Facilitating analysis of trace impurities in hydrogen: Enrichment based on the principles of pressure swing adsorption

A laboratory-scale gas sampling and impurity enrichment device (GSIED) based on the principles of pressure swing adsorption (PSA) has been designed, fabricated, and tested to show that such a device provides an effective method to enrich trace impurity species in hydrogen by a factor of 10 or more. With the availability of a high pressure sample gas at the hydrogen refueling stations, the device uses only a pressure sequence to enrich the impurities without need of a temperature cycle. Enrichment of the impurities allows the use of simpler and less expensive analytical instruments for hydrogen quality monitoring and certification purposes. A series of experiments was conducted using activated carbon as the PSA sorbent for impurity enrichment in a hydrogen gas containing N₂, CO, CH₄, and CO₂. The enrichment factor varied for the different species according to their affinity of adsorption. The measured impurity enrichment factors agreed well with theoretical analyses, and are functions of the pressure ratio (adsorption/desorption pressures) and adsorption affinity relative to hydrogen (selectivity). Depending on the species of interest and the volume of the enriched sample needed for analysis, the device can be designed to enrich the impurities in hydrogen in 40 min or less.     

Hydrogen permeation through a Pd-based membrane and RWGS conversion in H2/CO2, H2/N2/CO2 and H2/H2O/CO2 mixtures

This study investigated the effect of gases such as CO₂, N₂, H₂O on hydrogen permeation through a Pd-based membrane −0.012 m² – in a bench-scale reactor. Different mixtures were chosen of H₂/CO₂, H₂/N₂/CO₂ and H₂/H₂O/CO₂ at temperatures of 593–723 K and a hydrogen partial pressure of 150 kPa. Operating conditions were determined to minimize H₂ loss due to the reverse water gas shift (RWGS) reaction. It was found that the feed flow rate had an important effect on hydrogen recovery (HR). Furthermore, an identification of the inhibition factors to permeability was determined. Additionally, under the selected conditions, the maximum hydrogen permeation was determined in pure H₂ and the H₂/CO₂ mixtures. The best operating conditions to separate hydrogen from the mixtures were identified.     

Catalytic transformation of H2S for H2 production

Hydrogen sulfide (H₂S) gas is a by-product from natural gas refining, hydrodesulfurization of various fossil fuels, and syngas cleaning from pyrolysis and gasification. Catalytic pyrolysis of H₂S provides an alternative and effective pathway to recover both H₂ and sulfur. Catalysts from hydrotalcite of ZnAl, ZnNiAl, and ZnFeAl were employed for H₂S pyrolysis and compared with TiO₂ and MoS₂ at atmospheric pressure and temperatures in the range of 923–1123 K. Kinetic analysis was carried out in a packed bed reactor which revealed the effect of H₂S partial pressures to be of the order of 0.8–1 with respect to H₂S. The developed novel catalysts showed improved performance with significantly reduced activation energy compared to TiO₂ by 30 kJ/mol as well as higher H₂S conversion during pyrolysis (17% at 1173 K) than with MoS₂ catalyst, even at high H₂S partial pressure which is necessary for viable hydrogen production. The new approach showed an alternate economical and efficient pathway of catalyst design to obtain high activity and stability for simultaneous H₂ energy and pure sulfur recovery from unwanted H₂S resources.     

Effect of iron concentration on continuous H2 production using membrane bioreactor

The effect of FeSO₄ on continuous H₂ production in a membrane bioreactor (MBR) was investigated using anaerobic mixed microflora under mesophilic condition. The H₂ production of 41.6 l/day was obtained at 10.9 mg FeSO₄/l, which was 1.59 times higher than that at 2.7 mg FeSO₄/l. Between 2.7 and 13.7 mg FeSO₄/l, the H₂ production rate increased in parallel with the H₂ yield under high-cell-density condition. For the same amounts of FeSO₄, increases in butyric acid together with decreases in lactic acid promoted a reduction of the number of protons and the resultant release of H₂. The hydrogenase activity of 1.08 mg methylene blue (M.B) reduced/min at 10.9 mg FeSO₄/l was about sixfold higher than at 2.7 mg FeSO₄/l. These results suggest that the addition of iron and sulfur to an MBR is an important key factor in the enhancement of H₂ production.     

H2 production in silica membrane reactor via methanol steam reforming: Modeling and HAZOP analysis

The main aim of this work is the presentation of both qualitative safety and quantitative operating analyses of silica membrane reactor (MR) for carrying out methanol steam reforming (MSR) reaction to produce hydrogen. To perform the safety analysis, HAZOP method is used. Before the HAZOP analysis, a comprehensive investigation of most important operating parameters effects on silica MR performance is required. Therefore, for a quantitative analysis, a 1-dimensional and isothermal model is developed for evaluating the reaction temperature, reaction pressure, feed molar ratio (steam/methanol) and feed flow rate effects on silica MR performance in terms of methanol conversion and hydrogen recovery. The model validation results show good agreement with experimental data from literature. As a consequence, simulation results indicate that the reaction pressure and feed molar ratio have dual effect on silica MR performance. In particular, it is found that methanol conversion is decreased by increasing the reaction pressure from 1.5 to 4.0 bar, whereas over 4.0 bar, it is improved. Moreover, the hydrogen recovery is decreased by increasing the feed molar ratio from 1 to 5, while over 5, it was approximately constant. After the evaluation of modeling results, the HAZOP analysis for silica MR is carried out during MSR reaction. The analysed operating parameters in the modeling study have been considered as key parameters in the HAZOP analysis. The safety assessment results are presented in tables as check list. By considering the HAZOP results, safety pretreatment works are recommended before or during the experimental tests of MSR reaction in silica MR. According to different parameters consequences, reaction temperature is the most critical parameter in MSR reaction for the silica MR studied in this work. In particular, to avoid the consequences of temperature deviation, it is recommended to use a PID temperature controller in the silica MR for MSR reaction.     

Influence of hydrogen dilution on low-temperature polycrystalline silicon formation using RF excitation SiH4/H2 plasma

The effect of hydrogen dilution was investigated on polycrystalline silicon formation using radio frequency excitation SiH₄/ H₂ plasma. The hydrogen dilution reduces the growth rate of the a-Si : H films. The dark conductivity of the a-Si : H films increases with increasing H₂ dilution. The dark conductivity of the poly-Si films formed by recrystallization annealing of the a-Si : H film decrease with H₂ dilution. The grain size, with X-ray diffraction spectroscopy and scanning electron microscopy images of the poly-Si films, is in reverse ratio to the H₂ dilution.     

Effect of CO and CO2 impurities on performance of direct hydrogen polymer-electrolyte fuel cells

Mechanisms by which trace amounts of CO and CO₂ impurities in fuel may affect the performance of direct hydrogen polymer-electrolyte fuel cell stacks have been investigated. It is found that the available data on CO-related polarization losses for Pt electrodes could be explained on the basis of CO adsorption on bridge sites, if the CO concentration is less than about 100 ppm, together with electrochemical oxidation of adsorbed CO at high overpotentials. The literature data on voltage degradation due to CO₂ is consistent with CO production by the reverse water–gas shift reaction between the gas phase CO₂ and the H₂ adsorbed on active Pt sites. The effect of oxygen crossover and air bleed in “cleaning” of poisoned sites could be modeled by considering competitive oxidation of adsorbed CO and H by gas phase O₂. A model has been developed to determine the buildup of CO and CO₂ impurities due to anode gas recycle. It indicates that depending on H₂ utilization, oxygen crossover and current density, anode gas recycle can enrich the recirculating gas with CO impurity but recycle always leads to buildup of CO₂ in the anode channels. The buildup of CO and CO₂ impurities can be controlled by purging a fraction of the spent anode gas. There is an optimum purge fraction at which the degradation in the stack efficiency is the smallest. At a purge rate higher than the optimum, the stack efficiency is reduced due to excessive loss of H₂ in purge gas. At a purge rate lower than the optimum, the stack efficiency is reduced due to the decrease in cell voltage caused by the excessive buildup of CO and CO₂. It is shown that the poisoning model can be used to determine the limits of CO and CO₂ impurities in fuel H₂ for a specified maximum acceptable degradation in cell voltage and stack efficiency. The impurity limits are functions of operating conditions, such as pressure and temperature, and stack design parameters, such as catalyst loading and membrane thickness.     

Catalysts for H2 production using the ethanol steam reforming (a review)

This review aims to provide an overview of the main catalytic studies of H₂ production by ethanol steam reforming (ESR). The reaction is endothermic and produces H₂, CO₂, CH₄, CO and coke. The conversion and H₂ selectivity of these products depended greatly of the physicochemical properties of the catalysts, active metal, promoters, temperature, long-term reaction, water/ethanol ratio, space velocity, contact time, and presence of O₂. Initial total conversion has been reported in all catalysts evaluated between 300 and 850 °C. The noble catalysts with high selectivity to H₂ (more than 80%) were: Rh, Ru, Pd and Ir and non-noble metal catalysts were: Ni, Co and Cu. The support materials include CeO₂, ZnO, MgO, Al₂O₃, zeolites-Y, TiO₂, SiO₂, La₂O₂CO₃, CeO₂–ZrO₂ and hydrotalcites. The impregnation method produced the best noble metal catalysts in terms of selectivity and conversion. The decrease of coke was related with the presence of basic sites on the support.     

Direct high-purity hydrogen production from ammonia by using a membrane reactor combining V-10mol%Fe hydrogen permeable alloy membrane with Ru/Cs2O/Pr6O11 ammonia decomposition catalyst

The hydrogen production capabilities of the membrane reactor combining V-10 mol%Fe hydrogen permeable alloy membrane with Ru/Cs₂O/Pr₆O₁₁ ammonia decomposition catalyst are studied. The ammonia conversion is improved by 1.7 times compared to the Ru/Cs₂O/Pr₆O₁₁ catalyst alone by removing the produced hydrogen through the V-10mol%Fe alloy membrane during the ammonia decomposition. 79% of the hydrogen atoms contained in the ammonia gas are extracted directly as high-purity hydrogen gas. Both the Ru/Cs₂O/Pr₆O₁₁ catalyst and the V-10 mol% Fe alloy membrane are highly durable, and the initial performance of the hydrogen separation rate lasts for more than 3000 h. The produced hydrogen gas conforms to ISO 14687–2:2019 Grade D for fuel cell vehicles because the ammonia and nitrogen concentrations are less than 0.1 ppm and 100 ppm, respectively.     

Effect of UV irradiation on PC membrane and use of Pd nanoparticles with/without PVP for H2 selectivity enhancement over CO2 and N2 gases

The hydrogen-based economy is one of the possible approaches toward to eliminate the problem of global warming, which are increases because of the gathering of greenhouse gases. Palladium (Pd) is well-known material having a strong affinity to the hydrogen absorbing property and thus appropriate material to embed in the membrane for the improvement of selective permeation of hydrogen gas. In present work, we have functionalized polycarbonate (PC) membranes with the help of UV irradiation to embed the Pd nanoparticles in pores as well as on the surface of the PC membrane. Use of Pd Nanoparticles is helpful to enhance the H₂ selectivity over other gases (CO₂, N_2, etc.). Also, the UV based modification of membrane increases the attachment of Pd Nanoparticles. Further to enhance the Pd nanoparticles attachment, we used PVP binder with Pd nanoparticles solution. Gas permeability measurements of functionalized PC membranes have been carried out, and better selectivity of hydrogen has been found in the functionalized and Pd nanoparticle binded membrane. PC membrane with 48 h UV irradiated and Pd NPs with PVP have been found to have maximum selectivity and permeability for H₂ gas. All the samples being characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and UV–Vis spectroscopy for their morphological and structural investigation.     

Stability of Y2O3 hydrogen isotope permeation barriers in hydrogen at high temperatures

Hydrogen isotope permeation barriers (HIPB) have great potential applications in the fields of hydrogen energy and thermonuclear fusion energy. Here, we report the stability of Y₂O₃ HIPB in gaseous hydrogen at high temperatures including the structures, mechanical properties and electrical properties. With increasing hydrogen treatment time at 700 °C, the high-index diffractions of Y₂O₃ became weak gradually whereas the (400) diffraction was strengthened. The color of the Y₂O₃ HIPB changed from brown to gray. The bonding strength decreased by 61% with increasing hydrogen treatment time, and finally remained unchanged. Meanwhile, the electrical resistivity of the Y₂O₃ HIPB decreased from 8.2 × 10⁹ Ω cm by over two orders of magnitude and then tended to be constant. The oxygen loss as well as hydrogen incorporation was proposed to be responsible for these modifications and indications of the present work for preparation of HIPB with high reliability were discussed.     

CO2 methanation combined with NH3 decomposition by in situ H2 separation using a Pd membrane reactor

Combination of the reactions by means of membrane separation techniques are of interest. The CO₂ methanation was combined with NH₃ decomposition by in situ H₂ separation through a Pd membrane. The CO₂ methanation reaction in the permeate side was found to significantly enhance the H₂ removal rate of Pd membrane compared to the use of sweep gas. The reaction rate of CO₂ methanation was not influenced by H₂ supply through the Pd membrane in contrast to NH₃ decomposition in the retentate side. However, the CH₄ selectivity could be improved by using a membrane separation technique. This would be caused by the active dissociated H species which might immediately react with adsorbed CO species on the catalysts to CH₄ before those CO species desorbed. From the reactor configuration tests, the countercurrent mode showed higher H₂ removal rate in the combined reaction at 673 K compared to the cocurrent mode but the reaction rate in CO₂ methanation should be improved to maximize the perfomance of membrane reactor.     

Electrolysis of coal slurries to produce hydrogen gas: Relationship between CO2 and H2 formation

The purpose of this study was to produce hydrogen gas by electrolysis of coal slurries and to investigate the relation between hydrogen (H₂) and carbon dioxide (CO₂) formation. Electrolysis of coal slurries was evaluated at 40 °C and 1.0 V cell potential to examine H₂ and CO₂relationship. When electrolysis was performed after the coal slurry was mixed with Fe(II)/Fe(III) ions and stirred overnight (>12 h), no CO₂ gas was observed at the anode compartment. The results of total organic carbon (TOC) indicated that after electrolysis, few organic compounds were transformed into the solution and these organic compounds did not convert into CO₂. GC analysis, on the other hand, revealed that the H₂ collected at the cathode was pure and did not require any further purification process. Hydrogen generation or electrolysis efficiency of coal slurries cannot be calculated or estimated by examining CO₂ generation as reported in the literature. Low temperature and low cell potential were not sufficient to oxidize coal quantitatively.     

Quantification of “delivered” H2 by a volumetric method to test H2 storage materials

We set up and validated a volumetric method to quantify the amount of hydrogen “delivered” after saturation of a solid material as adsorber at different pressures (up to 100 kg_f/cm²) and temperatures (down to 77 K). This is the practically most relevant datum to quantify the effectiveness of an adsorbent for the present application. A complementary dynamic method has been also developed to take into account the reversibility of adsorption and to assess in at least a semi-quantitative way the strength of interaction between H₂ and the adsorbent. The method has been applied to compare the hydrogen storage capacity of some significant different carbon-based materials (two active carbons and one graphite), as supplied or after thermal treatments under oxidising or reducing conditions. The best results, ca. 7 wt% H₂ “delivered”, were achieved after saturation at 77 K, 20 kg_f/cm² with an active carbon with ca. 3000 m²/g of apparent specific surface area. The thermal treatments, almost always inducing a drop in surface area, showed effective only for saturation at 273 K, in particular the oxidising procedure. This was correlated to the formation of surface oxidised species, likely carboxylic groups, which improved the interaction strength between H₂ and the adsorbent.     

Hydrogen permeation in asymmetric La28 − xW4 + xO54 + 3x/2 membranes

Asymmetric supported La_28 − xW_4 + xO_54 + 3x/2 (La/W ≈ 5.6) membranes were investigated for their hydrogen permeation properties as a function of temperature and feed gas conditions. Dense membranes of thickness 25–30 μm supported on substrates with 25 and 40 vol.% porosity were compared. Above 850 °C under dry conditions, the hydrogen permeation rate was approximately constant as a function of temperature due to low concentration of protons in the material at high temperatures. Under humid conditions and above 960 °C enhanced permeation rates were observed. A hydrogen permeation as high as 0.14 NmL min⁻¹ cm⁻² was recorded at 1000 °C with 10 vol.% H₂ (2.5 vol.% H₂O) as feed gas.     

In-situ CO2 capture in a pilot-scale fluidized-bed membrane reformer for ultra-pure hydrogen production

A novel pilot fluidized-bed membrane reformer (FBMR) with permselective palladium membranes was operated with a limestone sorbent to remove CO₂in-situ, thereby shifting the thermodynamic equilibrium to enhance pure hydrogen production. The reactor was fed with methane to fluidize a mixture of calcium oxide (CaO)/limestone (CaCO₃) and a Ni-alumina catalyst. Experimental tests investigated the influence of limestone loading, total membrane area and natural gas feed rates. Hydrogen-permeate to feed methane molar ratios in excess of 1.9 were measured. This value could increase further if additional membrane area were installed or by purifying the reformer off-gas given its high hydrogen content, especially during the carbonation stages. A maximum of 0.19 mol of CO₂ were adsorbed per mole of CaO during carbonation. For the conditions studied, the maximum carbon capture efficiency was 87%. The reformer operated for up to 30 min without releasing CO₂ and for up to 240 min with some degree of CO₂ capture. It was demonstrated that CO₂ adsorption can significantly improve the productivity of the reforming process. In-situ CO₂ capture enhanced the production of hydrogen whose purity exceeded 99.99%.     

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H₂ production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H₂ and N₂) and mixtures (H₂ with N_2, CO or CO₂) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5, while it decreases until 0.66–1.35·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H₂–18%CO–12%CO₂) and a stoichiometric H₂O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h⁻¹. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.     

The adsorption of H2 on Fe-coated C5H5 and its application in hydrogen storage

Based on density functional theory, the capacities of FeC₅H₅, Fe₂C₅H₅ and one-dimensional (FeC₅H₅)_∞ nanowire as hydrogen storage media were investigated. The results show that FeC₅H₅ and Fe₂C₅H₅ can adsorb five and ten H₂ molecules, respectively, and form stable FeC₅H₅(H₂)₅ and Fe₂C₅H₅(H₂)₁₀ systems. The hydrogen storage capacities of the two systems are 7.63 wt% and 10.15 wt%, while the average adsorption energies are 0.49 and 0.73 eV/H², indicating that FeC₅H₅ and Fe₂C₅H₅ are excellent hydrogen storage media. In addition, (FeC₅H₅)_∞ nanowire can also adsorb H₂ molecules (1.62 wt%). Most importantly, the magnetic and electrical properties of the nanowire are sensitive to the additional H₂, thus (FeC₅H₅)_∞ can be used for selecting and detecting H₂ molecules.     

Convenient storage of concentrated hydrogen peroxide as a CaO2·2H2O2(s)/H2O2(aq) slurry for energy storage applications

Prior investigations have proposed, and successfully implemented, a stand-alone supply of aqueous hydrogen peroxide for use in fuel cells. An apparent obstacle for considering the use of aqueous hydrogen peroxide as an energy storage compound is the corrosive nature of the nominally required 50 wt.% maximum concentration. Here we propose storage of concentrated hydrogen peroxide in a high weight percent solid slurry, namely the equilibrium system of CaO₂·2H₂O₂(s)/H₂O₂(aq), that mitigates much of the risk associated with the storage of such high concentrations. We have prepared and studied surrogate slurries of calcium hydroxide/water that are assumed to resemble the peroxo compound slurries. These slurries have the consistency of a paste rather than a distinct two-phase (liquid plus solid) system. This paste-like property of the prepared surrogates enable them to be contained within a 200 lines-per-inch. (LPI) nickel mesh screen (33.6% open area) with no solids leakage, and only liquid transport driven by an adsorbent material is placed in physical contact on the exterior of the screen. This hydrogen peroxide slurry approach suggests a convenient and safe mechanism of storing hydrogen peroxide for use in, say, vehicle applications. This is because fuel cell design requires only aqueous hydrogen peroxide use, that can be achieved using the separation approach utilizing the screen material here. This proposed method of storage should mitigate hazards associated with unintentional spills and leakage issues arising from aqueous solution use.     

Promoted hydrogen release from 3LiBH4/MnF2 composite by doping LiNH2: Elimination of diborane release and reduction of decomposition temperature

The evolution of diborane accompanying H₂ release during the decomposition of transition metal borohydrides reduces the purity of evolved hydrogen and results in capacity loss during cycling. To solve the problem, a small amount of LiNH₂ is doped into a 3LiBH₄/MnF₂ composite and the decomposition properties are investigated. The results show that after doping LiNH₂, the formation of diborane during decomposition is effectively suppressed meanwhile the decomposition temperature is significantly reduced. Around 5 wt.% pure hydrogen can be released at 95–140 °C from 5 wt.% LiNH₂-doped 3LiBH₄/MnF₂ composite. These improvements in the decomposition performance are mainly attributed to the prevention of the formation of B–H–B bonds for B₂H₆ and the destabilization of B–H bonds in borohydrides by the interaction of BH₄⁻ and NH₂⁻.