Diffuse reflectance infrared spectrometry of powdered coals

Diffuse reflectance Fourier Transform infrared spectrometry has been shown to allow spectra of powdered coal samples to be measured at high sensitivity. Quantitative precision is good, so that the rank of individual coals and the composition of coal blends can be determined in <15 min. The degree of oxidation of coals, both for natural oxidation in the seam and for laboratory oxidation, can be determined from diffuse reflectance spectra of coals and from the second derivative of these spectra. Second-derivative spectra allow quantitative estimates of oxidation to be obtained without the application of spectral subtraction routines, which require standard reference samples that are not always available. The potential for using diffuse reflectance infrared spectrometry for monitoring reactions of powdered coals in-situ has been demonstrated.     

Preliminary studies on the aromaticity of Australian coals: Solid state n.m.r. techniques

The aromaticities of samples from nine Australian coal seams, including pairs of hand-picked vitrains and durains, have been determined by ¹³C cross-polarization n.m.r. spectroscopy with magic angle sample spinning. The results clearly show that the aromaticity (f_a) of the coals increases with increase in vitrinite reflectance and carbon content and decrease in atomic H/C ratio. For a given coal seam, durain (inertinite-rich coal) has a higher f_a value than vitrain (vitrinite-tich coal). The trends for carbon content and atomic H/C are in good agreement with results from North American coals, although the aromaticities of Australian coals obtained in this study appear to be slightly lower than some of those reported for North American coals of similar carbon content.     

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution ¹³C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame ¹H relaxation times (T_1p′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T_1p5 of ≈ ? 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.     

E.s.r. study of pyrolysis vapour of coal

Wyodak and Heatburg subbituminous coals were pyrolysed in-situ in an e.s.r. microwave cavity at ≈510 °C in an evacuated sealed tube. At least two kinds of radicals are detected; first, phenalenyl-like radicals and then, polymerized radicals from the initial ones.     

Nuclear magnetic proton relaxation studies of oxidized coals

Coals of NCB rank 301 a (coking), 502 (caking) and 802 (very weakly caking) are oxidized in air at 373 K or 383 K for up to 42 days. Spin-lattice and spin-spin relaxation times, T₁ and T₂ respectively, of oxidized coals are measured using a Bruker SXP 4–100 and FT spectrometer. Free radical concentrations in the coals are obtained using a JES PE e.s.r. spectrometer. Infrared spectra of oxidized coals are obtained and optical textures of cokes from fresh and oxidized coals are assessed by optical microscopy. For two coking coals, decreasing values of T₁, and increasing concentration of free radicals occurred with oxidation at 383 K to 16 and 28 days. Thereupon values of T₁, increased and free radical concentrations decreased with further progressive oxidation. At the point of inflexion in properties, resultant cokes from the coals ceased to shown any anisotropy in their optical textures and became isotropic resembling cokes from low-rank coals. For the caking coals, T₁ increased at all stages of oxidation to 42 days with decreasing concentrations of free radicals. Two values of T₂ were found in each coal corresponding to a rigid and mobile component ((T₂)_r < (T₂)_m). The rigid component (T₂)_r was not affected by oxidation but values of (T₂)_m decreased with increasing duration of oxidation. It is considered that coking and caking coals exhibit different effects of oxidation with perhaps phenols and quinones in caking coals acting as inhibitors to the growth of stable free radicals. Oxidized coking coal may behave like fresh caking coal.     

Thermal and oxidation chemistry of coal at low temperatures

The chemical reactions which occur when Illinois No. 6 (hv C) and Rawhide (SBB C) coals are thermally pretreated at 100°C and when Illinois No. 6 coal is subsequently oxidized at 100°C with O₂ have been studied using in-situ FT-i.r. differende spectroscopy. Significant spectroscopic changes were seen. Vacuum drying at 100°C resulted in the decomposition of carboxylic acid species to form a variety of new carbonyl species (in Rawhide) and decarboxylated or decarbonylated coal (Illinois No. 6). Oxidation of predried Illinois No. 6 coal leads to the formation of new carbonyl species. The assumption that drying does not alter the chemical composition of coal may not be correct. Thus, overall spectroscopic (and chemical) changes observed in moderate temperature reaction studies may depend upon sample pretreatment, drying and storage. In addition, the time/temperature profile used in a reaction study may affect the overall changes observed by altering the relative contribution of the different reactions.     

Kinetics of the thermo-oxidative and thermal cracking reactions of Athabasca bitumen

The thermo-oxidative and thermal cracking reactions of Athabasca bitumen were examined qualitatively and quantitatively using differential thermal analysis (DTA). Reaction kinetics of low temperature oxidation (LTO) and high temperature cracking (HTC) were determined. The rate of the LTO reaction was found to be first order with respect to oxygen concentration. The activation energy and the Arrhenius pre-exponential factor were 64 MJ kg^?1 mol^?1 and 10^5.4 s^?1, respectively. The effects of atmosphere, pressure, heating rate and support material on the thermal reactions of bitumen were studied. In general, it was found that partial pressures of oxygen > 10% O₂ favoured exothermic oxidation reactions. High pressure increased the rates of LTO and HTC as well as the exothermicity of these reactions. A major contribution of this study to thermal in-situ processes is that heating rate can be used effectively to control the extent of low temperature oxidation and hence fuel availability during in-situ combustion. Low linear heating rates (2.8 °C min^?1) favoured low temperature oxidative addition and fission reactions. The reaction products readily formed coke and combusted upon heating. High linear heating rates (24.5 °C min ^?1) led to rapid oxidation reactions in the high temperature zone; the high temperature and the energy released during oxidation appeared to promote combustion. Finally, when sand was used as the support material there appeared to be a catalytic effect in both LTO and HTC reactions.     

Coal liquefaction by in-situ hydrogen generation.: 1. Zinc-water-coal reaction

Liquefaction of coal was carried out in a zinc—water—solvent system to give a product with high concentration of pyridine and benzene solubles. In this system the metal reacts with water to produce the corresponding metal oxide and hydrogen. This hydrogen was used for in-situ hydrogenation of coal. The effects of reaction time, temperature, type of solvent, the quantity of metal used and the rank of coal were investigated. The solvent has a very marked effect on the conversion of coal to benzene-soluble materials, especially at short reaction times. A maximum benzene conversion of 96% for Taiheiyo coal was obtained when it was treated at 445 °C for 1 h using wash oil as solvent. With regard to the influence of coal rank it was found that low rank coals were more reactive than high rank coals. The amount of preasphaltene is only slightly influenced by coal rank but depends on the temperature and the type of solvent used.     

Voltammetric, in-situ spectroelectrochemical and in-situ electrocolorimetric characterization of phthalocyanines

In this work, electrochemical, and in-situ spectroelectrochemical characterization of the metallophthalocyanines bearing tetra-(1,1-(dicarbethoxy)-2-(2-methylbenzyl))-ethyl 3,10,17,24-tetra chloro groups were performed. Voltammetric and in-situ spectroelectrochemical measurements show that while cobalt phthalocyanine complex gives both metal-based and ring-based redox processes, zinc and copper phthalocyanines show only ring-based reduction and oxidation processes. The redox processes are generally diffusion-controlled, reversible and one-electron transfer processes. Differently lead phthalocyanine demetallized during second oxidation reaction while it was stable during reduction processes. An in-situ electrocolorimetric method, based on the 1931 CIE (Commission Internationale de l’Eclairage) system of colorimetry, has been applied to investigate the color of the electro-generated anionic and cationic forms of the complexes for the first time in this study.     

Evaluation of lignin and cellulose contributions to low-rank coal formation by alkaline cupric oxide oxidation

Oxidation with alkaline cupric oxide has been combined with solid-state ¹³C-n.m.r. spectroscopy to evaluate the cellulose and lignin input to the formation of low rank coals. Model studies carried out on lignin-cellulose mixtures, carbonified cellulose, synthetic coals and synthetic humic acids (melanoidins) have established m-hydroxybenzoic acid as a source indicator for cellulose. This product has been found specifically in the oxidation of bio- and geo-macromolecules containing cellulose and/or thermally altered cellulosic material and is chemically distinct from the characteristic oxidation products of lignin-derived materials. Systematic changes in the distribution of the major oxidation products from lignin provide a chemical fingerprint which, in general, can be utilized to trace the thermal history of the sample. Analysis of two lignite coals from the northern hemisphere has demonstrated their predominantly lignitic origin. On the other hand, a Victorian brown coal (pale lithotype) sample is shown to contain a significant amount of highly transformed carbohydrate materials which are presumably incorporated into the macromolecular structure as humic acid derivatives.     

An e.s.r. study of some coals under rapid passage condition at high temperatures and pressure

The e.s.r. spectra of Miike and Taiheiyo coals were measured under rapid passage conditions in the temperature range 150–450 °C. A parameter, R, was defined by a ratio of out-of-phase and in-phase spectral amplitudes and the ratios for Miike and Taiheiyo coals were estimated in this temperature range. It was found that the temperature dependence for R was different for the two coals examined, and the reason for the difference was discussed. Further, the ratios for those coals mixed with pyrene were estimated in the temperature range 150–400 °C at atmospheric and 1.1 MPa nitrogen pressure. Based on the temperature dependence of the ratio the coal liquefaction ability of pyrene for those coals was discussed.     

Deno oxidation. Isolation of high-molecular-weight aliphatic material from coals and further model compound studies/

Long-chain aliphatic materials present in coals are not completely oxidized using the procedure described by Deno (Fuel 1978, 57, 455). They are adsorbed on the filter cake during the work-up procedure and can be isolated by extracting the filter cake. The amounts present are similar to those observed by Hayatsu et al. (Fuel in press). Also-phenol is not completely oxidized under these conditions, but gives products with m/e as high as 310. Products from the oxidation of phenol include ethane and propane tricarboxylic acids and benzene tri- and tetracarboxylic acids.     

Influence of thermoplastic properties on coking pressure generation: Part 1 - A study of single coals of various rank

In this study a number of high coking pressure coals with different fluidities were evaluated alongside a number of low pressure coals also with differing fluidities. This was to confirm findings from an earlier study using a limited selection of coals, and to establish rheological parameters within which a coal may be considered potentially dangerous with regards to coking pressure. The results have confirmed and elaborated on previous findings which show that parallel plate displacement (ΔL) and axial force profiles can be used to distinguish between high and low pressure coals, with peak values indicating cell rupture and subsequent pore network formation. This is thought to correspond with plastic layer compaction in the coke oven.For low pressure coals pore coalescence occurs quite early in the softening process when viscosity/elasticity are decreasing and consequently a large degree of contraction/collapse is observed. For higher pressure coals the process is delayed since pore development and consequently wall thinning progress at a slower rate. If or when a pore network is established, a lower degree of contraction/collapse is observed because the event occurs closer to resolidification, where viscosity and elasticity are increasing. For the higher fluidity, high coking pressure coals, a greater degree of swelling is observed prior to cell rupture, and this is considered to be the primary reason for the high coking pressure observed with these coals. An additional consequence of these events is that high pressure coals are likely to contain a higher proportion of closed cells both at and during resolidification, reducing permeability in both the semi-coke and high temperature plastic layers, respectively.Using a rheological mapping approach to follow viscoelastic changes during carbonisation it has been possible to identify specific regions associated with dangerous coals. These tend to be fusible coals where at the onset of expansion, δ (elasticity) < 54° and η* (complex viscosity) > 5 × 10⁵ Pa s, and where in most cases δ_MAX does not exceed 65°.     

Quench solvent evaluation: An e.s.r. study

An in-situ radical-quenching experiment was performed in an e.s.r. microwave cavity by using a solution flow system. Diphenylmethyl radicals produced from pyrolysis of 1,1,2,2-tetraphenylethane were quenched by several H-donor solvents. Among the solvents used, indan was the fastest in quenching, followed by hydrophenanthrene, tetralin, mesitylene and cumene in decreasing order of quenching rate.     

Carbon doped TiO2 nanotubes photoanodes prepared by in-situ anodic oxidation of Ti-foil in acidic and organic medium with photocurrent enhancement

Carbon doped titanium oxide nanotubular arrays (C-TNT) were successfully fabricated in highly ordered arrays by in-situ anodic oxidation of titanium foil to enhance the photoelectrochemical performance of titanium oxide nanotubular arrays (TNT) under visible light. The carbon doped titanium oxide nanotube was achieved via an in-situ anodic oxidation of titanium foil at 20 V in acidic and organic media with 0.5 and 1 wt% carbon source (polyvinyl alcohol, PVA) at room temperature. The carbon was incorporated from PVA into the titanium oxide nanotubular arrays during the anodic oxidation process. FESEM micrographs of the nanotubular arrays of C-TNT showed uniform vertical nanotubes. The external shapes of the pores and structures of the nanotubular arrays of C-TNT were affected by the percentage of PVA in both of the electrolytes. The amounts of C incorporated into TNT increased linearly with the amount of PVA introduced into the electrolyte. The morphology of the C-TNT produced by in-situ doping is superior in terms of uniformity, and the nanotubes grow in the preferred z-direction compared to C-TNT obtained using a post doping technique. The influence of the carbon contents on the photocurrent densities of C-TNT photoanodes was tested in a photoelectrochemical cell, and the current–potential (I–V) profiles were established.     

Pyrolysis—gas chromatography of Australian coals. 2. Bituminous coals

Pyrolysis—gas chromatography (Py—g.c.) was used to characterize quantitatively a series of high- to low-volatile bituminous Permian Australian coals. The levels of n-alkanes, n-alkenes and triterpenoids released by pyrolysis all decrease as a function of increasing rank and thus, the coal samples can be classified into three distinct groups. Carbon Preference Indices (CPI's) for alkanes and alkene/alkane ratios also decrease as a function of rank. The triterpenoids have exclusively the hopane skeleton. The hopane isomeric distributions exemplify the geological maturity of bituminous coals relative to brown coal (lignite). A significant correlation has been established between the level of n-alkanes and n-alkenes released under Py-g.c. conditions and the predicted oil yield by pyrolysis of these coals. Further development and application of the techniqueshould enable much to be learnt relating to the quality and yield of flash pyrolysis tars as well as the original coal macromolecular structure.     

Quantitative solid-state C n.m.r. measurements on cokes, chars and coal tar pitch fractions

Bloch decay or single pulse excitation (SPE) ¹³C n.m.r., generally recognized as the best approach to obtain quantitatively reliable aromaticity values and other skeletal parameters for coals, was applied to partly carbonized coal samples, a biomass char and the toluene-insolubles from a coal tar and a corresponding pitch. As found previously for coals, the aromaticities and non-protonated carbon concentrations were generally higher than those estimated by cross-polarization (CP). Furthermore, in terms of accumulation times, the shorter ¹³C T₁'s of low-temperature chars makes SPE a more efficient technique than for coals. The higher concentrations of paramagnetic centres responsible for the shorter ¹³C T₁'s still result in observability of 75% of the carbon in the chars by the SPE technique. The ratios derived from the SPE measurements agree well with those obtained from elemental analysis.     

Carbonization of coals to produce anisotropic cokes.: 4. Improving co-carbonization behaviour of bituminous and subbituminous coals with pitch by pretreatment coals to remove cations

Several de-ashing pretreatments of selected coals have been examined to establish simple and effective procedures to improve, in terms of anisotropic development, the co-carbonization behaviour of the coals with pitches. Refluxing pretreatments of the coals in 1N HCI containing methanol and in boiling water containing EDTA-2Na (EDTA-2Na/coal = 7/100 byweight) improve the co-carbonization behaviour of Witbank, Miller, Taiheiyo and Wandoan coals, all of which, in their original, untreated form, are modified in terms of anisotropic development only very slightly in co-carbonizations with A240 petroleum pitch. Pretreatment of coals of very low rank appears to be ineffective in co-carbonizations with A240; however, co-carbonization with hydrogenated A240 shows that the pretreatments are effective. Analyses and FT-i.r. spectroscopy of mineral matter suggest that improved behaviour due to the pretreatment is related to the removal of divalent cations and to the modification of the oxygen functionality of the coals.     

Study of deuterium transfer,isotope effects and structural distributions of products of reactions of coals in deuterated tetralin using 2H and 13C FT-n.m.r. and solid-state 13C FT-n.m.r.

Four coals (bituminous, subbituminous, lignite and canneloid) are treated with tetralin-1,1,4,4,-d₄ or — 1,1 -d₂ or mixtures of tetralin-d₄ and tetralin-d₀ at 427 °C in degassed Pyrex vessels for times between 5 and 60 min. Deuterium depletion and scrambling in solvent-derived products are determined for degassed and air-saturated experiments. Deuterium distributions are determined for preasphaltene and asphaltene fraction (A + P) and light oils (LTO) by ²H FT-n.m.r., and solid coals and products are characterized by ¹³C CP/MAS and ¹³C FT-n.m.r. Illinois No. 6, PSOC 837 and PSOC 531 coals selectively consume tetralin-d₀ over tetralin-d₄ and exhibit isotope effects in the scrambling of deuterium from 1 — to 2-positions. Intersite deuterium scrambling in recovered tetralin is negligible at 10 min or shorter reaction times, but deuterium depletion from tetralin is significant at all reaction times. Deuterium is detected predominantly at benzylic-type and secondary aliphatic positions and to a lesser extent at aromatic positions of A + P and LTO fractions at reaction times of 5 min. The presence of air significantly enhances both the extent of deuterium scrambling and the rearrangement of tetralin to 1-methylindan at reaction times of 30–60 min.