Development of a hydrogen impurity analyzer based on mobile-gas chromatography for online hydrogen fuel monitoring

Hydrogen is an excellent alternative energy source, particularly for vehicles. Despite the expansion of a considerable number of infrastructures, such as hydrogen refueling stations, there is a lack of efficient inspection methods for monitoring the hydrogen fuel quality. In this study, a hydrogen impurity analyzer (HIA) based on mobile gas chromatography with a thermal conductivity detector is developed and evaluated for the quality assurance of hydrogen fuel. Accordingly, O₂, N₂, and Ar which help in monitoring air leaks at hydrogen refueling stations, and CH₄, which can also be detected by HIA, are selected as target impurities. The HIA reached limits of detection of 2.93, 0.72, 0.84, and 1.54 μmol/mol for O₂, Ar, N₂, and CH₄, respectively. Moreover, the ISO 14687 requirements are satisfied with respective HIA expanded uncertainties of 2.6, 8.7, 8.2, and 9.4% (coverage factor k = 2). The developed system is ISO-compliant and offers enhanced mobility for online inspections.     

Challenges in hydrogen fuel sampling due to contaminant behaviour in different gas cylinders

Increasing deployment of fuel cell electric vehicles (FCEVs) has led to implementation of hydrogen quality regulations (ISO 14687:2019) to prevent FCEV loss of performance. Hydrogen refuelling stations operators must be able to send representative samples of hydrogen fuel for analysis. Stability of contaminants in sampling vessels needs to be known at ISO 14687:2019 thresholds. A 4-month stability study was carried out on mixtures of ISO 14687 contaminants at amount fractions close to the thresholds in two types of sampling cylinders (SPECTRA-SEAL® and SGS? aluminium cylinders). SPECTRA-SEAL® cylinder allowed representative sampling of CO, CO₂, CH₄, C₂H₆, N₂, Ar, He, Cl₂CH₂, H₂O, O₂, CH₂O₂ in hydrogen fuel for 2 months. SGS? cylinder allowed representative sampling of CO, CO₂, CH4, C₂H₆, N₂, Ar, He, Cl₂CH₂, H₂O, O₂, H₂S for 4 months. Further work is needed to allow representative sampling of ammonia and formaldehyde.     

Energy efficient hydrogen drying and purification for fuel cell vehicles

High-purity standards are required for hydrogen used in fuel cell vehicles. The relative abundance of contaminants is highly influenced by the production pathway. Hydrogen obtained from water electrolysis presents three main pollutants: Nitrogen, Oxygen and Water. Herein, the engineering and implementation of removal techniques in a commercial 50 kW alkaline electrolyzer are reported. The full system was characterized with various analytical techniques including gas chromatography and mass spectrometry. A reduction of contaminant levels compatible with ISO 14687:2019 standard was achieved. From cold start, 100 min of operation are required to reach the desired nitrogen levels. Oxygen was removed in one step with a catalytic converter. Drying of hydrogen was achieved by using an innovative vacuum assisted pressure swing adsorption system. Sub-ppm levels of water are obtained with a power consumption of only 0.5 kWh/kg H₂ and 98.4% of product recovery.     

Supercritical water gasification mechanism of polymer-containing oily sludge

In the offshore petroleum industry, polymer-containing oily sludge (PCOS) hinders oil extraction and causes tremendous hazards to the marine ecological environment. In this paper, an effective pretreatment method is proposed to break the adhesive structure of PCOS, and the experiments of supercritical water gasification are carried out under the influencing factors including residence time (5–30 min) and temperature (400–750 °C) in batch reactors. The increase of time and temperature all show great promoting effects on gas production. Polycyclic aromatic hydrocarbons, including naphthalene and phenanthrene, are considered as the main obstacles for a complete gasification. Carbon gasification efficiency (CE) reaches maximum of 95.82% at 750 °C, 23 MPa for 30 min, while naphthalene makes up 70% of the organic compounds in residual liquid products. The highest hydrogen yield of 19.79 (mol H₂/kg of PCOS) is observed in 750 °C for 25 min. A simplified reaction pathway is presented to describe the gaseous products (H₂, CO, CO₂, CH₄). Two intermediates are defined for describing the reaction process bases on the exhaustive study on organic matters in residual liquid products. The results show that the calculated data and the experimental data have a high degree of fit and tar formation reaction is finished within 10 min.     

Enhancing resistance of carbon deposition and reaction stability over nickel loaded fibrous silica-alumina (Ni/FSA) for dry reforming of methane

Syngas production from the dry reforming of methane is now the most extensively utilized method for removing massive amounts of greenhouse emissions. Effective solutions towards the utilization of greenhouse gases such as CO₂ and CH₄ are scarce, except for power generation in the energy sector, which is a major source of CO₂. Herein, dry reforming of methane was experimented for the first time using an effective catalytic system composed of 5% Ni fibrous silica-alumina (FSA) that was successfully fabricated using a hydrothermal method. The characterization results from XRD, FESEM mapping, TEM, BET,XRF, FTIR, H₂-TPR, TGA/DTA, and Raman spectra demonstrated that Ni/FSA is composed of orderly Ni dispersion, small particles of Ni, robust basic sites, and high oxygen vacancies which enhanced the catalytic efficiency. The synthesized Ni/FSA also reduced coke formation and had long-term stability with no evidence of inactivation during and after the catalytic cycles. The superior activity of Ni/FSA was manifested in the high conversion rates of CH₄ and CO₂ at 97% and 92% respectively, with a H₂:CO ratio of ≈ 1. The stability of Ni/FSA was also sustained over 30 h of operation at 800 °C. The findings of the Raman, TEM, and TGA/DTA tests revealed that the spent Ni/FSA catalysts did not exhibit graphitic carbon or metal sintering in significant amounts when compared to commercial Ni–Si/Al catalysts.     

Screening and optimisation of hydrogen production by newly isolated nitrogen-fixing cyanobacterial strains

Recently, there has been a propensity to postpone dealing with the world's climate concerns until later, resulting in a 1.5 °C rise in temperature over the last century. Therefore, interest in biologically derived, inexhaustible energy sources based on solar energy is growing. Cyanobacteria have the potential to produce clean, renewable fuels in the form of hydrogen (H₂) gas, derived from solar energy and water. The current study reports the screening 11 cyanobacterial strains isolated from rice paddies and hotsprings for efficient H₂ producers. According to our findings, H₂ concentrations in the species ranged from 3.6 to 48.9 μmol mg⁻¹ Chl a h⁻¹. H₂ production by isolated species was shown to have a 2% positive influence on oxygen (O₂) and carbon dioxide (CO₂) concentrations and a 2% negative effect on all nitrogen gas (N₂) concentrations. It was discovered that at high CO₂ concentrations, photosynthesis is enhanced but H₂ production is suppressed. Anabaena variabilis BTA-1047 was found to be the most active H₂-producing species, with an H₂ production activity of 21.3 μmol mg⁻¹ Chl a h⁻¹. Moreover, a 1% O₂: 2% CO₂ gas mixture doubled the strain activity of H₂ production. The findings of the study called into the question the notion that only an anaerobic environment is required for H₂ production by N₂-fixing cyanobacterial species and explored whether H₂ productivity can be increased by stimulating the micro-anaerobic environment with a carbon source.     

Simultaneous biohydrogen (H2) and bioplastic (poly-β-hydroxybutyrate-PHB) productions under dark,photo, and subsequent dark and photo fermentation utilizing various wastes

The present study is focused on bio hydrogen (H₂) and bioplastic (i.e., poly-β-hydroxybutyrate; PHB) productions utilizing various wastes under dark fermentation, photo fermentation and subsequent dark-photo fermentation. Potential bio H₂ and PHB producing microbes were enriched and isolated. The effects of substrate (rice husk hydrolysate, rice straw hydrolysate, dairy industry wastewater, and rice mill wastewater) concentration (10–100%) and pH (5.5–8.0) were examined in the batch mode under the dark and photo fermentation conditions. Using 100% rice straw hydrolysate at pH 7, the maximum bio H₂ (1.53 ± 0.04 mol H₂/mol glucose) and PHB (9.8 ± 0.14 g/L) were produced under dark fermentation condition by Bacillus cereus. In the subsequent dark-photo fermentation, the highest amounts of bio H₂ and PHB were recorded utilizing 100% rice straw hydrolysate (1.82 ± 0.01 mol H₂/mol glucose and 19.15 ± 0.25 g/L PHB) at a pH of 7.0 using Bacillus cereus (KR809374) and Rhodopseudomonas rutila. The subsequent dark-photo fermentative bio H₂ and PHB productions obtained using renewable biomass (i.e., rice husk hydrolysate and rice straw hydrolysate) can be considered with respect to the sustainable management of global energy sources and environmental issues.     

Nickel-loaded red mud catalyst for steam gasification of bamboo sawdust to produce hydrogen-rich syngas

Ni/red mud (RM) catalysts were prepared by wet impregnation and used in the catalytic steam gasification of bamboo sawdust (BS) to produce hydrogen-rich syngas. The system was optimized in terms of the amount of added nickel (10%), reaction temperature (800 °C), and catalyst placement (separately behind the BS). The maximum H₂ yield was 17.3% higher than that using pure RM catalyst and 43.8% higher than that of BS gasification alone, and the H₂/CO ratio in the syngas reached 7.82. This Ni/RM catalyst also retained good activity after six cycles in a double-stage fixed bed reactor. Analysis using X-ray fluorescence, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and other methods revealed that the interaction of Ni, Fe, and Mg in Ni/RM produced bimetallic compounds containing active sites, such as NiFe₂O₄, MgNiO₂, and NiO. This explains the good catalytic performance in the tar conversion during the gasification process.     

Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

Turning glycerol surplus into renewable syngas through glycerol steam reforming over a sol-gel Ni–Mo2C-Al2O3 catalyst

In this work, a sol-gel Ni–Mo₂C–Al₂O₃ catalyst is employed for the first time in the glycerol steam reforming for syngas production. Catalyst stability and activity are investigated in the temperature range of 550 °C–700 °C and time on stream up to 30 h. As reaction temperature increases, from 550 °C to 700 °C, H₂ yield boosts from 22% to 60%. The stability test, carried out at milder conditions (600 °C and Gas-Hourly Space-Velocity (GHSV) of 50,000 mL h⁻¹.g_cat⁻¹), shows high catalyst stability, up to 30 h, with final conversion, H₂ yield, and H₂/CO ratio of 95%, 53% and 1.95, respectively. Both virgin and spent catalysts have been characterized by a multitude of techniques, e.g., Atomic-Absorption spectroscopy, Raman spectroscopy, N₂-adsorption-desorption, and Transmission Electron Microscopy (TEM), among others. Regarding the spent catalysts, carbon deposits’ morphology becomes more graphitic as the reaction temperature increases, and the total coke formation is mitigated by increasing reaction temperature and lowering GHSV.     

Detonation propagation characteristics of H2/O2/AR in multi-angle bifurcation tubes

The propagation characteristics of the detonation wave in the bifurcated tube with the angular variation range of 30°–90° are simulated with 25% AR as dilution gas for H₂/O₂ mixture fuel at chemical equivalence ratio using the solver DCRFoam built on the OpenFOAM platform. The diffraction and reflection phenomena of detonation waves passing through bifurcation tubes with different angles are studied and analyzed. The results show that the distance from regular reflection to Mach reflection increases with the increase of the bifurcation angle so that after one reflection, the detonation forms three reflection forms with the angle of the different bifurcation tubes. After the first reflection, the detonation waves are more likely to induce the formation of transverse waves in the low-angle bifurcation tube. The lowest collision pressure after the detonation collides with the upper wall to form a secondary reflection occurs in the bifurcation tube between 50° and 60°.     

Utilization of laterite ore as an oxygen carrier in chemical looping reforming of methane for syngas production

Growing energy demands in various sectors have resulted in overusing fossil fuel sources and rise in greenhouse gases in the atmosphere. This necessitates the need for reducing greenhouse gases and shifting to cleaner, renewable energy sources like H₂. Chemical looping is one such renewable method to produce clean H₂. The efficiency of this process depends on the oxygen carrier. Generally, oxygen carriers (OC) are transition metal oxides (Fe₂O₃ or NiO) or some complex metal oxides like spinel or perovskites, but usage of these OCs are restricted due to their availability and redox performance. One solution for selecting OCs can be using industrial waste like slag or low-grade ores because of their composition, which consists of metal oxides. One such low-grade ore is Ni-laterite ore or chromite overburden, a mining waste found in the chromite mines of Sukinda (India). In this work, we have focused on utilizing this laterite ore as an OC for the chemical looping reforming of methane to produce syngas. The reactivity analysis of laterite ore with CH₄ was performed in DSC-TG and the reaction products were analyzed in gas chromatography along with microscopy and spectroscopic techniques. Results showed the formation of H₂ and CO gases along with reduced metallic phases. The total H₂ yield at 750 °C is determined to 53.67 (±1.09) ml/g of OC which is comparable or even higher than existing CeO₂ based OCs. Further, thermodynamic calculations are presented to calculate the theoretical yield for our process and compared with the experimental H₂ yield. This study effectively demonstrates the performance of laterite ore as an OC for generating clean and renewable energy through chemical looping technique.     

Kinetics of formic acid decomposition in subcritical and supercritical water – a Raman spectroscopic study

The decomposition of formic acid is studied in a continuous sub- or supercritical water reactor at temperatures between 300 and 430 °C, a pressure of 25 MPa, residence times between 4 and 65 s, and a feedstock concentration of 3.6 wt%. In situ Raman spectroscopy is used to produce real-time data and accurately quantify decomposition product yields of H₂, CO₂, and CO. Collected spectra are used to determine global decomposition rates and kinetic rates for individual reaction pathways. First-order global Arrhenius parameters are determined as log A (s⁻¹) = 1.6 ± 0.20 and E_A = 9.5 ± 0.55 kcal/mol for subcritical decomposition, and log A (s⁻¹) = 12.56 ± 1.96 and E_A = 41.90 ± 6.08 kcal/mol for supercritical decomposition. Subcritical and supercritical Arrhenius parameters for individual pathways are proposed. The variance in rate parameters is likely due to changing thermophysical properties of water across the critical point. There is strong evidence for a surface catalyzed free-radical mechanism responsible for rapid decomposition above the critical point, facilitated by low density at supercritical conditions.     

HRT control as a strategy to enhance continuous hydrogen production from sugarcane juice under mesophilic and thermophilic conditions in AFBRs

The objective of this study was to evaluate the effects of hydraulic retention time (HRT) (8–1 h) on H₂ production from sugarcane juice (5000 mg COD L⁻¹) in mesophilic (30 °C, AFBR-30) and thermophilic (55 °C, AFBR-55) anaerobic fluidized bed reactors (AFBRs). At HRTs of 8 and 1 h in AFBR-30, the H₂ production rates were 60 and 116 mL H₂ h⁻¹ L⁻¹, the hydrogen yields were 0.60 and 0.10 mol H₂ mol⁻¹ hexose, and the highest bacterial diversities were 2.47 and 2.34, respectively. In AFBR-55, the decrease in the HRT from 8 to 1 h increased the hydrogen production rate to 501 mL H₂ h⁻¹ L⁻¹ at the HRT of 1 h. The maximum hydrogen yield of 1.52 mol H₂ mol⁻¹ hexose was observed at the HRT of 2 h and was associated with the lowest bacterial diversity (0.92) and highest bacterial dominance (0.52).     

Wind-powered 250 kW electrolyzer for dynamic hydrogen production: A pilot study

Alkaline water electrolysis is the most promising approach for the industrial production of green hydrogen. This study investigates the dynamic operational characteristics of an industrial-scale alkaline electrolyzer with a rated hydrogen production of 50 m³/h. Strategies for system control and equipment improvement in dynamic-mode alkaline electrolytic hydrogen production are discussed. The electrolyzer can operate over a 30%–100% rated power load, thereby facilitating high-purity (>99.5%) H₂ production, competitive DC energy efficiency (4.01–4.51 kW h/Nm³ H₂, i.e., 73.1%–65.0% LHV), and good gas–liquid fluid balance. A safe H₂ content of 2% in O₂ (50% LFL) can be guaranteed by adjusting the system pressure. In transient operation, the electrolyzer can realize minute-level power and pressure modulation with high accuracy. The results confirm that the proposed alkaline electrolyzer can absorb highly fluctuating energy output from renewables because of its capability to operate in a dynamic mode.     

Combined experimental and numerical study on the extinction limits of non-premixed H2/CH4 counterflow flames with varying oxidizer composition

Chemical reaction mechanisms with detailed kinetics are an important topic in combustion science and an essential prerequisite for the accurate modeling of reactive flows in combustors. Besides isolating and studying individual reactions, the development of reaction mechanisms is often based on well-defined experimental observables, such as the laminar burning velocity and the ignition delay time. While many optimization targets are associated with premixed combustion, the extinction strain rate (ESR) of non-premixed flames in the counterflow configuration is another well-defined experimental observable which, however, often receives less attention. In order to reduce the scarcity of corresponding datasets for the emerging fuel hydrogen and its blends with methane, this work reports ESR measurements for H₂, CH₄/H₂ and CH₄ counterflow diffusion flames considering a variation of the oxygen content in the oxidizer stream between 14 % and 21 %. The experimental investigation is complemented by calculations with a 1D counterflow model utilizing a temperature-control continuation method in order to determine the extinction limits numerically. The simulations are performed with six different well-established chemical reaction mechanisms. It is shown from both, experimental and numerical results, that with the substitution of CH₄ by H₂ the ESR increases and further, that the ESR decreases with a reduction of the oxygen content in the oxidizer stream. In addition, decreasing flame temperatures are observed at extinction as the H₂ content increases. Overall, all mechanisms are able to qualitatively recover the trends found for varying H₂ contents, fuel mole fraction, and oxygen content in the oxidizer. However, significant quantitative deviations are observed between the numerical results regarding the ESR values and the deviations are larger than for other important flame characteristics, such as the laminar burning velocity. The results suggest that the ESR could be a useful optimization target for further improving chemical reaction mechanisms which underlines the importance of datasets such as the one presented in this work.     

A review on recent advances in dry reforming of methane over Ni- and Co-based nanocatalysts

The recent environmental-related issues such as climate change and global warming have sparked scientists' interest in finding a way to reduce the emission of greenhouse gases through dry reforming of CH₄. As a result of this reaction, not only H₂ is produced, but also CO₂ and CH₄ are reduced. Catalysts are needed due to the enhancement of the kinetics of the reaction. Non-noble metals like Ni, Co, etc., have shown promising activity, they are readily available, and have low cost; consequently, they have been widely employed for the reaction. In this paper, the recent advances in the development of the Ni- and Co-based nanocatalysts for DRM reaction, including the use of different supports and promoters, the addition of alkaline earth metals, and new structures like mesoporous silica and dendritic fibrous nano silica as supports were reviewed.     

The role of oxygen vacancies in the CO2 methanation employing Ni/ZrO2 doped with Ca

The Ni/ZrO₂ catalyst doped with Ca and Ni/ZrO₂ were employed in the CO₂ methanation, a reaction which will possibly be used for storing intermittent energy in the future. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS, reduction in situ), X-ray diffraction (XRD, reduction in situ and Rietveld refinement), electron paramagnetic resonance (EPR), temperature-programmed surface reaction, cyclohexane dehydrogenation model reaction, temperature-programmed desorption of CO₂ and chemical analysis. The catalytic behavior of these catalysts in the CO₂ methanation was analyzed employing a conventional catalytic test. Adding Ca to Ni/ZrO₂, the metallic surface area did not change whereas the CO₂ consumption rate almost tripled. The XRD, XPS and EPR analyses showed that Ca⁺² but also some Ni²⁺ are on the ZrO₂ surface lattice of the Ni/CaZrO₂ catalyst. These cations form pairs which are composed of oxygen vacancies and coordinatively unsaturated sites (cus). By increasing the number of these pairs, the CO₂ methanation rate increases. Moreover, the number of active sites of the CO₂ methanation rate limiting step (CO and/or formate species decomposition, rls) is enhanced as well, showing that the rls occurs on the vacancies-cus sites pairs.     

Modulating Fischer-Tropsch synthesis performance on the Co3O4@SixAly catalysts by tuning metal-support interaction and acidity

ZIF-67 derived catalysts for Fischer-Tropsch synthesis have attracted much attention in recent years, while there is still a potential to improve their activity and selectivity. In this work, we prepared Si/Al co-immobilized Co₃O₄@Si_xAl_y catalysts by in-situ doping tetraethylorthosilicate and aluminum nitrate during the synthesis of ZIF-67. The effects of different Si/Al ratios on the metal-support interaction, acidity and FTS performance were explored. Results indicated that the Co₃O₄@Si₀Al₄ catalyst exhibited the best FTS performance with the CO conversion as high as 79.9% and CTY (cobalt time yield) value of 19.5 × 10^?5 mol_CO·g_Co^?1·s^?1, which was ascribed to the moderate metal-support interaction and the most active Co sites. Meanwhile, the Co₃O₄@Si₃Al₁ and Co₃O₄@Si₂Al₂ catalysts exhibited higher iso-paraffin and olefin selectivity due to more acidic sites.     

Dark fermentative biohydrogen production using pretreated Scenedesmus obliquus biomass under an integrated paradigm of biorefinery

In recent times, biohydrogen production from microalgal feedstock has garnered considerable research interests to sustainably replace the fossil fuels. The present work adapted an integrated approach of utilizing deoiled Scenedesmus obliquus biomass as feedstock for biohydrogen production and valorization of dark fermentation (DF) effluent via biomethanation. The microalgae was cultivated under different CO₂ concentration. CO₂-air sparging of 5% v/v supported maximum microalgal growth and carbohydrate production with CO₂ fixation ability of 727.7 mg L^?1 d^?1. Thereafter, lipid present in microalgae was extracted for biodiesel production and the deoiled microalgal biomass (DMB) was subjected to different pretreatment techniques to maximize the carbohydrate recovery and biohydrogen yield. Steam heating (121 °C) in coherence with H₂SO₄ (0.5 N) documented highest carbohydrate recovery of 87.5%. DF of acid-thermal pretreated DMB resulted in maximum H₂ yield of 97.6 mL g^?1 VS which was almost 10 times higher as compared to untreated DMB (9.8 mL g^?1 VS). Subsequent utilization of DF effluent in biomethanation process resulted in cumulative methane production of 1060 mL L^?1. The total substrate energy recovered from integrated biofuel production system was 30%. The present study envisages a microalgal biorefinery to produce biohydrogen via DF coupled with concomitant CO₂ sequestration.