Hydrogen production from glycerol by reforming in supercritical water over Ru/Al2O3 catalyst

Supercritical water is a promising medium for the reforming of hydrocarbons and alcohols for the production of hydrogen at high pressures in a short reaction time. Water serves both as a dense solvent as well as a reactant. In this work, hydrogen is produced from glycerol by supercritical water reforming over a Ru/Al₂O₃ catalyst with low methane and carbon monoxide formation. Experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 700–800 °C, feed concentrations up to 40 wt% glycerol, all at short reaction time of less than 5 s. Glycerol was completely gasified to hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At dilute feed concentrations, near-theoretical yield of 7 mol of hydrogen/mol of glycerol was obtained, which decreases with an increase in the feed concentration. Based on a kinetic model for glycerol reforming, an activation energy of 55.9 kJ/mol was observed.     

Effective hydrolysis of sodium borohydride driven by self-supported cobalt oxide nanorod array for on-demand hydrogen generation

Hydrogen storage, distribution and controlled release are of important concerns for hydrogen based economy. Sodium borohydride (NaBH₄) is one of the mostly studied chemical hydrides used for hydrogen storage and generation. However, it requires efficient catalysts to accelerate its dehydrogenation for controllable hydrogen production. In this paper, we demonstrate that the dehydrogenation of NaBH₄ in alkaline solutions can be driven by self-supported cobalt oxide nanorod array on Ti sheet (Co₃O₄ NA/Ti). Such Co₃O₄ NA/Ti shows high catalytic performance with a maximum hydrogen generation rate of 1940 mL/min/g_Co3O4 and an activation energy of 59.84 kJ/mol under ambient condition. Moreover, this catalyst exhibits no mass or activity loss even after 5 cycles with an obvious advantage of easy separation from the fuel solution. This development offers us a cost-effective and recyclable catalytic material toward hydrolytic hydrogen production for applications.     

Elucidation of hydrogen mobility in coal under reductive atmosphere using a tritium tracer method

Hydrogen exchange reaction of three Argonne coals (Illinois No. 6, Upper Freeport and Pocahontas #3) and Wandoan coal with tritiated gaseous hydrogen were performed at several temperatures. Hydrogen exchange reaction was performed in a flow reactor packed with 0.4 g of coal and 0.05 g of catalysts under the following conditions: pressure 15 kg/cm², temperature 200, 250, 300 °C, carrier gas H₂ or N₂ 5 ml/min. When a pulse of [³H]H₂ was introduced into a coal in H₂ carrier gas at several temperatures, the delay of [³H]H₂ pulse observed increased with increasing the reaction temperature and decreased with increasing coal rank. Further in the reaction of tritiated coals with gaseous hydrogen at constant temperature, the hydrogen exchange rate was estimated from the release rate of [³H]H₂. The apparent hydrogen exchange rate at 200 °C was higher than that at 250 °C. This shows that the hydrogen with low reactivity came to participate in the reaction at high temperature. When the reaction of tritiated coal with gaseous hydrogen was performed during heat treatment, one, two or three peaks of tritium concentration were observed in the outlet of the reactor depending on temperature (200, 250 or 300 °C, respectively) at which tritium was incorporated into coal initially. It was suggested that there were at least three kinds of hydrogen with different reactivity in coal.     

CO2 reforming of waste plastics

Carbon dioxide reforming of polyethylene was carried out. Pyrolysis and catalytic carbon dioxide reforming were combined. Polyethylene was packed at the bottom of the reactor and the catalyst, Pd/Al₂O₃, was packed at the top of the reactor. The pyrolysis of the polyethylene occurred at the bottom of the reactor, and the pyrolysis products reacted with carbon dioxide on the catalyst bed. Carbon dioxide reforming occurred on the catalyst bed zone. Hydrogen, carbon monoxide, methane, ethane, ethene were produced at 910 and 720 K which were the catalyst and polyethylene temperature, respectively. Polyethylene was completely reformed to carbon monoxide and hydrogen when catalyst temperature was increased or polyethylene temperature was decreased.     

Hydrogen production from wood vinegar of camellia oleifera shell by Ni/M/γ-Al2O3 catalyst

Hydrogen production from wood vinegar was investigated by catalytic reforming with Ni/M/γ-Al₂O₃ (M = Co, Cr, Fe) as the catalysts. The maximal H₂ yield rate and concentration were 22.03 mg/g sample and 64.33% respectively. And the selectivity sequence for hydrogen is Fe, Cr, Co. After catalytic reforming, the content of the compounds was decreased from 16% to 6%. Especially, the content of the acetic acid was decreased from 5.599% to 1.859%, while the content of the phenol was increased from 0.998% to 1.904% due to the demethylation or the demethoxyation of the phenolic compounds. The characteristic analysis showed that the metals of Fe and Ni were the active centers. The amount of carbon deposit was decreased from 5.53% to 2.66%. The distribution of carbon was also shifted to the lower temperature area.     

Modeling of synthesis gas and hydrogen production in a thermally coupling of steam and tri-reforming of methane with membranes

In this novel study, tri-reforming process was used as a heat source to proceed steam reforming of methane in a two membrane hydrogen perm-selective Pd/Ag thermally coupled reactor. Results illustrated that H₂/CO ratio at the output of steam and tri-reforming sides reached to 6.1 and 0.9, respectively. Additionally the results showed that methane conversion at the output of steam and tri-reforming sides reached to 31% and 96%, respectively. By increasing the feed flow rate of tri-reforming side from 28,120 to 140,600 kmol h⁻¹, methane conversion and H₂ molar flow rate enhanced 40% and 28.64%, respectively.     

Improvements in the performance of a medium-pressure-boiler through the adjustment of inlet fuels in a refinery plant

Hydrogen has been considered as a promising alternative for fossil fuel in recent years because it is very “clean”. Fossil fuel generates CO₂, CO, SO_x, unburned hydrocarbon and particles during combustion, while hydrogen only yields NO_x. In this study, a medium-pressure boiler with 130 ton/h boiler loading in a full-scale plant was studied with two inlet hydrogen-rich refinery gas (RG)/fuel oil (FO) volumetric flow rate ratios (inlet RG/FO ratio) and two residual O₂ concentration (vol.%) in flue gases (2%, 4%) to evaluate their influence on the emissions of NO_x and CO₂, flue gas temperatures and boiler efficiencies. The result shows significant improvements in both boiler efficiencies and emissions of air pollutants. By increasing the inlet RG/FO ratio from 1:5 to 1:1.5, the fuel cost was reduced by 11%, NO_x emission down by 12%, and the CO₂ emission 20,200 ton lower per year was achieved. Thus, better economic operating conditions for the boiler are suggested at inlet RG/FO ratio = 1:1.5 with the residual O₂ concentration in flue gases = 2%.     

Improvement in hydrogen production from hard-shell nut residues by catalytic hydrothermal gasification

The hydrothermal gasification of some hard-shell nut residues (hazelnut, walnut and almond shells) was performed in a batch type reactor at temperature and pressure ranges of 300–600 °C and 88–405 bar, respectively. The biomass samples were converted into gaseous product (hydrogen, carbon dioxide, methane, carbon monoxide and C₂–C₄ compounds), aqueous product (carboxylic acids, furfurals, phenols, aldehydes and ketones) and solid products after hydrothermal gasification. Hydrogen production was improved by using natural mineral catalysts (Trona, Dolomite and Borax). The activity of selected natural mineral catalysts in hydrothermal gasification can be ordered as being Trona [Na₃(CO₃)(HCO₃)·2H₂O] > Borax [Na₂B₄O₇·10H₂O] > Dolomite [CaMg(CO₃)₂]. The most effective catalyst was found to be Trona at 600 °C leading enhancement in hydrogen yields (mol H₂/kg C in biomass) for hazelnut, walnut and almond shells as 82.4%, 74.1% and 42.4%, respectively.     

Was pretreatment beneficial for more biogas in any process? Chemical pretreatment effect on hydrogen–methane co-production in a two-stage process

The study focused on the mesophilic anaerobic hydrogen production from PPS (pulp and paper sludge) and FW (food waste) pretreated by NaOH or H₂SO₄, and the subsequent thermophilic anaerobic methane production with the effluent in a two-stage process. The maximum hydrogen yield (78.35 mL g^?1 VS_fed) which was 50.21% higher than that of CK, was achieved when 10 g NaOH/100 g TS_substrate was used. However, the maximum methane yield (383.8 mL g^?1 VS_fed) was obtained in CK as well as 64% SCOD removal efficiency was achieved. In short, NaOH/H₂SO₄ pretreatment was suitable to enhance the hydrogen production.     

Tape-cast asymmetric membranes for hydrogen separation

Ceramic hydrogen separation membrane is a promising technology for obtaining pure hydrogen in a wide range of processes including power generation with pre-combustion CO₂ capture, water-gas shift, methane reforming, etc. This work presents for the first time the production of cer-cer asymmetrical composite membranes. BaCe_0.65Zr_0.20Y_0.15O_3-δ (BCZY) supported BCZY- Gd_0.2Ce_0.8O_2-δ (GDC) membranes were produced by tape casting. Three different sintering aid incorporation methods were investigated to enhance the final density of the BCZY-GDC layer. The optimization of the whole process leads to produce planar crack-free asymmetrical proton conductive membranes with Ø=12 mm, constituted by a porous 350 µm thick BCZY substrate with an open porosity of 48%, and a 20 µm thick gas tight BCZY-GDC layer.     

Hydrogen production by partial oxidation of methanol over bimetallic Au–Ru/Fe2O3 catalysts

Hydrogen production by partial oxidation of methanol (POM) was investigated over Au–Ru/Fe₂O₃ catalyst, prepared by deposition–precipitation. The activity of Au–Ru/Fe₂O₃ catalyst was compared with bulk Fe₂O₃, Au/Fe₂O₃ and Ru/Fe₂O₃ catalysts. The reaction parameters, such as O₂/CH₃OH molar ratio, calcination temperature and reaction temperature were optimized. The catalysts were characterized by ICP, XRD, TEM and TPR analyses. The catalytic activity towards hydrogen formation is found to be higher over the bimetallic Au–Ru/Fe₂O₃ catalyst compared to the monometallic Au/Fe₂O₃ and Ru/Fe₂O₃ catalysts. Bulk Fe₂O₃ showed negligible activity towards hydrogen formation. The enhanced activity and stability of the bimetallic Au–Ru/Fe₂O₃ catalyst has been explained in terms of strong metal–metal and metal–support interactions. The catalytic activity was found to depend on the partial pressure of oxygen, which also plays an important role in determining the product distribution. The catalytic behavior at various calcination temperatures suggests that chemical state of the support and particle size of Au and Ru plays an important role. The optimum calcination temperature for hydrogen selectivity is 673 K. The catalytic performance at various reaction temperatures, between 433 and 553 K shows that complete consumption of oxygen is observed at 493 K. Methanol conversion increases with rise in temperature and attains 100% at 523 K; hydrogen selectivity also increases with rise in temperature and reaches 92% at 553 K. The overall reactions involved are suggested as consecutive methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition is subsequently transformed into CO₂ by the water gas shift and CO oxidation reactions.     

Catalytic hydrogen production from 2-propanol in supercritical water: Comparison of some metal catalysts

The gasification of organics in supercritical water is a promising method for the direct production of hydrogen at high pressures, and in order to improve the hydrogen yield or selectivity, activities of various catalysts are evaluated. In this study, hydrogen production from 2-propanol over Ni/Al₂O₃ and Fe–Cr catalysts was investigated in supercritical water. The experiments were carried out in the temperature range of 400–600 °C and in the reaction time range of 10–30 s, under a pressure of 25 MPa. The hydrogen yields and selectivities of Ni/Al₂O₃ and Fe–Cr used in this study, and those of Pt/Al₂O₃ and Ru/Al₂O₃ used in our previous work were compared. The hydrogen contents of the gaseous products obtained by using Ni/Al₂O₃ and Fe–Cr were measured as 62 mol% and 70 mol%, respectively, at low temperatures and reaction times. However, the hydrogen yields remained in low levels when compared with that of Pt/Al₂O₃ used in previous study. Pt/Al₂O₃ was established to be the most effective and selective catalyst for hydrogen production. During the catalytic gasification of a 0.5 M solution of 2-propanol, hydrogen content up to 96 mol% and hydrogen yield of 1.05 mol/mol 2-propanol were obtained.     

Integration of wind,solar and biomass over a year for the constant production of CH4 from CO2 and water

In this paper we optimize the combination of biomass, wind and solar energy for the constant production of synthetic methane. Biomass is used for the production of power and/or hydrogen. Photovoltaic solar and wind energy are used to obtain power. Water is electrolyzed generating oxygen and hydrogen, which is used to synthesize methane with CO₂. The model is formulated as an MINLP. The optimization suggests the production of power using solar energy complemented with biomass. Biomass is processed using indirect gasification and steam reforming. The hydrogen is produced from water electrolysis. The investment and production costs are 175 M€ and 0.38 €/Nm³ respectively. A sensitivity analysis shows that biomass is preferred for prices and investment below 50 €/t and 1500 €/kW. Solar energy is used for high cost of biomass if solar incidence is above 1200 kWh/m² yr. Wind use is restricted to low solar incidence and wind velocities above 9 m/s.     

Effect of steam and sodium hydroxide for the production of hydrogen on gasification of dehydrochlorinated poly(vinyl chloride)

Dehydrochlorinated poly(vinyl chloride) (PVC) and activated carbon were pyrolyzed with sodium hydroxide in a flow of steam and nitrogen at 3.0 MPa and 560–660 °C. In both cases, hydrogen and sodium carbonate were the main products, and methane, ethane, and carbon dioxide were minor products. The gasification rate increased with partial steam pressure, and the reaction order with respect to steam partial pressure was 0.69. For both dehydrochlorinated PVC and activated carbon, the gasification rate increased with the NaOH/C molar ratio. However, the rate became saturated at NaOH/C ratios higher than 2.0. The activation energy of gasification of dehydrochlorinated PVC or activated carbon was 178 kJ/mol, assuming first-order reaction rate. These experimental results indicate that hydrogen was produced from the reaction: C+2NaOH+H₂O→Na₂CO₃+2H₂.     

Fabrication and electrochemical properties of SOFC single cells using porous yttria-stabilized zirconia ceramic support layer coated with Ni

A porous yttria-stabilized zirconia (YSZ) ceramic supported single cell with a configuration of porous YSZ support layer coated with Ni/Ni–Ce_0.8Sm_0.2O_1.9 (SDC) anode/YSZ/SDC bi-layer electrolyte/La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ cathode was fabricated. The porosity, mechanical strength, and microstructure of porous YSZ ceramics were investigated with respect to the amount of poly(methyl methacrylate) (PMMA) used as a pore former. Porous YSZ ceramics with 56 vol.% PMMA showed a mechanical strength of 24 ± 3 MPa and a porosity of 37 ± 1%. The electrochemical properties of the single cell employing the porous YSZ support layer were measured using hydrogen and methane fuels, respectively. The single cell exhibited maximum power densities of 421 mW/cm² in hydrogen and 399 mW/cm² in methane at 800 °C. Moreover, at a current density of 550 mA/cm², the cell maintained 91% of its initial voltage after operation in methane for 13 h at 700 °C.     

Fabrication and H2 flux measurement of asymmetric La27W3.5Mo1.5O55.5-δ − La0.87Sr0.13CrO3-δ membranes

Novel asymmetric hydrogen permeable membranes consist of a dense ceramic–ceramic (cercer) composite layer of La_0.87Sr_0.13CrO_3-δ and La₂₇W_3.5Mo_1.5O_55.5-δ deposited on a tubular porous support of the latter composition. The membranes were produced by extrusion and dip-coating with various thermal cycles required for adjusting the thermal shrinkage of the different layers and obtaining gas tight membrane layers. The produced asymmetric membranes have a dense cercer layer thicknesses ranging from 25 to 50 μm on supports exhibiting a porosity of up to 40 vol%. The effect of processing parameters, such as volume of pore former, coating steps, sintering temperature and soaking time on the microstructure of the membranes is discussed to highlight critical steps in the manufacturing protocol. Hydrogen fluxes were measured as a function of temperature with both wet and dry Ar sweep gas. Results are discussed with respect to membrane architectures and materials properties.     

Co-production of hydrogen and multi-wall carbon nanotubes from ethanol decomposition over Fe/Al2O3 catalysts

The co-production of hydrogen and carbon nanotubes (CNTs) from the decomposition of ethanol over Fe/Al₂O₃ at different temperatures and feeding rates of ethanol was investigated systematically. The results indicated that Fe/Al₂O₃ was a quite active catalyst for the co-production of hydrogen and CNTs and that its activity and stability depended strongly on the Fe loading. Among all catalysts tested, 10 mol% Fe/Al₂O₃ was the most effective catalyst based on the ratio of hydrogen production, the total H₂ yield, and the quality of the CNTs formed. The efficiency of hydrogen production from ethanol decomposition over 10 mol% Fe/Al₂O₃ reached a maximum of ∼80% at 800 °C and the yield of CNTs with well-oriented growth and uniform diameter was 141%. In addition, the reaction of hydrogen and CNTs co-produced from ethanol decomposition was proposed.     

Free-standing diamond wafers deposited by multi-cathode,direct-current,plasma-assisted chemical vapor deposition

Free-standing diamond wafers, 100 mm in diameter, have been deposited by the multi-cathode (seven-cathode) direct-current (DC) plasma-assisted chemical vapor deposition (PACVD) method. The input power was 17.5 kW and the pressure was 100 torr. The methane concentration in hydrogen was between 3.5% and 8% at a constant flow rate of 150 sccm. Intrinsic tensile stress was controlled by introducing thermal compressive stress with step-down control of the deposition temperature during diamond deposition. A higher growth rate of 10 μm h⁻¹ was obtained by raising the methane concentration to 8%, and the deposited diamond wafer showed good thermal conductivity of 12–14 W cm⁻¹ K⁻¹. Crack-free, homogeneous and flat diamond wafers with 100 mm diameter were obtainable.     

Optimization of carbamazepine removal in O3/UV/H2O2 system using a response surface methodology with central composite design

This study used an ozone/ultraviolet/hydrogen peroxide (O₃/UV/H₂O₂) system to remove carbamazepine (CBZ) from water using a second-order response surface methodology (RSM) experiment with a five-level full-factorial central composite design (CCD) for optimization. The effects of both the primary and secondary interactions of the photocatalytic reaction variables, including O₃ concentration (X₁), H₂O₂ concentration (X₂), and UV intensity (X₃), were examined. The O₃ concentration significantly influenced CBZ and total organic carbon (TOC) removal as well as total inorganic nitrogen ion production (T-N) (p < 0.001). However, CBZ, TOC removal, and T-N production were enhanced with increasing O₃ and H₂O₂ concentrations up to certain levels, and further increases in O₃ and H₂O₂ resulted in adverse effects due to hydroxyl radical scavenging by higher oxidant and catalyst concentrations. UV intensity had the most significant effect on T-N production (p < 0.001). Complete removal of CBZ was achieved after 5 min. However, only 34.04% of the TOC and 36.99% of T-N were removed under optimal concentrations, indicating formation of intermediate products during CBZ degradation. The optimal ratio of O₃ (mg L^? 1): H₂O₂ (mg L^? 1): UV (mW cm^? 2) were 0.91:5.52:2.98 for CBZ removal, 0.7:18.93:12.67 for TOC removal, and 0.94: 4.85:9.03 for T-N production, respectively.     

Bio-gas production by co-fermentation from the brown algae,Laminaria japonica

In this study, the optimization of bio-gas produced from Laminaria japonica through co-fermentation using hydrolysis and bio-gas production microorganisms was investigated. Bio-gas production was increased by using a mixed culture with Clostridium butyricum and Erwinia tasmaniensis, and the total hydrogen and methane levels were 327.47% and 354.99% higher, respectively. When lower oxygen contents were used in the flask, the bio-gas production yield increased. The optimual E/C ratio was determined to be 1/1, and the hydrogen and methane gas production levels under these conditions were 356.03 mL/L and 2243.59 mL/L, respectively.