CS₂), a liquid under ambient temperature and pressure—a commodity chemical that is also a feedstock for the synthesis of sulfuric acid. Pinch point analyses for H₂SMR were conducted to determine the reaction conditions necessary for no carbon lay down to occur. Calculations showed that to prevent solid carbon formation, low inlet CH₄ to H₂S ratios are needed. In this paper, we analyze H₂SMR with either a cryogenic process or a membrane separation operation for production of either liquid or gaseous hydrogen. Of the three H₂SMR hydrogen production flowsheets analyzed, direct liquid hydrogen generation has higher first and second law efficiencies of exceeding 80% and 50%, respectively.     

Delivery of cold hydrogen in glass fiber composite pressure vessels

We are proposing to minimize hydrogen delivery cost through utilization of glass fiber tube trailers at 200 K and 70 MPa to produce a synergistic combination of container characteristics with properties of hydrogen gas: (1) hydrogen cooled to 200 K is ∼35% more compact for a small increase in theoretical storage energy (exergy); and (2) these cold temperatures (200 K) strengthen glass fibers by as much as 50%, expanding trailer capacity without the use of much more costly carbon fiber composite vessels.     

Feasibility and sustainability analyses of carbon dioxide – hydrogen separation via de-sublimation process in comparison with other processes

Hydrogen (H₂) plays a vital role both as a reactant in petrochemical processes and as an energy carrier and storage medium. When produced from carbon-containing feed stocks, such as fossil fuels and biomass, hydrogen is typically produced as a mixture with carbon dioxide (CO₂), and must be subsequently separated by the associated energy, with an invertible energy penalty. In this study, the process for the removal of carbon dioxide from CO₂ - H₂ mixtures by de-sublimation was analysed. This process is particularly relevant to the production of liquid hydrogen (LH₂) at cryogenic temperatures, for which cooling of the H₂ stream is already necessary. The solid – gas equilibrium of CO₂ - H₂ was studied using the Peng-Robinson equation of state which provided a wide range of operating conditions for process simulation. The de-sublimation process was compared with selected conventional separation processes, including amine-based absorption, pressure swing adsorption and membrane separation. In the scenario in which the resulting products, carbon dioxide and hydrogen, were subsequently liquefied for transportation and storage at 10 bar and −46 °C, and 1 bar and −251.8 °C, respectively. The overall energy consumption per kg of CO₂ separated (MJ/kgCO₂₎, was found to follow the order: 8.19–11.21 for monoethanolamine (MEA) absorption; 1.81–8.93 for membrane separation; 1.53–5.69 for pressure swing adsorption; and 0.81–3.35 de-sublimation process. Each process was evaluated and compared on the bases of electricity demand, cooling water usage, high-pressure steam usage, and refrigeration energy requirements. Finally, the advantages and disadvantages were discussed and the feasibility and sustainability of the processes for application in the production of liquid hydrogen were assessed.