Coking Stability Research Articles

Methane Dry Reforming Catalysts Based on Pr-Doped Ceria–Zirconia Synthesized in Supercritical Propanol

This paper is devoted to the study of active and stable nickel catalysts for methane dry reforming based on Pr-doped ceria–zirconia obtained via the solvothermal continuous method. Studies on the physicochemical and catalytic properties of the 5%Ni/Ce0.75Zr0.25−xPrxO2 series have showed that Pr introduction leads to an increase in the amount of highly reactive oxygen in the oxide lattice. Praseodymium-based catalysts showed significantly higher reactant conversions. In addition to the nature of support, the method of nickel introduction was also studied; Ni was added both using impregnation and the one-pot procedure with mixed oxide preparation. The method of Ni addition was shown to have significant effect on the morphology of its particles and Ni-support interaction, and, respectively, on catalytic activity and coking stability. The 5%Ni/Ce0.75Zr0.15Pr0.1O2 catalyst prepared by one-pot method showed stable operation in the MDR reaction for 30 h at CO2 and CH4 conversions of ~40% and an H2 yield of ~18% (T = 700 °C, τ = 10 ms).

Approaches to the design of efficient and stable catalysts for biofuel reforming into syngas: doping the mesoporous MgAl2O4 support with transition metal cations.

The mesoporous MgAl2O4 support is promising for the design of efficient and stable to coking catalysts for natural gas and biofuel reforming into syngas. This work aims at doping this support with transition metal cations (Fe, Cr, Ti) to prevent the incorporation of Ni and rare-earth cations (Pr, Ce, Zr), loaded by impregnation, into its lattice along with providing additional sites for CO2 activation required to prevent coking. Doped MgAl1.9Me0.1O4 (Me = Fe, Ti, Cr) mesoporous supports prepared by the one-pot evaporation-induced self-assembly method with Pluronic P123 triblock copolymers were single-phase spinels. Their specific surface area varies in the range of 115-200 m2 g-1, decreasing to 90-110 m2 g-1 after successive addition of the supporting nanocomposite active component 10 wt% Pr0.3Ce0.35Zr0.35O2 + (5 wt% Ni + 1% Ru) by impregnation. Mössbauer spectroscopy for iron-doped spinels confirmed the spatially uniform distribution of Fe3+ cations in the lattice without clustering being mainly located at the octahedral positions. Fourier-transform infrared spectroscopy of the adsorbed CO molecules was performed to estimate the surface density of metal sites. In methane dry reforming, the positive effect of MgAl2O4 support doping was observed from both a higher turn-over frequency as compared with the catalyst on the undoped support as well as the highest efficient first-order rate constant for the Cr-doped catalyst as compared with published data for a variety of Ni-containing catalysts based on the alumina support. In the reaction of ethanol steam reforming, the efficiency of catalysts on the doped supports is comparable, while exceeding that of Ni-containing supported catalysts reported in the literature. Coking stability was provided by a high oxygen mobility in the surface layers estimated by the oxygen isotope heteroexchange with C18O2. A high efficiency and coking stability were demonstrated in the reactions of methane dry reforming and ethanol dry and steam reforming in concentrated feeds for the honeycomb catalyst with a nanocomposite active component on the Fe-doped MgAl2O4 support loaded on the FeCrAl-alloy foil substrate.

Applicative Coal Petrology for Industries: New Paradigms

Abstract Coal petrology plays a significant role in understanding coal behaviour during various industrial processes such as carbonization, gasification and liquefaction and helps in characterizing them accordingly. Proper use of fluorescence microscopy and vitrinite reflectance measurement is crucial; carbonization study shows that maceral composition and rank affect the thermoplasticity wherein vitrinite contributes most to the coke formation. Further, the vitrinite is catalyzed by the presence of exsudatinite. Liptinite, when associated with vitrinite, lowers the viscosity of coal during coke making. Coal petrology is successfully used to assess suitability of a coal for coking to predict coke strength and to evaluate coal for coal-blend designing. Composition, structure and behaviour of coke are revealed through petrographic study. The stability and reactivity of coke can also be realised through microscopy. Gasification of coal is performed best in bituminous coal while it is expensive in case of low rank or low grade coals. It can be a simple coal gasification, fixed bed gasification, fluidized-bed gasification, entrained-flow and molten-bath coal gasification. Though any coal may be used for gasification but coal with high reactive components are more suitable but bituminous coal with high inertinite is also suitable as per few researchers. Some minerals have catalytic effect while others act as inhibitors. Elemental composition of organic and inorganic matter of coal, its surface characteristics, porosity and intrinsic reactivity have important bearing on efficiency of gasification. Coal liquefaction is a clean fuel technology which requires proper petrological characterization of coal before processing it. Rank and type of coal along with its composition influence the liquefaction behaviour. Thus, it is imperative to carry out a complete coal microscopy before coal is utilized for making coke/coke-blend or liquid and gaseous hydrocarbon.

Spinel-type MnxCr3-xO4-based catalysts for ethanol steam reforming

For catalysts comprised of mixed manganese-chromium oxides MnxCr3-xO4 (x = 0.3–2.7) prepared by Pechini route with Ni and Ru supported by impregnation fundamental factors determining their performance in ethanol steam reforming have been elucidated using combination of structural (XRD, HRTEM), spectroscopic (UV–vis), surface science (XPS, FTIR spectroscopy of adsorbed CO) and kinetic (H2 and EtOH TPR, oxygen isotope heteroexchange with C18O2) methods. The most important feature is strong metal-support interaction stabilizing small clusters of metals/alloys and preventing carbon nucleation. The lattice oxygen mobility and reactivity increased with Mn content. The highest TOF was obtained for (Ni + Ru)–loaded oxide support containing cubic spinel phase of MnCr2O4 composition, which implies a positive effect of Ni-Ru interaction in mixed clusters on catalytic activity. This catalyst has also a high density of active sites, surface enriched by Mn and sufficient oxygen mobility providing coking stability, which makes it attractive for practical application.

Promotional Effect of Iron on Nickel-Based Catalyst for Combined Steam-Carbon Dioxide Reformation of Methane.

In this study, the effect by Iron with nickel-based catalyst for the combined steam and carbon dioxide reforming of methane was investigated. Fe-promoted and un-promoted Ni-Mg-Ce/γ-Al2O3 catalysts were prepared by co-impregnation and evaluated in a quartz fixed-bed reactor at H₂O:CO₂:CH₄ ratios of 0.9:1:1 and a temperature of 1073 K under atmospheric pressure. The physicochemical properties of the catalysts were investigated by N₂ adsorption-desorption, XRD, H₂-TPR, CO₂-TPD, TGA and FE-SEM. The iron-supported catalysts showed improved resistance to carbon deposition and suppressed sintering of nickel. As a result, NMC-Fe(5) showed the lowest coke and high stability over 70 h among all other catalysts.

Novel Ni/Ce(Ti)ZrO2 Catalysts for Methane Dry Reforming Prepared in Supercritical Alcohol Media

To achieve a high activity and coking stability of nickel catalysts in dry reforming of methane, materials comprised of ceria–zirconia doped by Ti were investigated as supports. Ceria–zirconia supports doped with titanium were prepared either via the Pechini method or by synthesis in supercritical alcohol media. Ni-containing catalysts were prepared by two techniques: standard incipient wetness impregnation and one-pot synthesis. The catalytic reaction of DRM to synthesis gas was carried out in the 600–750 °C range over 5% wt. Ni/Ce(Ti)ZrO2. Dried and calcined supports and catalysts were characterized by physicochemical methods including N2 adsorption, XRD, Raman, H2-TPR, and HRTEM. Both preparation methods led to formation of solid solution with cubic fluorite-like structure, as well as after addition of Ti. Introduction of Ti should provide improved oxygen storage capacity and mobility of support oxygen. The highest activity was observed with the catalyst of 5% wt. Ni/Ce0.75Ti0.2Zr0.05O2−δ composition due to optimized oxide support structure and support oxygen mobility.

Gas-Permeable Inorganic Shell Improves the Coking Stability and Electrochemical Reactivity of Pt toward Methane Oxidation

Solid oxide fuel cells produce electricity directly by oxidizing methane, which is the most attractive natural gas fuel, and metal nanocatalysts are a promising means of overcoming the poor catalytic activity of conventional ceramic electrodes. However, the lack of thermal and chemical stability of nanocatalysts is a major bottleneck in the effort to ensure the lifetime of metal-decorated electrodes for methane oxidation. Here, for the first time, this issue is addressed by encapsulating metal nanoparticles with gas-permeable inorganic shells. Pt particles approximately 10 nm in size are dispersed on the surface of a porous La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) electrode via wet infiltration and are then coated with an ultrathin Al2O3 layer via atomic layer deposition. The Al2O3 overcoat, despite being an insulator, significantly enhances the immunity to carbon coking and provides high activity for the electrochemical oxidation of methane, thereby reducing the reaction impedance of the Pt-decorated electrode by more than 2 orders of magnitude and making the electrode activity of the Pt-decorated sample at 650 °C comparable with those reported at 800 °C for pristine LSCM electrodes. These observations provide a new perspective on strategies to lower the operation temperature, which has long been a challenge related to hydrocarbon-fueled solid oxide fuel cells.

The Synthesis of Ce1 – xZr x O2 Oxides in Supercritical Alcohols and Catalysts for Carbon Dioxide Reforming of Methane on Their Basis

The effect of the features of starting zirconium compounds on the solvothermal synthesis of mixed Ce–Zr oxides in a flow reactor using ethanol and isopropanol as a supercritical medium was studied. The phase composition and structural properties of the synthesized samples were investigated using X-ray diffraction analysis (XRD) and Raman spectroscopy. The morphology and textural properties were studied by transmission electron microscopy (TEM) and thermal desorption of nitrogen. It was found that the use of zirconium oxychloride or acetate as the starting substances results in the formation of a mixture of phases enriched with cerium or zirconium, whereas the use of zirconium butoxide with acetylacetone as a complexing agent allows obtaining a homogeneous solid solution. The catalytic properties of the synthesized oxides with supported Ni were tested in methane dry reforming (MDR). The catalyst containing a single-phase oxide synthesized in the presence of acetylacetone exhibited much higher activity, selectivity and coking stability.

Electrochemically modified, robust solid oxide fuel cell anode for direct-hydrocarbon utilization

A main advantage of solid oxide fuel cells (SOFCs) operating at a high temperature (>650°C) is the flexibility of the fuel they use, specifically as they offer the possibility to utilize methane (natural gas). Unfortunately, however, the state-of-the-art SOFC anodes, composed of a nickel and an anionically conducting oxide such as yttria-stabilized zirconia (YSZ), are associated with Ni-catalyzed carbon deposition and the ensuing degradation of the anode performance. Here, we address these issues through the application of a simple, scalable, cost-effective ceramic coating method known as cathodic electrochemical deposition (CELD). Samaria-doped CeO2 (SDC) was chosen as the coating material due to its high chemical stability against carbon formation, high electronic and ionic conductivities, and favorable electrocatalytic activity toward fuel oxidation reaction. Nanostructured SDC layers with a high specific surface area were successfully coated onto Ni surfaces via CELD. The physical and chemical attributes of each coating were characterized by a range of analysis tools, in this case SEM, TEM, XRD, EDS, ICP-MS and Raman spectroscopy. An analysis of the AC impedance spectroscopy (ACIS) of Ni-patterned YSZ symmetric cells (anode|electrolyte|anode) with SDC coatings revealed significantly enhanced electrode activity toward fuel oxidation and coking stability under dry or wet methane fuel at 650°C. These results suggest that the Ni-surface modification via CELD can be a feasible solution for the direct use of hydrocarbon fuels in SOFCs.

Ni-loaded nanocrystalline ceria-zirconia solid solutions prepared via modified Pechini route as stable to coking catalysts of CH4 dry reforming

AbstractMixed nanocrystalline Ce-Zr-O oxides (Ce/Zr = 1 or 7/3) were prepared by modified Pechini route using ethylene glycol solutions of metal salts. Detailed characterization of their real structure and surface properties by X-ray diffraction on synchrotron radiation with the full-profile Rietveld analysis, high resolution electron microscopy with elemental analysis, Raman spectroscopy, UV-Vis and X-ray photoelectron spectroscopy revealed a high homogeneity of cations distribution in nanodomains resulting in stabilization of disordered cubic phase. This provides a high dispersion of NiO loaded on these mixed oxides by wet impregnation, a high reactivity and mobility of oxygen in these catalysts and strong interaction of Ni with support in the reduced state. This helps to achieve a high activity and coking stability of developed catalysts in CH4 dry reforming in feeds with CH4 concentration up to 15% and CH4/CO2 ratio =1.

Effect of modified sludge on the rheological properties and co-slurry mechanism of petroleum coke–sludge slurry

Abstract Poor stability and low gasification reactivity of petroleum coke–water slurry (PCWS) significantly limit large-scale gasification applications of PCWS. Co-slurry of sludge and petroleum coke can be used to solve the problems of poor stability and low gasification reactivity of PCWS. In this study, petroleum coke–sludge slurry (PCSS) samples were prepared by mixing petroleum coke with three kinds of sludge, namely, petrochemical, sewage, and paper mill paper. The rheological properties and co-slurry mechanism of PCSS were analyzed with different sludge modifiers and sludge mixing proportions. Results showed that the lowest apparent viscosity of PCSS could be obtained by using Ca(OH)2 modifier for the three kinds of sludge. Optimal dosage was approximately 8 wt.% to 10 wt.% based on dry sludge. Maximum mass concentration of PCWS with no stabilizer was 71.3 wt.% and the slurry exhibited shear-thickening behavior. However, PCSS exhibited shear-thinning behavior when approximately 6 wt.% to 8 wt.% of the sludge was added based on dry petroleum coke. Flow behavior of PCSS fitted the Herschel–Bulkley model perfectly. Good stability of PCSS could be obtained despite reducing maximum mass concentration of PCSS to approximately 8 wt.% compared with PCWS after almost 10 wt.% of sludge was added. The co-slurry mechanism of PCSS may have a significant relationship with the physical and chemical properties of sludge. The network structure of sludge floc and the network structure formed by a chemical bond between petroleum coke and sludge determined the rheological properties of PCSS.

Assessing the effectiveness of the technological system of coke stabilization. Part 2

The stabilization of coke is highly effective, no matter how the influence of its properties on the production costs of hot metal is assessed. Setting limits on the maximum effectiveness has little influence on the result. Thus, the number of stabilizing actions adopted (the number of stabilization-drum rotations) may be sharply reduced. In that case, the speed of the stabilizing drum may be low. The stabilization of coke offers untapped potential for reducing the cost of hot metal.

Assessing the effectiveness of coke stabilization. Part 1

The effectiveness of stabilization ($/t of hot metal) is assessed for ten coke samples. A method of comparing coke quality is proposed, on the basis of its influence on the coke consumption in hot-metal production. Three formulas for the dependence of the coke consumption on its quality are considered. The relation between the effectiveness of coke stabilization and its initial properties is found to be stochastic. Analysis shows that the effectiveness of stabilization is slightly reduced when the cost of stabilization is taken into account at levels of $0.05 and $0.1 per revolution of the stabilizing drum.

Syngas production by CO2 reforming of methane using LnFeNi(Ru)O3 perovskites as precursors of robust catalysts

LnFeNi(Ru)O3 perovskites synthesized via a modified Pechini method have been studied as catalyst precursors in CO2 reforming of methane. The structural and redox properties along with catalytic performance were found to depend upon Ln nature and Ru content in the perovskite. Active and stable catalysts have been formed from perovskite precursors in reaction media at high temperatures due to Fe–Ni–(Ru) alloy particles segregation from the perovskite lattice and their stabilization on the oxide surface. Coking stability of these catalysts in dry reforming of real natural gas containing admixtures of higher hydrocarbons is explained by combined effects of Ni dilution by Ru in alloy nanoparticles and high mobility and reactivity of surface/lattice oxygen in the disordered Ln ferrite support.

Influence of coke quality on blast-furnace performance

The relation between the thermal stability of coke and blast-furnace performance is discussed.

Stabilization of coke properties

Rational organization of coke stabilization is considered, for various examples. On the basis of the existing relations between the coke and blast-furnace shops, a method is proposed for determining the number of turns in the Micum drum required to obtain the maximum and most economical stabilization.

Rational coke preparation for blast furnaces

The relation between the CSR and CRI values of coke and its familiar characteristics is analyzed. The strength and reactivity of coke differ over the blast-furnace height. The economic importance of each of these properties may only be established for specified blast-furnace conditions and technology. The systems for coke stabilization must be selected on the basis of the specific properties of the coke. There can never be a general solution. The optimal stability must be determined for each coke-furnace combination. Literature sources that address the following issues are identified: the equipment for improving coke properties; the necessary processes and their regulation; and the method for determining optimal blast-furnace conditions on the basis of the characteristics of the specific coke-furnace system.

Transformation of CH 4 and liquid fuels into syngas on monolithic catalysts

Active components comprised of fluorite-like Ln x (Ce 0.5Zr 0.5) 1− x O 2− y (Ln = La, Pr, Sm) and perovskite-like La 0.8Pr 0.2Mn 0.2Cr 0.8O 3 mixed oxides and their composites with yttria-doped zirconia (YSZ) promoted by precious metals (Pt, Ru) and/or Ni were supported on several types of heat-conducting substrates (compressed Ni–Al foam, Fecralloy foil or gauze protected by corundum layer, Cr–Al–O microchannel cermets, titanium platelets protected by oxidic layer) as well as on honeycomb corundum monolithic substrate. These structured catalysts were tested in pilot-scale reactors in the reactions of steam reforming of methane, selective oxidation of decane and gasoline and steam/autothermal reforming of biofuels (ethanol, acetone, anisole, sunflower oil). Applied procedures of supporting nanocomposite active components on monolithic/structured substrates did not deteriorate their coking stability in real feeds with a small excess of oxidants, which was reflected in good middle-term (up to 200 h) performance stability promising for further up-scaling and long-term tests. Equilibrium yield of syngas at short contact times was achieved by partial oxidation of decane and gasoline without addition of steam usually required to prevent coking. For the first time possibility of successive transformation of biofuels (ethanol, acetone, anisole, sunflower oil) into syngas at short contact times on monolithic catalysts was demonstrated. This was provided by a proper combination of active component, thermal conducting monolithic substrates and unique evaporation/mixing unit used in this research.

Fissure formation in coke. 3: Coke size distribution and statistical analysis

A model of coke stabilization, based on a fundamental model of fissuring during carbonisation is used to demonstrate the applicability of the fissuring model to actual coke size distributions. The results indicate that the degree of stabilization is important in determining the size distribution. A modified form of the Weibull distribution is shown to provide a better representation of the whole coke size distribution compared to the Rosin–Rammler distribution, which is generally only fitted to the lump coke. A statistical analysis of a large number of experiments in a pilot scale coke oven shows reasonably good prediction of the coke mean size, based on parameters related to blend rank, amount of low rank coal, fluidity and ash. However, the prediction of measures of the spread of the size distribution is more problematic. The fissuring model, the size distribution representation and the statistical analysis together provide a comprehensive capability for understanding and predicting the mean size and distribution of coke lumps produced during carbonisation.

The Sydney coalfield of Nova Scotia, Canada

In size, production and remaining resources, the Sydney coalfield is the largest field in eastern Canada. It is nearly entirely submarine and extends from northeastern Cape Breton Island to almost as far as Newfoundland, occupying an area estimated at 36,300 km 2. During 205 years of mining, some 410 million t have been produced and the total remaining “demonstrated” resources, present in ten seams, have been calculated at 1,800 million short tons, T (1 short ton=0.907 t). Of this in situ tonnage about 300 million may be suitable for metallurgical purposes and 1,500 million T can be classed as thermal coal. Some 82% of the total estimate is contributed by four seams, of which the Harbour seam is the main producer. The present annual production is between 3 and 4 million T and all mining is done in the submarine area. The main problems with submarine mining are ventilation and haulage time. The latter increases with the distance from the shore and results in reduced production. A west to east cross-section through five seams illustrates the development of coal and shows the phenomenon of depositional splitting and rejoining, caused by the interaction of fluvial sedimentation and peat accumulation. Fossil rivers forming “wants” or “wash-outs” in the coal seams are the principle geological obstructions to mining. Structural difficulties are minor as the field is only gently folded and no main faults are present. All coal of the Sydney field is classed as high volatile A bituminous, but there are significant changes within and beyond this category. These are related to the observation that the coalification is essentially post-deformational. This has resulted in an increase in rank with depth, as well as regionally from west to east within the same seam. Coke stability data indicate that these rank changes are economically favourable, because the coking characteristics of the coal improve with depth and towards the east. Petrographically, a normal, banded bright coal is represented, consisting of alternating bands of vitrite, clarite, clarodurite, durite and fusite. Durite bands occur sporadically, rarely exceeding 3 cm, and are present as “inertinite-rich” durite and “exinite-rich” durite. The latter consists of a groundmass of matted exinite and some of these bands could be traced over a lateral distance of some 50 km within the Harbour seam section. Microlithotype analyses show that, within each seam section, four coal facies types can be recognized, namely: the forest-terrestrial-moor (Ftm), the forest-moor (FM), the reed-moor (RM) and the open-moor (OM) facies. All coal seams of the Sydney field have low ash yields, which range from 5% to 9%. However, the sulphur content is generally high and varies between seams from 2.5% to 6.2%. The average volatile matter content is 36% and calorific value averages 7,524 kcal/kg (13,545 Btu/lb).