Co-precipitated Ni–Mg–Al catalysts for hydrogen production by supercritical water gasification of glucose

Supercritical water gasification (SCWG) is a promising process for hydrogen production from biomass. In this study, a series of Ni–Mg–Al catalysts with different Mg/Al molar ratios has been synthesized by a co-precipitation method for hydrogen production by SCWG of glucose. Effects of Mg addition on the catalytic activity, hydrothermal stability and anti-carbon performance of alumina supported nickel catalyst were investigated. The highly dispersed nickel catalysts prepared by co-precipitation could greatly enhance the gasification efficiency of glucose in supercritical water. Among the tested Ni–Mg–Al catalysts, NiMg_0.6Al_1.9 showed the highest catalytic activity with the hydrogen yield of 11.77 mmol/g (912% as that of non-catalytic test). NiMg_0.6Al_1.9 also showed the best hydrothermal stability probably due to the formation of MgAl₂O₄. Mg could efficiently improve the anti-carbon ability of Ni–Al catalyst by inhibiting the formation of graphite carbon. It is also confirmed that MgO supported nickel catalyst is not suitable for SCWG process owing to the difficulty on nickel oxides reduction in the precursors and the phase change of MgO to Mg(OH)₂ under the hydrothermal condition.     

Comparison of co–gasification efficiencies of coal,lignocellulosic biomass and biomass hydrolysate for high yield hydrogen production

The diversity in the chemical composition of lignocellulosic feedstocks can affect the conversion technologies employed for hydrogen production. Gasification and co–gasification activities of lignocellulosic biomass, biomass hydrolysate, and coal were evaluated for hydrogen rich gas production. The hydrolysates of biomass materials showed the best performance for gasification. The results indicated that biomass hydrolysates obtained from lignocellulosic biomass were more sensitive to degradation and therefore, produced more hydrogen and gaseous products than that of lignocellulosic biomass. The effects of feed (kenaf and sorghum hydrolysate), flow rate (0.3–2.0 mL/min) and temperature (700–900 °C) on hydrogen production and gasification yields were investigated. It was observed that 0.5 mL/min the optimum feed flow rate for the maximum total gas and hydrogen production. Synergism effects were observed for co–gasification of coal/biomass and coal/biomass hydrolysate. In all co–gasification processes, the main component of the gas mixture was hydrogen (≥70%).     

Ni–Pt/Al nano-sized catalyst supported on TNPs for hydrogen and valuable fuel production from the steam reforming of plastic waste dissolved in phenol

In this research, titanium nanoparticles (TNPs) for Ni–Pt/Al nano-sized catalysts were prepared via the hydrothermal technique, and their catalytic performance for the polyethylene terephthalate (PET) as plastic waste and phenol steam reforming reaction was examined. Complementary characterization methods, such as BET, ICP, TEM, XRD, FTIR, NH₃-TPD, H₂-TPR, CO₂-TPD, TGA, and CHNS, were conducted to relate surface functionality and structure to the activity of catalysts. The catalytic activity and stability with ten days on stream at 700 °C were investigated. It was found that the catalyst properties such as surface area and the number of acid sites play a crucial role in catalyst activity. The feed conversion and hydrogen yield for the optimum catalyst that is Ni–Pt/Ti–Al were found to be 92% and 75%, respectively. This research has also emphasized the opportunities of this method to resolve the threat of PET plastic waste to the environment concerning the creation of valuable fuels such as benzene, toluene, styrene, methylindene, etc.     

Comparison of different copper–chlorine thermochemical cycles for hydrogen production

Copper–chlorine thermochemical cycles for hydrogen production are very promising water splitting cycles. In this paper, different types of copper–chlorine cycles with various numbers of steps are compared. The factors that determine the number and effective grouping of steps are analyzed. It is found that the water requirement in the hydrolysis step is affected by a combination of drying and hydrolysis steps. It is also found that hydrogen can be produced either from electrolysis of cuprous chloride, or from chlorination of copper by hydrogen chloride, which indicates a potential combination of disproportionation and chlorination steps. The major engineering advantages and disadvantages of these cycle variations with different amounts of steps will be analyzed and discussed.     

Performance of a PV–wind hybrid system for hydrogen production

This paper describes the performance of an integrated PV–wind hydrogen energy production system. The system consists of photovoltaic array, wind turbine, PEM electrolyser, battery bank, hydrogen storage tank, and an automatic control system for battery charging and discharging conditions. The system produced 130–140 ml/min of hydrogen, for an average global solar radiation and wind speed ranging between 200 and 800 W/m² and 2.0 and 5.0 m/s respectively. A mathematical model for each component in the system was developed and compared to the experimental results.     

A novel system for the production of pure hydrogen from natural gas based on solid oxide fuel cell–solid oxide electrolyzer

In this paper, a novel process for the production of pure hydrogen from natural gas based on the integration of solid oxide fuel cells (SOFCs) and solid oxide electrolyzer cells (SOECs) is presented. In this configuration, the SOFC is fed by natural gas and provides electricity and heat to the SOEC, which carries out the separation of steam into hydrogen and oxygen. Depending on the system layout considered, the oxygen available at the SOEC anode outlet can be either mixed with the SOFC cathode stream in order to improve the SOFC performance or regarded as a co-product. Two configurations of the cell stack are studied. The first consists of a stack with the same number of SOFCs and SOECs working at the same current density. In this case, since in typical operating conditions the voltage delivered by the SOFC is lower than the one required by the SOEC, the required additional power is supplied by means of an electric grid connection. In the second case, the electricity balance is compensated by providing additional SOFCs to the stack, which are fed by a supplementary natural gas feed. Simulations carried out with Aspen Plus show that pure hydrogen can be produced with a natural gas to hydrogen LHV-efficiency that is about twice the value of a typical water electrolyzer and comparable to that of medium-scale reformers.     

Ni/SiO2 core–shell catalysts for catalytic hydrogen production from waste plastics-derived syngas

Ni/SiO₂ core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO₂ core synthesized by the Stöber process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO₂ core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO₂ catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO₂ support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO₂ core–shell catalyst was synthesized in methanol (Ni/SiO₂–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H₂O/h. The Ni/SiO₂–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.     

Ni/CeO2/ZSM-5 catalysts for the production of hydrogen from the pyrolysis–gasification of polypropylene

The production of hydrogen from the two-stage pyrolysis–gasification of polypropylene using a Ni/CeO₂/ZSM-5 catalyst has been investigated. Experiments were conducted on CeO₂ loading, calcination temperature and Ni loading of the Ni/CeO₂/ZSM-5 catalyst in relation to hydrogen production. The results indicated that with increasing CeO₂ loading from 5 to 30 wt.% for the 10 wt.% Ni/CeO₂/ZSM-5 catalyst calcined at 750 °C, hydrogen concentration in the gas product and the theoretical potential hydrogen production were decreased from 63.0 to 49.8 vol.% and 50.4 to 21.6 wt.%, respectively. In addition, the amount of coke deposited on the catalyst was reduced from 9.5 to 6.2 wt.%. The calcination temperature had little influence on hydrogen production for the catalyst containing 5 wt.% of CeO₂. However, for the 10 wt.% Ni/CeO₂/ZSM-5 catalyst with a CeO₂ content of 10 or 30 wt.%, the catalytic activities reduced when the calcination temperature was increased from 500 to 750 °C. The SEM results showed that large amounts of filamentous carbons were formed on the surface of the catalysts. The investigation of different Ni content indicates that the Ni/CeO₂/ZSM-5 ((2-10)-5-500) catalyst containing 2 wt.% Ni showed poor catalytic activity in relation to the pyrolysis–gasification of polypropylene according to the theoretical potential H₂ production (7.2 wt.%). Increasing the Ni loading to 5 or 10 wt.% in the Ni/CeO₂/ZSM-5 ((2-10)-5-500) catalyst, high potential hydrogen production was obtained.     

Performance assessment of solar-driven integrated Mg–Cl cycle for hydrogen production

The present study develops a new solar energy system integrated with a Mg–Cl thermochemical cycle for hydrogen production and analyzes it both energetically and exergetically for efficiency assessment. The solar based integrated Mg–Cl cycle system considered here consists of five subsystems, such as: (i) heliostat field subsystem, (ii) central receiver subsystem, (iii) steam generation subsystem, (iv) conventional power cycle subsystem and (v) Mg–Cl subsystem. Also, the inlet and outlet energy and exergy rates of all of subsystems are calculated and illustrated accordingly. We also undertake a parametric study to investigate how the overall system performance is affected by the reference environment temperature and operating conditions. As a result, the overall energy and exergy efficiencies of the considered system are found to be 18.18% and 19.15%, respectively. The results show that the Mg–Cl cycle has good potential and attractive overall cycle efficiencies over 50%.     

Hydrogen-rich syngas produced from the co-pyrolysis of municipal solid waste and wheat straw

The co-thermochemical conversion of Municipal Solid Waste (MSW) and biomass is a new environmental technology and can produce hydrogen-rich syngas. This study investigated the co-pyrolysis of MSW and wheat straw, using a drop-tube furnace experiment. Using a temperature range of 500 °C–1000 °C, the study assessed pyrolysis gas yield, product distribution, gas low heating value, and carbon conversion of co-pyrolysis MSW with different amounts of wheat straw. Adding wheat straw only slightly increases the gas yield and carbon conversion, but improved the carbon monoxide and carbon dioxide in the syngas. At an experimental temperature below 700 °C, adding wheat straw promoted the cracking reaction of hydrocarbon gas, generated by the pyrolysis of MSW. At a temperature of 600 °C, adding 25% wheat straw improved carbon conversion in the blended sample. This study provides a basis for the application of MSW and WS thermo-chemical conversion.     

Performance investigation of magnesium–chloride hybrid thermochemical cycle for hydrogen production

In this paper, we study the yields of reactants in hydrolysis and chlorination chemical processes of the low temperature Mg–Cl hybrid thermochemical cycle to investigate the requirements of temperature, pressure and product ratios for individual reactors of the cycle. A simulation of both hydrolysis and chlorination processes is conducted using the Aspen Plus software. A Mg–Cl cycle is developed by considering the results obtained from the present simulations. Both energy and exergy efficiencies of Mg–Cl cycle are comparatively evaluated under varying system and environmental parameters, and an efficiency comparison of the cycle with other promising thermochemical water splitting cycles is conducted. The results show that, compared to other cycles, lower pressure, higher temperature and higher steam to magnesium–chloride ratio are required for full conversion of reactants in the hydrolysis step; and hence, lower temperature, higher pressure and higher chlorine to magnesium oxide ratio is required for full conversion in chlorination reactor. The efficiency results show that Mg–Cl cycle can compete with other low temperature thermochemical water splitting cycles and under influence of various internal and external parameters.     

Innovative concept for gasification for hydrogen based on the heat integration between water gas shift unit and coal–water–slurry gasification unit

In order to achieve the energy cascade utilization and improve the energy utilization efficiency of coal–water–slurry (CWS) gasification for hydrogen system, the heat integration scheme (HIS) between the water gas shift unit and the gasification unit is put forward. The effects of temperature change of CWS and oxygen on the gasification performance are investigated. Both the HIS and the non-heat integration scheme (NHIS) are analyzed by using gasification performance, energy conversion efficiency and exergy efficiency. The results show that the specific coal consumption and the specific oxygen consumption decrease by 2.7% and 6.5%, respectively, as the feedstock is preheated up to the temperature of 150 °C. The energy conversion efficiency of HIS and NHIS are nearly the same. The exergy efficiency of HIS (62.66%) is better than that of NHIS (62.02%). Therefore, the HIS is better than the NHIS by heat integration between the WGS unit and the gasification unit.     

Progress of international hydrogen production network for the thermochemical Cu–Cl cycle

This paper presents recent advances by an international team which is developing the thermochemical copper–chlorine (Cu–Cl) cycle for hydrogen production. Development of the Cu–Cl cycle has been pursued by several countries within the framework of the Generation IV International Forum (GIF) for hydrogen production with the next generation of nuclear reactors. Due to its lower temperature requirements in comparison with other thermochemical cycles, the Cu–Cl cycle is particularly well matched with Canada's Generation IV reactor, SCWR (Super-Critical Water Reactor), as well as other heat sources such as solar energy or industrial waste heat. In this paper, recent developments of the Cu–Cl cycle are presented, specifically involving unit operation experiments, corrosion resistant materials and system integration.     

Intensification of hydrogen production by B. licheniformis using kitchen waste as substrate

Bacillus licheniformis AP1 isolated from dairy waste cheese whey water possess pyruvate formate lyase (PFL) and formate hydrogen lyase (FHL) enzyme gene which can hydrolyze pyruvate and formate to produce hydrogen under anaerobic conditions. Molecular characterization of this strain was done using 16rRNA gene sequencing. Phylogenetic tree was formed on the basis of neighbor-joining method using MEGA5 which showed that no significant change occurred in 16s rRNA during the course of evolution. Biohydrogen production using this laboratory isolate was performed using pre-treated kitchen waste as substrate at optimized pH 6.5 with yield of 12.29 ± 1.2 mmolH₂/gCOD reduced. Effect of macronutrients and micronutrients were studied by varying concentrations on the hydrogen production. Hydrogen production substantially increased from 14.10 ± 1.4 mmolH₂/gCOD, 17.027 ± 1.7 mmolH₂/gCOD, 17.029 ± 1.7 mmolH₂/gCOD to 17.62 ± 1.8 mmol/gCOD reduced kitchen waste by B. licheniformis at optimized concentrations of –different metals like magnesium (MgCl₂) 0.59 g/L, nitrogen (NH₄Cl) 7 g/L, nickel (NiCl₂) 180 μg/L, and iron (II) (FeSO₄) 67 μg/L respectively. The optimized temperature for this process was found to be 34 ± 2 °C with the maximal hydrogen yield of 17.62 ± 1.8 mmol/g COD reduced kitchen waste. The end fermentation metabolites detected were acetic acid, isobutyl acid, butyric acid, and pyruvic acid in the proportion of 3.75:1:1:1 under the optimized conditions in batch experiment (30 ml MGY media broth). These are the products of pyruvate-formate lyase enzyme complex that indicates the major electron flux towards formate during hydrogen production by B. licheniformis in hydrolyzed kitchen waste.     

Multiphase reactor scale-up for Cu–Cl thermochemical hydrogen production

This paper examines selected design issues associated with reactor scale-up in the thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. The thermochemical cycle decomposes water into oxygen and hydrogen, through intermediate copper and chlorine compounds. In this paper, emphasis is focused on the hydrogen, oxygen and hydrolysis reactors. A sedimentation cell for copper separation and HCl gas absorption tower are discussed for the thermochemical hydrogen reactor. A molten salt reactor is investigated for decomposition of an intermediate compound, copper oxychloride (CuO·Cl₂), into oxygen gas and molten cuprous chloride. Scale-up design issues are examined for handling three phases within the molten salt reactor, i.e., solid copper oxychloride particles, liquid (melting salt) and exiting gas (oxygen). Also, different variations of hydrolysis reactions are compared, including 5, 3 and 2-step Cu–Cl cycles that utilize reactive spray drying, instead of separate drying and hydrolysis processes. The spray drying involves evaporation of aqueous feed by mixing the spray and drying streams. Results are presented for the required capacities of feed materials for the multiphase reactors, steam and heat requirements, and other key design parameters for reactor scale-up to a pilot-scale capacity.     

Multi-tube Pd–Ag membrane reactor for pure hydrogen production

An experimental apparatus carrying out a membrane process for producing pure hydrogen via ethanol steam reforming has been tested in order to measure the hydrogen production by varying operative parameters such as temperature, pressure and membrane sweeping mode.     

Ceria as a catalyst for hydrogen iodide decomposition in sulfur–iodine cycle for hydrogen production

In this work, ceria (CeO₂) prepared with different methods and at various calcination temperatures have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in sulfur–iodine (SI) cycle at various temperatures. The CeO₂ catalysts' strongly enhance the HI decomposition by comparison with blank test, especially gel CeO₂ 300. TG–FTIR, BET, XRD, TEM and TPR were performed for catalysts' characterization. The results show that the CeO₂ catalyst synthesized by citric-aided sol–gel method and calcined at low temperature (<500 °C) shows more lattice defects, smaller crystallites, larger surface area and better reducibility. Oxygen can promote the significantly rapid surface reaction, but simultaneously consume hydrogen species (H) contained in HI. Lattice defects, especially the reduced surface sites, i.e., Ce³⁺ and oxygen vacancy, play the dominant role in surface reactions of HI decomposition. A new reaction mechanism for HI catalytic decomposition over CeO₂ catalyst is proposed.     

Platinum–ceria–zirconia catalysts for hydrogen production in sulfur-iodine cycle

In this study, Pt/Ce_1−xZr_x catalysts with different Zr mole concentration (x = 0, 0.2, 0.5, 0.8, 1) have been tested to evaluate their effects on hydrogen iodide (HI) decomposition for hydrogen production in the sulfur-iodine (SI or IS) cycle at various temperatures. The Pt/Ce_1−xZr_x catalysts strongly enhanced the HI conversion to H₂ by comparison with blank test, especially the Pt/Ce_0.8Zr_0.2 catalyst. BET, XRD, TEM, EDS, TPR were performed for catalysts characterization. It was found that, through introducing ZrO₂ into Pt/CeO₂, a synergistic effect between Pt and CeO₂-ZrO₂ solid solution was different from Pt and CeO₂ yield, such as improvement of the thermal stability and increase of Pt-O-Ce reducibility. Among the three samples containing Zr, the one with 20 mol% displayed the best activity for hydrogen production.     

Fabrication using sequence wet-chemical coating and electrochemical performance of Ni–Fe-foam-supported solid oxide electrolysis cell for hydrogen production from steam

Ni–Fe-alloy-foam supported solid oxide electrolysis cell with an arrangement of nickle and Sc_0.1Ce_0.005Gd_0.005Zr_0.89O₂ (Ni-SCGZ) cathode, SCGZ electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) anode is successfully fabricated by the sequence wet-chemical coating. The multi-layer cathode with a gradient of thermal expansion coefficient (TEC) is deposited on the alloy-foam support. Two-step firing processes are applied including cathode pre-firing (1373 K, 2 h) and electrolyte sintering (1623 K, 4 h) using slow heating rate enhanced with compressive loading. The fabricated cell shows current density of ?0.95 Acm^?2 at 1.1 V with H₂O:H₂ = 70:30 and 1073 K, providing hydrogen production rate at 4.95 × 10^?6 mol s^?1. However, performance degradation was observed with the rate of 0.08 V h^?1, which can be ascribed to the delamination of BSCF anode under operating at high current density.