Ammonia as a hydrogen energy carrier

The gravimetric H₂ densities and the heats of combustion of tanks stored ammonia (ammonia storage tanks) were similar to those of the liquid H₂ tanks at the weight of 20–30ton, although the gravimetric H₂ density of liquid H₂ is 100 wt%. The volumetric H₂ densities and the heats of combustion of ammonia storage tanks were about 2 times higher than those of liquid H₂ tanks at 1–4 × 10⁴ m³. Gray ammonia is synthesized from hydrogen through process known as steam methane reforming, nitrogen separated from air and Haber-Bosch process. Blue ammonia is the same as gray ammonia, but with CO₂ emissions captured and stored. Green ammonia is produced by reacting hydrogen produced by electrolysis of water and nitrogen separated from air with Haber-Bosch process using renewable energies. The energy efficiencies of gray, blue and green ammonia were better than those of liquid hydrogen and methylcyclohexane (MCH) with high H₂ density and similar to the efficiency of H₂ gas. The energy efficiencies of ammonia decreased in the order, gray ammonia > blue ammonia > green ammonia. The production costs of green hydrogen energy carried increased in the order, ammonia < liquid H₂<MCH. The amounts of energy consumption by N₂ production and Haber-Bosch process were below 10% compared with the value of H₂ production from water electrolysis.     

Thermal conductivity measurements of magnesium hydride powder beds under operating conditions for heat storage applications

One of the major issues of the change in energy politics is the storage of renewable energy in order to facilitate a continuous energy supply to the grid. An efficient way to store energy (heat) is provided by the usage of Thermochemical Energy Storage (TES) in metal hydrides. Energy is stored in dehydrogenated metal hydrides and can be released by hydrogenation for consumption. One prominent candidate for high temperature (400 °C) heat storage is magnesium hydride. It is a well-known and investigated material which shows high cycling stability over hundreds of cycles. It is an abundant material, non-toxic and easy to prepare in bigger scales. One of the major drawbacks for heat storage applications is the low heat transfer capability of packed beds of magnesium hydrides. In this work we present results of effective thermal conductivity (ETC) which were measured under hydrogen pressure up to 25 bar and temperatures up to 410 °C in order to meet the operating conditions of magnesium hydride as a thermochemical heat storage material. We could show that the effective thermal conductivity of a magnesium hydride – hydrogen system at 410 °C and 25 bar hydrogen increases by 10% from 1.0 W m⁻¹ K⁻¹ to 1.1 W m⁻¹ K⁻¹ after 18 discharging and charging cycles. In dehydrogenated magnesium hydride this increase of the thermal conductivity was found to be at 50% from 1.20 W m⁻¹ K⁻¹ to 1.80 W m⁻¹ K⁻¹ at 21 bar hydrogen. These data are very important for the design and construction of heat storage tanks based on high temperature metal hydrides in the future.     

Polymer electrolytes based on modified natural rubber for use in rechargeable lithium batteries

Modified natural rubber (NR) polymer hosts having low transition glass temperatures have been investigated. Three types of modified NR, namely 25% epoxidised NR (ENR-25), 50% ENR (ENR-50) and polymethyl methacrylate grafted NR (MG-49) were employed. Results are reported for ionic conductivity and thermal properties for both unplasticised and plasticised polymer electrolyte systems. The samples were in the form of free standing films with the thickness 0.2–0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticisers. Unplasticised modified NR based systems exhibit ionic conductivities in 10⁻⁶–10⁻⁵ S cm⁻¹ range at ambient temperatures. Incorporating 50–100% of EC/PC by weight to the systems yielded mechanically stable films and ionic conductivities in 10⁻⁴–10⁻³ S cm⁻¹ range at ambient temperature. The thermal event of the systems has displayed an increasing trend of transition glass temperature at elevated salt concentration whereas incorporation of EC and PC into the systems leads to marked reduction in their T_g values.     

Research on systems for producing liquid hydrogen and LNG from hydrogen-methane mixtures with hydrogen expansion refrigeration

In industrial production processes, gas mixtures with hydrogen and methane as main useful components are often obtained as by-products, which are often not well utilized. In this paper, an innovative approach is proposed to produce both liquid hydrogen and LNG from industrial by-products with H₂ and CH₄ as main components. Taking the purified hydrogen-methane mixtures as the research object, four different separation-liquefaction processes (namely Open Loop-N₂, Open Loop-H₂, Closed Loop-N₂, Closed Loop-H₂) are constructed and optimized, with refrigeration supplied with hydrogen expansion at the cryogenic section and nitrogen or hydrogen expansion at the precooling section. A distillation column is set up before the mixture enters the cryogenic section to facilitate the production of high purity methane and hydrogen products. Every system achieves excellent energy integration, and the load of condenser and reboiler in the column is borne by the hydrogen expansion cycle in the cryogenic section. For each process, the influence of hydrogen mole proportion in feed gas between 10% and 90% on the process performance is analyzed. The results show that the purities of LNG and liquid hydrogen products obtained by the system are higher than 99.99%, and the specific energy consumption of the systems is within 18.01–41.72 kWh·kmol⁻¹ for different situations. At the same time, an open loop and a closed loop are constructed, respectively, to investigate the necessity of recovering cold energy of boil-off gas. The results suggest recommendation of open loop system with nitrogen precooling.     

A liquefied energy chain for transport and utilization of natural gas for power production with CO2 capture and storage – Part 3: The combined carrier and onshore storage

A novel energy and cost effective transport chain for stranded natural gas utilized for power production with CO₂ capture and storage is developed. It includes an offshore section, a combined gas carrier and an integrated receiving terminal. The combined carrier will transport liquid carbon dioxide (LCO₂) and liquid nitrogen (LIN) outbound, where natural gas (NG) is cooled and liquefied to LNG by vaporization of LIN and LCO₂ onboard the carrier. The same carrier is used to transport the LNG onshore, where the NG can be used for power production with CO₂ capture. The combined carrier consists of 10 cylindrical tanks with a diameter of 9.2 m and varying lengths from 14 to 40 m. The total ship volume is 13,000 m³. Assuming 85% capture rate of the CO₂, the maximum ship utilization factor (SUF) is 63.4%. Due to the combined use of the storage tanks, the SUF is decreased with 1.4% points to 62%. The ship is equipped with a bi-directional submerged turret loading for anchoring and loading of NG and unloading of CO₂. Two ships can deliver NG to and remove CO₂ from a 400 MW_net power plant, and still obtain continuous production of LNG offshore without intermediate storage. The investment cost for each gas carrier is 40 million EUR giving total transport cost of 16.9 EUR/tonne LNG. The cost for the offshore transfer system is 6.6 million EUR per tonne LNG, whereas the cost for onshore storage and loading system is 3.1 and 0.8 million EUR per tonne LNG, respectively. The total specific costs for the ship transport, including onshore storage, loading shipping and offshore unloading are 27.5 EUR per tonne LNG for a roundtrip of 5 days, including voyage, production of LNG, unloading, connecting and berthing.     

Improved hydrogen permeation through thin Pd/Al2O3 composite membranes with graphene oxide as intermediate layer

Here we proposed the decreasing in the roughness of asymmetric alumina (Al₂O₃) hollow fibers by the deposition of a thin graphene oxide (GO) layer. GO coated substrates were then used for palladium (Pd) depositions and the composite membranes were evaluated for hydrogen permeation and hydrogen/nitrogen selectivity. Dip coating of alumina substrates for 45, 75 and 120 s under vacuum reduced the surface mean roughness from 112.6 to 94.0, 87.1 and 62.9 nm, respectively. However, the thicker GO layer (deposited for 120 s) caused membrane peel off from the substrate after Pd deposition. A single Pd layer was properly deposited on the GO coated substrates for 45 s with superior hydrogen permeance of 24 × 10⁻⁷ mol s⁻¹m⁻² Pa⁻¹ at 450 °C and infinite hydrogen/nitrogen selectivity. Activation energy for hydrogen permeation through the Al₂O₃/GO/Pd composite membrane was of 43 kJ mol⁻¹, evidencing predominance of surface rate-limiting mechanisms in hydrogen transport through the submicron-thick Pd membrane.     

Sorption of hydrogen in titanium plates at low pressure

In this work we studied the influence of pressure and temperature on the sorption of hydrogen in titanium plates using a constant volume system at low pressure. The system consisted of a stainless steel vacuum chamber with an electrically isolated titanium plate inside. Before each sorption experiment the plate was degassed by heating at 750 °C and 10⁻⁶ mbar for several minutes. The pressure in the chamber for the hydrogen sorption was between 10⁻¹ and 10³ mbar and the temperature in the titanium samples was between 10 and 750 °C. The results suggest that the amount of absorbed hydrogen in the plates depends on the quantity of hydrogen present in the system, the cleanliness and thermal degassing of the titanium. The degassing process results as the most important condition, because the samples degassed three times before being in contact with hydrogen absorbed rapidly this gas at room temperature. The titanium samples that were degassed just once absorbed hydrogen at the typical conditions of 600–700 °C.     

Recycling phosphorus by fast pyrolysis of pig manure: Concentration and extraction of phosphorus combined with formation of value-added pyrolysis products

In order to recycle phosphorus from the livestock chain back to the land, fast pyrolysis of concentrated pig manure at different temperatures (400 °C, 500 °C, 600 °C), was undertaken to concentrate the phosphorus in the char fraction for recovery. Results show that 92%–97% of the phosphorus present in the pyrolysis feedstock ends up in the char fraction, while 60%–75% of that can be directly leached as ortho-phosphate, and 90% as total phosphorus. After char combustion, 100% of the phosphorus present can be leached as ortho-phosphate from the ash. Yields, heating values, and properties of the pyrolysis products have been analyzed. Expressed per tonne of fresh pig manure, the char phosphorus value is estimated at 0.81 € t⁻¹–0.86 € t⁻¹, energy application value at 2.4 € t⁻¹–3.6 € t⁻¹ (liquid organic phase) and 0.5 € t⁻¹–0.7 € t⁻¹ (char), and the fertilizer value of the aqueous phase at 0.10 € t⁻¹–0.18 € t⁻¹. Including costs for energy requirement, solid–liquid separation, and drying, pyrolysis costs are estimated around 0.4 € t⁻¹–4.4 € t⁻¹ for pig manure. It is concluded that pyrolysis costs compare positively with pig manure transportation costs of 0.06 € t⁻¹ km⁻¹, while it also offsets phosphorus extraction from the rapidly depleting phosphate rock.     

Flow electrification characteristics of liquid hydrogen in pipe flow

Flow electrification occurs when a dielectric liquid flows along the wall surface, and it may cause electrostatic hazards such as spark discharges. Flow electrification issues of liquid hydrogen should be carefully treated since its low electrical conductivity and dangerous flammability. In this study, flow electrification characteristics of liquid hydrogen in pipe flow are numerically investigated. A theoretical model coupling the electric field and the flow field is introduced to govern the behaviour and distribution of charges, and an interface discharge model is adopted to describe the charge transfer boundary condition. The theoretical model is validated by comparing the simulation with experiment data, and the results show a good agreement with the averaged related deviation below 10%. The result of a common case, with flow velocity u of 1 m/s, pipe radius a 0.01 m, and length L 1 m, shows that the charge density, streaming current, and the electric potential of liquid hydrogen flow are in the magnitude of 10⁻¹² C·m⁻³, 10⁻¹⁶ A and 10⁻² V, respectively. Flow parameters, including flow velocity and pipe size, have a certain effect on the flow electrification characteristics of liquid hydrogen flow. By dimensionless parameterization, it is found that Reynolds numbers (Re), r/a, and x/a are exactly three orthogonal parameters determining the charge density distribution. Furthermore, the effects of electrical conductivity on the distribution of charges and charge dissipation have also been discussed. Finally, the safety assessment of the liquid hydrogen transportation system has been discussed, with extra consideration of the impurities and gas-liquid two-phase flow regime. To sum up, this work presents an in-depth and comprehensive insight into the flow electrification of liquid hydrogen flow, which is of great significance to the transportation safety of liquid hydrogen.     

A novel MCFC hybrid power generation process using solar parabolic dish thermal energy

In this paper, a novel molten carbonate fuel cell hybrid power generation process with using solar parabolic dish thermal energy is proposed. The process contains MCFC, Oxy-fuel and Rankine power generation cycles. The Rankine power generation cycles utilized various types of working fluid to emphasize taking advantage of the cycles in different thermodynamic conditions. The required hot and cold energies are provided from solar dish parabolic thermal hot and liquefied natural gas (LNG) cold energies, respectively. The carbon dioxide (CO₂) from MCFC effluent stream is captured from the process at liquid state. The process total heat integrated and in this regards, no need to any hot and cold external sources with the net electrical power generation. The energy and exergy analysis are conducted to determine the approaches to improve the process performance. This integrated structure consumed 2.30 × 10⁶ kg h⁻¹ of air and 2.67 × 10⁶ kg h⁻¹ of LNG to generate 292597 kW of net power. The products of this integrated structure are 6.25 × 10⁴ kg h⁻¹ of condensates, 183 kg h⁻¹ of water vapor, 2.20 × 10⁶ kg h⁻¹ of MCFC effluent stream, 2.60 × 10⁶ kg h⁻¹ of natural gas and 1.10 × 10⁵ kg h⁻¹ of CO₂ in liquid state. The presented new integrated structure has overall thermal efficiency of 73.14% and total exergy efficiency of 63.19%. Also, sensitivity analysis is performed for determination of the process key parameters which affected the process operating performance.     

Shipping the sunshine: An open-source model for costing renewable hydrogen transport from Australia

Green hydrogen (H₂) is emerging as a future clean energy carrier. While there exists significant analysis on global renewable (and non-renewable) hydrogen generation costs, analysis of its transportation costs, irrespective of production method, is still limited. Complexities include the different forms in which hydrogen can be transported, the limited experience to date in shipping some of these carrier forms, the trade routes potentially involved and the possible use of different shipping fuels. Herein, we present an open-source model developed to assist stakeholders in assessing the costs of shipping various forms of hydrogen over different routes. It includes hydrogen transport in the forms of liquid hydrogen (LH₂), ammonia, liquified natural gas (LNG), methanol and liquid organic hydrogen carriers (LOHCs). It considers both fixed and variable costs including port fees, possible canal usage charges, fuel costs, ship capital and operating costs, boil-off losses and possible environmental taxes, among many others. The model is applied to the Rotterdam-Australia route as a case study, revealing ammonia ($0.56/kg_H2) and methanol ($0.68/kg_H2) as the least expensive hydrogen derivatives to transport, followed by liquified natural gas ($1.07/kg_H2), liquid organic hydrogen carriers ($1.37/kg_H2) and liquid hydrogen ($2.09/kg_H2). While reducing the transportation distance led to lower shipping costs, we note that the merit order of assumed underlying shipping costs remain unchanged. We also explore the impact of using hydrogen (or the hydrogen carrier) as a low/zero carbon emission fuel for the ships, which led to lowering of costs for liquified natural gas ($0.88/kg_H2), a similar cost for liquid hydrogen ($2.19/kg_H2) and significant increases for the remainder. Given our model is open-sourced, it can be adapted globally and updated to match the changing cost dynamics of the emerging green hydrogen market.     

Burner-heated dehydrogenation of a liquid organic hydrogen carrier (LOHC) system

For a hydrogen-based economy, safe and efficient hydrogen storage is essential. Compared to other chemical hydrogen storage technologies, such as ammonia or methanol, liquid organic hydrogen carrier (LOHC) systems allow for a reversible storage of hydrogen while being easy to handle in a diesel-like manner. In our contribution, we describe for the first time the successful utilization of the exhaust gas enthalpy of a porous media burner to directly supply the dehydrogenation heat for a kW-scale dehydrogenation of the hydrogen-rich LOHC compound perhydro dibenzyltoluene (H18-DBT). Our setup demonstrates the dynamics of the dehydrogenation unit at a realized maximum hydrogen power of 3.9 kW_th, based on the lower heating value of the released hydrogen. For the intended applications with fluctuating hydrogen demand, e.g. a hydrogen refueling station (HRS) or stationary heating in buildings, a dynamic hydrogen supply from LOHC is important. Methane, e.g. from a biogas plant, is utilized in our scenario as a fuel source for the burner. Hydrogen is released within 30 min after cold start of the system. The dehydrogenation unit exhibits a power density relative to the reactor volume of about 0.5 kW_therm l⁻¹ based on the lower heating value of the hydrogen and a catalyst productivity of up to 0.65 g_H2 g_Pt⁻¹ min⁻¹ for hydrogen release from H18-DBT. An analysis of the by-products and reaction intermediates shows low by-product formation (e.g. maximum 0.6 wt.-% for high boilers and 0.9 wt.- % for low boilers) and uniform distribution of intermediates after the reaction. Thus, a relatively homogeneous temperature distribution and a uniform LOHC flow in the reaction zone can be assumed. Our findings illustrate the dynamics (heating rates of about 10 K min⁻¹) and performance of direct heating of a release unit with a burner and represent a significant step towards LOHC-based hydrogen provisioning systems at technically relevant scales.     

Techno-economic analysis of fuel cell auxiliary power units as alternative to idling

This paper presents a techno-economic analysis of fuel-cell-based auxiliary power units (APUs), with emphasis on applications in the trucking industry and the military. The APU system is intended to reduce the need for discretionary idling of diesel engines or gas turbines. The analysis considers the options for on-board fuel processing of diesel and compares the two leading fuel cell contenders for automotive APU applications: proton exchange membrane fuel cell and solid oxide fuel cell. As options for on-board diesel reforming, partial oxidation and auto-thermal reforming are considered. Finally, using estimated and projected efficiency data, fuel consumption patterns, capital investment, and operating costs of fuel-cell APUs, an economic evaluation of diesel-based APUs is presented, with emphasis on break-even periods as a function of fuel cost, investment cost, idling time, and idling efficiency. The analysis shows that within the range of parameters studied, there are many conditions where deployment of an SOFC-based APU is economically viable. Our analysis indicates that at an APU system cost of $ 100 kW⁻¹, the economic break-even period is within 1 year for almost the entire range of conditions. At $ 500 kW⁻¹ investment cost, a 2-year break-even period is possible except for the lowest end of the fuel consumption range considered. However, if the APU investment cost is $ 3000 kW⁻¹, break-even would only be possible at the highest fuel consumption scenarios. For Abram tanks, even at typical land delivered fuel costs, a 2-year break-even period is possible for APU investment costs as high as $ 1100 kW⁻¹.     

The role of synthesis method in hydrogen evolution activity of Ce doped ZnO/CNTs photocatalysts: A comparative study

Cerium doped zinc oxide/carbon nanotubes (Ce doped ZnO/CNTs) composites are synthesized using sol-gel, hydrothermal deposition and one-pot hydrothermal methods. These composites are tested for photocatalytic hydrogen evolution from water-methanol mixture to check the effect of synthesis method on photocatalytic activity of these composites. Each synthesis method induces unique physiochemical properties in composite and hydrogen evolution rates. The composite prepared by one-pot hydrothermal method shows highest hydrogen evolution of 759 μmolh⁻¹g⁻¹ under sunlight. This hydrogen evolution rate is significantly higher than the sol-gel synthesized photocatalyst (579 μmolh⁻¹g⁻¹) and hydrothermal deposition method (621 μmolh⁻¹g⁻¹). The high hydrogen evolution activity of the prepared composites can be attributed to small crystallite size, low recombination of charge carriers, large active surface area, short diffusion pathway for photoinduced electrons and high oxidation potential of photogenerated holes. Focused on different methods, this study provides a pathway for production of efficient semiconductor photocatalysts for environmental applications.     

Proton conduction in ceria-doped Ba2In2O5 nanocrystalline ceramic at low temperature

Sintered pellets of Ce-doped Ba₂In₂O₅ (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300 °C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0–30 vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100–300 °C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2 × 10⁻⁶ K⁻¹ from 25 to 1250 °C.     

Lithium nitrate and lithium trifluoromethanesulfonate ammoniates for electrolytes in lithium batteries

The liquid ammonia solutions of lithium nitrate and lithium trifluoromethanesulfonate (triflate) have been found to be highly conductive inorganic electrolytes with low vapor pressures. The important phases of the LiNO₃ · xNH₃ solutions (1.5 < x < 3.1) and those of the LiSO₃CF₃ · yNH₃ solutions (1.5 < y < 3.5) are documented. In addition, the temperature dependence of their conductivities, their electrical stability windows, and their NH₃ vapor pressures were determined. In summary, the lithium triflate ammoniate (LiCF₃SO₃ · 2NH₃) remains a liquid down to −10 °C. It has an electroactivity range of 3.8 V and a conductivity of 0.6 × 10⁻³ ω⁻¹ cm⁻¹ at −10 °C. The NH₃ vapor pressure is less than 1 bar at 60 °C. The lithium nitrate ammoniate (LiNO₃ · 2NH₃) has an electroactivity range of 3.5 V and a conductivity of 2.5 × 10⁻² ω⁻¹ cm⁻¹ at 20 °C. The freezing point of the nitrate ammoniate is between 3 °C and −10 °C depending on the stoichiometry. Its NH₃ vapor pressure remains below 1 bar up to 40 °C. In addition, Li/MnO₂ batteries were constructed and tested using the above mentioned electrolytes.     

Thermodynamics analysis of hydrogen storage based on compressed gaseous hydrogen,liquid hydrogen and cryo-compressed hydrogen

Safe, reliable, and economic hydrogen storage is a bottleneck for large-scale hydrogen utilization. In this paper, hydrogen storage methods based on the ambient temperature compressed gaseous hydrogen (CGH₂), liquid hydrogen (LH₂) and cryo-compressed hydrogen (CcH₂) are analyzed. There exists the optimal states, defined by temperature and pressure, for hydrogen storage in CcH₂ method. The ratio of the hydrogen density obtained to the electrical energy consumed exhibits a maximum value at the pressures above 15 MPa. The electrical energy consumed consists of compression and cooling down processes from 0.1 MPa at 300 K to the optimal states. The recommended parameters for hydrogen storage are at 35–110 K and 5–70 MPa regardless of ortho-to parahydrogen conversion. The corresponding hydrogen density at the optimal states range from 60.0 to 71.5 kg m⁻³ and the ratio of the hydrogen density obtained to the electrical energy consumed ranges from 1.50 to 2.30 kg m⁻³ kW⁻¹. While the ortho-to para-hydrogen conversion is considered, the optimal states move to a slightly higher temperatures comparing to calculations without ortho-to para-hydrogen conversion.     

Evaluation of structural,electronic, thermoelectric,and optical results of C-doped HfO2 by first-principle's investigation

In this work, we report the ab initio numerical simulation investigation on the crystal lattice, electronic structure, optical, and transport properties of pure and C-doped crystalline hafnium dioxide (c-HfO₂) using FP-LAPW method. Different exchange correlation functionals like generalized gradient approximation (GGA) of PBE-sol and Tran and Blaha's modified Becke-Johnson exchange potential (mBJ) within density functional theory have been used. Two kinds of defects in cubic pure HfO₂ have been investigated: one is substitution of Hf atom by C impurity and other substitution of O atom by C impurity in crystalline HfO₂. The computed results indicate that impurity energy bands as a result of 2p states of C are found to present in the band gap of c-HfO₂. Few of these bands are present at the conduction band minimum, which results to a noteworthy band gap contraction, and hence electrons close to Fermi level get transferred in doped c-HfO₂. We have also analysed the dielectric function, absorption coefficient, optical conductivity, optical function, electron energy loss, and reflectivity for both pure HfO₂ and doped with C. Furthermore, the temperature-dependent transport properties of C-doped HfO₂ are also discussed in terms of Seeback coefficient, thermal conductivities, electronic conductivities, power factor, and figure of merit in the temperature range 0 to 1200 K. The calculated value of PF for pure HfO₂ was found to increase from 0.01 × 10¹² WK⁻²m⁻¹s⁻¹ at 50 K to 1.79 × 10¹² WK⁻²m⁻¹s⁻¹ at 1200 K and for HfO_{2(1 − x)}C_x it was found to increase from 0.06 × 10¹² WK⁻²m⁻¹s⁻¹ at 50 K to 0.25 × 10¹² WK⁻²m⁻¹s⁻¹ at 1200 K.     

Hydrogen and LNG production from coke oven gas with multi-stage helium expansion refrigeration

Here we propose a novel cryogenic system to simultaneously produce liquid hydrogen (LH₂) and liquefied natural gas (LNG) from coke oven gas. The coke oven gas, simplified as a mixture of methane and hydrogen, directly enters the cryogenic system. Due to the very low temperature of liquid hydrogen, helium is selected as the refrigerant, and the energy needed for the liquefaction is supplied by a multi-stage helium expansion refrigeration system. The high-purity liquid hydrogen and LNG products are obtained with the help of a cryogenic distillation column. The whole cryogenic process is simulated with the Aspen HYSYS software to determine the parameters of each process point and key component. We found that the process is able to produce LH₂ and LNG of very high purity. Using the power consumption of the product liquefaction as the major performance parameter for the analysis, optimum parameters of the multi-stage helium expansion liquefaction process could be found. The results show that the proposed system can achieve a methane recovery rate of 97.9% and a hydrogen recovery rate of 99.7% with acceptable energy consumption.     

Proton conduction of novel calcium phosphate nanocomposite membranes for high temperature PEM fuel cells applications

This work describes the synthesis and evaluation of nanocomposite membranes based on calcium phosphate (CP)/ionic liquids (ILs) for high-temperature proton exchange membrane (PEM) fuel cells. Several composite membranes were synthesized by varying the mass ratios of ILs with respect to the CP and all supported on porous polytetrafluoroethylene (PTFE). The membranes exhibit high proton conductivities. Two ionic liquids were investigated in this study, namely, 1-Hexyl-3- methylimidazolium tricyanomethanide, [HMIM][C₄N₃⁻], and 1-Ethyl-3-methylimidazolium methanesulfonate, [EMIM][CH₃O₃S⁻]. At room temperature, the CP/PTFE/[HMIM][C₄N₃⁻] composite membrane possessed a high proton conductivity of 0.1 S cm⁻¹. When processed at 200 °C, and fully anhydrous conditions, the membrane showed a conductivity of 3.14 × 10⁻³ S cm⁻¹. Membranes based on CP/PTFE/[EMIM][CH₃O₃S⁻] on the other hand, had a maximum proton conductivity of 2.06 × 10⁻³ S cm⁻¹ at room temperature. The proton conductivities reported in this work appear promising for the application in high-temperature PEMFCs operated above the boiling point of water.