Laboratory-scale coal reactivity testing for entrained gasification

A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO₂ or H₂O. It is shown that gasification reactivity increases with decreasing coal rank. The CO₂ and H₂O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO₂ gasification reaction has an activation energy of about 100 kJ mol^?1 for lignite and 220–230 kJ mol^?1 for bituminous coals and fluid petroleum coke. The activation energies for H₂O gasification are about 100 kJ mol^?1 for lignite, 290–360 kJ mol^?1 for bituminous coals and about 200 kJ mol^?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results.     

Influence of coal preoxidation and the relation between char structure and gasification potential

A study was carried out to ascertain the effects of coal preoxidation and carbonization conditions on the structure and relative gasification potential of a series of bituminous coal chars. Chars were prepared from two freshly mined bituminous coals and preoxidized samples derived from them. Carbonization conditions included a wide range of heating rate (0.2–10000K s^?1), temperature (1073–1273 K) and time (0.25–3600 s). Char properties were characterized in terms of analysis of char morphology, surface area, elemental composition, and gasification reactivity in air. Over the range of conditions used, preoxidation substantially reduced coal fluid behaviour and influenced macroscopic char properties (char morphology). Following slow heating (0.2 K s^?1), preoxidized coals yielded chars having higher total surface areas and higher reactivities toward gasification in air than did similar chars prepared from fresh coal. Following rapid heating (10000 K s^?1) and short residence times (0.25 s), chars prepared from preoxidized and fresh coals exhibited similar microstructural and chemical properties (surface area, $\text{C}\text{H}$ ratios, gasification rates). Carbonization time and temperature were found to be the critical parameters influencing char structure and gasification potential.     

Correlation of gasification rates of various coals measured by a rapid heating method in a steam atmosphere at relatively low temperatures

Twenty-five kinds of coals (carbon content on dry ash-free basis, C[%], ranges from 65.0 to 92.8%) were pyrolysed and gasified simultaneously by use of a rapid heating method (heating rate ≈ 1600 K min⁻¹) in steam at temperatures between 750 and 850 °C to clarify the factors which control the gasification rates of various coals. The relationships were examined in detail between the reactivity of each coal, represented by the initial gasification rate − r_cm0, and various properties such as pore surface area of char, ultimate and proximate analyses of coal, reflectance of coal, contents of metals in char, and the amount of oxygen trapped by char. For gasification at 800 °C, the relation between − r_cm0 and the carbon content C[%] changed abruptly at C ≈ 75–80%. For higher rank coals (C > 75–80%), − r_cm0 was rather small and was well correlated by C[%]. On the other hand, the plot of − r_cm0versus C % scattered largely for the lower rank coals (C < 75–80%). For these coals, the rate of CO₂ formation was much greater than that of CO formation, and was almost proportional to − r_cm0. The CO₂ formation reaction is known to be catalysed by alkali or alkaline earth metals such as Na, K and Ca. Then the reactivities of lower rank coals were supposed to be controlled mainly by the catalytic effect of the minerals in the coal.     

Synthesis of 9H-carbazole-9-carbothioic methacrylic thioanhydride,electropolymerization, characterization and supercapacitor applications

A novel organic molecule of 9H-carbazole-9-carbothioic methacrylic thioanhydride (CzCS₂metac) was synthesized by incorporating CS₂ and methacrylate groups into the carbazole monomer structure. CzCS₂metac was characterized by FTIR, ¹H-NMR and ¹³C-NMR spectroscopy. CzCS₂metac was electropolymerized in 0.1 M tetraethylammonium tetrafluoroborate (TEABF₄)/acetonitrile (CH₃CN) on glassy carbon electrode (GCE). The characterization of the electrocoated P(CzCS₂metac)/CFME thin film was studied by various techniques, such as cyclic voltammetry, scanning electron microscopy–energy-dispersive X-ray analysis and electrochemical impedance spectroscopy. The specific capacitance (C _sp) of P(CzCS₂metac)/MWCNT/GCE in the scan rate of 20 mV s^?1 (C _sp = 38.48 F g^?1 from area formula, C _sp = 38.52 F g^?1 from charge formula) was increased ~15.66 and ~15.64 times in area and charge formulas compared to P(CzCS₂metac)/GCE (C _sp = 2.46 F g^?1 from area and charge formulas). The same results were also obtained from Nyquist graphs. The specific capacitance value of composite film (C _sp = 1.09 × 10^?3 F) is ~15.66 times higher than the polymer film (C _sp = 6.92 × 10^?5 F). The composite film may be used as supercapacitor electrode material in energy storage devices.     

Iron impregnation on the amorphous shell of vapor grown carbon fibers and the catalytic growth of secondary nanofibers

Vapor grown carbon fibers (VGCFs) with diameters of several microns were synthesized and investigated by high resolution transmission electron microscopy. It was found that the shell of the VGCFs consisted of densely-packed domains embedded in loosely-packed matrix, and both were highly amorphous. Regular edge planes as observed on the surface of fishbone nanofibers do not exist on VGCFs. Hence, surface treatment is more important for the deposition of catalysts. Ammonium ferric citrate (AFC) was employed for the impregnation of iron, where the high viscosity of the aqueous solution of AFC is beneficial. Calcination was found to be a key step to improve the dispersion of the iron particles, which can be attributed to enhanced interactions between iron and carbon due to the gasification of carbon occurring at the iron–carbon interface. Quantitative analysis by X-ray photoelectron spectroscopy showed that the calcination of the supported AFC led to a higher atomic concentration of iron on the surface, indicating smaller particle size and a higher dispersion. Secondary carbon nanofibers were grown subsequently on the VGCFs from cyclohexane. The specific surface area was enhanced considerably, from less than 1 m² g^? 1 to 106 m² g^? 1 after the growth of the secondary nanofibers. The obtained composites are promising materials as structured support in heterogeneous catalysis.     

Gasification reaction kinetics on biomass char obtained as a by-product of gasification in an entrained-flow gasifier with steam and oxygen at 900-1000 °C

The purpose of this study was to investigate the gasification kinetics of biomass char, such as the wood portion of Japanese cedar char (JC), Japanese cedar bark char (JB), a mixture of hardwood char (MH) and Japanese lawngrass char (JL), each of which was obtained as a by-product of gasification in an entrained-flow type gasifier with steam and oxygen at 900-1000 °C. Biomass char was gasified in a drop tube furnace (DTF), in which gasification conditions such as temperature (T_g), gasifying agent (CO₂ or H₂O), and its partial pressure (P_g) were controlled over a wide range, with accompanying measurement of gasification properties such as gasification reaction ratio (X), gasification reaction rate (R_g), change of particle size and change of surface area. Surfaces were also observed with a scanning electric microscope (SEM). By analyzing various relationships, we concluded that the random pore model was the most suitable for the biomass char gasification reaction because of surface porosity, constant particle size and specific surface area profile, as well as the coincidence of R_g, as experimentally obtained from Arrhenius expression, and the value is calculated using the random pore model. The order of R_g was from 10⁻² to 10⁻¹ s⁻¹, when T_g = 1000 °C and P_g = 0.05 MPa, and was proportional to the power of P_g in the range of 0.2-0.22 regardless of gasifying agent. Reactivity order was MH > JC > (JB, JL) and was roughly dependent on the concentration of alkali metals in biomass feedstock ash and the O/C (the molar ratio of oxygen to carbon) in biomass char.     

Novel dye-substituted polyanilines: conducting and antimicrobial properties

Conducting and antimicrobial properties of chemically synthesized dye-substituted polyanilines were found to be affected by varying the dye moieties. The dye-polyanilines were characterized by various analytical techniques including UV–visible spectroscopy, IR spectroscopy, fluorescence spectroscopy, AC impedance and thermo-gravimetric analysis and X-ray diffraction. The temperature dependence of DC conductivity was studied by two-probe method to learn about the conduction behavior in the synthesized compounds. The conductivity of the dye-substituted polyanilines was found to be in the range of 10^?3–10^?2 Scm^?1. For the study of antimicrobial behavior of the synthesized polyanilines, different microorganisms, including the bacteria Escherichia coli (MTCC 442), Pseudomonas aeurginosa (MTCC 441), Staphylococus aureus (MTCC 96), and S. pyogenus (MTCC 443) and fungal strains Candida albicans (MTCC 227), Aspergillus niger (MTCC 282) and A. clavatus (MTCC 1323), were chosen based on their clinical and pharmacological importance.     

Importance of carbon active sites in the gasification of coal chars

A demineralized lignite has been used in a fundamental study of the role of carbon active sites in coal char gasification. The chars were prepared in N₂ under a wide variety of conditions of heating rate (10 K min^?1 to 10⁴ K s^?1), temperature (975–1475 K) and residence time (0.3 s–1 h). Both pyrolysis residence time and temperature have a significant effect on the reactivity of chars in 0.1 MPa air, determined by isothermal thermogravimetric analysis. The chars were characterized in terms of their elemental composition, micropore volume, total and active surface area, and carbon crystallite size. Total surface area, calculated from C0₂ adsorption isotherms at 298 K, was found not to be a relevant reactivity normalization parameter. Oxygen chemisorption capacity at 375 K and 0.1 MPa air was found to be a valid index of char reactivity and, therefore, gives an indication, at least from a relative standpoint, of the concentration of carbon active sites in a char. The commonly observed deactivation of coal chars with increasing severity of pyrolysis conditions was correlated with their active surface areas. The importance of the concept of active sites in gasification reactions is illustrated for carbons of increasing purity and crystallinity including a Saran char, a graphitized carbon black and a spectroscopically pure natural graphite.     

Char morphology and behaviour of Australian vitrinites of various ranks pyrolysed at various heating rates

This study concerns the relative importance of rank and heating rate on the development of plasticity during pyrolysis of several Australian vitrinites. Dispersed vitrinite particles, 100 μm in diameter, were heated to 1000 °C in nitrogen at linear heating rates ranging from 10^?1 to 10⁴ °Cs^?1 in a special electrical strip furnace. When pyrolysed at 10⁴ °C s^?1 all vitrinites became plastic and vesiculated except for vitrinite from anthracite, and gelinite from brown coal. The greatest plasticity developed in bituminous-rank vitrinite. Brown coal textinite and the lower-rank sample of the two subbituminous-rank vitrinites behaved similarly, whereas the behaviour of the higher-rank subbituminous coal resembled that of the semi-anthracite sample. At heating rates of 10^?1 °C s^?1 all the vitrinites retained their original morphologies. Cenospheres began to form in the vitrinites within the heating rate range of 1 °C s^?1 (for bituminous rank) to 10² °C s^?1 (for brown coal and semi-anthracite ranks). During pyrolysis, the differences in plastic behaviour attributable to rank could largely be eliminated by changing the heating rate by two orders of magnitude. The effects attributable to plasticity related to increasing heating rates reach a limit within five orders of magnitude of heating rate (for the conditions used in this study).     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript>-OSO<Subscript>3</Subscript>H: an efficient hierarchical nanocatalyst for the organic quinazolines syntheses

A sulfonic acid functionalized titanium dioxide quasi-superparamagnetic nanocatalyst Fe₃O₄@SiO₂@TiO₂-OSO₃H with average size of 61 nm and semispherical shape with surface area about 97 m² g^?1 with saturation magnetization 17.7 emu g^?1 and the coercivity 9.84 Oe was successfully synthesized. The structure and morphology of the nanocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy, X-ray diffraction pattern, transmission electron microscopy, field-emission scanning electron microscopy, vibrating sample magnetometer and Brunauer–Emmett–Teller surface area analysis. The catalytic usage of the nanocatalyst was exemplified in synthesis of 2,3-dihydroquinazolin-4(1H)-one and spiroquinazolin-4(3H)-one derivatives in deep eutectic solvents (DESs) based on choline chloride and urea. We suggest that the synergistic effects in catalytic activities of titanium dioxide, organic acid and the CO₂ capture property of DES are the main reasons for the improvement of catalytic activity. The synthesized spiroquinazolinones and dihydroquinazolinones derivatives were characterized by FT-IR, ¹H and ¹³C nuclear magnetic resonance spectroscopy. The magnetic nanocatalyst exhibit high catalytic activity and can be simply separated from reaction media by an external magnet in a few seconds and could be reused for six cycles without significant loos in activity, which indicates the good immobilization of sulfonic acid on the magnetic titanium dioxide support. Furthermore, the solvent which has been used in this work can be readily isolated and reused for several times.     

The reaction of hydroxyl radicals with carbon at 298 K

The reaction of free OH radicals with graphite was studied in a flow system by mass spectrometry, the OH being produced by the reaction H + NO₂ → OH + NO. The OH radicals react rapidly at 298 K to produce approximately equal amounts of CO and CO₂. The collision efficiency (γ) for gasification of the carbon is>5 × 10^?3. OH radicals are much more reactive than free oxygen atoms towards graphite at 298 K. Carbon is an efficient heterogeneous catalyst for the reaction H + OH → H₂O, and when free hydrogen atoms are present, this reaction is several times faster than the gasification of the carbon by OH. Carbon is also an efficient catalyst for the recombination of H atoms: 2H → H₂.     

Relationship between the colour of ochre from Roussillon and the content of iron-bearing minerals

Nine samples of ochre from Sentier des Ocres near Roussillon, France, were studied with Mössbauer spectroscopy and spectro-photo-colourimetry. Mössbauer spectroscopy was used for quantitative phase analysis of iron-containing minerals (goethite, hematite and kaolinite). Colourimetry enabled determination of the CIE-L*a*b* colour coefficients. Both a^? and b^? coordinates are responsible for the colour of the ochres. The colour coordinate a^? was positively correlated with the content of hematite, negatively with that of goethite and kaolinite. The coordinate b^? was positively correlated with the relative amount of goethite, negatively correlated with that of hematite, and weakly correlated with the amount of kaolinite. With respect to L^?, a^? showed negative correlation, and b^? showed positive correlation.     

Synthesis and electrochemistry of 5 V LiNi0.4Mn1.6O4 cathode materials synthesized by different methods

Spinel LiNi_0.4Mn_1.6O₄ has been successfully synthesized by ultrasonic-assisted co-precipitation (UACP) method. The structure and physicochemical properties of this as-prepared powder compared with the LiNi_0.4Mn_1.6O₄ synthesized by co-precipitation method were investigated by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test in detail. XRD and SEM show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; FT-IR reveals that the Mn(III)–O stretching band at 511 cm^?1 has a red shift to 503 cm^?1, and the Mn(IV)–O stretching band at 612 cm^?1 has a blue shift to 622 cm^?1 because of the doped Ni. CV confirms that the LiNi_0.4Mn_1.6O₄ sample (UACP) has bigger area of the reduction peaks than that of sample synthesized by co-precipitation method, indicating that the former has higher discharge capacity than that of the latter. Galvanostatic charge–discharge test indicates that the initial discharge capacities for the LiNi_0.4Mn_1.6O₄ (UACP) at C/5 and 1C are 129 and 116 mAh g^?1, respectively. After 100 cycles, their capacity retentions are 94.6% and 85.3%, respectively. EIS indicates that LiNi_0.4Mn_1.6O₄ samples synthesized by UACP method have smaller charge transfer resistance than that of samples synthesized by co-precipitation method corresponding to the extraction of Li⁺ ions.     

Green reduction of graphene oxide by aqueous phytoextracts

The reduction of graphene oxide (GO) by phytochemicals was investigated using aqueous leaf extracts of Colocasia esculenta and Mesua ferrea Linn. and an aqueous peel extract of orange (Citrus sinensis). The prepared GO and phytoextract reduced GO (RGO) were characterized by ultraviolet–visible spectroscopy, Raman spectroscopy and Fourier transform infrared analyses to provide a clear indication of the removal of oxygen-containing groups from the graphene and the formation of RGO. The extent of reduction was determined from elemental analysis. Formation of few layers of graphene was indicated by transmission electron microscopy. The obtained RGO exhibited good specific capacitance (17–21 Fg^?1), high electrical conductivity (3032.6–4006 Sm^?1) and high carbon to oxygen ratio (5.97–7.11).     

Characterization of CuInS2 thin films prepared by one-step electrodeposition

CuInS₂ thin films were fabricated by one-step electrochemical deposition from a single alkaline aqueous solution and using conductive glass as the substrate. The electrolyte consisted in 0.01 mol L^?1 CuCl₂, 0.01 mol L^?1 InCl₃, 0.5 mol L^?1 Na₂SO₃ and 0.2 mol L^?1 Na₃C₃H₅O(COO)₃ (CitNa) at pH 8. The films were analyzed using a variety of techniques such as X-ray diffractometry, micro-Raman spectroscopy, X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy and photoelectrochemistry. After carrying out a thermal treatment in sulfur vapor, chalcopyrite CuInS₂ thin films were obtained. Etching the films in KCN solution was found to be a key step, enabling a final adjustment in the stoichiometry. These thin films exhibited p-type semiconductor behavior with the bandgap of 1.43 eV. The results show that electrodeposition provides a cost-effective and versatile method for the preparation of thin films of CuInS₂, even when acidic precursors need to be avoided.     

Volatile trace element behaviour in the Sasol fixed-bed dry-bottom (FBDB)™ gasifier treating coals of different rank

Trace element simulation and validation of model predictions for the elements Hg, As, Se, Cd and Pb have recently been undertaken for the Sasol^® FBDB™ gasification process operating on lump coal. The validation was conducted by interpolating the residual trace elements content remaining behind in the solid coal/char/ash fractions after sequential mining of a quenched commercial-scale gasifier operating on low rank grade C bituminous Highveld coal used for gasification in South Africa. This paper extends the research understanding by comparing the volatile trace element behaviour of these same elements, using the same gasification technology, but operating on North Dakota lignite. The focus will be on the behaviour of the volatile Class III trace elements: Hg, As, Se, Cd and Pb within the Sasol^® FBDB™ gasifier as function of coal rank. This study excludes the downstream gas cleaning partitioning and speciation behaviour of these elements.Findings indicate that although the feed concentration and mode of occurrence of these elements differ quite substantially between the two coal types studied, that the volatilization profiles of the elements are indeed quite similar; being within 0.1%-15% lower in the case of the lignite when compared to the bituminous coal. In both cases, Hg was found to be the most volatile and As the least; with the volatility order varying slightly for the metals Se, Cd and Pb for the two coal types. The differences observed in the trace element volatilization rate are supported by the temperature profile which was inferred from the reflectance of vitrinite (RoV) measurements of the dissected fuel bed material. The highly reactive lignite, is successfully gasified at a lower temperature than is the case for bituminous coal using the Sasol^® FBDB™ gasification process. Speciation predictions have earlier shown that: H₂ Se, CdS, PbS/Pb/PbCl, and AsH₃ species possibly exist in the gas phase. In reality, organically-associated trace elements will also be volatilized into the gas phase, but due to a lack of thermodynamic data for the lignite organo-metallic species at this stage only inorganic associations could be modelled.     

Multi-stage activation of brown-coal chars with oxygen

Activation of xylitic brown-coal coke XBC 900 with water vapour and carbon dioxide, when modified by partial replacement of the basic activating agent with 10% oxygen at a lower temperature, results in products with an increased microporosity. Thus, oxygen as activating agent for xylitic coke develops, preferentially, micropores, and this property is more strongly pronounced for oxygen than for the carbon dioxide and water vapour. A drawback to the process of activation with oxygen, i.e. blockage of initially formed micropores by chemisorbed oxygen, can be eliminated by removal of the chemisorbed oxygen by heat treatment in argon (multi-stage oxygen activation). This increases the micropore volume of the xylitic brown-coal coke XBC 900 activated with oxygen to 70% total burnoff, from about 0.2 cm³ g^?1 to almost 0.5 cm³ g^?1. The increase of the total adsorptive volume (micropores and mesopores) of these samples is from 0.45 cm³ g^?1 to over 0.6 cm³ g^?1 and the surface area S_BET in benzene increases from 650 m² g^?1 to over 1200 m² g^?1. These last values are close to the limiting conditions for 70% activation obtainable for this material. Temperature of carbonization of the brown-coal char has a strong effect on the possibility of pore development through further activation. Multi-stage oxygen activation of xylitic brown-coal semicoke XBC 500 produces a material with a smaller micropore volume and a lower surface area than that of xylitic brown-coal coke XBC 900 similarly activated.     

Effect of operating conditions on gas components in the partial coal gasification with air/steam

With increasing environmental considerations and stricter regulations, coal gasification, especially partial coal gasification, is considered to be a more attractive technology than conventional combustion. Partial coal gasification was conducted in detail under various experimental conditions in a lab-scale fluidized bed to study the factors that affected gas components and heating value, including fluidized air flow rate, coal feed rate, and steam feed rate, gasification temperature, static bed height, coal type and catalyst type. The experiment results indicate that gasification temperature is the key factor that affects components and the heating value of gas is in direct proportion to gasification temperature. There exists a suitable range of fluidized air flow rate, coal feed rate, steam feed rate and static bed height, which show more complex effect on gas components. High rank bitumite coal is much more suitable for gasification than low rank bitumite coal. The concentrations of H₂, CO and CH₄ of bitumite coal are more than those of anthracite coal. Compounds of alkali/alkaline-earth metals, such as Ca, Na, K etc., enhance the gasification rate considerably. The catalytical effects of Na₂CO₃ and K₂CO₃ are more efficient than that of CaCO₃. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.