Theoretical Hydrogen Yield Research Articles

Highly Efficient Recycling Waste Plastic into Hydrogen and Carbon Nanotubes through a Double Layer Microwave-Assisted Pyrolysis Method.

Microwave-assisted pyrolysis of PE to hydrogen and carbon material has great potential to solve the problem of waste PE induced white pollution and provide a promising way to produce hydrogen energy. To increase the hydrogen yield, a new microwave-assisted pyrolysis procedure should be developed. In the present study, a facile double-layer microwave-assisted pyrolysis (DLMP) method is developed to pyrolyze PE. Within this method, PE can be converted to hydrogen, multiwalled carbon nanotubes with extremely high efficiency compared with the traditional methods. A high hydrogen yield of 66.4 mmolg-1 PE is achieved, which is ≈93% of the upper limit of the theoretical hydrogen yield generated from the PE pyrolysis process. The mechanism of high hydrogen yield during the microwave-assisted pyrolysis of PE using the DLMP method is also clarified in detail. The DLMP method paved the potential way for recycling plastic waste into high-value-added products.

In Situ Formation of Li2SiO3-Li-NaCl Interface on Si and Its Effect on Hydrogen Evolution

Silicon has emerged as a competitive candidate for hydrolytic hydrogen production due to its high theoretical hydrogen yield, low cost, and on-demand availability. However, the hydrolysis reaction is extremely restrained by passivated SiO2, including the original one on the Si surface and the generated one during hydrolysis, and almost no hydrogen is produced in pure water. Herein, the original SiO2 surface has been effectively removed by milling micro-Si mixed with a small amount of Li metal and NaCl. An artificial soluble interface on Si has been established containing Li2SiO3, Li, and NaCl. Once micro-Si is placed into water, fresh Si surface can be exposed and a weak LiOH solution can be generated due to the fast dissolution of the interface layer, resulting in the rapid liberation of hydrogen gas. Accordingly, the modified micro-Si displays a significantly enhanced hydrogen production in pure water at 30 °C (1213 mL g-1 H2 within 3.0 h), which is 2.0 and 4.7 times higher than that observed for ball-milled Si and raw Si in 0.06 M LiOH solution, respectively. In addition, it also exhibited an outstanding operation compatibility for practical uses. This work has proposed a green, effective, and scalable strategy to promote hydrogen production from the hydrolysis of Si-based systems.

Hydrogen recovery cascade from pretreated rice straw and its fermentative residuals using step-up potential-based sulfate reducing bacteria-bioelectrochemical system

Despite the availability of well-proven biohydrogen production technology, the uncapping of the biological theoretical hydrogen yield is still a challenge. This study explores the stimulation of step-up applied potential for hydrogen production in a sulfate-reducing bacteria-based bioelectrochemical system (SRB-BES), a sustainable and promising technology for organic waste recycling with resource recovery. This research focused on the application of a low applied potential to recover H2 from pretreated rice straw and its residual fermentative by-products. An applied potential of −40 mV could proficiently recover 1.5 times higher hydrogen from pretreated rice straw by completely inhibiting methanogens. The residual fermentative byproducts obtained at the first stage were further used in extra H2 recovery at a step-up applied potential of −150 mV, −300 mV, and −450 mV. The H2 recovery from fermentative residuals shows maxima at −300 mV. The acetic acid and iso-butyric acid production of 52.89 ± 15.67 and 56.93 ± 11.81 mM at −300 mV and −450 mV respectively contribute majorly to volatile fatty acids (VFAs). The more electronic equivalents of 2024.34 (mM) in R-450mV in comparison to 1850.803 (mM) in R-40mV (effluent recovered from AD-MEC) indicate the involvement of the higher applied potential in chain elongation of VFAs. So, optimization of step-up potential could lead to the bioelectrochemical synthesis of the desired fatty acids through chain elongation deserving various applications with hydrogen recovery. The gaseous data obtained were verified by Richard, Logistic, and modified Gompertz kinetic models to check H2 prediction validity using cumulative H2 production. This study demonstrated the technical foundation with a novel approach to maximize hydrogen recovery from the fermentation residuals by step-up applied potential.

Enhanced hydrogen generation from Al-water reaction mediated by metal salts

Hydrogen generation by the reaction of micrometer-aluminum powder with water at room temperature is hard to proceed due to the inhibition of alumina layer. In this study, a novel strategy of metal salts mediated Al-water reaction was proposed for more efficient and practical hydrogen generation. The effects of metal salt composition and dosage, and water injection rate and volume on hydrogen generation were investigated. The hydrogen yield of 230.0 mL was achieved in the Al/Ni/Cu/H2O system within 600 s under the following conditions: 0.24 g aluminum with the molar ratio of Al, Ni and Cu at 10:1:1 and 2 mL water at the injection rate of 2 mL/min, which was equivalent to 70.4% of the theoretical hydrogen yield. Based on the morphology, element composition, crystal structure and electrochemical test results of the obtained composites after reaction, the mechanism of hydrogen production by metal salts mediated Al-water reaction was proposed.

The effect of various cations/anions for MgH2 hydrolysis reaction

MgH2 is regarded as a potential hydrolysis material for the hydrogen generation due to its high theoretical hydrogen yield, abundant source on earth and environmentally friendly hydrolysates. However, the quickly formed passive magnesium hydroxide layer on the surface of MgH2 will hinder its further hydrolysis reaction, leading to sluggish reaction kinetics and low H2 yield. In this paper, we explore the improvement of different anions and cations in solutions for the hydrolysis of MgH2. It is found that the cations in the solution promote the reaction rate of MgH2 hydrolysis through the hydrolysate-induced growth effect, among which the fastest hydrogen yield can get 1664 mL/g within a few minutes in the Fe2(SO4)3 solution. As for the anions, it enables different microstructures of the Mg(OH)2 hydrolysate which give rise to enhanced water utilization. Specially, for the mixed 0.5 M MgCl2 + 0.05 M MgSO4 solution, the water utilization rate attains the optimum value of 51.3 %, much higher than that of the single MgCl2 or MgSO4 solutions. These findings are of great significance for the application of MgH2 hydrolysis as hydrogen generation.

Influence of process parameters on enhanced hydrogen evolution from alcoholysis of sodium borohydride with a boric acid catalyst

The hydrogen evolution via alcoholysis reaction of sodium borohydride with an H3BO3 catalyst was carried out for the first time. In the process of methanol and NaBH4 (NaBH4-MR), the effects of the H3BO3 and NaBH4 concentration, and temperature parameters were examined and evaluated. The hydrogen yields by the NaBH4-MR, NaBH4 ethanolysis (NaBH4-ER) and NaBH4 hydrolysis reactions (NaBH4-HR) with 0.2 M H3BO3 catalyst are 99, 62, and 88% compared to the theoretical hydrogen yield, respectively. The completion times of the NaBH4-MR using the H3BO3 concentrations of 0.2, 0.4, 0.5, 1 M, and saturated acid solution were about 50, 15, 10, 2 and 1 min, respectively. The hydrogen yields obtained with 50, 15, 10, 2, and 1 min for the same acid concentration values were about 100% compared to the theoretical hydrogen value. By increasing the H3BO3 concentration from 0.2 M to the saturated H3BO3 concentration, the completion time of this NaBH4-MR process was reduced by approximately 50 times, resulting in a significant result. The activation energy (Ea) of the NaBH4-MR with the H3BO3 catalyst was 57.3 kJ/mol.

Future district heating plant integrated with municipal solid waste (MSW) gasification for hydrogen production

Characterizing municipal solid waste (MSW) is a critical step in planning, designing, operating, or upgrading solid waste management systems. For a theoretical investigation of hydrogen production by gasification and water-gas shift reaction, we characterized Norwegian MSW and used the data. Three different gasification setups, named as ‘A-1’, ‘A&S-2’, and ‘S-3’ were modeled using Aspen plus simulation software for direct and indirect gasification processes according to the different gasification agents. The MSW characterization result showed a reasonable agreement with existing studies in different countries. The maximum hydrogen yield achieved in setup ‘S-3’ was around 94% of the maximum theoretical hydrogen yield from the specified MSW. At a steam to syngas ratio of 0.5, 199.6 g of hydrogen could be produced per one kg of MSW, with 4 L of water at 100 °C for district heating. The study indicates integrating an indirect gasifier in preexisting MSW-fired plants can play a significant role in recovering energy from MSW in the form of energy carrier hydrogen. However, if it is necessary to construct a new waste incinerator, the study results indicate building a direct gasification system.

Beyond the Theoretical Yields of Dark-Fermentative Biohydrogen.

Theoretical hydrogen (H2) yield by dark fermentative route is 12mol/mol of glucose. Biological H2 production yields of 3.8mol/mol of glucose by microbes have been reported. Transient gene inactivation in combination with adaptive laboratory evolution strategy has enabled the H2 yield to exceed the stoichiometric production values.

Nickel-based catalysts for hydrogen production by steam reforming of glycerol

As the renewable energy technologies are making progress every day, hydrogen energy technologies are taking huge part of this development. Nowadays, there are several industries using hydrogen. Also, the increase at biodiesel production amounts has increased the glycerol production as by-product. One of the main objectives of this study is to compare the effects Al2O3-, SiO2- and CeO2-supported nickel catalysts at steam reforming of glycerol in order to produce hydrogen. All catalysts were prepared by incipient to wetness method. The obtained steam reforming results showed that nickel catalysts supported on ceria showed the highest activity. Also the effect of nickel amount on CeO2 support material has been studied. The highest hydrogen amounts were obtained with 15 wt% nickel loading. Also the increase at water/glycerol ratio increased the hydrogen production amount. The highest hydrogen yield was obtained as 4.82 mol per glycerol mole, whereas the theoretical hydrogen yield is 7 mol, by using 15 wt% Ni/CeO2 catalyst, water/glycerol ratio of 15 and at 650 °C reaction temperature.

Kinetic performance of hydrogen generation enhanced by AlCl3 via hydrolysis of MgH2 prepared by hydriding combustion synthesis

Magnesium hydride (MgH2) is a very promising hydrogen storage material and it has been paid more and more attention on the application of supplying hydrogen on-board because the theoretical hydrogen yield is up to 1703 mL/g when it reacts with water. However, the hydrolysis reaction is inhibited rapidly by the passivation layer of Mg(OH)2 formed on the surface of MgH2. This paper reports that high purity MgH2 (∼98.7 wt%) can be readily obtained by the process of hydriding combustion synthesis (HCS) and the hydrogen generation via hydrolysis of the as-prepared HCSed MgH2 can be dramatically enhanced by the addition of AlCl3 in hydrolysis solutions. An excellent kinetics of hydrogen generation of 1487 mL/g in 10 min and 1683 mL/g in 17 min at 303 K was achieved for the MgH2-0.5 M AlCl3 system, in which the theoretical hydrogen yield (1685 mL/g) of the HCSed product was nearly reached. The mechanism of the hydrolysis kinetics enhancement was demonstrated by the generation of a large amounts of H+ from the Al3+ hydrolysis and the pitting corrosion (Cl−) of the Mg(OH)2 layer wrapped on the surface of MgH2 even at a low temperature. In addition, the apparent activation energies for the MgH2 hydrolysis in the 0.1 M AlCl3 and 0.5 M AlCl3 solutions are decreased to 34.68 kJ/mol and 21.64 kJ/mol, respectively, being far superior to that of reported in deionized water (58.06 kJ/mol). The results suggest that MgH2 + AlCl3 system may be used as a promising hydrogen generation system in practical application of supplying hydrogen on-board.

Hydrogen generation from Nd-Ni-Mg system by hydrolysis reaction

The generation of hydrogen from both the new NdNiMg15 ternary compound and the 1Nd - 1Ni - 15Mg mixtures (using NdH2.6 or NdCl3 as Nd precursors) by hydrolysis reaction were investigated. The Nd-Ni-Mg mixtures were prepared by ball milling process (for 1, 3 and 5 h) and the hydrolysis reaction was carried out in a 3.5 wt % NaCl solution (i.e. seawater). Independently of the composition, Nd-Ni-Mg mixtures show better hydrolysis performance compared with NdNiMg15 compound. The best hydrolysis performances were achieved with the mixtures 1NdH2.6 - 1Ni - 15Mg + 15 wt % NaCl and 1NdCl3 - 1Ni - 15Mg mixtures milled for 3 h. A 100% of theoretical hydrogen yield was obtained in 3 and 4 min respectively. The presence of chloride salts such as NaCl or NdCl3 during ball milling improves significantly the hydrolysis performance due to its ball milling and electrolyte properties. The activation energies of best mixtures, with and without adding salts (NdH2.6-Ni-15Mg (1 h BM) and NdH2.6-Ni-15Mg + 15 wt % NaCl (3 h BM)), were calculated using Avramie Erofeev model. A lower activation energy (24 kJ/mol < 31 kJ/mol) was found for NdH2.6-Ni-15Mg + 15 wt % NaCl (3 h BM) mixture, which demonstrates the beneficial effect of adding NaCl during ball milling.

Hydrogen generation via hydrolysis of H-CaMg2 and H-CaMg1.9Ni0.1

Hydrogen generation via hydrolysis of hydrides from hydrogenated CaMg2 (abbreviated as H-CaMg2 hereafter) and hydrogenated CaMg1.9Ni0.1 (abbreviated as H-CaMg1.9Ni0.1 hereafter) alloys has been investigated in pure water without addition of any catalyst. Experimental results show that the hydrolysis of H-CaMg2 is fast when immersed in water with the hydrogen generation yield of 800 mL/g within 1 min. For CaMg1.9Ni0.1 alloy, the addition of Ni element spurs the hydrogen absorption at room temperature and significantly enhances the hydrolysis properties with fast and continuous hydrogen release yield of 1053 mL/g in 12 min, which is 94.6% of the theoretical hydrogen yield of H-CaMg1.9Ni0.1. The excellent hydrolysis properties of Ca5Mg9H28 and the catalytic effect of MgNi2 particles are further clarified. The fast and constant hydrolysis rate of H-CaMg1.9Ni0.1 can reach higher even than 365 mL/(min g) in first 2 min. The apparent activation energy of H-CaMg1.9Ni0.1 hydrolysis in deionized water is determined to be 32.9 kJ/mol. The hydrolysis mechanism of H-CaMg2 and H-CaMg1.9Ni0.1 was also discussed.

Heat transfer analysis of thermal disassociation of ZnO for solar hydrogen production

Hydrogen production by the two-step solar thermochemical cycle has high cycle efficiency, low cost, and a great development space. Of special interest is the solar thermochemical cycle based on ZnO/Zn redox reactions since its high theoretical hydrogen yield and relatively low endothermic reaction temperature. In this paper, a steady heat transfer model for thermal ZnO dissociation in a solar thermochemical reactor is developed, coupling conduction, convection and radiation with chemical reaction. Accuracy was evaluated by comparison of results obtained from other references. Based on the new proposed reactor, the model is adopted to analyze the operating parameter effect on the conversion rate and fluid feature inside the solar reactor. The results show that the mass flow rate of ZnO and aperture gas temperature have a positive relation with ZnO conversion rate, however, the diameter of particles and aperture gas velocity has an inverse relation with ZnO conversion rate under specific condition. The results will provide useful foundation for improving the solar-to-fuel conversion rate in the near future.

Hydrogen storage and hydrogen generation properties of CaMg2-based alloys

The hydrogen storage and hydrogen generation of CaMg2 and CaMg1.9Ni0.1 alloys were investigated by X-ray diffraction (XRD) and pressure-composition-isotherm (PCI) measurements. The results confirmed that the CaMg2 alloy cannot absorb hydrogen at room temperature. While the addition of Ni to the CaMg2-based alloys resulted in room-temperature hydrogen absorption without an activation process, and a maximum hydrogen-absorption capacity of 5.65 wt%. The hydrolysis performance of hydrogenated CaMg2 and hydrogenated CaMg1.9Ni0.1 (abbreviated as H-CaMg2 and H-CaMg1.9Ni0.1 hereafter) was also evaluated. The hydrolysis reaction of H-CaMg2 occurred rapidly in water and resulted in a hydrogen yield of 800 mL/g. Furthermore, the hydrolysis properties of H-CaMg1.9Ni0.1 were significantly enhanced with the addition of Ni, as evidenced by a hydrogen yield of 1053 mL/g in 12 min, this yield is 94.7% of the theoretical hydrogen yield of H-CaMg1.9Ni0.1.

Biofuels as a promising source of hydrogen for fuel cell power plants

The state of the art in biomass conversion into liquid hydrocarbon biofuels aimed at obtaining synthesis gas and hydrogen for duel elements is analyzed. The most promising liquid hydrocarbon and oxygencontaining fuels for synthesis gas production are vegetable oils, diesel fuel, and biodiesel. Mathematical models are developed for the autothermal reforming, steam reforming and pre-reforming of biodiesel into synthesis gas and for the steam reforming of pre-reforming products integrated with the membrane separation of hydrogen. The results of calculations are verified against experimental data. The solution suggested here ensures 93.5% efficiency of the membrane separation of hydrogen from the reaction mixture and a theoretical hydrogen yield of 128 mol per kilogram of biodiesel.

Production of hydrogen, ethanol and volatile fatty acids from the seaweed carbohydrate mannitol

Fermentative hydrogen from seaweed is a potential biofuel of the future. Mannitol, which is a typical carbohydrate component of seaweed, was used as a substrate for hydrogen fermentation. The theoretical specific hydrogen yield (SHY) of mannitol was calculated as 5mol H2/mol mannitol (615.4mL H2/g mannitol) for acetic acid pathway, 3mol H2/mol mannitol (369.2mL H2/g mannitol) for butyric acid pathway and 1mol H2/mol mannitol (123.1mL H2/g mannitol) for lactic acid and ethanol pathways. An optimal SHY of 1.82mol H2/mol mannitol (224.2mL H2/g mannitol) was obtained by heat pre-treated anaerobic digestion sludge under an initial pH of 8.0, NH4Cl concentration of 25mM, NaCl concentration of 50mM and mannitol concentration of 10g/L. The overall energy conversion efficiency achieved was 96.1%. The energy was contained in the end products, hydrogen (17.2%), butyric acid (38.3%) and ethanol (34.2%).

Analysis of the catalytic steam gasification mechanism of biomass

The gasification of cellulose was here used to prove that the inner reaction of oxygen with carbon contained in the biomass was unavoidable during the gasification of biomass. It was also proven that the dehydrogenation reaction and conversion of oxygen in biomass to CO always caused the formation of residual carbon. Although, almost all of oxygen contained in the biomass could be converted into CO by the catalytic effect of ions, which in turn could be converted to CO2, but the CO2 was always methanized. This indicated that the hydrogen and syngas yield contained in the product gas of biomass could not practically achieve to the theoretical maximum hydrogen and syngas yield from biomass. The present study showed biomass gasification connected in series with coal gasification to be an excellent approach to large-scale conversion of biomass to hydrogen and syngas.

Elementary Flux Mode Analysis of Acetyl-CoA Pathway in Carboxydothermus hydrogenoformans Z-2901

Carboxydothermus hydrogenoformans is a carboxydotrophic hydrogenogenic bacterium species that produces hydrogen molecule by utilizing carbon monoxide (CO) or pyruvate as a carbon source. To investigate the underlying biochemical mechanism of hydrogen production, an elementary mode analysis of acetyl-CoA pathway was performed to determine the intermediate fluxes by combining linear programming (LP) method available in CellNetAnalyzer software. We hypothesized that addition of enzymes necessary for carbon monoxide fixation and pyruvate dissimilation would enhance the theoretical yield of hydrogen. An in silico gene knockout of pyk, pykC, and mdh genes of modeled acetyl-CoA pathway allows the maximum theoretical hydrogen yield of 47.62 mmol/gCDW/h for 1 mole of carbon monoxide (CO) uptake. The obtained hydrogen yield is comparatively two times greater than the previous experimental data. Therefore, it could be concluded that this elementary flux mode analysis is a crucial way to achieve efficient hydrogen production through acetyl-CoA pathway and act as a model for strain improvement.

Evaluation of hydrogen production from corn cob with the mesophilic bacterium Clostridium hydrogeniproducens HR-1

Corn cob is a promising hydrogen fermentation substrate, not only because of its abundant and low cost, but also because of its high cellulose and hemicellulose content. However, little information is available on the use of corn cob as a feedstock for hydrogen production. In this study, corn cob was hydrolyzed by cellulase after acid steam-explosion, alkali soaking, or steam-explosion pretreatment. The liquid products of pretreatment and the enzymatic hydrolysates were then used as carbon sources for hydrogen production by Clostridium hydrogeniproducens HR-1. Pretreatment followed by enzymatic hydrolysis yielded 720, 670, and 530 mg reducing sugars/g corn cob, and the hydrogen yield from corn cob reached 119, 100, and 83 ml H2/g corn cob, which is 55.9%, 46.7%, and 38.8% of the theoretical hydrogen yield from corn cob using C. hydrogeniproducens HR-1, respectively.

High-yield hydrogen production from glucose by supercritical water gasification without added catalyst

Continuous supercritical water gasification of glucose is investigated with a recently developed updraft gasification apparatus under various conditions: temperatures of 600–767 °C, residence times of 15–60 s, glucose concentrations of 1.8–15 wt% and without added a catalyst. The experimental gas yields are compared with predicted values at equilibrium that are estimated via Gibbs free energy minimization. Total gas yields and hydrogen gas yield increase with temperature. At 740 °C and 1.8 wt%, hydrogen gas yields become very high (10.5–11.2 mol/mol glucose). The hydrogen gas yields do not vary significantly with different residence times. The hydrogen gas yield decreases to 5.7 mol/mol glucose at 15 wt%, a value very close to the predicted value (6.3 mol/mol glucose). Only acetic acid is detected in the liquid effluents at temperatures above 740 °C, while 42 products are detected at 600 °C. The highest hydrogen gas yield obtained in this study is 11.5 mol/mol glucose at 25 MPa, 767 °C, and 1.8 wt%, for 60 s; this value is very close to the theoretical equilibrium hydrogen yield of 11.9 mol/mol glucose. Under these conditions, the carbon efficiency is very high (91%) and total organic carbon (TOC) in the liquid product is very low (23 ppm), indicating that glucose is almost completely converted to gaseous products. Comparison with other work under similar operating conditions shows that the current reactor is capable of attaining higher hydrogen gas yields at temperatures above 650 °C. Possible explanations for the higher hydrogen gas yields are presented.