Production of synthesis gas by autothermal reforming of iso-octane and toluene over metal modified Ni-based catalyst

The reforming process of gasoline is an attractive technique for fuel processor or hydrogen station applications. We investigated catalytic autothermal reforming (ATR) of iso-octane and toluene over transition metal supported catalysts. The catalysts were prepared by an incipient wetness impregnation method and characterized by N₂ physisorption, XRD, and TEM techniques before and after the reaction. Many of the tested catalysts displayed reasonably good activity towards the reforming reactions of iso-octane. Especially, Ni/Fe/MgO/Al₂O₃ catalyst showed more activity than the other catalysts tested in this study including commercial HT catalyst. Ni/Fe/MgO/Al₂O₃ catalyst showed good stability for 700 h in the ATR of iso-octane. No major change was observed in catalytic activity in ATR of iso-octane or in the structure of catalyst. Since iso-octane, toluene are surrogates of gasoline, Ni/Fe/MgO/Al₂O₃ catalyst can be considered as ATR catalyst for gasoline fuel processor and hydrogen station systems.     

Development of iso-octane fuel processor system for fuel cell applications

An iso-octane fuel processor system with three different reaction stages, autothermal reforming (ATR) reaction of iso-octane, high temperature shift (HTS) and low temperature shift (LTS) reactions, was developed for applications in a fuel cell system. Catalytic properties of the prepared Ni/Fe/MgO/Al₂O₃ and Pt–Ni/CeO₂ or molybdenum carbide catalysts were compared to those of commercial NiO/CaO/Al₂O₃ and Cu/Zn/Al₂O₃ catalysts for ATR and LTS reaction, respectively. It was found that the prepared catalysts formulations in the fuel processor system were more active than those of the commercial catalysts. As the exit gas of iso-octane ATR over the Ni/Fe/MgO/Al₂O₃ catalyst was passed through Fe₃O₄–Cr₂O₃ catalyst for HTS and Mo₂C or Pt–Ni/CeO₂ catalyst for LTS reaction, the concentration of CO in hydrogen-rich stream was reduced to less than 2400 ppm. The results suggest that the iso-octane fuel processor system with prepared catalysts can be applied to PEMFC system when a preferential partial oxidation reaction is added to KIST iso-octane reformer system.     

Partial Oxidation Reforming Catalyst for Fuel Cell-Powered Vehicles Applications

Transition metal oxide formulations for the partial oxidation (POX) reforming of isooctane were investigated for an onboard gasoline fuel processor. Ni/M/MgO/Al₂O₃ systems are more active than a commercial ICI catalyst. These catalysts showed better sulfur tolerance over the commercial ICI catalyst in the POX reforming of isooctane containing sulfur (Cs = 100 ppm). There was no apparent deactivation or modification of structure during 770h onstream. It was found that Ni/(Fe,Co)/MgO/Al₂O₃ catalyst is a promising candidate as POX reforming catalyst for gasoline fuel processor applications.     

A kinetic modeling study of self-ignition of low alkylbenzenes at engine-relevant conditions

The self-ignition of low alkylbenzenes at engine-relevant conditions has been studied with kinetic modeling. A previously developed chemical kinetic model for gasoline surrogate fuels [J.C.G. Andrae, R.A. Head, Combust Flame 156 (2009) 842-51] was extended with chemistry for ethylbenzene and m-xylene resulting in an overall model consisting of 150 species and 759 reactions. In model validation, comparisons were made between model predictions and experimental data of ignition delay times measured behind reflected shock waves, laminar burning velocities collected at elevated temperature and pressure and species profiles in a high-pressure single pulse shock tube. Generally good agreement was found and the model is sensitive to changes in mixture strength, pressure and temperature. Shock tube ignition delay modeling results for ethylbenzene and m-xylene also compare well to the ones for toluene. The rate controlling step for the ignition of ethylbenzene in the current mechanism is the reaction with ethylphenyl radical and oxygen. Ignition delay time for m-xylene was found to be very sensitive to reactions involving hydrogen atom abstraction from fuel by hydroxyl and oxygen and to branching reactions where methylbenzyl reacts with oxygen and hydroperoxide. The validated mechanism was used to study fuel chemistry effects when blending ethylbenzene with the paraffinic fuels iso-octane and n-heptane. A sensitivity- and flow path analysis showed that a higher consumption of hydroperoxide by ethylphenyl than expected from the contribution of neat ethylbenzene in a fuel mixture with iso-octane inhibits both iso-octane and ethylbenzene ignition. This can explain the observed increase in ignition delay time and octane number for fuel mixtures compared to neat fuels.     

PEM – Fuel Cell System for Residential Applications

Viessmann is developing a PEM fuel cell system for residential applications. The uncharged PEM fuel cell system has a 2 kW electrical and 3 kW thermal power output. The Viessmann Fuel Processor is characterized by a steam‐reformer/burner combination in which the burner supplies the required heat to the steam reformer unit and the burner exhaust gas is used to heat water. Natural gas is used as fuel, which is fed into the reforming reactor after passing an integrated desulphurisation unit. The low temperature (600 °C) fuel processor is designed on the basis of steam reforming technology. For carbon monoxide removal, a single shift reactor and selective methanisation is used with noble metal catalysts on monoliths. In the shift reactor, carbon monoxide is converted into hydrogen by the water gas shift reaction. The low level of carbon monoxide at the outlet of the shift reactor is further reduced, to approximately 20 ppm, downstream in the methanisation reactor, to meet PEM fuel cell requirements. Since both catalysts work at the same temperature (240 °C), there is no requirement for an additional heat exchanger in the fuel processor. Start up time is less than 30 min. In addition, Viessmann has developed a 2 kW class PEFC stack, without humidification. Reformate and dry air are fed straight to the stack. Due to the dry operation, water produced by the cell reaction rapidly diffuses through the electrolyte membrane. This was achieved by optimising the MEA, the gas flow pattern and the operating conditions. The cathode is operated by an air blower.     

iso-Octane partial oxidation over Ni-Sn/Ce0.75Zr0.25O2 catalysts

In this study, Ni/Ce_0.75Zr_0.25O₂ catalyst was doped with different amounts of Sn by co-impregnation method. The catalysts were characterized by BET, H₂ chemisorption, XRD, TPR, TEM, XPS and tested for iso-octane partial oxidation (iC8POX) to H₂ in the temperature range of 400–800 °C at atmospheric pressure. The results showed that most of Sn species were present on the surface of Ni particles and did not modify the reducibility of the support. Addition of a small amount of Sn (<0.5 wt.%) lowered the catalytic activity for iso-octane partial oxidation by less than 5% while the extent of carbon deposition was decreased by more than 50%. However, Sn loadings higher than 1 wt.% caused a massive drop in catalytic activity. This indicates that as long as the Ni surface is only partially covered with Sn species, the active sites for the partial oxidation of iso-octane remain intact, while the surface site ensembles required for carbon formation are blocked.     

An experimental and numerical analysis of the HCCI auto-ignition process of primary reference fuels,toluene reference fuels and diesel fuel in an engine,varying the engine parameters

For a future HCCI engine to operate under conditions that adhere to environmental restrictions, reducing fuel consumption and maintaining or increasing at the same time the engine efficiency, the choice of the fuel is crucial. For this purpose, this paper presents an auto-ignition investigation concerning the primary reference fuels, toluene reference fuels and diesel fuel, in order to study the effect of linear alkanes, branched alkanes and aromatics on the auto-ignition. The auto-ignition of these fuels has been studied at inlet temperatures from 25 to 120 °C, at equivalence ratios from 0.18 to 0.53 and at compression ratios from 6 to 13.5, in order to extend the range of investigation and to assess the usability of these parameters to control the auto-ignition. It appeared that both iso-octane and toluene delayed the ignition with respect to n-heptane, while toluene has the strongest effect. This means that aromatics have higher inhibiting effects than branched alkanes. In an increasing order, the inlet temperature, equivalence ratio and compression ratio had a promoting effect on the ignition delays. A previously experimentally validated reduced surrogate mechanism, for mixtures of n-heptane, iso-octane and toluene, has been used to explain observations of the auto-ignition process.     

Fuel composition effects on transportation fuel cell reforming

This work examines the effect of various hydrocarbons on fuel processor light-off and reforming. Major hydrocarbon fuel constituents, such as aliphatic compounds, napthanes, and aromatics have been compared with the fuel processing performance of blended fuel components and reformulated gasoline to examine synergistic or detrimental effects the fuel components have in a real fuel blend.

Short chained aliphatic hydrocarbons tend to have favorable light-off and reforming characteristics for catalytic autothermal reforming compared with longer-chained and aromatic components. Oxygenated hydrocarbons have lower light-off requirements than do pure hydrocarbons. Gas phase oxidation favors higher cetane # fuels, which tend to be longer chained hydrocarbons. Energy consumption during the start-up process shows a large fuel effect. Methanol and dimethylether (DME) show lower start-up energy demands for the fuel processor start-up than do high temperature reforming hydrocarbon fuels such as methane, gasoline and ethanol. Aromatics and longer chained hydrocarbons show a higher tendency for carbon formation, increasing the amount of carbon formed during the light-off phase while the addition of oxygenates tends to lower the carbon formed during the start-up process.     

Development of a detailed kinetic model for gasoline surrogate fuels

A detailed chemical kinetic model to describe the autoignition of gasoline surrogate fuels is presented consisting of the fuels iso-octane, n-heptane, toluene, diisobutylene and ethanol. Model predictions have been compared with shock tube ignition delay time data for surrogates of gasoline over practical ranges of temperature and pressure, and the model has been found to be sensitive to both changes in temperature and pressure. Moreover, the model can qualitatively predict the observed synergistic and antagonistic non-linear blending behaviour in motor octane number (MON) for different combinations of primary reference fuels (PRFs) and non-PRFs by correlating calculated autoignition delay times from peak pressures and temperatures in the MON test to experimental MON values. The reasons for the blending behaviour are interpreted in terms autoignition chemistry.     

Comparative studies of dehydrocyclization of n-octane and iso-octane on bifunctional and monofunctional Pt/Al2O3 catalysts

The dehydrocyclization of n-octane and iso-octane to ethyl benzene, and ortho-, para-, and meta-xylenes was investigated on mono- and bifunctional platinum/alumina catalysts in a microcatalytic reactor with hydrogen as carrier at 1.8 atm pressure and between temperatures of 573 and 763 K, using pulse technique. On bifunctional Pt/Al₂O₃ catalyst, the total conversion of both n-octane and iso-octane was found to start from a high value and decrease with increasing temperature for all pulse volumes investigated. However, iso-octane was found to be more reactive than n-octane. There was only one primary product, namely iso-octane, in the n-octane reaction. As regards the iso-octane reaction, two primary products, ethyl benzene and o-oxylene were identified. For both reactions, these primary products decreased to a minimum as temperatures increased. On monofunctional (non-acidic) Pt/Al₂O₃, the total conversion of n-octane increased with temperature and passed through a maximum. The primary products of the reaction were ethyl benzene and o-xylene.     

Catalytic reforming of model tar compounds from hot coke oven gas with low steam/carbon ratio over Ni/MgO-Al2O3 catalysts

The catalytic reforming of toluene and naphthalene was performed to investigate the possibility for directly converting tar components from hot coke oven gas (COG) with lower steam/carbon (S/C) molar ratios to light fuel gases. The NiO/MgO-Al₂O₃ catalysts reduced exhibited excellent catalytic activity, stability and sulphur tolerance. The effects of various reaction conditions and S/C ratios on the catalytic performance were investigated in detail. Toluene and naphthalene were completely converted into small gas molecules at 700-800 °C and S/C = 0.28. An appropriate amount of steam benefited the methanation reaction of CO and H₂. The effects of N₂, CH₄ or CO in COG were also discussed. Relative to N₂, CO contributed to the conversion of toluene and the formation of CH₄, but the opposite was true for CH₄. The sulphur tolerance was tested by adding H₂S in the feed gas. The reaction results were explained by a water cycle mechanism.     

Decane reforming reaction over Pt,Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite

Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on NaY- and HY-zeolite were examined as a catalyst for producing gasoline from n-decane via simultaneous reforming and cracking. The catalysts were prepared by calcining and reducing metal-ion-exchanged Y-zeolite with O₂ and H₂ at 300°C., respectively. Thus prepared catalysts were characterized by hydrogen chemisorption and temperature programmed desorption of ammonia. Pt-Ni/NaY and Pt-Ir/NaY bimetallic catalysts offered the improved activity maintenance compared to Pt/NaY monometallic catalyst. The catalysts supported on HY-zeolite showed higher selectivity toward C₅–C₇ and skeletal isomers of C₅–C₇- and C₈–C₁₀ than those of the catalysts supported on NaY-zeolite, which is a desired characteristic for increasing octane value of gasoline these days. However, deactivation with reaction time was much more pronounced on HY-zeolite-supported catalyst. When the catalyst was prcsulfided with H,S, the stability with time on stream was enhanced and the selectivity was quite different from that of the catalyst before presulfiding. The acidity of Y-zeolite and presulfiding of catalyst greatly influenced the activny, selectivity and stability of Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite in n-decane reforming reaction.     

Novel perovskite-based catalysts for autothermal JP-8 fuel reforming

Autothermal reforming is an attractive method for on-site production of hydrogen for use in proton exchange membrane (PEM) fuel cells. The use of liquid hydrocarbons as feedstock, however, remains a challenge as these fuels cause severe coking of the currently available catalysts. In this work, cerium- and nickel-substituted LaFeO₃ perovskites were investigated as potential low cost coking resistant catalysts for autothermal reforming of a JP-8 fuel surrogate. The high surface area complex oxides were prepared using aqueous (solution) combustion synthesis at fuel-rich conditions and characterized by BET and XRD techniques. The catalysts exhibited excellent stability during autothermal reforming at and 1 atm, with near-equilibrium hydrogen yield even at high GHSV values (). The addition of cerium significantly improved coking resistance, attributed to improved oxygen ion conductivity, resulting in carbon oxidation on the catalyst surface.     

A Multi‐Function Compact Micro‐Channel Reactor Coated with Sulphur Tolerant Catalyst for LPG Steam Reforming

Hydrogen fuelled polymer electrolyte fuel cells (PEFC) offer clear environmental benefits. Lack of viable hydrogen infrastructure in the near future means that a key issue is availability of hydrogen at the point of use. Liquefied petroleum gas (LPG) offers advantages as a fuel over other hydrocarbons because there is already an infrastructure in place for remote areas. Hydrogen supply via steam reforming of LPG is therefore a feasible avenue of achieving the environmental benefits. Commercial grade LPG unavoidably contain sulphur as an odorant, the sulphur needs to be removed from the fuel stream before it reaches the reformer catalyst and fuel cell. Utilizing sulphur tolerant catalysts in the reformer leads to a simpler fuel processor design. Thermal management and reforming efficiency has been a challenge for the sulphur tolerant catalysts. In this paper, a multi‐function compact micro‐channel reactor designed for hydrocarbon steam reforming was evaluated for use with LPG. A sulphur tolerant catalyst was wash‐coated on to the reforming layers. The reformer was tested over a wide range of reactor temperatures, steam to carbon ratios and fuel flow rates. Over 60% of H₂ composition can be achieved at high reforming temperatures with a LPG supply rate of 0.75 dm³ min⁻¹ (STP) and a S/C ratio of 4.     

液体碳氢燃料蒸汽重整制氢催化剂研究进展

液体碳氢燃料具有能量密度高、氢含量大及便于储存和运输的特点,以其为原料经重整制氢并应用到移动式的燃料电池/加氢站对民用设备及国防武器等具有现实意义。本文首先对液体碳氢燃料蒸汽重整机理进行概述,明确当前催化剂面临的积炭、硫中毒等主要问题,从而指导高性能催化剂的设计和开发;其次,总结了几种典型液体碳氢燃料（汽油、煤油、柴油、焦油、含硫碳氢燃料等）蒸汽重整催化剂的相关进展,对比了不同催化剂在相应工艺条件下的活性及稳定性;最后,归纳了几类蒸汽重整过程强化技术包括等离子体重整、化学链重整、吸附增强重整及反应与分离耦合重整,说明了各类强化技术的优点及存在的不足,提出通过构建高效催化剂与蒸汽重整强化技术耦合有望实现液体碳氢燃料的高效转化制氢。希望本综述能为进一步研究液体碳氢燃料重整制氢提供相关指导。     

The development and experimental validation of a reduced ternary kinetic mechanism for the auto-ignition at HCCI conditions,proposing a global reaction path for ternary gasoline surrogates

To acquire a high amount of information of the behaviour of the Homogeneous Charge Compression Ignition (HCCI) auto-ignition process, a reduced surrogate mechanism has been composed out of reduced n-heptane, iso-octane and toluene mechanisms, containing 62 reactions and 49 species. This mechanism has been validated numerically in a 0D HCCI engine code against more detailed mechanisms (inlet temperature varying from 290 to 500 K, the equivalence ratio from 0.2 to 0.7 and the compression ratio from 8 to 18) and experimentally against experimental shock tube and rapid compression machine data from the literature at pressures between 9 and 55 bar and temperatures between 700 and 1400 K for several fuels: the pure compounds n-heptane, iso-octane and toluene as well as binary and ternary mixtures of these compounds. For this validation, stoichiometric mixtures and mixtures with an equivalence ratio of 0.5 are used. The experimental validation is extended by comparing the surrogate mechanism to experimental data from an HCCI engine. A global reaction pathway is proposed for the auto-ignition of a surrogate gasoline, using the surrogate mechanism, in order to show the interactions that the three compounds can have with one another during the auto-ignition of a ternary mixture.     

Contributions of heterogeneous and homogeneous chemistry in the catalytic partial oxidation of octane isomers and mixtures on rhodium coated foams

Catalytic partial oxidation experiments with n-octane, 2,2,4-trimethylpentane (i-octane), and an n-octane:i-octane (1:1) mixture were performed on 80 and 45 ppi Rh-coated α-alumina foam supports at 2, 4, and 6 SLPM total flow rate in order to explore the effects of chemical structure for single components and binary mixtures on fuel reactivity and product distribution. When reacted as single components, the conversion of i-octane is greater than n-octane at C/O>1.1 (both fuel conversions are 100% for C/O<1.1). However, when reacted in an equimolar mixture, the conversion of n-octane is greater than i-octane. All three fuels give high selectivity to syngas (H₂ and CO) on 80 ppi supports for C/O<1. For C/O>1, n-octane produces high selectivity to ethylene while i-octane makes i-butylene and almost no ethylene. The fuel mixture produces these species proportional to the mole fractions of n-octane and i-octane within the reacting mixture. Increasing the support pore diameter decreases the selectivity to syngas and increases H₂O and olefin selectivity.The reforming of all three fuels is modeled using detailed chemistry by decoupling the heterogeneous and homogeneous chemistry in a two-zone plug flow model. Detailed homogeneous reaction mechanisms with several thousand elementary reactions steps and several hundred species are used to simulate experimentally observed olefin selectivities for all three fuels on 80 and 45 ppi monoliths at 2, 4, and 6 SLPM quite well. These results support the hypothesis that a majority of the observed olefins are made through gas-phase chemistry.     

Screening of Inorganic Adsorbents for Selective Adsorption of Thiophene from Model Gasoline

Hydrodesulfurization-treated (HDS-treated) gasoline with low sulfur content is an important source of primary fuel for fuel cells, although it contains sulfur compounds, thiophene (TP), benzothiophene (BTP), and thiophene alkylated derivatives, known as a poison for the reformer catalysts and the electrode catalysts of fuel cells. Adsorptive removal of TP from model organic liquid of HDS-treated gasoline was screened on different kinds of inorganic adsorbents: hydrous metal oxides, mixed metal oxides, aluminosilicates, acidic salts of multivalent metal, hetero polyacidic salt, and metal salts of iron hexacyanate. All the adsorbents showed very low TP uptake, less than 5% of the total TP amount when metal ions were not loaded on the adsorbent. On the other hand, some metal ion (Ag, Cu, and Ce) loaded adsorbents had good TP adsorptive properties. On simple metal oxides, Ag ion was better for the formation of adsorption center than Ce or Ni ions. In zeolite group, Ce-loaded Y-zeolite showed the largest TP uptake (99% of the total TP amount). Hydrous cerium oxide and the Ce-loaded adsorbents prepared from K₄[Fe(CN)₆], Silicagel, TiO₂, and ZrO₂ did not show TP selectivity. The effect of coexisting toluene on TP adsorption was studied from the TP solutions with and without toluene.     

Optimised Mixture Formation for Diesel Fuel Processing

Mixture formation plays an important role in the diesel reforming process. It is important to maintain proper O₂/C and H₂O/C ratios to avoid hot spots and coking. Fuel must be completely evaporated before entering the reaction zone in order to prevent catalyst damage by coking. Computational fluid dynamics (CFD) is used to optimise the mixing process. Turbulent mixing, diesel spray injections and evaporation and simplified chemical reactions have been calculated. This revealed critical parts of the existing construction. However, experimental verification is necessary. To identify thermodynamic conditions for a possible carbon formation process, experiments with idealised model fuels as well as with real diesel fuel were carried out. Flow visualisation experiments serve for the verification of the CFD simulations. Quartz glass reactors as models of the reformers were operated under real mixing temperatures (400 °C) to observe the effect of the flow profile on fuel sprays. Experiments with coloured fuels were used to visualise the flow and concentration profiles in the mixing chamber. Results were compared with CFD models. Two patented reformers were designed as a result of the CFD optimisation. These were operated for 500 h and 1,000 h respectively with a commercially available diesel, showing very promising results.     

Biogas Catalytic Reforming Studies on Nickel‐Based Solid Oxide Fuel Cell Anodes

Heterogeneous catalysis studies were conducted on two crushed solid oxide fuel cell (SOFC) anodes in fixed‐bed reactors. The baseline anode was Ni/ScYSZ (Ni/scandia and yttria stabilized zirconia), the other was Ni/ScYSZ modified with Pd/doped ceria (Ni/ScYSZ/Pd‐CGO). Three main types of experiments were performed to study catalytic activity and effect of sulfur poisoning: (i) CH₄ and CO₂ dissociation; (ii) biogas (60% CH₄ and 40% CO₂) temperature‐programmed reactions (TPRxn); and (iii) steady‐state biogas reforming reactions followed by postmortem catalyst characterization by temperature‐programmed oxidation and time‐of‐flight secondary ion mass spectrometry. Results showed that Ni/ScYSZ/Pd‐CGO was more active for catalytic dissociation of CH₄ at 750 °C and subsequent reactivity of deposited carbonaceous species. Sulfur deactivated most catalytic reactions except CO₂ dissociation at 750 °C. The presence of Pd‐CGO helped to mitigate sulfur deactivation effect; e.g. lowering the onset temperature (up to 190 °C) for CH₄ conversion during temperature‐programmed reactions. Both Ni/ScYSZ and Ni/ScYSZ/Pd‐CGO anode catalysts were more active for dry reforming of biogas than they were for steam reforming. Deactivation of reforming activity by sulfur was much more severe under steam reforming conditions than dry reforming; a result of greater sulfur retention on the catalyst surface during steam reforming.