Ammonia production using iron nitride and water as hydrogen source under mild temperature and pressure

Ammonia generation was studied in the reaction between water and nitrogen-containing iron at 323 K and atmospheric pressure. Similar to metallic Fe, the interstitial compound Fe₃N reduced water through Fe oxidation to produce hydrogen gas, while the N combined with atomic hydrogen to produce ammonia as a byproduct. The addition of carbon dioxide to this system accelerated the reaction with concomitant consumption of carbon dioxide. The promoted ammonia production upon addition of carbon dioxide can be attributed to the generation of atomic hydrogen from the redox reaction of carbonic acid and Fe, as well as removal of used Fe from the reaction system through the formation of a soluble carbonato complex. When carbonate was added to the reaction system, the production rates of ammonia and hydrogen increased further. The results here confirmed that ammonia can be synthesized from iron nitride under mild conditions by utilizing carbon dioxide.     

Hydrogen generation during the corrosion of carbon steel in crotonic acid and using some organic surfactants to control hydrogen evolution

The purpose of this paper is to describe and evaluate the corrosion of carbon steel in crotonic acid for hydrogen production and using polysorbate 20 (NS), dioctyl sodium sulfosuccinate (AS) and benzalkonium chloride (CS) to control hydrogen evolution. Measurements were conducted in tested solutions using hydrogen evolution and electrochemical impedance spectroscopy (EIS) measurements and complemented by scan electron microscope (SEM) and energy dispersive X-ray (EDX) investigations. It is shown that the hydrogen generation rate obtained during the corrosion of carbon steel in crotonic acid increased with increase in acid concentration, temperature and immersion time. The addition of organic surfactants inhibits the hydrogen generation rate. The inhibition occurs through adsorption of organic surfactants on the metal surface. Adsorption processes followed the Langmuir isotherm. The order of effectiveness of the surfactants was AS > NS > CS. The values of activation energy (E_a) and heat of adsorption (Q_ads) were calculated and discussed.     

Carbon nanotubes-promoted Co–B catalysts for rapid hydrogen generation via NaBH4 hydrolysis

In this work, multiwalled carbon nanotubes (MWCNTs) promoted Co–B catalysts for NaBH₄ hydrolysis have been designed and synthesized. The structural features of as-prepared catalysts have been investigated and discussed as a function of MWCNTs contents by X-ray diffraction, X-ray photoelectron spectra, N₂ adsorption/desorption isotherms, scanning electron microscope. The results show that the catalysts still maintain an amorphous structure with the addition of carbon nanotubes promoter. However, the appropriate amount of MWCNTs promoter in Co–B catalysts leads to large specific surface area, fine dispersion of active components, increased active sites and high electron density at active sites. Moreover, hydrogen spillover on the catalyst is promoted, which contributes to regeneration of active sites and accelerating catalytic cycle. Among all the experimental samples, it is found that the Co–B catalyst promoted by 10 wt% carbon nanotubes exhibits optimal catalytic activity with remarkably high hydrogen generation rate of 12.00 L min⁻¹·g_catalyst⁻¹ and relatively good stability.     

Carbon-neutral economy with fossil fuel-based hydrogen energy and carbon materials

Hydrocarbon fossil fuels can be considered as hydrogen ores for CO₂-free energy, and carbon ores for carbonaceous construction materials. Hydrogen fuel can be extracted from fossil fuels by decarbonization, and used as an energy resource. The carbon byproduct can be used as a versatile construction material. Carbon materials would sequester carbon, and replace CO₂-generating steel and concrete. Approximate comparison of the global consumption of energy and construction materials suggests a rough mass balance of energy and materials markets. The cost of foregoing the carbon energy content as a fuel can be easily offset by the value of the carbon-based construction material. The nature and properties of carbon materials and conventional infrastructural materials are compared.     

The cost of integration of zero emission power plants—A case study for the island of Cyprus

In this work, a technical, economic and environmental analysis is carried out for the estimation of the optimal option scenario for the Cyprus's future power generation system. A range of power generation technologies integrated with carbon capture and storage (CCS) were examined as candidate options and compared with the business as usual scenario. Based on the input data and the assumptions made, the simulations indicated that the integrated gasification combined cycle (IGCC) technology with pre-combustion CCS integration is the least cost option for the future expansion of the power generation system. In particular, the results showed that for a natural gas price of 7.9US$/GJ the IGCC technology with pre-combustion CCS integration is the most economical choice, closely followed by the pulverized coal technology with post-combustion CCS integration. The combined cycle technology can, also, be considered as alternative competitive technology. The combined cycle technologies with pre- or post-combustion CCS integration yield more expensive electricity unit cost. In addition, a sensitivity analysis has been also carried out in order to examine the effect of the natural gas price on the optimum planning. For natural gas prices greater than 6.4US$/GJ the least cost option is the use of IGCC technology with CCS integration. It can be concluded that the Cyprus's power generation system can be shifted slowly towards the utilization of CCS technologies in favor of the existing steam power plants in order not only to lower the environmental emissions and fulfilling the recent European Union Energy Package requirements but also to reduce the associated electricity unit cost.     

Climate policy: Bucket or drainer?

Worldwide, industry is responsible for about 40% of greenhouse gas (GHG) emissions, making it an important target for climate policy. Energy-intensive industries may be particularly vulnerable to higher energy costs caused by climate policy. If companies cannot offset rising energy costs and would face increased competition from countries without climate policy, they may decide to relocate their industrial production to the countries without climate policy. The resulting net effect of climate policy on GHG emissions in foreign countries is typically referred to as “carbon leakage”. Carbon leakage may lead to higher global GHG emissions due to the use of less advanced technology in less developed countries. Based on a literature review of climate policy, earlier environmental policy and analyses of historical trends, this paper assesses the carbon leakage effects of climate policy for energy-intensive industries. Reviews of past trends in production location of energy-intensive industries show an increased global production share of Non-Annex 1 countries. However, from empirical analyses we conclude that the trend is primarily driven by regional demand growth. In contrast, climate policy models show a strong carbon leakage. Even though future climate policy may have a more profound impact than environmental policies in the past, the modelling results are doubtful. Leakage generally seems to be overestimated in current models, especially as potential positive spillovers are often not included in the models. The ambiguity of the empirical analyses and the modelling results warrants further research in the importance of production factors for relocation.     

Production of hydrogen by Enterobacter aerogenes in an immobilized cell reactor

The production of hydrogen from glucose by using Enterobacter aerogenes ATCC 13048 (E. aerogenes) in an immobilized cell reactor (ICR) was investigated. The effect of several factors, such as the glucose concentration, feed flow rate, and fermentation time were examined. The highest amount of hydrogen (9.44 mmol H₂/g glucose) was obtained at a glucose concentration of 8 g/L, flow rate of 0.5 mL/min, retention time of 24 h and at a temperature of 30 °C. Meanwhile, the highest amount of carbon dioxide (1.68 mmol CO₂/g glucose) was obtained at a glucose concentration of 10 g/L, flow rate of 0.7 mL/min, hydraulic retention time of 24 h and at a temperature of 30 °C. The hydrogen and carbon dioxide production were affected by glucose concentration, hydraulic retention time (HRT) and fermentation time. This study showed that the ICR was a very efficient method for the production of hydrogen and carbon dioxide gases.     

Hydrogen production from methane hydrate with sequestering of carbon dioxide

Methane hydrate exists in large amounts in certain locations, in sea sediments and the geological structures below them and below artic regions permafrost, at low temperature and high pressure. It has recently been shown that there are suitable methods for producing methane, perhaps on a floating platform. There it could be reformed in an endothermic process to produce hydrogen and carbon dioxide. Some of the methane could be used to provide heat energy for a power plant on the platform to provide all needed power and support for the reforming process. After separation, hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform could be separated from other gases and then sequestered, in one of several possible forms. In this way, hydrogen could be made available without the release of carbon dioxide to the atmosphere and the hydrogen could be an enabling step toward a world hydrogen economy, free of particles and carbon dioxide pollution.     

Study on selective hydrogen sulfide removal over carbon dioxide by catalytic oxidative absorption method with chelated iron as the catalyst

H₂S is a detrimental impurity that must be removed for upgrading biogas to biomethane. H₂S removal selectivity over CO₂ employing catalytic oxidative absorption method and its influence factors were studied in this work. The desulfurization experiments were performed in a laboratory apparatus using EDTA-Fe as the catalyst and metered mixture of 60% (v/v) CH₄, 33% (v/v) CO₂ and 2000–3000 ppmv H₂S balanced by N₂ as the simulated biogas. It was found that for a given catalytic oxidative desulfurization system, it exists a critical pH, at which desulfurization selectivity achieves the highest. It was also observed that desulfurization selectivity increased along with the increase of chelated iron concentration, gas flow rate, and ratio of gas flow rate to liquid flow rate (G/L). This demonstrated that high selectivity and high efficiency for biogas desulfurization could both be achieved through optimizing these parameters. Specific to the desulfurization system of this work, when the gas flow rate was set as 1.1 L/min, after optimizing the above mentioned parameters, i.e. EDTA-Fe concentration of 0.084 mol/L, absorption solution pH of 7.8, and G/L of 55, the desulfurization selectivity factor reached 142.1 with H₂S removal efficiency attained 96.7%.     

Indirect electrochemical oxidation of cyanide by hydrogen peroxide generated at a carbon cathode

The oxidation of cyanide was performed in aqueous sodium hydroxide solutions. Cyanide was oxidized over 90% to cyanate by hydrogen peroxide electrochemically generated at a 60 ppi reticulated vitreous carbon electrode from oxygen reduction. Cyanide depletion was recorded as a function of time from the analysis of cyanide based on the titration procedure using silver nitrate with p$p$-dimethylamino-benzal-rhodanine indicator. Cyanate was further oxidized to mineralization by decreasing the pH of the solution obtaining a recovery of carbon dioxide over 90%. The employment of copper together with hydrogen peroxide to increase the destruction of cyanide was also studied. Different molar ratios of hydrogen peroxide/cyanide and copper/cyanide were tested achieving over 98% of cyanide destruction in a time period of 40 min by increasing either the concentration of hydrogen peroxide or copper ion.     

Experimental studies on hydrogen generation by methane autothermal reforming over nickel-based catalyst

This paper presents the experimental studies on the hydrogen generation by methane autothermal reforming method. An experimental system was built in-house for this study. The temperature profile along the axis of the reformer was measured and discussed. The peak temperature of the reformer appeared in the part of 1/4 to 2/4 of the reformer length from inlet to outlet. The maximum hydrogen yield, hydrogen mole numbers generated per mole of methane consumed of 2.71, was achieved at molar oxygen-to-carbon ratio of 1.68 and molar steam-to-carbon ratio of 2.5. Under this condition, the energy conversion efficiency of the reforming process reached 81.4% based on the lower heating values.     

Cascading pressure thermal reduction for efficient solar fuel production

Efficient two-step solar-thermochemical fuel production requires vacuum pumping or inert gas sweeping to lower the oxygen pressure in the thermal reduction step. Pumping is hampered by large oxygen volumetric flows, whereas sweeping is energy-intensive, requiring heat recovery at high temperature, and a dedicated inert gas purification plant. A novel pumping approach—using a cascade of chambers at successively lower pressures—is analyzed and shown to lead to over an order of magnitude pressure decrease compared to a single-chambered design. The resulting efficiency gains are substantial, and represent an important step toward practical and efficient solar fuel production on a large scale.     

Absorption of hydrogen in tensile strained iron and high-carbon steel studied by electrochemical permeation and desorption techniques

Absorption of hydrogen in gradually tensile strained Armco iron and high-carbon steel, cathodically charged in 0.1 M NaOH solution, was studied using the electrochemical permeation and desorption techniques. Measurements of hydrogen permeation through specimens in the form of a membrane allowed determining the lattice diffusivity and concentration of hydrogen (diffusible hydrogen). The lattice diffusivity of hydrogen in iron (D = 6.2 × 10⁻⁵ cm²/s) was about 280 times higher than that in high-carbon steel (D = 2.2 × 10⁻⁷ cm²/s). In turn, a detailed analysis of the desorption rate of hydrogen from previously hydrogen charged and strained, cylindrical specimens made it possible to characterize hydrogen reversibly attached to traps. This trapped hydrogen made nearly a whole and a majority (from 70% to 85%, depending on strain) of the reversibly absorbed hydrogen in iron and high-carbon steel, respectively. In both studied materials, the amount of the trapped hydrogen strongly increased with strain. Moreover, in contrast to the diffusible hydrogen, evenly distributed in the charged specimen, the trapped hydrogen was mainly located within a subsurface region of the specimen. The estimated thickness of this subsurface region in iron was about 0.44 mm, whereas that in high-carbon steel was only about 0.017 mm. Consequently, the subsurface concentration of hydrogen in high-carbon steel was extremely high. It may be one of the reasons for more intensive hydrogen embrittlement of high-carbon (high-strength) steels in comparison with that of iron.     

Partial substitution of hydrogen for conventional fuel in an aircraft by utilizing unused cargo compartment space

Options are being actively sought in aviation to switch from petroleum-based fuels to alternative fuels, of which hydrogen is a promising candidate, despite challenges associated with its production and storage. The possibility is demonstrated in this study of using hydrogen in place of some mission fuel without making substantial aircraft modifications and while utilizing only available unused baggage space in the lower-deck cargo compartments of aircraft. The environmental impact reduction and weight increase are obtained accounting for a broad range of factors including aircraft model, seat capacity, passenger and baggage load factors, annual landing and take off cycles, container type, and costs of metal hydride and gaseous hydrogen storage units of various sizes. It is found that, while there may be a cost increase, CO₂ emissions are substantially reduced, by 25,000–570,000 tonnes annually in several cases and by up to 1.1 million tonnes annually for the 10 types of aircraft considered. It is also determined that with present technology, despite the low density of hydrogen, the weight of storage systems constitutes more of a challenge than their volume in aviation. Large-body aircraft are found to have more difficulties than the narrow-body aircraft regarding storage system weight. For the most frequently used narrow- and large-body aircraft considered, the number of the available containers within the required limits of weight and volume respectively are found to be 3 and 4 for the B 737-800 aircraft and 2 and 10 for the A 340-300 aircraft. Overall, the combined usage of hydrogen and kerosene investigated here may be feasible in the future, but is a challenging option with present technology and aircraft due to various factors.     

Hydrogen evolution from water molecule reactions with Ge7 and Ge6Al clusters

The most stable structures of Ge₆M (M = Ge, Al) clusters and reactions of Ge₆M clusters with a single water molecule are investigated theoretically by density functional theory (DFT) calculation and reaction pathway search method at the same level. The calculated binding energies of Ge₇ and Ge₆Al clusters show that the stabilities of two clusters are close. The most stable geometric structures and electronic structures of Ge₆M@H₂O complex and reaction pathways of Ge₆M with a single H₂O molecule are predicted. All geometric structures of reactants, intermediate products, final products and transition states are confirmed by frequency analysis. Our results show that both of Ge₇ and Ge₆Al clusters can completely release H₂ from water after a three steps reaction and both reactions are endothermic. The calculated adsorption energies and energy barriers indicate that the dopant Al atom will improve the reactivity between Ge₇ cluster and water. The NPA charge of Ge₇O and Ge₆AlO means both of them can react with another H₂O molecule.     

Hydrogen generation under sunlight by self ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays generate a considerable interest for hydrogen generation by an electrochemical photocell, since ordered architecture of nanotube arrays provides a unidirectional electric channel for electron's transport. Here, we report the hydrogen generation by highly ordered TiO₂ nanotube arrays under actual sunlight in KOH electrolyte. The two-electrode electrochemical cell included an adjustable anode compartment capable of tracing the trajectory of the sun and a set of alkaline batteries connected with a rheostat for application of external bias. The results showed that the photocurrent responses of nanotube arrays match well with the intensity of solar irradiance on a clear summer day. Addition of ethylene glycol into KOH electrolyte as a hole scavenger enhanced the rate of hydrogen generation. A maximum photocurrent density of 31 mA/cm² was observed at 13:30 h, by focusing the sunlight with an intensity of 113 mW/cm² on the surface of the TiO₂ nanotube arrays in 1 M KOH electrolyte with 10 vol% ethylene glycol under an applied bias of 0.5 V. The observed hydrogen generation rate was 4.4 mL/h cm² under the focalized solar irradiance with an intensity between 104 mW/cm² and 115 mW/cm² from 10:00 to 14:20 h.