An XPS study of the oxidation of pyrite and pyrites in coal

X-ray Photoelectron Spectroscopy (XPS) was used to study mineral, synthetic and coal-associated pyrites, oxidized for various time intervals at low temperatures with humid air or oxygen. This was done to find out if XPS could detect, monitor and clarify pyrite surface-oxidative changes that influence surface-dependent coal-cleaning methods such as froth flotation, and could provide a means of directly analysing coal sulphur, by determining if oxidizing conditions existed which would effectively eliminate the surface pyrite whose XPS peak may occur at the same energy as the organic sulphur peak of coal. The conditions of study were as follows: a mineral and two coals containing pyrite were exposed to air at 24 ± 3 ° C and 33 ± 8% relative humidity up to 600 h; two mineral pyrites were exposed to oxygen at 100% relative humidity and 35 ° C for up to 200 h; and the two mineral and a synthetic pyrite were exposed to oxygen at 100% relative humidity and 55 ° C for up to 300 h and at 72°C for 25 h. The results indicated that the XPS S2p pyrite peak at ≈169 eV and the surface-oxidation-product(s) peak(s) at ≈163 eV could be detected and followed with XPS, although no conclusions could be made about the oxidation mechanism. The pyrite XPS peak became small compared to that of its oxidation products when the synthetic and mineral pyrites were exposed to 55 ° C oxygen at 100% relative humidity for 300 h. These conditions may prove useful in trying to determine directly the organic sulphur in coal.     

Optical properties of oxidized resinite

Resinite concentrate from a subbituminous coal (R_oil = 0.45%) was oxidized in air for 1 h intervals at fixed temperatures between 50 and 400 °C. The oxidized residues were examined using reflected white and fluorescent light microscopy. Three phases of oxidation were observed. Phase I (50–125°C) was marked by an oxidation rim with lower reflectance than the main mass of resinite, perhaps indicating chemisorption and decomposition of the chemisorbed components. Phase II (150–350°C) was apparent from the development of two oxidation rims, the outer of higher and the inner of lower reflectance than the main mass of resinite, perhaps indicating an ‘oxycoal’ phase. Phase III (〉 350°C) was marked by a sharp increase in reflectance of the outer oxidation rim and a similarity in reflectance between the inner oxidation rim and main mass of resinite, perhaps indicating a ‘combustion phase’. The fluorescence properties (colour, wavelength of maximum intensity and red-green quotient) of the oxidation rims shifted from green towards the red region of the spectrum with increasing oxidation temperature and were a good indicator of the progress of oxidation.     

Effect of air-oxidation on the pore-structure of coals and cokes or chars obtained from oxidized coals

Seven kinds of coals (C, 77.8–89.8 wt% daf) were oxidized with air at 150 °C for 1, 5 and 10 h. The oxidized coals were heat-treated at various temperatures between 300 and 1500 °C with intervals of 50 or 100°C. The pore-structure of the oxidized coals and the cokes or chars obtained from the oxidized coals was compared with those of parent coals and their cokes or chars. True densities were measured in methanol and straight-chain hexane and pore volumes were determined by the Dubinin-Polanyi procedure. For the coals, the methanol-density increased with extent of oxidation; the hexane-density increased at first, but then decreased and again increased in the course of the oxidation. The air-oxidation of coals has a marked and controlling effect on the development of the pore-structure of cokes and chars in the course of the carbonization.     

Oxidation of bituminous coal. 1. Expansion pressure

Experiments show that the oxidation of bituminous coal from the Zasyad’ko mine at 60°C in laboratory conditions increases its expansion pressure from 5.2 to 30.0 kPa in ~28.3 days. Oxidation occurs in stages, as already demonstrated for Ukrainian and imported coal of different metamorphic stages on oxidation in the laboratory and in industrial trials at other temperatures. The rate constant in the initial stage of oxidation is 0.4095 × 10^–4 min^–1 at 60°C and 3.8479 × 10^–4 min^–1 at 140°C. That indicates sharp increase in oxidation rate between 60 and 140°C. In oxidation, the actual coal density, the atomic ratio H/C, and the number of hydrocarbon rings per carbon atom decline, while the molar volume per g-atom of carbon increases. Saturation of the bituminous coal with oxygen on oxidation increases the viscosity of the plastic mass that forms and increases the volume of gas and vapor products. Ultimately, that results in increase in the expansion pressure as the coal is oxidized.     

Superacid coal chemistry: 1. HF:BF3 catalysed depolymerization—ionic hydroliquefaction of coals under mild conditions

HF:BF₃:H₂ catalysed depolymerization and hydroliquefaction of coal was studied. This superacidic system was found to be extremely effective for low temperature liquefaction of coal. Illinois No. 6 coal could be solubilized in pyridine to the extent of > 90% by treating it at ≈ 105 °C for 4 h. Under somewhat more elevated temperature (150–170 °C) cyclohexane extractabilities of up to 22% and distillability of up to 28% is achieved. A hydrogen donor solvent such as isopentane is shown to improve the efficiency of the superacidic catalyst for the conversion of coal to cyclohexane soluble products.     

Influence of Catalyst Pretreatments on Propane Oxidation Over Ru/γ-Al2O3

The influence of different treatments (in H₂ or in O₂ at 250 or 600 °C) of alumina supported Ru catalysts on the total oxidation of propane was investigated. Ruthenium catalysts were prepared using RuCl₃ as metal precursor and characterized by H₂ chemisorption, O₂ uptake, BET, XRD and TEM. The presence of chloride on the catalyst surface was found to exert an inhibiting effect on the activity of Ru. The reduced Ru/γ-Al₂O₃ catalysts after partial removing chlorine ions were more active than the same samples oxidized at 250 °C. The higher activity of the reduced Ru/γ-Al₂O₃ catalysts was attributed to the presence of a large amount of active sites on small Ru _x O _y clusters without well defined stoichiometry or on a poorly ordered layer of a ruthenium oxide on the larger Ru particles. The formation of highly dispersed, but in some extent crystallized RuO₂ phase in catalysts oxidized at 250 °C, leads to slightly lower activity of the Ru phase. Strong decline of the activity was found for catalysts oxidized at 600 °C. At this temperature, the Ru particles were completely oxidized to well-crystallized RuO₂ oxide, and the mean crystallite size of the Ru oxide phase was much higher (9–25 nm) than that of after oxidation at 250 °C (~4 nm). The effect of the regeneration treatment in H₂ on the activity of the Ru/γ-Al₂O₃ catalysts was also studied. The active ruthenium species for propane oxidation were discussed based on the catalytic and characterization data both before and after activity tests.     

Effect of pyrite and pyrrhotite on free radical formation in coal

The effects of pyrite (FeS₂) and pyrrhotite (Fe₇S₈) on free radical formation in a coal sample (81% carbon content) have been investigated by electron spin resonance (e.s.r.) spectroscopy. Changes in the e.s.r. parameters (spin concentration g^-1, n, linewidth ΔH and g-value) were monitored in samples of coal, coal+8% FeS₂ and coal+8% Fe₇S₈, as these samples were heated in vacuum or in hydrogen from room temperature to 500 °C, in steps of 50 °C for a residence time of 30 min at each temperature. In vacuum heating, changes in n begin to occur at 400 °C, 350 °C and 300 °C respectively for coal, coal+8%Fe₇S₈ and coal+8% FeS₂ samples whereas in H₂, the corresponding temperatures are 250 °C, 200 °C and 150 °C. Changes in ΔH and g were also observed at these temperatures. The maximum increase in n occured for coal+8% FeS₂ samples whereas the minimum increase was observed for the pure coal sample. It is argued that enhancement in n is due to two mechanisms: the pyrite to pyrrhotite conversion and the presence of pyrrhotite itself. The detailed nature of the catalytic activity of pyrrhotite is not known.     

Thermal Decomposition of Oxidized Long-Flame Coal

The influence of oxidation of long-flame coal pieces (at 100–250°C for 5–40 h) on the yield and composition of the pyrolytic products, the emission dynamics of volatiles, and the properties and porous structure of the semicoke is studied.     

Effectiveness of gases in desulphurization of coal

The effect of air, steam and hydrogen on the desulphurization of 10 U.S. high-volatile bituminous coals was investigated. Air treatment was most effective at 450 °C where an average of 38% total sulphur, comprising 51% of the inorganic sulphur and 20% of the organic sulphur, was removed. With steam at 600 °C, 61% of the total sulphur, 87% of inorganic and 25% of organic was lost. Hydrogen was not effective below 850 °C, but at 900 °C 86% of the total sulphur was dispelled, i.e. 94% of the inorganic and 76% of the organic sulphur. Without oxidative pretreatment the sulphur was much more difficult to remove; after oxidative pretreatment at 300 °C for 10 min followed by treatment with hydrogen at 900 °C, as much sulphur was removed in 4 min as in 60 min without the pretreatment. With raw coal, heating under nitrogen ‘cooked-in’ or fixed some of the sulphur making it more difficult to remove with hydrogen; whereas following oxidative pretreatment, heating for up to 1 h did not lessen the reduction of sulphur with hydrogen. For temperature-swelling coals with large quantities of organic sulphur, heating at 300 °C in air followed by reduction with hydrogen at 900 °C appears to permit rapid discharge (3–10 min) of the organic as well as the inorganic sulphur, to produce a smokeless product with a CV (per unit of product) similar to the fuel value of the untreated coal.     

Temperature dependence of processes during initial stages of oxidation of poly(acrylonitrile-co-acrylic acid) films

Poly(acrylonitrile-co-acrylic acid) films containing 1.8 percent acrylic acid as comonomer units in the copolymer were oxidized in air isothermally at different temperatures for periods of 1 and 5 hours. The physico-chemical properties such as thermogravimetry, differential scanning calorimetry, infrared spectral absorption and intrinsic viscosity were analysed for the oxidized films. The intrinsic viscosity shows that the molecules of the polymer crosslink at temperature as low as 100°C. TGA spectrum shows two regions of steep weight losses in the range of temperatures studied, one is at 275–300°C and the other at 395–485°C. The first region is the formation of ladder polymer with the elimination of NH₃, HCN and CO. The second region is due to the formation of aromatic structures with the elimination of HCN, NH₃, water vapour and higher hydrocarbons. DSC spectral analysis shows an endothermic effect up to 205°C and exothermic processes from 205–300°C with a peak at 276°C. The exothermic processes continue up to 360°C. The exothermic effect is reduced for the films oxidized at 242 and 275°C. A marked endothermic effect is noticed at 120°C for the films oxidized at 242 and 275°C. This shows that the cyclization accompanying with exothermic effect sufficiently advanced during isothermal treatment leaving less room for rapid cyclization occurring upon further heating. IR spectral data show the negative environment with a shoulder at 2210 cm^?1 which is associated with uptake of oxygen during oxidation. Distinct peaks at 810 and 1550–1700 cm^?1 are noticed for the oxidized films oxidized at 275°C which are due to the presence of conjugated double bonds of the type C ? N? C ? N. This type of conjugation is assumed in the ladder polymer.     

Phosphoric acid activation of nutshells for metals and organic remediation: Process optimization

Almond, pecan, English walnut, black walnut and macadamia nut shells were chosen as hard, lignocellulosic precursors for the production of granular activated carbons (GACs). They were activated with H₃PO₄ under a variety of conditions. Following activation, a portion of each GACs was oxidized in air at 300°C for 4 h in order to create a carbon surface presumably with more oxygen functional groups for the adsorption of metal cations. Also investigated was a streamlining of the production techniques used. Several of the samples were subjected to a ‘Continuous’ process in which the carbon was activated and upon cooling to 300°C was oxidized with air. Beyond this activation, methods were developed wherein the activation process took place under air and without a discrete, separate oxidation step. These processes were designed to determine if any of the carbon's capabilities would be lost or enhanced in comparison to the more standard activate–cool–wash–oxidize method. The carbons produced from these various activation/oxidation methods consistently, and without regard to precursor composition, sequestered over 90% of available copper from a 3 mM copper chloride test solution and often adsorbed organic contaminants as effectively as some commercial carbons. © 1998 SCI     

Effects of temperature,reaction time,atmosphere, and catalyst on hydrothermal liquefaction of Chlorella

Hydrothermal liquefaction (HTL) is the direct conversion of wet biomass into bio-oil at high temperature (200–400°C) and high pressure (10–25 MPa). In this work, we investigated HTL with 4.5 g of Chlorella and 45 ml of water/ethanol (1:1 vol. ratio) in a 100 ml reactor. Bio-oils produced are characterized via elemental analysis, thermogravimetric analysis, and gas chromatography–mass spectrometry (GC–MS). HTL of Chlorella was investigated at 240 and 250°C for 0 and 15 min under an air or H₂ atmosphere and with and without 5% zeolite Y. Temperature increased the bio-oil yield from 38.75% at 240°C to 43.04% at 250°C for 15 min reaction time. Longer reaction time increased the bio-oil yield at 250°C from 39.14% for 0 min to 43.04% for 15 min. The H₂ atmosphere had a significant effect for HTL at 240°C. Zeolite Y increased the bio-oil yield significantly from 32.03% to 43.06% at 250°C for 0 min. The carbon content of bio-oil increased with the temperature while the oxygen content decreased. The boiling point distribution of bio-oils in the range of 110–300°C varies with temperature, and atmosphere. At 240°C for 15 min, the 110–300°C range increased from 31.19% in air (240-15-air) to 39.25% in H₂ (240-15-H₂). The H₂ atmosphere increased the content of hydrocarbons, alcohols, and esters from 69.61% in air (240-0-air) to 82.83% in H₂ (240-0-H₂). Overall, temperature, reaction time, atmosphere, and catalyst all significantly influenced the yield and/or quality of bio-oils from HTL of Chlorella.     

Pro-Oxidant Effects of β-Carotene During Thermal Oxidation of Edible Oils

β-Carotene is one of the most important fat soluble pigments with well-known antioxidant and pro-vitamin A activity. It is used in industries as a food colorant and a source of vitamin A. The thermal induced degradation during processing of wide varieties of carotenoid-rich foods leads to color and properties losses. The thermal stability of edible oils is thus of great importance to food manufacturers. Corn oil, rapeseed, and sunflower oils were fortified with 50–300 μg/g of β-carotene and oxidized using a Rancimat apparatus (air flow rate 20 L/h) at 110 °C for 14 h. β-Carotene degradation was measured using high performance thin layer chromatography and confirmed by HPLC–DAD–MS. Triacylglycerols and polar compounds (PC) were determined using LC–ESI–MS. Results showed that most of the β-carotene was degraded during the first 5 h of the thermal oxidation. It was found that the addition of β-carotene produces significant effects (P < 0.05) on the peroxide index, free fatty acid values and radical scavenging activity of the three oils. Triacylglycerols containing high amounts of oleic acid show higher stability toward thermal oxidation and β-carotene treatment. Among the oils, rapeseed oil was the most stable oil in terms of the formation of polar compounds (PC), followed by corn oil, while sunflower oil was more prone to oxidation and thus higher amounts of PC were formed.     

The performance of CNT as catalyst support on CO oxidation at low temperature

A carbon nanotube (CNT) was used as catalyst support impregnated with transition metal cobalt for CO oxidation at low temperature. Catalyst properties were analyzed by X-ray powder diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and transmission electron microscope (TEM). Analytical results for TEM and XRD demonstrated that cobalt particles were highly dispersed on the carbon nanotube (20–30 nm) with nanosized cobalt particles (10–15 nm). These investigations indicated that Co/CNT generates about 99% of the high activity for CO conversion at 250 °C and thermally stability that is superior to Co/activated carbon (AC). The optimum reaction conditions for CO conversion were O₂ concentration 3%, operation temperature 250 °C, CO concentration 5000 ppm, and space velocity 156,000 h⁻¹. At 250 °C, CO may act as a reductant for NO reduction over Co/CNT in the presence of oxygen, whereas CO/NO = 2.5 showed that maximum NO reduction was 30%. Under H₂ rich conditions, the optimum reaction temperature for CO conversion was under 300 °C, and performance of CO₂ selectivity was better at 200 °C than 250 °C as the oxygen concentration increased.     

Supported Gold Nanoparticles Catalysts for Solvent-free Selective Oxidation of Benzylic Compounds into Ketones at 1 atm O2

Supported gold nanoparticles catalyst (Au/TiO₂) was investigated for the oxidation of benzylic compounds into corresponding ketones without any organic solvent at 1 atm O₂ under mild reaction conditions (≤100 °C). For instance, indan was oxidized with conversion of 46% and 1-indanone selectivity of 90% at 90 °C for 24 h. Effect of various reaction parameters viz., temperature, time, and effect of a range of supports was studied for the oxidation of indan. The conversion of indan and selectivity of 1-indanone over recycled catalyst remains almost same.     

Changes in coal composition during air oxidation at 200–250 °C

Air oxidation of two bituminous coals and a lignite was carried out in a fluidized bed reactor at 200–250 °C. The gaseous products were analysed by gas chromatography and solid samples were titrated to determine carboxylic and total acidity and were subjected to ¹³C n.m.r. spectrometry to determine the fraction of aromatic carbon. Elemental composition, heating value and ash content were also determined. During the first few hours oxidation-induced devolatilization proceeded simultaneously with oxidation. Oxidation of the high volatile bituminous coal for 12 h at 200 °C raised the carboxylic groups from 0.37 to 2.1 meq g⁻¹ and the total acidity from 1.5 to 5.3 meq g⁻¹. The acidic groups seem to be largely distinct from oxygenated groups that are precursors to CO and CO₂ products. Oxidation of the same coal at 200 °C consumed aromatic as well as aliphatic carbon at relative amounts 1:3 to 1:4.     

Kinetic study of the oxidation of Illinois No. 6 coal at low temperatures: Evidence for simultaneous reactions

The changes which occur during the low-temperature (25–100 °C) oxidation of thin sections of Illinois No. 6 coal were observed using time-resolved in-situ FT-i.r. difference spectroscopy. Graphical visualization of the spectral changes clearly demonstrates that multiple reactions occur. The presence of at least three interrelated reactions is inferred from the temporal behaviour of the absorbance changes. Consequently the overall oxygen-to-carbon ratio of the final oxidized coal will depend critically on both time/temperature conditions of the oxidation as well as the pretreatment and sample handling history of the coal.     

Structural analysis of NaOH-alcohol treated coals

Six vitrinite-concentrated coal samples were treated with NaOH-alcohol at 300 or 350 °C for 1 h. The products were nearly all soluble in pyridine except those from the oldest coal (52.4% of extraction yield). Structural indices of these pyridine extracts were calculated from ultimate analytical values, molecular weight and ¹H-n.m.r. data. The younger coals have tetralin-type nuclei and bituminous coal has 5–6 rings, about 2 of naphthene type. The younger coals were estimated to have more frequent ether linkages.     

ACCELERATION OF THE WET OXIDATION REACTION OF PIPERAZINE BY HETEROGENEOUS Ru/TiO2 CATALYST

Wet air oxidation is a candidate technique for the effective treatment of wastewater contaminated by nitrogenous organic pollutants. Piperazine (PZ) is a cyclic diamine representing this class of compounds. In the present work, the wet oxidation reaction of PZ was studied for the first time. It was found that, in the studied range of temperatures of 180°–230°C and O₂ partial pressures of 0.69–2.07 MPa, the oxidation process was slow. Total organic carbon (TOC) conversion at 230°C and 0.69 MPa O₂ partial pressure was just 52% after 2 h. The investigated reaction was accelerated by a heterogeneous Ru/TiO₂ catalyst. Maximum TOC conversion (91%) was achieved during catalytic wet oxidation at 210°C and 1.38 MPa O₂ pressure. Kinetic data were collected over the range of temperatures 180°–210°C, O₂ partial pressures 0.34–1.38 MPa, and catalyst loading 0.11–0.66 kg/m³. The lumped TOC concentration decay was a two-step first-order process.     

Low temperature—long time,high temperature-short time liquefaction of coal: The Hokudai process

A Japanese cola was hydrogenated in wash oil with fine iron dust and sulphur as catalyst under a reaction pressure of 12–13 MPa at 420 °C for 2 h and then at 500 °C for 0–20 min. The liquid yield boiling up to 600 °C amounted to 55–66 wt%. Pyridine conversion was ≈ 100 wt%, benzene conversion 82–90 wt% and n-hexane conversion 53–70 wt%. Compared with direct hydrogenation at 500 °C for 10 min the low temperature-long time plus high temperature-short time liquefaction process (the Hokudai process) is a very effective method for obtaining high liquid yield under relatively low hydrogen pressure without coking, using disposable catalyst and non-donor solvent.