Mineralogical characterization and washability of Indian coal from Jamadoba

Coal characterization becomes a prelude for designing of washing circuits and also utilization of washed products. In the present paper, an attempt has been made to characterize coal obtained from an operating washery (Jamadoba, Jharia) as a case study. Two approaches, viz., physical and chemical characterization approaches, have been attempted after crushing the coal to finer size (?3.0 mm) for improved liberation. In the first approach, physical characterization of feed coal was done by density fractionation (float and sink test) using mixtures of organic liquids, besides determination of Hardgrove Grindability Index to estimate the friability nature of the coal. In the second approach, mineralogical characterization of coal has been done by modern analytical methods such as X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier-Transform Infrared Spectroscopy (FTIR), thermogravimetric, and differential thermal analyses.

The results of the float–sink test indicated coal to possess difficult washing characteristics having its near-gravity material content of 31.5 at 1.52 g/cc washing density and is of ‘formidable type’ as per Bird's Scale of Classification. The results of Hardgrove Grindability Index (HGI) indicated that the coal to be medium hard. Further, the difficulty washing has been established by estimating the values of Washability Number and Washability Index. The results of mineralogical analysis on the inorganic mineral matter composition indicated that the coal to contain quartz as the major gangue mineral and kaolinite, illite, montmorillonite, rutile, calcite, siderite, and pyrite as minor gangue components. The present paper enumerates that for development of a beneficiation strategy, physical characterization studies (such as Washability Index and Washability Number), etc., are important. However, mineralogical and chemical characterizations place a vital role from the end utilization point of view.     

High temperature electrolysis using Molten Carbonate Electrolyzer

Molten Carbonate Fuel Cells (MCFC) are a well-developed and commercial technology that can operate also as an electrolyzer producing hydrogen from steam. In this study, a system for the production of hydrogen based on Molten Carbonate Electrolyzer (MCE) is presented. The system receives, as an external input, water and recovers internally the additional gas streams required as input to the electrolyzer. The system products are, separately, pure oxygen and hydrogen. A calculation sheet was implemented to analyze the energy equilibrium and gas mix compositions. The system can produce 0.074 Nl h^?1 cm^?2 of hydrogen with an inlet power density of 0.213 W cm^?2 for an energy consumption of 3.40 kWh Nm_H2^?3. Sensitivity studies on current density, utilization factors of both steam and CO₂ were analyzed considering energy equilibrium of the stack unit and the post processing processes. Results show how current density has higher impact on system equilibrium compared to the other parameters.     

Tungsten carbide cathodes for electrolysis of sulphuric acid solutions

Cathodes for the electrolysis of sulphuric acid solutions were prepared from a catalyst (WC), binding agent (PTFE), and pore-forming additive (Na₂SO₄). It is shown that the best characteristics are obtained with thin electrodes (d = 0.25?0.3 mm). Current densities up to 200 mA cm^?2 at ?200 mV vs HE reference in the same solutions are attained. After 4000 h operation at 200 mA cm^?2 the electrodes gave no evidence of increased polarization.     

Modelling the internal structure of nascent soot particles

In this paper we present studies of clusters assembled from polycyclic aromatic hydrocarbon (PAH) molecules similar in size to small soot particles. The clusters studied were comprised of coronene (C₂₄H₁₂) or pyrene (C₁₆H₁₀) molecules and represent the types of soot precursor molecule typically found in flame environments. A stochastic ‘basin-hopping’ global optimisation scheme was used to locate low-lying local minima on the potential energy surface of the molecular clusters. TEM-style projections of the resulting geometries show similarities with those observed experimentally in TEM images of soot particles. The mass densities of these clusters have also been calculated and are lower than bulk values of the pure crystalline PAH structures. They are also significantly lower than the standard value of 1.8 g/cm³ used in our soot models. Consequently we have varied the mass density between 1.0 g/cm³ and 1.8 g/cm³ to examine the effects of varying soot density on our soot model and observed how the shape of the particle size distribution changes. Based on similarities between nascent soot particles and PAH clusters a more accurate soot density is likely to be significantly lower than 1.8 g/cm³. As such, for modelling purposes, we recommend that the density of nascent soot should be taken to be the value obtained for our coronene cluster of 1.12 g/cm³.     

Hydrogen PEMFC stack performance analysis through experimental study of operating parameters by using response surface methodology (RSM)

Although many studies have been done on finding operating conditions of hydrogen-fed fuel cells before, it remains one of the most critical points in determining its parameters in the process. So this paper aims to investigate experimentally the reactant gases flow rate and cell voltage which have a significant impact on the current density of a 3-cell Proton Exchange Membrane fuel cell stack having a 150 cm² active layer. In this case, to determine the optimum values, Design of Experiment and Response Surface Methodology was applied to the experimental system at low 1.5 V, medium 1.8 V, and high 2.1 V. Then, they were compared with each other. In this context, keeping the hydrogen flow rate low and obtaining high current density is one of the main targets; at low voltage values, it was concluded that the flow rate should be increased due to the reaction rate increases with temperature. In general, the effect of humidification and cell temperature on performance was seen more prominently at 1.8 V. The highest current density values that were 313.66 mA/cm², 336.75 mA/cm², and 323.48 mA/cm², respectively, were reached at flow rates of 1 L/min,1.3 L/min,1.6 L/min.     

Polymeric ionic liquids and MXene synergistically improve proton conductivity and mechanical properties of polybenzimidazole-based high-temperature proton exchange membranes

A series of Polymeric ionic liquids (PILs) cross-linked amino polybenzimidazoles with MXene fillers were successfully prepared. By anion replacement of PILs, the OH^? of the system can interact with phosphoric acid (PA) to form H₂PO₄^? and HPO₄^2? to transfer protons, and the hydroxide existing on the surface of MXene is also conducive to the transfer of protons. Therefore, the synergistic effect of the two enables the membrane to have high proton conductivity with low PA absorption. Through the covalent cross-linking between PILs and PBI and the interaction between the oxygen-containing groups on the surface of MXene and the = N and –NH of imidazole, so the mechanical performance can be greatly improved. The proton conductivity of AmPBI-PIL-5-MXene-3 can reach 91.4 mS cm^?1 at 180 °C, which is twice that of pristine AmPBI. Moreover, the tensile stress after PA doping can reach 11.1 MPa, which is twice that of pristine AmPBI. Meanwhile, the power density of AmPBI-PIL-5-MXene-3 can reach 219 mW cm^?2 at 350 mA cm^?2, which is 1.8 times that of pristine AmPBI. In addition, there is no voltage loss after 100 h test at 160 °C and 200 mA cm^?2, which indicates the excellent stability of the membrane.     

FT-IR and micro-Raman spectroscopic characterization of minerals in high-calcium coal ashes

Two high-calcium coal ashes were prepared in a muffle furnace at 815 °C. The mineral matter in both coal ashes was characterized by Fourier transform infrared (FT-IR) spectroscopy, micro-Raman spectroscopy, and X-ray diffraction (XRD). The overlapping bands of original FT-IR spectra were resolved into individual ones by using second derivative method. The presence of two most intense absorption bands (1154 and 1120 cm^?1) in the original spectra indicate that both coal ashes contain high levels of anhydrite, consistent with the XRD result. The presence of amorphous silica and metakaolinite was found from the second derivative spectra. Calcite and anhydrite in both ashes show marked Raman bands at 1086 and 1017 cm^?1, respectively. In addition, the Raman intensity of anatase in both ashes is very strong, due to the high polarizability of TiOTi. FT-IR and micro-Raman spectroscopy are complementary for the identification of anhydrite in coal ashes. Moreover, a combination of both spectroscopic techniques can provide more information on mineral composition and structure as compared to XRD, since XRD fails to identify the presence of amorphous silica, metakaolinite, and anatase.     

The composite electrolyte with an insulation Sm2O3 and semiconductor NiO for advanced fuel cells

Novel Sm₂O₃?NiO composite was prepared as the functional electrolyte for the first time. The total electrical conductivity of Sm₂O₃?NiO is 0.38 S cm^?1 in H₂/air condition at 550 °C. High performance, e.g. 718 mW cm^?2, was achieved using Sm₂O₃?NiO composite as an electrolyte of solid oxide fuel cells operated at 550 °C. The electrical properties and electrochemical performance are strongly depended on Sm₂O₃ and NiO constituent phase of the compositions. Notably, surprisingly high ionic conductivity and fuel cell performance are achieved using the composite system constituting with insulating Sm₂O₃ and intrinsic p-type conductive NiO with a low conductivity of 4 × 10^?3 S cm^?1. The interfacial ionic conduction between two phases is a dominating factor giving rise to significantly enhanced proton conduction. Fuel cell performance and further ionic conduction mechanisms are under investigation.     

Construction of proton channels and reinforcement of physicochemical properties of oPBI/FeSPP/GF high temperature PEM via building hydrogen bonding network

Composite high temperature proton exchange membranes (HT-PEMs) comprising poly[4,4′-(diphenyl ether)-5,5′-bibenzimidazole] (oPBI), ferric sulfophenyl phosphate (FeSPP) and glass fiber (GF) were prepared by the hot-pressing method. Doping FeSPP as a novel insoluble proton conductor not only provided good proton conductivity at high temperature but also enhanced their methanol blocking property, dimensional stability and oxidative resistance. Good dispersion, construction of proton channels and reinforcement of the physicochemical properties were achieved by building hydrogen bonding network among oPBI, FeSPP and GF. After incorporation of 3wt% GF into the oPBI/FeSPP(30wt%) composite membrane, the tensile strength was enhanced by 370% while the swelling ratio reduced to around 55%. The oxidative stability and methanol resistance were also enhanced while the proton conductivity was slightly affected. The membranes were thermally stable in the working temperature range for HT-PEM fuel cells. The proton conductivity of oPBI/FeSPP(30wt%) and oPBI/FeSPP(30wt%)/GF(3wt%) membranes reached 0.089 and 0.074 S cm^?1 at 180 °C and 100% relative humidity, respectively. At 180 °C, the proton conductivity of oPBI/FeSPP(30wt%) and oPBI/FeSPP(30wt%)/GF(3wt%) was 0.052 and 0.042 S cm^?1 at 50% RH, respectively. oPBI/FeSPP(30wt%)/GF(3wt%) exhibited good selectivity of 3.84 × 10⁵ S s cm^?3 indicating good potential for applications in direct methanol fuel cells.     

Efficient and stable heterostructured air electrode for solid oxide steam electrolysis

High performance and excellent durability are essential for the practical application of solid oxide electrolysis cell (SOEC). Here we have demonstrated efficient and durable solid oxide steam electrolysis by constructing active La_0.8Sr_0.2CoO_3-δ/Gd_0.2Ce_0.8O_2-δ (LSC/GDC) heterointerface in air electrode using a simple co-impregnation method. The heterostructured air electrode exhibits the outstanding activity for oxygen evolution reaction, and its exchange current density (557 mA cm^?2) is 69 times higher than that of the traditional LSM-YSZ. The resulting cell reaches ?1.86 A cm^?2 @1.3 V and ?2.30 A cm^?2 @1.5 V at 800 °C and 50% absolute humidity (A.H), and the polarization resistance from the oxygen electrode only is 0.02 Ω cm². Most importantly, the heterostructured cell presents excellent long-term stability for the 1035 h steam electrolysis operation and excellent durability for 100 times charge-discharge cycles. In the heterostructured air electrode, the problem of electrode delamination is avoided due to the reduced oxygen partial pressure at anode/electrolyte resulting from easy diffusion of O^2? at the interphase, and the coarsening of LSC and GDC nanoparticles is limited because of the LSC/GDC percolative interfaces from phase segregation process. This work proposes a simple and effective strategy to design heterointerface for efficient and durable solid oxide steam electrolysis.     

Preparation of clean coal by flotation following ultra fine liberation

This paper reports the results of current fundamental research at the Department of Process Engineering, University of Miskolc on the processing of clean coal from Mecsek bituminous coal, Southern Hungary. The theoretical possibility of the separation of different petrographic components was proven experimentally and their liberation degree was determined based on the petrographic composition, flotation kinetic study of isolated components (groups of components), scanning electron microscopy and microprobe analyses. The mill with stirred ball media was chosen for the ultra-fine liberation of the coal components. It was revealed that along with the liberation of coal components, their surface oxidation and spontaneous agglomeration, entrapping the mineral impurities take place in ultra-fine grinding. This paper discusses the interfacial phenomena occurring in the ultra-fine grinding process and their influence on the flotation. The concept for the advanced preparation of clean coal was developed, tested and proved. The main steps of this concept are the ultra-fine liberation in the stirred-media mill, the de-agglomeration of flocs spontaneously formed during the ultra-fine grinding and the induced (hydrophobic) flocculation with the following two-step flotation in a flotation column.     

Hydrogen production by immobilized cells—I. light dependent dissimilation of organic substances by Rhodopseudomonas palustris

Photoproduction of H₂ from some organic acids by agar entrapped cells of Rhodopseudomonas palustris has been investigated. With an agar layer 3.5 mm thick, the rate of H₂ evolution from dl-malate is limited by the diffusion of the substrate into the agar when the concentration of bacterial cells is as high as 1.7 mg cells dry weight cm^?3 (ca. 0.59 mg cells d.w.cm^?2) while no limitation occurs with 0.425 mg cells d.w.cm^?3 (ca. 0.15 mg d.w.cm^?2). At the latter concentration of bacterial cells in the agar layer, the rate of H₂ evolution is light saturated at an energy flux of 2.7 × 10³ erg cm^?2 s^?1. Immobilized cells retain their H₂-producing activity much longer than the free cells kept in identical conditions. The conversion efficiency (H₂-formed divided by the the H₂-content of the substrate decomposed × 100) varied between 67% (succinate) and 40% (acetate).     

Mass production of Nickel@Carbon nanoparticles attached on single-walled carbon nanotube networks as highly efficient water splitting electrocatalyst

Herein, we develop a direct current arc discharge method which enables large-scale synthesis of nickel@carbon attached single-walled carbon nanotube networks as an electrocatalyst for highly efficient water splitting. Mass amount of Ni@C/SCN (～80 g) could be easily obtained. After optimization, the catalyst exhibits a superior performance of electrochemical water splitting, which allows a current density of 10 mA cm^?2, with an overpotential of only 260 mV for OER and 198 mV for HER. The electrolyzer can achieve a current density of 10 mA cm^?2 at 1.8 V.     

Fe/Ni bimetallic organic framework with varying anions as robust electrocatalyst for oxygen evolution reaction

The performance of the metal?organic frameworks (MOFs) will be affected when the anions added were different. Herein, bimetallic FeNi-MOF was synthesized by hydrothermal method with nickel foam as substrate, the effects of four anions (Cl^?, NO₃^?, CH₃COO^?, SO₄^2?) on the materials performance of MOF were investigated. The MOF prepared when added chloride ion with the overpotential at 100 mA?cm^?2 as 247 mV. Meanwhile, the stability test at 100 mA cm^?2 for 12 h had no obvious change which exhibited high electrochemical stability. The analysis demonstrated that the superior performance of the MOF prepared when added chloride ion was attributed to the low charge transfer resistance, increased active area, exposure more active sites. This work would shed some lights for facile synthesis of ultrahigh performance OER catalyst by adjusting the anion of the precursor.     

Gravity separation of oil shale and low-temperature pyrolysis characteristics of different density fractions

In this paper, gravity separation of Huadian? (HD) and Longkou? (LK) oil shales and low-temperature pyrolysis characteristics of their different density fractions have been studied. The gravity separation results showed that kerogen could be enriched using the gravity separation method. The low-temperature pyrolysis results showed that the highest oil contents of HD and LK were in the density fractions of 1.4–1.5 and 1.5–1.6 g·cm^?3, respectively. Meanwhile, for the low-temperature pyrolysis, the oil/gas ratio decreased with the density increase, indicating higher gas loss and lower oil yield with the increase of density. The mineralogical analysis showed that most of the organic matter were associated with clay minerals, and the organic matter could not fully liberate from the matrix under coarse particles. The migration and occurrence of minerals and organic matter in different density fractions generated various pyrolysis characteristics.     

Thermal decomposition of ethylene

Laser-schlieren profiles of incident shock waves in 2.5, 5, and 10% C₂H₄ in Ar were recorded for the ranges of shock front conditions 2000 < T₂ < 2540°K, 1.8 × 10^?6 < ? < 5.4 × 10^?6mol/cm³. Data analysis was accomplished by computer modeling using a 14-reaction mechanism. Most, but not all, previous observations could be accounted for with the final rate constant set. For C₂H₄ + M → C₂H₂ + H₂ + M the expression log(k₁/cm³ mol^?1 s^?1) = 17.47 – 340 kJ/RT, for C₂H₄ + M → C₂H₃ + H + M the expression log (k₂/cm³ mol^?1 s^?1) = 17.49 – 400 kJ/RT, and for C₂H₃ + H → C₂H₂ + H₂ the rate constant k₆ = 10¹³cm³ mol^?1 s^?1 were obtained.     

High-temperature solar pyrolysis of coal

Subbituminous coal from Western United States was pyrolyzed by directly exposing 50 mg powdered samples to concentrated solar radiation. It was found that exposure to flux levels > 200 W/cm² for 12.5 s devolatilized 51 per cent of the coal. At flux levels between 100 and 200 W/cm² devolatilization was slightly less. Gas yield was a maximum of 31 mmol/g coal at a flux of 100 W/cm² and decreased slightly with increasing flux. Gas yields were more than twice as great as those obtained by a laser technique developed to simulate solar pyrolysis. In experiments with spectral cut-off filters there was no effect due to changing the wavelength distribution of sunlight.     

Methane conversion to syngas and hydrogen in a dual phase Ce0.8Sm0.2O2-δ-Sr2Fe1.5Mo0.5O5+δ membrane reactor with improved stability

Coupling of partial oxidation of methane (POM) with water dissociation in an oxygen transport membrane is a promising technology for methane utilization. However, cobalt-based membrane materials show poor stability under the above harsh conditions. In this work, a nominal 60 wt % Ce_0.8Sm_0.2O_2-δ-40 wt % Sr₂Fe_1.5Mo_0.5O_5+δ (CSO-SFMO) dual phase membrane is reported, which was synthesized by using a one-pot EDTA-citric acid complexing method. The phase structure and morphology of the CSO-SFMO membrane were characterized by XRD, SEM and EDXS. It was found that a uniform distribution of CSO phase with a fluorite structure and SFMO phase with a perovskite structure was achieved in the dual phase membrane. The CSO-SFMO membrane exhibited an improved stability compared with cobalt based perovskite Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ, (BSCF) membrane under CO₂ or reductive gas atmospheres. The oxygen permeation flux of the dual phase membrane was investigated under different oxygen partial pressure gradients: air/He, air/CO₂, air/POM, and H₂O/POM. At 950 °C, the oxygen permeation fluxes of the CSO-SFMO membrane under air/POM and H₂O/POM gradients were 2.7 cm³ (STP) min^?1 cm^?2 and 0.75 cm³ (STP) min^?1 cm^?2, respectively, which were much higher than the oxygen flux of 0.1 cm³ (STP) min^?1 cm^?2 under air/He. Moreover, a CO selectivity of 98%, a CH₄ conversion of 97% on the POM side and a H₂ production of 1.5 cm³ (STP) min^?1 cm^?2 on the H₂O splitting side were achieved in CSO-SFMO membrane reactor under the oxygen partial pressure gradient of H₂O/POM, which was steadily run for 100 h before the measurement was intentionally stopped.     

Proton conductivity and performance in fuel cells of grafted membranes based on polymethylpentene with radiation-grafted crosslinked sulfonated polystyrene

In this work, a comparative study was carried out of the transport properties and performance in a hydrogen-air fuel cell of the membranes based on polymethylpentene (PMP) with grafted sulfonated polystyrene and the standard Nafion® 212 membrane. Grafted cation-exchange membranes (GCM) were obtained by radiation graft post-polymerization of styrene onto UV-exposed PMP film followed by sulfonation with chlorosulfonic acid. The proton-conductivity of the GCM membrane with an ion-exchange capacity of 2.9 ± 0.1 meq/g reaches 21 ± 1 mS cm^?1 at room temperature and 95% relative humidity, which is twice higher the conductivity of the Nafion® under the same conditions. The GCM-1 H₂-permeability of 2.06?10^?7 cm² s^?1 even slightly lower than that of the Nafion® 212 (2.14?10^?7 cm² s^?1). A comparison of these membranes in the membrane electrode assemblies (MEA) of hydrogen-air fuel cells (FC) shows that the use of the grafted membranes with the high ion-exchange capacity is highly promising. The maximum performance of FC with grafted and Nafion® 212 membrane are both close to 180 mW/cm² at the current density of 400 mA/cm². At the same time, the high degree of crosslinking of sulfonated polystyrene leads to a decrease in conductivity and does not give an advantage in gas permeability.     

Low temperature studies on rechargeable lithium cells

Rechargeable lithium cells using intercalating cathodes of TiS₂, a-MoS₃, and mixed a-MoS₃TiS₂ were studied at temperatures from 25 °C to ?40 °C. On the basis of conductivity investigations, LiAsF₆ and LiAlCl₄ electrolytes were selected for use in a binary solvent containing 24.4 mass % 4-butyrol actone in 1,2-dimethoxyethane. The Li/TiS₂ and Li/a-MoS₃TiS2 cells cycled well at 2 mA cm^?2 down to ?30 °C, but at 5 mA cm^?2 at these very low temperatures, cell capacities were significantly lower. At room temperatures all cells performed slightly better in 1 mol dm^?3 LiAsF₆ than in 0.8 mol dm^?3 LiAlCl₄ in 24 mass % 4-BL/DME. However, at temperatures below ?10 °C the latter electrolyte was found to be superior.