On-board reforming of biodiesel and bioethanol for high temperature PEM fuel cells: Comparison of autothermal reforming and steam reforming

In the 21st century biofuels will play an important role as alternative fuels in the transportation sector. In this paper different reforming options (steam reforming (SR) and autothermal reforming (ATR)) for the on-board conversion of bioethanol and biodiesel into a hydrogen-rich gas suitable for high temperature PEM (HTPEM) fuel cells are investigated using the simulation tool Aspen Plus. Special emphasis is placed on thermal heat integration. Methyl-oleate (C₁₉H₃₆O₂) is chosen as reference substance for biodiesel. Bioethanol is represented by ethanol (C₂H₅OH). For the steam reforming concept with heat integration a maximum fuel processing efficiency of 75.6% (76.3%) is obtained for biodiesel (bioethanol) at S/C = 3. For the autothermal reforming concept with heat integration a maximum fuel processing efficiency of 74.1% (75.1%) is obtained for biodiesel (bioethanol) at S/C = 2 and λ = 0.36 (0.35). Taking into account the better dynamic behaviour and lower system complexity of the reforming concept based on ATR, autothermal reforming in combination with a water gas shift reactor is considered as the preferred option for on-board reforming of biodiesel and bioethanol. Based on the simulation results optimum operating conditions for a novel 5 kW biofuel processor are derived.     

n-C4H10 autothermal reforming over MgO-supported base metal catalysts

We report n-C₄H₁₀ autothermal reforming over MgO-supported base metal catalysts at 723 K. Catalytic performance was investigated not only after H₂ treatment at 1073 K (reductive treatment) but also after subsequent O₂/Ar treatment at the reaction temperature (oxidative treatment) to mimic the shutdown and startup of a domestic fuel cell system. After reductive treatment, both Ni/MgO and Co/MgO exhibited high n-C₄H₁₀ conversion and hydrogen formation activity; the stability of Ni/MgO was better than that of Co/MgO. The reaction route was investigated by measuring activity at various contact times. The results revealed that n-C₄H₁₀ autothermal reforming over Ni/MgO is a multi-step reaction composed of combustion, steam reforming, water gas shift reaction, and methanation. In contrast, Cu/MgO and Fe/MgO did not show reforming activity but cracking and combustion of n-C₄H₁₀. Ni/MgO and Co/MgO catalyzed H₂ formation even after the oxidative treatment. However, the initial activity of Co/MgO after the oxidative treatment was lower than that after the reductive treatment and a decrease in H₂ formation rate was again observed after 6 h in Co/MgO, similar to the measurements after the reductive treatment.     

Thermodynamic analysis of carbon formation boundary and reforming performance for steam reforming of dimethyl ether

Thermodynamic analysis of dimethyl ether steam reforming (DME SR) was investigated for carbon formation boundary, DME conversion, and hydrogen yield for fuel cell application. The equilibrium calculation employing Gibbs free minimization was performed to figure out the required steam-to-carbon ratio (S/C = 0–5) and reforming temperature (25–1000 °C) where coke formation was thermodynamically unfavorable. S/C, reforming temperature and product species strongly contributed to the coke formation and product composition. When chemical species DME, methanol, CO₂, CO, H₂, H₂O and coke were considered, complete conversion of DME and hydrogen yield above 78% without coke formation were achieved at the normal operating temperatures of molten carbonate fuel cell (600 °C) and solid oxide fuel cell (900 °C), when S/C was at or above 2.5. When CH₄ was favorable, production of coke and that of hydrogen were significantly suppressed.     

Cobalt molybdenum carbides as anode electrocatalyst for proton exchange membrane fuel cell

Cobalt molybdenum (Co-Mo) carbides were prepared by the carburization of Co-Mo oxides at temperatures of 723–973 K in a stream of CH₄/H₂ gas. The carburized catalysts were evaluated using a single-stack fuel cell and three-electrode cell. The results showed high activities for the anodic electrooxidation of hydrogen over the Co-Mo catalysts carburized at 873 and 923 K. The 873 K carburized Co-Mo catalyst had the highest activity and achieved 10.9% of the performance of a commercial Pt/C catalyst in a single-stack fuel cell. The XRD, TPC, TPR and XPS results showed that the Co-Mo oxycarbide in the bulk and on the surface are the active species for the hydrogen oxidation reaction.     

Self-sustained operation of a kWe-class kerosene-reforming processor for solid oxide fuel cells

In this paper, fuel-processing technologies are developed for application in residential power generation (RPG) in solid oxide fuel cells (SOFCs). Kerosene is selected as the fuel because of its high hydrogen density and because of the established infrastructure that already exists in South Korea. A kerosene fuel processor with two different reaction stages, autothermal reforming (ATR) and adsorptive desulfurization reactions, is developed for SOFC operations. ATR is suited to the reforming of liquid hydrocarbon fuels because oxygen-aided reactions can break the aromatics in the fuel and steam can suppress carbon deposition during the reforming reaction. ATR can also be implemented as a self-sustaining reactor due to the exothermicity of the reaction. The kW_e self-sustained kerosene fuel processor, including the desulfurizer, operates for about 250 h in this study. This fuel processor does not require a heat exchanger between the ATR reactor and the desulfurizer or electric equipment for heat supply and fuel or water vaporization because a suitable temperature of the ATR reformate is reached for H₂S adsorption on the ZnO catalyst beds in desulfurizer. Although the CH₄ concentration in the reformate gas of the fuel processor is higher due to the lower temperature of ATR tail gas, SOFCs can directly use CH₄ as a fuel with the addition of sufficient steam feeds (H₂O/CH₄ ≥ 1.5), in contrast to low-temperature fuel cells. The reforming efficiency of the fuel processor is about 60%, and the desulfurizer removed H₂S to a sufficient level to allow for the operation of SOFCs.     

Stoichiometric analysis of autothermal fuel processing

Fuel processing is one of the major processes for generation of hydrogen for fuel cells. Stoichiometric analysis is used to develop a general framework for comparison of fuel reforming data, in the full range of steam reforming (SR) to combustion. This framework is then applied to determine the reforming reaction space for methanol, ethanol, methane, propane, isooctane, dodecane, and hexadecane. A simple approach is proposed for determination of the thermal efficiency for autothermal reforming (ATR) of a generalized fuel based on fuel atomic analysis and oxygen consumption.     

Hydrogen production from ethanol steam reforming over nickel based catalyst derived from Ni/Mg/Al hydrotalcite-like compounds

Nickel based catalysts derived from thermal decomposition of Ni/Mg/Al hydrotalcite-like precursors have been studied in ethanol steam reforming (ESR) for hydrogen production. X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and thermogravimetric analysis (TGA) were used to investigate the physic-chemical properties of the catalysts prepared. The catalysts being mainly composed of Ni–Mg–O solid solution phase exhibited high activity and stability for ethanol steam reforming. Ethanol could be completely converted even at 673 K, and hydrogen concentration tended to increase with increasing reaction temperature, gas hourly space velocity (GHSV) and Ni/Mg ratio. XRD and TEM investigations demonstrate that low Ni/Mg ratio led to insufficient Ni⁰ phase available, which may result in decreasing activity and stability due to coke formation observed on the NiMg10 (Ni/Mg = 1/10) catalyst. High reduction pretreatment temperature (>973 K) could promote the reduction of Ni⁰ metal, and effectively improve the catalytic activity and stability. The optimum reduction temperature might be 1073 K, at which proper amount of Ni⁰ species and good resistance to coke formation could be obtained.     

Power-law type rate equation for propane ATR over Pt–Ni/Al2O3 catalyst

Kinetics of autothermal reforming (ATR) of propane on bimetallic Pt–Ni catalyst supported over δ-Al₂O₃ is investigated at 673 K with the purpose of obtaining an easy-to-implement power-law type rate equation. The rate expression is proposed for conditions extending up to 20% propane conversion and has reaction orders of 1.64, 2.44 and −0.59 in propane, oxygen and steam partial pressures, respectively. Parameters estimated by non-linear regression analysis in the MATLAB™ environment can be reliably used for propane ATR in the steam-to-carbon ratio range of 2.0–3.0 and carbon-to-oxygen ratio range of 3.0–5.4. The apparent activation energy is calculated as 46 ± 4 kJ mol⁻¹ in the 653–693 K interval.     

Effect and behavior of cerium oxide in Ni/γ-Al2O3 catalysts on autothermal reforming of methane: CeAlO3 formation and its role on activity

Nickel supported γ-alumina (Ni/γ-Al₂O₃) catalysts are well-known to be highly active on the autothermal reforming of methane, but to be unstable due to coke deposition. Cerium oxide (CeO₂) is one of promising promoter to overcome the fast deactivation of nickel-based catalysts by coke formation. Herein, catalytic behavior of CeO₂ over Ni/γ-Al₂O₃ catalysts on the autothermal reforming of methane was investigated. The catalytic activity was maintained for 100 h with H₂/CO molar ratio of 1.9. The formation of CeAlO₃ is observed at the reduction and reaction conditions. In this work, it was found that the formation of CeAlO₃ promoted the catalytic oxidation toward CO₂ and prevented the formation of α-Al₂O₃ and nickel-aluminate, resulting in stable activity for autothermal reforming of methane.     

LDH-derived Ni–MgO–Al2O3 catalysts for hydrogen-rich syngas production via steam reforming of biomass tar model: Effect of catalyst synthesis methods

Steam reforming of toluene (SRT) as a model tar compound is studied on Ni–MgO–Al₂O₃ hydrotalcite synthesized by different methods: urea hydrolysis, coprecipitation, and wet impregnation. The two wet-impregnated catalysts were produced by immersing MgO–Al₂O₃ hydrotalcites synthesized by urea hydrolysis and coprecipitation in Ni²⁺ solution to produce the corresponding impregnated catalysts. Among all the catalysts, both the samples prepared by urea hydrolysis gave superior toluene conversion of ~85% and also improved the resistance to carbon deposits. The two coprecipitation catalysts had a low toluene conversion of ~63% and also produced more coke. The X-ray photoelectron spectroscopy studies showed that impregnated catalyst produced from urea hydrolysis imparted greater metal-support interaction; whereas the coprecipitation impregnation catalysts only weakly interacted with the support. The CO₂ temperature programmed desorption measurement of the reduced catalysts showed that urea hydrolysis catalysts possessed higher surface basicity as compared to coprecipitation catalysts. This high basic character aided in suppressing the coke formation. HRTEM results also revealed that urea hydrolysis produced smaller Ni⁰ particles (6–7 nm) and coprecipitation produced larger particles (10–20 nm). The excellent reforming properties of urea hydrolysis is due to smaller Ni⁰ particle size and greater surface basicity which aided in improving the catalytic performance and suppressing coke.     

A comparative assessment of homogeneous propane reforming at intermediate temperatures

The study compares the performance of different pathways for gas-phase (non-catalytic) fuel reforming between 600 and 1000 °C. Specifically, the conversion of propane to hydrogen-rich syngas was investigated numerically and experimentally for pyrolysis (Py), steam reforming (SR), partial oxidation (POx), and autothermal reforming (ATR). Experiments were conducted in a tubular quartz reactor, where temperatures were imposed externally; reactants were diluted with nitrogen to reduce the impact of endothermic/exothermic reactions on the variation of gas-phase temperatures. In experiments, product concentrations of hydrogen, carbon monoxide, carbon dioxide, methane, and a range of hydrocarbon species were measured at predetermined operating conditions. The performance of each homogeneous reforming process was evaluated and compared by assessing propane conversion and production efficiencies for hydrogen and other species of interest. At 600 °C, propane conversion was low, but increased substantially with temperature; complete conversion was achieved at 1000 °C. Furthermore, findings show improved hydrogen production efficiencies of POx/ATR when compared to Py/SR. Experimental results are substantiated by numerical simulations with detailed chemical kinetics; numerical results are in good agreement with experiments at identical operating conditions. Experimental and numerical results for non-catalytic propane reforming at all tested temperatures (600–1000 °C) imply a negligible impact of steam addition to the process, as results for SR resemble Py results, and ATR closely follows POx characteristics. As such, results clearly show that steam does not play an active role in gas-phase reforming of propane at intermediate temperatures.     

The study of the performance of Ni supported on gadolinium doped ceria SOFC anode on the steam reforming of ethanol

The catalytic performance of Ni/CeGd SOFC anodes prepared by co-precipitation for steam reforming of ethanol at different reaction temperatures was evaluated. The Ni/CeGd SOFC anode calcined at 1073 K exhibited the highest activity and the lowest by-products formation rates during SR at 773 K. The TG and SEM analyses of the used catalysts showed that the deactivation observed for SR at 773 K was associated with the formation of carbon filaments. It was also observed that the increase of reaction temperature from 773 to 1073 K decreased coke formation, which was no longer detected at 1073 K. This result was attributed to the reverse of the Boudouard reaction and the promoting effect of the support on carbon gasification.     

Thermodynamic analysis of hydrogen production via autothermal steam reforming of selected components of aqueous bio-oil fraction

From a technical and economic point of view, autothermal steam reforming offers many advantages, as it minimizes heat load demand in the reformer. Bio-oil, the liquid product of biomass pyrolysis, can be effectively converted to a hydrogen-rich stream. Autothermal steam reforming of selected compounds of bio-oil was investigated using thermodynamic analysis. Equilibrium calculations employing Gibbs free energy minimization were performed for acetic acid, acetone and ethylene glycol in a broad range of temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm) values. The optimal O₂/fuel ratio to achieve thermoneutral conditions was calculated under all operating conditions. Hydrogen-rich gas is produced at temperatures higher than 700 K with the maximum yield attained at 900 K. The ratio of steam to fuel and the pressure determine to a great extent the equilibrium hydrogen concentration. The heat demand of the reformer, as expressed by the required amount of oxygen, varies with temperature, steam to fuel ratio and pressure, as well as the type of oxygenate compound used. When the required oxygen enters the system at the reforming temperature, autothermal steam reforming results in hydrogen yield around 20% lower than the yield by steam reforming because part of the organic feed is consumed in the combustion reaction. Autothermicity was also calculated for the whole cycle, including preheating of the organic feed to the reactor temperature and the reforming reaction itself. The oxygen demand in such a case is much higher, while the amount of hydrogen produced is drastically reduced.     

Catalytic features of Ni/Ba–Ce0.9–Y0.1 catalyst to produce hydrogen for PCFCs by methane reforming

Methane reforming in steam (SR), auto-thermal (ATR) and partial oxidation (POX) conditions over Ni/Ba–Ce_0.9–Y_0.1 catalyst was investigated in the temperature range 500–700 °C. Catalyst presents a satisfying activity in POX condition only. BCY carrier was not stable in the presence of CO₂ and, irrespective of reaction conditions, it reacts with CO₂ giving rise to the formation of BaCO₃ and CeO₂. The very low activity observed in SR conditions was due to the negative role exerted by water strongly absorbed on catalyst surface, limiting so the accessibility and reduction state of Ni active sites. In POX condition catalyst is active and satisfying H₂ yield can be reached by operating at T = 700 °C. A significant reduction of coke formation was observed by operating in POX at 700 °C. On the contrary, in ATR condition at the same reaction temperature huge amount of filamentous coke was observed.     

New low cost mesoporous silica (MSN) as a promising support of Ni-catalysts for high-hydrogen generation via dry reforming of methane (DRM)

In this study, a new nano-sized mesoporous silica (MSN) as support for Ni-based catalysts was produced from natural resources and tested in the dry reforming of methane between 823 and 1023 K. The fresh and spent catalysts Ni-x/MSN (x = 5, 10 and 20 wt.%) were characterized by various techniques. All catalysts are selective for hydrogen production and exhibited long-term stability with low coke formation predominantly as carbon nanotubes, for Ni loadings less than 10% at 973 K. The catalytic results were correlated with the in situ generation of Ni nanoparticles which are highly dispersed on the MSN surface due to strong metal-support interactions thus preventing the sintering process. No significant deactivation was recorded along 25 h on stream meaning that the textural properties of the catalysts have not been altered by the coke deposition or reaction temperature. The prepared MSN is a potential support to be utilized for hydrogen generation.     

Autothermal reforming study of diesel for fuel cell application

Diesel is one of the best hydrogen storage systems, because of its very high hydrogen volumetric density (100 kg H₂ m⁻²) and gravimetric density (15% H₂). In this study, several catalysts were selected for diesel reforming. Three experimental catalysts (Pt on gadolinium-doped ceria, Rh and Ru on the same support) and two commercial catalysts (FCR-HC14 and FCR-HC35, Süd-Chemie, Inc.) were used to reform diesel. The effects of operating conditions, such as temperature, O₂/C16 and H₂O/C16 on autothermal reforming (ATR) were investigated. In addition, by analyzing the concentrations of products and the temperature profiles along the catalyst bed, we studied the reaction characteristics for a better understanding of the ATR reaction. The fuel delivery and heat transfer between the front exothermic part and the rear endothermic part of the catalyst bed were found to be significant. In this study, the characteristic differences between a surrogate fuel (C₁₆H₃₄) and commercial grade diesel for the ATR were also examined.     

Zirconia supported catalysts for bioethanol steam reforming: Effect of active phase and zirconia structure

Three new catalysts have been prepared in order to study the active phase influence in ethanol steam reforming reaction. Nickel, cobalt and copper were the active phases selected and were supported on zirconia with monoclinic and tetragonal structure, respectively. To characterize the behaviour of the catalysts in reaction conditions a study of catalytic activity with temperature was performed. The highest activity values were obtained at 973 K where nickel and cobalt based catalysts achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. Nickel supported on tetragonal zirconia exhibited the highest hydrogen production efficiency, higher than 4.5 mol H₂/mol EtOH fed. The influence of steam/carbon (S/C) ratio on product distribution was another parameter studied between the range 3.2–6.5. Nickel supported on tetragonal zirconia at S/C = 3.2 operated at 973 K without by-product production such as ethylene or acetaldehyde. In order to consider a further application in an ethanol processor, a long-term reaction experiment was performed at 973 K, S/C = 3.2 and atmospheric pressure. After 60 h, nickel supported on tetragonal zirconia exhibited high stability and selectivity to hydrogen production.     

Hydrogen rich gas production by the autothermal reforming of biodiesel (FAME) for utilization in the solid-oxide fuel cells: A thermodynamic analysis

The thermodynamics of the autothermal reforming (ATR) of biodiesel (FAME) for production of hydrogen is simulated and evaluated using Gibbs free minimization method. Simulations are performed with water-biodiesel molar feed ratios (WBFR) between 3 and 12, and oxygen-biodiesel molar feed ratio (O_XBFR) from 0 to 4.8 at reaction temperature between 300 and 800 °C at 1 atm. Yields of H₂ and CO are calculated as functions of WBFR, O_XBFR and temperature at 1 atm. Hydrogen rich gas can be produced by the ATR of biodiesel for utilization in solid-oxide fuel cells (SOFCs). The best operating conditions for the ATR reformer are WBFR≥9 and O_XBFR = 4.8 at 800 °C by optimization of the operating parameters. Yields of hydrogen and carbon monoxide are 68.80% and 91.66% with 54.14% and 39.2% selectivities respectively at the above conditions. The hydrogen yield from biodiesel is higher than from unmodified oils i.e., transesterification increases hydrogen yield. Increase in saturation of the esters, results in increase in methane selectivity, while an increase in unsaturation results in a decrease in methane selectivity. Increase in degree of both saturation and unsaturation of esters, increases coke selectivity. Similarly an increase in the linoleic content of esters, increases coke selectivity.     

Ni/Ru–Mn/Al2O3 catalysts for steam reforming of toluene as model biomass tar

The catalytic steam reforming of the major biomass tar component, toluene, was studied over two commercial Ni-based catalysts and two prepared Ru–Mn-promoted Ni-base catalysts, in the temperatures range 673–1073 K. Generally, the conversion of toluene and the H₂ content in the product gas increased with temperature. A H₂-rich gas was generated by the steam reforming of toluene, and the CO and CO₂ contents in the product gas were reduced by the reverse Boudouard reaction. A naphtha-reforming catalyst (46-5Q) exhibited better performance in the steam reforming of toluene at temperatures over 873 K than a methane-reforming catalyst (Reformax 330). Ni/Ru–Mn/Al₂O₃ catalysts showed high toluene reforming performance at temperatures over 873 K. The results indicate that the observed high stability and coking resistance may be attributed to the promotional effects of Mn on the Ni/Ru–Mn/Al₂O₃ catalyst.